EP4690341A1 - Electrolyte system - Google Patents

Abstract

Provided herein is an electrochemical cell comprising an anode, a cathode and an electrolyte system, wherein the electrolyte system comprises: (i) a first electrolyte comprising a solid electrolyte; and (ii) a second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof, wherein the second electrolyte has a polysulfide and/or polyselenide solubility sufficient to prevent shuttling and wherein the second electrolyte does not contact the anode. Also provided is a method of producing the electrochemical cell; and an electrochemical cell assembly comprising at least one electrochemical cell.

Description

Electrolyte System Related The present application claims priority from Great Britain Patent Application No. GB2304596.6, filed on 29 March 2023, the entire contents of which have been incorporated herein by reference. Field The present invention relates broadly to the field of battery technology. Specifically, the invention relates to an electrolyte system, an electrochemical cell comprising the electrolyte system, methods of manufacture of the electrochemical cell, and an electrochemical cell assembly comprising at least one of the electrochemical cells. In particular, the invention relates to an electrolyte system comprising a first electrolyte comprising a solid electrolyte and a second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof. Background The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field. In recent years there has been an increased demand for “green energy” due to the detrimental impact that fossil fuels have on the environment. One energy source that has received a great deal of interest is battery technology, in particular rechargeable batteries. Of the commonly available rechargeable battery technologies, lithium-ion (Li-ion) battery technology dominates the commercial market, as a result of its high energy density compared to competing technologies, such as nickel-cadmium batteries (Ni-Cd). However, Li-ion batteries are expensive to produce, highly flammable, and typically require the use of cobalt and/or nickel in the production of the cathodes. Both cobalt and nickel are costly materials, and there are concerns over the security of the supply chain. In addition, cobalt can be toxic if not handled correctly, increasing the operational complexity of both the manufacture and end of life recycling processes. Recently, chalcogen and chalcogenide materials, in particular sulfur, selenium, and combinations such as selenium sulfide have received a great deal of attention, given their promise for use in cathodes for rechargeable lithium batteries. In particular, lithium-sulfur (Li-S) cells have received widespread attention because of their advantages over Li-ion batteries. For instance, they have a higher gravimetric energy (i.e., the measure of how much energy a battery contains in proportion to its weight, which is typically measured in ”watt-hours per kilogram (Wh/kg)”, wherein a watt-hour is a measure of electrical energy that is equivalent to the consumption of one watt for one hour), a lower raw material cost, and are more environmentally friendly. Moreover, they do not require the use of nickel or cobalt in their manufacture. Furthermore, there are safety benefits associated with use of Li-S batteries over Li-ion batteries, as there is no longer a need for free metal ions in the materials. Instead, Li-S batteries proceed via a “conversion mechanism”, whereby sulfur and lithium react to form polysulfides. In addition, lithium-selenium (Li-Se) cells have also received attention given that selenium has a high electrical conductivity. Li-Se cells also operate via a “conversion mechanism”, whereby selenium and lithium react to form polyselenides. A disadvantage to conventional Li-S and Li-Se batteries is that polysulfides or polyselenides generated at the electrodes dissolve in the liquid electrolyte and undergo a “shuttling effect” between the anode and cathode, which results in an irreversible loss of sulfur/selenium from the cathode. This can result in capacity loss and be detrimental to cyclability of the battery (i.e., the measure of times they can be recharged before they start to break down). Moreover, another important disadvantage to conventional Li-S and Li-Se batteries is the degradation of the liquid electrolyte during operation due to the presence of lithium metal at the anode. As a result, a high loading of liquid electrolyte is often required to enable extended cyclability of the battery. However, high electrolyte loadings often result in an increase in the weight and volume of the cell, which negatively impacts the gravimetric and volumetric energy density (i.e., the amount of energy stored in the cell per volume in litres). One way that the effect of the polysulfide and polyselenide shuttle has been limited is through the addition of certain additives in the electrolyte, such as additives that include N-O bonds (e.g., lithium nitrate (LiNO3)). Without being bound by theory, the presence of additives like LiNO3 in the electrolyte is understood to result in formation of a passivation layer (commonly known as a solid electrolyte interphase (SEI) layer) on the anode that mitigates the polysulfide/polyselenide shuffle effect. However, there are numerous disadvantages associated with the use of these additives. For instance, LiNO3 forms nitrogen oxide gases above 40 degrees Celsius, which results in a narrowing of the operating and storage temperature window. Moreover, the presence of these additives results in cell swelling, due to the formation of gases during cycling, not to mention safety implications. Therefore, there is a need to eradicate or avoid the use of such additives. Instead of using electrolyte salts such as LiNO3 or solid-state electrolytes, previous attempts have included the combination of a low porosity cathode having an electrochemically active sulfur component with a liquid electrolyte having no or a low polysulphide solubility (which ultimately reduces polysulphide shuttling). However, such cells may still suffer from degradation of the liquid electrolyte during operation. Further, conventional Li-S and Li-Se batteries often use flammable liquids as the electrolyte, which has resulted in concern over their safety given the high loadings required to dissolve polysulfides and polyselenides. As a result, there has been a great deal of interest in solid state batteries (SSBs), which use an inorganic solid-state electrolyte that do not dissolve polysulfides or polyselenides during battery cycling. Whilst safety would be improved using a solid-state battery, the manufacture of solid- state batteries on a large scale is difficult, and there remains the issue of low sulfur utilisation and poor interfacial contact between the electrolyte and electrode in a solid- state battery, which may result in high impedance within the cell. Moreover, to maintain a good interfacial contact between the solid-state electrolyte and cathode, a high amount of pressure is generally required. Also, there is the issue of dendrite formation with solid state lithium batteries or sodium batteries. Lithium or sodium dendrites are tree-like microstructures, which can form on the surface of a lithium or sodium metal anode during charge/discharge cycles. Solid electrolytes are often brittle or polycrystalline in nature, which means they are susceptible to the growth of these dendrites. Formation of dendrites are problematic, as they impact the thermal stability of the cell, and can lead to short circuiting. In some cases, formation of lithium dendrites can cause a build-up of pressure, resulting in explosion. Therefore, formation of such dendrites impacts the overall safety of the battery. To try and address the drawbacks associated with solid-state batteries, there has been research into the combination of a solid-state electrolyte with an organic liquid electrolyte in lithium ion and lithium-sulfur cells. However, whilst such cells have better interfacial contact compared to solid-state batteries, such cells still require high liquid electrolyte loadings of the liquid electrolyte. There therefore remains a need for an electrochemical cell having not only improved cyclability, improved safety, and a broad operating/storage temperature window, but also having a high gravimetric energy and volumetric energy density. To achieve this, there remains a need to reduce liquid electrolyte loadings of a cell and ensure that the possibility of degradation at the anode/electrolyte interface is minimised or prevented altogether. It is an object of the present invention that at least one of the needs above is at least partially satisfied. It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least provide a useful alternative. Summary of the Invention The following description conveys exemplary embodiments of the present invention in sufficient detail to enable those of ordinary skill in the art to practice the present invention. Features or limitations of the various embodiments described do not necessarily limit other embodiments of the present invention or the present invention as a whole. Hence, the following detailed description does not limit the scope of the present invention, which is defined only by the claims. Accordingly, in a first aspect of the invention there is provided an electrochemical cell comprising an anode, a cathode and an electrolyte system, wherein the electrolyte system comprises: (i) a first electrolyte comprising a solid electrolyte; and (ii) a second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof; wherein the second electrolyte has a polysulfide and/or polyselenide solubility sufficient to prevent shuttling, and wherein the second electrolyte does not contact the anode. Electrolyte System Electrolyte systems as defined by the first aspect of the invention result in electrochemical cells having superior gravimetric energy and volumetric energy compared to existing hybrid cells. Such electrolyte systems have improved safety and cyclability when compared to conventional Li-S cells, Li-Se cells, and conventional hybrid cells. In preferred embodiments of the present invention, the first electrolyte acts as a physical barrier to prevent physical contact between the second electrolyte and the anode (meaning that there is no degradation of the second electrolyte during cycling), but it also acts as a barrier against the formation of lithium or sodium dendrites at the anode (in instances where the anode comprises lithium, sodium, an alloy comprising lithium, or an alloy comprising sodium). Moreover, the use of a second electrolyte which does not substantially dissolve polysulfides and/or polyselenides means that much leaner electrolyte loadings can be used when compared to existing hybrid systems, which require sufficient electrolyte loading to dissolve the sulfur/polysulfides and or selenium/polyselenides from the cathode. As such, the electrolyte system according to the first aspect of the invention provides for electrochemical cells with high specific energy densities (Wh/kg). By “lean” or “low” loadings of electrolyte, it is meant that relatively low volumes of liquid or gel electrolyte (in terms of the second electrolyte of the present invention) is used. In the present invention, a relatively “lean” or “low” loading of a liquid or gel electrolyte refers to amounts of less than about 3 µL/mAh. As used herein, “µL/mAh” relates to the electrolyte/sulfur ratio in the cell (i.e., µL of electrolyte per milliampere-hour of sulfur). It is also understood by the inventor that another benefit of a liquid or gel electrolyte with low polysulfide solubility (or, low solvent power) is that the dissolution of the solid electrolyte by the liquid or gel electrode is reduced, or ameliorated, or eliminated entirely. As the skilled person may appreciate, this advantage is further enhanced by a low liquid or gel electrolyte loading, which provides even further protection against degradation of the solid electrolyte. The term “electrolyte” takes its usual meaning in the art and relates to the medium that allows for ion transport between the anode and cathode. First Electrolyte In some embodiments, the first electrolyte comprises a ceramic material, a polymer material, or any combination thereof. As used herein, the term “ceramic material” takes its usual meaning in the art, and relates to an inorganic non-metallic solid made up of either metal or non-metal compounds. In certain embodiments, the first electrolyte comprises a ceramic material selected from an oxide, a carbonate, a nitride, a carbide, a sulfide, an oxysulfide, a metal oxynitride, a metalloid, or any combination thereof. The ceramic material may have a crystalline, polycrystalline, partially crystalline, or amorphous structure. Suitable ceramic materials include, but are not limited to, oxides, carbonates, nitrides, carbides, silicides, sulphides, oxysulphides, and/or oxynitrides of metals and/or metalloids. Where the electrolyte system is incorporated into an electrochemical cell with an anode comprising lithium metal or a lithium alloy, the ceramic material of the first electrolyte may comprise lithium; similarly, where the electrolyte system is incorporated into an electrochemical cell with an anode comprising sodium metal or a sodium alloy, the ceramic material of the first electrolyte may comprise sodium. However, all ceramic materials disclosed herein are compatible with all anode materials disclosed herein. Non-limiting examples of suitable ceramic materials having a sufficient ionic conductivity may be produced by a combination of various lithium compounds. Such ceramic materials including lithium include, but are not limited to, lithium oxides (Li2O, LiO, LiO2, LiRO2, where R is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and/or lutetium), lithium carbonate (Li2CO3), lithium nitrides (e.g., Li3N), lithium oxysulfide, lithium oxynitride, lithium garnet-type oxides (e.g., Li7La3Zr2O12)), Li10GeP2S12, lithium phosphorus oxynitride, lithium silicosulfide, lithium germanosulfide, lithium lanthanum oxides, lithium titanium oxides, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium halides, and combinations of the above. In certain cases, the ceramic material comprises a lithium oxide, a lithium nitride, or a lithium oxysulfide. In some embodiments, the ceramic includes a carbonate and/or a carbide. Examples of ceramic materials include but are not limited to, Li-containing oxides such as Li3.3La0.56TiO3; Nasicon structure such as LiTi(PO4)3; LiSICON (Li14Zn(GeO4)4); Li10GeP2S12; Garnet: Li7La3Zr2O12; Li2O; other oxides such as Al2O3, TiO2, ZrO2, SiO2, ZnO; sulfides such as LiS-P2S5; antiperovskites such as Li3OCl; hydrides such as LiBH4, LiBH4-LiX (where X = Cl, Br, or I), LiNH, LiNH2, LiAlH6, Li2NH; borates or phosphates such as Li2B4O7, Li3PO4, LiPON; carbonates or hydroxides such as Li2CO3, LiOH; fluorides such as LiF; nitrides such as Li3N; sulfides such as lithium borosulfides; lithium phosphosulfides, lithium aluminosulfides, oxysulfides, praseodymium oxide. At least one of said ceramic materials may be used, or a combination thereof. Optionally, the ceramic material is selected from at least one of an argyrodite, lithium lanthanum zirconium oxide (Li7La3Zr2O12) (LLZO), lithium aluminium titanium phosphate (Li1.3Al0.3Ti1.7(PO4)3) (LATP), lithium aluminium germanium phosphate (LAGP), lithium phosphorus oxynitride (LIPON), lithium phosphorous sulfide (LPS), lithium germanium phosphorus sulfide (Li10GeP2S12) (LGPS), or lithium sulfide-phosphorous pentasulfide (Li2S-P2S5). In some preferred embodiments, the ceramic material comprises argyrodite. As used herein, an “argyrodite” refers to materials of general formula Li7-pBS6-pXp, wherein B is phosphorous or arsenic, X is chlorine, bromine or iodine, and p is between 0 and 1. Optionally, B is phosphorous, X is chlorine, and p is 1 (i.e., wherein the argyrodite has the chemical formula: Li6PS5Cl). In some embodiments, the first electrolyte comprises a polymer material. Preferably, the polymer material is inherently ionically conductive, such as a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (e.g., Nafion^®). Alternatively, polymers blended with lithium (or sodium) salts, which can achieve bulk conductivities of greater than 10^-7 S/cm, may also be used. Examples of suitable polymers include, but are not limited to, ethylene oxide (EO) based polymers (for example PEO); acrylate based polymers (for example PMMA); polyamines (for example polyethyleneimine); siloxanes (for example poly(dimethylsiloxane)); polyheteroaromatic compounds (e.g., polybenzimidazole); polyamides (e.g. Nylons), polyimides (e.g. Kapton^®); polyvinyls (e.g. polyacrylamide, poly(2-vinyl pyridine), poly(N-vinylpyrrolidone), poly(methylcyanoacrylate), poly(vinyl acetate), poly (vinyl alcohol), poly(vinyl chloride), poly(vinyl fluoride)); inorganic polymers (e.g. polysilane, polysilazane, polyphosphazene, polyphosphonate); polyurethanes; polyolefins (e.g., polypropylene, polytetrafluoroethylene); polyesters (e.g., polycarbonate, polybutylene terephthalate), or a combination thereof. Optionally, co-block polymers such as a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion^®) may be used. At least one of said polymer materials may be used, or a combination thereof. In some embodiments, it may be the case that the first electrolyte contains ceramic particles in combination with one or more of the polymer materials disclosed herein. In some embodiments the first electrolyte may comprise a ceramic-polymer composite material. Examples of ceramic-polymer composite materials include, but are not limited to, metalcones (e.g., alucone, zincone, zircone, titacone, or combinations thereof). The term “composite” takes its usual meaning in the art and relates to materials made from two or more constituent materials having different chemical or physical properties from one another. When the two or more constituent materials are combined, the resultant composite material has properties different to the individual components present. In some embodiments, the first electrolyte comprises one or more of: an argyrodite; lithium germanium phosphorus sulfide (LGPS - Li10GeP2S12); lithium phosphorous sulfide (LPS); lithium lanthanum zirconium oxide (LLZO); lithium aluminium germanium phosphate (LAGP); lithium phosphorus oxynitride (LIPON); polyethylene oxide (PEO); or combinations thereof. In some preferred embodiments, the first electrolyte comprises an argyrodite. Argyrodites have a high ionic conductivity and are easily processable. In addition, argyrodites have high compatibility with the anode and cathode materials discussed herein. Without being bound to theory, it is understood that argyrodites are highly compatible with Li-S battery technologies thanks to their lower voltage window (typically between 1 and 3 V) when compared to Li-ion batteries (which can go above 4 V). Moreover, this material demonstrates good stability at the interface with the anode when part of an electrochemical cell. Optionally, the first electrolyte comprises an argyrodite of chemical formula Li6PS5Cl. In some embodiments, the first electrolyte further comprises a binder. The binder may comprise a copolymer. The copolymer may be a block copolymer. The binder may comprise a copolymer with a repeating unit comprising a carboxylic acid group or a conjugate base. In some embodiments, the solid electrolyte comprises two or more binders. For example, the solid electrolyte may comprise two or more binders, three or more binders, four or more binders, or five or more binders. In some embodiments, the binder comprises poly(ethylene-co-acrylic acid), carboxylated polystyrene, poly(ethylene-co-methacrylic acid), carboxylated rubber (e.g. carboxylated nitrile butadiene rubber or carboxylated styrene butadiene rubber), or any combination thereof. It is understood that the presence of at least one binder improves the elasticity of the first electrolyte, and therefore improves its processability. In addition, presence of at least one binder may also help to keep the first electrolyte layer intact when the cell is assembled, and/or when in operation. As the skilled person would appreciate, assembly and operation of a cell can cause mechanical stress on the components therein. For example, some of the causes of mechanical stress can include lithium diffusion, heat, or shocks. Such stress could cause some damage to the solid electrolyte (e.g., promotion of lithium or sodium dendrite formation when in operation). However, it is understood that the presence of a binder may reduce such risks. The binder may be present in the range of from 0.1 to 15% of the total weight of the first electrolyte, often in the range of from 1 to 10%, often in the range of from 2 to 7 %. In some embodiments, the first electrolyte comprises an argyrodite and a binder selected from poly(ethylene-co-acrylic acid), carboxylated polystyrene, poly(ethylene-co- methacrylic acid), carboxylated nitrile butadiene rubber, carboxylated styrene butadiene rubber, or a combination thereof. In some embodiments, the ionic conductivity of the first electrolyte is in the range of from 0.0001 mS/cm to 10 mS/cm, or in the range of 0.05 mS/cm to 7 mS/cm, or from 0.75 mS/cm to 5 mS/cm, or from 1 mS/cm to 7.5 mS/cm, or may be about 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5,. 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10 mS/cm, or any range therein. Ionic conductivities within these ranges result in an electrochemical cell having superior capacity at higher discharge rates. Ionic conductivity may be measured using any known technique, such as for example a High Temperature Conductivity Cell (HTCC) or impedance spectroscopy. in some embodiments, the thickness of the first electrolyte is in the range of from 5 µm to 100 µm, often in the range of from 10 µm to 80 µm, or in the range of from 15 µm to 70 µm, or in the range of from 20 µm to 60 µm, or in the range of from 30 µm to 50 µm, or may be about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 , 19, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 µm, or any range therein. Thicknesses within these ranges provide lighter electrochemical cells without compromising on cyclability and cell safety. Optionally, the porosity of the first electrolyte less than 30%, or less than 10%, or less than 1%. In some embodiments, the porosity of the first electrolyte is in the range of from 1% to 40%, or in the range of from 1% to 10%, or in the range of from 1% to 5%, or it may be about 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40% or any range therein. It is believed that a first electrolyte with a porosity in these ranges allow the first electrolyte to perform as a lithium and/or sodium dendrite barrier and also prevent the second electrolyte from diffusing through to the anode and causing any physical degradation. By “porosity” it is meant the volumetric fraction of the material that is a void or empty space, relative to the volume of the total material, expressed as a percentage of between 0% (entirely no voids or empty space) and 100% (entirely void or empty space). Each of the pores in a material may be discrete (i.e., may be embedded entirely in the material or access a single surface of the material) or they may be continuous (i.e., access two or more surfaces of the material). In some embodiments of the present invention, the first electrolyte contains no, or few, continuous pores which would allow contact between the second electrolyte and the anode. Second Electrolyte The second electrolyte according to the first aspect of the invention comprises a liquid electrolyte, a gel electrolyte, or a combination thereof; and has a polysulfide and/or polyselenide solubility sufficient to prevent shuttling. As the skilled person would be aware, and as mentioned above, a “shuttling effect” can occur in sulfur- and selenium-containing electrolytic cells, whereby dissolved polysulfides (or polyselenides) can dissolve into and diffuse through the electrolyte, eventually irreversibly contacting the anode. This loss of sulfur or selenium from the cathode can lead to a loss of capacity and cycle stability and so is preferably avoided. Hence, it is desirable to provide an electrolyte, in particular a liquid electrolyte, which has a low solubility for polysulfide or polyselenide species. Accordingly, in the present invention, the second electrolyte has a low solubility for polysulfide and/or polyselenide species, particularly a solubility that is sufficient to prevent, or ameliorate, or at least significantly or substantially reduce, the shuttling effect in an electrolytic cell. As the skilled person may appreciate, the complete precipitation (i.e., non-dissolution) of generated polysulfide or polyselenide species at or near the cathode is not required to prevent, or reduce, or at least significantly or substantially reduce the shuttling effect. However, in order to sufficiently prevent significant shuttling, a substantial amount of the generated polysulfide or polyselenide species must be restricted from being dissolved in a liquid electrolyte, or other restrained from diffusing to the anode, which can be achieved by providing a liquid electrolyte with low solubility for these species. In some embodiments, the second electrolyte has a low (or relatively low) polysulfide and/or polyselenide solubility at room temperature (approximately 20 °C) defined as less than about 2 M, or less than about 1 M, or less than about 750 mM, or less than about 500 mM, or less than about 400 mM, or less than about 200 mM, or less than about 150 mM, or less than about 100 mM, or less than about 10 mM, or less than about 1 mM, or it may be between about 1 M and about 500 mM, or between about 750 mM and about 250 mM, or between about 1 mM and about 500 mM, or between about 2 mM and about 250 mM, or between about 5 mM and about 100 M, or it may be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 20, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 mM or about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3 M or any range therein. It is expected that the shuttling effect is substantially or completely prevented, or at least significantly or substantially reduced, when the second electrolyte of the present invention has a polysulfide or polyselenide solubility such as that provided above. In some embodiments, the electrolyte may not dissolve polysulfides and/or polyselenides, or may not substantially dissolve polysulfides and/or polyselenides. For example, the electrolyte may have a polysulfide and/or polyselenide solubility in the range of from about 0.001 mM to about 50 mM, or about 0.01 to about 40 mM, or about 0.1 mM to about 20 mM, or about 1 mM to about 10 mM. Correspondingly, the second electrolyte may have a low solubility for sulfur-containing species (such as polysulfides and sulfur) or selenide-containing species (such as polyselenides and selenium) in general. As the skilled person may appreciate, the use of a second electrolyte having low, poor or no solubility of polysulfides and/or polyselenides can prevent polysulfide and/or polyselenide shuttling within an electrolyte and is therefore beneficial in cells such as lithium-sulfur cells, lithium-selenium cells, or lithium-selenium sulfide cells. As noted above, the polysulfide/polyselenide shuttle effect is an undesirable reaction, as it results in loss of coulombic efficiency and can impact cyclability. The second electrolyte of the present invention typically comprises a suitable solvent system, liquid or gel, or mixture of liquids and/or gels; and at least one alkali metal salt. Suitable organic solvents for use in the second electrolyte include at least one of ethers (e.g. linear ethers, diethyl ether (DEE), diglyme (e.g. 2-methoxyethyl ether), tetraglyme, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane (DME), dioxolane (DIOX)); carbonates (e.g. dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate, ethylene carbonate (EC), propylene carbonate (PC)); sulfones (e.g. dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), tetramethyl sulfone (TMS)); esters (e.g. methyl formate, ethyl formate, methyl propionate, methylpropylpropionate, ethylpropylpropionate, ethyl acetate and methyl butyrate); ketones (e.g. methyl ethyl ketone); nitriles (e.g. acetonitrile, propionitrile, isobutyronitrile); amides (e.g. dimethylformamide, dimethylacetamide, hexamethyl phosphoamide, N, N, N, N-tetraethyl sulfamide); lactams/lactones (e.g. N-methyl-2- pyrrolidone, butyrolactone); ureas (e.g. tetramethylurea); sulfoxides (e.g. dimethyl sulfoxide); phosphates (e.g. trimethyl phosphate, triethyl phosphate, tributyl phosphate); phosphoramides (e.g. hexamethylphosphoramide); or any combination thereof. Further suitable solvents include toluene, benzene, heptane, xylene, dichloromethane, and pyridine. In some embodiments, the second electrolyte may comprise one or more of ethers, carbonates, sulfones, esters, ketones, nitriles, amides, lactams, ureas, phosphates, and phosphoramides that are optionally halogenated; for example, they may be optionally fluorinated, and/or optionally chlorinated, and/or optionally iodinated, and/or optionally brominated. In certain embodiments, the second electrolyte comprises a mixture of halogenated and non-halogenated solvents. For example, the organic solvent may optionally comprise a mixture of one or more ethers and fluorinated ethers, or one or more carbonates and fluorinated carbonates. Non-limiting examples of fluorinated ethers include 1,1,2,2-tetrafluoroethyl-2,2,3,3- tetrafluoropropyl ether (TTE), hydrofluorinated ether (HFE) and 2,2,2-trifluoroethyl methyl ether ethylene glycol (TFEG). An example of a fluorinated carbonate is monofluoroethylene carbonate. Non-limiting examples of chlorinated ethers include dichlorodiethyl ether and perchlorodiethyl ether. An example of an ether that is both fluorinated and chlorinated is isoflurane. An example of a chlorinated carbonate is chloroethylene carbonate. The skilled person would easily be able to extrapolate to other halogenated solvents which may be suitable for use. In some embodiments, the second electrolyte may comprise one or more ionic liquids as the solvent. Said ionic liquids may comprise salts comprising organic cations such as imidazolium, ammonium, pyrrolidinium, and/or organic anions such as bis(trifluoromethanesulfonyl)imide TFSI-, bis(fluorosulfonyl)imide FSI-, triflate, tetrafluoroborate BF4- , dicyanamide DCA-, chloride Cl-. The ionic liquid is liquid at room temperature (20 °C). Examples of suitable ionic liquids include (N,N-diethyl-N-methyl- N(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl), N,N-diethyl-N-methyl-N- propylammonium bis(fluorosulfonyl)imide, N,N-diethyl-N-methyl-N-propylammonium bis(fluorosulfonyl)imide, N,N-dimethyl-N-ethyl-N-(3-methoxypropyl)ammonium bis(fluorosulfonyl)imide, N,N-dimethyl-N-ethyl-N-(3-methoxypropyl)ammonium bis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-benzyl ammonium bis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-Ethyl-N-phenylethyl ammonium bis(trifluoromethanesulfonyl)imide, N-Ethyl-N,N-dimethyl-N-(2- methoxyethyl)ammonium bis(fluorosulfonyl)imide, N-Ethyl-N,N-dimethyl-N-(2- methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, N-tributyl-N- methylammonium bis(trifluoromethanesulfonyl)imide, N-tributyl-N-methyl ammonium dicyanamide, N-tributyl-N-methylammonium iodide, N-trimethyl-N-butyl ammonium bis(trifluoromethanesulfonyl)imide, N-trimethyl-N-butylammonium bromide, N-trimethyl- N-hexylammonium bis(trifluoromethanesulfonyl)imide, N-trimethyl-N-propylammonium bis(fluorosulfonyl)imide, N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, (N,N-diethyl-N-methyl-N(2methoxyethyl)ammonium bis(fluorosulfonyl)imide, 1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide, 1-ethyl- 3-methylimidazolium bis(fluorosulfonyl)imide, 1-methyl-1-(2-methoxyethyl)pyrrolidinium bis(fluorosulfonyl)imide, N,N-diethyl-N-methyl-N-propylammonium bis(fluorosulfonyl)imide, N-Ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide, N-propyl-N-methylpiperidinium bis(fluorosulfonyl)imide, N- trimethyl-N-butyl ammonium bis(fluorosulfonyl)imide, N-methyl-N-butyl-piperidinium bis(trifluoromethanesulfonyl) imide, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, or a combination thereof. Alternatively, or additionally, the second electrolyte may be a gel electrolyte. As used herein, the term “gel electrolyte” refers to electrolytes where the liquid is in a gel matrix, whereby “gel” is understood to be a stationary or non-flowing amorphous liquid when measured at room temperature (i.e., at or about 20°C). As the skilled person may appreciate, any gel may melt at higher or elevated temperatures, such as those experienced by an electrolytic cell in use, as the kinetic energy of gel components exceeds the inter- and intramolecular forces that provide the gelation. In some embodiments, it may be an advantage to provide an electrolyte that is a gel at room temperature (i.e., when not in use) which then melts to be a liquid at elevated operating temperature, before then re-gelling as the temperature drops. In some embodiments, the gel electrolyte may comprise polyethylene oxide with a gelling liquid electrolyte, for example an ether such as dimethyl ether. In one example, the gel electrolyte may comprise polyethylene oxide in combination with LiTFSI in dimethylether. In certain embodiments, the second electrolyte comprises a solvent selected from linear ethers, diethyl ether (DEE), tetrahydrofuran (THF), Dimethoxyethane (DME), Dioxolane (DIOX), Diglyme, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl acetate (EA) and methyl butyrate (MB), methyl ethyl ketone, acetonitrile (ACN), propionitrile (PN), isobutyronitrile (iBN), Dimethylformamide (DMF), Dimethylacetamide (DMAc), N-Methyl-2-pyrrolidone (NMP), Tetramethyl urea (TMU), Dimethyl sulfoxide (DMSO), Trimethyl phosphate, Triethyl phosphate, Hexamethylphosphoramide, toluene, benzene, heptane, xylene, dichloromethane, ionic liquids, fluorinated ethers, fluorinated carbonates, fluorinated sulfones, fluorinated esters, fluorinated ketones, fluorinated nitriles, fluorinated amides, fluorinated lactams, fluorinated ureas, fluorinated phosphates, fluorinated phosphoramides, gels, or any combination thereof; and at least one alkali metal salt. Any combination of one or more of the above solvents may be included in the second electrolyte. For example, the second electrolyte may comprise the combination of an ionic liquid with a fluorinated ether, or the combination of an ionic liquid within a gel, or the combination of a fluorinated ether within a gel. It is believed that a skilled person could suitable and routinely adjust the solvent system as required. The second electrolyte may comprise a combination of two or more of any of the liquids and/or gels detailed above. In some embodiments, the alkali metal salt comprises lithium when the anode comprises lithium or a lithium alloy. In other embodiments, the alkali metal salt comprises sodium when the anode comprises sodium or a sodium alloy. When the alkali metal salt comprises lithium, the alkali metal salt may be at least one lithium salt selected from lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium perchlorate, lithium sulfate, lithium nitrate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethane)sulfonimide, lithium bis(fluorosufonyl)imide, lithium bis(oxalate) borate, lithium difluoro(oxalate)borate, lithium bis(pentafluoroethanesulfonyl)imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazole, or a combination thereof; or when the alkali metal salt comprises sodium, at least one sodium salt selected from sodium hexafluoroarsenate, sodium hexafluorophosphate, sodium perchlorate, sodium sulfate, sodium nitrate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethane)sulfonimide, sodium bis(fluorosufonyl)imide, sodium bis(oxalate) borate, sodium difluoro(oxalate)borate, sodium bis(pentafluoroethanesulfonyl)imide, sodium 2-trifluoromethyl-4,5-dicyanoimidazole, or any suitable combination thereof. In some embodiments, the alkali metal salt is lithium trifluoromethanesulfonate (also known as lithium triflate or LiOTf), lithium bis-trifluoromethanesulfonimide (LiTFSI), and/or lithium bis(fluorosulfonyl)imide (LiFSI). In conventional Li-S cells, LiFSI lacks stability in the presence of polysulfides, such that this salt would usually be considered unsuitable. However, with cathodes of the invention detailed below, which operate without the formation of polysulfides, the electrolyte can include salts and solvents, such as LiFSI, that otherwise would not be stable, resulting in a broader range of materials that can be used in the fabrication of the claimed cells. As the skilled person would be aware, any suitable mechanism for ensuring a low (or relatively low) polysulfide and/or low polyselenide solubility (i.e., sufficient to prevent, or reduce, or at least significantly or substantially reduce the shuttling effect) for the second electrolyte can be implemented. For instance, the low (or relatively low) solubility may be achieved through the selection of solvents, ionic liquids and/or gels in which polysulfides and/or polyselenides are insoluble, or substantially insoluble. Alternatively, or as well, increased concentration of dissolved salts in a solvent is also known to reduce analyte solubility in a solvent system, such as via the “Common-ion effect” or the like. Therefore, in some embodiments, the concentration of the at least one alkali metal salt is at least 75% of the saturation concentration of the electrolyte. As used herein, the term “saturation concentration” relates to the extent of solubility of a particular solute in a particular solvent. The point of saturation is where the addition of solute does not result in an increase in concentration. In certain embodiments, the concentration of the at least one alkali metal salt is at least 80% of the saturation concentration of the solvent system, or at least 85% of the saturation concentration of the solvent system, or at least 90% of the saturation concentration of the solvent system, or may be about 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 98.5, 99, 99.5, 99.9 or 99.99% or any range therein. It may be the case that the concentration of the at least one alkali metal salt is about 100% of the saturation concentration, i.e., the electrolyte is fully saturated, or substantially saturated, by the alkali metal salt. In some embodiments, the concentration of the alkali metal salt will be in the range of 75% to 90%, or 80% to 100%, or 80% to 90%, or 85% to 95%, or 90% to 99% of the saturation concentration of the solvent system in the electrolyte. For example, the concentration of lithium or sodium salt in the electrolyte may be within the range of 0.05 M to 10 M, or between 1 M to 5 M, or between 2 M and 4 M, for example, about 3 M. It may be the case that the lithium salt is present in the electrolyte at a concentration of 0.1 M to 6 M, or between 0.5 M to 5 M, or between 1 M and 4 M, or between 2.5 M and 3.5 M for example, about 3 M. As the skilled person would appreciate, the saturation concentration is commonly determined at room temperature, for example at about 20 °C. The saturation concentration of polysulfides and/or polyselenides is within a particular solvent may be determined by known methods, for example by determining the point at which just enough electrolyte is added to dissolve all solid residues. In embodiments of the present invention with a high dissolved salt concentration in the second (i.e., liquid or gel) electrolyte, such as those described above with at least 75% or higher salt saturation, it is further anticipated that such liquid electrolytes will have a protective effect on the first (i.e., solid) electrolyte. Without being bound to any particular theory, it is understood that a liquid electrolyte with a high salt concentration may significantly prevent not only the dissolution of polysulfides and/or polyselenides, but also the dissolution or degradation of the solid electrolyte, particularly in embodiments where the first (i.e., solid) electrolyte is a ceramic material which may be susceptible to degradation by liquid solvents, such as argyrodite or lithium phosphorous sulfide (LPS). It is an advantage of the present invention that low or lean levels of the second (i.e., liquid or gel) electrolyte are present in the electrolyte system of the present invention. In some preferred embodiments, the electrolyte loading of the second electrolyte is in the range of up to about 3 µL/mAh, such as from about 0.1 µL/mAh to about 3 µL/mAh, or in the range of from about 0.3 µL/mAh to about 2.5 µL/mAh, or in the range of about 0.5 µL/mAh to about 2 µL/mAh. Typically, conventional Li-S and Li-Se electrolytic cells require a high amount of electrolyte (i.e., high loading) to dissolve polysulfides and/or polyselenides contained in the cathode. The cells according to the present invention advantageously do not require a high electrolyte loading compared to conventional cells. As the skilled person would appreciate, low electrolyte loading is beneficial as it makes the overall cell lighter, resulting in higher gravimetric energy. Without being bound to any theory, it is understood by the inventor that the combination of a polysulfide (or polyselenide)-insoluble liquid or gel electrolyte, in combination with a low porosity solid electrolyte, allows for low loadings of liquid or gel electrolytes to be used, thereby providing increased gravimetric energy. Electrochemical Cells Advantageously, electrochemical cells according to the present invention have superior gravimetric energy density and volumetric energy density compared to existing hybrid cells, which is provided, at least in part, by a decrease in liquid electrolyte loading. Moreover, it is expected that such cells have improved safety and cyclability when compared to conventional Li-S or Li-Se cells, since: - there is a decrease in the volume of solvents present in the liquid portion of the electrolyte system, increasing safety of the cells in use (if flammable or explosive solvents are required); - the low-porosity first electrolyte acts as a physical barrier to prevent physical contact between the second electrolyte and the anode (meaning that there is no degradation of the second electrolyte during cycling), but it also acts as a barrier against the formation of lithium or sodium dendrites; and - the second electrolyte is selected such that the first electrolyte is not degraded or dissolved. Without being bound by theory, the charging and discharging cycles of the electrochemical cell according to the present invention is believed to operate via a solid- state (or pseudo-solid-state, or quasi-solid-state, or solid-state-like) mechanism. It is understood that this beneficial solid-state (or solid-state-like) mechanism may occur via the formation of solid (i.e., unsolvated) polysulfide and/or polyselenide species in the low-solubility second electrolyte, thereby approximating a solid-state electrolyte when used in combination with a solid electrolyte. In such solid-state or solid-state-like systems, cathodes according to conventional Li-S/Li-Se cells and Li-S/Li-Se solid state cells may have insufficient transport of lithium and/or sodium ions to the active sulfur and/or selenium species present in the cathode, and/or an insufficient cathode interface to enable high sulfur/selenium utilisations via a solid-state mechanism. However, the use of an electrolyte system according to the first aspect (i.e., a first electrolyte comprising a solid electrolyte combined with a second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof, with low polysulfide and/or selenide solubility) in an electrochemical cell of the present invention is expected to beneficially mitigate this issue via the formation of solid polysulfide and/or solid polyselenide species that remain in or near to the cathode. The inventor also anticipates that other properties of the polysulfide and/or polyselenide species may also contribute to the inhibition of the “shuttling” effect, such as the lack of ionic charge on polysulfide/polyselenide species present in the second electrolyte (particularly liquid electrolytes with a high dissolved salt concentration), or the specific species formed (such as longer chain polysulfides being preferentially formed in the liquid electrolyte). The term “anode” takes its usual meaning in the art and relates to the negative electrode of a cell. The anode releases electrons to the circuit (and effectively oxidises) during the electrochemical reaction. The term “cathode” takes its usual meaning in the art and relates to the positive electrode of a cell. The cathode acquires electrons from the circuit (and is effectively reduced) during the electrochemical reaction. In some embodiments, the first electrolyte has a first surface and a second opposing surface, wherein the first surface is in contact with a surface of the anode and wherein the second surface is in contact with the second electrolyte. It may be the case that at least a portion of the first surface of the first electrolyte is in direct contact with at least a portion of a surface of the anode. As used herein, the term “direct contact” means that there are no additional layers or material present between the first surface of the first electrolyte and the anode. Such a construction means that the second electrolyte will not come into contact with the anode, particularly when a low porosity first electrolyte (as described above) is used. Accordingly, in electrolytic cells of the present invention, there can be no liquid electrolyte, gel electrolyte, or a combination thereof as claimed between the solid electrolyte and anode, or in contact with the anode, or distributed throughout the first electrolyte, as is commonly the case with known cells that utilise a hybrid electrolyte. As used herein, the term “surface” takes its usual meaning, and relates to the exterior of an object, layer, or structure. In some embodiments the first electrolyte will be substantially planar, in the sense that it will comprise a sheet material, or a layer applied directly or indirectly to the surface of the anode. In certain embodiments, the cell further comprises an additional first electrolyte positioned on an opposing surface of the anode, such that the anode is positioned between two separate first electrolytes. Often, at least a portion of each of the surfaces of the anode are in direct contact with the two separate first electrolytes. In some embodiments, the electrochemical cell comprises a separator. The separator may be formed from a wide variety of materials. Examples of material used for the separator include, but are not limited to, polyolefin-based materials such as polyethylene, polypropylene, or combinations thereof. Anode In some embodiments, there is provided an electrochemical cell according to the first aspect of the invention, wherein the anode comprises an alkali metal, an alkali metal alloy, silicon, carbon, or a silicon-carbon composite material. In certain preferred embodiments, the alkali metal or alkali metal alloy comprises lithium and/or sodium. In some embodiments, the anode comprises a foil formed of lithium metal or lithium metal alloy. Examples of lithium alloys include, but are not limited to, lithium indium alloy, lithium aluminium alloy, lithium magnesium alloy and lithium boron alloy. In other embodiments the anode comprises a foil formed of sodium metal or sodium metal alloy. Examples of sodium alloys include, but are not limited to, sodium indium alloy, sodium aluminium alloy, sodium magnesium alloy and sodium boron alloy. Commonly, the anode is a lithium metal foil or a sodium metal foil because of their high specific capacity. In some embodiments, the anode may comprise silicon. Where the anode comprises silicon, it may be lithiated or sodiated. As used herein, the term “lithiated” takes its usual meaning in the art and refers to the combination or impregnation with lithium or a lithium compound. Similarly, the term “sodiated” takes its usual meaning in the art and refers to the combination or impregnation with sodium or a sodium compound. Preferably, the lithiation or sodiation step occurs before assembly of the electrolytic cell (i.e., the silicon comprises lithium or sodium ions before the initial charge/discharge cycle). In some embodiments, the anode may comprise carbon, for instance the anode may comprise carbon nanotubes, carbon nanofibers, graphene, graphene oxide, graphite, carbon black, or a combination thereof. Carbon-containing anodes may also be lithiated or sodiated in some embodiments. In some embodiments, the anode may comprise a silicon-carbon composite material. Examples of silicon-carbon composites include, but are not limited to, silicon-doped graphite. Composite silicon-carbon anodes may also be lithiated or sodiated in some embodiments. Cathode In some embodiments, the cathode comprises (i) selenium, sulfur, or a combination thereof; and (ii) a carbonaceous material, a metallic material, a metalloid material, a polymer, or a combination thereof. In such embodiments, the cathode comprises at least about 40 wt% sulfur and/or selenium based on the total weight of the cathode, or at least about 60 wt%, at least about 70 wt% or at least about 75 wt% sulfur and/or selenium, or the cathode may comprise 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 99 wt% sulfur and/or selenium based on the total weight of the cathode, or any range therein. The cathode may be porous, whereby “porous” and “porosity” have the same meanings as above for the first electrolyte. In some embodiments, the porosity of the cathode may be in the range of from about 10% to about 60%, or between about 15% and about 45%, or between about 20 wt% and about 40 wt%, such as about 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38 or 40 wt% or any range therein. A porosity in these ranges provides a good balance between penetration of the second electrolyte into the cathode and structural integrity of the cathode. The cathode may comprise a solid comprising at least one of a carbonaceous material, a metallic material, a metalloid material, a polymer, or any combination thereof. The solid may be present in the cathode at a level of at least about 10 wt%, at least about 20 wt%, or at least about 30 wt%, or between about 10 wt% and about 20 wt%, or between about 15 wt% and about 30 wt%, or in the range 0.1 to 30 wt%, or about 1 to about 20 wt%, or about 5 to about 10 wt%, such as about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40 wt% or any range therein. In one embodiment the cathode may comprise (i) selenium, sulfur, or a combination thereof; and (ii) a carbonaceous material, a metallic material, a metalloid material, a polymer, or a combination thereof is in the form of a composite. As noted above, the term “composite” takes its usual meaning in the art and relates to materials made from two or more constituent materials having different chemical or physical properties from one another. When the two or more constituent materials are combined, the resultant composite material has properties different to the individual components present. The composite can be manufactured by known techniques, such as melt diffusion, a solution-based process, or mechanical grinding or any method known to the skilled person. Thermal annealing could be performed as an optional step following the melt diffusion step. In some embodiments, the cathode comprises a carbon-sulfur composite, a metal sulfide, a polymer-sulfur composite, a carbon-selenium composite, a carbon-sulfur- selenium composite, a metal selenide, a polymer-selenium composite, a metal sulphoselenide, a metalloid sulfide, a metalloid selenide, or a combination thereof. When present, the carbonaceous material may comprise micropores, mesopores, or a combination of micropores and mesopores. In such embodiments, the micropores will be of pore diameter in the range of 0.1 nm to 2 nm, often in the range of 0.5 nm to 1.5 nm. Optionally, the mesopores will be in the range of 2 nm and 50 nm, often in the range of 5 nm and 30 nm. As used herein, the term “nm” takes its usual meaning and is the symbol denoting the unit of length “nanometre”. When present, the carbonaceous material may comprise carbon black (such as acetylene black, channel black, furnace black, lamp black and thermal black), activated carbon, graphene, reduced graphene oxide, carbon nanofibers, carbon nanotubes (CNT), multi- walled carbon nanotubes (MWCNT), microporous carbon, mesoporous carbon, carbon comprising micropores and mesopores, or a combination thereof. As used herein, the term “graphene” is intended to include two-dimensional graphene and three-dimensional graphene. In some embodiments, the graphene will be three-dimensional. It is understood that carbonaceous materials generally have a very high electron conductivity, which results in high charge/discharge capacities. As used herein, the term “microporous” takes its normal meaning in the art and refers to materials containing interconnected pores of less than 2 nm in size (i.e., micropores). As used herein, the term “mesoporous” takes its usual meaning in the art. For instance, according to IUPAC nomenclature, a mesoporous material is a nanoporous material containing pores with diameters between 2 nm and 50 nm (i.e., mesopores). In some embodiments, the carbonaceous material may be further doped with a heteroatom. Examples of dopants include, but are not limited to, nitrogen, boron, oxygen, sulfur, or phosphorous. In preferred embodiments, the carbonaceous material is doped with boron, or the carbonaceous material is boron-doped graphene. Without being bound to any theory, it is understood that doping the carbon network results in an increase in the electronic conductivity of the carbonaceous material and further improves the mechanical robustness of the resultant cathode. When present, the metallic material may comprise a metal, a metal oxide, a metal hydroxide, a metal sulfide, or a combination thereof. As used herein, the term “metal” is intended to include all metal elements, such as transition and post-transition metals, alkali metals, alkaline earth metals, lanthanides, and actinides. Examples of metals include, but are not limited to nickel, manganese, platinum, silver, gallium, copper, palladium, or a combination thereof. Examples of metal oxides include, but are not limited to, zinc oxide, aluminium oxide, titanium oxide, vanadium oxide, ruthenium oxide, nickel oxide, manganese oxide, or a combination thereof. Often, the metal oxide comprises manganese oxide. Examples of metal hydroxides include, but are not limited to, cobalt (II) hydroxide, nickel (II) hydroxide, or a combination thereof. An example of a metal sulfide includes, but is not limited to, molybdenum sulfide. Metallic materials allow cathodes with high structural rigidity and electron conductivity. When present, the metalloid material may comprise a metalloid, a metalloid oxide, a metalloid sulfide, a metalloid nitride, or a combination thereof. As used herein, “metalloid” has the same meaning common in the art to refer the chemical elements with characteristics between metals and non-metals. Examples of metalloids include, but are not limited to silicon, boron, germanium, antimony, arsenic, tellurium, or a combination thereof. Examples of metalloid oxides include, but are not limited to, silicon oxide, germanium oxide, boron oxide or a combination thereof. Examples of metalloid sulfides include, but are not limited to, boron sulfide, germanium sulfide, antimony sulfide, or any combination thereof. Examples of metalloid nitrides include, but are not limited to, boron nitride, germanium nitride, antimony nitride, tellurium nitride, or a combination thereof. Optionally, boron nitride may be in the form of a boron nitride aerogel, a boron nitride nanomesh, or boron nitride nanotubes. In preferred embodiments, the metalloid material comprises boron nitride nanotubes. When present, the polymer material may comprise at least one polymer selected from: polyacrylonitrile; cellulose; a polyether (an example includes, but is not limited to, polyethylene glycol (PEG)); polyvinylpyrrolidone (PVP); poly(3,4- ethylenedioxythiophene) (PEDOT); poly(3,4-ethylenedioxythiophene); polystyrene sulfonate (PEDOT:PSS); polythiophene (PTh); polydopamine (PDA); polyaniline (PANI); triallyl isocyanurate polymer; polypyrrole (PPY); an ionomer (examples include, but are not limited to, a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion^®)), and copolymers of ethylene and acrylic and/or methacrylic acid); an ethylene oxide (EO) based polymer (an example includes, but is not limited to, PEO); an acrylate based polymer (an example includes, but is not limited to, PMMA); a polyamine (an example includes, but is not limited to, polyethyleneimine); a siloxane (an example includes, but is not limited to, poly(dimethylsiloxane)); a polyheteroaromatic compound (an example includes, but is not limited to, polybenzimidazole); a polyamide (examples include, but are not limited to, Nylons), a polyimide (an example includes, but is not limited to, Kapton^®); a polyvinyl polymer (examples include, but are not limited to, poly(2-vinyl pyridine), poly(vinyl acetate), poly (vinyl alcohol), poly(vinyl chloride), and poly(vinyl fluoride)); a polycyanoacrylate (an example includes, but is not limited to, poly(methylcyanoacrylate)); an inorganic polymer (examples include, but are not limited to, polysilane, polysilazane, polyphosphazene, polyphosphonate); a polyurethane; a polyolefin (examples include, but are not limited to, polyacrylamide, polypropylene, polytetrafluoroethylene)); a polyester (examples include, but are not limited to, polycarbonate and polybutylene terephthalate); or any combination thereof. When two or more of the above polymers are present, these may be combined to form a polymer blend (i.e., at least two distinct homopolymer chains melted and mixed together without covalently bonding) or they may be co-polymers (i.e., where two or more different monomers are covalently bound in the same polymer chain) or any other suitable form known to the skilled person. As used herein, the term “ionomer” is intended to take its usual meaning in the art, and refers to synthetic polyelectrolytes, which consist of both electrically neutral and ionized groups along the polymer backbone. The electrically neutral and ionized groups can be regularly distributed or randomly distributed. The term “inorganic polymer” is intended to take its usual meaning in the art, and refers to polymers with an inorganic backbone, which is composed of atoms other than carbon. As used herein, the term “polyvinyl polymer” is intended to take its usual meaning in the art and refers to polymers derived by polymerization from compounds containing the vinyl group. In some preferred embodiments, the polymer may inherently be electrically or ionically conductive and comprise at least one of polyacrylonitrile, cellulose, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polythiophene (PTh), polydopamine (PDA), nylon, polyaniline, triallyl isocyanurate, polypyrrole, or any combination thereof. In certain embodiments, the carbonaceous material, the metallic material, the metalloid material, the polymer, or any combination thereof, when present, may be in the form of hollow core-shell particles. As used herein, the term “hollow core-shell particle” takes its usual meaning in the art and refers to particles comprising a shell surrounding a hollow core, which is effectively a single pore. The pore may be a void, or may contain an active or inactive material, such as sulfur or selenium, which may pass into and out of the pore during cycling or manufacture. In preferred embodiments of the electrolytic cell of the present invention, following cathode formation, sulfur and/or selenium is generally housed within the hollow core- shell particles. As such, following cathode formation, the hollow core-shell particles may be at least partially filled with sulfur and/or selenium, or largely or substantially or completely filled; however, it is advantageous if the particles are only partially filled (for example, in the range of between about 5 – 80 vol%, or about 10 – 50 vol%, or about 25—75 vol%, such as about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 or 80 vol%), as the inventor understand that this amount of sulfur and/or selenium reduces the mechanical stress undergone by the shell structure as sulfur and/or selenium expands or contracts during cycling, and enables extended cycle life. In some embodiments, the sulfur and/or selenium may at least partly covering the shell of the particle, optionally covering substantially all of the shell of the hollow core-shell particle, such that the sulfur permeates from the shell of the core-shell particle into the hollow core. As used herein, “covering substantially all of the shell of the hollow core-shell particle” is intended to mean that at least 70% of the shell is covered, or at least 80%, or at least 90%, such that the upper limit would be 100%, 99.9% or possibly 99%, that is, about 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, 99.9, 99.99 or 100% is covered, or any range therein. Incorporation of hollow core-shell particles comprising at least one of a carbonaceous material, a metallic material, a metalloid material, a polymer, or any combination thereof, allows for a mechanically stable host structure for the delithiation and lithiation of sulfur and/or selenium (and subsequent volume expansion). Moreover, without being bound by any theory, the inventor understands that particles having a hollow core-shell structure are generally electronically conductive, and when combined with sulfur and/or selenium (for instance using melt diffusion techniques), sulfur and/or selenium can be housed within the core of the particles and remain there during cycling. As such, sulfur and/or selenium utilisation is expected to be high, advantageously leading to higher charge/discharge capacities. In some embodiments, the hollow core-shell particles have an average particle diameter in the range of from 0.1 nm to 40 nm, or in the range of from 0.5 nm to 35 nm, or in the range of from 1 nm to 30 nm, or in the range of from 4 nm to 20 nm, or in the range of from 3 nm to 15 nm, such as about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40 nm. Average particle diameters in this range are expected to have high interfacial contact between sulfur and the core-shell particles, which allows for electrochemical cells having high sulfur utilisation. Particle size can be determined using any known suitable analysis technique, such as dynamic image analysis (DIA), static laser light scattering, dynamic light scattering (DLS), sieve analysis, or by visual analysis of Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM) images. When present, the hollow core-shell particles may have any suitable geometry. They may have one of a wide range of geometries including, but not limited to, spherical, cubic, prismatic, pentagonal, hexagonal, heptagonal, or octagonal. The geometries will often be mathematically imperfect, such that they may be “substantially” of a given geometry. As used herein, with regard to these geometries, the term “substantially” can be taken to mean clearly recognisable as a given geometry (for instance spherical), but not mathematically of that geometry (e.g., not a perfect sphere). This could include elongation along one axis by, perhaps, ±20% or ±10%, maybe in the range 20% or 10% to 1%; the presence of surface roughness be that protrusions or recesses in the surface of, perhaps, ±10% or less (maybe 10% - 1%) of the thickness of the shell. In certain embodiments, the hollow core-shell particles may be substantially spherical. Spherical hollow core-shell particles have a high surface area, which results in a high sulfur loading and therefore high sulfur utilisation. The hollow core-shell particles will generally form a complete shell surface. However, in some instances, it may be the case that at least a proportion of the particles are partially formed, such that there are holes present in the form of a missing face or faces (or part faces) of the surface of the shell. In such embodiments, at least about 75% of the hollow core-shell particles will form a complete shell surface, or at least about 80%, or at least about 85%, or at least about 90%, such that the upper limit would be about 100%, 99.9% or possibly 99%, for instance it may be about 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, 99.9, 99.99 or 100% complete. When at least 75% of the hollow core-shell particles form a complete shell surface, it is understood that the particles are more robust to cycling and more resistant to degradation during battery operation. When present, the hollow core-shell particles may have a unimodal, bimodal, or multimodal particle size distribution. Often, the hollow core-shell particles have a unimodal particle size distribution. When present, the hollow core-shell particles may have a shell thickness in the range of from about 0.01 and about 50 nm, or from about 0.1 nm to about 40 nm, or from about 0.5 to about 30 nm or from about 1 to about 25 nm, such as about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50 nm. The inventor understands that this range allows for improved structural rigidity and elasticity of the particles in some embodiment, such that they can better withstand cell swelling. The shell of the hollow core-shell particles may be porous, or partially porous, in addition to or instead of holes being present as described above. As used herein the term “porous” is to be given its common meaning in the art and refers to the presence of one or more pores, often many pores, in the shell. Each pore will typically be of cross- section in the range of from 0.1 to 3.0 nm, or in the range of from 0.3 to 2.0 nm or may be about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0 nm or any range therein. As mentioned above, the hollow core-shell particles may comprise a carbonaceous material, a metallic material, a metalloid material, a polymer, or a combination thereof. As such, all four components may be present, or three, or two, or just any one of the components. In some embodiments, the cathode may comprise a carbon-sulfur composite, a metal sulfide, a polymer-sulfur composite, a carbon-selenium composite, a carbon-sulfur- selenium composite, a polymer-selenium composite, a metalloid sulfide, or combination thereof. In certain embodiments, the carbon-sulfur composite and/or carbon-selenium composite comprises a carbonaceous material selected from at least one of graphene, reduced graphene oxide, carbon nanofibers, carbon nanotubes (CNT), multi-walled carbon nanotubes (MWCNT), microporous carbon, mesoporous carbon, carbon black (such as acetylene black, channel black, furnace black, lamp black and thermal black) and activated carbon. The carbonaceous material may be in the form of hollow core-shell particles (e.g., hollow core-shell carbon black particles). Carbonaceous hollow core-shell particles have a very high electron conductivity, which results in high charge/discharge capacities. Examples of carbon-sulfur composites include, but are not limited to, sulfur-graphene, sulfur-reduced graphene oxide, sulfur-carbon nanofibers, sulfur-CNT, sulfur-MWCNT, sulfur-microporous/mesoporous carbons (e.g., S-CNovel), sulfur-Black Pearls 2000®. Examples of carbon-selenium composites include, but are not limited to, selenium- graphene, selenium-reduced graphene oxide, selenium-carbon nanofibers, selenium- CNT, selenium-MWCNT, selenium-microporous/mesoporous carbons (e.g., S-CNovel), or combinations thereof. An Example of a carbon-sulfur-selenium composite includes, but is not limited to, carbon black-sulfur-selenium composites. Specific examples of carbon black may include, but is not limited to, CNovel® and MSC-30. Examples of polymer-sulfur composites include, but are not limited to, sulfur-nylon, sulfur-polyaniline, sulfur-triallyl isocyanurate, sulfur-polypyrrole, or combinations thereof. In some embodiments, the cathode may comprise a metal sulfide, a metal selenide, a metal sulphoselenide, a metalloid sulfide, a metalloid sulfide, or a combination thereof. In some embodiments, the cathode comprises a metal sulfide. Optionally, the metal sulfide has a one-dimensional structure including, but not limited to, nanotubes, wires, and rods. Such structures allow for a high metal/sulfur interface, which result in fast kinetics. In addition, the use of one-dimensional structures provides a cathode with good structural stability. Moreover, without being bound by theory, it is believed that the use of one-dimensional structures allows for higher sulfur loadings, which would result in a cell having both high gravimetric energy and volumetric energy densities. In other embodiments, the metal sulfide has a two-dimensional layered structure. Two- dimensional layered structures, such as two dimensional nanosheets, form networks through overlapping and stacking with one another. Without being bound by theory, these structures have a large metal/sulfur interface able to effectively trap the polysulfides formed, holding these in place through chemical bonds. The high metal/sulfur interface also generally results in faster reaction kinetics. In addition, without being bound by theory, it is believed that a layered structure is able to accommodate the volume expansion of sulfur and conduct lithium ions (Li⁺) and/or sodium ions (Na⁺). Moreover, a layered structure can be exfoliated to obtain small particles and increase the electrochemical performance of the battery. In some other embodiments, the metal sulfide may have a three-dimensional structure including, but not limited to, metal sulfide nanoparticles such as core-shell structured metal sulfides and flower-like metal sulfide nanomaterials. As the skilled person would appreciate, three-dimensional structures can withstand volume expansion of sulfur and/or selenium. Without being bound by theory, polysulfides could be held within three- dimensional structures. As such, use of three-dimensional structures provides a cathode with optimised kinetics. In addition, three-dimensional structures can have higher sulfur loadings compared to one or two-dimensional structures, which provides a cell with a higher gravimetric and volumetric energy density. The metal sulfide may comprise one or more metals, such that mono-metal sulfides may be used or mixed-metal sulfides comprising two, three or more metals (bi-metal, tri- metal or multi-metal systems). The mono-metal sulfide when present may have the structural formula MxSy, whereby M is a metal, 1≤x≤3, and 1≤y≤4. The metal may be a transition metal, an alkali earth metal, an alkali metal, or a post-transition metal (i.e., metals found in groups 13-16 of the periodic table). Optionally, the metal may be selected from molybdenum (Mo), tin (Sn), titanium (Ti), vanadium (V), tungsten (W), tantalum (Ta), hafnium (Hf), or rhenium (Re) or occasionally combinations thereof. The mono-metal sulfide may be selected from α-manganese sulfide (α-MnS), β- manganese sulfide (β-MnS), γ-manganese sulfide (γ-MnS), iron sulfide (FeS, Fe3S4), ferrous disulfide (FeS2), cobalt sulfide (CoS, CoS2, Co3S4, and Co9S8), zinc sulfide (ZnS), copper sulfide (CuS), bismuth (III) sulfide (Bi2S3), germanium sulfide (GeS), germanium disulfide (GeS2), lithium sulfide (Li2S), calcium sulfide (CaS), tin (II) sulfide (SnS), tin (IV) sulfide (SnS2), antimony trisulfide (Sb2S3), indium sulfide (In2S3), α-indium sulfide (α-In2S3), β-indium sulfide (β-In2S3), γ-indium sulfide (γ-In2S3), zirconium sulfide (ZrS), cerium sulfide (Ce2S3), molybdenum disulfide (MoS2), molybdenum trisulfide (MoS3), silver sulfide (Ag2S), cadmium sulfide (CdS), tungsten disulfide (WS2), nickel sulfide (NiS), vanadium sulfide (VS2), titanium sulfide (TiS2, Ti0.67S), lead sulfide (PbS), niobium sulfide (NbS), niobium disulfide (NbS2), tantalum disulfide (TaS2), tellurium disulfide (TeS2), rhodium(III) sulfide (Rh2S3), palladium sulfide (PdS), palladium disulfide (PdS2), rhenium disulfide (ReS2), osmium sulfide (Os2S3), platinum sulfide (PtS), iridium disulfide (IrS2), iridium(III) sulfide (Ir2S3), chromium sulfide (CrS), chromium(III) sulfide (Cr2S3), barium sulfide (BaS), strontium sulfide (SrS), caesium sulfide (Cs2S), rubidium sulfide (Rb2S), thallium(I) sulfide (Tl2S), beryllium sulfide (BeS), ytterbium sulfide (YbS), hafnium disulfide (HfS2), or combinations thereof. It is noted that the term “copper sulfide” includes chemical compounds and minerals with the formula CuxSy, where 0.5≤ Cu ≥2 and 0.5≤ S ≥2. For instance, the term copper sulfide may include Cu1.12S, Cu1.39S, Cu1.6S, Cu1.75S, Cu1.8S, Cu1.8S, or Cu1.96S. It is noted that the term “nickel sulfide” includes NiS2, Ni3+xS2, Ni3S2, Ni6S5, Ni7S6, Ni9S8, and Ni3S4. In some embodiments, the metal sulfide may be a mixed metal sulfide, wherein the metals may be selected from a transition metal ion, an alkali earth metal, an alkali metal, a post-transition metal, or combinations thereof. Optionally, the mixed metal sulfide comprises molybdenum (Mo), tin (Sn), titanium (Ti), vanadium (V), tungsten (W), tantalum (Ta), hafnium (Hf), or rhenium (Re), or combinations thereof. Examples of mixed-metal sulfides include, but are not limited to, Zn1-xCuxS, Cu3SbS4, Fe4.60Ni4.55S8, PbMoS2, Li5A1S4, KCrS2, Cu6WSnS8, Zn1-xCuxS, CuSbS2, Fe5.80Ni3.98S8, CdMoS2, Li2FeS2, KCr5S8, Cu6GeWS8, Zn1-xFexS, Cu5FeS6, FeMoS2, NbMoS2, Li4GeS4, CsTaS3, (CuGa)0.8Zn0.4S2, Zn1-xInxS, Cu12Sb4S13, CoMoS2, CoNi2S4, LiGaS2, Cs2Co3S4, Pb4FeSb6S14, Zn1-xMnxS, Cu2Sb8S13, CoMoS4, FeNi2S4, γ-Li3PS4, K2Ni3S4, Pb4MnSb6S14, Zn1-xCoxS, Cu2GeS3, Co0.5MoS2, ZnCo2S4, LiInS2, Rb2Ni3S4, Ag4MnSb2S6, Zn1-xCexS, CuGaS, Co1- _xRu_xS₂, Ni_0.33Co_0.67S₂, RbCr₅S₈, Cs₂Ni₃S₄, Ag(Fe,Ni)₈S₈, ZnY₂S₄, CuGaS₂, Co_1-xRh_xS₂, Sb_2- xBixS3, CSCr5S8, RbCu4S3, Ag2MnSnS4, Cd1-xZnxS, Cu2WS4, NiMoS2, NiMoS2, Ni0.5MoS2, Rb2Pt3S4, Bi0.94Sb1.06S3, Ni(Bi,Pb)2S2, Cd1-xMnxS, Cu3TaS4, MgMoS2, Rh1-xRuXS2, CS2Pt3S4, NiCoMoS, (CuIn)xZn2(1-x)S2, Sn1-xMoxS, Cu1-xTi2S4, PdMoS2, CoNi2S4, K2Pt4S6, Cu2ZnSnS4, Cu(In,Ga)(Se,S)₂, MnCr₂S₄, Cu_0.89Ti₂S₄, W_1-xMo_xS₂, SnCoS₄, Co_0.4Ru_0.6S₂, Cu₂FeSns₄, (Cu,Fe)(Re,Mo)4S8, CdCr2S4, Cu0.32TiS2, VMo2S4, AgInS4, No0.6Ru0.4S2, Cu2ZnGeS4, Cu10Fe3MoGe3S16, CdIn2S4, Cu0.92Ti2S4, Mo1-xWxS2, Ag3CuS2, NaInS2, CuPbSbs3, Cu10Fe3WGe3S16, [M4In16S33]^10-(where M = Mn, Co, Zn or Cd), Cu0.37TiS2, NiCr2S4, AgIn- 5S8, CuIr2S4, Cu6SnMoS8, Ag6(Cu4Fe2)sb4S12, Cu3VS4, NiCo2S4, AgBiS2, Na3NbS4, Cu2Fe5Ni2S8, (Cu,Fe)(Re,Mo)4S8, CuV2S4, NiV2S4, Ag2WS4, Na3TaS4, Cu10Cu2Sb4S13, Pb4Mo4VSbS15, CdSexS1-x, Cu2MoS4, Ni6MoS4, ZnLn2S4, Rb3NaS4, Cu12VAs3S16, AgMnPb3Sb5S12, CuCoS4, Cu3NbS4, Ni9Sn2S2, MnCo2S4, Rb3TaS4, Cu13VSn3S16, Pb5Mn3Ag2Sb6As4S24, CuInS2, CuCrS2, Ni1-xZnxS, MgIn2S4, K3NbS4, Cu13VGe3S16, Cu10Fe3WGe3S16, Cu1.0In2.0S3.5, CuFeS2, FeMo4S6, MgSc2S4, K3TaS4, CoFe(AsS)2, Cu13V(Sb,Sn,As)3S16, Cu2SnS3, Fe0.5Co0.5S2, FeNi2S4, Pd30Cu10S9, KFes2, Be3Mn4(SiO4)3S, Pb4Mo4VSbS15, Cu3SbS3, Fe3.63Ni5.39S8, FeV2S4, LiAlS2, NaCrS2, (Fe,Zn,Mn)S, or any combination thereof. In other embodiments, the metal sulfide is a metal disulfide. The metal disulfide may be selected from molybdenum disulfide (MoS2), tungsten disulfide (WS2), hafnium disulfide (HfS2), tin sulfide (SnS2), titanium sulfide (TiS2), vanadium sulfide (VS2), tantalum disulfide (TaS2), rhenium disulfide (ReS2) or any combinations thereof. Without being bound by theory, the transition metal disulfides that fall within the transition metal dichalcogenide family are particularly beneficial, as they can be in the form of a monolayer where the metal atom is located between two sulfur atoms. In some embodiments, the metal sulfide comprises molybdenum disulfide. It may be the case that the molybdenum disulfide is in the form of the 1T polymorph (1T-MoS2), 2H polymorph (2H-MoS2), or 3R polymorph (3R-MoS2). Often, molybdenum disulfide is in the form of the 1T polymorph. The octahedral or trigonal antiprismatic geometry of the 1T polymorph is able to form strong bonds with polysulfides, reducing the possibility of polysulfide shuffle. Moreover, the octahedral or trigonal antiprismatic geometry of the 1T polymorph can provide higher lithium diffusion, which leads to enhanced electrochemical performance. In certain embodiments, the metal sulfide is pre-lithiated. The terms “pre-lithiated” and pre-sodiated” take their usual meaning and relate to a pre-treatment step where lithium ions or sodium ions are added to the cell before operation. Without being bound by theory, lithiation of the metal sulfide may increase one or both the electronic and ionic conductivities of the metal sulfide, and consequently the cathode as well. It may be the case that the metal sulfide comprises molybdenum disulfide in the form of the 1T polymorph, and that the molybdenum disulfide in the form of the 1T polymorph is lithiated. In some embodiments, the metal sulfide may be in particulate form. The particles may be of a size in the range of from 1 µm to 20 µm, or in the range of from 1 µm to 5 µm or from 10 to 15 µm, such as about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 µm. It is expected that having metal sulfide particles falling within this size range results in higher sulfur utilisation, which leads to enhanced power performance. Particles can be obtained via any known conventional means including, but not limited to, chemical/physical exfoliation, bead milling, jet milling and/or ball milling. Particle size analysis can be determined using any known techniques, such as dynamic image analysis (DIA), static laser light scattering, dynamic light scattering (DLS), sieve analysis, or by visual analysis of Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM) images. It is expected that a skilled person could easy optimise this process. In certain embodiments, the cathode may further comprise elemental sulfur. The cathode may comprise a metal sulfide further comprising sulfur. For instance, the cathode may comprise metal sulfide-sulfur composites. The metal sulfide may instead or also comprise molybdenum disulfide further comprising sulfur. In embodiments where the cathode comprises sulfur and a metal sulfide, the sulfur may be incorporated into the metal sulfide through conventional methods. For instance, this could be achieved via melt infusion whereby metal sulfides are immersed in sulfur at approximately 150°C to 160°C. Without being bound by theory, when a melt infusion method is used, melted sulfur can diffuse throughout the pores of the metal sulfide. In such embodiments, the average pore diameters of the metal sulfide are in the range of from 0.1 nm and 20 nm, or in the range of from 1 nm and 10 nm, such as about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 nm. It is understood that pore sizes falling within these particular ranges allow for higher sulfur utilisation. As the skilled person would appreciate, average pore diameter can be measured using any known techniques, such as Brunauer– Emmett–Teller (BET) porosimetry or Mercury porosimetry. It may be the case that the metal sulfide has a porous one-dimensional, two- dimensional, or three-dimensional structure. In some embodiments, the metal sulfide further comprises selenium forming a metal sulphoselenide, such as wherein the metal sulphoselenide has the structural formula MS1-xSex, where M is a metal and where 0≤x≤1. The metal may be a transition metal ion, an alkali earth metal, an alkali metal, or a post-transition metal (i.e., metals found in groups 13-16 of the periodic table). It is understood by the inventor that use of a metal sulphoselenide has the advantage of having enhanced power in the cell, owing to the high electronic conductivity of Se. In some embodiments, the cathode may be in particulate form. The particles may be of a size in the range of from 1 µm to 20 µm, or in the range of from 1 µm to 5 µm, or in the range of between 5 to 15 µm, such as about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 µm. Having particles falling within this size range results in higher sulfur and or selenium utilisation, which leads to enhanced power performance of the cell. Particles can be obtained via conventional means including, but not limited to, chemical/physical exfoliation, bead milling, jet milling and/or ball milling. Particle size analysis can be determined using any known techniques, such as dynamic image analysis (DIA), static laser light scattering, dynamic light scattering (DLS), sieve analysis, or by visual analysis of Transmission Electron Microscopy (TEM) or Scanning Electron Microscopy (SEM) images. In some embodiments, the cathode further comprises a current collector. The current collector may comprise any suitable material, such as aluminium, carbon, copper, titanium, or stainless-steel. The current collector may comprise a metal foil, such as aluminium foil, copper foil, titanium foil, or stainless-steel foil. In preferred embodiments, the current collector comprises aluminium foil. The current collector may be further coated with a protective layer. When present, the protective layer may be a carbon-based layer, such that the current collector is a carbon-coated current collector. In embodiments where the current collector comprises aluminium (e.g., aluminium foil), copper (e.g., copper foil), titanium (e.g., titanium foil), or stainless-steel (e.g., stainless- steel foil), it may further be carbon coated. In other embodiments the current collector may comprise carbon coated aluminium foil. The inventor understands that carbon coatings may improve the corrosion resistance of the current collector and adhesion to the cathode materials. In some embodiments, the cathode may have a thickness in the range of from about 20 µm to about 300 µm, or in the range of about 50 µm to about 200 µm, or in the range of from about 75 µm to about 150 µm, such as about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290 or 300 µm. The cathode may be a single or double-sided cathode, although dimensions herein are quoted without the current collector, although the skilled person can easily make the necessary corrections as required. In some embodiments, the cathode may further comprise a binder. Without being bound by theory, the binder may act to bind the cathode components together. Additionally, or alternatively, the binder may also help bind the cathode components to the current collector. In doing so, the binder can provide a cathode with enhanced mechanical robustness and can improve the processability of the cathode. When present, the binder may be guar gum, xanthan gum, gum arabic, a polymeric binder, or any combination thereof. Preferably, the binder may be guar gum, xanthan gum, or a combination thereof. When the binder is a polymeric binder, it may be for example, a polyether such as poly(ethylene oxide)s, polyethylene glycols, polypropylene glycols, polytetramethylene glycols (PTMGs), polytetramethylene ether glycols (PTMEGs), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF- HFP), a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, carboxymethyl cellulose (CMC), styrene butadiene (SBR), polypyrrole, polythiophene, polyaniline, polyvinyl alcohol, poly(ethylene) imine, polyacetylene, polyphenylene vinylene, poly(3,4- ethylenedioxythiophene), polyphenylene sulphide, gelatine, or any mixtures or combinations thereof. In some embodiments, the binder may be selected from halogenated polymers, for instance, the binder may be selected from a fluorinated polymer. Examples of suitable binders include, but are not limited to, poly(vinylidene fluoride) (PVDF), often in the a form poly(trifluoroethylene) (PVF3); polytetrafluoroethylene (PTFE); copolymers of vinylidene fluoride with either hexafluoropropylene (HFP) or trifluoroethylene (VF3) or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE); fluoroethylene/propylene (FEP) copolymers; copolymers of ethylene with either fluoroethylene/propylene (FEP) or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE); perfluoropropyl vinyl ether (PPVE); perfluoroethyl vinyl ether (PEVE); and copolymers of ethylene with perfluoromethyl vinyl ether (PMVE); or blends or mixtures thereof. Other examples of suitable binders include, for instance, polyacrylonitrile, polyurethane, PVDF-acrylic co-polymer; polyacrylic acid, polyimides, and polyvinyl alcohol. Further suitable binders include rubber (e.g., styrene butadiene rubber), cellulose-based binders (e.g., carboxymethyl cellulose), or gelatine. When present, the cathode may comprise 0.05 to 20 wt% binder based on the total weight of the cathode, or between 0.5 to 10 wt%, for example 1 to 5 wt%, such as about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 wt% based on the total weight of the cathode, for example 2 to 3 wt%. In certain embodiments, the cathode may further comprise an ionically conductive material. The ionically conductive material may have a bulk ionic conductivity of greater than 10^-7 S/cm at 25 °C, for example greater than 10^-6 S/cm. Where the cathode contains an electroactive, ionically conductive material such as Li3PS4, or LixPySz, a further ionically conductive material may be absent. When present, the ionically conductive material is selected from a conducting ceramic material, an ionically conducting polymer, or a combination thereof. Presence of an ionically conductive material allows for an increase in the lithium cation conductivity within the cell, which results in improved power performance. The ceramic material may have a crystalline, polycrystalline, partially crystalline, or amorphous structure. Suitable ceramic materials include, but are not limited to, oxides, carbonates, nitrides, carbides, sulfides, oxysulfides, and/or oxynitrides of metals and/or metalloids. Where the anode comprises lithium, a lithium alloy, or silicon, the ceramic material may comprise lithium; similarly, where the anode comprises sodium or a sodium alloy, the ceramic material may comprise sodium. Non-limiting examples of suitable ceramic materials having a sufficient ionic conductivity for use in lithium-based systems or silicon-based systems may be produced by a combination of various lithium compounds, such as ceramic materials including lithium include lithium oxides (Li2O, LiO, LiO2, LiRO2, where R is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and/or lutetium), lithium carbonate (Li2CO3), lithium nitrides (e.g., Li3N), lithium oxysulfide, lithium oxynitride, lithium garnet-type oxides (e.g., Li7La3Zr2O12)), Li10GeP2S12, lithium phosphorus oxynitride, lithium silicosulfide, lithium germanosulfide, lithium lanthanum oxides, lithium titanium oxides, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium halides, and combinations of the above. In certain cases, the ceramic material comprises a lithium oxide, a lithium nitride, or a lithium oxysulfide. In some cases, the ceramic includes a carbonate and/or a carbide. Examples of ceramic materials that can be used as a lithium-ion containing conductive material include: an argyrodite (i.e., Li7-pBS6-pXp, wherein B is phosphorous or arsenic, X is chlorine, bromine or iodine, and p is between 0 and 1), Li-containing oxides such as Li3.3La0.56TiO3; Nasicon structure such as LiTi(PO4)3; LiSICON (Li14Zn(GeO4)4); Li10GeP2S12; Garnet: Li7La3Zr2O12; Li2O; other oxides such as Al2O3, TiO2, ZrO2, SiO2, ZnO; sulfides such as LiS-P2S5; antiperovskites such as Li3OCl; hydrides such as LiBH4, LiBH4-LiX (where X = Cl, Br, or I), LiNH, LiNH2, LiAlH6, Li2NH; borates or phosphates such as Li2B4O7, Li3PO4, LiPON; carbonates or hydroxides such as Li2CO3, LiOH; fluorides such as LiF; nitrides such as Li3N; sulfides such as lithium borosulfides; lithium phosphosulfides, lithium aluminosulfides, oxysulfides, and praseodymium oxide. At least one of said ceramic materials may be used, or a combination thereof. As noted above, where the anode comprises sodium metal or a sodium alloy, the sodium ion equivalent of any of these conductive materials may be utilised. In preferred embodiments, the argyrodite has the chemical formula Li6PS5Cl. In some embodiments, the ionically conductive material may be formed of a polymeric material which is inherently ionically conductive, such as a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion^®). Alternatively, polymers blended with lithium (or sodium) salts, which can achieve bulk conductivities of greater than 10^-7 S/cm, may also be used. Examples of suitable polymers include, but are not limited to, ethylene oxide (EO) based polymers (for example PEO); acrylate based polymer (for example PMMA); polyamines (polyethyleneimine); siloxanes (poly(dimethylsiloxane)); polyheteroaromatic compounds (e.g., polybenzimidazole); polyamides (e.g. Nylons), polyimides (e.g. Kapton^®); polyvinyls (e.g. polyacrylamide, poly(2-vinyl pyridine), poly(N-vinylpyrrolidone), poly(methylcyanoacrylate), poly(vinyl acetate), poly (vinyl alcohol), poly(vinyl chloride), poly(vinyl fluoride)); inorganic polymers (e.g. polysilane, polysilazane. polyphosphazene, polyphosphonate); polyurethanes; polyolefins (e.g., polypropylene, polytetrafluoroethylene); and polyesters (e.g., polycarbonate, polybutylene terephthalate). Optionally, co-block polymers such as a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion^®) may be used. At least one of said polymeric materials may be used, or a combination thereof. In some embodiments, the cathode contains ceramic particles in combination with one or more ionically conductive polymers. In certain embodiments, the conducting ceramic material may be selected from at least one of an argyrodite, lithium lanthanum zirconium oxide (Li7La3Zr2O12) (LLZO) , lithium aluminium titanium phosphate (Li1.3Al0.3Ti1.7(PO4)3) (LATP), lithium germanium phosphorus sulfide (Li10GeP2S12) (LGPS), lithium sulfide-phosphorous pentasulfide (Li2S- P2S5), or a combination thereof; and the ionically conductive polymer is selected from at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene vinylene and poly(3,4-ethylenedioxythiophene), or any combination thereof. In some embodiments, the cathode may contain from 1 to 60 % by weight of an ionically conductive material based on the total weight of the cathode. In some embodiments, the cathode may further comprise an electronically conductive carbon material. The electronically conductive carbon material may be selected from carbon nanotubes, carbon nanofibers, graphene, graphene oxide, graphite, carbon black (e.g., carbon black Super-P^®, KETJENBLACK^®), activated carbon (e.g., Maxsorb III^®), microporous carbon, mesoporous carbon, macroporous carbon, or any combination thereof. The electronically conductive carbon material may be present in the range of from 0.1 to 30 wt%, or between 1 to 20 wt%, or between 5 to 15 wt%, such as about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 wt% of the total weight of the cathode. Inclusion of an electronically conductive carbon material is expected to result in an increase of the electronic conductivity within the cathode. In addition, inclusion of an electronically conductive carbon material may add a degree of porosity to the cathode, allowing for better electrolyte penetration, which contributes to shortening the lithium-ion migration path within the cathode. As a result, power performance of the cell may be enhanced. The electronically conductive carbon material may comprise microporous carbon, mesoporous carbon, macroporous carbon, or a combination thereof. The microporous carbon, mesoporous carbon, macroporous carbon, or a combination thereof may have a disordered or ordered network and may be selected from the group consisting of carbon molecular sieves, activated carbon; carbon black, such as Super P carbon black (SPCB); or combinations thereof. It may be the case that the mesoporous materials are prepared using ordered mesoporous silica or magnesium oxide frameworks. The pore diameter of the mesoporous carbon material, when present, may be in the range of from about 5 nm to about 40 nm, or from about 10 nm to about 30 nm, or from about 15 nm to about 25 nm, such as about 5, 10, 15, 20, 25, 30, 35 or 40 nm or any range therein. the pore diameter of the macroporous carbon material, when present, may be in the range of from about 60 nm to about 500 nm, or from about 100 nm to about 300 nm, such as about 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480 or 500 nm or any range therein. Mesoporous and/or macroporous carbon having a pore diameter within these ranges provides for effective mass transport of the electrolyte, whilst also providing a cathode of sufficient strength to withstand external pressures when the cell is in use. When present, the mesoporous and/or macroporous carbon material is present in the range of from about 0.1 wt% to about 10 wt%, or from about 0.3 wt% to about 7 wt%, or from about 0.5 wt% to about 5 wt%, such as about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 wt% or any range therein, based on the total weight of the cathode. If a current collector is present, the total weight of the cathode excludes the weight of the current collector. Presence of the mesoporous and/or macroporous carbon material in the abovementioned amounts provides a balance between optimum porosity to allow for effective mass transport of the electrolyte and structural integrity of the cathode. The presence of a mesoporous and/or macroporous carbon material in the cathode provides pathways for some of the liquid or gel electrolyte, which allows for effective mass transport and good power capabilities. Without being bound by theory, the pores of the mesoporous and/or macroporous carbon material are empty because the mesoporous and/or macroporous carbon material is a separate component of the cathode to components (i) and (ii) detailed above, meaning no sulfur and/or selenium from (i) can be present in any of the pores of the mesoporous and/or macroporous carbon material, thereby providing voids for the liquid electrolyte to fill once the cell is assembled. As a result, the cell would facilitate the migration/diffusion of lithium/sodium cations throughout the cathode. As such, the mesoporous and/or macroporous carbon material adds a degree of porosity to the cathode, allowing for better electrolyte penetration, which contributes to shortening the lithium-ion/sodium-ion migration path within the cathode. However, this must be balanced by a need to keep the loading of liquid or gel electrolyte to a minimum, or “low” or “lean” level, which provides the present invention with an advantage. Moreover, the mesoporous and/or macroporous carbon material results in an increase of the electronic conductivity within the cathode. In some embodiments, the cathode is pre-lithiated or pre-sodiated. Pre-lithiation or pre- sodiation of the cathode results in an increase in energy density of the cell. In certain embodiments, the cathode is calendared. Without being bound by theory, calendaring may result in the reduction of the porosity of the cathode, which may allow for a lower electrolyte loading and result in an increase in volumetric energy density (Wh/L). As used herein, the term “volumetric energy” relates to the amount of energy stored in the cell per volume in litres. Moreover, calendaring may also bring about smoothing and levelling of the cathode, which can help extend the life cycle of the cell without affecting the cell utilization. Method of Production According to a second aspect of the invention, there is provided a method of producing an electrolyte system as defined in the first aspect of the invention. The method comprises the following steps: (i) generating a paste from the first electrolyte material; (ii) calendaring the paste to form the solid-state electrolyte; and (iii) providing the second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof, wherein the second electrolyte has a polysulfide and/or polyselenide solubility sufficient to prevent shuttling. The first electrolyte and second electrolyte are identical to the first electrolyte and second electrolyte discussed above with respect to the first aspect of the invention. As used herein, the term “calendaring” refers to a compaction process. Calendaring can be carried out via conventional methods, such as through the use of calendar rollers. In some embodiments, generating the paste may include combining the first electrolyte with a solvent, a binder, or a combination thereof, to the first electrolyte. The solvent may be polar, non-polar or a combination thereof. A suitable polar solvent may be selected from water, dimethyl sulfoxide (DMSO), tetrahydrofuran, acetone, ethyl acetate, dimethylformamide, dichloromethane, ethanol, methanol, isopropyl alcohol, or combinations thereof. A suitable non-polar solvent may be selected from pentane, hexane, diethyl ether, toluene, xylene, benzene, or combinations thereof. In preferred embodiments, the non-polar solvent is toluene, xylene, benzene, or combinations thereof. The solvent may be selected from water, dimethyl sulfoxide (DMSO), tetrahydrofuran, acetone, ethyl acetate, dimethylformamide, dichloromethane, ethanol, methanol, isopropyl alcohol, pentane, hexane, diethyl ether, toluene, xylene, benzene, or combinations thereof. In instances where the first electrolyte comprises an argyrodite as described herein, the solvent may be non-polar. Suitable or preferred non-polar solvents are toluene, xylene, or benzene. When present, the binder is as defined above. In some embodiments, the binder may comprise a copolymer with a repeating unit comprising a carboxylic acid group or a conjugate base. In other embodiments, the binder may comprise poly(ethylene-co- acrylic acid), carboxylated polystyrene, poly(ethylene-co-methacrylic acid), carboxylated rubber (e.g. carboxylated nitrile butadiene rubber or carboxylated styrene butadiene rubber), or a combination thereof. In some embodiments, the solid electrolyte may comprise two or more binders. For example, the solid electrolyte may comprise two or more binders, three or more binders, four or more binders, or five or more binders. It is understood by the inventor that the presence of at least one binder improves the elasticity of the first electrolyte, and therefore improves its processability. In addition, presence of at least one binder also helps keep the layer intact when the cell is assembled, and also when in operation. Where calendaring takes place via calendar rollers, the first electrolyte may be passed through rollers up to five times, or one or two times in most embodiments. The rollers may be made of any suitable material, for example steel, glass, or ceramics. A force may be applied on the rollers of 0 kN to 100 kN, often 0 to 80 kN, for example 20 to 80 kN. Calendaring may take place at room temperature (i.e., in the range of from 15 to 25 °C). Heating may optionally be applied to the rollers. The temperature of the rollers may be in the range of from 15 to 300 °C. During calendaring or pressing, the thickness of the cathode decreases. The thickness of the first electrolyte following calendaring or pressing may be from 1 to 50 µm, or from about 10 to about 40 µm, or from about 15 to about 30 µm. Calendaring may bring about smoothing and levelling of the first electrolyte, which can help extend the life cycle of the cell. The solid-state electrolyte may be in the form of a sheet following step (ii). In some preferred embodiments, the thickness of the first electrolyte is in the range of from about 5 µm to about 100 µm, or in the range of from about 10 µm to about 80 µm, or in the range of from about 15 µm to about 70 µm, or in the range of from about 20 µm to about 60 µm, or in the range of from about 30 µm to about 50 µm. The inventor expects that solid electrolyte thicknesses within these ranges provide lighter electrochemical cells without compromising on cyclability and cell safety. In some embodiments, the method includes the additional step of drying the solid-state electrolyte following calendaring of the paste. Drying may be conducted using any known technique, such as oven drying. In some embodiments, the method includes the step of cutting the first electrolyte into the desired footprint. The cutting step can be carried out using any known technique in the art, such as laser cutting, or die cutting. According to a third aspect of the invention, there is provided a method of producing an electrochemical cell according to the first aspect of the invention. The method comprises the following steps: (i) forming the cathode from cathode material, and cutting the cathode into the desired shape; (ii) forming the first electrolyte; (iii) attaching a surface of the first electrolyte to a surface of the anode; and (iv) providing of the second electrolyte. The first electrolyte and second electrolyte are identical to the first electrolyte and second electrolyte discussed above with respect to the first aspect of the invention. In some embodiments, step (i) comprises mixing the cathode material with a solvent to produce a slurry, and the solvent is removed to produce the cathode prior to cutting. The solvent according to the third aspect of the invention may be selected from water or a suitable organic solvent, such as N-Methyl-2-pyrrolidone (NMP) or the other solvents discussed herein. The current collector may comprise aluminium, carbon, copper, titanium, or stainless- steel. In preferred embodiments, the current collector may comprise aluminium, copper, titanium, or stainless steel. In some embodiments, the current collector comprises a metal foil, such as aluminium foil, copper foil, titanium foil, or stainless-steel foil. In preferred embodiments, the current collector comprises aluminium foil. The current collector may further be coated with a protective layer. Typically, the protective layer is a carbon-based layer, such that the current collector is a carbon-coated current collector. In instances where the current collector comprises aluminium (e.g., aluminium foil), copper (e.g., copper foil), titanium (e.g., titanium foil), or stainless-steel (e.g., stainless- steel foil), it may be carbon coated. The current collector may comprise carbon coated aluminium foil in certain embodiments. Carbon coatings are understood to improve the corrosion resistance of the current collector and adhesion to the cathode materials. In some embodiments, the second electrolyte may be held within a separator placed between the cathode and first electrolyte. The separator may be formed from a wide variety of materials. Examples of material used for the separator include, but are not limited to, polyolefin-based materials such as polyethylene, polypropylene, and combinations thereof. In some embodiments, the second electrolyte is at least partially absorbed within the separator. The method may further comprise attaching an additional first electrolyte to the opposing surface of the anode, such that the anode is positioned between two separate first electrolytes. In such embodiments, at least a portion of the surfaces of the anode are in direct contact with a surface of each of the two separate first electrolytes. In embodiments of the present invention, the electrolytic cell is a pouch cell, a prismatic cell, or a cylindrical cell. Preferably, the cell is a pouch cell. When the cell is a pouch cell, the method may include the additional step of stacking the cathode, first electrolyte, and anode generated in steps (i) to (iii) prior to provision of the second electrolyte; and a final step of sealing the pouch cell. In some embodiments, the method according to the third aspect of the invention further comprises the step of calendaring or pressing of the cathode prior to cutting. As noted above, the term “calendaring” refers to a compaction process. Calendaring can be carried out via conventional methods, such as through the use of calendar rollers. Where calendaring takes place via calendar rollers, the cathode may be passed through rollers up to five times, or preferably one or two times. The rollers may be made of any suitable material, for example steel, glass, or ceramics. A force may be applied on the rollers of 0 kN to 100 kN, often 0 to 80 kN, often example 20 to 80 kN. Calendaring may take place at room temperature (i.e., in the range of from 15 to 25 °C). Heating may optionally be applied to the rollers. The temperature of the rollers may be in the range of from 15 to 80 °C. During calendaring or pressing, the thickness of the cathode decreases. The thickness of the cathode following calendaring or pressing may be from 1 to 50 µm, often 10 to 40 µm, often 15 to 30 µm. Calendaring may result in the reduction of the porosity of the cathode, which allows for a lower electrolyte loading and results in an increase in volumetric energy density (Wh/L). As used herein, the term “volumetric energy” relates to the amount of energy stored in the cell per volume in litres. Moreover, calendaring may also bring about smoothing and levelling of the cathode, which can help extend the life cycle of the cell without affecting the cell utilisation. Battery According to a fourth aspect of the invention, there is provided an electrochemical cell assembly comprising at least one electrochemical cell according to the first aspect of the invention; and a means of applying pressure to the at least one electrochemical cell. As the skilled person would appreciate, during cycling of the cell, there is an expansion of sulfur and/or selenium, which results in swelling of the cathode. Application of pressure helps to retain the integrity of the cathode structure, which can be changed due to volume expansion of the sulfur and/or selenium within the cathode. In addition, application of pressure helps to retain the good physical contact between the anode and the first electrolyte. As a result, application of pressure is believed to help extend the life cycle of the cell and improve cycling performance. In such embodiments, the means of applying pressure comprises at least one of a band, wrap or tubing positioned on the outside of the cell assembly. A band, wrap or tubing positioned on the outside of the cell assembly allows for a stable constricting force to be applied during cycling. As used herein, the outside of the cell refers to the surface of the anode. Pressure may be applied across the entire surface of the anode, or substantially the entire surface of the anode. Alternatively, the force may be applied over a portion of the surface of the anode, such as over at least 20% of the surface of the anode or pressure may be applied over at least 40% of the surface of the anode, or over at least 60%, or over at least 80%. The cell assembly may comprise one or more plates located outside the cell. Where one or more plates are present, pressure may be applied to the one or more plates. The cell assembly may be located within a housing. When the cell is located within a housing, pressure may be applied to the housing. The band wrap or tubing can be made of any suitable material, such as elastic materials or shrink-wrap materials. Examples of suitable elastic materials include, but are not limited to, natural or synthetic rubber materials. Examples of shrink-wrap materials include, but are not limited to, polyvinyl chloride (PVC), polyethylene (PE), and polyolefin (POF). Pressure may be applied to the cell or plurality of cells present in the cell assembly continuously. Alternatively, the pressure may vary over time. Other means of applying pressure may include use of screws or weights. It is envisioned that a skilled person would be able to optimise the method of pressure application to the cell. Definitions Unless otherwise stated, each of the integers described may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly understood meaning in the art. Further, in the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, is to be construed as an implied statement that each intermediate value of said parameter, lying between the smaller and greater of the alternatives, is itself also disclosed as a possible value for the parameter. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). Also, the indefinite articles “a” and “an” preceding an element or component of the invention are intended to be non-restrictive regarding the number of instances (i.e., occurrences) of the element or component. Therefore “a” or “an” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular. Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, “%” will mean “weight %”, “ratio” will mean “weight ratio” and “parts” will mean “weight parts”. The terms “predominantly” and “substantially” as used herein shall mean comprising more than 50% by weight, unless otherwise indicated. As used herein, wt.% refers to the weight of a particular component relative to total weight of the referenced composition. In addition, unless otherwise stated, all numerical values appearing in this application are to be understood as being modified by the term "about". As used herein, with reference to numbers in a range of numerals, the terms “about”, “approximately” and “substantially” are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to + 1 % of the referenced number, most preferably -0.1 % to +0.1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth. The complete disclosures of the patents, patent documents and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. Examples In order that the invention may be more readily understood, it will be described further with reference to the figures and to the specific examples hereinafter. Figure 1 is a schematic illustration of a cross section of an electrochemical cell comprising an electrolyte system according to an embodiment of the invention. Figure 2 is a schematic illustration of a cross section of an anode located between two separate first electrolytes according to an embodiment of the invention. Figure 3 illustrates electrochemical performance data (charge-discharge voltage curve at a C/10 rate and room temperature) of a cell designed in accordance with Example 2. Figure 1 is a schematic illustration of a cross section of an electrochemical cell 100. Electrochemical cell 100 includes a first electrolyte 110, a second electrolyte 120, an anode 105, a cathode 115, and a current collector 125. The first electrolyte 110 can be any material as discussed above; the second electrolyte 120 can be any material discussed above; the anode 105 can be any material discussed above; the cathode 115 can be any material discussed above; and the current collector 125 can be any material discussed above. The first electrolyte 110 has a first surface 110a and a second opposing surface 110b. The first surface 110a is in contact with a surface of the anode 105 and the second surface 110b is in contact with the second electrolyte 120. Figure 2 is a schematic illustration of a cross section of an anode 205 positioned between two separate first electrolytes 210(i) and 210(ii). The anode 205 can be any material discussed above, and the two separate first electrolytes 210(i) and 210(ii) can be any material discussed above. In figure 2, the surfaces of the anode 205 are in direct contact with the two separate first electrolytes 210(i) and 210(ii). Example 1 An electrochemical cell is provided. The cathode can comprise 90 wt.% molybdenum sulphide/sulfur (1T-LixMoS2/S), wherein the ratio of 1T-LixMoS2:S is 25:75 (i.e., 25 wt. % 1T-LixMoS2 and 75 wt. % sulfur), as the active material and 10 wt.% PVDF as a binder. The cathode powder can be prepared by simple agitation and mixing methods with the use of a three-roll mill. The binder can be added in a second step to form a slurry which can be coated onto an aluminium based current collector to form a cathode. The first electrolyte can comprise 95 wt.% argyrodite of formula Li6PS5Cl and 5 wt.% carboxylated styrene butadiene rubber. The first electrolyte can be made by mixing argyrodite of formula Li6PS5Cl with carboxylated styrene butadiene rubber to form a paste. The paste can then be calendared to form the first electrolyte in the form of a sheet. The first electrolyte can then be dried in an optional additional step, and then cut to the desired size and shape for the electrochemical cell. The second electrolyte can contain a lithium salt, the salt being at a concentration above 75% of its saturation concentration. In this example, the liquid electrolyte may consist of lithium bis(fluorosufonyl)imide (LiFSI) dissolved within a 2:1 volume per volume (v:v) of Dimethoxyethane (DME):1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to a molar concentration of 4.5 M. Lithium metal foil 100 micron thick can be utilised as the negative electrode (anode). The second electrolyte component may be held within an inert separator placed between the cathode and first electrolyte. Example 2 An electrochemical cell is provided. The cathode comprises 90 wt.% Black Pearls 2000®/S as the active material and 10 wt.% PEO as a binder. The cathode powder was prepared by simple agitation and mixing methods with the use of a three-roll mill. The binder was added in a second step to form an aqueous slurry which was coated onto an aluminium based current collector to form a cathode. The first electrolyte comprises 97 wt.% argyrodite of formula Li6PS5Cl and 3 wt.% poly(ethylene-co-acrylic acid). The first electrolyte was made by mixing argyrodite of formula Li6PS5Cl with carboxylated styrene butadiene rubber to form a paste. The paste was then calendared to form the first electrolyte in the form of a sheet. The first electrolyte was dried, and then cut to the desired size and shape for the electrochemical cell. The second electrolyte contains a lithium salt, the salt being at a concentration above 75% of its saturation concentration. In this example, the liquid electrolyte consists of lithium bis(fluorosufonyl)imide (LiFSI) dissolved within a 3:1 volume per volume (v:v) of Dimethoxyethane (DME):1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to a molar concentration of 4 M. Lithium metal foil 100 micron thick was utilised as the negative electrode (anode). The second electrolyte component was held within an inert separator placed between the cathode and first electrolyte. Electrochemical performance data characteristic of the cell is provided in Figure 3 It would be appreciated that the process and apparatus of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above. Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms in particular features of any one of the various described examples may be provided in any combination in any of the other described examples. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.

Claims

Claims 1. An electrochemical cell comprising an anode, a cathode and an electrolyte system, wherein the electrolyte system comprises: (i) a first electrolyte comprising a solid electrolyte; and (ii) a second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof; wherein the second electrolyte has a polysulfide and/or polyselenide solubility sufficient to prevent shuttling and wherein the second electrolyte does not contact the anode.

2. The electrochemical cell according to claim 1, wherein the first electrolyte comprises a ceramic material, a polymer material, or a combination thereof.

3. The electrochemical cell according to claim 1 or claim 2, wherein the first electrolyte comprises an argyrodite, lithium germanium phosphorus sulfide (LGPS - Li10GeP2S12), lithium phosphorous sulfide (LPS), lithium lanthanum zirconium oxide (LLZO), lithium aluminium germanium phosphate (LAGP), lithium phosphorus oxynitride (LIPON), polyethylene oxide (PEO), or combinations thereof.

4. The electrochemical cell according to any preceding claim, wherein the first electrolyte comprises a binder comprising poly(ethylene-co-acrylic acid), carboxylated polystyrene, poly(ethylene-co-methacrylic acid), carboxylated nitrile butadiene rubber, carboxylated styrene butadiene rubber, or a combination thereof.

5. The electrochemical cell according to any preceding claim, wherein the ionic conductivity of the first electrolyte is in the range of from 0.01 to 10 mS/cm.

6. The electrochemical cell according to any preceding claim, wherein the thickness of the first electrolyte is in the range of from 5 µm to 100 µm.

7. The electrochemical cell according to any preceding claim, wherein the second electrolyte comprises a solvent selected from linear ethers, diethyl ether (DEE), tetrahydrofuran (THF), Dimethoxyethane (DME), Dioxolane (DIOX), Diglyme, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl acetate (EA) and methyl butyrate (MB), methyl ethyl ketone, acetonitrile (ACN), propionitrile (PN), isobutyronitrile (iBN), Dimethylformamide (DMF), Dimethylacetamide (DMAc), N-Methyl-2-pyrrolidone (NMP), Tetram ethyl urea (TMU), Dimethyl sulfoxide (DMSO), Trimethyl phosphate, Triethyl phosphate, Hexamethylphosphoramide, toluene, benzene, heptane, xylene, dichloromethane, ionic liquids, fluorinated ethers, gels, or a combination thereof; and at least one alkali metal salt.

8. The electrochemical cell according to claim 7, wherein the alkali metal salt comprises lithium when the anode comprises lithium or a lithium alloy; or wherein the alkali metal salt comprises sodium when the anode comprises sodium or a sodium alloy.

9. The electrochemical cell according to claim 8 wherein the alkali metal salt is at least one lithium salt selected from lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium perchlorate, lithium sulfate, lithium nitrate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethane)sulfonimide, lithium bis(fluorosufonyl)imide, lithium bis(oxalate) borate, lithium difluoro(oxalate)borate, lithium bis(pentafluoroethanesulfonyl)imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazole, and combinations thereof; or wherein the alkali metal salt is at least one sodium salt selected from sodium hexafluoroarsenate, sodium hexafluorophosphate, sodium perchlorate, sodium sulfate, sodium nitrate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethane)sulfonimide, sodium bis(fluorosufonyl)imide, sodium bis(oxalate) borate, sodium difluoro(oxalate)borate, sodium bis(pentafluoroethanesulfonyl)imide, sodium 2-trifluoromethyl-4,5-dicyanoimidazole, and combinations thereof.

10. The electrochemical cell according to any preceding claim, wherein the concentration of the at least one alkali metal salt is at least 75% of the saturation concentration of the second electrolyte.

11. The electrochemical cell according to any preceding claim, wherein the electrolyte loading of the second electrolyte is in the range of from 0.1 µL/mAh to 3 µL/mAh.

12. The electrochemical cell according to any preceding claim, wherein the solubility of the polysulphide and/or polyselenide in the second electrolyte which is sufficient to prevent shuttling is less than 2 M, or less than 1 M, or less than 750 mM, or less than 500 mM, or less than 400 mM, or less than 200 mM, or less than 100 mM.

13. The electrochemical cell according to any of claims 1 to 12, wherein: the anode comprises an alkali metal, an alkali metal alloy, silicon, carbon, or a silicon- carbon composite material.

14. The electrochemical cell according to any preceding claim, wherein the first electrolyte has a first surface and a second opposing surface, and wherein the first surface is in contact with a surface of the anode and wherein the second surface is in contact with the second electrolyte.

15. The electrochemical cell according to any preceding claim, wherein the cathode comprises (i) selenium, sulfur, or a combination thereof; and (ii) a carbonaceous material, a metallic material, a metalloid material, a polymer, or a combination thereof.

16. The electrochemical cell according to claim 15, wherein the cathode comprises a carbon-sulfur composite, a metal sulfide, a polymer-sulfur composite, a carbon-selenium composite, a carbon-sulfur-selenium composite, a metal selenide, a polymer-selenium composite, a metal sulphoselenide, a metalloid sulfide, a metalloid selenide, or a combination thereof.

17. The electrochemical cell according to any preceding claim, wherein the cathode is pre-lithiated or pre-sodiated.

18. The electrochemical cell according to claim 17, wherein the cathode is pre-lithiated.

19. The electrochemical cell according to any of claims 17 or 18, wherein the cathode comprises a metal sulfide comprising molybdenum disulfide in the form of the 1T polymorph, wherein the cathode is pre-lithiated, and wherein the cathode further comprises sulfur.

20. The electrochemical cell according to any preceding claim, wherein the cathode further comprises an ionically conductive material.

21. The electrochemical cell according to claim 20, wherein the ionically conductive material is selected from an ionically conducting ceramic material, an ionically conducting polymer, or a combination thereof.

22. A method of producing an electrolyte system as defined in any of claims 1 to 12, comprising the following steps: (i) generating a paste from the first electrolyte material; (ii) calendaring the paste to form the solid-state electrolyte; and (iii) providing the second electrolyte comprising a liquid electrolyte, a gel electrolyte, or a combination thereof, wherein the second electrolyte has a polysulfide and/or polyselenide solubility sufficient to prevent shuttling.

23. A method of producing a cell according to any of claims 1 to 21, comprising the following steps: (i) forming the cathode from cathode material, and cutting the cathode into the desired shape; (ii) forming the first electrolyte; (iii) attaching a surface of the first electrolyte to a surface of the anode; and (iv) providing the second electrolyte.

24. A method according to claim 23, further comprising calendaring or pressing the cathode prior to cutting.

25. An electrochemical cell assembly comprising at least one electrochemical cell according to any of claims 11 to 21; and a means of applying pressure to the at least one electrochemical cell.