CN107275551A - Lithium-sulfur cell and its component, and application of the functional material layer in lithium-sulfur cell - Google Patents

Abstract

The invention provides a lithium-sulfur battery, comprising a sulfur-based positive electrode; a lithium-based negative electrode; a diaphragm arranged between the sulfur-based positive electrode and the lithium-based negative electrode; and a diaphragm arranged between the sulfur-based positive electrode and the lithium-based negative electrode Between the functional material layer, the material of the functional material layer includes transition metal oxide with crystal water. The invention also provides the application of a composite diaphragm, an electrode assembly of a lithium-sulfur battery, a composite sulfur-based positive electrode, a composite lithium-based negative electrode and a functional material layer in a lithium-sulfur battery.

Description

Lithium-sulfur batteries and their components, and the application of functional material layers in lithium-sulfur batteries

technical field

The invention relates to the field of lithium batteries, in particular to the application of lithium-sulfur batteries, composite separators, lithium-sulfur battery electrode assemblies, composite sulfur-based positive electrodes, composite lithium-based negative electrodes and functional material layers in lithium-sulfur batteries.

Background technique

With the rapid development of the new energy automobile industry, the development of energy storage devices with high energy density has become an important direction of current research and development. With its theoretical specific capacity of 1675mAh/g and theoretical energy density of ~2500Wh/kg, lithium-sulfur batteries have become one of the most promising power battery systems to replace traditional lithium-ion batteries and achieve long-range battery life (>500Wh/kg). . However, due to the current problems of low cycle life and poor safety and stability of lithium-sulfur batteries, it still faces obstacles on the road to practical use. How to efficiently suppress the shuttle effect of lithium polysulfide is a key factor to improve the electrochemical performance and safety performance of lithium-sulfur batteries, and it is also a hot spot of international research in recent years.

The shuttle effect of lithium polysulfide is mainly caused by two aspects, one is the inevitable diffusion in thermodynamics, and the other is the accumulation of lithium polysulfide in the electrolyte due to the slower reaction kinetics. At present, the main methods to inhibit the shuttling of lithium polysulfides are physical barriers, polar adsorption and storage, and the promotion of lithium polysulfide conversion, and inhibit the shuttling of lithium polysulfides by coating sulfur cathodes or trapping sulfur in nanopores. Although the formation of a protective layer or protective network on the surface of sulfur can block lithium polysulfides to a certain extent, it is still difficult to achieve a long life cycle of the battery.

There have been a lot of researches on coating some transition metal oxides or sulfides on the separator as a functional material layer to improve the capacity and cycle performance of lithium-sulfur batteries. Some polar transition metal oxides or sulfide oxides, such as Fe ₂ O ₃ , Co ₃ O ₄ , Ti ₄ O ₇ , NiO, ZnO, V ₂ O ₃ , Cu ₂ O, etc. acidic sites to adsorb and store lithium polysulfide; other transition metal oxides, such as TiO ₂ , MnO ₂ , CuO, and VO ₂ , can also catalyze lithium polysulfide. In addition, since nanomaterials can be filled in the pores of the separator, it can also physically block lithium polysulfide to a certain extent under the premise of ensuring the normal passage of lithium ions. However, it is often found in practical applications that even if the above-mentioned transition metal oxides are used, the effect achieved in preventing lithium polysulfide shuttle is still unsatisfactory.

Contents of the invention

Based on this, in order to prevent the shuttle of lithium polysulfide more effectively, it is necessary to provide a lithium-sulfur battery, a composite separator, a lithium-sulfur battery electrode assembly, a composite sulfur-based positive electrode, a composite lithium-based negative electrode, and a functional material layer in a lithium-sulfur battery. in the application.

A lithium-sulfur battery, comprising a sulfur-based positive electrode; a lithium-based negative electrode; a separator arranged between the sulfur-based positive electrode and the lithium-based negative electrode; and a diaphragm arranged between the sulfur-based positive electrode and the lithium-based negative electrode The functional material layer, the material of the functional material layer includes transition metal oxide with crystal water.

A composite diaphragm, which is used in lithium-sulfur batteries, characterized in that the composite diaphragm includes a diaphragm and a functional material layer arranged on at least one surface of the diaphragm, and the material of the functional material layer includes Transition metal oxides in water of crystallization.

A lithium-sulfur battery electrode assembly, comprising a sulfur-based positive electrode, a separator, and a functional material layer stacked on each other, the functional material layer is arranged between the sulfur-based positive electrode and the separator, and the functional material layer materials include transition metal oxides with water of crystallization.

A lithium-sulfur battery electrode assembly, characterized in that it includes a lithium-based negative electrode, a separator, and a functional material layer stacked on each other, the functional material layer is arranged between the lithium-based negative electrode and the separator, the The material of the functional material layer includes a transition metal oxide with crystal water.

A composite sulfur-based positive electrode, comprising a positive electrode material layer, a positive electrode current collector, and a functional material layer stacked on each other, the positive electrode material layer is arranged between the functional material layer and the positive electrode current collector, the functional The material of the permanent material layer includes a transition metal oxide with crystal water.

A composite lithium-based negative electrode includes metal lithium and functional material layers stacked on each other, and the material of the functional material layer includes transition metal oxides with crystal water.

An application of a functional material layer in a lithium-sulfur battery, comprising coating the solid-liquid mixture containing the transition metal oxide with crystal water on at least one of the sulfur-based positive electrode, lithium-based negative electrode and separator surface, thereby forming the functional material layer between the sulfur-based positive electrode and the lithium-based negative electrode.

The present invention introduces the transition metal oxide with crystal water into the lithium-sulfur battery. Compared with the transition metal oxide with crystal water removed, the transition metal oxide with crystal water can have a larger specific surface area, thereby providing more The active sites can better play the role of adsorbing and storing lithium polysulfides and/or catalyzing lithium polysulfides, so as to effectively inhibit the shuttle of lithium polysulfides and improve the electrochemical performance of lithium-sulfur batteries.

Description of drawings

Fig. 1 is the structural representation of the lithium-sulfur battery of the embodiment of the present invention;

2 is a schematic structural view of an electrode assembly of a lithium-sulfur battery according to an embodiment of the present invention;

Fig. 3 is the SEM picture of functional material layer in PP@C&HTO-1 in embodiment 1;

Figure 4 is a comparison chart of the cycle performance of the lithium-sulfur battery using PP@C&HTO-1 in Example 1 and the lithium-sulfur battery using PP in the comparative example at 0.2C;

Figure 5 is a diagram of cycle performance and Coulombic efficiency at 1C for a lithium-sulfur battery using PP@C&HTO-1 in Example 1;

Figure 6 is a graph of the cycle performance and Coulombic efficiency of the lithium-sulfur battery using PP@C&TO-1 in the comparative example at 1C in Example 1;

Fig. 7 is the SEM figure of PP@C&HTO-2 functional material layer in embodiment 2;

Figure 8 is a comparison chart of the cycle performance of lithium-sulfur batteries using PP@C&HTO-2 and PP at 0.2C in Example 2;

Fig. 9 is a diagram of cycle performance and coulombic efficiency at 0.5C for the lithium-sulfur battery prepared by using PP@C&HTO-2 coating in Example 2.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Please refer to FIG. 1 and FIG. 2 , an embodiment of the present invention provides a lithium-sulfur battery, including a sulfur-based positive electrode 10, a lithium-based negative electrode 20, and a separator 30 disposed between the sulfur-based positive electrode 10 and the lithium-based negative electrode 20. The lithium-sulfur battery It further includes a functional material layer 32 disposed between the sulfur-based positive electrode 10 and the lithium-based negative electrode 20 . The material of the functional material layer 32 includes transition metal oxide with crystal water. The transition metal oxide can absorb and store and/or catalyze lithium polysulfide, and inhibit lithium polysulfide shuttling. In addition, due to the crystal water in the material, there may be a certain degree of reaction with lithium ions or the uniform distribution of lithium ions can be adjusted through the surface polarity, thereby inhibiting the growth of lithium dendrites.

The metal element of the transition metal oxide can be selected from at least one of titanium (Ti), ruthenium (Ru), molybdenum (Mo), vanadium (V), tungsten (W), iron (Fe) and cobalt (Co). kind.

The transition metal oxides with water of crystallization include but are not limited to TiO ₂ xH ₂ O, H ₂ Ti _n O _2n+1 H ₂ O, RuO ₂ xH ₂ O, MoO ₃ xH ₂ O, (H ₃ O) _x MoO ₃ xH ₂ O, _Hy V ₄ O ₁₀ xH ₂ O, _Hz V ₂ O ₅ xH ₂ O, V ₂ O ₅ xH ₂ O, V ₂ O ₄ xH ₂ O , WO ₃ xH ₂ O, Fe ₂ O ₃ xH ₂ O and Co ₂ O ₃ xH ₂ O, at least one of 2≤n≤9, 0.5≤x≤10, 0<y≤1,0 <z≤1.

The transition metal oxide with crystal water is preferably a nanoscale material, and the primary particle size of the transition metal oxide with crystal water is preferably 1 nm to 100 nm, more preferably 1 nm to 10 nm. When the particle size of the material is nanoscale, it can be effectively filled in the pores of the separator, and to a certain extent, it can also physically block lithium polysulfide shuttle.

The transition metal oxide with crystal water has a larger specific surface area than the transition metal oxide obtained after removing the crystal water, and the specific surface area of the transition metal oxide with crystal water is preferably 100m ² /g to 600m ² /g.

The thickness of the functional material layer 32 is preferably 10 nm to 200 μm, and the surface density is preferably 0.1 to 10 mg/cm.

Preferably, the material of the functional material layer 32 further includes an electronically conductive material and a binder, and the electronically conductive material and binder are uniformly mixed with the transition metal oxide having crystal water. The mass percent content of the transition metal oxide with crystal water in the functional material layer 32 is preferably 5%-99%. The mass ratio of the electronically conductive material to the binder is preferably 1:9˜9:1.

Preferably, the electronically conductive material is at least one selected from activated carbon, graphene, carbon nanotubes, Ketjen black, Super P, acetylene black and graphite.

Preferably, the binder is selected from polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), lauric acid acrylate (LA), poly At least one of tetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), epoxy resin, polyacrylic acid (PAA) and sodium carboxymethylcellulose (CMC).

The functional material layer 32 can be arranged on the surface of the sulfur-based positive electrode 10 facing the lithium-based negative electrode 20 (that is, facing the separator 30), at least one surface of the separator 30, or the lithium-based negative electrode 20 faces the The surface of the sulfur-based positive electrode 10 (that is, facing the separator 30). In a preferred embodiment, the functional material layer 32 is at least disposed on the surface of the separator 30 facing the sulfur-based positive electrode 10 . In one embodiment, the functional material layer 32 is disposed on both surfaces of the membrane 30 .

The sulfur-based positive electrode 10 includes a positive electrode material layer 12 and a positive electrode current collector 14, the positive electrode current collector 14 is used to support the positive electrode material layer 12 and conduct current, and the shape can be foil or mesh. The material of the positive current collector 14 can be selected from aluminum, titanium or stainless steel. The positive electrode material layer 12 is disposed on at least one surface of the positive electrode current collector 14 . The material of the positive electrode material layer 12 includes a sulfur-containing positive electrode active material, and further optionally includes a conductive agent and a binder. The conductive agent and the binder may be uniformly mixed with the sulfur-containing positive electrode active material. The sulfur-containing positive electrode active material is a sulfur-based material with electrochemical lithium storage capacity, such as at least one of sulfur element, sulfur-based composite material, and sulfurized conductive polymer. The sulfur-based composite material may be, for example, a core-shell composite material obtained by coating the surface of sulfur element particles with a conductive carbon layer, or a porous composite material obtained by disposing sulfur element particles in a porous carbon material. The sulfur-based conductive polymer, for example, can be selected from sulfurized polypyridine, sulfurized polystyrene, sulfurized polyethylene oxide, sulfurized polyvinyl alcohol, sulfurized polyvinylidene chloride, sulfurized polyvinylidene fluoride, sulfurized polyvinyl chloride, One or more of vulcanized polyvinyl fluoride, vulcanized polyvinyl dichloride, vulcanized polyvinylidene fluoride, vulcanized polymethyl methacrylate and vulcanized phenolic resin.

The functional material layer 32 may be disposed on the surface of the positive electrode material layer 12 facing the lithium-based negative electrode 20 (that is, facing the separator 30 ). The positive electrode material layer 12 is disposed between the functional material layer 32 and the positive electrode current collector 14 .

The functional material layer 32 is preferably in direct contact with the positive electrode material layer 12 , or directly in contact with the separator 30 . More preferably, the two surfaces of the functional material layer 32 are arranged in direct contact with the positive electrode material layer 12 and the separator 30 respectively. However, in some embodiments, other material layers, such as adhesive layers, The conductive layer or the ion-conducting layer can be used as long as it does not affect the functional material layer 32 to realize at least one of the above-mentioned functions (1) to (3).

The lithium-based negative electrode 20 may include a negative electrode active layer 22 , such as a lithium metal layer or a lithium alloy layer, such as a lithium tin alloy layer or a lithium aluminum alloy layer, and may further include a negative electrode current collector 24 . The negative electrode current collector 24 is used to support the negative electrode active layer 22 and conduct current, and the shape may be foil or mesh. The material of the negative electrode current collector 24 can be selected from copper, nickel or stainless steel.

The separator 30 can be a traditional lithium battery separator, capable of isolating electrons and allowing lithium ions to pass between the sulfur-based positive electrode 10 and the lithium-based negative electrode 20, and can be any one of an organic polymer separator or an inorganic separator. For example, it can be selected from but not limited to polyethylene porous membrane, polypropylene porous membrane, polyethylene-polypropylene double-layer porous membrane, polypropylene-polyethylene-polypropylene three-layer porous membrane, glass fiber porous membrane, non-woven fabric Any one of porous membrane, electrospun porous membrane, PVDF-HFP porous membrane and polyacrylonitrile porous membrane. The non-woven fabric separator can include polyimide nanofiber nonwoven fabric, polyethylene terephthalate (PET) nanofiber nonwoven fabric, cellulose nanofiber nonwoven fabric, aramid nanofiber nonwoven fabric, etc. Cloth, nylon nanofiber non-woven fabric and polyvinylidene fluoride (PVDF) nanofiber non-woven fabric. The electrospun porous membrane includes, for example, a polyimide electrospun membrane, a polyethylene terephthalate electrospun membrane, and a polyvinylidene fluoride electrospun membrane.

The lithium-sulfur battery further includes a non-aqueous electrolyte 40 disposed between the sulfur-based positive electrode 10 and the lithium-based negative electrode 20 , for example, may permeate the separator 30 . The non-aqueous electrolytic solution 40 includes a solvent and a lithium salt solute dissolved in the solvent, the solvent may be selected from but not limited to cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, nitriles and One or more of amides, such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate , ethyl propionate, diethyl ether, acetonitrile, propionitrile, anisole, butyrate, glutaronitrile, adiponitrile, γ-butyrolactone, γ-valerolactone, tetrahydrofuran, 1,2-dimethyl One or more of oxyethane, acetonitrile and dimethylformamide. The lithium salt solute can be selected from but not limited to lithium chloride (LiCl), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium methanesulfonate (LiCH ₃ SO ₃ ), lithium trifluoromethanesulfonate ( One or more of LiCF ₃ SO ₃ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ) and lithium bisoxalate borate (LiBOB).

The lithium-sulfur battery also includes a sealed case 50 , and the sulfur-based positive electrode 10 , lithium-based negative electrode 20 , separator 30 , functional material layer 32 and non-aqueous electrolyte 40 are arranged in the sealed case 50 .

The embodiment of the present invention also provides a composite diaphragm, which is used in the lithium-sulfur battery, and the composite diaphragm includes the diaphragm 30 and a functional material layer 32 disposed on at least one surface of the diaphragm 30 . In a preferred embodiment, the functional material layer 32 is disposed on the surface of the separator 30 facing the sulfur-based positive electrode 10 in the lithium-sulfur battery.

The embodiment of the present invention also provides a lithium-sulfur battery electrode assembly, including the sulfur-based positive electrode 10, the separator 30 and the functional material layer 32 stacked on each other, and the functional material layer 32 is arranged on the sulfur-based positive electrode 10 and the between the diaphragms 30 .

The embodiment of the present invention also provides a lithium-sulfur battery electrode assembly, including a lithium-based negative electrode 20 , a separator 30 , and a functional material layer 32 stacked on top of each other. The functional material layer 32 is arranged between the lithium-based negative electrode 20 and the separator 30 .

An embodiment of the present invention also provides a composite sulfur-based positive electrode, including a positive electrode material layer 12, a positive electrode current collector 14, and a functional material layer 32 stacked on each other, and the positive electrode material layer 12 is arranged between the functional material layer 32 and the functional material layer 32. Between the positive electrode collectors 14 .

The embodiment of the present invention also provides a composite lithium-based negative electrode, including metallic lithium 22 and functional material layers 32 stacked on each other.

The embodiment of the present invention provides the application of the functional material layer 32 in the lithium-sulfur battery, including coating the solid-liquid mixture containing the transition metal oxide with crystal water on the sulfur-based positive electrode 10 and the separator 30, so that the functional material layer 32 is formed between the sulfur-based positive electrode 10 and the lithium-based negative electrode 20.

The solid phase in the solid-liquid mixture includes the transition metal oxide with crystal water, and may further include the electronically conductive material and the binder; the liquid phase is preferably a solvent. In the solid-liquid mixture, the transition metal oxide with crystal water, electronically conductive material, binder and solvent are uniformly mixed. The function of the solvent is as the carrier of the transition metal oxide with water of crystallization, so it is necessary to select the transition metal oxide that cannot dissolve the water of crystallization, and do not chemically react with the transition metal oxide with water of crystallization. Reaction, and the solvent that can be removed completely under lower temperature (such as 30～120 ℃), for example low molecular weight volatile organic solvent, can be selected from N-methylpyrrolidone, water, methanol, ethanol, propanol, One or more of isopropanol, acetonitrile, acetone and ether.

The solid-liquid mixture can be a mixed liquid or a slurry. The difference between the mixed liquid and the slurry is only in the ratio of the solid and liquid phases. When the solid phase is more, it is a slurry, and when the liquid phase is more, it is a mixed liquid. The selection of slurry and mixed liquid, and the ratio of solid to liquid can be selected according to actual needs, for example, according to the method of coating. Of course, in order to facilitate the coating, the slurry preferably has proper fluidity; and in order to make the coating more efficient, the solid phase in the mixed solution preferably has a proper ratio. The coating method can be, for example, any one of the dipping method, spin coating method, doctor blade coating method, casting coating method, suction filtration (filtering) coating method, uniaxial stretching method and biaxial stretching method. A sort of. After the solid-liquid mixture is formed into a coating through the step of coating, the functional material layer 32 can be obtained only by removing the solvent in the coating. Therefore, the solid-liquid mixture can be coated on the desired component surface. When the solid-liquid mixture is applied to the sulfur-based positive electrode 10 , it may be applied to the surface of the positive electrode material layer 12 facing the separator 30 . When the solid-liquid mixture is applied to the separator 30 , it may be applied to one or both surfaces of the separator 30 .

After coating the solid-liquid mixture on the surface of at least one of the sulfur-based positive electrode 10 and the separator 30 , drying may be further included to remove the solvent in the coating. The drying method is, for example, vacuum drying in an environment with a temperature of 30-120° C. for 4-24 hours. It can be understood that the drying step is only to remove the liquid phase solvent and adsorbed water in the coating, and the temperature of the drying step is relatively low, so that the transition metal oxide in the functional material layer 32 still has crystallization after drying. Water, water molecules still exist in the functional material layer 32 in the form of crystal water.

After forming the functional material layer 32 on the required surface, such as the surface of the positive electrode material layer 12 of the sulfur-based positive electrode 10 and/or at least one surface of the separator 30, it further includes laminating the sulfur-based positive electrode 10 and the separator 30 Steps to set up.

In one embodiment, the step of stacking is to stack the functional material layer 32 between the sulfur-based positive electrode 10 and the separator 30 . For example, after the functional material layer 32 is formed on the surface of the positive electrode material layer 12 of the sulfur-based positive electrode 10 , the separator 30 may be paved on the surface of the functional material layer 32 . Or after the functional material layer 32 is formed on at least one surface of the separator 30, the separator 30 with the functional material layer 32 can face the positive electrode material layer 12 and be laid on the positive electrode material layer. Layer 12 surface.

In another embodiment, in the step of stacking, the functional material layer 32 is stacked on the surface of the separator 30 away from the sulfur-based positive electrode 10 . In this embodiment, by further laminating the lithium-based negative electrode 20 on the surface of the separator 30 having the functional material layer 32, the functional material layer 32 can also be arranged between the sulfur-based positive electrode 10 and the lithium-based Between negative poles 20.

After stacking the sulfur-based positive electrode 10, the functional material layer 32, the separator 30 and the lithium-based negative electrode 20, the stacked structure can be packaged in the sealed case 50 according to the traditional lithium-sulfur battery manufacturing process; and The electrolyte solution 40 is injected into the sealed case 50 .

The functional material layer 32 based on the transition metal oxide with crystal water has the function of absorbing and storing and/or catalyzing lithium polysulfide in the lithium-sulfur battery, and through the introduction of crystal water _H2O , the functional The diversity of crystal structures and nanometer dimensions of transition metal oxides in the material layer 32 improves the ion conductivity of the functional material layer 32 . The introduction of crystalline water H ₂ O can increase the specific surface area of the material, and a larger specific surface area can provide more active sites, thereby effectively inhibiting lithium polysulfide shuttle, and improving the electrochemical performance and safety of lithium-sulfur batteries. performance.

The technical solution of the present application breaks the traditional notion that water will cause harm to the electrochemical performance and safety of lithium-sulfur batteries, and it is found and proved through experiments that the introduction of crystal water into the functional material layer 32 will not only not affect lithium-sulfur batteries. The performance of the battery can also make the lithium-sulfur battery have excellent rate capacity and cycle stability. The lithium-sulfur battery using the functional material layer 32 has broad application prospects in energy storage fields such as electric vehicles, energy storage power stations, and lithium ion batteries in large-capacity electronic products.

In addition, most of the methods for preparing transition metal oxides are wet chemical methods (such as hydrothermal synthesis or sol-gel method). The products obtained by these methods are often hydrates. of crystal water. The direct use of transition metal oxides with crystal water in the functional material layer 32 omits the step of heat treatment to remove water, effectively reducing energy consumption and pollution in traditional methods, and the material preparation process is mild and controllable. , new materials and energy-saving and environmental protection industries have important influence and significance.

Example 1

1) Preparation of transition metal oxide-based functional material layer with crystal water: TiO ₂ xH ₂ O, Super P and PVDF were added to N-methylpyrrolidone at a mass ratio of 8:1:1 Mix to form a slurry, and then use the casting method to coat the above slurry on one side of the polypropylene separator, and then dry the slurry at 60°C for 10 hours in vacuum to obtain a transition metal oxide-based functional material with crystal water layer composite separator (hereinafter referred to as PP@C&HTO-1). The scanning electron microscope (SEM) image of the functional material layer in PP@C&HTO-1 is shown in Fig. 3.

2) Assembly of lithium-sulfur battery: Sublimed sulfur is used to prepare sulfur positive electrode, metal lithium sheet is used as negative electrode, PP@C&HTO-1 is used as separator, and electrolyte is a mixed solution of LiTFSI and LiNO ₃ in a mixed solvent of DME and DOL (DME The volume ratio to DOL is 1:1, the concentration of LiTFSI is 1mol/L, and the concentration of _LiNO3 is 0.2mol/L). A 2032-type coin cell was assembled in a glove box with a high-purity argon atmosphere with both water and oxygen content below 1 ppm.

Comparative example 1

Same as Example 1, the only difference is that the PP@C&HTO-1 in Example 1 is replaced by a commercialized lithium battery polypropylene separator (hereinafter referred to as PP), and the same 2032-type button battery as in Example 1 is assembled, the difference Just replace PP@C&HTO-1 with PP.

Comparative example 2

Same as Example 1, the only difference is that the TiO ₂ xH ₂ O in Example 1 is heated and dehydrated at 350°C to obtain TiO ₂ (hereinafter referred to as TO-1) material, and the functional material layer in Example 1 is prepared The TiO ₂ ·xH ₂ O in the step was replaced with TO-1 to obtain a composite separator with a transition metal oxide coating (hereinafter referred to as PP@C&TO-1), and the same 2032-type button battery as in Example 1 was assembled, with the difference Just replace PP@C&HTO-1 with PP@C&TO-1.

Example 2

Same as Example 1, the only difference is that TiO ₂ xH ₂ O in Example 1 is replaced by H ₂ Ti ₃ O ₇ , and the tape casting method is replaced by a doctor blade coating method to obtain a transition metal oxide coating The composite separator (hereinafter referred to as PP@C&HTO-2) was assembled with the same 2032-type button battery as in Example 1, the only difference being that PP@C&HTO-1 was replaced by PP@C&HTO-2.

The scanning electron microscope (SEM) image of the functional material layer in PP@C&HTO-2 is shown in Fig. 7.

Testing of battery electrochemical performance

Adopt LAND battery test system to carry out constant current charge and discharge cycle in the voltage range of 2.7V and 1.8V respectively in charge and discharge cut-off voltage, test the electrochemical cycle characteristics of the button cell of embodiment 1-2 and comparative example 1-2, The test data of the battery is shown in Table 1. Figure 4 is a comparison chart of the cycle performance of lithium-sulfur batteries using PP@C&HTO-1 and PP at 0.2C. Figure 5 is a diagram of the cycle performance and Coulombic efficiency of a lithium-sulfur battery using PP@C&HTO-1 at 1C. Figure 6 is a diagram of the cycle performance and coulombic efficiency of the lithium-sulfur battery using PP@C&TO-1 in Comparative Example 2 at 1C. Figure 8 is a comparison chart of the cycle performance of lithium-sulfur batteries using PP@C&HTO-2 and PP at 0.2C. Figure 9 is a diagram of the cycle performance and Coulombic efficiency of a lithium-sulfur battery using PP@C&HTO-2 at 0.5C.

From the cycle performance comparison in Figure 4, it can be seen that the initial discharge capacity of the lithium-sulfur battery using PP@C&HTO-1 is as high as 1735mAh/g, while the initial discharge capacity of the control battery using PP is only 979mAh/g. After 400 cycles, the lithium-sulfur battery using PP@C&HTO-1 can still maintain a stable specific capacity of 671mAh/g, which is 2.5 times the specific capacity of the control battery using PP. It can be seen from Figure 5 that at a large rate of 1C, the lithium-sulfur battery using PP@C&HTO-1 still has a reversible specific capacity of 420mAh/g after up to 1400 cycles, and the Coulombic efficiency is close to 100%. The "shuttle effect" of lithium is significantly weakened, and the battery exhibits excellent high-rate capacity and cycle stability.

Using PP@C&TO-1 and PP@C&HTO-1 to compare the advantages of crystal water-containing materials in lithium-sulfur batteries. It can be seen from Figure 6 that the first discharge capacity of the lithium-sulfur battery using PP@C&TO-1 is only 650mAh/g. In the next 1400 cycles, the specific capacity of the battery continued to decrease, and the specific capacity had dropped to 420mAh/g at 250 cycles. In Figure 5, under the same conditions, the lithium-sulfur battery of PP@C&HTO-1 is still higher than 420mAh/g after 1400 cycles. After 1400 cycles, the specific capacity of the lithium-sulfur battery of PP@C&TO-1 is only 130mAh/g. This is because the nano-TiO ₂ ·xH ₂ O crystal structure tends to coarsen and agglomerate during the high-temperature dehydration process, the particle size of the material becomes larger, and the specific surface area is greatly reduced, which in turn reduces the resistance of the active sites in the material to lithium polysulfide. Adsorption storage and catalysis lead to unsatisfactory electrochemical performance.

It can be known from the above experiments that in the preparation method of nano-oxides, the hydrates of oxides prepared by wet chemical methods (such as hydrothermal reaction or sol-gel reaction) have crystal water. Traditionally, it is believed that hydrates with crystal water need to be calcined at high temperature to remove water to obtain the final product. However, the inventors of the present application found that the material after high-temperature water removal is not ideal for the functional material layer used in lithium-sulfur batteries. In this application, the inventors of the present application avoided the high-temperature calcination, retained the crystal water in the material, and avoided the coarsening and agglomeration of the nanocrystalline structure in the process of high-temperature dehydration, so that the transition metal oxide has a large number of active sites, Adsorption storage and (or) catalysis of lithium polysulfide through a large number of active sites. Moreover, when the oxide has a smaller grain size, it can be more easily filled in the pores of the organic separator to physically block lithium polysulfide, and achieve a better effect of inhibiting lithium polysulfide shuttling in lithium-sulfur batteries.

From the cycle performance comparison in Figure 8, it can be seen that the initial discharge capacity of the lithium-sulfur battery using PP@C&HTO-2 is as high as 1536mAh/g, while the initial discharge capacity of the control battery using PP is only 979mAh/g. After 400 cycles, the lithium-sulfur battery using PP@C&HTO-2 can still maintain a stable specific capacity of 639mAh/g, which is 2.5 times the specific capacity of the control battery using PP. At a rate of 0.5C (Figure 9), the lithium-sulfur battery using PP@C&HTO-2 still has a reversible specific capacity of 442mAh/g after up to 1200 cycles, and the Coulombic efficiency is close to 100%. The "shuttle effect" is significantly weakened, and the battery exhibits excellent high-rate capacity and cycle stability.

Table 1

Current rate First discharge specific capacity The discharge point specific capacity of the Nth cycle Example 1 0.2C 1735mAh/g 671mAh/g, N=400 Example 1 1C 958mAh/g 420mAh/g, N=1400 Comparative example 1 0.2C 979mAh/g 263mAh/g, N=400 Comparative example 2 1C 650mAh/g 130mAh/g, N=1400 Example 2 0.2C 1536mAh/g 639mAh/g, N=400 Example 2 0.5C 694mAh/g 442mAh/g, N=1200

Example 3

1) Preparation of a transition metal oxide-based functional material layer with crystal water: MoO ₃ ·xH ₂ O, Ketjen Black and PVDF were added to an ethanol solvent at a mass ratio of 7:2:1 and mixed to form a slurry, Then use spin coating to coat the above slurry on both sides of the polyethylene separator, and then dry the slurry at 80°C for 10 hours in vacuum to obtain a composite separator with a transition metal oxide-based functional material layer with crystal water (hereinafter referred to as PE@C&HMO-3).

2) Assembly of lithium-sulfur battery: the same as in Example 1, the only difference is that PP@C&HTO-1 is replaced by PE@C&HMO-3.

Example 4

1) Preparation of a transition metal oxide-based functional material layer with crystal water: V ₂ O ₅ xH ₂ O, acetylene black, and LA were added to deionized water at a mass ratio of 85:15:5 and mixed to form a slurry , and then use the suction filtration (filtration) coating method to coat the above slurry on one side of the polyethylene-polypropylene double-layer separator, and then dry the slurry at 80°C for 10 hours in a vacuum to obtain a transition layer with crystal water. A composite separator with a metal oxide-based functional material layer (hereinafter referred to as PE/PP@C&HVO-4).

2) Assembly of lithium-sulfur battery: the same as in Example 1, the only difference is that sublimated sulfur is replaced by sulfur-carbon composite material, and PP@C&HTO-1 is replaced by PE/PP@C&HVO-4.

Example 5

1) Preparation of a transition metal oxide-based functional material layer with crystal water: WO ₃ ·xH ₂ O, carbon nanotubes, and PTFE were added to methanol at a mass ratio of 6:3:1 to form a slurry, and then Apply the above slurry on the surface of the positive electrode material layer made of sublimed sulfur by casting method, and then vacuum dry the slurry at 80°C for 10 hours to obtain a transition metal oxide-based functional material layer with crystal water Sulfur-based cathode (hereinafter referred to as S@C&HWO-5).

2) Lithium-sulfur battery assembly: S@C&HWO-5 is used as the positive electrode, metal lithium sheet is used as the negative electrode, the separator is a commercial lithium battery polypropylene-polyethylene-polypropylene separator, and the electrolyte is LiTFSI in DME and DOL A solution formed in a mixed solvent (the volume ratio of DME to DOL is 1:1, and the concentration of LiTFSI is 1mol/L). A 2032-type coin cell was assembled in a glove box with a high-purity argon atmosphere with both water and oxygen content below 1 ppm.

Example 6

1) Preparation of transition metal oxide-based functional material layer with crystal water: Fe ₂ O ₃ xH ₂ O, graphene and polyvinylidene fluoride were added to ethanol at a mass ratio of 70:15:15 and mixed to form Slurry, then use the doctor blade method to coat the above slurry on one side of the PAN porous membrane, and then dry the slurry at 60°C for 10 hours in vacuum to obtain a composite layer with a transition metal oxide-based functional material layer with crystal water Diaphragm (hereinafter referred to as PAN@C&HFO-6).

2) Assembly of lithium-sulfur battery: the same as in Example 1, the only difference is that the sublimated sulfur is replaced by a sulfur-carbon composite material, and PP@C&HTO-1 is replaced by PE/PP@C&HVO-6.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (16)

1. A lithium-sulfur battery, comprising: Sulfur-based cathode; Lithium-based negative electrode; a separator disposed between the sulfur-based positive electrode and the lithium-based negative electrode; and A functional material layer disposed between the sulfur-based positive electrode and the lithium-based negative electrode, the material of the functional material layer includes transition metal oxides with crystal water. 2. The lithium-sulfur battery according to claim 1, wherein the metal element in the transition metal oxide is selected from at least one of titanium, ruthenium, molybdenum, vanadium, tungsten, iron and cobalt. 3. The lithium-sulfur battery according to claim 1, wherein the transition metal oxides with water of crystallization include TiO ₂ ·xH ₂ O, H ₂ Ti _n O _2n+1 ·H ₂ O, RuO ₂ xH ₂ O, MoO ₃ xH ₂ O, (H ₃ O) _x MoO ₃ xH ₂ O, _{HyV 4} O ₁₀ xH ₂ O, H _z V ₂ O ₅ xH ₂ O, V ₂ O ₅ xH ₂ O, V ₂ O ₄ xH ₂ O, WO ₃ xH ₂ O, Fe ₂ O ₃ xH ₂ O and Co ₂ O ₃ xH ₂ O, 2≤n≤9 , 0.5≤x≤10, 0<y≤1, 0<z≤1. 4 . The lithium-sulfur battery according to claim 1 , wherein the primary particle size of the transition metal oxide with crystal water is 1 nanometer to 100 nanometers. 5 . The lithium-sulfur battery according to claim 1 , wherein the thickness of the functional material layer is 10 nm-200 μm, and the surface density is 0.1-10 mg/cm. 6. The lithium-sulfur battery according to claim 1, characterized in that, the material of the functional material layer further comprises an electronically conductive material and a binder, and the electronically conductive material and the binder are compatible with the The transition metal oxides are homogeneously mixed. 7. The lithium-sulfur battery according to claim 1, wherein the functional material layer is arranged on the surface of the sulfur-based positive electrode facing the lithium-based negative electrode, at least one surface of the separator, or the The lithium-based negative electrode faces the surface of the sulfur-based positive electrode. 8. The lithium-sulfur battery according to claim 1, wherein the functional material layer is disposed on both surfaces of the separator. 9. The lithium-sulfur battery according to claim 1, characterized in that, the mass percentage of the transition metal oxide with crystal water in the functional material layer is 5%-99%. 10. A diaphragm, which is used in lithium-sulfur batteries, characterized in that the diaphragm includes a diaphragm matrix and a functional material layer arranged on at least one surface of the diaphragm matrix, and the material of the functional material layer includes Transition metal oxides with water of crystallization. 11. A lithium-sulfur battery electrode assembly, characterized in that it comprises a sulfur-based positive electrode, a separator, and a functional material layer stacked on top of each other, and the functional material layer is arranged between the sulfur-based positive electrode and the separator, The material of the functional material layer includes transition metal oxide with crystal water. 12. A lithium-sulfur battery electrode assembly, characterized in that it comprises a lithium-based negative electrode, a diaphragm, and a functional material layer stacked on top of each other, and the functional material layer is arranged between the lithium-based negative electrode and the diaphragm, The material of the functional material layer includes transition metal oxide with crystal water. 13. A composite sulfur-based positive electrode, characterized in that it includes a positive electrode material layer, a positive electrode current collector, and a functional material layer stacked on each other, and the positive electrode material layer is arranged between the functional material layer and the positive electrode current collector. Between, the material of the functional material layer includes transition metal oxide with crystal water. 14. A composite lithium-based negative electrode, characterized in that it includes metal lithium and functional material layers stacked on each other, and the material of the functional material layer includes transition metal oxides with crystal water. 15. An application of a functional material layer, comprising coating the solid-liquid mixture containing the transition metal oxide with crystal water on the surface of at least one of the sulfur-based positive electrode, lithium-based negative electrode and separator , so that the functional material layer is formed between the sulfur-based positive electrode and the lithium-based negative electrode, thereby forming a lithium-sulfur battery. 16. The application of the functional material layer according to claim 15, further comprising: Drying and removing the solvent in the coating formed by the solid-liquid mixture at a temperature of 30-120°C.