DE102013011273A1 - Separator for a lithium-ion battery, and lithium ion battery containing the separator - Google Patents

Abstract

The invention relates to a separator for a lithium-ion battery, which separates the positive and the negative electrode of the lithium-ion battery and is permeable to lithium ions, characterized in that the separator at least one silica and at least one sulfur Component, as well as lithium-ion battery, comprising the separator.

Description

The present invention relates to a separator for a secondary battery, particularly a separator for a lithium-ion battery, preferably for a lithium-sulfur battery.

Secondary batteries, in particular lithium-ion batteries, are used as a driving force for mobile information devices because of their high energy density and high capacity. In addition, such batteries are used in tools, electric automobiles, and hybrid-powered automobiles. However, in order to be suitable for these uses, they should have high voltage, high capacity, and long life with high safety and reliability. However, it is known that under the influence of a high voltage, the performance and safety of the battery can be affected. For example, the separator located in the battery may be adversely affected. For example, undesirable growth of Li crystals, so-called Li dendrites or "lithium whiskers", can occur through the separator. These then connect the anode and the cathode of the battery together, which can result in a short circuit of the battery. This can lead to failure of the battery and / or affect the reliability and safety of the battery.

If the lithium-ion battery is designed as a lithium-sulfur battery, further adverse reactions can occur. For example, the polysulfides formed during the discharge at the sulfur electrode (cathode) can dissolve in the electrolyte of the battery and also remain dissolved there, which leads to a loss of active electrode mass. At the same time, polysulfide anions can migrate through the separator to the lithium metal electrode (anode) where they can form insoluble products. This also affects the performance of the battery.

It is an object of the present invention to provide a separator for a secondary battery, preferably a lithium-ion secondary battery, particularly for a lithium-sulfur secondary battery, which further improves the characteristics of separators, and which makes it possible to provide a battery as well remains as stable as possible at high voltages and is therefore durable, especially a lithium-sulfur secondary battery.

This object is achieved with a separator as defined in claim 1. Advantageous developments of the separator are defined in the claims dependent on claim 1.

First aspect of the invention - Separator according to the invention

According to a first aspect, the invention relates to a separator for a lithium-ion battery, which separates a positive and a negative electrode of the lithium-ion battery and is substantially transparent to lithium ions,
characterized in that
the separator comprises at least one silica and at least one sulfur component.

In one embodiment, the sulfur component is elemental sulfur or a sulfide, or a combination of both.

The inventors have found that a silica in combination with a sulfur component, preferably sulfur at least partially, preferably substantially, in the oxidation state 0 or -2, the formation of lithium dendrites or lithium whiskers in the separator of a lithium-ion Effectively prevent or at least reduce the battery. In the case of a lithium-sulfur battery, the silica in combination with the sulfur component can also effectively minimize or prevent the unwanted migration of polysulfide anions through the separator.

In addition, the inventors have surprisingly found that moisture can be effectively bound by the separator according to the invention in the event of a moisture intrusion into the lithium-ion battery, whereby the possible formation of hydrogen fluoride from fluorine-containing electrolytes can be effectively prevented or at least minimized.

The inventors have further found that even adverse gas formation in the battery, for example damage to the battery, can be prevented or at least minimized since gases can be absorbed by the silica and the sulfur component.

Further, the inventors have found that the dimensional stability of a lithium-ion battery using the separator of the present invention can be improved because the aging-frequently observed swelling or dimensional change of the battery is reduced. Likewise, dislocations in the battery caused by the manufacturing process can be minimized or advantageously compensated.

Secondary batteries comprising the separator according to the invention can thus have a high durability and safety, which is their use in tools, electrically powered automobiles and in hybrid-powered automobiles is extremely beneficial.

The terms defined below are defined within the meaning of the invention.

The term "separator" refers to the element of a lithium-ion battery which separates the anode and the cathode of the battery. The separator used for the battery must be substantially transparent to lithium ions in order to ensure the ion transport of the lithium ions between the positive and the negative electrode. On the other hand, the separator for electrons should be insulating or at least poorly conductive.

According to the invention, the separator comprises one or more silicas and one or more sulfur components.

The term "silicic acid" includes all known to the expert oxygen acids of silicon of the general formula H _{2n + 2} Si _n O _{3n + 1} , so for example monosilicic acid (orthosilicic acid) Si (OH) ₄ diclitic acid (pyrosilicic acid) (HO) ₃ Si-O- Si (OH) ₃ and trisilicic acid (HO) ₃ Si-O-Si (OH) ₂ -O-Si (OH) ₃ . The term also includes cyclic silicas such as. B. Cyclotrikieselsäure and Cyclotetrakieselsäure with the general empirical formula [Si (OH) ₂ -O-] _n and long-chain silicas of the general empirical formula H ₂ SiO ₃ , [-Si (OH) ₂ -O-] _n ), also referred to as meta-silicic acid. The term also includes amorphous colloids (silica sols) and silicas such as fumed silicas of the formula SiO ₂ . Furthermore, the term also includes salts of the acids, preferably the alkali metal salts, wherein alkali is preferably Li, and the term "silica gel".

The term "fumed silica" means amorphous silica powder, preferably with a diameter of 5-50 nm and a specific surface area of 5-800 m ² / g. Pyrogenic silicas can be prepared by known methods by flame hydrolysis or silicon tetrachloride.

The term "silica" also includes silica in the form of a xerogel. Such gels can be prepared by known methods from suitable silicon-containing precursor compounds, such as silicon-alkoxy compounds, by a sol-gel process wherein the sol phase is hydrolyzed and condensed to form a moist but solid gel phase becomes. By drying the gel phase, which i. A. does not occur under supercritical conditions, the fluid is removed from the gel to form a dried, monolithic matrix having an open network of pores ("xerogel"). The dried gel monolith may then be calcined to form a solid, glassy monolith having interconnected pores. This monolith can be further densified, for example by sintering, whereby the monolith can be converted into a glass or a ceramic. Of course, it is possible to comminute the xerogel for the use according to the invention to desired particle sizes, preferably by milling. Xerogels are preferred silicas for the purposes of the present invention.

In one embodiment, the xerogel is in particulate form, the particles having a spherical shape.

In another embodiment, the particles of xerogel may have a stretched and elongated shape.

Preferred silicic acids have a BET surface area of 5-800, preferably 10-500, particularly preferably 50-300 m ² / g.

Suitable silicic acids are commercially available or can be prepared by known methods, for example by methods such as DE 101 51 777 A1 disclosed.

Particularly suitable for the purposes of the invention, the silicas have proven, marketed under the name "Sipermat ^®" and "ident ^®" by the company Evonik (Germany).

The separator has sulfur at least partially, preferably substantially, in the oxidation state 0 or -2.

In one embodiment, the term "sulfur" refers to elemental sulfur (oxidation state 0). Elemental sulfur can be used in the known allotropic forms.

In a further embodiment, the term "sulfur" denotes a sulfide, ie compounds which contain the di-negatively charged sulfide anion S ^2- (oxidation state -2), preferably an inorganic sulfide, preferably a metal sulfide. Examples of sulfides are alkali metal, alkaline earth metal and earth metal sulfides and sulfides of the transition metals, such as iron, zinc, copper sulfide or molybdenum sulfide.

In one embodiment, the content of silica and sulfur, as present together in the separator, 0.1 to 60 wt .-% based on the total weight of the separator, preferably 0.5 to 50 wt .-%, more preferably 1 to 40 wt .-%.

In one embodiment, the weight ratio of silica to sulfur is Component 10: 1 to 1:10, preferably 5: 1 to 1: 5, more preferably 2.5: 1 to 1: 2.5.

In one embodiment, the weight ratio of silica to sulfur or the corresponding sulfur compound of the oxidation state is -2 or +6, 5: 1, more preferably 10: 1, more preferably 100: 1.

In one embodiment of the separator according to the invention, the separator has a polymer film.

In a further embodiment, the separator has woven polymer fibers.

In a further embodiment, the separator has a nonwoven web of nonwoven polymer fibers.

Preferably, the polymers used for the film or fibers are non-conductive to electrons, that is, to be electron-insulating.

The separator used for the battery must be permeable to lithium ions to ensure ion transport for lithium ions between the positive and negative electrodes.

In the case of a lithium-sulfur battery, the separator should be impermeable to sulfide and polysulfide anions. This prevents the circulation of such ions in the battery and their diffusion to the electrode comprising metallic lithium or a lithium alloy. This minimizes or even prevents the formation of undesirable sparingly soluble sulfides on this electrode.

The term "fleece" is used interchangeably with terms such as "nonwoven fabrics", "nonwoven material", "knits" or "felt". Instead of the term "unwoven" the term "not woven" is used.

Preferably, the polymers for the polymer film or fibers are selected from the group of polymers consisting of polyacrylonitrile, polyolefin, polyester, polyimide, polyetherimide, polysulfone, polyamide, polyether.

Suitable polyolefins are preferably polyethylene, polypropylene, polytetrafluoroethylene, or polyvinylidene fluoride.

Preferred polyesters are polyethylene terephthalates.

The polymer film or the woven or non-woven polymer fibers are preferably coated on one or both sides with a porous inorganic material.

In a preferred embodiment, the separator is formed as a fleece of nonwoven polymer fibers.

Particularly preferably, the separator has a porous inorganic coating on or on and in the nonwoven.

A preferred separator is marketed under the trade name "Separion ^®" by the company Evonik AG in Germany and above previously disclosed in the prior art. Processes for producing such separators are known, for example, from US Pat EP 1 017 476 B1 . WO 2004/021477 and WO 2004/021499 known.

In one embodiment, the polymer fibers or the nonwoven fabric of polymer fibers are coated on one or both sides with an ion-conducting inorganic material, and / or are penetrated by it.

In a further embodiment, the ion-conducting inorganic material is ion-conducting for lithium ions in a temperature range of -40 ° C to 200 ° C, wherein the material used for the coating at least one compound selected from the group of oxides, phosphates, sulfates, titanates, silicates Aluminosilicate is at least one of the elements zirconium, aluminum, silicon or lithium.

In a further embodiment, the ion-conducting material comprises or consists of aluminum oxide or zirconium oxide or aluminum oxide and zirconium oxide.

In one embodiment, the inorganic ion conducting material preferably comprises particles, preferably having 90% (D90) (or more) a largest diameter below 100 nm.

In principle, too large pores and holes in separators used in secondary batteries can lead to an internal short circuit. The battery can then discharge itself very quickly in a dangerous reaction. In this case, such large electrical currents can occur that a closed battery cell can even explode in the worst case. For this reason, the separator can contribute significantly to the safety or lack of security of a lithium high performance or Lithiumhochenergiebie battery.

The separators according to the invention stop at a certain temperature (the so-called "shut-down temperature") typically at about 120 ° C) any current transport through the electrolyte. This happens because at this temperature, the pore structure of the separator collapses and all pores are closed. The fact that no ions can be transported, the dangerous reaction that can lead to an explosion, comes to a standstill. However, if the cell continues to be heated due to external circumstances, the so-called "break-down temperature" is exceeded at approx. 150 to 180 ° C. From this temperature it comes in conventional separators to melt the separator, which contracts. In many places in the battery cell, there is now a direct contact between the two electrodes and thus to a large internal short circuit. This leads to an uncontrolled reaction, which can end with an explosion of the cell, or the resulting pressure must be reduced by a pressure relief valve (preferably a rupture disk) often under fire phenomena.

In the separator according to the invention comprising a fleece of nonwoven polymer fibers and an inorganic coating, which is used in a secondary battery, in particular a lithium-ion battery, it can only come to shutdown (shutdown) if the polymer structure of the carrier material melts due to the high temperature and penetrates into the pores of the inorganic material and thereby closes them. On the other hand, there is no such break-down (collapse) as the inorganic particles ensure that complete melting of the separator can not occur. This ensures that there are no operating states in which a large-area short circuit can occur. By the type of nonwoven used, which has a particularly suitable combination of thickness and porosity, separators can be produced that can meet the requirements for separators in high-performance batteries, especially lithium high-performance batteries. By the simultaneous use of particle size exactly matched oxide particles for the production of the porous (ceramic) coating, a particularly high porosity of the finished separator is achieved, wherein the pores are still sufficiently small to prevent unwanted growth of "lithium whiskers" through the separator to minimize.

In one embodiment of the separator according to the invention, in particular a separator of the type Separion ^® , which according to the invention additionally contains a silica and a sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2, the intergrowth of dendrites or whiskers on be minimized advantageous, as well as the migration of Polysulfidanionen.

Due to the high porosity in conjunction with the small thickness of the separator according to the invention, it is also possible to impregnate the separator completely or at least almost completely with the electrolyte, so that no or only small dead spaces in individual areas of the separator and thus in certain windings or laminations the battery cells may arise in which there is no electrolyte. This is achieved in particular by the compliance of the particle size of the oxide particles, the resulting separators are free or virtually free of closed pores, in which the electrolyte can not penetrate. The separators according to the invention used for the invention also have the advantage that partially adhere to the inorganic surfaces of the separator material, the anions of the conducting salt, which leads to an improvement in the dissociation and thus to a better ionic conductivity in the high current range. Another not inconsiderable advantage of the separator is the very good wettability. Due to the hydrophilic ceramic coating, wetting with electrolytes takes place very rapidly, which likewise leads to improved conductivity.

The separators according to the invention, preferably comprising a flexible nonwoven with a porous inorganic coating on and in this nonwoven, the material of the nonwoven being selected from nonwoven, non-electrically conductive polymer fibers, and further comprising a silica and a sulfur component, are also distinguished characterized in that the web has a thickness of less than 30 microns, a porosity of more than 50%, preferably from 50 to 97% and a pore radius distribution, wherein at least 50% of the pores have a pore radius of 75 to 150 microns.

Particularly preferably, a separator according to the invention comprises a nonwoven which has a thickness of 5 to 30 μm, preferably a thickness of 10 to 20 μm. Also particularly advantageous is a very homogeneous pore radius distribution in the nonwoven as indicated above. A maximized homogeneous distribution of pore radii in the fleece, in combination with optimally matched oxide particles of a certain size, leads to an optimized porosity of the separator. The thickness of the substrate has a great influence on the properties of the separator, since on the one hand the flexibility but also the sheet resistance of the electrolyte-impregnated separator depends on the thickness of the substrate. Due to the small thickness, a particularly low electrical resistance of the separator is achieved in the application with an electrolyte. The separator itself has a very high electrical resistance, since it itself should have insulating properties. In addition, thinner separators allow increased packing density in a battery stack so that you can store in the same volume a larger amount of energy.

Preferably, the web has a porosity of 60 to 90%, more preferably from 70 to 90%. The porosity is defined as the volume of the web (100%) minus the volume of the fibers of the web, ie the proportion of the volume of the web that is not filled by material.

The volume of the fleece can be calculated from the dimensions of the fleece. The volume of the fibers results from the measured weight of the fleece considered and the density of the polymer fibers. The large porosity of the substrate also allows a higher porosity of the separator, which is why a higher uptake of electrolytes with the separator can be achieved. In order to obtain a separator having insulating properties, it has as polymer fibers for the non-woven fabric preferably non-electrically conductive fibers of polymers as defined above, which are preferably selected from polyacrylonitrile (PAN), polyesters such. As polyethylene terephthalate (PET) and / or polyolefin (PO), such as. As polypropylene (PP) or polyethylene (PE), or mixtures of such polyolefins.

The polymer fibers of the nonwovens preferably have a diameter of from 0.1 to 10 .mu.m, more preferably from 1 to 4 .mu.m.

Particularly preferred flexible nonwovens have a basis weight of less than 20 g / m ² , preferably from 5 to 10 g / m ² .

Preferably, the nonwoven is flexible and has a thickness of less than 30 microns.

In one embodiment, a separator according to the invention has a porous, electrically insulating, ceramic coating, in particular on and in the polymer film or on or in the polymer fibers, preferably in the nonwoven web of nonwoven polymer fibers.

The porous inorganic coating on and in the film or the fibers, preferably in the nonwoven, preferably has oxide particles of the elements Li, Al, Si and / or Zr with an average particle size of 0.5 to 7 μm, preferably of 1 to 5 microns and most preferably from 1.5 to 3 microns.

Particularly preferably, a separator according to the invention has on and in the film or fibers, preferably a porous inorganic coating on and in the nonwoven, which has aluminum oxide particles. Preferably, these have an average particle size of 0.5 to 7 microns, preferably from 1 to 5 microns and most preferably from 1.5 to 3 microns. In one embodiment, the alumina particles are bonded to an oxide of elements Zr or Si.

In order to achieve the highest possible porosity, preferably more than 50% by weight and more preferably more than 80% by weight of all particles are within the abovementioned limits of average particle size. As already described above, the maximum particle size is preferably 1/3 to 1/5 and particularly preferably less than or equal to 1/10 of the thickness of the nonwoven used.

Preferably, a separator according to the invention has a porosity of from 30 to 80%, preferably from 40 to 75% and particularly preferably from 45 to 70%. The porosity refers to the achievable, ie open pores. The porosity can be determined by the known method of mercury porosimetry or can be calculated from the volume and density of the starting materials used, if it is assumed that only open pores are present. The separators used for the battery according to the invention are also distinguished by the fact that they can have a tensile strength of at least 1 N / cm, preferably of at least 3 N / cm and very particularly preferably of 3 to 10 N / cm. The separators can preferably be bent without damage to any radius down to 100 mm, preferably down to 50 mm, and most preferably up to a radius down to 1 mm.

The high tear strength and the good bendability of a separator according to the invention have the advantage that changes occurring in the charging and discharging of a battery of the geometries of the electrodes can be tolerated by the separator, without this being damaged. The flexibility also has the advantage that commercially standardized winding cells can be produced with this separator. In these cells, the electrode / separator layers are spirally wound together in a standardized size and contacted.

In one embodiment, it is possible to design a separator according to the invention so that it has the shape of a concave or convex sponge or pad or the shape of wires or a felt. This embodiment is well suited to compensate for volume changes in the battery. Corresponding preparation methods are known to the person skilled in the art.

In a further embodiment, the polymer fleece used in a separator according to the invention comprises a further polymer. Preferably, this polymer is between the separator and the negative electrode and / or the separator and the positive electrode, preferably in the form of a polymer layer.

In one embodiment, the separator is coated with this polymer on one or both sides.

Said polymer may be in the form of a porous membrane, i. H. as a film, or in the form of a nonwoven, preferably in the form of a nonwoven fabric of non-woven polymer fibers.

These polymers are preferably selected from the group consisting of polyester, polyolefin, polyacrylonitrile, polycarbonate, polysulfone, polyethersulfone, polyvinylidene fluoride, polystyrene, polyetherimide.

Preferably, the further polymer is a polyolefin. Preferred polyolefins are polyethylene and polypropylene.

The separator is preferably coated with one or more layers of the further polymer, preferably of the polyolefin, which is preferably also present as a nonwoven, that is to say as nonwoven polymer fibers.

Preferably, a non-woven of polyethylene terephthalate is used in the separator, which is coated with one or more layers of the further polymer, preferably of the polyolefin, which is preferably also present as non-woven, so as non-woven polymer fibers.

Particularly preferred is a separator of the above-described type of separation, which is coated with one or more layers of the other polymer, preferably the polyolefin, which is preferably also present as a nonwoven, so as non-woven polymer fibers.

The coating with the further polymer, preferably with the polyolefin, can be achieved by gluing, lamination, by a chemical reaction, by welding or by a mechanical connection. Such polymer composites and processes for their preparation are known from EP 1 852 926 known.

The fiber diameters of the polyethylene terephthalate fleece are preferably larger than the fiber diameters of the further polymer fleece, preferably the polyolefin fleece, with which the separator is coated on one or both sides.

Preferably, the nonwoven made of polyethylene terephthalate then has a higher pore diameter than the nonwoven, which is made of the other polymer.

Preferably, the nonwovens usable in the separator are made of nanofibers of the polymers used, whereby nonwovens are formed which have a high porosity with formation of small pore diameters. This can further reduce the risk of short-circuit reactions.

The use of a polyolefin in addition to the polyethylene terephthalate ensures increased safety of the electrochemical cell, since in unwanted or excessive heating of the cell, the pores of the polyolefin contract and the charge transport through the separator is reduced or terminated. Should the temperature of the electrochemical cell increase to such an extent that the polyolefin begins to melt, the polyethylene terephthalate effectively counteracts the melting together of the separator and thus an uncontrolled destruction of the electrochemical cell.

In one embodiment, a separator according to the invention preferably consists of or comprises a substantially material-permeable carrier, wherein the carrier is coated on at least one side with an inorganic material, wherein as an essentially permeable carrier preferably an organic material is used, which preferably is not woven web is configured, wherein the organic material is preferably a polymer and particularly preferably a polymer selected from polyethylene terephthalate, wherein the organic material is coated with an inorganic ion-conductive material, or is penetrated by this, which preferably in a temperature range of -40 ° C. is conductive to 200 ° C ion, wherein the inorganic, ion-conducting material is preferably at least one compound selected from the group of oxides, phosphates, sulfates, titanates, silicates, aluminosilicates at least one of the elements Zr, Al, Li, and wherein the inorganic material preferably has particles with a largest diameter below 100 nm, wherein the separator comprises at least one silica and at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2.

• (α1) im Polymerfilm; und/oder
• (α2) auf dem Polymerfilm; oder
• (β1) in den Polymerfasern; und/oder
• (β2) auf den Polymerfasern; oder
• (γ1) im ionenleitenden anorganischen Material; und/oder
• (γ2) auf dem ionenleitenden anorganischen Material.

In one embodiment of the separator, the at least one silica and the at least one sulfur component are present

• (α1) in the polymer film; and or
• (α2) on the polymer film; or
• (β1) in the polymer fibers; and or
• (β2) on the polymer fibers; or
• (γ1) in the ion-conducting inorganic material; and or
• (γ2) on the ion-conducting inorganic material.

In one embodiment, it is precluded that the separator according to the invention comprises a carbon component. The term "carbon" or "carbon component" as used herein includes all known carbon modifications and carbon forms of elemental carbon, preferably graphite, amorphous carbon, glassy carbon, graphene, activated carbon, carbon black, carbon nanotubes, carbon nanofoam, fullerenes, or mixtures of two or more from that.

Second Aspect of the Invention - Battery having the separator as defined in the first aspect

According to a second aspect, the invention relates to a lithium-ion battery which has the separator according to the invention.

• (a) eine positive Elektrode;
• (b) eine negative Elektrode;
• (c) einen erfindungsgemäßen Separator wie im ersten Aspekt definiert;
• (d) einen nicht-wässerigen Elektrolyt.

The lithium-ion battery has at least:

• (a) a positive electrode;
• (b) a negative electrode;
• (c) a separator according to the invention as defined in the first aspect;
• (d) a nonaqueous electrolyte.

The terms "lithium-ion battery" and "lithium-ion secondary battery" are used synonymously. The terms also include the terms "lithium battery", "lithium ion secondary battery" and "lithium ion cell". A lithium-ion battery generally consists of a serial or series connection of individual lithium-ion cells. The term "lithium-sulfur / -battery" includes terms such as "lithium-sulfur secondary battery"; "Lithium Sulfide Battery" "Lithium Sulfur Accumulator" "Lithium Sulfur Cell" and the like. This means that the term "lithium-ion battery" is used as a generic term for the terms mentioned in the prior art.

electrodes

The term "positive electrode" means the electrode that is capable of accepting electrons when the battery is connected to a consumer, such as an electric motor. So it represents the cathode.

The term "negative electrode" means the electrode that is capable of delivering electrons when in use. This electrode thus represents the anode.

In one embodiment, a cathode material comprising a lithium transition metal oxide is used for the lithium-ion battery according to the invention.

In one embodiment of the electrochemical cell of the present invention, the positive electrode contains a lithium mixed oxide.

Preferably, the mixed oxide contains one or more elements selected from nickel, manganese and cobalt.

Such electrode material is known in the art. These oxides used for the positive electrode are commercially available or can be prepared by known methods.

In one embodiment, the positive electrode comprises lithium iron phosphate. The phosphate may additionally contain Mn, Co or Ni, or combinations thereof.

In a further embodiment, the positive electrode comprises a lithium transition metal phosphate such as lithium manganese phosphate, lithium cobalt phosphate or lithium nickel phosphate.

The positive electrode may also contain mixtures of two or more of said substances.

The positive electrode preferably contains the lithium compound in the form of nanoparticles.

The nanoparticles can take any shape, that is, they can be coarse-spherical or elongated.

In one embodiment, the lithium compound has a particle size measured as D90 value of less than 15 microns. Preferably, the particle size is less than 10 microns.

In a further embodiment, the lithium compound has a particle size measured as D90 value between 0.005 μm to 10 μm. In a further embodiment, the lithium compound has a particle size measured as a D90 value of less than 10 μm, the D50 value being 4 μm ± 2 μm and the D10 value being less than 1.5 μm.

The values given are determined by measurement using static laser light scattering (laser diffraction, laser diffractometry) as known in the art.

Further, it is also possible that the lithium compound contains carbon to increase the conductivity. Such compounds can be prepared by known methods, for example by coating with carbon compounds such as acrylic acid or ethylene glycol. It is then pyrolyzed, for example at a temperature of 2500 ° C.

The negative electrode may be fabricated from a variety of materials known for use in a prior art lithium-ion battery. In principle, all materials that are capable of forming lithium intercalation compounds can be used.

Preferably, the negative electrode may contain lithium metal or lithium in the form of an alloy, either in the form of a foil, a grid, or in the form of particles held together by a suitable binder.

The use of lithium metal oxides such as lithium titanium oxide is also possible.

Suitable materials for the negative electrode also include graphite, synthetic graphite, carbon black, mesocarbon, doped carbon, fullerenes. Niobium pentoxide, tin alloys, titanium dioxide, tin dioxide, silicon are also usable.

The materials used for the positive as well as for the negative electrode are preferably held together by a binder holding these materials on the electrode. For example, polymeric binders can be used. As the binder, for example, polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylate, ethylene (propylene-diene) copolymer (EPDM), and mixtures and copolymers thereof can be used.

Particularly in the case of the inventive use of silica, preferably in the form of a xerogel or in the form of xerogels, this can have a favorable effect on the anode, in particular on the maintenance of the solid electrolyte interface layer (SEI layer). As is known, this layer prevents the penetration of electrolyte components into the anode and the reaction of these components with lithium. When this layer is damaged, uncontrolled ignition of the anode material can occur as a consequence, in particular if it has carbon. By suppressing or minimizing the formation of dendrites on the anode and a corresponding damage to the SEI layer is suppressed or minimized, which is extremely favorable for the safety and longevity of the battery according to the invention.

In the case of a lithium-sulfur battery, the electrode (b) comprises metallic lithium. When discharging the battery, (b) the negative electrode (anode) and the other electrode (a) are the positive electrode (cathode). The electrochemical reaction can be described as follows:

• (A) Cathode: S ₈ + 2Li ⁺ + e ^- → Li ₂ S ₈ ; Li ₂ S ₈ → Li ₂ S _n + (8 - n) S);
• (B) Anode: Li → Li ⁺ + e ^- .

Preferably, the positive electrode has a matrix of carbon in which the sulfur and / or the lithium sulfide are embedded.

In a further embodiment, the negative electrode comprises a lithium alloy. Suitable lithium alloys are preferably alloys of lithium with aluminum and tin, for example LiAl and Li ₂₂ Sn ₅ .

The lithium alloy is preferably embedded in a matrix of carbon. Preferably, in this embodiment, the positive electrode also comprises a matrix of carbon.

In one embodiment, the negative electrode comprises an alloy of lithium and tin together with carbon. The discharge electrochemical reaction can be described as follows:

• (A) Cathode: 11S + C + 22Li ⁺ + 22 ^e- → 11Li ₂ S / C;
• (B) Anode: Li ₂₂ Sn ₅ + C → 22Li ⁺ + 5Sn / C + 22 ^e- .

It is known that electrodes comprising metallic lithium or a lithium alloy can have the property of expanding during the charging process and contracting during the discharging process. This can lead to power loss of the battery. By using a lithium alloy in a matrix of carbon, it is possible to compensate for volume changes of the battery advantageous.

In a further embodiment, the negative electrode comprises silicon wires whose dimensions are in the nanoscale. Through the use of silicon as a nanowire can also the unwanted volume change of the anode during Charging or unloading counteracted. Silicon nanowire negative electrodes are also known from lithium ion batteries.

In another embodiment, the silicon (in the form of nanowires) replaces the carbon in the anode.

Non-aqueous electrolyte

Suitable electrolytes for the battery according to the invention are known from the prior art. The electrolytes preferably comprise a liquid and a conducting salt. Preferably, the liquid is a solvent for the conducting salt. Preferably, the electrolyte is present as an electrolyte solution.

Suitable solvents are preferably inert. Suitable solvents include, for example, solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, dipropyl carbonate, cyclopentanones, sulfolanes, dimethylsulfoxide, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, 1,2-diethoxymethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, nitromethane, 1,3-propanesultone.

In one embodiment, ionic liquids may also be used.

Ionic liquids are known in the art. They contain only ions. Examples of useful cations which may in particular be alkylated are imidazolium, pyridinium, pyrrolidinium, guanidinium, uronium, thiuronium, piperidinium, morpholinium, sulfonium, ammonium and phosphonium cations. Examples of useful anions are halide, tetrafluoroborate, trifluoroacetate, triflate, hexafluorophosphate, phosphinate and tosylate anions.

Examples of ionic liquids which may be mentioned are: N-methyl-N-propyl-piperidinium-bis (trifluoromethylsulfonyl) imide, N-methyl-N-butyl-pyrrolidinium-bis (trifluoromethyl-sulfonyl) -amide, N-butyl-N-trimethyl-ammonium bis (trifluoromethylsulfonyl) imide, triethylsulfonium bis (trifluoromethylsulfonyl) imide, N, N-diethyl-N-methyl-N- (2-methoxyethyl) -ammonium bis (trifluoromethylsulfonyl) -imide. Two or more of the above liquids can be used.

Preferred conductive salts are lithium salts which have inert anions and which are non-toxic. Suitable lithium salts are, for example, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis (trifluoromethylsulfonyl imide), lithium trifluoromethanesulfonate, lithium tris (trifluoromethylsulfonyl) methide, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate, lithium chloride, lithium bisoxalatoborate, lithium difluorooxalato borate, and mixtures of two or more thereof.

The use of gel electrolytes is also possible.

In the case of a lithium-sulfur battery, it is preferable to add polysulfide anions to the electrolyte, for example in the form of Li ₂ S ₃ , Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ . In one embodiment, the amount of polysulfide added is such that the electrolyte is saturated with polysulfide. Thus, the fading of the negative electrode to sulfur can be counteracted. The addition of polysulfide is preferably carried out before the battery is started up.

The electrolyte may include other adjuvants commonly used in electrolytes for lithium ion batteries. For example, these are free-radical scavengers such as biphenyl, flame retardant additives such as organic phosphoric acid esters or hexamethylphosphoramide, or acid scavengers such as amines. Additives such as vinylene carbonate, which can influence the formation of the "solid electrolyte interface" layer (SEI) on the electrodes, preferably carbon-containing electrodes, can also be used.

Separator and battery production

The preparation of the separator according to the invention can be carried out analogously to known methods.

It is possible to use all processes with which it is possible to incorporate a silica and a sulfur component at least partially, preferably substantially, in the oxidation state 0 or -2 into a material and / or apply to a material which acts as a separator in a lithium-ion battery can be used.

Silica and sulfur component at least partially, preferably substantially, in the oxidation state 0 or -2 are preferably used in powder form.

In one embodiment, the at least one silica and the at least one sulfur component are used in the form of a mixture.

In one embodiment, it is preferred to mix the at least one silica and the at least one sulfur component, at least in part, preferably substantially, in the oxidation state 0 or -2, with a material to be used as a separator and the mixture to process a separator, which now contains the at least one silica and the at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2.

In one embodiment, it is preferred to mix the at least one silica and the at least one sulfur component, preferably substantially, in the oxidation state 0 or -2 with a polymer and to extrude the mixture into a polymer film or polymer fiber, wherein the Polymer film or the polymer fiber containing at least one silica and the at least one sulfur component at least partially, preferably substantially, in the oxidation state 0 or -2.

In a further embodiment it is preferred to apply the at least one silica and the at least one sulfur component at least partially, preferably substantially, in the oxidation state 0 or -2, in paste form, preferably containing suitable binders, to a polymer film or polymer fiber. such that the at least one silicic acid and the at least one sulfur component, at least in part, preferably substantially, in the oxidation state 0 or -2, are present as a coating on the polymer film or the polymer fiber.

In a further embodiment it is preferred to mix the at least one silica and the at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2, with a ceramic material, and this mixture in paste form, which preferably suitable binder comprises applying to a polymer film or to a polymer fiber, wherein the resulting ceramic coating containing at least one silica and the at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2. Preferably, the ceramic (inorganic) material is ion conducting, preferably ion conducting for lithium ions.

In a further embodiment, it is preferred to apply the at least one silica and the at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2 in paste form, preferably containing suitable binders, to a ceramic layer of a separator, wherein a polymer film or polymer fiber is coated with the ceramic layer such that the at least one silica and the at least one sulfur component are at least partially, preferably substantially, in the oxidation state 0 or -2 as a coating on the ceramic layer of the separator ,

Optionally, these steps are followed by drying steps.

In a further embodiment, it is also preferable to process at least one silicic acid and at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2 separately from one another.

The preparation of the lithium-ion battery according to the invention may preferably be carried out by precipitating a suitable lithium compound as a powder on the electrode to produce the positive electrode and compacting it into a thin film, optionally with the use of a binder. The negative electrode may be laminated on the positive electrode, and the separator in the form of a foil is previously laminated on the negative or the positive electrode. It is also possible to simultaneously process the positive electrode, the separator and the negative electrode under mutual lamination.

A lithium-sulfur battery may be constructed from components (a) through (d) according to principles known in the art and commonly used for the production of lithium-sulfur batteries.

For example, to produce the positive electrode, sulfur may be ground with carbon, for example in the form of graphite, in a binder. The mass obtained can then be pressed onto aluminum foil, for example. To produce the negative electrode, for example, lithium foil or a lithium alloy foil may be pressed onto a suitable carrier. The separator is soaked in electrolyte and the electrodes are laminated to the impregnated separator. It will get an already charged battery.

In a further embodiment, it is also possible to produce the battery in the discharged state. For this purpose, a positive electrode is produced, which contains a composite of a lithium sulfide and carbon. The negative electrode comprises the support for the lithium metal but is free of lithium metal or lithium alloy. The separator is soaked in electrolyte and the electrodes are laminated to the impregnated separator. When charging the battery, the electrodes are transferred to the sulfur electrode and the electrode with lithium metal or lithium alloy.

Third aspect of the invention - Use of the battery according to the invention as defined in the second aspect

According to a third aspect, the present invention relates to the use of the battery according to the invention.

With the battery according to the invention, a high energy density and capacity can be made available at high voltage, wherein the battery has good stability even at high voltage output. Therefore, it can preferably be used for powering mobile information devices, tools, electric cars, and hybrid cars.

Preferably, the lithium battery according to the invention can be operated at ambient temperatures of -40 to + 100 ° C.

Preferred discharge currents of a battery according to the invention are greater than 100 A, preferably greater than 200 A, preferably greater than 300 A, more preferably greater than 400 A.

Fourth aspect of the invention - Use of the separator according to the invention as defined in the first aspect

According to a fourth aspect, the present invention relates to the use of at least one silicic acid and at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2, in a lithium-ion battery.

In one embodiment, the invention relates to the use of at least one silica and at least one sulfur component, at least in part, preferably substantially, in the oxidation state 0 or -2, in a separator of a lithium-ion battery.

• (j) Erniedrigen der Li-Dendriten- oder Whiskerbildung im Separator; und/oder zum
• (jj) Binden von Wasser und/oder Fluorwasserstoff in der Lithium-Ionen-Batterie; und/oder zum
• (jjj) Erhöhen der Dimensionsstabilität des Separators oder des Separators und der Lithium-Ionen-Batterie; und/oder zum
• (jv) Gasabsorbieren in der Lithium-Ionen-Batterie; und/oder zum
• (v) Erniedrigen der Diffusion von Polysulfidanionen durch den Separator.

In one embodiment, the invention relates to the use of at least one silica and at least one sulfur component, at least in part, preferably substantially, in the oxidation state 0 or -2, in a separator of a lithium-ion battery for

• (j) lowering Li-dendrite or whisker formation in the separator; and / or to
• (jj) binding of water and / or hydrogen fluoride in the lithium-ion battery; and / or to
• (jjj) increasing the dimensional stability of the separator or separator and the lithium-ion battery; and / or to
• (jv) absorbing gas in the lithium-ion battery; and / or to
• (v) lowering the diffusion of polysulfide anions through the separator.

In the use according to the invention, all advantages (j) to (v) are preferably achieved.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10151777 A1 [0022]
• EP 1017476 B1 [0043]
• WO 2004/021477 [0043]
• WO 2004/021499 [0043]
• EP 1852926 [0075]

Claims (16)

A separator for a lithium-ion battery, which separates a positive and a negative electrode of the lithium-ion battery and is substantially permeable to lithium ions, characterized in that the separator comprises at least one silica and at least one sulfur component , Separator according to claim 1, wherein the separator comprises sulfur in the sulfur component at least partially in the oxidation state 0 or -2. Separator according to claim 1 or 2, wherein the content of silica and of sulfur component together from 0.1 to 60 wt .-%, based on the total weight of the separator. A separator according to any one of the preceding claims, wherein the weight ratio of silica to sulfur component is from 5: 1 to 1: 5. Separator according to one of the preceding claims, wherein the separator comprises a polymer film or woven polymer fibers or a nonwoven web of nonwoven polymer fibers. A separator according to claim 5, wherein the polymer is selected from a group containing or consisting of: polyacrylonitrile, polyolefin, polyester, polyimide, polyetherimide, polysulfone, polyamide, polyether, or two or more of these materials. Separator according to one of claims 5 or 6, wherein the polymer film or the polymer fibers or the web of polymer fibers on one or both sides is coated with an ion-conducting inorganic material and / or is penetrated by this. Separator according to claim 7, wherein the ion-conducting inorganic material in a temperature range of -40 ° C to 200 ° C ion conducting for lithium ions, wherein the material used for the coating at least one compound selected from the group of oxides, phosphates, sulfates, titanates , Silicates, aluminosilicates at least one of zirconium, aluminum, silicon or lithium. A separator according to claim 7 or 8, wherein the ion-conductive material comprises or consists of alumina or zirconia or alumina and zirconia. Separator according to one of claims 7 to 9, wherein the inorganic ion-conducting material preferably comprises at least 90% of the particles (D90) having a maximum diameter below 100 nm. Separator according to one of claims 1 to 3, wherein the separator preferably comprises a substantially permeable material carrier, wherein the carrier is coated on at least one side with an inorganic material, and / or is penetrated by it, wherein as a substantially permeable material carrier preferably a organic material is used, which is preferably designed as a non-woven fabric, wherein the organic material is preferably a polymer and more preferably a polymer selected from polyethylene terephthalate, wherein the organic material is coated with an inorganic ion-conductive material, and / or is penetrated by this which is preferably ion-conducting in a temperature range from -40 ° C to 200 ° C, wherein the inorganic, ion-conductive material preferably at least one compound selected from the group of oxides, phosphates, sulfates, titanates, silicates, aluminosilicates at least one of the element e Zr, Al, Li is. Separator according to one of the preceding claims 7 to 11, wherein the at least one silica and the at least one sulfur component (α1) are in the polymer film; and or (α2) are on the polymer film; or (β1) are located in the polymer fibers; and or (β2) are on the polymer fibers; or (γ1) are in the ion-conducting inorganic material; and or (γ2) are on the ion-conducting inorganic material. Lithium-ion battery, comprising: (a) a positive electrode; (b) a negative electrode; (c) a separator as defined in any one of claims 1 to 12 which separates the positive and negative electrodes; (d) a nonaqueous electrolyte. A lithium ion battery according to claim 13, which comprises at least: (a) a positive electrode comprising sulfur and / or a lithium sulfide; (b) a negative electrode comprising metallic lithium; (c) a separator as defined in any one of claims 1 to 12 which separates the positive and negative electrodes; (d) an electrolyte in the separator. Use of a lithium-ion battery according to any one of the preceding claims for supplying power to mobile information devices, tools, electrically powered automobiles and to hybrid-powered automobiles. Use of at least one silica, preferably silicic acid in the form of a xerogel, and at least one sulfur component, at least partially, preferably substantially, in the oxidation state 0 or -2 in a separator of a lithium-ion battery for (j) lowering the Li-dendrite or whisker formation in the separator; and / or for (jj) binding of water and / or hydrogen fluoride in the lithium-ion battery; and / or for (jjj) increasing the dimensional stability of the separator or separator and the lithium-ion battery; and / or for (jv) gas absorbing in the lithium-ion battery; and / or for (v) lowering the diffusion of polysulfide anions through the separator.