DE102022204655A1 - Method for producing a separator for a lithium-ion battery - Google Patents

Abstract

The invention describes a method for producing a separator (26) for a lithium ion battery, comprising the steps: providing (S10) a first type of particles (10) comprising a first oxidic solid electrolyte material; Providing (S11) a second type of particle (11) comprising a second oxidic solid electrolyte material; Mixing (S14) the first type of particles (10) and second type of particles (11) and sintering (S16) the mixture comprising the first type of particles (10) and the second type of particles (11). It has now surprisingly been found that the combination of oxidic solid electrolyte materials in particular leads to separators with good electrochemical properties.

Description

The invention relates to a method for producing a separator for a lithium-ion battery, comprising the sintering of different types of particles with different oxidic solid electrolyte materials.

Rechargeable electrochemical storage systems are becoming increasingly important for many areas of daily life. High-capacity energy storage devices, such as lithium-ion batteries and capacitors, are being used in an increasing number of applications, including portable electronics, medical, transportation, grid-connected large-scale energy storage, renewable energy storage, and uninterruptible power supplies (UPS). In each of these applications, the charging and discharging time and the capacity of energy storage devices are the crucial parameters. In addition, the size, weight and/or cost of such energy storage devices are also important parameters. In addition, low internal resistance is required for high performance. The lower the resistance, the fewer restrictions the energy storage device faces when delivering electrical energy. For example, in the case of a battery, internal resistance affects performance by reducing the total amount of useful energy stored by the battery as well as the battery's ability to deliver high current. Furthermore, Li-ion batteries should best achieve the desired capacity and the desired cycling. However, Li-ion batteries in their current form often lack the energy capacity and number of charge/discharge cycles for these growing applications.

As described above, lithium-ion batteries are widely used today. In consumer electronics, for example, they are used in portable devices such as cell phones, smartphones, laptops and tablets and so on. In addition, lithium-ion batteries are an important part of electric vehicles, as electric batteries are used in electric cars and hybrid vehicles and have therefore become part of mass production. In addition to the performance requirements described above, requirements with regard to ecological aspects are also increasingly coming to the fore. The cell production of solid-state cells is very complex and is characterized by a large number of precise assembly steps in the area of cell construction.

DE 10 2018 217 507 A1 , DE 10 2018 212 889 A1 and EP 3 224 884 A1 describe solid electrolyte batteries.

However, the accumulators known from the prior art are not yet entirely satisfactory.

The development of lithium metal batteries is considered the most promising technology that can enable a high energy density system for energy storage. However, today's lithium metal batteries suffer from dendrite growth, which makes the practical application of lithium metal batteries in portable electronic devices and electric vehicles difficult. Over the course of several charge/discharge cycles, microscopic lithium fibers called dendrites form on the lithium metal surface and spread out until they touch the other electrode. Conducting electrical current through these dendrites can short-circuit the accumulator. One of the most difficult aspects of manufacturing a lithium metal battery is developing a stable and efficient solid electrolyte interface (SEI). A stable and efficient SEI provides an effective strategy to prevent dendrite growth and thus achieve improved cycling.

There is therefore still a need for improved solid separators for lithium-ion batteries with tailored properties.

According to the invention, this object is achieved by a method for producing a separator for a lithium-ion battery comprising the steps: providing a first type of particles comprising a first oxidic solid electrolyte material; Providing a second type of particle comprising a second oxidic solid electrolyte material; mixing the first type of particles and second type of particles; and sintering the mixture comprising the first type of particles and the second type of particles.

Different solid electrolytes have different properties. One is electrochemically stable to lithium, whereas the other has high particle conductivity. Some electrolyte particles are plastically deformable and others have better stability compared to ambient air. It has now surprisingly been found that, in particular, the combination of a first type of particles comprising a first oxidic solid electrolyte material with a second type of particles comprising a second oxidic solid electrolyte material leads to separators with particular advantages. This does not apply only for the manufacturing process, which can be improved as a result, but also for the properties of the separators.

If two different oxidic solid electrolyte materials are combined with one another, in addition to the general processability, the sintering temperatures, the process atmosphere, the dimensional stability, the internal stresses, the product properties, in particular the conductivity of the boundary layer on the grains, and also the mechanical and/or chemical stability , be optimized.

In connection with the present invention, particular attention is paid to the sintering process. Sintering is the process of producing or changing materials. Despite the heating, preferably under increased pressure, the shape of the workpiece is retained because the heating of the fine-grained ceramic or metallic materials preferably remains below the melting temperature.

Nevertheless, microscopic melting processes can occur at least at the grain boundaries, which lead to mixed phases being formed at the grain boundaries when using two different solid electrolyte materials, as in the case of the present invention, which contribute to particularly good electrochemical properties of the separator.

From a process engineering perspective, the necessary sintering temperature can be significantly reduced by sintering two oxidic materials.

In addition, mixed phases occur at the fused grain boundaries of the two materials. These mixing phases can also be understood as a partial “solid solution”. While in single-phase systems the properties are essentially determined by the chemical composition, in multi-phase systems they are also influenced by the distribution of the phases. Due to the mixing phases, the separator has a higher mechanical and chemical stability and also a lower melting temperature than simple ceramics, which improves processability. These mixed phases also lead to improved ionic conductivity and thus to improved properties of the separator and thus also of the accumulator as such.

In the context of the present invention, any inorganic material that contains oxygen as a component is referred to as an oxidic solid material. Oxidic material is understood to mean, on the one hand, oxides with predominantly purely ionic bonding components, such as in the case of lithium lanthanum zirconate or lithium lanthanum tantalate. In addition, compounds such as lithium aluminum titanium phosphate in which oxygen partially forms covalent bonds, for example as part of a phosphate group, are also considered to be included.

Nevertheless, melting processes can occur at least at the grain boundaries, which result in mixed phases being formed when two different solid electrolyte materials are used, as in the case of the present invention, which contribute to particularly good electrochemical properties of the separator.

In connection with the present invention, particular attention is paid to the sintering process. As the particles of the powdery starting material compact and pore spaces are compressed, shrinkage usually occurs during the process.

Basically, sintering processes are of great importance in ceramic production. A distinction must be made between solid-phase sintering and liquid-phase sintering, which also produces a melt, as has already been disclosed in connection with mixed phase formation.

The binding area of the grains in relation to the particle size is important for properties such as strength and conductivity. The variables that can be adjusted and controlled for the given first oxidic solid electrolyte and the given second oxidic solid electrolyte are, in particular, the temperature and the initial grain size, since the vapor pressure depends on the temperature.

The source of energy for solid state processes is the change in free energy between the neck and the surface of the particle. This energy creates material transfer in the fastest possible way. If transfer from the particle volume or the grain boundary between particles were to occur, particle reduction and pore destruction would occur. With many pores of uniform size and higher porosity, pore reduction occurs faster when the boundary diffusion distance is smaller.

Controlling the temperature is important for the sintering process because the grain boundary diffusion and the volume diffusion depend on the temperature, the size and distribution of the particles of the material and the material composition.

According to a preferred embodiment of the method, a further temperature treatment is carried out.

This gives the sintered product its final properties, such as strength, hardness or thermal conductivity. This can be controlled specifically in the sintering process, depending on requirements.

According to a preferred embodiment, the green body is formed in a previous process step. This allows the separator to be given a precisely fitting shape.

According to a preferred embodiment, the method is described, wherein the first oxidic solid electrolyte material comprises at least one lithium lanthanum zirconate and/or at least one lithium lanthanum tantalate.

According to a preferred embodiment, the method is described, wherein the first oxidic solid electrolyte material comprises a garnet, for example lithium lanthanum zirconate Li ₇ La ₃ Zr ₂ O ₁₂ .

According to a preferred embodiment, the method is described, wherein the second oxidic solid electrolyte material comprises at least one ceramic material of the NASICON type or LISICON structure type, which is represented by the general formula Li ₁ +xR _x M _2x (PO ₄ ) ₃ , where M consists of at least one element is selected from the group Ti, Ge, Zn, Si and Hf; R is selected from at least one element from the group AI, B, Sn, Zr and Ge and x is selected as 0 ≤ x < 3.

In this context, LISICON type or NASICON type refers to the structure of the solid electrolyte material.

NASICON stands for “Natrium Super ionic Conductor,” which usually refers to a family of solids with the chemical formula Na ₁ ⁺ xZr ₂ Si _x P _3-x O ₁₂ , where 0 < x < 3. In a broader sense it is also used for similar compounds where Na, Zr and/or Si are replaced by isovalent elements. NASICON compounds have high ionic conductivities on the order of magnitude that can compete with those of liquid electrolytes. They are caused by the jumping of Na ions between the interstitials of the NASICON crystal lattice.

According to a preferred embodiment, the method is described, wherein the second oxidic solid electrolyte material comprises lithium aluminum titanium phosphate as a NASICON-type or LISICON-type ceramic material.

According to a particularly preferred embodiment, the method is described, wherein the first oxidic solid electrolyte material comprises lithium lanthanum zirconate Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO) and the second oxidic solid electrolyte material comprises lithium aluminum titanium phosphate (LATP). Both ion conductors are preferably Li ion conductors. Garnets, perovskites and anti-perovskites also come into consideration.

According to a particularly preferred embodiment, the first oxidic solid electrolyte material comprises lithium lanthanum zirconate Li7La3Zr2O12, LLZO. The second oxidic solid electrolyte material comprises lithium aluminum titanium phosphate, LATP, both solid electrolyte materials being used in a quantitative ratio of 80:20 to 20.80, preferably 70:30 to 30:70% by weight, based on the total weight of the composition.

LLZO is stable, particularly stable to lithium metal, and has high grain conductivity. However, LLZO disadvantageously has a very high sintering temperature.

LATP also has good grain conductivity, but low grain boundary conductivity. In contrast to grain conductivity, grain boundary conductivity does not describe the conductivity within the grains, but rather the conductivity across the grain boundaries.

If both electrolytes are combined, in addition to the sintering temperatures, process atmosphere, dimensional stability and internal stresses, the product properties, in particular the conductivity of the boundary layers of the grains and the mechanical/chemical stability, can also be optimized.

According to a preferred embodiment, the method is described, the method further comprising: forming at least one coating on the separator designed as a substrate.

According to a further preferred embodiment, the method is described, wherein the coating is formed after sintering.

Such additional coatings can serve to further improve the properties of the separator. This embodiment is described as particularly preferred because it does not lead to any disadvantageous structural changes to the separator.

According to a preferred embodiment, the method for producing a separator for a lithium-ion battery is described, wherein the coating is formed as a cathode-side coating on the substrate.

According to a preferred embodiment, the method for producing a separator for a lithium-ion battery is described, wherein the coating is formed as an anode-side coating on the substrate.

According to a preferred embodiment, the described layer structures on the separator serve to form a gradient.

The first solid electrolyte and the second solid electrolyte can thus be homogeneously distributed in the separator membrane or have a distribution gradient. The formation of a gradient according to this embodiment is described below as an example. The specified quantities can be changed and adjusted by the specialist according to the requirements of each individual case. In this case, the first and second solid electrolytes are preferably present in a ratio of 50:50. The side of the solid electrolyte separator that is preferably oriented toward the anode consists essentially of 100% of the first solid electrolyte, while the side of the separator that is oriented toward the cathode side consists of 100% of the second solid electrolyte. The gradient is achieved via the solid electrolyte separator by applying different solid electrolyte mixtures in layers. By way of example, a first layer consisting only of the first solid electrolyte is created. A second layer is applied to this, which consists, for example, of a mixture of the first and second solid electrolytes in a ratio of 75:25. An optional third layer of first and second solid electrolyte in a mixing ratio of 50:50 is applied in the next step. This is followed by an optional fourth layer of first and second solid electrolyte in a mixing ratio of 25:75, which is applied using the coating process. In the example given, the conclusion is a layer consisting only of the second solid electrolyte.

A lithium-ion accumulator or a lithium-ion battery in the sense of the present invention is a rechargeable battery that contains lithium. Lithium ions migrate from the negative electrode through an electrolyte to the positive electrode when discharging and back to the negative electrode when charging. Lithium-ion batteries, for example, use an intercalated lithium compound on the positive electrode.

While conventional batteries known from the prior art typically have graphite on the negative electrode, the invention provides that the negative electrode comprises lithium metal, more preferably at least 80% by weight of lithium metal, more preferably at least 90% by weight. consists of lithium metal and even more preferably consists essentially of lithium metal.

According to a particularly preferred embodiment, the accumulator has, as a negative electrode, an electrode which comprises or consists of lithium metal, the separator comprising LLZO as an oxidic solid electrolyte material. LLZO is particularly suitable in combination with a lithium metal electrode as it is stable to lithium.

The battery according to the present invention uses a solid electrolyte in the separator layer.

In addition to production efficiency gains, this also results in improved performance.

The separator serves as a barrier that electrically isolates the two electrodes from each other in order to avoid internal short circuits. At the same time, however, the separator must be permeable to ions so that the electrochemical reactions can take place in the cell. A separator should be thin so that the internal resistance is as low as possible and a high packing density can be achieved.

• Die Sulfide Li₂S-P₂S₅, Li₂S-SiS₂ und Li₂S-GeS₂; und/oder
• die Oxide Li₇La₃Zr₂O₁₂ (LLZO) und Li_3xLa_2/3-3xTiO₃ (LLTO); und/oder
• die Li-Argyrodite Li₆PS₅X (X= Cl, Br and I), Li₇PS₆ und Li₇PSe₆.

In addition to the first oxidic solid electrolyte material and the second oxidic solid electrolyte material, further solid electrolyte materials may also be included. Such further materials that can optionally be used in addition to the necessarily present first oxidic solid electrolyte and the necessarily present second oxidic solid electrolyte are:

• The sulfides Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ and Li ₂ S-GeS ₂ ; and or
• the oxides Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO) and Li _3x La _2/3-3x TiO ₃ (LLTO); and or
• the Li argyrodites Li ₆ PS ₅ X (X= Cl, Br and I), Li ₇ PS ₆ and Li ₇ PSe ₆ .

• β-Li₃PS₄, Li₁₀SiP₂S₁₂, Li₁₀GeP₂S₁₂ mit LiH₂PO₄ Beschichtung zu Li, 77.5Li₂S-22.5P₂S₅, Lil-Li₂S-P₂S₅, 80Li₂S-20P₂S₅, Li₆PS₅Cl, Li_6.6P_0.4Ge_0.6S₅I, Li₃PS₄ Glass, 70Li₂S-29P₂S₅-1 P₂O₅, Li_1.3Al_0.3Ti_1.7(PO₄)₃, Li_6.6La₃Zr_1.6Ta_0.4O₁₂, Komposit von PEO-LiTFSI und Al-Li_6.75La₃Zr_1.75Ta_0.25O₁₂, Komposit von PBA-LiClO₄ und Li_1.5Al_0.5Ge_1.5(PO₄)₃, PEO-LiTFSI /oder SI-PEO-LiTFSI.

The following additional materials can also be used:

• β-Li ₃ PS ₄ , Li ₁₀ SiP ₂ S ₁₂ , Li ₁₀ GeP ₂ S ₁₂ with LiH ₂ PO ₄ coating to Li, 77.5Li ₂ S-22.5P ₂ S ₅ , Lil-Li ₂ SP ₂ S ₅ , 80Li ₂ S-20P ₂ S ₅ , Li ₆ PS ₅ Cl, Li _6.6 P _0.4 Ge _0.6 S ₅ I, Li ₃ PS ₄ Glass, 70Li ₂ S-29P ₂ S ₅ -1 P ₂ O ₅ , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _6.6 La ₃ Zr _1.6 Ta _0.4 O ₁₂ , composite of PEO-LiTFSI and Al-Li _6.75 La ₃ Zr _1.75 Ta _0.25 O ₁₂ , comp sit of PBA-LiClO ₄ and Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , PEO-LiTFSI /or SI-PEO-LiTFSI.

According to a further embodiment, the separator material only comprises oxidic solid electrolytes.

According to a preferred embodiment, the accumulator has a current collector. A current collector is a structure within the battery electrodes that is designed to allow current to flow between the cell poles and the active masses of the battery.

Current collectors are components for bridging lithium-ion batteries and external circuits and have a major influence on the capacity, performance and long-term stability of lithium-ion batteries. Conventional current collectors, Al and Cu foils have been used since the first commercial lithium-ion battery and over the past two decades the thickness of these current collectors has been reduced to increase energy density.

The positive electrode may preferably comprise a lithium-based positive electroactive material that can be subjected to lithium intercalation and deintercalation, alloying and dealloying, or plating and stripping while functioning as a positive terminal.

• NMC (NCM) - Lithium Nickel Cobalt Mangan Oxide (LiNiCoMnO₂);
• LFP - Lithium Eisen Phosphate (LiFePO₄/C);
• LNMO - Lithium Nickel Mangan Spinel (LiNi_0.5Mn_1.5O₄);
• NCA - Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO₂);
• LMO - Lithium Mangan Oxide (LiMn₂O₄) oder
• LCO - Lithium Cobalt Oxide (LiCoO₂).

Various inorganic lithium compounds can be used as cathode materials. For example:

• NMC (NCM) - Lithium Nickel Cobalt Manganese Oxide (LiNiCoMnO ₂ );
• LFP - Lithium Iron Phosphate (LiFePO ₄ /C);
• LNMO - Lithium Nickel Manganese Spinel (LiNi _0.5 Mn _1.5 O ₄ );
• NCA - Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO ₂ );
• LMO - Lithium Manganese Oxide (LiMn ₂ O ₄ ) or
• LCO - Lithium Cobalt Oxide (LiCoO ₂ ).

In particular, according to this alternative embodiment, the negative electrode may comprise a lithium metal and/or a lithium alloy. In other variations, the negative electrode may comprise a negative electroactive material based on silicon and comprising silicon, for example a silicon alloy, silicon oxide, or combinations thereof, which in certain cases may be further mixed with graphite.

According to the embodiments described below, the accumulator can have a layer structure. The advantageous layer structure is made possible by the use of the solid electrolyte. In such embodiments, the solid electrolyte is also referred to as a separator layer.

Furthermore, according to a preferred embodiment, a lithium-ion battery is described, wherein the separator layer has a thickness of 0.1 to 25 μm.

In addition, according to a preferred embodiment, a lithium-ion battery is described, which further comprises a cathode stack.

Furthermore, according to a preferred embodiment, a lithium-ion battery is described, which further comprises a cathode stack with a separator layer.

The stacking solution described provides an overall flexible system, in particular through the use of the flexible solid electrolyte layer or the separator layer. This is flexible due to the constitution and the manufacturing process. The core of the hybrid collector can compensate for mechanical stresses. This enables the production of cylindrical solid-state cells. Another advantage is that no additional sintering process is necessary during production.

Further refinements can be found in the dependent claims and their combination.

Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

• 1 eine Lithium-Ionen-Batterieanordnung mit Elektroden;
• 2 ein Verfahren zur Herstellung eines Separators gemäß einer Ausführungsform der Erfindung;
• 3a einen Sinterprozess für ein homogenes Gemisch von Partikeln;
• 3b einen Sinterprozess für ein Gemisch umfassend eine erste Art von Partikeln und eine zweite Art von Partikeln;
• 4 Korngrenzen eines Gemisches umfassend eine erste Art von Partikeln und eine zweite Art von Partikeln;
• 5 einen Separator mit weiterer Beschichtung gemäß einer Ausführungsform und
• 6 einen Separator mit weiteren Beschichtungen gemäß einer weiteren Ausführungsform.

The invention is explained below in exemplary embodiments with reference to the associated drawings. Show it:

• 1 a lithium-ion battery assembly with electrodes;
• 2 a method for producing a separator according to an embodiment of the invention;
• 3a a sintering process for a homogeneous mixture of particles;
• 3b a sintering process for a mixture comprising a first type of particles and a second type of particles;
• 4 Grain boundaries of a mixture comprising a first type of particles and a second type of particles;
• 5 a separator with further coating according to one embodiment and
• 6 a separator with further coatings according to a further embodiment.

1 shows a lithium-ion battery 20 with electrodes 22, 24. The positive electrode 24 and the negative electrode 22 are separated by the separator 26. This is able to conduct lithium ions between the negative electrode 22 and the positive electrode 24. The separator is in solid form. In conventional lithium-ion batteries, however, the electrolyte is a non-aqueous liquid electrolyte solution that contains a lithium salt dissolved in an organic solvent or a mixture of organic solvents. In contrast to such conventional solutions, the invention relates to a battery with a solid electrolyte. Various inorganic lithium compounds can be used as cathode materials. For example, lithium nickel cobalt manganese oxides (LiNiCoMnO ₂ ), lithium nickel manganese spinel (LiNi _0.5 Mn _1.5 O ₄ ) or lithium nickel cobalt aluminum oxides (LiNiCoAlO ₂ ) can be used. Furthermore, lithium manganese oxides (LiMn ₂ O ₄ ), or lithium cobalt oxides (LiCoO ₂ ) are also suitable materials. Graphite is conventionally used as the anode material, but lithium metal is preferably used in the present invention.

2 shows a method for producing a separator 26 according to an embodiment of the invention. The method shown in the flow diagram for producing the separator 26 for a lithium-ion battery first includes providing S10 of a first type of particles comprising a first oxidic solid electrolyte material.
Furthermore, particles of a second type comprising a second oxidic solid electrolyte material are added and the particles are mixed together S14. This is followed by sintering S16 of the mixture comprising the first type of particles 10 and the second type of particles 11, whereby the separator 26 is finally obtained.

The first oxidic solid electrolyte material includes lithium lanthanum zirconate Li ₇ La ₃ Zr ₂ O ₁₂ , LLZO. The second oxide solid electrolyte material includes lithium aluminum titanium phosphate, LATP. Both solid electrolyte materials were used and sintered in a ratio of approximately 50:50 based on weight. However, other amounts can also be used. This combination has proven to be particularly preferred over other combinations of solid electrolyte materials. For example, a combination of LLZO with perovskite or LATP with perovskite. However, perovskite or anti-perovskite are also possible. Grenades are also possible

3a shows a sintering process S16 for a homogeneous mixture of one type of particles. The homogeneous powder is first brought into the shape of the workpiece to be produced S16.1. Ceramic production involves shaping and, optionally, subsequent drying. If necessary, a binding agent can be used to ensure that the powder particles hold together. The green compact or green body resulting from the pressing is compacted by a subsequent heat treatment below the melting temperature S16.2 and then further heated in order to maintain the temperature S16.3. This is also the crucial difference to pure melt, because the starting materials are not completely melted. Sintering is therefore also assigned to the manufacturing process type of forming, although it can also “change material properties” and can therefore preferably be controlled by process control. The sintered product is then cooled S16.4.

3b shows a sintering process S16 for a mixture of particles comprising a first type of particles 10 and a second type of particles 11, as present in the case of the present invention.

After mixing the first particles 10 and the second particles 11, the powder mass is brought into the shape of the workpiece to be produced S16.1. The green compact is formed by shaping or pressing the mixed starting material under high pressure from a die. This now already corresponds to the shape of the desired sintered product.

In this case too, the green compact or green body resulting from the pressing is compacted by a subsequent heat treatment below the melting temperature S16.2. If a binder is used, elimination of the binder preferably takes place at temperatures between 300 and 800 ° C. The actual sintering takes place at temperatures of over 700 °C, preferably between 900 and 1200 °C according to step 16.3.

This is the actual sintering according to the invention, with the high-temperature treatment of the green compact causing the powder grains to enlarge and fuse. The open porosity of the sintered parts is significantly reduced. Only now do the desired properties of the component arise, such as strength, hardness and especially conductivity. In contrast to melting, the starting materials are not completely melted.

The sintered composition includes the first particles and the second particles, has a large internal surface and thus a large surface energy. Every system strives for a state of lowest free energy, which is used when sintering. The surface energy decreases because the individual grains enlarge.

This is particularly true in the systems with mixed oxidic particles as in the case of the invention. This is because microscopic melting processes occur at the grain boundaries, which result in mixed phases being formed at the grain boundaries when two different solid electrolyte materials are used, as in the case of the present invention, which contribute to particularly good electrochemical properties of the separator. From a process engineering perspective, the necessary sintering temperature can be significantly reduced by sintering two oxidic materials. The sintered product is then cooled S16.4.

4 shows the grain boundaries of a mixture comprising a first type of particles 10 and a second type of particles 11. The figure shows the grain boundary 14 between particles of the same type and the grain boundary 15 between particles of different types.

During sintering, the grain boundaries partially fuse. This preferably takes place at the grain boundaries 15 because of the colligative properties of the mixture of the first solid electrolyte material and the second solid electrolyte material. So 15 mixed phases appear at the fused grain boundaries, which can also be understood as a partial “solid solution”. While in single-phase systems the properties are essentially determined by the chemical composition, in multi-phase systems they are also influenced by the distribution of the phases. Due to the mixing phases, the separator has a higher mechanical and chemical stability and also a lower melting temperature than simple ceramics, which improves processability. These mixed phases, which are formed at the grain boundaries 15, also lead to improved ionic conductivity and thus to improved properties of the separator 26 and thus also of the accumulator as such.

5 shows a separator 26 according to an embodiment of the invention. The separator 26 is obtained by providing a sintered substrate 100 as described above. The substrate has been obtained by sintering the first particles 10 and second particles 11 and has correspondingly advantageous properties. The embodiment described here further designs the previously described separator 26 by forming further layers on the separator 26. The separator 26 according to this embodiment further has first layers 112, 122 of a first coating 110 or a second coating 120 on one or on both sides of the substrate 100. The first coating 110 is preferably arranged on the cathode side within the battery, while the second coating 120 is preferably arranged on the anode side. Sulphidic coatings applied to the cathode side are preferred. According to a preferred embodiment, the described layer structures on the separator serve to form a gradient based on the quantitative distribution of the first oxidic solid electrolyte and the second oxidic solid electrolyte by changing the respective quantitative ratio in the substrate and layers.

6 shows a separator 26 according to a further embodiment of the invention. The separator 26 is obtained by providing a substrate 100. The next step is to apply first compositions that form first layers 112, 122 of a first coating 110 and a second coating 120, respectively, on both sides of the substrate 100. Then, in a further step, second compositions forming second layers 114, 124 are applied to the first layers 112, 122 of the first coating 110 and the second coating 120. The first coating 110 is in turn preferably arranged on the cathode side within the battery, while the second coating 120 is preferably arranged on the anode side. According to a preferred embodiment, the further layer structures described on the separator serve to improve the already in 5 described gradients to be further differentiated based on the quantity distribution of the first oxidic solid electrolyte and the second oxidic solid electrolyte. The quantitative ratio in the further layers 114, 124 can be designed differently than in the first layers 112, 122 and/or the substrate 100 and thus the gradient can be designed in a more differentiated manner.

Reference symbols

S10

Providing a first type of particle

S11

Providing a second type of particle

S14

Mixing the first type of particles and second type of particles

S16

Sintering

S16.1

Shaping

S16.2

compression

S16.3

Warm up

S16.4

cooling down

10

first type of particles

11

second type of particles

14

Grain boundary between the same type of particles

15

Grain boundary between particles of different types

20

accumulator

22

Negative electrode

24

Positive electrode

26

separator

100

Separator substrate

110

First cathode-side coating of the separator

112

First layer of the separator

114

Second layer of the separator

120

Second anode-side coating of the separator

122

First layer of the separator

124

Second layer of the separator

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was 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 102018217507 A1 [0004]
• DE 102018212889 A1 [0004]
• EP 3224884 A1 [0004]

Claims (15)

Method for producing a separator (26) for a lithium-ion battery (20) comprising the steps: - Providing (S10) a first type of particle (10) comprising a first oxidic solid electrolyte material; - Providing (S11) a second type of particle (11) comprising a second oxidic solid electrolyte material; - Mixing (S14) the first type of particles (10) and second type of particles (11); and - Sintering (S16) the mixture comprising the first type of particles (10) and the second type of particles (11). Method according to the preceding claim, wherein the first oxidic solid electrolyte material comprises at least one lithium lanthanum zirconate and/or at least one first oxide with a garnet structure. A method according to the preceding claim, wherein the first oxidic solid electrolyte material comprises lithium lanthanum zirconate Li ₇ La ₃ Zr ₂ O ₁₂ . A method according to one or more of the preceding claims, wherein the second oxide solid electrolyte material comprises at least one LISICON-type or NASICON-type ceramic material represented by the general formula Li ₁ ⁺ xR _x M _2-x (PO ₄ ) ₃ , wherein M is selected from at least one element from the group Ti, Ge, ZN, Si and Hf; R is selected from at least one element from the group AI, B, Sn, Zr and Ge; and x is chosen as 0 ≤ x < 3. A method according to the preceding claim, wherein the second oxidic solid electrolyte material comprises lithium aluminum titanium phosphate. A method according to the preceding claim, wherein the method further comprises: a first temperature increase to temperatures between 300 and 800°C; and a further temperature increase to temperatures between 900 and 1200 °C. Method for producing a separator (26) for a lithium-ion battery (20), according to one of the preceding claims, the method further comprising: - Formation of at least one coating (110, 120) to form a gradient on the separator (26) designed as a substrate (100). Method for producing a separator (26) for a lithium-ion battery (20), according to the preceding claim, wherein a gradient is formed with the coating (110, 120) with respect to the quantity distribution of the first oxidic solid electrolyte material and the second oxidic solid material becomes. A method of producing a separator (26) for a lithium-ion battery (20) according to the preceding claim, wherein the coating is formed as a cathode-side coating (110) on the substrate (100). A method of producing a separator (26) for a lithium-ion battery (20) according to the preceding claim, wherein the coating is formed as an anode-side coating (120) on the substrate (100). Separator (26) for a lithium-ion battery (20) obtained by a method according to any one of the preceding claims. Method for producing a lithium-ion battery (20), the method comprising: - Providing a separator (26) according to the method of Claims 1 until 9 ; - Providing an anode (22) comprising lithium metal; - Providing a cathode (24). Lithium-ion battery (20) obtained by a method according to the preceding claim. Lithium-ion battery (20) according to the preceding claim, wherein the lithium-ion battery (20) is designed as a stack battery. Use of the lithium-ion battery (20) according to one of the two preceding claims in a motor vehicle.

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