DE102021101050A1 - Anode active material and lithium ion battery with the anode active material - Google Patents

Abstract

An anode active material for a lithium-ion battery (10) is specified, which has a multiplicity of particles (11), the particles (11) each having a core (12) which contains silicon. A surface structure (13) is arranged on the core (12) and only partially covers the core (12), the surface structure (13) having a material which is a lithium ion conductor and/or an electron conductor.

Description

The invention relates to an anode active material for a lithium-ion battery and a lithium-ion battery with such an anode active material.

In the following, the term "lithium ion battery" is used synonymously for all terms commonly used in the prior art for galvanic elements and cells containing lithium, such as lithium battery cell, lithium battery, lithium ion battery cell, lithium cell, Lithium ion cell, lithium polymer cell, lithium polymer battery and lithium ion accumulator. Specifically, rechargeable batteries (secondary batteries) are included. The terms "battery" and "electrochemical cell" are also used synonymously with the terms "lithium ion battery" and "lithium ion battery cell". The lithium-ion battery can also be a solid-state battery, for example a ceramic or polymer-based solid-state battery.

A lithium ion battery has at least two distinct electrodes, a positive electrode (cathode) and a negative electrode (anode). Each of these electrodes includes at least one active material, optionally together with additives such as electrode binders and electrical conductivity additives.

Graphite is currently typically used as an anode active material in lithium-ion batteries. An increase in the energy density or the specific energy is possible through the use of silicon-based anode active materials. This is particularly advantageous for use in electrically operated motor vehicles in order to increase the range. However, it has been found that silicon-based anode active materials exhibit a strong change in volume when lithium ions are taken up (battery charging) and lithium ions are released (battery discharging). The large change in volume can have a negative impact on mechanical stability and integrity. In order to improve the mechanical stability of the anode, the proportion of an electrode binder in the anode material can be increased. However, this can reduce the conductivity of the anode and thus the performance of the battery cell. With an increased use of electrode binders, the spec. Reduced energy or energy density.

A problem to be solved by the invention consists in making available an anode active material for a lithium-ion battery which is characterized by a high specific energy and energy density and, at the same time, a high conductivity.

This object is achieved by an anode active material according to the independent patent claim. Advantageous refinements and developments of the invention are the subject matter of the dependent claims.

According to one embodiment of the invention, the anode active material comprises a multiplicity of particles, each of which has a core, the core containing silicon. The core preferably contains from 3% to 100% by weight inclusive of silicon. For example, the core may include silicon, a silicon alloy, a silicon sub-oxide ("SiO"), or a silicon composite (e.g., a silicon-carbon composite). In addition to the silicon-based component, the core can contain carbon, in particular graphite, for example.

The core of the particles is, for example, at least approximately spherical. A surface structure is arranged on the core, which only partially covers the core. In particular, the core is not completely enveloped by the material that forms the surface structure. Rather, the surface structure forms a three-dimensional structure that extends outwards from the core. The surface structure has a material that is a lithium ion conductor or an electron conductor.

The invention is based in particular on the following considerations: With silicon-based anode materials, higher energy densities or specific energies can be achieved in lithium-ion batteries than, for example, with graphite, which is conventionally used. However, silicon-based materials exhibit a comparatively high volume change when lithium ions are taken up or released. Without suitable countermeasures, this can lead to a partial detachment of the anode active material from a current collector foil, typically a copper foil. Microscopic decoupling to an electrically conductive material (e.g. conductive soot) can also occur, which leads to a reduction in the current carrying capacity. In order to avoid this, the proportion of an electrode binder in which the particles of the anode active material are embedded can be increased. On the other hand, a higher proportion of the electrode binder in the anode material also leads to lower conductivity for lithium ions and electrons. With the anode active material proposed here, the conductivity of the anode for lithium ions or electrons is increased in that the particles of the anode active material each have a surface structure and the surface structure has a material that is a lithium ion conductor or an electron conductor. The surface structure is, in particular, a 3D structure which, starting from the core of the particles, passes through the electrode binder penetrates in which the particles are embedded. The core of the particles may partially abut the electrode binder and is partially covered by the surface structure that penetrates the electrode binder to form conductive "channels" for lithium ions or electrons.

According to one embodiment of the invention, the material of the surface structure is a lithium ion conductor. The lithium ion conductor can in particular have a material with a garnet structure, a material with a perovskite structure, a sulfide or a polymer. A suitable material with a garnet structure is, for example, in Li ₇ La ₃ Zr ₂ O ₁₂ . In addition to materials with a garnet structure, perovskites, sulfides and oxides can also be used. Particularly suitable structures are those derived from LISICON (Lithium (LI) Super (S) ionic (I) Conductor (CON)), for example Thio-LISICON Li _4-x M _1-y M' _y S ₄ with M = Si, Ge, P, and M' = P, Al, Zn, Ga, Sb, or NASISCON (Sodium (Na) Super (S) ionic (I) Conductor (CON)) of the general formula AMM'P ₃ O ₁₂ with A = Li+, Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , Mg ²⁺ , Ca ²⁺ , sr ²⁺ , Ba ²⁺ , H ⁺ , H ₃ O ⁺ , NH ⁴⁺ , Cu ⁺ , Ag ⁺ , Pb ²⁺ , Cd ²⁺ , Mn ²⁺ , Co ²⁺ , Mn ²⁺ , Co ²⁺ , Ni ²⁺ , Zn ²⁺ , Al ³⁺ , Ln ³⁺ , Ge ⁴⁺ , Zr ⁴⁺ , Hf ^{4 +} or unoccupied, M and M' = di-, tri-, tetra- or pentavalent transition metal ions selected from the group Zn ²⁺ , Cd ²⁺ , Ni ²⁺ , Mn ²⁺ , Co ²⁺ , Fe ³⁺ , Sc ^{3 +} , Ti ³⁺ , V ³⁺ , Al ³⁺ , In ³⁺ , Ga ³⁺ , Y ³⁺ , Lu ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Hf ⁴⁺ , Sn ⁴⁺ , Si ⁴⁺ , Ge ⁴⁺ , V ⁵⁺ , Nb ⁵⁺ , Ta ⁵⁺ , Sb ⁵⁺ , As ⁵⁺ , it also being possible for phosphorus to be partially substituted by Si or As.

A polymer suitable as a lithium ion conductor is, for example, a polymer electrolyte based on polyethylene oxide (PEO). Such PEO-based electrolytes are per se, for example, from the publication Z. Xue et al., "Poly(ethylene oxide)-based electrolytes for lithium-ion batteries", J. Mater. Chem. A, 2015, 3, 19218. The polymer electrolyte based on polyethylene oxide (PEO) contains a lithium conductive salt such as lithium tetraborate (LiBF ₄ ). Further polymer-based lithium ion conductors are known to the person skilled in the art, for example from the patent specification US 5,523,180A known.

According to one embodiment of the invention, the material of the surface structure is an electron conductor. The electron conductor can in particular have a carbon-based material, for example soot (carbon black), soft carbon, hard carbon, carbon nanotubes, graphite, graphene or carbon fibers.

In a preferred embodiment, the surface structure is in the form of fibers or tubes. The fibers or tubes advantageously form conductive channels for lithium ions or electrons. Elongated shapes such as fibers or tubes are particularly suitable for this. The fibers or tubes preferably have a length of 10 nm up to and including 10 μm, preferably of 25 nm up to and including 5 μm.

The core of the particles preferably has a diameter of 20 nm up to and including 50 μm. The diameter is preferably from 100 nm up to and including 20 μm.

The surface structure can be produced, for example, using one of the following methods: electrostatic deposition, nano-gluing, sputtering, vacuum deposition, sintering, spray coating, electrophoretic deposition.

The particles of the anode active material are advantageously incorporated into an electrode binder, with the core of the particles adjoining the electrode binder in some areas and the surface structure extending from the core into the electrode binder. A low conductivity of the electrode binder for lithium ions or electrons can be fully or partially compensated for by the surface structure.

A lithium-ion battery is also proposed, which has an anode with the anode active material described above. The anode can be made, for example, from a coating composition containing the anode active material, electrode binder and a carrier solvent. The anode active material is preferably arranged on a copper foil in the lithium ion battery.

The lithium-ion battery can, for example, only include a single battery cell or alternatively include one or more modules with multiple battery cells, it being possible for the battery cells to be connected in series and/or in parallel. The lithium ion battery includes at least an anode having the anode active material and a cathode having at least a cathode active material. Furthermore, the lithium-ion battery can have the other components of a lithium-ion battery known per se, in particular current collectors, a separator and an electrolyte.

The lithium ion battery according to the invention can be provided in particular in a motor vehicle or in a portable device. The portable device can in particular be a smartphone, an electric tool or power tool, a tablet or a wearable. Alternatively, the lithium-ion battery can also be used in a stationary energy store.

Further advantages and properties of the invention result from the following description of an exemplary embodiment in connection with the figures.

• 1 den Aufbau einer Lithium-Ionenbatterie gemäß einem Ausführungsbeispiel, und
• 2 ein Partikel des Anodenaktivmaterials bei dem Ausführungsbeispiel.

Specifically show schematic

• 1 the structure of a lithium-ion battery according to an embodiment, and
• 2 a particle of the anode active material in the embodiment.

The components shown and the proportions of the components among one another are not to be regarded as true to scale.

In the 1 The lithium-ion battery 10 shown purely schematically has a cathode 2 and an anode 5 . The cathode 2 and the anode 5 each have a current collector 1, 6, it being possible for the current collectors to be in the form of metal foils. The current collector 1 of the cathode 2 has, for example, aluminum and the current collector 6 of the anode 5 has copper.

The cathode 2 and the anode 5 are separated from one another by a separator 4 which is permeable to lithium ions but impermeable to electrons. Polymers can be used as separators, in particular a polymer selected from the group consisting of polyesters, in particular polyethylene terephthalate, polyolefins, in particular polyethylene and/or polypropylene, polyacrylonitriles, polyvinylidene fluoride, polyvinylidene hexafluoropropylene, polyetherimide, polyimide, aramid, polyether, polyetherketone, synthetic spider silk or mixtures thereof. Optionally, the separator can additionally be coated with ceramic material and a binder, for example based on Al ₂ O ₃ .

In addition, the lithium ion battery has an electrolyte 3 which is conductive for lithium ions and which can be a solid electrolyte or a liquid which includes a solvent and at least one lithium conductive salt dissolved therein, for example lithium hexafluorophosphate (LiPF ₆ ). The solvent is preferably inert. Examples of suitable solvents are organic solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate (FEC), sulpholane, 2-methyltetrahydrofuran, acetonitrile and 1,3-dioxolane. Ionic liquids can also be used as solvents. Such ionic liquids contain only ions. Preferred cations, which can be alkylated in particular, are imidazolium, pyridinium, pyrrolidinium, guanidinium, uronium, thiuronium, piperidinium, morpholinium, sulfonium, ammonium and phosphonium cations. Examples of anions that can be used are halide, tetrafluoroborate, trifluoroacetate, triflate, hexafluorophosphate, phosphinate and tosylate anions. Examples of ionic liquids which may be mentioned are: N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide, N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-butyl-N-trimethyl -ammonium bis(trifluoromethylsulfonyl)imide, triethylsulfonium bis(trifluoromethylsulfonyl)imide and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide. In a variant, two or more of the above liquids can be used. Preferred conductive salts are lithium salts which have inert anions and which are preferably non-toxic. Suitable lithium salts are, in particular, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) and mixtures of these salts. The separator 4 can be impregnated or wetted with the lithium salt electrolyte if it is liquid.

The cathode 2 has a cathode active material. The cathode active material can have a large number of particles which are bound into an electrode binder. The cathode active material can be a layered oxide such as a lithium nickel manganese cobalt oxide (NMC), a lithium nickel cobalt aluminum oxide (NCA), a lithium cobalt oxide (LCO) or a lithium nickel Have cobalt oxide (LNCO). The layered oxide can in particular be an overlithiated layered oxide (OLO, overlithiated layered oxide). Other suitable cathode active materials are compounds with a spinel structure such as lithium manganese oxide (LMO) or lithium manganese nickel oxide (LMNO), or compounds with an olivine structure such as lithium iron phosphate (LFP, LiFePO ₄ ) or lithium manganese - Iron phosphate (LMFP).

The anode 5 has an anode active material. The anode active material has a large number of particles that are bound into an electrode binder. A particle 11 of the anode active material is in 2 shown schematically. The particle 11 has a core 12 and a surface structure 13 . The core 12 of the particle 11 contains silicon. For example, the core 12 contains silicon, a silicon suboxide, a silicon alloy, a silicon-carbon composite, or consists of one of these materials. The core 12 preferably has from 3% by weight up to and including 100% by weight, in particular from 10% by weight up to and including 100% by weight, silicon.

A surface structure 13 is arranged on the core of the particles 11 of the anode active material, which surface structure preferably has an elongated shape, in particular a fiber or tube shape. The surface structure 13 covers the Core of the particles 11 each only partially. The surface structure 13 can penetrate an electrode binder 14 in which the particles 11 are embedded. The surface structure 13 thus forms channel-like conductive structures which, depending on the material of the surface structure 13, can form a lithium ion conductor or an electron conductor.

In order to form a lithium ion conductor, the surface structure 13 can in particular have a material with a garnet structure, a material with a perovskite structure, a sulfide or a polymer. In this case, the polymer is, for example, a polymer electrolyte based on polyethylene oxide (PEO). The result of the surface structure 13 on the cores 12 of the particles 11 in this configuration is that the lithium-ion conduction between the electrolyte 3 of the lithium-ion battery 10 and the anode active material is improved.

Electrostatic deposition, nano-gluing, sputtering, vacuum deposition, sintering, spray coating, electrophoretic deposition or mechanical methods can be used to produce the surface structure 13 of the particles.

In order to form an electron conductor, the surface structure 13 can have a material containing carbon, in particular soot (carbon black), carbon nanotubes, graphite, graphene or carbon fibers. In this embodiment, the surface structure 13 on the cores 12 of the particles 11 improves the electron conduction between the current collector 6 and the anode active material.

Although the invention has been illustrated and described in detail using exemplary embodiments, the invention is not restricted by the exemplary embodiments. On the contrary, other variations of the invention can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention as defined by the claims.

Reference List

1

current collector

2

cathode

3

electrolyte

4

separator

5

anode

6

current collector

10

Lithium Ion Battery

11

particles

12

core

13

surface texture

14

electrode ties

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited 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.

Patent Literature Cited

• US5523180A [0011]

Claims (11)

Anode active material for a lithium ion battery, wherein - the anode active material has a large number of particles (11), - the particles (11) each have a core (12) containing silicon, - A surface structure (13) is arranged on the core (12) which only partially covers the core (12), and - The surface structure (13) has a material which is a lithium ion conductor and/or an electron conductor. anode active material claim 1 , wherein the material of the surface structure (13) is a lithium ion conductor. anode active material claim 2 wherein the lithium ion conductor is a garnet structure material, a perovskite structure material, a sulfide or a polymer. anode active material claim 3 , wherein the polymer is a polyethylene oxide (PEO) based polymer electrolyte. anode active material claim 1 , wherein the material of the surface structure (13) is an electron conductor. anode active material claim 5 , wherein the electron conductor comprises carbon, soot, soft carbon, hard carbon, carbon nanotubes, graphite, graphene or carbon fibers. Anode active material according to one of the preceding claims, wherein the surface structure (13) has the form of fibers or tubes. anode active material claim 7 wherein the fibers or tubes have a length of 10 nm to 10 µm inclusive. Anode active material according to one of the preceding claims, wherein the core (12) of the particles (11) has a diameter of 20 nm up to and including 50 µm. Anode active material according to one of the preceding claims, wherein the particles (11) of the anode active material are bound into an electrode binder (14), the core (12) of the particles (11) adjoining the electrode binder (14) in regions and the surface structure (13) extending from the core (12) into the electrode binder (14). Lithium-ion battery (10) comprising at least one anode (2) with an anode active material according to one of Claims 1 until 10 .

Images