CN111326709A - Electrode active material with coating in multilayer system and lithium ion battery cell - Google Patents

Abstract

The invention relates to an electrode active material for a lithium ion battery, comprising active material particles (1) which have a first coating (2) consisting of a solid electrolyte, wherein the active material particles (1) have a second coating (3) consisting of an electron-conducting material, which is applied to the first coating (2), and wherein the first coating (2) is applied to the active material in a thickness which allows electron transport through the first coating (2), and to a secondary battery comprising the electrode active material according to the invention and to the use of the electrode active material for producing a battery cell, in particular for producing a traction battery for vehicles. Advantageously, with the electrode active material for lithium ion batteries according to the invention, it is possible to increase the efficiency of the anode and cathode active materials at voltages >4.2V, in particular at 4.9V, and to improve the service life and the high current carrying capacity.

Description

Electrode active materials and lithium-ion battery cells with coatings in multilayer systems

technical field

The present invention relates to a coating for an electrode active material of a lithium-ion battery, in particular as a traction battery for use in electric vehicles, which coating has the features of the preamble of claim 1 .

current technology

Coated electrode active materials are known in the prior art. German application publication DE 34 43 455 A1 describes a galvanic cell with polymer electrodes. As the electrode carrier, an aluminum substrate can be used, the surface of which comprises a usual oxide protective layer. In addition, the aluminum substrate can also be coated with an electron-conducting material, such as graphite or metal. Electrode materials including lithium ions are not mentioned.

Undesirable side reactions occur at high voltages >4.2 V between the active material of the electrode material, in particular the active material of the cathode, and the electrolyte in a lithium-ion battery cell because the cathode active material is in direct contact with the electrolyte. The result of the side reaction is the release of cations from the cathode active material, which results in a power degradation of the cathode active material and thus a decrease in the overall efficiency of the lithium ion battery cell. Particularly in the cathode active material LiNi _0.5 Mn _1.5 O ₄ , at a voltage of 4.9 V, nickel and manganese ions, which diffused through the separator to the anode and where metal deposition occurred, were dissolved from the structure.

Furthermore, this leads to the direct contact between the cathode active material and the electrolyte in the lithium-ion battery cell, leading to the decomposition of the electrolyte, especially at high voltages >4.2V. As a result, the efficiency of a lithium-ion battery cell decreases.

Therefore, it is definitely necessary to protect the cathode active material and the electrolyte from the above-mentioned degradation mechanism or degradation effect in order to stably maintain or extend the service life of a lithium ion battery cell.

Furthermore, an electrolyte for a lithium secondary battery is known from the European patent document EP 2 472 662 B1, the electrolyte comprising a lithium salt, a non-aqueous organic solvent and a compound selected from the group consisting of vitamins G, B ₄ , B ₅ , H, M , D ₂ , B _x , D ₃ and K ₁ additives. According to the above-mentioned document, the cathode may have a thin film on its surface, which film is formed by the oxidation of the additive by the initial application of the voltage.

Furthermore, such electrode materials for lithium-ion batteries are known, which are provided with a polymer coating as a protective layer for the active material, in particular against oxidation, or in which they are applied, in particular for the cathode active material There are solid electrolytes, for example as disclosed in US patent application US2017/0018760 A1 or in German application publication DE 10 2015217 749 A1.

In all the coated electrode materials known to date, the coating is used either as a protection for the sensitive active material or as a lithium ion conductor at the same time.

The disadvantage here, however, is that electron transport is hindered because the known coatings cannot conduct electrons. Solid electrolytes are purely ionic conductors, not electronic conductors. Furthermore, in view of the direct contact between the electrode active material and the solid electrolyte, the electrolyte is decomposed especially at high pressure, which leads to a decrease in the efficiency of the lithium-ion battery.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is therefore to provide an improved electrode active material, which has good protection of the active material and at the same time good electron conductivity. An improved efficiency, a higher high-voltage load capacity (load capacity) and an improved service life of the lithium-ion battery should thereby be achieved.

Said technical problem is solved according to the invention by an electrode active material having the technical features of claim 1 .

The present invention includes an electrode active material for a lithium ion battery, the electrode active material comprising active material particles having a first coating layer composed of a solid electrolyte.

According to the invention, the active material particles have a second coating consisting of an electron-conducting material, the second coating being applied on the first coating, and wherein the first coating (2) is used to allow the occurrence of The thickness of electron transport through the first coating ( 2 ) is deposited on the active material, or the first coating is deposited on the active material with such a thickness that electron transport through the first coating can take place or in other words Electron transport is enabled through the first coating.

Coatings with only conventional solid electrolytes electrically insulate the electrode particles from each other, since solid electrolytes are purely ionic conductors and cannot conduct electrons.

Advantageously, with the electrode active material according to the present invention, which can be both a cathode material and an anode material, it is possible to achieve ionic and electronic contact of the anode and cathode active material particles with each other in order to conduct lithium ions and at the same time transport electrons to the current arrester.

的传输系数由此应非常高，也即尽可能接近1。This is achieved in the first aspect of the invention by the fact that the solid electrolyte layer of the first coating is very thin, yet its thickness is sufficient to protect the active material particles. The solid electrolyte layer may be, for example, as thin as one atomic layer to several atomic layers. for electronic transitions across solid electrolytes

The transmission coefficient of should therefore be very high, ie as close to 1 as possible.

A second aspect of the invention consists in depositing a second layer on top of the first layer, which second layer conducts electrons very well. The second layer may have a lower Fermi energy and a lower work function (or work function).

Anode and cathode active material due to at least double coating of anode and cathode active material with a multilayer system by means of a high-voltage-stabilized solid electrolyte as the first coating and an electron-conducting layer with tunnel effect as the second coating The efficiency of the material is improved at voltages >4.2V, especially 4.9V.

This is because material dissolution and electrolyte decomposition are avoided. Therefore, the efficiency of the lithium-ion battery cell is improved. The improved efficiency of a lithium-ion battery cell refers in particular to a longer service life and a high current-carrying capacity.

In one embodiment of the invention, the first coating consists of a solid electrolyte comprising a solid electrolyte material selected from: NASICON solid electrolytes, especially LATP or LAGP; and (anti)perovskites, especially LLTO or _Li3OCl .

The deposition can be achieved by physical, wet-chemical or mechanical methods. Deposition or coating (coating) methods are generally known to those skilled in the art. For example, atomic layer deposition (ALD), molecular layer deposition (MLD), chemical vapor deposition (CVD), physical vapor deposition (PVD), electron beam deposition, laser deposition, plasma deposition, radio frequency sputtering, microemulsion deposition, Continuous ionic layer deposition, aqueous deposition, solid diffusion, sputter coating, sol-gel coating or powder coating.

By choosing the solid electrolyte as the first coating, it can be ensured that, depending on the electron type, cathode or anode material, very good ionic conductivity and at the same time good electrode active material protection are achieved. Decomposition of the solid electrolyte material due to high pressure is suppressed by utilizing the tunneling effect and the resulting electronic conductivity.

In one embodiment of the invention, the second coating consists of an electron-conducting material selected from the group consisting of: graphite; titanium; zirconium; boron; vanadium oxide; titanium oxide; niobium oxide; lithium metal alloys, in particular Zn-Li, Sn-Li, Al-Li; lithium metal oxides, especially Li ₂ ZrO ₃ , Li _3.5 Al ₂ O ₃ , Li ₄ Ti ₅ O ₁₂ ; and lithium metal fluorides, especially Li ₃ AlF ₆ , Li ₂ AlF ₄ , Li ₃ VF ₆ .

The material conducts electrons very well and has a low Fermi energy. In addition, it also has a lower work function WA. The deposition can be achieved by physical, wet-chemical or mechanical methods.

In another embodiment of the electrode material according to the invention, the electrode active material of the active material particles is LiNi _0.5 Mn _1.5 O ₄ .

By means of this design, a significant improvement in the high-voltage stability and thus longer service life of cells comprising this material can be achieved, especially for the cathode active material.

In another preferred embodiment of the invention, the first coating has a layer thickness of 0.05 nm to 100 nm, in particular a layer thickness of 0.1 nm to 80 nm, and preferably a layer thickness of 0.5 nm to 50 nm.

What can be achieved in this way is to exploit the tunnel effect, ie electrons traverse the path from the cathode active material to the second coating despite the presence of an electrically insulating solid electrolyte layer between the cathode active material and the second coating , the second coating is electronically conductive.

In other words, the first coating has a layer thickness preferably from one to several atomic layers and is applied by means of physical, wet-chemical or mechanical methods.

The second coating can be applied by means of physical, wet-chemical or mechanical methods.

Depending on the manufacturing process, the method for coating the electrode active material particles can be adjusted. As a suitable method thereof, for example, physical or chemical vapor deposition, atomic layer deposition (ALD), molecular layer deposition (MLD), chemical vapor deposition (CVD), physical vapor deposition (PVD), electron beam deposition, laser deposition can be used , plasma deposition, radio frequency sputtering, microemulsion deposition, continuous ionic layer deposition, aqueous phase deposition, solid phase diffusion, sputter coating, sol-gel coating or powder coating.

Suitable electrode active materials are all substances known for lithium-ion batteries. For example, it can be listed in the following list, but not limited to this:

Suitable oxide electrode active materials for cathodes are, for example: LiNiCoAlO ₂ ; LiNiCoMnO ₂ (NMC); LiMn _2-x M _x O ₄ , where M=Ni, Fe, Co or Ru and x=0 to 0.5; and LiCoO ₂ (LCO).

Suitable anode active materials are, for example, the following materials: V ₂ O ₅ , LiVO ₃ , Li ₃ VO ₄ and Li ₄ Ti ₅ O ₁₂ (LTP).

Also phosphate-containing compounds are suitable as electrode materials, such as Li ₃ V ₂ (PO4) ₃ or LiMPO ₄ for cathodes, where M=1/4 (Fe, Co, Ni, Mn), or for anodes LiM ₂ (PO ₄ ) ₃ or mixtures thereof, wherein M=Zr, Ti, Hf.

In another embodiment of the invention, a third coating consisting of a solid electrolyte is applied on the second coating, and optionally a fourth coating consisting of an electron-conducting material is applied on the third coating.

The order of the two layers is preserved, but more coatings are applied. As a result, an improvement (improvement) in the high-voltage stability and the long-term durability of the electrode material according to the invention can again be achieved. The present invention is not limited to a two-layer or four-layer multilayer coating. Likewise, within the scope of the present invention, further coatings are applied in the same sequence, in which case a solid electrolyte layer or an electron-conducting layer, respectively, should always be optionally provided as the outer layer.

Another technical solution of the present invention resides in a secondary battery including the electrode active material according to the present invention.

Likewise, the technical solution according to the invention consists in the use of the electrode active material according to the invention as described above in the production of battery cells, in particular in the production of cells for traction batteries for vehicles.

Description of drawings

There are numerous possibilities for designing and improving electrode active materials. To this end, reference is mainly made to the subclaims of claim 1 . Preferred embodiments of the invention will be explained in more detail below with the aid of the drawings and the associated description. In the attached image:

FIG. 1 shows a simplified schematic representation of a cross-section of an electrode material and shows in detail a part of a particle of such an electrode material according to the invention,

Figure 2 shows the energy curve of a coated active material according to the invention under an applied voltage in a simplified schematic diagram,

Figure 3 shows a cross-sectional view of an electrode material particle with a multilayer coating according to another aspect of the present invention in a simplified schematic view, and

Figure 4 shows a cross-sectional view of an electrode material particle with a multilayer coating according to another aspect of the present invention in a simplified schematic view.

Detailed ways

FIG. 1 schematically shows a cross-section of an electrode material according to the invention and an enlarged detail thereof. The electrode active material for a lithium-ion battery includes active material particles 1 having a first coating layer 2 composed of a solid electrolyte. According to the invention, the active material particles 1 have a second coating 3 of electron-conducting material, which is applied on the first coating 2 . The first coating layer 2 is deposited on the active material 1 in such a thickness that electron transport through the first coating layer 2 is allowed to take place.

Suitable oxide electrode active materials for cathodes are, for example: LiNiCoAlO ₂ ; LiNiCoMnO ₂ (NMC); LiMn _2-x M _x O ₄ , where M=Ni, Fe, Co or Ru and x=0 to 0.5; and LiCoO ₂ (LCO).

Suitable anode active materials are, for example, the following materials: V ₂ O ₅ , LiVO ₃ , Li ₃ VO ₄ and Li ₄ Ti ₅ O ₁₂ (LTP).

Also phosphate-containing compounds are suitable as electrode materials, such as Li ₃ V ₂ (PO4) ₃ or LiMPO ₄ for cathodes, where M=1/4 (Fe, Co, Ni, Mn), or for anodes LiM ₂ (PO ₄ ) ₃ or mixtures thereof, wherein M=Zr, Ti, Hf.

Preferably, the electrode active material of the active material particles 1 may be LiNi _0.5 Mn _1.5 O ₄ .

In other words, the coating of the anode and cathode active material particles is also achieved with a first coating 2, which is a very thin, ionically conductive, solid electrolyte layer of the order of one to several atomic layers. Since the solid electrolyte layer itself cannot conduct electrons, this layer 2 is applied very thinly so that the tunnel effect can be used.

High pressure stable hybrid or non-hybrid solid electrolytes, ie NASICON types such as LATP, LAGP or (anti)perovskites such as LLTO or Li ₃ OCl, are deposited on the anode or cathode active material particles 1 .

The following exemplifies some specific compounds suitable for use as solid electrolytes in this category, which should not be interpreted as limiting:

- oxides, such as Li _7-x La ₃ Zr ₂ Al _x O ₁₂ , where x=0 to 0.5, or Li ₇ La ₃ Zr _2-x Ta _x O ₁₂ , where x=0 to 0.5,

- lithium aluminium titanium phosphates, eg Li _1+x M _x Ti _2-x (PO ₄ ) ₃ , where x=0 to 7 and M=Al(LATP), Fe, Y or Ge,

- lithium lanthanum zirconate, wherein doping of tantalum, aluminium and iron can additionally be used,

- Lithium phosphorsulfide, into which germanium and selenium can be doped, eg Li ₇ P ₃ S ₁₁ , Li ₁₀ P ₃ S ₁₂ , Li ₁₀ M _x P _3-x S ₁₂ , where M=Ge, Se, and x=0 to 1, where M= _AyBz , where A=Si, Ge, and B=Sn, Si, and where _y =0 to 0.5, and z=1-y.

The first coating 2 can preferably have a layer thickness of 0.05 nm to 100 nm, in particular a layer thickness of 0.1 nm to 80 nm, and preferably a layer thickness of 0.5 nm to 50 nm.

A second important aspect of the invention is that on the first coating 2 there is deposited a layer 3 which conducts electrons very well and has a low Fermi energy (see E3 in Fig. 2) and a relatively low Fermi energy. Low work function (see WA(3) in Figure 2), such as graphite and metals (titanium, boron, zirconium, etc.), metal oxides (VO2, _TiO , _NbO2 , etc.), lithium metal alloys (Zn- Li, Sn-Li, Al-Li, etc.), lithium metal oxides (Li ₂ ZrO ₃ , Li _3.5 Al ₂ O ₃ , Li ₄ Ti ₅ O ₁₂ , etc.) or lithium metal fluorides (Li ₃ AlF ₆ , Li _{2 )} AlF ₄ , Li ₃ VF ₆ , etc.).

In addition, the lithium ions traverse the path from the active material or the solid electrolyte by means of tunneling via the electron conducting material, respectively.

Efficiency of anode and cathode active materials at voltages >4.2V, especially 4.9V, due to the coating of anode and cathode active materials with multilayer systems, solid electrolytes stabilized by high voltage and electron conducting layers with tunnel effect be increased.

This is because material dissolution and electrolyte decomposition are avoided. Therefore, the efficiency of the lithium-ion battery cell is improved. The improved efficiency of a lithium-ion battery cell refers in particular to a longer service life and a high current-carrying capacity.

The multi-layered coating consisting of the solid electrolyte 2 and the electron conducting material 3 on the anode and cathode active materials 1 is capable of conducting electrons in addition to lithium ions and is stable under high pressure. This has the consequence, inter alia, of achieving one or more of the advantages described below:

-Protection of electrolyte from decomposition due to high voltage.

- Protection of cathode active materials, especially LiNi _0.5 Mn _1.5 O ₄ , from material dissolution at high temperature and high voltage.

- Avoid structural changes in the cathode active material during cell cycling.

- Exploiting the tunneling effect of non-electronically conductive solid electrolytes;

- Improve the efficiency of cathode active materials, electrodes and lithium-ion battery cells composed therefrom.

Both coatings 2 and 3 are applied to the active material particles 1 using suitable methods known to those skilled in the art of lithium-ion battery cell manufacture, such as vapour deposition or the like. For example, atomic layer deposition (ALD), molecular layer deposition (MLD), chemical vapor deposition (CVD), physical vapor deposition (PVD), electron beam deposition, laser deposition, plasma deposition, radio frequency sputtering, microemulsion deposition, Continuous ionic layer deposition, aqueous deposition, solid diffusion, sputter coating, sol-gel coating or powder coating.

The energy curves of the anode or cathode active material particles 1 , of the solid electrolyte 2 and of the electron conductor 3 are shown schematically in FIG. 2 .

The effect of the present invention is that the tunnel effect is utilized, that is, electrons traverse from the cathode active material 1 to the second coating layer 3 despite the presence of the electrically insulating solid electrolyte layer 2 between the cathode active material 1 and the second coating layer 3 path, the second coating is electronically conductive.

When a voltage is applied on both sides of the barrier, eg in the operation of a battery, the Fermi levels E1 and E3 differ by eV from each other, since electrons are extracted on the right side 3 . An empty state for the electrons on the left side 1 is thus formed on the right side 3 , whereby tunneling, ie electron transport through the non-electron-conducting layer 2 is easily obtained.

3 schematically shows a cross-sectional view of an anode or cathode active material particle 1 according to the invention with a multilayer system consisting of a solid electrolyte layer 2 and an electron conductor layer 3, wherein the outermost layer is always the Solid electrolyte layer 2 .

4 schematically shows a cross-sectional view of an anode or cathode active material particle 1 according to the invention with a multilayer system consisting of a solid electrolyte layer 2 and an electron conductor layer 3, wherein the outermost layer is always the Electronic conductor layer 3.

The sequence of solid electrolyte layer 2, electron conductor layer 3 can be expanded here arbitrarily until ideal protection against degradation of the cathode active material and electrolyte is achieved, but an insulating effect has not yet been established.

Due to the coating of the anode and cathode active material 1 with a multilayer system, a solid electrolyte 2 stabilized by high voltage and an electron conducting layer 3 with tunneling effect, the anode and cathode active material are present at voltages >4.2V, in particular at 4.9V efficiency is improved.

This is because material dissolution and electrolyte decomposition are avoided. Therefore, the efficiency of the lithium-ion battery cell is improved. The improved efficiency of a lithium-ion battery cell refers in particular to a longer service life and a high current-carrying capacity.

List of reference signs

1 Electrode active material particles

2 first coat

3 Second coat

Claims (10)

1. An electrode active material for a lithium ion battery, comprising active material particles (1) having a first coating layer (2) of a solid electrolyte, characterized in that the active material particles (1) have a second coating layer (3) of an electron-conducting material, which is applied on the first coating layer (2), and wherein the first coating layer (2) is applied on the active material at a thickness which allows electron transport through the first coating layer (2) to take place.

2. The electrode active material according to claim 1, wherein the first coating layer (2) is composed of a solid electrolyte comprising a solid electrolyte material selected from the group consisting of: NASICON solid electrolytes, particularly LATP or LAGP; and (anti) perovskites, especially LLTO or Li₃OCl。

3. The electrode active material according to claim 1 or 2, characterized in that the second coating layer (3) is composed of an electron-conducting material selected from: graphite; titanium; zirconium; boron(ii) a Vanadium oxide; titanium oxide; niobium oxide; lithium metal alloys, especially Zn-Li, Sn-Li, Al-Li; lithium metal oxides, especially Li₂ZrO₃、Li_3.5Al₂O₃、Li₄Ti₅O₁₂(ii) a And lithium metal fluorides, especially Li₃AlF₆、Li₂AlF₄、Li₃VF₆。

4. An electrode active material according to any one of the preceding claims, wherein the electrode active material of the active material particles is LiNi_0.5Mn_1.5O₄。

5. The electrode active material according to any one of the preceding claims, characterized in that the first coating (2) has a layer thickness of 0.05nm to 100nm, in particular 0.1nm to 80nm, and preferably 0.5nm to 50 nm.

6. Electrode active material according to one of the preceding claims, characterized in that the first coating (2) has a layer thickness of a maximum of a plurality of atomic layers and is applied by means of a physical, wet-chemical or mechanical method.

7. Electrode active material according to any of the preceding claims, characterized in that the second coating (3) is applied by means of a physical, wet-chemical or mechanical method.

8. Electrode active material according to one of the preceding claims, characterized in that a third coating of solid electrolyte (2) is applied on the second coating (3).

9. A secondary battery comprising the electrode active material according to any one of the preceding claims.

10. Use of an electrode active material according to any one of the preceding claims 1 to 9 for the manufacture of a battery cell, in particular for the manufacture of a traction power battery for a vehicle.

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