DE102018221828A1 - Coating of anode and cathode active materials with high-voltage stable solid electrolytes and an electron conductor in a multi-layer system and lithium-ion battery cell - Google Patents

Abstract

The invention relates to an electrode active material for lithium-ion batteries, comprising active material particles (1) which have a first coating (2) made of a solid electrolyte, the active material particles (1) having a second coating (3) made of an electron-conducting material, which is applied to the first coating (2), and the first coating (2) is applied to the active material in such a thickness that electron transport can take place through the first coating (2), and a secondary battery comprising the electrode active material according to the invention and its Use in the manufacture of battery cells, in particular for traction batteries in vehicles. Advantageously, the electrode active material according to the invention for lithium-ion batteries can increase the performance of the anode and cathode active materials at voltages> 4.2 V, in particular at 4.9 V, and the service life as well as the high current load safety can be improved.

Description

The present invention relates to a coating of electrode active material for lithium-ion batteries, which are used in particular as traction batteries in electric vehicles, with the features of the preamble of claim 1.

Coated electrode active materials are known in the prior art. This is how the German published specification describes DE 34 43 455 A1 a galvanic element with a polymer electrode. An aluminum substrate can be used as the electrode carrier, the surface of which comprises a customary oxidic protective layer. The aluminum substrate can then be coated with an electron-conducting material such as graphite or a metal. An electrode material which comprises lithium ions is not mentioned.

At high voltages> 4.2 V, undesirable side reactions occur between the active material of the electrode material, in particular in the cathode, and the electrolyte in a lithium-ion battery cell, since these cathode active materials are in direct contact with the electrolyte. One consequence of the side reactions is the cation discharge from the cathode active material, which leads to a performance degradation of the cathode active material and thus to a reduction in the overall performance of the lithium-ion battery cell. In the case of the cathode active material LiNi _0.5 Mn _1.5 O _{4 in} particular, at the voltage of 4.9 V, nickel and manganese ions are released from the structure, which diffuse through the separator onto the anode and become metallic there.

Furthermore, the fact that the cathode active material and the electrolyte are in direct contact in a lithium-ion battery cell leads to decomposition of the electrolyte, especially at high voltages> 4.2 V. One consequence of this is a reduced performance of the lithium Ion battery cell.

Protection of the cathode active material and the electrolyte against the degradation mechanisms or effects mentioned is imperative in order to keep or extend the life of a lithium-ion battery cell.

It is also from the European patent EP 2 472 662 B1 an electrolyte for lithium secondary batteries is known, which comprises a lithium salt, a non-aqueous organic solvent and an additive from the group of vitamins G, B ₄ , B ₅ , H, M, D ₂ , B _x , D ₃ and K ₁ . According to the cited document, the cathode can have a thin film on its surface, which was produced from the additive by the first application of a voltage by oxidation.

In addition, such electrode materials for lithium-ion batteries are known which provide a polymeric coating to protect the active material, in particular against oxidation, or in which the cathode active material in particular is coated with a solid electrolyte, as described, for example, in the American patent application US 2017/0018760 A1 or in the German patent application DE 10 2015 217 749 A1 is disclosed.

In all previously known coated electrode materials, the coating serves either to protect the sensitive active material or at the same time as a lithium-ion conductor.

The disadvantage here, however, is that the electron transport is impaired by the fact that the known coatings cannot conduct electrons. Solid electrolytes are pure ion conductors and not electron conductors. In addition, the direct contact between the electrode active material and the electrolyte leads to decomposition of the electrolyte, especially at high voltages, which leads to a reduced performance of the lithium-ion battery.

The object of 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 has good electron conductivity. This is intended to enable improved performance, a high high-voltage load capacity and an improved lifespan of the lithium-ion battery.

According to the invention, this object is achieved by an electrode active material having the features of patent claim 1.

The invention comprises an electrode active material for lithium-ion batteries, comprising active material particles which have a first coating made of a solid electrolyte.

According to the invention, the active material particles have a second coating made of an electron-conducting material, which is applied to the first coating, and the first coating is applied to the active material in such a thickness that electron transport can take place through the first coating.

A coating with only a conventional solid electrolyte would electronically isolate the electrode particles from one another, because solid electrolytes are pure ion conductors and are not conductive for electrons.

Advantageously, with the electrode active material according to the invention, which can be both a cathode material and an anode material, the anode and cathode active material particles are in ionic and electronic contact with one another in order to conduct lithium ions and at the same time transport electrons to the current collector.

In a first aspect of the invention, this is achieved in that the solid electrolyte layer of the first coating is very thin, but thick enough to protect the active material particle. The solid electrolyte layer can be thin, for example, from one atomic layer to a few atomic layers. The transmission coefficient for the electronic transition through the solid electrolyte should be very high, i.e. as close as possible to 1.

The second aspect of the invention is that a second layer is deposited on this first layer, which can conduct electrons very well. It should have a low Fermi energy and a low work function.

As a result of the at least two-fold coating of the anode and cathode active material in the multilayer system with a high-voltage stable solid electrolyte as the first coating and an electron-conducting layer as the second coating, making use of the tunnel effect, the performance of the anode and cathode active materials at voltages> 4.2 V, especially at 4 , 9 V, increased.

The cause is the prevention of material dissolution and electrolyte decomposition. As a result, the performance of the lithium-ion battery cell is increased. The improved performance of a lithium-ion battery cell means, in particular, an extended service life and the high current carrying capacity.

In one embodiment of the invention, the first coating is made of a solid electrolyte, which comprises a solid electrolyte material from the group of NASICON solid electrolytes, in particular LATP or LAGP, and the (anti) perovskite, in particular LLTO or Li ₃ OCl.

The deposition can take place by means of physical, wet-chemical or mechanical methods. The deposition or coating processes are generally known to the person skilled in the art. Examples include ALD, MLD, CVD, PVD, electron beam deposition, laser deposition, plasma deposition, radio frequency sputtering, microemulsion deposition, successive ionic layer deposition, aqueous deposition, solid phase diffusion, sputter coating, sol-gel coating or powder coating.

By selecting the solid electrolytes mentioned as the first coating, it can be ensured that, depending on the type of electrode, cathode or anode material, very good ion conductivity and at the same time good protection of the electrode active material is achieved. Decomposition of the solid electrolyte material due to high voltages can be suppressed by utilizing the tunnel effect and the resulting electron conductivity.

In one embodiment of the invention, the second coating is made of an electron-conducting material which is selected from the group graphene, titanium, zirconium, boron, vanadium oxide, titanium oxide, niobium oxide, lithium metal alloy, in particular Zn-Li, Sn-Li, Al Li, lithium metal oxides, in particular Li ₂ ZrO ₃ , Li _3.5 Al ₂ O ₃ , Li ₄ Ti ₅ O ₁₂ , and lithium metal fluorides, in particular Li ₃ AlF ₆ , Li ₂ AlF ₄ , Li ₃ VF ₆ .

These materials can conduct electrons very well and have a low Fermi energy. In addition, they have a low work function WA. The deposition can take place by means of physical, wet-chemical or mechanical methods.

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

With this configuration, a significant improvement in the high-voltage stability and thus in the extended service life of a battery containing this material can be achieved, in particular for the cathode active material mentioned.

In a further 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.

In this way, the goal of using the tunnel effect can be achieved, that is, the electrons bridge the path from the cathode active material to the second layer, which is electron-conducting, even though there is an electronically insulating solid electrolyte layer in between.

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

The second coating can also 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 adapted. The physical or chemical vapor deposition, ALD, MLD, CVD, PVD, electron beam deposition, laser deposition, plasma deposition, radio frequency sputtering, microemulsion deposition, successive ionic layer deposition, aqueous deposition, solid phase diffusion, sputter coating, or sol-gel coating are examples of its suitable processes Called powder coating.

All substances known for lithium-ion batteries are suitable as electrode active materials. The following are examples, but are not limited to them:

The following are suitable as oxidic electrode active materials for the cathode: LiNiCoAlO ₂ , LiNiCoMnO ₂ (NMC), LiMn _2-x M _x O ₄ with M = Ni, Fe, Co or Ru and with x = 0 to 0.5 and LiCoO ₂ ( LCO).

The following materials are suitable as anode active materials: V ₂ O ₅ , LiVO ₃ , Li ₃ VO ₄ and Li ₄ Ti ₅ O ₁₂ (LTP).

Compounds comprising phosphates are also suitable as electrode materials, such as Li ₃ V ₂ (PO4) ₃ or LiMPO ₄ with M = ¼ (Fe, Co, Ni, Mn) for a cathode or LiM ₂ (PO ₄ ) ₃ with M = Zr , Ti, Hf or a mixture thereof for an anode.

In a further embodiment of the invention, a third coating made of a solid electrolyte is applied to the second coating and optionally a fourth coating made of an electron-conducting material is applied to this third coating.

The sequence of the two layers therefore remains the same, only more layers are applied. Improved high-voltage stability and long-term durability of the electrode material according to the present invention can thus again be achieved. The invention is also not limited to a two-layer or four-layer multi-layer coating. It is equally within the scope of the present invention to apply further coatings in the same sequence; a solid electrolyte layer or an electron-conducting layer should always be provided as the outer layer.

Another object of the present invention is a secondary battery comprising an electrode active material according to the invention.

It is equally the subject of the present invention that an electrode active material according to the invention, as described above, is used in the manufacture of battery cells, in particular for traction batteries in vehicles.

• 1 in einer stark schematisierten Darstellung einen Querschnitt eines Elektrodenmaterials und als Detailansicht ein Ausschnitt aus einem solchen Partikel des erfindungsgemäßen Elektrodenmaterials,
• 2 in einer stark schematisierten Darstellung ein Energiediagramm des erfindungsgemäßen beschichteten Aktivmaterials unter angelegter Spannung,
• 3 in einer stark schematisierten Darstellung als Schnittansicht einen Elektrodenmaterialpartikel mit einer Mehrlagenbeschichtung gemäß einem weiteren Aspekt der vorliegenden Erfindung, und
• 4 in einer stark schematisierten Darstellung als Schnittansicht einen Elektrodenmaterialpartikel mit einer Mehrlagenbeschichtung gemäß einem weiteren Aspekt der vorliegenden Erfindung.

There are a multitude of options for designing and developing the electrode active material. For this purpose, reference may first be made to the claims subordinate to claim 1. A preferred embodiment of the invention may be explained in more detail below with reference to the drawings and the associated descriptions. In the drawings:

• 1 in a highly schematic representation, a cross section of an electrode material and as a detailed view a section of such a particle of the electrode material according to the invention,
• 2nd a highly schematic representation of an energy diagram of the coated active material according to the invention under applied voltage,
• 3rd in a highly schematic representation as a sectional view an electrode material particle with a multilayer coating according to a further aspect of the present invention, and
• 4th in a highly schematic representation as a sectional view of an electrode material particle with a multilayer coating according to a further aspect of the present invention.

In 1 schematically shows a cross section of an electrode material according to the invention and an enlarged section thereof. The electrode active material for lithium-ion batteries comprises active material particles 1 which is a first coating 2nd have from a solid electrolyte. According to the invention, the active material particles have 1 a second coating 3rd made of an electron-conducting material on the first coating 2nd is applied. The first coating 2nd is in such a thickness on the active material 1 applied that electron transport through the first coating 2nd can take place.

The following are suitable as oxidic electrode active materials for the cathode: LiNiCoAlO ₂ , LiNiCoMnO ₂ (NMC), LiMn _2-x M _x O ₄ with M = Ni, Fe, Co or Ru and with x = 0 to 0.5 and LiCoO ₂ ( LCO).

The following materials are suitable as anode active materials: V ₂ O ₅ , LiVO ₃ , Li ₃ VO ₄ and Li ₄ Ti ₅ O ₁₂ (LTP).

Compounds comprising phosphates are also suitable as electrode materials, such as Li ₃ V ₂ (PO4) ₃ or LiMPO ₄ with M = ¼ (Fe, Co, Ni, Mn) for a cathode or LiM ₂ (PO ₄ ) ₃ with M = Zr , Ti, Hf or a mixture thereof for an anode.

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

In other words, the anode and cathode active material particles are coated with a first layer 2nd which is a very thin, on the order of one or more atomic layers, ion-conductive solid electrolyte layer. Since the solid electrolyte layer cannot conduct electrons per se, this layer becomes 2nd applied so thin that the tunnel effect can be used.

High-voltage stable doped or undoped solid electrolytes of the NASICON type like LATP, LAGP or (anti) perovskites like LLTO or Li3OCl are on anode and cathode active material particles 1 deposited.

• • - Oxide, wie beispielsweise Li_7-xLa₃Zr₂Al_xO₁₂ mit x = 0 bis 0,5 oder Li₇La₃Zr_2-xTa_xO₁₂ mit x = 0 bis 0,5,
• • - Lithiumaluminiumtitanphosphate, wie beispielsweise Li_1+xM_xTi_2-x(PO₄)₃ mit x = 0 bis 7 und M = Al (LATP), Fe, Y oder Ge,
• • - Lithiumlanthanzirkonate, wobei zusätzlich Dotierungen von Tantal, Aluminium und Eisen eingesetzt werden können,
• • - Lithiumphosphorsulfide, wobei Germanium und Selen eindotiert werden können, wie beispielsweise Li₇P₃S₁₁, Li₁₀P₃S₁₂, Li₁₀M_xP_3-xS₁₂ mit M = Ge, Se und x = 0 bis1, mit M = A_yB_z, wobei A = Si, Ge und B = Sn, Si und mit y = 0 bis 0,5 und z = 1 - y.

In the following, some specific compounds are listed as examples that are suitable as solid electrolytes in the aforementioned sense, without being understood as being restricted to them:

• Oxides, such as Li _7-x La ₃ Zr ₂ Al _x O ₁₂ with x = 0 to 0.5 or Li ₇ La ₃ Zr _2-x Ta _x O ₁₂ with x = 0 to 0.5,
• Lithium aluminum titanium phosphates, such as Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ with x = 0 to 7 and M = Al (LATP), Fe, Y or Ge,
• • lithium lanthanum zirconates, with additional doping of tantalum, aluminum and iron can be used,
• Lithium phosphorus sulfides, where germanium and selenium can be doped, such as Li ₇ P ₃ S ₁₁ , Li ₁₀ P ₃ S ₁₂ , Li ₁₀ M _x P _3-x S ₁₂ with M = Ge, Se and x = 0 to 1, with M = A _y B _z , where A = Si, Ge and B = Sn, Si and with y = 0 to 0.5 and z = 1 - y.

The first coating 2nd 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.

The second important aspect of the invention is that on this first layer 2nd a layer 3rd is deposited, which can conduct electrons very well and has a low Fermi energy ( E3 in 2nd ) and a low work function ( WA (3) in 2nd ), such as graphene 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 (Li2ZrO3, Li3.5Al2O3, Li4Ti5O12 etc.) or lithium metal fluorides (Li3AIF6, Li2AIF4, Li3VF6 etc.).

In addition, the lithium ions each bridge the path from the active material or solid electrolyte via the electronically conductive material by means of tunnels.

As a result of the coating of the anode and cathode active material in a multi-layer system with a high-voltage stable solid electrolyte and an electron-conducting layer using the tunnel effect, the performance of the anode and cathode active materials at voltages> 4.2 V, in particular at 4.9 V, is increased.

The cause is the prevention of material dissolution and electrolyte decomposition. As a result, the performance of the lithium-ion battery cell is increased. The improved performance of a lithium-ion battery cell means, in particular, an extended service life and the high current carrying capacity.

• - Schutz des Elektrolyten vor Zersetzung infolge hoher Spannungen.
• - Schutz des Kathodenaktivmaterials, insbesondere LiNi_0.5Mn_1.5O₄, vor Materialauflösung bei hoher Temperatur und hohen Spannungen.
• - Schutz vor Strukturveränderungen des Kathodenaktivmaterials während der Zyklisierung der Batteriezelle.
• - Nutzbarmachung des Tunneleffektes des elektronisch nicht leitenden Festelektrolyten;
• - Erhöhung der Leistungsfähigkeit des Kathodenaktivmaterials, der Elektrode und der Lithium-Ionen-Zelle daraus.

The multi-layer coating made of solid electrolyte 2nd and electron-conducting material 3rd on the anode and cathode active material 1 can conduct electrons in addition to lithium ions and is stable at high voltages. In particular, this has the consequence that one or more of the advantages listed below are achieved:

• - Protection of the electrolyte against decomposition due to high voltages.
• - Protection of the cathode active material, in particular LiNi _0.5 Mn _1.5 O ₄ , against material dissolution at high temperature and high voltages.
• - Protection against structural changes in the cathode active material during the cyclization of the battery cell.
• - Utilization of the tunnel effect of the electronically non-conductive solid electrolyte;
• - Increasing the performance of the cathode active material, the electrode and the lithium-ion cell therefrom.

Both coatings 2nd and 3rd are applied to the active material particles using suitable processes such as gas phase vapor deposition or the like, which are known to the person skilled in the art from the production of lithium-ion cells 1 upset. Examples include ALD, MLD, CVD, PVD, electron beam deposition, Laser deposition, plasma deposition, radio frequency sputtering, microemulsion deposition, successive ionic layer deposition, aqueous deposition, solid phase diffusion, sputter coating, sol-gel coating or powder coating are mentioned.

In 2nd Figure 3 is a schematic energy diagram of the anode or cathode active material particles 1 , of the solid electrolyte 2nd and the electron conductor 3rd shown.

One effect of the invention is to use the tunnel effect, that is, the electrons bridge the path from the cathode active material 1 to the second shift 3rd , which is electron-conductive, although there is an electronically insulating solid electrolyte layer in between 2nd located.

When a voltage is applied to both sides of the barrier, as is the case with a powered battery, the Fermi levels shift E1 and E3 against each other eV , because on the right 3rd Electrons are pulled out. As a result, there is on the right 3rd free states for left side electrons 1 , which causes tunneling, that is, electron transport through the non-electron-conducting layer 2nd , is relieved.

In 3rd is schematic as a cross-sectional view of the anode or cathode active material particle of the invention 1 with a multi-layer system made of layers of solid electrolyte 2nd and layers of electron conductors 3rd shown, the outermost layer always a solid electrolyte layer 2nd is.

In 4th is schematic as a cross-sectional view of the anode or cathode active material particle of the invention 1 with a multi-layer system made of layers of solid electrolyte 2nd and layers of electron conductors 3rd shown, the outermost layer is always an electron conductor layer.

The sequence of the solid electrolyte layer 2nd , electron-conducting layer 3rd can be expanded as often as necessary until optimal protection against degradation of the cathode active material and the electrolyte is achieved, but no isolating effects arise yet.

As a result of the coating of the anode and cathode active material 1 in a multi-layer system with a high-voltage stable solid electrolyte 2nd and an electron-conducting layer 3rd utilizing the tunnel effect, the performance of the anode and cathode active materials is increased at voltages> 4.2 V, in particular at 4.9 V.

The cause is the prevention of material dissolution and electrolyte decomposition. As a result, the performance of the lithium-ion battery cell is increased. Improved performance of a lithium-ion battery cell means, in particular, an extended service life and the high current carrying capacity.

Reference symbol list

1

Electrode active material particles

2nd

first coating

3rd

second coating

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 3443455 A1 [0002]
• EP 2472662 B1 [0006]
• US 2017/0018760 A1 [0007]
• DE 102015217749 A1 [0007]

Claims (10)

Electrode active material for lithium-ion batteries, comprising active material particles (1) which have a first coating (2) made of a solid electrolyte, characterized in that the active material particles (1) have a second coating (3) made of an electron-conductive material, which the first coating (2) is applied, and the first coating (2) is applied to the active material in such a thickness that electron transport can take place through the first coating (2). Electrode active material according to Claim 1 , characterized in that the first coating (2) is made of a solid electrolyte, which comprises a solid electrolyte material from the group of NASICON solid electrolytes, in particular LATP or LAGP, and the (anti) perovskite, in particular LLTO or Li ₃ OCl. Electrode active material according to Claim 1 or 2nd , characterized in that the second coating (3) is made of an electron-conducting material, selected from the group graphene, titanium, zirconium, boron, vanadium oxide, titanium oxide, niobium oxide, lithium metal alloy, in particular Zn-Li, Sn-Li, Al-Li, lithium metal oxides, in particular Li ₂ ZrO ₃ , Li _3.5 Al ₂ O ₃ , Li ₄ Ti ₅ O ₁₂ , and lithium metal fluorides, in particular Li ₃ AlF ₆ , Li ₂ AlF ₄ , Li ₃ VF ₆ . Electrode active material according to one of the preceding claims, characterized in that the electrode active material of the active material particles is LiNi _0.5 Mn _1.5 O ₄ . Electrode active material according to one of the preceding claims, characterized in that the first coating (2) 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 . Electrode active material according to one of the preceding claims, characterized in that the first coating (2) has a layer thickness of one to several atomic layers and is applied by means of physical, wet-chemical or mechanical methods. Electrode active material according to one of the preceding claims, characterized in that the second coating (3) is applied by means of physical, wet-chemical or mechanical methods. Electrode active material according to one of the preceding claims, characterized in that a third coating of a solid electrolyte (2) is applied to the second coating (3). Secondary battery comprising an electrode active material according to one of the preceding claims. Use of an electrode active material according to one of the preceding Claims 1 to 9 in the manufacture of battery cells, especially for traction batteries in vehicles.

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