Composite cathode material and battery cathode and solid-state battery

Abstract

The application discloses a composite positive electrode material and a battery positive electrode and a solid-state battery, and belongs to the technical field of batteries. The composite positive electrode material comprises a core part, a first coating layer and a second coating layer. The core part is a positive electrode active material. The first coating layer coats the core part. The first coating layer is a lithium-containing metal oxide. The second coating layer is a solid-state electrolyte. The first coating layer and the second coating layer are both non-continuous nanoscale island-shaped coating layers. The battery positive electrode is prepared by using the composite positive electrode material. The solid-state battery comprises the battery positive electrode. The application can improve the stability of a high-nickel single-crystal positive electrode material and improve solid-solid contact in the positive electrode.

Description

Technical Field

[0001] This invention generally relates to the field of battery technology, and more specifically, to a method for improving the stability of high-nickel single-crystal cathode materials and improving the solid-solid contact difference inside the cathode. Background Technology

[0002] Compared with traditional liquid lithium batteries, solid-state batteries have a wider operating temperature range, better safety and longer cycle life, and are widely regarded as an important direction for the future development of lithium batteries.

[0003] While solid-state batteries offer superior safety and cycle performance, the solid electrolyte and positive electrode form a solid-solid contact. This results in a significantly lower ionic conductivity within the positive electrode compared to a pure liquid electrolyte. Furthermore, persistent interfacial side reactions at the positive electrode interface lead to continuous capacity degradation, especially with higher nickel content. The poor wettability of the solid-solid contact interface between the positive electrode material and electrolyte in solid-state batteries creates numerous ion-conducting voids, resulting in poor ionic conductivity within the positive electrode and hindering its ability to achieve normal capacity. Addressing the solid-solid contact issue often involves applying extreme pressure to increase interfacial contact, which further complicates the industrialization of solid-state batteries.

[0004] Therefore, improving the stability of high-nickel single-crystal cathode materials and reducing the solid-solid contact difference inside the cathode are technical problems that the industry urgently needs to solve. Summary of the Invention

[0005] A primary objective of this invention is to overcome at least one of the deficiencies of the prior art and to provide a composite cathode material, battery cathode, and solid-state battery that can improve the stability of high-nickel single-crystal cathode materials and improve the solid-solid contact difference inside the cathode.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: According to one aspect of the present invention, a composite cathode material is provided, comprising a core, a first coating layer, and a second coating layer, wherein the core is a cathode active material, the first coating layer covers the core, the first coating layer is a lithium-containing metal oxide, the second coating layer is a solid electrolyte, and both the first coating layer and the second coating layer are discontinuous nanoscale island-shaped coating layers.

[0007] According to one embodiment of the present invention, the ionic conductivity of the positive electrode active material is 4.9*10⁻⁶. -3 S / cm, electronic conductivity 6.3*10 -3 S / cm, wherein the particle size of the positive electrode active material is 1-3μm or 3-5μm.

[0008] According to one embodiment of the present invention, the mass ratio of the positive electrode active material to the metal salt is 100:0.5, 100:0.2, or 100:0.1; the mass ratio of the positive electrode active material to the solid electrolyte is 100:0.5, 100:1, or 100:1.5.

[0009] According to one embodiment of the present invention, the general formula of the positive electrode active material is Li. a Ni x Co y Mn 1-x-y M b O2, wherein 0.9≤a≤1.1, 0.6≤x≤1, 0.00≤y<0.50, 0≤b<0.1, and M is selected from at least one of Mg, Ti, Al, Ca, Sn, W, Sb, Nb, Zn, La, Y, Zr, Cl, Br, I, B, and Si.

[0010] According to one embodiment of the present invention, the metal salt includes lithium difluorophosphate (LiPO2F2) and lithium titanate (Li4Ti5O2). 12 One or more combinations of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3).

[0011] According to one embodiment of the present invention, the solid electrolyte is LiAlCl 2.5 O 0.75 It is obtained by substituting Cl in LiAlCl4 with oxygen in Sb2O3. In Formula 1, the highest ionic conductivity is achieved when O:Li = 0.75. Formula 1 is as follows: .

[0012] According to one embodiment of the present invention, the preparation of the composite cathode material includes the following steps: S1. Lithium-containing metal oxide material coating: The positive electrode active material is mixed with lithium-containing metal oxide and sintered for the first time to obtain the first sintering product. The first sintering product is the positive electrode active material coated with lithium-containing metal oxide. S2. Solid electrolyte coating: The first sintering product is mixed with the electrolyte precursor and then sintered a second time to obtain the second sintering product. The second sintering product is coated with lithium metal oxide and solid electrolyte from the inside out.

[0013] According to one embodiment of the present invention, in S1, the first sintering temperature is 200℃-400℃, or 400℃-600℃; the heating rate is 2℃ / min-5℃ / min, or 5℃ / min-10℃ / min; the sintering time is 5h-10h, or 12h-24h; in S2, the third sintering temperature is 150℃-200℃, or 200℃-300℃; the heating rate is 2℃ / min-5℃ / min, or 5℃ / min-10℃ / min; the sintering time is 2h-10h, or 12h-24h; the mixing method in both S1 and S2 is ball milling, the ball milling speed is 200rpm / min-500rpm / min, or 500rpm / min-1000rpm / min; the ball milling time is 2h-12h, or 12h-24h.

[0014] According to a second aspect of the present invention, a battery positive electrode is provided, the battery positive electrode being prepared using the aforementioned composite positive electrode material.

[0015] According to a second aspect of the present invention, a solid-state battery is provided, the solid-state battery comprising the above-described battery positive electrode.

[0016] As can be seen from the above technical solution, the advantages and positive effects of the composite cathode material, battery cathode, and solid-state battery of the present invention are as follows: This invention can improve the stability of high-nickel single-crystal cathode materials and improve the solid-solid contact difference inside the cathode.

[0017] The first coating layer of this invention is a lithium-containing metal oxide material, which stabilizes the interface between the positive electrode and the solid electrolyte, improving the cycle stability of the positive electrode. The first coating is completed through solid-phase ball milling and sintering, resulting in a solid-phase island-like coating. The second coating layer is a solid electrolyte material with a low melting point. Through formation, this material effectively improves the contact between the positive electrode, the solid electrolyte, and other components, providing wetting. Simultaneously, it exhibits high ionic conductivity at room temperature. This second coating is also an island-like coating. By coating the positive electrode active material, this invention constructs an interface layer inside the solid-state battery positive electrode. This layer suppresses continuous side reactions between the positive electrode and the solid electrolyte, improving cycle stability. Furthermore, the flexible soft contact enhances the solid-solid contact between the positive electrode and the solid electrolyte, increasing the ionic conductivity within the positive electrode, increasing the proportion of positive electrode active material, improving cell energy density, reducing interface impedance, and enhancing rate capability and cycle performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process for preparing the coated cathode according to the present invention.

[0019] Figure 2This is a schematic diagram comparing the cell cycle data of various embodiments and comparative examples. Detailed Implementation

[0020] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0021] In the following description of various examples of the invention, reference is made to the accompanying drawings, which form part of the invention, and in which different exemplary structures, systems, and steps that can implement various aspects of the invention are shown by way of example. It should be understood that other specific embodiments of the components, structures, exemplary devices, systems, and steps may be used, and structural and functional modifications may be made without departing from the scope of the invention. Furthermore, while the terms “top,” “bottom,” “front,” “rear,” “side,” etc., may be used in this specification to describe various exemplary features and elements of the invention, these terms are used herein only for convenience, such as the orientation according to the examples shown in the drawings. Nothing in this specification should be construed as requiring a specific three-dimensional orientation of the structure to fall within the scope of the invention.

[0022] Example 1

[0023] refer to Figure 1 As shown, follow these steps: S1. Weigh 10g of positive electrode and 0.05g of LiPO2F2 according to the mass ratio of positive electrode active material and lithium metal oxide of 100:0.5, and mix them together and ball mill for 5h at a speed of 400rpm / min. Then, perform the first sintering at a temperature of 350℃ for 10h at a heating rate of 5℃ / min to obtain the first sintering product, which is a positive electrode active material coated with lithium metal oxide. S2. Weigh out 0.131g of LiAlCl4 and 0.054g of Sb2O3, the precursors of the electrolyte, according to a mass ratio of 100:1 for positive electrode active material and solid electrolyte. Mix the first sintering product with the precursors, ball mill for 10 hours at a speed of 400 rpm / min, and then perform a second sintering at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintering product. The second sintering product is a positive electrode active material coated with lithium metal oxide and solid electrolyte sequentially from the inside out. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0024] Example 2

[0025] refer to Figure 1 As shown, follow these steps: S1. Weigh 10g of positive electrode and 0.02g of LiPO2F2 according to the mass ratio of positive electrode active material and lithium metal oxide of 100:0.2, and mix them together and ball mill for 5h at a speed of 400rpm / min. Then, perform the first sintering at a temperature of 350℃ for 10h at a heating rate of 5℃ / min to obtain the first sintering product, which is a positive electrode active material coated with lithium metal oxide. S2. Weigh out 0.131g of LiAlCl4 and 0.054g of Sb2O3, the precursors of the electrolyte, according to a mass ratio of 100:1 for positive electrode active material and solid electrolyte. Mix the first sintering product with the precursors, ball mill for 10 hours at a speed of 400 rpm / min, and then perform a second sintering at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintering product. The second sintering product is a positive electrode active material coated with lithium metal oxide and solid electrolyte sequentially from the inside out. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0026] Example 3

[0027] refer to Figure 1 As shown, follow these steps: S1. Weigh 10g of positive electrode and 0.01g of LiPO2F2 according to the mass ratio of positive electrode active material and lithium metal oxide of 100:0.1, and mix them together and ball mill for 5 hours at a speed of 400 rpm / min. Then, perform the first sintering at a temperature of 350℃ for 10 hours at a heating rate of 5℃ / min to obtain the first sintering product, which is a positive electrode active material coated with lithium metal oxide. S2. Weigh out 0.131g of LiAlCl4 and 0.054g of Sb2O3, the precursors of the electrolyte, according to a mass ratio of 100:1 for positive electrode active material and solid electrolyte. Mix the first sintering product with the precursors, ball mill for 10 hours at a speed of 400 rpm / min, and then perform a second sintering at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintering product. The second sintering product is a positive electrode active material coated with lithium metal oxide and solid electrolyte sequentially from the inside out. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0028] Example 4

[0029] refer to Figure 1 As shown, follow these steps: S1. Weigh 10g of positive electrode and 0.02g of LiPO2F2 according to the mass ratio of positive electrode active material and lithium metal oxide of 100:0.2, and mix them together and ball mill for 5h at a speed of 400rpm / min. Then, perform the first sintering at a temperature of 350℃ for 10h at a heating rate of 5℃ / min to obtain the first sintering product, which is a positive electrode active material coated with lithium metal oxide. S2. Weigh out 0.065g of LiAlCl4 and 0.027g of Sb2O3 according to the mass ratio of positive electrode active material to solid electrolyte of 100:0.5. Mix the first sintering product with the precursors, ball mill for 10 hours at a speed of 400 rpm / min, and then perform a second sintering at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintering product. The second sintering product is a positive electrode active material coated with lithium metal oxide and solid electrolyte sequentially from the inside out. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0030] Example 5

[0031] refer to Figure 1 As shown, follow these steps: S1. Weigh 10g of positive electrode and 0.02g of LiPO2F2 according to the mass ratio of positive electrode active material and lithium metal oxide of 100:0.2, and mix them together and ball mill for 5h at a speed of 400rpm / min. Then, perform the first sintering at a temperature of 350℃ for 10h at a heating rate of 5℃ / min to obtain the first sintering product, which is a positive electrode active material coated with lithium metal oxide. S2. Weigh out 0.195g of LiAlCl4 and 0.081g of Sb2O3 according to the mass ratio of positive electrode active material to solid electrolyte of 100:1.5. Mix the first sintering product with the precursors, ball mill for 10 hours at a speed of 400 rpm / min, and then perform a second sintering at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintering product. The second sintering product is a positive electrode active material coated with lithium metal oxide and solid electrolyte sequentially from the inside out. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0032] Comparative Example 1 S1. Weigh 10g of positive electrode and 0.02g of LiPO2F2 according to the mass ratio of positive electrode active material and lithium metal oxide of 100:0.2, and mix them together and ball mill for 5 hours at a speed of 400 rpm / min. Then, perform the first sintering at a temperature of 350℃ for 10 hours at a heating rate of 5℃ / min to obtain the first sintering product, which is a positive electrode active material coated with lithium metal oxide. S2. The positive electrode active material is ball-milled for 10 hours at a speed of 400 rpm / min, and then sintered a second time at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintered product. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0033] Comparative Example 2 S1. The positive electrode active material is mixed and ball-milled for 5 hours at a speed of 400 rpm / min. The first sintering is then carried out at a temperature of 350℃ for 10 hours at a heating rate of 5℃ / min to obtain the first sintered product. S2. Weigh out each electrolyte precursor LiAlCl according to a mass ratio of positive electrode active material to solid electrolyte of 100:1. 4，Sb2O3 was added and the first sintering product was mixed with the precursor. The ball milling time was 10 h and the ball mill speed was 400 rpm / min. Then, a second sintering was carried out at a sintering temperature of 200℃, a holding time of 2 h, and a heating rate of 5℃ / min to obtain the second sintering product. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0034] Comparative Example 3 S1. The positive electrode active material is mixed and ball-milled for 5 hours at a speed of 400 rpm / min. The first sintering is then carried out at a temperature of 350℃ for 10 hours at a heating rate of 5℃ / min to obtain the first sintered product. S2. The positive electrode active material is ball-milled for 10 hours at a speed of 400 rpm / min, and then sintered a second time at a temperature of 200℃ for 2 hours at a heating rate of 5℃ / min to obtain the second sintered product. The above composite cathode material was assembled into a battery and tested at a current density of 0.1~0.5C.

[0035] By coating different cathode materials and cycling them in the battery, a comparison chart of cycling data for different cathode materials was obtained, such as... Figure 2 As shown in the figure. The problem indicates that the positive electrode with coating treatment exhibits better cycle performance than the untreated positive electrode (Comparative Example 3), but the cell's first-efficiency cycle stability is poor. The higher first-efficiency of the cell in Comparative Example 2 compared to Comparative Example 1 suggests better interfacial contact, which is more conducive to high energy density. However, their cycle stability is exactly opposite, indicating that this electrolyte material also exhibits side reactions with the positive electrode. The first coating layer, LiPO2F2, can generate a stable CEI layer (mainly composed of LiP) on the positive electrode surface through decomposition and reaction with residual surface alkali. x O y F z LiP x F y The presence of LiF blocks and inhibits the generation of side reactions; the second coating layer is LiAlCl. 2.5 O 0.75 Solid electrolytes have a low melting point of ≈160℃. Through high-temperature formation, the components inside the positive electrode can achieve good interfacial wetting and better utilize the cell capacity. In addition, the residual part of the solid electrolyte precursor will react with the residual alkali on the positive electrode surface to generate LiSbO3, which eliminates the residual alkali and forms a highly ionic conductive interfacial layer, which stabilizes the positive electrode interface to a certain extent.

[0036] Examples 1-3 compare the effects of different coating amounts on the stability of the cathode. It can be seen that as the coating amount increases, the initial efficiency of the cathode material gradually decreases, while better cycle performance is observed at a coating ratio of 100:0.2. In Examples 4 and 5, it can be seen that a coating ratio of 100:1 yields the best performance. A small amount of coating may result in insufficient interfacial contact, while excessive coating may affect the electronic conductivity of the coated cathode.

[0037] This patent first forms a stable CEI layer on the positive electrode surface by coating lithium difluorophosphate once, which alleviates the continuous side reaction with the solid electrolyte, improves the cycle performance of the battery, and reduces the transformation of the positive electrode interface structure to the rock salt phase. Then, it constructs a soft contact at the interface by coating electrolyte material twice, which reduces the problems of solid-solid contact ion conduction and capacity utilization.

[0038] Those skilled in the art should understand that the specific structures and processes shown in the above detailed embodiments are merely exemplary and not restrictive. Furthermore, those skilled in the art can combine the various technical features described above in various possible ways to form new technical solutions or make other modifications, all of which fall within the scope of this invention.

Claims

1. A composite cathode material, characterized in that, It includes a core, a first coating layer, and a second coating layer. The core is a positive electrode active material, the first coating layer covers the core, the first coating layer is a lithium-containing metal oxide, and the second coating layer is a solid electrolyte. Both the first coating layer and the second coating layer are discontinuous nanoscale island-shaped coating layers.

2. The composite cathode material according to claim 1, characterized in that: The ionic conductivity of the positive electrode active material is 4.9*10. -3 S / cm, electronic conductivity 6.3*10 -3 S / cm, wherein the particle size of the positive electrode active material is 1-3μm or 3-5μm.

3. The composite cathode material according to claim 1, characterized in that: The mass ratio of the positive electrode active material to the lithium-containing metal oxide is 100:0.5, 100:0.2, or 100:0.1; the mass ratio of the positive electrode active material to the solid electrolyte is 100:0.5, 100:1, or 100:1.

5.

4. The composite cathode material according to claim 1, characterized in that: The general formula of the positive electrode active material is Li a Ni x Co y Mn 1-x-y M b O2, wherein 0.9≤a≤1.1, 0.6≤x≤1, 0.00≤y<0.50, 0≤b<0.1, and M is selected from at least one of Mg, Ti, Al, Ca, Sn, W, Sb, Nb, Zn, La, Y, Zr, Cl, Br, I, B, and Si.

5. The composite cathode material according to claim 4, characterized in that: The lithium-containing metal oxides include lithium difluorophosphate (LiPO2F2) and lithium titanate (Li4Ti5O). 12 It can be one or more of the following: lithium niobate (LiNbO3), lithium tantalate (LiTaO3), etc.

6. The composite cathode material according to claim 5, characterized in that: The solid electrolyte is LiAlCl 2.5 O 0.75 It is obtained by substituting Cl in LiAlCl4 with oxygen in Sb2O3. In Formula 1, the highest ionic conductivity is achieved when O:Li = 0.

75. Formula 1 is as follows: 。 7. The composite cathode material according to any one of claims 1-6, characterized in that: The preparation of the composite cathode material includes the following steps: S1. Lithium-containing metal oxide material coating: The positive electrode active material is mixed with lithium-containing metal oxide and sintered for the first time to obtain the first sintering product. The first sintering product is the positive electrode active material coated with lithium-containing metal oxide. S2. Solid electrolyte coating: The first sintering product is mixed with the electrolyte precursor and then sintered a second time to obtain the second sintering product. The second sintering product is coated with lithium metal oxide and solid electrolyte from the inside out.

8. The composite cathode material according to claim 7, characterized in that: In S1, the first sintering temperature is 200℃-400℃, or 400℃-600℃; the heating rate is 2℃ / min-5℃ / min, or 5℃ / min-10℃ / min; the sintering time is 5h-10h, or 12h-24h. In S2, the second sintering temperature is 150℃-200℃, or 200℃-300℃; the heating rate is 2℃ / min-5℃ / min, or 5℃ / min-10℃ / min; the sintering time is 2h-10h, or 12h-24h. The mixing method in both S1 and S2 is ball milling, with a ball milling speed of 200rpm / min-500rpm / min, or 500rpm / min-1000rpm / min; the ball milling time is 2h-12h, or 12h-24h.

9. A battery positive electrode, characterized in that, The positive electrode of the battery is prepared using the composite positive electrode material according to any one of claims 1-8.

10. A solid-state battery, characterized in that, The solid-state battery includes the positive electrode according to claim 9.

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