Positive electrode composite, method for manufacturing the same, positive electrode sheet, and battery

Abstract

The application relates to the technical field of lithium batteries, in particular to a positive electrode composite material and a preparation method thereof, a positive electrode sheet and a battery. The application aims at solving the problem of poor interface stability and structural stability between a coating layer and a bulk material in the related art. The positive electrode composite material comprises a bulk material and a coating layer, the bulk material comprises a material of general formula Li w Ni a Co b Mn c X 1‑a‑b‑c O2, wherein X comprises one or more of Al, Ti, Zr, Mg and W, and 0.95<=w<=1.1, 0.6<=a<=1, b>=0 and c>=0; the material of the coating layer is of general formula Li α Ni β Co γ Mn δ O2, wherein 0<alpha<=1, 0<=beta<=0.6, 0<=gamma<=1, 0<=delta<=1, and beta, gamma and delta are not zero at the same time; and the interface between the bulk material and the coating layer is a coherent phase interface.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a positive electrode composite material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] The rapid development of the new energy vehicle industry has driven the rapid growth of power lithium-ion batteries.

[0003] High-nickel layered cathode materials have attracted widespread market attention due to their advantages such as high specific capacity, excellent cycle performance, and low production cost, enabling electric vehicles to achieve a single-charge range of over 300km. However, high-nickel layered cathode materials typically face complex electrode / electrolyte interface problems in practical applications: on the one hand, the high residual lithium compounds such as LiOH and Li₂CO₃ on the surface of these materials can easily exacerbate gelation and gas generation in the electrode slurry; on the other hand, under high charge, the H₂→H₃ phase transition causes anisotropic contraction or expansion of the crystal structure, continuously accumulating mechanical stress at the grain boundaries, inducing microcracks and particle breakage. The electrolyte can then seep into the active particles along these cracks, further aggravating the high activity of Ni in the high-nickel layered cathode material. 4+ Side reactions with the electrolyte ultimately lead to the failure of the high-nickel layered cathode material.

[0004] By preparing a coating layer on the surface of a high-nickel layered cathode material (also known as the bulk material), the high-nickel layered cathode material can be separated from the electrolyte, reducing the reactivity between the two. In a highly delithiated state, the coating layer can also prevent highly oxidized Ni. 4+ The irreversible phase transition from layered to disordered spinel and rock salt structures caused by electrolyte side reactions improves the cycle life of cathode materials. However, current coating materials are either electrochemically inert compounds or, although the coating materials have electrochemical properties, the coating material and the bulk material are physically bonded, making them prone to dissociation or detachment during charge and discharge. Therefore, the problem of poor interfacial stability between the bulk material and the electrolyte still exists. Summary of the Invention

[0005] Based on this, this application provides a positive electrode composite material and its preparation method, a positive electrode sheet and a battery, to solve the problem of poor interfacial stability and structural stability between the coating layer and the bulk material in related technologies.

[0006] In a first aspect, a positive electrode composite material is provided, comprising a bulk material and a coating layer;

[0007] The bulk material includes general formula Li w Ni a Co b Mn c X1-a-b-c The material of O2, wherein X includes one or more of Al, Ti, Zr, Mg and W, and 0.95≤w≤1.1, 0.6≤a≤1, b≥0, c≥0;

[0008] The general formula for the coating material includes Li α Ni β Co γ Mn δ The material is O2, wherein 0 ≤ α ≤ 1, 0 ≤ β ≤ 0.6, 0 ≤ γ ≤ 1, 0 ≤ δ ≤ 1, and β, γ and δ are not simultaneously 0;

[0009] The interface between the bulk material and the coating layer is a coherent phase boundary.

[0010] Optionally, in the crystal structure of both the bulk material and the coating material, oxygen ions are in a close-packed structure;

[0011] And / or,

[0012] The material of the cladding layer belongs to one or more of the space groups Fd-3m, Fm-3m, R-3m and C2 / m.

[0013] Optionally, the thickness of the coating layer is ≤200nm.

[0014] In a second aspect, a method for preparing the positive electrode composite material as described in the first aspect is provided, comprising:

[0015] Prepare or provide the body material;

[0016] The bulk material is mixed with a coating additive, and the cathode composite material is prepared by a topological transformation reaction.

[0017] Optionally, the bulk material is mixed with a coating additive, and the cathode composite material is prepared by a topological transformation reaction, comprising:

[0018] The bulk material and the coating additive are mixed;

[0019] The mixed materials are calcined in stages to prepare the positive electrode composite material;

[0020] The stepwise calcination includes two calcination steps. The first calcination step is carried out at a temperature of 400-600℃ for 1-5 hours. The second calcination step is carried out at a temperature of 600-800℃ for 3-10 hours. The atmosphere for the stepwise calcination is an oxygen-containing atmosphere.

[0021] The coating additive includes a first precursor and a reaction auxiliaries, wherein the first precursor includes: Ni x Co y Mn z (OH)2, Nix Co y Mn z OOH, Ni x Co y Mn z One of O, wherein 0≤x≤0.6, 0≤y≤1, 0≤z≤1, and x, y, and z are not simultaneously 0; the reaction aid includes one or more of lithium carbonate, lithium oxide, and lithium hydroxide;

[0022] Optionally, in the stepwise calcination, the first precursor has an oxygen-dense packing structure, and the space group includes one or more of Fd-3m, Fm-3m, R-3m and C2 / m;

[0023] Optionally, the first precursor satisfies one of the following conditions:

[0024] (1) The specific surface area of ​​the first precursor is ≥20 m² 2 / g;

[0025] (2) The molar ratio of the first precursor to the bulk material is 0.5 mol% ~ 10 mol%

[0026] (3) The total number of metal atoms in the first precursor is M, and the total number of residual lithium atoms in the reaction aid and the bulk material is L, wherein M and L satisfy 0.8. <L / M<1.2。

[0027] Optionally, the preparation of the bulk material includes:

[0028] In an oxygen-containing atmosphere, a high-nickel precursor and a lithium salt are mixed, heated and calcined, then cooled in the furnace and crushed and sieved.

[0029] Optionally, the bulk material is prepared to satisfy at least one of the following conditions:

[0030] (1) The high-nickel material precursor includes one or more of oxides and hydroxides;

[0031] (2) The lithium salt includes one or more of lithium carbonate and lithium hydroxide;

[0032] (3) The molar ratio of lithium atoms in the high-nickel material precursor and the reaction aid is 1.0:(0.9~1.1);

[0033] (4) The heating rate is 2~8℃ / min, the calcination temperature is 700~1100℃, and the time is 12h~24h.

[0034] Thirdly, a positive electrode sheet is provided, comprising: a positive electrode current collector, and a positive electrode material layer formed on at least one surface of the positive electrode current collector;

[0035] The cathode material layer includes the cathode composite material as described in the first aspect or the cathode composite material prepared by the preparation method as described in the second aspect.

[0036] Fourthly, a battery is provided, comprising: a positive electrode as described in the third aspect.

[0037] Compared with the prior art, this application has the following beneficial effects:

[0038] By forming a coating layer on the surface of a high-nickel layered cathode material (i.e., the bulk material), the good electrochemical activity of this coating layer can effectively reduce the battery capacity loss caused by the use of inert coating layers in related technologies. Furthermore, since the interface between the bulk material and the coating layer is a coherent phase boundary, on the one hand, the coating layer and the bulk material are chemically bonded, thus effectively improving the bonding stability between the coating layer and the bulk material; on the other hand, the coherent phase boundary between the two can effectively improve the interfacial stability and structural stability between the coating layer and the bulk material. Therefore, this coating layer can alleviate stress accumulation in the high-nickel layered cathode material during battery cycling, prevent direct contact between the high-nickel layered cathode material and the electrolyte, and thus effectively suppress Ni oxidation on the surface of the high-nickel layered cathode material. 4+ The coating layer reduces side reactions with the electrolyte, thereby effectively improving battery cycle performance. Furthermore, the formation of this coating layer can consume residual lithium compounds on the surface of the high-nickel layered cathode material, thus reducing residual lithium compounds and effectively reducing battery gas production. This solves the problem of poor interfacial and structural stability between the coating layer and the bulk material in related technologies. Attached Figure Description

[0039] Figure 1 The non-in-situ XRD patterns of high-nickel layered cathode materials at different temperature states in process S3 provided in the embodiments of this application;

[0040] Figure 2 A comparison chart of the specific capacity of Example 1 without coating and after coating as a function of the number of cycles, provided for the embodiments of this application;

[0041] Figure 3 A comparison diagram of the differential scanning calorimetry curves of Example 1 without coating and with coating, provided as an embodiment of this application. Detailed Implementation

[0042] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] The determination of surface residual alkali in this patent is performed in accordance with GB / T 41704-2022.

[0045] Based on the above technical problems, some embodiments of this application provide a positive electrode composite material, including: a bulk material and a coating layer; the bulk material includes general formula Li w Ni a Co b Mn c X 1-a-b-c The material for O2, wherein X includes one or more of Al, Ti, Zr, Mg and W, and 0.95≤w≤1.1, 0.6≤a≤1, b≥0, c≥0; the general formula of the coating material is Li. α Ni β Co γ Mn δ O2, where 0 < α ≤ 1, 0 ≤ β ≤ 0.6, 0 ≤ γ ≤ 1, 0 ≤ δ ≤ 1, and β, γ and δ are not simultaneously 0; the interface between the bulk material and the coating layer is a coherent phase boundary.

[0046] The aforementioned bulk material is a high-nickel layered cathode material, and the coating material is a low-nickel material. Furthermore, since the coating material contains elements with good electrochemical activity such as Ni, Co, and / or Mn, the coating material has high electrochemical activity.

[0047] Most crystalline materials are composed of many grains. The interface between grains belonging to the same solid phase but with different phases is called a grain boundary. In a crystal structure, if two grains have different structures, we say that these two grains with different structures have different crystalline phases, and the interface between two phases with different structures is called a phase boundary. A coherent phase boundary refers to an interface where atoms are located at the nodes of both phase lattices, meaning that the lattices of the two phases are connected to each other, and the atoms at the interface are shared by both. Here, the interface between the bulk material and the cladding layer is a coherent phase boundary, meaning that the bulk material and the cladding layer have different crystal structures, and the atoms at the interface of the two different crystal structures are shared by both the bulk material and the cladding layer.

[0048] In the cathode composite material provided in this application embodiment, a coating layer is formed on the surface of the high-nickel layered cathode material (i.e., the bulk material). Because this coating layer has good electrochemical activity, it can effectively reduce the battery capacity loss caused by the use of inert coating layers in related technologies. Simultaneously, since the interface between the bulk material and the coating layer is a coherent phase boundary, on the one hand, the coating layer and the bulk material are chemically bonded, thus effectively improving the bonding stability between the coating layer and the bulk material; on the other hand, the coherent phase boundary between the two can effectively improve the interface stability and structural stability between the coating layer and the bulk material. Therefore, this coating layer can alleviate the stress accumulation of the high-nickel layered cathode material during battery cycling, prevent direct contact between the high-nickel layered cathode material and the electrolyte, and thus effectively suppress Ni oxidation on the surface of the high-nickel layered cathode material. 4+ The coating layer reduces side reactions with the electrolyte, thereby effectively improving battery cycle performance. Furthermore, the formation of this coating layer can consume residual lithium compounds on the surface of the high-nickel layered cathode material, thus reducing residual lithium compounds and effectively reducing battery gas production. This solves the problem of poor interfacial and structural stability between the coating layer and the bulk material in related technologies.

[0049] In some embodiments, oxygen ions are in close-packed structures in both the bulk material and the cladding layer crystal structure; and / or, the cladding layer belongs to one or more of the space groups Fd-3m, Fm-3m, R-3m, or C2 / m.

[0050] The space group to which the coating layer belongs is one or more of Fd-3m, Fm-3m, R-3m or C2 / m, which can make the interface between it and the bulk material a coherent phase boundary.

[0051] In some embodiments, the thickness of the coating layer is ≤200nm.

[0052] In these embodiments, by controlling the thickness of the coating layer to ≤200nm, the coating layer can be coated on the surface of the bulk material in a thin and uniform manner. This can both protect the high-nickel layered cathode material from electrolyte attack and suppress side reactions, and reduce the obstruction to lithium diffusion during the insertion and extraction process.

[0053] Some embodiments of this application provide a method for preparing the positive electrode composite material as described above, including:

[0054] Preparation or provision of bulk materials;

[0055] The bulk material is mixed with a coating additive, and a positive electrode composite material is prepared by topological transformation reaction.

[0056] Topological chemistry refers to a chemical reaction in which the structure of the product is related to the structure of the reactants, and the reaction can proceed under conditions that maintain a certain crystal structure of the reactants.

[0057] In the method for preparing the cathode composite material provided in this application, on the one hand, residual lithium compounds on the surface of the high-nickel layered cathode material can be used to generate a coherent coating layer with a good and stable structure in situ, thereby effectively reducing the residual lithium compounds on the surface of the bulk material and reducing battery gas production. Furthermore, by using coating additives containing elements with high electrochemical activity such as Ni, Co, and Mn, the high reactivity can more effectively consume the residual lithium compounds on the surface of the bulk material. On the other hand, in the multi-step topological chemical reaction, by leveraging the synergistic effect of the first precursor and the reaction promoter, the secondary calcination process is controlled. Through the topological transformation of the continuous close-packed structure of oxygen ions, the co-lattice growth of the coating layer on the surface of the first calcination product A is achieved, reducing the diffusion effect of metal ions into the bulk phase. The resulting coherent coating layer can effectively improve the interfacial stability and structural stability between the coating layer and the bulk material. This can alleviate the stress accumulation of the high-nickel layered cathode material during battery cycling, avoid direct contact between the high-nickel layered cathode material and the electrolyte, and effectively suppress the Ni content on the surface of the high-nickel layered cathode material. 4+ Side reactions between the battery and the electrolyte can effectively improve battery cycle performance.

[0058] In some embodiments, the bulk material is mixed with a coating additive, and the cathode composite material is prepared by a topological transformation reaction, including:

[0059] The bulk material and the coating additive are mixed;

[0060] The mixed materials are calcined in stages to prepare the positive electrode composite material.

[0061] The specific spatial structure and calcination conditions of the coating additive in the calcination step are not specifically limited. As long as the residual lithium compounds of the coating additive and the bulk material can undergo multi-step topological transformation based on oxygen close packing structure during the entire calcination process to generate a coherent coating layer for the high-nickel layered cathode material, it is acceptable.

[0062] The stepwise calcination includes two calcination steps. The first calcination step is carried out at a temperature of 400-600℃ for 1-5 hours. The second calcination step is carried out at a temperature of 600-800℃ for 3-10 hours. The atmosphere for the stepwise calcination is an oxygen-containing atmosphere.

[0063] In these embodiments, by controlling the stepwise calcination, the first precursor has an oxygen close-packed structure, and the space group includes one or more of Fd-3m, Fm-3m, R-3m, and C2 / m, so that the coating layer can form a coherent phase boundary with the bulk material in the form of sharing an oxygen lattice, thereby forming a coherent coating layer. By limiting the temperature and time of the stepwise calcination within the above ranges, a multi-step topological transformation based on the oxygen close-packed structure can occur between the coating additive and the residual lithium compounds on the surface of the bulk material, generating a coherent coating layer with excellent performance.

[0064] Among them, the oxygen-containing atmosphere may include one or more of oxygen and dry air.

[0065] In some embodiments, the coating additive includes a first precursor and a reaction aid. The first precursor includes: Ni x Co y Mn z (OH)2, Ni x Co y Mn z OOH, Ni x Co y Mn z O, where 0 ≤ x ≤ 0.6, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x, y, and z are not all 0 at the same time. The reaction aid includes one or more of lithium oxide, lithium carbonate, and lithium hydroxide.

[0066] In some embodiments, the first precursor satisfies one of the following conditions:

[0067] (1) The specific surface area of the first precursor ≥ 20 m 2 / g;

[0068] (2) The molar ratio of the first precursor to the bulk material is 0.5 mol% - 10 mol%;

[0069] (3) The total number of metal atoms in the first precursor is M, and the total number of residual lithium atoms in the reaction aid and the bulk material is L. M and L satisfy 0.8 < L / M < 1.2.

[0070] In these embodiments, the particle size of the above first precursor can be in the micron range. In this way, the integrity of the coating layer preparation can be effectively improved. By controlling the molar ratio of the first precursor to the bulk material to be 0.5:100 - 10:100, the composition and content of the coating layer can be optimized; by controlling the total number of lithium atoms in the reaction aid and the residual lithium atoms in the bulk material to be L, and satisfying 0.8 < L / M < 1.2 with the total number of metal atoms M of the first precursor, the topological chemical reaction can be thorough and controllable, thereby ensuring the smooth progress of the multi-step topological chemical reaction and ensuring the generation of a coherent phase boundary.

[0071] In some embodiments, the preparation of the bulk material includes:

[0072] In an oxygen-containing atmosphere, a high-nickel precursor and a lithium salt are mixed, heated and calcined, then cooled in the furnace and crushed and sieved.

[0073] Optionally, the bulk material is prepared to satisfy one of the following conditions:

[0074] (1) High-nickel material precursors include one or more of oxides and hydroxides;

[0075] (2) Lithium salts include one or more of lithium carbonate and lithium hydroxide;

[0076] (3) The molar ratio of lithium atoms in the high-nickel material precursor and the reaction aid is 1.0:(0.9~1.1);

[0077] (4) The heating rate is 2~8℃ / min, the calcination temperature is 700~1100℃, and the time is 12h~24h.

[0078] Some embodiments of this application provide a positive electrode sheet, which includes: a positive current collector and a positive electrode material layer formed on the positive current collector, the positive electrode material layer including: a positive electrode composite material as described above or a positive electrode composite material prepared by the preparation method as described above.

[0079] The beneficial technical effects of the positive electrode sheet provided in this application embodiment are the same as those of the positive electrode composite material provided in this application embodiment, and will not be repeated here.

[0080] Some embodiments of this application provide a battery, including: a positive electrode as described above.

[0081] The battery example in this case could be a lithium-ion battery.

[0082] The beneficial technical effects of the battery provided in this application embodiment are the same as those of the high-nickel cathode composite material based on topological conversion reaction modification provided in this application embodiment, and will not be repeated here.

[0083] In order to objectively evaluate the technical effects of the embodiments of this application, the present application will be described in detail and by way of examples and comparative examples below.

[0084] In the following examples and comparative examples, all raw materials were commercially available, and to maintain the reliability of the experiments, the raw materials used in the following examples and comparative examples had the same physical and chemical parameters or underwent the same treatment.

[0085] Example 1

[0086] S1, Take 1000g of Ni 0.92 Co 0.04 Mn 0.03 Al 0.01 (OH)2 (D50 is 3.5μm, specific surface area is 20m²) 2 470g of LiOH·H2O and 470g of LiOH·H2O were mixed evenly using a high-speed mixer. The mixture was then placed in an oxygen atmosphere furnace and heated at a rate of 3℃ / min to 810℃. After holding at this temperature for 15 hours, the mixture was cooled with the furnace, crushed, and sieved to obtain the uncoated and unmodified primary calcined product (i.e., the aforementioned bulk material). The residual lithium compounds on the surface of the primary calcined product were tested, and the content of LiOH in the primary calcined product was found to be 5200ppm, and the content of Li2CO3 in the primary calcined product was 2700ppm. Both tests were conducted according to national standards.

[0087] S2. Mix 500g of the first calcination product with 1.675g of Li2O and 23.390g of the first precursor Co. 0.5 Mn 0.5 (OH)2 (specific surface area is 25m²) 2 / g) are mixed evenly to obtain a two-component mixture, wherein Co 0.5 Mn 0.5 The amount of (OH)2 used satisfies: Co 0.5 Mn 0.5 The molar ratio of (OH)₂ to the product from the first calcination is 5:100, and the first precursor Co... 0.5 Mn 0.5 The number of metal atoms in (OH)2 is M, and the total number of lithium atoms in the reaction aid Li2O and the residual lithium in the first calcination product is L, with L / M being 1.0.

[0088] S3. The above two mixtures are calcined again in oxygen in steps. The first step calcination temperature I is 450℃ for 2 hours; the second step calcination temperature II is 720℃ for 8 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified LiNi. 0.92 Co 0.04 Mn 0.03 Al 0.01 O2 materials.

[0089] Example 2

[0090] S1, Take 1000g of Ni 0.90 Co 0.06 Mn 0.03 Al 0.01 (OH)2 (D50 is 13.0 μm, specific surface area is 6 m²) 2455g of LiOH·H2O and 455g of LiOH·H2O were mixed evenly using a high-speed mixer. The mixture was then placed in an oxygen atmosphere furnace and heated to 775℃ at a rate of 4℃ / min. After holding at this temperature for 16 hours, the mixture was cooled with the furnace, crushed, and sieved to obtain the uncoated primary calcined product. The residual lithium compounds on the surface of the primary calcined product were tested, and the content of LiOH·H2O in the primary calcined product was found to be 4800ppm, and the content of Li2CO3 in the primary calcined product was 3700ppm.

[0091] S2. Mix 500g of the first calcination product with 0.170g of LiOH·H2O and 11.820g of the first precursor CoOOH (with a specific surface area of ​​55m²). 2 The mixture of CoOOH and the first calcined product is mixed evenly to obtain a second mixture, wherein the amount of CoOOH is satisfied as follows: the molar ratio of CoOOH to the first calcined product is 2.5:100, the number of metal atoms of the first precursor CoOOH is M, the total number of lithium atoms of the reaction aid LiOH·H2O and the residual lithium in the first calcined product is L, and L / M is 1.1.

[0092] S3. The above two mixtures are calcined again in oxygen in steps. The first step calcination temperature I is 450℃ for 3 hours; the second step calcination temperature II is 750℃ for 6 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified Ni. 0.90 Co 0.06 Mn 0.03 Al 0.01 (OH)2 material.

[0093] Example 3

[0094] S1, Take 1000g of Ni 0.92 Co 0.05 Mn 0.02 Zr 0.01 (OH)₂ (D₅₀ is 3.3 μm, specific surface area is 18 m²) 2 450 g of LiOH·H2O and 450 g of LiOH·H2O were mixed evenly using a high-speed mixer. The mixture was then placed in an oxygen atmosphere furnace and heated to 700℃ at a rate of 2℃ / min. After holding at this temperature for 12 h, the mixture was cooled with the furnace, crushed, and sieved to obtain the uncoated primary calcined product. The content of residual lithium compounds on the surface of the primary calcined product was tested, and the content of LiOH·H2O in the primary calcined product was found to be 5300 ppm, and the content of Li2CO3 in the primary calcined product was 3700 ppm.

[0095] S2. Mix 500g of the first calcination product with 11.614g of the first precursor Co. 0.33 Ni 0.33 Mn0.33 (OH)2 (specific surface area is 30m²) 2 / g) were mixed evenly to obtain a two-component mixture, without the addition of reaction aids, wherein Co 0.33 Ni 0.33 Mn 0.33 The amount of (OH)2 used satisfies: Co 0.33 Ni 0.33 Mn 0.33 The molar ratio of (OH)₂ to the product from the first calcination is 2.5:100, and the first precursor Co... 0.33 Ni 0.33 Mn 0.33 The number of metal atoms in (OH)2 is M, and the number of lithium atoms in the residual lithium in the first calcination product is L, with L / M being 1.1.

[0096] S3. The above two mixtures are calcined again in oxygen in steps. The first step calcination temperature I is 400℃ for 4 hours; the second step calcination temperature II is 800℃ for 10 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified LiNi. 0.92 Co 0.05 Mn 0.02 Zr 0.01 (OH)2 material.

[0097] Example 4

[0098] S1, Take 1000g of Ni 0.83 Co 0.11 Mn 0.05 W 0.01 (OH)₂ (D₅₀ = 10.5 μm, specific surface area = 8 m²) 2 480 g of LiOH·H2O and 480 g of LiOH·H2O were mixed evenly using a high-speed mixer. The mixture was then placed in an oxygen atmosphere furnace and heated at a rate of 8 °C / min to 1100 °C. After holding at this temperature for 24 h, the mixture was cooled with the furnace, crushed, and sieved to obtain the uncoated primary calcined product. The content of residual lithium compounds on the surface of the primary calcined product was tested, and the content of LiOH·H2O in the primary calcined product was found to be 5400 ppm, and the content of Li2CO3 in the primary calcined product was 5200 ppm.

[0099] S2. Mix 500g of the first calcination product with 0.292g of Li₂O and 23.002g of the first precursor Co. 0.5 Mn 0.5 (OH)2 (specific surface area is 25m²) 2 / g) are mixed evenly to obtain a two-component mixture, wherein Co 0.5 Mn 0.5 The amount of (OH)2 used satisfies: Co 0.5 Mn0.5 The molar ratio of (OH)₂ to the product from the first calcination is 5:100, and the first precursor Co... 0.5 Mn 0.5 The number of metal atoms in (OH)2 is M, and the total number of lithium atoms in the reaction aid Li2O and the residual lithium in the primary calcination product is L, with L / M being 0.85.

[0100] S3. The above two mixtures are calcined again in oxygen in steps. The first step calcination temperature I is 600℃ for 5 hours; the second step calcination temperature II is 600℃ for 3 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified LiNi. 0.83 Co 0.11 Mn 0.05 W 0.01 (OH)2 material.

[0101] Example 5

[0102] S1, Take 1000g of Ni 0.68 Co 0.12 Mn 0.195 Al 0.005 (OH)2 (D50 is 3.8 μm, specific surface area is 22 m²) 2 495g of LiOH·H2O was mixed uniformly using a high-speed mixer. The mixture was then placed in a dry air atmosphere furnace, heated at a rate of 4℃ / min to 920℃, held at that temperature for 18h, and then cooled with the furnace. The resulting product was crushed and sieved to obtain the uncoated, modified primary calcined product. The residual lithium compounds on the surface of the primary calcined product were analyzed, revealing that the content of LiOH in the primary calcined product was 3700ppm, and the content of Li2CO3 in the primary calcined product was 2900ppm.

[0103] S2. Mix 500g of the first calcination product with 7.523g of Li2O and 48.026g of the first precursor Co(OH)2 (with a specific surface area of ​​35m²). 2 The mixture of Co(OH)2 and Co(OH)2 is uniformly mixed to obtain a second mixture, wherein the amount of Co(OH)2 is satisfied as follows: the molar ratio of Co(OH)2 to the primary calcination product is 10:100, the number of metal atoms of the first precursor Co(OH)2 is M, the total number of lithium atoms of the reaction aid Li2O and the residual lithium in the primary calcination product is L, and L / M is 1.1.

[0104] S3. The above two mixtures are calcined again in dry air in steps. The first step calcination temperature I is 500℃ for 1 hour; the second step calcination temperature II is 600℃ for 3 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified LiNi. 0.68 Co 0.12 Mn 0.195Al 0.005 (OH)2 material.

[0105] Example 6

[0106] S1, Take 1000g of Ni 0.90 Co 0.05 Mn 0.04 Mg 0.01 (OH)2 (D50 is 3.0 μm, specific surface area is 25 m²) 2 455g of LiOH·H2O and 455g of LiOH·H2O were mixed evenly using a high-speed mixer. The mixture was then placed in a dry air atmosphere furnace, heated at a rate of 5℃ / min to 800℃, held at that temperature for 15h, and then cooled with the furnace. The resulting product was crushed and sieved to obtain the uncoated, modified primary calcined product. The residual lithium compounds on the surface of the primary calcined product were analyzed, revealing that the residual lithium compounds contained 6200ppm of LiOH·H2O and 4200ppm of Li2CO3 in the primary calcined product.

[0107] S2. Mix 500g of the product from a single calcination with 4.493g of LiOH·H2O and 27.765g of the first precursor Co. 0.5 Mn 0.5 OOH (specific surface area of ​​30m²) 2 / g) are mixed evenly to obtain a two-component mixture, wherein Co 0.5 Mn 0.5 The amount of OOH used satisfies: Co 0.5 Mn 0.5 The molar ratio of OOH to the product from the first calcination is 6:100, and the first precursor Co... 0.5 Mn 0.5 The number of metal atoms in OOH is M, and the total number of lithium atoms in the reaction aid LiOH·H2O and the residual lithium in the primary calcination product is L, with L / M being 0.95.

[0108] S3. The above two mixtures are calcined again in dry air in steps. The first step calcination temperature I is 450℃ for 5 hours; the second step calcination temperature II is 750℃ for 8 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified LiNi. 0.90 Co 0.05 Mn 0.04 Mg 0.01 (OH)2 material.

[0109] Example 7

[0110] S1, Take 1000g of Ni 0.88 Co 0.06 Mn 0.05 Zr 0.01(OH)2 (D50 is 8.5 μm, specific surface area is 22 m²) 2 480 g of LiOH·H2O and 480 g of LiOH·H2O were mixed evenly using a high-speed mixer. The mixture was then placed in a dry air atmosphere furnace and heated to 815 °C at a rate of 5 °C / min. After holding at this temperature for 15 h, the mixture was cooled with the furnace, crushed, and sieved to obtain the uncoated primary calcined product. The residual lithium compounds on the surface of the primary calcined product were tested, and the contents of LiOH·H2O and Li2CO3 in the primary calcined product were found to be 6400 ppm and 5500 ppm, respectively.

[0111] S2. Mix 500g of the first calcination product with 5.755g of LiOH·H2O and 27.974g of the first precursor Co. 0.33 Ni 0.33 Mn 0.33 O (specific surface area is 35m²) 2 / g) are mixed evenly to obtain a two-component mixture, wherein Co 0.33 Ni 0.33 Mn 0.33 The amount of O used satisfies: Co 0.33 Ni 0.33 Mn 0.33 The molar ratio of O to the primary calcination product is 7.5:100, and the first precursor Co... 0.33 Ni 0.33 Mn 0.33 The number of metal atoms in O is M, and the total number of lithium atoms in the reaction aid LiOH·H2O and the residual lithium in the first calcination product is L, with L / M being 0.9.

[0112] S3. The above two mixtures are calcined again in dry air in steps. The first step calcination temperature I is 400℃ for 4 hours; the second step calcination temperature II is 700℃ for 8 hours. After calcination, the mixture is cooled in the furnace to obtain coated and modified LiNi. 0.88 Co 0.06 Mn 0.05 Zr 0.01 O2 materials.

[0113] Comparative Example 1

[0114] In Comparative Example 1, steps S1 and S3 are the same as in Example 1. In step S2, 500g of the first calcination product is mixed with 1.675g of Li2O and 23.390g of the first precursor Co. 0.5 Mn 0.5 (OH)2 (specific surface area is 15m²) 2 / g) are mixed evenly to obtain a two-component mixture, wherein Co 0.5 Mn 0.5 The amount of (OH)2 used satisfies: Co0.5 Mn 0.5 The molar ratio of (OH)₂ to the product from the first calcination is 5:100, and the first precursor Co... 0.5 Mn 0.5 The number of metal atoms in (OH)2 is M, and the total number of lithium atoms in the reaction aid Li2O and the residual lithium in the first calcination product is L, with L / M being 1.0.

[0115] Comparative Example 2

[0116] In Comparative Example 2, steps S1 and S3 are the same as in Example 1. In step S2, 500g of the first calcination product and 23.390g of the first precursor Co are mixed. 0.5 Mn 0.5 (OH)2 (specific surface area is 25m²) 2 / g) were mixed evenly to obtain a two-component mixture, without the addition of reaction aids, wherein Co 0.5 Mn 0.5 The amount of (OH)2 used satisfies: Co 0.5 Mn 0.5 The molar ratio of (OH)₂ to the product from the first calcination is 5:100, and the first precursor Co... 0.33 Ni 0.33 Mn 0.33 The number of metal atoms in (OH)2 is M, and the number of lithium atoms in the residual lithium in the first calcination product is L, with L / M being approximately 0.5.

[0117] Comparative Example 3

[0118] In Comparative Example 3, steps S1 and S3 are the same as in Example 1. In step S2, 500g of the first calcination product is mixed with 3.596g of Li2O and 23.390g of the first precursor Co. 0.5 Mn 0.5 (OH)2 (specific surface area is 25m²) 2 / g) are mixed evenly to obtain a two-component mixture, wherein Co 0.5 Mn 0.5 The amount of (OH)2 used satisfies: Co 0.5 Mn 0.5 The molar ratio of (OH)₂ to the product from the first calcination is 5:100, and the first precursor Co... 0.5 Mn 0.5 The number of metal atoms in (OH)2 is M, and the total number of lithium atoms in the reaction aid Li2O and the residual lithium in the primary calcination product is L, with L / M being 1.5.

[0119] Comparative Example 4

[0120] In Comparative Example 4, steps S1 and S2 are the same as in Example 1. In step S3, the two mixtures are calcined again in oxygen at a temperature of 720°C for 12 hours.

[0121] The difference between Comparative Example 1 and Example 1 is that the first precursor selected in Comparative Example 1 has a smaller specific surface area and poorer reactivity. As a result, the modified material obtained does not form a complete coating layer, and the residual lithium compounds on the surface of the bulk material are not significantly improved.

[0122] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 only uses the residual lithium compound on the surface of the bulk material as a reaction aid, without adding any additional reaction aids. As a result, the amount of lithium salt in the coating additive is low, leading to an incomplete topological transformation reaction. Consequently, the coating layer in the modified material is not an oxygen-dense docking structure, and no coherent phase boundary is formed.

[0123] The difference between Comparative Example 3 and Example 1 is that the amount of lithium salt in the coating additive used in Comparative Example 3 is too high, which leads to the runaway topological transformation reaction. As a result, the coating layer in the modified material is not an oxygen close-packed structure and no coherent interface is generated. Furthermore, the residual lithium content on the surface of the product after the first calcination is too high, which can easily cause gas generation in the battery.

[0124] The difference between Comparative Example 4 and Example 1 is that the two-component calcination in Comparative Example 4 was changed to one-step calcination, which resulted in incomplete topological transformation reaction. Furthermore, the excessively long high-temperature calcination intensified the metal ion diffusion effect. As a result, the modified material obtained had no obvious surface coating layer. Therefore, no coherent interface was generated in the modified material.

[0125] Test case

[0126] 1. In-situ XRD tests were performed on the high-nickel layered cathode material (i.e., the bulk material) at different temperature states in process S3 of Example 1, and the in-situ XRD patterns of the high-nickel layered cathode material are shown below. Figure 1 As shown, in Figure 1 At 450℃, the XRD peaks mainly represent the R-3m structure of the bulk material, with some impurity peaks corresponding to the Fd-3m phase of the spinel structure. At 720℃, the XRD peaks still mainly represent the R-3m structure of the bulk material, with some impurity peaks corresponding to the Fd-3m phase of the spinel structure and the Fm-3m phase of the rock salt structure. After being cooled to room temperature RT with the furnace, the material completely transforms into the R-3m structure.

[0127] 2. Electrochemical performance testing:

[0128] (1) Preparation of positive electrode and lithium-ion battery:

[0129] The modified materials prepared in Examples 1-7 and Comparative Examples 1-4 were mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 90:5:5, and an appropriate amount of N-methylpyrrolidone was added as a dispersant. The mixture was then ground into a slurry. The slurry was then uniformly coated onto aluminum foil and vacuum dried at 120°C for 12 hours. The dried electrode was then rolled using a roller press, and the aluminum foil was cut into circular electrode sheets with a diameter of 10 mm using a slicing machine. The loading of the active material was controlled at 12 mg / cm². -2 about.

[0130] Then, half-cells were assembled in an argon atmosphere glove box, with water pressure ≤0.1ppm and oxygen partial pressure ≤0.1ppm. Using lithium metal as the counter electrode and 1M LiPF6 (EC / DMC, volume ratio 1:1) solution as the electrolyte, CR2032 type coin cells were assembled.

[0131] (2) Charge-discharge cycle test:

[0132] The battery was charged and discharged using a constant current charge-discharge mode at room temperature, with a voltage range of 2.5-4.3V and a current density of 100mA / g (0.5C rate) for 100 charge-discharge cycles. During this process, the battery's first-cycle charge specific capacity, first-cycle discharge specific capacity, first-cycle coulombic efficiency, and capacity retention after 100 cycles were tested.

[0133] Specific test results can be found in Table 1 below. Figure 2 As shown. Figure 2 This is a comparison graph showing the specific capacity of uncoated and coated samples in Example 1 as a function of the number of cycles.

[0134] Table 1

[0135]

[0136] From Table 1 and Figure 2 It can be seen that the modified high-nickel layered cathode materials all exhibit excellent charge-discharge capacity and cycle performance, and the coated material has a higher initial coulombic efficiency (>90%). Therefore, it can be seen that the coating layer obtained based on the topological transformation reaction can significantly improve the interfacial stability.

[0137] (3) Differential scanning calorimetry (DSC) test:

[0138] The positive electrode sheet charged to 4.3V was disassembled to extract the positive electrode powder, which was placed in a high-pressure crucible. 50 μL of electrolyte was added dropwise, and the temperature was increased from room temperature to a specified temperature at a rate of 2 °C / min. Differential scanning calorimetry (DSC) data for Comparative Examples 1-4 and Examples 1-7 are shown in Table 2 below, used to evaluate the safety and thermal stability of the batteries in Comparative Examples 1-4 and Examples 1-7. Additionally, as... Figure 3The figure shown is a comparison of the differential scanning calorimetry curves of uncoated and coated samples in Example 1.

[0139] Table 2

[0140]

[0141] From Table 2 and Figure 3 It can be seen that the high-nickel layered cathode material modified by topological conversion reaction has lower surface residual lithium compounds. DSC test shows that the modified high-nickel layered cathode material has a higher exothermic peak temperature and less heat generation, which effectively inhibits the precipitation of highly reactive oxygen from the bulk material and improves the safety of high-nickel materials.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0143] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode composite material, characterized in that, Including the body material and the coating layer; The bulk material includes the general formula Li w Ni a Co b Mn c X 1-a-b-c The material of O2, wherein X includes one or more of Al, Ti, Zr, Mg and W, and 0.95≤w≤1.1, 0.6≤a≤1, b≥0, c≥0; The coating layer includes the general formula Li α Ni β Co γ Mn δ The material is O2, wherein 0 ≤ α ≤ 1, 0 ≤ β ≤ 0.6, 0 ≤ γ ≤ 1, 0 ≤ δ ≤ 1, and β, γ and δ are not simultaneously 0; The interface between the bulk material and the coating layer is a coherent phase boundary; The thickness of the coating layer is ≤200nm.

2. The positive electrode composite material according to claim 1, characterized in that, In the crystal structures of both the bulk material and the coating layer, oxygen ions are in a close-packed structure. And / or, The space group to which the coating layer belongs includes one or more of Fd-3m, Fm-3m, R-3m and C2 / m.

3. A method for preparing the positive electrode composite material as described in claim 1 or 2, characterized in that, include: Prepare or provide the body material; The bulk material is mixed with a coating additive, and the cathode composite material is prepared by a topological transformation reaction. The coating additive includes a first precursor and a reaction auxiliaries, wherein the first precursor includes: Ni x Co y Mn z (OH)2, Ni x Co y Mn z OOH, Ni x Co y Mn z One of O, wherein 0 ≤ x ≤ 0.6, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x, y, and z are not simultaneously 0; the specific surface area of ​​the first precursor is ≥ 20 m². 2 / g; the total number of metal atoms in the first precursor is M, and the total number of residual lithium atoms in the reaction aid and the bulk material is L, wherein M and L satisfy 0.8 <L / M<1.2; The cathode composite material is prepared by mixing the bulk material with a coating additive and then performing a topological transformation reaction, comprising: The bulk material and the coating additive are mixed; The mixed materials are calcined in stages to prepare the positive electrode composite material; The stepwise calcination includes two calcination steps, wherein the first calcination is carried out at a temperature of 400~600℃ for 1~5h; and the second calcination is carried out at a temperature of 600~800℃ for 3~10h.

4. The preparation method according to claim 3, characterized in that, The atmosphere for the stepwise calcination is an oxygen-containing atmosphere.

5. The preparation method according to claim 3 or 4, characterized in that, The reaction aids include one or more of lithium oxide, lithium carbonate, and lithium hydroxide.

6. The preparation method according to claim 4, characterized in that, In the stepwise calcination, the first precursor has an oxygen-dense packing structure, and the space group includes one or more of Fd-3m, Fm-3m, R-3m and C2 / m.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the first precursor to the bulk material is 0.5 mol% to 10 mol.

8. The preparation method according to claim 5, characterized in that, The preparation of the bulk material includes: In an oxygen-containing atmosphere, a high-nickel precursor and a lithium salt are mixed, heated and calcined, then cooled in the furnace and crushed and sieved.

9. The preparation method according to claim 8, characterized in that, The bulk material is prepared to satisfy at least one of the following conditions: (1) The high-nickel material precursor includes one or more of oxides and hydroxides; (2) The lithium salt includes one or more of lithium carbonate and lithium hydroxide; (3) The molar ratio of lithium atoms in the high-nickel precursor to the reaction aid is 1.0:(0.9~1.1); (4) The heating rate is 2~8℃ / min, the calcination temperature is 700~1100℃, and the time is 12h~24h.

10. A positive electrode plate, characterized in that, include: A positive current collector, and a positive electrode material layer formed on at least one surface of the positive current collector; The positive electrode material layer includes the positive electrode composite material as described in claim 1 or 2, or the positive electrode composite material prepared by the preparation method as described in any one of claims 3 to 9.

11. A battery, characterized in that, include: The positive electrode as described in claim 10.

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