A method for preparing lithium cobalt oxide material, lithium cobalt oxide material and secondary battery

Abstract

This invention discloses a method for preparing lithium cobalt oxide material, the lithium cobalt oxide material itself, and a secondary battery, belonging to the field of cathode materials. Lithium cobalt oxide is prepared by sequentially performing acid leaching, primary phosphate coating, and secondary ammonium fluoride coating to obtain a lithium cobalt oxide material with a stable surface structure and good cycle performance. During the acid leaching process, lithium cobalt oxide reacts with H+ in the acid solution. + The reaction forms active sites on its surface; during subsequent coating processes, PO4 in the phosphate... 3‑ The phosphate reacts with the active sites to form a stable primary coating of lithium cobalt oxide. The phosphate is distributed in a dotted pattern on the surface of the lithium cobalt oxide, inhibiting electrolyte corrosion. During the secondary coating process, the NH4+ in the ammonium fluoride salt... 4+ The surface O of the uncoated area on the surface of the lithium cobalt oxide coated once. 2‑ The combination of water and ammonia forms a tightly packed fluoride coating. This fluoride coating effectively reduces the erosion of the cathode material by hydrofluoric acid produced by electrolyte decomposition, reduces the release of surface oxygen, and further stabilizes the surface structure of lithium cobalt oxide.

Description

Technical Field

[0001] This invention relates to the field of cathode materials, specifically to a method for preparing lithium cobalt oxide, the lithium cobalt oxide material, and a secondary battery. Background Technology

[0002] Lithium cobalt oxide (LiCoO2) is widely used in 3C electronic products due to its high compaction density. The development of 3C electronic products towards multi-functionality, miniaturization, and intelligence has placed higher demands on the volumetric energy density of lithium-ion batteries.

[0003] Currently, LiCoO2 cathode materials can effectively improve battery specific capacity by further increasing the charging voltage on a 4.50V platform, but this causes a sharp capacity decay during cycling and high-temperature storage. Poor cycle stability is also the main reason restricting the application of high-voltage, high-specific-capacity LiCoO2 cathode materials. During high-voltage cycling and storage, irreversible loss of active oxygen leads to phase transitions in the material's surface structure, and the dissolution of cobalt on the material's surface and the continuous thickening of the catalytic SEI film deposited on the negative electrode side cause battery polarization. These are two important factors causing capacity loss and cycle failure.

[0004] How to rationally control the surface structure of high-voltage LiCoO2 cathode materials is key to improving their cycling and high-temperature storage performance. Currently, the industry generally uses solid-state methods to prepare lithium cobalt oxide. However, solid-state coating materials are prone to detachment during high-voltage cycling, affecting cycle stability. At the same time, research shows that using only one coating material, such as fluoride, phosphate, or oxide, cannot completely solve the interface problem of lithium cobalt oxide under high voltage.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to provide a method for preparing lithium cobalt oxide material, lithium cobalt oxide material and secondary battery. After acid washing of lithium cobalt oxide, it is coated with phosphate and ammonium fluoride salt in sequence. After two coatings, a lithium cobalt oxide material with stable surface structure and good cycle performance is obtained.

[0007] To achieve the above objectives, the present invention provides a method for preparing lithium cobalt oxide material in a first aspect, comprising: lithium cobalt oxide pretreatment: dispersing lithium cobalt oxide in an acid solution and stirring the reaction, then filtering, washing and drying to obtain acid-treated lithium cobalt oxide;

[0008] One-time coating: The acid-treated lithium cobalt oxide is mixed with phosphate and then sintered once to obtain one-time coated lithium cobalt oxide;

[0009] Secondary coating: The lithium cobalt oxide material is obtained by mixing the primary coated lithium cobalt oxide with ammonium fluoride salt and then sintering it a second time.

[0010] In some embodiments, the acid in the acid solution includes at least one selected from oxalic acid, acetic acid, citric acid, phosphoric acid, and carbonic acid;

[0011] And / or, the phosphate includes at least one of Li3PO4, LiCoPO4, LiFePO4, LiNiPO4, LiH2PO4, Co3(PO4)2 and LiH2PO4;

[0012] And / or, the ammonium fluoride salt includes at least one of NH4BF4, (NH4)3AlF6, (NH4)2SiF6 and (NH4)2GeF6.

[0013] In some embodiments, the molar concentration of the acid solution is 0.01-0.20 mol / L;

[0014] And / or, the phosphate is 1wt%-3wt% of the acid-treated lithium cobalt oxide;

[0015] And / or, the ammonium fluoride salt is 0.1wt%-0.5wt% of the primary coated lithium cobalt oxide.

[0016] In some embodiments, the lithium cobalt oxide includes large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, wherein the large-particle lithium cobalt oxide satisfies 18μm≤D v The small-particle lithium cobalt oxide has a particle size of 50 ≤ 21 μm and satisfies 4.5 μm ≤ Dv50 ≤ 9.5 μm.

[0017] The solid-liquid mass ratio of the lithium cobalt oxide to the acid solution is 1:1-3.

[0018] In some embodiments, the temperature of the first sintering is 500-900°C and the time is 3-6 hours;

[0019] And / or, the secondary sintering temperature is 400-800℃ and the time is 3-6h;

[0020] And / or, the drying temperature is 60-120℃ and the time is 24-30h;

[0021] And / or, the stirring reaction time is 5-10 min.

[0022] In some embodiments, the preparation process of the lithium cobalt oxide includes: mixing a lithium source and an additive with large-particle cobalt tetroxide and small-particle cobalt tetroxide respectively, followed by sintering and crushing, to obtain the large-particle lithium cobalt oxide and the small-particle lithium cobalt oxide respectively.

[0023] In some embodiments, the large cobalt tetroxide particles satisfy 13.5 μm ≤ D v50≤18.5μm;

[0024] And / or, the small cobalt tetroxide particles satisfy 1.5 μm ≤ D v 50≤6.5μm;

[0025] And / or, the additive is an oxide, the oxide comprising at least one of the elements Ti, Mg, Al, Y, La, Zr and B;

[0026] And / or, the lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0027] In some embodiments, the additive is 0.3wt%-3.5wt% of the large-particle cobalt tetroxide or the small-particle cobalt tetroxide;

[0028] And / or, the molar ratio of lithium in the lithium source to cobalt in the large-particle cobalt tetroxide or the small-particle cobalt tetroxide is 1.07-1.09;

[0029] And / or, the sintering temperature is 1050-1100℃.

[0030] The second aspect of the present invention provides a lithium cobalt oxide material, which is prepared by the preparation method provided in the first aspect of the present invention.

[0031] A third aspect of the present invention provides a secondary battery comprising the lithium cobalt oxide material provided in the second aspect of the present invention.

[0032] The beneficial effects of this invention include:

[0033] This invention provides a method for preparing lithium cobalt oxide materials.

[0034] Lithium cobalt oxide was prepared by sequentially performing acid leaching, primary phosphate coating, and secondary ammonium fluoride coating to obtain a lithium cobalt oxide material with a stable surface structure and good cycling performance. During the acid leaching process, lithium cobalt oxide reacts with H+ in the acid solution. + The reaction occurs and active sites are formed on its surface; during subsequent coating processes, PO4 in the phosphate... 3- The phosphate reacts with the active sites to form a stable primary coating of lithium cobalt oxide. The phosphate is distributed in a dotted pattern on the surface of the lithium cobalt oxide, effectively inhibiting electrolyte corrosion. During the secondary coating process, the NH4+ in the ammonium fluoride salt... 4+ The surface O of the unsalted coated area on the surface of the primary coated lithium cobalt oxide 2- The combination of water and ammonia forms a tightly packed fluoride coating. This fluoride coating effectively reduces the erosion of the cathode material by hydrofluoric acid produced by electrolyte decomposition, reduces the release of surface oxygen, and further stabilizes the surface structure of lithium cobalt oxide. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a SEM image of the lithium cobalt oxide material provided in Example 1 of the present invention;

[0037] Figure 2 This is a SEM image of the lithium cobalt oxide material provided in Embodiment 2 of the present invention;

[0038] Figure 3 EDS diagram of lithium cobalt oxide material with respect to element P provided in Embodiment 1 of the present invention;

[0039] Figure 4 EDS diagram of the lithium cobalt oxide material provided in Embodiment 1 of the present invention with respect to element F;

[0040] Figure 5 The image shows the XRD pattern of the lithium cobalt oxide material provided in Embodiment 1 of the present invention. Detailed Implementation

[0041] The following detailed description, with appropriate reference to the accompanying drawings, discloses a method for preparing a lithium cobalt oxide material, the lithium cobalt oxide material itself, and a secondary battery according to the present invention. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Specifically, "()", ")", "[", and "]" represent intervals, where "()" or ")" represents an open interval, meaning the endpoints of the interval are not included; and "[" and "]" represent a closed interval, meaning the endpoints of the interval are included. A range defined in this way can include endpoints or not, and can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range.

[0043] Specifically, for example, if the ranges 60-120 and 80-110 are listed for a specific parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range “ab” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range “0-5” means that all real numbers between “0-5” have been listed herein, and “0-5” is merely a shortened representation of these numerical combinations. Additionally, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. If (10, 20) is listed, it is understood as any value in the interval 10-20 excluding 10 and 20; (10, 20] is understood as any value in the interval 10-20 excluding 10 but including 20.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0046] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] This invention provides a method for preparing lithium cobalt oxide material, comprising:

[0050] Lithium cobalt oxide pretreatment: Lithium cobalt oxide is dispersed in an acid solution and stirred to react, then filtered, washed and dried to obtain acid-treated lithium cobalt oxide;

[0051] One-time coating: The acid-treated lithium cobalt oxide is mixed with phosphate and then sintered once to obtain one-time coated lithium cobalt oxide;

[0052] Secondary coating: The lithium cobalt oxide material is obtained by mixing the primary coated lithium cobalt oxide with ammonium fluoride salt and then sintering it a second time.

[0053] This invention provides a method for preparing lithium cobalt oxide material. Lithium cobalt oxide is prepared by sequentially undergoing acid leaching, primary phosphate coating, and secondary ammonium fluoride coating to obtain a lithium cobalt oxide material with a stable surface structure and good cycle performance. During the acid leaching process, the acid solution etches the surface of the lithium cobalt oxide, and the H+ in the acid solution... + It reacts with lithium cobalt oxide and forms lithium and oxygen vacancies on its surface; in the subsequent encapsulation process, PO4 in the phosphate... 3- Upon entering oxygen vacancies, lithium ions enter lithium vacancies, forming a stable primary coated lithium cobalt oxide. However, because phosphate coating easily forms agglomerates on the material surface, primary coating alone cannot achieve complete coating of the lithium cobalt oxide material, leaving exposed surfaces. During the secondary coating process, the NH4+ in the ammonium fluoride salt... 4+ O with the bare surface of lithium cobalt oxide that is not coated with phosphate 2- The combination generates water and ammonia, which in turn form a tightly coated fluoride layer.

[0054] Phosphate coating can effectively inhibit the corrosion of lithium cobalt oxide by the electrolyte, while fluoride coating can effectively reduce the erosion of the cathode material by hydrofluoric acid produced by electrolyte decomposition, reduce the release of surface oxygen, further stabilize the surface structure of lithium cobalt oxide material, and help improve the cycle performance of lithium cobalt oxide material.

[0055] In some embodiments, the acid in the acid solution includes at least one of oxalic acid, acetic acid, citric acid, phosphoric acid, and carbonic acid. All acids in the acid solution are weak acids. Compared to weak acids, strong acids may react more violently with the particle surface, producing unwanted byproducts that could affect the quality and performance of the final product.

[0056] In some embodiments, the phosphate includes at least one of Li3PO4, LiCoPO4, LiFePO4, LiNiPO4, LiH2PO4, Co3(PO4)2, and LiH2PO4.

[0057] In some embodiments, the ammonium fluoride salt includes at least one of NH4BF4, (NH4)3AlF6, (NH4)2SiF6, and (NH4)2GeF6.

[0058] In some embodiments, the molar concentration of the acid solution is 0.01-0.20 mol / L. Too high or too low an acid solution concentration will affect the etching effect on the material; too high a concentration will result in excessive etching, leading to severe capacity loss in the cathode material; too low a concentration will be insufficient to form effective etching, further affecting the phosphate coating effect.

[0059] In some embodiments, the phosphate is 1 wt% to 3 wt% of the acid-treated lithium cobalt oxide.

[0060] In some embodiments, the ammonium fluoride salt is 0.1wt%-0.5wt% of a single-coated lithium cobalt oxide.

[0061] In some embodiments, lithium cobalt oxide includes large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, wherein the large-particle lithium cobalt oxide satisfies 18μm≤D v The small-particle lithium cobalt oxide has a particle size of 50 ≤ 21 μm and satisfies 4.5 μm ≤ Dv50 ≤ 9.5 μm.

[0062] In some embodiments, the solid-liquid mass ratio of lithium cobalt oxide to acid solution is 1:1-3.

[0063] In some implementations, the temperature for a single sintering is 500-900°C and the time is 3-6 hours.

[0064] In some embodiments, the secondary sintering temperature is 400-800℃ and the time is 3-6 hours.

[0065] In some embodiments, the drying temperature is 60-120°C and the time is 24-30 hours.

[0066] In some implementations, the stirring reaction time is 5-10 minutes.

[0067] In some embodiments, the preparation process of lithium cobalt oxide includes: mixing a lithium source and an additive with large-particle cobalt tetroxide and small-particle cobalt tetroxide respectively, followed by sintering and crushing to obtain large-particle lithium cobalt oxide and small-particle lithium cobalt oxide respectively.

[0068] The lithium source and additives are mixed with large-particle cobalt tetroxide and small-particle cobalt tetroxide respectively, and then sintered and crushed to obtain doped lithium cobalt oxide materials, namely large-particle lithium cobalt oxide and small-particle lithium cobalt oxide. Doping can alleviate the bulk lattice distortion of the material and improve the stability of the material.

[0069] In some embodiments, large cobalt tetroxide particles satisfy 13.5 μm ≤ D v 50≤18.5μm.

[0070] In some embodiments, the small cobalt tetroxide particles satisfy 1.5 μm ≤ D v 50≤6.5μm.

[0071] In some embodiments, the additive is an oxide, which includes at least one of the elements Ti, Mg, Al, Y, La, Zr, and B.

[0072] In some embodiments, the lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0073] In some embodiments, the additive is 0.3wt%-3.5wt% of cobalt tetroxide with large or small particles.

[0074] In some embodiments, the molar ratio of lithium in the lithium source to cobalt in large-particle cobalt tetroxide or small-particle cobalt tetroxide is 1.07-1.09.

[0075] In some embodiments, the sintering temperature is 1050-1100°C.

[0076] The second aspect of this invention provides a lithium cobalt oxide material, which is prepared by the method provided in the first aspect of this invention, and the lithium cobalt oxide material satisfies 16μm≤D v 50≤18μm.

[0077] A third aspect of the present invention provides a secondary battery, which includes the lithium cobalt oxide material provided in the second aspect of the present invention.

[0078] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0079] The features and performance of the present invention will be further described in detail below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0080] Example 1

[0081] (1) Preparation of lithium cobalt oxide:

[0082] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (15.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a large-particle lithium cobalt oxide with a particle size of 18.8 μm. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 2.3 wt% of large-particle cobalt tetroxide.

[0083] Preparation of small-particle lithium cobalt oxide: D v Cobalt tetroxide (3.2 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 5.5μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 1.2wt% of small-particle cobalt tetroxide.

[0084] (2) Pretreatment of lithium cobalt oxide: After mixing large-particle lithium cobalt oxide and small-particle lithium cobalt oxide at a mass ratio of 4:1, the mixed lithium cobalt oxide is dispersed in 0.1 mol / L citric acid solution at a solid-liquid mass ratio of 1:2. The mixture is stirred and reacted at room temperature for 10 min. Then the material is filtered and washed twice with deionized water. Finally, it is dried in an oven at 80℃ for 24 hours to obtain acid-treated lithium cobalt oxide.

[0085] (3) Primary coating: Acid-treated lithium cobalt oxide and lithium phosphate are mixed and sintered in a high-temperature box furnace at 800°C for 6 hours in air atmosphere. After cooling, the mixture is mechanically crushed to obtain primary coated lithium cobalt oxide; the lithium phosphate content is 1 wt% of the acid-treated lithium cobalt oxide.

[0086] (4) Secondary coating: After mixing the primary coated lithium cobalt oxide and ammonium fluoroaluminate, the mixture is sintered for 6 hours in a high-temperature box furnace at 700°C in an air atmosphere. After cooling, it is mechanically crushed to obtain the lithium cobalt oxide material. The ammonium fluoroaluminate is 0.2 wt% of the primary coated lithium cobalt oxide.

[0087] Example 2

[0088] The only difference between this embodiment and Example 1 is that the molar concentration of citric acid in step (2) is 0.2 mol / L, while the other steps are the same as in Example 1.

[0089] Example 3

[0090] The only difference between this embodiment and Example 1 is that the molar concentration of citric acid in step (2) is 0.05 mol / L, while the other steps are the same as in Example 1.

[0091] Example 4

[0092] The only difference between this embodiment and Example 1 is that the phosphate in step (3) is Co3(PO4)2, while the other steps are the same as in Example 1.

[0093] Example 5

[0094] The only difference between this embodiment and Example 1 is that the phosphate in step (3) is LiH2PO4, and the other steps are the same as in Example 1.

[0095] Example 6

[0096] The only difference between this embodiment and Example 1 is that the ammonium fluoride salt in step (4) is NH4BF4, and the other steps are the same as in Example 1.

[0097] Example 7

[0098] The only difference between this embodiment and Example 1 is that the ammonium fluoride salt in step (4) is (NH4)2SiF6, and the other steps are the same as in Example 1.

[0099] Example 8

[0100] (1) Preparation of lithium cobalt oxide:

[0101] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (13.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a 16.5μm large-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 0.3wt% of large-particle cobalt tetroxide.

[0102] Preparation of small-particle lithium cobalt oxide: D vCobalt tetroxide (1.5 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 3.3μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium, and titanium in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 0.3wt% of small-particle cobalt tetroxide.

[0103] (2) Pretreatment of lithium cobalt oxide: After mixing large-particle lithium cobalt oxide and small-particle lithium cobalt oxide at a mass ratio of 4:1, the mixed lithium cobalt oxide is dispersed in 0.01mol / L oxalic acid solution at a solid-liquid mass ratio of 1:3. The mixture is stirred and reacted at room temperature for 10min. Then the material is filtered and washed twice with deionized water. Finally, it is dried in an oven at 80℃ for 24 hours to obtain acid-treated lithium cobalt oxide.

[0104] (3) Primary coating: Acid-treated lithium cobalt oxide and lithium phosphate are mixed and sintered in a high-temperature box furnace at 500°C for 6 hours in air atmosphere. After cooling, the mixture is mechanically crushed to obtain primary coated lithium cobalt oxide; the lithium phosphate content is 2.5 wt% of the acid-treated lithium cobalt oxide.

[0105] (4) Secondary coating: After mixing the primary coated lithium cobalt oxide and ammonium fluoroaluminate, the mixture is sintered for 6 hours in a high-temperature box furnace at 800°C in an air atmosphere. After cooling, it is mechanically crushed to obtain the lithium cobalt oxide material. The ammonium fluoroaluminate is 0.5 wt% of the primary coated lithium cobalt oxide.

[0106] Example 9

[0107] (1) Preparation of lithium cobalt oxide:

[0108] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (18.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a 22μm large-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 3.5wt% of large-particle cobalt tetroxide.

[0109] Preparation of small-particle lithium cobalt oxide: D vCobalt tetroxide (6.5 μm) particles, lithium carbonate, and additives were mixed evenly and sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 9μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 3.5wt% of small-particle cobalt tetroxide.

[0110] (2) Pretreatment of lithium cobalt oxide: After mixing large-particle lithium cobalt oxide and small-particle lithium cobalt oxide at a mass ratio of 4:1, the mixed lithium cobalt oxide is dispersed in 0.2 mol / L acetic acid solution at a solid-liquid mass ratio of 1:1. The mixture is stirred and reacted at room temperature for 10 min. Then the material is filtered and washed twice with deionized water. Finally, it is dried in an oven at 80℃ for 24 hours to obtain acid-treated lithium cobalt oxide.

[0111] (3) Primary coating: Acid-treated lithium cobalt oxide and lithium phosphate are mixed and sintered in a high-temperature box furnace at 900°C for 6 hours in air atmosphere. After cooling, the mixture is mechanically crushed to obtain primary coated lithium cobalt oxide; the lithium phosphate content is 3 wt% of the acid-treated lithium cobalt oxide.

[0112] (4) Secondary coating: After mixing the primary coated lithium cobalt oxide and ammonium fluoroaluminate, the mixture is sintered for 6 hours in a high-temperature box furnace at 400°C in an air atmosphere. After cooling, it is mechanically crushed to obtain the lithium cobalt oxide material. The ammonium fluoroaluminate is 0.1 wt% of the primary coated lithium cobalt oxide.

[0113] Comparative Example 1

[0114] (1) Preparation of lithium cobalt oxide:

[0115] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (15.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a large-particle lithium cobalt oxide with a particle size of 18.8 μm. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 2.3 wt% of large-particle cobalt tetroxide.

[0116] Preparation of small-particle lithium cobalt oxide: D vCobalt tetroxide (3.2 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 5.5μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 1.2wt% of small-particle cobalt tetroxide.

[0117] (2) Primary coating: Large-particle lithium cobalt oxide and small-particle lithium cobalt oxide are mixed at a mass ratio of 4:1 and then mixed with lithium phosphate. The mixture is sintered in an air atmosphere in a high-temperature box furnace at 800℃ for 6 hours. After cooling, it is mechanically crushed to obtain primary coated lithium cobalt oxide. The lithium phosphate is 1 wt% of the sum of the mass of large-particle lithium cobalt oxide and small-particle lithium cobalt oxide.

[0118] (3) Secondary coating: After mixing the primary coated lithium cobalt oxide and ammonium fluoroaluminate, the mixture is sintered for 6 hours in a high-temperature box furnace at 700°C in an air atmosphere. After cooling, it is mechanically crushed to obtain the lithium cobalt oxide material. The ammonium fluoroaluminate is 0.2 wt% of the primary coated lithium cobalt oxide.

[0119] Comparative Example 2

[0120] (1) Preparation of lithium cobalt oxide:

[0121] Preparation of large-particle lithium cobalt oxide: Large-particle cobalt tetroxide (Dv50) of 15.5 μm, lithium carbonate, and additives were mixed evenly and sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain large-particle lithium cobalt oxide (Dv50) of 18.8 μm. The additives were prepared by mixing aluminum oxide, zirconium oxide, and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide was 1.08:1, and the additives amounted to 2.3 wt% of the large-particle cobalt tetroxide.

[0122] Preparation of small-particle lithium cobalt oxide: Small-particle cobalt tetroxide (Dv50) with a diameter of 3.2 μm, lithium carbonate, and additives were mixed evenly and sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain small-particle lithium cobalt oxide with a diameter of 5.5 μm. The additives were prepared by mixing aluminum oxide, zirconium oxide, and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide was 1.08:1, and the additives amounted to 1.2 wt% of the small-particle cobalt tetroxide.

[0123] (2) Pretreatment of lithium cobalt oxide: After mixing large-particle lithium cobalt oxide and small-particle lithium cobalt oxide at a mass ratio of 4:1, the mixed lithium cobalt oxide is dispersed in 0.1 mol / L citric acid solution at a solid-liquid mass ratio of 1:2. The mixture is stirred and reacted at room temperature for 10 min. Then the material is filtered and washed twice with deionized water. Finally, it is dried in an oven at 80℃ for 24 hours to obtain acid-treated lithium cobalt oxide.

[0124] (3) Coating: After mixing acid-treated lithium cobalt oxide and ammonium fluoroaluminate, the mixture is sintered twice in a high-temperature box furnace at 700°C for 6 hours in an air atmosphere. After cooling, it is mechanically crushed to obtain lithium cobalt oxide material; the ammonium fluoroaluminate is 0.2 wt% of the acid-treated lithium cobalt oxide.

[0125] Comparative Example 3

[0126] (1) Preparation of lithium cobalt oxide:

[0127] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (15.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a large-particle lithium cobalt oxide with a particle size of 18.8 μm. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 2.3 wt% of large-particle cobalt tetroxide.

[0128] Preparation of small-particle lithium cobalt oxide: D v Cobalt tetroxide (3.2 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 5.5μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 1.2wt% of small-particle cobalt tetroxide.

[0129] (2) Pretreatment of lithium cobalt oxide: After mixing large-particle lithium cobalt oxide and small-particle lithium cobalt oxide at a mass ratio of 4:1, the mixed lithium cobalt oxide is dispersed in 0.1 mol / L citric acid solution at a solid-liquid mass ratio of 1:2. The mixture is stirred and reacted at room temperature for 10 min. Then the material is filtered and washed twice with deionized water. Finally, it is dried in an oven at 80℃ for 24 hours to obtain acid-treated lithium cobalt oxide.

[0130] (3) Coating: Acid-treated lithium cobalt oxide and lithium phosphate are mixed and sintered in an air atmosphere in a high-temperature box furnace at 800°C for 6 hours. After cooling, the mixture is mechanically crushed to obtain lithium cobalt oxide material; the lithium phosphate content is 1 wt% of the acid-treated lithium cobalt oxide.

[0131] Comparative Example 4

[0132] (1) Preparation of lithium cobalt oxide:

[0133] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (15.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a large-particle lithium cobalt oxide with a particle size of 18.8 μm. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 2.3 wt% of large-particle cobalt tetroxide.

[0134] Preparation of small-particle lithium cobalt oxide: D v Cobalt tetroxide (3.2 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 5.5μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 1.2wt% of small-particle cobalt tetroxide.

[0135] (2) Lithium cobalt oxide treatment: Large-particle lithium cobalt oxide and small-particle lithium cobalt oxide are mixed at a mass ratio of 4:1, and the mixed lithium cobalt oxide is dispersed in a 0.1 mol / L citric acid solution at a solid-liquid mass ratio of 1:2. The mixture is stirred and reacted at room temperature for 10 min. The material is then filtered and washed twice with deionized water, and then dried in an oven at 80°C for 24 hours to obtain lithium cobalt oxide material.

[0136] Comparative Example 5

[0137] (1) Preparation of lithium cobalt oxide:

[0138] Preparation of large-particle lithium cobalt oxide: D vCobalt tetroxide (15.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a large-particle lithium cobalt oxide with a particle size of 18.8 μm. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 2.3 wt% of large-particle cobalt tetroxide.

[0139] Preparation of small-particle lithium cobalt oxide: D v Cobalt tetroxide (3.2 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 5.5μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08:1. The additive is 1.2wt% of small-particle cobalt tetroxide.

[0140] (2) Coating: Large-particle lithium cobalt oxide and small-particle lithium cobalt oxide are mixed at a mass ratio of 4:1 and then mixed with lithium phosphate. The mixture is sintered in an air atmosphere in a high-temperature box furnace at 800℃ for 6 hours. After cooling, it is mechanically crushed to obtain lithium cobalt oxide material. The lithium phosphate is 1 wt% of the sum of the mass of large-particle lithium cobalt oxide and small-particle lithium cobalt oxide.

[0141] Comparative Example 6

[0142] (1) Preparation of lithium cobalt oxide:

[0143] Preparation of large-particle lithium cobalt oxide: D v Cobalt tetroxide (15.5 μm) particles, lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1070 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is a large-particle lithium cobalt oxide with a particle size of 18.8 μm. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in large-particle cobalt tetroxide is 1.08:1. The additive is 2.3 wt% of large-particle cobalt tetroxide.

[0144] Preparation of small-particle lithium cobalt oxide: D vCobalt tetroxide (3.2 μm particles), lithium carbonate, and additives were mixed evenly and then sintered in an air atmosphere at 1020 °C for 10 h. After cooling, the mixture was coarsely crushed by a roller mill and finely crushed by an air jet mill to obtain D. v 50 is 5.5μm small-particle lithium cobalt oxide. The additive is a mixture of aluminum, zirconium and titanium oxide in a mass ratio of 2:1:1. The molar ratio of lithium in lithium carbonate to cobalt in small-particle cobalt tetroxide is 1.08. The additive is 1.2wt% of small-particle cobalt tetroxide.

[0145] (2) Coating: Large-particle lithium cobalt oxide and small-particle lithium cobalt oxide are mixed in a mass ratio of 4:1 and then mixed with ammonium fluoroaluminate. The mixture is sintered twice in a high-temperature box furnace at 700°C for 6 hours in an air atmosphere. After cooling, it is mechanically crushed to obtain lithium cobalt oxide material. The ammonium fluoroaluminate is 0.2 wt% of the total mass of large-particle lithium cobalt oxide and small-particle lithium cobalt oxide.

[0146] [Performance Testing]

[0147] Characterization of lithium cobalt oxide materials (1) Morphological characterization:

[0148] The lithium cobalt oxide material samples provided in Examples 1-2 were characterized using scanning electron microscopy. Figure 1 This is a SEM image of the lithium cobalt oxide material provided in Example 1. Figure 2 The image shows a SEM image of the lithium cobalt oxide material provided in Example 2. Because the acid solution concentration was increased from 1 mol / L to 2 mol / L during the lithium cobalt oxide pretreatment process in Example 2, it can be seen that... Figure 1 Lithium cobalt oxide materials have a relatively smooth surface. Figure 2 The surface of the lithium cobalt oxide material shows obvious acid etching marks.

[0149] (2) Characterization of encapsulation:

[0150] The EDS images of P and F elements on the surface of the lithium cobalt oxide material provided in Example 1 of the present invention were characterized using scanning electron microscopy-energy dispersive spectroscopy. Figure 3 and Figure 4 The EDS diagrams of the lithium cobalt oxide material provided in Example 1 regarding P and F elements show that, within the same region, P elements are present on the surface of the lithium cobalt oxide material and exhibit a blocky aggregation pattern. Figure 3 This is caused by the agglomeration of phosphates during the sintering process; in addition, there are areas on the surface of lithium cobalt oxide materials where F element is distributed in areas not covered by P element. Figure 4 ), which refers to the uncovered area of ​​the primary coated lithium cobalt oxide coated with ammonium fluoride.

[0151] (3) Structural characterization:

[0152] The structure of the lithium cobalt oxide material provided in Example 1 was characterized using an X-ray diffractometer. Figure 5 The image shows the XRD pattern of lithium cobalt oxide material. It can be seen from the image that the lithium cobalt oxide material has a good crystal structure.

[0153] 2. Electrochemical performance testing

[0154] Preparation of coin cell half-cells: Lithium cobalt oxide, conductive carbon, and polyvinylidene fluoride were mixed evenly with deionized water at a mass ratio of 95:2:3 and then coated onto aluminum foil to obtain the positive electrode. 1 mol / L LiPF6 was dissolved in a 1:1 volume mixture of EC and DEC, and then 3 wt% FEC was added to prepare the electrolyte. A PP / PE / PP composite membrane was used as the separator. The above positive electrode, lithium foil negative electrode, electrolyte, and separator were combined to form a coin cell half-cell; the coin cell half-cell test voltage was 2.3-4.58V.

[0155] Fabrication of coin cell full cells: Lithium cobalt oxide, conductive carbon, and polyvinylidene fluoride were mixed evenly with deionized water at a mass ratio of 95:2:3 and then coated onto aluminum foil to obtain the positive electrode. 1 mol / L LiPF6 was dissolved in a 1:1 volume mixture of EC and DEC, and 3 wt% FEC was added to prepare the electrolyte. A PP / PE / PP composite membrane was used as the separator. The above positive electrode, graphite negative electrode, electrolyte, and separator were combined to fabricate a coin cell full cell. The coin cell full cell was tested with a voltage of 3.0-4.53 V and a current density of 1 / 3 C.

[0156] (1) By preparing button half-cells, the first discharge specific capacity and first coulombic efficiency of each embodiment and comparative example were measured, and the results are shown in Table 1.

[0157] (2) By preparing button cells, the values ​​of each embodiment and comparative example at 25 μm were measured. o and 45 o The loop performance of C, and at 45 o The storage performance of C is shown in Table 1.

[0158] Table 1 Electrochemical performance of lithium cobalt oxide materials

[0159]

[0160] As can be seen from Table 1, compared with Example 1, the acid solution concentration in the pretreatment of lithium cobalt oxide in Example 2 was higher and the acid washing degree was too high, resulting in lower initial discharge specific capacity and initial coulombic efficiency; while in Example 3, the acid solution concentration in the pretreatment of lithium cobalt oxide was lower and the acid washing degree was too low, which reduced the primary coating effect of phosphate on the surface of lithium cobalt oxide, and the resulting lithium cobalt oxide material had poor cycle performance at 25°C and 45°C.

[0161] Compared to Examples 1-9, the lithium cobalt oxide materials prepared in Comparative Examples 1-6 were not prepared entirely according to the process of acid leaching, primary phosphate coating, and secondary ammonium fluoride coating. Therefore, the initial specific capacity, initial coulombic efficiency, cycling performance at 25°C and 45°C, and capacity retention after 30 days of storage of the resulting lithium cobalt oxide materials were relatively poor. In particular, Comparative Example 4, which was completely uncoated, resulted in lithium cobalt oxide materials with significantly lower initial coulombic efficiency, cycling performance at 25°C and 45°C, and capacity retention after 30 days of storage compared to the other examples.

[0162] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing lithium cobalt oxide material, characterized in that, The preparation method includes: lithium cobalt oxide pretreatment: dispersing lithium cobalt oxide in an acid solution and stirring the reaction, then filtering, washing and drying to obtain acid-treated lithium cobalt oxide; primary coating: mixing the acid-treated lithium cobalt oxide with phosphate and then sintering it once to obtain primary coated lithium cobalt oxide; secondary coating: mixing the primary coated lithium cobalt oxide with ammonium fluoride and then sintering it twice to obtain lithium cobalt oxide material.

2. The preparation method according to claim 1, characterized in that, The acid in the acid solution includes at least one of oxalic acid, acetic acid, citric acid, phosphoric acid, and carbonic acid; and / or, the phosphate includes at least one of Li3PO4, LiCoPO4, LiFePO4, LiNiPO4, LiH2PO4, Co3(PO4)2, and LiH2PO4; and / or, the ammonium fluoride includes at least one of NH4BF4, (NH4)3AlF6, (NH4)2SiF6, and (NH4)2GeF6.

3. The preparation method according to claim 1 or 2, characterized in that, The molar concentration of the acid solution is 0.01-0.20 mol / L; and / or, the phosphate is 1 wt%-3 wt% of the acid-treated lithium cobalt oxide; and / or, the ammonium fluoride is 0.1 wt%-0.5 wt% of the primary coated lithium cobalt oxide.

4. The preparation method according to claim 1, characterized in that, The lithium cobalt oxide includes large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, wherein the large-particle lithium cobalt oxide satisfies 18μm≤D v The small lithium cobalt oxide particles have a diameter of 50 ≤ 21 μm and satisfy 4.5 μm ≤ Dv50 ≤ 9.5 μm; the solid-liquid mass ratio of the lithium cobalt oxide to the acid solution is 1:1-3.

5. The preparation method according to claim 1, characterized in that, The primary sintering temperature is 500-900℃ and the time is 3-6h; and / or, the secondary sintering temperature is 400-800℃ and the time is 3-6h; and / or, the drying temperature is 60-120℃ and the time is 24-30h; and / or, the stirring reaction time is 5-10min.

6. The preparation method according to claim 4, characterized in that, The preparation process of the lithium cobalt oxide includes: mixing lithium source and additives with large-particle cobalt tetroxide and small-particle cobalt tetroxide respectively, followed by sintering and crushing to obtain the large-particle lithium cobalt oxide and the small-particle lithium cobalt oxide respectively.

7. The preparation method according to claim 6, characterized in that, The large-particle cobalt tetroxide satisfies 13.5μm≤D v 50≤18.5μm; and / or, the small cobalt tetroxide particles satisfy 1.5μm≤D v 50≤6.5μm; and / or, the additive is an oxide, the oxide including at least one of the elements Ti, Mg, Al, Y, La, Zr and B; and / or, the lithium source includes at least one of lithium carbonate and lithium hydroxide.

8. The preparation method according to claim 6 or 7, characterized in that, The mass of the additive is 0.3wt%-3.5wt% of the large-particle cobalt tetroxide or the small-particle cobalt tetroxide; and / or, the molar ratio of lithium in the lithium source to cobalt in the large-particle cobalt tetroxide or the small-particle cobalt tetroxide is 1.07-1.09; and / or, the sintering temperature is 1050-1100℃.

9. A lithium cobalt oxide material, characterized in that, The lithium cobalt oxide material is prepared by the preparation method according to any one of claims 1-8.

10. A secondary battery, characterized in that, The secondary battery includes the lithium cobalt oxide material as described in claim 9.

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