Positive electrode material, secondary battery comprising same, and electric device

Abstract

This application discloses a cathode material, a secondary battery containing the same, and an electrical device, relating to the field of electrochemical energy storage technology. The cathode material of this application has a nickel content of at least 70%, enabling it to maintain a high average voltage during charge and discharge, thereby improving the battery's volumetric and gravimetric energy density. Furthermore, the cathode material provided in this application exhibits a high nickel content after cycling. 3+ / Ni 2+ The proportion of oxidation states of Ni increased significantly. 2+ The reduction in Ni content helps to suppress the phase transition from layered structure to rock salt phase, and also effectively suppresses unstable Ni. 4+ The formation of [a specific substance] reduces the electrolyte decomposition kinetic rate and suppresses interfacial side reactions. Ultimately, the cathode material provided in this application exhibits superior interfacial stability and resistance to electrolyte decomposition, improving the stability between the cathode and electrolyte interface while maintaining a high energy density in the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a cathode material, a secondary battery containing the cathode, and an electrical device thereof. Background Technology

[0002] In the field of high-efficiency energy storage, lithium-ion batteries have attracted much attention due to their high energy density and long cycle life. Cathode materials, as a key component affecting battery performance, directly limit the battery's energy density due to their capacity characteristics, and their manufacturing cost also dominates the total cost of lithium-ion batteries. Among them, nickel-cobalt-manganese ternary cathode materials have become the main cathode material system due to their advantages of both high specific capacity and low cost. However, with the increasing scarcity and rising price of cobalt resources, ternary materials are continuously being optimized towards high-nickel and low-cobalt content.

[0003] Among related technologies, high-nickel polycrystalline materials (such as NCM811 and NCM90) have become core candidate materials for high-energy-density lithium-ion batteries due to their high specific capacity (>200 mAh / g) and energy density advantages. However, their polycrystalline structure faces significant challenges under high-nickel conditions: on the one hand, increased lattice distortion can lead to interlayer structure collapse during cycling (such as the R3m→Fm-3m phase transition), causing capacity decay; on the other hand, high nickel content enhances the surface activity of the material, making it prone to side reactions with the electrolyte, generating byproducts such as Li2CO3 and LiF, resulting in a decrease in initial coulombic efficiency (<85%) and gas release. At the same time, volume expansion during charge and discharge (>10%) can easily cause microcrack propagation in particles, accelerating material pulverization and capacity decay, and reducing the cycle life of the battery. In addition, the preparation of polycrystalline materials requires processes such as high-energy ball milling and high-temperature sintering, but high temperatures can easily aggravate lithium-nickel mixing, requiring the addition of excessive lithium salt, which in turn leads to severe particle agglomeration; while mechanical crushing can separate agglomerated particles, it may damage the crystal structure. Therefore, it is urgent to balance its high specific capacity advantage with structural stability and promote the industrial application of high-nickel polycrystalline materials in high-energy-density batteries.

[0004] Therefore, solving the problems of unstable interface structure and poor cycle life under high voltage in current high-nickel polycrystalline cathode materials is of great significance. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a cathode material, a secondary battery containing the cathode, and an electrical device thereof, aiming to solve the problems of unstable interface structure and poor cycle life under high voltage existing in current high-nickel polycrystalline cathode materials.

[0006] In the first aspect of the present application, a cathode material is proposed. The cathode material at least includes Li, Ni, Co, and Mn elements. Among the metal elements of the cathode material except Li, the molar content ratio of Ni is at least 70%. The cathode material satisfies 2.7 ≤ I ≤ 3.3, where I represents the ratio of the content of Ni obtained by performing XPS analysis on the cathode material after 100 cycles of testing on a coin cell assembled with the cathode electrode sheet containing the cathode material and a lithium sheet as the counter electrode under the conditions of a test voltage of 2.8 - 4.4 V at a current rate of 0.5 C. ,

[0016] and Ni 2+ content ratio.

[0007] In some embodiments, the chemical formula of the cathode material is Li a Ni x Co y Mn z A p O2, where 0.95 ≤ a ≤ 1.15, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.3, 0 ≤ p ≤ 0.05, and A includes at least one of Al, Zn, Zr, Ti, Mg, V, and B.

[0008] In some embodiments, the cathode material has a polycrystalline morphology.

[0009] In some embodiments, the median particle size Dv of the cathode material 50 is 0.1 - 3 μm.

[0010] In some embodiments, the powder compaction density of the cathode material under 30 kN is 3.10 - 3.35 g / cm 3 .

[0011] In some embodiments, at least a part of the surface of the cathode material is provided with a spinel structure layer.

[0012] In some embodiments, the spinel structure layer at least includes Fe element.

[0013] In some embodiments, the thickness of the spinel structure layer is 1 - 5 nm.

[0014] In the second aspect of the present application, a secondary battery is further proposed, including a negative electrode sheet and a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector. The positive electrode active material layer includes the above-mentioned cathode material.

[0015] In the third aspect of the present application, an electrical device is further proposed, including the above-mentioned secondary battery, and the secondary battery serves as the power supply of the electrical device.

[0016] This application also proposes a method for preparing the above-mentioned cathode material, including the following steps: S10. The hydroxide precursor and surface-modified salt are mixed in proportion and placed in a high-pressure reactor for a single reaction to obtain the cathode material precursor. S20. The cathode material precursor and eutectic molten salt are mixed in proportion and then sintered at high temperature to obtain the cathode material.

[0017] In some embodiments, the molar ratio of the surface-modified salt to the hydroxide precursor is (0.1~1):100.

[0018] In some embodiments, the molar ratio of the eutectic molten salt to the hydroxide precursor is (1~1.15):1.

[0019] In some embodiments, the method for preparing the cathode material includes at least one of the following (a1) to (a7): (a1) The hydroxide precursor includes nickel cobalt manganese hydroxide; (a2) Median particle size Dv of the hydroxide precursor 50 The size is 1~5μm; (a3) The surface-modifying salt includes one or both of chloride salts and nitrate salts; (a4) When (a3) ​​is included, the chloride salt includes at least one of manganese chloride, magnesium chloride, and calcium chloride; (a5) When (a3) ​​is included, the nitrate includes ferric nitrate; (a6) The eutectic molten salt includes lithium salt; (a7) When (a6) is included, the lithium salt includes at least one of lithium hydroxide, lithium chloride, lithium nitrate, and lithium acetate.

[0020] In some embodiments, the method for preparing the cathode material includes at least one of the following (b1) to (b6): (b1) The conditions for the first reaction are: reaction at 120~200°C for 4~8 hours; (b2) The cathode material precursor and the eutectic molten salt are ball-milled for 20-40 minutes to mix; (b3) The high-temperature sintering includes at least two sintering stages; (b4) When (b3) is included, the conditions for the first stage of sintering are: under an oxygen atmosphere, the temperature is increased from room temperature to 350-450°C at a heating rate of 3-10°C / min, and held for 0.5-1.5h. (b5) When (b3) is included, the conditions for the second stage sintering are: under an oxygen atmosphere, the temperature is increased from the temperature of the first stage sintering to 750-830°C at a heating rate of 1-5°C / min, and held for 10-14 hours. (b6) When (b4) or (b5) is included, the initial oxygen flow rate is 80~200 mL / min.

[0021] This application has at least the following beneficial effects: The cathode material of this application has a nickel content of at least 70%, which enables the cathode material to maintain a high average voltage during charge and discharge, thereby improving the volumetric and gravimetric energy density of the battery. Furthermore, the cathode material provided in this application, after cycling, exhibits a higher Ni content... 3+ / Ni 2+ The proportion of oxidation states of Ni increased significantly. 2+ The reduction in Ni content helps to suppress the phase transition from layered structure to rock salt phase, and also effectively suppresses unstable Ni. 4+ The formation of [a specific substance] reduces the electrolyte decomposition kinetic rate and suppresses interfacial side reactions. Ultimately, the cathode material provided in this application exhibits superior interfacial stability and resistance to electrolyte decomposition, improving the stability between the cathode and electrolyte interface while maintaining a high energy density in the secondary battery. Attached Figure Description

[0022] Figure 1 This is a SEM image of the modified polycrystalline material obtained in Example 1 of this application; Figure 2 Here is a SEM image of the polycrystalline material obtained in Comparative Example 1 of this application; Figure 3 This is a SEM image of the modified polycrystalline material obtained in Example 1 of this application after 200 cycles; Figure 4 This is a SEM image of the polycrystalline material obtained in Comparative Example 1 of this application after 200 cycles; Figure 5 This is a TEM image of the surface structure of the modified polycrystalline material obtained in Example 1 of this application; Figure 6 This is a TEM image of the interface structure of the modified polycrystalline material obtained in Example 1 of this application after cycling. Figure 7 This is a TEM image of the interface structure of the polycrystalline material obtained in Comparative Example 1 of this application after cycling. Figure 8 These are the Ni XPS peak spectra of the polycrystalline materials from Examples 1 and 1 of this application after cycling. Figure 9 The above are the C XPS peak spectra of the polycrystalline materials of Examples 1 and 1 of this application after cycling. Figure 10This is a sample differential capacity curve of the polycrystalline material in Example 1 of this application. Figure 11 This is a differential capacity curve of the polycrystalline material of Comparative Example 1 of this application after cycling. Figure 12 The results of the first charge-discharge test of the CR2032 coin cell prepared by the polycrystalline cathode material of Example 1 and Comparative Example 1 of this application; Figure 13 The charge-discharge cycle test results are for the CR2032 coin cell prepared from the polycrystalline cathode material of Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features. As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate small variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the terms may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two values ​​is less than or equal to ±10% of the average of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two values ​​can be considered "substantially" the same. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified. In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. In the following description, all figures disclosed in this application are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit (RL) and an upper limit (RU) is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable ranging from 1% to 100% with a 1% increment, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed. Throughout this specification, references to "implementation," "partial implementation," "one implementation," "another implementation," "specific method," or "partial method" mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment. In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated. Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

[0024] The term "polymer" refers to a polymeric compound prepared by polymerizing the same or different types of monomers. The general term "polymer" includes the terms "homopolymer," "copolymer," "trimer," and "interpolymer." The term "coating" refers to one or more layers applied to one or both sides of a porous substrate material. Functional coatings comprise a mixture of at least one organic binder and at least one inorganic filler. In addition to the organic binder and inorganic filler, the protective porous layer may also include one or more additives. Functional coatings can be single-layer, double-layer, or multi-layer structures. The term "binder" refers to a substance used to bond inorganic fillers to or to each other in a porous substrate material. Any organic binder that can bond inorganic fillers to or to each other in a porous substrate material may be used herein. Some non-limiting examples of organic binders include polyesters, polyamides, polyacrylic acid, polyethers, polyimides, polyolefins, rubbers, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, cellulose, cellulose derivatives, latexes, and combinations thereof.

[0025] The term "inorganic filler" refers to a non-conductive material. Some non-limiting examples of inorganic fillers include metal oxides, as well as non-oxide materials and non-metallic materials. Some non-limiting examples of metal oxides include alumina, zirconium oxide, barium titanate, lead zirconate titanate, ferrites, zinc oxide, and combinations thereof. Some non-limiting examples of non-oxide materials and non-metallic materials include silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium boride, molybdenum silicide, and combinations thereof. The term "water-soluble polymer" refers to a high molecular weight polymer that is soluble in water or uniformly dispersed in water. The term "oil-soluble polymer" refers to a high molecular weight polymer that is soluble in water or uniformly dispersed in an organic polar solvent, including but not limited to N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

[0026] Positive electrode active material: As used herein and in the claims, the term "positive electrode active material" (also known as cathode active material) is defined as a material that is electrochemically active in a positive electrode or cathode. Active material should be understood as a material capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.

[0027] <Cathode Materials> The first aspect of this application proposes a cathode material comprising at least Li, Ni, Co, and Mn elements. Among the metal elements excluding Li, the molar content of Ni is at least 70%. The cathode material satisfies the following condition: 2.7 ≤ I ≤ 3.3, where I represents the Ni content obtained after 100 cycles of a coin cell assembled with a cathode sheet containing the cathode material and a lithium sheet as the counter electrode, under a test voltage of 2.8~4.4 V at a current rate of 0.5 C. The analysis of the cathode material after cycling using XPS yields the Ni content. 3+ with Ni 2+ The content ratio.

[0028] The cathode material according to the embodiments of this application has at least the following beneficial effects: the cathode material of this application has a nickel content of at least 70%, which enables the cathode material to maintain a high average voltage during charging and discharging, thereby improving the volumetric and gravimetric energy density of the battery. Furthermore, the cathode material provided in this application, after cycling, exhibits a higher Ni content than its counterparts. 3+ / Ni 2+ The proportion of oxidation states of Ni increased significantly. 2+ The reduction in Ni content helps to suppress the phase transition from layered structure to rock salt phase, and also effectively suppresses unstable Ni. 4+ The formation of [a specific substance] reduces the electrolyte decomposition kinetic rate and suppresses interfacial side reactions. Ultimately, the cathode material provided in this application exhibits superior interfacial stability and resistance to electrolyte decomposition, improves the stability between the cathode material and electrolyte interface, mitigates the breakage of polycrystalline cathode materials during cycling, stabilizes the polycrystalline crystal structure, enhances the electrochemical performance of the polycrystalline cathode material, and simultaneously ensures high energy density in the secondary battery.

[0029] In some embodiments, the molar content of Ni is at least 70%, including: the molar content of Ni is at least 70%, the molar content of Ni is at least 80%, or the molar content of Ni is at least 90%.

[0030] In some embodiments, the positive electrode material satisfies: 2.7 ≤ I ≤ 3.3. Exemplarily, I can be 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, or within the range formed by any two of the above values.

[0031] In some embodiments, I represents the ratio of Ni obtained by XPS analysis of the positive electrode material after 100 cycles of testing a coin cell assembled with a positive electrode sheet containing the positive electrode material and a lithium sheet as the counter electrode under the conditions of a test voltage of 2.8 - 4.4 V at a current rate of 0.5 C. 3+ and Ni 2+ The specific test steps are as follows: Etch the positive electrode sheet after 100 cycles with XPS, and obtain the ratio of Ni 3+ and Ni 2+ by performing peak separation processing through Avantage software.

[0032] In some embodiments, the chemical formula of the positive electrode material is Li a Ni x Co y Mn z A p O2, where 0.95 ≤ a ≤ 1.15, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.3, 0 ≤ p ≤ 0.05, and A includes at least one of Al, Zn, Zr, Ti, Mg, V, B. The positive electrode material of this embodiment has both a relatively high energy density and cycle stability.

[0033] In some embodiments, the positive electrode material has a polycrystalline morphology. The polycrystalline morphology is beneficial to improving the kinetic performance of the secondary battery and enhancing the charge and discharge rate of the battery.

[0034] In some embodiments, the median particle size Dv / / 这里的Dv应该是D₅₀之类的具体粒径参数,原文未明确其具体含义,翻译时保留原文形式 50 of the positive electrode material is 0.1 - 3 μm. For example, it can be 1 - 2 μm. Exemplarily, the median particle size Dv 50 of the positive electrode material can be 0.1 μm, 0.5 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.5 μm, 3.0 μm, or within the range formed by any two of the above values.

[0035] After cycling, the oxidation state ratio of Ni <00​​​The reduction in content helps suppress the phase transition from layered structure to rock salt phase, thus alleviating the problem of polycrystalline secondary particle breakage and reducing the side reactions at the cathode / electrolyte interface between polycrystalline primary particles. The aforementioned polycrystalline cathode material, after surface structure remodeling modification, exhibits a regular polyhedral morphology, stronger secondary particle structure stability, and an initial discharge capacity greater than 200 mAh g. --1 After 200 charge-discharge cycles, the capacity retention rate is greater than 80%, and the cycle stability performance is better.

[0036] In some embodiments, the powder compaction density of the cathode material at 30 kN is 3.10~3.35 g / cm³. 3 For example, it can be 3.10 g / cm³. 3 3.15 g / cm 3 3.20 g / cm 3 3.25 g / cm 3 3.30 g / cm 3 3.35g / cm 3 The density of the cathode material powder must be within the range of any two of the above values, or within the range of any two of the above values. A compacted density of the cathode material powder within the above range is beneficial for improving the energy density of the secondary battery.

[0037] In some embodiments, at least a portion of the surface of the cathode material is provided with a spinel structure layer. After cycling, the cathode material can generate a spinel MnFe2O4 structure layer on its surface. The MnFe2O4 of the spinel is difficult to react with HF in the electrolyte, which improves the crystal structure stability between the cathode and electrolyte interface and enhances the electrochemical performance of the polycrystalline cathode material.

[0038] In some embodiments, the spinel structure layer includes at least Fe. The introduction of Fe helps improve the stability of the spinel structure layer, further enhancing the cycle stability of the cathode material.

[0039] In some embodiments, the thickness of the spinel structure layer is 1-5 nm. Exemplarily, it can be 1.0 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 4.0 nm, 4.5 nm, 5.0 nm, or within any two of the above values. A spinel structure layer thickness within the above range can effectively reduce electrolyte corrosion of the cathode material and improve the cycle stability of the cathode material.

[0040] This application also proposes a method for preparing the above-mentioned cathode material, including the following steps: S10. The hydroxide precursor and surface-modified salt are mixed in proportion and placed in a high-pressure reactor for a single reaction to obtain the cathode material precursor. S20. After mixing the cathode material precursor and eutectic molten salt in a certain proportion, high-temperature sintering is carried out to obtain the cathode material.

[0041] The method for preparing the cathode material according to the embodiments of this application has at least the following beneficial effects: This application utilizes a surface-modified salt to treat the surface of a hydroxide precursor, and then reconstructs the atomic arrangement (400°C) of the precursor surface under the treatment of a eutectic molten salt. This helps alleviate the problem of polycrystalline secondary particle breakage and can reduce the side reactions at the cathode / electrolyte interface between polycrystalline primary particles. Furthermore, this application reconstructs the precursor surface atoms under the action of the eutectic molten salt, generating a spinel MnFe2O4 structural layer on the surface. The spinel MnFe2O4 does not react with HF, improving the crystal structure stability at the cathode / electrolyte interface and enhancing the electrochemical performance of the polycrystalline cathode material. The polycrystalline cathode material obtained by the above preparation method, after surface structure reconstruction modification, has a regular polyhedral morphology, stronger secondary particle structure stability, and a first-cycle discharge capacity greater than 200 mAh g. --1 After 200 charge-discharge cycles, the capacity retention rate is greater than 80%, demonstrating better cycle stability. Furthermore, the polycrystalline modification process provided in this application is simple to prepare; the eutectic molten salt can both treat the precursor surface structure remodeling and serve as a lithium source, eliminating the need for an additional water washing step to remove flux, making it suitable for large-scale production. Ultimately, the cathode material modification method provided in this application improves the stability between the cathode and electrolyte interface, mitigates the breakage of polycrystalline cathode materials during cycling, stabilizes the polycrystalline crystal structure, and enhances the electrochemical performance of polycrystalline cathode materials, making it highly valuable for applications in the secondary battery field.

[0042] In some embodiments, the molar ratio of the surface-modifying salt to the hydroxide precursor is (0.1~1):100, preferably (0.3~0.8):100. Exemplarily, it can be 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, or within any range of two of the above values. This application introduces a surface-modifying salt to induce surface reconstruction modification of the hydroxide precursor using salt ions. Too low a salt concentration leads to insufficient interaction with the material surface and poor modification; too high a salt concentration may cause salt ions to form an excessively thick layer on the material surface, hindering subsequent reactions and also impeding modification. Therefore, this application sets the molar ratio of the surface-modifying salt to the hydroxide precursor to (0.1~1):100.

[0043] In some embodiments, the hydroxide precursor includes, but is not limited to, nickel cobalt manganese hydroxide.

[0044] In some embodiments, the median particle size Dv of the hydroxide precursor 50 The particle size is 1~5 μm, preferably 1~3 μm. Exemplarily, the median particle size Dv of the hydroxide precursor is... 50 It can be 1μm, 2μm, 3μm, 4μm, 5μm, or within the range of any two of the above values.

[0045] In some embodiments, the surface-modifying salt includes one or both of chloride salts and nitrate salts, but is not limited thereto.

[0046] In some embodiments, the chloride salt includes at least one of manganese chloride (MnCl2), magnesium chloride (MgCl2), and calcium chloride (CaCl2), but is not limited thereto.

[0047] In some embodiments, the nitrate includes ferric nitrate (Fe(NO3)3), but is not limited thereto.

[0048] In some embodiments, the surface-modifying salt includes manganese chloride hydrate and ferric nitrate hydrate.

[0049] Specifically, manganese chloride hydrates include manganese chloride monohydrate, manganese chloride dihydrate, or manganese chloride tetrahydrate.

[0050] Specifically, the hydrate of ferric nitrate is a nonahydrate, with the chemical formula Fe(NO3)3·9H2O.

[0051] In some specific embodiments, in step S10, the hydroxide precursor, manganese chloride hydrate, and ferric nitrate hydrate are mixed in a certain proportion and then placed in a high-pressure reactor for a single reaction to obtain the cathode material precursor. The purpose of this application is to provide a method for surface structure remodeling modification of polycrystalline cathode materials, in which components comprising the hydroxide precursor, manganese chloride hydrate, and ferric nitrate hydrate are reacted in a high-pressure reactor to obtain a cathode material precursor with remodeled surface structure.

[0052] In some embodiments, in step S10, the conditions for one reaction are: reacting at 120~200°C for 4~8 hours, preferably reacting at 160°C for 6 hours.

[0053] In some embodiments, in step S10, the hydroxide precursor, manganese chloride hydrate, and ferric nitrate hydrate are ultrasonically dispersed in deionized water, and then the mixture is placed in a high-pressure reactor and placed in a constant-temperature reactor, where it is reacted at 120~200°C for 4~8 hours.

[0054] In some embodiments, step S10, after the reaction is completed, further includes the step of cooling the high-pressure reactor to room temperature, separating the obtained solid material by centrifugation, washing it multiple times with deionized water and ethanol, and then freeze-drying it to obtain the processed cathode material precursor.

[0055] In some embodiments, the molar ratio of the eutectic molten salt to the hydroxide precursor is (1~1.15):1. Preferably, it is (1.03~1.08):1. Exemplarily, it can be 1.00:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.10:1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, 1.15:1, or within any range of two of the above values.

[0056] In some embodiments, the eutectic molten salt includes lithium salts, but is not limited thereto.

[0057] In some embodiments, the lithium salt includes at least one of lithium hydroxide (LiOH), lithium chloride (LiCl), lithium nitrate (LiNO3), and lithium acetate (CH3COOLi), but is not limited thereto.

[0058] In some embodiments, the eutectic molten salt is a LiOH / LiCl mixture (molar ratio 1:1) with a melting point of 366°C.

[0059] In some specific embodiments, in step S20, this application provides a method for preparing a cathode material using eutectic molten salt lithium salt, which uses eutectic molten salt treatment to reconstruct the surface structure of the precursor prepared in situ and the atomic arrangement as a lithium source.

[0060] In some embodiments, in step S20, the cathode material precursor is mixed with eutectic molten salt by ball milling for 20-40 minutes.

[0061] In some implementations, step S20, high-temperature sintering includes at least two sintering stages.

[0062] In some embodiments, in step S20, the conditions for the first stage of sintering are: under an oxygen-filled atmosphere, the temperature is increased from room temperature to 350-450°C at a heating rate of 3-10°C / min, and held at that temperature for 0.5-1.5 hours.

[0063] In some embodiments, in step S20, the conditions for the second stage of sintering are as follows: under an oxygen-filled atmosphere, the temperature is increased from the temperature of the first stage of sintering to 750-830°C at a heating rate of 1-5°C / min, and held for 10-14 hours.

[0064] In some embodiments, the final temperature of high-temperature sintering in step S20 is 780°C to 810°C.

[0065] In some embodiments, after the second sintering, step S20 further includes the step of cooling to room temperature at a cooling rate of 3~10°C / min.

[0066] In some embodiments, in step S20, during multi-stage high-temperature sintering, the initial oxygen flow rate is 80~200 mL / min.

[0067] In one specific embodiment, to improve the secondary particle breakage and cycle stability performance of polycrystalline materials, this application provides a method for preparing a cathode material. The method involves modifying the polycrystalline cathode material using a ball milling-assisted sintering method. Specific steps include: ultrasonically dispersing a hydroxide precursor, manganese chloride hydrate, and ferric nitrate hydrate in deionized water; then placing the mixture in a 100ml high-pressure reactor and reacting it at 160°C for 6 hours in a constant-temperature reactor; after the reaction, cooling the high-pressure reactor to room temperature; centrifuging the resulting solid material; washing it multiple times with deionized water and ethanol; and freeze-drying it to obtain the treated precursor; using LiOH / LiCl (molar ratio 1:1) as the eutectic molten salt; grinding and mixing the treated precursor with the eutectic molten salt for 30 minutes; then transferring the mixture to a ceramic boat and treating it at 400°C for 1 hour under oxygen, followed by treatment at 780°C for 8 hours to obtain the treated cathode material. This single-crystal material has a first-cycle discharge capacity exceeding 200mAh g⁻¹. -1 The retention rate exceeds 80% after 200 cycles.

[0068] Secondary batteries A second aspect of this application provides a secondary battery, including a negative electrode and a positive electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes the aforementioned positive electrode material.

[0069] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent.

[0070] In some embodiments, the mass percentage of each component, taking the positive electrode material, conductive agent, and binder as a whole, is as follows: positive electrode material 80-98%, conductive agent 1-10%, and binder 1-10%.

[0071] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders. In some embodiments, the positive electrode conductive agent may include at least one of carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0072] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0073] In some embodiments, the conductive layer may include at least one of carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon nanotube, carbon nanotube, activated carbon, and mesoporous carbon. In some embodiments, the preparation method of the positive electrode sheet includes the following steps: thoroughly mixing the positive electrode material, conductive agent, binder, and solvent according to a mass ratio, coating the mixture onto the positive electrode current collector, and then drying, cold pressing, and slitting to obtain the positive electrode sheet. The preparation method of the positive electrode sheet can adopt conventional methods in the industry, and this application does not limit it.

[0074] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0075] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0076] In some embodiments, the conductive layer may include at least one of carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0077] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode binder conductive agent.

[0078] In some embodiments, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, elemental Si, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0079] In some embodiments, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders. In some embodiments, the negative electrode conductive agent may include at least one of carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0080] In some embodiments, a method for preparing the above-mentioned negative electrode sheet is also provided, including the steps of: thoroughly mixing the negative electrode active material, conductive agent, and binder according to a mass ratio, coating the mixture onto the negative electrode current collector, and then drying, cold pressing, and slitting to obtain the negative electrode sheet. The preparation method of the negative electrode sheet can adopt conventional methods in the industry, and this application does not limit it.

[0081] In some implementations, the secondary battery includes a lithium-ion battery.

[0082] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator located between the positive and negative electrodes.

[0083] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures. Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate. In some embodiments, the porous substrate is, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer. In some embodiments, the coating is disposed on one side of the substrate. In some embodiments, the coating is disposed on both sides of the substrate.

[0084] In some embodiments, the coating includes inorganic fillers and adhesives.

[0085] In some embodiments, the inorganic filler comprises Al2O3, SiO2, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, TiN, AlN, Na2O.mTiO2, K2O.nTiO2, BaO x MTiO3 and combinations thereof, wherein m is 3 or 6, n is 1, 2, 4, 6 or 8, x is 1 or 2, and M is Ba, Sr or Ca. The inorganic filler may be spherical, plate-like, disc-like, needle-like, cylindrical, irregular or other known particle shapes.

[0086] In some embodiments, the inorganic filler includes one or more of alumina, hydrated alumina, boehmite, magnesium hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, and barium sulfate. In some implementations, the binder is a water-soluble polymer.

[0087] In some implementations, the water-soluble polymer is a homopolymer or copolymer. In some embodiments, the water-soluble binder includes at least one of polyamide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose, cyanoethyl cellulose, nitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0088] In some implementations, the binder is an oil-soluble polymer. In some embodiments, non-limiting examples of oil-soluble polymers include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyester, polyether, polyvinyl compounds, polyolefins, rubber, polyvinylpyrrolidone, polystyrene, nitrile rubber (NBR), styrene-butadiene rubber (SBR), latex, acrylonitrile-styrene-butadiene copolymer, halogenated polymers, fluorinated polymers, chlorinated polymers, unsaturated polymers, conjugated diene polymers, and combinations thereof.

[0089] In some embodiments, the electrolyte may include at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte. In some embodiments, the liquid electrolyte may include a non-aqueous solvent and a lithium salt.

[0090] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds. In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds. In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate. In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof. In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0091] <Electrical Equipment> In a third aspect, the present invention provides an electrical device comprising the aforementioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0092] The electrical equipment used in this application is not particularly limited and can be any electrical equipment known in the prior art. The purpose of the electrical equipment described in this application is not particularly limited, and it can be used with any electrical equipment known in the prior art. According to some embodiments of this application, the electrical equipment includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0093] Unless otherwise specified in the following examples, the techniques or conditions described in the literature in this field or in accordance with the product instructions shall apply. All reagents or instruments without a specified manufacturer are commercially available conventional products.

[0094] Example 1 Preparation of polycrystalline cathode materials: a) Preparation of modified precursor: Ni hydroxide precursor with an average diameter of 2 μm was prepared. 0.75 Co 0.05 Mn 0.2 (OH)₂, MnCl₂·4H₂O, and Fe(NO₃)₃·9H₂O were mixed in 45 mL of deionized water at a molar ratio of 1:0.005:0.01 and ultrasonically dispersed for 10 minutes using an ultrasonic cleaner. Then, 15 mL of 2 M NaOH solution was added to the solution with stirring, and stirring was continued for another 10 minutes. The aqueous solution was then transferred to a 100 mL autoclave and placed in a constant-temperature reactor at 160°C for 6 hours. After the reaction, the autoclave was cooled to room temperature, and the resulting solid material was separated by centrifugation, washed repeatedly with deionized water and ethanol, and then freeze-dried to obtain the cathode material precursor.

[0095] b) Treatment of the surface structure of the cathode material precursor using eutectic molten salt: LiOH / LiCl (molar ratio 1:1) was selected as the eutectic molten salt, with a melting point of 366°C. The cathode material precursor and the eutectic molten salt LiOH / LiCl were ground and mixed at a molar ratio of 1:1.05 for 30 minutes to obtain a mixture.

[0096] c) The mixture obtained in step b) is placed in a tube furnace with an oxygen flow rate of 100 mL / min. The furnace is first heated to 400 °C at a heating rate of 3 °C / min and held for 1 h, then heated to 780 °C at a heating rate of 3 °C / min and held for 8 h, and finally cooled to room temperature at a cooling rate of 3 °C / min to obtain a polycrystalline cathode material with the chemical formula LiNi. 0.75 Co 0.05 Mn0.2 O2, and the cathode material has a spinel-structured MnFe2O4 layer on its surface, and the median particle size Dv of the cathode material. 50 It is 2μm.

[0097] The above-mentioned positive electrode sheet and lithium sheet were used as counter electrodes to assemble a coin cell. Battery assembly process: The positive electrode material from Example 1 was mixed in a mass ratio of positive electrode material: conductive carbon: binder PVDF of 90:5:5. The viscosity of the positive electrode slurry was adjusted with N-methylpyrrolidone (NMP) solvent. The slurry was uniformly coated onto aluminum foil and dried in a vacuum oven at 120 °C for 12 h. The dried electrode was rolled and the coated aluminum foil was cut into 12 mm diameter discs using a slicing machine. These discs were then transferred to a glove box for battery assembly. The atmosphere inside the glove box was maintained at O2 < 0.1 ppm and H2O < 0.1 ppm. PP2400 was used as the separator, lithium metal as the negative electrode, and a 1 M LiPF6 solution as the electrolyte, with EC / DMC / EMC (volume ratio 1:1:1) as the solvent. The assembled coin cell was allowed to stand for 4 h to allow the electrolyte to fully impregnate it before electrochemical testing.

[0098] Performance Testing: The coin cells obtained above were cycled 100 times under a current rate of 0.5 C and a test voltage range of 2.8–4.4 V. After the test, the cells were disassembled, and the cathode material was analyzed by X-ray photoelectron spectroscopy (XPS) to determine the elemental composition, yielding Ni. 3+ with Ni 2+ The content ratio (i.e., I) = 2.95.

[0099] Example 2 The difference between this embodiment and Embodiment 1 is that the precursor Ni is adjusted. 0.75 Co 0.05 Mn 0.2 (OH)₂, MnCl₂·4H₂O, and Fe(NO₃)₃·9H₂O are mixed in a molar ratio of 1:0.0025:0.005. The obtained button cell was tested according to the test method of Example 1, and I=2.7 was obtained.

[0100] Example 3 The difference between this embodiment and Embodiment 1 is that the precursor Ni is adjusted. 0.75 Co 0.05 Mn 0.2 (OH)₂, MnCl₂·4H₂O, and Fe(NO₃)₃·9H₂O are mixed in a molar ratio of 1:0.0075:0.015. The obtained button cell was tested according to the test method of Example 1, and I=3.3 was obtained.

[0101] Example 4 The difference between this embodiment and Embodiment 1 is that Ni is used. 0.75 Co 0.05 Mn 0.2 The positive electrode material modified by (OH)2 and Al2O3 in a 1:0.005 molar ratio has the chemical formula Li. 0.95 Ni 0.70 Co 0.1 Mn 0.2 Al 0.05 O2 The corresponding preparation method is: a) using Ni 0.75 Co 0.05 Mn 0.2 (OH)₂ and Al₂O₃ are mixed at a molar ratio of 1:0.005, and then mixed with the lithium salt compound LiOH at a molar ratio of 1:1.05. b) Sintering: The mixture obtained in step a) is placed in an oxygen furnace with an oxygen flow rate of 100 mL / min (normal value). The oxygen furnace is first heated to 550°C at a heating rate of 3°C / min and held for 5 hours, then heated to 780°C at a heating rate of 3°C / min and held for 8 hours. Finally, it is cooled to room temperature at a cooling rate of 3°C / min to obtain undoped polycrystalline cathode material B with the chemical formula Li. 0.95 Ni 0.70 Co 0.1 Mn 0.2 Al 0.05 O2.

[0102] The obtained button cells were tested according to the test method of Example 1.

[0103] Example 5 The difference between this embodiment and Embodiment 1 is that the chemical formula of the positive electrode material is Ni. 0.75 Co 0.05 Mn 0.2 The chemical formula of the cathode material modified by (OH)₂ and MgO in a 1:0.005 molar ratio is Li. 0.95 Ni 0.75 Co 0.05 Mn 0.2 Mg 0.05 O2.

[0104] The corresponding preparation method is as follows: a) using Ni 0.75 Co 0.05 Mn 0.2(OH)₂ and MgO are mixed at a molar ratio of 1:0.005, and then mixed with the lithium salt compound LiOH at a molar ratio of 1:1.05. b) Sintering: The mixture obtained in step a) is placed in an oxygen furnace with an oxygen flow rate of 100 mL / min (normal value). The oxygen furnace is first heated to 550°C at a heating rate of 3°C / min and held for 5 hours, then heated to 780°C at a heating rate of 3°C / min and held for 8 hours. Finally, it is cooled to room temperature at a cooling rate of 3°C / min to obtain undoped polycrystalline cathode material B with the chemical formula Li. 0.95 Ni 0.75 Co 0.05 Mn 0.2 Mg 0.05 O2.

[0105] The obtained button cells were tested according to the test method of Example 1. Example 6 The difference between this embodiment and Embodiment 1 is that: a precursor Ni with a particle size of 0.1 μm is used. 0.75 Co 0.05 Mn 0.2 The median particle size Dv of the cathode material modified with (OH)2 50 It is 0.1μm.

[0106] The obtained button cells were tested according to the test method of Example 1. Example 7 The difference between this embodiment and Embodiment 1 is that a precursor Ni with a particle size of 3μm is used. 0.75 Co 0.05 Mn 0.2 The median particle size Dv of the cathode material modified with (OH)2 50 It is 3μm.

[0107] The obtained button cells were tested according to the test method of Example 1.

[0108] Examples 8-10 The difference from Example 1 is that Ni is adjusted. 0.75 Co 0.05 Mn 0.2 The spinel structure layer thickness was adjusted to 1, 3, and 5 nm by using (OH)2, MnCl2·4H2O and Fe(NO3)3·9H2O in molar ratios of 1:0.00025:0.005, 1:0.00075:0.015, and 1:0.00125:0.025.

[0109] Example 11 The difference from Example 1 is that Fe(NO3)3·9H2O is replaced with Al(NO3)3·9H2O to adjust the element of the spinel structure layer to Al.

[0110] Comparative Example 1 Compared with Example 1, Comparative Example 1 does not involve surface modification in the preparation of the polycrystalline cathode material, and its preparation process includes the following steps: a) Mixing: Ni hydroxide precursor with an average diameter of 2 μm is mixed with... 0.75 Co 0.05 Mn 0.2 (OH)2 and lithium salt compound LiOH are mixed at a molar ratio of 1:1.05 and ground for 30 minutes to obtain a mixture.

[0111] b) Sintering: The mixture obtained in step a) is placed in an oxygen furnace with an oxygen flow rate of 100 mL / min (normal value). The oxygen furnace is first heated to 550°C at a heating rate of 3°C / min and held for 5 hours, then heated to 780°C at a heating rate of 3°C / min and held for 8 hours. Finally, it is cooled to room temperature at a cooling rate of 3°C / min to obtain an undoped polycrystalline cathode material with the chemical formula LiNi. 0.75 Co 0.05 Mn 0.2 O2.

[0112] The rest is the same as in Example 1, and will not be repeated here.

[0113] Comparative Example 2 The difference between this comparative example and Example 1 is that molten salt is not used; the sintering method of Comparative Example 1 is used directly.

[0114] The obtained button cell was tested according to the test method of Example 1, and I=2.3 was obtained.

[0115] The rest is the same as in Example 1, and will not be repeated here.

[0116] The characteristics of the cathode materials prepared in the above embodiments and comparative examples are shown in the table below: Performance testing 1. SEM testing The polycrystalline cathode materials prepared in Example 1 and Comparative Example 1 were observed using scanning electron microscopy (SEM), and the results are as follows: Figure 1-2 : Figure 1 This is a SEM image of the modified polycrystalline material obtained in Example 1. Figure 2 The image shows the SEM image of the polycrystalline material obtained in Comparative Example 1.

[0117] Depend on Figure 1-2It can be seen that the modified sample of Example 1 ( Figure 1 Its overall morphology is similar to that of the unmodified Comparative Example 1 sample ( Figure 2 Compared to the previous example, there was no significant change, but the boundaries of the primary particles on the surface became blurred, and obvious flocculent matter could be observed on the surface. This phenomenon indicates that a uniform coating layer exists on the surface of the sample in Example 1, which may have a positive impact on the electrochemical performance of the material.

[0118] The surfaces of the polycrystalline cathode materials prepared in Example 1 and Comparative Example 1 after 200 cycles were observed using scanning electron microscopy (SEM). (Specifically, the cathode surface was polished using triion cutting and then observed under SEM). The results are as follows: Figure 3-4 : Figure 3 This is a SEM image of the polycrystalline material from Example 1 after 200 cycles. Figure 4 The image shows the SEM image of the polycrystalline material in Comparative Example 1 after 200 cycles.

[0119] As shown in the figure, in the material of Comparative Example 1, the particles around the crack gradually exhibit a loose distribution. This phenomenon indicates that during the lithium delithiation / lithiation process in the material of Comparative Example 1, the formation of a large amount of spinel and rock salt phases severely degraded the structure, significantly affecting the electrochemical performance and cycle stability of the material. In contrast, after long-term cycling, the material of Example 1 exhibited significant resistance to breakage. The material of Example 1 maintained the integrity and spherical structure of the particles well, without obvious cracks or breakage, indicating that a good cathode / electrolyte interface structure was maintained.

[0120] 2. TEM test The polycrystalline cathode material prepared in Example 1 before and after 200 cycles, and the polycrystalline cathode material prepared in Comparative Example 1 after cycling, were analyzed using spherical aberration transmission electron microscopy (TEM). The results are as follows: Figure 5-7 : Figure 5 This is a TEM image of the surface structure of the modified polycrystalline material obtained in Example 1. Figure 6 This is a TEM image of the interface structure of the modified polycrystalline material obtained in Example 1 after cycling. Figure 7 The image shows the TEM image of the interface structure of the polycrystalline material obtained in Comparative Example 1 after cycling.

[0121] Depend on Figure 5-7TEM images show a significant change in the layered structure at the polycrystalline interface after surface restructuring and modification, with a uniform 2nm spinel MnFe2O4 phase transition layer present at the interface. After cycling, the presence of a uniform 2nm spinel MnFe2O4 phase transition layer in the cathode of Example 1 helps resist HF and other side reactions at the interface, thus contributing to the stability of the cathode / electrolyte interface. In contrast, after cycling, the cathode of Comparative Example 1 exhibits a large area of ​​rock salt phase transition region in the cathode / electrolyte, with the thick phase transition layer severely hindering lithium ion (Li-) conversion. + The migration of ) leads to a rapid decay of the material's capacity.

[0122] 3. XPS Analysis Detailed elemental analysis was performed on the polycrystalline material samples of Example 1 and Comparative Example 1 after cycling using X-ray photoelectron spectroscopy (XPS). The results are as follows: Figure 8-9 As shown.

[0123] XPS analysis revealed that the binding energy peak position of the Ni 2p orbital did not show a significant shift, but Ni 3+ / Ni 2+ The proportion of oxidation states of Ni increased significantly. 2+ The decrease in content helps suppress the phase transition from layered structure to rock salt phase, a phenomenon highly consistent with the structural evolution trend observed in TEM images (e.g., Figure 8 (As shown). However, a large amount of unstable Ni is easily generated under high pressure conditions. 4+ This can trigger interfacial instability and accelerate electrolyte decomposition. The HF generated by the reaction further exacerbates interfacial instability. During cycling, the electrolyte penetrates into the particle interior through microcracks on the material surface, leading to the accumulation of carbon oxides (such as CO and C=O) from the surface to the bulk region. This phenomenon is clearly characterized in C1s spectra (e.g., ...). Figure 9 (As shown). The comparison shows that the content of carbon oxides such as CO / C=O in the material of Example 1 is significantly lower than that in Comparative Example 1, indicating that it has superior interfacial stability and resistance to electrolyte decomposition. Further research shows that the material of Example 1 effectively suppresses unstable Ni by regulating cation order and optimizing surface chemical state. 4+ The generation of [a substance] reduces the electrolyte decomposition kinetic rate, revealing the inhibition mechanism of its interfacial side reactions.

[0124] 4. Phase transition analysis Phase transition analysis was performed on the polycrystalline material samples of Example 1 and Comparative Example 1 using DQ / DV curves. The results are as follows: Figure 10-11 . As shown in the figure, with 200 cycles, the curves of Example 1 have a high degree of overlap, indicating that the degree of phase transition is small and the original layered structure is maintained. Figure 10The obvious shift in the peak of the curve in Comparative Example 1 indicates an irreversible phase transition that occurs during the cycling process. Figure 11 ).

[0125] 5. Electrochemical performance testing The polycrystalline cathode materials prepared in Example 1 and Comparative Example 1 were used as cathode active materials to prepare coin cells CR2032 and their electrochemical performance was tested, including the first charge-discharge test and charge-discharge cycle test.

[0126] Battery assembly process: The materials of the examples and comparative examples were mixed in a mass ratio of positive electrode active material: conductive carbon: binder PVDF of 90:5:5. The viscosity of the positive electrode slurry was adjusted with N-methylpyrrolidone (NMP) solvent. The slurry was uniformly coated onto aluminum foil and dried in a vacuum oven at 120 °C for 12 h. The dried electrode was rolled and the coated aluminum foil was cut into 12 mm diameter discs using a slicing machine. The discs were then transferred to a glove box for battery assembly. The atmosphere inside the glove box was maintained with O2 < 0.1 ppm and H2O < 0.1 ppm. PP2400 was used as the separator, lithium metal was used as the negative electrode, and the electrolyte was a 1M LiPF6 solution with EC / DMC / EMC solvent (volume ratio 1:1:1). The assembled button batteries were allowed to stand for 4 h to allow the electrolyte to fully impregnate them before electrochemical testing.

[0127] Electrochemical testing: First charge-discharge test, voltage range 2.8~4.4 V, rate 0.1 C; Charge-discharge cycle test, voltage range 2.8~4.4 V, rate 0.5 C.

[0128] The results are as follows Figure 12 (First cycle charge / discharge curve) Figure 13 (Charge-discharge cycle test curves) and Table 1 below: Table 1 name 0.1C capacity First effect 0.5C capacity 200-lap retention rate Example 1 205.74 93.6% 188.69 82.5% Example 2 202.47 92.1% 185.45 80.3% Example 3 201.48 93.2% 184.64 80.5% Example 4 200.87 91.3% 183.45 78.4% Example 5 201.83 92.5% 184.56 79.1% Example 6 207.44 93.8% 183.54 79.4% Example 7 203.13 92.6% 184.45 79.6% Example 8 203.48 91.5% 183.46 80.3% Example 9 200.37 92.5% 181.65 81.9% Example 10 199.86 92.9% 180.53 81.6% Example 11 200.48 92.1% 181.78 80.4% Comparative Example 1 195.43 89.6 % 175.43 73.4% Comparative Example 2 197.32 90.1% 177.32 75.3% By comparing the embodiments and comparative examples, it can be seen that the cathode material provided in this application, after cycling, produces Ni 3+ / Ni 2+ The proportion of oxidation states of Ni increased significantly. 2+ The reduction in Ni content helps to suppress the phase transition from layered structure to rock salt phase, and also effectively suppresses unstable Ni. 4+ The formation of [a specific substance] reduces the decomposition kinetics rate of the electrolyte and suppresses interfacial side reactions. Ultimately, the cathode material provided in this application exhibits superior interfacial stability and resistance to electrolyte decomposition, improves the stability of the cathode / electrolyte interface, mitigates the breakage of polycrystalline cathode materials during cycling, stabilizes the polycrystalline crystal structure, and enhances the electrochemical performance of polycrystalline cathode materials.

[0129] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this 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 modifications and improvements all fall within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The cathode material includes at least Li, Ni, Co and Mn elements, and among the metal elements other than Li in the cathode material, the molar content of Ni is at least 70%. The positive electrode material satisfies: 2.7 ≤ I ≤ 3.

3. I represents the result of 100 cycle tests on a coin cell assembled with a positive electrode containing the aforementioned positive electrode material and a lithium sheet as the counter electrode, under test conditions of 0.5 C current rate and 2.8~4.4 V. The positive electrode material after cycling is analyzed by XPS, yielding Ni... 3+ with Ni 2+ The content ratio.

2. The cathode material according to claim 1, characterized in that, The chemical formula of the positive electrode material is Li a Ni x Co y Mn z A p O2, where 0.95 ≤ a ≤ 1.15, 0.7 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.3, 0 ≤ p ≤ 0.05, and A includes at least one of Al, Zn, Zr, Ti, Mg, V, and B.

3. The cathode material according to claim 1, characterized in that, The cathode material has a polycrystalline morphology.

4. The cathode material according to claim 1, characterized in that, The median particle size Dv of the cathode material 50 The range is 0.1~3μm.

5. The positive electrode material according to claim 1, characterized in that, The compacted density of the cathode material at 30 kN is 3.10~3.35 g / cm³. 3 .

6. The cathode material according to claim 1, characterized in that, The cathode material has a spinel structure layer on at least a portion of its surface.

7. The cathode material according to claim 6, characterized in that, The spinel structure layer includes at least the element Fe.

8. The positive electrode material according to claim 1, characterized in that, The thickness of the spinel structure layer is 1~5nm.

9. A secondary battery, characterized in that, The device includes a negative electrode and a positive electrode, wherein the positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, and the positive active material layer includes the positive electrode material as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9, wherein the secondary battery serves as the power supply for the electrical equipment.

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