Coated positive electrode material and preparation method therefor, positive electrode sheet and secondary battery

Abstract

A coated positive electrode material and a preparation method therefor, a positive electrode sheet and a secondary battery, the coated positive electrode material comprising an inner core and a coating layer covering at least part of the outer surface of the inner core. The inner core contains lithium nickel oxide, and the coating layer contains a lithium-containing amorphous polymer, LiPO2F2 and metal fluoride being distributed in the lithium-containing amorphous polymer. The metal fluoride can reduce interfacial side reactions and avoid the erosion to the positive electrode material by HF, and the lithium-containing amorphous polymer and the metal fluoride distributed therein and having good stability help to avoid direct contact between the inner core and an organic electrolyte, thus alleviating electrode / electrolyte interfacial side reactions and impedance growth during cycling. The lithium-containing amorphous polymer has good lithium ion transmission capacity, and the LiPO 2F2 can form a low-impedance electrode / electrolyte interfacial film having high ionic conductivity and stable electrochemical performance, and the synergistic effect of the two improves the dynamic performance of the positive electrode material.

Description

Coated positive electrode material and preparation method thereof, positive electrode sheet and secondary battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311343444.0 filed with the State Intellectual Property Office of China on October 17, 2023, entitled “Coated positive electrode material and preparation method thereof, positive electrode sheet and secondary battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the technical field of lithium-ion batteries, and in particular to a coated positive electrode material and a preparation method thereof, a positive electrode plate and a secondary battery. Background Art

[0004] The rapid development of new energy vehicles is placing higher demands on the energy density of lithium-ion secondary batteries. Exploring low-cost, high-energy-density cathode materials to meet these demands has become a critical task. Lithium nickel oxide layered cathode materials have garnered widespread market attention due to their high gram capacity, excellent cycle performance, and low production cost, enabling electric vehicles to achieve a single-charge range of over 300 km. However, practical applications of these materials often face complex electrode / electrolyte interface issues and safety concerns.

[0005] In the related art, a coating layer is usually formed on the surface of the lithium nickel oxide layered positive electrode material in order to solve the electrode / electrolyte interface problem and safety issues, but it may also lead to the problem of increased interface impedance of the layered positive electrode material.

[0006] Summary of the Invention

[0007] Based on this, it is necessary to provide a coated positive electrode material and its preparation method, a positive electrode plate and a secondary battery, so as to reduce the interfacial impedance of the positive electrode material while solving the electrode / electrolyte interface problem and safety problems.

[0008] A first aspect of the present invention provides a coated positive electrode material, comprising:

[0009] a core comprising lithium nickel oxide; and

[0010] The coating layer is coated on at least a portion of the outer surface of the core, and the coating layer contains a lithium-containing amorphous polymer, in which LiPO2F2 and metal fluoride are distributed.

[0011] In some embodiments, the lithium-containing amorphous polymer includes a lithium-containing ether oligomer;

[0012] Optionally, the lithium-containing ether oligomer has at least one of the following characteristics:

[0013] (1) The lithium-containing ether oligomer includes an ether oligomer containing lithium at the end group;

[0014] (2) The repeating units of the lithium-containing ether oligomer include one or more of -CH2-O-, -CH2-CH2-O-, and -CH2-CH2-CH2-O-;

[0015] (3) The mass percentage of the lithium-containing ether oligomer to the mass percentage of the core is 0.05% to 3%;

[0016] (4) The degree of polymerization of the lithium-containing ether oligomer is an integer between 1 and 10.

[0017] In some embodiments, the LiPO2F2 has at least one of the following characteristics:

[0018] (1) The average particle size D50 of the LiPO2F2 is 1 nm to 100 nm;

[0019] (2) The mass of the LiPO2F2 accounts for 0.01% to 3% of the mass of the core.

[0020] In some embodiments, the metal fluoride has at least one of the following characteristics:

[0021] (1) The metal elements contained in the metal fluoride include one or more of Li, Mg, Zn, Al, Zr, Ti, Nb, V, Mo and W;

[0022] (2) The average particle size D50 of the metal fluoride is 1 nm to 100 nm;

[0023] (3) The mass of the metal fluoride accounts for 0.05% to 3% of the mass of the inner core.

[0024] In some embodiments, in the lithium nickel oxide, the molar ratio of nickel element to the total metal elements other than lithium element is 0.6-1;

[0025] Optionally, the chemical formula of the lithium nickel oxide is Li a Ni b M 1-b O2, M element is a metal element, 0.9≤a≤1.1, 0.6≤b≤1;

[0026] Further optionally, the M element includes one or more of Mn, Co, Al, Mg, Sr, B, Ti, Zr, Nb, Ta and W.

[0027] In some embodiments, the coated cathode material has at least one of the following characteristics:

[0028] (1) The thickness of the coating layer is 2nm-200nm;

[0029] (2) The average particle size D50 of the coated positive electrode material is 2 μm-18 μm;

[0030] (3) The specific surface area of ​​the coated positive electrode material is 0.3 m 2 / g-3.0m 2 / g;

[0031] (4) The water content of the coated positive electrode material is less than 500 ppm;

[0032] (5) The coated positive electrode material contains one or more of free LiOH and free Li2CO3;

[0033] Optionally, the content of free LiOH in the coated positive electrode material is 1500ppm-4000ppm;

[0034] Optionally, the content of free Li2CO3 in the coated positive electrode material is 1500ppm-4000ppm.

[0035] The second aspect of the present invention provides a method for preparing the coated positive electrode material of the first aspect of the present invention, comprising the following steps:

[0036] The core, the reaction medium and the carbonate solution containing LiPF6 are mixed and then aged to form the coating layer on at least a portion of the outer surface of the core to prepare the coated positive electrode material; wherein the core contains at least one of free LiOH and free Li2CO3;

[0037] Wherein, the reaction medium includes metal oxide; and the water content of the carbonate solution is less than 500 ppm.

[0038] In some embodiments, the method for preparing the coated positive electrode material includes at least one of the following conditions:

[0039] (1) The content of free LiOH in the core is 2000ppm-10000ppm;

[0040] (2) the content of free Li2CO3 in the core is 2000ppm-10000ppm;

[0041] (3) The water content of the core is less than 500 ppm;

[0042] (4) The metal elements contained in the metal oxide include one or more of Mg, Zn, Al, Zr, Ti, Nb, V, Mo and W;

[0043] (5) The mass ratio of the core to the reaction medium is 1:(0.0005-0.03);

[0044] (6) The specific surface area of ​​the reaction medium is 10m 2 / g-100m 2 / g;

[0045] (7) The reaction medium comprises primary particles having an average particle size D50 of 1 nm to 500 nm;

[0046] (8) The mass percentage concentration of LiPF6 in the carbonate solution is 5%-20%;

[0047] (9) the carbonate solvent contained in the carbonate solution includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate;

[0048] (10) The aging reaction temperature is 20°C-80°C; the aging reaction time is 6h-30h;

[0049] (11) The solid content of the slurry after the core, the reaction medium and the carbonate solution are mixed is 10%-80%.

[0050] The third aspect of the present invention provides a positive electrode plate, comprising the coated positive electrode material of the first aspect of the present invention or the coated positive electrode material prepared by the method of the second aspect of the present invention.

[0051] A fourth aspect of the present invention provides a secondary battery comprising the positive electrode sheet according to the third aspect of the present invention.

[0052] A fifth aspect of the present invention provides an electrical device comprising the secondary battery according to the fourth aspect of the present invention.

[0053] The above-mentioned coated positive electrode material and its preparation method, positive electrode plate and secondary battery, the coated positive electrode material includes a coating layer containing a lithium-containing amorphous polymer, lithium salt LiPO2F2 and metal fluoride are distributed in the lithium-containing amorphous polymer, and the coating layer has a CEI-like film structure, that is, the lithium-containing amorphous polymer and the lithium salt LiPO2F2 and metal fluoride distributed therein constitute an organic / inorganic composite structure; metal fluoride can reduce interfacial side reactions and avoid HF in the electrolyte from corroding the positive electrode material. Therefore, the lithium-containing amorphous polymer and the metal fluoride with good stability distributed therein help to avoid direct contact between the core and the organic electrolyte, alleviate the electrode / electrolyte interface side reactions and impedance growth during the cycle. In addition, the lithium-containing amorphous polymer has good lithium ion transport capability, and LiPO2F2 can form a low-impedance electrode / electrolyte interface film with high ionic conductivity and electrochemical stability. The synergistic effect of the two improves the kinetic performance of the positive electrode material and can also improve the long-cycle stability of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG1 is a SEM image of the coated positive electrode material prepared in Example 1;

[0055] FIG2 is a MALDI-TOF-MS spectrum of the coated cathode material prepared in Example 1;

[0056] FIG3 is a schematic diagram of rate performance test results of Example 1 and Comparative Examples 1-5. DETAILED DESCRIPTION

[0057] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0059] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0060] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0061] Only certain numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0062] The temperature parameters in the present invention, unless otherwise specified, allow for either constant temperature treatment or treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range controlled by the instrument.

[0063] In the description of the invention, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0064] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0065] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially.

[0066] Lithium nickel oxide layered cathode materials often face complex electrode / electrolyte interface problems and safety issues during practical applications. Technicians analyzed that the main reason is that the residual lithium compounds such as LiOH and Li2CO3 on the surface of lithium nickel oxide layered cathode materials are high, which easily aggravates the gelation of electrode slurry and battery gas production; and the highly active Ni 4+ The side reaction with the liquid electrolyte can induce the decomposition of the organic solvent in the electrolyte, forming an unstable cathode / electrolyte interface layer (CEI film), which accelerates battery failure.

[0067] In related technologies, a coating layer is usually formed on the surface of lithium nickel oxide layered positive electrode materials to inhibit interfacial side reactions, in order to solve electrode / electrolyte interface problems and safety issues; however, the electronic / ionic insulation and heavy coating layer may also lead to problems such as increased material impedance and decreased specific capacity. Therefore, it is urgent to optimize the coating modification process of lithium nickel oxide layered positive electrode materials, so as to ensure the high stability, integrity and uniformity of the coating layer, minimize interfacial side reactions, and reduce the damage of the modification process to the material surface structure to achieve a self-limiting coating reaction.

[0068] To address these challenges, the present invention provides a coated cathode material and its preparation method. This material utilizes a lithium nickel oxide layered cathode material as a core. Based on residual lithium compounds such as LiOH and Li2CO3 on the core's surface, a lithium-containing amorphous polymer coating is formed on the core's exterior through a self-limiting polymerization reaction. The lithium-containing amorphous polymer contains lithium salts LiPO2F2 and metal fluorides. This coating, characterized by these characteristics, mitigates side reactions at the electrode / electrolyte interface and impedance growth during cycling, while also improving the kinetic performance of the cathode material.

[0069] The first aspect of the present invention provides a coated positive electrode material, comprising a core and a coating layer coated on at least a portion of the outer surface of the core, wherein the core contains lithium nickel oxide, and the coating layer contains a lithium-containing amorphous polymer, in which LiPO2F2 and metal fluoride are distributed.

[0070] Understandably, the coated positive electrode material includes a coating layer containing a lithium-containing amorphous polymer, in which a lithium salt LiPO2F2 and a metal fluoride are distributed. The coating layer has a CEI-like film structure, that is, the lithium-containing amorphous polymer and the lithium salt LiPO2F2 and metal fluoride distributed therein constitute an organic / inorganic composite structure; the metal fluoride can reduce the side reaction at the interface and avoid the corrosion of the positive electrode material by HF in the electrolyte. Therefore, the lithium-containing amorphous polymer and the metal fluoride with good stability distributed therein help to avoid direct contact between the core and the organic electrolyte, alleviate the electrode / electrolyte interface side reaction and impedance growth during the cycle. In addition, the lithium-containing amorphous polymer has good lithium ion transport capacity, and LiPO2F2 can form a low-impedance electrode / electrolyte interface film with high ionic conductivity and electrochemical stability. The synergistic effect of the two improves the kinetic performance of the positive electrode material and can also improve the long-cycle stability of the positive electrode material.

[0071] In some embodiments, the lithium-containing amorphous polymer includes a lithium-containing ether oligomer.

[0072] In some optional embodiments, the lithium-containing ether oligomer includes an ether oligomer containing lithium at the end group; the end group lithium ions help to reduce the transmission energy barrier of lithium ions at the interface and reduce the interface impedance.

[0073] In some optional embodiments, the repeating units of the lithium-containing ether oligomer include one or more of -CH2-O-, -CH2-CH2-O-, and -CH2-CH2-CH2-O-.

[0074] In some optional embodiments, the mass percentage of the lithium-containing ether oligomer to the mass percentage of the core is 0.05%-3%; for example, it can be but not limited to 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3% or the range between any two of the above values. When the percentage of the mass of the lithium-containing ether oligomer to the mass of the core is within the above range, it helps to improve the integrity of the coating layer and the stability of the interface between the electrode material and the electrolyte.

[0075] In some optional embodiments, the degree of polymerization of the lithium-containing ether oligomer is an integer between 1 and 10; for example, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, etc., without specific limitation.

[0076] In some optional embodiments, the average particle size D50 of the LiPO2F2 is 1 nm to 100 nm; for example, it can be, but is not limited to, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range between any two of the foregoing values. When the average particle size D50 of the LiPO2F2 is within the above range, it helps to improve the electrochemical activity of the LiPO2F2 and achieve uniform distribution of the LiPO2F2 in the lithium-containing ether oligomer.

[0077] As a possible embodiment, the mass percentage of LiPO2F2 to the mass of the core is 0.01%-3%; for example, it can be but not limited to 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3% or the range between any two of the above values. When the percentage of the mass of LiPO2F2 to the mass of the core is within the above range, it is beneficial to reduce the battery interface impedance and improve the cycle performance of the battery.

[0078] In some optional embodiments, the metal elements contained in the metal fluoride include one or more of Li, Mg, Zn, Al, Zr, Ti, Nb, V, Mo and W; the metal fluoride containing the above metal elements helps to induce the decomposition of LiPF6 to generate metal fluoride and LiPO2F2 lithium salt.

[0079] In some optional embodiments, the average particle size D50 of the metal fluoride is 1 nm to 100 nm, such as, but not limited to, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range between any two of the foregoing values. When the average particle size D50 of the metal fluoride is within the above range, it helps to achieve uniform distribution of the metal fluoride in the lithium-containing ether oligomer.

[0080] As a possible embodiment, the mass percentage of metal fluoride to the mass percentage of the inner core is 0.05%-3%; for example, it can be but not limited to 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3% or the range between any two of the above values. When the percentage of the mass of the metal fluoride to the mass of the inner core is within the above range, it is helpful to achieve uniform distribution of the metal fluoride in the lithium-containing ether oligomer and improve interface stability.

[0081] In some embodiments, in lithium nickel oxide, the molar ratio of nickel element in the total metal elements other than lithium element is 0.6-1; for example, it can be but not limited to 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or a range between any two of the above values.

[0082] In some optional embodiments, the chemical formula of lithium nickel oxide is Li a Ni b M 1-b O2, M element is a metal element, 0.9≤a≤1.1, 0.6≤b≤1.

[0083] As a possible implementation manner, the M element includes one or more of Mn, Co, Al, Mg, Sr, B, Ti, Zr, Nb, Ta and W.

[0084] In some embodiments, the coating layer has a thickness of 2 nm to 200 nm, for example, but not limited to, 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or a range between any two of the foregoing values. When the coating layer has a thickness within the foregoing range, it helps to improve the stability of the interface between the electrode material and the electrolyte.

[0085] As one possible embodiment, the average particle size D50 of the coated positive electrode material is 2 μm-18 μm; for example, it can be, but is not limited to, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or a range between any two of the foregoing values. When the average particle size D50 of the coated positive electrode material is within the above range, the positive electrode material can have higher electrochemical activity and higher compaction density.

[0086] In some optional embodiments, the specific surface area of ​​the coated positive electrode material is 0.3 m 2 / g-3.0m 2 / g; for example, but not limited to 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2m 2 / g, 2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 2.9m 2 / g、3m 2 When the specific surface area of ​​the coated positive electrode material is within the above range, the positive electrode material may have higher electrochemical activity.

[0087] In some embodiments, the water content of the coated cathode material is less than 500 ppm.

[0088] In some embodiments, the coated positive electrode material contains free lithium-containing compounds.

[0089] In some optional embodiments, the free lithium-containing compound includes one or more of free LiOH and free Li2CO3.

[0090] It should be noted that the core is a secondary particle formed by the aggregation of multiple primary particles. The "free LiOH" and "free Li2CO3" mentioned above are both unreacted residual lithium compounds existing on the surface of the coated positive electrode material or between the core primary particles.

[0091] Optionally, the content of free LiOH in the coated positive electrode material is 1500ppm-4000ppm; for example, it can be, but is not limited to, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, 3100ppm, 3200ppm, 3300ppm, 3400ppm, 3500ppm, 3600ppm, 3700ppm, 3800ppm, 3900ppm, 4000ppm, or a range between any two of the above values. When the content of free LiOH in the coated positive electrode material is within the above range, the processability of the positive electrode material can be improved.

[0092] Optionally, the content of free Li2CO3 in the coated positive electrode material is 1500ppm-4000ppm; for example, it can be, but is not limited to, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, 3100ppm, 3200ppm, 3300ppm, 3400ppm, 3500ppm, 3600ppm, 3700ppm, 3800ppm, 3900ppm, 4000ppm, or a range between any two of the above values. When the content of free Li2CO3 in the coated positive electrode material is within the above range, the processability of the positive electrode material can be improved and battery gas production can be reduced.

[0093] The second aspect of the present invention provides a method for preparing the coated positive electrode material of the first aspect, comprising the following steps: mixing a core, a reaction medium and a carbonate solution containing LiPF6, and then performing an aging reaction to form a coating layer on at least a portion of the outer surface of the core to prepare the coated positive electrode material; wherein the core contains at least one of free LiOH and free Li2CO3.

[0094] A coating layer is formed on the surface of the core through a self-limiting polymerization reaction, and the coating layer has excellent coating integrity, uniformity and mechanical stability.

[0095] It should be noted that the self-limiting polymerization reaction utilizes the free lithium compounds (LiOH and Li2CO3) in the core to induce the cleavage of the ester bond in the carbonate solvent, and the degree of polymerization reaction to form the coating layer is controlled by the free lithium content.

[0096] The free LiOH and free Li2CO3 contained in the core can induce the cleavage of the ester bond in the carbonate solvent, and the carbonate undergoes in-situ self-limiting polymerization to obtain a lithium-containing amorphous polymer coating. Taking ethylene carbonate solvent as an example, the reaction process for generating ether oligomers is as follows:

[0097] The reaction medium can induce the decomposition of LiPF6 to generate metal fluoride and LiPO2F2 lithium salt, which are embedded in the ether oligomer coating layer.

[0098] It should be noted that the core is a secondary particle formed by the aggregation of multiple primary particles. The "free LiOH" and "free Li2CO3" mentioned above are both incompletely reacted residual lithium compounds existing on the surface of the core or between the primary particles of the core.

[0099] In some embodiments, the content of free LiOH in the core is 2000 ppm-10000 ppm; for example, it can be, but is not limited to, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm, 8500 ppm, 9000 ppm, 9500 ppm, 10000 ppm, or a range between any two of the foregoing values. When the content of free LiOH in the core is within the above range, it is more conducive to the in-situ self-limiting polymerization of the carbonate solvent, thereby improving the uniformity and integrity of the coating layer.

[0100] In some embodiments, the content of free Li2CO3 in the core is 2000ppm-10000ppm; for example, it can be, but is not limited to, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000ppm, 5500ppm, 6000ppm, 6500ppm, 7000ppm, 7500ppm, 8000ppm, 8500ppm, 9000ppm, 9500ppm, 10000ppm, or a range between any two of the foregoing values. When the content of free Li2CO3 in the core is within the above range, it is more conducive to the in-situ self-limiting polymerization of the carbonate solvent, thereby improving the uniformity and integrity of the coating layer.

[0101] In some embodiments, the water content of the core is less than 500 ppm, which helps to reduce the hydrolysis side reaction of LiPF6 and avoid the generation of HF and the corrosion of HF on the positive electrode material.

[0102] As a possible embodiment, the reaction medium includes a metal oxide, and the metal elements contained in the metal oxide include one or more of Mg, Zn, Al, Zr, Ti, Nb, V, Mo, and W. Taking MgO as an example, the reaction equation with LiPF6 in the carbonate solution is as follows: 2MgO + LiPF6 → 2MgF2 + LiPO2F2.

[0103] In some optional embodiments, the mass ratio of the core to the reaction medium is 1:(0.0005-0.03); for example, it can be, but is not limited to, 1:0.0005, 1:0.001, 1:0.002, 1:0.003, 1:0.004, 1:0.005, 1:0.006, 1:0.007, 1:0.008, 1:0.009, 1:0.01, 1:0.011, 1:0.012, 1:0.013, 1:0.014, 1:0.015, 1:0.016, 1:0.017, 1:0.018, 1:0.019, 1:0.02, 1:0.021, 1:0.022, 1:0.023, 1:0.024, 1:0.025, 1:0.026, 1:0.027, 1:0.028, 1:0.029, 1:0.03, or a range between any two of the above ratios. When the mass ratio of the core to the reaction medium is within the above range, reactant residue can be reduced, which is conducive to the reaction product meeting the specified requirements.

[0104] In some embodiments, the specific surface area of ​​the reaction medium is 10 m 2 / g-100m 2 / g; for example, but not limited to 10m 2 / g、15m2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g, 60m 2 / g、65m 2 / g、70m 2 / g、75m 2 / g、80m 2 / g、85m 2 / g、90m 2 / g、95m 2 / g、100m 2 When the specific surface area of ​​the reaction medium is within the above range, it helps to increase the chemical activity of the reaction medium, accelerate the reaction rate, and help the product meet the specified requirements.

[0105] As a possible embodiment, the reaction medium includes primary particles having an average particle size D50 of 1 nm to 500 nm. For example, the average particle size D50 of the primary particles included in the reaction medium can be, but is not limited to, 1 nm, 30 nm, 50 nm, 80 nm, 100 nm, 130 nm, 150 nm, 180 nm, 200 nm, 230 nm, 250 nm, 280 nm, 300 nm, 330 nm, 350 nm, 380 nm, 400 nm, 430 nm, 450 nm, 480 nm, 500 nm, or a range between any two of the foregoing values. When the average particle size D50 of the primary particles included in the reaction medium is within the above range, it helps to increase the chemical activity of the reaction medium, accelerate the reaction rate, and help the product meet the specified requirements.

[0106] It should be noted that the “primary particles” mentioned above refer to primary particles, that is, the reaction medium includes primary particles with an average particle size D50 of 1 nm to 500 nm.

[0107] In some embodiments, the mass percentage concentration of LiPF6 in the carbonate solution is 5%-20%, for example, but not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range between any two of the foregoing values. When the mass percentage concentration of LiPF6 in the carbonate solution is within the foregoing range, residual reactants can be reduced, and the reaction product meets the specified requirements.

[0108] In some embodiments, the carbonate solvent contained in the carbonate solution includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0109] As a possible implementation method, the water content of the carbonate solution is less than 500ppm; when the water content of the carbonate solution is higher than the above range, it will affect the copolymerization process, cause side reactions, and the polymerization effect is poor; and excessive water content causes the LiPF6 solute to hydrolyze to generate HF, resulting in a high content of metal fluoride on the surface of the material.

[0110] In some embodiments, the aging reaction temperature is 20°C-80°C; for example, it can be, but is not limited to, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or a range between any two of the above values. When the aging reaction temperature is within the above range, it is conducive to the polymerization reaction of the carbonate. The aging reaction time is 6 hours to 30 hours; for example, it can be, but is not limited to, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 17 hours, 20 hours, 22 hours, 25 hours, 27 hours, 30 hours, or a range between any two of the above values.

[0111] In some embodiments, the solid content of the slurry after mixing the core, the reaction medium and the carbonate solution is 10%-80%; for example, it can be but is not limited to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or a range between any two of the above values.

[0112] In some embodiments, the method for preparing the coated positive electrode material further comprises: filtering the reaction liquid after the aging reaction, drying the solid material after the filtration, cooling and screening, to obtain the coated positive electrode material.

[0113] In some optional embodiments, the solid matter after the filtration treatment is physically dried by vibration drying under vacuum conditions.

[0114] Optionally, the vibration drying temperature is 80°C-300°C; for example, it can be but not limited to 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, or a range between any two of the above values. The vibration drying time is 5h-20h; for example, it can be but not limited to 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or a range between any two of the above values.

[0115] In some embodiments, the method for preparing the core includes: mixing a precursor with a lithium source and then calcining the mixture to prepare the core; wherein the precursor contains Ni.

[0116] In some optional embodiments, the precursor further contains M elements, and the M elements include one or more of Mn, Co, Al, Mg, Sr, B, Ti, Zr, Nb, Ta and W.

[0117] In some optional embodiments, the precursor includes at least one of oxides, hydroxides, and carbonates containing Ni, and at least one of oxides, hydroxides, and carbonates containing the M element.

[0118] In some optional embodiments, the ratio between the molar amount of lithium element contained in the lithium source and the total molar amount of Ni and M elements contained in the precursor is (1-1.15):1; for example, it can be but is not limited to 1:1, 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, 1.1:1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, 1.15:1 or a range between any two of the above values.

[0119] In some embodiments, the calcination temperature is 700°C-1000°C; for example, it can be, but not limited to, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or a range between any two of the above values. The calcination time is 8h-20h; for example, it can be, but not limited to, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or a range between any two of the above values. The heating rate of the calcination is 1°C / min-5°C / min; for example, it can be, but not limited to, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, or a range between any two of the above values.

[0120] It should be noted that the above-mentioned heating rate refers to the rate at which the temperature of the material itself rises to the calcination temperature.

[0121] A third aspect of the present invention provides a positive electrode plate, comprising the coated positive electrode material of the first aspect or the coated positive electrode material prepared by the preparation method of the second aspect.

[0122] A fourth aspect of the present invention provides a secondary battery comprising the positive electrode sheet of the third aspect.

[0123] The secondary battery of the present invention comprises the above-mentioned coated positive electrode material and has excellent kinetic performance and long cycle stability.

[0124] A fifth aspect of the present invention provides an electrical device comprising the secondary battery of the fourth aspect. The electrical device may be an electric vehicle, an electric bicycle, an electric two-wheeled vehicle, an electric vehicle power system, an energy storage system, or a mobile storage device, without limitation.

[0125] The technical solution of the present invention is described in detail below with reference to specific embodiments.

[0126] 1. Preparation of positive electrode materials

[0127] Example 1

[0128] S1. Preparation of core material: 1000gNi 0.82 Mn 0.12 Co 0.06(OH)2 (as a precursor), 910.2gLiOH·H2O (as a lithium source), 5.196gTiO2 (as a precursor), and 5.280gZrO2 (as a precursor) are mixed evenly, with a Li / Me ratio of 1.05 (where Me represents the Ni and M elements contained in the precursor). The mixed material is then placed in an oxygen furnace and calcined at 820°C for 12h with a heating rate of 3°C / min. After calcination, the product is cooled in the furnace, crushed, and sieved to obtain the core material Li 1.022 Ni 0.812 Mn 0.119 Co 0.059 Ti 0.006 Zr 0.004 O2.

[0129] S2. Preparation of mixed slurry: 1000g of the above core material was taken and mixed with 5.0g of the reaction medium Al2O3. The average particle size D50 of the primary particles of Al2O3 used was 50nm and the specific surface area was 42.4m 2 / g, and then added into 1000g of ethylene carbonate solution containing LiPF6, the LiPF6 concentration was 10wt% and stirred evenly, the water content of the ethylene carbonate solution was 350ppm; then aged at 30℃ for 24h to obtain a mixed slurry.

[0130] S3. Preparation of coated positive electrode material: The mixed slurry was filtered, and the filter cake was placed in a vacuum vibration dryer at a drying temperature of 150° C. for 16 h. After cooling, the material was sieved through a 325-mesh sieve to obtain a coated positive electrode material.

[0131] Example 2

[0132] S1. Preparation of core material: 1000gNi 0.90 Co 0.10 (OH)2 (as a precursor), 452.5g LiOH·H2O (as a lithium source) and 11.000g Al2O3 (as a precursor), 12.500g WO3 (as a precursor) are mixed evenly, with a Li / Me ratio of 1.15 (where Me represents the Ni and M elements contained in the precursor). The mixed material is then placed in an oxygen furnace and calcined at 1000℃ for 8h with a heating rate of 5℃ / min. After calcination, the product is cooled in the furnace and crushed and sieved to obtain the core material Li 1.056 Ni 0.878 Co 0.0970 Al 0.02 W 0.005 O2.

[0133] S2. Preparation of mixed slurry: 1000g of the above core material was taken and mixed with 10.0g of the reaction medium Nb2O5 and 20.0g of the reaction medium MgO. The average particle size D50 of the primary particles of Nb2O5 used was 440nm and the specific surface area was 10.3m 2 / g, the average particle size D50 of MgO primary particles is 5.5nm, and the specific surface area is 96.6m 2 / g; then added to 9000g of ethylene carbonate solution containing LiPF6, the LiPF6 concentration was 20wt% and stirred evenly, the water content of the ethylene carbonate solution was 475ppm; then aged at 20°C for 30h to obtain a mixed slurry.

[0134] S3. Preparation of coated positive electrode material: The mixed slurry was filtered, and the filter cake was placed in a vacuum vibration dryer at a drying temperature of 300° C. for 5 h. After cooling, the material was sieved through a 325-mesh sieve to obtain a coated positive electrode material.

[0135] Example 3

[0136] S1. Preparation of core material: 1000g Ni 0.90 Mn 0.06 Co 0.04 (OH)2 (as a precursor), 453.65g LiOH·H2O (as a lithium source) and 5.510g Al2O3 (as a precursor), 10.545g ZrO2 (as a precursor) are mixed evenly, with a Li / Me ratio of 1.0 (where Me represents the Ni and M elements contained in the precursor). The mixed material is then placed in an oxygen furnace and calcined at 700°C for 20h with a heating rate of 1°C / min. After calcination, the product is cooled in the furnace and crushed and sieved to obtain the core material Li 0.978 Ni 0.884 Mn 0.059 Co 0.039 Al 0.01 Zr 0.008 O2.

[0137] S2. Preparation of mixed slurry: 1000g of the above core material was taken and mixed with 0.5g of the reaction medium ZnO. The average particle size D50 of the ZnO primary particles used was 15nm and the specific surface area was 64.3m 2 / g; then added to 250 g of ethylene carbonate solution containing LiPF6, the LiPF6 concentration was 5 wt% and stirred evenly, the water content of the ethylene carbonate solution was 320 ppm; then aged at 80 ° C for 6 h to obtain a mixed slurry.

[0138] S3. Preparation of coated positive electrode material: The mixed slurry was filtered, and the filter cake was placed in a vacuum vibration dryer at a drying temperature of 80° C. for 20 h. After cooling, the material was sieved through a 325-mesh sieve to obtain a coated positive electrode material.

[0139] Example 4

[0140] S1. Preparation of core material: 1000g Ni 0.92 Mn 0.06 Co 0.02 (OH)2 (as a precursor), 475.25gLiOH·H2O (as a lithium source) and 4.480g SrO (as a precursor), 2.260g B2O3 (as a precursor) are mixed evenly, and the Li / Me ratio is 1.10 (where Me represents the Ni and M elements contained in the precursor). The mixed material is then placed in an oxygen furnace and calcined at 780℃ for 16h with a heating rate of 5℃ / min. After calcination, the furnace is cooled, and the product is crushed and sieved to obtain the core material Li 1.060 Ni 0.911 Mn 0.059 Co 0.02 Sr 0.004 B 0.006 O2.

[0141] S2. Preparation of mixed slurry: 1000g of the above core material was taken and mixed with 10.0g of the reaction medium TiO2 and 10.0g of the reaction medium ZrO2. The average particle size D50 of the TiO2 primary particles used was 25nm and the specific surface area was 68.5m 2 / g, the average particle size D50 of ZrO2 primary particles is 35nm, and the specific surface area is 46.6m 2 / g; then added to 1800 g of dimethyl carbonate solution containing LiPF6, the LiPF6 concentration was 10 wt% and stirred evenly, the water content of the dimethyl carbonate solution was 457 ppm; then aged at 35 ° C for 30 h to obtain a mixed slurry.

[0142] S3. Preparation of coated positive electrode material: The mixed slurry was filtered, and the filter cake was placed in a vacuum vibration dryer at 80° C. for 21 h. After cooling, the material was sieved through a 325-mesh sieve to obtain a coated positive electrode material.

[0143] Example 5

[0144] S1. Preparation of core material: 1000g Ni 0.92 Mn 0.04 Co 0.04(OH)2 (as a precursor), 470.08g LiOH·H2O (as a lithium source) and 11.935g Ta2O5 (as a precursor), 7.180g Nb2O5 (as a precursor) are mixed evenly, with a Li / Me ratio of 1.12 (where Me represents the Ni and M elements contained in the precursor). The mixed material is then placed in an oxygen furnace and calcined at 900°C for 12h with a heating rate of 5°C / min. After calcination, the product is cooled in the furnace and crushed and sieved to obtain the core material Li 1.065 Ni 0.91 Mn 0.04 Co 0.04 Ta 0.005 Nb 0.005 O2.

[0145] S2. Preparation of mixed slurry: 1000g of the above core material was taken and mixed with 25g of the reaction medium WO3. The average particle size D50 of the primary particles of WO3 used was 45nm and the specific surface area was 82.5m 2 / g; then added to 500 g of dimethyl carbonate solution containing LiPF6, the LiPF6 concentration was 15 wt% and stirred evenly, the water content of the dimethyl carbonate solution was 285 ppm; then aged at 50 ° C for 18 h to obtain a mixed slurry.

[0146] S3. Preparation of coated positive electrode material: The mixed slurry was filtered, and the filter cake was placed in a vacuum vibration dryer at a drying temperature of 150° C. for 9 h. After cooling, the material was sieved through a 325-mesh sieve to obtain a coated positive electrode material.

[0147] Example 6

[0148] S1. Preparation of core material: 1000g Ni 0.95 Mn 0.04 Co 0.01 (OH)2 (as a precursor), 453.35g LiOH·H2O (as a lithium source) and 5.505g Al2O3 (as a precursor) were mixed evenly with a Li / Me ratio of 1.10 (where Me represents the Ni and M elements contained in the precursor). The mixed material was then placed in an oxygen furnace and calcined at 780°C for 10 hours at a heating rate of 1°C / min. After calcination, the product was cooled in the furnace and crushed and sieved to obtain the core material Li 1.040 Ni 0.94 Mn 0.04 Co 0.01 Al 0.01 O2.

[0149] S2. Preparation of mixed slurry: 1000g of the above core material was taken and mixed with 3g of the reaction medium V2O5. The average particle size D50 of the primary particles of V2O5 used was 120nm and the specific surface area was 22.8m 2 / g; then added to 1000 g of dimethyl carbonate solution containing LiPF6, the LiPF6 concentration was 15 wt% and stirred evenly, the water content of the dimethyl carbonate solution was 229 ppm; then aged at 60 ° C for 10 h to obtain a mixed slurry.

[0150] S3. Preparation of coated positive electrode material: The mixed slurry was filtered, and the filter cake was placed in a vacuum vibration dryer at a drying temperature of 180° C. for 5 h. After cooling, the material was sieved through a 325-mesh sieve to obtain a coated positive electrode material.

[0151] Comparative Example 1

[0152] The difference between Comparative Example 1 and Example 1 is that the core material Li prepared in step S1 is 1.022 Ni 0.812 Mn 0.119 Co 0.059 Ti 0.006 Zr 0.004 O2 washing was used to reduce free lithium carbonate and free lithium hydroxide. The washing time was 1 min and the solid content was 50 wt%. The washed material was then dried at 150 ° C for 4 h to obtain the core of the high nickel positive electrode material Li 1.022 Ni 0.812 Mn 0.119 Co 0.059 Ti 0.005 Zr 0.005 O2, and then proceed to subsequent S2 and S3 processing.

[0153] Comparative Example 2

[0154] The difference between Comparative Example 2 and Example 1 is that the reaction medium Al2O3 is not added in step S2.

[0155] Comparative Example 3

[0156] The difference between Comparative Example 3 and Example 1 is that there is no LiPF6 in the ethylene carbonate solution in step S2.

[0157] Comparative Example 4

[0158] The difference between Comparative Example 4 and Example 1 is that the ethylene carbonate solvent in S2 is replaced with anhydrous ethanol solvent.

[0159] Comparative Example 5

[0160] The difference between Comparative Example 5 and Example 1 is that the water content in the ethylene carbonate solution in step S2 is 800 ppm.

[0161] It should be noted that, in the above embodiments and comparative examples, physical and chemical characterizations including at least the following items were also carried out:

[0162] The average particle size D50, specific surface area, free LiOH content, free Li2CO3 content, and water content of the core; the thickness of the coating layer, the percentage of the mass of the ether oligomer in the coating layer to the mass of the core, the percentage of the mass of the LiPO2F2 lithium salt in the coating layer to the mass of the core, the percentage of the mass of the metal fluoride in the coating layer to the mass of the core, the average particle size D50 of the coated positive electrode material, the free LiOH content and free Li2CO3 content in the coated positive electrode material, the water content in the coated positive electrode material, and the morphology of the coated positive electrode material. The results are shown in Tables 1 and 2.

[0163] It should be noted that the test methods for the physical and chemical characterizations of the above embodiments and comparative examples are as follows:

[0164] (1) Morphology characterization: The sample morphology was observed using a scanning electron microscope (SEM); ultrathin sample slices were prepared by focused ion beam (FIB) cutting, and the thickness of the surface coating layer was tested by high-resolution transmission electron microscopy (HRTEM).

[0165] (2) Test method for average particle size D50: Use a particle size analyzer to test the particle size volume distribution of each sample to obtain the average particle size D50. Before performing the particle size analysis test, the sample can be subjected to wet ultrasonic treatment with an ultrasonic time of 60 s and an ultrasonic power of 20 W.

[0166] (3) Specific surface area test method: The specific surface area of ​​each sample was measured using a specific surface area tester and a nitrogen low-temperature adsorption method.

[0167] (4) LiOH and Li2CO3 content test: refer to GB / T 41704-2022.

[0168] (5) Trace water test: The water content of the coated cathode material, core and carbonate solution material was measured by Karl-Fischer titration.

[0169] (6) ICP test: The positive electrode material sample is dissolved in HCl and prepared into a solution of a certain concentration. The content of metal elements in the material and the content of P and F in the coated high-nickel positive electrode material are tested by inductively coupled plasma atomic emission spectrometry, and the content of LiPO2F2 and metal fluoride in the coating layer is calculated.

[0170] (7) Determination of ether oligomer content: Using organic element analysis, the ether oligomers in the high-nickel composite positive electrode material are decomposed at high temperature in a pure oxygen environment, and the carbon, hydrogen and oxygen element contents are determined to obtain the corresponding ether oligomer content.

[0171] (8) Characterization of oligomer functional groups: The MALDI-TOF-MS spectra of functional groups were obtained by using a German Bruker Autoflex MALDI-TOF-MS mass spectrometer. The method was to dissolve the test sample and 2,5-dihydroxybenzoic acid (DHB) matrix in acetonitrile solvent at a sample concentration of about 10 -6 mol / L, recording positive ions, and measuring the range of 150-3000 Da. The polymerization units and degree of polymerization were calculated from the MALDI-TOF-MS spectrum.

[0172] The scanning electron microscope scan results of the coated cathode material prepared in Example 1 are shown in Figure 1. As shown in Figure 1, the coated cathode material prepared in Example 1 is composed of secondary particles formed by the agglomeration of primary particles of about 400 nm, with a particle size of about 9.0 μm. The surface of the material has a clear coating layer, which embeds lithium salt LiPO2F2 and metal fluoride particles of about 30 nm.

[0173] The characterization results of oligomer functional groups of the coated cathode material prepared in Example 1 are shown in Figure 2. As can be seen from Figure 2, the m / z spacing between adjacent peak groups in the spectrum is about 160, and the degree of polymerization is 4. This regular repetitive pattern is mainly caused by the regular site breakage of the monomers in the polymer. Combined with the reaction mechanism, it can be inferred that the copolymer contains -(CH2-CH2-O)3-CH2-O- groups and is an ether oligomer. In addition, the m / z spacing between adjacent peaks in each peak group is about 6, which is mainly due to the fact that the H at the end of the polymer is replaced by Li + The oligomer coating obtained on the surface is replaced by lithium-containing ether oligomers.

[0174] The physical and chemical characterization results of the above examples are shown in Table 1.

[0175] Table 1

[0176] The physical and chemical characterization results of the above comparative examples are shown in Table 1.

[0177] Table 2

[0178] As can be seen from the results in Table 1 and Table 2, in Comparative Example 1, since the core material was washed with water, the residual lithium compounds on the surface were reduced, and the carbonate bonds on the surface could not be induced to break to form a copolymer coating layer. In Comparative Example 2, no reaction medium was added, and in Comparative Example 3, no LiPF6 was added, and neither could form LiPO2F2 lithium salt and metal fluoride by in-situ reaction. In Comparative Example 4, the carbonate solvent was changed to anhydrous ethanol, and no copolymerization reaction occurred, and no oligomer coating layer was generated. In Comparative Example 5, the water content in the carbonate solution was too high, which affected the copolymerization process, caused side reactions, and the polymerization effect was poor. In addition, the excessive water content caused the LiPF6 solute to hydrolyze to generate HF, resulting in a high content of metal fluoride on the surface of the material.

[0179] 2. Preparation of Secondary Batteries

[0180] The electrochemical properties of the materials in the above examples and comparative examples were tested using button cells and soft-pack batteries.

[0181] The specific production method of the button battery and its positive electrode sheet is as follows: the prepared positive electrode material powder is mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 96:2:2, an appropriate amount of N-methylpyrrolidone is added as a dispersant, and the mixture is ground into a slurry; the slurry is then evenly coated on one side of an aluminum foil, vacuum dried at 120°C for 12 hours, the dried electrode sheet is rolled with a roller mill, and the aluminum foil is cut with a slicer into circular electrode sheets with a diameter of 10 mm. The loading amount of active material is controlled at 12 mg / cm 2 The half-cell was assembled in an argon atmosphere glove box with a water partial pressure ≤ 0.1 ppm and an oxygen partial pressure ≤ 0.1 ppm. Metallic lithium was used as the counter electrode, and a 1M LiPF6 (EC / DMC, 1:1 volume ratio) solution was used as the electrolyte. The assembled specifications were CR2032 button cells.

[0182] The specific production method of soft-pack batteries and their positive electrode sheets is as follows: the prepared positive electrode material powder is mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 96:2:2, an appropriate amount of N-methylpyrrolidone is added as a dispersant, and the mixture is ground into a slurry; the slurry is then coated on both sides of aluminum foil and vacuum-dried at 120°C for 12 hours. The negative electrode is composed of graphite (MCMB), Super-P, CMC, and styrene-butadiene rubber in a weight ratio of 94:2:2:2. The average load density of the positive and negative electrodes is approximately 20 mg cm -2 and 13 mg cm -2 The battery design capacity is about 1Ah, and the positive and negative electrode capacity balance N / P ratio is set at around 1.10.

[0183] 3. Performance Testing

[0184] 1. First-cycle charge / discharge capacity and rate performance test method: Coin cells were charged and discharged at room temperature using constant current charge / discharge mode, with a voltage range of 2.8-4.25V and a current density of 40mA / g, i.e., a 0.2C rate. Rate performance of the coin cells was tested using current densities of 0.5C, 2C, 5C, and 10C.

[0185] 2. Lithium ion diffusion coefficient test method: The lithium ion diffusion coefficients of button cells made of different materials were compared using electrochemical impedance spectroscopy (EIS) testing. The test frequency range was 100 kHz to 0.01 Hz, and the amplitude was 10 mV.

[0186] 3. Capacity Retention and DC Internal Resistance (DCR) Testing: Soft-pack batteries were cycled at 45°C using a constant current charge / discharge mode with a voltage range of 2.8-4.2V and a current density of 100mA / g. Capacity retention after 200 cycles = (100-cycle discharge specific capacity / first-cycle discharge specific capacity) × 100%. The DC internal resistance test was performed using the HPPC method described in the FreedomCAR project's "Power Assisted Hybrid Electric Vehicle Battery Test Manual," measuring the DC internal resistance at 50% SOC during discharge. The increase in DC internal resistance after 200 cycles = (200-cycle DCR - first-cycle DCR) / first-cycle DCR × 100%.

[0187] The first-week charge / discharge specific capacity test results and lithium ion diffusion coefficient test results of each button battery prepared above, as well as the capacity retention rate test results and DC internal resistance test structure of each soft-pack battery prepared above are shown in Table 3.

[0188] Table 3

[0189] The rate performance test results of the button cells prepared above are shown in Table 4. The rate performance test results of Example 1 and Comparative Examples 1-5 are shown in FIG3 .

[0190] Table 4

[0191] As shown in Tables 3 and 4, the positive electrode materials and positive electrode sheets prepared in Examples 1-6 have higher first-cycle coulombic efficiencies, significantly higher capacity retention rates after 200 cycles than the control samples, and significantly lower DCR growth than the control samples, demonstrating superior interfacial stability. This indicates that the coated positive electrode materials prepared by the preparation method of the present invention have lower interfacial impedance, higher first-cycle efficiencies, and superior kinetic and cycling performance.

[0192] It can be seen from the lithium ion diffusion coefficient obtained from the EIS test that the coated positive electrode material prepared by the preparation method of the present invention has a higher lithium ion diffusion coefficient and stronger reaction kinetics.

[0193] In addition, as shown in Figure 3, the rate performance tests at different current densities from 0.5C to 10C show that the discharge capacity retention rate of the coated positive electrode materials in Examples 1-6 at a high rate of 10C (10C discharge capacity / 0.5C discharge capacity) is all above 70%, which is much higher than the discharge capacity retention rate of the positive electrode materials in the comparative example at a high rate of 10C (10C discharge capacity / 0.5C discharge capacity). This shows that the coated positive electrode material prepared by the preparation method of the present invention has excellent rate performance.

[0194] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0195] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A coated positive electrode material, characterized in that: include: a core comprising lithium nickel oxide; and The coating layer is coated on at least a part of the outer surface of the inner core, and the coating layer contains a lithium-containing amorphous polymer, in which LiPO2F2 and metal fluoride are distributed.

2. The coated positive electrode material according to claim 1, characterized in that The lithium-containing amorphous polymer includes a lithium-containing ether oligomer; Optionally, the lithium-containing ether oligomer has at least one of the following characteristics: (1) The lithium-containing ether oligomer includes an ether oligomer containing lithium at the end group; (2) The repeating units of the lithium-containing ether oligomer include one or more of -CH2-O-, -CH2-CH2-O-, and -CH2-CH2-CH2-O-; (3) The mass percentage of the lithium-containing ether oligomer to the mass percentage of the core is 0.05%-3%; (4) The degree of polymerization of the lithium-containing ether oligomer is an integer between 1 and 10.

3. The coated positive electrode material according to claim 1, characterized in that: The LiPO2F2 has at least one of the following characteristics: (1) The average particle size D50 of the LiPO2F2 is 1 nm-100 nm; (2) The mass of the LiPO2F2 accounts for 0.01%-3% of the mass of the core.

4. The coated positive electrode material according to claim 1, characterized in that: The metal fluoride has at least one of the following characteristics: (1) The metal elements contained in the metal fluoride include one or more of Li, Mg, Zn, Al, Zr, Ti, Nb, V, Mo and W; (2) The average particle size D50 of the metal fluoride is 1 nm to 100 nm; (3) The mass of the metal fluoride accounts for 0.05%-3% of the mass of the inner core.

5. The coated positive electrode material according to any one of claims 1 to 4, characterized in that: In the lithium nickel oxide, the molar ratio of nickel element in the total metal elements other than lithium element is 0.6-1; Optionally, the chemical formula of the lithium nickel oxide is Li a Ni b M 1-b O2, M element is a metal element, 0.9≤a≤1.1, 0.6≤b≤1; Further optionally, the M element includes one or more of Mn, Co, Al, Mg, Sr, B, Ti, Zr, Nb, Ta and W.

6. The coated positive electrode material according to any one of claims 1 to 4, characterized in that: The coated positive electrode material has at least one of the following characteristics: (1) The thickness of the coating layer is 2nm-200nm; (2) The average particle size D50 of the coated positive electrode material is 2 μm-18 μm; (3) The specific surface area of ​​the coated positive electrode material is 0.3 m 2 / g-3.0m 2 / g; (4) The water content of the coated positive electrode material is less than 500 ppm; (5) The coated positive electrode material contains one or more of free LiOH and free Li2CO3; Optionally, the content of free LiOH in the coated positive electrode material is 1500ppm-4000ppm; Optionally, the content of free Li2CO3 in the coated positive electrode material is 1500ppm-4000ppm.

7. A method for preparing a coated positive electrode material according to any one of claims 1 to 6, characterized in that: The steps include: The core, the reaction medium and the carbonate solution containing LiPF6 are mixed and then aged to form a solid phase on at least a portion of the core. The coating layer is formed on the surface to prepare the coated positive electrode material; wherein the core contains at least one of free LiOH and free Li2CO3; Wherein, the reaction medium includes metal oxides; and the water content of the carbonate solution is less than 500 ppm.

8. The method for preparing a coated positive electrode material according to claim 7, characterized in that: The method for preparing the coated positive electrode material comprises at least one of the following conditions: (1) The content of free LiOH in the core is 2000ppm-10000ppm; (2) the content of free Li2CO3 in the core is 2000ppm-10000ppm; (3) The water content of the inner core is less than 500 ppm; (4) The metal elements contained in the metal oxide include one or more of Mg, Zn, Al, Zr, Ti, Nb, V, Mo and W; (5) The mass ratio of the core to the reaction medium is 1:(0.0005-0.03); (6) The specific surface area of ​​the reaction medium is 10m 2 / g-100m 2 / g; (7) The reaction medium comprises primary particles having an average particle size D50 of 1 nm to 500 nm; (8) The mass percentage concentration of LiPF6 in the carbonate solution is 5%-20%; (9) the carbonate solvent contained in the carbonate solution includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; (10) The aging reaction temperature is 20°C-80°C; the aging reaction time is 6h-30h; (11) The solid content of the slurry after the core, the reaction medium and the carbonate solution are mixed is 10%-80%.

9. A positive electrode sheet, characterized in that: The invention comprises the coated positive electrode material as claimed in any one of claims 1 to 6 or the coated positive electrode material prepared by the method as claimed in any one of claims 7 to 8.

10. A secondary battery, characterized in that: Comprising the positive electrode sheet as claimed in claim 9.

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