High-nickel ternary positive electrode material, preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

The application provides a high-nickel ternary positive electrode material, a preparation method of the high-nickel ternary positive electrode material, a positive electrode sheet and a lithium ion battery. The preparation method of the high-nickel ternary positive electrode material comprises the following steps: providing a high-nickel ternary positive electrode base material with a chemical general formula of Li x Ni y Co z Mn 1‑y‑z O2, 1≤x≤1.15, 0.8≤y≤0.95, 0.02≤z≤0.18; and forming a coating layer on the surface of the high-nickel ternary positive electrode base material by plasma-enhanced chemical vapor deposition in a reaction gas atmosphere containing a carbon source gas and a fluorine source gas to prepare the high-nickel ternary positive electrode material. The coating layer of LiF-Li2CO3 formed in situ on the surface of the high-nickel ternary positive electrode base material blocks the corrosion of the electrolyte by the LiF coating layer, and the Li2CO3 coating layer provides a lithium ion channel, thereby forming a 'barrier-conductor' bifunctional interface, and the interface stability and ion transmission efficiency of the high-nickel ternary positive electrode material are significantly improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a high-nickel ternary cathode material and its preparation method, cathode sheet and lithium-ion battery. Background Technology

[0002] High-nickel ternary cathode material (LiNi) x Co y Mn z O2 or LiNi x Co y Al z O2 (where x≥0.8) has become a key material for achieving high energy density in lithium-ion batteries due to its high specific capacity (≥200 mAh / g) and low cost. However, with increasing nickel content, the material faces the following serious challenges: high content of residual alkalis such as LiOH and Li2CO3 on the material surface, and the original residual alkalis on the material surface are discontinuous, uneven, and have high impedance, which are harmful residual alkalis. Specifically, LiOH and Li2CO3 easily react with LiPF6 in the electrolyte to generate HF, leading to the dissolution of transition metals, gas evolution, and increased interfacial impedance; Ni 2+ (0.069 nm) and Li + The similar ionic radii (0.076 nm) lead to Li / Ni mixing, and the anisotropic volume change during charging and discharging generates microcracks, accelerating electrolyte erosion. High-nickel materials are prone to undergoing a transformation from layered structure to rock salt phase under high temperature or high voltage, releasing oxygen and causing safety hazards.

[0003] To overcome the above problems, traditional modifications, such as single coating layers like Al2O3 and Li3PO4, can suppress interfacial side reactions. However, traditional wet coating requires high-temperature sintering (≥500℃), which easily damages the material structure and results in poor uniformity. Atomic layer deposition (ALD) technology is costly and difficult to scale up. Fluorides such as LiF and AlF3 have high lithium-ion transference numbers (>0.9) and HF removal capabilities, but when these fluorides are used as sole coatings, their electronic conductivity is low, which may increase interfacial impedance. Therefore, it is difficult to achieve both interfacial stability and ion transport efficiency in cathode materials obtained by single-coating modifications on the surface of high-nickel ternary cathode materials. Summary of the Invention

[0004] Therefore, since a single coating on the surface of a high-nickel ternary cathode material cannot simultaneously ensure interface stability and ion transport efficiency, this application provides a high-nickel ternary cathode material, its preparation method, cathode sheet, and lithium-ion battery that can simultaneously ensure interface stability and ion transport efficiency by forming a composite coating containing LiF and Li2CO3 on the surface of a high-nickel ternary cathode substrate.

[0005] This application provides a method for preparing a high-nickel ternary cathode material, including the following steps:

[0006] A high-nickel ternary cathode substrate is provided; the chemical formula of the high-nickel ternary cathode substrate is Li. x Ni y Co z Mn 1-y-z O2, 1≤x≤1.15, 0.8≤y≤0.95, 0.02≤z≤0.18;

[0007] The high-nickel ternary cathode substrate is placed in a reaction gas atmosphere containing carbon source gas and fluorine source gas, and a coating layer is formed on the surface of the high-nickel ternary cathode substrate by plasma-enhanced chemical vapor deposition. The coating layer consists of LiF and Li2CO3 in a molar ratio of (0.7~2):1, thus preparing the high-nickel ternary cathode material.

[0008] In one embodiment, the reactant gas satisfies one or more of the following conditions:

[0009] (1) The volume ratio of the carbon source gas to the fluorine source gas is (10~20):(5~15);

[0010] (2) The carbon source gas includes one or more of carbon dioxide and trifluoromethane;

[0011] (3) The fluorine source gas includes one or more of carbon tetrafluoride, nitrogen trifluoride and hexafluoroethane.

[0012] In one embodiment, the plasma-enhanced chemical vapor deposition satisfies one or more of the following conditions:

[0013] (1) The reaction temperature is 100℃~250℃;

[0014] (2) The reaction pressure is 10 Pa to 500 Pa;

[0015] (3) The reaction time is 10 min to 60 min;

[0016] (4) The power output of the radio frequency plasma is 100W~250W;

[0017] (5) The rotation speed of the high-nickel ternary cathode substrate is 100 r / min to 200 r / min.

[0018] In one embodiment, the method for preparing the high-nickel ternary cathode substrate includes the following steps:

[0019] The high-nickel ternary precursor is mixed with a lithium source and then sintered to prepare the high-nickel ternary cathode substrate.

[0020] The chemical formula of the high-nickel ternary precursor is Niy Co z Mn 1-y-z (OH)2, 0.8≤y≤0.95, 0.02≤z≤0.18, the molar ratio of the metal element in the high-nickel ternary precursor to the lithium element in the lithium source is 1:(1.03~1.15).

[0021] In one embodiment, one or both of the following conditions are met:

[0022] (1) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate;

[0023] (2) The median particle size of the high-nickel ternary precursor is 5μm≤D50≤14μm.

[0024] In one embodiment, the sintering process includes a first sintering process and a second sintering process, satisfying one or more of the following conditions:

[0025] (1) The temperature of the first sintering treatment is 400℃~600℃;

[0026] (2) The first sintering treatment takes 3 to 8 hours;

[0027] (3) The temperature of the second sintering treatment is 700℃~850℃;

[0028] (4) The second sintering treatment takes 6 to 20 hours;

[0029] (5) The sintering process is carried out in an oxygen environment.

[0030] This application also provides a high-nickel ternary cathode material, which is prepared according to the above-described method for preparing high-nickel ternary cathode materials.

[0031] In one embodiment, the thickness of the coating layer is 6 nm to 15 nm.

[0032] Furthermore, this application provides a positive electrode sheet, including the high-nickel ternary positive electrode material as described above.

[0033] Furthermore, this application also provides a lithium-ion battery, including the positive electrode as described above.

[0034] Compared with the prior art, this application has the following advantages:

[0035] The method for preparing high-nickel ternary cathode material provided in this application utilizes a LiF-Li2CO3 coating layer formed in situ on the surface of the high-nickel ternary cathode substrate. The LiF coating layer blocks electrolyte corrosion, while the Li2CO3 coating layer provides lithium-ion channels, forming a "barrier-conductor" dual-functional interface, which significantly improves the interface stability and ion transport efficiency of the high-nickel ternary cathode material. Detailed Implementation

[0036] To facilitate understanding of this application, it 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 complete understanding of the disclosure of this application.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0038] As used herein, the term "and / or" encompasses any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" includes three parallel options: A, B, and "a combination of A and B".

[0039] In this document, unless otherwise stated, "one or more" means any one of the listed items or any combination of the listed items. Similarly, "one or more" and other instances of "one or more" are to be understood in the same way unless otherwise stated.

[0040] In this document, terms such as "further," "even further," "especially," "for example," "like," "example," and "exemplary" are used for descriptive purposes to indicate a connection in the coverage of different technical solutions presented earlier and later. However, they should not be construed as limitations on the preceding technical solution or on the scope of protection of this document. Unless otherwise specified, in this document, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0041] In this document, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "present" or "absent." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. In this application, descriptions such as "optionally contains" and "optionally includes" indicate "contains or does not contain." "Optional component X" indicates whether component X exists or does not exist, or whether component X is contained or not.

[0042] In this document, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood as not constituting a closed limitation on quantity.

[0043] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0044] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0045] The present application will be further described in detail below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0046] In the specific embodiments described below, the measurement parameters of the raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. For temperature and time parameters, acceptable deviations due to instrument testing accuracy or operational precision are permissible. "Ambient temperature" refers to 25°C; "atmospheric pressure" refers to 100 kPa or 101 kPa.

[0047] In this application, primary particles and secondary particles have the same meanings known in the art. "Primary particle" refers to a non-agglomerated particle. "Secondary particle" refers to an aggregated particle composed of two or more primary particles. Primary and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0048] "Primary particle size" refers to the statistical result obtained by randomly selecting 100 primary particles as a sample from the SEM image. The average value of the longest and shortest diagonals of each single crystal particle is taken as its particle size.

[0049] "Grain" refers to a single crystal or a single crystal in a single-crystal material, wherein the lattice of a single crystal is continuous and uninterrupted to its edge, and has no internal grain boundaries.

[0050] "Grain boundary" refers to a defect in the crystal structure of a grain. In polycrystalline materials, defects form an interface between two grains or microcrystals.

[0051] "Porosity" refers to the percentage of pore volume in a precursor to the total volume of the precursor under natural conditions.

[0052] "Particle size D10" refers to the particle size value corresponding to a cumulative particle size distribution percentage of 10%; "Particle size D50" refers to the particle size value corresponding to a cumulative particle size distribution percentage of 50%; and "Particle size D90" refers to the particle size value corresponding to a cumulative particle size distribution percentage of 90%. These values ​​can be measured using testing methods known in the art. For example, the national standard GB / T19077-2016 can be referenced, using a Malvern laser particle size analyzer for characterization testing.

[0053] "Diameter distance" refers to (D90-D10) / D50.

[0054] Specific surface area refers to the total surface area per unit mass of material. Specific surface area can be tested using methods well known to those skilled in the art. For example, the specific surface area of ​​a precursor can be calculated using the multi-point Brunauer-Emmett-Teller method after measuring the nitrogen isothermal adsorption-desorption curve of the material with a fully automated gas adsorption analyzer.

[0055] This application provides a method for preparing a high-nickel ternary cathode material, including the following steps:

[0056] We provide high-nickel ternary cathode substrates; the general chemical formula of the high-nickel ternary cathode substrate is Li. x Ni y Co z Mn 1-y-z O2, 1≤x≤1.15, 0.8≤y≤0.95, 0.02≤z≤0.18;

[0057] A high-nickel ternary cathode substrate is placed in a reaction gas atmosphere containing carbon source gas and fluorine source gas, and a coating layer is formed on the surface of the high-nickel ternary cathode substrate by plasma-enhanced chemical vapor deposition. The coating layer consists of LiF and Li2CO3 in a molar ratio of (0.7~2):1, thus preparing a high-nickel ternary cathode material.

[0058] This application utilizes a LiF-Li2CO3 coating layer formed in situ on the surface of a high-nickel ternary cathode substrate. The LiF coating layer blocks electrolyte corrosion, while the Li2CO3 coating layer provides lithium-ion channels, forming a "barrier-conductor" dual-functional interface, which significantly improves the interface stability and ion transport efficiency of the high-nickel ternary cathode material.

[0059] Specifically, the coating material may include, but is not limited to, LiF and Li2CO3 with molar ratios of 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1.

[0060] In some specific examples, the volume ratio of carbon source gas to fluorine source gas in the reaction gas is (10~20): (5~15). By utilizing the plasma activation characteristics of carbon source gas and fluorine source gas, a one-step in-situ composite coating of high-nickel ternary cathode substrate can be achieved, avoiding interface contamination caused by multi-step processes.

[0061] Understandably, the reaction gas atmosphere also includes diluent gases, and the volume ratio of carbon source gas, fluorine source gas, and diluent gas in the reaction gas is (10~20): (5~15): (65~85). Further, the diluent gases include one or more of argon, nitrogen, helium, and neon.

[0062] In some specific examples, the carbon source gas includes one or both of carbon dioxide and trifluoromethane (CHF3).

[0063] In some specific examples, the fluorine source gas includes one or more of carbon tetrafluoride (CF4), nitrogen trifluoride (NF3), and hexafluoroethane (C2H6).

[0064] In some specific examples, the reaction temperature in plasma-enhanced chemical vapor deposition is 100°C to 250°C. Specifically, the reaction temperature may be, but is not limited to, 100°C, 115°C, 130°C, 145°C, 160°C, 175°C, 190°C, 205°C, 220°C, 235°C, or 250°C.

[0065] In some specific examples, the reaction gas pressure in plasma-enhanced chemical vapor deposition is 10 Pa to 500 Pa. Specifically, the reaction gas pressure can be, but is not limited to, 10 Pa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, 250 Pa, 300 Pa, 350 Pa, 400 Pa, 450 Pa, or 500 Pa.

[0066] In some specific examples, the reaction time in plasma-enhanced chemical vapor deposition is 10 min to 60 min. Specifically, the reaction time can be, but is not limited to, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0067] In some specific examples, the power output of the radio frequency plasma in plasma-enhanced chemical vapor deposition is 100W to 250W. The power output of the radio frequency plasma can be, but is not limited to, 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W, 200W, 210W, 220W, 230W, 240W, or 250W.

[0068] In some specific examples, the high-nickel ternary cathode substrate is placed in the plasma reaction chamber, and the rotation speed of the plasma reaction chamber is controlled at 100 r / min to 200 r / min. Understandably, the rotation speed of the plasma reaction chamber, i.e., the rotation speed of the high-nickel ternary cathode substrate, can be, but is not limited to, 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, or 200 r / min.

[0069] It is evident that the plasma treatment in the above preparation method has a low temperature and mild reaction conditions, avoiding damage to the material structure caused by high temperature, ensuring safety, and improving the cycle life of the material while reducing energy consumption by more than 30%.

[0070] Understandably, plasma-enhanced chemical vapor deposition (PECVD) also includes cooling to room temperature in an inert gas atmosphere to prepare high-nickel ternary cathode materials. The inert gas may be, but is not limited to, one or more of argon, nitrogen, helium, and neon.

[0071] In some specific examples, the preparation method of the high-nickel ternary cathode substrate includes the following steps:

[0072] A high-nickel ternary cathode substrate is prepared by mixing a high-nickel ternary precursor with a lithium source and then sintering the mixture.

[0073] The chemical formula of the high-nickel ternary precursor is Ni. y Co z Mn 1-y-z (OH)₂, 0.8≤y≤0.95, 0.02≤z≤0.18, the molar ratio of the metal element in the high-nickel ternary precursor to the lithium element in the lithium source is 1:(1.03~1.15). The molar ratio of the metal element in the high-nickel ternary precursor to the lithium element in the lithium source can be, but is not limited to, 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 or 1:1.15.

[0074] In some specific examples, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0075] In some specific examples, the median particle size of the high-nickel ternary precursor is 5 μm ≤ D50 ≤ 14 μm. Understandably, the median particle size D50 of the high-nickel ternary precursor can be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or 14 μm.

[0076] In some specific examples, the sintering process includes a first sintering process and a second sintering process. Understandably, all of the above sintering processes are carried out in an oxygen atmosphere.

[0077] Furthermore, the temperature of the first sintering treatment is 400℃~600℃; the time of the first sintering treatment is 3h~8h. The temperature of the first sintering treatment can be, but is not limited to, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, or 600℃. The time of the first sintering treatment can be, but is not limited to, 3h, 4h, 5h, 6h, 7h, or 8h.

[0078] Furthermore, the temperature of the second sintering treatment is 700℃~850℃; the time of the second sintering treatment is 6h~20h. The temperature of the second sintering treatment can be, but is not limited to, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃.

[0079] This application also provides a high-nickel ternary cathode material, which is prepared according to the above-described method for preparing high-nickel ternary cathode materials.

[0080] Furthermore, the thickness of the coating layer in the high-nickel ternary cathode material is 6 nm to 15 nm. Specifically, the thickness of the coating layer in the high-nickel ternary cathode material can be, but is not limited to, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, or 15 nm.

[0081] Furthermore, this application provides a positive electrode sheet, including the high-nickel ternary positive electrode material as described above.

[0082] Specifically, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side of the surface of the positive current collector, wherein the positive active layer includes the aforementioned high-nickel ternary positive electrode material.

[0083] In some specific examples, the positive electrode active layer also includes a positive electrode conductive agent and a positive electrode binder.

[0084] Understandably, positive current collectors include metal foil materials and composite current collectors. Composite current collectors have a sandwich-like sandwich structure, with the middle polymer layer mainly consisting of materials such as high-molecular insulating resin. Metal layers are deposited on both sides of the middle polymer layer by electroplating, chemical plating, or other methods. Schematic, the high-molecular resin includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamide-imide, polycarbonate, and cyclic polymers. The material is selected from one or more of the following: olefins, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone and its derivatives, sodium carboxymethyl cellulose, styrene-butadiene rubber, fluorinated rubber, polyvinyl alcohol, or polyvinylidene fluoride. The metal layer is selected from at least one of aluminum, copper, nickel, cobalt, tungsten, tin, lead, iron, silver, or gold. Further, the current collector is aluminum foil.

[0085] Understandably, the positive electrode conductive agent includes at least one of carbon nanotubes, conductive carbon, graphite, acetylene black, metal fibers, organic conductive polymers, graphene, conductive carbon black (super-P), Ketjen black, carbon dots, and carbon nanofibers.

[0086] Understandably, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyurethane, PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0087] Fourthly, this application provides a lithium-ion battery, including the aforementioned positive electrode.

[0088] As is understandable, lithium-ion batteries also include negative electrode plates, separators, and electrolytes.

[0089] In some specific examples, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder.

[0090] Understandably, the negative electrode current collector can be a conventional metal foil or a composite current collector; for example, a metal material can be deposited on a polymer substrate to form a composite current collector. As an example, the negative electrode current collector can be copper foil.

[0091] Understandably, the negative electrode active material includes, but is not limited to, one or more of the following: artificial graphite, natural graphite, hard carbon materials, soft carbon, silicon-based materials, and tin-based materials. Among these, silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds, such as silicon suboxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. All of these materials are commercially available.

[0092] Understandably, negative electrode conductive agents include, but are not limited to, carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials may include particles such as carbon black, graphite, super-P, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fibers and nanotubes, graphene, etc. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene)polysulfonated styrene, etc.

[0093] Understandably, the negative electrode binder includes, but is not limited to, any one or a combination of at least two of the following: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyoxymethylene (POM), polycarbonate (PC), polyamide (PA), acrylic plastics, other polyolefins and their copolymers, polysulfone, polyphenylene ether (PPO), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC).

[0094] It should be noted that this application does not impose any particular restriction on the type of diaphragm; any well-known porous diaphragm with good chemical and mechanical stability can be selected. It is understood only that the diaphragm material can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular restriction. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular restriction.

[0095] In some specific examples, the electrolyte may be, but is not limited to, a solid electrolyte or a liquid electrolyte.

[0096] Furthermore, the electrolyte includes an electrolyte salt and a solvent.

[0097] Understandably, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0098] Understandably, the solvent includes one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0099] In some specific examples, the electrolyte also includes additives. These additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as additives that improve battery overcharge performance, high-temperature performance, and low-temperature performance.

[0100] The following are specific embodiments. They are intended to provide a more detailed description of this application to help those skilled in the art and researchers better understand it. The technical conditions described do not constitute any limitation on this application. Any modifications made within the scope of the claims of this application are protected by the claims.

[0101] Unless otherwise stated, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods. Experimental methods not specifying particular conditions in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0102] Example 1

[0103] This embodiment provides a method for preparing a high-nickel ternary cathode material, including the following steps:

[0104] (1) Preparation of LiNi 0.8 Co 0.1 Mn 0.1 O2 substrate: Ni with a particle size D50 of 8μm 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor and LiOH·H₂O were mixed at a molar ratio of 1:1.06, pre-calcined at 500℃ for 5 h in an oxygen atmosphere, and then sintered at 750℃ for 12 h to obtain LiNi. 0.8 Co 0.1 Mn 0.1 O2 substrate;

[0105] (2) For LiNi 0.8 Co 0.1 Mn 0.1 Plasma treatment of O2 substrate: LiNi 0.8 Co 0.1 Mn 0.1 The O2 substrate was placed in a plasma reaction chamber, evacuated to 10 Pa, and a CO2 / CF4 / Ar mixed gas (volume ratio 15%:10%:75%) was introduced, adjusting the pressure to 150 Pa. The temperature was raised to 120 °C, and the radio frequency plasma power supply (150 W) was started. The reaction chamber was rotated at 150 r / min for 20 min. After treatment, it was cooled to room temperature under an Ar atmosphere to prepare a high-nickel ternary cathode material.

[0106] Example 2

[0107] The difference between this embodiment and Embodiment 1 is that the volume ratio of the carbon source gas and the fluorine source gas is changed: the volume ratio of the CO2 / CF4 / Ar mixed gas is 20%:5%:75% to prepare a high-nickel ternary cathode material.

[0108] Example 3

[0109] The difference between this embodiment and Embodiment 1 is that the volume ratio of the carbon source gas and the fluorine source gas is changed: the volume ratio of the CO2 / CF4 / Ar mixed gas is 10%:15%:75% to prepare a high-nickel ternary cathode material.

[0110] Example 4

[0111] The difference between this embodiment and Embodiment 1 is that the volume ratio of the fluorine source gas to a mixture of NF3:CO2 / NF3 / Ar is changed to 15%:10%:75% to prepare a high-nickel ternary cathode material.

[0112] Example 5

[0113] The difference between this embodiment and Embodiment 1 is that the volume ratio of the fluorine source gas to a mixture of C2F6:CO2 / C2F6 / Ar is changed to 15%:10%:75% to prepare a high-nickel ternary cathode material.

[0114] Example 6

[0115] The difference between this embodiment and Embodiment 1 is that the plasma treatment is changed to 40 min to prepare high-nickel ternary cathode material.

[0116] Example 7

[0117] This embodiment provides a method for preparing a high-nickel ternary cathode material, including the following steps:

[0118] (1) Preparation of LiNi 0.8 Co 0.1 Mn 0.1 O2 substrate: Ni with a particle size D50 of 5μm 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor and LiOH·H₂O were mixed at a molar ratio of 1:1.03, pre-calcined at 400℃ for 8 hours in an oxygen atmosphere, and then sintered at 850℃ for 6 hours to obtain LiNi. 0.8 Co 0.1 Mn 0.1 O2 substrate;

[0119] (2) For LiNi 0.8 Co 0.1 Mn 0.1Plasma treatment of O2 substrate: LiNi 0.8 Co 0.1 Mn 0.1 The O2 substrate was placed in a plasma reaction chamber, and the vacuum was evacuated to below 10 Pa. A CO2 / CF4 / Ar mixed gas (volume ratio 15%:10%:75%) was introduced, and the pressure was adjusted to 10 Pa. The temperature was raised to 250 °C, and the radio frequency plasma power supply (power 250 W) was started. The reaction chamber was rotated at 200 r / min for 10 min. After treatment, it was cooled to room temperature under an Ar atmosphere to prepare a high-nickel ternary cathode material.

[0120] Example 8

[0121] This embodiment provides a method for preparing a high-nickel ternary cathode material, including the following steps:

[0122] (1) Preparation of LiNi 0.8 Co 0.1 Mn 0.1 O2 substrate: Ni with a particle size D50 of 14μm 0.8 Co 0.1 Mn 0.1 (OH)₂ precursor and LiOH·H₂O were mixed at a molar ratio of 1:1.15, pre-calcined at 600℃ for 3 h in an oxygen atmosphere, and then sintered at 700℃ for 20 h to obtain LiNi. 0.8 Co 0.1 Mn 0.1 O2 substrate;

[0123] (2) For LiNi 0.8 Co 0.1 Mn 0.1 Plasma treatment of O2 substrate: LiNi 0.8 Co 0.1 Mn 0.1 The O2 substrate was placed in a plasma reaction chamber, evacuated to 10 Pa, and a CO2 / CF4 / Ar mixed gas (volume ratio 15%:10%:75%) was introduced, adjusting the pressure to 500 Pa. The temperature was raised to 100 °C, and the radio frequency plasma power supply (100 W) was started. The reaction chamber was rotated at 100 r / min for 60 min. After treatment, it was cooled to room temperature under an Ar atmosphere to prepare a high-nickel ternary cathode material.

[0124] Comparative Example 1

[0125] The difference between this comparative example and Example 1 is that no carbon source gas is introduced; instead, argon gas is used to make up the difference. The volume ratio of the CF4 / Ar mixed gas is 10%:90%, and a high-nickel ternary cathode material with a pure LiF coating is prepared.

[0126] Comparative Example 2

[0127] The difference between this comparative example and Example 1 is that no fluorine source gas is introduced; instead, argon gas is used to make up the gas. The volume ratio of the CO2 / Ar mixed gas is 15%:85%, and a high-nickel ternary cathode material with a pure / rich Li2CO3 coating layer is prepared.

[0128] Comparative Example 3

[0129] The difference between this comparative example and Example 1 is that no carbon source gas is introduced, only C2F6 is introduced, and the volume ratio of the C2F6 / Ar mixed gas is 25%:75% to prepare a high-nickel ternary cathode material.

[0130] Comparative Example 4

[0131] The difference between this comparative example and Example 1 is that the volume ratio of the carbon source gas and the fluorine source gas is changed: the volume ratio of the CO2 / CF4 / Ar mixed gas is 5%:20%:75% to prepare a high-nickel ternary cathode material.

[0132] Comparative Example 5

[0133] The difference between this comparative example and Example 1 is that the plasma treatment temperature is 300°C, and a high-nickel ternary cathode material is prepared.

[0134] Comparative Example 6

[0135] The difference between this comparative example and Example 1 is that the alternative cathode material is LiFePO4, and the cathode material is prepared accordingly.

[0136] Performance testing and results analysis

[0137] The positive electrode materials prepared in the above examples and comparative examples were subjected to electrical performance tests according to the following method: The positive electrode material prepared above, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5 to form a slurry, which was then coated onto aluminum foil and pressed into a positive electrode sheet by a drying roller. A CR2032 coin cell was assembled using a lithium metal sheet as the negative electrode and Celgard 2325 as the separator. The electrolyte was 1M LiPF6 in EC:EMC:DMC = 1:1:1 (vol%).

[0138] Electrochemical testing:

[0139] Rate performance: Discharge specific capacity cycle performance was tested at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C within a voltage window of 2.8-4.3V. Capacity retention was calculated after 200 cycles at 1C rate.

[0140] Ion transport efficiency assessment: The lithium-ion diffusion coefficient (DLi) can be measured using galvanostatic intermittent titration (GITT). + The results are shown in Table 1 below.

[0141] Table 1

[0142]

[0143] As can be seen from the above embodiments, the composition of the coating layer can be changed by adjusting the selection of carbon and fluorine source gases, the volume relationship between the gases, the plasma treatment time, and the preparation parameters. The lithium-ion battery containing the cathode material of the embodiments retains a capacity of over 91%, and the ion transport efficiency can reach up to 6.2 × 10⁻⁶. -12 cm 2 It has a high discharge capacity under multiple discharge rate conditions and good rate performance.

[0144] Compared to Example 1, Example 2 saw an increase in the proportion of Li2CO3 and a decrease in the proportion of LiF in the coating layer due to the relatively sufficient supply of carbon source (CO2) and reduced supply of fluorine source (CF4) after adjusting the gas source ratio. The ratio of LiF to Li2CO3 decreased from 1.2:1 to 0.7:1, and the coating layer thickness increased from 8 nm to 10 nm due to the accumulation of reaction products. Therefore, in the electrochemical performance test, the low-rate (0.1C~1C) discharge capacity decreased slightly, and the high-rate (2C / 5C) performance decreased significantly. The 5C discharge capacity decreased by 8.1% compared to Example 1, and the capacity retention rate decreased to 92.5%. This may be because although Li2CO3 has better ionic conductivity than LiF, the increased coating layer thickness significantly prolonged the lithium-ion diffusion path; at the same time, the decreased LiF proportion weakened the electrolyte corrosion resistance of the coating layer, and the combined effect of these two factors led to a decrease in overall performance. In Example 3, due to the adjustment of the gas source ratio, the supply of fluorine source (CF4) was sufficient while the supply of carbon source (CO2) was insufficient. This resulted in an increase in the proportion of LiF and a decrease in the proportion of Li2CO3 in the coating layer. The ratio of LiF to Li2CO3 increased from 1.2:1 to 2.0:1, and the thickness of the coating layer decreased from 8 nm to 6 nm due to the more intense reaction of the fluorine source. Therefore, in the electrochemical performance test, the discharge capacity at low rates (0.1C~1C) remained basically the same, while the performance at high rates (2C / 5C) decreased slightly. Specifically, the 5C discharge capacity decreased by 1.8% compared to Example 1, and the ion transport efficiency decreased to 4.9 × 10⁻⁶. -12 cm 2 / s, with a capacity retention of 93.8%. This is mainly because LiF itself has poor ionic conductivity, and its high proportion offsets the diffusion advantage brought about by the thinning of the coating layer. The insufficient initial ionic conductivity limits the rate performance. Although the additional LiF generated by the subsequent reaction of Li2CO3 with HF decomposed in the electrolyte can improve the interfacial stability, it cannot make up for the initial conduction defects.

[0145] Compared to Example 1, Example 4, by replacing the fluorine source with NF3, adjusted the coating composition to LiF:Li2CO3 = 1.5:1 and reduced the thickness to 7 nm. In electrochemical performance testing, high-rate (2C / 5C) performance showed a slight improvement, with the 5C discharge capacity increasing by 1.3% compared to Example 1, the capacity retention rate rising to 94.0%, and the ion transport efficiency only slightly decreasing. This is mainly because NF3 has high reactivity, resulting in a more uniform and dense coating layer; the increased LiF content enhances the electrolyte's corrosion resistance; and the reduced thickness shortens the lithium-ion diffusion path.

[0146] Compared to Example 1, Example 5 changed the fluorine source to C2F6, adjusted the coating composition to a LiF:Li2CO3 ratio of 1:1, and increased the thickness to 9 nm. In electrochemical performance testing, high-rate (2C / 5C) performance decreased, with the 5C discharge capacity decreasing by 3.7% compared to Example 1, and the ion transport efficiency dropping to 5.0 × 10⁻⁶. -12 cm 2 / s, with a capacity retention of 93.2%. This is mainly because carbon impurities disrupt the ion conduction channels of the coating layer. At the same time, the coating layer thickens and the proportion of Li2CO3 increases, leading to a simultaneous decrease in rate capability and cycling performance.

[0147] Compared to Example 1, Example 6, by extending the processing time to 40 min, adjusting the coating composition to a ratio of LiF:Li₂CO₃ = 1.5:1, and increasing the coating thickness to 12 nm, showed a significant decrease in performance at all rates during electrochemical performance testing. Specifically, the 5C discharge capacity decreased by 14.2% compared to Example 1, and the ion transport efficiency dropped to 4.5 × 10⁻⁶. -12 cm 2 / s, with a capacity retention of 92.3%. This is mainly because the excessively thick coating layer significantly prolongs the lithium-ion diffusion path, and the overgrown coating layer is prone to peeling and cracking, failing to effectively isolate the contact between the electrolyte and the positive electrode substrate, and instead exacerbating the interfacial side reactions.

[0148] Compared to Example 1, Example 7 used a precursor with a smaller particle size and adjusted parameters to maintain the coating thickness at 8 nm. The corresponding rate performance showed a slight increase in the 0.1C discharge capacity to 213.2 mAh / g, the 0.2C discharge capacity to 208.5 mAh / g, and the 0.5C discharge capacity to 203.3 mAh / g. This indicates a certain degree of optimization in high-rate performance, with the ion transport efficiency increasing to 6.1 × 10⁻⁶. -12 cm 2 / s, with a capacity retention rate of 95.1%. This is mainly because the small particle size substrate has a larger specific surface area, which is conducive to the uniform adhesion of the coating layer. The thin coating layer significantly reduces the ion diffusion resistance, and the reasonably composed coating layer takes into account both ion conductivity and interface stability.

[0149] Compared to Example 1, Example 8 used a precursor with a larger particle size and increased the coating thickness to 15 nm after parameter adjustments. The corresponding rate performance showed a significant decrease in discharge capacity: 208.9 mAh / g at 0.1C, 204.1 mAh / g at 0.2C, and 195.2 mAh / g at 0.5C. High-rate performance degradation was significant, and ion transport efficiency and capacity retention also decreased markedly, with the ion transport efficiency reaching only 3.7 × 10⁻⁶. -12 cm 2 / s, with a capacity retention rate of 91.1%. This is mainly because the plasma dissociation efficiency is low under high voltage and low power, the fluorine source and carbon source do not react sufficiently, and the coating layer has many defects and is prone to falling off and failure. It cannot prevent electrolyte corrosion and seriously hinders lithium ion transport.

[0150] Although the gas sources selected in Comparative Examples 1 and 3 contained C and F elements, they could not form ideal LiF and Li₂CO₃ materials, resulting in a certain degree of decrease in capacity retention and ion transport efficiency, as well as a certain degree of decrease in rate performance. This shows that only specific gases can achieve a coating layer composed of LiF and Li₂CO₃. In Comparative Example 2, only carbon dioxide was used, resulting in a single Li₂CO₃ coating layer, which could not improve the ion transport efficiency and capacity retention of this electrode material. In Comparative Example 4, the proportion of LiF and Li₂CO₃ materials in the coating layer was too high, and the coating layer was too thick, resulting in a significant decrease in ion transport efficiency, only 1.8 × 10⁻⁶. -12 cm 2 / s, with a capacity retention rate of only 82.4%. The uneven coating in Comparative Example 5 and the lack of effective coating in Comparative Example 6 resulted in a significant decrease in the rate performance, ion transport efficiency, and capacity retention rate of the lithium-ion battery using this electrode material. It is evident that only by forming a coating layer of LiF and Li₂CO₃ with a specific composition and ratio, creating a "barrier-conductor" bifunctional interface, can the rate performance, interface stability, and ion transport efficiency of the cathode material be effectively improved.

[0151] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0152] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a high-nickel ternary cathode material, characterized in that, Includes the following steps: A high-nickel ternary cathode substrate is provided; the chemical formula of the high-nickel ternary cathode substrate is Li. x Ni y Co z Mn 1-y-z O2, 1≤x≤1.15, 0.8≤y≤0.95, 0.02≤z≤0.18; The high-nickel ternary cathode substrate is placed in a reaction gas atmosphere containing carbon source gas and fluorine source gas, and a coating layer is formed on the surface of the high-nickel ternary cathode substrate by plasma-enhanced chemical vapor deposition. The coating layer consists of LiF and Li2CO3 in a molar ratio of (0.7~2):1, thus preparing the high-nickel ternary cathode material.

2. The method for preparing the high-nickel ternary cathode material as described in claim 1, characterized in that, The reactant gas satisfies one or more of the following conditions: (1) The volume ratio of the carbon source gas to the fluorine source gas is (10~20):(5~15); (2) The carbon source gas includes one or more of carbon dioxide and trifluoromethane; (3) The fluorine source gas includes one or more of carbon tetrafluoride, nitrogen trifluoride and hexafluoroethane.

3. The method for preparing the high-nickel ternary cathode material as described in claim 1, characterized in that, The plasma-enhanced chemical vapor deposition satisfies one or more of the following conditions: (1) The reaction temperature is 100℃~250℃; (2) The reaction pressure is 10 Pa to 500 Pa; (3) The reaction time is 10 min to 60 min; (4) The power output of the radio frequency plasma is 100W~250W; (5) The rotation speed of the high-nickel ternary cathode substrate is 100 r / min to 200 r / min.

4. The method for preparing the high-nickel ternary cathode material according to any one of claims 1 to 3, characterized in that, The preparation method of the high-nickel ternary cathode substrate includes the following steps: The high-nickel ternary precursor is mixed with a lithium source and then sintered to prepare the high-nickel ternary cathode substrate. The chemical formula of the high-nickel ternary precursor is Ni y Co z Mn 1-y-z (OH)2, 0.8≤y≤0.95, 0.02≤z≤0.18, the molar ratio of the metal element in the high-nickel ternary precursor to the lithium element in the lithium source is 1:(1.03~1.15).

5. The method for preparing the high-nickel ternary cathode material as described in claim 4, characterized in that, One or two of the following conditions must be met: (1) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate; (2) The median particle size of the high-nickel ternary precursor is 5μm≤D50≤14μm.

6. The method for preparing the high-nickel ternary cathode material as described in claim 4, characterized in that, The sintering process includes a first sintering process and a second sintering process, and meets one or more of the following conditions: (1) The temperature of the first sintering treatment is 400℃~600℃; (2) The first sintering treatment takes 3 to 8 hours; (3) The temperature of the second sintering treatment is 700℃~850℃; (4) The second sintering treatment takes 6 to 20 hours; (5) The sintering process is carried out in an oxygen environment.

7. A high-nickel ternary cathode material, characterized in that, It was prepared according to the preparation method of the high-nickel ternary cathode material according to any one of claims 1 to 6.

8. The high-nickel ternary cathode material as described in claim 7, characterized in that, The thickness of the coating layer is 6nm to 15nm.

9. A positive electrode plate, characterized in that, Including the high-nickel ternary cathode material as described in claim 7 or 8.

10. A lithium-ion battery, characterized in that, Includes the positive electrode as described in claim 9.

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