Positive electrode active material, electrochemical device, and electronic device

Abstract

The invention discloses a positive electrode active material, an electrochemical device, and an electronic device. The positive electrode active material comprises lithium-containing cobalt oxide particles, the lithium-containing cobalt oxide particles comprise Mn element and Ni element, on the basis that the molar content of metal elements except the lithium element in the lithium-containing cobalt oxide particles is 100%, the content of the Mn element is A%, the content of the Ni element is B%, 0.1 < = A + B < 20, and 0.2 < = A / B < = 9. The structure of the positive electrode active material is kept relatively stable under high voltage, and the positive electrode active material has relatively high discharge capacity per gram and cycle retention rate.

Description

[0001] This application is a divisional application of the patent application filed on November 29, 2021, with application number CN202180013692.1 and invention title "Positive Electrode Active Material, Electrochemical Device and Electronic Device". Technical Field

[0002] This application relates to the field of energy storage, specifically to a positive electrode active material and an electrochemical and electronic device containing the positive electrode active material. Background Technology

[0003] Lithium-ion batteries are widely used in portable electronic products, electric transportation, and energy storage due to their advantages such as high energy density, good cycle performance, environmental friendliness, safety, and lack of memory effect. To meet the needs of social development, the search for lithium-ion batteries with higher energy and power densities is an urgent problem to be solved, which requires the cathode materials used to have higher specific capacity and a higher voltage platform.

[0004] Currently, commercially available lithium cobalt oxide cathode materials are facing challenges during high-voltage charging (>4.6V vs. Li / Li). + Crystal structure collapse and interface failure are prone to occur in the process, resulting in a discharge specific capacity that is lower than the theoretical value and rapid cycle decay, making it difficult to meet the needs of future higher energy density cathode active materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a positive electrode active material that maintains a relatively stable structure under high voltage and exhibits high discharge capacity and cycle retention rate.

[0006] In a first aspect, this application provides a positive electrode active material comprising lithium cobalt oxide particles, wherein the lithium cobalt oxide particles comprise Mn (manganese) and Ni (nickel) elements, and the molar content of the metal elements other than lithium in the lithium cobalt oxide particles is 100%, the molar content of Mn is A%, and the molar content of Ni is B%, wherein 0.1≤A+B<20 and 0.2≤A / B≤9.

[0007] According to some embodiments of this application, the positive electrode active material comprises lithium cobalt oxide particles having a P63mc structure.

[0008] In the lithium-containing cobalt oxide with the P63mc structure of this application, Ni can mix with Li, occupying Li sites and forming a pillar effect, thereby improving the interlayer structural stability of CoO6. Mn can occupy Co sites, increasing the Co migration barrier and inhibiting Co dissolution, thereby improving the intralayer structural stability of CoO6. By controlling the contents of Mn and Ni within the above-mentioned ranges, the interlayer and intralayer structural stability of CoO6 can be balanced, thus improving the overall crystal structure stability.

[0009] According to some embodiments of this application, 0.05 ≤ A < 11. In some embodiments, 0.05 ≤ B < 10.

[0010] In some implementations, 0.1 ≤ A + B < 10. In some implementations, 0.2 ≤ A / B ≤ 5.

[0011] According to some embodiments of this application, the positive electrode active material particle includes a first region and a second region. The first region is a region extending 100 nm from the surface of the positive electrode active material particle to the center of the positive electrode active material particle, and the second region is other regions outside the first region.

[0012] According to some embodiments of this application, lithium cobalt oxide particles include a first region and a second region, wherein the first region is a region extending 100 nm from the surface of the lithium cobalt oxide particle to the center of the lithium cobalt oxide particle, and the second region is other regions outside the first region.

[0013] According to some embodiments of this application, the content of Mn element in the first region is greater than the content of Mn element in the second region.

[0014] According to some embodiments of this application, the positive electrode active material satisfies at least one of conditions (a) to (e): (a) with the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of Mn in the first region A1% and the molar content of Mn in the second region A2% satisfy: 1 ​​< A1 / A2 < 5; (b) the molar content of Ni in the first region is greater than the molar content of Ni in the second region; (c) with the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of Ni in the first region B1% and the molar content of Ni in the second region B2% satisfy: 1 ​​< B1 / B2 < 5; (d) the molar content of Li in the first region is less than the molar content of Li in the second region; (e) the molar content of Li in the first region C1% and the molar content of Li in the second region C2% satisfy: 0.5 < C1 / C2 < 1.

[0015] In this application, the Mn and Ni content in the first region of the lithium-containing cobalt oxide particles is higher than that in the second region, while the Li content in the first region is lower than that in the second region. The surface layer of the lithium-containing cobalt oxide particles is more lithium-deficient than the interior. The lithium-deficient state of the surface-mounted lithium-containing cobalt oxide has higher conductivity than the fully lithium-mounted state, which is beneficial for its electrical performance. Furthermore, the P63mc structure of the lithium-containing cobalt oxide material provides a certain concentration of lithium vacancies, which makes the material more stable. Too few lithium vacancies can easily lead to phase transformation, forming an R-3m phase structure, which affects the structural stability of the lithium-containing cobalt oxide particles under high-voltage conditions.

[0016] According to some embodiments of this application, the positive electrode active material satisfies at least one of conditions (f) to (h): (f) in the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Mn 2p in the first region is greater than the intensity of the strongest characteristic peak of Mn 2p in the second region; (g) in the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Ni 2p in the first region is greater than the intensity of the strongest characteristic peak of Ni 2p in the second region; (h) in the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Li 1s in the first region is less than the intensity of the strongest characteristic peak of Li 1s in the second region.

[0017] According to some embodiments of this application, the positive electrode active material further includes an element M, wherein the element M includes at least one selected from aluminum (Al), magnesium (Mg), titanium (Ti), iron (Fe), zinc (Zn), copper (Cu), niobium (Nb), chromium (Cr), zirconium (Zr), or sodium (Na). According to some embodiments of this application, the positive electrode active material further includes an element Z, wherein the element Z includes at least one selected from boron (B), fluorine (F), phosphorus (P), sulfur (S), nitrogen (N), or silicon (Si). The introduction of the element M or element Z can further improve the structural stability of the material.

[0018] According to some embodiments of this application, the positive electrode active material includes particles with a median particle size Dv50 satisfying 3μm≤Dv50≤30μm. According to some embodiments of this application, the median particle size Dv50 of the lithium cobalt oxide particles satisfies 3μm≤Dv50≤30μm. When the particle size is less than 3μm, the specific surface area of ​​the positive electrode active material particles is too large, resulting in high reactivity and a tendency for side reactions to occur, thus affecting the performance of the electrochemical device. When the particle size exceeds 30μm, the positive electrode slurry containing this positive electrode active material presents processing difficulties in the process of forming the positive electrode sheet, and the excessively long ion migration path leads to a deterioration in the kinetic performance of the electrochemical device.

[0019] According to some embodiments of this application, the preparation method of the positive electrode active material includes subjecting a sodium cobalt oxide and a lithium compound to a solid-phase reaction, wherein the solid-phase reaction temperature is 180°C to 320°C and the solid-phase reaction time is 3h to 12h.

[0020] According to some embodiments of this application, the solid-phase reaction temperature is 180°C to 320°C. In some embodiments, the solid-phase reaction temperature is 200°C to 300°C. In some embodiments, the solid-phase reaction temperature is 220°C to 280°C. In some embodiments, the solid-phase reaction temperature is 240°C to 260°C. According to some embodiments of this application, the solid-phase reaction time is 3 hours to 12 hours. In some embodiments, the solid-phase reaction time is 4 hours to 8 hours.

[0021] According to some embodiments of this application, the sodium-containing cobalt oxide has a P63 / mmc structure. According to some embodiments of this application, the lithium-containing compound includes at least one of lithium sulfate, lithium carbonate, lithium nitrate, lithium halide, lithium carboxylate, lithium squaric acid, lithium alkoxide, or lithium hydroxide.

[0022] According to some embodiments of this application, the charge / discharge specific capacity of the positive electrode active material is greater than or equal to 210 mAh / g.

[0023] In a second aspect, this application provides an electrochemical device comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive current collector and a positive active layer disposed on the surface of the positive current collector, and the positive active layer comprises the positive active material of the first aspect.

[0024] According to some embodiments of this application, the charging cutoff voltage of the electrochemical device is greater than or equal to 4.6V.

[0025] Thirdly, this application provides an electronic device that includes the electrochemical device described in the second aspect.

[0026] The cathode active material of this application differs from that of conventional R-3m lithium cobalt oxide. Under high voltage, the cathode active material of this application is less prone to spinel phase transition, resulting in higher discharge specific capacity. Furthermore, the interlayer spacing of the cathode active material of this application is larger than that of conventional lithium cobalt oxide, leading to lower lithium-ion migration energy and better rate performance. Attached Figure Description

[0027] Figure 1 The image shows the XRD pattern of the sodium cobalt oxide in Example 1.

[0028] Figure 2 The images show the XRD patterns of the lithium cobalt oxide materials in Examples 1 to 7.

[0029] Figure 3The images show the XRD patterns of the lithium cobalt oxide materials in Comparative Examples 1 to 2 and Example 1.

[0030] Figure 4 XPS images of lithium cobalt oxide materials at different depths in Example 1.

[0031] Figure 5 XPS images of lithium cobalt oxide materials with different profile thicknesses in Comparative Example 3.

[0032] Figure 6 XPS images of lithium cobalt oxide material at different depths in Comparative Example 4. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0034] I. Positive Electrode Active Materials This application provides a positive electrode active material comprising lithium cobalt oxide particles, wherein the lithium cobalt oxide particles comprise Mn and Ni elements, and the molar content of Mn is A% and the molar content of Ni is B%, based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%, wherein 0.1≤A+B<20 and 0.2≤A / B≤9.

[0035] According to some embodiments of this application, the positive electrode active material includes lithium cobalt oxide particles having a P63mc structure.

[0036] In the lithium-containing cobalt oxide with the P63mc structure of this application, Ni can mix with Li, occupying Li sites and forming a pillar effect, thereby improving the interlayer structural stability of CoO6. Mn can occupy Co sites, increasing the Co migration barrier and inhibiting Co dissolution, thereby improving the intralayer structural stability of CoO6. By controlling the contents of Mn and Ni within the above-mentioned ranges, the interlayer and intralayer structural stability of CoO6 can be balanced, thus improving the overall crystal structure stability.

[0037] According to some embodiments of this application, 0.1 ≤ A + B < 20. In some embodiments, A + B is a range of 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 16, 18, 19, 19.9, or any combination of these values. In some embodiments, 0.1 ≤ A + B < 15. In some embodiments, 2 ≤ A + B < 10. In some embodiments, 2 ≤ A + B ≤ 9. When 2 ≤ A + B < 10, the positive electrode active material particles have a better Li / Mn mixing ratio, and the Co sites occupied by Mn are within a more suitable range, further improving the structural stability of the positive electrode active material particles.

[0038] According to some embodiments of this application, 0.2 ≤ A / B ≤ 9. In some embodiments, A / B is a range of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, or any combination of these values. In some embodiments, 0.3 ≤ A / B ≤ 5.

[0039] According to some embodiments of this application, with the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of Mn is A%, where 0.05 ≤ A < 11. In some embodiments, A is a range of 0.5, 1, 3, 5, 7, 9, or any combination of these values. In some embodiments, 1 ≤ A < 10. When the value of A is within the above range, the Li and Mn mixing ratio of the positive electrode active material particle crystals is in a preferred range.

[0040] According to some embodiments of this application, with the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of Ni is B%, where 0.05 ≤ B < 10. In some embodiments, B is a range of 0.5, 1, 3, 5, 7, 9, or any combination of these values. In some embodiments, 1 < B ≤ 7. When the value of B is within the above range, the proportion of Mn occupying Co sites is within a preferred range, thereby improving the stability of the crystal structure of the positive electrode active material particles.

[0041] According to some embodiments of this application, the positive electrode active material particle includes a first region and a second region, wherein the first region is a region extending 100 nm from the surface of the positive electrode active material particle to its center, and the second region is any region other than the first region. In some embodiments, the second region is a region extending 100 nm from the surface of the positive electrode active material particle to its center.

[0042] According to some embodiments of this application, the lithium cobalt oxide particles include a first region and a second region, wherein the first region is a region extending 100 nm from the surface of the lithium cobalt oxide particle to its center, and the second region is any region other than the first region. In some embodiments, the second region is a region extending 100 nm from the surface of the positive electrode active material particle to its center.

[0043] According to some embodiments of this application, the molar content of Mn element in the first region is greater than the molar content of Mn element in the second region. In some embodiments, the molar content of Mn element A1% in the first region and the molar content of Mn element A2% in the second region satisfy: 1 ​​< A1 / A2 < 5.

[0044] According to some embodiments of this application, the molar content of Ni in the first region is greater than that in the second region. In some embodiments, the molar content of Ni in the first region B1% and the molar content of Ni in the second region B2% satisfy: 1 ​​< B1 / B2 < 5.

[0045] According to some embodiments of this application, the molar content of Li in the first region is less than the molar content of Li in the second region. In some embodiments, the Li content C1% in the first region and the Li content C2% in the second region satisfy 0.5 < C1 / C2 < 1.

[0046] In this application, the Mn and Ni content in the first region of the lithium-containing cobalt oxide particles is higher than that in the second region, while the Li content in the first region is lower than that in the second region. The surface layer of the lithium-containing cobalt oxide particles is more lithium-deficient than the interior. The lithium-deficient state of the surface-mounted lithium-containing cobalt oxide has higher electrical conductivity than the fully lithium-mounted state, which is beneficial for its electrical performance. Furthermore, the P63mc structure of the lithium-containing cobalt oxide material provides a certain concentration of lithium vacancies, which makes the material more stable. Insufficient lithium vacancies can easily lead to phase transformation, forming an R-3m phase structure, which affects the structural stability of the lithium-containing cobalt oxide particles under high-voltage conditions.

[0047] According to some embodiments of this application, in the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Mn 2p in the first region is greater than the intensity of the strongest characteristic peak of Mn 2p in the second region. According to some embodiments of this application, in the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Ni 2p in the first region is greater than the intensity of the strongest characteristic peak of Ni 2p in the second region. According to some embodiments of this application, in the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Li 1s in the first region is less than the intensity of the strongest characteristic peak of Li 1s in the second region.

[0048] According to some embodiments of this application, the positive electrode active material further includes an element M, wherein the element M includes at least one selected from Al, Mg, Ti, Fe, Zn, Cu, Nb, Cr, Zr, or Na. According to some embodiments of this application, the positive electrode active material further includes an element Z, wherein the element Z includes at least one selected from B, F, P, S, N, or Si. The introduction of the element M or the element Z can further improve the structural stability of the material.

[0049] According to some embodiments of this application, with the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of element M is 0.01% to 3%.

[0050] According to some embodiments of this application, the positive electrode active material includes particles with a median particle size Dv50 satisfying 3μm≤Dv50≤30μm. According to some embodiments of this application, the median particle size Dv50 of the lithium cobalt oxide-containing particles satisfies 3μm≤Dv50≤30μm. In some embodiments, the median particle size Dv50 of the lithium cobalt oxide-containing particles is a range of 5μm, 10μm, 15μm, 20μm, 25μm, or any combination thereof. When the particle size is less than 3μm, the specific surface area of ​​the positive electrode active material particles is too large, resulting in high reactivity and a tendency for side reactions to occur, leading to failure. When the particle size exceeds 30μm, the positive electrode slurry containing this positive electrode active material presents processing difficulties in the process of forming a positive electrode sheet, and the kinetic performance of the electrochemical device deteriorates due to the excessively long ion migration path.

[0051] According to some embodiments of this application, the charge / discharge specific capacity of the positive electrode active material is greater than or equal to 210 mAh / g. In some embodiments, a coin cell battery is fabricated using lithium metal as the negative electrode. When charged at 0.1C to a voltage of 4.6V at 25°C and discharged at a rate of 0.1C, the discharge specific capacity of the positive electrode active material is greater than or equal to 210 mAh / g. In some embodiments of this application, the discharge voltage of the positive electrode active material is greater than or equal to 4.03V. The discharge voltage of the positive electrode active material can be measured using a Blue Battery Tester.

[0052] According to some embodiments of this application, a coin cell battery is fabricated using lithium metal as the negative electrode. When charged at 0.1C to a voltage of 4.7V at 25°C and discharged at 0.1C, the discharge specific capacity of the positive electrode active material is greater than or equal to 240mAh / g. In some embodiments of this application, the discharge voltage of the positive electrode active material is greater than or equal to 4.03V.

[0053] II. Preparation methods of positive electrode active materials This application also provides a method for preparing a positive electrode active material, which includes subjecting a sodium cobalt oxide and a lithium compound to a solid-phase reaction, wherein the solid-phase reaction temperature is 180°C to 320°C and the solid-phase reaction time is 3h to 12h.

[0054] According to some embodiments of this application, the solid-state reaction temperature is from 180°C to 320°C. In some embodiments, the solid-state reaction temperature is a range of 190°C, 210°C, 250°C, 260°C, 270°C, or any combination thereof. In some embodiments, the solid-state reaction temperature is from 200°C to 300°C. In some embodiments, the solid-state reaction temperature is from 220°C to 280°C. In some embodiments, the solid-state reaction temperature is from 240°C to 270°C.

[0055] According to some embodiments of this application, the solid-phase reaction time is 3 hours to 12 hours. In some embodiments, the solid-phase reaction time is 4 hours to 8 hours. In some embodiments, the solid-phase reaction time is 5 hours to 7 hours.

[0056] According to some embodiments of this application, the sodium-containing cobalt oxide has a P63 / mmc structure. According to some embodiments of this application, the preparation method of the sodium-containing cobalt oxide includes the following steps: S1: providing a compound containing cobalt, manganese, and nickel, and optionally containing M and / or Z elements; S2: mixing the compound in S1 with a sodium salt and calcining to generate sodium-containing cobalt oxide.

[0057] According to some embodiments of this application, in S2, the calcination temperature is 750°C to 1050°C, and the calcination time is 24 h to 72 h. In some embodiments, the sodium salt includes sodium carbonate. In some embodiments, the molar ratio of the compound to the sodium salt in S1 is 0.3:1 to 0.5:1.

[0058] According to some embodiments of this application, the preparation of the compound described in S1 may include the following steps: S11: mixing cobalt salt, manganese salt, nickel salt and optional M salt with a solvent to obtain a first mixed solution; S12: mixing the first mixed solution with a precipitant and optional complexing agent, and carrying out a precipitation reaction under conditions of pH 5 to 9 to obtain a precipitate; S13: optionally mixing the precipitate with a Z source and then calcining it, or directly calcining the precipitate.

[0059] According to some embodiments of this application, the preparation of the compound described in S1 includes the following steps: S11': mixing cobalt salt, manganese salt and nickel salt with a solvent to obtain a first mixed solution; S12': mixing the first mixed solution with a precipitant and an optional complexing agent, and carrying out a precipitation reaction under conditions of pH 5 to 9 to obtain a precipitate; S13': calcining the precipitate after mixing it with an optional M salt and / or Z source.

[0060] According to some embodiments of this application, the cobalt salt includes at least one selected from cobalt sulfate, cobalt nitrate, cobalt chloride, or cobalt acetate. According to some embodiments of this application, the manganese salt includes at least one selected from manganese sulfate, manganese nitrate, manganese chloride, or manganese acetate. According to some embodiments of this application, the nickel salt includes at least one selected from nickel sulfate, nickel nitrate, nickel chloride, or nickel acetate.

[0061] According to some embodiments of this application, the M salt includes at least one of chloride, acetate, sulfate, or nitrate containing the element M. In some embodiments, the element M includes at least one of Al, Mg, Ti, Fe, Zn, Cu, Nb, Cr, Zr, or Na.

[0062] According to some embodiments of this application, the Z source includes borides, oxides, sulfides, sulfates, chlorides, fluorides, or silicon-containing organic compounds. In some embodiments, the Z element includes at least one of B, F, P, S, N, or Si.

[0063] According to some embodiments of this application, in S13 and S13', the calcination temperature is 500°C to 750°C, and the calcination time is 8h to 24h.

[0064] According to some embodiments of this application, the solvent includes at least one of water, methanol, ethanol, acetone, isopropanol, or n-hexanol.

[0065] According to some embodiments of this application, the precipitant includes at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, or potassium carbonate.

[0066] According to some embodiments of this application, the complexing agent includes at least one of ammonia, ammonium carbonate, ammonium bicarbonate, urea, hexamethylenetetramine, ethylenediaminetetraacetic acid, citric acid, or ascorbic acid.

[0067] According to some embodiments of this application, the lithium-containing compound includes at least one of lithium sulfate, lithium carbonate, lithium nitrate, lithium halide, lithium carboxylate, lithium squaric acid, lithium alkoxide, or lithium hydroxide.

[0068] III. Electrochemical Device This application provides an electrochemical device including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive active layer disposed on the surface of the positive current collector. The positive active layer contains a positive active material of the first aspect.

[0069] According to some embodiments of this application, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0070] According to some embodiments of this application, a positive electrode active material and a binder (conductive materials and thickeners may be further used as needed) are mixed to form a sheet, which is then pressed onto a positive electrode current collector. Alternatively, these materials are dispersed in a liquid medium to form a slurry, which is then coated onto the positive electrode current collector and dried. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0071] According to some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative active layer disposed on the surface of the negative current collector.

[0072] According to some embodiments of this application, the negative electrode active layer includes a negative electrode active material, which may include a material capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloy, or transition metal oxide. In some embodiments, the negative electrode active material includes at least one of carbon material or silicon material, wherein the carbon material includes at least one of graphite and hard carbon, and the silicon material includes at least one of silicon, silicon oxide, silicon carbide, or silicon alloy.

[0073] According to some embodiments of this application, the negative electrode active layer includes an adhesive, and the adhesive may include various adhesive polymers. In some embodiments, the binder includes at least one selected from polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or styrene-butadiene rubber.

[0074] According to some embodiments of this application, the negative electrode active layer further includes a conductive material to improve the electrode conductivity. Any conductive material can be used as the conductive material, as long as it does not cause a chemical change. In some embodiments, the conductive material includes at least one selected from conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, or graphene.

[0075] According to some embodiments of this application, the negative electrode is lithium metal or a lithium-containing alloy. In some embodiments, the negative electrode is a lithium sheet.

[0076] According to some embodiments of this application, the charging cutoff voltage of the electrochemical device is greater than or equal to 4.6V.

[0077] The electrochemical device of this application also includes a separating membrane. The material and shape of the separating membrane used in the electrochemical device of this application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separating membrane comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0078] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0079] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0080] The inorganic layer comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0081] The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0082] The electrochemical device of this application also includes an electrolyte. The electrolyte that can be used in this application can be any electrolyte known in the prior art.

[0083] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The organic solvent of the electrolyte according to this application may be any organic solvent known in the art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the art. The additives of the electrolyte according to this application may be any additives known in the art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate. In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0084] In some embodiments, the electrochemical device of this application includes, but is not limited to, all types of primary batteries, secondary batteries, or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0085] IV. Electronic Devices This application further provides an electronic device that includes the electrochemical device described in the third aspect of this application.

[0086] The electronic devices or apparatus described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0087] Unless otherwise specified, all reagents, materials and instruments used in the following examples and comparative examples are commercially available.

[0088] Example 1 (1) Preparation of sodium cobalt oxide Cobalt sulfate (CoSO4), manganese sulfate (MnSO4), and nickel sulfate (NiSO4) were weighed according to a molar ratio of 94:5:1. Then, deionized water was added and stirred rapidly to dissolve them. Ammonium carbonate was then added to adjust the pH to 8 until the reaction was complete, forming a homogeneous carbonate precipitate. The precipitate was sintered at 650℃ for 12 hours. After crushing and sieving, Ni and Mn-doped Co3O4 metal oxide materials were obtained.

[0089] Sodium carbonate (Na₂CO₃) and the above-mentioned metal oxide were weighed and mixed evenly at a molar ratio of 0.35:1, and kept at 800℃ for 48 hours. After post-treatment, the corresponding sodium-cobalt oxide material was obtained. For example... Figure 1 As shown, XRD test results indicate that the obtained sodium-containing cobalt oxide has a P63 / mmc structure.

[0090] (2) Preparation of lithium-containing cobalt oxides The above-mentioned sodium cobalt oxide material, lithium nitrate and lithium acetate were mixed evenly in a molar ratio of 1:2:3, and placed in an alumina crucible. The mixture was then subjected to a solid-phase reaction at 250°C for 6 hours. After cooling, a mixture containing lithium cobalt oxide was obtained.

[0091] The above-mentioned mixture was crushed and then washed repeatedly with deionized water to remove soluble sodium and lithium salts until the conductivity of the supernatant was less than 200 μS / cm. The remaining powder was then subjected to filtration, drying, and sieving to obtain the target lithium-cobalt oxide material. The median particle size Dv50 of the obtained lithium-cobalt oxide material was approximately 14 µm. Figure 2 As shown, XRD test results indicate that the obtained lithium-containing cobalt oxide has a P63mc structure.

[0092] (3) Making button batteries The lithium-containing cobalt oxide obtained above was used as the positive electrode active material. Conductive carbon (SP) was used as a conductive agent, and polyvinylidene fluoride (PVDF) was used as a binder. They were mixed at a mass ratio of 90:5:5, and N-methyl-2-pyrrolidone (NMP) was added to form a slurry, which was then coated onto an aluminum foil with a thickness of 12 μm. The slurry was then dried in a 90°C forced-air drying oven for 4 hours and baked in a 110°C vacuum drying oven for 24 hours. The fully dried electrode sheet was then subjected to cold pressing, punching, and weighing processes to obtain the positive electrode.

[0093] A coin cell was assembled using the above-mentioned positive electrode, separator, negative electrode, and electrolyte under an inert atmosphere. The negative electrode was lithium metal; the electrolyte consisted of EC and DMC in a 1:1 volume ratio, and 1 M / L LiPF6.

[0094] Examples 2 to 7 Except for the adjustment of the solid-state reaction temperature in (2) for preparing lithium cobalt oxide, the other material preparation steps are the same as in Example 1. The solid-state reaction temperatures of Examples 2 to 7 are 200℃, 220℃, 240℃, 260℃, 280℃, and 300℃, respectively. The elemental composition of the lithium cobalt oxide in Examples 2 to 7 is shown in Table 1.

[0095] Examples 8 to 20 Except for adjustments to the elemental composition of the sodium-containing cobalt oxide used, the preparation steps were the same as in Example 1. The elemental compositions of the lithium-containing cobalt oxides in Examples 8 to 20 are shown in Tables 2 and 3.

[0096] Examples 21 to 28 Except for adjustments to the elemental composition of the sodium-containing cobalt oxide used, the preparation steps were the same as in Example 1. In the case of the aluminum-containing lithium cobalt oxide, aluminum was added to deionized water in the form of aluminum nitrate along with cobalt sulfate, manganese sulfate, and nickel sulfate. The elemental composition of the lithium-containing cobalt oxides in Examples 21 to 28 is shown in Table 4.

[0097] Examples 29 to 39 Except for adjustments to the elemental composition of the sodium cobalt oxide used, the preparation steps were the same as in Example 1. In the lithium cobalt oxide containing titanium, titanium was introduced in the form of titanium dioxide during the solid-state sintering stage of the sodium cobalt oxide. It is worth noting that the introduction of titanium is not limited to titanium dioxide; it can also be other titanium-containing compounds such as titanium sulfate or titanium nitrate. Furthermore, the introduction stage is not limited to the solid-state sintering stage of the sodium cobalt oxide; it can also be during the oxide precursor preparation stage. The elemental composition of the lithium cobalt oxides in Examples 29 to 39 is shown in Table 5.

[0098] Examples 40 to 44 Except for adjustments to the elemental composition of the sodium cobalt oxide used, the preparation steps were the same as in Example 1. In the fluorine-containing lithium cobalt oxide, fluorine was introduced in the form of cobalt fluoride during the solid-state sintering stage of the sodium cobalt oxide. The elemental composition of the lithium cobalt oxides in Examples 40 to 44 is shown in Table 6.

[0099] Comparative Example 1 Weigh 0.5 mol of cobalt sulfate (CoSO4) raw material, add deionized water and stir rapidly to dissolve it, then add ammonium carbonate and adjust the pH to 8 until the reaction is complete, forming a homogeneous cobalt carbonate precipitate. Sinter the precipitate at 650℃ for 12 h, and after crushing and sieving, obtain pure Co3O4 metal oxide material.

[0100] Lithium carbonate (Li₂CO₃) and the above-mentioned metal oxide were weighed and mixed evenly at a molar ratio of 1.05:1, and kept at 900℃ for 12 hours. After post-processing, the corresponding lithium cobalt oxide material was obtained. For example... Figure 3 As shown, XRD test results indicate that the obtained lithium cobalt oxide has an R-3m structure.

[0101] Comparative Examples 2 to 4 Except for the adjustment of the elemental composition of the sodium-containing cobalt oxide used, the other material preparation steps were the same as in Example 1. The elemental composition of the lithium-containing cobalt oxides in Comparative Examples 2 to 4 is shown in Table 1.

[0102] Comparative Examples 5 to 6 Except for adjustments to the elemental composition of the sodium-containing cobalt oxide used, the preparation steps were the same as in Example 1. The elemental composition of the lithium-containing cobalt oxides in Comparative Examples 5 and 6 is shown in Table 4.

[0103] Comparative Examples 7 to 8 Except for adjustments to the elemental composition of the sodium-containing cobalt oxide used, the preparation steps were the same as in Example 1. The elemental composition of the lithium-containing cobalt oxides in Comparative Examples 7 to 8 is shown in Table 5.

[0104] Comparative Examples 9 to 10 Except for adjustments to the elemental composition of the sodium-containing cobalt oxide used, the preparation steps were the same as in Example 1. The elemental composition of the lithium-containing cobalt oxides in Comparative Examples 9 and 10 is shown in Table 6.

[0105] Test methods 1. Discharge capacity and cycle capacity retention test After aging the coin cell at a constant temperature (25℃) for 24 hours, it was then subjected to a voltage range of 3V to x (where x can be 4.6V, 4.7V, or 4.8V, vs. Li / Li). + The voltage range was repeatedly tested for 20 charge-discharge cycles at a current density of 0.3 mA / cm². 2 .

[0106] The capacity of the second discharge is used as the reference benchmark for the cyclic capacity decay, i.e., the capacity retention rate of the nth discharge = the capacity of the nth discharge / the capacity of the second discharge × 100%; The discharge voltage is the battery voltage corresponding to 50% capacity discharge.

[0107] 2. High-temperature float charging performance test After the button cell was aged at a constant temperature (45℃) for 24 hours, it was subjected to an energy input of 0.3 mA / cm. 2 The battery was charged at a constant current density until the voltage reached 4.6V, and then charged at a constant voltage of 4.6V, yielding a curve showing the change of constant voltage charging current over time. Generally, the constant voltage charging current first decreases and then increases (a "sharpening" or "sharpening") as the constant voltage charging time increases. The current sharpening time is the time it takes for the current to reach its minimum value and then begin to increase again during constant voltage charging. The length of this time reflects, to some extent, the structural stability of the battery's positive electrode active material. Generally, the longer the current sharpening time, the better the structural stability of the positive electrode active material, and vice versa.

[0108] 3. XRD test The cathode material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with Cu Kα as the target material; the voltage and current were 40 kV / 35 mA, the scanning angle range was 10° to 60°, and the scanning rate was 5° / min.

[0109] 4. Elemental composition test of positive electrode active material The elemental composition of the cathode material was tested. The contents of elements such as Li and transition metals were measured using a Pepperl Optima 7000DV inductively coupled plasma optical emission spectrometer (ICP-OES), while the F content was measured using a Thermo Fisher ion chromatograph. Before the F content test, the cathode material to be tested needed to be dissolved in a certain amount of dilute nitric acid solution to completely form F. - The aqueous solution was then tested.

[0110] 5. XPS Test The experiment used a multifunctional X-ray photoelectron spectroscopy instrument (XPS, instrument model: ThermoFisher / ESCALAB Xi+) to test the surface of the positive electrode active material at different profiling depths.

[0111] Test Results Table 1 shows the effect of solid-state reaction temperature on the structure of lithium-containing cobalt oxide materials. Table 2 shows the effect of Mn and / or Ni doping on the performance of lithium-containing cobalt oxide materials and lithium-ion batteries containing these materials.

[0112] Wherein, A% represents the content of Mn element in the lithium cobalt oxide, with the total molar content of Co, Mn, and Ni elements being 100%; B% represents the content of Ni element in the lithium cobalt oxide, with the total molar content of Co, Mn, and Ni elements being 100%. The solid-phase reaction temperature in Examples 8 to 11 was 250°C.

[0113] Table 1

[0114] Table 2

[0115] Figure 2 XRD analysis results of the lithium-containing cobalt oxide materials from Examples 1 to 7 are presented. Figure 2 As can be seen, the solid-state reaction temperature has a significant impact on the phase composition of lithium cobalt oxide materials. When the solid-state reaction temperature is below 240℃, obvious residual sodium cobalt oxide with a P63mmc structure can be seen in the obtained lithium cobalt oxide material (main peak marked "1"), indicating that the reaction was not complete. When the solid-state reaction temperature is increased to 240℃ to 260℃, the obtained lithium cobalt oxide material is basically a pure phase of lithium cobalt oxide with a P63mc structure (main peak marked "2"). When the solid-state reaction temperature is further increased to 280℃ and above, a new impurity phase of lithium cobalt oxide with a new R-3m structure begins to appear (main peak marked "3").

[0116] Figure 4 , Figure 5 and Figure 6 XPS test results for different profile thicknesses of the lithium cobalt oxide materials in Examples 1, 3, and 4 are presented respectively. For the lithium cobalt oxide material in Example 1, when profiled 50 nm deeper from the surface, the strongest characteristic peak intensities of Co, Mn, and Ni are significantly higher than those at a depth of 200 nm, while the strongest characteristic peak intensity of Li is lower than that at a depth of 200 nm. Relative to the sum of the molar numbers of Ni, Co, and Mn, the surface layer n Li Approximately 0.3, inner layer n Li The value is approximately 0.92, indicating that the surface layer of the lithium-containing cobalt oxide material in Example 1 is more lithium-deficient than the inner layer. In contrast, the lithium-containing cobalt oxide materials in Comparative Examples 3 and 4, when analyzed at depths of 50 nm and 200 nm from the surface layer, show very similar intensity of their strongest characteristic peaks for Li 1s, Ni 2p, and Mn 2p. Relative to the sum of the molar numbers of Ni, Co, and Mn, the surface and inner layers have significantly different n... Li The values ​​are all close to 1, with no significant difference, which indicates that the metal elements in the surface and inner layers of the lithium-containing cobalt oxide materials in Comparative Examples 3 and 4 are uniformly distributed.

[0117] As shown in Table 2, the float current rise time is the shortest (approximately 150 hours) for lithium cobalt oxide materials without Mn and Ni doping, indicating the worst material stability at this time. After single doping with Mn or Ni, the float current rise time increases to approximately 200 hours, indicating improved structural stability. When Mn and Ni are co-doped in a certain ratio, the float current rise time increases significantly, exceeding 400 hours, indicating that Ni and Mn co-doping greatly improves the structural stability of lithium cobalt oxide materials.

[0118] Furthermore, compared to the lithium-containing cobalt oxide materials in Comparative Examples 3 and 4, the lithium-containing cobalt oxide material in Example 1 exhibited better high-temperature float charging performance. It is speculated that in addition to the improved structural stability of the lithium-containing cobalt oxide material due to Mn and Ni doping, the improved high-temperature float charging performance may also be related to the elemental distribution. For the lithium-containing cobalt oxide material in Example 1, the deep-profile XPS test results indicate that its surface layer is more lithium-deficient than its inner layer. The lithium-deficient state of the lithium-containing cobalt oxide has higher conductivity than the fully lithium-containing state, which is beneficial to its electrical performance. Furthermore, the P63mc structure of the lithium-containing cobalt oxide material itself contains a certain concentration of lithium vacancies. A reduction in lithium vacancies can lead to instability and a tendency to undergo a phase transition to R-3m. Therefore, the elemental gradient distribution on the surface of the lithium-containing cobalt oxide material in Example 1 is highly likely to further enhance the overall structural stability of the material.

[0119] Table 3 shows the effect of Mn and / or Ni doping content on the performance of lithium cobalt oxide materials and lithium-ion batteries containing such materials.

[0120] Wherein, A% represents the content of Mn element in the lithium cobalt oxide, with the total molar content of Co, Mn, and Ni elements being 100%; B% represents the content of Ni element in the lithium cobalt oxide, with the total molar content of Co, Mn, and Ni elements being 100%. The solid-phase reaction temperature in Examples 12 to 20 was 250°C.

[0121] Table 3

[0122] As shown in Table 3, with the increase of the total amount of Mn and Ni, the initial discharge specific capacity and discharge voltage of the lithium cobalt oxide material at 4.6V both show a decreasing trend. This is mainly because Mn... 4+ Relatively inert, it is difficult for Ni to contribute to the bulk density through valence changes, although 2+ / Ni 3+ Redox reactions can contribute some of the specific capacity, but their low redox potential leads to a decrease in discharge voltage.

[0123] Comparing Examples 12 to 20 with Comparative Examples 1 and 2, it can be seen that although the capacity retention of the lithium cobalt oxide material after 20 cycles at 3-4.6V initially increases and then decreases with the increase of the total amount of Mn and Ni doping, the cycle retention rates of Examples 12 to 20 are significantly higher than those of Comparative Examples 1 and 2. This indicates that Mn and Ni co-doping is beneficial to improving the structural stability of lithium cobalt oxide materials, thereby improving the cycle stability of lithium-ion batteries under high voltage. Meanwhile, when the Co content is greater than or equal to 90%, materials such as those in Example 8 and Example 16 exhibit both high discharge capacity and high cycle stability.

[0124] Table 4 shows the effect of Al doping on the performance of lithium cobalt oxide materials and lithium-ion batteries containing such materials.

[0125] Wherein, A% represents the content of Mn element in lithium cobalt oxide with the total molar content of Co, Mn, Ni and Al elements being 100%; B% represents the content of Ni element in lithium cobalt oxide with the total molar content of Co, Mn, Ni and Al elements being 100%.

[0126] The phase composition of the lithium cobalt oxide in Comparative Example 1 was R-3m. The solid-state reaction temperature of Comparative Examples 2, 5, 6 and Examples 21 to 28 was 250°C, and the phase composition of the lithium cobalt oxide obtained was P63mc.

[0127] Table 4

[0128] As shown in Table 4, Comparative Examples 1 and 2 are lithium cobalt oxides with R-3m and P63mc structures, respectively, without any element doping. When charged to 4.6V, their initial discharge capacities are 210 mAh / g and 218 mAh / g, respectively, and their capacity retention after 20 cycles is only about 60%. Comparative Examples 5 and 6 are lithium cobalt oxide materials with P63mc structures doped only with Mn or only with Ni, respectively. When charged to 4.6V, their cycle stability is improved, and their capacity retention after 20 cycles can be increased to about 70%. Example 21 is a lithium cobalt oxide with a P63mc structure co-doped with Mn and Ni in a 4:1 design ratio. Its capacity retention after 20 cycles is significantly improved, reaching 86.9%.

[0129] A comparison of Examples 22 to 28 with Example 21 also shows that, based on the co-doping of Mn and Ni elements, the introduction of Al element into the lithium-containing cobalt oxide material further enhances its cycle stability. The likely mechanism is that Al doping into the Co sites, and the stronger covalent nature of the Al-O bond compared to the Co-O bond, is beneficial for improving the structural stability of the transition metal layer composed of CoO6 octahedrons. Furthermore, Al doping at the Co sites increases the migration barrier of Co, which to some extent also inhibits Co dissolution.

[0130] Furthermore, Table 4 also shows that the cycling stability of lithium cobalt oxide materials with different Mn / Ni ratios varies. The lithium cobalt oxide material in Example 24 has a measured Mn / Ni ratio of 0.78, a high discharge capacity, and the best cycle stability. After 20 cycles, the capacity retention rate exceeds 90%, which is much higher than that of Comparative Examples 1, 2, 5, and 6.

[0131] Table 5 shows the effect of Ti doping on the performance of lithium cobalt oxide materials and lithium-ion batteries containing such materials.

[0132] Where A% represents the content of Mn element in lithium cobalt oxide with the total molar content of Co, Mn, Ni and Ti elements being 100%; B% represents the content of Ni element in lithium cobalt oxide with the total molar content of Co, Mn, Ni and Ti elements being 100%.

[0133] The phase composition of the lithium cobalt oxide in Comparative Example 1 was R-3m. The solid-state reaction temperature of Comparative Examples 2, 7, 8 and Examples 29 to 39 was 250°C, and the phase composition of the lithium cobalt oxide obtained was P63mc.

[0134] Table 5

[0135] As shown in Table 5, with the charging cut-off voltage increasing to 4.7V, the initial discharge specific capacity and discharge voltage of all lithium-ion cobalt oxide materials significantly improved compared to 4.6V, indicating that lithium-ion batteries at higher voltages have higher energy density. However, the cycle stability of all lithium-ion batteries decreased to varying degrees. Comparative Examples 1 and 2, undoped R-3m and P63mc structure lithium cobalt oxides respectively, retained only about 50% of their capacity after 20 cycles. Comparative Examples 7 and 8, single-doped Mn and single-doped Ni-containing lithium-ion cobalt oxide materials, showed similar cycle retention rates of about 50% to the undoped lithium cobalt oxide. However, after co-doping Mn and Ni, the capacity retention rate after 20 cycles increased by more than 30% compared to Comparative Examples 1, 2, 7, and 8.

[0136] A comparison of Examples 30 to 39 with Example 29 shows that the additional introduction of Ti further improves the cycle retention of the lithium cobalt oxide material. Similarly, a comparison of Examples 30 to 39 also shows that the ratio of Mn to Ni elements has a significant impact on cycle stability. Overall, the cycle retention of the lithium cobalt oxide material is better when the A / B ratio is between 0.2 and 5. Specifically, the A / B ratios in the lithium cobalt oxide materials of Examples 32 and 34 are 1.95 and 0.76, respectively, and their capacity retention exceeds 89% after 20 cycles in the 3V to 4.7V voltage range.

[0137] Table 6 shows the effect of F (fluorine) doping on the performance of lithium cobalt oxide materials and lithium-ion batteries containing such materials.

[0138] Wherein, A% represents the content of Mn element in lithium cobalt oxide with the total molar content of Co, Mn and Ni elements being 100%; B% represents the content of Ni element in lithium cobalt oxide with the total molar content of Co, Mn and Ni elements being 100%.

[0139] The phase composition of the lithium cobalt oxide in Comparative Example 1 was R-3m. The solid-state reaction temperature of Comparative Examples 2, 9, 10 and Examples 40 to 44 was 250°C, and the phase composition of the lithium cobalt oxide obtained was P63mc.

[0140] Table 6

[0141] As shown in Table 6, with the charging cut-off voltage further increased to 4.8V, the initial discharge voltage of all lithium cobalt oxide materials increased to above 4.05V, but the discharge specific capacity did not show a significant improvement compared to when the charging cut-off voltage was 4.7V. Furthermore, with the charging cut-off voltage increasing to 4.8V, the cycle stability of undoped lithium cobalt oxide materials and those doped with Mn or Ni elements decreased significantly. Comparative Examples 1 and 2 showed a sharp drop in capacity after 20 cycles, with the capacity decaying to zero. Comparative Examples 9 and 10 showed improved cycle performance, but the capacity retention after 20 cycles was only about 40%. However, the lithium cobalt oxide materials co-doped with Mn and Ni maintained good cycle stability, with a capacity retention of over 80% after 20 cycles. Further, introducing non-metallic element F into the lithium cobalt oxide materials could further improve the capacity retention after 20 cycles by 2% to 3%. However, excessive F doping would reduce the initial discharge specific capacity of the lithium cobalt oxide materials. The possible mechanism by which fluorine (F) doping improves cycle stability is that fluorine has a higher electronegativity than oxygen (O), which can pull down the O energy band, reducing the overlap of O and Co energy bands in the high delithiation state, thus avoiding the negative impact of O on cycle stability. 2- Oxygen is released when the material is oxidized, thereby enhancing its structural stability.

[0142] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A positive electrode active material comprising lithium cobalt oxide particles, wherein the lithium cobalt oxide particles comprise Mn and Ni elements, and with the molar content of the metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of Mn is A%, and the molar content of Ni is B%, wherein... 0.1≤A+B<20, 0.2≤A / B≤9; The positive electrode active material further includes elements M and / or Z, wherein the element M includes at least one of aluminum, magnesium, titanium, iron, zinc, copper, niobium, chromium, zirconium or sodium, and the element Z includes at least one of boron, fluorine, phosphorus, sulfur, nitrogen or silicon.

2. The positive electrode active material according to claim 1, wherein, The positive electrode active material includes lithium cobalt oxide particles with a P63mc structure.

3. The positive electrode active material according to claim 1, wherein 0.05 ≤ A < 11, and / or 0.05 ≤ B < 10.

4. The positive electrode active material according to claim 1, wherein, 0.1≤A+B<10, 0.2≤A / B≤5.

5. The positive electrode active material according to claim 1, wherein, The lithium-containing cobalt oxide particles comprise a first region and a second region, wherein the molar content of Mn element in the first region is greater than the molar content of Mn element in the second region. The first region is a 100nm region extending from the surface of the lithium cobalt oxide particle to the center of the lithium cobalt oxide particle, and the second region is any region other than the first region.

6. The positive electrode active material according to claim 5, wherein, The positive electrode active material satisfies at least one of conditions (a) to (e): (a) Assuming the molar content of metal elements other than lithium in the lithium cobalt oxide particles is 100%, the content of Mn element A1% in the first region and the content of Mn element A2% in the second region satisfy: 1 ​​< A1 / A2 < 5. (b) The molar content of Ni in the first region is greater than that in the second region; (c) Taking the molar content of metal elements other than lithium in the lithium cobalt oxide particles as 100%, the molar content of Ni element B1% in the first region and the molar content of Ni element B2% in the second region satisfy 1 < B1 / B2 < 5. (d) The molar content of Li in the first region is less than the molar content of Li in the second region; (e) Assuming the molar content of metal elements other than lithium in the lithium cobalt oxide particles is 100%, the molar content of Li element C1% in the first region and the molar content of Li element C2% in the second region satisfy 0.5 < C1 / C2 < 1.

7. The positive electrode active material according to claim 5, wherein, The positive electrode active material satisfies at least one of conditions (f) to (h): (f) In the XPS spectrum of the positive electrode active material, the intensity of the strongest characteristic peak of Mn 2p in the first region is greater than the intensity of the strongest characteristic peak of Mn 2p in the second region; (g) In the XPS spectrum of the positive electrode active material, the intensity of the strongest Ni 2p characteristic peak in the first region is greater than the intensity of the strongest Ni 2p characteristic peak in the second region; (h) In the XPS spectrum of the positive electrode active material, the intensity of the strongest Li 1s characteristic peak in the first region is less than the intensity of the strongest Li 1s characteristic peak in the second region.

8. The positive electrode active material according to claim 1, wherein, The median particle size Dv50 of the lithium cobalt oxide particles satisfies 3μm≤Dv50≤30μm.

9. The positive electrode active material according to claim 1, wherein, The method for preparing the positive electrode active material includes carrying out a solid-phase reaction between a sodium cobalt oxide and a lithium compound, wherein the solid-phase reaction temperature is 180°C to 320°C and the solid-phase reaction time is 3h to 12h.

10. The positive electrode active material according to claim 1, wherein, The charge / discharge capacity of the positive electrode active material is greater than or equal to 210 mAh / g.

11. An electrochemical device comprising a positive electrode and a negative electrode, the positive electrode comprising a positive current collector and a positive active layer disposed on the surface of the positive current collector, the positive active layer comprising a positive active material according to any one of claims 1 to 10.

12. The electrochemical device according to claim 11, wherein, The charging cutoff voltage of the electrochemical device is greater than or equal to 4.6V.

13. An electronic device comprising the electrochemical device of claim 11 or 12.

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