4.6-4.9 V high-voltage-resistant lithium cobalt oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a 4.6-4.9 V high-voltage-resistant lithium cobalt oxide positive electrode material as well as a preparation method and application thereof. The 4.6-4.9 V high-voltage-resistant lithium cobalt oxide positive electrode material comprises an outer coating layer, a transition layer and a lithium cobalt oxide layer which are tightly laminated in sequence. According to the invention, a high-pressure-resistant lithium cobalt oxide material comprising bulk phase / surface doping and surface coating is designed through a high-temperature solid-phase sintering method. The bulk phase / surface doped elements comprise one or more of Ti, Mg, Al, Zr, F, B and the like, the element introduced by surface coating is mainly a rare earth element Q, and the coated rare earth element can form a LiQOx (2 < = x < = 3) structure in a high-temperature sintering process, and the design can stabilize the bulk phase and surface structure of lithium cobalt oxide at the same time, inhibit cobalt dissolution and oxygen release, and improve the performance of lithium cobalt oxide. And the high-voltage stability of the electrolyte at the interface is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a 4.6V-4.9V high-voltage lithium cobalt oxide cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-metal batteries, using lithium metal as the negative electrode, were first researched in the early 20th century. However, due to serious problems such as high safety risks and low cycle life, they could not be put into practical use. Around 1990, the "rocking chair" lithium-ion battery, using lithium cobalt oxide as the positive electrode and graphite as the negative electrode, was introduced. During charging, lithium ions are extracted from the lithium cobalt oxide positive electrode and embedded in the graphite negative electrode. During discharging, lithium ions are extracted from the graphite negative electrode and re-embedded in the lithium cobalt oxide positive electrode, which greatly improves the safety performance of lithium-ion batteries. In the following thirty years, lithium-ion batteries developed rapidly. The positive electrode materials have expanded from the traditional lithium cobalt oxide positive electrode to layered lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, olivine-type lithium iron phosphate, lithium iron manganese phosphate, spinel-phase lithium-rich manganese oxide, and lithium-rich lithium nickel manganese oxide. The negative electrode materials have also evolved from the traditional graphite negative electrode to hard carbon negative electrodes, silicon-carbon negative electrodes, and silicon negative electrodes. In addition, lithium metal anodes with high energy density have also developed rapidly in the past 10 years, and the safety issues that existed in the past have been resolved to some extent in recent years.

[0003] Despite this, traditional lithium cobalt oxide cathodes hold a dominant position in consumer electronics due to their advantages such as high energy density, high tap density, high high tap density, high charging voltage, high ionic / electronic conductivity, and excellent cycle and rate performance. The theoretical capacity of lithium cobalt oxide is 274 mAh / g, but its actual capacity is limited by the charging cut-off voltage. Currently, the charging cut-off voltage of commercially available lithium cobalt oxide cathodes is around 4.55V, rarely exceeding 4.6V, which limits its actual discharge capacity to less than 200 mAh / g. A simple and effective strategy to further improve the energy density of lithium cobalt oxide is to increase its charging cut-off voltage. When the charging cut-off voltage is increased to 4.7V, the discharge capacity of lithium cobalt oxide exceeds 235 mAh / g. When the charging cut-off voltage is further increased to 4.9V, the discharge capacity reaches approximately 250 mAh / g. However, due to the large number of lithium ions inserted and extracted from lithium cobalt oxide, the lithium cobalt oxide undergoes drastic volume expansion and contraction, and cracks appear in the bulk phase of lithium cobalt oxide due to crystal slip. On the other hand, under high voltage, lithium cobalt oxide undergoes cobalt ion dissolution and lattice oxygen release on its surface. Some cobalt ions also occupy lithium vacancies, forming spinel and rock salt phases, which hinder lithium ion transport. Furthermore, under ultra-high voltage, the electrolyte becomes unstable and decomposes on the lithium cobalt oxide surface. The dissolved high-valence cobalt ions and oxygen free radicals further catalyze the decomposition of the electrolyte, exacerbating electrolyte consumption and damaging the surface structure of lithium cobalt oxide. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art and provide a 4.6V-4.9V high voltage lithium cobalt oxide cathode material.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned 4.6V-4.9V high voltage lithium cobalt oxide cathode material.

[0006] Another object of the present invention is to provide the application of the above-mentioned 4.6V-4.9V high voltage lithium cobalt oxide cathode material.

[0007] The technical solution of the present invention is as follows:

[0008] A 4.6V-4.9V high-voltage lithium cobalt oxide cathode material comprises a tightly stacked outer coating layer, a transition layer, and a lithium cobalt oxide layer, wherein...

[0009] The outer coating is primarily a monoclinic phase lithium rare earth metal oxide containing the rare earth element Q. This monoclinic phase is a composite monoclinic phase and / or a modified monoclinic phase. The structural formula of this lithium rare earth metal oxide is LiQO. x 2≤x≤3, Q is at least one of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu);

[0010] The lithium cobalt oxide layer is a bulk-doped or surface-doped lithium cobalt oxide material, and the doping element M of the bulk-doped or surface-doped material is at least one of Ti, Mg, Al, Zr, F and B.

[0011] The transition layer is a composite phase structure consisting of the phase structure of the lithium cobalt oxide layer and the phase structure of the outer coating layer.

[0012] In a preferred embodiment of the present invention, the monoclinic phase is a composite monoclinic phase with the structural formula LiQ. 1 m Q 2 n O x (2≤x≤3, 0≤m≤1, 0≤n≤1), Q is not limited to Q 1 Q 2 Two types are possible, or more than three types; or the monoclinic phase can be a modified monoclinic phase, with modification methods including element doping, creating vacancies, creating defects, etc. The doping element can be element N doped in the inner or outer layer structure of lithium cobalt oxide, or other alkali metal elements, transition metal elements, non-metal elements, and rare earth elements, etc. The structural formula is Li₂Q₃N₂. y O x(2≤x≤3,0.001≤y≤0.5), N is not limited to one type, but can be two or more types; or the monoclinic phase is a combination of the above-mentioned composite monoclinic phase and the above-mentioned modified monoclinic phase.

[0013] In a preferred embodiment of the present invention, the content of the dopant element M is 0.05-10 wt% (preferably 0.1-5 wt%, more preferably 0.2-2 wt%), and its sources include elemental metals, oxides, chlorides, fluorides, borides, hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, formates, acetates, borates, silicates, aluminates, aluminates, phosphates, oxalates, and acetylacetonates.

[0014] In a preferred embodiment of the present invention, the rare earth element Q is derived from metal elements, oxides, chlorides, fluorides, borides, hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, formates, acetates, borates, silicates, aluminates, metaaluminates, phosphates, oxalates, and acetylacetonates.

[0015] In a preferred embodiment of the present invention, the amount of the outer coating layer is 0.05-10 wt% (preferably 0.1-5 wt%, more preferably 0.5-3 wt%), and the thickness is 1-1000 nm (preferably 5-500 nm, more preferably 10-100 nm); the thickness of the transition layer is 0.5-100 nm (preferably 1-50 nm, more preferably 2-20 nm).

[0016] Preferably, the transition layer is mainly composed of a layered phase inside, gradually transitioning to a monoclinic phase on the outside. The two crystal planes of the two phases, whether identical or different, have a specific multiple relationship in their interplanar spacing, mainly 0.5 times, 1 times, or 2 times. This facilitates the epitaxial growth of the monoclinic phase through the coating layer via specific crystal planes, thus generating the transition layer.

[0017] The preparation method of the above-mentioned 4.6V-4.9V high-voltage lithium cobalt oxide cathode material includes the following steps:

[0018] (1) Take the source of rare earth element Q, the source of doping element M, cobalt source and lithium source and mix them evenly, wherein the molar ratio of lithium to cobalt is 0.8-1.2:1;

[0019] (2) The material obtained in step (1) is subjected to a first sintering and a second sintering in sequence. The temperature of the first sintering is 500-700℃ and the time is 2-10h. The temperature of the second sintering is 800-1200℃ and the time is 6-24h.

[0020] The purpose of the first sintering is to remove volatile substances such as water of crystallization from the material obtained in step (1), and the purpose of the second sintering is to synthesize lithium cobalt oxide material with a three-layer structure.

[0021] In a preferred embodiment of the present invention, the molar ratio of lithium to cobalt is 0.9-1.1:1 (more preferably 1.0-1.08:1).

[0022] Preferably, the lithium source and cobalt source include oxides, chlorides, fluorides, hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, formates, acetates, oxalates, acetylacetonates, etc.

[0023] In a preferred embodiment of the present invention, step (2) further includes a third sintering, wherein the temperature of the third sintering is 800-1000°C and the time is 6-24h.

[0024] The purpose of the third sintering is to remove residual defects and improve the uniformity and stability of the outer coating on the surface.

[0025] The atmosphere for the first to third sintering processes is one or a mixture of nitrogen, argon, and oxygen, or sintering can also be performed in an atmospheric atmosphere.

[0026] The above-mentioned 4.6V-4.9V high-voltage lithium cobalt oxide cathode material is used in the preparation of high-voltage lithium cobalt oxide batteries.

[0027] A high-voltage lithium cobalt oxide battery, characterized in that it comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte made of the aforementioned 4.6V-4.9V high-voltage lithium cobalt oxide positive electrode material.

[0028] The solute in the electrolyte is a lithium salt, including one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalato) phosphate, lithium tetrafluoro(oxalato) phosphate, lithium difluoroxanimide (LiFSI), lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, lithium tetrafluoroborate (LiBF4), lithium perchlorate, lithium nitrate, lithium oxalate, lithium formate, lithium chloride, lithium bromide, and lithium iodide; the solvent is an ester solvent, an ether solvent, or a sulfone solvent. Ester solvents include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), methyl acetate, ethyl acetate, methyl propionate, methyl butyrate, ethyl propionate, propyl propionate, and γ-butyrolactone; ether solvents include, but are not limited to, [the following categories]. Limited to one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, 15-5 crown ether, tetrahydrofuran (THF), and 2-methyltetrahydrofuran; or, the solvent is one or more of 1-methylimidazolium, acetonitrile, dimethyl sulfoxide, sulfolane, ethyl vinyl sulfone, and methyl isopropyl sulfone; the additives include at least one of fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), 1,4-butanesulfonyl lactone, 2,4-butanesulfonyl lactone, propane sulfonic anhydride, succinic anhydride, lithium difluorophosphate, succinic anhydride, adiponitrile, trans-butenedionitrile, glutaronitrile, 1,3,6-hexanetrionitrile or 1,2,3-tris(2-cyanoxy)propane, lithium bis(oxalato)borate, and lithium difluorooxalatoborate.

[0029] The active material of the negative electrode sheet is lithium metal, sodium metal, artificial graphite, natural graphite, hard carbon, silicon-carbon negative electrode, silicon negative electrode, etc. The lithium metal negative electrode includes lithium alloy and pure lithium metal. The alloying elements include one or more of nickel, cobalt, manganese, aluminum, magnesium and zirconium.

[0030] The release films include polyethylene release films, polypropylene release films, polypropylene / polyethylene / polypropylene composite release films, cellulose release films, PET nonwoven release films, as well as polyethylene release films, polypropylene release films, polypropylene / polyethylene / polypropylene composite release films, cellulose release films, and PET nonwoven release films modified by surface coating, grafting, etc.

[0031] The separator is coated or grafted onto at least one surface of the separator. The coating comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, manganese carbonate, calcium carbonate, aluminum borate, and magnesium borate.

[0032] The adhesive is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.

[0033] Grafting modification mainly involves cross-linking and polymerization of the separator surface through chemical bonding, including polydopamine, polyethylene glycol dimethacrylate, etc. Surface modification of the separator can improve the heat resistance, oxidation resistance and electrolyte wetting properties of the separator, and enhance the adhesion between the separator and the electrode.

[0034] In a preferred embodiment of the present invention, the method for preparing the positive electrode sheet includes: sieving the 4.6V-4.9V high-voltage lithium cobalt oxide positive electrode material to obtain large-particle-size powder with D50≈10-25μm and small-particle-size powder with D50≈2-10μm; then mixing the large-particle-size powder, small-particle-size powder, conductive agent, binder and dispersant to form a slurry, and coating it onto a support (aluminum foil, carbon-coated aluminum foil, aluminum mesh or carbon fiber self-supporting film) to obtain the positive electrode sheet.

[0035] The beneficial effects of this invention are:

[0036] 1. This invention designs a high-voltage resistant lithium cobalt oxide material comprising bulk / surface doping and surface coating via high-temperature solid-state sintering. The bulk / surface doping elements include one or more of Ti, Mg, Al, Zr, F, and B. The surface coating primarily introduces rare earth element Q, which forms LiQO during the high-temperature sintering process. x The (2≤x≤3) structure design can simultaneously stabilize the bulk and surface structure of lithium cobalt oxide, suppress cobalt dissolution and oxygen release, and improve the high-voltage stability of the electrolyte at the interface.

[0037] 2. In this invention, there is a transition region where two phases coexist between the surface of lithium cobalt oxide and the coating layer. This transition region can effectively connect the surface of the lithium cobalt oxide material and the coating layer together, and can adapt to the volume changes caused by the large-scale insertion and extraction of lithium ions under ultra-high voltage.

[0038] 3. The bulk / surface element doping of the present invention improves the stability of lithium cobalt oxide material under deep lithium ion extraction conditions, slows down the volume change caused by lithium cobalt oxide during the repeated lithium extraction / intercalation process, and the pillar or pinning effect generated by element doping also inhibits the generation of cracks in the bulk phase of lithium cobalt oxide, thereby improving the structural stability of lithium cobalt oxide under high voltage conditions and long-term charge and discharge processes.

[0039] 4. The lithium cobalt oxide in this invention contains LiMO with a transition metal surface. x (2≤x≤3) The coating layer is a lithium-ion conductor with a better ion conduction pathway, which helps to reduce the resistance of lithium-ion transport on the surface of lithium cobalt oxide during charging and discharging, and reduce the capacity loss caused by battery polarization.

[0040] 5. The LiMO in this invention x (2≤x≤3) The rare earth elements in the coating layer have unique 4f electron orbitals, strong conductivity, and strong oxygen bonding, which can effectively inhibit oxygen release, thereby indirectly inhibiting the dissolution of cobalt ions on the surface of lithium cobalt oxide and the resulting phase transition.

[0041] 6. This invention co-sintersects rare earth element precursors with lithium cobalt oxide precursors and doped element precursors, which can better achieve LiMO. x Uniform coating with (2≤x≤3) is superior to non-in-situ coating of LiMO on the outside of lithium cobalt oxide. x It also has advantages such as simple and environmentally friendly material preparation process and low cost. Attached Figure Description

[0042] Figure 1 The image shows a comparison of the lithium cobalt oxide powder prepared in Example 1 of this invention with the lithium cobalt oxide powder prepared in Comparative Examples 1, 2, and 3.

[0043] Figure 2 The X-ray diffraction patterns are shown in the comparison between the lithium cobalt oxide powder prepared in Example 1 of the present invention and the lithium cobalt oxide powder prepared in Comparative Examples 1, 2, and 3.

[0044] Figure 3 This is a scanning transmission electron microscope image of the lithium cobalt oxide powder prepared in Example 1 of the present invention.

[0045] Figure 4This is a schematic diagram of the assembly of the coin cell half-cell and the full cell of the high-voltage lithium cobalt oxide battery in Embodiment 1 of the present invention.

[0046] Figure 5 This is a comparison chart of the first charge-discharge cycle of the high-voltage lithium cobalt oxide battery in Example 1 of the present invention and the high-voltage lithium cobalt oxide batteries in Comparative Examples 1, 2, and 3.

[0047] Figure 6 This is a comparison chart of the cycle performance of the high-voltage lithium cobalt oxide battery in Example 1 of the present invention with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.7V.

[0048] Figure 7 This is a comparison diagram of the battery polarization of the high-voltage lithium cobalt oxide battery in Example 1 of the present invention with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.7V.

[0049] Figure 8 This is a comparison chart of the rate performance of the high-voltage lithium cobalt oxide battery in Example 1 of the present invention with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.7V.

[0050] Figure 9 This is a comparison chart of the cycle performance of the high-voltage lithium cobalt oxide battery in Example 1 of the present invention with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.9V.

[0051] Figure 10 This is a cycle performance diagram of the high-voltage lithium cobalt oxide battery in Example 7 of the present invention. Detailed Implementation

[0052] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0053] Example 1

[0054] Cobalt tetroxide, lithium carbonate, magnesium oxide, and yttrium oxide were added separately in a molar ratio of 1:1.05:0.005:0.01 and thoroughly mixed in a ball mill. The mixing speed was 600 r / min, and the mixing time was 12 h. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 h, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 h, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 h, to eliminate defects in the bulk phase and interface of lithium cobalt oxide and further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After three firings and subsequent particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. A detailed battery assembly diagram can be found in [link to diagram]. Figure 4 The ester electrolyte formulation in this embodiment is: 1M LiPF6, EC / EMC (mass ratio 3:7). This formulation is the most basic electrolyte formulation and is intended to illustrate the superiority of the material of the present invention.

[0055] Example 2

[0056] Cobalt tetroxide, lithium carbonate, titanium oxide, magnesium oxide, aluminum oxide, and terbium acetate were added separately in a molar ratio of 1:1.05:0.005:0.005:0.005:0.01 and thoroughly mixed in a ball mill. The mixture was then removed and subjected to three sintering processes in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 hours, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 hours, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 hours, to eliminate defects in the lithium cobalt oxide bulk phase and interface, and to further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After three firings and subsequent particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. The ester electrolyte formulation in this embodiment is: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0057] Example 3

[0058] Cobalt tetroxide, lithium carbonate, boron oxide, lithium fluoride, lanthanum oxide, and terbium acetate were added separately in an elemental molar ratio of 1:1.05:0.005:0.005:0.006:0.004 and thoroughly mixed in a ball mill. The mixture was then removed and subjected to three sintering processes in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 hours, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 hours, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 hours, to eliminate defects in the bulk phase and interface of lithium cobalt oxide, further improving the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After three firings and subsequent particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. The ester electrolyte formulation in this embodiment is: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0059] Example 4

[0060] Cobalt tetroxide, lithium carbonate, magnesium nitrate, aluminum nitrate, and gadolinium oxide were added in a molar ratio of 1:1.05:0.01:0.01:0.02 and thoroughly mixed in a ball mill. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃ for 6 hours to remove volatile impurities such as water of crystallization. The second sintering temperature was 1000℃ for 24 hours to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃ for 15 hours to eliminate defects in the bulk and interfacial phases of lithium cobalt oxide, further improving the adhesion and stability of the coating. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After the three sintering processes and particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. In this embodiment, the ester electrolyte formulation was: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0061] Example 5

[0062] Cobalt tetroxide, lithium carbonate, magnesium nitrate, aluminum nitrate, and dysprosium nitrate were added in a molar ratio of 1:1.05:0.01:0.02:0.01 and thoroughly mixed in a ball mill. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃ for 6 hours to remove volatile impurities such as water of crystallization. The second sintering temperature was 1000℃ for 24 hours to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃ for 15 hours to eliminate defects in the bulk and interfacial phases of lithium cobalt oxide, further improving the adhesion and stability of the coating. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After the three sintering processes and particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. In this embodiment, the ester electrolyte formulation was: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0063] Example 6

[0064] Cobalt tetroxide, lithium carbonate, magnesium acetate, aluminum acetate, zirconium acetate, and europium oxide were added separately in an elemental molar ratio of 1:1.05:0.01:0.02:0.01:0.01 and thoroughly mixed in a ball mill. The mixture was then removed and subjected to three sintering processes in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 hours, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 hours, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 hours, to eliminate defects in the lithium cobalt oxide bulk phase and interface, and to further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After three firings and subsequent particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. The ester electrolyte formulation in this embodiment is: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0065] Example 7

[0066] Cobalt tetroxide, lithium carbonate, magnesium oxide, and yttrium oxide were added separately in a molar ratio of 1:1.05:0.005:0.01 and thoroughly mixed in a ball mill. The mixing speed was 600 r / min, and the mixing time was 12 h. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 h, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 h, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 h, to eliminate defects in the bulk phase and interface of lithium cobalt oxide and further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After three firings and subsequent particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, graphite negative electrode sheet (N / P ratio approximately 1.05), PP separator, ester electrolyte, and other battery materials were used to assemble a high-voltage lithium cobalt oxide battery. The ester electrolyte formulation in this embodiment is: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0067] Comparative Example 1

[0068] Cobalt tetroxide and lithium carbonate were added separately at a cobalt:lithium molar ratio of 1:1.05 and thoroughly mixed in a ball mill. The mixing speed was 600 r / min, and the mixing time was 12 h. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 h, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 h, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 h, to eliminate defects in the bulk phase and interface of lithium cobalt oxide and further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After the three sinterings and particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. The comparative example ester electrolyte formulation was: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0069] Comparative Example 2

[0070] Cobalt tetroxide, lithium carbonate, and magnesium oxide were added in a cobalt:lithium:magnesium molar ratio of 1:1.05:0.01 and thoroughly mixed in a ball mill. The mixing speed was 600 r / min, and the mixing time was 12 h. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 h, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 h, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 h, to eliminate defects in the bulk phase and interface of lithium cobalt oxide and further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After the three sinterings and particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. The comparative example ester electrolyte formulation was: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0071] Comparative Example 3

[0072] Cobalt tetroxide, lithium carbonate, and yttrium oxide were added separately at a cobalt:lithium:yttrium molar ratio of 1:1.05:0.01 and thoroughly mixed in a ball mill. The mixing speed was 600 r / min, and the mixing time was 12 h. The mixture was then removed and sintered three times in a muffle furnace. The first sintering temperature was 500℃, and the sintering time was 6 h, to remove volatile impurities such as water of crystallization from the raw materials. The second sintering temperature was 1000℃, and the sintering time was 24 h, to synthesize lithium cobalt oxide material. The third sintering temperature was 900℃, and the sintering time was 15 h, to eliminate defects in the bulk phase and interface of lithium cobalt oxide and further improve the adhesion and stability of the coating layer. After each sintering, the lithium cobalt oxide particles were crushed using an air jet mill, sieved, and then proceeded to the next sintering step. After the three sinterings and particle crushing and sieving, lithium cobalt oxide powders of different particle sizes were obtained. Large-particle-size lithium cobalt oxide powder (D50≈10-20μm) and small-particle-size lithium cobalt oxide powder (D50≈2-10μm) were mixed uniformly in a 1:1 mass ratio using a rolling ball mill. 90g of the mixed lithium cobalt oxide powder was then poured into a container, and 5g of acetylene black conductive agent, 5g of polyvinylidene fluoride (PVDF) binder, and 150g of N-methylpyrrolidone (NMP) dispersant were added. The mixture was thoroughly stirred to form a uniform positive electrode slurry, which was then coated onto a 10μm thick aluminum foil to increase the electrode compaction density, resulting in a positive electrode sheet with better ion conduction and conductivity. Finally, the prepared positive electrode sheet, a 300μm thick lithium metal negative electrode sheet, a PP separator, and an ester electrolyte were used to assemble a high-voltage lithium cobalt oxide battery. The comparative example ester electrolyte formulation was: 1M LiPF6, EC / EMC (mass ratio 3:7).

[0073] Performance testing and analysis of the above embodiments and comparative examples

[0074] Figure 1 The image shows a comparison of the lithium cobalt oxide powder prepared in Example 1 with the lithium cobalt oxide powder prepared in Comparative Examples 1, 2, and 3. It can be seen that there is no significant difference in the external morphology of the lithium cobalt oxide materials before and after modification. Figure 2 The X-ray diffraction patterns of the lithium cobalt oxide powder prepared in Example 1 are compared with those of the lithium cobalt oxide powders prepared in Comparative Examples 1, 2, and 3. It can be seen that there is no significant difference in the crystal structure of the lithium cobalt oxide powders before and after modification; they remain NaFeO2 structures. Therefore, the modification of the lithium cobalt oxide powders has no significant impact on the morphology and structure of the bulk material.

[0075] Figure 3The image shown is a scanning transmission electron microscope image of the lithium cobalt oxide powder prepared in Example 1. It can be seen that the surface and near-surface structure of the lithium cobalt oxide powder is clearly divided into three regions: the internal NaFeO2 structure, the transition region NaFeO2 / LiMO... x Structure, and external LiMO x Structure. The transition region can improve the adhesion and stability of the coating layer. External LiMO x The coating layer provides a good lithium-ion conductivity pathway and also exhibits high-voltage stability.

[0076] Figure 4 This is a schematic diagram of the assembly of a button cell and a full cell. Figure 5 The chart shows a comparison of the first charge-discharge cycle of the high-voltage lithium cobalt oxide battery in Example 1 with those in Comparative Examples 1, 2, and 3. It can be seen that at a high cutoff voltage of 4.7V, the first-cycle discharge specific capacity of the high-voltage lithium cobalt oxide battery in Comparative Example 1 is approximately 250 mAh / g. Although the capacity of the modified lithium cobalt oxide is reduced, it is still around 225 mAh / g. These differences can be improved later using lithium replenishment technology.

[0077] Figure 6 This is a comparison graph showing the cycle performance of the high-voltage lithium cobalt oxide battery in Example 1 with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.7V. Figure 7 This is a comparison diagram of the high-voltage lithium cobalt oxide battery in Example 1 and the high-voltage lithium cobalt oxide batteries in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.7V. Figure 8 This is a comparison graph showing the rate performance of the high-voltage lithium cobalt oxide battery in Example 1 with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.7V. Figure 9 The graph shows a comparison of the cycle performance of the high-voltage lithium cobalt oxide battery in Example 1 with that in Comparative Examples 1, 2, and 3 at a charging cutoff voltage of 4.9V. It can be seen that, compared to the comparative examples, the high-voltage lithium cobalt oxide battery in Example 1 shows significant improvements in both cycle and rate performance. When the charging cutoff voltage is increased to 4.9V, the first-cycle discharge specific capacity of the high-voltage lithium cobalt oxide battery in Example 1 is nearly 250mAh / g, while also exhibiting ultra-high voltage cycle stability.

[0078] Figure 10 This is a full-cell cycle performance diagram of the high-voltage lithium cobalt oxide battery prepared in Example 7. The difference between the high-voltage lithium cobalt oxide battery in Example 7 and the high-voltage lithium cobalt oxide battery in Example 1 is that the lithium metal anode is replaced with a graphite anode, and the assembled battery is changed from a half-cell to a full-cell battery. As can be seen from the figure, the high-voltage lithium cobalt oxide cathode material of the present invention exhibits excellent cycle performance in both half-cell and full-cell configurations.

[0079] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A 4.6V-4.9V high-voltage lithium cobalt oxide cathode material, characterized in that: It includes a tightly stacked outer coating layer, a transition layer, and a lithium cobalt oxide layer, wherein, The outer coating is primarily a monoclinic phase lithium rare earth metal oxide containing the rare earth element Q. This monoclinic phase is a composite monoclinic phase and / or a modified monoclinic phase. The structural formula of this lithium rare earth metal oxide is LiQO. x , 2≤x≤3, Q is at least one of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; The lithium cobalt oxide layer is a bulk-doped or surface-doped lithium cobalt oxide material, and the doping element M of the bulk-doped or surface-doped material is at least one of Ti, Mg, Al, Zr, F and B. The transition layer is a composite phase structure consisting of the phase structure of the lithium cobalt oxide layer and the phase structure of the outer coating layer.

2. The 4.6V-4.9V high-voltage lithium cobalt oxide cathode material as described in claim 1, characterized in that: The content of the dopant element M is 0.05-10 wt%, and its sources include elemental metals, oxides, chlorides, fluorides, borides, hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, formates, acetates, borates, silicates, aluminates, aluminates, phosphates, oxalates, and acetylacetonates.

3. The 4.6V-4.9V high-voltage lithium cobalt oxide cathode material as described in claim 1, characterized in that: The rare earth element Q is derived from sources including elemental metals, oxides, chlorides, fluorides, borides, hydroxides, carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, formates, acetates, borates, silicates, aluminates, metaaluminates, phosphates, oxalates, and acetylacetonates.

4. A 4.6V-4.9V high-voltage lithium cobalt oxide cathode material as described in any one of claims 1 to 3, characterized in that: The outer coating layer has an amount of 0.05-10 wt% and a thickness of 1-1000 nm; the transition layer has a thickness of 0.5-100 nm.

5. A method for preparing a 4.6V-4.9V high-voltage lithium cobalt oxide cathode material according to any one of claims 1 to 4, characterized in that: Includes the following steps: (1) Take the source of rare earth element Q, the source of doping element M, cobalt source and lithium source and mix them evenly, wherein the molar ratio of lithium to cobalt is 0.8-1.2:1; (2) The material obtained in step (1) is subjected to a first sintering and a second sintering in sequence. The temperature of the first sintering is 500-700℃ and the time is 2-10h. The temperature of the second sintering is 800-1200℃ and the time is 6-24h.

6. The preparation method according to claim 5, characterized in that: The molar ratio of lithium to cobalt is 0.9-1.1:

1.

7. The preparation method according to claim 5 or 6, characterized in that: The step (2) also includes a third sintering, which is performed at a temperature of 800-1000℃ for 6-24 hours.

8. The use of the 4.6V-4.9V high-voltage lithium cobalt oxide cathode material according to any one of claims 1 to 4 in the preparation of high-voltage lithium cobalt oxide batteries.

9. A high-voltage resistant lithium cobalt oxide battery, characterized in that: The device comprises a positive electrode, a negative electrode, a separator, and an electrolyte made of the 4.6V-4.9V high-voltage lithium cobalt oxide positive electrode material as described in any one of claims 1 to 4.

10. A high-voltage resistant lithium cobalt oxide battery as described in claim 9, characterized in that: The method for preparing the positive electrode sheet includes: sieving the 4.6V-4.9V high-voltage lithium cobalt oxide positive electrode material to obtain large-particle-size powder with D50≈10-25μm and small-particle-size powder with D50≈2-10μm; then mixing the large-particle-size powder, small-particle-size powder, conductive agent, binder and dispersant to form a slurry, and coating it on a support to obtain the positive electrode sheet.

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