Lithium cobalt oxide positive electrode material preparation method, positive electrode material, positive electrode plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium cobalt oxide positive electrode material preparation method, a positive electrode material, a positive electrode plate and a battery. The invention provides a preparation method of a lithium cobalt oxide positive electrode material. The preparation method comprises the following steps: mixing a deep eutectic solvent, at least five metal salts, phosphate and a doping source, and carrying out solvothermal reaction to obtain a solvothermal product; carrying out pre-sintering, deep sintering and quenching treatment on the solvothermal product to obtain a coating material precursor; the pre-sintering temperature is lower than the deep sintering temperature, and the cooling rate of quenching treatment is gt; 20 DEG C / S; and coating the surface of the LCO material with the coating material precursor, drying, and carrying out gradient sintering to obtain the lithium cobalt oxide positive electrode material. The LCO positive electrode material is prepared by coating the surface of an LCO material with a composite material formed by mixing a high-entropy material, phosphate and fluoride or sulfide, and when the LCO positive electrode material works in a high-voltage environment of 4.5 V or above, irreversible phase change and interface side reaction of the LCO positive electrode material can be inhibited when the LCO positive electrode material works in the high-voltage environment of 4.5 V or above.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for preparing lithium cobalt oxide cathode material, cathode material, cathode sheet and battery. Background Technology

[0002] In the cathode material system of lithium-ion batteries, lithium cobalt oxide (LCO) has become the mainstream choice in the consumer electronics field due to its high volumetric energy density. However, when operating in a high-voltage environment above 4.5V, the delithiation of LCO material will cause distortion of the cobalt-oxygen octahedral structure, resulting in oxygen evolution in the lattice, which in turn induces an irreversible phase transition, leading to the obstruction of lithium-ion insertion and extraction channels and causing rapid capacity decay. At the same time, high voltage will also exacerbate the interfacial side reactions between LCO material and electrolyte, which not only consumes electrolyte but also increases interfacial impedance, further deteriorating the cycle life and rate performance of the battery. Summary of the Invention

[0003] In order to suppress the irreversible phase transition and interfacial side reactions of LCO materials when operating in a high voltage environment above 4.5V, this invention provides a method for preparing lithium cobalt oxide cathode material, cathode material, cathode electrode sheet and battery.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing lithium cobalt oxide cathode material includes the following steps: A solvothermal product is obtained by mixing a eutectic solvent, at least five metal salts, a phosphate, and a dopant source and then carrying out a solvothermal reaction; the dopant source includes fluorides or sulfides. The solvothermal product is subjected to pre-sintering, deep sintering, and rapid quenching to obtain a coating material precursor; the pre-sintering temperature is lower than the deep sintering temperature, and the cooling rate of the rapid quenching is >20℃ / s; and The lithium cobalt oxide cathode material is obtained by coating the precursor of the coating material onto the surface of the lithium cobalt oxide material, drying it, and then performing gradient sintering. The gradient sintering includes at least two sintering stages, with the temperature of the later sintering stage being higher than that of the previous sintering stage.

[0005] Preferably, the process of mixing a eutectic solvent, at least five metal salts, a phosphate, and a dopant source, followed by a solvothermal reaction to obtain a solvothermal product includes the following steps: Weigh at least five metal salts in equimolar ratio to form a metal salt solution with a total metal ion concentration of 0.2~1M, and dissolve it in a eutectic solvent to obtain the first mixed solution; A second mixed solution is obtained by dissolving diammonium hydrogen phosphate and ammonium fluoride or ammonium sulfide in ethylene glycol or water to prepare a 0.5-1.5M solution, which is then added dropwise to the first mixed solution. The second mixed solution is transferred to a reaction vessel and heated to 180-220°C at a heating rate of 3-5°C / min for 12-24 hours to obtain the solvothermal product.

[0006] Preferably, the solvothermal product comprises colloidal particles with a particle size of 10-30 nm.

[0007] Preferably, the process of pre-sintering, deep sintering, and rapid cooling of the solvothermal product to obtain the coating material precursor includes the following steps: Pre-sintering is carried out by heating to 300-400℃ at a rate of 2-5℃ / min under an inert atmosphere and holding for 1-3 hours to obtain the pre-sintered product. Deep sintering involves heating the pre-sintered product to 450-500°C at a rate of 3-5°C / min under an argon-hydrogen or nitrogen-hydrogen mixed atmosphere and holding it at that temperature for 1-5 hours to obtain the deep sintered product. Rapid cooling treatment is performed to rapidly cool the deep sintered product through airflow to obtain the coating material precursor, with a cooling rate >20℃ / s.

[0008] Preferably, the lithium cobalt oxide cathode material is obtained by coating the precursor of the coating material onto the surface of the lithium cobalt oxide material, followed by drying and gradient sintering, comprising the following steps: The lithium cobalt oxide particles are then surface-cleaned and dried. The coating material precursor is mixed with solvent and dispersant and then homogenized to obtain a coating slurry; The coating slurry is coated onto the surface of the lithium cobalt oxide particles using a ball milling or spraying process to obtain a preliminary coating product. The initial coating product was dried at 150-200°C to obtain a pre-formed cathode material. The pre-formed cathode material is subjected to gradient sintering in an inert atmosphere to obtain the lithium cobalt oxide cathode material. The gradient sintering includes a first sintering stage and a second sintering stage. The sintering temperature of the first sintering stage is 300-350℃, and the sintering time is 1-4 hours. The sintering temperature of the second sintering stage is 500-700℃, and the sintering time is 1-4 hours.

[0009] Preferably, the metal salt comprises at least five of the following metal elements: Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La.

[0010] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: A cathode material, wherein the cathode material is prepared by the above-described method for preparing lithium cobalt oxide cathode material.

[0011] Preferably, the cathode material comprises lithium cobalt oxide particles and a coating layer covering the lithium cobalt oxide particles. The coating layer comprises a phosphate-based high-entropy amorphous material with the structural formula (M)PO4-X, wherein the metal element M includes at least five of the following: Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La, and X is one of F or S.

[0012] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: A positive electrode sheet comprising the aforementioned positive electrode material.

[0013] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: A battery comprising the aforementioned positive electrode material.

[0014] Compared with the prior art, the method for preparing lithium cobalt oxide cathode material, the cathode material, the cathode sheet, and the battery provided by the present invention have the following beneficial effects: 1. A method for preparing a lithium cobalt oxide cathode material according to the present invention includes the following steps: mixing a eutectic solvent, at least five metal salts, a phosphate and a dopant source and then performing a solvothermal reaction to obtain a solvothermal product; the dopant source includes fluoride or sulfide; pre-sintering, deep sintering and rapid cooling of the solvothermal product to obtain a coating material precursor; the pre-sintering temperature is lower than the deep sintering temperature, and the cooling rate of the rapid cooling treatment is >20℃ / S; and coating the coating material precursor onto the surface of the lithium cobalt oxide material and then drying and gradient sintering to obtain the lithium cobalt oxide cathode material; the gradient sintering includes at least two sintering stages, the temperature of the later sintering stage is higher than that of the previous sintering stage. LCO cathode materials are prepared by coating the surface of LCO materials with a composite material formed by mixing high-entropy materials, phosphates, and fluorides or sulfides. When operating in a high-voltage environment above 4.5V, the structural distortion of the cobalt-oxygen octahedron in LCO materials can be suppressed, and oxygen evolution in the LCO lattice can be suppressed. In turn, the irreversible phase transition and interfacial side reactions of LCO cathode materials when operating in a high-voltage environment above 4.5V can be suppressed, enabling LCO cathode materials to have a wider range of applications.

[0015] 2. The present invention involves a solvothermal reaction of a eutectic solvent, at least five metal salts, a phosphate, and a dopant source to obtain a solvothermal product, comprising the following steps: Weighing at least five metal salts in equimolar ratio to form a metal salt solution with a total metal ion concentration of 0.2-1 M, dissolving it in the eutectic solvent to obtain a first mixed solution; dissolving diammonium hydrogen phosphate and ammonium fluoride or ammonium sulfide in ethylene glycol or water to prepare a 0.5-1.5 M solution, and adding it dropwise to the first mixed solution to obtain a second mixed solution; transferring the second mixed solution to a reaction vessel, and heating it to 180-220 °C at a heating rate of 3-5 °C / min for 12-24 hours to obtain the solvothermal product. The solvothermal reaction of the mixed solvent allows the five metal salt solutions to undergo amorphous nucleation-dominant growth, which is beneficial for promoting the formation of a high-entropy phase.

[0016] 3. The present invention provides a method for obtaining a coating material precursor by pre-sintering, deep sintering, and rapid quenching of a solvothermal product, comprising the following steps: pre-sintering, wherein the temperature is raised to 300-400°C at a rate of 2-5°C / min under an inert atmosphere and held for 1-3 hours to obtain a pre-sintered product; deep sintering, wherein the pre-sintered product is heated to 450-500°C at a rate of 3-5°C / min under an argon-hydrogen mixed atmosphere and held for 1-5 hours to obtain a deep sintered product; and rapid quenching, wherein the deep sintered product is rapidly quenched by an airflow to obtain a coating material precursor, with a cooling rate >20°C / s. The pre-sintering stage removes residual solvent and completes the phosphate condensation reaction, forming a stable (M)PO4-X framework structure; the deep sintering stage, by sintering under a reducing atmosphere, suppresses crystallization caused by the increase in the valence state of metal ions, maintaining disorder; and the rapid quenching, through rapid cooling, prevents atoms from arranging themselves in an orderly manner, further facilitating the maintenance of atomic disorder and promoting the formation of a high-entropy amorphous phase.

[0017] 4. The present invention provides a method for obtaining lithium cobalt oxide cathode material by coating a coating material precursor onto the surface of lithium cobalt oxide material, followed by drying and gradient sintering. This method includes the following steps: cleaning and drying the surface of lithium cobalt oxide particles; homogenizing the coating material precursor with solvent and dispersant to obtain a coating slurry; coating the coating slurry onto the surface of lithium cobalt oxide particles using ball milling or spraying to obtain a preliminary coating product; drying the preliminary coating product at 150-200°C to obtain a pre-formed cathode material; and gradient sintering the pre-formed cathode material in an inert atmosphere to obtain the lithium cobalt oxide cathode material. The gradient sintering includes a first sintering stage and a second sintering stage. The sintering temperature of the first sintering stage is 300-350°C, and the sintering time is 1-4 hours. The sintering temperature of the second sintering stage is 500-700°C, and the sintering time is 1-4 hours. The purpose of using a medium temperature in the first sintering stage is to promote a stable phase transformation; the purpose of using a high temperature in the second sintering stage is to promote Co-OP bonding. The bonding structure of Co-OP is beneficial for maintaining structural stability, and the high temperature also allows for the ashing of carbon-containing materials such as dispersants.

[0018] 5. The metal salts of the present invention comprise at least five of the following metal elements: Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La. The high-entropy material formed using these five metal salts can withstand a portion of the stress generated by internal lithium cobalt oxide lattice distortion, delaying the formation of microcracks and the overall collapse of the structure, thus enhancing structural stability.

[0019] 6. The cathode material of the present invention is prepared using the above-described method for preparing lithium cobalt oxide cathode material. 7. The cathode material of the present invention includes lithium cobalt oxide particles and a coating layer covering the lithium cobalt oxide particles. The coating layer includes a phosphate-based high-entropy amorphous material with the structural formula (M)PO4-X, wherein the metal element M includes at least five of Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La, and X is one of F or S. By combining the high-entropy material, phosphate, and F or S, when operating in a high-voltage environment above 4.5V, the structural distortion of the cobalt-oxygen octahedron in the LCO material can be suppressed, and oxygen evolution in the LCO lattice can be suppressed. This, in turn, can suppress the irreversible phase transition and interfacial side reactions of the LCO cathode material when operating in a high-voltage environment above 4.5V, enabling the LCO cathode material to have a wider range of applications.

[0020] 8. The positive electrode sheet of the present invention includes the above-mentioned positive electrode material and has the same beneficial effects as the above-mentioned method for preparing lithium cobalt oxide positive electrode material, which will not be described in detail here.

[0021] 9. The battery of the present invention includes the above-mentioned positive electrode material and has the same beneficial effects as the above-mentioned method for preparing lithium cobalt oxide positive electrode material, which will not be described in detail here. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the steps in the preparation method of lithium cobalt oxide cathode material provided in the first embodiment of the present invention.

[0024] Figure 2 This is a flowchart of step S1 in the method for preparing lithium cobalt oxide cathode material provided in the first embodiment of the present invention.

[0025] Figure 3 This is a flowchart of step S2 in the method for preparing lithium cobalt oxide cathode material provided in the first embodiment of the present invention.

[0026] Figure 4 This is a flowchart of step S3 in the method for preparing lithium cobalt oxide cathode material provided in the first embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] In the embodiments provided by this invention, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined based on A. However, it should also be understood that determining B based on A does not mean determining B solely based on A; B can also be determined based on A and / or other information.

[0029] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of the invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Those skilled in the art should also recognize that the embodiments described in the specification are optional embodiments, and the actions and modules involved are not necessarily essential to the invention.

[0030] In various embodiments of the present invention, it should be understood that the sequence number of each process does not necessarily imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0031] The flowcharts and block diagrams in the accompanying drawings illustrate methods and possible architectures, functions, and operations according to various embodiments of this application. In this regard, each block in the flowchart or block diagram may represent part of a step. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved.

[0032] Combination Figure 1 The first embodiment of the present invention provides a method for preparing lithium cobalt oxide cathode material, comprising the following steps: S1. A solvothermal product is obtained by mixing a eutectic solvent, at least five metal salts, a phosphate, and a dopant source and then performing a solvothermal reaction. The dopant source includes fluorides or sulfides. S2. The solvothermal products are pre-sintered, deeply sintered, and rapidly quenched to obtain a coating material precursor; the pre-sintering temperature is lower than the deep sintering temperature, and the cooling rate of the rapid quenching is >20℃ / s; and S3. After coating the precursor material onto the surface of the lithium cobalt oxide material, the material is dried and then subjected to gradient sintering to obtain the lithium cobalt oxide cathode material. The gradient sintering includes at least two sintering stages, with the temperature of the later sintering stage being higher than that of the previous sintering stage.

[0033] It is understandable that in LCO materials, cobalt (Co) atoms are surrounded by six oxygen (O) atoms in an octahedral shape, forming a cobalt-oxygen octahedral structure. During the delithiation process in LCO materials, due to the reduction of positive charge, in order to maintain the charge neutrality of the material, cobalt ions must be oxidized to compensate for the charge, i.e., from Co... 3+ to become Co 4+ And Co 4+ It is a very unstable cation with a stronger electron-acquiring ability and a stronger attraction (polarization) to surrounding oxygen ions than Co. 3+ Much stronger, due to Co 4+ The strong attraction to oxygen ions causes the entire cobalt-oxygen octahedron to shrink and distort, affecting structural stability and making it easier for oxygen ions to escape from the lattice. Under high voltage (>4.5V), excessive delithiation leads to Co... 4+ If the proportion is too high, its strong oxidizing properties cause oxygen to lose electrons. Combined with the structural instability caused by the contraction and distortion of the cobalt-oxygen octahedron, two adjacent lattice oxygen molecules will combine to form O2 molecules and precipitate (i.e., lattice oxygen evolution). Oxygen precipitation leads to a transformation of the crystal structure from an ordered layered structure to a disordered spinel or even rock salt phase, causing an irreversible phase transition. Simultaneously, Co... 4+ It is a very strong oxidizing agent, which strongly strips electrons from electrolyte molecules, thereby catalyzing the oxidative decomposition of the electrolyte. Oxygen released from the crystal lattice also has extremely strong oxidizing properties, accelerating electrolyte decomposition. Under high voltage, solvent molecules in the electrolyte are forced to lose electrons and undergo oxidation reactions, producing gases such as CO2 and CO, as well as various organic esters and polymers as byproducts. These byproducts do not completely dissolve; they deposit on the surface of LCO material particles, forming a cathode electrolyte interphase (CEI) film. Therefore, under high voltage environments above 4.5V, the interfacial side reactions between the LCO material and the electrolyte are intensified, leading to the formation of a thick and unstable cathode electrolyte interphase (CEI) film on the positive electrode surface, increasing interfacial impedance.

[0034] The method for preparing lithium cobalt oxide cathode material provided in the first embodiment of the present invention involves forming a coating material precursor through steps S1 and S2, and then coating the coating material precursor onto the surface of LCO material through step S3, thereby forming a coating layer on the surface of LCO material. The coating layer includes a high-entropy material formed by five metal salts and a phosphate-based high-entropy amorphous material formed by phosphate.

[0035] The PO bonds in the phosphate groups provided by the phosphate in the coating layer have extremely high bond energies. The robust three-dimensional network formed by these PO bonds can effectively "lock" oxygen ions, significantly increasing the energy barrier for oxygen evolution. This thermodynamically and kinetically inhibits lattice oxygen evolution, thereby suppressing structural phase transitions. Simultaneously, the phosphate material used in the coating layer also possesses a certain mechanical strength, capable of withstanding the stress generated by volume changes during LCO material cycling, preventing particle breakage, and maintaining interfacial integrity.

[0036] High-entropy materials in the coating layer can conduct Li more uniformly. + This can alleviate excessive delithiation and oxidation of Co ions at the interface to some extent, reducing Co at the source. 4+ The formation of high-entropy materials inhibits structural distortion of cobalt-oxygen octahedra; the high-entropy stabilizing effect of high-entropy materials also makes them very "inert" under high pressure, making them difficult to oxidize and decompose, thus inhibiting lattice oxygen evolution; the various cations of high-entropy materials can form stronger and more diverse metal-oxygen bonds with oxygen on the surface of LCO materials, directly "anchoring" oxygen atoms and increasing the energy barrier for oxygen evolution, even if the internal Co... 4+ In an attempt to pull oxygen outwards, the high-entropy structure on the surface can provide additional stability, preventing oxygen from escaping and inhibiting oxygen evolution in the lattice. High-entropy materials can also withstand some of the stress generated by the lattice distortion of the internal LCO material, delaying the formation of microcracks and the overall collapse of the structure, thus enhancing its stability.

[0037] In addition, doping sources such as S or F are introduced into the coating layer. The presence of F helps to form a LiF-rich cathode electrolyte interface (CEI) film in the early stages of cycling. LiF has high interfacial energy and high lithium-ion conductivity. Although the bulk conductivity is not high, the extremely thin LiF interface layer can effectively conduct Li-ion electrolytes. + Simultaneously, it prevents electrons from passing through and is extremely dense and stable, greatly reducing subsequent side reactions; the extremely high electronegativity of F can also regulate the electron cloud distribution of surrounding metal ions, further enhancing the strength of the MO bond (M represents the metal element in the metal salt) and improving the overall structural stability. The introduction of S will form Li2S and Li... x SO y Sulfur-containing compounds, such as those that are good lithium-ion conductors, can significantly reduce interface impedance and improve rate performance.

[0038] In summary, the lithium cobalt oxide cathode material preparation method provided in the first embodiment of the present invention prepares an LCO cathode material by coating a composite material formed by mixing a high-entropy material, phosphate, and fluoride or sulfide onto the surface of an LCO material. When operating in a high-voltage environment above 4.5V, it can suppress the structural distortion of the cobalt-oxygen octahedron in the LCO material and suppress oxygen evolution in the LCO material lattice. In turn, it can suppress the irreversible phase transition and interfacial side reactions of the LCO cathode material when operating in a high-voltage environment above 4.5V, thus enabling the LCO cathode material to have a wider range of applications.

[0039] Furthermore, in step S1, the eutectic solvent has both reducing and coordinating abilities, which can prevent the hydrolysis of metal ions and promote uniform dispersion. The solvothermal reaction can cause the metal ions to recombine and form an amorphous structure.

[0040] It is understandable that the uniform dispersion of high-entropy materials leads to lattice distortion, slow diffusion, and the cocktail effect, endowing high-entropy materials with excellent comprehensive properties. Amorphous structures, because they lack the defects of traditional crystalline materials such as grain boundaries and dislocations, usually possess extremely high hardness, strength, wear resistance, and fatigue resistance. When used as coating materials, they can mechanically suppress the volume expansion and structural breakage of electrode materials during cycling, further enhancing the stability of the structure.

[0041] Specifically, in one embodiment of the present invention, the eutectic solvent in step S1 can be prepared by mixing polyethylene glycol 200 and urea at a molar ratio of 2:1 and stirring in an oil bath at 60°C until a transparent liquid is formed. It is understood that in other embodiments, the eutectic solvent can also be prepared in other ways, as long as the same function can be achieved. The volume ratio of phosphate to dopant source is 3:1.

[0042] Further, in step S1, the metal salt contains at least five of the following metal elements: Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La. The type of metal salt can be one of nitrates, acetates, sulfates, or hydrochlorides. The phosphate salt includes one or more of the following materials: diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and triethyl phosphate. The dopant source includes one of the following: ammonium fluoride, ammonium sulfide, thiourea, and thioacetamide.

[0043] As a preferred approach, hydrochloride salts are used as the metal salts because the chloride ions in hydrochloride salts help form a porous structure. The pores within this porous structure can act as buffer spaces to absorb the mechanical stress generated by volume changes, preventing the material particles from breaking and pulverizing, thereby significantly improving the structural stability and cycle life of the material. As a preferred approach, five metal salts are used: TiCl4, ZrOCl2, MnCl2, FeCl3, and VCl3. As a preferred approach, diammonium hydrogen phosphate is used as the phosphate.

[0044] It is understandable that the temperature of pre-sintering in step S2 is lower than that of deep sintering, and the temperature of the next sintering stage in step S3 is higher than that of the previous sintering stage. The temperature referred to here is the peak temperature.

[0045] Combination Figure 2 The specific steps of step S1 include: S11. Weigh at least five metal salts in equal molar ratio to form a metal salt solution with a total metal ion concentration of 0.2~1M, and dissolve it in a eutectic solvent to obtain a first mixed solution; S12. Dissolve diammonium hydrogen phosphate and ammonium fluoride or ammonium sulfide in ethylene glycol or water to prepare a 0.5~1.5M solution, and add it dropwise to the first mixed solution to obtain a second mixed solution; S13. Transfer the second mixed solution to a reaction vessel and heat it to 180-220°C at a heating rate of 3-5°C / min for 12-24 hours to obtain a solvothermal product.

[0046] Specifically, in step S11, the mass ratio of the eutectic solvent to the metal salt is controlled between (1:3) and (1:5) to ensure sufficient complexation. It can be understood that the metal salt here refers to the total mass of at least five metals.

[0047] Specifically, in step S12, diammonium hydrogen phosphate and ammonium fluoride or ammonium sulfide are dissolved in ethylene glycol or water to prepare a 0.5-1.5M solution, which is then slowly added dropwise to the first mixed solution. The purpose of this slow addition is to force the at least five metal ions with different chemical properties from those in step S11 to co-precipitate synchronously and uniformly, thereby achieving a highly uniform mixture at the molecular level and ensuring that the high-entropy material is ultimately highly uniformly mixed at the atomic scale. Furthermore, the molar ratio of phosphate to total metal salt is 1.2:1 to ensure an excess of phosphate ions to compensate for volatilization losses.

[0048] As a preferred method, in step S11, at least five metal salts are weighed in equimolar ratio to form a metal salt solution with a total metal ion concentration of 0.5 M, which is then dissolved in a eutectic solvent to obtain a first mixed solution. In step S12, diammonium hydrogen phosphate and ammonium fluoride or ammonium sulfide are dissolved in ethylene glycol or water to prepare a 0.8 M solution, which is then added dropwise to the first mixed solution to obtain a second mixed solution. As a preferred embodiment, the reaction vessel in step S13 is a polytetrafluoroethylene-lined reactor. In other embodiments, other reaction vessels capable of achieving the same purpose may also be used.

[0049] It is understandable that the solvothermal reaction in step S13 can lead to amorphous nucleation-dominated growth, forming colloidal particles with a diameter of 10-30 nm. The reaction process requires controlling the heating rate to 3-5 °C / min to promote the formation of the high-entropy phase. These colloidal particles are understood to be primary nanoparticles of high-entropy amorphous phosphate (M)PO4-X. Due to their extremely small size and uniform dispersion in the solvent, they constitute a stable colloidal system. Forming colloidal particles enables high-entropy uniform mixing and lays the foundation for the amorphous structure. The nanoscale colloidal particles possess extremely high specific surface area and surface energy, allowing them to better adhere to the surface of lithium cobalt oxide (LCO) particles in subsequent processes, forming a dense and uniform thin layer through heat treatment. The particle size of 10-30 nm helps improve the uniformity and density of the coating, and after sintering, a thin layer of approximately 5-10 nm can be formed, enhancing ionic conductivity. In addition, the high specific surface area and high reactivity help the coating to form Co-OP more fully and efficiently with LCO, and the nano-sized amorphous particles have the effect of enhancing structural stability and buffering stress.

[0050] Combination Figure 3 The specific steps of step S2 include: S21. Pre-sintering: Under an inert atmosphere, the temperature is increased to 300-400℃ at a rate of 2-5℃ / min, and the temperature is held for 1-3 hours to obtain the pre-sintered product. S22. Deep sintering: The pre-sintered product is heated to 450-500℃ at 3-5℃ / min under an argon-hydrogen or nitrogen-hydrogen mixed atmosphere and held for 1-5 hours to obtain the deep sintered product. S23. Rapid cooling treatment: The deep sintered product is rapidly cooled by airflow to obtain the coating material precursor, with a cooling rate >20℃ / s.

[0051] Preferably, the inert atmosphere in step S21 is a nitrogen atmosphere.

[0052] It is understandable that the pre-sintering stage in step S21 removes residual solvent and completes the phosphate condensation reaction, forming a stable (M)PO4-X framework structure. The deep sintering stage in step S22, sintering under a reducing atmosphere, suppresses crystallization caused by the increase in the valence state of metal ions, maintaining disorder. The rapid cooling process in step S23 prevents atoms from arranging themselves in an orderly manner, further contributing to maintaining atomic disorder and promoting the formation of a high-entropy amorphous phase.

[0053] Furthermore, prior to step S21, a cleaning process is included to remove impurities and obtain pure, well-dispersed, easy-to-store and subsequently applied nanomaterials. This involves washing the solvothermal product with ethanol and deionized water 3 to 5 times, followed by pre-sintering, deep sintering, and rapid cooling.

[0054] Combination Figure 4 The specific steps of step S3 include: S31. The lithium cobalt oxide material particles are cleaned and dried. S32. The coating material precursor is mixed with solvent and dispersant and then homogenized to obtain coating slurry; S33. The coating slurry is coated onto the surface of lithium cobalt oxide material particles by ball milling or spraying to obtain the initial coating product; S34. The initial coated product is dried at 150~200℃ to obtain the pre-formed cathode material. S35. The preformed cathode material is placed in an inert atmosphere and subjected to gradient sintering to obtain lithium cobalt oxide cathode material. The gradient sintering includes a first sintering stage and a second sintering stage. The sintering temperature of the first sintering stage is 300~350℃ and the sintering time is 1~4h. The sintering temperature of the second sintering stage is 500~700℃ and the sintering time is 1~4h.

[0055] Preferably, the inert atmosphere in step S35 is an argon atmosphere.

[0056] Further, the specific steps of step S31 are as follows: ultrasonically clean the LCO material particles with anhydrous ethanol for 10-30 minutes, followed by vacuum drying at 100-150℃ for 20-50 minutes. The purpose is to remove residual alkali from the surface of the LCO material particles.

[0057] Further, the solvent in step S32 includes one or more of N-methylpyrrolidone, dimethylacetamide, ethanol, isopropanol, and water; the dispersant includes one or more of polyacrylic acid, ammonium polyacrylate, polyvinylpyrrolidone, and sodium carboxymethyl cellulose. Further, in step S32, the coating material precursor, solvent, and dispersant form a dispersion system, wherein the weight percentage of the dispersant in this dispersion system is 0.5 wt%, that is, the mass of the dispersant accounts for 0.5 wt% of the total mass of the entire dispersion system. Further, the solid content of the coating material precursor is 5-10 wt%, that is, the mass of the solid powder of the coating material precursor accounts for 5% to 10% of the total mass of the entire coating material precursor-solvent-dispersant system.

[0058] Furthermore, the homogenization process in step S32 specifically involves: ball milling the mixed material for 1 hour (300 rpm, zirconium oxide balls: slurry = 3:1) followed by ultrasonic dispersion for 30 minutes.

[0059] As a preferred embodiment, step S33 employs a spraying process to coat the LCO material surface, i.e., uniformly spraying the coating slurry onto the LCO material surface. Specifically, an ultrasonic atomizing nozzle is used, with an atomization pressure of 0.3~0.4MPa and a spraying distance of 150mm. A multi-layer thin-spray strategy is adopted, and the coating layer thickness is controllable by controlling the number of sprays.

[0060] First coating layer: low flow rate (8~15 mL / min) to form an initial adhesion layer of ≤20 nm.

[0061] Subsequent coating layers: Gradually increase the flow rate to 15-20 mL / min, with a 3-5 minute interval between each layer (to allow the solvent to evaporate). After each coating layer is completed, increase the flow rate by 2-5 mL / min.

[0062] It is understandable that using a spraying process to uniformly spray the coating material precursor onto the surface of LCO material can increase uniformity and controllable additive thickness. At the same time, the spraying process is much cheaper than physical / chemical deposition, more controllable than ball milling (micron-level) coating, can be controlled at the nanometer level, and can be transferred to continuous production lines, which is conducive to industrialization.

[0063] It is understandable that the purpose of using low-temperature drying in step S34 is to remove solvents and other substances introduced during the spraying process and to form an initial coating film.

[0064] It is understandable that the purpose of using medium temperature in the first sintering stage in step S35 is to promote stable phase transformation; the purpose of using high temperature in the second sintering stage is to promote Co-OP bonding. The Co-OP bonding structure is conducive to maintaining structural stability, and high temperature can also cause carbon-containing materials such as dispersants to ashed.

[0065] It is understandable that the coating material precursor can stabilize the LCO material lattice, reduce oxygen vacancy concentration, inhibit oxygen evolution, and suppress electrolyte corrosion through a multi-element "cocktail effect," while simultaneously allowing Li... + Rapid transport. The spraying process enables uniform dispersion of the coating material precursor on the LCO material surface, while the staged temperature control of gradient sintering avoids high-entropy phase segregation, ensuring uniform elemental distribution. The LCO cathode material prepared by the LCO cathode material preparation method provided in the first embodiment of this invention can suppress phase transitions and interfacial side reactions under high pressure and improve Li... + Diffusion kinetics and reversible insertion / extraction, as well as relieving lattice stress and enhancing mechanical / chemical stability, can give batteries advantages such as high voltage stability, high specific capacity, and high cycle life when used as a positive electrode.

[0066] The second embodiment of the present invention provides a cathode material, which is prepared by the lithium cobalt oxide cathode material preparation method provided in the first embodiment of the present invention.

[0067] Furthermore, the cathode material provided in the second embodiment of the present invention includes lithium cobalt oxide particles and a coating layer covering the lithium cobalt oxide particles. The coating layer includes a phosphate-based high-entropy amorphous material with the structural formula (M)PO4-X, wherein the metal element M includes at least five of Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La, and X is one of F or S.

[0068] As a preferred approach, the metallic element M includes five types: Ti, V, Zr, Mn, and Fe.

[0069] Furthermore, the thickness of the coating layer is 10~15 nm. Preferably, it is 10 nm.

[0070] It is understood that the cathode material provided in the second embodiment of the present invention has the same beneficial effects as the lithium cobalt oxide cathode material preparation method provided in the first embodiment of the present invention, and will not be described in detail here.

[0071] The third embodiment of the present invention provides a positive electrode sheet, which includes the positive electrode material provided in the second embodiment of the present invention.

[0072] To verify the performance of the positive electrode provided in the third embodiment of the present invention, the present invention was tested using the first positive electrode of Experimental Example 1.

[0073] Experimental Example 1: The first positive electrode sheet was prepared as follows: (1) The active material is a lithium cobalt oxide cathode material prepared using the lithium cobalt oxide cathode material preparation method provided in the first embodiment of the present invention. The specific preparation method is as follows: Step 1: Mix polyethylene glycol 200 and urea at a molar ratio of 2:1 and stir in an oil bath at 60°C until a transparent liquid is formed to prepare a eutectic solvent; Step 2: Weigh TiCl4, ZrOCl2, MnCl2, FeCl3, and VCl3 in equimolar ratio to form a metal salt solution with a total metal ion concentration of 0.5M. Dissolve the metal salt in a eutectic solvent to obtain the first mixed solution; the mass ratio of the metal salt to the eutectic solvent is 1:4. Step 3: Dissolve diammonium hydrogen phosphate ((NH4)2HPO4) and ammonium fluoride (NH4F) in a mixed solution of deionized water and ethylene glycol (volume ratio 1:2) to prepare a 0.8M solution, and add it dropwise to the first mixed solution to obtain a second mixed solution; the mass ratio of diammonium hydrogen phosphate to the first mixed solution is 1.2:1. Step 4: Transfer the second mixed solution to a polytetrafluoroethylene-lined reactor and heat it to 200°C at a heating rate of 4°C / min for 12 hours to obtain a solvothermal product. Step 5: Wash the solvothermal product three times each with deionized water and ethanol; Step 6: Pre-sintering, deep sintering, and rapid cooling of the solvothermal products: Pre-sintering: Under a nitrogen atmosphere, the temperature is increased to 350℃ at 2℃ / min and held for 2 hours to obtain the pre-sintered product; Deep sintering involves heating the pre-sintered product to 480°C at a rate of 5°C / min and holding it at that temperature for 3 hours under an argon-hydrogen mixed atmosphere to obtain the deep sintered product. Rapid cooling treatment: The deep sintered product is rapidly cooled by airflow to obtain the coating material precursor, with a cooling rate of 25℃ / s. Step 7: Cleaning LCO material particles. Use anhydrous ethanol to ultrasonically clean LCO material particles for 10 minutes, then vacuum dry them at 120°C for 30 minutes, and then lay them flat on an ultrasonic vibration spraying table.

[0074] Step 8: The coating material precursor is mixed with N-methylpyrrolidone (NMP) and 0.5 wt% polyacrylic acid (PAA) and then homogenized to obtain the coating slurry; wherein the solid content of the coating material precursor is 8 wt%. Step 9: Use an ultrasonic atomizing nozzle to spray the coating slurry onto the surface of the LCO material to obtain the initial coating product; atomization pressure: 0.35MPa, spraying distance: 150mm, spraying times: 2 times; the first spraying flow rate is 10mL / min to form a 5nm initial adhesion layer, and the second spraying flow rate is 15mL / min to obtain a 15nm coating layer; Step 10: Dry the initial coated product at 180°C for 2 hours, then sinter it at 350°C for 1 hour for the first sintering stage, and then sinter it at 600°C for 2 hours for the second sintering stage. After cooling, the lithium cobalt oxide cathode material is obtained.

[0075] (2) The preparation method of the positive electrode sheet is as follows: Step 1: Slurry preparation The high-entropy coated lithium cobalt oxide active material (i.e., the lithium cobalt oxide cathode material prepared above), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were precisely weighed at a mass ratio of 92:4:4. First, the PVDF powder was dissolved in N-methylpyrrolidone solvent to form a homogeneous slurry. Then, the conductive agent and active material were added sequentially, and the mixture was thoroughly stirred using a high-speed mixer to obtain a cathode slurry of suitable viscosity.

[0076] Step 2: Current collector preparation and coating Battery-grade aluminum foil is cut to the required size to serve as the current collector. The slurry prepared in step one is then uniformly coated onto the aluminum foil surface using a doctor blade coater, and the coating thickness is controlled to determine the areal loading of the active material.

[0077] Step 3: Drying the electrode sheets The coated electrode was initially dried in an 80°C forced-air drying oven to evaporate most of the solvent. Then, the electrode was transferred to a 120°C vacuum drying oven and continuously vacuum dried for more than 12 hours to completely remove residual solvent and moisture.

[0078] Step 4: Electrode rolling and cutting The completely dried electrode sheets are cold-pressed using a roller mill to compress their thickness to approximately 60% of their original thickness, thereby increasing the compaction density. Finally, the electrode sheets are punched into circular pieces of specified dimensions using a die to obtain the first positive electrode sheet, which is used for battery assembly.

[0079] (3) The first positive electrode sheet was prepared into a CR2032 coin cell with a lithium metal negative electrode according to the coin cell preparation process for electrical performance testing. The surface CEI film thickness, specific capacity (discharge rate 0.1C), and Li of the lithium cobalt oxide positive electrode material were tested. + Diffusion coefficient and cycling stability (capacity retention after 300 cycles at 4.6V / 0.5C).

[0080] The test results are as follows: The phase transition enthalpy of the lithium cobalt oxide cathode material of the present invention decreased by 62% when cycled at 4.6V using differential scanning calorimetry (DSC), which significantly enhanced the thermal stability of the bulk structure of the lithium cobalt oxide cathode material.

[0081] After cycling at 3.0V to 4.6V for 10 cycles, the surface CEI film thickness of the lithium cobalt oxide cathode material of the present invention was found to be 3 to 5 nm by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which is much lower than the traditional 15 nm.

[0082] The constant current charge-discharge test showed that the first discharge specific capacity at 4.6V / 0.1C rate reached 231mAh / g, and the first discharge specific capacity at 4.6V cutoff voltage was ≥230mAh / g.

[0083] Li was obtained by electrochemical impedance spectroscopy (EIS) analysis.+ The diffusion coefficient was increased to 3.8 × 10⁻⁶. -10 cm² / s.

[0084] Through constant current charge-discharge cycle testing, it was found that the capacity retention rate of the lithium cobalt oxide cathode material of the present invention is ≥85% after 300 cycles at 4.6V / 0.5C, which is 40% higher than that of traditional LCO cathode materials.

[0085] According to linear sweep voltammetry (LSV), the coating layer on the outside of the lithium cobalt oxide cathode material of the present invention increases the electrolyte decomposition initiation voltage to 4.8V (vs. Li+ / Li), while the electrolyte of conventional LCO material without coating layer begins to decompose at around 4.5V. It can be seen that the coating layer of the present invention effectively protects the lithium cobalt oxide cathode material and inhibits the oxidation of the electrolyte on its surface.

[0086] X-ray diffraction (XRD) showed that the XRD diffraction peaks were well maintained after 10 cycles of 3.0V to 4.6V, proving that the layered structure of the lithium cobalt oxide cathode material of the present invention was well maintained. Furthermore, SEM and TEM observations further confirmed that the lithium cobalt oxide cathode material of the present invention was free of microcracks and phase transitions.

[0087] The test results above show that the lithium cobalt oxide cathode material of the present invention can effectively suppress the irreversible phase transition and interfacial side reactions caused by LCO cathode material when working under a high voltage greater than 4.5V.

[0088] It is understood that the positive electrode provided in the third embodiment of the present invention has strong cycle stability under high voltage greater than 4.5V, can effectively reduce the thickness of CEI film on the surface of positive electrode material, and has the advantages of high specific capacity and long cycle life.

[0089] It is understood that the positive electrode sheet provided in the third embodiment of the present invention has the same beneficial effects as the lithium cobalt oxide positive electrode material preparation method provided in the first embodiment of the present invention, and will not be described in detail here.

[0090] The fourth embodiment of the present invention provides a battery including the positive electrode material provided in the second embodiment of the present invention. It can be understood that the battery provided in the fourth embodiment of the present invention has the same beneficial effects as the lithium cobalt oxide positive electrode material preparation method provided in the first embodiment of the present invention, and will not be described in detail here.

[0091] Furthermore, the battery provided in the fourth embodiment of the present invention includes a negative electrode, an electrolyte, a positive electrode provided in the third embodiment of the present invention, a separator, and a shell that contains the negative electrode, the electrolyte, the positive electrode, and the separator. The separator is located between the negative electrode and the positive electrode, and the electrolyte is filled inside the shell.

[0092] It is understandable that, since the positive electrode can operate under high voltage conditions above 4.5V, it can significantly improve energy density and achieve long battery life; at the same time, it has high power performance and can effectively reduce heat generation.

[0093] The foregoing has provided a detailed description of a method for preparing lithium cobalt oxide cathode material, the cathode material, the cathode sheet, and the battery disclosed in the embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing lithium cobalt oxide cathode material, characterized in that: Includes the following steps: A solvothermal product is obtained by mixing a eutectic solvent, at least five metal salts, a phosphate, and a dopant source and then carrying out a solvothermal reaction; the dopant source includes fluorides or sulfides. The solvothermal product is subjected to pre-sintering, deep sintering and rapid cooling to obtain a coating material precursor; the pre-sintering temperature is lower than the deep sintering temperature, and the cooling rate of the rapid cooling treatment is >20℃ / S; as well as The lithium cobalt oxide cathode material is obtained by coating the precursor of the coating material onto the surface of the lithium cobalt oxide material, drying it, and then performing gradient sintering. The gradient sintering includes at least two sintering stages, with the temperature of the later sintering stage being higher than that of the previous sintering stage.

2. The method for preparing lithium cobalt oxide cathode material as described in claim 1, characterized in that: The process of mixing a eutectic solvent, at least five metal salts, a phosphate, and a dopant source, followed by a solvothermal reaction to obtain a solvothermal product includes the following steps: Weigh at least five metal salts in equimolar ratio to form a metal salt solution with a total metal ion concentration of 0.2~1M, and dissolve it in a eutectic solvent to obtain the first mixed solution; A second mixed solution is obtained by dissolving diammonium hydrogen phosphate and ammonium fluoride or ammonium sulfide in ethylene glycol or water to prepare a 0.5-1.5M solution, which is then added dropwise to the first mixed solution. The second mixed solution is transferred to a reaction vessel and heated to 180-220°C at a heating rate of 3-5°C / min for 12-24 hours to obtain the solvothermal product.

3. The method for preparing lithium cobalt oxide cathode material as described in claim 2, characterized in that: The solvothermal products include colloidal particles with a particle size of 10-30 nm.

4. The method for preparing lithium cobalt oxide cathode material as described in claim 1, characterized in that: The process of pre-sintering, deep sintering, and rapid cooling of the solvothermal products to obtain the coating material precursor includes the following steps: Pre-sintering is carried out by heating to 300-400℃ at a rate of 2-5℃ / min under an inert atmosphere and holding for 1-3 hours to obtain the pre-sintered product. Deep sintering involves heating the pre-sintered product to 450-500°C at a rate of 3-5°C / min under an argon-hydrogen or nitrogen-hydrogen mixed atmosphere and holding it at that temperature for 1-5 hours to obtain the deep sintered product. Rapid cooling treatment is performed to rapidly cool the deep sintered product through airflow to obtain the coating material precursor, with a cooling rate >20℃ / s.

5. The method for preparing lithium cobalt oxide cathode material as described in claim 1, characterized in that: The process of coating the lithium cobalt oxide material with the coating material precursor, followed by drying and gradient sintering, yields the lithium cobalt oxide cathode material, comprising the following steps: The lithium cobalt oxide particles are then surface-cleaned and dried. The coating material precursor is mixed with solvent and dispersant and then homogenized to obtain a coating slurry; The coating slurry is coated onto the surface of the lithium cobalt oxide particles using a ball milling or spraying process to obtain a preliminary coating product. The initial coating product was dried at 150-200°C to obtain a pre-formed cathode material. The preformed cathode material is subjected to gradient sintering in an inert atmosphere to obtain the lithium cobalt oxide cathode material; the gradient sintering includes a first sintering stage and a second sintering stage, wherein the sintering temperature of the first sintering stage is 300~350℃ and the sintering time is 1~4h, and the sintering temperature of the second sintering stage is 500~700℃ and the sintering time is 1~4h.

6. The method for preparing lithium cobalt oxide cathode material as described in claim 1, characterized in that: The metal salt comprises at least five of the following metal elements: Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La.

7. A positive electrode material, characterized in that: The cathode material is prepared using the lithium cobalt oxide cathode material preparation method as described in any one of claims 1-6.

8. The cathode material as described in claim 7, characterized in that: The cathode material includes lithium cobalt oxide particles and a coating layer covering the lithium cobalt oxide particles. The coating layer includes a phosphate-based high-entropy amorphous material with the structural formula (M)PO4-X, wherein the metal element M includes at least five of the following: Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Mo, In, and La, and X is either F or S.

9. A positive electrode sheet, characterized in that: Including the cathode material as described in claim 7.

10. A battery, characterized in that: Including the cathode material as described in claim 7.

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