A high-voltage lithium cobalt oxide cathode material, a method for improving its spin state and use thereof

Abstract

The application discloses a high-voltage lithium cobalt oxide positive material, a method for improving spin state of the high-voltage lithium cobalt oxide positive material and application of the high-voltage lithium cobalt oxide positive material, and belongs to the technical field of battery preparation. The specific process is as follows: (1) preparing lithium cobalt oxide coarse material, and then crushing and screening the lithium cobalt oxide coarse material; (2) collecting the screened powder, and treating the powder by at least two of the following ways: magnetic field assistance, plasma treatment and calcination, so as to obtain the high-voltage lithium cobalt oxide positive material with improved spin state. The application cooperates different treatment ways of magnetic field, plasma and sintering treatment, and prepares the high-voltage lithium cobalt oxide positive material with high spin state Co 4+ , improves the lattice oxygen energy band coverage, and anchors the lattice oxygen sites; the volume expansion of the lithium cobalt oxide is inhibited by the magnetostriction effect, the ordered layered structure of the high-voltage lithium cobalt oxide positive material is arranged, and the Co 4+ dissolution in the high-voltage interval is inhibited, so that the defects of unstable material interface are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery preparation, and particularly relates to a high-voltage lithium cobalt oxide positive electrode material and a method and use for improving the spin state thereof. BACKGROUND

[0002] To cope with the excessive global carbon emissions, promote the transformation of green energy structure and form, and develop renewable clean energy is imperative. As a green energy storage product, lithium ion batteries have many advantages, including high energy density, high power density, long cycle life, no memory effect, and long service life. In recent years, they have been widely used in notebook computers, smart phones, digital cameras, camcorders and other small and medium-sized portable mobile devices. Lithium cobalt oxide (LiCoO2, hereinafter referred to as LCO) with a layered structure is the main component of the positive electrode of lithium ion batteries. Compared with lithium nickelate and lithium iron phosphate, the theoretical density of lithium cobalt oxide is higher, and the volume specific energy is the largest. With the in-depth research of LCO materials, the charging voltage of LCO has gradually increased from 4.2V to 4.45V, and even higher voltage levels, and the specific capacity can reach 185mAh g -1 Under the requirements of safety, environmental protection and long cycle application, the performance optimization of the new generation of lithium ion batteries should be strengthened to make them have fast charging properties and higher energy density, so as to better reflect the efficiency in actual use.

[0003] Currently, the consumer batteries that have been developed and utilized are mainly 4.2V lithium cobalt oxide / graphite systems, but with the national energy layout and expansion, the energy density of the batteries cannot meet the actual production needs. Increasing the charging cutoff voltage of lithium cobalt oxide (charged to 4.6V) is an effective way to achieve higher energy density. However, there are some difficulties in developing high-voltage LCO, which limits its application. When charged to 4.55V or above, a large number of lithium ions in LCO are removed, and the hexagonal crystal system with electrochemical activity is converted into a monoclinic crystal system without electrochemical activity. The occurrence of irreversible phase transition is accompanied by more irreversible sliding of Co-O layers; compared with the bulk phase, the destruction of the surface structure is also serious, and the high-oxidizing Co 4+ / O n- will cause irreversible harmful side reactions between the surface and the electrolyte, leading to O loss, Co dissolution and interface solvent decomposition, and at the same time, the surface will undergo structural degradation completely opposite to the synthesis process of LCO, i.e., the transformation from LiCoO2 to CoO, which will cause a sharp increase in surface resistance. This irreversible structural degradation process is always accompanied by continuous O loss and continuous failure in the surface region of LCO.

[0004] The capacity development of high-voltage lithium cobalt oxide positive electrode material is closely related to the evolution of its crystal structure and the stability of the positive electrode and electrolyte interface layer (CEI), therefore, it is crucial to stabilize the bulk phase structure of high-voltage lithium cobalt oxide and inhibit side reactions.

[0005] Currently, the lithium cobalt oxide positive electrode is mainly improved by means of surface coating, element doping, changing electrolyte components, etc. to improve the long cycle performance of the battery and reduce the loss of irreversible capacity of the battery. However, these technical means are only limited to improving the part of the active material transmission properties, delaying the rate of battery decay, and it is difficult to fundamentally solve the problems of poor reversibility of H1-3 / O1 phase change in the bulk phase and irreversible side reactions between the electrode and electrolyte, resulting in a significant reduction in the available active material, and the actual capacity development and the improvement of coulombic efficiency are very small. At present, there is still a high space for improvement in the research and development of high-voltage lithium cobalt oxide positive electrode material, therefore, it is crucial to design and develop a simple and effective synthesis method of high-voltage lithium cobalt oxide for improving its cycle stability, energy density and power density.

[0006] However, some documents report that oxygen-containing gas is continuously introduced into a calcination device, active oxygen (O + , O 2+ , O 3+ , etc.) with positive charge is generated by plasma discharge, the movement of the active oxygen is deflected by applying an electromagnetic field in the calcination device, the active oxygen is enriched near the powder material, on this basis, the utilization rate of active oxygen is improved, and the oxidation is strengthened and the required material is synthesized. However, it cannot solve the defects of poor reversibility of H1-3 / O1 phase change in the bulk phase and irreversible side reactions between the electrode and electrolyte of high-voltage lithium cobalt oxide positive electrode material during charging and discharging, and currently there is no related report on how to solve such problems. SUMMARY

[0007] In view of the above deficiencies in the prior art, the present application provides a high-voltage lithium cobalt oxide positive electrode material and a method for improving its spin state and use, the present application adopts at least two ways of magnetic field assistance, plasma treatment or high temperature sintering to prepare a high-voltage lithium cobalt oxide positive electrode material with high spin state Co 4+ , which can realize the arrangement of the ordered layered structure of the high-voltage lithium cobalt oxide positive electrode material, and can inhibit the dissolution of Co 4+ in the high-voltage interval, and solve the defect of unstable material interface.

[0008] To achieve the above object, the technical scheme adopted by the present application to solve its technical problems is:

[0009] A method for improving the spin state of a high-voltage lithium cobalt oxide positive electrode material, comprising the following steps:

[0010] (1) preparing lithium cobalt oxide coarse material, and then crushing and sieving it;

[0011] (2) Collect the sieved powder and treat the powder by at least two of the following methods: magnetic field assistance, plasma treatment and calcination, to obtain the high-voltage lithium cobalt oxide cathode material with elevated spin state.

[0012] Further, the lithium cobalt oxide is prepared by sintering or hydrothermal synthesis in step (1), and a magnetic field with a strength of 0.2-2.5T is applied during the preparation.

[0013] Further, the treatment process in step (2) is as follows: collect the sieved powder and place it in a magnetic field environment for sintering, to obtain the high-voltage lithium cobalt oxide cathode material with elevated spin state.

[0014] Further, the treatment process in step (2) is as follows: collect the sieved powder and place it in a magnetic field and plasma environment for sintering, to obtain the high-voltage lithium cobalt oxide cathode material with elevated spin state.

[0015] Further, the treatment process in step (2) is as follows: collect the sieved powder and place it in a plasma environment for sintering, to obtain the high-voltage lithium cobalt oxide cathode material with elevated spin state.

[0016] Further, the treatment process in step (2) is as follows: collect the sieved powder and place it in a magnetic field and plasma environment for sintering, to obtain the high-voltage lithium cobalt oxide cathode material with elevated spin state.

[0017] Further, the strength of the magnetic field applied in step (2) is 0.2-2.5T.

[0018] Further, the strength of the magnetic field applied in step (1) is 0.4-1T, and the strength of the magnetic field applied in step (2) is 0.4-1T.

[0019] Further, in step (1) for preparing the lithium cobalt oxide, the molar ratio of the cobalt source to the lithium source is 9:8-9:2, based on the molar ratio of cobalt to lithium.

[0020] Further, the molar ratio of the cobalt source to the lithium source is 9:4-3:1.

[0021] Further, in step (1) for preparing the lithium cobalt oxide, the cobalt source used is cobalt trioxide, cobalt oxide, cobalt hydroxide, cobalt sulfate or cobalt oxalate; and the lithium source is lithium carbonate, lithium hydroxide or lithium sulfate.

[0022] Further, after crushing in step (1), the powder is sieved, and the powder with a particle size of less than 100μm is collected for subsequent secondary sintering.

[0023] Further, the sintering temperature in step (1) is 750-950℃.

[0024] Further, the sintering time in step (1) is 14-20h.

[0025] Furthermore, the sintering temperature in step (2) is 750–950 °C.

[0026] Furthermore, the sintering time in step (2) is 14–20 h.

[0027] Furthermore, in step (2), the plasma treatment pressure is 3 to 10 Pa, the temperature during the treatment is 80 to 950 °C, and the working gas is H2 / N2.

[0028] Furthermore, in step (2), the plasma treatment pressure is 3-5 Pa, the temperature during the treatment is 100-300 °C, and the working gas is H2 / N2.

[0029] Furthermore, in step (2), the plasma treatment pressure is 5 Pa, the temperature during the treatment is 120-180 °C, and the working gas is H2 / N2.

[0030] A high-pressure lithium cobalt oxide cathode material with a high spin state was prepared using the method described above.

[0031] The above-mentioned high-voltage lithium cobalt oxide cathode material is used in the preparation of energy storage materials.

[0032] A lithium-ion battery that uses the aforementioned high-voltage lithium cobalt oxide as the positive electrode material.

[0033] The beneficial effects of this invention are:

[0034] 1. This invention prepares Co with high spin state by combining magnetic field assistance, plasma method and sintering. 4+ High-voltage lithium cobalt oxide cathode material. High-spin Co 4+ High-voltage lithium cobalt oxide cathode materials enhance Co-O electronic orbital coupling by altering the material's electronic state density, further modifying the local coordination structure of the CoO6 octahedron, especially improving Co-O6 performance under high cutoff voltage conditions. 4+ By anchoring lattice oxygen sites to the oxygen bandgap coverage, and suppressing the volume expansion of lithium cobalt oxide through the magnetostrictive effect, an ordered layered structure of high-voltage lithium cobalt oxide cathode is achieved; simultaneously, the high-voltage range can suppress Co 4+ Dissolution can solve the defect of unstable material interfaces.

[0035] 2. In the preparation of high-voltage lithium cobalt oxide cathode materials, this invention utilizes plasma treatment to improve the crystallinity of the material, increase its specific surface area, reduce agglomeration during material growth, and lower the temperature of the reaction system. Furthermore, the introduction of plasma can alter the surface properties of high-voltage lithium cobalt oxide, increase the formation energy of oxygen vacancies, and enhance the bonding force with the material by forming stable chemical bonds on the material surface, thereby improving the performance and lifespan of the cathode material.

[0036] 3、The high-voltage lithium cobalt oxide positive electrode material is prepared by adopting the two-step calcination mode, after the first sintering, the crystal lattice structure of the material is not completely stable, and defects and impurities may exist. In addition, the Li and Co ions in the material prepared by the first sintering also have the problem of uneven distribution, and the particles of the material have the phenomenon of mutual aggregation, which is easy to bring negative effects on the battery. Therefore, in order to eliminate these defects and impurities, the positive electrode material needs to be ground and sieved, and then the first sintering product with a suitable particle size is selected for the second sintering, so that the material is recrystallized, the crystal lattice is more stable, the defects and impurities are repaired and removed, and the battery performance and stability are improved. At the same time, the second sintering can also improve the particle size and distribution of the positive electrode material, improve the charge / discharge rate and cycle life, and further improve the battery performance.

[0037] 4、The high-voltage lithium cobalt oxide positive electrode material prepared by the application has a cut-off voltage of 4.6V, which is greatly improved compared with the charging voltage of 4.2V of the conventional (commercial) lithium cobalt oxide, and the potential of the lithium cobalt oxide material is fully developed, which can greatly improve the energy density of the battery. At the same time, the high-voltage lithium cobalt oxide positive electrode material has more Co 4+ content in the high-spin state than the conventional lithium cobalt oxide, and the Co 4+ in the high-spin state can inhibit the dissolution of Co 4+ , further improving the battery performance. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The first circle charge-discharge curve of the battery assembled by the high-voltage lithium cobalt oxide positive electrode material prepared in Example 1 of the application;

[0039] Figure 2 The long cycle curve of 300 cycles of charge-discharge of the battery assembled by the high-voltage lithium cobalt oxide positive electrode material prepared in Example 1 of the application;

[0040] Figure 3 The curve graph of the battery assembled by the high-voltage lithium cobalt oxide positive electrode material prepared in Example 1 of the application under different discharge rates;

[0041] Figure 4 The concentration detection of Co 4+ in the electrolyte after 10 cycles of the high-voltage lithium cobalt oxide positive electrode material prepared in Example 1 of the application;

[0042] Figure 5 The electron microscope graph of the electrode / electrolyte interface layer after 10 cycles of the high-voltage lithium cobalt oxide positive electrode material prepared in Example 1 and Comparative Example 3 of the application;

[0043] Figure 6 The schematic diagram of the device of the application. DETAILED DESCRIPTION

[0044] The specific embodiments of the present application are described below to enable those skilled in the art to understand the present application, but it should be clear that the present application is not limited to the scope of the specific embodiments, and that all the inventions utilizing the concept of the present application are within the scope of the present application as long as various changes are obvious to those skilled in the art within the spirit and scope of the present application defined and determined by the appended claims.

[0045] Example 1

[0046] A high-pressure lithium cobalt oxide positive electrode material with high spin state is prepared by magnetic field assisted sintering, and the specific process is as follows:

[0047] S1, preparation of lithium cobalt oxide material: 135g of tricobalt tetroxide is uniformly mixed with 26.8g of lithium carbonate (cobalt / lithium molar ratio 9:3.5), compacted, then loaded into a crucible, the electromagnetic field is turned on, the magnetic field strength is 1T, and sintering is carried out in an oxygen atmosphere at 850℃ in a muffle furnace for 16 hours. After sintering is completed, cooling is carried out for crushing and sieving, and the powder with a particle size less than 100μm is collected.

[0048] S2, the collected powder is mixed and compacted, then secondary sintering is carried out in an electromagnetic iron assisted (1T) muffle furnace at 850℃ in an oxygen atmosphere for 16 hours, and a micron-sized high-pressure lithium cobalt oxide positive electrode material is obtained.

[0049] Example 2

[0050] A high-pressure lithium cobalt oxide positive electrode material with high spin state is prepared by magnetic field assisted sintering, and the specific process is as follows:

[0051] S1, preparation of lithium cobalt oxide material: 135g of tricobalt tetroxide is uniformly mixed with 26.8g of lithium carbonate (cobalt / lithium molar ratio 9:3.5), compacted, then loaded into a crucible, the electromagnetic field is turned on, the magnetic field strength is 1T, and sintering is carried out in an oxygen atmosphere at 850℃ in a muffle furnace for 16 hours. After sintering is completed, cooling is carried out for crushing and sieving, and the powder with a particle size less than 100μm is collected.

[0052] S2, the collected powder is mixed and compacted, then secondary sintering is carried out in an electromagnetic iron assisted (1T) muffle furnace at 850℃ in an oxygen atmosphere for 16 hours, and a micron-sized high-pressure lithium cobalt oxide positive electrode material is obtained.

[0053] Example 3

[0054] A high-pressure lithium cobalt oxide positive electrode material with high spin state is prepared by magnetic field assisted and plasma method, and the specific process is as follows:

[0055] S1, Preparation of lithium cobaltate material: 93 g of cobalt hydroxide was added to 40 mL of absolute ethanol, continuously stirred for 30 minutes. At the same time, 9.3 g of lithium hydroxide was dissolved in 40 mL of deionized water, completely dissolved (cobalt / lithium molar ratio 9:3.5). Then, the LiOH solution was added dropwise to the cobalt hydroxide ethanol solution under vigorous stirring. The mixture was stirred for 2 hours to thoroughly mix the components. Subsequently, the solution was transferred to a 100 mL autoclave lined with polytetrafluoroethylene, then heated at 180°C for 24 hours. After cooling to room temperature, the precipitate was centrifuged and washed with ultrapure water and ethanol, then crushed and sieved after drying at 60°C for 12 hours.

[0056] S2, After the above collected powder was mixed and compacted, a lithium cobaltate precursor was treated in a H2 / N2 plasma atmosphere under the assistance of an electromagnet (1 T) to prepare a micron-sized high-pressure lithium cobaltate cathode material. The process was controlled to be carried out at a pressure of 8 Pa and a temperature of 120°C for 2 h.

[0057] Example 4

[0058] A plasma method for calcining to prepare a high-pressure lithium cobaltate cathode material with a high spin state, the specific process is as follows:

[0059] S1, Preparation of lithium cobaltate material: 93 g of cobalt hydroxide was added to 40 mL of absolute ethanol, continuously stirred for 30 minutes. At the same time, 9.3 g of lithium hydroxide was dissolved in 40 mL of deionized water, completely dissolved (cobalt / lithium molar ratio 9:3.5). Then, the LiOH solution was added dropwise to the cobalt hydroxide ethanol solution under vigorous stirring. The mixture was stirred for 2 hours to thoroughly mix the components. Subsequently, the solution was transferred to a 100 mL autoclave lined with polytetrafluoroethylene, then heated at 180°C for 24 hours. After cooling to room temperature, the precipitate was centrifuged and washed with ultrapure water and ethanol, then crushed and sieved after drying at 60°C for 12 hours.

[0060] S2, After the above collected powder was mixed and compacted, a lithium cobaltate precursor was treated in a H2 / N2 plasma atmosphere under the assistance of an electromagnet (1 T) to prepare a micron-sized high-pressure lithium cobaltate cathode material. The process was controlled to be carried out at a pressure of 8 Pa and a temperature of 120°C for 2 h.

[0061] Example 5

[0062] A magnetic field assisted plasma method for sintering to prepare a high-pressure lithium cobaltate cathode material with a high spin state, the specific process is as follows:

[0063] S1, Preparation of lithium cobalt oxide material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 2.5 T. Sintering was performed in an oxygen atmosphere at 850°C for 14 hours in a muffle furnace. After sintering was completed, the temperature was lowered and the powder was crushed and sieved. The powder with a particle size of less than 100 μm was collected.

[0064] S2, The collected powder was mixed and compacted, and then treated in an H2 / N2 plasma atmosphere to prepare micron-sized high-pressure lithium cobalt oxide positive electrode material. The process was controlled to be performed at a pressure of 5 Pa and a temperature of 150°C for 2 h. Secondary sintering was performed in an electromagnetic iron auxiliary (2.5 T) muffle furnace at 850°C in an oxygen atmosphere for 20 hours to obtain micron-sized high-pressure lithium cobalt oxide positive electrode material.

[0065] Example 6

[0066] A magnetic field assisted plasma sintering method for preparing high-pressure lithium cobalt oxide positive electrode material with high spin state, the specific process is as follows:

[0067] S1, Preparation of lithium cobalt oxide material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1.25 T. Sintering was performed in an oxygen atmosphere at 750°C for 16 hours in a muffle furnace. After sintering was completed, the temperature was lowered and the powder was crushed and sieved. The powder with a particle size of less than 100 μm was collected.

[0068] S2, The collected powder was mixed and compacted, and then treated in an H2 / N2 plasma atmosphere to prepare micron-sized high-pressure lithium cobalt oxide positive electrode material. The process was controlled to be performed at a pressure of 10 Pa and a temperature of 150°C for 2 h. Secondary sintering was performed in an electromagnetic iron auxiliary (1.2 T) muffle furnace at 750°C in an oxygen atmosphere for 14 hours to obtain micron-sized high-pressure lithium cobalt oxide positive electrode material.

[0069] Example 7

[0070] A magnetic field assisted sintering method for preparing high-pressure lithium cobalt oxide positive electrode material with high spin state, the specific process is as follows:

[0071] S1, Preparation of lithium cobalt oxide material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1 T. Sintering was performed in an oxygen atmosphere at 950°C for 16 hours in a muffle furnace. After sintering was completed, the temperature was lowered and the powder was crushed and sieved. The powder with a particle size of less than 100 μm was collected.

[0072] S2, the collected powder is mixed and compacted, and then secondarily sintered at 950°C in an oxygen atmosphere in a muffle furnace with the assistance of an electromagnet (1T) for 20 hours to obtain micron-sized high-pressure lithium cobalt oxide positive electrode materials.

[0073] Example 8

[0074] A method for magnetically assisted sintering to prepare high-pressure lithium cobalt oxide positive electrode materials with high spin states, the specific process is as follows:

[0075] S1, preparation of lithium cobalt oxide material: 135g of tricobalt tetroxide is uniformly mixed with 26.8g of lithium carbonate (molar ratio of cobalt to lithium 9:3.5), compacted, then loaded into a crucible, the electromagnetic field is turned on, the magnetic field strength is 1T, and sintered at 850°C in an oxygen atmosphere in a muffle furnace for 14 hours. After sintering, cool down and crush and sieve, collect the powder with particle size less than 100μm.

[0076] S2, the collected powder is mixed and compacted, and then secondarily sintered at 950°C in an oxygen atmosphere in a muffle furnace with the assistance of an electromagnet (1T) for 20 hours to obtain micron-sized high-pressure lithium cobalt oxide positive electrode materials.

[0077] Example 9

[0078] A method for magnetically assisted sintering to prepare high-pressure lithium cobalt oxide positive electrode materials with high spin states, the specific process is as follows:

[0079] S1, preparation of lithium cobalt oxide material: 135g of tricobalt tetroxide is uniformly mixed with 26.8g of lithium carbonate (molar ratio of cobalt to lithium 9:3.5), compacted, then loaded into a crucible, the electromagnetic field is turned on, the magnetic field strength is 1T, and sintered at 850°C in an oxygen atmosphere in a muffle furnace for 14 hours. After sintering, cool down and crush and sieve, collect the powder with particle size less than 100μm.

[0080] S2, the collected powder is mixed and compacted, and then secondarily sintered at 950°C in an oxygen atmosphere in a muffle furnace with the assistance of an electromagnet (1T) for 20 hours to obtain micron-sized high-pressure lithium cobalt oxide positive electrode materials.

[0081] Comparative Example 1

[0082] A method for magnetically assisted sintering to prepare high-pressure lithium cobalt oxide positive electrode materials, which is different from Example 1 in that the molar ratio of tricobalt tetroxide and lithium carbonate in the synthesis is different, the specific process is as follows:

[0083] Preparation of lithium cobaltate material: 135 g of tricobalt tetroxide and 20.1 g of lithium carbonate (cobalt / lithium molar ratio 9:8) were mixed uniformly and compacted, then loaded into a crucible, the electromagnetic field was turned on, the magnetic field strength was 1 T, and sintering was carried out at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours. After sintering was completed, the temperature was lowered and the mixture was crushed and sieved. The crushed mixture was compacted, and secondary sintering was carried out at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours to obtain micron-sized high-pressure lithium cobaltate positive electrode material.

[0084] Comparative Example 2

[0085] A method for synthesizing high-pressure lithium cobaltate positive electrode material with the assistance of a magnetic field, which is different from Example 1 in that the molar ratio of tricobalt tetroxide and lithium carbonate in the synthesis is different, and the specific process is as follows:

[0086] Preparation of lithium cobaltate material: 135 g of tricobalt tetroxide and 33.5 g of lithium carbonate (cobalt / lithium molar ratio 9:2) were mixed uniformly and compacted, then loaded into a crucible, the electromagnetic field was turned on, the magnetic field strength was 1 T, and sintering was carried out at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours. After sintering was completed, the temperature was lowered and the mixture was crushed and sieved. The crushed mixture was compacted, and secondary sintering was carried out at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours to obtain micron-sized high-pressure lithium cobaltate positive electrode material.

[0087] Comparative Example 3

[0088] A method for synthesizing high-pressure lithium cobaltate positive electrode material without the assistance of a magnetic field, which is different from Example 1 in that the synthesis process is carried out without applying a magnetic field, and the specific process is as follows:

[0089] Preparation of lithium cobaltate material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly and compacted, then loaded into a crucible, and sintering was carried out at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours. After sintering was completed, the temperature was lowered and the mixture was crushed and sieved. The crushed mixture was compacted, and secondary sintering was carried out at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours to obtain micron-sized high-pressure lithium cobaltate positive electrode material.

[0090] Comparative Example 4

[0091] A method for synthesizing high-pressure lithium cobaltate positive electrode material with the assistance of a magnetic field, which is different from Example 1 in that the synthesis process is carried out under a strong magnetic field, and the specific process is as follows:

[0092] Preparation of lithium cobaltate material: 135g of tricobalt tetroxide and 26.8g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 3T. The sample was sintered in an oxygen atmosphere at 850°C for 16 hours in a muffle furnace. After sintering was completed, the sample was cooled and crushed and sieved. The crushed mixture was compacted and then subjected to secondary sintering in an oxygen atmosphere at 850°C for 16 hours in a muffle furnace with the assistance of an electromagnet (1T), to obtain micron-sized high-pressure lithium cobaltate positive electrode material.

[0093] Comparative Example 5

[0094] A method for synthesizing high-pressure lithium cobaltate positive electrode material with the assistance of a magnetic field, which differs from Example 1 in that the temperature during synthesis is different, and the specific process is as follows:

[0095] Preparation of lithium cobaltate material: 135g of tricobalt tetroxide and 26.8g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1T. The sample was sintered in an oxygen atmosphere at 450°C for 16 hours in a muffle furnace. After sintering was completed, the sample was cooled and crushed and sieved. The crushed mixture was compacted and then subjected to secondary sintering in an oxygen atmosphere at 450°C for 16 hours in a muffle furnace with the assistance of an electromagnet (1T), to obtain micron-sized high-pressure lithium cobaltate positive electrode material.

[0096] Comparative Example 6

[0097] A method for synthesizing high-pressure lithium cobaltate positive electrode material with the assistance of a magnetic field, which differs from Example 1 in that the temperature during synthesis is different, and the specific process is as follows:

[0098] Preparation of lithium cobaltate material: 135g of tricobalt tetroxide and 26.8g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1T. The sample was sintered in an oxygen atmosphere at 1050°C for 16 hours in a muffle furnace. After sintering was completed, the sample was cooled and crushed and sieved. The crushed mixture was compacted and then subjected to secondary sintering in an oxygen atmosphere at 1050°C for 16 hours in a muffle furnace with the assistance of an electromagnet (1T), to obtain micron-sized high-pressure lithium cobaltate positive electrode material.

[0099] Comparative Example 7

[0100] A method for synthesizing high-pressure lithium cobaltate positive electrode material with the assistance of a magnetic field, which differs from Example 1 in that the sintering atmosphere during synthesis is different, and the specific process is as follows:

[0101] Preparation of lithium cobalt oxide material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1 T. The mixture was sintered in a muffle furnace at 850°C in an air atmosphere for 16 hours. After sintering was completed, the mixture was cooled and crushed and sieved. The crushed mixture was compacted and then sintered again in a muffle furnace at 850°C in an air atmosphere for 16 hours with the assistance of an electromagnet (1 T). A micron-sized high-voltage lithium cobalt oxide positive electrode material was obtained.

[0102] Comparative Example 8

[0103] A method for synthesizing a high-voltage lithium cobalt oxide positive electrode material with the assistance of a magnetic field, which differs from Example 1 in that the sintering time during synthesis is different, and the specific process is as follows:

[0104] Preparation of lithium cobalt oxide material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1 T. The mixture was sintered in a muffle furnace at 850°C in an air atmosphere for 16 hours. After sintering was completed, the mixture was cooled and crushed and sieved. The crushed mixture was compacted and then sintered again in a muffle furnace at 850°C in an air atmosphere for 16 hours with the assistance of an electromagnet (1 T). A micron-sized high-voltage lithium cobalt oxide positive electrode material was obtained.

[0105] Comparative Example 9

[0106] A method for synthesizing a high-voltage lithium cobalt oxide positive electrode material with the assistance of a magnetic field, which differs from Example 1 in that the sintering time during synthesis is different, and the specific process is as follows:

[0107] Preparation of lithium cobalt oxide material: 135 g of tricobalt tetroxide and 26.8 g of lithium carbonate (cobalt / lithium molar ratio 9:3.5) were mixed uniformly, compacted, and then loaded into a crucible. The electromagnetic field was turned on, with a magnetic field strength of 1 T. The mixture was sintered in a muffle furnace at 850°C in an air atmosphere for 16 hours. After sintering was completed, the mixture was cooled and crushed and sieved. The crushed mixture was compacted and then sintered again in a muffle furnace at 850°C in an air atmosphere for 16 hours with the assistance of an electromagnet (1 T). A micron-sized high-voltage lithium cobalt oxide positive electrode material was obtained.

[0108] Comparative Example 10

[0109] A method for synthesizing a high-voltage lithium cobalt oxide positive electrode material, which differs from Example 1 in that a finished lithium cobalt oxide is directly used to prepare a positive electrode material, and the specific process is as follows:

[0110] The finished lithium cobalt oxide was collected and sieved, and then a positive electrode material was prepared in the manner described in Example 1.

[0111] Comparative Example 11

[0112] A method for synthesizing high-voltage lithium cobaltate positive electrode material, which is different from example 1 in that only one sintering process is performed in the synthesis, and the specific process is as follows:

[0113] Preparation of lithium cobaltate material: 135g of tricobalt tetroxide is uniformly mixed with 20.1g of lithium carbonate (cobalt / lithium molar ratio 9:3.5), compacted, and then loaded into a crucible, and sintered at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours. After sintering, the temperature is lowered and the mixture is crushed and sieved to obtain micron-sized high-voltage lithium cobaltate positive electrode material.

[0114] Comparative example 12

[0115] A method for synthesizing high-voltage lithium cobaltate positive electrode material with magnetic field assistance, which is different from example 1 in that the sintering temperature is different in the two sintering processes in the synthesis, and the specific process is as follows:

[0116] Preparation of lithium cobaltate material: 135g of tricobalt tetroxide is uniformly mixed with 20.1g of lithium carbonate (cobalt / lithium molar ratio 9:3.5), compacted, and then loaded into a crucible, and sintered at 850°C in an oxygen atmosphere in a muffle furnace for 16 hours. After sintering, the temperature is lowered and the mixture is crushed and sieved to obtain micron-sized high-voltage lithium cobaltate positive electrode material.

[0117] The performance of the high-voltage lithium cobaltate positive electrode material prepared in the examples and comparative examples of the application and the performance of the batteries assembled based thereon are detected, and the specific process is as follows:

[0118] 1. The high-voltage lithium cobaltate positive electrode material prepared in examples 1-9 and comparative examples 1-9 is used to assemble batteries, and the positive and negative electrode active materials of the batteries are selected from the high-voltage lithium cobaltate and graphite synthesized above, and the electrolyte is 1 mol / L LiPF6-EC / DEC ester electrolyte.

[0119] Then the electrochemical performance is detected, and the results are shown in Table 1, and the specific process of electrochemical performance test is as follows:

[0120] (1) First, the battery is activated, and the voltage control range is 3.0-4.6V, and the charging capacity is obtained by charging at a current of 19mA / g to 4.6V, and the discharge capacity is obtained by discharging at a current of 19mA / g to 3.0V, and the discharge specific capacity is equal to the discharge capacity / the mass of the positive electrode active material.

[0121] (2) Then, the cycle test is performed, and the n-time capacity retention rate is equal to the n-time discharge capacity / the first discharge capacity.

[0122] (3) Spin state determination: The high spin Co content in the synthetic material was determined by a comprehensive physical property measurement system (PPMS).

[0123] (4) Co in the electrolyte 4+ Content testing: The chemical composition of the electrolyte in the high-voltage lithium cobalt oxide after five cycles was determined by inductively coupled plasma (ICP).

[0124] (5) Characterization of the electrode / electrolyte interface layer: The surface morphology and physical state of the high-voltage lithium cobalt oxide electrode / electrolyte interface layer were compared by transmission electron microscopy (TEM).

[0125] Table 1 Electrochemical performance of batteries assembled with different high-voltage lithium cobalt oxide cathode materials

[0126]

[0127] 2. The charge-discharge curves, rate curves, and Co content in the electrolyte of the high-voltage lithium cobalt oxide cathode materials prepared using Example 1 and Comparative Example 3 of this invention were measured. 4+ Solubility and interfacial layer transmission electron microscopy images are shown below. Figures 1-5 .

[0128] like Figure 1 As shown, the battery assembled using the high-voltage lithium cobalt oxide cathode material prepared in Example 1 of this invention has a first-cycle charge specific capacity of 257 mAh / g, a first-cycle discharge specific capacity of 226 mAh / g, an initial coulombic efficiency of 88.1%, and an energy density of 247 Wh / kg. Compared with Comparative Example 3 (without a magnetic field), magnetic field-assisted synthesis improved the first-cycle charge-discharge capacity and initial coulombic efficiency of the lithium cobalt oxide battery, fully utilized the active materials in the positive and negative electrode materials, and obtained a higher energy density.

[0129] like Figure 2 As shown, the battery assembled using the high-voltage lithium cobalt oxide cathode material prepared in Example 1 of this invention exhibits a long cycle curve of 300 charge-discharge cycles, with a capacity retention rate of 85.5%. Compared with Comparative Example 3, the cycle life of the high-voltage lithium cobalt oxide battery is improved, indicating that the chemical stability of the cathode material is enhanced under the influence of a magnetic field.

[0130] like Figure 3 As shown, compared with Comparative Example 3, the rate performance of the battery assembled using the high-voltage lithium cobalt oxide cathode material prepared in Example 1 of the present invention is improved, and the battery polarization is significantly improved under high current charge and discharge.

[0131] like Figure 4 As shown, after 10 cycles, the Co content in the electrolyte of the high-voltage lithium cobalt oxide prepared according to Example 1 of this invention is... 4+The concentration of Co is 0.28 ppm, which is much lower than 2.64 ppm of Comparative Example 3, proving that the technical solution can effectively inhibit Co 4+ dissolution, and improve the actual capacity of high-voltage lithium cobalt oxide.

[0132] As shown in Figure 5 Compared with Comparative Example 3, the electrode / electrolyte interface layer of high-voltage lithium cobalt oxide prepared by using the lithium cobalt oxide of Example 1 is thin and uniform after 10 cycles, indicating that the side reaction between the electrode and the electrolyte is inhibited, and the defect of unstable material interface is solved.

[0133] Finally, it should be pointed out that the above specific embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for enhancing the spin state of a high-voltage lithium cobalt oxide cathode material, characterized in that, Includes the following steps: (1) Prepare crude lithium cobalt oxide, and then crush and sieve it; (2) Collect the sieved powder and process it using at least two of the following methods: magnetic field assistance, plasma treatment and calcination, to obtain a high-pressure lithium cobalt oxide cathode material with increased spin state. In step (1), lithium cobalt oxide is prepared by sintering or hydrothermal synthesis; and a magnetic field with a strength of 0.2~2.5T is applied during the preparation process; In step (2), the plasma treatment pressure is 3~10 Pa, the temperature is 80~950℃, and the working gas is H2 / N2; The magnetic field strength applied in step (2) is 0.2~2.5T; The sintering temperature in step (1) is 750~950℃; the sintering temperature in step (2) is 750~950℃.

2. The method according to claim 1, characterized in that, In step (1), when preparing lithium cobalt oxide, the molar ratio of cobalt source to lithium source is 9:8 to 9:2, based on the molar ratio of cobalt to lithium.

3. The method according to claim 2, characterized in that, The cobalt source is cobalt tetroxide, cobalt oxide, cobalt hydroxide, cobalt sulfate, or cobalt oxalate; the lithium source is lithium carbonate, lithium hydroxide, or lithium sulfate.

4. A high-pressure lithium cobalt oxide cathode material with a high spin state, characterized in that, It is prepared by the method described in any one of claims 1 to 3.

5. The use of the high-voltage lithium cobalt oxide cathode material according to claim 4 in the preparation of energy storage materials.

6. A lithium-ion battery, characterized in that, The high-pressure lithium cobalt oxide described in claim 4 is used as the positive electrode material.

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