Positive electrode active material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of materials, in particular to a positive active material and a preparation method and application thereof. According to the preparation method provided by the invention, after the V2O5 and nano Al2O3 mixture reacts under the thermoelectric coupling field to obtain the material containing V2O5 and Al2O3, carbon coating is carried out on the material by taking CO2 as a carbon source, the obtained positive active material has the advantages of high coating rate, large specific surface area and multiple active sites, and the assembled battery has the advantages of large specific capacity, small first-circle loss rate and the like. Experiments show that when the positive active material provided by the invention is applied to the lithium ion battery, the conductivity is 9 * 10 <-4 >-4 * 10 <-3 > S / m; the charge transfer impedance is 438 to 201 omega; the thermal expansion coefficient is 4 * 10 <-6 >-7 * 10 <-6 > / The first discharge specific capacity is 273 to 289 mAh / g; the discharge capacity of the battery in 100 cycles is 253-278 mAh / g, and the cycle efficiency is 91%-96%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a positive electrode active material and a preparation method and application thereof. BACKGROUND

[0002] High-performance energy storage devices are major needs of China's strategic emerging industries and cutting-edge national defense equipment, and important technical support for achieving carbon peak and carbon neutrality. Lithium ions have advantages such as high energy density, green environmental protection, ultra-long cycle life, superior energy conversion efficiency, high-rate charging-discharging process, and no obvious memory effect.

[0003] At present, the mainstream positive electrode active material of lithium ion batteries can be roughly divided into three categories: layered transition metal oxides, polyanion compounds and other new compounds. The performance of the current lithium ion battery cathode is mainly limited by low energy density, and the specific capacity is significantly lower than the market expectation. Among them, layered transition metal oxides are considered as excellent high-capacity electrode materials due to their excellent structural stability and multi-electron reaction. Multi-electron reaction means that multiple Li + can be embedded and removed, thereby realizing higher specific capacity and improving energy density. Among the many transition metal elements, vanadium has multiple stable oxidation states, and the common valence is +5, +4, +3, +2, etc. Vanadium-based materials represented by V2O5 can realize reversible redox reactions in the charging and discharging process due to the conversion of vanadium among V 5+ , V 4+ , V 3+ , and thus provide higher energy density, and are a typical material that can realize multi-electron reaction.

[0004] Whittingham pointed out that today's commercialization can only reach 25% of its theoretical capacity. In the lithium field, one way to increase energy density while reducing cost is to perform multiple single-electron reactions at each redox center, for example, by embedding two lithium / sodium ions or one magnesium / calcium ion into the host structure. Within the stability limit of today's electrolytes, few transition metals have two redox couples, fortunately, V is one of them, and its redox action is easy to perform between +5 and +2. Vanadium is abundant, the fourth transition metal element, more than nickel and cobalt currently used. Multiple Li + embedding and removing processes cause serious structural degradation and rapid capacity decay of vanadium-based crystal nanomaterials, which are common problems faced by these materials.

[0005] V2O5 is an amphoteric acid-base oxide with fast dissolution rate, irreversible phase transition, severe volume expansion, and low electronic conductivity. Therefore, many strategies have been explored to improve the performance of vanadium-based electrode materials, such as studying bulk structure regulation, morphology regulation, ion pre-intercalation, valence bond transformation, crystal state transformation, and surface coating.

[0006] Surface coating with conductive coating, conductive substance doping, and reducing particle size are considered to be effective ways to improve the rate performance and cycle performance of V2O5 materials. Carbon-based substances such as carbon nanotubes and graphene have good electronic conductivity, which shortens the lithium ion diffusion length and ensures high rate performance. Mixing V2O5 with conductive substances (polyaniline (PANI), polypropylene glycol (PPY), poly (3, 4-ethylenedioxythiophene) (PEDOT), Cu, and conductive metal fabric) can improve its performance. Adding conductive additives can prevent aggregation and improve the effective conductivity of the entire electrode material. However, poor electrical contact at the interface between V2O5 nanoparticles and carbon additives and the lack of a continuous carbon skeleton still limit these materials to achieve high specific capacity at higher power rates.

[0007] CO2 is one of the main greenhouse gases, and its main uses are as a refrigerant, extinguishing agent, and industrial process raw material. However, due to the characteristics of CO2 adapting to high temperature and high pressure, the cost and maintenance cost are expensive, so its utilization is less, and the excessive emission of CO2 still aggravates the greenhouse effect, leading to global climate warming, air pollution, ocean acidification, and ecological balance destruction. The current application process of CO2 conversion to prepare carbon material positive electrode is challenging. SUMMARY

[0008] Therefore, the technical problem to be solved by the present application is to provide a positive electrode active material and a preparation method and application thereof. The preparation method provided by the present application reacts V2O5 and a nano-Al2O3 mixture under a thermoelectric coupling field to obtain a material containing V2O5 and Al2O3, and then performs carbon coating on the material containing V2O5 and Al2O3 using CO2 as a carbon source. The obtained positive electrode active material has high coating rate, large specific surface area, and many active sites. The battery assembled using the positive electrode active material has the advantages of large specific capacity and small first circle loss rate.

[0009] The present application provides a positive electrode active material, which comprises:

[0010] The active material comprises V2O5, V2O3, and Al2O3.

[0011] The carbon is coated on the active material.

[0012] The positive electrode active material provided by the application is specifically a carbon composite positive electrode active material of a lithium ion battery, and more specifically a carbon-coated multi-valence vanadium-based active material, which is a core-shell structure and comprises a capsule core (i.e., a core) and a capsule wall (i.e., a shell) coated on the capsule core, wherein the capsule core is an active material, the active material comprises V2O5, V2O3 and Al2O3, and is formed by reduction reaction of a material comprising V2O5 and Al2O3, and in the reduction reaction, part of the V2O5 in the material comprising V2O5 and Al2O3 is reduced to V2O3; the material comprising V2O5 and Al2O3 is prepared from V2O5 and nano-Al2O3, and specifically is obtained by reaction of a mixture of V2O5 and nano-Al2O3 under a thermal electric coupling field, and comprises V2O5 and Al2O3; and the capsule wall is carbon, which is formed by supercritical liquid reaction and double-function reaction of gaseous CO2. The positive electrode active material provided by the application has good electrochemical performance and high specific capacity, and also has excellent cycle resistance and mechanical strength, which is conducive to promoting sustainable development of the environment.

[0013] The application further provides a preparation method of the positive electrode active material, comprising the following steps:

[0014] The material comprising V2O5 and Al2O3 and ethylbenzene are subjected to carbonization treatment under a CO2 atmosphere, the carbonization treatment causes the V2O5 in the material comprising V2O5 and Al2O3 to be partially oxidized to V2O3, and the positive electrode active material is obtained; the pressure of the carbonization treatment is 7.8 MPa to 8.3 MPa, the temperature of the carbonization treatment is 450 DEG C to 530 DEG C, and the time of the carbonization treatment is 38 min to 44 min.

[0015] The material comprising V2O5 and Al2O3 is prepared from V2O5 and nano-Al2O3 with a mass ratio of (15-16):(1-2), preferably from V2O5 and nano-Al2O3 with a mass ratio of 16:1. The material comprising V2O5 and Al2O3 is sintered from V2O5 and nano-Al2O3 under a direct current voltage of 550 V-650 V; specifically, the material comprising V2O5 and Al2O3 is prepared by sintering V2O5 and nano-Al2O3 at 530℃-550℃ under a direct current voltage of 550 V-650 V for 2 h-3 h in a protective atmosphere to obtain the material comprising V2O5 and Al2O3. The heating rate of sintering in the present application is 8℃ / min-12℃ / min. The protective atmosphere in the present application is selected from one or more of nitrogen, helium, neon or argon, preferably selected from nitrogen or argon. In some embodiments of the present application, the V2O5 and Al2O3 are uniformly stirred and ground, and the mixture is reacted under a thermocouple coupled field, specifically, two electrode sheets are added on the side of the aluminum oxide sheet, the electrode sheets are connected to the positive and negative electrodes of a 600 V direct current voltage converter, respectively, and the reaction is carried out in a tubular heating furnace under an electric field and argon protection, the temperature is raised to 550℃ at a rate of 10℃ / min, and the temperature is maintained for 180 min to obtain the material comprising V2O5 and Al2O3. The temperature field dominates the nucleation rate and growth kinetics of the material, and the electric field directionally guides the growth direction of the nanocrystals through electrostatic interaction and magnetic dipole interaction, finally realizing accurate control of the size, morphology and crystal form of the nanomaterial, and solving the problem of poor structural uniformity in traditional single field control process. The material comprising V2O5 and Al2O3 is used to prepare a positive active material, which has low working voltage, high specific capacity, high first circle coulomb efficiency, high compaction density, high electronic and ionic conductivity, stable structure (small volume change), air stability, low cost and safety and non-toxicity. The material comprising V2O5 and Al2O3 in the present application is preferably selected from a material comprising V2O5 and Al2O3 with a particle size of less than 5 microns.

[0016] The material comprising V2O5 and Al2O3 and ethylbenzene are subjected to carbonization treatment under a CO2 atmosphere, which partially oxidizes V2O5 in the material comprising V2O5 and Al2O3 to V2O3 to obtain a positive active material. The flow rate of the CO2 atmosphere in the present application is 15 mL / min-25 mL / min; the mass ratio of the material comprising V2O5 and Al2O3 and ethylbenzene is 50:(8-12).

[0017] Specifically, the present application mixes a material including V2O5 and Al2O3 and ethylbenzene under a CO2 atmosphere, and then performs a carbonization treatment, during which ethylbenzene is introduced multiple times, the carbonization treatment causing V2O5 in the material including V2O5 and Al2O3 to be partially oxidized into V2O3, the product obtained after the carbonization treatment being ground after cooling to pass through a 400-mesh sieve to obtain a positive electrode active material. The flow rate of the CO2 atmosphere in the present application is 15 mL / min to 25 mL / min. The material including V2O5 and Al2O3 and ethylbenzene are mixed in a mass ratio of 50:(8 to 12) in the present application. The speed of introducing ethylbenzene in the present application is 1 mL / min to 2 mL / min.

[0018] More specifically, the present application mixes a material including V2O5 and Al2O3 and ethylbenzene under a CO2 atmosphere, and then sequentially performs a first-stage carbonization treatment, a second-stage carbonization treatment, and a third-stage carbonization treatment, the carbonization treatment causing V2O5 in the material including V2O5 and Al2O3 to be partially oxidized into V2O3, the product obtained after the carbonization treatment being ground after cooling to obtain a positive electrode active material; the first-stage carbonization treatment includes: introducing CO2 and raising the temperature to the temperature of the carbonization treatment, and then stably maintaining for 4 min to 6 min, and then introducing ethylbenzene for the first time and simultaneously performing carbonization treatment for 10 min to 12 min, and then stripping for 4 min to 6 min; the second-stage carbonization treatment includes: introducing CO2 and raising the temperature to the temperature of the carbonization treatment, and then stably maintaining for 1 min to 3 min, and then introducing ethylbenzene for the second time and simultaneously performing carbonization treatment for 14 min to 16 min, and then stripping for 4 min to 6 min; the third-stage carbonization treatment includes: introducing CO2 and raising the temperature to the temperature of the carbonization treatment, and then stably maintaining for 1 min to 3 min, and then introducing ethylbenzene for the third time and simultaneously performing carbonization treatment for 14 min to 16 min, and then stripping for 4 min to 6 min. The material including V2O5 and Al2O3 and ethylbenzene are mixed in a mass ratio of 50:(8 to 12) in the present application. The flow rate of the CO2 atmosphere in the present application is 15 mL / min to 25 mL / min. The speed of introducing ethylbenzene in the present application is 1 mL / min to 2 mL / min. The time of introducing ethylbenzene for the first time, introducing ethylbenzene for the second time, and introducing ethylbenzene for the third time in the present application is independently 1 min to 5 min less than the carbonization treatment time performed simultaneously. The speed of introducing ethylbenzene for the first time, introducing ethylbenzene for the second time, and introducing ethylbenzene for the third time in the present application is independently 1 mL / min to 2 mL / min. The carbonization treatment in the present application is the same as described above, and will not be described again. The tail gas generated by the carbonization treatment in the present application is preferably subjected to tail gas absorption treatment using a caustic soda solution. The positive electrode active material obtained after the carbonization treatment in the present application is stored in a dry environment. The stripping in the present application is preferably performed using CO2.

[0019] The preparation method of the positive electrode active material provided by the application adopts catalytic cracking process to carry out supercritical liquid reaction and double-function reaction, and indirectly uses gaseous CO as a carbon source to coat the capsule wall (i.e. shell), thereby realizing direct utilization of CO2 and efficient indirect utilization of the product CO. Specifically, in the preparation method of the positive electrode active material provided by the application, the V2O5 and Al2O3 mixture is reacted under a thermoelectric coupling field, the electric field controls the carrier concentration, and the temperature field optimizes the grain boundary, thereby synergistically improving the thermoelectric conversion efficiency; the temperature and pressure of the carbonization treatment are above the critical temperature and critical pressure of CO2, at this time, CO2 cannot be separated into gas and liquid two phases, and exists in a supercritical state, at this time, CO2 has the dual characteristics of gas and liquid, i.e. the density is close to that of liquid, the viscosity is similar to that of gas, and the diffusion coefficient is 10-100 times that of liquid, thus having strong solubility and good flow properties, and supercritical liquid reaction is carried out.

[0020] In the preparation method of the positive electrode active material provided by the application, the carbonization treatment process also carries out multiple function reactions, i.e. ethylbenzene reacts with CO2 to generate the product styrene and CO which have higher chemical value; wherein, CO2 is reduced to CO, at this time, CO carries out carbon coating on the materials including V2O5 and Al2O3 to form V2O5-Al2O3-C, and makes V 5+ partially reduced to V 3+ , thereby having high reaction efficiency, simple operation, energy saving and environmental protection. After CO coating, CO forms an amorphous carbon layer on the surface of the multi-valence vanadium-based composite material, constructs a "core-shell structure", inhibits vanadium dissolution, improves the electrical conductivity of the vanadium-based electrode, and improves the problem of excessive first-cycle specific capacity loss and low capacity retention rate after cycling. At the same time, after carbon coating, the vanadium-based electrode has excellent chemical stability and electrochemical performance, and can ensure the battery life and stability.

[0021] The application further provides a positive electrode, which comprises a current collector and a positive electrode material loaded on the current collector; the positive electrode material comprises the positive electrode active material according to any one of the technical solutions or the positive electrode active material obtained by the preparation method according to any one of the technical solutions. The current collector is preferably selected from aluminum foil. The loading amount of the positive electrode active material loaded on the positive electrode is preferably 1 mg / m 2 ~2 mg / m 2 .

[0022] Specifically, the positive electrode provided by the present application comprises the positive electrode active material, the binder and the conductive filler in a mass ratio of (6-10):(2-3):(1-2), preferably 7:2:1. The binder is preferably selected from polyvinylidene fluoride, and the conductive filler is preferably selected from conductive carbon black with a particle size of 1-10 microns.

[0023] The positive electrode provided by the present application is prepared by the following method: mixing the positive electrode active material, the binder and the conductive filler to obtain a mixed powder, adding a solvent to the mixed powder to obtain a slurry, coating the slurry on a current collector, drying, and cutting into a round sheet to obtain the positive electrode. The solvent added in the present application accounts for 18-22% of the mass of the mixed powder. The solvent is preferably N-methyl pyrrolidone.

[0024] The present application also provides a lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the positive electrode provided by any of the above technical solutions. The lithium ion battery provided by the present application has high conductivity, large specific capacity and small loss rate due to the use of the positive electrode material provided by the present application, i.e. the carbon-coated multi-valence vanadium-based active material powder.

[0025] The present application provides a positive electrode active material, a preparation method and application thereof. The preparation method provided by the present application can be used to coat a material comprising V2O5 and Al2O3 with carbon by taking CO2 as a carbon source. The obtained positive electrode active material has high coating rate, large specific surface area and many active sites. The battery assembled by using the positive electrode active material has large specific capacity and small first-cycle loss rate. Experiments show that the positive electrode active material provided by the present application has a conductivity of 9×10 -4 ~4×10 - 3 S / m, a charge transfer impedance of 438-201 ohms, a thermal expansion coefficient of 4×10 -6 ~7×10 -6 / K, a first discharge specific capacity of 273-289 mAh / g, a discharge capacity of 253-278 mAh / g after 100 cycles of the battery, and a cycle efficiency of 91-96%. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A schematic diagram of a thermoelectric coupling field device for preparing a V2O5 and nano-Al2O3 composite material of an embodiment of the present application;

[0027] Figure 2 An XRD pattern of a V2O5-Al2O3 composite material prepared in Example 4 of the present application and a carbon-coated multi-valence vanadium-based active material;

[0028] Figure 3 SEM image of carbon-coated multi-valence vanadium-based active material prepared for Example 4 of the present application;

[0029] Figure 4 Charge-discharge cycle curve cycle diagram of lithium ion battery assembled with carbon-coated multi-valence vanadium-based active material prepared for Example 4 of the present application;

[0030] Figure 5 X-ray photoelectron spectroscopy (XPS) test image of active material of Example 1 and Comparative Example 2;

[0031] Figure 6 Electrochemical impedance spectrogram of lithium ion battery respectively assembled with carbon-coated multi-valence vanadium-based active material prepared for Example 4 of the present application, V2O5 material prepared for Comparative Example 1, and conventional carbon-coated V2O5-Al2O3 composite material prepared for Comparative Example 3. DETAILED DESCRIPTION

[0032] The present application discloses a positive electrode active material, a preparation method and application thereof. Those skilled in the art can refer to the content herein and make appropriate improvements to the process parameters. It is particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the present application. The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the method and application herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0033] The present application is further described below in conjunction with examples:

[0034] Example 1

[0035] 10 parts of nano-Al2O3 and 90 parts of V2O5 were mixed by weight, stirred and ground uniformly, the obtained mixed raw materials were poured into a beaker, deionized water was added until completely wet, and then stirred for 30 min by a magnetic stirrer to form a slurry. The obtained slurry was placed in an oven and dried at 90-100 ℃ for 12 h. The obtained dried mixed raw materials were transferred to an alumina crucible sheet, which was placed in a glass tube of a tube furnace. The two side electrode sheets of the mixed materials were respectively connected to a 600V direct current voltage. The temperature was raised to 550 ℃ at a heating rate of 10 ℃ / min, and the temperature was kept for 180 min. The gas in the furnace was connected to a caustic soda solution for tail gas absorption treatment. After the end, the furnace was cooled to room temperature, and then taken out. A material including V2O5 and Al2O3 was obtained, which was called V2O5-Al2O3 composite material. A ball mill was used for sufficient grinding, and the V2O5-Al2O3 composite material powder with a particle size less than 5 microns was selected by sieving. Figure 1 As shown in the formula (1), the V2O5-Al2O3 composite material is prepared by mixing V2O5 and Al2O3, and then sintering at a high temperature. The V2O5-Al2O3 composite material is a composite material of V2O5 and Al2O3, and the V2O5-Al2O3 composite material is not a simple mixture of V2O5 and Al2O3. The V2O5-Al2O3 composite material is a material in which V2O5 and Al2O3 are combined together at the atomic level. Figure 1A schematic diagram of a thermoelectric coupling field device for preparing V2O5 and nano-Al2O3 composite material reaction of the embodiment of the present application.

[0036] 50 parts of V2O5-Al2O3 composite material powder and 10 parts of ethylbenzene are mixed by weight. The coating drying process is completed in a catalytic cracking micro-reaction evaluation device, and the ethylbenzene solution is added in three stages for carbonization treatment under a CO2 gas atmosphere during the process. The specific process is as follows:

[0037] The first stage treatment includes: passing CO2 gas in the device, the CO2 flow rate is 20 mL / min, the temperature is raised to 530°C, the pressure is 8 MPa, the temperature is stabilized for 5 min, then the first ethylbenzene is introduced and carbonization treatment is carried out at the same time for 11 min, and then stripping for 5 min; the rate of ethylbenzene introduction is 1.5 mL / min, and the time of ethylbenzene introduction is 10 min;

[0038] The second stage treatment includes: passing CO2 gas in the device, the CO2 flow rate is 20 mL / min, the temperature is raised to 530°C, the pressure is 8 MPa, the temperature is stabilized for 2 min, then the second ethylbenzene is introduced and carbonization treatment is carried out at the same time for 15 min, and then stripping for 5 min; the rate of ethylbenzene introduction is 1.5 mL / min, and the time of ethylbenzene introduction is 10 min;

[0039] The third stage treatment includes: passing CO2 gas in the device, the CO2 flow rate is 20 mL / min, the temperature is raised to 530°C, the pressure is 8 MPa, the temperature is stabilized for 2 min, then the third ethylbenzene is introduced and carbonization treatment is carried out at the same time for 15 min, and then stripping for 5 min; the rate of ethylbenzene introduction is 1.5 mL / min, and the time of ethylbenzene introduction is 10 min.

[0040] After the reaction is completed, the device is cooled to room temperature, the liquid in the condenser bottle and the carbon-coated multi-valence vanadium-based active material in the reaction furnace are collected, the carbon-coated multi-valence vanadium-based active material is ground through a 400 mesh sieve, and a positive electrode active material powder is obtained.

[0041] The positive active material powder, a binder (polyvinylidene fluoride), and conductive carbon black (particle size distribution 1-10 μm) powder in a mass ratio of 7:2:1 were mixed, and then dropped into an appropriate amount of solvent N-methylpyrrolidone (20 wt% of the powder) for ball milling. The obtained slurry was coated on an aluminum foil and dried. After vacuum drying at 60 °C for 12 hours, it was cut into a 12 mm diameter disc and used as a positive electrode. A lithium sheet was used as a reference electrode, and 1 M LiPF6 in a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1:1:1 v / v / v) was used as an electrolyte to prepare a CR2032 type button cell in an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). The cycle performance of the battery was tested using a LAND CT3001A battery test system. CHI660E was used for electrochemical impedance spectroscopy (EIS) testing, and the recorded frequency range was 10 -2 ~10 5 Hz, and the amplitude was 5 mV.

[0042] Examples 2-5

[0043] According to the preparation procedure of Example 1, V2O5-Al2O3 composite materials were prepared using different amounts of transition metal oxide V2O5 and nano-Al2O3 as shown in Table 1, and then using different amounts of V2O5-Al2O3 composite materials and ethylbenzene as shown in Table 2, the positive active material powders of Examples 2-5 were prepared.

[0044] Table 1

[0045]

[0046] Table 2

[0047]

[0048] Comparative Example 1

[0049] The dry V2O5 powder was ground thoroughly using a ball mill with a particle size less than 5 μm. The electrode was prepared by mixing the active material (V2O5 powder), conductive carbon black and polytetrafluoroethylene (PTFE) binder in a mass ratio of 7:2:1. The weighed V2O5 powder, conductive carbon black, binder, NMP solution and ball milling beads were put into an agate mortar and ground for 30 minutes at 300 r / min using a ball mill to obtain a uniform mixture. The slurry was uniformly coated onto an aluminum foil to obtain a uniform film (thickness 80 μm). The prepared cathode film was punched into a round sheet using a circular cutter with a diameter of 8 mm and then uniformly pasted onto an aluminum mesh. Then, a CR2032 coin cell (316L stainless steel, polypropylene gasket) was assembled in a glove box with the prepared cathode film as the cathode, 1 mol / L LiPF6 as the ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte, Celgard 2025 as the separator, and lithium sheet as the counter electrode. The charge and discharge performance of the comparative sample lithium ion battery under different current densities in the voltage range of 2.0-4.2 V was tested on an electrochemical workstation. The test data showed that the specific capacity of the first cycle was 270 mAh g -1 , and the capacity retention rate after 100 cycles was about 90%. In addition, the specific capacity of 220 mAh g -1 could be provided at a high current density of 85 mA g -1 after 300 cycles, equivalent to a capacity retention rate of 80%.

[0050] Comparative Example 2

[0051] 10 parts of nano-Al2O3 and 90 parts of V2O5 were mixed by weight, stirred and ground uniformly, and the obtained mixed raw materials were poured into a beaker and added with deionized water until completely wet. After stirring for 30 min with a magnetic stirrer, a slurry was formed. The obtained slurry was placed in an oven and dried at 90-100 ℃ for 12 h. The obtained dry mixed raw materials were transferred to an alumina crucible sheet, two electrode sheets were added to the side of the alumina sheet, and the electrode sheets were connected to the positive and negative electrodes of a 600V DC voltage converter. The tube furnace was heated to 550 ℃ at a heating rate of 10 ℃ / min under the action of an electric field and in an argon atmosphere, and the temperature was kept for 180 min. The gas in the furnace was connected to a caustic soda solution for tail gas absorption treatment. After the end, the furnace was cooled to room temperature, and then taken out. A material including V2O5 and Al2O3 was obtained, which was called V2O5-Al2O3 composite material. The V2O5-Al2O3 composite material powder with a particle size less than 5 μm was ground thoroughly using a ball mill;

[0052] V2O5-Al2O3 composite material powder, a binder (polyvinylidene fluoride), and conductive carbon black (particle size distribution 1-10 μm) powder in a mass ratio of 7:2:1 were mixed, then dropped into an appropriate amount of solvent N-methyl pyrrolidone (20 wt% of the powder) and ball milled, and the obtained slurry was coated on an aluminum foil and dried. After vacuum drying at 60 °C for 12 hours, it was cut into a 12 mm diameter disc and used as a positive electrode. A lithium sheet was used as a reference electrode, and 1 M LiPF6 in a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1:1:1 v / v / v) was used as an electrolyte, and a CR2032 type button cell was prepared in an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). The cycle performance of the battery was tested using a LAND CT3001A battery test system. CHI660E was used for electrochemical impedance spectroscopy (EIS) testing, and the recorded frequency range was 10 -2 ~10 5 Hz, and the amplitude was 5 mV.

[0053] Comparative Example 3

[0054] The V2O5-Al2O3 composite material powder was dispersed in deionized water and ultrasonically treated for 30 minutes to form a uniform suspension. Glucose was dissolved in deionized water (concentration of 0.5M) and stirred until completely dissolved. The glucose solution was slowly added to the composite material suspension (mass ratio of composite material: glucose = 1:0.2) and stirring was continued for 2 hours to allow the glucose to be uniformly adsorbed on the surface of the composite material. The mixed solution was evaporated to a gel at 60-80°C under stirring, and then transferred to an oven for drying at 80-100°C for 12 hours to obtain a precursor powder. The dried precursor was transferred to an alumina crucible and placed in a tube furnace for carbonization under a nitrogen atmosphere, with the temperature raised to 350°C at a rate of 5°C / min and held for 180 min to allow the glucose to pyrolyze and form an amorphous carbon layer coating the V2O5-Al2O3. After the end of the process, the furnace was allowed to cool to room temperature and then removed, to obtain a carbon-coated V2O5-Al2O3 composite material (V2O5-Al2O3@C). The V2O5-Al2O3@C was thoroughly ground to a particle size of less than 5μm, and an electrode was prepared by mixing the active material (V2O5-Al2O3@C), conductive carbon black and polytetrafluoroethylene (PTFE) binder in a mass ratio of 7:2:1. The weighed V2O5-Al2O3@C powder, conductive carbon black, binder, NMP solution and ball milling beads were placed in an agate mortar and ground using a ball mill at 300r / min for 30 minutes to obtain a uniform mixture. The slurry was uniformly coated onto an aluminum foil to obtain a uniform film (thickness of 80μm). The prepared cathode film was punched into a round sheet using a circular cutter with a diameter of 8mm, and then uniformly pasted onto an aluminum mesh. Then, a CR2032 type coin cell (316L stainless steel, polypropylene gasket) was used as the cathode, 1mol / L LiPF6 was used as the ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte, Celgard 2025 was used as the separator, and a lithium sheet was used as the counter electrode, to assemble a CR2032 type coin cell in a glove box. The charge-discharge performance of the comparative sample lithium ion battery under different current densities in the voltage range of 2.0-4.2V was tested on an electrochemical workstation.

[0055] The V2O5-Al2O3 composite material and the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application were subjected to X-ray diffraction testing, and the results are shown in Figure 2 Figure 2 The XRD pattern of the V2O5-Al2O3 composite material and the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application is shown in

[0056] The carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application was subjected to scanning electron microscope analysis, and the results are shown in Figure 3 Figure 3 The SEM pattern of the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application is shown in ​​

[0057] Charging-discharging cycle test and coulombic efficiency test were conducted on the lithium ion battery assembled by the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application, and the results are shown in Figure 4 Figure 4 Figure 4 is a charging-discharging cycle curve cycle diagram of the lithium ion battery assembled by the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application.

[0058] XPS test was conducted on the active materials of Example 1 and Comparative Example 2 of the present application, and the results are shown in Figure 5 Figure 5 Figure 3 is the XPS test diagram of the active materials of Example 1 and Comparative Example 2 of the present application. It can be seen from the figure that the pentavalent vanadium in the active material of the present application is partially reduced to trivalent vanadium. Figure 5

[0059] Electrochemical impedance test was conducted on the lithium ion batteries respectively assembled by the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application, the V2O5 material prepared in Comparative Example 1, and the conventional carbon-coated V2O5-Al2O3 composite material prepared in Comparative Example 3, Figure 6 Figure 5 is the electrochemical impedance spectrum diagram of the lithium ion batteries respectively assembled by the carbon-coated multi-valence vanadium-based active material prepared in Example 4 of the present application, the V2O5 material prepared in Comparative Example 1, and the conventional carbon-coated V2O5-Al2O3 composite material prepared in Comparative Example 3.

[0060] The performance of the lithium ion batteries assembled by the vanadium-based positive electrode materials prepared in the examples and comparative examples of the present application was tested, and the results are shown in Table 2:

[0061] Table 2

[0062]

[0063] From the above data, it can be seen that the present application provides a carbon-coated multi-valence vanadium-based active material, and the preparation raw materials include nano-Al2O3, transition metal oxide V2O5, ethylbenzene, and CO2. In the present application, the nano-Al2O3 and the transition metal oxide V2O5 are mixed at high temperature to obtain a V2O5-Al2O3 composite material, which is then fully mixed with ethylbenzene after grinding. A catalytic cracking micro-reaction evaluation device is used, CO2 gas is introduced, and supercritical liquid reaction, double-function reaction, and oxidation-reduction reaction are conducted to complete carbonization treatment, thereby obtaining a carbon-coated multi-valence vanadium-based active material powder. The powder is applied in a lithium ion battery, and the conductivity is 9×10 -4 ~4×10 -3 S / m; the charge transfer impedance is 438~201Ω; and the thermal expansion coefficient is 4×10 -6 ~7×10 -6 ​​​ / K; the first discharge specific capacity is 273-289 mAh / g; the battery 100 cycle discharge capacity is 253-278 mAh / g, and the cycle efficiency is 91%-96%.

[0064] The above merely provides the preferred but not limiting embodiments of the present application. Any person skilled in the art should understand that, within the technical scope of the present application, equivalent replacements or changes can be made to the technical solutions and the inventive concept of the present application, and all of them should be covered within the protection scope of the present application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material comprises: an active material comprising V2O5, V2O3 and Al2O3; carbon coated on the active material.

2. A method for producing the positive electrode active material according to claim 1, characterized by, The method comprises the following steps: subjecting a material comprising V2O5 and Al2O3 and ethylbenzene to a carbonization treatment under a CO2 atmosphere, the carbonization treatment causing V2O5 in the material comprising V2O5 and Al2O3 to be partially oxidized into V2O3, to obtain a positive electrode active material; the carbonization treatment is performed at a pressure of 7.8 MPa to 8.3 MPa, at a temperature of 450°C to 530°C, and for a time of 38 min to 44 min.

3. The production method according to claim 2, characterized by, The material comprising V2O5 and Al2O3 is prepared from V2O5 and nano-Al2O3 in a mass ratio of (15-16):(1-2).

4. The production method according to claim 3, characterized by, The material comprising V2O5 and Al2O3 is prepared by the following method: sintering V2O5 and nano-Al2O3 at 530°C to 550°C under a protective atmosphere and a direct current voltage of 550 V to 650 V for 2 h to 3 h to obtain the material comprising V2O5 and Al2O3.

5. The preparation method according to claim 2, characterized in that, The CO2 atmosphere has a flow rate of 15 mL / min to 25 mL / min. The mass ratio of the material comprising V2O5 and Al2O3 to ethylbenzene is 50:(8-12).

6. The production method according to claim 2, characterized by, Further comprising: multiple times of introducing ethylbenzene during the carbonization treatment; the introduction rate of ethylbenzene is 1 mL / min to 2 mL / min.

7. The production method according to any one of claims 2 to 6, characterized by, The method comprises the following steps: mixing the material comprising V2O5 and Al2O3 and ethylbenzene, and then sequentially performing a first-stage carbonization treatment, a second-stage carbonization treatment and a third-stage carbonization treatment; the first-stage carbonization treatment comprises: introducing CO2 and heating to the temperature of the carbonization treatment and stabilizing for 4 min to 6 min, then introducing ethylbenzene for the first time and simultaneously performing carbonization treatment for 10 min to 12 min, and then stripping for 4 min to 6 min; the second-stage carbonization treatment comprises: introducing CO2 and heating to the temperature of the carbonization treatment and stabilizing for 1 min to 3 min, then introducing ethylbenzene for the second time and simultaneously performing carbonization treatment for 14 min to 16 min, and then stripping for 4 min to 6 min; the third-stage carbonization treatment comprises: introducing CO2 and heating to the temperature of the carbonization treatment and stabilizing for 1 min to 3 min, then introducing ethylbenzene for the third time and simultaneously performing carbonization treatment for 14 min to 16 min, and then stripping for 4 min to 6 min.

8. The preparation method according to claim 6, characterized in that, The time for introducing ethylbenzene for the first time, the second time and the third time is independently 1 min to 5 min less than the simultaneous carbonization treatment time.

9. A positive electrode, characterized by comprising: The positive electrode material comprises the positive electrode active material of claim 1 or the positive electrode active material obtained by the preparation method of any one of claims 2-8. The battery comprises a positive electrode, a negative electrode and an electrolyte.

10. A lithium-ion battery, characterized by, The positive electrode is the positive electrode of claim 9. ​

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