A high-pressure-resistant lithium cobalt oxide cathode material coated with nano tin oxide and lithium aluminum titanium phosphate and a preparation method thereof

Abstract

The application discloses a kind of nano tin oxide and lithium titanium aluminum phosphate double-coated high-pressure-resistant lithium cobaltate positive electrode material and preparation method thereof.The positive electrode material is lithium cobaltate as matrix and is coated with ion conductor material lithium titanium aluminum phosphate and nano tin oxide on its surface;Nano tin oxide coating can inhibit the interface side reaction of lithium cobaltate positive electrode and electrolyte, and doped into the lattice vibration of body pegging layered structure, prevent the irreversible phase transition of material;Lithium titanium aluminum phosphate can construct interface with excellent ion and electron conductivity characteristics, further promote the rapid conduction of lithium ion in positive electrode material.Lithium cobaltate positive electrode coated with double coating has double-layer lithium ion conductor coating layer, to a certain extent, play the dual role of physical barrier and chemical stability, meet the high-pressure cycle stability required by lithium cobaltate positive electrode at present.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion batteries, in particular to a nano-tin oxide and lithium titanium aluminum phosphate double-coated high-voltage-resistant lithium cobalt oxide positive electrode material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of electric vehicles, portable electronic devices and other fields, the demand for lithium ion batteries with high energy density and high voltage stability is increasing. As an important part of lithium ion batteries, the positive electrode material has always been the focus of researchers. Improving the performance of the positive electrode material is the key to improving the performance of the lithium ion battery. It mainly reflects in the following two aspects: first, the specific capacity of the lithium ion battery positive electrode material increases by 50%, and the power density increases by 28%; second, the cost proportion of each component and the positive and negative electrode materials in the lithium ion battery is different, and the positive electrode material accounts for more than 40% of the cost. However, the positive electrode material used in the traditional lithium ion battery has problems such as accelerated degradation of the structure under high voltage, short cycle life and poor safety. Therefore, it is an urgent need to develop a lithium cobalt oxide positive electrode material suitable for high voltage.

[0003] At present, the research on high-voltage LCO is continuously deepened, and the irreversible transformation of the surface structure of lithium cobalt oxide, the dissolution of Co element and the unstable by-products of the surface interface are also one of the most important factors affecting the performance of the material. Therefore, the surface coating technology has developed rapidly, and many coating materials have been reported to improve the cycle performance and thermal stability of lithium cobalt oxide under high voltage. Lithium ion conductor materials: lithium-containing cathode materials, inorganic fast lithium ion conductors, lithium ion conductive polymers and other materials (high polarization dielectric material (TaTiO3), surface P-doped (Li-O-P glass phase)) have excellent ion conduction performance and chemical stability, which can promote the transmission of lithium ions and further improve the rate performance and high-temperature storage performance of the material. The octahedral stacking structure composed of part of metal ions and oxygen ions has good lattice compatibility with lithium cobalt oxide, so that a coating layer of metal oxide is formed on the surface of lithium cobalt oxide, which plays a dual role of physical blocking and chemical stability to a certain extent, and alleviates the dissolution of cobalt and the overflow of oxygen. Both of them can be used as a good coating layer of lithium cobalt oxide, and double coating can construct a more efficient and stable surface coating layer to improve the cycle performance and thermal stability of lithium cobalt oxide. SUMMARY

[0004] The purpose of the present application is to provide a nano-tin oxide and lithium titanium aluminum phosphate double-coated high-voltage-resistant lithium cobalt oxide positive electrode material and a preparation method thereof, which overcomes the above-mentioned deficiencies in the prior art and solves the problems of poor electrochemical performance, high safety risk and the like caused by the instability of the bulk phase and interface of the lithium cobalt oxide positive electrode material under high voltage.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is:

[0006] A nano tin oxide and titanium aluminum lithium phosphate double-coated high-pressure-resistant lithium cobaltate positive electrode material and a preparation method thereof, characterized by comprising the following steps:

[0007] (1) After dissolving the cobalt source into the microwave reaction kettle, a precipitating agent is added, and a microwave-assisted co-precipitation reaction is used, and then a lithium source and a tin source are added for ultrasonic treatment to obtain a tin oxide-coated lithium cobaltate precipitate mixture;

[0008] (2) The tin oxide-coated lithium cobaltate precipitate mixture is filtered, washed, dried, and calcined to obtain a primary calcined solid powder;

[0009] (3) After the calcination is completed, the primary calcined solid powder is thoroughly ground and then subjected to secondary calcination to obtain nano tin oxide-coated lithium cobaltate;

[0010] (4) The nano tin oxide-coated lithium cobaltate is ultrasonically dispersed in an organic solvent, and phosphoric acid, lithium nitrate, aluminum nitrate, and tetrabutyl titanate are introduced to obtain a reaction precursor solution 1, the pH value of the reaction precursor solution 1 is adjusted, and the reaction precursor solution 1 is thoroughly mixed and uniform to obtain a reaction precursor solution 2;

[0011] (5) The reaction precursor solution 2 is heated and stirred, evaporated to dryness, thoroughly ground, and then sintered in a tube furnace to obtain a nano tin oxide and titanium aluminum lithium phosphate double-coated high-pressure-resistant lithium cobaltate positive electrode material.

[0012] Preferably, step (1) comprises the following steps: the cobalt source is dissolved in 100 ml of deionized water, then 0.1 mol / L of a precipitating agent is added dropwise after being placed in a microwave reaction kettle, the microwave power is 300-800 W, the reaction temperature is heated to 50-80°C by microwave, and after 30-60 min of reaction, a lithium source and a tin source are added for ultrasonic treatment, the ultrasonic power is 300-800 W, and the ultrasonic time is 0.5-2 h.

[0013] The microwave, which can uniformly control the temperature, is used to help shorten the reaction time, avoid the long reaction time and high energy consumption of the ordinary co-precipitation method, and introduce ultrasonic treatment with high dispersion capacity, so that the tin oxide-coated lithium cobaltate particles formed have small particle size, the coating layer produced is thin and uniform, and the thickness is nano-level (5-10 nm).

[0014] Preferably, in step (1), the molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1:(1.02-1.12); the molar amount of tin in the tin source is 0.3-1.5% of the cobalt content; the cobalt source is one or more of cobalt hydroxide, cobalt chloride, and cobalt sulfate; the precipitating agent is one or more of NaOH, NH3·H2O, and Na2C2O4; the lithium source is lithium hydroxide and / or lithium carbonate; and the tin source is tin oxide and / or tin chloride.

[0015] Preferably, the tin oxide coated lithium cobaltate precipitate mixture in step (2) is dried at a temperature of 80-120°C; the temperature condition for the first calcination is 600-800°C, and the calcination is carried out at a temperature increasing rate of 1-5°C / min for 4-6h. In step (3), the second calcination is carried out at a rate of 1-5°C / min to a temperature of 800-1000°C, and the calcination is carried out in an oxygen or air atmosphere for 8-12h.

[0016] The first calcination and then the second grinding can make the mixture fully react in the presence of oxygen during the second calcination, and the Sn element migrates to the interior of the lithium cobaltate material after the second high-temperature calcination, thereby forming trace doping between the lithium cobaltate bodies.

[0017] The tin doped into the body can weaken the atomic thermal motion and pin the lattice vibration in the layered structure lithium cobaltate, thereby preventing the irreversible cubic spinel structure phase change of the lithium cobaltate cathode under high voltage and long cycle, and thus playing a role in stabilizing the body phase structure and interface of the cathode.

[0018] Preferably, in step (4), the organic solvent is one or more of anhydrous ethanol, isopropanol, and ethylene glycol, and the ultrasonic treatment time is 20-30min; a reaction precursor solution 1 is obtained by sequentially adding phosphoric acid, lithium nitrate, aluminum nitrate, and finally tetrabutyl titanate according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3, wherein 0.3≤x≤0.8. The pH value of the reaction precursor solution 1 is adjusted to 7-10; the mixing uniformity refers to stirring the reaction precursor solution 1 at a speed of 300-600rpm for 4-6h at room temperature after ultrasonic treatment for 30-60s, to obtain a reaction precursor solution 2.

[0019] The phosphoric acid which is easy to disperse is first added, then the solid particles of lithium nitrate and aluminum nitrate are added, and finally the tetrabutyl titanate which is easy to hydrolyze is added, which can ensure that a complete lithium titanium aluminum phosphate coating layer is formed on the surface of the nano tin oxide coated lithium cobaltate.

[0020] The ultrasonic treatment is beneficial to dispersing the nano powder and avoiding the agglomeration phenomenon thereof; the stirring at room temperature is convenient for controlling the synthesis of the reactants, so that a homogeneous coating layer material is formed in the solution. Too low temperature or too short time is not conducive to the synthesis of the coating layer material, and too high temperature or too long time will cause the organic solvent to volatilize too early, and the coating layer formation and coating are not complete.

[0021] Preferably, in step (5), the heating and stirring is to increase the temperature of the reaction precursor solution 2 to 80-100°C after stirring at room temperature; the evaporation to dryness refers to continuous stirring until the organic solvent in step (4) is volatilized; the grinding is to grind the mixture after evaporation to dryness; and the sintering is to increase the temperature to 400-700°C at a rate of 1-5°C / min, and sintering in an oxygen or air atmosphere for 7-10h.

[0022] After the reaction is completed and the coating layer is initially formed by heating and stirring, the organic solvent needs to be evaporated to form a thin and uniform lithium titanium aluminum phosphate coating layer on the surface of the nano-tin oxide coated lithium cobaltate particles; the evaporation temperature needs to be moderate to avoid side reactions or uneven coating due to too low temperature and too long evaporation time.

[0023] The application provides application of the lithium cobaltate coated with the nano-tin oxide and the lithium titanium aluminum phosphate in preparation of a positive electrode material of a lithium ion battery and can be used for performance improvement of the lithium ion battery under high voltage conditions.

[0024] The application has the following beneficial effects:

[0025] (1) The application obtains a high-pressure-resistant lithium cobaltate positive electrode material coated with the nano-tin oxide and the lithium titanium aluminum phosphate, that is, the lithium cobaltate substrate is coated with the tin oxide first, the SnO2 belongs to a lithium ion conductor active material, can improve lithium ion conductivity, and generates a thin and stable solid electrolyte interface film on the surface to inhibit the occurrence of surface side reactions. Meanwhile, the Sn element in the surface coating layer migrates to the inside of the lithium cobaltate material after high-temperature calcination, and the tin doped into the body can pin the lattice vibration in the layered structure lithium cobaltate, prevent irreversible phase change under high pressure, and thus improve the cycle stability of the lithium cobaltate positive electrode.

[0026] (2) The application obtains a high-pressure-resistant lithium cobaltate positive electrode material coated with the nano-tin oxide and the lithium titanium aluminum phosphate, that is, the lithium cobaltate coated with the tin oxide is further coated with the lithium titanium aluminum phosphate, the lithium titanium aluminum phosphate has high and excellent ion conduction performance and chemical stability, can construct an excellent ion and electron conduction characteristic interface, further promotes the rapid conduction of lithium ions in the positive electrode material, and plays a stable interface protection role and provides good kinetic conditions.

[0027] (3) The coating layer formed by the preparation method provided by the application is thin and uniform, and the thickness is nano-level (5-10 nm). The lithium cobaltate positive electrode coated by the double coating has a double-layer lithium ion conductor coating layer, plays a double role of physical blocking and chemical stability to a certain extent, constructs a more efficient and stable interface for the positive electrode material under high voltage, improves the structural stability of the positive electrode material under high voltage, and meets the high-pressure cycle stability required by the lithium cobaltate positive electrode material at present. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The XRD graph of the uncoated lithium cobaltate positive electrode material prepared in the comparative example 1 of the application and the high-pressure-resistant lithium cobaltate positive electrode material coated with the nano-tin oxide and the lithium titanium aluminum phosphate prepared in the example 1 of the application

[0029] Figure 2 The SEM graph of the uncoated lithium cobaltate positive electrode material prepared in the comparative example 1 of the application

[0030] Figure 3 SEM image of nano-tin oxide coated lithium cobalt oxide cathode material prepared for Inventive Example 1

[0031] Figure 4 SEM image of nano-tin oxide and lithium titanium aluminum phosphate double coated high voltage resistant lithium cobalt oxide cathode material prepared for Inventive Example 1

[0032] Figure 5 TEM image of nano-tin oxide and lithium titanium aluminum phosphate double coated high voltage resistant lithium cobalt oxide cathode material prepared for Inventive Example 1

[0033] Figure 6 Cycle curves of lithium ion batteries assembled with uncoated lithium cobalt oxide cathode material of Inventive Comparative Example 1, nano-tin oxide coated lithium cobalt oxide cathode material of Comparative Example 2, and nano-tin oxide and lithium titanium aluminum phosphate double coated high voltage resistant lithium cobalt oxide cathode material of Inventive Example 1 at room temperature, 3-4.6V, 200mA / g current density -1 DETAILED DESCRIPTION

[0034] The present application will be further described in conjunction with the following specific examples and drawings. The process, conditions, experimental methods, etc. for implementing the present application are the general knowledge and common sense in the art, and the present application has no special limitations.

[0035] Example 1

[0036] Dissolve 0.05 mol of CoS04·7H20 in 100 mL of deionized water, and then add sodium oxalate solution (0.1 mol / L) drop by drop after placing it in a microwave reactor. After 60 min of reaction at 70°C with a microwave power of 500 W, add 0.02625 mol of Li2C03 and 0.025 mol of SnCl4·5H20 for ultrasonic treatment, and then obtain a tin oxide coated lithium cobalt oxide precipitate mixture after 1 h of ultrasonic treatment with a power of 500 W.

[0037] Filter, wash, and dry the tin oxide coated lithium cobalt oxide precipitate mixture at 100°C, and then perform primary calcination in a tube furnace, with a calcination temperature of 650°C and a temperature increase rate of 4°C / min, for 6 h of calcination treatment, to obtain a primary calcination solid powder. After the primary calcination, fully grind the primary calcination solid powder and then place it back in the tube furnace to increase the temperature to 900°C at a rate of 4°C / min, and then perform secondary calcination in an air atmosphere for 10 h, to obtain nano-tin oxide coated lithium cobalt oxide.

[0038] ​The tin oxide nanocoated lithium cobalt oxide was ultrasonically dispersed in anhydrous ethanol, and phosphoric acid, lithium nitrate, aluminum nitrate were added in sequence according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3, wherein: x=0.3, and finally tetrabutyl titanate was added to obtain reaction precursor 1. The pH of the obtained reaction precursor 1 was adjusted to 7, and after ultrasonic treatment for 30 s, the reaction precursor 2 was stirred at room temperature at a speed of 300 rpm for 4 h.

[0039] After stirring at room temperature, the temperature of the reaction precursor 2 was increased to 80°C, and the stirring was continued until the anhydrous ethanol was completely volatilized. Then the mixture was fully ground and placed in a tube furnace to be heated to 700°C at a rate of 4°C / min, and sintered in an oxygen atmosphere for 8 h to obtain the tin oxide nanocoated lithium titanium aluminum phosphate lithium cobalt oxide positive electrode material.

[0040] The XRD of the tin oxide nanocoated lithium titanium aluminum phosphate lithium cobalt oxide positive electrode material obtained in the present example is shown in Figure 1 Compared with the XRD of the uncoated lithium cobalt oxide positive electrode material prepared in Comparative Example 1, it can be seen that the characteristic peaks of both correspond to the standard PDF card of lithium cobalt oxide, indicating that no impurity phase is generated and the coating does not affect the bulk structure and crystallinity of the lithium cobalt oxide.

[0041] The morphology of the tin oxide nanocoated lithium titanium aluminum phosphate lithium cobalt oxide positive electrode material obtained in the present example is shown in Figure 4 Figure 5 The existence of the surface coating layer is proved, and the thickness of the coating layer can be seen to be about 5-10 nm.

[0042] Example 2

[0043] 0.03 mol of CoSO4·7H2O was dissolved in 100 mL of deionized water, and then sodium oxalate solution (0.1 mol / L) was added dropwise. After 60 min of reaction at 70°C with a microwave power of 500 W, 0.01545 mol of Li2CO3 and 0.021 mol of SnCl4·5H2O were added for ultrasonic treatment, and the ultrasonic power was 500 W for 1 h to obtain a tin oxide coated lithium cobalt oxide precipitate mixture.

[0044] The tin oxide coated lithium cobalt oxide precipitate mixture was filtered, washed, and dried at 100°C, and then placed in a tube furnace for primary calcination. The calcination temperature was 650°C, the heating rate was 4°C / min, and the calcination treatment was 6 h to obtain a primary calcined solid powder. After the primary calcination, the primary calcined solid powder was fully ground and placed back in the tube furnace to be heated to 900°C at a rate of 4°C / min, and then secondary calcination was performed in an air atmosphere for 10 h to obtain tin oxide nanocoated lithium cobalt oxide.

[0045] ​The tin oxide-coated lithium cobalt oxide nanoparticles were ultrasonically dispersed in anhydrous ethanol, and phosphoric acid, lithium nitrate, aluminum nitrate were added in sequence according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3, wherein x=0.5, and finally tetrabutyl titanate was added to obtain reaction precursor solution 1. The pH of the reaction precursor solution 1 was adjusted to 9, and after ultrasonic treatment for 30 s, the solution was stirred at room temperature at a speed of 400 rpm for 4 h to obtain reaction precursor solution 2.

[0046] After stirring at room temperature, the temperature of the reaction precursor solution 2 was increased to 80°C, and stirring was continued until the anhydrous ethanol was completely volatilized. Then the mixture was fully ground and placed in a tube furnace, and was heated to 700°C at a rate of 4°C / min, and sintered in an oxygen atmosphere for 8 h to obtain the high-pressure-resistant lithium cobalt oxide anode material coated with tin oxide and lithium titanium aluminum phosphate.

[0047] Example 3

[0048] CoSO4·7H2O (0.05 mol) was dissolved in 100 mL of deionized water, and then sodium hydroxide solution (0.1 mol / L) was added dropwise. After reaction at 70°C for 60 min at a microwave power of 500 W, 0.02625 mol of Li2CO3 and 0.025 mol of SnCl4·5H2O were added for ultrasonic treatment, and after ultrasonic treatment for 1 h, a tin oxide-coated lithium cobalt oxide precipitate mixture was obtained.

[0049] The tin oxide-coated lithium cobalt oxide precipitate mixture was filtered, washed, and dried at 100°C, and then was placed in a tube furnace for primary calcination at a calcination temperature of 650°C at a heating rate of 4°C / min for 6 h. After primary calcination, the powder was fully ground and was placed in the tube furnace again and heated to 900°C at a rate of 4°C / min for secondary calcination in an air atmosphere for 10 h to obtain tin oxide-coated lithium cobalt oxide nanoparticles.

[0050] The tin oxide-coated lithium cobalt oxide nanoparticles were ultrasonically dispersed in anhydrous ethanol, and phosphoric acid, lithium nitrate, aluminum nitrate were added in sequence according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3, wherein x=0.5, and finally tetrabutyl titanate was added to obtain reaction precursor solution 1. The pH of the reaction precursor solution 1 was adjusted to 9, and after ultrasonic treatment for 30 s, the solution was stirred at room temperature at a speed of 400 rpm for 4 h to obtain reaction precursor solution 2.

[0051] After stirring at room temperature, the temperature of the reaction precursor solution 2 was increased to 80°C, and stirring was continued until the anhydrous ethanol was completely volatilized. Then the mixture was fully ground and placed in a tube furnace, and was heated to 700°C at a rate of 4°C / min, and sintered in an oxygen atmosphere for 8 h to obtain the high-pressure-resistant lithium cobalt oxide anode material coated with tin oxide and lithium titanium aluminum phosphate.

[0052] Example 4

[0053] 0.05 mol of CoSO4·7H2O was dissolved in 100 mL of deionized water and placed in a microwave reactor. Sodium hydroxide solution (0.1 mol / L) was then added dropwise. The reaction was carried out at 70 °C with a microwave power of 500 W for 60 min. Then, 0.02625 mol of Li2CO3 and 0.025 mol of SnCl4·5H2O were added for ultrasonic treatment at a power of 500 W for 1 h. This yielded a mixture of tin oxide-coated lithium cobalt oxide precipitates.

[0054] The mixture of tin oxide-coated lithium cobalt oxide precipitate was filtered, washed, dried at 100°C, and then calcined once in a tube furnace at 650°C with a heating rate of 4°C / min for 6 hours to obtain a first-calcined solid powder. After the first calcination, the first-calcined solid powder was thoroughly ground and then placed back into the tube furnace, heated to 900°C at a rate of 4°C / min, and calcined a second time in air for 10 hours to obtain nano-tin oxide-coated lithium cobalt oxide.

[0055] Lithium cobalt oxide nano-coated with tin oxide was ultrasonically dispersed in ethylene glycol. Simultaneously, phosphoric acid, lithium nitrate, and aluminum nitrate were added sequentially according to the molar ratio Li:Al:Ti:P = (1+x):x:(2-x):3, where x = 0.4. Finally, tetrabutyl titanate was added to obtain reaction precursor solution 1. The pH of reaction precursor solution 1 was adjusted to 7, and after ultrasonication for 30 seconds, it was stirred at 400 rpm for 4 hours at room temperature to obtain reaction precursor solution 2.

[0056] After stirring at room temperature, the temperature of the reaction precursor solution 2 was raised to 80°C and stirred continuously until the anhydrous ethanol was completely evaporated. Then, the mixture was thoroughly ground and placed in a tube furnace, and the temperature was raised to 700°C at a rate of 4°C / min. The mixture was sintered in an oxygen atmosphere for 10 hours to obtain a high-voltage lithium cobalt oxide cathode material with double coating of nano-tin oxide and lithium titanium aluminum phosphate.

[0057] Comparative Example 1

[0058] 0.05 mol of CoSO4·7H2O was dissolved in 100 mL of deionized water and placed in a microwave reactor. Sodium oxalate solution (0.1 mol / L) was then added dropwise. The reaction was carried out at 70 °C with a microwave power of 500 W for 60 min. Then, 0.02625 mol of Li2CO3 was added for ultrasonic treatment at a power of 500 W for 1 h. This resulted in an uncoated lithium cobalt oxide precipitate mixture.

[0059] The uncoated lithium cobalt oxide precipitate mixture was filtered, washed, dried at 100°C, and then calcined once in a tube furnace at 650°C with a heating rate of 4°C / min for 6 hours to obtain a first-calcined solid powder. After the first calcination, the powder was thoroughly ground and returned to the tube furnace, where the temperature was increased to 900°C at a rate of 4°C / min for a second calcination in air for 10 hours to obtain uncoated lithium cobalt oxide, with the morphology as shown below. Figure 2 As shown.

[0060] Comparative Example 2

[0061] 0.05 mol of CoSO4·7H2O was dissolved in 100 mL of deionized water and placed in a microwave reactor. Sodium oxalate solution (0.1 mol / L) was then added dropwise. The reaction was carried out at 70 °C with a microwave power of 500 W for 60 min. Then, 0.02625 mol of Li2CO3 and 0.025 mol of SnCl4·5H2O were added for ultrasonic treatment at a power of 500 W for 1 h. This yielded a mixture of tin oxide-coated lithium cobalt oxide precipitates.

[0062] The mixture of tin oxide-coated lithium cobalt oxide precipitate was filtered, washed, dried at 100°C, and then calcined once in a tube furnace at 650°C with a heating rate of 4°C / min for 6 hours to obtain a first-calcined solid powder. After the first calcination, the solid powder was thoroughly ground and returned to the tube furnace, where the temperature was increased to 900°C at a rate of 4°C / min for a second calcination in air for 10 hours to obtain nano-tin oxide-coated lithium cobalt oxide, with the morphology as shown in the figure. Figure 3 As shown.

[0063] To evaluate the electrochemical performance of the lithium cobalt oxide cathode material described in this invention, the following method was adopted:

[0064] Weigh 0.48g of the prepared positive electrode material, 0.06g of Super P as a conductive agent, and 0.06g of polyvinylidene fluoride (PVDF) as a binder. Grind them evenly, then add an appropriate amount of N,N-dimethylpyrrolidone and continue grinding until a paste is formed. Then, coat the paste evenly onto a 15mm thick aluminum foil. Place the coated aluminum foil in a vacuum drying oven and dry at 110℃ for 12 hours. Use a die-cutting machine to cut the electrode into 14mm diameter discs. Using lithium metal sheets as the negative electrode, a Celgard 2400 membrane as the separator, and an electrolyte composition of 1mol / L LiPF6 / EC+DMC, assemble CR2032 coin cells in an argon atmosphere glove box. Place the cells in a constant temperature chamber with a cutoff voltage of 3-4.6V and a capacity of 200mAg. -1 Charge-discharge cycle tests were conducted at a current density of [value missing].

[0065] like Figure 6The cycling curves are shown, at 3.0–4.6V and 200 mAg. -1 After 200 cycles at a current density, the discharge specific capacities of the lithium cobalt oxide cathode coated with nano-tin oxide and the lithium cobalt oxide cathode double-coated with nano-tin oxide and lithium titanium aluminum phosphate were 136 mAh / g and 164 mAh / g, respectively, with corresponding capacity retention rates of 66% and 82%. In contrast, the uncoated lithium cobalt oxide cathode had a discharge specific capacity of only 105 mAh / g and a capacity retention rate of only 50% after 200 cycles. These results indicate that double coating can significantly improve the cycling performance of lithium cobalt oxide cathode materials under high voltage, and the improvement of high-voltage cycling performance of lithium cobalt oxide by the double lithium-ion conductor coating layer is significantly higher than that of single-layer nano-tin oxide coating.

[0066] Table 1 lists the values ​​of relevant impedance parameters and lithium-ion diffusion coefficients based on equivalent circuits for Example 1 and Comparative Examples 1 and 2. Example 1 exhibits the lowest impedance and the highest lithium-ion diffusion coefficient, indicating that coating lithium-ion conductors with nano-tin oxide and lithium aluminum titanium phosphate further enhances the ion transport capability of lithium cobalt oxide, improves lithium insertion / extraction kinetics, thereby reducing the impedance of lithium cobalt oxide and increasing lithium-ion conductivity.

[0067] Table 1 Impedance parameters and Li in the examples and comparative examples + diffusion coefficient

[0068]

[0069] (R s R is the resistance of the solution. ct R is the charge transfer resistor. total D is the total impedance; Li+ For Li + (Diffusion coefficient).

Claims

1. A method for preparing a high-voltage resistant lithium cobalt oxide cathode material double-coated with nano-tin oxide and lithium titanium aluminum phosphate, characterized in that, Includes the following steps: (1) After dissolving the cobalt source, put it into a microwave reactor, add a precipitant, and use microwave-assisted co-precipitation reaction. Then add the lithium source and tin source and perform ultrasonic treatment to obtain a mixture of lithium cobalt oxide precipitate coated with tin oxide. (2) The mixture of tin oxide-coated lithium cobalt oxide precipitate was filtered, washed, dried and calcined to obtain a single-calcined solid powder; (3) After calcination, the solid powder from the first calcination is thoroughly ground and then calcined again to obtain lithium cobalt oxide coated with nano-tin oxide; (4) Disperse the nano-tin oxide-coated lithium cobalt oxide in an organic solvent by ultrasonication, and introduce phosphoric acid, lithium nitrate, aluminum nitrate and tetrabutyl titanate to obtain reaction precursor solution 1. Adjust the pH value of reaction precursor solution 1 and mix it thoroughly to obtain reaction precursor solution 2. (5) The reaction precursor liquid 2 is heated, stirred, evaporated, and ground thoroughly before being placed in a tube furnace for sintering to obtain a high-voltage lithium cobalt oxide cathode material with double coating of nano-tin oxide and lithium titanium aluminum phosphate.

2. The method for preparing a high-voltage resistant lithium cobalt oxide cathode material with dual coating of nano-tin oxide and lithium titanium aluminum phosphate as described in claim 1, characterized in that, Step (1) includes the following steps: Dissolve the cobalt source in 100ml of deionized water, put it into a microwave reactor, add 0.1mol / L precipitant dropwise, microwave power is 300-800W, heat to the reaction temperature of 50-80℃ by microwave, react for 30-60min, then add lithium source and tin source for ultrasonic treatment, ultrasonic power is 300-800W, ultrasonic time is 0.5-2h.

3. The method for preparing a high-voltage resistant lithium cobalt oxide cathode material with dual coating of nano-tin oxide and lithium titanium aluminum phosphate according to claim 1, characterized in that, In step (1), the molar ratio of cobalt in the cobalt source to lithium in the lithium source is 1:(1.02-1.12); the molar amount of tin in the tin source is 0.3-1.5% of the cobalt content; the cobalt source is one or more of cobalt hydroxide, cobalt chloride, and cobalt sulfate; the precipitant is one or more of NaOH, NH3·H2O, and Na2C2O4; the lithium source is lithium hydroxide and / or lithium carbonate; and the tin source is tin oxide and / or tin chloride.

4. The method for preparing a high-voltage resistant lithium cobalt oxide cathode material with dual coating of nano-tin oxide and lithium titanium aluminum phosphate according to claim 1, characterized in that, The drying temperature of the tin oxide-coated lithium cobalt oxide precipitate mixture in step (2) is 80-120℃; the temperature conditions for the first calcination are 600-800℃, and the calcination treatment is carried out at a heating rate of 1-5℃ / min for 4-6 hours; the second calcination in step (3) is to heat to 800-1000℃ at a rate of 1-5℃ / min and calcinate in an oxygen or air atmosphere for 8-12 hours.

5. The method for preparing a high-voltage resistant lithium cobalt oxide cathode material with dual coating of nano-tin oxide and lithium titanium aluminum phosphate according to claim 1, characterized in that, The organic solvent mentioned in step (4) is one or more of anhydrous ethanol, isopropanol, and ethylene glycol. The ultrasonic treatment time is 20-30 min. Phosphoric acid, lithium nitrate, and aluminum nitrate are added in sequence according to the molar ratio Li:Al:Ti:P=(1+x):x:(2-x):3, where: 0.3≤x≤0.

8. Finally, tetrabutyl titanate is added to obtain reaction precursor solution 1. The pH value of reaction precursor solution 1 is adjusted to 7-10. The term "mixing evenly" refers to ultrasonicating reaction precursor solution 1 for 30-60 s and then stirring it at 300-600 rpm at room temperature for 4-6 h to obtain reaction precursor solution 2.

6. The method for preparing a high-voltage resistant lithium cobalt oxide cathode material with dual coating of nano-tin oxide and lithium titanium aluminum phosphate according to claim 1, characterized in that, The heating and stirring in step (5) refers to raising the temperature of the precursor liquid 2 to 80-100℃ after stirring at room temperature; the evaporation refers to continuously stirring until the organic solvent in step (4) evaporates; the grinding refers to fully grinding the mixture after evaporation; the sintering refers to heating to 400-700℃ at a rate of 1-5℃ / min and sintering in an oxygen or air atmosphere for 7-10 hours.

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