A surface-doping modified lithium cobalt oxide material, a preparation method and application in high-voltage lithium batteries

Abstract

The application discloses a kind of surface doping modified lithium cobaltate materials and preparation method and application in high-voltage lithium battery.The material is the surface of lithium cobaltate material Doping Potassium Element, phosphorus element and fluorine element.The surface of the described surface doping modified lithium cobaltate material is doped and modified, and the reversible specific capacity of the material is 200-230 mAh / g at 1C rate in the voltage interval of 3.0-4.6V;The reversible specific capacity of the material is 115-155 mAh / g at 50C rate.The high-voltage fast-charging lithium cobaltate cathode material prepared by the application is modified by surface doping of potassium, phosphorus and fluorine elements.By optimizing raw materials, doping content and process, the material phase crystal structure reversibility and surface structure stability under high voltage are improved, and the ion conductivity and electronic conductivity of the material are also improved, realizing the improvement of high-voltage super-fast-charging performance and cycle stability of lithium cobaltate cathode material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a surface-doped modified lithium cobalt oxide material, its preparation method, and its application in high-voltage lithium batteries. Background Technology

[0002] Lithium cobalt oxide cathode materials occupy an important position in the market for portable electronic terminal devices such as computers, communications, and consumer electronics due to their advantages such as high compaction density, high volumetric energy density, and long cycle life. As electronic products develop towards diversification, thinner and lighter designs, high performance, and intelligence, the battery market urgently needs small energy storage devices with high energy density and high power density.

[0003] Improving the fast-charging performance and charging cut-off voltage of lithium cobalt oxide cathodes is a crucial way to enhance the energy density and power density of lithium-ion batteries. However, with the increase in fast-charging rate and charging cut-off voltage, the electrochemical performance of lithium cobalt oxide cathodes deteriorates significantly. This is mainly because at high charging cut-off voltages, the side reactions at the cathode material and electrolyte interface intensify, and the high degree of delithiation leads to irreversible phase transitions. Under fast charging, material polarization intensifies surface side reactions and generates irreversible phase transitions, thereby accelerating the degradation of the electrochemical performance of lithium cobalt oxide cathode materials.

[0004] Therefore, improving structural stability and reducing material polarization are key technical challenges that need to be overcome to enhance the fast-charging performance and charging cutoff voltage of lithium cobalt oxide cathodes, and are also important directions for the development of new advanced lithium-ion battery cathode materials in recent years. Summary of the Invention

[0005] In view of this, the present invention provides a surface-doped modified lithium cobalt oxide material, its preparation method, and its application in high-voltage lithium batteries. The main purpose is to solve the technical problem that the electrochemical performance of high-voltage fast-charging lithium cobalt oxide cathode materials needs to be improved.

[0006] On one hand, the present invention provides a surface-doped modified lithium cobalt oxide material, wherein the surface-doped modified lithium cobalt oxide material is a lithium cobalt oxide material doped with potassium, phosphorus and fluorine elements.

[0007] Optionally, the surface-doped modified lithium cobalt oxide material has a reversible specific capacity of 200-230 mAh / g at a rate of 1C within a voltage range of 3.0-4.6V, and a reversible specific capacity of 115-155 mAh / g at a rate of 50C.

[0008] Optionally, the reversible specific capacity of the surface-doped modified lithium cobalt oxide material at a 1C rate is selected from any value of 200, 205, 210, 215, 220, 225, 230 mAh / g or any range between the two.

[0009] Optionally, the surface-doped modified lithium cobalt oxide material has a reversible specific capacity at a rate of 50C of any value among 115, 120, 125, 130, 135, 140, 145, 150, and 155 mAh / g, or a range between any two.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned surface-doped modified lithium cobalt oxide material, the method comprising the following steps:

[0011] S1: Obtain lithium cobalt oxide;

[0012] S2: Mix the raw materials containing lithium cobalt oxide, potassium source, phosphorus source and fluorine source as described in step S1 to obtain the precursor dry material;

[0013] S3: The precursor dry material in step S2 is heated for I and kept at a constant temperature for I in air to obtain the surface-doped modified lithium cobalt oxide material.

[0014] Optionally, in step S2, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.0001~0.05):(0.0001~0.08):(0.0001~0.09).

[0015] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.0005~0.05):(0.0005~0.08):(0.0005~0.09).

[0016] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.001-0.05):(0.001-0.08):(0.001-0.09).

[0017] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.005~0.05):(0.005~0.08):(0.005~0.09).

[0018] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.01-0.05):(0.01-0.08):(0.01-0.09).

[0019] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.01-0.04):(0.01-0.07):(0.01-0.08).

[0020] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.01-0.03):(0.01-0.05):(0.01-0.06).

[0021] Optionally, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.02-0.03):(0.02-0.05):(0.02-0.06).

[0022] Another expression for the mass ratio of lithium cobalt oxide, potassium source, phosphorus source and fluorine source in this invention is: 100:x:y:z, 0.01%≤x≤5%, 0.01%≤y≤8%, 0.01%≤y≤9%;

[0023] x represents the mass fraction of the potassium source and the mass percentage of 100 parts of lithium cobalt oxide;

[0024] y represents the mass fraction of the phosphorus source and the mass percentage of 100 parts of lithium cobalt oxide;

[0025] z represents the mass fraction of the fluorine source and the mass percentage of 100 parts of lithium cobalt oxide.

[0026] Optionally, x is selected from any value among 0.01%, 0.50%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%, or a range between any two.

[0027] Optionally, y is selected from any value among 0.01%, 0.50%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, and 8.0%, or a range between any two.

[0028] Optionally, x is selected from any value or a range between 0.01%, 0.50%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, and 9%.

[0029] Optionally, in step S3, the temperature of heating I is 600-1000℃, and the time of heat preservation I is 2-12h.

[0030] Optionally, the temperature of heating I is selected from any value or a range between 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃.

[0031] Optionally, the heat preservation time I is selected from any value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12h or any range between the two.

[0032] Optionally, in step S2, the potassium source is selected from at least one of potassium carbonate, potassium bicarbonate, potassium chloride, potassium nitrate, and potassium hexafluorophosphate.

[0033] Optionally, in step S2, the phosphorus source is selected from at least one of phosphoric acid, potassium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and potassium hexafluorophosphate.

[0034] Optionally, in step S2, the fluorine source is selected from at least one of calcium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, and potassium hexafluorophosphate.

[0035] Optionally, in step S1, the lithium cobalt oxide is a product obtained by mixing cobalt tetroxide and a lithium source, heating in air medium (II), and holding at a certain temperature (II); it is nano-lithium cobalt oxide powder.

[0036] The unmodified lithium cobalt oxide used in this invention can also be obtained from existing technologies.

[0037] Optionally, the atomic molar ratio of cobalt tetroxide to the lithium source is 1:1 to 1.1; the temperature of heating II is 600 to 1000°C; and the holding time of heat II is 2 to 12 hours.

[0038] Optionally, the temperature of the heating II is selected from any value or a range between 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, and 1000°C.

[0039] Optionally, the duration of the heat preservation II is selected from any value among 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 hours or a range between any two.

[0040] Optionally, the atomic molar ratio of the cobalt tetroxide and the lithium source is selected from any value among 1:1, 1:1.05, and 1:1.1, or any range between the two.

[0041] Optionally, the cobalt tetroxide is the product of cobalt hydroxide being heated in air for a period of time (III) and then kept at that temperature (III); it is nano-cobalt tetroxide powder.

[0042] The cobalt tetroxide used in this invention can also be obtained from existing technologies.

[0043] Optionally, the temperature of heating III is 200–600°C, and the holding time of heat III is 2–6 hours.

[0044] Optionally, the temperature of heating III is selected from any value or a range between 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, and 600°C.

[0045] Optionally, in step S3, the heating rate of heating I is 5-20℃ / min; the heating rate of heating II is 2-20℃ / min; and the heating rate of heating III is 2-20℃ / min.

[0046] Optionally, the cobalt hydroxide is obtained by centrifuging, washing, and freeze-drying the product of cobalt salt and ammonia water heated to 600-100°C for 1-24 hours to obtain nano-cobalt hydroxide powder.

[0047] The cobalt hydroxide of the present invention can also be obtained from the prior art.

[0048] Optionally, the cobalt salt is selected from cobalt nitrate.

[0049] This invention provides a specific method for preparing a surface-doped modified high-voltage fast-charging lithium cobalt oxide cathode material, the method comprising the following steps:

[0050] S1. Preparation of nano-lithium cobalt oxide powder: Weigh 10-50g of polyvinylpyrrolidone and 1-20g of cobalt nitrate hexahydrate and disperse them in 0.5-1.0L of deionized water. Heat in an oil bath to 60-100℃. Add 5-30mL of 25% ammonia solution to the above solution, keep warm and stir at a stirring speed of 100-1000rpm for 1-24h. Centrifuge and wash the above reaction product, ultrasonically disperse and freeze-dry to obtain nano-cobalt hydroxide powder. Centrifuge speed is 4000-10000r / min. Place the above cobalt hydroxide powder in a muffle furnace and heat in air at a heating rate of 5-20℃ / min, at a temperature of 200-600℃ for 2-6h. After natural cooling, obtain nano-cobalt tetroxide powder.

[0051] Cobalt tetroxide and lithium source were weighed according to an atomic molar ratio of 1:1.05, mixed and ground to obtain the precursor dry material.

[0052] The above-mentioned dry precursor material was placed in a muffle furnace and heated and held in air at a rate of 5-20℃ / min for a temperature of 600-1000℃ for 2-12 hours. After the process was completed, the product was removed to obtain nano-lithium cobalt oxide powder.

[0053] S2. Preparation of surface-doped lithium cobalt oxide cathode material: Weigh lithium cobalt oxide, potassium source, phosphorus source and fluorine source according to the mass ratio of 100:x:y:z, where: 0.01%≤x≤5%, 0.01%≤y≤8%, 0.01%≤y≤9%; (x is the mass percentage of potassium source to 100 parts of lithium cobalt oxide; y is the mass percentage of phosphorus source to 100 parts of lithium cobalt oxide; z is the mass percentage of fluorine source to 100 parts of lithium cobalt oxide), mix and grind to obtain the precursor dry material.

[0054] The aforementioned dry precursor material was placed in a muffle furnace and heated and held in air at a rate of 5-20℃ / min for a temperature of 600-1000℃ for 2-12 hours. After the heating process was completed, the product was removed and air-quenched to obtain surface-doped lithium cobalt oxide cathode material.

[0055] Optionally, the polyvinylpyrrolidone in S1 is one or more of PVP-K12, PVP-K15, PVP-K17, PVP-K25, PVP-K30, PVP-K60, and PVP-K90.

[0056] Thirdly, the present invention provides a lithium cobalt oxide positive electrode, comprising a conductive substrate and a slurry coated on the surface of the conductive substrate; the raw material of the slurry comprises the aforementioned surface-doped modified lithium cobalt oxide material.

[0057] Optionally, the method for preparing the lithium cobalt oxide positive electrode is as follows: lithium cobalt oxide material is mixed with conductive carbon black and polyvinylidene fluoride binder at a mass ratio of (6-10):1:1 and ground, and then an appropriate amount of solvent is added to form a slurry; the slurry is uniformly coated on carbon-coated aluminum foil and dried to obtain a positive electrode sheet.

[0058] Fourthly, the present invention provides a high-voltage fast-charging lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode is the aforementioned lithium cobalt oxide positive electrode.

[0059] Optionally, the negative electrode is a lithium metal sheet, the separator is a Celgard 2400 membrane, and the electrolyte is an LB-372 high-voltage electrolyte.

[0060] Optionally, the battery is a CR2016 button cell battery.

[0061] Fifthly, the present invention provides the application of the above-mentioned surface-doped modified lithium cobalt oxide material in high-voltage ultra-fast charging lithium-ion batteries.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] 1) The lithium cobalt oxide cathode material prepared by this invention, which is suitable for high-voltage fast charging, is modified by surface doping with multiple elements such as potassium, phosphorus and fluorine. By optimizing the raw materials, doping content and preparation process, not only is the reversibility of the bulk crystal structure and the structural stability of the surface improved under high voltage, but also the ionic conductivity and electronic conductivity of the material are improved, thereby realizing the improvement of the high-voltage ultra-fast charging performance and cycle stability of the lithium cobalt oxide cathode material.

[0064] 2) The preparation method provided by the present invention has good controllability, is simple and easy to implement, and is suitable for large-scale production and industrialization. Attached Figure Description

[0065] Figure 1 This is a scanning electron microscope image of the potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material prepared in Example 1 of the present invention;

[0066] Figure 2 This is a scanning electron microscope image of the unmodified lithium cobalt oxide cathode material prepared in Comparative Example 1 of this invention;

[0067] Figure 3 The graph shows the rate performance test results of lithium-ion batteries assembled with potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material in Example 1 and unmodified lithium cobalt oxide cathode material in Comparative Example 1, under a constant temperature of 28°C, in the voltage range of 3.0-4.6V.

[0068] Figure 4 The charge-discharge curves of a lithium-ion battery assembled with the potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material prepared in Example 1 of the present invention at different rates within a voltage range of 3.0-4.6V at a constant temperature of 28℃.

[0069] Figure 5 The graph shows the cycle performance of a lithium-ion battery assembled with the potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material prepared in Example 1 of this invention at a constant temperature of 28°C, within a voltage range of 3.0-4.6V, and at a 1C rate. Detailed Implementation

[0070] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0071] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0072] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0073] Example 1 (Doped Lithium Cobalt Oxide Cathode Material)

[0074] Weigh 10g of polyvinylpyrrolidone and 15g of cobalt nitrate hexahydrate and disperse them in 1L of deionized water. Heat the solution in an oil bath to 60℃. Add 10mL of 25% ammonia solution to the above solution, keep warm and stir at a stirring speed of 400rpm for 2h. Centrifuge and wash the above reaction product, ultrasonically disperse and freeze dry to obtain nano cobalt hydroxide powder. The centrifugation speed is 6000r / min.

[0075] The cobalt hydroxide powder was placed in a muffle furnace and heated in air at a rate of 5°C / min to a temperature of 400°C for 2 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0076] Cobalt tetroxide and lithium carbonate were weighed according to a cobalt to lithium atom molar ratio of 1:1.05, mixed, and ground to obtain a dry precursor material. The dry precursor material was placed in a muffle furnace and heated in air at a rate of 5-20℃ / min to a temperature of 700℃ for 6 hours. After the process was completed, the product was removed to obtain nano-lithium cobalt oxide powder.

[0077] Lithium cobalt oxide, potassium carbonate, ammonium dihydrogen phosphate, and ammonium fluoride were weighed in a mass ratio of 1:0.01:0.02:0.02, mixed, and ground to obtain the dry precursor material.

[0078] The aforementioned dry precursor material was placed in a muffle furnace and heated and held in air at a rate of 5°C / min to a temperature of 800°C for 4 hours. After the heating process was completed, the product was removed to obtain surface-doped lithium cobalt oxide cathode material.

[0079] Example 2 (Doped Lithium Cobalt Oxide Cathode Material)

[0080] Weigh 20g of polyvinylpyrrolidone and 30g of cobalt nitrate hexahydrate and disperse them in 1L of deionized water. Heat the mixture in an oil bath to 60℃. Add 15mL of 25% ammonia solution to the above solution, keep warm and stir at a stirring speed of 400rpm for 2h. Centrifuge and wash the above reaction product, ultrasonically disperse and freeze dry to obtain nano cobalt hydroxide powder. The centrifugation speed is 6000r / min.

[0081] The cobalt hydroxide powder was placed in a muffle furnace and heated in air at a rate of 5°C / min to a temperature of 400°C for 2 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0082] Cobalt tetroxide and lithium carbonate were weighed according to a cobalt to lithium atom molar ratio of 1:1.05, mixed, and ground to obtain a dry precursor material. The dry precursor material was placed in a muffle furnace and heated in air at a rate of 5-20℃ / min to a temperature of 700℃ for 6 hours. After the process was completed, the product was removed to obtain nano-lithium cobalt oxide powder.

[0083] Weigh lithium cobalt oxide and potassium hexafluorophosphate at a mass ratio of 1:0.02, mix and grind them to obtain the precursor dry material.

[0084] The aforementioned dry precursor material was placed in a muffle furnace and heated and held in air at a rate of 5°C / min to a temperature of 900°C for 8 hours. After the heating process was completed, the product was removed to obtain surface-doped lithium cobalt oxide cathode material.

[0085] Example 3 (Doped Lithium Cobalt Oxide Cathode Material)

[0086] Weigh 20g of polyvinylpyrrolidone and 30g of cobalt nitrate hexahydrate and disperse them in 1L of deionized water. Heat the mixture in an oil bath to 60℃. Add 15mL of 25% ammonia solution to the above solution, keep warm and stir at a stirring speed of 400rpm for 2h. Centrifuge and wash the above reaction product, ultrasonically disperse and freeze dry to obtain nano cobalt hydroxide powder. The centrifugation speed is 6000r / min.

[0087] The cobalt hydroxide powder was placed in a muffle furnace and heated in air at a rate of 5°C / min to a temperature of 400°C for 2 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0088] Cobalt tetroxide and lithium carbonate were weighed according to a cobalt to lithium atom molar ratio of 1:1.05, mixed, and ground to obtain a dry precursor material. The dry precursor material was placed in a muffle furnace and heated in air at a rate of 5-20℃ / min to a temperature of 700℃ for 6 hours. After the process was completed, the product was removed to obtain nano-lithium cobalt oxide powder.

[0089] Lithium cobalt oxide, potassium carbonate, ammonium dihydrogen phosphate, and ammonium fluoride were weighed in a mass ratio of 1:0.01:0.02:0.02, mixed, and ground to obtain the dry precursor material.

[0090] The aforementioned dry precursor material was placed in a muffle furnace and heated in air at a rate of 5°C / min to a temperature of 700°C for 4 hours. After the heating process was completed, the product was removed to obtain surface-doped lithium cobalt oxide cathode material.

[0091] Example 4 (Doped Lithium Cobalt Oxide Cathode Material)

[0092] Weigh 20g of polyvinylpyrrolidone and 30g of cobalt nitrate hexahydrate and disperse them in 1L of deionized water. Heat the mixture in an oil bath to 60℃. Add 15mL of 25% ammonia solution to the above solution, keep warm and stir at a stirring speed of 400rpm for 2h. Centrifuge and wash the above reaction product, ultrasonically disperse and freeze dry to obtain nano cobalt hydroxide powder. The centrifugation speed is 6000r / min.

[0093] The cobalt hydroxide powder was placed in a muffle furnace and heated in air at a rate of 5°C / min to a temperature of 400°C for 2 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0094] Cobalt tetroxide and lithium carbonate were weighed according to a cobalt to lithium atom molar ratio of 1:1.05, mixed, and ground to obtain a dry precursor material. The dry precursor material was placed in a muffle furnace and heated in air at a rate of 5-20℃ / min to a temperature of 700℃ for 6 hours. After the process was completed, the product was removed to obtain nano-lithium cobalt oxide powder.

[0095] Lithium cobalt oxide, potassium carbonate, ammonium dihydrogen phosphate, and ammonium fluoride were weighed in a mass ratio of 1:0.01:0.01:0.01, mixed, and ground to obtain the dry precursor material.

[0096] The aforementioned dry precursor material was placed in a muffle furnace and heated and held in air at a rate of 5°C / min to a temperature of 800°C for 4 hours. After the heating process was completed, the product was removed to obtain surface-doped lithium cobalt oxide cathode material.

[0097] Comparative Example 1 (Undoped lithium cobalt oxide cathode material)

[0098] 20g of polyvinylpyrrolidone and 5g of cobalt nitrate hexahydrate were weighed and dispersed in 1.0L of deionized water, and heated to 80℃ in an oil bath. 15mL of 25% ammonia solution was added to the above solution, and the mixture was kept at this temperature and stirred at 400rpm for 1h. The reaction product was centrifuged, washed, ultrasonically dispersed, and freeze-dried to obtain nano-cobalt hydroxide powder.

[0099] The cobalt hydroxide powder was placed in a muffle furnace and heated in air at a rate of 5°C / min to a temperature of 450°C for 2 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0100] Cobalt tetroxide and lithium carbonate were weighed according to a cobalt to lithium atom molar ratio of 1:1.05, mixed, and ground to obtain a dry precursor material. The dry precursor material was placed in a muffle furnace and heated in air at 5℃ / min to a temperature of 800℃ for 3 hours. After the heating process was completed, the product was removed to obtain the lithium cobalt oxide cathode material.

[0101] Example 5 (Lithium-ion Battery)

[0102] The lithium cobalt oxide cathode materials prepared in Examples 1-4 and Comparative Example 1 were weighed with conductive carbon black and polyvinylidene fluoride binder in a mass ratio of 8:1:1, mixed and ground, and then an appropriate amount of N-methylpyrrolidone was added dropwise, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto carbon-coated aluminum foil and transferred to a vacuum oven at 100°C. After complete drying, the aluminum foil was cut into cathode sheets with a diameter of 12 mm for later use, resulting in 5 different cathode sheets.

[0103] Using lithium metal sheets as the negative electrode and Celgard 2400 membrane as the separator, and LB-372 high-voltage electrolyte provided by Duoduo Reagent Co., Ltd., CR2016 button batteries were assembled in a glove box under argon atmosphere protection to obtain five different lithium-ion batteries.

[0104] The present invention provides a method for evaluating the electrochemical performance of lithium cobalt oxide cathode materials as follows:

[0105] The five types of lithium-ion batteries were placed in a constant temperature chamber at 28°C, and rate and cycle charge-discharge tests were conducted within a voltage window of 3.0-4.6V. Rate performance testing within the 3.0-4.6V voltage range was performed as follows. Figure 3 As shown. The corresponding charge-discharge curves at different rates are as follows. Figure 4 As shown.

[0106] Correspondingly, the potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode materials prepared in Examples 1 to 4 of the present invention have a reversible specific capacity of 226.4 mAh / g at a rate of 1C and a reversible specific capacity of 136.2 mAh / g at a rate of 50C, with a capacity retention rate of 60%.

[0107] The undoped lithium cobalt oxide cathode material prepared in Comparative Example 1 has a reversible specific capacity of 167.3 mAh / g at 1C and a reversible specific capacity of 23.6 mAh / g at 50C, corresponding to a capacity retention of only 14%.

[0108] The comparison shows that the reversible specific capacity of the cathode material prepared in Comparative Example 1 is significantly lower than that of the potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material prepared in this invention. Specifically, the reversible specific capacity of the potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material prepared in this invention at a 1C rate is 226.4 mAh / g, while that of Comparative Example 1 is 167.3 mAh / g, meaning that this invention is 1.35 times that of Comparative Example 1. The reversible specific capacity of this invention at a 50C rate is 136.2 mAh / g, while that of Comparative Example 1 is 23.6 mAh / g, meaning that this invention is more than 5 times that of Comparative Example 1. The electrical performance of the lithium cobalt oxide cathode material after doping in this invention is significantly improved.

[0109] The above results demonstrate that the present invention can effectively improve the rate performance and reversible specific capacity of lithium cobalt oxide cathode materials by surface doping.

[0110] This invention first prepares nano-sized lithium cobalt oxide powder using a liquid-phase method and high-temperature annealing. Based on this, the nano-sized lithium cobalt oxide powder and doping elements are mixed uniformly according to a specific atomic ratio and then subjected to high-temperature annealing. This invention significantly improves the bulk structural stability of the lithium cobalt oxide cathode material, suppresses side reactions at the particle-electrolyte interface under high voltage, and greatly enhances the ionic and electronic conductivity of the lithium cobalt oxide cathode material. This improves the high-voltage fast-charging performance and high-voltage cycle stability of the lithium cobalt oxide cathode material. The preparation method provided by this invention is highly controllable, simple, and suitable for large-scale production and industrialization.

[0111] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A surface-doped modified lithium cobalt oxide material, characterized in that, The surface-doped modified lithium cobalt oxide material is a lithium cobalt oxide material with potassium, phosphorus and fluorine elements doped on its surface. The preparation method of the surface-doped modified lithium cobalt oxide material includes the following steps: S1: Obtain lithium cobalt oxide; S2: Mix the raw materials containing lithium cobalt oxide, potassium source, phosphorus source and fluorine source as described in step S1 to obtain the precursor dry material; S3: The precursor dry material in step S2 is heated for I and kept at a constant temperature for I in air to obtain the surface-doped modified lithium cobalt oxide material; In step S2, the mass ratio of the lithium cobalt oxide, the potassium source, the phosphorus source, and the fluorine source is 100:(0.0001~0.05):(0.0001~0.08):(0.0001~0.09).

2. The surface-doped modified lithium cobalt oxide material according to claim 1, characterized in that, The surface-doped modified lithium cobalt oxide material exhibits a reversible specific capacity of 200-230 mAh / g at a rate of 1C within a voltage range of 3.0-4.6V, and a reversible specific capacity of 115-155 mAh / g at a rate of 50C.

3. The surface-doped modified lithium cobalt oxide material according to claim 1, characterized in that, In step S3, the temperature of heating I is 600 ~ 1000℃, and the holding time I is 2 ~ 12h.

4. The surface-doped modified lithium cobalt oxide material according to claim 1, characterized in that, In step S2, the potassium source is selected from at least one of potassium carbonate, potassium bicarbonate, potassium chloride, potassium nitrate, and potassium hexafluorophosphate. The phosphorus source is selected from at least one of phosphoric acid, potassium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and potassium hexafluorophosphate. The fluorine source is selected from at least one of calcium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, and potassium hexafluorophosphate.

5. The surface-doped modified lithium cobalt oxide material according to claim 1, characterized in that, In step S1, the lithium cobalt oxide is the product of mixing cobalt tetroxide and a lithium source, heating it in air medium II, and holding it at a certain temperature II. The atomic molar ratio of cobalt tetroxide to the lithium source is 1:1 to 1.1; the temperature of heating II is 600 to 1000°C; and the holding time of heating II is 2 to 12 hours. The cobalt tetroxide is the product of cobalt hydroxide being heated (III) and held at a certain temperature (III) in air; wherein the temperature of heating (III) is 200 ~ 600℃, and the holding time (III) is 2 ~ 6h; In step S3, the heating rate of heating I is 5 ~ 20℃ / min; the heating rate of heating II is 2 ~ 20℃ / min; and the heating rate of heating III is 2 ~ 20℃ / min.

6. A lithium cobalt oxide positive electrode, comprising a conductive substrate and a paste coated on the surface of the conductive substrate; characterized in that, The raw material for the slurry includes the surface-doped modified lithium cobalt oxide material as described in claim 1 or 2.

7. A high-voltage fast-charging lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; characterized in that, The positive electrode is the lithium cobalt oxide positive electrode as described in claim 6.

8. A high-voltage fast-charging lithium-ion battery according to claim 7, characterized in that, The negative electrode is a lithium metal sheet, the separator is a Celgard 2400 membrane, the electrolyte is an LB-372 high-voltage electrolyte, and the battery is a CR2016 button cell.

9. The application of the surface-doped modified lithium cobalt oxide material according to claim 1 or 2 in high-voltage ultra-fast charging lithium-ion batteries.

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