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

Abstract

The application discloses a surface-modified lithium cobalt oxide material and a preparation method and application thereof in high-voltage lithium batteries. The material is a lithium cobalt oxide material modified by fluorinated phosphate surface coating. The surface-modified lithium cobalt oxide material has a reversible specific capacity of 200-225 mAh / g at a rate of 0.2 C in a voltage range of 3.0-4.6 V, and a reversible specific capacity of 150-190 mAh / g at a rate of 10 C. The high-voltage fast-charging lithium cobalt oxide cathode material prepared by the application is modified by fluorinated phosphate surface coating, and by optimizing raw materials, doping content and process, the material body phase crystal structure reversibility and surface structure stability at high voltage are improved, and the ion conductivity and electronic conductivity of the material are also improved, so that the high-voltage super-fast-charging performance and cycle stability of the lithium cobalt oxide cathode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a surface-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-modified lithium cobalt oxide material, its preparation method and its application in high-voltage lithium batteries, the main purpose of which 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-modified lithium cobalt oxide material, wherein the surface-modified lithium cobalt oxide material is lithium cobalt oxide modified by fluorinated phosphate, and the fluorinated phosphate is coated on the surface of the lithium cobalt oxide material.

[0007] Optionally, the number of phosphorus atoms in the fluorinated phosphate coating is 0.02% to 10% of the number of cobalt atoms in the lithium cobalt oxide.

[0008] Optionally, the number of phosphorus atoms in the fluorinated phosphate coating is a range of 0.02%, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, 5%, 5.3%, 5.5%, 5.8%, 6%, 6.3%, 6.5%, 6.8%, 7%, 7.3%, 7.5%, 7.8%, 8%, 8.3%, 8.5%, 8.8%, 9%, 9.3%, 9.5%, 9.8%, 10%, or any combination thereof.

[0009] Optionally, the surface-modified lithium cobalt oxide material has a reversible specific capacity of 200-225 mAh / g at a rate of 0.2C within a voltage range of 3.0-4.6V, and a reversible specific capacity of 150-190 mAh / g at a rate of 10C.

[0010] Optionally, the reversible specific capacity of the surface-modified lithium cobalt oxide material at a rate of 0.2C is selected from any value of 200, 205, 210, 215, 220, 225 mAh / g or any range between the two.

[0011] Optionally, the surface-modified lithium cobalt oxide material has a reversible specific capacity at 10C of any value or a range between 150, 155, 160, 165, 170, 175, 180, 185, and 190 mAh / g.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned surface-modified lithium cobalt oxide material, the method comprising the following steps:

[0013] S1: Obtain lithium cobalt oxide;

[0014] S2: Mix the raw materials containing lithium cobalt oxide, lithium source, fluorine source, phosphorus source and transition metal salt described in step S1 to obtain the precursor dry material;

[0015] S3: The precursor dry material in step S2 is heated for I and kept at a constant temperature for I in an inert atmosphere to obtain a lithium cobalt oxide cathode material with cobalt fluoride phosphate surface modification.

[0016] Optionally, in step S2, the atomic molar ratio of the lithium cobalt oxide, the lithium source, the fluorine source, the phosphorus source, and the transition metal salt is (1-2x):1x:1x:1x:1x, where 0.0002≤x≤0.1;

[0017] The atomic molar number of lithium cobalt oxide is expressed in terms of cobalt atomic molar number.

[0018] The atomic molar number of the lithium source is expressed in terms of lithium atomic molar number.

[0019] The atomic molar number of the fluorine source is expressed in terms of the number of fluorine atoms in molars.

[0020] The atomic molar number of the transition metal salt is calculated based on the corresponding metal atomic molar number.

[0021] In the above "(1-2x)" of this invention, "-" means 1 minus 2x.

[0022] In this invention, when the transition metal salt is a complex metal salt, its atomic molar number is the total number of metal atoms in the complex metal salt.

[0023] Optionally, x in step S2 is selected from any value or a range between 0.0002, 0.0005, 0.0008, 0.0010, 0.003, 0.005, 0.008, 0.010, 0.020, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1.

[0024] Optionally, in step S3, the temperature of heating I is 600-1000℃, and the time of heat preservation I is 2-6 hours.

[0025] Optionally, the inert atmosphere includes argon gas.

[0026] 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℃.

[0027] Optionally, the heat preservation time I is selected from any value of 2, 3, 4, 5, 6 hours or any range between two.

[0028] Optionally, in step S2, the lithium source is selected from at least one of lithium carbonate, lithium chloride, lithium hydroxide, and lithium fluoride.

[0029] Optionally, in step S2, the fluorine source is selected from lithium fluoride and / or ammonium fluoride.

[0030] Optionally, in step S2, the phosphorus source is at least one of phytic acid, phosphoric acid, lithium dihydrogen phosphate, and ammonium phosphate.

[0031] Optionally, in step S2, the transition metal salt is selected from at least one of cobalt acetate or nitrate, copper acetate or nitrate, lanthanum acetate or nitrate, and aluminum acetate or nitrate.

[0032] Optionally, in step S1, the lithium cobalt oxide is the product of mixing cobalt tetroxide and lithium carbonate, heating in air medium II, and holding at that temperature II.

[0033] The atomic molar ratio of cobalt tetroxide to lithium carbonate 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 6 hours.

[0034] Wherein, the atomic molar number of cobalt tetroxide is expressed in terms of cobalt atoms.

[0035] The number of molar atoms of lithium carbonate is expressed as the number of molar lithium atoms.

[0036] 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.

[0037] Optionally, the duration of the heat preservation II is selected from any value of 2, 3, 4, 5, 6 hours or a range between any two.

[0038] Optionally, the atomic molar ratio of cobalt tetroxide to lithium carbonate is selected from any value among 1:1, 1:1.05, and 1:1.1, or any range between the two.

[0039] Optionally, the cobalt tetroxide includes flake-shaped nano-cobalt tetroxide powder and spherical nano-cobalt tetroxide powder.

[0040] Optionally, the preparation method of the flake-shaped nano-cobalt tetroxide powder includes: heating cobalt salt and ammonia water at 60-100°C and holding at that temperature for 1-24 hours, followed by centrifugal drying to obtain nano-cobalt hydroxide powder; heating the nano-cobalt hydroxide powder in air medium for III and holding at that temperature for III to obtain the product; wherein the temperature of heating III is 600-1000°C, and the time of holding at that temperature for III is 2-6 hours.

[0041] Optionally, the temperature of heating III is selected from any value or a range between 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃.

[0042] Optionally, the duration of heat preservation III is selected from any value among 2, 3, 4, 5, and 6 hours or a range between any two.

[0043] Optionally, the preparation method of the spherical nano-cobalt tetroxide powder includes: the reaction solution of cobalt salt and sodium acetate under closed conditions at 100-250°C for 5-48 hours is separated and dried to obtain the product, wherein the drying temperature is 40-100°C.

[0044] Optionally, the cobalt salt used in the preparation of cobalt tetroxide is selected from at least one of cobalt acetate, cobalt sulfate, cobalt nitrate, and cobalt chloride.

[0045] The cobalt tetroxide used in this invention can also be obtained from existing technologies.

[0046] Optionally, in step S3, the heating rate of heating I is 5-20℃ / min; the heating rate of heating II is 5-20℃ / min; and the heating rate of heating III is 5-20℃ / min.

[0047] This invention provides a specific method for preparing a surface-modified high-voltage fast-charging lithium cobalt oxide cathode material, the method comprising the following steps:

[0048] S1. Preparation of spherical nano-cobalt tetroxide powder:

[0049] Weigh out 10-100 mg sodium acetate, 50-1000 mg polyvinylpyrrolidone, and 100-1000 mg cobalt nitrate hexahydrate and dissolve them step by step in 40-80 mL of deionized water. Stir at a constant speed of 100-1000 rpm for 0.5-3 hours.

[0050] Transfer the above solution to a 100ml hydrothermal reactor and react for 5-48 hours at a temperature of 100-250℃.

[0051] Take the solution after the above reaction, centrifuge and wash 2-3 times with deionized water at a speed of 4000-10000 r / min. Dry the separated product in an oven at 40-100℃ to obtain spherical nano-cobalt tetroxide powder.

[0052] S2. Preparation of sheet-like nano-cobalt tetroxide powder:

[0053] Weigh 1-20g of cobalt nitrate hexahydrate and disperse it in 0.5-1.0L of deionized water, then heat it in an oil bath to 60-100℃;

[0054] Add 5-30 mL of 25% ammonia solution to the above solution, keep warm and stir at a stirring speed of 100-1000 rpm, and keep warm for 1-24 hours.

[0055] The above reaction products were centrifuged, washed, ultrasonically dispersed, and freeze-dried to obtain nano-cobalt hydroxide powder. The centrifugation speed was 4000-10000 r / min.

[0056] The above-mentioned cobalt hydroxide powder was placed in a muffle furnace and heated and held in air at a rate of 5-20℃ / min for 600-1000℃ for 2-6 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0057] S3, Fluorinated phosphate surface-modified lithium cobalt oxide cathode material:

[0058] Weigh out the above cobalt tetroxide powder (either S1 or S2 can be selected) according to an atomic molar ratio of 1:1.05, mix and grind to obtain the precursor dry material. Place the above dry material in a muffle furnace and heat and hold in air at a rate of 5-20℃ / min, at a temperature of 600-1000℃, for a holding time of 2-6h.

[0059] According to the atomic molar ratio of 1-2x:x:x:x:x, where 0.02% ≤ x ≤ 10% (the % represents a numerical percentage, such as 0.02% is 0.0002, and 10% is 0.1), the prepared lithium cobalt oxide powder, lithium source, fluorine source, phosphorus source, and transition metal salt are weighed, mixed and ground to obtain the precursor dry material.

[0060] The aforementioned dry precursor material was placed in a tube furnace and heated and held at a temperature of 600-1000℃ in an argon atmosphere at a rate of 5-20℃ / min for 2-6 hours. After the heating process was completed, the product was removed to obtain lithium cobalt fluoride phosphate cathode material.

[0061] 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.

[0062] 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 includes the aforementioned surface-modified lithium cobalt oxide material.

[0063] 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.

[0064] 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.

[0065] Optionally, 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.

[0066] Optionally, the battery is a CR2016 button cell battery.

[0067] Fifthly, the present invention provides the application of the above-mentioned surface-modified lithium cobalt oxide material in high-voltage ultra-fast charging lithium cobalt oxide batteries.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] 1) The fast-charging high-voltage lithium cobalt oxide cathode material prepared by the present invention adopts fluorinated phosphate surface coating modification. By optimizing the raw materials, doping content and preparation process, it not only improves the reversibility of the bulk crystal structure and the structural stability of the surface of the material under high voltage, but also improves the ionic conductivity and electronic conductivity of the material, thereby realizing the improvement of the high-voltage ultra-fast charging performance and cycle stability of the lithium cobalt oxide cathode material.

[0070] 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

[0071] Figure 1 This is a scanning electron microscope image of the fluorinated phosphate surface-modified lithium cobalt oxide cathode material prepared in Example 1 of the present invention;

[0072] Figure 2 This is a scanning electron microscope image of the unmodified spherical lithium cobalt oxide cathode material prepared in Comparative Example 1 of this invention;

[0073] Figure 3 This is a scanning electron microscope image of the unmodified sheet-like lithium cobalt oxide cathode material prepared in Comparative Example 2 of this invention;

[0074] Figure 4 Rate performance tests were conducted on the lithium cobalt oxide cathode material with lanthanum fluoride lithium phosphate surface modification in Example 1 of the present invention and the unmodified lithium cobalt oxide cathode material in Comparative Example 1 at a constant temperature of 20°C within a voltage range of 3.0-4.6V.

[0075] Figure 5 The charge-discharge curves of the lithium lanthanum phosphate surface-modified lithium cobalt oxide cathode material of Example 1 of the present invention at a constant temperature of 20°C and within a voltage range of 3.0-4.6V, under different current densities.

[0076] Figure 6 Rate performance tests were conducted on the lithium cobalt oxide cathode material with lanthanum fluoride lithium phosphate surface modification in Example 2 of the present invention and the unmodified lithium cobalt oxide cathode material in Comparative Example 2, at a constant temperature of 20°C, within a voltage range of 3.0-4.5V.

[0077] Figure 7 The charge-discharge curves of the lithium cobalt oxide cathode material with lanthanum fluoride lithium phosphate surface modification in Example 2 of the present invention are shown at a constant temperature of 20°C and at different current densities within a voltage range of 3.0-4.5V. Detailed Implementation

[0078] 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.

[0079] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0080] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0081] Example 1 (Fluorophosphate-coated lithium cobalt oxide material)

[0082] Weigh out 10 mg of sodium acetate, 50 mg of polyvinylpyrrolidone, and 100 mg of cobalt nitrate hexahydrate and dissolve them stepwise in 40 mL of deionized water. Stir at a constant speed of 200 rpm for 0.5 h. Transfer the solution to a 100 mL hydrothermal reactor and react for 12 h at 180 °C.

[0083] The solution after the above reaction was centrifuged and washed twice with deionized water at a speed of 6000 r / min. The separated product was dried in an oven at 60℃ to obtain spherical nano-cobalt tetroxide powder.

[0084] Weigh out the above cobalt tetroxide powder and lithium carbonate according to a cobalt to lithium atom molar ratio of 1:1.05, mix and grind to obtain a dry precursor material. Place the above dry material in a muffle furnace and heat and hold in air at 5℃ / min for 700℃ for 3h to obtain lithium cobalt oxide powder.

[0085] The prepared lithium cobalt oxide powder, lithium carbonate, lithium fluoride, lithium dihydrogen phosphate, and lanthanum nitrate hexahydrate were weighed in sequence according to the molar ratio of cobalt atoms, lithium atoms, fluorine atoms, phosphorus atoms, and lanthanum atoms of 0.98:0.01:0.01:0.01:0.01 (i.e., 98:1:1:1:1), mixed and ground to obtain the precursor dry material.

[0086] The aforementioned dry precursor material was placed in a tube furnace and heated and held at 800℃ for 2 hours in an argon atmosphere at a rate of 5℃ / min. After the heating process was complete, the product was removed to obtain lithium cobalt oxide fluorinated phosphate cathode material. Figure 1 As shown.

[0087] Example 2 (Fluorophosphate-coated lithium cobalt oxide material)

[0088] 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 flake-shaped nano-cobalt hydroxide powder.

[0089] The above-mentioned flake-shaped nano-cobalt hydroxide powder was placed in a muffle furnace and heated and held at 450°C in air at a heating rate of 5°C / min for 2 hours. After natural cooling, nano-cobalt tetroxide powder was obtained.

[0090] Weigh out the above cobalt tetroxide powder and lithium carbonate according to a cobalt to lithium atom molar ratio of 1:1.05, mix and grind to obtain a dry precursor material. Place the above dry material in a muffle furnace and heat and hold in air at 5℃ / min for 700℃ for 3h to obtain lithium cobalt oxide powder.

[0091] The prepared lithium cobalt oxide powder, lithium carbonate, lithium fluoride, lithium dihydrogen phosphate, and lanthanum nitrate hexahydrate were weighed in sequence according to the molar ratio of cobalt atoms, lithium atoms, fluorine atoms, phosphorus atoms, and lanthanum atoms of 0.9:0.05:0.05:0.05:0.05 (i.e., 90:5:5:5:5), mixed and ground to obtain the precursor dry material.

[0092] The aforementioned dry precursor material was placed in a tube furnace and heated and held at 800℃ in an argon atmosphere at a rate of 5℃ / min for 2 hours. After the heating process was completed, the product was removed to obtain lithium cobalt oxide fluorinated phosphate cathode material.

[0093] Example 3 (Fluorophosphate-coated lithium cobalt oxide material)

[0094] Weigh out 10 mg of sodium acetate, 50 mg of polyvinylpyrrolidone, and 100 mg of cobalt nitrate hexahydrate and dissolve them stepwise in 40 mL of deionized water. Stir at a constant speed of 200 rpm for 0.5 h. Transfer the solution to a 100 mL hydrothermal reactor and react for 12 h at 180 °C.

[0095] The solution after the above reaction was centrifuged and washed twice with deionized water at a speed of 6000 r / min. The separated product was dried in an oven at 60℃ to obtain spherical nano-cobalt tetroxide powder.

[0096] Weigh out the above cobalt tetroxide powder and lithium carbonate according to a cobalt to lithium atom molar ratio of 1:1.05, mix and grind to obtain a dry precursor material. Place the dry material in a muffle furnace and heat and hold in air at 5℃ / min at a temperature of 800℃ for 3 hours to obtain lithium cobalt oxide powder.

[0097] The prepared lithium cobalt oxide powder, lithium carbonate, lithium fluoride, lithium dihydrogen phosphate, and copper nitrate hexahydrate were weighed out in sequence according to the molar ratio of cobalt atoms, lithium atoms, fluorine atoms, phosphorus atoms, and copper atoms of 0.98:0.01:0.01:0.01:0.01 (i.e., 98:1:1:1:1). They were mixed and ground to obtain the precursor dry material.

[0098] The aforementioned dry precursor material was placed in a tube furnace and heated and held at 700℃ for 2 hours in an argon atmosphere at a rate of 5℃ / min. After the heating process was completed, the product was removed to obtain lithium cobalt oxide fluorinated phosphate cathode material.

[0099] Example 4 (Fluorophosphate-coated lithium cobalt oxide material)

[0100] 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.

[0101] 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.

[0102] Weigh out the above cobalt tetroxide powder and lithium carbonate according to a cobalt to lithium atom molar ratio of 1:1.05, mix and grind to obtain a dry precursor material. Place the dry material in a muffle furnace and heat and hold in air at 5℃ / min for 900℃ for 3h to obtain lithium cobalt oxide powder.

[0103] The prepared lithium cobalt oxide powder, lithium carbonate, lithium fluoride, lithium dihydrogen phosphate, and aluminum nitrate were weighed in sequence according to the molar ratio of cobalt atoms, lithium atoms, fluorine atoms, phosphorus atoms, and aluminum atoms of 0.98:0.01:0.01:0.01:0.01 (i.e., 98:1:1:1:1), mixed and ground to obtain the precursor dry material.

[0104] The aforementioned dry precursor material was placed in a tube furnace and heated and held at 1000℃ in an argon atmosphere at a rate of 5℃ / min for 2 hours. After the heating process was completed, the product was removed to obtain lithium cobalt oxide fluorinated phosphate cathode material.

[0105] Comparative Example 1 (Unmodified Lithium Cobalt Oxide Material)

[0106] 10 mg of sodium acetate, 50 mg of polyvinylpyrrolidone, and 100 mg of cobalt nitrate hexahydrate were weighed and gradually dissolved in 40 mL of deionized water. The mixture was stirred at a constant speed of 200 rpm for 0.5 h. The solution was then transferred to a 100 mL hydrothermal reactor and reacted for 12 h at 180 °C. The resulting solution was centrifuged and washed twice with deionized water at 6000 rpm. The separated product was dried in a 60 °C oven to obtain spherical cobalt tetroxide nanoparticles.

[0107] Weigh out the above cobalt tetroxide powder and lithium carbonate according to a cobalt to lithium atom molar ratio of 1:1.05, mix and grind to obtain a dry precursor material. Place the above dry material in a muffle furnace and heat and hold in air at 5℃ / min for 3 hours to obtain spherical lithium cobalt oxide cathode material. Figure 2 ).

[0108] Comparative Example 2 (Unmodified Lithium Cobalt Oxide Material)

[0109] 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.

[0110] 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.

[0111] 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 and air-quenched to obtain sheet-like lithium cobalt oxide cathode material. Figure 3 ).

[0112] Example 5 (Lithium-ion Battery)

[0113] The lithium cobalt oxide cathode materials prepared in Examples 1-4 and Comparative Examples 1-2 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 6 different cathode sheets.

[0114] 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, resulting in 6 different types of batteries.

[0115] The method for evaluating the electrochemical performance of lithium cobalt oxide cathode materials in this invention is as follows:

[0116] The six types of 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 4 As shown. The corresponding charge-discharge curves at different rates are as follows. Figure 5 As shown.

[0117] The potassium / phosphorus / fluorine surface-doped modified lithium cobalt oxide cathode material prepared in Example 1 of this invention has a reversible specific capacity of 212.2 mAh / g at a rate of 0.2C and a reversible specific capacity of 168.7 mAh / g at a rate of 10C.

[0118] The unmodified lithium cobalt oxide cathode material prepared in Comparative Example 1 has a reversible specific capacity of 205.3 mAh / g at 0.2C and 132 mAh / g at 10C.

[0119] 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. These results demonstrate that the surface modification of lithium cobalt oxide cathode materials in this invention can effectively improve the rate performance and reversible specific capacity of the material.

[0120] This invention first uses a solid-state method to prepare nano-lithium cobalt oxide powder. Based on this, the nano-lithium cobalt oxide powder, lithium source, fluorine source, phosphorus source, and transition metal salt are mixed evenly in a certain atomic ratio and subjected to high-temperature annealing treatment to obtain fluorinated phosphate-coated lithium cobalt oxide cathode material.

[0121] This invention significantly improves the bulk structural stability of lithium cobalt oxide cathode materials, suppresses side reactions at the particle-electrolyte interface under high voltage, and greatly enhances the ionic and electronic conductivity of lithium cobalt oxide cathode materials, thereby improving their high-voltage fast-charging performance and high-voltage cycle stability. The preparation method provided by this invention is highly controllable, simple, and suitable for large-scale production and industrialization.

[0122] 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-modified lithium cobalt oxide material, characterized in that, The surface-modified lithium cobalt oxide material is lithium cobalt oxide modified with fluorinated phosphate, and the fluorinated phosphate is coated on the surface of the lithium cobalt oxide material; The number of phosphorus atoms in the fluorinated phosphate coating is 0.02% to 10% of the number of cobalt atoms in the lithium cobalt oxide.

2. The surface-modified lithium cobalt oxide material according to claim 1, characterized in that, The surface-modified lithium cobalt oxide material exhibits a reversible specific capacity of 200-225 mAh / g at a rate of 0.2C within a voltage range of 3.0-4.6V, and a reversible specific capacity of 150-190 mAh / g at a rate of 10C.

3. The method for preparing the surface-modified lithium cobalt oxide material according to any one of claims 1 to 2, characterized in that, The preparation method includes the following steps: S1: Obtain lithium cobalt oxide; S2: Mix the raw materials containing lithium cobalt oxide, lithium source, fluorine source, phosphorus source and transition metal salt 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 an inert atmosphere to obtain a fluorinated phosphate surface-modified lithium cobalt oxide material.

4. The method for preparing the surface-modified lithium cobalt oxide material according to claim 3, characterized in that, In step S2, the atomic molar ratio of the lithium cobalt oxide, the lithium source, the fluorine source, the phosphorus source, and the transition metal salt is (1-2x):1x:1x:1x:1x, where 0.0002≤x≤0.1; The atomic molar number of lithium cobalt oxide is expressed in terms of cobalt atomic molar number. The atomic molar number of the lithium source is expressed in terms of lithium atomic molar number. The atomic molar number of the fluorine source is expressed in terms of the number of fluorine atoms in molars. The atomic molar number of the transition metal salt is calculated based on the corresponding metal atomic molar number; The lithium source is selected from at least one of lithium carbonate, lithium chloride, lithium hydroxide, and lithium fluoride; The fluorine source is selected from lithium fluoride and / or ammonium fluoride; The phosphorus source is selected from at least one of phytic acid, phosphoric acid, lithium dihydrogen phosphate and ammonium phosphate. The transition metal salt is selected from at least one of cobalt acetate or nitrate, copper acetate or nitrate, lanthanum acetate or nitrate, and aluminum acetate or nitrate.

5. The method for preparing the surface-modified lithium cobalt oxide material according to claim 3, characterized in that, In step S3, the temperature of heating I is 600 ~ 1000℃, and the holding time I is 2 ~ 6h; the inert atmosphere includes argon gas.

6. The method for preparing the surface-modified high-voltage lithium cobalt oxide cathode material according to claim 3, characterized in that, In step S1, the lithium cobalt oxide is the product of mixing cobalt tetroxide and lithium carbonate, heating in air medium II, and holding at that temperature II. The atomic molar ratio of cobalt tetroxide to lithium carbonate 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 6 hours. Wherein, the atomic molar number of cobalt tetroxide is expressed in terms of cobalt atoms; The number of lithium atoms in the lithium carbonate is expressed as the number of lithium atoms in the molar number. The cobalt tetroxide comprises flake-shaped nano-cobalt tetroxide powder and spherical nano-cobalt tetroxide powder; wherein... The preparation method of the flake-shaped nano-cobalt tetroxide powder includes: heating cobalt salt and ammonia water at 60~100℃ and holding at that temperature for 1~24h, followed by centrifugal drying to obtain nano-cobalt hydroxide powder; heating the nano-cobalt hydroxide powder in air medium for III and holding at that temperature for III to obtain the product; wherein, the temperature of heating III is 600~1000℃, and the time of holding at that temperature for III is 2~6h; The preparation method of the spherical nano cobalt tetroxide powder includes: the reaction solution of cobalt salt and sodium acetate under closed conditions at 100~250℃ for 5~48h is separated and dried to obtain the product, wherein the drying temperature is 40~100℃. The cobalt salt used in the preparation process of cobalt tetroxide is selected from at least one of cobalt acetate, cobalt sulfate, cobalt nitrate, and cobalt chloride. In step S3, the heating rate of heating I is 5 ~ 20℃ / min; the heating rate of heating II is 5 ~ 20℃ / min; and the heating rate of heating III is 5 ~ 20℃ / min.

7. 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 materials for the slurry include the surface-modified lithium cobalt oxide material as described in any one of claims 1 to 2.

8. 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 7.

9. A high-voltage fast-charging lithium-ion battery according to claim 8, 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.

10. The application of the surface-modified lithium cobalt oxide material according to any one of claims 1 to 2 in high-voltage ultra-fast charging lithium-ion batteries.

Images