Positive electrode material and preparation method and application thereof
Through low-temperature freezing, three-dimensional porous structures are formed, electrostatic spraying is used to build a conductive network and sintered carbon coating at high temperature, which solves the problems of low conductivity and conductivity of lithium vanadium phosphate positive electrode materials and improves the performance of lithium-ion batteries.
Patent Information
- Application Number
- CN202510497235.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-21
- Publication Date
- 2025-07-25
AI Technical Summary
The low ionic conductivity and electronic conductivity of the lithium vanadium phosphate cathode material limit its application and development in lithium-ion batteries.
A three-dimensional porous structure is formed through low-temperature freezing technology, a conductive network is built with electrostatic spraying, and a carbon-coated positive electrode material is formed through high-temperature sintering to enhance its conductivity and ion diffusion rate.
It improves the rate performance and cycle stability of lithium-ion batteries, enhances the conductivity, ion diffusion rate and structural stability of the cathode material.
Smart Images
Figure BDA0005367380370000111
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a cathode material, a preparation method thereof, and an application thereof. Background Art
[0002] With the continuous growth of energy demand and the pursuit of sustainable development, lithium-ion batteries, as an efficient energy storage device, have been widely used in various fields. As an important component of lithium-ion batteries, the performance of the cathode material directly affects the performance of lithium-ion batteries. Currently, the commercially available cathode materials for lithium-ion batteries mainly include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), and ternary materials ([Li(Ni, Co, Mn)O2]4), etc. Different types of cathode materials for lithium-ion batteries have their own advantages and disadvantages. Lithium vanadium phosphate (Li3V2(PO4)3, LVP) has the advantages of high theoretical capacity (197 mAh / g), good safety performance, and high discharge voltage, but its relatively low ionic conductivity and electronic conductivity limit its further application and development.
[0003] To solve this defect of Li3V2(PO4)3, researchers have carried out modification research on it. The modification methods mainly include doping, surface coating, and particle nanosizing, etc. Through these methods, the conductivity of Li3V2(PO4)3 materials can be improved, thereby expanding its application scope in lithium-ion batteries. Summary of the Invention
[0004] The present application provides a cathode material, a preparation method thereof, and an application thereof, aiming to solve the problem of relatively low ionic conductivity and electronic conductivity of the lithium vanadium phosphate cathode material.
[0005] The first aspect of the present application provides a preparation method of a cathode material, including the following steps:
[0006] (1) Mix an aluminum-doped lithium vanadium phosphate material and a first solvent, perform low-temperature freezing treatment to form a solid, and then dry the solid to obtain a cathode material precursor;
[0007] (2) Perform a first calcination treatment on the cathode material precursor to obtain an intermediate product with a three-dimensional porous structure;
[0008] (3) Mix a conductive agent, a dispersant, and a second solvent to obtain a mixed solution, deposit the mixed solution on the surface of the intermediate product with a three-dimensional porous structure, and then perform a second calcination treatment to obtain an intermediate product with a three-dimensional synergistic conductive network;
[0009] (4) Mix the intermediate product with the three-dimensional collaborative conductive network, the carbon source, and the third solvent, and perform ball milling. After the ball milling is completed, dry the ball-milled product and then perform a third calcination treatment to obtain the positive electrode material.
[0010] According to some embodiments of the method for preparing the positive electrode material of the present application, the first solvent includes deionized water.
[0011] According to some embodiments of the method for preparing the positive electrode material of the present application, the mass ratio of the aluminum-doped lithium vanadium phosphate material to the first solvent is 1:(50 - 100).
[0012] According to some embodiments of the method for preparing the positive electrode material of the present application, the temperature of the cryogenic freezing treatment is -196°C, and the time of the cryogenic freezing treatment is 20 - 50 min.
[0013] According to some embodiments of the method for preparing the positive electrode material of the present application, the drying temperature is 60 - 100°C, and the drying time is 36 - 72 h.
[0014] According to some embodiments of the method for preparing the positive electrode material of the present application, the first calcination is carried out in an inert atmosphere.
[0015] According to some embodiments of the method for preparing the positive electrode material of the present application, the temperature of the first calcination is 700 - 900°C, and the time of the first calcination is 6 - 24 h.
[0016] According to some embodiments of the method for preparing the positive electrode material of the present application, the conductive agent includes a one-dimensional conductive agent and a two-dimensional conductive agent.
[0017] According to some embodiments of the method for preparing the positive electrode material of the present application, the one-dimensional conductive agent includes carbon nanotubes and conductive carbon black; the two-dimensional conductive agent includes at least one of graphene oxide, reduced graphene oxide, and graphene.
[0018] According to some embodiments of the method for preparing the positive electrode material of the present application, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is 1:(1 - 2).
[0019] According to some embodiments of the method for preparing the positive electrode material of the present application, the dispersant includes one or more of polyvinylpyrrolidone, polyacrylic acid, sodium polystyrene sulfonate, Tween series, and sodium carboxymethyl cellulose.
[0020] According to some embodiments of the method for preparing the positive electrode material of the present application, the second solvent includes absolute ethanol.
[0021] In some embodiments of the method for preparing the positive electrode material according to the present application, the mass ratio of the conductive agent to the dispersant is (10 - 20):(0.1 - 0.5).
[0022] In some embodiments of the method for preparing the positive electrode material according to the present application, the mass ratio of the conductive agent to the second solvent is (10 - 20):(50 - 100).
[0023] In some embodiments of the method for preparing the positive electrode material according to the present application, the deposition is electrostatic spray deposition.
[0024] In some embodiments of the method for preparing the positive electrode material according to the present application, during the deposition process, the mass ratio of the amount of the conductive agent to the mass of the intermediate product of the three-dimensional porous structure is (10 - 20):100.
[0025] In some embodiments of the method for preparing the positive electrode material according to the present application, the temperature of the second calcination is 500 - 700 °C, and the time of the second calcination is 60 - 90 min.
[0026] In some embodiments of the method for preparing the positive electrode material according to the present application, the carbon source includes one or more of graphene, glucose, sucrose, and starch.
[0027] In some embodiments of the method for preparing the positive electrode material according to the present application, the third solvent includes deionized water.
[0028] In some embodiments of the method for preparing the positive electrode material according to the present application, the mass ratio of the intermediate product having a three-dimensional synergistic conductive network to the carbon source is 1:(0.1 - 0.4), such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, etc.
[0029] In some embodiments of the method for preparing the positive electrode material according to the present application, the intermediate product having a three-dimensional synergistic conductive network, the carbon source, and the third solvent are mixed, and the solid content in the obtained mixed solution is 78% - 82%.
[0030] In some embodiments of the method for preparing the positive electrode material according to the present application, the rotation speed of the ball milling is 800 - 1200 rpm, and the time of the ball milling is 4 - 8 h.
[0031] In some embodiments of the method for preparing the positive electrode material according to the present application, the temperature of the drying is 60 - 100 °C, and the time of the drying is 0.5 - 1 h.
[0032] In some embodiments of the method for preparing the positive electrode material according to the present application, the temperature of the third calcination treatment is 700 - 900 °C, and the time of the third calcination treatment is 6 - 9 h.
[0033] According to some embodiments of the method for preparing the cathode material described in the present application, the heating rate of the third calcination treatment is 3-6 °C / min.
[0034] The second aspect of the present application provides a cathode material, which is prepared by the preparation method described in the first aspect of the present application.
[0035] The third aspect of the present application provides a lithium-ion battery, including the cathode material obtained by the preparation method described in the first aspect of the present application or the cathode material described in the second aspect of the present application.
[0036] The beneficial effects of the present application include: the cathode material described in the present application forms a three-dimensional porous structure through a low-temperature freezing technique, constructs a conductive network through electrostatic spraying, and forms a carbon-coated cathode material through high-temperature sintering, having strong conductivity, a high ion diffusion rate, and a relatively stable structure. The lithium-ion battery prepared from the cathode material described in the present application has high rate performance and cycle stability. Specific Embodiments
[0037] The embodiments of the present invention are described in detail below. The examples of the embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.
[0038] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without conflict, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples.
[0039] The embodiment of the present application provides a method for preparing a cathode material, including the following steps:
[0040] (1) Mix the aluminum-doped lithium vanadium phosphate material and the first solvent, perform a low-temperature freezing treatment to form a solid, and then dry the solid to obtain a cathode material precursor;
[0041] (2) Perform a first calcination treatment on the cathode material precursor to obtain an intermediate product with a three-dimensional porous structure;
[0042] (3) Mix the conductive agent, dispersant, and second solvent to obtain a mixed solution. Deposit the mixed solution on the surface of the intermediate product of the three-dimensional porous structure, and then perform a second calcination treatment to obtain an intermediate product with a three-dimensional synergistic conductive network.
[0043] (4) Mix the intermediate product with the three-dimensional synergistic conductive network, carbon source, and third solvent, and perform ball milling. After the ball milling is completed, dry the ball-milled product and then perform a third calcination treatment to obtain the positive electrode material.
[0044] The positive electrode material of the present application obtains a positive electrode material with a three-dimensional porous structure through a low-temperature freezing technique. Then, a mixed conductive slurry containing conductive carbon black, carbon nanotubes, etc. is sprayed on the above positive electrode material through an electrostatic spraying technique to form a three-dimensional synergistic conductive network on the surface and inside of the positive electrode material. After high-temperature sintering and carbon coating, ball milling is performed to obtain an aluminum-doped porous lithium vanadium phosphate positive electrode material. The positive electrode material has high conductivity and ion diffusion rate, and a stable structure. Using the positive electrode material as the positive electrode of a lithium battery can effectively improve the rate performance and cycle stability of the lithium battery.
[0045] In some embodiments of the present application, the preparation method of the aluminum-doped lithium vanadium phosphate material includes the following steps:
[0046] Mix the lithium source, vanadium source, aluminum source, phosphorus source, and organic dispersant to obtain a mixture. Magnetically stir the mixture into a colloid at 70-100°C, then place the colloid in an oven at 120-150°C to dry and grind it. Pre-calcine the ground product in a nitrogen environment at 300-500°C for 5-10 h, then perform tablet pressing, and then perform high-temperature calcination in a nitrogen environment at 700-900°C for 6-8 h to obtain the aluminum-doped lithium vanadium phosphate material.
[0047] In some embodiments of the present application, the molar ratio of the lithium source, vanadium source, aluminum source, and phosphorus source is 3:(1.9-2):(0.05-0.1):3.
[0048] In some embodiments of the present application, the organic dispersant includes one or more of polyvinylpyrrolidone, polyacrylic acid, sodium polystyrene sulfonate, Tween series, and sodium carboxymethyl cellulose.
[0049] In some embodiments of the present application, the first solvent includes deionized water.
[0050] In some embodiments of the present application, the mass ratio of the aluminum-doped lithium vanadium phosphate material to the first solvent is 1:(50-100), such as 1:50, 1:60, 1:80, 1:86, 1:93, 1:100, etc.
[0051] In some embodiments of the present application, the lithium vanadium phosphate doped with aluminum is mixed with a first solvent, and a double planetary stirring device is used to stir at a linear velocity of 6 - 10 m / s for 2 - 6 h for sufficient mixing.
[0052] In some embodiments of the present application, the temperature of the cryogenic freezing treatment is -196 °C, and the time of the cryogenic freezing treatment is 20 - 50 min; for example, 20 min, 28 min, 33 min, 36 min, 43 min, 50 min, etc. Freezing at -196 °C can significantly increase the freezing rate, avoid the formation of ice crystals, and directly convert the liquid sample into an amorphous glass state.
[0053] In some embodiments of the present application, the drying temperature is 60 - 100 °C, for example, 60 °C, 63 °C, 72 °C, 83 °C, 96 °C, 100 °C, etc., and the drying time is 36 - 72 h, for example, 36 h, 40 h, 45 h, 56 h, 63 h, 72 h, etc.
[0054] In some embodiments of the present application, the first calcination is carried out in an inert atmosphere.
[0055] In some embodiments of the present application, the temperature of the first calcination is 700 - 900 °C, for example, 700 °C, 760 °C, 820 °C, 860 °C, 900 °C, etc., and the time of the first calcination is 6 - 24 h, for example, 6 h, 12 h, 18 h, 22 h, 24 h, etc.
[0056] In some embodiments of the present application, the conductive agent includes a one-dimensional conductive agent and a two-dimensional conductive agent.
[0057] In some embodiments of the present application, the one-dimensional conductive agent includes carbon nanotubes and / or conductive carbon black; the two-dimensional conductive agent includes at least one of graphene oxide, reduced graphene oxide, and graphene.
[0058] The conductive carbon black can be at least one of conductive furnace black (CF), super conductive furnace black (SCF), extra conductive furnace black (XCF), and acetylene black. The conductive carbon black has a small particle size, a large specific surface area, and is hard, with a low resistivity, and can increase the electronic conductivity of the lithium iron phosphate skeleton.
[0059] In some embodiments of the present application, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is 1:(1 - 2). The one-dimensional conductive agent has a small particle size, a large specific surface area, and is hard, with a low resistivity, and can increase the electronic conductivity of the lithium iron phosphate skeleton; the two-dimensional conductive agent provides surface contact, and the one-dimensional conductive agent bridges the voids to reduce the interface resistance. By constructing a three-dimensional conductive network, its conductivity can be significantly improved, the pore structure of the material can be optimized, the interface contact can be enhanced, the dispersibility can be improved, and the cost can be balanced.
[0060] When the content of the one-dimensional conductive agent is excessive, entanglement and agglomeration may occur, and it is impossible to effectively bridge the two-dimensional sheets; the agglomerated one-dimensional conductive agent will form a local insulating region, hindering electron transport. In addition, the excessive one-dimensional conductive agent will also cause an increase in the brittleness of the film.
[0061] In some embodiments of the present application, the dispersant includes one or more of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), sodium polystyrene sulfonate (PSS), Tween series (such as Tween-60), and sodium carboxymethyl cellulose (CMC).
[0062] In some embodiments of the present application, the second solvent includes absolute ethanol;
[0063] In some embodiments of the present application, the mass ratio of the conductive agent to the dispersant is (10-20):(0.1-0.5), such as 10:0.1, 10:0.3, 10:0.5, 15:0.1, 15:0.2, 15:0.5, 20:0.1, 20:0.3, 20:0.5, etc.
[0064] In some embodiments of the present application, the mass ratio of the conductive agent to the second solvent is (10-20):(50-100), such as 10:50, 10:80, 10:100, 15:50, 15:70, 15:100, 20:50, 20:85, 20:100, etc.
[0065] In some embodiments of the present application, in step (3), the deposition is electrostatic spray deposition.
[0066] In some embodiments of the present application, during the deposition process, the mass ratio of the dosage of the conductive agent to the intermediate product of the three-dimensional porous structure is (10-20):100, such as 10:100, 12:100, 15:100, 18:100, 20:100, etc.
[0067] The conductive agent (such as carbon nanotubes, graphene or carbon black) is atomized into micron / nano-scale droplets by electrostatic spray technology to achieve uniform coverage of the surface of the lithium vanadium phosphate material particles, avoiding the agglomeration problem of traditional mechanical mixing. The one-dimensional (CNTs) or two-dimensional (graphene) conductive agent is deposited on the surface of the lithium vanadium phosphate material particles through electrostatic spray technology to form a penetration network, shortening the electron conduction path, and significantly improving the problem of the intrinsic low conductivity (10 -9 S / cm) of lithium vanadium phosphate.
[0068] In some embodiments of the present application, the temperature of the second calcination is 500-700 °C, such as 500 °C, 550 °C, 580 °C, 600 °C, 620 °C, 670 °C, 700 °C, etc., and the time of the second calcination is 60-90 min, such as 60 min, 70 min, 75 min, 80 min, 90 min, etc.
[0069] In some embodiments of the present application, the carbon source includes one or more of graphene, glucose, sucrose, and starch.
[0070] In some embodiments of the present application, the third solvent includes deionized water.
[0071] In some embodiments of the present application, the mass ratio of the intermediate product having a three-dimensional synergistic conductive network to the carbon source is 1:(0.1-0.4); such as 1:0.1, 1:0.2, 1:0.4, etc.
[0072] In some embodiments of the present application, the intermediate product having a three-dimensional synergistic conductive network, the carbon source, and the third solvent are mixed, and the solid content in the obtained mixed solution is 78%-82%, such as 78%, 80%, 82%, etc.
[0073] In some embodiments of the present application, the rotation speed of the ball milling is 800-1200 rpm, such as 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, etc., and the time of the ball milling is 4-8 h; such as 4 h, 5 h, 7 h, 8 h, etc.
[0074] In some embodiments of the present application, the temperature of the drying is 60-100 °C, such as 60 °C, 76 °C, 83 °C, 92 °C, 100 °C, etc., and the time of the drying is 0.5-1 h, such as 0.5 h, 0.8 h, 1 h, etc.
[0075] In some embodiments of the present application, the temperature of the third calcination treatment is 700-900 °C, such as 700 °C, 760 °C, 830 °C, 900 °C, etc., and the time of the third calcination treatment is 6-9 h; such as 6 h, 7 h, 9 h, etc.
[0076] In some embodiments of the present application, the heating rate of the third calcination treatment is 3-6 °C / min, such as 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, etc.
[0077] The embodiments of the present application further provide a positive electrode material, which is prepared by the preparation method described in the first aspect of the present application. The positive electrode material of the present application has a high ionic conductivity.
[0078] The embodiments of the present application further provide a lithium-ion battery, which includes the positive electrode material obtained by the preparation method described in the first aspect of the present application or the positive electrode material described in the second aspect of the present application. The lithium-ion battery described in the present application has high rate performance and cycle stability.
[0079] The technical solution of the present application will be further described below in conjunction with specific embodiments.
[0080] Example 1
[0081] A preparation method of a positive electrode material includes the following steps:
[0082] (1) Weigh lithium carbonate, vanadium pentoxide, alumina and phosphorus pentoxide with a molar ratio of 3:1.95:0.05:3, and mix them evenly with polyvinylpyrrolidone (the dosage of the organic dispersant polyvinylpyrrolidone is in a mass ratio of 1:100 to the total mass of the lithium source, vanadium source, aluminum source and phosphorus source). Stir the mixture into a colloid at 80 °C with magnetic stirring, then place the colloid in an oven at 120 °C for drying and grinding. Pre-calcine the ground product in a nitrogen environment at 350 °C for 5 h, further grind and press into tablets, and calcine the tablet product at 800 °C in a nitrogen environment for 8 h to obtain an aluminum-doped lithium vanadium phosphate material; Add the above aluminum-doped lithium vanadium phosphate material to deionized water (the mass ratio of the aluminum-doped lithium vanadium phosphate material to deionized water is 1:60), stir at a linear velocity of 6 m / s for 2 h, then place it in liquid nitrogen at -196 °C, freeze for 30 min, and then place it in a vacuum dryer at 80 °C for vacuum drying for 48 h to obtain a precursor of an aluminum-doped lithium vanadium phosphate positive electrode material;
[0083] (2) Sinter the positive electrode material precursor in an argon atmosphere at a temperature of 750 °C for 6 h to obtain a three-dimensional porous aluminum-doped lithium vanadium phosphate positive electrode material;
[0084] (3) Take carbon nanotubes and graphene with a mass ratio of 1:1, and polyvinylpyrrolidone as a dispersant (the dosage of the dispersant is in a mass ratio of 0.1:10 to the mass of the conductive agent), add them to an anhydrous ethanol solution and disperse evenly. The solid content in the obtained mixed solution is 65%; then deposit it on the three-dimensional porous structure intermediate product by electrostatic spraying method. During the deposition process, control the mass ratio of the dosage of the conductive agent to the three-dimensional porous structure intermediate product to be 15:100. After the deposition is completed, vacuum dry at 500 °C for 60 min in an argon atmosphere to obtain an intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network formed on the surface and inside;
[0085] (4) The intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network and graphene with a mass ratio of 1:0.3 are uniformly mixed and placed in a ball milling tank. Then, deionized water is added to make the solid content of the resulting mixed solution 80%. The mixture is stirred at 1200 rpm for 6 h, then dried at 80 °C for 0.5 h, and then placed in a sintering furnace. It is heated to 800 °C at a heating rate of 5 °C / min and calcined for 8 h, and then cooled to room temperature to obtain a carbon-coated composite porous material.
[0086] Example 2
[0087] The preparation method of the cathode material described in Example 2 is different from that of Example 1 only in that: during the preparation process of the cathode material described in Example 2, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is 1:3.
[0088] Example 3
[0089] The preparation method of the cathode material described in Example 3 is different from that of Example 1 only in that: during the preparation process of the cathode material described in Example 3, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is 1.2:1.
[0090] Example 4
[0091] The preparation method of the cathode material described in Example 4 is different from that of Example 1 only in that: during the preparation process of the cathode material described in Example 4, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is 2:1.
[0092] Example 5
[0093] The preparation method of the cathode material described in Example 5 is different from that of Example 1 only in that: the dispersant used during the preparation process of the cathode material described in Example 5 is Tween-60.
[0094] Example 6
[0095] The preparation method of the cathode material described in Example 6 is different from that of Example 1 only in that: the dispersant used during the preparation process of the cathode material described in Example 6 is sodium carboxymethyl cellulose.
[0096] Comparative Example 1
[0097] The preparation method of the cathode material described in Comparative Example 1 is different from that of Example 1 only in that: during the preparation process of the cathode material described in Comparative Example 1, the aluminum-doped lithium vanadium phosphate cathode material precursor was not subjected to low-temperature freeze-drying treatment.
[0098] The specific operation steps include:
[0099] (1) Weigh lithium carbonate, vanadium pentoxide, aluminum oxide, and phosphorus pentoxide with a molar ratio of 3:1.95:0.05:3, and mix them evenly with polyvinylpyrrolidone (the dosage of the organic dispersant polyvinylpyrrolidone is in a mass ratio of 1:100 to the total mass of the lithium source, vanadium source, aluminum source, and phosphorus source). Stir the mixture magnetically into a colloid at 80 °C, then dry the colloid in an oven at 120 °C and grind it. Pre-calcine the ground product in a nitrogen environment at 350 °C for 5 h, further grind and press it into tablets, and then calcine the tablet product in a nitrogen environment at 800 °C for 8 h to obtain an aluminum-doped lithium vanadium phosphate material; Place the above aluminum-doped lithium vanadium phosphate material in a vacuum dryer and vacuum dry it at 80 °C for 48 h to obtain a precursor of the aluminum-doped lithium vanadium phosphate cathode material;
[0100] (2) Sinter the precursor of the cathode material in an argon atmosphere at 750 °C for 6 h to obtain a three-dimensional porous aluminum-doped lithium vanadium phosphate cathode material;
[0101] (3) Take carbon nanotubes and graphene with a mass ratio of 1:1, and polyvinylpyrrolidone as a dispersant (the dosage of the dispersant is in a mass ratio of 0.1:10 to the mass of the conductive agent), add them to an anhydrous ethanol solution and disperse them evenly. The solid content in the obtained mixed solution is 65%; Then deposit it on the intermediate product with a three-dimensional porous structure by electrostatic spraying. During the deposition process, control the mass ratio of the dosage of the conductive agent to the intermediate product with a three-dimensional porous structure to be 15:100. After the deposition is completed, vacuum dry it at 500 °C for 60 min in an argon atmosphere to obtain an intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network formed on the surface and inside;
[0102] (4) Uniformly mix the intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network and graphene with a mass ratio of 1:0.3, place them in a ball mill tank, and then add deionized water to make the solid content of the obtained mixed solution 80%. Mix and stir at 1200 rpm for 6 h, then dry it at 80 °C for 0.5 h, then place it in a sintering furnace, heat it to 800 °C at a heating rate of 5 °C / min and calcine it for 8 h, and then cool it to room temperature to obtain a carbon-coated composite porous material.
[0103] Comparative Example 2
[0104] The difference between the preparation method of the cathode material described in Comparative Example 2 and that in Example 1 is only that: during the preparation of the cathode material described in Comparative Example 2, the intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network was not subjected to carbon coating treatment.
[0105] The specific operation steps include:
[0106] (1) Weigh lithium carbonate, vanadium pentoxide, aluminum oxide, and phosphorus pentoxide with a molar ratio of 3:1.95:0.05:3, and mix them evenly with polyvinylpyrrolidone (the dosage of the organic dispersant polyvinylpyrrolidone is in a mass ratio of 1:100 to the total mass of the lithium source, vanadium source, aluminum source, and phosphorus source). Stir the mixture into a colloid at 80 °C with magnetic stirring, then place the colloid in an oven at 120 °C to dry and grind it. Pre-calcine the ground product in a nitrogen environment at 350 °C for 5 h, further grind and tablet it, and then calcine the tablet product at 800 °C in a nitrogen environment for 8 h to obtain an aluminum-doped lithium vanadium phosphate material; Add the above-mentioned aluminum-doped lithium vanadium phosphate material to deionized water (the mass ratio of the aluminum-doped lithium vanadium phosphate material to deionized water is 1:60), stir it at a linear velocity of 6 m / s for 2 h, then place it in liquid nitrogen at -196 °C, freeze it for 30 min, and then place it in a vacuum dryer to vacuum dry at 80 °C for 48 h to obtain a precursor of the aluminum-doped lithium vanadium phosphate cathode material;
[0107] (2) Sinter the precursor of the cathode material in an argon atmosphere at 750 °C for 6 h to obtain a three-dimensional porous aluminum-doped lithium vanadium phosphate cathode material;
[0108] (3) Take carbon nanotubes and graphene with a mass ratio of 1:1, and polyvinylpyrrolidone as a dispersant (the dosage of the dispersant is in a mass ratio of 0.1:10 to the mass of the conductive agent), add them to an anhydrous ethanol solution and disperse them evenly. The solid content in the obtained mixed solution is 65%; Then deposit it on the three-dimensional porous structure intermediate product by electrostatic spraying method. During the deposition process, control the mass ratio of the dosage of the conductive agent to the three-dimensional porous structure intermediate product to be 15:100. After the deposition is completed, vacuum dry it at 500 °C for 60 min in an argon atmosphere to obtain an intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network formed on the surface and inside, that is, the cathode material described in Comparative Example 2.
[0109] Comparative Example 3
[0110] The difference between the preparation method of the cathode material described in Comparative Example 3 and that of Example 1 is only that: all the conductive agents used in the preparation process of the cathode material described in Comparative Example 3 are one-dimensional conductive agents.
[0111] The specific operation steps include:
[0112] (1) Weigh lithium carbonate, vanadium pentoxide, aluminum oxide, and phosphorus pentoxide with a molar ratio of 3:1.95:0.05:3, and mix them evenly with polyvinylpyrrolidone (the dosage of the organic dispersant polyvinylpyrrolidone is in a mass ratio of 1:100 to the total mass of the lithium source, vanadium source, aluminum source, and phosphorus source). Stir the mixture magnetically into a colloid at 80 °C, then place the colloid in an oven at 120 °C for drying and grinding. Calcinate the ground product in a nitrogen environment at 350 °C for 5 h, further grind and press it into tablets, and then calcinate the tablet product in a nitrogen environment at 800 °C for 8 h to obtain an aluminum-doped lithium vanadium phosphate material; place the above aluminum-doped lithium vanadium phosphate material in a vacuum dryer and vacuum dry it at 80 °C for 48 h to obtain a precursor of the aluminum-doped lithium vanadium phosphate cathode material;
[0113] (2) Place the precursor of the cathode material in an argon atmosphere and sinter it at 750 °C for 6 h to obtain a three-dimensional porous aluminum-doped lithium vanadium phosphate cathode material;
[0114] (3) Take carbon nanotubes and the dispersant polyvinylpyrrolidone (the dosage of the dispersant is in a mass ratio of 0.1:10 to the mass of the conductive agent) and add them to an anhydrous ethanol solution for uniform dispersion. The solid content in the obtained mixed solution is 65%; then deposit it on the intermediate product with a three-dimensional porous structure by electrostatic spraying. During the deposition process, control the mass ratio of the dosage of the conductive agent to the intermediate product with a three-dimensional porous structure to be 15:100. After the deposition is completed, vacuum dry it at 500 °C for 60 min in an argon atmosphere to obtain an intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network formed on the surface and inside;
[0115] (4) Uniformly mix the intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network and graphene with a mass ratio of 1:0.3, place them in a ball milling tank, and then add deionized water to make the solid content of the obtained mixed solution 80%. Mix and stir at 1200 rpm for 6 h, then dry it at 80 °C for 0.5 h, and then place it in a sintering furnace. Heat it to 800 °C at a heating rate of 5 °C / min for calcination for 8 h, and then cool it to room temperature to obtain a carbon-coated composite porous material.
[0116] Comparative Example 4
[0117] The difference between the preparation method of the cathode material described in Comparative Example 4 and that in Example 1 is only that: the conductive agents used in the preparation process of the cathode material described in Comparative Example 4 are all two-dimensional conductive agents.
[0118] The specific operation steps include:
[0119] (1) Weigh lithium carbonate, vanadium pentoxide, aluminum oxide, and phosphorus pentoxide with a molar ratio of 3:1.95:0.05:3, and mix them evenly with polyvinylpyrrolidone (the dosage of the organic dispersant polyvinylpyrrolidone is in a mass ratio of 1:100 to the total mass of the lithium source, vanadium source, aluminum source, and phosphorus source). Stir the mixture magnetically into a colloid at 80 °C, then place the colloid in an oven at 120 °C for drying and grinding. Pre-calcine the ground product in a nitrogen environment at 350 °C for 5 h, further grind and press it into tablets, and then calcine the pressed product in a nitrogen environment at 800 °C for 8 h to obtain an aluminum-doped lithium vanadium phosphate material; place the above aluminum-doped lithium vanadium phosphate material in a vacuum dryer and vacuum dry it at 80 °C for 48 h to obtain a precursor of the aluminum-doped lithium vanadium phosphate cathode material;
[0120] (2) Place the precursor of the cathode material in an argon atmosphere and sinter it at 750 °C for 6 h to obtain a three-dimensional porous aluminum-doped lithium vanadium phosphate cathode material;
[0121] (3) Take graphene and the dispersant polyvinylpyrrolidone (the dosage of the dispersant is in a mass ratio of 0.1:10 to the mass of the conductive agent), add them to an anhydrous ethanol solution and disperse them evenly. The solid content in the obtained mixed solution is 65%; then deposit it on the intermediate product with a three-dimensional porous structure by electrostatic spraying. During the deposition process, control the mass ratio of the dosage of the conductive agent to the intermediate product with a three-dimensional porous structure to be 15:100. After the deposition is completed, vacuum dry it at 500 °C for 60 min in an argon atmosphere to obtain an intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network formed on the surface and inside;
[0122] (4) Uniformly mix the intermediate product of aluminum-doped lithium vanadium phosphate with a three-dimensional synergistic conductive network and graphene with a mass ratio of 1:0.3, place them in a ball mill jar, and then add deionized water to make the solid content of the obtained mixed solution 80%. Mix and stir at 1200 rpm for 6 h, then dry it at 80 °C for 0.5 h, and then place it in a sintering furnace. Heat it to 800 °C at a heating rate of 5 °C / min for calcination for 8 h, and then cool it to room temperature to obtain a carbon-coated composite porous material.
[0123] Performance study of the cathode materials described in Examples 1-6 and Comparative Examples 1-4 of this application
[0124] According to the mass ratio of cathode material: SP: polyvinylidene fluoride (PVDF) = 97:1:2, respectively add the cathode materials described in Examples 1-10 and Comparative Examples 1-4 of this application, SP, and polyvinylidene fluoride into an agate mortar, and then drop an appropriate amount of NMP solvent and grind them evenly. Then uniformly coat the mixtures on the surface of aluminum foil and vacuum dry them at 110 °C for 12 h. Roll press the dried electrode sheets and cut them into circular pieces with a diameter of 12 mm. Use a lithium metal sheet as the counter electrode to make button-type lithium-ion batteries. Test the specific capacity performance, rate performance, and cycling performance of the above batteries.
[0125] Among them, the study on the performance of the gram capacity mainly tests the discharge gram capacity at 0.1C at 25°C; the study on the rate performance mainly tests the discharge gram capacity under constant current discharge at 3C and 5C at 25°C, and the study on the cycle performance mainly tests the capacity retention rate after 500 cycles at 3C at 25°C. The test results are shown in Table 1.
[0126] The method for measuring the 0.1C gram capacity is as follows: The prepared button cell is tested using a 5V 10mA LAND battery test system in an environment of 25°C ± 2°C. The test process is to charge at a constant current and constant voltage of 0.1C to 4.8V, with a cut-off current of 0.05C; after standing for 5 minutes, discharge at a constant current of 0.1C to the lower limit voltage of 3.0V, and then stand for 5 minutes; the 0.1C discharge gram capacity of the positive electrode (mAh / g) = 0.1C discharge capacity / ((weight of the electrode sheet - weight of the foil) * proportion of the active material).
[0127] The method for testing the 3C gram capacity: Adopt the constant current charge-discharge test method, with the voltage test range of 3.0 - 4.8V. After first testing the capacity of the button cell at 0.1C, change the charge-discharge current value to complete the 3C current value test, and calculate the discharge gram capacity of the positive electrode material at the 5th time of 3C.
[0128] The method for testing the 5C gram capacity: Adopt the constant current charge-discharge test method, with the voltage test range of 3.0 - 4.8V. After first testing the capacity of the button cell at 0.1C, change the charge-discharge current value to complete the 5C current value test, and calculate the discharge gram capacity of the positive electrode material at the 5th time of 5C.
[0129] The method for measuring the capacity retention rate at 25°C after 100 cycles at 3C is as follows: After first testing the capacity of the button cell at 0.1C, cycle the 3C capacity test process 100 times; the 100-cycle capacity retention rate = discharge capacity at the 100th cycle / discharge capacity at the 2nd cycle * 100%.
[0130] Table 1
[0131]
[0132] It can be seen from Table 1 that by comparing Example 1 with Comparative Example 3 and Comparative Example 4, it can be seen that the mixed use of one-dimensional conductive agents and two-dimensional conductive agents can significantly reduce the interfacial resistance of the material compared with the pure single use. The one-dimensional conductive agent bridges the voids, and the two-dimensional conductive agent provides surface contact. By constructing a three-dimensional conductive network, the conductivity is significantly improved, and the pore structure of the material is optimized to enhance the interfacial contact, thereby improving the electrochemical performance of the material.
[0133] Comparing Example 1 with Example 2 and Example 4, when using a mixture of one-dimensional and two-dimensional conductive agents, an imbalance in the ratio (too much or too little) will lead to a significant decline in material performance. When the proportion of one-dimensional conductive agent is too high, entanglement and aggregation will occur, and it cannot effectively bridge the two-dimensional sheets. The aggregated area will form local insulation, hindering electron transport and reducing the conductivity of the material. When the proportion of two-dimensional conductive agent is too high, sheet stacking will form, and the one-dimensional conductive agent cannot penetrate effectively, resulting in a discontinuous conductive network and a significant decrease in conductivity.
[0134] Comparing Example 1 with Comparative Example 1, it can be seen that creating a three-dimensional porous synergistic conductive network on the surface and inside of the aluminum-doped lithium vanadium phosphate precursor can further improve the conductivity and cycling performance of the material.
[0135] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limitations on the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.
Claims
1. A method for preparing a cathode material, characterized in that, It includes the following steps: (1) Mix the aluminum-doped lithium vanadium phosphate material with the first solvent, conduct low-temperature freezing treatment to form a solid, and then dry the solid to obtain a precursor of the positive electrode material; (2) Conduct the first calcination treatment on the precursor of the positive electrode material to obtain an intermediate product with a three-dimensional porous structure; (3) Mix the conductive agent, the dispersant and the second solvent to obtain a mixed solution, deposit the mixed solution on the surface of the intermediate product with the three-dimensional porous structure, and then conduct the second calcination treatment to obtain an intermediate product with a three-dimensional synergistic conductive network; (4) Mix the intermediate product with the three-dimensional synergistic conductive network, the carbon source and the third solvent, conduct ball milling treatment. After the ball milling is completed, dry the ball milling product and conduct the third calcination treatment in sequence to obtain the positive electrode material.
2. The preparation method of the cathode material according to claim 1, wherein, The first solvent includes deionized water; And / or, the mass ratio of the aluminum-doped lithium vanadium phosphate material to the first solvent is 1:(50 - 100); And / or, the temperature of the low-temperature freezing treatment is -196°C, and the time of the low-temperature freezing treatment is 20 - 50 min; And / or, the temperature of the drying is 60 - 100°C, and the time of the drying is 36 - 72 h.
3. The preparation method of the cathode material according to claim 1, characterized in that, The first calcination is carried out in an inert atmosphere; And / or, the temperature of the first calcination is 700 - 900°C, and the time of the first calcination is 6 - 24 h.
4. The preparation method of the cathode material according to claim 1, wherein The conductive agent includes a one-dimensional conductive agent and a two-dimensional conductive agent; Preferably, the one-dimensional conductive agent includes carbon nanotubes and / or conductive carbon black; the two-dimensional conductive agent includes at least one of graphene oxide, reduced graphene oxide and graphene; Preferably, the mass ratio of the one-dimensional conductive agent to the two-dimensional conductive agent is 1:(1 - 3).
5. The preparation method of the cathode material according to claim 1, characterized in that, The dispersant includes one or more of polyvinylpyrrolidone, polyacrylic acid, sodium polystyrene sulfonate, Tween series and sodium carboxymethyl cellulose; And / or, the second solvent includes absolute ethanol; And / or, the mass ratio of the conductive agent to the dispersant is (10 - 20):(0.1 - 0.5); And / or, the mass ratio of the conductive agent to the second solvent is (10 - 20):(50 - 100).
6. The preparation method of the cathode material according to claim 1, characterized in that, In step (3), the deposition is electrostatic spray deposition; And / or, during the deposition process, the mass ratio of the dosage of the conductive agent to the mass of the intermediate product with the three-dimensional porous structure is (10 - 20):100; And / or, the temperature of the second calcination is 500 - 700°C, and the time of the second calcination is 60 - 90 min.
7. The preparation method of the cathode material according to claim 1, characterized in that, The carbon source includes one or more of graphene, glucose, sucrose and starch; And / or, the third solvent includes deionized water; And / or, the mass ratio of the intermediate product with the three-dimensional synergistic conductive network to the carbon source is 1:(0.1 - 0.4); And / or, when the intermediate product with the three-dimensional synergistic conductive network, the carbon source and the third solvent are mixed, the solid content in the obtained mixed solution is 78% - 82%.
8. The preparation method of the cathode material according to claim 1, wherein The rotation speed of the ball milling is 800 - 1200 rpm, and the time of the ball milling is 4 - 8 h; And / or, the temperature of the drying is 60 - 100°C, and the time of the drying is 0.5 - 1 h; And / or, the temperature of the third calcination treatment is 700-900 °C, and the time of the third calcination treatment is 6-9 h; And / or, the heating rate of the third calcination treatment is 3-6 °C / min.
9. A cathode material, characterized in that, The positive electrode material is prepared by the preparation method according to any one of claims 1-8.
10. A lithium-ion battery, characterized in that, It includes the positive electrode material obtained by the preparation method according to any one of claims 1-8 or the positive electrode material according to claim 9.