Secondary sintering treatment method for battery cathode material

Abstract

The application discloses a secondary sintering treatment method of a battery positive electrode material and belongs to the technical field of lithium batteries. The secondary sintering treatment method of the battery positive electrode material comprises the following steps: mixing a lithium source, an iron source, a phosphorus source, a carbon source and a modified silane coupling agent, adding the mixture into an ethanol aqueous solution dispersant, performing ball milling to obtain a mixture; drying the mixture, tabletting, performing first-time sintering under an inert atmosphere to obtain a first-time sintering product; grinding and tabletting the first-time sintering product, performing second-time sintering under the inert atmosphere to obtain the battery positive electrode material. The battery positive electrode material prepared by the application has excellent electrochemical performance, the preparation process is simple, and the requirement of high-performance lithium iron phosphate batteries on the market can be met.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for secondary sintering of battery cathode materials. Background Technology

[0002] Since the advent of lithium-ion battery materials, their superior high-capacity characteristics and renewable properties have opened up broad prospects for new energy development in the new century. Lithium iron phosphate (LFP), as a cathode material that combines high safety, excellent cycle stability, and environmental friendliness, has long been a highly regarded research subject in the lithium battery field. Its applications are wide-ranging, covering various commercial vehicle battery systems, energy storage base stations, and numerous electronic and electrical devices. However, LFP materials themselves also have limitations, namely, their relatively low electronic and ionic conductivity, which leads to poor rate performance when used as cathode materials in lithium-ion batteries. In view of this, many companies and industry experts have devoted themselves to improving the performance of LFP cathode materials. Unfortunately, in pursuing high performance, it is often difficult to simultaneously control costs. This challenge has led to fierce competition and arduous tests for companies in the industrial production and market promotion of LFP cathode materials.

[0003] Secondary sintering refers to the process of sintering the cathode material twice at high temperatures. The first sintering primarily aims to induce initial crystallization in the cathode material, while the second sintering, while maintaining this initial crystallization, further promotes grain growth and improves grain density and compactness. Through secondary sintering, the crystals in the cathode material can become denser, forming a more regular crystal structure, thereby increasing the battery's energy density and power density, while also enhancing its cycle life and stability. This is of great significance for batteries used in electric vehicles, energy storage devices, and other applications requiring high performance and long lifespan.

[0004] Patent publication number CN112897491 B discloses a method for preparing and applying lithium iron phosphate cathode materials. This patent involves (1) dry mixing and refining an iron source, phosphorus source, lithium source, carbon source, and additives to obtain a mixture; (2) subjecting the mixture to a first sintering, followed by pulverization to obtain a pulverized material; and (3) subjecting the pulverized material to a second sintering, during which a gasifiable organic carbon source is introduced, followed by cooling to obtain the lithium iron phosphate cathode material. However, the battery cathode materials prepared by this patent and existing technologies still suffer from poor electrochemical performance. Summary of the Invention

[0005] In order to solve the problem that the battery cathode materials prepared by the prior art still have poor electrochemical performance, the purpose of this invention is to provide a secondary sintering treatment method for battery cathode materials.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for secondary sintering of battery cathode material includes the following steps:

[0008] Step A1: Mix lithium source, iron source, phosphorus source, carbon source, and modified silane coupling agent, add to 30 mL of ethanol aqueous solution dispersant, and ball mill to obtain a mixture; the modified silane coupling agent is a coupling agent containing triazole ring, amino group, and fluorine.

[0009] The lithium source, iron source, and phosphorus source are mixed in a stoichiometric ratio of Li:Fe:P = 1:1:1. The carbon source accounts for 10% of the total mass of the mixture, and the modified silane coupling agent accounts for 1.5%-3% of the total mass of the mixture. The volume fraction of the ethanol aqueous solution dispersant is 90%-95%, and the volume is 30 mL.

[0010] Step A2: Dry the mixture, compress it into tablets, and sinter it for the first time under an inert atmosphere to obtain the first sintered product;

[0011] Step A3: Grind and press the first sintering product into sheets, and then perform a second sintering under an inert atmosphere to obtain the battery cathode material.

[0012] Modified silane coupling agents contain both inorganic and organic affinity groups. Adding modified silane coupling agents before carbonization can improve the bonding force between the carbon source and the mixture, allowing the carbon source to fully cover and uniformly exist in the mixture. After carbonization, the carbon source uniformly coats the lithium iron phosphate, thereby improving the electrochemical performance of the lithium iron phosphate battery, greatly reducing the agglomeration of the carbon source after carbonization, and improving the utilization rate of the carbon source.

[0013] Further, in step A1, the lithium source is one or more of lithium carbonate, lithium chloride, lithium nitrate, lithium fluoride, lithium sulfate, and lithium hydroxide; the iron source is ferric oxide or iron(II,III) oxide; the phosphorus source is one or more of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and ammonium phosphate; and the carbon source is glucose or sucrose.

[0014] Furthermore, in step A1, the ball milling speed is 200-350 r / min, and the ball milling time is 4-12 h.

[0015] Furthermore, in step A2, the specific steps for the first sintering are as follows: the temperature of the tube furnace is raised from room temperature to 250-450℃, and the reaction is held at that temperature for 3-12 hours, after which the temperature is lowered to room temperature; during the first sintering process, the heating rate and the cooling rate are both 5-20℃ / min.

[0016] Furthermore, in step A3, the specific steps of the second sintering are as follows: the temperature of the tube furnace is raised from room temperature to 600-800℃, and the reaction is held at that temperature for 4-15 hours, and then the temperature is lowered to room temperature; during the second sintering process, the heating rate and the cooling rate are both 5-20℃ / min.

[0017] Furthermore, in step A3, the grinding speed is 300-450 r / min, and the grinding time is 5-20 h.

[0018] Furthermore, in steps A2 and A3, the pressure of the tablet is 15-20 MPa.

[0019] Furthermore, in steps A2 and A3, the inert gas is any one of nitrogen, argon, and helium.

[0020] Furthermore, the preparation method of the modified silane coupling agent is as follows:

[0021] 11-Azide-undecyltrimethoxysilane and 3-alkynyl-2-fluoroaniline were added to DMF and stirred. Potassium tert-butoxide was added simultaneously with the stirring. The reaction was carried out at room temperature for 3-5 hours. The reaction was terminated by adding saturated ammonium chloride solution. Ethyl acetate and water were then added, and the mixture was allowed to stand for phase separation. The resulting organic phase was washed twice with water, twice with saturated brine, and dried over anhydrous sodium sulfate to obtain the modified silane coupling agent.

[0022] The ratio of 11-azidoundecyltrimethoxysilane, 3-alkynyl-2-fluoroaniline, DMF, and potassium tert-butoxide is 0.32 g: 0.14 g: 2 mL: 0.11 g.

[0023] The azide group in 11-azidoundecyltrimethoxysilane undergoes an azide-alkynyl cycloaddition reaction with the alkynyl group in 3-alkynyl-2-fluoroaniline. Potassium tert-butoxide is used as a catalyst to catalyze the above reaction, yielding a modified silane coupling agent containing a triazole ring, an amino group, and fluorine.

[0024] The beneficial effects of this invention are:

[0025] 1. In the preparation of the battery cathode material, this invention incorporates a modified silane coupling agent into the mixture. The inorganic and organic groups in the modified silane coupling agent promote the uniform encapsulation of lithium iron phosphate by carbon source, thereby improving the electrochemical performance of the battery prepared from the cathode material of this invention. The triazole ring in the modified silane coupling agent can serve as a nitrogen source, forming a uniform thin N-doped carbon layer on the lithium iron phosphate particles after sintering. This N-doped carbon layer forms an excellent continuous electronic conductivity layer, effectively improving the rate performance of the material. Furthermore, the N-doped carbon coating layer effectively inhibits the growth and aggregation of lithium iron phosphate nanoparticles, resulting in smaller lithium iron phosphate nanoparticles, shortening the solid-state diffusion path of lithium ions, and improving battery performance. The modified silane coupling agent also contains fluorine, which expands the lattice of lithium iron phosphate due to fluorine doping, facilitating the insertion / extraction of Li+ ions, thereby improving the electrochemical performance of the battery.

[0026] 2. This invention, by precisely controlling the amount of modified silane coupling agent added, is beneficial for preparing lithium manganese iron phosphate cathode materials with better electrochemical performance. Too much or too little modified silane coupling agent will affect the overall performance of the battery. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Preparation Example 1

[0029] The preparation method of the modified silane coupling agent in this preparation example is as follows:

[0030] 0.32 g of 11-azidoundecyltrimethoxysilane and 0.14 g of 3-ynyl-2-fluoroaniline were added to 2 mL of DMF. While stirring, 0.11 g of potassium tert-butoxide was added. The reaction was carried out at room temperature for 3 h. The reaction was terminated by adding 2 mL of saturated ammonium chloride solution. Then, 25 mL of ethyl acetate and 15 mL of water were added. The mixture was allowed to stand and separate into layers. The resulting organic phase was washed twice with water and twice with saturated brine and dried over anhydrous sodium sulfate to obtain the modified silane coupling agent.

[0031] Preparation Example 2

[0032] The preparation method of the modified silane coupling agent in this preparation example is as follows:

[0033] 0.32 g of 11-azidoundecyltrimethoxysilane and 0.14 g of 3-ynyl-2-fluoroaniline were added to 2 mL of DMF. While stirring, 0.11 g of potassium tert-butoxide was added. The reaction was carried out at room temperature for 5 h. The reaction was terminated by adding 2 mL of saturated ammonium chloride solution. Then, 25 mL of ethyl acetate and 15 mL of water were added. The mixture was allowed to stand and separate into layers. The resulting organic phase was washed twice with water and twice with saturated brine and dried over anhydrous sodium sulfate to obtain the modified silane coupling agent.

[0034] Preparation Example 3

[0035] The preparation method of the modified silane coupling agent in this preparation example is as follows:

[0036] 0.32 g of 11-azidoundecyltrimethoxysilane and 0.12 g of 3-acetylene aniline were added to 2 mL of DMF. While stirring, 0.11 g of potassium tert-butoxide was added. The reaction was carried out at room temperature for 3 h. The reaction was terminated by adding 2 mL of saturated ammonium chloride solution. Then, 25 mL of ethyl acetate and 15 mL of water were added. The mixture was allowed to stand and separate into layers. The resulting organic phase was washed twice with water and twice with saturated brine and dried over anhydrous sodium sulfate to obtain the modified silane coupling agent.

[0037] Preparation Example 4

[0038] The preparation method of the modified silane coupling agent in this preparation example is as follows:

[0039] 0.32 g of 11-azidoundecyltrimethoxysilane and 0.12 g of 1-phenyl-1-propyne were added to 2 mL of DMF. While stirring, 0.11 g of potassium tert-butoxide was added. The reaction was carried out at room temperature for 3 h. The reaction was terminated by adding 2 mL of saturated ammonium chloride solution. Then, 25 mL of ethyl acetate and 15 mL of water were added. The mixture was allowed to stand and separate into layers. The resulting organic phase was washed twice with water and twice with saturated brine and dried over anhydrous sodium sulfate to obtain the modified silane coupling agent.

[0040] Preparation Example 5

[0041] The silane coupling agent used in this preparation example is KH550.

[0042] Example 1

[0043] This embodiment provides a method for secondary sintering of battery cathode materials, including the following steps:

[0044] Step A1: Mix 0.37g of lithium carbonate, 0.8g of ferric oxide, 1.15g of ammonium dihydrogen phosphate, 0.26g of sucrose, and 0.04g (accounting for 1.5% of the total mass of the mixture) with the modified silane coupling agent prepared in Example 1, add it to 30mL of 90% ethanol aqueous solution dispersant, and ball mill at 350r / min for 4h to obtain the mixture;

[0045] Step A2: After drying the mixture in an oven at 60°C, it is pressed into tablets under a pressure of 15 MPa. The temperature of the tube furnace is raised from room temperature to 250°C under a nitrogen atmosphere at a heating rate of 5°C / min, and the reaction is held at this temperature for 3 hours. Then the temperature is lowered to room temperature at a cooling rate of 15°C / min to obtain the first sintered product.

[0046] Step A3: Grind the first sintered product at 300 r / min for 5 h, press it into tablets under a pressure of 15 MPa, raise the temperature of the tube furnace from room temperature to 800℃ in a nitrogen atmosphere at a heating rate of 20℃ / min, hold the reaction at this temperature for 4 h, and then lower the temperature to room temperature at a cooling rate of 20℃ / min to obtain the battery cathode material.

[0047] Example 2

[0048] This embodiment provides a method for secondary sintering of battery cathode materials, including the following steps:

[0049] Step A1: Mix 0.69g of lithium nitrate, 0.77g of iron(III) oxide, 1.32g of ammonium hydrogen phosphate, 0.32g of sucrose, and 0.06g (accounting for 2% of the total mass of the mixture) of the modified silane coupling agent prepared in Example 1, add it to 30mL of 92% ethanol aqueous solution dispersant, and ball mill at 300r / min for 8h to obtain the mixture;

[0050] Step A2: After drying the mixture in an oven at 60°C, it is pressed into tablets under a pressure of 18 MPa. The temperature of the tube furnace is raised from room temperature to 450°C under a helium atmosphere at a heating rate of 20°C / min, and the reaction is held at this temperature for 12 hours. Then the temperature is lowered to room temperature at a cooling rate of 20°C / min to obtain the first sintered product.

[0051] Step A3: Grind the first sintered product at 380 r / min for 15 h, press it into sheets under a pressure of 18 MPa, raise the temperature of the tube furnace from room temperature to 700℃ in a helium atmosphere at a heating rate of 15℃ / min, hold the reaction at that temperature for 15 h, and then lower the temperature to room temperature at a cooling rate of 5℃ / min to obtain the battery cathode material.

[0052] Example 3

[0053] This embodiment provides a method for secondary sintering of battery cathode materials, including the following steps:

[0054] Step A1: Mix 0.24g of lithium hydroxide, 0.8g of ferric oxide, 1.15g of ammonium phosphate, 0.25g of glucose, and 0.08g (3% of the total mass of the mixture) of the modified silane coupling agent prepared in Example 2, add the mixture to 30mL of 95% ethanol aqueous solution dispersant, and ball mill at 350r / min for 12h to obtain the mixture.

[0055] Step A2: After drying the mixture in an oven at 60°C, it is pressed into tablets under a pressure of 20 MPa. The temperature of the tube furnace is raised from room temperature to 350°C under an argon atmosphere at a heating rate of 10°C / min, and the reaction is held at this temperature for 8 hours. Then the temperature is lowered to room temperature at a cooling rate of 5°C / min to obtain the first sintered product.

[0056] Step A3: Grind the first sintered product at 450 r / min for 20 h, press it into sheets under a pressure of 20 MPa, raise the temperature of the tube furnace from room temperature to 800 °C in an argon atmosphere at a heating rate of 5 °C / min, hold the reaction at that temperature for 10 h, and then lower the temperature to room temperature at a cooling rate of 10 °C / min to obtain the battery cathode material.

[0057] Comparative Example 1

[0058] This comparative example provides a secondary sintering treatment method for battery cathode materials. Compared with Example 1, the difference is that the modified silane coupling agent in Example 1 is replaced with the product prepared in Preparation Example 3, while the other raw materials and steps are the same as in Example 1.

[0059] Comparative Example 2

[0060] This comparative example provides a secondary sintering treatment method for battery cathode materials. Compared with Example 1, the difference is that the modified silane coupling agent in Example 1 is replaced with the product prepared in Preparation Example 4, while the other raw materials and steps are the same as in Example 1.

[0061] Comparative Example 3

[0062] This comparative example provides a secondary sintering treatment method for battery cathode materials. Compared with Example 1, the difference is that the modified silane coupling agent in Example 1 is replaced with the product prepared in Preparation Example 5, while the other raw materials and steps are the same as in Example 1.

[0063] Comparative Example 4

[0064] This comparative example provides a secondary sintering treatment method for battery cathode materials. Compared with Example 1, the difference is that "0.04g of the modified silane coupling agent prepared in Example 1" is replaced with "0.03g of the modified silane coupling agent prepared in Example 1". The other raw materials and steps are the same as in Example 1.

[0065] Comparative Example 5

[0066] This comparative example provides a secondary sintering treatment method for battery cathode materials. Compared with Example 3, the difference is that "0.08g of the modified silane coupling agent prepared in Example 3" is replaced with "0.09g of the modified silane coupling agent prepared in Example 3". The other raw materials and steps are the same as in Example 3.

[0067] The battery cathode materials prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to electrical performance tests, which were performed according to the following methods:

[0068] The battery cathode materials prepared in Examples 1-3 and Comparative Examples 1-5 were mixed with carbon black and PVDF at a mass ratio of 80:10:10 to prepare a slurry. The uniformly mixed slurry was coated onto aluminum foil and vacuum dried at 100°C for 4 hours. The dried aluminum foil was rolled using a roller press, then cut and weighed. 2032 button batteries were then assembled in an argon-atmosphere vacuum glove box, using lithium iron phosphate as the cathode, lithium metal sheets as the anode, CeL Gard 2300 as the separator, and 1 mol / L LiPF6 / (EC+DMC+EMC) electrolyte (volume ratio 1:1:1). The batteries were then sealed using a sealing machine and allowed to stand for 7-8 hours. Battery performance testing was conducted on the Shenzhen Xinwei Battery Testing System, using constant current charge-discharge testing within a voltage range of 2.5-4.2V. The test results are shown in Table 1.

[0069] Table 1

[0070]

[0071] As can be seen from Table 1, the batteries prepared in Examples 1-3 have excellent electrochemical performance.

[0072] The battery performance of Example 1 is better than that of Comparative Example 1, which does not contain fluorine. This indicates that the lattice of lithium iron phosphate is expanded due to F doping, which is beneficial for the insertion / extraction of Li+, thereby improving the electrochemical performance of the battery.

[0073] The battery performance of Example 1 is better than that of Comparative Example 2. Comparative Example 2 does not contain fluorine or amino groups, indicating that the inorganic and organic groups in the modified silane coupling agent can promote the uniform coating of lithium iron phosphate with carbon source, thereby improving the electrochemical performance of the battery cathode material.

[0074] The battery performance of Example 1 is better than that of Comparative Example 3. Comparative Example 3 does not contain fluorine, amino, or triazole rings, and its performance is worse than that of Comparative Example 1 and Comparative Example 2. This indicates that triazole rings can be used as a nitrogen source to form a uniform thin N-doped carbon layer on lithium iron phosphate particles after sintering. The N-doped carbon layer can form an excellent continuous electronic conductivity layer, which can effectively improve the rate performance of the material. Moreover, at a high current rate of 10C, the discharge specific capacity of Example 1 is still relatively high, indicating that the N-doped carbon coating layer can effectively inhibit the growth and aggregation of lithium iron phosphate nanoparticles, thereby producing smaller lithium iron phosphate nanoparticles and shortening the solid-state diffusion path of lithium ions.

[0075] The battery performance of Example 1 is better than that of Comparative Example 4, and the battery performance of Example 3 is better than that of Comparative Example 5. This shows that too much or too little modified silane coupling agent will affect the overall performance of the battery, and the amount selected in this invention is optimal.

[0076] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for secondary sintering of battery cathode material, characterized in that, Includes the following steps: Step A1: Mix lithium source, iron source, phosphorus source, carbon source, and modified silane coupling agent, add to ethanol aqueous solution dispersant, and ball mill to obtain a mixture; the modified silane coupling agent is a coupling agent containing triazole ring, amino group, and fluorine. Step A2: Dry the mixture, compress it into tablets, and sinter it for the first time under an inert atmosphere to obtain the first sintered product; Step A3: Grind and press the first sintering product into sheets, and then perform a second sintering under an inert atmosphere to obtain the battery cathode material; The modified silane coupling agent accounts for 1.5%-3% of the total mass of the mixture; The preparation method of the modified silane coupling agent is as follows: 11-Azide-undecyltrimethoxysilane and 3-alkynyl-2-fluoroaniline were added to DMF and stirred. Potassium tert-butoxide was added and the mixture was reacted at room temperature for 3-5 hours. A saturated ammonium chloride solution was added, followed by ethyl acetate and water. The mixture was allowed to stand and separate into layers. The resulting organic phase was washed and dried to obtain the modified silane coupling agent.

2. The secondary sintering treatment method for battery cathode material according to claim 1, characterized in that, In step A1, lithium source, iron source, and phosphorus source are mixed in a stoichiometric ratio of Li:Fe:P = 1:1:

1. Carbon source accounts for 10% of the total mass of the mixture, and modified silane coupling agent accounts for 1.5%-3% of the total mass of the mixture. The volume fraction of ethanol aqueous solution dispersant is 90%-95%, and the volume is 30 mL.

3. The secondary sintering treatment method for battery cathode material according to claim 1, characterized in that, In step A1, the lithium source is one or more of lithium carbonate, lithium chloride, lithium nitrate, lithium fluoride, lithium sulfate, and lithium hydroxide; the iron source is ferric oxide or iron tetroxide; the phosphorus source is one or more of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and ammonium phosphate; and the carbon source is glucose or sucrose.

4. The secondary sintering treatment method for battery cathode material according to claim 1, characterized in that, In step A1, the ball mill rotation speed is 200-350 r / min, and the ball milling time is 4-12 h.

5. The method for secondary sintering of battery cathode material according to claim 1, characterized in that, In step A2, the specific steps for the first sintering are as follows: raise the temperature of the tube furnace from room temperature to 250-450℃, hold the reaction at that temperature for 3-12 hours, and then lower the temperature to room temperature; during the first sintering process, the heating rate and the cooling rate are both 5-20℃ / min.

6. The method for secondary sintering of a battery cathode material according to claim 1, characterized in that, In step A3, the specific steps for the second sintering are as follows: raise the temperature of the tube furnace from room temperature to 600-800℃, hold the reaction at that temperature for 4-15 hours, and then lower the temperature to room temperature; during the second sintering process, the heating rate and cooling rate are both 5-20℃ / min; the grinding speed is 300-450r / min, and the grinding time is 5-20 hours.

7. The method for secondary sintering of a battery cathode material according to claim 1, characterized in that, In steps A2 and A3, the tableting pressure is 15-20 MPa.

8. The method for secondary sintering of a battery cathode material according to claim 1, characterized in that, In steps A2 and A3, the inert gas is any one of nitrogen, argon, and helium.

9. The method for secondary sintering of a battery cathode material according to claim 1, characterized in that, The ratio of 11-azidoundecyltrimethoxysilane, 3-alkynyl-2-fluoroaniline, DMF, and potassium tert-butoxide is 0.32 g: 0.14 g: 2 mL: 0.11 g.

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