Carbon-coated lithium iron phosphate anode material and preparation method thereof

Abstract

The application discloses a kind of carbon-coated lithium iron phosphate positive electrode material and preparation method thereof, belong to electrochemical energy material technical field. Binder and 80% solvent are stirred at 50-55 ℃ according to weight parts, conductive agent is added, and stirring is carried out below 40 ℃ for 2h;Carbon-coated lithium iron phosphate is added, stirring is carried out, 20% solvent is added, and stirring is carried out;After vacuumizing, pressure is kept, then vacuum is broken again, after being extracted into vacuum again, stirring is carried out, viscosity is tested, and positive electrode slurry is obtained;Coated on aluminum foil, roll-pressed, and positive electrode material is obtained.The binder is a firm three-dimensional network crosslinking structure inside, and simultaneously contains benzotriazole structure and abundant hydroxyl group, so that the binder has strong adhesion, and the non-polar part of the binder helps electrolyte to wet the electrode;Binder and the remaining raw materials have good compatibility, and play a synergistic role, and together give the carbon-coated lithium iron phosphate positive electrode material of the application excellent and stable cycle life and conductive performance, so that the comprehensive performance is excellent, and use is safer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy materials, and particularly relates to a carbon-coated lithium iron phosphate positive electrode material and a preparation method thereof. BACKGROUND

[0002] A lithium ion battery is a highly efficient energy storage device with extremely wide application range, and its development trend is towards higher energy density, super-long cycle life and high safety. Lithium iron phosphate, as one of the positive electrode materials of the lithium ion battery, is a positive electrode material that is widely used at present, and is particularly concerned by the industry due to its super-long cycle life, outstanding safety and low production cost. However, the lithium iron phosphate material also has the disadvantages of low tap density, low electronic conductivity and small lithium ion diffusion efficiency. In order to overcome the shortcomings of the lithium iron phosphate positive electrode material, a lot of research work has been done, and the conductivity of the lithium iron phosphate material is improved by modification. For example, a layer of conductive material such as carbon, manganese and cobalt is coated and doped on the surface of the lithium iron phosphate particles. The surface carbon coating is an important means for modifying the lithium iron phosphate positive electrode material.

[0003] At present, in the industrial production of lithium ion batteries, polyvinylidene fluoride (PVDF) is mostly used as a binder, and N-methyl pyrrolidone (NMP), N,N-dimethylformamide (DMF) and other small organic molecules are used as dispersants. Although the organic solvent system has good dispersibility, it has the disadvantages of easy volatilization, flammability, explosiveness and high toxicity. The volatilization of the organic solvent seriously pollutes the environment and seriously affects the health of the workers. At the same time, the production cost of the organic solvent system is high. Chinese patent CN105428658A discloses a water-based binder positive electrode material for lithium iron phosphate batteries and a preparation method thereof. The invention uses deionized water as a dispersant, and the binder is composed of carboxymethyl chitosan and polyethylene glycol (PEG) in a weight ratio of (2.8-3.3):1. Although the cost is greatly reduced and the battery performance is improved, the adhesion of the binder needs to be improved.

[0004] In addition, the adhesion between the existing positive electrode slurry and the aluminum foil is poor, and then the problems of material dropping, powder falling off, poor overall flexibility of the positive electrode sheet, and reduction of the unit volume energy density of the electrode sheet occur, which are not conducive to the performance of the final product battery.

[0005] Therefore, it is urgent to design and prepare a carbon-coated lithium iron phosphate positive electrode material to meet different market demands. SUMMARY

[0006] The purpose of the present application is to overcome the defects of the prior art, and provide a carbon-coated lithium iron phosphate positive electrode material and a preparation method thereof.

[0007] The object of the present application can be achieved by the following technical solutions.

[0008] A preparation method of a carbon-coated lithium iron phosphate positive electrode material, comprising the following steps:

[0009] 90-95 parts of carbon-coated lithium iron phosphate, 2-6 parts of conductive agent, 2-6 parts of binder and 75-80 parts of solvent are weighed by weight parts;

[0010] First, the binder and 80% of the solvent are mixed and stirred at 50-55℃ for 3h, then the conductive agent is added, and stirred below 40℃ for 2h, then the carbon-coated lithium iron phosphate is added and continues to stir for 3h, then 20% of the solvent is added and continues to stir for 2h, then the system is vacuumed, and the pressure is maintained for 10min, then the vacuum is broken, then the vacuum is re-applied and continues to stir for 40min until the foam is completely eliminated, the viscosity is tested, and the positive electrode slurry with a viscosity of 3000-4000mPa·s is obtained, finally the positive electrode slurry is coated on the aluminum foil, and then the rolling operation is performed, and the carbon-coated lithium iron phosphate positive electrode material is obtained.

[0011] Further, the carbon-coated lithium iron phosphate is prepared by the following steps:

[0012] First, lithium nitrate, phosphoric acid, iron chloride and glucose are dissolved in deionized water respectively; then the lithium nitrate solution, the phosphoric acid solution, the iron chloride solution and the glucose solution are slowly added to the deionized water in sequence, and fully stirred until completely mixed and uniform, then rotary evaporation is performed at 100℃, the precursor is obtained, the precursor is calcined at 200℃ with a temperature rising rate of 5℃ / min for 2h, then calcined at 800℃ with a temperature rising rate of 2℃ / min for 3h under nitrogen protection, and finally naturally cooled to room temperature, and the carbon-coated lithium iron phosphate is obtained; the amount ratio of lithium nitrate, phosphoric acid, iron chloride and glucose is 1.8g:2.2g:3.9g:10.8g.

[0013] The carbon-coated lithium iron phosphate improves the tap density, electronic conductivity and lithium ion diffusion efficiency of the positive electrode material. In addition, the carbon source of the carbon-coated lithium iron phosphate is obtained by carbonization of glucose, so the surface of the carbon-coated lithium iron phosphate has abundant carboxyl and hydroxyl groups, and the surface of the binder has abundant hydroxyl groups, therefore, the carbon-coated lithium iron phosphate and the binder can produce hydrogen bond interaction in deionized water, and the compatibility and dispersity of the two in the positive electrode slurry are improved, which can further improve the corresponding performance of the positive electrode material.

[0014] Further, the conductive agent is one or several of acetylene black, carbon black, ketjen black and carbon nanotube.

[0015] Further, the binder is prepared by the following steps:

[0016] S1, nitrogen replacement dry three-port flask in the air, and then add epichlorohydrin and chloroform, fully stirred to 65℃, then slowly add a mixture of benzotriazole and chloroform, after the completion of the addition at 65℃ for 3h, after the reaction was cooled to room temperature, reduced pressure distillation, column chromatography purification (eluent selection of chloroform and ether mixed solvent, chloroform and ether volume ratio of 9:1), reduced pressure distillation, to obtain intermediate 1; benzotriazole, epichlorohydrin and chloroform dosage ratio is 12.5g:7.8mL:120mL;

[0017] The control of benzotriazole and epichlorohydrin molar ratio is 1:1 and benzotriazole slightly excess, under heating conditions, the amino group of benzotriazole and the epoxy group of epichlorohydrin addition reaction, the reaction process is as follows:

[0018]

[0019] S2, nitrogen replacement dry three-port flask in the air, and then add D-glucosamine, triethylamine and dimethyl sulfoxide, stirring to dissolve after heating to 80℃, then slowly add a mixture of intermediate 1 and dimethyl sulfoxide, after the completion of the addition at 80℃ for 3h, after the reaction was cooled to room temperature, reduced pressure distillation, to obtain intermediate 2; D-glucosamine, intermediate 1, triethylamine and dimethyl sulfoxide dosage ratio is 18.4g:19g:16.3mL:180mL;

[0020] Triethylamine is an acid binding agent, control of D-glucosamine and intermediate 1 molar ratio is 1.1-1.2:1, D-glucosamine -NH2 and intermediate 1 -Cl substitution reaction, the reaction process is as follows:

[0021]

[0022] S3, under nitrogen protection, trimethylolpropane triacrylate, DBU (1,8-diazobis spiro [5.4.0] eleven-7-alkene) and dimethyl sulfoxide into three-port flask, stirring uniform after heating to 70℃, then slowly add intermediate 2, after the completion of the addition at 70℃ for 18h, after the reaction was cooled to room temperature, reduced pressure distillation, to obtain intermediate 3; intermediate 2, trimethylolpropane triacrylate, DBU and dimethyl sulfoxide dosage ratio is 32.6g:22.9mL:0.4g:200mL;

[0023] Under the catalysis of DBU, control of intermediate 2 and trimethylolpropane triacrylate molar ratio is 1.05-1.1:1, intermediate 2 and trimethylolpropane triacrylate Michael addition reaction, the reaction process is as follows:

[0024]

[0025] S4, nitrogen is bubbled into deionized water for 0.5h to remove oxygen in the deionized water, then carboxymethyl cellulose is added, and the reaction liquid is obtained by fully stirring to be clear and viscous, and is prepared for use; then intermediate 3, acrylic acid, butyl acrylate, N-hydroxy acrylamide and ammonium persulfate are added to the reaction liquid, and the reaction is stirred at 60 DEG C for 6h, after the reaction is completed, the reaction liquid is cooled to room temperature, and sodium hydroxide solution is slowly added to adjust the pH of the system to 6 to obtain the binder; the amount ratio of carboxymethyl cellulose, intermediate 3, acrylic acid, butyl acrylate, N-hydroxy acrylamide and ammonium persulfate is 1g:2.6g:4mL:1g:0.2g:0.15g.

[0026] Under the action of ammonium persulfate, the carbon-carbon double bond on intermediate 3 and the carbon-carbon double bond on acrylic acid, butyl acrylate and N-hydroxy acrylamide are chemically reacted and polymerized, and further form a firm three-dimensional network cross-linking structure with carboxymethyl cellulose, and in addition, the binder has abundant polar hydroxyl groups, so that the binder has excellent adhesion and can effectively improve the performance and service life of the finished battery.

[0027] The binder contains a benzotriazole structure, three nitrogen atoms of which are adjacent to the benzene ring, and has strong coordination ability, and can form a stable complex with aluminum on the aluminum foil current collector through a coordination bond, so that the positive electrode slurry can be adhered to the aluminum foil for a long time and is not easy to fall off, and further, the current transmission in the battery is more smooth. The benzene ring on intermediate 3 and the butyl group of butyl acrylate both provide non-polar parts for the binder, which helps the electrolyte to wet the electrode, and the electrolyte wetting the electrode improves the wettability of the electrode material, optimizes the distribution and reaction kinetics of the electrolyte on the electrode, and thus improves the performance, cycle life and capacity of the battery.

[0028] The abundant hydroxyl groups on the binder make the binder have good compatibility with the remaining raw materials of the positive electrode slurry, and each raw material of the positive electrode material can fully play its own role, and further, the carbon-coated lithium iron phosphate positive electrode material has excellent and stable cycle life and conductivity.

[0029] Further, the solvent is deionized water.

[0030] The application further discloses a carbon-coated lithium iron phosphate positive electrode material prepared according to the preparation method of the carbon-coated lithium iron phosphate positive electrode material.

[0031] The present application has the following advantages: the binder has a firm three-dimensional network cross-linking structure, contains benzotriazole structure and rich hydroxyl groups, and has strong adhesion; the binder has good compatibility with other raw materials, and cooperates with other raw materials to give the carbon-coated lithium iron phosphate positive electrode material excellent and stable cycle life and conductivity, and excellent comprehensive performance and safe use. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0033] Embodiment 1

[0034] The carbon-coated lithium iron phosphate is prepared by the following specific steps:

[0035] 1.8 g of lithium nitrate is dissolved in 80 mL of deionized water; 2.2 g of phosphoric acid is dissolved in 30 mL of deionized water, 3.9 g of iron chloride is dissolved in 60 mL of deionized water; 10.8 g of glucose is dissolved in 30 mL of deionized water; then the lithium nitrate solution, the phosphoric acid solution, the iron chloride solution and the glucose solution are slowly added to 100 mL of deionized water in sequence, and fully stirred until completely mixed and uniform; then rotary evaporation is performed at 100℃, to obtain a precursor; the precursor is calcined at 200℃ at a temperature increasing rate of 5℃ / min for 2 h, and then calcined at 800℃ at a temperature increasing rate of 2℃ / min for 3 h under nitrogen protection; finally, natural cooling is performed to room temperature, to obtain the carbon-coated lithium iron phosphate.

[0036] Embodiment 2

[0037] The binder is prepared by the following specific steps:

[0038] S1, nitrogen is used to replace the air in a 250 mL dry three-necked flask, then 7.8 mL of epichlorohydrin and 80 mL of chloroform are sequentially added, fully stirred, and then heated to 65℃, and then a mixed solution of 12.5 g of benzotriazole and 40 mL of chloroform is slowly added, after the addition is completed, reaction is performed at 65℃ for 3 h, after the reaction is completed, cooling is performed to room temperature, vacuum distillation is performed, column chromatography purification is performed (the eluent is a mixed solvent of chloroform and diethyl ether, and the volume ratio of chloroform to diethyl ether is 9:1), and vacuum distillation is performed, to obtain intermediate 1;

[0039] S2, nitrogen was used to replace the air in a 500 mL dry three-necked flask, and then 18.4 g of D-glucosamine, 16.3 mL of triethylamine and 140 mL of dimethyl sulfoxide were sequentially added. After stirring and dissolving, the temperature was raised to 80°C, and then a mixed solution of 19 g of intermediate 1 and 40 mL of dimethyl sulfoxide was slowly added. After the addition was completed, the reaction was carried out at 80°C for 3 h. After the reaction was completed, the temperature was cooled to room temperature, and then vacuum distillation was carried out to obtain intermediate 2.

[0040] S3, 22.9 mL of trimethylolpropane triacrylate, 0.4 g of DBU and 200 mL of dimethyl sulfoxide were added to a 500 mL three-necked flask under nitrogen protection. After stirring and dissolving, the temperature was raised to 70°C, and then 32.6 g of intermediate 2 was slowly added. After the addition was completed, the reaction was carried out at 70°C for 18 h. After the reaction was completed, the temperature was cooled to room temperature, and then vacuum distillation was carried out to obtain intermediate 3.

[0041] S4, nitrogen was bubbled into 120 mL of deionized water for 0.5 h to remove oxygen in the deionized water, and then 1 g of carboxymethyl cellulose was added. After stirring, a clear viscous reaction solution was obtained and was ready for use. Then 2.6 g of intermediate 3, 4 mL of acrylic acid, 1 g of butyl acrylate, 0.2 g of N-hydroxy acrylamide and 0.15 g of ammonium persulfate were added to the reaction solution. The reaction was carried out at 60°C for 6 h. After the reaction was completed, the temperature was cooled to room temperature, and then sodium hydroxide solution was slowly added to adjust the pH of the system to 6 to obtain the adhesive.

[0042] Example 3

[0043] The carbon-coated lithium iron phosphate positive electrode material was prepared by the following specific steps:

[0044] According to the weight parts of each raw material, 2 parts of the adhesive prepared in Example 2 and 60 parts of deionized water were mixed and stirred at 50°C for 3 h. Then 1 part of acetylene black and 1 part of carbon black were added and stirred below 40°C for 2 h. Then 90 parts of the carbon-coated lithium iron phosphate prepared in Example 1 were added and stirred for 3 h. Subsequently, 15 parts of deionized water were added and stirred for 2 h. Then the system was vacuumized and maintained for 10 min. Then the vacuum was broken. Then the system was vacuumized again and stirred for 40 min until the foam was completely eliminated. The viscosity was tested to obtain a positive electrode slurry with a viscosity of 3000-4000 mPa·s. Finally, the positive electrode slurry was coated on an aluminum foil, and then roll pressing was performed to obtain the carbon-coated lithium iron phosphate positive electrode material.

[0045] Example 4

[0046] The carbon-coated lithium iron phosphate positive electrode material was prepared by the following specific steps:

[0047] The raw materials were mixed by weight parts, 5 parts of the binder prepared in Example 2 and 62.4 parts of deionized water were mixed and stirred at 53℃ for 3h, then 3 parts of carbon black, 2 parts of Ketjen black were added and stirred at below 40℃ for 2h, then 93 parts of the carbon-coated lithium iron phosphate prepared in Example 1 was added and stirred for 3h, then 15.6 parts of deionized water was added and stirred for 2h, then the system was vacuumized and kept for 10min, then the vacuum was broken, then the system was vacuumized again and stirred for 40min until the foam was completely eliminated, the viscosity was tested, and the positive electrode slurry with a viscosity of 3000-4000mPa·s was obtained, finally the positive electrode slurry was coated on the aluminum foil, and then the rolling operation was performed, and the carbon-coated lithium iron phosphate positive electrode material was obtained.

[0048] Example 5

[0049] The carbon-coated lithium iron phosphate positive electrode material was prepared, and the specific steps were as follows:

[0050] The raw materials were mixed by weight parts, 5 parts of the binder prepared in Example 2 and 62.4 parts of deionized water were mixed and stirred at 53℃ for 3h, then 3 parts of carbon black, 2 parts of Ketjen black were added and stirred at below 40℃ for 2h, then 93 parts of the carbon-coated lithium iron phosphate prepared in Example 1 was added and stirred for 3h, then 15.6 parts of deionized water was added and stirred for 2h, then the system was vacuumized and kept for 10min, then the vacuum was broken, then the system was vacuumized again and stirred for 40min until the foam was completely eliminated, the viscosity was tested, and the positive electrode slurry with a viscosity of 3000-4000mPa·s was obtained, finally the positive electrode slurry was coated on the aluminum foil, and then the rolling operation was performed, and the carbon-coated lithium iron phosphate positive electrode material was obtained.

[0051] Comparative Example 1

[0052] The carbon-coated lithium iron phosphate positive electrode material was prepared, and the specific steps were as follows:

[0053] The remaining steps were unchanged, only the binder of Example 3 was replaced with carboxymethyl cellulose without any treatment, thereby preparing the carbon-coated lithium iron phosphate positive electrode material.

[0054] Performance test

[0055] The positive electrode materials prepared in Examples 3-5 and Comparative Example 1 were cut into small pieces of 4*10cm, and then the peel strength test was performed on the peel strength machine, and the test results are shown in Table 1 below:

[0056] Table 1

[0057] Test item Example 3 Example 4 Example 5 Comparative Example 1 Peeling strength N / m 3.83 3.98 4.21 3.51

[0058] The carbon-coated lithium iron phosphate positive electrode materials prepared in Examples 3-5 and Comparative Example 1 were respectively made into lithium iron phosphate batteries, and the following performance tests were performed.

[0059] (1) Lithium iron phosphate battery safety performance test: according to GB / T 31485-2015 standard to do overcharge, overdischarge and needle test, all qualified.

[0060] (2) According to GB / T 31484-2015 standard to do lithium iron phosphate battery cycle performance test; the results are shown in Table 2 as follows:

[0061] Table 2

[0062]

[0063] In the description of the specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does 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.

[0064] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or adopt similar ways to replace them, as long as they do not deviate from the invention or exceed the scope defined by the present claims.

Claims

1. A method for preparing a carbon-coated lithium iron phosphate positive electrode material, characterized in that: The following steps are involved: Weigh 90-95 parts of carbon-coated lithium iron phosphate, 2-6 parts of a conductive agent, 2-6 parts of a binder, and 75-80 parts of a solvent by weight; stir the binder and 80% of the solvent at 50-55° C., add the conductive agent, stir at below 40° C. for 2 hours, add the carbon-coated lithium iron phosphate, stir for 3 hours, add 20% of the solvent, stir for 2 hours, evacuate the system, maintain the pressure, break the vacuum, evacuate again, and stir for 40 minutes, test the viscosity to obtain a positive electrode slurry, coat it on aluminum foil, and roll-press to obtain a carbon-coated lithium iron phosphate positive electrode material; Wherein, the binder is prepared by the following steps: S1. Replace the air in the bottle with nitrogen, add epichlorohydrin and chloroform, stir and heat to 65°C, add benzotriazole and chloroform, react at 65°C for 3 hours, cool, distill under reduced pressure, purify by column chromatography, and distill under reduced pressure to obtain intermediate 1; S2. Replace the air in the bottle with nitrogen, add D-glucosamine, triethylamine and dimethyl sulfoxide, stir and heat to 80°C, add intermediate 1 and dimethyl sulfoxide, react at 80°C for 3 hours, cool, and distill under reduced pressure to obtain intermediate 2; S3. Trimethylolpropane triacrylate, DBU and dimethyl sulfoxide were added to a flask under nitrogen protection, and the temperature was raised to 70°C with stirring. Intermediate 2 was added and the reaction was carried out at 70°C for 18 hours. The mixture was cooled and distilled under reduced pressure to obtain Intermediate 3. S4. Nitrogen is bubbled into deionized water, carboxymethyl cellulose is added, and the mixture is stirred to obtain a reaction solution; intermediate 3, acrylic acid, butyl acrylate, N-hydroxyacrylamide, and ammonium persulfate are added to the reaction solution, reacted at 60° C. for 6 h, cooled, and sodium hydroxide solution is added to adjust the pH of the system to 6 to obtain a binder.

2. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: Carbon-coated lithium iron phosphate is prepared by the following steps: First, lithium nitrate, phosphoric acid, ferric chloride, and glucose were dissolved in deionized water respectively; then, lithium source solution, phosphorus source solution, iron source, and carbon source were added to deionized water in sequence, stirred, and rotary evaporated to obtain a precursor, which was calcined at 200°C for 2h, and then calcined at 800°C for 3h under nitrogen protection, and cooled to obtain carbon-coated lithium iron phosphate.

3. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: The usage ratio of benzotriazole, epichlorohydrin and chloroform in step S1 is 12.5 g:7.8 mL:120 mL.

4. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: The usage ratio of D-glucosamine, intermediate 1, triethylamine and dimethyl sulfoxide in step S2 is 18.4 g:19 g:16.3 mL:180 mL.

5. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: The usage ratio of intermediate 2, trimethylolpropane triacrylate, DBU and dimethyl sulfoxide in step S3 is 32.6 g:22.9 mL:0.4 g:200 mL.

6. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: The usage ratio of carboxymethyl cellulose, intermediate 3, acrylic acid, butyl acrylate, N-hydroxyacrylamide and ammonium persulfate in step S4 is 1 g:2.6 g:4 mL:1 g:0.2 g:0.15 g.

7. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 2, characterized in that: The usage ratio of lithium nitrate, phosphoric acid, ferric chloride and glucose is 1.8g:2.2g:3.9g:10.8g.

8. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: The conductive agent is one or more of acetylene black, carbon black, Ketjen black, and carbon nanotubes.

9. The method for preparing a carbon-coated lithium iron phosphate positive electrode material according to claim 1, characterized in that: The solvent is deionized water.

10. A carbon-coated lithium iron phosphate positive electrode material, characterized in that: It is prepared according to the method for preparing a carbon-coated lithium iron phosphate positive electrode material according to any one of claims 1-9.

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