A preparation method of a cathode material for a lithium iron phosphate battery

Abstract

The present invention relates to the technical field of lithium-ion batteries, and specifically to a preparation method of a cathode material for lithium iron phosphate batteries. In the present invention, aniline, o-toluidine, m-aminobenzenesulfonic acid, hydrochloric acid solution and ammonium persulfate are added to prepare polyaniline. Then, polyaniline with multiple branched chains is prepared using polyaniline, silane coupling agent KH560, deionized water and dimethyl sulfoxide as raw materials. A composite carbon source is prepared by adding polyaniline with multiple branched chains and graphene to dimethyl sulfoxide. Finally, the finished product is prepared using a lithium iron phosphate precursor, lithium carbonate and the composite carbon source as raw materials. The finished product prepared by the present invention has good conductivity and ion diffusion rate, and thus has broad application prospects in the field of lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and specifically to a preparation method for the cathode material of a lithium iron phosphate battery. Background Art

[0002] Lithium - ion batteries have high energy density, long cycle life, no memory effect, low self - discharge rate and good environmental compatibility. In the current situation of the increasingly depleted fossil energy and deteriorating environment, they play a crucial role in alleviating the energy crisis and curbing environmental deterioration. The modern values of lithium iron phosphate batteries include: (1) High safety: Compared with other lithium - ion battery chemicals, lithium iron phosphate batteries have higher thermal stability and lower spontaneous combustion risk, which makes them safer and more reliable in applications and reduces the risk of accidents. (2) High energy density: Lithium iron phosphate batteries have a relatively high energy density and can store more energy in a smaller volume or mass. (3) Long life: Lithium iron phosphate batteries have a long cycle life and long - term stability. They can withstand more charge - discharge cycles without significant capacity attenuation and are thus more durable and reliable. (4) Fast charging ability: Compared with other lithium - ion batteries, lithium iron phosphate batteries have better charging current characteristics. They can accept charging more quickly, shorten the charging time and provide a more convenient user experience. (5) Environmentally friendly: Lithium iron phosphate batteries do not contain toxic heavy metals such as cadmium and mercury and have no significant pollution risk to the environment, which makes them a more environmentally friendly energy storage option.

[0003] However, in the prior art, there are still some problems to be solved in commonly used lithium iron phosphate batteries. For example, the conductivity of lithium iron phosphate is relatively low, and the speed of charge transfer inside the cathode is slow. This results in relatively slow charging and discharging speeds of lithium iron phosphate batteries and certain limitations. In addition, the interfacial instability between the cathode material and the electrolyte of lithium iron phosphate batteries may lead to a decline in battery performance. The interfacial problem may cause battery polarization and instability of the electrochemical reaction.

[0004] In order to overcome the defects of the prior art, the present invention provides a preparation method for the cathode material of a lithium iron phosphate battery. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method for the cathode material of a lithium iron phosphate battery to solve the problems in the prior art.

[0006] To solve the above - mentioned technical problems, the present invention provides the following technical solutions:

[0007] A preparation method for the cathode material of a lithium iron phosphate battery, comprising the following steps:

[0008] Step 1: Under a nitrogen atmosphere, mix aniline, o-toluidine, m-aminobenzenesulfonic acid, and hydrochloric acid solution, stir at 0 - 5°C for 40 - 60 min, then dropwise add ammonium persulfate and continue stirring for reaction for 6 - 8 h. After the reaction is completed, wash, filter by suction, and dry under vacuum to obtain polyaniline; fully dissolve the polyaniline in 1 / 2 mass portion of dimethyl sulfoxide, then dropwise add silane coupling agent KH560 and react at 25 - 30°C for 50 - 60 h. After the reaction is completed, wash, filter by suction, and dry under vacuum to obtain a reaction intermediate; then fully dissolve the reaction intermediate in 1 / 2 mass portion of dimethyl sulfoxide, gradually add deionized water dropwise and react at 25 - 30°C for 50 - 60 h. After the reaction is completed, wash, filter by suction, and dry under vacuum to obtain multi-branched polyaniline;

[0009] Step 2: Add multi-branched polyaniline and graphene to dimethyl sulfoxide, stir ultrasonically for 20 - 30 min to obtain a mixed solution, subject the mixed solution to sedimentation, filtration by suction, washing, and drying under vacuum to obtain a composite carbon source;

[0010] Step 3: Mix iron phosphate precursor, lithium carbonate, and the composite carbon source, wet grind the mixture for 2 - 3 h after mixing, and after drying, carry out pre-sintering and high-temperature sintering in a nitrogen atmosphere in sequence to prepare the finished product.

[0011] Preferably, in Step 1, when preparing polyaniline, the molar ratio of aniline, o-toluidine, m-aminobenzenesulfonic acid, hydrochloric acid solution, and ammonium persulfate is (1 - 2):1:1:3:3.

[0012] Preferably, in Step 1, the component contents of the multi-branched polyaniline are as follows: in terms of mass portions, 1 - 2 parts of polyaniline, 450 - 500 parts of dimethyl sulfoxide, 0.15 - 0.30 parts of silane coupling agent KH560, and 1 - 2 parts of deionized water.

[0013] Preferably, in Step 1 or Step 2, when drying under vacuum, the temperature is 55 - 65°C and the time is 20 - 30 h.

[0014] Preferably, in Step 2, the mass ratio of the multi-branched polyaniline, graphene, and dimethyl sulfoxide is (0.05 - 0.07):1:44.

[0015] Preferably, in Step 3, the component contents of the finished product are as follows: in terms of mass fraction, 15 - 20% of lithium carbonate, 5 - 10% of the composite carbon source, and the balance is the iron phosphate precursor.

[0016] Preferably, in Step 3, pre-sinter at 350 - 400°C for 3 - 4 h; carry out high-temperature sintering at 800 - 900°C for 7 - 8 h.

[0017] Preferably, the method for preparing the iron phosphate precursor is as follows: dissolve ferric nitrate nonahydrate in 1 / 2 part by mass of deionized water to form Solution 1; dissolve ammonium dihydrogen phosphate in 1 / 2 part by mass of deionized water to form Solution 2; mix Solution 1 and Solution 2 evenly, then add ammonia water to adjust the pH to 1.0 - 1.5, continue stirring for 30 - 40 min, after the stirring ends, carry out oil bath heating, and then obtain the iron phosphate precursor through washing and drying.

[0018] Preferably, the mass ratio of ferric nitrate nonahydrate, ammonium dihydrogen phosphate and deionized water is 4:(1 - 1.5):80.

[0019] Preferably, during the oil bath heating, the temperature is 100 - 130 °C and the time is 6 - 8 h.

[0020] The beneficial effects of the present invention:

[0021] In the present invention, polyaniline is prepared by adding aniline, o-toluidine, m-aminobenzenesulfonic acid, hydrochloric acid solution and ammonium persulfate. Then, multi-branched polyaniline is prepared using polyaniline, silane coupling agent KH560, deionized water and dimethyl sulfoxide as raw materials. A composite carbon source is prepared by adding multi-branched polyaniline and graphene to dimethyl sulfoxide. Finally, the finished product is prepared using the iron phosphate precursor, lithium carbonate and the composite carbon source as raw materials.

[0022] The characteristics of the present invention are as follows: in Step 1, polyaniline is prepared by adding aniline, o-toluidine, m-aminobenzenesulfonic acid, hydrochloric acid solution and ammonium persulfate; then, multi-branched polyaniline is prepared using polyaniline, silane coupling agent KH560, deionized water and dimethyl sulfoxide. In the second step, the silane coupling agent KH560 is first introduced into polyaniline through a ring-opening reaction to obtain a reaction intermediate, and then deionized water is added for hydrolysis to prepare multi-branched polyaniline. The obtained multi-branched polyaniline has a unique conjugated multi-branched structure and a relatively low steric hindrance, which can reduce the internal resistance of the battery, reduce the hindrance to electrons and ions, improve the energy density of the battery, enable more charges to be transferred per unit time, and enhance the electron transfer rate and a higher ion diffusion coefficient.

[0023] In step 2, multi-branched polyaniline and graphene are added to dimethyl sulfoxide to prepare a composite carbon source. The principle of this reaction is to coat the surface of the graphene material with multi-branched polyaniline to obtain a composite carbon source material. On the one hand, the multi-branched polyaniline is coated on the surface of the graphene material. The multi-branched polyaniline can fully coat the graphene and interact with it through the π-π stacking interaction with the graphene, thereby preventing the agglomeration and accumulation of the graphene, and effectively improving the dispersibility and comprehensive performance of the graphene material; on the other hand, the multi-branched polyaniline has good electrical conductivity and can enhance the electrical conductivity of the graphene material. This can reduce the internal resistance of the electrode material, promote electron conduction and charge transfer, and improve the charge and discharge rate and power density of the battery. In addition, the coating of multi-branched polyaniline can also provide additional reaction interfaces and catalytic active sites, promote the insertion / deinsertion reaction of lithium ions, and improve the capacity and cycle stability of the battery.

[0024] In step three, a finished product is prepared using an iron phosphate precursor, lithium carbonate, and a composite carbon source as raw materials. By coating the composite carbon source around the lithium iron phosphate primary particles, not only does the migration of electrons and ions accelerate, but the coated primary particles also have a smaller particle size, increasing the reactive surface area of the electrode material and thus improving the electrode's reactivity. Furthermore, the presence of the carbon coating prevents the formation of side reaction products after direct contact between the positive electrode material and the electrolyte. DETAILED DESCRIPTION

[0025] The following will provide a clear and complete description of the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] Source of raw materials:

[0027] Graphene, provided by Jiangxi Shuobang New Materials Technology Co., Ltd., has a particle size of 3 μm. One portion is 1 g.

[0028] Example 1: Step 1: Under a nitrogen atmosphere, 1 mol of aniline, 1 mol of o-toluidine, 1 mol of m-aminobenzenesulfonic acid, and 3 mol of hydrochloric acid solution were mixed, stirred at 5 °C for 60 min, and then 3 mol of ammonium persulfate was added dropwise and the reaction was continued with stirring for 8 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 65 °C for 30 h to obtain polyaniline; 1 g of polyaniline was fully dissolved in 240 g of dimethyl sulfoxide, and then 0.15 g of silane coupling agent KH560 was added dropwise and reacted at 30 °C for 60 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 65 °C for 30 h to obtain a reaction intermediate; then the reaction intermediate was fully dissolved in 240 g of dimethyl sulfoxide, 1 g of deionized water was added dropwise and reacted at 30 °C for 60 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 65 °C for 30 h to obtain multi-branched polyaniline;

[0029] Step 2: 0.05 g of multi-branched polyaniline and 1 g of graphene were added to 44 g of dimethyl sulfoxide, and ultrasonically stirred for 30 min to obtain a mixed solution. The mixed solution was sedimented, filtered by suction, washed, and vacuum dried at 65 °C for 30 h to obtain a composite carbon source;

[0030] Step 3: 4 g of ferric nitrate nonahydrate was dissolved in 40 g of deionized water to form Solution 1; 1 g of ammonium dihydrogen phosphate was dissolved in 40 g of deionized water to form Solution 2; Solution 1 and Solution 2 were mixed evenly, and then ammonia water was added to adjust the pH to 1.5, and stirring was continued for 40 min. After the stirring was completed, it was heated in an oil bath at 130 °C for 8 h, and then washed and dried to obtain a ferric phosphate precursor;

[0031] Step 4: By mass fraction, 80% of the ferric phosphate precursor, 15% of lithium carbonate, and 5% of the composite carbon source were mixed, wet milled for 3 h after mixing, dried, and then pre-calcined at 400 °C for 4 h and sintered at 900 °C for 8 h in a nitrogen atmosphere in sequence to prepare the finished product.

[0032] Example 2: Step 1: Under a nitrogen atmosphere, 1 mol of aniline, 1 mol of o-toluidine, 1 mol of m-aminobenzenesulfonic acid, and 3 mol of hydrochloric acid solution were mixed, stirred at 4 °C for 55 min, and then 3 mol of ammonium persulfate was added dropwise and the reaction was continued with stirring for 7.5 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 63 °C for 27 h to obtain polyaniline; 1 g of polyaniline was fully dissolved in 240 g of dimethyl sulfoxide, and then 0.15 g of silane coupling agent KH560 was added dropwise and reacted at 29 °C for 57 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 63 °C for 27 h to obtain a reaction intermediate; then the reaction intermediate was fully dissolved in 240 g of dimethyl sulfoxide, 1 g of deionized water was added dropwise and reacted at 29 °C for 57 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 63 °C for 27 h to obtain multi-branched polyaniline;

[0033] Step 2: Add 0.05 g of multi-branched polyaniline and 1 g of graphene into 44 g of dimethyl sulfoxide, and ultrasonically stir for 27 min to obtain a mixed solution. The mixed solution is subjected to sedimentation, suction filtration, washing, and vacuum drying at 63 °C for 27 h to obtain a composite carbon source;

[0034] Step 3: Dissolve 4 g of ferric nitrate nonahydrate in 40 g of deionized water to form Solution 1; dissolve 1 g of ammonium dihydrogen phosphate in 40 g of deionized water to form Solution 2; mix Solution 1 and Solution 2 evenly, then add ammonia water to adjust the pH to 1.4, continue stirring for 37 min, after the stirring ends, heat in an oil bath at 120 °C for 7.5 h, and then wash and dry to obtain an iron phosphate precursor;

[0035] Step 4: Mix 80% iron phosphate precursor, 15% lithium carbonate, and 5% composite carbon source by mass fraction, wet grind the mixture for 2.7 h, dry it, and then carry out pre-sintering at 390 °C for 3.7 h and high-temperature sintering at 870 °C for 7.8 h in a nitrogen environment in sequence to prepare the finished product.

[0036] Example 3: Step 1: Under a nitrogen environment, mix 1 mol of aniline, 1 mol of o-toluidine, 1 mol of m-aminobenzenesulfonic acid, and 3 mol of hydrochloric acid solution, stir at 3 °C for 50 min, then dropwise add 3 mol of ammonium persulfate and continue stirring and reacting for 7 h. After the reaction ends, wash, carry out suction filtration, and vacuum dry at 60 °C for 25 h to obtain polyaniline; fully dissolve 1 g of polyaniline in 240 g of dimethyl sulfoxide, then dropwise add 0.15 g of silane coupling agent KH560 and react at 27 °C for 55 h. After the reaction ends, wash, carry out suction filtration, and vacuum dry at 60 °C for 25 h to obtain a reaction intermediate; then fully dissolve the reaction intermediate in 240 g of dimethyl sulfoxide, gradually add 1 g of deionized water dropwise and react at 27 °C for 55 h. After the reaction ends, wash, carry out suction filtration, and vacuum dry at 60 °C for 25 h to obtain multi-branched polyaniline;

[0037] Step 2: Add 0.05 g of multi-branched polyaniline and 1 g of graphene into 44 g of dimethyl sulfoxide, ultrasonically stir for 25 min to obtain a mixed solution. The mixed solution is subjected to sedimentation, suction filtration, washing, and vacuum drying at 60 °C for 25 h to obtain a composite carbon source;

[0038] Step 3: Dissolve 4 g of ferric nitrate nonahydrate in 40 g of deionized water to form Solution 1; dissolve 1 g of ammonium dihydrogen phosphate in 40 g of deionized water to form Solution 2; mix Solution 1 and Solution 2 evenly, then add ammonia water to adjust the pH to 1.3, continue stirring for 35 min, after the stirring ends, heat in an oil bath at 115 °C for 7 h, and then wash and dry to obtain an iron phosphate precursor;

[0039] Step 4: Mix 80% iron phosphate precursor, 15% lithium carbonate and 5% composite carbon source by mass fraction. After mixing, wet grind for 2.5 h, and after drying, successively carry out pre-sintering at 370 °C for 3.5 h and high-temperature sintering at 850 °C for 7.5 h under a nitrogen atmosphere to obtain the finished product.

[0040] Example 4: Step 1: Under a nitrogen atmosphere, mix 1 mol of aniline, 1 mol of o-toluidine, 1 mol of m-aminobenzenesulfonic acid and 3 mol of hydrochloric acid solution, stir at 2 °C for 45 min, then dropwise add 3 mol of ammonium persulfate and continue stirring and reacting for 6.5 h. After the reaction is completed, wash, filter by suction, and vacuum dry at 57 °C for 23 h to obtain polyaniline; fully dissolve 1 g of polyaniline in 240 g of dimethyl sulfoxide, then dropwise add 0.15 g of silane coupling agent KH560 and react at 26 °C for 53 h. After the reaction is completed, wash, filter by suction, and vacuum dry at 57 °C for 23 h to obtain the reaction intermediate; then fully dissolve the reaction intermediate in 240 g of dimethyl sulfoxide, gradually add 1 g of deionized water dropwise and react at 26 °C for 53 h. After the reaction is completed, wash, filter by suction, and vacuum dry at 57 °C for 23 h to obtain multi-branched polyaniline;

[0041] Step 2: Add 0.05 g of multi-branched polyaniline and 1 g of graphene to 44 g of dimethyl sulfoxide, ultrasonically stir for 23 min to obtain a mixed solution, and subject the mixed solution to sedimentation, filtration by suction, washing, and vacuum drying at 57 °C for 23 h to obtain the composite carbon source;

[0042] Step 3: Dissolve 4 g of iron(III) nitrate nonahydrate in 40 g of deionized water to form Solution 1; dissolve 1 g of ammonium dihydrogen phosphate in 40 g of deionized water to form Solution 2; mix Solution 1 and Solution 2 evenly, then add ammonia water to adjust the pH to 1.2, continue stirring for 33 min, after the stirring is completed, heat in an oil bath at 107 °C for 6.5 h, and then wash and dry to obtain the iron phosphate precursor;

[0043] Step 4: Mix 80% iron phosphate precursor, 15% lithium carbonate and 5% composite carbon source by mass fraction. After mixing, wet grind for 2.3 h, and after drying, successively carry out pre-sintering at 360 °C for 3.3 h and high-temperature sintering at 825 °C for 7.3 h under a nitrogen atmosphere to obtain the finished product.

[0044] Example 5: Step 1: Under a nitrogen atmosphere, 1 mol of aniline, 1 mol of o-toluidine, 1 mol of m-aminobenzenesulfonic acid, and 3 mol of hydrochloric acid solution were mixed, stirred at 0 °C for 40 min, then 3 mol of ammonium persulfate was added dropwise and stirring reaction continued for 6 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 55 °C for 20 h to obtain polyaniline; 1 g of polyaniline was fully dissolved in 240 g of dimethyl sulfoxide, then 0.15 g of silane coupling agent KH560 was added dropwise and reacted at 25 °C for 50 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 55 °C for 20 h to obtain a reaction intermediate; then the reaction intermediate was fully dissolved in 240 g of dimethyl sulfoxide, 1 g of deionized water was added dropwise and reacted at 25 °C for 50 h. After the reaction, it was washed, filtered by suction, and vacuum dried at 55 °C for 20 h to obtain multi-branched polyaniline;

[0045] Step 2: 0.05 g of multi-branched polyaniline and 1 g of graphene were added to 44 g of dimethyl sulfoxide, ultrasonically stirred for 20 min to obtain a mixed solution. The mixed solution was sedimented, filtered by suction, washed, and vacuum dried at 55 °C for 20 h to obtain a composite carbon source;

[0046] Step 3: 4 g of ferric nitrate nonahydrate was dissolved in 40 g of deionized water to form Solution 1; 1 g of ammonium dihydrogen phosphate was dissolved in 40 g of deionized water to form Solution 2; Solution 1 and Solution 2 were mixed evenly, then ammonia water was added to adjust the pH to 1.0, and stirring continued for 30 min. After the stirring ended, it was heated in an oil bath at 100 °C for 6 h, and then washed and dried to obtain a ferric phosphate precursor;

[0047] Step 4: By mass fraction, 80% of the ferric phosphate precursor, 15% of lithium carbonate, and 5% of the composite carbon source were mixed, wet milled for 2 h after mixing, dried, and then pre-calcined at 350 °C for 3 h and high-temperature sintered at 800 °C for 7 h in a nitrogen atmosphere to prepare the finished product.

[0048] Comparative Example 1: The preparation step of multi-branched polyaniline was removed, and the rest was the same as in Example 1. The specific steps were as follows: Step 1: 4 g of ferric nitrate nonahydrate was dissolved in 40 g of deionized water to form Solution 1; 1 g of ammonium dihydrogen phosphate was dissolved in 40 g of deionized water to form Solution 2; Solution 1 and Solution 2 were mixed evenly, then ammonia water was added to adjust the pH to 1.5, and stirring continued for 40 min. After the stirring ended, it was heated in an oil bath at 130 °C for 8 h, and then washed and dried to obtain a ferric phosphate precursor;

[0049] Step 2: By mass fraction, 80% of the ferric phosphate precursor, 15% of lithium carbonate, and 5% of graphene were mixed, wet milled for 3 h after mixing, dried, and then pre-calcined at 400 °C for 4 h and high-temperature sintered at 900 °C for 8 h in a nitrogen atmosphere to prepare the finished product.

[0050] Comparative Example 2: Replace the composite carbon source with the conventional carbon source glucose, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Dissolve 4 g of ferric nitrate nonahydrate in 40 g of deionized water to form Solution 1; dissolve 1 g of ammonium dihydrogen phosphate in 40 g of deionized water to form Solution 2; mix Solution 1 and Solution 2 evenly, then add ammonia water to adjust the pH to 1.5, continue stirring for 40 min, after the stirring ends, heat in an oil bath at 130 °C for 8 h, and then wash and dry to obtain the iron phosphate precursor;

[0051] Step 2: Mix 80% iron phosphate precursor, 15% lithium carbonate and 5% glucose by mass fraction, wet mill the mixture for 3 h, dry it, and then carry out pre-sintering at 400 °C for 4 h and high-temperature sintering at 900 °C for 8 h in a nitrogen environment in sequence to prepare the finished product.

[0052] Detection test:

[0053] Cyclic voltammetry test: Use the finished product prepared by the present invention as a sample, by controlling different scanning voltages, conduct multiple scanning tests on the sample within the selected test range, and record the corresponding current-potential curve. By observing the potential difference of the curve, the polarization and reversibility and other behaviors of the material can be reflected. The voltage range of the cyclic voltammetry test is 2.4 - 4.4 V, and the scanning speed is 1 mV / s.

[0054] AC impedance test: Use the finished product prepared by the present invention as a sample, apply a varying frequency signal to the sample, and obtain the relationship between the signal fluctuation feedback by the system and the electrode response. The parameters used in the experiment are: low frequency 0.01 Hz, high frequency 10 KHz. Substitute the measured impedance data into the diffusion coefficient formula of lithium ions to obtain the lithium ion diffusion coefficient.

[0055] The results are as follows in the table;

[0056]

[0057]

[0058] Conclusion: The dosages in Examples 1 to 5 remain unchanged, and only some reaction parameters are modified. From the experimental data, it can be seen that there are no obvious fluctuations in the various properties of the samples. Comparative Example 1: Remove the preparation steps of multi-branched polyaniline, and the rest is the same as in Example 1. From the experimental data, it can be seen that compared with Example 1, the potential difference increases to 0.48 V, and the lithium ion diffusion coefficient decreases to 3.15×10 -13, The analysis shows that: multi-branched polyaniline has good conductivity and electrochemical activity. Therefore, after removing the preparation of multi-branched polyaniline, only the graphene material is left as the carbon source to coat and modify the cathode material of the lithium iron phosphate battery, which will lead to more obvious polarization behavior of the material, decreased reversibility, and thus an increase in the potential difference; the conductivity decreases and the lithium ion diffusion coefficient decreases.

[0059] Comparative Example 2: Replace the composite carbon source with the conventional carbon source glucose, and the rest is the same as in Example 1. It can be seen from the experimental data that, compared with Example 1, the potential difference increases to 0.53 V and the lithium ion diffusion coefficient decreases to 2.73×10 -13 , The analysis shows that: the composite carbon source is obtained by coating the surface of the graphene material with multi-branched polyaniline. This composite carbon source has conductivity, charge-discharge rate, and can provide additional reaction interfaces and catalytic active sites to promote the intercalation / deintercalation reaction of lithium ions and improve the capacity and cycle stability of the battery; therefore, after replacing the composite carbon source with the conventional carbon source glucose, the potential difference increases and the lithium ion diffusion coefficient decreases.

[0060] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0061] Finally, it should be noted that: the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a cathode material for a lithium iron phosphate battery, characterized in that: It includes the following steps: Step 1: Under a nitrogen atmosphere, aniline, o-toluidine, m-aminobenzenesulfonic acid, and hydrochloric acid solution are mixed, stirred at 0 - 5 °C for 40 - 60 min, then ammonium persulfate is added dropwise and stirring reaction continues for 6 - 8 h. After the reaction ends, it is washed, filtered by suction, and dried under vacuum to obtain polyaniline; the polyaniline is fully dissolved in 1 / 2 mass portion of dimethyl sulfoxide, then silane coupling agent KH560 is added dropwise and reacted at 25 - 30 °C for 50 - 60 h. After the reaction ends, it is washed, filtered by suction, and dried under vacuum to obtain a reaction intermediate; then the reaction intermediate is fully dissolved in 1 / 2 mass portion of dimethyl sulfoxide, deionized water is added dropwise and reacted at 25 - 30 °C for 50 - 60 h. After the reaction ends, it is washed, filtered by suction, and dried under vacuum to obtain multi-branched polyaniline; Step 2: The multi-branched polyaniline and graphene are added to dimethyl sulfoxide, ultrasonically stirred for 20 - 30 min to obtain a mixed solution, and the mixed solution is subjected to sedimentation, filtration by suction, washing, and vacuum drying to obtain a composite carbon source; the mass ratio of the multi-branched polyaniline, graphene, and dimethyl sulfoxide is (0.05 - 0.07):1:44; Step 3: The iron phosphate precursor, lithium carbonate, and the composite carbon source are mixed, wet milled for 2 - 3 h after mixing, dried, and then pre-calcined and high-temperature sintered in a nitrogen atmosphere in sequence to prepare the finished product; pre-calcined at 350 - 400 °C for 3 - 4 h; high-temperature sintered at 800 - 900 °C for 7 - 8 h.

2. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 1, wherein: In Step 1, when preparing polyaniline, the molar ratio of aniline, o-toluidine, m-aminobenzenesulfonic acid, hydrochloric acid solution, and ammonium persulfate is (1 - 2):1:1:3:

3.

3. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 1, characterized in that: In Step 1, the component contents of the multi-branched polyaniline are as follows: in terms of mass portions, 1 - 2 parts of polyaniline, 450 - 500 parts of dimethyl sulfoxide, 0.15 - 0.30 parts of silane coupling agent KH560, and 1 - 2 parts of deionized water.

4. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 1, characterized in that: In Step 1 or Step 2, during vacuum drying, the temperature is 55 - 65 °C and the time is 20 - 30 h.

5. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 1, characterized in that: In Step 3, the component contents of the finished product are as follows: in terms of mass fraction, 15 - 20% lithium carbonate, 5 - 10% composite carbon source, and the balance is the iron phosphate precursor.

6. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 5, characterized in that: The preparation method of the iron phosphate precursor is: dissolve ferric nitrate nonahydrate in 1 / 2 mass portion of deionized water to form Solution 1; dissolve ammonium dihydrogen phosphate in 1 / 2 mass portion of deionized water to form Solution 2; mix Solution 1 and Solution 2 evenly, then add ammonia water to adjust the pH to 1.0 - 1.5, continue stirring for 30 - 40 min, after the stirring ends, perform oil bath heating, and then wash and dry to obtain the iron phosphate precursor.

7. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 6, characterized in that: The mass ratio of ferric nitrate nonahydrate, ammonium dihydrogen phosphate, and deionized water is 4:(1 - 1.5):

80.

8. The preparation method of a cathode material for a lithium iron phosphate battery according to claim 6, characterized in that: During oil bath heating, the temperature is 100 - 130 °C and the time is 6 - 8 h.

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