Preparation And Electrochemical Performance Of Lithium Iron Phosphate Cathode Material With Coated Organic Carbon Source

As a cathode material for lithium-ion batteries,lithium iron phosphate has the advantages of low price,safety,environmental protection,non-toxicity,and cycle stability,making it one of the first choices for power batteries.However,lithium iron phosphate is limited by its structure,and has disadvantages such as low electronic conductivity,low diffusion rate of lithium ions at the Fe PO₄/Li Fe PO₄two-phase interface,and low tap density,which make the actual capacity of lithium iron phosphate lower than its theoretical capacity.Although carbon coating modification can significantly improve the electrochemical performance of Li Fe PO₄,the influence mechanism of the carbonization process of different carbon sources,the structure and morphology of carbonized products on the electrochemical performance of Li Fe PO₄/C still needs to be further explored.This paper mainly studies the influence of precursor preparation and carbonization process operating conditions on the electrochemical performance and mechanism of Li Fe PO₄/C during the preparation of Li Fe PO₄/C by in-situ polymerization-carbothermal reduction method.The main research content and conclusions are as follows:（1）Using FeSO₄,NaH₂PO₄,AN（aniline）and H₂O₂as raw materials,Fe PO₄/PAN（polyaniline）was prepared by in-situ polymerization-coprecipitation method.The particle size test results show that the obtained Fe PO₄/PAN particle size is 530 nm.The XRD characterization results of the sample after heat treatment show that the sample obtained after heat treatment is pure phase Fe₂P₂O₇,and the iron element is reduced from trivalent to divalent,indicating that there is an organic carbon source in the precursor.The IR test result shows that this organic carbon The source is PAN instead of AN.（2）Conducted experimental research on the carbonization method.Based on the reduction performance and cost considerations,sucrose was selected as the reducing carbon source;based on the large temperature difference in the carbonization process of sucrose and polyaniline,and the PAN carbonization product was graphitized with high electronic conductivity for carbon,PAN is selected as the carbon source for coating.The carbonized product of sucrose is used to reduce Fe³⁺to Fe²⁺,and the carbonized product of polyaniline forms a carbon coating layer of Li Fe PO₄.A comparative experiment was carried out using sucrose as the reducing and coating carbon source,sucrose as the reducing carbon source,and polyaniline as the coating carbon source.The results showed that the different carbon sources used in this paper were used as the reducing and coating carbon sources.The obtained Li Fe PO₄/C has better electrochemical performance.（3）The effects of AN addition,polymerization temperature,sucrose addition,pyrolysis temperature and pyrolysis time on the electrochemical performance of Li Fe PO₄/C were investigated.The research results show that the precursor Fe PO₄/PAN is an iron source,and Li Fe PO₄/C with a smaller particle size can be obtained,corresponding to better electrochemical performance.This is because in the precursor preparation stage,aniline is polymerized in situ to form polyaniline,which can control the particle size of the precursor Fe PO₄,which in turn controls the particle size of Li Fe PO₄/C.In the carbothermic reduction reaction stage,when polyaniline is used as the coated carbon source,the specific capacity of Li Fe PO₄/C is greatly improved.This is because the organic polymer with benzene ring as the main component can obtain graphitized carbon with high electronic conductivity after pyrolysis,which effectively improves the electronic conductivity of lithium iron phosphate,and the electrochemical charge transfer resistance is reduced from505Ωto 294Ωat 0.1 C.Using the experimental method in this article,under suitable conditions,the prepared Li Fe PO₄/C has a discharge specific capacity of 163.7 m Ah/g at a rate of 0.1 C.After a high rate cycle of 10 C,the material still has a high specific capacity（170 m Ah/g）.It shows that the prepared cathode material has good structural stability.The capacity retention rate was 93.7%after 50 charge-discharge cycles.After cyclic voltammetry and AC impedance tests,the prepared Li Fe PO₄/C has good reversibility and a large lithium ion diffusion coefficient.Compared with commercial lithium iron phosphate materials,the samples obtained in this study have less electrochemical polarization.（4）The orthogonal experiment method was used to investigate the interactive effects of sucrose and polyaniline on the electrochemical performance of Li Fe PO₄/C.The analysis of variance showed that both polyaniline and sucrose have an effect on the specific discharge capacity of Li Fe PO₄/C,but the effect of polyaniline is more significant.The two carbon sources have an interactive effect on the specific discharge capacity of Li Fe PO₄/C.It is found through research that when the added amount of sucrose is close to the theoretical amount of reduced carbon,the electrochemical performance of the prepared Li Fe PO₄/C is better.Using the method in this paper,compared with the current method of the enterprise,each ton of Li Fe PO₄/C produced can save 2,410 yuan in cost.