Study On The Preparation Of Lithium Iron Phosphate From Wet-process Phosphoric Acid And Titanium Dioxide By-product Ferrous Sulfate

Lithium iron phosphate is considered to be a new generation of lithium ion battery cathode materials because of its safety,non-toxicity,environmental friendliness and high specific capacity.However,the research and development of excellent and inexpensive lithium iron phosphate precursors has been a problem that limits its further development.In this experiment,titanium iron by-product ferrous sulfate and wet-process phosphoric acid were used as raw materials to prepare lithium iron phosphate precursor by coprecipitation method,and then precursor was used to obtain lithium iron phosphate by roasting,which not only reduced the synthesis cost,but also solved the recycling of waste ferrous sulfate produced in production course of titanium dioxide.The precursor is synthesized by coprecipitation using wet-process phosphoric acid as a phosphorus source,which is relatively simple and easy to operate.Therefore,this experiment has very important significance and application value.Firstly,in this thesis,the precursors of lithium iron phosphate were prepared by co-precipitation method with pure FeSO4·7H2O,H3PO4 and LiOH·H2O.The results show that the optimized process conditions for preparing lithium iron phosphate precursor are:the lithium molar charge is 0.084mol,the phosphorus molar charge is 0.03mol,the iron molar charge is 0.025 mol,the reaction time is 1h,the reaction temperature is 30℃,the aging time is 2h.Under optimized process conditions,the precursor ratio is closest to 1:1:1.The results of XRD,thermo gravimetry and particle size analysis showed that the precursor prepared was a mixture of ferrous phosphate and lithium phosphate.The weight loss of the precursor tended to be stable after 500℃,and the volume average particle size was 4.96 um.Secondly,in order to prepare lithium iron phosphate with excellent performance,the precursor was doped with 7%sucrose and then calcined in a tube furnace to obtain LiFePO4/C powder material.The calcination time and calcination temperature of the precursor were studied.Studies have shown that the optimized calcination temperature is 750℃ and the optimized calcination time is 8h.Finally,the preparation of precursors was carried out by coprecipitation using ferrous sulfate and wet-process phosphoric acid as raw materials and sucrose as carbon source.The experimental results show that the optimum conditions for the preparation of precursors are:lithium molar charge is 0.24 mol,the phosphorus molar charge is 0.03 mol,and the iron molar charge is 0.025 mol.Under optimized process conditions,the precursor ratio is closest to 1:1:1.The LiFePO4/C powder material was prepared by calcination with a self-made precursor.The prepared materials were characterized by XRD,SEM,electrochemical performance test and cyclic voltammetry.The results show that the prepared material is a complete spherical structure,and basically consistent with the lithium iron phosphate standard map(81-1173).At the 0.1C rate,the first discharge specific capacity reached 112.0Ah·kg-1.after ten cycles,the specific capacity was not reduced but increased,showing excellent electrochemical performance.The cyclic voltammetry curve of the sample is a pair of redox peaks with good symmetry.The peaks after four cycles are basically coincident,indicating that the internal polarization of the sample is small.