Study On The Preparation And Modification Of Battery-grade Iron Phosphate

Due to depletion of the petrochemical energy and the rise in primary energy prices such as international crude and natural gas and the mature application of lithium ion batteries in the field of electric vehicles and energy storage materials,and the strong support of national industrial policies.The demand for high safety,high reliability and environmental-friendly lithium iron phosphate energy storage materials is increasing.At present,the main iron sources for synthesizing lithium iron phosphate are ferrous oxalate,ferric oxide,and iron phosphate.The stability problem of the first two ion sources is the most concern in the industry due to their non-skeleton and relatively simple synthesis process.However,the skeleton of iron phosphate is obvious shown in the performance of synthetic lithium iron phosphate.In this paper,the preparation of battery-grade iron phosphate was studied by precipitation method using iron powder and phosphoric acid as raw materials.Firstly,the optimal p H for the preparation of iron phosphate was obtained by analyzing the presence of phosphate in aqueous solution combining the solubility product rule,and a diffusion model was established.Secondly,effects of reaction conditions on the quality of product iron phosphate were studied.The optimal experimental parameters for synthesis iron phosphate:a reaction temperature of 70?,a reaction time of 1 hour,10%excess of H₂O₂,a H₂O₂ dropping time of 60 minutes and a sintering temperature of 550?.The effects of the concentration of phosphoric acid,dissolution time,dissolution temperature and molar ratio on the dissolution rate of iron powder were further studied.The optimal experimental parameters for the dissolution of iron powder:(1₃₄?(1_?60?=1:4,9)₀)?9)₃₄=1:3,a dissolution temperature of 60?,a dissolution time of 1 hour.Finally,a liquid phase method for preparation of lithium iron phosphate precursors is proposed.The effects of solid-liquid ratio,temperature,CO₂ flow rate,and time on the hydrogenation effect of lithium carbonate were investigated.The optimal experimental parameters for the hydrogenation of lithium carbonate:a liquid ratio of 1:25,a temperature of 25?,a CO₂ flow rate of 3 L/min,and a time of 40 minutes.Li Fe PO₄/C is obtained by sintering prepared precursor and added carbon source under these optimal experimental parameters.Electrochemical test results show that the sample obtained by the liquid phase method has better cycle performance and the first discharge capacity is 143m Ah/g at 0.2C.