Technology Research And Properties Of Lithium Iron Phosphate Synthesized From Iron(II) Oxalate Utilizing Water Based Ball-milling

The synthesis routes of lithium iron phosphate numerous, while solid-state method is most widely used route which used Li OH, NH4H2PO4, Fe C2O4 and sugar as the raw materials. In this method, large amount of ball-milling solvent was consumed, so the expense of Li Fe PO4 increase. If ethanol was replaced by other inexpensive solvent partially or totally, the expense will decrease greatly.In this article, two synthesis routes was used to modify the traditional solid-state method. Firstly, moderate amount of distilled water was utilized to replace partially ethanol, acetic acid was used to adjust p H to maintain the stability of the raw materials in the process of ball-milling.Secondly, ethanol was totally replaced by distilled water as ball-milled solvent medium, the utilization of citric acid to maintain the stability of the raw materials and prevent Fe2+ oxidized to Fe3+, In this method, optimized solid content, amount of citric acid and proportion of lithium source.At last, ethanol was totally replaced by distilled water. The research results were as follows:(1) Li OH, NH4H2PO4, Fe C2O4 and sugar were used as the raw materials, discussed different proportion ball-milling solvent mixed with ethanol and water(ethanol:water=0%-50%) impacted on the performance of the Li Fe PO4, the results showed that the discharge capacity of Li Fe PO4 increases with ethanol adding in 0-20% proportion, the performance of the sample is the best under the condition of 20% ethanol solution.However, the electrochemical performance of material change a little with the proportion increasing.(2) The discussion of p H, amount of carbon source and doped location effects of the structure and electrochemical performance of cathodes were investigated e at the condtion of using 20% ethanol solution as the ball-milling solvent. The results showed that, the most optimal material was synthesized under the conditions of p H was 4.5, amount of carbon source was 25%(The mass of theoretical prepared material). By discussing Fe-doped and Li-doed impacted on the structure of material, confirmed Fe-doped was better than Li-doed.The discharge capacity of optimal material in the 0.1C and 1.0 C.was 143.6 m Ah/g, 131.9m Ah/g. In the 1.0 C, the capacity always remained at 99.21% after cycling 20 times.(3) Li OH, NH4H2PO4, Fe C2O4 and citric acid were used as the raw materials, deionized water was utilized as ball milling medium to synthetize Li Fe PO4.The structure and electrochemical performance of cathodes were investigated at the different condition of solid content, amount of citric acid and excessive proportion of lithium source. The most optimal material was synthesized under the conditions of solid content was 30%, Fe C2O4 :citric acid was 1:1.2(Stoichiometric ratio), excessive proportion of lithium source was 3%. The discharge capacity of optimal material was 132.3m Ah/g in the 0.1 C and was 117.6m Ah/g in the 1.0 C; the capacity always remained at 98.98% after cycling 52 times, it showed that the material had a better electrochemical performance.