Enhanced electrochemical properties of lithium iron phosphate as a cathode material for lithium ion rechargeable batteries

Intrinsically poor conductivity of LFP has hindered the realization of its high theoretical capacity (170 mAhg-1). In an attempt to solve these issues, in this work we have investigated the enhancement in electrochemical properties of LFP by process modification and surface modification. Firstly, the electrochemical improved performance of bare LFP with surfactant processing is introduced. The addition of surfactant as a dispersing agent during vibratory ball milling of LiFePO4 (LFP) precursor showed better size uniformity, morphology control, and reduced particle size when anionic surfactant (Avanel S-150) was used. Electrodes fabricated from LFP particles by solid state reaction involving vibratory milling showed a 22% decrease in capacity after 50 cycles, whereas the performance of electrode prepared by surfactant processed LFP showed only 3% loss in capacity. Secondly, in order to improve the electrical conductivity of LFP cathode, metal (Cu nano-flakes with very high surface area) with a polyethylene glycol (PEG) as carbon source and dispersant was incorporated in the cathode by ball milling Cu nano-flakes. Uniformly dispersed Cu flakes subsequently transformed to CuO during the calcination process. Interestingly, Cu flakes was used as a catalyst for transforming carbon from disordered to graphitic carbon from the analysis of I D/IG ratio with the help of Cu flakes during calcinations process. The Cu incorporated LFP composite cathode showed a high capacity of 161 mAhg-1, displayed excellent high rate and cyclic performance. Lastly, In order to improve the electrical conductivity of LFP cathode with a consideration of a reduced cost of the coating material, metal oxide was employed. This idea was originated from the transformation of metal to metal oxide as mentioned in the above. ZnO/Carbon was incorporated in the cathode by ball milling ZnO, PEG and LFP particles together. Herein, the catalytic property of ZnO for carbon transformation was confirmed again through the analysis of ID/IG ratio. The uniformly dispersed carbon and ZnO on the surface of LFP led to a good electronic contact between the LFP grains. Thus, an excellent high rate performance up to 10C was successfully achieved.