Improving the Performance of LiFePO4 Cathode Material By: Finding out an Effective Mixing Ratio for Cathode Slurry and Implementing Calendaring Process

The olivine structured lithium iron (II) phosphate (LiFePO4) is a promising cathode material for use in lithium-ion batteries. It has a high operating voltage (~3.4 V vs Li/Li), nontoxic and environmentally benign [1]. Although It has high specific theoretical capacity (~ 170 mAh g − 1 ), at high ‘C’ rates the discharge capacity decreased exponentially. To get optimum and consistent discharge capacity at different ‘C’ rates, the conductivity has to be improved. Different percentage of PVDF and carbon black were used to prepare slurry mixture of LiFePO4 and then coated on bare aluminum and carbon coated aluminum foil to make the cathode electrodes. Coin cells were made and tested at 1/10 C, 1/5 C, ½ C and 1C rates. Also to compare the effect of binder on cell performance, distinct percentages of water based binder were used. For this experiment each sample cathode electrode were calendared to different densities. A comparison of uncalendered and calendared cathode electrode (with carbon-coated current collector and also non-carbon coated current collector) were made. Before calendaring, material density was 0.8424 gcm -3 at 146 µm thickness of cathode electrode and after calendaring, density increased to 1.59 g/cm -3 at 97 µm thickness. Discharge capacity at different “C” rates shows that the calendared electrode provide consistent and better discharge capacity performance than the uncalendered electrode. Electrochemical impedance spectroscopy (EIS) test shows the calendaring of electrode exhibits a large decrease in contact resistance. Reference: [1] Seung-Ah Hong,Su Jin Kim, Kyung Yoon Chung, Myung-Suk Chun, Byung Gwon Lee, Jaehoon Kim, “Continuous synthesis of lithium iron phosphate (LiFePO4) nanoparticles in supercritical water: Effect of mixing tee”, The Journal of Supercritical Fluids, Elsevier, 2013.