Electrochemical study on lithium iron phosphate/hard carbon lithium-ion batteries

The electrochemical performances of lithium iron phosphate (LiFePO4), hard carbon (HC) materials, and a full cell composed of these two materials were studied. Both positive and negative electrode materials and the full cell were characterized by scanning electron microscopy, transmission electron microscopy, charge-discharge tests, and alternating current (a. c.) impedance techniques. Experimental results show that the LiFePO4/HC full cell exhibits a gradually decreased cell voltage, and it is capable of delivering a reversible discharge capacity of 122.1 mAh g(-1) at 0.2-C rate. At the higher rate of 10 C, the efficiency of the full cell remains almost unchanged from that of 0.2 C. Furthermore, the LiFePO4/HC battery demonstrated a long life of 2,450 cycles with 40% of capacity change at a 10-C high rate. The internal resistance of the full cell is rather low as it is revealed from a. c. impedance measurements. These properties make the LiFePO4/HC battery an attractive option for high rate and long cycle life power applications.