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.