Amphoteric effects of Fe(2)P on electrochemical performance of lithium iron phosphate-carbon composite synthesized by ball-milling and microwave heating

Abstract

Lithium iron phosphate-carbon (LiFePO(4)-C) Composites with various amounts of Fe(2)P are synthesized by ball-milling coupled with microwave heating to serve as cathodes for lithium-ion batteries. LiFePO(4)-C in which Fe(2)P is restrained below a critical concentration gives as very high discharge capacity of 165 mAh g(-1), excellent rate capability (85.4% C/50-rate discharge capacity at 2C) and stable cyclic retention for 250 cycles. Above the critical concentration however, electrochemical performance deterioated. Analysis and debate, based on a comparison of the physical and electrochemical properties among LiFePO(4)-C composites with the variation of Fe(2)P, proceeded to the conclusion that below the critical concentration, Fe(2)P enhanced the conductivity of LiFePO(4)-C, whereas above the critical concentration, it blocked the one-dimensional Li(+) pathways in LiFePO(4) and might hinder Li(+) movement in LiFePO(4). Therefore, in order to obtain a LiFePO(4)-C composite that enhances electrochemical performance, it is concluded that the amount of Fe(2)P should be carefully controlled below its critical concentration. (C) 2008 Elsevier B.V. All rights reserved.