Electrochemical performance of LiFePO_4/Si composites as cathode material for lithium ion batteries

摘要

LiFeP04/Si composites are synthesized via a simple milling isopropanol mixtures process, and the effects of Si-modification on the electrochemical performances of LiFePO_4 are investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine LiFePO_4, LiFePO_4/Si-nanoparticle shows better cyclability and higher rate capability, especially at elevated temperature. An analysis of the electrochemical measurements indicates that Si incorporation could significantly improve the electrochemical performance at high charge/ discharge rate and elevated temperature. Among the investigated samples, (LiFePO_4)_(98)/(Si)_2 sample shows the best electrochemical performance with 150 mAhg~(-1) at 0.5C at 60 ℃. The enhancement could be mainly attributed to the lower charge-transfer resistance and higher lithium diffusion coefficients. In addition, the dangling bonds of Si and fluorosilica compounds are responsible for suppressing the dissolution of Fe~(2+) from olivine phase and preventing the rise of the surface resistance and charge transfer resistance.