Improving the electrochemical properties of nanosized LiFePO4-based electrode by boron doping

Electrode materials with homogeneous distribution of boron were obtained by heating mixtures of nanosized carbon-coated lithium iron phosphate and BPO4 in 3-9% weight at 700 degrees C. The materials can be described as nanocomposites containing i) LiFePO4, possibly doped with a low amount of boron, ii) FePO4 and iii) an amorphous layer based on Li4P2O7-derived material that surrounds the phosphate particles. The thermal treatment with BPO4 also triggered changes in the carbon coating graphitic order. Galvanostatic and voltammetric studies in lithium half-cells showed smaller polarisation, higher capacity and better cycle life for the boron-doped composites. For instance, one of the solids, called B-6-LiFePO4, provided close to 150 and 140 mAhg(-1) (87% and 81% of theoretical capacity, respectively) under C/2.5 and C regimes after several cycles. Improved specific surface area, carbon graphitization, conductivity and lithium ion diffusivity in the boron-doped phospholivine network account for this excellent rate performance. The properties of an amorphous layer surrounding the phosphate particles also account for such higher performance. (C) 2014 Elsevier Ltd. All rights reserved.