Towards High Capacity Li-ion Batteries Based on Silicon-Graphene Composite Anodes and Sub-micron V-doped LiFePO4 Cathodes

Lithium iron phosphate, LiFePO4 (LFP) has demonstrated promising performance as a cathode material in lithium ion batteries (LIBs), by overcoming the rate performance issues from limited electronic conductivity. Nano-sized vanadium-doped LFP (V-LFP) was synthesized using a continuous hydrothermal process using supercritical water as a reagent. The atomic % of dopant determined the particle shape. 5 at. % gave mixed plate and rod-like morphology, showing optimal electrochemical performance and good rate properties vs. Li. Specific capacities of >160 mAh g-1 were achieved. In order to increase the capacity of a full cell, V-LFP was cycled against an inexpensive micron-sized metallurgical grade Si-containing anode. This electrode was capable of reversible capacities of approximately 2000 mAh g-1 for over 150 cycles vs. Li, with improved performance resulting from the incorporation of few layer graphene (FLG) to enhance conductivity, tensile behaviour and thus, the composite stability. The cathode material synthesis and electrode formulation are scalable, inexpensive and are suitable for the fabrication of larger format cells suited to grid and transport applications.