Boosting the intrinsic kinetics of lithium vanadium phosphate via an electrochemically active cross-link framework

Abstract

The monoclinic lithium vanadium phosphate Li3V2(PO4)3 (LVP) is considered a promising cathode for lithium-ion batteries (LIBs) due to its high working voltage (>4.0 V, vs. Li+/Li) and high theoretical specific capacity (197 mAh g−1). However, the electrochemical procedure accompanied by three-electron reactions in LVP has proven challenging due to the complexity or asymmetry of the reaction pathways, thus limiting its wide application. Herein, an electrochemically active cross-link framework of LVP, LiFe0.3Mn0.7PO4 (LFMP) and graphene are successfully synthesized by an in situ catalytic process, which enables stable cycling and high-rate capabilities up to 4.8 V (vs. Li+/Li). Graphene-like carbon can be formed in situ with VOx as the catalyst and polyvinyl alcohol as the carbon source, and LFMP also inhibits the growth of LVP particles, allowing rapid Li+ and electron transport in the cathodes. Both in situ and ex situ X-ray diffraction prove that the cross-link framework efficiently smooths the lattice mismatch and achieves highly reversible structural phase transitions. The prepared 0.9LVP·0.1LFMP is able to provide a superior rate capability of 123 mAh g−1 at 20 C. After 150 cycles, the 0.9LVP·0.1LFMP shows 97.4 % capacity retention even under a voltage of 4.8 V (vs. Li+/Li). This work develops a new strategy for the future design of high-voltage and high-power cathode materials for LIBs.