Unravelling the regulating role of graphene coating on improving the electrochemical performance of pyrophosphate cathode material: A first-principles study

Abstract

Pyrophosphate (Li2FeP2O7, LFPO) is proposed as a promising cathode material for Li-ion batteries on account of the high voltage and the two-dimensional lithium ions diffusion channel. Graphene coating could effectively improve the inherent poor ionic and electronic conductivities of Li2FeP2O7 material, however, the interfacial interaction and regulating role of the graphene coating on the graphene/Li2FeP2O7 (G/LFPO) composite structures are lack of research at the atomic scale. With the aid of first-principles calculations and ab initio molecular dynamics (AIMD) simulations, the interaction mechanism of graphene on the LFPO cathode material has been systematically investigated in terms of the geometrical structure, thermodynamical stability, interfacial charge distribution and electronic property. The analysis of electron localization function (ELF), charge density differences, and density of states strongly suggest the G/LFPO(001) and G/LFPO(010) heterostructures exhibit high electrochemical performance. The AIMD simulations show that the parallel and perpendicular G/LFPO(001) and G/LFPO(010) heterostructures have high thermodynamical stabilities and electronic conductivities. The diffusion coefficients of Li+ ions in the G/LFPO heterostructures are noticeably enhanced. Our present work would not only provide a fundamental understanding of interfacial interaction and electrochemical properties of G/LFPO composite, but also shed light on the regulating mechanism for the potential phosphate-based cathode material with high electrochemical performance.