Electrode/Electrolyte Interface of Composite α-Li3V2(PO4)3 Cathodes in a Nonaqueous Electrolyte for Lithium Ion Batteries and the Role of the Carbon Additive

Abstract

Transition-metal phosphates (TMPs) are potential materials for large-scale applications of lithium ion batteries (LIBs). Yet, high-voltage TMP cathodes have not met commercial success due to ill understood failure mechanisms. In this article we studied the surface chemistry of Li3V2(PO4)3 composite electrodes using X-ray photoelectron spectroscopy (XPS) post-electrochemical cycling in a stable electrochemical window of 3.0–4.2 V vs Li/Li+ and in the wider window of 3.0–4.8 V vs Li/Li+ where a dramatic fade in capacity is noted. In addition, we performed aging experiments in LiPF6 EC/DEC electrolyte with no electrochemical bias applied to investigate a possible spontaneous solid electrolyte interphase (SEI) formation as has been described for lithium transition-metal oxide (LixMyOz) electrodes. An SEI was found on the Li3V2(PO4)3 composite electrodes cycled in both potential windows and after aging with similar chemical compositions including ethers, alkoxides, esters, carboxylates, and carbonates as well ...