Electrolyte Optimization of a Substituted-LiCo1-xFexPO4 Cathode

Abstract

Lithium cobalt phosphate (LiCoPO4) is an attractive cathode material due to its high discharge potential (4.8 V vs. Li/Li+) and specific capacity (167 mAh g-1), resulting in an impressive specific energy of ~802 Wh kg-1. The development of LCP has proven difficult owing to the instability of the electrode and the tendency of the electrolyte to perpetually decompose (oxidize), leading to a highly resistive passivation layer. In this report, a substituted lithium cobalt iron phosphate (s-LiCo1-xFexPO4 or s-LCFP) cathode material was tested with various solvents and additives to find an optimized electrolyte that limits electrode polarization and improves cycle life. The s-LCFP cathode performed best with a 1M LiPF6 solution of EC/EMC (3/7 wt%) with 2% of additive ARL1. Comparing ARL1 to the baseline electrolyte, the fade rate was reduced from 0.014% per cycle to 0.005% per cycle and the shift in charge voltage (due to polarization) was reduced from 39mV to 19mV through 50 cycles.