Stabilization of Lithium Cobalt Phosphate Cathodes via Artificial Interphases

Olivine LiCoPO4 (LCP) exhibits a rare combination of high theoretical capacity (167 mAh g−1), excellent thermal stability, and high redox potential (4.8 V vs vs Li/Li+), making it a promising candidate for high voltage lithium batteries. Despite these attractive properties, practical implementation of this electrode chemistry has been limited by stability issues at the cathode-electrolyte interface, including parasitic electrolyte reactions, surface decomposition of the electrode material, and Co dissolution. Carbon coating and substitutions of Co by Fe and other cations improve the performance, however the cycling stability needs further improvement. In an effort to address these issues, we deposited thin, conformal metal oxide surface coatings on substituted LCP powder and investigated the effects of these coatings on the performance of carbon-coated substituted LCP/MCMB graphite full cells with a standard carbonate electrolyte. Remarkably, some of these coatings clearly improved operation of carbon-coated substituted LCP cells as compared to the as-prepared cathode powder. Observed improvements in capacity retention relate to stabilization of the cathode-electrolyte interface and suppression of electrolyte oxidation, as measured by online electrochemical mass spectroscopy (OEMS) of evolved gases within the cell. Together, these results suggest artificial interphases are a viable pathway toward stabilizing LCP and achieving commercial viability.