5V-class high-voltage batteries with over-lithiated oxide and a multi-functional additive

Abstract

Over-lithiated oxides are promising cathode materials for 5V-class high-voltage batteries, however, their widespread adoption has been seriously restricted owing to their complicated chemical and electrochemical limitations. To resolve both of these issues at once, we suggest a multi-functional additive, tris(trimethylsilyl)phosphite (TMSP), with a comprehensive working mechanism that is demonstrated by systematic spectroscopic analyses combined with first-principles calculations. First, TMSP remarkably reduces the internal pressure because trivalent phosphorus effectively scavenges the oxygen gas in the cell. Second, TMSP greatly enhances the overall chemical stability of electrolytes because electrophilic phosphorus and silicon readily remove nucleophilic lithium oxide species by means of a chemical scavenging reaction. Third, TMSP affords a phosphite component in the protection layer on the electrode surface, inhibiting additional electrolyte decomposition under a high working potential. Finally, TMSP provides a silyl ether component in the protection layer, which is responsible for preventing transition metal dissolution through a fluoride scavenging reaction. Based on these verified effects, TMSP-controlled cells offer remarkable cycle performance with 90.2% capacity retention for 100 cycles.