Superior Stability Secured by a Four-Phase Cathode Electrolyte Interface on a Ni-Rich Cathode for Lithium Ion Batteries

Abstract

A multi-functional coating with high electronic and ionic conductivity is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM) to boost the battery stability upon cycling and during storage as well. Phosphoric acid reacts with residual lithium species on the pristine NCM to form Li3PO4 coating with extra CNTs penetrating through, which shows high ionic and electronic conductivity. NCM, Li3PO4, CNTs, and the electrolyte jointly form a four-phase cathode electrolyte interface, which plays a key role in the great enhancement of capacity retention, from 50.3% for pristine NCM to 84.8% for modified one after 500 cycles at 0.5C at room temperature. The modified NCM also deliveries superior electrochemical performances at high cut-off voltage (4.5 V), high temperature (55 ℃) and high rate (10C). Furthermore, it can deliver 154.2 mA h g-1 at the 500th cycle after exposed to air with high humidity for two weeks. These results demonstrate that the well-constructed multi-functional coating can remarkably enhance the chemical and electrochemical performances of NCM. The improved cycling, storage and rate performance are attributed to the four-phase cathode electrolyte interface delivering high electron and ionic conductivity, and securing the cathode against attack. This work broadens the horizon of constructing effective electrode/electrolyte interface for electrochemical energy storage and conversion.