Surface-Modified Ni-Rich Layered Oxide Cathode Via Thermal Treatment of Poly(Vinylidene Fluoride) for Lithium-Ion Batteries

Abstract

Combination of poly(vinylidene fluoride) (PVDF) with Ni-rich layered cathode material create artificial cathode-electrolyte interphases by thermal decomposition of PVDF and residual Li+ species. The pressure of the cell cycled with PVDF-treated cathode materials is markedly decreased, since the thermal treatment with PVDF selectively reduces the amounts of Li+ species. The cycling performance is improved compared to nontreated Ni-rich layered cathodes because the artificial cathode–electrolyte interphases effectively suppress the electrolyte decomposition as determined by systematic characterization of particle hardness, surface morphology, and electrochemical impedance spectroscopy. Additional high temperature storage tests performed with 3450-dimensioned pouch cells indicate much improved recovery rates, as well as smaller open circuit voltage drops, smaller increases in internal resistance, and less swelling for cells cycled with the PVDF-treated Ni-rich layered cathode than with a nontreated Ni-rich layered cathode.