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.