Achieving a Highly Stable Electrode/Electrolyte Interface for a Nickel-Rich Cathode via an Additive-Containing Gel Polymer Electrolyte

The nickel-rich cathode LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) is deemed as a prospective material for high-voltage lithium-ion batteries (LIBs) owing to its merits of high discharge capacity and low cobalt content. However, the unsatisfactory cyclic stability and thermostability that originate from the unstable electrode/electrolyte interface restrict its commercial application. Herein, a novel electrolyte composed of a polyethylene (PE) supported poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) based gel polymer electrolyte (GPE) strengthened by a film-forming additive of 3-(trimethylsilyl)phenylboronic acid (TMSPB) is proposed. The porous structure and good oxidative stability of the P(VdF-HFP)/PE membrane help to expand the oxidative potential of GPE to 5.5 V compared with 5.1 V for the liquid electrolyte. The developed GPE also has better thermal stability, contributing to improving the safety performance of LIBs. Furthermore, the TMSPB additive constructs a low-impedance and stable cathode electrolyte interphase (CEI) on the NCM811 cathode surface, compensating for GPE's drawbacks of sluggish kinetics. Consequently, the NCM811 cathode matched with 3% TMSPB-containing GPE exhibits remarkable cyclicity and rate capability, maintaining 94% of its initial capacity after 100 cycles at a high voltage range of 3.0-4.35 V and delivering a capacity of 133.5 mAh g^-1 under 15 C high current rate compared with 68% and 75.8 mAh g^-1 for the one with an additive-free liquid electrolyte. By virtue of the enhanced stability of the NCM811cathode, the cyclability of graphite||NCM811 full cell also increases from 48 to 81% after 100 cycles. The incorporation of P(VdF-HFP)-based GPE and TMSPB electrolyte additive points out a viable and convenient pathway to unlock the properties of high energy density and satisfactory safety for next-generation LIBs.