High‐voltage poly (ethylene oxide) all‐solid‐state lithium batteries enabled by high‐concentration interfacial layer

Abstract Poly (ethylene oxide) (PEO) solid electrolytes hold great promise in all‐solid‐state lithium batteries (ASSLBs) with high‐energy and safety capabilities. However, the PEO electrolyte is hardly resistant to degrade electrochemically at high voltages (>4 V) in ASSLBs. Herein, we design and prepare a highly efficient and stable PEO‐based solid electrolyte (denoted as PEO‐L/DT‐PEO) applied to high‐voltage ASSLBs, in which the Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO)‐containing PEO (PEO‐L) serves as a bulk of the electrolyte and the PEO with dual‐salts (LiDFOB and high‐concentration LiTFSI) forms an ultrathin coating layer (DT‐PEO) covering on PEO‐L. With 3% coating layer, the PEO‐L/DT‐PEO electrolyte exhibits an enhanced decomposition potential (> 4.9 V vs. Li/Li + ) originating from the high concentration of LiTFSI as well as renders Al foil current collector high anticorrosion by the introduction of LiDFOB. Upon coupling with high‐voltage NCM811 cathode, the DT‐PEO efficiently suppresses the interfacial degradation kinetics between electrolyte and cathode, and slows down the irreversible phase change of NCM811. The assembled PEO‐L/DT‐PEO‐based Li/NCM811 battery exhibits an excellent cycling stability of remaining 63.0% after 400 cycles at a cutoff voltage of 4.2 V as well as an initial discharge specific capacity of 164.5 mAh g −1 at a rate of 0.4C. This work offers a facile and feasible strategy to overcoming interface decomposition of the PEO electrolyte matching perfectly with high‐voltage cathode for high‐performance ASSLBs.