Improving interfacial stability by in situ protective layer formation in 4.2V poly(ethylene oxide) based solid state lithium batteries

The poly(ethylene oxide) based composite solid electrolyte(PEO-CSE) is an effective solution for developing high-performance solid-state lithium battery. However, the poly(ethlene oxide)(PEO) based solid-state lithium battery using 4.0 V cathode suffers from severe interfacial instability problems. In this work, we add additive lithium difluorophosphate(LiPO2F2) into the PEO-CSE to form a stable and low resistance interphase at the cathode/electrolyte interface during charge/discharge process. The electrochemical stability window of PEO-CSE increases to ∼5.0 V. Besides, the electrochemical performance of PEO based solid-state lithium battery with LiCoO2 as cathode is excellent. The discharge capacity of LiCoO2/Li cell with LiPO2F2 reaches 108.5 mAh g−1 at 1.0C. In contrast, the discharge capacity that without LiPO2F2 is only 60.0 mAh g−1. Meanwhile, the PEO-CSE with LiPO2F2 cell delivers stable cycle performance at 4.2 V. The capacity retention maintains 88.5% compared with 16.1%(without LiPO2F2) after 100 cycles. Furthermore, it's still maintains 83.3% after 150 cycles. In addition, the cathode/electrolyte interface is analyzed by transmission electron microscope(TEM) and X-ray photoelectron spectroscopy(XPS). Galvanostatic intermittent titration test(GITT) is used to analyze the dynamic diffusion performance. This strategy provides a simple and effective way to improve the high voltage stability of the cathode/electrolyte interface.