A Liquid-Free Poly(butylene oxide) Electrolyte for Near-Room-Temperature and 4-V Class All-Solid-State Lithium Batteries

Abstract

Solid polymer electrolyte (SPE) is a promising class of solid electrolytes for building All-solid-state lithium batteries (ASSLBs) due to their flexibility and compatibility with electrodes. However, the requirement of an elevated operating temperature (> 60 oC), the high-voltage instability, and mechanical vulnerability to Li dendrites penetration remain major drawbacks for the most commonly used poly(ethylene oxide) (PEO) based SPEs. Our group is making efforts to improve the PEO based ASSLBs from various approaches, including glass fiber reinforcement and vertically-aligned composite polymer electrode to realize high areal capacity [1], self-healing electrostatic shielding additive for Li dendrites suppression [2], hierarchical hybrid electrolytes of “ceramic-in-polymer” and “polymer-in-ceramic” [3], and atomic layer deposited interfacial protection for polysulfides inhibition. More inspiring strategies are discussed in details in our recent review on solid-state hybrid electrolytes [4], but polymer electrolytes without liquid phases rarely afford feasible battery performance near room temperature.Alternatively, poly(butylene oxide) (PBO) is another promising member of the polyether family that PEO belongs to. Although PBO based SPEs have been previously reported to have favorable ionic conductivity at room temperature, its application in ASSLBs is scarce, probably due to challenges of engineering methodology and interfacial instability with electrodes. Herein, we develop a solvent-free route for fabricating PBO SPE membranes for application in ASSLBs with feasible performance near room temperature. We also demonstrate a facile activation method to stabilize the electrode/electrolyte interface for the PBO based ASSLBs. As a result, the ASSLB with PBO SPE and a LiFePO4 cathode delivers a stable specific capacity of ~140 mAh g-1 at 0.1C with almost 100% retention after 100 cycles at ~28 oC. Moreover, in spite of the poor high-voltage stability of PEO, we found that the PBO SPE demonstrates good compatibility with 4-V class cathodes without extra modifications, achieving good cycling stability with LiCoO2 and LiNi0.8Mn0.1Co0.1O2 cathodes. For extended application, interfacial protection based on PBO SPEs can futher enable Li metal compatibility for the superionic halide solid electrolytes (which exhibit highly promising performance with high-voltage cathodes but fall short of low-potential stability [5-6]). The versatile applications of PBO SPEs shall lead to new opportunities for high-performance ASSLBs.