Fiber-reinforced quasi-solid polymer electrolytes enabling stable Li-metal batteries

Abstract

With high ionic conductivity and good contact/adhesion with electrodes, quasi-solid polymer electrolytes (QPEs) are considered as one of the most promising options to address the safety concerns of next-generation rechargeable batteries. A trade-off exists between mechanical strength and ionic conductivity, e.g., a high electrolyte uptake ratio leads to high ionic conductivity while low mechanical strength, and vice versa. Constructing QPEs with integrated high ionic conductivity and mechanical robustness is crucial in promoting the practical use of safe and long-cycling lithium (Li)-metal batteries (LMBs). Herein, by integrating the poly(propylene) fiber (PPF) and a rationally designed polymer network, i.e., poly[poly(ethylene glycol) methyl ether methacrylate)-r-(2-ethylhexyl acrylate)-r-sodium (p-styrene sulfonate)-r-polyethylene glycol dimethacrylate] (PPES), a mechanically reinforced PPES@PPF film is obtained with a decent Young's modulus of ∼190 MPa. This fiber reinforced QPE (rQPE) exhibits a high ionic conductivity of 1.1 mS cm⁻¹ at 60 °C. The resulting Li/rQPE/LiFePO₄ (LFP) cell shows excellent cycling stability with a capacity retention of 91% over 900 cycles. Moreover, a cell with ultra-thin QPE (tQPE, ∼10 µm) and a high-voltage LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathode was also assembled, and delivers stable cycling performance over 300 cycles with a capacity retention of 80%. The current design of fiber-reinforced QPE not only surpasses the mechanical strength–ionic conductivity trade-off of QPEs, but also sheds light on the application of solid electrolytes for high-energy density LMBs.