Janus nanofibers with multiple Li+ transport channels and outstanding thermal stability for all-solid-state composite polymer electrolytes

Abstract

Solid electrolytes with high ionic conductivity, dendrite suppression, and compatibility with high-voltage electrodes are needed for application in all-solid-state lithium metal batteries (ASSLMBs). Here, an optimized composite polymer electrolyte (CPE) that can meet the above-mentioned requirements by introducing a Janus nanofiber membrane prepared by side-by-side electrospinning technology into a PEO-based electrolyte, is reported. Janus nanofibers have asymmetric structural characteristics, with positively charged oxygen vacancy enriched yttrium oxide (Y₂O₃) doped zirconium dioxide (ZrO₂) (YSZ) nanoparticle interconnected nanofibers on one side and poly-m-phenyleneisophthalamide (PMIA) nanofibers on the other side. The former YSZ nanoparticle interconnected nanofiber has a permeable ceramic phase inside and can also form continuous organic–inorganic interfaces with the PEO matrix outside, achieving fast Li⁺ transport. Additionally, the oxygen vacancies on the surface of YSZ can also combine with anions of lithium salt, releasing more Li⁺. The latter PMIA nanofibers provide a robust skeleton support for the CPEs, ensuring outstanding mechanical strength and safety for the thin CPEs even at elevated temperatures. Therefore, the CPEs presented prominent ionic conductivity (1.61 × 10⁻⁴ S cm⁻¹) and excellent ionic transference number (0.50) at 50 °C. Meanwhile, the Li‖Li cells have remarkable lithium stripping/plating reversibility, and the LiFePO₄‖Li cells display ultra-long stable cycle life over 5000 cycles. Besides, the CPEs also present excellent compatibility with LiNi_0.8Mn_0.1Co_0.1O₂. More strikingly, the CPEs have excellent cycling stability even at 40 °C, and the LiFePO₄‖Li flexible pouch cells cycle normally even under folding, piercing, and cutting. The research will provide new insight into the construction of Janus nanofibers for CPEs towards the prospect of practical high-energy ASSLMBs.