With the merits of both solid polymer electrolytes (SPEs) and inorganic ceramic electrolytes (ICEs), composite polymer electrolytes (CPEs) prepared by coupling polymer matrix with inorganic fillers are broadly utilized in solid lithium metal batteries (SLMBs). However, CPEs fabricated by a single filler with polymer matrix often exhibit unsatisfactory performance. Here, prepared by coupling poly (ethylene oxide) (PEO) matrix with a natural additive carboxymethyl cellulose lithium (CMC-Li) and an inorganic filler mineral hectorite (Ht), an efficient CPE is reported. Detailedly, CMC-Li is considered to act as a “bridge”, which connects the Ht nanosheets distributed in PEO, thus establishing continuous Li⁺ transmission channels. Ht with a nanolayers structure vividly acts as “bricks”, pave the way for ion transference. In addition, oxygen atoms in CMC-Li contribute to adequately dissociating lithium salts, hydrogen bonding generated by hydroxyl groups is propitious to anchor anions to increase the Li⁺ transference number. Under the synergistic effect brought by CMC-Li and Ht, the electrolyte membrane PEO-10%Ht-4%CMC-Li (PHCL, in mass fraction) displays a high Li⁺ transfer number (0.73) and exceptional Li⁺ conductivity at 25 ℃ (2.5 × 10⁻⁴ S/cm). Our work demonstrates a powerful mean to fabricate the efficient electrolyte membrane for SLMBs.

The rational design of green chemical, low-cost, and highly efficient solid-state electrolytes for Li-metal anode is a promising but still challenging strategy for preventing Li dendrite growth and developing safe and ultralong cycle life Li-metal batteries. Herein, a homogeneous composite solid polymer electrolyte (CSPE) is fabricated with water as the ideal dispersion medium, hectorite (Ht) as nanofiller, and poly (ethylene oxide) (PEO) as the matrix, to guide uniform Li plating/stripping. Benefiting from the merit of Ht can form uniformly dispersed nanosheets in water, the obtained CSPE inheres to a low melting point, robust mechanical property, and high Li⁺ transference number. Moreover, the fabricated Li symmetric battery using PEO-Ht-LiClO₄ CSPE keeps cycling steadily for 4000 h. The well demonstrated water-based CSPE paves the way for developing low-cost, environmentally friendly, and safe solid-state electrolytes for Li-metal batteries.