Asymmetric quasi-solid-state composite electrolytes via self-assembly of molecular brushes and hairy nanoparticles for dendrite-free lithium metal batteries

The practical application of lithium metal batteries is severely hindered by flammable liquid electrolytes and uncontrollable lithium dendrite growth. In this study, we propose a novel asymmetric quasi-solid-state composite electrolyte (denoted as QSCE-BPL/LPE/PDL) designed to overcome these challenges. QSCE-BPL/LPE/PDL is fabricated by evaporation-induced self-assembly of one-dimensional molecular brush BC-g-PLiSTFSI [BC = bacterial cellulose, PLiSTFSI = poly(lithium 4-styrenesulfonyl-(trifluoromethylsulfonyl) imide)] and zero-dimensional hairy nanoparticle LL-g-PEGMA [LL = Li_6.4La₃Zr_1.4Ta_0.6O₁₂, PEGMA = poly(oligo(ethylene glycol) methyl ether methacrylate)], followed by in situ cationic ring-opening polymerization of 1,3-dioxolane. The resulting ultrathin QSCE-BPL/LPE/PDL (19 μm) possesses a unique asymmetric architecture comprising a rigid layer of hairy nanoparticles to suppress dendrite penetration and a composite layer to ensure good interfacial contact with the cathode. The grafted PLiSTFSI side chains enable single Li⁺ conduction to reduce concentration polarization, and the PEGMA side chains promote lithium salt dissociation to accelerate Li⁺ transport. This design yields a three-dimensional porous network that provides continuous and fast Li⁺ transport pathways. The optimized electrolyte achieves a high ionic conductivity of 5.44 × 10⁻⁴ S cm⁻¹ and a Li⁺ transference number of 0.67 at room temperature. Consequently, Li/LiFePO₄ cells with QSCE-BPL/LPE/PDL can operate stably for 200 cycles with a high-capacity retention of 94% at 0.5 C. This study provides a feasible molecular engineering strategy for developing high-performance and safe lithium metal batteries.