Enabling wide-temperature-adaptive, anode-less solid sodium batteries via electrolyte–substrate co–engineering

Single-ion polymer conductor (SIPC) electrolytes emerge as a promising solution for the construction of solid-state sodium metal batteries (SSMBs) by preferentially facilitating the Na⁺ transport, meanwhile suppressing anion mobility and concentration polarization. However, their practical use for pouch cell prototyping is hindered by insufficient ionic conductivity at room temperature (RT), poor mechanical strength, and interfacial incompatibility with reactive Na metal. Herein, this study proposed a SSMB configuration with a lean amount of Na metal source (N/P ratio of 0.4) that integrates a plasticized SIPC electrolyte with a pre-sodiated deposition substrate. The modular design of SIPC synergistically involves the mechanical stiff bacterial cellulose (BC) fibers, anion anchored poly(sodium 4-styrenesulfonate) salt (PSSNa) as well as in-situ polymerized vinyl ethyl carbonate (PVEC) with the optimized plasticizer. Upon the thin-layer (15 μm) membrane formation, the BC-PSSNa-PVEC/P electrolyte achieves impressive tensile strength (51.4 MPa), ionic conductivity (1.42 × 10⁻⁴ S cm⁻¹ at 30 °C) and close-to-unit cation transference ( t _Na+=0.92). Additionally, a 2 μm pre-sodiated Na₁₅Sn₄ interphase is constructed on the Cu foil, which enhances Na⁺ affinity and secures interfacial compatibility with the SIPC electrolyte. Upon the layered-stack assembly into a pouch-format cell, the Na₁₅Sn₄@Cu|BC-PSSNa-PVEC/P|Na₃V₂(PO₄)₃ model achieves the balanced energy density of 345.7 Wh kg⁻¹, extreme power output of 891.3 W kg⁻¹, as well as cycling endurance across a wide temperature range (−10–90 °C). Operando phase and electrochemical characterizations collectively confirm the reversible lattice breathing of cathode at both RT and 0 °C, along with the boosted Na⁺ diffusion kinetics at the pre-sodiated substrate/SIPC interphase, highlighting the feasibility and extendibility of the proposed lean-Na-metal SSMB design.