Constructing a Stable Elastomer Electrolyte Containing Tin‐Based Additives for High‐Performance Na‐Metal Batteries

Abstract Solid polymer electrolytes (SPEs), attractive for Na‐metal batteries due to low cost, non‐toxicity and flexibility, often exhibit the low ionic conductivity or poor extensibility. Herein, Sn salt‐containing plastic crystal/elastomer‐based polymer electrolyte (Sn‐PCEPE) is developed for Na metal batteries. Butyl acrylate (BA)‐based elastomer framework displays excellent mechanical toughness (elongation at break of 340%), which makes Sn‐PCEPE accommodate Na anode volume change over cycling. Dense and stable solid electrolyte interphase (SEI) induced by Sn salt and fluoroethylene carbonate (FEC) significantly inhibits side reactions between Na and Sn‐PCEPE. Especially, the theoretical/experimental data suggest that Sn salt reacts with Na to form NaSn alloy, which reduces Na + diffusion energy barrier, resulting in low Na plating/stripping overpotentials and Na dendrite‐free growth. Furthermore, the plastic crystal introduction greatly enhances ionic conductivity (0.77 mS cm −1 ) of Sn‐PCEPE. Therefore, the Sn‐PCEPE‐based symmetric battery exhibits high cycling stability for 1800 h and low overpotentials of 0.13 V under 0.1 mA cm −2 . When coupled with Na 3 V 2 (PO 4 ) 3 cathodes, the full batteries with Sn‐PCEPE display higher capacity‐retention rate (86%) after 1100 cycles at 1C (1C = 117 mA g −1 ), lower voltage hysteresis, and better rate performance compared with the PCEPE‐based batteries. More interestingly, the Sn‐PCEPE‐containing pouch batteries normally work even under harsh testing conditions.