Covalently Anchored Multifunctional Interlayer Enables Ultrastable and Fast - Charging Composite Solid - State Sodium Metal Batteries.

Xu, Shuangwu; Xiang, Shaoe; Mao, Pengcheng; Sun, Huapeng; Tu, Jian; Sun, Dan; Ji, Xiaobo; Tang, Yougen et al. · Adv Mater · 2026

basic_science · Level V

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Abstract

The practical application of composite solid-state sodium metal batteries is critically limited by poor organic-inorganic compatibility, causing particle agglomeration, high interfacial resistance, and dendrite growth. Here, a covalent surface grafting strategy constructs a multifunctional interlayer covalently anchored on Na<sub>3</sub>Zr<sub>2</sub>Si<sub>2</sub>PO<sub>12</sub>, featuring a cross‑linked siloxane network and terminal ─NH<sub>2</sub> groups. Covalent anchorage transforms inert particle surfaces into dispersible units, while ─NH<sub>2</sub> groups anchor TFSI<sup>-</sup> and confine residual solvent via hydrogen bonding and Lewis acid‑base interactions. This dual regulation decouples ion transport from side reactions, yielding a high Na<sup>+</sup> transference number (0.58) and a stable, NaF‑rich, thin solid‑electrolyte interphase (SEI). The optimized electrolyte enables symmetric cells with exceptional cycling stability and high critical current density (CCD). Full cells achieve fast‑charging (92 mAh g<sup>-1</sup> at 15 C) and ultralong cycle life (76.4% retention after 7000 cycles at 10 C). A flexible pouch cell retains 97% capacity after 150 cycles. This work establishes that precise molecular‑level interfacial design, rather than simple physical blending, is key to high‑performance, dendrite‑resistant solid‑state sodium batteries.