Synergistic PAM@MXene hydrogel interlayer regulates Sn deposition behavior for highly stable Sn anodes in aqueous tin-ion batteries

Aqueous tin-ion batteries represent a promising candidate for safe and cost-effective energy storage, owing to the dendrite-free property of Sn metal anode, but their development is hindered by interfacial instability that leads to the “dead Sn” accumulation and severe side reactions. Herein, an integrated organic-inorganic PAM@MXene composite hydrogel interlayer is constructed on the Sn metal anode to engineer a stable interface. The hydrophilic PAM network guides Sn²⁺ migration and confines interfacial water, while the MXene homogenizes the electric field, promotes ion transport and provides uniform nucleation sites. Their synergy fundamentally optimizes the nucleation kinetics, deposition morphology and interfacial reactivity, leading to the effective inhibition of “dead Sn” accumulation and side reactions. As a result, the symmetric cell assembled with PAM@MXene-Sn electrodes exhibits stable operation for 2,600 h, and the PAM@MXene-Sn||Cu asymmetric cell achieves an ultra-long life of 20,000 cycles with an average Coulombic efficiency of 99.99%. Also, the PAM@MXene-Sn||MnO₂ full cell exhibits negligible capacity decay after 6,000 cycles at 20 mA cm^-2. This work not only presents an effective interfacial design for stable Sn anodes, but also demonstrates a generalizable strategy of organic-inorganic synergy for regulating interfacial behavior for developing highly reversible tin-ion batteries.