Checkerboard-structured Ga₄Na–In alloy interface for mechanically reinforced and dendrite-free sodium metal anodes

Dendritic proliferation and intrinsic instability of solid-electrolyte interfaces (SEIs) continue to impede the practical deployment of sodium metal anodes in sodium metal batteries (SMBs). In this study, a checkerboard-structured Ga₄Na–In alloy interfacial layer was introduced, formed through a spontaneous in situ reduction-alloying reaction between metallic sodium and GaCl₃/InCl₃ precursors. Within this architecture, the Ga₄Na intermetallic matrix functions as a rigid “chessboard” that homogenizes Na⁺ flux and resists dendrite penetration, whereas the dispersed metallic In particles, acting as compliant “chess pieces”, accommodate local stress during cycling. Guided by the intrinsic reactivity hierarchy (Ga > Zn > In), this multi-phase configuration yielded a dense, ion-conductive, and mechanically reinforced interfacial layer. Sodium symmetric cells incorporating this alloy interface achieved ultrastable cycling for more than 1600 h at 1 mA cm⁻², with minimal polarization. The full cells coupled with Na₃V₂(PO₄)₃ cathodes retained 90.1 % of their capacity after 600 cycles, markedly surpassing the performance of conventional sodium batteries. This study establishes a chessboard-inspired alloy interface engineering strategy that integrates chemical selectivity with mechanical adaptability, providing a scalable route toward dendrite-free sodium metal anodes and enabling substantial improvements in long-term electrochemical stability and durability.