Design of Soft/Hard Interfaces with Stress Variation for Improved Sodium Ion Storage

Abstract Alloy anode materials experience substantial volume changes during electrochemical cycling, necessitating effective stress management to improve cycling performance. This study introduces a novel soft−hard interface design approach, which modifies the interlayer structure of Bi 2 Te 3 /MXene for the first time. Bi 2 Te 3 is systematically assembled between MXene nanosheets via van der Waals forces, yielding a mechanically stratified architecture that combines both soft and hard components. In this configuration, MXene serves as a flexible buffer layer, mitigating the significant volume fluctuations of Bi 2 Te 3 during Na‐ion intercalation and de‐intercalation, while concurrently establishing a conductive network that promotes rapid charge transfer. In‐situ TEM analysis demonstrates a rapid and reversible intercalation/de‐intercalation process between the Bi 2 Te 3 and MXene layers, which is pivotal for enhancing rate capability and cycling stability of the material. Theoretical calculations and COMSOL simulations further elucidate that MXene markedly improves charge transfer in Bi 2 Te 3 and mitigates its volume expansion. As a result, the Bi 2 Te 3 /MXene composite exhibits exceptional electrochemical performance. This work not only showcases an effective synthesis strategy but also highlights the critical role of interfacial interactions and structural design in stress alleviation development.