Ternary Heterostructures With Gradient Built-In Electric Fields Through Stepwise Screening for Highly Reversible Sodium Storage at Low Temperature.

Abstract

Heterostructure engineering is considered a promising approach to improve sodium storage at low temperatures (LTs). However, the trial-and-error fabrication method as well as insufficient interface control dimensions in traditional two-component heterojunctions result in low efficiency and limited electrochemical performance improvement. Herein, a screening-driven strategy guided by theoretical descriptors is proposed to identify MoS₂/MoO₂ as the optimal binary heterostructure for improving sodium storage performance at LTs. Importantly, this result reveals a clear relationship between heterostructure configuration and electrochemical performance, where the work function (W_f) difference and the resulting charge redistribution regulate Na⁺ storage behavior. Inspired by this understanding, Ti₃C₂T_x MXene is introduced to construct a multi-interface system with cascaded W_f alignment, establishing a gradient built-in electric field that overcomes the localized modulation of conventional binary heterostructures. Such heterostructure induces an electron-enriched region that acts as a Na⁺ reservoir, thereby facilitating efficient Na⁺ storage and transport at LTs. Meanwhile, the multiphase heterointerface optimizes the reaction pathway and mitigates kinetic limitations. Consequently, the MoS₂/MoO₂/Ti₃C₂T_x ternary heterostructure delivers high reversible capacity, excellent rate performance, and robust cycling stability even at -20°C. This work establishes a general and predictive strategy for accelerating the rational design of high-performance electrodes through the proposed screening framework.