Upshifted d-Band Center and Electron Delocalization in High-Entropy MXene Enabling Highly Reversible Anode-Free Sodium Batteries.

Anode-free sodium metal batteries (AFSMBs) have attracted significant attention owing to their exceptionally high theoretical energy density and low-cost advantages. However, their practical application is severely hindered by uncontrolled sodium dendrite growth and unstable electrode/electrolyte interfaces. Herein, we propose an interface modification strategy based on high-entropy MXene, (Ti1/5V1/5Zr1/5Nb1/5Ta1/5)2CTx (HE-MXene), to regulate the electronic structure of the current collector. It has been demonstrated that the synergistic interactions among multiple transition metal elements in HE-MXene upshift the d-band center and induce electron delocalization, which effectively enhance sodium ion adsorption and promote uniform charge transfer, ultimately facilitating homogeneous sodium deposition and the formation of an inorganic-rich SEI. As a result, the HE-MXene-modified electrode reduces the sodium nucleation overpotential to 6.2 mV. Specifically, the half-cell achieves stable cycling for over 400 h at 0.5 mA cm-2 and 1 mAh cm-2, while the symmetric cell delivers an extended lifespan exceeding 1500 h at 1 mA cm-2 and 1 mAh cm-2. This work elucidates the electronic mechanism by which interfacial modification layers optimize sodium deposition behavior and SEI chemistry at the atomic scale, offering perspectives for the design of high-performance AFSMBs.