Synergistic Engineering of Electronic Structure and Interfacial Field via a 3D Heterostructure for Stable Sodium Metal Batteries

Abstract

Uneven distribution of electric field and sodium ion on the sodium metal anode surface is identified as the key factor triggering dendrite growth, which severely compromises the energy density and cycle life of batteries. Herein, a sodiophilic heterostructure with Sn₄P₃ nanoparticles encapsulated in N/P codoped graphene-like nanotubes (Sn₄P₃/NPGTs) is synthesized through the integration of chemical vapor deposition and in situ phosphorization. Rich active sites constructed by N/P codoping modulate the local electronic structure effectively, facilitating uniform Na⁺ distribution and adsorption while reducing the nucleation overpotential. The interfacial electric field formed at the heterogeneous interface exerts electrostatic forces on Na⁺, inducing ionic rectification, directional migration, and confined deposition of Na⁺ within the channels. In addition, the synergistic mechanism for improved Na⁺ deposition behavior is unraveled in-depth through in situ optical microscopy characterization, COMSOL simulations, in situ XRD analysis, and density functional theory calculations at multiple scales. Asymmetric cells remain stable for 1500 cycles at 3.0 mA cm^-2 and 1.0 mAh cm^-2, and the corresponding symmetric cells display a lifespan exceeding 2000 h. Pairing with either low-voltage (NaTi₂(PO₄)₃) or high-voltage (Na₃V₂(PO₄)₃) cathodes, the full cells exhibit excellent cycling stability.