Regulating sodium deposition and interfacial chemistry via sulfur-embedded carbon spheres enables high-power Ah-level sodium-metal batteries

Sodium metal batteries offer high energy density and abundant resources, yet their cycling stability is hindered by uncontrolled Na dendrite growth, especially under high capacity and high-rate conditions. Although three-dimensional sodiophilic matrixes can enable uniform Na deposition, the large specific surface area often exacerbates interfacial side reactions, while excessive mass/volume fraction compromises the overall energy density and power performance. Herein, we design sulfur-embedded mesoporous hollow carbon spheres as a matrix for Na metal negative electrodes. The sulfur species not only guide confined nucleation and uniform deposition of Na within the carbon spheres, but also participate in forming Na2S nanocrystals in the solid electrolyte interphase. These nanocrystals facilitate the decomposition of fluoroethylene carbonate, contributing to a NaF-rich robust solid electrolyte interphase that stabilizes the interface. With only 5 wt% sulfur-embedded mesoporous hollow carbon spheres, the sodium composite electrode achieves stable cycling at high current density (up to 40 mA cm−2) and high areal capacity (up to 40 mAh cm−2). Notably, the pouch cells deliver high specific energy up to 178 Wh kg−1 and high specific power up to 420 W kg−1 when coupled with Na3V2(PO4)3, based on total cell mass, highlighting a feasible matrix design for practical high-performance sodium metal batteries. Sodium metal batteries offer high energy density but suffer from dendritic Na growth and unstable interphases. Here, authors design sulfur-embedded mesoporous carbon spheres that regulate Na deposition and form a robust NaF-rich interphase, enabling high power Ah-level sodium metal batteries with long cycle life.