Gradient-Structured sodiophilic skeleton integrated with spatial confinement effect Enables high-rate and ultra-stable Na metal batteries

Abstract

Despite the dendrite growth and volume change faced by Na metal anodes (SMAs) can be suppressed by constructing sodiophilic three-dimensional (3D) skeleton, the long-term cycling stability of SMAs under harsh work conditions (>10 mA cm⁻²; >5 mA h cm⁻²) is still unsatisfactory. Herein, a gradient-structured sodiophilic carbon skeleton, composed of carbon foam decorated with gradient-distributed Ag nanoparticles (Ag NPs@CF), is elaborately designed to enable the stable operation of SMAs even in harsh work environments. Firstly, the gradient sodiophilic structure of Ag NPs@CF directionally regulates the Na⁺ nucleation/growth behavior, homogenizing Na⁺ flux and electric field near the electrode and inhibiting dendrites formation. Secondly, the sodiophilic Ag NPs promote the formation of gradient solid electrolyte interphase, enhancing the interfacial stability and expediting Na⁺ transport kinetics at the interface. Furthermore, the open 3D structure of CF spatially confines Na deposition without volume change during cycling. Consequently, the Na-Ag NPs@CF symmetrical battery demonstrates stable cycling for over 2200h with an ultralow overpotential of 10.2 mV under harsh conditions of 10 mA cm⁻²/10 mA h cm⁻². Meanwhile, the assembled Na-Ag NPs@CF||NVPOF full cells show superior rate capability and cycling stability. The gradient sodiophilic structure proposed in this work sparks new insights for designing high-performance SMAs.