In situ composite solid electrolyte interphases enabling dendrite-free sodium metal batteries

Abstract

Given the limited reserves and high cost of lithium resources, research into cost-effective, high-performance energy storage devices beyond lithium-ion batteries has gained increasing attention. Sodium metal anodes, with their abundant reserves, low cost, high specific capacity (1160 mA h g⁻¹), and low redox potential (−2.714 V vs. the Standard Hydrogen Electrode (SHE)), are considered one of the most promising next-generation anode materials. However, the unstable solid electrolyte interphase (SEI) in sodium metal anodes leads to non-uniform diffusion and deposition of Na⁺, resulting in uncontrollable dendrite growth. During repeated charging/discharging processes, the growth of dendrites and the continuous fracture and regeneration of the SEI layer lead to the continuous loss of active sodium and coulombic efficiency (CE). To address this issue, this study reports an in situ generated organic/inorganic hybrid multifunctional solid electrolyte interface to effectively enhance the stability of the sodium metal anode. The inorganic components, NaF and Na₂S, serve as high ionic conductivity components, accelerating the transfer of Na⁺. The rich amide groups in the organic component exert a polar attraction to Na⁺, regulating the Na⁺ flux and alleviating the “tip effect” during metal deposition. Experiments show that the Na‖Na symmetric battery using this anode exhibits extremely low overpotential and stable plating/stripping behavior (cycling for over 2500 hours at 1 mA cm⁻² and 1 mA h cm⁻², with an ultra-low voltage of 15 mV). The full cell assembled with Na₃V₂(PO₄)₃ (NVP) demonstrates excellent rate and cycling performance, with a capacity retention rate of 90.3% after 1000 cycles at 1C and 89.2% after 800 cycles at a high rate of 5C.