Interfacial Protection Engineering of Sodium Nanoparticles toward Dendrite‐Free and Long‐Life Sodium Metal Battery

Abstract The instability of interfacial solid‐electrolyte interphase (SEI) layer of metallic sodium (Na) anode during cycles results in the rapid capacity decay of sodium metal batteries (SMBs). Herein, the concept of interfacial protection engineering of Na nanoparticles (Na‐NPs) is proposed first to achieve stable, dendrite‐free, and long‐life SMB. Employing an ion‐exchange strategy, conformal Sn‐Na alloy‐SEI on the interface of Na‐NPs is constructed, forming Sn@Na‐NPs. The stable alloy‐based SEI layer possesses the following three advantages: 1) significantly enhancing the transport dynamics of Na + ions and electrons; 2) enabling the well‐distributed deposition of Na + ions to avoid the growth of dendrites; and 3) protecting the Sn@Na‐NPs anode from the attack of electrolyte, thereby reducing the parasitic reaction and boosting the Coulombic efficiency of SMBs. Because of these virtues, the symmetric Sn@Na‐NPs cell shows an ultralow voltage hysteresis of 0.54 V at 10 mA cm −2 after 600 h. Paired with the Na 3 V 2 (PO 4 ) 2 O 2 F (NaVPF) cathode, the NaVPF‐Sn@Na‐NPs full cell exhibits an initial discharge capacity of 89.2 mAh g −1 at 1 C and a high capacity retention of 81.6% after 600 cycles.