Long Cycle Life and High‐Rate Sodium Metal Batteries Enabled by an Active/Inactive Co‐Sn alloy Interface

Abstract Sodium‐metal batteries (SMBs) are considered as a promising route to realize a high energy density battery, showing potential for applications in large‐scale energy storage. However, the cycling stability and reversibility of the Na‐metal anode suffer from significant challenges because of the growth of Na dendrites. This study reports an active/inactive Co‐Sn alloy interface to suppress the growth of Na dendrites under harsh test conditions. In this interface, Sn provides abundant nucleation sites and Co plays a synergistic role in alleviating volume variation of Sn nanoparticles and increasing the interaction between Na and substrate, significantly promoting the uniform Na deposition and preventing the Na plating from the root of the deposited Na. Under High‐current‐density (12 mA cm −2 ) with a high depth of discharge (DOD, 66.67%), Na||Na can achieve stable cycling for over 4200 h at 4 mA h cm −2 . When paired with a high‐loading NaTi 2 (PO 4 ) 3 cathode (10 mg cm −2 ), SMB delivers an excellent performance (800 cycles) at a negative‐to‐positive electrode capacity (N/P) ratio up to 2.