Observation and suppression of metallic and metallic-like plating on hard carbon for high-performance sodium-ion batteries

Increasing the lifespan of Na-ion batteries (NIBs) is one of the primary requirements for stationary energy storage. Metallic and metallic-like Na plating on hard carbon (HC) could be one of the main causes for degraded performance during cycling, but the mechanism remains unclear. Here, we systematically investigate the plating phenomenon on HC under various cycling conditions in NIBs. We reveal that underpotential deposition (UPD) could potentially trigger the metallic-like plating on the surface of HC electrodes. In-situ distribution of relaxation time (DRT) analysis provides an effective indictor to identify the occurring of metallic and metallic-like Na plating on HC electrode by probing the time constant for charge transfer process. Based on the understanding, we apply a uniform nano porous coating layer on HC electrode to restrict potential UPD on the HC electrode surface but allow uniform Na+ transport across interface, which greatly suppress the plating phenomenon, leading to significantly improved cycling stability of NIBs.