A Simple Electrode‐Level Chemical Presodiation Route by Solution Spraying to Improve the Energy Density of Sodium‐Ion Batteries

The formation of a solid electrolyte interface (SEI) on the surface of a carbon anode consumes the active sodium ions from the cathode and reduces the energy density of sodium‐ion batteries (SIBs). Herein, a simple electrode‐level presodiation strategy by spraying a sodium naphthaline (Naph‐Na) solution onto a carbon electrode is reported, which compensates the initial sodium loss and improves the energy density of SIBs. After presodiation, an SEI layer is preformed on the surface of carbon anode before battery cycling. It is shown that a large irreversible capacity of 60 mAh g −1 is replenished and 20% increase of the first‐cycle Coulombic efficiency is achieved for a hard carbon anode using this presodiation strategy, and the energy density of a Na 0.9 [Cu 0.22 Fe 0.30 Mn 0.48 ]O 2 ||carbon full cell is increased from 141 to 240 Wh kg −1 by using the presodiated carbon anode. This simple and scalable electrode‐level chemical presodiation route also shows generality and value for the presodiation of other anodes in SIBs.