Manipulating irreversible phase transition of NaCrO2 towards an effective sodium compensation additive for superior sodium-ion full cells

During the first charge process of full cells, a solid electrolyte interphase (SEI) film is formed when the active ion from the cathode is consumed, resulting in irreversible capacity loss. This phenomenon has shown to be more serious in sodium-ion full cells than in lithium-ion full cells. Although many strategies have been employed to alleviate the loss of sodium ions, such as presodiation and construction of an artificial solid electrolyte interface, they are both cumbersome and time-consuming. For the first time, NaCrO2 was used as an effective self-sacrificing sodium compensation additive in sodium-ion full cells due to the irreversible phase transition of NaCrO2 in a high voltage region can deliver an irreversible capacity of up to 230 mAh g−1. Based on this design, sodium-ion full cells coupled with hard carbon as the anode exhibited higher capacity, less polarization, greater energy density, and superior cycle stability than those of a pristine electrode. This is mainly attributed to the removal of sodium ions from NaCrO2, which compensates for the loss of sodium ions consumed during the formation of the SEI film on the anode surface during the first charge process. Overall, this work opens up a new avenue for exploring sodium compensation strategy and contributing to practical application of sodium-ion full cells.