Bifunctional sodium compensation of anodes for hybrid sodium-ion capacitors

The low initial Coulombic efficiency (ICE) for the electrodes which stems from electrolyte decomposition and irreversible sodium uptake by the material itself, is one of the reasons limiting the large-scale sodium-ion capacitors (SICs). Here, we report a simple but precise bifunctional presodiation of the Nb2O5 anode (as a typical example) using sodium naphthalene/2-methyltetrahydrofuran as a pre-sodiated agent. The pre-sodiated agent realizes the pre-activation to achieve stable cycling of NaxNb(2)O(5), thus compensating the irreversible Na uptake. Moreover, this process offsets the electrolyte decomposition loss, and facilitates the formation of a robust inorganic-rich solid electrolyte interphase layer. Stable and high-energy SIC devices are achieved by compensating the interphase and bulk sodium loss of Nb2O5 anodes. This work provides new insights into tuning the ICE of sodium-storage electrodes for next-generation and scaled-up applications of SICs.