Electronic Structure Modulation Enables Sodium Compensation in Cathode Organic Additives for Sodium-Ion Batteries

Abstract

To address the issue of reduced energy density in sodium-ion full cells due to irreversible sodium ion losses, the cathode sodium compensation additive method is the usual approach nowadays; however, finding efficient, low-voltage, and low-cost additives remains a challenge. This work develops a class of organic additives, i.e., N-substituted main-chain C organic compounds. Compared with all-C or O-substituted organics, the N-substituted organics show lower decomposition potentials due to the stronger electron-donating effect of N, and the potentials will be further reduced if other electron-donating groups are introduced. When introduced as an additive into a P2–Na_2/3Ni_1/3Mn_1/3Ti_1/3O₂ cathode, an addition of 10 wt % enhances the initial charging capacity from 96.3 to 189.4 mAh g^–1 and does not cause cycling or rate capability deterioration. The full cells paired with hard carbon anode exhibit higher energy densities (150.6 vs 235.1 Wh kg^–1), suggesting that such additives offer great potential for practical applications.