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

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–Na2/3Ni1/3Mn1/3Ti1/3O2 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.