High-Entropy Cl Substitution Promotes High Specific Capacity and Specific Energy Release from Sodium Manganate for Sodium-Ion Batteries

Poor electronic conductivity, low potential plateau, rapid capacity decay, and poor rate capability are critical challenges hindering the development of layered transition metal oxides such as P2-Na 0.7 MnO 2 . To address these issues, a high-entropy design combined with Cl substitution has been implemented, resulting in the material P2-Na 0.7 Li 0.02 K 0.02 Mg 0.02 Fe 0.05 Cu 0.05 Ni 0.25 Ti 0.02 Nb 0.02 Mn 0.59 O 1.93 Cl 0.07 . Hall effect tests reveal a transition from hole-dominated to electron-dominated conduction, significantly improving the Na + transport kinetics, enhancing electronic conductivity, and facilitating the release of a high specific capacity and specific energy. Notably, the bulk carrier concentration increases from 1.63 × 10 11 to 2.63 × 10 12 cm –3, the surface carrier concentration rises from 2.47 × 10 10 to 2.16 × 10 11 cm –2, and the mobility improves from 322.7 to 455.9 cm 2 (V s) −1 . Consequently, the electronic conductivity undergoes a remarkable 20-fold increase from 8.44 × 10 –6 to 1.915 × 10 –4 S cm –1 . The material delivers a reversible capacity of 196.80 mAh g –1 and a specific energy of 587.07 Wh kg –1 at a current rate of 0.05 C.