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

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_0.7MnO₂. To address these issues, a high-entropy design combined with Cl substitution has been implemented, resulting in the material P2-Na_0.7Li_0.02K_0.02Mg_0.02Fe_0.05Cu_0.05Ni_0.25Ti_0.02Nb_0.02Mn_0.59O_1.93Cl_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 × 10¹¹ to 2.63 × 10¹² cm^-3, the surface carrier concentration rises from 2.47 × 10¹⁰ to 2.16 × 10¹¹ cm^-2, and the mobility improves from 322.7 to 455.9 cm² (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.