Cationic High-Entropy Doping Endows O3-Type Na-Ni-Mn-O-Layered Cathode with High Energy Density and Sustainable Sodium Storage

Abstract

Although O3-type layered oxides featuring an open framework demonstrate potential as high-capacity cathode materials for sodium-ion batteries, such cathode materials are confronted with commercial limitations, including intricate phase transition mechanisms, structural degradation, and sluggish sodium ion diffusion kinetics, culminating in rapid capacity fading and severe performance deterioration. Cationic high-entropy doping was adopted to fabricate the O3-Na_0.95Mg_0.045Ni_0.22Fe_0.045Cu_0.08Co_0.08Ti_0.08Mn_0.45O₂ (HE-NNMO) cathode. The HE-NNMO cathode manifests acceptable Na storage capability, rapid electron transmission, apparent pseudocapacitance effect, and preferable structural integrity. HE-NNMO achieved an initial discharge specific capacity of 142.2 mAh g⁻¹ at a current density of 50 mA g⁻¹ and maintained a capacity retention rate of 93.0% after 100 cycles at a current density of 500 mA g⁻¹. Additionally, it achieved an ultrahigh specific energy of 431.8 Wh kg⁻¹ (based on the cathode active material) at a current density of 0.05 A g⁻¹, and the Coulombic efficiency reached 89%. Notably, in the full cell, HE-NNMO//H`C maintained capacity retention rates of 78.8% and 65.7% after 200 and 1200 cycles at current densities of 200 mA g⁻¹ and 1 A g⁻¹, respectively, demonstrating its practical applicability. This study provides insights for the high-entropy design of O3-type layered oxides in sodium-ion batteries.