Mechanism and cost of Zn substitution to boost the specific capacity of NaNi1/3Fe1/3Mn1/3O2 for sodium-ion batteries

This paper explores the mechanism and cost of partially replacing nickel with zinc to boost the specific capacity of NaNi_1/3Fe_1/3Mn_1/3O₂ cathode material for sodium-ion batteries. The specific capacity of Na_0.9Ni_4/15Fe_1/3Mn_1/3Zn_1/15O₂ material increases by lowering the voltage for the P3-OP2 phase transition within the voltage range of 2.0–4.0 V, although its theoretical capacity reduces due to the decline in optimal sodium content and the electrochemical inactivity of zinc. Besides, the reversible P3-OP2 phase transition shows negligible effects on its cycling performance. However, the OP2-O3′ phase transition, coupled with the oxidation and release of lattice oxygen, occurs at a cut-off voltage exceeding 4.0 V, which deteriorates its cycle performance. The paper presents a novel approach for designing an O3-type cathode with a high specific capacity, which maximizes the reversible phase transition within the targeted voltage range by selecting appropriate components.