Synthesis, structure, and electrochemical properties of O′3-type monoclinic NaNi0.8Co0.15Al0.05O2 cathode materials for sodium-ion batteries

Abstract

Sodium-ion batteries (SIBs) have shown great promise in stationary energy storage due to the abundance of low-cost sodium and the similar electrochemical mechanism to that of commercial lithium-ion batteries. O3-type layered NaNiO₂ is considered as one of the most promising cathode materials for SIBs. However, it suffers from irreversible phase transitions, sluggish kinetics and poor mass-production techniques, incurring rapid capacity fading, poor rate performance and limited practical applications. Herein, a novel O′3-type layered NaNi_0.8Co_0.15Al_0.05O₂ with a monoclinic phase structure is synthesized by a scalable co-precipitation method followed by a high-temperature calcination process. The substitution of similar ionic radii and same valence Co³⁺ and Al³⁺ for Ni³⁺ enhances the structural stability and improves the reversibility of phase transitions during (de)sodiation processes. The hierarchical architecture of microspheres and assembling of primary nanocrystals, can provide high compacted density and supply short diffusion paths for sodium ion/electron transport simultaneously. Because of these superior merits, the monoclinic NaNi_0.8Co_0.15Al_0.05O₂ microspheres exhibit an initial reversible capacity of 153.9 mA h g⁻¹ with a coulombic efficiency of 89.1% at 0.1C and remarkable capacity retention of 86.7% after 200 cycles at 1C, potentially serving as a high capacity and stable cathode material for SIB applications.