Copper and Zirconium Codoped O3-Type Sodium Iron and Manganese Oxide as the Cobalt/Nickel-Free High-Capacity and Air-Stable Cathode for Sodium-Ion Batteries

Abstract

Considering the abundance of iron and manganese within the Earth's crust, the cathode O3-NaFe_0.5Mn_0.5O₂ has shown great potential for large-scale energy storage. Following the strategy of introducing specific heteroelements to optimize the structural stability for energy storage, the work has obtained an O3-type NaFe_0.4Mn_0.49Cu_0.1Zr_0.01O₂ that exhibits enhanced electrochemical performance and air stability. It displays an initial reversible capacity of 147.5 mAh g^-1 at 0.1C between 2 and 4.1 V, a capacity retention ratio exceeding 69.6% after 100 cycles at 0.2C, and a discharge capacity of 70.8 mAh g^-1 at a high rate of 5C, which is superior to that of O3-NaFe_0.5Mn_0.5O₂. The codoping of Cu/Zr reserves the layered O3 structure and enlarges the interlayer spacing, promoting the diffusion of Na⁺. In addition, the structural stability and air stability observed by Cu-doping is well maintained <i>via</i> the incorporation of extra Zr favoring a highly reversible phase conversion process. Thus, this work has demonstrated an efficient strategy for developing cobalt/nickel-free high-capacity and air-stable cathodes for sodium-ion batteries.