A stable tunnel-type cathode material based on Al-O bonds for sodium-ion batteries

Na_0.44MnO₂, a tunnel-type cathode material for sodium-ion batteries, has attracted attention because of its low cost and abundant raw materials. However, the cathode material has the problems of structural instability of manganese ion dissolution and migration caused by the Jahn-Teller effect during Na⁺ extraction and insertion. The bonding energy of the Al-O bond formed by Al substituted for Mn was higher than that of the Mn-O bond, which could alleviate the problems of lattice strain as well as the dissolution and migration of Mn ions during the cycle. Therefore, Na_0.44Mn_0.95Al_0.05O₂ was prepared by a high-temperature solid-state method. The structure and surface morphology of the prepared cathode material were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performance and kinetic properties of the cathode material were investigated. The cathode displayed a smooth charge-discharge curve with a highly reversible capacity of 127.8 mAh/g. Na⁺ storage was mainly governed by a capacitive mechanism.