Lattice regulation strategy for constructing high-rate performance Na0.44Mn0.895Ti0.1Mg0.005O2 sodium-ion batteries cathode materials

Na0.44MnO2 has received much interest as a potential cathode material for Sodium-ion batteries (SIBs) because of its unique tunnel structure and the ease of Na+ insertion/extraction. Therefore, the size and stability of the tunnel structure are critical factors in solving its low-rate performance and cycle stability. Herein, a lattice regulation strategy to enlarge the size in favor of Na+ insertion/extraction and to maintain the stability of the tunnel structure of Na0.44MnO2 by Ti and trace Mg co-doping is reported for the first time. Subsequently, the Na0.44Mn0.895Ti0.1Mg0.005O2 (NMO-TM) material is synthesized with Ti/Mg co-doping. The structure and phase composition of the as-synthesized samples are investigated through X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The results indicate that Ti/Mg has been effectively doped into the crystal structure of Na0.44MnO2 while it maintains the stability of the tunnel structure. The material was used as cathode materials of rechargeable sodium-ion batteries. As a result, at a 1 C rate, the NMO-TM sample exhibits a considerable capacity of 110 mAh g-1, with retention rates of up to 93.6 % after 200 cycles. Even at a higher cycle rate of 20 C, the NMO-TM sample maintains a specific capacity of 80.0 mAh g-1, with a retention rate of 67 % after 2000 cycles. This work provides a facile strategy for regulating the tunnel structure to get stable and high-rate performance of cathode materials.