Effect of sodium concentration on the structure and electrochemical properties of Na MnO2+ cathode materials

Sodium-ion batteries (SIBs) experience a re-emerging academic interest due to their low cost and high abundance as compared with lithium-ion batteries (LIBs) which have considerably increased the worldwide cost due to high actual demand. At present, a representative amount of cathode/anode SIBs materials are developed; facilitating the Na+ insertion mechanism understanding and the respective influence on structure change, which in most cases it is directly related to sodium concentration. In this work, the rheological phase reaction method is used to synthesize five types of NaxMnO2+z materials with different sodium content and use them as the cathode materials for SIBs. The physical properties and electrochemical performances of NaxMnO2+z materials with different concentrations are investigated by physical characterization means, electrochemical tests, and a series of computational methods. Inductively coupled plasma optical emission spectrometer (ICP-OES) test results indicate that the right materials have been successfully synthesized, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements show how the changes in sodium concentration significantly impact the morphology of the formed particles. In the results of electrochemical investigations, NMO-0.67 material has a high initial specific discharge capacity, but NMO-0.44 material has a reasonable cycling stability, keeping its discharge specific capacity of 83.06 mAh/g after 1000 cycles at a high current density of 360 mA g−1. Galvanostatic intermittent titration technique (GITT) testing and pseudo-capacitance analyses are also used to disclose the dynamic properties of NMO-0.44 material. In conclusion, the rheological phase reaction approach may be used to successfully create NaxMnO2+z materials, and variations in sodium content have a big impact on their structure and electrochemical performance.