Excellent\nPerformance of Sodium Ion Battery Cathode\nMaterials Benefiting from the Inorganic Acid Regulating Strategy

The cathode material NaNi<sub>1/3</sub>Fe<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub> (NFM111) is known as an O3-type layered\noxide for sodium\nion batteries. It has the advantages of high energy density and easy\nsynthesis. However, the residual alkali leads to capacity decay and\nair stability decline. And its storage and application are limited.\nThe residual alkali content on the surface of NFM111 is reduced through\nphosphoric acid treatment. The initial discharge capacity of the modified\nmaterial is 162 mA h g<sup>–1</sup> at 0.1 C. Meanwhile, the\nmaterial still has a capacity of 140.7 mA h g<sup>–1</sup> at\n0.1 C after exposure to air. This treatment strategy increases the\nspecific discharge capacity of the material at 25 and −20 °C\nand improves the cycle stability and air stability. It provides an\neffective and reliable method for the production and application of\nsodium ion battery cathode materials.