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A new strategy of cobalt boride coating diamond phase Prussian white cathode material to improve its structural stability

News from our correspondent (reporter Liu Runan) Recently, Zhao Junmei, a researcher in the Green Chemical Research Department of the Institute of Process Engineering, Chinese Academy of Sciences, teamed up with the team of the Institute of Physics, Chinese Academy of Sciences, and proposed a new strategy of coating diamond phase Prussian white cathode materials with cobalt boride at room temperature to improve their structural stability. The relevant research results were recently published in the Journal of Applied Chemistry in Germany.

The rhombic Prussian white lattice has less water of crystallization, high sodium content, high voltage and capacity, and is an excellent cathode material for sodium ion batteries. However, Prussian white, which is rich in manganese, is prone to trigger the Ginger Taylor effect during the charging and discharging process, ultimately leading to corrosion and dissolution of material particles, generation of intergranular cracks, continuous increase in interface impedance, and severe degradation of bulk structure. Introducing a suitable coating layer on its surface is the main solution to this problem. Conventional strategies such as carbon coating and metal oxide coating typically require high-temperature sintering, which will damage the Prussian white structure. Therefore, developing a strategy that can achieve encapsulation at room temperature is particularly important.

Cobalt boronate, as a type of "metallic glass", not only can achieve full coating of Prussian white, but also has good mechanical toughness, which can effectively suppress the side reactions between it and the electrolyte, reduce the dissolution of manganese elements, and constrain and buffer the anisotropic volume changes of Prussian white particles, thereby alleviating the generation of intergranular microcracks. In addition, cobalt boronate also exhibits dual conductivity of mixed electrons and ions, which can enhance the kinetic performance of Prussian white.

In the study, the author coated cobalt borate on the surface of Prussian white using a chemical wet coating method. The experimental results showed that the coated Prussian white exhibited a capacity retention rate of 80% after 1000 cycles at 5C magnification, while the uncoated sample only achieved a capacity retention rate of 41%. Based on the calculation of the total mass of positive and negative active substances, the energy density of the Prussian white full battery coated in the laboratory is close to the energy density of lithium iron phosphate under the same conditions. In addition, according to experimental calculations, the energy cost and cycle life cost of the Prussian white full battery coated with cobalt borohydride with hard carbon as the negative electrode are relatively low.