ИСТИНА

Sodium-ion batteries (SIBs) are the most promising post-lithium batteries available today. They possess several advantages over other post-lithium systems as well as lithium-ion batteries themselves. For instance, SIBs are more environmentally friendly and less expensive due to the widespread availability of sodium in the Earth's crust. High initial coulombic efficiency (ICE), high specific capacity, and good stability are required for the anode materials to commercialize this technology. Hard carbon is a non-graphitizable form of carbon that contains curved graphene-like layers in its structure. The structural disorder of hard carbon enables sodium ions to intercalate into expanded interlayer space of carbon and occupy other positions, such as closed pores. This material is the best candidate for the role of anode material in SIBs due to its high electrochemical capacity compared to graphite, which has limited sodium ion intercalation [1]. Numerous synthesis methods for hard carbon exist, some of which aim to increase the specific capacity of hard carbon. Template-based synthesis methods are used to create materials with a high microporosity, where salts of metals such as magnesium gluconate or citrate can serve as templates. This approach enables the production of materials with very high specific capacities of up to 480 mAh/g [2]. The aim of this work is to carry out template synthesis of hard carbon with high specific capacity using magnesium and calcium salts as template. For the synthesis of hard carbon, carbonization of a glucose solution in air followed by high-temperature annealing was employed. After the initial annealing, which took place at temperatures of 600/800 °C in an inert atmosphere, the templates were removed by one molar hydrochloric acid. Following that, the material was subjected to a secondary annealing at temperatures of 1300/1500 °C in an inert atmosphere. The samples were analyzed using low temperature nitrogen adsorption, X-ray diffraction, and scanning electron microscopy techniques. Additionally, electrochemical tests were conducted on the obtained materials in sodium half-cells. The obtained samples exhibited a discharge capacity of 260 mAh/g and an ICE of 59% for the magnesium-based material, and a discharge capacity of 228 mAh/g with an ICE of 58% for the calcium-based material. Based on galvanostatic testing results, hard carbons obtained through annealing at 600°C followed by a secondary annealing at 1300°C demonstrated the highest values of discharge capacity and ICE. It was found that insufficient removal of oxides reduces the discharge capacity of materials. In the future, the work will be aimed at optimizing the removal conditions to improve the discharge capacity. This work is supported by Russian Science Foundation (Project No. 17-73-30006-P).