Hard carbon as anode material for metal-ion batteries

The development of large-scale energy storage systems based on the mature technology of lithium-ion batteries is hampered by the high cost of lithium. Therefore, analogous technologies based on other alkali metals (sodium and potassium) are being developed. Among various types of negative electrode (anode) materials for such batteries, carbon materials are most promising; in particular, hard carbon is of most interest. The present review addresses the current state of research on the structure, composition and properties of this type of material and gives analysis of methods of its preparation and investigation. Description of the microstructure of hard carbon is a highly ambiguous and challenging problem; therefore, the review pays special attention to various microstructural models. In addition, the methods of synthesis are systematized and the results of studies of the physicochemical properties of hard carbon are analyzed. The correlations between the preparation method, characteristics and electrochemical properties in metal-ion batteries are identified. A large array of results of electrochemical studies is considered, the views on the mechanisms of electrochemical interactions of Na⁺ and K⁺ cations with hard carbon are systematized, and the currently existing contradictions in various models of the interaction mechanisms are shown.Bibliography — 247 references.