Sodium-ion battery technology rapidly develops in the post-lithium-ion landscape. Among the variety of studied anode materials, hard carbons appear to be the realistic candidates because of their electrochemical performance and relative ease of production. This class of materials can be obtained from a variety of precursors, and the most ecologically important and interesting route is the synthesis from biomass. In the present work, for the first time, hard carbons were obtained from Heracleum sosnowskyi, a highly invasive plant, which is dangerous for humans and can cause skin burns but produces a large amount of green biomass in a short time. We proposed a simple synthesis method that includes the pretreatment stage and further carbonization at 1300 °C. The effect of the pretreatment of giant hogweed on the hard carbon electrochemical properties was studied. Obtained materials demonstrate >220 mAh g⁻¹ of the discharge capacity, high values of the initial Coulombic efficiency reaching 87% and capacity retention of 95% after 100 charge-discharge cycles in sodium half-cells. Key parameters of the materials were examined by means of different analytical, spectroscopic and microscopic techniques. The possibility of using the giant hogweed-based hard carbons in real batteries is demonstrated with full sodium-ion cells with NASICON-type Na₃V₂(PO₄)₃ cathode material.

With sodium-ion batteries (SIBs) finding widespread application, the demand grows for hard carbon, the most popular anode material for SIBs. Hydrothermal carbonization facilitates the production of hard carbon with desired characteristics from various sources. Despite the considerable volume of literature addressing this subject, there is a notable absence of investigations elucidating the relationship between synthesis conditions and the electrochemical characteristics of the product. Here we study systematically the influence of hydrothermal carbonization parameters on hard carbon characteristics and emphasize the potential of hard carbon as an anode material for SIBs. The initial Coulombic efficiency (ICE) is significantly affected by the particle size of the glucose-derived hard carbon, which, in turn, depends on glucose concentration in the initial solution, pH, and stirring regime. By optimizing the hydrothermal carbonization parameters, the ICE up to 91% and a good reversible capacity of ∼300 mAh g⁻¹ in a half cell are achieved. Full cells with Na₃(VO)₂(PO₄)₂F cathode material demonstrate ICE of about 80% and reversible capacity of up to 100 mAh g⁻¹ _cath. Considering the effective performance of pouch-cell SIB prototypes based on Na₃(VO)₂(PO₄)₂F and hard carbon, hydrothermal carbonization of glucose yields hard carbon with the necessary characteristics required for its successful application in SIBs.

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.

In the present work, we focus onthe experimental screening of selected electrolytes, which have been reported earlier in different works, as a good choice for high-voltage Li-ion batteries. Twenty-four solutions were studied by means of their high-voltage stability in lithium half-cells with idle electrode (C+PVDF) and the LiNi_0.5Mn_1.5O₄-based composite as a positive electrode. Some of the solutions were based on the standard 1 M LiPF₆ in EC:DMC:DEC = 1:1:1 with/without additives, such as fluoroethylene carbonate, lithium bis(oxalate) borate and lithium difluoro(oxalate)borate. More concentrated solutions of LiPF₆ in EC:DMC:DEC = 1:1:1 were also studied. In addition, the solutions of LiBF₄ and LiPF₆ in various solvents, such as sulfolane, adiponitrile and tris(trimethylsilyl) phosphate, atdifferent concentrations were investigated. A complex study, including cyclic voltammetry, galvanostatic cycling, impedance spectroscopy and ex situ PXRD and EDX, was applied for the first time to such a wide range of electrolytesto provide an objective assessment of the stability of the systems under study. We observed a better anodic stability, including a slower capacity fading during the cycling and lower charge transfer resistance, for the concentrated electrolytes and sulfolane-based solutions. Among the studied electrolytes, the concentrated LiPF₆ in EC:DEC:DMC = 1:1:1 performed the best, since it provided both low SEI resistance and stability of the LiNi_0.5Mn_1.5O₄ cathode material.