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With the increasing demand for the efficient utilization of global resources, green strategies for the transformation of inferior coals to highly value-added products are largely required. In this study, a green approach was demonstrated for the conversion of inferior coals into crystalline graphite using a simple purification and high-efficiency electrochemical method. After being processed in the molten CaCl2 salt under 2.6 V at 950 °C for 6 h, the products presented a highly graphitic structure with high degree of graphitization. The as-prepared graphite was employed as a negative electrode material for lithium-ion batteries, delivering a highly reversible capacity of 510 mA h g−1 at 1C. High-performance lithium-ion storage represents an efficient green strategy to reuse inferior coals for conversion into value-added products via a more sustainable route. [ABSTRACT FROM AUTHOR]

It is extremely important to design and fabricate high capacitance and stable Coulombic efficiency capacitors for energy storage. Herein, nitrogen-doped graphene coated on flexible tantalum foil is developed as a cathode for aluminum-ion hybrid supercapacitors which are based on an ionic liquid electrolyte with 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl)/AlCl3. The results demonstrate that the nitrogen-doped graphene cathode offers a high capacitance of 254 F g−1, a Coulombic efficiency of ∼90% and a cycle life of 1000 at a current density of 0.3 A g−1. Meanwhile, the nitrogen-doped graphene cathode shows a capacitance of ∼130 F g−1, a Coulombic efficiency of almost 100% and a cycle life of 2000 at a higher current density of 2.0 A g−1. Moreover, the energy storage mechanism of the nitrogen-doped graphene in the aluminum-ion hybrid supercapacitors, that is, the dominant electrical double-layer capacitance (the adsorption and desorption of AlCi4− on the surface), and the intercalation/deintercalation in the nitrogen doped graphene, are confirmed. [ABSTRACT FROM AUTHOR]

A new Al-ion battery based on an affordable and nontoxic liquid electrolyte made from molten AlCl3/urea was assembled. As the cathode material, natural graphite shows two well-defined discharge voltage plateaus at about 1.9 and 1.5 V with a high specific capacity of 93 mA h g−1 and excellent coulombic efficiency (＞99%). The attractive capacity (about 78 mA h g−1) is retained even at a high current density of 1000 mA g−1. Moreover, no faster fading in capacity is observed after 500 cycles. This electrolyte could provide a new system for Al ion batteries, which can be used for large scale energy storage, owing to its cost advantages, high-rate capability and durability. [ABSTRACT FROM AUTHOR]