Self-redox reaction of carbon in molten salt for anode materials of lithium/sodium-ion batteries

Preparation of carbonaceous anode with excellent electrochemical performance is important for the utilization of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, carbon powder was synthesized from CaCO3 and CaC2 in CaCl2-NaCl molten salt. The reaction mechanism was discussed in thermodynamics and kinetics. Microstructure of the carbon powder was systemically characterized. Electrochemical performance of the carbon powder was evaluated as anode materials of LIBs and SIBs. The results showed that molten salt can transfer the carbonization process from a solid-solid process to a liquid-solid process. The kinetic barrier of CaO layers on the raw materials was removed in molten salt. The products exhibited better lithium (reversible capacity of ~480 mAhg−1 after 200 cycles and reversible capacity of ~250 mAh·g−1 at 1000 mAg−1) and sodium (reversible capacity of ~290 mAhg−1 after 200 cycles and reversible capacity of ~180 mAh·g−1 at 5000 mA·g−1) storage performance than commercial graphite. This method was easy and efficient to recover more than 70 wt% of carbon in the raw materials within 15 min •Carbon material was prepared by self-redox reaction of C element in molten salt.•Molten salt transferred a solid-solid reaction to a liquid-solid reaction.•CaO barrier for carbonization was removed by CaCl2-based molten salt.•Morphology and structure of products were modified by varying working temperature.•Carbon product presented superior performance than commercial graphite anode.