High Performance Carbon Anode Materials For Sodium Ion Batteries Derived From Coal Based Heavy Organic Matters

Lithium-ion batteries,sodium-ion batteries and other secondary batteries will play an increasingly important role in the development and utilization of clean renewable energy such as wind energy,solar energy and water energy.At the same time,the development of electric vehicles and large-scale energy storage systems will require a sharp rise in the number of energy storage and conversion equipment.Because of the abundant sodium resources and relatively low cost,the replacement of lithium-ion batteries in energy storage grid and other occasions with low energy density requirements will greatly relieve the pressure brought by the lack of lithium resources and reduce the economic cost of the development of new energy technology.At present,due to the size effect of sodium ions and other problems,no suitable anode material has been developed for commercial application of sodium ion batteries.Carbon-based materials are expected to become ideal anode materials for sodium ion batteries because of their good electrochemical characteristics.Carbon precursors with a wide range of sources and low cost can be used to prepare high-performance carbon anode materials for sodium ion batteries on a large scale with practical significance.In order to meet the above problems and practical needs,hard carbon and sulfur-doping carbon anode materials with large interlayer spacing were prepared by wet oxidation pretreatment and heteroatom introduction using cheap and easily available coal-based heavy organic compounds as precursors.The specific research contents are as follows:A mild wet oxidation strategy for preparation of hard carbon anodes with low-cost coal liquefaction residue?CLR?extract as precursor is reported.The introduction of oxygen-containing functionalities by wet oxidation with hydrogen peroxide at a mild condition not only triggers the thermoplastic to thermoset transition of the precursor but also inhibits its graphitization tendency in the high-temperature carbonization process.The obtained hard carbon?carbonized at 1200 ??anode with the interlayer space of 0.376 nm showed a high reversible capacity(301.2 m Ah g^-1)and an excellent cycling performance,displaying a capacity retention rate of 94% after 100 cycles.In addition,the current mild wet oxidation strategy can be extended to other carbon precursors to facilitate the low-cost and high-performance hard carbon anodes for SIBs.Sulfur-doped pitch-based carbon materials with high sulfur content were successfully prepared by two-step heat treatment at low and high temperatures,using medium-temperature coal tar pitch as carbon source and sublimated sulfur as sulfur source.The effects of carbonization temperature on the composition,structure and electrochemical properties of the materials were investigated.The experimental results show that with the increase of carbonization temperature,the sulfur content in the material decreases obviously,while the loss of sulfur leads to the change of carbon structure,and the specific surface area and interlayer spacing of the material increase gradually.Among them,the sulfur content of the material carbonized at 800 ??SC-800?reaches 20.19 wt.%,and the interlayer spacing is 0.368 nm.At the current density of 0.1 A g^-1,the reversible capacity reaches 482.8 m Ah g^-1 at the first time.At the current density of 0.5 A g^-1 and 5 A g^-1,the specific capacity of the material remains 245.9 m Ah g^-1 and 103.7 m Ah g^-1 after 500 cycles and 1000 cycles,showing the best sodium storage performance which is attributed to the high sulfur content,large interlayer spacing and suitable pore structure.