近年来,人们对利用低温炭化工艺制备煤基无定形炭材料作为锂离子电池(LIBs)和钠离子电池(SIBs)的负极材料产生了兴趣.然而,煤衍生炭材料的炭化机制仍然不太清楚.因此,本文选取烟煤为原料,探究了煤炭到无定形炭材料的化学、微晶和孔隙结构演变过程.随着温度的升高(低于 1000℃),材料结构发生局部变化,碳层的迁移和小分子物质的释放导致了层间距(3.69-3.82Å)和缺陷密度(1.26-1.90)逐渐增大,并且产生了丰富的纳米微孔结构.当温度升至1000~1600℃时,层间距和缺陷密度开始逐渐减小.在LIBs中,经 1000℃炭化制备的样品表现出最佳的电化学性能.在 0.1 C倍率测试下可逆容量达到384 mAh g-1,在5C倍率下仍能保持170 mAh g-1,表现出优异的倍率性能.在SIBs中,经1200 ℃炭化制备的样品在 0.1 C倍率测试下具有 270.1 mAh g-1 的可逆容量和高达 86.8%的首次库伦效率.本研究为煤基炭材料的精细化制备提供了理论支撑.
Insights into the carbonization mechanism of bituminous coal-derived carbon materials for lithium-ion and sodium-ion batteries
Despite recent interest in the low-temperature carbonization of coal to prepare disordered carbon materials for the an-odes of lithium-ion(LIBs)and sodium-ion batteries(SIBs),the carbonization mechanism is still poorly understood.We selected bitu-minous coal as the raw material and investigated the chemical,microcrystal,and pore structure changes during the carbonization pro-cess from coal to the resulting disordered carbon.These structural changes with temperature below 1000℃ show an increase in both interlayer spacing(3.69-3.82Å)and defect concentration(1.26-1.90),accompanied by the generation of a large amount of nano-mi-croporous materials.These changes are attributed to the migration of the local carbon layer and the release of small molecules.Fur-thermore,a decrease in interlayer spacing and defect concentration occurs between 1000℃ and 1600℃.In LIBs,samples carbon-ized at 1000℃ showed the best electrochemical performance,with a reversible capacity of 384 mAh g-1 at 0.1 C and excellent rate performance,maintaining 170 mAh g-1 at 5 C.In SIBs,samples carbonized at 1200℃ had a reversible capacity of 270.1 mAh g-1 at 0.1 C and a high initial Coulombic efficiency of 86.8%.This study offers theoretical support for refining the preparation of carbon materials derived from coal.