Abstract:

Coal resources in China are rich, diverse, inexpensive and widely distributed. Converting coal into new materials is an effective way to improve its added value and technical content. Coal has high carbon content and rich aromatic ring structure, and pyrolytic carbonization can prepare hard carbon anode materials for sodium-ion batteries. This paper uses Xinjiang bituminous coal as the carbon source, adopts a two-step process of low-temperature pyrolysis and high-temperature carbonization, and adjusts the corresponding process conditions. The effect of the development process of bituminous coal mesophase on the structure of hard carbon and its sodium storage electrochemical behavior was studied. We have found that changing the temperature range, carrier gas flow rate, and heating rate of low-temperature pyrolysis can adjust the decomposition and depolymerization reactions in the formation stage of colloids, then adjust the degree of volatile matter generation and escape, and the degree of colloidal solidification, so as to adjust the specific surface area, graphitization degree and heteroatom content of the obtained hard carbon. The result of electrochemical performance test demonstrated that the carbonized anode electrode material under low-speed heating range of 350—550℃, carrier gas flow rate of 60 ml·min^-1, and heating rate of 1℃·min^-1 has the best reversible specific capacity and initial coulombic efficiency, reaching 314.3 mA·h·g^-1 and 82.8% at a current density of 0.02 A·g^-1, respectively. These excellent performances should be attributed to the coordination between the ordered carbon structure and the defect structure of the coal-based hard carbon material.

Key words: electrochemistry, sodium-ion batteries, anode material, bituminous coal, carbonization conditions, pyrolysis, preparation

摘要：

我国煤炭资源丰富多样、价格低廉、分布广泛，将煤转化为新材料，是提高其附加价值和技术含量的有效途径。煤含碳量高、芳环结构丰富，热解炭化可制备钠离子电池硬炭负极材料。以新疆烟煤为碳源，采用低温热解复合高温炭化的两步过程，并调控相应工艺条件，研究了烟煤中间相的发展过程对硬炭结构及其储钠行为的影响。经研究发现，改变低温热解的温度区间、载气流速和升温速率，可以调节胶质体生成阶段内的分解和解聚反应，调节挥发分生成和逸出以及胶质体固化等过程进行的程度，从而调控硬炭的比表面积和石墨化程度等。在温度区间为350~550℃、载气流速为60 ml·min^-1、升温速率为1℃·min^-1条件下，炭化得到的硬炭负极可逆比容量和首周库仑效率最佳，在0.02 A·g^-1的电流密度下分别达到314.3 mA·h·g^-1和82.8%，良好的性能归因于煤基硬炭材料中有序结构和缺陷结构的协调和平衡。

关键词: 电化学, 钠离子电池, 负极材料, 烟煤, 炭化条件, 热解, 制备