微扩层改性对煤基石墨微观结构和储锂性能的影响

Effect of mildly-expanded modification on coal-based graphite microstructure and lithium storage performance

以自制煤基石墨为前体,浓硫酸为插层剂,高锰酸钾为氧化剂,采用液相氧化插层-热处理工艺对煤基石墨进行微扩层改性处理,制备出微扩层煤基石墨。利用X射线衍射仪、扫描电子显微镜、透射电子显微镜、拉曼光谱测试、低温氮气吸附和X射线光电子能谱等手段分析不同微扩层煤基石墨的微观结构,并测试其用作锂离子电池负极材料的电化学储锂特性,系统研究微扩层改性对煤基石墨微观结构和储锂性能的影响。研究表明,微扩层改性处理不仅可增加石墨微晶片层的层间距,还可以在石墨基体中引入纳米孔道和C==O、C—O—H及C—O—C等含氧官能团。氧化剂用量是影响微扩层煤基石墨微观结构的重要因素。通过调节氧化剂用量可实现微扩层煤基石墨微晶层间距、纳米孔道和表面官能团等微观结构的有效调控。当氧化剂用量为煤基石墨的0.30倍时,微扩层煤基石墨的层间距为0.3374nm,其纳米孔道主要由1~2nm微孔和2~6nm中孔组成,比表面积为24.6m^(2)/g,且富含C==O、C—O—H及C—O—C等含氧官能团。微扩层煤基石墨用作锂离子电池负极材料展现出优异的电化学储锂性能,其在0.1C低电流密度下的可逆比容量最高可达511.1mAh/g,在5C高电流密度下为348.7mAh/g,且经300次循环充放电后,其比容量仍可维持在313.3mAh/g,容量保持率为89.9%,综合性能远高于煤基石墨。微扩层煤基石墨优异的电化学储能特性与其微观结构中富含石墨微晶片层、纳米孔道和含氧官能团等密切相关。

The mildly-expanded coal-based graphite was prepared from coal-based graphite via liquid oxidation-thermal reduction process using concentrated H_(2)SO4 as intercalator and KMnO4 as oxidant.The microstructures of mildly-expanded coal-based graphite were characterized by XRD、SEM、TEM、Raman、nitrogen adsorption-desorption and XPS,and their lithium ions storage performance and the effect of the degree of mildly-expanded modification on their structure were further investigated.The results demonstrated that the mildly-expanded modification not only could expand the interlayer spacing of graphite crystallites,decrease the crystallite size and increase the content of nanopores,but also could introduce oxygen-containing functional groups such as carbonyl,hydroxyl and alkoxy groups into coal-based graphite.When the amount of oxidant is 0.30 times that of coal-based graphite,the interlayer distance of the mildly-expanded coal-based graphite was 0.3374nm,and its nanopore channels mainly consisted of 1—2nm micropores and 2—6nm mesopores with a specific surface area of 24.6m^(2)/g and was rich in oxygen-containing functional groups such as C==O,C—O—H and C—O—C.Mildly-expanded coal-based graphite as anode for lithium-ion batteries exhibited excellent electrochemical performance,in which the reversible specific capacity could reach up to 511.1mAh/g at 0.1C and 348.7mAh/g at high current density of 5C,and the specific capacity at 5C could still be maintained at 313.3mAh/g after 300 cycles with a capacity retention rate of 89.9%.Its comprehensive performance was much higher than that of coal-based graphite.The excellent electrochemical energy storage properties of mildly-expanded coal-based graphite were closely related to its microstructure,which is rich in graphite microcrystal layers,nanopores and oxygen-containing functional groups.