CN105070916B - 一种高压实碳包覆天然石墨材料的制备方法 - Google Patents
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Abstract
本发明提供了一种高压实碳包覆天然石墨材料的制备方法，以层间距介于0.3470～0.3700的膨胀天然石墨为原料，经有机溶剂溶解、抽滤后，再于高压下恒压，再于50～70℃添加适量的过硫酸钾和亚硫酸氢钠的混合液，制得在石墨端面形成高分子膜的材料；最后于900～1900℃进行碳化处理，得到高压实碳包覆天然石墨材料。本发明方法仅对天然石墨的端面进行包覆，不采用任何挥发性的有机溶剂，环境友好；且加工工艺节能、加工周期短的优点；且采用本发明方法制备的产品可在未对其它电性能并有不良影响条件下，有效提高材料的压实密度和降低的材料电阻率。
Description
技术领域
本发明涉及一种石墨材料制备方法，特别涉及一种高压实碳包覆天然石墨材料的制备方法。
背景技术
天然石墨是一种层状架构发达的晶体材料，用作锂离子电池负极材料时，具有容量高、压实高、导电性能好、低温性能优良的特点。然而，天然石墨在用于锂离子电池负极材料也具有明显的缺陷：电解液会与锂离子形成溶剂化，而后共嵌入石墨内部发生还原反应，反应生成的气体可以造成石墨晶体粉化失效，这就会破会电池的使用寿命，目前多采用简单地固相包覆技术，尽管可以保证所得材料循环性能有明显改善，但同时材料也会延生出压实降低，粉末电阻率提高的问题，最终导致材料能量密度及低温性能变差。采用喷雾干燥包覆或其它液相包覆工艺，尽管可以兼顾天然石墨负极材料的循环性能、能量密度和低温性能，但加工工艺存在大量有机溶剂挥发引起环境污染的问题，并且这类包覆技术对设备要求苛刻，加工成本高。
发明内容
本发有旨在提供一种可制备得到长循环寿命、高压实、低粉末电阻率包覆天然石墨材料的制备方法。本发明通过以下方案实现：
一种高压实碳包覆天然石墨材料的制备方法，包括以下步骤：
(Ⅰ)以层间距介于0.3470～0.3700的膨胀天然石墨为原料，将其加入至-40℃的丙烯腈溶剂中，混合均匀后于-40℃温度下抽真空浸渍2h以上，之后加压至5个大气压并在该压力下恒压8～15h，后于室温常压条件抽滤；
(Ⅱ)将第(Ⅰ)步抽滤后得到的滤饼加入水中，升温并于50～70℃恒温，而后添加适量的过硫酸钾和亚硫酸氢钠的混合液，制得在石墨端面形成高分子膜的材料；
(Ⅲ)将第(Ⅱ)步得到的材料于900～1900℃进行碳化处理，保温时间0～24h，得到高压实碳包覆天然石墨材料。
实验发现，以下工艺参数的优化，包覆效果较好，材料性能较优：
1.第(Ⅱ)步中添加的过硫酸钾的质量浓度为4％，亚硫酸氢钠的质量浓度为1％；过硫酸钾和亚硫酸氢钠的添加量为每1KG滤饼添加的过硫酸钾溶液体积为50ml，每1KG滤饼添加的亚硫酸氢钠溶液体积为10ml；滤饼加入水中后升温的速率为10℃/min。
2.第(Ⅲ)步碳化处理的升温速度为，起始温度～900℃时，升温速率为100℃/h，900℃～最高碳化温度时，升温速率为200℃/h。
与现有技术相比，本发明所具有以下有益效果：
1.本发明的方法可实现仅对天然石墨的端面进行包覆，所需包覆量远低于液相包覆和固相包覆，不采用任何挥发性的有机溶剂。从原材料角度讲，该工艺具备生产成本低、加工工艺环境友好。
2.本发明方法中，第Ⅲ步的碳化工艺温度介于900～1900℃，热处理工艺所需时间少于24h，而固相包覆法为了尽可能增加材料的压实并降低其粉末电阻率，一般采用的热处理温度为2400～3200℃，热处理工艺所需时间为25～35D，由此可见，从工艺角度讲，本发明的方法具备节能、加工周期短的优点。
3.采用本发明方法产品，由于仅在核心天然石墨的端面包覆无定形碳，不仅可以阻止溶剂化锂离子嵌入石墨层中，还降低了包覆层对天然石墨压实以及导电性能的影响。
具体实施方式
实施例1
一种高压实碳包覆天然石墨材料的制备方法，步骤如下：
(Ⅰ)以层间距介于0.3470～0.3700的膨胀天然石墨为原料，将其加入至-40℃的丙烯腈溶剂中，混合均匀后于-40℃温度下抽真空浸渍2h以上，之后加压至5个大气压并在该压力下恒压10h，后于室温常压条件抽滤；
(Ⅱ)将第(Ⅰ)步抽滤后得到的滤饼加入水中，按速率为10℃/min升温至60℃，恒温，使滤饼完全分散于水中，之后按每1KG滤饼加入50ml质量浓度为4％过硫酸钾溶液和10ml质量浓度为1％的亚硫酸氢钠之添加比例，加入过硫酸钾和亚硫酸氢钠的混合液，制得在石墨端面形成高分子膜的材料；
(Ⅲ)将第(Ⅱ)步得到的材料于1900℃进行碳化处理1小时，得到高压实碳包覆天然石墨材料。碳化处理的升温速度为：起始温度～900℃时，升温速率为100℃/h，900℃～1900时℃，升温速率为200℃/h。
试验表明采用本发明方法制备的产品，在被用于制作锂离子电池负极材料后，其电容量为365～370mAh/g，压实在2.0g/cm3，粉末电阻率为8～9mΩcm，-20℃做0.2C倍率充放电，容量可保持为室温容量的90％。作为比较例，采用现有常规的简单固相包覆工艺下制得的碳包覆天然石墨容量通常为360～365mAh/g，压实在1.7～1.8g/cm3，粉末电阻率为12～18mΩcm，-20℃做0.2C倍率充放电，容量可保持为室温容量的85％。可以看出，采用本发明方法制备的产品可以有效提高材料的压实密度，并且材料电阻率也大大降低，但其它电性能并未有不良影响。
Claims (4)
1.一种高压实碳包覆天然石墨材料的制备方法，其特征在于：包括以下步骤，
（Ⅰ）以层间距介于0.3470~0.3700的膨胀天然石墨为原料，将其加入至-40℃的丙烯腈溶剂中，混合均匀后于-40℃温度下抽真空浸渍2h以上，之后加压至5个大气压并在该压力下恒压8~15h，后于室温常压条件抽滤；
（Ⅱ）将第（Ⅰ）步抽滤后得到的滤饼加入水中，升温并于50~70℃恒温，而后添加适量的过硫酸钾和亚硫酸氢钠的混合液，制得在石墨端面形成高分子膜的材料，所述过硫酸钾的质量浓度为 4%，亚硫酸氢钠的质量浓度为1%；
（Ⅲ）将第（Ⅱ）步得到的材料于900~1900℃进行碳化处理，保温时间1~24h，得到高压实碳包覆天然石墨材料。
2.如权利要求1所述的一种高压实碳包覆天然石墨材料的制备方法，其特征在于：所述过硫酸钾和亚硫酸氢钠的添加量为每1KG滤饼添加的过硫酸钾溶液体积为 50ml，每1KG滤饼添加的亚硫酸氢钠溶液体积为 10ml。
3.如权利要求1或2所述的一种高压实碳包覆天然石墨材料的制备方法，其特征在于：所述第（Ⅱ）步中滤饼加入水中后升温的速率为10℃/min。
4.如权利要求1或2所述的一种高压实碳包覆天然石墨材料的制备方法，其特征在于：所述第（Ⅲ）步碳化处理的升温速度为，起始温度至900℃时，升温速率为100℃/h，900℃至最高碳化温度时，升温速率为200℃/h。
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| CN102623684A (zh) * | 2012-04-18 | 2012-08-01 | 长沙理工大学 | 一种特殊壳层结构石墨基碳负极复合材料及制备方法 |
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