成膜添加剂对石墨电极性能改善的研究

发布时间：2018-04-14 05:25

本文选题：锂离子电池 + 电解液　；参考：《中国矿业大学》2014年硕士论文

【摘要】：锂离子电池技术由于可作为电动汽车的动力电源而在近年来日益显示其重要性。锂离子电池在首次充放电过程中形成的固体电解质相界面膜对电池的性能起到关键的影响作用。选择合适的电解液成膜添加剂，促进电极表面形成有利于电池性能提高的SEI膜是改善锂离子电池最简单、经济的手段之一。本文研究了碳酸钾、碳酸钠、氟化锂等无机盐作为锂离子电池电解液成膜添加剂对石墨电极性能的影响，首次创新性地提出将维生素E用作电解液成膜添加剂，研究了石墨负极在含有不同添加剂电解液中的电化学性能，深入研究了石墨电极性能改善的机理。测试手段包括充放电测试、循环伏安法、电化学阻抗谱、扫描电子显微镜等，实验主要内容和结论如下：（1）在1mol/L LiPF6-EC:DEC电解液中添加饱和K2CO3，运用循环伏安法、充放电测试和电化学阻抗谱测试研究了K2CO3对电池性能的影响。通过扫描电镜分析了添加K2CO3前后SEI膜形貌及组成的变化，结果表明两种电解液中形成的SEI膜拥有不同的形貌，组分也发生一定程度的改变；CV结果显示，K2CO3的加入可以有效抑制电解液溶剂EC的还原分解，，从而改善了石墨电极的电化学性能；EIS结果表明，加入K2CO3使得电极的整体阻抗和SEI膜阻抗都有所减小，有利于电池性能的提高。（2）研究了碳酸钠作为成膜添加剂对锂离子电池石墨电极的影响。运用扫描电子显微镜观察了在未添加和添加了Na2CO3的电解液中石墨电极表面SEI膜形貌和结构的变化；采用循环伏安法和电化学阻抗谱测试技术研究了Na2CO3对石墨电极电化学性能的影响。结果表明，在1mol/L LiPF6-EC:DEC电解液中添加饱和Na2CO3可以促进形成更加光滑致密的SEI膜，增大电极反应的可逆性，有效抑制电化学过程中电解液的还原分解，从而提高石墨电极的电化学循环性能。（3）研究了1mol/L LiPF6-EC:DEC:DMC电解液中维生素E和LiF的加入对石墨电极表面SEI膜形貌、结构和电化学性能的影响。SEM图观察结果表示，LiF和维生素E添加到电解液中，促进了SEI膜的形成，改善了SEI膜结构；充放电结果表明，该两种添加剂均可以显著提高石墨电极的首次充放电容量和库伦效率；CV研究结果表明，电解液中添加3%维生素E和LiF能抑制首次循环过程中EC的第一步还原反应，提高锂离子嵌入脱出的可逆性，从而提高首次可逆容量，改善循环性能。
[Abstract]:Lithium - ion battery technology has become more and more important in recent years because of the power supply which can be used as an electric automobile . The solid electrolyte phase interface film formed during the first charge and discharge of lithium ion battery plays a key role in improving the performance of the lithium ion battery . It is first proposed to use the inorganic salt of potassium carbonate , sodium carbonate and lithium fluoride as the electrolyte forming additive to improve the performance of the graphite electrode . The mechanism of improving the performance of graphite electrode is studied . The test method includes the charge and discharge test , cyclic voltammetry , electrochemical impedance spectrum , scanning electron microscope , etc . The experimental results are as follows :

( 1 ) The effects of K _ 2CO _ 3 on the performance of the battery were studied by cyclic voltammetry , charge - discharge test and electrochemical impedance spectroscopy . The morphology and composition of the SEI films were investigated by SEM . The results showed that the SEI films formed in the two electrolytes had different morphology and the components were changed to some extent .
CV results show that the addition of co3 can effectively inhibit the reduction and decomposition of electrolyte solvent EC , thus improving the electrochemical performance of graphite electrode ;
EIS results show that the addition of co3 can decrease the overall impedance and SEI film impedance of the electrode , which is beneficial to the improvement of cell performance .

( 2 ) The effect of sodium carbonate as film - forming additive on graphite electrode of Li - ion battery was studied .
The effect of Na2CO3 on the electrochemical properties of graphite electrode was studied by cyclic voltammetry and electrochemical impedance spectroscopy . The results show that adding saturated Na2CO3 in 1 mol / L lip6 - EC : DEC electrolyte can promote the formation of more smooth and dense SEI film , increase the reversibility of electrode reaction , and effectively inhibit the reduction and decomposition of electrolyte in electrochemical process , so as to improve the electrochemical cycle performance of graphite electrode .

( 3 ) The effects of the addition of vitamin E and LiF on the morphology , structure and electrochemical properties of SEI film on the surface of graphite electrode were studied . The results showed that LiF and E were added to the electrolyte , which promoted the formation of SEI film and improved the structure of SEI film .
The charge - discharge results show that the first charge - discharge capacity and coulombic efficiency of graphite electrode can be obviously improved by the two kinds of additives .
CV results show that the addition of 3 % vitamin E and LiF in the electrolyte can inhibit the first reduction reaction of EC during the first cycle and improve the reversibility of lithium ion intercalation , so as to improve the first reversible capacity and improve the cycle performance .

【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912;U469.72

【参考文献】