高压镍锰酸锂电池电解液体系探索研究

Explorative investigation of electrolytes utilized for high-voltage LiNi_(0.5)Mn_(1.5)O_4 batteries

新型正极材料高压镍锰酸锂的平台电位在4.75Vvs Li^+/Li,因此普遍认为电解液在高电位下的氧化分解是限制其应用的瓶颈。我们的研究工作发现,在半电池内、以纯碳酸酯为溶剂,镍锰酸锂表现出较好的循环稳定性,常规溶剂组合可以实现循环300周后容量保持80%以上,溶剂优化后,甚至达到92%以上的保持率。这表明高压镍锰酸锂电池正极一侧对添加剂的需求并不迫切。但是,我们发现部分常用石墨负极添加剂会对高压镍锰酸锂的循环性产生负面作用。本文中列举了碳酸亚乙烯酯(VC)和亚硫酸乙烯酯(ES)的氧化行为,发现它们分别在4.6V和4.05Vvs Li^+/Li会有明显分解反应。含有VC、ES添加剂的电解液使得镍锰酸锂电池的放电容量显著降低,在其电极表面有一层厚厚的沉积物,同时电池的阻抗显著增加。实验结果表明,在商品电池内广泛使用的负极添加剂,可能会优先在高压镍锰酸锂一侧发生正极氧化分解。因此,镍锰酸锂电池需要重新设计电解液体系。

The main challenge of high-voltage LiNi_(0.5)Mn_(1.5)O_4(LNMO),which is one of the most promising cathodes with the redox plateau of^4.75 Vvs Li+/Li,is the decomposition of electrolyte.In fact,our studies show that LNMO presents the good capacity retention ratio,higher than 80%after 300 cycles,in the electrolyte with the mixture of pure carbonate solvents.Even 92% of the initial capacity in the 300 th cycle is remained in the optimal composition.Obviously,high-voltage LiNi_(0.5)Mn_(1.5)O_4 can get excellent cycle performance without any special additives.In addition,we studied the electrochemical behavior of vinylene carbonate(VC)and ethylene sulfite(ES)in high potential.The results indicate that ES and VC can be electrochemically oxidized at 4.05 Vand 4.6Vvs Li+/Li,respectively.In the cells with the electrolytes containing VC and ES respectively,the discharge capacities are significantly diminished.Also the thick and high-resistance sediment layers are formed on the surface of LNMO.We concluded that the SEI-forming additives widely used in commercial batteries may firstly decompose on cathode side.Therefore the electrolyte systems should be redesigned for graphite-LNMO batteries.