VC劣化电解液高电压性能的原因探索

Exploring the causes of VC deteriorating high voltage performance of electrolyte

碳酸亚乙烯酯(VC)常用作锂离子电池电解液添加剂,可在石墨负极形成固体电解质相界面(SEI)膜,但可能影响碳酸盐电解质的高电压性能。研究VC在LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)高电压正极中的电化学性能及副反应,结果表明:VC添加剂在一定程度上降低了碳酸酯体系电解液的氧化分解电位,从而导致难以在高电压电池中应用。分析不同充电过程中的表观容量,证实VC在正极材料的平台电位4.75 V下就会发生一定的分解;而在设定的恒压(4.95 V)充电段,会发生一个缓慢而持久的氧化分解过程,且存在较大的反应电流,使电池体系无法停止充电,造成电解液更持久的氧化。全电池循环性能测试结果表明:含VC的碳酸酯体系电解液的循环寿命较短,且在充电过程会有气体产生,导致电池鼓胀。

Vinyl carbonate(VC) was commonly used as electrolyte additive for Li-ion battery.It could form solid electrolyte phase interface(SEI) film on graphite anode, but it might affect the high voltage performance of carbonate electrolyte.The electrochemical performance and side reaction analysis of VC in LiNi_(0.5)Mn_(1.5)O_(4)(LNMO) high voltage cathode were studied.The results showed that VC additive reduced the oxidative decomposition potential of carbonate electrolyte, which made it difficult to be applied in high voltage battery.By analyzing the apparent capacity in different charging processes, it was confirmed that VC would decompose when the platform potential of cathode material was 4.75 V.At the set potentiostatic charging section of 4.95 V,a slow and lasting oxidation decomposition process would occur, there was a large reaction current, which made the battery system unable to stop charging, resulting in more lasting oxidation of electrolyte.The cycle performance test results of full battery revealed that the cycle life of the carbonate electrolyte containing VC was short, would produce gas during charging and resulting in battery swelling.