双(氟磺酰)亚胺锂对LiPF_(6)电解液热稳定性的影响及作用机制

Lithium Bis(fluorosulfonyl)imide Improving Chemical Stability of LiPF_(6)-based Electrolyte and Mechanism

六氟磷酸锂(LiPF_(6))是商业化锂离子电池电解液的主导电盐,但LiPF_(6)电解液热稳定性差的问题严重制约了耐高温电池技术的发展。LiPF_(6)电解液中存在的微量氟化氢(HF)和质子性杂质是导致电解液分解的关键因素。通过在LiPF_(6)电解液中引入双(氟磺酰)亚胺锂(LiFSI),使用核磁共振技术(NMR)探究了在高温存储过程中LiFSI对LiPF_(6)电解液化学分解行为的影响。研究结果表明,高温85℃分别存储14、30、180 d后,在含LiFSI的电解液中只检测到极微量的LiPF_(6)分解产物,未分解的LiPF_6的摩尔百分含量高达99.1%、99%、99%。LiFSI可以清除电解液中残留的HF杂质,从而抑制LiPF_(6)的分解,最终显著改善LiPF_(6)电解液的高温稳定性。通过对含LiFSI的电解液进行加水存储实验进一步验证了LiFSI可以有效清除HF并抑制LiPF_(6)分解的能力。

LiPF_(6)is the dominating lithium salt in commercial carbonate electrolyte due to its well compromised properties,however,the unexpected degradation of LiPF_(6)-based electrolyte at elevated temperature restricts the implement of lithium-ion batteries in extreme circumstances.It has been reported that trace hydrogen fluoride(HF)and protonic impurities are prime culprits for the decompositions of LiPF_(6)-based electrolyte.Herein,by using nuclear magnetic resonance(NMR),the impact of lithium bis(fluorosulfonyl)imide(LiFSI)on the thermal stability of LiPF_(6)-based electrolyte during storage at elevated temperature was investigated.Only a very small amount of LiPF_(6)decomposition products were detected in LiFSI-containing electrolyte and the amounts of intact LiPF_(6)remained as high as 99.1%,99%,99%after storage at 85℃for 14,30,180 d,respectively.LiFSI can chemically eliminate HF impurity in the LiPF_(6)-based electrolyte,thus suppressing the decomposition of LiPF_(6)and dramatically improving the electrolyte stability.The HF-eliminating functionality of LiFSI to inhibit LiPF_(6)decomposition was further manifested in the storage test by adding H 2 O into the LiFSI-containing electrolyte.