Lee Jinhong, Kim Yun-Jung, Jin Hyun Soo, Noh Hyungjun, Kwack Hobeom, Chu Hyunwon, Ye Fangmin, Lee Hongkyung, Kim Hee-Tak
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea.
Advanced Battery Center, KAIST Institute for the NanoCentury, Korea Advanced Institute of Science and Technology, 335 Gwahangno, Yuseong-gu, Daejeon 34141, Republic of Korea.
ACS Omega. 2019 Feb 14;4(2):3220-3227. doi: 10.1021/acsomega.8b03022. eCollection 2019 Feb 28.
Various electrolytes have been reported to enhance the reversibility of Li-metal electrodes. However, for these electrolytes, concurrent and balanced control of Li-metal and positive electrode interfaces is a critical step toward fabrication of high-performance Li-metal batteries. Here, we report the tuning of Li-metal and lithium cobalt oxide (LCO) interfaces with fluoroethylene carbonate (FEC)-containing electrolytes to achieve high cycling stability of Li/LCO batteries. Reversibility of the Li-metal electrode is considerably enhanced for electrolytes with high FEC contents, confirming the positive effect of FEC on the stabilization of the Li-metal electrode. However, for FEC contents of 50 wt % and above, the discharge capacity is significantly reduced because of the formation of a passivation layer on the LCO cathodes. Using balanced tuning of the two interfaces, stable cycling over 350 cycles at 1.5 mA cm is achieved for a Li/LCO cell with the 1 M LiPF FEC/DEC = 30/70 electrolyte. The enhanced reversibility of the Li-metal electrode is associated with the formation of LiF and polycarbonate in the FEC-derived solid electrolyte interface (SEI) layer. In addition, electrolytes with high FEC contents lead to lateral Li deposition on the sides of Li deposits and larger dimensions of rodlike Li deposits, suggesting the elastic and ion-conductive nature of the FEC-derived SEI layer.
据报道，各种电解质可增强锂金属电极的可逆性。然而，对于这些电解质而言，同时且平衡地控制锂金属与正极界面是制造高性能锂金属电池的关键一步。在此，我们报道了通过含氟代碳酸乙烯酯（FEC）的电解质对锂金属与钴酸锂（LCO）界面进行调控，以实现Li/LCO电池的高循环稳定性。对于含高FEC含量的电解质，锂金属电极的可逆性显著增强，这证实了FEC对锂金属电极稳定化的积极作用。然而，当FEC含量达到50 wt%及以上时，由于在LCO阴极上形成了钝化层，放电容量显著降低。通过对两个界面进行平衡调控，采用1 M LiPF₆ - FEC/DEC = 30/70电解质的Li/LCO电池在1.5 mA cm⁻²下可实现350次循环的稳定循环。锂金属电极可逆性的增强与FEC衍生的固体电解质界面（SEI）层中LiF和聚碳酸酯的形成有关。此外，高FEC含量的电解质会导致锂在锂沉积物侧面横向沉积，且棒状锂沉积物尺寸更大，这表明FEC衍生的SEI层具有弹性和离子传导性。
