原位构建富氟SEI的凝胶电解质用于金属锂二次电池  

LiF-rich SEI generated by in-situ gel polymer electrolyte process for lithium metal rechargeable batteries

作　　者：李文涛 林慧娟 钟海 LI Wentao;LIN Huijuan;ZHONG Hai(Institute of New Energy Technology,Jinan University,Guangzhou 510632,Guangdong,China)

机构地区：[1]暨南大学新能源技术研究院,广东广州510632

出　　处：《化工学报》2022年第7期3240-3250,共11页CIESC Journal

基　　金：国家自然科学基金项目(21805113,62035006);广东省基础与应用研究基金项目(2019A1515011656)。

摘　　要：以六氟磷酸锂(LiPF6)为四氢呋喃的聚合引发剂制备凝胶电解质,同时作为氟源在金属锂负极表面原位构建富含LiF的固态电解质界面层(solid electrolyte interface,SEI)来抑制锂枝晶的生长以及金属锂/电解液之间的副反应。所制备的凝胶电解质具有较高的室温离子电导率(1.33 mS·cm^(−1))和较宽的电化学稳定窗口(4.5 V)。原位聚合方式组装金属锂对称电池循环后,锂负极表面没有明显的锂枝晶和被损毁的形貌出现;XPS结果表明锂负极表面生成了富含LiF的SEI。组装的LiFePO4全电池在1 C的电流密度下,稳定循环400周后仍保持118.7 mAh·g^(−1)的放电比容量。得益于四氢呋喃在开环聚合反应过程中,促进了LiPF6分解反应平衡的正向移动,在锂负极表面形成稳定的富含LiF的SEI,能够抑制锂枝晶的生长并防止其被持续性的腐蚀破坏。A gel electrolyte was prepared by using lithium hexafluorophosphate(LiPF6)as the polymerization initiator of tetrahydrofuran,and at the same time as a fluorine source,a LiF-rich solid electrolyte interface(SEI)was constructed in-situ on the surface of the lithium metal anode to suppress the growth of lithium dendrites and side reactions between metallic lithium/electrolyte.The as-prepared gel polymer electrolyte presents an ionic conductivity of 1.33 mS·cm^(−1)at room temperature and shows a high electrochemical stability up to 4.5 V.Compared with linear sweep voltammetry in 335C electrolyte,lower reduction current is observed at the range of 0-1.5 V(vs Li/Li+)in the cell with gel polymer electrolyte,which indicates that gel polymer electrolyte can mitigate the side reaction of metallic lithium with electrolyte.The lithium metal anode in the symmetric-cell with in-situ polymerization gel polymer electrolyte exhibits no obvious lithium dendrite and damaged morphology.X-Ray photoelectron spectroscopy results further reveal that the lithium metal anode in gel polymer electrolyte is formed a stable SEI with LiF-rich compound,which is much enhanced than that of in 335C electrolyte.Consequently,the Li|LiFePO4 cells with gel polymer electrolyte exhibits a long-term cycling stability,which can release a reversible capacity 118.7 mAh·g^(−1)after 400 cycles at a current density of 1 C,as well as coulombic efficiency of 99.5%.Benefit from the ring opening polymerization process of tetrahydrofuran,PF5 participates the formation reaction of intermediate product[(THF)+(PF5)−],which caused the equilibrium of the decomposition reaction shift to the right and therefore increase the formation of LiF on the surface of lithium metal anode.This process results in a great enhancement of the cyclability due to LiF-rich formed in the SEI.Therefore,the growth of lithium dendrite can be prevented by the stable SEI,as well as the side reaction between lithium metal and electrolyte.

关 键 词：氟化锂 固态电解质界面层 原位聚合 凝胶聚合物电解质 金属锂电池 

分 类 号：TQ125.1[化学工程—无机化工]