基于聚苯乙烯磺酸的锂金属负极界面保护层的设计

Lithium Polystyrene Sulfonate Based Interfacial Protective Layer for Lithium Metal Anodes

将聚苯乙烯磺酸(PSS)进行锂化处理后,涂覆在锂箔表面,在锂金属表面构筑一层均匀的聚苯乙烯磺酸锂(PSSLi)界面保护层,形成PSSLi@Li复合电极.通过红外光谱(FTIR)、电化学阻抗谱(EIS)、电池性能分析和有限元多物理场仿真模拟等方法,对该复合电极进行了结构和性能研究.结果表明,PSSLi界面保护层能有效地避免电解液与锂金属的直接接触,抑制了“死锂”和锂枝晶的生成.聚苯乙烯磺酸锂具有整齐排布的磺酸基团,为锂离子提供了稳定的传输通道,能够均匀化锂离子的迁移速率,调节锂离子在电极表面的浓度分布,并实现均匀的锂金属沉积/剥离.电化学实验数据表明,将该PSSLi界面层涂覆在铜箔表面进行库仑效率测试,循环350次实验后仍然能够保持在99.5%以上;利用PSSLi@Li复合电极组装形成的对称电池,在1 mA/cm^(2)的电流密度、1 mA·h/cm^(2)的面积容量下,能够稳定循环1200 h以上;PSSLi@Li与磷酸铁锂正极材料组装的全电池,在1C倍率下循环500次后,仍具有115 mA·h/g的容量,容量保持率可达81%以上;在8C的高倍率下,该电池的容量可达到105 mA·h/g.

Due to the ultrahigh theoretical specific capacity(3860 mA·h/g)and lowest negative electrochemical potential[‒3.04 V(vs.SHE)],lithium metal has long been considered as an ideal anode for next-generation high-energy-density lithium batteries.However,several critical issues such as volume expansion,lithium dendrite,and side reaction have restricted its practical application.Here,lithium polystyrene sulfonic(PSSLi)was evenly coated on the surface of commercial lithium metal foil to form the PSSLi@Li composite electrode.Fourier transform infrared spectroscopy(FTIR),electrochemical impedance(EIS),battery performance test and finite-element-based solver simulation were used to analyze the physical and electrochemical properties of this composite anode.The results indicated the PSSLi layer can effectively avoid the side reaction between electrolyte and Li metal,restricting the formation of"dead Li".In addition,PSSLi with the neatly arranged sulfonic groups can homogenize the Li ions flux and distribution on the electrode surface,which ensures the uniform plating/stripping of Li metal.The electrochemical test showed that the coulombic efficiency of the PSSLi@Cu composite electrode can remain above 99.5%after 350 cycles.And the symmetrical cell assembled with PSSLi@Li composite electrodes presents an excellent cycling life over 1200 h under the current density of 1 mA/cm^(2) and area capacity of 1 mA·h/cm^(2).Moreover,the LiFePO_(4)(LFP)coupled full cell can maintain at 115 mA·h/g under the rate of 1C after 500 cycles and realize an ideal capacity retention(81%).The full cell also exhibits an excellent rate performance of 105 mA·h/g at the rate of 8C.