Electrochemical Properties of Prelithated Silicon-Graphite Mixtures As an Anode Material for Quasi-Solid-State Battery

To guarantee the minimum safety of Li-ion battery, quasi-solid electrolyte such as gel polymer is one of potential candidates by retarding the fire. With the safety issue, the requirement of higher energy density is still main issue for the next generation Li-ion battery. To enhance the energy density, Silicon (Si) is well known as potential anode due to its much higher theoretical specific capacity than that of graphite. Nevertheless, Si’s large volumetric changes during cycles hinder its application for the next generation Li-ion battery. Here, specially designed process to prelithiate Si nanoparticles with size of several hundred nanometers were developed, and physical mixture of Si and graphite was applied to coin-type full cell with quasi-solid electrolyte. Specifically, Si nanoparticles were annealed with Li-sources such as Li 2 CO 3 or LiOH in reduction atmosphere. Simultaneously, Carbon (C) sources such as Toluene or ethylene was injected to Si nanoparticles to form C- layer to gain electrical conductivity of Si. Prelithiated Si and graphite were mixed with various composition from 0:100 to 50:50 (in wt.%), and the mixture was applied as anode material with Ni-rich cathode and gel electrolyte for assembly of coin-type cell. Specific capacity of prelithiated Si exhibited around 1,300 mAh/g with extremely high initial capacity of 88%. Microstructure of the Si nanoparticles were studied by using XRD, SEM and HR-TEM analysis. Various gel electrolyte was applied not only for separator but also for inside of cathode and anode. Effect of types and compositions of gel electrolytes on electrochemical properties such as cycle performance of quasi-solid-state Li-ion battery was investigated. Also, interface properties especially between anode materials and gel electrolyte were precisely investigated through the EIS (Electrochemical Impedance Spectroscopy) measurements to enhance the cycle performances. This quasi-solid-state Li-ion battery can solve the safety problem as well as low energy density at the same time.