(Digital Presentation) Ex Situ Electrochemical Pre-Lithiation of Silicon for Lithium-Ion Battery Anodes

Abstract

Crystalline silicon as an anode material for lithium-ion batteries (LIBs) has a theoretical capacity greater than 3600 mAh/g, an order of magnitude larger than the current anode materials of choice, graphite (~370 mAh/g). However, the use of silicon is hampered by several issues that hinder its widespread usage in LIBs. Chief among these is the large volume expansion that accompanies lithiation (>300%), which results in the self-pulverization of silicon during cycling and the degradation in stability and performance that accompanies it. Silicon also suffers from active lithium loss in its first cycle from the formation of Li x Si and the solid-electrolyte interphase (SEI), which irreversibly consumes lithium and decreases gravimetric/volumetric capacity (typically >20% capacity loss after the formation cycle). This capacity loss coupled with mechanical and chemical degradation leads to poor capacity retention and short cycle life. Pre-lithiation of silicon and other potential anode materials (e.g. SiOx), a process of inserting additional Li into Si prior to battery operation, is thus desired to compensate for lithium consumption and to maintain the high capacity associated with silicon. Here, we demonstrate a simple and scalable method for the ex situ (i.e. outside the cell) electrochemical synthesis of pre-lithiated silicon. In this method, a current is driven though an electrochemical stir-tank reactor composed of Si powder in electrolyte suspension and a Li containing anode. When Si particles contact the conductive inner surface of the reaction vessel, lithium ions in the electrolyte are reduced on the surface to form lithium-silicon compounds. The degree of lithiation is controlled by the applied current density, applied voltage, and/or runtime. This talk will describe the chemical and structural characteristics of pre-lithiated silicon synthesized with this technique, basic electrochemical properties of our lithiated material, and the specific advantages presented by the method vs other methods.