An Ab Initio Study of Lithization of Two-Dimensional Silicon-Carbon Anode Material for Lithium-Ion Batteries.

Alexander Galashev,Alexey Vorob'Ev

doi:10.3390/ma14216649

Abstract

This work is devoted to a first-principles study of changes in the structural, energetic, and electronic properties of silicene anodes during their lithium filling. Anodes were presented by silicene on carbon substrate and free-standing silicene. The ratio of the amount of lithium to silicon varied in the range from 0.06 to 1.125 for silicene on bilayer graphene and from 0.06 to 2.375 for free-standing silicene. It is shown that the carbon substrate reduces the stability of the silicene sheet. Silicene begins to degrade when the ratio of lithium to silicon (NLi/NSi) exceeds ~0.87, and at NLi/NSi = 0.938, lithium penetrates into the space between the silicene sheet and the carbon substrate. At certain values of the Li/Si ratio in the silicene sheet, five- and seven-membered rings of Si atoms can be formed on the carbon substrate. The presence of two-layer graphene imparts conductive properties to the anode. These properties can periodically disappear during the adsorption of lithium in the absence of a carbon substrate. Free-standing silicene adsorbed by lithium loses its stability at NLi/NSi = 1.375.

Highlights

Modern automobile manufacturing and large stationary energy storage devices require cheap and high-capacity batteries
Graphite anodes currently used in lithium-ion batteries (LIBs) have a low theoretical specific capacity (372 mAh·g−1 ), which does not allow the creation of LIBs with a high energy density [1]
The present density functional theory (DFT) study of polyatomic adsorption of lithium was carried out on models of a stand-alone silicene sheet and a silicene sheet located on bilayer graphene

Summary

Introduction

Modern automobile manufacturing and large stationary energy storage devices (used to smooth out loads in smart grids) require cheap and high-capacity batteries. Graphite anodes currently used in LIBs have a low theoretical specific capacity (372 mAh·g−1 ), which does not allow the creation of LIBs with a high energy density [1]. Bulk crystalline or amorphous silicon cannot serve as a good anode material for LIB because of the large (up to 300%) volume change during cycling and low electrical conductivity [3]. An ab initio study of the adsorption of lithium on free-standing single-layer silicene showed that the specific capacity of such an anode, which did not experience bond rupture, should be 1196 mAh·g−1 [7]. A similar study performed for two-layer free-standing silicene showed that a bond rupture, initiated as a result of lithium adsorption, limits the specific capacity of such electrode at the level of 955 mAh·g−1 [8]

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