In-plane staging in lithium-ion intercalation of bilayer graphene

TL;DR

This study uncovers four distinct in-plane intercalation stages in bilayer graphene during lithium insertion, revealing unique mechanisms and limits that differ from bulk graphite, with implications for enhancing Li-ion battery capacity.

Contribution

It identifies four in-plane intercalation stages in bilayer graphene and elucidates the underlying stacking transition mechanism using magnetotransport and DFT calculations.

Findings

Four distinct intercalation stages identified

Transition from AB to AA stacking at specific Li density

Lower Li storage capacity compared to graphite

Abstract

The ongoing efforts to optimize Li-ion batteries led to the interest in intercalation of nanoscale layered compounds, including bilayer graphene. Its lithium intercalation has been demonstrated recently but the mechanisms underpinning the storage capacity remain poorly understood. Here, using magnetotransport measurements, we report in-operando intercalation dynamics of bilayer graphene. Unexpectedly, we find four distinct intercalation stages that correspond to well-defined Li-ion densities. We refer to these stages as 'in-plane', with no in-plane analogues in bulk graphite. The fully intercalated bilayers represent a stoichiometric compound C14LiC14 with a Li density of 2.7x10^{14} cm^{-2}, notably lower than fully intercalated graphite. Combining the experimental findings and DFT calculations, we show that the critical step in bilayer intercalation is a transition from AB to AA stacking which occurs at a density of 0.9x10^{14} cm^{-2}. Our findings reveal the mechanism and limits for electrochemical intercalation of bilayer graphene and suggest possible avenues for increasing the Li storage capacity.