Surface Structural Disordering in Graphite upon Lithium Intercalation/Deintercalation

TL;DR

This study investigates how lithium intercalation and deintercalation cause surface structural disordering in graphite anodes, revealing that low lithium concentrations induce damage, while higher stage compounds mitigate it, impacting battery performance.

Contribution

The paper identifies the relationship between lithium concentration stages and surface disordering, highlighting the mechanisms behind structural damage during cycling.

Findings

Surface disordering is most severe at low lithium concentrations (x < 0.16).

Higher stage compounds (x > 0.33) reduce surface damage.

Delithiated electrodes show higher interfacial impedance.

Abstract

We report on the origin of the surface structural disordering in graphite anodes induced by lithium intercalation and deintercalation processes. Average Raman spectra of graphitic anodes reveal that cycling at potentials that correspond to low lithium concentrations in LixC (0 \leq x < 0.16) is responsible for most of the structural damage observed at the graphite surface. The extent of surface structural disorder in graphite is significantly reduced for the anodes that were cycled at potentials where stage-1 and stage-2 compounds (x > 0.33) are present. Electrochemical impedance spectra show larger interfacial impedance for the electrodes that were fully delithiated during cycling as compared to electrodes that were cycled at lower potentials (U < 0.15 V vs. Li/Li+). Steep Li+ surface-bulk concentration gradients at the surface of graphite during early stages of intercalation processes, and the inherent increase of the LixC d-spacing tend to induce local stresses at the edges of graphene layers, and lead to the breakage of C-C bonds. The exposed graphite edge sites react with the electrolyte to (re)form the SEI layer, which leads to gradual degradation of the graphite anode, and causes reversible capacity loss in a lithium-ion battery.