Dendrite/Volume Expansion-Free Lithium Deposition Inside the Enclosed Nanoscale Space of Electrochemically Modified Graphite

Abstract

Though over-lithiation of graphite can increase the initial specific capacity of the anodes, the cycling stability is unsatisfactory as metallic lithium depositing on the surface of graphite has poor reversibility. In this work, we utilize electrochemical co-intercalation of Li+ and diethylene glycol dimethyl ether (DEGDME) to prepare [Li-DEGDME]+-graphite co-intercalation compounds ([Li-DEGDME]-Gr) from pristine graphite. The expanded d-spacing and abundant cross-layer voids in the intralayer structure of [Li-DEGDME]-Gr owing to the co-intercalation of [Li-DEGDME]+ complex ions and parasitic chemical reactions between solvent molecules and graphene layers promotes the migration of bare Li+ and provides sufficient interior space for extra lithium-storage. As a result, a much higher lithium-storage capacity of 810 mAh g-1 can be successfully achieved. The extra lithium-storage is proved to originate from the deposition of lithium metal inside the enclosed nanoscale space of the as modified graphite, which inhibits the formation of lithium dendrites, isolates lithium metal from electrolytes and avoids volumetric expansion, enabling the [Li-DEGDME]-Gr electrodes to exhibit better cycling stability with high specific capacity. This work proposes a new strategy to enhance the reversibility of lithium metal plating/stripping by accommodating lithium deposition inside modified carbon materials, thus effectively increases the reversible capacity of graphite-based anode materials.