Diffusion‐Controlled Lithium Trapping in Graphite Composite Electrodes for Lithium‐Ion Batteries

Abstract

Although graphite‐based composite electrodes currently are widely used as negative electrodes in lithium‐ion batteries due to their good cycle performances, improvements of their long‐time cycling stability are still desirable. Herein, a series of lithium‐metal half‐cell experiments is performed to demonstrate that the diffusion‐controlled lithium‐trapping effect constitutes an additional, and so far, largely unrecognized, aging mechanism for graphite‐based electrodes. This trapping effect, which stems from incomplete delithiation due to diffusion‐controlled redistribution of intercalated lithium in graphite, is shown to account for around 30% of the total accumulated capacity loss during long‐time cycling. The trapping effect is caused by the concentration gradients present at the end of the lithiation steps as these gradients result in lithium (i.e., coupled Li+ and e−) diffusion in the electrodes. As a result, a small fraction of the lithium becomes inaccessible on the timescale of the subsequent delithiation step. The results, however, also show that the inclusion of constant‐voltage delithiation steps can increase the delithiation efficiency and decrease the influence of the lithium‐trapping effect. This work consequently demonstrates that diffusion‐controlled lithium‐trapping effects need to be considered when trying to increase the lifetimes of graphite‐based electrodes.

Keywords

• diffusion
• graphite electrodes
• lithium trapping
• lithium-ion batteries
• lithium–metal half cells