Journal
ADVANCED ENERGY AND SUSTAINABILITY RESEARCH
Volume 3, Issue 8, Pages -Publisher
WILEY
DOI: 10.1002/aesr.202200042
Keywords
diffusion; graphite electrodes; lithium trapping; lithium-ion batteries; lithium-metal half cells
Categories
Funding
- Swedish Research Council [VR-2019-04276]
- Angstrom Advanced Battery Center
- StandUp
- Swedish Research Council [2019-04276] Funding Source: Swedish Research Council
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Although graphite-based composite electrodes are commonly used in lithium-ion batteries for their good cycle performance, their long-time cycling stability still needs improvement. The diffusion-controlled lithium-trapping effect, which accounts for around 30% of the total capacity loss during long-time cycling, is shown to be an additional and largely unrecognized aging mechanism in graphite-based electrodes. It is caused by incomplete delithiation due to diffusion-controlled redistribution of intercalated lithium in graphite. However, constant-voltage delithiation steps can increase the delithiation efficiency and decrease the influence of the lithium-trapping effect.
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.
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