Li-ion batteries have advantages including high energy density, high output voltage, and the absence of the memory effect, and so are recognized as promising candidates for energy storage.
Li-ion batteries operate through the migration of Li ions between the electrodes. Therefore, non-destructive observation of the migration with high spatial resolution is important.
Layered materials are commonly used as electrode materials for Li-ion batteries. When charging and discharging, Li-ions are extracted or inserted into the interlayers, which causes changes in volume. Scanning probe microscopy (SPM) can allow high resolution imaging of these volume changes, which enables us to investigate Li-ion migration without destruction. Here, we present our results of LiCoO2 cathodes in Li-ion batteries.
The active materials in the electrodes were layered LiCoO2 and graphite, which are commonly used in the batteries. Li-ions migrated between LiCoO2 and the graphite during the charging/discharging cycle, which led to changes in the volume of the active materials. SPM is capable of imaging properties inducing strains in a sample non-destructively and with a high spatial resolution.
Volume changes of LiCoO2 generated by Li insertion/extraction are very small, 10-2, and so they hardly appeared in our obtained images. However, the LiCoO2 particles were imaged as dark portions with no signal as shown by (b), because changes in volume in the interspace were detected. We concluded that electrolyte flux induced by the gradient of Li-ion concentration in the cathode caused the volume changes in the interspace. Graphite or silicon yields large volume changes by changing/discharging, which induces electrolyte flux. This often causes dry-out of electrolyte. In the case of LiCoO2, the concentration gradient of Li ions induced the electrolyte flux.
This electrolyte flux is one of the most important issues for increasing the energy density of lithium ion batteries.
- Our presented method is a powerful tool for research & development of the Li-ion battery.
- Great advances in the research & development should be achieved.
- Our method is very simple and easy. Anyone can try it.
- We presented fruitful results for developmen