| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeP |
| Session: | Energy Harvesting & Storage Poster Session |
| Presenter: | Keisuke Nakayama, Kansai University, Japan |
| Correspondent: | Click to Email |
In recent years, world's energy consumption has been steadily increasing, and prompt efforts are needed to decrease CO2 and other greenhouse gas emissions. Li-ion batteries are becoming increasingly important in the world market of energy storage and conversion devices. Compared with other commonly used batteries, 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 are applied to mobile electronic devices and these are an essential part of the full hybrid electric vehicles (HEVs) and/or plug-in electric vehicles (PHEVs) owing to their high energy densities and low weight-to-volume ratios.
Li-ion batteries are operated by the Li ions migration. Therefore, it is important to observe the migration of lithium-ions with a high spatial resolution and non-destruction.
The active materials in the electrodes of the lithium-ion batteries have been generally used LiCoO2 cathode and graphite carbon anode that were layered materials. Graphitic materials, which are representative of carbon materials have been used the most for anode materials because of their low working potential, which is close to the metallic lithium anode. During charging and discharging, Li-ions migrate between LiCoO2 and graphite, and intercalation/deintercalation are induced. Intercalation/deintercalation induce 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.
Our samples to observe were as follows. LiCoO2 particles around 10 µm in diameter were coated with the Al current collector. The thickness of the coated layer was around 30 µm. A 20-µm-thick polypropylene separator with the electrolyte was sandwiched between the LiCoO2 cathode and the graphite anode.
We observed volume changes in the LiCoO2 cathode using SPM, and successfully imaged the distribution of the volume changes corresponding to the LiCoO2 particles. Volume changes in the interspace were significantly larger than those in the particles. Therefore, the large volume changes are caused by electrolyte flux induced by changes in concentration of Li ions.