Lithium ion thin-film electrodes for all-solid-state and electrochromic applications
Establishing thin-film technologies for lithium ion batteries is an important step towards all-solid-state batteries. Solid thin-film electrodes expose significantly higher charge and discharge rates than standard composite electrodes, thus have the potential to increase the power density of thin-film batteries. Sol-gel procedures are established in battery research for synthesizing active material powders with controlled particle sizes. Here, we prepared single- and multi-layer films of active materials viadip-coating method. Both electrode single-layer systems exhibit excellent electrochemical properties such as high reversibility and low polarization in long-term CV measurements and show almost full capacity retention at charge and discharge currents up to 100 C. Furthermore, applied on transparent conducting oxides, the electrodes were of high optical quality and showed intense color changes upon charging and discharging which positions them as interesting electrochromic compounds. Both materials are well known for their high reversibility and low cost compared to commonly known electrochromic metal oxides such as tungsten oxide. The combination of their highly stable and very fast cycling capabilities with their color switching properties, make the presented transparent thin film electrodes promising candidates for high-power all-solid-state and electrochromic applications. This paper shows transparent Li4Ti5O12 and LiMn2O4 thin film electrodes characterized by the above mentioned electrochemical measurements and their optical properties with the help of UV-vis spectroscopy. Additionally, material characterization is demonstrated via X-ray diffraction, XPS and SEM imaging.