Mar 13 2019
At the Tokyo Institute of Technology (Tokyo Tech) and Okayama University, researchers have discovered that when LiCoO2 cathodes in Li-ion batteries (LIBs) are decorated with BaTiO3 nanodots, their performance can be considerably improved.
Three cathodes were fabricated: a standard bare one (left), one coated with a layer of BaTiO3 (middle), and one coated with several BaTiO3 nanodots (right). The one with the nanodots exhibited greatly enhanced performance. (Image credit: Nano Letters)
Most significantly, the researchers also described the mechanism behind the quantified results, drawing a conclusion that a unique interface is created by BaTiO3 nanodots through which Li ions can circulate effortlessly, even at extreme high charge/discharge rates.
Unsurprisingly, batteries have facilitated a countless number of applications in relation to electronic and electric devices. At present, due to contemporary developments in electrical devices as well as vehicles, there is a demand for more improved batteries, especially in terms of charging speeds, stability, and rechargeability.
Although LIBs have been demonstrated to be extremely useful, they cannot be charged rapidly with high currents without encountering issues like sudden reduction in output capacity and cyclability because of their inherent high resistance and undesirable side reactions.
Due to these unfavorable effects of undesirable reactions, the use of LiCoO2 (LCO) as a cathode material in LIBs is considerably hindered. One of the negative effects involves the dissolution of Co4+ ions into the battery’s electrolyte solution at the time of the charge/discharge cycles. Another negative effect is that a solid electrolyte interface is formed between the electrode and the active material in these kinds of batteries, thus obstructing the movement of Li ions and degrading the performance.
In an earlier study, researchers reported that the high-rate performance of LCO cathodes can be considerably improved by utilizing materials that have a high dielectric constant, for example, BaTiO3 (BTO). Conversely, the mechanism behind the perceived enhancements was not evident. Hence, to further explain this potential method, Tokyo Tech scientists, headed by Professor Mitsuru Itoh, Dr Shintaro Yasui, and Mr Sou Yasuhara, examined LCO cathodes with BTO applied in various ways to comprehensively establish what exactly occurs at the BTO–LCO interface.
In this regard, the scientists developed three entirely different LCO cathodes—a bare LCO cathode, one coated with a BTO layer, and one decorated with BTO nanodots (see the above image). The researchers also designed an LCO cathode using one BTO nanodot and eventually predicted that the current density proximal to the edge of the BTO nanodot was extremely high, which was a rather interesting finding. The existence of this specific area, known as the triple phase interface (BTO–LCO–electrolyte), considerably improved the electrical performance of the cathode coated with tiny BTO nanodots.
As anticipated, after the scientists tested and compared the three cathodes prepared by them, they discovered that the one coated with a layer of a BTO dots showed a relatively better performance, in terms of discharge capacity as well as stability.
Our results clearly demonstrate that decorating with BTO nanodots plays an important role in improving cyclability and reducing resistance.
Mitsuru Itoh, Professor, Tokyo Institute of Technology.
Once the researchers realized that the BTO dots had a major impact on the motility of Li ions in the cathode, they started to look for an explanation.
After analyzing their measurements results, the researchers eventually reached a conclusion that BTO nanodots produce a unique interface through which Li ions can effortlessly intercalate and de-intercalate, even at extremely high charge/discharge rates. This is attributed to the concentration of the electric field around materials having a high dielectric constant. In addition, the creation of a solid electrolyte interface is also considerably suppressed close to the triple phase interface, which otherwise would lead to poor cyclability.
The mechanism by which the formation of a solid electrolyte interface is inhibited near the triple phase interface is still unclear.
Mitsuru Itoh, Professor, Tokyo Institute of Technology.
Although more research on this subject has to be carried out, the outcomes achieved by the scientists appear to be promising and could provide a new means to considerably enhance the performance of LIBs. This can prove to be a major step for addressing the requirements of contemporary and futuristic devices.