UNIST Develops Innovative Electrolyte Additive

The Ulsan National Institute of Science and Technology (UNIST) announced on Feb. 14 that its research team led by energy and chemical engineering professors Choi Nam-soon and Kwak Sang-kyu and chemistry professor Hong Sung-you developed an innovative electrolyte additive with which an EV battery can retain more than 80 percent of its initial capacity even after hundreds of charges and discharges.

With the demand for large-capacity batteries rising, a number of research projects are underway to replace the electrodes of commercial lithium-ion batteries with high Ni and Si as high-capacity materials. However, the former is problematic in terms of chemical stability and the latter is not mechanically durable as its volume repeatedly increases and decreases more than three-fold as a result of charging and discharging.

In the additive developed by the team, a protective film covers the surface of the Si-containing negative electrode and the highly flexible and elastic film ensures a high level of lithium-ion mobility. As a result, the additive is capable of reducing a mechanical overload attributable to repeated Si volume changes and enabling rapid charging. In addition, the additive blocks nickel outflow from the anode by HF removal from the electrolyte. The amount of the metal inside the anode is the very factor that determines the capacity of a battery.

The team applied the additive to a large-capacity battery including a high Ni anode and a Si-containing cathode, charged and discharged the battery 400 times, and confirmed that the battery retained 81.5 percent of its capacity. The outcome is a 10 percent to 30 percent improvement on existing commercial additives such as fluoroethylene carbonate and vinylene carbonate.

Details of the research have been published, as Editors’ Highlights, in the Feb. 5 edition of Nature Communications.