UBE Industries, which last week announced a new electrolyte development center for large Li-ion batteries in Europe (earlier post), is targeting the development of functional electrolytes for Li-ion batteries for automotive applications. At the Advanced Automotive Battery Conference (AABC) in Pasadena this week, Yoshihiro Ushigoe, manager of the electrolyte development team for UBE provided an overview of the company’s efforts.
The electrolyte is one of the four main components of a Li-ion battery, the other three being the separator, the cathode, and the anode. In his AABC tutorial on battery materials, Prof. Martin Winter from the University of Muenster noted that the electrolyte is a key system component, and should be treated as such.
UBE has been a leader in the development of the concept of functional electrolytes, reporting on them for the first time in 1999. Functional electrolytes are small amounts of chemical additives mixed in a highly-purified electrolyte base to introduce a specific high-performance functionality, or role, in the electrolyte system.
Due to the high purity of UBE’s base electrolyte, electrolyte decomposition itself is inhibited, UBE notes. Consequently, a small amount of additive is deliberately decomposed on the anode surface to produce the solid electrolyte interphase (SEI) to improve battery performance.
Various compounds are already in use as electrolyte additives, including agents for anode passivation (SEI), cathode protection (cathode SEI), overcharge protection, wettability improvement, flame retardation, trapping of undesired components, and improving electrolyte conductivity, among many others.
|Novolyte functional additives for electrolytes|
|In a separate presentation at AABC, Martin Payne from Novolyte presented results showing that Novolyte’s new D5 additive shows equal or better performance in cell testing at equal additive levels and is an acceptable replacement for the industry stand-by vinylene carbonate (VC).|
|Payne also noted that several approaches can be taken to solve high temperature challenges, each dependent on cell chemistry and specific electrolyte components.|
|Novolyte is also developing a series of new additives that reduce flammability and enhance safety. The NF additive also sow improved performance in cycling, capacity retention, rate performance and storage.|
In 2007, in a paper in the Journal of the Electrochemical Society, UBE researchers reported a novel type of anode additive containing a triple-bonded moiety, which produces a thin and dense SEI, improving battery performance, especially in cycleability.
A practical electrolyte may contain more than one additive. In a subsequent paper published in 2008, the UBE researchers observed a novel and unique effect of an additive combination. The combination of triple-bonded compounds and double-bonded compounds showed much improved battery performance, especially in cycleability and gas evolution, than the case when they are singly used.
In this specific case, the team suggested that the higher battery performance of the combination effect resulted not only from the thin and dense SEI on the negative electrode but also from the positive electrode surface co-polymerized film produced by the synergetic decomposition of the additives.
UBE is now focusing on the development of an electrolyte able to be utilized at a higher working voltage (for higher capacities) and over a wider working temperature. Complicating matters, lithium-ion batteries (LIBs) at higher working voltages or temperatures have inherent problems of property degradation or gas evolution.
Koji Abe, Takashi Hattori, Kazuyuki Kawabe, Yoshihiro Ushigoe, and Hideya Yoshitake (2007)Functional Electrolytes J. Electrochem. Soc. 154, A810 doi: 10.1149/1.2746570
Koji Abe, Kazuhiro Miyoshi, Takashi Hattori, Yoshihiro Ushigoe, Hideya Yoshitake (2008) Functional electrolytes: Synergetic effect of electrolyte additives for lithium-ion battery, Journal of Power Sources, Volume 184, Issue 2, Pages 449-455 doi: 10.1016/j.jpowsour.2008.03.037.