Ludwigshafen, Germany – BASF has developed a new rubber binder for lithium-ion batteries. The speciality chemicals company will present the innovation at the 241st Electrochemical Society (ECS) Meeting in Washington D.C. from May 14 to 19, 2017. The new binder is based on a polyurethane-ionic liquid (PU-IL) and is used in the production of silicon anodes. Thanks to this new binder, the anodes can expand freely during use and do not break. This is a prerequisite for long battery life in electric cars.

Currently, graphite is used as the active material in the anodes of lithium-ion batteries. However, graphite has a theoretical energy density that is only 60 percent of that of silicon. This means that silicon-based anodes have the potential to more than double the energy density of lithium-ion batteries and, as a result, significantly increase their range. To do this, the silicon must be able to expand by up to 400 percent during use without breaking.

The new binder developed by BASF meets this challenge. It is based on a polyurethane and an ionic liquid. The ionic liquid is a salt in which the ions are not bound to each other by conventional chemical bonds, but by attractive forces. As a result, the ionic liquid is liquid even at low temperatures. The combination of the two materials provides the silicon anode with the ideal properties for use in lithium-ion batteries: The anode can expand without breaking and the electrolyte is not adversely affected.

"With our new binder, we are enabling the use of silicon in anodes for the first time. This is a major step forward in the development of lithium-ion batteries," says Hans-Jürgen Kuhn, Head of Battery Materials Europe at BASF.

BASF offers a comprehensive portfolio of ingredients for the production of lithium-ion batteries. These include cathode materials, such as nickel manganese cobalt (NMC) and nickel cobalt aluminum (NCA) as well as battery separators and electrolytes. BASF also offers active pharmaceutical ingredients (APIs) for the production of cathode materials. In addition, the company provides a broad range of polymer binders for the electrodes.