Prior to filing for bankruptcy in October, A123 had received about half of its grant.
Thune and Grassley had earlier raised questions in August about a failed attempt by Wanxiang, an auto parts supplier, to rescue faltering A123.
That $465 million rescue deal fell apart when A123 was unable to meet some conditions of the agreement.
Republicans have latched on to A123’s bankruptcy as another example of the Obama administration’s failed attempt to kickstart the U.S. clean energy sector.
The Obama administration has defended its efforts, arguing that despite some high profile bankruptcies, most of its investments have been successful and have to helped to double renewable energy output from wind and solar.