Lithium ion batteries (LIBs) have been emerging as a major power source for portable electronic devices and hybrid electric vehicles (HEV) with their superior performance to other competitors. The performance aspects of energy density and rate capability of LIBs should, however, be further improved for their new applications. Towards this end, many Li-alloy materials, metal oxides, and phosphides have been tested, some of which have, however, been discarded because of poor activity at ambient temperature. Here, it is shown that the In-Cu binary intermetallic compound (Cu7In3), which shows no activity at room temperature as a result of activation energy required for In-Cu bond cleavage, can be made active by discharge-charge cycling at elevated temperatures. Upon lithiation at elevated temperatures (55-120 degrees C), the Cu7In3 phase is converted into nanograins of metallic Cu and a lithiated In phase (Li13In3). The underlying activation mechanism is the formation of new In-rich phase (CuIn). The de-lithiation temperature turns out to be the most important variable that controlling the nature of the In-rich compounds.