Physical Sciences Inc. (PSI) proposes to develop a silicon whisker and carbon nanofiber composite anode for lithium ion batteries on a Phase I program. This anode provides high capacity, high power, and improved cycle life at a competitive cost. Silicon is low cost and has a theoretical capacity of 4200 mAh/g but it has a limited cycle life. The nanocomposite design provides a synergistic improvement in reversible capacity and electrochemical cycling as a result of the unique silicon architecture and structural reinforcement provided by the nanofibers. In the Phase I program, PSI will demonstrate a technology readiness level of 3 with an anode capacity of greater than 1000 mAh/g for over 100 cycles (100% depth-of-discharge) using 2 mAh cells. These performance goals will result in an overall battery energy density of greater than 300 Wh/kg. In the Phase II program, PSI will increase cell size to 2500 mAh and optimize cell design to further improve cycle life.