Compositionally-graded silicon-copper helical arrays as anodes for lithium-ion batteries

Restrictions in silicon based anodes have been the subject of many researches for years. As an innovative approach, we have adopted ion assisted deposition technique to glancing angle deposition method and have used compositionally-graded structuring. A unique helical shaped gradient film has been produced in which the Cu/Si atomic ratio decreases from the bottom to the top of the coating. With such a unique film (high surface area) more spaces have been created promoting mechanical integrity and reaction between active materials (silicon) with lithium ions. The highly adherent film is formed as a result of ion assisted deposition process and the gradual change in Cu/Si atomic ratio diverts stress through the helices. To compare the performance of the SiCu electrode, a pure Si film is deposited in the same experimental condition. Galvanostatic test results show that although the film with pure Si helices fails after 30th cycles, the compositionally graded anode exhibits a capacity of 1228 mAh g^-1 at the 100th cycles with 99.5% coulombic efficiencies when cycled at 100 mA g^-1, and delivers 815 mAh g^-1 when cycled with a rate of 400 mA g^-1.