One-minute deposition of micrometre-thick porous Si-Cu anodes with compositional gradients on Cu current collectors for lithium secondary batteries

We report micrometre-thick porous Si-Cu anodes that are rapidly co-deposited on Cu current collectors in 1 min. This rapid deposition is realized by heating Si and Cu powders to ∼2000 °C and elevating their vapour pressures, while the porous and amorphous anode structure is realized by keeping the substrates at 100 °C. The films spontaneously form a 2-4.5-μm-thick composition gradient that changes from a Cu-rich region at the bottom to a Si-rich region at the top of the film, because of the higher vapour pressure for Cu than Si. A small addition of 5 wt% Cu to the Si source enhances the cycle performance of the film remarkably in a half-cell test, yielding a gravimetric capacity of 1250 mAh g_film^-1, a volumetric capacity of 1956 mAh cm_film^-3, and an areal capacity of 0.96 mAh cm_anode^-2 at the 100th cycle. However, excess addition of Cu causes partial Si crystallization in the films, which results in poorer cycle performance. While further improvement is needed, this rapid vapour deposition method yields Si-Cu films with compositional gradients on Cu current collectors in 1 min using inexpensive and safe Si and Cu powder sources, and is attractive for practical Si-based anode fabrication.