The structural evolution and lithiation behavior of vacuum-deposited Si film with high reversible capacity

The silicon film (6 μm) was prepared by vacuum deposition method on a surface modified copper foil as anode for lithium-ion batteries with high capacity and long cycle life. The modified copper foil has a rough and pyramid-like surface which helps the deposited Si film to connect toughly. The deposited hill-like Si is favorable to reduce the mechanical stress coming from the volume expansion and shrinkage of active materials during lithiation and de-lithiation. Moreover, the Si film exists mostly in an amorphous state. After cycling, partial amorphous phase transforms into the polycrystalline Si grains, forming a combination of amorphous and crystalline structure. Cyclic voltammograms (CVs) and electrochemical impedance spectra (EIS) research indicate that the vacuum-deposited thick Si film has a good reversibility of lithiation/de-lithiation. As a consequence, the thick Si film exhibits an excellent cycling performance with high reversible capacity.