Functionally Graded Si Based Thin Films as Negative Electrodes for Next Generation Lithium Ion Batteries

A functionally graded SiCu film is deposited by magnetron sputtering to overcome the quick failure problem of the Si thick film electrode. As the stress induced by lithium intercalation along the electrode and the embrittlement caused by lithium segregation at the electrode-current collector interface are believed to be the main reasons for capacity fade, depositing a pure Cu layer first, then providing a gradual increase in Si is believed to be a promising solution for future high capacity next generation lithium-ion battery (LIB) anodes. This electrode delivers 2073 mAh g^-1 with 80% coulombic efficiency in the first cycle and retains 70% of its initial capacity after 100^th cycle. We believe that pure Cu layer at the bottom minimizes the segregation of Li due its inactive behavior and increases the adhesion of the coating. Moreover, the gradual decrease of Cu in the first 1.7 micron of the film diverts the stress propagation along the thickness while improving the deformation characteristic during cycling. And, the existence of 10% at. Cu atoms at the top region (around 0.7 micron) along with Si atoms, improves the physical as well as the mechanical properties of the electrode leading to a high electrochemical performance.