The effect of copper coating on nanocolumnar silicon anodes for lithium ion batteries

• Silicon nanocolumn arrays are produced via oblique angle deposition method.
• Copper layer is deposited on silicon nanocolumns to improve the anode performance.
• Copper layer acts as a glue to improve the physical and the mechanical properties.
• Intermetallic formation enhances cycleability of the electrode.

In this work, a very thin (20 nm) copper (Cu) coated silicon (Si) nanocolums are produced by an oblique angle deposition method. Galvanostatic half-cell measurements show that, the Cu coated Si nanocolumn arrays perform 1700 mAh g− 1 in the first cycle, then after 10 cycles its performance is stabilized to 500 mAh g− 1 with 99% coulombic efficiency for 90 cycles. This high performance is related to its particular morphology and physical properties: having homogenously distributed nano-sized porosities in the Cu coated film increase the mechanical tolerance of the electrode against the volumetric changes occurred during galvanostatic test, plus the ductile behavior of the Cu film holds the electrode together to prevent the electronic isolation, pulverization or delamination of the coating, moreover the formation of Cu15Si4 intermetallic increases the mechanical resistances of the coating against the stress generated in the electrode, and the existence of the Cu top coat between the Si nanocolumns and the electrolyte changes the surface reactivity of the electrode, hence its interaction with the electrolyte leading to higher coulombic efficiency once a stable passive forms on the anode.