Effect of multilayer structure on cyclic performance of Si/Fe anode electrode in Lithium-ion secondary batteries

A buffer-strengthened Si/Fe multilayer film, consisting of amorphous silicon layers and polycrystalline Fe layers, is investigated as the anode for Li-ion batteries. This film can achieve a stable cycle-life performance with a high capacity. Decreasing the thickness of the Fe layer can lead to a higher capacity, which is related to the fast transport of the Li ion, but the cyclic performance deteriorates with repeated cycling. In contrast, increasing the thickness of the Fe buffer layers and the number of deposit stacks improves the cycle life with high reversibility. Because of the strain in the Si layers suppressed by the primary multilayer structure, the long-term strength is preserved and the substantial fracture toughness is enhanced by the increasing numbers of effective grain boundaries and interfacial layers. In addition, we demonstrate that the Ti underlayer promotes the electrochemical properties in the Si/Fe multilayer for various Fe layer thicknesses because of the enhanced adhesion of the interfacial electrode and current collector. The mechanically optimized Si/Fe multilayer films can have superior cycle-life performances and higher capacities. Notably, the 16-bilayer deposited electrode exhibits an excellent capacity retention of ∼95% with ∼204 mAh g^-1 over 300 cycles at a 1 C rate.