The effect of annealing and multilayer structure on promoting the electrochemical performance of Al/Si thin film anodes

•Al interlayers can enhance the structural stability of Si-based thin film anodes.•The mechanism of annealing to improve the stability of the SEI layers is discussed.•C/(Al/Si)4/TiO2-30 min anode achieves 80.5 % capacity retention rate after 500 cycles.•The stable block structure can improve the electrochemical performance of the anode. C/(Al/Si)n/TiO2 multilayer thin films with the controllable number of (Al/Si) layers (n = 1, 2, 3, 4) were prepared by magnetron sputtering. The effect of the inserted Al layers and annealing process on the electrochemical performance of the anodes have been discussed. Among the samples before annealing, C/(Al/Si)4/TiO2 thin film anode exhibits a better capacity retention rate after 500 cycles. The annealing process was performed to facilitate the diffusion of Al and Si layers in the film, improving the conductivity of the anode. The result is a decrease in the resistance and an increase in the Li+ diffusion rate of the anode. The annealing process also forms the Al-Si phase. During the cycling process, the Al-Si phase reacts with the electrolyte to form a Li-Al-Si ternary phase, which can improve the stability of the solid electrolyte interphase (SEI) layer. C/(Al/Si)4/TiO2 thin film anode annealed at 300 °C for 30 min (C/(Al/Si)4/TiO2-30 min) forms a stable block structure during cycling, which can alleviate volume expansion, enhance Li+ diffusion rate and exhibit adaptability to high current densities of the thin film anode. It is shown that C/(Al/Si)4/TiO2-30 min thin film anode obtains an initial discharge capacity of 2419 mA h g−1 and a capacity retention of 80.5 % after 500 cycles. In addition, this thin film anode exhibits superior rate performance, maintaining a capacity of 1453 mA h g−1 after 500 cycles at 5 A/g and a capacity above 1463 mAhg−1 even at 30 A/g.