Study Of Si/Ge Films And Si/MXene Composites For Lithium-Ion Storage

Si anode has ten times theoretical specific capacity of commercial graphite,which is very attractive.However,the volume change during charging/discharging and poor electrical conductivity reduce the promotion of Si anodes in the field of energy storage.Therefore,suppress the volume change and improve the conductivity of the Si anode is an important research of lithium-ion batteries.In this Paper,low Ge content of Si/Ge film anode and different structures of Si/MXene anode materials were prepared by magnetron sputter deposition and wet etching.Take the excellent electrical conductivity of Ge and special two-dimensional structure of MXene materials.Which can alleviate the volume change during charging/discharging and improve the conductivity of Si anodes.Investigate the effects of different Si anode materials on the cycling performance and rate capability performance of Si anode.The main research contents of this Paper are listed as follows:（1）The low Ge content of Si/Ge film were prepared by magnetron sputtering technology at the room temperature and the Ge content was only 12%.At the thickness of125 nm,compare with the same thickness of the Si film anode,the cycle performance of the Si/Ge film cannot produce the optimization of the cycling performance.But the cycle performance is significantly improved when the thickness is increased to 250 nm and500 nm.At a rate of 0.2 C after 100 cycles,the capacity retention rate respectively increase 13.6%and 41.7%.In the rate capability tests,at the rate of 1 C,the capacity retention rate of 250 nm and 500 nm Si/Ge film compare with the same thickness Si film anode also increased 1.39%and 5.7%.（2）The annealing process was used to further optimize the Si/Ge thin film anode,and the effect of annealing temperature on the lithium storage performance of the Si/Ge thin film anode was investigatd.The annealed 250 nm and 500 nm thick of Si/Ge film anodes have the best cycling performance at 300℃and 400℃.At a rate of 0.2 C after100 cycles the capacities are 1326 m Ah/g and 875 m Ah.All the rate capability performance is the best at 400℃.The analysis shows that the cycle of the Si/Ge thin film anode is affected by the crystallinity of Ge and the release of internal stress by annealing,while the rate performance is affected by the crystallinity of Ge and the degree of diffusion for Si and Ge.（3）The single-layer Ti₃C₂ and multi-layer Ti₃C₂ are compounded with Si NPs and Si NWs to prepare different structures of Si/MXene anode materials.By analyzing the battery cycle performance,the optimal combination of Si and Ti₃C₂ was studied.The results show that the free-standing Si/MXene anode has low capacity due to the tight Ti₃C₂ structure that prevents the enter of electrolyte.The composite of multi-layer Ti₃C₂and Si NWs has poor cycling performance,That’s because the large aspect ratio of Si NWs makes it difficult to enter the open structure of Ti₃C₂.The composite of multi-layer Ti₃C₂and Si NPs has excellent cycling performance,That’s because the open structure of the multi-layer Ti₃C₂ can effectively accommodate and protect the Si NPs to improve the cycling performance of the material.