Investigation On NiTi/Si Negative Electrode Composite For Li-ion Batteries

Li-ion rechargeable batteries have attracted high attention comparing with other rechargeable batteries because of their high energy density,long cycle life,and low cost for applications in various fields.In commercial Li-ion batteries,graphic carbon has been used as an anode material with the theoretical capacity of 372mAh/g.In order to improve the capacity of Li-ion batteries,silicon(Si)is quite a promising candidate for anode material due to its high theoretical capacity(3578mAh/g),which is 11 times larger than that of graphic carbon.Unfortunately,Si electrode shows poor cycle life,which originates from the large volume change of Si(~400%)during charge-discharge(lithiation-delithiation)process,causing surface cracking and even pulverization and leading to poor electrical performance.In recent times,many researches have been made to solve this problem by enhancing the adhesion between the Si film and a current collector(substrate)to restrain the generation of stress.Among them,NiTi alloys are promising candidates for substrate material because of the shape memory effect,and several attempts have been tried recently.In this study,Si/NiTi composite film was produced by hot pressed sintering and magnetron sputtering and the relationship between structure,phase constitution,and electrical performance was evaluated.The main results achieved are listed in the following:1.Si/ NiTi composite film was produced by hot pressed sintering,and the relationship between structure and electrical performance was evaluated.The cell battery assembled by the Si/NiTi thin film electrode has significant capacity fading in the initial cycles,while it has a constant capacity of ~550 mAh/g after 40 cycles.So the cycle performance of the produced Si/NiTi composite film electrode is better than Si electrodes on traditional current collectors.2.Si/ NiTi composite film was produced by magnetron sputtering and the relationship between structure,phase constitution,and electrical performance was evaluated.Near equlatomic NiTi film was produced by adjusting the composition of the target,and the Si layer has a thickness of about 1.3?m while the NiTi layer has a thickness of 1.1?m or so.The capacity fading of the Si/NiTi thin film electrode has been restrained and it has a constant capacity of ~1546 mAh/g after 100 cycles,higher than Si electrodes on traditional current collectors.In conclusion,the Si/ NiTi composite films produced by hot pressed sintering and magnetron sputtering have better cycle performance and higher constant capacity.What's more,by adjusting the target composition and process parameter,better crystallized B2-NiTi and Si composite film can be produced as quite promising negative electrode material for Li-ion batteries.