Abstract
To meet the environmental concern for global issue, lithium-ion batteries have been used for electric vehicle (EV) and hybrid electric vehicle (HEV) to save oil and to decrease exhaust emissions. Besides, the increasing demands for high energy density and high power density of batteries have attracted investigators to develop new materials for lithium-ion batteries. In this study, the concept of architecture control is introduced to explore advanced negative materials. In general, Sn-based anode material is an alternative candidate for high energy lithium-ion batteries, due to its higher theoretical capacity than commercial graphite. The first part of this study aims to develop porous Sn-Cu alloy thin film battery by a sputtering technique. Cu source is introduced to increase Cu6Sn5 and to serve as a buffer during cycling. The 1st charge capacity of Sn-Cu thin film anode is 635 mAhg-1, and the 1st efficiency is even higher than 97%. The capacity remains higher than 500 mAhg-1 after 15 cycles. It is displayed that the porous structure of Sn-Cu alloy can accommodate huge volume change during cycling, further enhancing the cycling stability. To further advance the rate capability of Sn-based anodes, carbon-coated SnO2 hollow nanospheres are developed by novel shell-by-shell synthesis. Hollow structure provides a rapid lithium transport path and facilitates the C-rate capability. Moreover, ductile carbon matrix relieves the stress induced by volume change upon cycling and eliminates pure metallic Sn from agglomeration. Thus, hollow structure with 15 nm in SnO2 thickness exhibits an outstanding reversible capacity of 500 mAhg-1 at 5 C. The extraordinary performance is associated with the ultrathin SnO2 shell and the carbon layer, accommodating the volume changes and preventing the agglomeration of Sn particles during cycling. Spinel Li4Ti5O12 is also a promising anode material, due to its 3-D lithium ion diffusion pathway and negligible structure change. Nevertheless, the relatively low electronic conductivity will limit the commercialization of spinel Li4Ti5O12. Hereafter, shortening lithium transport path via architecture control to promote the rate capability of spinel Li4Ti5O12 anodes is investigated in this study. Initially, mesoporous spinel Li4Ti5O12 spheres are synthesized via conventional hard template method. The functionality of mesoporous structure will be systematically investigated. Afterwards, to increase the specific surface area of spinel Li4Ti5O12 anodes to greatly accelerate their rate capability, nanoflower-like architecture is introduced via hydrothermal process by LiOH. The nanoflower-like spinel lithium titanate shows outstanding rate capability The reversible capacity at 30 C even remains over 80 % of that at 0.5 C. Besides, the nanoflower-like spinel lithium titanate shows superior low temperature performance of 145, 142, 139, 134, 124 mAhg-1 at 0.5, 1, 3, 5, 10 C at 0 oC, respectively. Even at -20 oC, the reversible capacity at 1 C is higher than 130 mAhg-1. Spinel lithium titanate with nanoflower shape can retain both remarkable rate capability and superior temperature tolerance ability. In summary, the nanoflower-like spinel lithium titanate is expected to be a promising anode material for integrating both ultrahigh rate and extremely low temperature applications for next-generation LIBs.