Studies On Applications Of Super-aligned Carbon Nanotube Macroscopic Architectures In Lithium Batteries

The energy demand in this era is much higher than ever.Batteries become more and more important for its ability to store and supply energy.Lithium batteries,with high specific capacities and long cycle life,have drawn more and more attention.As the development of the electronic devices,small grids,and electrical vehicles,batteries with better electrochemical performances are in great demand.Therefore,it is crucial to achieve higher energy densities and capacities for lithium batteries.They are composed of two parts,active materials and inert materials.These two aspects can be the start points to improve the performances of lithium batteries.Super-aligned carbon nanotubes?SACNTs?,with clean surface and strong interactions among the carbon nanotubes,can be directly drawn from the SACNT arrays to form a continuous SACNT films and construct a 3D SACNT sponge by a self-assembly method.The energy densities and specific capacities of lithium batteries would be greatly improved if SACNT macroscopic structures were applied into them because of the unique electrical and mechanical properties of SACNTs.In this work,we focus on the conductive agent with regard to inert materials.A sandwich-structured electrode was designed with cross-stacked SACNT films as conductive layers.In this electrode,the amount of Super P was cut down obviously.In the sandwich-structured electrodes,both long-range and short-range electron transport pathways could be well satisfied by SACNT conductive layers and Super P powders.The performances of the electrodes would not be undermined as the thickness increased,as a result of the characteristics of the sandwich structure to keep the same electron transport circumstances for active materials in each separate layer.The sandwich-structured electrodes with better electrochemical performances and less amount of conductive agent demonstrated higher energy densities.In addition,the sandwich structure can be applied to various kinds of active materials.In regard to active materials,sulfur is chosen as an active material for its high theoretical capacity and energy density.Broad adaption of Li-S batteries,however,has been hampered by the low electronic/ionic conductivity of sulfur and Li₂S,the shuttle effect of polysulfides and the large volumetric change of sulfur species.To address these problems,MoS₂ nanosheets was loaded onto a cross-stacked SACNT film to construct a MoS₂/CNT interlayer.With the functional interlayer,the polysulfides could be effectively entrapped and an efficient deposition interface for Li₂S was formed.Besides,the self-discharge was alleviated and the electrochemical performances were improved.In addition,the S@SACNT sponge with high areal density was fabricated.The porosity of SACNT sponge provided the sulfur with abundant reactive sites.The 3D hierarchical structure and superior absorption of the sponge could effectively suppress the dissolution and diffusion of the polysufides.The SACNT sponge facilitated the sulfur electrode with outstanding electrical conductivity and its honeycomb-like structure could accommodate volume expansion of the sulfur species.As a result,the S@SACNT sponge exhibited excellent electrochemical performances.