An Investigation On Carbon Nanotube As Binder In Electrode For Flexible Lithium Ion Batteries

With the continuous development of technologies,Lithium-ion batteries?LIBs?play a more and more important role in our lives.Especially for 3C products,as well as the smart wearable devices and electric vehicles,that should be charged and discharged quickly with higher energy density,flexibility and safety.The energy density of the traditional LIBs is mainly limited by the weight of the metallic current collector and the binder.In addition,the rate capability cannot be increased for high contact resistance among the active material,binder and metallic current collector.Moreover,the LIBs become unsafe as short circuit occurs.The above issues should be explored urgently.Carbon nanotubes?CNTs?,as a new type of carbon material with high aspect ratio,have many excellent properties,including high electrical conductivity,high thermal conductivity and low density.Thereby,it indicates potential applications in LIBs.In the early stage of our group,we prepared free-standing CNT macro-film?CMF?by CVD method,and the flexible LIBs based on the CNT current collectors displayed an excellent electrochemical performance.In this thesis,an integrated binder-free LiCoO₂?LCO?,Li₄Ti₅O₁₂?LTO?and Graphite?Gra?electrode for LIBs was prepared by a spraying method based on the CMF technologies.The obtained LIBs suggest excellent electrochemical performances.The main results are as follows:?1?An integrated electrode without a binder and current collector was prepared by spraying method at CNTs process with CVD method.The different types of electrodes can be batch prepared quickly in scale with a wide range of particle size and mass loading of active materials.?2?The active materials were segregated by CNT bundles with three-dimensional network and formed integrated electrode.The surface of the obtained electrode indicates a low electrical resistance of 3??the value of the traditional electrode is about 100??.The electrode also can be easily bent,folded even after hundreds of operation and thereby it display excellent flexibility.The mass of active material would account for 95%of the whole electrode.Due to active materials in the CNT networks,the contact resistance of the electrode would be decreased,and the energy density of the LIBs could be increased significantly?304.6 Wh/kg?.?3?The good cycle stability and rate capability of the full cells based on the electrode has been demonstrate.The specific capacity of the LCO-CNTs/LTO-CNTs battery is 134.89 mAh/g at 10 C(the corresponding metallic LIB is 33.87 mAh,and the value of the LCO-CNTs/Gra-CNTs battery is 87 mAh/g at 10 C?the correnponding metallic LIB is 59 mAh/g?.?4?The integrated LIBs show excellent foldability,and they could not be affected even after hundreds of folds.Furthermore,the integrated structure of the batteries suggest increased electrical resistance when the shortcircuit occurrs.