Fabrication And Application Of New Current Collectors Based On Carbon Nanotubes And Copper Coated Carbon Fibers For Lithium Ion Battery

As a secondary energy storage battery with high energy density,lithium-ion battery?LIB?has drawn much attention.LIB is mainly composed of anode,cathode,electrolyte,separator and battery case.The capacity of the battery is mainly provided by the active material in the anode and cathode.The lithium-ion battery electrode is mainly composed of an active material layer and a current collector.The active material layer mainly includes active material,binder and conductive agent.With the blossom of its application areas,more efforts are focused on fabricating high-performance new LIBs with higher energy,higher power density and longer life cycle.In order to comply with this trend,modification of electrode materials has become a hot research topic in LIBs.However,the electrochemical performances of LIBs depend not only on active materials but also other components and factors,such as the electrode structure,current collector,binder,separator,electrolyte,and so on.The component current collector plays a critical role in electronically connecting the active material layer with an external circuit,which is regarded as an indispensable part of LIBs.Two new current collectors with particular structures are fabricated based on multi-walled carbon nanotubes?MWCNTs?and copper-coated carbon fibers.Their effects on the electrochemical performance of lithium-ion batteries are also studied.The fabrication processes of the new current collector and the electrodes for LIBs are studied and introduced in detail in this study.The specific research work is as follows:?1?A conductive layer made of MWCNTs,with micro-cracks and micro/nano porous structure is fabricated on the surface of Cu foil and Al foil in this study.The coating thickness of MWCNTs-based conductive layer?MCL?varies in the range of 25-100?m.For comparison,a normal MCL with a smooth and firm surface and a comparable thickness was also prepared by fully coating dispersed MWCNTs slurry onto the surface of Cu or Al foil.The mesocarbon-microbeads?MCMB?anode and the LiCoO₂ cathode are fabricated by using the new current collector.The binding forces between the active material and the current collector are studied.Finally,the optimal coating thickness is obtained.?2?The electrodes with micro-cracked MWCNTs conductive layers or normal MWCNTs conductive layers are assemblied into lithium-ion half-cell.Their influences on electrochemical performance of the anode and cathode for LIB are studied by charge/discharge test and electrochemical impedance spectroscopy?EIS?test.?3?The copper coated carbon fibers stirring electroplating process is studied by the control of chopped carbon fiber concentration,electroplating time and electroplating current to prepare better copper coated carbon fibers.And then the copper coated carbon fibers are sintered onto the surface of the 9?m thick copper foil by high temperature sintering process.Finally prepare copper-coated carbon fiber current collector.?4?Four kinds of copper coated carbon fiber current collectors with different structures are prepared by controlling the quality of copper coated carbon fiber,and then the anodes for LIBs are prepared with MCMB as active material.Lithium-ion half-cells are assembled with lithium palate as the counter electrode.The influences of the three-dimensional porous structure of copper coated carbon fiber current collectors on the electrochemical performance of the electrodeare investigated discharge/charge test and EIS test.?5?The position of the MWCNTs layer is changed at the copper coated carbon fiber electrodes to prepare three different electrodes.The effects of MWCNTs layers on the electrochemical performance of the copper coated carbon fiber electrodes are studied by cyclic charge/discharge test and EIS test.