Research On High-voltage Flexible Lithium-ion Battery Based On Electrolyte-repellent Carbon Nanotube Macroscopic Membrane Current Collector

Flexible lithium ion batteries?LIBs? have received great attention as a promising power source for rapid development of the wearable electronic devices.Due to the stable electrochemical performance and bendability of the LIBs,developing flexible LIBs with high energy density become a major issue in recent years.The key component of the batteries is electrode,flexible current collector should be explored for flexible electrode.Carbon materials,such as carbon nanotubes?CNTs? or graphite?graphene? are suitable for flexible substrates for their excellent properties.CNT macro-films?CMF? were used as current collectors for anode Li₄Ti₅O₁₂?LTO? and cathode LiCoO₂?LCO?,to achieve high specific capacity and long life of the foldable LIBs before.However,the low output voltage?2.5 V? of the battery limits their practical applications.To solve the problem,fluorinated CMF was used as anode current collector for flexible LIBs with high output voltage and energy density.In this thesis,CNTs were preapred by chemical vapor deposition?CVD? and then CMFs were assembledthrough CNT socks.Next,the CMFs with low surface free energy,modified by perfluoroalky were obtained through plasma enhanced chemical vapor deposition?PECVD? technique.ATR-FTIR,XPS results confirmed that the fluorine groups are grafting of on CNTs successfully.The composition,morphology and structure of the CMF were also characterized by XRD,SEM,HR-TEM and Raman.These results indicate the structure and morphology of the fluorinated CMFs?CCMFs? have not been deteriorated by the modification processes.The obtained CCMFs demonstrated excellent conductivity and flexibility for foldable current collectors.CCMF was used as current collector to loading graphite with low potential for anode electrode.The graphite are adhered on CCMF tightly for porous morphology of the CCMF.The CCMF-Graphite/Li half-cell displays a high specific capacity of 319.6mAh/g at first charge.After 50 cycles,the specific capacity retention is as high as95.9%.The results indicated lithium ions have not been intercalated into the CCMF at 0.9 V.Thereby the electrochemical performances of the battery can be improved.The full battery of CCMF-Graphite/CMF-LCO suggests a specific capacity of133.6 mAh/g at first discharge,the output voltage increases to 3.7 V,and the mass energy density increases to 247 Wh/kg?cathode mass loading is⁵ mg/cm²?.Compared to CMF-LTO/CMF-LCO battery,the output voltage?from 2.5 V to 3.7 V? and mass energy density?from 170 Wh/kg to 247 Wh/kg? of the present battery have been improved.