Synthesis Of The Flexible Current Collectors Of Graphene/Aluminium Foil And Their Performance In Various Lithium Battery System

Flexible batteries with high-performance used in the flexible electronic devices exhibit widely application prospects in the fields of portable electronic devices,wearable product and medical device.The ideal flexible batteries can operate while it is bending,folding and stretching,and it also exhibit high energy and power density at the same time.The performance of the flexible batteries is determined by the flexible current collector.This dissertation investigated the electrochemical performance of two kinds of flexible current collectors in various lithium batteries,which prepared by using the aluminum foil modified with a silane coupling agent and prepared by using a graphene solution,respectively.Many advanced techniques,such as X-ray powder diffraction method,energy spectrum,scanning electron microscopy,contact angle measurement,peel strength test,cyclic voltammetry curve,electrochemical impedance spectroscopy and charge and discharge test,were employed to investigate the key factors which determine the electrochemical performance of flexible current collectors.The main conclusions as following:1.The silane can form a self-assembled monolayer on the surface of aluminum foil in an appropriate hydrolysis condition.The as-prepared aluminum foil modified by a self-assembled monolayer（Al-SAM）exhibit good electrochemical corrosion-resistant properties in the electrolyte with HF solution.The Al-SAM exhibit the first cycle capacity of 135.9 m Ah·g^-1 and the coulombic efficiency of 89.9%in the battery system of gel polymer electrolyte/Li Fe PO₄ cathode materials（Gel-Li Fe PO₄）.In a continuous charge-discharge test with various current,the Gel-Li Fe PO₄ exhibit the first cycle capacity of 162.4m Ah·g^-1（0.1C）and 142.6 m Ah·g^-1（1C）,respectively.2.The as-prepared flexible graphene current collector（GCC）and the GCC after bending for 500 cycles were investigated the electrochemical performance in the cell with Li Fe PO₄ cathode.Compared to the normal aluminum foil current collector,the Li Fe PO₄-flexible GCC cathode exhibit higher capacity and voltage platform.The Li Fe PO₄-flexible GCC cathode exhibits the first cycle discharge capacity of 165.2 m Ah·g^-1 and the coulombic efficiency of 81.8%at 0.1C rate.In a continuous charge-discharge test with various current,the Li Fe PO₄-flexible GCC cathode exhibits the first cycle capacity of 168.2m Ah·g^-1（0.1C）and 134.8 m Ah·g^-1（5C）,respectively.While charge-discharged at 0.1C rate,the Li Fe PO₄-flexible GCC cathode after bending for 500 cycles exhibits the first cycle discharge capacity of 153.5 m Ah·g^-1 and the coulombic efficiency of 85.7%;and exhibits the 200th cycle discharge capacity of 121.4 m Ah·g^-1 and the coulombic efficiency of100.1%.In a continuous charge-discharge test with various current,the Li Fe PO₄-flexible GCC cathode after bending for 500 cycles exhibits the first cycle capacity of 162.5 m Ah·g^-1（0.1C）and 27.7 m Ah·g^-1（5C）,respectively.3.The as-prepared flexible graphene current collectors（GCC）and the GCC after bending for 500 cycles were investigated the electrochemical performance in a Li-S cell.The sulphur/carbon-flexible GCC cathode（S/C-flexible GCC cathode）exhibits the first cycle discharge capacity of 952.5 m Ah·g^-1 and the coulombic efficiency of 100%at 0.1C rate.The S/C-flexible GCC cathode after bending for 500 cycles exhibits the first cycle discharge capacity of 792.7 m Ah·g^-1 at 0.1C rate.In a continuous charge-discharge test,the S/C-flexible GCC cathode after bending for 500 cycles exhibits the first cycle capacity of864.6 m Ah·g^-1（0.1C）and 343.9 m Ah·g^-1（2C）,respectively.