Preparation And Properties Study Of PVDF-HFP/MWCNT Of Inverse Opal Structural Gel Electrolyte And Lithium-ion Capacitor

Possessing the merits of high energy density,power density and long cycle life,lithium-ion capacitors（LIC）integrating battery-type electrodes,supercapacitor-type electrodes and separators have abroad applications for power storage devices,new energy vehicles,and portable wearable devices.Currently,high-performance lithium-ion capacitors are limited by factors such as the low ion transport rate of the electrolyte,electrochemical window,mechanical strength,and thermal stability,making it difficult for the device to achieve ideal performance and a wide range of applications.To overcome above difficulties,the methods of roll pressing,hot pressing and site occupancy etching are herein proposed to prepare polyvinylidene fluoride-hexafluoropropylene（PVDF-HFP）/multi-walled carbon nanotube（MWCNT）of inverse opals structural gel Electrolytes（GPEs）with ordered structure and controllable pores.By constructing a polymer 3D porous network and the formation of intermolecular hydrogen bonds between PVDF-HFP and MWCNT,the inherent defects of the inverse opal structure gel electrolyte were overcome,resulting in inverse opal structure separator（prepared with Si O₂ size of 660 nm,silica content of 75%and MWCNT addition of 3 wt.%）with excellent properties:1)high ionic conductivity(1.78×10^-3 S·cm^-1);2)high mechanical strength（9.2 MPa）;3)good thermal stability（thermal shrinkage at 160°C）.After assembling it to the LIC,the device exhibits excellent cycling stability with a capacity retention of 68%after 8,000 cycles at a high current density of 1 A g^-1.Meanwhile,the device can keep working under different pressure and temperature（the coulombic efficiency is close to 100%）,which shows good application ability.The main work of this paper is as following:（1）To realize the controllable preparation of porous structures of gel polymer electrolytes,silica（Si O₂）nanospheres with different particle sizes（440 nm,490 nm,660 nm,710 nm）were prepared by the St（?）ber method to achieve precise control of the pore size and porosity of the inverse opal structure.At the same time,in order to eliminate the defects of the inverse opal structure,the commercial MWCNTs were modified with diazonium salts to improve their dispersibility and functionalize the surface.Doping of modified MWCNTs with polymers eliminates the inherent defects of the inverse opal structure.（2）In order to study the change of fillers on the performance of inverse opal polymer gel electrolytes,the microstructure of inverse opal and the mechanism of interaction between fillers and polymers were characterized by SEM and FT-IR.And,the ion transport rate,mechanical strength and thermal stability of gel electrolyte were tested by electrochemical tests,thermal shrinkage tests and tensile stress tests to highlighting the superiority of the inverse opal structure and the promotion of MWCNT for ion transport in polymer electrolytes.（3）The inverse opal structure PVDF-HFP/MWCNT gel electrolyte and electrodes were assembled into lithium-ion capacitors,which showed excellent rate performance(0.1～3 A g^-1)and charge-discharge capacity（8000 times of charge and discharge,coulombic efficiency is close to 100%）.And the lithium-ion capacitors were charged and discharged multiple times under different temperature gradients（25,40,75°C）and different pressures（0,1,1.5,2 MPa）,and the results showed that the device has stable and efficient charge and discharge capabilities（the Coulombic efficiency is close to100%）to provide new ideas for efficient energy storage in complex environments.