A Functional Energy Storage Device Based On Carbon/Carbon Hybrid Foam And Its Performance

As an indispensable part of portable electronic products,supercapacitors are required to maintain stable electrochemical performance under various deformations(such as compression,bending,etc.)as well as a wide temperature range(-30℃～50℃).Therefore,the development of supercapacitors with compressibility and antifreeze function is of great significance to promote the practical application of portable electronic products.This thesis mainly includes the following aspects:(1)In this work,using melamine sponge(MS)as matrix,nanocellulose/carbon nanotubes(CNF/MWCNT)aerogel sheets were uniformly stacked in a three-dimensional mesh framework of MS by freeze-drying,and then carbon/carbon foam(CF)hybrid materials were prepared by high temperature carbonization.The hybrid material can not only withstand 70%compression deformation,but also has high conductivity and high surface area,which provides a good platform for the loading of active substances.Therefore,Fe3O4-CF was used as a platform to introduce electroactive material.The results show that the area capacity of Fe3O4-CF can reach 727.6 mF/cm2(=169.2 F/g)at the current density of 1 mA/cm2.In addition,polypyrrole(PPy)active material was introduced to produce PPy-CF positive electrode material,and PPy-CF//Fe3O4-CF-ASC asymmetric compressible supercapacitor was assembled,which could be reversibly charged/discharged under the voltage window of 1.6 V.It also has significant specific capacity and energy density values of 172.5 F/g and 59.9 Wh/kg,and maintains good electrochemical performance even under different compression degrees(10%～50%).(2)Herein,a multi-hydrogen bond cross-linked hydrogel was prepared based on the copolymerization of acrylic acid(AA)and acrylamide(AM),using hyperbranched resin as the cross-linking agent,NaAc and LiCl as the complex electrolyte.The results show that the hydrogel not only exhibits good reparability,adhesion and flexibility,but also has a wide voltage window of 1.4 V and excellent frost resistance.The ionic conductivity reached 3.45 S/m at-30℃(even at the extremely low temperature of-50℃,the ionic conductivity can still reach 1.53 S/m).In order to further demonstrate its application in energy storage devices.In this paper,a sandwich supercapacitor with energy density of 26.87 Wh/kg and power density of 554.0 W/kg was assembled by using carbon/carbon hybrid foam(named GCF)modified by graphene as electrode and hydrogel electrolyte as electrode.As expected,the device also showed excellent electrochemical performance at low temperatures.For example,at-30℃,the mass specific capacity at 1 A/g is 73.7 F/g,and the capacity retention rate can reach 75.57%of that at normal temperature(25℃).In addition,after 5000 cycles at different temperatures(25 ℃、0℃、and-30℃),the capacitance retention of the device reached more than 95%.In conclusion,the assembled supercapacitor not only has excellent antifreeze function,but also has excellent electrochemical performance.