Capillary Shrinkage Mechanism Of Graphene Hydrogels And Its Application

Since its discovery in 2004,graphene has received extensive attention from thescientific and industrial community for its special monolayer structure and novel properties.Our research group is dedicated to designing and synthesizing the graphene-based high volumetric capacity electrode materials.We have prepared graphene-based three-dimensional(3D)hydrogels through the liquid-phase assembly of graphene.Moreover,the capillary evaporative drying strategy has been invented to obtain dense-yet-nanoporous graphene monolith(HPGM)composed of tightly overlapped graphene with a density of 1.6 g cm^-3,about 70%of the density of graphite,which is much higher than other carbon nanomaterials or porous carbon.It has provided a simple but effective strategy to balance the porous property and high density of carbon materials,which also proposes a solution for building compact carbon-based electrode with high volumetric capacity.This paper systematically studied the capillary shrinkage process and mechanism ofgraphene-based three-dimensional hydrogels.It is found that the interfacial interaction between the solvent inside the gel and the graphene nanoplates during the evaporation process is precisely controlled by changing the composition of the solvent inside the gel.The density and porosity of the carbon material can be regulated continuously and controllably.Based on the concept of material bulk modulus(K),the formula of the relationship between the deformation of the graphene-based materials and the capillary force during the capillary evaporation of the solvent is proposed,which reveals the essence of capillary evaporation drying strategy theoretically.In addition,the interfacial interaction between solvent and graphene sheets during capillary evaporation has been regulated by using solvents with different surface tensions.The shrinkage&densification process of graphene hydrogels has been analyzed and its mechanism has been proposed for the first time to construct three-dimensional macro materials by capillary evaporation,which provides both experimental and theoretical basis for the preparation of dense porous electrode materials.At last,we extended the application of the capillary evaporation method by selecting microcrystalline(MC)graphite as raw material to successfully prepare MC graphene-based hydrogel using functional modification and liquid phase assembly.The as-designed carbon material exhibits high volumetric capacity performance when used as electrode material for supercapacitors.The evaluation methods and main factors of volumetric capacity performance of supercapacitors have been summarized and proposed,respectively,and finally,a normalization formula was proposed to further standardize the evaluation criteria of volumetric capacity performance.The construction of MC graphene-based 3D assembly opens up a new way for the application of MC graphite in electrochemical compact energy storage and proposes a new direction for the further rational development of MC graphite resources in China.