Preparation Of Carbon Fiber Three-dimensional Network And Its Application In Energy Storage

With the acceleration of the industrialization process of human society and the rapid development of economy,people put forward higher requirements for energy storage,transformation and use.The storage and transformation of electrical energy represented by lithium-ion battery and thermal energy represented by phase change materials have become the focus of researchers.The area specific capacity of the lithium-ion battery is a crucial parameter in the practical applications of various electronic devices,electric vehicles,aerospace and other fields,however,the traditional electrode material is designed by coating powder material on the current collector,so as to increase the loading of the active material,the obtained electrode is easy to fall off during the cycle.Therefore,the construction of high specific capacity anode materials with high loading capacity and stable mechanical properties has become an important research direction.In addition,the Heat Energy Storage and conversion device can use the latent heat of the phase change material to improve the energy utilization rate.However,the common organic phase change materials have the problems of low thermal conductivity and high leakage,which seriously affect the efficiency of energy storage conversion.Therefore,in this paper,carbon fiber is used as the main material,and three-dimensional carbon fiber network is prepared by slurry molding method,which has high conductivity,high thermal conductivity,low density and high structure stability,it is not only suitable for lithium-ion battery to improve its area specific capacity,but also can provide three dimensional support structure and fast thermal conduction channel for PCM to improve its thermal conductivity and thermal cycle stability.This paper focuses on the following three aspects:(1)Graphite fiber(GMF)and phenolic carbon(PC)were used to prepare3D-GMFT as negative electrode materials.The three-dimensional self-supporting structure improves the loading of the active material(50 mg cm^-2)and exhibits excellent electrochemical performance.Compared with the low area specific capacity(1.64 m Ah cm^-2)of the conventional coated electrode,its reversible capacity is increased to 5.94 m Ah cm^-2.In addition,3D-GMFT has good cyclic performance.Under the current density of 4 m A cm^-2,the specific capacity of 3D-GMFT can reach2.09 m Ah cm^-2for 90 cycles,and the capacity retention of 3D-GMFT is 68.7%.(2)Carbon fiber(MCF),phenolic carbon(PC)and carbon nanotube(CNT)as raw materials,micro-nano composite network was prepared by slurry molding.The composite was used as a thick electrode(HNT-MCF-CNT/PC)for lithium-ion battery.Compared with the pure carbon fiber network thick electrode(HNT-MCF/PC)and the pure carbon nanotube thick electrode(HNT-CNT/PC),the HNT-MCF-PC exhibits excellent electrochemical properties.The first discharge specific capacity is 37.57m Ah cm^-2.Even at 10 m A cm^-2current density,the reversible capacity is 2.5 m Ah cm^-2,which is higher than that of HNT-MCF/PC and HNT-CNT/PC.(3)3D-GMFT networks were prepared from graphite fibers with different fiber lengths,and phase change energy storage composites were prepared by vacuum impregnation with paraffin.The characterization of thermal conductivity and the analysis of thermal conductivity model show that the thermal conductivity of the composite increases from 1mm to 5mm,and the thermal conductivity of the composite increases to 13.6 W/m K^-1(0.3g/cm³),while the thermal conductivity of the composite increases to 26.81 W/m K^-1(111.7 times)with 5mm fiber length compared with that of paraffin(0.24 W/m K^-1).In addition,the carbon fiber network can effectively alleviate the problem of high leakage during the paraffin phase transition.After 40 thermal cycles,it still has a high quality retention rate of 87.83%.