Preparation Of Carbon Fiber Nano Graphite Flake Network And Its Application In Energy Storage Materials

The development,design and preparation of energy materials are important components.Energy storage materials require their own thermal,electrical conductivity,low density,corrosion resistance and stable structure.The prepared materials often cannot integrate all the properties.In this paper,a composite network of carbon fibers(CF)and nano-graphite sheets(GNP)was prepared by slurry molding method using phenolic resin as precursor of carbon binder.The network is a pure carbon skeleton reinforcement that integrates the functions of heat conduction,electricity conduction,low density and stable structure.The network body is applied to phase change energy storage and lithium ion battery energy storage.CF-GNP/paraffin phase change composite materials CF-GNP-5000 and CF-GNP-5010 are prepared by vacuum impregnation of paraffin,which are applied to the storage and release of heat energy.The carbon-coated network bodies 5010-Ni O-PDA12 and 5010-Ni O-PDA40 were prepared by loading nickel oxide on the network bodies through hydrothermal method,and then the carbon-coated network bodies 5010-Ni O-PDA12and 5010-Ni O-PDA40 were obtained by impregnating 5010-Ni O with different concentrations of dopamine(PDA).These network bodies were then applied to the energy storage of lithium ion batteries.The composition,morphology,structure,physical and chemical properties of the composite were characterized by SEM,XRD,Raman,and CV.The results show that the addition of GNP in network of CF-GNP can improve the thermal conductivity and thermal stability of the composite;improve the energy storage stability and rate performance of the network lithium-ion battery;low concentration of PDA carbon coating can further improve the energy storage stability and rate performance of the network lithium-ion battery.SEM shows that the bonding point of CF-GNP network will become rough after adding GNP.With the increase of GNP and phenolic content,GNP blocks will appear,and other various connection paths will also appear in CF-GNP network,which can be used to improve the defect of slow heat conduction of paraffin phase change materials.The thermal conductivity efficiency of CF-GNP/paraffin phase change energy storage composite material is greatly increased compared with pure paraffin phase change material.With the increase of CF content,the time required for the CF-GNP/paraffin composite to heat up from 7?to 65?is shortened,from 1/4 of the time required for pure paraffin to about 1/7.However,the addition of GNP further enhances the heat conduction enhancement effect of the network body,and the lower the CF content of the network body,the more obvious the heat conduction enhancement effect of GNP.Thermal stability tests show that the CF-GNP/paraffin composite materials prepared in this study have good thermal stability.The CF-GNP network significantly improved the two major problems of low thermal conductivity and poor thermal stability of paraffin phase change materials.The stability and rate of lithium storage of CF-GNP-5010 added with GNP is better than that of CF-GNP-5000 without GNP.CF-GNP-5010 and CF-GNP-5000 both have higher specific discharge capacity per unit area of the first turn,reaching 23.5m Ah cm^-2 and 16.9 m Ah cm^-2 respectively.CF-GNP-5010 and CF-GNP-5000 have specific capacity per unit area of 2.5 m Ah cm^-2 and 1.47 m Ah cm^-2 respectively after100 cycles at a discharge density of 2 m A cm^-2.CV and EIS show that CF-GNP-5010has better cycle stability and Li⁺diffusion resistance in electrolyte solution is smaller.Nitrogen adsorption test results show that CF-GNP-5010 has a larger specific surface area than CF-GNP-5000 and reaches 136.1 m2/g.The load of Ni O improved the specific discharge capacity per unit area of the network 5010-Ni O and 5000-Ni O based on CF-GNP-5010 and 5000-Ni O,reaching 45 m Ah cm^-2 and 23 m Ah cm^-2 respectively,but the stability and rate performance of lithium storage and discharge of both did not improve.The lithium storage stability and rate performance of 5010-Ni O-PDA12obtained by coating 5010-Ni O network with PDA have been greatly improved.When carrying out rate performance test at current density of 1?3?5?8?5?3 m A cm^-2,its average discharge reversible capacity is 7?4.7?3.4?1.7?2.5?3.7 m Ah cm^-2 respectively.After 120 cycles with a current density of 5 m A cm^-2,it still maintained 1.6 m Ah cm^-2.