Preparation Of Biomass Carbon Composites And Research On Their Energy Storage And Wave Absorption Properties

With the rapid development of science and technology and the continuous improvement of people’s living standards,intelligence is entering people’s lives with lightning speed.In the whole environment system of smart home,whether it is smart devices,products or short-range wireless communication technology,needs the support of electrochemical energy storage devices and equipment such as batteries and capacitors.The continuous innovation of products has also brought forward higher requirements for the support of its electrochemical energy storage devices and equipment.On the other hand,while smart home provides human beings with a comfortable environment and experience,its electromagnetic waves and other radiation have brought a certain threat to health,and electromagnetic wave absorbing materials have also become a research hotspot.Against this background,this study uses the biomass material sodium alginate(SA)as a soft template,using its gel properties to chelate ferric ions in order to obtain an iron alginate skeleton(FA),and then introduces small molecular carbon source p-phenylenediamine for polymerization and carbonization at 600～800℃ in order to obtain a new type of magnetic iron-based core-shell nitrogen-doped carbon(Fe3C@N-doped C)composite.After a series of characterization methods,it was confirmed that carbon composites with high nitrogen content(5.84 wt%)can be synthesized at low temperature with 5～8 layers of graphite-like structure wrapped with Fe3C as the core center.Fe3C@N-doped C series materials at different carbonization temperatures were used as electrode materials to explore their electrochemical properties in energy storage devices such as supercapacitors and lithium-ion capacitors,and to explore their wave-absorbing properties.The results are as follows:(1)The multi-layer graphitized Fe3C@N-doped C composite with high micropore content was used as an electrode material in a supercapacitor for a series of electrochemical performance tests.The results show that the Fe3C@N-doped C-600 composite with a specific surface area of 446 m2 g-1 possesses a specific capacity of 175 F g-1 in 6 M KOH electrolyte and 132 F g-1 in 1 M H2SO4 electrolyte.The capacity retention was 66.7%after 10,000 cycles in a two-electrode system in an acidic 1 M H2SO4 electrolyte at a current density of 20 A g-1.(2)Fe3C@N-doped C composites were used as electrode materials in lithium-ion batteries(LIBs)for a series of electrochemical performance tests and characterizations.The results show that all the specific capacities of Fe3C@N-doped C series electrode materials carbonized at 600～800℃ are much higher than the theoretical value of graphite(372.0 mAh g-1)at 0.1 A g-1,reaching 500.5～566.0 mAh g-1.Among them,Fe3C@N-doped C-700 exhibits a more prominent specific capacity,and still maintains a discharge specific capacity of 136.6 mAh g-1 which means a capacity retention rate of 91%after 5000 cycles.Based on the above conclusions,Fe3C@N-doped C-600 and 700 were used as anode materials in lithium-ion capacitors(LICs)for a series of electrochemical performance tests and characterizations.The results show that Fe3C@N-doped C-700 has a specific capacity of 29.6 mAh g-1,a specific energy of 86.6 Wh kg-1,and a corresponding specific power of 293.5 W kg-1 when the current density is 0.1 A g-1.Under the working voltage of 2.0～3.8 V,the high specific energy of 44.3 Wh kg-1 and the high specific power of 14.0 kW kg-1 are still maintained at the current of 5.0 A g-1.And after 10,000 charge/discharge cycles,LIC still retains almost 100%of the initial capacity,making it a candidate material for future LICs.(3)The effects of different filling amounts and different carbonization temperatures on the absorbing properties of magnetic Fe3C@N-doped C series materials were investigated.The results show that when the mixing ratio is 1:2,the order of the maximum reflection loss is:-39.72 dB(Fe3C@N-doped C-700@1.5 mm)<-13.88 dB(Fe3C@N-doped C-600@1.8 mm)<-12.91 dB(Fe3C@N-doped C-800@1.0 mm),while the effective absorbing frequency band is ordered as 4.01 GHz(Fe3C@N-doped C-700)>3.55 GHz(Fe3C@N-doped C-600)>1.72 GHz(Fe3C@N-doped C-800).In general,Fe3C@N-doped C-700 composites have the best absorbing properties and excellent performance,which can be used as high-quality candidate materials in the field of corrosion-resistant absorbing materials in the future.