The use of high-quality and high-value coal liquefaction residues, the main by-products in the coal liquefaction process, has an inestimable impact on the resource utilization and economics of the coal liquefaction process, and is an important issue for improving the direct coal liquefaction technology. The typical composition of coal liquefaction residues is: heavy oil, asphaltene, pre-asphaltene and tetrahydrofuran insolubles (including unreacted coal and minerals). Among them, asphaltene and pre-asphaltene molecules are mainly composed of element C. The basic structural unit is a fused aromatic ring composed of multiple aromatic rings as the core, and there are several alkyl side chains of different lengths connected around the aromatic ring or The naphthenic ring has high aromaticity and high carbon content, is easy to polymerize or crosslink, and is suitable as a precursor for preparing carbon materials.
Recently, the team of Song Yan, a researcher from the Institute of Coal Chemistry, Chinese Academy of Sciences, used asphaltene or pre-asphaltene in coal liquefaction residue as the carbon source, and successfully produced a flexible porous nano-carbon fiber nonwoven fabric through electrostatic spinning combined with infusible and carbonized treatment. The method of nitric acid pretreatment combined with air infusibility and the addition of benzoic acid in the spinning dope solution effectively solved the fusion phenomenon between fibers during the infusible process. Clarified the evolution of product structure and morphology of electrospinning, infusible, carbonization and other processes, and explored the application of the nonwoven fabric in new electrochemical energy storage devices such as supercapacitors, lithium ion batteries and potassium ion batteries (ACS Sustainable Chem Eng, 2019, 7 (6): 5742-5750; Energy Fuels, 2020, 34 (2): 2445-2451, patent application number: 201711362163.4, 201810491436.3, 201810641716.8, 201810641705.X and 201811315964.X).
Since 2011, the team has carried out the preparation and structural control of flexible nano-carbon fiber non-woven fabrics, using thermosetting phenolic resin as the carbon source and polyvinyl alcohol as the spinning aid, using electrostatic spinning, curing and carbonization to successfully prepare porous Nano carbon fiber non-woven fabric (Mater Lett, 2012, 76: 211-214; patent authorization numbers: CN201110319102.6 and CN201110319111.5). By adding a pore-forming agent to the spinning dope or subsequent activation treatment, the specific surface area and pore structure of the nano-carbon fiber non-woven fabric are adjusted, and the nano-carbon fiber non-woven fabric rich in micropores or mesopores is prepared. And to some extent improved its electrochemical performance (Carbon, 2013, 51: 290-300; Chem Eng J, 2014, 249: 216-225; J Electrochem Soc, 2014, 161 (9): A1330-A1337; RSC Adv, 2015, 5 (51): 40884-40891; New Carbon Materials, 2012, 27 (2): 129-134). By adopting a nitrogen-rich precursor as a carbon source or an ammonia gas post-treatment method, a nitrogen-containing functional group is introduced into the manufactured flexible nano-carbon fiber non-woven fabric to improve its electrochemical performance (Int J Electrochem Sci, 2012, 7: 7587 – 7599; J Colloid Interface Sci, 2013, 395: 217-223 .; Electrochim Acta, 2015, 185: 40-51; New Carbon Materials, 2015, 30 (4): 295-301). By adding graphene oxide to the spinning dope, a nano-carbon fiber nonwoven fabric with graphitized structure was prepared, which improved its electrochemical performance (Electrochim Acta, 2017, 247: 1060-1071).
In addition, by introducing metal oxides or metal sulfides with high theoretical specific capacity, composite electrode materials with high specific capacity and long cycle life were prepared. When it is used as a positive electrode material for supercapacitors, the specific capacity of 1 A g-1 current density is as high as 1088.5 F g-1. Even if the current density is increased to 20 A g-1, the capacity of 860.3 F g-1 remains. When used as a negative electrode material for lithium ion batteries, it still shows good performance (Appl Surf Sci, 2018, 434: 49-56; Appl Surf Sci, 2019, 465: 635-642).