High Performance Graphene Fiber

Graphene fiber(GF),consisting of well-aligned 2D graphene sheets,is a brand new carbonaceous fiber with high performances and rich functionalities.It has triggered tremendous interest due to the remarkable prospect as lightweight electrical conductors,wearable energy devices,and smart actuators.However,the combined performances of GFs,especially the mechanical strength and electrical conductivity,are still far inferior to the high expectation of single graphene,which will severely hinder their further application.Therefore,it is urgent to upgrade the performance of GFs and to develop large scale manufacturing technique to push the prototype of GFs from conception in lab to industrial production.Accordingly,this dissertation focused on the high performance and scalable fabrication of GFs,and presented systematic studies on the relationship between microstructures and macroscopic functionalities.(1)To achieve high performance GFs,we presented a full-scale synergetic defect engineering strategy to manage all the possible defects at all levels by a rational combination of flowing-stretching,fining,and graphitization.The resultant GFs possessed ultrahigh stiffness of 400 GPa and record tensile strength of 2.2 GPa,as well as the outstanding electrical conductivity of 0.8 MS/m and superb ampacity of 23 GA/m2.The exceptional combination of strength,modulus,electrical conductivity,and ampacity of our GF is unmatched by any known non-metallic macroscopic materials,making it the best-performing macroscopic graphene material.(2)Based on the well-established wet-spinning technique for single filament GF,we realized the large-scale production of qualified 100-filament GF on a home-made spinning apparatus.The protocol we established for making multifilament GFs is very simple yet controllable,and highly compatible with those of conventional polymer fibers and carbon fibers,promising industrial productivity and low cost of GFs.(3)We proposed a post-doping strategy to boost the conductivity of GFs by introducing donor type(K)or acceptor type dopant(FeCl 3,Br2)into neat GFs.After doping,the electrical conductivity of GFs significantly increased by more than one order of magnitude and was on par with those of benchmark metals.We confirmed that the soaring conductivity was ascribed to the effective increment in carrier concentration,together with the high carrier mobility of the graphene units.Importantly,the doped GFs can compete with metals in the specific conductivity.For example,the specific conductivity of K-doped GF surpassed copper and silver over 2 times and nickel about 8 times,and even competed with aluminum.This will promote the high-value use in the weight-economic applications.The well-understood doping method here is not only effective to upgrade the conductivity of GFs,but also useful in the fabrication of other dimensional graphene macroscopic materials,such as film and aerogel.(4)We successfully fabricated flexible and continuous graphene-based superconducting fibers via a well-established calcium(Ca)intercalation strategy using neat GFs as host materials.The resultant Ca-intercalated graphene fiber(Ca-GF)showed a superconducting transition at?11 K,which was almost two orders of magnitude higher than that of early reported alkali metal intercalated graphite,and even comparable to that of micro-sized intercalation compounds CaC6 and commercial superconducting NbTi wire.Considering the merits of lightness,low-cost and easy preparation of neat GFs,the superconducting Ca-GF would be useful in the field of low-temperature physics and power transmission system.In summary,targeting the realization of high performance GFs,three kinds of high performance GFs,namely,ultrastiff and strong GFs,superb electrically conductive GFs,and superconducting GFs were developed.The systematic investigation of the fabrication,structure and performance of GFs in this dissertation will contribute to further development of macroscopic assembly of graphene.