Research On Structure Engineering Of Laser-induced Graphene-based Electrodes And Their Electrochemical Energy Storage Performance

Graphene has been considered as an ideal material for energy storages due to its unique two-dimensional structures,as well as excellent mechanical,thermal,and electrical properties.Among different types of graphene materials,laser-induced graphene(LIG)has the advantages of high crystallinity,high conductivity and easy-to-fabricate,comparing with other types of graphene materials prepared via traditional methods,such as oxidation-reduction and chemical vapor deposition.Thus,LIG has aroused much attention in the field of energy storages.However,the electrodes based on bare LIG usually suffer from few-layered structures(less than 10layers)and electric-double layer capacitance(a theoretic capacitance of 550 F/g)of nanosheets.Hence,it's meaningful to study LIG composite electrodes in order to realize high performance of graphene-based electrodes.As we know,electrode structure is key for high performance devices.How to quickly and efficiently realize the regulation and optimization of the structure of LIG composite electrodes is of great significance to the preparation and application of high-performance LIG composite electrodes and devices.This thesis focuses on the design of laser-induced graphene hybrid frameworks to improve the electrochemical performance of energy storage devices,mainly using laser-induced graphene as a carrier,and construct three kinds of high-quality graphene-based functional hybrid 3D network electrodes,while their electrochemical energy storage characteristics and the growth mechanism of laser-induced graphene were also studied.The main research and the conclusions are described as follows:1.The intrinsic relationship between laser-induced process parameters and characteristics of LIG was studied,and the growth mechanism of LIG based on fused vapor deposition was proposed.Further elucidation through COMSOL Multiphysics simulation analysis was carried out.The experimental and simulation results showed that the LIG obtained under focus conditions,with a power of 5 W and a scan rate of 30 cm/s,has a highly conductive sheet structure,with less than 10 layers,and the surface temperature field distribution is sufficient to make the precursor polyimide(PI)undergo a phase change;under defocus conditions,at a power of 6 W,and a scan rate of 30 cm/s,the resulting LIG is a highly conductive,fibrous structure with less than10 layers and the same surface temperature can cause PI to change phase.2.A unique laser-induced bi-metal sulfide/graphene nanoribbon(GR)hybrid framework for high-performance all-in-one flexible FSCs has been constructed.It's proposed that the synergistic effects of bi-metal sulfide as well as the unique laser-induced three-dimensional frameworks has greatly improved the electrochemical performances of the as-designed framework electrodes.The fiber-like electrode based on laser-induced molybdenum disulfide/manganese sulfide/GR(MoS₂/MnS/GR)hybrid frameworks exhibit a high areal specific capacitance of 58.3 m F/cm²at 50?A/cm²,which is 36.7,3.4 and 2.7 times larger than the pristine LIGR,MoS₂/LIG and MnS/LIG fiber-based electrode,respectively.In addition,the as-assembled all-in-one flexible FSCs based on laser-induced molybdenum disulfide/manganese sulfide/GR(MoS₂/MnS/GR)hybrid frameworks exhibit a high areal energy density of 7.0?Wh/cm²at 50?A/cm²,a high areal power density of 49.9?W/cm²at 50?A/cm²,as well as a high cycling stability(93.6%,10000 cycles).3.The one-step laser scribing technique is applied to produce MnO/Mn₃O₄/Ndoped-graphene(MNLIG)hybrid frameworks in-situ anchored on Cu current collectors as binder-free anodes for high-performance Li-ion batteries.Rational design and scalable construction of unique three-dimensional structures with high electronic conductivity and excellent electrolyte penetration,which can greatly improve the electrochemical performance of lithium ion batteries.The experimental results indicate that the resultant MNLIG composites perform exceptionally well as Li-ion batteries anode,specifically,a high reversible capacity of 992 m Ah g^-1at 0.2 A g^-1and excellent rate capacity of 365 m Ah g^-1at 2.0 A g^-1,as well as a high cycling stability(699 m Ah g^-1after 400 cycles at 0.2 A g^-1)were achieved.The binder free MNLIG electrode shows enhanced rate performance,and higher charge-discharge capacities in comparison with binder free pristine NLIG electrode,MNLIG electrode with PVDF binder,and commercial MnO/Mn₃O₄electrode with PVDF binder.4.A new route to rationally constructe three-dimensional(3D)N-doped porous carbons decorated with ZnO nanoparticles(NPs)through a laser-induced micro-explosion method and used as a high-efficiency shuttle inhibitor of polysulfide in lithium-sulfur batteries was presented.The laser-induced“micro-explosion”of the molecular fuel leads to the formation of unique 3D porous architectural LNPCs-ZnO hybrid frameworks with high a specific surface area.The high active surface area and high conductivity of the unique graphene hybrid frameworks,combined with the shuttle inhibiting effect of ZnO nanoparticles,can greatly enhance the sulfur content,rate and cycle performance of the cathode.The experimental results indicate that the unique structure of LNPCs-ZnO hybrid frameworks not only exhibited high cycling stability(capacity retention of 72.8%),high areal sulfur utilization(areal sulfur loading up to 6.3 mg cm^-2),as well as an excellent rate performance(3C)of Li-S battery were achieved.The DFT calculations proposed that the intrinsic interaction between lithium polysulfides(Li PSs)/S₈ and ZnO NPs was the main factor to suppress the shuttling effect of LiPSs.