Preparation And Hybrid Capacitor Properties Of Graphene Based Multicomponent Electrode Materials With High Performance

As the two mainstream energy storage devices,in the past decades supercapacitors and lithium ion batteries have been explored for wide range of energy applications,from mobile devices to hybrid electric vehicles.Recently,novel hybrid capacitors,lithium ion capacitors use lithium-insertion-type anode and non-faradaic capacitor-type cathode.The combination of two type electrodes can effectively overcome the energy densities limitation of supercapacitors and the poor power densities in lithium ion batteries.Recently,metal oxides have been proposed as high-performance electrode material for supercapacitors and lithium ion capacitors.However,they suffer from the intrinsic low ionic and electronic conductivity,which restricts the electrochemical kinetics,leading to limited rate capability.One of reported approaches to overcome this hurdle is compositing metal oxides with conductive carbon materials.In this article,we construct six different systems of metal oxides/graphene composites and undertake the detailed evaluations of electrochemical performance.Firstly,boron and nitrogen co-doped graphene with nickel cobaltite nanosheets(NCO/BN-G)hybrid was fabricated by a facile soft-chemical method for asymmetric supercapacitors.The effect of heteroatom doping on electrochemical properties of the hybrids is systematically investigated.The NCO/BN-G hybrid have a specific capacitance of 766.6 F h g^-1 at the current density of 0.5 A g^-1 and capacitance retention of 96.8%after10000 cycles at 5 A g^-1,much better than those of the pure NiCo₂O₄ and its hybrid with N-doped graphene.Moreover,an asymmetric supercapacitor device,assembled with NCO/BN-G and activated carbon(NCO/BN-G//AC),exhibits a maximum energy density of 45.6 Wh kg^-1 and an excellent cycling stability.The improved electrochemical performance of the NCO/BN-G hybrid is attributed to the highly conductive BN-G,the uniformly distributed NiCo₂O₄ nanosheets and the synergetic efforts between them.The incorporation of spacers between graphene sheets has been investigated as an effective method to improve the electrochemical performance of graphene papers(GP).We construct the design of free-standing GP@NiO and GP@Ni in which NiO nanoclusters and Ni nanoparticles are encapsulated into graphene sheets through electrostatic assembly and subsequent vacuum filtration.The encapsulated NiO nanoclusters and Ni nanoparticles can mitigate the restacking of graphene sheets,providing sufficient spaces for high-speed ion diffusion and electron transport.In addition,the spacers strongly bind to graphene sheets,which can efficiently improve the electrochemical stability.Therefore,at a current density of 0.5 A g^-1,the GP@NiO and GP@Ni electrodes exhibit higher specific capacitances of 306.9 and 246.1 F g^-1 than the GP electrode(185.7 F g^-1).The GP@Ni O and GP@Ni electrodes exhibit capacitance retention of 98.7% and 95.6% after 10000 cycles,demonstrating an outstanding cycling stability.Additionally,the GP@NiO//GP@Ni delivers excellent cycling stability(93.7%after 10000 cycles) and high energy density.The orthorhombic niobium oxide nanosheets supported on nitrogen and sulfur co-doped graphene(T-Nb₂O₅/NS-G) was prepared by a facile two-step hydrothermal method.X-ray diffraction and morphological analysis show that the T-Nb₂O₅ nanosheets successfully and uniformly distributed on the NS-G sheets.The T-Nb₂O₅/NS-G hybrid exhibits great rate capability(capacity retention of 63.1% from 0.05 to 5 A g^–1)and superior cycling stability(a low capacity fading of?6.4%after 1000 cycles at 0.5 A g^–1).The lithium ion capacitor consisting of T-Nb₂O₅/NS-G and activated carbon results in high energy density(69.2 W h kg^-1 at 0.1 A g^–1),high power density(9.17 kW kg^-1)and excellent cycling stability(95%of the initial energy after 3000 cycles).This excellent performance is mainly attributed to the highly conductive NS-G sheets,the uniformly distributed T-Nb₂O₅ nanosheets and the synergetic efforts between them.The M-Nb₂O₅@C/rGO composite has been obtained through a reaction at room temperature followed by heat treatment.The graphene support could provide sufficient electronic conductivity for fast electron transport and uniform M-Nb₂O₅@C nanoparticles with unique porous structure enhance Li ion penetration and diffusion,leading to superior rate capability and cycling stability.Therefore,the M-Nb₂O₅@C/rGO electrode exhibits high reversible capacity of 192 m Ah g^-1at 0.05 A g^-1,excellent rate capability with a reversible capacity of?97 m Ah g^-1 at 5 A g^-1 and long cycle life(capacity retention of 90.5% after 1000cycles).More appealingly,the M-Nb₂O₅@C/r GO//activated carbon lithium ion capacitor shows maximum energy density of 71.5 W h kg^-1(at 0.247 k W kg^-1),high power density of3.9 k W kg^-1(at 18.3 W h kg^-1)and excellent cycling stability(94%of initial capacity after 2500 cycles).These results prove that the M-Nb₂O₅@C/r GO composite could be promising electrode material for high performance Li-ion capacitors.The new nanocomposite(TNO/HG)with Ti Nb₂O₇ network nanostructure in situ anchored onto the holey graphene was formed by solvothermal reaction.The electrochemical analyses show that the good rate performance(capacity retention of 73.5%from 0.05 to 5 A g^-1)and long cycle life up to 1000 cycles at 1 A g^-1(a capacity retention of91.5%)are attained.Furthermore,the lithium ion capacitor consisting of this nanocomposite and activated carbon exhibits excellent cycling stability(90.2%of initial capacity after 3000cycles),high energy density of 86.3 W h kg^-1(at 237.7 W kg^-1)and power density of 3.88kW kg^-1(at 28.7 W h kg^-1).This study ascribes the unprecedented performance to the high conductive holey graphene with abundant mesopores,the uniformly distributed TiNb₂O₇network nanostructure and the synergetic effect between them.The new LiNbO₃@rGO composite was successfully synthesized using a soft chemical method,which was used as electrode material for lithium ion capacitor.The high conductivity graphene and the uniformly distributed Li Nb O₃ nanoparticles provide fast ion and electron transport channels.The electrochemical results show that the LiNbO₃@rGO composite electrode exhibits high capacity(165 m A h g^-1 at 0.05 A g^-1),great rate capability(68 m A h g^-1 at 5 A g^-1),and excellent cycle stability(1 A g^-1,80% of initial capacity after 1000 cycles).In addition,the lithium ion capacitor assembled with Li Nb O₃@r GO composites and activated carbon have the highest energy density of 66.1 W h kg^-1(at 296.7W kg^-1),high power density of 4.87 kW kg^-1(at 15.9 W h kg^-1)and superior cycle stability(92% of initial capacity after 2000 cycles).