| Supercapacitor is a new energy storage device that combines the advantages of conventional capacitors,and high power density,long cycle life and high rate performance of batteries.However,the large-scale application is inhibited by its lower energy density.Designing and developing high performance electrode materials is the key to address this issue.On one hand,traditional transition metal oxides have a series of problems such as poor conductivity,structural instability,and poor mechanical properties.Transition metal sulfides and phosphides are considered as an ideal candidate material because of low electronegativity,high electrical conductivity and excellent electrochemical activity properties.On the other hand,with the rapid development of flexible electronics,the demand for wearable energy storage devices is gradually increasing,but metal collectors such as foamed nickel and copper foam are not suitable for flexible energy storage devices.In this regard,we firstly study the carbonization and phosphating of metal organic framework(MOFs)with unique microstructure,and get a conclusion that the double metal phosphide shows much better energy storage performance than the corresponding oxide;Then we design and prepare one-dimensional Ni-Co bimetallic phosphorus.The hierarchical structure of the structure was discussed,and the formation mechanism of the special hierarchical structure was discussed.The two-step ion exchange method was extended to other bimetallic systems.Finally we realized high-performance bimetallic sulfide/carbon nanotube constructed composite film flexible electrodes.The main contents are summarized as follows:(1)Using the MOFs with special microstructure as bimetallic sources,the bimetallic oxide/carbon and phosphide/carbon nanocomposites with high specific surface area were prepared by controlling the carbonization,phosphating temperature and reaction time.The resulting products were characterized in detail.The performance of the two kinds of composite materials was analyzed and made a comparison.The results show that the Mn-Co phosphides/carbon has a specific capacitance of 2992.7 F g-1,which is much higher than the corresponding oxide(1760.4 F g-1).At the same time,the capacity retention reached 98.2%after 3000 charge-dischage cycles,which was also higher than the corresponding oxide(87.3%).(2)Through low temperature phosphorization,porous hexagonal microsheets constructed by porous NiCoP-CoP NWs were successfully prepared in a tubular furnace via a reaction of the Ni-Co precursors prepared by the above-mentioned first-step hydrothermal with sodium hypophosphite.Due to the high specific surface area,high conductivity and synergistic effect,the NiCoP-CoP electrode material has a high specific capacitance of 1968.5 F g-1(at 1 A g-1).When the current density increases to 10 A g-1,the capacitance remains 83.1%.Especially the electrode shows high cycle stability with capacitance retention of 95%after 10,000 charge-discharge cycles at the current density of 20 A g-1.All-solid-state asymmetric supercapacitors with NiCoP-CoP as the positive electrode and the nitrogen-doped graphene hydrogel film as the negative electrode deliver an energy density of 38.7 Wh kg-1 at a power density of 1784 W kg-1.Additionally,a new type of multilayer capacitor in series connection was designed,and a single device with four layers has a wide voltage window of reaching 7.2 V.The proposed device will achieve higher performance and hold great promise in wearable applications for miniaturized electronic devices.(3)High-quality carbon nanotube film(CNTF)is obtained by floating catalyst chemical vapor deposition,and then two-step acidification treatment enables effective separation between adjacent carbon nanotubes to obtain an open porous structure,giving an active base to the surface of the carbon nanotube.This converts hydrophobic CNTF to a high degree of hydrophilicity to promote uniform growth of the high load precursor,and optimization of the vulcanization results in a nanoporous coating of nanoparticle construction.The optimal MnCo9S10/CNTF electrode has a ultrahigh volumetric capacitance reaching 449 F cm-3 at 10 mA cm-2,much superior over previously reported values for CNT or CF based composites.Also,only 1.6%capacitance loss was observed after 10,000 cycles at a high current density of 80 mA cm-2.All-solid-state MnCo9S10/CNTF//A-CNTFs ASC delivers exceptionally high energy density of 67 mWh cm-3(at 10 W cm-3)with an excellent cycling stability.In particular,the lightweight devices are deformable due to outstanding flexibility and stability without structural failure and performance loss even after repeated hammering and folding during discharging.This work opens a new route to high-performance CNTF-based power sources for wearable electronics. |
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