Interfacial Design Of Electrodes For Capacitive Energy Storge

High power electrochemical capacitors and high energy batteries have some differences in the charge storage mechanism,high-efficiency energy storage requires an excellent interface between the electronic-transporting phase?electrode?and the ionic-transporting phase?electrolyte?.Considerable amounts of attentions have been paid to interface and entire electrode system to solve all kinds of technological challenges for the development.We introduce two powerful strategies for well-controlled integration?step-by-step integration and slury-pasting?.We want to integrate individual materials components and optimization.Step-by-step integration provides contact between working materials and substrates.Nanoscale building blocks as solution-processable precursors are potentially low cost alternative and promising for the bulk production.Flexible step-by-step assembly by combining step-by-step integration with nanoscale building blocks may be a powerful way for interface chemistry of electrochemical energy storage.Porous nickel foams with reduced graphene oxide?reduced graphite oxide?coating were prepared by a simple‘dip and dry'process,the reduced graphite oxide/nickel foams were used as substrates for adhering to coerce nickel-cobalt-hydroxide nanoscale building blocks on the reduced graphite oxide/nickel foam.Consequently,with different nickel-doping and dipping numbers,the nickel-cobalt-hydroxide/reduced graphite oxide/nickel foam exhibit a balance of high specific capacitances between the electroactive materials and the electrodes with adjustable specific energy and power.Co?OH?₂/reduced graphite oxide/nickel foam has a better capacitve behavior,the specific capacitance for Co?OH?₂/reduced graphite oxide/nickel foam?dipping number:4?is still over 3 F·cm^-2 after 2000 cycling.While,high Ni-doping cobalt-nickel-hydroxide/reduced graphite oxide/nickel foam?dipping number:4?has a worse retention,but the specific capacitance still over 4 F·cm^-2 after 2000 cycling.The interfacial assembly process could be repeated easily and conveniently,which promotes an optimal electrode/electrolyte interface with a large mass loading for potential applications in lithium-ion batteries,electrochemical or photocatalysis,and energy conversion storage.NiCo₂O₄ nanosheets stretching out of the Ni foam skeleton surface loosely is obtained by a solution-grown and'dip-dry'process?in a cobalt-nickel-hydroxide solution?followed by annealing;the NiCo₂O₄ nanosheets are filled in the pores of the Ni scaffold via a'chemical bath deposition'process followed by annealing.The surface and space of scaffolds could be filled with the NiCo2O4.Compared with'pasted'NiCo2O4,'tailored'NiCo2O4 has a smaller size,but a larger crystallite size.The tailored process could be beneficial for the specific capacitance with an area unit.The unit area capacitance of the obtained electrode is as high as3.23 F·cm^-2 at 10 mA·cm^-2,while the specific capacitance of the electroactive materials reaches 1029 F·g^-1 at 10 mA·cm^-2.The specific capacitance remains about 4 F cm^-2 after 1800cycling,even higher than intial.The cycling test results implies that the'pasted'and'tailored'NiCo2O4/Ni foams exhibit an intermediate electrochemical behaviour between a supercapacitor and a battery.The specific thermodynamic hysteresis promotes the‘broken'and‘fused'behaviour.The preparation strategy is useful for the design of new electrodes from surface to space.Co-Ni-hydroxide precursors were prepared by hybrid quasi-two-dimensional nanosheets and accumulated nanomaterials.Followed by a dip-dry and annealing,NiCo2O4 could adhere to the nickel foams robustly with a solution-based surface treatment.As quasi-two-dimensional nanosheets added,the specific capacitance with an area unit could be increased.The electrode of the highest quasi-two-dimensional nanosheets content has the highest specific capacitance with an area unit,it could reach about 8.5 F·cm^-1 and 900 F·g^-1.Specific factor is calculated to discover a feasible link between the results.All k values are0.6-0.7,between an ideal battery?k=1?and an ideal supercapacitor?k=0.5?.The results indicate that all the electrodes have similar hybrid processes of‘supercapacitor'and‘battery'.It inspires us some new design ideas as the following:An electrode could combine‘supercapacitor'with‘battery'rather than two asymmetric electrodes;Spinel NiCo2O4 is a better electronic conductor than insertion battery materials.It may be attractive to design an aqueous high-power battery:It is possible that a pseudocapacitive behavior could be received by binary cooperative battery and double-layer materials.NiCo2S4 nanosheets have been directly grown on nickel foams using a stepwise solution-based growth method.The as-prepared electrodes with controllable mass loadings and microstructures show excellent electrochemical performance,indicating their potential application as supercapacitors.High mass loadings could be achieved with increased deposition numbers.Afterwards,shape-retented NiCo₂S₄ could be obtained from NiCo₂O₄ via a facile anion exchange reaction.Electrochemical measurements exhibit that the NiCo₂S₄/nickel foam electrode has a competitive areal specific capacitance?10.82 F·cm!² at10 mA·cm!²?,relatively high rate capability?40.3%capacitance retention at 80 mA·cm!²?and good cycling stability?92%capacitance retention after 1500 cycles at 20 mA cm!²?.Moreover,it promotes a facile interface design method for controlling the mass loading of electrodes,which might be useful for the fabrication of high-performance supercapacitors.