Construction of hierarchical three-dimensional interspersed flower-like nickel hydroxide for asymmetric supercapacitors

Low-cost and easily obtainable electrode materials are crucial for the application of supercapacitors.Nickel hydroxides have recently attracted intensive attention owning to their high theoretical specific capacitance,high redox activity,low cost,and eco-friendliness.In this study,novel three-dimensional (3D) interspersed flower-like nickel hydroxide was assembled under mild conditions.When ammonia was used as the precipitant and inhibitor and CTAB was used as an exfoliation agent,the obtained exfoliated ultrathin Ni(OH)2 nanosheets were assembled into 3D interspersed flower-like nickel hydroxide.In this novel 3D structure,the ultrathin Ni(OH)2 nanosheets not only provided a large contact area with the electrolyte,reducing the polarization of the electrochemical reaction and providing more active sites,but also reduced the concentration polarization in the electrode solution interface.Consequently,the utilization efficiency of the active material was improved,yielding a high capacitance.The electrochemical performance was improved via promoting the electrical conductivity by mixing the as-synthesized Ni(OH)2 with carbon tubes (N-4-CNT electrode),yielding excellent specific capacitances of 2,225.1 F·g-1 at 0.5 A·g-1 in a three-electrode system and 722.0 F·g-1 at 0.2 A·g-1 in a two-electrode system.The N-4-CNT//active carbon (AC) device exhibited long-term cycling performance (capacitance-retention ratio of 111.4％ after 10,000 cycles at 5 A·g-1) and a high specific capacitance of 180.5 F·g-1 with a high energy density of 33.5 W·h·kg-1 and a power density of 2,251.6 W·kg-1.     

Hollow multi-nanochannel carbon nanofiber/MoS2 nanoflower composites as binder-free lithium-ion battery anodes with high capacity and ultralong-cycle life at large current density

The electrode materials with high pseudocapacitance can enhance the rate capability and cycling stabil-ity of lithium-ion storage devices.Herein,we fabricated MoS2 nanoflowers with ultra-large interlayer spacing on N-doped hollow multi-nanochannel carbon nanofibers(F2-MoS2/NHMCFs)as freestanding binder-free anodes for lithium-ion batteries(LIBs).The ultra-large interlayer spacing(0.78～1.11 nm)of MoS2 nanoflowers can not only reduce the internal resistance,but also increase accessible active sur-face area,which ensures the fast Li+intercalation and deintercalation.The NHMCFs with hollow and multi-nanochannel structure can accommodate the large internal strain and volume change during lithi-ation/delithiation process,it is beneficial to improving the cycling stability of LIBs.Benefiting from the above combined structure merits,the F2-MoS2/NHMCFs electrodes deliver a high rate capability 832 mA h g-1 at 10 A g-1 and ultralong cycling stability with 99.29 and 91.60％capacity retention at 10 A g-1 after 1000 and 2000 cycles,respectively.It is one of the largest capacities and best cycling stability at 10 A g-1 ever reported to date,indicating the freestanding F2-MoS2/NHMCFs electrodes have potential applications in high power density LIBs.     

Fe~(3+) -stabilized Ti_3C_2T_x MXene enables ultrastable Li-ion storage at low temperature

It is highly important to develop ultrastable electrode materials for Li-ion batteries(LIBs),especially in the low temperature.Herein,we report Fe³⁺-stabilized Ti₃C₂T_x MXene(donated as T/F-4:1)as the anode material,which exhibits an ultrastable low-temperature Li-ion storage property(135.2 m A h g^-1after300 cycles under the current density of 200 m A g^-1at-10℃),compared with the negligible capacity for the pure Ti₃C₂T_x MXene(26 m A h g^-1at 200 m A g^-1).We characterized as-made T/F samples via the Xray photoelectron spectroscopy(XPS),Fourier transformed infrared(FT-IR)and Raman spectroscopy,and found that the terminated functional groups(-O and-OH)in T/F are Li⁺ storage sites.Fe³⁺-stabilization makes-O/-OH groups in MXene interlayers become active towards Li⁺,leading to much more active sites and thus an enhanced capacity and well cyclic stability.In contrast,only-O/-OH groups on the top and bottom surfaces of pure Ti₃C₂T_x MXene can be used to adsorb Li⁺,resulting in a low capacity.Transmission electron microscopy(TEM)and XPS data confirm that T/F-4:1 holds the highly stable solid electrolyte interphase(SEI)layer during the cycling at-10℃.Density functional theory(DFT)calculations further uncover that T/F has fast diffusion of Li⁺ and consequent better electrochemical performances than pure Ti₃C₂T_x MXene.It is believed that the new strategy used here will help to fabricate advanced MXene-based electrode materials in the energy storage application.     

Metal-organic framework derived hierarchical NiCo2O4 triangle nanosheet arrays@SiC nanowires network/carbon cloth for flexible hybrid supercapacitors

To overcome the disadvantages of traditional powder electrodes,such as the insufficient performance,the aggregation of active materials,and the complex fabrication process,rationally constructing free-standing electrode materials with hierarchical architecture is an effective and promising method,which could further improve the electrochemical properties.Herein,using metal-organic framework nanoar-rays (MOFNAs) as self-sacrificial templates and SiC nanowires (SiCNWs) network as nanoscale conductive skeletons,we successfully fabricated the hierarchical core-shell SiCNws@NiCo2O4NAs on carbon cloth (CC)substrate.Taking advantages of structural merits,such as hierarchical porous triangle-like NiCo2O4NAs,the interwoven SiCNWs network and conductive CC substrate,when evaluated as a binder-free superca-pacitor electrode,the CC/SiCNWs@NiCo2O4NAs shows a high specific capacitance of 1604.7 F g-1 (specific capacity of 222.9 mA h g-1) at 0.5 A g 1,good rate performance,and excellent cycling stability.Signifi-cantly,the hybrid supercapacitor assembled with CC/SiCNWs@NiCo2O4NAs as the cathode and MOF derived CC/SiCNWs@CNAs as the anode,could deliver a high specific density of 49.9 W h kg-1 at a specific power of 800 W kg-1,stable cycling performance,and good flexibility.Impressively,this feasible strategy for fabricating hierarchical structure displays great potential in the field of energy storage.     

中空Cu_7S_4纳米立方的制备及其电化学电容性能

本文以化学沉淀法制备出立方体Cu_2O,以Cu_2O为模板用水热离子交换法制备出纳米Cu_7S_4。利用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对Cu_7S_4进行测试,结果显示Cu_7S_4具有中空立方体结构,平均尺寸在550nm左右。使用三电极体系,采用循环伏安法、恒流充放电、电化学阻抗谱和循环稳定性分析研究了Cu_7S_4的电化学性能。测试结果表明,当电流密度为1A·g~(-1)时,Cu_7S_4的比电容为275F·g~(-1)。在电流密度为4A·g~(-1)时,Cu_7S_4循环1000次仍能保留94.8%的比电容,展示出良好的循环性能。     

Micro-nano structured VNb9O25 anode with superior electronic conductivity for high-rate and long-life lithium storage

The oxygen vacancies and micro-nano structure can optimize the electron/Li+migration kinetics in anode materials for lithium batteries(LIBs).Here,porous micro-nano structured VNb9O25 composites with rich oxygen vacancies were reasonably prepared via a facile solvothermal method combined with annealing treatment at 800℃for 30 h(VNb9 O25-30 h).This micro-nano structure can enhance the contact of active material/electrolyte,and shorten the Li+diffusion distance.The introduction of oxygen vacancies can further boosts the intrinsic conductivity of VNb9O25-30 h for achieving excellent LIB performance.The as-prepared VNb9O25-30 h anode showed advanced rate capability with reversible capacity of 122.2 mA h g-1 at 4 A g-1,and delivered excellent capacity retention of～100％after 2000 cycles.Meanwhile,VNb9O25-30 h provides unexpected long-cycle life(i.e.,reversible capacity of 165.7 mA h g-1 at 1 A g-1 with a high capacity retention of 85.6％even after 8000 cycles).Additionally,coupled with the LiFePO4 cathode,the LiFePO4//VNb9O25-30 h full cell delivers superior LIB properties with high reversible capacities of 91.6 mA h g-1 at 5C for 1000 cycles.Thus,such reasonable construction method can assist in other high-performance niobium-based oxides in LIBs.     

NiCo_2O_4微球的制备及其电化学性能

通过简单的水热法以及后续热处理,成功合成介孔NiCo_2O_4微球。利用FESEM、TEM、XPS和电化学工作站对样品的表面形貌、元素价态和电化学性能进行表征。结果表明:合成的NiCo_2O_4拥有丰富的多孔纳米针状结构,表现出较高的比表面积。由于这种三维多孔纳米结构,当NiCo_2O_4微球作为电极材料时,展现出优异的电容特性,在1A·g-1的电流密度下比电容高达1 554F·g-1,而且当电流密度增加到20A·g-1时,电容保持率为87.5%。另外,在5A·g-1的电流密度下,经过2 000次的充放电循环后,比电容仍能保持初始电容的90.4%。良好的电化学性能表明,NiCo_2O_4微球是一种理想的超级电容器电极材料。     

Facile one-pot synthesis of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> hollow spheres with controllable number of shells for high-performance supercapacitors

In this work,single-and double-shelled NiCo2O4 hollow spheres have been synthesized in situ by a one-pot solvothermal method assisted by xylose,followed by heat treatment.Employed as supercapacitor electrode materials,the double-shelled NiCo2O4 hollow spheres exhibit a remarkable specific capacitance (1,204.4 F·g-1 at a current density of 2.0 A·g-1) and excellent cycling stability (103.6％ retention after 10,000 cycles at a current density of 10 A·g-1).Such outstanding electrochemical performance can be attributed to their unique internal morphology,which provides a higher surface area with a larger number of active sites available to interact with the electrolyte.The versatility of this method was demonstrated by applying it to other binary metal oxide materials,such as ZnCo2O4,ZnMn2O4,and CoMn2O4.The present study thus illustrates a simple and general strategy for the preparation of binary transition metal oxide hollow spheres with a controllable number of shells.This approach shows great promise for the development of next-generation high-performance electrochemical materials.     

Biowaste derived porous carbon sponge for high performance supercapacitors

Here,an agricultural waste (the stem pith of helianthus annuus,SPHA) is firstly used as the precursor for preparing three-dimensional (3D) porous carbon sponge (PCS).The as-prepared 3D PCS (SPHA-700) pos-sesses unique sponge-like structure,large specific surface area (SSA) and high nitrogen doping level (4.52 at.％),which benefit the enhancement of conductivity (5.8 S cm-1) and wettability.As a binder-free elec-trode for solid-state symmetric supercapacitor,SPHA-700 delivers a relatively high specific capacitance of 137.1 F g-1 at 0.5 A g-1.Moreover,activated SPHA-700 (SPHA-ac-700-2) displays an even higher specific capacitance (403.6 F g-1 at 0.5 A g-1) in 6.0 M KOH electrolyte.The SPHA-ac-700-2-based symmetrical supercapacitor can offer high specific capacitance (271 F g-1 at 1 A g-1) and good rate capability (82.1％of capacitance retention at 1-80 A g-1) in 6.0 M KOH electrolyte,together with high energy density(23.3 Wh kg-1 at 450 W kg-1) in 1.0 M Na2SO4 electrolyte.Such excellent performance of SPHA-ac-700-2 is believed to have originated from the crushed sponge-like structure,O/N-co-doping (10.6 at.％ O and 3.3 at.％ N),high SSA,large total pore volume,and hierarchical pore structure.     

Tungsten diselenide nanoplates as advanced lithium/sodium ion electrode materials with different storage mechanisms

Transition-metal dichalcogenides (TMDs) exhibit immense potential as lithium/sodium-ion electrode materials owing to their sandwich-like layered structures.To optimize their lithium/sodium-storage performance,two issues should be addressed:fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs.In this study,WSe2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery (LIB/SIB) electrode materials.For LIBs,the WSe2-nanoplate electrodes achieved a stable reversible capacity and a high rate capability,as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g-1.Most importantly,in situ Raman spectroscopy,ex situ X-ray diffraction (XRD),transmission electron microscopy,and electrochemical impedance spectroscopy measurements performed during the discharge-charge process clearly verified the reversible conversion mechanism,which can be summarized as follows:WSe2 + 4Li+ + 4e-←→ W + 2Li2Se.The WSe2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes.Ex situ XRD and Raman spectroscopy results demonstrate that WSe2 reacted with Na+ more easily and thoroughly than with Li+ and converted to Na2Se and tungsten in the 1st sodiated state.The subsequent charging reaction can be expressed as Na2Se → Se + 2Na+ + 2e-,which differs from the traditional conversion mechanism for LIBs.To our knowledge,this is the first systematic exploration of the lithium/sodium-storage performance of WSe2 and the mechanism involved.     

Three-Dimensional Self-assembled Hairball-Like VS4 as High-Capacity Anodes for Sodium-Ion Batteries

Sodium-ion batteries(SIBs)are considered to be attractive candidates for large-scale energy storage systems because of their rich earth abundance and consistent performance.However,there are still challenges in developing desirable anode materials that can accommodate rapid and stable insertion/extraction of Na+and can exhibit excellent electrochemical performance.Herein,the self-assembled hairball-like VS4 as anodes of SIBs exhibits high discharge capacity(660 and 589 mAh g−1 at 1 and 3 A g−1,respectively)and excellent rate property(about 100%retention at 10 and 20 A g−1 after 1000 cycles)at room temperature.Moreover,the VS4 can also exhibit 591 mAh g−1 at 1 A g−1 after 600 cycles at 0°C.An unlike traditional mechanism of VS4 for Na+storage was proposed according to the dates of ex situ characterization,cyclic voltammetry,and electrochemical kinetic analysis.The capacities of the final stabilization stage are provided by the reactions of reversible transformation between Na2S and S,which were considered the reaction mechanisms of Na–S batteries.This work can provide a basis for the synthesis and application of sulfur-rich compounds in fields of batteries,semiconductor devices,and catalysts.     

新型复合相变储能材料Na/Paraffin的制备与性能分析

为提升广泛应用于相变储能领域的石蜡的导热系数,在手套箱内将导热系数高、熔点低、密度小的金属Na与石蜡复合为Na/paraffin新型相变储能材料,并对其导热系数、相变潜热及储/放热特性进行研究。结果表明:5%Na/95%paraffin复合相变储能材料导热系数较纯石蜡提高了17.6倍,储/放热速率均较纯石蜡提升了1倍;经过200次循环实验后,3%Na/97%paraffin复合相变储能材料相变温度由60.58℃下降到59.65℃,相变潜热由166.7520J·g~(-1)下降到160.5632J·g~(-1),热导率由2.33W·m~(-1)·K~(-1)减少到1.98W·m~(-1)·K~(-1)。     

Novel porous starfish-like Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@nitrogen-doped carbon as an advanced anode for lithium-ion batteries

A Co-based metal-organic framework (Co-MOF) with a unique three-dimensional starfish-like nanostructure was successfully synthesized using a simple ultrasonic method.After subsequent carbonization and oxidation,a nanocomposite of nitrogen-doped carbon with a Co3O4 coating (Co3O4@N-C) with a porous starfish-like nanostructure was obtained.The final hybrid exhibited excellent lithium storage performance when evaluated as an anode material in a lithiumion battery.A remarkable and stable discharge capacity of 795 mAh·g-1 was maintained at 0.5 A·g-1 after 300 cycles.Excellent rate capability was also obtained.In addition,a full Co3O4@N-C/LiFePO4 battery displayed stable capacity retention of 95％ after 100 cycles.This excellent lithium storage performance is attributed to the unique porous starfish-like structure,which effectively buffers the volume expansion that occurs during Li+ insertion/deinsertion.Meanwhile,the nitrogendoped carbon coating enhances the electrical conductivity and provides a buffer layer to accommodate the volume change and accelerate the formation of a stable solid electrolyte interface layer.     

石墨烯负载花球状二氧化锰复合材料制备及其电容性能研究

利用高锰酸钾与乙醇之间的氧化还原反应,在多孔石墨烯表面沉积纳米二氧化锰花球,获得了一种新型的复合电极材料。通过XRD,TG,SEM,TEM等分析手段确定了材料的晶体结构、化学成分、微观形貌特征。电化学性能测试表明:纳米二氧化锰花球具有优异的比电容,但是倍率性能和循环性能不足。通过在石墨烯表面负载纳米二氧化锰花球,能够显著增加石墨烯的比电容,同时改善纳米二氧化锰花球的倍率性能和循环性能。采用0.5mol/L K_2SO_4电解液,进行三电极循环伏安测试,复合电极材料在2mV·s^-1扫速下的比电容高达295F·g^-1,在1000mV·s^-1扫速下,比电容仍然可达102F·g^-1,同时100mV·s^-1,1000次循环后,电容循环保持率可达96.3%。这表明石墨烯负载花球状二氧化锰材料是一种极具潜力的超级电容器电极材料。     

LiMn2O4/LiPF6-(EC+DEC)溶液界面电化学研究

用交流阻抗谱结合循环伏安曲线研究了LiMn2O4粉末微电极在充放电循环及贮存情况下，LiMn2O4／LiPF6-(EC DEC)溶液界面性质变化．结果表明，LiMn2O4经充放电循环，其表面膜电阻及膜电容在循环初期增加显著，但后期变化不大，界面电荷传递电阻显著增加而界面电容变化不明显；经贮存，其膜电阻在贮存初期减小，后期反而稍有增加，界面电荷传递电阻呈增加趋势，尤其在初期增加幅度较大，膜电容及界面电容变化不明显，对引起这些界面参数变化的可能原因进行了解释。     

NiS2/三维多孔石墨烯复合材料作为超级电容器电极材料的电化学性能

选用合适的软模板,通过简便的一步溶剂热法成功制备了NiS₂/三维多孔石墨烯（3D rGO）复合材料。利用FESEM、TEM、XPS和电化学工作站对样品的表面形貌、元素价态和电化学性能进行表征。结果表明:制备的NiS₂/3D rGO复合材料存在石墨烯三维堆叠的孔道结构,且具备较大的比表面积,为57.51 m2g-1。电化学测试表明,在1 Ag-1的电流密度下NiS₂/3D rGO复合材料的比电容高达1 116.7 Fg-1,而且当电流密度增加到5 Ag-1时NiS₂/3D rGO复合材料的比电容为832.2 Fg-1,比电容保持率为1 Ag-1时的74.5%。在4 Ag-1电流密度下,经过1 000次循环后,NiS₂/3D rGO复合材料的比电容仍能保持91.2%。因此,NiS₂/3D rGO复合材料可作为一种理想的超级电容器电极材料。      

Hierarchically porous carbon derived from renewable Chingma Abutilon Seeds for high-energy supercapacitors

The cost-effectively biomass-derived porous carbon is highly promising for usage in electrochemical energy storage as the electrode materials. Herein, a series of hierarchically porous carbons with biomass Chingma Abutilon Seeds as the renewable precursor were synthesized via KOH activation and high-temperature carbonization technique. The resulting carbon material possessed an interconnected structure, high specific surface area (120–3566 m² g^?1), hierarchical pores as well as the heteroatom-substituted functional groups. Based on the synergistic effect of the above-mentioned merits, the optimized material exhibited the remarkably electrochemical performance with high specific capacitance (389 F g^?1 at 0.5 A g^?1) and excellent rate stability (72% capacitance retention at 20 A g^?1) in the three-electrode configuration. More significantly, the symmetric two-electrode device assembled in 6 M KOH delivered a high energy density of 39.2 Wh kg^?1 and excellent chemical stability (90% capacitance retention after 10,000 cycles at 5 A g^?1). Such prominent results might provide a new perspective on the value-added application of the renewable biomass resources in the electrochemical field.     

碳包覆介孔四氧化三铁纳米阵列:高性能Ni/Fe水相电池阴极材料

阴极材料的开发对于可充电水相电池的发展具有重要意义.本文通过自牺牲模板法和碳包覆法相结合制备了碳包覆介孔Fe₃O₄纳米阵列阴极材料(Fe₃O₄@C MNAs).得益于包覆碳层、介孔结构和纳米阵列结构的优异特性, Fe₃O₄@C MNAs电极表现出良好的倍率性能和优秀的循环稳定性.在组装的Ni/Fe电池器件中, Fe₃O₄@C MNAs表现出较高的能量密度及功率密度(在能量密度为213.3 W h kg^-1时功率密度为0.658 kW kg^-1和在功率密度为20.7 kW kg^-1时能量密度为113.9 W h kg^-1)和出色的循环稳定性(约5000次循环后保持81.7%).     

Interface-modulated fabrication of hierarchical yolk–shell Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/C dodecahedrons as stable anodes for lithium and sodium storage

Transition-metal oxides (TMOs) have gradually attracted attention from researchers as anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) because of their high theoretical capacity.However,their poor cycling stability and inferior rate capability resulting from the large volume variation during the lithiation/sodiation process and their low intrinsic electronic conductivity limit their applications.To solve the problems of TMOs,carbon-based metal-oxide composites with complex structures derived from metal-organic frameworks (MOFs) have emerged as promising electrode materials for LIBs and SIBs.In this study,we adopted a facile interface-modulated method to synthesize yolk-shell carbon-based Co3O4 dodecahedrons derived from ZIF-67 zeolitic imidazolate frameworks.This strategy is based on the interface separation between the ZIF-67 core and the carbon-based shell during the pyrolysis process.The unique yolk-shell structure effectively accommodates the volume expansion during lithiation or sodiation,and the carbon matrix improves the electrical conductivity of the electrode.As an anode for LIBs,the yolk-shell Co3O4/C dodecahedrons exhibit a high specific capacity and excellent cycling stability (1,100 mAh·g-1 after 120 cycles at 200 mA·g-1).As an anode for SIBs,the composites exhibit an outstanding rate capability (307 mAh·g-1 at 1,000 mA·g-1 and 269 mAh·g-1 at 2,000 mA·g-1).Detailed electrochemical kinetic analysis indicates that the energy storage for Li+ and Na+ in yolk-shell Co3O4/C dodecahedrons shows a dominant capacitive behavior.This work introduces an effective approach for fabricating carbonbased metal-oxide composites by using MOFs as ideal precursors and as electrode materials to enhance the electrochemical performance of LIBs and SIBs.     

Extremely high-rate aqueous supercapacitor fabricated using doped carbon nanoflakes with large surface area and mesopores at near-commercial mass loading

Achieving a satisfactory energy-power combination in a supercapacitor that is based on all-carbon electrodes and operates in benign aqueous media instead of conventional organic electrolytes is a major challenge.For this purpose,we fabricated carbon nanoflakes (20-100 nm in thickness,5-μm in width) containing an unparalleled combination of a large surface area (3,000 m2·g-1 range) and mesoporosity (up to 72％).These huge-surface area functionalized carbons (HSAFCs) also had a substantial oxygen and nitrogen content (～10 wt.％ combined),with a significant fraction of redox-active carboxyl/phenol groups in an optimized specimen.Their unique structure and chemistry resulted from a tailored single-step carbonization-activation approach employing (2-benzimidazolyl) acetonitrile combined with potassium hydroxide (KOH).The HSAFCs exhibited specific capacitances of 474 F·g-1 at 0.5 A·g-1 and 285 F·g-1 at 100 A·g-1 (charging time ＜ 3 s) in an aqueous 2 M KOH solution.These values are among the highest reported,especially at high currents.When tested with a stable 1.8-V window in a 1 M Na2SO4 electrolyte,a symmetric supercapacitor device using the fabricated nanoflakes as electrodes yielded a normalized active mass of 24.4 Wh·kg-1 at 223 W·kg-1 and 7.3 Wh·kg-1 at 9,360 W·kg-1.The latter value corresponds to a charge time of ＜3 s.The cyclability of the devices was excellent,with 93％ capacitance retention after 10,000 cycles.All the electrochemical results were achieved by employing electrodes with near-commercial mass loadings of 8 mg·cm-2.