Insights into Formation and Li-Storage Mechanisms of Hierarchical Accordion-Shape Orthorhombic CuNb_(2)O_(6) toward Lithium-Ion Capacitors as an Anode-Active Material

The orthorhombic CuNb_(2)O_(6)(O-CNO)is established as a competitive anode for lithium-ion capacitors(LICs)owing to its attractive compositional/structural merits.However,the high-temperature synthesis(>900℃)and controversial charge-storage mechanism always limit its applications.Herein,we develop a low-temperature strategy to fabricate a nano-blocks-constructed hierarchical accordional O-CNO framework by employing multilayered Nb_(2)CT_(x)as the niobium source.The intrinsic stress-induced formation/transformation mechanism of the monoclinic CuNb_(2)O_(6)to O-CNO is tentatively put forward.Furthermore,the integrated phase conversion and solid solution lithium-storage mechanism is reasonably unveiled with comprehensive in(ex)situ characterizations.Thanks to its unique structural merits and lithium-storage process,the resulted O-CNO anode is endowed with a large capacity of 150.3 mAh g^(-1)at 2.0 A g^(-1),along with long-duration cycling behaviors.Furthermore,the constructed O-CNO-based LICs exhibit a high energy(138.9 Wh kg^(-1))and power(4.0 kW kg^(-1))densities with a modest cycling stability(15.8%capacity degradation after 3000 consecutive cycles).More meaningfully,the in-depth insights into the formation and charge-storage process here can promote the extensive development of binary metal Nb-based oxides for advanced LICs.

Sub-nanoscale Engineering of MoO_(2) Clusters for Enhanced Sodium Storage

Smart construction of battery-type anodes with high rate and good mechanical properties is significant for advanced sodium ion capacitors(SICs).Herein,a flexible film consisting of MoO_(2) subnanoclusters encapsulated in nitrogen-doped carbon nanofibers(MoO_(2) SCs@N-CNFs)is designed and synthesized via electrospinning toward SICs as anodes.The strong N-Mo interaction guarantees the stable yet uniform dispersion of high loading MoO_(2) SCs(≈40 wt.%)in the flexible carbonaceous substrate.The sub-nanoscale effect of SCs restrains electrode pulverization and improves the Na+diffusion kinetics,rendering better pseudocapacitance-dominated Na+-storage properties than the nanocrystal counterpart.The MoO_(2) SCs@N-CNFs paper with mass loadings of 2.2–10.1 mg cm^(−2) can be directly used as free-standing anode for SICs,which exhibit high reversible gravimetric/areal capacities both in liquid and quasi-solid-state electrolytes.The assembled flexible SICs competitively exhibit exceptional energy density and cycling stability.More significantly,the sub-nanoscale engineering strategy here is promisingly generalized to future electrode design for other electrochemical energy-related applications and beyond.

Binary molten salt in situ synthesis of sandwich-structure hybrids of hollowβ-Mo2C nanotubes and N-doped carbon nanosheets for hydrogen evolution reaction

Focused exploration of earth-abundant and cost-efficient non-noble metal electrocatalysts with superior hydrogen evolution reaction(HER)performance is very important for large-scale and efficient electrolysis of water.Herein,a sandwich composite structure(designed as MS-Mo2C@NCNS)ofβ-Mo2C hollow nanotubes(HNT)and N-doped carbon nanosheets(NCNS)is designed and prepared using a binary NaCl–KCl molten salt(MS)strategy for HER.The temperature-dominant Kirkendall formation mechanism is tentatively proposed for such a three-dimensional hierarchical framework.Due to its attractive structure and componential synergism,MS-Mo2C@NCNS exposes more effective active sites,confers robust structural stability,and shows significant electrocatalytic activity/stability in HER,with a current density of 10 mA cm-2 and an overpotential of only 98 mV in 1 M KOH.Density functional theory calculations point to the synergistic effect of Mo2C HNT and NCNS,leading to enhanced electronic transport and suitable adsorption free energies of H*(ΔGH*)on the surface of electroactive Mo2C.More significantly,the MS-assisted synthetic methodology here provides an enormous perspective for the commercial development of highly active non-noble metal electrocatalysts toward efficient hydrogen evolution.

Boosting sodium-storage properties of hierarchical Na_(3)V_(2)(PO_(4))_(3)@C micro-flower cathodes by tiny Cr doping:The effect of“four ounces moving a thousand pounds”

Na_(3)V_(2)(PO_(4))_(3)(NVP),as a great potential cathode candidate for Na-ion batteries(NIBs),has attracted enormous interest due to its three-dimensional(3D)large open framework for convenient Na+transport,yet its practical application is still limited by its inferior electron conductivity and sluggish Na+diffusion kinetics.Herein,the tiny Cr doped hierarchical NVP micro-flower cathodes(i.e.,Na_(3)V_(2-x)Crx(PO_(4))_(3)@C,x≤0.1),which are self-assembled with single-crystal nanoflake subunits in-situ coated with carbon nano-shell,are designed and fabricated via a scalable avenue.The optimized cathode,i.e.,Na_(3)V_(1.94)Cr_(0.06)(PO_(4))_(3)@C(NVCP-6),was endowed with more electro-active Na(2)sites and higher electronic/ionic conductivity for efficient sodium storage.Benefiting from these competitive merits,the NVCP-6,when evaluated as a cathode towards NIBs,exhibits an ultrahigh-rate capability of 99.8 mAh·g^(-1)at 200 C and superior stability of 82.2%over 7300 cycles at 50 C.Furthermore,the NVCP-6 based full NIBs display remarkable electrochemical properties in terms of both high-rate capacities and long-duration cycling properties at different temperatures(-20–50°C).The contribution,i.e.,the design of“four ounces can move a thousand pounds”,here will promote the practical industrial application of NVP towards advanced NIBs.

Conductive metal-organic frameworks: Recent advances in electrochemical energy-related applications and perspectives

Metal-organic frameworks(MOFs),typically constructed with metallic nodes and organic linkers,have influenced the development of modular solid materials.Their adjustable molecular structure provides a remarkable variety of MOF-based solid-state structures towards diverse applications.However,the low conductivity of traditional MOFs extremely hinders their applications in electronic and electrochemical devices.The emerging conductive MOFs,generally possessing twodimensional layered structures,are endowed with both the structural merits of common MOFs and exceptional electronic/ionic conductivities.Besides,the selection and optimization of ligands and metal centers,as well as synthetic methods enormously affects the intrinsic conductivity of conductive MOFs.The distinctive crystal structures and superb conductivity promise their appealing applications in electrochemical energy-related fields.In the review,we mainly summarize representative crystal features,conducting mechanisms and recent advances in rational design and synthesis of conductive MOFs,along with their versatile applications as electrodes for electrochemical capacitors and rechargeable batteries,and as catalysts towards electrocatalysis.Finally,the involved challenges and future trends/prospects of the conductive MOFs for electrochemical energyrelated applications are further proposed.

钠离子电容器MoO_(3)/Mo_(2)CT_(x)负极材料的原位构建及其电化学性能

钠离子电容器(SIC)兼具超级电容器和可充电电池的双重优势,实现了高能量密度和高功率密度的共存.然而,电池型负极的动力学短板严重阻碍了器件储钠性能的进一步提升.在此,我们提出了一种简单且高效的不完全原位氧化策略,构建了多层堆叠式MoO_(3)/Mo_(2)CT_(x)复合材料,用于SIC的负极.通过对热氧化反应的精准调控,MoO_(3)/Mo_(2)CT_(x)具备了丰富的活性位点、高导电性和结构稳定性,可实现有效储钠.结合以上优势,MoO_(3)/Mo_(2)CT_(x)负极表现出优异的倍率性能和长循环性能.此外,基于MoO_(3)/Mo_(2)CT_(x)负极所构建的SIC在10 kW kg^(−1)下的能量密度为19.4 Wh kg^(−1),在1 A g^(−1)下的5000次循环中的电容衰减仅为21.5%.本文的贡献在于对MoO3基材料的精准设计和优势共建,以推动其实际应用进程.

Coordination polymer nanowires/reduced graphene oxide paper as flexible anode for sodium-ion batteries

构建基于有机材料的高性能柔性储钠电极面临诸多挑战.本工作通过可控组装及还原的方式,实现了铁基配位聚合物纳米线/还原氧化石墨烯柔性薄膜的构筑.多维复合薄膜可直接用作钠离子电池自支撑负极,且具有较高的储钠容量(200 mA g^−1电流密度下可逆容量为319 mA h g^−1)和优异的倍率性能(3000 mA g^−1大电流密度下比容量可保持在∼120 mA h g^−1).研究表明有机配体(氨三乙酸)中的羧基及氨基为储钠活性位点,而配位金属离子(Fe^2+)不参与电化学反应.

Laser irradiation construction of nanomaterials toward electrochemical energy storage and conversion:Ongoing progresses and challenges

The emerging use of laser irradiation in synthesis smartly bridges“nanotech-nology”and“light”,and has attracted enormous attention as an efficient syn-thetic methodology for versatile nanomaterials toward electrochemical energy storage and conversion devices(ESCDs).In this review,recent contributions and progress regarding the laser-induced nanomaterials for ESCDs are com-prehensively summarized,with a special focus on their practical utilization in rechargeable batteries,supercapacitors and electrocatalysis.The laser-induced synthesis strategies and corresponding mechanisms involved in nano-architecture generation/regulation,including pulsed laser deposition and laser irradiation in liquid,are also discussed in detail.With the in-depth insights into the mechanisms and revolutionary advancements of laser irradiation tech-nology,the comprehensive performances of ESCDs have been strikingly opti-mized.Finally,the existing challenges and future directions in this booming research field are outlined.This review will exert the significant guidance for future design and purposeful fabrication of advanced laser-induced nano-materials with appealing properties for advanced ESCDs and beyond.

In-situ growth of hybrid NaTi8O13/NaTiO2 nanoribbons on layered MXene Ti3C2 as a competitive anode for high-performance sodium-ion batteries

In the work,we successfully explore a two-step hydrothermal method for scalable synthesis of the hybrid sodium titanate(NaTi8O13/NaTiO2) nanoribbons well in-situ formed on the multi-layered MXene Ti3C2(designed as NTO/Ti3C2).Benefiting from the inherent structural and componential superiorities,the resulted NTO/Ti3C2 composite exhibits long-duration cycling stability and superior rate behaviors when evaluated as a hybrid anode for advanced SIBs,which delivers a reversible and stable capacity of^82 mAh/g even after 1900 cycles at 2000 mA/g for SIBs.

Facile hydrothermal construction of Nb2CTx/Nb2O5 as a hybrid anode material for high-performance Li-ion batteries

Herein,a simple yet efficient hydrothermal strategy is developed to in-situ convert multi-layered niobium-based MXene(Nb2 CTx)to hierarchical Nb2 CTx/Nb2O5 composite.In the hybrid,the Nb2O5 nanorods are well dispersed in and/or on the Nb2 CTx.Thanks to the synergetic contributions from the high capacity of Nb2O5 and superb electrical conductivity of the two-dimensional Nb2 CTx itself,the resultant Nb2 CTx/Nb2O5 hybrid exhibits excellent rate behaviors and stable long-term cycling behaviors,when evaluated as anodes for Li-ion batteries.

Solid-state template-free fabrication of uniform Mo2C microflowers with lithium storage towards Li-ion batteries

Herein,we first report one-step synthesis of uniform Mo2 C microflowers(MCMFs)from low-cost precursors via industrialized solid-state strategy.With fine optimization in precursor ratio and pyrolysis temperatures,the as-fabricated MCMFs are assembled well with interconnected single-crystalline nanosheet subunits.More encouragingly,the resultant MCMFs are further highlighted as a competitive anode with robust and long-duration lithium-storage behaviors towards high-performance Li-ion batteries.