A Universal Room-Temperature 3D Printing Approach Towards porous MOF Based Dendrites Inhibition Hybrid Solid-State Electrolytes.

Hybrid solid-state electrolytes (HSSEs) provide new opportunities and inspiration for the realization of safer, higher energy-density metal batteries. The innovative application of 3-dimensional printing in the electrochemical field, especially in solid-state electrolytes, endows energy storage devices with fascinating characteristics. In this paper, effective dendrite-inhibited PEO/MOFs HSSEs is innovatively developed through universal room-temperature 3-dimensional printing (RT-3DP) strategy. The prepared HSSEs display enhanced dendrite inhibition due to the porous MOF filler promoting homogeneity of lithium deposition and the formation of C-OCO3 Li, ROLi, LiF mesophases, which further improve the migration of Li+ in PEO chain and comprehensive performances. This universal strategy realizes the fabrication of different slurry components (PEO with ZIF-67, MOF-74, UIO-66, ZIF-8 fillers) HSSEs at RT environment, providing new inspirations for the exploration of next-generation advanced solid-state batteries.

Tailoring Pore Structures of 3D Printed Cellular High-Loading Cathodes for Advanced Rechargeable Zinc-Ion Batteries.

Developing high-loading cathodes with superior electrochemical performance is desirable but challenging in aqueous zinc-ion batteries (ZIBs) for commercialization. Advanced 3D printing of cellular and hierarchical porous cathodes with high mass loading for superior ZIBs is explored here. To obtain a high-performance 3D printable ink, a composite material of iron vanadate and reduced holey graphene oxide is synthesized as the ink component. A cellular cathode with hierarchical porous architecture for aqueous ZIBs is then designed and fabricated by 3D printing for the first time. The unique structures of 3D printed composite cathode provide interpenetrating transmission paths as well as channels for electrons and ions. 3D printed cathodes with high mass loading over 10 mg cm-2 exhibit a high specific capacity of 344.8 mAh g-1 at 0.1 A g-1 and deliver outstanding cycling stability over 650 cycles at 2 A g-1 . In addition, the printing strategy enables the ease increase in mass loading up to 24.4 mg cm-2 , where a remarkably high areal capacity of 7.04 mAh cm-2 is reached. The superior electrochemical performance paves the new way to design the state-of-the-art cathodes for ZIBs.

Direct Ink Writing of Li1.3 Al0.3 Ti1.7 (PO4 )3 -Based Solid-State Electrolytes with Customized Shapes and Remarkable Electrochemical Behaviors.

All-solid-state lithium batteries have received extensive attention due to their high safety and promising energy density and are considered as the next-generation electrochemical energy storage system. However, exploring solid-state electrolytes in customized geometries without sacrificing the ionic transport is significant yet challenging. Herein, various 3D printable Li1.3 Al0.3 Ti1.7 (PO4 )3 (LATP)-based inks are developed to construct ceramic and hybrid solid-state electrolytes with arbitrary shapes as well as high conductivities. The obtained inks show suitable rheological behaviors and can be successfully extruded into solid-state electrolytes using the direct ink writing (DIW) method. As-printed free-standing LATP ceramic solid-state electrolytes deliver high ionic conductivity up to 4.24 × 10-4  S cm-1 and different shapes such as "L", "T," and "+" can be easily realized without sacrificing high ionic transport properties. Moreover, using this printing method, LATP-based hybrid solid-state electrolytes can be directly printed on LiFePO4 cathodes for solid-state lithium batteries, where a high discharge capacity of 150 mAh g-1 at 0.5 C is obtained. The DIW strategy for solid-state electrolytes demonstrates a new way toward advanced solid-state energy storage with the high ionic transport and customized manufacturing ability.

Superior Hydrogen Evolution Reaction Performance in 2H-MoS2 to that of 1T Phase.

In the hydrogen evolution reaction (HER), energy-level matching is a prerequisite for excellent electrocatalytic activity. Conventional strategies such as chemical doping and the incorporation of defects underscore the complicated process of controlling the doping species and the defect concentration, which obstructs the understanding of the function of band structure in HER catalysis. Accordingly, 2H-MoS2 and 1T-MoS2 are used to create electrocatalytic nanodevices to address the function of band structure in HER catalysis. Interestingly, it is found that the 2H-MoS2 with modulated Fermi level under the application of a vertical electric field exhibits excellent electrocatalytic activity (as evidenced by an overpotential of 74 mV at 10 mA cm-2 and a Tafel slope of 99 mV per decade), which is superior to 1T-MoS2 . This unexpected excellent HER performance is ascribed to the fact that electrons are injected into the conduction band under the condition of back-gate voltage, which leads to the increased Fermi level of 2H-MoS2 and a shorter Debye screen length. Hence, the required energy to drive electrons from the electrocatalyst surface to reactant will decrease, which activates the 2H-MoS2 thermodynamically.

Recent Advances in Nanowire-Based, Flexible, Freestanding Electrodes for Energy Storage.

The rational design of flexible electrodes is essential for achieving high performance in flexible and wearable energy-storage devices, which are highly desired with fast-growing demands for flexible electronics. Owing to the one-dimensional structure, nanowires with continuous electron conduction, ion diffusion channels, and good mechanical properties are particularly favorable for obtaining flexible freestanding electrodes that can realize high energy/power density, while retaining long-term cycling stability under various mechanical deformations. This Minireview focuses on recent advances in the design, fabrication, and application of nanowire-based flexible freestanding electrodes with diverse compositions, while highlighting the rational design of nanowire-based materials for high-performance flexible electrodes. Existing challenges and future opportunities towards a deeper fundamental understanding and practical applications are also presented.

Carbon-MEMS-Based Alternating Stacked MoS2 @rGO-CNT Micro-Supercapacitor with High Capacitance and Energy Density.

A novel process to fabricate a carbon-microelectromechanical-system-based alternating stacked MoS2 @rGO-carbon-nanotube (CNT) micro-supercapacitor (MSC) is reported. The MSC is fabricated by successively repeated spin-coating of MoS2 @rGO/photoresist and CNT/photoresist composites twice, followed by photoetching, developing, and pyrolysis. MoS2 @rGO and CNTs are embedded in the carbon microelectrodes, which cooperatively enhance the performance of the MSC. The fabricated MSC exhibits a high areal capacitance of 13.7 mF cm-2 and an energy density of 1.9 µWh cm-2 (5.6 mWh cm-3 ), which exceed many reported carbon- and MoS2 -based MSCs. The MSC also retains 68% of capacitance at a current density of 2 mA cm-2 (5.9 A cm-3 ) and an outstanding cycling performance (96.6% after 10 000 cycles, at a scan rate of 1 V s-1 ). Compared with other MSCs, the MSC in this study is fabricated by a low-cost and facile process, and it achieves an excellent and stable electrochemical performance. This approach could be highly promising for applications in integration of micro/nanostructures into microdevices/systems.

Single-Nanowire Electrochemical Probe Detection for Internally Optimized Mechanism of Porous Graphene in Electrochemical Devices.

Graphene has been widely used to enhance the performance of energy storage devices due to its high conductivity, large surface area, and excellent mechanical flexibility. However, it is still unclear how graphene influences the electrochemical performance and reaction mechanisms of electrode materials. The single-nanowire electrochemical probe is an effective tool to explore the intrinsic mechanisms of the electrochemical reactions in situ. Here, pure MnO2 nanowires, reduced graphene oxide/MnO2 wire-in-scroll nanowires, and porous graphene oxide/MnO2 wire-in-scroll nanowires are employed to investigate the capacitance, ion diffusion coefficient, and charge storage mechanisms in single-nanowire electrochemical devices. The porous graphene oxide/MnO2 wire-in-scroll nanowire delivers an areal capacitance of 104 nF/µm(2), which is 4.0 and 2.8 times as high as those of reduced graphene oxide/MnO2 wire-in-scroll nanowire and MnO2 nanowire, respectively, at a scan rate of 20 mV/s. It is demonstrated that the reduced graphene oxide wrapping around the MnO2 nanowire greatly increases the electronic conductivity of the active materials, but decreases the ion diffusion coefficient because of the shielding effect of graphene. By creating pores in the graphene, the ion diffusion coefficient is recovered without degradation of the electron transport rate, which significantly improves the capacitance. Such single-nanowire electrochemical probes, which can detect electrochemical processes and behavior in situ, can also be fabricated with other active materials for energy storage and other applications in related fields.

In Situ Investigation of Li and Na Ion Transport with Single Nanowire Electrochemical Devices.

In the past decades, Li ion batteries are widely considered to be the most promising rechargeable batteries for the rapid development of mobile devices and electric vehicles. There arouses great interest in Na ion batteries, especially in the field of static grid storage due to their much lower production cost compared with Li ion batteries. However, the fundamental mechanism of Li and Na ion transport in nanoscale electrodes of batteries has been rarely experimentally explored. This insight can guide the development and optimization of high-performance electrode materials. In this work, single nanowire devices with multicontacts are designed to obtain detailed information during the electrochemical reactions. This unique platform is employed to in situ investigate and compare the transport properties of Li and Na ions at a single nanowire level. To give different confinement for ions and electrons during the electrochemical processes, two different configurations of nanowire electrode are proposed; one is to fully immerse the nanowire in the electrolyte, and the other is by using photoresist to cover the nanowire with only one end exposed. For both configurations, the conductivity of nanowire decreases after intercalation/deintercalation for both Li and Na ions, indicating that they share the similar electrochemical reaction mechanisms in layered electrodes. However, the conductivity degradation and structure destruction for Na ions is more severe than those of Li ions during the electrochemical processes, which mainly results from the much larger volume of Na ions and greater energy barrier encountered by the limited layered spaces. Moreover, the battery performances of coin cells are compared to further confirm this conclusion. The present work provides a unique platform for in situ electrochemical and electrical probing, which will push the fundamental and practical research of nanowire electrode materials for energy storage applications.

Synergistic effect of hierarchical nanostructured MoO2/Co(OH)2 with largely enhanced pseudocapacitor cyclability.

Pseudocapacitors have demonstrated an ability to deliver high energy and power densities. The main limitation is their poor cyclability and for this reason the architectural design of electrode materials has attracted considerable attention. Here we report the synthesis of hierarchical nanostructured material by growing Co(OH)2 nanoflakes onto MoO2 thin film. The electrode material exhibits a high capacitance of 800 F g(-1) at 20 A g(-1) with only 3% capacitance loss after 5000 cycles and high rate capability with increasing current density from 2 to 40 A g(-1), which are better than those of individual component. The enhanced pseudocapacitor performances benefit from the synergistic effect of the hierarchical nanostructure: (1) faster ion diffusion and electron transport at electrode/electrolyte interface, and (2) mitigation of the electrode destruction caused by ion insertion/deinsertion during charge-storage process. This facile design and rational synthesis offers an effective strategy to enhance the electrochemical performance of pseudocapacitors and shows promising potential for large-scale application in energy storage.

Nanowire templated semihollow bicontinuous graphene scrolls: designed construction, mechanism, and enhanced energy storage performance.

Graphene scrolls have been widely investigated for applications in electronics, sensors, energy storage, etc. However, graphene scrolls with tens of micrometers in length and with other materials in their cavities have not been obtained. Here nanowire templated semihollow bicontinuous graphene scroll architecture is designed and constructed through "oriented assembly" and "self-scroll" strategy. These obtained nanowire templated graphene scrolls can achieve over 30 µm in length with interior cavities between the nanowire and scroll. It is demonstrated through experiments and molecular dynamic simulations that the semihollow bicontinuous structure construction processes depend on the systemic energy, the curvature of nanowires, and the reaction time. Lithium batteries based on V3O7 nanowire templated graphene scrolls (VGSs) exhibit an optimal performance with specific capacity of 321 mAh/g at 100 mA/g and 87.3% capacity retention after 400 cycles at 2000 mA/g. The VGS also shows a high conductivity of 1056 S/m and high capacity of 162 mAh/g at a large density of 3000 mA/g with only 5 wt % graphene added which are 27 and 4.5 times as high as those of V3O7 nanowires, respectively. A supercapacitor made of MnO2 nanowire templated graphene scrolls (MGSs) also shows a high capacity of 317 F/g at 1A/g, which is over 1.5 times than that of MnO2 nanowires without graphene scrolls. These excellent energy storage capacities and cycling performance are attributed to the unique structure of the nanowire templated graphene scroll, which provides continuous electron and ion transfer channels and space for free volume expansion of nanowires during cycling. This strategy and understanding can be used to synthesize other nanowire templated graphene scroll architectures, which can be extended to other fabrication processes and fields.

Wrinkled-graphene enriched MoO3 nanobelts with increased conductivity and reduced stress for enhanced electrochemical performance.

MoO3 has long suffered from poor conductivity and cyclability, which limit its high rate performance and ultralong cycling ability. Increasing the electronic conductivity with electron pathways of cathode materials can effectively enhance the lithium storage properties with stable cyclability and rate capability theoretically. Here the MoO3-reduced graphene oxide (rGO) hybrid nanobelts were designed and prepared and were tested as cathode materials for lithium batteries. It is demonstrated that the rGO is wrinkled and twisted around MoO3 nanobelts after reacting under high temperature and pressure conditions. The unique morphology of rGO, which has continuous electron pathways and stress buffering effects, endows the MoO3-rGO hybrid nanobelts with significantly increased rate capability and cycling ability. Meanwhile, it is demonstrated that MoO3-rGO hybrid nanobelts are promising cathode materials for use in rechargeable lithium batteries and our synthesis strategy is also versatile for exploiting advanced materials for Li-ion batteries.

Achieving desirable charge transport by porous frame engineering for superior 3D printed rechargeable Ni-Zn alkaline batteries.

Rechargeable 3D printed batteries with extraordinary electrochemical potential are typical contenders as one of the promising energy storage systems. Low-cost, high-safety, and excellent rechargeable aqueous alkaline batteries have drawn extensive interest. But their practical applications are severely hampered by poor charge carrier transfer and limited electrochemical activity at high loading. Herein, we report a unique structure-based engineering strategy in 3D porous frames using a feasible 3D printing technique and achieve 3D printed full battery devices with outstanding electrochemical performance. By offering a 3D porous network to provide prominently stereoscopic support and optimize the pore structure of electrodes, the overall charge carrier transport of engineered 3D printed Ni-Zn alkaline batteries (E3DP-NZABs) is greatly enhanced, which is directly demonstrated through a single-wired characterization platform. The obtained E3DP-NZABs deliver a high areal capacity of 0.34 mA h cm-2 at 1.2 mA cm-2, and an outstanding capacity retention of 96.2% after 1500 cycles is also exhibited with an optimal electrode design. Particularly, parameter changes such as a decrease in pore sizes and an increase in 3D network thickness are favorable to resultant electrochemical performance. This work may represent a vital step to promote the practical application progress of alkaline batteries.

Design of internally integrated in-plane electrodes for superior flexible hybrid zinc-ion capacitor devices.

A unique configuration based on internally integrated electrodes is proposed for flexible hybrid zinc-ion capacitor (HZIC) devices. An in-depth charge storage process is studied, confirming the high electrochemical promise of HZICs for future practical applications.

Multi-Channel Engineering of 3D Printed Zincophilic Anodes for Ultrahigh-Capacity and Dendrite-Free Quasi-Solid-State Zinc-Ion Microbatteries.

Zinc-ion microbatteries (ZIMBs) are regarded as one of most promising miniaturized energy storage candidates owing to their high safety, compatible device size, superior energy density, and cost efficiency. Nevertheless, the zinc dendrite growth during charging/discharging and the inflexible device manufacturing approach seriously restrict practical applications of ZIMBs. Herein, we report a unique material extrusion 3D printing approach with reinforced zincophilic anodes for ultrahigh-capacity and dendrite-free quasi-solid-state ZIMBs. A 3D printed N-doped hollow carbon nanotube (3DP-NHC) multichannel host is rationally designed for desirable dendrite-free zinc anodes. Favorable structural metrics of 3DP-NHC hosts with abundant porous channels and high zincophilic active sites enhance the ion diffusion rate and facilitate uniform zinc deposition behavior. Rapid zinc-ion migration is predicted through molecular dynamics, and zinc dendrite growth is significantly suppressed with homogeneous zinc-ion deposition, as observed by in situ optical microscopy. 3D printed symmetric zinc cells exhibit an ultralow polarization potential, a glorious rate performance, and a stable charging/discharging process. Accordingly, 3D printed quasi-solid-state ZIMBs achieve an outstanding device capacity of 11.9 mA h cm-2 at 0.3 mA cm-2 and superior cycling stability. These results reveal a feasible approach to effectively restrain zinc dendrite growth and achieve high performance for state-of-the-art miniaturized energy storage devices.

3D Printing for Solid-State Energy Storage.

Ever-growing demand to develop satisfactory electrochemical devices has driven cutting-edge research in designing and manufacturing reliable solid-state electrochemical energy storage devices (EESDs). 3D printing, a precise and programmable layer-by-layer manufacturing technology, has drawn substantial attention to build advanced solid-state EESDs and unveil intrinsic charge storage mechanisms. It provides brand-new opportunities as well as some challenges in the field of solid-state energy storage. This review focuses on the topic of 3D printing for solid-state energy storage, which bridges the gap between advanced manufacturing and future EESDs. It starts from a brief introduction followed by an emphasis on 3D printing principles, where basic features of 3D printing and key issues for solid-state energy storage are both reviewed. Recent advances in 3D printed solid-state EESDs including solid-state batteries and solid-state supercapacitors are then summarized. Conclusions and perspectives are also provided regarding the further development of 3D printed solid-state EESDs. It can be expected that advanced 3D printing will significantly promote future evolution of solid-state EESDs.

3D printing of cellular materials for advanced electrochemical energy storage and conversion.

3D printing, an advanced layer-by-layer assembly technology, is an ideal platform for building architectures with customized geometries and controllable microstructures. Bio-inspired cellular material is one of most representative 3D-printed architectures, and attracting growing attention compared to block counterparts. The integration of 3D printing and cellular materials offer massive advantages and opens up great opportunities in diverse application fields, particularly in electrochemical energy storage and conversion (EESC). This article gives a comprehensive overview of 3D-printed cellular materials for advanced EESC. It begins with an introduction of advanced 3D printing techniques for cellular material fabrication, followed by the corresponding material design principles. Recent advances in 3D-printed cellular materials for EESC applications, including rechargeable batteries, supercapacitors and electrocatalysts are then summarized and discussed. Finally, current trends and challenges along with in-depth future perspectives are provided.

Rapid, all dry microfabrication of three-dimensional Co3O4/Pt nanonetworks for high-performance microsupercapacitors.

On-chip electrochemical energy storage devices have attracted growing attention due to the decreasing size of electronic devices. Various approaches have been applied for constructing the microsupercapacitors. However, the microfabrication of high-performance microsupercapacitors by conventional and fully compatible semiconductor microfabrication technologies is still a critical challenge. Herein, unique three-dimensional (3D) Co3O4 nanonetwork microelectrodes formed by the interconnection of Co3O4 nanosheets are constructed by controllable physical vapor deposition combined with rapid thermal annealing. This construction process is an all dry and rapid (≤5 minutes) procedure. Afterward, by sputtering highly electrically conductive Pt nanoparticles on the microelectrodes, the 3D Co3O4/Pt nanonetworks based microsupercapacitor is fabricated, showing a high volume capacitance (35.7 F cm-3) at a scan rate of 20 mV s-1 due to the unique interconnected structures, high electrical conductivity and high surface area of the microelectrodes. This microfabrication process is also used to construct high-performance flexible microsupercapacitors, and it can be applied in the construction of wearable devices. The proposed strategy is completely compatible with the current semiconductor microfabrication and shows great potential in the applications of the large-scale integration of micro/nano and wearable devices.

Porous Nickel-Iron Selenide Nanosheets as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction.

Exploring non-noble and high-efficiency electrocatalysts is critical to large-scale industrial applications of electrochemical water splitting. Currently, nickel-based selenide materials are promising candidates for oxygen evolution reaction due to their low cost and excellent performance. In this work, we report the porous nickel-iron bimetallic selenide nanosheets ((Ni0.75Fe0.25)Se2) on carbon fiber cloth (CFC) by selenization of the ultrathin NiFe-based nanosheet precursor. The as-prepared three-dimensional oxygen evolution electrode exhibits a small overpotential of 255 mV at 35 mA cm(-2) and a low Tafel slope of 47.2 mV dec(-1) and keeps high stability during a 28 h measurement in alkaline solution. The outstanding catalytic performance and strong durability, in comparison to the advanced non-noble metal catalysts, are derived from the porous nanostructure fabrication, Fe incorporation, and selenization, which result in fast charge transportation and large electrochemically active surface area and enhance the release of oxygen bubbles from the electrode surface.

Graphene Oxide Templated Growth and Superior Lithium Storage Performance of Novel Hierarchical Co2V2O7 Nanosheets.

Hierarchical Co2V2O7 nanosheets consisted of interconnected nanoparticles are synthesized by a facile method using graphene oxide as the template. The electrochemical reaction mechanism of the Co2V2O7 nanosheets is thoroughly investigated by in situ XRD and ex situ TEM. The initial Co2V2O7 transforms into CoO nanoparticles and vanadium oxides in the first cycle, and the following reversible conversion reaction mainly occurs between CoO and Co and lithiation/delithiation of the vanadium oxides. The Co2V2O7 nanosheet displays a high reversible capacity (962 mAh/g at 0.5 A/g) and remarkable high rate capability. When cycled at 5.0 A/g, a reversible capacity of 441 mAh/g can be retained after 900 cycles. The stable high capacity and excellent rate capability make the hierarchical Co2V2O7 nanosheets a promising anode material for lithium-ion batteries.