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Nanosized energy storage, energy-harvesting, and functional devices are the three key components for integrated self-power systems. Here, we report on nanoscale electrochemical devices with a nearly three-fold enhanced stored charge under the field effect. We demonstrated the field-effect transistor can not only work as a functional component in nanodevices but also serve as an amplifier for the nanosized energy storage blocks. This unusual increase in energy storage is attributed to having a wide range of accessible electronic density of states (EDOS), hence redox reactions are occurring within the nanowire and not being confined to the surface. Initial results with MoS2 suggest that this field effect modulated energy storage mechanism may also apply to many other redox-active materials. Our work demonstrates the novel application of the field-effect in energy storage devices as a universal strategy to improve ion diffusion and the surface-active ion concentration of the active material, which can greatly enhance the charge storage ability of nanoscale devices. The fabrication process of the field-effect energy storage device is also compatible with microtechnology and can be integrated into other microdevices and nanodevices., Comment: 18 pages, 4 figures

Surface redox pseudocapacitance, which enables short charging times and high power delivery, is very attractive in a wide range of sites. To achieve maximized specific capacity, nanostructuring of active materials with high surface area is indispensable. However, one key limitation for capacitive materials is their low volumetric capacity due to the low tap density of nanomaterials. Here, we present a promising mesoscale TiO2 structure with precisely controlled mesoporous frameworks as a high-density pseudocapacitive model system. The dense-packed mesoscopic TiO2 in micrometer size offers a high accessible surface area (124 m2 g-1) and radially aligned mesopore channels, but high tap density (1.7 g cm-3) that is much higher than TiO2 nanoparticles (0.47 g cm-3). As a pseudocapacitive sodium-ion storage anode, the precisely designed mesoscopic TiO2 model achieved maximized gravimetric capacity (240 mAh g-1) and volumetric capacity (350 mAh cm-3) at 0.025 A g-1. Such a designed pseudocapacitive mesostructure further realized a commercially comparable areal capacity (2.1 mAh cm-2) at a high mass loading of 9.47 mg cm-2. This mesostructured electrode that enables fast sodiation in dense nanostructures has implications for high-power applications, fast-charging devices, and pseudocapacitive electrode design.

Sodium-ion storage technologies are promising candidates for large-scale grid systems owing to the abundance and low cost of sodium. However, compared to well-understood lithium-ion storage mechanisms, sodium-ion storage remains relatively unexplored. Herein, we systematically determine the sodium-ion storage properties of anatase titanium dioxide (TiO2(A)). During the initial sodiation process, a thin surface layer (~3 to 5 nm) of crystalline TiO2(A) becomes amorphous but still undergoes Ti4+/Ti3+ redox reactions. A model explaining the role of the amorphous layer and the dependence of the specific capacity on the size of TiO2(A) nanoparticles is proposed. Amorphous nanoparticles of ~10 nm seem to be optimum in terms of achieving high specific capacity, on the order of 200 mAh g-1, at high charge/discharge rates. Kinetic studies of TiO2(A) nanoparticles indicate that sodium-ion storage is due to a surface-redox, capacitor-like reaction mechanism that is not dependent on nanoparticle size in contrast to the lithiation of TiO2(A) which is a diffusion-limited intercalation process. The surface-redox properties of TiO2(A) result in excellent rate capability, cycling stability and low overpotentials. Moreover, the surface-redox mechanism is instrumental in enabling thick electrodes of TiO2(A) retain high rate properties, and represent a promising direction for high-power sodium-ion storage.

Sodium-ion storage devices are highly desirable for large-scale energy storage applications owing to the wide availability of sodium resources and low cost. Transition metal nitrides (TMNs) are promising anode materials for sodium-ion storage, while their detailed reaction mechanism remains unexplored. Herein, we synthesize the mesoporous Mo3N2 nanowires (Meso-Mo3N2-NWs). The sodium-ion storage mechanism of Mo3N2 is systematically investigated through in-situ XRD, ex-situ experimental characterizations and detailed kinetics analysis. Briefly, the Mo3N2 undergoes a surface pseudocapacitive redox charge storage process. Benefiting from the rapid surface redox reaction, the Meso-Mo3N2-NWs anode delivers high specific capacity (282 mAh g−1 at 0.1 A g−1), excellent rate capability (87 mAh g−1 at 16 A g−1) and long cycling stability (a capacity retention of 78.6% after 800 cycles at 1 A g−1). The present work highlights that the surface pseudocapacitive sodium-ion storage mechanism enables to overcome the sluggish sodium-ion diffusion process, which opens a new direction to design and synthesize high-rate sodium-ion storage materials.

Fast charging and high-power delivering batteries are highly demanded in mobile electronics, electric vehicles and grid energy storage, but there are full of challenges. The star-material Li3V2(PO4)3 is demonstrated as a promising high-rate cathode material meeting the above requirements. Herein, we report the carbon decorated Li3V2(PO4)3 (LVP/C) cathode prepared via a facile method, which displays a remarkable high-rate capability and long-term cycling performance. Briefly, the prepared LVP/C delivers a high discharge capacity of 122 mAh g−1 (~93% of the theoretical capacity) at a high rate up to 20 C and a superior capacity retention of 87.1% after 1000 cycles. Importantly, by applying a combination of X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering, we clearly elucidate the structural and chemical evolutions of LVP upon various potentials and cycle numbers. We show unambiguous spectroscopic evidences that the evolution of the hybridization strength between V and O in LVP/C as a consequence of lithiation/delithiation is highly reversible both in the bulk and on the surface during the discharge-charge processes even over extended cycles, which should be responsible for the remarkable electrochemical performance of LVP/C. Our present study provides not only an effective synthesis strategy but also deeper insights into the surface and bulk electrochemical reaction mechanism of LVP, which should be beneficial for the further design of high-performance LVP electrode materials.

Sodium-ion storage technologies are promising candidates for large-scale grid systems due to the abundance and low cost of sodium. However, compared to well-understood lithium-ion storage mechanisms, sodium-ion storage remains relatively unexplored. Herein, we systematically determine the sodium-ion storage properties of anatase titanium dioxide (TiO2(A)). During the initial sodiation process, a thin surface layer (~3 to 5 nm) of crystalline TiO2(A) becomes amorphous but still undergoes Ti4+/Ti3+ redox reactions. A model explaining the role of the amorphous layer and the dependence of the specific capacity on the size of TiO2(A) nanoparticles is proposed. Amorphous nanoparticles of ~10 nm seem to be optimum in terms of achieving high specific capacity, on the order of 200 mAh g−1, at high charge/discharge rates. Kinetic studies of TiO2(A) nanoparticles indicate that sodium-ion storage is due to a surface-redox mechanism that is not dependent on nanoparticle size in contrast to the lithiation of TiO2(A) which is a diffusion-limited intercalation process. The surface-redox properties of TiO2(A) result in excellent rate capability, cycling stability and low overpotentials. Moreover, tailoring the surface-redox mechanism enables thick electrodes of TiO2(A) to retain high rate properties, and represents a promising direction for high-power sodium-ion storage.

We report the synthesis of a Na-ion-conducting ionogel (IG) electrolyte using a one-pot, siloxane-modified sol–gel approach. The resulting pseudosolid electrolyte provides a nonflammable alternativ...

By introducing a compatible reducing agent (2-ethylimidazole) into a mono-micelle assembly process, we present a type of ordered mesoporous TiO2 microspheres that combines radially aligned mesostructure with Ti3+ defects in mesoporous frameworks. Such reductant acts as a building block of mesostructured frameworks and reduces Ti4+ in situ to generate defects during calcination, giving rise to the coexistence of bulk Ti3+ defects and an ordered mesostructure. The mesoporous TiO2 has both excellent mesoporosity (a high surface area of 106 m2 g-1 , a mean pore size of 18.4 nm) and stable defects with an extended photoresponse. Such integration of unique mesoscopic architecture and atomic vacancies provide both effective mass transportation and enhanced light utilization, leading to a remarkable increase in H2 generation rate. A maximum H2 evolution rate of 19.8 mmol g-1 h-1 can be achieved, along with outstanding stability under solar light.

Commercial carbon clothes have the potential to be utilized as supercapacitor electrodes due to their low cost and high conductivity. However, the negligible surface area of the carbon clothes serves as a serious impediment to their utilization. Herein, we report a facile calcination activation method for carbon cloths to realize remarkable comprehensive electrochemical performance. The activated carbon cloths deliver a high areal capacitance (1700 mF/cm2), good rate capability, and stable cycling performance up to 20,000 cycles. Owing to the stability in the wide potential window, a designed symmetric capacitor can function in a cell voltage of 2.0 V and delivers high volumetric and gravimetric energy densities of 7.62 mWh/cm3 and 18.2 Wh/kg, respectively. The remarkable electrochemical performance is attributed to rich microporosity with high surface area, superior electrolyte wettability, and stability in wide potential window.

PNb9O25, a Wadsley–Roth compound whose structure is obtained by appropriate crystallographic shear of the ReO3 structure, is a high-power electrode material that can reach 85% of the equilibrium ca...

The large overpotential and poor cycle stability caused by inactive redox reactions are tough challenges for lithium-oxygen batteries (LOBs). Here, a composite microsphere material comprising NiCo

Electrochemical sodium-ion storage technologies have become an indispensable part in the field of large-scale energy storage systems owing to the widespread and low-cost sodium resources. Molybdenum carbides with high electron conductivity are regarded as potential sodium storage anode materials, but the comprehensive sodium storage mechanism has not been studied in depth. Herein, Mo

Sodium-ion batteries (SIBs) show practical applications in large-scale energy storage systems. But, their power density is limited by the sluggish Na

Among the various VO

Tuning the uniformity and size of binary metal oxide nanodots on graphene oxide (BMO NDs@GO) is significant but full of challenges in wet-chemistry, owing to the difficulties of controlling the complicated cation/anion co-adsorption, heterogeneous nucleation, and overgrowth processes. Herein, the aim is to tune these processes by understanding the functions of various alcohol solvents for NDs growth on GO. It is found that the polyol solvation effect is beneficial for obtaining highly uniform BMO NDs@GO. Polyol shell capped metal ions exhibit stronger hydrogen-bond interactions with the GO surface, leading to a uniform cation/anion co-adsorption and followed heterogeneous nucleation. The polyol-solvated ions with large diffusion energy barrier drastically limit the ion diffusion kinetics in liquids and at the solid/liquid interface, resulting in a slow and controllable growth. Moreover, the synthesis in polyol systems is highly controllable and universal, thus eleven BMO and polynary metal oxide NDs@GO are obtained by this method. The synthetic strategy provides improved prospects for the manufacture of inorganic NDs and their expanding electrochemical applications.

Batteries and supercapacitors serve as the basis for electrochemical energy-storage devices. Although both rely on electrochemical processes, their charge-storage mechanisms are dissimilar, giving rise to different energy and power densities. Pseudocapacitive materials store charge through battery-like redox reactions but at fast rates comparable to those of electrochemical double-layer capacitors; these materials, therefore, offer a pathway for achieving both high energy and high power densities. Materials that combine these properties are in demand for the realization of fast-charging electrochemical energy-storage devices capable of delivering high power for long periods of time. In this Review, we describe the fundamental electrochemical properties of pseudocapacitive materials, with emphasis on kinetic processes and distinctions between battery and pseudocapacitive materials. In addition, we discuss the various types of pseudocapacitive materials, highlighting the differences between intrinsic and extrinsic materials; assess device applications; and consider the future prospects for the field. Pseudocapacitive materials can bridge the gap between high-energy-density battery materials and high-power-density electrochemical capacitor materials. In this Review, we examine the electrochemistry and physical signatures of pseudocapacitive charge-storage processes and discuss existing pseudocapacitive materials.

Summary Magnesium-ion batteries (MIBs) show great potential for large-scale energy storage because of the advantages of low cost and safety, but their application is severely hindered by the difficulty in finding desirable electrode materials. Herein, we develop a bilayer-structured vanadium oxide (Mg0.3V2O5·1.1H2O) with synergistic effect of Mg2+ ions and lattice water as the cathode material for MIBs. The pre-intercalated Mg2+ ions provide high electronic conductivity and excellent structural stability. The lattice water enables fast Mg2+ ions mobility because of its charge shielding effect. As a result, the Mg0.3V2O5·1.1H2O exhibits excellent rate performance and an unprecedented cycling life with capacity retention of 80.0% after 10,000 cycles. In addition, the Mg0.3V2O5·1.1H2O exhibits good electrochemical performance in full MIBs. This scalable Mg2+ host material is a promising candidate as a cathode for MIBs, and its high performance is expected to meet the requirements for large-scale storage applications.

The aqueous zinc ion batteries (ZIBs) composed of inexpensive zinc anode and nontoxic aqueous electrolyte are attractive candidates for large-scale energy storage applications. However, their development is limited by cathode materials, which often deliver inferior rate capability and restricted cycle life. Herein, the VO2 nanorods show significant electrochemical performance when used as an intercalation cathode for aqueous ZIBs. Specifically, the VO2 nanorods display high initial capacity of 325.6 mAh g–1 at 0.05 A g–1, good rate capability, and excellent cycling stability of 5000 cycles at 3.0 A g–1. Furthermore, the VO2 unit cell expands in a, b, and c directions sequentially during the discharge process and contracts back reversibly during the charge process, and the zinc storage mechanism is revealed to be a highly reversible single-phase reaction by operando techniques and corresponding qualitative analyses. Our work not only opens a new door to the practical application of VO2 in ZIB systems but a...

Transition-metal chalcogenides (TMCs) have emerged as attractive anode materials for rechargeable batteries due to their excellent performance and abundant resources. Here, for the first time, we disclose a unique copper (Cu)-driven conversion process in TMC-based battery systems that involves classic Cu current collector and is considered to be an “activation process”. According to state-of-the-art characterization techniques, Cu was evidenced to gradually replace the transition-metal elements in TMCs to be the active material during cycling. Based on this unique Cu-driven conversion mechanism, we used a facile method to design a new type of sulfur-based battery that presents excellent performance: a reversible capacity of 1.045 mAh cm−2 after 700 cycles at 2 A g−1, and a good rate capability up to a capacity of 0.33 mAh cm−2 at 20 A g−1. With respect to the large family of TMC compounds, this study introduces a new direction for the design of high-performance energy storage systems.

Aqueous zinc-ion batteries are highly desirable for large-scale energy storage because of their low cost and high-level safety. However, achieving high energy and high power densities simultaneously is challenging. Herein, a VO

Highlights Layered iron vanadate ultrathin nanosheets (FeVO UNSs) with a thickness of ~ 2.2 nm were synthesized by a sonicate-assisted method. Pseudocapacitive Na+ intercalation of FeVO UNSs anode delivers high initial coulombic efficiency (93.86%), high reversible capacity (292 mAh g−1), excellent rate capability, and remarkable cycling stability. A pseudocapacitor–battery hybrid SIC is assembled with the elimination of presodiation and delivers high energy and power densities. Electronic supplementary material The online version of this article (10.1007/s40820-020-00567-2) contains supplementary material, which is available to authorized users., High-performance and low-cost sodium-ion capacitors (SICs) show tremendous potential applications in public transport and grid energy storage. However, conventional SICs are limited by the low specific capacity, poor rate capability, and low initial coulombic efficiency (ICE) of anode materials. Herein, we report layered iron vanadate (Fe5V15O39 (OH)9·9H2O) ultrathin nanosheets with a thickness of ~ 2.2 nm (FeVO UNSs) as a novel anode for rapid and reversible sodium-ion storage. According to in situ synchrotron X-ray diffractions and electrochemical analysis, the storage mechanism of FeVO UNSs anode is Na+ intercalation pseudocapacitance under a safe potential window. The FeVO UNSs anode delivers high ICE (93.86%), high reversible capacity (292 mAh g−1), excellent cycling stability, and remarkable rate capability. Furthermore, a pseudocapacitor–battery hybrid SIC (PBH-SIC) consisting of pseudocapacitor-type FeVO UNSs anode and battery-type Na3(VO)2(PO4)2F cathode is assembled with the elimination of presodiation treatments. The PBH-SIC involves faradaic reaction on both cathode and anode materials, delivering a high energy density of 126 Wh kg−1 at 91 W kg−1, a high power density of 7.6 kW kg−1 with an energy density of 43 Wh kg−1, and 9000 stable cycles. The tunable vanadate materials with high-performance Na+ intercalation pseudocapacitance provide a direction for developing next-generation high-energy capacitors. Electronic supplementary material The online version of this article (10.1007/s40820-020-00567-2) contains supplementary material, which is available to authorized users.

The polymer binders used in most lithium-ion batteries (LIBs) serve only a structural role, but there are exciting opportunities to increase performance by using polymers with combined electronic and ionic conductivity. To this end, here we examine dihexyl-substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx₂) as an electrochemically stable π-conjugated polymer that becomes electrically conductive (up to 0.1 S cm⁻¹) upon electrochemical doping in the potential range of 3.2 to 4.5 V (vs Li/Li⁺). Because this family of polymers is easy to functionalize, can be effectively fabricated into electrodes, and shows mixed electronic and ionic conductivity, PProDOT-Hx₂ shows promise for replacing the insulating polyvinylidene fluoride (PVDF) commonly used in commercial LIBs. A combined experimental and theoretical study is presented here to establish the fundamental mixed ionic and electronic conductivity of PProDOT-Hx₂. Electrochemical kinetics and electron spin resonance are first used to verify that the polymer can be readily electrochemically doped and is chemically stable in a potential range of interest for most cathode materials. A novel impedance method is then used to directly follow the evolution of both the electronic and ionic conductivity as a function of potential. Both values increase with electrochemical doping and stay high across the potential range of interest. A combination of optical ellipsometry and grazing incidence wide angle X-ray scattering is used to characterize both solvent swelling and structural changes that occur during electrochemical doping. These experimental results are used to calibrate molecular dynamics simulations, which show improved ionic conductivity upon solvent swelling. Simulations further attribute the improved ionic conductivity of PProDOT-Hx₂ to its open morphology and the increased solvation is possible because of the oxygen-containing propylenedioxythiophene backbone. Finally, the performance of PProDOT-Hx₂ as a conductive binder for the well-known cathode LiNi_(0.8)Co_(0.15)Al_(0.05)O₂ relative to PVDF is presented. PProDOT-Hx₂-based cells display a fivefold increase in capacity at high rates of discharge compared to PVDF-based electrodes at high rates and also show improved long-term cycling stability. The increased rate capability and cycling stability demonstrate the benefits of using binders such as PProDOT-Hx₂, which show good electronic and ionic conductivity, combined with electrochemical stability over the potential range for standard cathode operation.

By introducing a compatible reducing agent (2-ethylimidazole) into a mono-micelle assembly process, we present a type of ordered mesoporous TiO

With the increasing interest in transition metal chalcogenides, sulfide minerals containing the disulfide unit (S22-) have gained intensive attention for potential applications in energy storage devices, such as lithium-ion batteries (LIBs). Vanadium tetrasulfide (VS4) possesses a unique linear-chain structure with a Peierls distortion and shows great promise for application in LIBs. However, its electrochemical reaction mechanism is still controversial, mainly due to the amorphous nature of the intermediates and final products. Here, by applying multiple X-ray spectroscopies, we reveal that VS4 undergoes lithium intercalation and conversion reactions sequentially during the first discharge process, which are partially reversible in the subsequent charge process. However, an anomalous intercalation/conversion mixed reaction mechanism is dominant for the second cycle, mainly owing to the amorphization of the VS4 electrode during the first cycle. In addition, the sulfur atoms are also involved in the redox reaction during cycling, with the anionic contribution of S22- ↔ 2S2- transformation. Furthermore, we find that the formation process of the solid electrolyte interphase is highly dynamic during the discharge and charge processes. The present study provides deeper insights into the complex reaction mechanism of VS4. This knowledge can accelerate the development of high-performance VS4-based electrode materials for LIBs.

Pseudocapacitive charge storage has been regarded as a promising mechanism to achieve both high specific energy and power energy storage devices. Some pseudocapacitive anode materials show great high-rate performance, however, it remains a significant challenge to develop the cathode ones. Herein, for the first time, we report a layered iron vanadate (Fe5V15O39(OH)9⋅9H2O, named as kazakhstanite) nanosheets (FeVO NSs) with featuring ultrathin layer thickness (

A facile water bath method was developed to synthesize layered iron vanadate Fe5V15O39(OH)9·9H2O (FVO) nanosheets. As a cathode material FVO delivers a high capacity of 385 mA h g−1 at 0.1 A g−1 due to the high proportion of variable valence elements (Fe and V). A remarkable cycling performance at a high current density is achieved in a Zn(TFSI)2 electrolyte.

Layered transition metal oxides are promising cathodes for sodium ion capacitors due to their high specific capacity. In this work, we present a layered birnessite sodium manganese dioxide (Na0.77MnO2·0.5H2O) supported by a two-dimensional conductive network (denoted as b-NMO/C) as a cathode for non-aqueous sodium ion capacitor (SIC). The interlayer crystal water and carbon networks promote the ion/electron transport kinetics and overcome the structural instability, leading to largely enhanced electrochemical performance. As a result, the as-synthesized b-NMO/C cathode delivers a capacity of 192 mA h g−1 at 0.25C and 43 mA h g−1 even at a high rate of 100C. The attained performance is compared favorably with those of state-of-the-art Mn-based cathodes for sodium ion storage. Furthermore, the assembled asymmetric SIC (b-NMO/C//graphite) exhibits the highest energy (91 W h kg−1 achieved at ∼84 W kg−1) and power (5816 W kg−1 achieved at ∼37 W h kg−1) densities within the voltage range of 0.5–3.8 V.