A Gradient Composite Structure Enables a Stable Microsized Silicon Suboxide-Based Anode for a High-Performance Lithium-Ion Battery.

The practical application of microsized anodes is hindered by severe volume changes and fast capacity fading. Herein, we propose a gradient composite strategy and fabricate a silicon suboxide-based composite anode (d-SiO@SiOx/C@C) consisting of a disproportionated microsized SiO inner core, a homogeneous composite SiOx/C interlayer (x ≈ 1.5), and a highly graphitized carbon outer layer. The robust SiOx/C interlayer can realize a gradient abatement of stress and simultaneously connect the inner SiO core and carbon outer layer through covalent bonds. As a result, d-SiO@SiOx/C@C delivers a specific capacity of 1023 mAh/g after 300 cycles at 1 A/g with a retention of >90% and an average Coulombic efficiency of >99.7%. A full cell assembled with a LiNi0.8Co0.15Al0.05O2 cathode displays a remarkable specific energy density of 569 Wh/kg based on total active materials as well as excellent cycling stability. Our strategy provides a promising alternative for designing structurally and electrochemically stable microsized anodes with high capacity.

Hierarchical Metal Sulfide/Carbon Spheres: A Generalized Synthesis and High Sodium-Storage Performance.

The development of suitable anode materials is far from satisfactory and is a major scientific challenge for a competitive sodium-ion battery technology. Metal sulfides have demonstrated encouraging results, but still suffer from sluggish kinetics and severe capacity decay associated with the phase change. Herein we show that rational electrode design, that is, building efficient electron/ion mixed-conducting networks, can overcome the problems resulting from conversion reactions. A general strategy for the preparation of hierarchical carbon-coated metal sulfide (MS⊂C) spheres through thermal sulfurization of metal glycerate has been developed. We demonstrate the concept by synthesizing highly uniform hierarchical carbon coated vanadium sulfide (V2 S3 ⊂C) spheres, which exhibit a highly reversibly sodium storage capacity of 777 mAh g-1 at 100 mA g-1 , excellent rate capability (410 mAh g-1 at 4000 mA g-1 ), and impressive cycling ability.

Facile Synthesis of Nitrogen-Containing Mesoporous Carbon for High-Performance Energy Storage Applications.

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen-containing mesoporous carbon with high SSA (1390 m(2) g(-1)), a suitable pore size distribution (1.5-8.1 nm), and a nitrogen content of 4.7 wt % through a facile one-step self-assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium-sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g(-1) at 1 A g(-1) and an excellent rate capability (180 F g(-1), 10 A g(-1)). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium-sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g(-1) at 837.5 mA g(-1) and an extraordinary cycling stability with 70.3% capacity retention after 100 cycles.

Heteroatom-Doped Porous Carbon Nanosheets: General Preparation and Enhanced Capacitive Properties.

High-performance electrical double-layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion-diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten-salt method and chemical activation to prepare N-doped carbon nanosheets with high surface area (654 m2 g-1 ) and adjustable porous structure is presented. Owing to their structural features, the N-doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g-1 (area-normalized capacitance up to 37 µF cm-2 ) at a current density of 0.5 A g-1 in aqueous electrolyte, high rate capability (179 F g-1 at 20 A g-1 ), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom-doped carbon nanosheets for high-performance EDLCs, which could also be extended to other polymer precursors and even waste biomass.

Self-templated formation of uniform NiCo2O4 hollow spheres with complex interior structures for lithium-ion batteries and supercapacitors.

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities.

Photo-Energized MoS2/CNT Cathode for High-Performance Li-CO2 Batteries in a Wide-Temperature Range.

Li-CO2 batteries are considered promising energy storage systems in extreme environments such as Mars; however, severe performance degradation will occur at a subzero temperature owning to the sluggish reaction kinetics. Herein, a photo-energized strategy adopting sustainable solar energy in wide working temperature range Li-CO2 battery was achieved with a binder-free MoS2/carbon nanotube (CNT) photo-electrode as cathode. The unique layered structure and excellent photoelectric properties of MoS2 facilitate the abundant generation and rapid transfer of photo-excited carriers, which accelerate the CO2 reduction and Li2CO3 decomposition upon illumination. The illuminated battery at room temperature exhibited high discharge voltage of 2.95 V and mitigated charge voltage of 3.27 V, attaining superior energy efficiency of 90.2% and excellent cycling stability of over 120 cycles. Even at an extremely low temperature of - 30 °C, the battery with same electrolyte can still deliver a small polarization of 0.45 V by the photoelectric and photothermal synergistic mechanism of MoS2/CNT cathode. This work demonstrates the promising potential of the photo-energized wide working temperature range Li-CO2 battery in addressing the obstacle of charge overpotential and energy efficiency.

Tailoring Zn2+ Flux by an Ion Acceleration Layer Modified Separator for High-Rate Long-Lasting Zn Metal Anodes.

A large concentration gradient originating from sluggish ion transport on the surface of Zn metal anodes will result in uneven Zn2+ flux, giving rise to severe dendrite growth, especially at high current density. Herein, an ion acceleration layer is introduced by a facile separator engineering strategy to realize modulated Zn2+ flux and dendrite-free deposition. Zinc hexacyanoferrate as the modifying agent featuring strong zincophilicity and rapid diffusion tunnel can enable fast trap for Zn2+ near the electrode surface and immediate transport onto deposition sites, respectively. The ion acceleration effect is substantiated by improved ion conductivity, decreased activated energy, and promoted Zn2+ transference number, which can moderate concentration gradient to guide homogenous Zn2+ flux distribution. As a result, the separator engineering guarantees Zn||Zn symmetrical cells with long-term stability of 2700 h at 2 mA cm-2, and 1770 h at a large current density of 10 mA cm-2. Moreover, cycling stability and rate capability for full cells with different cathodes can be substantially promoted by the modified separator, validating its superior practical feasibility. This study supplies a new scalable approach to tailoring ion flux near the electrode surface to enable robust Zn metal anodes at a high current density.

Advanced inorganic nanomaterials for high-performance electrochromic applications.

Electrochromic materials and devices with the capability of dynamic optical regulation have attracted considerable attention recently and have shown a variety of potential applications including energy-efficient smart windows, multicolor displays, atuto-diming mirrors, military camouflage, and adaptive thermal management due to the advantages of active control, wide wavelength modulation, and low energy consumption. However, its development still experiences a number of issues such as long response time and inadequate durability. Nanostructuring has demonstrated that it is an effective strategy to improve the electrochromic performance of the materials due to the increased reaction active sites and the reduced ion diffusion distance. Various advanced inorganic nanomaterials with high electrochromic performance have been developed recently, significantly contributing to the development of electrochromic applications. In this review, we systematically introduce and discuss the recent advances in advanced inorganic nanomaterials including zero-, one-, and two-dimensional materials for high-performance electrochromic applications. Finally, we outline the current major challenges and our perspectives for the future development of nanostructured electrochromic materials and applications.

Encapsulating sulfur into hierarchically ordered porous carbon as a high-performance cathode for lithium-sulfur batteries.

A three-dimensional (3D) hierarchical carbon-sulfur nanocomposite that is useful as a high-performance cathode for rechargeable lithium-sulfur batteries is reported. The 3D hierarchically ordered porous carbon (HOPC) with mesoporous walls and interconnected macropores was prepared by in situ self-assembly of colloidal polymer and silica spheres with sucrose as the carbon source. The obtained porous carbon possesses a large specific surface area and pore volume with narrow mesopore size distribution, and acts as a host and conducting framework to contain highly dispersed elemental sulfur. Electrochemical tests reveal that the HOPC/S nanocomposite with well-defined nanostructure delivers a high initial specific capacity up to 1193 mAh g(-1) and a stable capacity of 884 mAh g(-1) after 50 cycles at 0.1 C. In addition, the HOPC/S nanocomposite exhibits high reversible capacity at high rates. The excellent electrochemical performance is attributed exclusively to the beneficial integration of the mesopores for the electrochemical reaction and macropores for ion transport. The mesoporous walls of the HOPC act as solvent-restricted reactors for the redox reaction of sulfur and aid in suppressing the diffusion of polysulfide species into the electrolyte. The "open" ordered interconnected macropores and windows facilitate transportation of electrolyte and solvated lithium ions during the charge/discharge process. These results show that nanostructured carbon with hierarchical pore distribution could be a promising scaffold for encapsulating sulfur to approach high specific capacity and energy density with long cycling performance.

Porous nitrogen-doped carbon nanotubes derived from tubular polypyrrole for energy-storage applications.

Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m(2) g(-1)) and a large pore volume (1.28 cm(3) g(-1)) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium-sulfur (Li-S) batteries. At a current density of 0.5 A g(-1), PNCNT presents a high specific capacitance of 210 F g(-1), as well as excellent cycling stability at a current density of 2 A g(-1). When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341 mA h g(-1) at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mA h g(-1). The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution.

General strategy for designing core-shell nanostructured materials for high-power lithium ion batteries.

Because of its extreme safety and outstanding cycle life, Li(4)Ti(5)O(12) has been regarded as one of the most promising anode materials for next-generation high-power lithium-ion batteries. Nevertheless, Li(4)Ti(5)O(12) suffers from poor electronic conductivity. Here, we develop a novel strategy for the fabrication of Li(4)Ti(5)O(12)/carbon core-shell electrodes using metal oxyacetyl acetonate as titania and single-source carbon. Importantly, this novel approach is simple and general, with which we have successfully produce nanosized particles of an olivine-type LiMPO(4) (M = Fe, Mn, and Co) core with a uniform carbon shell, one of the leading cathode materials for lithium-ion batteries. Metal acetylacetonates first decompose with carbon coating the particles, which is followed by a solid state reaction in the limited reaction area inside the carbon shell to produce the LTO/C (LMPO(4)/C) core-shell nanostructure. The optimum design of the core-shell nanostructures permits fast kinetics for both transported Li(+) ions and electrons, enabling high-power performance.

Stable lithium metal anode enabled by in situ formation of a Li3N/Li-Bi alloy hybrid layer.

A hybrid protective layer containing a Li3N and Li-Bi alloy is fabricated on a Li-metal anode as an artificial SEI layer to guide dendrite-free Li deposition. Noteworthily, the hybrid interface could not only facilitate homogeneous Li plating but also provide rapid Li+ transportation, enabling a long-term stability of ∼2400 h at 0.5 mA cm-2 with a low steady overpotential of 10 mV.

A 3D-Printed Proton Pseudocapacitor with Ultrahigh Mass Loading and Areal Energy Density for Fast Energy Storage at Low Temperature.

The sluggish ionic transport in thick electrodes and freezing electrolytes has limited electrochemical energy storage devices in lots of harsh environments for practical applications. Here, a 3D-printed proton pseudocapacitor based on high-mass-loading 3D-printed WO3 anodes, Prussian blue analog cathodes, and anti-freezing electrolytes is developed, which can achieve state-of-the-art electrochemical performance at low temperatures. Benefiting from the cross-scale 3D electrode structure using a 3D printing direct ink writing technique, the 3D-printed cathode realizes an ultrahigh areal capacitance of 7.39 F cm-2 at a high areal mass loading of 23.51 mg cm-2 . Moreover, the 3D-printed pseudocapacitor delivers an areal capacitance of 3.44 F cm-2 and excellent areal energy density (1.08 mWh cm-2 ). Owing to the fast ion kinetics in 3D electrodes and the high ionic conductivity of the hybrid electrolyte, the 3D-printed supercapacitor delivers 61.3% of the room-temperature capacitance even at -60 °C. This work provides an effective strategy for the practical applications of energy storage devices with complex physical structure at extreme temperatures.

Discovery of fast and stable proton storage in bulk hexagonal molybdenum oxide.

Ionic and electronic transport in electrodes is crucial for electrochemical energy storage technology. To optimize the transport pathway of ions and electrons, electrode materials are minimized to nanometer-sized dimensions, leading to problems of volumetric performance, stability, cost, and pollution. Here we find that a bulk hexagonal molybdenum oxide with unconventional ion channels can store large amounts of protons at a high rate even if its particle size is tens of micrometers. The diffusion-free proton transport kinetics based on hydrogen bonding topochemistry is demonstrated in hexagonal molybdenum oxide whose proton conductivity is several orders of magnitude higher than traditional orthorhombic molybdenum oxide. In situ X-ray diffraction and theoretical calculation reveal that the structural self-optimization in the first discharge effectively promotes the reversible intercalation/de-intercalation of subsequent protons. The open crystal structure, suitable proton channels, and negligible volume strain enable rapid and stable proton transport and storage, resulting in extremely high volumetric capacitance (~1750 F cm-3), excellent rate performance, and ultralong cycle life (>10,000 cycles). The discovery of unconventional materials and mechanisms that enable proton storage of micrometer-sized particles in seconds boosts the development of fast-charging energy storage systems and high-power practical applications.

A Dendrite-Free Zn Anode Co-modified with In and ZnF2 for Long-Life Zn-Ion Capacitors.

Aqueous Zn (zinc) metal batteries have gotten a lot of interest and research because of their great volumetric capacity, low production cost, and high use safety. However, the coulombic efficiency of the Zn metal anode is low due to Zn dendrites formed during the charging and discharging processes of the battery, and the corrosion problem of the Zn anode in the electrolyte also reduces the battery's cycling stability and hinders its practical application. In this paper, InF3 has been used to decorate the surface of Zn foil, and In (indium) and ZnF2 coatings have been introduced to the surface of metal Zn simultaneously. After 1400 h of plating and stripping cycles, a symmetrical battery assembled from the modified Zn foil can still maintain a low voltage hysteresis of 30 mV. The Zn-ion capacitor assembled by the InF3-modified Zn foil (Zn@In&ZnF2) and activated carbon delivers an energy density of 33.5 Wh kg-1 and a power density of 1608 W kg-1 at a current density of 2 A g-1 and can still maintain almost 100% capacity after 10,000 cycles. This work is helpful to improve the cycling stability and the corrosion problem of aqueous Zn-based batteries.

Electrochemical Proton Storage: From Fundamental Understanding to Materials to Devices.

Simultaneously improving the energy density and power density of electrochemical energy storage systems is the ultimate goal of electrochemical energy storage technology. An effective strategy to achieve this goal is to take advantage of the high capacity and rapid kinetics of electrochemical proton storage to break through the power limit of batteries and the energy limit of capacitors. This article aims to review the research progress on the physicochemical properties, electrochemical performance, and reaction mechanisms of electrode materials for electrochemical proton storage. According to the different charge storage mechanisms, the surface redox, intercalation, and conversion materials are classified and introduced in detail, where the influence of crystal water and other nanostructures on the migration kinetics of protons is clarified. Several reported advanced full cell devices are summarized to promote the commercialization of electrochemical proton storage. Finally, this review provides a framework for research directions of charge storage mechanism, basic principles of material structure design, construction strategies of full cell device, and goals of practical application for electrochemical proton storage.

Kinetic photovoltage along semiconductor-water interfaces.

External photo-stimuli on heterojunctions commonly induce an electric potential gradient across the interface therein, such as photovoltaic effect, giving rise to various present-day technical devices. In contrast, in-plane potential gradient along the interface has been rarely observed. Here we show that scanning a light beam can induce a persistent in-plane photoelectric voltage along, instead of across, silicon-water interfaces. It is attributed to the following movement of a charge packet in the vicinity of the silicon surface, whose formation is driven by the light-induced potential change across the capacitive interface and a high permittivity of water with large polarity. Other polar liquids and hydrogel on silicon also allow the generation of the in-plane photovoltage, which is, however, negligible for nonpolar liquids. Based on the finding, a portable silicon-hydrogel array has been constructed for detecting the shadow path of a moving Cubaris. Our study opens a window for silicon-based photoelectronics through introducing semiconductor-water interfaces.

Niobium Tungsten Oxide in a Green Water-in-Salt Electrolyte Enables Ultra-Stable Aqueous Lithium-Ion Capacitors.

Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost, high safety and eco-friendliness. However, the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications. Here, we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm-1 as a green "water-in-salt" electrolyte, providing wide voltage window up to 2.8 V. It facilitates the reversible function of niobium tungsten oxide, Nb18W16O93, that otherwise only operations in organic electrolytes previously. The Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance, high areal capacity, and ultra-long cycling stability. An aqueous lithium-ion hybrid capacitor is developed by using Nb18W16O93 as negative electrode combined with graphene as positive electrode in lithium acetate-based "water-in-salt" electrolyte, delivering a high energy density of 41.9 W kg-1, high power density of 20,000 W kg-1 and unexceptionable stability of 50,000 cycles.

Bacterial cellulose-derived carbon nanofibers as both anode and cathode for hybrid sodium ion capacitor.

Hybrid ion capacitors (HICs) based on insertion reactions have attracted considerable attention due to their energy density being much higher than that of the electrical double-layer capacitors (EDLCs). However, the development of hybrid ion capacitors with high energy density at high power density is a big challenge due to the mismatch of charge storage capacities and electrode kinetics between the battery-type anode and capacitor-type cathode. In this work, N and O dual doped carbon nanofibers (N,O-CNFs) were combined with carbon nanotubes (CNTs) to compose a complex carbon anode. N,O dual doping effectively tuned the functional group and surface activity of the CNFs while the integration of CNTs increased the extent of graphitization and electrical conductivity. The carbon cathode with high specific surface area and high capacity was obtained by the activation of CNFs (A-CNFs). Finally, a hybrid sodium ion capacitor was constructed by the double carbon electrode, which showed a superior electrochemical capacitive performance. The as-assembled HIC device delivers a maximum energy density of 59.2 W h kg-1 at a power density of 275 W kg-1, with a high energy density of 38.7 W h kg-1 at a power density of 5500 W kg-1.

Alloying Reaction Confinement Enables High-Capacity and Stable Anodes for Lithium-Ion Batteries.

The current insertion anode chemistries are approaching their capacity limits; thus, alloying reaction anode materials with high theoretical specific capacity are investigated as potential alternatives for lithium-ion batteries. However, their performance is far from being satisfactory because of the large volume change and severe capacity decay that occurs upon lithium alloying and dealloying processes. To address these problems, we propose and demonstrate a versatile strategy that makes use of the electronic reaction confinement via the synthesis of ultrasmall Ge nanoparticles (10 nm) uniformly confined in a matrix of larger spherical carbon particles (Ge⊂C spheres). This architecture provides free pathways for electron transport and Li+ diffusion, allowing for the alloying reaction of the Ge nanoparticles. The thickness change of electrodes containing such a material, monitored byan in situ electrochemical dilatometer, is rather limited and reversible, confirming the excellent mechanical integrity of the confined electrode. As a result, these electrodes exhibit high reversible capacity (1310 mAh g-1, 0.1C) and very impressive cycling ability (92% after 1000 cycles at 2C). A prototype device employing such an alloying electrode material in combination with LiNi0.8Mn0.1Co0.1O2 offers a high energy density of 250 Wh kg-1.