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.

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.

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 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.

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 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.

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.

Ultrathin Ti2 Nb2 O9 Nanosheets with Pseudocapacitive Properties as Superior Anode for Sodium-Ion Batteries.

Sodium-ion batteries are emerging as promising candidates for grid energy storage because of the abundant sodium resources and low cost. However, the identification and development of suitable anode materials is far from being satisfactory. Here, it is demonstrated that the Ti2 Nb2 O9 nanosheets with tunnel structure can be used as suitable anode materials for sodium-ion batteries. Ti2 Nb2 O9 nanosheets are synthesized by liquid exfoliation combined with topotactic dehydration, delivering a high reversible capacity of 250 mAh g-1 at 50 mA g-1 at a suitable average voltage of ≈0.7 V. It is found that a low energy diffusion barrier, enlarged interlayer spacing, and exceptional nanoporosity together give rise to high rate performance characterized by pseudocapacitive behavior. The observed high reversible capacity, excellent rate capability, and good cyclability of Ti2 Nb2 O9 nanosheets make this material competitive when compared to other sodium insertion anode materials.

Cross-Linking Hollow Carbon Sheet Encapsulated CuP2 Nanocomposites for High Energy Density Sodium-Ion Batteries.

Sodium-ion batteries (SIB) are regarded as the most promising competitors to lithium-ion batteries in spite of expected electrochemical disadvantages. Here a "cross-linking" strategy is proposed to mitigate the typical SIB problems. We present a SIB full battery that exhibits a working potential of 3.3 V and an energy density of 180 Wh kg-1 with good cycle life. The anode is composed of cross-linking hollow carbon sheet encapsulated CuP2 nanoparticles (CHCS-CuP2) and a cathode of carbon coated Na3V2(PO4)2F3 (C-NVPF). For the preparation of the CHCS-CuP2 nanocomposites, we develop an in situ phosphorization approach, which is superior to mechanical mixing. Such CHCS-CuP2 nanocomposites deliver a high reversible capacity of 451 mAh g-1 at 80 mA g-1, showing an excellent capacity retention ratio of 91% in 200 cycles together with good rate capability and stable cycling performance. Post mortem analysis reveals that the cross-linking hollow carbon sheet structure as well as the initially formed SEI layers are well preserved. Moreover, the inner electrochemical resistances do not significantly change. We believe that the presented battery system provides significant progress regarding practical application of SIB.

Challenges and Perspectives for NASICON-Type Electrode Materials for Advanced Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have attracted increasing attention in the past decades, because of high overall abundance of precursors, their even geographical distribution, and low cost. Apart from inherent thermodynamic disadvantages, SIBs have to overcome multiple kinetic problems, such as fast capacity decay, low rate capacities and low Coulombic efficiencies. A special case is sodium super ion conductor (NASICON)-based electrode materials as they exhibit - besides pronounced structural stability - exceptionally high ion conductivity, rendering them most promising for sodium storage. Owing to the limiting, comparatively low electronic conductivity, nano-structuring is a prerequisite for achieving satisfactory rate-capability. In this review, we analyze advantages and disadvantages of NASICON-type electrode materials and highlight electrode structure design principles for obtaining the desired electrochemical performance. Moreover, we give an overview of recent approaches to enhance electrical conductivity and structural stability of cathode and anode materials based on NASICON structure. We believe that this review provides a pertinent insight into relevant design principles and inspires further research in this respect.

Carbon-Coated Li3 VO4 Spheres as Constituents of an Advanced Anode Material for High-Rate Long-Life Lithium-Ion Batteries.

Lithium-ion batteries are receiving considerable attention for large-scale energy-storage systems. However, to date the current cathode/anode system cannot satisfy safety, cost, and performance requirements for such applications. Here, a lithium-ion full battery based on the combination of a Li3 VO4 anode with a LiNi0.5 Mn1.5 O4 cathode is reported, which displays a better performance than existing systems. Carbon-coated Li3 VO4 spheres comprising nanoscale carbon-coating primary particles are synthesized by a morphology-inheritance route. The observed high capacity combined with excellent sample stability and high rate capability of carbon-coated Li3 VO4 spheres is superior to other insertion anode materials. A high-performance full lithium-ion battery is fabricated by using the carbon-coated Li3 VO4 spheres as the anode and LiNi0.5 Mn1.5 O4 spheres as the cathode; such a cell shows an estimated practical energy density of 205 W h kg-1 with greatly improved properties such as pronounced long-term cyclability, and rapid charge and discharge.

Peapod-like Li3 VO4 /N-Doped Carbon Nanowires with Pseudocapacitive Properties as Advanced Materials for High-Energy Lithium-Ion Capacitors.

Lithium ion capacitors are new energy storage devices combining the complementary features of both electric double-layer capacitors and lithium ion batteries. A key limitation to this technology is the kinetic imbalance between the Faradaic insertion electrode and capacitive electrode. Here, we demonstrate that the Li3 VO4 with low Li-ion insertion voltage and fast kinetics can be favorably used for lithium ion capacitors. N-doped carbon-encapsulated Li3 VO4 nanowires are synthesized through a morphology-inheritance route, displaying a low insertion voltage between 0.2 and 1.0 V, a high reversible capacity of ≈400 mAh g-1 at 0.1 A g-1 , excellent rate capability, and long-term cycling stability. Benefiting from the small nanoparticles, low energy diffusion barrier and highly localized charge-transfer, the Li3 VO4 /N-doped carbon nanowires exhibit a high-rate pseudocapacitive behavior. A lithium ion capacitor device based on these Li3 VO4 /N-doped carbon nanowires delivers a high energy density of 136.4 Wh kg-1 at a power density of 532 W kg-1 , revealing the potential for application in high-performance and long life energy storage devices.

Dual-Functionalized Double Carbon Shells Coated Silicon Nanoparticles for High Performance Lithium-Ion Batteries.

To address the challenge of huge volume change and unstable solid electrolyte interface (SEI) of silicon in cycles, causing severe pulverization, this paper proposes a "double-shell" concept. This concept is designed to perform dual functions on encapsulating volume change of silicon and stabilizing SEI layer in cycles using double carbon shells. Double carbon shells coated Si nanoparticles (DCS-Si) are prepared. Inner carbon shell provides finite inner voids to allow large volume changes of Si nanoparticles inside of inner carbon shell, while static outer shell facilitates the formation of stable SEI. Most importantly, intershell spaces are preserved to buffer volume changes and alleviate mechanical stress from inner carbon shell. DCS-Si electrodes display a high rechargeable specific capacity of 1802 mAh g-1 at a current rate of 0.2 C, superior rate capability and good cycling performance up to 1000 cycles. A full cell of DCS-Si//LiNi0.45 Co0.1 Mn1.45 O4 exhibits an average discharge voltage of 4.2 V, a high energy density of 473.6 Wh kg-1 , and good cycling performance. Such double-shell concept can be applied to synthesize other electrode materials with large volume changes in cycles by simultaneously enhancing electronic conductivity and controlling SEI growth.

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.

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.