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The lattice oxygen redox (LOR) reaction, known for its potential to augment the capacity of layered transition metal oxides in sodium-ion batteries (SIBs), has attracted widespread attention. However, the utilization of the LOR reaction often leads to irreversible release of lattice oxygen, causing damage to the crystal structure and deterioration in electrochemical performance, thereby impeding its practical application. Here, we demonstrate a method to significantly enhance the electrochemical performance of P3-type Na0.6Li0.2Mn0.8O2 cathodes by concurrently applying surface NaBO2 coatings and boron doping. We reveal that the NaBO2 coating efficiently mitigates electrolyte corrosion and side reactions on the electrode surface. In addition, boron doping enhances the involvement of manganese in the redox process, thereby boosting capacity, while inhibiting the irreversible Li migration, thereby stabilizing the crystal structure of the material. The synergistic effect of surface NaBO2 coating and bulk phase boron doping enables 6%B-NLMO to exhibit improved electrochemical performance, achieving a discharge capacity of 98.7 mA h g−1 and 95.8% retention after 100 cycles at 20 mA g−1. This synergistic strategy, employing multiple modification techniques, offers a potential way to improve the performance of anion redox cathode materials. [ABSTRACT FROM AUTHOR]

The Na-ion hybrid capacitor (NIC) has exhibited its potential applications for devices that need high energy and power densities with low cost. Nevertheless, due to their “Daniell-type” mechanism, conventional NIC devices require massive electrolytes to provide a good ionic conductivity during charging, which could decrease the packaged energy density. Herein, we report a novel “Rocking-Chair” Na-ion hybrid capacitor (RC-NIC) employing Na-ions as charge carriers, Na3V2O2(PO4)2F@PEDOT as the cathode material and activated carbon (AC) as the anode material. RC-NIC efficiently improves the energy density by minimizing the amount of electrolyte like secondary batteries because Na-ion is de-intercalated from the cathode while it is adsorbed to the anode during charging. The Na3V2O2(PO4)2F@PEDOT//AC (peanut shell derived carbon) RC-NIC delivers high energy density of ∼158 W h kg−1 and power density of ∼7000 W kg−1 based on the total mass of active materials in both electrodes, respectively, in the voltage window of 1.0–4.2 V. This is one of the highest energy densities among the previously reported NICs. This concept provides a new route to build sodium-ion hybrid capacitors that meet dual criteria of battery and supercapacitor characters. [ABSTRACT FROM AUTHOR]

Spinel ZnFe2O4 (ZFO) has recently gained prominence as a fascinating anode for lithium-ion batteries (LIBs) owing to its intrinsic merits. However, serious electrode pulverization and modest electrical conductivity hugely hinder its commercial application. Herein, we describe the deliberate fabrication of a multi-functional yolk–shell hollow architecture, designated as H-ZFO–C@void@C, where hollow ZFO sub-microspheres with an internal well-distributed carbon network were prepared in a template-free manner as a yolk, along with a conductive N-doped carbon nanoshell and functional void interspace. Structural/geometric simulations and experiments confirm that the well-defined internal void and hollow interior of the yolk can efficiently accommodate volumetric expansion over lithiation without breaking the outer nanoshell while ensuring good yolk–shell electronic contact and a thin yet stable solid–electrolyte-interphase film on the outer surface. The conducting nano-carbon shell and continuous internal carbon network prevent the serious aggregation of nano-ZFO subunits, and facilitate convenient charge transfer during repeated lithiation/delithiation processes. Benefiting from the synergetic contributions of these appealing design rationales, our integrated H-ZFO–C@void@C anode delivers a high initial coulombic efficiency of ∼76.8%, a remarkable reversible capacity of ∼775 mA h g−1 at 2000 mA g−1, and long-term cyclability after 500 cycles at a high rate of 1000 mA g−1. More promisingly, our design here offers a competitive metal oxide-based anode structure for advanced LIBs. [ABSTRACT FROM AUTHOR]

There is an urgent need but it is still a huge challenge to integrate high energy and power density with high safety in a single energy storage device. Addressing this issue largely depends on design of new energy storage systems with novel electrode architectures. Herein, a novel electrochemical energy storage device called a quasi-solid-state Na-ion capacitor (QSS-NIC) is designed based on a 3D self-supported Na2Ti3O7 nanoribbon array/graphene foam (NTO/GF) anode and graphene foam (GF) cathode, and a Na-ion conducting gel polymer as the electrolyte and separator, without any binders, conducting additives or metal current collectors. Benefiting from the unique 3D self-supported cathode and anode, the GF//NTO/GF configuration achieves a high energy density of 70.6 W h kg−1 and high power density of 4000 W kg−1 on the basis of the mass of both electrodes, and a prominent cycling stability over 5000 cycles (capacitance retention ∼73.2%). This work successfully demonstrates a proof of concept of QSS-NIC as a high performance energy storage device based on two self-supported electrodes, which could provide a feasible approach to bridge the performance gap between capacitors and Na-ion batteries. [ABSTRACT FROM AUTHOR]

Developing flexible and lightweight energy storage systems for miniaturized electronic equipment and high volumetric performance is arousing increasing interest. For practical applications, the parameters of gravimetric and volumetric performance should both be taken into account and given the same importance. Here, a novel hierarchical structure of free-standing, binder-free electrodes of corrugated NiCo2O4 nanosheets on nitrogen doped graphene/carbon nanotubes (NGN/CNTs) film has been designed for use in high-performance supercapacitors. This unique lightweight electrode structure achieved extremely high electrochemical performance, with a volumetric capacitance of 482.7 F cm−3, a gravimetric capacitance of 2292.7 F g−1 at 5 A g−1, and very long-term cycle stability (125% capacitance retention after 10 000 circles at 30 A g−1). Optimal supercapacitive performance was also achieved in our fabricated asymmetric supercapacitor (ASC) by using NiCo2O4/NGN/CNTs as the cathode and NGN/CNTs as the anode. The device exhibited high gravimetric energy densities of 42.71 W h kg−1 at 775 W kg−1 and of 24.69 W h kg−1 at a high gravimetric power density of 15 485 W kg−1; it even demonstrated a high volumetric energy density of 25.90 W h L−1 and a high volumetric power density of 9389 W L−1. This strategy provides a new method to design flexible high-performance electrodes for a new generation of energy storage applications. [ABSTRACT FROM AUTHOR]

Hierarchical hollow porous architectures with intriguing hetero-interfaces are currently of particular interest in emerging energy-related fields. In this investigation, we report a smart template-free methodology to purposefully fabricate high-quality uniform hollow hetero-NiCo2S4/Co9S8 (NCCS) submicro-spindles with well-dispersed hetero-nanodomains at the nanoscale. High-yield hollow mesocrystal nickel cobalt carbonate spindles are first solvothermally synthesized as the intermediate, and a subsequent shape-preserving conversion into hetero-NCCS submicro-spindles via a hydrothermal anion-exchange reaction occurs. The underlying template-free formation mechanism of the hollow structures is tentatively proposed. When evaluated as a promising electrode for supercapacitors, the resultant hollow mesoporous hetero-NCCS electrode with a mass loading of 5 mg cm−2 delivers a good pseudocapacitance of ∼749 F g−1 at a current rate of 4 A g−1, and holds at approximately 620 F g−1 at 15 A g−1 as a result of intrinsic synergetic contributions from structural/compositional/componental merits. Furthermore, an asymmetric device based on hollow mesoporous hetero-NCCS achieves an encouraging energy density of around 33.5 W h kg−1 at a power density of 150 W kg−1, and exceptional cycling behavior with capacitance degradation of ∼0.007% per cycle over 5000 consecutive cycles at 5 A g−1. Comprehensive investigations unambiguously highlight that the unique hollow mesoporous hetero-NCCS submicro-spindles would be a powerful electrode platform for advanced next-generation supercapacitors. [ABSTRACT FROM AUTHOR]

Porous NiCo2O4 nanotubes have been successfully synthesized using a facile and cost-effective electrospinning method and used as a noble-metal-free catalyst for rechargeable Li–O2 batteries. The as-synthesized NiCo2O4 nanotubes possess hollow cavities and porous walls, and were found to significantly improve the electrochemical performance of Li–O2 batteries, by endowing them with a high initial discharge capacity, reduced overpotential as well as good rate capability. Excellent cycling stability over 110 cycles with a highly discharged voltage platform of 2.4 V at 200 mA gc−1 was achieved. By means of FESEM, XRD, Raman spectroscopy and GITT analysis, toroidal-shaped Li2O2 particles were identified as the dominant discharge product and it was revealed that the Li2O2 can be completely decomposed during the charging process, indicating its superior reversibility as an effective bifunctional catalyst for Li–O2 batteries. All the results indicated that the porous NiCo2O4 nanotubes expressed intriguing properties and great potential applications as a noble-metal-free effective bifunctional catalyst for rechargeable Li–O2 batteries. [ABSTRACT FROM AUTHOR]

Homogeneous ZnCo2O4 nanoflowers have been synthesized on a 3D layered structure of carbon nanotubes/nitrogen-doped graphene (NGN/CNTs) film by a hydrothermal process and subsequent calcination method. The ZnCo2O4 nanoflowers have an average diameter of 4 μm, and are composed of petals less than 100 nanometers. The as-synthesized ZnCo2O4/NGN/CNT film can be directly used as a flexible electrode with a high specific capacitance of 1802 F g−1 at 1 A g−1 and excellent cycling stability (almost 0% fade after 4000 sustaining charge/discharge at 10 A g−1). These results suggest that the obtained electrode has a promising application prospect in flexible energy conversion/storage devices. In addition, a binder-free asymmetric supercapacitor has been synthesized with the ZnCo2O4/NGN/CNT film as the positive electrode and the NGN/CNT film as the negative electrode. This demonstrates superior energy density (≈37.19 W h kg−1 at 750 W kg−1) and power density (≈14.992 kW kg−1 at 14.16 W h kg−1). [ABSTRACT FROM AUTHOR]

Hybrid sodium-ion capacitors (NICs) have tremendous potential in large-scale energy storage applications due to their low cost, long lifetime and high power. However, it remains a great challenge to find a desirable anode material with fast kinetics and superior cycle life. Here an applicable strategy to in situ grow Na2Ti3O7 on 1D CNTs as an anode material for sodium-ion capacitors is presented. Benefiting from the unique 1D nanostructure and the presence of pseudocapacitive charge storage mechanism, the Na2Ti3O7@CNT electrode exhibits excellent electrochemical performance with high rate capability and superb cycling stability. Moreover, a high performance hybrid NIC is also fabricated by using Na2Ti3O7@CNTs as an anode and activated carbon derived from the outer peanut shell as a cathode, which delivers high energy density (58.5 W h kg−1), high power density (3000 W kg−1), and long term cycle life (retaining ca. 75% of its original capacity at 0.4 A g−1 after 4000 cycles). [ABSTRACT FROM AUTHOR]

Hybrid supercapacitors are a very appealing power source with high energy density and power density because they employ both the merits of lithium ion batteries and supercapacitors. To balance such hybrid systems, the rate of the redox component must be substantially comparative to the levels of the double layer process. As far as the insertion-host material TiNb2O7 is concerned, we have used facile step electrode design consisting of the physically assisted template infusion of Ti–Nb sol into the pores of AAO followed by in situ conversion into porous TiNb2O7 nanotubes within the AAO walls under calcination, and finally making those templates dissolve away. Using such an electrode as the battery type anode and a graphene grass electrode as the capacitor type cathode, we successfully constructed a novel hybrid supercapacitor. Within a voltage range of 0–3 V, a high energy density of ∼74 W h kg−1 is achieved and it could remain as much as ∼34.5 W h kg−1 at a power of 7500 W kg−1. The present research sheds new light on the development of energy storage devices with both high energy density and high power density. [ABSTRACT FROM AUTHOR]

In this work, a solvothermal strategy combined with following calcination was developed to synthesize a mesoporous NaTi2(PO4)3/CMK-3 (NTP/C) nanohybrid as a high-performance anode for next-generation Na-ion batteries (NIBs). Physicochemical characterizations demonstrated that NASICON-type structured NaTi2(PO4)3 (NTP) nanoparticles (NPs) with high crystallinity were homogeneously embedded in the mesoporous CMK-3 matrix. The mesoporous NTP/C nanohybrid as the anode for NIBs exhibited excellent electrochemical performance with high charge–discharge capability, good rate performance and long cycle life in non-aqueous electrolytes. The nanohybrid electrode delivered large specific capacities of 101, 76, 58, 39 mA h g−1 at 0.2, 0.5, 1.0 and 2.0 C, respectively, and retained it as high as 62.9 mA h g−1 even after 1000 cycles at 0.5 C. Compared to the pure NTP electrode, the mesoporous NTP/C hybrid anode with unique “meso–nano” architecture exhibited better Na-storage ability and indicated its promising application for rechargeable NIBs. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) working at room temperature offer promising opportunities for renewable energy storage applications because of the abundant supply and low cost of sodium, low capacity, inferior rate capability and limited cycle life remain a significant challenge in their electrochemical operations. Herein, we report the preparation of hierarchically Na3V2(PO4)3/nitrogen-decorated carbon hybrids via solvothermal reaction using biomolecule of adenosine 5′-triphosphate disodium salt (ATP), as a novel precursor and environmentally friendly multifunctional source, simultaneously including sodium, phosphorus, carbon, nitrogen. The results demonstrate that Na3V2(PO4)3 nanocrystals are encapsulated in interconnected carbon nanosheets with moderate nitrogen doping (2.88%) to form a bundle-like structure, where the carbon nanosheets not only serve as a highly conducting pathway facilitating electron and ion transport, but as a shielding matrix to accommodate volume changes upon electrochemical cycling; thus, improving stability and reversibility of the Na3V2(PO4)3 cathode. Thus, the obtained materials deliver a high reversible capacity of 110.9 mA h g−1 at a low current rate of 0.2 C, as well as outstanding rate performance, suggesting that the Na3V2(PO4)3/nitrogen-doped carbon hybrids are promising cathode materials to be used in high-performance sodium ion batteries. [ABSTRACT FROM AUTHOR]

A uniform and thin Li2TiO3 layer with various amounts was coated on the surface of nanostructured LiNi0.5Mn1.5O4 (LNMO) materials by in situ hydrolysis of tetrabutyl titanate (TBOT) followed by the lithiation process. The morphology and structure of the samples were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) with an energy-dispersive X-ray spectroscope (EDS). Electrochemical tests illustrate that Li2TiO3 as a Li+-conductive coating layer remarkably improved the rate and cycling performance of the LNMO spinel cathode. Particularly, the 3 wt% and 5 wt% Li2TiO3-surface modified samples deliver high discharge capacities of 95 mA h g−1 and 90 mA h g−1 even at a high current density of 5 C, while the bare one only has a discharge capacity of 70 mA h g−1. At a current density of 1 C at elevated temperature, the 3 wt% and 5 wt% Li2TiO3-surface modified LNMO samples show excellent cyclability. After 50 cycles, the capacity retention of 3 wt% and 5 wt% Li2TiO3 modified LNMO is 88.1% and 94.1%, while only 77.1% for the bare sample. [ABSTRACT FROM AUTHOR]

The development of high-energy batteries is highly attractive for powering advanced communication equipment and electric vehicles in future. Lithium-sulfur batteries have attracted much attention in recent years due to their low cost, high theoretical specific capacity and energy density. However, lithium-sulfur batteries have not been commercialized because of their intrinsic shortcomings, including the insulation of the active cathode materials, the high solubility of lithium polysulfides in organic liquid electrolytes, and the lithium dendrite in the anode. In this feature article, recent research progress in cathode materials, electrolytes, anode materials, and others is reviewed and commented upon. Some perspectives and directions on future development of lithium-sulfur batteries are pointed out based on knowledge from previous studies and our experience. [ABSTRACT FROM AUTHOR]

We have developed a facile yet scalable polymer-assisted chemical solution route to prepare a three-dimensional (3D) hierarchical porous network-like NiCo2O4 framework for advanced electrochemical capacitors (ECs). The unique interconnected hierarchical porous framework is constructed by nanosized spinel NiCo2O4 building blocks of 20–30 nm size, thus, a 3D continuous electron transport expressway, convenient electrolyte penetration–diffusion and large electrode–electrolyte interface are obtained simultaneously. The combination of these appealing structural features in the striking network-like NiCo2O4 framework results in a drastically enhanced kinetic behavior, large specific capacitance (SC) and a remarkable cycling stability at high rates. The unique network-like NiCo2O4 electrode features a SC of 587 F g−1 at 2 A g−1, and can deliver up to 518 F g−1 at a large current density of 16 A g−1. Also, a SC deterioration of ∼6% of the maximum SC is evident after continuous 3500 charge–discharge cycles at varying current densities, ranging from 2 to 16 A g−1. Furthermore, the synthetic strategy presented here can be easily extended to fabricate other binary complex metal oxides and/or ternary metal oxides with a controlled composition and porous structure, which may be promising candidates for high-performance ECs, and even advanced Li-ion batteries. [ABSTRACT FROM AUTHOR]