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Selenium‐based materials are considered as desirable candidates for potassium‐ion and sodium‐ion storage. Herein, an in situ fabrication method is developed to prepare an integrated cuprous selenide electrode by means of directly chemical selenization of the copper current collector with commercial selenium powder. Interestingly, only the electrolyte of 1 m potassium hexafluorophosphate dissolved in 1,2‐dimethoxyethane with higher highest occupied molecular orbital energy and lower desolvation energy facilitates the formation of polyselenide intermediates and the further selenization of the copper current collector. Benefiting from the unique thin‐film‐like nanosheet morphology and the robust structural stability of the integrated electrode, the volume change and the loss of selenide species could be effectively restrained. Therefore, high performance is achieved in both potassium‐ion batteries (462 mA h g−1 at 2 A g−1 for 300 cycles) and sodium‐ion batteries (775 mA h g−1 at 2 A g−1 for 4000 cycles). The facile fabrication strategy paves a new direction for the design and preparation of high‐performance electrodes. [ABSTRACT FROM AUTHOR]

Aqueous‐ion batteries have received much attention owing to the merits of high safety, low cost, and environmental friendliness. Among potential cathode candidates, transition metal sulfides drew little attention since they suffer from low capacity, low working potential, and fast capacity fading. Here, advantage is taken of the chemical instability of VS2 in aqueous electrolyte to in situ fabricate a heterostructural VS2/VOx material. Benefiting from the internal electric field at heterointerfaces, high conductivity of vanadium sulfide and high chemical stability of vanadium oxides, heterostructural VS2/VOx delivers an enhanced working potential by 0.25 V, superior rate capability with specific capacity of 156 mA h g−1 at 10 A g−1, and long‐term stability over 3000 cycles as Zn2+ storage electrode. In addition, heterostructural VS2/VOx is employed as the cathode for aqueous NH4+ ion storage with high reversible capacity over 150 mA h g−1 and long lifespan over 1000 cycles, surpassing the state‐of‐the‐art materials. VS2/VOx is proved to demonstrate a (de)intercalation process for Zn2+ storage, while a conversion reaction accompanied by insertion is responsible for nonmetal NH4+. The strong insight obtained in this study sheds light on a new methodology of exploring the potential of transition metal sulfides‐based cathode materials for aqueous ion batteries. [ABSTRACT FROM AUTHOR]

Sodium‐ and potassium‐ion batteries have attracted intensive attention recently as low‐cost alternatives to lithium‐ion batteries with naturally abundant resources. However, the large ionic radii of Na+ and K+ render their slow mobility, leading to sluggish diffusion in host materials. Herein, hierarchical FeSe2 microspheres assembled by closely packed nano/microrods are rationally designed and synthesized through a facile solvothermal method. Without carbonaceous material incorporation, the electrode delivers a reversible Na+ storage capacity of 559 mA h g−1 at a current rate of 0.1 A g−1 and a remarkable rate performance with a capacity of 525 mA h g−1 at 20 A g−1. As for K+ storage, the FeSe2 anode delivers a high reversible capacity of 393 mA h g−1 at 0.4 A g−1. Even at a high current rate of 5 A g−1, a discharge capacity of 322 mA h g−1 can be achieved, which is among the best high‐rate anodes for K+ storage. The excellent electrochemical performance can be attributed to the favorable morphological structure and the use of an ether‐based electrolyte during cycling. Moreover, quantitative study suggests a strong pseudocapacitive contribution, which boosts fast kinetics and interfacial storage. [ABSTRACT FROM AUTHOR]

Selenium (Se) has received extensive attention as the most competitive cathode material for next generation high‐energy batteries. However, the shuttle effect of polyselenide and volume change lead to inferior electrochemical properties. To solve these issues, a porous bamboo‐derived carbon (PBC) with abundant meso/micropores is prepared as a framework to effectively encapsulate elemental selenium. For Li–Se batteries, Se/PBC electrode delivers an outstanding capacity of 509 mAh g−1 after 200 cycles at 0.2 C (1 C = 675 mA g−1) with a low capacity fade of 0.036% per cycle. The Se/PBC composite also reveals a satisfied electrochemical performance for Na–Se batteries with an excellent capacity of 409 mAh g−1 after 200 cycles at 0.2 C. Moreover, Se/PBC electrode also presents excellent long‐term cycle performance and rate performance at 15 C for Li–Se batteries and 10 C for Na–Se batteries. The outstanding properties are attributed to the specific 3D structure and high conductivity of PBC, which significantly inhibits the shuttle effect and enhances the reaction kinetics. Herein, not only the great application potential of bamboo in energy storage systems is demonstrated, but also an effective approach and low‐cost strategy for improving the performance of lithium/sodium–selenium batteries is offered. [ABSTRACT FROM AUTHOR]

The high electrochemical performance of Li2MnO3‐derived Li‐rich layered oxides suggests that Na2MnO3 might be a promising cathode material for sodium‐ion batteries for its effective anionic oxygen redox. However, experimental and theoretical evidence for anionic redox and enhanced Na+ capacity of Na2MnO3 has not been established. In the present work, the structural and thermal stability, and the anionic oxygen redox mechanism of Na2MnO3 were studied by using first‐principle calculations based on density functional theory. About 1.75 Na+ per formula unit were extracted from Na2‐xMnO3 through partial O2− oxidation while the local structure remained intact, resulting in a large theoretical capacity of 315 mA h g−1. Surface Na+ was extracted before bulk Na+, which might have led to oxygen loss and structural transformation from the surface to the material bulk. Given the importance of high capacity in practical applications, Na2MnO3 and its derived Na‐rich layered oxides might be considered promising cathode materials for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Identifying suitable electrode materials for sodium‐ion and potassium‐ion storage holds the key to the development of earth‐abundant energy‐storage technologies. This study reports an anode material based on self‐assembled hierarchical spheroid‐like KTi2(PO4)3@C nanocomposites synthesized via an electrospray method. Such an architecture synergistically combines the advantages of the conductive carbon network and allows sufficient space for the infiltration of the electrolyte from the porous structure, leading to an impressive electrochemical performance, as reflected by the high reversible capacity (283.7 mA h g−1 for Na‐ion batteries; 292.7 mA h g−1 for K‐ion batteries) and superior rate capability (136.1 mA h g−1 at 10 A g−1 for Na‐ion batteries; 133.1 mA h g−1 at 1 A g−1 for K‐ion batteries) of the resulting material. Moreover, the different ion diffusion behaviors in the two systems are revealed to account for the difference in rate performance. These findings suggest that KTi2(PO4)3@C is a promising candidate as an anode material for sodium‐ion and potassium‐ion batteries. In particular, the present synthetic approach could be extended to other functional electrode materials for energy‐storage materials. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid potassium‐ion capacitors (KICs) show great promise for large‐scale storage on the power grid because of cost advantages, the weaker Lewis acidity of K+ and low redox potential of K+/K. However, a huge challenge remains for designing high‐performance K+ storage materials since K+ ions are heavier and larger than Li+ and Na+. Herein, the synthesis of hierarchical Ca0.5Ti2(PO4)3@C microspheres by use of the electrospraying method is reported. Benefiting from the rich vacancies in the crystal structure and rational nanostructural design, the hybrid Ca0.5Ti2(PO4)3@C electrode delivers a high reversible capacity (239 mA h g−1) and superior rate performance (63 mA h g−1 at 5 A g−1). Moreover, the KIC employing a Ca0.5Ti2(PO4)3@C anode and activated carbon cathode, affords a high energy/power density (80 W h kg−1 and 5144 W kg−1) in a potential window of 1.0–4.0 V, as well as a long lifespan of over 4000 cycles. In addition, in situ X‐ray diffraction is used to unravel the structural transition in Ca0.5Ti2(PO4)3, suggesting a two‐phase transition above 0.5 V during the initial discharge and solid solution processes during the subsequent K+ insertion/extraction. The present study demonstrates a low‐cost potassium‐based energy storage device with high energy/power densities and a long lifespan. [ABSTRACT FROM AUTHOR]

Abstract: A facile chemical vapor deposition method is developed for the preparation of carbon nanofiber (CNF) composite Na3V2(PO4)2F3@C as cathodes for sodium‐ion batteries. In all materials under investigation, the optimized composite content, denoted as NVPF@C@CNF‐5, shows excellent sodium storage performance (86.3 % capacity retention over 5000 cycles at 20 C rate) and high rate capability (84.3 mA h g−1 at 50 C). The superior sodium storage performance benefits from the enhanced electrical conductivity of the working electrode after formation of a composite with CNF. Furthermore, the full cell using NVPF@C@CNF‐5 and hard carbon as the cathode and anode, respectively, demonstrates an impressive electrochemical performance, realizing an ultrahigh rate charge/discharge at a current rate of 30 C and long‐term stability over 1000 cycles. This approach is facile and effective, and could be extended to other materials for energy‐storage applications. [ABSTRACT FROM AUTHOR]

Mg-Li hybrid batteries have attracted wide interest in recent years because of their potential safety as well as their cost benefit and high volumetric capacity. However, slow kinetic properties strongly hinder their commercial application. In this study, we have prepared spinel LiCrTiO4 by a solid-state reaction and have conducted a comprehensive study aimed at improving the performance of Mg-Li hybrid batteries by optimizing the dual-salt electrolyte. LiCrTiO4 has been found to show reversible discharge/charge capacities of 178 and 169 mA h g−1 in electrolytes of 1 m LiCl and 0.3 m APC (all-phenyl-complex), respectively. When the concentration of APC was increased to 0.4 m, LiCrTiO4 showed a high capacity retention of 95 % after 30 cycles. In addition, no phase transition could be observed for an LiCrTiO4 electrode in a dual-salt system, suggesting high electrochemical reversibility. Ex situ EDX and SEM studies have indicated that only Li+ ions are inserted into the cathode side, while Mg2+ ions are reversibly deposited on the surface of Mg metal without dendrite-like growth, indicative of good safety of the Mg-Li hybrid batteries. [ABSTRACT FROM AUTHOR]

It remains a big challenge to identify high-performance anode materials to promote practical applications of sodium-ion batteries. Herein, the facile synthesis of CoS nanoflowers wrapped in reduced graphene oxides (RGO) is reported, and their sodium storage properties are systematically studied in comparison with bare CoS. The CoS@RGO nanoflowers deliver a high reversible capacity of 620 mAh g−1 at a current density of 100 mA g−1 and superior rate capability with discharge capacity of 329 mAh g−1 at 4 A g−1, much higher than those of the bare CoS. Evidenced by electrochemical impedance spectra and ex-situ SEM images, the improvement in the sodium storage performance is found to be due to the introduction of RGO which serves as a conducting matrix, to not only increase the kinetic properties of CoS, but also buffer the volume change and maintain the integrity of working electrodes during (de)sodiation processes. More importantly, the pseudocapacitive contribution of more than 89 % is only observed in the CoS@RGO nanocomposites, owing to the enhanced specific area and surface redox behavior. [ABSTRACT FROM AUTHOR]

Ag2Mo2O7 micro-rods are prepared by one-step hydrothermal method and their lithium electrochemical properties, as the anode for lithium-ion batteries, are comprehensively studied in terms of galvanostatic charge-discharge cycling, cyclic voltammetry, and rate performance measurements. The electrode delivers a high reversible capacity of 825 mAh g−1 at a current density of 100 mA g−1 and a superior rate capability with a discharge capacity of 263 mAh g−1 under the high current density of 2 Ag−1. The structural transition and phase evolution of Ag2Mo2O7 were investigated by using ex situ XRD and TEM. The Ag2Mo2O7 electrode is likely to be decomposed into amorphous molybdenum, Li2O, and metallic silver based on the conversion reaction. Silver nanoparticles are not involved in the subsequent electrochemical cycles to form a homogeneous conducting network. Such in situ decomposition behavior provides an insight into the mechanism of the electrochemical reaction for the anode materials and would contribute to the design of new electrode materials in future. [ABSTRACT FROM AUTHOR]

Li-rich layered oxide Li1.18Ni0.15Co0.15Mn0.52O2 (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium-ion battery and its Na+ storage properties are comprehensively studied in terms of galvanostatic charge-discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium-ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g−1 at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g−1 for 200 cycles at 5 C rate. Moreover, ex situ ICP-OES suggests interesting mixed-ions migration processes: In the initial two cycles, only Li+ can intercalate into the LNCM cathode, whereas both Li+ and Na+ work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge-discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Cu3V2O8 nanoparticles with particle sizes of 40-50 nm have been prepared by the co-precipitation method. The Cu3V2O8 electrode delivers a discharge capacity of 462 mA h g−1 for the first 10 cycles and then the specific capacity, surprisingly, increases to 773 mA h g−1 after 50 cycles, possibly as a result of extra lithium interfacial storage through the reversible formation/decomposition of a solid electrolyte interface (SEI) film. In addition, the electrode shows good rate capability with discharge capacities of 218 mA h g−1 under current densities of 1000 mA g−1. Moreover, the lithium storage mechanism for Cu3V2O8 nanoparticles is explained on the basis of ex situ X-ray diffraction data and high-resolution transmission electron microscopy analyses at different charge/discharge depths. It was evidenced that Cu3V2O8 decomposes into copper metal and Li3VO4 on being initially discharged to 0.01 V, and the Li3VO4 is then likely to act as the host for lithium ions in subsequent cycles by means of the intercalation mechanism. Such an 'in situ' compositing phenomenon during the electrochemical processes is novel and provides a very useful insight into the design of new anode materials for application in lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Silver molybdate, Ag2Mo2O7, has been prepared by a conventional solid-state reaction. Its electrochemical properties as an anode material for sodium-ion batteries (SIBs) have been comprehensively examined by means of galvanostatic charge-discharge cycling, cyclic voltammetry, and rate performance measurements. At operating voltages between 3.0 and 0.01 V, the electrode delivered a reversible capacity of nearly 190 mA h g−1 at a current density of 20 mA g−1 after 70 cycles. Ag2Mo2O7 also demonstrated a good rate capability and long-term cycle stability, the capacity reaching almost 100 mA h g−1 at a current density of 500 mA g−1, with a capacity retention of 55 % over 1000 cycles. Moreover, the sodium storage process of Ag2Mo2O7 has been investigated by means of ex situ XRD, Raman spectroscopy, and HRTEM. Interestingly, the anode decomposes into Ag metal and Na2MoO4 during the initial discharge process, and then Na+ ions are considered to be inserted into/extracted from the Na2MoO4 lattice in the subsequent cycles governed by an intercalation/deintercalation mechanism. Ex situ HRTEM images revealed that Ag metal not only remains unchanged during the sodiation/desodiation processes, but is well dispersed throughout the amorphous matrix, thereby greatly improving the electronic conductivity of the working electrode. The 'in situ' decomposition behavior of Ag2Mo2O7 is distinct from that of chemically synthesized, metal-nanoparticle-coated electrode materials, and provides strong supplementary insight into the mechanism of such new anode materials for SIBs and may set a precedent for the design of further materials. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) have attracted much interest as a low-cost and environmentally benign energy storage system, but more attention is justifiably required to address the major technical issues relating to the anode materials to deliver high reversible capacity, superior rate capability, and stable cyclability. A SnSe/reduced graphene oxide (RGO) nanocomposite has been prepared by a facile ball-milling method, and its structural, morphological, and electrochemical properties have been characterized and compared with those of the bare SnSe material. Although the redox behavior of SnSe remains nearly unchanged upon the incorporation of RGO, its electrochemical performance is significantly enhanced, as reflected by a high specific capacity of 590 mA h g−1 at 0.050 A g−1, a rate capability of 260 mA h g−1 at 10 A g−1, and long-term stability over 120 cycles. This improvement may be attributed to the high electronic conductivity of RGO, which also serves as a matrix to buffer changes in volume and maintain the mechanical integrity of the electrode during (de)sodiation processes. In view of its excellent Na+ storage performance, this SnSe/RGO nanocomposite has potential as an anode material for SIBs. [ABSTRACT FROM AUTHOR]

Tin-iron-carbon nanocomposite is successfully prepared by a sol-gel method followed by a chemical vapor deposition (CVD) process with acetylene gas as the carbon source. The structural properties, morphology, and electrochemical performances of the nanocomposite are comprehensively studied in comparison with those properties of tin-carbon and iron-carbon nanocomposites. Sheet-like carbon architecture and different carbon contents are induced thanks to the catalytic effect of iron during CVD. Among three nanocomposites, tin-iron-carbon demonstrates the highest reversible capacity of 800 mA h g−1 with 96.9 % capacity retention after 50 cycles. It also exhibits the best rate capability with a discharge capacity of 420 mA h g−1 at a current density of 1000 mA g−1. This enhanced performance is strongly related to the carbon morphology and content, which can not only accommodate the large volume change, but also improve the electronic conductivity of the nanocomposite. Hence, the tin-iron-carbon nanocomposite is expected to be a promising anode for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

H2V3O8 nanowires wrapped by reduced graphene oxide (RGO) are synthesized successfully through a simple hydrothermal process. The structural properties of the samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman scattering, and X-ray photoelectron spectroscopy. The RGO nanosheets modify the surfaces of the H2V3O8 nanowires through VC linkages. The H2V3O8/RGO composite exhibits a remarkably enhanced electrochemical performance in terms of its reversible capacity, cyclic performance, and rate capability. The material shows high discharge capacities of 256 and 117 mA h g−1 at the current densities of 0.1 and 1 A g−1, respectively, with almost no capacity fading after fifty charge/discharge cycles. Cyclic voltammetry and electrochemical impedance spectroscopy show that the superior electrochemical performance of H2V3O8/RGO can be attributed to the cooperation of RGO, which provides better mechanical flexibility, higher electronic conductivity, and smaller charge-transfer resistance. [ABSTRACT FROM AUTHOR]

Since the discovery of Ti3C2Tx in 2011, the family of two‐dimensional transition metal carbides, carbonitrides, and nitrides (collectively known as MXenes) has quickly attracted the attention of those developing energy storage applications such as electrodes for supercapacitors with acidic aqueous electrolytes. The excellent performance of these MXenes is attributed to a pseudocapacitive energy storage mechanism, based on the non‐rectangular shape of cyclic voltammetry curves and changes in the titanium oxidation state detected by in situ X‐ray absorption spectroscopy. However, the pseudocapacitive mechanism is not well understood and no dimensional changes due to proton insertion have been reported. In this work, in situ X‐ray diffraction and density functional theory are used to investigate the charge storage mechanism of Ti3C2Tx in 1 m H2SO4. Results reveal that a 0.5 Å expansion and shrinkage of the c‐lattice parameter of Ti3C2Tx occur during cycling in a 0.9 V voltage window, showing that the charge storage mechanism is intercalation pseudocapacitance with implication for MXene use in energy storage and electrochemical actuators. [ABSTRACT FROM AUTHOR]

Thanks to low costs and the abundance of the resources, sodium‐ion (SIBs) and potassium‐ion batteries (PIBs) have emerged as leading candidates for next‐generation energy storage devices. So far, only few materials can serve as the host for both Na+ and K+ ions. Herein, a cubic phase CuSe with crystal‐pillar‐like morphology (CPL‐CuSe) assembled by the nanosheets are synthesized and its dual functionality in SIBs and PIBs is comprehensively studied. The electrochemical measurements demonstrate that CPL‐CuSe enables fast Na+ and K+ storage as well as the sufficiently long duration. Specifically, the anode delivers a specific capacity of 295 mA h g−1 at current density of 10 A g−1 in SIBs, while 280 mA h g−1 at 5 A g−1 in PIBs, as well as the high capacity retention of nearly 100% over 1200 cycles and 340 cycles, respectively. Remarkably, CPL‐CuSe exhibits a high initial coulombic efficiency of 91.0% (SIBs) and 92.4% (PIBs), superior to most existing selenide anodes. A combination of in situ X‐ray diffraction and ex situ transmission electron microscopy tests fundamentally reveal the structural transition and phase evolution of CuSe, which shows a reversible conversion reaction for both cells, while the intermediate products are different due to the sluggish K+ insertion reaction. [ABSTRACT FROM AUTHOR]

Room‐temperature rechargeable sodium‐ion batteries appear to be promising alternatives for grid and other storage applications to lithium‐ion batteries because of the natural abundance, low cost, and environmental benignity of sodium. In response to the ever‐increasing development for these technologies, an intensive exploration for appropriate electrode materials with high energy density is still underway. This Progress Report highlights the recent research in the investigation of amorphous materials, whose isotropic physical and chemical properties can provide multiple pathways for ions and facilitate ion diffusion. This Progress Report focuses on sodium‐ion batteries, but it is hoped that the engineering strategies may provide guidance on further research and design of functional materials for both sodium and potassium‐ion batteries. Amorphous materials appear to be promising energy storage materials for room‐temperature rechargeable sodium‐ion batteries. The recent progress in this field is discussed in this progress report, both in cathode and anode electrodes. The isotropic physical and chemical properties resulting from the unique long‐range disordered and short‐range ordered structure of amorphous materials can provide various advantages for ion diffusion. [ABSTRACT FROM AUTHOR]