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Controlling morphology, adopting metal cations and introducing crystal water are three effective strategies to improve the electrochemical performance of various battery electrodes. However, the effects of simultaneously applying these three strategies to aqueous rechargeable zinc batteries (ARZBs) are rarely demonstrated. Herein, hierarchical H11 Al2 V6 O23.2 (HAVO) microspheres were successfully prepared using a simple hydrothermal method, and used as cathode material for ARZBs. The as-prepared HAVO microspheres exhibited superior electrochemical performance than the dehydrated AlV3 O9 (AVO) microspheres, i. e. they have a larger specific capacity of 390.4 mA h g-1 at 100 mA g-1 , a better rate capability of 191.4 mA h g-1 at 5000 mA g-1 and a higher cycling stability of up to 1000 cycles with a capacity retention of 80.9 %. The excellent electrochemical performance of HAVO is due to the synergistic effects of the shortened ion diffusion distance in primary HAVO nanosheets, the improved electronic conductivity, and structural stability by adopting Al3+ into the lattice, the enhanced charge transfer properties and ion diffusion coefficient of the electrode due to the existence of crystal water. Therefore, this work may offer a new route for the design and synthesis of more advanced electrode materials for ARZBs.

Titanium-substituted LiTix Fe1-2x SO4 F (x=0, 0.01, 0.02, 0.03) cathode materials were synthesized by a solvothermal method. X-ray diffraction, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy were used to investigate the effects of Ti substitution on the structure of LiFeSO4 F, and it was shown that Ti substitutes the Fe(2) site. First-principles calculations and UV-visible spectroscopy demonstrate that Ti substitution reduces the bandgap of LiFeSO4 F which improves the electronic conductivity from 8.3×10-12 S cm-1 to 3.9×10-11 S cm-1 . CI-NEB and BV calculations show that the Li diffusion energy barriers along the (100), (010) and (101) directions are decreased after Ti substitution, and the Li diffusion coefficient is increased from 4.99×10-11 cm2 S-1 to 1.59×10-10 cm2 S-1 . The improved electronic conductivity and ionic diffusivity mean that the Ti-substituted material shows improved electrochemical properties compared to the pristine LiFeSO4 F.

Transition metal oxides and sulfides have been intensively investigated as host materials for the S cathode in lithium-sulfur (Li-S) batteries; however, the distinctions between them in battery operation have remained unclear. In this study, VO2 and VS2 nanosheets were systematically studied as host materials for Li-S batteries through theoretical calculations and experimental testing. First-principles calculations demonstrated that VS2 showed more favorable properties, including the inherent semi-metallic conductivity of VS2 , moderate adsorption strength for Li2 Sn , fast Li+ transport with a low diffusion barrier, and accelerated surface redox reactions with a low Li2 S decomposition barrier. In comparison, the low electronic conductivity and strong adsorption strength of VO2 increased Li+ diffusion as well as Li2 S decomposition barriers of the electrode, resulting in relatively poor rate capability and cycle stability. In experiments, the VS2 @S electrode exhibited superior electrochemical performance compared with VO2 @S, giving a large capacity of 713 mAh g-1 at 5 C and a low capacity fading rate of 0.13 % per cycle over 200 cycles at 1 C. The constructed relationships between S cathode and host materials could guide the future design of high-performance S cathodes for Li-S batteries.

Advanced functional materials 32(16), 2110674 (2022). doi:10.1002/adfm.202110674, Herein, an eco-friendly and high safety aqueous Mg-ion electrolyte (AME) with a wide electrochemical stability window (ESW) $≈$ 3.7 V, containing polyethylene glycol (PEG) and low-concentration salt (0.8 m Mg(TFSI)$_2$), is proposed by solvation structure reorganization of AME. The PEG agent significantly alters the Mg$^{2+}$ solvation and hydrogen bonds network of AMEs and forms the direct coordination of Mg$^{2+}$ and TFSI-, thus enhancing the physicochemical and electrochemical properties of electrolytes. As an exemplary material, V$_2$O$_5$ nanowires are tested in this new AME and exhibit initial high discharge/charge capacity of 359/326 mAh g$^{-1}$ and high capacity retention of 80% after 100 cycles. The high crystalline $α$-V$_2$O$_5$ shows two 2-phase transition processes with the formation of $ε$-Mg$_{0.6}$V$_2$O$_5$ and Mg-rich Mg$_x$V$_2$O$_5$ (x $≈$1.0) during the first discharge. Mg-rich Mg$_x$V$_2$O$_5$ (x $≈$ 1.0) phase formed through electrochemical Mg-ion intercalation at room temperature is for the first time observed via XRD. Meanwhile, the cathode electrolyte interphase (CEI) in aqueous Mg-ion batteries is revealed for the first time. MgF$_2$ originating from the decomposition of TFSI- is identified as the dominant component. This work offers a new approach for designing high-safety, low-cost, eco-friendly, and large ESW electrolytes for practical and novel aqueous multivalent batteries., Published by Wiley-VCH, Weinheim

Nanostructures can improve battery capacity and cycle life, especially with sulfide electrodes. In this work, a freestanding flexible electrode, consisting of MnS nanoparticles embedded onto carbon nanofibers, was prepared by electrospinning. The produced hybrid was used as an electrode for lithium-ion and sodium-ion batteries. MnS nanoparticles have a size of about 5 nm and the particles are evenly distributed in the carbon nanofibers. Carbon nanofibers act as electronic conductors and buffer the volume change, while MnS nanoparticles react through rapid electrochemical reaction. As a Li-ion battery anode, this hybrid electrode exhibits specific capacities from 240 mAh g-1 at a high current density of 5 A g-1 , up to 600 mAh g-1 at 200 mA g-1 .

LiFePO4 @C/reduced graphene oxide (rGO) hierarchical microspheres with superior electrochemical activity and a high tap density were first synthesized by using a Fe3+ -based single inorganic precursor (LiFePO4 OH@RF/GO; RF=resorcinol-formaldehyde, GO=graphene oxide) obtained from a template-free self-assembly synthesis followed by direct calcination. The synthetic process requires no physical mixing step. The phase transformation pathway from tavorite LiFePO4 OH to olivine LiFePO4 upon calcination was determined by means of the in situ high-temperature XRD technique. Benefitting from the unique structure of the material, these microspheres can be densely packed together, giving a high tap density of 1.3 g cm-3 , and simultaneously, defectless LiFePO4 primary nanocrystals modified with a highly conductive surface carbon layer and ultrathin rGO provide good electronic and ionic kinetics for fast electron/Li+ ion transport.

The size and conductivity of the electrode materials play a significant role in the kinetics of sodium-ion batteries. Various characterizations reveal that size-controllable VS4 nanoparticles can be successfully anchored on the surface of graphene sheets (GSs) by a simple cationic-surfactant-assisted hydrothermal method. When used as an electrode material for sodium-ion batteries, these VS4 @GS nanocomposites show large specific capacity (349.1 mAh g-1 after 100 cycles), excellent long-term stability (84 % capacity retention after 1200 cycles), and high rate capability (188.1 mAh g-1 at 4000 mA g-1 ). A large proportion of the capacity was contributed by capacitive processes. This remarkable electrochemical performance was attributed to synergistic interactions between nanosized VS4 particles and a highly conductive graphene network, which provided short diffusion pathways for Na+ ions and large contact areas between the electrolyte and electrode, resulting in considerably improved electrochemical kinetic properties.

Co9S8 has been regarded as a desirable anode material for sodium ion batteries because of its high theoretical capacity. In this study, a Co9S8 anode material containing 5.5 wt% Co (Co9S8/Co) was prepared by a solid-state reaction. The material's electrochemical properties were studied with carbonate-based and ether-based electrolytes (the latter, EBE), which showed that the material had a longer cycling life and better rate capability in the EBE. This excellent electrochemical performance was attributed to the low apparent activation energy and the low over-potential for Na deposition in the ether based electrolyte, which improved the electrode kinetic properties. Also, EBE suppressed side reactions of the electrode and electrolyte, which avoided the formation of a solid electrolyte interphase film.

An integrated WS2@CMK-3 nanocomposite has been prepared by a one-step hydrothermal method and then used as the anode material for lithium-ion and sodium-ion batteries. Ultrathin WS2 nanosheets have been successfully embedded into the ordered mesoporous carbon (CMK-3) framework. Owing to the few-layered nanostructure of WS2, as well as the high electronic conductivity and the volume confinement effect of CMK-3, the material shows larger discharge capacity, better rate capability, and improved cycle stability than pristine WS2. When tested in lithium-ion batteries, the material delivers a reversible capacity of 720 mA h g−1 after 100 cycles at a current density of 100 mA g−1. A large discharge capacity of 307 mA h g−1 is obtained at a current density of 2 A g−1. When used in sodium-ion batteries, the material exhibits a capacity of 333 mA h g−1 at 100 mA g−1 without capacity fading after 70 cycles. A discharge capacity of 230 mA h g−1 is obtained at 2 A g−1. This excellent performance demonstrates that the WS2@CMK-3 nanocomposite has great potential as a high-performance anode material for next-generation rechargeable batteries.

Ag2 Mo2 O7 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 Ag2 Mo2 O7 were investigated by using ex situ XRD and TEM. The Ag2 Mo2 O7 electrode is likely to be decomposed into amorphous molybdenum, Li2 O, 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.

The demand for large-scale and high-safe energy storage is increasing rapidly due to the strong push for smartphone and electric vehicles. The Li+/Mg2+ hybrid-ion batteries (LMIBs) combing a dendrite-free deposition of Mg anode and Li+ intercalation cathode attract considerable attentions. Here we report a LMIB using the hydrothermal-prepared MoS2 nano flowers as the cathode material. The battery showed remarkable electrochemical properties with a large discharge capacity (243 mAh g-1 at the 0.1 C rate), excellent rate capability (108 mAh g-1 at the 5 C rate) and long cycle life (87.2 % capacity retention after 2,300 cycles). Electrochemical analysis showed that the reactions occurred in the battery cell involved Mg stripping/plating at the anode side and Li+ intercalation at the cathode side with a small contribution from Mg2+ adsorption. The excellent electrochemical performance and extremely safe cell system lead to an opportunity for its practical application.

Cu3 V2 O8 nanoparticles with particle sizes of 40-50 nm have been prepared by the co-precipitation method. The Cu3 V2 O8 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 Cu3 V2 O8 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 Cu3 V2 O8 decomposes into copper metal and Li3 VO4 on being initially discharged to 0.01 V, and the Li3 VO4 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.

Silver molybdate, Ag2 Mo2 O7 , 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. Ag2 Mo2 O7 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 Ag2 Mo2 O7 has been investigated by means of ex situ XRD, Raman spectroscopy, and HRTEM. Interestingly, the anode decomposes into Ag metal and Na2 MoO4 during the initial discharge process, and then Na(+) ions are considered to be inserted into/extracted from the Na2 MoO4 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 Ag2 Mo2 O7 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.

The fabrication of silicon (Si) anode materials derived from high silica-containing plants enables effective utilization of subsidiary agricultural products. However, the electrochemical performances of synthesized Si materials still require improvement and thus need further structural design and morphology modifications, which inevitably increase preparation time and economic cost. Here, the conversion of corn leaves into Si anode materials is reported via a simple aluminothermic reduction reaction without other modifications. The obtained Si material inherits the structural characteristics of the natural corn leaf template and has many inherent advantages, such as high porosity, amorphous/crystalline mixture structure, and high-valence SiOx residuals, which significantly enhance the material's structural stability and electrode adhesive strength, resulting in superior electrochemical performances. Rate capability tests show that the material delivers a high capacity of 1200 mA h g-1 at 8 A g-1 current density. After 300 cycles at 0.5 A g-1 , the material maintains a high specific capacity of 2100 mA h g-1 , with nearly 100% capacity retention during long-term cycling. This study provides an economical route for the industrial production of Si anode materials for Lithium-Ion batteries.

A sponge-like V2O5 nanomaterial is prepared by a freeze–drying method and evaluated as a cathode material for sodium-ion batteries. The sponge-like structure is self-assembled from V2O5 nanosheets that can sustain high pressure (400 times their own weight), thus leading to a high structure stability. The numerous macropores in the spongy structure can effectively soak up the electrolyte. Moreover, the exposed (001) facet of the nanosheets is favorable for charge transfer at the electrolyte/electrode interface. The thin nanosheets along the [001] axis provide short diffusion pathways for sodium ions. Electrochemical experiments show that the material has a high discharge capacity of 216 mAh g−1 at a current density of 20 mA g−1. In addition, the material shows a good capacity retention of 73 % in 100 charge–discharge cycles at a current density of 100 mA g−1.

A series of V2O5-based cathode materials that include V2O5 and Al0.14 V2O5 nanoparticles, V2O5/reduced graphene oxide (RGO), and Al0.16 V2O5/RGO nanocomposites are prepared by a simple soft chemical method. XRD and Raman scattering show that the Al ions reside in the interlayer space of the materials. These doping ions strengthen the V−O bonds of the [VO5] unit and enhance the linkage of the [VO5] layers, which thus increases the structural stability of V2O5. SEM and TEM images show that the V2O5 nanoparticles construct a hybrid structure with RGO that enables fast electron transport in the electrode matrix. The electrochemical properties of the materials are studied by charge-discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Of all the materials tested, the one that contained both Al ions and RGO (Al0.16 V2O5/RGO) exhibited the highest discharge capacity, the best rate capability, and excellent capacity retention. The superior electrochemical performance is attributed to the synergetic effects of Al(3+) doping and RGO modification, which not only increase the structural stability of the V2O5 lattice but also improve the electrochemical kinetics of the material.

H2 V3 O8 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 H2 V3 O8 nanowires through VC linkages. The H2 V3 O8 /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 H2 V3 O8 /RGO can be attributed to the cooperation of RGO, which provides better mechanical flexibility, higher electronic conductivity, and smaller charge-transfer resistance.

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 A 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.

H2V3O8 nanowires wrapped by reduced graphene oxide (RGO) as composite cathodes for Li-ion batteries are hydrothermally prepared by ultrasonication of a suspension of V2O5, H2O2, and a graphene oxide derived by a modified Hummers method (autoclave, 200 °C, 5 d).

Li3V2(PO4)3/Cu composite cathode material was prepared via sol–gel method by adding of 1.8 wt% Cu powder into the precursor solution. The structural and physical properties, as well as the electrochemical performance of the material were compared with those of Cu-free Li3V2(PO4)3. X-ray diffraction showed that Cu did not enter the crystal structure of Li3V2(PO4)3. The Li3V2(PO4)3/Cu composite material had a higher electronic conductivity comparing with that of Cu-free Li3V2(PO4)3. Electrochemical impedance spectroscopy showed that the adding of Cu decreased the charge transfer resistance of the electrode. In addition, the lithium diffusion coefficient was prominently enhanced from 1.3 × 10−9 to 2.8 × 10−8 cm2 s−1. Based on the these advantages, the Li3V2(PO4)3/Cu composite material exhibited much better cycling performance than the Cu-free Li3V2(PO4)3.

A uniform and high crystalline Cu0.04V2O5 powder was prepared by precipitation method. The effects of Cu doping on the electrochemical properties of crystalline V2O5 were investigated by means of galvanostatic charge–discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that slight Cu doping significantly improved the electrochemical properties of V2O5. Cu-doped Cu0.04V2O5 exhibited promising electrochemical performance, with a reversible energy density of 450 Wh/kg and a power density of 275 W/kg.