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TiO2 has been intensively investigated as an anode material for lithium-ion batteries (LIBs) in 1.0-3.0 V (vs Li+/Li). However, it is a challenge to realize its theoretical capacity (336 mAh g-1) in this limited potential range. Extending the potential range below 1.0 V would increase its capacity but usually at the expense of its cyclic stability owing to the sluggish ionic diffusion and unsatisfactory structural stability. Here, three-dimensional (3D) macroporous TiO2 microspheres with interconnected pores and nanocrystalline thin walls have been constructed through a scalable template-assisted spray drying method to overcome these obstacles. When applied to LIBs, high and stable discharge capacity (300 mAh g-1 at 0.1 A g-1) as well as superior cyclic stability (242 mAh g-1 after 1000 cycles at 1.0 A g-1) can be achieved under deep discharging/charging conditions (0.01-3.0 V vs Li+/Li). Furthermore, the 3D macroporous structure is well preserved under deep discharging/charging and the in situ X-ray diffraction (XRD) patterns and Raman spectra reveal the dominant pseudocapacitive contribution at low potentials (0.01-1.0 V). This work not only develops a facile method to synthesize macroporous metal oxides but also provides insight into the lithium storage mechanism of TiO2 under deep discharging/charging conditions.

Composite solid electrolytes (CSEs) hold great promise toward safe lithium metal batteries with high energy density, due to integration of the merits of polymer matrixes and fillers. Rational design of filler nanostructures has attracted increasing attention for improving the ionic transport of CSEs in solid batteries. In this work, we fabricated open-structured Li0.33La0.557TiO3 (LLTO) nanotubes (NTs) as ion-conductive fillers in CSEs by a gradient electrospinning method for the first time. Different from nanoparticles (NPs) and nanowires (NWs), our nanotubes are composed of connected small NPs, which offer three-dimensional (3D) Li+-accessible pathways, large polymer/filler interfacial ionic conduction regions, and enhanced wettability against the polymer matrix. As a result, the solid electrolytes based on LLTO NTs and polyacrylonitrile (PAN) can display a high ionic conductivity of up to 3.6 × 10-4 S cm-1 and a wide electrochemical window of 5 V at room temperature (RT). Furthermore, Li-Li symmetric cells using the LLTO NTs/PAN CSE can work stably over 1000 h with a polarization of 20 mV. LiFePO4-Li full cells exhibit a high capacity of 142.5 mAh g-1 with a capacity retention of 90% at 0.5 C after 100 cycles. All of these results demonstrate that the design of open-structured nanotubes as fillers is a promising strategy for high-performance solid electrolytes.

Solid-state lithium metal battery (SSLMB) is regarded as a safer energy storage system compared to the liquid one. The performance of the SSLMB depends on the cathode performance and the side reactions derived from the interface of the cathode and the electrolyte, which becomes much severe at high temperatures. Herein, we carried out a facile spray-drying route to prepare a CNTs/LiV3O8/Y2O3 (M-LVO-Y) composite. The synthesized cathode material exhibits an outstanding Li+ storage performance with a high reversible capacity of 279.9 mA h g-1 at 0.05 A g-1, excellent power capability (182.5 mA h g-1 at 2 A g-1), and a long cycle lifespan of 500 cycles with a capacity retention of 66.5% at a current density of 1 A g-1. The fabricated rechargeable solid-state Li/M-LVO-Y-2 lithium metal battery (LMB) with a poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE) achieves a high discharge capacity of 302.1 mA h g-1 at 0.05 A g-1 and a stable cycling performance with the highest capacity of 72.1% after 100 cycles at 0.2 A g-1 and 80 °C. The above battery performance demonstrates that SSLMBs with the CNTs/LiV3O8/Y2O3 cathode and the PEO-based SPE film can provide high energy density and are suitable for applying in a high-temperature environment.

Poor cycle and rate performance caused by volume effects and sluggish kinetics is the main bottleneck for most lithium-ion battery (LIB) anode materials run on the conversion reaction. Although nan...

The shuttle effect of lithium polysulfides (Li2Sn) in electrolyte and the low conductivity of sulfur are the two key hindrances of lithium sulfur (Li-S) batteries. In order to address the two issues, we propose a three-dimensional porous nitrogen-doped carbon nanosheet with embedded NixCo3-xS4 nanocrystals derived from metal-organic frameworks for the durable-cathode host material in Li-S batteries. Experiments and density functional theory simulations show that the large porosity, robust N-doped carbon framework, and evenly embedded NixCo3-xS4 nanocrystals with high polarity act as strong "traps" for the immobilization of Li2Sn, which leads to an effective suppressing of the shuttle effect and promotes efficient utilization of sulfur. The NixCo3-xS4/N-doped carbon hybrid material exhibits a high reversible capacity of 1122 mAh g-1 at a current density of 0.5 C after 100 cycles. Even at high areal sulfur loadings of 10 and 12 mg cm-2, the hybrid cathode materials can maintain good areal capacities of 7.2 and 7.6 mAh cm-2 after 100 cycles. The present study sheds light on the principles of the anchoring behaviors of Li2Sn species on bimetallic sulfide hybrid materials and reveals an attractive route to design the highly desirable cathode materials for Li-S batteries.

A two-dimensional (2D) layer-structured material is often a high-capacity ionic storage material with fast ionic transport within the layers. This appears to be the case for nonconversion layer str...

Mn3O4 is a potential anode for alkali-metal (Li/Na/K)-ion batteries because of the high capacity, abundant resources, and eco-friendliness. However, its ion storage performance is limited by poor e...

Porous carbons have been extensively studied in supercapacitors. However, it remains a grand challenge for porous carbons to achieve a volumetric capacitance (Cv) of over 200 F cm–3 because of the low intrinsic density and limited capacitance. Herein, we propose a pomegranate-like carbon microsphere (PCS) constructed by monodisperse, submicron, N-doped microporous carbon spheres for high-volumetric-capacitance supercapacitors. The assembly of submicron carbon spheres into pomegranate-like structures significantly reduces the required binder amount (2.0 wt %) for electrode preparation, diminishes the interparticle resistance, and most importantly, endows the PCS with a high packing density (0.75 g cm–3). Benefited from the high surface area (1477 m2 g–1), N-doping (3.0 wt %), and high packing density, the PCS demonstrates a high Cv (254 F cm–3), four times that of unassembled monodisperse carbon spheres. This work opens a new avenue to enhance the Cv of porous carbons without compromising the rate capabili...

Cryptomelane-type α-MnO2 has been demonstrated as a promising anode material for high-energy Li-ion batteries because of its high capacity and intriguing [2 × 2] tunnel structure. However, applications of MnO2 electrode, especially at high current rates and mass active material loading, are limited by the poor mechanical stability, unstable solid electrolyte interphase layer, and low reversibility of conversion reactions. Here, we report a design of homogeneous core–shell MnO2 nanowires (NWs) created by near-surface gradient Ti doping (Ti-MnO2 NWs). Such a structurally coherent core–shell configuration endowed gradient volume expansion from the inner core to the outer shell, which could effectively release the stress of the NW lattice during cycling and avoid pulverization of the electrode. Moreover, the gradiently doped Ti is able to avoid the Mn metal coarsening, reducing the metal particle size and improving the reversibility of the conversion reaction. In this way, the Ti-MnO2 NWs achieved both high r...

As a novel and potential transition metal dichalcogenide (TMDC), NbSe2 has low ion diffusion barrier when applied in energy-storage systems, such as traditional lithium-ion batteries and novel magnesium-ion batteries (MIBs). In this work, we have developed a novel hexagonal NbSe2 material with a nanosized surface via a facile microwave-hydrothermal method. The Li+-storage mechanism of NbSe2 with surface conversion and internal intercalation is thoroughly revealed by in situ X-ray diffraction (XRD), ex situ high-resolution transmission electron microscopy, and ex situ scanning electron microscopy. Besides, Mg2+ intercalation mechanism is confirmed via ex situ XRD and ex situ X-ray photoelectron spectroscopy for the first time. In addition, as the cathode for MIBs, NbSe2 with a nanosized surface exhibits a high rate capacity of 101 mA h g-1 at 200 mA g-1 with a high discharge plateau at 1.30 V. Our work builds a deep understanding of ion-storage mechanisms in TMDCs and provides guidance for designing new electrode materials with high electrochemical performances.

Dual ion batteries based on Na+ and PF6– received considerable attention due to their high operating voltage and the abundant Na resources. Here, cheap and easily obtained graphite that served as a cathode material for dual ion battery delivered a very high average discharge platform (4.52 V vs Na+/Na) by using sodium hexafluorophosphate in propylene carbonate as electrolyte. Moreover, the all-carbon dual ion batteries with graphite as cathode and hard carbon as anode exhibited an ultrahigh discharge voltage of 4.3 V, and a reversible capacity of 62 mAh·g–1 at 40 mA·g–1. Phase changes have been investigated in detail through in situ X-ray diffraction and in situ Raman characterizations. The stable structure provides long life cycling performance, and the pseudocapacitance behavior also demonstrates its benefits to the rate capability. Thus, dual ion batteries based on sodium chemistry are very promising to find their applications in future.

With high theoretical capacity, good ionic conductivity, and suitable working plateaus, Li3VO4 has emerged as an eye-catching intercalation anode material for lithium storage. However, Li3VO4 suffers from poor electrical conductivity and 20% volume variation under deep discharging/charging conditions. Herein, we present a “double-carbon decoration” strategy to tackle both issues. Deflated balloon-like Li3VO4/C/reduced graphene oxide (LVO/C/rGO) microspheres with continuous electron transport pathways and sufficient free space for volume change accommodation are fabricated through a facile spray-drying method. Under deep discharging/charging conditions (0.02–3.0 V), LVO/C/rGO achieves a high intercalation capacity of 591 mA h g–1. With high capacity and outstanding stability, LVO/C/rGO outperforms other intercalation anode materials (such as graphite, Li4Ti5O12, and TiO2). In situ X-ray diffraction measurement reveals that the lithium storage is realized through both solid-solution reaction and two-phase r...

Sodium-ion batteries (SIBs) are considered as one of the most favorable alternative devices for sustainable development of modern society. However, it is still a big challenge to search for proper anode materials which have excellent cycling and rate performance. Here, zinc selenide microsphere and multiwalled carbon nanotube (ZnSe/MWCNT) composites are prepared via hydrothermal reaction and following grinding process. The performance of ZnSe/MWCNT composites as a SIB anode is studied for the first time. As a result, ZnSe/MWCNTs exhibit excellent rate capacity and superior cycling life. The capacity retains as high as 382 mA h g–1 after 180 cycles even at a current density of 0.5 A g–1. The initial Coulombic efficiency of ZnSe/MWCNTs can reach 88% and nearby 100% in the following cycles. The superior electrochemical properties are attributed to continuous electron transport pathway, improved electrical conductivity, and excellent stress relaxation.

Rationally generating oxygen vacancies in electrocatalysts is an important approach to modulate the electrochemical activity of a catalyst. Herein, we report a remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCo2O4 supported on hollow carbon spheres (HCS) achieved through generating abundant oxygen vacancies within the surface lattice. This catalyst exhibits enhanced ORR activity (larger limiting current density of ∼−5.8 mA cm–2) and higher stability (∼90% retention after 40 000 s) compared with those of NiCo2O4/HCS and NiCo2O4. The results of X-ray photoelectron spectroscopy (XPS) characterizations suggest that the introduction of oxygen vacancies optimizes the valence state of active sites. Furthermore, we carried out density functional theory (DFT) calculations to further confirm the mechanism of oxygen vacancies, and results show that oxygen vacancies enhance the density of states (DOS) near the Fermi level, decrease work function, and lower the calculated overpotential of NiCo2O4.

Symmetric sodium-ion batteries (SIBs) are considered as promising candidates for large-scale energy storage owing to the simplified manufacture and wide abundance of sodium resources. However, most symmetric SIBs suffer from suppressed energy density. Here, a superior congeneric Na4V2(PO4)3 anode is synthesized via electrochemical preintercalation, and a high energy density symmetric SIB (Na3V2(PO4)3 as a cathode and Na4V2(PO4)3 as an anode) based on the deepened redox couple of V4+/V2+ is built for the first time. When measured in half cell, both electrodes show stabilized electrochemical performance (over 3000 cycles). The symmetric SIBs exhibit an output voltage of 3.0 V and a cell-level energy density of 138 W h kg–1. Furthermore, the sodium storage mechanism under the expanded measurement range of 0.01–3.9 V is disclosed through an in situ X-ray diffraction technique.

Constructing novel heterostructures has great potential in tuning the physical/chemical properties of functional materials for electronics, catalysis, as well as energy conversion and storage. In this work, heterostructured Bi2S3-Bi2O3 nanosheets (BS-BO) have been prepared through an easy water-bath approach. The formation of such unique BS-BO heterostructures was achieved through a controllable thioacetamide-directed surfactant-assisted reaction process. Bi2O3 sheets and Bi2S3 sheets can be also prepared through simply modifying the synthetic recipe. When employed as the sodium-ion battery anode material, the resultant BS-BO displays a reversible capacity of ∼630 mA h g-1 at 100 mA g-1. In addition, the BS-BO demonstrates improved rate capability and enhanced cycle stability compared to its Bi2O3 sheets and Bi2S3 sheets counterparts. The improved electrochemical performance can be ascribed to the built-in electric field in the BS-BO heterostructure, which effectively facilitates the charge transport. This work would shed light on the construction of novel heterostructures for high-performance sodium-ion batteries and other energy-related devices.

Aqueous zinc-ion batteries attract increasing attention due to their low cost, high safety, and potential application in stationary energy storage. However, the simultaneous realization of high cycling stability and high energy density remains a major challenge. To tackle the above-mentioned challenge, we develop a novel Zn/V2O5 rechargeable aqueous hybrid-ion battery system by using porous V2O5 as the cathode and metallic zinc as the anode. The V2O5 cathode delivers a high discharge capacity of 238 mAh g–1 at 50 mA g–1. 80% of the initial discharge capacity can be retained after 2000 cycles at a high current density of 2000 mA g–1. Meanwhile, the application of a “water-in-salt” electrolyte results in the increase of discharge platform from 0.6 to 1.0 V. This work provides an effective strategy to simultaneously enhance the energy density and cycling stability of aqueous zinc ion-based batteries.

One-dimensional heterostructures have attracted significant interests in various applications. However, the selective deposition of shell material on specific sites of the backbone material remains a challenge. Herein, a facile facet-selective deposition strategy has been developed for the construction of heterostructured α-MoO3@FeOx nanobelts. Because of the anisotropic feature of α-MoO3 nanobelts, the FeOx nanoparticles selectively deposit on the edges of α-MoO3 nanobelts, that is, the {100} and {001} facets. Such a heterostructure facilitates the electron transfer in lithium storage. As a result, the α-MoO3@FeOx nanobelts exhibit high capacities of 913 mA h g–1 after 100 cycles at 200 mA g–1 and 540 mA h g–1 after 100 cycles at 1000 mA g–1. The facet-selective deposition strategy developed here would be extended to the construction of other novel heterostructures with fascinating physical/chemical properties and wide potential applications.

Magnesium-based batteries have received much attention as promising candidates to next-generation batteries because of high volumetric capacity, low price, and dendrite-free property of Mg metal. Herein, we reported H2V3O8 nanowire cathode with excellent electrochemical property in magnesium-based batteries. First, it shows a satisfactory magnesium storage ability with 304.2 mA h g–1 capacity at 50 mA g–1. Second, it possesses a high-voltage platform of ∼2.0 V vs Mg/Mg2+. Furthermore, when evaluated as a cathode material for magnesium-based hybrid Mg2+/Li+ battery, it exhibits a high specific capacity of 305.4 mA h g–1 at 25 mA g–1 and can be performed in a wide working temperature range (−20 to 55 °C). Notably, the insertion-type ion storage mechanism of H2V3O8 nanowires in hybrid Mg2+/Li+ batteries are investigated by ex situ X-ray diffraction and Fourier transform infrared. This research demonstrates that the H2V3O8 nanowire cathode is a potential candidate for high-performance magnesium-based batteries.

The employment of nanomaterials and nanotechnologies has been widely acknowledged as an effective strategy to enhance the electrochemical performance of lithium-ion batteries (LIBs). However, how to produce nanomaterials effectively on a large scale remains a challenge. Here, the highly crystallized Zn3V2O7(OH)2·2H2O is synthesized through a simple liquid phase method at room temperature in a large scale, which is easily realized in industry. Through suppressing the reaction dynamics with ethylene glycol, a uniform morphology of microflowers is obtained. Owing to the multiple reaction mechanisms (insertion, conversion, and alloying) during Li insertion/extraction, the prepared electrode delivers a remarkable specific capacity of 1287 mA h g–1 at 0.2 A g–1 after 120 cycles. In addition, a high capacity of 298 mA h g–1 can be obtained at 5 A g–1 after 1400 cycles. The excellent electrochemical performance can be attributed to the high crystallinity and large specific surface area of active materials. The sm...

Herein, a graphene oxide (GO)-wired manganese silicate (MS) hollow sphere (MS/GO) composite is successfully synthesized. Such an architecture possesses multiple advantages in lithium and sodium storage. The hollow MS structure provides a sufficient free space for volume variation accommodation; the porous and low-crystalline features facilitate the diffusion of lithium ions; meanwhile, the flexible GO sheets enhance the electronic conductivity of the composite to a certain degree. When applied as the anode material for lithium-ion batteries (LIBs), the as-obtained MS/GO composite exhibits a high reversible capacity, ultrastable cyclability, and good rate performance. Particularly, the MS/GO composite delivers a high capacity of 699 mA h g-1 even after 1000 cycles at 1 A g-1. The sodium-storage performance of MS/GO has been studied for the first time, and it delivers a stable capacity of 268 mA h g-1 after 300 cycles at 0.2 A g-1. This study suggests that the rational design of metal silicates would render them promising anode materials for LIBs and SIBs.

The hybrid magnesium–lithium-ion batteries (MLIBs) combining the dendrite-free deposition of the Mg anode and the fast Li intercalation cathode are better alternatives to Li-ion batteries (LIBs) in large-scale power storage systems. In this article, we reported hybrid MLIBs assembled with the VO2 cathode, dendrite-free Mg anode, and the Mg–Li dual-salt electrolyte. Satisfactorily, the VO2 cathode delivered a stable plateau at about 1.75 V, and a high specific discharge capacity of 244.4 mA h g–1. To the best of our knowledge, the VO2 cathode displays the highest energy density of 427 Wh kg–1 among reported MLIBs in coin-type batteries. In addition, an excellent rate performance and a wide operating temperature window from 0 to 55 °C have been obtained. The combination of VO2 cathode, dual-salt electrolyte, and Mg anode would pave the way for the development of high energy density, safe, and low-cost batteries.

In this article, we report NiSe2 nanooctahedra as a promising anode material for sodium-ion batteries (SIBs). They exhibit outstanding long-term cyclic stability (313 mAh/g after 4000 cycles at 5 A/g) and excellent high-rate capability (175 mAh/g at 20 A/g). Besides, the initial Coulombic efficiency of NiSe2 is also very impressive (over 90%). Such remarkable performances are attributed to good conductivity, structural stability, and the pseudocapacitive behavior of the NiSe2. Furthermore, the sodium ion storage mechanism of NiSe2 is first investigated by in situ XRD and ex situ XRD. These highlights give NiSe2 a competitive strength for rechargeable SIBs.

Metal chalcogenides have emerged as promising anode materials for lithium ion batteries (LIBs) and sodium ion batteries (SIBs). Herein, a free-standing membrane based on ultralong Sb2Se3 nanowires has been successfully fabricated via a facile hydrothermal synthesis combined with a subsequent vacuum filtration treatment. The as-achieved free-standing membrane constructed by pure Sb2Se3 nanowires exhibits good flexibility and integrity. Meanwhile, we investigate the lithium and sodium storage behavior of the Sb2Se3 nanowire-based free-standing membrane. When applied as the anode for LIBs, it delivers a reversible capacity of 614 mA h g-1 at 100 mA g-1, maintaining 584 mA h g-1 after 50 cycles. When applied as the anode for SIBs, it delivers a reversible capacity of 360 mA h g-1 at 100 mA g-1, retaining 289 mA h g-1 after 50 cycles. Such difference in electrochemical performance can be attributed to the more complex sodiation process relative to the corresponding lithiation process. This work may provide insight on developing Sb2Se3-based anode materials for high-performance LIBs or SIBs.

Exploring non-noble and high-efficiency electrocatalysts is critical to large-scale industrial applications of electrochemical water splitting. Currently, nickel-based selenide materials are promising candidates for oxygen evolution reaction due to their low cost and excellent performance. In this work, we report the porous nickel-iron bimetallic selenide nanosheets ((Ni0.75Fe0.25)Se2) on carbon fiber cloth (CFC) by selenization of the ultrathin NiFe-based nanosheet precursor. The as-prepared three-dimensional oxygen evolution electrode exhibits a small overpotential of 255 mV at 35 mA cm(-2) and a low Tafel slope of 47.2 mV dec(-1) and keeps high stability during a 28 h measurement in alkaline solution. The outstanding catalytic performance and strong durability, in comparison to the advanced non-noble metal catalysts, are derived from the porous nanostructure fabrication, Fe incorporation, and selenization, which result in fast charge transportation and large electrochemically active surface area and enhance the release of oxygen bubbles from the electrode surface.

Herein, a successful application of V2O5·nH2O film as hole transporting layer (HTL) instead ofPSS in polymer solar cells is demonstrated. The V2O5·nH2O layer was spin-coated from V2O5·nH2O sol made from melting-quenching sol-gel method by directly using vanadium oxide powder, which is readily accessible and cost-effective. V2O5·nH2O (n ≈ 1) HTL is found to have comparable work function and smooth surface to that ofPSS. For the solar cell containing V2O5·nH2O HTL and the active layer of the blend of a novel polymer donor (PBDSe-DT2PyT) and the acceptor of PC71BM, the PCE was significantly improved to 5.87% with a 30% increase over 4.55% attained withPSS HTL. Incorporation of V2O5·nH2O as HTL in the polymer solar cell was found to enhance the crystallinity of the active layer, electron-blocking at the anode and the light-harvest in the wavelength range of 400-550 nm in the cell. V2O5·nH2O HTL improves the charge generation and collection and suppress the charge recombination within the PBDSe-DT2PyT:PC71BM solar cell, leading to a simultaneous enhancement in Voc, Jsc, and FF. The V2O5·nH2O HTL proposed in this work is envisioned to be of great potential to fabricate highly efficient PSCs with low-cost and massive production.

Metal vanadates suffer from fast capacity fading in lithium-ion batteries especially at a high rate. Pseudocapacitance, which is associated with surface or near-surface redox reactions, can provide fast charge/discharge capacity free from diffusion-controlled intercalation processes and is able to address the above issue. In this work, we report the synthesis of macroporous CoV2O6 nanosheets through a facile one-pot method via acetylene black induced heterogeneous growth. When applied as lithium-ion battery anode, the macroporous CoV2O6 nanosheets show typical features of pseudocapacitive behavior: (1) currents that are mostly linearly dependent on sweep rate and (2) redox peaks whose potentials do not shift significantly with sweep rate. The macroporous CoV2O6 nanosheets display a high reversible capacity of 702 mAh g(-1) at 200 mA g(-1), excellent cyclability with a capacity retention of 89% (against the second cycle) after 500 cycles at 500 mA g(-1), and high rate capability of 453 mAh g(-1) at 5000 mA g(-1). We believe that the introduction of pseudocapacitive properties in lithium battery is a promising direction for developing electrode materials with high-rate capability.

Hierarchical Co2V2O7 nanosheets consisted of interconnected nanoparticles are synthesized by a facile method using graphene oxide as the template. The electrochemical reaction mechanism of the Co2V2O7 nanosheets is thoroughly investigated by in situ XRD and ex situ TEM. The initial Co2V2O7 transforms into CoO nanoparticles and vanadium oxides in the first cycle, and the following reversible conversion reaction mainly occurs between CoO and Co and lithiation/delithiation of the vanadium oxides. The Co2V2O7 nanosheet displays a high reversible capacity (962 mAh/g at 0.5 A/g) and remarkable high rate capability. When cycled at 5.0 A/g, a reversible capacity of 441 mAh/g can be retained after 900 cycles. The stable high capacity and excellent rate capability make the hierarchical Co2V2O7 nanosheets a promising anode material for lithium-ion batteries.

Hierarchical copper silicate hydrate hollow spheres-reduced graphene oxide (RGO) composite is successfully fabricated by a facile hydrothermal method using silica as in situ sacrificing template. The electrochemical performance of the composite as lithium-ion battery anode was studied for the first time. Benefiting from the synergistic effect of the hierarchical hollow structure and conductive RGO matrix, the composite exhibits excellent long-life performance and rate capability. A capacity of 890 mAh/g is achieved after 200 cycles at 200 mA/g and a capacity of 429 mAh/g is retained after 800 cycles at 1000 mA/g. The results indicate that the strategy of combining hierarchical hollow structures with conductive RGO holds the potential in addressing the volume expansion issue of high capacity anode materials.

Operating as the "rocking-chair" battery, sodium ion battery (SIB) with acceptable high capacity is a very promising energy storage technology. Layered vanadium oxide xerogel exhibits high sodium storage capacity. But it undergoes large lattice breathing during sodiation/desodiation, resulting in fast capacity fading. Herein, we develop a facile hydrothermal method to synthesize iron preintercalated vanadium oxide ultrathin nanobelts (Fe-VOx) with constricted interlayer spacing. Using the Fe-VOx as cathode for SIB, the lattice breathing during sodiation/desodiation is largely inhibited and the interlayer spacing is stabilized for reversible and rapid Na(+) insertion/extraction, displaying enhanced cycling and rate performance. This work presents a new strategy to reduce the lattice breathing of layered materials for enhanced sodium storage through interlayer spacing engineering.

Olivine-type LiMnPO4 has been extensively studied as a high-energy density cathode material for lithium-ion batteries. To improve both the ionic and electronic conductivities of LiMnPO4, a series of carbon-decorated LiMnPO4·Li3V2(PO4)3 nanocomposites are synthesized by a facile sol-gel method combined with the conventional solid-state method. The optimized composite presents a three-dimensional hierarchical structure with active nanoparticles well-embedded in a conductive carbon matrix. The combination of the nanoscale carbon coating and the microscale carbon network could provide a more active site for electrochemical reaction, as well as a highly conductive network for both electron and lithium-ion transportation. When cycled at 20 C, an initial specific capacity of 103 mA h g(-1) can be obtained and the capacity retention reaches 68% after 3000 cycles, corresponding to a capacity fading of 0.013% per cycle. The stable capacity and excellent rate capability make this carbon-decorated LiMnPO4·Li3V2(PO4)3 nanocomposite a promising cathode for lithium-ion batteries.

Recently, layered transition-metal dichalcogenides (TMDs) have gained great attention for their analogous graphite structure and high theoretical capacity. However, it has suffered from rapid capacity fading. Herein, we present the crumpled reduced graphene oxide (RGO) decorated MoS2 nanoflowers on carbon fiber cloth. The three-dimensional framework of interconnected crumpled RGO and carbon fibers provides good electronic conductivity and facile strain release during electrochemical reaction, which is in favor of the cycling stability of MoS2. The crumpled RGO decorated MoS2 nanoflowers anode exhibits high specific capacity (1225 mAh/g) and excellent cycling performance (680 mAh/g after 250 cycles). Our results demonstrate that the three-dimensional crumpled RGO/MoS2 nanoflowers anode is one of the attractive anodes for lithium-ion batteries.