Metallic tin has been considered as one of the most promising anode materials both for lithium (LIBs) and sodium ion battery (NIBs) because of a high theoretical capacity and an appropriate low discharge potential. However, Sn anodes suffer from a rapid capacity fading during cycling due to pulverization induced by severe volume changes. Here we innovatively synthesized pipe-wire TiO2–Sn@carbon nanofibers (TiO2–Sn@CNFs) via electrospinning and atomic layer deposition to suppress pulverization-induced capacity decay. In pipe-wire TiO2–Sn@CNFs paper, nano-Sn is uniformly dispersed in carbon nanofibers, which not only act as a buffer material to prevent pulverization, but also serve as a conductive matrix. In addition, TiO2 pipe as the protection shell outside of Sn@carbon nanofibers can restrain the volume variation to prevent Sn from aggregation and pulverization during cycling, thus increasing the Coulombic efficiency. The pipe-wire TiO2–Sn@CNFs show excellent electrochemical performance as anodes for both LIBs and NIBs. It exhibits a high and stable capacity of 643 mA h/g at 200 mA/g after 1100 cycles in LIBs and 413 mA h/g at 100 mA/g after 400 cycles in NIBs. These results would shed light on the practical application of Sn-based materials as a high capacity electrode with good cycling stability for next-generation LIBs and NIBs.Keywords: binder-free flexible anode; electrospinning; lithium and sodium ion batteries; Pipe-wire structure; TiO2−Sn@carbon nanofibers;

Porous h-MoO3@C nanofibers with a large specific surface area of 400.2 m2 g−1 were successfully synthesized with hot HNO3 oxidizing MoO2@C nanofibers without obvious damage to carbon shells. As anodes for lithium ion batteries (LIBs), the porous h-MoO3@C nanofibers electrodes show a reversible capacity of 302.9 mA h g−1 at 2 A g−1 after 500 cycles. As anodes for sodium ion batteries (SIBs), they also can deliver a good rate capacity and hold 108.9 mA h g−1 at 2 A g−1 after 500 cycles, even can have 91 mA h g−1 at 5 A g−1 after 1200 cycles. The excellent electrochemical performances of the porous h-MoO3@C nanofibers are attributed to the unique structure which not only can maintain the structure stability but also provide enough active sites for Li+/Na+. At the same time, the tunnel structure of h-MoO3 can lead to separate electron–hole and offer a great deal of special positions for cation (Li+/Na+) insertion/extraction. The present method may be helpful for the synthesis of transition metal oxides (TMOs)-carbon composites with high valence metal atoms in the field of batteries and catalysts.基于金属氧化物存储机制, MoO3比MoO2具有更高的理论容量. 本文通过热的硝酸氧化MoO2@C纳米线成功制备出具有400.2 m2 g−1高比表面积的多孔h-MoO3@C纳米纤维, 且碳壁没有明显破坏. 作为锂离子电池的负极, 与MoO2@C纳米线相比多孔h-MoO3@C纳米纤维电极表现出更好的性能, 其中在2 A g−1的电流密度下500循环后展现出302.9 mA h g−1的可逆容量. 作为钠离子电池的负极, h-MoO3@C电极同样具有很好的倍率性能. 在2 A g−1的电流密度下500循环后仍具有108.9 mA h g−1的容量, 并且在2 A g−1的电流密度下1200循环后还能保持91 mA h g−1的容量. 由于碳壁可以维持结构的完整性且可提高导电性; 同时h-MoO3 的隧道结构可作为分离电子孔并为Li+/Na+ 嵌入脱出提供更多的特有位置,使得该复合纳米线作为电极材料表现出更好的性能. 本工作为合成具有高价的过渡金属氧化物/碳复合材料在电池和催化剂领域的运用提供了依据.

•Cr dopant and structure designing grant SnO2 the best electrochemical properties.•Cr-doped SnO2 can easily get quantum dots structure with diameter lower than 3 nm.•Electrodes deliver a stable reversible capacity without apparent capacity fading.Designing heteroatom doped metal oxides and modifying them with carbonaceous materials can grant metal oxides with good Li+ storage performance because of the improved structure stability and enhanced electric conductivity. Herein, monodispersed Cr-doped SnO2 quantum dots fixed by graphene nanosheets and carbon layers (C/Cr-SnO2/G) were successfully assembled, which showed excellent cyclic stability, high reversible capacity and remarkable rate capability for Li+ storage. According to the characteristics results, 3.8 wt% Cr were uniformly incorporated into SnO2 lattice in form of Cr3 +, resulting the decrease of SnO2 diameters. The C/Cr-SnO2/G electrodes displayed an excellent reversible capacity of 672 mA h g− 1 after 200 cycles at 100 mA g− 1 without apparent capacity fading throughout the test, and still retained a stable specific capacity of 296 mA h g− 1 even at 5 A g− 1. The enhanced electrochemical performances of C/Cr-SnO2/G can be related to incorporation of Cr into lattice of SnO2 and the double structure protections by graphene nanosheets and carbon layers, which can easily obtain quantum dots structure, increase the conductivity, and keep the structure stability.

•A yolk-shell structure is proposed for anodes of lithium-ion batteries.•Cr2O3@carbon@graphene is fabricated via a spray drying route.•The multi-protection makes sure the excellent properties to store lithium-ions.Cr2O3 is of high theoretical capacity for lithium-ion (Li+) storage. However, its cyclic stability is very poor due to the large volume change during lithiation/delithiation. In addition, the low conductivity of Cr2O3 blocked the fast transfer of electrons, resulting in an inferior rate capacity. In this study, we design yolk-shell Cr2O3 composites using carbon/Cr2O3 as core and graphene as shell to improve the conductivity of electrode materials and provide spaces for the volume change of Cr2O3. Therefore, this composites (Cr2O3@C@G) exhibit a higher specific capacity and stable cyclic performance achieved the remarkable reversible capacity of 648 mA hg−1 after 120 cycles at 0.1 A g−1, even a capacity of 347 mA hg−1 is obtained after 600 cycles at 1 A g−1. Due to the space between carbon sphere and graphene, they not only effectively alleviate the volume expansion of Cr2O3, but also enhance the electrochemical properties of the composites. Eventually the electronic conductivity and Li+ diffusion rate more pleasantly during cycling due to the excellent structural characteristics.Download high-res image (343KB)Download full-size image

Uniform Co3O4–SnO2 nanoboxes have been synthesized successfully by a facile annealing treatment. Their hollow and cubic structure can be retained successfully during calcination. Due to their hollow structure and PN junction, these Co3O4–SnO2 nanobox sensors can detect H2S with high sensitivity at a low temperature of 180 °C. In addition, it was found that the Co3O4–SnO2 nanobox sensors obtained at a higher annealing temperature displayed a higher sensitivity and lower recovery time to H2S in a temperature range of 500 to 700 °C. X-ray photoelectron spectroscopy (XPS) was employed to confirm that the changes in resistance and the high sensitivities of the sensors are significantly attributable to the transformation of Co3O4 to CoSx with high conductivity under an H2S atmosphere.

An electrode’s conductivity, ion diffusion rate, and flexibility are critical factors in determining its performance in a lithium-ion battery. In this study, NiO–carbon fibers were modified with multifunctional graphene sheets, resulting in flexible mats. These mats displayed high conductivities, and the transformation of active NiO to inert Ni0 was effectively prevented at relatively low annealing temperatures in the presence of graphene. The mats were also highly flexible and contained large gaps for the rapid diffusion of ions, because of the addition of graphene sheets. The flexible NiO–graphene–carbon fiber mats achieved a reversible capacity of 750 mA h/g after 350 cycles at a current density of 500 mA/g as the binder-free anodes of lithium-ion batteries. The mats’ rate capacities were also higher than those of either the NiO–carbon fibers or the graphene–carbon fibers. This work should provide a new route toward improving the mechanical properties, conductivities, and stabilities of mats using multifunctional graphene.Keywords: carbon fibers; flexible mats; graphene; lithium-ion batteries

Enhanced lithium-ion storage performance of carbon nanofiber networks decorating with uniformly dispersed Cr2O3 quantum nanodots (∼4 nm) totally embedded within them were fabricated via a facile electrospinning method. The composite networks were directly employed as free-standing anode materials for Li ion batteries, which exhibited high specific capacity and stable cyclic performance (527 mAh g−1 in the 100th cycle). The outstanding electrochemical properties of carbon nanofiber networks could be ascribed to the existence of multifunctional Cr2O3 quantum nanodots and the synergistic effect between the Cr2O3 quantum nanodots and carbon. On one hand, Cr2O3 with high theoretical capacity can improve the specific capacity of composites. On the other hand, the embedded Cr2O3 quantum nanodots can effectively promote the defects concentration of carbon nanofibers, resulting in extra lithium-ion storage sites in carbon fiber. In addition, the carbon nanofibers can provide sufficient room to accommodate the huge volume changes of Cr2O3 quantum nanodots during cycling, and also enhance the electronic conductivity and ion diffusion rate as well as granting a good free-standing matrix.

•Ultrafine ferrites/C nanofibers are synthesized by an electrospinning method.•ZnFe2O4/Ni/Fe/C nanofibers exhibit an excellent performance of li-ion battery.•Codoping with moderate Ni and Fe can greatly improve the conductivity.•The amorphous carbon can relieve the stress arising from the volumetric expansion.•1D network can enhance the interaction between active materials and electrolyte.This work discusses codoping moderate metal nanoparticles (Ni, Fe) on the ferrite/C composite nanofibers to improve the electronic conductivity. The ultrafine Ni0.5Zn0.5Fe2O4/Ni/C, ZnFe2O4/Ni/Fe/C, and ZnO/Ni/Fe/C nanofibers are synthesized by electrospinning and subsequent annealing at 450, 550 and 650 °C, respectively. Their growth mechanism, morphologies and lithium ion storage properties are investigated in detail. ZnFe2O4/Ni/Fe/C exhibits the best electrochemical performance. The composite shows an initial discharge capacity of 1316 mA h g−1 and manages to achieve a capacity of 793 mA h g−1 after 200 cycles at 100 mA g−1. A high capability of 450 mA h g−1 is still obtained when the current density increases to 1 A g−1. We also compare the lithium ion storage properties of pure ZnFe2O4, ZnFe2O4/C and ZnFe2O4/Ni/Fe/C to demonstrate the positive effect of codoping ferrites by Ni and Fe nanoparticles with amorphous carbon mixed.

Nickel-cobalt sulfide arrays with different loading densities were fixed on nickel foam via a facile hydrothermal method in ethanol. Their loading densities could be easily adjusted via changing the amount of reactants. It was found that the nickel-cobalt sulfide arrays on Ni foam with moderate loading density showed excellent electrochemical performance for supercapacitors. The best sample not only exhibited an outstanding areal capacitance of 4.84 F cm−2 at 10 mA cm−2 but also showed the best cycle stability and rate performance compared with the samples with other loading densities. Remarkably, this method to control the loading densities of nickel-cobalt sulfide on nickel foammay provide a new strategy for the investigation of other nanoarrays on various substrates for catalysts and lithium-ion batteries other than supercapacitors.本文以无水乙醇为溶剂通过水热反应在泡沫镍上生长了不同负载密度的镍钴硫阵列. 它们的负载密度可以通过简单方法来调节. 而 且, 通过实验发现, 在泡沫镍上生长负载密度适中的镍钴硫阵列时, 能获得优异的超电容电化学性能. 本实验中, 性能最好的实验组不仅在 10 mA cm−2时表现出了4.84 F cm−2的杰出面电容, 同时也表现出了比其他负载密度实验组更加优异的循环稳定性以及倍率性能. 值得注意 的是, 这种控制镍钴硫阵列负载密度的实验方案, 还能够为除了超电容以外的催化及锂电池研究提供一种将其他纳米阵列长在各种衬基 上的新策略.

Tin oxides with high theoretical capacities as anodes for lithium-ion batteries always suffer from the electrical disconnect issue of active materials owing to huge volume changes. In this work, flexible mats composed of ultra-small SnOx nanoparticles, graphene, and carbon fibers are synthesized by reducing graphene oxide with stannous ions at room temperature following treatments. SnOx nanoparticles, including SnO and SnO2, with diameters of approximately 4 nm are embedded in the matrix composed of carbon fiber and graphene to form composite fibers that are woven into flexible mats without any binders. As binder-free anodes for lithium-ion batteries, SnOx–graphene–carbon fiber mats can deliver a high reversible capacity of 545 mA h g−1 after 1000 cycles at a current density of 200 mA g−1, which is much better than those of SnOx–carbon fiber mats. The improved performance of SnOx–graphene–carbon fiber mats can be attributed to the ultra-small size of SnOx nanoparticles and the double protection of both graphene and carbon fibers.

ZnS/graphene composites are prepared using a facile solvothermal process by combining the reduction of graphene oxide with the growth of ZnS aggregates in one step. ZnS aggregates with diameters of 50–90 nm assembled from ZnS nanocrystals are homogeneously anchored on graphene sheets as spacers to keep the neighboring sheets separated. As anode materials for lithium-ion batteries, the ZnS/graphene composite electrode exhibits discharge and charge capacities of 1464 and 1010 mA h g−1 for the initial cycle at 100 mA g−1, and shows excellent cyclability with a capacity of 570 mA h g−1 after 200 cycles at a current density of 200 mA g−1. The total specific capacity of ZnS/graphene composites is higher than the sum of pure graphene and ZnS, highlighting the importance of aggregates of ZnS and the anchoring structure of aggregates on graphene sheets for maximum utilization of active ZnS aggregates and graphene for energy storage applications in high-property lithium-ion batteries.

SnxSb intermetallic composites as high theoretical capacities anodes for lithium ion batteries (LIBs) suffer from the quick capacity fading owing to their huge volume change. In this study, flexible mats made up of SnxSb-graphene-carbon porous multichannel nanofibers are fabricated by an electrospinning method and succedent annealing treatment at 700 °C. The flexible mats as binder-free anodes show a specific capacity of 729 mA h/g in the 500th cycle at a current density of 0.1 A/g, which is much higher than those of graphene-carbon nanofibers, pure carbon nanofibers, and SnxSb-graphene-carbon nanofibers at the same cycle. The flexible mats could provide a reversible capacity of 381 mA h/g at 2 A/g, also higher than those of nanofibers, graphene-carbon nanofibers, and SnxSb-carbon nanofibers. It is found that the suitable nanochannels could accommodate the volume expansion to achieve a high specific capacity. Besides, the graphene serves as both conductive and mechanical-property additives to enhance the rate capacity and flexibility of the mats. The electrospinning technique combined with graphene modification may be an effective method to produce flexible electrodes for fuel cells, lithium ion batteries, and super capacitors.Keywords: binder free electrodes; flexible mats; good electrical performance; lithium-ion batteries; SnxSb-graphene-carbon porous multichannel nanofibers

NiO–CoO nanoneedles are grown on carbon fibers by a solvothermal strategy to form nanobrushes. The density of nanobrushes can be easily controlled by altering the solvents. The synthesis mechanism of NiO–CoO/carbon fiber nanobrushes is investigated by the time-dependent experiments in detail. As anodes for lithium ion batteries, the NiO–CoO/carbon fiber nanobrushes synthesized in ethanol show excellent properties with a discharge capacity of 801 mA h g–1 after 200 cycles at a current density of 200 mA g–1. The improvement can be ascribed to the carbon fibers as the highway for electrons and the interspace between NiO–CoO nanoneedles to accommodate the volume change and maintain the structural stability.Keywords: carbon fibers; lithium ion batteries; NiO/carbon fiber nanobrushes; NiO−CoO nanoneedles; NiO−CoO/carbon fiber nanobrushes; solvents

The spike-piece-structured Ni(OH)2 multilayer nanoplate arrays on nickel foams are directly synthesized by a facile hydrothermal method at 160 °C for 4 h. A possible mechanism for the growth of those nanostructures is proposed based on the experimental results. It is discovered that the surface of nickel foams could affect the orientation of the Ni(OH)2 nanoplates. This unique multilayer nanoplate array structure significantly enhances the electroactive surface areas of Ni(OH)2, leading to shorter ion-diffusion paths, and displays a capacity of 2.83 F/cm2 at a current density of 6 mA/cm2 in 0–0.48 V versus the saturated calomel electrode. It also exhibits a good cycling performance, with 51.5% of its initial capacity after about 3000 cycles at a large current density of 24 mA/cm2. The present results may provide a new strategy for the synthesis and application of nickel-foam-based composites for energy storage.Keywords: hydrothermal synthesis; nickel foams; nickel hydroxides; supercapacitors;

Highly sensitive and fast responding humidity sensors were fabricated based on Sb-doped ZnSnO3 fine nanoparticles, which were synthesized via a dual-hydrolysis-assisted liquid precipitation reaction and subsequent hydrothermal procedure. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible spectrophotometry. The results demonstrated that ZnSnO3 nanocubes evolved into Sb-doped ZnSnO3 nanoparticles with doping by Sb. This evolution facilitated their application in humidity sensing. At room temperature, the resistance of the humidity sensors based on Sb-doped ZnSnO3 at 30% relative humidity (RH) was 130 times greater than that in air with 85% RH. The response and recovery times were 7.5 s and 33.6 s, respectively, when the sensors were switched between 30% and 85% RH. These results are much better than those reported so far. The present results may present new opportunities for the practical application of high-performance humidity sensors at room temperature.

Novel CoSx/functionalized multi-walled carbon nanotube (CoSx/fMWCNTs) shell/core composites are successfully prepared via a simple hydrothermal route. The CoSx nanoparticles with diameters of about 6 nm are decorated on the carbon nanotubes to form a shell. The electrochemical performance of the composites was investigated using a three-electrode system. The results show that CoSx/fMWCNTs exhibit the highest specific capacitance of 1324 F g−1 at a current density of 10 A g−1, better than published results for supercapacitors based on CoSx, CoSx/CNTs, and CoSx/graphene. Even at a higher current density of 50 A g−1, the CoSx/fMWCNTs composites still could deliver a relatively high specific capacitance of 796 F g−1. The CoSx/fMWCNTs composite electrodes show improved cyclic properties which show about 13% decay in available specific capacity after 2000 cycles. The facile synthesis of the CoSx/fMWCNTs shell/core composites with superior electrochemical performance may provide a new candidate for energy storage devices with high efficiency.

Tin oxides with high theoretical capacities as anodes for lithium-ion batteries always suffer from the electrical disconnect issue of active materials owing to huge volume changes. In this work, flexible mats composed of ultra-small SnOx nanoparticles, graphene, and carbon fibers are synthesized by reducing graphene oxide with stannous ions at room temperature following treatments. SnOx nanoparticles, including SnO and SnO2, with diameters of approximately 4 nm are embedded in the matrix composed of carbon fiber and graphene to form composite fibers that are woven into flexible mats without any binders. As binder-free anodes for lithium-ion batteries, SnOx–graphene–carbon fiber mats can deliver a high reversible capacity of 545 mA h g−1 after 1000 cycles at a current density of 200 mA g−1, which is much better than those of SnOx–carbon fiber mats. The improved performance of SnOx–graphene–carbon fiber mats can be attributed to the ultra-small size of SnOx nanoparticles and the double protection of both graphene and carbon fibers.

ZnS/graphene composites are prepared using a facile solvothermal process by combining the reduction of graphene oxide with the growth of ZnS aggregates in one step. ZnS aggregates with diameters of 50–90 nm assembled from ZnS nanocrystals are homogeneously anchored on graphene sheets as spacers to keep the neighboring sheets separated. As anode materials for lithium-ion batteries, the ZnS/graphene composite electrode exhibits discharge and charge capacities of 1464 and 1010 mA h g−1 for the initial cycle at 100 mA g−1, and shows excellent cyclability with a capacity of 570 mA h g−1 after 200 cycles at a current density of 200 mA g−1. The total specific capacity of ZnS/graphene composites is higher than the sum of pure graphene and ZnS, highlighting the importance of aggregates of ZnS and the anchoring structure of aggregates on graphene sheets for maximum utilization of active ZnS aggregates and graphene for energy storage applications in high-property lithium-ion batteries.