Sandwich structure of carbon-coated silicon/carbon nanofiber anodes for lithium-ion batteries

For electrospun silicon/carbon nanofiber composites, the surface precipitation of silicon nanoparticles can cause poor cycle stability. To solve this, a carbon-coated silicon/carbon nanofiber (Si/C@C) composite with a ‘sandwich’ structure is constructed by hydrothermal reaction of glucose and an electrospun silicon/carbon nanofiber, followed by high-temperature carbonization. The effects of the thickness of the carbon coating layer and calcining temperature on the electrochemical performance are studied. The results showed that carbon is uniformly and continuously coated on the surface of the composite fibers, which avoid direct exposure of precipitated silicon on the surface of the nanofibers to the electrolyte, reduce the occurrence of side reactions and is conducive to the stable formation of SEI films. At the same time, the carbon shell inhibit the volume expansion of silicon to a certain extent and improve the conductivity of the composites. Consequently, the obtained Si/C@C exhibit good rate performance and cycle stability. With the optimised carbon coating thickness and calcination temperature, the obtained electrodes deliver a reversible capacity of 1120 and 683 mA h g^-1 at a current density of 0.1 and 2 A g^-1 respectively, and a specific capacity of 602 mAh∙g^-1 at a current density of 1 A g^-1 after 100 cycles, a capacity retention rate of 80%. The facilely synthesised Si/C@C composite shows potential applications in high-capacity silicon-based anode materials.     

A biomass-derived biochar-supported NiS/C anode material for lithium-ion batteries

Nickel sulfides are perfect anode materials for high-capacity and low-cost lithium-ion batteries (LIBs); however, with the shortcoming of polysulfide intermediate dissolution, volume expansion exceeding the limit during cycling also restricts their development. Herein, NiS/C composite materials are successfully anchored on chestnut shell fluff (CSF)-derived biochar by a glucose-auxiliary hydrothermal method along with an annealing treatment. The CSF biochar acts as an effective electron transmission channel for the rapid lithiation/delithiation of NiS and as a fixed sulfur carrier for inhibiting the dissolution of polysulfide. Glucose restrains the accumulation of NiS particles and then transforms into uniform amorphous carbon during annealing, which is more effective in buffering for rapid volume variation. Moreover, the CSF-NiS/C electrode exhibits a remarkable specific capacity of 1522.8 mAh g^-1 (0.1 A g^-1) and distinguished rate performance with 295 mAh g^-1 capacity (3 A g^-1), which are better than those of the pure NiS/C anode material displays. Researchers may be inspired by both of these reasonable design and synthesis strategies that are beneficial for the development of high-performance nickel-based sulfide anode materials for LIBs.     

Encapsulation of SnO2 by carbon nanotubes and WS2 to form high-performance lithium-ion batteries materials

Optimizing the structure of materials has proven to be an efficient solution for improving the electrochemical performance of lithium-ion batteries. In this work, SnO₂-WS₂-CNTS (SWC) ternary composites were prepared by hydrothermal and ball milling methods to first obtain SnO₂-WS₂ mixture, which was then embedded on CNTS to form a special multi-level structure. Due to the special 2D structure of transition metal sulfide WS₂ and CNTS, the de-intercalation speed of lithium ions is greatly increased and the inherent particle aggregation phenomenon of SnO₂ is weakened. The three materials show their advantages while compensating for each other's disadvantages, forming an interesting synergistic effect which results in extremely stable anode materials. At 0.2Ag^-1, the capacity of SWC reaches 930.71 mAhg^-1 after 100 cycles, and reaches 1043 mAhg^-1 after 1000 cycles at 1.0Ag^-1. It is worth noting that after multiple cycles, SWC still exhibits an extremely stable state in the SEM image. The above results confirm that the special structure of SWC leads to excellent electrochemical performance, and its simple preparation method makes it a potential leading battery anode material in the future.     

Facile synthesis of MnO/C anode materials for lithium-ion batteries

Cubic MnO with particle sizes of ∼200 nm and ∼600 nm was synthesized by decomposition of MnCO₃. The corresponding MnO/C composite was obtained by thermal treatment of mixture of MnCO₃ and sucrose. The structure and morphology of the products were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical experiments showed that the as-prepared MnO/C exhibited promising electrochemical properties, and could potentially be used as anode material in lithium-ion batteries. MnO/C delivered a reversible capacity of about 470 mAh/g after cycling 50 times, when testing at 75 mA/g. The reversible capacity, when tested at 150, 375, 755 mA/g, reached 440, 320, 235 mAh/g, respectively. The good electrochemical performance was ascribed to the smaller particle size and the efficient carbon coating on MnO.     

Encapsulating homogenous ultra-fine SnO2/TiO2 particles into carbon nanofibers through electrospinning as high-performance anodes for lithium-ion batteries

Homogenous ultra-fine SnO₂/TiO₂ particles encapsulated into carbon nanofibers (SnO₂/TiO₂@CNFs) with a uniform and ordered one-dimensional fibrous structure are fabricated through facile electrospinning technique and subsequent heat treatments, which are confirmed by XRD, Raman, TG, SEM, TEM, and XPS analyses. The battery performance reveals that the SnO₂/TiO₂@CNFs-1.5:1 (1.5:1 denotes the mole ratio of SnO₂ to TiO₂ in the carbon nanofibers) electrode displays the optimal electrochemical properties among the whole samples, which can deliver the initial charge and discharge specific capacity of 1061.2 and 1494.8 mAh/g with a coulombic efficiency of 71.0% at 100 mA/g, and exhibit a remarkable specific capacity of 766.1 mAh/g after 200 cycles. Moreover, the SnO₂/TiO₂@CNFs-1.5:1 electrode displays a high pseudocapacitive contribution of 73.9% at the scan rate of 2 mV/s and the lithium ion diffusion coefficient of approximately 1.20 × 10^?15 cm² s^?1. The excellent electrochemical performance of the SnO₂/TiO₂@CNFs-1.5:1 electrode is closely correlated with the synergetic effect of the proper amount of TiO₂ that enhances the electrochemical stability of the electrode and provides fractional capacity, and the flexible and conductive carbon nanofiber matrix that accommodates volume changes and increases overall electronic conductivity. The detailed investigations of the as-prepared electrode materials by a facile electrospinning process may pave possible instructions for the next generation SnO₂-based anodes and other related electrospun anodes for the energy storage device.     

Preparation and characterization of Six-Co0.6B0.6Al0.2/modified graphite sphere composites as anodes for lithium-ion batteries

In order to improve the cyclic property of Si as anode for lithium-ion battery, Si_x-Co_0.6B_0.6Al_0.2/modified graphite sphere composites (labeled as Si_x-Co_0.6B_0.6Al_0.2/MGS, x = 0.72, 1.12, 1.68) were synthesized using high energy ball milling (HEBM) technique. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the compositions and morphology of composite materials. The electrochemical behaviors of Si_x-Co_0.6B_0.6Al_0.2/MGS were investigated by galvanostatic charge-discharge technique and electrochemical impedance spectroscopy (EIS). The results indicate that Co, B, Al and MGS have a good synergistic effect in improving the electrochemical performance of Si powder-based electrode. Compared to Si/MGS and Si_1.12-Co_0.6B_0.6Al_0.2, the cyclic performance and coulombic efficiency of Si_1.12-Co_0.6 B_0.6Al_0.2/MGS are significantly enhanced from the 2nd cycle. The first reversible capacity of Si_1.12-Co_0.6B_0.6Al_0.2/MGS is 533 mAh g⁻¹ and 90% of the capacity may be obtained after 80 cycles. EIS and SEM measurements indicate that the microstructural stability of the composite during cycling appears to be the main reason contributing to the good cycleability.     

Nano-porous Si/C composites for anode material of lithium-ion batteries

Nano-porous silicon composite incorporated with graphite and pyrolyzed carbon was synthesized and investigated as a promising anode material for lithium-ion batteries. The nano-porous Si/graphite composite was prepared via two-step ball-milling followed by etching process. Then carbon was incorporated by using different approaches. The nano-porous Si/graphite/C composite exhibits a reversible capacity of about 700 mAh/g with no capacity loss up to the 120th cycle at a constant current density of 0.2 mA/cm². The superior electrochemical characteristics are attributed to the nanosized pores in Si particles, which suppress the volume effect, and buffering action as well as excellent electronic and ionic conductivity of carbon materials.     

Fabrication of NiO-ZnO/RGO composite as an anode material for lithium-ion batteries

NiO-ZnO/RGO composite was obtained by the annealing of an Ni (OH)₂-Zn (OH)₂/RGO precursor, which has been fabricated by in situ ultrasonic agitation. Moreover, the NiO-ZnO nanoflakes are evenly distributed on the RGO sheets based on the scanning electron microscope (SEM) and transmission electron microscope (TEM) characterization results. When the NiO-ZnO/RGO composite was used as an anode material in lithium-ion batteries (LIBs), the electrodes exhibited a high reversible capacity of 1017 mA h/g at a current density of 100 mA/g after 200 cycles and a specific capacity of 458 mA h/g at 500 mA/g even after 400 cycles. The electrode even reached a capacity of 185 mA h/g at a current density of 2000 mA/g. The excellent electrochemical properties of the NiO-ZnO/RGO composite might be attributable to the NiO-ZnO nanoflakes offering rich electrochemical reaction sites and shortening the diffusion length for lithium ion (Li⁺), as well as the RGO sheets improving the transfer rates of Li⁺ and electron during the charge-discharge process.     

Hematite nanoflakes as anode electrode materials for rechargeable lithium-ion batteries

Hematite (α-Fe₂O₃) nanoflakes and nanocubes were synthesized by liquid-solid-solution method and their properties as anode electrode materials for rechargeable Li⁺-ion batteries were measured. When changing the water to ethanol volume ratio in the synthesis system, the nanocrystals can be changed from α-Fe₂O₃ to α-FeOOH, with shapes being tuned from nanoflakes to nanocubes, non-uniform particles and nanowires. When assembled as the anode electrode materials in rechargeable Li⁺-ion batteries, the hematite nanoflakes showed one more plateau in the first discharge progress of the voltage-composition curves than hematite nanocrystals with other shapes in the literature. X-ray diffraction, high-resolution transmission electron microscope and electrochemical data showed that this extra plateau came from the formation of Li₂Fe₃O₄ nanoclusters and amorphous Li₂O. This experiment showed that like sizes, shapes of nanocrystals may also affect the detailed electrochemical progress.     

Electrochemical performance of arc-produced carbon nanotubes as anode material for lithium-ion batteries

The effects of etching process on the morphology, structure and electrochemical performance of arc-produced multiwalled carbon nanotubes (CNTs) as anode material for lithium-ion batteries were systematically investigated by TEM and a variety of electrochemical testing techniques. It was found that the etched CNTs exhibited four times higher reversible capacity than that of raw CNTs, and possessed excellent cyclability with almost 100% capacity retention after 30 cycles. The kinetic properties of three kinds of CNTs electrodes involving the pristine (CNTs-1), etched (CNTs-2) as well as etch-carbonized samples (CNTs-3) were characterized via ac impedance measurement. It was indicated that, after 30 cycles the exchange current density i₀ of etched CNTs ((7.6-7.8) × 10⁻³ A cm⁻²) was higher than that of the raw CNTs (5.9 × 10⁻³ A cm⁻²), suggesting the electrochemical activity of CNTs was enhanced by the etching treatment. The storage characteristics of the CNTs electrodes at room temperature and 50 °C were particularly compared. It was found that the film resistance on CNTs electrode generally tended to become large with the elongation of storage time, especially storage at high temperature. In comparison with CNTs-1 and CNTs-3, CNTs-2 exhibited more distinctly increase of film resistance, which is related with the surface properties.     

Synthesis and electrochemical performance of lithium vanadium oxide nanotubes as cathodes for rechargeable lithium-ion batteries

A new kind of cathode materials for rechargeable lithium-ion batteries, lithium vanadium oxide nanotubes synthesized by a combined sol-gel reaction and hydrothermal treatment procedure is reported in this paper. SEM, TEM, XRD and XPS techniques were performed to investigate the morphology and structure of the resulting materials. The results confirmed that the synthetic materials are composed of uniformly open-ended multiwalled nanotubes with a length from 1 to 3 μm. The inner and the outer diameters of the obtained nanotubes vary from 30 to 50 nm and 50 to 120 nm, respectively. The electrochemical performance as a cathode material was examined and evaluated by cyclic voltammetry, galvanostatic charge-discharge cycling and AC impedance spectroscopy techniques. The results indicated that the resultant lithium vanadium oxide nanotubes have a high initial discharge capacity of 457 mAh g⁻¹ in the potential range of 1.0-4.0 V (vs. Li/Li⁺) and good cycling performance. The improved electrochemical performance of the products should be due to its special one-dimensional multiwalled tubular structure and the contribution of lithium-ions.     

CMOS-compatible metal-stabilized nanostructured Si as anodes for lithium-ion microbatteries

The properties of fully complementary metal-oxide semiconductor (CMOS)-compatible metal-coated nanostructured silicon anodes for Li-ion microbatteries have been studied. The one-dimensional nanowires on black silicon (nb-Si) were prepared by inductively coupled plasma (ICP) etching and the metal (Au and Cu) coatings by successive magnetron sputtering technique. The Cu-coated nb-Si show the most promising electrochemical performance enhancements for the initial specific capacity as well as their cyclability compared to pristine nb-Si. The electrochemical and microstructural properties before and after cycling of the metal-coated nb-Si compared to their pristine counterparts are discussed in detail.     

Graphitized boron-doped carbon foams: Performance as anodes in lithium-ion batteries

The electrochemical performance as potential anodes in lithium-ion batteries of several boron-doped and non-doped graphitic foams with different degree of structural order was investigated by galvanostatic cycling. The boron-doped foams were prepared by the co-pyrolysis of a coal and two boron sources (boron oxide and a borane–pyridine complex), followed by heat treatment in the 2400–2800 °C temperature interval. The extent of the graphitization process of the carbon foams depends on boron concentration and source. Because of the catalytic effect of boron, lightweight graphite-like foams were prepared. Boron in the foams was found to be present as carbide (B₄C), in substitutional positions in the carbon lattice (B–C), bonded to nitrogen (B–N) and forming clusters. Larger reversible lithium storage capacities with values up to ∼310 mA h g⁻¹ were achieved by using the boron oxide-based carbon foams. Moreover, since the electrochemical anodic performance of these boron-doped foams with different degree of structural order is similar, the beneficial effect of the presence of the B–C boron phase was inferred. However, the bonding of boron with nitrogen in the pyridine borane-based has a negative effect on lithium intercalation.     

Electrochemical characteristics and intercalation mechanism of ZnS/C composite as anode active material for lithium-ion batteries

ZnS/C composites were synthesized by a combined precipitation with carbon coating method. Morphology and structure of the as-prepared ZnS/C composite materials with carbon content of 4.6 wt%, 9.3 wt% and 11.4 wt% were characterized using TEM and XRD technique. TEM observation demonstrated that the ZnS/C (9.3 wt% C) composite showed excellent microstructure with 20–30 nm ZnS nanoparticles uniformly dispersed in conductive carbon network. Electrochemical tests showed that the ZnS/C (9.3 wt% C) composite presented superior performance with initial charge and discharge capacity of 1021.1 and 481.6 mAh/g at a high specific current of 400 mA/g, after 300 cycles, the discharge capacity of ZnS/C electrode still maintained at 304.4 mAh/g, with 63.2% of its initial capacity. The rate capability and low temperature performance of the ZnS/C (9.3 wt% C) composite were compared with commercial MCMB anode. The results showed that the ZnS/C (9.3 wt%) composite exhibited much better cycle capability and low temperature performance than MCMB anode. ZnS/C composite seems to be a promising anode active material for lithium ion batteries. Intercalation mechanism of the ZnS/C composites for lithium ion insertion–extraction is proposed based on the ex situ X-ray diffraction analysis incorporating with its electrochemical characteristics.     

Waste catkins-derived graphitic carbon/Co3O4 composites as long-life and high-rate anodes for lithium-ion battery

Upgrading waste re-utilization has been regarded as an important concept to promote the sustainable development of social economy. Herein, waste catkins were used as carbon source and template to prepare graphitic carbon/Co₃O₄ composites through cobalt salt immersion, in-situ carbonization and calcination. The obtained Co₃O₄/C composites inherit the microtubular structure of catkins with ultra-thin tube wall and large tube cavity. Particularly, the sample (Co₃O₄/C-280) calcined at 280 °C in air shows a morphology of the hollow Co₃O₄ spheres (av. 50 nm) evenly embedded on the biocarbon tube. As an anode for lithium-ion battery, such unique structure is more conductive to alleviate volume expansion. As expected, Co₃O₄/C-280 electrode has excellent rate capability at 5 A g⁻¹ and stable long-cycle performance (647.3 mA h g⁻¹, 1800 cycles, 1 A g⁻¹). The presence of pseudo-capacitance behavior plays an important role in improving the capacity of material. The good electrochemical properties of Co₃O₄/C-280 can be ascribed to the synergistic effect of hollow tubular structure and graphitic carbon. Therefore, the strategy of making waste profitable is in line with the theme of green and sustainable development, and provides a reference for improving lithium storage performance of Co₃O₄-based anode materials.     

A new high-performance cathode material for rechargeable lithium-ion batteries: Polypyrrole/vanadium oxide nanotubes

Polypyrrole/vanadium oxide nanotubes (PPy/VOx-NTs) as a new high-performance cathode material for rechargeable lithium-ion batteries are synthesized by a combination of hydrothermal treatment and cationic exchange technique. The morphologies and structures of the as-prepared samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetry and differential scanning calorimeter (TG-DSC) and X-ray powder diffraction (XRD). The results indicate that the organic templates are mainly substituted by the conducting polymer polypyrrole without destroying the previous nanotube structure. Their electrochemical properties are evaluated via galvanostatic charge/discharge cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is found that PPy/VOx-NTs exhibit high discharge capacity and excellent cycling performance at different current densities compared to vanadium oxide nanotubes (VOx-NTs). After 20 cycles, the reversible capacity of PPy/VOx-NTs (159.5 mAh g⁻¹) at the current density of 80 mA g⁻¹ is about four times of magnitude higher than that of VOx-NTs (37.5 mAh g⁻¹). The improved electrochemical performance could be attributed to the enhanced electronic conductivity and the improved structural flexibility resulted from the incorporation of the conducting polymer polypyrrole.     

Carbon-coated porous Si/C composite anode materials via two-step etching/coating processes for lithium-ion batteries

A highly stable Si/SiO_x/C composite was synthesized in this study through NaOH etching and carbon-coating approaches for use as an anode material in Li-ion batteries (LIBs). The two-step process not only enhanced the electronic conductivity of the as-synthesized Si/SiO_x/C composite by using the two-step etching/coating processes to enhance the columbic efficiency of Si during cycling processes but also architecturally provided an amorphous Si/SiO_x composite to buffer volume expansion. The Raman spectroscopy and X-ray diffraction results demonstrate that the etching process involves a transition from crystalline Si to amorphous SiO_x. The Fourier transform infrared spectroscopy results further confirm that the vibration mode of Si–O bonding changes from symmetric to asymmetric. The Brunauer–Emmett–Teller analysis reveals that we can control specific surface area and pore-size distribution of NaOH-modified Si by tuning the parameters pertaining to the solid content of Si in NaOH solution. After optimizing the etching and carbon-coating processes, the modified Si/C composite delivered ~780 mAh g⁻¹ for more than 200 cycles at 0.5C, which was better than un-modified one of 315 mAh g⁻¹ after 200 cycles. The results clearly indicate that we could improve cycle stability of Si anode drastically through the NaOH etching process and carbon coating modification. The proposed methodology may provide a potential approach to promoting the synthesis of Si-based anodes for use in the commercial applications of LIBs.     

SnO2-MoO3 nanoparticles anchored in carbon nanotubes as a large-capacity,high-rate,and long-lifetime anode for lithium-ion batteries

SnO₂-MoO₃ hybrid nanoparticles are anchored in a few-walled carbon nanotube (CNT) network to synthesize SnO₂-MoO₃-CNT nanocomposite by hydrothermal and ball grinding methods. The CNTs can alleviate the volume expansion of SnO₂, improve conductivity and shorten the transmission paths of the electrons and Li⁺. The SnO₂-MoO₃-CNT composite has a high initial coulombic efficiency of 80.9% and shows a large invertible capacity of 1372.2 mAhg⁻¹ after 280 cycles at 0.2 Ag^-1 and the coulomb efficiency holds more than 98.0% after the second cycle, high-rate property of 743.6 mAhg⁻¹ at 5.0 Ag^-1 and long-term cycling capacity of 886.3 mAhg⁻¹ at 1.0 Ag^-1 after 950 cycles. Because of its outstanding properties, ternary SnO₂-MoO₃-CNT nanocomposite is a confident anode material for lithium-ion batteries.     

Electrochemical properties of SnO2/carbon composite materials as anode material for lithium-ion batteries

SnO₂/carbon composite anode materials were synthesized from SnCl₄·5H₂O and sucrose via a hydrothermal route and a post heat-treatment. The synthesized spherical SnO₂/carbon powders show a cauliflower-like micro-sized structure. High annealing temperature results in partial reduction of SnO₂. Metallic Sn starts to emerge at 500 °C. High Sn content in SnO₂/carbon composite is favorable for the increase of initial coulombic efficiency but not for the cycling stability. The SnO₂/carbon annealed at 500 °C exhibits high specific capacity (∼400 mAh g⁻¹), stable cycling performance and good rate capability. The generation of Li₂O in the first lithiation process can prevent the aggregation of active Sn, while the carbon component can buffer the big volume change caused by lithiation/delithiation of active Sn. Both of them make contribution to the better cycle stability.     

Electrochemical performance of flowerlike CaSnO3 as high capacity anode material for lithium-ion batteries

Nanosized CaSnO₃ is synthesized by a hydrothermal process and characterized by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The SEM observation shows the sample has a porous flowerlike morphology. The electrochemical results exhibit that the stable and reversible capacity of 547 mAh g⁻¹ is obtained after 50 cycles at 60 mA g⁻¹ (0.1 C) and the corresponding charge capacity is determined to be 316 mAh g⁻¹ at the current density of 2.5 C. Cyclic voltammetry and electrochemical impedance spectroscopy data are analyzed to complement the galvanostatic results. The observed excellent performance is attributed to the porous structure and large surface area of flowerlike CaSnO₃.