Growth of Ultrafine SnO 2 Nanoparticles within Multiwall Carbon Nanotube Networks: Non-Solution Synthesis and Excellent Electrochemical Properties as Anodes for Lithium Ion Batteries

Carbon-Coated Tin-Titanate derived SnO2/TiO2 nanowires as High-Performance anode for Lithium-Ion batteries

Tin dioxide (SnO2) is a promising alternative material to graphite anode, but the large volume change induced electrode pulverization issue has limited its application in lithium-ion batteries (LIBs). In contrast, titanium dioxide (TiO2) anode shows high structure stability upon lithium insertion/extraction, but with low specific capacity. To overcome their inherent disadvantages, combination of SnO2 with TiO2 and highly conductive carbon material is an effective way. Herein, we report a facile fabrication method of carbon-coated SnO2/TiO2 nanowires (SnO2/TiO2@C) using tin titanate nanowires as precursor, which are prepared by reacting SnCl2·2H2O with layered sodium titanate (Na2Ti3O7) nanowires in the aqueous solution though the ion exchange between Sn2+ and Na+. After annealing under argon atmosphere, the hydrothermally carbon-coated tin-titanate nanowires decompose, forming a unique hybrid structure, where ultrafine SnO2 nanoparticles are uniformly embedded within the TiO2 substrate with carbon coating. Consequently, the SnO2/TiO2@C nanowires demonstrate excellent lithium storage capacity with high pseudocapacitance contribution, excellent reversible capacity, and long-term cycling stability (673.7/510.5 mAh/g at 0.5/1.0 A/g after 250/800 cycles), owing to the unique hybrid structure, as the well-dispersion of ultra-small SnO2 within TiO2 nanowire substrate with simultaneous carbon coating efficiently suppresses the volume changes of SnO2, provides abundant reactive sites for lithium storage, and enhances the electrical conductivity with shortened ion transport distance.

MWCNT/Ruthenium hydroxide aerogel supercapacitor production and investigation of electrochemical performances

In this study, the material obtained from the sonication of the double-walled carbon nanotube and ruthenium chloride was produced as an aerogel. Then, symmetrical supercapacitor devices were made using them, and their electrochemical properties were investigated. XRD and FTIR were used in the structural analysis of the aerogel, STEM in surface images, and elemental analyses in EDX. Electrochemical analysis was performed by galvanostat/potentiostat. From the cyclic voltammetry analysis, the highest specific capacitance for MWCNT/Ruthenium hydroxide aerogels was achieved as 423 F/g at 5 mV/s. On the other hand, the corresponding values calculated from the charge–discharge curves were found to be 420.3 F/g and 319.9 F/g at the current densities of 0.5 A/g and 10.0 A/g, respectively. The capacitance retention of as-synthesized aerogel was 96.38% at the end of the 5000 consecutive consecutive cyclic voltammetry cycles.

Self-Supported Fibrous Sn/SnO2@C Nanocomposite as Superior Anode Material for Lithium-Ion Batteries

Low-cost and simple methods are constantly chased in order to produce less expensive lithium-ion batteries (LIBs) while possibly increasing the energy and power density as well as the volumetric capacity in order to boost a rapid decarbonization of the transport sector. Li alloys and tin-carbon composites are promising candidates as anode materials for LIBs both in terms of capacity and cycle life. In the present paper, electrospinning was employed in the preparation of Sn/SnO_x@C composites, where tin and tin oxides were homogeneously dispersed in a carbonaceous matrix of carbon nanofibers. The resulting self-standing and light electrode showed a greatly enhanced performance compared to a conventional electrode based on the same starting materials that are simply mixed to obtain a slurry then deposited on a Cu foil. Fast kinetics were achieved with more than 90% of the reaction that resulted being surface-controlled, and stable capacities of about 300 mAh/g over 500 cycles were obtained at a current density of 0.5 A/g.

Hollow nanoparticle-assembled hierarchical NiCo2O4 nanofibers with enhanced electrochemical performance for lithium-ion batteries

Hollow NiCo₂O₄ nanoparticle-assembled electrospun nanofibers showed tailorable electrochemical activity and tunable lithium storage properties.

Porous N-doped carbon nanoflakes supported hybridized SnO2/Co3O4 nanocomposites as high-performance anode for lithium-ion batteries

Alloy-/conversion-type metal oxides usually exhibit high theoretical lithium storage capacities but suffer from the large volume change induced electrode pulverization and the poor electric conductivity, which limit their practical applications. Hybrid/mixed metal oxides with different working mechanisms/potentials can display advantageous synergistic enhancement effect if delicate structure engineering is performed. Herein, atomically hybridized SnO₂/Co₃O₄ nanocomposites with amorphous nature are successfully cast onto the porous N-doped carbon (denoted as NC) nanoflakes through facile pyrolysis of the tin (II) 2-ethylhexanoate (C₁₆H₃₀O₄Sn) and cobalt (II) 2-ethylhexanoate (C₁₆H₃₀O₄Co) mixture within NC nanoflakes in air at 300 °C for 1 h. The Sn/Co atomic ratio and the loading amount of SnO₂/Co₃O₄ can be readily controlled, whose effect on lithium storage are investigated as anodes for lithium ion batteries (LIBs). Notably, SnO₂/Co₃O₄@NC (R_Sn/Co = 1.25) nanoflakes exhibit the most excellent lithium storage properties, delivering a reversible capacity of 1450.3 mA h g^-1 after 300 cycles at 200 mA g^-1, which is much higher than that of the single metal oxide SnO₂@NC and Co₃O₄@NC electrodes.

Casting amorphorized SnO2/MoO3 hybrid into foam-like carbon nanoflakes towards high-performance pseudocapacitive lithium storage

We report an amorphorization-hybridization strategy to enhance lithium storage by casting atomically mixed amorphorized SnO₂/MoO₃ into porous foam-like carbon nanoflakes (denote as SnO₂/MoO₃@CNFs, or SMC in short), which are simply prepared by annealing tin(II)/molybdenum(IV) 2-ethylhexanoate within CNFs under ambient atmosphere at a low temperature (300 °C). The SnO₂/MoO₃ loading amount within CNFs can be easily adjusted by controlling the Sn/Mo/C precursors. When examined as lithium ion battery (LIB) anode materials, the amorphorized SnO₂/MoO₃@CNFs with carbon content of 32 wt% (also denote as SMC-32, in which the number represents the carbon content) deliver a high reversible capacity of 1120.5 mA h/g after 200 cycles at 200 mA/g and then 651.5 mA h/g after another 300 cycles at 2000 mA/g, which is much better than that of the crystalline SnO₂/CNFs (carbon content of 34 wt%), MoO₃/CNFs (carbon content of 22.7 wt%), or SnO₂/MoO₃@CNFs (with lower carbon contents of 11 and 25 wt%). The electrochemical measurements as well as the ex situ structure characterization clearly suggest that combination of amorphorization and hybridization of SnO₂/MoO₃ with CNFs synergistically contributes to the superior lithium storage performance with high pseudocapacitive contribution.

Chemical vapor deposition growth of carbon nanotube confined nickel sulfides from porous electrospun carbon nanofibers and their superior lithium storage properties

Multidimensional architecture design is a promising strategy to explore unique physicochemical characteristics by synergistically integrating different structural and compositional materials. Herein, we report the facile synthesis of a novel dendritic hybrid architecture, where carbon nanotubes (CNTs) with nickel sulfide nanoparticles encapsulated inside are epitaxially grown out of the porous electrospun N-doped carbon nanofibers (CNFs) (denoted as CNT@NS@CNFs) through a combined strategy of electrospinning and chemical vapor deposition (CVD). The adopted thiophene (C₄H₄S) not only serves as a carbon source for the growth of CNTs but also as a sulfur source for the sulfurization of Ni particles and S-doping into carbon matrices. When examined as an anode material for lithium-ion batteries (LIBs), the dendritic CNT@NS@CNFs display superior lithium storage properties including good cycle stability and high rate capability, delivering a high reversible capacity of 630 mA h g^-1 at 100 mA g^-1 after 200 cycles and 277 mA h g^-1 at a high rate of 1000 mA g^-1. These outstanding electrochemical properties can be attributed to the novel hybrid architecture, in which the encapsulation of nickel sulfide nanoparticles within the CNT/CNFs not only efficiently buffers the volume changes upon lithiation/delithiation, but also facilitates charge transfer and electrolyte diffusion owing to the highly conductive networks with open frame structures.

Integrating TiO₂/SiO₂ into Electrospun Carbon Nanofibers towards Superior Lithium Storage Performance

In order to overcome the poor electrical conductivity of titania (TiO₂) and silica (SiO₂) anode materials for lithium ion batteries (LIBs), we herein report a facile preparation of integrated titania⁻silica⁻carbon (TSC) nanofibers via electrospinning and subsequent heat-treatment. Both titania and silica are successfully embedded into the conductive N-doped carbon nanofibers, and they synergistically reinforce the overall strength of the TSC nanofibers after annealing (Note that titania⁻carbon or silica⁻carbon nanofibers cannot be obtained under the same condition). When applied as an anode for LIBs, the TSC nanofiber electrode shows superior cycle stability (502 mAh/g at 100 mA/g after 300 cycles) and high rate capability (572, 518, 421, 334, and 232 mAh/g each after 10 cycles at 100, 200, 500, 1000 and 2000 mA/g, respectively). Our results demonstrate that integration of titania/silica into N-doped carbon nanofibers greatly enhances the electrode conductivity and the overall structural stability of the TSC nanofibers upon repeated lithiation/delithiation cycling.

Template synthesis of graphitic hollow carbon nanoballs as supports for SnOx nanoparticles towards enhanced lithium storage performance

To address the volume change-induced pulverization problem of tin-based anodes, a concept using hollow carbon nanoballs (HCNBs) as buffering supports is herein proposed. HCNBs with hollow interior, flexibility and graphitic crystallization are first prepared by a combined method of chemical vapor deposition (CVD) and template-synthesis using CH4 as the carbon source and CaCO3 as the conformal template. The ultrafine SnO2 nanoparticles are loaded onto the HCNBs (denoted as SnO2@HCNBs) via pyrolysis of tin(ii) 2-ethylhexanoate at 300 °C in air. On further annealing SnO2@HCNBs in Ar, SnO2 is partially reduced to SnOx by consuming a part of carbon of HCNBs as the reducing agent, and thus SnOx@HCNBs are obtained (note that SnOx represents a composite consisting of SnO2, SnO and Sn phases). When applied as anode materials for lithium ion batteries (LIBs), HCNBs deliver high reversible capacities of 841 mA h g-1 after 125 cycles at 200 mA g-1, and 726 mA h g-1 after 400 cycles even at 1000 mA g-1, while SnO2@HCNBs and SnOx@HCNBs exhibit discharge capacities of 1042 and 1299 mA h g-1 after 400 cycles at 200 mA g-1, respectively. Notably, all of them display gradually increased capacity with retention over 100% even after long-term cycling, which is attributed to the novel robust characteristic of the HCNBs as revealed by the ex situ TEM analysis. The flexible hollow HCNBs with high graphitic crystallization not only efficiently tolerate the volume changes of the Li-Sn alloying-dealloying but also facilitate the electrolyte/charge transfer owing to the hollow structure and high conductivity of the HCNBs.