Core-shell Ti@Si coaxial nanorod arrays formed directly on current collectors for lithium-ion batteries

Metallic and porous Ti nanorod arrays for visible-IR light absorption and dendrite-free stable lithium-metal batteries

It is still a challenging task to prepare highly porous nanorod arrays of metals formed on substrates for optical and energy storage applications. Herein, we demonstrate the design and synthesis of black color, metallic and highly porous Ti nanorod arrays as novel current collectors for dendrite-free and highly stable Li-metal anodes. The high porosity of metallic nanorod arrays provides numerous heterogeneous nucleation sites and huge contact area and large space for the accommodation of Li metal. The conductive metallic Ti nanorod arrays enhance electrode integration. Effectively, it eliminates formation Li dendrites and demonstrates superior cycling stability over 300 cycles. Additionally, the unique porous structures of the nanorod arrays can decrease the amplitude of forced vibration in narrow space leading to light absorption. Interestingly, the metal is black instead of metallic color. The black metallic nanorod arrays can absorb more than 96% of both visible and infra-red lights. This black color metallic porous nanorod arrays may find additional applications in aerospace, energy, biomedical, defence, and chemical industries.

WSi2 nanodot reinforced Si particles as anodes for high performance lithium-ion batteries

Si-based anodes are attracting enormous attention due to the super-high theoretical capacity of silicon (3579 mA h g⁻¹ at room temperature) as an anode of lithium-ion batteries.

Insights into defective TiO2 in electrocatalytic N2 reduction: combining theoretical and experimental studies

Artificial N2 fixation via the Haber-Bosch process requires high temperature and high pressure at the expense of CO2 release. Electrochemical NH3 synthesis is emerging as an environmentally friendly alternative that operates under ambient conditions, calling for electrocatalysts with efficient N2 reduction reaction (NRR) performance. In this paper, we experimentally and theoretically prove that defective TiO2 on Ti mesh (d-TiO2/TM) acts as an electrocatalyst for the NRR. In 0.1 M HCl, d-TiO2/TM achieves a much higher NH3 yield of 1.24 × 10-10 mol s-1 cm-2 and FE of 9.17% at -0.15 V (versus reversible hydrogen electrode) than pristine TiO2 (NH3 yield: 0.17 × 10-10 mol s-1 cm-2; FE: 0.95%). Notably, d-TiO2/TM also shows great electrochemical stability and durability. Theoretical investigation further reveals the possible catalytic mechanism involved.

Electrodeposited Cu/MWCNT composite-film: a potential current collector of silicon-based negative-electrodes for Li-Ion batteries

With the aim of developing the potential high theoretical capacity of Si as a negative electrode material for Li-ion batteries, a new type of composite current collector in which multi-walled carbon nanotubes (MWCNTs) are immobilized on a Cu surface was developed using an electroplating technique. For the Si electrode with a flat-Cu substrate, voltage plateaus related to the stepwise electrochemical lithiation were observed below 0.27 V (vs. Li/Li⁺), whereas the Cu/MWCNT substrate distinctly decreased the overvoltage to enhance charge/discharge capacities to approximately 1.6 times that obtained in the flat-Cu system. Field-emission scanning microscopy revealed that MWCNTs immobilized on the Cu surface extended inside the active material layer. Adhesion strength between the substrate and electrode mixture layer was reinforced by MWCNTs to increase the reversibility of change in electrode thickness before and after cycling: the expansion ratio was 200% and 134% for flat-Cu and Cu/MWCNT systems, respectively. Electrochemical impedance analysis demonstrated that MWCNTs served as an electron conduction pathway inside the electrode. By controlling the upper cutoff voltage from 2.0 V to 0.5 V, synergetic effects including improved adhesion strength and a more developed conduction pathway became noticeable: a reversible capacity of 1100 mA h g⁻¹ with 64% capacity retention was achieved even after the 100th cycle. The results indicate that the Cu/MWCNT is a promising current collector for expansion/contraction-type active materials for rechargeable batteries.

To develop the potential high theoretical capacity of Si as a negative electrode material for Li-ion batteries, a new type of composite current collector in which carbon nanotubes (CNTs) are immobilized on a Cu surface was developed using an electroplating technique.

The role of thermal annealing on the microstructures of (Ti, Fe)-alloyed Si thin-film anodes for high-performance Li-ion batteries

Here, we studied the effect of thermal annealing on the microstructure and cyclic stability of a (Ti, Fe)-alloyed Si thin-film fabricated by a simple sputtering deposition method for Li-ion battery (LIB) anodes. The anode samples annealed at different temperatures (300-600 °C) were subjected to microstructure analysis and LIB performance test. The (Ti, Fe)-alloyed Si thin-film anode delivered a high capacity of 1563 mA h g-1 for 100 cycles at 0.1 A g-1 with nearly 100% capacity retention. Post-mortem analysis using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) disclosed the microstructural changes of the cycled anodes, revealing that (Ti, Fe) silicides served as a structural buffer against the large volume change of active Si during cycling for enhanced LIB performance.

Si/Ag/C Nanohybrids with in Situ Incorporation of Super-Small Silver Nanoparticles: Tiny Amount, Huge Impact

Silicon (Si) has been regarded as one of the most promising anodes for next-generation lithium-ion batteries (LIBs) due to its exceptional capacity, appropriate voltage profile, and reliable operation safety. However, poor cyclic stability and moderate rate performance have been critical drawbacks to hamper the practical application of Si-based anodes. It has been one of the central issues to develop new strategies to improve the cyclic and rate performance of the Si-based lithium-ion battery anodes. In this work, super-small metal nanoparticles (2.9 nm in diameter) are in situ synthesized and homogeneously embedded in the in situ formed nitrogen-doped carbon matrix, as demonstrated by the Si/Ag/C nanohybrid, where epoxy resin monomers are used as solvent and carbon source. With tiny amount of silver (2.59% by mass), the Si/Ag/C nanohybrid exhibits superior rate performance compared to the bare Si/C sample. Systematic structure characterization and electrochemical performance tests of the Si/Ag/C nanohybrids have been performed. The mechanism for the enhanced rate performance is investigated and elaborated. The temperature-dependent I-V behavior of the Si/Ag/C nanohybrids with tuned silver contents is measured. Based on the model, it is found that the super-small silver nanoparticles mainly increase charge carrier mobility instead of the charge carrier density in the Si/Ag/C nanohybrids. The evaluation of the total electron transportation length provided by the silver nanoparticles within the electrode also suggests significantly enhanced charge carrier mobility. The existence of tremendous amounts of super-small silver nanoparticles with excellent mechanical properties also contributes to the slightly improved cyclic stability compared to that of simple Si/C anodes.

Group IVA Element (Si, Ge, Sn)-Based Alloying/Dealloying Anodes as Negative Electrodes for Full-Cell Lithium-Ion Batteries

To satisfy the increasing energy demands of portable electronics, electric vehicles, and miniaturized energy storage devices, improvements to lithium-ion batteries (LIBs) are required to provide higher energy/power densities and longer cycle lives. Group IVA element (Si, Ge, Sn)-based alloying/dealloying anodes are promising candidates for use as electrodes in next-generation LIBs owing to their extremely high gravimetric and volumetric capacities, low working voltages, and natural abundances. However, due to the violent volume changes that occur during lithium-ion insertion/extraction and the formation of an unstable solid electrolyte interface, the use of Group IVA element-based anodes in commercial LIBs is still a great challenge. Evaluating the electrochemical performance of an anode in a full-cell configuration is a key step in investigating the possible application of the active material in LIBs. In this regard, the recent progress and important approaches to overcoming and alleviating the drawbacks of Group IVA element-based anode materials are reviewed, such as the severe volume variations during cycling and the relatively brittle electrode/electrolyte interface in full-cell LIBs. Finally, perspectives and future challenges in achieving the practical application of Group IVA element-based anodes in high-energy and high-power-density LIB systems are proposed.

Silicon hollow sphere anode with enhanced cycling stability by a template-free method

Silicon is a promising alternative anode material since it has a ten times higher theoretical specific capacity than that of a traditional graphite anode. However, the poor cycling stability due to the huge volume change of Si during charge/discharge processes has seriously hampered its widespread application. To address this challenge, we design a silicon hollow sphere nanostructure by selective etching and a subsequent magnesiothermic reduction. The Si hollow spheres exhibit enhanced electrochemical properties compared to the commercial Si nanoparticles. The initial discharge and charge capacities of the Si hollow sphere anode are 2215.8 mAh g^-1 and 1615.1 mAh g^-1 with a high initial coulombic efficiency (72%) at a current density of 200 mA g^-1, respectively. In particular, the reversible capacity is 1534.5 mAh g^-1 with a remarkable 88% capacity retention against the second cycle after 100 cycles, over four times the theoretical capacity of the traditional graphite electrode. Therefore, our work demonstrates the considerable potential of silicon structures for displacing commercial graphite, and might open up new opportunities to rationally design various nanostructured materials for lithium ion batteries.

SnS2 Nanowall Arrays toward High-Performance Sodium Storage

Cost-effective sodium ion batteries (SIBs) are emerging as a desirable alternative choice to lithium ion batteries in terms of application in large-scale energy storage devices. SnS₂ is regarded as a potential anode material for SIBs because of its unique layered structure and high theoretical specific capacity. However, the development of SnS₂ was hindered by the sluggish kinetics of the diffusion process and the inevitable volume change during repeated sodiation-desodiation processes. In this work, SnS₂ with a unique nanowall array (NWA) structure is fabricated by one-step pulsed spray evaporation chemical vapor deposition (PSE-CVD), which could be used directly as binder-free and carbon-free anodes for SIBs. The SnS₂ NWA electrode achieves a high reversible capacity of 576 mAh g^-1 at 500 mA g^-1 and enhanced cycling stability. Attractively, an excellent rate capability is demonstrated with ∼370 mAh g^-1 at 5 A g^-1, corresponding to a capacity retention of 64.2% at 500 mA g^-1. The superior sodium storage capability of the SnS₂ NWA electrode could be attributed to outstanding electrode design and a rational growth process, which favor fast electron and Na-ion transport, as well as provide steady structure for elongated cycling.

Well-constructed silicon-based materials as high-performance lithium-ion battery anodes

Silicon has been considered as one of the most promising anode material alternates for next-generation lithium-ion batteries, because of its high theoretical capacity, environmental friendliness, high safety, low cost, etc. Nevertheless, silicon-based anode materials (especially bulk silicon) suffer from severe capacity fading resulting from their low intrinsic electrical conductivity and great volume variation during lithiation/delithiation processes. To address this challenge, a few special constructions from nanostructures to anchored, flexible, sandwich, core-shell, porous and even integrated structures, have been well designed and fabricated to effectively improve the cycling performance of silicon-based anodes. In view of the fast development of silicon-based anode materials, we summarize their recent progress in structural design principles, preparation methods, morphological characteristics and electrochemical performance by highlighting the material structure. We also point out the associated problems and challenges faced by these anodes and introduce some feasible strategies to further boost their electrochemical performance. Furthermore, we give a few suggestions relating to the developing trends to better mature their practical applications in next-generation lithium-ion batteries.

Si/Ti2O3/Reduced Graphene Oxide Nanocomposite Anodes for Lithium-Ion Batteries with Highly Enhanced Cyclic Stability

Silicon (Si) has attracted tremendous attention as a high-capacity anode material for next generation Li-ion batteries (LIBs); unfortunately, it suffers from poor cyclic stability due to excessive volume expansion and reduced electrical conductivity after repeated cycles. To circumvent these issues, we propose that Si can be complexed with electrically conductive Ti2O3 to significantly enhance the reversible capacity and cyclic stability of Si-based anodes. We prepared a ternary nanocomposite of Si/Ti2O3/reduced graphene oxide (rGO) using mechanical blending and subsequent thermal reduction of the Si, TiO2 nanoparticles, and rGO nanosheets. As a result, the obtained ternary nanocomposite exhibited a specific capacity of 985 mAh/g and a Coulombic efficiency of 98.4% after 100 cycles at a current density of 100 mA/g. Furthermore, these ternary nanocomposite anodes exhibited outstanding rate capability characteristics, even with an increased current density of 10 A/g. This excellent electrochemical performance can be ascribed to the improved electron and ion transport provided by the Ti2O3 phase within the Si domains and the structurally reinforced conductive framework comprised of the rGO nanosheets. Therefore, it is expected that our approach can also be applied to other anode materials to enable large reversible capacity, excellent cyclic stability, and good rate capability for high-performance LIBs.

Ultrafine Mo2C nanoparticles encapsulated in N-doped carbon nanofibers with enhanced lithium storage performance

The as-synthesized Mo₂C–NCNFs hybrid showed excellent lithium storage performance when used as an anode material for lithium ion batteries.

Synthesis of curved Si flakes using Mg powder as both the template and reductant and their derivatives for lithium-ion batteries

Mg powder was used as both active template for SiO₂ shell coating and reductant to subsequently reduce SiO₂ sheaths into Si to obtain curved Si flakes for lithium storage.