Junwen Deng

Cu-Si nanocable arrays as high-rate anode materials for lithium-ion batteries.

There is a surge in developing rechargeable lithium-ion batteries (LIBs) with higher energy densities and higher rate performance for application in powering future advanced communications equipment and electric vehicles (EVs). [ 1–6 ] The development of the electrode materials is essential for the improvement of the electrochemical properties of LIBs. [ 7–10 ] Among various anode materials tested for LIBs, Si has triggered signifi cant research effort because of its low Li-uptake potential and the high theoretical capacity (4200 mA h g − 1 ). [ 6 , 11–19 ] However, the main disadvantage that restricts the application of Si is the large volume changes of Si during Li + insertion and extraction, which results in a pulverization of the Si particles, a peeling off the current connection network, and, consequently, a rapid capacity decline upon cycling. [ 11–17 ] To overcome this issue, Si nanostructures, such as Si nanowires and nanotubes, have been fabricated. [ 6 , 11 , 18–23 ] The procedures for the fabrication of the Si nanostructures have also been well developed. [ 24–26 ] These nanostructures can provide spaces to accommodate the large volume variation during charge and discharge processes and thus allow for facile strain relaxation, which prevents pulverization upon lithium insertion. [ 11–19 , 27 ] The cycle stability of the Si anode has been signifi cantly improved by using these nanostructures. [ 11–17 , 27 ] Nevertheless, the rate capability of these materials highly needed for EVs is still not satisfying. This is possibly due to the lack of favorable electronic conductivity and the continuous growth of the unstable solid electrolyte interphase (SEI) at the Si/electrolyte interface upon cycling. Therefore, a new design for the structure of the Si anode is in high demand to achieve both longer cycling life and higher rate capability. Our previous work suggested that the application of nanocable structures in LIBs electrodes can signifi cantly improve the batteries’ electrochemical performance, especially the high

Naturally Rolled‐Up C/Si/C Trilayer Nanomembranes as Stable Anodes for Lithium‐Ion Batteries with Remarkable Cycling Performance

Lithium-ion batteries (LIBs) have attracted considerable interest because of their wide range of environmentally friendly applications, such as portable electronics, electric vehicles (EVs), and hybrid electric vehicles (HEVs). For the next generation of LIBs with high energy and high power density, improvements on currently used electrode materials are urgently needed. Among various anode materials, Si has been extensively studied owing to its highest theoretical capacity (4200 mAhg ), abundance in nature, low cost, and nontoxicity. However, Si-based anodes are notoriously plagued by poor capacity retention resulting from large volume changes during alloy/de-alloy processes (400%). The intrinsic strain generated during such expansion and contraction easily leads to electrode pulverization and capacity fading. Thus, it is a big challenge to achieve both excellent cyclability and enhanced capacity of Si-based anode materials. Significant efforts have been devoted to circumvent this issue caused by the volume change of silicon. Recently, a number of Si nanostructures, including nanoparticles, nanowires/nanorods, nanotubes, and porous nanostructures 22] as well as their composites, have been fabricated to achieve improved cycling performance. Among them, tubular structures, with extra interior space for electron and ion transport, as well as for accommodating volume changes, are one of the most attractive and promising configurations for LIBs. However, such anode materials are still far from commercialization, and new strategies for the synthesis of novel structures with superior cycling performance and stability are still much sought-after. Herein, we report a new tubular configuration made from naturally rolled-up C/Si/C trilayer nanomembranes, which exhibits a highly reversible capacity of approximately 2000 mAh g 1 at 50 mA g , and approximately 100 % capacity retention at 500 mA g 1 after 300 cycles. The sandwich-structured C/Si/C composites, with moderate kinetic properties toward Li ion and electron transport, are of the highest quality. The excellent cycling performance is related to the thin-film effect combined with carbon coating, which play a structural buffering role in minimizing the mechanical stress induced by the volume change of Si. The energy reduction in C/Si/C trilayer nanomembranes after rolling up into multi-winding microtubes results in a significantly reduced intrinsic strain, which can improve capacity and cycling performance. This synthetic process could be compatible with existing industrial sputtering deposition processes as well as roll-to-roll thin-film fabrication technology. The strategy for the self-release of C/Si/C trilayer nanomembranes using rolled-up nanotechnology to form multilayer C/Si/C microtubes is shown in Scheme 1. First, a sacrificial layer (red color, photoresist ARP 3510) was deposited on top of the Si substrates by spin-coating, then trilayer C/Si/C (10/40/10 nm, respectively) nanomembranes were sequentially deposited by radio frequency sputtering, during which the intrinsic strain caused by thermal expansion effects was generated. When the sacrificial layer was selectively under-

Highly Conductive and Strain‐Released Hybrid Multilayer Ge/Ti Nanomembranes with Enhanced Lithium‐Ion‐Storage Capability

Highly conductive and hybridized microtubes relying on strain-released ultrathin Ti/Ge bilayer nanomembranes are reported. These hybrid multilayer microtubes show a remarkably enhanced reversible capacity up to 1495 mA h g(-1) with a high first-cycle Coulombic efficiency of 85%, and demonstrate an excellent capacity of ≈930 mA h g(-1) after 100 cycles.

Sandwich-Stacked SnO2/Cu Hybrid Nanosheets as Multichannel Anodes for Lithium Ion Batteries

We have introduced a facile strategy to fabricate sandwich-stacked SnO2/Cu hybrid nanosheets as multichannel anodes for lithium-ion batteries applying rolled-up nanotechnology with the use of carbon black as intersheet spacer. By employing a direct self-rolling and compressing approach, a much higher effective volume efficiency is achieved as compared to rolled-up hollow tubes. Benefiting from the nanogaps formed between each neighboring sheet, electron transport and ion diffusion are facilitated and SnO2/Cu nanosheet overlapping is prevented. As a result, the sandwich-stacked SnO2/Cu hybrid nanosheets exhibit a high reversible capacity of 764 mAh g(-1) at 100 mA g(-1) and a stable cycling performance of ~75% capacity retention at 200 mA g(-1) after 150 cycles, as well as a superior rate capability of ~470 mAh g(-1) at 1 A g(-1). This synthesis approach presents a promising route to design multichannel anodes for high performance Li-ion batteries.

Hierarchically Designed SiOx/SiOy Bilayer Nanomembranes as Stable Anodes for Lithium Ion Batteries

Hierarchically designed SiOx /SiOy rolled-up bilayer nanomembranes are used as anodes for lithium-ion batteries. The functionalities of the SiO(x,y) layers can be engineered by simply controlling the oxygen content, resulting in anodes that exhibit a reversible capacity of about 1300 mA h g(-1) with an excellent stability of over 100 cycles, as well as a good rate capability.

MoS2 nanosheets decorated with gold nanoparticles for rechargeable Li–O2 batteries

We demonstrate here a facile one-step hydrothermal synthesis to prepare molybdenum disulfide nanosheets decorated with gold nanoparticles (MoS2/AuNPs) for rechargeable Li–O2 batteries. The fabricated Li–O2 battery exhibits enhanced specific capacity and cycle efficiency, which are ascribed to the two-dimensional structure of MoS2/AuNP nanohybrids and the synergistic catalytic effects of both MoS2 nanosheets and AuNPs.

Free-standing Fe2O3 nanomembranes enabling ultra-long cycling life and high rate capability for Li-ion batteries

With Fe2O3 as a proof-of-concept, free-standing nanomembrane structure is demonstrated to be highly advantageous to improve the performance of Li-ion batteries. The Fe2O3 nanomembrane electrodes exhibit ultra-long cycling life at high current rates with satisfactory capacity (808 mAh g−1 after 1000 cycles at 2 C and 530 mAh g−1 after 3000 cycles at 6 C) as well as repeatable high rate capability up to 50 C. The excellent performance benefits particularly from the unique structural advantages of the nanomembranes. The mechanical feature can buffer the strain of lithiation/delithiation to postpone the pulverization. The two-dimensional transport pathways in between the nanomembranes can promote the pseudo-capacitive type storage. The parallel-laid nanomembranes, which are coated by polymeric gel-like film and SEI layer with the electrolyte in between layers, electrochemically behave like numerous “mini-capacitors” to provide the pseudo-capacitance thus maintain the capacity at high rate.

A Single Rolled‐Up Si Tube Battery for the Study of Electrochemical Kinetics, Electrical Conductivity, and Structural Integrity

A lab-on-chip device is demonstrated for probing the electrochemical kinetics, electrical properties, and structure integrity of a single Si rolled-up tube as the anode in lithium-ion batteries. Cyclic voltammetry of the tube exhibits better-resolved peaks than of the planar film due to the enhanced diffusion. The tube is wrinkled after cycling. The tube could be used as a promising ultra-microelectrode for other voltammetry research.