Wenping Si

On chip, all solid-state and flexible micro-supercapacitors with high performance based on MnOx/Au multilayers

In this work, we introduce a new concept to fabricate on chip, all solid-state and flexible micro-supercapacitors based on MnOx/Au multilayers, which are compatible with current microelectronics. The micro-supercapacitor exhibits a maximum energy density of 1.75 mW h cm−3 and a maximum power density of 3.44 W cm−3, which are both much higher than the values obtained for other solid-state supercapacitors. At a scan rate of 1 V s−1, a volumetric capacitance of 32.8 F cm−3 is obtained for MnOx/Au multilayer electrodes, which is much higher than the bare MnOx electrode. Electrochemical impedance spectroscopy (EIS) and evolution complex capacitance confirm that the electrical conductivity of MnOx is improved due to the incorporation of gold, and a low relaxation time constant around 5 ms is observed. The MnOx/Au multilayer micro-supercapacitor also shows good long-term cycling stability, with a capacitance retention rate of 74.1% after a large cycling number of 15000 times. Compared with other supercapacitors, which are not portable and are relatively bulky, the device demonstrated here allows fast and reliable applications in a portable and smart fashion. Furthermore, the nature of the process allows the micro-supercapacitor to be integrated with other micro-devices, to meet the need for micro-scale energy storage.

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 Nanoarchitecture of Si/Reduced Graphene Oxide Bilayer Nanomembranes for Li-Ion Batteries with Long Cycle Life

The large capacity loss and huge volume change of silicon anodes severely restricts their practical applications in lithium ion batteries. In this contribution, the sandwich nanoarchitecture of rolled-up Si/reduced graphene oxide bilayer nanomembranes was designed via a strain released strategy. Within this nanoarchitecture, the inner void space and the mechanical feature of nanomembranes can help to buffer the strain during lithiation/delithiation; the alternately stacked conductive rGO layers can protect the Si layers from excessive formation of SEI layers. As anodes for lithium-ion batteries, the sandwiched Si/rGO nanoarchitecture demonstrates long cycling life of 2000 cycles at 3 A g(-1) with a capacity degradation of only 3.3% per 100 cycles.

High-defect hydrophilic carbon cuboids anchored with Co/CoO nanoparticles as highly efficient and ultra-stable lithium-ion battery anodes

We propose an effective strategy to engineer a unique kind of porous carbon cuboid with tightly anchored cobalt/cobalt oxide nanoparticles (PCC–CoOx) that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The host carbon cuboid features an ultra-polar surface reflected by its high hydrophilicity and rich surface defects due to high heteroatom doping (N-/O-doping both higher than 10 atom%) as well as hierarchical pore systems. We loaded the porous carbon cuboid with cobalt/cobalt oxide nanoparticles through an impregnation process followed by calcination treatment. The resulting PCC–CoOx anode exhibits superior rate capability (195 mA h g−1 at 20 A g−1) and excellent cycling stability (580 mA h g−1 after 2000 cycles at 1 A g−1 with only 0.0067% capacity loss per cycle). Impressively, even after an ultra-long cycle life exceeding 10000 cycles at 5 A g−1, the battery can recover to 1050 mA h g−1 at 0.1 A g−1, perhaps the best performance demonstrated so far for lithium storage in cobalt oxide-based electrodes. This study provides a new perspective to engineer long-life, high-power metal oxide-based electrodes for lithium-ion batteries through controlling the surface chemistry of carbon host materials.

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.

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.

Bifunctional Au–Pd decorated MnOx nanomembranes as cathode materials for Li–O2 batteries

The search for new stable and efficient cathode materials for nonaqueous Li–O2 batteries has become an urgent task to satisfy the ever-growing needs for high capacity and high energy efficiency. To circumvent above issues, we have designed and synthesized isolated Au and Pd decorated MnOx nanomembranes, which act as bifunctional catalysts for Li–O2 batteries with a high specific capacity of 3200 mA h g−1 at 500 mA g−1 which is 9.8 and 3.2 times that of Super P and bare MnOx, respectively. In addition, with such novel structured catalysts, lithium ions, electrons and oxygen-containing intermediates can be rapidly transported, thus greatly improving the performance of Li–O2 batteries by significantly lowering the polarization and extending the cycle life to 120 times. The encouraging electrochemical property of such Au–Pd decorated MnOx nanomembranes leads to potential applications of the materials for high-performance Li–O2 batteries.

Schottky contact on ultra-thin silicon nanomembranes under light illumination

By repeating oxidation and subsequent wet chemical etching, we produced ultra-thin silicon nanomembranes down to 10 nm based on silicon-on-insulator structures in a controllable way. The electrical property of such silicon nanomembranes is highly influenced by their contacts with metal electrodes, in which Schottky barriers (SBs) can be tuned by light illumination due to the surface doping. Thermionic emission theory of carriers is applied to estimate the SB at the interface between metal electrodes and Si nanomembranes. Our work reveals that the Schottky contacts with Si nanomembranes can be influenced by external stimuli (like light luminescence or surface state) more heavily compared to those in the thicker ones, which implies that such ultra-thin-film devices could be of potential use in optical detectors.