Reducing the Charge Carrier Transport Barrier in Functionally Layer‐Graded Electrodes

Lithium‐ion batteries (LIBs) are primary energy storage devices to power consumer electronics and electric vehicles, but their capacity is dramatically decreased at ultrahigh charging/discharging rates. This mainly originates from a high Li‐ion/electron transport barrier within a traditional electrode, resulting in reaction polarization issues. To address this limitation, a functionally layer‐graded electrode was designed and fabricated to decrease the charge carrier transport barrier within the electrode. As a proof‐of‐concept, functionally layer‐graded electrodes composing of TiO₂(B) and reduced graphene oxide (RGO) exhibit a remarkable capacity of 128 mAh g⁻¹ at a high charging/discharging rate of 20 C (6.7 A g⁻¹), which is much higher than that of a traditionally homogeneous electrode (74 mAh g⁻¹) with the same composition. This is evidenced by the improvement of effective Li ion diffusivity as well as electronic conductivity in the functionally layer‐graded electrodes.     

石墨烯/硫酸铅复合材料的制备及其在铅酸电池中的电化学性能

利用简单的浸渍法制备了石墨烯/硫酸铅复合材料,使得硫酸铅可以直接用作铅酸电池负极材料。该复合材料分别以100 mA·g^-1、200 mA·g^-1和300 mA·g^-1电流密度放电时,平均放电比容量分别可达到110、94和69 mAh·g^-1,而硫酸铅仅为49、5和0.5 mAh·g^-1,显示出复合材料在高倍率充放电下更好的比容量和再接受充电能力。循环伏安测试表明石墨烯的电容效应随扫描速率增大而增强,同时析氢也变得严重,使得复合材料在充放电过程中充电效率比纯硫酸铅低20%。在充放电过程中,石墨烯能够提高硫酸铅1倍以上的放电容量,并将充电电压提高0.1 V。XRD和SEM结果显示硫酸铅均匀分布在石墨烯片层上,没有出现团聚现象。     

Capacity of graphene anode in ionic liquid electrolyte

The graphene anode was investigated in an ionic liquid electrolyte (0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂)) in room temperature ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPPyrNTf₂)). SEM and TEM images suggested that the electrochemical intercalation/deintercalation process in the ionic liquid electrolyte without vinylene carbonate (VC) leads to small changes on the surface of graphene particles. However, a similar process in the presence of VC results in the formation of a coating (SEI—solid electrolyte interface) on the graphene surface. During charging/discharging tests, the graphene electrode working together with the 0.7 M LiNTf₂ in MPPyrNTf₂ electrolyte lost its capacity, during cycling and stabilizes at ca. 200 mAh g^?1 after 20 cycles. The addition of VC to the electrolyte (0.7 M LiNTf₂ in MPPyrNTf₂?+?10 wt.% VC) considerably increases the anode capacity. Electrodes were tested at different current regimes: ranging between 50 and 1,000 mA g^?1. The capacity of the anode, working at a low current regime of 50 mA g^?1, was ca. 1,250 mAh g^?1, while the current of 500 mA g^?1 resulted in capacity of 350 mAh g^?1. Coulombic efficiency was stable and close to 95 % during ca. 250 cycles. The exchange current density, obtained from impedance spectroscopy, was 1.3?×?10^?7 A cm^?2 (at 298 K). The effect of the anode capacity decrease with increasing current rate was interpreted as the result of kinetic limits of the electrode operation.     

石墨烯/硫酸铅复合材料的制备及其在铅酸电池中的电化学性能

利用简单的浸渍法制备了石墨烯/硫酸铅复合材料,使得硫酸铅可以直接用作铅酸电池负极材料。该复合材料分别以100 mA.g-1、200 mA.g-1和300 mA.g-1电流密度放电时,平均放电比容量分别可达到110、94和69 mAh.g-1,而硫酸铅仅为49、5和0.5 mAh.g-1,显示出复合材料在高倍率充放电下更好的比容量和再接受充电能力。循环伏安测试表明石墨烯的电容效应随扫描速率增大而增强,同时析氢也变得严重,使得复合材料在充放电过程中充电效率比纯硫酸铅低20%。在充放电过程中,石墨烯能够提高硫酸铅1倍以上的放电容量,并将充电电压提高0.1 V。XRD和SEM结果显示硫酸铅均匀分布在石墨烯片层上,没有出现团聚现象。     

Charging and discharging rate studies of polypyrrole films in AlCl3: 1-methyl-(3-ethyl)-imidazolium chloride molten salts and in CH3CN

The chronocoulometric charging and discharging of polypyrrole films in basic AlCl₃/1-methyl-(3-ethyl)-imidazolium chloride molten salts and CH₃CN have been investigated. Both processes follow a t^{$\text{1}\text{2}$} time dependence and are significantly faster in the molten salts. Comparison with redox polymer and porous electrode models shows that neither model is satisfactorily applicable over the entire potential region studied. The charging and discharging rates are limited by ion migration in the polymer and for potential steps in the “double layer charging” region polypyrrole behaves as a porous electrode material. In this region there is a good correlation between the charging/discharging rates and the solvent conductivity.     

Electrochemical Determination of Hydrogen Peroxide Using a Glassy Carbon Electrode Modified with Three-Dimensional Copper Hydroxide Nanosupercages and Electrochemically Reduced Graphene Oxide

Three-dimensional copper hydroxide nanosupercages and electrochemically reduced graphene oxide were used to modify the glassy carbon electrode for the selective determination of hydrogen peroxide. The morphology and electrochemistry properties of copper hydroxide nanosupercage/electrochemically reduced graphene oxide/glassy carbon electrode were characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectra, Raman spectra, cyclic voltammetry, and electrochemical impedance spectroscopy. The resulting copper hydroxide nanosupercage/electrochemically reduced graphene oxide/glassy carbon electrode showed favorable performance for the electrocatalytic reduction of hydrogen peroxide. The amperometric current–time curve of the electrochemical sensor exhibited a wide linear range from 0.5 to 1030?µM with a limit of detection of 0.23?µM at a signal-to-noise ratio of three. Moreover, the sensor provided favorable selectivity, reproducibility, and stability and was used for the determination of H₂O₂ in tap water.     

Bipolar Resistive Switching Behavior of PVP-GQD/HfOx/ITO/Graphene Hybrid Flexible Resistive Random Access Memory

We have investigated highly flexible memristive devices using reduced graphene oxide (RGO) nanosheet nanocomposites with an embedded GQD Layer. Resistive switching behavior of poly (4-vinylphenol):graphene quantum dot (PVP:GQD) composite and HfOx hybrid bilayer was explored for developing flexible resistive random access memory (RRAM) devices. A composite active layer was designed based on graphene quantum dots, which is a low-dimensional structure, and a heterogeneous active layer of graphene quantum dots was applied to the interfacial defect structure to overcome the limitations. Increasing to 0.3–0.6 wt % PVP-GQD, V_f changed from 2.27–2.74 V. When negative deflection is applied to the lower electrode, electrons travel through the HfOx/ITO interface. In addition, as the PVP-GQD concentration increased, the depth of the interfacial defect decreased, and confirmed the repetition of appropriate electrical properties through Al and HfOx/ITO. The low interfacial defects help electrophoresis of Al⁺ ions to the PVP GQD layer and the HfOx thin film. A local electric field increase occurred, resulting in the breakage of the conductive filament in the defect.     

利用过硫酸钠化学抽取制备脱锂态电极材料

介绍了一种通过常规化学反应制备锂离子电池脱锂态电极材料的方法。首先将氧化剂Na₂S₂O₈与锂离子电池电极材料混合于去离子水中,对混合液进行振荡和搅拌,使脱锂反应充分进行,获得不溶于水的脱锂态电极材料和溶于水的其他生成物,然后将溶于水的生成物过滤掉,最后对不溶于水的脱锂态电极材料进行反复清洗并干燥,便获得所需材料。此方法操作简便,容易控制,计算锂含量方便准确,并且可以得到足够量和纯净的脱锂态电极材料,克服了充放电法制备和采用其他氧化剂进行化学     

In situ Investigations of Interfacial Degradation and Ion Migration at CH3NH3PbI3 Perovskite/Ag Interfaces

Interfacial properties between perovskite layers and metal electrodes play a crucial role in the device performance and the long-term stability of perovskite solar cells. Here, we report a comprehensive study of the interfacial degradation and ion migration at the interface between CH₃NH₃PbI₃ perovskite layer and Ag electrode. Using in situ photoemission spectroscopy measurements, we found that the Ag electrode could induce the degradation of perovskite layers, leading to the formation of PbI₂ and AgI species and the reduction of Pb²⁺ ions to metallic Pb species at the interface. The unconventional enhancement of the intensities of I 3d spectra provides direct experimental evidences for the migration of iodide ions from CH₃NH₃PbI₃ subsurface to Ag electrode. Moreover, the contact of Ag electrode and perovskite layers induces an interfacial dipole of 0.3 eV at CH₃NH₃PbI₃/Ag interfaces, which may further facilitate iodide ion di usion, resulting in the decomposition of perovskite layers and the corrosion of Ag electrode.     

Biomolecular Release Stimulated by Electrochemical Signals at a Very Small Potential Applied

DNA release electrochemically stimulated by applying ?10 mV on the modified electrode was studied. The release process was based on the local (interfacial) pH change produced upon H₂O₂ reduction electrocatalyzed by the immobilized microperoxidase‐11. SiO₂ nanoparticles attached to the electrode surface and functionalized with trigonelline and boronic acid species changed their electrical charge from positive to negative upon the interfacial pH change, thus allowing electrostatic adsorption of negatively charged DNA on the positive interface and then its repulsion/release from the negative interface. The loaded/released DNA molecules were labeled with a fluorescent dye to allow easy detection of the released DNA molecules. The important feature of the developed system is the controlled DNA release upon applying very small electrical potential on the modified electrode.     

Preparation of 3D MnO2/Polyaniline/Graphene Hybrid Material via Interfacial Polymerization as High‐Performance Supercapacitor Electrode

MnO₂/polyaniline/graphene composite as a supercapacitor electrode material was synthesized through an interfacial polymerization approach in the interface of oil/water phase. The as‐synthesized MPG is characterized by infrared spectroscopy, XRD, XPS, SEM and TEM, and its electrochemical performance is measured by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The 3D nanostructure of MPG and loose nanorod structure of polyaniline (PANI) coated with round MnO₂ pellets could be clearly observed. The maximum energy density of MPG is 45.4 Wh/kg (at a power density of 67.8 kW/kg) and the highest power density is 229.2 kW/kg (at an energy density of 25.7 Wh/kg). The capacitance retentions after 500 cycles at the scan rate of 5 mV/s for MGP composite and PANI/graphene are 70.4% and 59.1%, respectively, and the capacitance values after 500 cycles are 158.4 F/g and 114.8 F/g, respectively. The improved performance of MPG is due to the 3D nanostructure, loose nanorod structure of PANI and stable support of graphene, which prevent the mechanical deformation effectively during the fast charge/discharge process and facilitate the diffusion of the electrolyte ions into the inner region of active materials. The composite material is very promising for the next generation of high‐performance supercapacitors electrode.     

Solvation of Calcium–Phosphate Headgroup Complexes at the DPPC/Aqueous Interface

The effects of sodium (Na⁺) and calcium (Ca²⁺) cations on model zwitterionic dipalmitoylphosphatidylcholine (DPPC) monolayers spread on metal chloride salt solutions are investigated by means of vibrational sum frequency generation (VSFG) and heterodyne‐detected (HD)‐VSFG spectroscopy. VSFG and HD‐VSFG spectra in the OH stretching region reveal cation‐specific effects on the interfacial water′s H‐bonding network, knowledge of which has been limited to date. It is found that low‐concentrated Ca²⁺ more strongly perturbs interfacial water organization relative to highly concentrated Na⁺. At higher Ca²⁺ concentrations, the water H‐bonding network at the DPPC/CaCl₂ interface reorganizes and the resulting spectrum closely follows that of the bare air/CaCl₂ interface up to ～3400 cm^?1. Most interesting is the appearance of a negative band at ～3450 cm^?1 in the DPPC/CaCl₂ Im χ_s⁽²⁾ spectra, likely arising from an asymmetric solvation of Ca²⁺–phosphate headgroup complexes. This gives rise to an electric field that orients the net OH transition moments of a subset of OH dipoles toward the bulk solution.     

NMR investigations on the lithiation and delithiation of nanosilicon-based anodes for Li-ion batteries

Lithiation and delithiation of nanosilicon anodes of 100–200 nm diameter have been probed by ex situ solid-state high-resolution ⁷Li nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) methods. Samples were charged within pouch cells up to capacities of 1,500 mAh/g at 0.1 C, and subsequently discharged at the same rate. The NMR spectra reveal important quantitative information on the local lithium environments during the various stages of the charging/discharging process. The TEM experiments show that the electrochemical lithiation of nanosilicon particles results in core-shell materials, consisting of Li_xSi shells surrounding a core of residual silicon. The NMR spectra yield approximate Li/Si ratios of the lithium silicides present in the shells, based on the distinct local environments of the various types of ⁷Li nuclei present. The combination of NMR with TEM gives important quantitative conclusions about the nature of the electrochemical lithiation process: Following the initial formation of the solid electrolyte interphase layer, which accounts for an irreversible capacity of 240 mAh/g, lithium silicide environments with intermediate Li concentrations (Li₁₂Si₇, Li₇Si₃, and Li₁₃Si₄) are formed at the 500 to 1,000 mAh/g range during the charging process. At a certain penetration depth, further lithiation does not progress any further toward the interior of the silicon particles but rather leads to the formation of increasing amounts of the lithium-richest silicide, Li₁₅Si₄-type environments. Delithiation does not result in the reappearance of the intermediate-stage phases but rather only changes the amount of Li₁₅Si₄ present, indicating no microscopic reversibility. Based on these results, a detailed quantitative model of nanophase composition versus penetration depth has been developed. The results indicate the power and potential of solid-state NMR spectroscopy for elucidating the charging/discharging mechanism of nano-Si anodes.     

High-performance supercapacitor based on tantalum iridium oxides supported on tungsten oxide nanoplatelets

Here we report on a novel supercapacitor electrode based on IrO₂–Ta₂O₅ nanoparticles supported on WO₃ nanoplatelets. The nanoplatelets were directly grown on a W plate using a facile hydrothermal method, whereas the IrO₂–Ta₂O₅ nanoparticles were formed via a thermal decomposition technique which can be easily scaled up. The structural, morphological, and electrochemical properties of the WO₃ nanoplatelets and the formed trimetallic oxide nanocomposite have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV), and charging/discharging techniques. The fabricated trimetallic oxide nanocomposite exihibited rectangular cyclic voltamograms even tested at high potential scan rates, a high specific capacitance and high charging/discharging stability, promising utilization in the design of high-performance devices for energy storage.     

锂电池电极过程的原位电化学原子力显微镜研究进展

随着人类对能源的使用与存储需求不断增加,高能量密度和高安全性能的二次锂电池体系正在被不断地开发与完善.深入理解充放电过程中锂电池内部电极/电解质界面的电化学过程以及微观反应机理,有利于指导电池材料的优化设计.原位电化学原子力显微镜将原子力显微镜的高分辨表界面分析优势与电化学反应装置相结合,能够在电池运行条件下实现对电极/电解质界面的原位可视化研究,并进一步从纳米尺度上揭示界面结构的演化规律与动力学过程.本文总结了原位电化学原子力显微镜在锂电池电极过程中的最新研究进展,主要包括基于转化型反应的正极过程、固体电解质中间相的动态演化以及固态电池界面演化与失效分析.     

界面扩张流变法研究C12mimBr对Gemini12-2-12在空气/水界面聚集行为的影响

采用界面扩张流变技术研究了季铵盐偶联表面活性剂C₁₂-(CH₂)₂-C₁₂·2Br (Gemini12-2-12)及其与离子液体表面活性剂溴化1-十二烷基-3-甲基咪唑(C₁₂mimBr)复配体系的动态界面张力、扩张流变性质和界面弛豫过程等, 探讨了C₁₂mimBr 对C₁₂mimBr/Gemini12-2-12 混合体系界面性质的影响及C₁₂mimBr 对Gemini12-2-12界面聚集行为影响的机制. 结果表明, 随着离子液体表面活性剂的不断引入, 体系界面吸附达到平衡所需的时间逐渐缩短, 扩张模量和相角明显降低, 界面吸附膜由粘弹性膜转变为近似纯弹性膜; 同时, 界面及其附近的弛豫过程也发生显著变化, 慢弛豫过程消失, 快弛豫过程占主导地位, 且离子液体浓度越高, 快弛豫的贡献越大. 这些界面性质的变化主要归因于离子液体表面活性剂C₁₂mimBr参与界面形成及两表面活性剂在界面竞争吸附的结果. 少量离子液体表面活性剂C₁₂mimBr 的加入可以填补疏松的Gemini12-2-12 界面上的空位, 形成混合界面吸附膜. 随着C₁₂mimBr 含量的增加, 嵌入界面的C₁₂mimBr 分子数不断增多, 导致界面上相互缠绕的Gemini12-2-12烷基链“解缠”, 在体相和界面分子扩散交换的过程中“解缠”的Gemini12-2-12分子从界面上解吸回到体相, 与此同时, C₁₂mimBr 分子相对较小的空间位阻及较强的疏水作用促使其优先扩散至界面进而取代Gemini12-2-12分子, 最终界面几乎完全被C₁₂mimBr分子所占据.     

Graphene‐Functionalized 3D‐Carbon Fiber Electrodes – Preparation and Electrochemical Characterization

Graphene nanosheets were produced on the surface of carbon fibers by in situ electrochemical procedure including oxidative and reductive steps to yield first graphene oxide, later converted to graphene. The electrode material composed of graphene‐functionalized carbon fibers was characterized by scanning electron microscopy (SEM) and cyclic voltammery demonstrating superior electrochemical kinetics comparing with the original carbon paper. The interfacial electron transfer rate for the reversible redox process of [Fe(CN)₆]^3?/4? was found ca. 4.5‐fold higher after the electrode modification with the graphene nanosheets. The novel electrode material is suggested as a promising conducting interface for bioelectrocatalytic electrodes used in various electrochemical biosensors and biofuel cells, particularly operating in vivo.     

Hybrid materials utilizing polyelectrolyte-derivatized carbon nanotubes and vanadium-mixed addenda heteropolytungstate for efficient electrochemical charging and electrocatalysis

Preparation and electrochemical behavior of new hybrid materials composed of multi-walled carbon nanotubes (CNTs) that were derivatized with poly(diallyldimethylammonium) chloride and modified with vanadium-mixed addenda Dawson-type heteropolytungstate, [P₂W₁₇VO₆₂]^8?, is described here. These nanostructured composite systems exhibited fast dynamics of charge propagation. They were characterized by the transport (effectively diffusional) kinetic parameter of approximately 8?×?10^?8 cm^?2 s^?1/2 and the specific capacitance parameter of 82 F g^?1 (at the charging/discharging current of 200 mA g^?1). The latter parameter for bare CNTs was found to be only 50 F g^?1 under analogous conditions. These observations were based on the results of galvanostatic charging–discharging, cyclic voltammetric, and AC impedance spectroscopic measurements. The improved capacitance properties were attributed to the systems’ pseudocapacitive features originating from the fast redox transitions of the [P₂W₁₇VO₆₂]^8? polyanions. In addition to the fast redox conduction, the proposed organic–inorganic hybrid materials exhibited interesting electrocatalytic activity toward reduction of bromate in the broad concentration range (sensitivity, 0.24 mA cm^?2 mmol^?1 dm³).     

The Structure of Water Bonded to Phosphate Groups at the Electrified Zwitterionic Phospholipid Membranes/Aqueous Interface

Gaining insight into the water structure at the electrified phospholipid membranes/aqueous interface is vital and essential for elucidating the mechanism of many biochemical reactions, but still remains a formidable challenge. Herein, based on the superiority of surface enhanced infrared absorption (SEIRA) spectroscopy combined with electrochemistry in interfacial analysis, the evolution of local water structure at the zwitterionic phospholipid membranes/aqueous interface with an external electric field is revealed by means of ion perturbation. The strongly hydrogen‐bonded water directly bonded to the phosphate groups (PO₂^?) has a strong mechanical strength to resist potential perturbations, and that portion of water greatly affects the electrostatic properties of the phospholipid membranes. This study innovates the basic understanding of electric double layer (EDL) at the membranes/aqueous interface.