Accelerating electrochemistry with metal nanowires

Scalable, solution-phase syntheses of metal nanowires are enabling their increased use in electrochemical processes. This review highlights recent results demonstrating how metal nanowires can exhibit better durability and higher activity than traditional metal nanoparticle electrocatalysts on carbon supports. Metal nanowires can also form interconnected two-dimensional and three-dimensional (3D) networks that eliminate the need for a carbon support, thus eliminating the detrimental effects of carbon corrosion. Porous 3D networks of nanowires can be used as flow-through electrodes with the highest specific surface areas and mass transport coefficients obtained to date, enabling dramatic increases in the productivity of electrochemical reactions. Nanowire networks are also serving as 3D current collectors that improve the capacity of batteries. The tunable surface structure and dimensions of metal nanowires offer researchers a new opportunity to create electrodes that are tailored from the atomic scale to the microscale to improve electrochemical performance.     

不同维度Co3O4纳米材料的水热合成研究进展

过渡金属氧化物Co_3O_4的晶体结构及表面特性与其形貌、尺寸和微观结构密切相关。本文将不同形貌Co_3O_4纳米材料按尺寸分为:纳米球、立方块、多面体等零维材料,纳米线、纳米棒、纳米管、纳米柱等1D材料,纳米片、纳米薄膜等2D材料,海胆状、微米球等由纳米单元构成的微米尺寸3D超结构。探讨了对形貌形成的影响因素,重点研究其水热合成过程,总结了可能的形成机理,以利于对不同维度材料的形成规律有较深入的理解,进而能在理论上指导特定维度、特定形貌材料的可控合成。     

Redox flow batteries for energy storage: their promise,achievements and challenges

Redox flow batteries continue to be developed for utility-scale energy storage applications. Progress on standardisation, safety and recycling regulations as well as financing has helped to improve their commercialisation. The technical progress of redox flow batteries has not considered adequately the significance of electrolyte flow velocity, mass transfer and plug flow reactor modelling, despite steps in the right direction. 3D simulations of fluid flow, pressure drop, current distribution and mechanical resistance using commercial software are becoming more common, but satisfactory validation by experiments is still unusual. The majority of research tends to report short-term studies on small electrodes, often in poorly defined flow channels; long-term evaluation of electrode and membrane durability on a pilot scale is needed. Digital imaging of electrode structure using X-ray computed tomography is increasingly being used. Much activity is directed to organic and non-aqueous systems. However, scale-up and high, sustained charge capacity using electrolytes of moderate cost, which are environmentally acceptable to source, store, transport and handle, require considerable attention. Recommendations for future work are discussed.     

Improved kinetics of LiNi(1/3)Mn(1/3)Co(1/3)O2 cathode material through reduced graphene oxide networks

An electronically conducting 3D network of reduced graphene oxide (RGO) was introduced into LiNi(1/3)Mn(1/3)Co(1/3)O(2) (LNMC) cathode material in a special nano/micro hierarchical structure. The rate test and cycling measurement showed that the hierarchical networks remarkably improve the high rate performance of LNMC electrode for lithium-ion batteries. The effect of RGO conducting networks on kinetic property was investigated by electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration (PITT). The EIS results reveal that the RGO network greatly decreases the resistance of lithium batteries, especially the charge transfer resistance which can be attributed to the significantly improved conducting networks. The enhancement of apparent diffusion coefficient by the RGO conducting networks is shown by PITT. The power performance was found to be limited by the electrical conduction in the two-phase region, which can be greatly facilitated by the hierarchical RGO network together with carbon black. The as-obtained LNMC/RGO cathode exhibits an outstanding electrochemical property supporting the design idea of electronically conducting 3D networks for the high-energy and high-power lithium-ion batteries.     

固态锂电池界面优化策略的研究进展

固态锂电池具有安全性好、能量密度高等优点,在新能源汽车和智能电子等领域具有广泛的应用前景。然而,由化学/电化学和物理因素引起的界面副反应与高界面阻抗问题制约了其进一步发展。先前的综述已对解决化学/电化学界面问题的方法有了相对全面的阐述,但并未细致讨论不同结构固态电池中物理界面的影响及应对策略。本文将简要介绍化学/电化学界面问题及其解决方案;重点按结构特点将固态锂电池分为三明治结构、粉末复合结构和3D一体化结构,细致地分析不同电池结构的物理界面特点与优化策略,并对各种策略的优缺点进行比较分析;最后,对固态锂电池电极/电解质界面的未来研究方向进行展望。     

一种有助于稳定锂金属循环的富氟化位点框架结构

锂金属是下一代高能量密度二次电池的理想负极材料,然而它的应用仍然受制于较差的循环稳定性。近期,二维氟化界面被广泛用于改善锂金属负极的成核机制、沉积形貌和循环稳定性。本工作通过将体积缩小化的氟化石墨颗粒与锂离子传导网络结合,获得了一种富氟化位点的三维框架结构。实验结果证明此类三维氟化结构可显著提升锂金属负极在不同电流密度和容量下的循环稳定性,且优于二维氟化界面结构。通过本工作的研究,证明了相较于单纯的二维氟化界面,三维锂离子传导网络和富氟化位点的合理结合可以成为一种改进的界面结构用于锂金属负极保护,为高能量密度锂金属电池的负极保护提供了新的设计思路。     

Frontispiece: Stainless Steel-Like Passivation Inspires Persistent Silicon Anodes for Lithium-Ion Batteries

Passivation of stainless steel by additives forming mass-transport blocking layers is widely practiced, where Cr element is added into bulk Fe−C forming the Cr₂O₃-rich protective layer. Here we extend the long-practiced passivation concept to Si anodes for lithium-ion batteries, incorporating the passivator of LiF/Li₂CO₃ into bulk Si. The passivation mechanism is studied by various ex situ characterizations, redox peak contour maps, thickness evolution tests, and finite element simulations. The results demonstrate that the passivation can enhance the (de)lithiation of Li-Si alloys, induce the formation of F-rich solid electrolyte interphase, stabilize the Si/LiF/Li₂CO₃ composite, and mitigate the volume change of Si anodes upon cycling. The 3D passivated Si anode can fully retain a high capacity of 3701 mAh g⁻¹ after 1500 cycles and tolerate high rates up to 50C. This work provides insight into how to construct durable Si anodes through effective passivation.     

基于三维集流体的无枝晶锂金属负极

随着电化学储能市场的迅猛发展, 当前商用锂离子电池难以满足人们对高能量密度储能器件的需求. 锂金属具有高比容量和低氧化还原电位等优点, 被认为是下一代二次电池的理想负极材料. 然而, 锂金属负极在充放电过程中会出现体积变化大、 枝晶生长、 界面不稳定等问题, 严重阻碍了其在二次电池中的实际应用. 三维多孔材料具有骨架/空间互穿网络结构、 比表面积大、 孔隙发达和机械性能好等物理特性, 用作金属锂负极的集流体, 在锂沉积/溶解过程中可以起到降低局部有效电流密度、 均匀电场分布和降低锂离子浓度梯度的作用, 有望实现锂的均匀成核和无枝晶沉积, 同时抑制了电极的体积膨胀. 尽管有关三维集流体的研究报道不断出现, 但综合系统评价现有各种三维集流体体系的工作鲜见报道. 本文聚焦锂金属负极三维集流体的构建及应用研究进展, 首先分析了三维集流体抑制锂枝晶生长的基本原理及局限性, 继而重点关注了三维集流体的结构调控、 表面改性和功能化等应对策略对锂成核、 沉积过程的影响, 并对不同材质三维集流体的优缺点进行了归纳总结. 最后, 面向实用化, 分析并展望了三维集流体应用于锂金属电池的发展前景.     

Towards High-performance Lithium-Sulfur Batteries: the Modification of Polypropylene Separator by 3D Porous Carbon Structure Embedded with Fe3C/Fe Nanoparticles

Lithium-sulfur(Li-S) batteries with high energy densities have received increasing attention. However, the electrochemical performance of Li-S batteries is still far from the satisfactory of the practical application, which can be mainly attributed to the shuttling of polysulfides and the slow reaction kinetics of polysulfide conversion. To address this issue, a 3D porous carbon structure constructed by 2D N-doped graphene and 1D carbon nanotubes with embedded Fe₃C/Fe nanoparticles(NG@Fe₃C/Fe) was designed and prepared by a simple programmed calcination method for the modification of polypropylene(PP) separator. The Fe₃C/Fe nanoparticles demonstrate an excellent catalytic conversion and strong chemisorption towards polysulfides, while the unique architecture of N-doped graphene promotes the Li⁺/electron transfer and the physical adsorption of polysulfides. The electrochemical performance of the Li-S batteries with the NG@Fe₃C/Fe-modified separator is significantly improved. A large discharge capacity of 1481 mA∙h∙g^-1 is achieved at 0.2 C(1 C=1675 mA/g), and a high capacity of 601 mA∙h∙g^-1 is maintained after discharged/charged for 500 cycles at a current rate of 1 C. This work provides a new approach for the development of high-performance Li-S batteries through the modification of the PP separator by rationally designed composites with large adsorption capability to polysulfides, good wettability to the electrolyte and high catalytic property.     

Highly Stable Lithium Metal Batteries Enabled by Regulating the Solvation of Lithium Ions in Nonaqueous Electrolytes

Safe and rechargeable lithium metal batteries have been difficult to achieve because of the formation of lithium dendrites. Herein an emerging electrolyte based on a simple solvation strategy is proposed for highly stable lithium metal anodes in both coin and pouch cells. Fluoroethylene carbonate (FEC) and lithium nitrate (LiNO₃) were concurrently introduced into an electrolyte, thus altering the solvation sheath of lithium ions, and forming a uniform solid electrolyte interphase (SEI), with an abundance of LiF and LiN_xO_y on a working lithium metal anode with dendrite‐free lithium deposition. Ultrahigh Coulombic efficiency (99.96 %) and long lifespans (1000 cycles) were achieved when the FEC/LiNO₃ electrolyte was applied in working batteries. The solvation chemistry of electrolyte was further explored by molecular dynamics simulations and first‐principles calculations. This work provides insight into understanding the critical role of the solvation of lithium ions in forming the SEI and delivering an effective route to optimize electrolytes for safe lithium metal batteries.     

Multiphoton lithography of nanocrystalline platinum and palladium for site-specific catalysis in 3D microenvironments

Integration of catalytic nanostructured platinum and palladium within 3D microscale structures or fluidic environments is important for systems ranging from micropumps to microfluidic chemical reactors and energy converters. We report a straightforward procedure to fabricate microscale patterns of nanocrystalline platinum and palladium using multiphoton lithography. These materials display excellent catalytic, electrical, and electrochemical properties, and we demonstrate high-resolution integration of catalysts within 3D defined microenvironments to generate directed autonomous particle and fluid transport.     

Microscale 3-D hydrogel scaffold for biomimetic gastrointestinal (GI) tract model

Here we describe a simple and efficient method for fabricating natural and synthetic hydrogels into 3-D geometries with high aspect ratio and curvature. Fabricating soft hydrogels into such shapes using conventional techniques has been extremely difficult. Combination of laser ablation and sacrificial molding technique using calcium alginate minimizes the stress associated with separating the mold from the hydrogel structure, and therefore allows fabrication of complex structures without damaging them. As a demonstration of this technique, we have fabricated a microscale collagen structure mimicking the actual density and size of human intestinal villi. Colon carcinoma cell line, Caco-2 cells, was seeded onto the structure and cultured for 3 weeks until the whole structure was covered, forming finger-like structures mimicking the intestinal villi covered with epithelial cells. This method will enable construction of in vitro tissue models with physiologically realistic geometries at microscale resolutions.     

石墨烯作为硫载体在锂硫电池中的研究进展

锂硫电池因其超高的理论能量密度以及硫资源丰富、成本低廉、无毒的优点,被认为是极具发展潜力与应用前景的新一代储能设备。然而,硫正极导电性差、体积膨胀以及穿梭效应严重等问题严重制约了其商业化应用。石墨烯具有高比表面积、高导电性和高柔韧性,并且易于进行表面化学修饰及组装,是一种理想的硫载体材料。本文主要综述了近年来三维石墨烯、表面化学修饰的石墨烯、石墨烯基复合材料以及石墨烯基柔性材料在锂硫电池正极中的研究现状,并展望了石墨烯作为硫载体在锂硫电池正极中的发展趋势。     

Wetting Phenomena and their Effect on the Electrochemical Performance of Surface‐Tailored Lithium Metal Electrodes in Contact with Cross‐linked Polymeric Electrolytes

Li metal batteries (LMBs) containing cross‐linked polymer electrolytes (PEs) are auspicious candidates for next‐generation batteries. However, the wetting behavior of PEs on uneven Li metal surfaces has been neglected in most studies. Herein, it is shown that microscale defect sites with curved edges play an important role in a wettability‐dependent electrodeposition. The wettability and the viscoelastic properties of PEs are correlated, and the impact of wettability on the nucleation and diffusion near the Li|PE interface is distinguished. It is found that the curvature of the edges is a key factor for the investigation of wetting phenomena. The appearance of microscale defects and phase separation are identified as main causes for erratic nucleation. It is emphasized that the implementation of stable and consistent long‐term cycling performance of LMBs using PEs requires a deeper understanding of the “soft‐solid”–solid contact between PEs and inherently rough Li metal surfaces.     

计算模拟在锂金属负极研究中的应用

锂金属以其高比容量和低电极电势,在高能量密度电池领域具有极大潜力,然而界面反应复杂、枝晶生长难以抑制等问题,导致电池易燃易爆、容易击穿短路,极大地限制了锂电池的应用。计算模拟有助于科研工作者认识反应机理、预测筛选电极材料以及优化电池设计,与实验相辅相成。本文对近年计算模拟在锂金属电极中的应用进行综述,重点在于利用分子动力学、第一性原理计算等计算方法,研究界面反应、固体电解质膜以及锂形核。此外,新开发的固态电解质很好地解决了传统锂电池易燃易爆等问题,提高了能量密度,但也存在界面阻力大、传导性能差以及枝晶生长等问题,对此,我们就计算模拟在固态电解质锂电池中锂负极的应用进行综述。最后,我们论述了该领域潜在研究方向。     

Synthesis of self-assembled 3D flowerlike SnS2 nanostructures with enhanced lithium ion storage property

In this work, we reported a facile ethanol solvothermal approach to fabricate highly dispersive 3D flowerlike SnS₂ architectures. The effects of synthetic conditions, such as the solvent system and the concentration of thiourea, on the morphology of the products were investigated. A possible growth mechanism for the formation of 3D flowerlike architectures was preliminarily propounded on the basis of the evolution of the structure and the morphology with increasing the reaction time. As anode materials of rechargeable Li-ion batteries, the as-prepared flowerlike SnS₂ structures exhibited exceptional good electrochemical properties, which revealed a higher reversible capacity about 502 mA h g^?1 and more stable cyclic retention at 50th cycle than the as-prepared SnS₂ nanoplates. The reasons for the improved electrochemical performance of the flowerlike structures have been proposed. All the results demonstrated that they were potential anode materials in Li-ion batteries.     

Partial Hydrolysis of Cyanide Coordination Polymers Induced by a Pillar Ligand with Optimized Electrochemical Kinetics for Rechargeable Alkaline Batteries

Coordination polymers are promising cathode materials for rechargeable alkaline batteries. Therefore, the precise modulation of these cathodes by chemical structure and in-depth structure transform study is necessary. Here, two model coordination polymer battery cathodes were designed to demonstrate the dynamic structure–performance relationship. We studied the electrochemical performance of two kinds of nickel-based coordination polymer, comprising a planar 2D cyanide-bridged network and a 3D cyanide-bridged network pillared by pyrazine molecules. The 2D coordination polymer showed serious voltage degradation with poor rate capability, whereas the 3D coordination polymer exhibited stable voltage output coupled with high rate at various current densities. The investigation revealed the underlining relationship of plateau voltage degradation and hydrolysis process of electrodes. It was revealed that the pyrazine pillar molecules in the 3D coordination polymer could suppress the hydrolysis and lead to the in situ formation of partially hydrolyzed structure with excellent electrochemical kinetics; this exhibited obvious smaller peak separation (27 mV compared with 149 mV) and hence an almost twofold increase in capacity retention (31.9 to 50.0 %) and energy density retention (18.2 to 35.9 %) at 10 A g⁻¹.     

ReaxFF MD局部区域反应追踪与物理性质可视化分析

Recently, the application of ReaxFF based reactive molecular dynamics simulation (ReaxFF MD) in complex processes of pyrolysis, oxidation and catalysis has attracted considerable attention. The analysis of the simulation results of these processes is challenging owing to the complex chemical reactions involved, coupled with their dynamic physical properties. VARxMD is a leading tool for the chemical reaction analysis and visualization of ReaxFF MD simulations, which allows the automated analysis of reaction sites to get overall reaction lists, evolution trends of reactants and products, and reaction networks of specified reactants and products. The visualization of the reaction details and dynamic evolution profiles are readily available for each reactant and product. Additionally, the detailed reaction sites of bond breaking and formation are available in 2D chemical structure diagrams and 3D structure views; for specified reactions, they are categorized on the basis of the chemical structures of the bonding sites or function groups in the reacting species. However, the current VARxMD code mainly focuses on global chemical reaction information in the simulation system of the ReaxFF MD, and is incapable of locally tracking the chemical reaction and physical properties in a 3D picked zone. This work extends the VARxMD from global analysis to a focused 3D zone picked interactively from the 3D visualization modules of VARxMD, as well as physical property analysis to complement reaction analysis. The analysis of reactions and physical properties can be implemented in three steps: picking and drawing a 3D zone, identifying molecules in the picked zone, and analyzing the reactions and physical properties of the picked molecules. A 3D zone can be picked by specifying the geometric parameters or drawing on a screen using a mouse. The picking of a cuboid or sphere was implemented using the VTK 3D view libraries by specifying geometric parameters. The interactive 3D zone picking was implemented using a combination of observer and command patterns in the VTK visualization paradigm. The chemical reaction tracking and dynamic radial distribution function (RDF) of the 3D picked zone was efficiently implemented by inheriting data obtained from the global analysis of VARxMD. The reaction tracking between coal particles in coal pyrolysis simulation and dynamic structure characterization of carbon rich cluster formation in the thermal decomposition of an energetic material are presented as application examples. The obtained detailed reactions between the coal particles and comparison of the reaction between the locally and globally picked areas in the cuboid are helpful in understanding the role of micro pores in coal particles. The carbon to carbon RDF analysis and comparison of the spherical region picked for the layered molecular clusters in the pyrolysis system of the TNT crystal model with the standard RDF of the 5-layer graphene demonstrate the extended VARxMD as a chemical structure characteristic tool for detecting the dynamic formation profile of carbon rich clusters in the pyrolysis of TNT. The extended capability of VARxMD for a 3D picked zone of a ReaxFF MD simulation system can be useful for interfacial reaction analysis in a catalysis system, hot spot formation analysis in the detonation of energetic material systems, and particularly the pyrolysis or oxidation processes of coal, biomass, polymers, hydrocarbon fuels, and energetic materials.     

石墨烯嵌锂的拉曼成像

锂离子电池由于具有高能量密度,高循环寿命,低自放电率的优势,成为当前使用最为广泛的储能器件。层状材料是极为常用的负极材料,其微观嵌锂行为的研究对提高电池的能量密度和循环寿命有重要意义。本工作发展了一种新的平板微电池结构,可用于研究锂离子在各类二维层状纳米材料中的嵌锂行为。我们用机械剥离的单片少层石墨烯为正极,热蒸镀的锂金属为负极,构成石墨烯电池,用恒电压放电的方法进行嵌锂测试。采用拉曼成像技术收集石墨烯G峰信号的空间分布,实现对锂的嵌入过程的显微观测。发现了锂在石墨烯中沿层间扩散迁移,以及石墨烯断层对锂扩散的阻碍作用。这些结果有助于理解放电时锂在石墨烯电极中扩散过程,并且这项研究开发的平板微电池结构可用于多种材料的电化学过程中的微观过程表征,同时可实现与光学、电学、电子显微学等多种表征手段的兼容,具有较好的应用前景。     

Ionic Liquid Mediated Synthesis of Lath Shaped CuO Micro‐Assembles as Extremely Stable Anode Material for Lithium‐Ion Batteries

A novel lath‐shaped CuO microassemble consisting of well‐crystalized ultrafine nanocrystals was prepared by an ionothermal method with the assistance of ionic liquids (ILs , 1‐butyl‐3‐methylimidazolium tetrafluoroborate). As anode material of lithium ion batteries, the ILs‐CuO exhibits high specific capacity, durability and good rate performance, superior to bare CuO . At a high current density of 1000 mA •g⁻¹, after 100 cycles, ILs‐CuO still retains a discharge capacity of 483.2 mAh •g⁻¹. The improved electrochemical performances could be ascribed to the unique microscale lath‐shape CuO assembles composed of ultrafine nanostructure.