Neutron-based characterization techniques for lithium-ion battery research

During the past decades, Li-ion batteries have been one of the most important energy storage devices. Large-scale energy storage requires Li-ion batteries which possess high energy density, low cost, and high safety. Other than advanced battery materials, in-depth understanding of the intrinsic mechanism correlated with cell reaction is also essential for the development of high-performance Li-ion battery. Advanced characterization techniques, especially neutron-based techniques,have greatly promoted Li-ion battery researches. In this review, the characteristics or capabilities of various neutron-based characterization techniques, including elastic neutron scattering, quasi-elastic neutron scattering, neutron imaging, and inelastic neutron scattering, for the related Li-ion-battery researches are summarized. The design of in-situ/operando environment is also discussed. The comprehensive survey on neutron-based characterizations for mechanism understanding will provide guidance for the further study of high-performance Li-ion batteries.     

用于全固态锂电池的有机-无机复合电解质

固态电解质被认为是解决传统液态锂金属电池安全隐患和循环性能的关键材料，但仍然存在离子电导率低，界面兼容性差等问题.设计兼顾力学性能、离子电导率和电化学窗口的有机-无机复合型固态电解质材料是发展全固态锂电池的明智选择.近年来，基于无机填料与聚合物电解质的有机-无机复合电解质备受关注.设计与优化复合电解质结构对提高复合电解质综合性能具有重要意义.本文详细梳理了有机-无机复合固态电解质在全固态锂电池中展现的多方面优势，从满足不同性能需求的复合电解质结构设计角度出发，综述了有机-无机复合电解质在锂离子传导、锂枝晶的抑制、界面稳定性和相容性等方面的研究进展，并对有机-无机复合电解质的未来发展趋势和方向进行了展望.     

All-solid-state thick-film battery

An all-solid-state Li-ion secondary battery based on Li/LiSiPO/LiCoO₂ has been developed and the cell performance has been evaluated. The electrolyte and cathode were fabricated by tape casting. The charge and discharge behaviour of the cell at constant current was investigated in view of the fact of lower conductivities of solid conductors compared to liquid electrolytes and the internal resistance of the solid-solid interface. Solutions to these problems have been investigated by varying the fabrication methods. A major advantage was the application of pyrolyzable pore formers in the cathode green tape in order to produce a porous cathode matrix. This result indicates that the interfacial contacts between solid electrolytes and electrodes can be greatly improved. Also, the internal resistance may be further decreased by tape casting of thinner electrolyte films. In conclusion, the tape casting method is very promising for the development of high performance all-solid-state Li-ion batteries.     

High-throughput theoretical design of lithium battery materials

The rapid evolution of high-throughput theoretical design schemes to discover new lithium battery materials is reviewed, including high-capacity cathodes, low-strain cathodes, anodes, solid state electrolytes, and electrolyte additives.With the development of efficient theoretical methods and inexpensive computers, high-throughput theoretical calculations have played an increasingly important role in the discovery of new materials. With the help of automatic simulation flow,many types of materials can be screened, optimized and designed from a structural database according to specific search criteria. In advanced cell technology, new materials for next generation lithium batteries are of great significance to achieve performance, and some representative criteria are: higher energy density, better safety, and faster charge/discharge speed.     

Thermal transport in phosphorene and phosphorene-based materials: A review on numerical studies

The recently discovered two-dimensional(2D) layered material phosphorene has attracted considerable interest as a promising p-type semiconducting material. In this article, we review the recent advances in numerical studies of the thermal properties of monolayer phosphorene and phosphorene-based heterostructures. We first briefly review the commonly used first-principles and molecular dynamics(MD) approaches to evaluate the thermal conductivity and interfacial thermal resistance of 2D phosphorene. Principles of different steady-state and transient MD techniques have been elaborated on in detail. Next, we discuss the anisotropic thermal transport of phosphorene in zigzag and armchair chiral directions. Subsequently, the in-plane and cross-plane thermal transport in phosphorene-based heterostructures such as phosphorene/silicon and phosphorene/graphene is summarized. Finally, the numerical research in the field of thermal transport in 2D phosphorene is highlighted along with our perspective of potentials and opportunities of 2D phosphorenes in electronic applications such as photodetectors, field-effect transistors, lithium ion batteries, sodium ion batteries, and thermoelectric devices.     

L型石墨纳米结的热输运

利用非平衡格林函数方法研究了由半无限长扶手椅型和锯齿型边界石墨纳米带连接而成的L型石墨纳米结的热输运性质.结果表明,L型石墨纳米结的热导依赖于L型石墨纳米结的夹角和石墨纳米带的宽度.在L型石墨纳米结的夹角从30°增加到90°再增加到150°过程中,其热导显著增大.夹角为90°的L型石墨纳米结的热导随着扶手椅型纳米带宽度增加时,在低温区热导随着宽度的增大而降低,在高温区热导随宽度的增大而升高.对于夹角为150°的L型石墨纳米结,其热导无论是在低温区还是在高温区都随着锯齿型纳米带宽度的增加而降低.利用声子透射谱对这些热输运现象进行了合理的解释.研究结果阐明了不同L型石墨纳米结中的热输运机理,为设计基于石墨纳米结的热输运器件提供了重要的物理模型和理论依据. 关键词： 石墨纳米结 热输运 热导     

Nanomaterials for electrochemical energy storage

The development of nanotechnology in the past two decades has generated great capability of controlling materials at the nanometer scale and has enabled exciting opportunities to design materials with desirable electronic, ionic, photonic, and mechanical properties. This development has also contributed to tile advance in energy storage, which is a critical technology in this century. In this article, we will review how the rational design of nanostructured materials has addressed the challenges of batteries and electrochemical capacitors and led to high-performance electrochemical energy storage devices. Four specific material systems will be discussed： i） nanostructured alloy anodes for Li-batteries, ii） nanostructured sulfur cathodes for Li-batteries, iii） nanoporous open- framework battery electrodes, and iv） nanostructured electrodes for electrochemical capacitors.     

电动汽车锂离子电池热管理系统研究进展

锂离子电池作为电动汽车最广泛使用的动力源,对工作温度高度敏感,为保证其高性能和安全运行,电池热管理系统必不可少.本文综述了近年来锂离子电池热管理系统的研究进展.首先讨论了由高低温环境和电池温度不均匀引起的临界热问题.在此基础上,对设计原则和现有的电池热管理系统进行了广泛的介绍和阐述.然后进一步分析了用于未来电池热管理系统的热电器件和内部加热方法等新兴技术.分析表明,被动和主动冷却/加热方法的组合有望满足苛刻的热要求,特别是在功率波动剧烈的动态条件下.此外,电池在变工况下所输出的电流、电压等均不相同,因此建议对电动汽车动力电池进行动态性能实时管理,从而延长电池使用寿命。     

Review of 5-V electrodes for Li-ion batteries: status and trends

Lithium-ion batteries have dominated the battery industry for the past several years in portable electronic devices due to their high volumetric and gravimetric energy densities. The success of these batteries in small-scale applications translates to large-scale applications, with an important impact in the future of the environment by improving energy efficiency and reduction of pollution. We present the progress that allows several lithium-intercalation compounds to become the active cathode element of a new generation of Li-ion batteries, namely the 5-V cathodes, which are promising to improve the technology of energy storage and electric transportation, and address the replacement of gasoline engine by meeting the increasing demand for green energy power sources. The compounds considered here include spinel LiNi_0.5Mn_1.5O₄ and its related doped-structures, olivine LiCoPO₄, inverse spinel LiNiVO₄ and fluorophosphate Li₂CoPO₄F. LiNi_0.5Mn_1.5O₄ thin films, nanoscale prepared materials and surface-modified cathode particles are also considered. Emphasis is placed on the quality control that is needed to guarantee the reliability and the optimum electrochemical performance of these materials as the active cathode element of Li-ion batteries. The route to increase the performance of Li-ion batteries with the other members of the family is also discussed.     

A molecular dynamics study on interfacial heat transport of alkanethiol surfactant coated nanofluids-effect of chain length and stiffness

The thermal transport across the alkanethiol surfactant layer at the nanoparticle/base fluid interface in nanofluids was investigated by molecular dynamics simulation, with consideration of the conformation of the surfactant layer with different surfactant chain lengths and backbone stiffness. The variation of temperature drop at nanoparticle-surfactant interface reveals that the interfacial thermal conductance was mediated by the chain length, possibly due to the difference in the adsorption density of surfactant on the surface of the nanoparticles, because of the blocking effect from the bending of the long alkyl chains. The intrinsic thermal conductivity of the surfactant layer increased with decreasing chain length and increasing chain stiffness because of the phonon scattering effect from the bending and cross-linking of the alkyl chains. We quantified the modes of heat flow across the surfactant layer and found that the contribution of intramolecular bonded interaction was much higher than that of atomic translation and nonbonded interaction separately. By analysing the variation of bonded interaction contrition with chain length and stiffness, it is demonstrated that the increased thermal conductivities benefited from the enhanced thermal transfer through the covalent bonds of surfactant molecules. The results can provide insights into the design of thermally conductive surfactants.     

Thermal properties of transition-metal dichalcogenide

Beyond graphene, the layered transition metal dichalcogenides(TMDs) have gained considerable attention due to their unique properties. Herein, we review the lattice dynamic and thermal properties of monolayer TMDs, including their phonon dispersion, relaxation time, mean free path(MFP), and thermal conductivities. In particular, the experimental and theoretical studies reveal that the TMDs have relatively low thermal conductivities due to the short phonon group velocity and MFP, which poses a significant challenge for efficient thermal management of TMDs-based devices. Importantly,recent studies have shown that this issue could be largely addressed by connecting TMDs and other materials(such as metal electrode and graphene) with chemical bonds, and a relatively high interfacial thermal conductance(ITC) could be achieved at the covalent bonded interface. The ITC of MoS_2/Au interface with chemical edge contact is more than 10 times higher than that with physical side contact. In this article, we review recent advances in the study of TMD-related ITC.The effects of temperature, interfacial vacancy, contact orientation, and phonon modes on the edge-contacted interface are briefly discussed.     

低维纳米材料量子热输运与自旋热电性质 ——非平衡格林函数方法的应用

低维材料不断涌现的新奇性质吸引着科学研究者的目光. 除了电子的量子输运行为之外, 人们也陆续发现和确认了热输运中显著的量子行为, 如 热导低温量子化、声子子带、尺寸效应、瓶颈效应等. 这些小尺度体系的热输运性质可以很好地用非平衡格林函数来描述. 本文首先介绍了量子热输运的特性、声子非平衡格林函数方法及其在低维纳米材料中的研究进展; 其次回顾了近年来在 一系列低维材料中发现的热-自旋输运现象. 这些自旋热学现象展现了全新的热电转换机制, 有助于设计新型的热电转换器件, 同时也给出了用热产生自旋流的新途径; 最后介绍了线性响应理论以及在此理论框架下结合声子、电子非平衡格林函数方法进行的一些有益的探索. 量子热输运的研究对热效应基础研究以及声子学器件、能量转换器件的发展有着不可替代的重要作用.     

Interfacial water studies and their relevance for the energy sector

ABSTRACT

Interfacial water is ubiquitous, and its investigation has attracted the interest of many for both fundamental and applied purposes. This perspective provides a few highlights concerning how molecular and sometimes multi-scale investigations on the properties of interfacial water could be of practical relevance for the energy sector. The discussion focuses on the transport of electrolytes through narrow pores, and on the solubility and transport properties of confined hydrocarbons, with particular attention in attempting to describe how interfacial water can affect such properties, especially within narrow pores. Recent results on the self-assembly of surfactants on heterogeneous surfaces are also briefly discussed. Finally, a few possible directions for future research are suggested. It should be stressed that this is not a comprehensive review on the possible impact of interfacial water studies on the energy sector, but rather a brief commentary on some personal interests, with the intent of stimulating debate.     

A brief review of thermal transport in mesoscopic systems from nonequilibrium Green’s function approach

With the rapidly increasing integration density and power density in nanoscale electronic devices, the thermal management concerning heat generation and energy harvesting becomes quite crucial. Since phonon is the major heat carrier in semiconductors, thermal transport due to phonons in mesoscopic systems has attracted much attention. In quantum transport studies, the nonequilibrium Green’s function (NEGF) method is a versatile and powerful tool that has been developed for several decades. In this review, we will discuss theoretical investigations of thermal transport using the NEGF approach from two aspects. For the aspect of phonon transport, the phonon NEGF method is briefly introduced and its applications on thermal transport in mesoscopic systems including one-dimensional atomic chains, multi-terminal systems, and transient phonon transport are discussed. For the aspect of thermoelectric transport, the caloritronic effects in which the charge, spin, and valley degrees of freedom are manipulated by the temperature gradient are discussed. The time-dependent thermoelectric behavior is also presented in the transient regime within the partitioned scheme based on the NEGF method.     

Li-ion batteries: Phase transition

Progress in the research on phase transitions during Li+extraction/insertion processes in typical battery materials is summarized as examples to illustrate the significance of understanding phase transition phenomena in Li-ion batteries.Physical phenomena such as phase transitions(and resultant phase diagrams) are often observed in Li-ion battery research and already play an important role in promoting Li-ion battery technology. For example, the phase transitions during Li+insertion/extraction are highly relevant to the thermodynamics and kinetics of Li-ion batteries, and even physical characteristics such as specific energy, power density, volume variation, and safety-related properties.     

Cruising in ceramics—discovering new structures for all-solid-state batteries—fundamentals,materials, and performances

Energy storage research has drawn much attention recently due to increasing demand for carbon neutral electrical energy from renewable energy sources such as solar, wind, and hydrothermal. Various electrochemical energy storage and conversion technologies are being considered for their integration into smart grid systems, of which batteries seem to play a vital role due to their wide range of energy densities. In this review, we provide the current status and recent advances in solid-state (ceramic) electrolytes based on inorganic compounds for all-solid-state batteries. This paper is specifically focused on the fundamentals, materials, and performances of solid electrolytes in batteries. A wide spectrum of inorganic solid-state electrolytes is presented in terms of their chemical composition, crystal structure, and ion conduction mechanism. Furthermore, the advantages and main issues associated with different types of inorganic solid electrolytes, including β-alumina, NASICON and LISICON-type, perovskites, and garnet-type for all-solid-state batteries are presented. Among these solid electrolytes, Zr and Ta-based Li-stuffed garnets exhibit high Li-ion conductivity, electrochemical stability window (up to 6  V/Li at room temperature), and chemical stability against reaction with molten elemental Li. However, their stability under humidity and carbon dioxide should be improved to decrease the fabrication and operational costs.     

Impact of thermostat on interfacial thermal conductance prediction from non-equilibrium molecular dynamics simulations

The knowledge of interfacial thermal conductance (ITC) is key to understand thermal transport in nanostructures. The non-equilibrium molecular dynamics (NEMD) simulation is a useful tool to calculate the ITC. In this study, we investigate the impact of thermostat on the prediction of the ITC. The Langevin thermostat is found to result in larger ITC than the Nose-Hoover thermostat. In addition, the results from NEMD simulations with the Nose-Hoover thermostat exhibit strong size effect of thermal reservoirs. Detailed spectral heat flux decomposition and modal temperature calculation reveal that the acoustic phonons in hot and cold thermal reservoirs are of smaller temperature difference than optical phonons when using the Nose-Hoover thermostat, while phonons in the Langevin thermostat are of identical temperatures. Such a non-equilibrium state of phonons in the case of the Nose-Hoover thermostat reduces the heat flux of low-to-middle-frequency phonons. We also discuss how enlarging the reservoirs or adding an epitaxial rough wall to the reservoirs affects the predicted ITC, and find that these attempts could help to thermalize the phonons, but still underestimate the heat flux from low-frequency phonons.     

聚噻吩单链量子热输运的第一性原理研究

聚噻吩块体通常被视为绝热材料,其热导率小于1W·m~(-1)·K~(-1).但近年发现对于室温下沿聚噻吩分子链方向排列的无定形聚噻吩纳米纤维,其热导率高于聚噻吩块体,可达4.4W·m~(-1)·K~(-1).为了相对准确地揭示纳米尺度聚噻吩单链热输运的微观特征,从量子力学出发,在密度泛函理论计算的基础上,应用中间插入延展方法结合非平衡格林函数方法,对长度为25.107nm、包含448个原子的聚噻吩单链的量子热输运及其同位素效应进行了研究,并与分子动力学方法模拟的结果进行了详细比较.结果表明:室温下32 nm长的纯聚噻吩单链热导率上限高达30.2 W·m~(-1)·K~(-1),与铅的热导率35 W·m~(-1).K~(-1)相近;相同掺杂比例(原子百分数)下C元素热导的同位素效应比S元素显著;室温下聚噻吩单链中~(12)C,~(13)C等比例随机掺杂时的同位素效应最为显著,此时聚噻吩单链的平均热导至少降低了30%;室温下纯聚噻吩单链的热导随C的相对原子质量增加近似呈反比例减小,随S的相对原子质量增加呈非线性单调增加.该研究对认识和调控聚噻吩这种新型功能材料的热输运特性具有积极的价值.     

Scientific and technological challenges toward application of lithium–sulfur batteries

Recent progress in improving Li–S batteries' cathodes, anodes, and electrolytes via different approaches is summarized. The poor conductivity of sulfur cathodes, the dissolution of polysulfide intermediates, and the high reactivity of metal Li anodes currently motivate a great deal of research. Urgent challenges concerning Li anodes are also emphasized.     

多空穴错位分布对石墨纳米带中热输运的影响

利用非平衡格林函数方法研究了石墨纳米带中三空穴错位分布对热输运性质的影响.研究结果发现:三空穴竖直并排结构对低频声子的散射较小,导致低温区域三空穴竖直并排时热导最大,而在高频区域,三空穴竖直并排结构对高频声子的散射较大,导致较高温度区域三空穴竖直并排时热导最小;三空穴的相对错位分布仅能较大幅度地调节面内声学模高频声子的透射概率,而三空穴的相对错位分布能较大幅度地调节垂直振动膜高频声子和低频声子的透射概率,导致三空穴的相对错位分布不仅能大幅调节面内声学模和垂直振动模的高温热导,也能大幅调节垂直振动模的低温热导.研究结果阐明了空穴位置不同的石墨纳米带的热导特性,为设计基于石墨纳米带的热输运量子器件提供了有效的理论依据.