Effect of nickel coating on electrochemical performance of graphite anodes for lithium ion batteries

Among the different materials often studied and proposed as negative electrodes for lithium-ion batteries, graphite anodes are the most used in commercial batteries. For this study, synthetic graphite was tested. During the first discharge 0.2 Li ions were consumed for the formation of the SEI film and the capacity reaches about 387 mAh/g. But at the end of the first charge only 72% of the initial charge was recovered (the reversible capacity is about 279 mAh/g). In order to improve this performance we have deposited metallic nickel on graphite with the intention to obtain a homogeneous thin layer able to modify the nature of the SEI film, to allow the diffusion of lithium ions through the protective layer, and also to increase the performance of graphite electrodes. The results show a decrease of the irreversible capacity loss (16% instead of 28% for pure graphite electrodes) as well as better cycleability for a nickel-deposited graphite electrode with only 11% weight ratio of nickel. On the other hand, an increase of the nickel content decreases this performance.     

Facile synthesis of N-doped carbon-coated Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode for application in high-rate lithium ion batteries

A facile sol-gel approach for the synthesis of lithium titanate composite decorated with N-doped carbon material (LTO/NC) is proposed. Urea is used as a nitrogen source in the proposed approach. The LTO/NC exhibits superior electrochemical performances as an electrode material for lithium-ion batteries, delivering a discharge capacity of as high as 103 mAh g^?1 at a high rate of 20 C and retaining a stable reversible capacity of 90 mAh g^?1 after 1000 cycles, corresponding to 100% capacity retention. These excellent electrochemical performances are proved by the nanoscale structure and N-doped carbon coating. NC layers were uniformly dispersed on the surface of LTO, thus preventing agglomeration, favoring the rapid migration of the inserted Li ion, and increasing the Li⁺ diffusion coefficient and electronic conductivity. LTO with the appropriate amount of NC coating is a promising anode material with applications in the development of high-powered and durable lithium-ion batteries.     

双相多孔锂离子电池液/固界面的声反射与声透射

采用传递矩阵法,同步联立改进的Biot理论,对含液固界面的双相多孔锂离子电池的超声反射与透射系数进行理论求解。考虑锂离子的摇摆特性对电极力学性能的影响,计算了对应状态下液/固界面的双相多孔锂离子电池声反射及透射系数的角度谱与频率谱。同时,构建了不同荷电状态时含单元锂离子电池的频域仿真模型,以萃取对应的超声反射及透射角度谱及频率谱,并与理论计算结果对比吻合良好。随后,以多单元锂离子电池为例,在不同的荷电状态下,分析了反射与透射系数随斜入射角度、入射波频率的变化关系,并分别指出了其角度谱及频率谱特征点随荷电状态的变化特征,为锂离子电池运行状态的超声无损测量提供了理论基础。     

Analysis of the Properties of Fractional Heat Conduction in Porous Electrodes of Lithium-Ion Batteries

Research on the heat transfer characteristics of lithium-ion batteries is of great significance to the thermal management system of electric vehicles. The electrodes of lithium-ion batteries are composed of porous materials, and thus the heat conduction of the battery is not a standard form of diffusion. The traditional heat conduction model is not suitable for lithium-ion batteries. In this paper, a fractional heat conduction model is used to study the heat transfer properties of lithium-ion batteries. Firstly, the heat conduction model of the battery is established based on the fractional calculus theory. Then, the temperature characteristic test was carried out to collect the temperature of the battery in various operating environments. Finally, the temperature calculated by the fractional heat conduction model was compared with the measured temperature. The results show that the accuracy of fractional heat conduction model is higher than that of traditional heat conduction model. The fractional heat conduction model can well simulate the transient temperature field of the battery. The fractional heat conduction model can be used to monitor the temperature of the battery, so as to ensure the safety and stability of the battery performance.     

Structure and ionic interactions of organic-inorganic composite polymer electrolytes studied by solid-state NMR and Raman spectroscopy

Solid-state NMR studies of composite polymer electrolytes are reported. The materials consist of polyethylene oxide and an organic inorganic composite, together with a lithium salt, and are candidates for electrolytes in solid-state lithium ion batteries. Silicon and aluminum MAS and multiple quantum MAS are used to characterize the network character of the organic-inorganic composite, and spin diffusion measurements are used to determine the nanostructure of the polymer/composite blending. Multiple quantum spin counting is used to measure the ion aggregation. The NMR results are supported by Raman spectra, calorimetry, and impedance spectroscopy. From these experiments it is concluded that the composite suppresses polymer crystallization without suppressing its local mobility, and also suppresses the tendency for the ions to aggregate. This polymer composite thus appears very promising for application in lithium ion batteries.     

Phenomenon of enhanced diffusion of lithium-ion in LiMn2O4 induced by electrochemical cycling

Lithium-ion diffusion in insertion-host materials is of significant interest because of its importance in improving the power density of lithium-ion batteries. In this study, the dependence of the chemical diffusion coefficient (D) of lithium-ion in spinel LiMn₂O₄ cathode material on electrochemical cycling has been investigated by the capacity intermittent titration technique (CITT). Results show that there are two minimum peaks in the curves of D∼E respectively at ∼3.95 and ∼4.12 V in the voltage range from 3.85 to 4.30 V. The curves of D∼E at different cycles show an interesting phenomenon that the values of D tend to increase with the cycling numbers. This phenomenon indicates an enhanced diffusion of lithium-ion in LiMn₂O₄ cathode material induced by the electrochemical cycling.     

锂离子电池负极材料CuSn的Li嵌入性质的研究

使用基于混合基表示的第一原理赝势法，研究了锂离子电池非碳类负极材料CuSn的Li嵌入时的形成能以及相应的电子结构.还给出了Li嵌入时的体积变化，能带结构、电子态密度以及电荷密度分布等性质, 并讨论了CuSn作为负极材料的特点.计算发现，Cu-Sn化合物在闪锌矿结构时，Li嵌入主体材料时的嵌入形成能大致在3.5eV附近. 关键词： 锂离子电池 负极材料 CuSn 电子结构     

冠醚对废旧锂离子电池浸出液中Li+选择性密度泛函理论研究

本文基于密度泛函理论研究了在水溶液中不同结构冠醚对Li~+的选择性.通过对几何结构、结合能和热力学的计算,发现15-冠-5(15C5)对Li~+的选择性强于12-冠-4(12C4)和18-冠-6(18C6).苯并15-冠-5(B15C5)与Li~+的结合能小于15C5,但在溶液巾结合Li~+时具有更低的自山能.研究了B15C5和Li、Co、Ni水合离子之间的交换反应,表明B15C5与水合锂离子之间的反应占据优势.上述结果表明采用B15C5从废旧钾离子电池浸出液中回收锂具有一定的可行性.     

Strategies to curb structural changes of lithium/transition metal oxide cathode materials & the changes' effects on thermal & cycling stability

Structural transformation behaviors of several typical oxide cathode materials during a heating process are reviewed in detail to provide in-depth understanding of the key factors governing the thermal stability of these materials. We also discuss applying the information about heat induced structural evolution in the study of electrochemically induced structural changes. All these discussions are expected to provide valuable insights for designing oxide cathode materials with significantly improved structural stability for safe, long-life lithium ion batteries, as the safety of lithium-ion batteries is a critical issue; it is widely accepted that the thermal instability of the cathodes is one of the most critical factors in thermal runaway and related safety problems.     

多层多孔锂离子电池结构的导波频散特征及其应用EI北大核心CSCD

采用状态矩阵与勒让德级数联合法,同步联立Biot理论,构建多层多孔锂离子电池声传播特性理论模型,以厚1.9 mm软包钴酸锂电池为例,数值分析了荷电状态(State of Charge,SOC)对多模态频散曲线的影响规律。同时,建立了电池中的声传播特性频域仿真模型,提取频域仿真中的超声导波频散曲线。此外,以体积小、柔性强的压电纤维复合材料(Macro Fiber Composite,MFC)为基础,实验探究了不同SOC对锂离子电池中声学行为的影响。采用互相关分析获取电池放电过程中声波渡越时间的偏移规律,建立了1.9 mm软包钴酸锂电池的声学波动行为与电池SOC间的映射关系。     

Structure and electrochemical characteristics of LiFePO4 cathode materials for rechargeable Li-Ion batteries

Complex investigations of cathode materials for rechargeable lithium-ion batteries have been carried out using the following techniques: scanning electron microscopy, microanalysis, extended X-ray absorption fine structure (EXAFS) spectroscopy, Mössbauer spectroscopy, and porosimetry. Investigations have been performed on samples prepared according to the original technology at the St. Petersburg State Institute of Technology (Technical University) (SPbSTI (TU)) and on four commercial cathode materials. It has been established that there is a correlation between the nanostructured morphology of the cathode materials, their chemical composition, and electrochemical capacity. It has been found that the internal resistance of the LiFePO₄ cathode material is linearly dependent on the diffusion coefficient of lithium ions. The valence state and local coordination of Fe ions have been studied using the ⁵⁷Fe Mössbauer effect. It has been shown that more than 90% of the iron ions are in the valence state Fe²⁺. Based on the data available in the literature on the methods of synthesizing LiFePO₄ and data on the diagnosis of the studied samples, conclusions have been drawn about a modification of the synthesis for producing high-quality cathode materials for Li-ion batteries.     

Theoretical prediction of honeycomb carbon as Li-ion batteries anode material

First principles calculations are performed to study the electronic properties and Li storage capability of honeycomb carbon. We find its right model consistent with the experimental result, the honeycomb carbon and its Li-intercalated configurations are all metallic which is beneficial to the electrode materials for lithium-ion batteries. The model 1 configuration shows fast Li diffusion and theoretical Li storage capacity of 319 mAh/g. Moreover, the average intercalation potentials for honeycomb carbon material is calculated to be low relatively. Our results suggest that the honeycomb carbon would be a new promising pure carbon anode material for Li-ion batteries.     

一种求解锂离子电池单粒子模型液相扩散方程的新方法

电解液中的锂离子浓度表达是锂离子电池电化学模型求解的基本任务之一.为了平衡单粒子模型的液相动态性能和计算效率,假设反应仅发生在集电极和电解质界面上,为此,提出一种基于液相扩散方程无穷级数解析解的界面浓度求解新方法.在恒流工况下,利用数列单调收敛准则将解析解转化为一个收敛和函数.在动态工况下,将该解析解简化为输入与和函数的无限离散卷积.利用和函数随时间单调衰减并收敛至零的特性对其进行截断,从而得到有限离散卷积求解算法.对比专业有限元分析软件,该方法在恒流工况和动态工况下均能以较少的计算时间获得相当好的精度.而且,该方法仅有一个配置参数.因此,所提方法将有效减小应用于实时电池管理系统上的电化学模型计算负担.     

一种求解锂离子电池单粒子模型液相扩散方程的新方法

电解液中的锂离子浓度表达是锂离子电池电化学模型求解的基本任务之一.为了平衡单粒子模型的液相动态性能和计算效率,假设反应仅发生在集电极和电解质界面上,为此,提出一种基于液相扩散方程无穷级数解析解的界面浓度求解新方法.在恒流工况下,利用数列单调收敛准则将解析解转化为一个收敛和函数.在动态工况下,将该解析解简化为输入与和函数的无限离散卷积.利用和函数随时间单调衰减并收敛至零的特性对其进行截断,从而得到有限离散卷积求解算法.对比专业有限元分析软件,该方法在恒流工况和动态工况下均能以较少的计算时间获得相当好的精度.而且,该方法仅有一个配置参数.因此,所提方法将有效减小应用于实时电池管理系统上的电化学模型计算负担.     

Hollow Silica Spheres Embedded in a Porous Carbon Matrix and Its Superior Performance as the Anode for Lithium‐Ion Batteries

Silica (SiO₂) is regarded as one of the most promising anode materials for lithium‐ion batteries due to the high theoretical specific capacity and extremely low cost. However, the low intrinsic electrical conductivity and the big volume change during charge/discharge cycles result in a poor electrochemical performance. Here, hollow silica spheres embedded in porous carbon (HSS–C) composites are synthesized and investigated as an anode material for lithium‐ion batteries. The HSS–C composites demonstrate a high specific capacity of about 910 mA h g^?1 at a rate of 200 mA g^?1 after 150 cycles and exhibit good rate capability. The porous carbon with a large surface area and void space filled both inside and outside of the hollow silica spheres acts as an excellent conductive layer to enhance the overall conductivity of the electrode, shortens the diffusion path length for the transport of lithium ions, and also buffers the volume change accompanied with lithium‐ion insertion/extraction processes.     

离子辐照引起的金属／绝缘体界面混合与相变研究

载能离子穿过固体界面引起界面原子迁移使界面原子混合和物质成分变化，从而导致界面发生材料相变。简要介绍了载能离子辐照引起金属／绝缘体界面混合效应及相变现象的主要实验研究进展、低能离子和高能离子辐照引起金属／绝缘体界面现象差异，并对离子辐照引起界面混合及相变的机制进行了初步探讨。When penetrating an interface between two kind of solids, energetic ions can induce atomic diffusion at both sides of the interface and then result in intermixing, atom re-distribution or composition change, as well as phase transformation. Main progress on the study of intermixing and phase change at metal/insulator interface induced by energetic ion irradiations, the difference of phenomena occurred at metal/insulator interfaces induced by high-and low-energy ions were briefly reviewed. Furthermore, the possible mechanisms related to intermixing and phase change at metal/insulator interface produced by energetic ion irradiations were also discussed in short words.     

Nb‐based MXenes for Li‐ion battery applications

Li‐ion batteries depend critically on the stability and capacity of the electrodes. In this respect the recently synthesized two‐dimensional MXenes are promising materials, as they combine an excellent Li‐ion capacity with very high charging rates. We employ density functional theory to investigate the impact of Li adsorption on the structural and electronic properties of monolayer Nb₂C and Nb₂CX₂. The Li ions are predicted to migrate easily on the pristine MXene due to a diffusion barrier of only 36 meV, whereas larger diffusion barriers are obtained for the functionalized MXenes. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Multinuclear NMR Study of Structure and Mobility in Cyclic Model Lithium Conducting Systems

The transport of the lithium ions is the basis of lithium ion conductivity of currently used electrolytes. Understanding how the transport of lithium ions within the matrix is influenced by the interactions with solvating moieties is needed to improve their performance. Along these lines well-defined model compounds based on cyclotriphosphazene (CTP) and hexaphenylbenzene (HPB) cores, bearing side groups of ethylene carbonate, a common solvent for lithium salts used as electrolytes in Li-ion batteries (Thielen et al. Chem. Mater, 23, 2120, 2011) and blended with different amounts of Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) have been studied by multinuclear nuclear magnetic resonance (NMR) spectroscopy. The local dynamics of the matrix was probed by ¹H and ³¹P NMR, while the local dynamics of the Li⁺ cations was unraveled by ⁷Li and ¹³C NMR. Transport of both ions was studied by pulsed-field gradient (PFG) NMR. Based on the different temperature dependences of the dynamics the bulk ion transport is not attributed to local dynamics, but to translational diffusion best characterized by PFG NMR. Although the glass transition temperatures of the blends are low, their conductivities are only in the range of typical polymer electrolytes. The results of NMR spectroscopy are in accord with the conjecture that the coordination between the cyclic carbonate functionality and the Li⁺-ion is too tight to allow for fast ion dynamics.     

用离子辐照模拟研究反应堆结构材料中金属/金属界面原子扩散行为

介绍了利用载能离子辐照模拟研究反应堆结构材料中金属／金属界面原子扩散行为的实验进展,特别是辐照参数（如辐照剂量、辐照温度、核能损、电子能损以及膜结构等）对界面原子扩散行为的影响,并对可能的机理进行了简要的评述。 Atom diffusion at metal/metal interfaces is very important for property of reactor structural materials, which can be simulated by using energetic ion irradiations. The present situation of experimental studies on atom diffusion at metal/metal interfaces induced by energetic ion irradiations is reviewed. The influence of experimental parameters such as the irradiation dose, irradiation temperature, electronic energy loss, nuclear energy loss and the interface structure on the intermixing is emphatically introduced. In addition, the possible mechanisms of metal/ metal intermixing are also briefly described.     

Identification of solid electrolyte interphase formed on graphite electrode cycled in trifluoroethyl aliphatic carboxylate-based electrolytes for low-temperature lithium-ion batteries

Trifluoroethyl aliphatic carboxylates with different length of carbon-chain in acyl groups have been introduced into carbonate-based electrolyte as co-solvents to improve the low-temperature performance of lithium-ion batteries, both in capacity retention and lowering polarization of graphite electrode. To identify the further influence of trifluoroethyl aliphatic carboxylates on graphite electrode, the components and properties of the surface film on graphite electrode cycled in different electrolytes are investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The IR and XPS results show that the chemical species of the solid electrolyte interphase (SEI) on graphite electrode strongly depend on the selection of co-solvent. For instance, among those species, the content of RCOOLi increases with an increasing number of carbon atoms in RCOOCH₂CF₃ molecule, wherein R was an alkyl with 1, 3, or 5 carbon atoms. We suggest that the thickness and components of the SEI film play a crucial role on the enhanced low-temperature performance of the lithium-ion batteries.