Thin film solid electrolytes and electrodes for rechargeable lithium-ion batteries

Various modifications of chemical vapour deposition (CVD), and electrostatic spray deposition (ESD) have been developed recently for the production of solid-state battery components. In addition, the DSM-Solufill^™ process will be explored for the production of thin films of these battery components. The principles of these techniques will be discussed, with examples of materials used for these thin film Li-ion batteries.     

锂离子电池热失控仿真研究进展

锂离子电池作为常见的储能和动力装置在生产生活中得到了广泛应用,但其在滥用条件下会引发热失控,对其安全性的研究很有必要.热失控仿真因其独有的优势,成为研究锂离子电池热失控的重要手段.本文通过对近期文献的研究,从热失控仿真、热蔓延仿真以及热失控仿真的应用三个方面对热失控仿真的研究现状进行了总结.着重介绍了不同诱因(热滥用、机械滥用和电滥用)导致热失控的产热机理和仿真方法,电池组内热蔓延仿真的研究现状和如何抑制热蔓延以及对热失控预测方法的研究.当前的热失控模型已经具有较好的精确度,可以模拟出电池发生热失控时主要的放热副反应,但电池内部十分复杂,混合了化学反应和物理变化,相关参数难以测量和计算,因此锂离子电池热失控仿真还需进一步研究.     

Research on thermal runaway test platform design for energy-storage lithium-ion batteries

介绍了锂离子储能电池热失控研究的目的和意义,探讨了储能电池与动力电池在热失控检测实验研究关注上的异同,从理论分析和实验研究两方面归纳了影响储能电池热失控的促发条件及对应的关键阈值.在此基础上,完成了模拟热失控促发条件和满足阈值要求的检测实验平台设计及功能验证,并对此平台的应用前景进行了展望.     

New anions as supporting electrolytes for rechargeable lithium batteries

Each of the two most commonly used salts in ambient-temperature rechargeable lithium batteries has problems involving safety and long-term stability. For example, solutions of LiClO₄ in 1,3-dioxolane are shock sensitive while LiAsF ₆/ether electrolytes degrade (both thermochemically and electrochemically) with time. Studies have been undertaken on the solubility, conductivity, and stability towards lithium of seven new lithium salts in both tetrahydrofuran (THF) and sulfolane. Of the seven salts, LiTaF₆, Li₂C₂F₄(SO₃)₂ and Li₂C₄F₈ (SO₃)₂ provide reasonable conductivities and good stability in sulfolane at 70 °C.     

Pure ionic liquid electrolytes compatible with a graphitized carbon negative electrode in rechargeable lithium-ion batteries

Ambient temperature ionic liquids composed of bis(fluorosulfonyl)imide (FSI) as an anion and 1-ethyl-3-methylimidazolium (EMI) or N-methyl-N-propylpyrrolidinium (P-13) as a cation have the following desirable physicochemical properties, particularly for a battery electrolyte: a high ionic conductivity, low viscosity, and a low melting point. While an irreversible cationic intercalation into graphene interlayers at ca. 0.5 V versus Li/Li⁺ has been a significant and common problem with usual ionic liquids, we found that ionic liquids containing FSI with the Li cation can prevent such an irreversible reaction and provide reversible Li intercalation into graphene interlayers. Our experimental results found the reversible capacity of a graphite negative electrode, in a half-cell with EMI-FSI containing the Li cation as an electrolyte, to be a stable value of approximately 360 mAh g⁻¹ during 30 cycles at a charge/discharge rate of 0.2 C, The present paper may be the first report that a “pure” ionic liquid can provide a stable, reversible capacity for a graphitized negative electrode at an ambient temperature without any additives or solvents when an appropriate counter anion, e.g., FSI, is selected.     

Development of coin-type lithium-ion rechargeable batteries

We developed coin-type lithium-ion rechargeable batteries made of crystalline V₂O₅ for the cathode and pitch-based carbon for the anode. We optimized the capacity balance of cathode and anode materials. The batteries have a high operating voltage of about 2.7 V and excellent charge/discharge cycle characteristics. We also designed the batteries whose cathode potential is over 3 V versus lithium when the batteries are overdischarged to 0 V. Therefore, the batteries have excellent recovery characteristics even after overdischarge. The batteries have high energy density (about 100 Wh/l) which is about two times that of the coin-type NiCd batteries. It can serve as a memory backup power source with a single battery.     

Ionic liquid and plastic crystalline phases of pyrazolium imide salts as electrolytes for rechargeable lithium-ion batteries

A new member of the plastic crystal, pyrazolium imide family, N,N′-diethyl-3-methylpyrazolium bis-(trifluoromethanesulfonyl)imide (DEMPyr123) was prepared. It showed a single, plastic crystalline phase that extends from 4.2 °C to its melting at 11.3 °C. When 10 mol% LiTFSI salt was added, the mixture showed ionic conductivities reaching 1.7 × 10⁻³ S cm⁻¹ at 20 °C, in the liquid state and 6.9 × 10⁻⁴ S cm⁻¹ at 5 °C, in the solid, plastic phase. A wide electrochemical stability window's of 5.5 V was observed by cyclic voltammetry of the molten salt mixture. Batteries were assembled with LiFePO₄/Li₄Ti₅O₁₂ electrodes and the salt mixture as an electrolyte. They showed a charge/discharge efficiency of 93% and 87% in the liquid and the plastic phase, respectively. The capacity retention was very good in both states with 90% of the initial capacity still available after 40 cycles. In general, the batteries showed good rate capability and cycle life performance in the ionic liquid phase that were sustained when the electrolyte transformed to the plastic phase. Comparison of the battery results with those of a classic (non-plastic crystal) ionic liquid has proven the advantage of the dual state of matter character in this electrolyte.     

Characterization of low-flammability electrolytes for lithium-ion batteries

In an effort to develop low-flammability electrolytes for a new generation of Li-ion batteries, we have evaluated physical and electrochemical properties of electrolytes with two novel phosphazene additives. We have studied performance quantities including conductivity, viscosity, flash point, and electrochemical window of electrolytes as well as formation of solid electrolyte interphase (SEI) films. In the course of study, the necessity for a simple method of SEI characterization was realized. Therefore, a new method and new criteria were developed and validated on 10 variations of electrolyte/electrode substrates. Based on the summation of determined physical and electrochemical properties of phosphazene-based electrolytes, one structure of phosphazene compound was found better than the other. This capability helps to direct our further synthetic work in phosphazene chemistry.     

Ceramic and polymeric solid electrolytes for lithium-ion batteries

Lithium-ion batteries are important for energy storage in a wide variety of applications including consumer electronics, transportation and large-scale energy production. The performance of lithium-ion batteries depends on the materials used. One critical component is the electrolyte, which is the focus of this paper. In particular, inorganic ceramic and organic polymer solid-electrolyte materials are reviewed. Solid electrolytes provide advantages in terms of simplicity of design and operational safety, but typically have conductivities that are lower than those of organic liquid electrolytes. This paper provides a comparison of the conductivities of solid-electrolyte materials being used or developed for use in lithium-ion batteries.     

Crosslinkable fumed silica-based nanocomposite electrolytes for rechargeable lithium batteries

Electrochemical and rheological properties are reported of composite polymer electrolytes (CPEs) consisting of dual-functionalized fumed silica with methacrylate and octyl groups + low-molecular weight poly(ethylene glycol) dimethyl ether (PEGdm) + lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, lithium imide) + butyl methacrylate (BMA). The role of butyl methacrylate, which aids in formation of a crosslinked network by tethering adjacent fumed silica particles, on rheology and electrochemistry is examined together with the effects of fumed silica surface group, fumed silica weight percent, salt concentration, and solvent molecular weight. Chemical crosslinking of the fumed silica with 20% BMA shows a substantial increase in the elastic modulus of the system and a transition from a liquid-like/flocculated state to an elastic network. In contrast, no change in lithium transference number and only a modest decrease (factor of 2) on conductivity of the CPE are observed, indicating that a crosslinked silica network has minimal effect on the mechanism of ionic transport. These trends suggest that the chemical crosslinks occur on a microscopic scale, as opposed to a molecular scale, between adjacent silica particles and therefore do not impede the segmental mobility of the PEGdm. The relative proportion of the methacrylate and octyl groups on the silica surface displays a nominal effect on both rheology and conductivity following crosslinking although the pre-cure rheology is a function of the surface groups. Chemical crosslinked nanocomposite polymer electrolytes offer significant higher elastic modulus and yield stress than the physical nanocomposite counterpart with a small/negligible penalty of transport properties. The crosslinked CPEs exhibit good interfacial stability with lithium metal at open circuit, however, they perform poorly in cycling of lithium–lithium cells.     

Composite gel-type polymer electrolytes for advanced,rechargeable lithium batteries

The main goal of this work was to determine whether the dispersion of ceramic fillers have any promotion effect on the properties of solid-like, gel-type lithium conducting polymer electrolytes. Using a series of different but complementary techniques, which included SEM analysis, voltammetry and impedance spectroscopy, we demonstrate that the dispersion of surface functionalized fumed silica and alumina, respectively, to PVdF–carbonate solvent–lithium salt systems, while not greatly influencing the transport properties, does stabilize the lithium metal interface and the mechanical properties of the resulting composite GPE electrolytes. The relevance of these features in view of practical application is here demonstrated by the response of lithium batteries based on selected GPEs.     

Industrial progress of nonaqueous liquid electrolytes for lithium-ion batteries

电解质是锂离子电池的关键材料,作为锂离子传输的媒介,其选择直接影响锂离子电池的能量密度、循环性能、倍率性能、储存性能及安全性等特性。我国电解液产业经过十多年的快速发展,已经具备了一定的国际竞争力。本文以锂离子电池电解液产业国产化进程为切入点,梳理了该产业的发展脉络,对国内电解液企业的市场份额和竞争格局进行了重点剖析;以电解液常用添加剂的专利持有情况为例,评述了国内外主要企业在电解液专利申请方面的差别;介绍了3C电池电解液、动力电池电解液、储能电池电解液以及功能性电解液等四大类产品的性能特点,着重阐述了前两类产品的设计开发思路;对我国锂离子电池电解液行业标准亦作了简述;展望了电解液材料的技术发展方向和产业前景。     

Thermal stability and flammability of electrolytes for lithium-ion batteries

Safety is the key-feature of large-size lithium-ion batteries and thermal stability of the electrolytes is crucial. We investigated the thermal and flammability properties of mixed electrolytes based on the conventional ethylene carbonate-dimethyl carbonate (1:1 wt/wt)-1 M LiPF₆ and the hydrophobic ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI). The results of thermogravimetric analyses and flammability tests of mixed electrolytes of different compositions are reported and discussed. An important finding is that though the mixtures with high contents of ionic liquid are more difficult to ignite, they burn for a longer time, once they are ignited.     

Recent progress in rechargeable nickel/metal hydride and lithium-ion miniature rechargeable batteries

VARTA is searching for alternative battery solutions for memory back-up and bridging applications, and for this, it is developing nickel/metal hydride and lithium-ion button cells. Presented are the results on different sizes and forms of lithium-ion cells (621, 1216 and 2025) containing different electrode materials and shapes. Presently, the most favoured cathode material is lithiated manganese dioxide. The electrodes are made from both solid and porous materials and, together with an organic electrolyte, result in a cell system with a voltage level of approximately three. Included are results, both from these lithium-ion cells, and also from ones using the nickel/metal hydride system.     

Polymer electrolytes containing guanidinium-based polymeric ionic liquids for rechargeable lithium batteries

The electrochemical properties of solvent-free, quaternary polymer electrolytes based on a novel polymeric ionic liquid (PIL) as polymer host and incorporating 1g13TFSI ionic liquid, LiTFSI salt and nano-scale silica are reported. The PIL-LiTFSI-1g13TFSI-SiO₂ electrolyte membranes are found to be chemically stable even at 80 °C in contact with lithium anode and thermally stable up to 320 °C. Particularly, the quaternary polymer electrolytes exhibit high lithium ion conductivity at high temperature, wide electrochemical stability window, time-stable interfacial resistance values and good lithium stripping/plating performance. Batteries assembled with the quaternary polymer electrolyte at 80 °C are capable to deliver 140 mAh g⁻¹ at 0.1C rates with very good capacity retention.     

Room temperature rechargeable polymer electrolyte batteries

Polyacrylonitrile (PAN)- and poly(vinyl chloride) (PVC)-based Li⁺-conductive thin-film electrolytes have been found to be suitable in rechargeable Li and Li-ion cells. Li/Li_xMn₂O_y and carbon/LiNiO₂ cells fabricated with these electrolytes have demonstrated rate capabilities greater than the C-rate and more than 375 full depth cycles. Two-cell carbon/LiNiO₂ bipolar batteries could be discharged at pulse currents as high as 50 mA/cm².     

Properties and potential application of silica-gelled electrolytes for lithium-ion batteries

The properties of gelled electrolytes based on liquid organic electrolytes are investigated. The gelation agents are highly dispersed silica (HDS) which are added in a quantity of a few wt.%. Drying conditions for the HDS are described as well as the analytical values for the residual water. Two basically different types of HDS are investigated: (i) hydrophilic and (ii) hydrophobic material. Whereas the hydrophilic HDS contains SiOH groups on the surface of the silica particles, in the hydrophobic HDS, these SiOH are normally methylated. With hydrophilic HDS, thixotropic gels can be prepared. Conductivity data for EC—DMC/LiTFMSI gels are comparable with the values obtained for the liquid electrolyte. The electrochemical stability window for such a gel electrolyte is at least between 0–4, 1 V versus lithium. Metallic lithium and the intercalation cathodes (LiCoO₂, LiMn₂O₄) can be reversibly cycled in this electrolyte. No specific detremental effects due to the addition of HDS were observed.     

Electrochemical performance of a tin-coated carbon fibre electrode for rechargeable lithium-ion batteries

An Sn-carbon fibre composite electrode is fabricated by electrodepositing a thin film (0.5 ± 0.1 μm) of Sn with an ultrafine grain size (350 ± 50 nm) on the 7.5 ± 1.5 μm diameter fibres of a carbon fibre paper (CFP). The electrochemical performance of the Sn-CFP composite being considered as an anode material for rechargeable Li-ion batteries is evaluated by conducting galvanostatic charge-discharge cycling tests. The Sn-CFP electrode displays a reversible planar capacity of 2.96 mAh cm⁻² with a capacity retention of 50% after twenty cycles, compared to the 23% measured for a 2.2 ± 0.2 μm thick Sn coating deposited on a Cu foil. The enhanced cycling performance of the Sn-CFP electrode is attributed to the double role played by carbon fibres, which act as randomly oriented current collectors in addition to being an active material. The small thickness and large surface area of the Sn coating on the carbon fibres enhances the coating's chemical reactivity and tolerance for volume change. It is suggested that transforming Sn to Sn oxides in Sn-CFP electrodes may improve the cycling performance of these composites as anode materials for rechargeable Li-ion batteries.