Safety evaluation of rechargeable cells with lithium metal anodes and amorphous V2O5 cathodes

Rechargeable cells with lithium metal anodes have a very large theoretical energy density and are a promising cell system. However, rechargeable lithium metal cells are not yet currently commercially available. One of the biggest problems with the cells is the poor safety aspect resulting from the high chemical reactivity of lithium. We have been studying a cell system consisting of an amorphous (a-)V2O5P2O5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte in fabricating an AA-size prototype. In this paper, we report recent progress on our rechargeable lithium metal cell focusing on its safety.     

Cycling performance and safety of rechargeable lithium cells with binary and ternary mixed solvent electrolytes

The influence of electrolyte composition on the cycling performance and safety of AA rechargeable cells with a lithium metal anode, and an amorphous (a-) V₂O₅-P₂O₅ cathode was examined. The cells were cycled at a discharge current of 1000 mA and a charging current of 200 mA. The electrolytes were composed of ethylene carbonate (EC)/2-methyltetrahydrofuran (2MeTHF) binary and EC/propylene carbonate (PC)/2MeTHF ternary mixed solvents containing 40–70 vol% 2MeTHF to provide higher conductivity. The solute was 1.5mol dm^–3 LiAsF₆. The cycle life of the AA cells was evaluated by setting the end of cycle life at the cycle number where the discharge capacity fell to 50% of its maximum value. Cells with EC/2MeTHF (50:50) exhibited the longest cycle life among all the electrolytes examined here. Cells with EC/PC/2MeTHF (15:45:40) had the longest cycle life among the ternary mixed solvents systems. Fundamental abuse tests were also carried out on AA cells, which were cycled twice (fresh cells), cycled 100 times and cycled until the end of their cycle life. Neither the fresh nor the cycled cells with EC/PC/2MeTHF (15:45:40 ) smoked nor ignited in a 150 °C heating test or in an external short circuit test. However, the fresh cell with EC/2MeTHF (50:50) ignited in the 150 °C heating test. Summarizing the cycling and the abuse test results, the EC/PC/2MeTHF (15:45:40) ternary mixed systems exhibited the best performance. However, in terms of practical use, cell safety still requires further improvement.     

离子液体电解质在锂二次电池中的应用

锂二次电池作为动力电池,被寄予厚望。但锂二次电池面临的安全隐患也是不容忽视的,是当前亟需解决的问题,而这与电解质的性质有着紧密的联系。离子液体由于具有较宽电化学窗口、良好的导电性、高热稳定性、几乎无挥发及不燃烧等优良的特性,正在作为一种新型绿色替代溶剂被电化学领域所关注。离子液体的不燃烧特性,对于替代传统有机电解质具有十分重要的意义。本文阐述了新型溶剂“离子液体”作为电解质在锂二次电池中的应用,其中重点阐述了在碳、硅、钛酸锂(Li₄Ti₅O₁₂)、磷酸亚铁锂(LiFePO₄)、钴酸锂LiCoO₂、镍锰酸锂(LiNi_xMn_yO_z),镍钴锰锂(LiNi_xCo_yMn_zO_w)及在锂硫(Li-S)电池中的应用。     

锂离子二次电池添加剂初探

本文介绍了碳酸亚乙烯酯作为碳阳极的锂离子二次电池的添加剂对二次锂电池性能的影响，并比较了含稳定荆的碳酸亚乙烯酯和不舍稳定剂的碳酸亚乙烯酯对电池性能的影响，说明了不合稳定荆的碳酸亚乙烯酯能够稳定和提高放电能力，改变电极的表面性质，减缓电池衰退，提高电池的稳定性。     

Safety and capacity retention of lithium ion cells after long periods of storage

This paper provides the results of simple preliminary tests on the storage characteristics of lithium ion cells in relation to their use for UPS or BPS. Commercial cylindrical 18 650 size cells with a discharge capacity of around 1200 mAh were used in the experiments. The cells consisted of an amorphous carbon anode, a LiCoO₂ cathode and an organic electrolyte. Cells were stored for 1–12 months and then their capacity was measured after constant voltage charging (similar to trickle charging) at 4.1 or 4.2 V and 21 or 60 °C. After measuring the capacity, the cells were crushed with a round 15 mm bar in diameter as an example of a fundamental abuse test. The residual cell capacity after 10 years of 4.2 V constant charging at 20 °C was predicted to be approximately 65%. This exceeds our tentative target of 50%. We also found that no cells smoked, ignited or exploded when crushed. We also measured the cell capacity after simple storage (i.e., after self-discharge).     

α‐Al2O3 improves the properties of gel polyacrylonitrile nanocomposite electrolytes used as electrolyte materials in rechargeable lithium batteries

In this investigation, a series of gel polyacrylonitrile (PAN)/α‐Al₂O₃ nanocomposite electrolyte materials that incorporate various fractions of PAN, α‐Al₂O₃ inorganic powders, propylene carbonate and ethylene carbonate as cosolvents, and LiClO₄ were prepared. X‐ray diffraction revealed that the gel nanocomposite electrolyte materials contained amorphous PAN in which was uniformly dispersed α‐Al₂O₃. The gel PAN/α‐Al₂O₃ nanocomposite electrolytes had lower glass‐transition temperatures (as determined by dynamic mechanical analysis) and higher conductivity than a similar electrolyte prepared in the absence of α‐Al₂O₃. The conductivity of the PAN/α‐Al₂O₃ nanocomposite films was inversely proportional to the size of the α‐Al₂O₃ particles and directly proportional to (I) the amount of α‐Al₂O₃ (up to 7 wt %), (II) the F value [LiClO₄/CH₂CH(CN) ratio], and (III) the amount of plasticizer (propylene carbonate/ethylene carbonate = 1 : 1). Cyclic voltammetry revealed that adding α‐Al₂O₃ significantly increased the electrochemical stability of the composite electrolyte system. A rechargeable lithium battery prepared using this gel nanocomposite electrolyte system exhibited good cyclability and a stable capacity. The coulombic efficiency for the recharge/discharge process was approximately 75%, even after 100 cycles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

可充镁电池电解质研究现状

综述了可充镁电池电解质材料的研究进展;介绍了有机格氏试剂盐系列电解质和可传导镁离子的聚合物电解质(GPE);简述了相应的制备工艺和存在的主要问题;最后提出可充镁电池电解质的发展趋势.     

锂离子二次电池正极材料锰酸锂的研究进展

锂离子电池正极材料锰酸锂的理论比容量较高,但由于多次循环过程中衰减严重,阻碍其商业化应用.综述了近年来其发展状况,总结了尖晶石型锰酸锂正极材料具备比容量较高、原料资源丰富、价格便宜、环境友好等特点,以及各方面应用情况.论述了其结构特点、工作原理、存在缺陷等.着重总结了近期的材料制备方法和稀土掺杂改性研究的进展情况,分类指出了一元稀土掺杂及多元稀土掺杂对材料改性的影响并指出了存在的问题,同时提出了未来的研究方向和发展前景.     

Purification process for an inorganic rechargeable lithium battery and new safety concepts

We have investigated an inorganic lithium battery system in which LiCoO₂ is used as the positive electrode and lithium, intercalated into graphite, serves as negative electrode. The conducting salt is lithium tetrachloroaluminate (LiAlCl₄). The electrolyte is based on SO₂. It has been shown that a layer of lithium hydroxide is present on the surface of the lithium cobalt oxide. This has a negative impact on the stability of the electrode. To improve stability, we have developed a purification process for removing the lithium hydroxide from the surface of the positive electrode. After purification the cells show no significant change in either capacity or internal resistance when cycled. Up to 70% of the theoretical capacity of electrodes which have been purified in this way can be used without any negative effects being observed. To prevent the deposition of metallic lithium leading to a hazardous situation, a new safety concept was developed whereby local short circuits are allowable. Safe functioning of the new concept has been demonstrated with tests on complete cells.     

Ternary and quaternary mixed electrolytes for lithium cells

This paper reports the influence of composition of mixed solvent electrolyte composition on the discharge capacity and charge–discharge cycle life of lithium metal/amorphous V2O5–P2O5 (95:5 in molar ratio) cells. The solvents used were ethylene carbonate (EC), propylene carbonate (PC), 2-methyltetrahydrofuran (2MeTHF) and THF. LiAsF6 was used as the solute. The electrolyte solutions examined here contain ternary and quaternary mixed systems. The purpose of this work is to obtain an electrolyte solution which realizes a higher rate capability and/or a longer cycle life than the previously studied EC:PC:2MeTHF (15:70:15) ternary mixed system. Of the electrolyte systems examined here, the EC:PC:2MeTHF (30:40:30 in volume) ternary mixed solvent system showed the best cell performance. In addition, a heating test was carried out on an AA- size lithium cell with EC:PC:2MeTHF (30:40:30) as a fundamental abuse test to ensure cell safety.     

Characteristics of an aqueous rechargeable lithium battery (ARLB)

Electrochemical performance of an aqueous rechargeable lithium battery (ARLB) containing a LiV₃O₈ (negative electrode) and LiCoO₂ (positive electrode) in saturated LiNO₃ aqueous electrolyte was studied. These two electrode materials are stable in the aqueous solution and intercalation/deintercalation of lithium ions occurs within the window of electrochemical stability of water. The obtained capacity of this cell system is about 55 mAh/g based on the mass of the positive electrode, which is lower than the corresponding one in the non-aqueous lithium ion battery. However, its specific capacity can be compared with those of the lead acid and Ni-Cd batteries. In addition, initial results show that this cell system is good in cycling.     

锂离子二次电池电解质四氟硼酸锂制备技术研究进展

四氟硼酸锂由于具有较好的热稳定性,因而在锂离子二次电池电解液中的使用比例越来越大。介绍了国内外锂离子二次电池电解质四氟硼酸锂的制备技术研究进展,包括4种制备方法,即气-固反应法、水溶液法、混合溶剂法、氟化氢溶液反应法。总结了各种制备方法的优缺点,并且展望了四氟硼酸锂的发展方向。指出制备高纯度的四氟硼酸锂将是未来的研究重点之一,同时四氟硼酸锂在离子液体中的使用,以及和其他新型锂盐特别是含氟磺酰锂盐的配合使用都将是今后的研究重点。     

Effect of purification of 2-methyltetrahydrofuran/ethylene carbonate mixed solvent electrolytes on cyclability of lithium metal anodes for rechargeable cells

The effects of the purification of LiAsF₆–2-methyl tetrahydrofuran (2MeTHF)/ethylene carbonate (EC) mixed solvent organic electrolytes on the charge–discharge cyclability of lithium metal anodes has been investigated by using an accelerated method for evaluating lithium cycling efficiency. This method involves cycle tests on coin cells with an amorphous V₂O₅–P₂O₅ (95:5 molar ratio) cathode and an anode containing a small amount of lithium. Using this method, the cycle life of the cell was determined over a short period simply from the lithium cycling efficiency. The lithium cycling efficiency in LiAsF₆–2MeTHF/EC was improved by removing both water and organic impurities such as peroxides. An electrolyte containing less than 14ppm of water and 20ppm of organic impurities had a high lithium cycling efficiency of 97.2%.     

原位构建富氟SEI的凝胶电解质用于金属锂二次电池

以六氟磷酸锂（LiPF₆）为四氢呋喃的聚合引发剂制备凝胶电解质,同时作为氟源在金属锂负极表面原位构建富含LiF的固态电解质界面层（solid electrolyte interface,SEI）来抑制锂枝晶的生长以及金属锂/电解液之间的副反应。所制备的凝胶电解质具有较高的室温离子电导率（1.33 mS·cm^-1）和较宽的电化学稳定窗口（4.5 V）。原位聚合方式组装金属锂对称电池循环后,锂负极表面没有明显的锂枝晶和被损毁的形貌出现;XPS结果表明锂负极表面生成了富含LiF的SEI。组装的LiFePO₄全电池在1 C的电流密度下,稳定循环400周后仍保持118.7 mAh·g^-1的放电比容量。得益于四氢呋喃在开环聚合反应过程中,促进了LiPF₆分解反应平衡的正向移动,在锂负极表面形成稳定的富含LiF的SEI,能够抑制锂枝晶的生长并防止其被持续性的腐蚀破坏。     

原位构建富氟SEI的凝胶电解质用于金属锂二次电池

以六氟磷酸锂（LiPF₆）为四氢呋喃的聚合引发剂制备凝胶电解质,同时作为氟源在金属锂负极表面原位构建富含LiF的固态电解质界面层（solid electrolyte interface,SEI）来抑制锂枝晶的生长以及金属锂/电解液之间的副反应。所制备的凝胶电解质具有较高的室温离子电导率（1.33 mS·cm^-1）和较宽的电化学稳定窗口（4.5 V）。原位聚合方式组装金属锂对称电池循环后,锂负极表面没有明显的锂枝晶和被损毁的形貌出现;XPS结果表明锂负极表面生成了富含LiF的SEI。组装的LiFePO₄全电池在1 C的电流密度下,稳定循环400周后仍保持118.7 mAh·g^-1的放电比容量。得益于四氢呋喃在开环聚合反应过程中,促进了LiPF₆分解反应平衡的正向移动,在锂负极表面形成稳定的富含LiF的SEI,能够抑制锂枝晶的生长并防止其被持续性的腐蚀破坏。     

新型电解质锂盐-氟烷基膦酸锂的研究现状

本文综述了锂电池电解质锂盐的研究现状,介绍了一种新型的电解质锂盐-氟烷基膦酸锂的合成方法,并对其具体工艺条件进行了描述.     

锂离子电池安全添加剂的研究进展

锂离子电池具有高能量密度和良好的循环性能,是目前最为理想的动力电源储能体系。然而,由于大容量和高功率锂离子电池技术尚未成熟,存在安全隐患,导致其商业化应用受到了很大程度的限制。锂离子电池的安全问题主要有机械力破坏、异常充电、气体积聚和热失控等,本文分析了上述危险因素产生的原因以及抑制的方法。在这些增强电池安全性的方法中,使用安全添加剂是最为经济有效的手段,但要在电解液中找到一种对电池具有高安全性能且不牺牲其他性能的实用添加剂并不容易,未来同时具备多功能的添加剂将会是对电池性能提升最有希望的研究方向。本文分析了成膜添加剂、阻燃添加剂和防过充添加剂的作用机理,并对相关领域的发展方向进行了展望。     

制备锂电池电解质六氟磷酸锂的工艺探讨

分析了目前国内外锂电池的发展状况,并对其中一种电解质六氟磷酸锂的制备工艺作了一些探讨。简要介绍了国外已经研究出的六氟磷酸锂的替代产品———氟烷基磷酸锂用作锂电池电解质。     

锂离子电池高压电解液研究进展

传统碳酸酯类电解液在高压(>4.3 V, vs. Li/Li+)下易发生氧化分解反应,导致锂离子电池不可逆容量增加、循环性能下降. 为解决这一问题,需从理论和实验两方面对电解液溶剂、锂盐、添加剂及其基本组成等进行针对性设计. 耐高压溶剂是提升电解液稳定性的关键因素之一,既经济又有效,添加高浓锂盐是近年来研究较多的可提升电解液电化学窗口和循环稳定性的新策略. 本工作从耐高压溶剂、高压添加剂和高浓锂盐三方面综述了近几年锂离子电池高压电解液的研究进展.     

锂离子二次电池电解质锂盐的研究进展及其发展前景

从作为锂离子二次电池电解质的导电锂盐的分类、组成、结构和性能等方面进行分析，通过比较存在的差异，阐述了它们的优缺点及其在锂离子电池中的应用与研究进展。最后展望了锂离子二次电池电解质的发展方向和前景。