Electrochemistry of L-niobium pentoxide a lithium/non-aqueous cell

The electrochemical behaviour of L-Nb₂O₅ (orthorhombic; a = 6.162, b = 3.661, c = 3.919 Å) was examined in a 1 M LiClO₄-propylene carbonate/ tetrahydrofuran (1:1) solution at 30 °C. L-Nb₂O₅ exhibited an S-shaped discharge curve (mid-point about 1.58 V) under a low, continuous drain below 5 mA g⁻¹ without addition of any conductive binder (such as graphite or acetylene black) and it could be reduced up to 2 F mol⁻¹. The performance of Li/Nb₂O₅ cells was examined: these were found to belong to the 1.5 V class of lithium cell at both low and high discharge rates.The reaction mechanism of L-Nb₂O₅ in a lithium/non-aqueous cell was investigated by ex situ X-ray diffraction analysis together with a chronopotentiometric technique. Reversibility tests indicated that the reaction of L-Nb₂O₅ was basically reversible over 0 – 2 F mol⁻¹ of reduction, which agreed with the analytical results of ex situ XRD studies. The electrochemistry of L-Nb₂O₅, especially the characteristic S-shaped electrode potential curve, is discussed in terms of a homogeneous phase reaction.     

Effects of carbon coating on the electrochemical properties of sulfur cathode for lithium/sulfur cell

Carbon-coated sulfur cathodes were prepared by sputtering method and electrochemical properties of lithium/sulfur cells were investigated. As a result of charge/discharge test, sulfur cathode having carbon layer of 180 Å showed the highest capacity of 1178 mA hg⁻¹ at first discharge. Moreover, discharge capacity showed about 500 mA hg⁻¹ until 50th cycle, which is two times larger than that of no-coated sulfur cathode. This capacity increase could be considered due to the decrease of polysulfides dissolution and the enhancement of electrical contact by surface carbon layer. The changes of sulfur cathode during discharge process were investigated by SEM observation, XRD and DSC measurements. From these results, a discharge reaction mechanism of lithium/carbon-coated sulfur cell was suggested.     

Galvanostatic cycling of vanadium oxide (V6O13) in a nonaqueous secondary lithium cell

The galvanostatic cycling of Li(Al)-V₆O₁₃ cells in 1M LiAsF₆/propylene carbonate (PC)-acetonitrile (AN) and 1M LiAsF₆/PC electrolytes is reported. The discharge capacity and voltage of the Li(Al)-V₆O₁₃ cell were shown to be consistently higher than those of the corresponding Li(Al)-TiS₂ cell. Discharge rates of 1.2, 2.5, 5.0 and 10.0 mA cm^?2 with active material utilisations of 20 – 60% were obtained from the Li(Al)-V₆O₁₃ cell. The addition of fresh PC-AN electrolyte resulted in an improvement in cell capacity, but did not stop capacity decline on cycling. Cycle life of Li(Al)-V₆O₁₃ cells was normally less than 50 cycles. It was also found that exposure of the V₆O₁₃ electrode to moist air reduced the OCV and the discharge capacity of the cell. Short circuiting and complete discharge of the cell resulted in lower capacity and this may have been due to some degree of irreversible reduction of the V₆O₁₃.     

Optimization of the vanadium oxide (V6O13) electrode in a nonaqueous secondary lithium cell

The V₆O₁₃ electrode was tested in a nonaqueous lithium cell using 1M LiAsF₆ in propylene carbonate- acetonitrile mixture as the electrolyte. It was shown that incorporation of acetylene black in the V₆O₁₃ electrodes improved cell performance in terms of active material utilisation. Also, cells using hydrophilic microporous polypropylene separators, e.g., Celgard 5511 and 3501, displayed less resistive losses enabling larger charge/discharge rates to be used. Voltage changes in the cell were shown to be controlled almost entirely by the V₆O₁₃ electrode. Analysis of the exhausted V₆O₁₃ electrodes showed that they contained at least 4 moles of lithium per mole of V₆O₁₃.     

Rechargeable lithium sulfide electrode for a polymer tin/sulfur lithium-ion battery

In this work we investigate the electrochemical behavior of a new type of carbon-lithium sulfide composite electrode. Results based on cyclic voltammetry, charge (lithium removal)-discharge (lithium acceptance) demonstrate that this electrode has a good performance in terms of reversibility, cycle life and coulombic efficiency. XRD analysis performed in situ in a lithium cell shows that lithium sulfide can be converted into sulfur during charge and re-converted back into sulfide during the following discharge process. We also show that this electrochemical process can be efficiently carried out in polymer electrolyte lithium cells and thus, that the Li₂S-C composite can be successfully used as cathode for the development of novel types of rechargeable lithium-ion sulfur batteries where the reactive and unsafe lithium metal anode is replaced by a reliable, high capacity tin-carbon composite and the unstable organic electrolyte solution is replaced by a composite gel polymer membrane that is safe, highly conductive and able to control dendrite growth across the cell. This new Sn-C/Li₂S polymer battery operates with a capacity of 600 mAh g⁻¹ and with an average voltage of 2 V, this leading to a value of energy density amounting to 1200 Wh kg⁻¹.     

Factors impact charging process in lithium/sulfur batteries

为了探究多硫离子在多孔碳材料表面的氧化过程,组装了三电极模拟电池和两电极扣式电池。比较了高硫浓度下和低硫浓度下硫电极的循环伏安曲线和充放电曲线;研究了充放电过程中电解液颜色和极片表面颜色的变化;比较了硫浓度、电解液种类、碳材料比表面积对硫电极在2.6 V处氧化峰电流的影响。结果表明：维持硫的适当过饱和度,对硫电极充电过程的完成是必要的;充电过程中可产生单质硫,同时多硫离子还可通过化学过程生成硫。碳比表面积增大,将使氧化峰电流增大;碳酸酯电解液由于对硫和多硫离子溶解度小,氧化峰电流较小;随着硫浓度的增大,氧化峰电流先线性增大,后快速下降。使用醚类电解液时,合适的总硫浓度为0.125 mol/L。     

Research progress on sulfur cathode of lithium sulfur battery

锂硫电池具有能量密度高、原料低廉、绿色环保等优势,已成为下一代高性能二次电池的研究热点,但是活性材料利用率低、容量衰减较快、自放电严重等问题,极大地阻碍了该电池的实用化进程。正极是电池的核心部件,要实现锂硫电池的性能提升,必须对硫正极的组分结构进行合理的设计与构建。本文首先分析锂硫电池的工作原理、存在问题及解决途径,然后分别从硫正极的活性材料、集流体、表面涂层、黏结剂、添加剂等5个方面对当前的研究现状进行总结,最后对其未来的发展前景做出展望,文章指出,硫正极更应关注真实的能量密度水平,而锂硫电池的研究视野不应局限于正极材料。     

Design of a safe cylindrical lithium/thionyl chloride cell

Cell design criteria have been established which can result in a safe lithium/thionyl chloride cell. A cell vent, a low area internal anode design, cel     

Research progress of safe lithium sulfur batteries

锂硫电池由于其原料来源广泛、成本低廉并且具有理论容量高以及环境友好等优点,被认为是最有潜力的新一代高能量密度电池技术之一。近年来,随着固硫化学的发展和硫电极结构设计的优化,锂硫电池技术发展已经取得了长足的进步。但是,锂硫电池的实用化仍然面临着一系列的挑战,如高载量硫正极的设计,少液体系或固态体系中硫的催化活化、稳定的电极/电解液界面、安全性能的提升等。其中,安全性能是阻碍锂硫电池商业化进程的关键问题之一。目前,已有众多的研究者对锂硫电池的安全性能提出了改进策略,包括金属锂负极的保护、阻燃电解液的开发、修饰隔膜乃至固体电解质的使用,以及通过电极结构设计缓解电池体积变化等。本文从锂硫电池的化学特性和影响安全性的关键部件出发,在基础研究方面,从负极锂枝晶生长、充放电过程中电极的体积变化以及电解液体系的问题等几方面总结了锂硫电池安全性问题的来源,针对这些问题提出了解决锂硫电池安全性问题的关键需求,总结了近年来安全性锂硫电池研究工作的进展,并对未来发展态势及方向进行探讨。由于缺乏直接的电芯和模块的数据测试,在大型器件上的安全性测试问题上,亟待其他科研工作者补充总结。     

Rechargeable lithium/sulfur battery with liquid electrolytes containing toluene as additive

The effect of incorporating varying amounts (in the range 2.5–10 vol%) of toluene additive in 1 M LiCF₃SO₃ in tetra(ethylene glycol) dimethyl ether (TEGDME) liquid electrolyte on the electrochemical performance of Li/S cell at room temperature was studied. Cyclic voltammetry measurements showed the same active voltage range for the electrolytes with and without toluene, consisting of an oxidation peak at 2.5 V and a pair of reduction peaks at 2.35 and 1.9 V. Electrolytes with toluene have higher redox currents resulting from increased ion mobility and ionic conductivity. Toluene addition enhanced initial discharge capacity; a maximum of 750 mAh g⁻¹ (45% of the theoretical specific capacity of sulfur) was obtained with 5% of toluene, which was 1.8 times that of the cell without toluene. The electrolyte with 5% toluene exhibited a stable cycle performance with the highest discharge capacity and charge–discharge efficiency. AC impedance analyses of Li/S cells with the electrolytes showed that toluene addition resulted in a lower initial interfacial resistance and a fast stabilization of electrode/electrolyte interfaces in the cell. Addition of toluene in low amounts is thus an effective means to enhance the electrochemical performance of 1 M LiCF₃SO₃ in TEGDME electrolyte in Li/S cells at room temperature.     

Polysulfide rubber-based sulfur-rich composites as cathode material for high energy lithium/sulfur batteries

Novel sulfur-rich polymer composites were prepared from the commercial polysulfide rubber through facile vulcanization methods and were firstly used as cathode material for lithium/sulfur batteries. The sulfur enriched in the composites includes three parts, the first part was inserted into the main chains of the polysulfide rubber, the second part formed insoluble polysulfide (-S_n-)through self-polymerization and the third part was trapped inside the network of the above two polymer chains. The obtained sulfur-rich polymer composites have high sulfur content over 80%. Compared with the pure sulfur electrode, the composites showed better cycle stability and coulomb efficiency.     

Fundamental scientific aspects of lithium ion batteries(Ⅺ)--Lithium air and lithium sulfur batteries

提高能量密度是可充放锂电池研发最重要的目标.近年来,锂硫电池与锂空气电池由于具有高的理论能量密度而受到广泛关注,这两种电池仍然面临较多的科学与技术问题,处于电池开发早期研究阶段.在本文中,重点介绍了锂空气电池的基本工作原理,基本结构组成,所面临的问题和两种特殊体系的锂空气电池, 同时简要介绍了锂硫电池.     

Nitrogen/sulfur co-doped disordered porous biocarbon as high performance anode materials of lithium/sodium ion batteries

Nitrogen/sulfur co-doped disordered porous biocarbon was facilely synthesized and applied as anode materials for lithium/sodium ion batteries. Benefiting from high nitrogen (3.38 wt%) and sulfur (9.75 wt%) doping, NS_1-1 as anode materials showed a high reversible capacity of 1010.4 mA h g⁻¹ at 0.1 A g⁻¹ in lithium ion batteries. In addition, it also exhibited excellent cycling stability, which can maintain at 412 mAh g^-1 after 1000 cycles at 5 A g⁻¹. As anode materials of sodium ion batteries, NS_1-1 can still reach 745.2 mA h g⁻¹ at 100 mAg^-1 after 100 cycles. At a high current density (5 A g^-1), the reversible capacity is 272.5 mA h g⁻¹ after 1000 cycles, which exhibits excellent electrochemical performance and cycle stability. The preeminent electrochemical performance can be attributed to three effects: (1) the high level of sulfur and nitrogen; (2) the synergic effect of dual-doping heteroatoms; (3) the large quantity of edge defects and abundant micropores and mesopores, providing extra Li/Na storage regions. This disordered porous biocarbon co-doped with nitrogen/sulfur exhibits unique features, which is very suitable for anode materials of lithium/sodium ion batteries.     

Preparation of iron sulfides and the study of their electrochemical characteristics for use in a nonaqueous—lithium battery

A variety of iron sulfides was prepared by changing both the mixing ratio of iron to sulfur and the reaction heating temperatures. Samples were then subjected to chemical and X-ray diffraction analyses to check their composition. These iron sulfides were polarized in a nonaqueous electrolyte. As a result, the sample prepared with a S/Fe ratio of 1.1/1 and heated at 800 °C showed the highest electrochemical capacity and had the molecular formula FeS. A button-type, nonaqueous electrolyte—lithium battery using the FeS as the cathode material was constructed and evaluated. The energy density of the battery was calculated to be 0.448 W h/cm³ and 0.137 W h/g.     

Improvement of cycle property of sulfur-coated multi-walled carbon nanotubes composite cathode for lithium/sulfur batteries

A novel sulfur-coated multi-walled carbon nanotubes composite material (S-coated-MWCNTs) was prepared through capillarity between the sulfur and multi-walled carbon nanotubes. The results of the TEM and XRD measurements reveal that S-coated-MWCNTs have a typical core-shell structure, and the MWCNTs serve as the cores and are dispersed individually into the sulfur matrices. The charge–discharge experiments of the lithium/sulfur cells demonstrated that the S-coated-MWCNTs cathode could maintain a reversible capacity of 670 mAh g⁻¹ after 60 cycles, showing a greatly enhanced cycle ability as compared with the sulfur cathode with simple MWCNTs addition (S/MWCNTs) and the cathode using sulfur-coated carbon black composite (S-coated-CB). The EIS and SEM techniques were used to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors to the improvement in the cycle life of the sulfur cathode were discussed.     

Capacity fade analysis of a lithium ion cell

A physics-based single particle model was used to simulate the life cycling data of a lithium ion cell. The simulation indicates that there are probably three stages of capacity fade in a lithium ion cell used at low rates. In the first stage, lithium ions are lost to a film formation reaction (e.g. SEI formation) and, consequently, the cathode becomes less intercalated during cycling. In the second stage, the loss of active cathode material outpaces the loss of lithium ions and the cathode gradually becomes more intercalated at the end of discharge. The anode is the limiting electrode in stages one and two and the change in the anode voltage causes the cell to reach end of discharge voltage. In the third stage, the limiting electrode shifts from the anode to the cathode, and the anode becomes increasingly less discharged at the end of discharge. Thus, more and more “cyclable” lithium ions are left inside the anode, which causes additional capacity fade.     

Behavior of a sodium-sulfur cell with a dynamic sulfur electrode

A sodium-sulfur cell was constructed with sodium polysulfide circulating in a narrow annulus around a β-alumina tube. The absence of carbon mat in the electrode reduced the current collector surface area appreciably, localized the electrochemical reactions, and ultimately led to film formation on the electrode. The results are consistent with existing models and interpretations of sulfur electrode behavior. Film formation on the electrode is responsible for the rather poor electrical characteristics of the cell.     

Optimal charge rates for a lithium ion cell

The optimum charge rate for a lithium ion cell at each cycle is determined to maximize the useful life of the cell without using optimization algorithms. In previous work, we showed that by applying a dynamic optimization routine the number of cycles can be increased by approximately 29.4% with respect to the case with one optimal charge current [7]. The dynamic optimization results indicated that the optimum charge rates are the minimum currents at which the constraints for the useful life are satisfied. This is due to the minimum charge rate resulting in minimum side reaction rate and capacity fade. Useful cell life is defined as the number of cycles before the end of discharge voltage (EODV) drops below 3.0 V or the cell discharge capacity becomes less than 20% of the original discharge capacity. The new approach presented in this work is able to find the optimal charge rates in a few minutes while the previous optimization algorithm takes at least one day, and improves the useful cell life by approximately 41.6% with respect to using only one optimal charge current.     

Analysis of internal short-circuit in a lithium ion cell

An electrochemical thermal model was developed to study the internal short-circuit behavior of a lithium ion cell. The model was used to understand several experimental observations: several short-circuit scenarios possible in a lithium ion cell were simulated and the power generated from each case was calculated. Influence of parameters like the SOC and initial temperature of the cell was studied.Experiments were carried out to verify the predictions made using the model. Some pointers are provided towards design of a safer cell.