Idit Weissman

On the correlation between surface chemistry and performance of graphite negative electrodes for Li ion batteries

This paper discusses some important aspects of the correlation between surface chemistry, 3D structure, and the electrochemical behavior of lithiated graphite electrodes. By reviewing results obtained with diAerent electrolyte solutions (e.g. ethylene carbonate-based solutions, propylene carbonate solutions, and ether-based systems), we describe the stabilization and capacity fading mechanisms of graphite electrodes. One of the failure mechanisms occurs at potentials >0.5 V Li/Li + , and relates to an increase in the electrode’s impedance due to improper passivation and a simultaneous change in the electrode’s morphology, probably due to gas formation. At low potentials (depending on the electrolyte solution involved), phenomena such as exfoliation and amorphization of the graphite electrodes can be observed. Stabilization mechanisms are also discussed. In general, surface stabilization of the graphite is essential for obtaining reversible lithiation and a long electrode cycle life. The latter usually relates to precipitation of highly compact and insoluble surface species, which adhere well, and irreversibly, to the active surface. Hence, the choice of appropriate electrolyte solutions in terms of solvents, salts and additives is very critical for the use of graphite anodes in Li batteries. The major analytical tools for this study included FTIR and impedance spectroscopies, XPS, and in situ and ex situ XRD in conjunction with standard electrochemical techniques. # 1999 Elsevier Science Ltd. All rights reserved.

Recent studies on the correlation between surface chemistry, morphology, three-dimensional structures and performance of Li and Li-C intercalation anodes in several important electrolyte systems

Abstract This paper reviews some advances in the comparative study of lithium and graphite electrodes in a large matrix of solvents, salts and additives. The major purpose of this work was to support RD (ii) successful and useful application of AFM and EQCM in order to study the surface film formation and Li-deposition processes; (iii) understanding the correlation between the reversibility and stability of graphite electrodes in Li-intercalation processes and their surface chemistry, and (iv) finding an interesting correlation between the three-dimensional structure of graphite electrodes, the diffusion coefficient of Li + and their voltammetric behaviour in Li-intercalation processes.

Correlation between surface chemistry, morphology, cycling efficiency and interfacial properties of Li electrodes in solutions containing different Li salts

The influence of the Li salt used on the behaviour of Li electrodes in tetrahydrofurane (THF) and propylene carbonate (PC) solutions was investigated. The salts studied included Li halides (LiBr, LiI), LiBF4, LiPF6, LiSO3CF3 and LiN(SO2CF3)2. The correlation between the electrochemical properties, surface chemistry and morphology of Li electrodes in the above systems was studied using impedance spectroscopy, surface sensitive in situ and ex situ FTIR, X-ray microanalysis, electron microscopy and standard experiments of charge discharge cycling. It was found that all the salt anions explored have strong effects on all the above aspects, eg they strongly affect Li surface chemistry in solutions and participate in the build-up of surface films. The electrical properties of the Li-solution interphase formed in the different salt solutions are remarkably dependent on the salt anion. Consequently, the morphology and Li utility in repeated charge-discharge cycling are also strongly influenced by the salt used. Except for the Li halides, all the salts studied seem to be more reactive to lithium than LiClO4 and LiAsF6. They are worse than the commonly used LiAsF6 for rechargeable Li battery systems because their strong involvement in the Li surface chemistry adversely affects Li cycling efficiency.

Recent studies of the lithium-liquid electrolyte interface Electrochemical, morphological and spectral studies of a few important systems

Our recent studies on the correlation between Li-cycling efficiency, morphology, interfacial properties and surface chemistry in a variety of Li battery electrolyte solutions are reviewed. The solvent systems include alkyl carbonate mixtures, ether and ether alkyl carbonate mixtures, and methyl formate solutions. The techniques include surface sensitive Fourier-transform infrared spectroscopy and standard electrochemical techniques. The principal points are: (i) the surface chemistry of Li is determined by a delicate balance between reduction processes of the solvents, salts and common contaminants; (ii) the surface films initially formed are subjected to ageing processes which gradually change their structure and properties; (iii) the heterogeneous chemical structure of the Li electrodes surface films induces non-uniform Li deposition; (iv) the cycling efficiency is high in systems where Li deposition is smooth and/or the Li deposited is efficiently passivated by the surface species instantaneously formed on it, and (v) it is evident that less hygroscopic surface species passivate the active metal in solution (e.g., Li2CO3, LiF) more effectively.

On the role of water contamination in rechargeable Li batteries

Abstract Many cathode materials such as LiMnO 2 can be highly hygroscopic and thus, introduce considerable water contamination into Li batteries. Water reacts with the Li anode, and this strongly affects its surface chemistry. In this work, we investigated some phenomena related to water contamination due to the cathode material in LiLi x MnO 2 cells containing 1–3 dioxolane/LiAsF 6 solutions. When these cells contain cathodes which were exposed to air, their electrolyte solutions become contaminated with water, which reacts with lithium and thus, hydrogen gas is formed. We discovered that discharging cells containing wet cathodes stops this liberation of hydrogen. We explored several possible explanations for this phenomenon. It was concluded that lithiation of water-containing Li x MnO 2 considerably inhibits the liberation of water into the electrolyte solution. The effect of the presence of water in solutions on the properties of the Li anode is discussed.

The Correlation Between Charge/Discharge Rates and Morphology, Surface Chemistry, and Performance of Li Electrodes and the Connection to Cycle Life of Practical Batteries

We investigated the correlation among surface chemistry, morphology, and current densities of the charge-discharge processes and the performance of lithium electrodes in Li vs. Li half-cell testing and practical rechargeable AA Li-Li x MnO 2 batteries (Tadiran Batteries, Limited). The electrolyte system was LiAsF 6 /tributylamine (stabilizer)/1,3 dioxolane solution. It was found that the performance of the lithium anodes in practical batteries depends on the current densities at which the batteries are operated. These determine the surface chemistry of the anodes in the following manner: at sufficiently high discharge rates (Li dissolution) the native films which cover the active metal are replaced completely and rapidly by surface films which originate from solvent-reduction processes. These films induce uniform, dendrite-free Li deposition. At too-low discharge rates, part of the native films remains, and thus the surface films are too heterogeneous. This leads to dendritic Li deposition. Charging the batteries at too-high rate (Li deposition) leads to the exposure of fresh Li to the solution, which reacts predominantly with the salt anion (AsF 6 - ). The surface films thus formed (comprised of LiF, Li x AsF y species, etc.) lead to nonuniform Li deposition. It is possible to adjust charging rates which lead to lithium deposition with a very minor exposure of fresh lithium, and thereby change the Li surface chemistry to that dominated by solvent reduction. This leads to an extended cycle life of the Li anodes due to the uniform Li deposition that the surface films thus formed induce.

Safety and Performance of Tadiran TLR‐7103 Rechargeable Batteries

In this paper the authors report on the characteristics and performance of a new rechargeable Li-Li{sub x}MnO{sub 2} 3 V battery system developed at Tadiran. The behavior of AA cells of an 800 to 750 mAh capacity is described in terms of charge-discharge curves, cycle life, and low-temperature and high-current performance. At charging regimes around C/10, more than 350 cycles at 100% DOD could be obtained. These batteries have a unique cell chemistry based on LiAsF{sub 6}/1,3-dioxolane/tributyl amine electrolyte solutions which provide internal safety mechanisms that protect the cells from short circuit, overcharge, and thermal runaway upon heating up to 135 C. This behavior is due to the fact that the electrolyte solution is stable at low-to-medium temperatures but polymerizes at temperatures over 125 C.

LiC(SO2CF3)3, a new salt for Li battery systems. A comparative study of Li and non-active metal electrodes in its ethereal solutions using in situ FTIR spectroscopy

Abstract The surface chemistry of lithium electrodes and non-active electrodes polarized to low potentials in LiC(SO 2 CF 3 ) 3 solutions in 1-3-dioxolane (DN) and tetrahydrofuran (THF) was rigorously investigated using three different modes of in situ FTIR measurements. One method is based on external reflectance (SNIFTIRS type) and two methods are based on internal reflectance modes. In addition, Li electrodes treated in these solutions were also studied using ex situ FTIR external reflectance mode. For a comparison, the surface chemistry of these electrodes in LiAsF 6 and LiN(SO 2 CF 3 ) 2 solutions in the same solvents was also investigated using in situ and ex situ FTIR spectroscopy. It was found that while in LiAsF 6 solutions the surface chemistry developed is dominated mostly by the solvent reduction, in the other two salt solutions, the salt anion reduction products are the major constituents in the surface films formed. The LiN(SO 2 CF 3 ) 2 is more reactive towards Li than LiC(SO 2 CF 3 ) in these systems. The differences in Li cycling efficiency and morphology observed in the three salt solutions are discussed in light of the difference in the surface chemistry developed on lithium.

More details on the new LiMnO2 rechargeable battery technology developed at Tadiran

Abstract This paper describes the performance of LiMnO 2 rechargeable AA batteries developed at Tadiran. The advancement, achieved recently in this technology in terms of cycle life, capacity, energy density, low-temperature performance and high discharge currents, is presented. In spite of the use of lithium metal as the anode and liquid electrolyte solutions, these cells are considered safe due to their internal safety mechanisms based on polymerization of the solvent 1,3-dioxolane, in abuse cases.

On the possibility of LiH formation on Li surfaces in wet electrolyte solutions

Fresh lithium reacts with gaseous hydrogen to form surface species which are probably LiH. Li may also react with the H2 that is formed by its reaction with H2O contamination in 1–3 dioxolane solutions. The LiH, when formed, is metastable because it reacts with trace water and the solvent.