P. Dan

Factors Which Limit the Cycle Life of Rechargeable Lithium (Metal) Batteries

Failure mechanisms due to high charging rates of rechargeable lithium batteries comprised of Li metal anodes, cathodes (tunneled structure), and electrolyte solutions based on the combination of 1,3‐dioxolane (DN), , and tributylamine (antipolymerization stabilizer) were explored with the aid of postmortem analysis. It was found that at high charging rates, lithium deposition produces small grains, which are too reactive toward the electrolyte solution, in spite of the excellent passivation of lithium in this solution. In practical batteries such as AA cells with spirally wound configurations, the amount of solution is relatively small, and the solution is spread throughout the battery in a thin layer. Therefore, upon cycling, the Li‐solution reactions deplete the amount of the solution below a critical value, so that only part of the active materials continues to function. This leads to a pronounced increase in the internal resistance of these batteries, which fail as a result of their high impedance and the decrease in the effective working electrodes area. Another failure mechanism relates to the extremely high charge‐discharge current densities developed as the active electrode area decreases. These high currents, developed after prolonged cycling, lead to the formation of dendrites that short‐circuit the battery, thus terminating its life.

Attempts to Improve the Behavior of Li Electrodes in Rechargeable Lithium Batteries

In this work we studied properties of modified lithium electrodes in an attempt to improve the high rate performance of rechargeable Li (metal) batteries containing liquid electrolyte solutions. Li (metal)-Li 0.3 MnO 2 AA batteries with solutions containing 1,3-dioxolane (DN), LiAsF 6 , and a basic stabilizer became commercial several years ago but failed to compete with Li-ion battery technology because of a very limited cycle life at high charging rates. The problem relates to intensive reactions between Li deposited at high rates and the electrolyte solutions, which dry the batteries. The lithium-solution reactivity was modified through several approaches. Li anodes doped by Li 3 N, Al, and Mg were tested, as well as solutions containing derivatives of DN that are expected to be less reactive toward lithium than DN. It was concluded that reduction of the Li anode-solution reactivity by these approaches cannot solve the problem, because it is impossible to modify the rough morphology, high surface of lithium electrodes when charging (Li deposition) rates are high (>1 mA/cm 2 ). Since there is no hermetic passivation of any Li surface in liquid electrolyte solutions, the high-surface-area Li deposits react with solution components. Therefore, upon charge-discharge cycling of practical Li (metal) batteries, the electrolyte solution is consumed in these reactions. Hence, the future of Li (metal) rechargeable batteries lies either in the use of solid electrolyte matrices instead of the liquid solutions, or in applications where low charging rates are tolerable.

Development and testing of nanomaterials for rechargeable lithium batteries

Abstract The use of nanoparticles in composite electrodes for Li batteries may have considerable kinetic advantages due to the reduction of the diffusion length for lithium insertion in the active mass, and also because of the reduction of the overall charge transfer resistance of the electrodes. We report herein on the synthesis of various types of nanomaterials for rechargeable lithium batteries and their testing as active mass in anodes and cathodes. These include SnO, VO x , Li x MnO 2 , and various types of carbon nanotubes. Sonochemistry was applied for the synthesis of part of the nanophases. The tools for this study included X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and standard electrochemical techniques (CV, SSCV, chronopotentiometry and impedance spectroscopy).

Structural and Electrochemical Studies of 3 V Li x MnO2 Cathodes for Rechargeable Li Batteries

X-ray diffraction studies (XRD) were carried out for the investigation of the synthesis and electrochemical reduction of lithiated MnO 2 . The optimal Li:Mn ratio for a heat-treated mixture of LiNO 3 + γ-MnO 2 at 370°C (20 h) with a minimum of impurities, such as γ-β-MnO 2 or spinel, was shown to be equal to 0.33. A combined application of the open-circuit voltage (OCV), slow-scan-rate cyclic voltammetry and XRD measurements was used for the investigation of the intercalation mechanism. The initial compound, Li 0.33 MnO 2 , was shown to undergo only one essential reversible transition during its electrochemical reduction to Li 0.75 MnO 2 , with a voltage plateau appearing around 3 V. It was conclusively demonstrated that both a thermal synthesis in a certain range of Li:Mn ratio and electrochemical reduction upon cycling result in the phase transition from Li 0.3 MnO 2 to Li 0.5 MnO 2 spinel. The characteristic feature of the latter reduction process is that it is essentially irreversible and occurs in a thin surface layer of the initial material. The formation of this thin layer seems to be responsible for a drop in the capacity of practical electrodes during their charge-discharge cycling. A plausible explanation for this effect is discussed.

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.

Performances and safety behaviour of rechargeable AA-size Li/LixMnO2 cell

Abstract An Li/LixMnO2 rechargeable system was developed. The AA cell based on a lithium metal anode and lithiated manganese dioxide cathode, organic electrolyte and polypropylene separator, exhibits excellent performance and safety behaviour. The cell possesses an energy density of 125 to 140 Wh/kg and 280 to 315 Wh/l. An accumulated capacity of about 200 Ah can be achieved under cycling. The system incorporates a chemical mechanism preventing explosion, fire and venting with fire under abuse conditions such as short circuit, overcharge, deep discharge, etc.

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.

The electrochemical behaviour of 2-methyltetrahydrofuran solutions

Abstract The electrochemical behaviour of 2-methyltetrahydrofuran (2Me-THF) solutions with lithium and noble metal electrodes was investigated. Surface-sensitive FTIR, X-ray microanalysis and scanning electron microscopy were applied in conjunction with electrochemical techniques in order to characterize the electrode surfaces in solutions and to correlate the cycling efficiency and surface morphology of lithium electrodes with their surface chemistry in solutions. The influence of a variety of contaminants, including oxygen, water, CO 2 , nitrogen, furans and paraffin oil, on the Li cycling efficiency, morphology and surface chemistry was also studied. It was found that the surface films formed on lithium in 2Me-THF contained several types of alkoxides. The presence of trace O 2 , water, CO 2 ; and furans modifies the structure of these surface films and influences both the morphology and the Li cycling efficiency. The best efficiency of Li electrodes in charge-discharge cycling was obtained with uncontaminated LiAsF 6 + 2Me-THF solutions.