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)- Li0.3MnO2 AA batteries with solutions containing 1,3-dioxolane (DN), LiAsF6, 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 Li3N, 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/cm2). 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. © 2002 The Electrochemical Society. All rights reserved.

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-LiMn02 batteries (Tadiran Batteries, Limited). The electrolyte system was LiAsF,/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'). The surface films thus formed (comprised of LIF, LiAsF 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.

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 + y-MnO 2 at 370OC (20 h) with a minimum of impurities, such as y-4-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,,, 33 MnO 2 , was shown to undergo only one essential reversible transition during its electrochemical reduction to Li 0 5 ,,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 ,,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.

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The calr chloride battery is a very promising candidate for high-energydensity and high-power-density applications ~1,2~ It has been found to be safer than high-rate lithium batteries. A laboratory prototype based on Ca(AICl4)~ electrolyte successfully resisted abuse charge and overdischarge tests, a partial compression test, short-circuit tests and heating up to 300oC ~1,2~ It can be discharged over a temperature range of -40 to +200~ ~ After being fully developed, it is expected to have a volumetric energy density greater than the Li-S0~ battery by 30~ or more;(i.e., 5.5Ahfor a C-size cell or 12Ah for a D-size cell).The major drawback of this Ca-TC cell has been rapid corrosion of the calcium anode (i.e., too short a shelf lifel.The calciumthionyl chloride cell is a SEI (Solid Electrolyte lnterphase) battery ~4~ The calcium anode is covered by a thin CaCI~ film which appears to be an anionic conductor. The properties of this film govern the quality and performance of the battery. The rapid selfdischarge of the calcium-thionyl chloride battery results from unsuitable properties of this SEI which may be: too high solubility in the electrolyte, non-compact structure, and a combination of a high anionic transference number (t_~l) and the large difference between the equivalent volume of CaCl= and that of calcium.