Lithium manifests a transient passivation when it is anodically polarized to ∼ −2.66 NHE in normalLiOH electrolytes. The duration of the passivation ranges from seconds to hours. The occurrence of the passivation is independent of electrolyte concentration, flow velocity, anode‐cathode contact pressure, and of the polarization technique used. The duration of the transient is proportional to electrolyte concentration, the more dilute the solution the shorter the time. The passivation is believed due to the formation of an insulating, but unstable aggregate of Li2O which nucleates at active Li sites at the base of the pores in the protective normalLiOH film. The recovery of the surface to the active state is due to the conversion of the Li2O to normalLiOH in the presence of water at the Li surface.

The anodic passivation of lithium in flowing alkaline electrolytes was studied chronopotentiometrically. The experimental results reveal that the passivation follows the classical diffusion‐limited process. An empirical relationship similar to the Sand equation, but including a term for the critical current, inormalc , is observed)(i−inormalc=ktnormalp−1/2A theoretical model of the dissolving lithium anode has been formulated to explain the dependence of the time to passivation, tnormalp , on the experimental variables. This model involves the diffusion of the soluble species through a fixed porous solid layer on the electrode surface and through the electrolyte diffusion layer. The assumption made for the initial boundary condition requires the existence at OCV of a concentration gradient within the porous oxide layer. It has led to an analytical solution which can successfully represent the i−tnormalp relationship for metals in highly corrosive media.

The corrosion of Li was studied in 3-5M LiOH at 25~ and in 4.5M LiOI-I at 4~176The Arrhenius relationship is obeyed and the apparent activation energy for the Li corrosion reaction is found to be 15.5 kcal mole -1. An empirical relationship is derived from which the corrosion rate vf can be obtained at any molar LiOH. At 25~ ,f(kA m -2) ----0.31 ). An equation is also given which allows calculation of the Li corrosion rate when the metal is anodically polarized. The kinetics of the He evolution reaction (e.r.) on Li were determined, the transfer coefficient ~ has a value of 0.14. The rate-controlling process of the Li dissolution reaction is the highly polarized I-I2 evolution at cathodic sites. Based on the ~ value obtained, the enthalpy of activation for the He e.r. on Li at OCV is calculated to be 22.8 kcal mole -1. It is proposed that the protective film on Li has a duplex structure with a thin oxide/ hydroxide layer adjacent to the metal and an outer porous hydrated layer through which the reaction products and reactants can pass freely.The rapid dissolution of Li in alkaline aqueous solutions can be utilized electrochemically to produce high rate battery systems (1). This is possible because the corrosion (parasitic) reaction in 3-5M LiOH can be virtually eliminated if the metal is anodically polarized by about 300 mV. It has been found that the rate of the Li dissolution reaction Lt + H~O-> LiOH -5 Yz H2[i]is essentially constant at constant temperature from OCV to the above-mentioned polarization level. Unlike conventional batteries, in Li-H20 cells the current efficiency is governed by the ratio of two competing reactions, namely, the anodic dissolution reaction and the parasitic reaction (2, 3). The current, efficiency increases with an increase in the anodic dissolution rate (i.e., the current density), and if decreases at elevated temperatures where the corrosion reaction is stimulated. Since current efficiency is critical to cell performance, a fundamental understanding of the factors which influence the parasitic reaction is important.No prior investigations of the corrosion of Li immersed in aqueous electrolytes have been reported. Papers on the electrochemistry of the system have been concerned with anodic passivation and mathematical modeling. This corrosion study of Li in flowing electrolyte under conditions identical to battery operation was undertaken to gain knowledge of three aspects of the Li-H20 reaction.(i) Information on the reaction at various LiOH concentrations and temperatures provides data for the determination of the reaction rate constant. This then allows calculation of corrosion rates in practical battery systems.(it) To characterize the processes which occur across the oxide/hydroxide film in a Li-H20 cell, knowledge of the H20 activity at the active Li surface is necessary.The assumption of the previous mathematical modeling paper (2) was that the exchange current density for the parasitic hydrogen evolution reaction is proportional to the 0.5 power of water activity at the a...

The influence of electrolyte flow velocity, concentration, and contact pressure on the anodic behavior of lithium at constant temperatures in LiOH was studied. The experimental results reveal that, under constant load polarization, a steady-state i-E curve is obtained consisting of resistance and concentration polarization components. A method to accurately determine the film thickness was devised. It was found that the oxide film at the anode surface is quite thick, ca. 10 -2 cm, and its thickness remained constant irrespective of polarization level at constant electrolyte concentration, flow rate, and anode-cathode contact pressure. The effective diffusion layer at the Li active surface is thin, ca. 10 -3 cm. The fraction of active surface area was found to change significantly with LiOH concentration (ranging from 0.05 in 4.84M to 0.39 in 2.9UM), but it was virtually independent of flow velocity and contact pressure. Likewise, electrolyte concentration has far greater influence on film resistance than flow rate or contact pressure. Electrolyte flow velocity variation is, however, an effective means to alter power output from the cell. The oxide/hydroxide film which forms on Li anodes in aqueous, strongly alkaline electrolytes has some tmusual properties. For example, even though it is fairly thick (ca. 5 X 10 -2 cm) it will support high * Electrochemical Society Active Member.

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