Zinc is the most commonly used battery electrode, and zinc primary batteries have found numerous applications. The zinc electrode is electrochemically reversible in alkaline electrolytes, and there is a strong incentive to develop a practical secondary battery based on this metal. However, secondary batteries that use zinc electrodes typically exhibit short lifetimes, because of problems with zinc material redistribution and undesirable zinc morphologies that form during recharge. There has been a worldwide effort to develop a long-lived secondary alkaline zinc electrode, and marked improvements in cell lifetimes have resulted. This article reviews these efforts, paying particular attention to research and development during the period 1975-1990.

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In situ laser Raman spectra of electrochemically precipitated thin-film Ni(OH)2 electrodes in alkaline NaOH electrolytes were recorded, and the effect of repeated charge-discharge cycling on the structure and phase composition of the discharged and charged films was investigated. Careful deconvolution analyses of the Raman and surface-enhanced Raman spectra showed that freshly precipitated films of Ni(OH)2 contain not only an a-like phase but also small amounts of a 3-phase. By combining cyclic voltammetry with in situ Raman spectroscopy, spectral changes that accompanied charge-discharge cycling could be associated with a partial transformation of the predominant a-phase into a disordered -Ni(OH)2 phase. A new phase characterized by a vibration at 522 cm was also discovered in the film at the end of the cycling procedure. Analysis of the Raman spectra of the oxidized electrode (NiOOH active material) revealed for the first time a slight variation of the 477/559 cm peak pair ratio, which corresponds to phase transitions in the Ni(III) hydrous oxide film, as the electrode was cycled. Significant differences between the low-frequency-region Raman spectra of chemically synthesized a,3-Ni(OH)2 and those of highly disordered hydrous Ni(OH)2 films, as well as the absence of characteristic vibrations in the OH stretching region of the in situ Raman spectra of the Ni(OH)2 electrode, suggest that chemically prepared a,13-nickel hydroxides should not be regarded as structural models for electrochemically precipitated thin-film materials.

A baseline cell chemistry was identified as a carbon anode, LiNi 0.8 Co 0.2 O 2 cathode, and diethyl carbonate-ethylene carbonate LiPF 6 electrolyte, and designed for high power applications. Nine 18650-size advanced technology development cells were tested under a variety of conditions. Selected diagnostic techniques such as synchrotron infrared microscopy, Raman spectroscopy, scanning electronic microscopy, atomic force microscopy, gas chromatography, etc., were used to characterize the anode, cathode, current collectors and electrolyte taken from these cells. The diagnostic results suggest that the four factors that contribute to the cell power loss are solid electrolyte interphase deterioration and nonuniformity on the anode; morphology changes, increase of impedance, and phase separation on the cathode; pitting corrosion on the cathode current collector; and decomposition of the LiPF 6 salt in the electrolyte at elevated temperature.

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Thin-film LiMn2O4 electrodes, which were exposed to pure dimethyl carbonate (DMC) or to a mixture of ethylene carbonate (EC) and DMC (1:1 by volume) containing 1 M LiPF6 at elevated temperatures, were studied by using X-ray diffraction, current-sensing atomic force microscopy (CSAFM), cyclic voltammetry, ordinary Raman spectroscopy, and surface-enhanced Raman spectroscopy (SERS). Thin, electronically insulating surface layers were detected by CSAFM and SERS on all electrodes. The surface layer formed by exposure to DMC at 70°C was uniform and preserved the electrode structure, however, it led to complete electrode deactivation, probably due to loss of surface electronic conductivity and slower lithium-ion transport rates through the surface layer. A similar surface layer was formed when the electrodes were exposed to EC­DMC­LiPF6, however, the layer formed at 70°C did not prevent LiMn2O4 decomposition and consequent electrode capacity loss. In this case, manganese dissolution was observed, accompanied by the formation of λ­MnO2. SER spectra of the surface layers suggest that they were formed as a result of DMC decomposition at the LiMn2O4 surface. The SER spectra displayed bands characteristic of Li-O-R, carbonate, and carboxyl groups. Derivatives of carbon-oxygen triple bonds or silver-carbon-oxygen groups, which are possibly a result of interactions between the surface layer and silver microparticles, were also detected. © 2001 The Electrochemical Society. All rights reserved.

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