The Microstructure of Sintered Silver Electrodes

Wales, Charles P.

doi:10.1149/1.2408189

Cited by 4 publications

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“…S7. EIS measurements support the speculation that the increase in capacity is attributed to an increase in the active surface area of the limiting Ag electrode, leading to higher material utilization as a result of flexing (39)(40)(41)(42)(43)(44)(45). Thus, the electromechanical characterization demonstrated that constructing the battery around the helical band spring current collector resulted in a device resilient to repetitive dynamic mechanical load.…”

Section: Electrochemical and Mechanical Performance Of Flexible Wire ...supporting

confidence: 60%

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Section: Electrochemical and Mechanical Performance Of Flexible Wire ...supporting

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“…As AgO formed from Ag20 in 8.4M CsOH (Fig. 8) the active material as a whole looked identical to what had been found earlier in 8.4M KOH (11).…”

Section: Discussionsupporting

confidence: 84%

“…This was Paper 30 presented at the Boston, Massachusetts, Meeting of the Society, Oct. [7][8][9][10][11]1973. Any discussion of this paper will appear in a Discussion Section to be published in the December 1974 JOURNAL.…”

Section: Discussionmentioning

confidence: 99%

Oxidation of Silver Electrodes in CsOH Solutions

Wales

1974

J. Electrochem. Soc.

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Sintered Ag electrodes were cycled under several conditions in aqueous CsOH or KOH solutions. Over a wide range of charge rates the capacity accepted at the Ag/Ag20 potential plateau increased as electrolyte concentration decreased, but charge acceptance at the Ag20/AgO plateau increased as concentration increased and was larger in CsOH than in KOH. Polarization was greater in CsOH than in KOH of the same concen.tration. Cross sections through electrodes were examined by optical microscopy. The structures that formed in CsOH tended to be similar to those that formed in a more concentrated KOH. After several cycles the average Ag particle size became larger in KOH than was typical in CsOH. Results indicated that concentration gradients were higher in. CsOH.The charge and discharge reactions are well known for the Ag electrode in alkaline solutions. First, Ag is oxidized to Ag20 and then to AgO during charge. The opposite reactions take place during discharge. The work reported in the literature has been done most often in aqueous KOH solutions and less often in NaOH solutions. The products of charge and discharge are the same in both electrolytes. Nevertheless, electrolyte concentration has a definite effect on the characteristics of Ag electrodes (1-5).Variations between results in different KOH concentrations may be effects of changes in ionic mobility or in the amount of free water. Dirkse has pointed out the importance of the mobility of OH-ions and of hydration of the various ions in the electrolyte (2). Comparison of results in different KOH concentrations can indicate the influence of water concentration.Another factor that may have an influence on the characteristics of Ag electrodes is the particular alkaline metal cation involved. The cation can have a noticeable effect even though it does not enter into an electrode reaction. For example, the capacity obtained when sheet Zn was oxidized in KOH was a little larger than in CsOH or RbOH, an effect probably related to solubility of Zn oxidation products (6).The use of CsOH instead of KOH should indicate if the cation of the electrolyte has a strong effect on the Ag electrode. The atomic weight of Cs is 3.4 times that of K. CsOH and KOH solutions having the same molar concentration of cation will contain different amounts of water. The ionic radius of Cs (as measured in crystals) is about 1.26 times as large as K, but hydration of the ions decreases this size difference. A recent review points out the considerable disagreement among various workers as to the actual solvation numbers of most ions (7). It seems reasonable, however, to consider the ionic radius of hydrated Cs to be approx~ imately 1.19 times as large as hydrated K. Thus, it is of interest to determine some of the characteristics of Ag electrodes in aqueous CsOH solutions because results may differ significantly from those obtained in KOH solutions of the same concentration. A better understanding of the behavior of Ag electrodes in alkaline solutions can result in improvements in high energy ba...

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“…Discharge at the AgO/Ag20 potentiaL--Most of the active material is converted to AgO during the charge of a sintered Ag electrode to oxygen evolution. The remainder of the active material consists of Ag20 and Ag in varying amounts depending on electrode structure, electrolyte, and cycling conditions (7,(9)(10)(11) duction of this AgO gives the familiar potential plateau usually found at the beginning of a discharge, except when current is high enough to polarize the electrode down to the Ag20/Ag potential during the entire discharge. The AgO/Ag20 potential can be seen at the beginning of most of the discharges in Fig.…”

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Reduction of the Silver Oxide Electrode in CsOH Solutions

Wales¹

1974

J. Electrochem. Soc.

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The electrical characteristics and changes in structure when sintered Ag electrodes were cycled in 8.4M or 3.6M CsOH solutions were compared with results for similar electrodes cycled in KOH solutions. The products of reduction were the same in the two electrolytes. Solutions of CsOH gave a better capacity when the Ag electrodes were cycled repeatedly using slow discharges, because the Ag which formed during reduction had a smaller average particle size in CsOH than in KOH as a result of lower ionic mobility in the CsOH. But polarization was higher in CsOH, so KOH was preferable to CsOH at moderate and high rates of discharge.Reduction of the silver oxide electrode has usually been studied in aqueous KOH solutions [(1-7) and references in (8)]. Since the ionic radius and atomic weight of Cs are larger than those of K, the use of CsOH instead of KOH should indicate if the cation of the electrolyte has a strong effect on the Ag electrode. In addition, CsOH and KOH solutions having the same molar concentration contain different amounts of water. It is of interest, therefore, to determine some of the characteristics of Ag electrodes in aqueous CsOH solutions, because results may differ significantly from those obtained in KOH solutions.A previous paper has described the oxidation of sintered silver electrodes in CsOH solutions (9). The present work is concerned with reduction or discharge of these electrodes and gives the effect of CsOH on electrical characteristics and on electrode structure. ExperimentalOnly a brief description of experimental procedure is given here, since details have already been presented (9). Test cells contained sintered silver electrodes whose average dimensions were 43.7 mm wide, 36.0 mm high, and 0.87 mm thick. Particle size distribution in an unused electrode was given earlier (7). Cells contained an excess of electrolyte. Two other sintered Ag electrodes served as counterelectrodes. All electrodes were wrapped with five layers of either cellulosic separator or crosslinked polyethylene separator. Each cell also contained a Ag/Ag20 reference electrode. Electrodes were always charged (anodically oxidized) to oxygen evolution before beginning a discharge. The 20-hr constant current charge rate was used except where otherwise stated. Temperature was 24 ~ • I~ Discharges began immediately after the end of a charge, without any stand period. Some electrodes were always discharged (reduced) using the 20-hr rate of constant current, and others were always discharged at the 1-hr rate. Discharges were ended when potential dropped about 200-250 mV below the observed Ag/Ag20 potential plateau. One or more samples were

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The Microstructure of Sintered Silver Electrodes

Cited by 4 publications

References 9 publications

Flexible and stretchable power sources for wearable electronics

Flexible and stretchable power sources for wearable electronics

Oxidation of Silver Electrodes in CsOH Solutions

Reduction of the Silver Oxide Electrode in CsOH Solutions

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