Electrolytes water-activated batteries

Reserve batteries have been developed for appHcations that require a long inactive shelf period foUowed by intense discharge during which high energy and power, and sometimes operation at low ambient temperature, are required. These batteries are usually classified by the mechanism of activation which is employed. There are water-activated batteries that utilize fresh or seawater electrolyte-activated batteries, some using the complete electrolyte, some only the solvent gas-activated batteries where the gas is used as either an active cathode material or part of the electrolyte and heat-activated or thermal batteries which use a soHd salt electrolyte activated by melting on appHcation of heat. 

In the reserve stmcture, one of the key components of the cell is separated from the remainder of the cell until activation. In this inert condition, chemical reaction between the cell components (self-discharge) is prevented, and the battery is capable of long-term storage. The electrolyte is the component that is usually isolated, though in some water-activated batteries the electrolyte solute is contained in the cell and only water is added. 

The battery is constracted dry, stored in the dry condition, and activated at the time of use by the addition of water or an aqueous electrolyte. Most of the water-activated batteries use magnesium as the anode material. Several cathode materials have been used successfully in different types of designs and applications. 

Immersion batteries are designed to be activated by immersion in the electrolyte. They have been constmcted in sizes to produce from 1.0 V to several hundred volts at currents up to 50 A. Discharge times can vary from a few seconds to several days. A typical immersion-type water-activated battery is shown in Fig. 17.1. 

Voltage versus Current Density. Figures 17.6 and 17.7 are representative voltage versus current density curves for several water-activated battery systems at 35 and 0°C, respectively, using a simulated ocean water electrolyte. 

FIGURE 17.24 Discharge curves of magnesium/cuprous chloride water-activated batteries at 20°C electrolyte tapwater. 

When immersed in water, the explosives in water-activated contrivances are initiated by electric current as water (acting as an electrolyte) immerses the electrodes of specially designed batteries by chemical reaction with water and by pressure sensors triggered at certain depths. These contrivances include ammunition, signal flares and other pyrotechnics, sounding devices (which are dropped by ships to determine depth), and actuating cartridges for gas cylinders that automatically inflate life rafts and jackets. 

Electrolyte inside the battery cells has two functions, which is to conduct electricity and heat. If the electrolyte is below the plate level, the area that is not covered by the electrolyte is not electrochemically active. The inactive area causes a concentration of heat in other parts of the cell and promotes grid corrosion. Periodically adding water to maintain the electrolyte level can provide an indication of charging efficiency. If the water consumption... 

Seawater-activated batteries are designed to operate in an infinite electrolyte, namely, the oceans of the world. However, for design, development, and quality control purposes, it is not practical to use ocean water. Thus it is common practice throughout the industry to use a simulated ocean water. A commercial product, composed of a blend of all the ingredients required, simplifies the manufacture of simulated ocean water test solutions. 

Dunk-type batteries, activated by pouring the electrolyte into the battery where it is absorbed by the separator, can utilize water or seawater when the temperature is above freezing. At lower temperatures special electrolytes can be used. The use of a conducting aqueous electrolyte will result in faster voltage buildup. However, the introduction of salts in the electrolyte will increase the rate of self-discharge. 

The de-plasticized (extracted or otherwise) cells are then packaged into vapor-impermeable, flexible, multilayer polymer-aluminum bags, dried under reduced pressure and elevated temperature to remove any adsorbed water, activated with a measured amount of liquid electrolyte solution, and sealed. The liquid electrolyte is rapidly absorbed into the microporous structure of the electrodes and separator, thus making the spillage of the liquid electrolyte from an open battery highly improbable. 

Water-activated cells and batteries are supplied sealed. The caustic (potassium hydroxide) electrolyte and the lime flake are present in Ae dry form. The cell is activated by removing the seals and adding the appropriate amount of water to dissolve the potassium hydroxide. Periodic inspection and addition of water are the only required maintenance. 

Electrolytes are ubiquitous and indispensable in all electrochemical devices, and their basic function is independent of the much diversified chemistries and applications of these devices. In this sense, the role of electrolytes in electrolytic cells, capacitors, fuel cells, or batteries would remain the same to serve as the medium for the transfer of charges, which are in the form of ions, between a pair of electrodes. The vast majority of the electrolytes are electrolytic solution-types that consist of salts (also called electrolyte solutes ) dissolved in solvents, either water (aqueous) or organic molecules (nonaqueous), and are in a liquid state in the service-temperature range. [Although nonaqueous has been used overwhelmingly in the literature, aprotic would be a more precise term. Either anhydrous ammonia or ethanol qualifies as a nonaqueous solvent but is unstable with lithium because of the active protons. Nevertheless, this review will conform to the convention and use nonaqueous in place of aprotic .]... 

In considering the selection of anodes for high energy density (HED) storage (or secondary) batteries (SB), we note that there are some 19 metals whose free-energy density (TED) of reaction with oxidants such as O2, Cl2, and F2 are higher than those of Zn with the same oxidants. Most of these metals react violently with water. The remainder are passivated by water. Therefore other electrolytes must be considered for these metals, based on non-aqueous, molten salt, or solid-state ionic conductors. Much experimental work has been carried out during the last two decades on primary and secondary batteries based on anhydrous electrolytes, aimed at utilization of the active metals. 

Hydrates could play an important role in electrolytes for batteries with active metals. The water, being involved in the hydrate structure, is less active than at the compositions on the water side of the diagram, i.e. between the eutectic and pure water. The rate of the anodic dissolution of the alkali and... 

FICs are useful as electrochemical sensors, electrolytes and electrodes in batteries and in solid state displays (Farrington Briant, 1979 Ingram Vincent, 1984). If a FIC material containing mobile M ions separates two compositions with different activities of M, a potential is set up across the FIC that can be related to the difference in the chemical activities of M. By fixing the activity on one side, the unknown activity on the other can be determined. This principle forms the basis of a number of ion-selective electrodes LaFj doped with 5% SrF2 is used for monitoring fluoride ion concentration in drinking water. Similarly, calcia-stabilized-zirconia is used in cells of the type... 

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