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. 

Magnesium-Cuprous Chloride Water Activated Battery (Indian Patent No. 106820) Central Electrochemical Research Institute Non-Technical Note. Accessed on www.cecri.res.in/Technology/batteries... 

MA8M06 (Russia) which is produced specially for use in water activated Mg-AgCl batteries is also suitable for use in Mg-air cells. 

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... 

In previous sections of this chapter, magnesium anodes have been considered as replacements for zinc in Leclanche and air-depolarized cells. In sea water-activated reserve batteries, magnesium anodes are coupled with either silver chloride, lead chloride, manganese dioxide or, occasionally,... 

Fig. 3.34 Schematic diagram of a sea water-activated battery. (By courtesy of Uitralife,)...

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. 

To avoid this accident, for Li-ion batteries, carbon is utilized as the negative active material instead of lithium metal, and Li-containing transition metal oxides are used for the positive active material. The combination of these positive and negative materials gives more than 3 V potential. An organic liquid or polymer electrolyte is used for Li-ion batteries. Water-based electrolytes decompose to oxygen and hydrogen at more than 1.23 V in such batteries. 

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. 

Water-activated batteries Activation by fresh- or seawater. 

System Conventional system Water-activated batteries Metal/air batteries Lithium/ water batteries Manually activated Automatically activated... 

The water-activated battery was first developed in the 1940s to meet a need for a high-energy-density, long-shelf-life battery, with good low-temperature performance, for military... 

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. 

Because of the high cost of silver, the impracticality of recovering it after use, other nonsilver water-activated batteries were developed, primarily as the power source for antisubmarine warfare (ASW) equipment. 

Magnesium seawater-activated batteries, using dissolved oxygen in the seawater as the cathode reactant, also have been developed for application in buoys, communications, and underwater propulsion. These batteries, as well as the use of other metals as anodes for water-activated batteries, are covered in Chaps. 16 and 38. 

The advantages and disadvantages of the various water-activated magnesium batteries are given in Table 17.1. 

The principal overall and current-producing reactions for the water-activated magnesium batteries are as follows ... 

Water-activated batteries are manufactured in the following basic types ... 

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. 

A summary of the performance characteristics of the major water-activated batteries currently available is given in Table 17.4. 

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. 

---