10 - Manganese dioxide-magnesium perchlorate primary batteries

Abstract

The magnesium cell has an open-circuit voltage of around 2.0 V, compared to 1.5 V for the zinc dry cell. In addition to this higher voltage, the magnesium dry cell has several other advantages over the conventional dry cell. It has the capability of giving twice the gravimetric energy density of the dry cell at medium discharge rates. Manganese dioxide-magnesium perchlorate batteries are available in reserve and non-reserve forms. This chapter focuses on reserve types; the reserve battery is activated by electrolyte addition, either manually or automatically, by electrical or mechanical means. The heat of corrosion of the magnesium anode, at a controlled rate, enhances operation over a wide range of temperature and discharge rates. The batteries are non-hazardous, being vented to atmosphere, and non-explosive; the electrolyte is far less corrosive than that used in conventional alkaline batteries. The positive plates are high-conductivity expanded metal grids and the negative plates are fabricated from magnesium sheet. The operating and storage temperatures, respectively, are -54 to + 18°C and -68 to + 18°C. Batteries are available with volumes of 4 g cm3 upwards and 28 g cm3 upwards. A shelf life of 3-5 years is claimed at 20°C, reducing to 3 months at 71°C.