GB2112561A - Solid state electrochemical devices - Google Patents

Abstract

Electrochemical devices suitable for room temperature, low current density applications may be made from a combination of an electrode which is an active light metal, in particular magnesium, and a solid electrolyte of the form B4AX5-nYn, where B is Ag or Cu, A is K, NH4 or Rb and X and Y are Cl, Br or I. n can take values between 0 and 4; Ag4RbI5 is a typical example. Such devices include electrochemical cells, typical of which is a cell comprising an anode compartment consisting of magnesium powder mixed with the electrolyte, an electrolyte layer of the type specified and a suitable cathode material such as iodine, iodine-containing complexes and oxides of transition metals. In an alternative cell the electrolyte layer is omitted and the anode is placed in direct contact with a suitable cathode material, either elemental iodine or an iodine-containing complex such as iodine-perylene.

Description

SPECIFICATION Solid state electrochemical devices This invention relates to solid-state electrochemic al devices such as electrochemical cell, batteries, coulometers, and elapsed- time measuring devices.

According to one aspect of the present invention, a solid-state electrochemical device comprises an electrode of magnesium or other polyvalent active metal, in conjunction with a solid electrolyte of the form B4A X > nYn where B is silver or copper, A is potassium or rubidium orammonium, and X, Y are chlorine, bromine or iodine; n can take values between 0 and 4. An example is Ag4Rbl5.

The above mentioned combination of anode and electrolyte materials provide unexpectedly good performance in solid-state electrochemical devices.

The applicants believe that this is attributable to the fact that the relative ionic dimensions of the alkali metals and halogens in the electrolyte provide vacant sites for the conducting species namely silver, copper, or the polyvalent electrode metal which enhance ionic mobility.

According to another aspect of the invention a solid-state electrochemical device comprises an electrode of magnesium or other polyvalent active metal, in conjunction with another electrode consisting of iodine in the elemental or an alternative appropriate form e.g. a polyiodide or iodine complex, of manganese dioxide, in the absence of a deliberately incorporated solid electrolyte. It is believed that, in such a device, an electrolyte is formed in situ but the nature of this autogenous electrolyte has not been determined.

A solid-state electrochemical cell embodying the first aspect of the invention was prepared as follows: An electrolyte was prepared by slowly cooling a melt of rubidium iodide (lug) and silver iodide (4.4219g) to form silver rubidium iodide.

Atestcell utilising such an electrolyte was made in the following way. A layer of anode material, composed of fine magnesium powder mixed with powdered electrolyte material, was put into the base of a die chamber at room temperature and lightly compacted. A layer of silver rubidium iodide was placed above the anode layer and lightly compacted.

A layer of suitable cathode material was placed above the electrolyte and the pellet was pressed at 3.5 Mom~2 for a suitable period. The pellet formed the test cell and was suitably mounted so that voltage readings could be taken.

Suitable cathodes include iodine, polyiodides, iodine-containing complexes e.g. perylene-iodine complexes, and manganese dioxide.

Cells produced in this manner have produced open circuit voltages in excess of 1.2 volts. When cells have been tested under load, voltages in excess of 0.55V have been maintained while a current of 6~wAwas being drawn.

A solid-state electrochemical cell embodying the second aspect of this invention was prepared by compacting a layer of Mg powder directly in contact with a layer of compacted elemental iodine. Cells prepared in this manner have produced open circuit voltages in excess of 1 .5V; when cells have been tested under load, voltages greater than 1.1 5V have been maintained whilst a current of 1 2,aA was being drawn and voltages greater than 0.75 volts have been maintained whilst a current of 75,uA was being drawn.

Iodine-containing complexes suitable for use as cathodes in direct contact with an anode of magnesium or other polyvalent active metal include iodine-perylene, iodine - 2 - vinyl pyridine, rubidium triiodide, ammonium triiodide, or tetraalkyl ammonium polyiodides.

Claims (3)

1. A battery or related electrochemical device comprising an active light metal anode and an electrolyte of the form B4 A X SnYn where B is silver or copper, A is potassium, ammonium or rubidium and X, Y are chlorine, bromine or iodine; n can take values between 0 and 4.

2. A device as claimed in claim 1 in which the anode is magnesium.

3. A battery comprising magnesium or calcium in direct contact with iodine or an iodine-containing complex, in the absence of a deliberately incorporated solid electrolyte.