GB2107510A - Electrochemical device - Google Patents

Abstract

Electrochemical devices suitable for room temperature, low current density applications, are made from a combination of an electrode which is an active light metal (in particular aluminium, calcium or magnesium) and a solid electrolyte formed by an organic Group VI- onium silver or copper halide salt

Description

SPECIFICATION Electrochemical devices This invention relates to solid electrolyte material for use in electrochemical devices, including solid state electrochemical cells, solid state batteries comprising an assembly of such cells, elapsed-time measuring devices, coulometer and other devices.

Miniaturization in electronics has rapidly advanced in recent years and has resulted in increased demand for highly ionically conduct- ing solid electrolytes comparable to electronic components employed in the circuitry. Such electrolytes can be employed in solid state electro-chemical devices such as cells and timers. Such devices do not suffer from leakage problems as the electrolyte is solid. Further, because the tendency for material migration in a solid system is low, devices containing solid electrolytes have a long shelf life.

The solid electrolytes employed in solid state devices are ionic conductors which facilitate ionic flow during the operation of the solid state devices. A reasonable performance is obtained from solid state devices containing solid electrolytes which possess high ionic conductivity but low electronic conductivity at room temperature, and for which the transport number of the predominant conducting species approaches unity.

Our United Kingdom Patent Specification No. 1474246 concerns a solid electrolyte material for electro-chemical devices, comprising an organic Group Vl-onium silver or copper halide salt. More specifically, the electrolyte comprises a complex or compound of silver (or copper) iodide with either a sulphonium iodide or a selenonium iodide or a telluoronium iodide.

It has been found that such solid electrolytes have high ionic conductance at room temperature and in particular can have conductivities exceeding 2.10 - 4(ohm-cm) - 1 which is that of silver iodide, together with negligible electronic conductivity.

According to Specification No. 1474246, the solid electrolyte is used with an anode comprising silver or cooper, which anode may also incorporate the above-mentioned electrolyte or another electrolyte.

Electrochemical cells using the above-mentioned solid electrolytes with silver or copper at the anode have the disadvantage of a relatively low voltage, typically about 0.6 volts.

It It has now been found, surprisingly, that solid electrolytes of the above mentioned kind can be used in conjunction with an anode of an active light metal, e.g. aluminium, calcium, and in particular magnesium, to give a substantially higher voltage in room-temperature, low-current-density operation. Cell voltages over 1.5 volts can be obtained.

The present invention provides an electrochemical device comprising in combination an active light metal electrode and a solid electrolyte formed by an organic Group VI- onium silver or copper halide salt.

The invention also provides an electrochemical device comprising in combination an active light metal electrode and a solid electrolyte of the form n Ag I, Z+l or n Ag, Z22+2l-; where Z+ is of the form R,R2R3Y or R,R5Y or R7Y and Z22+ is of the form R,R2Y R8YR3R4 or R5YR8YR,R2 or R5YR8YR6 or

in which R1, R2, R3, R4, are straight or branched chain organic groups, R5 Y and Y R6 are cyclic organic groups containing Y, R7Y is a cyclic organic group containing Y adjacent to a double bond, R8 and R9 are organic bridge groups linking two Y groups and R, and R9 inclusive can contain or not contain heteroatoms; Y is S+, Se + or Toe +.

Silver can be replaced by copper.

Preferred values of the group weighting coefficient are below 7.0 for S+, and below 4.5 for Se+.

Stated in another way, the present inven tion provides an electro-chemical device com prising a light metal, in particular magnesium, electrode in conjunction with a solid electro lyte which consists of an organic sulphonium iodide of the form Mn(R,R2R3VI) In + 1 or Mn(R1R2VI(CH2)mVlR3R4)1n+2; where B1, R2, R, R4 can be straight or branched chains contain ing or not containing heteroatoms, or alterna tively R, and R2 and/or R3 and R4 are oppo site ends of a chain or branched chain, con taining or not containing heteroatoms in which case the cyclic structure embodying the group VI entity is produced; VI is S, Se or Te; m is 2,3 etc.; M is Ag (silver) or Cu (copper).

Preferred values of n are in the range 0 to 40.

The electrolyte materials are based on silver salts and no deliberate attempt is made to incorporate ionic, metallic, complexed or other forms of the active light metal into the electro lyte, prior to cell operation.

Suitable cathodes include transition metal oxides e.g. manganese dioxide, iodine, group VI onium polyiodides, quaternary ammonium polyiodides or iodine-containing complexes e.g. peryleneiodine complexes, sometimes in timately mixed with a conductor e.g. finely divided carbon power with or without the addition of a finely ground suitable electrolyte.

The electrolyte material used in the cathode can be a silver group VI onium iodide or another material which is high silver or suit able metal ion conductor.

The electrolytes described above can also be used with a variety of cathode materials including polyiodides of monovalent cations, e.g. RblS. Iodine may be totally or partially replaced by other halogens.

A test cell was prepared as follows: An electrolyte with a conductivity of 9 X l0-3(ohm cm)-' was prepared by adding powdered cuprous iodide (4.1 323g) to 4 methyl-1, 4-oxathianium iodide (lug) (84 mol.%: 16 mol.%). The materials were ground together in an agate pestle and mortar and then dried over P205 for 72 hours.

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 the copper group VI onium electrolyte material was then placed above the anode layer in the die chamber and lightly compacted. A layer of suitable cathode material was placed above the electrolyte layer and the pellet thus formed was pressed at 350 M Pa for a suitable period e.g. 30 sec.

The pellet formed the test cell and was suitably mounted so that voltage readings could be taken.

With such cells, after an induction period of up to 700 hours, voltages of about 1.5V can be maintained for several weeks under a load of 75 kohm, corresponding to a current of 20yA and a current density of 15yA cm-2.

Currents as high as 140ELA can be drawn with minimum voltage loss. Anode mass efficiencies up to 30% have been achieved.

Claims (7)

1. An electrochemical device comprising in combination an active light metal electrode and a solid electrolyte formed by an organic Group VI-onium silver or copper halide salt.

2. An electrochemical device comprising in combination an active light metal electrode and a solid electrolyte of the form n Agl, Z+l- or n Agl, Z22+21-; where Z+ is of the form R1R2R3Y or R,R5Y or R7Y and Z22+ is of the form R,R2YR8YR3R4 or R5YR8YR,R2 or R5YR8YR6 or

in which R,, R2, R3, R4 are straight or branched chain organic groups, R9Y and YR, are cyclic organic groups containing Y, R7Y is a cyclic organic group containing Y adjacent to a double bond, R8 and Rg are organic bridge groups linking two Y groups and R, and Rg inclusive can contain or not contain heteroatoms; Y is S+, Se+ or Te+

3. A device as claimed in claim 2 in which n is O to 40.

4. A device as claimed in claim 2 or 3 having a group weighting coefficient below 7.0 for S+.

5. A device as claimed in claim 2 or 3 having a group weighting coefficient below 4.5 for Se+.

6. A device as claimed in claim 2,3,4 or S in which Ag is replaced by Cu.

7. A device as claimed in any preceding claim in which the active light metal is Al, Ca or Mg.