GB2108312A - Electrochemical cells - Google Patents

Abstract

An electrochemical cell with a lithium anode, an electrolyte solution comprising an electrolyte salt dissolved in sulfuryl chloride and a cathode doped with a macrocyclic complex of a transition metal such as CoPc, FePc or (CoPc)n.

Description

SPECIFICATION Electrochemical cells An electrochemical cell based on lithium-sulfuryi chloride (LiiSO2Cl2) electrochemical system offers a potentially higher energy performance than the lithium thionyl chloride (Li/SOCI2) system. Poor electrochemical discharge and relatively narrow operating temperature range have, however, hindered a practical cell development. One of the factors believed responsible for poor discharge performance is cathode substrate. High surface area Teflon (trademark of E.l. du Pont DeNemours)bonded carbon cathodes, where S02C12 undergoes reduction, and irreversibility of the cathode reaction contribute excessive cathode overpotential. Another factor contributing to premature cell failure, particularly at high discharge rates, is the presence of reactive intermediate reduction species.

According to the present invention, there is provided an electrochemical cell with an improved current producing capability, the cell comprising a metal anode; a sulfuryl chloride depolarizer and an electrolyte salt; and a cathode doped with a macrocyclic complex of a transition metal.

The catalysts may be such as polymeric and monomeric cobalt and iron phthalocyanines.

It has been discovered that the rate of S02C12 reduction can be increased substantially by doping the porous carbon cathodes with CoPo, FePc and (CoPc) catalysts. Both monomeric CoPe and FePc are soluble in acid (AICI3/SQ2CI2) as well as neutral (LiAlClSO2Cl2) electrolytes. However, the heat treated (500 to 600 C) polymeric (CoPcXn, which is synthesized by heating a mixture of 3,3,4, 4-benzophenone tetracarboxylic dianhydride (BTDA), CoCI2 and urea at 200 C for one hour, does not dissolve and is stable in both acid and neutral electrolytes.

A preferred cathode material is Shawinigan (Registered Trade Mark) carbon black. A binder, such as Teflon (trademark of E.l. du Pont DeNemours) may also be included.

Embodiments of the present invention will now be described. A number of cells were constructed employing a lithium anode, a sulfuryl chloride depolarizer and lithium tetrachloroaluminate elec troiyte salt, and porous carbon cathodes doped with a macrocyclic complex of a transition metal. Experiments, as described below, were performed on these various cells having cathodes catalyzed with FePc, CoPo, or (CoPc) and compared to a cell with uncatalyzed cathode. Catalyst doping of cathodes can be achieved by mixing the catalyst with carbon before cathode fabrication or, in the case of FePc and CoPc, by dissolving the catalyst in the electrolyte.

Each of the cells for which data is given in Table 1 below comprised a lithium anode, an electrolyte of 1.5 mole solution of lithium tetrachloroaluminate in sulfuryl chloride and a porous carbon cathode.

In the cells with FePc and CoPe, the catalyst doping of the cathode was accomplished by adding catalyst to the electrolyte. Approximately 3 milligrams of catalyst per cc of electrolyte were used. It has been found, however, that much smaller amounts of the catalyst, i.e. less than 0.5 milligrams per cc of electrolyte, produce a significant improvement in the cell operation. On the other hand, much larger amounts of the catalyst will, beyond a certain point, not produce any further improvement.

Cathode doping with (CoPc) was accomplished by adding it to the cathode during the manufacture of the cathode. The cathode was formed by mixing (CoPc) with Shawinigan (R.T.M.) carbon black in approximate ratio of 5% to 95% and heat treating the mixture at 55000 or higher for two or morn hours.

Upon cooling, a scurry was formed by adding to the mixture a nonaqueous solvent and binder, such as Teflon. The scurry was then shaped into the desired cathode shape and allowed to dry.

Although in the specific example given here, the ratio of (CoPc) to carbon was almost 5% to 95%, it has been found that the amount of (CoPc) could vary from 0.5% to 20% by weight based on the weight of carbon. Preferrably, from 2% to 10% by weight, based on the weight of carbon, is employed.

TABLE 1 POLARIZATION CHARACTERISTICS OF Li/SO2Sl2 CELLS WITH VARIOUS CATALYSTS (1.SM LiALCl,,'SO2Cl2 at 72 F)

CURRENT CELL VOLTAGE-volts milliamperes per cm No Catalyst FePc CoPc (CoPc)n 5 3.55 3.52 3.55 3.58 10 3.17 3.25 3.48 3.50 20 3.05 3.15 3.37 3.45 30 3.00 3.10 3.30 3.38 40 2.95 3.06 3.25 3.33 As can be seen from Table 1 above, the cells doped with FePc, CoPc, and (CoPc) produced significantly higher voltages.The greatest improvement throughout the entire current rate discharge range was shown by the cell having its cathode catalyzed by (CoPc).

Table 2 below comparative polarization character istics of cells similartothose represented byTable 1, but utilizing 2.3M AICI3/SO2CI2 as the electrolyte.

TABLE 2 POLARIZATION CHARECTERISTICS Li/SO2Cl2 CELLS WITH VARIOUS CATALYSTS (2.3M AlCl3/SO2Cl2 AT72 F.

CURRENT CELL VOTAGE - volts milliamperes per cm No Catalyst FePc CoPc (CoPc)n 10 3.21 3.76 3.31 3.85 20 3.02 3.30 3.45 3.55 30 2.94 3.21 3.37 3.34 40 2.88 3.15 3.32 3.28 60 2.75 3.05 3.20 3.13 80 2.45 2.90 3.11 3.04

Claims (7)

1. An electrochemical cell comprising d petal anode; a sulfuryl chloride depolari.r and an electro lyte salt; and a cathode doped with a macrocyclic complex of a transition metal.

2 The electrochemical cell of Claim 1, wherein the cathode is doped with a catalyst selected from CoPc, FePc and (CoPc)n.

3. The cell of Claim 1 or 2, wherein the cathode consists primarily of carbon.

4 The cell of Claim 3,wherein said carbon comprises Shawinigan carbon black.

5. The cell of any one of Claim 1 to 4, wherein said electrolyte salt is lithium tetrachloroaluminate or aluminium chloride.

6. The cell of any one of the preceding claims, wherein the anode is an alkaline metal, for example lithium.

7. An electrochemical cell substantially as herein described.