HIGH RATE METAL OXYHALIDE CELLS

Abstract: Improved catalysts for the reduction of oxyhalide depolarizers such as SOCl2 and SO2Cl2 in active-metal non-aqueous cells are provided which are easier to prepare and less expensive than phthalocyanine complexes and which are generally more stable in the cell environment. These catalysts include certain macrocyclic complexes of Schiff's base prepared by the reaction of an aldehyde with a primary diamine. The preferred embodiments include mononuclear metal macrocyclic complexes made from salicylaldehyde and o-phenylenediamine and binuclear metal macrocyclic complexes of 5-methyl isophthalaldehyde and 1,3-diaminopropane.

Description: HIGH RATE METAL OXYHALIDE CELLS BACKGROUND OF THE INVENTION The invention herein described was made in the source of or under a contract or subcontract thereunder with the Department of the Army. Field of the Invention The present invention relates generally to the field of non-aqueous electrochemical cells and, more particularly to a class of catalysts for the reduction of oxyhalide depolarizers such as SOCI2 and SO2CI2 in such cells. Description of the Prior Art Much work has been done in the field of high energy battery systems utilizing highly reactive anode materials such as alkali or alkaline earth metals in combination with a non-aqueous electrolyte. The electrolyte is normally composed of a solute which is commonly a metal salt or a complex metal salt of the anode metal dissolved in a compatible non-aqueous solvent depolarizer such as SO2, SOCI2, or SO2CI2. An inert cathode, usually of carbon black, is also used in such cells. The potential of electrochemical couples, such as those mentioned above as high rate, high-power batteries, has not been fully realized mainly because of excessive cathode polarization particularly at high discharge rates and low operating temperatures. This causes a deterioration of cell performance after a short period of operation. For this reason, much research has been conducted concerning the development of additives such as catalysts to reduce the cathode depolarizer, thereby improving the rate capability of the cathodes. Some improvement in the rate capability of these carbon cathodes has been achieved by doping them with metals such as platinum or metal halides. However, high amounts of the metals or -metal halides are required to effectively increase the rate capability of cells such as Li/SOCl2 cells. Also, the cell performance of these dopants deteriorates with thinner electrodes and at the higher temperatures required for certain applications. More recently, metal-phthalocyanine complexes have been shown to possess significant catalytic activity for the electrochemical reduction of solvent depolarizers such as thionyl chloride or sulfural chloride, thereby increasing cell capacity. Examples of such are found in U.S. patents 4,252,875 and 4,405,693. The need still exists for the provision of catalyzed cathodes for cells such as Li/S0Cl2 cells which are stable and effective over a wide temperature range and which are sufficiently stable in the cell to be used in both active and reserve configurations. SUMMARY OF THE INVENTION By means of the present invention, improved catalysts for the reduction of oxyhalide depolarizers such as SOCI2 and SO2CI2 are provided which are easier to prepare and less expensive than phthalocyanine complexes and which are generally more stable in the cell environment. These catalysts include certain macrocyclic complexes of Schiffs base prepared by the reaction of an aldehyde with a primary diamine. The preferred embodi¬ ments include mononuclear metal macrocyclic complexes made from salicylaldehyde and o-phenylenediamine of a structure such as and binuclear metal macrocyclic complexes of 5-methyl isophthaialdehyde and 1,3-diaminopropane having a structure such as where M or Me represents a metal selected from the group consisting of iron and cobalt and m and n represent integers. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIGURE 1 is a graphical representation of the discharge characteristics of a Li/SOCl2 cell employing prior art catalysts cobalt phthalocyanine (CoPc) and iron phthalocyanine (FePc) dissolved in the electrolyte compared with the uncatalyzed baseline. FIGURE 2 is a graphical representation showing the discharge characteristics of a Li/SOCl2 cell using mononuclear CoSB catalyst compared with the uncatalyzed baseline. FIGURE 3 is a graphical representation of polarization characteristics of a Li/SOCl 2 cell using binuclear metal complexes FeMac and CoMac of the invention; FIGURE 4 is a graphical representation of the discharge characteristics of a cell of FIGURE 2 at 23°C and 63°C with and without CoSB. DESCRIPTION OF THE PREFERRED EMBODIMENT*. Catalyst Preparation The syntheses of FeMac and CoMac were carried out using the method of Pilkington et al, Australian Journal of Chemistry Vol. 23, 2225 (1970). The synthese of CoSB and FeSB were carried out using a method described in Jahnke et al. Topics in Current Chemistry, Vol. 1 , 133 (1979) . Example 1 A solution of 5-methyl isophthalaldehyde (0.05 mole) dissolved in the minimum volume of boiling methano was added to a suspension formed by mixing 1,3-diamino- propane (0.05M) with a saturated solution of cobalt chloride in methanol. The mixture was heated under reflux for 1 hour. Methanol was removed by boiling at atmospheric pressure. The product was poured into ten times its volume of tetrahydrofuran. The product was filtered, washed with water and dried. Example 2 The process of Example 1 was repeated except that iron chloride was substituted for cobalt chloride of Example 1. The process of Examples 1 and 2 produced binuclear metal macrocyclic complexes CoMac and FeMac, repectively, of the following structure: where M represents iron or cobalt and m and n are integers. Example 3 A solution of salicylaldehyde (0.05M), o-phenyl¬ enediamine (0.05M) and cobalt acetate (0.025M) was refluxed in ethanol for about 30 minutes. The resulting product was washed with cold methanol and dried at 120°C. Ex ample 4 Example 3 was repeated substituting iron acetat for the cobalt acetate. The structure of the complexes formed in Examples 3 and 4 known as CoSB and FeSB, respectively, was as follows: Performance of Catalyst in Cells Tables 1 and 2 show a comparison of discharge characteristics of cells using a prior art catalyst, the catalyst of Example 3, and no catalyst. TABLE 1. DISCHARGE CHARACTERISTICS OF Li/SOCl 2 CELLS WITH VARIOUS CATALYSTS WITH A CONSTANT CURREN DENSITY OF 30 MA/cm 2 AT 23°C Cell Voltage Discharge Life Catalyst (V) (Minutes) None 2.92 34 Iron Phthalocyanine (FePc) 3.30 52 Mononuclear Couples with Schiff*s Base (CoSB) 3.30 70 • ELECTROLYTE - (0.5 M LiAlCl 4 + 1.0 M A1C1 3 )/S0C1 2 • CATHODE THICKNESS = 1.0 millimeter TABLE 2. DISCHARGE CHARACTERISTICS OF Li/SOCl2 CELLS WITH AND WITHOUT COSB COMPLEX AT A CONSTANT CURRENT LOAD OF 10 MA/cm 2 AT DIFFERENT OPERATING TEMPERATURES -32°C -18°C 23°C 63°C Voltage at Voltage at Voltage at Voltage at 50% DOD DOD 50% DOD DOD 50% DOD DOD 50% DOD DO atalyst (V) (min) (V) (min) (V) (min) (V) (mi one 2.70 55 2.80 80 3.12 105 3. 36 16 oSB 2.72 60 2.94 90 3.39 182 3.44 19 10 FIGURE 1 shows the discharge characteristics of prior art cells using cobalt phthalocyanine (CoPc) and iron phthalocyanine (FePc) catalysts dissolved in the electrolyte. It should be noted that the FePc exhibits a somewhat higher catalytic activity. FIGURES 2-4 show 15 data derived using the catalysts of the present invention. In FIGURES 2-4, the discharge characteristics of Li/SOCl2 cells catalyzed by various metal macrocyclic 20 complexes are compared to an uncatalyzed cell. All catalyzed cells showed substantial improvement in both cell voltage and specific cathode capacity over the uncatalyzed cell. These complexes have shown as good or better catalytic activity for the reduction of SOCI2 than 25 the iron phthalocyanine catalyst. In the case of metal pthalocyanine catalysts, FePc showed the best catalytic activity, whereas, cobalt tetraphenylporphyrin (CoTPP) and cobalt Schiffs base complexes (CoSB) posses superior catalytic activity for SOCI2 reduction than the iron complexes of these macrocyclic rings. Electronic charge density on the central metal ion, extent of orbital overlapping backbonding and the nature of the specific interaction of the complex with the carbon surface, are some of the factors that can influence the catalytic activity of these complexes for the reduction of SOCI2. In the case of the binuclear macrocyclic complexes the iron couples appear to be superior. The operating temperature also appears to influence the catalytic activity as shown in Table 2. I general, the cell performance improved with catalyzed cells irrespective of operating temperatures and current densities. At low operation temperatures, however, the catalytic activity of cobalt Schiff*s base complex is rather reduced but the significance of this behavior is not yet understood. However, one of the factors could b the specific interaction of the CoSB complex with carbon cathode surface. A better way of impregnating the complex onto carbon should show better results since the performance of cells with this catalyst is drastically improved at high operating temperatures. The catalyst stability is projected to be responsible for the superio performance at high operating temperatures.

Claims: O 2__£ The embodiments of the invention in which an exclusive property or right is claimed are defined as follows: 1. In a non-aqueous electrochemical cell system having an active metal anode, a cathode and a non-aqueous electrolyte having an oxyhalide depolarizer, the improve¬ ment comprising: a catalyst for the reduction of said oxyhalide depolar- izer comprising a metal complex of Schiffs base, said Schiffs base being selected from the group consisting of macrocyclic complexes of 5-methyl isophthalaldehyde and a diamino alkane and complexes of salicylaldehyde and o-phenylenediamine, and wherein the metal in said metal complex is selected from the group consisting of iron and cobalt. 2. The cell of claim 1 wherein said metal is cobalt. 3. The cell of claim 1 wherein said metal is ron. 4. The cell of claim 1 wherein said Schiffs base is one made from salisaldehyde and o-phenylene¬ diamine and said metal complex is mononuclear. 5. The cell of claim 3 wherein said metal is coba t. 6. The cell of claim 3 wherein said metal is iron. 7. The cell of claim 1 wherein said Schiffs base is one made from 5-methyl isophthalaldehyde and 1,3-diaminoρropane and wherein said metal complex is binuclear. 8. The cell of claim 5 wherein said metal is cobalt. 9. The cell of claim 5 wherein said metal is iron. 10. In a non-aqueous electrochemical cell havin a lithium anode, a carbon cathode and a non-aqueous electrolyte comprising LiAlCl 4 salt in S0C1 2 depolarizer solvent the improvement comprising: a catalyst for the reduction of said oxyhalide depolar¬ izer comprising a metal complex of Schiffs base, said shift base being selected from the group consisting of macrocyclic complexes of 5-methyl (Claim 10 continued) isophthalaldehyde and a diamino alkane and complexes of salicylaldehyde and o-phenylenediamine, and wherein the metal in said metal complex is selected from the group consisting of iron and cobalt. 11. The cell of claim 10 wherein said metal is cobalt. 12. The cell of claim 10 wherein said metal is iron.

Inventors: DODDAPANENI NARAYAN, DODDAPANENI, NARAYAN
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1985
Main classification: H01M6
IPC codes: H01M4, H01M6