Novel composite cathodes, eletrochemical cells comprising novel composite cathodes, and processes for fabricating same

Abstract

The present invention pertains to composite cathodes suitable for use in an electrochemical cell, said cathodes comprising: (a) an electroactive sulfur-containing cathode material, wherein said electroactive sulfur-containing cathode material, in its oxidized state, comprises a polysulfide moiety of the formula —Sm—, wherein m is an integer equal to or greater than 3; and, (b) an electroactive transition metal chalcogenide composition, which encapsulates said electroactive sulfur-containing cathode material, and which retards the transport of anionic reduction products of said electroactive sulfur-containing cathode material, said electroactive transition metal chalcogenide composition comprising an electroactive transition metal chalcogenide having the formula Mj Yk (OR)l wherein: M is a transition metal; Y is the same or different at each occurrence and is oxygen, sulfur, or selenium; R is an organic group and is the same or different at each occurrence; j is an integer ranging from 1 to 12; k is a number ranging from 0 to 72; and l is a number ranging from 0 to 72; with the proviso that k and l cannot both be 0. The present invention also pertains to methods of making such composite cathodes, cells comprising such composite cathodes, and methods of making such cells.

Description

RELATED APPLICATION [0001] This application is a continuation of U.S. patent application Ser. No. 08 / 859,996 filed 21 May 1997, now U.S. Pat. No. ______, which claims priority to U.S. provisional patent application Ser. No. 60 / 018,115 filed 22 May 1996, the contents of both of which are incorporated herein by reference in their entirety.TECHNICAL FIELD [0002] The present invention pertains generally to the field of cathodes and rechargeable electric current producing cells. More particularly, the present invention pertains to composite cathodes which comprise (a) an electroactive sulfur-containing cathode material, wherein said electroactive sulfur-containing cathode material, in its oxidized state, comprises a polysulfide moiety of the formula —Sm—, wherein m is an integer equal to or greater than 3; and, (b) an electroactive transition metal chalcogenide composition, which encapsulates said electroactive sulfur-containing cathode material, and which retards the transport of anioni...

AI Technical Summary

Benefits of technology

[0023] (b) an electroactive transition metal chalcogenide composition, which encapsulates said electroactive sulfur-containing cathode material, and which retards the transport of anionic reduction products of said electroactive sulfur-containing cathode material, said electroactive transition metal chalcogenide composition comprising an electroactive transition metal chalcogenide having the formula Mj Yk(OR)l wherein: M is a transition metal;

Problems solved by technology

The depolymerization which occurs during the discharging of the cell results in lower molecular weight polymeric and monomeric species, namely soluble anionic organic sulfides, which can dissolve into the electrolyte and cause self-discharge as well as reduced capacity, thereby severely reducing the utility of the organo-sulfur material as cathode-active material and eventually leading to complete cell failure.

The result is an unsatisfactory cycle life having a maximum of about 200 deep discharge-charge cycles, more typically less than 100 cycles as described in J. Electrochem. Soc., Vol. 138, pp.

A significant drawback with cells containing cathodes comprising elemental sulfur, organosulfur and carbon-sulfur materials relates to the dissolution and excessive out-diffusion of soluble sulfides, polysulfides, organo-sulfides, carbon-sulfides and / or carbon-polysulfides, hereinafter referred to as anionic reduction products, from the cathode into the rest of the cell.

This process leads to several problems: high self-discharge rates, loss of cathode capacity, corrosion of current collectors and electrical leads leading to loss of electrical contact to active cell components, fouling of the anode surface giving rise to malfunction of the anode, and clogging of the pores in the cell membrane separator which leads to loss of ion transport and large increases in internal resistance in the cell.

Also there is no mention of improved capacity and battery cycle stability and life by the use of an electroactive transition metal chalcogenide with the elemental sulfur electroactive material.

This reduced energy density is a disadvantage of derivatives of organo-sulfur materials when utilized to overcome the dissolution problem.

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