Single component sulfur-based cathodes for lithium and lithium-ion batteries

Abstract

The present invention pertains to the selection of cathode materials. The cathode materials of concern are the conducting polymer or backbone and the redox active species or sulfur species. The selection of the materials is based on the characteristics of the materials relating to the other components of the batteries and to each other. The present invention also pertains to the resultant cathode materials, particularly a selected cathode material of a single component sulfur-based conducting polymer with the sulfur species covalently linked to the conducting polymer, and most particularly a thiophene based polymer with covalently linked sulfur species. The conducting polymers have been covalently-derivatized with sulfides and / or sulfide-containing groups as battery cathode materials. The present invention also pertains to a battery employing the selection method and resultant cathode materials.

Description

RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional patent application 60 / 118,068, the contents of which are incorporated herein by reference in their entirety.TECHNICAL FIELD [0002] The present invention relates generally to cathodes for rechargeable batteries. More particularly, the present invention relates to cathode materials based on conducting polymers and sulfur or selenide species and the method of selecting conducting polymers and sulfur or selenide species. The selection method accounts for characteristics of the conducting polymer and the sulfur or selenide species and the specific capacity, capacity fade, charge and discharge rate, physical and chemical stability, safety and other characteristics associated with battery cycles. More particularly, the present invention relates to a single component sulfur-based conducting polymer for use in lithium batteries and the synthesis of such material. BACKGROUND [0003] Increasing reliance on sophisti...

AI Technical Summary

Benefits of technology

[0019] In one embodiment, the selection of cathode materials is based on one or more of the following characteristics of the conducting polymer and / or the sulfur or selenide species: ease of fabrication using straightforward synthetic procedures; ionically conductive for Li+ ions; no labile protons in the material; a high density of electroactive species per weight and volume (i.e. large inherent charge capacity); good overlap of the thermodynamic redox potentials of the electroactive substituents and the conducting polymer backbone; reasonable electronic conductivity of the composite: no solubility in typical electrolyte solutions; and electrochemically, physically, and chemically stable to many repeated charge and discharge cycles. In a preferred embodiment, the selection of the cathode materials is based on all of the above identified characteristics for both the conducting polymer and the sulfur or selenide species.

[0020] In one embodiment, the selection of cathode materials is based on the overlap of the thermodynamic potentials of the electroactive substituents of the sulfur species and the conducting polymer. The cathode materials are chosen based on the redox mediation window. The conducting polymer mediates electrons between the current collector and the sulfur or selenium species. Conducting polymers exhibit potential-dependent conductivities. When the potential is in the “double-layer” region of the conducting polymer (that is, when the conducting polymer is releasing or accepting electrons), the conductivity of the polymer is much higher than when the potential is more negative or more positive of that region. If the conducting polymer is inherently in a less-conductive state in the potential region where the sulfur or selenium species exhibits redox species behavior, mediation of electrons between the current collector and the sulfur or selenium species is poorly effected, the material is less desirable, and the battery performance is poorer.

[0024] In a preferred embodiment, the sulfur species is NOT covalently linked to the conducting polymer backbone. An example of this system is that comprising a mixture of poly(3,4-ethylenedioxythiophene) (PEDT) and 2,5-dimercapto-1,3,4-thiadiazole, dilithium salt (Li2DMcT). PEDT is available as an aqueous dispersion. Li2DMcT is dissolved directly into the PEDT dispersion at high concentrations. Properly treated films cast from that mixture are used as cathode materials in lithium and lithium-ion cells. Alternately, films are prepared by electrochemical or chemical oxidation of the PEDT monomer and Li2DMcT from the same or different solutions in a homogeneous or layered arrangement. Li2DMcT contains no labile protons, so its use in the cathode is attractive. PEDT has a wide potential window of conductivity, contains no labile protons, and is not proton-doped, so its use in the cathode is attractive.

Problems solved by technology

If the conducting polymer is inherently in a less-conductive state in the potential region where the sulfur or selenium species exhibits redox species behavior, mediation of electrons between the current collector and the sulfur or selenium species is poorly effected, the material is less desirable, and the battery performance is poorer.

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