University of California

Polystor Corporation

Robert L Morrison

Steven T Mayer

Richard W Pekala

James L Kaschmitter

Eric Nolin

A method for fabricating thin, flat carbon electrodes by infiltrating highly porous carbon papers, membranes, felts, metal fibers/powders, or fabrics with an appropriate carbon foam precursor material. The infiltrated carbon paper, for example, is then cured to form a gel-saturated carbon paper, which is subsequently dried and pyrolyzed to form a thin sheet of porous carbon. The material readily stays flat and flexible during curing and pyrolyzing to form thin sheets. Precursor materials include polyacrylonitrile (PAN), polymethylacrylonitrile (PMAN), resorcinol/formaldehyde, catechol/formaldehyde, phenol/formaldehyde, etc., or mixtures thereof. These thin films are ideal for use as high power and energy electrodes in batteries, capacitors, and fuel cells, and are potentially useful for capacitive deionization, filtration and catalysis.

Method for making thin carbon foam electrodes

The present invention provides a method of preparing carbon electrodes for use in electrochemical energy storage cells such as lithium ion batteries. The process involves a step of precipitating a polymer from a concentrated solution to yield a structure having at least a partially fractious morphology. The solvent from which the polymer has been precipitated (the 'primary solvent') is then exchanged with another solvent (the 'secondary solvent') in which the polymer is relatively insoluble. Thereafter, the secondary solvent is removed from the precipitated polymer and the dry polymer is contacted with a dopant such as phosphorous. Subsequently, the polymer with dopant is pyrolyzed to yield a carbon material which is assembled into an electrode.

Preparation of carbon electrodes by polymer-precipitation

Biofoam is a rigid, opaque microcellular organic foam made from organic materials derived from natural products and biological organisms. Typical organic materials are agar, agarose, gelatin, algin, alginates, gellan gum, and microcrystalline cellulose. The organic material is dissolved in a polar solvent, typically water, and the solution can be gelled immediately. The gel is frozen and freeze-dried to form the biofoam. Alternatively, a nonpolar solvent is added to the solution and emulsified. The resulting emulsion is then gelled, frozen, and freeze-dried. A variety of crystalline, fibrous, or metallic additives may be added to produce lightweight composite materials with enhanced strength and insulating properties. The amount of dilution of the organic material in the solvent(s) determines the density of the resulting biofoams, which ranges from about 1.0 mg/cm.sup.3 to about 500 mg/cm.sup.3.

Biofoam

Biofoam is a rigid, microcellular organic foam made from organic materials derived from natural products and biological organisms. Starting materials include agar, agarose, gelatin, algin, alginates, gellan gum, and microcrystalline cellulose. The organic material is dissolved in a polar solvent, typically water, and the mixture is gelled. The water in the gel pores is replaced at least once with another solvent to reduce the pore size of the final biofoam. The solvent in the gel pores may be replaced several times. After the final replacement of solvent, the gel is frozen and freeze-dried to form a biofoam. Translucent biofoams are formed by selecting a final solvent that forms very small crystals. A variety of crystalline, fibrous, amorphous, or metallic additives may be incorporated into the foam structure to produce lightweight composite materials with enhanced strength and insulating properties.

Biofoam II

A polymeric foam precursor, wetted with phosphoric acid, is pyrolyzed in an inert atmosphere to produce an open-cell doped carbon foam, which is utilized as a lithium intercalation anode in a secondary, organic electrolyte battery. Tests were conducted in a cell containing an organic electrolyte and using lithium metal counter and reference electrodes, with the anode located therebetween. Results after charge and discharge cycling, for a total of 6 cycles, indicated a substantial increase in the energy storage capability of the phosphorus doped carbon foam relative to the undoped carbon foam, when used as a rechargeable lithium ion battery.

Growing community of inventors

Modesto, CA, United States of America

Robert L Morrison