No part of the invention described herein was the result of Federally sponsored research or development.
The invention relates to the fields of electrode manufacturing, web coating, energy storage, energy efficiency, batteries, secondary batteries, and lithium ion batteries.
Rechargeable batteries play an important role in everyday modern life. From portable electronics to hybrid electric and electric vehicles, rechargeable batteries are an indispensable part of our society. The advent of lithium ion batteries was an important development in the field of rechargeable batteries. Lithium ion batteries typically comprise two electrodes, those being the anode and the cathode, each formed separately on a metal foil backing called a current collector. In a cell, the exposed surfaces of the electrodes are faced towards each other and an ion permeable, electrically insulating barrier membrane, called the separator, is disposed between the open electrode faces to prevent their direct contact. An electrolyte containing solution is introduced between the layers to provide a medium for ion conduction between the electrodes through the separator while electrons migrate between current collectors via an external electrical circuit to produce work.
Traditionally, lithium ion battery electrodes are made by spreading a thick slurry that contains active material particles onto a metal foil support that also acts as a current collector. One reason for applying liquid electrode coatings to metal foil supports is to ensure good electrical contact between the electrode and the current collector bound to it. To act as a support for manufacturing, however, the metal foils need to be sufficiently thick enough to withstand the mechanical forces applied to the foil during unwinding, processing, and rewinding during production activities.
In many situations, the thickness of a metal foil is driven more by mechanical issues than electrical requirements. As a result, an electrode often requires a thicker foil than is electrically necessary. The additional metal foil thickness adds to the overall weight, volume, and cost of the resulting battery. Accordingly, there is a need to reduce the amount of metal foil needed to produce a battery because lowering costs and reducing weight in lithium ion batteries are important goals towards the electrification of transportation, an important step in the reduction of human-caused greenhouse gas emission.
An example of a typical lithium ion battery cell found in the prior art can be seen in
a & 2b depict another typical battery cell with a thermal shut-down separator shown in cross-section found in the prior art. Here, the separator comprises three parts, Outer Layers 125a and 125c with Shutdown Separator 125b therebetween. When a cell containing a shutdown separator experiences higher than normal operating temperatures, Shutdown Separator 125b softens to close off its pores thus rendering it non-ion-permeable. In-turn, the cell shuts down due to the breaking of the electrolyte circuit within the cell between the anode and cathode.
The invention disclosed herein provides for methods and devices arising therefrom for making batteries with minimal to zero amounts of metal foil to lower costs and reduce battery weight.
The invention provides, in one aspect, methods for making battery electrodes comprising the steps of: providing an ion permeable electrically insulating substrate having a surface; applying an active material suspension onto the substrate surface to produce an active material layer having first and second active material layer surfaces, the first active material layer surface being adjacent to the substrate surface, the active material suspension comprising: active material particles capable of reversibly lithiating and de-lithiating; conductive particles capable of conducting electrons; and, binder polymer; applying a conductive layer upon the active material layer wherein the conductive layer is in electrical communication with the coating layer.
In some embodiments, the substrate may comprise a battery separator, preferably a battery separator suitable for use in lithium ion batteries. The battery separator may comprise a material selected from the group of polymers and polymer precursors including, but not limited to: polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyurethane, polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), polytetraethylene glycol diacrylate, and, copolymer.
In some embodiments, the substrate may comprise a first microporous membrane and a second ceramic/porous polymer composite layer, wherein the ceramic composite layer consists of a porous polymer and inorganic particles composed as a matrix, the matrix being one or a combination of: silicon dioxide (SiO2); aluminum oxide (Al2O3); calcium carbonate (CaCO3); titanium dioxide (TiO2); SiS2; and, SiPO4. Preferably, the inorganic particles make up from 5% to 80% by weight of the ceramic composite layer In other embodiments, the inorganic particles make up from 40% to 60% by weight of the ceramic composite layer.
In some embodiments, the substrate may comprise one or a combination of: polyacrylates (AA); acrylonitrile-butadiene-styrene (ABS); ethylene vinyl alcohol (E/VAL); fluoroplastics (PTFE), (FEP, PFA, CTFE); high impact polystyrene (HIPS); melamine formaldehyde (MF); poly liquid crystal polymer (LCP); polyacetal (POM); acrylo nitrile (PAN); phenol-formaldehyde plastic (PF); polyamide (PA); polyamide-imide (PAI); polyaryletherketone (PAEK)′ polyetheretherketone (PEEK); 2. cis 1,4-poly butadiene (PBD); trans 1,4-poly butadiene (PBD); poly 1-butene (PB); poly butylene terephthalate (PBT); poly caprolactam; poly carbonate (PC); polycarbonate/acrylonitrile butadiene styrene (PC/ABS); poly 2,6-dimethyl-1,4-phenylene ether (PPE); polydicyclopentadiene (PDCP); polyester (PL); poly ether ether ketone (PEEK); poly etherimide (PEI); poly ethylene (PE, LDPE, MDPE, HDPE, UHDPE); polyethylenechlorinates (PEC); poly(ethylene glycol) (PEG); poly ethylene hexamethylene dicarbamate (PEHD); poly ethylene oxide (PEO); polyethersulfone (PES); poly ethylene sulphide (PES); poly ethylene terephthalate (PET); Phenolics (PF); poly hexamethylene adipamide (PHMA); poly hexamethylene sebacamide (PHMS); polyhydroxyethylmethacrylate (HEMA)poly imide (PI); poly isobutylene (PIB); polyektone (PK); polylactic acid (PLA); poly methyl methacrylate (PMMA); poly methyl pentene (PMP); poly m-methyl styrene (PMMS); poly p-methyl styrene (PPMS); poly oxymethylene (POM); poly pentamethylene hexamethylene dicarbamate (PPHD); poly m-phenylene; isophthalamide (PMIA); poly phenylene oxide (PPO); poly p-phenylene sulphide (PPS); poly p-phenylene terephthalamide (PPTA); polyphthalamide (PTA); poly propylene (PP); poly propylene oxide (PPDX); poly styrene (PS); polysulfone (PSU); poly tetrafluoro; ethylene (PTFE); poly(trimethylene terephthalate) (PTT); poly polyurethane (PU); Polyvinyl butyral (PVB); poly vinyl chloride (PVC); polyvinylidene chloride (PVDC); poly vinyledene fluoride (PVDF); poly vinyl methyl ether (PVME); poly(vinyl pyrrolidone) (PVP)silicone(SI); styrene-acrylonitrile resin (SAN); thermoplastic elastomers (TPE); thermoplastic polymer (TP); and, urea-formaldehyde (UF).
In some embodiments, the electrode support may act in a way that helps to prevent thermal runaway resulting from dendrite formation within the battery, preferably by having the electrode support comprises two or more layers of polymer sheets with different melting points being laminated to provide the electrode support.
In one aspect of the invention, the support surface may further comprise a hydrophilic coating upon the surface. In some embodiments, the substrate may have upon its surface a hydrophilic coating comprising a polymer, or combination of polymers, such as: acrylonitrile butadiene styrene (ABS); polyacrylonitrile (PAN) or Acrylic; polybutadiene; poly(butylene terephthalate) (PBT); poly(ether sulphone) (PES, PES/PEES); polyether ether ketones (PEEK, PES/PEEK); polyethylene (PE); poly(ethylene glycol) (PEG); poly(ethylene terephthalate) (PET); polypropylene (PP); polytetrafluoroethylene (PTFE); styrene-acrylonitrile resin (SAN); poly(trimethylene terephthalate) (PTT); polyurethane (PU); Polyvinyl butyral (PVB); polyvinylchloride (PVC); polyvinylidenedifluoride (PVDF); poly(vinyl pyrrolidone) (PVP); polyhydroxyethylmethacrylate (HEMA); butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, acrylonitrile, methyl methacrylate, trimethylolpropane triacrylate (TMPTA), and, cyanoacrylate.
In some embodiments, the applying step may comprise a coating method that includes one or a combination of: spray deposition; electrostatic assisted spray deposition; electrokinetic deposition; electrophoretic deposition; mist deposition; curtain coating; slurry coating; slot-die coating; gravure coating; and, coating involving a doctor blade.
In some embodiments, the first conductive layer may comprise a metal foil, the metal foil adhering to the coating layer upon contact, preferably wherein the metal foil adheres to the coating layer through a conductive adhesive. In some embodiments, the first conductive layer is applied to the electrode in liquid form, and where preferably the liquid comprises conductive particles and a binder polymer. In preferred embodiments, the conductive particles may comprise carbon, and more preferably, carbon nanotubes.
In preferred embodiments, the active material may comprise a material comprising one or a combination of: LiC6; LiCo1/3Ni1/3Mn1/3O2; LiCoO2; LiFePO4; Li2FePO4F; Li4.4Ge; Li(LiaNixMnyCOz)O2; LiMnO2; LiMn2O4; LiNixCOyMnzO2; LiNiO2; Li4.4Si; Li4Ti5O12; Si; Sn; SnO2; and, graphite. In particularly preferred embodiments, the active material may comprise Li2Mn2-xMexO4-zFz, wherein Me is selected from the group consisting of: aluminum; chromium; zinc; cobalt; nickel; lithium; magnesium; iron; copper; titanium; and, silicon, and wherein x and z range from 0 to 0.5.
Another aspect of the invention provides for methods of applying materials to substrates. In a highly preferred embodiment, the active material suspension may be applied to the substrate surface by spraying, preferably by air spraying, airless spraying, or, electrostatic spraying. In some embodiments, the active material suspension may be applied to the substrate surface by electrokinetic deposition, preferably by electrophoretic deposition. In some embodiments, material application is done by slurry coating, preferably by slot-die or gravure coating. In some embodiments, the substrate moves past an active material suspension applicator during the applying step. Preferably, the substrate is unwound from a reel prior to the applying step and, the substrate is rewound subsequent to the applying step.
In some embodiments, the invention provides for an electrode comprising a substrate having a surface and being ion permeable and electrically insulating. In some embodiments, an electrode may comprise an active material layer having first and second active material layer surfaces, the first active material layer surface being bonded to the substrate surface, the active material layer comprising: active material particles capable of reversibly lithiating and de-lithiating; conductive particles capable of conducting electrons; and, binder polymer; a conductive layer upon the active material layer, wherein the conductive layer is in electrical communication with the coating layer. In some embodiments, the conductive particles comprise carbon nanotubes, preferably multi-walled carbon nanotubes.
In some embodiments, the substrate may comprise a battery separator membrane, preferably comprising one or more polymers. In some embodiments, the substrate may comprise at least two different polymer types, at least two types having different melting temperatures. In some embodiments, the substrate may comprise glass fiber. In some preferred embodiments, the substrate may comprise a plurality of polymer layers, preferably three polymer layers. In some preferred embodiments, the substrate may comprise a thermal shutdown battery separator.
In some embodiments, the substrate and the active material layer may be adhesively bonded to each other, preferably where the substrate and active materials are adhered together by a conductive adhesive comprising conductive particles, preferably carbon nanotubes.
In one aspect of the invention, the electrode support may act as a battery separator. In some embodiments, the electrode support functions as a battery separator that comprises a polymer sheet having thereupon an electrode material, the polymer sheet being disposed adjacent another electrode, for example, but not limited to, a cathode or an anode, wherein the electrode support with its electrode material and the other electrode are situated within a liquid electrolyte, a gel electrolyte, or a molten salt battery. In preferred embodiments, the separator prevents physical contact between anode and cathode material and may serve as an electrolyte reservoir to provide for ionic transport between the electrodes through the pores of the separator. In some embodiments, the separator may participate in an electrochemical reaction, for example, but not limited to, lithium ion secondary storage processes. In some embodiments, ion permeability and dielectric properties of the separator may be improved to improve energy density, power density, cycle life and safety of the battery, and preferably the separator may be stable against acidic, basic, aqueous, organic, and electrolytic battery environments. The preferred separator may have additives that afford chemical and electrochemical stability, and mechanical strength to prevent dendrite growth. Structural and/or chemical variants may be incorporated into the battery and/or the separator to minimize self-discharge and penetration of metal dendrites formed during charging for a secondary battery. For high energy and power densities, the separator should be very thin, highly porous, and capable of withstanding high temperature incurred by fast discharge.
In some embodiments, the electrode support may comprise two or more polymer materials each having a different or the same melting temperature.
In some embodiments, the electrode support may act in a way that helps to prevent thermal runaway resulting from dendrite formation within the battery in that the electrode support comprises two or more layers of polymer sheets with different melting points being laminated to provide the electrode support, when used as a battery separator, with thermal shutdown capability.
Another aspect of the invention provides for battery separators having disposed thereon a material capable of reversibly sequestering metal atoms.
In preferred embodiments, the metal atoms are alkaline metal atoms. In particularly preferred embodiments, the alkaline metal atom may be lithium. In some embodiments, the metal atom may be a metal ion. A highly preferred embodiment, the metal ion may be lithium ion.
a & 1b depict a typical battery cell shown in cross-section found in the PRIOR ART.
a & 2b depict another typical battery cell with a thermal shut-down separator shown in cross-section found in the PRIOR ART.
a & 3b depict a typical three-layer battery separator found in the PRIOR ART.
a through 4c depict a typical three layer thermal shut-down separator found in the PRIOR ART.
a & 5b depict a preferred embodiment of the invention of a battery cell in cross-section showing the electrode materials bonded to the separator prior to application of the current collectors.
a through 6c depict an exemplary cell embodiment of the invention.
a & 8b depict an exemplary embodiment cell of the invention in perspective view.
a through 9e depict stepwise the preferred method for making exemplary electrodes of the invention.
a & 10b depict, in perspective view, an exemplary cell provided for by the invention.
The invention provides, in one aspect, for rechargeable battery cells manufactured by applying electrode material to a surface of a non-electrically conductive substrate. The non-electrically conductive substrate may be permeable, or non-permeable to ions. In addition to applying the electrode material to the surface of the substrate, an additional electrically conductive layer may be applied to the surface of the substrate prior to applying the electrode material to provide for a current collecting conductive layer adjacent the substrate, or the conductive layer may be applied after the application of the electrode material to the surface of the substrate to provide a current collector conductive layer distal to the substrate. In some embodiments, the current collector layer may further comprise an electrically conductive tab for establishing electrical communication between the electrode and an electrical circuit external to the cell.
The invention provides for electrodes that may be used in different cell configurations.
Another cell configuration offered by the invention is shown in
In one embodiment, the electrodes provided for by the invention may be mated together and rolled up into a spiral or “jelly” roll configuration as shown in
The invention provides, in one aspect, for cells having in-situ formed current collectors.
The conductive coating described in the preceding paragraph may further be used to affix a thin metal foil to serve as a current conductor. As shown in
In some embodiments, the electrode support surface may be made hydrophilic prior to the immersing step and/or the carbon nanotubes are deposited upon the hydrophilic layer. In particularly preferred embodiments, the hydrophilic layer comprises a polymer selected from the group consisting: acrylonitrile butadiene styrene (ABS); polyacrylonitrile (PAN) or Acrylic; polybutadiene; poly(butylene terephthalate) (PBT); poly(ether sulphone) (PES, PES/PEES); poly(ether ether ketone)s (PEEK, PES/PEEK); polyethylene (PE); poly(ethylene glycol) (PEG); poly(ethylene terephthalate) (PET); polypropylene (PP); polytetrafluoroethylene (PTFE); styrene-acrylonitrile resin (SAN); poly(trimethylene terephthalate) (PTT); polyurethane (PU); Polyvinyl butyral (PVB); polyvinylchloride (PVC); polyvinylidenedifluoride (PVDF); poly(vinyl pyrrolidone) (PVP); polyhydroxyethylmethacrylate (HEMA); butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, acrylonitrile, methyl methacrylate, trimethylolpropane triacrylate (TMPTA), and, cyanoacrylate.
Preferred embodiments of the invention may have the electrode support further comprise a conductive layer upon the electrode support surface with variants that include having: the conductive layer comprises carbon nanotubes; the conductive layer comprises an elemental metal, preferably on that is selected from the group consisting of: aluminum; copper, gold, nickel, or silver; the electrode support having bonded thereto a second substrate having properties different from the electrode support to form a laminate, the laminate being ion permeable, preferably where the laminate further comprises a third substrate bonded thereto to form a three-layer laminate that is ion permeable; the second substrate has electrically conductive properties; the electrode support has dielectric properties, preferably where the laminate has dielectric properties; the electrode support has conductive properties and the second substrate has dielectric properties the first and third substrates have electrically conductive properties, preferably where the electrode support comprises pores ranging in size from 0.1 nanometers to 1000 nanometers. Some particularly preferred embodiments of the invention include having the electrode support be permeable to lithium ions and/or where the nanoparticles are selected from the group consisting of: lithium, cobalt, manganese, silicon; carbon nanotubes; and, graphite.
The invention provides, in certain embodiments, coating methods selected from the group comprising: spray deposition; electrostatic assisted spray deposition; electrokinetic deposition; electrophoretic deposition; mist deposition; curtain coating; slurry coating; slot-die coating; gravure coating; and, coating involving a doctor blade. Some embodiments of the invention provide for a second layer formation by immersing the electrode substrate into a second solvent bath having a counter electrode, a solvent, carbon nanotubes, and, nanoparticles, and applying an electrical potential to the counter electrode and the conductive layer upon the electrode support surface so that the carbon nanotubes and silicon nanoparticles deposit upon the electrode support surface. In particularly preferred embodiments, the nanoparticles comprise a material that can reversibly retain a metal atom.
Preferred embodiments of the invention provide for a cathode material layer being deposited upon the electrode support, the cathode materials comprises materials including, but not limited to, gold; silver; silver oxide; silver chloride; lead; indium; indium oxide; tin; tin indium oxide; nickel; nickel tin oxide; ruthenium; ruthenium oxide; manganese; manganese oxide; aluminum; aluminum oxides; vanadium; vanadium oxide; iron; iron oxides; cobalt; cobalt oxides; tellurium; tellurium oxides; gallium; gallium oxides; tungsten; tungsten oxides; lithium; lithium oxides; polymers; protein; nucleic acid; lipid; mineral; salt; colloidal particles; sulfur; sulfur dioxide; thionyl dichloride; LiCoO2; LiMn2O4; LiMnO2; LiNiO2; LiFePO4; LiNixCOyMnzO2; metal fluoride; bismuth fluoride; bismuth oxyfluoride; copper difluoride; zinc; zinc nitride; and nitrides. In certain embodiments the formula CuMexFzOw wherein Me is selected from the group consisting of: iron; cobalt; nickel; manganese; vanadium; molybdenum; lead; antimony; bismuth; tin; niobium; chromium; silver; zinc; zinc nitride; and, nitrides. In particularly preferred embodiments, the cathode material comprises an alloy, for example, but not limited to, Li2Mn2-xMexO4-zFz wherein said Me is selected from the group consisting of: aluminum; chromium; zinc; cobalt; nickel; lithium; magnesium; iron; copper; titanium; and, silicon, and wherein x and z range from 0 to 0.5.
Preferred embodiments of the invention provide for a anode material layer being deposited upon the electrode support, the anode materials comprises materials including, but not limited to: graphite; graphene; copper; copper oxides; silicon; silicon oxides; silicon nanoparticles; germanium; germanium oxides; Li4Ti5O12;
The invention provides for embodiments where the deposited electrode layer comprises a conductive material. In some embodiments, the conductive material may comprise one or more of the following: tin, antimony, vanadium, chromium, titanium, manganese, iron, cobalt, nickel, copper, zinc, titanium, graphite; carbon black; carbon fibers; and, nanostructures. The conductive layer may be deposited from a suspension of conductive material particles having an average dimension ranging from 1 to 1000 nanometers, more preferably from 1 to 500 nanometers, still more preferably from 1 to 200 nanometers. In particularly preferred embodiments, the conductive material may be a nanostructure comprising carbon nanostructures including fullerenes, Buckminster fullerenes, carbon nanotubes are single walled and/or multiple walled. The nanostructures may have structural distortions and features, be spherical, oblong, tubular, or branched hollow structures with open and/or closed portions. In some embodiments, the carbon nanostructure has a surface that is charged and/or modified. Preferable methods for charging a nanostructure include exposing the nanostructures to acidic, basic, or oxidizing conditions with or without charged ions present. Nanostructure surface modification may include covalently, ionically, physically, or chemically attaching or adsorbing a charged material.
The supported electrodes of the invention can, in some embodiments, be stacked together. Electrical communication between electrode layers may be achieved, in preferred embodiments, by using conductive interconnections between the conductive stacked electrodes. For example, but not limited to, using metal foil to form an electrically conductive trace from a first to a second electrode element.
Preferable solvents are dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylene carbonate (PC), .gamma.-butyrolactone (.gamma.-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene and methyl acetate (MA). These second solvents may be employed singly or in a combination of two or more. More desirably, this solvent should be selected from those having a donor number of 16.5 or less. The viscosity of this second solvent should preferably be 28 cps or less at 25.degree. C.
The mixing ratio of the aforementioned ethylene carbonate in a mixed solvent should preferably be 10 to 80% by volume. If the mixing ratio of the ethylene carbonate falls outside this range, the conductivity of the solvent may be lowered or the solvent tends to be more easily decomposed, thereby deteriorating the charge/discharge efficiency. More preferable mixing ratio of the ethylene carbonate is 20 to 75% by volume. When the mixing ratio of ethylene carbonate in a non-aqueous solvent is increased to 20% by volume or more, the solvating effect of ethylene carbonate to lithium ions will be facilitated and the solvent decomposition-inhibiting effect thereof can be improved.
Examples of preferred mixed solvents are a composition comprising EC and MEC; comprising EC, PC and MEC; comprising EC, MEC and DEC; comprising EC, MEC and DMC; and comprising EC, MEC, PC and DEC; with the volume ratio of MEC being controlled within the range of 30 to 80%. By selecting the volume ratio of MEC from the range of 30 to 80%, more preferably 40 to 70%, the conductivity of the solvent can be improved. With the purpose of suppressing the decomposition reaction of the solvent, an electrolyte having carbon dioxide dissolved therein may be employed, thereby effectively improving both the capacity and cycle life of the battery.
The electrolytic salts to be incorporated into a non-aqueous electrolyte may be selected from a lithium salt such as lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-metasulfonate (LiCF.sub.3SO.sub.3) and bis-trifluoromethyl sulfonylimide lithium [LiN(CF.sub.3SO.sub.2).sub.2]. Among them, LiPF.sub.6, LiBF.sub.4, and LiN(CF.sub.3SO.sub.2).sub.2 are preferred. The content of aforementioned electrolytic salts in the non-aqueous solvent is preferably 0.5 to 2.0 mol/l.
Electrodes provided for by the invention may be arranged in a manner including, but not limited to, serpentine, co-planar; co-axial; zigzag; folded stack; folded staircase; wrinkled; non-planar; and spiral, flat spiral, and the electrodes are spaced apart by a separator or polymer electrolyte structure.
In another aspect of the invention, the resulting electrodes can be combined with electrodes made by one of deposition methods of the invention, or by a different electrode forming method. Exemplary uses of the resulting batteries include, but are not limited to, incorporation into a system selected from the group consisting of uninterrupted power supply; audio headset; wireless headset; portable telephone; cellular phone; satellite telephone; portable digital imaging; camcorder; portable video game player; portable medical diagnostic; portable defibrillator; pacemaker; portable drug infusion pump; uninterrupted power supply; photographic light flash unit; prop-up battery; automobile power storage; handheld radar device; portable computational device; and, laptop computer.
The surfaces of two 25 mm by 75 mm porous polyethylene battery separator membranes were exposed to plasma for 10 minutes. A poly-(hydroxymethyl methacrylate) (pHEMA) coating was then applied to the treated separator membrane. Monomeric HEMA was mixed with water at a 5% v/v ratio to which the catalyst FeCl2 was added to yield a final FeCl2 solution molarity of 2.5×10−4. The treated separator membrane was promptly immersed into the HEMA solution for 3 hours, removed from the solution, rinsed with water, rinsed in ethanol, and allowed to air dry.
The plasma treated membrane was placed upon an aluminum foil sheet covering one side of a 25 mm by 75 mm standard microscope slide to form a membrane/foil/glass slide sandwich and was held together with small binder clips to form a membrane-electrode sandwich.
Multi-walled carbon nanotubes (MWCNTs) were readied by suspending 2400 mg of MWCNT in 160 ml of 15.6M H2(NO3) and refluxed for 10 hours using an oil bath at 125° C. and collected and dried by filtration. The average length and diameter of the MWCNTs ranged from 5 to 50 μm and 2-25 nm, respectively. After drying, 60 mg of the acid treated MWCNTs was suspended in 20 ml of 200 proof ethanol in a beaker placed for 45 minutes placed in a 70 watt ultrasonic cleaning water bath operating at 40 kHz to yield a stock MWCNT solution.
LiNi1/3Mn1/3CO1/3O2 nanoparticles were formed by the following method. The following aqueous solutions were combined:
To the above mixture was added 5.7 grams of citric acid. The mixture was constantly stirred while on a hotplate. The mixture temperature was brought to 180° C. and then ramped over a one hour period to a final temperature of 280° C. where the mixture began to boil and degas. After one hour at 280° C., the mixture yielded a loose brown powder. The powder was pulverized with a laboratory mortar and pestle, placed in a 50 cc alumina crucible, and sintered in a small box furnace at 700° C. for three hours to yield a dark brown powder. The resulting powder was used in the electrode formation process described below.
The stock MWCNT solution was diluted by adding enough 200 proof ethanol to 1.8 ml of stock MWCNT to a final volume of 20 ml in a beaker and was placed in a sonicating water bath for 20 minutes. To the diluted MWCNT mixture was added 15 mg of Mg(NO3)2 by way of a stock 50 mg/ml Mg(NO3)2 solution. The MWCNT mixture beaker was placed in a sonicating water bath for 10 minutes and then poured into a tray having a graphite counter electrode located against an interior wall of the tray submerging the graphite electrode in the mixture. The prepared membrane/electrode sandwich was then immersed in mixture within the tray and situated on the side of the tray opposite the counter electrode. An electrical potential was applied from an external power supply across the electrodes with the foil adjacent the membrane being the negative pole. The electrical current was held constant (2.5 mA/cm2) while power was supplied for 30 seconds to deposit form an electrically conductive MWCNT layer upon the exposed surface of the separator membrane. The sandwich was then removed from the tray and allowed to air dry.
A MWCNT and silicon nanoparticle (MWCNT/SiNP)/ethanol stock solution was made by diluting 1.8 ml of the stock MWCNT solution and 12.6 mg of dry silicon nanoparticles to 20 ml total volume using 200 proof ethanol. The MWCNT/SiNP stock solution was placed in the ultrasonication bath for 30 minutes. To the MWCNT/SiNP stock solution was added 45 mg of Mg2(NO3)2 then diluted to 60 ml total volume with 200 proof ethanol and placed in the ultrasonication bath for 5-10 minutes.
Using the MWCNT/Si nanoparticle stock solution, a second layer active material layer was then coated upon the electrically conductive MWCNT layer to form a active material layer by the following process. The membrane/electrode/slide sandwich was removed from the tray so that a strip of aluminum foil could be placed at each end of the slide length in direct contact with the conductive MWCNT layer to facilitate electrical communication of the MWCNT layer with the external power supply. A constant current electrical potential was applied between the MWCNT layer and the graphite counter electrode and held between 30 and 40 milliamps for 30 seconds. The sandwich was then removed and allowed to air dry. During the drying step, the MWCNT/SiNP solution was subjected to further ultrasonication to prevent aggregation of the suspended nanoparticles. An additional 30 second immersion in the MWCNT/SiNP solution with constant electrical current exposure was performed followed by an additional six rounds of 60 second immersion/exposures to build up the thickness of the resulting MWCNT/SiNP layer. Between each round, the solution was further ultrasonicated to prevent aggregation of the MWCNT nanotubes and SiNP nanoparticles.
To 62.1 mg of the LiNi1/3Mn1/3CO1/3O2 nanoparticles from the above example was added 5.4 mg of CNT by way of the stock CNT solution described above to which 15 mg of Mg(NO3)2 was then added. The suspension was subjected to ultrasonication as described above. The ultrasonicated suspension was then used to perform the deposition method described above with the following parameters: 2.5 mA/cm2 constant current.
Like above, a second diluted MWCNT mixture was made and to it 15 mg of Mg(NO3)2 was added by way of a stock 50 mg/ml Mg(NO3)2 solution. The MWCNT mixture was placed in the cleaner bath for 10 minutes and then poured into a tray having a graphite counter electrode located against an interior wall of the tray thereby submerging the graphite electrode in the mixture.
The MWCNT-MWCNT/SiNP coated membrane/electrode sandwich was then immersed in mixture into the tray and situated on the side of the tray opposite the counter electrode. An electrical potential was applied from an external power supply across the electrodes with the foil adjacent the membrane being the negative pole. The electrical current was held constant and ranged from 30 to 40 milliamps as the power was supplied for 30 seconds to deposit form an electrically conductive MWCNT layer upon the previously formed MWCNT/SiNP layer. The membrane sandwich was then removed form the mixture and allowed to air dry.
The electrode materials described in the Examples above were tested in a full-cell environment by making coin cells from the
This application claim priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/298,893 by Du, et al., filed on Jan. 27, 2010, which is herein incorporated by reference in its entirety for all purposes, and the specific purposes described herein.
Number | Date | Country | |
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61298893 | Jan 2010 | US |