US20060177732A1 - Battery cell with barrier layer on non-swelling membrane - Google Patents

Battery cell with barrier layer on non-swelling membrane Download PDF

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US20060177732A1
US20060177732A1 US11/377,090 US37709006A US2006177732A1 US 20060177732 A1 US20060177732 A1 US 20060177732A1 US 37709006 A US37709006 A US 37709006A US 2006177732 A1 US2006177732 A1 US 2006177732A1
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lithium
structure
barrier layer
membrane
electrolyte
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US11/377,090
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Steven Visco
Bruce Katz
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Polyplus Battery Co Inc
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Polyplus Battery Co Inc
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Priority to US10/193,652 priority patent/US7070632B1/en
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/056Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565Polymeric materials, e.g. gel-type or solid-type
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/42Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2/00Constructional details or processes of manufacture of the non-active parts
    • H01M2/14Separators; Membranes; Diaphragms; Spacing elements
    • H01M2/16Separators; Membranes; Diaphragms; Spacing elements characterised by the material
    • H01M2/1686Separators having two or more layers of either fibrous or non-fibrous materials
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134Electrodes based on metals, Si or alloys
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/362Composites
    • H01M4/366Composites as layered products
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/58Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/581Chalcogenides or intercalation compounds thereof
    • H01M4/5815Sulfides
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00Primary cells; Manufacture thereof
    • H01M6/14Cells with non-aqueous electrolyte
    • H01M6/18Cells with non-aqueous electrolyte with solid electrolyte
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00Primary cells; Manufacture thereof
    • H01M6/14Cells with non-aqueous electrolyte
    • H01M6/18Cells with non-aqueous electrolyte with solid electrolyte
    • H01M6/187Solid electrolyte characterised by the form
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00Electrolytes
    • H01M2300/0088Composites
    • H01M2300/0094Composites in the form of layered products, e.g. coatings
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00Metal working
    • Y10T29/49Method of mechanical manufacture
    • Y10T29/49002Electrical device making
    • Y10T29/49108Electric battery cell making
    • Y10T29/49112Electric battery cell making including laminating of indefinite length material

Abstract

Battery cells having separator structures which include a substantially impervious active metal ion conducting barrier layer material, such as an ion conducting glass, formed on an active metal ion conducting membrane in which elongation due to swelling on contact with liquid electrolyte is constrained in at least two of three orthogonal dimensions of the membrane. The non-swelling character of the membrane prevents elongation in the x-y (or lateral, relative to the layers of the composite) orthogonal dimensions of the membrane when it is contacted with liquid electrolyte that would otherwise cause the barrier layer to rupture. Substantial swelling of the membrane, if any, is limited to the z (or vertical, relative to the layers of the composite) dimension.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • This application is a continuation of U.S. patent application Ser. No. 10/193,652, filed Jul. 9, 2002 and titled ELECTROCHEMICAL DEVICE SEPARATOR STRUCTURES WITH BARRIER LAYER ON NON-SWELLING MEMBRANE, which claims priority to U.S. Provisional Patent Application No. 60/307,981, filed Jul. 25, 2001 and titled PROTECTED ANODE USING NON-SWELLING MEMBRANE; incorporated herein by reference in their entirety for all purposes.
  • In addition, this application is related to U.S. patent application Ser. No. 09/086,665 filed May 29, 1998, now U.S. Pat. No. 6,025,094 issued: Feb. 15, 2000, titled PROTECTIVE COATINGS FOR NEGATIVE ELECTRODES, and naming Steven J. Visco and May-Ying Chu as inventors. This application is also related to U.S. patent application Ser. No. 09/139,603 filed Aug. 25, 1998, now U.S. Pat. No. 6,402,795 issued: Jun. 11, 2002, titled “PLATING METAL NEGATIVE ELECTRODES UNDER PROTECTIVE COATINGS,” and naming May-Ying Chu, Steven J. Visco and Lutgard C. DeJonghe as inventors. This application is also related to U.S. patent application Ser. No. 09/139,601 filed Aug. 25, 1998, now U.S. Pat. No. 6,214,061 issued: Apr. 10, 2001, titled “METHOD FOR FORMING ENCAPSULATED LITHIUM ELECTRODES HAVING GLASS PROTECTIVE LAYERS,” and naming Steven J. Visco and Floris Y. Tsang as inventors. Each of these patent applications is incorporated herein by reference for all purposes.
  • BACKGROUND OF THE INVENTION
  • 1. Field of the Invention
  • The present invention relates generally to electrodes for use in batteries. More particularly, this invention relates to methods of forming alkali metal electrodes having a reinforced glassy protective layers.
  • 2. Description of Related Art
  • In theory, some alkali metal electrodes could provide very high energy density batteries. The low equivalent weight of lithium renders it particularly attractive as a battery electrode component. Lithium provides greater energy per volume than the traditional battery standards, nickel and cadmium. Unfortunately, no rechargeable lithium metal batteries have yet succeeded in the market place.
  • The failure of rechargeable lithium metal batteries is largely due to cell cycling problems. On repeated charge and discharge cycles, lithium “dendrites” gradually grow out from the lithium metal electrode, through the electrolyte, and ultimately contact the positive electrode. This causes an internal short circuit in the battery, rendering the battery unusable after a relatively few cycles. While cycling, lithium electrodes may also grow “mossy” deposits which can dislodge from the negative electrode and thereby reduce the battery's capacity.
  • To address lithium's poor cycling behavior in liquid electrolyte systems, some researchers have proposed coating the electrolyte facing side of the lithium negative electrode with a “protective layer.” Such protective layer must conduct lithium ions, but at the same time prevent contact between the lithium electrode surface and the bulk electrolyte. Many techniques for applying protective layers have not succeeded.
  • Some contemplated lithium metal protective layers are formed in situ by reaction between lithium metal and compounds in the cell's electrolyte which contact the lithium. Most of these in situ films are grown by a controlled chemical reaction after the battery is assembled. Generally, such films have a porous morphology allowing some electrolyte to penetrate to the bare lithium metal surface. Thus, they fail to adequately protect the lithium electrode.
  • Various pre-formed lithium protective barrier layers have been contemplated. For example, U.S. Pat. No. 5,314,765 (issued to Bates on May 24, 1994) describes an ex situ technique for fabricating a lithium electrode containing a thin layer of sputtered lithium phosphorus oxynitride (“LiPON”) or related material. LiPON is a glassy single ion conductor (conducts lithium ion) which has been studied as a potential electrolyte for solid state lithium microbatteries that are fabricated on silicon and used to power integrated circuits (See U.S. Pat. Nos. 5,597,660, 5,567,210, 5,338,625, and 5,512,147, all issued to Bates et al.).
  • One difficulty encountered with providing such glassy electrolyte/protective barrier layers for the protection of lithium electrodes in battery cells is that the battery cell components on which the protective layer may be formed are not generally dimensionally stable, particularly where liquid electrolyte systems are used. For example, conventional polymeric electrode separator materials, such as porous polyolefins (e.g., CELGARD materials), polyacrylonitrile, etc., take up solvent and swell when contacted with liquid electrolyte. Such swelling results in elongation of the separator along its orthogonal x, y and z axes. As a result of this elongation in the x and y dimensions, a glassy protective layer formed on the surface of the separator is liable to crack and break into islands, thereby destroying its protective function.
  • It would desirable to be able to form separators coated with ionically conductive glassy electrolyte/protective layers and integrated lithium electrodes/separators with such glassy protective coatings as battery cell components in which the glassy protective layers would not be fractured when these components are subsequently incorporated into battery cells and brought into contact with liquid electrolytes.
  • Accordingly, improved methods and structures for providing protected lithium (or other active metal) electrodes for use in batteries would be desirable.
  • SUMMARY OF THE INVENTION
  • The present invention provides electrochemical device separator structures which include a substantially impervious active metal ion conducting barrier layer material, such as an ion conducting glass, is formed on an active metal ion conducting membrane in which elongation due to swelling on contact with liquid electrolyte is constrained in at least two of three orthogonal dimensions of the membrane. Suitable membrane materials include fiber-reinforced polymers, such as polyvinylidene fluoride (PVDF) reinforced with polytetrafluorethylene (PTFE) fibers, and ionomeric polymers, such as a per-fluoro-sulfonic acid polymer film (e.g., du Pont NAFION)), reinforced with PTFE fibers, for example the product Gore-Select. Non-fiber-reinforced materials, such as porous polyolefin membranes impregnated with an ionically conductive material may also be used. These membranes are sometimes referred to referred to herein as “non-swelling membranes.” These composite materials may be advantageously incorporated into active metal electrochemical structures, such as, for example lithium metal batteries and components, where the barrier layer prevents deleterious reaction between active metal ions and separator membrane. The non-swelling character of the membrane constrains elongation in the x-y dimensions of the membrane when it is contacted with liquid electrolyte that would otherwise cause the barrier layer to rupture.
  • Thus, structures in accordance with the present invention provide robust barrier layers on non-swelling separator material membranes. The structures of the invention may further incorporate an active metal negative electrode and current collector on the barrier layer to create an integrated anode/separator structure that can subsequently be incorporated into a battery cell by pairing with a suitable positive electrode, such as an active sulfur electrode. Such a battery cell may include a liquid electrolyte without risk to the integrity of the barrier layer (and therefore the cell performance) and may include, but may not require, an additional separator beyond the non-swelling separator material membranes.
  • In one aspect, the invention pertains to an electrochemical device separator structure. The structure includes a separator having a layer of a membrane material characterized in that elongation due to swelling on contact with liquid electrolyte is constrained in at least two of three orthogonal dimensions of the membrane material. The structure further includes a substantially impervious barrier layer on the membrane material layer. Both the separator and barrier layer are conductive to ions of an active metal. The structure may be combined with further elements to form integrated separator/anodes and battery cells.
  • In another aspect, the invention pertains to method of fabricating an electrochemical device separator structure. The method involves forming a substantially impervious barrier layer on a layer of a membrane material characterized in that elongation due to swelling on contact with liquid electrolyte is constrained in at least two of three orthogonal dimensions of the material. Both the membrane material layer and the barrier layer are conductive to ions of an active metal. In alternative embodiments, a negative electrode may be formed on the barrier layer to produce an integrated separator/anode structure. In another embodiment, a positive electrode may be formed on the barrier layer and a battery cell formed.
  • These and other features of the invention will be further described and exemplified in the drawings and detailed description below.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a schematic illustrations of the formation of a separator structure according to a one embodiment of the present invention.
  • FIGS. 2-4 are schematic illustrations of the formation of an integrated separator/anode structure according to a one embodiment of the present invention.
  • FIG. 5 is a block diagram of a battery formed from a separator structure in accordance with the present invention.
  • FIGS. 6A and B show scanning electron microscope (SEM) imaging of a fiber-reinforced membrane in accordance with the present invention having a lithium-ion conducting glass coated on its surface before (6A) and after (6B) swelling in electrolyte.
  • FIGS. 7A and B show scanning electron microscope (SEM) imaging of a non-fiber-reinforced membrane having a lithium-ion conducting glass coated on its surface before (7A) and after (7B) swelling in electrolyte.
  • FIG. 8 depicts a graph of capacity versus cycles for a lithium anode protected by a glass layer coated on a reinforced ionomeric membrane.
  • DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
  • Reference will now be made in detail to specific embodiments of the invention. Examples of the specific embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to such specific embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.
  • When used in combination with “comprising,” “a method comprising,” “a structure comprising” or similar language in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.
  • Introduction
  • The present invention provides electrochemical device separator structures which include a substantially impervious active metal ion conducting barrier layer material, such as an ion conducting glass, is formed on an active metal ion conducting membrane in which elongation due to swelling on contact with liquid electrolyte is constrained in at least two of three orthogonal dimensions of the membrane. Suitable membrane materials include fiber-reinforced polymers such as PVDF reinforced with fibers of polytetrafluorethylene (PTFE), polyolefins, such as polyethylene and polypropylene, or polyethylene terephthalate. In a specific embodiment, ionomeric polymers, such as a per-fluoro-sulfonic acid polymer film (e.g., du Pont NAFION)), reinforced with polytetrafluorethylene fibers, for example the product GORE-SELECT, available from W.L. Gore and Associates, are used. Dimensionally stable non-fiber-reinforced materials, such as porous polyolefin membranes, impregnated with an ionically conductive material may also be used. All of these membranes are sometimes referred to referred to herein as “non-swelling membranes.” These composite materials may be advantageously incorporated into active metal electrochemical structures, such as, for example lithium metal batteries and components, where the barrier layer prevents deleterious reaction between active metal ions and separator membrane. The non-swelling character of the membrane prevents elongation in the x-y (or lateral, relative to the layers of the composite) orthogonal dimensions of the membrane when it is contacted with liquid electrolyte that would otherwise cause the barrier layer to rupture. Substantial swelling of the membrane, if any, is limited to the z (or vertical, relative to the layers of the composite) dimension.
  • Thus, structures in accordance with the present invention provide robust barrier layers on non-swelling separator material membranes. The structures of the invention may further incorporate an active metal negative electrode and current collector on the barrier layer to create an integrated anode/separator structure that can subsequently be incorporated into a battery cell by pairing with a suitable positive electrode, such as an active sulfur electrode. Such a battery cell may include a liquid electrolyte without risk to the integrity of the barrier layer (and therefore the cell performance) and may include, but may not require, an additional separator beyond the non-swelling separator material membranes.
  • The present invention involves providing a substantially impervious ion-conducting barrier layer (i.e., a sufficient barrier to battery solvents and other materials that would be damaging to an active metal electrode material to prevent any such damage that would degrade electrode performance from occurring when the barrier is disposed between an active metal electrode and such materials) on an at least two-dimensionally constrained membrane (elongation constrained in at least two orthogonal dimensions). For example, a suitable barrier layer may be a glass, such as lithium phosphorus oxynitride (LiPON) and more highly conductive sulfide glasses such as Li2S—GeS2, LiI—Li2S—P2S5, and Li2S—Li3PO4—SiS2.
  • Fabrication Methods
  • In the following description, the invention is presented in terms of certain specific compositions, configurations, and processes to help explain how it may be practiced. The invention is not limited to these specific embodiments. For example, while much of the following discussion focuses on lithium systems, the invention pertains more broadly to other active metal battery systems as well (e.g., batteries having negative electrodes of alkali metals, alkaline earth metals, and certain transition metals).
  • FIGS. 1-4 illustrate a specific fabrication process for an electrochemical device separator structure 101 in accordance with the present invention. Referring first to FIG. 1, an at least two-dimensionally stable porous membrane 102 is used as a substrate for deposition of a thin glass barrier/electrolyte 104. Both the membrane and the barrier layer are ionically conductive, preferably to a single active metal ion. The membrane may be for example, a gel type polymer such as polyvinylidene fluoride (PVDF) or polyacrylonitrile (PAN) and reinforced with non-swelling fibers or porous polymer sheet, for example composed of PTFE or other polymer as noted above. The membrane may also be, for example, a microporous polyolefin membrane impregnated with an ionically conductive material such as a gel-type polymer electrolyte, for example, PVDF, or an ionomer, for example, a per-fluoro-sulfonic acid polymer, polyacrylic acid or polysulfonic acid to confer ionic conductivity to the porous non-swelling membrane. In a specific embodiment, the membrane may be a fiber reinforced ionomeric polymer membrane, for example a PTFE fiber reinforced proton exchange membrane (PEM), e.g., a per-fluoro-sulfonic acid polymer film.
  • The base membrane may be a highly porous/permeable material such as is conventionally used as separators in battery cells, generally, but not necessarily polymeric. It should also resist attack by the electrolyte and other cell components under the potentials experienced within the cell. Examples of suitable separators include porous polymer membranes known to those in the art such as porous polyolefin materials (polyethylene, polypropylene or combination) marketed under the trade name CELGARD ( e.g., CELGARD 2300 or CELGARD 2400) available from Hoechst Celanese of Dallas, Tex.
  • Where the membrane is reinforced, it should be understood that the reinforcement material may take a number of forms including fibers as noted above, but also and punched sheets and woven mats or mesh.
  • Particularly suitable porous membrane materials are fiber reinforced ionomeric polymers available from several commercial sources, including the product GORE-SELECT (available from Gore) in which a composite of NAFION (a per-fluoro-sulfonic acid polymer) and PTFE fibers make up a thin conductive membrane, which when exposed to solvent expands mainly in the z-direction and very little in the x-y direction. In this way solvent uptake of the membrane does not rupture the thin glass film deposited on the membrane.
  • NAFION may be represented by the chemical formula:
    Figure US20060177732A1-20060810-C00001
  • Nafion can also be represented by:
    —(CF2CF2)m—CF2CF(OCF2CF(CF3)OCF2CF2SO3H))n
    where m is 5 to 10 typically, and n can be very large, for example, up to 1000 and more. Similar materials are available from other manufactures, including Dow Chemical Co., Asahi Chemical Co., and Chloride Engineers Ltd. NAFION is a single ion conducted for a number of active metals including alkali metals, alkaline earth metals or certain transition metals as described more fully in the prior applications of the present inventors previously incorporated by reference herein. Further information on this material and techniques for forming materials of this type may be found in “A First Course in Ion Permeable Membranes,” by Thomas A. Davis, J. David Genders and Derek Pletcher, and U.S. Pat. No. 4,661,411 “Method For Depositing A Fluorocarbonsulfonic Acid Polymer From A Solution” Apr. 28, 1987; Inventors: C. W. Martin, B. R. Ezzell, J. D. Weaver; Assigned to Dow Chemical Co., Midland Mich., both of which are incorporated herein by reference in their entirety for all purposes. In specific embodiments, the active metal used in structures of the present invention may be lithium, sodium or potassium or alloys thereof. Lithium and alloys thereof are particularly preferred.
  • One advantageous feature of NAFION and the like ionomeric membranes is that they can carry charge without the addition of a salt. NAFION can be ion exchanged and thereby be an ionic conductor (e.g., of lithium). When undergoing ion exchange the sulfonic acid exchanges its hydrogen for a positively charged ion (e.g., Li+) in solution. The chemical formula for the Li+ ion exchange reaction with NAFION is:
    R—SO3—H+Li+→R—SO3—Li+H+.
    In the case of a lithium-sulfur battery, this ionomeric characteristic allows for ionic conductivity while preventing polysulfides from reaching the glass barrier where they could deleteriously react with Li and cause the glass to delaminate from the membrane.
  • Fiber reinforced membranes in accordance with the present invention may have a thickness between about 20 and 100 microns. The thickness may be as low as 20 microns without risking the structural integrity of the membrane due to the strength conferred by the fibrous reinforcement.
  • Referring to FIGS. 2-4, the structure of FIG. 1 may be added to to form an integrated separator/anode structure 210. As shown in FIG. 2, a negative electrode (anode) material (Li, Na, etc.) or a bonding layer (Al, Sn, etc.) 206 could be deposited by evaporation (or other appropriate deposition technique such as are know to those of skill in the art) onto the glass barrier layer 104. The glass layer 104 prevents direct interaction of the highly reducing anode 206 with the microporous membrane 102 and/or liquid electrolyte therein.
  • Referring to FIG. 3, a technique for laminating an electrode to the electrode material or bonding layer 206 is shown. A layer of lithium 206′ on a copper current collector 208 is contacted and bound with the electrode material/bonding layer 206. The resulting structure 210 shown in FIG. 4 in which the ionomeric membrane 102, such as PTFE fiber reinforced NAFION (ion-exchanged to the Li form), is protected against reaction with the metallic Li electrode 207 by the glassy barrier layer 104. The lithium (or other active metal) electrode is in turn protected from ambient by the bound current collector 208.
  • The current collector includes a first surface which is exposed to the ambient and a second surface which intimately contacts the active metal electrode layer. The active metal electrode includes a first surface which forms the interface with the current collector and a second surface which intimately contacts the protective layer. In turn, the protective layer includes a first surface which contacts the second surface of the active metal electrode and a second surface which contacts the ionomeric membrane. The interfaces at the surfaces of the active metal electrode should be sufficiently continuous or intimate that moisture, air, electrolyte, and other agents from the ambient are prevented from contacting the active metal. In addition, the interface the active metal electrode and the current collector should provide a low resistance electronic contact. Finally, the interface between the active metal and the protective layer should provide a low resistance ionic contact.
  • Preferably, the current collectors employed with this invention form a physically rigid layer of material that does not alloy with active metal (e.g., lithium). They should be electronically conductive and unreactive to moisture, gases in the atmosphere (e.g., oxygen and carbon dioxide), electrolytes and other agents they are likely to encounter prior to, during, and after fabrication of a battery. Examples of materials useful as current collectors for this invention include copper, nickel, many forms of stainless steel, zinc, chromium, and compatible alloys thereof. The current collector should not alloy with, easily migrate into, or otherwise detrimentally effect the electrochemical properties of the active metal alloy layer. This also ensures that the current collector material does not redistribute during the charge and discharge cycles in which active metal is alternately plated and electrolytically consumed. The thickness of the current collector depends upon the material from which it is made. For many embodiments of interest, the current collector is between about 1 and 25 micrometers thick, more preferably between about 6 and 12 micrometers thick.
  • The current collector may be provided as a metallized plastic layer. In this case, the current collector may be much thinner than a free-standing current collector. For example, the metal layer on plastic may be in the range of 500 angstroms to 1 micrometer in thickness. Suitable plastic backing layers for use with this type of current collector include polyethylene terephthalate (PET), polypropylene, polyethylene, polyvinylchloride (PVC), polyolefins, polyimides, etc. The metal layers put on such plastic substrates are preferably inert to lithium (e.g., they do not alloy with lithium) and may include at least those materials listed above (e.g., copper, nickel, stainless steel, and zinc). One advantage of this design is that it forms a relatively lightweight backing/current collector for the electrode.
  • The current collector may be prepared by a conventional technique for producing current collectors. The current collectors may be provided as sheets of the commercially available metals or metallized plastics. The surfaces of such current collectors may be prepared by standard techniques such as electrode polishing, sanding, grinding, and/or cleaning. Alternatively, the current collector metals may be formed by a more exotic technique such as evaporation of the metal onto a substrate, physical or chemical vapor deposition of the metal on a substrate, etc. Such processes may be performed as part of a continuous process for constructing the structure. Each step in the continuous process would be performed under vacuum.
  • The integrated structure 210 may not need a separate separator when incorporated into a battery cell. The use of Li-NAFION or other related ionomer also has the advantage of single-ion conduction, and lack of concentration polarization during cell operation. The use of an at least two dimensionally stable membrane support for the protective layer, such as described, protects the protective layer (e.g., glass film) against expansion which may crack the protective layer. The protective layer protects the microporous membrane against reaction with lithium.
  • The integrated anode/separator structure may be incorporated into a lithium metal battery cell by pairing with a suitable positive electrode, such as an active sulfur electrode, such as described in U.S. Pat. No. 5,686,201 titled RECHARGEABLE POSITIVE ELECTRODES, issued Nov. 11, 1997, incorporated by reference here in its entirety and for all purposes. As noted above, and described further below with reference to FIG. 5, such a battery cell may include a liquid electrolyte without risk to the integrity of the barrier layer (and therefore the cell performance) and may include, but may not require, an additional separator beyond the non-swelling separator material membranes.
  • Preferably, the entire fabrication process described above is conducted in a continuous fashion and under a vacuum. This ensures a high throughput for manufacturing and clean fresh surfaces for forming each layer of the laminate.
  • Most generally, the lithium metal with which the invention is most often described above can be replaced with any metal, any mixture of metals capable of functioning as a negative electrode. However, the protective layers of this invention will find most use in protecting alloys of highly reactive metals such as alkali metals and alkaline earth metals. The thickness of the metal layer used in the electrodes of this invention depends upon the cell construction, the desired cell capacity, the particular metal employed, etc. For many applications, the active metal alloy thickness will preferably lie between about one and one hundred micrometers.
  • In one preferred embodiment, the materials for the negative electrodes include a metal such lithium or sodium or an alloy of one of these with one or more additional alkali metals and/or alkaline earth metals. Preferred alloys include lithium aluminum alloys, lithium silicon alloys, lithium tin alloys, and sodium lead alloys (e.g., Na4Pb). Other metallic electrode materials may include alkaline earth metals such as magnesium and their alloys, aluminum, and transition metals such as, zinc, and lead and their alloys. The protective layer must be made from a compatible material. The material should be conductive to ions of the electrochemically active metal or metals in the negative electrode.
  • Protective Layer Composition
  • The protective layer serves to protect the active metal alloy in the electrode during cell cycling. It should protect the active metal alloy from attack from the electrolyte and reduce formation of dendrites and mossy deposits. In addition, protective layer should be substantially impervious to agents from the ambient. Thus, it should be free of pores, defects, and any pathways allowing air, moisture, electrolyte, and other outside agents to penetrate though it to the active metal alloy layer. In this regard, the composition, thickness, and method of fabrication may all be important in imparting the necessary protective properties to the protective layer. These features of the protective layer will be described in further detail below.
  • Preferably, the protective layer is so impervious to ambient moisture, carbon dioxide, oxygen, etc. that a lithium alloy electrode can be handled under ambient conditions without the need for elaborate dry box conditions as typically employed to process other lithium electrodes. Because the protective layer described herein provides such good protection for the lithium (or other active metal), it is contemplated that electrodes and electrode/electrolyte composites of this invention may have a quite long shelf life outside of a battery. Thus, the invention contemplates not only batteries containing a negative electrode, but unused negative electrodes and electrode/electrolyte laminates themselves. Such negative electrodes and electrode/electrolyte laminates may be provided in the form of sheets, rolls, stacks, etc. Ultimately, they are integrated with other battery components to fabricate a battery. The enhanced stability of the batteries of this invention will greatly simplify this fabrication procedure.
  • The protective layer should be a glass or amorphous material that conducts lithium (or other active metal) ion but does not significantly conduct other ions. In other words, it should be a single ion conductor. It should also be stable for the voltage window employed in the cell under consideration. Still further it should be chemically stable to a battery electrolyte, at least within the voltage window of the cell. Finally, it should have a high ionic conductivity for the lithium (or other active metal) ion.
  • The protective layer may be formed directly on a carrier or electrolyte by any suitable process. It can be deposited on these substrates by techniques such as physical vapor deposition and chemical vapor deposition. In a preferred embodiment, it is deposited by plasma enhanced chemical vapor deposition (PECVD). Examples of suitable physical vapor deposition processes include sputtering and evaporation (e.g., electron-beam evaporation). A PECVD technique is described in U.S. patent application Ser. No. 09/086,665, filed on May 19, 1998, and titled PROTECTIVE COATINGS FOR NEGATIVE ELECTRODES, which was previously incorporated herein by reference. In another preferred embodiment the protective layer is deposited by electron beam evaporation.
  • The protective layer is preferably composed of a glass or amorphous material that is conductive to metal ions of the negative electrode metal. Preferably, the protective layer does not conduct anions such as S8=generated on discharge of a sulfur electrode (or other anions produced with other positive electrodes), or anions present in the electrolyte such as perchlorate ions from dissociation of lithium perchlorate.
  • In order to provide the needed ionic conductivity, the protective layer typically contains a mobile ion such as a metal cation of the negative electrode metal. Many suitable single ion conductors are known. Among the suitable glasses are those that may be characterized as containing a “modifier” portion and a “network former” portion. The modifier is often an oxide of the active metal in (i.e., the metal ion to which the protective layer is conductive). The network former is often a polymeric oxide or sulfide. One example is the lithium silicate glass 2 Li2O.1 SiO2 and another example is the sodium borosilicate glass 2 Na2O.1 SiO2.2B2O3.
  • The modifier/network former glasses employed in this invention may have the general formula (M2O).X(AnDm), where M is an alkali metal, A is boron, aluminum, silicon, or phosphorous, D is oxygen or sulfur. The values of n and m are dependent upon the valence on A. X is a coefficient that varies depending upon the desired properties of the glass. Generally, the conductivity of the glass increases as the value of X decreases. However, if the value of X becomes too small, separate phases of the modifier and network former arise. Generally, the glass should remain of a single phase, so the value of X must be carefully chosen.
  • The highest concentration of M2O should be that which yields the stoichiometry of the fully ionic salt of the network former. For instance SiO2 is a polymeric covalent material; as Li2O is added to silica O—O bonds are broken yielding Si—O Li+. The limit of Li2O addition is at the completely ionic stoichiometry, which for silica would be Li4SiO4, or 2Li2O.SiO2 (Li2O.0.5SiO2). Any addition of Li2O beyond this stoichiometry would necessarily lead to phase separation of Li2O and Li4SiO4. Phase separation of a glass composition typically happens well before the fully ionic composition, but this is dependent on the thermal history of the glass and cannot be calculated from stoichiometry. Therefore the ionic limit can be seen as an upper maximum beyond which phase separation will happen regardless of thermal history. The same limitation can be calculated for all network formers, i.e. Li3BO3 or 3 Li2O.B2O3.Li3AlO3 or 3 Li2O.Al2O3, etc. Obviously, the optimum values vary depending upon the modifier and network former employed.
  • Examples of the modifier include lithium oxide (Li2O), lithium sulfide (Li2S), lithium selenide (Li2Se), sodium oxide (Na2O), sodium sulfide (Na2S), sodium selenide (Na2Se), potassium oxide (K2O), potassium sulfide (K2S), potassium selenide (K2Se), etc., and combinations thereof. Examples of the network former include silicon dioxide (SiO2), silicon sulfide (SiS2), silicon selenide (SiSe2), boron oxide (B2O3), boron sulfide (B2S3), boron selenide (B2Se3), aluminum oxide (Al2O3), aluminum sulfide (Al2S3), aluminum selenide (Al2Se3), phosphorous pentoxide (P2O5), phosphorous pentasulfide (P2S5), phosphorous pentaselenide (P2Se5), phosphorous tetraoxide (PO4), phosphorous tetrasulfide (PS4), phosphorous tetraselenide (PSe4), germanium sulfide (GeS2), gallium sulfide GaS2 and related network formers.
  • “Doped” versions of the above two-part protective glasses may also be employed. Often the dopant is a simple halide of the ion to which the glass is conductive. Examples include lithium iodide (LiI), lithium chloride (LiCl), lithium bromide (LiBr), sodium iodide (Nal), sodium chloride (NaCl), sodium bromide (NaBr), etc. Such doped glasses may have general formula (M2O).X(AnDm).Y(MH) where Y is a coefficient and MH is a metal halide.
  • The addition of metal halides to glasses is quite different than the addition of metal oxides or network modifiers to glasses. In the case of network modifier addition, the covalent nature of the glass is reduced with increasing modifier addition and the glass becomes more ionic in nature. The addition of metal halides is understood more in terms of the addition of a salt (MH) to a solvent (the modifier/former glass). The solubility of a metal halide (MH) in a glass will also depend on the thermal history of the glass. In general it has been found that the ionic conductivity of a glass increases with increasing dopant (MH) concentration until the point of phase separation. However, very high concentrations of MH dopant may render the glass hygroscopic and susceptible to attack by residual water in battery electrolytes, therefore it might be desirable to use a graded interface where the halide concentration decreases as a function of distance from the negative electrode surface. One suitable halide doped glass is Li2O.YLiCl.XB2O3.ZSiO2.
  • Single ion conductor glasses are particularly preferred as a protective layer used with this invention. One example is a lithium phosphorus oxynitride glass referred to as LiPON which is described in “A Stable Thin-Film Lithium Electrolyte: Lithium Phosphorus Oxynitride,” J. Electrochem. Soc., 144, 524 (1997) and is incorporated herein by reference for all purposes. An example composition for LiPON is Li2.9PO3.3N0.5. Examples of other glass films that may work include 6LiI—Li3PO4—P2S5 and B2O3—LiCO3—Li3PO4, and glasses based on Li2S—GeS2, Li2S—GaS2, and Li2S—Li3PO4—SiS2
  • Regarding thickness, protective layer should be as thin as possible while still effectively protecting the active metal alloy electrode. Thinner layers have various benefits. Among these are flexibility and low ionic resistance. If a layer becomes too thick, the electrode cannot bend easily without cracking or otherwise damaging the protective layer. Also, the overall resistance of the protective layer is a function of thickness. However, the protective layer should be sufficiently thick to prevent electrolyte or certain aggressive ions from contacting the underlying alkali metal. The appropriate thickness will depend upon the deposition process. If the deposition process produces a high quality protective layer, then a rather thin layer can be employed. A high quality protective layer will be smooth and continuous and free of pores or defects that could provide a pathway for lithium metal or deleterious agents from the electrolyte.
  • For many protective layers, the optimal thickness will range between about 50 angstroms and 5 micrometers. More preferably, the thickness will range between about 100 angstroms and 3,000 angstroms. Even more preferably, the thickness will range between about 500 angstroms and 2,000 angstroms. For many high quality protective layers, an optimal thickness will be approximately 1000 angstroms.
  • In addition, the composition of the protective layer should have an inherently high ionic conductivity (e.g., between about 10−8 and about 10−2 (ohm-cm)−1). Obviously, if a relatively good quality thin layer can be deposited, a material with a relatively low conductivity may be suitable. However, if relatively thicker layers are required to provide adequate protection, it will be imperative that the composition of the protective layer have a relatively high conductivity.
  • Battery Design
  • Batteries of this invention may be constructed according to various known processes for assembling cell components and cells. Generally, the invention finds application in any cell configuration. The exact structure will depend primarily upon the intended use of the battery unit. Examples include thin film with porous separator, thin film polymeric laminate, jelly roll (i.e., spirally wound), prismatic, coin cell, etc.
  • Generally, batteries employing the negative electrodes of this invention will be fabricated with an electrolyte. It is possible, however, that the protective layer could serve as a solid state electrolyte in its own right. If a separate electrolyte is employed, it may be in the liquid, solid (e.g., polymer), or gel state. It may be fabricated together with the negative electrode as a unitary structure (e.g., as a laminate). Such unitary structures will most often employ a solid or gel phase electrolyte.
  • The negative electrode is spaced from the positive electrode, and both electrodes may be in material contact with an electrolyte separator. Current collectors contact both the positive and negative electrodes in a conventional manner and permit an electrical current to be drawn by an external circuit. In a typical cell, all of the components will be enclosed in an appropriate casing, plastic for example, with only the current collectors extending beyond the casing. Thereby, reactive elements, such as sodium or lithium in the negative electrode, as well as other cell elements are protected.
  • Referring now to FIG. 5, a cell 400 in accordance with a preferred embodiment of the present invention is shown. Cell 400 includes a negative current collector 412 which is formed of an electronically conductive material. The current collector serves to conduct electrons between a cell terminal (not shown) and a negative electrode 414 (such as an active metal alloy) to which current collector 412 is affixed. Negative electrode 414 is made from lithium or other similarly active metal alloy material, and includes a protective layer 408 formed opposite current collector 412. Either negative electrode 414 or protective layer 408 contacts an electrolyte in an electrolyte region 416. The electrolyte may be liquid, gel, or solid (e.g., polymer). To simplify the discussion of FIG. 4, the electrolyte will be referred to as “liquid electrolyte” or just “electrolyte.” An example of a solid electrolyte is polyethylene oxide. An example of gel electrode is polyethylene oxide containing a significant quantity of entrained liquid such as an aprotic solvent.
  • A separator including a non-swelling separator material in accordance with the present invention in region 416 prevents electronic contact between the positive and negative electrodes. A positive electrode 418 abuts the side of separator layer 416 opposite negative electrode 414. As electrolyte region 416 is an electronic insulator and an ionic conductor, positive electrode 418 is ionically coupled to but electronically insulated from negative electrode 414. Finally, the side of positive electrode 418 opposite electrolyte region 416 is affixed to a posit