Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/06—Electrodes for primary cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/50—Methods or arrangements for servicing or maintenance, e.g. for maintaining operating temperature
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M12/00—Hybrid cells; Manufacture thereof
  • H01M12/04—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type
  • H01M12/06—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type with one metallic and one gaseous electrode
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0002—Aqueous electrolytes

Definitions

• the present invention relates generally to an improved electrochemical cell and a method of forming such a cell and, more specifically, the invention relates to an improved electrochemical cell having a lithium anode which is activated by contact with an aqueous electrolyte.
• Electrochemical cells utilizing aqueous electrolytes and anodes of highly chemically and electrochemically reactive metals, such as sodium and lithium, are well known. Such cells are described in detail in Rowley U.S. Patent No. 3,791,871, Momyer U.S. Patent No. 4,001,043 and Momyer et al U.S. Patent No. 4,269,907, the disclosures of which are all hereby incorporated by reference.
• a reactive metal anode is spaced from a cathode, initially by an electrically insulating film formed on the anode.
• Activation of the cell is effected by contact of the anode and cathode with an aqueous electrolyte.
• the insulating film on the anode dissolves in the electrolyte, and the water reacts with the anode-forming metal to form an alkaline electrolyte solution, generally an alkali metal hydroxide solution. As the reaction proceeds, the insulating film is further eroded, and the cathode is placed in electrochemical contact with the anode through the electrolyte. In some cases, as in Momyer et al 4,269,907, an additional element such as a nonconductive screen or other porous element is disposed between the anode and cathode to maintain proper spacing. Alkali metal electrochemical cells utilizing lithium anodes are very popular due to the relatively high energy density obtainable therewith.
• Lithium anodes are especially desirable when the cathode comprises a so-called "air cathode” in which depolarization at the cathode is accomplished by reduction of oxygen in the air.
• Giner U.S. Patent No. 3,438,815 the disclosure of which is hereby incorporated by reference, provides a good disclosure of a fuel cell utilizing an air cathode.
• activation be deferred until it is desired to utilize the cell.
• activation be effected with a minimum of delay.
• the lithium anode be protected and spaced from the cathode by an insulating film and that the film be subject to rapid decomposition upon addition of the aqueous electrolyte to the cell for activation.
• the electrolyte-soluble insulating film was typically formed on the anode by prior contact with an aqueous lithium hydroxide solution.
• films formed in this manner tend to contain an excess of free moisture, which is known to catalyze the room temperature reaction between lithium and nitrogen in the atmosphere to form lithium nitride (Li 3 N).
• the formation on a lithium anode of a hydrated lithium hydroxide film tends to promote the formation of lithium nitride occlusions in the film if the anode is subject to contact with the atmosphere.
• the formation of lithium nitride on an anode surface is undesirble as it decreases the rate of battery activation and reduces the shelf life of the cell. Further, the ultimate power output of the cell is substantially reduced by the presence of lithium nitride on an anode.
• the present invention is directed to overcoming one or more of the problems described above.
• the lithium anode of an electrochemical cell is provided with an electrolyte-soluble, electrically insulating film by reaction of the lithium metal of the anode with oxygen or carbon dioxide, in the substantial absence of moisture.
• the resulting protective film of lithium oxides or lithium carbonate prevents lithium nitride formation, resulting in an electrochemical cell which has long shelf life, is rapidly activated and produces high power output.
• lithium nitride (Li 3 N) on lithium metal is the only known reaction which occurs between a metal and atmospheric nitrogen at room temperature.
• the formation of lithium nitride on a lithium anode is undesirable for a variety of reasons.
• the formation on an anode of an insulating film which contains free moisture (defined as water which is capable of catalyzing the lithium-nitrogen reaction) must be avoided.
• an electrolyte-soluble insulating protective film can be formed on a lithium anode of an elecrochemical cell by reaction of the lithium in the anode with substantially moisture free oxygen, preferably from the atmosphere, or with carbon dioxide.
• the resulting films comprise lithium oxides and lithium carbonate, respectively.
• the films may be formed in a straightforward manner.
• a thin film of one or more lithium oxides is readily formed on a lithium anode by exposure of the anode to air at room temperature in a low humidity environment. It has been found that air with a relative humidity of 3% or less is suitable, and that the resulting film is substantially devoid of "free" moisture.
• the anode in the case of lithium carbonate, can readily be reacted with gaseous carbon dioxide to form a lithium carbonate (Li 2 CO 3 ) film.
• the resulting thin, opaque lithium carbonate film on the lithium anode surface retards or substantially eliminates the normal oxidation processes which occur in the atmosphere.
• the lithium carbonate film on the anode does not contain any waters of hydration ("free" moisture), which explains the effectiveness of the film in eliminating lithium nitride formation.
• lithium carbonate is relatively insoluble in aqueous lithium hydroxide electrolyte solutions, thus resulting in a relatively slow activation rate for the cell.
• air oxidation of the anode is the preferred procedure in carrying out the invention.
• the resulting lithium oxide film is also substantially devoid of "free” moisture. It will be appreciated that the prior method of "filming" a lithium anode with an aqueous lithium hydroxide electrolyte is unsatisfactory because excess moisture inevitably present in the film tends to catalyze lithium nitride formation unless air is rigorously excluded from the cell structure after assembly. Without such air exclusion, the possibility exists for lithium nitride formation during assembly and activation of the battery. This problem is particularly acute with an air cathode because the porous structure allows nitrogen from the air supply to contact the lithium anode surface prior to and during the activation sequence. This problem is not encountered with the method of the present invention.
• an electrically insulating electrode separator disposed between the anode and cathode is required in order to eliminate possible short circuiting of the electrical cell before or at activation.
• Various non-conductive structures are suitable, such as metal screens coated with Teflon (polytetrafluoroethylene) or various plastic resins such as Vexar brand low and high density polyethylene or polypropylene netting. The use of such non-conductive screens is disclosed in Momyer et al 4,269,907.
• the protected anode and method of the invention are applicable to any type of electrochemical cell having a lithium anode and activated by addition of an aqueous electrolyte
• the invention is especially applicable to primary batteries utilizing an aqueous electrolyte and an air cathode because the lithium anode is generally subjected to prolonged exposure to air prior to activation.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Hybrid Cells (AREA)
• Inert Electrodes (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Primary Cells (AREA)

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• 1983
  • 1983-12-14 WO PCT/US1983/001985 patent/WO1984003177A1/en unknown
  • 1983-12-14 EP EP84900440A patent/EP0135506A1/en not_active Withdrawn
• 1984
  • 1984-02-03 IT IT8447648A patent/IT8447648A0/it unknown
  • 1984-02-07 ES ES529525A patent/ES8501570A1/es not_active Expired

Non-Patent Citations (1)

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