WO1994010708A1

WO1994010708A1 - Battery assembly emloying a check valve

Info

Publication number: WO1994010708A1
Application number: PCT/US1993/010020
Authority: WO
Inventors: Scot S. Cheu
Original assignee: Valence Technology, Inc.
Priority date: 1992-10-29
Filing date: 1993-10-21
Publication date: 1994-05-11
Also published as: AU5585594A

Abstract

A one-way check valve is incorporated into the protective shell for protecting a laminar battery cell using a lithium anode. After the protective shell is sealed to form a battery chamber for housing the battery cell, the battery chamber is then evacuated. This permits the sealing operation to be performed outside of a vacuum chamber.

Description

BATTERY ASSEMBLY EMPLOYING A CHECK VALVE

Background of the Invention

This invention relates in general to battery vacuum packages, and in particular to a battery assembly employing a check valve for evacuating the battery assembly.

A solid-state battery is advantageous, since it possesses a number of very desirable characteristics, including the absence of liguid leakage or gassing, long shelf life, and operation over a wide temperature range. A number of solid-state batteries has been proposed.

One such battery which has received wide attention is one employing a lithium anode. For an example of a lithium anode battery, see U.S. Patent No. 4,997,732 issued to Austin et al. ("Austin et al.") . One problem in the manufacture of lithium battery cells is that lithium is highly reactive, so that a lithium anode battery cell must be sealed in a protective material to exclude air, water and- other gases from contacting the lithium. For this reason, it is necessary to evacuate any moisture, air or other gases within the protective layer protecting the battery, so as to prevent the lithium from reacting with water or other reactive gases. Typically, the battery is enclosed by a protec¬ tive shell material and both of them placed in a vacuum. The protective shell material is then heated and pressed, causing at least a portion of the shell material to melt in order to seal the shell edges which envelop the battery.

The above-described sealing method is cumbersome, since it must be performed in a vacuum. This is especially the case since particular care sometimes should be taken when sealing the edges around electrodes to prevent the electrodes from inadvertently breaking off during the sealing process, while at the same time a sufficient pressure must be applied to the edges to seal around the electrodes in order to ensure an air and water impermeable seal. It is therefore desirable to provide an improved battery assembly and method for evacuating the assembly in which the above-described difficulties are not present.

finmfflΛTγ o the Invention Applicant discovered that by employing a check valve connected to the protective shell, it is possible to evacuate the chamber within the protective shell after it has been sealed around the battery cell and portions of the electrically conductive terminals. This renders the sealing process much simpler and easier to accomplish.

One aspect of the invention is directed towards a battery assembly comprising a laminar battery cell, a pair of electrically conductive terminals integral with or in electrical contact with said cell, and a protec¬ tive shell defining a chamber therein enveloping said cell and portions of the terminals to protect the cell from an environment. The assembly further comprises a check valve connected to the shell for controlling the passage of fluids between the chamber and the environ¬ ment.

Another aspect of the invention is directed towards a method for evacuating at least one of the above- described battery assemblies. The method comprises causing a pressure differential between the chamber of at least one battery assembly and the environment, said differential being such that any gas (including mois- ture) present in the battery chamber will escape through the check valve through the environment to evacuate the battery chamber. The method further comprises removing the pressure differential.

Yet another aspect of the invention is directed towards a method for making a battery assembly, compris¬ ing connecting a one-way check valve to a protective shell and enclosing a laminar battery cell and portions of a pair of electrically conductive terminals integral with or in electrical contact with said cell by sealing said protective shell around said cell and portions of said terminals. The shell defines a battery chamber to protect the cell from an environment. The method further comprises causing an environment surrounding the battery chamber to be at a lower pressure than the chamber, thereby causing gas, including moisture, in the chamber to escape through the valve from the chamber to the environment without permitting gas from the environ¬ ment to enter the chamber.

Brief Description of the Drawings Fig. 1 is an exploded perspective view of the components of a battery assembly to illustrate one embodiment of the invention.

Figs. 2 and 3 are exploded perspective views of the components of a battery assembly forming the protective shell to illustrate two additional embodiments of the invention.

Fig. 4 is a schematic view of a check valve and a portion of a package wall or shell to illustrate the invention. Fig. 5 is a cross-sectional view of a battery assembly with a check valve to illustrate the operation of the invention.

Fig. 6 is a partly cross-sectional and partly schematic view of a battery assembly and a vacuum chamber to illustrate a method for evacuating the package according to the invention.

Fig. 7 is a cross-sectional view of a battery assembly and a vacuum hose to illustrate an alternative method for evacuating the battery assembly.

Detailed Description of the Preferred Embodiment Fig. 1 is an exploded perspective view of the components of a battery assembly to illustrate one embodiment of the invention. The assembly 10 includes a battery cell 12 which includes a cell body 14 and two terminals 16, 18. The body 14 has two flat surfaces 14a, 14b and four edge surfaces 14c, 14d, 14e, 14f.

As shown in Fig. 1, body 14 is in the shape of a rectangular plate with two large flat surfaces 14a, 14b. The protective shell includes two flexible sheets 20, 22 facing the two flat surfaces 14a, 14b, respectively, of body 14; the sheets 20 and 22 have surface areas larger than the two flat surfaces 14a, 14b of body 14. The protective shell also includes a continuous band 24 forming a protective frame of a shape which would fit onto the side surfaces 14c, 14d, 14e, 14f.

The method of assembly of cell 12 is described, for example, in the above-referenced patent to Austin et al. Terminals 16, 18 may be integral with body 14 or be electrically connected and physically attached to body 14. Thus, when flexible sheets 20, 22 are moved along arrows labeled A, B and band 24 is moved toward cell along arrow C, body 14 is enclosed by the band 24 and sheets 20, 22. Since sheets 20, 22 have larger areas than surfaces 14a, 14b, the four edges of the sheets 20, 22 will bend over to touch band 24 and each other. Heat and pressure may then be applied to sheets 20, 22 and band 24 to form a moisture and gas permeable protective shell around body 14 and portions of terminals 16, 18, and enclosing a chamber for holding the body and portions of the terminals.

Band 24 is provided with grooves 24a, 24b for accommodating terminals 16, 18 respectively during the above assembly process. After the assembly process, terminal 16, 18 will fit into grooves 24a, 24b and appear in phantom positions 16', 18', respectively. Band 24 also has a check valve 30 on one side, so that after the above-described assembly and sealing process, the check valve 30 controls the passage of fluids between the environment and the battery chamber enclosed by the protective shell formed by sheets 20, 22 and band 24 after the above-described assembly and sealing process. The method for evacuating the battery chamber using valve 30 is described in detail below.

Sheets 20 and 22 should be large enough so that the edges would wrap around body 14 after the assembly to envelop a portion of each of the terminals 16, 18 forming an edge of the protective shell in order to securely seal the chamber of the terminals 16, 18, while exposing a portion of each of the two terminals to provide external electrical connections to the battery cell 12. Sheets 20, 22 and band 24 may be sealed together by means of an adhesive where heat and pressure are applied in a manner described in the above-refer¬ enced patent to Austin et al.

Figs. 2 and 3 are exploded schematic views of the components for making a protective shell for the battery cell with the cell itself omitted to illustrate addi- tional embodiments of the invention. Instead of employing two flexible sheets and a rectangular band forming a plastic frame with a through hole sandwiched between the two flexible sheets as in Fig. 1, the protective shell in both Figs. 2 and 3 is formed by a rectangular rigid container 50 with a flexible sheet 52 as the lid of the container. Since the container 50 has a bottom, the second flexible sheet on the other side of sheet 52 is no longer necessary. Container 50 is a ridged container having a flange 50a, so that when flexible sheet 52 is placed on top of the flange 50a, the flange would contact the flexible sheet for conve¬ nient sealing. In this manner, the sealing process is simplified compared to that of Fig. 1. For simplicity, identical components in the Figures of this application are labeled by the same numerals. The embodiments of Figs. 2 and 3 differ, however, in their terminal con¬ figuration. In Fig. 2, terminals 46, 48 are provided on the short side surface 50b of the container 50. In the embodiment of Fig. 3, however, the terminals take the form of elongated flat strips 56, 58 which are placed on top of flange 50a with portions 56a, 58a bent downwards in contact with the inside surface 50c of the container 50. Thus in the configurations of both Figs. 2 and 3, the terminals are connected and/or attached to the battery cell body (not shown, such as that of Fig. 1) . In Fig. 2, side surface 50d is provided with a check valve 30; in the embodiment of Fig. 3, the check valve 30 is provided at surface 50c.

To make the battery assembly in the embodiments of Figs. 2 and 3, the battery cell (e.g., cell 12 of Fig. l without the protruding terminals) is placed in container 50, where the terminals 46, 48 or 56, 58 are connected to the anodes and cathodes of the battery cell in a known manner. Flexible sheet 52 is then placed on top of flange 50a with an adhesive already placed on top of the flange. Heat and pressure may then be applied to flange 50a and sheet 52 in order to form a moisture and gas impermeable protective shell enclosing a battery chamber with a battery cell therein. The battery assembly so completed is labeled 10', 10" in Figs. 2 and 3. Fig. 4 is a schematic view of a one-way check valve 30 and a portion of the package wall with a hole therein to illustrate the invention. One-way check valve 30 is available commercially, for example, from Robert Bosch Corporation, 15 Seely Ave. , Piscapaway, New Jersey 08854. In order to incorporate valve 30 into the sidewalls 24, 50d, 50c and 24 of Figs. 1, 2 and 3, these sidewalls or bands are first provided with a hole 60 as shown in Fig. 4. Check valve 30 has an inlet 30a and an outlet 30b. Check valve 30 also has a flange 30c adapted to contact and be attached to a package wall (24, 50c, 50d) . Flange 30c may be attached to the package wall by an element 64, which may be a tape with adhesives on both sides, or a heat seal layer composed of a material such as low density polyethylene or Surlyn ® brand glue from Dupont. After inlet 30a of the valve 30 is aligned with hole 60, flange 30c is brought into contact with the package wall so that the adhesive element 64 attaches flange 30c to the package wall. If necessary, a fixture is used to apply pressure between flange 30c and the package wall, and heat is supplied where necessary. Such fixture and heating operation is similar to those employed in bottle capping or sticker operations or fitmounts mounting operations. Instead of heating the valve in order to seal the flange 30c to the protective wall, ultrasonic energy may be applied to the flange to accomplish the same result.

After the valve is thus incorporated into a portion of the protective shell, the above-described protective shell, assembled as described above in reference to Figs. 1-3, may then be employed to seal the battery cell 12 within a protective shell, which encloses the battery cell within a battery chamber 70. Such configuration is shown in Fig. 5. Fig. 5 is a cross-sectional view of a battery assembly with a battery cell 12 enclosed within a protective shell 11 which encloses both the battery cell within a chamber 70, where check valve 30 controls the passage of fluids between chamber 70 and the environment 72 outside shell 11. The sealing element may also comprise a portion of the valve, the portion including a material 30c (Fig. 4) such as low density polyethylene or plastic resin.

The method for evacuation is illustrated in Figs. 6 and 7. In Fig. 6, the package assembly of any of the configurations described above (10, 10', 10'¹) is placed in vacuum chamber 100, so that the pressure differential between battery chamber 70 and vacuum chamber 100 causes moisture, air and any other gases inside the battery chamber to escape through check valve 30 into the vacuum chamber, where they are drawn through outlet 102 by vacuum pump (not shown) . After chamber 70 has been evacuated, the battery assembly is retrieved from vacuum chamber 100, thereby restoring a balanced pressure between chamber 70 and the environment. Check valve 30 only permits one-way movement of moisture and gas from its inlet to its outlet, but does not permit entry of moisture, air or any other gas from outlet 30b to the battery chamber 70. The lithium anode in cell 12 is therefore securely isolated from moisture, air and other gases in the atmosphere. While only one battery assembly is shown being evacuated in vacuum chamber 100, obviously a plurality of battery assemblies may be placed in chamber 100 and evacuated simultaneously to increase the efficiency of the system. Fig. 7 illustrates another method for evacuating the battery assembly. As shown in Fig. 7, instead of placing the assembly in a vacuum chamber, a vacuum hose is connected to the check valve, where the vacuum hose is connected to a vacuum pump (not shown) . In this manner, moisture, air and other gases in battery chamber 70 are evacuated through the outlet 30b of check valve 30.

Thus, the overall method for making the battery assembly is as follows. First, a one-way check valve 30 is connected to a protective shell such as described above in reference to Fig. 4. Then a laminar battery cell body (e.g., cell body 14) and portions of a pair of electrically conductive terminals integral with or in electrical contact with the cell are held in a battery chamber enclosed by the protective shell by sealing the shell around the battery cell and portions of the terminals. The shell thus encloses a battery chamber to protect the cell from the environment. Then, in the manner described above in reference to Figs. 6 and 7, the battery chamber is evacuated.

From the above, it will be evident that the formation of the protective shell and a sealed battery chamber enclosing the battery cell may be performed under atmospheric pressure instead of under vacuum conditions. This renders a sealing operation much easier to perform. This is especially the case since the sealing operation must ensure that the protective shell securely seals around the two terminals by applying pressure and the heat thereto without breaking or otherwise damaging the terminals.

Additionally, as shown in Fig. 5, the one-way check valve 30 has safety benefits. A defective battery may produce gases in the battery chamber 70. The one-way check valve 30 allows these gases to escape from the battery assembly and prevents the battery assembly from bursting at the seal. When the internal pressure in the battery chamber is greater than the atmospheric pres¬ sure, the one-way check valve 30 allows gases to escape from the battery chamber 70. While the invention has been described by reference to various embodiments, it will be understood that various modifications may be made without departing from the scope of the invention, which is to be limited only by the appended claims.

Claims

WHAT IS CLAIMED IS;

1. A battery assembly comprising: a laminar battery cell; a pair of electrically conductive terminals integral with or in electrical contact with said cell; a protective shell defining a chamber therein enveloping said cell to protect the cell from environ¬ ment; and a check valve connected to the shell for control¬ ling the passage of fluids between the chamber and the environment.

2. The assembly of claim 1, wherein said check valve is a one-way check valve that allows gas to escape from the chamber to the environment but does not permit any significant amount of gas from the environment to enter the chamber.

3. The assembly of claim 1, said shell defining a hole therein for holding the valve, said assembly further comprising means for sealing the valve to the shell at the hole.

4. The assembly of claim 3, said sealing means comprising an adhesive.

5. The assembly of claim 3, said sealing means comprising a portion of the valve, said portion includ¬ ing a low density polyethylene or plastic resin.

6. The assembly of claim 1, wherein said protec¬ tive shell further envelopes portions of said terminals.

7. A method for evacuating a battery assembly which comprises: (a) a laminar battery cell; (b) a pair of electrically conductive terminals integral with or in electrical contact with said cell; (c) a protective shell defining a battery chamber therein enveloping said cell to protect the cell from an environment; and a check valve connected to the shell for controlling the passage of fluids between the chamber and the environ¬ ment, said method comprising: causing a pressure differential between the battery chamber of at least one battery assembly and the environment, said differential being such that any gas present in the battery chamber will escape through the check valve to the environment to evacuate the battery chamber; and removing the pressure differential.

8. The method of claim 7, wherein said causing step includes the steps of placing said assembly into an vacuum chamber and continuously evacuating said vacuum chamber.

9. The method of claim 7, wherein said causing step includes the steps of connecting said check valve to a vacuum pump and operating said pump.

10. A method for making a battery assembly comprising: connecting a one-way check valve to a protective shell; enclosing a laminar battery cell by sealing said protective shell around said cell, said shell defining a battery chamber to protect the cell from environment; and evacuating the battery chamber.

11. The method of claim 10, said shell comprising a rigid frame and a flexible lid for sealing the frame, said frame defining a hole therein, said connecting step including the steps of: aligning the valve with said hole; and sealing the valve to the frame at the hole.

12. The method of claim 11, wherein said sealing step employs an adhesive material.

13. The method of claim 12, wherein said valve is made of or coated with a hot melt adhesive, and wherein said sealing step includes heating the valve or provid¬ ing ultrasonic energy to the valve.

14. The method of claim 10, wherein said laminar battery cell enclosing step includes enclosing portions of a pair of electrically conductive terminals integral with or in electrical contact with said cell by sealing said protective shell around said cell and portions of said terminals.