Patent Abstract:
A hermetically sealed coin cell is described. The coin cell has the opposite polarity terminals isolated from one another by a glass-to-metal seal. Glassing a conductive disc inside a ring of greater diameter and height forms this seal. The height of the ring is equivalent to the desired height of the cell. The disc acts as one cell terminal, which can be positive or negative, and the ring serves as the other terminal. In plan view, both terminals are on the same side of the cell. This allows for easy mounting and connection to an electric circuit board, and the like.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present application claims priority from U.S. provisional application Serial No. 60/441,015, filed Jan. 17, 2003. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to a hermetically sealed coin-type cell. The cell is of either a primary or a secondary chemistry.  
           [0004]    2. Prior Art  
           [0005]    Implantable electrochemical cells are in widespread use. These cells are hermetically sealed using an insulating glass to separate the terminal pin from the case. Power sources of this type prevent internal components, such as the electrolyte, from coming into contact with body tissue or sensitive electrical components of the associated implantable medical device. These cells are easily manufactured in large sizes. However, as cell size becomes smaller, it becomes increasingly more complicated to perform the required welding and fabrication processes.  
           [0006]    Often, coin cells are used in applications that require a very small power source. A top and bottom terminal crimped together with an insulating gasket characterizes coin cells. Contact between the electrodes and their current collectors are achieved by using stack pressure, which eliminates the need for welding the electrodes to the terminals. Also, since the number of parts is relatively small in a coin cell, this minimizes the need for many manufacturing operations. The problem with coin cells is, however, that the insulating gasket is typically of a polymeric or plastic material. Plastics are porous and do not constitute a hermetic seal. Also, these seals are unreliable and prone to leaking. As such, coin cells of the prior art are not suitable for implantable applications.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention coin cell is distinguishable from those of the prior art in that the opposite polarity terminals are isolated from one another using a glass-to-metal seal. Glassing a conductive disc inside a ring of greater diameter and height forms this seal. The height of the ring is equivalent to the desired height of the cell. The disc acts as one cell terminal, which can be positive or negative, and the ring serves as the other terminal. In plan view, both terminals are on the same side of the cell. This allows for easy mounting and connection to an electronic circuit board, and the like.  
           [0008]    These and other aspects of the present invention will become more apparent to those of ordinary skill on the art by reference to the following description and the appended drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a top plan view of the coin cell  10  of the present invention.  
         [0010]    [0010]FIG. 2 is a bottom plan view of the coin cell  10  shown in FIG. 1.  
         [0011]    [0011]FIG. 3 is a cross-sectional view along line  3 - 3  of FIG. 1.  
         [0012]    [0012]FIG. 4 is a cross-sectional view of the ring  12  and disc  14  for the coin cell  10 .  
         [0013]    [0013]FIG. 5 is a cross-sectional view showing the insulative glass  20  sealing between the ring  12  and disc  14  of FIG. 4.  
         [0014]    [0014]FIG. 6 is a cross-sectional view showing the positioning of the first and second electrodes  22  and  26  of the coin cell of FIG. 5.  
         [0015]    [0015]FIG. 7 is a cross-sectional view showing the electrolyte  28  activating the electrodes  22 ,  26  of FIG. 6.  
         [0016]    [0016]FIG. 8 is a cross-sectional view showing the plate  30  closing the coin cell of FIG. 7.  
         [0017]    [0017]FIG. 9 is a schematic showing a laser  32  welding the plate  30  to the ring  12  to hermetically close the coin cell of FIG. 8.  
         [0018]    [0018]FIG. 10 is a cross-sectional view showing an alternate embodiment of a coin cell  100  according to the present invention.  
         [0019]    [0019]FIG. 11 is a cross-sectional view showing another embodiment of a coin cell  10 A having a spring  36  captured between the second electrode  26  and lid  30  to provide stack pressure for the electrode assembly. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to the drawings, FIGS.  1  to  9  show a coin cell  10  according to the present invention. The coin cell  10  comprises a cylindrically shaped ring  12  surrounding a circular disc  14 . The ring  12  has a cylindrical outer wall  12 A that is coaxial with a cylindrical inner wall  12 B. The outer and inner walls  12 A,  12 B of the ring  12  extend to and meet with a spaced apart and perpendicularly oriented bottom or lower end  12 C and a top or upper end  12 D. The upper end  12 D includes an annular step  16  adjacent to the inner wall  12 B.  
         [0021]    The disc  14  serves as a base for one of the electrodes and comprises a cylindrically shaped outer wall  14 A extending to a perpendicularly oriented bottom or lower end  14 B and a top or upper end  14 C. A circular recess  18  is provided in the disc. The recess  18  comprises a cylindrical inner wall  14 D extending to an inner bottom wall  14 E. The disc lower end  14 B and the inner lower wall  14 E are parallel to each other. Further, the outer and inner cylindrical walls  14 A,  14 D are coaxial. The height of the inner wall  14 D is from about 10% to about 90% of that of the outer wall  14 A. This means that the thickness of the disc between the lower end  14 B and the inner lower wall  14 E is from about 10% to about 90% of the height of the outer wall  14 A.  
         [0022]    The disc  14  is sized to fit inside the ring  12 . As shown in FIGS.  3  to  9 , with the ring lower end  12 C aligned coplanar with the disc lower end  14 B, the disc upper end  14 C is spaced from and below the ring upper end  12 D. With the disc in a coaxial relationship with the ring, the disc outer wall  14 A is spaced from the ring inner wall  12 B. An insulative glass  20  seals in an annular manner between the ring inner wall  12 B and the disc outer wall  14 A (FIG. 5). This serves to hermetically seal the disc to the ring.  
         [0023]    A first electrode  22  of an electrode active material is nested in the recess  18 . The first electrode comprises spaced apart upper and lower major sides. The upper electrode side is shown substantially coplanar with the disc upper end  14 C; however, this is not necessary. The electrode upper side can be spaced above disc upper end  14 C, if desired.  
         [0024]    An insulating separator  24  resting on the disc upper end  14 C spans the entire area surrounded by the ring inner wall  12 B. A second electrode  26  of an opposite polarity as the first electrode is then positioned on the opposite side of the separator  24 .  
         [0025]    As previously discussed, the coin cell  10  is of either a primary chemistry or a secondary, rechargeable chemistry. However, the coin cell will be described with respect to the second electrode  26  being the anode or negative electrode and the first electrode  22  being the cathode or positive electrode. For both the primary and secondary types, the anode active metal of the second electrode  26  is selected from Groups IA, IIA and IIIB of the Periodic Table of the Elements, including lithium, sodium, potassium, etc., and their alloys and intermetallic compounds including, for example, Li—Si, Li—Al, Li—B, Li—Mg, and Li—Si—B alloys. The preferred metal comprises lithium. An alternate negative electrode comprises a lithium alloy, such as lithium-aluminum alloy. The greater the amounts of aluminum present by weight in the alloy, however, the lower the energy density of the cell.  
         [0026]    For a primary coin cell, the anode  26  is a thin metal sheet or foil or pellet of the lithium material. In secondary electrochemical systems, the anode or negative electrode comprises an anode material capable of intercalating and de-intercalating the anode active material, such as the preferred alkali metal lithium. A carbonaceous negative electrode comprising any of the various forms of carbon (e.g., coke, graphite, acetylene black, carbon black, glassy carbon, etc.), which are capable of reversibly retaining the lithium species, is preferred. A “hairy carbon” material is particularly preferred due to its relatively high lithium-retention capacity. “Hairy carbon” is a material described in U.S. Pat. No. 5,443,928 to Takeuchi et al. This patent is assigned to the assignee of the present invention and incorporated herein by reference. Graphite is another preferred material. Regardless of the form of the carbon, fibers of the carbonaceous material are particularly advantageous because they have excellent mechanical properties, which permit them to be fabricated into rigid electrodes that are capable of withstanding degradation during repeated charge/discharge cycling. Moreover, the high surface area of carbon fibers allows for rapid charge/discharge rates.  
         [0027]    A typical negative electrode for a secondary cell is fabricated by mixing about 90 to 97 weight percent “hairy carbon” or graphite with about 3 to 10 weight percent of a binder material, which is preferably a fluoro-resin powder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylenetetrafluoroethylene (ETFE), polyamides, polyimides, and mixtures thereof.  
         [0028]    In either the primary or secondary system, the reaction at the positive electrode  22  involves conversion of ions, which migrate from the negative electrode  26  to the positive electrode into atomic or molecular forms. For a primary cell, the cathode active material comprises a carbonaceous chemistry or at least a first transition metal chalcogenide constituent which may be a metal, a metal oxide, or a mixed metal oxide comprising at least a first and a second metals or their oxides, and possibly a third metal or metal oxide, or a mixture of a first and a second metals or their metal oxides incorporated in the matrix of a host metal oxide. The cathode active material may also comprise a metal sulfide.  
         [0029]    Carbonaceous active materials are preferably prepared from carbon and fluorine, which includes graphitic and nongraphitic forms of carbon, such as coke, charcoal or activated carbon. Fluorinated carbon is represented by the formula (CF x ) n , wherein x varies between about 0.1 to 1.9 and preferably between about 0.5 and 1.2, and (C 2 F) n , wherein n refers to the number of monomer units, which can vary widely.  
         [0030]    The metal oxide or the mixed metal oxide is produced by the chemical addition, reaction, or otherwise intimate contact of various metal oxides, metal sulfides and/or metal elements, preferably during thermal treatment, sol-gel formation, chemical vapor deposition or hydrothermal synthesis in mixed states. The active materials thereby produced contain metals, oxides and sulfides of Groups IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIII, which include the noble metals and/or other oxide and sulfide compounds. A preferred cathode active material is a reaction product of at least silver and vanadium.  
         [0031]    One preferred mixed metal oxide has the general formula SM x V 2 O y  where SM is a metal selected from Groups IB to VIIB and VIII of the Periodic Table of Elements, and wherein x is about 0.30 to 2.0 and y is about 4.5 to 6.0 in the general formula. One exemplary cathode active material comprises silver vanadium oxide having the general formula Ag x V 2 O y  in any one of its many phases, i.e., β-phase silver vanadium oxide having in the general formula x=0.35 and y=5.8, γ-phase silver vanadium oxide having in the general formula x=0.80 and y=5.40 and ε-phase silver vanadium oxide having in the general formula x=1.0 and y=5.5, and combination and mixtures of phases thereof. For a more detailed description of such cathode active materials reference is made to U.S. Pat. No. 4,310,609 to Liang et al. This patent is assigned to the assignee of the present invention and incorporated herein by reference.  
         [0032]    Another preferred composite cathode active material for primary cells has the general formula Cu x Ag y V 2 O z , (CSVO) and the range of material compositions is preferably about 0.01≦x≦1.0, about 0.01≦y≦1.0 and about 5.01≦z≦6.5. For a more detailed description of this cathode active material, reference is made to U.S. Pat. Nos. 5,472,810 to Takeuchi et al. and 5,516,340 to Takeuchi et al., both of which are assigned to the assignee of the present invention and incorporated herein by reference.  
         [0033]    In addition to the previously described fluorinated carbon, silver vanadium oxide and copper silver vanadium oxide, Ag 2 O, Ag 2 O 2 , CuF 2 , Ag 2 CrO 4 , MnO 2 , V 2 O 5 , MnO 2 , TiS 2 , Cu 2 S, FeS, FeS 2 , copper oxide, copper vanadium oxide, and mixtures thereof are contemplated as useful active materials.  
         [0034]    In secondary coin cell, the positive electrode  22  preferably comprises a lithiated material that is stable in air and readily handled. Examples of such air-stable lithiated cathode active materials include oxides, sulfides, selenides, and tellurides of such metals as vanadium, titanium, chromium, copper, molybdenum, niobium, iron, nickel, cobalt and manganese. The more preferred oxides include LiNiO 2 , LiMn 2 O 4 , LiCoO 2 , LiCo 0.92 Sn 0.08 O 2  and LiCo 1−x Ni x O 2 .  
         [0035]    To charge such secondary coin cells, lithium ions comprising the positive electrode  22  are intercalated into the carbonaceous negative electrode  26  by applying an externally generated electrical potential to the cell. The applied recharging electrical potential serves to draw lithium ions from the cathode active material, through the electrolyte and into the carbonaceous material of the negative electrode to saturate the carbon. The resulting Li x C 6  negative electrode can have an x ranging from 0.1 to 1.0. The cell is then provided with an electrical potential and is discharged in a normal manner.  
         [0036]    An alternate secondary cell construction comprises intercalating the carbonaceous material with the active lithium material before the negative electrode is incorporated into the cell. In this case, the positive electrode body can be solid and comprise, but not be limited to, such active materials as manganese dioxide, silver vanadium oxide, titanium disulfide, copper oxide, copper sulfide, iron sulfide, iron disulfide and fluorinated carbon. However, this approach is compromised by problems associated with handling lithiated carbon outside of the cell. Lithiated carbon tends to react when contacted by air or water.  
         [0037]    The above described cathode active materials, whether of a primary or a secondary chemistry, are formed into an electrode body for incorporation into a coin cell by mixing one or more of them with a binder material. Suitable binders are powdered fluoro-polymers; more preferably powdered polytetrafluoroethylene or powdered polyvinylidene fluoride present at about 1 to about 5 weight percent of the cathode mixture. Further, up to about 10 weight percent of a conductive diluent is preferably added to the cathode mixture to improve conductivity. Suitable materials for this purpose include acetylene black, carbon black and/or graphite or a metallic powder such as powdered nickel, aluminum, titanium and stainless steel. The preferred cathode active mixture thus includes a powdered fluoro-polymer binder present at about 1 to 5 weight percent, a conductive diluent present at about 1 to 5 weight percent and about 90 to 98 weight percent of the cathode active material.  
         [0038]    Whether the coin cell  10  is constructed as a primary or secondary electrochemical system, the separator  24  physically segregates the anode  26  and cathode active materials  22 . The separator is of an electrically insulative material to prevent an internal electrical short circuit between the electrodes, and also is chemically unreactive with the anode and cathode active materials and both chemically unreactive with and insoluble in the electrolyte. In addition, the separator material has a degree of porosity sufficient to allow flow there through of the electrolyte during the electrochemical reaction of the cell. The form of the separator typically is a sheet placed between the anode and cathode electrodes. Illustrative separator materials include fabrics woven from fluoropolymeric fibers including polyvinylidine fluoride, polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylene used either alone or laminated with a fluoropolymeric microporous film, non-woven glass, polypropylene, polyethylene, glass fiber materials, ceramics, a polytetrafluoroethylene membrane commercially available under the designation ZITEX (Chemplast Inc.), a polypropylene membrane commercially available under the designation CELGARD (Celanese Plastic Company, Inc.) and a membrane commercially available under the designation DEXIGLAS (C. H. Dexter, Div., Dexter Corp.).  
         [0039]    After the electrodes  22 ,  26  are housed in the ring/disc assembly, an electrolyte  28  is filled therein. The electrolyte is provided into the disc recess  18  and the ring  12  in an amount substantially level with the step  16  meeting the ring inner wall  12 B. Suitable nonaqueous electrolytes comprise an inorganic salt dissolved in a nonaqueous solvent, and more preferably an alkali metal salt dissolved in a mixture of aprotic organic solvents comprising a low viscosity solvent including organic esters, ethers and dialkyl carbonates, and mixtures thereof, and a high permittivity solvent including cyclic carbonates, cyclic esters and cyclic amides, and mixtures thereof. Suitable nonaqueous solvents are substantially inert to the anode and cathode electrode materials and preferred low viscosity solvents include tetrahydrofuran (THF), methyl acetate (MA), diglyme, triglyme, tetraglyme, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), 1,2-dimethoxyethane (DME), and mixtures thereof. Preferred high permittivity solvents include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, γ-butyrolactone (GBL), γ-valerolactone, N-methyl-pyrrolidinone (NMP), and mixtures thereof.  
         [0040]    Known lithium salts that are useful as a vehicle for transport of alkali metal ions from the anode to the cathode, and back again include LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiClO 4 , LiAlCl 4 , LiGaCl 4 , LiC(SO 2 CF 3 ) 3 , LiO 2 , LiNO 3 , LiO 2 CCF 3 , LiN(SO 2 CF 3 ) 2 , LiSCN, LiO 3 SCF 2 CF 3 , LiC 6 F 5 SO 3 , LiO 2 CF 3 , LiSO 3 F, LiB(C 6 H 5 ) 4 , LiCF 3 SO 3 , and mixtures thereof. Suitable salt concentrations typically range between about 0.8 to 1.5 molar.  
         [0041]    A preferred electrolyte for a secondary cell of an exemplary carbon/LiCoO 2  couple comprises a solvent mixture of EC:DMC:EMC:DEC. Most preferred volume percent ranges for the various carbonate solvents include EC in the range of about 20% to about 50%; DMC in the range of about 12% to about 75%; EMC in the range of about 5% to about 45%; and DEC in the range of about 3% to about 45%. In a preferred form of the coin cell  10 , the electrolyte is at equilibrium with respect to the ratio of DMC:EMC:DEC. This is important to maintain consistent and reliable cycling characteristics. It is known that due to the presence of low-potential (anode) materials in a charged cell, an un-equilibrated mixture of DMC:DEC in the presence of lithiated graphite (LiC 6 ≈0.01 V vs. Li/Li + ) results in a substantial amount of EMC being formed. When the concentrations of DMC, DEC and EMC change, the cycling characteristics and temperature rating of the cell changes. Such unpredictability is unacceptable. This phenomenon is described in detail in U.S. patent application Ser. No. 10/232,166, filed Aug. 30, 2002, which is assigned to the assignee of the present invention and incorporated herein by reference. Electrolytes containing the quaternary carbonate mixture of the present invention exhibit freezing points below −50° C., and lithium ion secondary cells activated with such mixtures have very good cycling behavior at room temperature as well as very good discharge and charge/discharge cycling behavior at temperatures below −40° C.  
         [0042]    A circular plate serving as a lid  30  is then fitted into the step  16 . The lid is of a size and thickness to rest on the step with its upper surface  30 A coplanar with the ring upper end  12 D. Next, the cell  10  is hermetically sealed closed by securing the lid  30  to the ring  12 . This is done by any one of a number of methods including soldering and welding. If the later technique is used, a laser  32  provides the weld  34  between the ring  12  and the lid  30 , as shown in FIG. 9. Preferably, the cell is set in a heat-sinking fixture (not shown) during welding to minimize heating of the cell components.  
         [0043]    After the lid  30  is welded in place, a compressive force is applied to the center of the lid. In that manner, the lid compresses the electrode materials  22 ,  26  housed inside cell. The resulting stack pressure is illustrated in the completed cell of FIG. 3 where the first and second electrode  22 ,  26  are in a tightly fitting relationship captured between the disc inner lower wall  14 E and the lid  30 .  
         [0044]    An important aspect of the present coin cell is the materials of construction for the ring  12 , disc  14 , glass  20  and lid  30 . The selection of materials for these parts is critical as they must be compatible with the chemistry and potential expected in the cell to prevent possible corrosion. Also, the ring  12 , disc  14  and glass  20  must be capable of forming a hermetic glass-to-metal seal. A compression seal is typically used to provide the reliability required for an implantable application. In such a seal, the coefficient of thermal expansion of the ring  12  is greater than that of the glass  20 , which, in turn, is greater than that of the disc  14 . When the first electrode  22  is the cathode and the second electrode  26  is the anode, suitable exemplary materials for the disc  14  are titanium, and molybdenum, and alloys thereof, which have a relatively low coefficient of linear expansion. Stainless steel, which has a high coefficient of linear expansion, is suitable for the ring  12  and lid  30 . If desired, these metal parts are coated with a secondary metal or carbon to provide compatibility with the desired electrochemical system.  
         [0045]    It is also contemplated by the scope of the present invention that the first electrode  22  is the anode and the second electrode  26  is the cathode. In that case, nickel, titanium, and molybdenum, and alloys thereof are a suitable material for the disc  14  while stainless steel is suitable for the ring  12  and lid  30 .  
         [0046]    [0046]FIG. 10 shows an alternate embodiment of a coin cell  100  according to the present invention. The coin cell  100  comprises a cylindrically shaped ring  112  surrounding a circular disc  114 . The ring  112  has a cylindrical outer wall  112 A coaxial with a cylindrical inner wall  112 B. The outer and inner walls  112 A,  112 B extend to and meet with spaced apart perpendicularly oriented lower and upper ends  112 C and  112 D.  
         [0047]    The disc  114  comprises a cylindrically shaped outer wall  114 A extending to perpendicularly oriented outer lower end  114 B and upper end  114 C. The disc  114  is sized to fit inside the ring  112 . With the ring lower end  112 C aligned coplanar with the disc lower end  114 B, the disc upper end  114 C is spaced from and below the ring upper end  112 D. With the disc in a coaxial relationship with the ring, the disc outer wall  114 A is spaced from the ring inner wall  112 B. An insulative glass  116  seals in an annular manner between the ring inner wall  112 B and the disc outer wall  114 A. This serves to hermetically seal the disc to the ring.  
         [0048]    A first electrode  118  of an electrode active material is positioned on the disc upper end  114 C. A ring  120  of an insulative material surrounds the first electrode. An insulating separator  122  spans the entire area surrounded by the ring inner wall  112 B. A second electrode  124  of an opposite polarity as the first electrode is then positioned on the opposite side of the separator  122 . Preferably, the insulative ring  120  and the separator  122  are of one the polymeric materials previously described as being suitable for the separator  24  of coin cell  10 . An electrolyte  126  is provided in the cavity formed by the disc  114  glassed to the ring  112 . Then, a lid  128  secured to the ring upper end  112 D by weld  130  completes the cell  110 .  
         [0049]    An alternative embodiment of the present coin cell  10 A is shown in FIG. 11 having a spring  36  captured between the second electrode  26  and the lid  30  to provide stack pressure. The spring  36  is preferably of a Belleville type having its small diameter biasing against the second electrode  26  and its large diameter biasing against the lid  30 . This spring orientation applies an axial stack pressure to the electrodes  22 ,  26  that helps promote complete and efficient discharge. If desired, a wave spring (not shown) can be used instead of the Belleville spring.  
         [0050]    Thus, it is apparent that various embodiments of hermitically sealed coin cells of both a primary and a secondary chemistry have been described. Such cells have many applications where a power source of a relatively small size is desirable. However, a particularly preferred application is powering an implantable medical device, such as a cardiac pacemaker, defibrillator, neurostimulator, and the like. These devices require a long life, hermetically sealed power source. The present coin cells  10 ,  10 A and  100  fulfill this requirement.  
         [0051]    It is appreciated that various modifications to the present inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the scope of the present invention as defined by the herein appended claims.

Technology Classification (CPC): 8