Abstract:
An electrochemical cell with a non-prismatic casing and solid cathode is the present invention. The casing has a front side wall, a back side wall, a right side wall, a left side wall, a top wall, and bottom wall. The non-prismatic function is obtained by having the right and left side walls having tapered widths—wide near the top wall and narrower near the bottom wall. A solid anode having a uniform height is positioned against the front side wall and/or the back side wall. A solid cathode is surrounded by a separator and has at least a tapered height to correspond to the tapered right and left side walls wherein the anode&#39;s front side is parallel with the front major sidewall and the anode&#39;s back side is parallel with the back major sidewall. This non-prismatic design decreases the formation of voids and maximizes the amount of cathode in non-prismatic casing designs to obtain the optimal electrochemical capabilities.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Application Ser. No. 60/952,879, filed Jul. 31, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is directed to electrochemical cells for generating electrical energy by chemical reaction. More specifically, the invention relates to an electrochemical cell housed in a generally wedge-shaped casing. Such a casing shape contrasts with those where the active components are housed in either prismatic or cylindrical casings, which are well known. The wedge-shaped casing is useful in applications requiring non-traditional shapes. 
         [0004]    2. Prior Art 
         [0005]    Recent developments in small electronic devices having various shape and size requirements necessitate comparably small-sized electrochemical cells that are easily manufactured and used in such devices. Preferably, these types of cells are of a high energy density, such as is provided by those predicated on a lithium chemistry. One widely used configuration is to house a high energy density lithium cell in a prismatic-shaped casing  10 . An example is shown in  FIG. 1 . Whether the cell is of a primary or a secondary chemistry is not important. The casing  10  includes a planar front sidewall  12  opposite a planar back sidewall (not shown), both of which extend to and meet with a right end wall  14  and an opposed left end wall (not shown). The front and back sidewalls and the right and left end walls extend to and meet with a planar bottom wall (not shown) in a unitary construction to form a deep drawn container having an upper opening. The open ended container has a generally rectangular shape with the front and back sidewalls being parallel to each other and the right and left end walls being parallel to each other as well. An alternate construction is to provide individual plates which are connected together as sidewalls and end walls to form the open ended container. 
         [0006]    In any event, the open end of the container is closed by a generally planar lid  16 . The lid  16  has a rectangular shape and is welded about its periphery to the upper edges of the respective sidewalls and end walls. The lid includes a fill opening  18  and a terminal pin opening  20 . The fill opening  18  is a port for providing an electrolyte into the casing after an electrochemical couple is housed therein. The fill port is closed by a closure member  22 , such as a ball, sealed therein. 
         [0007]    The terminal pin opening  20  supports a glass-to-metal seal comprising a ring of insulative glass  24  surrounding a terminal pin  26  having its interior end (not shown) connected to one of the anode and cathode housed inside the casing  10 . That way, the terminal pin  26  serves as one of the cell leads. The casing  10 , insulated from the terminal pin  26  by the glass-to-metal seal  24 , serves as the lead for the other electrode. 
         [0008]    While the prismatic shaped casing  10  is widely used for a variety of power source applications, there exists a need for cells that are of different shapes, such as those having a wedge shape in cross-section. 
         [0009]    In U.S. Pat. No. 6,267,790, Daroux et al. wrote, “[w]hile metal . . . containers are sturdy and volume efficient, they are somewhat shape restrictive. Typically, metal . . . containers are most suitable and cost effective when traditional cylindrical shapes (especially for metal enclosures) or rectangular shapes are required. However, when a specific application or product requires a battery having an unusual shape, such as an extremely thin battery or a non-planar or non-prismatic battery, the assembly of a battery in an unusually shaped metal . . . enclosure becomes more difficult.” 
         [0010]    Alternative shapes for cell casings are disclosed in U.S. Pat. No. 5,958,088 to Vu et al., U.S. Pat. No. 7,074,520 to Probst et al. and U.S. Pat. No. 6,831,827 to Zayatz, the latter two being commonly assigned. Zayatz discloses that an electrochemical cell can be housed in a cylindrical casing. 
         [0011]    The Vu et al. patent discloses a prismatic casing having partially contoured sidewalls. The casing includes opposed major side walls, one having a concave arc while the other has an opposed convex arc. The electrodes are disposed within the casing and deflected in a spring like manner to follow the arcs of the opposed sidewalls. That way, the casing maintains a positive pressure against the cell electrodes. 
         [0012]    The Probst et al. patent discloses an electrochemical cell housed in a casing of mating clamshell portions. The first clamshell portion has a first major sidewall extending to and meeting with a first surrounding sidewall and the second clamshell portion has a second major sidewall extending to and meeting with a second surrounding sidewall. The first and second clamshells are mated to each other with a first outer edge of the first surrounding sidewall facing the second major sidewall and a second outer edge of the second surrounding sidewall facing the first major sidewall. At least a portion of the first surrounding sidewall overlaps a portion of the second surrounding sidewall. The casing is then provided as a sealed enclosure with the first outer edge hermetically secured to the second surrounding sidewall. The first and second major sidewalls deflect in a similar direction. 
         [0013]    A common feature in both a standard prismatic-shaped casing and the alternative casing shapes discussed above in the Vu et al., Probst et al. and Zayatz patents is that the distances between opposite sidewalls and end walls are equidistant. Equidistant separation between opposed casing walls, even when curved or cylindrical, is not always desirable for all electrochemical cell applications. 
         [0014]    The previously discussed Probst et al. patent also describes a cell casing in which the opposed major sidewalls, even though they are curved, are not equidistant. In this patent, even though the back sidewall has a greater curvature than the front sidewall, the sidewalls curve in a similar direction. That type of casing construction is also not always desirable. 
         [0015]    In that respect, the present invention provides a casing having a wedge-shape in which at least two directly opposed sidewalls angle away from each other. The term “opposed sidewalls” means a pair of sidewalls diametrically opposed to each other. 
       SUMMARY OF THE INVENTION 
       [0016]    Accordingly, the present invention is directed to an electrochemical cell of either a primary or a secondary, rechargeable chemistry housed in a generally wedge-shaped casing. The casing has a front sidewall, a back sidewall, a right end wall and a left end wall, all of them extending from a bottom wall to an open end closed by a lid. The wedge-shaped form factor is provided by the opposed right and left end walls having tapered widths. That is, the right and left end walls are wider near the top lid and narrower near the bottom wall. The spaced apart front and back sidewalls extending to and meeting with the opposed right and left end walls can either be planar or at least partly radiused to have a convex shape. In a case negative design, two anode portions are positioned against the respective front and back sidewalls. A solid cathode enveloped in a separator is located intermediate the front and back anode portions and has a wedge shape characterized by a tapered width that generally corresponds to the taper of the right and left end walls. Preferably, the front face of the front anode portion is parallel with the front major sidewall and the back face of the back anode portion is parallel with the back major sidewall. 
         [0017]    The present non-prismatic or wedge-shaped casing designs are particularly well suited for modern tools and devices requiring a self container power source provided with a “V-shaped” receptacle for the power source. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of a cell  10  comprising a conventional prismatic casing. 
           [0019]      FIG. 2  is a perspective view of one embodiment of a wedge shaped casing  100  according to the present invention. 
           [0020]      FIG. 3  is a cross-sectional view taken along the line  3 - 3  of  FIG. 2 . 
           [0021]      FIG. 4  is a cross-sectional view taken along the line  4 - 4  of  FIG. 2 . 
           [0022]      FIG. 5  is another embodiment of a wedge shaped casing  200  according to the present invention. 
           [0023]      FIG. 6  is a cross-sectional view taken along the line  6 - 6  of  FIG. 5 . 
           [0024]      FIG. 7  is a cross-sectional view taken along the line  7 - 7  of  FIG. 5 . 
           [0025]      FIG. 8  is another embodiment of a wedge shaped casing  300  according to the present invention. 
           [0026]      FIG. 9  is another embodiment of a wedge shaped casing  400  according to the present invention. 
           [0027]      FIG. 10  is a cross-sectional view taken along the line  10 - 10  of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Turning now to the drawings,  FIGS. 2 to 4  illustrate one embodiment of an electrochemical cell  100  housed in a wedge-shaped casing  101  according to the present invention. Prior to describing the casing construction in detail, it should be understood that many different chemistries can be housed in the wedge-shaped casing. This includes either an alkali metal/solid cathode or alkali metal/oxyhalide chemistry of both solid cathode and liquid electrolyte types. In the primary solid cathode type, for example a lithium-solid cathode cell, a solid cathode active material such as silver vanadium oxide or copper silver vanadium oxide, is contained within the casing and surrounded by a separator, such as of a polypropylene fabric or cloth. Lithium is the anode active material. 
         [0029]    The casing  101  comprises a wedge-shaped open-ended container  102  closed by a header comprising a lid  104 . The container  102  and lid  104  are preferably of a conductive material selected from the group of nickel, aluminum, stainless steel, mild steel, tantalum, titanium, and combinations thereof. More preferably, the container  102  and lid  104  are of the same conductive material. The lid  104  has a generally rectangular shape with radiused corners and is secured about its periphery to the upper edges of the respective sidewalls and end walls comprising the container  102  by weld  106 . The lid  104  includes a fill opening  108  and a terminal pin opening  110 . The fill opening  108  is a port for providing an electrolyte into the casing  101  to activate an electrochemical couple housed therein. The port is closed by a closure member  112 , such as the ball or plug, sealed therein by weld  113 . 
         [0030]    The terminal pin opening  110  supports a glass-to-metal seal comprising a ring of insulative glass  114  surrounding a terminal pin  116  having its interior or proximal end  116 A connected to one of the anode and cathode electrodes housed inside the casing  101 . That way, the terminal pin  110  serves as one of the cell leads. The casing  101  insulated from the terminal pin  110  by the glass-to-metal seal  114  serves as the lead for the other electrode. 
         [0031]    According to the present invention, the casing container  102  comprises front and back sidewalls  118 ,  120  extending to and meeting with right and left end walls  122  and  124 , respectively. The wall pairs  118 ,  120  and  122 ,  124  are each in a non-parallel relationship with respect to each other. More particularly, the wedge-shaped open-ended container  102  of the casing  101  comprises a generally planar, wedge-shaped front sidewall  118  opposite a generally planar, wedge-shaped back sidewall  120  ( FIG. 3 ), both of which extend to and meet with opposed generally planar wedge-shaped right and left end walls  122  and  124  ( FIG. 4 ) at radiused or curved corners. The wedge-shaped front and back sidewalls  118 ,  120  and the wedge-shaped right and left end walls  122 ,  124  extend in a unitary construction from an arcuate or curved bottom wall  126  to an open end. This provides the container  102  as a deep-drawn member having a generally trapezoidal, wedge shape with the front and back sidewalls  118 ,  120  and the right and left end walls  122 ,  124  forming respective pairs of walls that angle upwardly and outwardly with respect to each other along their entire extent from the bottom wall  126  to the open container end. An alternate construction is to provide individual plates which are connected together as sidewalls and end walls to form the trapezoidal, wedge shaped casing. 
         [0032]    In  FIG. 2  this generally trapezoidal, wedge shape is shown by the distance between the edges of the end walls  122 ,  124  increasing moving in an upwardly direction from adjacent to the bottom wall  126  toward the open end. These non-uniform widths are shown by the relative distance “A” of end wall  122  adjacent to the bottom wall  126  being less than the distance “B” being less than the distance “C” adjacent to the open end of the container. Furthermore, that portion of the relative distances “A”, “B” and “C” on either side of an imaginary bisecting line  122 A are substantially equal. The opposed end wall  124  is similarly shaped. This angled relationship is shown by imaginary lines  122 B and  124 B projecting from the planar surface of the respective end walls  122 ,  124  meeting at a location below the bottom wall  126 . Of course, if the end walls were parallel to each other, their projected imaginary lines would not meet each other. 
         [0033]    Similarly, the widths of the respective sidewalls  118 ,  120  increase moving in an upwardly direction from adjacent to the bottom wall  126  toward the open end. This is shown by the relative distance “X” of sidewall  118  adjacent to the bottom wall  126  being less than the distance “Y” being less than the distance “Z” adjacent to the open end of the container. Furthermore, that portion of the relative distances “X”, “Y” and “Z” on either side of an imaginary bisecting line  118 A are substantially equal. The opposed sidewall  120  is similarly shaped. This angled relationship is shown by imaginary lines  118 B and  120 B projecting from the planar surface of the respective sidewalls  118 ,  120  meeting at a location below the bottom wall  126 . 
         [0034]    A significant characterizing feature of the casing  101  is that the front and back major sidewalls  118 ,  120  are significantly wider at their maximum width than are the right and left end walls  122 ,  124 . 
         [0035]    As shown in  FIGS. 3 and 4 , the thusly described casing  101  houses an electrode assembly comprising an anode  130  in electrical association with a cathode  132 . The anode  130  and cathode  132  are physically segregated from contacting each other by an intermediate separator  134 . The form of the anode  130  may vary, but preferably it comprises two portions  130 A and  130 B in the form of thin metal sheets or foils of anode active material, preferably lithium, pressed against the inner surface of the sidewalls  118 ,  120  serving as the anode terminal. The anode portions  130 A,  130 B can also comprise a perforated current collector (not shown), such as of nickel foil, having two sheets of anode active material, preferably lithium, pressed to its opposed major sides. That way, the lithium locks to itself through the current collector perforations. Titanium, titanium alloy, copper, tungsten and tantalum are also suitable materials for the anode current collector. The anode current collector is then integrally contacted by a weld to an inner surface of the wedge-shaped sidewalls  118 ,  120  of the casing  100  serving as the anode terminal. 
         [0036]    The cathode  132  is of an electrically conductive material that serves as the other cell electrode. The cathode  132  is preferably of a solid cathode active material comprising a metal, a metal oxide, a mixed metal oxide and a metal sulfide, and combinations thereof. The cathode active material is formed by the chemical addition, reaction, or otherwise intimate contact of various metal oxides, metal sulfides 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 other oxide and sulfide compounds. A preferred cathode active material is a reaction product of at least silver and vanadium. 
         [0037]    Preferably, the cathode  132  is a solid cathode active material such as silver vanadium oxide, carbon monofluoride (of, for example, a Li/CF x  cell), or copper silver vanadium oxide, contained within the wedge-shaped casing  101  and physically segregated from the anode by the separator  134 . Contemplated solid cathode active materials are not limited to silver vanadium oxide, carbon monofluoride, and copper silver vanadium oxide, but, can also be manganese dioxide, cobalt oxide, nickel oxide, copper oxide, copper sulfide, iron sulfide, iron disulfide, titanium disulfide, copper vanadium oxide, and mixtures thereof. 
         [0038]    By way of example in an illustrative primary lithium cell, the cathode active material is a silver vanadium oxide material as described in U.S. Pat. Nos. 4,310,609 and 4,391,729 to Liang et al., or copper silver vanadium oxide as described in U.S. Pat. Nos. 5,472,810 and 5,516,340 to Takeuchi et al., all assigned to the assignee of the present invention and incorporated herein by reference. 
         [0039]    In any event, the cathode active material is mixed with a conductive diluent and a binder material and the thusly formed active admixture is pressed into the desired shape. Typically, the cathode  132  is made from a mixture of 80 to 95 weight percent of a cathode active material, 1 to 10 weight percent of a conductive diluent and 3 to 10 weight percent of a binder. The binder is preferably a fluoro-resin powder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylenetetrafluoroethylene (ETFE), polyamides, polyimides, and mixtures thereof. It is preferably used in a powdered form. Suitable conductive diluents include acetylene black, carbon black and/or graphite. Metals such as nickel, aluminum, titanium and stainless steel in powder form are also useful as conductive diluents when mixed with the above listed active materials. 
         [0040]    The cathode active mixture is contacted to a suitable current collector selected from titanium, titanium alloy, copper, tungsten, tantalum, and nickel. Titanium is a preferred material; however, if the cathode active material is CF x , the titanium current collector preferably has a coating of a graphite material on at least the surface contacted therewith. 
         [0041]    An important feature of the cathode  132  is that it is at an intermediate location between the anode sheet portions  130 A,  130 B and is shaped to match the taper of the wedge-shaped casing  101 . The cathode  132  enveloped in the separator  134  has an upper width  132 A at a position nearest the lid  104  that is greater than its lower width  132 B nearest the bottom wall  126 . Preferably, the taper of the cathode  132  matches that of the end walls  122 ,  124 . On the other hand, the anode portions  130 A,  130 B have similar thicknesses  136  while their respective heights measured from adjacent to the bottom wall  126  to adjacent the lid  104  are equal or approximately equal to the height of the cathode  132 . As shown in  FIG. 4 , the anode  130  and the cathode  132  have similar widths adjacent to the lid  104 , as indicated by arrow  138 , and adjacent to the bottom wall  126 , as indicated by arrow  140 . Providing the anode portions  130 A,  130 B having essentially the same thicknesses and height as each other with the cathode  132  having a shape emulating the wedge-shaped casing  101  of the present invention minimizes the void (inactive) volume and maximizes the amount of active materials in the cell  100  having a non-traditional shaped, i.e. one that is neither prismatic or cylindrical. 
         [0042]    As previously discussed, the anode  130  is physically segregated or separated from the cathode  132  by the separator  134 . The separator  134  is an electrically insulative material that is chemically unreactive with the anode and cathode active materials. The separator  150  is also chemically unreactive with and insoluble in the electrolyte. Additionally, the separator material has sufficient porosity to allow flow therethrough of the electrolyte during the electrochemical reactions of the cell. Illustrative separator materials comprise 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.). 
         [0043]    A preferred separator construction comprises a non-woven polypropylene fabric and polypropylene membrane. Preferably the non-woven fabric faces the cathode and the membrane faces the anode. That way, the non-woven layer acts as a wicking material to more effectively wet the cathode and act as a barrier to puncture of the membrane from loose cathode active materials such as carbon particles (CF x ). 
         [0044]    An insulator  160  is positioned between the lid  104  and the electrode assembly comprising the anode  130  and the cathode  132 . The insulator  160  is a non-conductive material that securely positions the anode and cathode in the proper positions within the casing to obtain the desired battery capabilities. The thickness of the insulator  160  is shown exaggerated for purposes of illustration and it has an opening that allows an electrolyte filled into the casing  101  to contact the electrode assembly. 
         [0045]    In that respect, the electrochemical cell  100  further includes a nonaqueous, ionically conductive electrolyte that serves as a medium for migration of ions between the anode  130  and the cathode  132  during the electrochemical reactions of the cell. The electrochemical reactions at the electrodes involve conversion of ions in atomic or molecular forms that migrate from the anode  130  to the cathode  132 . Thus, suitable nonaqueous electrolytes are substantially inert to the anode and cathode materials, and they exhibit those physical properties necessary for ionic transport, namely, low viscosity, low surface tension and wettability. 
         [0046]    A suitable electrolyte has an inorganic, ionically conductive salt dissolved in a mixture of aprotic organic solvents comprising a low viscosity solvent and a high permittivity solvent. In the case of an anode comprising lithium, preferred lithium salts that are useful as a vehicle for transport of lithium ions from the anode  130  to the cathode  132  include LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiClO 4 , LiO 2 , LiAlCl 4 , LiGaCl 4 , LiC(SO 2 CF 3 ) 3 , LiN(SO 2 CF 3 ) 2 , LiSCN, LiO 3 SCF 3 , LiC 6 F 5 SO 3 , LiO 2 CCF 3 , LiSO 6 F, LiB(C 6 H 5 ) 4 , LiCF 3 SO 3 , and mixtures thereof. 
         [0047]    Low viscosity solvents include esters, linear and cyclic ethers and dialkyl carbonates such as tetrahydrofuran (THF), methyl acetate (MA), diglyme, trigylme, tetragylme, dimethyl carbonate (DMC), 1,2-dimethoxyethane (DME), diethyl carbonate (DEC), and mixtures thereof, and high permittivity solvents include cyclic carbonates, cyclic esters and cyclic amides such as propylene carbonate (PC), ethylene carbonate (EC), acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, γ-valerolactone, γ-butyrolactone (GBL), N-methyl-pyrrolidinone (NMP), and mixtures thereof. In the present invention, a preferred anode is lithium metal and the preferred electrolyte is 1.0M to 1.4M LiBF 4  in γ-butyrolactone for a Li/CF x  cell and a 1.0M to 1.2M LiAsF 6  or LiPF 6  in a 50:50, by volume, mixture of DME and PC. 
         [0048]    In the preferred Li/SVO cell  100 , the cathode current collector (if present) is of titanium, the terminal lead  116  is of molybdenum, the electrolyte is a 1.0M to 1.4M solution of LiAsF 6  or LiPF 6  in a 50:50 mixture of, by volume, 1,2-dimethoxyethane and propylene carbonate, the glass seal  114  is of TA-23 hermetic sealing glass, and closure  112  is of stainless steel. The lithium anode is preferable in sheet form contacted to both sides of a nickel foil current collector. 
         [0049]    While a primary solid cathode type, for example a lithium-solid cathode cell, has been used as an exemplary chemistry for the purpose of describing the construction of the wedge-shaped casing  101  shown in  FIGS. 2 to 4 , the type of chemistry that can be contained therein should not be so limited. The cell  100  can also be of a liquid cathode/electrolyte or catholyte type cell, for example a lithium-oxyhalide cell where a liquid catholyte fills the casing interior and is in operative contact with the anode  130  and the cathode element  132  is a carbonaceous material serving as a current collector. A separator  134  is disposed between the anode  130  and the carbonaceous cathode  132 . For a more detailed description of such a cell reference is made to U.S. Pat. No. 4,246,327 to Skarstad et al., which is assigned to the assignee of the present invention and incorporated herein by reference. 
         [0050]    The cell can also be of a secondary, rechargeable chemistry where the anode  130  comprises an anode material capable of intercalating and de-intercalating the anode active material, such as the preferred lithium. A carbonaceous material comprising any of the various forms of carbon, e.g., coke, graphite, acetylene black, carbon black, glass carbon, meso-carbon microbeads (MCMB), and “hair carbon”, which are capable of reversibly retaining the lithium species is preferred for the anode. “Hairy carbon” is a material described in U.S. Pat. No. 5,443,928 to Takeuchi et al., which 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. 
         [0051]    Also in secondary systems, the cathode  132  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 . 
         [0052]    A preferred electrolyte for a secondary cell is described in U.S. application Ser. No. 09/669,936, which is assigned to the assignee of the present invention and incorporated herein by reference. 
         [0053]    As illustrated in  FIGS. 3 and 4 , a preferred form of the electrochemical cell  100  is a case-negative design. This means that the anode/cathode couple is inserted into the conductive metal casing  101  electrically connected to the anode  130  serving as the negative terminal. A preferred material for the casing container  102  is titanium although stainless steel, mild steel, nickel, nickel-plated mild steel and aluminum are also suitable. The casing header comprising the metallic lid  104  is of a material similar to that of the container  101  and has a sufficient number of openings to accommodate the glass-to-metal seal/terminal pin feedthrough for the cathode  130 . An additional opening is provided for the electrolyte. The casing  101  is thereafter filled with the electrolyte solution described hereinabove and hermetically sealed such as by close-welding the stainless steel closure member  112  into the fill hole or port  108 , but not limited thereto. The cell  100  can also be constructed in a case-positive design, as is well known by those skilled in the art. 
         [0054]      FIGS. 5 to 7  illustrate another embodiment of an electrochemical cell  200  comprising a casing  201  according to the present invention. The casing  201  comprises a container  202  closed by a header comprising the lid  104  shown in  FIGS. 2 to 4 . The casing container  202  comprises front and back sidewalls  218 ,  220  extending to and meeting with right and left end walls  222  and  224 , respectively, at radiused or curved corners. At least some portions of the wall pairs  218 ,  220  and  222 ,  224  are in a non-parallel relationship with respect to each other. More particularly, the wedge-shaped open-ended container  202  of the casing  201  comprises a compound planar, wedge-shaped front sidewall  218  opposite a compound planar, wedge-shaped back sidewall  220  ( FIG. 6 ), both of which extend to and meet with opposed compound planar, wedge-shaped right and left end walls  222  and  224  ( FIG. 7 ). The wedge-shaped front and back sidewalls  218 ,  220  and the wedge-shaped right and left end walls  222 ,  224  extend in a unitary construction from an arcuate or curved bottom wall  226  to an open end. This provides the container  202  as a deep-drawn member having a generally wedge shape with the front and back sidewalls  218 ,  220  and the right and left end walls  222 ,  224  forming respective pairs of walls that angle upwardly and outwardly with respect to each other along at least a portion of their lengths extending from the bottom wall  226  to the open container end. 
         [0055]    In  FIG. 5  this wedge shape is shown by the relative distance “D” of end wall  222  adjacent to the bottom wall  226  being less than the distance “E” being substantially the same as the distance “F” adjacent to the open end of the container. The opposed end wall  124  is similarly shaped. Similarly, the width of the sidewall  218  is shown by the relative distance “G” adjacent to the bottom wall  226  being less than the distance “H” being substantially the same as the distance “I” adjacent to the open end of the container. The opposed sidewall  220  is similarly shaped. 
         [0056]    A significant characterizing feature of the casing  201  is that the front and back major sidewalls  218 ,  220  are significantly wider at their maximum width than are the right and left end walls  222 ,  224 . 
         [0057]    In that respect, casing container  202  has wall pairs  218 ,  220  that comprise respective lower planar portions  218 A,  220 A that angle upwardly and outwardly with respect to each other and respective upper planar portions  218 B,  220 B that are substantially parallel to each other. The lower portions  218 A,  220 A account for the distances “G” being less that the distances “H” while the upper planar portions  218 B and  220 B account for the distances “H” being substantially the same as the distances “I”. The transition from the lower portions  218 A,  220 A to the upper portions  218 B,  220 B is curved or radiused. Furthermore, that portion of the relative distances “G”, “H” and “I” on either side of an imaginary bisecting line  218 C are substantially equal. 
         [0058]    In a like manner, the wall pairs  222 ,  224  comprise respective lower planar portions  222 A,  224 A and respective upper planar portions  222 B,  224 B. The lower portions  222 A,  224 A account for the distances “D” being less that the distances “E” while the upper planar portions  222 B,  224 B account for the distances “E” being substantially the same as the distances “F”. The transition from the lower portions  222 A,  224 A to the upper portions  222 B,  224 B is curved or radiused. Furthermore, that portion of the relative distances “D”, “E” and “F” on either side of an imaginary bisecting line  222 C are substantially equal. 
         [0059]      FIG. 8  illustrates another embodiment of an electrochemical cell  300  comprising a casing  301  according to the present invention. The casing  301  comprises a container  302  closed by a header comprising the lid  104  shown in  FIGS. 2 to 4 . The casing container  302  comprises front and back sidewalls  318 ,  320  extending to and meeting with right and left end walls  322  and  324 , respectively, at radiused or curved corners. The wall pairs  318 ,  320  and  322 ,  324  are each in a non-parallel relationship with respect to each other. More particularly, the wedge-shaped open-ended container  302  of the casing  301  comprises a generally planar rectangular-shaped front sidewall  318  opposite a generally planar rectangular-shaped back sidewall  320 , both of which extend to and meet with opposed generally planar wedge-shaped right and left end walls  322  and  324 . The rectangular-shaped front and back sidewalls  318 ,  320  and the wedge-shaped right and left end walls  322 ,  324  extend in a unitary construction from an arcuate or curved bottom wall  326  to an open end. This provides the container  302  as a deep-drawn member having a generally wedge shape with the front and back sidewalls  318 ,  320  and the right and left end walls  322 ,  324  forming respective wall pairs with only the sidewalls  318 ,  320  angling upwardly and outwardly with respect to each other along their entire extent from the bottom wall  326  to the open container end. The end walls  322 ,  324  are in a substantially parallel relationship with respect to each other. 
         [0060]    In  FIG. 8  this wedge shape is shown by the relative distance “J” of end wall  322  adjacent to the bottom wall  326  being less than the distance “K” being less than the distance “L” adjacent to the open end of the container. Furthermore, that portion of the relative distances “J”, “K” and “L” on either side of an imaginary bisecting line  322 A are substantially equal. The opposed end wall  324  is similarly shaped. 
         [0061]    In contrast, the widths of the respective sidewalls  318 ,  320  are shown by the relative distance “M” of sidewall  318  adjacent to the bottom wall  226  being substantially the same as the distance “N” being substantially the same as the distance “O” adjacent to the open end of the container. Furthermore, that portion of the relative distances “M”, “N” and “O” on either side of an imaginary bisecting line  318 A are substantially equal. The opposed sidewall  320  is similarly shaped. 
         [0062]    A significant characterizing feature of the casing  301  is that the front and back major sidewalls  318 ,  320  are significantly wider at their maximum width than are the right and left end walls  322 ,  324 . 
         [0063]      FIGS. 9 and 10  illustrate another embodiment of an electrochemical cell  400  housed in a casing  402  having a wedge-shape according to the present invention. The wedge-shaped casing  402  includes a first or front clamshell portion  404  and a second or back clamshell portion  406  mated or otherwise secured to each other. The front clamshell  404  comprises a front major face wall  404 A having a uniform width extending from adjacent a bottom portion of the casing to a lid portion. The lid portion includes a fill opening closed by a plug  408  and the terminal pin opening  410  supporting the glass-to-metal seal  412  and the terminal pin  414 . The surrounding sidewall of the first clamshell extending from the front face wall  404 A includes a right tapered end wall portion  404 B, a left tapered end wall portion  404 C, the right and left end wall portions  404 B,  404 C meeting a lid portion  404 D and an arcuate bottom wall portion  404 E. In that respect, the wall portions  404 B,  404 C,  404 D and  404 E comprise the surrounding sidewall of the front clamshell  404  of the casing  402 . 
         [0064]    Likewise, the back clamshell  406  comprises a surrounding sidewall extending from the front face wall  406 A. The surrounding sidewall includes a right end wall portion  406 B, a left tapered end wall portion  406 C, the right and left end wall portions  406 B,  406 C meeting a lid portion  406 D and an arcuate bottom wall portion  406 E. In that respect, the wall portions  406 B,  406 C,  406 D and  406 E comprise the surround sidewall of the front clamshell  406  of the casing  402 . 
         [0065]    A characterizing feature of the second clamshell portion  402  is that the wall portions  406 B,  406 C,  406 D and  406 E all have a similar height measured from where they meet the back face wall  406 A to their distal edge. On the other hand, the height of the right and left end walls  404 B,  404 C of the first clamshell portion  404  having increasing heights measured from where they meet the front face wall  404 A to their distal edges. This is illustrated by the combined widths of the right end wall portions  404 B and  406 B shown by the relative distance “P” adjacent to the bottom wall portion  404 E,  406 E being less than their combined widths at intermediate location “Q” being less that their combined widths “R” adjacent to the lid portions  404 D and  406 D. The opposed left end wall portions  404 C and  406 C are similarly shaped. 
         [0066]    The non-right angling of front face wall  404 A and the vertical orientation of the back face wall  406 A are confirmed by comparing the imaginary line  420  projecting from the plane of front face wall  404 A to the imaginary line  422  projecting from the back face wall  406 A. These lines  420  and  422  intersect along the vertical path of the back face wall  406 A. 
         [0067]    The clam shells may be butted together before they are sealed. This means that instead of the sidewall of one of the clamshells  404  or  406  being able to be partially housed or covered by the sidewall of the other clamshell, the sidewalls are of equal lengths and abut each other. The butted edges are sealed together such as by welding to form a hermetic enclosure. 
         [0068]    In one embodiment, the front clamshell  504  has a front edge  424  and the back clamshell  406  has a back edge  426 . The front edge  424  is relatively straight while the back edge  426  is a partial chicane shape (S-shaped) that receives the front edge  424 . The respective front and back edges  424 ,  426  of the front and back clam shells  404 ,  406  are then secured to each other at hermetic seal  428 . Other hermetic seals for mating clamshells are described in commonly assigned U.S. Pat. No. 7,074,520 to Probst et al. 
         [0069]    It is also within the scope of the present invention that instead of the casing shape shown in  FIGS. 9 and 10  being provided by mating clamshell portions, this wedge-shape can be provided by a casing of the type described with respect to cells  100 ,  200  and  300 . That is cells are housed in casing comprising a container closed by a lid, but having the shape shown with respect to cell  400 . The seam between the clamshell portions would delineate one pair of major sidewalls or pair of end walls having one of the walls being in a vertical orientation while the other wall of the pair was in a angled relationship therewith. The included angle is acute. 
         [0070]    The electrode assembly housed inside the casing  402  includes an anode  430  positioned against the interior surface of the back clamshell  404  and a cathode  432  positioned against the front clamshell  404 . A separator  434  completely envelopes the cathode  432  and maintains physical separation between the anode and cathode while providing for ionic flow therethrough. The cathode  432  is connected to the terminal pin  414  serving as the positive terminal electrically insulated from the casing by a glass-to-metal seal  436 . The anode  430  is in direct contact with the casing  402  serving as the negative terminal in the case negative cell design. Alternatively, the anode can de provided in two portions on opposite side of an intermediate cathode in a similar manner as the electrode assembly described with respect to the cell  100  shown in  FIGS. 2 to 4 . An insulator  460 , preferably of a polymeric material, is provided as a ring-shaped member at an intermediate location between the weld  428  sealing the clamshell portion  404  and  406  together and the electrode assembly comprising the anode  430  and the cathode  432 . The insulator  460  is for the purpose of preventing heat generated during the welding process from damaging the anode, cathode and separator  434 . 
         [0071]    Thus, various casing shapes and configurations have been shown and described having a “wedge-shape”. The wedge=shape is characterized by at least one of the casing sidewalls being in a non-parallel relationship with a diametrically opposed sidewall. In some designs, both opposed sidewalls are in an angled alignment with respect to an imaginary vertical axis. In any event, such casing shapes are particularly useful where the cell is received in a “V-shaped” receptacle as may be demanded by modern tools and devices requiring a self container power source. 
         [0072]    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 spirit and scope of the present invention as defined by the herein appended claims.