Abstract:
The present invention relates to a bushing forming a terminal for a storage battery, made through an opening connecting to either side of a wall comprising two opposing surfaces, which comprises: two electrically insulating washers, each comprising a bearing portion resting by the surface thereof under pressure against one of the surfaces of the wall and a guiding portion projecting from the bearing portion and resting under pressure against the edge of the opening; two electrically conductive parts, in which a male part is adjusted clamped inside the female part, each one of the parts comprising a bearing portion resting by the surface thereof under pressure against a bearing portion of the washers, the female part resting by the surface thereof under pressure against the guiding portions of the washers. The material(s) of the parts is/are fitted, and the section(s) thereof is/are sized so as to enable the flow of an electric current with a value of no less than 100 A.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a bushing forming a terminal for a lithium storage battery, such as a lithium-ion storage battery, and to such a storage battery. 
         [0002]    The invention relates more particularly to a lithium-ion (Li-ion) storage battery with a high capacity, typically more than 10 ampere-hours (Ah), and having a capability for the flow of heavy currents, typically more than 100 A. 
         [0003]    The invention more particularly relates to the production of a bushing of a housing making it possible for the high-capacity Li-ion storage battery equipped therewith to be able to deliver heavy currents. 
         [0004]    By “bushing”, it is to be pointed out that the usual sense is intended, that is to say a device used to pass an electrically conductive element through a wall while insulating the conductor from this wall. 
       PRIOR ART 
       [0005]    As schematically represented, a lithium-ion battery or storage battery usually comprises at least one electrochemical cell consisting of an electrolyte constituent between a positive electrode, or cathode, and a negative electrode, or anode, a current collector connected to the cathode, a current collector connected to the anode and, lastly, a package intended to contain the electrochemical cell in a leaktight fashion while some of the current collectors pass through it. 
         [0006]    The electrolyte constituent may be in the form of a solid, liquid or gel. In the latter form, the constituent may comprise a separator made of polymer or microporous composite, impregnated with electrolyte(s) of the organic type or of the ionic liquid type, which allows the lithium ion to move from the cathode to the anode for charging and in the reverse direction for discharging, which generates the current. The electrolyte is generally a mixture of organic solvents, for example carbonates to which a lithium salt, typically LiPF 6 , is added. 
         [0007]    The positive electrode, or cathode, consists of materials with lithium cation intercalation, which are generally composites, such as LiFePO 4 , LiCoO 2 , LiNi 0.33 Mn 0.33 Co 0.33 O 2 . 
         [0008]    The negative electrode, or anode, very often consists of graphite carbon or Li 4 TiO 5 O 12  (titanate material), optionally also based on silicon or silicon-based composite. 
         [0009]    The current collector connected to the positive electrode is generally made of aluminum. 
         [0010]    The current collector connected to the negative electrode is generally made of copper, nickel-plated copper or aluminum. 
         [0011]    A lithium-ion battery or storage battery may, of course, comprise a plurality of electrochemical cells which are stacked on one another. 
         [0012]    Traditionally, an Li-ion battery or storage battery uses a pairing of materials at the anode and at the cathode which allow it to operate with a high voltage level, typically equal to 3.6 volts. 
         [0013]    A Li-ion battery or storage battery comprises a rigid package when the applications envisioned are robust and a long lifetime is desired, for example with much higher pressures to be withstood and a more stringent required level of leaktightness, typically below 10 −8  mbar.l/s, or in very demanding environments, such as the aeronautical or space sectors. 
         [0014]    Furthermore, to date a rigid package has consisted of a metal housing, typically made of stainless steel (inox 316L or inox 304), aluminum (Al 1050 or Al 3003) or titanium. 
         [0015]    Currently, two types of rigid housing are manufactured. 
         [0016]    The first type consists of a rigid housing, made with a machined bottom and a cover, which are laser-welded to one another at their periphery. The current collectors consist partly of metal wires or pins. The pin or pins is (are) welded by electrical or ultrasonic welding to the corresponding current collector part, which is itself connected to one of the electrodes of an electrochemical cell or of a stack of electrochemical cells. In order to establish electrical insulation between the metal cover of the housing and the metal pin, a glass bead encapsulates the pin, thus constituting what is commonly referred to as a glass/metal bushing (GMB). Furthermore, in order to establish leaktightness with the cover of the housing, a ring around the glass bead, and generally made of the same metal as the housing, is welded to the latter. Certain configurations make it possible to use a single GMB, the housing constituting the other terminal, also referred to as a pole, of the storage battery. 
         [0017]    The second type also consists of a rigid housing, made with a crimped cup and a cover, which are laser-welded to one another at their periphery. Conversely, the current collectors comprise a bushing with a part which projects on the top of the housing and forms an emergent terminal, also referred to as a pole, of the battery. 
         [0018]    A first assembly example of such a bushing  1  forming a terminal with the current collector  2  and with the cover  3  of a housing is shown in  FIG. 1 : the collector  2 , typically made of copper, in the form of an internally threaded male piece, is fixed by screwing with the aid of a nut  2  of the M5 or M8 type. Two washers  5 A,  5 B made of electrically insulating material, typically polypropylene, and placed on one another are interposed, one  5 A between the cover  3  and the other bearing washer  6  of the nut  4 , and the other  5 B between the cover  3  and the collector  2 . These washers  5 A,  5 B establish the leaktightness and electrical insulation of the collector  2  with respect to the housing cover  3 . More precisely, in this first example illustrated, the two insulating washers  5 A,  5 B are identical and each comprise a bearing portion  50 A,  50 B and a guiding and centering portion  51 A,  51 B. The bearing portion  50 A bears with its surface under pressure both against the face  30  of the wall of the cover  3  and against the bearing washer  6  of the nut  4 . Similarly, the bearing portion  50 B bears with its surface both against the opposite face  31  of the cover  3  and against the bearing portion  20  of the current collector  2 . The guiding and centering portions  51 A,  51 B, for their part, bear with their surface under pressure both against the edge of the orifice  32  passing through the cover  2  and against the collector  2 . These guiding and centering portions  51 A,  51 B make it possible to guide and center both the washers  5 A,  5 B in the through-orifice  32  and the male collector  2  in said washers  5 A,  5 B. 
         [0019]    A second assembly example of a bushing  1  forming a terminal with the current collector  2  and with the cover  3  of a housing is shown in  FIG. 2 : the collector  2 , typically made of copper, in the form of an internally threaded male piece, is fixed by crimping the collector on the bearing washer  6 . Here again, there are the two washers  5 A,  5 B made of electrically insulating material, with their bearing portions  50 A,  50 B and their guiding and centering portions  51 A,  51 B, which are arranged in an identical way and fulfil the same functions as in the first example. Conversely, the fastening by crimping according to this second example is carried out without using an additional piece, such as the screwing nut  4  of the first example. This is because the crimping is carried out by mechanically crushing a crimping portion  21 , arranged on the outside of the cylindrical part of the collector  2 , against the bearing washer  6 . 
         [0020]    A third assembly example of a bushing forming a terminal with the current collector and with the cover of a housing is described in the Patent Application FR 2798227. 
         [0021]    As mentioned above, an Li-ion battery or storage battery uses a pairing of materials at the anode and at the cathode allowing it to operate at a high voltage level, typically equal to 3.6 volts. 
         [0022]    Other material pairings, delivering a lower voltage level, are possible. For example, a material pairing of LiFePO 4 /graphite delivers a medium voltage level of between 3.0 and 3.2 volts during operation. Also by way of example, a material pairing of LiFePO 4 /Li 4 TiO 5 O 12  delivers a medium voltage level of between 1.6 and 1.8 volts during operation. 
         [0023]    The Inventors have been confronted with a need to propose an Li-ion storage battery provided with a housing, with the connection terminals, making it possible to pass very heavy currents, typically more than 100 A, with medium voltage levels lower than that equal to 3.6 volts which is typically used. This is because, for so-called power applications, a high-capacity storage battery must deliver at its terminals a very high power, that is to say a product of the current and voltage which are very high. Because of the use of pairings with lower voltage levels, however, it is necessary to deliver heavier currents than traditionally. 
         [0024]    The Inventors have come to the conclusion that none of the bushings, proposed according to the prior art through a package housing of an Li-ion storage battery, such as those mentioned above, is suitable for passing very heavy currents, typically more than 100 A. In particular, the solution proposed in the aforementioned Application FR 2798227 is not suitable for passing heavy currents, because doing so would entail generating a loss of contact by decohesion between the male piece and the female piece during heating, which leads to thermal expansions, in particular because of the geometries of said pieces and the absence of laser welding, etc. 
         [0025]    Furthermore, whatever the type of assembly envisioned, it is necessary to provide perfect leaktightness of the bushing, and to do so throughout the working life of an li-ion storage battery, typically more than 5 years. 
         [0026]    There is therefore a need to improve a bushing forming a terminal for a lithium-ion storage battery and formed through a housing of the storage battery, in particular with a view to allowing a high-capacity storage battery equipped therewith to be able to deliver heavy currents, and with a view to obtaining perfect leaktightness of the bushing, and doing so throughout its working life. 
       SUMMARY OF THE INVENTION 
       [0027]    To this end, according to one of its aspects, the invention relates to a bushing forming a terminal for a lithium-ion (Li-ion) storage battery, formed through an orifice opening on either side of a wall having two opposite faces, comprising:
       two electrically insulating washers, each having a bearing portion bearing with its surface under pressure against one of the faces of the wall, and a guiding portion projecting from the bearing portion, the guiding portion bearing with pressure against the edge of the orifice of the wall,   two electrically conductive pieces, of which a male piece is fitted tightly in the female piece, each of the conductive pieces having a bearing portion bearing with its surface under pressure against a bearing portion of the washers, the female piece furthermore bearing with its surface under pressure against the guiding portions of the washers,       
 
         [0030]    in which bushing the material(s) of the pieces is (are) adapted, and their cross sections are dimensioned, in order to allow an electric current with a value at least equal to 100 A to flow through. 
         [0031]    In other words, according to the invention, the following are carried out in combination:
       tight fitting between male and female electrical connection pieces, which allows both axial compression (along the axis of the bushing) of the two insulating washers and radial tightening of the male and female pieces between one another and of the two insulating washers between the female piece and the edge of the orifice, which ensures perfect leaktightness and very good mechanical holding of the bushing on the wall;   selection of material(s) of the male and female pieces and of their cross sections in order to allow heavy currents to flow through the bushing.       
 
         [0034]    The term “perfect leaktightness” is intended to mean leaktightness at a level among the most stringent required, typically to below 10 −8  mbar.l/s for helium. 
         [0035]    Advantageously, the material(s) of the pieces may be adapted, and their cross sections are dimensioned, in order to allow an electric current with a value at most equal to 500 A to flow through. 
         [0036]    According to an advantageous embodiment, the female piece is open and is welded by a continuous weld bead to the male piece on the emergent end of the latter. The term “emergent end” is intended to mean the end of the male piece visible on the side of the female piece when the tight fitting is carried out. The welding may be electrical or carried out using a laser. Such an embodiment is advantageous because it allows permanent reinforcement of the mechanical connection between the end of the male piece and the base of the female piece. Furthermore, a continuous weld bead is perfectly leaktight and will supplement and ensure the perfect leaktightness of the bushing of the wall according to the invention, and will do so throughout the working life of the Li-ion storage battery. Further to the leaktightness, the welding will ensure mechanical cohesion in relation to the thermal expansions caused by the heating of the terminal under the effect of heavy current. Preferably, according to this advantageous embodiment, the arrangement of the male piece in the female piece is such that the height difference between the end of the male piece and the end of the female piece is less than 0.3 mm, whether the male piece projects or is set back relative to the female piece. In particular, provision is advantageously made for the ends of the male and female pieces to define a plane surface, that is to say with a substantially zero height difference between them. Such an arrangement, with a very small height difference, makes it possible to promote on the one hand welding of the male and female pieces to one another and, on the other hand, subsequent welding of the connection means. 
         [0037]    Preferably, the male and female pieces are made of the same material. They may be made of electrolytic copper CuAl or of copper weakly alloyed with tellurium, CuTe. 
         [0038]    The insulating washers may advantageously be made of polyetherimide (PEI), the mechanical and thermal properties of which are compatible with a heavy current flow. 
         [0039]    Preferably, the contact cross section S 1  between the male piece and the female piece is greater than 8 mm 2 , preferably greater than 10 mm 2 . 
         [0040]    Also preferably, the smallest cross section S 2  of the male piece is greater than 8 mm 2 , preferably greater than 10 mm 2 . 
         [0041]    According to another of its aspects, the invention also relates to a bushing forming a terminal for a lithium-ion (Li-ion) storage battery, formed through an orifice opening on either side of a wall having two opposite faces, comprising:
       two electrically insulating washers, each having a bearing portion bearing with its surface under pressure against one of the faces of the wall, and a guiding portion projecting from the bearing portion, the guiding portion bearing with pressure against the edge of the orifice of the wall,   two electrically conductive pieces, of which a male piece is fitted tightly in the female piece, each of the conductive pieces having a bearing portion bearing with its surface under pressure against a bearing portion of the washers, the female piece furthermore bearing with its surface under pressure against the guiding portions of the washers,       
 
         [0044]    in which bushing the female piece is open and is welded by a continuous weld bead to the male piece on the emergent end of the latter. 
         [0045]    According to yet another aspect, the invention also relates to a lithium-ion (Li-ion) battery or storage battery comprising a housing with a cover through which a bushing as described above is formed. 
         [0046]    According to one characteristic, the male piece is of the internally threaded type and projects outside the housing. 
         [0047]    The cover may be made of aluminum, such as aluminum 1050 or 3003. 
         [0048]    The material of the negative electrode(s) may be selected from the group comprising graphite, lithium, titanate oxide Li 4 TiO 5 O 12 ; and the material of the positive electrode(s) may be selected from the group comprising LiFePO 4 , LiCoO 2 , LiNi 0.33 Mn 0.33 Co 0.33 O 2 . 
         [0049]    Lastly, the invention relates to a method for producing a bushing as described above, according to which the following steps are carried out: 
         [0050]    a/ insertion through the orifice, from each of the two opposite faces of the wall, of one of the guiding portions of the washers, in such a way that they bear against the edge of the orifice of the wall, 
         [0051]    b/ insertion, from one face of the wall, of the female piece into one of the washers; 
         [0052]    c/ force-fitting, from the opposite face of the wall, of the male piece, in such a way that each of the bearing portions of the male and female pieces bears under pressure against a bearing portion of the washers, which itself bears with pressure against the edge of the orifice, the female piece furthermore bearing with pressure against the guiding portions of the washers, which themselves bear under pressure against the edge of the orifice of the wall. 
         [0053]    The force-fitting which allows bearing with pressure, according to step c/ is advantageously carried out by pressing with a force greater than or equal to 1 metric tonne-force. 
     
    
     
       DETAILED DESCRIPTION 
         [0054]    Other advantages and characteristics of the invention will become clearer on reading the details description of exemplary embodiments of the invention, provided by way of illustration and without implying limitation with reference to the appended figures, in which: 
           [0055]      FIG. 1  is a view in axial section of a bushing forming a terminal of an Li-ion storage battery according to one example of the prior art; 
           [0056]      FIG. 2  is a view in axial section of a bushing forming a terminal of an Li-ion storage battery according to another example of the prior art; 
           [0057]      FIG. 3  is a perspective view in axial section of a bushing forming a terminal of an Li-ion storage battery according to one example according to the invention; 
           [0058]      FIG. 4  illustrates the curves of the variation in temperature as a function of time according to the example of  FIG. 3  and with different dimensionings; 
           [0059]      FIG. 4A  is an enlarged view of  FIG. 4 ; 
           [0060]      FIG. 5  is a perspective view of a cylindrical housing of an Li-ion storage battery, with a cover through which a bushing forming a terminal according to the invention is formed; 
           [0061]      FIGS. 5A and 5B  are perspective views respectively from above and from below of a cover with a circular cross section fixed on a housing of  FIG. 5 ; 
           [0062]      FIG. 5C  is a reproduction of a photograph from below of a cover with a circular cross section fixed on a housing such as according to  FIG. 5 ; 
           [0063]      FIG. 6  is a perspective view of a prismatically shaped housing of an Li-ion storage battery, with a cover through which a bushing forming a terminal according to the invention is formed. 
       
    
    
       [0064]      FIGS. 1 and 2  relate to two different examples of a bushing forming a terminal of an Li-ion storage battery according to the prior art. These  FIGS. 1 and 2  have already been discussed in the introduction, and are therefore not discussed below. 
         [0065]    For the sake of clarity, references which are the same, denoting the same elements of bushings according to the prior art and according to the invention, are used for all of  FIGS. 1 to 6 . 
         [0066]    In the rest of the present application, the terms “lower”, “upper”, “low”, “high”, “below” and “above” are to be understood with reference to an Li-ion storage battery housing positioned vertically with its cover on top and the bushing projecting upward out of the housing. 
         [0067]      FIG. 3  represents an example of a bushing forming a terminal  1  of an Li-ion storage battery, according to the invention. 
         [0068]    The bushing  1  according to the invention is formed through an orifice  32  opening on either side of a cover  3  of an Li-ion storage battery housing. This cover comprising two opposite faces  30 ,  31 . The bushing  1  extends along an axis X parallel to the axis of the housing of the Li-ion storage battery. 
         [0069]    The bushing  1  according to the invention firstly comprises two identical electrically insulating washers  5 A,  5 B. The washers  5 A,  5 B represented have a high electrical resistivity coefficient, greater than 1.10 15  μohm.cm. They may be made of polyetherimide PEI. Each washer comprising a bearing portion  50 A,  50 B and a guiding portion  51 A,  51 B projecting from the bearing portion. The bearing portion of the upper washer  5 A bears with its surface under pressure against the upper face  30  of the cover  3 , and its guiding portion  51 A bears with pressure against the edge of the orifice  32  of the cover  3 . Similarly, the bearing portion of the lower washer  5 B bears with its surface under pressure against the lower face  30  of the cover  3 , and its guiding portion  51 B bears with pressure against the edge of the orifice  32  of the cover  3 . 
         [0070]    The bushing  1  according to the invention comprises a male piece  7  fitted tightly in a female piece  8 . The male piece  7  represented is internally threaded, typically according to a diameter  of the M5 type. The male  7  and female  8  pieces represented are electrically conductive: in other words, they have a low electrical resistivity coefficient, typically between 1.7 and 1.9 μohm.cm. They may be made of electrolytic copper CuAl or of copper weakly alloyed with tellurium, CuTe. They may also consist of the same material as the cover  3 , typically aluminum 1050 or 3003, the electrical resistivity coefficient of which is of the order of 2.6 μohm.cm. In this case, care is of course taken so that the material is chemically compatible with the materials constituting the electrochemical cell or cells of the Li-ion storage battery contained in the housing. Preferably, these male  7  and female  8  pieces are made of the same material. 
         [0071]    Each of the male  7  and female pieces comprises a bearing portion  70 ,  80 . The bearing portion  70  of the male piece  7  bears with its surface under pressure against the bearing portion  50 A of the upper washer  5 A, while the bearing portion  80  of the female piece bears with its surface under pressure against the bearing portion  50 B of the lower washer  5 B. As illustrated in  FIG. 3 , the female piece  8  furthermore bears with its surface under pressure against the guiding portions  51 A,  51 B of the washers. 
         [0072]    According to the invention, the material(s) of the male  7  and female  8  pieces is (are) selected, and their cross sections are dimensioned, in order to allow an electric current with a value at least equal to 100 A to flow through. This heavy current capable of flowing through a bushing  1  according to the invention is a continuous current for a duration of at least 3 minutes. 
         [0073]    The path of a current I with more than 100 A through the bushing  1  according to the invention has been symbolized by the black arrowed line. 
         [0074]    The dimensioning of the male  7  and female  8  pieces represented in  FIG. 3  relates to the length dimensions of each of the pieces  7 ,  8 , the contact height H between the two pieces  7 ,  8 , defining a cross section S 1  symbolized by a dashed rectangle, and lastly the wall thickness on the female piece  8 , defining a cross section S 2  symbolized by a dashed circle. It is to be pointed out that the cross section S 1  is a band of height H on the periphery of the male piece  7 , i.e. S 1 =π*H*D. Likewise, S 2  corresponds to the smallest cross section of the male piece  7 , that is to say transversely to its axis X, level with the bore of diameter . 
         [0075]    Preferably, S 1  is greater than 8 mm 2 , more preferably greater than 10 mm 2 . Preferably, S 2  is greater than 8 mm 2 , more preferably greater than 10 mm 2 . 
         [0076]    A plurality of bushings  1  were produced as illustrated in  FIG. 3 , but according to different dimensionings Nos 1 to 4. These, as well as the various values of current I which can flow through the bushing  1 , are indicated in the table below, given on the one hand that the diameter D corresponds to that of the part of the male piece  8  which defines the contact height H with the female piece  7 , and on the other hand that the current I must be continuous for a duration of at least 3 minutes. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Dimensioning of the 
               
             
          
           
               
                 bushing according to the 
                 No. 
               
             
          
           
               
                 invention 
                 1 
                 2 
                 3 
                 4 
               
               
                   
               
             
          
           
               
                 Diameter D in mm 
                 6.0 
                 7.0 
                 8.0 
                 9.0 
               
               
                 Cross section S1 in mm 2   
                 14.3 
                 26.0 
                 40.5 
                 56 
               
               
                 Cross section S2 in mm 2   
                 40 
                 52 
                 60 
                 67 
               
               
                 Current I in A 
                 200-230 
                 320-360 
                 450-500 
                 &gt;500 
               
               
                   
               
             
          
         
       
     
         [0077]    Tests were carried out on a bushing with dimensioning No. 1, that is to say with a diameter D equal to 6 mm, in order to corroborate the selection of the materials and the dimensioning of their cross sections. These tests consisted in making various current levels flow, respectively ranging from 50 to 500 A, increasing at intervals of 50 A to change from one level to the other. Measurements were then made of the heating observed in the bushing as a function of time, that is to say its temperature rise counting from the initial instant at which the current I is delivered through the female piece  8  and flows as symbolized in  FIG. 3 . It is to be pointed out that these tests were carried out for a bushing  1  according to the invention forming a negative terminal. It is to be pointed out that, for these tests, the male  7  and female pieces are made of CuAl, the washers are made of PEI and the wall  3  is made of aluminum 1050. 
         [0078]    The various curves shown in  FIGS. 4 and 4A  illustrate the results of these heating measurements. 
         [0079]    From these curves, it can be seen that, with a current of 200 A, the temperature rise measured is about 30° C., and that with a current of 250 A it is about 50° C. 
         [0080]    It may be concluded therefrom that these measurement results show that it is possible for a bushing  1  with dimensioning No. 1 to carry:
       very heavy currents up to at least 500 A;   heavy currents of between 200 and 250 A continuously for a consequent duration without excessive temperature rise, which furthermore has a tendency to stabilize after a certain amount of time.       
 
         [0083]    In order to produce a bushing according to the invention, the following steps are carried out. 
         [0084]    One of the guiding portions  51 A,  51 B of the washers  5 A,  5 B is inserted through the orifice  32 , from each of the two faces  30 ,  31  of the cover  3 , in such a way that they bear against the edge of the orifice  32 . 
         [0085]    The female piece  8  is inserted into the lower washer  5 B from the lower face  31  of the cover  3 . 
         [0086]    The male piece  7  is force-fitted from the upper face  30  opposite the lower face  31  of the cover  3 . The force-fitting makes it possible to have each of the bearing portions  70 ,  80  of the male  7  and female pieces  8  bearing with its surface under pressure against a bearing portion  50 ,  50 B of the washers  5 A,  5 B, itself bearing under pressure against the edge of the orifice  32 . Furthermore, the female piece  8  bears under pressure against the guiding portions  51 A,  51 B of the washers  5 A,  5 B, themselves bearing with their surface under pressure against the edge of the orifice  32 . 
         [0087]    Various tests under pressure were carried out with various forces applied for the force-fitting. These tests showed that it is preferable to apply a force-fitting force at least equal to 1 metric ton-force in order to obtain on the one hand perfect leaktightness between the pieces  7 ,  8 , washers  5 A,  5 B and cover  3 , and on the other hand very strong cold mechanical tightening between the male  7  and female  8  pieces. 
         [0088]    The bushing  1  according to the invention may be formed on a cover  3  of a housing  10  of an Li-ion storage battery both according to a cylindrical geometry ( FIGS. 5 to 5C ) and according to a prismatic geometry ( FIG. 6 ). In these various configurations, the terminal  1  according to the invention is for example negative, it being possible for the positive terminal  11  to be produced, for example, directly by welding, likewise on the cover  3 , as illustrated in  FIGS. 5 to 6 . 
         [0089]    In order to further reinforce the mechanical connection between the male  7  and female  8  pieces, it is advantageous to form a continuous leaktight weld bead  12  at the periphery and at the emergent end  71  of the male piece  7 , as illustrated in  FIG. 5C . This continuous bead  12  may be produced by electrical welding or laser welding. This continuous bead  12  supplements and ensures perfect leaktightness of the bushing  1  according to the invention, and does so throughout the working life of the Li-ion storage battery, which is preferably more than 5 years. 
         [0090]    Although not mentioned above, it is ensured that the base of the female piece  8 , that is to say the cross section which defines its bearing surface  80 , has a sufficient area to be able to electrically connect a connection means internal to the housing and itself electrically connected to the electrochemical assembly, usually referred to as a bundle, consisting of one or more electrochemical cells. Electrical connection between the internal connection means and the base  80  of the female piece may be produced by welding. The invention is not limited to the examples described above; in particular, characteristics of the examples illustrated may be combined with one another in the scope of variants which are not illustrated. 
         [0091]    The expression “comprising one” should be understood as being synonymous with “comprising at least one”, unless the contrary is indicated.