Feed-through forming a terminal for a metal-ion electrochemical accumulator, integrating a gas relief valve, associated accumulator

Abstract

The invention relates to a feed-through comprising a terminal for a metal-ion electrochemical accumulator, produced through an orifice emerging either side of a wall comprising two opposite faces, comprising: a closure means in abutment against the chamfer of at least one through passage forming a seat inside the feed-through; a compression means housed in the through duct, the compression means being adapted to keep the closure means pressed against its seat along a continuous peripheral surface, up to a predetermined pressure of the gases prevailing inside the accumulator, beyond which pressure said gases may escape towards the outside of the accumulator through the passage and the through duct.

Claims

1. A feed-through forming a terminal for a metal-ion electrochemical accumulator, produced through an orifice emerging either side of a wall comprising two opposite faces, comprising: a closure means in abutment against a chamfer of at least one through passage forming a seat inside the feed-through; and a compression means housed in a through duct, the compression means comprising two ends and being adapted to keep the closure means pressed against the seat along a continuous peripheral surface, up to a predetermined pressure of gases prevailing inside the accumulator, beyond which pressure said gases may escape towards the outside of the accumulator through the passage and the through duct, wherein the closure means is a ball, the compression means being adapted, on the one hand, to allow the passage of an end of a tool so as to allow an initial plastic deformation of the ball by pressing against the seat and, on the other hand, to keep the deformed ball pressed against the seat up to the predetermined pressure of the gases prevailing inside the accumulator, beyond which pressure said gases may escape towards an outside of the accumulator, and wherein the ball is made in a material and the seat is made in another material so that, the material of the ball has an elastic limit lower than the elastic limit of the material of the seat to allow the plastic deformation of the ball to be performed in order to ensure the seal at the interface between the ball surface and the seat, and wherein the material of the ball is compatible with an electrochemistry used in the metal-ion accumulator and ensures chemical resistance to prevent, on the one hand, any risk of corrosion and potential source of pollution of an inside of the accumulator and, on the other hand, any damage to the surface of the ball through a chemical attack originating from one or more salts and solvents contained in an electrolyte or gases that form during an operation of the accumulator.

2. The feed-through according to claim 1, further comprising: two electrically insulating washers, each comprising an abutment portion in pressured surface abutment against one face of the faces of the wall and a guide portion projecting relative to the abutment portion and in contact with an edge of the orifice; and one electrically conductive female part and one electrically conductive male part, a portion of the male part being press-fitted in a bored portion of the female part, each of the conductive parts comprising an abutment portion in pressured surface abutment against an abutment portion of the washers, a base of the bored portion comprising the through passage, the through passage comprising the chamfer, a fitted portion of the male part comprising the duct emerging both outside the accumulator and facing the through passage of the female part.

3. The feed-through according to claim 1, the compression means being a compression spring.

4. The feed-through according to claim 3, the compression spring being made of AISI 316 or 316L, or even of AISI 304 or 304L, grade stainless steel.

5. The feed-through according to claim 2, the female part being made of a Cu—Al copper grade, in the H14 type strain-hardened state, whereas the ball is made of a Cu—Al copper grade in the 0-state.

6. The feed-through according to claim 2, the female part being made of a 1050 aluminum alloy grade, in the H14, H16 or H18 type strain-hardened state, whereas the ball is made of an aluminum grade in the 0-type annealed state.

7. The feed-through according to claim 2, the male part being made of a copper-based alloy or an aluminum-based alloy.

8. The feed-through according to claim 1, the chamfer of the through passage forming the seat being a conical chamfer.

9. The feed-through according to claim 2, the press-fitting of the fitted portion of the male part in the bored portion of the female part is an N9p7 type fitting.

10. The feed-through according to claim 2, the through duct comprising a tapped central hole of the male part.

11. A metal-ion battery or accumulator comprising a casing with a cover, through which the feed-through according to claim 2 is produced.

12. The metal-ion battery or accumulator according to claim 11, the male part being of an internally threaded type and projecting towards the outside of the casing.

13. The metal-ion battery or accumulator according to claim 11, the cover being made of aluminum.

14. The metal-ion battery or accumulator according to claim 11, the metal-ion battery or accumulator being a Li-ion battery or accumulator, the female part of the feed-through being made of aluminum alloy and soldered to an aluminum-based current collector that is soldered to an aluminum-based electrode strip supporting an active material for inserting metal-ions.

15. The metal-ion battery or accumulator according to claim 11, the metal-ion battery or accumulator being a Li-ion battery or accumulator the female part of the feed-through being Cu—Al copper-based and soldered to a copper-based current collector that is soldered to a copper-based electrode strip supporting an active material for inserting metal-ions.

16. A method for producing the feed-through according to claim 2, wherein the following steps are performed: a/ inserting one of the guide portions of the washers through the orifice, from each of the two opposite faces of the wall, so that they are in abutment against the edge of the orifice of the wall; b/ inserting the aluminum female part into one of the washers from a face of the wall; c/ housing the closure means along an axis of the through passage inside the bored portion of the female part, so that it comes to rest in surface abutment on the chamfer at an end of the through passage; d/ housing the compression means in a part of the through duct of the male part forming a housing, so that one of the ends of the compression means is in abutment or is held on a base of the housing, whereas the other one of the ends projects beyond a portion of the male part to be fitted; and e/ press fitting, from the opposite face of the wall, the male part, so that the fitted portion of the male part is in abutment against the base of the bored portion of the female part and so that each of the abutment portions of the male and female parts is in pressured surface abutment against an abutment portion of the washers that is guided against the edge of the orifice.

17. The method according to claim 16, the fitting according to step e/ being carried out under a press with a force greater than or equal to 1 ton-force so as to obtain an N9p7 type fitting between the fitted portion of the male part and the bored portion of the female part.

18. The method according to claim 16 comprising, after step e/, the following steps: f/ all the steps of assembling the accumulator and a casing, comprising: f1/ inserting an electrochemical assembly inside a lateral enclosure of the housing, said assembly comprising at least one cell wound around itself, each cell being formed by a cathode, an anode and a separator film interposed between the anode-cathode; f2/ completing electrical connections, on the one hand, between an end of the electrochemical assembly and the casing of the accumulator corresponding to one of the polarities and, on the other hand, between another end of the assembly and the feed-through; f3/ sealed closing of the accumulator casing; f4/ filling an inside of the accumulator with a liquid or gel electrolyte through a fill hole in the accumulator casing, then sealingly closing the fill hole; and g/ electrically connecting positive and negative terminals of the accumulator in order to produce its electric formation.

19. The method according to claim 18, the closure means being a ball comprising, once the step g/ of electric formation of the accumulator is complete, the following step: h/ inserting a pressing tool into the through duct of the male part from the outside of the accumulator through the compression means, so as to plastically deform the ball in abutment against the seat.

Description

DETAILED DESCRIPTION

(1) Further advantages and features of the invention will become more clearly apparent upon reading the detailed description of embodiments of the invention that is provided by way of a non-limiting illustration, with reference to the accompanying figures, in which:

(2) FIG. 1 is a perspective view of a Li-ion accumulator with cylindrical geometry according to an example of the prior art;

(3) FIG. 2 is a perspective view of a Li-ion accumulator with prismatic geometry according to another example of the prior art;

(4) FIG. 3 shows, in the form of curves, the result of tests carried out for a cylindrical format, 50-125 type Li-ion accumulator according to the prior art with LiFePO.sub.4/Graphite type electrochemistry;

(5) FIG. 4 is an axial section and exploded view of a feed-through forming a terminal of a metal-ion accumulator through the cover of the casing, the feed-through integrating a gas relief device according to the invention;

(6) FIG. 4A is a detailed view of FIG. 4 showing the position of the ball of the gas relief device on its seat;

(7) FIGS. 5A, 5B and 5C are axial section views showing the various steps of producing a feed-through according to the invention integrating a gas relief device;

(8) FIG. 6 is an axial section view of the feed-through forming a terminal of a metal-ion accumulator according to the invention obtained following the step of plastic deformation of the ball of FIG. 5C;

(9) FIGS. 7A and 7B are detailed axial section views of the ball of the gas relief device, as it is positioned on its seat, respectively before and after the step of plastic deformation of the ball of FIG. 5C;

(10) FIGS. 8A and 8B are detailed axial section views of two variations of a pressing tool for implementing the step of plastic deformation of the ball of FIG. 5C;

(11) FIG. 9 shows, in the form of curves, the result of tests carried out for a cylindrical format, 50-125 type Li-ion accumulator according to the invention with LiFePO.sub.4/Graphite type electrochemistry;

(12) FIGS. 1 to 3 relate to Li-ion accumulators according to the prior art. These FIGS. 1 to 3 have already been discussed in the preamble and therefore are not discussed further hereafter.

(13) For the sake of clarity, the same reference numerals denoting the same feed-through elements according to the prior art and according to the invention are used for all FIGS. 1 to 9B.

(14) Throughout the present application, the terms “lower”, “upper”, “low”, “high”, “bottom” and “top” are to be understood with reference to a vertically positioned metal-ion accumulator casing with the cover thereof on top and the feed-through projecting outside the housing towards the top.

(15) It is to be noted that, for the sake of clarity, the cover 3 of the accumulator casing through which the feed-through 1 according to the invention is produced, as well as the washers 6A, 6B providing the seal, are only shown in FIG. 4. It is obvious that, even though they are not shown, these elements exist for all the other views of a feed-through according to the invention.

(16) FIG. 4 shows a first example of a feed-through forming a terminal 1 of a metal-ion accumulator integrating a gas relief device according to the invention.

(17) The feed-through 1 according to the invention is produced through an orifice 32 emerging either side of a cover 3 of a metal-ion accumulator casing, with this cover comprising two opposite faces 30, 31. The cover 3 typically can be made of 1050 or 3003 aluminum, the electric resistivity coefficient of which is approximately 2.6 μohm.Math.cm.

(18) The feed-through 1 extends along an axis X parallel to the axis of the Li-ion accumulator casing.

(19) The feed-through 1 according to the invention comprises a male part 4 tightly fitted in a female part 5. The male 4 and female 5 parts that are shown are electrically conductive, in other words, they have a low electric resistivity coefficient, typically included in a range of 1.7 and 1.9 μohm.Math.cm. The male part 4 advantageously can be made of 5754 aluminum or of Cu—Al electrolytic copper, preferably with a nickel coating. The female part 5 advantageously can be made of 1050 aluminum or of Cu—Al electrolytic copper, preferably with a nickel coating.

(20) Each of the male 4 and female 5 parts comprises an abutment portion 40, 50, which comes into pressured surface abutment against an upper washer 6A and a lower washer 6B, respectively. The washers 6A, 6B shown have a high electric resistivity coefficient, greater than 1.10.sup.15 μohm.Math.cm. They can be made of polyetherimide PEI. Each washer comprises an abutment portion in direct pressured abutment against one of the abutment portions 40, 50 of the washers and a guide portion projecting relative to the abutment portion. The guide portions guide and center the female part 5 in the orifice of the cover.

(21) The male part 4 comprises a cylindrical portion 41 that is tightly fitted in the bored hole 51 of the female part 5.

(22) The height L1 of the cylindrical portion 41 is determined to at least ensure a minimum fitting height between the cylindrical portion 41 and the bored hole 51. Typically, the height L1 is greater than 2 mm.

(23) The height L2 of the bored hole 51 is determined to at least ensure a minimum fitting height between the cylindrical portion 41 and the bored hole 51. Typically, the height L2 is greater than 2 mm.

(24) Preferably, the outer diameter of the cylindrical portion 41 and the internal diameter D1 of the bored hole 51 so as to comply with press fitting subject to a force greater than or equal to 1 ton-force for this cylindrical part 41 in the bored hole 51 of the female part 5. Typically, an N9p7 type fitting is defined between these two cylindrical portions 41, 51. The assembly of the male 4 and female parts 5 and the washers 6A and B provides a perfect seal at the orifice of the cover 3.

(25) According to the invention, the terminal 1 integrates a device for relieving gases in the event of overpressure inside the accumulator.

(26) This device comprises a set of perforations produced in the two male 4 and female 5 parts, through which gases originating from inside the accumulator are able to pass in order to escape towards the outside of the accumulator, as well as a ball 7 and a compression spring 8.

(27) The ball 7 diameter is greater than both the diameter outside its seat 54 and the outer diameter of the compression spring 8.

(28) In the compressed state the compression spring 8 will allow the ball 7 to be maintained on its seat 54 in a continuous line over the entire periphery of said seat so as to obtain a perfect seal between the inside and the outside of the accumulator, under the force of the spring 8, which typically is greater than an equivalent force of 2 bar pressure through the through hole 53, above which the ball 7 is positioned.

(29) The perfect seal level that is achieved, as will be explained hereafter, is typically less than 10.sup.−8 mbar.Math.l/s for helium, i.e. equivalent to that of the metal-ion accumulator casing assembly, in particular around the orifice 32 of the cover 3 at the washers 6A, 6B.

(30) More specifically, the male part 4 comprises a housing 43 intended to house the compression spring 8. This housing 43 is connected to the internally threaded hole 42, typically with a diameter of the M5 or M6 type, via a through passage 44.

(31) Preferably, a constriction 45 is produced at the upper end of the housing 43. This constriction 45 allows the spring 8 to be kept in position after it is positioned in the male part 4.

(32) This constriction 45 may be produced either by machining or by moving material along the wall of the bore of the housing 43 so as to form a continuous or partial line of catch-type overthicknesses positioned in threes at 120° or in fours at 90°.

(33) The female part 5, in particular, is perforated in its base 52 at the end of the bored hole 51 of a through passage 53, the end of which 54 forms the seat of the ball 7 and which, as shown in FIG. 6, is facing the housing 43 for the spring 8.

(34) Thus, by its very construction, without blocking by the ball 7 under the pressure force of the spring 8, the threaded hole 42, the housing 43, the through passages 44 and 53 communicate together so as to allow gases to pass from the inside of the accumulator to the outside through the male parts 4 and 5 of the feed-through 1.

(35) The seat 54 of the ball 7 is advantageously formed by a conical chamfer, typically at approximately 45°, which allows, in addition to the aforementioned desired sealing function, the ball 7 to position itself independently along the axis X of the passage 53 and the feed-through 1 during its installation step.

(36) Preferably, a chamfered widening 46 is produced on the lower end of the housing 43.

(37) Preferably, the internal diameter D3 of the housing 43 for the spring 8 is defined so as to be greater than approximately 10% of the outer diameter of the spring 8. This thus avoids any friction and possibly jamming upon compression of the spring 8.

(38) Preferably, the height L3 of the housing 43 for the spring 8 is defined so that, when the male part 4 is tightly fitted in the female part 5 with the end of the cylindrical portion 41 in abutment against the base 52 of the bored hole 51, the compression rate of the spring 8 corresponds to the level of force to be applied to the ball to contain an opening pressure that will be defined as being included in a range of two pressure values, respectively low P1 and high P2, for discharging gases from the inside of the accumulator to the outside.

(39) In order to be compatible with the normal and desired dimensions and space for a metal-ion accumulator feed-through 1, the ball 7 advantageously is small, typically with an outer diameter included in a range of 1.6 and 3 mm.

(40) Similarly, the ball 7 is positioned on a chamfer 54 of the through passage 53, the diameter of which is preferably included in a range of 1 and 2 mm.

(41) When the female part 5 is made of nickel-coated Cu—Al copper, the ball 7 preferably is also made of Cu—Al copper, preferably at least 99.9% copper.

(42) When the female part 5 is made of nickel-coated 1050 aluminum, the ball 7 is made of 1000 grade aluminum, such as 1050 aluminum, for example, with at least 99.5% aluminum.

(43) As explained hereafter, in order to ensure a seal at the aforementioned required level on the chamfer 54 of the through hole 53, provision advantageously is made for a final step of plastic deformation of the ball 7 against the female part 5 to be carried out, when assembling the feed-through 1, as will be described hereafter.

(44) Furthermore, in order to comply with these plastic deformation constraints, when the female part 5 of the terminal is made of nickel-coated Cu—Al copper, the following advantageous selection can be made: for the female part 5, a Cu—Al copper grade of the H14 type in the strain-hardened state, which is expressed by breaking strength greater than 300 N/mm.sup.2 with an elastic limit greater than 250 N/mm.sup.2; for the ball 7, a Cu—Al copper grade in the 0-state with annealing, which is expressed by breaking strength greater than 200 N/mm.sup.2 with a maximum elastic limit of 120 N/mm.sup.2.

(45) When the female part 5 of the terminal is made of 1050 type aluminum, the following advantageous selection can be made: for the female part 5, a 1050 aluminum grade of the H14, H16 or H18 type in the strain-hardened state, which is expressed, for the H14 state, by breaking strength greater than 105 N/mm.sup.2 with an elastic limit greater than 85 N/mm.sup.2; for the ball 7, an aluminum grade in the 0-state with annealing, which is expressed by breaking strength included in a range of 65 and 95 N/mm.sup.2 with a maximum elastic limit of 40-50 N/mm.sup.2.

(46) According to an advantageous variation, the difference in mechanical strength between the ball 7 and the base of the female part 5 also can be accentuated.

(47) To this end, it is possible, as a function of the diameter of the ball 7, to increase the wall thickness E of the base to a certain extent between the lower end of the through passage 53 and the lower end of the chamfer 54.

(48) Table 1 below provides preferred values of this thickness E as a function of the outer diameter Ø of the ball 7.

(49) TABLE-US-00001 TABLE 1 Outer diameter Ø 1.8 to 2.4 2.4 to 2.8 2.8 to 3.3 to 4 of the ball 7 3.3 (mm) Wall thickness E of the 2.0 to 3.0   3 to 3.5 3.5 to 4   4 to 5 base of the female part 5 (mm)

(50) In order to be compatible with the normal and desired dimensions and space for a metal-ion accumulator feed-through 1, the spring 8 advantageously is small, typically with an outer diameter less than or equal to 4 mm and a length in the free state less than or equal to 8 mm.

(51) The compression spring 8 is preferably made of AISI 316-316L, or possibly AISI 304-304L, grade stainless steel, which also have the advantage of being grades that are widely used and are compatible with the electrochemistry of a Li-ion accumulator.

(52) By way of an example, the compression spring 8 can be one of the wire-based springs made of 316 stainless steel marketed by SPEC.

(53) Thus, preferably, for a cylindrical portion 41 diameter D1 of approximately 6 mm, a spring from SPEC advantageously can be selected, the features of which are summarized in table 2 below:

(54) TABLE-US-00002 TABLE 2 Commercial references C0088-008-0190X Material 316 stainless steel Stiffness R (N/mm) 0.51 Outer diameter (mm) 2.24 Wire diameter (mm) 0.2  Length in free state (mm) 4.83

(55) More preferably, for a cylindrical portion 41 diameter D1 included in a range of 7 and 8 mm, a spring from SPEC advantageously can be selected, the features of which are summarized in table 3 below:

(56) TABLE-US-00003 TABLE 3 Commercial references C0120-008-0190X Material 316 stainless steel Stiffness R (N/mm) 0.47 Outer diameter (mm) 3.05 Wire diameter (mm) 0.25 Length in free state (mm) 6.35

(57) In order to produce an accumulator with a feed-through 1 integrating the gas relief device according to the invention, the following steps are performed.

(58) One of the guide portions of the washers 6A, 6B is inserted through the orifice 32, from each of the two faces 30, 31 of the cover, so that they are in abutment against the edge of the orifice 32.

(59) The female part 5 is inserted into the lower washer 6B from the lower face 31 of the cover 3.

(60) The ball 7 is placed inside the female part 5 so that it comes to rest on the chamfer 54 along the axis X of the through passage 53.

(61) The compression spring 8 is then placed in the housing 43 of the male part 4. The spring 8 snaps into the base of the housing 43 at the constriction 5 via one of its ends, whereas the other one of its ends projects beyond the cylindrical portion 41 of the male part 4 (FIG. 5A).

(62) The male part 4 is press fitted, from the upper face 30 opposite the lower face 31 of the cover 3. The press fitting allows each of the abutment portions 40, 50 of the male 4 and female 5 parts to be in pressured surface abutment against an abutment portion of the washers 6A, 6B, which are in pressured abutment against the edge of the orifice 32 (FIG. 5B). Furthermore, the female part 5 is in pressured abutment against the guide portions of the washers 6A, 6B, which are in pressured surface abutment against the edge of the orifice 32. Preferably, a press fitting force is applied that is at least equal to 1 ton-force in order to obtain, on the one hand, a seal between the parts 4, 5, the washers 6A, 6B and the cover 3 and, on the other hand, highly resistant cold mechanical clamping between the male 4 and female 5 parts.

(63) At the end of this step, the obtained sealing level is already high. With the aforementioned components, a helium tested level included in a range of 10.sup.−5 et 10.sup.−7 mbar.Math.l/s can be provided. This sealing level is sufficient for carrying out the electric formation step of a metal-ion accumulator.

(64) The assembly of the various components of the feed-through according to the invention is then complete.

(65) All the normal steps for assembling a metal-ion accumulator are carried out as follows: an electrochemical assembly is inserted inside a lateral enclosure of the housing, said assembly comprising at least one cell wound around itself, each cell being formed by a cathode, an anode and a separator film interposed between the anode-cathode; the electrical connections are completed, on the one hand, between an end of the electrochemical assembly and the casing of the accumulator corresponding to one of the polarities, for example, the positive polarity and, on the other hand, between the other end of the assembly and the terminal-feed-through 1 wall of the cover 3 of the accumulator according to the invention, which corresponds to the other one of the polarities, for example, the negative polarity); the accumulator casing is closed in a sealed manner; the inside of the accumulator is filled with an electrolyte liquid through a fill hole provided to this end on the cover 3 of the accumulator casing, for example. This fill hole is then reclosed to provide a perfectly sealed accumulator casing.

(66) With the accumulator according to the invention being assembled, it is then possible to proceed to the step of electric formation by electrically connecting its positive and negative terminals to a known item of equipment.

(67) To this end, the first charge and discharge cycles are carried out by passing a charge or discharge current through two negative and positive polarity terminals of the accumulator.

(68) As mentioned in the preamble of this application, during this step of electric formation, which can last up to 48 to 72 hours, the internal pressure may increase, which is more generally observed during the first charge cycle.

(69) Before this pressure increase, the previously obtained sealing level, of approximately 10.sup.−5 and 10.sup.−7 mbar.Math.l/s for helium, is sufficient since, a priori, the air or the ambient humidity cannot enter the accumulator.

(70) By virtue of the ball 7 and spring 8 gas relief device, as previously described, the overpressure gases will overcome the force of the spring 8 and thus lift the ball 7 and thereby will be able to be relieved outwards through the threaded hole 42, the housing 43, the through passages 44 and 53, respectively.

(71) FIG. 9 shows, in the form of graphs, the result of tests carried out for a cylindrical format, 50-125 type Li-ion accumulator according to the invention with LiFePO.sub.4/Graphite type electrochemistry, with the ball 7 and the compression spring 8 being made of the aforementioned materials and having the aforementioned dimensions.

(72) Upon reading the curve of the pressure inside the accumulator, it can be seen that: when the internal pressure reaches the exhaust pressure from which the ball 7 may be lifted from its seat 54, approximately 2.5 bar at point A in the example shown, gas will escape from the inside of the accumulator when gas is generated inside the accumulator; then the ball 7 closes back onto its seat, from point B in the example shown, when this generation of gas stops.

(73) As a final step, on completion of electric formation, provision advantageously is made for a step of plastic deformation of the ball 7, which will allow an accumulator sealing level to be permanently provided with a value that is at least greater than 10.sup.−8 mbar.Math.l/s for helium, as explained hereafter.

(74) This final step is shown in FIG. 5C: a pressing tool 9 is inserted into the axis X of the male part 4 of the terminal 1, then the threaded body 90 of this tool 9 is screwed into the threaded hole 42 of the terminal 1.

(75) The threaded body 90 is extended by a cylindrical end 91, which is introduced at the center of the spring turns when the body 90 is screwed into the threaded hole 42 until this end 91 comes into contact with the upper dome of the bore 7.

(76) As shown by the arrow F in FIG. 5C, during screwing a pressing force is transferred by the end 91 of the tool in order to press the ball 7 against the chamfer 54 and thus cause the deformation thereof. The deformation progressively moves the volume of material of the ball 7 in order to crush its faces interfacing with the entry of the chamfer 54. Plastic deformation of the ball 7 is then obtained.

(77) This irreversible deformation of the ball 7 allows the surfaces facing the ball and the chamfered profile 54 at the end of the through passage 53 of the base of the female part 5 to coincide over a significant length and, consequently, the possible paths of gas leaks to be blocked that could have existed before the completion of the pressing operation by the tool 9.

(78) The evolution of the shape of the ball 7 as it is pressed is respectively shown in FIGS. 7A and 7B: the ball 7 initially has a perfectly spherical diameter, which progressively increases at the chamfered entry 54 of the through passage 53 of the female part 54 through the movement of its material from the center outwards subject to the pressing force F of the tool 9.

(79) The diameter of the ball 7 at the chamfered entry 54 thus transitions from a value Ø.sub.1 (FIG. 7A) to a higher value Ø.sub.2 (FIG. 7B) in its plastically deformed state. As can be seen in FIG. 7B, the contact surface between the plastically deformed ball 7 and the entry of the through passage 53 has increased relative to the initial contact surface between the non-deformed spherical ball 7 and the chamfer 54.

(80) FIGS. 8A and 8B show two examples of different profiles 91 at the end of the pressing tool 9 of the ball. These end profiles 91 advantageously are axisymmetrical in order to apply 360° contact from the top of the ball 7. The central part of the tool 9, which is in the extension of the body 90, may be relatively long. Preferably, precedence is given to the shortest central part in the case of a ball 7 made of harder material (FIG. 8A), such as when the ball 7 is made of copper, for example. The longest central part is instead given precedence in the case of a ball 7 made of softer material (FIG. 8B), such as when the ball 7 is made of aluminum, for example.

(81) During the step of plastic deformation of the ball 7, provision advantageously may be made for the upper surface of the terminal-feed-through 1 of the accumulator to be cleaned, in order to eliminate any traces and residues of pollution caused by the degassing during the step of electric formation.

(82) An example of the sizing of the previously described feed-through 1 will now be described with a ball 7/compression spring 8 gas relief device to allow the gases inside the accumulator to escape when they generate a pressure of approximately 2.5 to 3 bar.

(83) The range of operating pressures expected between the lower pressure P1 and the upper pressure P2 is determined by computing from the dimensions of the various components selected to produce the gas relief device.

(84) The selected compression spring 8 is that marketed by SPEC, the features of which are shown in table 2 above.

(85) The selected ball 7 is a Cu—Al copper ball with an outer diameter Ø.sub.1 equal to 2.4 mm. After plastic deformation, the outer diameter Ø.sub.2 is equal to at least 2.5 mm.

(86) The diameter of the through passage 53 perforated through the base of the female part 5 is equal to 1.4 mm.

(87) The base of the female part 5 is made of nickel-coated Cu—Al copper with an average thickness of 3.0 mm.

(88) The ball 7 is positioned in the axis X of the through passage 53 and self-centers on the profile 54 obtained by a chamfer of between 0.4 to 0.6 mm at 45°.

(89) The end of the bored housing 43 of the male part 4 comprises a chamfer of between 0.25 to 0.4 mm at 60°.

(90) The dimension of the depth L.sub.3 of the housing 43 for the spring 8 is now determined. This depth or height L.sub.3 is equal to the sum of the length Lx of the spring 8 in the compressed state and of the overthick part of the ball 7 above the plane inside the female part 5. The dimensions L.sub.3 and Lx are clearly shown in FIG. 6.

(91) In the example shown, taking into account the outer diameter of the spherical ball 7 and the value of the chamfer 54, the surface S of the ball 7 on which the internal pressure P of the gases is applied can be considered to be approximately 1.85 mm.sup.2.

(92) It is thus possible to deduce therefrom the respective forces Fn that correspond to various levels of applied pressure of P1 to P5 between 2.5 bar and 4.5 bar by applying the formula Fn=P×S.

(93) Table 4 summarizes the forces.

(94) TABLE-US-00004 TABLE 4 Pressures P1 P2 P3 P4 P5 Pressure values (bars) 2.5  3.0  3.5  4.0  4.5  Applied forces 0.462 0.554 0.647 0.739 0.831 (N)

(95) Table 5 below indicates, for each of the applied forces, the compression lengths xn of the spring 8 based on the formula Fn=R*xn (with R being the stiffness of the spring), as well as the compressed spring lengths Lxn, based on the formula Lxn=Lo−xn (with Lo being the spring length in the free state).

(96) TABLE-US-00005 TABLE 5 Compression length xn of the spring 8 (mm) x1 x2 x3 x4 x5 0.906 1.087 1.268 1.449 1.630 Length Lxn of the compressed spring 8 (mm) Lxl Lx2 Lx3 Lx4 Lx5 3.924 3.743 3.562 3.381 3.200

(97) Given the results obtained for Lx1 and Lx2, an average compressed length (Lx) can be defined for this type of spring 8 as being equal to 3.85 mm with a tolerance of +/−0.1 mm.

(98) Based on these hypotheses, and with a ball 7 with a diameter equal to 2.4 mm and the selected spring 8 dimensions, the height L.sub.3 of the housing 43 for the spring 8 that is to be provided in the bored part of the male part 8 must be included in a range of 3.8 mm and 4.3 mm.

(99) The operating pressure of the ball 7 with its spring 8, i.e. the pressure that allows it to be lifted from its seat 54 in order to allow degassing of the inside of the accumulator, therefore is between a minimum value P1 of approximately 2.3 bar and a maximum value P2 of approximately 3.1 bar.

(100) The feed-through 1 integrating the ball 7, spring 8 gas relief device according to the invention can be produced on a cover 3 of a Li-ion accumulator casing 10 both with a cylindrical geometry and with a prismatic geometry. In these various configurations, the terminal 1 according to the invention is negative, for example, with the positive terminal 2 also being able to be produced on the cover 3 directly by soldering, for example, as shown in FIGS. 1 and 2.

(101) Even though it has not been previously specified, provision is made for the surface of the base of the female part 5, i.e. the section that defines its abutment surface, to be sufficient to electrically connect a connector inside the housing that is electrically connected to the electrochemical assembly that is commonly called spool, formed by one or more electrochemical cells. The electric connection between the internal connector and the base of the female part can be produced by soldering.

(102) Other advantages and improvements may be provided without necessarily departing from the scope of the invention.

(103) The invention is not limited to the aforementioned embodiments, in particular features of embodiments shown within non-illustrated variations may be combined together.

(104) The term “comprising a/one” must be understood as being synonymous with “comprising at least one”, unless otherwise specified.