Electrochemical accumulator with housing and output terminal made of aluminium alloy

Abstract

An electrochemical accumulator including: at least one electrochemical cell made of at least one cathode and one anode and, on either side of an electrolyte, two current collectors, one of which is connected to the anode and the other to the cathode; a housing made of aluminium alloy arranged such as to sealingly contain the electrochemical cell(s); two current-output terminals, one of which is welded to a wall of the housing, the output terminal welded to the housing being made of an aluminium alloy having a magnesium content (Mg) that is no lower than 0.01% and no higher than 4%, and a copper content that is no lower than 0.05% and no higher than 0.3%, the aluminium alloy of the output terminal welded to the housing having a metallurgical state which grants same a breaking strength (Rm) of no less than 60 MPa.

Claims

1. An electrochemical accumulator including: at least one electrochemical cell consisting of at least one cathode and one anode and on either side of an electrolyte, two current collectors one of which is connected to the anode and the other to the cathode, a casing made of aluminum alloy, arranged to contain the electrochemical cell(s) with seal tightness, two current output terminals, one of which is welded to a wall of the casing, the output terminal welded to the casing being made of an aluminum-based alloy comprising a magnesium (Mg) content higher than or equal to 0.01% and lower than or equal to 4%, and a copper content higher than or equal to 0.05% and lower than or equal to 0.3%, the aluminum alloy of the output terminal welded to the casing having a metallurgical state providing it with a yield strength (Rm) higher than or equal to 160 MPa.

2. The accumulator as claimed in claim 1, the aluminum alloy of the output terminal welded to the casing being a 3003 grade with an H.sub.18 temper.

3. The accumulator as claimed in claim 2, constituting an Li-ion accumulator.

4. The accumulator as claimed in claim 1, the aluminum alloy of the output terminal welded to the casing being a 5754 grade.

5. The accumulator as claimed in claim 1, the aluminum alloy of the output terminal welded to the casing being a 6060 grade.

6. The accumulator as claimed in claim 1, the aluminum alloy of the output terminal welded to the casing being the positive terminal.

7. The accumulator as claimed in claim 1, the aluminum alloy of the output terminal welded to the casing being covered with a layer of nickel (Ni).

8. The accumulator as claimed in claim 7, the layer of Ni having a thickness comprised between 2 and 20 microns.

9. The accumulator as claimed in claim 1, the other output terminal being fastened by crimping or screwing through a wall of the casing.

10. The accumulator as claimed in claim 1, the other output terminal being made of copper (Cu) covered with a layer of Ni or made of a CuNibased alloy or an aluminum-based alloy.

11. A battery, referred to as a battery pack, including a plurality of accumulators, wherein said accumulators are as defined in claim 1, and said accumulators are connected together in electrical parallel or series, at least the positive output terminals of said accumulators being connected pairwise by means of a metal strip, referred to as a bus bar, fixed by screwing to each of the terminals.

12. The battery as claimed in claim 11, the screwing torque applied to each of the output terminals being higher than 4 N.m.

13. A process for producing an accumulator wherein said accumulator is as defined in claim 1, including the step i/ consisting in welding the output terminal made of aluminum alloy to the cover or to the bottom of the casing.

14. The process as claimed in claim 13, the step i/ being carried out by means of a laser at the base of the terminal the inclined profile of which, with respect to the axis X1 along which the output terminal extends, is adapted to prevent the reflection at 180 of a beam coming from the laser.

Description

DETAILED DESCRIPTION

(1) Other advantages and features will become more clearly apparent on reading the detailed description that is given by way of illustration and with reference to the following figures, in which:

(2) FIG. 1 is an exploded perspective schematic view showing the various elements of a lithium-ion accumulator;

(3) FIG. 2 is a front view showing a lithium-ion accumulator with its flexible packaging according to the prior art;

(4) FIG. 3 is a perspective view of a lithium-ion accumulator according to the prior art with its rigid packaging consisting of a casing of cylindrical shape;

(5) FIG. 4 is a top view of the casing cover of a lithium-ion accumulator with a positive output terminal according to the invention;

(6) FIG. 4A is a cross-sectional detailed view of a positive output terminal according to the invention showing the step of its welding to the casing cover of an Li-ion accumulator;

(7) FIG. 4B is a perspective photographic reproduction showing a positive output terminal according to the invention such as it is welded to the casing cover of a lithium-ion accumulator;

(8) FIGS. 5 and 5A are perspective and cross-sectional photographic reproductions, respectively, showing a positive output terminal according to the invention, made of an alloy of grade 5754 aluminum, such as it is welded to the casing cover of a lithium-ion accumulator;

(9) FIGS. 6 and 6A are perspective and cross-sectional photographic reproductions, respectively, showing a positive output terminal according to the invention, made of an alloy of grade 6060 aluminum, such as it is welded to the casing cover of a lithium-ion accumulator;

(10) FIG. 7 is a schematic representation of a testing device intended to measure the electrical contact resistance between a positive output terminal of an Li-ion accumulator and a copper strip representative of a bus bar;

(11) FIG. 8 illustrates the curves of the results of tests carried out with the device in FIG. 7 both on an output terminal made of aluminum alloy according to the prior art and on output terminals according to the invention;

(12) FIGS. 9A and 9B are perspective views of a lithium-ion accumulator with a positive output terminal according to the invention and a negative terminal, which terminals are both welded to a cover of a casing of cylindrical and prismatic shape, respectively;

(13) FIGS. 10A to 10C are side views of a lithium-ion accumulator with a casing of cylindrical shape illustrating various variants of arrangement of a positive output terminal according to the invention welded to the casing bottom and a negative terminal welded to the casing cover;

(14) FIGS. 11A to 11C are similar to FIGS. 10A to 10C but with a casing of prismatic shape;

(15) FIG. 12 is a schematic view showing a battery pack of two modules in series of Li-ion accumulators according to the invention, each module consisting of four rows of accumulators in parallel, each row consisting of six accumulators in series.

(16) For the sake of clarity, the same references have been used to designate the same elements of a lithium-ion accumulator according to the prior art and according to the invention in all of FIGS. 1 to 12.

(17) It will be noted that the various elements according to the invention are shown merely for the sake of clarity and that they are not to scale.

(18) Lastly it will be noted that here and throughout the present application, the terms lower, upper, vertical, raised, lowered, below and above are to be understood with reference to an Li-ion accumulator in vertical position with its cover on the top end of the casing.

(19) FIGS. 1 to 3 have already been discussed in detail in the preamble. They are therefore not described below.

(20) A lithium-ion accumulator A according to the invention has been shown in FIG. 4.

(21) The accumulator A firstly includes at least one electrochemical cell C (not shown) consisting of at least one anode and one cathode on either side of an electrolyte impregnated in a separator.

(22) The anode and cathode are made of lithium-insertion material and may be deposited, using a conventional technique, in the form of an active layer on a metal sheet forming a current collector. By way of example, the anode is made of Li.sub.4Ti.sub.5O.sub.12, the cathode of LiFePO.sub.4 and the current-collector sheets of aluminum.

(23) The Li-ion accumulator includes two current collectors one of which is connected to the anode and the other to the cathode of each cell C.

(24) By way of rigid packaging, the accumulator includes a casing 6 of a shape that is elongate along a longitudinal axis (X).

(25) The casing 6 includes a cylindrical lateral jacket 7 and a bottom 8 forming a container, and a cover 9 assembled by crimping and welding to the container at the opposite end to the bottom 8.

(26) The cover 9 bears the terminals or poles 40, 50 through which the current is output.

(27) One of the output terminals (poles), for example the positive terminal 40, is welded to the cover 9 whereas the other output terminal, for example the negative terminal 50, passes through the cover 9 with interposition of a seal (not shown) that electrically insulates the negative terminal 50 from the cover.

(28) The casing 6, i.e. the container formed by the jacket 7 and the bottom 8, and the cover 9, are all made of an alloy of 1050 aluminum.

(29) According to the invention, the positive terminal 40 is made of an aluminum alloy comprising a magnesium (Mg) content lower than or equal to 4%, and a copper content lower than or equal to 0.3%, the aluminum alloy having a metallurgical state providing it with a yield strength (Rm) higher than or equal to 160 MPa.

(30) With such values, as explained below, the inventors have been able to prove that it is possible to produce a reliable electrical and mechanical connection with a metal interconnecting strip screwed to the positive terminal 40.

(31) To weld the positive terminal 40 made of aluminum alloy according to the invention to the cover 9 of the casing 6, laser welding was performed as shown in FIG. 4A.

(32) The positive terminal 40 is placed in abutment against the planar face of the cover 9 beforehand.

(33) The beam of a laser L is then directed toward the base 41 of the terminal 40 as symbolized by the downward arrow in FIG. 4A.

(34) As illustrated, the profile of the base 41, which profile is inclined with respect to the axis X1 along which the output terminal extends 40, is adapted to prevent the reflection 180 of a beam coming from the laser. Thus, reflection of the laser beam toward the lens of its optical system is prevented. The entire periphery (360) of the base 41 is laser welded.

(35) The terminal 40 is thus welded via its base 41 along the weld line Ls to the cover 9, as illustrated in FIG. 4B.

(36) FIGS. 5 and 5A illustrate the welding of a positive terminal 40 made of an alloy of grade 5754 aluminum. The penetration depth of the weld was measured to be 0.286 mm and the cross section of flow of the current is equal to 22.4 mm.sup.2.

(37) FIGS. 6 and 6A illustrate welding with an alloy of 6060 grade aluminum. The penetration depth of the weld was measured to be 0.169 mm and the cross section of flow of the current is equal to 17.1 mm.sup.2.

(38) Tests were carried out to characterize the clamping torque of threads tapped in positive terminals 40 according to invention, which terminals were each welded to a casing 6 made of 1050 grade aluminum.

(39) The results are given in the table below for an alloy of grade 5754 aluminum and one of grade 6060.

(40) TABLE-US-00001 Value of the Al alloy positive Clamping screw Tap length clamping torque in terminal 40 diameter in mm N .Math. m 5754 M5 6 6.14 6 8.01 6 8.08 8 8.3 8 9.82 8 higher than 9.3 10 higher than 11.4 10 higher than 10 10 higher than 10 6060 6 higher than 3.6 6 7.5 6 7.24 8 10.4 8 higher than 10 8 higher than 10 10 higher than 10.3 10 higher than 10 10 higher than 10

(41) These results show that it is possible to envision clamping torques of about or higher than 4 N.Math.m with a conventional M5 screw.

(42) Tests for characterizing the contact resistance between the surface of a positive terminal 40 and that of a strip made of nickel-coated copper representative of a bus bar, as a function of the nature of the aluminum material of the positive terminal and of the clamping torque obtained by screwing using an M5 screw, were also carried out.

(43) The testing device used is shown in FIG. 7: a strip 10 made of nickel-coated copper is clamped by screwing to the positive terminal 40 welded to a cover 9 of an Li-ion accumulator. It is clarified here that the clamping screw used is an M5*8 BHC screw, a washer of trade name Onduflex and a Z5 steel washer being interposed between the screw and the positive terminal 40. The same screw washers are used to clamp an electrical supply wire to the negative terminal 50.

(44) Another electrical supply wire is fastened to the strip 10.

(45) To carry out the tests, the strip 10 was supplied electrically using a supply 21 delivering a high current of 200 A, then the electrical potential between the strip 10 and the positive terminal 40 was measured using a voltmeter 20, this allowing by calculation the contact resistance between the two parts to be deduced therefrom.

(46) The results of the test are illustrated in the form of curves in FIG. 8 for positive terminals 40 made of 5754 and 6060 alloys according to the invention and, by way of comparison, for a terminal 40 made of 1050 alloy.

(47) From these characterization tests it is possible to conclude that it is clearly possible to decrease the contact resistance between a copper strip 10 and the surface of a positive terminal 40 made of an alloy of 5754 or 6060 aluminum with clamping torques higher than 5 N.Math.m.

(48) Furthermore it will be noted that, with a positive terminal 40 made of an alloy of 1050 Al, it is not possible under the same test conditions to carry out clamping with a clamping torque higher than 5 N.Math.m without irreversible degradation of the threads of its tap.

(49) The assembly by laser welding of the base 41 of inclined profile of the output terminal 40 to a wall of the housing is simple to implement and allows the various following arrangements to be envisioned: positive terminal 40 made of aluminum alloy according to the invention and negative terminal 50 both supported by the cover 9 of a casing 6 of cylindrical shape (FIG. 9A) or prismatic shape (FIG. 9B); positive terminal 40 made of aluminum alloy according to the invention supported by the bottom 8 of a casing 6 and negative terminal 50 supported by the cover 9 of a casing 6 of cylindrical shape, with the negative terminal 50 shifted laterally relative to the axis X of the casing 6 and the positive terminal on the axis X of the casing 6 (FIG. 10A), or both positive and negative terminals 40, 50 on the axis X of the casing (FIG. 10B), or both positive and negative terminals 40, 50 shifted laterally from the axis X of the casing (FIG. 10C); positive terminal 40 made of aluminum alloy according to the invention supported by the bottom 8 of a casing 6 and negative terminal 50 supported by the cover 9 of a casing 6 of prismatic shape, with the negative terminal 50 shifted laterally relative to the axis X of the casing 6 and the positive terminal on the axis X of the casing 6 (FIG. 11A), or both positive and negative terminals 40, 50 on the axis X of the casing (FIG. 11B), or both positive and negative terminals 40, 50 shifted laterally from the axis X of the casing (FIG. 11C).

(50) The invention that was just described makes it possible to envision the production of battery packs including a plurality of Li-ion accumulators that are connected together in electrical series or parallel and at least the positive output terminals 40 of which are connected pairwise by means of a copper bus bar 10, 11, 12 fastened by screwing to each of the terminals with a screwing torque applied to each of the output terminals higher than 4 N.Math.m.

(51) Such a battery pack is shown in FIG. 12: it consists of two modules M1, M2 of identical Li-ion accumulators A that are connected together in series, each module M1, M2 consisting of four rows of accumulators connected in parallel, each row consisting of Li-ion accumulators that are in number equal to six.

(52) As shown, the electrical and mechanical connection between two Li-ion accumulators of a given row is made by screwing bus bars 10 made of Cu each connecting a positive terminal 40 and a negative terminal 50. The connection between the two modules M1, M2 is ensured by a bus bar 11 made of Cu and the connection between two rows of accumulators in parallel within a given module M1 or M2 is ensured by a bus bar 12 made of Cu.

(53) The invention is not limited to the examples described above and it is in particular possible to combine features of the illustrated examples in unillustrated variants.

(54) Thus, although in the illustrated examples the terminal (pole) according to the invention was the positive terminal 40 of the battery, it may also be a battery pack terminal. The output terminal according to the invention may also not be connected to an electrochemical cell. It may instead be connected to components of the battery or to systems connected to the battery.