Patent Application
20190341201
The present invention relates to the field of metal-ion electrochemical generators, which function according to the principle of insertion or deinsertion, or in other words intercalation-deintercalation, of metal ions in at least one electrode.
It relates more particularly to a metal-ion electrochemical storage battery comprising at least one electrochemical cell consisting of an anode and a cathode on either side of an electrolyte-impregnated separator, two current collectors, one of which is connected to the anode and the other to the cathode, and a case of a shape that is elongated along a longitudinal axis (X), the case being arranged to house the electrochemical cell hermetically while being traversed by a portion of the current collectors forming the output terminals, also called poles.
The separator may consist of one or more films.
The case may comprise a cover and a container, or may comprise a cover, a base and a lateral envelope joined both to the bottom and to the cover.
The present invention aims to improve the design of a part of the electrical connection between at least one electrochemical cell of the storage battery and its output terminals integrated with its case.
It aims more particularly to improve the method of compacting the lateral bands of electrodes lacking active insertion material, onto which, once compacted, a current collector in the form of a plate is welded.
Although described with reference to a lithium-ion storage battery, the invention applies to any metal-ion electrochemical storage battery, i.e. also sodium-ion, magnesium-ion, aluminum-ion, etc.
The invention also applies to the production of an electrochemical bundle of a supercapacitor and the connection to its case.
As illustrated schematically in
The architecture of the conventional lithium-ion batteries is an architecture that may be described as monopolar, as there is a single electrochemical cell comprising an anode, a cathode and an electrolyte. Several types of geometry of monopolar architecture are known:
The electrolyte constituent may be in the form of solid, liquid or gel. In this last-mentioned form, the constituent may comprise a separator made of polymer or of microporous composite impregnated with organic electrolyte(s) or of the ionic liquid type which allows movement of the lithium ion from the cathode to the anode for charging and vice versa for discharging, which generates the current. The electrolyte is generally a mixture of organic solvents, for example of carbonates in which a lithium salt, typically LiPF6, is added.
The positive electrode or cathode consists of lithium cation insertion materials, which are generally composite, such as lithiated iron phosphate LiFePO4, lithiated cobalt oxide LiCoO2, lithiated manganese oxide, optionally substituted, LiMn2O4 or a material based on LiNixMnyCozO2 with x+y+z=1, such as LiNi0.33Mn0.33CO0.33O2, or a material based on LiNixCoyAlzO2 with x+y+z=1, LiMn2O4, LiNiMnCoO2 or lithiated nickel cobalt aluminum oxide LiNiCoAlO2.
The negative electrode or anode very often consists of carbon, graphite or is made of Li4TiO5O12 (titanate material), optionally also based on silicon or based on lithium, or based on tin and alloys thereof or of a composite formed on the basis of silicon. This negative electrode, like the positive electrode, may also contain electron conducting additives as well as polymer additives which endow it with mechanical properties and electrochemical performance suitable for the lithium-ion battery application or for its method of implementation.
The anode and the cathode made of lithium insertion material may be deposited continuously by a usual technique in the form of an active layer on a metal sheet or strip constituting a current collector.
The current collector connected to the positive electrode is generally made of aluminum.
The current collector connected to the negative electrode is generally made of copper, nickel-plated copper or aluminum.
Conventionally, a lithium-ion storage battery or accumulator uses a pair of materials at the anode and at the cathode that allow it to operate at a high voltage level, typically between 3 and 4.1 V.
A lithium-ion storage battery or accumulator comprises a rigid container or case when the intended applications are restrictive, where a long service life is required, with for example much higher pressures to be withstood and a more stringent required level of hermeticity, typically below 10−6 mbar·l/s of helium, or in environments with high stresses such as the aeronautical or space sector. The main advantage of rigid containers is thus their high hermeticity that is maintained over time because the cases are closed by welding, generally by laser welding.
The geometry of most of the rigid cases for containers of Li-ion storage batteries is cylindrical, as most of the electrochemical cells of storage batteries are wound by winding according to a cylindrical geometry. Prismatic shapes of cases have also already been produced.
One type of rigid case of cylindrical shape, usually made for a high-capacity Li-ion storage battery with a service life longer than 10 years, is illustrated in
The case 6 with a longitudinal axis X comprises a cylindrical lateral envelope 7, a base 8 at one end, and a cover 9 at the other end. The cover 9 supports the poles or output terminals 40, 50 for the current. One of the output terminals (poles), for example the positive terminal 40, is welded on 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) which insulates the negative terminal 50 electrically from the cover.
Here, and in the context of the invention, “uncoated band” or “edge” means a lateral portion of a metal sheet, also called strips, forming a current collector, which is not covered with an insertion material for metal ions, such as lithium in the case of a lithium-ion battery.
The aim of manufacturers of batteries is to increase the autonomy of a cell making up the battery or their ability to function under high power regimes while improving their service life, i.e. their possible number of cycles, their lightness and the costs of production of these components.
The routes for improving Li-ion batteries mainly relate to the nature of the materials and the methods of production of the electrochemical cell components.
Other possible routes for improvements, less numerous, relate to the battery cases and the methods and means for electrical connection of an electrochemical bundle to the two output terminals, also called poles of different polarity of the battery.
Up to now, when we want to make an electrical connection between the electrochemical bundle and the output terminals of a lithium-ion battery of cylindrical or prismatic geometry, which is of high quality, the following design rules are observed as far as possible:
In the literature describing solutions for producing an electrochemical bundle of a battery of cylindrical or prismatic shape and electrical connection thereof to the output terminals integrated with its case, we may mention the following documents.
Patent FR 2094491 discloses an alkaline battery in which the electrical connection between the wound electrochemical cell and output terminals is obtained by cutting into the edges of the electrodes with regularly spaced slits, and then radial crimping of these slit edges from the exterior to the interior in the form of superposed scales in order to form a substantially flat base on which a current collector is finally welded, consisting if applicable of the cover of the case.
Patent application EP 1102337 discloses a lithium-ion battery in which the electrical connection between the wound electrochemical cell and output terminals is obtained by a single pressing of each end of the electrode strips of the wound cell, along the winding axis, by means of a pressing mandrel and then by laser welding of each end of the electrode strips to a terminal current collector consisting of foil in the form of a disk and a connecting tab itself laser-welded afterwards to the cover of the case at one end, and to the base of the case at the other end. Ribs are made, each on a diameter of the disk, and they themselves are pressed prior to welding against the ends of pressed electrode strips.
Patent application EP 1596449 describes a lithium-ion battery in which the electrical connection between the wound electrochemical cell and output terminals is obtained firstly by multiple pressing of each lateral end delimited by the bands not covered with electrodes of the wound cell, by means of a pressing mandrel with an outside diameter between 15 and 20 mm. The pressing mandrel moves over a very short course alternately from the exterior to the interior of the cell parallel to the winding axis, sweeping the entire lateral surface of the bands not covered with electrodes to produce entanglement between the latter by forming a dense, flat base on which a terminal current collector is welded by laser or by transparency consisting of a foil in the form of a flat connecting band in its turn welded by laser or by transparency afterwards to an output terminal integrated with the cover at one lateral end and to the base of the case at the other lateral end.
Patent EP1223592B1, which relates more to the field of supercapacitors, describes a technique for electrical connection of current collectors to the electrochemical bundle by directly supporting the collectors in the form of a plate on the edges.
U.S. Pat. No. 6,631,074B2, which also relates to supercapacitors, describes a solution that consists of spraying an electrically conductive substance, such as aluminum, on the surfaces at each end of the electrochemical bundle, so as to obtain, for each end, continuity of electrical contact surface between all the strips at the level of the electrode edges, each surface then being welded by laser welding to the current collector.
On analyzing all the known solutions for producing an electrochemical bundle of a lithium battery and of electrical connection thereof to the output terminals of the battery, as described above, the inventors came to the conclusion that the latter could be further perfected in many aspects.
Firstly, the weight and volume of the lateral bands not covered with electrodes (edges) necessary for electrical connection to the current collectors according to the prior art are not necessarily optimized, which ultimately means that the weight and volume of the battery have also not yet been optimized.
Next, the inventors found that in fact the edges of one and the same lateral end were not necessarily connected together electrically, in particular the portions of these edges located in the most peripheral zone of the bundle. This means a reduced real specific capacity of the electrochemical bundle, which may be detrimental in particular for the high power applications for the battery.
Furthermore, the step of filling the electrolyte in an electrochemical bundle of a lithium battery may prove relatively long and difficult because the current collectors according to the prior art, being welded on the edges of the electrochemical bundle of a battery, constitute an appreciable obstacle to passage of the electrolyte.
Finally, regarding the techniques with axial compacting of the electrode strips at the level of their edges, several specific drawbacks may arise.
Thus, the mechanical stress of compression to be applied during compacting to obtain a layer of dense folded edges must be high. Now, at present, all the metal strips of the electrodes of one and the same polarity have the same mechanical durability over the entire width of the bundle. This may lead to a difference in folding between the strips, in particular with greater folding at the level of the core of the bundle, which may even result in short-circuits.
Such a configuration is shown in
Moreover, when the layer of compacted edge is insufficient, the operation of welding a metallic part forming a current collector or of different wound portions of one and the same strip may produce strong heating, which may be propagated as far as the separator, which then melts, which also causes short-circuits.
There is therefore a need to improve the production of an electrochemical bundle of a lithium battery, and more generally of a metal-ion battery or of a supercapacitor and of electrical connection thereof to the output terminals, notably with a view to better control of the axial compacting of the electrode edges while uniformly densifying it over the full width of the electrochemical bundle.
The aim of the invention is to meet this need at least partly.
For this purpose, in one of its aspects the invention relates to an electrode for an electrochemical bundle of a metal-ion battery or of a supercapacitor, comprising a substrate formed of a metal strip that supports, in its central portion, an active metal-ion insertion material, whereas its lateral band, the so-called edge, lacks active insertion material, the lateral band comprising an end zone where the properties of its metallic material and/or its geometry is (are) modified relative to the rest of the strip in the edge and in the central portion, so as to cause localized plastic buckling on the end zone when a predetermined compressive stress (E) is applied on said end zone, the central portion not deforming under the predetermined compressive stress.
“Plastic buckling” is to be understood in its usual sense, i.e. buckling caused by compressive stress, leading to irreversible mechanical deformation.
According to an advantageous embodiment, the lateral band comprises an intermediate zone, between the central portion and the end zone, in which the properties of its metallic material and/or its geometry are selected in such a way that said intermediate zone does not deform under the predetermined compressive stress. This intermediate zone makes production safer, by mechanically protecting the core of the electrochemical bundle comprising the active insertion materials, during the steps of compacting and welding of the current collector to the compacted end zone.
To modify the material properties in the zones to be deformed so as to obtain a gradient of mechanical properties over the height of the electrochemical bundle, according to another variant embodiment, the Young's modulus and/or the elastic limit of the end zone is (are) modified by applying one or more thermomechanical treatments. The strip may also have a gradient of metallurgical state between the end zone and the intermediate zone.
Thus, it is possible to modify the microstructure (grain size, work-hardening, appearance of precipitates) of the end zone by various thermomechanical treatments (control of quenching rates, choice of tempering temperature), which generates a gradient of microstructure between the intermediate zone and the end zone.
It is preferable to use usual heat treatments (quenching, tempering, annealing), which lead to a change in mechanical properties in the existing crystalline structure, rather than chemical treatments, which could cause contamination. Reference may be made to publication [1] for these usual treatments.
The geometry of the end zone may be modified independently.
Thus, according to another variant, the thickness of the strip in the end zone may be less than that of the rest of the strip in the edge and in the central portion.
For localized thickness reduction, localized rolling of the metal strip may be carried out prior to coating thereof in its central portion with the active insertion material.
According to yet another variant embodiment, the intermediate zone may comprise stiffeners distributed uniformly along its length, i.e. over the height of the electrochemical bundle.
To weaken the strip mechanically, it may advantageously be pierced with holes or slits or cavities uniformly distributed in the end zone.
The strip may also advantageously be provided with at least one continuous groove along the length of the end zone. Thus, the modified geometry of the end zone with structural defects (cavities, continuous groove) or thickness reductions (holes, slits) will promote the development of instability of deformation of said zone during axial compacting of the bundle at this end.
The width of the end zone, once the compressive stress is applied, is preferably between 0.5 and 4 mm.
Preferably, the strip may have a thickness between 5 and 20 μm in the end zone and a thickness between 10 and 20 μm in the central portion.
The electrode strip may be of aluminum or of copper.
In another aspect, and according to a first alternative, the invention also relates to a method for producing an electrochemical bundle (F) of a metal-ion battery (A) such as a lithium-ion battery, or of a supercapacitor, with a view to electrical connection thereof to the output terminals of the battery, comprising the following steps:
a/ supplying an electrochemical bundle (F) comprising at least one electrochemical cell (C) consisting of a cathode as described above and an anode as described above, on either side of a separator suitable for being impregnated with an electrolyte, the bundle having an elongated shape along a longitudinal axis X1, with the lateral band of the anode at one lateral end, and the lateral band of the cathode at the other lateral end;
b/ axial compacting along axis X1 of at least one of the lateral bands of the electrochemical bundle; axial compacting being carried out once or twice so as to obtain, on at least one lateral end of the bundle, a compacted end zone forming a substantially flat, continuous base, intended to be welded to a current collector.
According to a second alternative, the following steps may be carried out:
a′/ supplying an electrochemical bundle (F) comprising at least one electrochemical cell (C) consisting of a cathode and an anode on either side of a separator suitable for being impregnated with an electrolyte, the cathode and the anode each comprising a substrate, formed of a metal strip that supports, in its central portion, an active metal-ion insertion material, whereas its lateral band, called edge, lacks active insertion material and the properties of its metallic material and its geometry are identical to the rest of the strip in the edge and in the central portion, the bundle having an elongated shape along a longitudinal axis X1, with the lateral band of the anode at one lateral end and the lateral band or bands of the cathode at the other lateral end;
b′/ axial compacting along axis X1 of at least one of the lateral bands of the electrochemical bundle with, beforehand or simultaneously, modification of the temperature of an end zone of said lateral band, the axial compacting being carried out once or twice so as to obtain, on at least one lateral end of the bundle, a compacted end zone forming a substantially flat, continuous base, intended to be welded to a current collector.
According to a third alternative, the following steps may be carried out:
a″/ supplying an electrochemical bundle (F) comprising at least one electrochemical cell (C) consisting of a cathode and an anode on either side of a separator suitable for being impregnated with an electrolyte, the cathode and the anode each comprising a substrate, formed of a metal strip that supports, in its central portion, an active metal-ion insertion material, whereas its lateral band, called edge, lacks active insertion material and the properties of its metallic material and its geometry are identical to the rest of the strip in the edge and in the central portion, the bundle having an elongated shape along a longitudinal axis X1, with the lateral band of the anode at one lateral end and the lateral band or bands of the cathode at the other lateral end;
b″/ axial compacting along axis X1 of at least one of the lateral bands of the electrochemical bundle with, simultaneously, clamping radially to axis X1, of an intermediate zone of said lateral band, leaving one end zone free radially, the axial compacting being carried out once or twice so as to obtain, on at least one lateral end of the bundle, a compacted end zone forming a substantially flat, continuous base, intended to be welded to a current collector.
Thus, according to the second and third alternatives, the end zone modified relative to the rest of the electrode is so during the compacting process.
In other words, here it is possible to start from ordinary electrodes and modify the conditions (localized heating of the end of the bundle, localized stiffening of the intermediate zone of the electrodes by radial clamping) of the process to modify the mechanical behavior of the end zone during the compression due to the axial compacting.
The height of the compacted end zone on a lateral end is preferably less than 4 mm, preferably between 0.5 and 2.5 mm.
According to an advantageous embodiment, the electrochemical bundle consists of a single electrochemical cell wound on itself by winding.
According to this embodiment, the gap between the anode strip and the cathode strip, considered in their central portion after winding, is preferably between 100 and 500 μm.
In another of its aspects, the invention also relates to a method for producing an electrical connection portion between an electrochemical bundle (F) of a metal-ion battery (A) and one of the output terminals of the battery, comprising the following steps:
The invention finally relates to a metal-ion battery or accumulator, such as a lithium (Li-ion) battery or a supercapacitor comprising a case comprising:
Preferably, for a lithium-ion battery or accumulator:
The invention that has just been described offers many advantages:
Other advantages and features of the invention will become clearer on reading the detailed description of embodiment examples of the invention, provided for purposes of illustration, and nonlimiting, referring to the following figures, where:
For clarity, the same references denoting the same elements of a lithium-ion battery according to the prior art and according to the invention are used for all
It should be noted that the various elements according to the invention are only shown for the sake of clarity and they are not to scale.
It should also be noted that the terms “length” and “lateral” referring to an electrode relate to when it is flat, before winding.
The terms “height” and “lateral” referring to the electrochemical bundle relate to the vertical configuration of its lateral ends respectively at the top and at the bottom.
To improve the electrical connection between an electrochemical bundle of a lithium-ion battery and its output terminals, the inventors propose a new design of electrode and a new method for producing the electrochemical bundle starting from this electrode.
The metal strips of square or rectangular section supporting the active insertion materials of electrodes may have a thickness between 5 and 50 μm. For an anode strip 3, it may advantageously be a strip of copper with a thickness of the order of 12 μm. For a cathode strip 2, it may advantageously be a strip of aluminum with a thickness of the order of 20 μm.
According to the invention, a positive electrode 2 or a negative electrode 3 comprises a lateral metal band with an end zone 21 or 31 for which the properties of its metallic strip material and/or its geometry is (are) modified relative to the rest of the strip, i.e. in an intermediate zone 23 or 33 of the edge 20 or 30 and in the central portion 22 or 32.
Thus, owing to this modified end zone 21 or 31, as described hereunder, in the operation of axial compacting of the bundle on one and/or other of its lateral ends, i.e. compacting applied on said end zone, there will be inelastic buckling localized on just the end zone.
The intermediate zone 23 or 33 provides security of mechanical protection during compacting as it will not deform.
Conversely, the central portion and if applicable an intermediate safety zone in the band devoid of active insertion material does not deform during compacting.
In this example, the strip has the same thickness over its whole area. However, the end zone 21 has undergone heat treatment, such as annealing, differentiated with respect to the intermediate zone 23 and the central portion 22 intended to be covered with the lithium insertion material. Typically, after treatment, the end zone 21 may have a breaking strength coefficient Rm lower than that of the rest of the surface (zone 23, central portion 22).
Also typically, after an annealing treatment, the end zone 21 may have a metallurgical state, slightly hardened, of type 0, H12, or H22 and H24 for aluminum, whereas the rest of the surface (zone 23, central portion 22) retains a work-hardened state, of type H14 to H18 for aluminum.
The same procedure is followed for producing an end zone 31 on a metal strip 3S of anode 3.
This variant according to
The various steps of this method of production according to the invention will now be described, referring to
Step a/:
The anode 3, the cathode 2 and at least one separator film 4 of the electrochemical cell C are wound by winding around a support (not shown).
The bundle is therefore of cylindrical shape elongated along a longitudinal axis X1, with, at one 10 of its lateral ends, a band 30 of uncoated anode 3 with an end zone 31 modified relative to the intermediate zone 33 and, at the other 11 of its lateral ends, a band 20 of uncoated cathode 2 with an end zone 31 modified relative to the intermediate zone 33.
Step b/:
Axial compacting is then carried out along the axis X1 of bands 20, 30 of the electrochemical bundle, on the entire surface of the lateral ends 10, 11.
The axial compacting consists of compression with a flat or structured tool with a bearing surface approximately equal to the surface of each of the lateral ends of the bands 20 or 30.
When the geometry required for the battery is cylindrical, the tool and the electrochemical bundle are arranged coaxially during the axial compacting.
Axial compacting is carried out once or more than once. It may consist of compression in one or more reciprocating relative movements, i.e. at least one movement to and fro along axis X1 of the bundle, until either a desired bundle dimension along X1, or a predetermined value of maximum compressive stress, is reached.
During application of this compressive stress, the end zones 21 and 31 undergo inelastic buckling and bend, whereas the intermediate zones 23 and 33 and the central portions 22 and 32 covered with the insertion materials do not deform.
A substantially flat base is thus obtained on the compacted portion of surface 20T, 30T, not bent down, of each lateral end.
Then, at one of the lateral ends 11 of the bundle, the base formed by the compacted portion 20T of the cathode (positive edges) is welded to a usual current collector 14 in the form of a full disk, itself intended to be welded afterwards to the base 8 of the battery case 6 (
In the same way, at the other lateral end 10 of the bundle, the base formed by the compacted portion 30T of the anode (negative edges) is welded to a portion of a usual current collector 13 in the form of a full disk pierced at its center and a tab 130 projecting laterally from the disk 13 (
The definitive production of the battery is finalized in the usual way.
Thus, although not shown, the bundle with the collector 13 is introduced into a rigid aluminum container forming only the lateral envelope 7 of the case 6. In particular, during this step it is necessary to ensure that the tab 130 does not hamper introduction. For this purpose, the latter is advantageously folded upwards.
The collector 14 is welded to the base 8 of the case 6.
The collector 13 is welded to a negative pole 50 forming a lead-in of a cover 9 of case 6.
Then the cover 9 is welded to the rigid metal container 7.
This is followed by a step of filling the case 6 with an electrolyte, through a through-hole (not shown) made in the cover 9.
Production of the Li-ion battery according to the invention ends with sealing the filling hole.
Other variants and improvements may be made while remaining within the scope of the invention.
Finally, although the case 6 in the embodiments illustrated that have just been presented in detail is made of aluminum, it may also be made of steel, or of nickel-plated steel. In a variant of this kind, a case made of steel or of nickel-plated steel constitutes the negative pole, with the lead-in 9 then constituting the positive pole.
The invention is not limited to the examples that have just been described; notably, features of the examples illustrated may be combined in variants that are not illustrated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1655541 | Jun 2016 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/063910 | 6/8/2017 | WO | 00 |
