FR3059159A1 - ELECTRODE FOR ELECTROCHEMICAL BEAM OF A METAL-ION BATTERY WITH HIGH ENERGY DENSITY, CYLINDRICAL OR PRISMATIC ACCUMULATOR - Google Patents

Abstract

The present invention relates to an electrode, intended to be wound by winding around an axis or core to form a part of an electrochemical bundle of a metal-ion accumulator, the electrode comprising a substrate formed of a metal strip comprising at least one lateral band, devoid of active insertion material, and a central portion supporting, on at least one of its main faces, a layer of active material, which has an increasing thickness along the length of the central portion which constitutes the length of winding around the axis or core, the lowest value of the thickness being at the beginning of the winding of the electrode, and / or which has a thickness gradient over the height of the central portion, the height being the dimension considered parallel to the axis or core, the gradient being such that the thickness decreases from each lateral end zone of the central portion to a zone median in which the thickness is substantially constant.

Description

Holder (s): COMMISSIONER OF ATOMIC ENERGY AND ALTERNATIVE ENERGIES Public establishment.

Extension request (s)

Agent (s): NONY CABINET.

L— 3S

FR 3 059 159 - A1 (34) ELECTRODE FOR ELECTROCHEMICAL BEAM OF A METAL-ION ACCUMULATOR WITH HIGH ENERGY DENSITY, ASSOCIATED CYLINDRICAL OR PRISMATIC ACCUMULATOR.

©) The present invention relates to an electrode, intended to be wound by winding around an axis or core to form part of an electrochemical beam of a metal-ion accumulator, the electrode comprising a substrate formed of a strip metallic comprising at least one side strip, devoid of active insertion material, and a central portion supporting, on at least one of its main faces, a layer of active material, which has an increasing thickness over the length of the central portion which constitutes the length of winding around the axis or core, the lowest value of the thickness being at the start of the winding of the electrode, and / or which has a thickness gradient over the height of the portion central, the height being the dimension considered parallel to the axis or core, the gradient being such that the thickness is decreasing from each lateral end zone of the central portion to a middle zone in which the thickness is substantially constant.

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ELECTRODE FOR ELECTROCHEMICAL BEAM OF A METAL-ION ACCUMULATOR WITH HIGH ENERGY DENSITY, CYLINDRICAL OR PRISMATIC ACCUMULATOR THEREOF

Technical area

The present invention relates to the field of metal-ion electrochemical generators, which operate on the principle of insertion or de-insertion, or in other words intercalation-deintercalation, of metal ions in at least one electrode.

It relates more particularly to a metal-ion electrochemical accumulator comprising at least one electrochemical cell wound on itself forming an electrochemical bundle, the cell consisting of an anode and a cathode on either side of a separator impregnated with electrolyte, two current collectors, one of which is connected to the anode and the other to the cathode, and a box of elongated shape along a longitudinal axis (X), the box being arranged to house the electrochemical cell with sealing while being traversed by a part of the current collectors forming the output terminals, also called poles.

The separator can consist of one or more films.

The case may include a cover and a container, usually called a cup, or may include a cover, a bottom and a side casing assembled both to the bottom and to the cover.

The present invention aims to improve heat dissipation and therefore the life of metal-ion accumulators obtained by winding, in particular those with high capacity.

Although described with reference to a Lithium-ion accumulator, the invention applies to any electrochemical metal-ion accumulator, that is to say also Sodium-ion, Magnesium-ion, Aluminum-ion ...

Prior art

As illustrated diagrammatically in FIGS. 1 and 2, a lithium-ion battery or accumulator usually comprises at least one electrochemical cell C consisting of a separator impregnated with an electrolyte component 1 between a positive electrode or cathode 2 and a negative electrode or anode 3, a current collector 4 connected to the cathode 2, a current collector 5 connected to the anode 3 and finally, a package 6 arranged to contain the electrochemical cell with sealing while being traversed by a part of the current collectors 4, 5, forming the output terminals.

The architecture of conventional lithium-ion batteries is an architecture that can be described as monopolar, because with a single electrochemical cell comprising an anode, a cathode and an electrolyte. Several types of geometry of monopolar architecture are known:

- a cylindrical geometry as disclosed in the patent application US 2006/0121348,

- a prismatic geometry as disclosed in US patents 7348098, US 7338733;

- a stacked geometry as disclosed in patent applications US 2008/060189, US 2008/0057392, and US patent 7335448.

The electrolyte component can be solid, liquid or gel. In the latter form, the constituent can comprise a separator made of polymer or microporous composite soaked with organic electrolyte (s) or of ionic liquid type which allows the displacement of the lithium ion from the cathode to the anode for a charge and vice versa for a discharge, which generates the current. The electrolyte is generally a mixture of organic solvents, for example carbonates to which is added a lithium salt typically LIPP6.

The positive electrode or cathode consists of materials for inserting the Fithium cation which are generally composite, such as lithiated iron phosphate FiFePCL, lithiated cobalt oxide FiCoCF, lithiated manganese oxide, optionally substituted, LiMmCh or a material based on FiNi _x Mn _y CozO2 with x + y + z = 1, such as FiNio.33Mno.33Coo.33O2, or a material based on FiNi _x Co _y Al _z O2 with x + y + z = 1, FiMmCL, FiNiMnCoO2 or FiNiCoAlO2 lithium cobalt aluminum nickel oxide.

The negative electrode or anode is very often made of carbon, graphite or F4TiO5Oi2 (titanate material), possibly also based on silicon or based on lithium, or based on tin and their alloys or formed composite based of silicon. This negative electrode, like the positive electrode, can also contain electronic conductive additives as well as polymer additives which give it mechanical properties and electrochemical performance suitable for the lithiumion battery application or its implementation process.

The anode and the cathode of Fithium insertion material can be continuously deposited according to 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.

Traditionally, a Li-ion battery or accumulator uses a couple of materials at the anode and at the cathode allowing it to operate at a voltage level typically between 1.5 and 4.2 Volt.

Depending on the type of application targeted, it is sought to produce either a fm and flexible lithium-ion accumulator or a rigid accumulator: the packaging is then either flexible or rigid and in the latter case constitutes a sort of case.

Flexible packaging is usually made from a multilayer composite material consisting of a stack of aluminum layers covered by one or more polymer film (s) laminated by gluing.

FIG. 3 illustrates this type of flexible packaging 6 which is arranged to contain the electrochemical cell C with sealing while being traversed by a part 40, 50 of two strips 4, 5 forming the poles and which extend in the plane of the electrochemical cell. As shown in FIG. 3, reinforcements made of polyolefin-based polymer 60 can be provided to improve the heat sealing of the packaging 6 around the strips 4, 5. The main advantage of flexible packaging is their lightness. Li-ion batteries with the highest energy densities therefore have flexible packaging. The major drawback of these flexible packages is that their seal deteriorates greatly over time due to the chemical non-resistance of the seal produced.

Rigid packaging is used when the intended applications are restrictive or where a long service life is sought, for example with pressures to be supported much higher and a required level of tightness more strict, typically less than 10 ⁸ mbar. .l / s, or in environments with high constraints such as aeronautics or space.

The main advantage of rigid packaging is thus their high tightness and maintained over time because the closure of the boxes is carried out by welding, generally by laser welding.

The geometry of most rigid Liion battery packagings is cylindrical, since most of the electrochemical cells of accumulators are wound by winding in a cylindrical geometry. The cylindrical cells are moreover necessarily integrated in a rigid casing, since it would be very difficult to preform flexible packaging with a desired cylindrical design.

One of the types of rigid case of cylindrical shape, usually manufactured for a Li-ion accumulator of high capacity and with a lifetime greater than 10 years, is illustrated in FIG. 4.

The housing 6 with a longitudinal axis X comprises a cylindrical lateral envelope 7, a bottom 8 at one end, a cover 9 at the other end. The cover 9 supports the poles or output terminals of the current 40, 50. One of the output terminals (poles), for example the positive terminal 40 is soldered to the cover 9 while the other output terminal, for example the terminal negative 50, passes through the cover 9 with the interposition of a seal (not shown) which electrically isolates the negative terminal 50 from the cover.

There is shown in Figure 5 a longitudinal sectional view of such a housing 6 of axisymmetric geometry around the central axis 10 and housing an electrochemical beam F of elongated shape and comprising a single electrochemical cell consisting of an anode 3 and d 'A cathode 4 on either side of a separator 1 adapted to be impregnated with the electrolyte. FIG. 5 shows the bundle F obtained, usually by winding around a central winding axis 10 inside the cylindrical box 6.

Figure 6 shows a top view of an electrochemical bundle already formed by cylindrical winding, before it is housed in a cylindrical case. As can be seen in this figure 6, the diameter of the beam depends mainly on the length of the cell components, the diameter of the winding axis and the thicknesses of the electrodes and separators.

Prismatic forms of housings are also widely used. Such a form of case 6 with its cover 9 is shown diagrammatically in FIG. 7.

Such rigid prismatic housings can accommodate either a beam obtained by winding a single cell or a generally prismatic beam obtained by stacking rectangular electrochemical cells. The main advantages of prismatic housings are:

- to allow heat dissipation on the faces of the cell or stacked cells which are of large unit area, and therefore to increase the size of the electrodes and thereby the capacity of the cells;

- to be able to integrate physically, easily in a battery pack while minimizing the remaining dead volume, thanks to their flat faces.

Thus, among the Li-ion battery designs, the prismatic geometry with a beam obtained by winding is very interesting for high energy density applications, thanks to its ability to easily dissipate the heat produced during operation.

FIG. 8 shows such a case 6 of prismatic geometry with an electrochemical bundle F of elongated shape and comprising a single electrochemical cell consisting of an anode 3 and a cathode 4 on either side of a separator 1 adapted to be impregnated with the electrolyte.

Figure 9 shows a top view of an electrochemical beam already formed by prismatic winding around a parallelepipedic core 10, before it is housed in a prismatic housing. As can be seen in this figure 9, the thickness of the beam mainly depends on the length of the cell components, the thickness of the winding core and the thicknesses of the electrodes and separators.

There is shown, respectively in FIGS. 10A and 10B and in FIGS. 11A and 11B, a positive electrode or cathode 2 and a negative electrode or anode 3 from which a current electrochemical beam is produced by winding with a separator 1 interposed between cathode 2 and anode 3. The cathode 2 consists of a substrate 2S formed of a metal strip which supports in its central portion 22, a continuous layer of active lithium insertion material 21, while its lateral strip (edge) 20 is free of active insertion material. Similarly, the anode 3 consists of a substrate 3S formed of a metal strip which supports in its central portion 32, a continuous layer of active lithium insertion material 31, and its edge 30 is devoid of active material of insertion. Each metal strip 2S, 3S is produced in one piece, that is to say with the same geometric and metallurgical characteristics over its entire surface.

By “uncoated strip” or “strand” is meant here and within the framework of the invention, a lateral portion of a metal sheet, also called strip, forming a current collector, which is not covered with a metal ion insertion material, such as lithium in the case of a Li-ion battery.

These electrodes 2, 3 for Li-ion accumulators are usually produced according to a continuous process by a technique of coating the active insertion material on the metal strip in order to constitute the active continuous layer. These coating techniques are known by the Anglo-Saxon terms "slot die" or "roll to roll transfer".

Although satisfactory in many aspects, Li-ion batteries with electrochemical bundle wound by winding pose significant problems of heat dissipation due to their intrinsic design.

We can refer first to publications [1] to [3] which study the influence of the type of design of Li-ion cylindrical cylinders.

FIGS. 12A to 12C show an electrochemical bundle F of a cylindrical geometry accumulator with a capacity of 20 Ah, according to a design with respectively:

- dimensions, qualified as nominal in the publication [4], typically with a ratio between height and diameter of the order of 2.15 (FIG. 12A),

- typically a great height with a ratio between height and diameter of around 12.5 (Figure 12B),

- a large diameter typically with a ratio between height and diameter of the order of 0.17 (Figure 12C).

The value of the height of the cylinder of the electrochemical beam influences the performance and the lifespan of an accumulator.

Indeed, a very high beam as shown in FIG. 12B, induces higher temperature increases at the level of the current connectors, due to the long path that the electrons must travel. The point heatings at the longitudinal ends of the accumulator correspond to areas which will degrade faster than those in the center of the accumulator which are at a lower temperature. These phenomena are well highlighted by simulations of thermal gradients of Li-ion accumulators in operation, published in the studies in reference [3],

The value of the cylinder diameter of the electrochemical bundle also influences the performance and the lifespan of an accumulator, as highlighted by the publication [4]. At the start of the life of a large-diameter electrochemical beam accumulator, such as that shown in FIG. 12C, the regions which are most stressed for cycling are those close to the positive and negative connectors. Similarly, the core of the electrochemical bundle has a higher temperature rise compared to the periphery of the latter, since the heat dissipation is less favorable at this location, compared to the areas close to the walls of the housing. As a result, the areas near the connectors and the center of the beam will have higher degradations during the life of the accumulator and will be the areas where the capacity loss and the impedance will be the highest.

Finally, in absolute terms, the values of the dimensions of the cylinder of a bundle also influence the heat dissipation and therefore the performance and lifetime of an accumulator.

Publication [5] discloses an experiment which characterizes this influence. Three accumulators of different format, namely in order of increasing size, 18650, "oval cell" and 50 900 respectively, were placed in a thermal enclosure to assess their ability to dissipate heat thermally. We specify that we must understand here by an “oval cell” format a prismatic format with two large rays, of type 256490 with a thickness of 25mm (two rays of 12.5 mm), a total width of 64mm and a total height 90mm. It is also specified that during this experiment, the separator between anode and cathode which generally a three-layer film of polyolefin PP / PE / PP, ensures a barrier effect, and thus prevents the electrodes from being short-circuited.

For a temperature within the enclosure of 140 ° C., it can be seen that the larger accumulator, in the format 50 900 has thermal runaway. The smaller accumulator, in size 18 650, is the only one that dissipates heat sufficiently, when the enclosure is at 150 ° C. And at a temperature of 160 ° C, none of the three batteries cannot withstand heat.

Furthermore, there are numerous examples in the literature showing that, by comparison with a Li-ion accumulator with cylindrical geometry, wound accumulators with prismatic geometry obtained by winding and by stacking have better heat dissipation on the faces of the accumulator. , which may have a large area.

In addition, whether in cylindrical geometry or in prismatic geometry, the increase in capacity and density of energy by volume is most commonly done by the use of very thick electrodes, typically of thickness greater than 160 μm, and with a high grammage for the positive or negative active insertion material.

In summary, Li-ion, and more generally metal-ion, in particular high capacity accumulators have limits in their design, because beyond these limits such as with a large diameter, a large height or high overall dimensions , localized overheating appears which induces a reduction in service life and performance, in particular with a high risk of electrical and safety malfunction.

There is therefore a need to improve the life and performance of lithium accumulators, and more generally metal-ion accumulators, in particular of high capacity, whose electrochemical bundles with cylindrical or prismatic geometry, are obtained by winding.

In particular, there is a need to improve the heat dissipation within lithium batteries, and more generally metal-ion batteries, in particular with high capacity.

The object of the invention is to respond at least in part to this (s) need (s).

Statement of the invention

To do this, the invention relates, in one of its aspects, and according to a first alternative, an electrode, intended to be wound by winding around a winding axis or core to form part of a bundle electrochemical of a metal-ion accumulator, the electrode comprising a substrate formed by a metal strip comprising a lateral strip, called the edge, devoid of active insertion material, and a central portion supporting, on at least one of its faces main, a layer of active metal ion insertion material, which has an increasing thickness over the length of the central portion which constitutes the winding length around the winding axis or core, the lowest value of the thickness being at the start of the winding of the electrode.

According to a second alternative, the invention relates to an electrode, intended to be wound by winding around a winding axis or core to form part of an electrochemical bundle of a metal-ion accumulator, the electrode comprising a substrate formed by a metal strip comprising a lateral strip, called a bank, devoid of active insertion material, and a central portion supporting, on at least one of its main faces, a layer of active metal ion insertion material , which has a thickness gradient over the height of the central portion, the height being the dimension considered parallel to the winding axis or core, the gradient being such that the thickness is decreasing from each lateral end zone from the central portion to a median zone in which the thickness is substantially constant.

According to a third alternative, the invention relates to an electrode according to the combination of the first and second alternatives, that is to say an electrode intended to be wound by winding around a winding axis or core to form a part d '' an electrochemical bundle of a metal-ion accumulator, the electrode comprising a substrate formed by a metal strip comprising a lateral strip, called the edge, devoid of active insertion material, and a central portion supporting, on at least one from its main faces, a layer of active metal ion insertion material, which has both:

an increasing thickness over the length of the central portion which constitutes the length of winding around the winding axis or core, the smallest value of the thickness being at the start of the winding of the electrode,

a thickness gradient over the height of the central portion, the height being the dimension considered parallel to the winding axis or core, the gradient being such that the thickness is decreasing from each lateral end zone of the central portion to a median zone in which the thickness is substantially constant.

The preferred ranges have been synthesized in the following table, as well as examples of the dimensions of the accumulators to which the different alternatives according to the invention which have just been described, are preferably applied.

It is specified that:

- for a geometry of a cylindrical accumulator, the value H indicated corresponds to the height of the electrochemical beam, while the value D corresponds to its diameter;

- for a prismatic accumulator geometry, the value H indicated corresponds to the height of the electrochemical beam, the value W corresponds to the width while the value T corresponds to its thickness.

Battery geometry First alternative according to the invention Second alternative according to the invention Third alternative according to the invention Format cylindrical Typology Large diameter Great height Large diameter and great height Range favorite H <2D with D> 20mm H> 4D with D> 20mm 2 D <H <4D with D> 20 mm Example 1 H = 70 mm D = 50 mm H = 166 mm D = 40 mm H = 160 mm D = 50 mm Example 2 H = 90 mm D = 60 mm H = 222 mm D = 54 mm H = 230 mm D = 65mm Example 3 H = 380 mm D = 55 mm - Format prismatic Typology Large thickness (T) and large width (W) Great height (H) Large thickness (T) and great height (H) Range favorite T> 1/3 H W> H with T> 10mm T <1/5 H H> 2 W with T> 10mm T> 1/3 H H> 2 W (with T> 10mm) Example 1 T = 25 mm W = 80 mm H = 60 mm T = 25 mm W = 70 mm H = 185 mm T = 55 mm W = 70 mm H = 150 mm Example 2 T = 40 mm W = 120 mm H = 100 mm T = 40 mm W = 80 mm H = 220 mm T = 70 mm W = 96 mm H = 200 mm

According to an alternative embodiment, the increasing thickness is a continuous linear increasing thickness over the entire length of the central portion. Preferably, the thickness variation (e2-el) between the start and the end of the central portion is between 10 pm and 150 pm.

According to another alternative embodiment, the decreasing thickness is a continuous linear decreasing thickness up to the middle zone. Preferably, the variation in thickness (e5-el) between each end zone and the middle zone is between 10 μm and 100 μm.

The central portion may comprise a layer of active material on only one of its main faces,

Preferably, the continuous part of the layer of active material has a thickness (e2) greater than 160 μm in an area at the end of winding of the electrode.

More preferably, the strip can have a thickness of between 10 and 20 μm.

The electrode strip can be made of aluminum or copper.

Thus, the invention essentially consists in producing an electrode, the layer of active insertion material of which has one or more thickness gradients which make it possible to locally adapt the heat dissipation required by the accumulator in order to lower the temperature in usually the most thermally stressed areas.

In other words, the thickness of the active insertion material is locally reduced in the areas likely to be subjected to significant thermal conditions, during the lifetime of the accumulator. These areas are no longer subject to these important thermal conditions, will no longer degrade quickly and therefore will not generate premature aging unlike electrodes according to the state of the art.

It is thus possible to produce accumulator formats usually dedicated to high capacities without the risk of seeing excessive localized heating which would degrade the service life.

For a large diameter type accumulator format, as shown in FIG. 12C, the first alternative of the invention is preferred, namely a small thickness of electrode at the heart of the electrochemical bundle and an increase in thickness depending on the length of the electrode.

For a format of accumulator of great height type, as shown in FIG. 12B, the second alternative of the invention is preferred, namely a greater thickness of electrode at the longitudinal ends of the electrochemical bundle and a reduction in thickness towards the center of the beam.

Finally, for an accumulator format which is both large in diameter and large in height, the two alternatives of the invention are combined.

The invention also relates in another aspect, and according to a first alternative, to a method of producing an electrochemical bundle of a metalion accumulator such as a Li-ion accumulator, with a view to its electrical connection to the output terminals of the accumulator, comprising the following stages:

a / supply of at least one electrochemical cell consisting of a cathode and an anode on either side of a separator adapted to be impregnated with an electrolyte, the cathode and / or the anode being as described previously.

b / winding on itself by winding the electrochemical cell so as to constitute an electrochemical bundle, of elongated shape along a longitudinal axis, with at one of its lateral ends, the lateral strip of the anode and at the other of its lateral ends the lateral strip of the cathode.

Step b / can be performed either around a winding axis so as to obtain a beam with cylindrical geometry, or around a winding axis so as to obtain a beam with prismatic geometry.

Preferably, after step b /, there is an axial packing step along the longitudinal axis of the wound electrochemical bundle, of at least one of the side bands; the axial packing being carried out in one or more occasions so as to obtain, on at least one lateral end of the bundle, a packed end zone forming a substantially flat and continuous base, intended to be welded to a current collector.

The invention also relates in another of its aspects, to a method of producing an electrical connection part between an electrochemical bundle (F) of a metal-ion accumulator (A) and one of the output terminals of the 'accumulator, comprising the following stages:

- Production of an electrochemical bundle (F) in accordance with the process which has just been described;

- welding of the base obtained to a current collector itself intended to be linked or electrically connected to an output terminal of the accumulator.

The invention finally relates to a metal-ion battery or accumulator, such as a lithium (Li-ion) accumulator or a supercapacitor comprising a case comprising:

- a bottom to which is welded one of the current collectors welded to the electrochemical bundle in accordance with the method described above; and

- a cover with a bushing forming an output terminal to which the other of the current collectors is welded welded to the electrochemical bundle in accordance with the method described above.

Preferably, for a li-ion battery or accumulator: the housing is based on aluminum;

- the metal strip of negative electrode (s) is made of copper;

- the active material for inserting negative electrode (s) is chosen from the group comprising graphite, lithium, titanate oxide Li ^ iOsOn; or based on silicon or based on lithium, or based on tin and their alloys;

- the metal strip of positive electrode (s) is made of aluminum;

the active material for inserting a positive electrode (s) is chosen from the group comprising lithium iron phosphate LiFePCri, lithium cobalt oxide LiCoCh, lithium manganese oxide, optionally substituted, LiMmCh or a material based on LiNixMnyCozCh with x + y + z = 1, such as LiNio.33Mno.33Coo.33O2, or a material based on LîNixCo _y Al _z O2 with x + y + z = 1, LiMmCri, LiNiMnCoO2 or l ' cobalt nickel oxide lithium aluminum LiNiCoAlO2.

detailed description

Other advantages and characteristics of the invention will emerge more clearly on reading the detailed description of examples of implementation of the invention made by way of illustration and not limitation, with reference to the following figures among which:

- Figure 1 is a schematic exploded perspective view showing the different elements of a lithium-ion battery,

FIG. 2 is a front view showing a lithium-ion accumulator with its flexible packaging according to the state of the art,

- Figure 3 is a perspective view of a lithium-ion battery according to the state of the art with its flexible packaging;

- Figure 4 is a perspective view of a lithium-ion battery according to the state of the art with its rigid packaging consisting of a housing with cylindrical geometry;

- Figure 5 is a longitudinal sectional view of a lithium-ion battery according to the state of the art, showing the electrochemical bundle consisting of a single electrochemical cell wound on itself by winding according to a cylindrical geometry at l inside the housing;

- Figure 6 is a cross-sectional view of an electrochemical bundle wound in a cylindrical geometry, intended to be housed inside a housing as shown in Figure 5;

- Figure 7 is a perspective view of a lithium-ion battery according to the state of the art with its rigid packaging consisting of a housing with prismatic geometry;

- Figure 8 is a longitudinal sectional view of a lithium-ion battery according to the state of the art, showing the electrochemical bundle consisting of a single electrochemical cell wound on itself by winding according to a prismatic geometry at l 'inside the case;

- Figure 9 is a cross-sectional view of an electrochemical bundle wound in a prismatic geometry, intended to be housed inside a box as shown in Figure 8;

- Figures 10A and 10B are respectively side and top views of a positive electrode of the electrochemical beam according to the state of the art;

- Figures 11A and 11B are respectively side and top views of a negative electrode of the electrochemical beam according to the state of the art;

- Figures 12A to 12C are perspective views of an electrochemical bundle wound in a cylindrical geometry respectively of nominal dimensions, of great height, and of large diameter;

- Figures 13 and 13 A are views respectively from above and in section along A-A of a first example of a negative electrode of an electrochemical bundle according to the invention;

- Figure 14 is a schematic perspective view of a large diameter cylindrical accumulator which incorporates a wound electrochemical bundle, consisting of negative and positive electrodes according to the first example of the invention;

- Figures 14A to 14C are sectional views respectively along the axes A, B, and C of the negative electrode of the electrochemical bundle according to Figure 14;

- Figures 15 and 15A are views respectively from above and in section along A-A of a second example of a negative electrode of an electrochemical bundle according to the invention;

- Figure 16 is a schematic perspective view of a cylindrical accumulator of great height which incorporates a wound electrochemical bundle, consisting of negative and positive electrodes according to the second example of the invention;

- Figures 16A to 16C are sectional views respectively along the axes A, B, and C of the negative electrode of the electrochemical beam according to Figure 16;

- Figures 17, 17A and 17B are views respectively from above, in section along A-A and according to B-B of a third example of a negative electrode of an electrochemical beam according to the invention;

- Figure 18 is a schematic side view of an installation part for producing an electrode according to the invention according to a coating technique called "slotdie";

- Figures 19A to 19C are perspective views of a nozzle for injecting active insertion material in the form of ink, which is integrated into the installation of Figure 18, the figures respectively showing the nozzle in closed, open and open configuration with the positioning of a mask according to the invention inside the nozzle chamber;

- Figure 20 is a side view of a mask according to the invention positioned in the injection nozzle as according to Figure 19C;

- Figure 21 is a schematic view of calendering rollers of an electrode according to the invention once coated with its layer of active insertion material;

- Figure 22 shows in profile form the evolution that the air gap of the calendering rollers according to Figure 21 must follow, when the strip of the electrode according to the invention moves in order to obtain a homogeneous porosity within it .

For the sake of clarity, the same references designating the same elements of a lithium-ion battery according to the state of the art and according to the invention are used for all of the figures 1 to 21.

It is specified that the various elements according to the invention are represented only for the sake of clarity and that they are not to scale.

It is also specified that the term "length" and "lateral" referring to an electrode is to be considered when it is flat before its winding.

The terms "height" and "lateral" referring to the wound electrochemical bundle is to be considered in vertical configuration with its lateral ends respectively on the top and on the bottom.

Figures 1 to 12C have already been discussed in detail in the preamble. They are therefore not described below.

As detailed in the preamble, the inventors have found that a Li-ion battery, in particular with a high capacity, as it is currently produced with its electrochemical beam with cylindrical geometry, can have a short lifespan.

Indeed, the electrochemical bundle wound by winding undergoes localized heating in certain zones, during the operation of the accumulator, with a high risk of electrical dysfunction, and of safety and therefore can induce premature aging of the accumulator.

Also, to improve the lifespan of a Li-ion accumulator, in particular at high capacity, the inventors propose a new embodiment of an electrode and a new method of producing the electrochemical beam from this electrode.

This new embodiment of electrode makes it possible to better anticipate the thermal conditions of the accumulator in operation, avoiding excessive localized heating.

The metal strips of square or rectangular section supporting the active electrode insertion materials can have a thickness of between 5 and 50 μm. For an anode strip 3, it may advantageously be a copper strip with a thickness of the order of 12 μm. For a cathode strip 2, it may advantageously be an aluminum strip with a thickness of the order of 20 μm.

A positive 2 or negative 3 electrode according to the invention, as usual comprises a metal lateral strip or edge 20 or 30 devoid of active insertion material.

According to a first alternative of the invention, a layer of active insertion material 31 is produced, which has an increasing thickness over the length of the central portion which constitutes the length of winding around the winding axis 10, the lowest value of the thickness being at the start of the winding of the electrode.

Figures 13 and 13 A show an embodiment of a negative electrode 3 produced in accordance with this first alternative of the invention.

In this example, the metal strip supports on one of its main faces, a layer 31 deposited by a coating technique as explained below, the thickness of which has a continuous linear growth and goes from a value el to start of the winding at a value e2 at the end of the winding.

Thus, this electrode 31 has an increasing thickness gradient from the heart of the electrochemical beam to its outer surface.

This first alternative therefore allows preferential heat dissipation at the heart of the electrochemical bundle of the accumulator.

An electrode produced according to this first alternative is rather dedicated to the production of large diameter accumulators, as illustrated in FIG. 14.

In FIGS. 14A to 14C, we see the continuous increase in the thickness of the active material layer since, starting from a value el at the start of winding, it reaches a value e3 at the end of this area of start of winding. (figure 14A) then e4 in an intermediate zone between the start of winding and the end of winding (figure 14B) and finally a value e2 in the end of winding area (figure 14C), that is to say say on the outer surface of the beam in contact with the walls of the battery case 6.

According to a second alternative of the invention, a layer of active insertion material 31 is produced, which has a thickness gradient over the height of the central portion, the height being the dimension considered parallel to the axis or core d winding, the gradient being such that the thickness is decreasing from each lateral end zone of the central portion to a middle zone in which the thickness is substantially constant.

Figures 15 and 15 A show an exemplary embodiment of a negative electrode 3 produced in accordance with this second alternative of the invention.

In this example, the metal strip supports on one of its main faces, a layer 31 deposited by a coating technique as explained below, the thickness of which has a continuous linear decrease from each lateral end zone of the central portion and goes from a value e5 to a value el. This value el is constant in the middle zone.

Thus, this electrode 31 has an increasing thickness gradient from the center of the electrochemical beam to the lateral ends directly connected to the output connectors.

This second alternative therefore allows preferential heat dissipation on the lateral ends (top and bottom) of the electrochemical bundle of the accumulator.

An electrode produced according to this second alternative is rather dedicated to the production of tall batteries, as illustrated in FIG. 16.

In FIGS. 16A to 16C, we see the variation in the thickness of the active material layer since from a value e5 at the bottom of the electrochemical beam it reaches el, less than e5, (FIG. 16A) then remains constant in a middle zone (FIG. 16B) and returns to its initial value e5 at the top of the beam (FIG. 16C).

According to a third alternative, the first and the second alternative are combined.

Figures 17, 17A and 17B show an exemplary embodiment of a negative electrode 3 produced in accordance with this third alternative of the invention.

In this example, the metal strip supports on one of its main faces, a layer 31 deposited by a coating technique as explained below, the thickness of which has a continuous linear decrease from each lateral end zone of the central portion and goes from a value e5 to a constant value el in the middle zone (FIG. 17B). This value is constant only on a given line since it increases in a continuous linear fashion over the length of the electrode from the value el at the start of winding to the value e2 at the end of winding (Figure 17A).

Thus, this electrode 31 has a gradient of increasing thickness from the center of the electrochemical beam to the lateral ends directly connected to the output connectors.

This third alternative therefore allows preferential heat dissipation both of the electrochemical bundle and on its lateral ends.

A description will now be given in relation to FIGS. 18 to 22, of a method of production according to a coating technique designated in English under the slot-die terminology of an electrode according to the third alternative of the invention.

As shown in FIG. 18, the ink of active insertion material which flows through from the cavity 12 of an injection nozzle 11 is continuously coated on a metal strip 3S while scrolling at Re drive means.

The injection nozzle 11 can be that usually used, that is to say with an internal surface 12 and an injection lip 13, as shown in its closed position in FIG. 19A. The injection nozzle can be opened (FIG. 19B) to accommodate therein, inside its chamber, a mask 14 adapted to produce the thickness gradient over the height of the electrode (FIG. 19C).

A conforming mask 14 is shown in FIG. 20: this mask has a constant depth el but less significant in its central zone than those on its peripheral edges which have a continuous linear decrease until obtaining a depth equivalent to e5.

Thus, when the ink of active insertion material will coat a 3S strip in transverse travel below the nozzle 11, the layer 31 deposited will have a thickness with a continuous linear decrease from each lateral end zone of the portion central and goes from a value e5 to a constant value el in the middle zone.

To obtain a layer thickness 31 which increases continuously linearly from the start of its length to the end of its length, two different methods can be used.

The first method consists in adapting the running speed of the metal strip forming the 3 S current collector, below the nozzle. Thus, with a low speed of movement, the thickness of ink of active insertion material deposited on the strip will be greater than with a high speed. It is thus possible to linearly decrease the speed of travel of the metal strip from the start of the injection corresponding to the start of the length of the electrode until the end of the length to obtain the desired thickness gradient.

The second method is to adjust the ink injection pressure through the chamber of the injection nozzle. Thus, the higher the injection pressure of the ink via the nozzle, the greater the thickness deposited.

The thickness gradients of the layer of active insertion material must not generate an inhomogeneity of porosity in the layer deposited on the metal strip.

Also, the inventors propose to modify the usual step of calendering the electrodes in order to obtain a homogeneous porosity, whatever the thickness gradient of layer of active material that one seeks to obtain.

To do this, it is possible to provide adequate control of the spacing e of the calendering rollers Re of the calender device during the continuous running of the electrode strip 3 (FIG. 21).

FIG. 22 illustrates in the form of a curve the spacing cycle which is subjected to the calendering rollers Rc in order to obtain a homogeneous porosity over the length of electrode 3. According to a pitch of length equal to the length of an electrode , the two calendering rollers Rc are brought towards each other from a value e2 corresponding to the greatest thickness to a value el corresponding to the least thickness. Then, the process is repeated continuously to obtain a multitude of electrodes according to the invention with homogeneous porosity.

We will now describe the different stages of a process for producing a beam and an accumulator according to the invention, integrating such a beam.

Anode 3, cathode 2 and at least one separator film 4 of the electrochemical cell C are supplied and wound by winding around a support not shown, such as a winding axis 10 for a cylindrical geometry or of a rectangular core for a prismatic geometry. Anode 3 and / or cathode 2 is (are) made in accordance with the invention.

The beam obtained therefore has a cylindrical shape or a prismatic shape elongated along a longitudinal axis with at one of its lateral ends an anode strip 3 of uncoated and, at the other of its lateral ends, a strip 20 of cathode 2 not coated.

An axial packing is then carried out along the longitudinal axis of the strips 20, 30 of the electrochemical bundle, over the entire surface of the lateral ends.

The axial compaction consists of compression by a flat or structured tool with a support surface substantially equal to the surface of each of the lateral ends of the strips 20 or 30.

When the desired geometry of the accumulator is cylindrical, the tool and the electrochemical bundle are arranged coaxially during axial compaction.

The axial packing is carried out one or more times. It can consist of compression according to one or more relative movements back and forth, ie at least one return trip according to Tax of the beam, and this until reaching either a desired dimension of beam according to Tax, or a maximum compression force whose value is predetermined beforehand.

There is thus obtained on the packed surface portion and not folded down of each lateral end, a substantially flat base.

The base formed by the packed part of the cathode (positive edges) is then welded to one of the lateral ends of the bundle with a usual current collector in the form of a solid disc, itself intended to be welded subsequently. with the bottom 8 of the case 6 of accumulator of cylindrical or prismatic shape.

One proceeds in the same way to the other of the lateral ends of the bundle, the base formed by the packed part of the anode (negative edges) with a part of usual current collector in the form of a solid disc pierced with sound. center and a tongue projecting laterally from the disc.

To finalize the final realization of the accumulator, we proceed as usual.

Thus, although not shown, the beam is introduced with the collector in a rigid aluminum container forming only the side envelope of the housing 6. In particular, during this step, care is taken to ensure that the tongue does not interfere with the introduction. To do this, it is folded advantageously upwards.

The collector is welded with the bottom 8 of the case 6.

The collector is welded to a negative pole 50 forming a crossing of a cover 9 of case 6.

The cover 9 is then welded to the rigid metal container 7.

Then a step of filling the case 6 is carried out using an electrolyte, through a through opening, not shown, which is made in the cover 9.

The production of the Li-ion accumulator according to the invention ends by plugging the filling opening.

Other variants and improvements can be made without departing from the scope of the invention.

An electrode according to the invention can be produced whatever the active material and the components of the electrode (collector, binders, electronic conductors, additives).

Although the case 6 in the illustrated embodiments which have just been detailed is made of aluminum, it can also be made of steel, or of nickel-plated steel. In such a variant, a steel or nickel-plated steel case constitutes the negative potential, the crossing then constituting the positive pole.

In all the examples illustrated, the thickness gradients of the insertion materials are produced for a single face of the electrodes. It goes without saying that the invention also applies to the two faces of the same electrode, that is to say with thickness gradients symmetrically on the two faces.

The invention also applies to an accumulator whose two electrodes superimposed during winding, ie anode and cathode, have a thickness gradient of insertion material, but also to a configuration in which only one of the two electrodes has a thickness gradient and the other is produced as usual with a constant large thickness. In particular, in a Li-ion accumulator with known electrochemistry, the positive electrode may have a thickness gradient of active insertion material in accordance with the invention while the negative electrode, opposite the positive electrode has a high constant thickness.

Furthermore, all the examples illustrated relate to coiled accumulators with cylindrical geometry. The invention also applies to wound prismatic geometries.

The invention is not limited to the examples which have just been described; one can in particular combine together characteristics of the examples illustrated within variants not illustrated.

References cited [1]: Al Hallaj S, Maleki H, Hong JS, Selman JR. "Thermal modeling and design considerations of lithium-ion batteries". J Power Sour 1998; 83: 1-8.

[2]: Y. Inui, Y. Kobayashi, Y. Watanabe, Y. Watase, Y. Kitamura, "Energy Conversion and 5 Management" 48 (2007) 2103-2109.

[3]: "Multi-Scale Multi-Dimensional Li-ion Battery Model for Better Design and

Management ”, PRÎME2008, 214th Electrochemical Society Pacific Rim Meeting Honolulu, 2008.

[4]: "Modeling of Nonuniform Degradation in Large-Format Li-ion Batteries", 215th 10 Electrochemical Society Meeting San Francisco, CA May 25-29 Kandler Smith, 2009.

[5]: "Analysis of Heat Dissipation in Li-ion Cells & Modules for Modeling of Thermal Runaway", 3rd International Symposium on Large Lithium Ion Battery Technology and Application, Gi-Heon Kim, 2007 California.

Claims (18)

1. Electrode (2, 3), intended to be wound by winding around a winding axis or core to form part of an electrochemical bundle (F) of a metal-ion accumulator, the electrode comprising a substrate (2S, 3S) formed of a metal strip comprising at least one lateral strip, called the edge (20, 30), devoid of active insertion material, and a central portion (22, 32) supporting, on at least one from its main faces, a layer of active metal ion insertion material, which has an increasing thickness over the length of the central portion which constitutes the length of winding around the winding axis or core, the most low value of the thickness being at the beginning of the winding of the electrode. 2. Electrode (2, 3), intended to be wound by winding around a winding axis or core to form part of an electrochemical bundle (F) of a metal-ion accumulator, the electrode comprising a substrate (2S, 3S) formed of a metal strip comprising at least one lateral strip, called the edge (20, 30), devoid of active insertion material, and a central portion (22, 32) supporting, on at least one from its main faces, a layer of active metal ion insertion material, which has a thickness gradient over the height of the central portion, the height being the dimension considered parallel to the winding axis or core, the gradient being such that the thickness is decreasing from each lateral end zone of the central portion to a median zone in which the thickness is substantially constant. 3. Electrode (2, 3) according to claim 1 in combination with the claim 2. 4. Electrode (2, 3) according to one of claims 1 or 3, the increasing thickness being a continuous linear increasing thickness over the entire length of the central portion. 5. Electrode (2, 3) according to claim 4, the variation in thickness (e2-el) between the start and the end of the central portion being between 10 and 150 µm. 6. Electrode (2, 3) according to one of claims 2 or 3, the decreasing thickness being a continuous linear decreasing thickness up to the middle zone. 7. The electrode (2, 3) according to claim 6, the variation in thickness (e5-el) between each end zone and the central zone being between 10 and 100 μm. 8. Electrode (2, 3) according to one of the preceding claims, the central portion comprising, on one of its main faces, a layer of active material. 9. Electrode (2, 3) according to one of the preceding claims, the layer of active material having a thickness (e2) greater than 160 μm in an area at the end of winding of the electrode. 10. Electrode (2, 3) according to one of the preceding claims, the strip having a thickness of between 10 and 20 μm. 11. Electrode (2, 3) according to one of the preceding claims, the strip being made of aluminum or copper. 12. Method for producing an electrochemical bundle (F) of a metal-ion accumulator (A) such as a Li-ion accumulator, with a view to its electrical connection to the output terminals of the accumulator, comprising the steps following: aJ supply of at least one electrochemical cell (C) consisting of a cathode (2) and an anode (3) on either side of a separator (4) adapted to be impregnated with an electrolyte, the cathode (2) and / or the anode being according to one of the preceding claims, b / winding on itself by winding the electrochemical cell (C) so as to constitute an electrochemical bundle (F), of elongated shape along a longitudinal axis, with at one of its lateral ends, the lateral strip (30) of the anode and at the other of its lateral ends the lateral strip (20) of the cathode. 13. A method of producing an electrochemical beam according to claim 12, step b / being carried out, either around a winding axis so as to obtain a beam with cylindrical geometry, or around an axis of winding so as to obtain a beam with prismatic geometry. 14. Method for producing an electrochemical bundle according to one of claims 12 or 13, comprising after step b /, a step of axial packing along the longitudinal axis of the wound electrochemical bundle, of at least one side bands (20, 30); the axial packing being carried out in one or more occasions so as to obtain, on at least one lateral end of the bundle, a packed end zone forming a substantially flat and continuous base, intended to be welded to a current collector. 15. Method for producing an electrical connection part between an electrochemical bundle (F) of a metal-ion accumulator (A) and one of the output terminals of the accumulator, comprising the following steps: - production of an electrochemical bundle (F) in accordance with the method according to claim 14; - welding of the base obtained to a current collector in the form of a plate, itself intended to be linked or electrically connected to an output terminal (40, 50) of the accumulator. 16. Metal-ion battery or accumulator, such as a lithium-ion 5 (Li-ion) accumulator comprising a case (6) comprising: - a bottom (8) to which is welded one of the current collectors welded to the electrochemical bundle in accordance with the method according to claim 15; and - a cover (9) with a bushing forming an output terminal to which the other of the current collectors is welded welded to the electrochemical bundle in accordance with 10 method according to claim 15. 17. Li-ion battery or accumulator according to claim 16, in which: - the case is made from aluminum; - the metal strip of negative electrode (s) is made of copper; the active material for insertion of negative electrode (s) is chosen from the group comprising graphite, lithium, titanate oxide LuTiOsOii; or based on silicon or based on lithium, or based on tin and their alloys; - the metal strip of positive electrode (s) is made of aluminum; - the active material for inserting a positive electrode (s) is chosen from the group comprising lithium iron phosphate LiFePCL, lithium cobalt oxide LiCoCh, oxide 20 lithiated manganese, optionally substituted, LiA / huCU or a material based on LiNixMnyCozCh with x + y + z = 1, such as LiNio 33Mno 33C00 33Ο2, or a material based on LiNixCoyAlzCh with x + y + z = 1, LiMmCU , LiNiMnCoCh or lithium cobalt aluminum oxide lithium LiNiCoAICh 1/8 2/8