Storage device and method of manufacture

Abstract

To allow the manufacture of an electrode (12), especially, for a micro battery.SOLUTION: Electrodes (12) are generated in multi-layers with an intermediate step of masking a first layer, which leaves a part of the first layer exposed to generate removal of a material that eliminates defects. After a masking layer (16) has been removed, a second layer can be formed. After that, the other layers can be followed in the same way.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to the field of electrochemical energy storage, in particular to microelectronic devices with electrodes in the form of microbatteries (thus implementing electrochemical microstorage components). The invention finds application in the manufacture of microelectronic devices providing such storage. By microelectronic devices is meant any type of device manufactured by microelectronic means. These devices include in particular micromechanical or electromechanical (MEMS, NEMS, etc.) devices and optical or optoelectronic (MOEMS, etc.) devices, in addition to devices of purely electronic purpose. This includes applications of electrochemical microstorage component types (microbatteries, microsupercapacitors, all types of solid-state ionic components).

[0002] Of particular interest to the present invention is therefore the manufacture of electrochemical energy storage devices, including in particular battery-type devices, in particular microelectronic scale devices called microbatteries, accumulators or capacitors, using an electrolyte, preferably solid state. [Background technology]

[0003] Electrochemical energy storage systems are typically produced by sequential deposition of a first current collector, a first electrode, an ionic electrolyte or conductor, a second electrode, and a second current collector onto a substrate. Encapsulation by deposition of additional layers or transfer of a cap is often required to protect the system from chemical reactions with oxygen and water vapor.

[0004] Device miniaturization involves the ability to generate energy sources of small size, especially a few millimeters square, that can store sufficient amounts of energy for the application. The capacity of a microbattery is directly proportional to the volume of the two electrodes, especially the positive electrode. The active surface of the latter is largely limited by the final size of the microbattery, so that it can be integrated into the final device without excessively detrimental bulk. Therefore, one method that can be used to increase the capacity of a battery while minimizing its size is to increase the thickness of the electrodes, especially the positive electrode. Usually, a thickness of more than 10 μm is required.

[0005] However, increasing this thickness causes surface defects related to the deposition method, which can cause short circuits in the energy storage device. In particular, electrode materials such as LiCoO2 are deposited by cathode sputtering, which is usually limited to small thicknesses of less than about 10 microns. Furthermore, as the electrode thickness increases, volume defects such as cracks and delamination occur. The structure of the thick layers of the electrode itself is not well controlled (grain size, crystal orientation), which leads to poor electrochemical performance.

[0006] An attempt at a solution to the above problem is proposed in US Pat. No. 9,899,661, which presents the formation of an electrode by successive depositions. In particular, the deposition of LiCoO2 under argon is alternated with the deposition of LiCoO2 under an argon / oxygen mixture. The resulting multilayer assembly causes the rupture of the growth nucleation and then renucleation. A reduction in the annealing temperature of the material, necessary to obtain the correct crystalline phase from the electrochemical point of view, is also applied. The document states that by this method it is possible to obtain LiCoO2 film thicknesses of more than 10 μm. However, this multilayer deposition causes inhomogeneity of the electrode, both in composition and in crystal structure, and therefore inhomogeneity of performance between the various layers. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 9,899,661 Summary of the Invention [Problem to be solved by the invention]

[0008] One objective is therefore to propose an electrode manufacturing method that, for a comparable thickness, offers a manufacturing quality (especially due to reduced defects) and improved electrical properties compared to known electrodes, which may, for example, allow for large thicknesses, even if this is not very detrimental to the performance of the electrode, or even detrimental, or even advantageous from an electrical point of view in particular.

[0009] Other objects, features and advantages will become apparent from a consideration of the following detailed description and the accompanying drawings, and of course other advantages may be incorporated. [Means for solving the problem]

[0010] To this end, one embodiment provides a method for manufacturing an electrode, in particular an electrode for an electrochemical energy storage device, which electrode is obtained by the formation of a number of layers.

[0011] Advantageously, the method comprises the steps of: (i) forming a first electrode layer by physical vapor deposition; (ii) forming a masking layer on the first electrode layer configured to cover a first portion of an exposed surface of the first electrode layer without covering a second unmasked portion of the exposed surface of the first electrode layer, the second portion including a relief having an extension in a thickness dimension of the electrode that is greater than a maximum extension of the first portion along the thickness dimension of the electrode; (iii) removing material of the first electrode layer from the second portion by applying an etching solution to the first electrode layer; (iv) removing the masking layer; (v) fabricating a second electrode layer directly over the exposed surface of the first electrode layer; Includes.

[0012] This allows the production of all or part of the layers of the electrode produced using physical vapor deposition techniques, but this technique generally causes very detrimental defects and limits the thickness of the electrode that can be produced. This method preferably makes it possible to obtain high thicknesses, which are advantageous for good energy storage, with good quality layers and with a manufacturing method that is itself well controlled, which is physical vapor deposition.

[0013] Advantageously, LiCoO2 is used in at least one layer of the electrode produced.

[0014] The invention also relates to a method for producing an electrochemical energy storage device, comprising the production of at least one first electrode by the method described above. Advantageously, a first collector is formed on the support, then a first electrode is produced on the first collector. Preferably, the method comprises forming another element on top of the previous one, which may in particular be the case of a preferably solid electrolyte, then a second electrode and a second collector.

[0015] Another aspect relates to an electrochemical energy storage device obtainable by the method of the invention.

[0016] Another embodiment relates to an electrode for an electrochemical energy storage device comprising a plurality of stacked layers, a first electrode layer of the plurality of stacked layers comprising at least one cavity formed hollow in its thickness, and a second electrode layer of the plurality of stacked layers located immediately above the first electrode layer at least partially covering an exposed surface of the first electrode layer and filling the at least one cavity.

[0017] Optionally, the at least one cavity includes a cavity that extends through the entire thickness of the first layer, so that in this case the filling of the material of the second layer can reach and contact the material of the layer below the first layer, which may be the surface of the support of the surface of the other layer located directly below the layer containing the cavity.

[0018] Another aspect relates to an electrochemical energy storage device comprising a stack on a support, a first collector, a first electrode, an electrolyte, a second electrode, and a second collector, comprising at least one of the first electrode and the second electrode.

[0019] The objects, objects, features and advantages of the present invention will be more clearly understood from the following detailed description of the embodiments thereof, illustrated in the accompanying drawings. [Brief description of the drawings]

[0020] [Figure 1] 1 shows a schematic of a stack of layers for forming a microbattery. [Diagram 2] 1 shows an example of the steps for producing an electrode layer of a first microbattery. [Diagram 3] 3 shows an example of steps for producing a microbattery electrode following the steps of FIG. 2. [Figure 4] This shows a step subsequent to that of FIG. [Diagram 5] 3A and 3B illustrate the formation of a second electrode layer. [Figure 6] An example of incorporating a multilayer cathode into a microbattery is shown. [Figure 7] 2 is a curve demonstrating the advantageous results of the present invention in terms of the capacity obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The drawings are given by way of example and not of limitation of the invention: they constitute schematic, schematic representations intended to facilitate understanding of the invention and do not necessarily correspond to the scale of an actual application.

[0022] Before commencing a detailed discussion of the embodiments of the present invention, some optional features that may be used in conjunction with or instead of the embodiments are described below. Annealing of the first layer is carried out after removal of the masking layer and before the second electrode layer is produced. The annealing of the second layer is carried out after its production or, if at least one third layer is subsequently formed, advantageously after removing the masking layer on the second layer. The second electrode layer 122 is produced by physical vapour deposition. - Material is removed from the second portion by applying an etching solution to the first electrode layer 121. -LiCoO2 is used to produce at least one of the first electrode layer 121 and the second electrode layer 122. Producing at least one third electrode layer on the second electrode layer 122 comprises repeating steps (ii) to (iv). Each electrode layer can be annealed before applying another layer on top. The thickness of the last electrode layer of the electrode 12, remote from the first electrode layer 121, is less than the thickness of the other electrode layers. The formation of the masking layer 16 includes the formation of at least one pattern 1212 directly through the thickness of the masking layer 16 so as to expose a third portion of the first electrode layer 121, the removal of which is configured to result in the removal of additional material from the third portion. The electrode layer has a thickness of ≧1 μm and / or ≦10 μm. at least two directly successive layers of the electrode layers have the same thickness. The masking layer 16 can be formed in a resin deposition step, preferably by spin coating.

[0023] In the context of the present invention, the terms "on" or "on top" are stated as not necessarily meaning "in contact with". Thus, for example, depositing one layer on another layer does not necessarily mean that the two layers are in direct contact with each other, but rather that one layer is in direct contact with the other or at least partially covers the other while being separated therefrom by a membrane or another layer or element. Furthermore, a layer may be composed of multiple sublayers of the same or different materials, which is particularly true in the case of electrode layers as described below.

[0024] In the context of the present invention, the thickness of a layer or substrate is stated as being measured in a direction perpendicular to the surface along which said layer or substrate has its greatest elongation. If a layer is not perfectly flat, especially since it has imperfections that tend to be in relief on the exposed surface of said layer, its thickness refers to the dimension of said layer outside said imperfections.

[0025] Some parts of the device of the invention may have an electrical function. Some are used for their electrical conducting properties, and the term electrode, collector or equivalent means in this application means an element made of at least one material that has sufficient electrical conductivity to fulfill the required function. Conversely, an electrical insulator or dielectric means in this application a material that performs an electrical insulating function.

[0026] By electrochemical energy storage device is meant a device that functions with a layer of electrolyte, preferably in solid form, with a lower conductive functional part and an upper conductive functional part, surrounding the electrolyte layer, allowing the storage of energy in the form of an increase in potential difference or the discharge of energy in the form of a decrease in potential difference. In the field of microelectronics, this may be the case for microbatteries, which means devices with dimensions on the microelectronic scale, in particular with an overall thickness of a few tens of microns, for example less than 100 microns.

[0027] In general, electrochemical energy storage devices contain two electrodes separated by an electrolyte. During discharge, the anode (negative electrode) is a sheet of oxidation, and ions pass through the electrolyte and undergo reduction at the cathode (positive electrode) while being inserted into a specific material (host material), and the electrons thus produced provide energy to the external circuit. During charging, the ions make the reverse path and electrons are supplied from the external circuit.

[0028] FIG. 1 shows a purely schematic view of the stack of the various layers to form a microbattery. In this context, the support 10 is capable of receiving the remaining stack and is formed, for example, of a semiconducting material such as silicon or any other organic or inorganic material, for example glass. If the support 10 is electrically conductive, it may comprise at least one surface electrically insulating layer. This arrangement is not shown in the schematic view of FIG. 1. The reference number 11 corresponds to the first current collector. Within the meaning of the present application, the term "collector" means a part of the device whose function is to connect an electrode to an element external to the device, i.e. generally located outside the stack of layers of the encapsulated device. For this part, a metal with good electrical conductivity can be used. This is the case of platinum, but also cheaper materials such as titanium are possible.

[0029] The electrode in question in this example is here a first electrode 12 placed on and in contact with a first collector, which serves as a support for forming the electrode 12. The term electrode means, for its part, a part of the device in electrical communication with the active layer (particularly the electrolyte, preferably solid, in the case of electrochemical storage). The first electrode 12 (or the positive electrode used in conventional lithium or sodium accumulators) can use various materials such as LiCoO2, V2O5, TiS2, LiMn2O4, NaMnO2 or NaCoO2. It may comprise a material of composition ABX, where A is an alkali metal, preferably Li, B is a transition metal, preferably Co, and X is oxygen (O) or phosphate (PO4). In general, in the present invention, materials based on lithium cobalt and / or lithium manganese can be used. As indicated above, it is generally required that the first electrode (here the cathode) is rather thick in order to be able to store a sufficient amount of energy with a limited surface area. Here, it is possible to use a thickness of 10 μm or more, preferably 20 μm or more.

[0030] Opposite to the contact with the first collector 11, the first electrode 12 is in contact with an electrolyte 13. Ion-conducting glasses and alkaline chalcogenides are among the inorganic solid electrolytes that can be applied in all-solid-state batteries. The corresponding materials can be selected from the series of sulfide and glassy oxysulfide electrolyte systems, as well as sulfide-based superionic glass ceramics Li2S-P2S5, of which the Li2S-P2S5 is the Li + The ionic conductivity is comparable to that of liquid electrolytes. As for electrolytes for sodium batteries, the same types of glasses exist, for example Na3PS4.

[0031] Figure 1 then shows a second electrode, here forming the anode, on the other side of the electrolyte 13. It can be silicon, for example. On top of it is placed a second collector 15. As before, titanium or another metal with electrical conductivity can be used.

[0032] Generally, in the normal context of the first electrode 12, with reference to Fig. 1, it is difficult to achieve a thickness of 10 μm without a prohibitive effect on the quality of the first electrode, in particular with regard to its electrical efficiency after manufacture, since an increase in the thickness of the electrode leads to a high degree of morphological defects, often resulting in significant roughness and curvature of the surface of said electrode, and in some cases to delamination between the electrode and the current collector layer of the previous level, resulting in a decrease in the electrical response of the component, often in the form of short circuits and / or high leakage currents.

[0033] The method of the invention provides a solution to this problem and, with reference to FIG. 2, presents a step in which a first electrode layer 121 is formed on the collector 11. Preferably, physical vapor deposition, commonly known by the acronym PVD, is used. The conditions of this deposition can be conventional. They give rise to defects, as revealed by the parts 1210 and 1211. These can be growth defects in the form of crusts with a poorly controlled crystal structure. Some defects are such that they can extend throughout the thickness of the layer 121, as represented by the defect 1210. Other defects are more superficial, such as the defect marked with reference 1211. These defects form reliefs beyond the average surface of the layer 121 that are oriented substantially perpendicular to the thickness dimensions of the various layers. In particular, these reliefs are greater than 1 μm, or even greater than 2 μm, or even possible 3 μm. This may be, for example, more than 30% of the thickness of the layer deposited in a single deposition step, or may be of the same order of magnitude as the thickness of the layer deposited in a single deposition step, e.g., 2 to 3 microns for a 3 micron layer, and 10 to 15 microns for a 20 micron layer.

[0034] In Fig. 3, a masking layer 16 is formed on the first layer 121. This formation is configured to cover parts of the layer 121 that are not affected by the relief defects 1210, 1211. Thus, despite the presence of the masking layer 16, parts of the defects are now exposed. It will be appreciated that the thickness of the masking layer 16 is configured to be fine enough not to completely cover the relief of the defects. Typically, the thickness of the masking layer 16 may be at least 1 μm and / or preferably less than 4 μm, more preferably at least 1.5 μm and / or less than 2.5 μm. For example, the masking layer 16 may measure 2 μm thick with a margin of + / - 0.2 μm.

[0035] The spin-coating technique is perfectly suitable for producing the masking layer 16. Usually, the first step is to apply a resin to the exposed surface of the layer 121, which results in a rotation of the support. The centrifugal force thus generated distributes the resin on the surface. Depending on the conditions of the rotation, in particular the time and speed, it is possible to obtain a layer of the required thickness. The resin can then be hardened by evaporating its solvent. The result shown in FIG. 3 shows a first part of the first electrode layer 121 that has been coated, while a second part of the electrode layer 121 remains exposed and not protected by the masking layer 16. According to one example, the thickness of the masking layer 16 represents at least 20% of the thickness of the first electrode layer 121, alternatively or additionally, the thickness of the masking layer 16 may represent up to 70% of the thickness of the first electrode layer 121, preferably up to 30% of said thickness. Generally, the formation of the masking layer is configured to fill the space around at least some of the reliefs 1210, 1211, filling only a part of the height separating the recesses (or the average surface and the top of the highest relief of the layer in question). Thus, advantageously, the second portion comprises at least one region in the form of a small island of material of the first electrode layer 121 surrounded by the masking layer, an island of material due to the protruding nature of the defect relief. The surface of said island is thus formed on the exposed surface of the first layer 121. The surface of said island has a higher elevation than the masking layer. It forms the top that is not covered during masking.

[0036] It is noted that other parts of the first electrode layer 121 are optionally exposed as well. This can be done by patterning the material of the masking layer 16 by a photolithography step to define unprotected areas 161 of the layer 121. In particular, it can be seen that in a next step it is possible to laterally delimit the first electrode in that layer 121.

[0037] This is because the next stage shown in FIG. 4 is the stage of removing the material of the first electrode layer 121. The parts not protected by the masking layer 16 can be the places of attack by application of an etching solution. This can be a wet etching. The etching is carried out, for example, in a bath of H2SO4, the speed of the etching being in particular about 6 μm / min. For an initial layer 121 with a thickness of 10 μm outside the defect, an etching of the order of 1 minute is suitable. In some cases, it is not desirable for this removal to be configured to reach the bottom of the layer 121 in order to completely remove the patterns. This is because some of them are in the form of a crust and have a fragile interface with the rest of the layer 121, so that they tend to be removed in the form of blocks. In this case, even if not extended, the etching can reach the interface of the defect and separate it. Naturally, in other cases, the effect of the etching is a more gradual removal. In general, the etching is configured to remove the material of the first electrode layer 121 at least over the average surface of the layer 121 and throughout the excess thickness of the defects 1210, 1211. More preferably, the etch is configured to completely remove the defects, which is why the etch times indicated above are relatively critical with respect to the thickness of layer 121.

[0038] In the preferred case where the removal is considered to exceed the average surface of the layer 121, said removal generates cavities in the unmasked parts that extend into the thickness of the layer 121. Optionally, the cavities extend through the entire thickness of the layer 121. Generally, there are multiple cavities in a layer. Multiple layers, whether immediately successive or not, can each contain one or multiple cavities. The cavities in a layer can have different forms and dimensions, in particular different depths.

[0039] As indicated above, the removal step in question may also serve to form the first electrode 12 in that part formed by the first layer 121. In this connection, the reference number 1212 in FIG. 4 denotes an etching carried out simultaneously with the removal of the deposit in order to laterally delimit the pattern of the first electrode. It is therefore understood that the step of the invention for removing the unwanted relief on the layer 121 does not take place in the context of a complementary step, but rather in the context of another step which is generally necessary. Moreover, it is noted that the situation in FIG. 4 corresponds to the situation after the removal of the masking layer 16, following the removal of the material of the first electrode layer 121.

[0040] The step in question may be a step involving the shaping of the electrode layer, in particular to constrain it laterally, and / or the electrical connection or encapsulation.

[0041] 5 then shows the production of a second electrode layer 122 on the thus reprocessed first layer 121. Preferably, a PVD method is also used to form said second layer. The depressions left by the previous removal step can be attenuated by this deposition.

[0042] According to a first possibility, the top layers of the stack, ie the electrolyte, the second electrode and the second collector, are secondly constructed.

[0043] According to another possibility, the steps of Figures 3 to 5 are repeated to produce at least a third layer of the first electrode on the second electrode 122. Thus, the steps of forming a masking layer, removing material (this time in the second electrode layer), removing the masking layer and depositing material of the third electrode layer are used again. It is noted that it is possible to continue forming a pattern having properties equivalent to those of the exposed areas 161 and etched pattern 1212 described above.

[0044] It is possible to increase the number of sub-layers forming the first electrode 12, and FIG. 6 gives an example of four sub-layers, 12a, 12b, 12c and 12d respectively.

[0045] According to a first embodiment, the thicknesses of these layers are the same. According to another possibility, the thickness is reduced, or at least the last layer (the layer intended to be in contact with the electrolyte) is thinner than the others, or at least thinner than the layer immediately below it.

[0046] In particular, it is possible to use layers having a thickness of at least 1 μm and / or less than 10 μm.

[0047] Optionally, it is possible to use different materials for each layer of the first electrode, or for at least two of them.

[0048] Conventionally, the manufacture of the device of the invention follows, in the case of an electrochemical energy storage device, the formation of the electrolyte 13, followed by the formation of a second electrode and a second collector, respectively having the references 14 and 15 in FIG. 6. Optionally, the second electrode 14 can be manufactured using the method described above for the first one. The electrolyte 13 can be the support for the deposition of one or more layers to form the second electrode 14.

[0049] Figure 7 gives an illustration of the considerable technological advance brought about by the present invention. It shows two capacitance / voltage curves of two microbatteries that are otherwise comparable but are distinguished by the formation of their first electrodes. In the first case, it is the first electrode produced according to the present invention with three layers of LiCoO2, each 3 μm thick. In the other case, the first electrode is of the same material but formed in a single piece according to conventional methods and has a thickness of 10 μm. Despite the slightly larger thickness in the second case, the operation of the microbattery is of much lower quality, taking into account the difference in capacity observed.

[0050] The invention is not limited to the embodiments described above, but extends to all embodiments covered by the claims. [Explanation of symbols]

[0051] 10 Support 11 First Collector 12 First electrode 12a sublayer 12b sublayer 12c sublayer 12d sublayer 13 Electrolytes 14 Second electrode 15 Second Collector 16 Masking Layers 161 Unprotected Areas 121 First electrode layer 122 Second electrode layer 1210 Relief 1211 Relief 1212 Etching Pattern

Claims

1. A method for producing an electrode (12) for an electrochemical energy storage device, said electrode (12) being obtained by the formation of a plurality of stacked layers (121, 122), The method further comprising: (i) producing a first electrode layer (121) on a support by physical vapor deposition, said vapor deposition creating defects in the first electrode layer (121) forming protruding reliefs (1210, 1211); (ii) forming a masking layer (16) on the first electrode layer (121) configured to completely not cover the relief (1210, 1211) so as to cover a first portion of the exposed surface of the first electrode layer (121) without covering a second unmasked portion of the exposed surface of the first electrode layer (121), the second portion comprising a relief (1210, 1211) having an extension in a thickness dimension of the electrode (12) that is greater than a maximum extension of the first portion along a thickness dimension of the electrode (12); (iii) removing material of the first electrode layer (121) from the second portion by applying an etching solution to the first electrode layer (121); (iv) removing said masking layer (16); (v) forming a second electrode layer (122) directly over the exposed surface of the first electrode layer (121); 1. A method for producing an electrode (12), comprising:

2. The method of claim 1 , wherein the second electrode layer (122) is produced by physical vapor deposition.

3. LiCoO ２ The method according to claim 1 or 2, wherein a first electrode layer (121) and a second electrode layer (122) are produced by a method comprising the steps of:

4. 4. The method of claim 1, further comprising producing at least a third electrode layer on the second electrode layer (122) by repeating steps (ii) to (v).

5. 5. The method according to claim 1, wherein the thickness of the last electrode layer of the electrode (12), which is furthest from the first electrode layer (121), is less than the thickness of the other electrode layers constituting the electrode (12).

6. 6. The method of claim 1, wherein forming the masking layer (16) comprises forming at least one pattern (1212) directly through a thickness of the masking layer (16) to expose a third portion of the first electrode layer (121), and the removal is configured to produce a removal of additional material from the third portion (1212).

7. 7. A method for producing an electrochemical energy storage device comprising producing at least a first electrode (12) by carrying out the method according to any one of claims 1 to 6.

8. 8. The method according to claim 7, comprising the steps of forming a first collector (11) on a support (10) and then producing said first electrode (12) on said first collector (11).

9. 9. The method according to any one of the preceding claims, wherein forming the masking layer (16) comprises depositing a resin by spin coating.

10. An electrode for an electrochemical energy storage device comprising a plurality of stacked layers (121, 122), characterized in that a first electrode layer (121) of the plurality of stacked layers (121, 122) comprises at least one cavity formed hollow in its thickness, and a second electrode layer (122) of the plurality of stacked layers located directly above the first electrode layer at least partially covers an exposed surface of the first electrode layer (121) and fills the at least one cavity.

11. The electrode of claim 10 , wherein the at least one cavity comprises a cavity extending through the entire thickness of the first electrode layer (121 ).

12. 12. The electrode according to claim 10 or 11, wherein an electrode layer in the plurality of stacked layers (121, 122) has a thickness of 1 μm or more and / or 10 μm or less.

13. 13. The electrode according to any one of claims 10 to 12, wherein at least two directly successive layers of the plurality of stacked layers (121, 122) have the same thickness.

14. Electrochemical energy storage device comprising a first collector (11), a first electrode (12), an electrolyte (13), a second electrode (14) and a second collector (15) in a stack on a support (10), wherein at least one of the first electrode (12) and the second electrode (14) is according to any one of claims 10 to 13.

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