Negative electrode for electric battery incorporating a natural binder

Abstract

Negative electrode for electric battery comprising at least one first binder selected from one of the following compounds: egg yolk, egg white, glutinous rice, flax seeds or a mixture thereof.

Description

Title of the invention: Negative electrode for an electric battery incorporating a natural binder. Technical field

[0001] The present invention relates, in general, to electric batteries, in particular an electric battery for a motor vehicle.

[0002] More specifically, the invention relates to a method for manufacturing a negative electrode for an electric battery incorporating a natural binder, a negative electrode assembly comprising such a negative electrode positioned on a current collector, an electrochemical cell of an electric battery incorporating such a negative electrode, an electric battery comprising such an electrochemical cell and a motor vehicle comprising such an electric battery. Previous techniques

[0003] An electrochemical cell of an electric battery comprises a positive electrode called the "cathode", a negative electrode called the "anode", an electrolyte allowing the circulation of ions between the anode and the cathode, and anodic and cathodic current collectors carrying, respectively, the anode and the cathode and connecting them to the external circuit.

[0004] Classically, the electrodes consist of an active material, the majority of which receives the ions that move between the positive and negative electrodes during the charging and discharging cycles of the battery, an electronic conductive agent which ensures the passage of electrons from the current collector to the active material, and a binder which allows the mechanical strength of the electrodes and the adhesion of the different compounds to the current collector.

[0005] Conventional electrodes include a chemical binder, often formed by a fluorinated polymer such as polyvinylidene fluoride PVDF, cellulose-based binders such as carboxymethyl cellulose CMC or even gum, such as styrene-butadiene rubber SBR.

[0006] These chemical binders, which are not found naturally in the environment, need to be synthesized and the production sites of such binders may be far away, which affects their availability as well as their cost.

[0007] Furthermore, the presence of chemical binder complicates the recycling of the electrodes. Description of the invention

[0008] The present invention therefore aims to overcome the aforementioned drawbacks by providing a negative electrode for an electric battery whose recycling is facilitated. and manufacturing is simplified by limiting its production cost and improving the availability of the binder it incorporates.

[0009] In the description of the invention which will be made, the expression "at least one" used shall be considered equivalent to the expression "one or more".

[0010] Furthermore, it is specified that the expression "between ... and ..." used in this description of the invention should be understood as including each of the limits mentioned.

[0011] The present invention relates to a negative electrode for an electric battery comprising at least a first binder chosen from one of the following compounds: egg yolk, egg white, glutinous rice, flax seeds or a mixture thereof.

[0012] Preferably, the first binder comprises a content of between 3 and 30% by mass of egg yolk, egg white, flaxseed, glutinous rice or a mixture thereof relative to the total mass of the negative electrode.

[0013] More preferably, the first binder comprises a content of between 5 and 20% by mass relative to the total mass of the negative electrode.

[0014] The said ranges of values ​​of the content of first binder in % mass refer to compounds in anhydrous form, i.e. without water.

[0015] Preferably, the first binder comprises egg yolk, egg white, glutinous rice in the form of flour or flaxseed in the form of powder.

[0016] Advantageously, the negative electrode further comprises at least one active material and at least one electronically conductive agent.

[0017] Preferably, the active material content is between 85 and 97% by mass relative to the total mass of the negative electrode.

[0018] The active material can, for example, be chosen from one of the following compounds: graphite LiC6, Silicon (oxide SiOx or metallic, Li4Ti50i2 (LTO)), hard carbon.

[0019] The electronic conducting agent may, for example, be carbon black, acetylene black, carbon nanotubes or graphene.

[0020] Advantageously, the negative electrode may include, in addition to the first binder, a second binder different from the first binder.

[0021] Preferably, the second binder is a chemical binder.

[0022] In the present invention, chemical binder means a binder synthesized by man, which is not found naturally in the environment, unlike a natural binder such as egg yolk, egg white, glutinous rice and flax seeds.

[0023] For example, the second binder is chosen from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, or a gum such as styrene-butadiene rubber SBR, a polyacrylic acid, or a mixture of these.

[0024] Preferably, the total content of first and second binders is between 5 and 20% by mass relative to the total mass of the negative electrode.

[0025] In the present invention, the total mass of the negative electrode means the mass of the active material, the electronic conductive agent, the first binder, and optionally the second binder when present.

[0026] In one embodiment, the negative electrode may consist of an active material, an electronic conductive agent, a first binder chosen from one of the following compounds: egg yolk, egg white, glutinous rice, flax seeds or a mixture thereof.

[0027] According to an alternative, the negative electrode can consist of an active material, an electronic conducting agent, a first binder chosen from one of the following compounds: egg yolk, egg white, glutinous rice, flax seeds or a mixture thereof, and a second binder different from the first binder, preferably a second chemical binder.

[0028] For example, the second binder is chosen from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, or a gum such as styrene-butadiene rubber SBR, a polyacrylic acid, or a mixture of these.

[0029] Preferably, the porosity of the negative electrode is between 20 and 60%.

[0030] The invention also relates to a negative electrode assembly comprising a negative electrode as previously described and a current collector on which the negative electrode is positioned.

[0031] For example, the current collector can be made of copper.

[0032] In one embodiment, the current collector may be made of foam, such as copper foam. In this case, the negative electrode is positioned on the surface and within the porosity of the foam collector.

[0033] Alternatively, the current collector can be at least partially covered with an adhesive layer comprising a conductive material, such as carbon black, and a second binder. In this case, the negative electrode is positioned on the surface of the adhesive layer.

[0034] Advantageously, the second binder for forming the adhesion layer can be chosen from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, or a gum such as styrene-butadiene rubber SBR, a polyacrylic acid, or a mixture thereof.

[0035] Preferably, the second binder for forming the adhesion layer is identical to the second binder of the negative electrode when the latter incorporates a second binder.

[0036] Preferably, the thickness of the adhesion layer is between 1 and 5 nm.

[0037] In one embodiment, the negative electrode comprises egg white and is positioned on a foam current collector, such as copper foam.

[0038] In one embodiment, the negative electrode comprises egg white and is positioned on a current collector having an adhesion layer comprising a conductive material, such as carbon black, and a second binder.

[0039] The invention also relates to an electrochemical cell for an electric battery comprising a negative electrode and / or a negative electrode assembly as previously described.

[0040] In addition, the electrochemical cell may, for example, comprise a liquid electrolyte LPX based on carbonate and a lithium salt, comprising 1 mol / L of lithium salt LiPF6 in Ethylene carbonate (EC): Dimethyl carbonate (DMC): Ethyl methyl carbonate (EMC) in the following proportions 1:1:1 by volume.

[0041] The invention also relates to an electric battery comprising at least one electrochemical cell as described above.

[0042] Such an electric battery can be integrated into any type of system incorporating an electric battery, stationary or not, such as, for example, a motor vehicle, a bus, a scooter, a motorcycle, a portable electronic device, etc.

[0043] Such an electric battery is, for example, a Li-ion battery or a Na-ion battery.

[0044] The invention also relates to a motor vehicle comprising at least one electric battery as previously described.

[0045] The invention also relates to a method for manufacturing a negative electrode as previously described, comprising the following steps:

[0046] a) mixing an active material, an electronic conductive agent, said first binder, optionally the second binder, and optionally a solvent, to form an ink;

[0047] b) coat the ink obtained onto a current collector;

[0048] c) dry the coating;

[0049] d) to proceed with calendering; and

[0050] e) recover the negative electrode obtained.

[0051] Step a) includes bringing together the active material, the electronic conductive agent, and the first binder to form the ink.

[0052] The first binder is chosen from one of the following compounds: egg yolk, egg white, glutinous rice, flax seeds or a mixture of these.

[0053] Preferably, the first binder comprises a content of between 3 and 30% by mass of egg yolk, egg white, flaxseed, glutinous rice or a mixture thereof relative to the total mass of the negative electrode.

[0054] More preferably, the first binder comprises a content of between 5 and 20% by mass relative to the total mass of the negative electrode.

[0055] The said ranges of values ​​of the content of first binder in % mass refer to compounds in anhydrous form, i.e. without water.

[0056] Flax seeds can be added to the mixture in step a) in powder form.

[0057] Glutinous rice can be added to the mixture in step a) in the form of flour.

[0058] The active material may, for example, be chosen from one of the following compounds: Graphite LiC6, Silicon (SiOx oxide or metallic, Li4Ti50i2 (LTO)), hard carbon.

[0059] The electronic conducting agent can, for example, be carbon black, acetylene black, carbon nanotubes, graphene.

[0060] In one embodiment, a solvent may also be added to the mixture to form the ink.

[0061] The solvent is, for example, water, demineralized water, N-Methyl-2-pyrrolidone (NMP).

[0062] Preferably, the solvent is an aqueous solvent, in which the first natural binder is easily dissolved and which facilitates the recycling of the negative electrode.

[0063] In one embodiment, the first binder comprises or consists of egg white and / or egg yolk. Egg white and egg yolk naturally contain a large amount of water, so in this case, the amount of solvent can be limited or even eliminated. Reducing the solvent leads to a decrease in the manufacturing cost of the negative electrode.

[0064] Preferably, when the first binder added in step a) comprises or consists of egg white, the water content of the added egg white is between 80 and 90% relative to the total mass of egg white added. This value can be measured using a heated desiccant balance.

[0065] In one embodiment, a second binder, such as a second chemical binder, may also be added to the mixture.

[0066] Preferably, the second binder is a chemical binder.

[0067] For example, the second binder is chosen from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC or a gum, such as styrene-butadiene rubber SBR, polyacrylic acid or a mixture of these.

[0068] In step b), the ink obtained at the end of step a) is coated onto a current collector.

[0069] In one embodiment, the ink deposited on the collector can be deposited by liquid coating. The coated ink is liquid.

[0070] According to an alternative, the ink deposited on the collector can be deposited by semi-solid coating. The coated ink is a gel or a paste.

[0071] For example, the current collector on which the ink is coated can be made of copper.

[0072] In one embodiment, the current collector may be made of foam, such as copper foam. In this case, the ink is coated onto the surface and within the porosity of the foam collector.

[0073] Alternatively, the current collector can be at least partially covered with an adhesive layer comprising a conductive material, such as carbon black, and a second binder. In this case, the ink is coated onto the surface of the adhesive layer.

[0074] Advantageously, the second binder for forming the adhesion layer can be chosen from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, or a gum such as styrene-butadiene rubber SBR, a polyacrylic acid, or a mixture thereof.

[0075] Preferably, the second binder for forming the adhesion layer is identical to the second binder of the ink when the latter incorporates a second binder.

[0076] Preferably, the thickness of the adhesion layer is between 1 and 5 nm.

[0077] The ink coated on the current collector is then dried in step c) in order to remove the solvent added in step a) and / or the water naturally present in the first binder such as, for example, the water from the egg white.

[0078] The ink is advantageously dried by heating in one or more stages, at a temperature between 50 and 90 °C.

[0079] The assembly formed by the current collector and the dried ink disposed on the surface of the current collector is subjected to a step d) of calendering between two rollers in order to apply homogeneous pressure over the entire surface of the coating and thus control its final thickness and porosity.

[0080] Preferably, calendering is carried out until a porosity of the negative electrode is obtained between 20 and 60%.

[0081] The negative electrode obtained formed on the current collector is recovered in step e). Examples

[0082] Example 1: Formation of a negative electrode incorporating a first binder comprising egg yolk and formation of an electrochemical half-cell incorporating such a negative electrode

[0083] A negative electrode ink is obtained by mixing an active material formed by graphite, an electronic conductive agent formed by carbon black, a solvent formed by demineralized water and a binder formed by egg yolk.

[0084] The content of the ink formed in active material and electronic conductive agent is, respectively, 80% by mass and 2% by mass relative to the total mass of the ink.

[0085] In addition, the ink comprises an 18% mass content of egg yolk, considered anhydrous.

[0086] The water content contained in the egg yolk which is added to form the ink is approximately 25% by mass.

[0087] The content of demineralized water is 67% by mass relative to the total mass of the ink.

[0088] The egg yolk is added in three stages to the rest of the mixture, with a mixing step after each addition.

[0089] The ink from the mixture is coated onto a copper current collector.

[0090] The coating was then dried at 80°C for 100.

[0091] After drying, calendering was carried out until a porosity of 50% was reached.

[0092] A negative electrode incorporating a binder comprising egg yolk is thus obtained.

[0093] Two button cell batteries were assembled and then cycled.

[0094] The electrolyte is a liquid LPX electrolyte based on lithium carbonate and lithium salt, comprising 1 mol / L of lithium salt LiPF6 in Ethylene carbonate (EC): Dimethyl carbonate (DMC): Ethyl methyl carbonate (EMC) in the following proportions 1:1:1 by volume.

[0095] The applied cycling comprises three training cycles at a C / 10 regime at 25°C. The capacity and efficiency results obtained for the first and third training cycles are reported in Table 1.

[0096] For comparison purposes, the results obtained on electrochemical half-cells incorporating a mixture of common binders are reported in Table 2. The mixture of common binders is formed by CMC and SBR in a 1:1 ratio by mass.

[0097] [Tables 1] First binder: egg white 1st cycle 3rd cycle Capacity (mAh / g) 261 240 Efficiency (%) 88 84

[0098] [Tables2] Common binders: CMC / SBR 1st cycle 3rd cycle Capacity (mAh / g) 384 360 Efficiency (%) 92 99

[0099] As can be seen, the particularly high capacity and efficiency obtained make it possible to consider replacing all or part of the usual chemical binders of the negative electrodes with natural binders such as egg yolk, which is naturally present in the environment, easily accessible and available.

[0100] Furthermore, the presence of water in the composition of the egg yolk made it possible to reduce the amount of solvent used and therefore to lower the manufacturing cost of the negative electrode. Its recycling is thus facilitated.

[0101] Example 2: Formation of a negative electrode incorporating a first binder comprising egg white

[0102] A negative electrode ink is obtained by mixing an active material, an electronic conductive agent, a first binder formed by egg white and a solvent formed by distilled water.

[0103] The quantity of egg white, considered anhydrous, added to the mixture is between 5 and 20% by mass.

[0104] The mixture may include a second binder, such as selected from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC or a gum, such as styrene-butadiene rubber SBR, polyacrylic acid or a mixture thereof.

[0105] The egg white was added in three stages to the rest of the mixture.

[0106] The quantity of water in the egg white was previously checked and adjusted using a heated desiccant balance so as to be between 80 and 90%.

[0107] The distilled water content is 20% by mass relative to the total mass of the ink.

[0108] The different compounds are mixed at a speed of between 1000 and 2000 rotations per minute. The resulting ink has the appearance of an airy foam, which is due to the mixing speed.

[0109] It is possible to reduce this mixing speed to between 100 and 500 rotations per minute to maintain a less aerated structure.

[0110] In a first embodiment, the ink obtained is deposited on a copper current collector coated with an adhesion layer between 1 and 5 nm thick. The adhesion layer comprises carbon and a binder.

[0111] Preferably, the binder of the adhesion layer is identical to the second binder of the ink when a second binder is added to the ink.

[0112] The adhesion layer on the current collector ensures better adhesion of the ink to the collector. Without this adhesion layer, the material tends to slide on the copper surface.

[0113] The coating thickness is between 100 and 250 µm, which ensures good distribution of the material on the current collector.

[0114] In a second embodiment, the ink obtained is deposited on a copper foam current collector. The foamy-looking ink becomes intercalated in the porosity of the copper foam collector.

[0115] The coatings obtained in the first and second embodiments are dried at 80°C for 10 minutes. The structure of the electrode solidifies during this drying step due to the presence of the egg white.

[0116] Following these steps, calendering was carried out until a porosity of between 20 and 60% was achieved.

[0117] In the second embodiment in which a foam collector is used, the porosity of the negative electrode may be less than the porosity of the negative electrode obtained in the first embodiment, which increases the density of the electrode.

[0118] Two negative electrodes incorporating a binder comprising egg white were thus obtained.

[0119] The high water content of egg yolk made it possible to reduce the amount of solvent used and therefore lower the manufacturing cost of the negative electrode. This also facilitates its recycling.

[0120] Egg white provides a foamy structure to the negative electrode, which improves the mechanical strength of silicon-based electrodes, particularly in the case of volumetric expansion during charge and discharge cycles.

[0121] From a rheological point of view, the foamy structure of the ink allows better stability over time, slows down the sedimentation effect of the materials that compose it and fixes the porosity of the electrode from the moment of coating.

[0122] Example 3: Formation of a negative electrode incorporating a first binder comprising rice flour, by liquid coating

[0123] In a first step, a gel is prepared by mixing glutinous rice flour, known as Oryza sativa L, and demineralized water. The glutinous rice flour content of the gel is between 2 and 8% by mass.

[0124] A negative electrode ink is formed by mixing an active material, an electronic conductive agent and the gel.

[0125] The mixture may include a second binder, such as one selected from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, or a polyacrylic acid or even a rubber, such as styrene-butadiene rubber (SBR) or a mixture thereof.

[0126] The quantity of glutinous rice flour, considered anhydrous, added to the mixture is between 5 and 20% by mass.

[0127] The gel is added in three stages to the rest of the mixture.

[0128] The ink obtained is deposited on a copper current collector. The coating thickness is between 100 and 250 µm to ensure good distribution of the material on the current collector.

[0129] Initially, the coating is heated to a temperature between 40°C and 60°C for approximately 30 minutes in order to further gel the ink.

[0130] Then, in a second step, the coating is dried at 80°C for 10 minutes in order to remove all the water.

[0131] Following these drying steps, calendering was carried out until a porosity of between 20 and 60% was reached.

[0132] A negative electrode incorporating a binder comprising glutinous rice flour was thus obtained.

[0133] Example 4: Formation of a negative electrode incorporating a first binder comprising rice flour, by semi-solid coating

[0134] A negative electrode ink is formed by mixing an active material, an electronic conductive agent, a first binder made from glutinous rice flour, known as Oryza sativa L, and demineralized water.

[0135] The mixture may include a second binder, such as selected from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, a polyacrylic acid or a gum, such as styrene-butadiene rubber SBR or a mixture thereof.

[0136] The quantity of solvent added, here water, is advantageously less than 10% of the total mass of the ink, which allows the ink to be formed in paste form.

[0137] The quantity of glutinous rice flour, considered anhydrous, added to the mixture is between 3 and 30% by mass.

[0138] The paste can be obtained via several types of mixers: extruder, Z-arm mixer, etc. The paste is then passed through a rolling mill to form a film with a thickness between 100 and 300 µm.

[0139] A second hot lamination step allows the paste to be coated onto a copper current collector with a thickness between 4 and 15 pm.

[0140] The coating obtained was dried at 80°C for approximately 10 minutes in order to remove all the water.

[0141] A calendering process was then carried out until a porosity of between 20 and 60% was achieved.

[0142] A negative electrode incorporating a binder comprising glutinous rice flour was thus obtained.

[0143] Example 5: Formation of a negative electrode incorporating a first binder comprising flaxseed powder

[0144] Flax seeds are ground using a marble mortar and pestle for 5 to 15 minutes or using a blender with cutting blades at a speed of approximately 10,000 rpm. The resulting flour-like powder has a particle size between 100 µm and 300 µm.

[0145] A negative electrode ink is formed by mixing an active material, an electronic conductive agent, a first binder formed by the obtained linseed flour, and a solvent formed by demineralized water.

[0146] The mixture may include a second binder, such as selected from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC or a gum, such as styrene-butadiene rubber SBR or a mixture thereof.

[0147] The flaxseed flour was added in two stages to the rest of the mixture.

[0148] As soon as water is added, the ink gels and allows the particles to remain in the mixture. This is due to the presence of mucilage from flax seeds, composed of polysaccharides, which have the property of swelling on contact with water, giving the ink a viscous and sticky consistency.

[0149] After mixing, the resulting ink is deposited onto a copper current collector. The coating thickness is between 100 and 250 µm to ensure good distribution of the material on the current collector.

[0150] The coating is then dried at 80°C for 10 minutes in order to remove all the water.

[0151] Finally, calendering is carried out until a porosity of between 20 and 60% is reached.

[0152] A negative electrode incorporating a binder comprising linseed flour is thus obtained.

[0153] The gelling power of flaxseed flour is superior to that of common chemical binders.

Claims

Demands

1. Negative electrode for electric battery comprising at least a first binder selected from one of the following compounds: egg yolk, egg white, glutinous rice, flaxseed or a mixture thereof.

2. Negative electrode according to claim 1, wherein the first binder comprises a content of between 3 and 30% by mass of egg yolk, egg white, flaxseed, glutinous rice or a mixture thereof relative to the total mass of the negative electrode, preferably a content of between 5 and 20% by mass relative to the total mass of the negative electrode.

3. Negative electrode according to claim 1 or 2, comprising at least a second binder different from the first binder, preferably the second binder being a chemical binder, such as selected from one of the following compounds: a fluorinated polymer such as polyvinylidene fluoride PVDF, a cellulose-based compound such as carboxymethyl cellulose CMC, a polyacrylic acid or a gum, such as styrene-butadiene rubber SBR or a mixture thereof.

4. Negative electrode assembly comprising a negative electrode as defined in any one of the preceding claims and a current collector on which the negative electrode is positioned.

5. Assembly according to claim 4, wherein the current collector is made of foam, such as copper foam.

6. A method for manufacturing a negative electrode as defined in any one of claims 1 to 3, comprising the following steps: a) mixing an active material, an electronic conductive agent, said first binder, optionally the second binder, and optionally a solvent, to form an ink; b) coating the resulting ink onto a current collector; c) drying the coating; d) calendering; and e) recovering the resulting negative electrode.

7. A manufacturing method according to claim 6, wherein the current collector on which the ink is deposited in step b) is made of foam, such as a copper foam current collector.

8. 13 Electrochemical cell for electric battery comprising a negative electrode according to any one of claims 1 to 3 and / or a negative electrode assembly according to any one of claims 4 or 5.

9. Electric battery comprising at least one electrochemical cell according to claim 8.

10. Motor vehicle comprising at least one electric battery according to claim 9, such as a lithium-ion battery.