Current collector coating

Abstract

An electrode comprising: - a planar current collector, - a coating covering at least partially one or both faces of the current collector, the coating comprising carbon nanotubes or carbon nanofibers or a mixture thereof, and optionally one or more binders, the longitudinal axis of at least 50% of the carbon nanotubes or carbon nanofibers forming an average angle of less than 30° with respect to the plane of the current collector, - an active material composition layer in contact with the coating, said active material composition layer comprising at least one active material and optionally one or more electronically conductive compounds and one or more binders. Abbreviated figure: Figure 2b

Description

Title of the invention: Coating for current collector technical field

[0001] The present invention relates to the field of electrodes for secondary electrochemical elements, more especially lithium-ion type electrochemical elements. It relates in particular to the field of manufacturing processes for coatings intended to improve the stability of electronic conductivity between a coated active material composition layer and a current collector during the cycling operation of a lithium-ion electrochemical element. Background

[0002] An electrode of an electrochemical element generally comprises a current collector and a layer of active material composition deposited on at least one face of this current collector. The current collector may be in the form of a grid, a foam, or a solid or perforated metal strip.

[0003] During the charge / discharge cycles of the electrochemical element, the active material composition layer undergoes a succession of expansions and contractions that gradually detach it from the surface of the foil. This detachment can also result from vibrations experienced by the element during transport or use. The detachment of the active material composition layer is also called delamination. Delamination leads to a progressive decrease in the element's capacity and a reduction in its lifespan.

[0004] It is known to apply a coating prior to the deposition of the active material composition layer in order to improve the electronic conductivity between the foil and the active material composition layer and / or to improve the adhesion of the active material composition layer to the foil. The objective of this coating is to achieve this conductivity improvement primarily at the beginning of the electrochemical element's life, particularly to increase its performance under high-speed conditions.

[0005] We are looking for an electrode coating which on the one hand has a high electronic conductivity in a direction parallel to the longitudinal plane of the electrode and which on the other hand limits the effect of delamination on the decrease in the electronic conductivity of the electrode, making it possible to increase the lifetime of the electrochemical element without impacting its initial performance. Summary

[0006] To this end, the invention proposes an electrode comprising: - a flat current collector, - a coating covering at least partially one or both faces of the current collector, the coating comprising carbon nanotubes or carbon nanofibers or a mixture thereof, and possibly one or more binders, the longitudinal axis of at least 50% of the carbon nanotubes or carbon nanofibers forming an average angle of less than or equal to 30° with respect to the plane of the current collector, - a layer of active material composition in contact with the coating, said layer of active material composition comprising at least one active material and possibly one or more electronically conductive compounds and one or more binders.

[0007] It has been discovered that by coating the current collector with a coating comprising carbon nanotubes and / or carbon nanofibers and by orienting these nanotubes and / or nanofibers in a direction forming an average angle of less than or equal to 30° with respect to the longitudinal plane of the current collector, it is possible to obtain a current collector exhibiting high electronic conductivity. Typically, electronic conductivity values ​​in the range of 10² to 10⁴ S·cm¹ are obtained. Therefore, such a coating makes it possible to limit the decrease in the electrode's electronic conductivity in the event of delamination.

[0008] According to one embodiment, the coating has greater adhesion to the active material composition layer than to the current collector.

[0009] According to one embodiment, the longitudinal axis of the carbon nanotubes or carbon nanofibers forms an average angle less than or equal to 20° with respect to the plane of the current collector.

[0010] According to one embodiment, the longitudinal axis of the carbon nanotubes or carbon nanofibers forms a mean angle less than or equal to 10° with respect to the plane of the current collector.

[0011] According to one embodiment, the entire face or faces of the current collector are covered by the coating.

[0012] According to one embodiment, the carbon nanotubes and / or carbon nanofibers have a form factor of at least 1000.

[0013] According to one embodiment, the carbon nanotubes or carbon nanofibers have a diameter ranging from 0.1 to 30 nm.

[0014] According to one embodiment, the carbon nanotubes or carbon nanofibers have a diameter ranging from 0.5 to 2 nm.

[0015] According to one embodiment, the coating has an electronic conductivity ranging from 102 to 104 S.cm1, the electronic conductivity being measured along the longitudinal direction of the coating.

[0016] According to one embodiment, the coating has a thickness greater than or equal to 1 pm and less than or equal to 5 pm.

[0017] According to one embodiment, the coating is free of carbon black.

[0018] The invention also relates to a lithium-ion electrochemical element comprising: - at least one positive electrode, - at least one negative electrode, said at least one positive electrode and / or said at least one negative electrode being an electrode as defined above, - a solid electrolyte.

[0019] The invention also relates to a method for manufacturing an electrode as defined above, said method comprising: a) the preparation of a mixture comprising carbon nanotubes or carbon nanofibres or a mixture thereof, an aqueous or non-aqueous solvent, and one or more binders, b) the deposition on one of the faces of a current collector of the mixture from step a), (c) evaporation of the solvent to obtain a current collector coated with a coating comprising carbon nanotubes or carbon nanofibres or a mixture thereof, and said one or more binders, d) the deposition of a layer of active material composition onto the coating to obtain an electrode, said layer of active material composition comprising at least one active material and optionally one or more electronically conductive compounds and one or more binders, e) electrode compression.

[0020] According to one embodiment, the mixture in step a) contains the constituents in the following mass proportions: - 0.1 to 10% of carbon nanotubes or carbon nanofibers or a mixture thereof, - 0.3 to 2% of one or more binders, - the remainder being made up of one or more solvents.

[0021] According to one embodiment, the process does not include a coating compression step between steps c) and d). Brief description of the figures

[0022] [Fig.la] schematically represents a cross-section of an electrode comprising a current collector coated with carbon nanotubes or nanofibers whose longitudinal axis forms an angle ul less than or equal to 30° with respect to the plane of the current collector.

[0023] [Fig.lb] schematically represents a cross-section of an electrode comprising a current collector coated with carbon nanotubes or nanofibers whose longitudinal axis forms an angle u2 greater than 30° with respect to the plane of the current collector.

[0024] [Fig.2a] schematically represents a cross-section of an electrode comprising a current collector coated with carbon black particles, which are covered with particles of active material.

[0025] [Fig.2b] schematically represents a cross-section of an electrode comprising a current collector coated with carbon nanotubes, which are covered with particles of active material. Detailed description of embodiments Electrode coating

[0026] An electrode according to the invention comprises a current collector, at least one face of which is coated with a coating comprising carbon nanotubes or carbon nanofibers or a mixture thereof, the coating itself being covered with a layer of active material composition. "Active material composition" means a composition comprising one or more active materials and optionally one or more binders and one or more electronically conductive materials.

[0027] Carbon nanotubes and nanofibers inherently exhibit a high aspect ratio. The aspect ratio is the ratio of the length of a nanofiber or nanotube to its diameter. This high aspect ratio promotes electron transport within the nanotubes and nanofibers. The electron transfer resistance between two nanotubes in contact with each other (or between two nanofibers in contact with each other) is minimized. The longitudinal axis of at least 50% of the nanotubes and / or nanofibers forms a mean angle θ with respect to the current collector surface of less than or equal to 30°, or less than or equal to 20°, or less than or equal to 10°, or less than or equal to 5°.In the case of curved carbon nanotubes or nanofibers, we consider the mean angle u which is the integral over the length of the nanofiber or nanotube of the angle values ​​u(x) at any point x of the nanofiber or nanotube, (u(x) being the angle formed between the tangent of the nanofiber or nanotube and the collector), divided by the length of the nanotube or carbon nanofiber considered, i.e.: .

[0028] [Math.l] Jou(x)xdx û = —L”“ where L denotes the length of the nanofiber or nanotube.

[0029] This average angle can be evaluated by taking a scanning electron microscopy (SEM) photograph of the electrode cross-section and analyzing the resulting image by computer. Sample preparation methods for SEM imaging are known to those skilled in the art. A suitable preparation method may involve using an ion polishing sectioning technique on the nanotube or nanofiber deposit on the current collector.

[0030] It has been observed that, for a given coating thickness and a given number of carbon nanofibers or nanotubes in that coating, a coating in which the carbon nanofibers or nanotubes form an angle of 30° or less with respect to the current collector plane exhibits significantly higher electronic conductivity than a coating in which the carbon nanofibers or nanotubes form an angle greater than 30° with respect to the current collector plane. These two situations are schematically represented in Figures 1a and 1b, respectively, assuming that the nanofibers or nanotubes are straight. In the situation of [Fig. 1a] according to the invention, there are 28 fibers. They are arranged in 4 layers, each consisting of 7 fibers. The fibers are inclined at an angle λ of 30° or less. In the situation of [Fig. 1b] outside the invention, there are also 28 fibers.They are arranged in 2 layers, each consisting of 14 fibers. The fibers are inclined at an angle u2 greater than 30°. The coating thickness is identical in both cases, and the number of carbon nanotubes or nanofibers is also identical. However, the electronic conductivity of the coating in [Fig. 1a] is significantly higher than that of the coating in [Fig. 1b].

[0031] A high aspect ratio of carbon nanotubes and nanofibers, combined with a specific orientation of the nanotubes and nanofibers, makes it possible to obtain a coating with high electronic conductivity in the longitudinal direction. The electronic conductivity value is in the range of 10² to 10⁴ S·cm⁻¹ or 5 x 10⁻¹ to 10⁻¹⁰ S·cm⁻¹, preferably in the range of 10⁻¹⁰ to 10⁻¹⁰ S·cm⁻¹. These values ​​are given for a coating thickness of 5 µm or less.

[0032] The form factor can be greater than or equal to 100 or greater than or equal to 500 or greater than or equal to 1000.

[0033] Carbon nanotubes or nanofibers can have a diameter ranging from 0.1 to 30nm or from 0.2 to 1nm or from 0.5 to 2nm.

[0034] Carbon nanotubes or nanofibers can have a length ranging from 500nm to 50pm.

[0035] Carbon nanotubes can be single-walled or multi-walled. According to one embodiment, they are single-walled carbon nanotubes with a diameter ranging from 0.5 to 2 nm and a length ranging from 500 nm to 100 pm.

[0036] The diameter and length of the carbon nanotubes and nanofibers can be determined by photography taken using a scanning electron microscope.

[0037] Typically, the coating has a thickness of less than 20 µm, or less than or equal to 1 µm, or less than or equal to 5 µm, for example between 1 and 3 µm. This thinness of the coating ensures that the volumetric capacity of the element is not negatively impacted.

[0038] The coating preferably further comprises one or more binders.

[0039] According to one embodiment, the coating further comprises one or more surfactants.

[0040] According to one embodiment, the coating consists solely of carbon nanotubes and / or nanofibers and one or more binders.

[0041] According to one embodiment, the coating consists solely of carbon nanotubes and / or nanofibers, one or more binders and one or more surfactants.

[0042] Preferably, at least 75% or at least 90% or at least 95% or at least 99% of the carbon nanotubes or nanofibers form an average angle of less than or equal to 30° with respect to the plane of the current collector.

[0043] Preferably, the coating uniformly covers the surface of the current collector. Uniformly means the absence of cracks or areas where the surface of the current collector is not covered by the coating. The presence of cracks prevents high longitudinal electronic conductivity. A continuous coating maximizes electronic conductivity in the longitudinal direction of the electrode. The difference between the smallest and largest values ​​of the coating thickness may be less than or equal to 500 nm, less than or equal to 200 nm, less than or equal to 100 nm, less than or equal to 50 nm, or less than or equal to 100 nm.

[0044] Preferably, the coating covers at least 90% or at least 95% or at least 99% or 100% of the area of ​​one face of the current collector.

[0045] It is essential that the adhesion of the nanotube and / or carbon nanofiber coating to the current collector be less than the adhesion of the coating to the active material composition layer. To this end, during the electrode manufacturing process, the calendering step will preferably be carried out after the active material composition layer has been deposited on the coating. Preferably, no calendering will be carried out between the deposition of the coating and the deposition of the active material composition layer on the coating. The absence of calendering between the deposition of the coating and the deposition of the active material composition layer on the coating prevents alteration of the adhesion zone constituted by the end nanotubes and / or nanofibers are used to promote the adhesion of the coating to the active ingredient layer. Preferably, the nanotube and / or nanofiber layer has a porosity of 60% or higher, or 70% or higher, before being coated with the active ingredient.

[0046] The coating may be present on one or both faces of the current collector.

[0047] In addition to achieving high electronic conductivity in the longitudinal direction of the electrode, the coating limits the decrease in the electrode's electronic conductivity in the event of delamination. Figure 2a schematically shows a cross-section of an electrode (1) comprising a current collector (2) coated with a layer of carbon black particles (3), which is itself covered with a layer of active material particles (4). A portion (5) of the active material particle layer is detached from the current collector and contributes significantly less to current generation than the portions of the active material particle layer located on either side of the detached portion. Figure 2b schematically shows a cross-section of an electrode (1) comprising a current collector (2) coated with a layer of carbon nanotubes (3), which is itself covered with a layer of active material particles (4).A portion (5) of the active material particle layer is detached from the current collector. Despite this detachment, the carbon nanotube coating (3) adheres to the active material particle layer. The detached portion of the active material particle layer contributes more to current generation than the detached portion of [Fig. 2a]. The carbon nanotubes or nanofibers exhibit a greater affinity for the active material particles than for the current collector, which may explain why they follow the deformation of the active material particle layer.Since, on the one hand, the value of the electronic conductivity of the coating in the longitudinal direction is high and, on the other hand, the coating of nanotubes and / or carbon nanofibers adheres to the active material composition layer, in the event of delamination, such a coating makes it possible to limit the decrease in the electronic conductivity of the electrode in the delaminated area and thus avoids a loss of capacity of the element. Electrode

[0048] The electrode according to the invention can be a positive or negative electrode of a lithium-ion type electrochemical element. Positive electrode:

[0049] The positive active material can be any positive active material known in lithium electrochemical element technology. It can be a lithium oxide of at least one transition metal or a lithium phosphate of at least one metal. transition. The invention is of particular interest in the case of active materials with low electronic conductivity, such as transition metal lithia phosphates.

[0050] The lithium oxide of at least one transition metal may be chosen from: i) a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMnyCozMt)O2(NMC) where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; ii) a lithium oxide of nickel, cobalt and aluminium of formula Liw(NixCoyAlzMt)O2(NCA) where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; iii) a compound of formula Lii+xMi.xO2.yFy with cubic crystal structure where 0 <x<0,5 et 0<y<l et M représente un élément choisi dans le groupe constitué de Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd et Sm et des mélanges de ceux-ci ; (iv) a lithium nickel manganese oxide (NMX) of formula Lia(Nii_x y zMnxCoyMz)O2 with 0.9 <a<l,l ; 0,60<l-x-y-z<0,80 ; 0<x ; 0<y<0,02 ; 0<z ; et M étant choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La et des mélanges de ceux-ci ; (v) a lithium oxide of nickel and manganese of formula Liw(NixMnyCozMt)O2 where 1.1 <w<1,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci. vi) a lithium oxide of nickel and manganese of formula LixMn2.y.zM'yM"zO4.ô where M' and M" are chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; M' and M" being different from each other, and 1 <x<1,4 ; 0<y<0,6 ; 0<z<0,2 ; 0<ô<l, and mixtures of different compounds of categories i) to vi).

[0051] The lithium phosphate of at least one transition metal may be chosen from: a) a lithium iron phosphate of formula LixFei yMyPO4 (LFP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; b) a lithium manganese phosphate of formula LixMni yMyPO4 (LMP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; c) a lithium manganese and iron phosphate of formula: LixMni y zFeyMzPO4 (LMFP) where 0.8 <x<l,2 ; 0,5<l-y-z<l; 0<y+z<0,5 ; 0<y<0,50 et 0<z<0,2 et M est choisi dans le groupe constitué de Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S, Hf, Bi, Se et des mélanges de ceux-ci ; d) and mixtures of different compounds from categories a) to c).

[0052] Lithified phosphate particles, in particular lithium manganese iron phosphate (LMFP), can be coated with a layer of carbon in order to increase their electronic conductivity.

[0053] The current collector of the positive electrode is a solid or perforated metal strip which may be made of aluminum or an aluminum alloy. Its thickness may be in the range of 6 to 30 µm or 5 to 20 µm or 10 to 15 µm, preferably 10 to 15 µm.

[0054] The positive active material(s) may be mixed with one or more binders which may be selected from poly(vinylidene fluoride) (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl or butyl methacrylate), poly(vinyl chloride) (PVC), poly(vinyl formalin), polyester, sequenced polyetheramides, acrylic acid polymers, methacrylic acid polymers, acrylamide polymers, itaconic acid polymers, sulfonic acid polymers, elastomers, and cellulosic compounds such as carboxymethylcellulose (CMC). The elastomers that can be used as a binder can be chosen from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR).Preferably, said at least one binder is an aqueous dispersible binder, such as polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR) and polyvinyl alcohol (PVA).

[0055] The positive active material(s) may be mixed with one or more electronically conductive materials which may be selected from graphite, carbon black, acetylene black, soot, graphene, carbon fibers, nanotubes of carbon or a mixture thereof. The carbon fibers and carbon nanotubes may be the same as or different from those used in the coating.

[0056] The composition of the positive active ingredient may consist of: - 80 to 98% or 90 to 95% by mass of one or more positive active substances,

[0057] - 1 to 10% or 2 to 5% by mass of one or more binders,

[0058] - from 0.1 to 10% or from 2 to 5% by mass of one or more conductive materials electronics. Negative electrode:

[0059] The negative active material may be a material capable of incorporating lithium into its structure, such as graphite, coke, carbon black, and vitreous carbon. It may also be tin, silicon, carbon-silicon compounds, carbon-tin compounds, and carbon-tin-silicon compounds. It may be lithiased titanium oxides or titanium oxides capable of being lithiased.

[0060] Lithified titanium oxides and titanium oxides capable of being lithified may be selected from: i) compounds of formula Lix_aMaTiy_bM'bO4_c_dXc in which 0 <x<3 ; l<y<2,5 ; 0<a<l ; 0<b<l ; 0<c<2 et -2,5<d<2,5 ; l’indice d représente une lacune en oxygène et peut être inférieur ou égal à 0,5, M represents at least one element chosen from the group consisting of Na, K, Mg, Ca, B, Mn, Fe, Co, Cr, Ni, Al, Cu, Ag, Pr, Y and La; M' represents at least one element chosen from the group consisting of B, Mo, Mn, Ce, Sn, Zr, Si, W, V, Ta, Sb, Nb, Ru, Ag, Fe, Co, Ni, Zn, Al, Cr, La, Pr, Bi, Sc, Eu, Sm, Gd, Ce, Y and Eu; X represents at least one element chosen from the group consisting of S, F, Cl and Br. This family includes the compounds with the formula Li4Ti50i2, Li2TiO3 Li2Ti3O7 LiTi2O4 and Li2 Na2Ti60i4. ii) compounds of formula HxTiyO4 in which 0 <x<l ; 0<y<2. Cette famille inclut H2Ti60i3, H2Ti12O25 et TiO2 ; et iii) a mixture of compounds i) and ii).

[0061] Titanium and niobium oxides may have the formula LixTia_yMyNbb.ZM zO((x+4a+5b) / 2)-c-dXc where 0 <x<5 ; 0<y<l ; 0<z<2 ; l<a<5 ; l<b<25 ; 0,25<a / b<2 ; 0<c<2 et 0<d<2 ; a-y> 0; bz>0. The index d represents an oxygen vacancy. The index d can be less than or equal to 0.5. M and M' each represent at least one element chosen from the group consisting of Li, Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd and Sm; X represents at least one element chosen from the group consisting of S, F, Cl and Br;

[0062] This family includes the compounds of formula TiNb2O7, Ti2Nb2O9 and Ti2NbiO29.

[0063] The invention is of particular interest in the case of weakly conductive active materials, such as lithium titanium oxides of the type Lq TisOi2.

[0064] The negative current collector is a solid or perforated metal strip that can be made of copper or a copper-based alloy, or of aluminum or an aluminum alloy, or of stainless steel. Its thickness can range from 3 to 10 µm, preferably from 5 to 8 µm.

[0065] The composition of the negative active ingredient may consist of: - 85 to 98% or 90 to 98% by mass of one or more negative active ingredients, - 1 to 10% or 1 to 5% by mass of one or more binders, - 0 to 5% by mass or 1 to 5% of one or more electronically conductive materials.

[0066] The binder(s) of the negative active material composition may be chosen from the same list as that mentioned in relation to the positive active material composition. Within this same list, the binder(s) of the negative electrode may be different from those of the positive electrode. Similarly, the electronically conductive material(s) of the negative active material composition may be chosen from the same list as that mentioned in relation to the positive active material composition. Within this same list, the electronically conductive material(s) of the negative electrode may be different from those of the positive electrode. Electrode manufacturing process

[0067] The process according to the invention makes it possible to obtain a coating in which the longitudinal axis of the carbon nanotubes or nanofibers forms an average angle of less than or equal to 30° with respect to the plane of the current collector. The process according to the invention comprises the following steps: a) the preparation of a mixture comprising carbon nanotubes or nanofibers or a mixture thereof, an aqueous or non-aqueous solvent, and one or more binders, possibly one or more surfactants, b) the deposition on at least one of the faces of a current collector of the mixture from step a), (c) evaporation of the solvent to obtain a current collector coated with a coating comprising the carbon nanotubes or nanofibers or a mixture thereof, and said one or more binders, d) the deposition of an active material composition onto the coating to obtain an electrode, said active material composition comprising at least one active material and optionally one or more electronically conductive compounds and one or more binders, e) compression of the electrode by calendering.

[0068] To ensure a small mean angle, the carbon nanotubes and / or nanofibers must be deagglomerated. Carbon nanotubes and nanofibers are commercially available as a dispersion or suspension, aqueous or non-aqueous. To deagglomerate the carbon nanotubes and / or nanofibers, the dispersion or suspension is subjected to ultrasound prior to step a). Sonication can be performed using a probe immersed in the dispersion or suspension. The device used can be a Hielscher UP200St sonotrode (200 W; 26 kHz) set to an amplitude of 100%, pulses of 30%, and a power of 60%. Sonication can be carried out in six 3-minute stages, with two sonication stages separated by a 5-minute rest stage to prevent excessive heating of the dispersion / suspension. The addition of the binder(s) is generally carried out after sonication.The mixing of carbon nanotubes and / or nanofibres with the binder(s) can be carried out using a planetary mixer.

[0069] The process according to the invention is characterized in particular by the use in step a) of a dispersion containing a small proportion of carbon nanotubes and / or nanofibers and a small proportion of binder. This makes it possible to obtain a uniform and homogeneous coating which adheres to the active material composition in the event of delamination, as illustrated in [Fig. 2b].

[0070] By "small proportion of carbon nanotubes and / or nanofibers", we mean a proportion generally ranging from 0.1 to 10% or from 0.2 to 5% or from 0.5 to 2% or from 0.5 to 1%, the other constituents of the dispersion being one or more binders, one or more solvents and possibly one or more surfactants.

[0071] By "low proportion of binder" is meant a proportion generally ranging from 0.1 to 2% or from 0.3 to 2% or from 0.5 to 1%, the other constituents of the dispersion being carbon nanotubes and / or nanofibers, one or more solvents and possibly one or more surfactants.

[0072] The mass ratio between the carbon nanotubes and / or nanofibers and the binder(s) preferably ranges from 4 / 6 to 6 / 4. Within this range, the appearance of the coating is homogeneous. Beyond a value of 6 / 4, the mechanical strength of the coating may be insufficient.

[0073] The mixture in step a) may contain: - 0.1 to 10% of carbon nanotubes or carbon nanofibers or a mixture thereof, - 0.3 to 2% of one or more binders, - the remainder being made up of one or more solvents.

[0074] The mixture in step a) may contain: - 0.1 to 1% of carbon nanotubes or carbon nanofibers or a mixture thereof, - 0.1 to 1% of one or more binders, - the remainder being made up of one or more solvents.

[0075] The mixture in step a) may contain: - 0.2 to 1% of carbon nanotubes or carbon nanofibers or a mixture thereof, - 0.5 to 1% of one or more binders, - the remainder being made up of one or more solvents.

[0076] The solvent can be organic or inorganic. Preferably, it is water.

[0077] The binder is preferably water-dispersible. It can be a cellulose derivative, such as carboxymethylcellulose.

[0078] The mixture of nanotubes and nanofibers can be prepared using a planetary mixer.

[0079] Gradual evaporation of the solvents is achieved by fractional drying at different temperatures to reduce binder migration, thereby preventing degradation of the coating's mechanical properties. To this end, temperatures ranging from 40 to 100°C are used successively without the application of a vacuum. Thanks to this drying process, the resulting deposit is significantly thinner while remaining highly uniform. According to one embodiment, the electrode manufacturing process does not include any step conducted at a temperature exceeding 100°C.

[0080] Preferably, step e) of electrode compression (calendering) takes place after the active material composition has been deposited. According to this embodiment, there is no compression step between step c) of solvent evaporation and step d) of deposition of the active material composition onto the coating. As explained above, this ensures that the adhesion of the nanotube and / or carbon nanofiber coating to the current collector is less than the adhesion of the nanotube and / or carbon nanofiber coating to the active material composition layer. Electrochemical element

[0081] The nature of the other components of the electrochemical element, such as the separator and the electrolyte, is not particularly limited. The electrochemical element comprises an electrolyte, which may be liquid or solid. The electrochemical element may be of the lithium-ion, sodium-ion, potassium-ion, magnesium-ion, or calcium-ion type.

[0082] The present invention can advantageously be implemented in the manufacture of a solid electrolyte electrochemical element. Indeed, such an element generally exhibits lower electrical conductivity than an element with a liquid electrolyte. The present invention makes it possible to compensate for the low conductivity of the element by providing a positive or negative electrode with increased electronic conductivity. Furthermore, delamination problems are more frequently encountered in a solid electrolyte element.

[0083] A preferred electrochemical element is a solid electrolyte lithium-ion electrochemical element.

[0084] A first type of solid electrolyte is that of inorganic solid electrolytes formed from an inorganic material in the crystalline or glassy state, such as LiBH4 or a compound of formula Li6PS5X of the argyrodite type obtained by reaction between Li2S, P2S5 and optionally LiX where X designates a halogen atom, or halide electrolytes such as Li3YCl6.

[0085] A second type of solid electrolyte is that of organic polymers having ionic conduction properties because they are capable of dissociating lithium salts, for example polyethers, polyesters, single-ion conducting polymer electrolytes (SIPEs), and poly(ionic liquids). Examples include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl ethacrylate, and polyvinyldiene chloride. The ionic conductivity of these polymers can be improved by the addition of plasticizers consisting of solvents such as linear and cyclic carbonate solvents, fluorinated carbonate solvents, nitrile solvents, linear or cyclic liquid polyethers, fluorinated polyether solvents and their mixtures and lithium salts such as LiFSI, LiTFSI, LIPF6, LiBF4, LiDFOB, LiNO3.Polymer electrolytes can be considered gel electrolytes composed of crosslinking polymers such as the olefin polymer family, particularly the low- or medium-density acrylate family such as polyethylenes (LDPE, MDPE), and methyl acrylates (EMA). These latter polymers allow the production of gel electrolytes by thermal crosslinking with an initiator, azobisisobutyronitrile (AIBN), and associated with a liquid electrolyte consisting of lithium salts such as LiFSI, LiTFSI, LIPF6, LiBF4, LiDFOB, LiNO3 primarily, and solvents such as linear and cyclic carbonate solvents, fluorinated carbonate solvents, nitrile solvents. linear or cyclic liquid polyethers, fluorinated polyether solvents and their mixtures.

[0086] A third type of solid electrolyte is that of organic polymers that are not ionically conductive, even in the presence of lithium salts. They form a matrix in which ionically conductive inorganic particles are embedded. They are called "composites" or "hybrids" because of the coexistence of organic polymers with inorganic particles. Examples

[0087] A first coating was applied to a substrate which is a sheet of a non-electrically conductive polymeric material so as not to interfere with the electronic conductivity measurements. This coating consists of carbon black particles.

[0088] A second coating was applied to a substrate of the same nature as the first coating. This second coating consists of carbon nanotubes whose longitudinal axis forms a mean angle of less than or equal to 30° with respect to the plane of the substrate. The orientation of the carbon nanotubes was measured by scanning electron microscopy.

[0089] The Table indicates the formulations of the two coatings: [Tables 1] Constituents Carbon black particle-based coating Carbon nanotube-based coating Carboxymethylcellulose (binder) 0.8% 0.6% Water 97.2% 99% Carbon nanotubes - 0.4% Carbon black 2% -

[0090] The electronic conductivity of the two coatings in the longitudinal direction was measured using a multimeter. A template mask was used to delimit the areas of the first and second coatings so that they were identical. It also served to fix the locations of the measurement points. The two measurement points are located in the longitudinal plane of the coating. The measured electronic conductivity is therefore the electronic conductivity of the coating in the longitudinal direction. The table below shows the measurement results.

[0091] [Tables2] Carbon black part-based coating Carbon nanotube-based coating Coating thickness (µm) 40 3 Electronic conductivity (S.cm1) 5.0 x 10⁹ 8.13 x 10³

[0092] It is observed that the second coating exhibits a significantly higher electronic conductivity than the first coating. The thickness of the second coating is less than that of the first coating. Despite this smaller thickness, the electronic conductivity of the second coating is higher than that of the first coating. The high value of 8.13 x 10³ S·cm⁻¹ is explained by the fact that the carbon nanotubes have a high aspect ratio and, secondly, by the fact that the longitudinal axis of these nanotubes forms a mean angle of less than or equal to 30° with respect to the plane of the substrate.

Claims

Demands

1. Electrode comprising: - a planar current collector, - a coating covering at least partially one or both faces of the current collector, the coating comprising carbon nanotubes or carbon nanofibers or a mixture thereof, and optionally one or more binders, the longitudinal axis of at least 50% of the carbon nanotubes or carbon nanofibers forming a mean angle less than or equal to 30° with respect to the plane of the current collector, - a layer of active material composition in contact with the coating, said layer of active material composition comprising at least one active material and optionally one or more electronically conductive compounds and one or more binders.

2. Electrode according to claim 1, wherein the coating has greater adhesion to the active material composition layer than its adhesion to the current collector.

3. Electrode according to claim 1 or 2, wherein the longitudinal axis of the carbon nanotubes or carbon nanofibers forms a mean angle less than or equal to 20° with respect to the plane of the current collector.

4. Electrode according to claim 3, wherein the longitudinal axis of the carbon nanotubes or carbon nanofibers forms a mean angle less than or equal to 10° with respect to the plane of the current collector.

5. Electrode according to any one of the preceding claims, wherein the entire face or faces of the current collector is covered by the coating.

6. Electrode according to any one of the preceding claims, wherein the carbon nanotubes and / or carbon nanofibers have a form factor of at least 1000.

7. Electrode according to any one of the preceding claims, wherein the carbon nanotubes or carbon nanofibers have a diameter ranging from 0.1 to 30 nm.

8. Electrode according to claim 7, wherein the carbon nanotubes or carbon nanofibers have a diameter ranging from 0.5 to 2 nm.

9. Electrode according to any one of the preceding claims, wherein the coating has an electronic conductivity ranging from 102 to 104 S.cm1, the electronic conductivity being measured along the longitudinal direction of the coating.

10. Electrode according to any one of the preceding claims, wherein the coating has a thickness greater than or equal to 1 pm and less than or equal to 5 pm.

11. Electrode according to any one of the preceding claims, wherein the coating consists of carbon nanotubes or carbon nanofibers or a mixture thereof and one or more binders.

12. Lithium-ion electrochemical element comprising: - at least one positive electrode, - at least one negative electrode, said at least one positive electrode and / or said at least one negative electrode being an electrode according to one of the preceding claims, - a solid electrolyte.

13. A method for manufacturing an electrode according to any one of claims 1 to 11, said method comprising: a) preparing a mixture comprising carbon nanotubes or carbon nanofibers or a mixture thereof, an aqueous or non-aqueous solvent, and one or more binders, b) deposition of the mixture from step a onto one face of a current collector, c) evaporating the solvent to obtain a current collector coated with a coating comprising the carbon nanotubes or carbon nanofibers or a mixture thereof, and said one or more binders, d) deposition of an active material composition layer onto the coating to obtain an electrode, said active material composition layer comprising at least one active material and optionally one or more electronically conductive compounds and one or more binders, e) compressing the electrode.

14. A process according to claim 13, wherein the mixture in step a) contains the constituents in the following mass proportions: - from 0.1 to 10% of carbon nanotubes or carbon nanofibers or a mixture thereof, - from 0.3 to 2% of one or more binders, - the remainder being one or more solvents.

15. A method according to any one of claims 13 to 14, not comprising a coating compression step between steps c) and d).

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