An additive to an electrode paste and a method to prepare the additive

Abstract

The invention provides an electrically conductive additive to electrode material comprising single walled and / or double walled carbon nanotubes and dispersant, wherein single walled and / or double walled carbon nanotubes are between 10 to 80 wt. % on dry basis of the additive, wherein mixing the additive in a mass ratio of 1:99 with N-methyl-2-pyrrolidone results in the formation of a suspension with median particle size D50 not less than 50 μm, while mixing the additive in a mass ratio of 1:99 with water leads to the formation of a suspension with median size D50 not more than 30 μm. The technical result high quality of electrodes prepared with such an additive, which is manifested in high specific capacitance and stability in successive charge-discharge cycles. The invention also provides the method to produce the additive.

Description

[0001] IPC: H01M4 / 02, H01M4 / 04, H01M4 / 62, H01M4 / 139, H01M10 / 0525; C01B32 / 158.

[0002] An additive to an electrode paste and a method to prepare the additive.

[0003] Background of the invention

[0004] Field of the invention

[0005] The invention relates to the field of materials used to produce electrodes of chemical power sources, including lithium-ion batteries. The invention provides an electrically conductive additive that reduces the internal resistance of the electrode material and increases electrode cycling stability, i.e., the number of charge and discharge cycles that the electrode of a lithium-ion battery can withstand before its capacitance decreases by a certain amount from the initial capacitance, e.g., by 20 % of the initial capacitance.

[0006] Conventional art

[0007] The use of single-walled and / or double-walled carbon nanotubes in the electrodes of lithium-ion batteries makes it possible to increase the capacity of electrodes and batteries in general, reduce their internal resistance, and increase the lifespan, i.e. the number of chargedischarge cycles of lithium-ion battery electrodes, especially silicon-containing anodes of lithium-ion batteries, for example as the Patent Application EP 4230581 teaches.

[0008] Hereinafter, the term “electrode” means a cathode or an anode, the term "electrode paste" means a cathode paste or an anode paste, and the term "active electrode material" means an active cathode material or an active anode material.

[0009] Single-walled and double-walled carbon nanotubes are prone to agglomeration due to van der Waals forces to form bundles of carbon nanotubes and also agglomerates of more complex geometry, in which the bundles of nanotubes combine into thicker ones and, conversely, separate into thinner ones. This ability is a feature of single-walled and doublewalled carbon nanotubes, and is not characteristic of multi-walled carbon nanotubes and other carbon materials. After being obtained, for example, by the Chemical Vapour Deposition (CVD) method, this material is sticky flakes of macroscopic size, resembling pieces of rag or cotton wool, which consists of a huge number of interconnected loops and rings of bundles of single-walled and / or double-walled carbon nanotubes. The introduction of this material into various coatings and composite materials, including electrode pastes used for the manufacture of lithium-ion battery electrodes, does not allow obtaining a material with a uniform distribution of well-dispersed carbon nanotubes.

[0010] In this regard, it is necessary to pre-divide the agglomerates of single-walled and / or double-walled carbon nanotubes into thinner bundles. It is known that suspensions of predispersed single-walled and double-walled carbon nanotubes in suitable solvents, e.g., in water can be used to introduce the carbon nanomaterial, as taught, for example, by the inventions JP 6860740 and RU 2777040. Such solutions make it possible to obtain high-quality electrode pastes and, subsequently, electrodes for lithium-ion batteries. However, the processes of production, storage, transportation and use of dispersions of single wall carbon nanotubes have a large number of disadvantages that are very difficult or impossible to eliminate, as they are caused by an insurmountable conflict between the need for a high degree of dispersion of carbon nanotubes without any re-agglomeration and sedimentation of carbon nanotubes on the one hand, and the undesirability of high viscosity of dispersion on the other hand. Patents JP 6860740, RU2777040, EP3333946 and some others offer various trade-off's between the viscosity of the dispersion, which should not be too high, and the stability of the dispersion, which should allow it to be stored and transported without reagglomeration and sedimentation of the nanotubes. An additional disadvantage of dispersions of single-walled and double-walled carbon nanotubes is the complexity and high cost of the manufacturing process itself, which requires special equipment, such as, for example, high-pressure homogenizers or ultrasonic dispersers, and also high energy consumption. Due to the low concentration of carbon nanotubes in the dispersions (usually not more than 1 wt.%), the volume and mass of the stored and transported dispersion are very large. Another important disadvantage is that the dispersions of carbon nanotubes are suitable only for technologies based on “wet” mixing methods and cannot be used in the production of electrodes using the so-called "dry mixing" methods.

[0011] The invention US11824201 aims to produce inexpensive and reliable coherent active material components containing dispersed discrete carbon nanotubes for energy storage and collection devices via dry, i.e., less than 10,000 ppm solvent, fabrication methods. As a proposed solution, an electrode manufacturing composition comprising is described: less than about 10,000 ppm, based on the total weight of the composition, of an aqueous or non-aqueous solvent, a plurality of discrete carbon nanotubes in the form of reaggregated bundles or clumps, and at least one additive dispersed within the bundles wherein the at least one additive at least partially coats a surface of the discrete carbon nanotubes, wherein the composition is dry.

[0012] The description and examples of the US 11824201 invention involve the preparation of suspensions of discrete carbon nanotubes and dispersants in a solvent, followed by solvent separation by filtration and drying of the cake to the desired residual solvent content. The resulting material "reaggregated discrete nanotubes" is a composition containing discrete carbon nanotubes in form of reaggregated bundles and additive, which is dispersed within the bundles and at least partially coats a surface of the discrete carbon nanotubes.

[0013] The proposed solution has a number of advantages: there is no need to store and transport a lot of solvent, the composition can be used in dry mixing methods. In essence, the US11824201 invention simply provides for the removal of a solvent from a suspension and / or dispersion of discrete carbon nanotubes, and to do so in the simplest and most obvious way for a person skilled in the art, i.e., filtration and drying. This solution, which is obvious to any specialist, has several significant drawbacks, especially if the carbon nanotubes used are singlewalled and / or double-walled.

[0014] First, to produce this composition, it is first necessary to create a dispersion of discrete carbon nanotubes, a very energy -intensive process in which it is necessary to separate bundles of single-walled and / or double-walled carbon nanotubes into "discrete carbon nanotubes" that will be stabilized with an additive that at least partially coats a surface of the discrete carbon nanotubes. After that, the solvent must be separated and / or vaporized from the resulting mixture of carbon nanotubes and the additive, during which the "discrete carbon nanotubes" are "reaggregated into bundles". This process is also energy consuming.

[0015] Secondly, the "reaggregated bundles" do not have the strength and electrical conductivity of the initial bundles of single-walled and / or double-walled carbon nanotubes, since the additive disrupts the direct contact of carbon nanotubes with each other, and the forces of intermolecular interaction between the molecules of the additive are much less than the van der Waals forces (71-71 stacking) between single-walled and / or double-walled carbon nanotubes. In this regard, it is necessary to find another solution that does not have the above two disadvantages of the obvious solution offered by the patent US11824201.

[0016] Thus, there is a technical problem of preparing an electrode paste containing singlewalled and / or double-walled carbon nanotubes and fabricating a lithium-ion battery anode with high quality, which is manifested in high specific capacitance and stability in successive charge-discharge cycles. Known solutions using dispersions of single-walled and / or doublewalled carbon nanotubes in solvents, including water, as raw materials for the preparation of electrodes, allow to achieve acceptable results, but have significant limitations related to their high viscosity or their low stability, as well as the impossibility of using them in technological processes based on dry mixing. Removing water or other solvent by filtration and subsequent drying incurs additional energy costs and results in less impact on the specific capacity and stability of lithium-ion batteries.

[0017] Description of the invention.

[0018] The solution to the problem described above could be a material that contains singlewalled and / or double-walled carbon nanotubes pre-dispersed into bundles of the required thickness and a dispersant that separates these bundles and prevents their reaggregation but does not contain or contains a small amount of solvent, such as water. Our research has shown that the technical challenge is to manufacture a high-quality lithium-ion battery electrode, which is manifested in high specific capacitance and stability of operation in successive chargedischarge cycles can be solved by using an electrically conductive additive to the electrode material which is a powder or granular material comprising single walled and / or double walled carbon nanotubes and dispersant, wherein single walled and / or double walled carbon nanotubes are between 10 to 80 wt. % on dry basis of the additive, wherein D50(NMP) is not less than 50 pm and D50(W) is not more than 30 pm, where D50(NMP) is the volume-weighted median of the particle size distribution, as determined by laser diffraction, in the suspension of the additive in N-methyl-2-pyrrolidone with mass ratio of 1 :99, and where D50(W) is the volume-weighted median of the particle size distribution, as determined by laser diffraction, in the suspension of the additive in water with mass ratio of 1 :99.

[0019] «Suspension of the additive in N-methyl-2-pyrrolidone with mass ratio of 1 :99» in this specification is the suspension, obtained by mixing the additive with N-methyl-2-pyrrolidone in a mass ratio of 1 : 99 when stirred with a disc sawtooth impeller with an angular velocity of 1000 rpm for 10 min. «Suspension of the additive in water with mass ratio of 1:99» in this specification is the suspension, obtained by mixing the additive with water in a mass ratio of 1 :99 when stirred with a disc sawtooth impeller with an angular velocity of 1000 rpm for 10 min. The sawtooth impellers should preferably have diameter between 40 and 50 mm.

[0020] Hereinafter, the volume-weighted particle size distribution (p.s.d.) means the distribution as it is calculated from the laser diffraction, i.e. from measuring the angular variation in intensity of light scattered as a laser bundle passes through a suspension sample. Large particles scatter light at small angles relative to the laser bundle and small particles scatter light at large angles. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter (VESD). Laser diffraction gives exact p.s.d. only for spherical particles, and the application of this method for measuring p.s.d. of particles with high aspect ratio (e.g. fibers or nanotubes) is disputed in literature. It is known that laser difraction represents data on the size of the particle projection on the plane, which is normal to the laser bundle (despite it is usually reported as the volume equivalent sphere diameter). Therefore, the measured size of a non-spherical particle depends on its orientation with respect to the bundle. In the state-of-the-art laser diffraction particles size analizers non-spherical particles are aligned by laminar flow in the measuring cell. Therefore the measured p.s.d. may significantly differ from that measured by the other methods. Despite these drawbacks, the ease of use and wide measuring range make laser diffraction the most widely used method for characterization of the dispersions of nanotubes. That is why in this patent we characterize p.s.d. for suspensions of the additive in water and in NMP by means of laser diffraction. We acknowledge that these data do not represent the exact distribution of volume equivalent sphere diameters of particles in these suspensions. However, these data are well reproducible and representative of the particle size and shape distribution. To avoid misinterpretation, we clearly note here that particle size distributions are measured by means of laser diffraction. In description below we will refer to such data as “particle size distribution” or “p.s.d.” without further mentioning laser diffraction.

[0021] It is also important that particle size is reported as a volume equivalent sphere diameter (VESD), This quantity is the diameter of an imaginary sphere that has the same volume V as the particle:

[0022] VESD= ft (!)■

[0023] It is important to note that carbon nanotubes and their bundles are particles whose shape is very different from spherical. The VESD value for such particles is always greater than the bundle diameter and always less than the bundle length. For cylindrical bundles VESD =31^ =31^} D (2).

[0024] For example, if the aspect ratio (L / D) of the bundle is 667, then the diameter of the bundle is 10 times less than the diameter of the volume equivalent sphere, VESD. VESD of 10 micrometers can correspond to carbon nanotube bundles of about 1 pm and a length of 667 pm. VESD of 30 micrometers can correspond to carbon nanotube bundles of about 2 pm and 4.5 mm long.

[0025] P.s.d. in aqueous suspension was chosen as a characteristic of the degree of dispersion of carbon nanotube and dispersant bundles. It must have median particle size D50(W) not more than 30 pm, since highly dispersed bundles are important for the performance of the additive in the final application - in electrode paste.

[0026] P.s.d. in an aprotic solvent using N-methyl-2-pyrrolidone is chosen as a characteristic of the grain size of the additive. It must have median D50(NMP) not less than 50 pm.

[0027] The method of obtaining suspensions of the additive - mixing with a disc sawtooth impeller with an angular velocity of 1000 rpm for 10 min - was chosen as a method that provides a sufficiently good suspension of the powder in the liquid, which at the same time cannot destroy van der Waals forces (71-71 stacking) between single-walled and / or double-walled carbon nanotubes and therefore does not lead to a noticeable change in the diameter or length of the bundles of single walled and / or double walled carbon nanotubes. Preferably, the sawtooth impeller should have diameter of 40 to 50 mm. It should be noted that another method of preparation of suspensions for characterization could have been chosen, but the numerical values of p.s.d. in these suspensions may differ for suspensions prepared by different methods.

[0028] For a material containing single walled and / or double walled carbon nanotubes to be an effective additive to the electrode material and to solve the specified technical problem, it is necessary that its suspension in water and its suspension in an aprotic solvent, which can be N-methyl-2-pyrrolidone, have significantly different particle size distributions. Note that when using an additive, that is, in the process of preparing the electrode material, an aprotic solvent may not be used at all. It should also be noted that the technological process of preparing the electrode material may not include the stages of dispersion or suspension of the additive in water. The preparation of suspensions of the additive in water and in N-methyl-2-pyrrolidone and the study of the particle size distribution in these suspensions are used here only as methods for experimental determination of the textural characteristics of the additive. Another polar or non-polar aprotic solvent (e.g., hexane or other aliphatic hydrocarbon or other solvent, but not limited to the examples given) could have been used as an aprotic solvent for the purpose of such textural characterization. The texture of the additive could also be determined by other methods, for example, by making thin slices with a cryotome and examining micrographs of a large number of these slices to provide sufficient statistical sampling. However, the production of such sections and their microscopic examination are much more labor-intensive than the method used here.

[0029] The particle size in the aqueous suspension characterizes the degree of pre-dispersion of the single walled and / or double walled carbon nanotubes in the additive. After the additive was mixed with water (without intentional additional dispersion using high shear rates, ultrasound, high-pressure homogenizers, and other known dispersion methods), the water molecules are absorbed by the dispersant in the additive between the carbon nanotube bundles, the bundles are separated by swelling of the dispersant during water absorption. Then stirring with a conventional disc sawtooth impeller with a diameter of 40 to 50 mm at a speed of 1000 rpm for 10 minutes leads to the formation of a suspension of bundles of single walled and / or double walled carbon nanotubes, the surface of which is stabilized with a dispersant.

[0030] The smallness of the median particle size in the resulting aqueous suspension of the additive is a necessary requirement for the additive. It is important that the median D50(W) particle size is not more than 30 pm, i.e. that particles with a size of 30 pm or less make up more than 50% in volume of all particles. This VESD can correspond to carbon nanotube bundles with a diameter of less than 2-3 pm and a length of less than 3-4 mm.

[0031] The viscosity of the suspension depends on the aspect ratio of the suspension particles: the higher the aspect ratio, the greater the viscosity. The aqueous suspension of the additive is characterized by high viscosity since the particles in it are long and thin bundles of carbon nanotubes, rather than their spherical balls. For this reason, it is preferable that 1 wt.% aqueous suspension of the additive has a dynamic viscosity of at least 1000 mPa s at a shear rate of 1 s’1and a temperature of 25 °C. It should be noted that the resulting suspension is a non-ideal pseudoplastic fluid and its viscosity depends on the shear rate, therefore at shear rates greater than 1 s’1, the dynamic viscosity may be lower, including less than 1000 mPa s.

[0032] It is preferred that the median particle size D50(W) in 1 wt.% aqueous suspension was not more than 30 pm, most preferably from 10 to 30 pm. Preferably, D90 should be not more than 50 pm, i.e. less that 10% in volume of particles have VESD of 50 pm. For some applications, it is preferable that the aqueous suspension of the additive thus obtained contains simultaneously much smaller particles (thin and / or short bundles of carbon nanotubes) and rather large agglomerates (long and thick bundles of carbon nanotubes). Accordingly, it is preferable that DIO is not more than 3 pm, i.e. more that 10% in volume of particles have VESD of 3 pm. For some of embodiments it is preferrable that DIO is in a range of 0.7 - 3 micrometers.

[0033] In this case, it is preferable that the viscosity of the 1 wt.% aqueous suspension is not less than 5000 mPa s at a shear rate of 1 s'1and a temperature of 25 °C, for some embodiments it is preferable that dynamic viscosity of the 1 wt.% aqueous suspension is not less than 10000 mPa s at a shear rate of 1 s'1and a temperature of 25 °C. It is important to note that for this additive, the high viscosity of the resulting suspension is not a disadvantage, since it is not used in the actual technological process, but for characterization of the properties of the additive.

[0034] Limiting the median D50 by not less than 50 pm particles in the additive suspension in the aprotic solvent is another necessary additive requirement. In our studies we used N-methyl- 2-pyrrolidone (NMP) as the aprotic solvent. It is important that the median particle size in such a suspension is at least 50 pm, i.e., that at least 50 % in volume of the particles in the suspension in NMP have a particle size of 50 pm or greater according to the results of the laser diffraction study.

[0035] It is preferred that the median particle size of D50(NMP) in 1 wt.% suspension of the additive in NMP is not less than 100 pm, most preferably D50(NMP) in 1 wt.% suspension of the additive in NMP is not less than 200 pm. Preferably D10 in 1 wt.% suspension of the additive in NMP is not less than 70 pm, i.e. more than 10 % of particles in volume have VESD 70 pm or greater.

[0036] It is preferable that the viscosity of 1 wt.% suspension of the additive in the NMP aprotic solvent is not more than 100 mPa s at a shear rate of 1 s'1and a temperature of 25 °C. The median particle size in the additive suspension in the aprotic solvent is a characteristic of the grain size in the additive granules. The low viscosity of the NMP suspension indicates a small length-to-diameter ratio of the grains, so the minimum and maximum sizes of the agglomerate are of the same order of magnitude as the size determined by laser diffraction. The absence or small number of particles with a size of a few micrometers and submicron particles in the suspension means that the additive is processable and that submicron particles will be scarce or absent in the air as well when using this additive.

[0037] The content of single-walled and / or double-walled carbon nanotubes in the additive should be not less than 10 wt.% on dry basis and not more than 80 wt.% on dry basis. It is preferred that the content of single-walled and / or double-walled carbon nanotubes in the additive is not less than 20 wt.% on dry basis, even more preferred that it is not less than 40 wt.% on dry basis. For some embodiments it is preferred that the content of single-walled and / or double-walled carbon nanotubes in the additive is not more than 70 wt.% on dry basis, for some other embodiments it is preferrable that it is not more than 50 wt.% on dry basis.

[0038] It is preferred that one of the water-absorbing polymers be used as the dispersant, e.g., carboxymethyl cellulose or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol and copolymers thereof, but not limited to these examples, or a mixture of two or more superabsorbent polymers.

[0039] In some applications, the presence of water does not impair the properties of the additive, for example, if water is further used in the preparation of the electrode paste. In this case, it is preferable not to remove the dispersant-absorbed or nanotube-adsorbed water before preparing the additive. In this regard, the presence of 5 to 20 wt.% of water in the additive will be preferable. In some embodiments, it is permissible and even preferable that the additive contains 20 wt.% or more of water, e.g., 20 to 40 or 20 to 60 wt.% of water or 60 to 80 wt.% of water.

[0040] In other applications, it is preferable to limit or eliminate the presence of water. In some embodiments, it is preferable that the additive contains no water or contains only small amount of water. It is preferable that the additive contains only water introduced into its composition by the moisture content of the single walled and / or double walled carbon nanotubes. It is known that single walled and / or double walled carbon nanotubes are distinguished by a large specific surface area and can adsorb up to 6 wt.% water. Therefore, it is preferable that the additive contains no more than 5 wt.% water. For some embodiments, it is preferable that the additive contains no more than 1 wt.% water. In this case, single walled and / or double walled carbon nanotubes and dispersant used for its production must be pre-dried, and the production process of the additive must be carried out in a room with controlled low air humidity (in a dry room).

[0041] It is preferable that single-walled and / or double-walled carbon nanotubes in the additive are of high quality and contain as few as possible defects and impurities of other allotropic carbon modifications, such as carbon black or amorphous carbon. A quantitative indicator characterizing the content of defects in the structure of single-walled and / or double-walled carbon nanotubes is the ratio of the intensities of the G and D lines in the Raman spectrum: the higher this ratio, the fewer defects the carbon nanotubes contain. Preferably, the ratio of the intensity of the G and D lines in the 532 nm Raman light scattering spectrum is at least 30, it is more preferable that the ratio of the intensity of the G and D lines in the 532 nm Raman light scattering spectrum is at least 60, and it is even more preferable that the ratio of the intensity of the G and D lines in the 532 nm Raman light spectrum is at least 80, it is most preferable that the ratio of the intensities of the G and D lines in the Raman spectrum with a wavelength of 532 nm is not less than 100.

[0042] It is important to note that the presence of impurities of other allotropic carbon modifications, such as soot, amorphous carbon, graphene, multi-walled carbon nanotubes, graphite-like particles, is tolerated in many end-use applications and, therefore, the additive may contain these or other allotropic carbon modifications.

[0043] The surface of single-walled and / or double-walled carbon nanotubes in the additive can be modified by functional groups. The expediency of modifying the surface of the single walled and / or double walled carbon nanotubes is determined by the final formulation of the electrode material. For some end-use applications, it is preferable that the surface of the carbon nanotubes in the additive contains functional groups containing elements with an electronegativity higher than carbon, e.g., hydroxyl, carboxyl, chlorine-containing: -Cl, -O-Cl, fluorine-containing, but not limited to the examples given. The presence of these groups allows for the best adhesion of carbon nanotubes to the particles of the active component of the electrode material. Functional groups can be obtained on the surface of carbon nanotubes by various methods known in the art. For example, carboxyl functional groups can be prepared on the surface of carbon nanotubes by heat treatment in a nitric acid solution, and chlorine-containing functional groups can be prepared by one of the methods described in the EP4023598 invention, but not limited to the examples given. Methods for functionalizing carbon nanotubes are not the subject of the present invention. The ends of single-walled and / or double-walled carbon nanotubes may be closed, and the inner channel of the tubes may be inaccessible to the molecules, or, otherwise, the ends of single-walled and / or double-walled carbon nanotubes may be decapped. In the latter case, the inner surface of the nanotubes is accessible to molecules, for example, it is accessible to water molecules and ions dissolved in it. This can be quantified by BET from nitrogen adsorption isotherms. The value of the specific surface area of the open (decapped) single-walled or double-walled carbon nanotubes is much higher than that for the closed (capped) nanotubes. It even may exceed the maximal theoretical specific surface area of the ideal graphene layer, 1315 m2 / g. For some applications, it is preferable that at least some of the single walled and / or double walled carbon nanotubes in the additive have internal channels open and the specific surface area of the carbon nanotubes determined by the BET method is at least 800 m2 / g. For other applications, it is preferable that the specific surface area of carbon nanotubes determined by the BET method is not less than 1000 m2 / g, more preferably not less than 1200 m2 / g, it is most preferable that the value of the specific surface area of carbon nanotubes determined by the BET method is more than 1315 m2 / g.

[0044] The present invention also states a method for preparing the described additive. To obtain an additive having the described characteristics, it is necessary to carry out successively the stages of (1) mixing single-walled and / or double-walled carbon nanotubes in an aggregated state with dispersant powder in proportions from 1 :9 to 4: 1 by weight and (2) grinding the resulting mixture using a roller mill with a friction ratio of at least 1.05. By “an aggregated state” we mean the state in which single-walled and / or double-walled carbon nanotubes are bundled under the action of van der Waals forces (71-71 stacking). Preferably, these bundles are in turn aggregated into flakes or mats of a nonwoven fabric consisting of loops of combining and separating nanotube bundles. The aggregated state of nanotubes reduces or even eliminates the floatation of nanotubes in the air of the working area during the process of mixing nanotubes and dispersant powder. In some cases, it is preferred that the carbon nanotube aggregates have been pre-granulated by one of the known methods.

[0045] The proportion of single-walled and / or double-walled carbon nanotubes to dispersant should be chosen in the range from 1 :9 to 4: 1 by weight to get the additive of the desired composition. For some embodiments the proportion of single-walled and / or double-walled carbon nanotubes to dispersant should be preferably chosen in the range from 1 :4 to 4: 1. For other embodiments it is preferable to mix single-walled and / or double-walled carbon nanotubes and dispersant in proportions from 1 :4 to 1 :2.5, or from 1 :2.5 to 1 : 1, or from 1 :1 to 4:1.

[0046] The stage of grinding the mixture of single-walled and / or double-walled carbon nanotubes and dispersant is preferably carried out using a roller mill at a friction ratio of at least 1.05. Friction ratio is the ratio of the rolls rotation speed. As such a mill, for example, a two-roll mill, a three-roll mill, or a five-roll mill can be used. The most preferable is the use of a three-roll mill. Grinding in roller mills is repeated until the required quality of mixing and dispersion of carbon nanotubes and dispersant is achieved. Preferably, the friction ratio of the mill is at least 1.1, most preferably the friction ratio is at least 2. Roller mills can be used for grinding in the mode of a set gap between the rollers or in the mode of a set force (or pressure) between the rollers, the size of the gap or the value of the force is selected for a particular mill depending on the diameter and length of the rollers to achieve the required mixing quality with the minimum number of grinding repetitions. However, it is also possible to mix and disperse single-walled and / or double-walled carbon nanotubes and dispersant using other equipment, such as a planetary or ball mill.

[0047] To increase the grinding efficiency in the roller mill, it is preferable to add water to the mixture of single-walled and / or double-walled carbon nanotubes and dispersant at stage (1) until the moisture content of the mixture is between 20 wt.% and 90 wt.% or, between stages

[0048] (1) and (2), add water to the mixture of single-walled and / or double-walled carbon nanotubes and dispersant until the moisture content of the mixture is between 20 wt.% and 90 wt.%. For applications where the moisture content of the additive must be limited (e.g. not more than 5 wt.% water, or 5 to 20 wt.% water, or from 20 to 40 wt.%, or from 20 to 60 wt.% water, or 60 to 80 wt.%) after stage (2), it is additionally preferable to dry the additive to the required humidity. The drying stage can be carried out by any known method, for example, in drum dryers, in vacuum dryers, in IR dryers, in shelf cabinets with a convective flow of hot dry air, etc. After drying, the additive can be lumps of irregular shapes and different sizes, in which case it is preferable to grind them to a powder for better further processability. The dried additive can be milled in any suitable mill, such as a knife mill or any other available mill. However, the additive can also be used immediately after drying, the milling stage of the dried additive is not necessary to achieve the declared technical result.

[0049] If it is necessary to ensure a water content of not more than 1 wt. % mixing is preferably carried out without adding water to the mixture of single-walled and / or double-walled carbon nanotubes and dispersant in a humidity-controlled room (dry room).

[0050] The important advantage of the additive proposed by this invention is that it can be used in technological processes for the preparation of electrode paste by dry mixing methods, which is manifested in high specific capacitance and stability of operation in successive chargedischarge cycles. The present invention provides a method for preparing an electrode paste, wherein it comprises the stage of adding the above additive to the active material of the electrode or to the binder or mixture comprising the active electrode material and binder, and a mixing stage until a homogeneous consistency of the paste is obtained. The sequence of adding the additive, binder and active ingredient can be any, only the subsequent thorough mixing is important until a homogeneous consistency of the paste is obtained.

[0051] However, the additive can also be used in technological processes that use solvents to prepare an electrode paste. The present invention provides a method for preparing an electrode paste characterized by the fact that it includes the stages of

[0052] (1) adding the above additive to the solvent,

[0053] (2) stirring until even consistency mixture is obtained,

[0054] (3) adding active material to the mixture obtained in stage (2), and

[0055] (4) stirring until a homogeneous consistency of the paste is obtained.

[0056] For some applications, it is preferable to add a binder, e.g., carboxymethyl cellulose or its salt or other binder used in the manufacture of the electrode, to the solvent at the same time as the additive in stage 1. For some applications, it is preferable to add the binder in stage 3. For other applications, it is preferable to implement the additional stage of adding binder to the solvent prior to stage (1) or to further implement such an additional stage prior to stage (4).

[0057] If necessary, a solvent, such as water or another solvent, may be added to the electrode paste in stages (3) and / or (4) to produce an electrode paste of desired viscosity.

[0058] An electrode active material refers to a cathode active material or an anode active material. A cathode active material is any material that has the following set of properties [M.S. Wittingham, Lithium Batteries and Cathode Materials, Chem.Rev. 2004, Vol. 104, pp. 4271- 4301]: (1) contains a readily reduced / oxidizable ion, e.g., a transition metal cation; (2) is able to enter into a reversible interaction with lithium that does not lead to a radical change in its structure; (3) the reaction of the material with lithium has a high free energy (Helmholtz potential) of the reaction; (4) The reaction of the material with lithium proceeds at a high rate. For example, the active material of the cathode paste may be one of the following types: LiTiS?, LiVSe?, LiCoCh, LiNiCL, LiFePCU (also called LFP), LiNixMnyCozO2 (where x, y, z are positive numbers less than 1, such as x+y+z=l, also called NMC, e.g., NMC 811 for LiNio.sMno.iCoo.iCL), or another, but not limited to the above examples, or a mixture of several such materials. It is most preferable to use LiFePO4 (also referred to as LFP) in the cathode paste of the present invention.

[0059] An anode active material is a material that can absorb significant amounts of reduced lithium. The anode active material may be a graphite phase, a silicon phase, or a silicon oxide phase, SiOx, where x is a positive number less than or equal to 2, or a combination of silicon and silicon oxide SiOxwith a total atomic ratio of oxygen: silicon elements in the composition of the anode active material greater than 0 and less than 1.8, or another known anode active material, described, for example, in the review [H. Cheng; J.G. Shapter; Y. Li, G. Gao, Recent progress of advanced anode materials of lithium-ion batteries. Recent progress of advanced anode materials of lithium-ion batteries, Journal of Energy Chemistry, Volume 57, 2021, Pages 451-468. ISSN 2095-4956. https: / / d .2020.08.056.1.

[0060] The additive can also be used in other methods of producing electrode material. In case the process of preparing the electrode paste is carried out using water as a solvent, the additive can be pre-mixed with water. The resulting dispersion will be similar in properties to the dispersions described in patent RU2777040. If this is preferable for some reason, the dispersion thus obtained can be used to make the electrode paste.

[0061] In case the process of preparing the electrode paste is carried out using water as a solvent, the additive can be pre-mixed with water. The resulting dispersion will be similar in properties to those described in patent RU2777040. If this is preferred for some reason, the dispersion thus obtained can be used to prepare the electrode paste.

[0062] The invention described above provides an electrically conductive additive to electrode material, the additive being a powder or granular material comprising single walled and / or double walled carbon nanotubes and dispersant, wherein the content of single walled and / or double walled carbon nanotubes is between 10 to 80 wt% on dry basis of the additive; wherein median grain diameter of the additive as determined by laser diffraction in the suspension of the additive in N-methyl-2-pyrrolidone is not less than 50 pm; wherein single walled and / or double walled carbon nanotubes are aggregated into bundles, and median size of bundles of carbon nanotubes in the additive as determined by laser diffraction in the suspension of the additive in water is not more than 30 pm. This electrically conductive additive increases electrode cycling stability, i.e., the number of charge and discharge cycles that the electrode of a lithium-ion battery can withstand before its capacitance decreases by a certain amount from the initial capacitance.

[0063] The Invention is illustrated by the following Figures and Examples, which are for illustrative purposes only and do not limit the possible uses of the invention. Brief Description of the Attached Drawings.

[0064] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0065] Fig- 1- Electron micrographs of the Tuball™ carbon nanotubes used in Example 1.

[0066] Fig- 2. Laser diffraction data on the cumulative volume particle size distribution (carbon nanotube bundles) in 1 wt.% suspension in water (dotted line) and in N-methyl-2-pyrrolidone (solid line) of the additive by Example 1.

[0067] Fig. 3. Dynamic viscosity (mPa s) as a function of the shear rate (s'1) of 1 wt.% suspension in water (circles, solid line) and in N-methyl-2-pyrrolidone (triangles, dotted line) of the additive by Example 1.

[0068] Fig. 4. Electron micrograph of the mixture of single-walled and double-walled carbon nanotubes used in Example 2.

[0069] Fig. 5. Graph of the capacity of the battery with the anode by Example 7 on cycle number.

[0070] Fig. 6. Charge and discharge curves of an anode cell by Example 8.

[0071] Fig. 7. Graph of the capacity of the battery with the anode by Example 8 on cycle number.

[0072] Fig. 8. Graph of the capacity of the battery with the anode by Example 9 on cycle number.

[0073] Fig. 9. Graph of the capacity of the battery with the anode by Example 10 on cycle number.

[0074] Fig. 10. Graph of the capacity of the battery with the anode by Example 11 on cycle number.

[0075] Fig. 11. Graph of the capacity of the battery with the anode by Example 12 on cycle number.

[0076] Fig. 12. Graph of the capacity of the battery with the anode by Example 13 on cycle number.

[0077] Fig. 13. Graph of the capacity of the battery with the anode by Example 14 on cycle number.

[0078] Fig. 14. Graph of the capacity of the battery with the anode by Example 15 on cycle number.

[0079] Fig. 15. Graph of the capacity of the battery with the anode by Example 16 on cycle number.

[0080] Fig. 16. Graph of the capacity of the battery with the anode by Example 17 on cycle number.

[0081] Detailed Description of Embodiments of the Invention.

[0082] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. For convenience, the information on the provided examples is also provided in the Tables 1-5 below.

[0083] Table 1 shows the composition of additives by Examples 1-6.

[0084] Table 2 shows the data on the particle size distribution measured by laser diffraction and on viscosity of the 1 wt.% suspensions of additives by Examples 1-6 in water and in NMP.

[0085] Table 3 shows composition of anode pastes by Examples 7-12, prepared using the additives by Examples 1-6.

[0086] Table 4 shows composition of cathode pastes by Examples 13-17, prepared using the additives by Examples 2-6.

[0087] Examples.

[0088] Example 1.

[0089] The additive contains 50 wt.% on dry basis of Tuball™ single wall carbon nanotubes and 50 wt.% on dry basis of Na carboxymethylcellulose salt Blanose 7L (both values on a dry basis). The moisture content of the additive is 3.2 wt.%. The diameter of the SWCNT is distributed in the range from 1.2 to 2.1 nm and with an average diameter of 1.54 nm (the diameter was determined by the methods of TEM of the dry residue of the additive, as well as by the positions of the absorption bands Si-i in the optical absorption spectrum of the additive). Raman spectroscopy with a wavelength of 532 nm shows the presence of a strong G band at 1580 cm characteristic of single-walled carbon nanotubes, and a D band at ca. 1330 cm’1, characteristic of other allotropic forms of carbon and defects of single-walled carbon nanotubes. The intensity ratio of the G / D bands is 80. The specific surface area determined from the nitrogen adsorption isotherms is 1220 m2 / g. The SWCNTs used for the preparation of the additive were further modified with chlorine by the method described in invention [EP4023598], According to the data of energy dispersive spectroscopy, the chlorine content in the Tuball SWCNTs is 0.25 wt.%. According to inductively coupled plasma atomic emission spectroscopy (ICP-AES), the SWCNTs used contain an impurity of 0.46 wt.% of group 8 metal - iron. Micrographs of transmission electron microscopy of carbon nanotubes used in the additive are shown in Fig. 1.

[0090] To prepare the additive, 1 kg of SWCNT Tuball was mixed with 1 kg of Na- carboxymethylcellulose salt powder and 1.5 kg of water. The resulting mixture was ground 5 times in a Buhler Trias 300 three-roll mill with roll speeds of 30, 90, and 270 rpm, friction ratio was 3. The obtained material was dried in an air flow at 60 °C to the required humidity of less than 4 wt.% (according to the measurement results, the humidity is 3.2 wt.%) and ground to an easy-to-use powder on a knife mill IKA MultiDrive basic M20 for 10 min at 5000 rpm.

[0091] 1 g of the additive was mixed with 99 g of water when stirred using an overhead stirrer at 1000 rpm for 10 minutes. The particle size distribution of the suspension, as determined by laser diffraction on the Malvern Mastersizer 3000, is shown in FIG. 2 dashed curve. According to Fig. 2 particle size distribution has a median D50(W) of about 10.5 pm. A similar particle size distribution curve of 1 wt.% suspensions in N-methyl-2-pyrrolidone are shown in Fig. 2 is a solid curve with a median D50(NMP) of about 270 pm. Values of characteristic particle size values: D10, D50, and D90 for 1 wt.% aqueous suspension and 1 wt. % suspensions in NMP are given in Table 2.

[0092] Dynamic viscosity (mPa s) on the shear rate (s'1) is shown in Fig. 3 for 1 wt.% suspension of the additive in water by circles and a solid line and for 1 wt.% suspension of the additive in N- methyl-2-pyrrolidone by triangles and a dotted line. At a shear rate of 1 s'1, the dynamic viscosity of the aqueous suspension is 17800 mPa s, and the dynamic viscosity of the suspension in the aprotic liquid (N-methyl-2-pyrrolidone) is 75 mPa s.

[0093] Example 2.

[0094] The additive is similar to Example 1, but it contains 50 wt.% on dry basis mixtures of single-walled and double-walled carbon nanotubes with diameters from 1.2 to 2.8 nm and an average diameter of 1.8 nm (the diameter was determined by TEM methods of the dry residue of the suspension, as well as by the positions of the bands of the respiratory mode in the Raman spectra). The ratio of the intensity of the G / D bands in the spectrum of Raman light with a wavelength of 532 nm is 34. The presence of double-walled carbon nanotubes, combined in a bundle together with single-walled carbon nanotubes, is confirmed by electron micrographs shown in Fig. 4. Experimental data on characteristic values of particle size: D10, D50 and D90, for 1 wt.% aqueous suspension and 1 wt.% suspension in NMP as well as the dynamic viscosity of these suspensions at shear rates of 1 s'1and 25 °C and the moisture content of the dispersion are given in Table 2. To prepare the additive, 2 kg of SWCNT Tuball was mixed with 2 kg of Na salt of carboxymethyl cellulose Blanose 7L and 2 kg of water. The resulting mixture was ground 10 times in a Buhler Trias 300 3-roll mill with roll rotation speed of 30, 90, and 270 rpm. Friction ratio was 3. The resulting material was dried in an air flow at 60 °C to the required moisture content of less than 4 wt. % (according to the results of the measurement, the humidity was 2.8 wt. %) and ground to an easy-to-use powder in an MTI jet mill at 5000 rpm.

[0095] Example 3.

[0096] The additive is similar to Example 1, but contains 32 wt.% on dry basis of single-walled Tuball carbon nanotubes. The moisture content in the additive is 9 wt.%. Single-walled carbon nanotubes used for dispersion preparation are SWCNT Tuball™. The diameter of the SWCNT is distributed in the range of 1.2 to 2.1 nm and the average diameter is 1.62 nm, the intensity ratio of the G / D bands is 46, the specific surface area determined from the nitrogen adsorption isotherms is 580 m2. According to thermogravimetry data in a flow of 5 vol.% oxygen in Ar, the ash residue after oxidation of the material at 950 °C is about 20 wt.%. According to X-ray diffraction, the ash residue contains predominantly iron oxide Fe2O3, and the CNTs used contain the nanodispersed metal iron phase. According to the data of energy dispersive spectroscopy, the Fe content in the used SWCNTs is 14.2 wt.%, which is consistent with the data on ash residue mass. Experimental data on characteristic values of particle size: D10, D50 and D90, for 1 wt.% aqueous suspension and 1 wt.% suspension in NMP as well as the dynamic viscosity of these suspensions at shear rates of 1 s'1and 25 °C and the moisture content of the dispersion are given in Table 2.

[0097] Example 4.

[0098] The additive is prepared from chlorine-modified single-walled carbon nanotubes Tuball™, same as were used in the preparation of the additive according to Example 1, but their content in the additive is 20 wt.% on dry basis, the additive also contains 80 wt.% on dry basis of Li salt of carboxymethyl cellulose (Li-CMC). At the first stage, 32 g of chlorine- modified Tuball™ SWCNTs were mixed with 68 g of Li-CMC powder, and 200 g of water was added to the resulting mixture. Grinding of the mixture of CNT, Li-CMC, and water was carried out using a two-roll mill Zamak LM 200 / 400 with rollers diameter of 200 mm and length of 400 mm with friction ratio 1.2. After that, the additive was dried to a moisture content of 40 wt.% and granulated using a flat-die pelletizer with a hole diameter of 2.5 mm.

[0099] Experimental data on characteristic values of particle size: D10, D50 and D90, for 1 wt.% aqueous suspension and 1 wt.% suspension in NMP as well as the dynamic viscosity of these suspensions at shear rates of 1 s'1and 25 °C and the moisture content of the dispersion are given in Table 2.

[0100] Example 5.

[0101] The additive is similar to Example 1, but the content of single-walled carbon nanotubes Tuball™ is 80 wt.% on dry basis, and the additive also contains 20 wt.% on dry basis K-salt of carboxymethylcellulose. To prepare the additive, 800 g of SWCNT Tuball™ was mixed with 200 g of K-salt carboxymethyl cellulose powder and 700 g of water. The resulting mixture was processed on a 3-roll mill Exakt 120 with rolls diameter of 120 mm, rotation speeds of 100, 300, and 600 rpm. Friction factor between the 1stand the 2ndrollers was 3, between the 2ndand the 3rdrollers it was 2. After processing in a 3-roll mill, the material was granulated using a flat-die pelletizer with a hole diameter of 2.5 mm. For additive preparation SWCNT Tuball™ 01RW03 were used. These SWCNTs were preliminarily purified from impurities of iron and amorphous carbon, as well as decapped, i.e. most nanotubes have an open internal channel. The diameter of the SWCNT is distributed in the range from 1.2 to 2.0 nm and with an average diameter of 1.56 nm, the intensity ratio of the G / D bands is 103, the specific surface area determined from the nitrogen adsorption isotherms is 1350 m2. According to thermogravimetry data in a flow of 5 vol.% oxygen in Ar, the ash residue after oxidation of the material at 950 °C is about 0.7 wt.%. According to ICP AES, the content of iron impurities is less than 500 ppm. Experimental data on characteristic values of particle size: D10, D50 and D90, for 1 wt.% aqueous suspension and 1 wt.% suspension in NMP as well as the dynamic viscosity of these suspensions at shear rates of 1 s'1and 25 °C and the moisture content of the dispersion are given in Table 2.

[0102] Example 6.

[0103] The additive is similar to Example 5, but the content of single-walled carbon carbon nanotubes Tuball™ is 67 wt.% on dry basis, and the additive also contains 33 wt.% on dry basis of Li-salt of carboxymethyl cellulose. Experimental data on characteristic values of particle size: D10, D50 and D90, for 1 wt.% aqueous suspension and 1 wt.% suspension in NMP as well as the dynamic viscosity of these suspensions at shear rates of 1 s'1and 25 °C and the moisture content of the dispersion are given in Table 2.

[0104] Examples 7-12 illustrate the preparation options for the anode paste and anode of a lithium-ion battery.

[0105] Example 7. Anode paste and anode of a lithium-ion battery prepared using an additive according to Example 1.

[0106] To prepare the anode paste, 0.8 g of the additive according to Example 1 was dissolved in 99.2 g of water with an overhead stirrer at 1000 rpm for 10 min. 97.5 g of 2 wt. % CMC solution, 12.5 g of the resulting dispersion and 15.5 g of water were mixed on an overhead stirrer at 1000 rpm for 10 minutes, then 1 g of conductive carbon black SuperP was added and stirred for next 30 min. Then active anode materials: 20 g of silicon oxide and 74.95 g of graphite were added and mixed for 4 hours and 30 minutes at 1500 rpm.

[0107] Anodes were obtained by applying a paste to copper foil on a coater, followed by drying at 60°C and pressing using calender to a density of 1.3 g / cm3. The anode mass loading was 6.3 mg / cm2A lithium-ion battery with such an anode was assembled with an NCM811 cathode at a mass loading of 15 mg / cm2. The final composition of the anode material is shown in Table 3.

[0108] The battery was tested at charge and discharge rates of 1C in the voltage range of 2.7- 4.2 V. Fig. 5 shows the graph of the battery capacity from the cycle number. The battery life before the capacity reduction to 80 % of the original capacity was 540 cycles.

[0109] Example 8. Anode paste and anode of a lithium-ion battery prepared using an additive according to Example 2.

[0110] To prepare the anode paste, 1.5 g of carboxymethyl cellulose (binder) was added to 148.5 g of water (solvent). 0.1 g of additive by Example 2 and 1 g of conductive carbon black SuperP was added to the obtained 150 g of 1% carboxymethyl cellulose solution and stirred with an overhead stirrer at a speed of 1000 rpm for 5 min. Active anode materials: 40 g of silicon monoxide and 53.95 g of graphite were added and the mixture was stirred with an overhead stirrer at a speed of 1500 rpm for 1 hour and 30 min. Finally, 4 g of 50 wt.% SBR latex was added and the mixture was stirred for another 30 minutes at 1500 rpm until a homogeneous paste is obtained. The finished paste was applied to copper foil and dried at 60°C. Anode mass loading was 4.6 mg / cm2The electrode was pressed with a calender to a density of 1.35 g / cm3. The final composition of the anode material is shown in Table 3.

[0111] A round electrode with a diameter of 16 mm was cut using a punching press, cell 2032 was assembled with it and the charge-discharge characteristic was measured at a current of 70 mA / g in the potential range from 20 mV to 1.5 V. The specific capacitance of the anode was 770 mAh / g, The charge and discharge curves of the cell are shown in the graph in Fig. 6.

[0112] The lithium-ion battery was assembled with an NCM811 cathode, cycled at a charge and discharge rate of 1C in the voltage range of 2.7-4.2 V, the dependence of capacity on the cycle number is shown in Fig. 7. Battery life before losing 20 % of original capacity is 420 cycles.

[0113] Example 9. Anode paste and anode of a lithium-ion battery prepared using an additive according to Example 3.

[0114] To produce the anode paste, 1.8 g of CMC was dissolved in 80 g of water, 312 mg of additive by Example 3 and 1 g of conductive carbon black Super P were added and stirred at 1500 rpm for 10 min. After that 50 g of silicon-containing active anode material with a specific capacitance of 720 mAh / g were added and the mixture was stirred at 1500 rpm for 30 min. Then, another 44.9 g of same silicon-containing active material and 4 g of SBR latex with a dry matter content of 50 wt.% were added to the mixture and finally, the mixture was stirred at 1500 rpm for 20 minutes until obtaining homogeneous consistency of the paste.

[0115] Anodes were obtained by applying a paste to copper foil on a coater, followed by drying at 80°C and pressing on a calender to a density of 1.5 g / cm3. The anode mass loading was 4.5 mg / cm2. A lithium-ion battery with such an anode was assembled with an NCM811 cathode with a mass loading of 15 mg / cm2. The final composition of the anode material is shown in Table 3.

[0116] The battery was cycled at charge and discharge rates of 1C in the voltage range of 2.7- 4.2 V. Fig. 8 shows a graph of the capacity from the cycle number. After 200 cycles, the residual battery capacity is more than 94%.

[0117] Example 10. Anode paste and anode of a lithium-ion battery prepared using an additive according to Example 4.

[0118] To produce the anode paste, 1 g of additive by Example 4 was added to 100 g of 1.2 wt.% solution of CMC and stirred for 10 minutes using an overhead stirrer at a speed of 1000 rpm. After that 96.3 g of anode material with a specific capacity of 460 mAh / g was added to the mixture and stirred for 3 hours at 2000 rpm until the homogeneous consistency of the paste. After that 3 g of 50 wt.% SBR latex was added to the paste and the paste was stirred for another 30 minutes.

[0119] Anode was obtained by applying the paste to copper foil on a coater, followed by drying at 50°C and pressing on a calender to a density of 1.55 g / cm3. The anode loading was 5 mg / cm2. The final composition of the anode material is shown in Table 3. A lithium-ion battery with such an anode was assembled with an NCM811 cathode with a loading of 15 mg / cm2.

[0120] The battery was cycled at charge and discharge rates of 2C in the voltage range of 2.7- 4.2 V at a temperature of 45°C. After 200 cycles, the residual battery capacity was more than 94%.

[0121] Example 11. Anode paste and anode of a lithium-ion battery prepared using an additive according to Example 5. To prepare anode paste, 6.87 g of CMC was dissolved in 450 g of water and 4.8 g of additive by Example 5 with a moisture content of 35 wt.% was added to the resulting solution, stirred with an overhead stirrer at 2000 rpm for 10 min. After that 232.5 g of silicon-containing active material with a specific capacitance of 1800 mAh / g was added and stirred for 20 min at 1000 rpm. After that, 15 g of SBR latex with a dry matter content of 50% was added to the mixture and, finally, the mixture was stirred for 4 hours at 1000 rpm until homogeneous consistency of the paste is achieved.

[0122] Anodes were obtained by applying a paste to copper foil on a coater, followed by drying at 120°C and pressing on a calender to a density of 1.2 g / cm3. The final composition of the anode material is shown in Table 3. The anode mass loading was 4.2 mg / cm2A lithium-ion battery with such an anode was assembled with an NCA cathode with a mass loading of 25 mg / cm2. The battery was cycled at charge and discharge rates of 1C in the voltage range of 2.7- 4.2 V. Fig. 10 shows a graph of the capacity from the cycle number. On cycle 400, the residual capacity of the battery was more than 80%.

[0123] Example 12. Anode paste and anode of a lithium-ion battery prepared using an additive according to Example 6.

[0124] To prepare the anode paste, 388 g of silicon-containing active material was mixed with 7.16 g of CMC powder and 0.12 g of additive by Example 6 in The Eirich Intensive Mixer Type ELI during 30 min. After that 200 g of the resulting mixture was added to 320 g of water and stirred using an overhead stirrer at 1000 rpm for 10 min, then the remaining mixture was added in and stirred for another 20 minutes at 2000 rpm. After that, 9.6 g of SBR latex with 50 wt.% dry matter content was added to the resulting mixture and finally the mixture was stirred at 2000 rpm for 4 hours until a homogeneous consistency of the paste was obtained.

[0125] Anodes were prepared by applying the paste to copper foil on a coater, followed by drying at 40°C and pressing on a calender to a density of 1.5 g / cm3. The anode mass loading was 7 mg / cm2. The final composition of the anode material is shown in Table 3. A lithium-ion battery with such an anode was assembled with an NCM911 cathode with a mass loading of 15 mg / cm2. The battery was cycled at charge and discharge rates of 1C in the voltage range of 2.7-4.2 V. Fig. 11 shows a graph of the capacity from the cycle number. After 350 cycles, the residual capacity of the battery was more than 85%.

[0126] Example 13. Cathode paste and cathode of a lithium-ion battery prepared using an additive according to Example 6.

[0127] To prepare the cathode paste, 6.3 g of CMC was dissolved in 365 g of water, 12.6 g of Super P and 42 mg of additive by Example 6 were added and the mixture was stirred at 1500 rpm for 10 min using an overhead stirrer. After that 200 g of active cathode material LFP was added and mixture was stirred for 30 min. Then 193.5 g of LFP was added to the mixture, stirred for 20 min. After that, 15.1 g of SBR latex with a dry matter content of 50% was poured in and finally the mixture was stirred for 6 hours until the homogeneous consistency of the paste.

[0128] Cathodes were obtained by applying the paste to aluminum foil on a coater, followed by drying at 80°C and pressing on a calender to a density of 2.3 g / cm3. The cathode mass loading was 15 mg / cm2. The final composition of the cathode material is presented in Table 4. A lithium-ion battery with such a cathode was assembled with a graphite anode with a mass loading of 7 mg / cm2. The battery was tested at charge and discharge rates of 2C in the voltage range of 2-3.6 V. Fig. 12 shows a graph of the battery capacity from the cycle number. On the 8000 cycle, the residual capacity of the battery was more than 96%

[0129] Example 14. Cathode paste and cathode of a lithium-ion battery prepared using an additive according to Example 2.

[0130] To produce cathode paste, 3 g of CMC was dissolved in 242 g of water, 3 g of conductive carbon black Super was added the mixture was stirred at 1500 rpm for 10 min. Then 290.9 g of active material LFP was added and mixture was stirred for 30 min. After that 90 mg of the additive by Example 2 was added and, finally, the mixture was stirred for 3 hours until the homogeneous consistency of the paste was achieved.

[0131] Cathodes were obtained by applying paste to aluminum foil on a coater, followed by drying at 40°C and pressing on a calender to a density of 2.35 g / cm3. The cathode mass loading was 40 mg / cm2The final composition of the cathode material is presented in Table 4. A lithium-ion battery with such a cathode was assembled with a graphite anode with a mass loading of 18 mg / cm2. The battery was tested at charge and discharge rates of 0.5°C in the voltage range of 2-3.6 V. Fig. 13 shows a graph of the capacitance from the cycle number. After 7500 cycles, the residual battery capacity was more than 99.5%.

[0132] Example 15. Cathode paste and cathode of a lithium-ion battery prepared using an additive according to Example 3.

[0133] To produce cathode paste, 2.5 g of the additive by Example 3 with a residual water content of 20 wt.% was dissolved on an overhead stirrer in 100 ml of water at 1000 rpm for 20 min. After that 20 g of CMC was dissolved in 1616 g of water, the additive solution was added to the CMC solution and the mixture was stirred at 1500 rpm for 10 min. 1958 g of active material LFP was added and the mixture was mixed 1 hours. After that, 6 g of SBR latex with a dry matter content of 50% was poured in and finally the mixture was stirred at 1500 rpm for 1 hour until the homogeneous consistency of the paste was achieved.

[0134] Cathodes were obtained by applying the paste to aluminum foil on a coater, followed by drying at 100°C and pressing on a calender to a density of 2.4 g / cm3. The cathode mass loading was 25 mg / cm2. The final composition of the cathode material is presented in Table 4. A lithium-ion battery with such a cathode was assembled with a graphite anode with a mass loading of 11.5 mg / cm2. The battery was tested at charge and discharge rates of 1C in the voltage range of 2-3.6 V. Fig. 14 shows a graph of the capacity from the cycle number. After 6500 cycles, the residual battery capacity was more than 95%.

[0135] Example 16. Cathode paste and cathode of a lithium-ion battery prepared using an additive according to Example 4.

[0136] To produce cathode paste, 30 mg of the additive by Example 4 with a moisture content of 35% was added to 46 ml of water and stirred with an overhead stirrer at 1000 rpm, then, without stopping stirring, 1 g of CMC was added and the mixture was stirred until the CMC was completely dissolved. Then, 2 g of conductive carbon black SuperP was added, and the mixture was stirred at 1500 rpm for 10 min. After that 95.5 g of active material LFP were added and the mixture was stirred at 1500 rpm for next 10 h. After that, 3 g of SBR latex with a dry matter content of 50 wt.% was poured in and, finally, the mixture was stirred at 1500 rpm until the homogeneous consistency of the paste was achieved.

[0137] Cathodes were obtained by applying a paste to nickel foil on a coater, followed by drying at 50°C and pressing on a calender to a density of 2.3 g / cm3. The cathode mass loading was 10 mg / cm2. The final composition of the cathode material is shown in Table 4. Alithium- ion battery with such a cathode was assembled with a graphite anode with a mass loading of 5 mg / cm2The battery was tested at charge and discharge rates of 3C in the voltage range of 2- 3.6 V. Fig. 15 shows a graph of the capacity from the cycle number. After 15000 cycles, the residual capacity of the battery was 88%.

[0138] Example 17. Cathode paste and cathode of a lithium-ion battery prepared using an additive according to Example 5.

[0139] To produce cathode paste, 0.5 g of conductive carbon black Super P was added to 50 ml of 2 wt.% CMC solution and the mixture was stirred for 2 hours at a rotation speed of 3000 rpm, then 47.47 g of active material LFP was added, the mixture was stirred for 2 hours at 1000 rpm, after that 25 mg of additive by Example 5 was added to the mixture, and, finally, the mixture was stirred for 3 hours at 1000 rpm until the homogeneous consistency of the paste was achieved.

[0140] Cathodes were obtained by applying a paste to nickel foil on a coater, followed by drying at 120°C and pressing on a calender to a density of 2.3 g / cm3. The cathode mass loading was 7 mg / cm2. The final composition of the cathode material is shown in Table 4. A lithium- ion battery with such a cathode was assembled with a graphite anode with a mass loading of 3.2 mg / cm2.

[0141] The battery was tested at charge rates 1C and discharge rates 5C in the voltage range of 2-3.8 V. Fig. 16 shows a graph of the capacity from the cycle number. After 10000 cycles, the residual capacity of the battery was more than 98%.

[0142] Table 1. Additive formulations.

[0143] Table 2. Properties of additives.

[0144] Table 3. Composition of anode pastes by Examples 7-12. Table 4. Composition of anode pastes by Examples 13-17.

Claims

CLAIMS1. An electrically conductive additive to electrode material , the additive being a powder or granular material comprising single walled and / or double walled carbon nanotubes and dispersant, wherein single walled and / or double walled carbon nanotubes are between 10 to 80 wt.% on dry basis of the additive, wherein D50(NMP) is not less than 50 pm and D50(W) is not more than 30 pm, where D50(NMP) is the volume-weighted median of the particle size distribution, as determined by laser diffraction, in the suspension of the additive in N-methyl-2- pyrrolidone with mass ratio of 1 :99, and where D50(W) is the volume-weighted median of the particle size distribution, as determined by laser diffraction, in the suspension of the additive in water with mass ratio of 1 :99.

2. The additive of claim 1, wherein it comprises a superabsorbent polymer as a dispersant.

3. The additive of claim 2, wherein it comprises carboxymethyl cellulose and / or a salt thereof as a dispersant.

4. The additive of claim 1, wherein the additive doesn’t contain water or contains less than 5 wt. % of water.

5. The additive of claim 1, wherein it contains water from 5 to 20 wt. %.

6. The additive of claim 1, wherein D50(NMP) is at least 100 pm.

7. The additive of claim 6, wherein its suspension in N-methyl-2-pyrrolidone with a mass ratio of 1 :99 has volume-weighted particle size distribution with median D50 of at least 200 pm and with D10 of at least 70 pm, as determined by laser diffraction.

8. The additive of claim 1, wherein its suspension in water with a mass ratio of 1 : 99 has volume-weighted particle size distribution with median D50(W) of 10 to 20 micrometers, D10 in a range of 0.7 to 3 micrometers, and D90 of not more than 50 pm, as determined by laser diffraction,9. The additive of claim 1, wherein its suspension in N-methyl-2-pyrrolidone with a mass ratio of 1 :99 has dynamic viscosity not more than 100 mPa s at shear rate of 1 s'1and at 25 °C.

10. The additive of claim 1, wherein its suspension in water with a mass ratio of 1 : 99 has dynamic viscosity not less than 1000 mPa s at shear rate of 1 s'1and at 25 °C.

11. The additive of claim 1, wherein at least a portion of single walled and / or double walled carbon nanotubes therein have open internal channels and the specific surface area of the carbon nanotubes determined by the BET method is not less than 800 m2 / g.

12. The additive of claim 1, wherein the ratio G / D of the intensity of the G-line and D- line in Raman spectrum with wavelength of 532 nm is not less than 30, or not less than 60, or not less than 80, or not less than 100.

13. A method for preparing an additive to electrode material comprising a sequence of stages (1) mixing single-walled and / or double-walled carbon nanotubes in an aggregated state with dispersant in a ratio from 1 :9 to 4: 1 by weight and (2) grinding the resulting mixture using a roller mill with a friction ratio of at least 1.05.

14. The method of claim 13, wherein water is additionally added to the mixture at stage (1) until the moisture content of the mixture is between 20 wt. % and 90 wt. %, or between stages (1) and (2), water is added to the mixture of single-walled and / or double-walled carbon nanotubes and dispersant until the moisture content of the mixture is between 20 wt.% and 90 wt.%.

15. The method of claim 14, wherein, after stage (2), the additive is additionally dried to the desired moisture content.

16. A method for preparing an electrode paste, wherein it comprises the stage of adding the additive of claim 1 to the active material of the electrode or to the binder or to a mixture comprising the active electrode material and the binder, and a subsequent agitation stage until a homogeneous consistency of the paste is obtained.

17. A method for preparing an electrode paste, wherein it comprises the stages of (1) adding the additive of claim 1 to the solvent, (2) stirring until even consistency mixture is obtained, (3) adding active material to the mixture obtained in stage (2), and (4) stirring until a homogeneous consistency of the paste is obtained.

18. The method for preparing the electrode paste of claim 16, wherein a binder is added to the solvent in stage 1, or a binder is also added to the mixture in stage 3, or a binder is added to the solvent in an additional stage prior to stage (1), or a binder is additionally added to the mixture in an additional stage prior to stage (4).

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