Improved carbonaceous coating materials for battery electrode materials

Abstract

The present invention relates to a coating material for coating primary particles, the coating material comprising a petroleum-derived pitch product, the pitch product having a melt viscosity index log 2 of 1.2 to 3.0 at 220° C. and 1.0 to 2.5 at 240° C. 10 (visc) * 100 / SPM, where visc=melt viscosity (mPa.s) and SPM=Mettler softening point °C. The invention also relates to the use of said coating material for coating primary particles of electrode material in the manufacture of battery electrodes, more particularly lithium ion batteries. The invention further relates to battery electrodes comprising a coating made of said coating material, as well as to batteries comprising electrodes having a coating made of said coating material. In addition, the invention relates to a method for obtaining a petroleum-derived pitch product as described above, said method comprising a petroleum vacuum distillation process step for obtaining a petroleum-derived distillation residue. Furthermore, the invention relates to a method for producing a battery electrode comprising said method for producing a pitch product.

Description

[Technical field]

[0001] Technical Field The present invention relates generally to a coating material comprising a petroleum-derived pitch product for coating primary particles.

[0002] Furthermore, the present invention relates to the use of said coating materials for coating primary particles with a carbon surface layer of electrode materials such as graphite, silicon, silicon oxide or carbonaceous particles and composites thereof, etc. These carbon-coated electrode materials can be used in the manufacture of battery electrodes, more particularly lithium-ion batteries.

[0003] Additionally, the present invention relates to battery electrodes comprising electrode materials having particle coatings made from such coating materials. [Background technology]

[0004] background Commercially available negative electrode materials used in lithium-ion batteries are traditionally graphite-based, but are increasingly based on silicon oxide, silicon metal, silicon alloys, and composites of carbon or graphite with silicon, tin, and other based materials.

[0005] Many of these anode materials are coated with carbon coating materials using coal tar and petroleum based pitches as precursors. Numerous processes are known for obtaining suitable coatings. Typically, the application of the coating to the electrode material particle surface is performed by a wet process, by dissolving the pitch in an organic solvent or dispersing finely ground pitch powder in water, mixing the solution or suspension with the particles, and drying the mixture, which is then heat treated at high temperatures of 600°C to 1300°C under an inert gas atmosphere. A dry coating process is also used, in which finely ground pitch is mixed with the electrode material particles. The mixture is then heated under an inert gas atmosphere to melt the pitch and form a surface carbon layer, which is finally carbonized at high temperatures and, if necessary, graphitized.

[0006] The first problem, known in the art, is that conventional carbon coatings are not always homogeneously distributed on the electrode particle surface, and a relatively large amount, i.e., a relatively thick carbon film, is required to completely cover the particle surface, which is necessary to reduce the BET surface area, the electrochemically active surface area wetted by the battery electrolyte, and the reactivity of the electrode material to the electrolyte. Low surface area carbon coatings improve the electrochemical parameters of carbon particles by reducing charge loss and improving cell safety and charge / discharge cycle stability. However, thinner coatings are preferred because the carbon formed on the particle surface has a lower contribution to the reversible capacity of the electrode material compared to the particle core, and the thickness of the carbon layer also affects the rate of lithium ion insertion into the bulk.

[0007] The second problem is that typical pitches derived from coal tar and petrochemical sources contain not only small carbon particles, but also metallic impurities that adversely affect the quality of the coating layer formed. These particle impurities are usually measured as quinoline insoluble matter (QI content), which is an indicator of pitch quality. To obtain good carbon film quality, the QI content should be low. In addition, some types of metallic particle impurities, such as iron, copper and zinc, cause safety issues in lithium-ion cells. The insoluble components reflected in the QI and TI values ​​are particularly disadvantageous in wet coating processes, where the pitch is dissolved in an organic solvent, such as THF, toluene, xylene or hexane, before mixing with the substrate to be coated. Specific requirements for QI and TI for coating materials are relevant for wet coating processes.

[0008] A third problem is that typical surface coating processes based on coating electrode particles with coal tar pitch in a dry or wet mixing process followed by carbonization at high temperature under inert gas atmosphere result in hydrophobic particle surfaces. This hydrophobicity leads to further problems associated with the use of binders in aqueous electrode manufacturing processes. To solve this problem, EP 3177651 A1 proposes coating with non-graphitic carbon followed by oxidation.

[0009] Another problem with coal tar pitch in particular is that it contains several polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene, B[a]P, which are carcinogenic and harmful to health and the environment.

[0010] In addition, changes in steelmaking, particularly away from blast furnaces, to reduce greenhouse gas emissions will significantly reduce the availability of coal tar as a feedstock for coal tar pitch in the future, and as a result, the availability of high quality coal tar will also decrease. Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the above, the present invention aims to provide a coating material for coating primary particles, comprising a pitch product, having suitable characteristics to result in a thin coating layer, typically a few tens of nanometers thick.

[0012] Furthermore, the present invention also aims at the use of a coating material for coating primary particles for the manufacture of battery electrodes, said coating material having suitable characteristics to result in a thin coating layer, typically a few tens of nanometers thick.

[0013] Without being bound to any theory, it is envisaged that the coating material exhibits good wetting and impregnation properties of the particle surface, resulting in a thin homogeneous coating, which can be adjusted by the composition and suitable viscosity of the pitch in the molten state.

[0014] Another object of the present invention is the use of pitch products as coating materials to improve the quality of the carbon coating layer formed on the surface of primary particles for the manufacture of battery electrodes.

[0015] Another object is to provide a pitch-based carbon coating that is suitable for aqueous electrode manufacturing processes.

[0016] Further objectives are to reduce safety issues and specific charge loss in lithium-ion cells, as well as to increase charge / discharge cycle stability.

[0017] It is a further general object of the present invention to provide an alternative to coal tar pitch based coatings that is reliably available and meets the necessary requirements for use as a hydrocarbon coating material in the manufacture of battery electrodes, particularly lithium ion batteries.

[0018] It is another general object of the present invention to provide an alternative pitch-based coating that provides similar coke values ​​and softening points, and that provides similar processing and performance of battery electrodes, particularly lithium ion batteries.

[0019] It is a further general object of the present invention to provide a more environmentally friendly alternative to coal tar pitch based coatings. [Means for solving the problem]

[0020] overview In a first aspect, the present invention provides a coating material for coating primary particles, the material comprising a petroleum-derived pitch product, wherein the pitch product has a melt viscosity index log 2 (log 2 ) of 1.2 to 3.0 at 220° C. and 1.0 to 2.5 at 240° C.10 (visc) * 100 / SPM (where visc = melt viscosity (mPa.s) and SPM = softening point Mettler (°C)).

[0021] In particular, the present invention provides the use of said coating material for coating primary particles for the manufacture of electrodes, and in particular battery electrodes.

[0022] In a second aspect of the invention, there is provided a battery electrode comprising a coating made from the pitch product.

[0023] In a third aspect of the invention, there is provided a battery comprising an electrode having a coating made from the pitch product.

[0024] In a fourth aspect according to the invention there is provided a process for obtaining a petroleum derived pitch product for use as described in the first aspect, said process comprising a petroleum vacuum distillation process step for obtaining a petroleum derived distillation residue.

[0025] In a fifth aspect of the present invention, there is provided a process for producing a battery electrode comprising the process described above for producing a pitch product. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Detailed Description In a first aspect, the present invention provides a coating material for coating primary particles, comprising a petroleum-derived pitch product as a coating material for primary particles, the pitch product having a melt viscosity index log 2 of 1.2 to 3.0 at 220° C. and 1.0 to 2.5 at 240° C. 10 (visc) * 100 / SPM (where visc = melt viscosity in mPa.s and SPM = Mettler softening point in °C).

[0027] In the context of the present invention, primary particles include particles of carbon, graphite, silicon, silicon metal, silicon alloys, silicon oxide, metals, carbonaceous particles and composites, or any combination thereof, or any type of primary particle suitable for the manufacture of battery electrode materials.

[0028] More preferably, the pitch product has a melt viscosity index log of 1.8 to 2.5 at 220° C. and 1.5 to 2.1 at 240° C. 10 (visc) * 100 / SPM (where visc=melt viscosity in mPa.s and SPM=Mettler softening point in °C).

[0029] Even more preferably, the pitch product has a melt viscosity index log of 2.0 to 2.5 at 220° C. and 1.7 to 2.1 at 240° C. 10 (visc) * 100 / SPM (where visc=melt viscosity in mPa.s and SPM=Mettler softening point in °C).

[0030] By using such coating materials as carbon precursor products, thin and uniform coating layers of carbon can be formed on the surfaces of electrode material particles with small amounts of precursor. The ability to form such thin and uniform coating layers of carbon is particularly important in the manufacture of battery electrodes, particularly negative electrodes for lithium ion batteries.

[0031] In one embodiment of the present invention, the pitch product contained in the coating material has a melt viscosity of 100-500, preferably 150-400 mPa.s at 220°C and 50-200, preferably 75-150 mPa.s at 240°C, while having an SPM of 110-130°C.

[0032] In another embodiment of the invention, the pitch product contained in the coating material has a melt viscosity at 220°C of 500-5000, preferably 1000-3000 mPa.s and at 240°C of 100-1000, preferably 400-900 mPa.s, while having an SPM of 140-160°C.

[0033] In yet another embodiment of the present invention, the pitch product contained in the coating material has a melt viscosity of 5000-50000, preferably 10000-35000 mPa.s at 220°C and 500-10000, preferably 2000-7000 mPa.s at 240°C, while having an SPM of 170-190°C.

[0034] The adjusted melt viscosity enhances the wetting and impregnation of the particle surface, which allows the thin carbon film to be distributed homogeneously on the particle surface. The high surface wetting and impregnation ensures good coverage of not only the geometric particle surface, but also the micro- and mesopores and irregularities that are usually found on the particle surface.

[0035] The uses described throughout this specification are offered as an alternative to the use of coal tar pitch based coatings for battery electrodes that meet the requirements of the battery manufacturing industry and have the advantage of being readily available.

[0036] In one embodiment of the present invention, the petroleum-derived pitch product included in the coating material may have an asphaltene concentration of at least 70%, or at least 75%, or at least 80%, as measured by the SARA method (clay-gel absorption chromatography according to ASTM D2007), resulting in an increased coke value, respectively. The pitch product ensures a dense (porosity) and homogenous carbon coating on the electrode material surface, reducing the surface reactivity towards the electrolyte and the surface area of ​​the electrode material in direct contact with the battery electrolyte, and also provides good electrical conductivity and particle contact of the electrode material in the battery cell electrode.

[0037] In one embodiment of the present invention, the pitch product included in the coating material may have a resin content (SARA) of less than 20%, which may contribute to a high coke yield.

[0038] In another embodiment of the present invention, the pitch product contained in the coating material may have a B(a)P content of less than 5000 ppm, or even less than 3000 ppm, or even less than 2000 ppm, and / or a total value of 16 EPA-PAHs (polycyclic aromatic hydrocarbons according to the United States Environmental Protection Agency (EPA)) of less than 7% by weight, or even less than 5% by weight. A sufficiently low B(a)P content and / or a total value of 16 EPA-PAHs allows a clear improvement in environmental friendliness compared to pitch products derived from pure coal tar.

[0039] In further embodiments, the pitch product contained in the coating material may have a coke yield of at least 35% Alcane, or at least 45% Alcane, or at least 50% Alcane, or at least 55% Alcane at a Mettler softening point of 110-185°C. Since the coating material is converted to carbon during the carbonization process, a sufficiently high coke yield allows high porosity in the resulting graphite particles to be avoided due to the low volatiles formed during the carbonization process. Post-treatment in a fluidized bed or rotary furnace at temperatures of 400-1000°C in air may be used to increase the hydrophilicity of the carbon surface, thereby improving the processing of the carbon-coated electrode material in aqueous electrode manufacturing processes. A dense carbon layer may be formed with a morphology favorable for the formation of an efficient solid electrolyte interfacial phase at the electrode particle surface. In addition, the nature and quality of the carbon film formed at the particle surface affects the charge loss as well as the electrochemically active electrode surface area in direct contact with the electrolyte of the battery cell.

[0040] In a further embodiment, the pitch product included in the coating material may have a flash point of at least 200° C., preferably at least 220° C., which allows the pitch product to be handled in accordance with safety requirements that may be required in high temperature mixing processes.

[0041] In one embodiment of the present invention, the pitch product included in the coating material may have a Mettler softening point of 110-190° C., which is a target range for the manufacture of battery electrodes.

[0042] According to the present invention, the pitch product included in the coating material may have a quinoline insoluble content range of less than 1 wt.% and / or a toluene insoluble content of less than 40 wt.% or less than 20 wt.%. Preferably, the pitch product may have a quinoline insoluble content range of less than 1 wt.% and a toluene insoluble content of less than 5 wt.%, which may enhance its applicability as a coating material for primary particles in solvent-based coating processes due to the improved solubility of the low toluene insoluble content.

[0043] In a preferred embodiment of the present invention, the pitch product contained in the coating material may have a melt viscosity of 500-50,000 mPa.s at 220°C, a coke yield of 35%-70% Alcan, and a quinoline insoluble content range of less than 1% by weight.

[0044] In accordance with the present invention, the coating material may contain other petroleum-derived or coal tar-derived components in addition to pitch products.

[0045] In certain embodiments, the coating material may consist solely of pitch products.

[0046] In certain embodiments, the coating materials of the present invention are composed exclusively of petroleum-derived components, i.e., do not contain any coal tar-derived components.

[0047] In certain embodiments, the pitch product included in the coating material is composed exclusively of petroleum-derived components.

[0048] In certain embodiments, the pitch product included in the coating material is comprised of petroleum-derived distillation residues.

[0049] In certain other embodiments, the pitch product included in the coating material does not include any coal tar derived components.

[0050] In a second aspect of the invention, there is provided a battery electrode comprising a coating made from the pitch product. Such a coating may comprise 6methylenediaminetetraacetate (6Methylenediaminetetraacetate) used as the electrode material in the electrode. 2 For spherical natural graphite with a BET SSA of 1000 / g and an average particle size of 15 microns, a pitch amount of 5 wt.% can reduce the BET surface area by at least 40%. 2 / g) can be increased to over 90%.

[0051] In a third aspect of the present invention, the present invention provides a battery comprising an electrode having a coating made of the coating material, in which the lithium-ion cell performance may be favorably affected, in particular low specific charge loss and high coulombic efficiency, good energy and power density and specific energy and power, and cycle stability of the cell.

[0052] In a fourth aspect of the present invention, there is provided a process for obtaining a petroleum-derived pitch for inclusion in a coating material of the present invention, said process comprising a petroleum vacuum distillation process step for obtaining a petroleum-derived distillation residue.

[0053] An advantage of the process of the present invention is that the amount of asphaltenes as measured by SARA can be maintained at a similar level compared to known coal tar-based battery electrode coating precursors, and other pitch properties can be not degraded compared to known coal tar coating precursors.

[0054] An additional advantage is that such a process may enable the coke value of the pitch product to be maintained at a high level, e.g., at least 40% ALCAN, with a target softening point, e.g., a Mettler softening point of 110-190°C.

[0055] In contrast to the production of pitch products by the process of the present invention, conventional coal tar pitch coating precursors are produced by distillation at atmospheric pressure and higher temperatures, optionally followed by air blasting. The disadvantages of these products resulting from distillation at atmospheric pressure are the high mesophase and toluene insoluble content due to the high process temperatures, which cause cracks and mesophase formation. Other disadvantages are low coke yields, high volatile content, and high viscosity, which reduces the impregnation and binding properties and worsens the processability of the pitch, as well as a low flash point, which causes safety issues in the electrode manufacturing process.

[0056] A further disadvantage of distillation at atmospheric pressure is that petroleum tar distillation is reactive and the temperatures required for distillation at atmospheric pressure already initiate conversion to solid carbon components in the heating chamber and column, which can lead to excessive fouling rates during pitch production and, as a result, plant reliability problems.

[0057] In one embodiment of the present invention, the distillation process step is carried out at a reduced pressure level of 0.1-400 mbar, preferably 0.1-250 mbar, and at a temperature of 200-400°C, preferably 280-370°C.

[0058] The process according to the invention allows precise control and prevention of the formation of potential intermediate phases associated with low secondary quinoline insolubles in the pitch, resulting in a thin and homogeneous coating on the particle surface.

[0059] Additionally, the process of the present invention provides a high level of reliability by achieving the required softening point and viscosity of the pitch product at lower temperatures compared to conventional atmospheric distillation, thus resulting in better plant reliability. The lower distillation temperatures used in the vacuum distillation process avoid cracking reactions such as interphase and coke formation that lead to plant fouling and periodic shutdowns.

[0060] Furthermore, the process of the present invention can result in a pitch product for use in battery electrodes that is of high quality and reliability, has low viscosity, sufficiently high coke value and low 16 EPA PAH content, and the resulting binder has lower 16 EPA PAH levels than pure coal tar derived products, resulting in a more environmentally friendly material. EXAMPLES

[0061] Examples 1 to 6: Table 1 below provides examples of petroleum-derived pitch products and properties that can be included in a coating material according to one embodiment of the present invention.

[0062] [Table 1]

[0063] Table 2 further shows the performance of the coated natural graphite materials obtained by coating with coating materials composed of the pitch products of Examples 3 and 4 and subsequent carbonization at 1100°C.

[0064] [Table 2]

[0065] The following table provides a summary of the analytical methods for the product parameters used herein.

[0066] [Table 3]

[0067] Example 7: - Preparation of coated natural graphite samples: Spherical natural graphite was mixed with pitch powder from the petroleum-derived pitch product described throughout this specification in a high shear mixer for 5 minutes at room temperature and ground to an average particle size of about 3-5 μm. The mixture was heat treated at 1100° C. for 5 hours under nitrogen atmosphere with a heating rate of 100° C. / h.

[0068] - Electrochemical testing of carbon-coated natural graphite materials: The graphite samples were dispersed in a solution of carboxymethyl cellulose (CMC) in water and then an SBR latex binder material was added to achieve a final composition of 96 wt% graphite, 2 wt% CMC and 2 wt% SBR. The aqueous slurry was spread onto copper foil by doctor blade method and the resulting coated foil was dried at 120°C. The dried sheet was roll pressed and then the final electrodes with a diameter of 17 mm were punched from the sheet. Approximately 8.5 mg / cm 2 Mass loading of approximately 1.65g / cm 3 The electrodes, with a density of about 100 μm and a thickness of about 70 μm, were dried under vacuum at 100° C. and tested in a lithium coin half-cell using 1M LiPF6EC / DEC (1:1 by weight) electrolyte and a porous polypropylene separator. The initial coulombic efficiency and reversible specific charge of the electrode were measured by discharging the half-cell at 0.1 C to 5 mV vs. Li / Li+ and holding the cell at this potential until the current dropped to 0.7 mA, then charging the cell to 1.5 V vs. Li / Li+ and holding the cell at this potential until the cell current dropped to 0.7 mA. The coulombic efficiency of the first charge / discharge cycle was calculated in percent from reversible specific charge / (reversible specific charge+irreversible specific charge)=measured mAh(first charge) / measured mAh(first discharge).

Claims

1. A coating material for coating primary particles of carbon, graphite, silicon, metallic silicon, silicon alloys, silicon oxide, metals, carbonaceous particles and composites, or any combination thereof, or any type of primary particles suitable for the production of battery electrode materials, said coating material comprising a petroleum-derived pitch product, said pitch product having a melt viscosity index log(I) of 1.2 to 3.0 at 220°C and 1.0 to 2.5 at 240°C. 10 1. A coating material characterized by having (visc)*100 / SPM, where visc = melt viscosity (mPa.s) and SPM = Mettler softening point (°C).

2. 2. The coating material of claim 1, wherein the pitch product has a melt viscosity of 100 to 500 mPa.s at 220°C and 50 to 200 mPa.s at 240°C, while having an SPM of 110 to 130°C.

3. 2. The coating material of claim 1, wherein the pitch product has a melt viscosity of 500 to 5000 mPa.s at 220°C and 100 to 1000 mPa.s at 240°C, while having an SPM of 140 to 160°C.

4. 2. The coating material of claim 1, wherein the pitch product has a melt viscosity of 5,000 to 50,000 mPa.s at 220°C and 500 to 10,000 mPa.s at 240°C, while having an SPM of 170 to 190°C.

5. 10. The coating material of claim 1, wherein the pitch product has a coke yield of at least 35% Alcan.

6. 10. The coating material of claim 1, wherein the pitch product has a quinoline insoluble content range of less than 1 wt. % and / or a toluene insoluble content of less than 40 wt. %.

7. 10. The coating material of claim 1, wherein the pitch product has a coke yield of 35% to 70% Alcant and a quinoline insoluble content range of less than 1 wt.%.

8. 10. The coating material of claim 1, wherein the pitch product has a resin content (SARA) of less than 20%.

9. 10. The coating material of claim 1, wherein the pitch product has a B(a)P content of less than 5000 ppm and / or a combined 16 EPA-PAH value of less than 7 wt.%.

10. 10. The coating material of claim 1, wherein the pitch product is comprised of petroleum-derived distillation residues.

11. Use of the coating material according to any one of claims 1 to 10 for coating primary particles for the production of battery electrodes.

12. 12. Use according to claim 11 for coating and / or bonding electrode material particles for the negative electrode of a lithium ion battery.

13. 12. The use of claim 11 in a solvent-based coating process, wherein the pitch product has a quinoline insoluble content range of less than 1 wt. % and a toluene insoluble content of less than 5 wt. %.

14. The use of claim 12 in a solvent-based coating process, wherein the pitch product has a quinoline insoluble content range of less than 1 wt. % and a toluene insoluble content of less than 5 wt. %.

15. A battery electrode comprising an electrode material comprising the coating material of any one of claims 1 to 10.

16. A lithium ion battery comprising the electrode of claim 15.

17. 11. A method for obtaining a petroleum-derived pitch product for inclusion in the coating material of any one of claims 1 to 10, comprising a petroleum vacuum distillation process step to obtain a petroleum-derived distillation residue.

18. 18. The method of claim 17, wherein the distillation process step is carried out at a vacuum level of 0.1 to 250 mbar and at a temperature of 200 to 370°C.

19. 20. A method for manufacturing a battery electrode comprising the method of claim 17.