Improved thermoplastic carbon precursor material for the manufacture of battery electrodes

Abstract

The present invention relates to the use of a carbon precursor material in the manufacture of battery electrodes, characterized in that the carbon precursor material comprises at least 50% by weight of petroleum-derived pitch product, an Alcan coking value of 44-80% by weight measured in accordance with ASTM D4715, and a concentration of at least 80% by weight of asphaltene measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

Description

Technical Field

[0001] The present invention generally relates to the use of certain thermoplastic carbon precursor materials in the manufacture of battery electrode materials for use in the negative electrodes of batteries, particularly Li-Ion batteries.

[0002] More specifically, the present invention relates to the use of the carbon precursor material as a coating material for carbon-coated particles, or for binding and aggregating the crystallites of primary particles into larger aggregates or carbon-containing particle composites, or for embedding primary particles in a carbon matrix in which the crystallites of the primary particles are completely embedded, in the manufacture of carbonaceous battery electrode materials.

[0003] Furthermore, the present invention relates to battery electrodes, particularly for Li-Ion batteries, and includes the carbon precursor material in a conversion state.

Background Art

[0004] Conventionally, hydrocarbon pitch materials in coating, binding, or impregnation processes for manufacturing carbonaceous battery electrode material powders used in battery cell electrodes, particularly in Li-Ion batteries, are coal tar pitches. Furthermore, particularly when aggregating fine graphite primary particles into equiaxed secondary particles that lead to an advantageous structure of a porous battery electrode based on an electrode particle assembly, compared to typical platelet-shaped graphite particles, coal tar-based pitches are usually used as binder materials in the aggregation process because they convert to electrochemically active carbon with a high yield.

[0005] Furthermore, in order to increase the energy density of battery cells, particles of silicon, silicon oxide, or silicon alloys are often directly mixed with graphite particles in the electrode or added to the negative battery electrode in the form of composites with graphite or carbon. Such silicon-based particles can be coated with a film of coal tar pitch-based material to enhance their compatibility with the battery electrolyte. In the form of composites, silicon is often aggregated or completely embedded in a coal tar pitch-based carbon matrix.

[0006] However, the problem is that while coal tar has always been readily available as a byproduct of metallurgical coke production used in blast furnaces for steelmaking, recently, the production of metallurgical coke has decreased due to lower demand for virgin iron, and therefore, the availability of coal tar has decreased. The increased recycling of iron or steel scrap using electric arc furnaces contributes to this trend. Furthermore, the shift in steelmaking away from high-CO2 emission manufacturing processes such as blast furnaces that use metallurgical coal as a reducing medium, towards directly reducing iron ore with hydrogen, is another reason why the availability of coal tar is expected to decline.

[0007] Another drawback of coal tar pitch binders is the relatively high amount of benzo(a)pyrene (B[a]P), which is classified as carcinogenic (approximately 10,000 ppm in a typical viscosity range). In addition to the B[a]P content, several other polycyclic aromatic compounds are also considered harmful to health and the environment. Generally, 16EPA-PAH can be used to calculate toxicity index values ​​for these polycyclic aromatic compounds.

[0008] Another drawback of coal tar pitch binders is the relatively high amount of sulfur impurities, which is considered a crucial factor affecting the electrochemical performance of carbonaceous electrodes. This is particularly problematic when the carbon precursor is not graphitized, as volatile sulfur is typically released from the carbon above 1600°C, even though the carbon precursor is carbonized at relatively low temperatures.

[0009] Petroleum-derived pitch is being considered in an attempt to produce an alternative pitch with a lower benzo[a]pyrene content than coal tar pitch, ensuring future supply.

[0010] However, conventionally used petroleum-derived pitches, when used purely in electrode production processes, do not achieve the same quality parameters of manufactured carbon artifacts as coal tar pitch. The first drawback is that they typically have a lower carbon yield than coal tar pitch.

[0011] Furthermore, existing industrial petroleum-based pitches may have flash points starting at 200°C (far below the typical flash point of coal tar pitch), thus raising potential safety concerns in battery electrode material manufacturing processes that may involve hot mixing processes at temperatures above 200°C. This also limits the proportion to which petroleum pitch can be mixed with coal tar pitch.

[0012] In summary, none of the prior art attempts have provided a suitable alternative carbon precursor material to coal tar pitch that can be used in a substantial quantity / mixing ratio to stably supply sufficient production volumes to the battery industry.

[0013] Therefore, a general objective of the present invention is to provide the use of an alternative carbon precursor that has enhanced supply availability and meets the necessary requirements as a precursor for conductive carbon in the manufacture of battery electrodes.

[0014] Another object of the present invention is to provide an alternative carbon precursor for use in impregnation processes that provide equivalent carbon yield (or Alcan coking value) and similar processability and performance in battery electrodes, particularly Li-ion batteries, for coating, binding, agglomerating, or embedding particles.

[0015] A further object of the present invention is to provide an alternative carbon precursor having a lower total content of B[a]P and 16EPA-PAH for use in the manufacture of battery electrodes for coating, binding, agglomerating, or embedding particles, or in impregnation processes.

[0016] In particular, the objective is to provide alternative carbon precursor materials for use in the manufacture of battery electrodes, as coating materials for carbon-coated particles, or for bonding and agglomerating primary particle grains into larger aggregates or carbon-containing particle composites, or for embedding primary particles in a carbon matrix in which primary particle grains are completely embedded.

[0017] In particular, the objective is to provide the use of alternative carbon precursors for agglomerating and / or coating primary carbon particles onto secondary particles, or for embedding primary particles in a carbon matrix, in the manufacture of porous battery electrodes.

[0018] In particular, a special objective is to provide alternative carbon precursors for agglomerating and / or coating silicon-based particles, or for embedding (nano) silicon in a carbon matrix, in the manufacture of battery electrodes. [Overview of the project]

[0019] In a first aspect of the present invention, the use of a carbon precursor material in the manufacture of a battery electrode is provided, characterized in that the carbon precursor material comprises at least 50 wt% of petroleum-derived pitch product, 44-80 wt% of Alcan coking value measured in accordance with ASTM D4715, and at least 80 wt% of asphaltene measured by SARA analysis via Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

[0020] Petroleum-derived pitch products are distillation products derived from petroleum-based raw materials, which are produced by the thermal decomposition of petroleum flows and have an asphaltene concentration of at least 40% by weight, as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

[0021] A second aspect of the present invention provides a battery electrode, particularly a Li-ion battery electrode, that includes the carbon precursor material in a converted state. [Modes for carrying out the invention]

[0022] A first aspect of the present invention provides the use of a carbon precursor material in the manufacture of a battery electrode, characterized in that the carbon precursor material comprises at least 50 wt% of petroleum-derived pitch product, an Alcan coking value of 44-80 wt% measured in accordance with ASTM D4715, and at least 80 wt% of asphaltene measured by SARA analysis via the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

[0023] As is well known, asphaltenes are hydrocarbon solids that are insoluble in paraffinic solvents and have high melting points, and due to their highly condensed aromatic ring structure and high molecular weight, they tend to readily form isotropic coke. For example, asphaltenes may be insoluble in pentane or heptane (see, for example, EP0072243B1).

[0024] SARA analysis is a commonly used method for measuring aromatics, distillates, and feedstocks in saturated heavy oils, asphaltenes, resins, and heavy crude oils. Other SARA analysis methods besides Clay-Gel (ASTM D-2007) may include TLC / FID in accordance with IP-469, or preparative HPLC following IP-143 (IP-368).

[0025] Furthermore, the amounts of asphaltenes mentioned throughout this specification may include losses as defined in ASTM D-2007.

[0026] The high Alcan coking value of the carbon precursor material used in this invention allows for high-yield carbon formation, which limits the amount of volatile substances formed during the carbonization process. A high amount of volatile substances leads to porous carbon, resulting in a high BET specific surface area (BET SSA). High aromatic content, such as condensed aromatic rings, is also necessary for the ideal carbon form of the dense coating layer formed on the particle surface. In this way, homogeneous coating and complete surface coating are achieved with thin layers using small amounts of carbon and carbon precursors.

[0027] Particularly with respect to the formation of the carbon matrix in which the primary particles are embedded, a high Alcan coking value results in a high-density carbon matrix with limited or no porosity.

[0028] The thermoplastic carbon precursor material used in the present invention, in combination with a low B[a]P content, can exhibit a high carbon yield in combination with a high flash point and low viscosity in the molten state. Furthermore, it can exhibit a quinoline insolubility content of less than 1 wt%, which indicates a low amount of impurities such as mesophase carbon and coke particles, as well as metal particles and solid carbon particles, and a sulfur level of less than 2500 ppm. In addition, it can exhibit a toluene insolubility content suitable for the particle coating process (i.e., typically less than 50%) and good milling properties for the dry particle coating process. It can also be environmentally friendly due to a low B[a]P concentration and / or improved toxicity indicators, and exhibit a high flash point and low viscosity for safe and efficient mixing with powder in the binding and coating processes. (Finding: There may be a sweet spot here. On the one hand, a high carbon yield of the carbon precursor is required to produce a significant amount of low-porosity carbon. At the same time, some of the heavier volatiles contribute to the binding properties, similar to how the lower viscosity of a carbon precursor with a lower metric softening point has a positive effect on the binding properties. Therefore, an ideal carbon precursor for binding will have components that provide a high-density carbon matrix (usually high-melting-point components), some low-melting-point components that provide low viscosity, and some heavy volatiles that provide some additional binding effect.)

[0029] Due to the high flash point and low viscosity in the molten state, the carbon precursor material can also be applicable to direct coating in the liquid state. In this case, the newly produced carbon precursor material can be directly sprayed into the particles fluidized by a coated intensive mixer or a fluidized bed. Also, the newly produced liquid carbon precursor may be directly used for the binding and aggregation of particles. In this case, the hot liquid precursor is directly sprayed onto the particles treated by high shear force in a heated mixer for aggregation.

[0030] The carbon precursor material used in the present invention has good impregnation and wetting properties, which are shown by low viscosity at high shear stress exceeding the softening point of the meter and rapid recovery of viscosity when the shear stress is released. The strong thixotropic properties of the carbon precursor in the molten state are different from those of the coal tar pitch precursor, which is known to exhibit Newtonian rheology (see Harry Marsh, Introduction in Carbon Science). The thixotropic melt viscosity combined with a number of aromatic components characterized by the asphaltene and resin content characterized by the SARA method enables ideal wetting and impregnation of the particle surface, and a high-density carbon form that can be graphitized during heat treatment can be produced.

[0031] In one embodiment of the present invention, the use of the carbon precursor material described throughout this specification is provided for coating the particles of the electrode material for the manufacture of battery electrodes. The particles to be coated can be all types of carbon such as graphite, soft and hard carbon, carbon black, carbon nanotubes, graphene, etc., but can also be silicon, tin, or aluminum, as well as other electrochemically active metals or metal alloys based on silicon oxide and tin oxide, thereby obtaining a carbonaceous powder material or powder composite.

[0032] In a specific embodiment, the use of the carbon precursor material described throughout this specification is provided for binding primary particles to form secondary particle aggregates used as electrode materials in battery electrodes. Due to the composition of the carbon precursor characterized by a high asphaltene level, the carbon precursor is converted to carbon with a high carbon yield. The formed soft carbon can crystallize at a high processing temperature and finally be graphitized at a temperature exceeding 2000°C. The product has a rheology in the molten state characterized by high viscous recovery after shear stress and is suitable for the construction of secondary particle aggregates required in technical applications.

[0033] In another particular object of the present invention, the use of carbon precursor materials, as described throughout this specification, is provided for embedding primary particles in a carbon matrix in which the crystal grains of primary particles are completely embedded.

[0034] The properties of the primary particles that are aggregated or embedded can be all types of carbon, such as graphite, soft and hard carbon, carbon black, carbon nanotubes, and graphene, but they can also be silicon, tin, or aluminum, as well as other electrochemically active metals or metallic alloys based on silicon oxide and tin oxide.

[0035] In addition, the carbon precursor material according to the present invention allows for the application of coal tar pitch at a significantly higher mixing ratio than conventional petroleum-derived pitch, thereby achieving the objective of strengthening the supply of high-quality carbon precursor material to flow users.

[0036] According to the present invention, the petroleum-derived pitch product is characterized by an Alcan coking value of 44-80% by weight, as measured in accordance with ASTM D4715, and is a distillation product derived from a petroleum-based raw material produced by the thermal decomposition of a petroleum stream, the petroleum-based raw material having a concentration of at least 40% by weight of asphaltene, as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007. More specifically, the petroleum-derived pitch product is a distillation residue derived from the petroleum-based raw material having a concentration of at least 40% by weight of asphaltene. Such distillation can usually be carried out at a temperature T = 280-400°C, preferably 320-380°C, under a typical pressure of P = 0.1 mbar-100 mbar.

[0037] In a preferred embodiment, the petroleum-based raw material produced by the thermal decomposition of the petroleum flow may have an asphaltene concentration of at least 50% by weight, as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007. These aforementioned amounts of asphaltene may include losses as defined in ASTM D2007.

[0038] Furthermore, the petroleum-based raw materials may be characterized by a resin concentration of 20% to 35% by weight, preferably 25% to 35% by weight, as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

[0039] In one embodiment of the present invention, the petroleum-derived pitch product may contain at least 80% by weight, or at least 85% by weight, or at least 90% by weight, or at least 95% by weight of asphaltene, as measured by SARA analysis (Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007).

[0040] Furthermore, the material may have a resin concentration of 1–20% by weight, as measured by SARA analysis. In addition, the amount of asphaltene mentioned above may include losses as defined by ASTM D2007.

[0041] While not bound by any particular theory, starting with petroleum-based raw materials containing at least 40% by weight of asphaltene and concentrating the asphaltene to a concentration exceeding 80% by weight may contribute to the high Alcan coking value of the carbon precursor used in this invention. This ensures a high-density (low-porosity) and uniform carbon coating on the electrode material surface, reducing surface reactivity to the electrolyte and decreasing the surface area of ​​the electrode material in direct contact with the battery electrolyte. In addition, the morphological carbon layer formed on the particle surface during the subsequent carbonization of the carbon precursor ensures good conductivity and particle contact of the electrode material within the battery cell electrode.

[0042] In embodiments of the present invention, the carbon precursor material may have a Mettler softening point of 130 to 300°C, preferably 150 to 280°C, and more preferably 160 to 260°C. Considering particle coating applications, a Mettler softening point above 120°C may allow the carbon precursor to be milled into fine particles used in dry particle coating processes.

[0043] Furthermore, the carbon precursor material may have an Alcan coking value of at least 44% by weight, or at least 55% by weight, preferably more than 60% by weight, or more preferably more than 70% by weight, resulting in lower porosity of carbon artifacts after carbonization / graphitization, leading to better properties in subsequent use as an electrode material for battery cells.

[0044] According to the present invention, petroleum-derived pitch products may have a B[a]P content of less than 1500 mg / kg, or less than 1200 mg / kg, preferably less than 1000 mg / kg, and / or a total of less than 5% (m / m) of 16EPA-PAH in accordance with the U.S. Environmental Protection Agency (EPA).

[0045] In one embodiment of the present invention, the carbon precursor material may have an Alcan coking value of at least 44%, a B[a]P content of less than 1500 mg / kg, or less than 1200 mg / kg, preferably less than 1000 mg / kg, and a Mettler softening point higher than 150°C.

[0046] In another embodiment, the carbon precursor material may have an Alcan coking value of at least 70%, a B[a]P content of less than 250 mg / kg, and a Mettler softening point greater than 240°C.

[0047] Since the carbon precursor material is converted to carbon during the carbonization process, which is a heat treatment in an inert gas atmosphere or vacuum, if the coke yield is sufficiently high, the amount of volatile substances formed during the carbonization process is small, thus avoiding high porosity in the resulting graphite particles. The low amount of volatile substances in the furnace exhaust gas makes exhaust gas management easier. Furthermore, several heavy volatile components contribute to the binding effect of the carbon precursor and the low viscosity of the molten carbon precursor. The binding of particles can lead to the formation of a high-density carbon layer on the surface of aggregated particles or carbon matrix in which primary particles are embedded in a form favorable for the efficient formation of a solid electrolyte interface on the electrode particle surface (i.e., a passivation layer formed from electrolyte decomposition products formed during the electrochemical reduction of the negative electrode in the electrochemically active electrode surface region that is in contact with the electrolyte during the cell charging process). In the case of liquid electrolytes, this passivation layer is formed in the electrochemically active electrode surface region that is wetted by the liquid electrolyte. The properties and quality of the carbon film formed on the particle surface positively influence the solid electrolyte interface phase, and therefore affect several battery cell parameters such as specific charge loss, discharge and charge performance of the current rate, stability of the charge / discharge cycle, and safety performance of the battery cell.

[0048] The thixotropic behavior of the carbon precursor materials used in this invention, with its rapid recovery rate of molten viscosity measured for molten precursors above the Mettler softening point, facilitates handling and processing at low viscosity with high shear forces introduced during particle formation, such as mixing of primary particles and molten carbon precursors, and rapid viscosity recovery after the shear stress is released. In particular, for carbon precursor materials consisting solely of petroleum-derived pitch products, the dynamic viscosity at 40°C above the Mettler softening point, measured at a shear rate of 10 1 / s, can range from 14,000 to 35,000 mPa·s, and viscosity recovery after 60 seconds can exceed 90%. If the carbon precursor material also contains a predetermined amount of coal tar-based pitch, such mixtures can have viscosities of up to 50,000 or even up to 60,000 mPa·s.

[0049] The aforementioned low melting viscosity promotes the bonding effect, as well as wetting and impregnation of the aggregated particle surface, resulting in a thin, high-density film of uniformly dispersed carbon on the particle surface. Improved surface wetting and impregnation ensures good coating not only of the geometric particle surface but also of the micro- and mesopores, while also achieving the roughness typically found on particle surfaces.

[0050] The carbon precursor material of the present invention may comprise 25 to 75% by weight, preferably 50 to 75% by weight, or at least 50% by weight, more preferably at least 80% by weight, or even more than 95% by weight of the petroleum-derived pitch product and coal tar-based pitch. Alternatively, bio-based components such as phenolic resins, lignin-based materials, or tall oil-based materials may be used instead of or in combination with coal tar-based pitch.

[0051] In a more preferred embodiment of the present invention, the carbon precursor material may consist solely of the petroleum-derived pitch product, i.e., it may contain 100% by weight of the petroleum-derived pitch product.

[0052] The following table shows examples of carbon precursor material formulations according to embodiments of the present invention. Specifically, Table 1 provides Examples 1 to 4 of carbon precursor materials containing only petroleum-derived pitch products, and Example 5 of a carbon precursor material containing 50% coal tar-based pitch.

[0053] [Table 1] JPEG2026521166000002.jpg132159

[0054] The following table outlines the analytical procedures for the product parameters used herein. [Table 2]

Claims

1. The use of a thermoplastic carbon precursor material in the manufacture of battery electrodes, wherein the carbon precursor material comprises at least 50% by weight of petroleum-derived pitch product, an Alcan coking value of 44-80% by weight measured in accordance with ASTM D4715, and a concentration of at least 80% by weight of asphaltene measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

2. The use according to claim 1, wherein the petroleum-derived pitch product has a Mettler softening point of 130°C to 300°C.

3. The use according to claim 1, wherein the petroleum-derived pitch product has an Alcan coking value of 50 to 76% by weight.

4. The use according to claim 1, wherein the petroleum-derived pitch product has an asphaltene concentration of at least 85% by weight, as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

5. The use according to claim 1, wherein the petroleum-derived pitch product has a resin content of less than 20%, as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

6. The use according to claim 1, wherein the petroleum-derived pitch product has a B[a]P content of less than 1500 mg / kg and / or a total of 16EPA-PAH of less than 5% (m / m) in accordance with the U.S. Environmental Protection Agency (EPA).

7. The use according to any one of the above claims, wherein the petroleum-derived pitch product has an Alcan coking value of at least 44% by weight, a B[a]P content of less than 1500 mg / kg, and a Mettler softening point greater than 150°C.

8. The use according to any one of the above claims, wherein the petroleum-derived pitch product has an Alcan coking value of at least 70%, a B[a]P content of less than 250 mg / kg, and a Mettler softening point greater than 240°C.

9. The use according to any one of the above claims, wherein the petroleum-derived pitch product is a distillation product derived from a petroleum-based raw material, the petroleum-based raw material is produced by the thermal decomposition of a petroleum stream, and the petroleum-based raw material has a concentration of at least 40% by weight of asphaltene as measured by the Clay-Gel Absorption Chromatographic Method in accordance with ASTM D2007.

10. The use according to any one of claims 1 to 9, wherein the carbon precursor material consists solely of the petroleum-derived pitch product.

11. The use according to any one of claims 1 to 9, wherein the carbon precursor material comprises 50 to 75% by weight of the petroleum-derived pitch product and coal tar-based pitch.

12. The use according to any one of claims 1 to 11 for binding primary particles together to form a secondary particle aggregate.

13. The use according to any one of claims 1 to 11 for embedding primary particles in a carbon matrix in which the primary particles are completely embedded.

14. A battery electrode comprising a converted carbon precursor material used in any of claims 1 to 13.

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