Artificial graphite anode material

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Artificial graphite anode material, its preparation method, and anode for lithium-ion batteries. Document number: 15131492. Publication date: August 10, 2018, 08:04. Navigation: X Technology > Latest Patents > Manufacturing and synthesis of inorganic chemicals and their compounds; Applied technologies. The present invention pertains to the field of lithium-ion battery technology. In particular, it relates to an anode material for power lithium-ion batteries and its preparation method, as well as the anode for lithium-ion batteries prepared using this anode material. Background Technology: With the development of technology, electric vehicles are gradually becoming more popular. Looking at future trends, lithium-ion batteries will become one of the main power sources for electric vehicles. Electric vehicles equipped with lithium-ion batteries are already on the market today, and the market prospects for power-type lithium-ion batteries are even more promising in the future. Power-type lithium-ion batteries must possess better rate charge/discharge performance, excellent performance at high and low temperatures, a long cycle life, and a low price in order to meet market demands. Currently, to meet the requirement for long lifespan, synthetic graphite is the preferred anode material for lithium-ion batteries. Compared to natural graphite, synthetic graphite exhibits better cycle stability, better compatibility with electrolytes, and lower volume changes during cycling, making it more suitable for power lithium-ion batteries. However, since artificial graphite has a layered structure, the decrease in electrolyte conductivity at low temperatures prevents it from meeting the demands of high-rate charging and discharging under such conditions. To address the above issues, existing technologies involve treating synthetic graphite by mixing in hard carbon or coating it with hard carbon. However, during this process, the stringent requirements regarding moisture control posed by hard carbon not only prolong the production cycle but also affect production capacity ； Moreover, the artificial graphite used must undergo a high-temperature graphitization process; this graphitization process, along with the processes of mixing in hard carbon or coating with hard carbon, results in significantly increased production costs. Summary of the invention: The objective of this invention is to provide an artificial graphite anode material that is low in cost and possesses good rate performance, along with a method for its preparation, as well as a lithium-ion battery anode. To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing artificial graphite anode material, comprising the following steps: subjecting the finished graphite produced from needle coke or petroleum coke raw materials to grading treatment, and screening out fine artificial graphite powder with an average particle size of 1.5–4 μm ； Mix the sieved fine powder of synthetic graphite with coal tar pitch in a mass ratio of 1:2.5 to 1:5.5 ； The mixed material was added to a horizontal reactor, where granulation was carried out under an inert gas atmosphere to yield a mixed precursor of monomeric particles and secondary particles with an average particle size of 4–7.5 μm ； The precursor is subjected to sintering and carbonization, and the carbonized secondary particle graphite is screened to obtain a secondary particle synthetic graphite anode material with an average particle size of 4–12 μm. More specifically, the average particle size of the coal tar pitch is 5–8 μm. More specifically, the softening point of the coal tar pitch is 100°C to 300°C. More specifically, the granulation time is 8 to 24 hours, and the temperature is 500 to 800°C. More specifically, the sintering and carbonization temperature is 600–1200°C, with a time of 6–12 hours. The artificial graphite anode material is prepared using the aforementioned preparation method. Anode for lithium-ion batteries, comprising: a current collector and an anode slurry coated on the current collector. The anode slurry is prepared by dissolving an anode mixture in a solvent; the anode mixture includes a conductive agent, a binder, and the aforementioned synthetic graphite anode material. As can be seen from the above technical solutions, the present invention uses fine artificial graphite powder with a small particle size as the main raw material, which significantly reduces the cost of the material. Moreover, by using artificial graphite powder as the raw material, there is no need for graphitization, as is the case in existing technologies where petroleum coke or needle coke is used as the raw material ； In this invention, artificial graphite powder is placed in a horizontal reactor for granulation; the material remains in a weightless state throughout the mixing process. Compared with conventional heating and mixing granulation methods, which rely on stirring to facilitate bonding between materials, the granulation process of this invention allows for more thorough mixing of graphite particles with asphalt particles, resulting in good encapsulation while preventing excessive bonding between the particles. The present invention effectively addresses the problem of high-rate charging and discharging of batteries at low temperatures. It enables rapid high-rate charging and discharging of lithium-ion batteries while preventing lithium deposition on the surface of the anode sheet. Additionally, by utilizing the superior electrolyte compatibility and long cycle life inherent in fine artificial graphite powder, the cycling performance and low-temperature cycling characteristics of the battery are improved. Moreover, the surface of the small-particle artificial graphite is coated with coal tar pitch; after carbonization treatment, its kinetic properties are enhanced. This prevents the formation of lithium dendrites during high-current charging, thereby contributing to an improvement in the overall safety performance of the battery. Description of the drawings: Figure 1 is an electron micrograph of the artificial graphite anode material prepared in Example 1 of the present invention ； Figure 2 shows the cycle curves at room temperature for lithium-ion batteries fabricated using the anode materials prepared in Examples 1–3 and the comparative example ； Figure 3 shows the cycle curves at 0°C for lithium-ion batteries fabricated using the anode materials prepared in Examples 1–3 and the comparative example. The following provides a more detailed description of the specific embodiments of the present invention, with reference to the accompanying drawings. Specific Embodiments: To make the above-mentioned and other objectives, features, and advantages of the present invention more apparent, examples of embodiments of the present invention are given below for a detailed explanation. Unless otherwise specified, the reagents, materials, and instruments used in the following descriptions are all conventional ones that can be purchased commercially. The relevant reagents can also be synthesized using standard synthetic methods. Example 1: The artificial graphite anode material of the present invention uses artificial graphite fine powder with an average particle size (D50) of 1.5–4 μm as the main raw material. Artificial graphite with a small particle size possesses good rate performance and is also relatively inexpensive. The artificial graphite fine powder is subjected to the following processing steps to produce secondary-particle artificial graphite anode material. Step 1: The graphite produced from needle coke or petroleum coke raw materials is subjected to grading treatment, so as to separate out artificial graphite fine powder with an average particle size of 1.5–4 μm ； Step 2: Mix the artificial graphite fine powder with coal tar pitch having an average particle size of 5–8 μm. The mixing ratio of coal tar pitch to artificial graphite fine powder is 1:2.5–1:5.5 (by mass), and the softening point of the coal tar pitch used is 100°C–300°C℃ ； Small-particle coal tar pitch is mixed with small-particle synthetic graphite in order to coat the pitch on the small-particle synthetic graphite and bond the graphite particles together ； Step 3: The mixed material is added to a horizontal reactor, where granulation takes place under nitrogen protection. The granulation time ranges from 8 to 24 hours, and the temperature is between 500 and 800°C, resulting in a precursor composed of both single particles and secondary particles with an average particle size of 4 to 7.5 μm ； Due to the presence of paddle blades that rotate in opposite directions on two axes inside the horizontal reactor, the material is in a state of temporary weightlessness during mixing, achieving a gravity-free mixing effect. This allows for more thorough mixing of graphite particles with asphalt particles, resulting in good coating and preventing excessive sticking between the particles ； Step 4: The precursor is subjected to sintering and carbonization treatment at a sintering temperature of 600–1200°C for 6–12 hours. The graphite obtained after carbonization is then screened to yield secondary particle artificial graphite anode material with an average particle size of 4–12 μm (Figure 1). After carbonization, the material strength of the particles increases, their capacity improves, and their overall performance becomes more stable. The prepared artificial graphite anode material was mixed with single-walled nanocarbon tubes, super-p, binder (SBR), CMC (sodium carboxymethyl cellulose), and solvent in a twin-screw mixer to obtain the anode mixture ； The amount of single-walled carbon nanotubes added to the anode mixture is 0.3% of the total mass of all materials; the amount of Super-P added is 1.5% of the total mass of all materials; the amount of binder added is 1.5% of the total mass of all materials; the amount of CMC added is 0.5% of the total mass of all materials. The remainder consists of secondary-particle synthetic graphite anode material ； A solvent is added to the anode mixture to produce an anode slurry with a solid content of 42% ； The negative electrode slurry is applied to the surface of copper foil; after drying and compression by a roller press, the negative electrode of the battery is obtained. After punching the prepared anode and cathode sheets, they were stacked in a Z-shape to form a bare cell. After adding the electrolyte, it was sealed to produce a square soft-packaged battery measuring 75 mm × 50 mm × 7 mm. In this embodiment, the cathode uses ternary nickel-cobalt-manganese (NCM) as the cathode active material. The cathode active material is mixed with a binder (PVDF) and conductive carbon black to obtain a cathode mixture, which consists of 94% NCM, 3% PVDF, and 3% conductive carbon black ； A solvent (N-methylpyrrolidone, abbreviated as NMP) is added to the cathode mixture to produce a cathode slurry with a solid content of 75% ； The positive electrode slurry is coated on both sides of aluminum foil; after drying and compression by a roller press, the positive electrode of the battery is obtained. The electrolyte in this embodiment includes lithium hexafluorophosphate (1M) and a mixed solvent, which is composed of ethylene carbonate, dimethyl carbonate, and 1,2-propanediol carbonate in a volume ratio of 1:1:1. In this embodiment, both the cathode and the electrolyte are prepared using conventional processes and materials. Example 2: The difference between this example and Example 1 is that the negative electrode mixture does not contain single-walled carbon nanotubes; only Super-P is used as the conductive agent. Example 3: This example differs from Example 1 in that the amount of CMC added to the negative electrode mixture is 1.5%. The comparative example differs from Example 1 in that the synthetic graphite particles in the negative electrode mixture are conventional synthetic graphite particles. Their particle size is similar to that of the secondary-particle synthetic graphite negative electrode material in Example 1; however, they have not undergone the treatments described in Steps 2, 3, and 4 of the process of the present invention. The batteries prepared in Examples 1–3 and the battery prepared in the comparative example were subjected to charge-discharge cycle tests, and the data for discharge at different rates are shown in Table 1. Table 1 shows that batteries made using the secondary small-particle artificial graphite anode material of the present invention exhibit excellent rate performance. When using the same formulation, conventional artificial graphite anode materials have significantly inferior high-rate discharge performance compared to those of the present invention. Furthermore, by comparing the discharge data of Examples 1–3, it can be seen that compared to using only SUPER-P as a conductive agent or adding single-walled nanocarbon tubes to the conductive agent, the battery exhibits significantly improved high-rate discharge performance. This indicates that the combination of single-walled nanocarbon tubes and SUPER-P helps to form an excellent conductive network in the negative electrode, reducing electrode polarization and thus facilitating high-rate discharge. Increasing the amount of thickener has an adverse effect on high-rate discharge. Figure 2 shows the cycle performance curves at room temperature for lithium-ion batteries fabricated using the anode materials prepared in Examples 1–3 and the comparative example. It can be seen from Figure 2 that the batteries made from the secondary small-particle synthetic graphite anode material of the present invention maintain a good capacity retention rate after 2C/2C charge-discharge cycles. Figure 3 shows the cycle curves at 0°C for lithium-ion batteries fabricated using the anode materials prepared according to Examples 1–3 and the comparative example. It can be seen from Figure 3 that the secondary small-particle synthetic graphite anode material of the present invention exhibits better low-temperature cycling performance, indicating that treating small-particle synthetic graphite with a special process can significantly improve its low-temperature cycling properties. The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will instead conform to the broadest scope consistent with the principles and novel features disclosed herein. Technical features: 1. A method for preparing artificial graphite anode materials, characterized by comprising the following steps: subjecting the finished graphite produced from needle coke or petroleum coke raw materials to grading treatment, and screening out artificial graphite fine powder with an average particle size of 1.5–4 μm ； Mix the sieved fine powder of synthetic graphite with coal tar pitch in a mass ratio of 1:2.5 to 1:5.5 ； The mixed material was added to a horizontal reactor, where granulation was carried out under an inert gas atmosphere to yield a mixed precursor of monomeric particles and secondary particles with an average particle size of 4–7.5 μm ； The precursor is subjected to sintering and carbonization, and the carbonized secondary particle graphite is screened to obtain a secondary particle synthetic graphite anode material with an average particle size of 4–12 μm. 2. The method for preparing the artificial graphite anode material as described in Claim 1, characterized in that: the average particle size of the coal tar pitch is 5–8 μm. 3. The method for preparing the artificial graphite anode material as described in claim 1 or 2, characterized in that: the softening point of the coal tar pitch is 100°C to 300°C. 4. The method for preparing the artificial graphite anode material as described in Claim 1, characterized in that: the granulation time is 8 to 24 hours, and the temperature is 500 to 800°C. 5. The method for preparing the artificial graphite anode material as described in Claim 1, characterized in that the temperature for sintering and carbonization is 600–1200°C, and the time is 6–12 hours. 6. Artificial graphite anode material, characterized in that it is prepared by the method described in any one of claims 1 to 5. 7. A negative electrode for lithium-ion batteries, comprising: a current collector and a negative electrode slurry coated on the current collector; the negative electrode slurry being prepared by dissolving a negative electrode mixture in a solvent, the negative electrode mixture including a conductive agent, a binder, and artificial graphite negative electrode material; characterized in that the artificial graphite negative electrode material is the artificial graphite negative electrode material as described in claim 6. In terms of technical summary, the preparation method for artificial graphite anode materials is as follows: Artificial graphite anode materials, their preparation methods, and high-quality graphite used in lithium-ion battery anodes are sorted, and fine artificial graphite powder with an average particle size of 1.5–4 μm is isolated through screening ； Mix artificial graphite powder with coal tar pitch at a mass ratio of 1:2.5 to 1:5.5 ； The mixed material was added to a horizontal reactor where granulation took place under an inert gas atmosphere, resulting in a mixed precursor of primary and secondary particles with an average particle size of 4–7.5 μm ； The precursor is subjected to sintering and carbonization, and the carbonized secondary particle graphite is screened to obtain a secondary particle synthetic graphite anode material with an average particle size of 4–12 μm. The present invention solves the problem of high-rate charging and discharging of batteries at low temperatures, and simultaneously takes advantage of the good electrolyte compatibility and long cycle life inherent in artificial graphite powder to improve the battery’s cycle performance, low-temperature cycle performance, and safety performance.