Soft carbon particles for lithium-ion battery negative electrode material and preparation method thereof

Abstract

The present invention provides soft carbon particles for lithium ion battery negative electrode materials and a preparation method thereof. The preparation method comprises the following steps: (1) mixing a soft carbon raw material and a first modifier to obtain a solid mixture A, blending the solid mixture A in a liquid state to obtain a carbonized precursor, carbonizing the carbonized precursor, crushing, and screening to obtain modified soft carbon particles A; (2) mixing a soft carbon raw material, a second modifier, and a conductive agent to obtain a solid mixture B, blending the solid mixture B in a liquid state, cooling, and obtaining a bulk product, crushing, and screening the bulk product to obtain modified soft carbon precursor particles B; (3) mixing the modified soft carbon particles A and the modified soft carbon precursor particles B, and then coating them, followed by carbonization, crushing, and screening to obtain the soft carbon particles for lithium ion battery negative electrode materials. When the soft carbon particles prepared by the present invention are used as the negative electrode of a lithium ion battery, the lithium battery has high capacity and excellent fast charging performance.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and relates to soft carbon particles for lithium ion battery negative electrode materials and a preparation method thereof, and in particular to high-performance soft carbon particles for lithium ion battery negative electrode materials suitable for continuous production and a preparation method thereof. Background Art

[0002] The theoretical capacity of natural and artificial graphite anode materials is 372 mAh / g. Currently, the capacity of commercially available high-quality graphite anode materials can reach 365 mAh / g, but further improvement in this performance is difficult to achieve significant results. As the energy density and other comprehensive performance requirements of power batteries continue to increase, natural and artificial graphite anode materials are gradually failing to meet the requirements of high-energy-density batteries.

[0003] Soft carbon materials exhibit a pattern of capacity that decreases and then increases during the carbonization process. Carbon materials carbonized at medium temperatures of 1000-2000°C exhibit a long-range ordered structure and high specific capacity. However, these ordered soft carbon materials have limited lithium ion insertion channels, resulting in unsatisfactory fast-charging performance. Therefore, soft carbon materials need to be modified to meet the market's higher demands for soft carbon materials.

[0004] Generally, more lithium insertion sites can be added by doping with elements such as B, N, and P, thereby improving the specific capacity of soft carbon materials. However, element doping modification has almost no effect on improving the fast charging performance of the material. In addition, soft carbon materials can also be modified using carbon sources that have hard carbon properties after carbonization. Because the interlayer spacing of the hard carbon 002 crystal plane is larger, there are more voids and disordered layer structures, thereby improving the specific capacity and fast charging performance of the soft carbon material. However, doping a large amount of hard carbon into the soft carbon often leads to too low a first coulombic efficiency of the final material.

[0005] CN102082272A discloses a lithium-ion battery negative electrode material containing a hard carbon coating and a preparation method thereof. The preparation method mainly comprises the following steps: fully mixing graphite with a coating material, heat treating the material under the protection of an inert atmosphere, cooling the material after heat preservation for 0.5-6 hours, and then performing a secondary high-temperature graphitization treatment under the protection of an inert atmosphere. The heteroatom modifier can change the structure of the hard carbon in the coating material, and the selected hard carbon precursor has the characteristics of dissolving and undergoing a condensation reaction with the soft carbon precursor asphalt, which can improve the uniformity and operability of the coated graphite particles. The ratio formula among the three has an important influence on the performance of the three. The invention achieves the purpose of increasing the capacity of the negative electrode material and improving its cycle performance by optimizing the application ratio formula of the heteroatoms, hard carbon precursors and soft carbon precursors in the graphite coating material. However, the fast charging performance of the negative electrode material of the invention has not been improved.

[0006] Therefore, in this field, it is expected to develop a method for preparing soft carbon particles for lithium-ion battery negative electrode materials with high capacity and fast charging performance. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention provides soft carbon particles for lithium-ion battery anode materials and a method for preparing the same. The present method is simple and can continuously and efficiently produce a uniform carbonized precursor of the soft carbon material. Furthermore, when the prepared soft carbon particles are used as anode materials for lithium-ion batteries, the lithium-ion batteries exhibit high capacity and excellent fast-charging performance.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing soft carbon particles for lithium ion battery negative electrode materials, the preparation method comprising the following steps:

[0010] (1) mixing a soft carbon raw material and a first modifier to obtain a solid mixture A, then blending the solid mixture A in a liquid state using a heating and stirring device, cooling to room temperature to obtain a carbonized precursor, carbonizing the carbonized precursor, crushing, and screening to obtain modified soft carbon particles A;

[0011] (2) mixing a soft carbon raw material, a second modifier, and a conductive agent to obtain a solid mixture B, then blending the solid mixture B in a liquid state using a heating and stirring device, cooling to obtain a block product, and crushing and sieving the block product to obtain modified soft carbon precursor particles B;

[0012] (3) mixing the modified soft carbon particles A and the modified soft carbon precursor particles B, and then coating the modified soft carbon particles A with the modified soft carbon precursor particles B, followed by carbonization, crushing, and screening to obtain the soft carbon particles for the negative electrode material of the lithium ion battery;

[0013] The particle size of the modified soft carbon precursor particles B in step (2) is 3-10 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0014] In the present invention, modified soft carbon precursor particles B, which exhibit good fluidity at medium temperatures, are used as a surface modifier to coat and modify modified soft carbon particles A. The resulting soft carbon particles, when used as negative electrode materials for lithium-ion batteries, provide high capacity and excellent fast-charging performance. Furthermore, the preparation method of the present invention is simple, low-cost, and enables the continuous and efficient production of a uniform carbonized precursor.

[0015] In the present invention, the modified soft carbon particles A obtained by modifying the soft carbon raw material with the first modifier have high capacity, and the carbonized product of the modified soft carbon precursor particles B obtained by modifying the soft carbon raw material with the second modifier has good fast charging performance.

[0016] In the present invention, the particle size of the modified soft carbon precursor particles B is controlled within 3-10 μm, which can better achieve the coating of the modified soft carbon precursor particles B on the modified soft carbon particles A. If the particle size of the modified soft carbon precursor particles B is less than 3 μm, it is very easy to cause agglomeration of the soft carbon particles in the final product, resulting in excessive particle size of the final product. If the particle size of the modified soft carbon precursor particles B is greater than 10 μm, the coating effect of B on A is poor, and the final product is approximately a physical mixture product of the carbides of particles A and particles B.

[0017] Preferably, the soft carbon raw material in step (1) includes any one of petroleum asphalt, coal tar, petroleum coke or needle coke, or a combination of at least two of them.

[0018] Preferably, the soft carbon raw material in step (2) includes any one of petroleum asphalt, coal tar, petroleum coke or needle coke, or a combination of at least two of them.

[0019] Preferably, the first modifier comprises any one of melamine, melamine phosphate, polyamide, melamine resin, ammonium phosphate, ammonium polyphosphate, phytic acid, phosphoric acid or boric acid, or a combination of at least two thereof.

[0020] Preferably, the second modifier includes any one or a combination of at least two of polyethylene, polypropylene, polystyrene, polyvinyl pyrrolidone, phenolic resin, polyamide, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, sucrose, glucosamine, wheat starch, rice starch, potato starch, chitosan, glycine or tryptophan. The second modifier can increase the amorphous region of the modified soft carbon precursor particles B after carbonization, thereby increasing the lithium ion transmission channel to achieve the purpose of improving the fast charging performance of the lithium ion battery.

[0021] Preferably, the conductive agent comprises any one of conductive carbon black, graphene, graphite oxide, carbon nanotubes, or whisker carbon nanotubes, or a combination of at least two. The graphene of the present invention comprises unoxidized graphene and / or graphene oxide. The conductive agent can enhance the electrical conductivity of the soft carbon material, providing good electronic conductivity for the negative electrode of the lithium-ion battery during high-rate charge and discharge, allowing for smooth insertion and deintercalation of lithium ions.

[0022] Preferably, the mass ratio of the soft carbon raw material to the first modifier in step (1) is 100:(10-50), for example, 100:10, 100:15, 100:20, 100:25, 100:30, 100:35, 100:40, 100:45 or 100:50, etc.

[0023] Preferably, the mass ratio of the soft carbon raw material to the second modifier in step (2) is 100:(10-100), for example, 100:10, 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90 or 100:100, etc.

[0024] Preferably, the mass ratio of the soft carbon raw material to the conductive agent in step (2) is 100:(0-10), for example, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8 or 100:9, etc.

[0025] Preferably, the mass ratio of the modified soft carbon particles A to the modified soft carbon precursor particles B in step (3) is 100:(1-20), for example, 100:1, 100:3, 100:5, 100:8, 100:10, 100:13, 100:15, 100:18 or 100:20, etc.

[0026] Preferably, the mixed processing environment in step (1), step (2) and step (3) is independently 10-25°C (for example, 10°C, 13°C, 15°C, 18°C, 20°C, 23°C or 25°C, etc.), and the humidity is less than 75% (for example, 73%, 70%, 65%, 60%, 55%, 50%, 45% or 40%, etc.).

[0027] As a preferred technical solution of the present invention, the processing environment described herein is one in which the soft carbon material can maintain its morphology well. Poor processing environments, such as high humidity, can cause the soft carbon material to absorb water and aggregate, resulting in poor processing performance and poor product quality. High temperatures can cause the soft carbon material to become sticky and aggregate, hindering the production of the final product. Low temperatures can also hinder the operation of processing equipment. Therefore, a processing environment of 10-25°C and humidity <75% is preferred in the present invention.

[0028] Preferably, the mixing equipment in step (1) includes any one of a homogenizing and dispersing barrel, a high-speed mixer, a zero-gravity mixer, a V-type mixer or a VC high-efficiency mixer.

[0029] Preferably, the mixing equipment in step (2) includes any one of a homogenizing and dispersing barrel, a high-speed mixer, a zero-gravity mixer, a V-type mixer or a VC high-efficiency mixer.

[0030] Preferably, the mixing frequency in step (1) is 20-50 Hz, for example, 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz or 50 Hz, and the mixing time is 10-60 min, for example, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc.

[0031] Preferably, the mixing frequency in step (2) is 20-50 Hz, for example, 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz or 50 Hz, and the mixing time is 10-60 min, for example, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc.

[0032] Preferably, the heating and stirring device in step (1) comprises any one of an open mill, a kneading pot, a stirring tank, a high-temperature stirring reactor, an internal mixer or a twin-screw extruder.

[0033] Preferably, the heating and stirring device in step (2) comprises any one of an open mill, a kneading pot, a stirring tank, a high-temperature stirring reactor, an internal mixer or a twin-screw extruder.

[0034] Preferably, the temperature of the heating and stirring device in step (1) and step (2) is independently divided into 5 sections. Among them, the first section: 150-200°C (for example, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C, etc.), the temperature of this section should be lower than the softening temperature of the soft carbon raw material to ensure that the material can enter the stirring chamber smoothly and without sticking. The second section: 200-240°C (for example, 200°C, 210°C, 220°C, 230°C or 240°C, etc.), the temperature of this area should soften the soft carbon material to ensure that there is a certain shearing effect between the material and the stirring rotor. The third section: 230-270°C (for example, 230°C, 240°C, 250°C, 260°C or 270°C, etc.), the temperature of this area should be higher than the flow temperature of the soft carbon to ensure that the material entering the liquid phase has good fluidity, the material is subjected to strong shearing and can be fully mixed. Section 4: 240-280°C (e.g. 240°C, 250°C, 260°C, 270°C or 280°C, etc.). As the shear rate gradually increases, the shear force on the material gradually increases, and the temperature is increased accordingly to ensure that the motor load of the heating and stirring device is within the normal range. Section 5: 220-260°C (e.g. 220°C, 230°C, 240°C, 250°C or 260°C, etc.). The temperature in this section should be slightly lower than that in Section 4 to reduce the volatilization of small molecules, ensure that the product in this step has good melt flow properties, and protect the environment.

[0035] Preferably, the rotor speed of the heating and stirring device in step (1) and step (2) is independently 300-600 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm. The rotor speed is controlled within the range of 300-600 rpm to ensure that the materials can be mixed evenly by a strong shearing action and to ensure a certain yield.

[0036] Preferably, the speed of the auxiliary motors in the feeding zones of the heating and stirring device in step (1) and step (2) is independently 30-80 rpm, for example, 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm or 80 rpm. The speed of the auxiliary motors in the feeding zones of the heating and stirring device is controlled within the range of 30-80 rpm to ensure that the chambers in each zone of the heating and stirring device are fully filled without causing an excessive load on the main motor of the heating and stirring device.

[0037] Preferably, the carbonization in step (1) is carried out in a carbonization furnace.

[0038] Preferably, the carbonization in step (1) is carried out under the protection of a protective gas.

[0039] Preferably, the protective gas comprises nitrogen or argon.

[0040] Preferably, the carbonization temperature in step (1) is 1300-2000°C, for example, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C or 2000°C, etc. The carbonization temperature is not lower than 1300°C, so that most of the heteroatoms in the soft carbon material can be removed, ensuring the first coulomb efficiency. The carbonization temperature is also not higher than 2000°C, which can ensure that the graphite interlayer spacing of the modified soft carbon particles A is greater than 0.34nm, so as to ensure that the soft carbon negative electrode material has a higher capacity. The carbonization time is 4-10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc. The carbonization time is not less than 4h, so as to ensure that the small molecular substances in the soft carbon raw material and the first modifier can be fully condensed to form a regular large planar structure. The carbonization time is not higher than 10h, so as to save energy.

[0041] Preferably, the processing environment for the crushing and screening in step (1) is 10-25°C (for example, 10°C, 13°C, 15°C, 18°C, 20°C, 23°C or 25°C, etc.), and the humidity is less than 75% (for example, 73%, 70%, 65%, 60%, 55%, 50%, 45% or 40%, etc.).

[0042] Preferably, the processing environment for the crushing and screening in step (2) is 10-25°C (for example, 10°C, 13°C, 15°C, 18°C, 20°C, 23°C or 25°C, etc.), and the humidity is less than 75% (for example, 73%, 70%, 65%, 60%, 55%, 50%, 45% or 40%, etc.).

[0043] Preferably, the particle size of the modified soft carbon particles A in step (1) is 10-18 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm or 18 μm.

[0044] Preferably, the coating treatment in step (3) is carried out in a vertical converter.

[0045] Preferably, the coating treatment temperature in step (3) is 200-400° C., for example, 200° C., 230° C., 250° C., 280° C., 300° C., 330° C., 350° C., 380° C., or 400° C., and the coating treatment time is 1-4 hours, for example, 1 hour, 1.3 hours, 1.5 hours, 1.8 hours, 2 hours, 2.3 hours, 2.5 hours, 2.8 hours, 3 hours, 3.3 hours, 3.5 hours, 3.8 hours, or 4 hours. By controlling the coating treatment temperature and time within the above ranges, it is possible to ensure that the modified soft carbon precursor particles B can be evenly coated on the surface of the modified soft carbon particles A and that the material will not be pyrolyzed in large quantities.

[0046] Preferably, in order to ensure that the modified soft carbon precursor particles B can be effectively coated on the surface of the modified soft carbon particles A in liquid state, the coating treatment in step (3) is carried out under stirring, and the stirring frequency is 20-60 Hz, for example, 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz, 50 Hz, 55 Hz or 60 Hz, etc.

[0047] Preferably, the carbonization in step (3) is carried out in a carbonization furnace.

[0048] Preferably, the carbonization in step (3) is carried out under the protection of a protective gas.

[0049] Preferably, the protective gas comprises nitrogen or argon.

[0050] Preferably, the carbonization temperature in step (3) is 600-1000°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, etc. The carbonization temperature is not lower than 600°C to ensure that the first coulombic efficiency of the soft carbon particles for lithium ion battery negative electrode materials is not less than 85%, and the carbonization temperature is not higher than 1000°C to ensure that the fast charging performance 2C / 0.2C of the soft carbon particles for lithium ion battery negative electrode materials is not less than 35%, and the carbonization time is 4-10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc.

[0051] Preferably, the particle size of the soft carbon particles for the lithium ion battery negative electrode material in step (3) is 10-20 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, etc.

[0052] Preferably, the soft carbon particles for lithium-ion battery negative electrode materials in step (3) have a core-shell structure, wherein the core is the modified soft carbon particles A and the shell is the modified soft carbon precursor particles B.

[0053] In a second aspect, the present invention provides soft carbon particles for lithium-ion battery negative electrode materials prepared by the preparation method described in the first aspect.

[0054] Preferably, when the soft carbon particles for lithium-ion battery negative electrode material are applied to the lithium battery negative electrode, the first coulombic efficiency of the lithium battery is 85-89%, such as 85%, 88% or 89%, etc., the charge and discharge reversible capacity is 403-450mAh / g, such as 403mAh / g, 430mAh / g or 450mAh / g, etc., and the 2C / 0.2C fast charging performance is 37%-43%, such as 37%, 38%, 40% or 43%, etc.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) The present invention can continuously and efficiently prepare a uniform carbonization precursor of a soft carbon material;

[0057] (2) The present invention uses modified soft carbon precursor particles B with good fluidity at medium temperature as a surface modifier to coat and modify the modified soft carbon particles A. When the prepared soft carbon particles are used as the negative electrode of a lithium-ion battery, the lithium-ion battery has a high capacity (first charge and discharge reversible capacity: 403-450 mAh / g) and excellent fast charging performance (2C / 0.2C fast charging performance: 37%-43%). DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0059] Example 1

[0060] In this embodiment, a method for preparing soft carbon particles for lithium-ion battery negative electrode materials is provided, the preparation method comprising the following steps:

[0061] (1) The soft carbon raw material and the first modifier were mixed in a homogeneous dispersion barrel at a mass ratio of 100:50 at a mixing frequency of 20 Hz for 60 min to obtain a uniformly dispersed solid mixture A, and then the solid mixture A was blended in a liquid state using a heating and stirring device. After cooling at room temperature, a carbonized precursor was obtained. The carbonized precursor was carbonized in a carbonization furnace in a nitrogen-protected environment at a carbonization temperature of 1300°C and a carbonization time of 10 h. The carbonized product was crushed and sieved using a crushing device to control its particle size to 10 μm, thereby obtaining modified soft carbon particles A;

[0062] (2) The soft carbon raw material and the second modifier were mixed in a homogenizing dispersion barrel at a mass ratio of 100:40 at a mixing frequency of 20 Hz for 60 min to obtain a solid mixture B, and then the solid mixture B was blended in a liquid state using a heating and stirring device, cooled to obtain a block product, and the block product was crushed and sieved using a crushing device to control its particle size to 3 μm to obtain modified soft carbon precursor particles B;

[0063] (3) The modified soft carbon particles A and the modified soft carbon precursor particles B are uniformly mixed in a mass ratio of 100:1, and then the modified soft carbon precursor particles B are coated on the modified soft carbon particles A in a vertical converter. The coating treatment temperature is 200°C, and the coating treatment time is 4 hours. The coating treatment is carried out under stirring, and the stirring frequency is 20 Hz. The treated product is carbonized in a carbonization furnace. The carbonization environment is a nitrogen-protected environment. The carbonization temperature is 600°C and the carbonization time is 10 hours. The carbonized product is crushed and sieved to control its particle size to 10 μm to obtain the soft carbon particles for the negative electrode material of the lithium ion battery.

[0064] Among them, the soft carbon raw material in step (1) is needle coke, the soft carbon raw material in step (2) is petroleum asphalt; the first modifier is polyamide; and the second modifier is sucrose.

[0065] The processing parameters of the heating and stirring device in step (1) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section: 200°C, the second section: 240°C, the third section: 270°C, the fourth section: 280°C, and the fifth section: 260°C; the rotor speed of the heating and stirring device is 300 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 30 rpm.

[0066] The processing parameters of the heating and stirring device in step (2) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section: 150°C, the second section: 200°C, the third section: 230°C, the fourth section: 240°C, and the fifth section: 220°C; the rotor speed of the heating and stirring device is 300 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 30 rpm.

[0067] The heating and stirring device in this embodiment is a twin-screw extruder.

[0068] Example 2

[0069] In this embodiment, a method for preparing soft carbon particles for lithium-ion battery negative electrode materials is provided, the preparation method comprising the following steps:

[0070] (1) The soft carbon raw material and the first modifier were mixed in a homogeneous dispersion barrel at a mass ratio of 100:40 at a mixing frequency of 50 Hz for 10 minutes to obtain a uniformly dispersed solid mixture A, and then the solid mixture A was blended in a liquid state using a heating and stirring device. After cooling at room temperature, a carbonized precursor was obtained. The carbonized precursor was carbonized in a carbonization furnace in a nitrogen-protected environment at a carbonization temperature of 2000°C and a carbonization time of 4 hours. The carbonized product was crushed and sieved using a crushing device to control its particle size to 18 μm, thereby obtaining modified soft carbon particles A;

[0071] (2) The soft carbon raw material, the second modifier and the conductive agent were mixed in a homogenizing dispersion barrel at a mass ratio of 100:60:2 at a mixing frequency of 50 Hz for 10 minutes to obtain a solid mixture B, and then the solid mixture B was blended in a liquid state using a heating and stirring device, cooled to obtain a block product, and the block product was crushed and sieved using a crushing device to control its particle size to 6 μm to obtain modified soft carbon precursor particles B;

[0072] (3) The modified soft carbon particles A and the modified soft carbon precursor particles B are uniformly mixed in a mass ratio of 100:5, and then the modified soft carbon precursor particles B are coated on the modified soft carbon particles A in a vertical converter. The coating treatment temperature is 350°C and the coating treatment time is 3 hours. The coating treatment is carried out under stirring at a frequency of 60 Hz. The treated product is carbonized in a carbonization furnace in a nitrogen-protected environment. The carbonization temperature is 650°C and the carbonization time is 9 hours. The carbonized product is crushed and sieved to control its particle size to 20 μm to obtain the soft carbon particles for the negative electrode material of the lithium ion battery.

[0073] Among them, the soft carbon raw materials in step (1) are all coal tar, and the soft carbon raw materials in step (2) are petroleum asphalt; the first modifier is boric acid; the second modifier is polyethylene; and the conductive agent is carbon nanotubes.

[0074] The processing parameters of the heating and stirring device in step (1) and step (2) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section: 180°C, the second section: 230°C, the third section: 260°C, the fourth section: 270°C, and the fifth section: 250°C; the rotor speed of the heating and stirring device is 600 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 80 rpm.

[0075] The heating and stirring device in this embodiment is a twin-screw extruder.

[0076] Example 3

[0077] In this embodiment, a method for preparing soft carbon particles for lithium-ion battery negative electrode materials is provided, the preparation method comprising the following steps:

[0078] (1) The soft carbon raw material and the first modifier were mixed in a high-speed mixer at a mass ratio of 100:45 at a mixing frequency of 30 Hz for 40 min to obtain a uniformly dispersed solid mixture A, and then the solid mixture A was blended in a liquid state using a heating and stirring device. After cooling at room temperature, a carbonized precursor was obtained. The carbonized precursor was carbonized in a carbonization furnace in a nitrogen-protected environment at a carbonization temperature of 1800°C and a carbonization time of 8 h. The carbonized product was crushed and sieved using a crushing device to control its particle size to 15 μm, thereby obtaining modified soft carbon particles A;

[0079] (2) The soft carbon raw material, the second modifier and the conductive agent were mixed in a high-speed mixer at a mass ratio of 100:100:3 at a mixing frequency of 40 Hz for 20 min to obtain a solid mixture B, and then the solid mixture B was blended in a liquid state using a heating and stirring device, cooled to obtain a block product, and the block product was crushed and sieved using a crushing device to control its particle size to 4 μm to obtain modified soft carbon precursor particles B;

[0080] (3) The modified soft carbon particles A and the modified soft carbon precursor particles B are evenly mixed in a mass ratio of 100:10, and then the modified soft carbon precursor particles B are coated on the modified soft carbon particles A in a vertical converter. The coating temperature is 350°C and the coating time is 3 hours. The coating treatment is carried out under stirring at a frequency of 30 Hz. The treated product is carbonized in a carbonization furnace in a nitrogen-protected environment. The carbonization temperature is 700°C and the carbonization time is 7 hours. The carbonized product is crushed and sieved to control its particle size to 15 μm to obtain the soft carbon particles for the negative electrode material of the lithium ion battery.

[0081] Among them, the soft carbon raw material in step (1) is petroleum asphalt, the soft carbon raw material in step (2) is coal asphalt; the first modifier is ammonium polyphosphate; the second modifier is polystyrene; and the conductive agent is graphene oxide.

[0082] The processing parameters of the heating and stirring device in step (1) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section is 150°C, the second section is 200°C, the third section is 230°C, the fourth section is 240°C, and the fifth section is 220°C; the rotor speed of the heating and stirring device is 400 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 45 rpm.

[0083] The processing parameters of the heating and stirring device in step (2) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section is 180°C, the second section is 230°C, the third section is 260°C, the fourth section is 270°C, and the fifth section is 250°C; the rotor speed of the heating and stirring device is 500 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 60 rpm.

[0084] The heating and stirring device in this embodiment is an open mixing mill.

[0085] Example 4

[0086] In this embodiment, a method for preparing soft carbon particles for lithium-ion battery negative electrode materials is provided, the preparation method comprising the following steps:

[0087] (1) The soft carbon raw material and the first modifier were mixed in a high-speed mixer at a mass ratio of 100:25 at a mixing frequency of 40 Hz for 20 min to obtain a uniformly dispersed solid mixture A, and then the solid mixture A was blended in a liquid state using a heating and stirring device. After cooling at room temperature, a carbonized precursor was obtained. The carbonized precursor was carbonized in a carbonization furnace in an argon-protected environment at a carbonization temperature of 1500°C and a carbonization time of 5 h. The carbonized product was crushed and sieved using a crushing device to control its particle size to 12 μm, thereby obtaining modified soft carbon particles A;

[0088] (2) The soft carbon raw material, the second modifier and the conductive agent were mixed in a high-speed mixer at a mass ratio of 100:10:4 at a mixing frequency of 30 Hz for 40 min to obtain a solid mixture B, and then the solid mixture B was blended in a liquid state using a heating and stirring device, cooled to obtain a block product, and the block product was crushed and sieved using a crushing device to control its particle size to 5 μm to obtain modified soft carbon precursor particles B;

[0089] (3) The modified soft carbon particles A and the modified soft carbon precursor particles B are uniformly mixed in a mass ratio of 100:8, and then the modified soft carbon precursor particles B are coated on the modified soft carbon particles A in a vertical converter. The coating treatment temperature is 300°C and the coating treatment time is 3.5 hours. The coating treatment is carried out under stirring at a frequency of 40 Hz. The treated product is carbonized in a carbonization furnace in an argon-protected environment. The carbonization temperature is 800°C and the carbonization time is 6 hours. The carbonized product is crushed and sieved to control its particle size to 14 μm to obtain the soft carbon particles for the negative electrode material of the lithium ion battery.

[0090] Wherein, the soft carbon raw materials in step (1) and step (2) are both coal tar; the first modifier is phosphoric acid; the second modifier is polypropylene; and the conductive agent is conductive carbon black.

[0091] The processing parameters of the heating and stirring device in step (1) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section is 190°C, the second section is 235°C, the third section is 265°C, the fourth section is 270°C, and the fifth section is 250°C; the rotor speed of the heating and stirring device is 500 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 60 rpm.

[0092] The processing parameters of the heating and stirring device in step (2) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section is 200°C, the second section is 240°C, the third section is 270°C, the fourth section is 280°C, and the fifth section is 260°C; the rotor speed of the heating and stirring device is 400 rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 50 rpm.

[0093] The heating and stirring device in this embodiment is a high-temperature stirring reactor.

[0094] Example 5

[0095] In this embodiment, a method for preparing soft carbon particles for lithium-ion battery negative electrode materials is provided, the preparation method comprising the following steps:

[0096] (1) The soft carbon raw material and the first modifier were mixed in a VC high-efficiency mixer at a mass ratio of 100:10 at a mixing frequency of 25 Hz for 50 min to obtain a uniformly dispersed solid mixture A, and then the solid mixture A was blended in a liquid state using a heating and stirring device. After cooling at room temperature, a carbonized precursor was obtained. The carbonized precursor was carbonized in a carbonization furnace in an argon-protected environment at a carbonization temperature of 1400°C and a carbonization time of 9 h. The carbonized product was crushed and sieved using a crushing device to control its particle size to 16 μm, thereby obtaining modified soft carbon particles A;

[0097] (2) The soft carbon raw material, the second modifier and the conductive agent were mixed in a VC high-efficiency mixer at a mass ratio of 100:60:10 at a mixing frequency of 25 Hz for 50 min to obtain a solid mixture B, and then the solid mixture B was blended in a liquid state using a heating and stirring device, cooled to obtain a block product, and the block product was crushed and sieved using a crushing device to control its particle size to 10 μm to obtain modified soft carbon precursor particles B;

[0098] (3) The modified soft carbon particles A and the modified soft carbon precursor particles B are evenly mixed in a mass ratio of 100:20, and then the modified soft carbon precursor particles B are coated on the modified soft carbon particles A in a vertical converter. The coating treatment temperature is 400°C, and the coating treatment time is 1 hour. The coating treatment is carried out under stirring, and the stirring frequency is 50 Hz. The treated product is carbonized in a carbonization furnace. The carbonization environment is an argon-protected environment. The carbonization temperature is 1000°C and the carbonization time is 4 hours. The carbonized product is crushed and sieved to control its particle size to 20 μm to obtain the soft carbon particles for the negative electrode material of the lithium ion battery.

[0099] The soft carbon raw materials in step (1) and step (2) are both petroleum asphalt; the first modifier is melamine phosphate; the second modifier is phenolic resin; and the conductive agent is graphite oxide.

[0100] The processing parameters of the heating and stirring device in step (1) and step (2) are as follows: the temperature of the entire device is divided into 5 sections, wherein the first section is 160°C, the second section is 210°C, the third section is 240°C, the fourth section is 250°C, and the fifth section is 230°C; the rotor speed of the heating and stirring device is 450rpm; and the auxiliary motor speed of the feeding zone of the heating and stirring device is 50rpm.

[0101] The heating and stirring device in this embodiment is a twin-screw extruder.

[0102] Example 6

[0103] The only difference between this embodiment and embodiment 5 is that the processing parameters of the heating and stirring device in step (1) and step (2) are as follows, and the temperature of the entire device is divided into 5 sections, and the temperature of each section is 250°C.

[0104] Comparative Example 1

[0105] The only difference between this comparative example and Example 2 is that the first modifier is not added in step (1), that is, step (1) includes the following steps: carbonizing the coal tar in a carbonization furnace, the carbonization environment is a nitrogen-protected environment, the carbonization temperature is 2000°C, the carbonization time is 4 hours, and the carbonized product is crushed and sieved using crushing equipment to control its particle size to 18 μm to obtain soft carbon particles A. The other conditions are the same as those in Example 1.

[0106] Comparative Example 2

[0107] The only difference between this comparative example and Example 2 is that the second modifier is not added in step (2), and the other conditions are the same as those in Example 1.

[0108] Comparative Example 3

[0109] The only difference between this comparative example and Example 2 is that the soft carbon raw material petroleum asphalt in step (2) is replaced by an equal amount of hard carbon raw material polyethylene.

[0110] Comparative Example 4

[0111] The only difference between this comparative example and Example 2 is that the particle size of the modified soft carbon precursor particles B obtained in step (2) is 2 μm, and the other conditions are the same as those in Example 1.

[0112] Comparative Example 5

[0113] The only difference between this comparative example and Example 2 is that the particle size of the modified soft carbon precursor particles B obtained in step (2) is 12 μm, and the other conditions are the same as those in Example 1.

[0114] The performance of the soft carbon particles for lithium ion battery negative electrode materials prepared in Examples 1-6 and Comparative Examples 1-5 was tested using the following method:

[0115] (1) Sample preparation: The positive electrode material is lithium sheet; the negative electrode material is soft carbon particles (Examples 1-6), styrene-butadiene rubber, sodium carboxymethyl cellulose, and conductive carbon black prepared in a ratio of 94.5:2.5:1.5:1.5; then after pulping, coating, electrode baking, electrode rolling, electrode punching, electrode weighing, assembly, and activation, a button battery for testing is obtained.

[0116] (2) First charge and discharge reversible capacity test: Use the Arbin blue battery tester to test the first charge and discharge performance of the button battery at a rate of 0.02C.

[0117] (3) First coulombic efficiency: Calculate the ratio of the first discharge capacity to the first charge capacity from the test results in (2).

[0118] (4) 2C / 0.2C fast charging performance: Using the Arbin blue battery tester, after the button battery has been cycled for 2 weeks, its discharge performance at 0.2C and 2C rates is tested, and the ratio of the latter to the former is calculated.

[0119] The performance test results are shown in Table 1.

[0120] Table 1

[0121]

[0122] It can be seen from Table 1 that when the soft carbon particles prepared in Examples 1-5 are used as the negative electrode of lithium-ion batteries, the lithium-ion batteries have excellent first coulombic efficiency (85%-89%), first charge and discharge reversible capacity (403-450 mAh / g) and 2C / 0.2C fast charging performance (37%-43%).

[0123] Compared with Example 5, when the soft carbon particles prepared in Example 6 are used as the negative electrode of a lithium-ion battery, the first charge and discharge reversible capacity and 2C / 0.2C fast charging performance of the lithium-ion battery are slightly reduced.

[0124] Compared with Example 2, when the soft carbon particles prepared in Comparative Example 1 are used for the negative electrode of a lithium ion battery, the first charge and discharge reversible capacity of the lithium ion battery is significantly reduced, which indicates that the addition of the first modifier can increase the capacity of the lithium battery. When the soft carbon particles prepared in Comparative Example 2 are used for the negative electrode of a lithium ion battery, the 2C / 0.2C fast charging performance of the lithium ion battery is significantly reduced, which indicates that the addition of the second modifier can improve the fast charging performance of the lithium battery.

[0125] Compared with Example 2, when the soft carbon particles prepared in Comparative Example 3 are used for the negative electrode of a lithium ion battery, the first coulombic efficiency and the first charge and discharge reversible capacity of the lithium ion battery are slightly reduced, and the 2C / 0.2C fast charging performance is significantly reduced.

[0126] Compared with Example 2, when the soft carbon particles prepared in Comparative Example 4 are used as the negative electrode of a lithium ion battery, the performance of the lithium ion battery does not change much. However, since the particle size of the modified soft carbon precursor particles B is too small, it is very easy to cause the soft carbon particles to agglomerate, which is not conducive to use.

[0127] Compared with Example 2, when the soft carbon particles prepared in Comparative Example 5 are used for the negative electrode of a lithium ion battery, the first charge and discharge reversible capacity and 2C / 0.2C fast charging performance of the lithium ion battery are slightly reduced.

[0128] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the soft carbon particles for lithium-ion battery negative electrode materials and the preparation method thereof, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for various raw materials in the products of the present invention, addition of auxiliary components, selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing soft carbon particles for lithium ion battery negative electrode materials, characterized in that: The preparation method comprises the following steps: (1) mixing a soft carbon raw material and a first modifier to obtain a solid mixture A, then blending the solid mixture A in a liquid state using a heating and stirring device to obtain a carbonization precursor, carbonizing the carbonization precursor, crushing, and screening to obtain modified soft carbon particles A; (2) mixing the soft carbon raw material, the second modifier, and the conductive agent to obtain a solid mixture B, then blending the solid mixture B in a liquid state using a heating and stirring device, cooling to obtain a block product, crushing and screening the block product to obtain modified soft carbon precursor particles B; (3) mixing the modified soft carbon particles A and the modified soft carbon precursor particles B, and then coating the modified soft carbon particles A with the modified soft carbon precursor particles B, followed by carbonization, crushing, and screening to obtain the soft carbon particles for the negative electrode material of the lithium ion battery; The particle size of the modified soft carbon precursor particles B in step (2) is 3-10 μm; The soft carbon raw materials in step (1) and step (2) each independently include any one of petroleum asphalt, coal tar, petroleum coke or needle coke, or a combination of at least two thereof; The first modifier comprises any one or a combination of at least two of melamine, melamine phosphate, polyamide, melamine resin, ammonium phosphate, ammonium polyphosphate, phytic acid, phosphoric acid or boric acid; The second modifier comprises any one or a combination of at least two of polyethylene, polypropylene, polystyrene, polyvinyl pyrrolidone, phenolic resin, polyamide, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer, sucrose, glucosamine, wheat starch, rice starch, potato starch, chitosan, glycine or tryptophan; The temperatures of the heating and stirring devices in step (1) and step (2) are independently divided into five sections, wherein the first section is 150-200°C, the second section is 200-240°C, the third section is 230-270°C, the fourth section is 240-280°C, and the fifth section is 220-260°C.

2. The preparation method according to claim 1, characterized in that The conductive agent includes any one of conductive carbon black, graphene, graphite oxide, carbon nanotubes or whisker carbon nanotubes, or a combination of at least two thereof.

3. The preparation method according to claim 1, characterized in that The mass ratio of the soft carbon raw material to the first modifier in step (1) is 100:(10-50).

4. The preparation method according to claim 1, characterized in that The mass ratio of the soft carbon raw material to the second modifier in step (2) is 100:(10-100).

5. The preparation method according to claim 1, characterized in that The mass ratio of the soft carbon raw material to the conductive agent in step (2) is 100:(0-10).

6. The preparation method according to claim 1, characterized in that The mass ratio of the modified soft carbon particles A to the modified soft carbon precursor particles B in step (3) is 100: (1-20).

7. The preparation method according to claim 1, characterized in that The mixing equipment in step (1) and step (2) independently includes any one of a homogenizing dispersion barrel, a high-speed mixer, a zero-gravity mixer, a V-type mixer or a VC high-efficiency mixer.

8. The preparation method according to claim 1, characterized in that The mixing frequencies in step (1) and step (2) are each independently 20-50 Hz, and the mixing time is each independently 10-60 min.

9. The preparation method according to claim 1, characterized in that The rotor speeds of the heating and stirring devices in step (1) and step (2) are independently 300-600 rpm.

10. The preparation method according to claim 1, characterized in that The speed of the auxiliary motor in the feeding zone of the heating and stirring device in step (1) and step (2) is independently 30-80 rpm.

11. The preparation method according to claim 1, characterized in that The carbonization in step (1) is carried out in a carbonization furnace.

12. The preparation method according to claim 1, characterized in that The carbonization in step (1) is carried out under the protection of protective gas.

13. The preparation method according to claim 12, characterized in that The protective gas includes nitrogen or argon.

14. The preparation method according to claim 1, characterized in that The carbonization temperature in step (1) is 1300-2000°C, and the carbonization time is 4-10 h.

15. The preparation method according to claim 1, characterized in that The particle size of the modified soft carbon particles A in step (1) is 10-18 μm.

16. The preparation method according to claim 1, characterized in that The coating treatment in step (3) is carried out in a vertical converter.

17. The preparation method according to claim 1, characterized in that The coating treatment temperature in step (3) is 200-400°C, and the coating treatment time is 1-4 h.

18. The preparation method according to claim 1, characterized in that The coating treatment in step (3) is carried out under stirring, and the stirring frequency is 20-60 Hz.

19. The preparation method according to claim 1, characterized in that The carbonization in step (3) is carried out in a carbonization furnace.

20. The preparation method according to claim 1, characterized in that The carbonization in step (3) is carried out under the protection of protective gas.

21. The preparation method according to claim 20, characterized in that The protective gas includes nitrogen or argon.

22. The preparation method according to claim 1, characterized in that The carbonization temperature in step (3) is 600-1000°C, and the carbonization time is 4-10 h.

23. The preparation method according to claim 1, characterized in that The particle size of the soft carbon particles used as the negative electrode material for lithium-ion batteries in step (3) is 10-20 μm.

24. Soft carbon particles for lithium ion battery negative electrode material prepared by the preparation method according to any one of claims 1 to 23.

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