A high-rate graphite negative electrode material and its preparation method and use

Abstract

The present invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a high rate graphite negative electrode material and its preparation method and use. The present invention adds a large amount of low carbon residue value organic carbon as a binder and small particle carbon material (D 50 5-8μm) are kneaded, and during the isostatic pressing process, the organic carbon tightly binds the small carbon particles to form a block. After the high-temperature roasting process, the organic carbon is carbonized to form a low-content hard carbon (0.8-2%). The graphite block automatically dissociates, and the hard carbon can bind the small carbon particles into firm secondary particles (D 50 This solves the disadvantage of natural graphite, which is difficult to form secondary particles between particles due to surface inertness, and also solves the defect of artificial graphite granulation, which is that the pitch is converted into graphite carbon through high-temperature graphitization, resulting in limited improvement in rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery negative electrode materials, in particular to a high-rate graphite negative electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, due to their high operating voltage, high energy density, long cycle life, low self-discharge, and lack of memory effect, have become the next generation of secondary batteries since the 1990s, following nickel-metal hydride batteries. The development of lithium-ion battery technology has resulted in continuous improvements in battery quality and reductions in production costs. Anode materials have played a significant role in this advancement.

[0003] Currently, graphite-based materials are still the dominant anode material for commercial lithium-ion batteries. Due to structural limitations, their capacity has reached its upper limit, making significant breakthroughs in the energy density of anode materials difficult to achieve. Against this backdrop, various end markets are placing more urgent demands on battery rate capabilities. Whether in the 3C (computers, communications, and consumer electronics) sector or the EV sector, anode materials with high-rate performance are a common development trend.

[0004] To overcome the drawback of graphite's low charge-discharge rate, graphite modification is often necessary. Chinese patent document CN201410787061.7 discloses the use of asphalt-coated graphite and high-temperature graphitization to prepare a fast-charging graphite lithium-ion battery anode material. The asphalt coated on the graphite surface undergoes high-temperature graphitization to transform it into graphite carbon. While the performance of graphite carbon is similar to that of bulk graphite, its rate performance is limited.

[0005] Natural graphite has the advantages of high specific capacity, low price and abundant resources, and is widely used in the field of digital battery negative electrode materials. However, its poor compatibility with electrolyte, large initial irreversible capacity, poor charge and discharge rate performance, poor cycle performance, and large electrode expansion rate have limited its application in power batteries. Among the methods for improving the electrochemical performance of carbon negative electrode materials, the secondary granulation process is a very effective way. Secondary granulation is a small particle carbon precursor with surface activity (D 50 5-8μm), with the help of adhesive asphalt or other organic matter, high temperature heat treatment is bonded into secondary particles (D 50 The process of producing a graphite-based composite material with a thickness of 14-20 μm can shorten the transmission path of lithium ions, improve rate performance, increase isotropy, and reduce the isotropic expansion of the electrode. Chinese patent document CN201710069655.8 discloses a graphite-based composite material, a preparation method thereof, and a lithium-ion battery containing the composite material, which includes the following steps:

[0006] (1) Activated natural graphite and asphalt are mixed uniformly in proportion, added to a fusion machine and introduced with inert gas, and then granulated at a certain temperature; (2) the granulated product is carbonized or graphitized to obtain a graphite-based composite material. The obtained graphite-based composite material has an initial delithiation capacity of more than 360.1 mAh / g, an initial efficiency of more than 91.5%, and a capacity retention rate of more than 90% after 300 cycles of charge and discharge at a rate of 1C at room temperature for the finished battery. However, the preparation of this material requires oxidation and amination of the natural graphite to functionalize the surface of the natural graphite before secondary granulation can be performed. Such a preparation process is complex and costly. Summary of the Invention

[0007] In order to improve the deficiencies of the prior art, the present invention provides a high-rate graphite negative electrode material for lithium-ion batteries, and a preparation method and use thereof. The negative electrode material is suitable for high-rate battery systems and can be charged faster at a larger current. The method has a simple preparation process, low preparation cost, high product yield, and does not introduce unnecessary impurity components.

[0008] The present invention adopts the following technical solutions:

[0009] A method for preparing a high-rate graphite negative electrode material, the method comprising the following steps:

[0010] (1) kneading the carbon material and the organic carbon to obtain a kneaded material;

[0011] (2) pressing the mixed material obtained in step (1) to obtain a block;

[0012] (3) calcining the block obtained in step (2) to obtain the high-rate graphite negative electrode material, wherein the mass percentage of hard carbon in the high-rate graphite negative electrode material is 0.8-2%.

[0013] According to an embodiment of the present invention, in step (1), the carbon material is at least one of natural graphite, needle coke, petroleum coke and pitch coke. The average particle size D of the carbon material is 50 The particle size of the natural graphite is 5 μm to 8 μm, for example, 5 μm, 6 μm, 7 μm or 8 μm. The particle shape of the natural graphite is spherical, approximately spherical, oval or potato-shaped.

[0014] According to an embodiment of the present invention, in step (1), the organic carbon is at least one of petroleum resin (such as petroleum resin C5 and / or petroleum resin C9), phenolic resin, epoxy resin, starch, glucose and cellulose.

[0015] According to an embodiment of the present invention, in step (1), the residual carbon value of the organic carbon is 3-15%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0016] According to an embodiment of the present invention, in step (1), the mass ratio of the organic carbon to the carbon material is (10-20):100, for example, 10:100, 11:100, 12:100, 13:100, 14:100, 15:100, 16:100, 17:100, 18:100, 19:100 or 20:100.

[0017] According to an embodiment of the present invention, in step (1), the kneading includes, for example: placing organic carbon and carbon material in a kneader, controlling the temperature at 60-100° C., rotating at 50-500 r / min, and processing for 1-300 min to obtain a kneaded material.

[0018] According to an embodiment of the present invention, in step (1), the kneading is performed in an air atmosphere. During the kneading process, the organic carbon will be coated on the surface of the carbon material to achieve coating of the carbon material.

[0019] According to an embodiment of the present invention, in step (1), the kneading is carried out in a kneader, and the kneader is selected from at least one of a high-speed modified VC kneader, a cone kneader and a kneader.

[0020] According to an embodiment of the present invention, in step (2), the molding is performed by cold isostatic pressing, wherein the pressure of the cold isostatic pressing is 3 MPa-10 MPa, the holding time is 3-10 minutes, and the temperature is room temperature. The molding is mainly performed to press the carbon material powder coated with organic carbon into a block.

[0021] According to an embodiment of the present invention, in step (3), by selecting organic carbon with a suitable residual carbon value and further adjusting the mass ratio of organic carbon to carbon material, a high-rate graphite negative electrode material with a hard carbon mass percentage of 0.8-2% can be obtained. More importantly, in the process of obtaining the high-rate graphite negative electrode material, no processing process such as crushing is required. The block obtained after pressing will automatically dissociate into a suitable size (D 50 The study found that when the mass percentage of hard carbon in the obtained high-rate graphite negative electrode material is more than 2%, the block after calcination cannot achieve automatic dissociation due to the high amount of residual carbon. If you want to obtain a suitable size (D 50The negative electrode material with a hard carbon content of 14-20 μm still needs to be pulverized, and impurity iron will be introduced at this time. In addition, the pulverization process will lead to problems such as excessive pulverization and peeling of the hard carbon layer, resulting in a low yield of the obtained negative electrode material and reduced initial efficiency and cycle performance of the product. When the mass percentage of hard carbon in the obtained high-rate graphite negative electrode material is less than 0.8%, due to the low amount of residual carbon, the block after calcination cannot achieve bonding and will automatically dissociate into the original carbon material particle size (D 50 The negative electrode material with a thickness of 5-8μm cannot be used at high rates.

[0022] According to an embodiment of the present invention, in step (3), the calcination temperature is 900-1100°C, exemplified by 900°C, 950°C, 1000°C, 1050°C or 1100°C. The calcination time is 4-24 hours, for example, 2-12 hours, exemplified by 4 hours or 6 hours. The calcination is carried out in an air atmosphere. The heating rate of the calcination is 15-30°C / min, exemplified by 20°C / min or 25°C / min. Further, after the calcination treatment is completed, the obtained product is allowed to cool naturally.

[0023] According to an embodiment of the present invention, in step (3), the D of the high-rate graphite negative electrode material 50 14-20 μm, for example, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0024] According to an embodiment of the present invention, in step (3), when the carbon material is needle coke, petroleum coke, or pitch coke, after calcination, a graphitization treatment is required, and the graphitization treatment temperature is 2800-3200°C, exemplarily 2800°C, 2900°C, and 3000°C. Furthermore, the graphitization treatment time is 12-24 hours, exemplarily 18 hours or 20 hours.

[0025] The present invention also provides a negative electrode material prepared by the above method.

[0026] According to an embodiment of the present invention, the negative electrode material is a high-rate graphite negative electrode material.

[0027] According to an embodiment of the present invention, the negative electrode material has a secondary particle structure, that is, hard carbon is a small particle carbon material (D 50 5-8μm) bonded into large particles (D 50 The graphite negative electrode material has a thickness of 14-20 μm, wherein the mass percentage of hard carbon is 0.8-2%.

[0028] According to an embodiment of the present invention, the charging capacity of the negative electrode material is ≥358 mAh / g, such as 358 mAh / g to 363 mAh / g, and the initial charge and discharge efficiency is ≥90%.

[0029] According to an embodiment of the present invention, when the negative electrode material is natural graphite (the carbon material is natural graphite), the capacity retention rate after 1000 cycles of 2C charge and discharge at room temperature is above 90%; when the negative electrode material is artificial graphite (the carbon material is at least one of needle coke, petroleum coke and asphalt coke), the capacity retention rate after 1000 cycles of 5C charge and discharge at room temperature is above 80%.

[0030] The present invention also provides a use of the negative electrode material, which is used in lithium-ion batteries.

[0031] The beneficial effects of the present invention are:

[0032] The present invention adds a large amount of organic carbon with low residual carbon value as a binder and small particle carbon material (D 50 5-8μm) are kneaded, and during the isostatic pressing process, the organic carbon tightly binds the small carbon particles to form a block. After the high-temperature roasting process, the organic carbon is carbonized to form a low-content hard carbon (0.8-2%). The graphite block automatically dissociates, and the hard carbon can bind the small carbon particles into firm secondary particles (D 50 14-20μm). On the one hand, it solves the disadvantage of natural graphite that it is difficult to form secondary particles between particles due to surface inertness. On the other hand, it solves the defect that the asphalt is converted into graphite through high-temperature graphitization during the granulation of artificial graphite, resulting in limited improvement in rate performance. The natural graphite and artificial graphite negative electrode materials prepared by the method of the present invention have maximum charge and discharge rates of 4C and 10C respectively, with long cycle life and stable product properties. Not only that, the present invention can ensure that the pressed block automatically dissociates into negative electrode materials of suitable particle size after roasting treatment by adjusting the content of hard carbon in the negative electrode material. In this process, there is no need to crush and pulverize the material, which can ensure the yield of the product without generating tailings and avoid the introduction of iron elements due to pulverization, thereby significantly improving the performance of the negative electrode material. DETAILED DESCRIPTION

[0033] The preparation method of the present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection intended by the present invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0035] Example 1

[0036] Spherical natural graphite (D 50 5μm) and petroleum resin C5 (residual carbon value is 15%) are added to the kneader in a mass ratio of 100:10, the speed is adjusted to 120r / min, and after mixing at 100°C for 1.5 hours, the mixture is cooled to obtain the mixture; the mixture is cold isostatically pressed at room temperature (3MPa, holding pressure for 10min) to obtain a block. The block is placed in a crucible, and the crucible is placed in a roasting furnace (air atmosphere), and the temperature is rapidly increased to 1100°C at a heating rate of 25°C / min. The temperature is kept for 2 hours, and the product is cooled naturally to obtain a natural graphite negative electrode material. The mass content of hard carbon is 1.5%.

[0037] Example 2

[0038] Spherical natural graphite (D 50 7μm) and phenolic resin (residual carbon value is 12%) are added into a kneader in a mass ratio of 100:15, the speed is adjusted to 240r / min, and after mixing at 100°C for 3 hours, the mixture is cooled to obtain a mixture; the mixture is cold isostatically pressed at room temperature (8MPa, holding pressure for 4min) to obtain a block. The block is placed in a crucible, and the crucible is placed in a roasting furnace (air atmosphere), and the temperature is rapidly increased to 1000°C at a heating rate of 20°C / min, kept warm for 3 hours, and the product is cooled naturally to obtain a natural graphite negative electrode material. The mass content of hard carbon is 1.8%.

[0039] Example 3

[0040] The needle coke (D 50 8μm) and phenolic resin (residual carbon value is 8%) are added to the kneader in a mass ratio of 100:15, the speed is adjusted to 200r / min, and after mixing at 100°C for 3 hours, the mixture is cooled to obtain the mixture; the mixture is cold isostatically pressed at room temperature (6MPa, holding pressure for 6min) to obtain a block. The block is placed in a crucible, and the crucible is placed in a roasting furnace (air atmosphere), and the temperature is quickly raised to 1000°C at a heating rate of 20°C / min, kept warm for 3 hours, and the product is cooled naturally. Then it is placed in a graphitization furnace and heated to 2800°C, kept warm for 14 hours, and the product is cooled naturally to obtain an artificial graphite negative electrode material. The mass content of hard carbon is 1.2%.

[0041] Example 4

[0042] Petroleum coke (D 505μm) and starch (residual carbon value is 5%) are added to the kneader in a mass ratio of 100:20, the speed is adjusted to 200r / min, and after mixing at 100°C for 3 hours, the mixture is cooled to obtain the mixture; the mixture is cold isostatically pressed at room temperature (6MPa, holding pressure for 6min) to obtain a block. The block is placed in a crucible, and the crucible is placed in a roasting furnace, and the temperature is quickly raised to 900°C at a heating rate of 20°C / min, kept warm for 3 hours, and the product is cooled naturally. Then it is placed in a graphitization furnace and heated to 3000°C, kept warm for 18 hours, and the product is cooled naturally to obtain an artificial graphite negative electrode material. The mass content of hard carbon is 1.0%.

[0043] Comparative Example 1

[0044] Spherical natural graphite (D 50 5μm) and petroleum resin C5 (residual carbon value is 5%) are added to a kneader in a mass ratio of 100:10, the speed is adjusted to 120r / min, and after mixing at 100°C for 1.5 hours, the mixture is cooled to obtain a kneaded material; the kneaded material is cold isostatically pressed at room temperature (3MPa, holding pressure for 10min) to obtain a block. The block is placed in a crucible, and the crucible is placed in a roasting furnace, and the temperature is rapidly increased to 1200°C at a heating rate of 25°C / min, and kept warm for 2 hours to obtain a natural graphite negative electrode material. The mass content of hard carbon is 0.5%.

[0045] Comparative Example 2

[0046] Spherical natural graphite (D 50 5μm) and petroleum resin C5 (residual carbon value is 15%) are added to a kneader in a mass ratio of 100:40, the speed is adjusted to 120r / min, and after mixing at 100°C for 1.5 hours, the mixture is cooled to obtain a mixture; the mixture is cold isostatically pressed at room temperature (3MPa, holding pressure for 10min) to obtain a block. The block is placed in a crucible, and the crucible is placed in a roasting furnace, and the temperature is quickly raised to 1200°C at a heating rate of 25°C / min, and kept warm for 2 hours to obtain a natural graphite negative electrode material block, which is then crushed and sieved to obtain a natural graphite negative electrode material. The mass content of hard carbon is 6.0%.

[0047] The physical and chemical indicators of Examples 1-4 and Comparative Examples 1-2 were tested as follows:

[0048] Electrochemical performance test

[0049] Semi-electric test method: The graphite anode materials prepared in Examples 1-4 and Comparative Examples 1-2 were mixed uniformly with conductive carbon black (SP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) in a mass ratio of 95:1:1.5:2.5, coated onto copper foil, and dried in a 120°C vacuum drying oven for 12 hours. Simulated battery assembly was performed in an argon-protected Braun glove box. The electrolyte consisted of 1M LiPF6 + EC:DEC:DMC (1:1:1 by volume), with a lithium metal sheet as the counter electrode. Simulated battery testing was performed in a 5V, 10mA Xinwei battery test cabinet with a charge and discharge voltage of 0.01-1.5V and a charge and discharge rate of 0.2C. The initial discharge capacity and initial charge and discharge efficiency obtained are listed in Table 1.

[0050] Full battery test method: A full battery was assembled using the materials prepared in Examples 1-4 and Comparative Examples 1-2 as the negative electrode, lithium cobalt oxide as the positive electrode, and 1M-LiPF6+EC:DEC:DMC (volume ratio 1:1:1) solution as the electrolyte. The battery was charged and discharged at room temperature at rates of 2C and 5C, with a voltage range of 3.0-4.2V. The cycle performance obtained from the test is listed in Table 1.

[0051] Maximum charge rate test method: Charge the battery cell to 100% SOC at different rates, disassemble the battery cell, and observe the lithium deposition on the negative electrode.

[0052] Table 1 Test results of physical and chemical properties and electrochemical properties of graphite anode materials

[0053]

[0054] “-” means not tested.

[0055] As can be seen from Table 1, the graphite negative electrode material prepared by the present invention has better rate performance and cycle performance. The present invention has a simple preparation process, low cost, and high practicality. It is suitable for lithium-ion batteries for mobile electronic devices such as mobile phones and digital cameras, and power lithium-ion batteries for electric vehicles, thereby significantly reducing costs.

[0056] From Comparative Example 2, when the mass content of hard carbon-free material is higher than 2.0%, the prepared graphite negative electrode material must be crushed before it can become a negative electrode material with suitable particle size. During the crushing process, on the one hand, excessive Fe will be introduced into the negative electrode material, which cannot meet the use requirements of lithium-ion batteries; on the other hand, it will also cause the hard carbon layer on the surface of the graphite negative electrode material to peel off, reducing its initial efficiency and cycle performance.

[0057] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-rate graphite negative electrode material, the method comprising the following steps: (1) kneading the carbon material and the organic carbon to obtain a kneaded material; (2) Pressing the mixed material obtained in step (1) to obtain a block; (3) calcining the block obtained in step (2) to obtain the high-rate graphite negative electrode material; In step (1), the kneading comprises: placing the organic carbon and the carbon material in a kneader, controlling the temperature at 60-100° C., rotating at 50-500 r / min, and processing for 1-300 min to obtain a kneaded material; In step (1), the residual carbon value of the organic carbon is 3-15%; In step (1), the mass ratio of the organic carbon to the carbon material is (10-20):100; In step (1), the organic carbon is at least one of phenolic resin, epoxy resin, starch, glucose and cellulose; In step (2), the molding is performed by cold isostatic pressing, the pressure of the cold isostatic pressing is 3MPa-10MPa, the holding time is 3-10min, and the temperature is room temperature; The negative electrode material has a secondary particle structure, that is, hard carbon D 50 Carbon materials with a thickness of 5-8 μm are bonded into D 50 The graphite negative electrode material is 14-20 μm, wherein the mass percentage of hard carbon is 0.8-2%.

2. The preparation method according to claim 1, wherein In step (1), the carbon material is at least one of natural graphite, needle coke, petroleum coke and pitch coke.

3. The preparation method according to claim 1, wherein In step (3), the calcination temperature is 900-1100°C; the calcination time is 4-24 hours; The calcination is carried out in an air atmosphere; the heating rate of the calcination is 15-30°C / min.

4. The preparation method according to any one of claims 1 to 3, wherein In step (3), when the carbon material is needle coke, petroleum coke or pitch coke, after roasting, graphitization treatment is required, and the temperature of the graphitization treatment is 2800~3200℃; the time of the graphitization treatment is 12-24 hours.

5. A negative electrode material prepared by the method according to any one of claims 1 to 4.

6. The negative electrode material according to claim 5, wherein The negative electrode material has a secondary particle structure, that is, hard carbon D 50 Carbon materials with a thickness of 5-8 μm are bonded into D 50 The graphite negative electrode material is 14-20 μm, wherein the mass percentage of hard carbon is 0.8-2%.

7. Use of the negative electrode material according to claim 5 or 6 in a lithium ion battery.

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