Negative electrode material and preparation method and application thereof

Abstract

The invention discloses a negative electrode material and a preparation method and application thereof. The preparation method of the negative electrode material comprises the following steps: carbonizing a mixture containing graphite and a coating agent, wherein the coating agent comprises a molecular sieve and liquid phase pitch; the mass ratio of the molecular sieve to the liquid phase pitch is 5-25%; the mass ratio of the coating agent to the graphite is 1%-15%. The negative electrode material comprises a graphite matrix and a composite coating layer coating the surface of the graphite matrix, the composite coating layer comprises amorphous carbon and a molecular sieve skeleton, and the composite coating layer contains pores; wherein the mass ratio of the composite coating layer to the graphite matrix is 1%-15%. The preparation method can optimize the pore size and other parameters of the obtained negative electrode material and the comprehensive performance of the obtained battery, and also has the advantages of low cost, simple process, easy large-scale production and the like.

Description

Technical Field

[0001] This invention relates to a negative electrode material, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of electric vehicles and energy storage technologies, lithium-ion batteries, as a core energy carrier, have faced increasingly higher performance requirements. Users have placed higher demands on battery fast-charging capabilities, cycle life, and cost control. However, traditional graphite anode materials suffer from significant technical bottlenecks in high-rate charge-discharge and long-term cycling processes, making it difficult to meet the growing application demands.

[0003] In fast-charging scenarios, graphite anode materials face limitations imposed by lithium-ion transport kinetics. Due to the slow diffusion rate of lithium ions between graphite layers, high-rate charging can easily lead to increased electrode polarization, insufficient capacity utilization, and even lithium dendrite growth, posing safety hazards. Furthermore, during long-term cycling, the solid electrolyte interphase (SEI) film formed on the graphite surface exhibits poor stability, easily cracking and remodeling, resulting in continuous electrolyte decomposition, ongoing loss of active lithium, and ultimately, battery capacity decay and shortened cycle life. Currently, research on the modification of graphite anodes mainly focuses on surface modification and structural optimization. For example, carbon coating can improve the conductivity of the material and optimize the lithium-ion transport path, thereby improving fast-charging performance, but its stabilizing effect on the SEI film is limited, making it difficult to significantly improve long-cycle performance. On the other hand, while elemental doping can enhance the structural stability of the material, its preparation process is complex, costly, and technically challenging, limiting its large-scale application.

[0004] Therefore, there is an urgent need to develop a graphite anode modification method that can simultaneously improve fast charging performance, cycle stability, and cost-effectiveness. Summary of the Invention

[0005] To overcome the technical shortcomings of existing graphite anode materials and their modification methods, such as poor fast-charging performance, cycle performance, and safety performance, this invention provides an anode material, its preparation method, and its applications. This preparation method is based on a double coating of molecular sieves and liquid-phase pitch, forming a high-density composite coating layer. This optimizes parameters such as pore size and volume of the resulting anode material, as well as the overall performance of the resulting battery, including fast-charging performance, rate performance, and cycle stability. Furthermore, this preparation method offers advantages such as low cost, simple process, and ease of large-scale production, demonstrating significant economic benefits and market application potential.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] This invention provides a method for preparing a negative electrode material, the method comprising the following steps: obtaining the material by carbonization treatment of a mixture containing graphite and a coating agent; wherein,

[0008] The coating agent includes molecular sieves and liquid-phase asphalt;

[0009] The mass ratio of the molecular sieve to the liquid phase asphalt is 5%-25%;

[0010] The mass ratio of the coating agent to the graphite is 1%-15%.

[0011] In this invention, after carbonization treatment with the above mixture, molecular sieves and liquid-phase pitch can simultaneously liquid-phase coat graphite. This method can construct a highly dense and uniform functional layer (composite coating layer) on the graphite surface. The molecular sieve retains its porous structure after carbonization, presenting an overall porous molecular sieve framework, while the liquid-phase pitch forms corresponding amorphous carbon, ultimately forming a composite coating layer with a porous structure. The graphite itself undergoes almost no change in its physicochemical properties. Furthermore, research has found that this composite coating layer can optimize the lithium-ion transport path of the negative electrode material. When applied to batteries, it can effectively improve the lithium-ion diffusion rate, thereby improving fast-charging performance. Simultaneously, this composite coating layer can also effectively improve the conductivity, rate performance, and cycle stability of the resulting negative electrode material and the resulting battery.

[0012] In some embodiments, the mass ratio of the coating agent to the graphite is 3%-15%, for example 3.625%, 4.25% or 14.5%.

[0013] In some embodiments, the mass ratio of the molecular sieve to the liquid phase pitch is 5%-16%, preferably 5%-15%, for example 8%.

[0014] In this invention, the type of molecular sieve can be conventional in the art; preferably, the molecular sieve includes one or more of 3A molecular sieve, 4A molecular sieve and 5A molecular sieve.

[0015] In this invention, the type of liquid phase asphalt can be conventional in the art.

[0016] Specifically, the liquid phase asphalt includes, for example, oil asphalt and / or coal tar pitch.

[0017] Specifically, the liquid-phase asphalt includes, for example, modified asphalt and / or solvent-based asphalt. Modified asphalt refers to asphalt material obtained by modifying asphalt with fillers such as rubber, resin, and polymers; solvent-based asphalt refers to asphalt material obtained by dissolving asphalt in an organic solvent.

[0018] In some embodiments, the coking value of the liquid phase bitumen is 10%-30%, for example, 15%.

[0019] In some embodiments, the density of the liquid phase asphalt is 0.5-1.5 g / cm³. 2 .

[0020] In some embodiments, the sulfur content of the liquid phase asphalt is not higher than 0.15 wt%, for example 0.5 wt%.

[0021] In some embodiments, the ash content of the liquid phase bitumen is less than 0.03 wt%.

[0022] In some embodiments, the volatile content of the liquid phase asphalt is 85wt%-95wt%, for example 90wt%.

[0023] In this invention, the graphite may be conventional in the art, such as natural graphite and / or artificial graphite.

[0024] In some embodiments, the graphite has a particle size Dv50 of 10-11 μm, for example 10.23 μm.

[0025] In this invention, the carbonization process may include a heating step beforehand; that is, the carbonization process begins when the temperature reaches a holding temperature. The carbonization temperature refers to the holding temperature. Those skilled in the art will understand its specific meaning.

[0026] In some embodiments, the heating rate before carbonization is 2-3 °C / min, for example 2.5 °C / min.

[0027] In some embodiments, the carbonization process is carried out at a temperature of 1000-1200°C, for example, 1150°C.

[0028] In some implementations, the carbonization process takes 4-8 hours, for example, 6 hours.

[0029] In some implementations, the carbonization process further includes a cooling and sieving step.

[0030] Preferably, the mesh size of the sieve is 200-400 mesh, for example, 300 mesh.

[0031] In some embodiments, the preparation of the mixture includes the following steps: first mixing the molecular sieve and liquid pitch once, then mixing it with the graphite a second time, and then fusing them.

[0032] The terms "primary mixing" and "secondary mixing" are used only to distinguish different steps. Each of these processes can be a conventional mixing operation in the art, requiring only that the materials be mixed uniformly (without producing entirely new substances). Those skilled in the art will understand their specific meaning.

[0033] In the fusion step, the mixture is fused under the action of external mechanical force to form a completely new substance; it is not simply a matter of mixing. Those skilled in the art will understand its specific meaning.

[0034] The fusion is performed, for example, in a fusion machine.

[0035] The fusion rotation speed is preferably 800-1100 rpm, for example 900 rpm.

[0036] The fusion time is preferably 3-8 minutes.

[0037] The present invention also provides a negative electrode material, the negative electrode material comprising a graphite matrix and a composite coating layer covering the surface of the graphite matrix, the composite coating layer comprising amorphous carbon and a molecular sieve framework, and the composite coating layer containing pores; wherein,

[0038] The mass ratio of the composite coating layer to the graphite matrix is ​​1%-15%.

[0039] In some embodiments, the mass ratio of the composite coating to the graphite matrix is ​​3%-15%, for example 3.625%, 4.25% or 14.5%.

[0040] In some implementations, the thickness of the composite coating layer is 0.7-2 μm.

[0041] In some embodiments, the particle size Dv10 of the negative electrode material is 6-8 μm, for example 6.48 μm, 6.95 μm, 6.97 μm, 6.98 μm or 7.21 μm.

[0042] In some embodiments, the particle size Dv50 of the negative electrode material is 10-13 μm, for example 10.98 μm, 11.34 μm, 11.48 μm, 11.76 μm or 12.21 μm.

[0043] In some embodiments, the particle size Dv90 of the negative electrode material is 18-20 μm, for example 18.07 μm, 18.34 μm, 18.57 μm, 18.76 μm or 19.68 μm.

[0044] In some embodiments, the specific surface area of ​​the negative electrode material is 1.0-1.5 m². 2 / g, for example 1.02m 2 / g, 1.05m 2 / g, 1.06m 2 / g or 1.08m 2 / g.

[0045] In some embodiments, the total pore volume of the negative electrode material is 0.0050-0.0055 cm³. 3 / g, for example 0.0049cm 3 / g, 0.0050cm 3 / g or 0.0052cm 3 / g.

[0046] In some embodiments, the particle strength of the negative electrode material is 0.920-0.950, for example 0.921, 0.923, 0.924 or 0.926.

[0047] The present invention also provides a negative electrode material, which is prepared by the method described above.

[0048] In some implementations, the negative electrode material is as defined above.

[0049] The present invention also provides an application of the aforementioned negative electrode material in lithium-ion batteries.

[0050] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0051] The reagents and raw materials used in this invention are all commercially available.

[0052] The positive and progressive effects of this invention are as follows:

[0053] The preparation method of this invention is based on the dual coating of molecular sieve and liquid pitch, forming a high-density composite coating layer on the graphite surface, thereby optimizing the lithium-ion transport path of the resulting negative electrode material. When used in a battery, it can effectively improve the lithium-ion diffusion rate and reduce the desolvation energy barrier; and effectively alleviate the dendrite deposition problem during fast charging, thus significantly enhancing the fast charging performance, cycle life and safety of lithium-ion batteries; and the entire method can effectively improve the adhesion performance of the composite coating layer and reduce the risk of peeling.

[0054] In addition, this preparation method has the advantages of low cost, simple process, and easy large-scale production, and has significant economic benefits and market application potential. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the structure of the negative electrode material obtained in Example 1 of the present invention.

[0056] The attached figures are labeled as follows:

[0057] 1-Graphite matrix, 2-Composite coating layer, 3-Porous structure.

[0058] Figure 2 This is a SEM image (magnification of 1000×) of the negative electrode material obtained in Example 1 of the present invention.

[0059] Figure 3 This is a SEM image (magnification of 500×) of the negative electrode material obtained in Example 1 of the present invention.

[0060] Figure 4 The image shows the EIS impedance diagram obtained from testing lithium-ion batteries assembled using the negative electrode materials obtained in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0061] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0062] Unless otherwise specified, the information on the raw materials used in the following examples and comparative examples is as follows:

[0063] (1) Molecular sieve: Specifically, 3A molecular sieve, purchased from Anhui Juteng New Material Technology Co., Ltd.;

[0064] (2) Liquid phase asphalt: specifically modified asphalt with a coking value of 15%, a volatile matter content of 90%, a sulfur content of 0.5%, and a density of 0.5-1.5 g / cm³. 2 Ash content less than 0.03 wt%;

[0065] (3) Graphite: specifically artificial graphite.

[0066] Example 1

[0067] The negative electrode material of this embodiment was prepared by the following steps:

[0068] (1) Mix and stir 3A molecular sieve and liquid phase asphalt at a mass feeding ratio of 16% to obtain material 1;

[0069] (2) Mix material 1 from step (1) with graphite at a mass feeding ratio of 7.25% to obtain material 2, wherein the particle size of graphite is Dv50=10.23μm;

[0070] (3) Put the material 2 from step (2) into the fusion machine for fusion, set the process parameters as 900 rpm and 8 min, and discharge the material 3;

[0071] (4) The material 3 in step (3) is put into the track kiln and heated to 1150°C at a heating rate of 2.5°C / min. The temperature is kept constant for 6 hours to carry out carbonization treatment. The material is then cooled and discharged to obtain the precursor.

[0072] (5) The precursor in step (4) is mixed (without adding other substances, only further mixed by itself), and then sieved through a 300-mesh sieve to obtain the negative electrode material of Example 1.

[0073] A schematic diagram of the structure of the negative electrode material is shown below. Figure 1 As shown, it specifically includes a graphite matrix 1 and a composite coating layer 2, wherein the composite coating layer 2 forms a corresponding pore structure 3 due to the presence of a molecular sieve framework; and the mass ratio of the composite coating layer to the graphite matrix is ​​7.25% (the theoretical value calculated based on the amount of raw materials fed).

[0074] Example 2

[0075] The only difference between this embodiment and Embodiment 1 is that:

[0076] In step (1), the mass ratio of 3A molecular sieve to liquid phase asphalt is 8wt%, and the other conditions are the same as in Example 1.

[0077] Example 3

[0078] The only difference between this embodiment and Embodiment 1 is that:

[0079] In step (1), the mass ratio of 3A molecular sieve to liquid phase asphalt is 24wt%, and the other conditions are the same as in Example 1.

[0080] Example 4

[0081] The only difference between this embodiment and Embodiment 1 is that:

[0082] In step (2), the mass ratio of material 1 to graphite aggregate is 3.625 wt%, and the other conditions are the same as in Example 1.

[0083] Example 5

[0084] The only difference between this embodiment and Embodiment 1 is that:

[0085] In step (2), the mass ratio of material 1 to graphite aggregate is 14.5wt%, and the other conditions are the same as in Example 1.

[0086] Comparative Example 1

[0087] The only difference between this comparative example and Example 1 is that:

[0088] Instead of using 3A molecular sieve, in step (2), liquid phase asphalt and graphite are directly mixed at a mass feeding ratio of 7.25wt%, and the remaining conditions are the same as in Example 1.

[0089] Effect Example

[0090] The negative electrode materials of Examples 1-5 and Comparative Example 1 were tested using the following methods:

[0091] 1. Microscopic morphological characterization:

[0092] The microstructure of the negative electrode material obtained in Example 1 was determined by SEM electron microscopy, and the results are as follows: Figure 2 and Figure 3 As shown in the figure, the graphite matrix surface is uniformly coated with amorphous carbon.

[0093] 2. Characterization of particle sizes Dv10, Dv50, and Dv90:

[0094] The test was conducted using a Malvern MS3000 laser particle size analyzer, and the test results are shown in Table 1.

[0095] 3. Characterization of specific surface area and total pore volume:

[0096] The tests were conducted using the NOVAtouch™ fully automated specific surface area and pore size analyzer from CANTA Instruments, USA. The test results are shown in Table 1.

[0097] 4. Particle strength characterization:

[0098] The ratio of the D50 particle size of the sample under 2T powder pressing to the Dv50 particle size before powder pressing is obtained. The test results are shown in Table 1.

[0099] 5. Electrochemical performance related tests:

[0100] Lithium-ion batteries were fabricated using the negative electrode materials of Examples 1-5 and Comparative Example 1, respectively, according to the following procedures, and electrochemical performance tests were performed:

[0101] (1) Preparation of negative electrode and lithium-ion battery:

[0102] The negative electrode materials obtained in Examples 1-5 and Comparative Example 1, the binder (CMC and SBR, mass ratio of 1.5:1.5) and the conductive agent SP were mixed in a mass ratio of 95.5:3:1.5 (total 100g), and then 130g of deionized water was added and mixed to obtain a negative electrode slurry. This slurry was coated on copper foil and then vacuum dried and rolled to prepare a negative electrode sheet.

[0103] Electrolyte formulation: The concentration of LiPF6 is 1 mol / L, and the mixed solvent is prepared in a volume ratio of ethyl carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1.

[0104] A button cell battery was assembled using a polypropylene microporous membrane as the separator and a lithium metal sheet as the positive electrode in an inert gas glove box system filled with argon.

[0105] (2) Electrochemical performance related tests:

[0106] The charge and discharge tests of the button cells were conducted on the LAND battery testing system of Wuhan Landian Electronics Co., Ltd. Specifically, under normal temperature conditions, constant current charge and discharge were performed at 0.1C, and the charge and discharge voltage was limited to 0.005-2V.

[0107] The specific test parameters and corresponding methods are as follows:

[0108] ①EIS test: The prepared battery was first discharged at a rate of 0.2C to 0.005V, then discharged at a constant voltage of 0.005V until the current was ≥0.05mA, and then charged at a rate of 2C for 15min. After activation, EIS test was performed on an electrochemical workstation (EC-lab).

[0109] ② Charge specific capacity: The prepared battery is first discharged at a rate of 0.2C to 0.005V, and then charged at a rate of 0.1C to 2V to obtain the charge specific capacity.

[0110] ③ Initial Coulomb efficiency (%): First discharge capacity / charge specific capacity × 100.

[0111] ④ Rate Performance: The prepared battery was first discharged at a rate of 0.2C to 0.005V, then charged at a rate of 0.2C to 2V. Subsequently, it was discharged at 0.5C and charged at 0.2C, discharged at 1C and charged at 0.2C, discharged at 2C and charged at 0.2C, and discharged at 3C and charged at 0.2C. The discharge capacity was tested, and the capacity retention rate at 3C was calculated. The capacity retention rate at 3C (%) = 3C discharge capacity / 0.2C discharge capacity × 100.

[0112] The test results obtained are as follows Figure 4 As shown in Table 2.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] As shown in Table 1, the particle size Dv50 of the negative electrode materials obtained in Examples 1-5 of this invention is between 10.98 and 12.21 μm, while the graphite particle size Dv50 is 10.23 μm; indicating that the thickness of the composite coating layer is between 0.7 and 2 μm. Furthermore, the negative electrode materials obtained in Examples 1-5 also simultaneously satisfy the following requirements: particle size Dv10 between 6.48 and 7.21 μm, particle size Dv90 between 18.07 and 19.68 μm, and specific surface area between 1.02 and 1.08 m². 2 The total pore volume is between 0.0049 and 0.0055 cm³ / g. 3 The particle strength is between 0.921 and 0.926, with a value between 0.921 and 0.926.

[0118] From Table 2 and Figure 4 As can be seen, the negative electrode materials obtained in Examples 1-5 of this invention, when used in lithium-ion batteries, exhibit significantly lower impedance and can simultaneously achieve excellent capacity performance, initial coulombic efficiency, and fast-charging performance. Specifically, the resulting lithium-ion batteries can achieve an EIS of less than 5.9Ω, a charge specific capacity of more than 359mAh / g, an initial coulombic efficiency of more than 92.0%, and a capacity retention rate of more than 5.7% at 3C.

[0119] Compared to Example 1, Comparative Example 1, without the use of molecular sieves, resulted in a significant reduction in the total pore volume of the anode material. Even though its specific surface area, particle strength, and particle size distribution were generally comparable to those of the Example, the battery still exhibited a significant increase in EIS (from 5.2Ω to 6.2Ω, a difference of 19%), and a significant decrease in charge specific capacity, initial coulombic efficiency, and capacity retention under 3C.

[0120] This indicates that by using molecular sieves and pitch for liquid-phase coating, the parameters of the anode material itself can be optimized while improving the lithium-ion transport path. When applied to batteries, this can effectively increase the lithium-ion diffusion rate and reduce the desolvation energy barrier, thereby improving the cycle performance and fast-charging performance of lithium-ion batteries.

Claims

1. A method for preparing a negative electrode material, characterized in that, The preparation method of the negative electrode material includes the following steps: a mixture containing graphite and a coating agent is carbonized to obtain the material; wherein, The coating agent includes molecular sieves and liquid-phase asphalt; The mass ratio of the molecular sieve to the liquid phase asphalt is 5%-25%; The mass ratio of the coating agent to the graphite is 1%-15%.

2. The method for preparing the negative electrode material as described in claim 1, characterized in that, The mass ratio of the coating agent to the graphite is 3%-15%, for example, 3.625%, 4.25%, or 14.5%. And / or, the mass ratio of the molecular sieve to the liquid phase pitch is 5%-16%, preferably 5%-15%, for example 8%; And / or, the molecular sieve includes one or more of 3A molecular sieve, 4A molecular sieve and 5A molecular sieve.

3. The method for preparing the negative electrode material as described in claim 1, characterized in that, The liquid phase asphalt includes oil asphalt and / or coal tar pitch; And / or, the liquid phase asphalt includes modified asphalt and / or solvent asphalt; And / or, the coking value of the liquid phase asphalt is 10%-30%, for example, 15%; And / or, the density of the liquid phase asphalt is 0.5-1.5 g / cm³. 2 ; And / or, the sulfur content of the liquid phase asphalt is not higher than 0.15 wt%, for example 0.5 wt%; And / or, the ash content of the liquid phase asphalt is less than 0.03 wt%; And / or, the volatile content of the liquid phase asphalt is 85wt%-95wt%, for example 90wt%.

4. The method for preparing the negative electrode material as described in claim 1, characterized in that, The graphite is natural graphite and / or artificial graphite; And / or, the graphite has a particle size Dv50 of 10-11 μm, for example 10.23 μm.

5. The method for preparing the negative electrode material as described in claim 1, characterized in that, The heating rate before carbonization is 2-3℃ / min, for example 2.5℃ / min; And / or, the carbonization treatment temperature is 1000-1200°C, for example 1150°C; And / or, the carbonization treatment time is 4-8 hours, for example 6 hours.

6. The method for preparing the negative electrode material as described in claim 1, characterized in that, The preparation of the mixture includes the following steps: The molecular sieve and liquid pitch are first mixed once, then mixed with the graphite a second time, and then fused together. The fusion is performed, for example, in a fusion machine; the fusion speed is preferably 800-1100 rpm, for example 900 rpm; and the fusion time is preferably 3-8 min. And / or, the carbonization process further includes a cooling and sieving step; Preferably, the mesh size of the sieve is 200-400 mesh, for example, 300 mesh.

7. A negative electrode material, characterized in that, The negative electrode material comprises a graphite matrix and a composite coating layer covering the surface of the graphite matrix. The composite coating layer includes amorphous carbon and a molecular sieve framework, and contains pores. The mass ratio of the composite coating layer to the graphite matrix is ​​1%-15%.

8. The negative electrode material as described in claim 7, characterized in that, The mass ratio of the composite coating layer to the graphite matrix is ​​3%-15%, for example, 3.625%, 7.25%, or 14.5%. And / or, the thickness of the composite coating layer is 0.7-2 μm; And / or, the particle size Dv10 of the negative electrode material is 6-8 μm; And / or, the particle size Dv50 of the negative electrode material is 10-13 μm; And / or, the particle size Dv90 of the negative electrode material is 18-20 μm; And / or, the specific surface area of ​​the negative electrode material is 1.0-1.5 m². 2 / g; And / or, the total pore volume of the negative electrode material is 0.0050-0.0055 cm³. 3 / g; And / or, the particle strength of the negative electrode material is 0.920-0.

950.

9. A negative electrode material, characterized in that, The negative electrode material is prepared by the method for preparing the negative electrode material as described in any one of claims 1-6.

10. The application of the negative electrode material as described in any one of claims 7-9 in a lithium-ion battery.

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