Negative electrode material and preparation method thereof, negative electrode sheet, and battery

Abstract

In order to solve the problem in the prior art that the fast charging performance and high temperature performance of graphite materials cannot be simultaneously guaranteed, the present invention provides a negative electrode material, a preparation method thereof, and a battery. The negative electrode material includes carbon particles a, carbon particles b, and carbon fine powder. The carbon particles a, carbon particles b, and carbon fine powder are all graphitized carbon materials, the carbon particles a are secondary particles, and the carbon particles b are single particles; the particle size of the carbon fine powder is ≤2μm; in the negative electrode material, the amount content of the carbon fine powder is 20%~40%, and the volume content of the carbon fine powder is 0.1%~2%.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a negative electrode material and a preparation method thereof, a negative electrode sheet, and a battery. Background Art

[0002] Lithium-ion batteries are developing rapidly and are widely used in various electronic products. They have put forward higher requirements for performance, especially stability and safety under extreme temperature conditions. Under high temperature environment, the negative electrode materials of traditional lithium-ion batteries, such as artificial graphite and natural graphite, will have serious problems such as reduced lithium ion insertion / deinsertion efficiency, accelerated SEI film reconstruction, and increased volume expansion at high temperature (≥60°C), which will lead to shortened battery cycle life, reduced thermal stability and increased safety hazards. The current solutions to improve the high-temperature performance of materials are mainly: (1) using needle coke and calcined needle coke with less volatile matter as raw materials; (2) increasing the graphite particle size; (3) reducing the functional groups on the graphite surface; (4) optimizing the material structure. Among these solutions, using needle coke and calcined needle coke with less volatile matter as raw materials is the main strategy currently expected by downstream companies. In order to further improve the high-temperature performance, if the graphite particle size is increased under the premise of using the above raw materials, the fast charging performance of artificial graphite materials will be reduced. Therefore, it is urgent to improve the high-temperature performance requirements of modified graphite materials while also ensuring the fast charging performance of the materials. Summary of the Invention

[0003] In response to the problem in the prior art that the fast charging performance and high temperature performance of graphite materials cannot be guaranteed at the same time, the present invention provides a negative electrode material and a preparation method thereof, a negative electrode sheet, and a battery.

[0004] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0005] In a first aspect, the present invention provides a negative electrode material comprising carbon particles a, carbon particles b, and carbon fine powder, wherein the carbon particles a, carbon particles b, and carbon fine powder are all graphitized carbon materials, the carbon particles a are secondary particles, and the carbon particles b are single particles; the particle size of the carbon fine powder is ≤2 μm;

[0006] In the negative electrode material, the amount content of the carbon fine powder is 20% to 40%, and the volume content of the carbon fine powder is 0.1% to 2%.

[0007] Optionally, in the negative electrode material, the amount content of the carbon fine powder is 28% to 32%, and the volume content of the carbon fine powder is 0.2% to 0.7%.

[0008] Optionally, the number ratio of the carbon particles a to the carbon particles b is (50-70): (30-50).

[0009] Optionally, the negative electrode material satisfies the following relationship: 5≤Dv50 / Dn50≤6, Dv50 is the volume median particle size of the negative electrode material, and Dn50 is the number median particle size of the negative electrode material.

[0010] Optionally, the Dv50 is 12~16μm, and the Dn50 is 2~3.2μm.

[0011] Optional, 5.3≤Dv50 / Dn50≤5.6.

[0012] Optionally, the carbon particles a, carbon particles b and carbon fine powder are each independently selected from one or more of artificial graphite, natural graphite and composite graphite;

[0013] And / or, the compaction density of the negative electrode material is greater than 1.75 g / cc, and the gram capacity is greater than 356 mAh / g.

[0014] In a second aspect, the present invention provides a method for preparing the negative electrode material as described in any one of the above, comprising the following steps:

[0015] Crushing and graphitizing the graphite raw material to obtain graphitized carbon material;

[0016] Screening the graphitized carbon material to obtain carbon fine powder and carbon particles b;

[0017] Part of the carbon particles b are subjected to secondary granulation treatment using asphalt to obtain carbon particles a;

[0018] The carbon particles a, carbon particles b and carbon fine powder are mixed to obtain a negative electrode material.

[0019] In a third aspect, the present invention provides a negative electrode sheet comprising a current collector and an active material layer arranged on at least one side of the current collector, wherein the active material layer comprises the negative electrode material as described above, or comprises the negative electrode material prepared by the preparation method described above.

[0020] In a fourth aspect, the present invention provides a battery comprising the negative electrode sheet as described above.

[0021] In the present invention, the negative electrode material containing fine carbon powder particles, when meeting the following conditions: a particle size of ≤2μm, a content of 20% to 40% by volume, and a volume content of 0.1% to 2%, benefits from the large specific surface area of ​​the fine carbon powder. This excessive binder usage during the formation of the negative electrode slurry from the negative electrode material results in a lower binder content on the surfaces of other large-sized particles (such as carbon particles a and carbon particles b). Furthermore, since the fine carbon powder has a smaller particle size and better kinetic properties, the surface binder does not deteriorate the kinetic properties of the material and can also serve to bond large particles within the negative electrode sheet. Furthermore, the fine carbon powder fills the gaps between carbon particles a and carbon particles b, further improving the compaction of the negative electrode material. The presence of carbon particles a and carbon particles b during the battery's charge and discharge processes reduces interfacial polarization, improves the surface polarization of the negative electrode material, shortens charging time under high-temperature cycling, and improves high-temperature standstill time under high voltage, thereby improving the material's high-temperature cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of a negative electrode material provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0024] One embodiment of the present invention provides a negative electrode material, comprising carbon particles a, carbon particles b, and carbon fine powder, wherein the carbon particles a, carbon particles b, and carbon fine powder are all graphitized carbon materials, the carbon particles a are secondary particles, and the carbon particles b are single particles; the particle size of the carbon fine powder is ≤2 μm;

[0025] In the negative electrode material, the amount content of the carbon fine powder is 20% to 40%, and the volume content of the carbon fine powder is 0.1% to 2%.

[0026] In the present invention, the negative electrode material containing fine carbon powder particles, when meeting the following conditions: a particle size of ≤2 μm, a content of 20% to 40% by volume, and a volume content of 0.1% to 2%, benefits from the large specific surface area of ​​the fine carbon powder. This excess binder is consumed during the formation of the negative electrode slurry from the negative electrode material, resulting in a lower binder content on the surfaces of other larger particles (such as carbon particles a and carbon particles b). Furthermore, since the fine carbon powder has a smaller particle size and better dynamic properties, the surface binder does not degrade the dynamic properties of the material and can also serve to bond large particles within the negative electrode sheet. Furthermore, the fine carbon powder fills the gaps between carbon particles a and carbon particles b, further improving the compaction of the negative electrode material. The presence of carbon particles a and carbon particles b during battery charge and discharge reduces interfacial polarization, improves the surface polarization of the negative electrode material, shortens charging time under high-temperature cycling, and improves high-temperature standstill time under high voltage, thereby improving the material's high-temperature cycling performance.

[0027] Specifically, the amount of carbon fines includes but is not limited to 20%, 23%, 26%, 29%, 32%, 35%, 38% or 40%.

[0028] The volume content of the carbon fines includes, but is not limited to, 0.1%, 0.3%, 0.6%, 0.9%, 1.2%, 1.5%, 1.8% or 2%.

[0029] In a preferred embodiment, the amount of the fine carbon powder in the negative electrode material is 28% to 32%, and the volume content of the fine carbon powder is 0.2% to 0.7%. Fine carbon powder within the above amount and volume content ranges in the negative electrode material can further improve the high-temperature performance of the battery while ensuring its fast charging performance.

[0030] In some embodiments, the mass ratio of the carbon particles a to the carbon particles b is (50-70): (30-50).

[0031] In some embodiments, the negative electrode material satisfies the following relationship: 5 ≤ Dv50 / Dn50 ≤ 6, where Dv50 is the volume median particle size of the negative electrode material, and Dn50 is the number median particle size of the negative electrode material. When the negative electrode material satisfies this relationship, the carbon fine powder fills the gaps between carbon particles a and carbon particles b. The negative electrode material composed of particles a, carbon particles b, and carbon fine powder can improve the compaction of the negative electrode material during use and improve the surface polarization of the negative electrode material.

[0032] Specifically, the value of Dv50 / Dn50 includes, but is not limited to, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.

[0033] In some embodiments, the Dv50 is 12-16 μm, and the Dn50 is 2-3.2 μm. By selecting the negative electrode material within the above particle size range, the negative electrode material has a higher compaction density.

[0034] In a preferred embodiment, 5.3≤Dv50 / Dn50≤5.6. When the negative electrode material satisfies the above relationship, the use compaction of the negative electrode material can be further improved, and the surface polarization of the negative electrode material can be improved.

[0035] In some embodiments, the carbon particles a, carbon particles b, and carbon fine powder are each independently selected from one or more of artificial graphite, natural graphite, and composite graphite.

[0036] In some embodiments, the compaction density of the negative electrode material is greater than 1.75 g / cc, and the gram capacity is greater than 356 mAh / g, so as to increase the energy density of the battery and improve the fast charging performance of the battery.

[0037] An embodiment of the present invention provides a method for preparing the negative electrode material as described above, comprising the following steps:

[0038] The graphite raw material is crushed and graphitized to obtain a graphitized carbon material; specifically, the average volume particle size D50 of the crushed graphite raw material is 6-12 μm.

[0039] Screening the graphitized carbon material to obtain carbon fine powder and carbon particles b;

[0040] Part of the carbon particles b is subjected to secondary granulation treatment using asphalt to obtain carbon particles a; specifically, the average volume particle size D50 of the carbon particles a after secondary granulation is 12-16 μm.

[0041] The carbon particles a, carbon particles b and carbon fine powder are mixed to obtain a negative electrode material.

[0042] One embodiment of the present invention provides a negative electrode sheet, comprising a current collector and an active material layer arranged on at least one side of the current collector, wherein the active material layer comprises the negative electrode material as described above, or comprises the negative electrode material prepared by the preparation method described above.

[0043] An embodiment of the present invention provides a battery, comprising the negative electrode sheet described above.

[0044] The present invention is further described below with reference to the following examples.

[0045] Example 1

[0046] This embodiment is used to illustrate the electrode and battery disclosed in the present invention, and includes the following steps:

[0047] Preparation of negative electrode materials:

[0048] The graphite of the coke raw material is crushed to a particle size D50 of 6-12 μm. The coke raw material is then graphitized. The graphitized carbon material is sieved using sieves of different mesh sizes to screen out carbon fines with a particle size of 2 μm or less. A portion of the remaining carbon particles (b) are then granulated using pitch to obtain a secondary particle size of 12-16 μm. The graphitized secondary particles, graphitized single particles, and graphitized carbon fine powder are physically mixed to obtain the negative electrode material. The carbon fine powder has a number content (W) of 30% and a volume content (V) of 0.5%. The negative electrode material has a Dv50 of 14 μm, a Dn50 of 2.55 μm, and a Dv50 / Dn50 ratio of 5.5. The mass ratio of carbon particles a to carbon particles b is 60:40.

[0049] Negative electrode sheet: The negative electrode material, conductive carbon black SP, CMC and SBR are mixed in a proper amount of deionized water at a mass ratio of 95.5:1.0:1.5:2.0 to form a uniform negative electrode slurry. The slurry is evenly coated on the negative electrode current collector Cu foil, vacuum-dried in a 110°C vacuum drying oven for 6 hours, and cold-pressed to obtain the negative electrode sheet.

[0050] Positive electrode:

[0051] The positive electrode active material lithium cobalt oxide, the conductive agent CNT, and the adhesive PVDF are fully stirred and mixed in NMP solvent at a weight ratio of 97:1.5:1.5. The slurry is coated on aluminum foil and then processed through drying, cold pressing, slitting, sheeting, welding the pole ears, and gluing to produce a positive electrode sheet that meets the requirements.

[0052] Production of lithium-ion batteries:

[0053] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The process is then wound into a bare cell. The bare cell is placed in an outer packaging bag, and the prepared electrolyte is injected into the dried battery. The battery is then vacuum packaged, allowed to rest, formed, and shaped to complete the process.

[0054] Example 2-12

[0055] The examples are used to illustrate the electrode and battery disclosed in the present invention, including most of the operating steps in Example 1, except that the formula in Table 1 is used.

[0056] Comparative Examples 1-8

[0057] The comparative example is used to compare and illustrate the electrode and battery disclosed in the present invention, including most of the operating steps in Example 1, except that the formula in Table 1 is used.

[0058] Table 1

[0059]

[0060] Performance Testing

[0061] 1. The batteries prepared in the above examples and comparative examples were subjected to the following performance tests:

[0062] 1. Cycle stability test: Place the battery in a 45±2℃ environment for 4 hours, and cycle it for 400 cycles at a standard charge and discharge rate of 1C / 1C and a voltage of 3.0-4.4V. Calculate the capacity retention rate of the battery after the cycle. The calculation formula is as follows:

[0063] The nth cycle capacity retention rate (%) = (nth cycle discharge capacity) / (first cycle discharge capacity) * 100%.

[0064] 2. Charging time is the constant current time + constant current and constant voltage time during the charging process.

[0065] The test results are shown in Table 2.

[0066] Table 2

[0067]

[0068] Depend on Figure 1 It can be seen that the negative electrode material contains carbon particles a, carbon particles b and carbon fine powder.

[0069] The test results for Example 1 and Comparative Example 1 in Table 2 show that the inclusion of fine carbon powder in the negative electrode material improves the material's high-temperature cycling performance and shortens the charging time under high-temperature cycling. The test results for Examples 1-6 and Comparative Examples 2-4, 7, and 8 show that when the amount of fine carbon powder is 28% to 32% and the volume content is 0.3% to 0.7%, the battery exhibits good capacity retention at 45°C.

[0070] The test results of Examples 1, 7-12, and Comparative Examples 5 and 6 show that using carbon particles a alone or carbon particles b mixed with fine carbon powder enhances battery charging time at high temperatures. However, using a negative electrode material made from a mixture of carbon particles b and fine carbon powder fails to achieve a compaction density of 1.75 g / cc, further impacting the battery's energy density. Batteries with a mass ratio of carbon particles a to carbon particles b in the negative electrode material of (50-70):(30-50) and a Dv50 / Dn50 ratio of 5-6 exhibit shorter charging times under high-temperature cycling.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that The negative electrode material is obtained by physically mixing carbon particles a, carbon particles b and carbon fine powder, wherein the carbon particles a, carbon particles b and carbon fine powder are all graphitized carbon materials, the carbon particles a are secondary particles, and the carbon particles b are single particles; the particle size of the carbon fine powder is ≤2 μm; In the negative electrode material, the amount content of the carbon fine powder is 20% to 40%, and the volume content of the carbon fine powder is 0.1% to 2%; The negative electrode material satisfies the following relationship: 5≤Dv50 / Dn50≤6, Dv50 is the volume median particle size of the negative electrode material, and Dn50 is the number median particle size of the negative electrode material.

2. The negative electrode material according to claim 1, characterized in that In the negative electrode material, the amount content of the carbon fine powder is 28% to 32%, and the volume content of the carbon fine powder is 0.2% to 0.7%.

3. The negative electrode material according to claim 1, characterized in that The mass ratio of the carbon particles a to the carbon particles b is (50-70): (30-50).

4. The negative electrode material according to claim 1, characterized in that The Dv50 is 12~16μm, and the Dn50 is 2~3.2μm.

5. The negative electrode material according to claim 1, characterized in that 5.3≤Dv50 / Dn50≤5.

6.

6. The negative electrode material according to claim 1, characterized in that The carbon particles a, carbon particles b and carbon fine powder are each independently selected from one or more of artificial graphite, natural graphite and composite graphite; And / or, the compaction density of the negative electrode material is greater than 1.75 g / cc, and the gram capacity is greater than 356 mAh / g.

7. A method for preparing the negative electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Crushing and graphitizing the graphite raw material to obtain graphitized carbon material; Screening the graphitized carbon material to obtain carbon fine powder and carbon particles b; Part of the carbon particles b are subjected to secondary granulation treatment using asphalt to obtain carbon particles a; the carbon particles a, carbon particles b and carbon fine powder are mixed to obtain a negative electrode material.

8. A negative electrode sheet, characterized in that: The invention comprises a current collector and an active material layer provided on at least one side of the current collector, wherein the active material layer comprises the negative electrode material according to any one of claims 1 to 6, or comprises the negative electrode material prepared by the preparation method according to claim 7.

9. A battery, characterized in that: Including the negative electrode sheet according to claim 8.

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