Hard carbon material, negative active material, preparation method of negative active material, negative plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a hard carbon material, a negative active material, a preparation method, a negative plate and a battery. The preparation method of the hard carbon material comprises the following steps: S1, adding phenolic resin into a curing agent for pre-curing; s2, carrying out instantaneous Joule thermal reaction on the product in the step S1 to obtain a hard carbon material crude product; and S3, treating the crude product to obtain the hard carbon material. The technical scheme has remarkable values in the aspects of improving the battery performance, reducing the production cost, promoting industrial application and the like.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a hard carbon material, a negative electrode active material and its preparation method, a negative electrode sheet and a battery. Background Technology

[0002] With the rapid development of modern electronic devices and new energy vehicles, the performance requirements for lithium-ion batteries are increasing. As a crucial component of lithium-ion batteries, the performance of the anode material has a critical impact on the battery's energy density, cycle life, and charge / discharge rate. Traditional graphite anode materials are gradually approaching their theoretical limits in terms of energy density, making it difficult to meet the ever-growing demand for high performance.

[0003] The selection and performance optimization of lithium-ion battery anode materials face significant bottlenecks: traditional graphite anodes have a low theoretical capacity (only 372 mAh / g), making it difficult to meet the demands of high-energy-density batteries; while silicon anodes possess extremely high theoretical capacity (4200 mAh / g), they experience approximately 300% volume expansion during charge and discharge, easily leading to electrode pulverization and a sharp decline in cycle performance, thus limiting their practicality; hard carbon anode materials, due to their unique structure and properties, exhibit a higher theoretical specific capacity than graphite anodes, showing broad application prospects in the lithium-ion battery field and becoming one of the current research hotspots. However, existing hard carbon material preparation processes often suffer from problems such as improper control of the pyrolysis atmosphere and incomplete impurity removal, resulting in unstable conductivity and lithium-ion migration efficiency, and limited capacity improvement potential when used alone as an anode. Furthermore, some composite processes of hard carbon and silicon anodes suffer from uneven mixing and high interfacial impedance, failing to fully leverage the synergistic advantages of the two materials. Additionally, some preparation processes suffer from unclear parameters, high costs, or difficulty in industrial scale-up. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a hard carbon material, a negative electrode active material and preparation method, a negative electrode sheet and a battery.

[0005] To achieve the above objectives, this application adopts the following solution:

[0006] A method for preparing a hard carbon material includes the following steps: S1: adding phenolic resin to a curing agent for pre-curing; S2: subjecting the product of step S1 to a transient Joule heating reaction to obtain a crude hard carbon material; S3: processing the crude product to obtain the hard carbon material.

[0007] The specific steps of step S1 are as follows: dissolve the phenolic resin in a solvent, add a curing agent, and heat to cure.

[0008] Preferably, the curing agent is hexamethylenetetramine; the amount of curing agent added is 10-15% of the mass of the phenolic resin;

[0009] Preferably, the solvent is methanol, ethanol, acetone or ethyl acetate; the mass-to-volume ratio of the phenolic resin to the solvent is 100g:(100-500ml); preferably 100g:300ml.

[0010] Preferably, the heating temperature is 150–200°C and the reaction time is 2–3 hours.

[0011] The specific steps of step S2 are as follows: After grinding, the product of step S1 is placed in a Joule heating reaction apparatus, and high-purity nitrogen or argon is introduced to replace the temperature and raise it to 800-1200℃, and the temperature is maintained for 1-3 hours.

[0012] The specific steps of step S3 are as follows: grind the cooled product of step S2 into powder, put it into an acid solution for acid washing, wash it with deionized water, dry it, and then carry out a low-temperature annealing reaction to obtain hard carbon material.

[0013] Preferably, the acid solution is a hydrochloric acid solution with a concentration of 0.5–2 mol / L; more preferably, it is 1 mol / L.

[0014] Preferably, the low-temperature annealing temperature is controlled at 150-250℃, and the annealing time is 1-5 hours; preferably 3 hours.

[0015] The present invention also includes a hard carbon material obtained by the preparation method described above.

[0016] The present invention also includes a negative electrode active material, comprising the aforementioned hard carbon material and silicon material; preferably, the mass ratio of the hard carbon material to the silicon material is (6-8):(2-4).

[0017] The particle size of the negative electrode active material is 4–7 μm.

[0018] The present invention also includes a method for preparing the aforementioned negative electrode active material, comprising the following steps: ball milling and mixing hard carbon material and silicon material, followed by cleaning and drying; preferably, the ball milling speed is 400-800 r / min.

[0019] The present invention also includes a negative electrode sheet comprising the aforementioned negative electrode active material.

[0020] The present invention also includes a battery comprising the aforementioned negative electrode.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. A method for preparing hard carbon materials with controllable process and low cost is provided. By precisely controlling the pyrolysis conditions and optimizing the impurity removal steps, the purity, conductivity and lithium ion intercalation / deintercalation performance of hard carbon materials are improved.

[0023] 2. Achieve efficient composite of hard carbon materials and silicon anodes, utilizing the complementary properties of the two materials to alleviate the volume expansion problem of silicon anodes, while improving the overall capacity and cycle stability of composite anodes;

[0024] 3. Finally, a composite anode active material suitable for high-energy-density lithium batteries was obtained, and the entire preparation process has the potential for industrial scale-up, providing a feasible solution for improving the performance and practical application of lithium battery anode materials. Attached Figure Description

[0025] Figure 1 An electron microscope image of Example 3 is shown;

[0026] Figure 2 The XRD pattern of Example 3 is shown. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] Example 1: A method for preparing hard carbon materials, comprising the following steps:

[0029] S1: Add phenolic resin to the curing agent for pre-curing; Phenolic resin dissolution: Take 100g of phenolic resin powder, add 300mL of ethanol, stir at 50℃ for 2 hours until completely dissolved, add 12g of hexamethylenetetramine, heat to 180℃ and cure for 2-3 hours, dry after curing, and grind to obtain a particle size ≤5μm.

[0030] S2: The product of step S1 is subjected to instantaneous Joule heating to obtain crude hard carbon material; the product of step S1 is ground and placed in a Joule heating apparatus, high-purity nitrogen gas (purity 99.999%) is introduced and heated to 1000℃, and kept at that temperature for 2 hours.

[0031] Cooling and grinding: Stop heating and allow nitrogen to flow through for natural cooling for 2.5 hours. Remove the hard carbon sample and grind it with an agate mortar until the particle size is ≤5μm.

[0032] S3: The crude product is processed to obtain hard carbon material. The crude hard carbon powder is added to a 1 mol / L hydrochloric acid solution (solid-liquid ratio 1:10) and stirred at room temperature for 3 hours; it is then washed with deionized water by centrifugation until the pH of the filtrate is ≈7, and annealed at 150℃ to obtain the hard carbon material.

[0033] The preparation method of the negative electrode active material includes the following steps: take the above-mentioned hard carbon material and polycrystalline silicon material (mass ratio 7:3), put them into a ball mill, grind them at 600 r / min for 2 hours, and then clean and dry them for later use.

[0034] Example 2: A method for preparing hard carbon materials, comprising the following steps:

[0035] S1: Add phenolic resin to the curing agent for pre-curing; Phenolic resin dissolution: Take 100g of phenolic resin powder, add 250mL of acetone, stir at 40℃ for 3 hours until completely dissolved, add 10g of hexamethylenetetramine, heat to 200℃ and cure for 2-3 hours, dry after curing, and grind to obtain a particle size ≤5μm.

[0036] S2: The product of step S1 is subjected to an instantaneous Joule heating reaction to obtain crude hard carbon material; the product of step S1 is ground and placed in a Joule heating reaction apparatus, high-purity argon gas is introduced, the temperature is instantly raised to 800℃, and held at that temperature for 3 hours.

[0037] Cooling and grinding: Cool with argon gas for 3 hours, then grind until the particle size is ≤5μm.

[0038] S3: The crude product was processed to obtain hard carbon material. The mixture was stirred at room temperature for 2 hours with 1 mol / L hydrochloric acid, washed until pH≈7, and then annealed at 200℃.

[0039] The preparation method of the negative electrode active material includes the following steps: hard carbon and polycrystalline silicon (mass ratio 6:4) are ball-milled at 400 r / min for 3 hours, and then cleaned and dried for later use.

[0040] Example 3: A method for preparing hard carbon materials, comprising the following steps:

[0041] S1: Add phenolic resin to the curing agent for pre-curing; take 100g of phenolic resin powder, add 350mL of ethanol, stir at 60℃ for 1.5 hours until completely dissolved, add 15g of hexamethylenetetramine and heat to 150℃ to cure for 2-3 hours.

[0042] S2: The product of step S1 is subjected to an instantaneous Joule heating reaction to obtain a crude hard carbon material; the product of step S1 is ground and placed in a Joule heating reaction apparatus, high-purity nitrogen is introduced, the temperature is instantly raised to 1200℃, and held at that temperature for 1 hour.

[0043] Cooling and grinding: Cool with nitrogen for 2 hours and grind until the particle size is ≤5μm.

[0044] S3: The crude product was processed to obtain hard carbon material. The mixture was stirred at room temperature for 4 hours with 1 mol / L hydrochloric acid, washed until pH≈7, and then annealed at 250℃.

[0045] The preparation method of the negative electrode active material includes the following steps: hard carbon and polycrystalline silicon (mass ratio 8:2) are ball-milled at 800 r / min for 1 hour, and then cleaned and dried for later use.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that no inert gas is introduced in step S2, and the product of step S1 is placed in a Joule heating reactor after grinding, without nitrogen gas is introduced, and the temperature is directly raised to 1000°C in the air atmosphere and held for 2 hours (the remaining steps are the same as in Example 1).

[0048] Comparative Example 2

[0049] The difference between Comparative Example 2 and Example 1 is that the low-temperature annealing step is omitted: the ground hard carbon powder is directly acid-washed with hydrochloric acid and washed with deionized water until pH≈7, and then dried at 90°C for 18 hours.

[0050] Comparative Example 3

[0051] The difference between Comparative Example 3 and Example 1 is that the product of step S1 was ground and placed in a Joule heating reactor, protected by nitrogen, heated to 700°C (below 800°C), and kept at that temperature for 2 hours.

[0052] Comparative Example 4

[0053] The difference between Comparative Example 4 and Example 1 is that the preparation method of the negative electrode active material is different. Hard carbon and polycrystalline silicon are ball-milled at 300 r / min (less than 400 r / min) for 2 hours.

[0054] The negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-4 were assembled into button cells for electrical performance characterization: The negative electrode material, conductive carbon black, and binder polyacrylic acid were mixed in a ratio of 80:10:10, thoroughly ground, and then dispersed in a homogenizer for 15 minutes to obtain a viscous active material slurry. The slurry was uniformly coated onto copper foil using a scraping method, and the coated negative electrode sheet was transferred to a vacuum oven at 80°C and dried for 12 hours. After drying, the electrode sheet was rolled and then punched into a circular electrode sheet with a diameter of 12 mm and weighed. The weighed electrode sheet was immediately transferred to a glove box under Ar atmosphere protection for button cell assembly. After assembly and sealing, the battery was allowed to stand at room temperature for 24 hours before being subjected to charge-discharge tests on an Arbin battery testing system. The results are shown in the table below, with a charge-discharge voltage range of 0.001–2V. The morphology and dimensions of the above examples, the key performance characteristics of the negative electrodes in the examples and comparative examples, and the battery performance were characterized. The results are shown in Tables 1 and 2.

[0055] Example 1 consisted of silicon particles and hard carbon microspheres, resulting in a composite anode active material with a size of 4 μm; Example 2 had a size of 7 μm; and Example 3 had a size of 5 μm. Figure 1 An electron microscope image of Example 3 is shown; Figure 2 The Xrd spectrum is shown, showing a clear silicon peak. Since hard carbon is amorphous carbon, the peaks are not obvious in the spectrum.

[0056] Table 1 Results of key performance indicators for the negative electrode:

[0057]

[0058] Table 2

[0059]

[0060] The results show that, under a high-purity inert atmosphere, the instantaneous Joule heating method described in this application can overcome the problems of slow and medium-speed heating in existing pyrolysis atmospheres, lack of protection, temperature fluctuations, or arbitrary cooling methods that lead to material oxidation and structural instability. It achieves high temperature control precision, forms a hard carbon microstructure, and ensures its conductivity and lithium-ion migration performance. Furthermore, after acid washing, a low-temperature annealing process is added, resulting in higher crystallinity and the removal of unstable oxygen-containing groups; it also closes the micropores opened by the acid. The hard carbon material and polycrystalline silicon are ground together in a planetary ball mill at a speed of 400–800 r / min. The grinding process generates intense shearing, extrusion, and friction forces, thus efficiently grinding the hard carbon and silicon materials. This achieves uniform dispersion of the two materials, retaining the high capacity advantage of silicon while mitigating its volume expansion with the help of hard carbon, thus exhibiting synergistic performance.

[0061] In summary, the technical solution of this application has the following characteristics:

[0062] 1. Improved Cycle Performance and Capacity: The composite design of hard carbon material and silicon anode combines the advantages of good cycle stability of hard carbon and high theoretical capacity (4200mAh / g) of silicon material. Uniform mixing is achieved through ball milling at 400–800 r / min, which can alleviate the volume expansion of silicon during charge and discharge, and significantly improve the cycle life and rate performance of the composite electrode.

[0063] 2. Process controllability and economy: The parameters of the entire preparation process (dissolution, pyrolysis, acid washing, and compounding) are clearly defined (such as temperature, time, and rotation speed range), making it easy to scale up industrially; the use of conventional organic solvents, hydrochloric acid for acid washing, and deionized water for washing results in low cost and environmental friendliness, avoiding the use of expensive reagents or complex equipment.

[0064] 3. Enhanced structural stability: The pyrolysis process under inert gas (nitrogen / argon) protection can effectively suppress material oxidation and ensure the integrity of the hard carbon skeleton; the subsequent grinding and washing processes further ensure the uniformity of the material, reduce the interfacial impedance during electrode preparation, and improve the overall performance of the battery.

[0065] With the advantages mentioned above, this technical solution has significant value in improving battery performance, reducing production costs, and promoting industrial applications.

[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0067] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0068] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a hard carbon material, characterized in that, The process includes the following steps: S1: Pre-curing phenolic resin by adding a curing agent; S2: The product of step S1 is subjected to a transient Joule heating reaction to obtain a crude hard carbon material; S3: The crude product is processed to obtain a hard carbon material.

2. The method for preparing hard carbon material according to claim 1, characterized in that, The specific steps of step S1 are as follows: dissolve the phenolic resin in a solvent, add a curing agent, and heat to cure. Preferably, the curing agent is hexamethylenetetramine; the amount of curing agent added is 10-15% of the mass of the phenolic resin; Preferably, the solvent is methanol, ethanol, acetone or ethyl acetate; the mass-to-volume ratio of the phenolic resin to the solvent is 100g:(250-350ml); preferably 100g:300ml. Preferably, the heating temperature is 150–200°C and the reaction time is 2–3 hours.

3. The method for preparing hard carbon material according to claim 1, characterized in that, The specific steps of step S2 are as follows: After grinding, the product of step S1 is placed in a Joule heating reaction apparatus, high-purity nitrogen or argon is introduced for purging, the temperature is raised to 800-1200℃, and the temperature is maintained for 1-3 hours.

4. The method for preparing hard carbon material according to claim 1, characterized in that, The specific steps of step S3 are as follows: grind the cooled product of step S2 into powder, put it into an acid solution for acid washing, wash it with deionized water, dry it, and then carry out a low-temperature annealing reaction to obtain hard carbon material. Preferably, the acid solution is a hydrochloric acid solution with a concentration of 0.5–2 mol / L; more preferably, it is 1 mol / L. Preferably, the low-temperature annealing temperature is controlled at 150-250℃, and the annealing time is 1-5 hours.

5. A hard carbon material obtained by the preparation method according to any one of claims 1-4.

6. A negative electrode active material, characterized in that, It includes the hard carbon material as described in claim 5 and silicon material; preferably, the mass ratio of the hard carbon material to the silicon material is (6-8):(2-4).

7. The negative electrode active material according to claim 6, characterized in that, The particle size of the negative electrode active material is 4–7 μm.

8. A method for preparing the negative electrode active material according to claim 7, characterized in that, The process includes the following steps: ball milling and mixing hard carbon material and silicon material, followed by cleaning and drying; preferably, the ball milling speed is 400-800 r / min.

9. A negative electrode sheet, characterized in that, Includes the negative electrode active material as described in claim 6 or 7.

10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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