Silicon-carbon negative electrode material preparation method

Abstract

The application relates to the technical field of battery materials, and discloses a preparation method of a silicon-carbon negative electrode material, which comprises the following steps: step one, mixing nano silicon powder, a carbon source material and a conductive additive according to a certain proportion, and performing ball milling treatment; step two, mixing the mixture after the ball milling with an interface stabilizer, and performing ball milling treatment again; step three, drying the mixed material; step four, performing carbonization treatment on the dried mixture; step five, mixing the material after the carbonization with an alloying material, and performing alloying treatment; step six, mixing the treated material with a binder and a solvent to prepare a slurry; and step seven, coating the slurry on a current collector to form a negative electrode material coating. By introducing the conductive additive and the alloying material, the lithium ion battery can store more electric energy under the same volume or weight, so that the overall energy density of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a preparation method of silicon-carbon negative electrode material. BACKGROUND

[0002] With the rapid development of electric vehicles, wearable devices and energy storage systems, the demand for high-performance lithium-ion batteries is increasing. Although traditional graphite negative electrode materials have high electrical conductivity and stable cycle life, their theoretical specific capacity (about 372 mAh / g) has reached the limit and cannot meet the increasing demand for energy density. Therefore, developing new high-capacity negative electrode materials has become a hot research topic.

[0003] Silicon is one of the most promising negative electrode materials due to its extremely high theoretical specific capacity (about 4200 mAh / g) and abundant natural reserves. However, silicon material will undergo significant volume change (more than 300%) during charging and discharging, which will lead to particle crushing, destruction of the conductive network, and increase of side reactions with electrolyte, thereby seriously affecting the cycle life and initial coulombic efficiency of the battery. These defects greatly limit the widespread use of silicon materials in practical applications.

[0004] In order to solve these problems of silicon material, various methods have been used in the prior art to improve the performance of silicon-based negative electrode materials. Common methods include compounding silicon with carbon material to form silicon-carbon composite material, which can alleviate the volume expansion problem of silicon through the flexibility and conductivity of carbon. However, simple silicon-carbon composite is still insufficient to completely solve the problems of cycle stability and initial coulombic efficiency. In addition, the selection of binder and the control of interface stability also have an important influence on the performance of the material, but the existing research and application still have many deficiencies in this regard. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a preparation method of silicon-carbon negative electrode material, which solves the problems of insufficient cycle stability, initial coulombic efficiency and specific capacity of silicon negative electrode material.

[0006] To achieve the above purpose, the present application is realized by the following technical scheme: a preparation method of silicon-carbon negative electrode material, comprising the following steps:

[0007] Step one, mix nano-silicon powder, carbon source material and conductive additive in a certain proportion, and perform ball milling treatment;

[0008] Step two, mix the ball-milled mixture with an interface stabilizer and perform ball milling treatment again;

[0009] Step three, dry the mixed material;

[0010] Step four, carbonize the dried mixture;

[0011] Step five, mixing the carbonized material with alloying material for alloying treatment;

[0012] Step six, mixing the treated material with binder and solvent to prepare slurry;

[0013] Step seven, coating the slurry on the current collector to form a negative electrode material coating;

[0014] Step eight, secondary drying and tabletting of the coated negative electrode material to obtain a silicon-carbon negative electrode material.

[0015] Preferably, the addition ratio of the nanosilicon powder, carbon source material and conductive additive in step one is 5-7:2-3:5-10.

[0016] Preferably, the ball milling time in step one is 10-20 hours.

[0017] Preferably, the interfacial stabilizer in step two is one of lithium fluoride or silicon dioxide, and the addition ratio is 1%-5%.

[0018] Preferably, the drying treatment temperature in step three is 80-120°C, and the drying time is 8-12 hours.

[0019] Preferably, the carbonization treatment temperature in step four is 600-900°C, and the treatment time is 2-4 hours.

[0020] Preferably, the alloying material in step five is one of tin, indium or gallium, and the addition ratio is 5-15%, the alloying treatment temperature is 300-500°C, and the treatment time is 1-3 hours.

[0021] Preferably, the binder in step six is one of carboxymethyl cellulose, polyacrylic acid or conductive polymer.

[0022] Preferably, the secondary drying temperature of the coated negative electrode material in step eight is 80-120°C, and the drying time is 8-12 hours.

[0023] Preferably, the ball milling treatment step includes using a high-energy ball mill for treatment to ensure that the materials are fully mixed and the particle size is reduced.

[0024] The present application provides a method for preparing a silicon-carbon negative electrode material. It has the following advantages:

[0025] 1. The present application optimizes the preparation method of the silicon-carbon negative electrode material, introduces conductive additives and alloying materials, significantly improves the specific capacity of the negative electrode material, enables the lithium ion battery to store more electric energy under the same volume or weight, and thus improves the overall energy density of the battery.

[0026] 2、The present application improves the structural stability and interface stability of the silicon-carbon negative electrode material in the charging and discharging process by adding an interface stabilizer and a modified binder in the preparation process. The material breakage and shedding caused by volume expansion and contraction of the silicon material during the cycle process are effectively slowed down, and the cycle life and capacity retention rate of the battery are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The method flowchart of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] Embodiment one:

[0030] Please refer to the accompanying Figure 1 The present application provides a silicon-carbon negative electrode material preparation method, which comprises the following steps:

[0031] Step one, mix nano-silicon powder (50g), graphite (30g) and carbon nanotubes (20g) in a ratio of 5:3:2, and perform ball milling treatment for 15 hours.

[0032] Step two, mix the ball-milled mixture with lithium fluoride (2g), and perform ball milling treatment again for 5 hours.

[0033] Step three, dry the mixed material at 100°C for 10 hours.

[0034] Step four, carbonize the dried mixture at 800°C for 3 hours.

[0035] Step five, mix the carbonized material with tin powder (10g), and perform alloying treatment at 400°C for 2 hours.

[0036] Step six, mix the treated material with carboxymethyl cellulose (5g) and NMP to prepare a slurry.

[0037] Step seven, coat the slurry on a copper foil to form a negative electrode material coating.

[0038] Step eight, dry the coated negative electrode material at 100°C for 10 hours, and perform tabletting treatment to obtain a silicon-carbon negative electrode material.

[0039] Example Two:

[0040] Please refer to the attached Figure 1 The embodiment of the present application provides a preparation method of silicon-carbon negative electrode material, comprising the following steps:

[0041] Step one, mix nano-silicon powder (60g), graphite (25g) and conductive carbon black (15g) in the ratio of 6:2.5:1.5, and perform ball milling treatment for 12 hours.

[0042] Step two, mix the ball-milled mixture with silicon dioxide (3g), and perform ball milling treatment again for 4 hours.

[0043] Step three, dry the mixed material at 90°C for 12 hours.

[0044] Step four, carbonize the dried mixture at 750°C for 2.5 hours.

[0045] Step five, mix the carbonized material with indium powder (8g), and perform alloying treatment at 350°C for 2 hours.

[0046] Step six, mix the treated material with polyacrylic acid (6g) and NMP to prepare a slurry.

[0047] Step seven, coat the slurry on a copper foil to form a negative electrode material coating.

[0048] Step eight, dry the coated negative electrode material at 90°C for 9 hours, and perform tabletting treatment to obtain a silicon-carbon negative electrode material.

[0049] Example Three:

[0050] Please refer to the attached Figure 1 The embodiment of the present application provides a preparation method of silicon-carbon negative electrode material, comprising the following steps:

[0051] Step one, mix nano-silicon powder (55g), carbon nanotubes (25g) and graphene (20g) in the ratio of 5.5:2.5:2, and perform ball milling treatment for 18 hours.

[0052] Step two, mix the ball-milled mixture with lithium fluoride (2.5g), and perform ball milling treatment again for 6 hours.

[0053] Step three, dry the mixed material at 110°C for 8 hours.

[0054] Step four, carbonize the dried mixture at 850°C for 3.5 hours.

[0055] Step five, mix the carbonized material with gallium powder (12g), and perform alloying treatment at 450℃ for 2.5 hours.

[0056] Step six, mix the treated material with conductive polymer (4g) and NMP to prepare a slurry.

[0057] Step seven, coat the slurry on a copper foil to form a negative electrode material coating.

[0058] Step eight, dry the coated negative electrode material at 110℃ for 10 hours, and perform tabletting treatment to obtain a silicon-carbon negative electrode material.

[0059] Example four:

[0060] Please refer to the attached Figure 1 The embodiment of the present application provides a silicon-carbon negative electrode material preparation method, which comprises the following steps:

[0061] Step one, mix nano-silicon powder (65g), graphite (20g) and carbon nanotubes (15g) in a ratio of 6.5:2:1.5, and perform ball milling treatment for 20 hours.

[0062] Step two, mix the ball-milled mixture with silicon dioxide (4g), and perform ball milling treatment again for 5 hours.

[0063] Step three, dry the mixed material at 85℃ for 10 hours.

[0064] Step four, carbonize the dried mixture at 900℃ for 3 hours.

[0065] Step five, mix the carbonized material with tin powder (12g), and perform alloying treatment at 500℃ for 3 hours.

[0066] Step six, mix the treated material with carboxymethyl cellulose (5g) and NMP to prepare a slurry.

[0067] Step seven, coat the slurry on a copper foil to form a negative electrode material coating.

[0068] Step eight, dry the coated negative electrode material at 100℃ for 12 hours, and perform tabletting treatment to obtain a silicon-carbon negative electrode material.

[0069] Example five:

[0070] Please refer to the attached Figure 1 The embodiment of the present application provides a silicon-carbon negative electrode material preparation method, which comprises the following steps:

[0071] Step one, mix nano-silicon powder (70g), graphite (25g) and conductive carbon black (5g) in the ratio of 7:2.5:0.5, and perform ball milling treatment for 14 hours.

[0072] Step two, mix the ball-milled mixture with lithium fluoride (3g), and perform ball milling treatment again for 6 hours.

[0073] Step three, dry the mixed material at 95℃ for 12 hours.

[0074] Step four, carbonize the dried mixture at 700℃ for 2 hours.

[0075] Step five, mix the carbonized material with indium powder (10g), and perform alloying treatment at 400℃ for 1.5 hours.

[0076] Step six, mix the treated material with polyacrylic acid (6g) and NMP to prepare a slurry.

[0077] Step seven, coat the slurry on a copper foil to form a negative electrode material coating.

[0078] Step eight, dry the coated negative electrode material at 85℃ for 9 hours, and perform tabletting treatment to obtain a silicon-carbon negative electrode material.

[0079] Comparative experimental example:

[0080] Compare the unimproved silicon-carbon negative electrode material with the silicon-carbon negative electrode materials of Examples 1-5, and the specific experimental steps are as follows:

[0081] I. Preparation of unimproved silicon-carbon negative electrode material

[0082] Step one: mix nano-silicon powder (60g) and graphite (40g) in the ratio of 6:4, and perform ball milling treatment for 12 hours.

[0083] Step two: dry the mixed material at 100℃ for 10 hours.

[0084] Step three: carbonize the dried mixture at 800℃ for 3 hours.

[0085] Step four: mix the carbonized material with carboxymethyl cellulose (5g) and NMP to prepare a slurry.

[0086] Step five: coat the slurry on a copper foil to form a negative electrode material coating.

[0087] Step six: dry the coated negative electrode material at 100℃ for 10 hours, and perform tabletting treatment to obtain an unimproved silicon-carbon negative electrode material.

[0088] II. Preparation of improved silicon-carbon negative electrode material

[0089] Prepared according to the specific steps of the preceding Examples 1-5.

[0090] III. Battery assembly

[0091] Material preparation: The negative electrode material prepared above and commercial positive electrode material, separator and electrolyte were prepared.

[0092] Electrode slicing: The negative electrode material and positive electrode material were sliced into 14mm diameter discs.

[0093] Assembled button cell: In an inert gas-protected glove box, button cells were assembled using the negative electrode material, positive electrode material, separator and electrolyte.

[0094] IV. Electrochemical performance test

[0095] First charge-discharge test:

[0096] Charging and discharging tests were performed using constant current-constant voltage (CC-CV) mode.

[0097] The test current was set to 0.1C.

[0098] The first charge-discharge capacity and first coulombic efficiency of each sample were recorded.

[0099] Cycle performance test:

[0100] The test current was set to 0.5C.

[0101] Cycle charging and discharging tests were performed in the voltage range of 0.01V to 1.5V.

[0102] The capacity and capacity retention rate of each sample after 500 cycles were recorded, and the experimental data are shown in Table 1

[0103]

[0104] Experimental analysis:

[0105] From the experimental data, it can be seen that the improved silicon-carbon negative electrode material is significantly better than the unimproved silicon-carbon negative electrode material in terms of first charge-discharge capacity, first coulombic efficiency and capacity retention rate after 500 cycles. The specific analysis is as follows:

[0106] First charge-discharge capacity:

[0107] The first charge-discharge capacity of the improved samples (Examples 1-5) was higher than that of the unimproved sample, with the highest being 1850mAh / g (Example 3).

[0108] ​The first coulombic efficiency of the improved sample is significantly improved, and the highest reaches 86% (Example III).

[0109] Cycling performance: The capacity retention rates of the improved samples all reach 90% after 500 cycles, indicating that the improved materials have excellent long cycle stability.

[0110] Sample Initial charge-discharge capacity (mAh / g) Initial coulombic efficiency (%) Capacity after 500 cycles (mAh / g) Capacity retention rate (%) Unimproved 1500 80 900 60 Example one 1800 85 1620 90 Example two 1750 83 1575 90 Example three 1850 86 1665 90 Example four 1700 82 1530 90 Example five 1800 84 1620 90

[0111] Table I

[0112] Experimental conclusion: By adding conductive additives, interfacial stabilizers, binder modifiers and alloying materials, and optimizing the process parameters, the improved silicon-carbon negative electrode material significantly improves the comprehensive performance of lithium ion batteries, especially in high capacity, long cycle life and high coulombic efficiency.

[0113] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing silicon-carbon anode materials, characterized in that, Includes the following steps: Step 1: Mix nano-silicon powder, carbon source material and conductive additives in a certain proportion and then ball mill them. Step 2: Mix the ball-milled mixture with the interface stabilizer, and then ball-mill again; Step 3: Dry the mixed materials. Step 4: Carbonize the dried mixture; Step 5: Mix the carbonized material with the alloying material and perform alloying treatment; Step 6: Mix the treated material with the binder and solvent to prepare a slurry; Step 7: Apply the slurry onto the current collector to form a negative electrode material coating; Step 8: The coated anode material is subjected to secondary drying and pressing to obtain silicon-carbon anode material; The interface stabilizer in step two is either lithium fluoride or silicon dioxide, and the addition ratio is 1% to 5%. The alloying material in step five is one of tin, indium, or gallium, with an addition ratio of 5-15%. The alloying temperature is 300℃~500℃, and the processing time is 1~3 hours.

2. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The addition ratio of nano-silicon powder, carbon source material and conductive additive in step one is 5-7:2-3:5-10.

3. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The ball milling time in step one is 10 to 20 hours.

4. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The drying temperature in step three is 80℃~120℃, and the drying time is 8~12 hours.

5. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The carbonization temperature in step four is 600℃~900℃, and the processing time is 2~4 hours.

6. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The adhesive used in step six is ​​one of carboxymethyl cellulose, polyacrylic acid, or a conductive polymer.

7. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The secondary drying temperature of the coated negative electrode material in step eight is 80℃~120℃, and the drying time is 8~12 hours.

8. The method for preparing silicon-carbon anode material according to claim 1, characterized in that, The ball milling process includes processing with a high-energy ball mill to ensure that the materials are fully mixed and that the particle size is reduced.

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