Preparation method of negative electrode material for energy storage lithium ion battery

Abstract

The invention discloses a preparation method of a negative electrode material for an energy storage lithium ion battery, which includes: selecting pitch coke with high isotropy and crushing it to a particle size of D50 = 10 - 50 μm, performing low-temperature graphitization at a temperature of 2000 - 2600 °C for 6 - 24 h, crushing and classifying, removing fine powder, and obtaining a graphite precursor material with a particle size distribution of D90 / D10 ≤ 4; adding metallic lithium and a polymer to an organic solvent, filtering, and performing vacuum drying to obtain a lithium supplement agent; adding the graphite precursor material, the lithium supplement agent, and a binder to a ball mill, mixing evenly, raising the temperature to 300 - 400 °C for pre-carbonization for 1 - 6 h for secondary granulation, and then raising the temperature to 800 - 1100 °C under an inert atmosphere and introducing a carbon source gas for vapor deposition for 1 - 6 h to obtain the product. The material of the invention has good high-temperature storage performance, high initial efficiency, and excellent cycle performance.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of lithium-ion battery materials, and specifically relates to a method for preparing a negative electrode material for an energy storage lithium-ion battery. Background Art

[0002] With the increasing market demand for long-life energy storage batteries, and the negative electrode material being a key factor affecting its cycle performance, the current negative electrode materials are mainly artificial graphite single particles or a mixture of secondary particles and single particles, with isotropic coke as the raw material and having advantages such as low expansion. However, due to defects existing on the surface of the material itself, there are many side reactions during its cycling process, resulting in a reduction in cycle performance. At the same time, the self-expansion of the material during charge and discharge causes the SEI film to continuously repair and consume lithium ions, which also leads to a reduction in cycle performance. And there are many factors to improve the cycle of the material, such as selecting isotropic coke with few defects, coating the surface of the material with a material with good kinetics to improve the kinetic performance, reducing fine powder to reduce side reactions, and improving storage and its cycle performance. For example, Chinese Patent Application No. 201711354909.7 discloses a method for manufacturing a fast-charging and long-cycle graphite negative electrode sheet, including the steps of: mixing petroleum coke particles, high-temperature pitch binder, and stearic acid, performing multi-stage temperature coating and bonding, incorporating Fe2O3 for graphitization treatment, magnetization treatment, and drying to obtain the finished product. This method can not only improve the graphitization degree and greatly reduce the graphitization temperature of various amorphous carbons, improve the first charge-discharge efficiency and cycle stability of the graphite negative electrode material, but also coat magnetic nanoparticles Fe3O4 on the surface and perform magnetization treatment, greatly reducing the OI value of the electrode sheet. However, the residual Fe3O4 in the material reduces the battery safety performance and self-discharge, which is not beneficial to the cycle, and defects will be left on the surface of the material during the volatilization process of Fe3O4, reducing the cycle performance of the material. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a negative electrode material for an energy storage lithium-ion battery with characteristics such as good high-temperature storage, high first efficiency, and excellent cycle performance, overcoming the above-mentioned drawbacks.

[0004] A method for preparing a negative electrode material for an energy storage lithium-ion battery according to the present invention includes the following steps:

[0005] Step S1: Select pitch coke with high isotropy and crush it to a particle size D50 = 10 - 50 μm, perform low-temperature graphitization at a temperature of 2000 - 2600 °C for 6 - 24 h, crush and classify, and remove fine powder to obtain a graphite precursor material with a particle size distribution D90 / D10 ≤ 4;

[0006] Step S2: According to the mass ratio of metallic lithium: polymer: organic solvent = 1 - 5: 10 - 30: 100, add metallic lithium and polymer to the organic solvent, filter, and vacuum dry to obtain a lithium supplement agent;

[0007] Step S3: According to the mass ratio of graphite precursor material: lithium supplement agent: binder = 100: 0.5 - 2: 1 - 5, add the graphite precursor material, lithium supplement agent and binder to a ball mill, mix evenly, heat up to 300 - 400 °C for pre-carbonization for 1 - 6 h for secondary granulation, and then heat up to 800 - 1100 °C under an inert atmosphere, and introduce a carbon source gas for vapor deposition for 1 - 6 h to obtain the product.

[0008] For the preparation method of the negative electrode material used in the above-mentioned energy storage lithium-ion battery, among them: the polymer described in Step S2 is one of polyalkylene carbonate, polyalkylene oxide, polyalkylsiloxane, polyacrylate alkyl ester or polymethacrylate alkyl ester; the organic solvent is one of N-methylpyrrolidone, carbon tetrachloride or cyclohexane.

[0009] For the preparation method of the negative electrode material used in the above-mentioned energy storage lithium-ion battery, among them: the binder described in Step S3 is one of carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, carboxyisopropyl cellulose, sodium cellulose, sodium nitrate cellulose or sodium carboxyalkyl cellulose.

[0010] For the preparation method of the negative electrode material used in the above-mentioned energy storage lithium-ion battery, among them: the carbon source gas described in Step S3 is one of carbon fluoride, methyl chloride, methylene chloride, trifluoromethane or difluoromethane. Compared with the prior art, the present invention has obvious beneficial effects. From the above technical solutions, it can be seen that: the present invention improves the layer spacing of the material through low-temperature graphitization to reduce expansion, improves the cycle performance, and at the same time controls the fine powder content to reduce side reactions and improve the high-temperature storage performance and its cycle performance. By coating the polymer-coated lithium powder on the surface of the material, the polymer-coated lithium powder dissolves in the electrolyte, and releases lithium ions during the charge and discharge process to improve the rate performance of the material and improve the power performance; at the same time, the lithium powder releases lithium ions during the charge and discharge process to reduce the lithium ions consumed by the SEI during the cycle process and improve the cycle performance. The obtained material has characteristics such as good high-temperature storage, high initial efficiency and excellent cycle performance when applied to lithium-ion batteries. Description of the Drawings

[0011] Figure 1 SEM diagram of the graphite composite material prepared in Example 1. Detailed Description of the Invention

[0012] Example 1

[0013] A preparation method of a negative electrode material used in an energy storage lithium-ion battery includes the following steps:

[0014] Step S1: Crush the pitch coke to a particle size of D50 = 30 μm, then perform low-temperature graphitization at 2400 °C for 12 h, crush and classify, and remove the fine powder to obtain a graphite precursor material with a particle size distribution of D90 / D10 = 3.8;

[0015] Step S2: Add 3 g of metallic lithium and 20 g of polyalkylene carbonate to 100 g of N-methylpyrrolidone organic solvent, filter, and vacuum dry at 80 °C for 24 h to obtain a lithium supplement agent;

[0016] Step S3: Add 100 g of graphite precursor material, 1 g of lithium supplement agent, and 3 g of carboxymethyl cellulose binder to a ball mill and mix evenly, then raise the temperature to 350 °C for pre-carbonization for 3 h for secondary granulation, and then raise the temperature to 900 °C under an argon inert atmosphere and introduce carbon fluoride gas (flow rate 100 ml / min) for vapor deposition for 3 h to obtain the product.

[0017] Example 2

[0018] A preparation method of a negative electrode material for an energy storage lithium-ion battery, comprising the following steps:

[0019] Step S1: Crush the pitch coke with high isotropy to a particle size of D50 = 10 μm, then perform low-temperature graphitization at 2000 °C for 6 h, crush and classify, and remove the fine powder to obtain a graphite precursor material with a particle size distribution of D90 / D10 = 3.4;

[0020] Step S2: Add 1 g of metallic lithium and 10 g of polyalkylene oxide to 100 g of carbon tetrachloride organic solvent, filter, and vacuum dry at 80 °C for 24 h to obtain a lithium supplement agent;

[0021] Step S3: Add 100 g of graphite precursor material, 0.5 g of lithium supplement agent, and 1 g of carboxyethyl cellulose to a ball mill and mix evenly, then raise the temperature to 300 °C for pre-carbonization for 6 h for secondary granulation, and then raise the temperature to 800 °C under an argon inert atmosphere and introduce monochloromethane gas (flow rate 100 ml / min) for vapor deposition for 6 h to obtain the product.

[0022] Example 3

[0023] A preparation method of a negative electrode material for an energy storage lithium-ion battery, comprising the following steps:

[0024] Step S1: Crush the pitch coke with high isotropy to a particle size of D50 = 50 μm, then perform low-temperature graphitization at 2600 °C for 24 h, crush and classify, and remove the fine powder to obtain a graphite precursor material with a particle size distribution of D90 / D10 = 3.6;

[0025] Step S2: Add 5 g of metallic lithium and 30 g of polyalkylsiloxane to 100 g of cyclohexane organic solvent, filter, and dry in vacuum at 80 °C for 24 h to obtain a lithium supplement agent;

[0026] Step S3: Add 100 g of graphite precursor material, 2 g of lithium supplement agent, and 5 g of carboxyisopropyl cellulose to a ball mill and mix evenly. Then, heat up to 400 °C for pre-carbonization for 1 h for secondary granulation. After that, heat up to 1100 °C under an argon inert atmosphere and introduce dichloromethane carbon source gas (flow rate 100 ml / min) for vapor deposition for 1 h to obtain the product.

[0027] Comparative Example 1:

[0028] A preparation method of a negative electrode material for an energy storage lithium-ion battery includes the following steps:

[0029] Different from Example 1, no lithium supplement agent is added, and the others are the same as in Example 1.

[0030] Comparative Example 2:

[0031] A preparation method of a negative electrode material for an energy storage lithium-ion battery includes the following steps:

[0032] Different from Example 1, no carbon fluoride gas is added, and the others are the same as in Example 1.

[0033] Experimental Example 1: Physical and chemical property test

[0034] (1) SEM test

[0035] Perform SEM test on the graphite composite material prepared in Example 1, and the test results are as Figure 1 shown. It can be seen from the figure that the graphite composite material is a single-particle structure, and the particle size is between (10 - 15) μm.

[0036] (2) Powder conductivity test

[0037] Perform powder conductivity test on the graphite composite materials in Examples 1 - 3 and Comparative Examples 1 - 2. The test method of powder conductivity is as follows: Press the powder into a block structure on a powder compaction density meter under a pressure of 2 T, and then use a four-probe tester to perform powder conductivity test. The test results are shown in Table 1.

[0038] (3) Specific surface area, particle size, tapped density, OI value test

[0039] Test the conductivity, specific surface area, particle size, and tapped density according to GB / T 24533 - 2019 "Graphite-based negative electrode materials for lithium-ion batteries", and use XRD to test the OI value of the powder material. The test results are shown in Table 1.

[0040] Table 1 Test Results of Physical and Chemical Properties

[0041]

[0042] As can be seen from Table 1, compared with Example 1, in Comparative Example 1, the lithium supplement agent is not added, the OI value of its material is larger, and the isotropy is poor, resulting in a poor electronic conductivity of its material; compared with Example 1, in Comparative Example 2, the outer shell is not coated with carbon fluoride, resulting in a deviation in its electronic conductivity and a reduction in the tap density of its material.

[0043] Experimental Example 2: Coin Cell Test

[0044] The graphite materials in Examples 1-3 and Comparative Examples 1-2 were assembled into coin cells respectively. The assembly method was as follows: a binder, a conductive agent and a solvent were added to the negative electrode material, stirred to make a slurry, coated on a copper foil, and dried and rolled to obtain a negative electrode sheet. The binder used was LA132 binder, the conductive agent was SP, the negative electrode materials were the graphite composite materials in Examples 1-3 and Comparative Examples 1-2 respectively, and the solvent was secondary distilled water. The proportion of each component was: negative electrode material: SP: LA132: secondary distilled water = 95 g: 1 g: 4 g: 220 mL; the electrolyte was LiPF6 / EC+DEC (the concentration of LiPF6 was 1.2 mol / L, and the volume ratio of EC and DEC was 1:1), the metal lithium sheet was the counter electrode, and the separator was a polyethylene (PE), polypropylene (PP) or polyethylene-propylene (PEP) composite film. The assembly of the coin cell was carried out in a glove box filled with argon, and the electrochemical performance test was carried out on a Wuhan Blue Electric CT2001A battery tester. The charge-discharge voltage range was 0.005 V to 2.0 V, the charge-discharge rate was 0.1 C, and its rate performance (1C / 0.1C) was tested. The test results are shown in Table 2.

[0045] Table 2

[0046] Initial discharge capacity (mAh / g) Initial efficiency (%) Rate (1C / 0.1C) Example 1 361.3 97.1 93.4％ Example 2 360.2 96.8 93.0％ Example 3 359.4 97.8 93.7％ Comparative Example 1 353.2 93.2 90.5％ Comparative Example 2 355.2 96.2 91.4％

[0047] As can be seen from Table 2, the initial discharge capacity and the initial charge-discharge efficiency of the lithium-ion batteries using the composite negative electrode materials obtained in Examples 1-3 are significantly higher than those in Comparative Examples 1-2. The reason is that the graphite surface is coated with a lithium supplement agent, which releases lithium ions during the charge-discharge process, reduces the irreversible capacity of its material, and improves the initial efficiency and its rate performance.

[0048] Experimental Example 3: Soft Pack Battery Test

[0049] Using the graphite composite materials in Examples 1-3 and Comparative Examples 1-2 as the negative electrode materials, negative electrode sheets were prepared. Using ternary materials (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3Using O2 as the positive electrode, a LiPF6 solution (with EC + DEC as the solvent in a volume ratio of 1:1 and a LiPF6 concentration of 1.3 mol / L) as the electrolyte, and celegard 2400 as the separator, 5 Ah soft-pack batteries were prepared respectively. Then, the cycle performance of the soft-pack batteries was tested.

[0050] Cycle performance test conditions: charge-discharge current 1C / 1C, voltage range 2.8 - 4.2V, number of cycles 500 times. The test results are shown in Table 3.

[0051] Table 3

[0052]

[0053]

[0054] As can be seen from Table 3, the cycle performance of the graphite composites prepared in Examples 1 - 3, as the negative electrode of the soft-pack battery, is better than that of Comparative Examples 1 - 2. The reason is that in terms of the cycle performance at a 1C / 1C rate, relying on the lithium supplement agent on the graphite surface to supply sufficient lithium ions to improve the cycle performance, and at the same time, the carbon fluoride on the surface has the characteristic of stable structure, which improves the cycle performance, thereby increasing the service life of the soft-pack battery.

[0055] In summary, the graphite composite material prepared by the present invention has high conductivity and tap density, and the graphite composite material has a high first discharge capacity and first efficiency in the coin cell, and has good cycle performance in the soft-pack battery.

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a negative electrode material for an energy storage lithium-ion battery, comprising the following steps: Step S1: Select isotropic pitch coke and crush it to a particle size D50 = 10 - 50 μm, perform low-temperature graphitization at a temperature of 2000 - 2600 °C for 6 - 24 h, crush and classify, remove fine powder, and obtain a graphite precursor material with a particle size distribution D90 / D10 ≤ 4; Step S2: According to the mass ratio of lithium metal: polymer: organic solvent = 1 - 5: 10 - 30: 100, add lithium metal and polymer to the organic solvent, filter, and vacuum dry to obtain a lithium supplement agent; the polymer is one of polyalkylene carbonate, polyalkylene oxide, polyalkylsiloxane, polyacrylate alkyl ester, or polymethacrylate alkyl ester; Step S3: According to the mass ratio of graphite precursor material: lithium supplement agent: binder = 100: 0.5 - 2: 1 - 5, add the graphite precursor material, lithium supplement agent, and binder to a ball mill and mix evenly, raise the temperature to 300 - 400 °C for pre-carbonization for 1 - 6 h for secondary granulation, and then raise the temperature to 800 - 1100 °C in an inert atmosphere and introduce a carbon source gas for vapor deposition for 1 - 6 h to obtain; the carbon source gas is one of methyl chloride, dichloromethane, trifluoromethane, or difluoromethane.

2. The preparation method of the negative electrode material for an energy storage lithium-ion battery according to claim 1, wherein: The organic solvent described in Step S2 is one of N-methylpyrrolidone, carbon tetrachloride, or cyclohexane.

3. The preparation method of the negative electrode material used in a lithium-ion energy storage battery as described in claim 1, wherein: The binder described in Step S3 is one of carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, carboxyisopropyl cellulose, sodium nitrate cellulose, or carboxyalkyl cellulose sodium.

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