Positive electrode lithium supplementing material and preparation method and application thereof

Abstract

The invention discloses a positive electrode lithium supplementing material and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The invention discloses a preparation method of a positive electrode lithium supplementing material. The preparation method comprises the following steps: S1, dispersing lithium oxide in a first organic solvent to obtain lithium oxide slurry; s2, dispersing a graphene material in a second organic solvent to obtain a coating suspension; s3, uniformly mixing the coating suspension and the lithium oxide slurry to form a mixed solution; and S4, drying the mixed solution, and sintering the dried mixed solution in an argon atmosphere to obtain the positive electrode lithium supplementing material. According to the preparation method of the positive electrode lithium supplementing material disclosed by the invention, the surface of the lithium oxide is coated with the graphene material, the coating layer can protect the lithium oxide from being influenced by moisture and CO2 in air, meanwhile, the conductivity of the positive electrode material is improved, and the initial charging specific capacity of a lithium ion battery is remarkably improved; and meanwhile, the method has the advantages of simple coating process, low cost and high economic benefit.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium replenishment material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as one of the most promising high-energy-density storage devices, possess advantages such as high energy density, long cycle life, high safety, and environmental friendliness. Therefore, they are widely used in electronic products, electric vehicles, aerospace, and large-scale energy storage power stations. With the rapid development of new energy vehicles and the increase in driving range, even higher demands are being placed on the energy density of lithium-ion batteries.

[0003] To improve the energy density of lithium-ion batteries, lithium replenishment at the positive or negative electrode is an effective method. Compared to negative electrode lithium replenishment, positive electrode lithium replenishment is simpler, has lower requirements for equipment and environment, is safer to use, and is relatively cheaper. Lithium oxide, as a positive electrode lithium replenishment additive, theoretically has a high specific capacity, but its chemical reactivity means it easily absorbs moisture and CO2 from the air, deteriorating into LiOH and Li2CO3. This results in lower specific capacity and poor lithium replenishment effect on the positive electrode; furthermore, it causes side reactions with the electrolyte, leading to severe gas production and affecting lithium-ion battery performance. Therefore, lithium oxide coating is necessary, and several patents have explored this approach.

[0004] Patent document CN 117038938A discloses a positive electrode lithium supplement agent, its preparation method, and its application. The positive electrode lithium supplement agent includes lithium oxide and a coating layer, wherein the coating layer is a dibenzo-18-crown ether-6 derivative, coated on the surface of the lithium oxide. The dibenzo-18-crown ether-6 derivative coating layer isolates carbon dioxide and moisture in the air. The preparation method of the dibenzo-18-crown ether-6 derivative is as follows: dibenzo-18-crown ether-6 and phenylbutanol are added sequentially to polyphosphoric acid, the temperature is raised to 70-80℃, and the reaction is carried out for 6-8 hours. After the reaction is completed, the temperature is naturally cooled to room temperature, water is slowly added dropwise to the reaction solution, and after stirring for 15-20 minutes, dichloromethane is added for extraction. The organic phase is first washed 2-3 times with 20-30% sodium hydroxide solution, then washed with distilled water until neutral, concentrated under reduced pressure to obtain a crude product, and recrystallized from toluene and n-heptane to obtain the final product.

[0005] Patent document CN 114927779A discloses a positive electrode lithium supplement additive, its preparation method, and its application. The positive electrode lithium supplement additive is a porous material with a core-shell structure. The core material is submicron-sized lithium oxide, and the shell material is nano-sized carbon nanotubes. Nitrogen gas and lithium nitride are adsorbed in the voids between the core and shell structures and in the interlayer of the carbon nanotubes. The preparation method of the positive electrode lithium supplement additive includes the following steps: 1) Mixing nano-sized carbon nanotubes, a polar organic solvent, a dispersant, and a non-polar organic solvent, ball milling, then adding micron-sized lithium carbonate, continuing ball milling, and drying to obtain a dried mixture; 2) Calcination of the dried mixture under a high-pressure nitrogen atmosphere, wherein the nitrogen pressure is not less than 70 kPa, to obtain the positive electrode lithium supplement additive.

[0006] Existing technologies have limitations in terms of complex coating methods, high costs, and residues that may lead to side reactions and affect the performance of lithium-ion batteries. They also have limitations in improving the capacity and first charge-discharge efficiency of lithium-ion rechargeable batteries. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention aims to provide a method for preparing a positive electrode lithium replenishment material that is simple to coat, low in cost, and leaves no coating residue; another objective of the present invention is to provide a positive electrode lithium replenishment material with no coating residue and better conductivity; yet another objective of the present invention is to provide a lithium-ion battery with a higher specific capacity during the first charge.

[0008] This invention discloses a method for preparing a positive electrode lithium replenishment material, comprising the following steps:

[0009] S1: Lithium oxide is dispersed in a first organic solvent to obtain a lithium oxide slurry;

[0010] S2: Disperse graphene-like materials in a second organic solvent to obtain a coated suspension;

[0011] S3: Mix the coating suspension and the lithium oxide slurry evenly to form a mixture;

[0012] S4: Dry the mixture and then sinter it in an argon atmosphere to obtain a positive electrode lithium replenishment material.

[0013] The first organic solvent is selected from at least one of n-hexane, n-pentane, cyclohexane, benzene, toluene, xylene, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0014] The second organic solvent is selected from at least one of dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone.

[0015] Graphene-based materials include at least one of graphene, graphene oxide, and reduced graphene oxide.

[0016] Graphene is a two-dimensional material composed of carbon atoms, possessing excellent electrical, thermal, and mechanical properties. Graphene oxide is the product of graphene oxidation, rich in surface functional groups and exhibiting high catalytic activity. Reduced graphene oxide is produced by reducing graphene oxide, losing functional groups and thus becoming stable.

[0017] Sintering the dried mixture helps the raw material particles bond together, improving the bonding between graphene-like materials and lithium oxide.

[0018] Furthermore, the lithium oxide has a particle size D50 of less than 1 μm; the first organic solvent includes N-methylpyrrolidone.

[0019] Furthermore, the mass ratio of lithium oxide to the first organic solvent in the lithium oxide slurry is (4-6):45.

[0020] Furthermore, in step S2, the graphene-like material includes reduced graphene; the second organic solvent includes dimethylformamide.

[0021] Using reduced graphene and dimethylformamide can achieve better first-week charge capacity.

[0022] Furthermore, in step S2, the mass percentage of the graphene-like material in the coating suspension is 1-3%.

[0023] Furthermore, in step S3, the mass ratio of the coating suspension to the lithium oxide slurry is (2-3):25.

[0024] Furthermore, in step S4, the mixture is dried under vacuum to remove the first organic solvent and the second organic solvent; after drying, the mixture is sintered in an argon atmosphere at a temperature of 450-550°C for 2-4 hours.

[0025] Sintering the dried mixture helps the raw material particles bond together, improving the bonding between graphene-like materials and lithium oxide.

[0026] The present invention also discloses a positive electrode lithium replenishment material, which is prepared by the preparation method described above.

[0027] The present invention also discloses a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises the positive electrode lithium replenishment material as described above.

[0028] Furthermore, the positive electrode sheet also includes Co3O4 and conductive carbon black; the mass ratio of the positive electrode lithium replenishment material, the mass of Co3O4 and the mass of conductive carbon black in the positive electrode sheet is (4-5): (4-5):1.

[0029] Co3O4 is a catalyst used to catalyze the decomposition of lithium oxide, and conductive carbon black is added to improve conductivity.

[0030] This invention discloses a method for preparing a positive electrode lithium replenishment material, which involves coating the surface of lithium oxide with graphene-like materials. The coating layer can protect lithium oxide from the effects of moisture and CO2 in the air, while improving the conductivity of the positive electrode material and significantly increasing the first charge specific capacity of the lithium-ion battery. It also has the advantages of simple coating process, low cost and high economic benefits. Attached Figure Description

[0031] Figure 1 This is a SEM image of the positive electrode lithium replenishment material prepared in Example 1 of this invention. Detailed Implementation

[0032] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] Preparation of cathode lithium supplementation materials:

[0035] The preparation of S1 lithium oxide slurry involves adding 10g of Li2O to 90g of N-methylpyrrolidone solvent and ultrasonically dispersing for 2 hours (ultrasonic power 900W, frequency 40kHz) to obtain lithium oxide slurry. The dispersed Li2O particle size D50 reaches less than 1μm.

[0036] S2 prepares the coating suspension by adding the corresponding graphene materials in the second organic solvent according to Table 1 and ultrasonically dispersing for 2 hours to obtain the coating suspension with the corresponding mass fraction of graphene materials.

[0037] S3. Prepare a mixture by taking 10g of the coated suspension obtained in step S2 and mixing it with the lithium oxide slurry obtained in step S1, and then ultrasonically dispersing it for 2 hours.

[0038] S4 The mixed solution is then vacuum dried to control the water content to below 50 ppm, and then sintered at 500°C for 3 hours in an argon atmosphere to obtain the positive electrode lithium replenishment material.

[0039] The positive electrode lithium replenishment material obtained in Example 1 was examined by scanning electron microscopy, and the results are as follows: Figure 1As shown, the lithium oxide particles themselves are smooth, but the surface of the lithium oxide particles is relatively rough after coating, which proves that a coating layer is formed on the surface of the lithium oxide particles.

[0040] Table 1. Composition of the coated suspensions in Examples 1-12

[0041] serial number Graphene-like materials Second organic solvent The mass fraction of graphene-based materials Example 1 graphene dimethylformamide 1% Example 2 graphene dimethylformamide 2% Example 3 graphene dimethylformamide 3% Example 4 Graphene oxide dimethylformamide 1% Example 5 Graphene oxide dimethylformamide 2% Example 6 Graphene oxide dimethylformamide 3% Example 7 Reduced graphene oxide dimethylformamide 1% Example 8 Reduced graphene oxide dimethylformamide 2% Example 9 Reduced graphene oxide dimethylformamide 3% Example 10 Reduced graphene oxide Dimethyl sulfoxide 1% Example 11 Reduced graphene oxide Dimethyl sulfoxide 2% Example 12 Reduced graphene oxide Dimethyl sulfoxide 3%

[0042] Example 2-12

[0043] The differences between Examples 2-12 and Example 1 are: the graphene-based material used, the second organic solvent, and the mass fraction of graphene-based material in the coating suspension. The specific differences are shown in Table 1.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 1 is that the positive electrode lithium replenishment material is uncoated lithium oxide.

[0046] Comparative Example 2

[0047] 0.125g of carbon nanotubes and 10g of lithium carbonate were added to 100g of N-methylpyrrolidone. The mixture was ball-milled using a high-energy ball mill for 5 hours to ensure thorough mixing. The mixture was then dried in a 100 °C drying oven for 10 hours. The mixture was then placed in a tube furnace and calcined under an argon atmosphere at 1500 °C for 10 hours. Finally, the mixture was pulverized, ground, and sieved to obtain carbon nanotube-coated lithium oxide.

[0048] Test the performance of the prepared lithium supplement material:

[0049] 1. Preparation of positive electrode sheet

[0050] 4.5g of the lithium-supplementing material obtained in the examples and comparative examples were added sequentially to 40g of N-methylpyrrolidone solvent, 4.5g of Co3O4 catalyst, and 1g of conductive carbon black. The mixture was stirred thoroughly and then coated onto the surface of aluminum foil with a coating density of 14g / m². 2 (Single-sided, based on the mass of solid components excluding solvent), then dried and cold-pressed to complete the preparation of the positive electrode sheet.

[0051] 2. Electrolyte preparation

[0052] In an argon atmosphere glove box with a water content of <10ppm and an oxygen content of <10ppm, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate are mixed at mass percentages of 20%, 30%, 40%, and 10%, respectively, to obtain a mixed organic solvent. Then, fully dried lithium hexafluorophosphate is dissolved in the above mixed organic solvent at a concentration of 1 mol / L. The additive is vinylene carbonate, accounting for 1% of the electrolyte mass percentage. After stirring evenly, the electrolyte is obtained.

[0053] 3. Prepare the diaphragm

[0054] A porous polyethylene membrane coated with alumina ceramic on both sides is used as the diaphragm.

[0055] 4. Assemble into a battery

[0056] The positive electrode sheet is cut into 12 mm diameter discs. The positive electrode sheet, separator, and lithium metal sheet (0.6 mm thick, 99.9% purity) are stacked in sequence, with the separator in the middle to provide isolation, to assemble a coin cell. The electrolyte amount added to each coin cell is 150 μL.

[0057] At 25°C, the assembled battery was charged at a constant current of 0.1C to a voltage of 4.1V, and then charged at a constant current of 0.01C to a voltage of 4.35V. This was the first charging process. The electrode conductivity and the specific capacity of the lithium-ion battery at 25°C during the first charge of Examples 1-12 and Comparative Examples 1-2 were tested respectively. The test results are shown in Table 2.

[0058] Table 2 shows the performance test results of the embodiments and comparative examples.

[0059] serial number Electrode conductivity S / cm First week charging capacity (mAh / g) Electrode specific capacity (mAh / g) during the first week of charging after being placed at 10% humidity for 3 days Example 1 0.0125 1427.8 489.3 Example 2 0.0131 1432.3 506.8 Example 3 0.0134 1435.5 513.6 Example 4 0.0120 1406.2 526.7 Example 5 0.0128 1410.4 540.6 Example 6 0.0131 1413.7 547.5 Example 7 0.0130 1452.1 553.0 Example 8 0.0138 1465.6 572.4 Example 9 0.0142 1470.9 578.2 Example 10 0.0127 1442.3 542.0 Example 11 0.0130 1456.8 564.8 Example 12 0.0134 1461.2 570.6 Comparative Example 1 0.0110 1385.7 402.0 Comparative Example 2 0.0118 1402.3 476.4

[0060] As shown in Table 2, the electrode conductivity, first charge specific capacity, and first charge specific capacity of the electrodes in Examples 1 to 3 after being placed in an environment with 10% humidity for 3 days were significantly better than those in Comparative Example 1. It can be seen that by coating lithium oxide, the stability of the pre-lithiated cathode in air can be significantly improved and the conductivity can be improved, thereby effectively increasing the first charge specific capacity. Moreover, the higher the proportion of coating, the higher the first charge specific capacity.

[0061] The electrode conductivity and initial charge specific capacity of Examples 4 to 6 are inferior to those of Examples 1 to 3. However, the initial charge specific capacity of the electrode after being placed in an environment with 10% humidity for 3 days is significantly better than that of Examples 1 to 3. This is because the surface of graphene oxide obtained after the graphene material oxidation treatment contains a large number of functional groups, which makes it have better electrochemical activity and stability. However, too many functional groups will hinder the transmission of electrons and reduce the conductivity of the material.

[0062] The electrode conductivity, initial charge specific capacity, and initial charge specific capacity of the electrodes in Examples 7 to 9 after being placed in an environment with 10% humidity for 3 days were significantly better than those in Examples 1 to 6. This is because the reduced graphene oxide obtained by the reduction treatment of graphene oxide can provide higher conductivity and stability, making the reduced graphene oxide have great application potential in electrode materials.

[0063] The electrode conductivity, initial charge specific capacity, and initial charge specific capacity of the electrodes in Examples 10 to 12 after being placed in an environment with 10% humidity for 3 days were all lower than those in Examples 7 to 9. This is because the solvent has strong polarity, which may destroy the structure of the reduced graphene oxide, introduce too many defects, and affect conductivity and stability.

[0064] In Comparative Example 1, since the lithium oxide was not coated, it could not isolate moisture and CO2 in the air, causing some of the lithium oxide to react with moisture and CO2 in the air and become inactive, which had a certain impact on the specific capacity of the battery during the first charge.

[0065] In Comparative Example 2, the electrode conductivity and initial charge specific capacity were lower than those in Examples 1 to 12. This is because the carbon nanotubes in Comparative Example 2 are one-dimensional hollow tubular structures that construct a conductive network through "line-point" contact, requiring a higher addition amount to achieve the desired effect. In contrast, the graphene-like materials in the examples are two-dimensional sheet structures with a large specific surface area (approximately 400-600 m² / g), which can form "surface-point" contact with the active material. They have a low conductivity threshold, and a small amount can significantly improve conductivity, making them particularly suitable for batteries with high rate performance requirements.

[0066] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a positive electrode lithium replenishment material, characterized in that, Includes the following steps: S1: Lithium oxide is dispersed in a first organic solvent to obtain a lithium oxide slurry; S2: Disperse graphene-like materials in a second organic solvent to obtain a coated suspension; S3: Mix the coating suspension and the lithium oxide slurry evenly to form a mixture; S4: Dry the mixture and then sinter it in an argon atmosphere to obtain a positive electrode lithium replenishment material.

2. The method for preparing a positive electrode lithium replenishment material according to claim 1, characterized in that, In step S1, the particle size D50 of the lithium oxide is less than 1 μm; the first organic solvent includes N-methylpyrrolidone.

3. The method for preparing a positive electrode lithium replenishment material according to claim 2, characterized in that, The mass ratio of lithium oxide to the first organic solvent in the lithium oxide slurry is 4-6:

45.

4. The method for preparing a positive electrode lithium replenishment material according to claim 1, characterized in that, In step S2, the graphene-like material includes reduced graphene; the second organic solvent includes dimethylformamide.

5. The method for preparing a positive electrode lithium replenishment material according to claim 1, characterized in that, In step S2, the mass percentage of the graphene-like material in the coating suspension is 1-3%.

6. The method for preparing a positive electrode lithium replenishment material according to claim 1, characterized in that, In step S3, the mass ratio of the coating suspension to the lithium oxide slurry is 2-3:

25.

7. The method for preparing a positive electrode lithium replenishment material according to claim 1, characterized in that, In step S4, the mixture is dried under vacuum to remove the first organic solvent and the second organic solvent; after drying, the mixture is placed in an argon atmosphere and sintered at 450-550°C for 2-4 hours.

8. A positive electrode lithium replenishment material, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode includes the positive electrode lithium replenishment material as described in claim 8.

10. A lithium-ion battery according to claim 1, characterized in that, The positive electrode sheet also includes Co3O4 and conductive carbon black; the mass ratio of the positive electrode lithium replenishment material, the mass of Co3O4 and the mass of conductive carbon black in the positive electrode sheet is 4-5:4-5:1.

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