Nanoscale Li2C2O4 positive electrode lithium supplement agent and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly discloses a nanoscale Li2C2O4 positive electrode lithium supplement agent and a preparation method and application thereof. The preparation method comprises the following steps: mixing Li2C2O4 with a solvent, and uniformly stirring to obtain a mixed solution A; adding a conductive skeleton into the mixed solution A, and uniformly stirring to obtain a mixed solution B; adding a dispersing agent into the mixed solution B, and uniformly stirring to obtain a mixed solution C; and transferring the mixed solution C into a hydrothermal reaction kettle, heating to a certain temperature, preserving heat for 2 hours, cooling to room temperature, carrying out suction filtration, and drying to obtain the nanoscale Li2C2O4 positive electrode lithium supplement agent. The invention discloses a nanoscale Li2C2O4 positive electrode lithium supplement agent and a preparation method and application thereof.The nanoscale Li2C2O4 positive electrode lithium supplement agent is low in decomposition voltage platform, high in capacity release rate, good in air stability and capable of providing sufficient reaction sites in the electrochemical reaction process and shortening the ion transmission path, and the method is simple in technological process, low in cost and suitable for industrial production. And the method has remarkable industrial benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a nano-scale Li 2 C 2 O 4 positive electrode lithium supplement agent and its preparation method and application. Background Art

[0002] With the increasing demand for high energy density lithium-ion batteries, silicon-based anode materials have become a research hotspot for lithium-ion battery anode materials due to their high specific capacity (3579 mAh / g), low working potential (0.4 V vs. Li / Li + ) and high cost-effectiveness. However, silicon-based materials will undergo huge volume expansion (300%-400%) during charge and discharge, resulting in the rupture and continuous regrowth of the solid electrolyte interface (SEI), consuming a large amount of active lithium ions, thereby reducing the initial Coulomb efficiency (ICE) of the battery and shortening the cycle life. In addition, the volume expansion of the silicon-based anode will also damage the electrode structure, causing the active material to fall off from the current collector, further deteriorating the battery performance.

[0003] To solve these problems, researchers have carried out various modification strategies, including nanostructure design, surface engineering, composite material preparation, etc., but these methods can only partially alleviate the volume expansion problem. As an effective solution, prelithiation technology can supplement the lithium ions consumed by silicon-based anodes during the first charge and discharge, thereby improving the initial Coulomb efficiency and cycle life of the battery. However, there are many challenges in the negative electrode prelithiation technology, such as incompatibility with existing manufacturing processes, difficulty in controlling lithium foil prelithiation, and safety hazards caused by high chemical activity, which limit its large-scale application. The positive electrode prelithiation technology has received more and more attention due to its high compatibility with commercial lithium-ion battery manufacturing processes, especially its seamless integration with the positive electrode slurry preparation process. Currently reported positive electrode prelithiation materials include composites of metals and binary lithium-rich compounds, binary lithium compounds, and ternary lithium-rich compounds, etc., but these materials have problems such as by-product generation, poor air stability, and affecting the slurry adhesiveness. Lithium oxalate (Li 2 C 2 O 4 ) as a positive electrode lithium supplement material has a high theoretical capacity, low cost, and good air stability, showing good application prospects. However, its inherent low electronic conductivity and slow decomposition kinetics limit its further application. Although introducing oxide dopants (such as NiO, Mo 2 C) can improve the kinetic performance of Li 2 C 2 O 4 , these metal catalysts will reduce the energy density and cycle life of the full battery. Summary of the Invention

[0004] The present invention aims to provide a nano-level Li 2 C 2 O 4 positive electrode lithium supplement and its preparation method and application. This nano-level Li 2 C 2 O 4 positive electrode lithium supplement has a low decomposition voltage platform, a high capacity release rate, good air stability, can provide sufficient reaction sites during the electrochemical reaction process, and shorten the ion transport path.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of a nano-level Li 2 C 2 O 4 positive electrode lithium supplement, comprising the following steps:

[0007] S1. Mix Li 2 C 2 O 4 with a solvent, stir evenly to obtain a mixed solution A;

[0008] S2. Add a conductive framework to the mixed solution A obtained in S1, stir evenly to obtain a mixed solution B;

[0009] S3. Add a dispersant to the mixed solution B obtained in S2, stir evenly to obtain a mixed solution C;

[0010] S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reaction kettle, heat to a certain temperature, keep warm for 2 h, cool to room temperature, filter by suction, and dry to obtain the nano-level Li 2 C 2 O 4 positive electrode lithium supplement.

[0011] Preferably, in S1, the mass ratio of Li 2 C 2 O 4 to the solvent is 1-50:1-100; the solvent is one or two of pure water or absolute ethanol.

[0012] Preferably, in S1, mix Li 2 C 2 O 4 with the solvent and stir evenly at 60-90 °C; the stirring speed is 500-1000 rpm, and the stirring time is 1-10 h.

[0013] Preferably, in S2, the mass ratio of the mixed solution A to the conductive framework is 1-100:1-50; the conductive framework is one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphite flakes.

[0014] Preferably, in S2, a conductive framework is added to the mixed solution A obtained in S1, and the mixture is stirred evenly at 60-90 °C; the stirring speed is 500-1000 rpm, and the stirring time is 1-10 h.

[0015] Preferably, in S3, the mass ratio of the mixed solution B to the dispersant is 1-100:1-10; the dispersant is one or more of cetyltrimethylammonium bromide, polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate, and polyvinyl alcohol.

[0016] Preferably, in S3, a dispersant is added to the mixed solution B obtained in S2, and the mixture is stirred evenly at 60-90 °C; the stirring speed is 500-1000 rpm, and the stirring time is 1-10 h.

[0017] Preferably, in S4, the mixed solution C obtained in S3 is transferred to a hydrothermal reaction kettle, heated at a heating rate of 5 °C / min to 150 °C, held for 2 h, cooled to room temperature, filtered by suction, and dried at 80 °C for 1-10 h to obtain a nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent.

[0018] The present invention also provides the nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent prepared by the preparation method.

[0019] The present invention also provides the application of the nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent or the nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent prepared by the preparation method in a lithium-ion battery.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The present invention uses a one-step hydrothermal method to prepare a nanoscale grain size of Li 2 C 2 O 4 positive electrode lithium supplement agent. Through hydrothermal treatment, the grain size of Li 2 C 2 O 4The grain size. Under hydrothermal conditions, high temperature and high pressure accelerate the diffusion of Li 2 C 2 O 4 molecules in the solvent, especially having a significant dissolving effect on crystal defects and high surface energy sites. After forming a supersaturated solution, Li 2 C 2 O 4 molecules move violently, the collision frequency increases, and it promotes the rapid formation of lithium oxalate crystal nuclei. The formation of a large number of crystal nuclei consumes Li 2 C 2 O 4 in the solution, reduces the concentration for grain growth, thereby inhibiting grain growth, and finally obtaining nanoscale Li 2 C 2 O 4 grains. These nanograins provide sufficient reaction sites in the electrochemical reaction, shorten the ion transport path, and after being compounded with carbon nanotubes, significantly improve the decomposition kinetic performance of Li 2 C 2 O 4 , increasing the release capacity of commercial Li 2 C 2 O 4 from 115 mAh / g to more than 512 mAh / g, and reducing the decomposition voltage from 4.7 V to 4.2 V. This method is simple to operate, low in cost, suitable for industrial production, and the prepared nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent can significantly improve the first-cycle Coulombic efficiency and cycle life of lithium-ion batteries, having significant technical effects and cost advantages.

[0022] Next, through the drawings and embodiments, the technical solutions of the present invention will be further described in detail. Description of the Drawings

[0023] Figure 1 The electron microscope scanning image of the nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent provided in Example 1, the scale bar is 100 nm;

[0024] Figure 2 The electron microscope scanning image of the nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent provided in Example 2, the scale bar is 100 nm;

[0025] Figure 3 The electron microscope scanning image of the nanoscale Li 2 C 2 O 4Electron microscopy scan of the positive electrode lithium supplement, scale bar is 100 nm;

[0026] Figure 4 The nanoscale Li provided for Example 4 2 C 2 O 4 Electron microscopy scan of the positive electrode lithium supplement, scale bar is 100 nm;

[0027] Figure 5 The nanoscale Li provided for Example 5 2 C 2 O 4 Electron microscopy scan of the positive electrode lithium supplement, scale bar is 100 nm;

[0028] Figure 6 The nanoscale Li provided for Examples 1 - 3 2 C 2 O 4 Grain size statistical chart of the positive electrode lithium supplement;

[0029] Figure 7 The nanoscale Li provided for Examples 1 - 3 2 C 2 O 4 Results of the delithiation voltage plateau of the positive electrode lithium supplement;

[0030] Figure 8 The commercial Li provided for Comparative Example 1 2 C 2 O 4 Delithiation voltage plateau of the positive electrode lithium supplement. Detailed implementation manners

[0031] The technical solution of the present invention will be further described below through the accompanying drawings and examples.

[0032] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the field to which the present invention belongs.

[0033] In the present invention, unless otherwise specified, other test materials and instrument equipment are all conventional test materials in the art and can be obtained through commercial channels.

[0034] Example 1

[0035] A nanoscale Li 2 C 2 O 4 Positive electrode lithium supplement, the preparation method includes the following steps:

[0036] S1. Mix Li 2 C 2 O 4Mix with pure water at a mass ratio of 1:9, stir at a speed of 500 r / min at 90 °C for 2 h to obtain mixed solution A;

[0037] S2. Add single-walled carbon nanotubes to the mixed solution A obtained in S1. The mass ratio of the mixed solution A to the single-walled carbon nanotubes is 10:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain mixed solution B;

[0038] S3. Add polyvinylpyrrolidone to the mixed solution B obtained in S2. The mass ratio of the mixed solution B to the polyvinylpyrrolidone is 20:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain mixed solution C;

[0039] S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reaction kettle, heat at a heating rate of 5 °C / min, keep warm at 150 °C for 2 h, cool to room temperature, filter by suction, and dry at 80 °C for 3 h to obtain nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent.

[0040] Example 2

[0041] A nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent, the preparation method includes the following steps:

[0042] S1. Mix Li 2 C 2 O 4 with pure water at a mass ratio of 3:7, stir at a speed of 500 r / min at 90 °C for 2 h to obtain mixed solution A;

[0043] S2. Add single-walled carbon nanotubes to the mixed solution A obtained in S1. The mass ratio of the mixed solution A to the single-walled carbon nanotubes is 10:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain mixed solution B;

[0044] S3. Add polyvinylpyrrolidone to the mixed solution B obtained in S2. The mass ratio of the mixed solution B to the polyvinylpyrrolidone is 20:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain mixed solution C;

[0045] S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reaction kettle, heat at a heating rate of 5 °C / min, keep warm at 150 °C for 2 h, cool to room temperature, filter by suction, and dry at 80 °C for 3 h to obtain nanoscale Li 2 C 2 O4 Positive electrode lithium supplement agent

[0046] Example 3

[0047] A nanoscale Li 2 C 2 O 4 Positive electrode lithium supplement agent, the preparation method includes the following steps:

[0048] S1. Mix Li 2 C 2 O 4 with pure water at a mass ratio of 1:1, stir at a stirring speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution A;

[0049] S2. Add single-walled carbon nanotubes to the mixed solution A obtained in S1, where the mass ratio of the mixed solution A to the single-walled carbon nanotubes is 10:1, stir at a stirring speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution B;

[0050] S3. Add polyvinylpyrrolidone to the mixed solution B obtained in S2, where the mass ratio of the mixed solution B to the polyvinylpyrrolidone is 20:1, stir at a stirring speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution C;

[0051] S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reaction kettle, heat at a heating rate of 5 °C / min, keep warm at 150 °C for 2 h, cool to room temperature, filter by suction, and dry at 80 °C for 3 h to obtain the nanoscale Li 2 C 2 O 4 Positive electrode lithium supplement agent.

[0052] Example 4

[0053] A nanoscale Li 2 C 2 O 4 Positive electrode lithium supplement agent, the preparation method includes the following steps:

[0054] S1. Mix Li 2 C 2 O 4 with pure water at a mass ratio of 1:9, stir at a stirring speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution A;

[0055] S2. Add graphite flakes to the mixed solution A obtained in S1, where the mass ratio of the mixed solution A to the graphite flakes is 10:1, stir at a stirring speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution B;

[0056] S3. Add polyvinylpyrrolidone to the mixed solution B obtained in S2. The mass ratio of the mixed solution B to polyvinylpyrrolidone is 20:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution C;

[0057] S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reactor, heat it at a heating rate of 5 °C / min, keep it at 150 °C for 2 h after heating, cool it to room temperature, carry out suction filtration, and dry it at 80 °C for 3 h to obtain a nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent.

[0058] Example 5

[0059] A nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent, and the preparation method includes the following steps:

[0060] S1. Mix Li 2 C 2 O 4 with pure water at a mass ratio of 1:9, stir at a speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution A;

[0061] S2. Add single-walled carbon nanotubes to the mixed solution A obtained in S1. The mass ratio of the mixed solution A to single-walled carbon nanotubes is 10:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution B;

[0062] S3. Add cetyltrimethylammonium bromide to the mixed solution B obtained in S2. The mass ratio of the mixed solution B to cetyltrimethylammonium bromide is 20:1. Stir at a speed of 500 r / min at 90 °C for 2 h to obtain a mixed solution C;

[0063] S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reactor, heat it at a heating rate of 5 °C / min, keep it at 150 °C for 2 h after heating, cool it to room temperature, carry out suction filtration, and dry it at 80 °C for 3 h to obtain a nanoscale Li 2 C 2 O 4 positive electrode lithium supplement agent.

[0064] Comparative Example 1

[0065] This comparative example uses commercial Li 2 C 2 O 4 as the positive electrode lithium supplement agent, and commercial Li 2 C 2 O 4It was purchased from Macklin Reagent Co., Ltd. in Shanghai.

[0066] The nano-scale Li 2 C 2 O 4 positive electrode lithium supplement agents provided in the above Examples 1-5 were verified through the following tests.

[0067] 1. The nano-scale Li 2 C 2 O 4 positive electrode lithium supplement agents provided in the above Examples 1-5 were subjected to electron microscopy scanning, and the results are as Figures 1 - 5 .

[0068] It can be seen from Figures 1 - 5 that as the content of lithium oxalate in the solution gradually increases and the amount of carbon nanotubes added to the solution remains unchanged, after hydrothermal treatment, the higher the content of lithium oxalate in the solution, the more lithium oxalate recrystallizes on the surface of the carbon nanotubes. As shown in Figure 3 the scanning electron microscopy, due to the excessive amount of lithium oxalate recrystallized on the surface of the carbon nanotubes, the carbon nanotubes agglomerate and stick together. It can be seen that the content of lithium oxalate in the solution has an important influence on the recrystallization process of lithium oxalate and the morphology of the lithium supplement agent. As shown in Figure 4 , when the content of lithium oxalate in the solution is constant and the conductive framework carbon nanotubes are replaced with graphite flakes, lithium oxalate can still recrystallize on the surface of the graphite flakes. It can be seen that the structure of the conductive framework does not affect the lithium oxalate recrystallization process. As shown in Figure 5 , when the dispersant polyvinylpyrrolidone in the solution is replaced with cetyltrimethylammonium bromide, lithium oxalate can still recrystallize on the surface of the carbon nanotubes. It can be seen that the type of dispersant in the solution does not affect the lithium oxalate recrystallization process.

[0069] 2. The grain sizes of the nano-scale Li 2 C 2 O 4 positive electrode lithium supplement agents provided in the above Examples 1-5 were measured. The measurement method is as follows: The prepared lithium supplement agent was subjected to X-ray diffraction testing, and the grain size of the sample can be calculated using the Scherrer formula.

[0070] Scherrer formula: Dhkl = kλ / βcosθ, where Dhkl is the grain diameter along the direction perpendicular to the crystal plane (hkl), k is the Scherrer constant (usually 0.89), λ is the wavelength of the incident X-ray (the Cuka wavelength is 0.15406 nm), θ is the Bragg diffraction angle (°), and β is the full width at half maximum of the diffraction peak (rad). The grain size calculation of specific samples is as shown in Figure 6 .

[0071] It can be seen from Figure 6It can be seen that when the mass ratio of lithium oxalate to pure water is 1:1, the grain size calculated by the Scherrer formula is 79.3. When the mass ratio of lithium oxalate to pure water is 3:7, the grain size calculated by the Scherrer formula is 75.1. When the mass ratio of lithium oxalate to pure water is 1:9, the grain size calculated by the Scherrer formula is 54.9. Thus, it can be known that when the content of lithium oxalate is too high,

[0072] Li 2 C 2 O 4 molecules in the solution move violently, the collision frequency increases, which promotes the rapid formation of lithium oxalate crystal nuclei. Since there are still a large number of Li 2 C 2 O 4 left in the solution after the formation of a large number of crystal nuclei, the concentration for grain growth is relatively high, which leads to continuous growth of the grains. Eventually, the Li 2 C 2 O 4 grain size is relatively large. When the concentration of Li 2 C 2 O 4 in the solution is relatively low, the large number of crystal nuclei formed consume Li 2 C 2 O 4 in the solution, reducing the concentration available for grain growth, thus inhibiting grain growth and finally obtaining Li 2 C 2 O 4 grains with a relatively small grain size.

[0073] 3. Perform delithiation voltage plateau tests on the nano-scale Li 2 C 2 O 4 cathode lithium supplement agent provided in Examples 1-5 and the commercial lithium oxalate provided in Comparative Example 1. The test method is as follows: Mix the prepared Li 2 C 2 O 4 cathode lithium supplement agent, acetylene black and PVDF in a mass ratio of 7:2:1 to obtain a mixed powder. Then add NMP and stir evenly to prepare a slurry (the mass ratio of the mixed powder to NMP is 1:1). Coat the uniformly mixed slurry evenly on an aluminum foil with a thickness of 9 μm. After drying at 110°C for 12 hours, cut the prepared electrode sheet into small round pieces with a diameter of φ1.2 cm. Then assemble the small round pieces into 2032 button cells for electrochemical charging tests. The test current is 0.01C (5.25 mA), and the results are as Figures 7 - 8 .

[0074] From Figure 7It can be seen that for the lithium oxalate cathode lithium supplement agent prepared after hydrothermal treatment, the de-lithiation voltage plateau is significantly lower than 5V, and the smaller the grain size of lithium oxalate, the lower the de-lithiation voltage plateau. This is because these smaller nano-grained lithium oxalate provide sufficient reaction sites in the electrochemical reaction, shorten the ion transport path, and significantly improve the decomposition kinetic performance of Li 2 C 2 O 4 , so the de-lithiation voltage plateau is significantly reduced.

[0075] It can be seen from Figure 8 that since commercial lithium oxalate has not undergone hydrothermal recrystallization treatment and has too large a grain size, resulting in insufficient reaction sites in the electrochemical reaction and a long ion transport path, the decomposition kinetic performance of Li 2 C 2 O 4 is poor, so the de-lithiation voltage plateau is relatively high (4.7V).

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a nano-scale Li2C2O4 positive electrode lithium supplement, characterized in that: The following steps are involved: S1. Mix Li2C2O4 and solvent and stir evenly to obtain a mixed solution A; S2, adding the conductive skeleton to the mixed solution A obtained in S1, stirring evenly, to obtain a mixed solution B; S3, adding a dispersant to the mixed solution B obtained in S2, stirring evenly, to obtain a mixed solution C; S4. Transfer the mixed solution C obtained in S3 to a hydrothermal reactor, heat it to a certain temperature and keep it warm for 2 hours, cool it to room temperature, filter it, and dry it to obtain a nano-scale Li2C2O4 positive electrode lithium supplement.

2. The preparation method according to claim 1, characterized in that: In S1, the mass ratio of Li2C2O4 to the solvent is 1-50:1-100; the solvent is one or both of pure water or anhydrous ethanol.

3. The preparation method according to claim 1, characterized in that: In S1, Li2C2O4 is mixed with a solvent and stirred evenly at 60-90°C; the stirring speed is 500-1000 rpm, and the stirring time is 1-10 h.

4. The preparation method according to claim 1, characterized in that: In S2, the mass ratio of the mixed solution A to the conductive skeleton is 1-100:1-50; the conductive skeleton is one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and graphite sheets.

5. The preparation method according to claim 1, characterized in that: In S2, the conductive skeleton is added to the mixed solution A obtained in S1, and stirred evenly at 60-90° C.; the stirring speed is 500-1000 rpm, and the stirring time is 1-10 h.

6. The preparation method according to claim 1, characterized in that: In S3, the mass ratio of the mixed solution B to the dispersant is 1-100:1-10; the dispersant is one or more of cetyltrimethylammonium bromide, polyvinyl pyrrolidone, polyethylene glycol, sodium lauryl sulfate, and polyvinyl alcohol.

7. The preparation method according to claim 1, characterized in that: In S3, a dispersant is added to the mixed solution B obtained in S2, and the mixture is stirred evenly at 60-90° C. The stirring speed is 500-1000 rpm, and the stirring time is 1-10 h.

8. The preparation method according to claim 1, characterized in that: In S4, the mixed solution C obtained in S3 is transferred to a hydrothermal reactor, heated to 150°C at a heating rate of 5°C / min, and then kept warm for 2 hours, cooled to room temperature, filtered, and dried at 80°C for 1-10 hours to obtain a nano-scale Li2C2O4 positive electrode lithium supplement.

9. The nanoscale Li2C2O4 positive electrode lithium supplement prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nanoscale Li2C2O4 positive electrode lithium replenisher as claimed in claim 9 or the nanoscale Li2C2O4 positive electrode lithium replenisher prepared by the preparation method according to any one of claims 1 to 8 in lithium ion batteries.

Images