Modified ternary positive electrode material, preparation method and application thereof

Abstract

The application provides a modified ternary positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing the ternary positive electrode material and water, and adjusting the pH to 11-12 to obtain a suspension; (2) mixing the suspension obtained in the step (1) and a phosphate to control the pH of a reaction solution to 11-12 to perform a reaction; and (3) performing spray pyrolysis on the obtained mixed solution to obtain the modified ternary positive electrode material. The application combines water washing and coating processes, is simple to operate, has a short process, has high industrial feasibility, and effectively reduces the production cost of ternary material modification and repair.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and relates to a modified ternary positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Surface modification treatment is an effective means to improve the cycle stability of the ternary positive electrode material. Coating some metal compounds, lithium salts or conductive carbon materials with appropriate thickness on the surface of the ternary material can isolate the direct contact between the active material and the electrolyte, reduce the occurrence of side reactions and inhibit the dissolution of transition metal ions.

[0003] CN110190254A discloses a preparation method of lithium phosphate coated lithium ion battery ternary positive electrode material, which comprises the following steps: (1) dissolving a phosphoric acid source in an organic solvent to form a solution, and the mass fraction of the phosphoric acid source in the solution is 0.05-0.8%; (2) adding lithium ion battery ternary positive electrode material to the solution in step (1), stirring for 5-120 minutes to make it uniformly dispersed, and then drying until the organic solvent is completely evaporated to obtain lithium phosphate coated lithium ion battery ternary positive electrode material.

[0004] As a good lithium ion conductor with stable electrochemical performance, lithium phosphate is selected as a commonly used coating agent for positive electrode materials. Traditional lithium phosphate coating methods include solid phase method and liquid phase method. The coating effect of the phase coating method is greatly influenced by the particle size of the coating material, and there is a problem of uneven coating layer. The liquid phase coating method generally selects an organic solvent such as ethanol as a dispersant. The organic solvent is flammable and relatively high in price, so that the method does not have advantages in cost and production safety.

[0005] During the preparation process of the ternary material, an excess of lithium salt is generally added to prevent lithium loss during the sintering process. Therefore, free lithium ions always exist on the surface of the material, which can easily react with H2O and CO2 in the air to generate basic substances LiOH and Li2CO3. The formation of surface residual alkali seriously hinders the performance of the ternary material itself, so it is necessary to perform water washing on the ternary material to reduce residual alkali.

[0006] CN114011795A discloses a lithium battery material water washing method and device. The method adds lithium battery material particulate material and water into a container, and then introduces gas into the bottom of the container. The gas forms bubbles in the water, and the bubbles are used to carry the material upwards. The material sinks under the action of its own gravity, so that the material is continuously tumbled and washed in the water.

[0007] The existing technology still has many problems in the control process of water washing to remove residual alkali. While ensuring that the residual alkali on the surface of the material is completely removed, the lithium ion inside the material cannot be prevented from being precipitated and lost, and the performance improvement of the ternary material is still very limited. SUMMARY

[0008] The application aims to provide a modified ternary positive electrode material, a preparation method and application thereof.

[0009] To achieve the above object, the application adopts the following technical scheme:

[0010] In the first aspect, the application provides a preparation method of a modified ternary positive electrode material, which comprises the following steps:

[0011] (1) mixing the ternary positive electrode material and water to obtain a suspension with a pH of 11-12;

[0012] (2) mixing the suspension obtained in step (1) and a phosphate to control the pH of the reaction solution to 11-12 for reaction;

[0013] (3) spray pyrolyzing the obtained mixed solution to obtain the modified ternary positive electrode material.

[0014] The ternary material and pure water are mixed and stirred to obtain a suspension, and the residual alkali on the surface of the ternary material is dissolved in the aqueous solution to form OH - In this process, lithium in the material may also be dissolved to form LiOH and Li2CO3, further contributing part of OH - The pH value of the ternary material dispersed in water is generally 10.0-12.5, and when there is residual alkali on the surface of the material, the pH value is generally 11.0-12.5, and after the water washing alkali removal process, the pH value can be reduced to below 11.0, but at this time, a small amount of lithium in the material has been dissolved, and the dissolved lithium forms new residual alkali in the drying process, which cannot completely remove the surface residual alkali, and also loses the internal active lithium, resulting in reduced battery performance, which is the biggest disadvantage of the water washing alkali removal process in industry.

[0015] The residual alkali component of the ternary material surface is utilized, the conventional water washing alkali removal process and the water phase coating process are combined, the pH of the water washing suspension is regulated to be between 11.0 and 12.0, the water washing degree can be controlled, the residual alkali on the material surface is reserved, the lithium dissolution in the material structure is inhibited, the residual alkali on the material surface after water washing can interact with the weak acid phosphate added to form a lithium phosphate coating layer on the ternary material surface in situ.

[0016] Preferably, the chemical formula of the ternary positive electrode material in step (1) is LiMO2, wherein M=Ni x Co y Mn z , 0 < x < 1, 0 < y < 1, 0 < z < 1.

[0017] Preferably, the Li / M ratio of the ternary positive electrode material is 1.02-1.20, for example, 1.02, 1.04, 1.1, 1.15 or 1.2, preferably 1.05-1.10.

[0018] Preferably, the solid content of the suspension in step (1) is 100-300 g / L, for example, 100 g / L, 150 g / L, 200 g / L, 250 g / L or 300 g / L.

[0019] Preferably, when the pH of the suspension is greater than 12.0, suction filtration is performed, and the filter cake is dispersed into an aqueous solution again, the water washing and suction filtration are repeated until the pH of the suspension is less than or equal to 12.0.

[0020] Preferably, the phosphate in step (2) includes any one or a combination of at least two of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate or phosphoric acid.

[0021] Preferably, the mass of the phosphate radical in the phosphate in step (2) is 0.1-10% of the mass of the ternary positive electrode material, for example, 0.1%, 0.5%, 1%, 2%, 8% or 10%, preferably 2-4%.

[0022] Preferably, the temperature of the spray pyrolysis in step (2) is 400-800℃, for example, 400℃, 500℃, 600℃, 700℃ or 800℃, preferably 500-600℃.

[0023] Preferably, the time of the spray pyrolysis is 5-20s, for example: 5s, 6s, 8s, 10s, 15s or 20s, etc.

[0024] Compared with the traditional filtering, drying and sintering steps, the spray pyrolysis method shortens the process flow and further avoids the loss of lithium phosphate during the filtration of the aqueous solution, so as to realize the accurate control of the content of the lithium phosphate coating layer.

[0025] In the second aspect, the application provides a modified ternary positive electrode material, which is prepared by the method of the first aspect, and the modified ternary positive electrode material comprises a ternary positive electrode material core and a lithium phosphate coating layer arranged on the surface of the ternary positive electrode material core.

[0026] The lithium phosphate coating layer can improve the surface and interface stability of the ternary material, avoid the generation of new residual alkali when the material is exposed to air in the subsequent process, and compared with the traditional oxide coating layer, the lithium phosphate as a good lithium ion conductor can not only block the contact between the ternary material and the electrolyte, but also reduce the interface electrochemical impedance between the ternary material and the electrolyte, so that the rate performance and cycle stability of the coated ternary material are significantly improved.

[0027] Preferably, the mass fraction of the lithium phosphate coating layer is 0.1-8% based on 100% of the mass of the modified ternary positive electrode material, for example: 0.1%, 0.5%, 1%, 2%, 6% or 8%, etc., preferably 1-3%.

[0028] In the third aspect, the application provides a positive electrode sheet, which comprises the modified ternary positive electrode material of the second aspect.

[0029] In the fourth aspect, the application provides a lithium ion battery, which comprises the positive electrode sheet of the third aspect.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] (1) In the preparation process of the modified ternary positive electrode material, the pH of the suspension is controlled to be 11.0-12.0, so that a small amount of residual alkali is left on the surface of the material, and in the subsequent steps, these residual alkalis are converted into a lithium phosphate layer structure, thereby inhibiting the further dissolution of lithium in the material. After adding the phosphate, the pH of the mixed solution is further controlled to be 11.0-12.0, at which time the phosphate reacts with the residual alkali on the surface of the material to generate lithium phosphate. By controlling the amount of phosphate added, the residual alkali can be completely removed, and at the same time, this lithium phosphate layer structure can also improve the surface and interface stability of the material, so as to avoid the generation of new residual alkali when the material is exposed to air in the subsequent process.

[0032] (2) The method is suitable for various ternary positive electrode materials, and can significantly improve the rate performance and cycle performance of the ternary positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a preparation process flow chart of the modified ternary positive electrode material according to Embodiment 1 of the present application.

[0034] Figure 2 is a battery performance comparison chart of the modified ternary material according to Embodiment 1 and Comparative Examples 1 and 2 of the present application. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations on the present application.

[0036] Embodiment 1

[0037] This embodiment provides a modified ternary positive electrode material, and a preparation process flow chart of the modified ternary positive electrode material is shown as follows: Figure 1 The preparation method of the modified ternary positive electrode material is as follows:

[0038] (1) The NCM811 positive electrode material and pure water are mixed and stirred to prepare a suspension, the solid-liquid ratio is 200 g / L, the pH of the suspension is 12.02, and the suspension is filtered and the filter cake is dispersed into an aqueous solution again, and the pH of the suspension is controlled to be 11.77;

[0039] (2) 3wt% (based on the amount of phosphate) of ammonium dihydrogen phosphate is added to the suspension of step (2) to obtain a mixed solution, and the pH of the mixed solution is controlled to be 11.35;

[0040] (3) The mixed solution of step (2) is sprayed into a pyrolysis furnace through an atomizer, and after staying at 650℃ for 5s, it is introduced into a dust removal equipment through an induced draft fan, and a modified ternary positive electrode material uniformly coated with 2.5wt% lithium phosphate is collected.

[0041] Embodiment 2

[0042] This embodiment provides a modified ternary positive electrode material, and the preparation method of the modified ternary positive electrode material is as follows:

[0043] (1) The NCM811 positive electrode material and pure water are mixed and stirred to prepare a suspension, the solid-liquid ratio is 200 g / L, the pH of the suspension is 12.10, and the suspension is filtered and the filter cake is dispersed into an aqueous solution again, and the pH of the suspension is controlled to be 11.89;

[0044] (2) Add 3wt% (in terms of the amount of phosphate) diammonium hydrogen phosphate to the suspension of step (2) to obtain a mixed solution, and control the pH of the mixed solution to be 11.58;

[0045] (3) Spray the mixed solution of step (2) into a pyrolysis furnace through an atomizer, and after staying at 650°C for 5s, introduce it into a dust removal device through an induced draft fan, and collect a modified ternary positive electrode material uniformly coated with 2.5wt% lithium phosphate.

[0046] Example 3

[0047] This example provides a modified ternary positive electrode material, and the preparation method of the modified ternary positive electrode material is as follows:

[0048] (1) Mix and stir NCM622 positive electrode material and pure water to obtain a suspension, the solid-liquid ratio is 200g / L, and the pH of the suspension is 11.75, without water washing and filtration;

[0049] (2) Add 2wt% (in terms of the amount of phosphate) lithium dihydrogen phosphate to the suspension of step (2) to obtain a mixed solution, and measure the pH of the mixed solution to be 11.56;

[0050] (3) Spray the mixed solution of step (2) into a pyrolysis furnace through an atomizer, and after staying at 550°C for 5s, introduce it into a dust removal device through an induced draft fan, and collect a modified ternary positive electrode material uniformly coated with 1.6wt% lithium phosphate.

[0051] Example 4

[0052] (1) Mix and stir NCM523 positive electrode material and pure water to obtain a suspension, the solid-liquid ratio is 200g / L, and the pH of the suspension is 11.50, without water washing and filtration;

[0053] (2) Add 2wt% (in terms of the amount of phosphate) lithium dihydrogen phosphate to the suspension of step (2) to obtain a mixed solution, and measure the pH of the mixed solution to be 11.38;

[0054] (3) Spray the mixed solution of step (2) into a pyrolysis furnace through an atomizer, and after staying at 550°C for 5s, introduce it into a dust removal device through an induced draft fan, and collect a modified ternary positive electrode material uniformly coated with 1.6wt% lithium phosphate.

[0055] Example 5

[0056] The difference between this example and Example 1 is only that the amount of added ammonium dihydrogen phosphate (in terms of the amount of phosphate) is 0.1% of the mass of the positive electrode material, and other conditions and parameters are the same as those of Example 1.

[0057] Example 6

[0058] The embodiment differs from Example 1 only in that the amount of ammonium dihydrogen phosphate (based on the amount of phosphate) added is 5% of the mass of the positive electrode material, and other conditions and parameters are exactly the same as in Example 1.

[0059] Comparative Example 1

[0060] The comparative example uses the NCM811 positive electrode material described in Example 1.

[0061] Comparative Example 2

[0062] The comparative example uses the NCM811 positive electrode material prepared by the method described in step (1) in Example 1, and is uniformly mixed with 2.5wt% lithium phosphate, sintered at 650°C for 5h to obtain a lithium phosphate-coated NCM811 material.

[0063] Comparative Example 3

[0064] The comparative example differs from Example 1 only in that the pH of the mixed solution is controlled to be 12.5, and other conditions and parameters are exactly the same as in Example 1.

[0065] Comparative Example 4

[0066] The comparative example differs from Example 1 only in that the pH of the mixed solution is controlled to be 10.5, and other conditions and parameters are exactly the same as in Example 1.

[0067] Performance test:

[0068] The ternary material prepared in the examples and comparative examples is mixed with conductive agent Super P and binder PVDF in a mass ratio of 8:1:1, and dissolved in N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry is scraped and dried on an aluminum foil, and then cut into φ14mm round pieces as the positive electrode, a lithium metal sheet as the negative electrode, a polyethylene film as the separator, and the solute of the electrolyte is 1M LiPF6, the solvent is a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1. The CR2016 button lithium ion battery is assembled by stacking and pressing in the order of negative electrode shell, negative electrode, electrolyte, separator, electrolyte, positive electrode, current collector and positive electrode shell.

[0069] The lithium ion battery prepared is subjected to electrochemical performance test, the test voltage is 3.0-4.3V, the initial discharge specific capacity and the initial coulombic efficiency are tested at 0.1C, the capacity retention rate after 100 cycles of charge-discharge is tested at 1C, and the test results are shown in Table 1:

[0070] Table 1

[0071]

[0072]

[0073] As can be seen from Table 1, it can be obtained from Examples 1-4 that the method described in the application is suitable for various ternary positive electrode materials, and can significantly improve the rate performance and cycle performance of the ternary positive electrode materials.

[0074] As can be obtained from the comparison between Example 1 and Examples 5-6, the amount of the phosphate added in the preparation process of the modified ternary positive electrode material will affect the performance of the modified ternary positive electrode material. If the amount of the phosphate (calculated by the mass of the phosphate radical) is controlled to be 2-4% of the ternary positive electrode material, the performance of the modified ternary positive electrode material is better. If the amount of the phosphate is too large, the content of the non-active substance is too high, which leads to a slight decrease in the specific discharge capacity of the material. If the amount of the phosphate is too small, it is not enough to form a stable lithium phosphate coating layer, and there is still part of residual alkali, which affects the performance of the material.

[0075] The battery performance comparison chart of the ternary materials described in Example 1 and Comparative Examples 1-2 is shown in FIG. 1. Figure 2 As can be obtained from the comparison between Example 1 and Comparative Example 1, the coating layer of the modified ternary positive electrode material prepared by the method described in the application can improve the surface interface stability of the ternary material, avoid the generation of new residual alkali in the subsequent exposure of the material to air, and compared with the traditional oxide coating layer, the lithium phosphate as a good lithium ion conductor can not only block the contact between the ternary material and the electrolyte, but also reduce the interfacial electrochemical impedance between the ternary material and the electrolyte, so that the rate performance and cycle stability of the coated ternary material are both significantly improved.

[0076] As can be obtained from the comparison between Example 1 and Comparative Example 2, the modified ternary material is prepared by directly pyrolyzing the above suspension liquid by spray pyrolysis one-step reaction. Compared with the filtering, drying and sintering steps of the traditional water washing process, the process flow is shortened, and the loss of lithium phosphate during the filtering of the aqueous solution is avoided, so that the content of the lithium phosphate coating layer can be accurately controlled. At the same time, compared with the lithium phosphate coating layer formed by the traditional solid-phase grinding mixing (Comparative Example 2), the uniformity of the lithium phosphate layer is better, which is more conducive to the capacity development and stability improvement of the ternary material.

[0077] As can be obtained from the comparison between Example 1 and Comparative Examples 3-4, the pH of the reaction solution needs to be strictly controlled in the range of 11-12 in the preparation process of the modified ternary positive electrode material. If the pH is too low, it means that the active lithium inside the structure of the ternary material is lost, the discharge capacity of the material is significantly decreased, and the structural stability is poor, and the capacity attenuation is too fast during the cycle process. If the pH is too high, there is still a small amount of residual alkali on the surface of the ternary material, which also affects the performance of the ternary material.

[0078] The applicant states that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought out by those skilled in the art, and all of them fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a modified ternary cathode material, characterized in that, The preparation method includes the following steps: (1) Mix the ternary cathode material with water and adjust the pH to 11-12 to obtain a suspension; (2) Mix the suspension obtained in step (1) with phosphate and control the pH of the reaction solution to 11-12 for reaction; (3) The obtained mixture is subjected to spray pyrolysis to obtain the modified ternary cathode material; Step (1) The method for adjusting pH includes: when the pH of the suspension is >12.0, perform vacuum filtration, redisperse the filter cake into the aqueous solution, and repeat water washing and vacuum filtration until the pH of the suspension is ≤12.0; The solid content of the suspension in step (1) is 100~300 g / L; The spray pyrolysis temperature in step (3) is 500~600℃, and the spray pyrolysis time is 5~20s.

2. The preparation method according to claim 1, characterized in that, The chemical formula of the ternary cathode material mentioned in step (1) is LiMO2, where M = Ni x Co y Mn z 0 <x<1,0<y<1,0<z<1。 3. The preparation method according to claim 2, characterized in that, The Li / M ratio of the ternary cathode material is 1.02~1.

20.

4. The preparation method according to claim 3, characterized in that, The Li / M ratio of the ternary cathode material is 1.05~1.

10.

5. The preparation method according to claim 1, characterized in that, The phosphate in step (2) includes any one or a combination of at least two of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, or lithium dihydrogen phosphate.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass of phosphate ions in the phosphate is 0.1 to 10% of the mass of the ternary cathode material.

7. The preparation method according to claim 6, characterized in that, In step (2), the mass of phosphate in the phosphate is 2-4% of the mass of the ternary cathode material.

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