Method for reducing residual alkali on surface of high-nickel layered positive electrode material, high-nickel layered positive electrode material and lithium ion battery

Abstract

This application provides a method for reducing residual alkali on the surface of a high-nickel layered cathode material, the high-nickel layered cathode material itself, and a lithium-ion battery, relating to the field of lithium-ion batteries. The method for reducing residual alkali on the surface of a high-nickel layered cathode material includes: mixing an organic acid with an organic alcohol solution to obtain a cleaning solution; mixing the high-nickel layered cathode material with the cleaning solution and washing it; filtering the washed slurry to obtain filter residue; and sequentially subjecting the filter residue to freeze-drying and drying treatments to obtain a high-nickel layered cathode material with reduced residual alkali content. This application can efficiently reduce the surface residual alkali of the product without damaging the material's performance. Furthermore, this application eliminates the need for secondary reheating of the product after alkali reduction, significantly reducing processing costs.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a method for reducing residual alkali on the surface of a high-nickel layered cathode material, the high-nickel layered cathode material, and a lithium-ion battery. Background Technology

[0002] The cathode is one of the most important components in lithium-ion batteries, determining the battery's energy density, cycle stability, and thermal stability. Ternary layered oxides, due to their high energy density, are widely used in battery products across various fields. Depending on the content of Ni, Co, and Mn elements within the system, ternary materials are mainly classified into low-nickel, medium-nickel, and high-nickel ternary oxides. Low-nickel and medium-nickel ternary technologies are mature and widely used, while high-nickel ternary oxide systems, with their higher energy density, still need to overcome interference from factors such as surface residual alkali during application. Because high-nickel ternary materials are limited by the preparation temperature (requiring relatively low temperatures; high temperatures in high-nickel systems can cause lithium-nickel mixing within the structure, affecting material performance), excess lithium source participating in the reaction cannot fully volatilize and remains on the product surface. Upon contact with moisture and CO2 in the air, residues including LiOH, Li2CO3, and a small amount of LiHCO3 are formed on the surface, collectively referred to as surface residual alkali. If the residual alkali on the product surface is not treated, it will cause the sample slurry to form a poorly fluid slurry (known in the industry as gelling) during the subsequent preparation of battery electrodes, making it impossible to prepare the battery normally.

[0003] Current alkali reduction processes mainly involve washing the product with water. This is done by washing and stirring the product with deionized water or ultrapure water in a specific ratio, followed by filtration and drying. This method utilizes the solubility of LiOH and Li₂CO₃ in water to efficiently remove residual alkali from the surface. However, due to the high polarity of water molecules, the H₂ in the water... + Ions will react with Li within the high-nickel ternary structure + Ion replacement occurs, forming an oxygen-depleted layer on the surface and creating oxygen vacancies, which leads to a significant reduction in the material's performance.

[0004] Since common cleaning solutions (such as deionized water) can cause surface damage to high-nickel ternary materials or cause structural deoxidation during subsequent drying, the products must be re-fired at high temperature in an oxygen-rich environment after cleaning, which greatly increases the production cost of the products. Summary of the Invention

[0005] The purpose of this application is to provide a method for reducing residual alkali on the surface of high-nickel layered cathode materials, high-nickel layered cathode materials, and lithium-ion batteries to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution: A method for reducing residual alkali on the surface of a high-nickel layered cathode material includes: The cleaning solution is obtained by mixing an organic acid with an organic alcohol solution. The high-nickel layered cathode material is mixed with a cleaning solution and then washed. The washed slurry is filtered to obtain filter residue; The filter residue was subjected to freezing and drying treatments in sequence to obtain a high-nickel layered cathode material with reduced residual alkali content.

[0007] According to embodiments of this application, the organic acid includes at least one of formic acid, acetic acid, and propionic acid; The organic alcohol includes at least one of methanol and ethanol.

[0008] According to an embodiment of this application, the concentration of organic acid in the cleaning solution is 0.01-0.3 mol / L.

[0009] According to embodiments of this application, the chemical formula of the high-nickel layered cathode material is LiNi. x Co y M 1-x-y O2, where x≥0.8, 0≤y≤0.1, and M includes at least one of Mn and Al; And / or, the solid-liquid ratio of the high-nickel layered cathode material to the cleaning solution is 1:1-1:20 kg / L.

[0010] According to an embodiment of this application, the washing is carried out under stirring conditions, the stirring speed is 100-1000 r / min, and the washing time is 1-60 min; And / or, the washing temperature is 15-80°C.

[0011] According to an embodiment of this application, the freezing temperature is below -10°C, and the freezing time is 0.5 to 120 min.

[0012] According to embodiments of this application, the freezing process satisfies any one of the following conditions: (1) The freezing process is carried out using a cryogenic medium, which includes at least one of liquid nitrogen, liquid helium, dry ice, ice salt bath, sulfur hexafluoride, liquid oxygen, and liquid argon, and the freezing time is 0.5 to 10 min. (2) The freezing process is carried out using a cold trap, and the freezing time is 1 to 120 min.

[0013] According to an embodiment of this application, the drying process is carried out in a vacuum environment with a vacuum degree of less than 150 Pa; And / or, the drying temperature is 20-100°C, and the drying time is 1-20h.

[0014] This application also provides a high-nickel layered cathode material, wherein the high-nickel layered cathode material is the high-nickel layered cathode material obtained by the method described above.

[0015] This application also provides a lithium-ion battery, which includes the high-nickel layered cathode material described above.

[0016] Compared with the prior art, the beneficial effects of this application include: This application uses a mixture of organic alcohols and organic acids as the cleaning solution, and employs both freeze-drying and drying post-treatment methods to efficiently reduce surface residual alkali in the product without damaging the material properties. Specifically, residual alkali is slightly soluble in organic alcohols, and the introduction of organic alcohols facilitates the removal of residual alkali; moreover, organic alcohols have weak polarity, causing less damage to the high-nickel ternary cathode. The organic acids in the cleaning solution can undergo an acid-base neutralization reaction with the residual alkali on the cathode material surface, further reducing the residual alkali. Moreover, organic acids have high solubility in organic alcohols, which is beneficial for efficient alkali removal. In addition, this application uses freeze-drying and drying treatments, which can achieve product drying at low temperatures and efficiently remove residual organic acids and their byproducts from the material surface, while eliminating the need for secondary re-firing of the dealkali-reduced product, greatly reducing processing costs. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0018] Figure 1 XPS images of the high-nickel layered cathode materials obtained by the methods in Examples 1-3 and Comparative Example 1; Figure 2 The above are charge-discharge curves for Examples 1-3. Detailed Implementation

[0019] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0020] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0021] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0022] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0023] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0024] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0025] A method for reducing residual alkali on the surface of a high-nickel layered cathode material includes: The cleaning solution is obtained by mixing an organic acid with an organic alcohol solution. The high-nickel layered cathode material is mixed with a cleaning solution and then washed. The washed slurry is filtered to obtain filter residue; The filter residue was subjected to freezing and drying treatments in sequence to obtain a high-nickel layered cathode material with reduced residual alkali content.

[0026] According to embodiments of this application, the organic acid includes at least one of formic acid, acetic acid, and propionic acid. Formic acid, acetic acid, and propionic acid are weak organic acids with higher priority in acid-base neutralization reactions, thus greatly reducing damage to the surface of the high-nickel ternary cathode, and their acidity is precisely what allows them to react with Li2CO3. Moreover, compared to inorganic acids, organic acids have higher solubility in organic alcohols, which is more conducive to efficient alkali removal.

[0027] The organic alcohol includes at least one of methanol and ethanol. LiOH is slightly soluble in organic alcohols, and by adding organic alcohols, LiOH in residual alkali on the surface of the cathode material can be washed away. Moreover, organic alcohols have weak polarity and cause less damage to the high-nickel ternary cathode.

[0028] According to an embodiment of this application, the concentration of organic acid in the cleaning solution is 0.01-0.3 mol / L.

[0029] For example, the concentration of organic acid in the cleaning solution can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, or any value between 0.01 and 0.3 mol / L.

[0030] According to embodiments of this application, the chemical formula of the high-nickel layered cathode material is LiNi. x Co y M 1-x-y O2, where x≥0.8, 0≤y≤0.1, and M includes at least one of Mn and Al; In some embodiments, the chemical formula of the high-nickel layered cathode material is LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0031] And / or, the solid-liquid ratio of the high-nickel layered cathode material to the cleaning solution is 1:1-1:20 kg / L.

[0032] For example, the solid-liquid ratio of the high-nickel layered cathode material to the cleaning solution can be any value between 1:1 kg / L, 1:5 kg / L, 1:10 kg / L, 1:15 kg / L, 1:20 kg / L, or 1:1-1:20 kg / L.

[0033] According to an embodiment of this application, the washing is carried out under stirring conditions, the stirring speed is 100-1000 r / min, and the washing time is 1-60 min.

[0034] For example, the stirring speed can be any value between 100 r / min, 300 r / min, 500 r / min, 800 r / min, 1000 r / min or 100-1000 r / min; the washing time can be any value between 1 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min or 1-60 min.

[0035] In some embodiments, the washing temperature is 15-80°C. For example, the washing temperature is any value between 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or 15-80°C.

[0036] According to an embodiment of this application, the freezing temperature is below -10°C, and the freezing time is 0.5 to 120 min.

[0037] For example, the freezing time can be 0.5 min, 1 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or any value between 0.5 and 120 min.

[0038] According to embodiments of this application, the freezing process satisfies any one of the following conditions: (1) The freezing process is carried out using a cryogenic medium, which includes at least one of liquid nitrogen, liquid helium, dry ice, ice-salt bath (a mixture of salt and ice water), sulfur hexafluoride (SF6), liquid oxygen, and liquid argon, and the freezing time is 0.5 to 10 min. (2) The freezing process is carried out using a cold trap, and the freezing time is 1 to 120 min.

[0039] Freezing can quickly solidify any residual weak organic acids on the material surface, preventing excessive damage to the surface.

[0040] According to an embodiment of this application, the drying process is carried out in a vacuum environment with a vacuum degree of less than 150 Pa; And / or, the drying temperature is 20-100°C, and the drying time is 1-20h.

[0041] For example, the drying temperature is any value between 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or 20-100°C, and the drying time is any value between 1h, 5h, 10h, 15h, 20h or 1-20h.

[0042] Organic acids and their reaction byproducts typically have high boiling points. Existing technologies usually employ long-term high-temperature drying to remove organic acids. However, this method can easily induce structural deoxidation in high-nickel cathodes, affecting the electrochemical performance of the materials.

[0043] This application employs cryogenic treatment and drying to remove residual organic acids from the material surface. The solid organic acids after cryogenic treatment can rapidly volatilize at low temperatures under vacuum, and the lower drying temperature does not induce deoxidation in the high-nickel ternary cathode, which is beneficial to the electrochemical performance of the material. Moreover, this technology eliminates the need for secondary re-firing of the product after alkali reduction, thus achieving energy saving and cost reduction.

[0044] This application also provides a high-nickel layered cathode material, wherein the high-nickel layered cathode material is the high-nickel layered cathode material obtained by the method described above.

[0045] This application also provides a lithium-ion battery, which includes the high-nickel layered cathode material described above.

[0046] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0047] Example 1 Example 1 provides a method for reducing residual alkali on the surface of a high-nickel layered cathode material, comprising: (1) Mix a certain amount of formic acid and ethanol to prepare a formic acid ethanol solution with a formic acid concentration of 0.3 mol / L, which is the cleaning solution; (2) At 25°C, the cleaning solution was mixed with the positive electrode material (LiNi) at a solid-liquid ratio of 1:20 kg / L. 0.8 Co 0.1 Mn 0.1 Mix with O2 and wash; wash at a stirring speed of 100-1000 r / min for 60 min; (3) The washed slurry is filtered by a filter press to obtain filter residue; (4) The filter residue was frozen with liquid nitrogen for 5 minutes. Then the sample was placed in a vacuum oven for drying. The vacuum was adjusted to less than 130 Pa until it stabilized. The temperature was then raised to 80°C and kept for 10 hours to obtain a high-nickel layered cathode material with reduced residual alkali content.

[0048] Example 2 The difference between Example 2 and Example 1 is that the cleaning solution in step (1) is an acetic acid-ethanol solution. Everything else is the same as in Example 1.

[0049] Example 3 The difference between Example 3 and Example 1 is that the cleaning solution in step (1) is a propionic acid ethanol solution. Everything else is the same as in Example 1.

[0050] Comparative Example 1 Comparative Example 1 is the cathode material that has not undergone washing treatment.

[0051] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the cleaning solution is deionized water, and the liquid nitrogen cooling step is omitted in step (4). The filter residue is directly placed in a vacuum oven and kept at 80°C for 10 hours. Everything else is the same as in Example 1.

[0052] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the cleaning solution is deionized water. Everything else is the same as in Example 1.

[0053] Figure 1 XPS images of the high-nickel layered cathode materials obtained by the methods in Examples 1-3 and Comparative Example 1; Figure 1 The characteristic peak near 290 eV is a characteristic peak of the carbon-oxygen double bond, originating from the residual Li₂CO₃ alkali on the surface of the ternary material. The intensity of the characteristic peak indirectly reflects the concentration of the residual alkali. Figure 1 It can be seen that the residual alkali concentration on the surface of the cathode material in Examples 1-3 is lower than that on the surface of the cathode material in Comparative Example 1, indicating that the method of this application can effectively reduce the amount of residual alkali on the surface of the cathode material compared with the untreated cathode material.

[0054] The pH values ​​of the cathode material products obtained in the examples and comparative examples were measured using a pH meter.

[0055] The cathode materials obtained in the examples and comparative examples were assembled into batteries under the same conditions. Specifically, the process included: thoroughly mixing the above-mentioned ternary cathode material, conductive carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10, adding N-methylpyrrolidone to obtain a cathode slurry, coating the prepared slurry onto aluminum foil, cold pressing, baking and die-cutting to prepare cathode sheets.

[0056] The negative electrode is a lithium metal sheet.

[0057] Electrolyte preparation: 1 mol of LiPF6 was used as the lithium salt, and the solvent was a mixed solvent composed of EC / DC / EMC (volume ratio of 1:1:1).

[0058] The positive and negative electrodes are separated by a diaphragm, electrolyte is added, and pressure is applied in a glove box to form a button half-cell.

[0059] The coin cells prepared above were subjected to performance tests under the same conditions, with a charge-discharge range of 2.7-4.3V (0.1C rate). The test results of the examples and comparative examples are shown in Table 1.

[0060] Table 1 Summary of pH values ​​and discharge specific capacities of the examples and comparative examples

[0061] From Table 1 and Figure 2 It can be seen that the methods in Examples 1-3 can effectively reduce the residual alkali on the surface of the cathode material without damaging the material properties.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0063] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for reducing residual alkali on the surface of a high-nickel layered cathode material, characterized in that, include: Organic acids and organic alcohols are mixed to obtain a cleaning solution; The high-nickel layered cathode material is mixed with a cleaning solution and then washed. The washed slurry is filtered to obtain filter residue; The filter residue was subjected to freezing and drying treatments in sequence to obtain a high-nickel layered cathode material with reduced residual alkali content.

2. The method for reducing residual alkali on the surface of high-nickel layered cathode material according to claim 1, characterized in that, The organic acid includes at least one of formic acid, acetic acid, and propionic acid; The organic alcohol includes at least one of methanol and ethanol.

3. The method for reducing residual alkali on the surface of high-nickel layered cathode materials according to claim 2, characterized in that, The concentration of organic acid in the cleaning solution is 0.01-0.3 mol / L.

4. The method for reducing residual alkali on the surface of high-nickel layered cathode material according to claim 1, characterized in that, The chemical formula of the high-nickel layered cathode material is LiNi. x Co y M 1-x-y O2, where x≥0.8, 0≤y≤0.1, and M includes at least one of Mn and Al; And / or, the solid-liquid ratio of the high-nickel layered cathode material to the cleaning solution is 1:1-1:20 kg / L.

5. The method for reducing residual alkali on the surface of high-nickel layered cathode material according to claim 1, characterized in that, The washing is carried out under stirring conditions, the stirring speed is 100-1000 r / min, and the washing time is 1-60 min; And / or, the washing temperature is 15-80°C.

6. The method for reducing residual alkali on the surface of high-nickel layered cathode material according to claim 1, characterized in that, The freezing temperature is below -10°C, and the freezing time is 0.5 to 120 minutes.

7. The method for reducing residual alkali on the surface of high-nickel layered cathode material according to claim 6, characterized in that, The freezing process satisfies any one of the following conditions: (1) The freezing process is carried out using a cryogenic medium, which includes at least one of liquid nitrogen, liquid helium, dry ice, ice salt bath, sulfur hexafluoride, liquid oxygen, and liquid argon, and the freezing time is 0.5 to 10 min. (2) The freezing process is carried out using a cold trap, and the freezing time is 1 to 120 min.

8. The method for reducing residual alkali on the surface of high-nickel layered cathode materials according to any one of claims 1-7, characterized in that, The drying process is carried out in a vacuum environment with a vacuum degree of less than 150 Pa. And / or, the drying temperature is 20-100°C, and the drying time is 1-20h.

9. A high-nickel layered cathode material, characterized in that, The high-nickel layered cathode material is the high-nickel layered cathode material obtained by the method described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the high-nickel layered cathode material as described in claim 9.

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