Modification method and application of lithium-rich manganese-based positive electrode material

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a modification method and application of a lithium-rich manganese-based positive electrode material. The modification method of the lithium-rich manganese-based positive electrode material comprises the following steps: mixing an organic reducing agent solution and the lithium-rich manganese-based positive electrode material to obtain a mixed solution, dropwise adding the mixed solution to the surface of a heating plate, enabling the mixed solution to generate a Leidenfrost effect, and performing reduction modification on the surface of the lithium-rich manganese-based positive electrode material to obtain the lithium-rich manganese-based positive electrode material. And forming a carbon coating layer on the surface of the lithium-rich manganese-based positive electrode material to obtain the modified lithium-rich manganese-based positive electrode material. The surface of the lithium-rich manganese-based positive electrode material particle is subjected to reduction modification by using the reducibility of the organic reducing agent and the instantaneous high-temperature heat conduction under the Leidenfrost effect, and the carbon coating layer is formed on the surface, so that the method has the advantages of short treatment time, no waste material generation in the treatment process, low energy consumption and the like; and the capacity, the first coulombic efficiency and the cycle capacity retention ratio of the material can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a method for modifying lithium-rich manganese-based cathode materials and its application. Background Technology

[0002] Lithium-rich manganese-based cathode materials are a key choice for next-generation lithium-ion battery cathode materials, possessing advantages such as high specific capacity, low cost, environmental friendliness, and abundant resources. However, the initial coulombic efficiency and cycle stability of lithium-rich manganese-based cathode materials still need improvement.

[0003] Existing technologies often employ post-processing modification methods for lithium-rich manganese-based cathode materials. However, current solutions mostly utilize liquid-phase methods for post-processing, which involve stirring the material and modifying agents in a liquid for a period of time, followed by washing, filtration, drying, and then secondary sintering. This method suffers from problems such as long processing time, wastewater generation during processing, and increased energy consumption due to secondary sintering.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a method for modifying lithium-rich manganese-based cathode materials. By utilizing the reducing properties of organic reducing agents and the instantaneous high-temperature heat conduction under the Leidenfrost effect, the surface of lithium-rich manganese-based cathode material particles is reduced and modified to form a carbon coating layer. This method not only improves the initial coulombic efficiency and cycle stability of the material, but also has advantages such as short processing time, no waste generation during the processing, and low energy consumption.

[0006] The second objective of this invention is to provide a method for modifying lithium-rich manganese-based cathode materials and its application in the preparation of cathode active materials, cathode sheets, and secondary batteries.

[0007] A third objective of this invention is to provide a lithium-ion battery.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] This invention first provides a method for modifying lithium-rich manganese-based cathode materials, comprising the following steps: mixing an organic reducing agent solution and lithium-rich manganese-based cathode materials to obtain a mixed solution, then dripping the solution onto the surface of a heating plate to induce the Leiden-Frost effect in the mixed solution, thereby reducing and modifying the surface of the lithium-rich manganese-based cathode material and forming a carbon coating layer on the surface of the lithium-rich manganese-based cathode material to obtain the modified lithium-rich manganese-based cathode material.

[0010] Furthermore, the organic reducing agent in the organic reducing agent solution includes at least one of glyoxal, formic acid, and ascorbic acid.

[0011] Further, the solvent in the organic reducing agent solution includes water.

[0012] Further, the mass fraction of the organic reducing agent in the organic reducing agent solution is 0.05% - 5%.

[0013] Further, the ratio of the volume of the organic reducing agent solution to the mass of the lithium-rich manganese-based cathode material is 60 - 100 mL: 2 g.

[0014] Further, the method of mixing includes ultrasonic treatment.

[0015] Further, during the mixing process, the temperature of the mixed solution is 2 - 8°C.

[0016] Further, the temperature of the hot plate is 300 - 600°C.

[0017] Further, the dropping is performed using a pipette.

[0018] Further, the thickness of the carbon coating layer is 1 - 5 nm.

[0019] Further, the general formula of the lithium-rich manganese-based cathode material is Li 1+x M 1-x O2, where 0 < x < 1, and M includes at least one of Ni, Co, and Mn elements. The present invention further provides the application of the modification method of the above lithium-rich manganese-based cathode material in the preparation of cathode active materials, cathode sheets, and secondary batteries.

[0020] The present invention also provides a lithium-ion battery, which includes a cathode sheet, an anode sheet, a separator, and an electrolyte, wherein the cathode sheet includes the modified lithium-rich manganese-based cathode material prepared by the modification method of the above lithium-rich manganese-based cathode material.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The modification method of the lithium-rich manganese-based cathode material provided by the present invention uses the reducibility of the organic reducing agent and the instantaneous high-temperature heat conduction under the Leidenfrost effect to perform reduction modification on the surface of the lithium-rich manganese-based cathode material particles, which can reduce the valence state of the transition metal elements on the surface of the lithium-rich manganese-based cathode material, form oxygen vacancies, thereby improving the initial Coulomb efficiency of the material, and at the same time, the formed carbon coating layer can inhibit the erosion of the electrolyte, thereby improving the cycle stability of the material.

[0023] (2) The modification method of the lithium-rich manganese-based cathode material provided by the present invention has the advantages of simple operation, short process, short processing time, high efficiency, no waste generation, and low energy consumption. Description of the Drawings

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 A schematic diagram illustrating the principle of the Leidenfrost effect provided by this invention;

[0026] Figure 2 A comparison of charge-discharge curves of batteries assembled with the materials of Example 1 and Comparative Example 1 provided by the present invention;

[0027] Figure 3 A comparison chart of the cycle performance of batteries assembled with the materials of Example 1 and Comparative Example 1 provided by the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0029] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0030] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0031] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0032] In a first aspect, the present invention provides a method for modifying lithium-rich manganese-based cathode materials, specifically comprising the following steps:

[0033] The organic reducing agent solution and the lithium-rich manganese-based cathode material are mixed evenly to obtain a mixed solution.

[0034] The mixed solution is dropped onto the surface of the heating plate to induce the Leiden-Frost effect, thereby reducing and modifying the surface of the lithium-rich manganese-based cathode material and forming a carbon coating layer on the surface of the lithium-rich manganese-based cathode material. After the mixed solution is evaporated to dryness, the powder is collected to obtain the modified lithium-rich manganese-based cathode material.

[0035] The Leidenfrost effect refers to the phenomenon where, when a liquid comes into contact with an object whose boiling point is far above its boiling point, a layer of insulating vapor forms on the liquid's surface, significantly slowing down the boiling process. For example, if a drop of water is placed on a hot iron plate, and the plate's temperature is only slightly above the water's boiling point (100°C), the water will hiss and boil rapidly. However, when the iron plate's temperature exceeds a certain threshold, the Leidenfrost effect occurs, causing the water droplet to roll around on the plate, maintaining its high temperature and slowly evaporating.

[0036] See Figure 1 The diagram shown is a schematic representation of the Leidenfrost effect occurring in this invention.

[0037] This invention utilizes the reducing properties of organic reducing agents and the instantaneous high-temperature heat conduction under the Leidenfrost effect to reduce and modify the surface of lithium-rich manganese-based cathode material particles, forming a carbon coating. Specifically, the organic reducing agent reduces the valence states of cobalt and manganese on the surface of the lithium-rich manganese-based cathode material (hereinafter referred to as lithium-rich material), lowering their valence states. As the reduction proceeds, oxygen vacancies are further formed to maintain a neutral valence state. This is observed from the charge-discharge curve (see...). Figure 2 It can be known that Co 3+ The oxidation level decreases and the plateau shortens, which improves the material's initial coulombic efficiency (i.e., first-efficiency). Simultaneously, after the droplets evaporate, they remain on the heating plate, and the residual organic reducing agents on the material surface carbonize at high temperatures, forming a thin carbon coating that inhibits electrolyte erosion. This improves the material's cycle stability (see [link to relevant documentation]). Figure 3 ).

[0038] Furthermore, the modification method for lithium-rich manganese-based cathode materials provided by this invention has the advantages of simple operation, short process, short processing time, high efficiency, no waste generation during processing, and low energy consumption.

[0039] In some specific embodiments, the organic reducing agent in the organic reducing agent solution includes at least one of glyoxal, formic acid, and ascorbic acid.

[0040] In some specific embodiments, the solvent in the organic reducing agent solution includes water.

[0041] In some specific embodiments, the mass fraction of the organic reducing agent in the organic reducing agent solution (i.e., the concentration of the organic reducing agent solution) is 0.05% to 5%, including but not limited to any one of 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, and 5%, or a range between any two. The effect of the Leidenfrost effect is related to the concentration of the organic reducing agent solution.

[0042] In some specific embodiments, the volume ratio of the organic reducing agent solution to the mass ratio of the lithium-rich manganese-based cathode material is 60–100 mL (e.g., 70 mL, 80 mL, or 90 mL): 2 g.

[0043] In some specific implementations, the mixing method includes ultrasound.

[0044] In some specific embodiments, during the mixing process, the temperature of the mixed solution is 2–8°C, including but not limited to any one of 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, and 8°C, or a range between any two. A lower solution temperature avoids raising the solution temperature during the ultrasonic step, thereby maintaining the temperature difference between the liquid and the heating plate, which is beneficial for the Leidenfrost effect. Furthermore, if the temperature is too high, glyoxal may undergo a polymerization reaction, resulting in precipitation or thickening; if the temperature is too low, there is a risk of solution solidification. Controlling the temperature within this range is beneficial for the Leidenfrost effect and maintains the stability of the mixed solution.

[0045] In some specific embodiments, the temperature of the hot plate is 300 to 600°C, including but not limited to any one of 300°C, 320°C, 350°C, 380°C, 400°C, 500°C, and 600°C, or a range between any two.

[0046] The key to the Leidenfrost effect lies in the temperature difference between the mixed solution and the heating plate.

[0047] In some specific embodiments, the addition is performed using a pipette. Using a pipette prevents the droplets from becoming too large and thus affecting the Leidenfrost effect.

[0048] In some specific embodiments, the thickness of the carbon coating layer is 1 to 5 nm, including but not limited to a point value of any one of 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm, or a range between any two.

[0049] In some specific embodiments, the general formula of the lithium-rich manganese-based cathode material is Li 1+x M 1-x O2, where 0 < x < 1, and M includes at least one of Ni, Co, and Mn elements. Second, the present invention provides an application of the modification method of the lithium-rich manganese-based cathode material in the preparation of cathode active materials, cathode sheets, and secondary batteries.

[0050] The modified lithium-rich manganese-based cathode material prepared by the modification method of the lithium-rich manganese-based cathode material can be used in cathode sheets, secondary batteries, and electrical equipment, which is beneficial to improving the capacity, initial efficiency, and cycle performance of secondary batteries.

[0051] Third, the present invention provides a lithium-ion battery, which includes a cathode sheet, an anode sheet, a separator, and an electrolyte, wherein the cathode sheet contains the modified lithium-rich manganese-based cathode material prepared according to the above modification method of the lithium-rich manganese-based cathode material.

[0052] The lithium-ion battery using the modified lithium-rich manganese-based cathode material has the advantages of high capacity, high initial efficiency, and high cycle capacity retention rate.

[0053] In some specific embodiments, the cathode sheet further includes a binder and / or a conductive agent, and the present invention does not limit this.

[0054] The following will describe the embodiments of the present invention in detail in conjunction with the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchases.

[0055] Example 1

[0056] [[ID=​​​​​​​​​​​​​(2) Fix the alumina ceramic heating plate on a precisely temperature-controlled heating platform and set the temperature to 400°C. Then use a pipette to drop the above mixed solution onto the surface of the alumina ceramic heating plate, so that the mixed solution undergoes the Leidenfrost effect. The droplets are lifted by the vapor film and float and roll for several seconds before evaporating completely, thereby achieving the reduction modification of the surface of the lithium-rich manganese-based cathode material particles and forming a carbon coating layer on the surface of the lithium-rich manganese-based cathode material. After all the mixed solutions have been processed (the mixed solutions have been completely evaporated), collect the powder to obtain the modified lithium-rich manganese-based cathode material.

[0059] The thickness of the carbon coating layer of the modified lithium-rich manganese-based cathode material is 3 nm.

[0060] Example 2

[0061] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the glyoxal aqueous solution is replaced with an aqueous solution of formic acid of equal volume, equal mass fraction and equal temperature.

[0062] Example 3

[0063] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the glyoxal aqueous solution is replaced with an ascorbic acid aqueous solution of equal volume, equal mass fraction and equal temperature.

[0064] Example 4

[0065] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass fraction of the glyoxal aqueous solution is replaced with 3%.

[0066] Example 5

[0067] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the temperature of the mixed solution is controlled to be 6°C during the ultrasonic process.

[0068] Example 6

[0069] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), Li is used. 1.2 Mn 0.6 Ni 0.2 O2-rich lithium-manganese-based cathode material.

[0070] Example 7

[0071] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the volume of the glyoxal aqueous solution is replaced with 60 ml.

[0072] The thickness of the carbon coating layer of the modified lithium-rich manganese-based cathode material prepared in this embodiment is 1 nm.

[0073] Example 8

[0074] The modification method of the lithium-rich manganese-based cathode material provided in this embodiment is basically the same as that in Example 1, except that in step (2), the temperature of the alumina ceramic heating plate is controlled at 300°C.

[0075] Comparative Example 1

[0076] Unmodified Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The O2-rich lithium-manganese-based cathode material has the same chemical formula as in Example 1.

[0077] Comparative Example 2

[0078] The lithium-rich manganese-based cathode material was modified using a conventional liquid-phase method, as follows:

[0079] Take 80 ml of a 1.5% glyoxal aqueous solution at 3°C, and add 2 g of Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The O2-rich lithium manganese-based cathode material was stirred for 10 minutes (while maintaining the temperature of the mixture at 3°C), then filtered, washed with water, and dried. Subsequently, it was sintered at 300°C for 4 hours to obtain the modified lithium-rich manganese-based cathode material.

[0080] Experimental Example

[0081] Lithium-ion batteries were fabricated using the modified lithium-rich manganese-based cathode materials prepared in each embodiment and each comparative example as cathode active materials. The electrochemical performance of each lithium-ion battery was tested, and the results are shown in Table 1.

[0082] The preparation method of lithium-ion batteries is as follows: The lithium-rich manganese-based cathode materials prepared in each embodiment and each comparative example are used as cathode active materials. Cathode slurry is prepared according to the mass ratio of cathode active material, PVDF and Super-P of 95:3:2 and coated on aluminum foil. After drying, stamping and weighing, the slurry is assembled into button batteries in a glove box.

[0083] The electrochemical performance testing method is as follows: After the assembled half-cell is left to stand for 6 hours, it is charged to 4.6V with a constant current density of 1C and a constant voltage, and the cutoff current is 0.1C. Then it is discharged to 2V with a current density of 1C and cycled for 100 cycles.

[0084] Table 1 Electrochemical performance test results of each battery

[0085]

[0086] As can be seen from Table 1, the batteries using the modified lithium-rich manganese-based cathode materials of each embodiment have higher capacity, higher initial coulombic efficiency, and higher cycle retention.

[0087] Specifically, the comparison chart of charge-discharge curves of the batteries assembled from the materials of Example 1 and Comparative Example 1 can be found in [reference needed]. Figure 2 See the comparison chart of cycle performance of batteries assembled from the materials of Example 1 and Comparative Example 1. Figure 3 Comparing Example 1 and Comparative Example 1, it can be seen that in Example 1, glyoxal reduces the valence states of cobalt and manganese on the surface of the lithium-rich manganese-based cathode material, lowering their valence states. As the reduction proceeds, oxygen vacancies are further formed to maintain a neutral valence state. Figure 2 The charge-discharge curves show that Co 3+ The oxidation rate decreases and the plateau shortens, which improves the material's initial coulombic efficiency. Simultaneously, the remaining glyoxal on the heating plate after droplet evaporation carbonizes at high temperatures, forming a thin carbon coating that inhibits electrolyte erosion, thus improving the material's cycle stability. Figure 3 ).

[0088] Furthermore, comparing Example 1 and Comparative Example 2, it can be seen that Comparative Example 2, due to the use of conventional liquid phase modification, not only has problems such as long processing time, wastewater generation during processing, and increased energy consumption due to secondary sintering, but also has low battery capacity, low initial efficiency, and low cycle retention rate.

[0089] In summary, this invention utilizes the reducing properties of organic reducing agents and the instantaneous high-temperature heat conduction under the Leiden-Frost effect to reduce and modify the surface of lithium-rich manganese-based cathode material particles, forming a carbon coating layer on their surface. This not only has the advantages of short processing time, no waste generation during the process, and low energy consumption, but also improves the material's capacity, initial coulombic efficiency, and cycle capacity retention.

[0090] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can 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, without departing from the spirit and scope of the present invention; and these 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 the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for modifying a lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: After mixing the organic reducing agent solution and the lithium-rich manganese-based cathode material to obtain a mixed solution, the solution is dropped onto the surface of a heating plate to induce the Leiden-Frost effect, thereby reducing and modifying the surface of the lithium-rich manganese-based cathode material and forming a carbon coating layer on the surface of the lithium-rich manganese-based cathode material, thus obtaining the modified lithium-rich manganese-based cathode material.

2. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The organic reducing agent in the organic reducing agent solution includes at least one of glyoxal, formic acid and ascorbic acid; And / or, the solvent in the organic reducing agent solution includes water.

3. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The organic reducing agent in the organic reducing agent solution has a mass fraction of 0.05% to 5%; And / or, the volume ratio of the organic reducing agent solution to the mass ratio of the lithium-rich manganese-based cathode material is 60-100 mL: 2 g.

4. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The mixing method includes ultrasound; And / or, during the mixing process, the temperature of the mixed solution is 2 to 8°C.

5. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The temperature of the hot plate is 300–600°C.

6. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The addition was performed using a pipette.

7. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The thickness of the carbon coating layer is 1–5 nm.

8. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The general formula of the lithium-rich manganese-based cathode material is Li 1+x M 1-x O2, where 0 < x < 1 and M includes at least one of Ni, Co, and Mn elements.

9. The application of the modification method of lithium-rich manganese-based cathode material according to any one of claims 1 to 8 in the preparation of cathode active materials, cathode sheets and secondary batteries.

10. 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 a modified lithium-rich manganese-based positive electrode material prepared by the modification method of the lithium-rich manganese-based positive electrode material as described in any one of claims 1 to 8.

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