Pre-lithiated positive electrode, preparation method, and lithium-ion battery

Abstract

A pre-lithiated positive electrode, a preparation method, and a lithium-ion battery, relating to the technical field of lithium-ion batteries. The pre-lithiated positive electrode comprises a positive electrode current collector and a positive electrode active layer. The positive electrode active layer comprises coated lithium oxide and a conductive agent; and raw materials of the coated lithium oxide include, in parts by weight, 2-8 parts of lithium oxide and 0.1-0.8 parts of an acid. The coated lithium oxide is used as a positive electrode lithium replenishment additive, and a coating layer has a protective effect on the lithium oxide to isolate moisture and carbon dioxide in the air, preventing the lithium oxide from reacting to generate LiOH and Li2CO3, and effectively improving the stability of the pre-lithiated positive electrode in the air, thereby improving the electrical properties of assembled lithium-ion batteries.

Description

A pre-lithiated cathode, its preparation method, and a lithium-ion battery Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a pre-lithiated cathode, its preparation method, and a lithium-ion battery. Background Technology

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

[0003] To further improve the energy density of lithium-ion batteries, replenishing lithium to either the positive or negative electrode is an effective method. Compared to replenishing lithium to the negative electrode, replenishing lithium to the positive electrode is simpler, has lower requirements for equipment and environment, is safer to use, and is relatively cheaper.

[0004] Chinese patent CN107863567A discloses a lithium-ion supplement additive, its preparation method, and its application. By doping lithium oxide powder with copper, the conductivity of the lithium oxide powder is improved, allowing it to be used as a lithium-ion supplement additive. While lithium oxide, as a positive electrode lithium-ion supplement additive, offers high specific capacity, its chemical reactivity means it readily absorbs moisture and carbon dioxide from the air, reacting to form LiOH and Li₂CO₃. This leads to a decrease in specific capacity and poor lithium-ion supplementation; furthermore, the generated LiOH and Li₂CO₃ undergo side reactions with the electrolyte, resulting in severe gas production and affecting the performance of the lithium battery. Summary of the Invention

[0005] The present invention aims to provide a chemically stable pre-lithiation cathode; another objective of the present invention is to provide a method for preparing a chemically stable pre-lithiation cathode; yet another objective of the present invention is to provide a lithium-ion battery with superior initial charge-discharge capacity and coulombic efficiency.

[0006] This invention provides a pre-lithiated cathode, comprising a cathode current collector and a cathode active layer, wherein the cathode active layer comprises coated lithium oxide and a conductive agent; by weight, the raw materials for the coated lithium oxide include:

[0007] 2-8 parts of lithium oxide;

[0008] 0.1-0.8 parts acid.

[0009] Furthermore, by weight, the raw materials for coating lithium oxide include:

[0010] 2-8 parts of lithium oxide;

[0011] 0.4-0.8 parts acid.

[0012] Increasing the amount of acid appropriately can increase the thickness of the lithium oxide coating, thereby improving the stability of the coated lithium oxide.

[0013] The positive current collector is aluminum foil. The conductive agent is selected from one or more of conductive carbon black, carbon nanotubes, and Ketjen black.

[0014] When an appropriate amount of acid reacts with lithium oxide under suitable conditions, a coating layer is formed on the surface of the lithium oxide, thereby isolating the lithium oxide from the air and effectively preventing the lithium oxide from reacting with water and carbon dioxide in the air.

[0015] Furthermore, in the raw material for coating lithium oxide, the acid is selected from one or more of boric acid, phosphoric acid, polyphosphoric acid, oxalic acid, and silicic acid.

[0016] Furthermore, in the raw material for coating lithium oxide, the acid is selected from boric acid, phosphoric acid, and polyphosphoric acid.

[0017] Boric acid, phosphoric acid, and polyphosphoric acid can form a more thermodynamically and kinetically stable coating layer on the surface of lithium oxide.

[0018] This invention also provides a method for preparing a pre-lithiated cathode, comprising the following steps:

[0019] S1. Prepare the positive current collector;

[0020] S2. Preparation of coated lithium oxide slurry: Lithium oxide and organic solvent are mixed evenly to obtain lithium oxide slurry; acid and organic solvent are mixed evenly to obtain acid solution; acid solution is added to lithium oxide slurry, stirred thoroughly, and reacted evenly to obtain coated lithium oxide slurry;

[0021] S3. Preparation of positive electrode active layer slurry: Add conductive agent to the coated lithium oxide slurry obtained in step S2 above, stir thoroughly and mix evenly to obtain positive electrode active layer slurry;

[0022] S4. Coat the surface of the positive electrode current collector with the positive electrode active layer slurry obtained in step S3.

[0023] S5. Dry and cold press to obtain the pre-lithiated cathode as described above.

[0024] Further, in step S2, the organic solvent is selected from N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, ethylene glycol dimethyl ether, 1,3-dioxane, 1,3-dioxane, dimethyl sulfoxide, and polyethylene glycol.

[0025] Furthermore, in step S2, the organic solvent is selected from one of N-methylpyrrolidone, dimethyl sulfoxide, and 1,3-dioxolane.

[0026] Furthermore, in step S2, by mass, the lithium oxide slurry contains lithium oxide at a ratio of 1:2-6 to the organic solvent; and the acid solution contains acid at a mass ratio of 1-2% of the acid solution.

[0027] Furthermore, in step S3, the ratio of lithium oxide: acid: conductive agent by mass is 2-6:0.1-0.6:1.

[0028] Furthermore, in step S4, the surface density of the positive electrode active layer slurry, based on the mass of the solid components excluding solvent, is 10-20 g / m². 2 .

[0029] The present invention also provides a lithium-ion battery, comprising a pre-lithiated positive electrode prepared by the preparation method described above.

[0030] The present invention discloses a pre-lithiated cathode that uses coated lithium oxide as a lithium supplementation additive for the cathode. The coating layer has a protective effect on the lithium oxide, which can isolate moisture and carbon dioxide in the air and prevent the lithium oxide from reacting to form LiOH and Li2CO3. This effectively improves the stability of the pre-lithiated cathode in air, thereby improving the electrical performance of the assembled lithium-ion battery. Detailed Implementation

[0031] The following examples illustrate the contents of this application in more detail. However, the examples are only for illustrating the contents of this application and are not intended to limit it. Therefore, any changes that are equivalent in meaning and scope to the claims of this application should be considered to be included within the scope of the claims.

[0032] The reagents, methods, and equipment used in this application are conventional in this technical field. Unless otherwise specified, all reagents and materials used in this application are commercially available. Example

[0033] Preparation of pre-lithiated cathode:

[0034] (1) Prepare aluminum foil as the positive current collector.

[0035] (2) Preparation of coated lithium oxide slurry: Add 4g of lithium oxide to 16g of solvent N-methylpyrrolidone and stir thoroughly to obtain a lithium oxide slurry. Add 0.2g of boric acid to solvent N-methylpyrrolidone to prepare 20g of acid solution. Slowly add the acid solution dropwise into the lithium oxide slurry and stir thoroughly to obtain a coated lithium oxide slurry.

[0036] (3) Preparation of positive electrode active layer slurry: Add 1g of conductive carbon black to the coated lithium oxide slurry and stir thoroughly to make the reaction uniform.

[0037] (4) The positive electrode active layer slurry is uniformly coated on the surface of the aluminum foil, with a coating surface density of 14.6 g / m². 2 (Single-sided, based on the mass of solid components excluding solvent).

[0038] (5) Dry, cold press, and make a pre-lithiated cathode. Example

[0039] The preparation process is the same as in Example 1, except that the amount of boric acid added in step (2) is different, which is 0.4g. Example

[0040] The preparation process is the same as in Example 1, except that the acid in step (2) is 0.2g of phosphoric acid. Example

[0041] The preparation process is the same as in Example 1, except that the acid in step (2) is 0.4g of phosphoric acid. Example

[0042] The preparation process is the same as in Example 1, except that the acid in step (2) is 0.2g of polyphosphoric acid. Example

[0043] The preparation process is the same as in Example 1, except that the acid in step (2) is 0.4g of polyphosphoric acid. Example

[0044] The preparation process is the same as in Example 2, except that the solvent for the acid in step (2) is different, which is dimethyl sulfoxide. Example

[0045] The preparation process is the same as in Example 2, except that the solvent for the acid in step (2) is different, which is 1,3-dioxolane. Example

[0046] The preparation process is the same as in Example 1, except that the acid in step (2) is 0.4g of oxalic acid. Example

[0047] The preparation process is the same as in Example 1, except that the acid in step (2) is 0.4g of silicic acid.

[0048] The preparation process is the same as in Example 1, except that no acid solution is added in step (2).

[0049] The composition of Examples 1-10 is shown in Table 1.

[0050] Table 1 Composition of Examples 1-10

[0051] Example 1: N-methylpyrrolidone boric acid (5% by mass of lithium oxide) Example 2: N-methylpyrrolidone boric acid (10% by mass of lithium oxide) Example 3: N-methylpyrrolidone phosphoric acid (5% by mass of lithium oxide) Example 4: N-methylpyrrolidone phosphoric acid (10% by mass of lithium oxide) Example 5: N-methylpyrrolidone polyphosphate (5% by mass of lithium oxide) Example 6: N-methylpyrrolidone polyphosphate (10% by mass of lithium oxide) Example 7: Dimethyl sulfoxide boric acid (10% by mass of lithium oxide) Example 8: 1,3-dioxolane boric acid (10% by mass of lithium oxide) Example 9: N-methylpyrrolidone oxalic acid (10% by mass of lithium oxide) Example 10: N-methylpyrrolidone silicate (10% by mass of lithium oxide) Comparative Example: N-methylpyrrolidone /

[0052] Assemble into a lithium-ion battery:

[0053] The pre-lithiated positive electrodes prepared in Examples 1-10 and the comparative examples were assembled with negative electrodes, separators, and electrolytes to form lithium-ion batteries.

[0054] Electrolyte preparation:

[0055] In an argon atmosphere glove box with a water content of <10 ppm and an oxygen content of <10 ppm, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate are mixed at mass percentages of 20%, 30%, 40%, and 10%, respectively, to obtain a mixed organic solvent. Then, fully dried lithium hexafluorophosphate is dissolved in the above mixed organic solvent at a concentration of 1 mol / L. The additive is vinylene carbonate, accounting for 1% of the electrolyte mass percentage. After stirring evenly, the electrolyte is obtained.

[0056] Separator: A porous polyethylene membrane coated with alumina ceramic on both sides is used as the separator.

[0057] Negative electrode: Lithium metal sheet (0.6mm thick, 99.9% purity) is used as the negative electrode.

[0058] Converting the assembly into a lithium-ion battery:

[0059] The pre-lithiated positive electrode sheets prepared in Examples 1-10 and the comparative example were cut into 12 mm diameter discs. The positive electrode sheets, separators and lithium metal sheets were stacked in sequence, with the separator in the middle to act as a separator, and assembled into coin cells. The electrolyte addition amount for each coin cell was 150 μL.

[0060] At 25°C, the lithium-ion batteries assembled in Examples 1-10 and the comparative example were first charged at a constant current of 0.02C to a voltage of 3.2V, then charged at a constant current of 0.2C to a voltage of 4.1V, and then charged at a constant current of 0.01C to a voltage of 4.35V. This was the first charging process. The first charging specific capacity was tested for batteries assembled immediately after the positive electrode was prepared and batteries placed in an environment with 10% humidity at 25°C for 3 days before being assembled. The test results of the examples are shown in Table 2.

[0061] Table 2. Initial charge specific capacity of lithium-ion batteries in Examples 1-10 and comparative examples.

[0062] Electrode No. Initial State First Week Charging Specific Capacity (mAh / g) Electrode Placed in 10% Humidity Environment for 3 Days First Week Charging Specific Capacity (mAh / g) Example 1 14 10.3 34 4.9 Example 2 13 87.2 42 6.8 Example 3 14 05.8 31 3.8 Example 4 13 56.8 35 6.7 Example 5 14 01.2 32 5.6 Example 6 13 67.2 38 7.4 Example 7 14 15.9 41 6.7 Example 8 14 08.9 42 0.8 Example 9 13 15.3 28 4.4 Example 10 13 34.8 25 8.6 Comparative Example 1 42 5.0 4.2

[0063] Results analysis:

[0064] Compared with Examples 1-10, Comparative Example 1 did not coat lithium oxide, which caused lithium oxide to react with moisture and CO2 in the air, resulting in failure. The specific capacity of the charge was greatly reduced in the first week after placement.

[0065] Compared with Examples 9-10, after the electrode was placed in an environment with 10% humidity for 3 days, the first charge specific capacity of the lithium-ion battery was significantly better than that of Examples 9-10. This is because the added boric acid, phosphoric acid or polyphosphoric acid coated the lithium oxide, and the resulting lithium borate or lithium phosphate coating layer has significantly better stability in air than the lithium oxalate or lithium silicate coating layer. Therefore, it can significantly improve the stability of the pre-lithiated cathode in air and effectively improve the first charge specific capacity.

[0066] Compared with Examples 2, 4, and 6, Examples 1, 3, and 5 had a lower specific capacity for the first charge after being placed in an environment with 10% humidity for 3 days due to the smaller amount of acid added and insufficient coating thickness. This indicates that sufficient acid needs to be added to form a coating layer of sufficient thickness in order to isolate moisture and CO2 in the air.

[0067] The first charge specific capacity of the lithium-ion batteries in Examples 7 and 8 (after the electrode was placed in an environment with 10% humidity for 3 days) was similar to that in Example 2, indicating that the solvent had virtually no effect on the coating results.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A pre-lithiated positive electrode, comprising a positive electrode current collector and a positive electrode active layer, characterized in that, The positive electrode active layer includes lithium oxide coating and a conductive agent; The raw materials for coating lithium oxide, by weight, include: 2-8 parts of lithium oxide; 0.1-0.8 parts acid.

2. The pre-lithiated cathode according to claim 1, characterized in that, In the raw material for coating lithium oxide, the acid is selected from one or more of boric acid, phosphoric acid, polyphosphoric acid, oxalic acid, and silicic acid.

3. The pre-lithiated cathode according to claim 1, characterized in that, In the raw material for coating lithium oxide, the acid is selected from boric acid, phosphoric acid, and polyphosphoric acid.

4. A method for preparing a pre-lithiated cathode, characterized in that, Includes the following steps: S1. Prepare the positive current collector; S2. Preparation of coated lithium oxide slurry: Lithium oxide and organic solvent are mixed evenly to obtain lithium oxide slurry; acid and organic solvent are mixed evenly to obtain acid solution; acid solution is added to lithium oxide slurry, stirred thoroughly, and reacted evenly to obtain coated lithium oxide slurry; S3. Preparation of positive electrode active layer slurry: Add conductive agent to the coated lithium oxide slurry obtained in step S2 above, stir thoroughly and mix evenly to obtain positive electrode active layer slurry; S4. Coat the surface of the positive electrode current collector with the positive electrode active layer slurry obtained in step S3. S5. Drying and cold pressing to obtain the pre-lithiated cathode as described in any one of claims 1-3.

5. The method for preparing a pre-lithiated cathode according to claim 4, characterized in that, In step S2, the organic solvent is selected from N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, ethylene glycol dimethyl ether, 1,3-dioxane, 1,3-dioxane, dimethyl sulfoxide, and polyethylene glycol.

6. The method for preparing a pre-lithiated cathode according to claim 5, characterized in that, In step S2, the organic solvent is selected from one of N-methylpyrrolidone, dimethyl sulfoxide, and 1,3-dioxolane.

7. The method for preparing a pre-lithiated cathode according to claim 4, characterized in that, In step S2, by mass, the lithium oxide slurry contains lithium oxide at a ratio of 1:2-6 to organic solvent; and the acid solution contains acid at a mass ratio of 1-2% of the acid solution.

8. The method for preparing a pre-lithiated cathode according to claim 4, characterized in that, In step S3, the ratio of lithium oxide to acid to conductive agent by mass is 2-6:0.1-0.6:

1.

9. The method for preparing a pre-lithiated cathode according to claim 4, characterized in that, In step S4, the surface density of the positive electrode active layer slurry, based on the mass of the solid components excluding solvent, is 10-20 g / m². 2 .

10. A lithium-ion battery, characterized in that, This includes the pre-lithiated cathode prepared by the preparation method as described in any one of claims 5-9.