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

Abstract

The present invention discloses a pre-lithiation positive electrode, a preparation method and a lithium-ion battery, belonging to the technical field of lithium-ion batteries. A pre-lithiation positive electrode comprises a positive electrode current collector and a positive electrode active layer, wherein the positive electrode active layer comprises coated lithium oxide and a conductive agent; in parts by weight, the raw materials of the coated lithium oxide comprise 2-8 parts of lithium oxide and 0.1-0.8 parts of acid. A pre-lithiation positive electrode disclosed by the present invention uses coated lithium oxide as a positive electrode lithium supplement additive, and the coating layer has a protective effect on the lithium oxide, can isolate moisture and carbon dioxide in the air, prevent lithium oxide from reacting to generate LiOH and Li2CO3, effectively improve the stability of the pre-lithiation positive electrode in the air, and thus improve the electrical performance of the assembled lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a pre-lithiation positive electrode, a preparation method and a lithium ion battery. Background Art

[0002] As one of the most promising high-energy-density storage devices, lithium-ion batteries offer advantages such as high energy density, long cycle life, high safety, and environmental friendliness. They are widely used in electronics, electric vehicles, aerospace, large-scale energy storage power stations, and other fields. The rapid development of new energy vehicles and the increase in driving range have placed higher demands on battery energy density.

[0003] To further increase the energy density of lithium-ion batteries, replenishing lithium at the positive or negative electrodes is an effective method. Compared to replenishing lithium at the negative electrode, replenishing lithium at the positive electrode is simpler, has relatively lower equipment and environmental requirements, is safer to use, and is relatively inexpensive.

[0004] Chinese patent CN107863567A discloses a lithium supplement additive, its preparation method, and its application. By doping lithium oxide powder with copper, the additive improves its conductivity and serves as a lithium supplement additive. While lithium oxide has a high specific capacity as a positive electrode supplement, its chemically active nature allows it to absorb moisture and carbon dioxide from the air, reacting to form LiOH and Li2CO3. This reduces the specific capacity and reduces the effectiveness of the supplement. Furthermore, the generated LiOH and Li2CO3 react with the electrolyte, leading to significant gassing and negatively impacting lithium battery performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a pre-lithiation positive electrode with stable chemical properties; another purpose of the present invention is to provide a method for preparing a pre-lithiation positive electrode with stable chemical properties; another purpose of the present invention is to provide a lithium-ion battery with better initial charge and discharge capacity and coulombic efficiency.

[0006] The present invention provides a pre-lithiation positive electrode, comprising a positive electrode current collector and a positive electrode active layer, wherein the positive electrode active layer comprises coated lithium oxide and a conductive agent; in parts by weight, the raw materials for the coated lithium oxide include:

[0007] 2-8 parts of lithium oxide;

[0008] Acid 0.1-0.8 parts.

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

[0010] 2-8 parts of lithium oxide;

[0011] Acid 0.4-0.8 parts.

[0012] Properly increasing the amount of acid can increase the thickness of the lithium oxide coating layer, thereby improving the stability of the coated lithium oxide.

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

[0014] An appropriate amount of acid reacts with lithium oxide under suitable conditions to form a coating layer on the surface of lithium oxide, thereby isolating the lithium oxide from the air, thereby 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 one of 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] The present invention also provides a method for preparing a pre-lithiation positive electrode, comprising the following steps:

[0019] S1. Prepare the positive electrode current collector;

[0020] S2, preparing coated lithium oxide slurry: mixing lithium oxide and an organic solvent to obtain lithium oxide slurry; mixing acid and an organic solvent to obtain an acid solution; adding the acid solution to the lithium oxide slurry, stirring thoroughly, reacting uniformly, and obtaining coated lithium oxide slurry;

[0021] S3, preparing a positive electrode active layer slurry: adding a conductive agent to the coated lithium oxide slurry obtained in step S2 above, stirring thoroughly, and mixing uniformly to obtain a positive electrode active layer slurry;

[0022] S4, coating the positive electrode active layer slurry obtained in step S3 on the surface of the positive electrode current collector;

[0023] S5. Drying and cold pressing to obtain the pre-lithiation positive electrode as described above.

[0024] Furthermore, in step S2, the organic solvent is selected from one of N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl 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-dioxolane, 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, in the lithium oxide slurry, the ratio of lithium oxide to organic solvent is 1:2-6 by mass; and in the acid solution, the mass ratio of the acid to the acid solution is 1-2%.

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

[0028] Furthermore, in step S4, the coating surface density of the positive electrode active layer slurry is 10-20 g / m 2 .

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

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

[0031] The contents of the present application are described in more detail below through examples. However, the following examples are only used to illustrate the contents of the present application rather than to limit them. Therefore, any changes within the meaning and scope equivalent to the claims of the present application should be deemed to be included in the scope of the claims.

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

[0033] Example 1

[0034] Preparation of pre-lithiation cathode:

[0035] (1) Prepare aluminum foil as the positive electrode current collector.

[0036] (2) Preparation of coated lithium oxide slurry: 4 g of lithium oxide was added to 16 g of N-methylpyrrolidone solvent and stirred thoroughly to obtain a lithium oxide slurry. 0.2 g of boric acid was added to the N-methylpyrrolidone solvent to prepare a 20 g acid solution. The acid solution was slowly dripped into the lithium oxide slurry and stirred thoroughly to obtain a coated lithium oxide slurry.

[0037] (3) Preparation of positive electrode active layer slurry: Add 1g of conductive carbon black to the coated lithium oxide slurry and stir thoroughly to achieve uniform reaction.

[0038] (4) The positive electrode active layer slurry is evenly coated on the surface of the aluminum foil with a coating density of 14.6 g / m 2 (single side, based on the mass of the solid component excluding the solvent).

[0039] (5) Drying and cold pressing to produce a pre-lithiation positive electrode.

[0040] Example 2

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

[0042] Example 3

[0043] The preparation process is the same as that of Example 1, except that the acid in step (2) is 0.2 g of phosphoric acid.

[0044] Example 4

[0045] The preparation process is the same as that of Example 1, except that the acid in step (2) is 0.4 g of phosphoric acid.

[0046] Example 5

[0047] The preparation process is the same as that of Example 1, except that the acid in step (2) is 0.2 g of polyphosphoric acid.

[0048] Example 6

[0049] The preparation process is the same as that of Example 1, except that the acid in step (2) is 0.4 g of polyphosphoric acid.

[0050] Example 7

[0051] The preparation process is the same as that of Example 2, except that the solvent of the acid in step (2) is different, namely dimethyl sulfoxide.

[0052] Example 8

[0053] The preparation process is the same as that of Example 2, except that the solvent of the acid in step (2) is different, namely 1,3-dioxolane.

[0054] Example 9

[0055] The preparation process is the same as that of Example 1, except that the acid in step (2) is 0.4 g of oxalic acid.

[0056] Example 10

[0057] The preparation process is the same as that of Example 1, except that the acid in step (2) is 0.4 g of silicic acid.

[0058] Comparative Example

[0059] The preparation process is the same as that of Example 1, except that no acid solution is added in step (2).

[0060] The compositions of Examples 1-10 are shown in Table 1.

[0061] Table 1 Composition of Examples 1-10

[0062] serial number solvent solute 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 Polyphosphoric acid (5% by mass of lithium oxide) Example 6 N-Methylpyrrolidone Polyphosphoric acid (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 Silicic acid (10% by mass of lithium oxide) Comparative Example N-Methylpyrrolidone /

[0063] Assemble into lithium-ion battery:

[0064] The pre-lithiated positive electrodes prepared in Examples 1-10 and the comparative example were assembled with the negative electrode, the separator, and the electrolyte to form a lithium-ion battery.

[0065] Preparation of electrolyte:

[0066] In an argon atmosphere glove box with a water content of <10 ppm and an oxygen content of <10 ppm, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate and fluoroethylene carbonate are mixed in proportions of 20%, 30%, 40% and 10% by mass to obtain a mixed organic solvent. Then, sufficiently dried lithium hexafluorophosphate is dissolved in the mixed organic solvent, wherein the concentration of the lithium hexafluorophosphate is 1 mol / L. The additive is vinylene carbonate, which accounts for 1% by mass of the electrolyte. After uniform stirring, an electrolyte is obtained.

[0067] Diaphragm: A polyethylene porous membrane coated with alumina ceramic on both sides is used as the diaphragm.

[0068] Negative electrode: A metallic lithium sheet (0.6 mm thick, 99.9% purity) was used as the negative electrode.

[0069] Convert to lithium-ion battery:

[0070] The pre-lithiated positive electrode sheets prepared in Examples 1-10 and the comparative example were cut into discs with a diameter of 12 mm, and then the positive electrode sheets, separators and metal lithium sheets were stacked in order with the separator in the middle to act as an isolater, and assembled into button batteries. The amount of electrolyte added to each button battery was 150 μL.

[0071] Battery performance test:

[0072] 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 charge specific capacity of the battery was tested when the positive electrode was prepared and immediately assembled into a battery and when the battery was placed in an environment of 25°C and 10% humidity for 3 days before being assembled into a battery. The test results of the examples are shown in Table 2.

[0073] Table 2 Initial charge specific capacity of the lithium ion batteries of Examples 1-10 and Comparative Examples

[0074]

[0075] Result analysis:

[0076] Compared with Examples 1-10, in Comparative Example 1, since the lithium oxide was not coated, the lithium oxide reacted with moisture and CO2 in the air, resulting in failure. The charging capacity in the first week after placement was greatly reduced.

[0077] Compared with Examples 9-10, the first charge specific capacity of the lithium-ion battery in Examples 1-8 is significantly better than that in Examples 9-10 after the electrode is placed in an environment with 10% humidity for 3 days. This is because the added boric acid, phosphoric acid or polyphosphoric acid is used to coat the lithium oxide, and the resulting lithium borate or lithium phosphate coating is significantly more stable in the air than the lithium oxalate or lithium silicate coating. Therefore, it can significantly improve the stability of the pre-lithiation positive electrode in the air and effectively improve the first charge specific capacity.

[0078] Compared with Examples 2, 4, and 6, in Examples 1, 3, and 5, the amount of acid added is small and the coating thickness is insufficient. Therefore, the first charge specific capacity of the electrode after being placed in an environment with a humidity of 10% for 3 days is lower than that of Examples 2, 4, and 6. It can be seen that sufficient acid needs to be added to form a coating layer of sufficient thickness to isolate moisture and CO2 in the air.

[0079] The initial charge specific capacity of the lithium-ion batteries of Examples 7 and 8 (after the electrodes were placed in a 10% humidity environment for 3 days) was similar to that of Example 2, indicating that the solvent had little effect on the coating results.

[0080] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a pre-lithiation positive electrode, characterized in that: The following steps are involved: S1. Prepare the positive electrode current collector; S2. Prepare coated lithium oxide slurry: mix lithium oxide and an organic solvent to obtain lithium oxide slurry; mix acid and an organic solvent to obtain an acid solution; add the acid solution to the lithium oxide slurry, stir thoroughly, and react uniformly to obtain coated lithium oxide slurry; in parts by weight, the raw materials of the coated lithium oxide include 2-8 parts of lithium oxide; 0.1-0.8 parts of acid; the acid is boric acid; S3, preparing a positive electrode active layer slurry: adding a conductive agent to the coated lithium oxide slurry obtained in step S2 above, stirring thoroughly, and mixing uniformly to obtain a positive electrode active layer slurry; S4, coating the positive electrode active layer slurry obtained in step S3 on the surface of the positive electrode current collector; S5. Drying and cold pressing to obtain a pre-lithiated positive electrode.

2. The method for preparing a pre-lithiation positive electrode according to claim 1, wherein: In step S2, the organic solvent is selected from one of N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl 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-dioxolane, 1,3-dioxane, dimethyl sulfoxide, and polyethylene glycol.

3. The method for preparing a pre-lithiation positive electrode according to claim 2, wherein: In step S2, the organic solvent is selected from one of N-methylpyrrolidone, dimethyl sulfoxide, and 1,3-dioxolane.

4. The method for preparing a pre-lithiation positive electrode according to claim 1, wherein: In step S2, in the lithium oxide slurry, the ratio of lithium oxide to organic solvent is 1:2-6 by mass; and in the acid solution, the mass ratio of the acid to the acid solution is 1-2%.

5. The method for preparing a pre-lithiation positive electrode according to claim 1, wherein: In step S3, the ratio of the lithium oxide: the acid: the conductive agent is 2-6:0.1-0.6:1 by mass.

6. The method for preparing a pre-lithiation positive electrode according to claim 1, wherein: In step S4, the coating surface density of the positive electrode active layer slurry is 10-20 g / m2 based on the mass of the solid component excluding the solvent. 2 .

7. A pre-lithiation positive electrode, characterized in that The method is prepared according to any one of claims 1 to 6.

8. A lithium-ion battery, characterized in that: Comprising the pre-lithiation positive electrode as claimed in claim 7.

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