An interface pretreatment liquid for pre-lithiation of a positive electrode, a lithium supplementing battery and a preparation method thereof

Abstract

The application discloses an interface pretreatment liquid for prelithiation of a positive electrode, a lithium supplementing battery and a preparation method thereof, and relates to the technical field of lithium ion batteries.The interface pretreatment liquid comprises one or more of lithium polysulfide, hydrobromic acid and hydriodic acid as solutes, and comprises 0.1-10% of the solutes and 90-99.9% of solvents in percentage by mass.The solvents are one or more of N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, gamma-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, dimethyl sulfoxide and dimethyl sulfide.The interface pretreatment liquid has the advantages of simple preparation method, simple use method, short soaking time of lithium supplementing positive electrode sheets in the interface pretreatment liquid, good effect, high production efficiency and suitability for industrial production.

Description

An interfacial pretreatment solution for prelithiated cathode, a lithium-compensating battery and its preparation method Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly to an interfacial pretreatment solution for prelithiated cathode, a lithium-compensating battery and its preparation method. Background Art

[0002] As one of the most promising high-energy density storage devices, silicon lithium-ion batteries have the advantages of high energy density, long cycle life, high safety, environmental friendliness, etc., and are widely used in fields such as electronic products, electric vehicles, aerospace, and large-scale energy storage power stations. With the rapid development of new energy vehicles and the improvement of the cruising range, higher requirements are put forward for the energy density of batteries.

[0003] To further improve the energy density of lithium-ion batteries, lithium compensation for the positive electrode or negative electrode is an effective method. Compared with lithium compensation for the negative electrode, the positive electrode lithium compensation process is simple, has relatively low requirements for equipment and the environment, is safer during use, and the cost is also relatively low. Some patents have studied this.

[0004] Chinese Patent with application number CN201710867438.3 discloses a lithium compensation additive for the positive electrode of a lithium-ion battery and its application. The lithium compensation additive for the positive electrode of this application is a conductive metal-doped lithium oxide powder. By doping copper in the lithium oxide powder, the conductivity of the lithium oxide powder is improved, enabling it to be used as a lithium compensation additive.

[0005] Chinese Patent with application number CN201410707478.8 discloses a positive electrode, its preparation method and a lithium secondary battery using the positive electrode. The positive electrode includes a conductive matrix, a positive electrode active material layer, and a lithium compensation layer provided between the conductive matrix and the positive electrode active material layer. The lithium compensation layer contains at least one lithium-containing compound, at least one conductive agent, and at least one binder. The lithium-containing compound is selected from the group consisting of compounds represented by the formula LixA, where A is O, P, S or N, and 0 < x ≤ 3. The positive electrode of this application has a lithium compensation function and can effectively compensate for the irreversible capacity loss during the charge and discharge process of the lithium secondary battery, improving the energy density of the battery.

[0006] However, as a positive electrode lithium compensation additive, although lithium oxide has a lithium compensation specific capacity as high as 1794 mAh / g, its chemical properties are active and it is easy to absorb moisture and CO2 in the air and deteriorate into LiOH and Li2CO3. On the one hand, this leads to a low specific capacity and a poor lithium compensation effect on the positive electrode; on the other hand, side reactions with the electrolyte cause serious gas generation, affecting the battery performance, and there are limitations in improving the capacity and the first charge-discharge efficiency of lithium-ion secondary batteries. Summary of the Invention

[0007] This application addresses the shortcomings of existing technologies by providing an interface pretreatment solution for a pre-lithiated cathode, a lithium-filled battery, and a method for preparing the same. By selecting the types of solvents and solutes and adjusting the dosage of solutes and solvents, the solvent in this application can fully wet the internal pores of the lithium-filled cathode sheet, and the solute can react with the pre-lithiated cathode material lithium oxide, thereby improving the stability of the cathode surface to air and the stability of the cathode interface film (CEI film), and synergistically enhancing the battery capacity and first charge-discharge efficiency.

[0008] Specifically, in order to achieve the above technical solution, in a first aspect, this application provides an interface pretreatment solution for a pre-lithiated cathode, comprising, by mass percentage, 0.1% to 10% solute and 90% to 99.9% solvent; the solute is one or more of lithium polysulfide, hydrobromic acid, and hydroiodic acid; the solvent is one or more of 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 propionate, propyl propionate, ethyl butyrate, propyl butyrate, dimethyl sulfoxide, ethylene glycol dimethyl ether, 1,3-dioxolane, polyethylene glycol dimethyl ether, and dimethyl sulfoxide.

[0009] Preferably, the mixture comprises 0.5% to 8% solute and 92% to 99.5% solvent by mass percentage.

[0010] Preferably, the mixture comprises 1% to 5% solute and 95% to 99% solvent by mass percentage.

[0011] Preferably, the solvent is selected from one or more of the following: ethylene glycol dimethyl ether, 1,3-dioxolane, polyethylene glycol dimethyl ether, and dimethyl sulfide.

[0012] Preferably, the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 6 to 10:1.

[0013] Secondly, this application provides a method for preparing a lithium-ion battery, comprising the following steps:

[0014] A positive electrode slurry containing a positive electrode active material is coated on the surface of the positive electrode current collector. After drying, an initial positive electrode sheet with a positive electrode film on the surface of the positive electrode current collector is obtained. Then, a layer of lithium oxide is deposited on the surface of the positive electrode film to obtain a lithium-supplemented positive electrode sheet.

[0015] A negative electrode slurry containing a negative electrode active material is coated on the surface of the negative electrode current collector. After drying, a negative electrode sheet with a negative electrode film disposed on the surface of the negative electrode current collector is obtained.

[0016] In an inert gas atmosphere, with water content <1ppm and oxygen content <1ppm, the lithium-added cathode sheet is immersed in an interface pretreatment solution for pre-lithiation cathode for 1min to 25min, and then dried in an inert environment at room temperature for 1-3h to obtain the cathode material.

[0017] The positive electrode material, separator, and negative electrode sheet are assembled into a lithium battery cell;

[0018] The lithium-ion battery cell is placed in a battery packaging shell, injected with electrolyte, and sealed to obtain a lithium-ion battery.

[0019] Preferably, the lithium-added cathode sheet is immersed in the interface pretreatment solution for 2 min to 15 min.

[0020] Preferably, the lithium-added cathode sheet is immersed in the interface pretreatment solution for 5 to 10 minutes.

[0021] Thirdly, this application provides a supplemental lithium battery, which is prepared by a supplemental lithium battery preparation method provided in any embodiment of this application.

[0022] This application has the following beneficial effects: The interface pretreatment solution provided in this application, by adjusting the ratio between solute and solvent, selects specific solutes and solvents. These specific solvents have good chemical stability, strong solubility, and moderate surface tension. Using these reagents as solvents for the interface pretreatment solution allows for sufficient wetting of the internal pores of the lithium-added cathode sheet. The specific solutes can react with lithium oxide to obtain products with good stability. These products have good mechanical properties and electrochemical stability, effectively suppressing side reactions and making the CEI film formed on the surface of the pre-lithiated cathode more stable, thereby improving the battery capacity and first charge-discharge efficiency. Compared with the prior art, the interface pretreatment solution preparation method of this application is simple and easy to use. In the application process, it is only necessary to immerse the lithium-added cathode sheet in the interface pretreatment solution. The immersion time is short, the effect is good, and the production efficiency is high, making it suitable for industrial production. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is a schematic flowchart of the preparation method of the lithium battery according to Embodiment 1 of this application. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] The present invention will be further described below with reference to specific embodiments.

[0028] Example 1

[0029] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0030] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 1% lithium polysulfide and 99% ethylene glycol dimethyl ether; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 7:1.

[0031] (2) The method for preparing the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is as follows:

[0032] In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether was added to an aluminum-plastic bottle, and then sulfur and lithium sulfide were added to the aluminum-plastic bottle in a molar ratio of 7:1. The mixture was stirred for 1 hour until the sulfur and lithium sulfide were completely dissolved, thus preparing an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 1wt%.

[0033] (3) Preparation of lithium-ion batteries; Please refer to Figure 1 for a preferred embodiment. This embodiment provides a method for preparing a lithium-ion battery, including the following steps:

[0034] S1: Prepare the positive electrode sheet; use the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride binder were mixed in a mass ratio of 97:0.5:0.5:2. N-methylpyrrolidone solvent was added, and the mixture was thoroughly stirred to obtain a homogeneous positive electrode slurry. This slurry was then coated onto both surfaces of the positive electrode current collector aluminum foil. The coating mass of the positive electrode slurry was 1.524 g / 76.2 cm². 2 (Single-sided, based on the mass of solid components excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet.

[0035] S2: Preparation of lithium-supplemented positive electrode sheet; Lithium oxide and conductive carbon black SP are mixed at a mass ratio of 1:1, and thoroughly stirred to obtain a lithium-supplemented slurry, which is then coated onto both surfaces of the positive electrode sheet with a coating density of 14.6 g / m². 2 (Double-sided, based on the mass of solid components excluding solvent), then dried and cold-pressed to obtain a lithium-added positive electrode sheet.

[0036] S3: Perform interface pretreatment on the lithium-added positive electrode sheet; in an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, immerse the cut lithium-added positive electrode sheet in the interface pretreatment solution of this embodiment for 5min, and then dry it at room temperature under argon atmosphere for 2h to obtain the negative electrode material.

[0037] S4: Preparation of electrolyte; In an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, 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, dried lithium hexafluorophosphate is dissolved in the above mixed organic solvent at a concentration of 1mol / L. In addition, ethylene carbonate at a mass percentage of 1% of the electrolyte is added as an additive. After stirring evenly, the electrolyte is obtained.

[0038] S5: Prepare a diaphragm; use a polyethylene porous membrane coated with alumina ceramic on both sides as the diaphragm.

[0039] S6: Battery preparation; stack the positive electrode, separator, and negative electrode material in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining a lithium-ion battery cell. Place the lithium-ion battery cell in a battery packaging shell, inject the prepared electrolyte, and seal it to obtain a lithium-ion battery.

[0040] Example 2

[0041] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0042] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% lithium polysulfide and 98% ethylene glycol dimethyl ether; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 7:1.

[0043] (2) The method for preparing the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is as follows:

[0044] In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether was added to an aluminum-plastic bottle, and then sulfur and lithium sulfide were added to the aluminum-plastic bottle in a molar ratio of 7:1. The mixture was stirred for 1 hour until the sulfur and lithium sulfide were completely dissolved, thus preparing an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 2wt%.

[0045] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0046] Example 3

[0047] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0048] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 3% lithium polysulfide and 97% ethylene glycol dimethyl ether; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 7:1.

[0049] (2) The method for preparing the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is as follows:

[0050] In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether was added to an aluminum-plastic bottle, and then sulfur and lithium sulfide were added to the aluminum-plastic bottle in a molar ratio of 7:1. The mixture was stirred for 1 hour until the sulfur and lithium sulfide were completely dissolved, thus preparing an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 3wt%.

[0051] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0052] Example 4

[0053] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0054] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 1% hydrobromic acid and 99% ethylene glycol dimethyl ether.

[0055] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether and hydrobromic acid are added to an aluminum-plastic bottle in sequence and stirred for 1 hour until the hydrobromic acid is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 1wt%.

[0056] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0057] Example 5

[0058] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0059] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% hydrobromic acid and 98% ethylene glycol dimethyl ether.

[0060] (2) The method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with water content <1Pppm and oxygen content <1ppm, ethylene glycol dimethyl ether and hydrobromic acid are added to an aluminum-plastic bottle in sequence and stirred for 1h until the hydrobromic acid is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 2wt%.

[0061] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0062] Example 6

[0063] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0064] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 3% hydrobromic acid and 97% ethylene glycol dimethyl ether.

[0065] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether and hydrobromic acid are added to an aluminum-plastic bottle in sequence and stirred for 1 hour until the hydrobromic acid is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 3wt%.

[0066] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0067] Example 7

[0068] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0069] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% hydroiodic acid and 98% ethylene glycol dimethyl ether.

[0070] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether and hydroiodic acid are added to an aluminum-plastic bottle in sequence and stirred for 1 hour until the hydroiodic acid is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 2wt%.

[0071] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0072] Example 8

[0073] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0074] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% hydroiodic acid and 98% ethylene glycol dimethyl ether.

[0075] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, ethylene glycol dimethyl ether and hydroiodic acid are added to an aluminum-plastic bottle in sequence and stirred for 1 hour until the hydroiodic acid is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 2wt%.

[0076] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0077] Example 9

[0078] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0079] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% hydroiodic acid and 98% ethylene glycol dimethyl ether.

[0080] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, ethylene glycol dimethyl ether and hydroiodic acid are added to an aluminum-plastic bottle in sequence and stirred for 1 hour until the hydroiodic acid is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 2wt%.

[0081] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0082] Example 10

[0083] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0084] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% lithium polysulfide and 98% 1,3-dioxolane; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 7:1.

[0085] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, 98% of 1,3-dioxolane is added to an aluminum-plastic bottle, and then sulfur and lithium sulfide are added to the aluminum-plastic bottle in a molar ratio of 7:1. The mixture is stirred for 1 hour until the sulfur and lithium sulfide are completely dissolved, and an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 2wt% is prepared.

[0086] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0087] Example 11

[0088] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0089] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% lithium polysulfide and 98% polyethylene glycol dimethyl ether; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio.

[0090] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, diethylene glycol dimethyl ether is added to an aluminum-plastic bottle, and then sulfur and lithium sulfide are added to the aluminum-plastic bottle in a molar ratio of 7:1. The mixture is stirred for 1 hour until the sulfur and lithium sulfide are completely dissolved, and an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 2wt% is prepared.

[0091] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0092] Example 12

[0093] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0094] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 2% lithium polysulfide and 98% dimethyl sulfide; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 7:1.

[0095] (2) The specific method for preparing the interface pretreatment solution for the pre-lithiated cathode in this embodiment is as follows: In an argon atmosphere glove box with a water content of <1ppm and an oxygen content of <1ppm, dimethyl sulfide is added to an aluminum-plastic bottle, and then sulfur and lithium sulfide are added to the aluminum-plastic bottle in a molar ratio of 7:1. The mixture is stirred for 1 hour until the sulfur and lithium sulfide are completely dissolved, and an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 2wt% is prepared.

[0096] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0097] Example 13

[0098] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0099] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 0.5% lithium polysulfide and 99.5% ethylene glycol dimethyl ether; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 8:1.

[0100] (2) The specific preparation method of the interface pretreatment solution used for the pre-lithiation cathode in this comparative example is as follows: In an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, ethylene glycol dimethyl ether is added to an aluminum-plastic bottle, and then sulfur and lithium sulfide are added to the aluminum-plastic bottle in a molar ratio of 8:1. Stir for 1 hour until sulfur and lithium sulfide are completely dissolved to prepare an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 0.5wt%.

[0101] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0102] Example 14

[0103] This embodiment provides an interface pretreatment solution for pre-lithiated cathodes, its preparation method, and its application.

[0104] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiated cathode in this embodiment is: 8% lithium polysulfide and 92% ethylene glycol dimethyl ether; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 8:1.

[0105] (2) The specific preparation method of the interface pretreatment solution used for the pre-lithiation cathode in this comparative example is as follows: In an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, ethylene glycol dimethyl ether is added to an aluminum-plastic bottle, and then sulfur and lithium sulfide are added to the aluminum-plastic bottle in a molar ratio of 8:1. Stir for 1 hour until sulfur and lithium sulfide are completely dissolved to prepare an interface pretreatment solution with lithium polysulfide as the solute and a solute mass fraction of 8wt%.

[0106] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0107] Comparative Example 1

[0108] The lithium-ion battery in this comparative example is exactly the same as that in Example 1, except that the interface pretreatment of the lithium-added positive electrode is not performed.

[0109] Comparative Example 2

[0110] The interface pretreatment solution for the pre-lithiated cathode provided in this comparative example is ethylene glycol dimethyl ether, and the preparation process of the lithium-ion battery is the same as in Example 1.

[0111] Comparative Example 3

[0112] The interface pretreatment solution for the pre-lithiated cathode provided in this comparative example is 1,3-dioxolane, and the preparation process of the lithium-ion battery is the same as in Example 1.

[0113] Comparative Example 4

[0114] The interface pretreatment solution for the pre-lithiated cathode provided in this comparative example is polyethylene glycol dimethyl ether, and the preparation process of the lithium-ion battery is the same as in Example 1.

[0115] Comparative Example 5

[0116] The interface pretreatment solution for the pre-lithiated cathode provided in this comparative example is dimethyl sulfide, and the preparation process of the lithium-ion battery is the same as in Example 1.

[0117] Comparative Example 6

[0118] This comparative example provides an interface pretreatment solution for a pre-lithiated cathode, its preparation method, and its application.

[0119] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiation cathode in this comparative example is: 2% dilute hydrochloric acid and 98% ethylene glycol dimethyl ether.

[0120] (2) The specific preparation method of the interface pretreatment solution used for the pre-lithiation cathode in this comparative example is as follows: In an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, ethylene glycol dimethyl ether and dilute hydrochloric acid are added to an aluminum-plastic bottle in sequence and stirred for 1h until the dilute hydrochloric acid is completely dissolved, so as to prepare an interface pretreatment solution with a solute mass fraction of 2wt%.

[0121] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0122] Comparative Example 7

[0123] This comparative example provides an interface pretreatment solution for a pre-lithiated cathode, its preparation method, and its application.

[0124] (1) By mass percentage, the composition of the interface pretreatment solution used for the pre-lithiation cathode in this comparative example is: 2% dilute silica and 98% ethylene glycol dimethyl ether.

[0125] (2) The preparation method of the interface pretreatment solution used for the pre-lithiation cathode in this comparative example is as follows: In an argon atmosphere glove box with water content <1ppm and oxygen content <1ppm, ethylene glycol dimethyl ether and dilute silica are added to an aluminum-plastic bottle in sequence and stirred for 1h until the dilute silica is completely dissolved to prepare an interface pretreatment solution with a solute mass fraction of 2wt%.

[0126] (3) The preparation process of the lithium-ion battery is the same as in Example 1.

[0127] The composition of the interface pretreatment solution in Examples 1 to 14 and Comparative Examples 1 to 7 is shown in Table 1.

[0128] Table 1: Composition of the interfacial pretreatment solution in Examples 1 to 14 and Comparative Examples 1 to 7

[0129]

[0130]

[0131] The batteries of Examples 1 to 14 and Comparative Examples 1 to 7 were tested respectively:

[0132] At 25°C, the battery was first charged at a constant current of 0.02C to a voltage of 3.9V, and then charged at a constant current of 0.2C to a voltage of 4.25V. After standing for 5 minutes, the battery was discharged at a constant current of 0.2C to a voltage of 2.5V. This was the first charge and discharge process. The first charge and discharge test results of the lithium-ion batteries in the example and comparative examples are shown in Table 2.

[0133] Table 2: Performance test results of Examples 1 to 14 and Comparative Examples 1 to 7

[0134] Number | First Week Discharge Capacity (Ah) | First Charge / Discharge Efficiency | Example 1 | 4.36 | 87.1% | Example 2 | 4.38 | 87.5% | Example 3 | 4.38 | 87.6% | Example 4 | 4.32 | 86.3% | Example 5 | 4.34 | 86.8% | Example 6 | 4.35 | 87.0% | Example 7 | 4.35 | 87.0% | Example 8 | 4.37 | 87.3% | Example 9 | 4.37 | 87.4% | Example 10 | 4.36 | 87.2% % Example 1 14.37 87.4% Example 1 24.36 87.1% Example 1 34.20 84.0% Example 1 44.23 84.6% Comparative Example 1 4.05 81.0% Comparative Example 2 4.06 81.2% Comparative Example 3 4.09 81.8% Comparative Example 4 4.07 81.4% Comparative Example 5 4.08 81.5% Comparative Example 6 4.09 81.8% Comparative Example 7 4.08 81.6% surface

[0135] As shown in Table 2, the first charge-discharge efficiency and cycle performance of the lithium-ion batteries in Examples 1-14 are significantly better than those in the comparative example. This indicates that by performing interface pretreatment on the lithium-added cathode sheet, the interfacial film formation of the pre-lithiated cathode can be significantly improved, thereby effectively enhancing the first charge-discharge efficiency. In Comparative Example 1, because no interface pretreatment was performed on the lithium-added cathode sheet, the CEI film formed on the surface of the pre-lithiated cathode was not stable enough, which aggravated the side reactions between the CEI film and the electrolyte, thus affecting the first charge-discharge efficiency of the battery. The composition and structure of the CEI film were not improved, and thermodynamically and kinetically unstable substances such as alkyl lithium carbonate and alkyl lithium were subsequently generated, resulting in insufficient CEI stability, which in turn affected the first charge-discharge efficiency of the battery.

[0136] In Comparative Examples 6 and 7, the reaction of the solute with lithium oxide to form unstable substances failed to improve the interfacial film formation of the pre-lithiated cathode, thus affecting the initial charge-discharge efficiency of the lithium-ion secondary battery. Therefore, it is necessary to add a suitable solute to react with lithium oxide to form a thermodynamically and kinetically stable interfacial layer.

[0137] The above are merely preferred embodiments of this application; however, the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and its improved concept, should be covered within the scope of protection of this application.

Claims

1. A method for preparing a lithium-ion battery, characterized in that, The process includes the following steps: A positive electrode slurry containing positive electrode active material is coated onto the surface of the positive electrode current collector. After drying, an initial positive electrode sheet with a positive electrode film on the surface of the positive electrode current collector is obtained. Then, a layer of lithium oxide is deposited on the surface of the positive electrode film to obtain a lithium-supplemented positive electrode sheet. A negative electrode slurry containing negative electrode active material is coated onto the surface of the negative electrode current collector. After drying, a negative electrode sheet with a negative electrode film on the surface of the negative electrode current collector is obtained. Under an inert gas atmosphere, with water content <1 ppm and oxygen content <1 ppm, the lithium-supplemented positive electrode sheet is immersed in an interface pretreatment solution used for pre-lithiation of the positive electrode for 1 min to 25 min, and then dried in an inert environment at room temperature for 1-3 h to obtain the positive electrode material. The positive electrode material, separator, and negative electrode sheet are assembled into a lithium-supplemented battery cell. The immersion time of the lithium-supplemented positive electrode sheet in the interface pretreatment solution is 2... min~15min; the interface pretreatment solution for the pre-lithiated cathode, by mass percentage, comprises 0.1%~10% solute and 90%~99.9% solvent; the solute is one or more of lithium polysulfide, hydrobromic acid and hydroiodic acid; the solvent is one or more of 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 propionate, propyl propionate, ethyl butyrate, propyl butyrate, dimethyl sulfoxide, ethylene glycol dimethyl ether, 1,3-dioxolane, polyethylene glycol dimethyl ether and dimethyl sulfoxide; the lithium polysulfide is prepared by mixing sulfur and lithium sulfide in a molar ratio of 6~10:

1.

2. The method for preparing a lithium-ion battery according to claim 1, characterized in that, The lithium-added cathode sheet is immersed in the interface pretreatment solution for 5 to 10 minutes.

3. A lithium-ion battery, characterized in that, The lithium-ion battery is prepared by any one of the lithium-ion battery preparation methods described in claims 1-2.

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