CN115172739A - Pre-lithiation method of secondary lithium ion battery positive electrode material - Google Patents

Abstract

The invention discloses a pre-lithiation method of a secondary lithium ion battery anode material. Mixing a secondary lithium ion battery anode powder material with a conductive agent, a binder and nitrogen-tetramethyl pyrrolidone to prepare slurry, uniformly coating the slurry on a carbon paper electrode, and drying to obtain a pre-lithiation electrode; (2) Dissolving lithium fluoride powder in an aqueous solution to prepare a saturated lithium fluoride solution, and adding lithium perchlorate powder to prepare an electrochemical solution system; (3) Placing the dried prelithiation electrode serving as a working electrode in the electrochemical solution system prepared in the step (2) to form a three-electrode system together with a platinum electrode and a reference electrode; or form a double-electrode system with the lithium titanate electrode; and (3) placing the prelithiation electrode at a lower voltage and keeping the constant voltage state for 0.5-2 hours, taking out the prelithiation electrode from the solution and drying, and finishing the prelithiation process. The method adopts an electrochemical pretreatment mode, and excess Li ions are embedded into the electrode material, so that the material performance is obviously improved, and the application prospect is wide.

Description

A kind of pre-lithiation method of positive electrode material of secondary lithium ion battery

Technical field:

The invention belongs to the technical field of preparation of electrode positive electrode materials, and in particular relates to a pre-lithiation method for positive electrode materials of secondary lithium ion batteries.

Background technique:

With the increasingly severe global energy and environmental problems, all countries and industries are actively seeking to develop new energy sources and explore the path of energy conservation and environmental protection. Secondary lithium-ion batteries have the advantages of high energy, long life, high cost performance, and less pollution, and are widely used in new energy vehicles, consumer electronics, energy storage power stations and other fields. In the lithium-ion battery manufacturing process, there is a common problem: during the first charging process of the lithium-ion battery, the organic electrolyte is reduced and decomposed on the surface of the negative electrode material such as graphite to form a solid electrolyte interface film (SEI), and this SEI The formation of the film will cause the consumption of lithium in the positive electrode. This process is irreversible. At the same time, the formation and consumption of the SEI film requires the consumption of lithium in the positive electrode, resulting in a low coulombic efficiency of the first cycle and reducing the capacity of lithium-ion batteries. and energy density. The electrode material is supplemented with lithium by pre-lithiation to offset the irreversible lithium loss caused by the formation of the SEI film, so as to improve the total capacity and energy density of the battery. The common pre-lithiation method of negative electrode lithium supplement technology is negative electrode supplement lithium, such as lithium foil supplement, lithium powder supplement, etc., which are all pre-lithiation processes that are currently being developed. The pre-lithiation of the positive electrode usually adopts a chemical synthesis method, adding a lithium source in the process of synthesizing the material. This method is suitable for commercial applications, but how to find a stable lithium source is the direction to be broken now.

Invention content:

In order to solve the above technical problems and make up for the deficiencies in the prior art, the present invention provides a pre-lithiation treatment method for a positive electrode material of a secondary lithium ion battery by means of electrochemical reduction.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A pre-lithiation method for a positive electrode material of a secondary lithium ion battery, comprising the following steps:

(1) Mix the positive electrode powder material of the secondary lithium ion battery with the conductive agent, binder and nitrogen-tetramethylpyrrolidone (NMP) to prepare a slurry, uniformly coat it on the carbon paper electrode, and then heat it at 60-90 ℃ drying in an oven to obtain a dried pre-lithiated electrode;

(2) Dissolving lithium fluoride powder in an aqueous solution to make a saturated lithium fluoride solution, and adding an 8 mol/L lithium perchlorate solution to make an electrochemical solution system;

(3) placing the dried pre-lithiated electrode as a working electrode in the electrochemical solution system prepared in step (2) to form a three-electrode system with a platinum electrode and a reference electrode; or form a double electrode with a lithium titanate electrode system; after placing the pre-lithiation electrode at a lower voltage and maintaining a constant voltage state for 0.5-2 hours, it is taken out from the solution and dried, and the pre-lithiation process is over.

Preferably, in the above method for pre-lithiation of positive electrode materials for secondary lithium ion batteries, the proportion by weight of each component in step (1) is: 85 to 99 parts of positive electrode powder materials for secondary lithium ion batteries, 0.5 ~10 parts of conductive agent, 0.5 to 5 parts of adhesive, 2-10 parts of nitrogen-tetramethylpyrrolidone.

Preferably, in the above-mentioned pre-lithiation method for the positive electrode material of a secondary lithium ion battery, the conductive agent in step (1) is a mixture of one or more of carbon black, graphite, graphene powder or carbon nanotubes .

Preferably, in the pre-lithiation method for the positive electrode material of a secondary lithium ion battery, the binder in step (1) is PVDF or PTFE powder or a mixture thereof.

Preferably, in the pre-lithiation method for the positive electrode material of the secondary lithium ion battery, the positive electrode powder material of the secondary lithium ion battery in step (1) is Li ₂ IrO ₃ , LiFePO ₄ , Li ₄ Ti ₅ O ₁₂ or LiCoO ₂ .

Preferably, in the pre-lithiation method for the positive electrode material of the secondary lithium ion battery, the volume ratio of the saturated lithium fluoride solution and the 8 mol/L concentration lithium perchlorate solution in step (2) is 1:10~ Between 10:1.

Preferably, in the above-mentioned method for pre-lithiation of the positive electrode material of a secondary lithium ion battery, the low voltage in step (3) refers to a voltage between negative 0.2 V and 0.8 V.

Compared with the prior art, the present invention has the following beneficial effects: the present invention adopts the electrochemical reduction method for the first time in the pre-lithiation treatment method of the positive electrode material of the secondary lithium ion battery. The present invention uses the electrochemical pretreatment method to embed excess Li ions into the electrode material, which significantly improves the material performance and has broad application prospects.

Description of drawings

Fig. 1 is the data of electrochemical constant voltage lithium charging in Example 1;

FIG. 2 is an SEM image of the electrode after electrochemical pre-lithiation treatment in Example 1. FIG.

Fig. 3 is that embodiment 2 shows the spectrogram before prelithiation;

Fig. 4 shows the sample spectrogram after pre-lithiation in Example 2;

FIG. 5 is an SEM image of the electrode after electrochemical pre-lithiation treatment in Example 2. FIG.

Detailed ways

The present invention will be described in further detail below with reference to specific examples, only for illustrating the present invention, rather than for limiting the scope of the present invention.

Example 1: Pre-lithiation treatment of Li ₂ IrO ₃ electrode material.

1. The Li ₂ IrO ₃ powder material and carbon black, PVDF, and nitrogen-tetramethylpyrrolidone solution were prepared from the following components by weight: 85 parts of positive active material, 1 part of carbon black, 5 parts of PVDF, 8 parts of Nitrogen-tetramethylpyrrolidone was uniformly mixed to prepare a slurry, which was uniformly coated on the carbon paper electrode and dried in an oven at 75°C.

2. Dissolve excess lithium fluoride in 100ml of solution, filter the supernatant for use. In 100 ml of saturated lithium fluoride solution, 851 mg of lithium perchlorate powder was added to prepare a lithium perchlorate solution with a concentration of 8 mol/L, and the solution was heated to 70 °C while stirring. After all the powder is dissolved, cool down to room temperature naturally.

3. The dried pre-lithiated electrode is placed as a working electrode in a mixed solution of saturated lithium fluoride and 8M lithium perchlorate to form a dual-electrode system with the lithium titanate electrode. After placing the pre-lithiated electrode at a voltage of 0.4 V vs Ag/AgCl and maintaining a constant voltage state for 1 hour, it was removed from the solution and dried, and the pre-lithiation process was over. The electrode after pre-lithiation treatment was tested for lithium charging effect. As shown in Figure 1, the initial charging current of the electrode reached 8 mA. Although the current declines rapidly, the absolute current of 1 mA is still maintained for more than 30 minutes, indicating that the lithium charging effect of the electrode is obvious. Figure 2 shows the SEM image of the electrode after electrochemical pre-lithiation treatment. It can be observed that the material particles have a uniform appearance and are tightly covered on the electrode. The pre-lithiation experiment did not damage the morphology and structure of the electrode material.

Example 2: Pre-lithiation of LiCoO ₂ electrode material.

1. A solution of LiCoO ₂ powder material with carbon nanotubes, PTFE, and nitrogen-tetramethylpyrrolidone was made of the following components by weight: 99 parts of positive active material, 9 parts of carbon nanotubes, 1 part of PTFE, 3 parts of Nitrogen-tetramethylpyrrolidone was uniformly mixed to prepare a slurry, which was uniformly coated on the carbon paper electrode and dried in an oven at 85°C.

2. Dissolve excess lithium fluoride in 100 ml of solution, filter the supernatant for use. In 100 ml of saturated lithium fluoride solution, 212.8 mg of lithium perchlorate powder was added to prepare a 2 mol/L concentration of lithium perchlorate solution, and the solution was heated to 70 °C while stirring. After all the powder is dissolved, cool down to room temperature naturally.

3. The dried prelithiated electrode is placed in a mixed solution of saturated lithium fluoride and 2M lithium perchlorate as a working electrode to form a three-electrode system with a platinum electrode and a reference electrode. After placing the pre-lithiated electrode at negative 0.2 V vs Ag/AgCl voltage and maintaining a constant voltage state for 2 hours, it was removed from the solution and dried, and the pre-lithiation process was over. The electrode after pre-lithiation was subjected to 7Li solid-state nuclear magnetic test. Figure 3 shows the spectrum before pre-lithiation, and Figure 4 shows the sample spectrum after pre-lithiation. At a chemical shift of 0 ppm, the peak intensity becomes more obvious, indicating that the lithium charging process has changed the internal lithium ion chemical environment, and there are more free lithium ions, indicating that the electrode has an obvious lithium charging effect. Figure 5 is an SEM image of the electrode after electrochemical pre-lithiation treatment, and it can be observed that the material particles are closely covered on the electrode.

Claims (7)

1. A pre-lithiation method for a secondary lithium ion battery positive electrode material is characterized by comprising the following steps:

(1) Mixing a secondary lithium ion battery anode powder material with a conductive agent, a binder and nitrogen-tetramethyl pyrrolidone to prepare slurry, uniformly coating the slurry on a carbon paper electrode, and drying the carbon paper electrode in a drying oven at the temperature of 60-90 ℃ to obtain a dried pre-lithiation electrode;

(2) Dissolving lithium fluoride powder in an aqueous solution to prepare a saturated lithium fluoride solution, and adding a lithium perchlorate solution with the concentration of 2-10 mol/L to prepare an electrochemical solution system;

(3) Placing the dried prelithiation electrode serving as a working electrode in the electrochemical solution system prepared in the step (2) to form a three-electrode system together with a platinum electrode and a reference electrode; or form a double-electrode system with the lithium titanate electrode; and (3) placing the prelithiation electrode at a lower voltage and keeping the constant voltage state for 0.5-2 hours, taking out the prelithiation electrode from the solution and drying, and finishing the prelithiation process.

2. The prelithiation method of a secondary lithium ion battery positive electrode material according to claim 1, wherein the weight parts of the components in step (1) are: 85 to 99 parts of secondary lithium ion battery anode powder material, 0.5 to 10 parts of conductive agent, 0.5 to 5 parts of adhesive and 2 to 10 parts of nitrogen-tetramethyl pyrrolidone.

3. The prelithiation method of a positive electrode material of a secondary lithium ion battery according to claim 1, wherein the conductive agent in step (1) is one or more of carbon black, graphite, graphene powder, and carbon nanotubes.

4. The method for prelithiation of a positive electrode material in a secondary lithium ion battery according to claim 1, wherein the binder of step (1) is PVDF or PTFE powder or a mixture thereof.

5. The prelithiation method of a positive electrode material for a secondary lithium ion battery according to claim 1, wherein the positive electrode powder material for a secondary lithium ion battery in step (1) is Li ₂ IrO ₃ 、LiFePO ₄ 、Li ₄ Ti ₅ O ₁₂ Or LiCoO ₂ 。

6. The prelithiation method of the positive electrode material of the secondary lithium ion battery according to claim 1, wherein the volume ratio of the saturated lithium fluoride solution to the 2 to 8 mol/L lithium perchlorate solution in the step (2) is 1:10 to 10: 1.

7. The prelithiation method of a positive electrode material for a secondary lithium ion battery according to claim 1, wherein said low voltage in step (3) is a voltage between negative 0.2 and 0.8V.

Images