A method for pre-lithiation of cathode materials for secondary lithium-ion batteries

Abstract

This invention discloses a pre-lithiation method for a secondary lithium-ion battery cathode material. The method includes: (1) mixing secondary lithium-ion battery cathode powder with a conductive agent, binder, and N-tetramethylpyrrolidone to prepare a slurry, uniformly coating it onto a carbon paper electrode, and then drying it to obtain a pre-lithiated 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 pre-lithiated electrode as the working electrode in the electrochemical solution system prepared in step (2), forming a three-electrode system with a platinum electrode and a reference electrode; or forming a two-electrode system with a lithium titanate electrode; placing the pre-lithiated electrode at a low voltage and maintaining a constant voltage state for 0.5-2 hours, then removing it from the solution and drying it, thus ending the pre-lithiation process. This invention uses an electrochemical pretreatment method to embed excess Li ions into the electrode material, significantly improving material performance and showing broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of electrode cathode material preparation technology, specifically, it relates to a pre-lithiation method for a secondary lithium-ion battery cathode material. Background Technology

[0002] With the increasingly severe global energy and environmental problems, countries and industries are actively seeking to develop new energy sources and explore energy-saving and environmentally friendly paths. Secondary lithium-ion batteries, with their advantages of high energy density, long lifespan, high cost-effectiveness, and low pollution, are widely used in new energy vehicles, consumer electronics, and energy storage power stations. A common problem in lithium-ion battery manufacturing is that during the first charge, the organic electrolyte undergoes reduction and decomposition on the surface of negative electrode materials such as graphite, forming a solid electrolyte interphase (SEI) film. This SEI film formation causes irreversible lithium consumption in the positive electrode. Furthermore, both the formation and consumption of the SEI film require lithium from the positive electrode, resulting in low coulombic efficiency in the first cycle and reducing the capacity and energy density of the lithium-ion battery. Pre-lithiation replenishes lithium to the electrode materials to offset the irreversible lithium loss caused by the SEI film formation, thereby improving the battery's total capacity and energy density. Common pre-lithiation methods for negative electrode replenishment include lithium foil replenishment and lithium powder replenishment, which are currently key pre-lithiation processes under development. Cathode pre-lithiation is usually achieved through chemical synthesis, which involves adding a lithium source during the synthesis process. This method is suitable for commercial applications, but finding a stable lithium source is the direction that needs to be addressed. Summary of the Invention

[0003] To address the aforementioned technical problems and overcome the shortcomings of existing technologies, this invention provides a pre-lithiation treatment method for secondary lithium-ion battery cathode materials using electrochemical reduction.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for pre-lithiation of a cathode material for a secondary lithium-ion battery includes the following steps:

[0006] (1) The positive electrode powder material of secondary lithium-ion battery is mixed with conductive agent, binder and nitrogen-tetramethylpyrrolidone (NMP) to prepare slurry, which is uniformly coated on carbon paper electrode and then dried in an oven at 60-90℃ to obtain dried pre-lithiation electrode.

[0007] (2) Dissolve lithium fluoride powder in an aqueous solution to prepare a saturated lithium fluoride solution, and add an 8 mol / L lithium perchlorate solution to prepare an electrochemical solution system;

[0008] (3) Place the dried pre-lithiation electrode as the working electrode in the electrochemical solution system prepared in step (2) to form a three-electrode system with the platinum electrode and the reference electrode; or form a two-electrode system with the lithium titanate electrode; after placing the pre-lithiation electrode at a low voltage and maintaining a constant voltage state for 0.5-2 hours, remove it from the solution and dry it, and the pre-lithiation process ends.

[0009] Preferably, in the above-mentioned pre-lithiation method for secondary lithium-ion battery cathode material, the weight ratio of each component in step (1) is: 85-99 parts of secondary lithium-ion battery cathode powder material, 0.5-10 parts of conductive agent, 0.5-5 parts of binder, and 2-10 parts of nitrogen-tetramethylpyrrolidone.

[0010] Preferably, in the above-mentioned pre-lithiation method for secondary lithium-ion battery cathode materials, the conductive agent in step (1) is one or a mixture of carbon black, graphite, graphene powder or carbon nanotubes.

[0011] Preferably, in the above-mentioned pre-lithiation method for secondary lithium-ion battery cathode materials, the binder in step (1) is PVDF or PTFE powder or a mixture thereof.

[0012] Preferably, in the above-mentioned pre-lithiation method for secondary lithium-ion battery cathode materials, the secondary lithium-ion battery cathode powder material in step (1) is Li2IrO3, LiFePO4, or Li4Ti5O. 12 Or LiCoO2.

[0013] Preferably, in the above-mentioned pre-lithiation method for secondary lithium-ion battery cathode materials, the volume ratio of the saturated lithium fluoride solution and the 8 mol / L lithium perchlorate solution in step (2) is between 1:10 and 10:1.

[0014] Preferably, in the above-mentioned pre-lithiation method for secondary lithium-ion battery cathode materials, the low voltage in step (3) refers to a voltage between -0.2 and 0.8 V.

[0015] Compared with existing technologies, this invention has the following advantages: This invention is the first to employ an electrochemical reduction method for the pre-lithiation treatment of cathode materials in secondary lithium-ion batteries. By using electrochemical pretreatment, this invention embeds excess Li ions into the electrode material, significantly improving material performance and demonstrating broad application prospects. Attached Figure Description

[0016] Figure 1 The data are from the electrochemical constant voltage lithium charging in Example 1;

[0017] Figure 2 The image shows the SEM image of the electrode after electrochemical pre-lithiation treatment in Example 1.

[0018] Figure 3 The spectrum before pre-lithiation is shown for Example 2;

[0019] Figure 4 The spectrum of the sample after pre-lithiation is shown for Example 2;

[0020] Figure 5 This is a SEM image of the electrode after electrochemical pre-lithiation treatment in Example 2. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific examples, which is only for illustrating the present invention and not for limiting the scope of the present invention.

[0022] Example 1: Pre-lithiation treatment of Li2IrO3 electrode material.

[0023] 1. The Li2IrO3 powder material, carbon black, PVDF, and nitrogen-tetramethylpyrrolidone solution are prepared by uniformly mixing the following components in parts by weight: 85 parts positive electrode active material, 1 part carbon black, 5 parts PVDF, and 8 parts nitrogen-tetramethylpyrrolidone. The slurry is then uniformly coated onto a carbon paper electrode and dried in an oven at 75°C.

[0024] 2. Dissolve excess lithium fluoride in 100 ml of solution, filter and set aside the supernatant. Add 851 mg of lithium perchlorate powder to 100 ml of saturated lithium fluoride solution to prepare an 8 mol / L lithium perchlorate solution. Heat the solution to 70°C while stirring. After all the powder has dissolved, allow it to cool naturally to room temperature.

[0025] 3. The dried pre-lithiated electrode was placed as the working electrode in a mixed solution of saturated lithium fluoride and 8M lithium perchlorate, forming a dual-electrode system with the lithium titanate electrode. The pre-lithiated electrode was subjected to a 0.4 V vs Ag / AgCl voltage and maintained at a constant voltage for 1 hour, then removed from the solution and dried, completing the pre-lithiation process. The pre-lithiated electrode was then tested for lithium charging performance. Figure 1 As shown, the initial lithium charging current of the electrode reached 8 mA. Although the current decayed rapidly, it still maintained an absolute current of 1 mA for more than 30 minutes, indicating that the lithium charging effect of the electrode was significant. Figure 2 The image shows the SEM image of the electrode after electrochemical pre-lithiation treatment. It can be observed that the material particles are uniform in appearance and tightly cover the electrode. The pre-lithiation experiment did not damage the morphology and structure of the electrode material.

[0026] Example 2: Pre-lithiation treatment of LiCoO2 electrode material.

[0027] 1. The LiCoO2 powder material, carbon nanotubes, PTFE, and nitrogen-tetramethylpyrrolidone solution were prepared by uniformly mixing the following components in parts by weight: 99 parts positive electrode active material, 9 parts carbon nanotubes, 1 part PTFE, and 3 parts nitrogen-tetramethylpyrrolidone. The slurry was then uniformly coated onto a carbon paper electrode and dried in an oven at 85°C.

[0028] 2. Dissolve excess lithium fluoride in 100 ml of solution, filter and set aside the supernatant. Add 212.8 mg of lithium perchlorate powder to 100 ml of saturated lithium fluoride solution to prepare a 2 mol / L lithium perchlorate solution. Heat the solution to 70°C while stirring. After all the powder has dissolved, allow it to cool naturally to room temperature.

[0029] 3. The dried pre-lithiated electrode was placed as the working electrode in a mixed solution of saturated lithium fluoride and 2M lithium perchlorate, forming a three-electrode system with a platinum electrode and a reference electrode. The pre-lithiated electrode was subjected to a negative 0.2 V vs Ag / AgCl voltage and maintained at a constant voltage for 2 hours, then removed from the solution and dried, completing the pre-lithiation process. The pre-lithiated electrode was then subjected to solid-state NMR spectroscopy on 7Li. Figure 3 The spectrum before pre-lithiation is shown. Figure 4 The spectrum of the sample after pre-lithiation is shown. At a chemical shift of 0 ppm, the peak intensity becomes more pronounced, indicating that the lithium charging process alters the internal lithium-ion chemical environment and results in more free lithium ions, demonstrating a significant lithium charging effect on the electrode. Figure 5 The image shows an SEM image of the electrode after electrochemical pre-lithiation treatment, which reveals that the material particles are tightly covered on the electrode.

Claims

1. A method for pre-lithiation of a secondary lithium-ion battery cathode material, characterized in that... Includes the following steps: (1) The positive electrode powder material of secondary lithium-ion battery is mixed with conductive agent, binder and nitrogen-tetramethylpyrrolidone to prepare slurry, which is uniformly coated on carbon paper electrode and then dried in an oven at 60-90℃ to obtain dried pre-lithiation electrode. (2) Dissolve lithium fluoride powder in an aqueous solution to prepare a saturated lithium fluoride solution, and add a lithium perchlorate solution with a concentration of 2-10 mol / L to prepare an electrochemical solution system; (3) Place the dried pre-lithiation electrode as the working electrode in the electrochemical solution system prepared in step (2) to form a three-electrode system with the platinum electrode and the reference electrode; or form a two-electrode system with the lithium titanate electrode; after placing the pre-lithiation electrode at a low voltage and maintaining a constant voltage state for 0.5-2 hours, remove it from the solution and dry it, and the pre-lithiation process ends. The volume ratio of the saturated lithium fluoride solution and the 2-10 mol / L lithium perchlorate solution in step (2) is between 1:10 and 10:

1. The low voltage mentioned in step (3) refers to a voltage between -0.2 and 0.8 V; The weight ratio of each component in step (1) is as follows: 85-99 parts of secondary lithium-ion battery positive electrode powder material, 0.5-10 parts of conductive agent, 0.5-5 parts of binder, and 2-10 parts of nitrogen-tetramethylpyrrolidone. The conductive agent mentioned in step (1) is one or a mixture of several of carbon black, graphite, graphene powder or carbon nanotubes; The adhesive used in step (1) is PVDF or PTFE powder or a mixture thereof; The secondary lithium-ion battery cathode powder material mentioned in step (1) is Li2IrO3, LiFePO4, or Li4Ti5O. 12 Or LiCoO2.

Images