A method for preparing a lithium titanate reference electrode and performing a one-step in-situ lithiation.

Abstract

This invention proposes a method for preparing a lithium titanate (LTO) reference electrode and performing a one-step in-situ lithiation, specifically relating to the field of energy storage technology. The method includes the following steps: LTO reference electrode coating, four-electrode battery fabrication, and one-step in-situ lithiation of the LTO reference electrode. Compared to traditional LTO reference electrode preparation methods, this method avoids the disassembly and transfer process of the LTO reference electrode in non-in-situ lithiation methods, and optimizes the two lithiation steps into a one-step lithiation process, thereby simplifying the LTO reference electrode preparation process and saving manufacturing costs.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and more specifically, to a method for preparing a lithium titanate reference electrode and a one-step in-situ lithiation method. Background Technology

[0002] Lithium-ion batteries, with their advantages of high voltage, high energy density, long cycle life, and low cost, are widely used in consumer electronics, mobile vehicles, and energy storage. To obtain detailed information on the electrochemical processes of each electrode, one or more reference electrodes can be implanted inside the battery to provide a standard potential, allowing for in-situ testing of the potentials and electrochemical impedance spectroscopy of the positive and negative electrodes. Lithium titanate (LTO), as a lithium intercalation material with a stable platform, can overcome the problems of potential drift, short lifespan, and poor stability of traditional lithium metal reference electrodes when used as a reference electrode active material. However, LTO needs to be lithiated to obtain a stable potential before it can be used as a reference electrode. Currently, LTO reference electrode manufacturing technology typically employs a non-in-situ lithiation method, where the LTO electrode is placed between two lithium foils to form a battery, undergoing two lithiation processes to obtain the LTO reference electrode, which is then implanted into the battery under test. Therefore, the existing LTO reference electrode lithiation process is complex, and the battery implantation steps are cumbersome.

[0003] Based on the above, the present invention proposes a simple and easy-to-implement method for lithiation of LTO reference electrode, which is of great significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the process of implanting the LTO reference electrode into the battery in the prior art is cumbersome, the lithiation process is too complicated, and the lithiation cost is high.

[0005] The technical solution adopted by this invention to solve this technical problem is: to provide a method for preparing a lithium titanate reference electrode and a one-step in-situ lithiation method, that is, coating LTO active material onto a current collector with good lithium-ion permeability, and directly implanting it into the battery during cell manufacturing, achieving one-step in-situ lithiation by controlling the magnitude of the lithiation current and the lithiation time. This overcomes the shortcomings of existing technologies (CN111082151, CN112430833) and academic journals (J. Power Sources, 2013, 240, 273), such as cumbersome reference electrode implantation steps, complex lithiation processes, and high lithiation costs. The specific steps are as follows:

[0006] (1) LTO reference electrode coating

[0007] A certain mass of LTO active material, conductive carbon black, and polyvinylidene fluoride (PVDF) were placed in a grinding jar at a molar ratio of (7.5–8.5):(0.5–1.5):(0.5–1.5). An appropriate amount of NMP was then added for grinding and mixing to obtain a uniform and glossy LTO slurry. The LTO slurry was then dipped into a current collector and placed in a constant temperature drying oven at 60–80°C for 6–15 hours. After drying to constant weight, a reference electrode coated with the LTO active material was obtained.

[0008] (2) Fabrication of a four-electrode battery

[0009] Lithium foil material is welded to the electrode tabs to obtain a lithium foil strip reference. After drying the positive and negative electrodes in a vacuum drying oven, the battery cells are assembled in the following order: positive electrode, separator, LTO reference electrode, separator, lithium foil strip reference, separator, and negative electrode. The battery cells are then subjected to insulation testing. Batteries that pass the insulation test are then liquid-filled and packaged to obtain a four-electrode lithium-ion battery containing an LTO reference electrode and a lithium foil strip reference.

[0010] In step (1) above, the current collector can be one of aluminum mesh, aluminum wire, copper wire and nickel foam, the positive electrode can be one of lithium nickel cobalt manganese oxide (NCM811), lithium cobalt oxide and lithium iron phosphate, and the negative electrode material can be one of graphite and activated carbon.

[0011] In step (2) above, the diaphragm can be one of polypropylene diaphragm and glass fiber diaphragm.

[0012] The electrolyte in step (2) above can be a 1 mol / L LiPF6 solution (dissolved in a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate), a 1 mol / L LiPF6 solution (dissolved in a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate), or a 1 mol / L LiPF6 solution (dissolved in a 1:1:1 volume ratio mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate).

[0013] (3) One-step in-situ lithiation of LTO reference electrode

[0014] The positive and negative electrodes of the four-electrode battery are combined to form a dual-electrode battery and charged to a preset voltage. Then, the LTO electrode and the negative electrode are combined to form a dual-electrode battery and discharged until the LTO is lithium intercalated. During the LTO lithium intercalation process, the real-time potential of the lithium foil reference electrode and the LTO reference electrode relative to the lithium foil reference is measured using an auxiliary channel. This enables real-time in-situ monitoring of the entire LTO reference electrode lithiation process, ensuring that the potential after lithiation is at a stable voltage platform. In subsequent use, the potential of the LTO reference electrode can still be calibrated using the lithium foil strip reference, ensuring the reliability of the main reference electrode test results.

[0015] The method for preparing a lithium titanate reference electrode and performing a one-step in-situ lithiation provided by the embodiments of the present invention has at least the following beneficial effects:

[0016] First, the design of this invention fully considers key issues such as the fabrication process, implantation method, and lithiation steps of the LTO reference electrode. It innovatively employs an in-situ lithiation method, avoiding the process of re-implanting the non-in-situ lithiated LTO reference electrode into the battery under test. Furthermore, thanks to the excellent ion permeability of the current collector, lithium ions can migrate and embed into both sides of the LTO reference electrode, thereby achieving one-step in-situ lithiation and reducing the difficulty of reference electrode fabrication.

[0017] Second, compared with the traditional lithiation method, the present invention no longer requires two metal lithium foils as lithium sources to lithiate the LTO reference electrode, thus achieving the goal of saving manufacturing costs.

[0018] Third, this invention embeds lithium foil strips as a reference electrode into a battery to form a four-electrode battery, thereby achieving real-time in-situ monitoring of the entire lithiation process of the LTO mesh reference electrode, ensuring a stable lithiation potential, as per the reference. Figure 3 In subsequent use, the lithium foil strip reference can be used to calibrate the potential of the LTO reference electrode to ensure the reliability of the main reference electrode test results. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a scanning electron microscope image of the LTO mesh reference electrode in Embodiment 1 of the present invention;

[0021] Figure 2 These are the front and side views of the four-electrode battery cell structure in Embodiment 1 of the present invention;

[0022] Figure 3 This is a graph showing the charging (lithium intercalation) process of NCM811-graphite in Embodiment 1 of the present invention.

[0023] Figure 4 This is a potential curve diagram of the lithium-ion battery in Example 1 during charge and discharge cycles between the positive and negative electrodes, and between the positive and negative electrodes and the mesh reference electrode, respectively.

[0024] Figure reference numerals: 1-NCM811 positive electrode, 2-lithium foil strip reference electrode, 3-LTO mesh reference electrode, 4-graphite negative electrode, 5-separator. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of 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. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0027] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the various embodiments and features described below can be combined with each other.

[0028] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0029] Example 1

[0030] The purpose of this embodiment is to provide a method for preparing a lithium titanate mesh reference electrode and a one-step in-situ lithiation method, as detailed below:

[0031] (1) LTO reference electrode coating

[0032] 1) Mixing: Weigh a fixed amount of LTO using a balance, convert the mass of conductive carbon black and PVDF according to the ratio of LTO:carbon black:PVDF of 8:1:1, and weigh them. Mix and grind them in a clean and dry agate mortar in sequence. 2) Slurry preparation: Add an appropriate amount of NMP evenly to the well-mixed and ground material, place it in a ball mill jar, and grind at 500 r / min for 6 h to obtain LTO composite active material. 3) Coating: Treat the aluminum mesh with fuming hydrochloric acid for 5 seconds, wash it clean and dry it, and then use it to dip the active material obtained in step (1), trying to coat it evenly. Then place the mesh reference electrode coated with active material in a vacuum drying oven at 75℃ for 12 h to obtain LTO mesh reference electrode. SEM image of LTO mesh reference electrode is shown in [link to image]. Figure 1 . Figure 1 (a) Schematic of LTO mesh reference electrode at 30x magnification. Figure 1 (b) is a 20,000x SEM image of the LTO mesh reference electrode.

[0033] (2) Fabrication of an NCM811-graphite four-electrode lithium-ion battery containing an LTO mesh reference electrode and a lithium foil strip reference electrode.

[0034] Lithium foil material is soldered to the electrode tabs to obtain a lithium foil strip reference. After drying the NCM811 positive electrode and graphite negative electrode in a vacuum drying oven, the battery cell is assembled in the following order: positive electrode, glass fiber separator, LTO reference electrode, glass fiber separator, lithium foil strip reference, glass fiber separator, and graphite negative electrode. Its structure is as follows: Figure 2 As shown. Then, the above-mentioned cells are subjected to insulation tests. The batteries that pass the insulation test are then liquid-filled and packaged to obtain a four-electrode lithium-ion battery containing an LTO reference electrode and a lithium foil strip reference.

[0035] The electrolyte is a 1 mol / L LiPF6 solution (dissolved in a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1), and the amount added to each battery group is 1 mL.

[0036] After the four-electrode battery was fabricated, it was left to stand for 5 hours, and then transferred to a 40°C constant temperature chamber to complete the formation at a charge-discharge rate of 0.1C.

[0037] (3) One-step in-situ lithiation of LTO mesh reference electrode

[0038] The positive and negative electrodes of the four-electrode battery are combined to form a dual-electrode battery and charged to a preset voltage of 3.80V. Then, the LTO electrode and the negative electrode are combined to form a dual-electrode battery and discharged to a stable voltage plateau before termination of discharge. The stable potential was tested to be approximately 1.56V relative to the lithium foil strip reference.

[0039] During the LTO lithium intercalation process described above, an auxiliary channel needs to be added to the LTO-lithium foil dual electrode to read the real-time potential of the LTO reference electrode relative to the lithium foil strip reference. This enables real-time in-situ monitoring of the entire lithiation process of the LTO mesh reference electrode, ensuring that the potential after lithiation remains on a stable voltage platform (e.g., ...). Figure 3 (As shown).

[0040] (4) Use LTO mesh reference electrode to test the positive and negative electrode potential curves.

[0041] The lithium-ion battery was placed in a 25°C constant temperature chamber and subjected to charge-discharge cycle experiments at a rate of 0.5C within a voltage range of 2.80–4.20V. The potential curves between the positive and negative electrodes and the reference electrode were measured using an auxiliary channel, as shown below. Figure 4 As shown, this further verifies the reliability of the reference electrode.

[0042] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a lithium titanate reference electrode and performing a one-step in-situ lithiation, characterized in that, The process includes the following steps: coating LTO active material onto a lithium-ion permeable current collector, embedding it inside a three-electrode battery during cell fabrication, and achieving one-step in-situ lithiation by controlling the magnitude of the lithiation current and the lithiation time. The specific steps include: (1) LTO reference electrode coating: LTO active material, conductive carbon black, and PVDF are ground thoroughly in a mortar at a molar ratio of 8:1:

1. An appropriate amount of NMP is then added to mix the materials, resulting in an LTO reference electrode active material. The active material is then dipped into a current collector and vacuum dried at 65℃~80℃ for 6~15h to obtain a reference electrode coated with the LTO active material. (2) Fabrication of a four-electrode battery: Lithium foil material is welded to the electrode tabs to obtain a lithium foil strip reference. After the positive and negative electrode sheets are dried in a vacuum drying oven, the battery cells are assembled in the following order: positive electrode sheet, separator, LTO reference electrode, separator, lithium foil strip reference, separator, and negative electrode sheet. Then, the battery cells are subjected to insulation testing. The batteries that pass the insulation test are injected with liquid and encapsulated to form a four-electrode lithium-ion battery containing an LTO reference electrode and a lithium foil strip reference. (3) One-step in-situ lithiation of LTO reference electrode: The positive and negative electrodes of the four-electrode battery are combined to form a dual-electrode battery and charged to a preset voltage. Then, the LTO electrode and the negative electrode are combined to form a dual-electrode battery and discharged to the LTO reference electrode to obtain a stable potential. It also includes the following steps: During LTO lithium intercalation, an auxiliary channel is added to the LTO-lithium foil dual electrode to read the real-time potential of the LTO reference electrode relative to the lithium foil strip reference; in subsequent use, the potential of the LTO reference electrode is calibrated using the lithium foil strip reference. The LTO is intercalated to a lithium base until the real-time potential of the LTO reference electrode reaches a stable state relative to the lithium foil strip reference.

2. The method for preparing a lithium titanate reference electrode and performing a one-step in-situ lithiation as described in claim 1, characterized in that, The current collector includes aluminum mesh, aluminum wire, copper wire, or nickel foam; the positive electrode includes lithium nickel cobalt manganese oxide or lithium iron phosphate; and the negative electrode material includes graphite.

3. The method for preparing a lithium titanate reference electrode and performing a one-step in-situ lithiation as described in claim 1, characterized in that, In step (2), the diaphragm includes a polypropylene diaphragm or a glass fiber diaphragm.

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