Reference electrode, three-electrode cell, method for preparing a three-electrode cell

Abstract

This invention provides a reference electrode for use in an electrode assembly. The electrode assembly includes an electrode sheet and a reference electrode. The reference electrode includes: a metal mesh; and an active coating coated on the surface of the metal mesh, containing lithium titanate or lithium iron phosphate as the main component. The areal weight of the main component in the active coating is no more than 1 / 10 of the areal weight of the active material in the electrode sheet. Using the above technical solution, the uniformity of current distribution can be significantly improved, the electrode impedance can be greatly reduced, thereby effectively improving the testing accuracy and avoiding signal distortion. This invention also provides a three-electrode battery and a method for preparing a three-electrode battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a reference electrode, a three-electrode battery, and a method for preparing a three-electrode battery. Background Technology

[0002] In the design and research of lithium-ion batteries, it is often necessary to independently analyze parameters such as the potential and impedance of the positive and negative electrodes. For example, during fast charging, the potential of the graphite negative electrode is monitored to assess the risk of lithium plating; during cycling, the changes in the potential and impedance of the positive and negative electrodes are monitored to analyze electrode degradation patterns and battery failure mechanisms. Such independent testing is difficult to achieve in a conventional two-electrode system and usually requires the introduction of a third electrode, namely a reference electrode, to form a three-electrode system.

[0003] Currently, the commonly used reference electrode is the lithium / copper wire reference electrode, but its preparation and use process is quite cumbersome. For example, it requires not only pretreatment and polishing of the copper wire, but also embedding the unlithiated copper wire inside the battery cell during the cell stacking or winding process. After the battery cell is packaged, injected with electrolyte, and formed, metallic lithium is electrochemically deposited twice on both sides of the copper wire using a small current to obtain the lithium / copper reference electrode. In addition, this type of reference electrode has many problems: 1) Metallic lithium has extremely high chemical activity and will irreversibly form an SEI layer in the electrolyte, resulting in its actual potential not being pure Li. + / Li potential, but rather manifests as Li + @SEI / Li potential; at the same time, its potential magnitude and stability are highly sensitive to the initial amount of lithium deposition and deposition uniformity, usually requiring a small current of 20-50 μA for 10-24 hours of deposition, which seriously reduces the testing efficiency; 2) The electrode lifespan is short, generally only lasting 1-2 days, which is difficult to meet the requirements of long-term cycling or long-term testing; 3) The potential of metallic lithium drifts significantly with current and temperature, with a temperature coefficient of 1-2 mV / ℃ (this data comes from J. Am. Chem. Soc. 2021, 143, 2264), and the potential stability is poor.

[0004] Existing reference electrodes include lithium / silver, lithium / tin, and lithium / aluminum alloys. These electrodes usually need to be pre-lithiated before being implanted into the battery cell, and the preparation process needs to be carried out in a dry room or glove box to avoid contamination. They also have problems such as complex preparation process, strict environmental requirements, and insufficient potential stability, making it impossible to achieve efficient, convenient, and long-term reliable testing.

[0005] Existing technologies also disclose reference electrodes with lithium titanate or lithium iron phosphate loaded on the surface of a metal wire. The preparation method involves coating a pretreated copper wire surface with a slurry containing lithium titanate or lithium iron phosphate. By rationally controlling the copper wire diameter, slurry coating thickness, and coating speed, the lithium titanate or lithium iron phosphate slurry is uniformly coated on the copper wire surface, and the coating thickness is controlled within a suitable range. This results in a lithium titanate or lithium iron phosphate-based reference electrode with dimensions matching the coating thickness. This type of electrode has the advantages of stable potential and long service life. Compared to lithium / copper, lithium / silver, lithium / tin, and lithium / aluminum alloy reference electrodes using pre-lithiated metal surfaces, this type of electrode effectively avoids side reactions between metallic lithium and the electrolyte, ensuring potential stability and solving the problem of short service life.

[0006] Regardless of the reference electrode used, its structure is always filamentous or linear. These filamentous and linear reference electrodes generally suffer from inherent defects: current can only propagate axially along the thin metal wire and diverge radially. Skin effect easily occurs at the ends and bends, causing a sudden increase in local current density and high ohmic impedance. Even a small current can trigger a significant ohmic voltage drop, leading to potential measurement deviations. Essentially, this results in uneven radial current and ion transport distribution and an overall high electrode impedance. Furthermore, artifacts or signal distortion are prone to occur in electrochemical impedance spectroscopy (EIS) testing, especially in large-capacity, large-size cells, severely affecting the accuracy of EIS analysis results. Therefore, how to provide a reference electrode that can significantly improve current distribution uniformity, substantially reduce electrode impedance, and thus effectively improve testing accuracy and avoid signal distortion has become a pressing technical problem to be solved in this field. Summary of the Invention

[0007] The present invention provides the following technical solution to solve the above-mentioned technical problems.

[0008] This invention provides a reference electrode for use in an electrode assembly, the electrode assembly comprising an electrode sheet and a reference electrode, the reference electrode comprising:

[0009] Metal mesh;

[0010] An active coating is applied to the surface of the metal mesh and contains lithium titanate or lithium iron phosphate as the main component. The areal loading of the main component in the active coating is not higher than 1 / 10 of the areal loading of the active material in the electrode sheet.

[0011] By adopting the above technical solution, the uniformity of current distribution can be significantly improved and the electrode impedance can be greatly reduced, thereby effectively improving the test accuracy and avoiding signal distortion.

[0012] Optionally, the metal mesh is a stretched metal mesh or a woven metal mesh, and the metal mesh satisfies one or more of the following: thickness of 10-80μm, wire diameter of 10-80μm, and aperture of 50-500μm.

[0013] Optionally, the metal mesh is made of copper or aluminum.

[0014] Optionally, the surface loading of the main component in the active coating is not higher than 1 / 10 of the surface loading of the active material in the electrode sheet.

[0015] Optionally, the active coating further contains a conductive agent and a binder, wherein the main component, the conductive agent, and the binder account for 70%~95%, 2%~20%, and 2%~10% of the active coating by mass, respectively.

[0016] Optionally, the mass ratio of the main component, conductive agent, and binder is 7:2:1.

[0017] Optionally, the solid content of the slurry for preparing the active coating is 40%-80%, and / or the viscosity of the slurry for preparing the active coating is 4000-6000 mPa. s.

[0018] The present invention also provides a three-electrode battery, including an electrode assembly, wherein the electrode assembly includes a reference electrode, a positive electrode, and a negative electrode as described in any of the above embodiments, the positive electrode, the reference electrode, and the negative electrode are arranged in sequence at intervals, and a separator is respectively provided between the positive electrode and the reference electrode and between the negative electrode and the reference electrode.

[0019] By adopting the above technical solution, the three-electrode battery provided by the present invention, through the introduction of an ultra-thin and lightweight mesh reference electrode, can achieve accurate real-time monitoring of the working electrode potential without significantly occupying the internal space of the battery, damaging the electrode plates, or interfering with the normal insertion and extraction of lithium ions. This effectively improves the accuracy of battery electrochemical performance testing, internal resistance analysis, and lifespan research. At the same time, it is easy to assemble, has a stable structure, and is suitable for mechanism research and performance characterization of various lithium-ion batteries.

[0020] The present invention also provides a method for preparing a three-electrode battery, comprising:

[0021] Assembling the three-electrode battery includes hot-pressing, encapsulating, and injecting electrolyte into the electrode assembly to obtain the assembled three-electrode battery.

[0022] The reference electrode is activated at 0.01-0.50 A g. -1The reference electrode is charged or discharged to a preset cutoff voltage of the main component using a current density of 0.01-0.50 A g. -1 The current density is used to discharge or charge the reference electrode to 30% to 70% of its capacity to activate the reference electrode.

[0023] By adopting the above technical solution, the reference electrode can be precisely activated after the battery is encapsulated and injected with electrolyte, so that its potential can be quickly stabilized in the working range. This avoids potential drift in the initial stage of testing caused by insufficient activation of the reference electrode, significantly improving the response accuracy and data reliability of the three-electrode battery in electrochemical testing. At the same time, the process is mild and easy to operate, and does not affect the original performance of the positive electrode, negative electrode and separator.

[0024] Optionally, the preset cutoff voltage of the lithium titanate is 2.8-2.9V, and the preset cutoff voltage of the lithium iron phosphate is 2.0V. Attached Figure Description

[0025] Figure 1 The potential-SOC curve of the three-electrode battery with reference electrode assembly in Embodiment 1 of the present invention is shown during the first fast charge (0–100% SOC) process.

[0026] Figure 2 The potential-SOC curve of the three-electrode battery with reference electrode assembly in Embodiment 1 of the present invention is shown during the 200th fast charge (0–100% SOC) process.

[0027] Figure 3 The potential-SOC curve of the three-electrode battery with reference electrode assembly in Comparative Example 1 of the present invention is shown during the 20th fast charge (0–100% SOC) process.

[0028] Figure 4 is a comparison chart of the EIS test results of the three-electrode battery in Example 1 and Comparative Example 2. Detailed Implementation

[0029] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0030] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0032] This invention provides a reference electrode for use in an electrode assembly. The electrode assembly includes an electrode sheet and a reference electrode. The reference electrode includes a metal mesh and an active coating coated on the surface of the metal mesh. The active coating contains lithium titanate or lithium iron phosphate as the main component, wherein the areal weight of the main component in the active coating is not higher than 1 / 10 of the areal weight of the active material in the electrode sheet.

[0033] It should be noted that areal loading refers to the coating mass per unit area, usually expressed in mg / cm² or g / m². Specifically, the areal loading of the main component refers to the mass of the main component coated in the active coating per unit area of ​​the metal mesh. The actual measurement method is as follows: weigh the metal mesh before and after the active coating is applied, calculate the difference to obtain the total mass of the active coating, then calculate the mass of the main component based on the active coating's formulation ratio, and divide this mass by the effective coating area of ​​the metal mesh to obtain the areal loading of the main component. The areal loading of the active material in the electrode sheet refers to the mass of the active material coated per unit area of ​​the electrode sheet. Its calculation method is the same as for the areal loading of the active coating: measure the mass of the electrode sheet before and after the active material is applied, calculate the mass of the active material based on the difference, and then divide this mass by the effective coating area of ​​the electrode sheet to obtain the areal loading of the active material in the electrode sheet.

[0034] It is understandable that active materials refer to the core materials in electrode sheets that participate in electrochemical reactions and undertake the functions of lithium ion insertion / extraction. The active materials of positive electrode sheets are usually ternary materials, lithium iron phosphate, etc., while the active materials of negative electrode sheets are usually graphite, silicon-based materials, etc. The above materials, along with lithium titanate and lithium iron phosphate, the main components of the active coating of the reference electrode, are all commonly used electrochemical active materials in the field of lithium-ion batteries.

[0035] It should be further explained that, since the electrode sheet includes a positive electrode sheet and a negative electrode sheet, the above-mentioned "the areal loading of the main component is not higher than 1 / 10 of the areal loading of the active material in the electrode sheet" specifically means that the areal loading of the main component in the active coating is not higher than 1 / 10 of the smaller value between the areal loading of the active material in the positive electrode sheet and the areal loading of the active material in the negative electrode sheet.

[0036] In the above technical solution, this invention abandons the traditional filamentary or linear reference electrode structure and instead uses a metal mesh as a conductive substrate, with an active coating coated on its surface. Simultaneously, the areal loading of the main component in the active coating is controlled to be no more than 1 / 10 of the areal loading of the active material in the electrode sheet (the smaller of the areal loading of the positive and negative electrode active materials). This design enables the reference electrode to form a planar porous mesh conductive structure, with multiple ribs intersecting within the mesh to form numerous parallel conductive paths. After coating with an active coating containing lithium titanate (LTO) or lithium iron phosphate (LFP), the test current can be uniformly distributed across the entire mesh surface, without any concentrated current "hot spots," resulting in a uniform current density. Furthermore, the mesh structure has a larger conductive path cross-sectional area, significantly reducing the overall ohmic impedance and generating almost no ohmic voltage drop under small test currents, thus ensuring accurate and reliable potential measurement. Therefore, this invention effectively solves the problems of uneven radial current and ion transport distribution and high overall electrode impedance commonly found in existing filamentary and wire-shaped reference electrodes, avoiding artifacts or signal distortion in electrochemical impedance spectroscopy (EIS) testing, and particularly improving the accuracy of EIS analysis results in large-capacity, large-size cells. Meanwhile, compared to conventional metal wire or filamentary reference electrodes, metal mesh has a larger specific surface area, allowing it to load more bulk components. This not only ensures that the state of charge remains relatively stable under small currents during testing, thus guaranteeing potential stability, but also effectively extends the lifespan of the reference electrode and enhances long-term operational stability. Furthermore, it is easily cut into different sizes to adapt to diverse cell structures, and its internal interlaced ribs further reduce electrode impedance and ohmic voltage drop, thereby further improving the accuracy of potential measurement.

[0037] Furthermore, in the above embodiments, the areal loading of the main component in the active coating is not less than 1 / 100 of the areal loading of the active material in the electrode sheet. This provides sufficient electrochemical active sites for the reference electrode, ensuring stable electrode potential and reliable response.

[0038] Furthermore, in the above embodiments, the metal mesh is a stretched metal mesh or a woven metal mesh, and satisfies one or more of the following conditions: thickness of 10–80 μm, wire diameter of 10–80 μm, and aperture of 50–500 μm.

[0039] Using stretched or woven metal mesh as a substrate creates a continuous conductive network, which facilitates uniform coating of the active coating and ensures sufficient electrolyte wetting and rapid ion transport within the cell, thus maintaining a stable reference electrode potential. Controlling the thickness within the aforementioned range ensures the mechanical strength of the reference electrode while preventing damage to the positive and negative electrode active material layers due to excessive thickness, which could affect the overall electrochemical performance of the cell. Controlling the wire diameter within the aforementioned range balances conductivity and structural flexibility, providing sufficient structural support without increasing overall thickness or damaging the electrodes due to excessive wire diameter. Limiting the pore size within the aforementioned range ensures sufficient electrolyte wetting and smooth ion transport while maintaining the overall flatness and structural stability of the mesh, preventing coating peeling due to excessively large pores or ion transport efficiency due to excessively small pores. Preferably, stretched metal mesh is used, which, compared to woven metal mesh, avoids excessive local thickness at the interlacing points of the metal wires, thus preventing pressure damage to the positive and negative electrode material layers and affecting the cell's electrical performance.

[0040] Furthermore, in the above embodiments, the metal mesh simultaneously satisfies the following requirements: thickness of 10–80 μm, wire diameter of 10–80 μm, and pore size of 50–500 μm. In the prior art, metal wires are commonly used as the reference electrode substrate. The core purpose is to minimize the space occupied by the reference electrode and avoid indentation of the electrode sheet due to excessive structural size, thereby interfering with the normal electrochemical processes such as lithium-ion insertion and extraction within the battery cell. Research shows that the present invention uses a metal mesh as the reference electrode substrate. By coordinating and precisely controlling the thickness, wire diameter, and pore size of the metal mesh, it not only avoids problems such as excessive space occupation and damage to the electrode sheet, but also fully leverages the advantages of the metal mesh structure while ensuring an ultra-thin and low-space reference electrode. This effectively optimizes current distribution, promotes ion transport, and reduces electrode impedance, solving the technical pain point of the difficulty in applying metal mesh to reference electrodes in the prior art. Preferably, the thickness is 20-50 μm, the wire diameter is 20-50 μm, and the pore size is 250-500 μm.

[0041] Furthermore, in the above embodiments, the metal mesh is made of copper or aluminum. Copper and aluminum possess excellent electrical conductivity and mechanical flexibility, which can further reduce the ohmic impedance of the electrodes. At the same time, their good ductility makes them less likely to damage the electrode plates during assembly, resulting in better compatibility with the battery cell system. This can further improve the stability and accuracy of potential measurement while ensuring structural stability.

[0042] Furthermore, in the above embodiments, the metal mesh can be pretreated before the active coating is applied to its surface. Pretreatment may include acid immersion, plasma cleaning, electropolishing, or sandpaper polishing to remove the oxide layer and adhering impurities from the metal mesh surface, thereby improving the adhesion of the active coating. Acid immersion is preferred; specifically, the metal mesh is suspended in concentrated acid for 0.2-2 minutes using a fine thread of the same material as the mesh, then removed and cleaned sequentially with deionized water and ethanol, and dried. Copper mesh is preferably immersed in concentrated sulfuric acid, and aluminum mesh is preferably immersed in concentrated hydrochloric acid.

[0043] Furthermore, in the above embodiments, the areal loading of the main component in the active coating is no more than 1 / 10 of the areal loading of the active material in the electrode sheet. It should be noted that the active coating can be applied to one or both sides of the metal mesh, and the active slurry can also be applied to both sides of the electrode sheet. The areal loading of the main component in the active coating mentioned here refers to the areal loading of the main component coated only on a single surface of the metal mesh; the corresponding areal loading of the active material in the electrode sheet refers to the areal loading of the active material on a single surface of the electrode sheet.

[0044] This ensures that the reference electrode has a sufficiently stable potential response, effectively controls the coating thickness and overall volume, avoids problems such as excessive space occupation and electrode extrusion caused by excessive load of the main component, and allows the reference electrode to maintain a basically constant state of charge under small test current, without significant potential drift due to test disturbances, further improving the accuracy and long-term stability of potential measurement.

[0045] Regarding the above technical solution, in practical operation, the apparent area S of the cut metal mesh (the overall outline area of ​​the cut metal mesh, i.e., the geometric area calculated based on its external length and width, without deducting the hollow areas inside the mesh) can be measured. The masses m1 and m2 of the metal mesh before and after applying the active coating can be weighed respectively, and the mass difference Δm can be calculated. Then, combined with the mass percentage w1 of the main component in the active coating, the single-sided surface load of the main component (Δm) can be calculated. (w1 / S). The surface loading should be controlled to be less than 1 / 10 of the smaller value of the surface loading of the positive or negative electrode sheet.

[0046] Furthermore, in the above embodiments, the active coating can be applied to the surface of the metal mesh by roller coating, spraying, or direct dipping in slurry. Dipping is preferred to ensure that the slurry adheres evenly to the metal mesh without clogging the mesh openings. In practice, the metal mesh can be cut to the required size, dipped in slurry, and then suspended in a 60–90°C forced-air oven to dry. Finally, the dried metal mesh can be flattened using a roller press or hydraulic press.

[0047] Furthermore, in the above embodiments, the surface loading of the main component in the active coating is not less than 1 / 100 of the surface loading of the active material in the electrode sheet.

[0048] Furthermore, in the above embodiments, the active coating also contains a conductive agent and a binder, with the main component, conductive agent, and binder accounting for 70%-95%, 2%-20%, and 2%-10% of the active coating by mass, respectively. This formulation design ensures a high proportion of active material while maintaining good conductivity and adhesion of the coating. A higher proportion of active material ensures that the reference electrode's state of charge remains largely unchanged under small test currents, thus maintaining potential stability; an appropriate amount of conductive agent effectively reduces ohmic impedance and potential measurement losses; and the addition of a suitable binder enhances the coating's mechanical strength, making it less prone to detachment even after long-term use in an electrolyte environment.

[0049] Furthermore, in the above embodiments, the mass ratio of the main component, conductive agent, and binder is 7:2:1. This ratio can significantly improve the conductivity of the coating and reduce impedance while ensuring sufficient active material content to maintain potential stability, and also possesses excellent adhesion strength, making the active coating less prone to detachment during electrolyte wetting and long-term testing, thus balancing potential stability, conductivity, and structural reliability. The conductive agent can be selected from one or more of carbon black, graphene, Ketjen black, acetylene black, single-walled carbon nanotubes, and multi-walled carbon nanotubes, preferably a combination of carbon black and carbon nanotubes. The binder can be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and polyacrylonitrile (PAN), preferably polyvinylidene fluoride (PVDF).

[0050] Furthermore, in the above embodiments, the solid content of the slurry for preparing the active coating is 40%-80%, preferably 50%-60%, and / or the viscosity of the slurry for preparing the active coating is 3000-10000 mPa. s, preferably 4000~6000 mPa By controlling the solid content within the above range, sufficient active material per unit volume can be ensured, resulting in uniform coating load and stable potential response. Controlling the viscosity within the above range allows the slurry to possess suitable coatability and adhesion, preventing dripping and missed areas during coating. The resulting coating is smooth, uniform, and tightly bonded to the metal mesh substrate, which helps improve the overall consistency and reliability of the reference electrode.

[0051] Furthermore, the active coating may also contain a dispersant. The dispersant may be a solvent that can uniformly disperse lithium titanate (LTO) or lithium iron phosphate (LFP) active material, conductive agent and binder, such as water, ethanol, isopropanol, acetone, N-methylpyrrolidone (NMP), etc., preferably NMP.

[0052] This invention provides a three-electrode battery, including an electrode assembly. The electrode assembly includes a reference electrode, a positive electrode, and a negative electrode as described in any of the above embodiments. The positive electrode, the reference electrode, and the negative electrode are arranged sequentially at intervals, and a separator is respectively provided between the positive electrode and the reference electrode, and between the negative electrode and the reference electrode.

[0053] The three-electrode battery provided by this invention, by introducing an ultra-thin and lightweight mesh reference electrode, can achieve accurate real-time monitoring of the working electrode potential without significantly occupying the internal space of the battery, damaging the electrode plates, or interfering with the normal insertion and extraction of lithium ions. This effectively improves the accuracy of battery electrochemical performance testing, internal resistance analysis, and lifespan research. At the same time, it is easy to assemble, has a stable structure, and is suitable for mechanism research and performance characterization of various lithium-ion batteries.

[0054] The present invention also provides a method for preparing a three-electrode battery according to the above embodiments, comprising:

[0055] Assembling a three-electrode battery includes hot-pressing, encapsulating, and injecting electrolyte into the electrode components described in the above embodiments to obtain the assembled three-electrode battery.

[0056] Activate the reference electrode at 0.01-0.50 Ag. -1 The reference electrode is charged or discharged to a preset cutoff voltage of the bulk component using a current density of 0.01-0.50 A g. -1 The current density is used to discharge or charge the reference electrode to 30% to 70% of its capacity in order to activate the reference electrode.

[0057] By adopting the above technical solution, the reference electrode can be precisely activated after the battery is encapsulated and injected with electrolyte, so that its potential can be quickly stabilized in the working range. This avoids potential drift in the initial stage of testing caused by insufficient activation of the reference electrode, significantly improving the response accuracy and data reliability of the three-electrode battery in electrochemical testing. At the same time, the process is mild and easy to operate, and does not affect the original performance of the positive electrode, negative electrode and separator.

[0058] Further, in the above embodiments, the preset cutoff voltage of lithium titanate is 2.8–2.9V, specifically 2.85V, and the preset cutoff voltage of lithium iron phosphate is 2.0V. Specifically, if lithium titanate (LTO) is used as the main component of the reference electrode, the positive electrode needs to be connected to the reference electrode and charged to 2.8–2.9V at the above current density. After activation, the reference electrode potential stabilizes at approximately 1.55V. If lithium iron phosphate (LFP) is used as the main component of the reference electrode, the negative electrode needs to be connected to the reference electrode and discharged to approximately 2.0V at the above current density. After activation, the reference electrode potential stabilizes at approximately 3.22V.

[0059] Furthermore, in the above embodiments, in the step of activating the reference electrode, 0.01-0.50 Ag is used. -1 The reference electrode is charged or discharged to a preset cutoff voltage of the bulk component using a current density, and then 30%–70% of its capacity is released or charged to the reference electrode using the same current density to activate it. Preferably, 40%–60% of the capacity is released or charged at a current density of 0.1–0.2 A g. -1 In actual operation, based on the mass of the LTO or LFP main component coated on the metal mesh, the reference electrode can be charged and discharged to the corresponding cutoff voltage through the positive or negative electrode at the above current density, and the total capacity Q1 can be recorded. Then, the charge can be charged and discharged in the reverse direction at the same current density for 0.4 to 0.6Q1.

[0060] The technical solution of the present invention will be further described below with reference to specific embodiments and comparative examples.

[0061] Example 1

[0062] 1) Preparation of reference electrode:

[0063] Select an aluminum mesh with a thickness of 40μm, a pore size of 400μm, and a wire diameter of 40μm, and cut it into square aluminum meshes of 2cm×2cm. Soak the aluminum meshes in commercially available concentrated hydrochloric acid (mass fraction of 37%) for 30 seconds, then remove them and rinse them twice each with deionized water and anhydrous ethanol. After drying, weigh them for later use.

[0064] Lithium iron phosphate (LFP) powder, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1 were weighed separately, and then N-methylpyrrolidone (NMP) was added in an amount 1.2 times the mass of the LFP powder to obtain a slurry for preparing the active coating. The solid content of the slurry for preparing the active coating was 60%, and the viscosity of the slurry for preparing the active coating was 5000 mPa. s. Immerse the pretreated aluminum mesh in the above slurry, remove it after dipping, and dry it in an 80°C forced-air oven for 2 hours. Repeat the dipping and drying operation three times to obtain the reference electrode. The single-sided surface loading of the main component in the above active coating is 1 / 20 of the single-sided surface loading of the active material in the electrode sheet. The reference electrode is then flattened on a hydraulic press under a pressure of 300 kgf for later use.

[0065] 2) Assemble a three-electrode battery:

[0066] The reference electrode is placed between the positive and negative electrode plates, and square separators with dimensions of 2.5cm × 2.5cm are placed between the reference electrode and the positive electrode, and between the reference electrode and the negative electrode, respectively, to obtain the electrode assembly. The electrode assembly is then hot-pressed and sealed, and then an electrolyte is injected to obtain the assembled three-electrode battery.

[0067] 2) Activate the reference electrode:

[0068] For the three-electrode battery formation, after formation is complete, the negative electrode and reference electrode are connected to the battery charging and discharging equipment at 0.1 A. g -1 The reference electrode is discharged to 2.0V at a current density and the total discharge capacity Q1 is recorded. Then, 0.5Q1 of the charge is charged to the reference electrode at the same current density. After activation, the LFP reference electrode can be used for battery fast charging, impedance and other related performance tests.

[0069] Example 2

[0070] 1) Preparation of reference electrode:

[0071] Select a copper mesh with a thickness of 20μm, an aperture of 300μm, and a wire diameter of 20μm, and cut it into a 3cm×3cm square metal copper mesh; immerse the above metal copper mesh in commercially available concentrated sulfuric acid (mass concentration of 98%) for 120s, then take it out and rinse it twice each with deionized water and anhydrous ethanol, blow it dry, weigh it and set it aside for later use.

[0072] Lithium iron phosphate (LTO) powder, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1 were weighed separately. Then, N-methylpyrrolidone (NMP) was added at 1.2 times the mass of the LTO powder to obtain a slurry for preparing the active coating. The solid content of the slurry for preparing the active coating was 60%, and the viscosity of the slurry was 5000 mPa. s. The pretreated aluminum mesh is immersed in the above slurry, dipped, and then removed. It is dried in a 60°C forced-air oven for 3 hours. The dipping and drying process is repeated three times to obtain the reference electrode. The surface loading of the main component in the active coating is 1 / 15 of the surface loading of the active material in the electrode sheet. The reference electrode is then flattened on a hydraulic press under a pressure of 300 kgf for later use.

[0073] 2) Assemble a three-electrode battery:

[0074] The reference electrode is placed between the positive and negative electrode plates, and square separators with dimensions of 3.5cm × 3.5cm are placed between the reference electrode and the positive electrode, and between the reference electrode and the negative electrode, respectively, to obtain the electrode assembly. The electrode assembly is then hot-pressed, sealed, and injected with electrolyte to obtain the assembled three-electrode battery.

[0075] 2) Activate the reference electrode:

[0076] For the three-electrode battery formation, after formation is complete, the positive electrode and reference electrode are connected to the battery charging and discharging equipment at 0.1 A. g -1 The reference electrode is charged to 2.85V using a current density, and the total charging capacity Q2 is recorded. Then, 0.5Q2 of the charge is released to the reference electrode using the same current density. After activation, the LTO reference electrode can be used for battery fast charging and other related performance tests.

[0077] Comparative Example 1

[0078] 1) Preparation of reference electrode:

[0079] Select copper wire with a diameter of 20μm, immerse the copper wire in commercially available concentrated sulfuric acid (mass concentration of 98%) for 120s, remove it, rinse it twice with deionized water and twice with anhydrous ethanol, blow it dry and weigh it for later use.

[0080] 2) Assemble a three-electrode battery:

[0081] The reference electrode is placed between the positive and negative electrode plates, and separators are placed between the reference electrode and the positive electrode, and between the reference electrode and the negative electrode, to obtain an electrode assembly. The electrode assembly is then hot-pressed, encapsulated, and injected with electrolyte to obtain the assembled three-electrode battery.

[0082] 3) Activate the reference electrode:

[0083] After formation, the negative electrode of the cell and the copper wire (reference electrode lead-out end) are connected to the battery charging and discharging equipment and discharged at a current of 30μA for 12 hours. After discharge, the positive electrode of the cell and the copper wire are connected to the battery charging and discharging equipment and charged at a current of 30μA for 12 hours. After the reference electrode potential stabilizes, the lithium / copper reference electrode can continue to be used for battery fast charging and other related performance tests.

[0084] Comparative Example 2

[0085] 1) Preparation of reference electrode:

[0086] Select aluminum wire with a diameter of 20μm, immerse the aluminum wire in commercially available concentrated hydrochloric acid (mass fraction of 37%) for 30 seconds, remove it, rinse it twice with deionized water and twice with anhydrous ethanol, blow it dry, weigh it and set it aside.

[0087] Lithium iron phosphate (LFP) powder, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1 were weighed separately, and then methylpyrrolidone (NMP) was added in an amount 1.2 times the mass of the LFP powder to obtain a slurry for preparing the active coating. The solid content of the slurry for preparing the active coating was 60%, and the viscosity of the slurry for preparing the active coating was 5000 mPa. s. Immerse a portion of the pretreated metal wire in the above slurry, remove it, and dry it in an 80°C forced-air oven for 2 hours. Repeat the immersion and drying process three times to obtain the reference electrode. The areal loading of the main component in the active coating is 1 / 80 of the single-sided areal loading of the active material in the electrode sheet. It should be noted that the areal loading of the main component in the active coating refers to the mass of the main component coated on a unit area of ​​aluminum wire in the active coating.

[0088] 2) Assemble a three-electrode battery:

[0089] The reference electrode is placed between the positive and negative electrode plates, and rectangular separators large enough to cover the metal wires are placed between the reference electrode and the positive electrode, and between the reference electrode and the negative electrode, respectively, to obtain the electrode assembly. The electrode assembly is then hot-pressed, encapsulated, and injected with electrolyte to obtain the assembled three-electrode battery.

[0090] 2) Activate the reference electrode:

[0091] For the three-electrode battery formation, after formation is complete, the negative electrode and reference electrode are connected to the battery charging and discharging equipment at 0.1 A. g -1 The reference electrode is discharged to 2.0V at a current density and the total discharge capacity Q1 is recorded. Then, 0.5Q1 of the charge is charged to the reference electrode at the same current density. After activation, the LFP reference electrode can be used for battery fast charging and other related performance tests.

[0092] The three-electrode battery assembled with the reference electrode prepared in Example 1 was subjected to fast charge-discharge cycle tests at room temperature. Battery voltage and negative parameter potential data were recorded during the 1st and 200th fast charge cycles (0-100% SOC range), resulting in the potential-SOC curves shown in Figures 1 and 2. The horizontal axis represents the battery state of charge, the left vertical axis represents the battery terminal voltage (in V), corresponding to the upward-trending black curve reflecting the overall charge-discharge characteristics of the battery, and the right vertical axis represents the negative parameter potential (in V), which is the working negative electrode potential relative to the Li, measured with the reference electrode as a reference in the three-electrode system. + The potential of / Li corresponds to the red curve showing a decreasing trend, which is used to monitor the change in the true potential of the negative electrode.

[0093] As shown in Figure 1, the reference electrode of this invention can accurately and stably monitor the negative electrode potential during the first fast charge without abnormal fluctuations. As shown in Figure 2, even after 200 long cycles, the reference electrode can still operate stably with minimal potential drift, without exhibiting the potential shift and failure problems common in traditional reference electrodes. This also proves that the reference electrode provided by this invention has excellent long-term electrochemical stability and can continuously and accurately monitor the true potential of the negative electrode (or positive electrode) during the long cycle of the power battery. It fully meets the testing needs of multiple scenarios such as long-cycle performance testing of power batteries, fast-charging performance evaluation, and electrochemical impedance analysis, fundamentally solving the industry pain points of short cycle life, easy potential drift, and inability to adapt to long-cycle testing of traditional reference electrodes.

[0094] Meanwhile, the inventors also conducted the aforementioned fast charge-discharge cycle test on a three-electrode battery assembled using the reference electrode prepared in Comparative Example 1, under the same room temperature conditions. They recorded the battery voltage and reference electrode potential data during the 20th fast charge cycle (0-100% SOC range), obtaining the potential-SOC curve shown in Figure 3. The horizontal axis represents the battery state of charge, the left vertical axis represents the battery terminal voltage (corresponding to the upward-trending black curve), reflecting the overall charge-discharge characteristics of the battery, and the right vertical axis represents the negative reference potential, i.e., the working potential of the battery's negative electrode relative to the Li, measured with the reference electrode as a reference in the three-electrode system. + / Li potential (vs Li) + / Li), corresponding to the red curve showing a downward trend, is used to monitor the change in the true potential of the negative electrode.

[0095] As shown in Figure 3, after testing, the reference electrode showed significant potential drift after only 20 battery cycles. The negative reference potential began to show abnormalities in the low SOC range, and the negative reference potential was below 0 V in a relatively wide SOC range of 30%–60%, indicating that the reference electrode had failed.

[0096] The EIS tests of the three-electrode batteries in Example 1 and Comparative Example 2 were performed, and the results are shown in Figure 4. As can be seen from Figure 4, when using the common linear reference electrode in Comparative Example 2, the obtained EIS spectrum shows significant distortion, with an overall high impedance. Furthermore, a large portion of the high-frequency curve is located in the fourth quadrant, which is a typical manifestation of impedance spectrum artifacts or distortion. This indicates that the reference electrode introduced non-uniform electron and ion currents during the test, resulting in greater impedance and significantly hindering subsequent impedance analysis, thus masking the true impedance characteristics of the battery to some extent. In contrast, when using the mesh reference electrode of Example 1, the obtained EIS spectrum exhibits the typical characteristics of a semi-circular high-frequency region and a straight low-frequency diffusion region characteristic of lithium-ion batteries. This indicates that the reference electrode did not introduce additional interference and can accurately reflect the interface impedance, charge transfer impedance, and diffusion process inside the battery, making the test data reliable. Therefore, the mesh reference electrode of Example 1 is significantly superior to the linear reference electrode of Comparative Example 2 in terms of stability and anti-interference capability, and is more suitable for EIS testing of three-electrode systems.

[0097] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A reference electrode, applied to an electrode assembly, the electrode assembly comprising electrode plates and a reference electrode, characterized in that, include: Metal mesh; An active coating is applied to the surface of the metal mesh and contains lithium titanate or lithium iron phosphate as the main component. The areal loading of the main component in the active coating is not higher than 1 / 10 of the areal loading of the active material in the electrode sheet.

2. The reference electrode according to claim 1, characterized in that, The metal mesh is a stretched metal mesh or a woven metal mesh, and the metal mesh meets one or more of the following conditions: thickness of 10-80μm, wire diameter of 10-80μm, and aperture of 50-500μm.

3. The reference electrode according to claim 1, characterized in that, The metal mesh is made of copper or aluminum.

4. The reference electrode according to claim 1, characterized in that, The surface loading of the main component in the active coating is no higher than 1 / 10 of the surface loading of the active material in the electrode sheet.

5. The reference electrode according to claim 1, characterized in that, The active coating also contains a conductive agent and a binder, and the main component, conductive agent, and binder in the active coating have a mass ratio of 70%~95%, 2%~20%, and 2%~10%, respectively.

6. The reference electrode according to claim 5, characterized in that, The mass ratio of the main component, conductive agent, and binder is 7:2:

1.

7. The reference electrode according to claim 1, characterized in that, The solid content of the slurry used to prepare the active coating is 40% to 80%, and / or the viscosity of the slurry used to prepare the active coating is 3000-10000 mPa·s.

8. A three-electrode battery, characterized in that, The device includes an electrode assembly comprising a reference electrode, a positive electrode, and a negative electrode as described in any one of claims 1-7, wherein the positive electrode, the reference electrode, and the negative electrode are arranged in sequence at intervals, and an isolation membrane is provided between the positive electrode and the reference electrode, and between the negative electrode and the reference electrode.

9. A method for preparing the three-electrode battery according to claim 8, characterized in that, include: Assembling the three-electrode battery includes hot-pressing, encapsulating, and injecting electrolyte into the electrode assembly to obtain the assembled three-electrode battery. The reference electrode is activated at 0.01-0.50 A g. -1 The reference electrode is charged or discharged to a preset cutoff voltage of the main component using a current density of 0.01-0.50 A g. -1 The current density is used to discharge or charge the reference electrode to 30% to 70% of its capacity to activate the reference electrode.

10. The method for preparing a three-electrode battery according to claim 9, characterized in that, The preset cutoff voltage of the lithium titanate is 2.8-2.9V, and the preset cutoff voltage of the lithium iron phosphate is 2.0V.

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