A reference electrode assembly, its preparation method and use

Abstract

The application relates to the field of secondary batteries, in particular to a reference electrode assembly and a preparation method and application thereof, which comprises a main reference electrode, a first auxiliary reference electrode and a second auxiliary reference electrode arranged between a working electrode and a counter electrode, the main reference electrode is located at the center position between the first auxiliary reference electrode and the second auxiliary reference electrode; the main reference electrode comprises a first base material and an electroactive material containing a lithium element coated on the surface of the first base material; the first auxiliary reference electrode and the second auxiliary reference electrode both comprise a second base material and a lithium layer connected to the surface of the second base material. The reference electrode assembly can realize in-situ potential adjustment, can long-term and real-time monitor the potential of the reference electrode assembly, can quickly, simply and efficiently prepare the sample of the reference electrode assembly, can improve the sample preparation quality and test precision of the reference electrode assembly, and the auxiliary reference electrode can calibrate the potential of the main reference electrode at any time, thereby prolonging the service life of the reference electrode assembly.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, specifically to a reference electrode assembly, its preparation method, and its application. Background Technology

[0002] Since its introduction, lithium-ion batteries have been widely used in fields such as digital products, energy storage, and new energy vehicles due to their advantages such as high specific energy, self-discharge, long life, no memory effect, and environmental friendliness. They have become the most widely used battery system.

[0003] In commercial applications, the common lithium-ion battery system is a mixed solution system of LCO / NCM / LFP, graphite, and organic compounds. This system is prone to lithium plating under high-rate or low-temperature operating conditions. LCO stands for lithium cobalt oxide, NCM for nickel-cobalt-manganese ternary lithium, and LFP for lithium iron phosphate. In-situ testing of the negative electrode potential in a three-electrode battery is a commonly used method for monitoring lithium plating. This method typically uses micron-sized copper wire, coated with lithium, and then implanted between the positive and negative electrodes of the cell to serve as a reference electrode. This reference electrode is placed between the positive and negative electrodes, and the negative electrode potential is measured. A negative electrode potential of 0V is used as the standard; when the negative electrode potential is less than 0V, lithium plating is considered to have occurred. Chinese patent CN116207357A discloses a three-electrode cell structure, a three-electrode battery, and a method for monitoring the negative electrode potential. The three-electrode lithium-ion battery includes a casing, an electrolyte, a cell under test, and a reference cell containing at least two reference electrodes. The reference cell is encapsulated inside the casing and located outside the cell under test. A reference cell with multiple reference electrodes is positioned outside the cell under test. By monitoring the potential difference between the negative electrode of the cell under test and the reference electrodes at different stages, the negative electrode potential is accurately tested, and the lithium plating status of the negative electrode is determined. However, copper wire lithium plating has significant drawbacks. The copper wire is thin, limiting the amount of lithium plating. During the test, lithium is partially or completely consumed, exposing the entire copper surface, resulting in large fluctuations in the measured potential data, and thus failing to accurately monitor changes in the negative electrode potential.

[0004] Lithium iron phosphate (LFP) reference electrodes offer advantages over lithium-plated copper wire reference electrodes, including greater testing stability, higher accuracy, simpler operation, and lower cost, making them highly valuable for applications. Chinese patent CN109585907A discloses a three-electrode lithium-ion battery and its manufacturing method, comprising a battery casing, a separator, a battery electrolyte, a positive electrode, a negative electrode, a copper wire, and a lithium iron phosphate electrode sheet. The battery electrolyte is sealed within the battery casing, and the positive electrode, negative electrode, copper wire, and lithium iron phosphate electrode sheet are all immersed in the electrolyte. The positive and negative electrodes are separated by a separator, and both the copper wire and lithium iron phosphate electrode sheet are separated from the positive electrode and from the negative electrode by separators. The patent describes a lithium iron phosphate reference electrode that exhibits higher stability and a longer service life compared to a lithium-plated copper wire reference electrode. Chinese patent CN114784224A discloses a reference electrode, a three-electrode battery cell, and a lithium-ion battery. The reference electrode includes a porous substrate and a lithium iron phosphate layer coated on the substrate framework. The lithium iron phosphate reference electrode described herein has significant advantages over lithium metal reference electrodes.

[0005] The above-mentioned solutions are all beneficial attempts in this field. However, the lithium iron phosphate (LFP) has a lithium-to-lithium operating potential range of 2.0V to 3.8V, while its stable lithium-to-lithium potential is 3.3V to 3.5V due to the intrinsic properties of the material. Therefore, based on the requirement of a stable reference electrode potential, it is necessary to adjust the potential of the LFP reference electrode to make it a reference electrode based on a stable potential. Both of the existing solutions mentioned above lack technical means for adjusting and monitoring the potential of the reference electrode. Summary of the Invention

[0006] The purpose of this invention is to provide a reference electrode assembly, its preparation method, and its application. This invention enables in-situ potential adjustment of the reference electrode assembly and real-time monitoring of its potential. Consequently, it allows for rapid, simple, and efficient sample preparation of the reference electrode assembly, improving sample quality and testing accuracy. Furthermore, the auxiliary reference electrode can perform potential calibration of the main reference electrode at any time, extending the service life of the reference electrode assembly.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a reference electrode assembly, including a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode disposed between a working electrode and a counter electrode. The main reference electrode is located at the center between the first auxiliary reference electrode and the second auxiliary reference electrode. The main reference electrode includes a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. Both the first and second auxiliary reference electrodes include a second substrate and a lithium layer connected to the surface of the second substrate. By charging or discharging the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode, respectively, in-situ regulation of lithium on the main reference electrode is achieved.

[0009] Furthermore, the first substrate is selected from at least one of copper, aluminum, gold, nickel, tin, silver, and platinum;

[0010] The electroactive material is selected from at least one of lithium iron phosphate, lithium manganese phosphate, lithium titanate, lithium titanium phosphate, lithium aluminum alloy, lithium gold alloy, lithium tin alloy, and lithium bismuth alloy.

[0011] Furthermore, the second substrate is selected from at least one of lithium, copper, aluminum, gold, nickel, tin, silver and platinum.

[0012] Furthermore, the thickness of the lithium layer on the surface of the second substrate is 3–150 μm.

[0013] Furthermore, the first auxiliary reference electrode and the second auxiliary reference electrode are identical in material, shape, and size.

[0014] Furthermore, a diaphragm is arranged between the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode, which serves as an insulating and separating membrane.

[0015] The base membrane material of the diaphragm is at least one of PP, PE, PI, PES and non-woven fabric.

[0016] Secondly, the present invention provides a method for preparing a reference electrode assembly, which includes the following steps:

[0017] The main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, and the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are led out from the same side or opposite side of the battery cell under test.

[0018] The first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode are connected to charge or discharge respectively until the plateau stable voltage range of the main reference electrode is met. Then the charging or discharging is stopped, so as to realize the in-situ regulation of lithium element on the main reference electrode, that is, to complete the fabrication of the reference electrode assembly.

[0019] Furthermore, the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are located on the same plane, and this plane is arranged parallel to the plane where the working electrode is located or the plane where the counter electrode is located. The main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are insulated from each other by a membrane.

[0020] Furthermore, after arranging and implanting the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode between the working electrode and the counter electrode of the battery cell under test, edge sealing, baking, aging, formation, and secondary sealing are performed.

[0021] Furthermore, the baking process specifically involves baking in a vacuum environment at a temperature of 85–105°C until the moisture content of the reference electrode assembly is ≤150 ppm.

[0022] Furthermore, the in-situ adjustment of lithium on the main reference electrode specifically includes: connecting the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively for charging or discharging at a preset rate; collecting the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode, and the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode; and stopping charging or discharging when f(U1,U2) meets the plateau stable voltage requirements of the main reference electrode, thus completing the fabrication of the reference electrode assembly; wherein f(U1,U2) is a preset calculation formula.

[0023] Furthermore, the plateau voltage requirement of the main reference electrode is reasonably set based on the electroactive material on the main reference electrode. Specifically...

[0024] When the electroactive material on the main reference electrode is lithium iron phosphate, the range of f(U1,U2) is 3.3V to 3.5V;

[0025] When the electroactive material on the main reference electrode is lithium manganese phosphate, the range of f(U1,U2) is 4.0V to 4.2V.

[0026] When the electroactive material on the main reference electrode is lithium titanate, the range of f(U1,U2) is 1.45V to 1.65V;

[0027] When the electroactive material on the main reference electrode is lithium titanium phosphate, the range of f(U1,U2) is 2.35V to 2.55V;

[0028] When the electroactive material on the main reference electrode is a lithium-aluminum alloy, the range of f(U1,U2) is 0.2V to 0.4V.

[0029] When the electroactive material on the main reference electrode is a lithium-gold alloy, the range of f(U1,U2) is 0.3V to 0.5V;

[0030] When the electroactive material on the main reference electrode is a lithium-tin alloy, the range of f(U1,U2) is 0.4V to 0.6V;

[0031] When the electroactive material on the main reference electrode is a lithium-bismuth alloy, the range of f(U1,U2) is 0.7V to 1.0V.

[0032] Thirdly, the present invention provides the application of the above-described reference electrode assembly or the reference electrode assembly prepared by the above-described method in lithium batteries.

[0033] Furthermore, the lithium battery includes a casing, a first tab and a second tab disposed on the casing, and a plurality of working electrodes and counter electrodes arranged alternately in the casing; the reference electrode assembly described above or the reference electrode assembly prepared by the above method is arranged between a group of adjacent working electrodes and counter electrodes.

[0034] The beneficial effects of this invention are:

[0035] 1. In this invention, a reference electrode assembly arranged between the working electrode and the counter electrode is configured as a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. The main reference electrode is located at the center between the first and second auxiliary reference electrodes. The main reference electrode includes a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. Both the first and second auxiliary reference electrodes include a second substrate and a lithium layer connected to the surface of the second substrate. During the sample preparation of the reference electrode assembly, the first auxiliary reference electrode is connected to the main reference electrode, and the second auxiliary reference electrode is connected to the main reference electrode. During charging or discharging, the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode, as well as the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode, are collected in real time. When f(U1,U2) meets the plateau stable voltage requirement of the main reference electrode, charging or discharging is stopped. This achieves in-situ potential adjustment of the reference electrode assembly, enabling rapid, simple, and efficient sample preparation of the reference electrode assembly. This improves the sample quality of the reference electrode assembly and ensures the testing accuracy of the battery cell under test, thereby enabling rapid identification and analysis of lithium plating in the battery cell under test.

[0036] 2. This invention achieves real-time monitoring of the reference electrode potential by acquiring the voltage U1 between the main reference electrode and the first auxiliary reference electrode, or between the second auxiliary reference electrode and the main reference electrode, and the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode in real time. Based on the calculation formula f(U1,U2), the real-time potential of the reference electrode assembly is obtained. Furthermore, after the battery has been used for a period of time, charging and discharging can be performed by connecting the first auxiliary reference electrode and the main reference electrode, or the second auxiliary reference electrode and the main reference electrode, respectively. This allows for real-time lithium replenishment of the main reference electrode, extending the lifespan of the reference electrode assembly. Consequently, it eliminates the error caused by lithium loss in the reference electrode assembly to the test accuracy, improving the accuracy of reference voltage detection and the lifespan of the reference electrode.

[0037] 3. Because the main reference electrode is located at the center between the first auxiliary reference electrode and the second auxiliary reference electrode (i.e., the first and second auxiliary reference electrodes are symmetrically arranged around the main reference electrode), this invention can eliminate the influence of concentration polarization on the voltage U1 between the main reference electrode and the first auxiliary reference electrode, or between the main reference electrode and the second auxiliary reference electrode. This effectively improves the accuracy of in-situ adjustment of the main reference electrode and enhances the testing accuracy of the reference electrode. Simultaneously, the first and second auxiliary reference electrodes are connected to the main reference electrode respectively, and small-current charging and discharging are used to adjust the potential of the main reference electrode in situ. This effectively reduces the impact on the working electrode and the counter electrode, maintaining the stability and consistency of the cell's capacity and other electrical properties.

[0038] 4. In traditional three-electrode systems, the potential adjustment of in-situ sample preparation mainly relies on charging or discharging the working electrode and counter electrode with the reference electrode to achieve stable reference electrode sample preparation. The effectiveness of reference electrode sample preparation is mainly determined by the voltage value between the reference electrode and the working electrode and counter electrode. However, in practical applications, the lithium concentration in various parts of the cell is non-uniform. This non-uniformity will cause concentration potential, affecting the accuracy of potential measurement between the reference electrode and the working electrode and counter electrode in traditional three-electrode systems, thus affecting the sample preparation of the reference electrode. This application employs a five-electrode system, namely a working electrode, a counter electrode, a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. In the five-electrode system, the first and second auxiliary reference electrodes are symmetrically arranged around the main reference electrode during the charging and discharging adjustment potential process with the main reference electrode. The voltage U1 between the main reference electrode and the auxiliary reference electrode, and the voltage U2 between the first and second auxiliary reference electrodes can be detected and eliminated by calculating f(U1,U2), thereby improving the sample preparation quality of the main reference electrode and enhancing the monitoring accuracy of the main reference electrode. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention.

[0040] Figure 1 This is a schematic diagram of the structure of the reference electrode assembly described in an embodiment of the present invention;

[0041] Figure 2 This is a flowchart illustrating the preparation method of the reference electrode assembly described in this embodiment of the invention.

[0042] Figure 3 This is a schematic diagram of the structure of the lithium-ion battery described in an embodiment of the present invention;

[0043] Figure 4 This is a cross-sectional schematic diagram of the lithium-ion battery described in an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram of the reference electrode assembly prepared according to Embodiment 1 of the present invention for monitoring the potential changes of the positive and negative electrode voltages of the battery cell under test as the cycle proceeds.

[0045] In the figure, 1—reference electrode assembly, 11—main reference electrode, 12—first auxiliary reference electrode, 13—second auxiliary reference electrode, 2—working electrode, 3—counter electrode, 4—diaphragm, 5—first tab, 6—second tab, 7—housing. Detailed Implementation

[0046] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0047] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0048] In-situ testing of the negative electrode potential in three-electrode batteries is a commonly used method for monitoring lithium plating. This method typically uses micron-sized copper wire, coated with lithium, and then implanted between the positive and negative electrodes of the cell to serve as a reference electrode. This reference electrode is placed between the positive and negative electrodes, and the negative electrode potential is measured, using 0V as the standard. When the negative electrode potential is less than 0V, lithium plating is considered to have occurred. However, the thinness of the copper wire limits the amount of lithium plating. During the test, some or even all of the lithium is consumed, exposing the entire copper surface, resulting in large fluctuations in the measured potential data. Consequently, it is impossible to accurately monitor changes in the negative electrode potential.

[0049] Furthermore, lithium iron phosphate (LFP) offers significant advantages over copper-plated lithium reference electrodes, including greater testing stability, higher accuracy, simpler operation, and lower cost, making it highly valuable for applications. However, LFP's operating potential range for lithium is 2.0V–3.8V, while its stable potential for lithium is 3.3V–3.5V due to intrinsic material properties. Therefore, based on the requirement for a stable reference electrode potential, it is necessary to adjust the potential of the LFP reference electrode to make it a reference electrode with a stable potential. Currently, existing solutions lack the technical means for adjusting and monitoring the potential of the reference electrode.

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0051] In one specific implementation, see Figure 1 As shown, the present invention provides a reference electrode assembly, including a main reference electrode 11, a first auxiliary reference electrode 12, and a second auxiliary reference electrode 13 disposed between a working electrode and a counter electrode. The main reference electrode 11 is located at the center between the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13. The main reference electrode 11 includes a first substrate and an electroactive material containing lithium coated on the surface of the first substrate; the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13 each include a second substrate and a lithium layer connected to the surface of the second substrate. By charging or discharging the first auxiliary reference electrode 12 and the main reference electrode 11, and the second auxiliary reference electrode 13 and the main reference electrode 11 respectively, in-situ regulation of lithium on the main reference electrode 11 is achieved.

[0052] In traditional three-electrode systems, the potential adjustment for in-situ sample preparation mainly relies on charging or discharging the working electrode and counter electrode with the reference electrode to achieve stable reference electrode sample preparation. The effectiveness of reference sample preparation is mainly determined by the voltage values ​​between the reference electrode and the working electrode and counter electrode. However, in practical applications, the lithium concentration in different parts of the cell is non-uniform. This non-uniformity will cause concentration potential, affecting the accuracy of potential measurement between the reference electrode and the working electrode and counter electrode in traditional three-electrode systems, thus affecting the sample preparation of the reference electrode. This application employs a five-electrode system, namely a working electrode, a counter electrode, a main reference electrode 11, a first auxiliary reference electrode 12, and a second auxiliary reference electrode 13. In the five-electrode system, the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13 are symmetrically arranged around the main reference electrode 11 during the charging and discharging adjustment potential process with the main reference electrode 11. By detecting the voltage U1 between the main reference electrode 11 and the auxiliary reference electrode (the first auxiliary reference electrode 12 or the second auxiliary reference electrode 13), and the voltage U2 between the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13, and eliminating them by calculating f(U1,U2), the sample preparation quality of the main reference electrode 11 is improved, and the monitoring accuracy of the main reference electrode 11 is enhanced.

[0053] Since the main reference electrode 11 is located at the center between the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13, i.e., the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13 are symmetrically arranged around the main reference electrode, the influence of concentration polarization on the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode can be eliminated, effectively improving the accuracy of in-situ adjustment of the main reference electrode and enhancing the testing accuracy of the reference electrode. Furthermore, the first and second auxiliary reference electrodes are connected to the main reference electrode respectively, and small-current charging and discharging are used to adjust the potential of the main reference electrode in situ, effectively reducing the impact on the working electrode and the counter electrode, thus maintaining the stability of the cell's capacity and other electrical properties. Simultaneously, the combination design of the first / second auxiliary reference electrodes and the main reference electrode enables real-time long-term calibration of the reference electrode, extending its lifespan and achieving monitoring stability and non-destructive dynamic monitoring throughout the cell's entire lifespan.

[0054] It should be noted that the number of the first auxiliary reference electrode and the second auxiliary reference electrode is not limited to one shown in the figure, and two or more can be arranged according to the actual application.

[0055] See Figure 2 As shown, the present invention also provides a method for preparing the reference electrode assembly, which includes the following steps:

[0056] S1, prepare the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode;

[0057] S2, the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, and the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are led out from the same side or opposite side of the battery cell under test.

[0058] S3 undergoes edge sealing, baking, aging, chemical formation, and secondary sealing.

[0059] S4 connects the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively for charging or discharging until the plateau stable voltage range of the main reference electrode is met, then stops charging or discharging, thus completing the fabrication of the reference electrode assembly.

[0060] Example 1: A method for preparing a reference electrode assembly, comprising the following steps:

[0061] S1, fabricating a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. The main reference electrode comprises a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. The first substrate is a copper wire with a purity of 99.99% or higher, and the electroactive material is lithium iron phosphate. The coated electroactive material has a thickness of 20 μm. Both the first and second auxiliary reference electrodes are lithium metal sheets, meaning the second substrate is selected from lithium. The thickness of the lithium metal sheet is 100 μm.

[0062] S2, in an environment with a temperature of 25±2℃ and humidity <10%, the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13, i.e., the reference electrode assembly 1, are arranged... Figure 3 and Figure 4 The reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, and the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are led out from the side of the battery cell under test. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are located on the same plane, and this plane is arranged parallel to the plane where the working electrode or the counter electrode is located. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are insulated from each other.

[0063] S3 involves top and edge sealing, followed by baking in a vacuum environment at 95℃ until the moisture content of the reference electrode assembly is ≤150ppm. The baked battery cell is then injected with electrolyte and its sides are sealed. The sealed battery is then aged and formed. Finally, the formed battery undergoes a second sealing process.

[0064] S4, the first auxiliary reference electrode 12 and the main reference electrode 11, and the second auxiliary reference electrode 13 and the main reference electrode 11 are respectively connected for charging at a preset rate. The voltage U1 between the main reference electrode 11 and the first auxiliary reference electrode 12 or between the main reference electrode 11 and the second auxiliary reference electrode 13, and the voltage U2 between the first auxiliary reference electrode 12 and the second auxiliary reference electrode 13 are collected. When f(U1,U2) meets the plateau stable voltage requirement of the main reference electrode, the charging is stopped, and the fabrication of the reference electrode assembly is completed. The f(U1,U2) is a preset calculation formula.

[0065] In this embodiment,

[0066] In this embodiment, since the electroactive material on the main reference electrode is lithium iron phosphate, the adjustment range of f(U1,U2) is set to 3.3V to 3.5V. Preferably, charging is stopped when f(U1,U2) is adjusted to 3.4V, thus completing the fabrication of the reference electrode assembly.

[0067] This invention achieves in-situ potential adjustment of the reference electrode assembly 1 by charging the first auxiliary reference electrode 12 and the main reference electrode 11, and the second auxiliary reference electrode 13 and the main reference electrode 11 respectively. This enables rapid, simple, and efficient sample preparation of the reference electrode assembly 1, improves the sample preparation quality of the reference electrode assembly 1, and ensures the testing accuracy of the battery cell under test, thereby enabling rapid identification and analysis of lithium plating in the battery cell under test.

[0068] This invention obtains the real-time potential of the reference electrode assembly based on the calculation formula f(U1,U2), realizing real-time monitoring of the reference electrode potential. Furthermore, after the battery has been used for a period of time, it can be charged by connecting the first auxiliary reference electrode 12 and the main reference electrode 11, and the second auxiliary reference electrode 13 and the main reference electrode 11 respectively, thereby replenishing the lithium of the main reference electrode 11, extending the service life of the reference electrode assembly, and thus eliminating the error caused by lithium loss in the reference electrode assembly 1 to the test accuracy, improving the accuracy of reference voltage detection.

[0069] The prepared reference electrode assembly was applied to a lithium battery, see [link to relevant documentation]. Figure 3 and Figure 4The lithium battery includes a casing 7, a first tab 5 and a second tab 6 disposed on the casing 7, and several working electrodes 2 and counter electrodes 3 alternately stacked within the casing. The working electrodes are connected to the first tab 5, and the counter electrodes 3 are connected to the second tab 6. A separator 4 is arranged between adjacent working electrodes and counter electrodes, and between the working electrodes, counter electrodes, and the reference electrode assembly 1. This separator 4 serves as insulation and separation. The base material of the separator 4 is at least one of PP, PE, PI, PES, and non-woven fabric. The prepared reference electrode assembly is arranged between a group of adjacent working electrodes 2 and counter electrodes 3, forming a "five-electrode system" together with the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13.

[0070] See Figure 5 As shown, the prepared reference electrode assembly was used to monitor the potential changes of the positive and negative electrode voltages of the battery cell under test during cycling. The X-axis of the figure represents the charge and discharge time, the left Y-axis represents the measured total voltage value and the positive electrode potential / negative electrode potential (measured using a regulated lithium iron phosphate as the reference electrode), and the right Y-axis represents the converted positive electrode potential / negative electrode potential (VS Li). The test cycle charge and discharge rate was 0.5C. From the potential monitoring during the cycling process, it can be seen that within 1000 hours, the electrode potential monitored by the main reference electrode with lithium iron phosphate as the electroactive material has high stability and consistency as the cycling progresses, further demonstrating the stability and reliability of the prepared lithium iron phosphate five-electrode system.

[0071] The prepared reference electrode assembly was cycled at a rate of 1.5C. The changes in the positive and negative electrode potentials before and after cycling are shown in Table 1.

[0072] Table 1 compares the changes in positive and negative electrode potentials of the prepared reference electrode assembly before and after cycling at a 1.5C rate.

[0073]

[0074]

[0075] As shown in Table 1, the cells were charged and discharged at 1 / 3C before and after cycling, and then charged to 50% SOC. After being left to stand at room temperature for 12 hours, the changes in the potential of the main and auxiliary reference electrodes were observed. The comparison of the positive and negative electrode potentials measured by the main reference electrode (lithium iron phosphate) and the auxiliary reference electrode (lithium sheet) before and after cycling shows that the stability of the lithium iron phosphate reference electrode in the five-electrode system decreases as cycling progresses.

[0076] Example 2: A method for preparing a reference electrode assembly, comprising the following steps:

[0077] S1, fabricating a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. The main reference electrode comprises a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. The first substrate is a copper wire with a purity of 99.99% or higher, and the electroactive material is lithium manganese phosphate. The coated electroactive material has a thickness of 20 μm. Both the first and second auxiliary reference electrodes are lithium metal sheets, meaning the second substrate is selected from lithium. The thickness of the lithium metal sheet is 100 μm.

[0078] S2, in an environment with a temperature of 25±2℃ and humidity <10%, the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13, i.e., the reference electrode assembly 1, are arranged... Figure 3 and Figure 4 The electrodes are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, with the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 led out from the side of the battery cell under test. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are located on the same plane, and this plane is parallel to the plane containing the working electrode or the plane containing the counter electrode. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are insulated from each other.

[0079] S3 involves top and edge sealing, followed by baking in a vacuum environment at 95℃ until the moisture content of the reference electrode assembly is ≤150ppm. The baked battery cell is then injected with electrolyte and its sides are sealed. The sealed battery is then aged and formed. Finally, the formed battery undergoes a second sealing process.

[0080] S4, connect the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively for preset rate charging, collect the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode, and the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode. When f(U1,U2) meets the plateau stable voltage requirement of the main reference electrode, stop charging, thus completing the fabrication of the reference electrode assembly; f(U1,U2) is a preset calculation formula.

[0081] In this embodiment,

[0082] In this embodiment, since the electroactive material on the main reference electrode is lithium manganese phosphate, the adjustment range of f(U1,U2) is set to 4.0V to 4.2V. Preferably, when f(U1,U2) is adjusted to 4.0V, charging is stopped and the fabrication of the reference electrode assembly is completed.

[0083] Example 3: A method for preparing a reference electrode assembly, comprising the following steps:

[0084] S1, fabricating a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. The main reference electrode comprises a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. The first substrate is a copper wire with a purity of 99.99% or higher, and the electroactive material is lithium manganese phosphate. The thickness of the coated electroactive material is 30 μm. Both the first and second auxiliary reference electrodes are lithium metal sheets, meaning the second substrate is selected from lithium. The thickness of the lithium metal sheet is 60 μm.

[0085] S2, in an environment with a temperature of 25±2℃ and humidity <10%, the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13, i.e., the reference electrode assembly 1, are arranged... Figure 3 and Figure 4 The electrodes are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, with the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 led out from the side of the battery cell under test. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are located on the same plane, and this plane is parallel to the plane containing the working electrode or the plane containing the counter electrode. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are insulated from each other.

[0086] S3 involves top and edge sealing, followed by baking in a vacuum environment at 95℃ until the moisture content of the reference electrode assembly is ≤150ppm. The baked battery cell is then injected with electrolyte and its sides are sealed. The sealed battery is then aged and formed. Finally, the formed battery undergoes a second sealing process.

[0087] S4, connect the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively for preset rate charging, collect the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode, and the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode. When f(U1,U2) meets the plateau stable voltage requirement of the main reference electrode, stop charging to complete the fabrication of the reference electrode assembly; f(U1,U2) is a preset calculation formula.

[0088] In this embodiment,

[0089] In this embodiment, since the electroactive material on the main reference electrode is lithium manganese phosphate, the adjustment range of f(U1,U2) is set to 4.0V to 4.2V. Preferably, when f(U1,U2) is adjusted to 4.1V, charging is stopped, and the fabrication of the reference electrode assembly is completed.

[0090] Example 4: A method for preparing a reference electrode assembly, comprising the following steps:

[0091] S1, fabricating a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. The main reference electrode comprises a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. The first substrate is a copper wire with a purity of 99.99% or higher, and the electroactive material is lithium titanate, with a coating thickness of 20 μm. Both the first and second auxiliary reference electrodes are lithium metal sheets, meaning the second substrate is selected from lithium. The thickness of the lithium metal sheet is 100 μm.

[0092] S2, in an environment with a temperature of 25±2℃ and humidity <10%, the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13, i.e., the reference electrode assembly 1, are arranged... Figure 2 and Figure 3 The electrodes are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, with the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 led out from the side of the battery cell under test. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are located on the same plane, and this plane is parallel to the plane containing the working electrode or the plane containing the counter electrode. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are insulated from each other.

[0093] S3 involves top and edge sealing, followed by baking in a vacuum environment at 105℃ until the moisture content of the reference electrode assembly is ≤150ppm. The baked battery cell is then injected with electrolyte and its sides are sealed. The sealed battery is then aged and formed. Finally, the formed battery undergoes a second sealing process.

[0094] S4, connect the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively to perform a preset rate discharge, collect the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode, and the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode. When f(U1,U2) meets the plateau stable voltage requirement of the main reference electrode, stop the discharge to complete the fabrication of the reference electrode assembly; f(U1,U2) is a preset calculation formula.

[0095] In this embodiment,

[0096] In this embodiment, since the electroactive material on the main reference electrode is lithium titanate, the adjustment range of f(U1,U2) is set to 1.45V to 1.65V. Preferably, when f(U1,U2) is adjusted to 1.55V, the discharge is stopped, and the fabrication of the reference electrode assembly is completed.

[0097] Example 5: A method for preparing a reference electrode assembly, comprising the following steps:

[0098] S1, fabricating a main reference electrode, a first auxiliary reference electrode, and a second auxiliary reference electrode. The main reference electrode comprises a first substrate and an electroactive material containing lithium coated on the surface of the first substrate. The first substrate is a copper wire with a purity of 99.99% or higher, and the electroactive material is lithium titanate, with a coating thickness of 20 μm. Both the first and second auxiliary reference electrodes are lithium metal sheets, meaning the second substrate is selected from lithium. The thickness of the lithium metal sheet is 100 μm.

[0099] S2, in an environment with a temperature of 25±2℃ and humidity <10%, the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13, i.e., the reference electrode assembly 1, are arranged... Figure 2 and Figure 3 The electrodes are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, with the main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 led out from the side of the battery cell under test. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are located on the same plane, and this plane is parallel to the plane containing the working electrode or the plane containing the counter electrode. The main reference electrode 11, the first auxiliary reference electrode 12, and the second auxiliary reference electrode 13 are insulated from each other.

[0100] S3 involves top and edge sealing, followed by baking in a vacuum environment at 105℃ until the moisture content of the reference electrode assembly is ≤150ppm. The baked battery cell is then injected with electrolyte and its sides are sealed. The sealed battery is then aged and formed. Finally, the formed battery undergoes a second sealing process.

[0101] S4, connect the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively to discharge at a preset rate, collect the voltage U1 between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode, and the voltage U2 between the first auxiliary reference electrode and the second auxiliary reference electrode. When f(U1,U2) meets the plateau stable voltage requirement of the main reference electrode, stop discharging, thus completing the fabrication of the reference electrode assembly; f(U1,U2) is a preset calculation formula.

[0102] In this embodiment,

[0103] In this embodiment, since the electroactive material on the main reference electrode is lithium titanium phosphate, the adjustment range of f(U1,U2) is set to 2.35V to 2.55V. Preferably, when f(U1,U2) is adjusted to 2.45V, the discharge is stopped, and the fabrication of the reference electrode assembly is completed.

[0104] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a reference electrode assembly, characterized in that, Includes the following steps: The main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, and the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are led out from the same side or opposite side of the battery cell under test. The first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode are connected respectively for charging or discharging, and the voltage between the main reference electrode and the first auxiliary reference electrode or between the main reference electrode and the second auxiliary reference electrode is collected. U 1, and the voltage between the first auxiliary reference electrode and the second auxiliary reference electrode. U 2, in f ( U 1, U 2) When the plateau voltage requirement of the main reference electrode is met, charging or discharging is stopped, thus completing the fabrication of the reference electrode assembly; f ( U 1, U 2) = U 1 － U 2÷2.

2. The method for preparing the reference electrode assembly according to claim 1, characterized in that: The main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are located on the same plane, and this plane is arranged parallel to the plane where the working electrode is located or the plane where the counter electrode is located. The main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are insulated from each other by a membrane.

3. The method for preparing the reference electrode assembly according to claim 1, characterized in that: After the main reference electrode, the first auxiliary reference electrode, and the second auxiliary reference electrode are arranged and implanted between the working electrode and the counter electrode of the battery cell under test, edge sealing, baking, aging, formation, and secondary sealing are performed.

4. The method for preparing the reference electrode assembly according to claim 3, characterized in that, The baking process involves baking in a vacuum environment at a temperature of 85–105°C until the moisture content of the reference electrode assembly is ≤150 ppm.

5. The method for preparing the reference electrode assembly according to claim 1, characterized in that, The plateau voltage requirement of the main reference electrode is set reasonably based on the electroactive material on the main reference electrode.

6. The method for preparing the reference electrode assembly according to claim 1, characterized in that: The main reference electrode includes a first substrate and an electroactive material containing lithium coated on the surface of the first substrate; Both the first auxiliary reference electrode and the second auxiliary reference electrode include a second substrate and a lithium layer connected to the surface of the second substrate; By charging or discharging the first auxiliary reference electrode and the main reference electrode, and the second auxiliary reference electrode and the main reference electrode respectively, in-situ regulation of lithium elements on the main reference electrode can be achieved.

7. The method for preparing the reference electrode assembly according to claim 6, characterized in that: The first substrate is selected from at least one of copper, aluminum, gold, nickel, tin, silver and platinum; The electroactive material is selected from at least one of lithium iron phosphate, lithium manganese phosphate, lithium titanate, lithium titanium phosphate, lithium aluminum alloy, lithium gold alloy, lithium tin alloy, and lithium bismuth alloy.

8. The method for preparing the reference electrode assembly according to claim 6, characterized in that: The second substrate is selected from at least one of lithium, copper, aluminum, gold, nickel, tin, silver and platinum.

9. The method for preparing the reference electrode assembly according to claim 6, characterized in that: The thickness of the lithium layer on the surface of the second substrate is 3~150μm.

10. The method for preparing the reference electrode assembly according to claim 1, characterized in that: The first and second auxiliary reference electrodes are identical in material, shape, and size.

11. The method for preparing the reference electrode assembly according to claim 2, characterized in that: The base film material of the insulating diaphragm is at least one of PP, PE, PI, PES and non-woven fabric.

12. The application of the reference electrode assembly prepared by the method of any one of claims 1 to 11 in lithium batteries.

13. The application according to claim 12, characterized in that: The lithium battery includes a casing, a first tab and a second tab disposed on the casing, and a plurality of working electrodes and counter electrodes arranged alternately in the casing. The reference electrode assembly prepared by the method of any one of claims 1 to 11 is arranged between a group of adjacent working electrodes and counter electrodes.

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