Reference electrode, lithium ion battery and potential measuring method of lithium ion battery

Abstract

The invention relates to a reference electrode, a lithium ion battery and a potential measurement method thereof, the reference electrode comprises a current collector layer and coating layers covering two sides of the current collector layer, and the coating layers are lithium foils; the current collector layer comprises a lithium storage region (1) and a measurement region (2) extending outwards from the lithium storage region (1); a lithium storage tab (4) is arranged on the lithium storage area (1), and a measuring tab (5) is arranged on the measuring area (2) deviating from the lithium storage area (1). Compared with the prior art, two sets of independent references are not used for calibration conversion, the same lithium foil is integrally formed and is divided into a lithium storage end and a measurement end, the lithium storage end and the measurement end are electrically communicated to form a single Li metal reference system, and the measurement end is directly placed in an ion channel between a positive electrode and a negative electrode to improve the authenticity and dynamic response of potential sampling. And the lithium storage end provides sufficient lithium source to maintain the interface stability and long service life of the measuring end.

Description

Reference electrode, lithium-ion battery and its potential measurement method Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a reference electrode, a lithium-ion battery, and a method for measuring the potential of the same. Background Technology

[0002] With the increasing application of lithium-ion batteries, research on their materials, performance, and safety is also growing. To better study the performance of the positive and negative electrodes of lithium-ion batteries, a reference electrode is often introduced. Using the reference electrode as a standard, the potential of the positive or negative electrode relative to the reference electrode is tested. This allows for research on battery cycle performance, high and low temperature charge-discharge, and rate charge-discharge, starting from the internal reaction mechanism of the battery. It has significant guiding significance for battery structure design, electrode design, positive and negative electrode ratio, material matching, and electrolyte composition optimization.

[0003] Existing technologies, such as CN110797569B, propose a "four-electrode" measurement approach. This involves placing a main reference electrode and an auxiliary reference electrode within the battery cell. The main reference electrode is made of the same material as the positive / negative electrode or its current collector, essentially serving as a "pseudo-reference" rather than a Li / Li+ reference. The auxiliary reference electrode is a lithium-plated copper wire with a diameter of approximately 40–80 μm. Its primary function is not to directly measure the positive and negative electrode potentials over a long period, but rather to calibrate the main reference electrode and obtain the positive and negative electrode potentials through conversion. This approach requires superimposing / differentially converting multiple measurements. For example, during each measurement, the auxiliary reference is used to "calibrate" the main reference to obtain V3, and then the pseudo-positive and negative electrode potentials are obtained through conversions such as V+=V1+V3 and V-=V2+V3. Its measurement link is long and involves many variables. Furthermore, the spatial positions of each electrode and the ion transport environment differ, making it prone to the superposition of various error sources such as solution potential drop, concentration polarization, interface drift, and sampling channel noise. This makes the conversion results highly sensitive to changes in operating conditions. In long-term testing across multiple cycles, multiple SOCs, and multiple rates, the superposition and drift effects of these error sources are more likely to accumulate, making it difficult to maintain a stable and consistent reference standard for the obtained potential. This, in turn, affects the interpretation of detailed processes such as electrode phase transition plateaus and polarization evolution, especially for signals like the negative electrode potential that are sensitive to the reference position. In addition, the lithium-plated copper wire auxiliary reference itself has a limited lithium storage capacity, and the interface state evolves with cycles. Calibration frequency, calibration time, and auxiliary reference decay all further amplify the conversion uncertainty, making it difficult for this scheme to simultaneously achieve "reference stability" and "potential accuracy" in long-term monitoring. Summary of the Invention

[0004] To address the aforementioned issues, this application proposes a reference electrode, a lithium-ion battery, and a potential measurement method thereof. The reference electrode is an integrated lithium metal reference electrode structure. By setting a lithium storage region and a measurement region located between the positive and negative electrodes on the same reference electrode, the measurement region is directly positioned at the ion channel between the electrodes, reducing the impact of spatial potential deviation on potential sampling from the source. This allows for a direct output of potentials closer to the true positive and negative electrodes without the need for multi-electrode calibration and multiple conversions. Simultaneously, the lithium storage region provides sufficient lithium to maintain the long-term stability of the reference electrode, preventing reference drift or failure due to insufficient lithium storage. Furthermore, by setting lithium storage tabs and measurement tabs, and utilizing the threshold judgment of the potential difference between the two paths under a static open-circuit state, online self-verification of anomalies such as reference electrode disconnection, leakage / short circuit can be achieved. This ensures accuracy, stability, and diagnosability of potential measurement under long-term, multi-condition testing.

[0005] The objective of this invention can be achieved through the following technical solution: One objective of this invention is a reference electrode, comprising: a current collector layer, and a coating layer covering both sides of the current collector layer, wherein the coating layer is a lithium foil; the current collector layer includes a lithium storage region and a measurement region extending outward from the lithium storage region; a lithium storage tab is disposed on the lithium storage region, and a measurement tab is disposed at one end of the measurement region away from the lithium storage region.

[0006] Furthermore, the current collector layer is a copper foil, and the thickness of the current collector layer is 2-10 μm.

[0007] Furthermore, the thickness of the coating layer is 20-30 μm.

[0008] Furthermore, the lithium storage area is rectangular or strip-shaped.

[0009] Furthermore, the width of the measurement area is less than 1 mm.

[0010] The second objective of this invention is to provide a lithium-ion battery, characterized in that it comprises a positive electrode, a negative electrode, and a reference electrode, wherein the reference electrode is as described above; the negative electrode comprises a negative current collector, a negative active material coated on the negative current collector, and a negative electrode tab extending from the negative current collector, wherein a separator, a lithium storage region, and a separator are sequentially disposed between the negative current collector and the negative active material; the positive electrode has a positive electrode tab extending from it, and a separator, a measurement region, and a separator are sequentially disposed between the positive electrode and the negative electrode.

[0011] Furthermore, the negative electrode tab and the positive electrode tab are located on the same side, and the lithium storage tab is located on the opposite side of the negative electrode tab.

[0012] The third objective of this invention is to provide a potential measurement method for a lithium-ion battery, wherein the lithium-ion battery is as described above. The potential measurement method includes the following steps: measuring the potential of the positive electrode plate (V1) using a lithium storage tab led out from the lithium storage region; measuring the potential of the negative electrode plate (V2) using a lithium storage tab led out from the lithium storage region; measuring the potential of the positive electrode plate (V3) using a measuring tab led out from the measurement region; measuring the potential of the negative electrode plate (V4) using a measuring tab led out from the measurement region; and defining the potential difference between the positive electrode plate measured by the lithium storage tab and the measuring tab as ΔV+ = |V1-V3|, and the potential difference between the negative electrode plate measured by the lithium storage tab and the measuring tab as ΔV- = |V2-V4|.

[0013] When the battery is in a static open-circuit state, ΔV+ and ΔV- should be less than the static threshold V5, where the static threshold V5 is 5-10mV.

[0014] Compared to existing technologies, this invention does not use two independent references for calibration and conversion. Instead, it uses a single lithium foil integrally formed, consisting of a lithium storage end and a measurement end. The two ends are electrically connected to form a single Li metal reference system. The measurement end is directly placed in the ion channel between the positive and negative electrodes to improve the accuracy and dynamic response of the potential sampling, while the lithium storage end provides a sufficient lithium source to maintain the stability and long lifespan of the measurement end interface. Therefore, there is no need to introduce additional auxiliary reference electrodes, nor does it rely on a measurement path converted after calibration. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the reference electrode in this invention; Figure 2 is a schematic diagram of the lithium-ion battery in this invention; Figure 3 shows the positive electrode potential measured at the lithium storage end and the measurement end of the lithium-ion battery in this invention; Figure 4 shows the negative electrode potential measured at the lithium storage end and the measurement end of the lithium-ion battery in this invention; the numbers in the figures indicate: 1-Lithium storage area; 2-Measurement area; 3-Separator; 4-Lithium storage tab; 5-Measurement tab; 6-Negative electrode current collector; 7-Negative electrode active material; 8-Positive electrode sheet; 9-Positive electrode tab; 10-Negative electrode tab; 11-Negative electrode sheet. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0017] Example 1

[0018] This embodiment provides a reference electrode, the specific structure of which is shown in Figure 1. It includes: a current collector layer and a coating layer covering both sides of the current collector layer, wherein the coating layer is a lithium foil; the current collector layer includes a lithium storage region 1 and a measurement region 2 extending outward from the lithium storage region 1; a lithium storage tab 4 is provided on the lithium storage region 1, and a measurement tab 5 is provided at the end of the measurement region 2 opposite to the lithium storage region 1.

[0019] In this embodiment, the current collector layer is a copper foil, and the thickness of the current collector layer is 2-10 μm.

[0020] In this embodiment, the thickness of the coating layer is 20-30 μm.

[0021] In this embodiment, the lithium storage area 1 is rectangular or strip-shaped.

[0022] In this embodiment, the width of the measurement area 2 is less than 1 mm.

[0023] The fabrication method of the reference electrode in this embodiment is shown in Figure 1. The reference electrode includes a current collector layer and a lithium metal layer. The current collector layer is made of copper foil with a thickness of 8 μm. Lithium foil with a thickness of 20-30 μm is laminated and covered on both surfaces of the copper foil. The lamination process is carried out under an inert gas atmosphere (such as argon), preferably in a glove box with a water content and oxygen content of less than 1 ppm. The copper foil is laid flat on a clean, dry workbench, and then the lithium foil is applied to both sides of the copper foil. The lithium foil and copper foil are tightly bonded by rolling or pressing to reduce interfacial contact resistance and improve structural integrity. After pressing, the reference electrode is visually inspected to ensure that the lithium layer is continuous, wrinkle-free, perforated, and free of obvious burrs or free lithium debris at the edges. Under inert gas protection, the reference electrode base material is cut and shaped using laser cutting to obtain a predetermined size that meets the battery assembly requirements. The laser cutting path can be set to a rectangular, strip-shaped, or irregularly shaped structure with an extended measuring end, depending on the cell structure. The width of the extended measuring end is preferably less than 1mm to ensure stable structural connection while minimizing size. After cutting, the cut edges are cleaned to remove any residual metal shavings and avoid potential short-circuit risks. The final product is a structurally complete reference electrode, which is then sealed and temporarily stored in an inert gas environment for subsequent battery assembly.

[0024] Example 2

[0025] This embodiment provides a lithium-ion battery, the specific structure of which is shown in Figure 2. It includes a positive electrode 8, a negative electrode, and a reference electrode. The reference electrode is the reference electrode as described in Embodiment 1. The negative electrode includes a negative current collector 6, a negative active material 7 coated on the negative current collector 6, and a negative electrode tab 10 led out from the negative current collector 6. A separator 3, a lithium storage region 1, and a separator 3 are sequentially provided between the negative current collector 6 and the negative active material 7. A positive electrode tab 9 is led out from the positive electrode 8. A separator 3, a measurement region 2, and a separator 3 are sequentially provided between the positive electrode 8 and the negative electrode.

[0026] In this embodiment, the negative electrode tab 10 and the positive electrode tab 9 are on the same side, and the lithium storage tab 4 is on the opposite side of the negative electrode tab 10.

[0027] Specifically, the lithium-ion battery preparation method in this embodiment is as follows: This embodiment uses the reference electrode obtained in Example 1 to construct a multi-electrode lithium-ion battery containing the reference electrode. The assembly process is carried out under an inert gas protective atmosphere, preferably in a glove box where the water and oxygen content are both below 1 ppm. The positive electrode sheet and the negative electrode sheet are prepared according to conventional processes and cut to a predetermined size. The positive electrode sheet and the negative electrode sheet are respectively provided with positive electrode tabs and negative electrode tabs. The main body of the reference electrode (lithium storage end 1) of Example 1 is arranged in the negative electrode current collector interlayer area, that is, the negative electrode current collector is cut open so that the lithium storage end 1 is embedded in the negative electrode copper foil interlayer, ensuring that the separator is completely covered on both sides of the reference electrode to avoid short circuit; a Z-shaped stacking process is used (the reference electrode tabs are located on the opposite sides of the positive and negative electrode tabs) to stack and assemble the negative electrode sheet with the lithium storage end 1 with other electrodes and separators. Special attention should be paid to ensuring that during assembly, the measuring end 2 of the reference electrode passes through the separator and extends into the separator layer region between the positive and negative electrodes, and that the measuring end 2 is completely covered by the separator to ensure that it has no direct contact with the positive electrode active layer, the negative electrode active layer, and the current collectors of both electrodes; after the stacking is completed, the positive electrode tab, the negative electrode tab, and the reference electrode tab (lithium storage tab 4 and measuring tab 5) are led out respectively, and insulating tape is placed at the point where the tabs pass through the aluminum-plastic film to prevent the tabs from overlapping; the assembled cell is placed into the aluminum-plastic film shell or a designated battery shell, dried in a high-temperature vacuum chamber, and after cooling, an electrolyte matching the cell capacity is injected into the battery under negative pressure. The electrolyte is a lithium salt-organic solvent system electrolyte, preferably a carbonate system electrolyte, and more preferably, the lithium salt includes, but is not limited to, lithium salt solutes such as LiPF6, LiBF4, and LiTFSI, and the organic solvent includes, but is not limited to, one or more of EC, DEC, EMC, and DMC, and may contain film-forming additives or flame-retardant additives. In this embodiment, 1M LiPF6 is used in a mixed solvent of EC:DMC:DEC, with a volume ratio of EC:DMC:DEC of 1:1:1. During the drying and liquid injection processes, attention is paid to the electrical insulation treatment and protection of the reference electrode and the positive and negative electrodes. After the battery is first vacuumed and sealed, it undergoes formation and sorting, followed by a second vacuuming and sealing to obtain a lithium-ion battery with a reference electrode.

[0028] The potential measurement method of this lithium-ion battery includes the following steps: measuring the potential of the positive electrode plate 8 using the lithium storage tab 4 led out from the lithium storage region 1 as V1, measuring the potential of the negative electrode plate using the lithium storage tab 4 led out from the lithium storage region 1 as V2; measuring the potential of the positive electrode plate 8 using the measuring tab 5 led out from the measurement region 2 as V3, measuring the potential of the negative electrode plate using the measuring tab 5 led out from the measurement region 2 as V4, and the results are shown in Figures 3-4; as shown in Figure 3, the positive electrode potential V1 measured by the lithium storage tab 4 led out from the lithium storage region 1 and the positive electrode potential V3 measured by the measuring tab 5 led out from the measurement region 2 have a consistent overall trend, but there is a deviation in the end range of capacity, indicating that the lithium storage region 1 may introduce potential measurement errors due to different arrangement positions. Furthermore, as shown in Figure 4, the negative electrode potential is more sensitive to the reference position: the negative electrode potential V4 measured by the measuring tab 5 more clearly reflects the characteristic changes (discharge plateau and terminal polarization, etc.) during the negative electrode phase transition process, while the negative electrode potential V2 measured by the lithium storage tab 4 is relatively smoother and has a larger deviation at the capacity end, indicating that the negative electrode potential measured in lithium storage region 1 has obvious systematic errors and is difficult to use for characterizing fine processes such as phase transition plateau. Therefore, this method uses V3 and V4 measured by the measuring tab 5 as the effective measurement results of the positive and negative electrode potentials, and uses V1 and V2 measured by the lithium storage tab 4 as the verification measurement results to judge the electrical connection status of the reference electrode and the reliability of the measurement circuit.

[0029] The positive electrode potential difference measured by the lithium storage electrode 4 and the measuring electrode 5 is ΔV+ = |V1-V3|, and the negative electrode potential difference measured by the lithium storage electrode 4 and the measuring electrode 5 is ΔV- = |V2-V4|.

[0030] When the battery is in a static open-circuit state, ΔV+ and ΔV- should be less than the static threshold V5, where the static threshold V5 is 5-10mV; if ΔV+ or ΔV- is greater than the static threshold V5 in the static open-circuit state, it is determined that the reference electrode may have an abnormal electrical connection (including but not limited to a disconnection between measurement area 2 and lithium storage area 1, abnormal tab lead-out connection, or an abnormal leakage path).

[0031] Compared to CN110797569B, the potential measurement method in this embodiment does not use two independent references for calibration and conversion. Instead, it uses a single lithium foil integrally formed, consisting of a lithium storage end and a measurement end. The two are electrically connected to form a single Li metal reference system. The measurement end is directly placed in the ion channel between the positive and negative electrodes to improve the accuracy and dynamic response of the potential sampling, while the lithium storage end provides a sufficient lithium source to maintain the stability and long lifespan of the measurement end interface. Therefore, there is no need to introduce additional auxiliary reference electrodes, nor does it rely on a measurement path converted after calibration.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A reference electrode, characterized in that, include: The current collector layer and the coating layer covering both sides of the current collector layer, the coating layer being a lithium foil; the current collector layer includes a lithium storage region (1) and a measurement region (2) extending outward from the lithium storage region (1); a lithium storage tab (4) is provided on the lithium storage region (1), and a measurement tab (5) is provided at one end of the measurement region (2) away from the lithium storage region (1).

2. A reference electrode according to claim 1, characterized in that, The current collector layer is a copper foil, and the thickness of the current collector layer is 2-10 μm.

3. A reference electrode according to claim 1, characterized in that, The thickness of the coating layer is 20-30 μm.

4. A reference electrode according to claim 1, characterized in that, The lithium storage area (1) is rectangular or strip-shaped.

5. A reference electrode according to claim 1, characterized in that, The width of the measurement area (2) is less than 1 mm.

6. A lithium-ion battery, characterized in that, The device includes a positive electrode (8), a negative electrode (11), and a reference electrode, wherein the reference electrode is the reference electrode as described in any one of claims 1-5; the negative electrode (11) includes a negative current collector (6), a negative active material (7) coated on the negative current collector (6), and a negative electrode tab (10) led out from the negative current collector (6); a separator (3), a lithium storage region (1), and a separator (3) are sequentially provided between the negative current collector (6) and the negative active material (7); a positive electrode tab (9) is led out from the positive electrode (8); a separator (3), a measurement region (2), and a separator (3) are sequentially provided between the positive electrode (8) and the negative electrode (11).

7. A lithium-ion battery according to claim 6, characterized in that, The negative electrode tab (10) and the positive electrode tab (9) are on the same side, and the lithium storage tab (4) and the measuring tab (5) are on the opposite side of the negative electrode tab (10) and the positive electrode tab (9).

8. A method for measuring the potential of a lithium-ion battery, wherein the lithium-ion battery is the lithium-ion battery as described in claims 6-7, characterized in that, The potential measurement method includes the following steps: measuring the potential of the positive electrode (8) with the lithium storage tab (4) led out from the lithium storage region (1) as V1, measuring the potential of the negative electrode with the lithium storage tab (4) led out from the lithium storage region (1) as V2; measuring the potential of the positive electrode (8) with the measuring tab (5) led out from the measurement region (2) as V3, measuring the potential of the negative electrode with the measuring tab (5) led out from the measurement region (2) as V4; measuring the potential difference of the positive electrode with the lithium storage tab (4) and the measuring tab (5) as ΔV+ = |V1-V3|, measuring the potential difference of the negative electrode with the lithium storage tab (4) and the measuring tab (5) as ΔV- = |V2-V4|.

9. A method for measuring the potential of a lithium-ion battery according to claim 8, characterized in that, When the battery is in a static open-circuit state, ΔV+ and ΔV- should be less than the static threshold V5, where the static threshold V5 is 5-10mV.

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