A three-electrode battery for testing

Abstract

This invention discloses a three-electrode battery for testing, comprising a cell and a reference electrode. The cell includes a positive electrode, a separator, and a negative electrode, with both ends of the cell serving as negative electrodes. The cell is arranged sequentially in the order of negative electrode, separator, positive electrode, separator, and negative electrode. Holes are drilled at the test locations on the positive and negative electrodes, and the reference electrode passes through both the negative and positive electrode holes sequentially. This invention eliminates the need for an additional separator, directly characterizing the potential at the test location. Furthermore, the position and distance of the reference electrode can be set as needed, simplifying operation. It can be used to study battery positive and negative electrode design, cycle failure, capacity decay mechanisms, etc., providing important guidance for improving battery performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a three - electrode battery for testing. Background Art

[0002] Three - electrode battery systems have been widely used to study the electrochemical changes of batteries. Compared with two - electrode batteries, three - electrode batteries can well obtain the impedance data and their change values of each part, and can quickly judge the reasons for battery capacity attenuation. The three parts constituting the three - electrode battery system include a working electrode, a reference electrode, and a counter electrode. These three electrodes do not contact each other (otherwise there will be a short circuit), but are jointly immersed in the electrolyte.

[0003] For lithium - ion batteries, the positive electrode and the negative electrode respectively correspond to the working electrode and the counter electrode, and the reference electrode is a lithium reference electrode, usually made of copper wire or platinum wire coated with lithium. At present, most of the production of three - electrode batteries is in the soft - package battery system, button - type battery system, as well as the cylindrical three - electrode model and groove - type three - electrode model sold on the market. The research cell system is relatively small. Secondly, in the prior art, two separators are arranged in the middle of the opposite surfaces of the positive and negative electrode sheets, and the reference electrode is arranged in these two separators to avoid contact between the reference electrode and the positive and negative electrodes. This will cause the measured data to deviate from the true value. Summary of the Invention

[0004] In order to solve the existing problems, the present invention provides a three - electrode battery for testing, and the specific scheme is as follows:

[0005] A three - electrode battery for testing includes a cell and a reference electrode. The cell includes a positive electrode sheet, a separator, and a negative electrode sheet. The two end faces of the cell are negative electrode sheets, and the cell is arranged in the order of negative electrode sheet, separator, positive electrode sheet, separator, and negative electrode sheet in turn. Holes are punched at the measured positions of the positive electrode sheet and the negative electrode sheet, and the reference electrode passes through the negative - electrode hole and the positive - electrode hole in turn.

[0006] Preferably, the positive - electrode hole and the negative - electrode hole can arbitrarily select the punching positions according to the measured positions, and the aperture of the positive - electrode hole is larger than that of the negative - electrode hole.

[0007] Preferably, the aperture of the positive - electrode hole is 1mm ≤ A ≤ 8mm.

[0008] Preferably, the aperture of the negative - electrode hole is 0.5mm ≤ B ≤ 4mm.

[0009] Preferably, the negative - electrode hole covers the positive - electrode hole, and the minimum distance C between the edges of the two holes is between 0.25mm < C < 2mm.

[0010] Preferably, the cell can be a square - shell cell or a soft - package cell.

[0011] Preferably, the reference electrode is a lithium reference electrode, which can be formed by a copper wire coated with lithium at one end, a platinum wire coated with lithium at one end, a pure copper wire, a copper-tin-plated wire, or a platinum wire electroplated with lithium.

[0012] Preferably, the diameter D of the pure copper wire, tin-plated copper wire, or platinum wire is ≤50μm, the tin plating layer thickness of the tin-plated copper wire is 0.5~15μm, and the length is 0.1~6mm; and the lithium plating length is 0.1~5mm.

[0013] Preferably, the lithium plating ratio between the positive electrode and the reference, and between the negative electrode and the reference, is ≤0.05C, and the plating time H is 2h. <H<5h。

[0014] Preferably, the positive and negative electrode sheets can be normal or failed electrode sheets of ternary lithium batteries, lithium iron phosphate batteries, lithium-rich manganese-based batteries, sodium batteries, or lithium iron manganese batteries.

[0015] The beneficial effects of this invention are as follows:

[0016] This invention eliminates the need for additional separators, directly characterizing the potential at the measured location. Furthermore, the position and distance of the reference electrode can be customized as needed, making operation simple. It can be used to study battery positive and negative electrode design, cycle failure, capacity decay mechanisms, etc., providing significant guidance for improving battery performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 Example 1: A schematic diagram of a test cell and a reference electrode located in the middle of a lithium-ion battery cell;

[0019] Figure 2 Example 1: 1C discharge curve of a three-electrode battery;

[0020] Figure 3 Example 2: A schematic diagram of a test lithium-ion battery cell and a reference electrode;

[0021] Figure 4 Example 2: 1C discharge curve of a three-electrode battery;

[0022] Figure 5 Example 3: A schematic diagram of a test cell and a reference electrode at the middle position of a lithium-ion battery cell;

[0023] Figure 6, Schematic diagram of the middle position of the lithium-ion battery cell and the reference electrode in the comparative example;

[0024] Figure 7 , Discharge curve of the three-electrode battery at 1C in the comparative example. Specific implementation mode

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] Such as Figures 1 to 7 , A three-electrode battery for testing, comprising a battery cell and a reference electrode 4. The battery cell includes a positive electrode sheet 1, a separator 3, and a negative electrode sheet 2. The two end faces of the battery cell are negative electrode sheets 2, and the battery cell is arranged in the order of negative electrode sheet 2, separator 3, positive electrode sheet 1, separator 3, and negative electrode sheet 2 in sequence. Through holes are formed at the measured positions of the positive electrode sheet 1 and the negative electrode sheet 2, and the reference electrode 4 passes through the negative electrode hole 6 and the positive electrode hole 5 in sequence.

[0027] The punching positions of the positive electrode hole 5 and the negative electrode hole 6 can be arbitrarily selected according to the measured position, and the aperture of the positive electrode hole 5 is larger than that of the negative electrode hole 6. Preferably, the aperture range of the positive electrode hole 5 is 1mm ≤ A ≤ 8mm. The aperture range of the negative electrode hole 6 is 0.5mm ≤ B ≤ 4mm. The negative electrode hole 6 covers the positive electrode hole 5, and the minimum distance C between their hole edges is between 0.25mm < C < 2mm.

[0028] The battery cell can be a square shell battery cell or a soft package battery cell. The reference electrode 4 is a lithium reference electrode 4, which can be formed by a copper wire with lithium wrapped at one end, a platinum wire with lithium wrapped at one end, a pure copper wire, a copper-tin plated wire, or lithium plating on a platinum wire. The diameter D of the pure copper wire, the copper-tin plated wire or the platinum wire ≤ 50μm, the tin plating layer thickness of the copper-tin plated wire is 0.5 - 15μm, and the length is 0.1 - 6mm; and the lithium plating length is 0.1 - 5mm. The lithium plating rate between the positive electrode and the reference electrode, and between the negative electrode and the reference electrode ≤ 0.05C, and the plating time H, 2h < H < 5h. The positive electrode sheet 1 and the negative electrode sheet 2 can be normal electrode sheets or failed battery electrode sheets of ternary lithium batteries, lithium iron phosphate batteries, lithium-rich manganese-based batteries, sodium batteries, or lithium manganese iron batteries.

[0029] Example 1: Schematic diagram of the prepared three-electrode battery is as Figure 1 shown.

[0030] Specifically, a 5mm diameter punch is used to punch a hole in the center of the positive electrode 1. Following the principle of negative enveloping positive, a 3mm diameter mold is used to punch a hole in the negative electrode 2. The battery cell is then assembled according to the battery cell assembly process.

[0031] Lithium reference electrode 4 fabrication: Place both ends of a copper wire with an insulating coating and a diameter of D1 = 50 μm into sulfuric acid for 30 min to remove the surface coating, and then soak it in alcohol or acetone for 30 min each, and set it aside for use.

[0032] Method 1: In a glove box, wrap one end of the cleaned copper wire with lithium until the lithium completely covers one end of the copper wire to complete the lithium reference battery fabrication; weld the positive and negative electrode sheets and reference electrode 4 with external tabs, then perform liquid injection, formation, and capacity testing to produce a three-electrode battery.

[0033] Method 2: Insert the cleaned copper wire directly into the drilled hole in the battery. Weld the positive and negative electrodes and reference electrode 4 to the outer tabs, then perform electrolyte injection, formation, and capacity testing to fabricate a three-electrode battery. Charge the circuit formed by the positive electrode and copper wire at a current density of 0.04C for 2 hours; then charge the circuit formed by the negative electrode and copper wire at a current density of 0.04C for 2 hours; finally, electroplate lithium onto the lithium wire to complete the lithium reference battery fabrication.

[0034] Method 3: Insert the tin-plated copper wire directly into the drilled hole in the battery. Weld the positive and negative electrodes and reference electrode 4 to the external tabs, then perform electrolyte injection, formation, and capacity testing to fabricate a three-electrode battery. Charge the circuit formed by the positive electrode and the tin-plated copper wire at a current density of 0.04C for 2 hours; then charge the circuit formed by the negative electrode and the tin-plated copper wire at a current density of 0.04C for 2 hours; this lithium-ionizes the tin layer to form a lithium-tin alloy, thus completing the fabrication of the lithium reference battery.

[0035] When the battery is operating normally, if a potential measurement is to be performed at a certain location on the positive electrode 1, the outer tab of the positive electrode 1 and the outer tab of the lithium reference electrode 4 need to be electrically connected to the test equipment respectively for measurement. Similarly, if a potential measurement is to be performed at a certain location on the negative electrode 2, the outer tab of the negative electrode 2 and the outer tab of the lithium reference electrode 4 need to be electrically connected to the test equipment respectively for measurement.

[0036] Example 2:

[0037] A hole is drilled at the lower right corner of the cell, and the remaining steps are the same as in Example 1 for the preparation of a three-electrode battery.

[0038] Example 3:

[0039] Drill holes at five different locations in the cell, but not limited to these five locations. You can measure the locations that need to be measured as required. The rest of the steps are the same as in Example 1 for the preparation of a three-electrode battery.

[0040] Comparative example:

[0041] A copper wire with a diameter D1 = 50 μm and an insulating coating is immersed at both ends in sulfuric acid for 30 minutes to remove the surface coating. It is then further soaked in alcohol or acetone for 30 minutes each. Three-electrode lithium-ion battery cell: The positive electrode 1, separator 1, the treated copper wire, separator 2, and negative electrode 2 are arranged as follows... Figure 6 The electrodes are stacked sequentially as shown. The copper wire is located between two separators. The positive and negative electrodes, along with the reference electrode, are welded together with external tabs. Electrolyte injection, formation, and capacity testing are then performed to fabricate a three-electrode battery. The circuit formed by the positive electrode and the copper wire is charged at a current density of 0.04C for 2 hours; then the circuit formed by the negative electrode and the copper wire is charged at a current density of 0.04C for 2 hours. Lithium is then electroplated onto the lithium wire, thus completing the fabrication of the lithium reference battery.

[0042] After the prepared battery underwent normal capacity testing, formation, and pre-lithiation, it was charged and discharged at a 1C current density at 25°C, and the voltage between the positive electrode and the reference electrode and the voltage between the negative electrode and the reference electrode were monitored.

[0043] Example 1 shows that the battery has an initial charging capacity of 38.8mAh with a 91.6% efficiency, and a constant current charge ratio of 96.6%. This position allows for accurate measurement of the positive and negative electrode reference potentials. Furthermore, subtracting the negative reference from the positive one results in a potential that is well-matched with the full battery potential. At 94% SOC, the battery reaches 0V, posing a risk of lithium plating. Therefore, the battery supports 1C direct charging to 94% SOC.

[0044] Example 2: The battery has an initial efficiency of 91.2%, a charging capacity of 27.8mAh, and a constant current charge ratio of 93.8%. The positive and negative electrode reference potentials were collected at this location, and the discharge curves of the composite lithium iron phosphate and graphite were obtained. However, the voltage difference between the two is slightly different from the full cell curve. Similarly, at 92%, the negative electrode potential is below 0V, which poses a risk of lithium plating.

[0045] The comparative battery has an initial efficiency of 88.6%, a charging capacity of 35.5mAh, and a constant current charge ratio of 90%. The potential difference between the positive electrode, negative electrode, and reference electrode is well matched with the full cell potential. At 88% SOC, the negative electrode potential to the reference electrode is below 0V, which poses a risk of lithium plating.

[0046] The batteries prepared in Examples 1 and 2 of this invention can maintain the original design capacity, with both the initial efficiency and charging capacity being higher than those of the comparative example. This is because the comparative example uses a double-layer separator, which increases the lithium-ion migration path, leading to increased system polarization and reduced capacity. Comparing the potentials collected by the reference electrode 4 in the comparative example and the comparative example, the negative reference electrode in the comparative example quickly reaches the lithium plating potential, making it impossible to accurately measure the lithium plating potential at the designed current density. This is because the comparative example typically uses a separator to separate the three electrodes from the positive and negative electrodes, resulting in a double-layer separator between the positive and negative electrodes. This increased polarization causes the results to deviate from reality.

[0047] This invention effectively avoids the need for dual-layer separators, eliminating the need for additional separators and accurately characterizing the actual potential at different electrode locations. Furthermore, the position and distance of the reference electrode 4 can be set as needed, simplifying operation. It can be used to study battery positive and negative electrode design, cycle failure, capacity decay mechanisms, etc., providing important guidance for improving battery performance.

[0048] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-electrode battery for testing, comprising a cell and a reference electrode, wherein the cell comprises a positive electrode, a separator, and a negative electrode, characterized in that: Both end faces of the battery cell are negative electrodes, and the battery cell is arranged in the order of negative electrode, separator, positive electrode, separator, and negative electrode in turn. Holes are punched at the measured positions of the positive electrode and the negative electrode, and the reference electrode passes through the negative electrode hole and the positive electrode hole in turn. The aperture of the positive electrode hole is larger than that of the negative electrode hole; the negative electrode hole covers the positive electrode hole, and the minimum distance C between the edges of the two holes satisfies 0.25 mm < C < 2 mm; the reference electrode is a lithium reference electrode, which is formed by a copper wire with lithium wrapped at one end, a platinum wire with lithium wrapped at one end, a pure copper wire, a copper-tin plated wire, or lithium plating on a platinum wire; the diameter D of the pure copper wire, the copper-tin plated wire or the platinum wire is ≤ 50 μm, and the thickness of the tin plating layer of the copper-tin plated wire is 0.5 - 15 μm.

2. The three-electrode battery according to claim 1, characterized in that: The punching positions of the positive electrode hole and the negative electrode hole can be arbitrarily selected according to the measured positions.

3. The three-electrode battery according to claim 2, characterized in that: The aperture of the positive electrode hole satisfies 1 mm ≤ A ≤ 8 mm.

4. The three-electrode battery according to claim 2, characterized in that: The aperture of the negative electrode hole satisfies 0.5 mm ≤ B ≤ 4 mm.

5. The three-electrode battery according to claim 1, characterized in that: The battery cell is a square shell battery cell or a soft package battery cell.

6. The three-electrode battery according to claim 1, characterized in that: The length of the tin plating layer of the copper-tin plated wire is 0.1 - 6 mm; and the length of the lithium plating is 0.1 - 5 mm.

7. The three-electrode battery according to claim 1, characterized in that: The lithium plating rate between the positive electrode and the reference electrode and between the negative electrode and the reference electrode is ≤ 0.05C, and the electroplating time H satisfies 2 h < H < 5 h.

8. The three-electrode battery according to claim 1, characterized in that: The positive electrode and the negative electrode are normal electrode plates or failed battery electrode plates of a lithium cobaltate battery, a lithium iron phosphate battery, a lithium-rich manganese-based battery, a sodium battery, or a lithium manganese iron battery.

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