Three-electrode battery for testing

Abstract

The invention discloses a three-electrode battery for testing, which comprises a battery cell and a reference electrode, the battery cell comprises a positive plate, a diaphragm and negative plates, the negative plates are arranged on the two end surfaces of the battery cell, the battery cell is arranged according to the sequence of the negative plates, the diaphragm, the positive plate, the diaphragm and the negative plates, and holes are punched in the tested positions of the positive plates and the negative plates. And the reference electrode sequentially penetrates through the negative electrode hole and the positive electrode hole. According to the invention, additional diaphragm barrier is not needed, the potential of the measured position can be directly represented, the position and distance of the reference electrode can be set according to requirements, and the operation is simple. The method can be used for researching the design, cycle failure, capacity attenuation mechanism and the like of the positive and negative plates of the battery, and has important guiding significance for improving the performance of the battery.

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 the attenuation of battery capacity. The three parts that make up 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, short - circuit will occur), but are jointly immersed in the electrolyte.

[0003] For lithium - ion batteries, the positive electrode and the negative electrode correspond to the working electrode and the counter electrode respectively, and the reference electrode is a lithium reference electrode, usually made of copper wire or platinum wire plated with lithium. At present, most of the production of three - electrode batteries is in the soft - package battery system, coin - type battery system, and the cylindrical three - electrode model and groove - type three - electrode model sold on the market. The research on the cell system is relatively small. Secondly, in the prior art, two diaphragms 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 diaphragms to avoid the 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 diaphragm, 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, diaphragm, positive electrode sheet, diaphragm, and negative electrode sheet in sequence. 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 sequence.

[0006] Preferably, the punching positions of the positive electrode hole and the negative electrode hole can be arbitrarily selected 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 satisfies 1mm ≤ A ≤ 8mm.

[0008] Preferably, the aperture of the negative electrode hole satisfies 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 with lithium coated on one end, a platinum wire with lithium coated on one end, a pure copper wire, a copper tinned wire, or a platinum wire electroplated with lithium.

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

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

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

[0015] The beneficial effects of the present invention are:

[0016] The present invention does not require the addition of an additional diaphragm barrier, can directly characterize the potential of the measured position, and the position and distance of the reference electrode can be set according to needs, and the operation is simple. It can be used to study the design of positive and negative electrode sheets of batteries, cycle failure, capacity attenuation mechanism, etc., and has important guiding significance for improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

[0019] Figure 2 , 1C discharge curve of the three-electrode battery in Example 1;

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

[0021] Figure 4 , 1C discharge curve of the three-electrode battery in Example 2;

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

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

[0024] Figure 7 , 1C discharge curve of a three-electrode battery for a comparative example. Detailed implementation manners

[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. Apparently, 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] As Figures 1 to 7 , A three-electrode battery for testing includes a cell and a reference electrode 4. The cell includes a positive electrode sheet 1, a separator 3, and a negative electrode sheet 2. The two end faces of the cell are the negative electrode sheets 2, and the 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 made 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 cell can be a square shell cell or a soft package 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 is ≤ 50um, the tin plating layer thickness of the copper-tin plated wire is 0.5 - 15um, 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, and between the negative electrode and the reference is ≤ 0.05C, and the plating time H is 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 a ternary lithium battery, a lithium iron phosphate battery, a lithium-rich manganese-based battery, a sodium battery, or a lithium manganese iron battery.

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

[0030] Specifically, a punching machine with a diameter of 5 mm is used to punch a hole in the center of the positive electrode sheet 1. According to the principle of negative covering positive, a die with a diameter of 3 mm is used to punch a hole in the negative electrode sheet 2. The battery cell is assembled according to the battery cell assembly process.

[0031] Preparation of lithium reference electrode 4: Put both ends of a copper wire with a diameter of D1 = 50 um and an insulating coating on the surface into sulfuric acid for 30 minutes to remove the surface coating, and then soak it in alcohol or acetone for 30 minutes each for standby use.

[0032] Method 1: In a glove box, one end of the cleaned copper wire is coated with lithium so that the lithium completely covers one end of the copper wire to complete the production of the lithium reference battery; the positive and negative electrodes and the reference electrode 4 are welded to the outer ears, and the liquid is injected, formed, and the capacity is divided to form a three-electrode battery.

[0033] Method 2: Insert the cleaned copper wire directly into the punched position of the battery. Weld the positive and negative electrodes and the reference electrode 4 to the outer ear, inject liquid, form, and divide the capacity to make a three-electrode battery. Charge the loop formed by the positive electrode and the copper wire for 2 hours at a current density of 0.04C; then charge the loop formed by the negative electrode 2 and the copper wire for 2 hours at a current density of 0.04C; electroplate the lithium wire with lithium to complete the production of the lithium reference battery.

[0034] Method 3: Insert the tinned end of the copper tinned wire directly into the punched position in the battery. Weld the positive and negative electrodes and the reference electrode 4 to the outer ear, inject liquid, form, and divide the capacity to make a three-electrode battery. Charge the loop formed by the positive electrode and the copper tinned wire at a current density of 0.04C for 2 hours; then charge the loop formed by the negative electrode 2 and the copper tinned wire at a current density of 0.04C for 2 hours; lithiate the tin layer to form a lithium-tin alloy, and the lithium reference battery is completed.

[0035] The battery is tested when it is operating normally. If the potential at a certain position on the positive electrode sheet 1 is measured, the outer tab of the positive electrode sheet 1 and the outer tab of the lithium reference electrode 4 need to be electrically connected to the test equipment respectively for measurement. If the potential at a certain position on the negative electrode sheet 2 is measured, the outer tab of the negative electrode sheet 2 and the outer tab of the lithium reference electrode 4 need to be electrically connected to the test equipment respectively for measurement.

[0036] Embodiment 2:

[0037] A hole was punched at the lower right corner of the battery cell, and the remaining steps were the same as in Example 1 to prepare a three-electrode battery.

[0038] Embodiment 3:

[0039] Holes are punched at five different positions of the battery cell, but are not limited to these five positions. The positions that need to be measured can be measured according to needs, and the remaining steps are the same as those in Example 1 to prepare a three-electrode battery.

[0040] Comparative Example:

[0041] Place both ends of a copper wire with a diameter of D1 = 50um and an insulating coating on the surface in sulfuric acid for 30 minutes to remove the surface coating, and then soak it in alcohol or acetone for 30 minutes each. Three-electrode lithium-ion battery cell: Place the positive electrode sheet 1, diaphragm 1, treated copper wire, diaphragm 2, and negative electrode sheet 2 as shown in the figure. Figure 6 As shown, they are stacked in sequence. The copper wire is located between two layers of diaphragms. The positive and negative electrodes and the reference electrode are welded to the outer tabs, injected with liquid, formed, and divided into capacities to make a three-electrode battery. The loop formed by the positive electrode and the copper wire is charged for 2 hours at a current density of 0.04C; the loop formed by the negative electrode and the copper wire is charged for 2 hours at a current density of 0.04C; the lithium wire is electroplated with lithium to complete the production of the lithium reference battery.

[0042] After the prepared battery is subjected to normal capacity division, formation, and pre-lithiation, it is charged and discharged at 25°C with a current density of 1C, and the voltage between the positive electrode and the reference electrode and the voltage between the negative electrode and the reference are monitored.

[0043] Example 1 The battery's first efficiency is 91.6% and the charging capacity is 38.8mAh. The constant current charging ratio is 96.6%. This position can well measure the positive and negative reference potentials, and the positive reference minus the negative reference. The potential can be well matched with the full battery potential, and 94% SOC reaches 0V, which has the risk of lithium deposition. That is, the battery supports 1C direct charging to 94% SOC.

[0044] The first efficiency of the battery in Example 2 is 91.2%, the charging capacity is 27.8mAh, and the constant current charging ratio is 93.8%. The positive and negative electrodes are collected at this position to obtain the reference potential, and the discharge curve trend of the composite lithium iron phosphate and graphite is obtained, but the voltage difference between the two is slightly different from the full battery curve. Similarly, at 92%, the negative electrode potential is lower than 0V, and there is a risk of lithium plating.

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

[0046] The batteries prepared in Examples 1 and 2 of the present invention can well maintain the original design capacity of the battery, and the first effect and charging capacity are higher than those in the comparative example. The reason is that the comparative example uses a double-layer diaphragm to increase the migration path of lithium ions, which increases the polarization of the system and reduces the capacity. The potential collected by the comparative example and the comparative example reference electrode 4 is that the negative reference of the comparative example quickly reaches the lithium deposition potential, and the lithium deposition potential measured at the designed current density cannot be accurately measured. This is because the comparative example usually uses a diaphragm to separate the three electrodes from the positive and negative electrodes, and a double-layer diaphragm will exist between the positive and negative electrodes, resulting in increased polarization, which makes the results deviate from reality.

[0047] The method of the present invention avoids the design of two-side diaphragms, does not require the addition of additional diaphragms, and can accurately characterize the actual potentials at different electrode positions. The position and distance of the reference electrode 4 can be set according to requirements, and the operation is simple. It can be used to study the design of positive and negative electrode sheets of batteries, cycle failure, capacity attenuation mechanism, etc., and has important guiding significance for improving battery performance.

[0048] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions 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 battery cell and a reference electrode, wherein the battery cell comprises a positive electrode sheet, a separator, and a negative electrode sheet, characterized in that: Negative electrode sheets are located at both ends of the battery cell, and the battery cell is arranged in the order of negative electrode sheet, diaphragm, positive electrode sheet, diaphragm, and negative electrode sheet. 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 sequence.

2. The three-pole battery according to claim 1, characterized in that: The positive electrode hole and the negative electrode hole can be punched at any position according to the measured position, and the hole diameter of the positive electrode hole is larger than the hole diameter of the negative electrode hole.

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

4. The three-pole battery according to claim 2, characterized in that: The diameter of the negative electrode pore is 0.5mm≤B≤4mm.

5. The three-pole battery according to claim 2, characterized in that: The negative electrode hole covers the positive electrode hole, and the minimum distance between the two hole edges is C, 0.25mm <C<2mm。 6. The three-pole battery according to claim 1, characterized in that: The battery cell may be a square-shell battery cell or a soft-pack battery cell.

7. The three-pole battery according to claim 1, characterized in that: The reference electrode is a lithium reference electrode, which can be a copper wire with lithium wrapped at one end, a platinum wire with lithium wrapped at one end, a pure copper wire, a copper tinned wire, or a platinum wire electroplated with lithium.

8. The three-pole battery according to claim 7, characterized in that: The diameter D of the pure copper wire, copper tinned wire or platinum wire is ≤50um, the thickness of the tinned layer of the copper tinned wire is 0.5-15um, and the length is 0.1-6mm; and the length of the lithium plating is 0.1-5mm.

9. The three-pole battery according to claim 7, characterized in that: The lithium plating rate between positive electrode and reference, negative electrode and reference is ≤0.05C, plating time is H, 2h <H<5h。 10. The three-pole battery according to claim 1, characterized in that: The positive electrode sheet and the negative electrode sheet may be normal electrode sheets or failed battery electrode sheets of a ternary lithium battery, a lithium iron phosphate battery, a lithium-rich manganese-based battery, a sodium battery, or a manganese iron lithium battery.

Images