A method for detecting current density distribution of a reference battery cell

Abstract

The application discloses a method for detecting current density distribution of a reference battery, which comprises the following steps: treating copper wires with insulating enamel wires, burying the treated copper wires between positive plates and negative plates, and performing insulation separation treatment to prepare a battery, leading out the copper wires from a steel shell for subsequent testing, charging and discharging the reference battery, detecting voltage changes of corresponding reference electrodes, and obtaining distribution conditions by understanding lithium intercalation and current size of the reference electrodes.

Description

Technical Field

[0001] This invention relates to the field of battery cell testing technology, and in particular to a method for detecting the current density distribution of a reference battery cell. Background Technology

[0002] Cylindrical lithium-ion batteries are widely used in energy storage and power applications due to their high energy density, low manufacturing cost, and high safety. Cell aging has heterogeneous origins. Uneven electrolyte distribution within the cell affects the kinetics of lithium insertion / extraction at local sites, indirectly causing uneven current density distribution. This uneven current generates temperature gradients. Furthermore, the electrochemical reactions within the cell are highly temperature-dependent, further exacerbating the uneven current distribution. In addition, the degree of side reactions between the electrolyte and materials varies, resulting in inconsistent thickness of the solid electrolyte interfacial film formed on the negative electrode surface due to electrolyte side reactions. Therefore, uneven electrolyte distribution can trigger a domino effect in the cell aging mechanism, accelerating cell aging.

[0003] Therefore, detecting the electrolyte distribution inside a lithium-ion battery cell can provide valuable guidance for improving cell performance. However, in reality, the battery cell remains a closed system throughout its entire operating life to prevent electrolyte leakage and adverse reactions caused by humidity, posing a significant challenge to understanding its internal structure. While non-destructive probes using high-energy X-rays and neutrons with high material penetration can provide spatial information about the cell's interior, their testing costs are prohibitively high.

[0004] If impedance and voltage data from the undefined portions of the positive and negative terminals can be obtained, signals reflecting the relevant current distribution can be obtained. The introduction of a reference electrode provides a good medium for acquiring local voltage data at various points within the battery cell. Therefore, there is an urgent need to develop a method for detecting the current density inside the battery cell using a reference electrode. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting the current density distribution of a reference cell. By using multiple reference electrodes at different positions, the distribution of electrolyte and the current within the cell can be characterized based on the polarization voltage corresponding to the positive and negative electrodes at different positions.

[0006] The technical solution adopted in the method for detecting current density distribution of a reference battery cell disclosed in this invention is as follows:

[0007] A method for detecting the current density distribution of a reference battery cell includes the following steps:

[0008] S1. Prepare several copper wires of equal length L with insulated enameled wire, and immerse one end of the copper wire in dimethyl sulfoxide for water bath heating.

[0009] S2, remove the enameled wire that has been soaked in dimethyl sulfoxide on the surface of the copper wire, strip it, clean the copper wire with alcohol and dry it;

[0010] S3, in the cell manufacturing process, during the electrode winding process, one side of the enameled wire of the copper wire is stripped and buried in a specific electrode position, and the copper wire is insulated and separated from the positive and negative electrode plates.

[0011] S4, the other end of the copper wire is led out through a small hole on the surface of the steel shell. After being led out, the small hole is solidified and sealed, and the copper wire is soldered to the reference electrode tab with solder wire to facilitate subsequent test clamping.

[0012] S5. After the cell is prepared, lithium plating is performed on the copper wire. The positive electrode is connected to each reference electrode, and lithium is deposited on the surface of the copper wire in a constant current manner until the voltage between the positive electrode and the reference electrode stabilizes at 3-3.6V, thus completing the preparation of the reference cell.

[0013] S6, charge and discharge the cell once with a current of magnitude I;

[0014] S7, and use a voltage acquisition device to collect the voltage change of the negative electrode relative to the reference electrode at different positions, with a sampling interval of t0, t0≤1s;

[0015] S8. After the charging and discharging is completed, the cell is charged and discharged once again with a current of nI. The voltage acquisition device is used to collect the voltage change of the negative electrode relative to the reference electrode at different positions at the same time interval.

[0016] S9, at the instant the current stops and remains stationary, the voltage changes during time t0 and 2t0 are recorded. as well as Record the voltage change after t0 as follows: and Where k represents the reference electrode number of the negative electrode pair.

[0017] Let Δsk be the value of K. Δsk can characterize the lithium intercalation and current magnitude of the reference electrode corresponding to K, and obtain the distribution.

[0018] As a preferred embodiment, in step S1, each copper wire is immersed to the same depth in dimethyl sulfoxide.

[0019] As a preferred embodiment, in step S13, the copper wire is separated from the negative electrode by the cell's own diaphragm, and from the positive electrode by a small diaphragm placed on top.

[0020] As a preferred embodiment, in steps S6 and S8, the charging and discharging voltage range is 2.5-3.75V, wherein each time the voltage is 3.75V, the cell is left to stand for 10 minutes.

[0021] As a preferred solution, due to the instantaneous changes in current, ohmic polarization, concentration polarization, and electrochemical polarization cause instantaneous voltage jumps. The charging to resting phase leads to an instantaneous rise in the negative electrode voltage relative to the reference electrode, while the discharging to resting phase leads to an instantaneous drop in the negative electrode voltage relative to the reference electrode. The recovery times for these three polarizations differ: ohmic polarization occurs instantaneously, electrochemical polarization occurs in microseconds, and concentration polarization occurs in seconds. Within a short time, the ohmic internal resistance RΩ changes relatively little. The relationship between ohmic polarization voltage and current is expressed by the following equation:

[0022]

[0023] The ohmic polarization voltage is directly proportional to the magnitude of the current, and its sign is determined by the direction of the current.

[0024] When the battery cell is charged with different current rates successively, and the second current is n times the first current, To multiply it by n times, we can express it by the following formula:

[0025]

[0026] The overall polarization is the sum of ohmic polarization, electrochemical polarization, and concentration polarization. Both electrochemical polarization and concentration polarization are related to the electrode reactions of lithium ions, and are defined as polarization caused by the lithium intercalation reaction.

[0027] When the current is I:

[0028]

[0029] When the current is nI:

[0030]

[0031] We can obtain the following using (4)-nx(3):

[0032]

[0033] Therefore, by subtracting n times the polarization voltage when charging or discharging with a current of nI, we can subtract the ohmic polarization and obtain the signal. The polarization voltage caused by lithium is defined for convenience as follows: Let Δs be the value collected by multiple reference electrodes. This value can be used to characterize the lithium insertion at different locations and the current magnitude, thus obtaining the distribution.

[0034] The beneficial effect of the reference cell manufacturing method disclosed in this invention is that by setting multiple reference electrodes inside the cell and placing the reference electrodes at different positions, and by collecting corresponding data using multiple reference electrodes according to the polarization voltage corresponding to the positive and negative electrodes at different positions, the distribution of electrolyte and current inside the cell can be characterized. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the winding positions of multiple reference electrodes in a method for detecting the current density distribution of a reference cell according to the present invention.

[0036] Figure 2 This is a physical diagram of multiple reference electrodes for a method of detecting current density distribution in a reference cell according to the present invention.

[0037] Figure 3 This is a diagram showing the change of the negative electrode voltage to each reference voltage during the charging and discharging process of a method for detecting the current density distribution of a reference cell according to the present invention.

[0038] Figure 4 These are electrode plates obtained from disassembling battery cells. Detailed Implementation

[0039] The present invention will be further described and illustrated below with reference to specific embodiments and the accompanying drawings:

[0040] A method for detecting the current density distribution of a reference battery cell includes the following steps:

[0041] S1. Prepare several copper wires of equal length L=100mm with insulated enameled wire. Immerse one end of the copper wire in dimethyl sulfoxide and heat in a water bath for 120 minutes. The immersion depth of each copper wire in dimethyl sulfoxide is the same. In this embodiment, four reference electrodes are used.

[0042] S2, the copper wire soaked in dimethyl sulfoxide is mechanically removed, and after stripping, the copper wire is cleaned with alcohol and dried.

[0043] Please refer to Figure 1 S3, In the cell manufacturing process, during the electrode winding process, the enameled wire of the copper wire is stripped on one side and buried in a specific electrode position. The copper wire is then insulated from the positive and negative electrodes. Specifically, the copper wire is separated from the negative electrode by the cell's own separator, and from the positive electrode by a small separator placed on top.

[0044] In this embodiment, the four reference electrodes are embedded at positions 6 / 30, 10 / 30, 14 / 30, and 22 / 30 of the negative electrode, and the reference electrode labels K correspond to 6, 10, 14, and 22, respectively.

[0045] Please refer to Figure 2S4, the other end of the copper wire is led out through a small hole on the surface of the steel shell. After being led out, the small hole is sealed with UV glue and soldered to the reference electrode tab with solder wire for easy clamping during subsequent testing.

[0046] S5. After the cell is prepared, lithium plating is performed on the copper wire. The positive electrode is connected to each reference electrode, and lithium is deposited on the surface of the copper wire for 3 hours with a constant current of 5uA until the voltage between the positive electrode and the reference electrode stabilizes at 3-3.6V, thus completing the preparation of the reference cell.

[0047] S6, charge and discharge the cell once with a current of I. In this example, I = 0.025A;

[0048] S7, and use a voltage acquisition device to collect the voltage change of the negative electrode relative to the reference electrode at different positions. The sampling interval is t0, t0≤1s. In this embodiment, the voltage acquisition device used is manufactured by Agilent Technologies, and t0=1. The charging and discharging voltage range is 2.5-3.75V. Each time the voltage is 3.75V, the cell is left to stand for 10 minutes.

[0049] S8. After the charging and discharging is completed, the cell is charged and discharged again with a current of nI for one cycle. The voltage acquisition device is used to collect the voltage change of the negative electrode to the reference electrode at different positions at the same time interval. In this embodiment, n=4. The same charging and discharging voltage range is 2.5-3.75V. When the voltage is 3.75V each time, the cell is left to stand for 10 minutes.

[0050] S9, at the instant the current stops and remains stationary, the voltage changes during time t0 and 2t0 are recorded. as well as Record the voltage change after t0 as follows: and Where k represents the reference electrode number of the negative electrode pair.

[0051] Due to the instantaneous changes in current, ohmic polarization, concentration polarization, and electrochemical polarization cause instantaneous voltage jumps. During the charging to resting phase, the negative electrode voltage relative to the reference electrode instantaneously increases, and during the discharging to resting phase, the negative electrode voltage relative to the reference electrode instantaneously decreases. The recovery times for these three polarizations differ: ohmic polarization occurs instantaneously, electrochemical polarization occurs in microseconds, and concentration polarization occurs in seconds. Within a short time, the ohmic internal resistance RΩ changes relatively little. The relationship between ohmic polarization voltage and current is expressed by the following equation:

[0052]

[0053] The ohmic polarization voltage is directly proportional to the magnitude of the current, and its sign is determined by the direction of the current.

[0054] When the battery cell is charged with different current rates successively, and the second current is n times the first current, To multiply it by n times, we can express it by the following formula:

[0055]

[0056] The overall polarization is the sum of ohmic polarization, electrochemical polarization, and concentration polarization. Both electrochemical polarization and concentration polarization are related to the electrode reactions of lithium ions, and are defined as polarization caused by the lithium intercalation reaction.

[0057] When the current is I:

[0058]

[0059] When the current is nl:

[0060]

[0061] We can obtain the following using (4)-nx(3):

[0062]

[0063] Therefore, by subtracting n times the polarization voltage when charging or discharging with a current of nl from the polarization voltage when charging or discharging with a current of l, we can subtract the ohmic polarization and obtain the signal. The polarization voltage caused by lithium is defined for convenience as follows: Let Δs be the value collected by multiple reference electrodes. This value can be used to characterize the lithium insertion at different locations and the current magnitude, thus obtaining the distribution.

[0064] Please refer to Figure 3 ,therefore, Let Δsk be the value, which characterizes the lithium intercalation and current magnitude of the reference electrode corresponding to K. The distribution is shown in Table 1. The data obtained from calculations from 6 to 10 to 14 to 22 are shown in Table 2.

[0065] Table 1 shows the EIS test results and the test fitting results:

[0066]

[0067] Table 2 shows the first second. And Δsk:

[0068] Voltage difference between positive and negative electrodes (mV) Negative electrode pressure difference relative to reference 6 (mV) Negative terminal relative to reference voltage #60 (V) Negative electrode voltage difference relative to reference 14 (mV) Negative electrode voltage difference relative to reference 22 (mV) Pressure difference after 1A charging and standing still for 1 second 25.4802 -14.70506 -15.32045 -17.342166 -16.792211 Pressure difference after 0.25A charging and standing still for 1 second 3.9624 -2.88686 -2.9906 -3.33821 -3.17709 50 times the power after 0.25A charging and 1 second of stillness 15.8496 -11.54744 -11.9624 -13.35284 -12.70836 Δs 9630.6 -3157.62 -3358.05 -3989.326 -4083.851

[0069] The positions from 6 to 10 to 14 to 22 represent the positions from the inside to the outside of the core. From Δsk in Table 2, we can see that Δsjk gradually increases from 6 to 10 to 14 to 22, meaning the polarization voltage caused by lithium gradually increases from the inside to the outside. Therefore, the actual lithium intercalation rate gradually decreases. Since the generation of current requires the transfer of charge through the lithium intercalation reaction as a prerequisite, the current density is lower where lithium intercalation is lower. This is consistent with... Figure 4 The results obtained from the disassembly of the battery cells shown are consistent. Figure 4 The results of disassembling a battery cell, one of which was obtained from disassembly under high-rate charging, show that during the charging process, lithium intercalation at the negative electrode will form LixC6 compounds. As the amount of lithium intercalation increases, it will change from gray to blue to red to yellow. Based on this, it can be determined that the amount of lithium intercalation gradually increases from position 6 to 10 to 14 to 22. This is consistent with the lithium intercalation distribution obtained using Δsk, which verifies the accuracy of the method.

[0070] This invention provides a method for detecting current density distribution in a reference cell. By setting multiple reference electrodes inside the cell and placing them at different positions, and collecting corresponding data based on the polarization voltages at different positions corresponding to the positive and negative electrodes, the distribution of electrolyte and current within the cell can be characterized.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for detecting current density distribution in a reference battery cell, characterized in that, Includes the following steps: S1. Prepare several copper wires of equal length L with insulated enameled wire, and immerse one end of the copper wire in dimethyl sulfoxide for water bath heating. S2, remove the enameled wire that has been soaked in dimethyl sulfoxide on the surface of the copper wire, strip it, clean the copper wire with alcohol and dry it; S3, in the cell manufacturing process, during the electrode winding process, one side of the enameled wire of the copper wire is stripped and buried in a specific electrode position, and the copper wire is insulated and separated from the positive and negative electrode plates. S4, the other end of the copper wire is led out through a small hole on the surface of the steel shell. After being led out, the small hole is solidified and sealed, and the copper wire is soldered to the reference electrode tab with solder wire to facilitate subsequent test clamping. S5. After the cell is prepared, lithium plating is performed on the copper wire. The positive electrode is connected to each reference electrode, and lithium is deposited on the surface of the copper wire in a constant current manner until the voltage between the positive electrode and the reference electrode stabilizes at 3-3.6V, thus completing the preparation of the reference cell. S6, charge and discharge the cell once with a current of magnitude I; S7, and use a voltage acquisition device to collect the voltage change of the negative electrode relative to the reference electrode at different positions, with a sampling interval of t0, t0≤1s; S8. After the charging and discharging is completed, the cell is charged and discharged once again with a current of nI. The voltage acquisition device is used to collect the voltage change of the negative electrode relative to the reference electrode at different positions at the same time interval. S9, the voltage change during time t0 is recorded at the instant the current stops and the system is at rest. as well as Where k represents the reference electrode number of the negative electrode pair. Let Δsk be the value of K, which represents the lithium insertion and current magnitude of the reference electrode corresponding to K, and then we can obtain the distribution.

2. The method for detecting current density distribution in a reference cell as described in claim 1, characterized in that, In step S1, each copper wire is immersed to the same depth in dimethyl sulfoxide.

3. The method for detecting current density distribution in a reference cell as described in claim 1, characterized in that, In step S3, the copper wire is separated from the negative electrode by the cell's own diaphragm, and from the positive electrode by a small diaphragm placed on top.

4. The method for detecting current density distribution in a reference cell as described in claim 1, characterized in that, In steps S6 and S8, the charging and discharging voltage range is 2.5-3.75V, and each time the voltage is 3.75V, the cell is left to stand for 10 minutes.

5. The method for detecting current density distribution in a reference cell as described in claim 1, characterized in that, Due to the instantaneous changes in current, ohmic polarization, concentration polarization, and electrochemical polarization cause instantaneous voltage jumps. During the charging to resting phase, the negative electrode voltage relative to the reference electrode instantaneously increases, and during the discharging to resting phase, the negative electrode voltage relative to the reference electrode instantaneously decreases. The recovery times for these three polarizations differ: ohmic polarization occurs instantaneously, electrochemical polarization occurs in microseconds, and concentration polarization occurs in seconds. Within a short time, the ohmic internal resistance... With relatively small changes, the relationship between the ohmic polarization voltage and the current is expressed by the following formula: （1） The ohmic polarization voltage is directly proportional to the magnitude of the current, and its sign is determined by the direction of the current. When the battery cell is charged with different current rates successively, and the second current is n times that of the first, To multiply it by n times, we can express it by the following formula: （2） The overall polarization is the sum of ohmic polarization, electrochemical polarization, and concentration polarization. Both electrochemical polarization and concentration polarization are related to the electrode reactions of lithium ions, and are defined as polarization caused by the lithium intercalation reaction. : When the current is I: （3） When the current is nI: （4） We can obtain the following using (4)-nx(3): Therefore, the signal is obtained by subtracting n times the polarization voltage when charging or discharging with a current of nI from the polarization voltage when the current is I, and then subtracting the ohmic polarization. The polarization voltage caused by lithium is defined for convenience. Let Δs be the value collected by multiple reference electrodes. This value can be used to characterize the lithium insertion at different locations and the current magnitude, thus obtaining the distribution.

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