Battery self-discharge type detection method

Abstract

The invention discloses a battery self-discharge type detection method, which comprises the following steps: carrying out charge-discharge pre-cycle on a battery, and recording a first DQ / DV-Voltage curve; after the battery is charged to a preset SOC, the battery stands for a first standing time in a normal-temperature environment; carrying out constant-temperature standing on the battery for a second standing time in a preset high-temperature environment; standing the battery in a normal temperature environment for a third standing time; carrying out charging and discharging circulation on the battery again, and recording a second DQ / DV-Voltage curve; and comparing the shapes, peak positions and capacity fading of the first DQ / DV-Voltage curve and the second DQ / DV-Voltage curve, and giving out a judgment result of physical self-discharge / chemical self-discharge according to a comparison result. According to the method, under the preset SOC of the battery, the internal reaction of the battery is accelerated at high temperature, and the DQ / DV-Voltage curve is used for distinguishing whether the battery is subjected to chemical self-discharge or physical self-discharge, so that the self-discharge type checking time is effectively shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a method for detecting the type of battery self-discharge. Background Art

[0002] The self-discharge phenomenon of lithium-ion batteries refers to the phenomenon that a battery with a certain capacity experiences a voltage drop and capacity loss after being stored at a certain temperature for a period of time. However, abnormal self-discharge of the battery easily leads to overcharging or over-discharging of the batteries assembled into a battery pack, posing a safety hazard. Therefore, the self-discharge phenomenon of lithium-ion batteries is a key indicator for measuring the stability of the battery. The self-discharge of lithium-ion batteries is mainly divided into chemical self-discharge and physical self-discharge. Chemical self-discharge is caused by side reactions of electrode materials (SEI film growth, electrolyte decomposition), and physical self-discharge is caused by internal micro-short circuits, burrs on the electrode plates, or external leakage in the battery.

[0003] Currently, the screening time for the self-discharge of lithium-ion batteries is relatively long, it is impossible to distinguish between chemical and physical self-discharge, and it is easily interfered by environmental temperature and SOC fluctuations. The existing K-value method (voltage drop rate) requires a long time and it is difficult to accurately locate the self-discharge caused by physical defects and chemical defects.

[0004] For example, in the Chinese patent application CN113917347A, a patent application document named Method for Evaluating Battery Self-Discharge Standard, by placing the battery in a super-low temperature condition of liquid nitrogen and standing still, the chemical self-discharge of the battery can be completely inhibited, so that the pure physical self-discharge situation of the battery can be accurately measured. For example, in the Chinese patent application CN118519051A, a patent application document named A Method, Device and Medium for Detecting the Type of Battery Self-Discharge, provides a method for detecting the type of battery self-discharge, which uses the frequency response characteristics of the physical self-discharge and chemical self-discharge of the battery to perform self-discharge testing, and can quickly screen whether there is a physical self-discharge phenomenon in the battery to be tested by monitoring the voltage change trend of the battery.

[0005] As described above, in the existing technologies, since the existing technologies use voltage monitoring under ultra-low temperature and after pulse to determine the physical self-discharge battery, the operation process is cumbersome and it is difficult to promote it to the mass production line, and the determination time of the physical self-discharge battery is relatively long. Therefore, there is an urgent need for a fast, high-precision, and quantifiable method for detecting physical self-discharge. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies and defects of the existing technologies, and provide a method for detecting the type of battery self-discharge. Under the preset SOC of the battery, the present invention uses high temperature to accelerate the internal reaction of the battery and the DQ / DV-Voltage curve to distinguish whether the battery is chemically or physically self-discharged, which can effectively shorten the time for troubleshooting the type of self-discharge.

[0007] The present invention is implemented as follows:

[0008] A method for detecting the type of self-discharge of a battery includes the following steps:

[0009] S1. Perform charge and discharge pre-cycling on the battery and record the first DQ / DV-Voltage curve;

[0010] S2. Charge the battery to a preset SOC and then let it stand for a first standing time at room temperature;

[0011] S3. Keep the battery at a constant temperature in a preset high-temperature environment for a second standing time;

[0012] S4. Place the battery in a room-temperature environment and let it stand for a third standing time;

[0013] S5. Perform charge and discharge cycling on the battery again and record the second DQ / DV-Voltage curve;

[0014] S6. Compare the shapes, peak positions, and capacity decays of the first DQ / DV-Voltage curve and the second DQ / DV-Voltage curve, and based on the comparison results, give a judgment result of physical self-discharge / chemical self-discharge.

[0015] Preferably, in step S2, for a battery of the LFP system, the preset SOC is 5% - 25% SOC; for a battery of the NCM system, the preset SOC is 30% - 50% SOC.

[0016] Preferably, in step S2, the first standing time is at least 8h; the temperature of the room-temperature environment is 25°C ± 4°C.

[0017] Preferably, in step S3, the preset high-temperature environment is 60°C ± 3°C, and the constant-temperature standing is carried out in an incubator.

[0018] Preferably, in step S3, the second standing time is at least 24h.

[0019] Preferably, in step S4, the third standing time is at least 12h; the temperature of the room-temperature environment is 25°C ± 4°C.

[0020] Preferably, in step S5, if the peak position shift of the two curves is lower than the shift threshold and the capacity decay is lower than the first decay threshold, it is determined as physical self-discharge.

[0021] Preferably, the shift threshold is 2mV, and the first decay threshold is 1%.

[0022] Preferably, in step S5, if the peak position shift of the curve is greater than or equal to the shift threshold or the capacity decay is greater than or equal to the second decay threshold, it is attributed to chemical self-discharge caused by side reactions of the material.

[0023] Preferably, in step S5, the offset threshold is 2 mV and the second decay threshold is 2%.

[0024] The method of the present invention is based on the curve shape, peak position and capacity decay comparison of two DQ / DV-Voltage curves before and after high-temperature accelerated aging and high temperature to detect whether the battery has physical self-discharge. It can eliminate the influence of chemical self-discharge, effectively distinguish the physical self-discharge and chemical self-discharge of the battery, and at the same time greatly shorten the detection cycle. Brief Description of the Drawings

[0025] Figure 1 is a flowchart of the method for detecting the type of battery self-discharge of the present invention.

[0026] Figure 2 is a DQ / DV-charging curve of the test battery before and after high-temperature static storage in the embodiment of the present invention.

[0027] Figure 3 is a DQ / DV-discharging curve of the test battery before and after high-temperature static storage in the embodiment of the present invention.

[0028] Figure 4 is a schematic diagram of the battery interface after the test battery in the embodiment of the present invention is disassembled. Detailed Description of the Embodiments

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] In the exemplary embodiment of the present application, under a preset SOC, the internal reaction of the battery is accelerated by high temperature and the DQ / DV-Voltage curves before and after high-temperature static storage are compared to distinguish whether the battery has chemical or physical self-discharge.

[0031] Please refer to Figure 1 As shown, a method for detecting the type of battery self-discharge includes the following steps:

[0032] S1. Perform charge and discharge pre-cycling on the battery and record the first DQ / DV-Voltage curve;

[0033] S2. Charge the battery to the preset SOC and then statically store it for the first static storage time in a normal temperature environment;

[0034] S3. Constantly statically store the battery in a preset high-temperature environment for the second static storage time;

[0035] S4. Place the battery in a normal temperature environment and statically store it for the third static storage time;

[0036] S5. Recharge and discharge the battery again, and record the second dQ / dV-Voltage curve;

[0037] S6. Compare the shapes, peak positions, and capacity attenuation of the first dQ / dV-Voltage curve and the second dQ / dV-Voltage curve. Based on the comparison results, give the judgment result of physical self-discharge / chemical self-discharge.

[0038] In step S1, by performing charge-discharge pre-cycling on the battery, the internal electrochemical performance of the battery can be activated, and the SEI film on the negative electrode surface and the CEI film on the positive electrode surface can be stabilized. Among them, when performing charge-discharge pre-cycling, a square lithium iron phosphate battery can be charged and discharged in multiple cycles (such as 5 cycles) at 0.33C (2.5V - 3.65V) to eliminate the electrochemical instability factors inside the battery. For batteries of different systems, a charge-discharge cycle process suitable for them can be adopted, not limited to this, and it is specifically determined according to the battery system.

[0039] In step S2, the preset SOC can be selected in the charge region where the battery electrochemical reaction is intense. More preferably, the low charge region where the battery electrochemical reaction is intense is selected. Specifically, the low charge region varies according to different battery systems. Specifically, in implementation, it is specifically determined according to different battery systems. For example, for a battery of the LFP system, the preset SOC is 5% - 25% SOC; for a battery of the NCM system, the preset SOC is 30% - 50% SOC. Taking a lithium iron phosphate battery of the LFP system as an example, the low charge range where its battery electrochemical reaction is intense is a data within 5% - 25% SOC. Through experiments, when the SOC is 23%, the battery electrochemical reaction is the most intense, and the preset SOC is preferably 23% SOC.

[0040] In the step of charging the battery to the preset SOC and then standing for the first standing time at room temperature (25°C ± 4°C) in step S2, the room temperature environment is generally 25°C. The standing time is preferably 8h, which can ensure uniform lithium ion diffusion and reduce polarization; if the standing time is too short, the purpose of uniform lithium ion diffusion and polarization reduction cannot be achieved, and if the standing time is too long, it will waste the detection time. It is determined to be 8h through experiments. Of course, for batteries of different systems, the corresponding standing time can be specifically determined according to the situation to achieve the purpose of uniform lithium ion diffusion and polarization reduction in the battery.

[0041] In step S3, in the step of keeping the battery at a constant temperature for a second standing time in a preset high-temperature environment (60°C ± 3°C), taking a lithium iron phosphate battery as an example, the lithium iron phosphate battery is placed in an incubator at 60°C and left standing for 24 h to accelerate the electrochemical reaction and charge loss inside the battery. If the standing time is too short, the purpose of accelerating the electrochemical reaction and charge loss inside the battery cannot be achieved; if the standing time is too long, it will waste the detection time. Through experiments, it is determined to be 24 h. Of course, for batteries of different systems, the corresponding standing time can be specifically determined according to the situation to achieve the purpose of accelerating the electrochemical reaction and charge loss inside the battery. The temperature of the high temperature is preferably kept constant at 60°C. For a lithium iron phosphate battery, this temperature is sufficient to achieve the purpose of accelerating the electrochemical reaction and charge loss inside the battery. Excessive temperature will cause the test battery to have a risk of thermal runaway, and too low temperature cannot achieve the purpose of accelerating the electrochemical reaction and charge loss inside the battery.

[0042] In step S4, in the step of placing the battery in a normal-temperature environment (25°C ± 4°C) and leaving it standing for a third standing time, taking a lithium iron phosphate battery as an example, the battery after high temperature is placed in an environment at 25°C for normal-temperature standing for 12 h to eliminate the influence of temperature gradient on the DQ / DV-Voltage curve. If the standing time is too short, the purpose of eliminating the influence of temperature gradient on the DQ / DV-Voltage curve cannot be achieved; if the standing time is too long, it will waste the detection time. Through experiments, it is determined to be 12 h. Of course, for batteries of different systems, the corresponding standing time can be specifically determined according to the situation to achieve the purpose of eliminating the influence of temperature gradient on the DQ / DV-Voltage curve.

[0043] In step S5, in the step of performing charge and discharge cycles on the battery again and recording the second DQ / DV-Voltage curve, taking a lithium iron phosphate battery as an example, with a current of 0.33C, the battery is charged and discharged again for 5 cycles, and the DQ / DV-Voltage curve is recorded. For batteries of different systems, a charge and discharge cycle process suitable for them can be adopted, not limited to this, and it is specifically determined according to the battery system.

[0044] In step S6, comparing the shapes, peak positions and capacity attenuation of the first DQ / DV-Voltage curve and the second DQ / DV-Voltage curve, and based on the comparison results, giving a judgment result of physical self-discharge / chemical self-discharge, including: if the peak position shift of the two curves is lower than the shift threshold and the capacity attenuation is lower than the first attenuation threshold (percentage), it is determined as physical self-discharge. Exemplarily, the shift threshold is 2 mV, and the first attenuation threshold is 1%.

[0045] Exemplarily, in step S5, it further includes: if the peak position shift of the curve is greater than or equal to the shift threshold or the capacity decay is greater than or equal to the second decay threshold, it is attributed to the chemical self-discharge caused by the side reaction of the material. Exemplarily, in step S5, the shift threshold is 2 mV and the second decay threshold is 2%.

[0046] Specifically, compare the DQ / DV-Voltage curves before and after high-temperature standing: if the curve shapes are the same (peak position shift < 2 mV) and the capacity decay < 1%, chemical self-discharge can be excluded and it is determined as physical self-discharge; if the curve is distorted (peak position shift ≥ 2 mV) or the capacity decay > 2%, it is attributed to the chemical self-discharge caused by the side reaction of the material.

[0047] According to a large amount of test data, the peak position shift caused by chemical self-discharge is usually ≥ 2 mV, and the peak position shift of physical self-discharge is usually < 2 mV. Therefore, the above peak position shift threshold is selected in this application.

[0048] According to a large amount of test data, the capacity decay of chemical self-discharge > 2%, and the capacity decay of physical self-discharge < 1%. Therefore, in the embodiments of this application, the capacity decay of 1% is the upper limit for determining physical self-discharge, and the capacity decay of 2% is the lower limit for determining chemical self-discharge.

[0049] For the fuzzy interval where the capacity decay is between 1% and 2%, it is impossible to quickly determine whether it is physical self-discharge or chemical self-discharge. For this interval, the following method of combining tests and determinations can be used:

[0050] 1) DQ / DV curve peak position shift judgment: if the peak position shift < 2 mV, it tends to be physical self-discharge; if the peak position shift ≥ 2 mV, it tends to be chemical self-discharge.

[0051] 2) Cycle capacity recoverability judgment: if the capacity can be fully recovered after recharging, it is physical self-discharge; if there is irreversible loss of capacity and the capacity is not fully recovered after charging, it is chemical self-discharge;

[0052] 3) EIS test: Use EIS (electrochemical impedance spectroscopy) to judge. Chemical self-discharge is usually accompanied by a significant increase in the SEI film impedance (RSEI).

[0053] Example:

[0054] Select 1 square lithium iron phosphate battery (capacity 324 Ah) for testing with a battery K value of 0.0612 mV / h. The average K value of the same batch of batteries is 0.0213 mV / h. The battery with a K value of 0.0612 mV / h is a self-discharging battery, but it is unknown whether it is chemical self-discharge or physical self-discharge.

[0055] One battery is subjected to charge-discharge pre-cycling (2.5V - 3.65V) at 0.33C for 5 cycles, and the first DQ / DV-Voltage curve is recorded. After the charge-discharge pre-cycling, it is left standing at room temperature of 25°C for 12h when charged to 23% SOC, and then placed in a high temperature of 60°C for heat preservation for 24h; after the heat preservation at 60°C is completed, the battery is left standing at room temperature of 25°C for 12h, and the internal temperature of the battery is reduced to room temperature of 25°C. After standing at 25°C, the battery is subjected to charge-discharge cycling (2.5V - 3.65V) again at 0.33C for 5 cycles, and the second DQ / DV-Voltage curve is recorded. For the DQ / DV-Voltage curves of the two charge-discharge cycles before and after high temperature, please refer to Figure 2 、 Figure 3 as shown.

[0056] Through Figure 2 、 Figure 3 , it can be seen that the curve shapes of the DQ / DV-charge curves before and after high temperature are basically the same, there is no peak shift, and the capacity attenuation is only 0.3%; the curve shapes of the DQ / DV-discharge curves before and after high temperature are basically the same, the peak shifts by 1.1mV, and the capacity attenuation is only 0.16%. Therefore, chemical self-discharge can be excluded, and it is inferred that the type of this self-discharge is physical self-discharge.

[0057] After disassembling and observing the battery after the test, it is found that there are particulate foreign matters at the interface of the test battery with a large K value, such as Figure 4 as shown in the two figures, there are two particulate foreign matters of self-discharge, which are verified as physical self-discharge.

[0058] The method of the embodiment of the present application can be used for the physical self-discharge detection of lithium iron phosphate batteries, and can also be used for the physical self-discharge detection of batteries in other systems. The self-discharge detection method of the embodiment of the present application does not require complex equipment, is suitable for quickly determining the types of defective batteries, has strong industrial applicability, excludes the influence of temperature and material side reactions based on the comparison of the curves before and after high temperature with a preset SOC, and has strong anti-interference ability; and the detection period is relatively shorter than the traditional technology. Through experiments, it can be completed in 7 days for the detection that takes several months by the traditional method, and the physical / chemical self-discharge is clearly distinguished, which is efficient and accurate;

[0059] The above shows and describes the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic features of the present invention;

[0060] Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0061] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative manner of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. Method for detecting battery self-discharge type, characterized in that, It includes the following steps: S1. Perform charge-discharge pre-cycling on the battery and record the first DQ / DV-Voltage curve; S2. Charge the battery to a preset SOC and then let it stand for a first standing time at room temperature; S3. Keep the battery at a preset high temperature environment for a second standing time; S4. Place the battery in a room temperature environment for a third standing time; S5. Perform charge-discharge cycling on the battery again and record the second DQ / DV-Voltage curve; S6. Compare the shapes, peak positions, and capacity attenuation of the first DQ / DV-Voltage curve and the second DQ / DV-Voltage curve, and give a judgment result of physical self-discharge / chemical self-discharge according to the comparison results.

2. The battery self-discharge type detection method according to claim 1, wherein, In step S2, for the battery of the LFP system, the preset SOC is 5% - 25% SOC, and preferably 23% SOC; for the battery of the NCM system, the preset SOC is 30% - 50% SOC.

3. The battery self-discharge type detection method according to claim 1, characterized in that In step S2, the first standing time is at least 8h; the temperature of the room temperature environment is 25°C ± 4°C.

4. The battery self-discharge type detection method according to claim 1, wherein In step S3, the preset high temperature environment is 60°C ± 3°C, and the constant temperature standing is carried out in an incubator.

5. The battery self-discharge type detection method according to claim 1, wherein In step S3, the second standing time is at least 24h.

6. The battery self-discharge type detection method according to claim 1, wherein In step S4, the third standing time is at least 12h; the temperature of the room temperature environment is 25°C ± 4°C.

7. The battery self-discharge type detection method according to claim 1, wherein In step S5, if the peak position offset of the two curves is lower than the offset threshold and the capacity attenuation is lower than the first attenuation threshold, it is determined as physical self-discharge.

8. The method for detecting the type of self-discharge of a battery according to claim 7, characterized in that, The offset threshold is 2mV, and the first attenuation threshold is 1%.

9. The battery self-discharge type detection method according to claim 1, characterized in that In step S5, if the curve peak position offset is greater than or equal to the offset threshold or the capacity attenuation is greater than or equal to the second attenuation threshold, it is attributed to chemical self-discharge caused by material side reactions.

10. The battery self-discharge type detection method according to claim 9, characterized in that In step S5, the offset threshold is 2mV, and the second attenuation threshold is 2%.

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