Self-discharge test method
By placing the battery's target SOC and recording the voltage changes, and combining the capacity required for charging recovery, estimating the SOC loss of the battery during self-discharge, the problem of low accuracy of SOC estimation in the prior art is solved, and more efficient self-discharge testing is achieved, reducing costs and time expenditures.
Patent Information
- Application Number
- CN202510006348.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-03
- Publication Date
- 2025-04-22
AI Technical Summary
In the prior art, the accuracy of estimating SOC by open circuit voltage is low, and estimating SOC before and after shelved by capacity loss method is time-consuming and time-consuming, which is not conducive to cost reduction and efficiency improvement.
Adjust the battery to the target SOC and stand still with the temperature not changing, recording the initial voltage U0. After the interval test time, the voltage Un is recorded. If Un is less than U0, the charge is until the voltage reaches U0 again, and the capacity of the SOC is estimated to be lost, thereby obtaining the relationship between self-discharge SOC and time.
This method can more accurately estimate the SOC loss of the battery during self-discharge, improve the accuracy of the test, reduce the inconvenience of frequent removal of large-scale batteries, and facilitate cost reduction and efficiency improvement.
Smart Images
Figure CN119861298A_ABST
Abstract
Description
Technical Field
[0001] The invention specifically relates to a self-discharge testing method. Background Art
[0002] Battery self-discharge refers to the phenomenon that the battery voltage drops and the capacity decreases in the open circuit state. It is one of the main parameters to measure battery performance. Excessive self-discharge of a single battery often causes its own voltage to drop rapidly, which in turn weakens the charge retention ability of the entire power battery pack. As a result, the voltage difference between batteries is large. Some batteries are basically fully charged, some batteries have been over-discharged, and some batteries have even been short-circuited due to overcharging and over-discharging. Therefore, the detection of battery self-discharge is particularly important.
[0003] At present, the self-discharge test methods include capacity consumption method and open circuit voltage method, which are widely used. For iron-lithium batteries, due to the existence of voltage platforms, SOC and OCV are not the only relationship, and there are basically no differences in the voltages corresponding to multiple SOCs. Therefore, the accuracy of using the open circuit voltage method to estimate the SOC of iron-lithium batteries may be low. For a test such as self-discharge for 30 days, the capacity can be maintained after 30 days to calculate the SOC, so the capacity loss method is used to estimate the SOC before and after shelving. However, for the SOC estimation of the intermediate process within 30 days, if large-scale battery storage is used, a few batteries are taken out at intervals. This method will increase the amount of battery testing. For enterprises, it increases material, human and financial resources, which is not conducive to reducing costs and increasing efficiency. For this reason, we propose a self-discharge test method. Summary of the invention
[0004] The purpose of the present invention is to provide a self-discharge test method to solve the problems in the above background technology that the existing SOC estimation by open circuit voltage has low accuracy, and the SOC estimation before and after shelving by capacity loss method is time-consuming and not conducive to cost reduction and efficiency improvement.
[0005] To achieve the above object, the present invention provides the following technical solution: a self-discharge test method, comprising the following steps:
[0006] Step A: Adjust to the target SOC and keep the temperature constant. Leave it for a while until the voltage stabilizes. Record the voltage at this time as U0.
[0007] Step B: wait for the required test time, and then record the voltage at this time as Un. When Un is less than U0, charge until the voltage reaches U0 again.
[0008] Step C: Based on the capacity consumed in charging to U0 in step B, that is, the capacity estimated as the SOC loss in step B, the relationship between the self-discharge SOC and time is obtained, and the SOC in the intermediate state is obtained.
[0009] It is convenient to charge the battery to a specific SOC and keep the battery at this SOC for a certain period of time. During this process, the battery is in a static state, that is, there is no external load and no charging or discharging. Tests are performed at required time intervals to record the battery voltage at different time points. The key to this process is to capture the voltage change caused by self-discharge when the battery is not charged or discharged. Charging to restore the SOC helps to estimate the amount of power lost by the battery during self-discharge. The capacity consumed by charging is the self-discharge loss capacity during this time period.
[0010] Preferably, the temperature range tested in step A is 20°C-65°C, and a temperature fluctuation range within 2°C is regarded as constant.
[0011] This is convenient to avoid being affected by external temperature during testing, which may cause inaccurate testing.
[0012] Preferably, the test temperature in step A is 45°C.
[0013] Preferably, in step A, the voltage does not exceed 5 mV within 10 minutes, which is considered to be stable.
[0014] It is convenient to ensure the stability of the voltage so that the self-discharge loss capacity can be accurately tested later.
[0015] Preferably, in step B, charging is performed with a small current of C / 5000-C / 10000.
[0016] It is convenient to ensure a very slow charging rate. This charging rate is used to charge the battery very gently and at a low speed to protect the health of the battery, extend its service life, and avoid battery damage caused by over-fast charging.
[0017] Preferably, in step B, charging is performed at a current of C / 5000.
[0018] This is convenient for ensuring the constancy of the current during charging, so as to reduce the impact of current fluctuations on the battery.
[0019] Preferably, the testing time in step B is 7-30 days.
[0020] Preferably, the target SOC in step A is one of 90% SOC to 10% SOC.
[0021] It is convenient to measure the SOC self-discharge loss capacity under different conditions.
[0022] Preferably, in step B, charging is performed by constant current, and the current fluctuation range of the constant current is within ±1%.
[0023] It is convenient to charge with a constant current to reduce the impact of large current fluctuations on the battery stack.
[0024] Preferably, in step B, when Un is greater than or equal to U0, the voltage is detected again after a period of time, and charging is then performed until Un is less than U0.
[0025] It is convenient to charge at the appropriate voltage to estimate the lost capacity.
[0026] Compared with the prior art, the present invention has the following beneficial effects:
[0027] The present invention facilitates the estimation of the SOC during the self-discharge process, and obtains a relationship diagram and a relationship expression between the SOC and time, which is convenient for research and development personnel to analyze its self-discharge performance. For the iron-lithium battery with a voltage platform, a self-discharge test method that is more suitable for its battery characteristics is obtained, and the open circuit voltage method that is not suitable for it is eliminated, thereby improving the accuracy of the test. The principle is simple and the feasibility is strong. It is convenient to judge the self-discharge loss of a large number of batteries through the method, reduce the inconvenience of frequently taking out the battery for testing, and is conducive to reducing costs and increasing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 It is a curve diagram showing the relationship between 80% SOC and time of the present invention;
[0029] Figure 2 It is a curve diagram showing the relationship between 50% SOC and time of the present invention;
[0030] Figure 3 It is a curve diagram showing the relationship between 20% SOC and time of the present invention. DETAILED DESCRIPTION
[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0032] See also Figure 1-Figure 3 The present invention provides a technical solution: a self-discharge test method, comprising the following steps:
[0033] Step A: Adjust to the target SOC, where SOC is the charge capacity of the state, and keep the temperature unchanged. Let it stand for a while until the voltage stabilizes. The voltage at this time is recorded as U0, so that the battery can reach the required SOC through appropriate charging and discharging;
[0034] Step B: wait for the required test time, and then record the voltage at this time as Un. When Un is less than U0, charge until the voltage reaches U0 again.
[0035] Step C: Based on the capacity consumed when charging to U0 in step B, that is, the capacity estimated as the SOC loss in step B, the relationship between the self-discharge SOC and time is obtained, and the intermediate state SOC is obtained, which makes it easy to calculate the self-discharge rate of the battery by recording the voltage changes at different time points, and then obtain the self-discharge characteristics of the battery at different SOCs.
[0036] It is convenient to charge the battery to a specific SOC and keep the battery at this SOC for a certain period of time. During this process, the battery is in a static state, that is, there is no external load and no charging or discharging. Tests are performed at required time intervals to record the battery voltage at different time points. The key to this process is to capture the voltage change caused by self-discharge when the battery is not charging or discharging. Charging to restore the SOC helps to estimate the amount of power lost by the battery during self-discharge. The capacity consumed by charging is the self-discharge loss capacity during this period of time. This process helps estimate the self-discharge loss of the battery over a period of time by monitoring the voltage change of the battery and combining it with the capacity required for charging recovery. It can provide important data for battery performance analysis, especially the impact of self-discharge during long-term use or storage of the battery.
[0037] Preferably, the temperature range tested in step A is 20°C-65°C, and a temperature fluctuation range within 2°C is regarded as constant.
[0038] This is to avoid being affected by the external temperature during the test, which may cause inaccurate testing. That is, the temperature change of the battery should be kept within a very small range, which can ensure that the temperature of the battery does not change significantly during the static period, thereby ensuring the accuracy of the test results.
[0039] Preferably, the test temperature in step A is 45° C. 45° C. is generally considered to be a temperature that will not cause excessive damage to the battery over a long period of time, which helps to evaluate the self-discharge characteristics of the battery and facilitates simulating the performance of the battery in a real working environment.
[0040] Preferably, in step A, the voltage does not exceed 5 mV within 10 minutes, which is considered to be stable.
[0041] It is convenient to effectively ensure that the battery is in a stable state at the target SOC. This standard helps to eliminate errors caused by small fluctuations or unstable factors, and ensures the stability of the voltage so that the self-discharge loss capacity can be accurately tested later.
[0042] Preferably, in step B, charging is performed with a small current of C / 5000-C / 10000.
[0043] It is convenient to ensure a very slow charging rate. This charging rate is used to charge the battery very gently and at a low speed to protect the health of the battery, extend its service life, and avoid battery damage caused by over-fast charging.
[0044] Preferably, in step B, charging is performed at a current of C / 5000.
[0045] It is convenient to ensure the constancy of current during charging and achieve an extremely slow charging rate, thereby avoiding any unstable factors caused by charging too fast to the battery, ensuring the accuracy of test data and the long-term stability of the battery, so as to reduce the impact of current fluctuations on the battery.
[0046] Preferably, the testing time in step B is 7-30 days.
[0047] The performance of the battery will change over time, especially as the number of charge and discharge cycles increases, the chemical reactions and physical structure inside the battery may change. By testing within a time range of 7 to 30 days, the stability and aging rate of the battery during long-term use can be better evaluated. Self-discharge means that the charge inside the battery will slowly decrease even when the battery is not connected to a load. By testing for a long time of 7 to 30 days, the self-discharge rate of the battery and other performance changes related to self-discharge can be accurately measured.
[0048] Preferably, the target SOC in step A is one of 90% SOC to 10% SOC.
[0049] It is convenient to start charging or discharging operation when the battery power is low according to different energy requirements to ensure the stability of the system and measure the SOC self-discharge loss capacity under different states.
[0050] Preferably, in step B, charging is performed by constant current, and the current fluctuation range of the constant current is within ±1%.
[0051] It is convenient to charge with a constant current to reduce the impact of a large current fluctuation range on the battery. The advantage of constant current charging is that the battery charging process is more stable and efficient. When the current fluctuation is small, the charging system can track the battery charging status more accurately and make corresponding adjustments to optimize the energy conversion during the charging process. When the battery is charging, if the current fluctuates greatly, it may cause instability in the chemical reaction inside the battery, thereby accelerating the battery's degradation. By ensuring that the current fluctuation is within the range of ±1%, the uncertainty of the chemical reaction inside the battery can be reduced, reducing the negative impact on the battery life.
[0052] Preferably, in step B, when Un is greater than or equal to U0, the voltage is detected again after a period of time, and charging is then performed until Un is less than U0.
[0053] It is convenient to detect self-discharge, and charging is performed only at a suitable voltage to estimate the lost capacity.
[0054] Working principle and testing method of the present invention:
[0055] First, discharge and charge the battery 4 times, with the last cycle of discharge capacity being C0. Then adjust the battery to the target SOC, and adjust the capacity released by the SOC to C1. The adjustment rates of the SOC and the constant capacity are the same, and the battery is cut off at the percentage of the capacity C0. Let the battery stand for a while until the voltage fluctuation does not exceed 5mV within 10 minutes. Record the voltage U0. Disconnect all connections for testing. Leave the battery in an open circuit state.
[0056] Some test standards require 0 hours, 24 hours, 2 days, 3 days, 5 days, etc. Then test the voltage at the required time. When the voltage is lower than U0, perform constant current charging until the voltage reaches U0. The current is selected as a small current, C / 5000 to C / 10000; C / 5000 means that the charging current is 1 / 5000 of the battery capacity, which means that the charging current is equivalent to 1 / 5000 of the nominal capacity of the battery, and the charged capacity is the self-discharge loss capacity in a certain period of time;
[0057] After the required time is reached, discharge and charge at the same rate for 4 times. The discharge capacity of the first cycle is C2, and the discharge capacity of the last cycle is C0. For example, if the self-discharge test is required to be 30 days, then the self-discharge capacity loss in 30 days is C1-C2. SOC estimation 0d=C0 / C0, 24 hours=Ccharge / C0, 2d=Cchargen / C0, ... and so on.
[0058] Table 1: Charging capacity at different shelf times at 80% SOC and 45°C environment:
[0059]
[0060] Table 2: Charging capacity at different shelf times at 50% SOC and 45°C environment:
[0061]
[0062] Table 3: Charging capacity at different shelf times at 20% SOC and 45°C environment:
[0063]
[0064] Table 1-3 records the self-discharge loss capacity of the battery under different storage conditions. Specifically:
[0065] Initial SOC value: As described in Table 1, the battery was initially at 80% SOC and tested at 45°C.
[0066] Shelf time: records the changes in self-discharge capacity of the battery at different shelf times, such as 0 hours, 24 hours, 2 days, 3 days, 5 days, etc.
[0067] Charged capacity: For each idle period, when the battery voltage is lower than the initial U0 value, the amount of electricity charged when the battery is restored to the target voltage U0 through constant current charging is the self-discharge loss capacity of that period.
[0068] Through these, the self-discharge performance of the battery at different times, different SOCs and different environmental conditions can be systematically measured and analyzed. Finally, by estimating the self-discharge capacity of the battery in a specific time period, the relationship between the battery's SOC change and time can be obtained. This method is particularly suitable for evaluating the long-term storage performance of batteries, especially for batteries with voltage platform characteristics, such as lithium iron phosphate batteries. It can effectively avoid the inaccuracy of the traditional open circuit voltage method and provide more accurate test results. This method provides important data support for battery design and development, and also helps to further optimize the battery management system and improve the accuracy of battery life prediction.
[0069] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A self-discharge test method, characterized in that: The steps include: Step A: Adjust to the target SOC and keep the temperature constant. Leave it for a while until the voltage stabilizes. Record the voltage at this time as U0. Step B: wait for the required test time, and then record the voltage at this time as Un. When Un is less than U0, charge until the voltage reaches U0 again. Step C: Based on the capacity consumed in charging to U0 in step B, that is, the capacity estimated as the SOC loss in step B, the relationship between the self-discharge SOC and time is obtained, and the SOC in the intermediate state is obtained.
2. A self-discharge testing method according to claim 1, characterized in that: The temperature range tested in step A is 20° C.-65° C., and the temperature fluctuation range within 2° C. is considered to be constant.
3. A self-discharge testing method according to claim 2, characterized in that: The test temperature of step A is 45°C.
4. A self-discharge testing method according to claim 1, characterized in that: In step A, if the voltage does not exceed 5 mV within 10 min, the voltage is considered stable.
5. A self-discharge testing method according to claim 1, characterized in that: In the step B, charging is performed with a small current of C / 5000-C / 10000.
6. A self-discharge testing method according to claim 5, characterized in that: In the step B, charging is performed at a current of C / 5000.
7. A self-discharge testing method according to claim 1, characterized in that: The testing time in step B is 7-30 days.
8. A self-discharge testing method according to claim 1, characterized in that: The target SOC in step A is one of 90% SOC and 10% SOC.
9. A self-discharge testing method according to claim 1, characterized in that: In the step B, charging is performed by constant current, and the current fluctuation range of the constant current is within ±1%.
10. A self-discharge testing method according to claim 1, characterized in that: In the step B, when Un is greater than or equal to U0, the voltage is detected again after a period of time, and charging is then performed until Un is less than U0.