CN115128489A - Method for measuring direct current resistance of high-power battery - Google Patents

Abstract

The invention relates to a method for measuring direct current resistance of a high-power battery, which comprises the following steps: (1) charging and discharging the battery to be tested by using XC current to obtain the average capacity of the battery to be tested; (2) fully charging the battery to be tested by using the current of XC; (3) discharging the battery to be tested by using the current of XC and standing; (4) discharging the battery to be tested by using the current of YC and standing; (5) discharging the battery to be tested; (6) repeating the steps (4) and (5); (7) fully charging the battery to be tested by using the current of XC; (8) discharging the battery to be tested by using the current of XC and standing; (9) charging the battery to be tested with current of nYC and standing; (10) discharging the battery to be tested; (11) and (5) repeating the steps (9) and (10) to finish the measurement. The measuring method provided by the invention is suitable for the pulse charging and discharging current with 3C or more than 3C high multiplying power.

Description

A method for measuring the DC resistance of high-power batteries

technical field

The invention belongs to the technical field of lithium ion batteries, and relates to a method for measuring the direct current resistance of a high-power battery.

Background technique

Lithium-ion batteries are currently widely used, first and foremost because it is a rechargeable secondary battery. Lithium-ion batteries, also known as rocking chair batteries, mainly rely on the shuttle movement of lithium ions between the positive and negative electrodes to achieve a working mode of back-and-forth insertion and extraction of lithium ions. During charging, lithium ions are extracted from the positive electrode and inserted into the negative electrode through the electrolyte; during discharge, lithium ions are extracted from the negative electrode and inserted into the positive electrode through the electrolyte.

After years of development, lithium-ion batteries have become the focus of research and development due to their advantages of no memory effect, light weight, high energy density, high voltage platform, low self-discharge rate, high output power and long cycle life.

With the increasing application of lithium-ion batteries in daily life, people have higher and higher performance requirements for lithium-ion batteries. The performance of lithium-ion batteries is mainly determined by the voltage, capacity, internal resistance, power and cycle life of the battery. Among them, internal resistance is one of the important parameters for evaluating battery performance. Internal resistance can usually be divided into AC internal resistance (ACR) and DC internal resistance (DCR). The AC internal resistance is to apply a fixed frequency and current to the battery. Generally, the frequency is 1KHz and the current is 50mA. Then the corresponding voltage is collected, and the internal resistance value of the battery is calculated after rectification and filtering. The DC internal resistance is based on the formula (1), through the test equipment, let the battery pass a constant DC current in a short time (several seconds, ten seconds or tens of seconds), measure the voltage at both ends of the battery, and follow the formula (1) Calculate the current internal resistance of the battery. The AC internal resistance reflects the state of the battery when it is static, and the DC internal resistance reflects the resistance received by the current flowing through the battery when the battery is working. The size of the DC internal resistance can directly reflect the performance of the battery during operation, and is often used Reflects the attenuation of the battery.

R=V/I Formula (1)

The specific test method HPPC (HybridPulse Power Characterization) of DC internal resistance is described in the battery test manual "Battey Test Manual ForPlug-In Hybrid Electric Vehicles" published in 2014. The purpose of the HPPC test is to evaluate the dynamic power capability of the battery pack under current pulse conditions, including 10-second charging power and 10-second discharging power. In addition, by processing the current-voltage curve of the HPPC test data, the relationship between the DC internal resistance of the battery and the SOC can also be obtained; at the same time, this method can also be used to evaluate the aging degree of the battery in the aging test of the battery.

The specific test method of HPPC is: apply the pulse discharge current and pulse charge current determined to the battery for 10 seconds every 10% SOC, and calculate the DC internal resistance and power of the charge and discharge.

Among them, SOC (state of charge) refers to the state of charge of the battery. When the battery is used for a period of time or left unused for a long time, the ratio of the remaining capacity to the capacity of the fully charged state is usually expressed as a percentage, and the value ranges from 0 to 1. . When SOC=0, it means that the battery is fully discharged, and when SOC=1, it means that the battery is fully charged.

However, in the actual use process, it is found that for small rate (≤5C) pulse charge and discharge batteries (energy type batteries), the test method has high accuracy; but for large rate (such as 50C) pulse charge and discharge batteries (power type batteries) ), if you continue to use this method to test the DC internal resistance, the 10s pulse discharge or charge will cause a large shift in the current SOC state of the battery, for example: after the battery performs 60C&10s pulse discharge, the battery SOC will drop by 60C* 10s/3600s=16.7%, which leads to a large difference in the SOC of the battery during the current pulse charge and discharge, and the actual test results will have serious deviations.

In view of the above defects, no effective and suitable improvement method has been disclosed. How to accurately measure the DC resistance of the high-rate pulsed charge-discharge battery is a technical problem that needs to be solved urgently in the technical field of lithium-ion batteries.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a method for measuring high-power DC resistance, which accurately controls the SOC value of the high-power battery after pulse charging and discharging, and divides the process of pulse discharge and pulse charging into two parts. cycle, further improving the accuracy of the high-power battery SOC value.

For this purpose, the present invention adopts the following technical solutions:

The invention provides a method for measuring the DC resistance of a high-power battery, the method comprising the following steps:

(1) Charge and discharge the high-power battery to be measured with the current of XC to obtain the average capacity of the high-power battery to be measured;

(2) Fully charge the high-power battery to be tested with the current of XC;

(3) Discharge the high-power battery to be measured with the current of XC and let it stand;

(4) Discharge the high-power battery to be measured with the current of YC and let it stand;

(5) Discharge the power battery to be measured;

(6) repeat step (4) and step (5);

(7) Fully charge the high-power battery to be tested with the current of XC;

(8) Discharge the high-power battery to be measured with the current of XC and let it stand;

(9) Charge the high-power battery to be measured with the current of nYC and let it stand;

(10) Discharge the power battery to be measured;

(11) Repeat step (9) and step (10) to complete the measurement of the DC resistance of the high-power battery;

Wherein, X≤1, and X<Y, n≠0.

The method provided by the invention is improved on the basis of the original HPPC test method. First, the cycle of pulse discharge is completed, the discharge amount is adjusted in the process so that the SOC value is accurately controlled, and then the cycle of pulse charge is carried out after fully charged. The amount of discharge allows the SOC value to be precisely controlled. The method accurately controls the SOC value of the high-power battery after pulse charging and discharging, and further improves the accuracy of the SOC value of the high-power battery by dividing the pulse discharge and pulse charging processes into two cycles.

In the method provided by the present invention, pulse discharge is performed first and then pulse charge is performed, because at the highest test point SOC (such as 95% SOC), if the pulse charge is performed first, it is likely to cause the battery to be overcharged, exceeding the battery charge. cut-off voltage, and if the safety cut-off voltage is set, it may lead to insufficient high-current pulse charging time, and the final test result is wrong.

X≤1, for example, can be 0.01, 0.05, 0.1, 0.2, 0.5, 0.8, 0.9, 0.95 or 1, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

The current of the YC in the present invention is a large current that is at least greater than 1C, so as to realize the pulse charging and discharging of the high-power battery.

Preferably, the number of times of charging and discharging in step (1) is 2-5 times, for example, it can be 2 times, 3 times, 4 times or 5 times, but is not limited to the listed values, and other unlisted values within the numerical range The same applies.

Preferably, the discharge capacity in step (3) is 5-20% SOC, such as 5% SOC, 10% SOC, 12% SOC, 15% SOC or 20% SOC, but not limited to the listed values, The same applies to other non-recited values within the numerical range.

Preferably, the standing time in step (3) is 0.8-1.2h, for example, it can be 0.8h, 0.9h, 1h, 1.1h or 1.2h, but is not limited to the listed values, and other values within the range of values are not listed The same value applies.

Preferably, the discharge time in step (4) is 5-20s, for example, it can be 5s, 8s, 10s, 12s, 15s or 20s, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable .

Preferably, the standing time described in step (4) is 5-20min, for example, it can be 5min, 8min, 10min, 12min, 15min or 20min, but is not limited to the enumerated numerical values, and other unenumerated numerical values within the numerical range are the same Be applicable.

Preferably, the capacity size of the discharge in step (5) is the capacity size of the discharge in step (3) minus the capacity size of the discharge in step (4).

Preferably, the discharge current in step (5) is XC.

Preferably, the repetition times of step (6) are 5-20 times, such as 5 times, 10 times, 12 times, 15 times or 20 times, but are not limited to the listed values, and other values are not listed within the numerical range The same value applies.

Preferably, the discharge capacity in step (8) is 5-20% SOC, such as 5% SOC, 10% SOC, 12% SOC, 15% SOC or 20% SOC, but not limited to the listed values, The same applies to other non-recited values within the numerical range.

Preferably, the standing time in step (8) is 0.8-1.2h, for example, it can be 0.8h, 0.9h, 1h, 1.1h or 1.2h, but is not limited to the listed values, and other values are not listed in the range of values The same value applies.

Preferably, the charging time in step (9) is 5-20s, for example, it can be 5s, 8s, 10s, 12s, 15s or 20s, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable .

Preferably, the standing time described in step (9) is 5-20min, such as 5min, 8min, 10min, 12min, 15min or 20min, but is not limited to the enumerated values, and other unenumerated values in the numerical range are the same Be applicable.

Preferably, in step (9), n<1, for example, it can be 0.01, 0.05, 0.1, 0.2, 0.5, 0.8, 0.9 or 0.95, but not limited to the listed values, and other unlisted values within the numerical range are also applicable .

In the method provided by the present invention, the current of the discharge pulse is greater than that of the charging pulse, because for most current research and commercial mass-produced lithium batteries, the discharge design capability of the battery is higher than the charging design capability, so the current of the discharge pulse is It should be larger than the current of the charging pulse, and the current size is within the range of the battery's charging and discharging capacity, otherwise it may cause the battery to fail.

Preferably, the value of n described in step (9) is 0.5-0.8, such as 0.5, 0.6, 0.7, 0.75 or 0.8, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

Preferably, the discharging capacity in step (10) is the sum of the discharging capacity in step (8) and the charging capacity in step (9).

Preferably, the discharge current in step (10) is XC.

Preferably, the repetition times of step (11) are 5-20 times, such as 5 times, 10 times, 12 times, 15 times or 20 times, but are not limited to the listed values, and other values are not listed in the numerical range The same value applies.

Preferably, the Y≧3, for example, may be 3, 5, 10, 20, 50 or 60, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

The measurement method provided by the present invention is suitable for the pulse charge and discharge current of 3C and above with large magnification.

Compared with the prior art, the present invention at least has the following beneficial effects:

(1) The method provided by the present invention is improved on the basis of the original HPPC test method. First, the cycle of pulse discharge is completed, the discharge amount is adjusted in the process so that the SOC value is accurately controlled, and then the cycle of pulse charge is carried out after fully charged. The SOC value is also precisely controlled by adjusting the discharge amount. The method accurately controls the SOC value of the high-power battery after pulse charging and discharging, and further improves the accuracy of the SOC value of the high-power battery by dividing the pulse discharge and pulse charging processes into two cycles.

(2) The measurement method provided by the present invention is suitable for the pulse charge and discharge current of 3C and above with large magnification.

Detailed ways

In order to facilitate the understanding of the present invention, examples of the present invention are as follows. It should be understood by those skilled in the art that the embodiments are only for helping the understanding of the present invention, and should not be regarded as a specific limitation of the present invention.

High-power battery to be tested: 8Ah ternary soft-pack lithium-ion battery for HEV.

Example 1

This embodiment provides a method for measuring the DC resistance of a high-power battery, and the method includes the following steps:

(1) Charge and discharge the high-power battery to be measured three times with a current of 1C to obtain the average capacity of the high-power battery to be measured;

(2) Fully charge the high-power battery to be tested with a current of 1C;

(3) Discharge the high-power battery to be tested with a current of 1C, the discharge capacity is 10% SOC, and stand for 1h;

(4) Discharge the high-power battery to be tested for 10s with a current of 10C, and let it stand for 10min;

(5) Discharge the high-power battery to be measured, and the discharge capacity is (10% SOC-100C/3600);

(6) Repeat steps (4) and (5) 8 times to complete the pulse discharge cycle of the high-power battery at 90% SOC, 80% SOC, 70% SOC...10% SOC;

(7) Fully charge the high-power battery to be tested with a current of 1C;

(8) Discharge the high-power battery to be tested with a current of 1C, the discharge capacity is 10% SOC, and let it stand for 1h;

(9) Charge the high-power battery to be tested for 10s with a current of 7.5C, and let it stand for 10min;

(10) Discharge the high-power battery to be measured, and the discharge capacity is (10%SOC+75C/3600);

(11) Repeat step (9) and step (10) 8 times, the high-power battery is in a pulse charging cycle of 90% SOC, 80% SOC, 70% SOC ... 10% SOC, to complete the measurement of the DC resistance of the high-power battery .

Example 2

This embodiment provides a method for measuring the DC resistance of a high-power battery, and the method includes the following steps:

(1) Charge and discharge the high-power battery to be measured twice with a current of 0.5C to obtain the average capacity of the high-power battery to be measured;

(2) Fully charge the high-power battery to be tested with a current of 0.5C;

(3) Discharge the high-power battery to be tested at a current of 0.5C, the discharge capacity is 5% SOC, and stand for 0.8h;

(4) Discharge the high-power battery to be tested for 5s with a current of 3C, and let it stand for 5min;

(5) Discharge the high-power battery to be measured, and the discharge capacity is (5% SOC-15C/3600);

(6) Repeat steps (4) and (5) 18 times to complete the pulse discharge cycle of the high-power battery at 95% SOC, 90% SOC, 85% SOC...5% SOC;

(7) Fully charge the high-power battery to be tested with a current of 0.5C;

(8) Discharge the high-power battery to be tested with a current of 0.5C, the discharge capacity is 5% SOC, and stand for 0.8h;

(9) Charge the high-power battery to be tested for 5s with a current of 2.25C, and let it stand for 5min;

(10) Discharge the high-power battery to be measured, and the discharge capacity is (5%SOC+11.25C/3600);

(11) Repeat steps (9) and (10) for 18 times, and the high-power battery is in a pulse charging cycle of 95% SOC, 90% SOC, 85% SOC...5% SOC to complete the measurement of the DC resistance of the high-power battery .

Example 3

This embodiment provides a method for measuring the DC resistance of a high-power battery, and the method includes the following steps:

(1) Charge and discharge the high-power battery to be measured at a current of 1C for 5 times to obtain the average capacity of the high-power battery to be measured;

(2) Fully charge the high-power battery to be tested with a current of 1C;

(3) Discharge the high-power battery to be tested with a current of 1C, the discharge capacity is 20% SOC, and stand for 1.2h;

(4) Discharge the high-power battery to be tested for 20s with a current of 20C, and let it stand for 20min;

(5) Discharge the high-power battery to be measured, and the discharge capacity is (20% SOC-400C/3600);

(6) Repeat steps (4) and (5) 4 times to complete the pulse discharge cycle of the high-power battery at 80% SOC, 60% SOC, 40% SOC, and 20% SOC;

(7) Fully charge the high-power battery to be tested with a current of 1C;

(8) Discharge the high-power battery to be tested with a current of 1C, the discharge capacity is 20% SOC, and stand for 1.2h;

(9) Charge the high-power battery to be tested for 20s with a current of 15C, and let it stand for 20min;

(10) Discharge the high-power battery to be measured, and the discharge capacity is (20%SOC+300C/3600);

(11) Repeat step (9) and step (10) for 4 times, and the high-power battery is in a pulse charging cycle of 80% SOC, 60% SOC, 40% SOC, 20% SOC to complete the measurement of the DC resistance of the high-power battery .

Example 4

This embodiment provides a method for measuring the DC resistance of a high-power battery. The remaining process steps are the same as those in Embodiment 1 except that the discharge capacity in step (5) is 10% SOC.

Example 5

This embodiment provides a method for measuring the DC resistance of a high-power battery. Except that the discharge capacity in step (10) is 10% SOC, the remaining process steps are the same as those in Embodiment 1.

Example 6

This embodiment provides a method for measuring the DC resistance of a high-power battery. Except that Y=50, the remaining process steps are the same as those in Embodiment 1.

Example 7

This embodiment provides a method for measuring the DC resistance of a high-power battery, except that the charging current in step (9) is 10C, and the discharging capacity in step (10) is (10%SOC+100C/3600). , and the rest of the process steps are the same as in Example 1.

Example 8

This embodiment provides a method for measuring the DC resistance of a high-power battery, except that the charging current in step (9) is 15C, and the discharging capacity in step (10) is (10%SOC+150C/3600). , and the rest of the process steps are the same as in Example 1.

Comparative Example 1

This comparative example provides a method for measuring the DC resistance of a lithium ion battery, and the measuring method is a conventional HPPC test method, comprising the following steps:

(1) Charge and discharge the lithium-ion battery to be tested three times with a current of 1C to obtain the average capacity of the lithium-ion battery to be tested;

(2) Fully charge the lithium-ion battery to be tested with a current of 1C;

(3) Discharge the lithium-ion battery to be tested with a current of 1C, the discharge capacity is 10% SOC, and let it stand for 1h;

(4) Discharge the lithium-ion battery to be tested for 10s with a current of 3C and let it stand for 40s;

(5) Charge the lithium-ion battery to be tested for 10s with a current of 2.25C, and let it stand for 10min;

(6) Repeat steps (3) to (5) for 8 times, 90% SOC, 80% SOC, 70% SOC...

Comparative Example 2

This comparative example provides a measurement method for a lithium-ion battery DC battery, except that Y=50, the remaining process steps are the same as in Comparative Example 1.

Comparative Example 3

This comparative example provides a method for measuring the DC resistance of a high-power battery, the method comprising the following steps:

(1) Charge and discharge the high-power battery to be measured three times with a current of 1C to obtain the average capacity of the high-power battery to be measured;

(2) Fully charge the high-power battery to be tested with a current of 1C;

(3) Discharge the high-power battery to be tested with a current of 1C, the discharge capacity is 10% SOC, and stand for 1h;

(4) Charge the high-power battery to be tested for 10s with a current of 7.5C, and let it stand for 10min;

(5) Discharge the high-power battery to be measured, and the discharge capacity is (10%SOC+75C/3600);

(6) Repeat steps (4) and (5) 8 times to complete the pulse charging cycle of the high-power battery at 90% SOC, 80% SOC, 70% SOC...10% SOC;

(7) Fully charge the high-power battery to be tested with a current of 1C;

(8) Discharge the high-power battery to be tested with a current of 1C, the discharge capacity is 10% SOC, and let it stand for 1h;

(9) Discharge the high-power battery to be tested for 10s with a current of 10C, and let it stand for 10min;

(10) Discharge the high-power battery to be measured, and the discharge capacity is (10% SOC-100C/3600);

(11) Repeat step (9) and step (10) 8 times, the high-power battery is in a pulse charging cycle of 90% SOC, 80% SOC, 70% SOC ... 10% SOC, to complete the measurement of the DC resistance of the high-power battery .

The error analysis results of the above measurement process are shown in Table 1.

Table 1

From Table 1, the following conclusions can be drawn:

(1) It can be seen from Examples 1-3 and 6-8 that the method provided by the present invention has been improved on the basis of the original HPPC test method, and is suitable for the pulse charge and discharge current of 3C and above. First complete the pulse discharge cycle, adjust the discharge amount in the process so that the SOC value is accurately controlled, and then perform the pulse charging cycle after fully charged, and also adjust the discharge amount to accurately control the SOC value. The method accurately controls the SOC value of the high-power battery after pulse charging and discharging, and further improves the accuracy of the SOC value of the high-power battery by dividing the pulse discharge and pulse charging processes into two cycles.

(2) It can be seen from the comparison between Examples 4 and 5 and Example 1 that when the steps provided by the present invention are changed, the SOC value under the pulse cannot be precisely adjusted, and the pulse charge and discharge current of 3C and above cannot be satisfied.

(3) It can be seen from the comparison of Comparative Examples 1 and 2 with Examples 1 and 8 that the present invention realizes the DC resistance measurement of pulse charge and discharge currents of 3C and above with large magnification on the basis of the original HPPC test method.

(4) It can be seen from the comparison between Comparative Example 3 and Example 1 that when pulse charging is performed first and then pulse discharging is performed, the SOC value under the pulse cannot be precisely adjusted, and the pulse charge and discharge current of 3C and above cannot be satisfied.

To sum up, the method provided by the present invention is improved on the basis of the original HPPC test method, and is suitable for the pulse charge and discharge current of 3C and above with a large rate. First complete the pulse discharge cycle, adjust the discharge amount in the process so that the SOC value is accurately controlled, and then perform the pulse charging cycle after fully charged, and also adjust the discharge amount to accurately control the SOC value. The method accurately controls the SOC value of the high-power battery after pulse charging and discharging, and further improves the accuracy of the SOC value of the high-power battery by dividing the pulse discharge and pulse charging processes into two cycles.

The present invention illustrates the detailed technological process of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed technological process, that is, it does not mean that the present invention must rely on the above-mentioned detailed technological process to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (10)

1. A method of measuring the dc resistance of a high power battery, the method comprising the steps of:

(1) charging and discharging the high-power battery to be tested by using XC current to obtain the average capacity of the high-power battery to be tested;

(2) fully charging the high-power battery to be tested by using the current of XC;

(3) discharging the high-power battery to be tested by using the current of XC and standing;

(4) discharging the high-power battery to be tested by using the current of YC and standing;

(5) discharging the high-power battery to be tested;

(6) repeating the step (4) and the step (5);

(7) fully charging the high-power battery to be tested by using the current of XC;

(8) discharging the high-power battery to be tested by using the current of XC and standing;

(9) charging the high-power battery to be tested at nYC current and standing;

(10) discharging the high-power battery to be tested;

(11) repeating the step (9) and the step (10) to complete the measurement of the direct current resistance of the high-power battery;

wherein X is less than or equal to 1, Y is less than X, and n is not equal to 0.

2. The method for measuring the direct current resistance of the high-power battery according to claim 1, wherein the number of charging and discharging in step (1) is 2-5 times.

3. The method for measuring the direct current resistance of a high power battery according to claim 1 or 2, wherein the capacity of the discharge in the step (3) is 5-20% SOC;

preferably, the standing time of the step (3) is 0.8-1.2 h.

4. The method for improving DC resistance of high power battery according to any one of claims 1-3, wherein the discharging time in step (4) is 5-20 s;

preferably, the standing time of the step (4) is 5-20 min.

5. The method for improving DC resistance of high power battery according to any one of claims 1-4, wherein the discharged capacity of step (5) is the discharged capacity of step (3) minus the discharged capacity of step (4);

preferably, the current discharged in step (5) is XC;

preferably, the number of repetitions of step (6) is 5 to 20.

6. The method for improving DC resistance of high power battery according to any one of claims 1-5, wherein the discharge capacity of step (8) is 5-20% SOC;

preferably, the standing time of the step (8) is 0.8-1.2 h.

7. The method for improving DC resistance of high power battery according to any one of claims 1-6, wherein the charging time in step (9) is 5-20 s;

preferably, the standing time of the step (9) is 5-20 min;

preferably, n < 1 in step (9);

preferably, n in step (9) has a value of 0.5 to 0.8.

8. The method for improving DC resistance of high power battery according to any one of claims 1-7, wherein the discharged capacity of step (10) is the sum of the discharged capacity of step (8) and the charged capacity of step (9);

preferably, the current of the discharge in step (10) is XC.

9. The method for improving the DC resistance of a high power battery according to any one of claims 1-8, wherein the repetition of step (11) is performed 5-20 times.

10. The method for improving DC resistance of high power battery according to any one of claims 1-9, wherein Y is 3 or more.