CN113093038B - An analysis method of internal resistance composition of power battery based on pulse charge and discharge test - Google Patents

Abstract

The invention provides a power battery internal resistance composition analysis method based on pulse charge and discharge tests. The method comprises the steps of adjusting to an SOC value to be tested, testing an alternating current internal resistance value, discharging with constant current pulses and obtaining a terminal voltage time sequence in the pulse discharging process, standing, charging with constant current pulses and obtaining a terminal voltage time sequence in the pulse charging process, analyzing the terminal voltage time sequence, and obtaining an electrochemical polarization internal resistance value and a concentration polarization internal resistance value of the power battery in the pulse discharging and charging processes respectively. The method uses simple and convenient steps to obtain the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance which form the internal resistance of the power battery, and has scientific and reasonable method, good stability and no dependence on expensive and complex instruments.

Description

An analysis method of internal resistance composition of power battery based on pulse charge and discharge test

technical field

The invention relates to the field of lithium-ion power batteries, in particular to a method for analyzing the internal resistance composition of a power battery based on a pulse charge-discharge test.

Background technique

Lithium-ion power batteries have been widely used due to their high energy density, good environmental adaptability, and high power density. The rate performance, charge-discharge capacity, and heat-generating power of lithium-ion power batteries are largely affected by internal resistance. If the internal resistance of the lithium-ion battery is large, the rate performance and charge-discharge capacity will decrease, the heat generation power will increase, and the thermal management difficulty will increase. The total internal resistance of lithium-ion power batteries mainly includes three major components: ohmic internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance. Among them, the ohmic internal resistance is caused by ohmic polarization, and its occurrence is instantaneous; the electrochemical internal resistance is caused by electrochemical polarization. It is short-lived; the internal resistance of concentration polarization is related to concentration polarization, which is the polarization caused by the diffusion rate of lithium ions participating in the reaction is lower than the electrochemical reaction rate. The polarization rate is relatively ohmic and electrochemical. Much lower, concentration polarization is generally believed to be completed within seconds. Obtaining the total internal resistance and its composition under different SOCs (State of Charge) of lithium-ion power batteries is very important for the design and process quality analysis, performance evaluation and life prediction of lithium-ion power batteries. Usually, people get the AC internal resistance of lithium-ion power battery by testing the AC resistance tester, and it is approximated that the AC internal resistance value is equal to the ohmic internal resistance; while the lithium-ion power battery includes ohmic internal resistance, electrochemical polarization internal resistance and concentrated internal resistance. The total internal resistance including the three parts of the differential internal resistance is obtained through the pulse charge-discharge test, and the most typical test scheme is the HPPC (Hybrid PulsePowerCharacteristic, that is, the hybrid power pulse capability characteristic) test.

In the current known technical solutions, in order to accurately obtain the total internal resistance composition of the lithium-ion power battery, it is necessary to use an electrochemical workstation to perform AC impedance and other tests, which not only relies on expensive and sophisticated professional instruments with complicated operations, but can only be used for experiments. Test chamber samples rather than actual complete power battery products. The pulse charge-discharge test for battery products only gives the total internal resistance of the battery. Therefore, it is urgent to develop an analysis method for the internal resistance test and its composition of the actual product of lithium-ion power battery that is easy to operate, scientific and reasonable.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a convenient, scientific and reasonable method for analyzing the internal resistance of a power battery based on a pulse charge and discharge test, and uses simple and convenient steps to obtain the ohmic internal resistance, electrochemical The method of polarization internal resistance and concentration polarization internal resistance is scientific and reasonable, with good stability and does not depend on expensive and complicated instruments.

To achieve the above object, the present invention adopts the following technical solutions:

A method for analyzing the internal resistance of a power battery based on a pulse charge-discharge test, the operation steps are as follows:

(1), charge and discharge the power battery, adjust to the SOC value required to be tested, and leave it aside for 1 hour ± 1 minute, measure and record the open circuit voltage value U _oc ;

(2), use the AC resistance tester to test and record the AC internal resistance value R ₀ of the power battery;

(3) Discharge the power battery with a constant current pulse of I ₁ for 10±0.5 seconds, and record the change of the terminal voltage of the power battery with time during the discharge process at a fixed time interval of Δt, and obtain the terminal voltage time series of the pulse discharge process { U _di }, where I ₁ is the current value corresponding to the rate of 1C to 10C, Δt is not greater than 0.001 seconds, and U _di represents the ith terminal voltage value in the power battery terminal voltage time series during the pulse discharge process;

(4), put the power battery on hold for 40±1 seconds, measure and record the open-circuit voltage value U _od at the end of the lay-up;

(5) Charge the power battery with a constant current pulse of I ₂ for 10 seconds, and record the change of the power battery terminal voltage with time during the charging process at a fixed time interval of Δt, and obtain the pulse charging process terminal voltage time series {U _ci }, where I ₂ is the current value corresponding to the rate between 1C and 5C, Δt is not greater than 0.001 seconds, and U _ci represents the ith terminal voltage value in the terminal voltage time series during the pulse charging process;

(6) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _di } obtained in the pulse discharge process obtained in step (3), and obtain the electrochemical polarization internal resistance value R of the power battery in the pulse discharge process _de and concentration polarization internal resistance R _dm ;

(7) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _ci } obtained in step (5) during the pulse charging process, and obtain the electrochemical polarization internal resistance value R of the power battery during the pulse charging process _ce and concentration polarization internal resistance R _cm .

Preferably, the present invention constitutes an analysis method for the internal resistance of a power battery based on a pulse charge-discharge test, and the specific operation steps of the step (6) are as follows:

(6.1) Based on the terminal voltage time series {U _di } in the pulse discharge process, each terminal voltage value is subtracted from the next terminal voltage value adjacent to it to obtain the terminal voltage difference time series {ΔU _di } in the pulse discharge process, Among them, ΔU _di represents the ith terminal voltage difference in the time series of power battery terminal voltage difference during the pulse discharge process:

ΔU _di =U _di -U _d(i+1) (1)

(6.2) Based on the time series {ΔU _di } of the terminal voltage difference during the pulse discharge process, compare each terminal voltage difference with the first terminal voltage difference ΔU _d1 in sequence, until the first satisfying ΔU _dk <fΔU is obtained. The k-th terminal voltage difference ΔU _dk for the condition of _d1 and record the k value, where f is a fixed value between 0.1 and 0.5;

(6.3), calculate the electrochemical polarization internal resistance R _de of the power battery during the pulse discharge process:

R _de =(U _oc -U _dk )/I ₁ -R ₀ (2)

In the formula, U _oc represents the open-circuit voltage value obtained in step (1); U _dk represents the k-th terminal voltage value in the power battery terminal voltage time series during the pulse discharge process, and the k value is obtained in step (6.2); I ₁ is step (3) ) in the pulse discharge current value; R ₀ is the AC internal resistance value obtained in step (2);

(6.4), calculate the concentration polarization internal resistance value R _dm of the power battery during the pulse discharge process:

R _dm =(U _oc -U _dn )/I ₁ -R ₀ -R _de (3)

In the formula, U _oc represents the open-circuit voltage value obtained in step (1); U _dn represents the last terminal voltage value in the power battery terminal voltage time series during the pulse discharge process; I ₁ is the pulse discharge current value in step (3); R ₀ is the AC internal resistance value obtained in step (2); R _de is the electrochemical polarization internal resistance value of the power battery obtained in step (6.3) during the pulse discharge process.

Preferably, the present invention constitutes an analysis method for the internal resistance of a power battery based on a pulse charge-discharge test, and the specific steps of the step (7) are:

(7.1) Based on the terminal voltage time series {U _ci } in the pulse charging process, starting from the second terminal voltage value, subtract the adjacent previous terminal voltage value from each terminal voltage value to obtain the terminal voltage during the pulse charging process. Difference time series {ΔU _ci }, where ΔU _ci represents the ith terminal voltage difference in the power battery terminal voltage difference time series during the pulse charging process:

ΔU _ci =U _c(i+1) −U _ci (4)

(7.2) Based on the time series {ΔU _ci } of the terminal voltage difference during the pulse charging process, compare each terminal voltage difference with the first terminal voltage difference ΔU _c1 in sequence, until the first ΔU _cs < pΔU is obtained. The sth terminal voltage difference ΔU _cs of the condition of _c1 and record the s value, where p is a fixed value between 0.1 and 0.5;

(7.3), calculate the electrochemical polarization internal resistance R _ce of the power battery during the pulse charging process:

R _ce = (U _cs -U _od )/I ₂ -R ₀ (5)

In the formula, U _od represents the open-circuit voltage value obtained in step (4); U _cs represents the s-th terminal voltage value in the power battery terminal voltage time series during the pulse charging process, and the s value is obtained in step (7.2); I ₂ is step (5) ) in the pulse charging current value; R ₀ is the AC internal resistance value obtained in step (2);

(7.4), calculate the concentration polarization internal resistance value R _cm of the power battery during the pulse charging process:

R _cm = (U _cn -U _od )/I ₂ -R ₀ -R _ce (6)

In the formula, U _od represents the open-circuit voltage value obtained in step (4); in the formula, U _cn represents the last terminal voltage value in the power battery terminal voltage time series during the pulse charging process; I ₂ is the pulse charging current value in step (5); R ₀ is the AC internal resistance value obtained in step (2); R _ce is the electrochemical polarization internal resistance value of the power battery obtained in step (7.3) during the pulse charging process.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and remarkable advantages:

1. The present invention uses the actual lithium-ion power battery product as the test and analysis object. The test itself only needs to carry out the conventional AC resistance and pulse charge and discharge tests, and does not rely on expensive and complicated instruments such as electrochemical workstations. It is easy to operate and can directly Test the power battery product itself;

2. According to the difference in the occurrence rates of the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance that constitute the total internal resistance of the lithium-ion power battery, the present invention analyzes the rate of change of the terminal voltage to discharge the pulse discharge. Or the stage where the terminal voltage rapidly drops or rises in a short period of time during the charging process is regarded as the effect of ohmic internal resistance and electrochemical polarization internal resistance, and the change in terminal voltage at the end of the discharge pulse is regarded as the effect of the total internal resistance of the battery. The measured AC resistance value is used as the ohmic internal resistance value, so that the accurate values of the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance can be obtained respectively through simple operations. This scheme is scientific and reasonable. , good stability;

3. The present invention obtains the voltage difference time series based on the pulse charging and discharging terminal voltage time series, and then compares each difference value in the sequence with the first difference value in sequence, and finds the inflection point where the difference value changes from fast to slow. As the starting point of the concentration polarization internal resistance, this data analysis method effectively distinguishes the sum of the ohmic internal resistance and the electrochemical polarization internal resistance from the concentration polarization internal resistance, and the calculation amount is small but simple. efficient.

Description of drawings

FIG. 1 is a flowchart of a method for analyzing the internal resistance composition of a power battery based on a pulse charge-discharge test in a preferred embodiment of the present invention.

Detailed ways

The preferred embodiments of the present invention are described in detail as follows in conjunction with the accompanying drawings:

Example 1:

Referring to Figure 1, a method for analyzing the internal resistance of a power battery based on a pulse charge-discharge test, the operation steps are as follows:

(1), charge and discharge the power battery, adjust to the SOC value required to be tested, and leave it aside for 1 hour ± 1 minute, measure and record the open circuit voltage value U _oc ;

(2), use the AC resistance tester to test and record the AC internal resistance value R ₀ of the power battery;

(3) Discharge the power battery with a constant current pulse of I ₁ for 10 seconds ± 0.5 seconds, and record the change of the power battery terminal voltage with time during the discharge process at a fixed time interval of Δt to obtain the pulse discharge process terminal voltage time series {U _di }, where I ₁ is the current value corresponding to the rate of 1C to 10C, Δt is not greater than 0.001 seconds, and U _di represents the ith terminal voltage value in the power battery terminal voltage time series during the pulse discharge process;

(4), put the power battery on hold for 40 seconds ± 1 second, measure and record the open-circuit voltage value U _od at the end of the putting aside;

(5) Charge the power battery with a constant current pulse of I ₂ for 10 seconds ± 0.5 seconds, and record the change of the power battery terminal voltage with time during the charging process at a fixed time interval of Δt, and obtain the pulse charging process terminal voltage time series {U _ci }, where I ₂ is the current value corresponding to the rate of 1C to 5C, Δt is not greater than 0.001 seconds, and U _ci represents the ith terminal voltage value in the time series of terminal voltages during the pulse charging process;

(6) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _di } obtained in the pulse discharge process obtained in step (3), and obtain the electrochemical polarization internal resistance value R of the power battery in the pulse discharge process _de and concentration polarization internal resistance R _dm ;

(7) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _ci } obtained in step (5) during the pulse charging process, and obtain the electrochemical polarization internal resistance value R of the power battery during the pulse charging process _ce and concentration polarization internal resistance R _cm .

In this example, simple and convenient steps are used to obtain the ohmic internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance that constitute the internal resistance of the power battery. The method is scientific and reasonable, with good stability and does not depend on expensive and complicated instruments

Embodiment 2:

Referring to Figure 1, a method for analyzing the internal resistance of a power battery based on a pulse charge-discharge test is divided into the following steps:

(1), charge and discharge the power battery, adjust to the SOC value required to be tested, and set aside for 1 hour, measure and record the open circuit voltage value U _oc ;

(2), use the AC resistance tester to test and record the AC internal resistance value R ₀ of the power battery;

(3) Discharge the power battery with a constant current pulse of I ₁ for 10 seconds, and record the change of the power battery terminal voltage with time during the discharge process at a fixed time interval of Δt, and obtain the pulse discharge process terminal voltage time series {U _di }, where I ₁ is the current value corresponding to the rate between 1C and 10C, Δt is not greater than 0.001 seconds, and U _di represents the ith terminal voltage value in the power battery terminal voltage time series during the pulse discharge process;

(4), put the power battery on hold for 40 seconds, measure and record the open-circuit voltage value U _od at the end of the hold;

(5) Charge the power battery with a constant current pulse of I ₂ for 10 seconds, and record the change of the power battery terminal voltage with time during the charging process at a fixed time interval of Δt, and obtain the pulse charging process terminal voltage time series {U _ci }, where I ₂ is the current value corresponding to the rate between 1C and 5C, Δt is not greater than 0.001 seconds, and U _ci represents the ith terminal voltage value in the terminal voltage time series during the pulse charging process;

(6) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _di } obtained in the pulse discharge process obtained in step (3), and obtain the electrochemical polarization internal resistance value R of the power battery in the pulse discharge process _de and concentration polarization internal resistance R _dm ;

In the present embodiment, step (6) is specifically divided into the following sub-steps:

(6.1) Based on the terminal voltage time series {U _di } in the pulse discharge process, each terminal voltage value is subtracted from the next terminal voltage value adjacent to it to obtain the terminal voltage difference time series {ΔU _di } in the pulse discharge process, Among them, ΔU _di represents the ith terminal voltage difference in the time series of power battery terminal voltage difference during the pulse discharge process:

ΔU _di =U _di -U _d(i+1) (1)

(6.2) Based on the time series {ΔU _di } of the terminal voltage difference during the pulse discharge process, compare each terminal voltage difference with the first terminal voltage difference ΔU _d1 in sequence, until the first satisfying ΔU _dk <fΔU is obtained. The k-th terminal voltage difference ΔU _dk for the condition of _d1 and record the k value, where f is a fixed value between 0.1 and 0.5;

(6.3), calculate the electrochemical polarization internal resistance R _de of the power battery during the pulse discharge process:

R _de =(U _oc -U _dk )/I ₁ -R ₀ (2)

In the formula, U _dk represents the k-th terminal voltage value in the power battery terminal voltage time series in the pulse discharge process, and the k value is obtained from step (6.2); I ₁ is the pulse discharge current value in step (3); R ₀ is step ( 2) AC internal resistance value obtained;

(6.4), calculate the concentration polarization internal resistance value R _dm of the power battery during the pulse discharge process:

R _dm =(U _oc -U _dn )/I ₁ -R ₀ -R _de (3)

In the formula, U _dn represents the last terminal voltage value in the power battery terminal voltage time series in the pulse discharge process; I ₁ is the pulse discharge current value in step (3); R ₀ is the AC internal resistance value obtained in step (2); R _de is the electrochemical polarization internal resistance value of the power battery obtained in step (6.3) during the pulse discharge process.

(7) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _ci } obtained in step (5) during the pulse charging process, and obtain the electrochemical polarization internal resistance value R of the power battery during the pulse charging process _ce and concentration polarization internal resistance R _cm .

Referring to Figure 1, step (7) is specifically divided into the following sub-steps:

(7.1) Based on the terminal voltage time series {U _ci } in the pulse charging process, starting from the second terminal voltage value, subtract the adjacent previous terminal voltage value from each terminal voltage value to obtain the terminal voltage during the pulse charging process. Difference time series {ΔU _ci }, where ΔU _ci represents the ith terminal voltage difference in the power battery terminal voltage difference time series during the pulse charging process:

ΔU _ci =U _c(i+1) −U _ci (4)

(7.2) Based on the time series {ΔU _ci } of the terminal voltage difference during the pulse charging process, compare each terminal voltage difference with the first terminal voltage difference ΔU _c1 in sequence, until the first ΔU _cs < pΔU is obtained. The sth terminal voltage difference ΔU _cs of the condition of _c1 and record the s value, where p is a fixed value between 0.1 and 0.5;

(7.3), calculate the electrochemical polarization internal resistance R _ce of the power battery during the pulse charging process:

R _ce = (U _cs -U _od )/I ₂ -R ₀ (5)

In the formula, U _od represents the open-circuit voltage value obtained in step (4); in the formula, U _cs represents the s-th terminal voltage value in the power battery terminal voltage time series during the pulse charging process, and the s value is obtained in step (7.2); I ₂ is the step The pulse charging current value in (5); R ₀ is the AC internal resistance value obtained in step (2);

(7.4), calculate the concentration polarization internal resistance value R _cm of the power battery during the pulse charging process:

R _cm = (U _cn -U _od )/I ₂ -R ₀ -R _ce (6)

In the formula, U _od represents the open-circuit voltage value obtained in step (4); in the formula, U _cn represents the last terminal voltage value in the power battery terminal voltage time series during the pulse charging process; I ₂ is the pulse charging current value in step (5); R ₀ is the AC internal resistance value obtained in step (2); R _ce is the electrochemical polarization internal resistance value of the power battery obtained in step (7.3) during the pulse charging process.

The embodiments are further described below with reference to the accompanying drawings.

The nominal capacity of a square aluminum shell lithium-ion power battery is 13Ah, the nominal voltage is 3.8V, and the discharge cut-off voltage is 3.2V. Now the internal resistance composition of the power battery at 90% SOC state is tested and analyzed. The test process is at room temperature. Completed below, the flow chart is shown in Figure 1.

First, the battery was discharged to 3.2V at a constant current rate of 1C (ie, a current of 13A), and then charged to a SOC state of 90% at a rate of 1C after leaving it for 0.5 hours. After standing for 1 hour, measure and record the open circuit voltage value U _oc =4.250V, and use an AC resistance tester to test and record the AC internal resistance value R ₀ =0.0012Ω of the power battery.

Then, pulse discharge the power battery with a constant current of I ₁ =78A (equivalent to a rate of 6C) for 10 seconds, and record the change of the terminal voltage of the power battery with time during the discharge process at a fixed time interval of 0.0005 seconds to obtain the pulse discharge process. Terminal voltage time series {U _di }, put on hold for 40 seconds, measure and record the open-circuit voltage value U _od =3.876V at the end of the hold.

Next, charge the power battery with a constant current of I ₂ =39A (equivalent to a 3C rate) for 10 seconds, and record the change of the terminal voltage of the power battery with time during the charging process at a fixed time interval of 0.0005 seconds to obtain the pulse charging process. Terminal voltage time series {U _ci }.

Now begin to analyze the test data of the pulse discharge process.

First, based on the terminal voltage time series {U _di } in the pulse discharge process, each terminal voltage value is subtracted from the next terminal voltage value adjacent to it to obtain the terminal voltage difference time series {ΔU _di } in the pulse discharge process, where ΔU _di represents the ith terminal voltage difference in the time series of power battery terminal voltage difference during the pulse discharge process:

ΔU _di =U _di -U _d(i+1) (1)

Wherein, the first terminal voltage difference ΔU _d1 =U _d1 -U _d2 =4.052-4.002=0.040V is obtained by calculation.

Secondly, taking f=0.3, based on the time series of terminal voltage difference {ΔU _di } in the pulse discharge process, compare each terminal voltage difference with the first terminal voltage difference ΔU _d1 in sequence, and find that the sixth terminal voltage difference The voltage ΔU _d6 =0.0151V, which begins to satisfy the condition of ΔU _dk <fΔU _d1 , and the corresponding k value is 6.

Therefore, U _d6 = 3.826V is found from the terminal voltage time series {U _di } during the pulse discharge process, and the electrochemical polarization internal resistance value of the power battery during the pulse discharge process is calculated R _de =(U _oc -U _dk )/I ₁ -R ₀ =(4.250-3.826)/78-0.0012=0.0042Ω.

The last terminal voltage value U _dn = 3.72V in the power battery terminal voltage time series {U _di } during the pulse discharge process, so the concentration polarization internal resistance value of the power battery during the pulse discharge process is calculated R _dm = (U _oc -U _dn ) /I ₁ -R ₀ -R _de =(4.250-3.72)/78-0.0012-0.0042=0.0014Ω.

Therefore, the ohmic internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance of the tested power battery I ₁ =78A during constant current pulse discharge are 0.0012Ω, 0.0042Ω and 0.0014Ω, respectively.

Next, the test data of the pulse charging process is analyzed.

First, based on the terminal voltage time series {U _ci } in the pulse charging process, starting from the second terminal voltage value, each terminal voltage value is subtracted from the adjacent previous terminal voltage value to obtain the terminal voltage difference during the pulse charging process. Time series {ΔU _ci }, where ΔU _ci represents the ith terminal voltage difference in the time series of power battery terminal voltage difference during the pulse charging process:

ΔU _ci =U _c(i+1) −U _ci (4)

Wherein, the first terminal voltage difference ΔU _c1 =U _c2 -U _c1 =3.995-3.986=0.009V is obtained by calculation.

Secondly, take p=0.3, based on the time series of terminal voltage difference {ΔU _ci } in the pulse charging process, compare each terminal voltage difference with the first terminal voltage difference ΔU _c1 in sequence, and find that the tenth terminal The voltage ΔU _c10 =0.0021V, which begins to satisfy the condition of ΔU _cs <pΔU _c1 , and the corresponding s value is 10.

Therefore, U _c10 =4.068V is found from the terminal voltage time series {U _ci } during the pulse charging process, and the electrochemical polarization internal resistance value of the power battery during the pulse charging process is calculated R _ce =(U _cs -U _od )/I ₂ -R ₀ =(4.068-3.876)/39-0.0012=0.0037Ω.

The last terminal voltage value U _cn =4.118V in the power battery terminal voltage time series {U _ci } during the pulse charging process, so the concentration polarization internal resistance value of the power battery during the pulse charging process is calculated R _cm =R _cm =(U _cn - U _od )/I ₂ -R ₀ -R _ce =(4.118-3.876)/39-0.0012-0.0037=0.0013Ω.

Therefore, the ohmic internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance during the constant current pulse charging process of the tested power battery I ₂ =39A are 0.0012Ω, 0.0037Ω and 0.0013Ω, respectively.

The method for analyzing the internal resistance composition of a power battery based on the pulse discharge test provided in this embodiment performs conventional AC resistance and pulse charge-discharge tests on actual lithium-ion power battery products without relying on expensive and complicated instruments such as electrochemical workstations. It is simple and the measurement method is direct; according to the difference in the occurrence rate of the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance, which constitute the total internal resistance of the lithium-ion power battery, through the analysis of the rate of change of the terminal voltage, the The rapid drop (or rise) of the terminal voltage in a short period of time during the pulse discharge (or charge) process is regarded as the effect of the ohmic internal resistance and the electrochemical polarization internal resistance, and the change of the terminal voltage at the end of the pulse discharge is regarded as the total battery. The effect of internal resistance, and then the measured AC resistance value is used as the ohmic internal resistance value, so that the accurate values of the ohmic internal resistance, the electrochemical polarization internal resistance and the concentration polarization internal resistance can be obtained respectively through simple operations. , this scheme is scientific and reasonable, and has good stability; in the process of data analysis, for the time series of terminal voltage difference, compare each difference in the sequence with the first difference in order, and find that the difference changes from fast to slow The inflection point is taken as the starting point for the concentration polarization internal resistance to act, thus effectively distinguishing the sum of the ohmic internal resistance and the electrochemical polarization internal resistance from the concentration polarization internal resistance. The computational complexity is small but simple and effective.

To sum up, the above embodiments constitute an analysis method for the internal resistance of a power battery based on a pulse charge-discharge test. The method of the above embodiment includes adjusting to the SOC value required to be tested, testing the AC internal resistance value, discharging with a constant current pulse and obtaining a time series of terminal voltage during the pulse discharge process, shelving, charging with a constant current pulse and obtaining the terminal voltage during the pulse charging process. Time series and analysis of the time series of the upper end voltage to obtain the electrochemical polarization internal resistance value and the concentration polarization internal resistance value of the power battery during the pulse discharge and charging process respectively. The above embodiment method uses simple and convenient steps to obtain the ohmic internal resistance, electrochemical polarization internal resistance and concentration polarization internal resistance that constitute the internal resistance of the power battery. The method is scientific and reasonable, has good stability and does not depend on expensive and complicated. instrument.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and various changes can also be made according to the purpose of the invention and creation of the present invention. Changes, modifications, substitutions, combinations or simplifications should be equivalent substitution methods, as long as they meet the purpose of the present invention, as long as they do not deviate from the technical principles and inventive concepts of the present invention, all belong to the protection scope of the present invention.

Claims (2)

1. a power battery internal resistance composition analysis method based on pulse charge-discharge test, is characterized in that, operating steps are as follows: (1), charge and discharge the power battery, adjust to the SOC value required to be tested, and leave it aside for 1 hour ± 1 minute, measure and record the open circuit voltage value U _oc ; (2), use the AC resistance tester to test, and record the AC internal resistance value R ₀ of the power battery; (3) Discharge the power battery with a constant current pulse of I ₁ for 10 seconds ± 0.5 seconds, and record the change of the power battery terminal voltage with time during the discharge process at a fixed time interval of Δt to obtain the pulse discharge process terminal voltage time series {U _di }, where I ₁ is the current value corresponding to the rate of 1C to 10C, Δt is not greater than 0.001 seconds, and U _di represents the ith terminal voltage value in the power battery terminal voltage time series during the pulse discharge process; (4), put the power battery on hold for 40 seconds ± 1 second, measure and record the open-circuit voltage value U _od at the end of the putting aside; (5) Charge the power battery with a constant current pulse of I ₂ for 10 seconds ± 0.5 seconds, and record the change of the power battery terminal voltage with time during the charging process at a fixed time interval of Δt, and obtain the pulse charging process terminal voltage time series {U _ci }, where I ₂ is the current value corresponding to the rate of 1C to 5C, Δt is not greater than 0.001 seconds, and U _ci represents the ith terminal voltage value in the time series of terminal voltages during the pulse charging process; (6) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _di } obtained in the pulse discharge process obtained in step (3), and obtain the electrochemical polarization internal resistance value R of the power battery in the pulse discharge process _de and concentration polarization internal resistance R _dm ; (7) Combine the AC internal resistance value R ₀ obtained in step S2, analyze the terminal voltage time series {U _ci } obtained in step (5) during the pulse charging process, and obtain the electrochemical polarization internal resistance value R of the power battery during the pulse charging process _ce and concentration polarization internal resistance R _cm ; The concrete operation steps of described step (6): (6.1) Based on the terminal voltage time series {U _di } in the pulse discharge process, each terminal voltage value is subtracted from the next terminal voltage value adjacent to it to obtain the terminal voltage difference time series {ΔU _di } in the pulse discharge process, Among them, ΔU _di represents the ith terminal voltage difference in the time series of power battery terminal voltage difference during the pulse discharge process: ΔU _di =U _di -U _d(i+1) (1) (6.2) Based on the time series {ΔU _di } of the terminal voltage difference during the pulse discharge process, compare each terminal voltage difference with the first terminal voltage difference ΔU _d1 in sequence, until the first satisfying ΔU _dk <fΔU is obtained. The k-th terminal voltage difference ΔU _dk for the condition of _d1 and record the k value, where f is a fixed value between 0.1 and 0.5; (6.3), calculate the electrochemical polarization internal resistance R _de of the power battery during the pulse discharge process: R _de =(U _oc -U _dk )/I ₁ -R ₀ (2) In the formula, U _oc represents the open-circuit voltage value obtained in step (1); U _dk represents the k-th terminal voltage value in the power battery terminal voltage time series during the pulse discharge process, and the k value is obtained in step (6.2); I ₁ is step (3) ) in the pulse discharge current value; R ₀ is the AC internal resistance value obtained in step (2); (6.4), calculate the concentration polarization internal resistance value R _dm of the power battery during the pulse discharge process: R _dm =(U _oc -U _dn )/I ₁ -R ₀ -R _de (3) In the formula, U _oc represents the open-circuit voltage value obtained in step (1); U _dn represents the last terminal voltage value in the power battery terminal voltage time series during the pulse discharge process; I ₁ is the pulse discharge current value in step (3); R ₀ is the AC internal resistance value obtained in step (2); R _de is the electrochemical polarization internal resistance value of the power battery obtained in step (6.3) during the pulse discharge process. 2. the power battery internal resistance composition analysis method based on pulse charge-discharge test according to claim 1, is characterized in that, the concrete operation steps of described step (7): (7.1) Based on the terminal voltage time series {U _ci } in the pulse charging process, starting from the second terminal voltage value, subtract the adjacent previous terminal voltage value from each terminal voltage value to obtain the terminal voltage during the pulse charging process. Difference time series {ΔU _ci }, where ΔU _ci represents the ith terminal voltage difference in the power battery terminal voltage difference time series during the pulse charging process: ΔU _ci =U _c(i+1) −U _ci (4) (7.2) Based on the time series {ΔU _ci } of the terminal voltage difference during the pulse charging process, compare each terminal voltage difference with the first terminal voltage difference ΔU _c1 in sequence, until the first ΔU _cs < pΔU is obtained. The sth terminal voltage difference ΔU _cs of the condition of _c1 and record the s value, where p is a fixed value between 0.1 and 0.5; (7.3), calculate the electrochemical polarization internal resistance R _ce of the power battery during the pulse charging process: R _ce = (U _cs -U _od )/I ₂ -R ₀ (5) In the formula, U _od represents the open-circuit voltage value obtained in step (4); U _cs represents the s-th terminal voltage value in the power battery terminal voltage time series during the pulse charging process, and the s value is obtained in step (7.2); I ₂ is step (5) ) in the pulse charging current value; R ₀ is the AC internal resistance value obtained in step (2); (7.4), calculate the concentration polarization internal resistance value R _cm of the power battery during the pulse charging process: R _cm = (U _cn -U _od )/I ₂ -R ₀ -R _ce (6) In the formula, U _od represents the open-circuit voltage value obtained in step (4); U _cn represents the last terminal voltage value in the power battery terminal voltage time series during the pulse charging process; I ₂ is the pulse charging current value in step (5); R ₀ is the AC internal resistance value obtained in step (2); R _ce is the electrochemical polarization internal resistance value of the power battery obtained in step (7.3) during the pulse charging process.

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