A lithium titanate battery power testing method

Abstract

The application discloses a lithium titanate battery power test method and belongs to the technical field of battery performance test. The method solves the problem that the existing battery power density test method cannot be applied to the continuous pulse power discharge working condition. The application comprises the following steps: based on the HPPC method, adjusting the pulse discharge test time to 18s, standing for 40s-5min, and subtracting the 18s discharge cutoff voltage from the voltage after standing; alternately charging or discharging the battery in the test, discharging for 10s, charging to the capacity consistent with that before discharging, recording the voltage, and calculating the power capacity; calculating the power change curve at different discharge times; the internal resistance obtained by the test presents a trend of first increasing and then decreasing with the increase of the discharge time, which is affected by the cell polarization and temperature rise; the JEVS method is used to obtain the maximum charging or discharging current; and the power verification of the final result is performed. The application is used for the battery power density test under the continuous pulse power discharge working condition.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery performance test, and particularly relates to a lithium titanate battery power test method. BACKGROUND

[0002] With the continuous development of the new energy industry, higher requirements are put forward for the high power and high energy of power lithium ion batteries. The parameters such as the charging and discharging power of the lithium ion power battery, which affect the safe use, need to be accurately measured and input to the BMS for control. If the power parameters are not clear, it may lead to the use of super battery design power, thereby causing the battery to be overcharged or overdischarged. If the power is directly verified, it may cause the battery to be damaged.

[0003] In addition, there are various methods for testing the power density of lithium ion batteries:

[0004] (1) Average power method, that is, the energy released per unit time, P = E / t, but the discharge time is short at high rate, and the error is large. This method is limited by the accuracy of the test equipment and the sampling frequency;

[0005] (2) The power density test method of the U.S. FreedomCAR project (referred to as HPPC method), in which the battery is tested by the HPPC method to calculate the discharge internal resistance Rdis through a 10s pulse charge-discharge test, the maximum discharge current is Imax = (UOC-Umin) / Rdis, and the discharge power Pmax = Umin x Idmax, wherein UOC is the open circuit voltage, Umin is the minimum voltage, and Pmax is the maximum power;

[0006] (3) The power density test method of the Japan Electric Vehicle Society (referred to as JEVS method), in which the test current and voltage curve is obtained by alternately charging 10s and discharging 10s at different rates under 0-100% state of charge (SOC), and the maximum discharge current corresponding to the cutoff voltage at the SOC is obtained by fitting, Pmax = Udis-cutoff x Idmax, and Udis-cutoff is the discharge cutoff voltage;

[0007] (4) 2s pulse discharge method, in which the battery is charged to the cutoff voltage with a 1C current, then discharged with different currents for 2s, and the maximum current Idmax and the product of the voltage at the end of 2s Pmax = U2s x Idmax are calculated, and U2s is the voltage at the end of 2s;

[0008] (5) Peak power method, in which the peak power density Pmax = U15 ms x Idmax is obtained when the current from 0A increases to the set current value, and the voltage at the end of 15ms U15 ms is the voltage at the end of 15ms.

[0009] The traditional HPPC method is mainly designed for the pulsed operating conditions commonly used in electric vehicles. However, it may not be applicable to continuous pulsed power discharge conditions, resulting in inaccurate power values ​​obtained from the test. Summary of the Invention

[0010] The purpose of this invention is:

[0011] To address the issue that the existing HPPC method for testing battery power density is not applicable to continuous pulse power discharge conditions, a power testing method for lithium titanate batteries is provided.

[0012] The technical solution adopted in this invention is as follows:

[0013] A method for testing the power of a lithium titanate battery includes the following steps:

[0014] A. Based on the HPPC method, adjust the pulse discharge test time to 18s, let it stand for 40s to 5min, and subtract the discharge cutoff voltage after 18s from the voltage after standing. The formula is as follows:

[0015] Discharge power capability = V min ×(V OC,dis -V min ) / R dis ;

[0016] Charging power capability = V max ×(V max -V OC,cha ) / R cha ;

[0017] R dis =-(V t1 -V t0 ) / (I t1 -I t0 );

[0018] R cha =(V t3 -V t2 ) / (I t3 -I t2 );

[0019] In the formula:

[0020] V max V min This is the operating voltage that will be cut off during charging or discharging.

[0021] V OC,cha V OC,dis V is the open-circuit voltage of the corresponding SOC before charging or discharging. OC,cha ≠V OC,dis ;

[0022] R cha 、R dis R is the internal resistance of the corresponding SOC charging or discharging;

[0023] V t0 V is the voltage before discharging, V t1 V is the voltage at the end of discharging, V t2 V is the voltage before charging at the end of the rest after discharging, V t3 V is the voltage at the end of charging;

[0024] I t0 I is the current before discharging, I t1 I is the current at the end of discharging, I t2 I is the current before charging at the end of the rest after discharging, I t3 I is the current at the end of charging;

[0025] B, high and low rate currents are used in the test, the high rate discharging current is 15C, the low rate discharging current is 5C, at the state of charge intervals of 10% DOD, the battery is alternately charged or discharged with a current ratio of Ieha / Iis=0.75, the discharging time is 10s, the battery is charged to the capacity consistent with that before discharging, the battery charging or discharging voltage is recorded during the test, and the battery charging or discharging internal resistance and charging or discharging power capability are calculated by the formula of step A;

[0026] C, the JEVS method is used to calculate the power change curve at different discharging times, and the continuous discharging power is obtained;

[0027] D, the internal resistance obtained by the test increases first and then decreases with the increase of the discharging time, which is affected by the polarization and temperature rise of the battery cell;

[0028] E, the JEVS method is used to obtain the maximum charging or discharging current;

[0029] F, the final result is verified.

[0030] Further, the method for obtaining the continuous discharging power in step C is that if the discharging time is between 10s and 30s, the discharging power gradually decreases with the increase of the discharging time, when the discharging time is > 30s, the discharging power remains unchanged, then the 30s discharging power is finally determined as the continuous discharging power.

[0031] Further, the test method in step E is that the test capacities are 90%, 70%, 50%, 30%, 20% and 10%, respectively, discharging for 40s, resting for 5min, and testing static 1C, 5C, 10C, 20C, 25C, 30C discharging; charging tests 90% soc 1C charging; 70% soc 2C charging, and the charging capacity is sequentially corresponding to the discharging rate.

[0032] Therefore, by adopting the technical scheme, the application has the beneficial effects:

[0033] The application changes the working condition on the basis of the HPPC method, tests the charge-discharge power capability and internal resistance of the battery, obtains the power variation curve at different discharge times, and then calculates the power and internal resistance variation curve through the JEVS method, so as to analyze the power under the continuous discharge working condition, thereby overcoming the technical defect that the method in the prior art cannot accurately obtain the battery power under the continuous discharge, and the result is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a test flow parameter diagram under the typical test procedure of the HPPC method;

[0035] Figure 2 is a discharge power parameter diagram varying with the discharge time of the application;

[0036] Figure 3 is an internal resistance parameter diagram varying with the discharge time of the application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the application more clear and understandable, the application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0038] A lithium titanate battery power testing method, comprising the following steps:

[0039] A、The application is based on the HPPC typical test method as shown in Figure 1 , and combines the power and internal resistance test method in GB31467, adjusts the pulse discharge test time to 18s, and rests for 40s to 5min, preferably, the resting time can be 40s, 50s, 1min, 2min, 3min, 4min or 5min;

[0040] Subtract the 18s discharge cutoff voltage from the voltage after resting, and the formula is as follows:

[0041] Discharge power capability = V min ×(V OC,dis -V min ) / R dis ;

[0042] Charging power capability = V max ×(V max -V OC,cha ) / R cha ;

[0043] R dis = -(V t1 -V t0 ) / (I t1 -I t0 );

[0044] R cha =(V t3 -V t2 ) / (I t3 -I t2 );

[0045] In the formula:

[0046] V max , V min are the charging or discharging cut-off operating voltage;

[0047] V OC,cha , V OC,dis are the open-circuit voltage of the corresponding SOC before charging or discharging, V OC,cha ≠ V OC,dis ;

[0048] R cha , R dis are the internal resistance of the corresponding SOC charging or discharging;

[0049] V t0 is the voltage before discharging, V t1 is the voltage at the end of discharging, V t2 is the voltage after discharging and before charging, and V t3 is the voltage at the end of charging;

[0050] I t0 is the current before discharging, I t1 is the current at the end of discharging, I t2 is the current after discharging and before charging, and I t3 is the current at the end of charging;

[0051] B. In the test, high and low rate currents are used, the high rate discharging current is 15C, and the low rate discharging current is 5C. At the state of charge intervals of 10% DOD, the battery is alternately charged or discharged at a current ratio of Ieha / Iis=0.75. The discharging time is 10s, and the charging is carried out to the same capacity as before discharging. The battery charging or discharging voltage is recorded during the test. The battery charging or discharging internal resistance and charging or discharging power capability are calculated by the formula of step A;

[0052] C. The JEVS method is used to calculate the power change curve at different discharging times, and the continuous discharging power is obtained;

[0053] D, the internal resistance obtained by the test increases first and then decreases with the increase of the discharge time, which is the influence of the cell polarization and temperature rise;

[0054] E, the maximum charging or discharging current is obtained by using the JEVS method;

[0055] F, the power verification of the final result is carried out.

[0056] Preferably, the method for obtaining the continuous discharge power in step C is that if the discharge time is between 10s and 30s, the discharge power gradually decreases with the increase of the discharge time, when the discharge time is greater than 30s, the discharge power remains unchanged, then the 30s discharge power is finally determined as the continuous discharge power.

[0057] Preferably, the test method in step E is that the static 1C, 5C, 10C, 20C, 25C and 30C discharges are tested respectively under the conditions of 90%, 70%, 50%, 30%, 20% and 10% of the test electric quantity, discharging for 40s, standing for 5min, and then charging is tested, 90% soc 1C charging and 70% soc 2C charging are tested respectively, and the charging capacity is corresponded to the discharge rate.

[0058] The application changes the working condition on the basis of the HPPC method, tests the charging and discharging power capacity and internal resistance of the battery, obtains the power change curve of different discharge times, and then calculates the power and internal resistance change curve through the JEVS method, so as to analyze the power under the continuous discharge condition, overcomes the technical defects that the method in the prior art cannot accurately obtain the battery power under the continuous discharge, and the result is more accurate.

[0059] The above only describes the preferred embodiments of the application and is not used to limit the application, any modification, equivalent replacement and improvement made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method of testing the power of a lithium titanate battery, characterized by, It comprises the following steps: A. Based on the HPPC method, the pulse discharge test time is adjusted to 18 s, and the voltage after standing for 40 s to 5 min is subtracted from the 18 s discharge cutoff voltage, and the formula is as follows: Discharge power capability = V min x (V OC,dis - V min ) / R dis ; Charging power capability = V max x (V max - V OC,cha ) / R cha ; R dis = -(V t1 -V t0 ) / (I t1 -I t0 ); R cha = (V t3 -V t2 ) / (I t3 -I t2 ); In the formula: V max , V min Vcharge or discharge cut-off operating voltage; V OC,cha , V OC,dis OCV of the corresponding SOC before charging or discharging, V OC,cha ≠ V OC,dis ; R cha , R dis internal resistance of charging or discharging the respective SOC; V t0 Vpre is the voltage before discharge t1 Vend is the voltage at the end of discharge t2 Vpost is the voltage after discharge and before rest t3 Vend is the voltage at the end of charge I t0 is the current before discharge, I t1 is the current at the end of discharge, I t2 is the current at the end of rest after discharge, I t3 is the current at the end of charge; B. In the test, high and low rate currents are used, the high rate discharge current is 15C, and the low rate discharge current is 5C. At the charge states with intervals of 10% DOD, the battery is alternately charged or discharged at a current ratio of Ieha / Iis=0.75, the discharge time is 10 s, and the battery is charged to the same capacity as before discharge. The battery charging or discharging voltage is recorded during the test, and the battery charging or discharging internal resistance and charging or discharging power capability are calculated by the formula in step A; C. The JEVS method is used to calculate the power change curve at different discharge times to obtain the continuous discharge power; D. The internal resistance obtained by the test increases first and then decreases with the increase of the discharge time, which is affected by the polarization and temperature rise of the battery; E. The JEVS method is used to obtain the maximum charging or discharging current; F. The final result is verified by power.

2. The method of claim 1, wherein, The method for obtaining the continuous discharge power in step C is that if the discharge time is between 10 s and 30 s, the discharge power gradually decreases with the increase of the discharge time, and when the discharge time is > 30 s, the discharge power remains unchanged, then the 30 s discharge power is finally determined as the continuous discharge power.

3. The method of claim 1, wherein the lithium titanate battery power test is performed by: The test method in step E is that the test capacity is 90%, 70%, 50%, 30%, 20% and 10%, respectively, and the static 1C, 5C, 10C, 20C, 25C and 30C discharges are tested after discharging for 40 s and standing for 5 min. The charging test is 90% soc 1C charging and 70% soc 2C charging, and the charging capacity is corresponding to the discharge rate in turn.

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