A method for testing the composite pulse power of a lithium battery

Abstract

The present invention discloses a method for testing the composite pulse power of a lithium battery, comprising the following steps: Step 1, preset the charging current as I ch0 , and the discharging current as I dis0 , and perform charging and discharging tests on the lithium battery using the HPPC test method; Step 2, execute Step 1 at preset different temperatures T to obtain a T-SOC-Imax table; Step 3, perform cumulative difference processing on the T-SOC-Imax table data, let ΔIi = |Ii - I0|, i ∈ N, to obtain a T-SOC-ΔIi table; Step 4, correct Δi to obtain a corrected T-SOC-I’max table; Step 5, perform charging and discharging tests on the lithium battery using the HPPC test method with the corrected charging and discharging currents; Step 6, execute Step 5 at preset different temperatures T to obtain a T-SOC-P’max table. The entire test process of the present invention is relatively simple and easy to implement compared to JEVS, and reduces the errors of traditional HPPC in the low SOC discharge and high SOC charge regions.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly relates to a method for testing the composite pulse power of a lithium battery. Background Art

[0002] With the soaring international oil prices, HEV, PHEV, and BEV have been highly pursued by people for their cleanliness and economy. In 2021, the production and sales of new energy vehicles were 3.545 million and 3.521 million respectively, and the market share continued to rise. Lithium batteries are widely used in new energy vehicles due to their high energy density and excellent power performance. Among the technologies in the new energy field, the most challenging one is the SOP algorithm, which is related to factors such as driving range, energy feedback ability, and service life. Among them, the SOP power ability belongs to real-time feedback data, especially for hybrid vehicles, and the requirement for data accuracy is very high.

[0003] Currently, the main methods for testing the power of lithium batteries are the Hybrid Pulse Power Characterization (HPPC) method based on the FreedomCAR standard, the JEVS battery peak power density test method, and the constant current charge and discharge test method at a fixed time. Each of these three methods has its own advantages and disadvantages. The HPPC test includes discharge pulses and charge pulses. By charging and discharging at a certain current to the cut-off voltage within a fixed time, a U-I-t graph is obtained, and then R, Imax, and Pmax can be derived through formulas.

[0004] Its entire test process is relatively simple and the test efficiency is high. However, since the HPPC tests with a fixed charge and discharge current, and the DCR of the battery has a non-linear relationship with I in different SOC dimensions, especially in the high SOC range during charging and the low SOC range during discharge, the DCR will increase sharply, which results in the measured results changing with the change of the I value and does not conform to the output mode of the battery under actual complex working conditions.

[0005] The JEVS test method measures the voltage value within the cut-off time by changing the value of I within a fixed time. Taking I as the abscissa and U as the ordinate, a U-I graph is obtained. The U-I curve is fitted by the linear interpolation method to obtain the I corresponding to the cut-off voltage, which is Imax. Although this method can obtain relatively accurate data, the test process is extremely complex and requires testing multiple groups of currents. Moreover, since the DCR changes during the process, the relationship between U and I is not linear, which is prone to fitting errors.

[0006] The timed constant current charge-discharge method selects different currents to charge and discharge until the cut-off voltage, obtains the I-t relationship diagram, and performs non-linear fitting to obtain Imax within a fixed time. Although the timed constant current method avoids the path of deriving Imax from DCR, like the JEVS method, this method also has the drawback of complex processes. Moreover, compared with the JEVS method, this method has certain requirements for the selection of the I value range; otherwise, there is a fitting uncertainty and a risk of serious deviation.

[0007] Therefore, there is an urgent need to innovate a set of simple and reliable test methods to solve all the above problems. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to implement a simple and reliable composite pulse power test method for lithium batteries.

[0009] To achieve the above object, the technical solution adopted by the present invention is: a composite pulse power test method for lithium batteries, including the following steps:

[0010] Step 1: Preset the charging current as I ch0 , and the discharge current as I dis0 , and use the HPPC test method to conduct charging and discharging tests on the lithium battery;

[0011] Step 2: Execute Step 1 at preset different temperatures T to obtain the T-SOC-Imax table;

[0012] T-SOC-Imax: A two-dimensional matrix table of the maximum current with respect to the temperature T and SOC.

[0013] Record the maximum current Imax corresponding to the temperature T and the corresponding SOC;

[0014] Step 3: Perform cumulative difference processing on the T-SOC-Imax table data, let ΔIi = |Ii - I0|, i ∈ N, to obtain the T-SOC-ΔIi table;

[0015] I0 is the maximum initial current value corresponding to 10% SOC at each temperature;

[0016] Ii is the maximum initial current value corresponding to different temperatures and different SOCs;

[0017] ΔIi is the difference between the above two values, simply referred to as the current difference;

[0018] i is a subscript number representing each data in the table; it can be written as I.

[0019]

[0020] T-SOC-ΔIi: A two-dimensional matrix table of the current difference with respect to the temperature T and SOC.

[0021] Record the current difference ΔIi corresponding to the temperature T and the corresponding SOC.

[0022]

[0023] Step 4: Correct Δi to obtain the corrected T-SOC-I’max table;

[0024] Δi is ΔIi in the T-SOC-ΔIi two-dimensional chart.

[0025] Step 5: Use the corrected charge and discharge current to conduct charge and discharge tests on the lithium battery using the HPPC test method;

[0026] Step 6: Execute Step 5 at different preset temperatures T to obtain the T-SOC-P’max table.

[0027] In the said Step 1, during charging, SOC = [0% 10% 20% 30% 40% 50% 60% 70% 80% 90%], and during discharging, SOC = [10% 20% 30% 40% 50% 60% 70% 80% 90% 100%].

[0028] In the said Step 1, the I dis0 is set to n times the capacity value, with a value of nC, and I ch0 is 0.75I dis0 , with a value of 0.75nC, where n ∈ R and R > 0.

[0029] In the said Step 1, the charging upper limit voltage is set to Umax, and the discharging lower limit voltage is set to Umin.

[0030] In the said Step 2, the preset different temperatures T adopt a temperature matrix, T = [T1 T2 T3... Tn], and the temperature difference between each temperature is 10°C;

[0031] The SOC matrix is set to SOC = [SOC1 SOC2 SOC3... SOCn], SOC1 = 0%, SOCn = 100%, and the difference between each SOC is 10%.

[0032] In the said Step 2, the calculation methods of R ch , R dis , I chmax , and I dismax are as follows:

[0033] R ch = (U0 - U1) / I ch ;

[0034] R dis = (U3 - U4) / I dis ;

[0035] I chmax =(Umax - Uocv) / R ch ;

[0036] I dismax =(Uocv - Umin) / R dis 。

[0037] In step 4, the correction method for Δi: if Δi ≤ 1C, then Δi = 0; if Δi > 1C, then the value of Δi remains unchanged. Replace the Ii value corresponding to Δi with I0 in step 3, and loop like this until the SOC boundary to obtain the repaired T - SOC - Δi' table. Where Ii = Δi' + I0, then the corrected T - SOC - I'max table is obtained.

[0038] 1C represents the current magnitude, and T represents the temperature.

[0039] In step 5, during charging, i0 is the current value at SOC = 90%, and during discharging, it is the current value at SOC = 10%.

[0040] In step 6, the preset different temperatures T adopt a temperature matrix, T = [T1 T2 T3... Tn], and the temperature difference between each is 10°C;

[0041] The SOC matrix is set as SOC = [SOC1 SOC2 SOC3... SOCn], SOC1 = 0%, SOCn = 100%, and the difference between each SOC is 10%.

[0042] In step 6, calculate the P value according to the HPPC power calculation method. Record the time t under each T - SOC dimension during the process. Let x = t / t0, where t0 is the pulse time in the HPPC test method in step 1. Then the corrected Pmax = P * t / t0, and the T - SOC - P'max table is obtained.

[0043] In step 6, P chmax 、P dismax The calculation methods are as follows:

[0044] R ch =(U0 - U1) / I ch ;

[0045] R dis =(U3 - U4) / I dis ;

[0046] P chmax =(Umax - Uocv)*Umax*t / (Rch*t0);

[0047] P dismax=(Uocv - Umin) * Umin * t / (Rdis * t0).

[0048] The parameters collected in the T - SOC - Δi’ table are T - SOC - Δi, and the parameters collected in the T - SOC - I’max are T - SOC - Δii. Both are used to record the corrected current values corresponding to the temperature T and the SOC, as shown in the following table:

[0049]

[0050] The P value represents the P power, the T - SOC dimension represents the relationship between temperature and SOC values, the time t is the time for constant - current discharge to the cut - off voltage, X is the correction factor, and Pmax is the maximum power.

[0051]

[0052] The power test method of the present invention first performs prior processing on the maximum current of each temperature and SOC interval with a certain I0 value to obtain an approximate maximum value I1, and then uses the approximate maximum value I1 to perform the HPPC test. The entire test process is relatively simple and easy to implement compared to JEVS, and reduces the errors of traditional HPPC in the low - SOC discharge and high - SOC charge regions. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The following briefly describes the content expressed in each drawing in the specification of the present invention:

[0054] Figure 1 is the flowchart of the composite pulse power test method for lithium batteries;

[0055] Figure 2 is the U - I - t diagram of the HPPC part in the first step of Example 1;

[0056] Figure 3 is the U - I - t diagram of the pulse discharge part in the fifth step of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0057] The following, with reference to the drawings, through the description of the embodiments, further details are given on the specific implementation manners of the present invention, such as the shapes, structures of the various components involved, the mutual positions and connection relationships between the various parts, the functions and working principles of each part, the manufacturing process, and the operation and use methods, to help those skilled in the art have a more complete, accurate, and in - depth understanding of the inventive concept and technical solutions of the present invention.

[0058] The present invention provides a method for testing the composite pulse power of a lithium battery. The method aims to first perform prior processing on the maximum current in each temperature and SOC range using a certain I0 value to obtain an approximate maximum value Imax, and then use the approximate maximum value Imax to perform an HPPC test (the HPPC test is a characteristic test used to reflect the pulse charge and discharge performance of a power battery), and perform correction processing on the test results. The method for testing the composite pulse power of the lithium battery in the present invention solves the problem that the traditional HPPC test method cannot accurately estimate Pmax due to the deviation in I selection in different temperature and SOC ranges, and can also solve the problem that the traditional JEVS process is complex and prone to overfitting due to problems with I selection and calculation methods.

[0059] The vehicle output mode generally refers to constant power output within a certain period of time. Then, at any moment Pτ = Iτ * Uτ, where τ ∈ (0, t). Therefore, the problem is simplified to obtaining Pτ at any moment as Pmax. According to the HPPC power expression P = |Uocv - U 截止 | / R * U 截止 , Uocv is the thermodynamic equilibrium electromotive force, which conforms to the Nernst equation E = Eθ - RT / nF ln J. Therefore, Uocv is only related to the reactant concentration (C suf / C max = SOC) and temperature. After specifying the charge and discharge cut-off voltages, the power P is only related to the DC internal resistance R. R satisfies Δu / ΔI for U (ordinate) and I (abscissa) at τ ∈ (0, t). The principle of JEVS is to obtain the mathematical expectation of Δu / ΔI (DC internal resistance) in the time range of 0 - t by testing the relationship between different currents and voltages, and then obtain the current value I0 at the U cut-off moment, that is, calculate Pmax. From the above derivation, it can be seen that HPPC is a special value when the JEVS test current is only I.

[0060] Based on the above theory, the method for testing the composite pulse power of a lithium battery is as follows:

[0061] 1) Adopt the HPPC test method, with the charging current being I ch0 , and the discharging current being I dis0 , to conduct charging and discharging tests on the lithium battery. The HPPC test is carried out at different temperatures respectively. The temperature matrix is set as T = [T1 T2 T3... Tn], with the unit being °C, and the temperature difference between each temperature is 10 °C;

[0062] The SOC matrix is set as SOC = [SOC1 SOC2 SOC3... SOCn], SOC1 = 0%, SOCn = 100%, and the difference between each SOC is 10%;

[0063] During charging, SOC = [0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%]; during discharging, SOC = [10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%];

[0064] I dis0 Set to n times the capacity (ah) value, i.e., nC, I ch0 Is 0.75I dis0 , i.e., 0.75nC, where n ∈ R, R > 0;

[0065] Set the charging upper limit voltage to Umax and the discharging lower limit voltage to Umin;

[0066] Among them, the calculation formulas for Rch, Rdis, Ichmax, and Idismax are as follows:

[0067] Rch = (U0 - U1) / Ich;

[0068] Rdis = (U3 - U4) / Idis;

[0069] Ichmax = (Umax - Uocv) / Rch;

[0070] Idismax = (Uocv - Umin) / Rdis;

[0071] 2) Perform cumulative difference processing on the T-SOC-Imax tabular data, let ΔIi = Ii - I0, i ∈ N, to obtain a T-SOC-ΔIi two-dimensional chart;

[0072] 3) Correct ΔIi, the rules are as follows. If -1C ≤ ΔIi ≤ 1C, then ΔIi = 0. If ΔIi > 1C or ΔIi < -1C, then the value of ΔIi remains unchanged. Replace the Ii value corresponding to ΔIi with I0 in the second step, and so on until the SOC boundary to obtain the repaired T-SOC-ΔIi', where Ii = ΔIi' + I0, and calculate to obtain the corrected T-SOC-I'max two-dimensional table;

[0073] 4) Adopt the HPPC test method, use the corrected charge and discharge currents in the third step to conduct charge and discharge tests on the lithium battery, calculate the P value according to the HPPC power calculation method, record the time t under each T-SOC dimension during the process, let x = t / t0, where t0 is the HPPC pulse time in the first step, then the corrected Pmax = P * t / t0, and obtain the T-SOC-Pmax two-dimensional table.

[0074] During charging, i0 is the current value when SOC = 90%; during discharging, it is the current value when SOC = 10%;

[0075] This HPPC test step is carried out at different temperatures. The temperature T, SOC values are the same as those in 1), and the charge and discharge cut-off voltages are also the same as those in 1). The temperature matrix is set as T = [T1 T2 T3... Tn], with the unit of °C, and the temperature difference between each is 10 °C; the SOC matrix is set as SOC = [SOC1 SOC2 SOC3... SOCn], SOC1 = 0%, SOCn = 100%, and the difference between each SOC is 10%.

[0076] The calculation formulas for Pchmax and Pdismax are as follows:

[0077] Rch = (U0 - U1) / Ich;

[0078] Rdis = (U3 - U4) / Idis;

[0079] Pchmax = (Umax - Uocv)*Umax*t / (Rch*t0);

[0080] Pdismax = (Uocv - Umin)*Umin*t / (Rdis*t0).

[0081] The explanations of some terms are as follows:

[0082] Rch: Charging internal resistance;

[0083] Ich: Charging current;

[0084] Rdis: Discharging internal resistance;

[0085] Idis: Discharging current;

[0086] Ichmax: Maximum charging current;

[0087] Idisma→Idismax: Maximum discharging current;

[0088] Umax: Charging cut-off voltage;

[0089] Umin: Discharging cut-off voltage;

[0090] Uocv: Static voltage;

[0091] Pchmax: Maximum charging power;

[0092] Pdismax: Maximum discharging power;

[0093] t: Charge and discharge time before current correction;

[0094] t0: Charge and discharge time after current correction.

[0095] The present invention has been described by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for testing the composite pulse power of a lithium battery, characterized in that, It includes the following steps: Step 1. Preset the charging current as I ch0 , and the discharging current as I dis0 , and conduct charging and discharging tests on the lithium battery using the HPPC test method; Step 2: Execute Step 1 at different preset temperatures T to obtain a T-SOC-Imax table; Step 3: Perform cumulative difference processing on the T-SOC-Imax table data, let ΔI i = |I i - I0|, i ∈ N, to obtain a T-SOC-ΔI i table; Step 4: Correct Δi to obtain a corrected T-SOC-I’max table; Step 5: Use the HPPC test method to charge and discharge the lithium battery with the corrected charge and discharge current; Step 6: Execute Step 5 at different preset temperatures T to obtain a T-SOC-P’max table; I0 is the maximum initial current value corresponding to 10% SOC at each temperature; I i is the maximum initial current value corresponding to different temperatures and different SOCs; ΔIi is the difference between the two values of I0 and Ii.

2. The lithium battery composite pulse power test method according to claim 1, wherein: In Step 1, during charging, SOC = [0% 10% 20% 30% 40% 50% 60% 70% 80% 90%], and during discharging, SOC = [10% 20% 30% 40% 50% 60% 70% 80% 90% 100%].

3. The lithium battery composite pulse power test method according to claim 2, wherein: In step 1, the I dis0 is set to n times the capacity value, with a value of nC. The I ch0 is 0.75I dis0 , with a value of 0.75nC, where n ∈ R and R > 0; In Step 1, the charging upper limit voltage is set to Umax, and the discharging lower limit voltage is set to Umin.

4. The lithium battery composite pulse power test method according to claim 1, 2 or 3, characterized in that: In Step 2, the different preset temperatures T adopt a temperature matrix, T = [T1 T2 T3... Tn], and the temperatures are separated by 10°C; The SOC matrix is set to SOC = [SOC1 SOC2 SOC3... SOCn], SOC1 = 0%, SOCn = 100%, and the SOCs are separated by 10%.

5. The lithium battery composite pulse power test method according to claim 1 or 4, characterized in that: In Step 4, the correction method of Δi: If Δi ≤ 1C, then Δi = 0; if Δi > 1C, then the value of Δi remains unchanged. Replace the I i value corresponding to Δi with I0 in Step 3, and loop until the SOC boundary to obtain a repaired T-SOC-Δi’ table. Where I i = Δi’ + I 0, then a corrected T-SOC-I’max table is obtained.

6. The lithium battery composite pulse power test method according to claim 5, wherein: In Step 5, during charging, i0 is the current value when SOC = 90%, and during discharging, it is the current value when SOC = 10%.

7. The lithium battery composite pulse power test method according to claim 6, wherein: In Step 6, the different preset temperatures T adopt a temperature matrix, T = [T1 T2 T3... Tn], and the temperatures are separated by 10°C; The SOC matrix is set to SOC = [SOC1 SOC2 SOC3... SOCn], SOC1 = 0%, SOCn = 100%, and the SOCs are separated by 10%.

8. The lithium battery composite pulse power test method according to claim 7, characterized in that: In Step 6, calculate the P value according to the HPPC power calculation method. Record the time t under each T-SOC dimension during the process, let x = t / t0, where t0 is the pulse time in the HPPC test method in Step 1. Then the corrected Pmax = P * t / t0 to obtain a T-SOC-P’max table.

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