A method for analyzing the consistency of lithium batteries

Abstract

A method for analyzing the consistency of lithium batteries belongs to the technical field of lithium battery analysis. The present invention comprises the following steps: step S1, removing batteries with capacity exceeding the range, and pre-dividing into n groups in sequence according to the capacity of all remaining batteries; step S2, measuring the synthetic impedance and polarization voltage of all remaining batteries, and removing batteries with at least one value exceeding the range; step S3, respectively calculating the median value of the synthetic impedance and the median value of the polarization voltage in each group of batteries; step S4, dividing the batteries in each group whose synthetic impedance and polarization voltage are both greater than the median value into a group with a larger capacity, and dividing the batteries in each group whose synthetic impedance and polarization voltage are both less than the median value into a group with a smaller capacity, so as to form at most n+2 groups of batteries. The present invention can comprehensively consider various factors, rationally sort and match groups, and maximize the performance of batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery analysis, and in particular to a method for analyzing the consistency of a lithium battery. Background Art

[0002] In recent years, lithium-ion batteries have made great progress in the field of power batteries and energy storage, and one of the main factors affecting their endurance is the inconsistency of battery production. Especially in the use of power batteries, batteries need to be used in groups. When there are differences in capacity and polarization between batteries, the battery cannot fully perform under discharge conditions, and the overall group capacity efficiency is low.

[0003] The consistency of lithium battery manufacturing and grouping has become a key factor affecting the battery life and service life of the PACK. When there are differences between the batteries in the group, the battery will not be able to fully perform due to the barrel effect, which is manifested as low charging capacity and low discharge capacity under working conditions. In actual use, the voltage difference between the batteries in the group will gradually increase, and due to the polarization of each battery, the capacity of each battery when charging and discharging reaches the cut-off voltage is quite different, which seriously affects the battery life and service life. Most lithium battery companies use the more traditional voltage, capacity, and internal resistance static sorting and grouping methods to sort and group lithium-ion batteries, and then group them. The battery consistency of the battery pack produced in this way cannot be guaranteed.

[0004] In the prior art, for example, a Chinese invention patent application with application number 202011580099.9 discloses a lithium-ion battery consistency sorting method, comprising the steps of: performing a battery capacity test and a battery energy test on each lithium-ion battery to be grouped at a predetermined voltage value and a predetermined charge and discharge current value; adjusting the state of charge of the lithium-ion batteries that have undergone the battery capacity test and the battery energy test to a preset value; storing the adjusted lithium-ion batteries in a preset environment for a preset time; collecting the internal resistance and voltage of each lithium-ion battery after storage; and grouping the lithium-ion batteries according to a preset grouping method, the tested battery capacity, the tested battery energy, the collected voltage and internal resistance, the preset grouping method indicating the groups in which different ranges of discharge capacity, discharge energy, internal resistance and voltage are located.

[0005] The above-mentioned sorting method still sorts and groups lithium batteries according to voltage, capacity, and internal resistance, but does not take into account the impact of battery polarization. This type of sorting and grouping method has the disadvantage of being not comprehensive enough. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a method for analyzing the consistency of lithium batteries, which can comprehensively consider various factors, reasonably classify and group, and maximize the performance of the battery.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] A method for analyzing the consistency of a lithium battery comprises the following steps:

[0009] Step S1, removing batteries with capacities exceeding the range, and pre-dividing all remaining batteries into n groups according to their capacities;

[0010] Step S2, calculating the synthetic impedance and polarization voltage parameters of all remaining batteries, and removing batteries with at least one value out of range;

[0011] Step S3, respectively calculating the median value of the synthetic impedance and the median value of the polarization voltage parameter in each group of batteries;

[0012] Step S4, the batteries in each group whose combined impedance and polarization voltage parameters are greater than the median value are divided into a group with a larger capacity, and the batteries in each group whose combined impedance and polarization voltage parameters are less than the median value are divided into a group with a smaller capacity, so as to form a maximum of n+2 groups of batteries.

[0013] As a preferred embodiment of the present invention, the method for calculating the battery synthetic impedance in step S2 is specifically:

[0014] Step S2.1, after the charged battery is left for a period of time, the disturbance current I 1 Test the AC impedance R of each battery ct ;

[0015] Step S2.2, the battery is charged with a current I 2 The constant current is used for n-stage discharge, and the test discharge time is t D1 ,t D2 ……t Dn The DC resistance R C1 , R C2 ……R Cn ;

[0016] Step S2.3, calculate the combined impedance of each battery:

[0017] .

[0018] As a preferred embodiment of the present invention, the method for calculating the battery polarization voltage parameter in step S2 is specifically:

[0019] Step S2.4, recording the cut-off voltage U of each discharge in the n-stage discharge of step S2.2 1 , U 2 … …U n , and the rest time t after each discharge U1 ,t U2 ,……t Un The voltage after U1 '、U 2 '、U 3 '……U n ';

[0020] Step S2.5, calculate the polarization voltage parameters of each battery:

[0021] .

[0022] As a preferred embodiment of the present invention, the constant current discharge in step S2.2 needs to be performed when the battery state of charge is between 5% and 95%.

[0023] As a preferred embodiment of the present invention, the holding time in step S2.1 is 30 minutes to 120 minutes, and the disturbance current I 1 The current is 0.2A~2A, and the frequency range is 0.1Hz~5Hz.

[0024] As a preferred embodiment of the present invention, the I in step S2.2 2 is 0.01A~2A, and the n-stage holding time t in step 2.4 U1 ,t U2 ,……t Un The following are 30S, 60S, 90S...30*nS respectively.

[0025] As a preferred embodiment of the present invention, the method for eliminating batteries whose synthetic impedance exceeds the range in step 2 is specifically: calculating the average value of the synthetic impedance of all batteries, and eliminating batteries whose synthetic impedance is greater than twice the average value.

[0026] As a preferred embodiment of the present invention, the method for eliminating batteries whose polarization voltage parameters are out of range in step 2 is specifically: calculating the average value of the polarization voltage parameters of all batteries, and eliminating batteries whose polarization voltage parameters are greater than 1.2 times the average value.

[0027] As a preferred embodiment of the present invention, the step S1 specifically includes:

[0028] Step S1.1, all batteries are charged and discharged in the same process to obtain the capacity of all batteries;

[0029] Step S1.2, dividing all batteries into n groups according to their capacity;

[0030] Step S1.3, calculate the average capacity C of each group of batteries respectively a , remove the battery capacity in each group C a -a~C a +Batteries outside the range of a; a≤2%C a .

[0031] As a preferred embodiment of the present invention, the charge and discharge current I in step S1.1 is 0.2A-2A, and the cut-off voltage is 3.6-3.7V.

[0032] The advantages of the present invention are that the electrochemical properties of the battery can be fully considered, the battery can be reasonably sorted and grouped, the grouping efficiency can be improved, and the performance of each battery can be maximized, thereby prolonging the service life of the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of a method for analyzing lithium battery consistency according to the present invention;

[0034] Figure 2 A synthetic impedance calculation table according to an embodiment of the present invention;

[0035] Figure 3 A calculation table of polarization voltage parameters in one embodiment of the present invention;

[0036] Figure 4 This is a grouping table according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] like Figure 1 As shown, the present invention provides a method for analyzing the consistency of a lithium battery, comprising the following steps:

[0039] Step S1, taking 22 batteries with a nominal capacity of 110Ah as an example, at an ambient temperature of 25°C, the batteries are charged and discharged once under the conditions of a charge and discharge current of 1.5A, a charge cut-off voltage of 3.65V, a cut-off current of 0.05A, and a discharge cut-off voltage of 2.5V, to obtain the actual capacity of each battery.

[0040] The 22 batteries are arranged in descending order of capacity as A01 to A22 and divided into three groups. The capacity range of group C1 is 110Ah to 112Ah, including A01 to A07; the capacity range of group C2 is 107Ah to 110Ah, including A08 to A14; the capacity range of group C3 is 105Ah to 107Ah, including A15 to A22. Figure 4 What is shown is the final grouping situation, that is, the situation after the synthetic impedance and polarization voltage parameters have been considered, so not all 22 batteries are shown.

[0041] Then the average capacity of each group of batteries was calculated and the batteries with a deviation of more than 2% from the average capacity within the group, namely A06 and A16, were eliminated.

[0042] Step S2: Charge all batteries to 3.65V with constant current and constant voltage and leave them for 30 minutes. Test the AC impedance of each battery with a disturbance current of 2A at an ambient temperature of 25°C and record the real impedance R of the disturbance current at 1Hz. ct .

[0043] All batteries were discharged at 5% to 95% of charge in two stages of constant current, and the DC impedance R was tested when the discharge time was 30S and 60S respectively. c1 and R c2 .

[0044] Calculate the combined impedance of each battery:

[0045] .

[0046] Then calculate the average combined impedance of all batteries and remove the battery whose combined impedance is greater than 2 times the average value, i.e. A22. Figure 2 As shown. (V / S) 2

[0047] In the above-mentioned two-stage constant current discharge process of the battery, after the first stage of discharge, leave t u1 (30S), record the cut-off voltage U after the first discharge 1 And the voltage after shelving U 1 ’ ; After the second discharge, leave t u2 (60S), record the cut-off voltage U after the second discharge 2 And the voltage after shelving U 2 ’ . This is used to calculate the polarization voltage parameters of each battery:

[0048]

[0049] Similarly, the average polarization voltage parameters of all batteries are calculated, and the batteries with polarization voltage parameters greater than 1.2 times the average value, i.e. A10, are eliminated. Figure 3 shown.

[0050] As mentioned above, the combined impedance and polarization voltage parameters are two important indicators of battery performance, and each indicator will affect the best performance that the battery can achieve. And the two are relatively independent, that is, the battery with higher combined impedance may have lower polarization voltage parameters. Therefore, we need to fully consider the impact of the two indicators on the final performance of the battery to ensure that the battery performance in the final group is close.

[0051] Step S3, respectively calculate the median value of the synthetic impedance R of the remaining batteries in the three groups C1, C2, and C3, and the median value of the polarization voltage parameter P. The batteries with synthetic impedance greater than the median value in each group are recorded as R1, and those with synthetic impedance less than the median value are recorded as R2; similarly, the batteries with planned voltage greater than the median value are recorded as P1, and those with planned voltage less than the median value are recorded as P2. In this way, there may be at most four types of batteries in each group: (P1, R1), (P1, R2), (P2, R1), (P2, R2).

[0052] Step S4, according to the above results, the battery marked as (P1, R1), that is, the battery whose P and R are ahead of other batteries in this group, will not be able to exert its maximum performance once it is paired with other batteries in this group, so we will promote it to a group with higher capacity. The battery marked as (P2, R2), that is, the battery whose P and R are behind other batteries in this group, will affect the performance of other batteries once it is paired with other batteries in this group, so we will move it down to a group with lower capacity.

[0053] Specifically, Figure 4 As shown, there is no battery (P1, R1) in group C1, so there is no need to lift it up, and battery A05 marked as (P2, R2) in group C1 is lowered to group C2 with lower capacity, which is the final group B. The remaining batteries in group C1, including batteries marked as (P1, R2) and (P2, R1), form group A.

[0054] There is no battery marked (P1, R1) in group C2, so there is no need to lift it up. Batteries A12 and A13 marked (P2, R2) are lowered to group C3, which is the final group C. The remaining batteries in group C2 form group B.

[0055] The batteries A15 and A18 marked as (P1, R1) in group C3 were moved up to group C2 with higher capacity, which is the final group B. The battery A17 marked as (P2, R2) was originally supposed to be moved down to a group with lower capacity. However, considering that only one battery needed to be moved down and a group with lower capacity needed to be newly built, and considering its poor performance, we directly screened it out. The remaining batteries in group C3 formed group C.

[0056] The final grouping is as follows:

[0057] Group A: A01, A02, A03, A04, A07;

[0058] Group B: A05, A08, A09, A11, A14, A15, A18;

[0059] Group C: A12, A13, A19, A20, A21.

[0060] The above is only a preferred specific embodiment of the present invention, which is an implementation method based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for analyzing the consistency of a lithium battery, characterized in that: The steps include: Step S1, pre-dividing all batteries into n groups according to their capacities, and removing batteries in each group whose capacities exceed the range; Step S2, calculating the synthetic impedance and polarization voltage parameters of all batteries, and removing batteries with at least one value out of range; the method for calculating the synthetic impedance of the battery in step S2 is specifically: Step S2.1, after the charged batteries are left for a period of time, the AC impedance R of each battery is tested with a disturbance current I1. ct ; Step S2.2, discharge the battery at a constant current of I2 for n steps, and the test discharge time is t D1 ,t D2 ……t Dn The DC resistance R C1 , R C2 ……R Cn ; Step S2.3, calculate the combined impedance of each battery: ； Step S3, respectively calculating the median value of the synthetic impedance and the median value of the polarization voltage parameter in each group of batteries; Step S4, the batteries in each group whose combined impedance and polarization voltage parameters are greater than the median value are divided into a group with a larger capacity, and the batteries in each group whose combined impedance and polarization voltage parameters are less than the median value are divided into a group with a smaller capacity, so as to form a maximum of n+2 groups of batteries.

2. A method for analyzing the consistency of a lithium battery according to claim 1, characterized in that: The method for calculating the battery polarization voltage parameter in step S2 is specifically as follows: Step S2.4, recording the cut-off voltages U1, U2, ..., U1, U2, ..., U2 ... n , and the rest time t after each discharge U1 ,t U2 ,……t Un The voltage after U1', U2', U3'...U n '; Step S2.5, calculate the polarization voltage parameters of each battery: 。 3. A method for analyzing the consistency of a lithium battery according to claim 1, characterized in that: The constant current discharge in step S2.2 needs to be performed when the battery state of charge is between 5% and 95%.

4. A method for analyzing the consistency of a lithium battery according to claim 1, characterized in that: The standby time in step S2.1 is 30 min to 120 min, the disturbance current I1 is 0.2 A to 2 A, and the frequency range is 0.1 Hz to 5 Hz.

5. A method for analyzing the consistency of a lithium battery according to claim 2, characterized in that: I2 in step S2.2 is 0.01A to 2A, and the n-stage holding time t in step 2.4 is U1 ,t U2 ,……t Un The following are 30S, 60S, 90S...30*nS respectively.

6. A method for analyzing the consistency of a lithium battery according to claim 1, characterized in that: The method for eliminating batteries whose combined impedance exceeds the range in step 2 is specifically: calculating the average value of the combined impedance of all batteries, and eliminating batteries whose combined impedance is greater than twice the average value.

7. A method for analyzing the consistency of a lithium battery according to claim 1, characterized in that: The method for eliminating batteries whose polarization voltage parameters are out of range in step 2 is specifically: calculating the average value of the polarization voltage parameters of all batteries, and eliminating batteries whose polarization voltage parameters are greater than 1.2 times the average value.

8. A method for analyzing the consistency of a lithium battery according to claim 1, characterized in that: The step S1 specifically includes: Step S1.1, all batteries are charged and discharged in the same process to obtain the capacity of all batteries; Step S1.2, dividing all batteries into n groups according to their capacity; Step S1.3, calculate the average capacity C of each group of batteries respectively a , remove the battery capacity in each group C a -a~C a +Battery outside the range of a; a≤2%C a .

9. A method for analyzing the consistency of a lithium battery according to claim 8, characterized in that: The charge and discharge current I in step S1.1 is 0.2A-2A, and the cut-off voltage is 3.6-3.7V.

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