Method suitable for curing short-circuit test parameters of lithium battery

Abstract

The invention discloses a short circuit test parameter curing method suitable for a lithium battery, which comprises the following steps: carrying out breakdown on a battery cell diaphragm to obtain a minimum breakdown voltage value, determining a test voltage, confirming a test voltage parameter, carrying out gradient verification on dwell time and discharge time, carrying out parameter setting, and obtaining voltage drop distribution; and determining the dwell time and the discharge time of each type of battery. And finally, carrying out a cell sample running test to obtain boosting time, actual voltage and voltage drop parameter values, carrying out interception and disassembly analysis on the cell at a voltage drop discrete point after short circuit is eliminated, and further determining whether a missed killing condition exists or not. According to the method, reasonable short-circuit test parameters can be reasonably and effectively solidified, over-killing can be avoided, and yield loss caused by mistaken killing of part of good battery cells due to irrational parameter setting can be avoided.

Description

Technical Field

[0001] The invention relates to the field of lithium ion battery testing, and in particular to a method for curing parameters of lithium battery short circuit testing. Background Art

[0002] The overall safety of lithium batteries is composed of a variety of complex factors, among which thermal runaway problems caused by short circuits account for a considerable proportion, and the damage of the internal diaphragm is also one of the important reasons for internal short circuits. In order to avoid serious accidents caused by short-circuited batteries failing to pass the test and flowing out, short-circuit testers are generally added in some processes during the production of battery cells to intercept the short-circuited batteries and prevent them from continuing to flow. In order to achieve good short-circuit detection, it is necessary to set reasonable short-circuit test parameters. The short-circuit test parameters mainly include test voltage, holding time (TK), discharge time (TF), and voltage drops at different stages (Vd1, Vd2, Vd3). The setting of short-circuit parameters is particularly important. Reasonable short-circuit test parameters can avoid missed killing and over-killing of battery cells; avoiding missed killing can prevent microcircuit batteries from being unable to be detected, and the finished product output phenomenon will flow to the client. Avoiding over-killing can avoid the mistaken killing of some good batteries due to unreasonable parameter settings, resulting in production losses. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a method for curing short-circuit test parameters of lithium batteries, so as to better cure the battery test voltage.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for curing parameters of a lithium battery short circuit test, comprising the following steps:

[0005] S1. Copper powder particles of different diameters are injected into the battery cell respectively, and the battery cell diaphragm is broken down at different temperatures and pressures according to the preset voltage gradient to obtain the minimum breakdown voltage value of copper powder of different diameters and determine the test voltage;

[0006] S2. Set the short-circuit test time: the sum of the voltage holding time TK and the discharge time TF is greater than the preset multiple of the boost time TP. Perform voltage holding time TK gradient verification based on the test voltage to obtain the voltage drop Vd distribution, further determine the voltage holding time TK for each type of battery, and complete the solidification of the voltage holding time TK parameter.

[0007] Furthermore, the aforementioned method for curing short-circuit test parameters of lithium batteries also includes curing of discharge time TF parameters, specifically: setting the short-circuit test time: the sum of the voltage holding time TK and the discharge time TF is greater than a preset multiple of the boost time TP, performing discharge time TF gradient verification based on the test voltage, obtaining the voltage drop Vd distribution, further determining the discharge time TF of each type of battery, and completing the curing of the discharge time TF parameters.

[0008] Furthermore, the aforementioned method for solidifying lithium battery short-circuit test parameters also includes solidifying the voltage drop Vd parameter, specifically: performing a cell running test to obtain the boost time TP, actual voltage VP, and voltage drop Vd parameter values, excluding NG type short circuits and SC severe short circuits corresponding to abnormal boost time TP and actual voltage VP parameters, and when the boost time TP and actual voltage VP parameters are normal, intercepting and disassembling the cell at the discrete point of the voltage drop Vd for analysis to determine whether there is a short circuit point. If so, it is determined that there is a missed kill situation at the discrete point of the voltage drop Vd, otherwise it is confirmed that the discrete point of the voltage drop Vd has passed the inspection.

[0009] Furthermore, in the aforementioned method for curing parameters of a lithium battery short-circuit test, in step S1, the copper powder particles are verified using μm units, the particle size is 5 μm, and the gradient is 5 μm; the preset voltage gradient is 200V, and the starting voltage is 200V.

[0010] Furthermore, the aforementioned method for curing parameters of a lithium battery short-circuit test is characterized in that when setting the short-circuit test time, the sum of the voltage holding time TK and the discharge time TF is greater than seven times or more of the voltage boost time TP.

[0011] Furthermore, in the aforementioned method for curing parameters of a short-circuit test for a lithium battery, when setting the short-circuit test time, the sum of the pressure holding time TK and the discharge time TF is greater than 200 ms.

[0012] Furthermore, in the aforementioned method for curing parameters of a lithium battery short-circuit test, the setting range of the boost time TP is: 18-22ms.

[0013] Furthermore, the aforementioned method for solidifying lithium battery short circuit test parameters determines NG type short circuit and SC severe short circuit type with boost time TP as the first priority, actual voltage VP as the second priority, and voltage drop Vd as the third priority.

[0014] Compared with the prior art, the beneficial technical effects of the present invention using the above technical solution are as follows:

[0015] Accurate control of the diaphragm test voltage can be used as a standardized verification method; reasonable setting of TK and TF time can avoid large VD parameter errors caused by large setting errors, which can cause false kills; reasonable setting of VD1 parameters can reduce or lower false kills without missing kills, save costs and improve production capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the voltage drop Vd parameter distribution diagram.

[0017] Figure 2 It is a scatter plot of Vd parameters under normal data of boost time TP and actual voltage VP.

[0018] Figure 3 This is the open circuit alarm waveform during the boost time TP.

[0019] Figure 4 This is the actual voltage VP severe short circuit waveform. DETAILED DESCRIPTION

[0020] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0021] Various aspects of the invention are described herein with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the invention are not limited to those described in the accompanying drawings. It should be understood that the invention is implemented by any of the various concepts and embodiments described above, as well as the concepts and embodiments described in detail below, because the concepts and embodiments disclosed in the invention are not limited to any implementation. In addition, some aspects disclosed in the invention may be used alone or in any appropriate combination with other aspects disclosed in the invention.

[0022] The present invention provides a method for curing parameters of a lithium battery short circuit test, comprising the following steps:

[0023] S1. Copper powder particles of different diameters are injected into the battery cell respectively, and the battery cell diaphragm is broken down at different temperatures and pressures according to the preset voltage gradient to obtain the minimum breakdown voltage value of copper powder of different diameters and determine the test voltage;

[0024] S2. Set the short-circuit test time: the sum of the voltage holding time TK and the discharge time TF is greater than the preset multiple of the boost time TP. Perform voltage holding time TK gradient verification based on the test voltage to obtain the voltage drop Vd distribution, further determine the voltage holding time TK for each type of battery, and complete the solidification of the voltage holding time TK parameter.

[0025] Furthermore, as a preferred embodiment of the present invention, it also includes solidification of the discharge time TF parameter, specifically: setting the short-circuit test time: the sum of the voltage holding time TK and the discharge time TF is greater than a preset multiple of the boost time TP, performing a discharge time TF gradient verification based on the test voltage, obtaining the voltage drop Vd distribution, further determining the discharge time TF of each type of battery, and completing the solidification of the discharge time TF parameter.

[0026] Furthermore, as a preferred embodiment of the present invention, it also includes solidifying the voltage drop Vd parameter, specifically: performing a cell running test to obtain the boost time TP, the actual voltage VP, and the voltage drop Vd parameter values, excluding the NG type short circuit and SC severe short circuit corresponding to the abnormal boost time TP and the actual voltage VP parameters, and when the boost time TP and the actual voltage VP parameters are normal, intercepting and disassembling the cell at the discrete point of the voltage drop Vd for analysis to determine whether there is a short circuit point. If so, it is determined that there is a missed kill situation at the discrete point of the voltage drop Vd, otherwise it is confirmed that the discrete point of the voltage drop Vd has passed the inspection.

[0027] Example 1, when testing voltage curing, the Ruijie pulse short circuit test instrument breakdown mode is used for verification, and the copper powder is artificially plugged inside the battery cell for verification. It is recommended to use the μm unit for verification of copper powder particles, and gradient verification is performed, using 5μm, 10μm, 15μm, 20μm.......; according to the research results, the breakdown voltage of the commonly used diaphragm is 1500-2000V under normal conditions, and the breakdown voltage is set in a gradient, 2000V, 1800V, 1600V.........400V, 200V. Refer to Table 1 below:

[0028] Table 1

[0029]

[0030]

[0031] According to the above table, the specific values ​​of the minimum breakdown voltage under different copper powder particle states can be obtained. This experiment is related to the process problem. The test temperature and pressure breakdown voltage values ​​are different under different processes. On this basis, the verification of different temperatures T and pressures F is added to obtain relatively accurate minimum voltage breakdown parameters and determine the test voltage value.

[0032] In Example 2, in step S2, the pressure holding time TK and the discharge time TF of each type of battery are determined, as follows: according to the use requirements of the pulse short-circuit tester, the short-circuit test time (TK+TF) is more than 7 times greater than the boost time (TP); taking a 200V, 95Ah battery cell as an example, the TP boost time is about 18-22ms; (TK+TF) is recommended to be set to more than 200ms; based on this, the TK and TF time gradients are verified by designing experiments, and the voltage drop distribution is observed and analyzed, as shown in Table 2 below;

[0033] Table 2

[0034] Serial number TK time (ms) TF time (ms) Investment output Pass rate Vd1 Vd2 Vd3 1 20 250 \ \ \ \ \ \ 2 70 200 \ \ \ \ \ \ 3 120 150 \ \ \ \ \ \ 4 170 100 \ \ \ \ \ \ 5 220 50 \ \ \ \ \ \

[0035] (1)① The Vd parameters are obtained based on the above experimental results. The subsequent Vd parameter scatter plot is not guaranteed. The number of samples in each group of TK and TF verification tests is more than 50;② Each group of experiments uses the same batch of samples to eliminate the influence of the results caused by the battery cells;③ A unified process is used for experimental verification to ensure that the battery cells are tested under the same pressure and temperature. Figure 1 The Vd distribution results were tested with 50 samples in each group under the conditions of 200V test voltage, 25℃ and 200kg pressure.

[0036] (2)①Based on Figure 1 Analysis shows that the voltage drop distribution in the Vd1 stage is not affected by TK and TF; ② After the TK time is 20ms, the voltage drop distribution in Vd2 reaches a stable state. This phenomenon may be caused by the voltage not being completely stable in the voltage holding stage, resulting in an unstable voltage, which reflects a large voltage drop. Therefore, it is recommended that the TK time be selected to be greater than 20ms, and the appropriate TK parameters for the specific type of battery be found through experiments. After the TK parameters are determined, the TF parameters are determined; ③ The TF drop is consistent with the time and is linear, with no obvious abnormal points.

[0037] In Example 3, in step S3, the voltage drop Vd parameter is solidified as follows:

[0038] (1) The Vd parameter mainly records the voltage fluctuations during the short circuit process inside the battery cell during the boost, voltage maintenance and free discharge stages. The short circuit process is mainly caused by the melting of foreign objects, the folding of the pole ears, etc., which cause the positive and negative poles to be directly short-circuited. After the short circuit, the resistance decreases instantly to form an instantaneous voltage fluctuation. The short circuit tester quickly captures the real-time fluctuation of the voltage pulse on the battery cell, and determines the short circuit and micro-short circuit problems of the battery cell based on the voltage fluctuation and the parameter characteristics of the battery cell when receiving the high-voltage pulse.

[0039] (2) Introduction to the judgment principle of the short circuit tester: The first priority is the TP time judgment. When the battery is detected to be open circuit, it may be due to poor contact or disconnection of the connecting wire. The TP time is generally short, between 2-5s. The waveform is as follows Figure 3As shown; this type of NG short circuit is generally an OC open circuit type. OC open circuit alarm, the positive and negative poles of the battery cell are not effectively connected to the test circuit, the tester open circuit alarm, the waveform output voltage holding stage is voltage maintenance, and a voltage drop occurs when entering free discharge. The battery cell has not been tested with a high-voltage pulse. It is a problem with the production line test organization and the wiring harness, and the battery cell status is uncertain. The second priority is the VP voltage judgment. The VP voltage is the actual voltage applied to the battery cell by the short circuit tester. When a serious short circuit occurs, the voltage cannot rise, and the actual voltage VP is lower than the set voltage threshold; taking the 200V test voltage as an example, when a serious short circuit occurs, the VP voltage is generally between 10-50V, which is quite different from the 200V voltage. The waveform is as shown Figure 4 As shown, this type of NG short circuit is generally a severe SC short circuit type; the third priority is the Vd voltage drop parameter determination; no matter the drop amplitude of Vd1, Vd2, and Vd3 exceeds the manually set control parameters, it is considered an NG short circuit cell. VP is abnormal, the voltage has almost no effective climb, and cannot reach the set voltage amplitude standard. This type of cell has the positive and negative poles directly connected together through a reliable short-circuit point.

[0040] (3) According to the parameter determination principle of the short-circuit tester, after confirming the test voltage, TK, and TF parameters, a small batch of battery cells can be tested, and the TP, VP, d1, Vd2, and Vd3 measurement parameters can be recorded, and the pulse short-circuit test waveform diagram can be plotted. It is preferred to exclude abnormal data of TP and VP parameters. This type of data is OC and SC type, and is determined by TP and VP parameters. Vd parameters are not determined and are not processed as Vd parameter analysis type data. Under the premise that TP and VP parameters are normal, data processing and analysis of Vd parameters are performed, refer to Figure 2 , Experimental conditions: ① Experimental process: peripheral welding process; ② Vd parameter control specifications: Vd1 set to 7V; Vd2 set to 18V; Vd3 set to 18V; ③ Vd parameter scatter plot under normal TP and VP data; Example analysis is as follows: According to the analysis of the discrete graph of the test, the discrete points of the normal battery with TP and VP data are all within the control range, indicating that the current setting parameters are not overkill. The discrete point battery cells are intercepted and disassembled to confirm whether there is a risk of missing parameters. This experiment needs to be classified according to the situation of each process. The discrete point battery cells may not be easy to remove obvious short-circuit points. It is recommended to perform a long-term disassembly process. If no short-circuit point is found, it is determined that this discrete degree can be released. If the obvious short-circuit point is removed, it is considered that there is a missed kill under this parameter, and the parameters are further tightened to determine the final parameters.

[0041] The above description is not intended to limit the present invention. A person skilled in the art of the present invention may make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for curing parameters of lithium battery short circuit test, characterized in that: The steps include: S1. Copper powder particles of different diameters are injected into the battery cell respectively, and the battery cell diaphragm is broken down at different temperatures and pressures according to the preset voltage gradient to obtain the minimum breakdown voltage value of copper powder of different diameters and determine the test voltage; S2. Set the short-circuit test time: the sum of the voltage holding time TK and the discharge time TF is greater than the preset multiple of the boost time TP. Perform voltage holding time TK gradient verification based on the test voltage to obtain the voltage drop Vd distribution, further determine the voltage holding time TK for each type of battery, and complete the solidification of the voltage holding time TK parameter.

2. A method for curing lithium battery short circuit test parameters according to claim 1, characterized in that: It also includes the solidification of the discharge time TF parameter, specifically: setting the short-circuit test time: the sum of the voltage holding time TK and the discharge time TF is greater than the preset multiple of the boost time TP, performing the discharge time TF gradient verification based on the test voltage, obtaining the voltage drop Vd distribution, and further determining the discharge time TF of each type of battery to complete the solidification of the discharge time TF parameter.

3. A method for curing parameters of lithium battery short circuit test according to claim 1, characterized in that: It also includes solidifying the voltage drop Vd parameters, specifically: conducting a cell running test to obtain the boost time TP, actual voltage VP, and voltage drop Vd parameter values, excluding NG type short circuits and SC serious short circuits corresponding to abnormal boost time TP and actual voltage VP parameters; when the boost time TP and actual voltage VP parameters are normal, intercepting and disassembling the cells at the discrete points of the voltage drop Vd for analysis to determine whether there are short circuit points. If there are short circuit points, it is determined that there are missed points at the discrete points of the voltage drop Vd. Otherwise, it is confirmed that the discrete points of the voltage drop Vd have passed the inspection.

4. A method for curing parameters of lithium battery short circuit test according to claim 1, characterized in that: In step S1, the copper powder particles are verified using μm units, the particle size is 5 μm, and the gradient is 5 μm; the preset voltage gradient is 200V, and the starting voltage is 200V.

5. A method for curing lithium battery short circuit test parameters according to claim 1 or 2, characterized in that: When setting the short-circuit test time, the sum of the voltage holding time TK and the discharge time TF is greater than seven times or more of the voltage boost time TP.

6. A method for curing lithium battery short circuit test parameters according to claim 1, characterized in that: When setting the short-circuit test time, the sum of the voltage holding time TK and the discharge time TF is more than 200ms.

7. A method for curing lithium battery short circuit test parameters according to claim 1 or 2, characterized in that: The setting range of boost time TP is: 18-22ms.

8. A method for curing lithium battery short circuit test parameters according to claim 1, characterized in that: The NG type short circuit and the SC severe short circuit type are determined with the boost time TP as the first priority, the actual voltage VP as the second priority, and the voltage drop Vd as the third priority.

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