Self-discharge test system and method for battery cell

Abstract

The application relates to the technical field of battery cells, in particular to a self-discharge test system and method for a battery cell, which comprises a measuring instrument electrically connected with the battery cell and used for measuring the voltage of the battery cell in real time; a controller electrically connected with the measuring instrument and used for receiving the voltage data fed back by the measuring instrument in real time; a programmable constant current source electrically connected with the controller and the battery cell and used for receiving the instruction of the controller to provide constant current for the battery cell; a power supply electrically connected with the controller and the programmable constant current source and used for providing electric energy for the controller and the programmable constant current source; wherein, when the controller does not issue an instruction to the programmable constant current source, the controller calculates the discharge voltage change rate according to the voltage data fed back by the measuring instrument; when the controller issues an instruction to the programmable constant current source, the programmable constant current source provides constant current for the battery cell, and the controller calculates the charging voltage change rate according to the voltage data fed back by the measuring instrument; and the controller calculates the self-discharge current according to the discharge voltage change rate and the charging voltage change rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery cells, in particular to a self-discharge test system and method for battery cells. BACKGROUND

[0002] During use, if the self-discharge of a battery is too large, the battery will run out of power soon after being fully charged. In addition, large self-discharge will increase the risk of thermal runaway. Therefore, the self-discharge of a battery cell needs to be tested before it is shipped.

[0003] For power or energy storage scenarios that require multiple series and parallel use, the self-discharge test of the battery is particularly important. Not only the qualified value needs to be measured, but also the qualified value needs to be classified and sorted, so that the self-discharge of each battery cell in the overall battery pack is basically equal. Only in this way, the use of the entire battery pack will not be affected by the different self-discharges of each battery cell.

[0004] The traditional method for testing the self-discharge of a battery cell is open-circuit voltage test. In order to obtain a reliable difference in open-circuit voltage, a long period of time (usually 1 week to 1 month) is required. Due to the long storage period, the storage and cost of the factory are greatly affected. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a self-discharge test system and method for battery cells, aiming to solve the problem of long self-discharge test period of existing battery cells, which leads to high storage and cost of the factory.

[0006] To achieve the above-mentioned purpose, the present application provides a self-discharge test system for battery cells, comprising:

[0007] a measuring instrument, electrically connected to the battery cell, for measuring the voltage of the battery cell in real time;

[0008] a controller, electrically connected to the measuring instrument, for receiving the voltage data fed back by the measuring instrument in real time;

[0009] a programmable constant current source, electrically connected to the controller and the battery cell, for receiving instructions from the controller to provide a constant current to the battery cell;

[0010] a power supply, electrically connected to the controller and the programmable constant current source, for providing power to the controller and the programmable constant current source;

[0011] The controller does not issue an instruction to the programmable constant current source, and the controller calculates a discharge voltage change rate according to voltage data fed back by the measuring instrument; the controller issues an instruction to the programmable constant current source, and the programmable constant current source provides a constant current for the battery cell, and the controller calculates a charging voltage change rate according to voltage data fed back by the measuring instrument; and the controller calculates a self-discharge current according to the discharge voltage change rate and the charging voltage change rate.

[0012] As one of the examples, the measuring instrument is a direct current voltmeter.

[0013] As one of the examples, the method further comprises:

[0014] An analog / digital converter (ADC) is electrically connected to the measuring instrument and the controller, and is configured to convert the voltage of the battery cell measured in real time from an analog signal into a digital signal and input the digital signal into the controller.

[0015] As one of the examples, the method further comprises:

[0016] A communication interface is electrically connected to the controller, and is configured to transmit the obtained self-discharge current value to a mobile terminal.

[0017] As one of the examples, the mobile terminal comprises a mobile phone and a computer.

[0018] The application further provides a self-discharge test method for a battery cell, comprising the following steps:

[0019] Step 1: turn off the programmable constant current source;

[0020] Step 2: continuously collect voltage data of the battery cell for N times;

[0021] Step 3: calculate a discharge K value of the battery cell according to the N voltage data;

[0022] Step 4: the programmable constant current source outputs a constant current I1 to charge the battery cell;

[0023] Step 5: again collect voltage data of the battery cell for N times;

[0024] Step 6: calculate a charging K value of the battery cell according to the N voltage data;

[0025] Step 7: calculate a self-discharge current I0 according to the discharge K value and the charging K value;

[0026] Step 8: update the constant current I1 output by the programmable constant current source according to the self-discharge current I0;

[0027] Step 9: at least cyclically execute steps 4-8 twice to obtain the self-discharge current I0.

[0028] Further, in step 3 and step 6, specifically:

[0029] Formula (1): Q=U*C;

[0030] Formula (2): Q=I*t;

[0031] According to formula (1) and formula (2), formula (3) is obtained: U=t*I / C; let K=I / C in formula (3), then K=ΔU / Δt;

[0032] Wherein, Q is the electric quantity, the unit is C; U is the voltage, the unit is V; C is the capacitance, the unit is F; I is the current, the unit is A; t is the time, the unit s.

[0033] Further, according to K=I / C, the following equation group is established:

[0034]

[0035] According to the equation group, the self-discharge current is:

[0036] Wherein, K0 is the discharge K value, K1 is the charge K value.

[0037] Further, in step 9, specifically:

[0038] Step 1: turn off the programmable constant current source;

[0039] Step 2: collect the voltage data of the battery cell for N times continuously;

[0040] Step 3: calculate the discharge K value of the battery cell according to N voltage data;

[0041] Step 4: the programmable constant current source outputs constant current I2 to charge the battery cell;

[0042] Step 5: collect the voltage data of the battery cell for N times continuously again;

[0043] Step 6: calculate the charge K value of the battery cell according to N voltage data;

[0044] Step 7: calculate the self-discharge current I0 according to the discharge K value and the charge K value, specifically: according to K=I / C, the following equation group is established:

[0045]

[0046] According to the equation group, the self-discharge current is:

[0047] Wherein, K0 is the discharge K value, K2 is the charge K value calculated by the second programmable constant current source outputting constant current.

[0048] The self-discharge test system and method for the battery cell have the advantages that:

[0049] The controller calculates the discharge voltage change rate of the battery cell when the programmable constant current source does not provide a constant current to the battery cell, and calculates the charging voltage change rate of the battery cell when the programmable constant current source provides a constant current to the battery cell, and the self-discharge current can be obtained according to the two voltage change rates, and the constant current provided by the programmable constant current source to the battery cell is changed according to the obtained self-discharge current, and the discharge voltage change rate is calculated again, and the new self-discharge current is obtained according to the charging voltage change rate and the new discharge voltage change rate, and the self-discharge current can reach an accuracy of 1% after two iterations. Compared with the conventional open-circuit voltage test method with a weekly test period and the constant potential method with a typical test time of 8-24 hours, the test speed of the battery cell self-discharge test by the self-discharge test system of the present application can be greatly improved, and the test time required for one test is only about 20 minutes, the test time of two iterations is about 40 minutes, and the overall test time can be shortened to less than 1 hour, thereby reducing the warehouse and cost pressure of the factory. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is one of the circuit block diagrams of the self-discharge test circuit of the embodiment of the present application;

[0051] Figure 2 is the second circuit block diagram of the self-discharge test circuit of the embodiment of the present application;

[0052] Figure 3 is the third circuit block diagram of the self-discharge test circuit of the embodiment of the present application;

[0053] Figure 4 is the flowchart of the self-discharge test method of the embodiment of the present application;

[0054] Figure 5 is the experimental data graph of measuring the self-discharge current of the battery cell by using the self-discharge test method of the present application. DETAILED DESCRIPTION

[0055] The present application will be further described below in combination with the drawings and specific embodiments.

[0056] The self-discharge of the battery is the leakage current inside the battery, and since the leakage current is only affected by the battery material system, the influence of external environmental factors on the detection can be excluded, so that the leakage current value measured can more accurately predict the self-discharge of the battery. The idea of the present application is to detect the leakage current inside the lithium battery, and judge the self-discharge of the battery according to the size of the leakage current, i.e. the self-discharge current in the following text, so that the quality and storage time of the battery can be judged.

[0057] AsFigure 1 As shown, the present invention provides a self-discharge testing system for battery cells, comprising:

[0058] The measuring instrument is electrically connected to the battery cell and is used to measure the voltage of the battery cell in real time.

[0059] The controller is electrically connected to the measuring instrument and is used to receive voltage data fed back by the measuring instrument in real time.

[0060] A programmable constant current source, electrically connected to the controller and the battery cell, is used to receive instructions from the controller to provide a constant current to the battery cell;

[0061] The power supply is electrically connected to the controller and the programmable constant current source, and is used to provide power to the controller and the programmable constant current source.

[0062] In one scenario, the controller does not issue commands to the programmable constant current source; instead, it calculates the discharge voltage change rate based on the voltage data fed back by the measuring instrument. When the controller issues commands to the programmable constant current source, the programmable constant current source provides a constant current to the battery cell, and the controller calculates the charging voltage change rate based on the voltage data fed back by the measuring instrument. Finally, the controller calculates the self-discharge current based on the discharge voltage change rate and the charging voltage change rate.

[0063] The controller of this invention first calculates the rate of change of the discharge voltage of the battery cell when the programmable constant current source does not provide a constant current to the battery cell, and then calculates the rate of change of the charging voltage of the battery cell when the programmable constant current source provides a constant current to the battery cell. The self-discharge current can be obtained from these two voltage rate of change. Simultaneously, the magnitude of the constant current provided by the programmable constant current source to the battery cell is changed based on the obtained self-discharge current, and the discharge voltage rate of change is calculated again. A new self-discharge current is obtained based on the charging voltage rate of change and the new discharge voltage rate of change. After two iterations, an accuracy of 1% can be achieved. Compared with the conventional open-circuit voltage test method with its weekly test cycle and the typical 8-24 hour test time of the constant potential method, the self-discharge test system of this invention significantly improves the test speed. A single test takes only about 20 minutes, and two iterative tests take about 40 minutes, reducing the overall test time to less than one hour, thus alleviating the factory's warehousing and cost pressures.

[0064] Understandably, the measuring instrument is a DC voltmeter.

[0065] like Figure 2 As shown, in some embodiments, the self-discharge test system further includes:

[0066] An analog-to-digital converter (ADC) is electrically connected to the measuring instrument and controller to convert the real-time measured voltage of the battery cell from an analog signal into a digital signal before inputting it to the controller.

[0067] likeFigure 3 As shown, in some embodiments, the self-discharge test system further comprises:

[0068] The communication interface is electrically connected with the controller, and is configured to transmit the obtained self-discharge current value to a mobile terminal.

[0069] It can be understood that the mobile terminal includes a mobile phone and a computer. A user can view the self-discharge current of the battery cell through a display device such as a mobile phone or a computer.

[0070] As shown, the application further provides a self-discharge test method of a battery cell, comprising the following steps:

[0071] Step 1: turn off the programmable constant current source;

[0072] Step 2: continuously collect voltage data of the battery cell for N times;

[0073] Step 3: calculate the discharge K value of the battery cell according to the N voltage data;

[0074] Step 4: the programmable constant current source outputs a constant current I1 to charge the battery cell;

[0075] Step 5: again continuously collect voltage data of the battery cell for N times;

[0076] Step 6: calculate the charge K value of the battery cell according to the N voltage data;

[0077] Step 7: calculate the self-discharge current I0 according to the discharge K value and the charge K value;

[0078] Step 8: update the constant current I1 output by the programmable constant current source according to the self-discharge current I0;

[0079] Step 9: at least cyclically execute steps 4-8 twice to obtain the self-discharge current I0.

[0080] The application obtains the discharge voltage change rate of the battery cell by continuously collecting voltage data of the battery cell for N times, then provides a constant current to the battery cell by the programmable constant current source, again collects the voltage data of the battery cell for N times to obtain the charging voltage change rate, and obtains the self-discharge current according to the two voltage change rates, changes the constant current provided by the programmable constant current source to the battery cell according to the obtained self-discharge current, and again calculates the discharge voltage change rate, obtains the new self-discharge current according to the charging voltage change rate and the new discharge voltage change rate, and the self-discharge current can reach 1% accuracy after two iterations. Compared with the conventional open circuit voltage test method with a weekly test cycle and the constant potential method with a typical test time of 8-24 hours, the test speed of the battery cell self-discharge test by the self-discharge test system of the application can be greatly improved, the test time required for one test is only about 20 minutes, the test time of two iteration tests is about 40 minutes, and the overall test time can be shortened to less than 1 hour, thereby reducing the warehouse and cost pressure of the factory.

[0081] Further, in steps 3 and 6, specifically:

[0082] Formula (1): Q=U*C;

[0083] Formula (2): Q=I*t;

[0084] According to formula (1) and formula (2), formula (3) is obtained: U=t*I / C; let K=I / C in formula (3), then K=ΔU / Δt;

[0085] Wherein, Q is the electric quantity, the unit is C; U is the voltage, the unit is V; C is the capacitance, the unit is F; I is the current, the unit is A; t is the time, the unit is s.

[0086] Further, according to K=I / C, the following equation group is established:

[0087]

[0088] According to the equation group, the self-discharge current is:

[0089] Wherein, K0 is the discharge K value, and K1 is the charging K value.

[0090] Further, in step 9, specifically:

[0091] Step 1: turn off the programmable constant current source;

[0092] Step 2: continuously collect voltage data of the battery cell for N times;

[0093] Step 3: calculate the discharge K value of the battery cell according to N voltage data;

[0094] Step 4: The programmable constant current source outputs constant current I2 to charge the battery;

[0095] Step 5: Collect the voltage data of the battery again for N times continuously;

[0096] Step 6: Calculate the charging K value of the battery according to the N voltage data;

[0097] Step 7: Calculate the self-discharge current I0 according to the discharge K value and the charging K value, specifically: according to K=I / C, the following equation group is established:

[0098]

[0099] According to the equation group, the self-discharge current is:

[0100] Wherein, K0 is the discharge K value, and K2 is the charging K value calculated by the second programmable constant current source output constant current. The I0 calculated by K2 can reach an accuracy of 1%.

[0101] The specific method for updating the constant current I1 output by the programmable constant current source in step 8 is: when the constant current I1 is greater than the discharge current I0, the constant current I1 output by the programmable constant current source is updated to I2, and I2<I1; when the constant current I1 is less than the discharge current I0, the constant current I1 output by the programmable constant current source is updated to I2, and I2>I1.

[0102] The ordinary cylindrical 18650 lithium ion battery screened from the production line is taken as the three battery samples to be measured, and the open circuit voltage test method is used to measure that the No. 1 is an unqualified battery, and the No. 2 and No. 3 are qualified batteries.

[0103] It is known that the K value of the No. 1 battery deviates from the normal range, and the K values of the No. 2 and No. 3 are in the normal range. The three measured battery samples are placed in the incubator, and the temperature in the incubator is about 30℃.

[0104] As shown in Figure 5 It is not difficult to see from the comparison of the self-discharge currents I1, I2 and I3 that the self-discharge current I1 of the No. 1 battery is about 165uA, and the self-discharge currents I2 of the No. 2 and I3 of the No. 3 are about 30uA, which are quite different. In addition, with the slight fluctuation of the temperature in the incubator, the self-discharge current values of the three battery samples also change.

[0105] The Figure 5It can be known that the self-discharge test method of the application has obvious difference in self-discharge current between qualified battery cells and unqualified battery cells, which shows the effectiveness of the self-discharge test method of the application on the self-discharge test of the battery cells.

[0106] The above is only the preferred embodiment of the application, and does not limit the technical scope of the application, so any slight modification, equivalent change and modification of the above embodiment according to the technical essence of the application still belongs to the technical solution of the application.

Claims

1. A self-discharge test system for a battery cell, the system comprising: The application relates to a self-discharge current measuring device for a battery, comprising: a measuring instrument electrically connected with a battery, for measuring the voltage of the battery in real time; a controller electrically connected with the measuring instrument, for receiving the voltage data fed back by the measuring instrument in real time; a programmable constant current source electrically connected with the controller and the battery, for receiving the instruction of the controller and providing constant current for the battery; a power supply electrically connected with the controller and the programmable constant current source, for providing power for the controller and the programmable constant current source; wherein the controller does not issue an instruction to the programmable constant current source, and the controller calculates the discharge voltage change rate according to the voltage data fed back by the measuring instrument; the controller issues an instruction to the programmable constant current source, the programmable constant current source provides constant current for the battery, and the controller calculates the charging voltage change rate according to the voltage data fed back by the measuring instrument; and the controller calculates the self-discharge current according to the discharge voltage change rate and the charging voltage change rate.

2. The self-discharge test system of battery cells of claim 1, wherein, The measuring instrument is a direct current voltmeter.

3. The self-discharge test system of battery cells of claim 1, wherein, The application further comprises: an analog / digital converter (ADC) electrically connected with the measuring instrument and the controller, for converting the voltage of the battery measured in real time from an analog signal into a digital signal and inputting the digital signal into the controller.

4. The self-discharge test system of battery cells of claim 1, wherein, The application further comprises: a communication interface electrically connected with the controller, for transmitting the obtained self-discharge current value to a mobile terminal.

5. The self-discharge test system of battery cells of claim 4, wherein, The mobile terminal comprises a mobile phone and a computer.

6. A method of self-discharge testing of a battery cell, the method comprising: The application comprises the following steps: Step 1: turn off the programmable constant current source; Step 2: continuously collect voltage data of the battery for N times; Step 3: calculate the discharge K value of the battery according to the N voltage data; Step 4: the programmable constant current source outputs constant current I1 to charge the battery; Step 5: again collect voltage data of the battery for N times; Step 6: calculate the charging K value of the battery according to the N voltage data; Step 7: calculate the self-discharge current I0 according to the discharge K value and the charging K value; Step 8: update the constant current I1 output by the programmable constant current source according to the self-discharge current I0; Step 9: at least execute steps 1-8 twice to obtain the self-discharge current I0.

7. The self-discharge test method according to claim 6, characterized in that In steps 3 and 6, the following equations are established: Formula (1): Q=U*C; Formula (2): Q=I*t; According to formula (1) and formula (2), formula (3) is obtained: U = t·I / C; let K = I / C in formula (3), formula (4) is obtained: U = K·t, and the derivative or difference with respect to time is ; wherein Q is electric quantity, U is voltage, C is capacitance, I is current, and t is time.

8. The self-discharge test method of claim 7, wherein, In step 7, the following equation group is established according to K=I / C: , from the discharge current according to the system of equations: ; wherein K0 is the discharge K value, and K1 is the charging K value.

9. The self-discharge test method of claim 8, wherein, In step 9, the following steps are executed: Step 1: turn off the programmable constant current source; Step 2: continuously collect voltage data of the battery for N times; Step 3: calculate the discharge K value of the battery according to the N voltage data; Step 4: the programmable constant current source outputs constant current I2 to charge the battery; Step 5: again collect voltage data of the battery for N times; Step 6: calculate the charging K value of the battery according to the N voltage data; Step 7: calculate the self-discharge current I0 according to the discharge K value and the charging K value, and the following equation group is established according to K=I / C: , the discharge current from the equation set: ; Wherein, K0 is the discharge K value, K2 is the charging K value calculated by the constant current output of the second programmable constant current source.

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