A method for measuring the effect of temperature on lithium-ion battery pack power performance

Abstract

The application discloses a kind of temperature influence measurement methods of lithium ion battery pack power performance.It is to solve the influence of temperature gradient on lithium ion battery pack power performance, the application includes the following steps: the battery is placed in temperature controllable constant temperature room;Regulate the temperature outside the battery, so that temperature gradient difference is formed between the battery;HPPC test is carried out to the battery;After repeating several times according to the same method under the same condition in the third step, stop experiment, and record experimental data, according to experimental data, evaluate the influence of temperature on lithium ion battery power performance.The advantage is suitable for all types of existing lithium ion batteries, strong applicability, simple operation, low measurement cost, help lithium ion battery module design and development.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a method for measuring the effect of temperature on the power performance of lithium-ion battery packs. Background Technology

[0002] To meet the energy and power requirements of electric vehicles, power batteries consist of numerous lithium-ion batteries connected in parallel and series. Due to manufacturing and structural tolerances, lithium-ion batteries generate uneven thermal stress during operation. Furthermore, the anisotropic thermal conduction of lithium-ion power batteries leads to temperature gradients within the battery pack, potentially causing severe thermal runaway. Compared to energy, the temperature gradient has a more significant impact on the power of lithium-ion batteries, making the optimization of temperature distribution crucial for improving the power output of lithium-ion battery packs. However, many studies have neglected the influence of thermal distribution on unbalanced discharge between batteries.

[0003] For example, a method for testing the power characteristics of a lithium-ion battery, disclosed in Chinese patent literature (CN109633468B, publication date December 1, 2020), is characterized by including continuous charge-discharge power characteristic testing, continuous charge-discharge power characteristic ratio testing, and pulse power characteristic testing. Testing the battery's continuous power characteristics at different temperatures better reflects the battery's power characteristics under actual conditions. The proposed continuous charge-discharge power characteristic ratio better reflects the quality of battery power characteristics, facilitating comparison of product power characteristics. Pulse power characteristic testing more comprehensively tests and simulates the battery's power characteristics under different ambient temperatures and states of charge. Battery voltage changes can be tested based on actual power usage. However, this invention neglects the influence of temperature on battery power characteristics, has technical limitations, and cannot meet the actual technical requirements of lithium-ion power batteries. Summary of the Invention

[0004] This invention primarily addresses the impact of temperature gradients on the power performance of lithium-ion battery packs; it provides a method for measuring the effect of temperature on the power performance of lithium-ion battery packs, accurately measuring the temperature sensitivity of the power performance of parallel lithium-ion battery packs, and proposes an optimization scheme.

[0005] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0006] This invention includes the following steps:

[0007] S1: Place the battery in a temperature-controlled constant temperature room;

[0008] S2: Regulate the external temperature of the battery to create a temperature gradient difference between the batteries;

[0009] S3: HPPC (Hybrid Pulse Power Characteristic) test is performed on the battery;

[0010] S4: After step S3, the experiment is stopped after repeating the same method several times under the same conditions, and the experimental data is recorded, and the influence of temperature on the power performance of lithium ion battery is evaluated according to the experimental data.

[0011] The innovation of the present application is that the influence of temperature on the power performance of lithium ion battery is evaluated, and the charging and discharging power of lithium ion power battery pack at different temperatures is accurately evaluated by using a test device with forced temperature gradient.

[0012] As a preferred, the lithium ion battery used is a soft package laminated structure, the design capacity is 10-20 Ah, the thickness is 8-10 mm, the positive electrode material is one or two or three of lithium iron phosphate / layered transition metal oxide / lithium manganate, and the negative electrode material is one or two or three of natural graphite / artificial graphite / mesocarbon microbeads. This is to make the current of the lithium ion battery stable during charging and discharging, and the temperature of the battery will not change too much.

[0013] As a preferred, the step S1 comprises the following steps:

[0014] S11: Place all test devices and lithium ion batteries in a temperature controllable constant temperature room, and package each single cell of the lithium ion battery in a separate copper chamber, and fix each copper chamber on a copper rail;

[0015] S12: Connect all negative electrodes of the six lithium ion batteries, connect all positive electrodes, and connect the negative and positive electrodes of the lithium ion battery with the wires of the charging and discharging test cabinet;

[0016] S13: Place the lithium ion battery for 2-3h before starting the test.

[0017] This is to keep the temperature of the battery at 25℃ and make the battery reach temperature balance.

[0018] As a preferred, the inner surface of the copper chamber is uniformly covered with a heat conducting foil, the surface of the copper rail is wound with a cooling pipe, the cooling pipe contains a cooling liquid, the copper rail is connected with a heating source, and a cooling liquid driving pump is installed at each end of the copper rail. The purpose of winding the cooling pipe is to improve the adjustability of the temperature of the copper rail and the copper chamber.

[0019] As preferred, in step S2, the power of the heating source is regulated by controlling the voltage, the control range of the power is 30-100 kW, the flow speed of the cooling liquid is controlled within 0.5 m / s-4.0 m / s by driving the pump of the cooling liquid, the temperature of the two packs of batteries in the middle position is 25℃, the temperature of the other batteries on both sides decreases in turn, and the temperature difference between the adjacent two packs of batteries is 1.0-1.5℃. This is to control the temperature of the batteries in gradient, and the temperature difference between the adjacent batteries is not large, which will not seriously interfere with the experimental results.

[0020] As preferred, step S3 comprises the following steps:

[0021] S31: the charge-discharge test cabinet charges the lithium ion battery at a 0.3C rate current through a wire;

[0022] S32: when charged to 20% SOC (State of Charge, i.e. the state of charge, which is used to reflect the remaining capacity of the battery, and its value is defined as the ratio of the remaining capacity to the battery capacity, commonly expressed in percentage), the battery is left for 30-60 min;

[0023] S33: pulse charging at a 3-10C rate current, charging for 10-20 s, and leaving the battery for 30-60 s after charging is completed;

[0024] S34: pulse discharging at the same rate current as charging, discharging for 10-20 s, and leaving the battery for 30-60 s after discharging is completed;

[0025] S35: repeating steps S32, S33 and S34 every 20% SOC until the battery reaches 100% SOC.

[0026] The HPPC test reflects the pulse charge-discharge performance of the power battery.

[0027] As preferred, the discharge power and charge power calculation method is:

[0028] Charge power = Vmax(Vmax-OCV) ÷ DCR charge;

[0029] Discharge power = Vmin(OCV-Vmin) ÷ DCR discharge;

[0030] Wherein, the charging direct current resistance DCR charge = (Vt1-Vt0) / (It0-It1), the discharging direct current resistance DCR discharge = (Vt0-Vt1) / (It1-It0), Vmin is the lower limit of the battery voltage, Vmax is the upper limit of the battery voltage, OCV is the open circuit voltage, Vt0 is the voltage at t0, Vt1 is the voltage at t1, It0 is the current at t0, and It1 is the current at t1.

[0031] The application has the advantages of being applicable to all types of lithium ion batteries, high applicability, simple operation, low measurement cost, and being helpful for lithium ion battery module design and development. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a structural diagram of a power test device with a temperature gradient for a temperature influence on lithium ion battery pack power performance measurement method of the application.

[0033] Figure 2 is a temperature diagram of a lithium ion single battery in a forced temperature gradient device for a temperature influence on lithium ion battery pack power performance measurement method of the application.

[0034] Figure 3 is a mixed pulse power test current-time change schematic diagram for a temperature influence on lithium ion battery pack power performance measurement method of the application.

[0035] In the figure, 1 is a charge-discharge test cabinet, 2 is a copper rail coated with a heat-conducting paste, 3 is a driving pump, 4 is a lithium ion cell, 5 is a heat-conducting foil, and 6 is a heating source. DETAILED DESCRIPTION

[0036] The technical solutions of the application are further specifically described below by means of examples and in combination with the drawings.

[0037] Example:

[0038] The temperature influence on lithium ion battery pack power performance measurement method of the example includes the following steps:

[0039] S1: Place the battery in a temperature-controllable constant temperature room, and also place all test devices in the temperature-controllable constant temperature room, such as a constant temperature room. Figure 1As shown, all test devices and lithium ion batteries are placed in a temperature-controllable thermostat, and the single cells of each lithium ion battery are packaged in a separate copper chamber, and the inner surface of the copper chamber is uniformly covered with a high thermal conductivity resin film (including one of graphene film, polyimide film, boron nitride thermal film, aluminum plastic film, etc.) or metal foil (including one of silver, gold, copper, aluminum, platinum, zinc, etc.), the thickness of the film or foil is 0.5-1mm, and the distance between the foil and the surface of the battery is ensured to be 2-4mm during the experiment. Within this distance range, it can ensure that the battery is heated quickly and uniformly, and it can also avoid the contact between the battery and the inner wall of the copper chamber, which can cause the external pressure to increase. The purpose of covering the high thermal conductivity film or foil is to increase the heat transfer and the heating speed of the battery. All the copper chambers are fixed on a copper rail with screws according to the designed spacing, and the size of the copper rail is determined according to the experimental requirements. The surface of the copper rail is wrapped with cooling pipes, and the cooling pipes contain cooling liquid. The composition of the cooling liquid is one of alcohol type, glycerol type and ethylene glycol type. The purpose of wrapping the cooling pipes is to improve the adjustability of the temperature of the copper rail and the copper chamber. The contact area between the copper chamber and the copper rail is filled with thermal conductive glue to reduce the interface heat transfer resistance. The copper rail is connected with the heating source, and each end is equipped with a cooling liquid driving pump. In order to reduce the heat loss of the copper rail in the air and maintain the temperature stability during the test, the above test device is placed in a thermostat or a thermostat. Connect the negative and positive electrodes of the lithium ion battery with the wires of the charge and discharge test cabinet; before the test starts, the lithium ion battery is placed for 2-3h.

[0040] S2: Adjust the temperature of the battery outside to form a temperature gradient difference between the batteries. In order to accurately simulate the actual use conditions, the power of the heating source is controlled by controlling the voltage, and the control range of the power is 30-100kW. The flow speed of the cooling liquid is controlled within 0.5m / s-4.0m / s by the cooling liquid driving pump, so that the temperature of the middle position 3# and 4# battery is 25℃, and the temperature of the batteries on both sides decreases in turn, and the temperature difference between the adjacent two batteries is 1.0-1.5℃.

[0041] S3: HPPC test of the battery. First, the charge and discharge test cabinet is charged to the lithium ion battery at 0.3C rate current; when charged to 20% SOC, the battery is placed for 30-60min; pulse charging at 3-10C rate current, charging for 10-20s, and after charging, the battery is placed for 30-60s; then pulse discharge at the same rate current as charging, discharge for 10-20s, and after discharging, the battery is placed for 30-60s; repeat steps S32, S33 and S34 every 20% SOC until the battery reaches 100% SOC. Figure 2 is a schematic diagram of the change of current with time during HPPC test, Figure 2 Take pulse current 5C, pulse time 18S, and rest time 40S as an example.

[0042] S4: Repeat step S3 three times under the same conditions and in the same way, then stop the experiment and record the experimental data. Evaluate the effect of temperature on the power performance of lithium-ion batteries based on the experimental data.

[0043] The method for calculating the charging or discharging power of a lithium-ion battery at a certain target SOC is as follows:

[0044] Charging power = Vmax(Vmax-OCV) ÷ DCR charging;

[0045] Discharge power = Vmin(OCV - Vmin) ÷ DCR discharge;

[0046] Where the charging DC internal resistance DCR is (Vt1-Vt0) / (It0-It1); the discharging DC internal resistance DCR is (Vt0-Vt1) / (It1-It0), Vmin is the lower limit of battery voltage, Vmax is the upper limit of battery voltage, OCV is the open circuit voltage, Vt0 is the voltage at t0, Vt1 is the voltage at t1, It0 is the current at t0, and It1 is the current at t1.

[0047] To improve the accuracy of the results, the experiment was repeated three times under the same conditions and using the same method. The lithium-ion battery used was a pouch-type stacked structure with a designed capacity of 10-20 Ah and a thickness of 8-10 mm. The positive electrode material was one or more of lithium iron phosphate, layered transition metal oxide, and lithium manganese oxide, and the negative electrode material was one or more of natural graphite, artificial graphite, and mesophase carbon microspheres.

[0048] like Figure 2 The table shows the actual temperatures of the lithium-ion batteries during the test. It can be seen that within the device with a forced temperature gradient, the temperature gradually decreases from batteries #3 and #4 in the middle, with the temperature difference between adjacent battery packs not exceeding 1.5℃. Batteries #3 and #4 have the highest temperatures. In the comparative test, when the temperature was maintained at 25℃, the power performance of all lithium-ion batteries showed no significant difference, indicating good battery consistency (see table below). After applying the temperature gradient, the power performance differences of the lithium-ion batteries increased significantly, as shown in the table below. At all SOC levels, batteries #3 and #4, with higher temperatures, had the best charge and discharge power performance, while the outermost batteries #1 and #6 had the lowest power. At 60% SOC, the discharge power difference between batteries #1 and #3 was the highest, approximately 4.8%. This value leads to significant battery inconsistency, causing a decrease in the overall power performance of the module. The discharge power difference between batteries #1 and #2, with lower temperature differences, was approximately 1.8%. This data indicates that the power of lithium-ion batteries is highly sensitive to temperature. Considering the impact of temperature during the production of lithium-ion battery modules is an unavoidable step in achieving reliable and safe use.

[0049] The method and structure provide important technical references for lithium ion power battery module structure, cooling mode and management method.

[0050]

[0051] Table 1

[0052] It should be understood that the embodiments are only used for illustrating the present application but not for limiting the scope of the present application. Furthermore, it should be understood that after reading the content of the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims

1. A method of measuring the effect of temperature on lithium-ion battery pack power performance, characterized by, The method comprises the following steps: S1: placing the battery in a temperature-controllable constant temperature chamber, the single cell of each lithium ion battery is packaged in a separate copper chamber, each copper chamber is fixed on a copper rail, the inner surface of the copper chamber is covered with a heat-conducting foil, the surface of the copper rail is wrapped with a cooling pipe, the copper rail is connected with a heating source, and a cooling liquid driving pump is installed at both ends of the copper rail; S2: by controlling the power of the heating source and the flow rate of the cooling liquid, the temperature of the two batteries at the middle position is 25℃, the temperature of the batteries on both sides decreases in turn, and the temperature difference between the adjacent two batteries is 1.0-1.5℃, forming a temperature gradient difference; S3: HPPC test is performed on the battery; S4: after repeating the same method several times under the same conditions, the experiment is stopped, and the experimental data is recorded, and the influence of temperature on the power performance of the lithium ion battery is evaluated according to the experimental data.

2. The method of claim 1, wherein the temperature is measured at a temperature of 25°C. The lithium ion battery used is a soft package laminated structure, the designed capacity is 10-20 Ah, the thickness is 8-10 mm, the positive electrode material is one or two or three of lithium iron phosphate / layered transition metal oxide / lithium manganate, and the negative electrode material is one or two or three of natural graphite / artificial graphite / mesocarbon microbeads.

3. The method of claim 1, wherein the temperature is measured at a temperature of 25°C. Step S1 comprises the following steps: S11: placing all test devices and lithium ion batteries in a temperature-controllable constant temperature chamber, the single cell of each lithium ion battery is packaged in a separate copper chamber, and each copper chamber is fixed on a copper rail; S12: connecting all negative electrodes of a plurality of lithium ion batteries, connecting all positive electrodes, and connecting the negative electrodes and positive electrodes of the lithium ion battery with the wires of the charge-discharge test cabinet; S13: the lithium ion battery is placed for 2-3h before the test starts.

4. The method of claim 3, wherein the temperature is measured at a temperature of 25°C. The inner surface of the copper chamber is uniformly covered with a high-thermal-conductivity resin film or a metal foil, the thickness of the high-thermal-conductivity resin film or the metal foil is 0.5-1mm, and the distance between the high-thermal-conductivity resin film or the metal foil and the surface of the battery during the experiment is 2-4mm.

5. The method of claim 3 or 4, wherein the temperature is measured at a temperature of 25°C. In step S2, the power of the heating source is controlled by controlling the voltage, the power control range is 30-100kW, and the flow speed of the cooling liquid is controlled within 0.5 m / s-4.0m / s by the cooling liquid driving pump, so that the temperature of the two batteries at the middle position is 25℃, the temperature of the batteries on both sides decreases in turn, and the temperature difference between the adjacent two batteries is 1.0-1.5℃.

6. The method of claim 1, wherein the temperature is measured at a temperature of 25°C. Step S3 comprises the following steps: S31: the charge-discharge test cabinet charges the lithium ion battery at a 0.3C rate current through the wires; S32: when charged to 20% SOC, the battery is placed for 30-60min; S33: pulse charging at a rate current of 3-10C, charging for 10-20s, and placing the battery for 30-60s after charging is completed; S34: pulse discharging at the same rate current as charging, discharging for 10-20s, and placing the battery for 30-60s after discharging is completed; S35: repeating steps S32, S33 and S34 every 20% SOC until the battery reaches 100% SOC.

7. The method of claim 5, wherein the temperature is measured at a temperature of 25°C. The discharge power and the charging power are calculated as follows: Charging power = Vmax(Vmax-OCV) ÷ DCR charging; Discharge power = Vmin (OCV - Vmin) ÷ DCR discharge; Wherein the charging direct current resistance DCR charge = (Vt1-Vt0) / (It0-It1); the discharging direct current resistance DCR discharge = (Vt0-Vt1) / (It1-It0), Vmin is the lower limit of battery voltage, Vmax is the upper limit of battery voltage, OCV is open circuit voltage, Vt0 is the voltage at t0, Vt1 is the voltage at t1, It0 is the current at t0, It1 is the current at t1.

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