Power battery specific heat capacity quasi-steady-state measurement method

Abstract

The invention relates to a power battery specific heat capacity quasi-steady-state measurement method, which comprises the following steps of: respectively arranging heating films on two large surfaces of a power battery, and uniformly and symmetrically arranging a plurality of thermocouples on the heating film on one large surface along the diagonal direction of the power battery, thermocouples with the same number are reversely and symmetrically arranged on the heating film on the surface of the other large surface along the direction of the other crossed diagonal line of the power battery, and an insulating material is wrapped outside the power battery; placing the processed power battery in a temperature control box, connecting the temperature control box with external test equipment through a connecting line, and adjusting and controlling the temperature control box to keep the initial temperature constant; the temperature rise rate is calibrated through heat loss calibration in the heating temperature rise stage and the slow cooling stage, and the specific heat capacity of the power battery is calculated based on the calibrated temperature rise rate. The specific heat capacity of the power battery can be obtained without extra heat loss calibration test, the method is suitable for stylized data algorithm processing, the data processing time is short, and the test result is accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a quasi-steady-state measurement method for specific heat capacity of a power battery. Background Art

[0002] Specific heat capacity is an important thermophysical parameter of power batteries. It indicates the rate at which the battery heats up and is a key thermophysical parameter for effective thermal management of the battery. Especially for thermal runaway suppression scenarios, accurate measurement of battery specific heat is conducive to accurate prediction of battery temperature and precise thermal protection design. However, traditional power battery specific heat capacity test devices usually use separate heat loss calibration and heating temperature equalization test to determine the specific heat capacity of the power battery. The specific heat capacity needs to be calculated once in each time period. Although the specific heat capacity of the power battery can be obtained, the heat loss curve needs to be calibrated separately, and the test time is long. Especially for power batteries of different specifications, additional heat loss calibration is required. This heat loss calibration generally takes more than 4-6 hours, the test time is long, and manual calculation is required. The calculation process is cumbersome and error-prone. Therefore, it needs to be improved. Summary of the invention

[0003] Based on this, it is necessary to provide a quasi-steady-state measurement method for the specific heat capacity of a power battery in view of the fact that the specific heat capacity test device of the traditional power battery needs to calculate the specific heat capacity once in each time period. Although the specific heat capacity of the power battery can be obtained, the heat loss curve needs to be calibrated separately, and the test time is long. Especially for power batteries of different specifications, additional heat loss calibration is required, the test time is long, manual participation in the calculation is required, and the calculation process is cumbersome and prone to errors.

[0004] The present invention provides a quasi-steady-state measurement method for specific heat capacity of a power battery, comprising:

[0005] Arrange heating films on the two large surfaces of the power battery respectively, arrange multiple thermocouples evenly and symmetrically on the heating film on one of the large surfaces along the diagonal direction of the power battery, and arrange the same number of thermocouples on the heating film on the other large surface in the opposite direction along the other cross diagonal direction of the power battery, and wrap the power battery with insulating material;

[0006] Place the treated power battery in a temperature control box and connect it to the external test equipment through a wire, and adjust and control the temperature control box to keep the initial temperature constant;

[0007] The temperature rise rate is calibrated by heat loss calibration through the heating temperature rise stage and the slow cooling stage, and the specific heat capacity of the power battery is calculated based on the calibrated temperature rise rate.

[0008] In one embodiment, the heat loss calibration is performed through the heating temperature rise stage and the slow cooling stage to calibrate the temperature rise rate, and the specific heat capacity of the power battery is calculated based on the temperature rise rate, including:

[0009] Turn on the heating film and heat the power battery at a constant power until the heating reaches the predetermined maximum average temperature, then stop heating, record the time and temperature rise of the heating stage, and calculate the instantaneous heating power and actual heating rate;

[0010] After stopping heating, allow the power battery to cool down naturally for a period of time until the temperatures of the thermocouples on the surface of the power battery tend to be consistent, and record the time and temperature rise of the natural cooling stage;

[0011] After the power battery is cooled naturally for a period of time, it enters a slow cooling stage, records the temperature and time of the power battery surface during the slow cooling stage, and fits the exponential function of temperature and time through the slow cooling stage to obtain the change rate of heat loss rate over time and the temperature rise rate of the power battery;

[0012] The temperature rise rate is compensated during the quasi-steady-state heating process in the heating stage, and the specific heat capacity of the power battery is calculated based on the compensated temperature rise rate.

[0013] In one embodiment, the quasi-steady-state heating process in the heating temperature rise stage compensates the temperature rise rate, and calculates the specific heat capacity of the power battery based on the compensated temperature rise rate, including:

[0014] According to the change of the average temperature rise of the battery over time, the linear temperature rise function equation in the heating stage and the exponential function of the temperature rise and time in the slow cooling stage are fitted respectively;

[0015] The first-order derivative of the exponential function equation is calculated to obtain the cooling rate or heat loss function of the power battery at each stage. The instantaneous heat loss rate calculation formula in the heating stage is as follows:

[0016]

[0017] Among them, C 3 is the fitting constant, ΔT ave Indicates temperature rise;

[0018] According to the law of energy conservation, the actual temperature rise of the power battery during the heating stage and the compensated heat loss, the specific heat capacity of the power battery is calculated. The specific heat capacity calculation formula of the power battery is as follows:

[0019]

[0020] Among them, m b is the mass of the power battery, m ht Indicates the mass of the heating film, c htrepresents the specific heat capacity of the heating film, P is the instantaneous heating power, t 1 is the heating stage time, t 0 is the transient heating time of the power battery, t 0 =0.5*ρ*(cb)*L*2 / k, ρ is the density of the power battery, L is the half thickness of the power battery, and k is the normal thermal conductivity of the power battery.

[0021] In one of the embodiments, the heating stage time ranges from 80 seconds to 10 minutes, the battery transient heating time ranges from 50 seconds to 300 seconds, and the heating stage time is greater than the battery transient heating time.

[0022] In one of the embodiments, the temperature standard deviation and the temperature extreme difference of the transient heating time of the power battery are within 85% of the maximum temperature difference of the entire heating stage, and increase with the increase of the thickness of the power battery.

[0023] In one embodiment, the natural cooling stage ends 80 to 200 seconds after the end of the accelerated heating stage, and is gradually extended as the thickness of the power battery increases.

[0024] In one embodiment, the slow cooling stage lasts between 1000 seconds and 6000 seconds, and is gradually prolonged as the thickness of the power battery increases.

[0025] In one of the embodiments, one side of the heating film is coated with glue and adheres to the middle part of the power battery, and the coverage area of ​​the heating film is greater than or equal to 80% of the large surface area of ​​the power battery.

[0026] In one embodiment, the heating film is composed of an outer electrical insulating material film covering an inner electrical heating film layer, the thermal conductivity resistance of the heating film is smaller than the thermal conductivity resistance of the insulating layer itself, and the thickness of the heating film is 0.05 mm to 0.2 mm.

[0027] In one of the embodiments, the thermal insulation layer is made of an aerogel layer or a foamed nitrile rubber material, and the thermal conductivity resistance of the thermal insulation layer is greater than the convection heat dissipation resistance from its surface to the environment.

[0028] The above-mentioned quasi-steady-state measurement method for specific heat capacity of power batteries can obtain the temperature rise and heat loss results of power batteries in one test, thereby facilitating the calculation of specific heat capacity of power batteries. No additional heat loss calibration test is required, and it is suitable for programmed data algorithm processing. It can quickly obtain the heat loss rate and specific heat of power batteries, reducing the workload of manual data processing. It has the advantages of simple form and convenient calculation, short measurement time and data processing time, and accurate test results. It is particularly suitable for the measurement and characterization of batteries of various sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 It is a schematic flow chart of a quasi-steady-state measurement method for specific heat capacity of a power battery in one embodiment;

[0031] Figure 2 A schematic diagram of a process for calibrating the temperature rise rate by heat loss calibration during the heating and slow cooling stages in one embodiment;

[0032] Figure 3 It is a schematic diagram of a flow chart of calculating the specific heat capacity of a power battery based on the compensated temperature rise rate in one embodiment;

[0033] Figure 4 A diagram showing a structural layout of a method for quasi-steady-state measurement of specific heat capacity of a power battery in an embodiment in a scenario in application example 1;

[0034] Figure 5 A schematic diagram of the change of the power battery temperature over time in a power battery specific heat capacity test in an embodiment;

[0035] Figure 6 is the heating time [t 0 , t 1 ] The variation diagram of the surface temperature rise in the interval and the fitting function expression;

[0036] Figure 7 A graph showing the change of the cooling time and the surface temperature drop in the slow cooling stage in one embodiment and a fitting function expression;

[0037] Figure 8 A schematic diagram showing a comparison between the temperature change during the total cooling time and the 1 / 3 cooling curve fitting in one embodiment;

[0038] Fig. 9 A structural diagram of the scenario layout of a quasi-steady-state measurement method for specific heat capacity of a power battery in an embodiment in application example three.

[0039] Reference numerals:

[0040] 410, heating film; 420, thermocouple; 430, insulation layer. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it may be directly on the other component or there may be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may be a central component at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in the specification of the present invention are for illustrative purposes only and do not represent the only implementation method.

[0043] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0044] In the present invention, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first feature is directly in contact with the second feature, or the first feature and the second feature are indirectly in contact through an intermediate medium. Moreover, a first feature being “above”, “above” or “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below” or “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0045] Unless otherwise defined, all technical and scientific terms used in the specification of the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the specification of the present invention includes any and all combinations of one or more related listed items.

[0046] Combine the following Figure 1-Figure 9 The present invention describes the quasi-steady-state measurement method of the specific heat capacity of a power battery.

[0047] like Figure 1 As shown, in one embodiment, a quasi-steady-state measurement method for specific heat capacity of a power battery comprises the following steps:

[0048] Step S100, respectively arrange heating films on the two large surfaces of the power battery, evenly and symmetrically arrange multiple thermocouples on the heating film on one of the large surfaces along the diagonal direction of the power battery, and arrange the same number of thermocouples on the heating film on the other large surface in the opposite symmetrical direction along the other cross diagonal direction of the power battery, and wrap the power battery with insulating material.

[0049] It should be noted that cracks must be avoided when wrapping the insulating material around the power battery to avoid affecting the measurement accuracy.

[0050] Step S200, placing the treated power battery in a temperature control box, connecting it to an external test device via a wire, and adjusting and controlling the temperature control box to keep the initial temperature constant.

[0051] It should be noted that the initial temperature T 0 The fluctuation is within 0.5℃.

[0052] Step S300, calibrating the temperature rise rate by heat loss calibration in a heating temperature rise stage and a slow cooling stage, and calculating the specific heat capacity of the power battery based on the calibrated temperature rise rate.

[0053] The quasi-steady-state measurement method for specific heat capacity of power batteries can obtain the temperature rise and heat loss results of power batteries in one test, thereby facilitating the calculation of specific heat capacity of power batteries. No additional heat loss calibration test is required, and the method is suitable for programmed data algorithm processing. The method can quickly obtain the heat loss rate and specific heat capacity of power batteries, reducing the workload of manual data processing. The method has the advantages of concise form and convenient calculation, short measurement time and data processing time, and accurate test results, and is particularly suitable for the measurement and characterization of batteries of various sizes.

[0054] In this embodiment, see Figure 2 The heat loss calibration and temperature rise rate calibration are performed in the heating temperature rise stage and the slow cooling stage, and the specific heat capacity of the power battery is calculated based on the temperature rise rate, including the following steps:

[0055] Step S310, turn on the heating film, heat the power battery at a constant power until the heating reaches a predetermined maximum average temperature, stop heating, record the time and temperature rise of the heating stage, and calculate the instantaneous heating power and actual heating rate.

[0056] Heat for a period of time to t 1 After reaching the maximum average temperature T ave1 , the temperature rise is ΔT ave1 (t 1), the instantaneous heating power is P.

[0057] Step S320, after stopping heating, the power battery is cooled naturally for a period of time until the temperatures of the thermocouples on the surface of the power battery tend to be consistent, and the time and temperature rise of the natural cooling stage are recorded.

[0058] When the temperature drops for a period of time to time t 2 At this time, the temperatures of the thermocouples on the surface of the power battery also tend to be consistent, and the fluctuation range, such as the standard deviation or range of the thermocouple readings, quickly decreases to a low level, such as t 1 When the temperature rises to 10% to 30% of the time, the temperature rise is ΔT ave2 (t 2 ).

[0059] Step S330, after the power battery is cooled naturally for a period of time, it enters a slow cooling stage, records the temperature and time of the power battery surface during the slow cooling stage, and fits the exponential function of temperature and time through the slow cooling stage to obtain the rate of change of heat loss rate over time and the temperature rise of the power battery.

[0060] Natural convection slowly cools down and dissipates heat until time t 3 Then stop the test.

[0061] Step S340 , compensating the temperature rise rate during the quasi-steady-state heating process in the heating stage, and calculating the specific heat capacity of the power battery based on the compensated temperature rise rate.

[0062] In this embodiment, see Figure 3 The quasi-steady-state heating process in the heating temperature rise stage compensates the temperature rise rate, and calculates the specific heat capacity of the power battery based on the compensated temperature rise rate, comprising the following steps:

[0063] Step S341 , according to the change of the average temperature rise of the battery over time, respectively fit the linear temperature rise function equation in the heating stage and the exponential function of the temperature rise and time in the slow cooling stage.

[0064] According to the average temperature T of the recorded battery cooling ave Changes with time t, in the interval [t 2 , t 3 ] is fitted as an exponential function of the average temperature rise versus time ΔT = exp[C 3 (tB 3 )], ΔT=T ave (t)-T 0 , T 0 is the initial temperature, and the heat loss function is d(ΔT) / dt=C 3 *ΔT, the form is simple and easy to calculate, where B 3 , C 3 is the fitting constant.

[0065] A polynomial function ΔT=ΔT(t) is fitted according to the heat dissipation curve of the power battery during the heating process, which facilitates the subsequent calculation of the specific heat capacity of the power battery.

[0066] An exponential function that is more in line with the cooling law is used to fit the cooling rate and heat loss function in the slow cooling stage. It is more concise, efficient, and accurate than the usual polynomial fitting function. The calculation is simple, which is conducive to programmed rapid calculation and reduces calculation errors. At the same time, the exponential function has strong regularity and does not require the entire cooling process to obtain an excellent fit, thereby shortening the cooling process time by several times. The entire battery test time is controlled within 1 to 2 hours, saving test time. It is suitable for testing batteries of various sizes. In the same measurement process, both heating measurement and calibration process are performed, and heat loss calibration and measurement are realized at the same time, thereby greatly saving actual measurement time.

[0067] Step S342, taking the first-order derivative of the exponential function equation to obtain the cooling rate or heat loss function of the power battery at each stage, wherein the instantaneous heat loss rate calculation formula in the heating stage is as follows:

[0068]

[0069] Among them, C 3 is the fitting constant, ΔT ave Indicates temperature rise.

[0070] Step S343, calculating the specific heat capacity of the power battery according to the law of energy conservation, the actual temperature rise of the power battery during the heating stage, and the compensated heat loss. The specific heat capacity calculation formula of the power battery is as follows:

[0071]

[0072] Among them, m b is the mass of the power battery, m ht Indicates the mass of the heating film, c ht represents the specific heat capacity of the heating film, P is the instantaneous heating power, t 1 is the heating stage time, t 0 is the transient heating time of the power battery, t 0 =0.5*ρ*(cb)*L*2 / k, ρ is the density of the power battery, L is the half thickness of the power battery, k is the normal thermal conductivity of the power battery, which can be calculated by series superposition of the thermal resistance of the layered structure of the internal materials of the battery.

[0073] See also Figure 5 , Figure 5 This is a schematic diagram of the change of power battery temperature over time in the power battery specific heat capacity test. At time t 0 Indicates the quasi-steady-state heating stage, time t1 ,t 2 ,t 3 They correspond to the end time of heating, the start time of slow cooling and the end time of slow cooling, respectively, and the average temperature T ave1 、T ave2 、T ave3 .

[0074] In this embodiment, the heating stage time t 1 The range of the battery transient heating time t is 80 seconds to 10 minutes. 0 The range is 50 seconds to 300 seconds, and the heating stage time is greater than the transient heating time of the battery, that is, t 1 >t 0 .

[0075] In this embodiment, the temperature standard deviation and the temperature extreme difference of the power battery transient heating time reach the entire heating stage, that is, t 1 The temperature difference is within 85% of the maximum temperature difference at the moment, and increases with the thickness of the power battery.

[0076] In this embodiment, the natural cooling stage ends 80 to 200 seconds after the end of the accelerated heating stage, and is gradually extended as the thickness of the power battery increases.

[0077] It should be noted that the natural cooling stage [t 1 , t 2 There is a significant temperature difference between the various temperatures of the power battery, and the slope is steep. The slope of the slow cooling stage is significantly slowed down, and the temperature difference between the various temperatures tends to be consistent. When the standard deviation or range of each temperature is reduced to t 1 When the temperature is within 10% to 30% of the time, it corresponds to the time when the natural cooling stage ends. 2 .

[0078] In this embodiment, the slow cooling stage [t 2 , t 3 ] The time is between 1000 seconds and 6000 seconds, and gradually increases with the increase of the thickness of the power battery.

[0079] In this embodiment, one side of the heating film is coated with glue and adheres to the middle part of the power battery, and the coverage area of ​​the heating film is greater than or equal to 80% of the large surface area of ​​the power battery.

[0080] In this embodiment, the heating film is composed of an outer electrical insulating material film covering an inner electrical heating film layer. The thermal resistance of the heating film is smaller than the thermal resistance of the insulating layer itself. The thickness of the heating film is 0.05 mm to 0.2 mm.

[0081] In this embodiment, the heat insulating layer is made of an aerogel layer or a foamed nitrile rubber material, and the heat conduction resistance of the heat insulating layer is greater than the convection heat dissipation resistance from its surface to the environment.

[0082] Application example 1:

[0083] Power batteries can be of various shapes, such as square hard shell batteries, soft pack batteries, and blade batteries.

[0084] This embodiment uses a square hard-shell power battery with dimensions of 148mm x 92mm x27mm, a capacity of 50AH, and a mass of 0.84kg. Figure 4 A heating film is applied to each of the two large surfaces of the power battery, with an instantaneous heating power of 36W. The two parts of the heating film are attached to the outer surface of the power battery. Five thermocouples are evenly arranged on the surface of each large surface of the power battery, and there are a total of 10 thermocouples on the two large surfaces. The insulation layer wraps the power battery, heating film and thermocouple and is placed in a temperature control box.

[0085] Preset heating film heating time t for power battery 1 =493s. To reduce the test error, the temperature rise of the power battery shall not be less than 10°C. Considering the thermal safety of the power battery, its maximum preheating temperature shall not be higher than the maximum allowable temperature of the battery, such as 70°C.

[0086] The insulation layer is used to wrap the power battery, reducing the heat dissipation rate to ensure uniform temperature inside and outside the battery. At the same time, the thermal conductivity formed is greater than the convection thermal resistance, thereby reducing the measurement error caused by the fluctuation of the convection thermal resistance. Considering the convection heat transfer coefficient of 10W / m 2 K, corresponding to thermal resistance of 0.1Km 2 / W. A 10mm thick aerogel layer is selected as the insulating layer, and its thermal conductivity is 0.02W / mK. The thermal resistance of the aerogel layer is 0.01 / 0.02=0.5Km 2 / W, significantly larger than the convection thermal resistance of 0.1Km 2 / W. If foamed nitrile rubber is used, the thermal conductivity is 0.036W / mK, and the thickness is about 10mm. The thermal resistance of foamed nitrile rubber is 0.01 / 0.036=0.3Km 2 / W, which is also significantly larger than the convection thermal resistance, which can greatly reduce the heat dissipation rate fluctuation and measurement error caused by convection instability. It also helps to ensure the uniformity of the temperature inside and outside the battery, which helps with measurement accuracy.

[0087] The various test processes include heating, natural cooling, and slow cooling. The main steps include:

[0088] 1. The initial temperature of the temperature control box cavity is preset to T 0= 8℃, the power battery is heated by the heating film for 493s, where the heating time is greater than the pre-calculated battery transient temperature rise time t 0 = 135s. Stop heating and allow it to cool down naturally for the first time t 2 ~100s(surface temperature rise ΔT 2 ), and then enter the slow cooling stage until time t = 8300s.

[0089] 2. See Figure 6 and Figure 7 , when the initial temperature T 0 The temperature change of the power battery during heating and slow cooling at 20°C. ave It is the average temperature of 10 temperature measurement points on the surface of the power battery.

[0090] Heating stage [t 1 , 493s], fitting the first-order or second-order polynomial function of temperature rise versus time t, here the fitting is the first-order polynomial ΔT ave =3.879E-02*t+7.167, fitting coefficient R 2 =0.9996, indicating that the fitting accuracy is excellent in the above range. It should be noted that the fitting constants in the fitting polynomials are all retained to 4 significant decimal places to avoid measurement errors caused by insufficient calculation accuracy.

[0091] The end time of natural cooling can be determined by estimating the temperature difference. 2 Generally in t 1 After 100s to 200s, the time will be extended as the thickness of the power battery increases. 1 , t 2 ] There is a significant temperature difference between the various temperatures of the power battery, and the slope is steep. When the temperature difference between the various temperatures tends to be consistent, when the standard deviation or range of each temperature is reduced to t 1 When the temperature is within 10% to 30% of the time, it corresponds to the time when the natural cooling ends. 2 , where t 2 =603s.

[0092] In the slow cooling stage, the full temperature section [603s, 8300s] was fitted with the 1 / 2 cooling section [400s, 4400s] time interval to obtain the exponential function ΔT ave =20.40exp(-1.079E-04*t), where the fitted exponential coefficient C 3 =-1.079E-4, good fitting accuracy, R 2 =0.9999.

[0093] The specific heat capacity calculation formula of the power battery can be used to calculate the specific heat value of the power battery to be 1054J / kgK. The influence of the heat capacity of the heating film itself (~1%) has been eliminated in the calculation process. This test can be completed using a local cooling curve. The measurement time is about 1 hour, which is much shorter than the conventional adiabatic acceleration measurement instrument and the additional heat loss calibration time. It is suitable for testing batteries of various specifications and sizes.

[0094] Application example 2:

[0095] A simulation model for power battery measurement is established in the simulation model to simulate each test process, including heating, natural cooling, and slow cooling. The main steps include:

[0096] 1. The initial temperature of the temperature control box cavity is preset to T 0 = 8°C, heat the power battery for 300s through the heating film, stop heating and let it cool down naturally for 100s, that is, time t 2 ~400s(surface temperature rise ΔT 2 ), and then enter the slow cooling stage until time t = 10000s.

[0097] 2. See Figure 6 , Figure 7 and Figure 8 , when the initial temperature T 0 The temperature change during the power battery specific heat capacity test at 20°C. ave It is the average temperature of 10 temperature measurement points on the surface of the power battery.

[0098] Fitting the quasi-steady-state heating stage [t 1 , t 2 ], [150, 300s], average temperature rise of power battery ΔT ave The functional relationship over time is a first-order polynomial.

[0099] According to the temperature difference change in the natural cooling stage, it is estimated that at t 2 = 400s, then enter the slow cooling stage. Figure 8 In the slow cooling stage, the full temperature section [400s, 10000s] is fitted with the 1 / 3 cooling section [400s, 3400s] time interval to obtain ΔT ave =13.02exp(-1.151E-04*t), C 3 =-1.151E-4, fitting coefficient R 2 =0.9999. The local cooling curve can be used to obtain the fitting relationship of all slow cooling stages with a small deviation, and the root mean square deviation is RMSE = 0.03 °C.

[0100] The calculated specific heat value of the power battery is 1099.6 J / kgK, which is 1078 J / kgK, and the error is 2.0%. The influence of the heat capacity of the heating film itself (~1%) has been eliminated in the calculation process. The error is very small, indicating that the measurement accuracy of this method is high, and the local cooling curve can be used to complete the test in about 1 hour, which is much shorter than the 4 to 8 hours of conventional adiabatic acceleration measurement instruments and the additional heat loss calibration time.

[0101] If the preset temperature T is changed in the above process 0 Repeat the above steps to measure the specific heat of power batteries at different temperatures. The initial box temperature of the temperature control box is T 0 By adjusting from low temperature to high temperature, the specific heat capacity of the power battery under different operating temperatures can be tested.

[0102] Application Example 3:

[0103] There is no specific limit on the size of the power battery, and it is suitable for one or more square batteries, soft-pack batteries and blade batteries arranged symmetrically, which can be set according to the specific situation. In order to facilitate the heat conduction of the heating film and reduce additional heat loss, the heating film material includes an internal conductive material and an external lightweight electrical insulating film material, such as polyimide. Fig. 9 The test device and thermocouple diagram of a battery pack consisting of two power batteries. In order to ensure rapid heating of the battery, in addition to the large surface of the power battery, heating films and thermocouples are arranged on the two sides facing the power battery. The heating heat flux density, that is, the ratio of power to area, is consistent with the heating heat flux density of the large surface of the battery. The heating power on the battery side is included in the total power P, and the thermocouple reading is included in the calculation of the average battery temperature.

[0104] In this embodiment, the mass of the power battery is known. By calculating the heat generated by the heating film, the temperature change of the power battery, and the heat loss calibration, the temperature-time change curve of the power battery is obtained, and the specific heat value is directly determined without the need for additional multiple calculations and averaging.

[0105] The method of the present invention also uses a standard stainless steel 304 sample for comparative testing. The specific heat capacity of stainless steel of the same size at room temperature is obtained by the same calculation method as 508 J / kgK, which deviates from the standard value of 490 in the literature (Thermophysical Properties, ASM Handbook, 15, 2008: 468-481) by 3.6%, thereby verifying the accuracy of the measurement method.

[0106] The present invention provides a method for measuring the specific heat capacity of a power battery with short measurement time, accurate test results, low cost, easy implementation, and the ability to test different operating temperatures. It can provide reliable specific heat capacity test data of power batteries for power battery manufacturers, electric vehicle companies and other institutions, and can be directly used for battery thermal management design.

[0107] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above-described embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A quasi-steady-state measurement method for specific heat capacity of a power battery, characterized in that: include: Arrange heating films on the two large surfaces of the power battery respectively, arrange multiple thermocouples evenly and symmetrically on the heating film on one of the large surfaces along the diagonal direction of the power battery, and arrange the same number of thermocouples on the heating film on the other large surface in the opposite direction along the other cross diagonal direction of the power battery, and wrap the power battery with insulating material; Place the treated power battery in a temperature control box and connect it to external test equipment through wires, and adjust and control the temperature control box to keep the initial temperature constant; The temperature rise rate is calibrated by heat loss calibration through the heating temperature rise stage and the slow cooling stage, and the specific heat capacity of the power battery is calculated based on the calibrated temperature rise rate.

2. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 1, characterized in that: The heat loss calibration is performed through the heating temperature rise stage and the slow cooling stage to calibrate the temperature rise rate, and the specific heat capacity of the power battery is calculated based on the temperature rise rate, including: Turn on the heating film and heat the power battery at a constant power until the heating reaches the predetermined maximum average temperature, then stop heating, record the time and temperature rise of the heating stage, and calculate the instantaneous heating power and actual heating rate; After stopping heating, allow the power battery to cool down naturally for a period of time until the temperatures of the thermocouples on the surface of the power battery tend to be consistent, and record the time and temperature rise of the natural cooling stage; After the power battery is cooled naturally for a period of time, it enters a slow cooling stage, records the temperature and time of the power battery surface during the slow cooling stage, and fits the exponential function of temperature and time through the slow cooling stage to obtain the change rate of heat loss rate over time and the temperature rise rate of the power battery; The temperature rise rate is compensated during the quasi-steady-state heating process in the heating stage, and the specific heat capacity of the power battery is calculated based on the compensated temperature rise rate.

3. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 2, characterized in that: The quasi-steady-state heating process in the heating temperature rise stage compensates the temperature rise rate, and calculates the specific heat capacity of the power battery based on the compensated temperature rise rate, including: According to the change of the average temperature rise of the battery over time, the linear temperature rise function equation in the heating stage and the exponential function of the temperature rise and time in the slow cooling stage are fitted respectively; The first-order derivative of the exponential function equation is calculated to obtain the cooling rate or heat loss function of the power battery at each stage. The instantaneous heat loss rate calculation formula in the heating stage is as follows: Where C3 is the fitting constant, ΔT ave Indicates temperature rise; According to the law of energy conservation, the actual temperature rise of the power battery during the heating stage and the compensated heat loss, the specific heat capacity of the power battery is calculated. The specific heat capacity calculation formula of the power battery is as follows: Among them, m b is the mass of the power battery, m ht Indicates the mass of the heating film, c ht represents the specific heat capacity of the heating film, P is the instantaneous heating power, t1 is the heating stage time, t0 is the transient heating time of the power battery, t0=0.5*ρ*(cb)*L*2 / k, ρ is the density of the power battery, L is the half thickness of the power battery, and k is the normal thermal conductivity of the power battery.

4. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 3, characterized in that: The time range of the heating stage is 80 seconds to 10 minutes, the time range of the battery transient heating is 50 seconds to 300 seconds, and the time of the heating stage is greater than the battery transient heating time.

5. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 4, characterized in that: The temperature standard deviation and the temperature extreme difference of the transient heating time of the power battery are within 85% of the maximum temperature difference of the entire heating stage, and increase with the increase of the thickness of the power battery.

6. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 5, characterized in that: The natural cooling stage ends 80 to 200 seconds after the end of the accelerated heating stage, and is gradually prolonged as the thickness of the power battery increases.

7. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 6, characterized in that: The time of the slow cooling stage is between 1000 seconds and 6000 seconds, and is gradually prolonged as the thickness of the power battery increases.

8. The quasi-steady-state measurement method for specific heat capacity of a power battery according to any one of claims 1 to 7, characterized in that: One side of the heating film is coated with glue and adhered to the middle part of the power battery. The covering area of ​​the heating film is greater than or equal to 80% of the large surface area of ​​the power battery.

9. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 8, characterized in that: The heating film is composed of an outer electrical insulating material film covering an inner electrical heating film layer. The thermal conductivity resistance of the heating film is smaller than the thermal conductivity resistance of the insulating layer itself. The thickness of the heating film is 0.05 mm to 0.2 mm.

10. The quasi-steady-state measurement method for specific heat capacity of a power battery according to claim 9, characterized in that: The heat insulating layer is made of an aerogel layer or a foamed nitrile rubber material, and the heat conduction resistance of the heat insulating layer is greater than the convection heat dissipation resistance from the surface of the heat insulating layer to the environment.

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