Method and device for testing specific heat capacity of energy storage battery

Abstract

The invention relates to a method and device for testing the specific heat capacity of an energy storage battery, and the method comprises the steps: arranging heating films on the two large surfaces of the energy storage battery respectively, and enabling the heating film on one large surface to be uniformly and symmetrically provided with a plurality of thermocouples in the diagonal direction of the energy storage 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 energy storage battery, and the energy storage battery is wrapped with a heat insulation layer material; placing the processed energy storage battery in a temperature control box, connecting the temperature control box with external test equipment through a connecting wire, and adjusting and controlling the temperature control box to keep the initial temperature constant; and respectively fitting a function relation between the time and the temperature rise of the energy storage battery for the heating temperature rise stage, the rapid cooling stage and the slow cooling stage, and calculating the specific heat capacity of the energy storage battery based on the fitted function relation. The method is short in measurement time and data processing time, accurate in test result and suitable for measurement characterization of batteries of different specifications and sizes.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage battery testing, and in particular to a method and device for testing the specific heat capacity of an energy storage battery. Background Art

[0002] Energy storage batteries, mainly lithium-ion batteries, are increasingly being used in passenger vehicles and energy storage power stations due to their high power density, long cycle life, and convenient energy storage and conversion. However, energy storage batteries generate a lot of heat during operation, and if they are not dissipated in time, it is easy to cause battery capacity and life decay, and even thermal runaway. In order to improve the thermal safety and thermal reliability of energy storage batteries, it is necessary to experimentally measure the thermal physical parameters of the battery to understand the thermal characteristics of the battery and perform thermal management on the energy storage battery. Among them, specific heat capacity is an important thermal physical parameter of energy storage batteries, which indicates the battery heating rate and is a key thermal physical parameter for effective thermal management of batteries. Especially for thermal runaway suppression scenarios, accurate determination of battery specific heat capacity is conducive to accurate prediction of battery temperature and precise thermal protection design. However, traditional adiabatic accelerated measurement instruments (abbreviated as ARC) are relatively large in size and slow in temperature balance. It takes 4 to 8 hours to test a single battery. For a large number of tests on different types of batteries, the test time is long and the equipment cost is high. An ARC device for measuring large batteries costs millions of yuan. Therefore, it is necessary to improve the measurement method and device to reduce the test time and cost while ensuring measurement accuracy. Summary of the invention

[0003] Based on this, it is necessary to provide a specific heat capacity testing method and device for energy storage batteries to address the problems of slow temperature equilibrium of traditional adiabatic acceleration measuring instruments, long testing time and high equipment cost for large-scale testing of different types of batteries.

[0004] The present invention provides a method for testing the specific heat capacity of an energy storage battery, comprising:

[0005] Arrange heating films on two large surfaces of the energy storage battery respectively, arrange multiple thermocouples evenly and symmetrically on the heating film on one large surface along the diagonal direction of the energy storage battery, 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 energy storage battery, and wrap the energy storage battery with an insulating layer material;

[0006] Place the treated energy storage 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 functional relationship between the time and temperature rise of the energy storage battery is fitted for the heating stage, the rapid cooling stage and the slow cooling stage, and the specific heat capacity of the energy storage battery is calculated based on the fitted functional relationship.

[0008] In one embodiment, fitting the functional relationship between the time and the temperature rise of the energy storage battery in the heating temperature rising stage, the rapid cooling stage, and the slow cooling stage, respectively, and calculating the specific heat capacity of the energy storage battery based on the fitted functional relationship, includes:

[0009] Turn on the heating film and heat the energy storage 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;

[0010] After stopping heating, the energy storage battery is cooled down rapidly under natural cooling conditions for a period of time until the temperatures of the thermocouples on the surface of the energy storage battery tend to be consistent, and the time and temperature rise of the rapid cooling stage are recorded;

[0011] Keep the energy storage battery to dissipate heat naturally, and slowly cool down and dissipate heat through heat conduction of the insulation layer, natural convection or stable convection for a period of time, and record the time of the slow cooling stage and the temperature of the energy storage battery surface after slow cooling;

[0012] According to the heat loss relationship, the functional relationship between the average temperature rise of the energy storage battery and time is fitted for the heating stage, the rapid cooling stage and the slow cooling stage respectively, and the specific heat capacity of the energy storage battery is calculated according to the fitted functional relationship.

[0013] In one embodiment, the heating time is between 30 seconds and 10 minutes, and the heating time is prolonged as the thickness of the energy storage battery increases.

[0014] In one embodiment, the time of the rapid cooling stage is between 50 seconds and 500 seconds, and the time of the slow cooling stage is between 1000 seconds and 5000 seconds. The time of the rapid cooling stage and the time of the slow cooling stage are gradually extended as the thickness of the battery increases.

[0015] In one embodiment, the function relationship between the average temperature rise of the energy storage battery and time is fitted for the heating stage, the rapid cooling stage, and the slow cooling stage according to the heat loss relationship, and the specific heat capacity of the energy storage battery is calculated according to the fitted function relationship, including:

[0016] Fitting the slow cooling curve through exponential or logarithmic function to obtain the exponential or logarithmic function relationship between heat loss and time and the difference between the energy storage battery and the ambient temperature;

[0017] The derivative of the time to temperature difference in each stage is obtained through the polynomial of the difference between time and temperature in each stage to obtain the cooling rate of the energy storage battery. The cooling rate calculation formula of the energy storage battery is as follows:

[0018] L cool =d(ΔT) / dt=ΔT ave / A3,

[0019] Where A3 is the fitting constant, ΔT ave represents temperature rise, ΔT represents the average temperature drop of the energy storage battery due to heat loss;

[0020] Based on the principle of integral conversion, the average temperature drop of the energy storage battery caused by heat loss is calculated;

[0021] According to the law of energy conservation and the heat loss of the energy storage battery during heating and cooling, the specific heat capacity of the energy storage battery is calculated. The specific heat capacity calculation formula of the energy storage battery is as follows:

[0022]

[0023] or,

[0024] Among them, c b is the specific heat capacity of the energy storage battery, m b is the mass of the energy storage battery, m ht Indicates the mass of the heating film, c ht represents the specific heat capacity of the heating film, ΔT ave2 =T ave (t2)-T0, ΔT ave3 =T ave (t3)-T0, represents the difference between the energy storage battery temperature and the initial temperature T0, P is the instantaneous heating power, ΔT L1 Indicates the average temperature drop of the energy storage battery caused by heat loss during the heating stage [0, t1], ΔT L2 Indicates the average temperature drop of the energy storage battery caused by heat loss during the rapid cooling stage [t1, t2], ΔT L3 It represents the average temperature drop of the energy storage battery caused by heat loss during the slow cooling stage [t2, t3].

[0025] In one of the embodiments, the thermocouples on the energy storage battery are fixed by an aluminum-plastic film with adhesive backing.

[0026] In one of the embodiments, the area of ​​the heating film covers more than 80% of the area of ​​the large surface of the energy storage battery.

[0027] The present invention also provides a specific heat capacity testing device for an energy storage battery, comprising:

[0028] The heating film is attached to the two large surfaces of the energy storage battery;

[0029] The thermocouple is evenly and symmetrically fixed on the surface of the heating film through an aluminum-plastic film with adhesive backing;

[0030] A heat-insulating layer, wrapped around the outer surface of the energy storage battery;

[0031] Temperature control box, used to control the initial temperature of the energy storage battery;

[0032] Wherein, adjacent heating films are connected in series, half of the thermocouples are evenly fixed on the diagonal direction of a large surface of the energy storage battery, and the other half of the thermocouples are symmetrically fixed on the other cross diagonal direction of another large surface of the energy storage battery, and the thermocouples are located between the heating film and the insulation layer.

[0033] 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.

[0034] In one of the embodiments, the thickness of the heating film is 0.05-0.2 mm, and the thermal conductivity resistance of the heating film is smaller than the thermal conductivity resistance of the insulation layer itself.

[0035] The above-mentioned specific heat capacity testing method and device of the energy storage battery can obtain the temperature rise and heat loss results of the energy storage battery in one measurement, thereby obtaining the specific heat capacity of the energy storage battery, without the need for additional heat loss calibration. It is suitable for computer programming to solve the temperature drop effect and specific heat value caused by heat loss of the energy storage battery, and can avoid introducing too much manual calculation. At the same time, the measurement time and data processing time are short, the test results are accurate, and it is suitable for the measurement and characterization of batteries of various specifications and sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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.

[0037] Figure 1 It is a schematic flow chart of a method for testing the specific heat capacity of an energy storage battery in one embodiment;

[0038] Figure 2 A schematic diagram of a flow chart of fitting the relationship between the time and temperature rise of the energy storage battery in each stage in an embodiment;

[0039] Figure 3 It is a schematic diagram of a process of calculating the specific heat capacity of an energy storage battery according to a relational expression in one embodiment;

[0040] Figure 4 It is a structural schematic diagram of a specific heat capacity testing device for an energy storage battery in one embodiment;

[0041] Figure 5A schematic diagram of battery temperature changing over time in a specific heat capacity test of an energy storage battery in one embodiment;

[0042] Figure 6 A graph showing a change in heating time and surface temperature rise during a heating and temperature rise phase in an embodiment and a fitting function expression;

[0043] Figure 7 A graph showing the change of the cooling time and the surface temperature drop during the rapid cooling stage in one embodiment and a fitting function expression;

[0044] Figure 8 A graph showing the change of the cooling time and the surface temperature drop during the slow cooling stage in one embodiment and a fitting function expression;

[0045] Fig. 9 A schematic diagram of the standard deviation and temperature range of thermocouples on the surface of an energy storage battery in one embodiment;

[0046] Fig.10 It is a schematic structural diagram of a specific heat capacity testing device for a battery pack composed of two energy storage batteries in one embodiment.

[0047] Reference numerals:

[0048] 410, heating film; 420, thermocouple; 430, insulation layer; 440, temperature control box. DETAILED DESCRIPTION

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Combine the following Figure 1-Figure 10 The invention describes a method and device for testing the specific heat capacity of an energy storage battery.

[0055] like Figure 1 As shown, in one embodiment, a method for testing the specific heat capacity of an energy storage battery comprises the following steps:

[0056] Step S100, respectively arrange heating films on the two large surfaces of the energy storage battery, evenly and symmetrically arrange multiple thermocouples on the heating film on one of the large surfaces along the diagonal direction of the energy storage 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 energy storage battery, and wrap the energy storage battery with an insulating layer material.

[0057] It should be noted that cracks must be avoided when wrapping the insulation material around the energy storage battery to avoid affecting the measurement accuracy.

[0058] Step S200, placing the treated energy storage 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.

[0059] It should be noted that the initial temperature fluctuation is within 0.5°C.

[0060] Step S300, fitting the functional relationship between the time and the temperature rise of the energy storage battery in the heating temperature rising stage, the rapid cooling stage and the slow cooling stage respectively, and calculating the specific heat capacity of the energy storage battery based on the fitted functional relationship.

[0061] By dividing the cooling process into a rapid cooling process and a slow cooling process, and using the slow cooling process for heat loss calibration, the test time is saved and the additional heat loss calibration curve is avoided. The additional heat loss calibration generally takes 4 to 6 hours and is time-consuming.

[0062] The specific heat capacity testing method of the energy storage battery can obtain the temperature rise and heat loss results of the energy storage battery in one measurement, thereby obtaining the specific heat capacity of the energy storage battery, without the need for additional heat loss calibration. It is suitable for computer programming to solve the temperature drop effect and specific heat value of the energy storage battery caused by heat loss, and can avoid introducing too much manual calculation. At the same time, the measurement time and data processing time are short, the test results are accurate, and it is suitable for the measurement and characterization of batteries of various specifications and sizes.

[0063] In this embodiment, see Figure 2 , respectively fitting the functional relationship between the time and the temperature rise of the energy storage battery in the heating temperature rising stage, the rapid cooling stage and the slow cooling stage, and calculating the specific heat capacity of the energy storage battery based on the fitted functional relationship, including the following steps:

[0064] Step S310, turn on the heating film, heat the energy storage 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.

[0065] Step S320, after stopping heating, the energy storage battery is cooled down rapidly under natural cooling conditions for a period of time until the temperatures of the thermocouples on the surface of the energy storage battery tend to be consistent, and the time and temperature rise of the rapid cooling stage are recorded.

[0066] Step S330, keep the energy storage battery to dissipate heat naturally, and slowly cool down and dissipate heat through heat conduction of the insulation layer, natural convection or stable convection for a period of time, and record the time of the slow cooling stage and the temperature of the surface of the energy storage battery after the slow cooling.

[0067] Step S340, fitting the functional relationship between the average temperature rise of the energy storage battery and time for the heating stage, the rapid cooling stage and the slow cooling stage according to the heat loss relationship, and calculating the specific heat capacity of the energy storage battery according to the fitted functional relationship.

[0068] By fitting the function of separate time and temperature rise for the rapid cooling process, the heat loss relationship of the battery in the rapid cooling process can be obtained more accurately, thereby improving the measurement accuracy.

[0069] In this embodiment, the duration of the heating stage is between 30 seconds and 10 minutes, and the heating time is prolonged as the thickness of the energy storage battery increases.

[0070] In this embodiment, the time of the rapid cooling stage is between 50 seconds and 500 seconds, and the time of the slow cooling stage is between 1000 seconds and 5000 seconds. The time of the rapid cooling stage and the time of the slow cooling stage are gradually extended as the thickness of the battery increases.

[0071] It should be noted that during the rapid cooling stage, there is an obvious temperature difference among the thermocouple temperatures of the energy storage battery, which is greater than 1°C, generally in the range of 1°C to 5°C, and decreases rapidly with time. However, the average temperature slope of the slow cooling process slows down significantly, and the temperature difference between the thermocouple temperatures tends to be consistent. When the standard deviation or range of each thermocouple temperature drops rapidly to a low level, such as 10% to 30% of the level at time t1, it corresponds to time t2 when the rapid cooling ends.

[0072] In this embodiment, see Figure 3 According to the heat loss relationship, the functional relationship between the average temperature rise of the energy storage battery and time is respectively fitted for the heating temperature rising stage, the rapid cooling stage and the slow cooling stage, and the specific heat capacity of the energy storage battery is calculated according to the fitted functional relationship, including the following steps:

[0073] Step S341, fitting the slow cooling curve through an exponential or logarithmic function to obtain an exponential or logarithmic function relationship between heat loss and time and the difference between the energy storage battery and the ambient temperature.

[0074] According to the recorded average temperature rise of the energy storage battery ΔT ave Changes with time t, and fits the heating stage [0, t1] and the rapid cooling process [t1, t2] stage t=t(ΔT ave ) and the logarithmic function equation of time versus temperature rise in the slow cooling stage [t2, t3] t=A3lnΔT ave +B3, or temperature rise ΔT ave Exponential function ΔT with time t ave (t) = exp[(t-B3) / A3], where A3 and B3 are fitting constants, ΔT ave =T ave (t)-T0, where T0 is the initial temperature.

[0075] Step S342, the derivative of the temperature difference of each stage time is obtained through the polynomial of the difference between the time and the temperature of each stage, so as to obtain the cooling rate of the energy storage battery. The cooling rate calculation formula of the energy storage battery is as follows:

[0076] L cool =d(ΔT) / dt=ΔT ave / A3,

[0077] Where A3 is the fitting constant, ΔT ave represents temperature rise, and ΔT represents the average temperature drop of the energy storage battery caused by heat loss.

[0078] Step S343, based on the integral conversion principle, calculate the average temperature reduction of the energy storage battery due to heat loss.

[0079] Since the energy storage battery has heat loss in the heating stage, rapid cooling stage and slow cooling stage, the average temperature drop of the energy storage battery caused by heat loss is ΔT L1 , ΔT L2 , ΔT L3 .

[0080] For the heating stage: t = D1ΔT ave 3 +A1ΔT ave 2 +B1ΔT ave +C1.

[0081] Among them, A1, B1, C1, and D1 are fitting coefficients. If the energy storage battery and the ambient temperature are the same at the beginning of heating, ΔT ave =0, then C1=0.

[0082] ΔT L1 The calculation method is:

[0083]

[0084] Among them, mc is the product of the total mass of the energy storage battery and the heating film and the specific heat, which can be expressed as:

[0085] mc=m b c b +m ht c ht .

[0086] Among them, m b Indicates the mass of the energy storage battery, c b Represents the specific heat capacity of the energy storage battery, m ht Indicates the mass of the heating film, c ht Represents the specific heat capacity of the heating film.

[0087] For the rapid cooling stage, the cooling relationship can be expressed as a third-order or higher-order polynomial. If it is fitted as a third-order polynomial t = D2ΔT ave 3 +A2ΔT ave 2 +B2ΔT ave +C2, where A2, B2, C2, and D2 are fitting coefficients.

[0088] ΔT L2 The calculation method is:

[0089]

[0090] For the slow cooling stage [t2, t3], the temperature-time curve can be fitted as an exponential function or a polynomial of second order or higher. If an exponential function is used, the temperature rise ΔT ave Exponential function ΔT with time t ave (t) = exp[(t-B3) / A3], where A3 and B3 are fitting constants, ΔT ave =T ave (t)-T0, where T0 is the initial temperature.

[0091] ΔT L3 It can be expressed in the following concise form:

[0092] ΔT L3 =ΔT ave3 -ΔT ave2 ,

[0093] Where, ΔT ave2 is the temperature rise at the end of rapid cooling, ΔT ave3 It is the temperature rise at the end of slow cooling.

[0094] The measurement process takes the influence of the heat capacity of the heating film into consideration, eliminates the heat capacity effect of the heating film, and improves the measurement accuracy of the specific heat of the energy storage battery.

[0095] See also Figure 5 , Figure 5 This is a schematic diagram of the change of the temperature of the energy storage battery over time in the specific heat capacity test of the energy storage battery. The temperatures corresponding to the times t1, t2, and t3 are T ave1 、T ave2 、T ave3 .

[0096] Step S344, based on the law of energy conservation and the heat loss of the energy storage battery during the heating and cooling process, the specific heat capacity of the energy storage battery is calculated. The specific heat capacity calculation formula of the energy storage battery is as follows:

[0097]

[0098] or,

[0099] Among them, c b is the specific heat capacity of the energy storage battery, ΔT ave2 =T ave (t2)-T0, ΔT ave3 =T ave (t3)-T0, represents the difference between the energy storage battery temperature and the initial temperature T0, P is the instantaneous heating power, ΔT L1 Indicates the average temperature drop of the energy storage battery caused by heat loss during the heating stage [0, t1], ΔT L2 Indicates the average temperature drop of the energy storage battery caused by heat loss during the rapid cooling stage [t1, t2], ΔT L3 It represents the average temperature drop of the energy storage battery caused by heat loss during the slow cooling stage [t2, t3].

[0100] The exponential or logarithmic function that is more in line with the cooling law is used to fit the cooling rate and heat loss function in the heating stage, the rapid cooling stage, and the slow cooling stage. It is more concise, efficient, and accurate than the usual polynomial fitting function, and the calculation is simpler, which is conducive to programmed fast calculation and reduces calculation errors. At the same time, the exponential or logarithmic function has strong fitting properties, and an excellent fit can be obtained without the entire cooling process, which shortens the cooling process time by several times. For batteries of different sizes, the entire test time is controlled within 1 to 2 hours, which saves test time and is suitable for testing batteries of various sizes. The heating measurement and calibration process are carried out in the same measurement process, and the heat loss calibration and measurement are realized at the same time, which greatly saves the actual measurement time.

[0101] In this embodiment, the thermocouples on the energy storage battery are all fixed by using an aluminum-plastic film with adhesive backing.

[0102] In this embodiment, the area of ​​the heating film covers more than 80% of the area of ​​the large surface of the energy storage battery.

[0103] Application example 1 is as follows:

[0104] Using 51AH square aluminum shell ternary lithium battery, various test processes are carried out, including heating, rapid cooling, and slow cooling. The main steps include:

[0105] 1. The initial temperature of the temperature control box cavity is preset to T0 = 17 ° C. The energy storage battery is heated by the heating film for 502s. The heating is stopped to allow it to first undergo a rapid cooling time of t2 to 110s (surface temperature rise ΔT2), and then enter a slow cooling stage until time t = 8000s.

[0106] 2. See Figure 6 , Figure 7 and Figure 8, when the initial temperature T0 is 20℃, the temperature change of the energy storage battery during the specific heat capacity test. ave It is the average temperature of 10 temperature measurement points on the surface of the energy storage battery.

[0107] Fitting the time t of each stage of the energy storage battery with the average temperature rise ΔT ave The change function relationship is a polynomial.

[0108] Heating stage [0,502s], the fitting polynomial equation is t = -0.02816ΔT ave 3 +1.634ΔT ave 2 -4.3103ΔT ave , zero crossing, fitting coefficient R 2 =0.9998, indicating that the fitting accuracy is excellent. It should be pointed out that the fitting constants in the above fitting polynomials are retained to 4 significant decimal places to avoid measurement errors caused by insufficient calculation accuracy.

[0109] The third-order polynomial fitting has sufficient accuracy in the rapid cooling stage [503s, 613s], t = -1.581ΔT ave 3 +109.8ΔT ave 2 -2542ΔT ave +20140,R 2 =0.9874, the fitting accuracy is excellent. Figure 4 and Fig. 9 At t1=502s, the temperature difference between the center thermocouple #1 and the edge thermocouple #3 on the surface of the energy storage battery is 3°C, and the temperature of thermocouple #2 is between the temperatures of thermocouple #1 and thermocouple #3. Ignoring this value has little effect on the average temperature and temperature difference. In actual testing, this point can be removed to reduce the number of test points. After t2=613s, the temperature difference between the center thermocouple #1 and the edge thermocouple #3 on the surface of the energy storage battery drops to about 0.6°C, and the energy storage battery enters a slow cooling stage.

[0110] In the slow cooling stage, the full temperature section [613s, 8000s] is fitted with the 1 / 2 cooling section [613s, 4000s] time interval to obtain the exponential function ΔT ave =20.61exp(-1.243E-04t), logarithmic function t=-8.040E+03ln(ΔT ave )+24330, fitting coefficient R 2 =0.9996. Figure 8, where the red line represents the change of cooling time and surface temperature drop in the full temperature section [613s, 8000s] of the slow cooling stage, and the blue line represents the change of cooling time and surface temperature drop in the 1 / 2 cooling section [613s, 4000s] of the slow cooling stage. After comparison, it can be seen that the use of local cooling curves can obtain the fitting relationship of all slow cooling stages with small deviation. The temperature drop caused by heat loss in different stages can be calculated based on the formula:

[0111] ΔT L1 =-1.058°C, ΔT L2 =-0.994°C, ΔT L3 =-19.28℃.

[0112] According to the calculation formula of specific heat capacity of energy storage battery, the specific heat value of energy storage battery is 1042J / kgK.

[0113] Application example 2 is as follows:

[0114] A simulation model for 100AH ​​energy storage battery measurement was established using the simulation model. Each test process was simulated, including heating, rapid cooling, and slow cooling. The main steps include:

[0115] 1. The initial temperature of the temperature control box cavity is preset to T0 = 20°C. The energy storage battery is heated for 300s through the heating film. The heating is stopped to allow it to first undergo a rapid cooling time of t2 to 100s (surface temperature rise ΔT2), and then enter a slow cooling stage until time t = 10000s.

[0116] 2. Calculate T ave is the average temperature of 10 temperature measurement points on the surface of the energy storage battery; similar steps can be used to calculate the temperature drop caused by heat loss at different stages. Among them, in the slow cooling stage, the full temperature section [401s, 10000s] is fitted with the 1 / 3 cooling section [401s, 3600s] time interval to obtain the exponential function ΔT ave =13.03exp(-1.154E-04t), R 2 =0.9999, thus obtaining the heat loss temperature drop at each stage:

[0117] ΔT L1 =-0.333°C, ΔT L2 =-0.2263°C, ΔT L3 =-12.51℃.

[0118] Based on the specific heat capacity calculation formula of the energy storage battery, the specific heat capacity of the energy storage battery can be calculated to be 1093.7J / kgK. Compared with the actual battery input specific heat capacity parameter of 1078J / kgK, the error is 1.45%. Here, the heat capacity influence of the heating film itself (~1%) has been eliminated according to the specific heat capacity calculation formula of the energy storage battery. The error of this simulation model is very small, indicating that the measurement accuracy of this method is high, and the test can be completed by using a local cooling curve. The measurement time is about 1 hour, which is much shorter than the 4 to 8 hours of conventional adiabatic acceleration measurement instruments, as well as the additional heat loss calibration time.

[0119] If the preset temperature T0 is changed and the above steps are repeated, the specific heat capacity of batteries at different temperatures can be measured. The initial box temperature T0 of the temperature control box is adjusted from low temperature to high temperature, and the specific heat capacity of energy storage batteries under different working temperatures can be tested.

[0120] Application example three is as follows:

[0121] There is no specific limit on the number of energy storage batteries, one or more, which can be set according to specific circumstances. In order to facilitate heat conduction of the heating film and reduce additional heat loss, the heating film material includes internal conductive material and external lightweight electrical insulating film material, such as polyimide, etc., and thermal insulating material is wrapped on the outside of the battery. Fig.10 The test device and thermocouple diagram of a battery pack composed of two energy storage batteries. In order to ensure rapid heating of the energy storage battery, in addition to the large surface of the energy storage battery, heating films and thermocouples are arranged on the two sides facing the energy storage 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 energy storage battery. The heating power on the side of the energy storage battery is included in the total power P, and the thermocouple reading is included in the calculation of the average battery temperature.

[0122] In this embodiment, the mass of the energy storage battery is known. By calculating the heat generated by the heating film, the temperature change of the energy storage battery, and the heat loss calibration, the temperature-time change curve of the energy storage battery is obtained, and the specific heat value is directly determined without the need for multiple additional calculations and averaging.

[0123] The method of the present invention is also compared with a standard stainless steel 304 sample. The specific heat of stainless steel of the same size at room temperature is obtained by the same calculation method as 501 J / kgK, which deviates from the standard value of 490 J / kgK in the literature (Thermophysical Properties, ASM Handbook, 15, 2008: 468-481) by 2.24%, thereby verifying the accuracy of the measurement method.

[0124] The present invention provides a device with simple device, short measurement time, accurate test results, low cost, easy implementation, and can test the specific heat capacity of energy storage batteries under different operating temperatures. It can provide reliable specific heat capacity test data of energy storage batteries for energy storage battery manufacturers, electric vehicle companies and other institutions, and can be directly used for battery thermal management design.

[0125] The specific heat capacity test method of this energy storage battery adds a slow cooling heat loss calibration process, performs heating measurement and calibration process in the same measurement process, and realizes heat loss calibration and measurement at the same time. It saves actual measurement time, improves measurement efficiency, and is suitable for measuring energy storage batteries of various sizes. An exponential function that is more in line with the cooling law is used to fit the cooling process, and accurate heat loss results are obtained in a shorter time. It is simpler, time-saving and accurate than the previous additional calibration polynomial fitting, and the calculation is simpler, which is conducive to programmed fast calculation and reduces calculation errors. Thereby saving actual measurement time, it is suitable for performance testing of energy storage batteries of various models and sizes. Since the surface temperature of the heating film is equal to that of the energy storage battery, it is necessary to remove the specific heat effect of the heating film by about 0.6%.

[0126] like Figure 4 As shown, the present invention also provides a specific heat capacity testing device for an energy storage battery, comprising a heating film 410 , a thermocouple 420 , an insulating layer 430 and a temperature control box 440 .

[0127] The heating film 410 is attached to two large surfaces of the energy storage battery. The energy storage battery can be a battery of various shapes, such as a square hard shell battery, a soft pack battery, and a blade battery.

[0128] The thermocouple 420 is evenly and symmetrically fixed on the surface of the heating film 410 through an aluminum-plastic film with adhesive backing.

[0129] The heat insulating layer 430 is wrapped around the outer surface of the energy storage battery.

[0130] The temperature control box 440 is used to control the initial temperature of the energy storage battery.

[0131] Among them, adjacent heating films 410 are connected in series, half of the thermocouples 420 are evenly fixed on the diagonal direction of a large surface of the energy storage battery, and the other half of the thermocouples 420 are symmetrically fixed on the other cross diagonal direction of another large surface of the energy storage battery, and the thermocouples 420 are located between the heating film 410 and the insulation layer 430.

[0132] In this embodiment, the heat insulating layer 430 is made of an aerogel layer or a foamed nitrile rubber material, and the heat conduction resistance of the heat insulating layer 430 is greater than the convection heat dissipation resistance from its surface to the environment.

[0133] In this embodiment, the thickness of the heating film 410 is 0.05-0.2 mm, and the thermal conductivity resistance of the heating film 410 is smaller than the thermal conductivity resistance of the insulation layer 430 itself.

[0134] The specific application scenarios are as follows:

[0135] A square hard-shell energy storage battery with a size of 148mm x 92mm x27mm, a capacity of 48AH, and a mass of 0.74kg is used. A heating film 410 is applied to each of the two large surfaces of the energy storage battery, and the total heating power is 36W. The two parts of the heating film 410 are attached to the outer surface of the energy storage battery, and five thermocouples 420 are evenly arranged on each large surface of the energy storage battery, with a total of ten thermocouples 420 on the two large surfaces. The insulation layer 430 wraps the energy storage battery, the heating film 410 and the thermocouple 420 and is placed in a temperature control box 440.

[0136] The heating film 410 is preset to heat the energy storage battery for a heating time t1 = 300s. To reduce test errors, the temperature rise of the energy storage battery is not less than 10°C. Considering the thermal safety of the energy storage battery, its maximum preheating temperature is not higher than the maximum allowable temperature of the energy storage battery, such as 70°C.

[0137] The insulation layer 430 is used to wrap the energy storage battery, reducing the heat dissipation rate to ensure that the temperature inside and outside the energy storage battery is uniform. 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 10 mm thick aerogel layer is selected as the thermal insulation layer 430, and its thermal conductivity is 0.02 W / mK. The thermal resistance of the aerogel layer is 0.01 / 0.02 = 0.5 Km 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.

[0138] 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.

[0139] 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 method for testing the specific heat capacity of an energy storage battery, characterized in that: include: Arrange heating films on two large surfaces of the energy storage battery respectively, arrange multiple thermocouples evenly and symmetrically on the heating film on one large surface along the diagonal direction of the energy storage battery, 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 energy storage battery, and wrap the energy storage battery with an insulating layer material; Place the treated energy storage 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; The functional relationship between the time and temperature rise of the energy storage battery is fitted for the heating stage, the rapid cooling stage and the slow cooling stage, and the specific heat capacity of the energy storage battery is calculated based on the fitted functional relationship.

2. The specific heat capacity testing method of the energy storage battery according to claim 1, characterized in that: The method of fitting the functional relationship between the time and the temperature rise of the energy storage battery in the heating temperature rising stage, the rapid cooling stage and the slow cooling stage, and calculating the specific heat capacity of the energy storage battery based on the fitted functional relationship, includes: Turn on the heating film and heat the energy storage battery at a constant power until the heating reaches a predetermined maximum average temperature, then stop heating, record the time and temperature rise of the heating stage, and calculate the instantaneous heating power; After stopping heating, the energy storage battery is cooled down rapidly under natural cooling conditions for a period of time until the temperatures of the thermocouples on the surface of the energy storage battery tend to be consistent, and the time and temperature rise of the rapid cooling stage are recorded; Keep the energy storage battery to dissipate heat naturally, and slowly cool down and dissipate heat through heat conduction of the insulation layer, natural convection or stable convection for a period of time, and record the time of the slow cooling stage and the temperature of the energy storage battery surface after slow cooling; According to the heat loss relationship, the functional relationship between the average temperature rise of the energy storage battery and time is fitted for the heating stage, the rapid cooling stage and the slow cooling stage respectively, and the specific heat capacity of the energy storage battery is calculated according to the fitted functional relationship.

3. The specific heat capacity testing method of the energy storage battery according to claim 2, characterized in that: The duration of the heating stage is between 30 seconds and 10 minutes, and the heating time is prolonged as the thickness of the energy storage battery increases.

4. The method for testing the specific heat capacity of an energy storage battery according to claim 3, characterized in that: The time of the rapid cooling stage is between 50 seconds and 500 seconds, and the time of the slow cooling stage is between 1000 seconds and 5000 seconds. The time of the rapid cooling stage and the time of the slow cooling stage are gradually prolonged as the thickness of the battery increases.

5. The method for testing the specific heat capacity of an energy storage battery according to claim 4, characterized in that: The method of fitting the functional relationship between the average temperature rise of the energy storage battery and time in the heating stage, the rapid cooling stage and the slow cooling stage according to the heat loss relationship, and calculating the specific heat capacity of the energy storage battery according to the fitted functional relationship, includes: Fitting the slow cooling curve through exponential or logarithmic function to obtain the exponential or logarithmic function relationship between heat loss and time and the difference between the energy storage battery and the ambient temperature; The derivative of the time to temperature difference in each stage is obtained through the polynomial of the difference between time and temperature in each stage to obtain the cooling rate of the energy storage battery. The cooling rate calculation formula of the energy storage battery is as follows: L cool =d(ΔT) / dt=ΔT ave / A3, Where A3 is the fitting constant, ΔT ave represents temperature rise, ΔT represents the average temperature drop of the energy storage battery due to heat loss; Based on the principle of integral conversion, the average temperature drop of the energy storage battery caused by heat loss is calculated; According to the law of energy conservation and the heat loss of the energy storage battery during heating and cooling, the specific heat capacity of the energy storage battery is calculated. The specific heat capacity calculation formula of the energy storage battery is as follows: or, Among them, c b is the specific heat capacity of the energy storage battery, m b is the mass of the energy storage battery, m ht Indicates the mass of the heating film, c ht represents the specific heat capacity of the heating film, ΔT ave2 =T ave (t2)-T0, ΔT ave3 =T ave (t3)-T0, represents the difference between the energy storage battery temperature and the initial temperature T0, P is the instantaneous heating power, ΔT L1 Indicates the average temperature drop of the energy storage battery caused by heat loss during the heating stage [0, t1], ΔT L2 Indicates the average temperature drop of the energy storage battery caused by heat loss during the rapid cooling stage [t1, t2], ΔT L3 It represents the average temperature drop of the energy storage battery caused by heat loss during the slow cooling stage [t2, t3].

6. The method for testing the specific heat capacity of an energy storage battery according to claim 5, characterized in that: The thermocouples on the energy storage battery are all fixed by using an aluminum-plastic film with adhesive backing.

7. The method for testing the specific heat capacity of an energy storage battery according to any one of claims 1 to 6, characterized in that: The area of ​​the heating film covers more than 80% of the area of ​​the large surface of the energy storage battery.

8. A specific heat capacity testing device for an energy storage battery, characterized in that: include: The heating film is attached to the two large surfaces of the energy storage battery; The thermocouple is evenly and symmetrically fixed on the surface of the heating film through an aluminum-plastic film with adhesive backing; A heat-insulating layer, wrapped around the outer surface of the energy storage battery; Temperature control box, used to control the initial temperature of the energy storage battery; Wherein, adjacent heating films are connected in series, half of the thermocouples are evenly fixed on the diagonal direction of a large surface of the energy storage battery, and the other half of the thermocouples are symmetrically fixed on the other cross diagonal direction of another large surface of the energy storage battery, and the thermocouples are located between the heating film and the insulation layer.

9. The specific heat capacity testing device of the energy storage battery according to claim 8, 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.

10. The specific heat capacity testing device of the energy storage battery according to claim 9, characterized in that: The thickness of the heating film is 0.05-0.2 mm, and the thermal conductivity resistance of the heating film is smaller than the thermal conductivity resistance of the insulation layer itself.

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