CN110736764B - Lithium battery specific heat capacity measuring method and device based on differential adiabatic tracing - Google Patents
Lithium battery specific heat capacity measuring method and device based on differential adiabatic tracing Download PDFInfo
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/005—Investigating or analyzing materials by the use of thermal means by investigating specific heat
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
Abstract
The invention discloses a device and a method for measuring the specific heat capacity of a lithium battery based on differential adiabatic tracing. And suspending the lithium battery pack and the aluminum block pack in a heat measuring cavity of the adiabatic accelerated calorimeter. Starting the adiabatic acceleration calorimeter, setting the adiabatic acceleration calorimeter as an adiabatic tracing mode, and creating an approximate adiabatic condition. Two heating plates are arranged to output variable power, and the temperature rise rates of the lithium battery pack and the aluminum block pack are controlled to be constant and the same. Recording temperature rise information of the lithium battery pack and the aluminum block pack and real-time output power curves of the two heating plates in upper computer software; and (4) the measured data is compared and subjected to difference solving to eliminate errors existing in the specific heat capacity measurement, so that the specific heat capacity of the lithium battery is accurately measured. The invention eliminates the measurement error of the specific heat capacity of the lithium battery caused by the non-ideal heat insulation environment in the measurement of the specific heat capacity of the lithium battery in the prior art.
Description
Technical Field
The invention relates to the field of battery safety detection, in particular to a method and a device for measuring the specific heat capacity of a lithium battery based on differential adiabatic tracing.
Background
With the gradual exhaustion of petrochemical energy and the worsening of environmental pollution, the development and utilization of new energy are increasingly gaining attention. In the process, the research and development and the application of the lithium battery are rapidly developed. Lithium batteries are becoming a widely used energy storage medium. However, during the charging and discharging processes of the lithium battery, a large amount of heat is generated inside the battery to cause the temperature change of the battery, wherein ohmic heat is the maximum heat source[1]. This temperature variation not only affects battery life and performance, but also, more seriously, the user's safety of life and property. For example, the mobile phone and the notebook computer can be used for burning and exploding lithium batteries, the electric automobile can explode, the lithium battery factory can be used for fire accidents, and the like. Therefore, the research on the thermal characteristics of the lithium battery is to promote the technical development of the lithium batteryThe method is an important measure, and the measurement of the specific heat capacity of the lithium battery is a basic link of the research. Therefore, a method capable of accurately measuring the specific heat capacity of the lithium battery is urgently needed to be invented, and support is provided for promoting the development of the lithium battery technology.
The existing methods for measuring the specific heat capacity mainly comprise the following methods:
the first method comprises the following steps: the lithium battery to be measured is placed into the adiabatic calorimeter, an approximately adiabatic measuring environment is provided through the calorimeter, the heating sheet is used for heating the lithium battery to be measured, and meanwhile, the temperature rise of the lithium battery to be measured is measured. And calculating the specific heat capacity of the lithium battery to be detected by using a relation between the temperature rise and the specific heat capacity deduced under an ideal condition according to the heat provided by the heating sheet and the temperature rise data of the lithium battery to be detected. The disadvantages of this method are: the heat loss caused by heat absorption of the heating sheet is ignored, and the heat loss caused by the fact that the adiabatic acceleration calorimeter provides a non-ideal adiabatic environment in a practical condition is also ignored, and the defect can influence the accuracy of the specific heat capacity measurement of the lithium battery.
And the second method comprises the following steps: relaxation calorimetry (relaxation calorimetry) is a specific heat measurement technique adopted by a comprehensive Physical Property Measurement System (PPMS) developed by Quantum Design corporation. In the method, in the process of heating a sample to be measured, the specific heat value is obtained by measuring the thermal response of the sample[2]. The relaxation calorimetry has limitation in measuring the specific heat capacity, and a sample to be measured has higher thermal conductivity, so that the sample can be quickly consistent with the temperature of a sample table in the heating process, and the application of the method in the measurement of the specific heat capacity of the lithium battery is not found.
And the third is that: the specific heat capacity of a sample is measured by a differential scanning calorimeter, and the temperature of the sample is scanned under the same condition with a standard substance with known specific heat capacity. And analyzing the heat flow signal obtained by scanning to obtain the specific heat capacity of the sample to be detected. The differential scanning calorimeter is adopted to measure the specific heat capacity of a sample, the good contact between the sample to be measured and a crucible needs to be ensured, and the requirement on the dosage control of the sample to be measured is also met[3]. The method is not suitable for measuring the specific heat capacity of the lithium battery.
In addition, as a method for measuring the specific heat capacity of a lithium battery, for example, patent application publication No. CN103809126A discloses an evaluation method for the specific heat capacity of a lithium ion battery, which mathematically fits the relationship between the internal resistance to heat generation and the temperature of the battery under specific operating conditions. And then obtaining the specific heat capacity of the sample through mathematical derivation according to the relation among the specific heat capacity, the heat generation internal resistance and the temperature, the relation between the temperature rise rate and the temperature of the battery under a specific working condition and the relation between the heat dissipation rate and the temperature of the battery under a standing condition. Although the method has low measurement requirement and short measurement period, the measurement result of the method is excessively dependent on mathematical fitting, and system errors are easily caused. For another example, patent with publication number CN208654076U discloses a device for testing specific heat capacity of a power lithium battery body. The device is through placing the lithium cell that awaits measuring in the less mineral oil of specific heat capacity, builds an approximate adiabatic environment in order to reduce thermal loss simultaneously. Although the method reduces the heat loss in the measuring process, the measuring device is still a traditional adiabatic acceleration calorimeter in nature, and the problem of inaccurate specific heat capacity measurement caused by non-ideal adiabatic heat insulation in the measuring process still exists. Also, as disclosed in patent publication No. CN105806884A, a method for measuring the specific heat capacity of a lithium ion battery is disclosed, which is the same as the first method, and therefore, the specific heat capacity of the lithium ion battery cannot be measured accurately.
Reference to the literature
[1] Liu shoi Hui, Gao Xiao Yan, He pei Run, etc. the research dynamics of the thermal model of the lithium ion battery is J, the statement of power supply, 2019,17(01) is 95-103.
[2] Schlegm, Shicheng, Yi nan, low temperature calorimetric principle and application in materials research [ J ]. scientific notice, 2016,61(Z2):3100- & 3119.
[3] Influence factors of a differential scanning calorimeter and a test technology [ J ] analytical instrument of Su Xiao Qin, Longwei, Liu Xiulan and the like, 2019(04) 74-79.
Disclosure of Invention
Aiming at the defects of the existing battery specific heat capacity measuring method in the background art, the invention provides a lithium battery specific heat capacity measuring method and device based on differential adiabatic tracing, so that the lithium battery specific heat capacity measuring error caused by non-ideal adiabatic conditions is eliminated, and the lithium battery specific heat capacity measuring accuracy is improved.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
the utility model provides a lithium cell specific heat capacity measuring device based on differential adiabatic pursuit, based on adiabatic acceleration calorimeter principle, respectively distributed two heating rods in the top of calorimetric cavity and the bottom of calorimetric cavity, eight heating rods have been distributed in the chamber wall of calorimetric cavity, and top, bottom, the chamber wall of calorimetric cavity respectively have a thermocouple. Two movable sample thermocouples and two ceramic heating plates with the same parameters and variable power output are arranged in the calorimetric cavity. The adiabatic acceleration calorimeter controls an internal heating rod by using the sample temperature measured by a thermocouple and the temperature of each point of a calorimetric cavity, so that the temperature of the calorimetric cavity tracks the temperature of a sample, and an approximate adiabatic environment is provided. And suspending the target lithium battery pack and the target aluminum block pack in a heat measuring cavity of the adiabatic acceleration calorimeter.
Most of the heat generated by the heating sheet in the measurement process is absorbed by the target lithium battery and the target aluminum block, and a small part of the heat is absorbed by the heating sheet and is dissipated due to the non-ideal heat insulation environment. Through the following operation steps and calculation method, the measured data of the target lithium battery pack and the target aluminum block pack are compared and calculated, and the specific heat capacity measurement error caused by heat absorbed by the heating sheet and heat dissipated by a non-ideal heat-insulating environment is eliminated.
A method for measuring the specific heat capacity of a lithium battery based on differential adiabatic tracing comprises the following steps:
two target square lithium batteries to be detected with the same parameters are selected, two target square aluminum blocks with the same geometric shapes as the target square lithium batteries are selected, and two target heating pieces with the same heating areas as the target square lithium batteries and the target square aluminum block binding surfaces are selected. And selecting one target heating sheet, fixing the target heating sheet between two target square lithium batteries to form a battery pack, sticking a thermocouple on the outer surface of one target square lithium battery, and finally binding the battery pack by using a wire and hanging the battery pack in a heat measuring cavity of the adiabatic acceleration calorimeter. And fixing the other target heating plate between the two square aluminum blocks in the same way to form an aluminum block bag, sticking a thermocouple on the outer surface of one target square aluminum block, and finally binding the aluminum block bag by using a wire and hanging the aluminum block bag in a heat measuring cavity of the adiabatic acceleration calorimeter. During suspension, the lithium battery pack and the aluminum block pack are suspended at the same height, and a certain distance is kept to prevent mutual contact.
And (4) checking the line connection, starting the adiabatic acceleration calorimeter without error, setting a target initial temperature, and waiting for the target lithium battery pack temperature, the target aluminum block pack temperature and the calorimetric cavity temperature to be balanced. Under the approximate adiabatic condition provided by the adiabatic tracking mode of the adiabatic acceleration calorimeter, the output of the two target heating plates is set to be a constant-temperature rate-of-rise mode (the same rate of temperature rise of the target lithium battery pack and the target aluminum block pack is realized by changing the power output of the two target heating plates). And heating for a period of time, and acquiring the temperature rise of the target lithium battery pack and the target aluminum block pack in the period of time and the real-time output power curves of the two target heating plates by using upper computer software.
And substituting the data measured in the above operation steps into a specific heat capacity relational expression, and carrying out simultaneous solving to eliminate errors existing in measurement so as to obtain the specific heat capacity of the target square lithium battery.
The specific heat capacity relational expression is subjected to simultaneous calculation, and the specific heat capacity of the target square lithium battery is obtained through the following steps:
the specific heat capacity relation is shown in formulas (1) and (2):
wherein the formula (1) is a relational expression containing the specific heat capacity of the target lithium battery. Equation (2) is a relational expression containing the specific heat capacity of the target aluminum block. In the two formulae, t1－t0For the length of heating, Pout lithiumFor the output power of the heating sheet in the target lithium battery pack, Pout aluminumAnd outputting power for the heating sheet in the target aluminum block package. In the scheme, the two heating plates have different output powers, and in order to ensure that the temperature rise rates of the target lithium battery pack and the target aluminum block pack are consistent, the output powers of the two heating plates are differentAnd changing in real time according to the thermocouple feedback signal of the sample. CLithium ion source、CAluminiumAnd CAddingThe specific heat capacity of the target square lithium battery, the specific heat capacity of the target square aluminum block and the specific heat capacity of the target heating sheet are respectively. And the delta T is the temperature rise of the target lithium battery pack and the target aluminum block pack and is also the temperature rise of the target square lithium battery and the target square aluminum block. MLithium ion source、MAluminiumAnd MAddingThe quality of the target square lithium battery, the quality of the target square aluminum block and the quality of the target heating plate are respectively. Ploss lithiumAnd Ploss aluminumIn order to measure the power dissipated by the non-ideal heat insulation environment, the lithium battery pack and the aluminum block pack in the measuring process. The heat dissipation power of an object is related to the contact area, temperature difference and heat conductivity of the object. The contact area of the lithium battery pack and the air of the calorimetric cavity and the contact area of the aluminum block pack and the air of the calorimetric cavity are the same in the measurement, the measurement condition is approximate to adiabatic real-time temperature difference and is extremely small and the same, the heat-conducting property of the lithium battery is similar to that of aluminum, and therefore P is measuredloss lithiumAnd Ploss aluminumThe dissipated power is considered equal.
Under the condition of isothermal rate of rise, the heat absorbed by the heating sheets in the lithium battery pack and the heating sheets in the aluminum block pack are equal, and the heat dissipated by the lithium battery pack and the aluminum block pack under the non-ideal heat insulation condition is also equal. And (3) subtracting the formula (1) and the formula (2) to eliminate the heat absorption error of the heating sheet and the heat dissipation error under the non-ideal adiabatic condition in the measurement to obtain a formula (3):
according to the formula (3), the specific heat capacity C of the lithium battery to be tested can be accurately obtainedLithium ion source。
Preferably, two sample thermocouples and two same-parameter variable power output heating plates are arranged in the heat measuring cavity of the adiabatic accelerated calorimeter.
Preferably, the aluminum block and the lithium battery are used for comparison and measurement in the measurement process, and the geometric shape of the aluminum block is consistent with that of the lithium battery.
Preferably, the temperature rise rates of the lithium battery and the aluminum block in the measurement process are the same.
Compared with the prior art for measuring the specific heat capacity of the lithium battery, the invention has the following advantages that:
compared with the existing method for measuring the specific heat capacity of the lithium battery, the method has the advantages that the group of aluminum blocks with the same geometric shapes are added as a reference, so that the measurement error of the specific heat capacity of the lithium battery caused by a non-ideal heat insulation environment in the conventional method for measuring the specific heat capacity of the lithium battery is eliminated, and the accuracy of the measurement result of the specific heat capacity of the lithium battery is improved.
Drawings
FIG. 1 is a graph of temperature versus time for a lithium battery and an aluminum block under a constant rate of rise of temperature in accordance with the present invention;
FIG. 2 is a graph of the real-time output power of a heating plate in a lithium battery pack according to the present invention;
FIG. 3 is a graph of real-time output power of heating plates in an aluminum block pack according to the present invention;
FIG. 4 is a flow chart of the measurement method steps of the present invention;
fig. 5 is a structural view of a battery pack according to the present invention;
FIG. 6 is a block diagram of the aluminum block pack of the present invention;
fig. 7 is a schematic view of the measurement sample of the present invention in a designed adiabatic acceleration calorimeter.
Detailed Description
In order to make the steps, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described more clearly, in detail and completely in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are some, not all embodiments of the invention.
As shown in fig. 5 to 7, a differential adiabatic tracing-based lithium battery specific heat capacity measuring device is based on the principle of an adiabatic acceleration calorimeter, two heating rods (4) are respectively distributed on the top (2) of a calorimetric cavity (1) and the bottom (3) of the calorimetric cavity, eight heating rods are respectively distributed on the cavity wall (5) of the calorimetric cavity, and a thermocouple is respectively arranged on the top, the bottom and the cavity wall of the calorimetric cavity. Two movable sample thermocouples (6) and two ceramic heating plates (7) and (8) with the same parameters and variable power output are arranged in the calorimetric cavity. The adiabatic acceleration calorimeter controls an internal heating rod by using the sample temperature measured by a thermocouple and the temperature of each point of a calorimetric cavity, so that the temperature of the calorimetric cavity tracks the temperature of a sample, and an approximate adiabatic environment is provided. And (3) suspending the target lithium battery pack (9) and the target aluminum block pack (10) in a calorimetric cavity of an adiabatic acceleration calorimeter.
Specifically, the method comprises the following steps: two target square lithium batteries (11) to be detected with the same parameters, two target square aluminum blocks (12) with the same geometric shapes and the same target square lithium batteries and two target heating sheets (7) and (8) with the same heating areas as the target square lithium batteries and the target square aluminum block binding surfaces are selected to ensure that the target square lithium batteries and the target square aluminum blocks are heated uniformly, and the two selected target heating sheets can be output in a variable power mode according to the temperature signals fed back.
When the heating plate is used for heating the lithium battery and the aluminum block, in order to prevent the heating plate from exchanging heat with the environment, the aluminum foil adhesive tape with good heat conduction performance is used, and the target square lithium battery and the target heating plate are packaged in a mode that the target heating plate is tightly bonded with one layer of target heating plate in the middle of the two layers of target square lithium batteries. And forming a target square lithium battery layer, a target heating sheet layer and a battery pack (9) with a sandwich-like structure of the target square lithium battery layer, and packaging the target square aluminum block and the target heating sheet in the same way to form an aluminum block pack (10).
Two sample thermocouples (6) in the heat measuring cavity of the adiabatic accelerated calorimeter are respectively stuck on the outer surface of a square lithium battery in a battery pack and the outer surface of a square aluminum block in an aluminum block pack by using aluminum foil adhesive tapes. Two sample thermocouples were used to monitor the temperature change of the target cell pack and the target aluminum block pack during the measurement. And binding the target battery pack and the target aluminum block pack through a nylon rope, and suspending the target battery pack and the target aluminum block pack in a heat measuring cavity of the adiabatic acceleration calorimeter. And during suspension, the target lithium battery pack and the target aluminum block pack are suspended at the same height and are kept at a certain distance to prevent mutual contact.
And (5) confirming that the circuit connection between the adiabatic acceleration calorimeter and the heating plate is correct, and starting the adiabatic acceleration calorimeter. Setting a starting temperature T higher than the current ambient temperature0After long-time temperature equalization, the temperature of the calorimetric cavity, the temperature of the target lithium battery pack and the temperature of the target aluminum block pack reachTo a target starting temperature T0. The adiabatic acceleration calorimeter is set to be in an adiabatic tracing mode, an approximate adiabatic environment is provided (the mode is used for controlling a heating rod in the adiabatic acceleration calorimeter to realize temperature tracing by passing temperature signals fed back by a thermal cavity top thermocouple, a thermal cavity bottom thermocouple, a thermal cavity wall thermocouple and a sample thermocouple), two target heating plates are set to output a constant temperature rate-of-rise mode (the two target heating plates are controlled to output variable power by sample temperature signals fed back by the two sample thermocouples to realize the same rate of temperature rise of a lithium battery pack and an aluminum block pack) to heat delta t0Time. Recording heating delta t using host computer software0Temperature rise delta T of the target lithium battery pack and the target aluminum block pack within time, and real-time output power curves of the two target heating plates.
And integrating the real-time output power curves of the two target heating sheets with time to obtain the heat released by the two target heating sheets. Because the real-time output power of the two heating sheets is different, the released heat quantity is also different. And comparing the measured data of the target battery pack and the target aluminum block pack, substituting the data into the specific heat capacity relational expression, performing simultaneous calculation to eliminate errors caused by heat absorption of the heating sheet and a non-ideal heat insulation environment, and solving the specific heat capacity of the target square lithium battery.
The relation of the specific heat capacity is shown in the formulas (3) and (4).
Wherein t is0、t1For measuring the start time and end time of constant rate heating during the process,. DELTA.t0＝t1-t0To measure the duration. Pout lithiumReal-time output power P of heating sheets in a target lithium battery packout aluminumThe real-time output power of the heating sheet in the target aluminum block package is different in the embodiment, so that the target lithium battery package is ensuredAnd the temperature rise rate of the target aluminum block package is consistent, and the two powers change in real time according to the temperature signal fed back by the sample thermocouple. CLithium ion source、CAluminiumAnd CAddingRespectively is the specific heat capacity of a target square lithium battery, the specific heat capacity of a target square aluminum block and the specific heat capacity of a target heating sheet, wherein CAluminiumIs the specific heat capacity of aluminum, a known quantity, CLithium ion sourceAnd CAddingIs an unknown quantity. And the delta T is the temperature rise of the target lithium battery pack and the target aluminum block pack and is also the temperature rise of the target square lithium battery and the target square aluminum block, and is controlled by the measuring process. MLithium ion source、MAluminiumAnd MAddingThe mass of the target square lithium battery, the mass of the target square aluminum block and the mass of the target heating plate are measured by balance measurement. Ploss lithiumAnd Ploss aluminumIn order to measure the power dissipated by the non-ideal heat insulation environment, the lithium battery pack and the aluminum block pack in the measuring process. From the thermal theory, the heat dissipation power of the object is related to the contact area, the temperature difference and the heat conduction performance of the object. The contact area of the lithium battery pack and the air of the calorimetric cavity and the contact area of the aluminum block pack and the air of the calorimetric cavity are the same in the measurement, the measurement condition is approximate to adiabatic real-time temperature difference and is extremely small and the same, the heat-conducting property of the lithium battery is similar to that of aluminum, and therefore P is measuredloss lithiumAnd Ploss aluminumThe dissipated power is considered equal.
And (3) subtracting the formula (4) through the joint formula (3), and eliminating an error term caused by the dissipated power and an error term caused by the heat absorbed by the heating plate in the formula. De type (5)
Division of C in equation (5)Lithium ion sourceThe other quantities are known quantities, so that the specific heat capacity C of the lithium battery to be measured can be accurately obtained by solving the equation (5)Lithium ion source。
The experiment is carried out by using the measuring device and the method, and the relation between the temperature and the time of the target square lithium battery and the target square aluminum block under the condition of constant temperature and speed rise is shown as figure 1, the real-time output power of the heating plate in the lithium battery pack is shown as figure 2, the real-time output power of the heating plate in the aluminum block pack is shown as figure 3, and the experimental data of the aluminum block and the lithium battery are shown as table 1.
TABLE 1 lithium cell and aluminum block Experimental data
The experimental data are substituted into the formulas (3), (4) and (5) to calculate, and the specific heat capacity of the lithium battery measured in the embodiment is obtained. The specific heat capacity of the lithium battery was measured using the first method in the background art as a comparative experiment. The specific heat capacity of the lithium battery measured by the two methods is shown in table 2.
TABLE 2 method for measuring specific heat capacity of lithium battery
As can be seen from Table 2, the specific heat capacity of the lithium battery measured by the method has a significant difference from the results obtained by other methods. Because the specific heat capacity of the lithium battery is an uncertain value, the data measured in the table 2 are difficult to judge the effectiveness of the invention. Therefore, a set of experiments is added, and the lithium battery with unknown specific heat capacity in the experiments is replaced by the iron blocks with known specific heat capacity and equal geometric shapes by adopting the measuring method and the measuring device. The experimental data for the iron and aluminum blocks are shown in table 3.
TABLE 3 iron and aluminum block Experimental data
The experimental data are calculated by the method to obtain the specific heat capacity of the iron block measured by the embodiment. The specific heat capacity of the iron block was measured using the first method in the background art as a comparative experiment. The specific heat capacity of the iron block and the actual specific heat capacity of the iron block measured by the two methods are shown in Table 4.
Table 4 shows that the specific heat capacity of the iron blocks and the actual specific heat capacity of the iron blocks are measured by two methods
From table 4, it can be seen that the specific heat capacity of the iron block measured by the method is closer to the true value than the specific heat capacity of the iron block measured by other methods, so that the specific heat capacity of the lithium battery measured by the method is more accurate than the specific heat capacity of the lithium battery measured by other methods.
In summary, the method and the device for measuring the specific heat capacity of the lithium battery provided by the invention eliminate the specific heat capacity measurement error of the lithium battery caused by the non-ideal heat insulation environment in the conventional method and device for measuring the specific heat capacity of the lithium battery. Therefore, the achievement of the invention has great significance for improving the measurement accuracy of the specific heat capacity of the lithium battery.
Claims (1)
1. A lithium battery specific heat capacity measuring method based on differential adiabatic tracing is characterized in that a measuring device in the method is based on the principle of an adiabatic acceleration calorimeter, and the specific structure of the device is as follows: two heating rods are respectively distributed at the top and the bottom of the calorimetric cavity, and eight heating rods are distributed on the wall of the calorimetric cavity; the top, the bottom and the cavity wall of the calorimetric cavity are respectively provided with a thermocouple, and the calorimetric cavity is internally provided with two movable sample thermocouples and two ceramic heating sheets with the same parameters and variable power output; the adiabatic acceleration calorimeter uses the sample temperature measured by a thermocouple and the temperature of each point of a calorimetric cavity so as to control an internal heating rod, and the temperature of the calorimetric cavity tracks the temperature of a sample, thereby providing an approximate adiabatic environment, and the method is characterized by comprising the following steps:
(1) selecting two target square lithium batteries to be detected with the same parameters, two target square aluminum blocks with the same geometric shapes as the target square lithium batteries to be detected, and two target heating sheets with the same heating areas as the target square lithium batteries to be detected and the target square aluminum blocks;
(2) selecting one target heating sheet, fixing the target heating sheet between two target square lithium batteries to form a lithium battery pack, sticking a thermocouple on the outer surface of one target square lithium battery, and finally binding and suspending the target heating sheet in a heat measuring cavity of the adiabatic acceleration calorimeter by using a wire;
(3) fixing the other target heating plate between the two target square aluminum blocks in the same way to form an aluminum block bag, sticking a thermocouple on the outer surface of one target square aluminum block, and finally tying and suspending the thermocouple in a heat measuring cavity of the adiabatic acceleration calorimeter by using a wire;
(4) the method comprises the steps that a circuit connection is checked, an adiabatic acceleration calorimeter is started without errors, a target initial temperature is set, and the temperature of a lithium battery pack, an aluminum block pack and a calorimetric cavity is waited to be balanced;
(5) under the approximate adiabatic condition provided by the adiabatic tracking mode of the adiabatic acceleration calorimeter, setting the output of the two target heating sheets as a constant temperature rate-of-rise mode, namely realizing the same rate of temperature rise of the lithium battery pack and the aluminum block pack by the variable power output of the two target heating sheets;
(6) heating for a period of time, recording the temperature rise of the lithium battery pack and the aluminum block pack in the period of time, and recording real-time output power curves of the two target heating sheets;
(7) substituting the measured data into a specific heat capacity relational expression, carrying out simultaneous solving to eliminate errors existing in a measurement system, and solving the specific heat capacity of the target square lithium battery;
in the step (7), the measured data is substituted into the specific heat capacity relational expression, simultaneous solving is carried out to eliminate errors existing in the measurement, and the specific heat capacity of the target square lithium battery is obtained through the following process:
the specific heat capacity relational expression is according to the formula:
wherein t is1－t0Is the heating time; pout lithiumFor the output power, P, of the heating plate in the lithium battery packout aluminumOutputting power for a heating plate in the aluminum block bag; cLithium ion source、CAluminiumAnd CAddingRespectively is the specific heat capacity of the target square lithium battery and the specific heat capacity of the target square aluminum blockThe specific heat capacity of the target heating sheet; the temperature rise of the battery pack and the aluminum block pack is shown as delta T, and the temperature rise of the target square lithium battery and the target square aluminum block is also shown as delta T; mLithium ion source、MAluminiumAnd MAddingThe mass of a target square lithium battery, the mass of a target square aluminum block and the mass of a target heating plate are respectively; ploss lithiumAnd Ploss aluminumIn order to measure the power dissipated by the non-ideal heat insulation environment, the lithium battery pack and the aluminum block pack in the measuring process;
under the condition of isothermal rate of rise, the heat absorbed by the heating sheets in the lithium battery pack and the heating sheets in the aluminum block pack are equal, and the heat dissipated by the lithium battery pack and the aluminum block pack under the non-ideal heat insulation condition is also equal; and (3) subtracting the formula (1) and the formula (2) to eliminate the heat absorption error of the heating sheet and the heat dissipation error under the non-ideal adiabatic condition in the measurement to obtain a formula (3):
the specific heat capacity C of the target square lithium battery to be measured can be accurately obtained according to the formula (3)Lithium ion source。
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