阅读说明：本技术 一种隔膜闭孔温度的测定方法 (Method for measuring closed pore temperature of diaphragm ) 是由 袁海朝 徐锋 豆赛赛 苏碧海 于 2019-09-12 设计创作，主要内容包括：本发明公开了一种隔膜闭孔温度的测定方法,在温度升温过程中,测量隔膜试样与参考物之间的热流差,对隔膜试样的DSC曲线做一阶导数,形成一阶导数曲线,一阶导数曲线最高点对应温度为吸收热量最快温度,此时隔膜受热接触面积最大,隔膜完全闭孔,该温度即为隔膜完全闭孔温度。本方法,通过一次测试,可以得到多种实验结果,既能测试隔膜一般热性能,也可以侦测隔膜闭孔温度,从而避免购买专用仪器的损耗,节约测试时间和增加测试效率。(The invention discloses a method for measuring diaphragm closed pore temperature, which comprises the steps of measuring heat flow difference between a diaphragm sample and a reference object in the temperature rising process, making a first derivative on a DSC curve of the diaphragm sample to form a first derivative curve, wherein the temperature corresponding to the highest point of the first derivative curve is the temperature with the highest heat absorption rate, the heated contact area of a diaphragm is the largest at the moment, the diaphragm is completely closed, and the temperature is the diaphragm completely closed pore temperature. The method can obtain various experimental results through one-time test, can test the general thermal property of the diaphragm, and can also detect the closed pore temperature of the diaphragm, thereby avoiding the loss of purchasing special instruments, saving the test time and increasing the test efficiency.)

1. A method for measuring the closed pore temperature of a diaphragm is characterized in that: in the temperature rising process, measuring the heat flow difference between the diaphragm sample and a reference object, and making a first derivative on a DSC curve of the diaphragm sample to form a first derivative curve, wherein the temperature corresponding to the highest point of the first derivative curve is the fastest temperature for absorbing heat, the heated contact area of the diaphragm is the largest at the moment, the diaphragm is completely closed, and the temperature is the completely closed-pore temperature of the diaphragm.

2. The method for measuring a closed cell temperature of a separator according to claim 1, wherein: the method adopts a differential scanning calorimeter, and the specific closed pore temperature of the diaphragm comprises the following steps:

step 1, sample pretreatment: placing a diaphragm in an environment with the temperature of 23 +/-2 ℃ and the relative humidity of 50 +/-10% for at least 4 h;

step 2, sampling and weighing: shearing a diaphragm sample from the geometric center of a diaphragm by using a pair of scissors, punching a wafer with the diameter slightly smaller than the inner diameter of a sample crucible by using a puncher, taking about 5-10mg of the diaphragm sample to be accurate to 0.1mg, flatly paving the diaphragm sample in the sample crucible, covering, and piercing the center of the cover by using a steel needle; weighing the weight of the sample crucible and the weight of the reference crucible after the diaphragm sample is placed, and accurately obtaining the weight of 0.01 mg;

step 3, temperature scanning:

3.1 at room temperature, placing the sample crucible and the reference crucible into a sample chamber, and cleaning the sample crucible and the reference crucible for 5min in advance by using nitrogen before starting temperature rise operation, wherein the flow rate is 50 mL/min;

3.2 starting to heat up and record at the speed of 20 ℃/min, heating the sample crucible to 20-30 ℃ above the estimated melting temperature of the diaphragm so as to eliminate the previous thermal history of the test material, and keeping for a certain time at the temperature;

3.3 cooling the instrument to room temperature, taking out the sample crucible, observing whether the sample crucible is deformed or whether the sample overflows, re-weighing the sample crucible to be accurate to +/-0.01 mg, opening the crucible and checking the sample if the mass loss exists, discarding the experimental result if the sample is degraded, and selecting a lower upper limit temperature for re-testing;

and 4, data processing:

and generating a DSC test curve graph of the test diaphragm sample, then making a first derivative on the DSC test curve to obtain a first derivative curve of the test diaphragm sample, marking the position of the DSC test curve corresponding to the peak value of the first derivative curve, wherein the temperature corresponding to the intersection point of the tangent line at the mark position and the tangent line of the base line is the diaphragm closed pore temperature.

Technical Field

The invention relates to a method for measuring the closed pore temperature of a diaphragm.

Background

The lithium ion battery has the advantages of high specific energy, high working voltage, no memory effect, long cycle life, little environmental pollution and the like. With the wide application of lithium ion batteries, the safety of the batteries is receiving more and more attention. At present, the safety of the lithium ion battery is still one of the key problems which prevent the lithium ion battery from being applied to the fields of electric vehicles, energy storage and the like on a large scale. In an unexpected situation, the lithium ion battery can be subjected to fire and explosion accidents, which causes great personal injury and property loss.

The battery mainly comprises a positive electrode material, a negative electrode material, electrolyte and a diaphragm, wherein the diaphragm is an important component of the battery, and the diaphragm mainly comprises a microporous film or a non-woven fiber sheet, separates the positive electrode and the negative electrode of the battery in the battery, plays a role in preventing short circuit of the two electrodes, and has electronic insulation property and ionic conductivity. Under the condition of temperature rise, the diaphragm has the protection effect of self-closing of the micropores, and explosion caused by short circuit of the battery can be prevented. When the temperature is too high, the separator may melt to cause the disappearance of micropores, and once the internal temperature of the battery further increases, the melt viscosity of the separator decreases, and the separator may crack upon reaching a certain temperature, resulting in direct contact of the electrodes, which is very dangerous. Therefore, the study on the closed cell temperature of the separator is very important for improving the safety of the battery.

Currently, many diaphragm manufacturers use the following test methods: and measuring the air permeability of the diaphragm or observing the diaphragm by an electron microscope. The air permeability test method requires a special test instrument. The electron microscope observation method needs to conduct electricity on the diaphragm, is high in cost and cannot quantify.

In comparison with the similar conductivity test method, they use a closed device, are placed in a high temperature environment, and then are tested. There are several disadvantages as follows: 1. the high temperature easily causes the conductive liquid to volatilize and leak, and the high air pressure that produces also can influence the test result. 2. If the measurement time is too long, the conductive liquid is volatilized and leaked to increase the conductive resistance, so that the test result is influenced. 3. The testing device is relatively complex and has high requirement on the sealing property. The above method has high requirements for equipment, and a common battery manufacturer may not have the above two devices.

Therefore, it is still meaningful to find a simpler, more convenient and more accurate test method for detecting the closed-cell temperature and the membrane rupture temperature of the membrane.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide the method for measuring the closed pore temperature of the diaphragm, the method is simple and convenient to operate and high in measuring speed, and the general thermal performance of the diaphragm can be measured and the closed pore temperature of the diaphragm can be detected through one test, so that the measuring time is greatly saved and the measuring efficiency is improved.

A method for measuring the closed pore temperature of a diaphragm comprises the steps of measuring the heat flow difference between a diaphragm sample and a reference object in the temperature rising process, and making a first derivative on a DSC curve of the diaphragm sample to form a first derivative curve, wherein the temperature corresponding to the highest point of the first derivative curve is the temperature at which heat is absorbed most quickly, the heated contact area of the diaphragm is the largest at the moment, the diaphragm is completely closed, and the temperature is the completely closed pore temperature of the diaphragm.

In the technical scheme, a differential scanning calorimeter is adopted, and the specific measurement steps of the diaphragm closed pore temperature are as follows:

step 1, sample pretreatment: placing a diaphragm in an environment with the temperature of 23 +/-2 ℃ and the relative humidity of 50 +/-10% for at least 4 h;

step 2, sampling and weighing: shearing a diaphragm sample from the geometric center of a diaphragm by using a pair of scissors, punching a wafer with the diameter slightly smaller than the inner diameter of a sample crucible by using a puncher, taking about 5-10mg of the diaphragm sample to be accurate to 0.1mg, flatly paving the diaphragm sample in the sample crucible, covering, and piercing the center of the cover by using a steel needle; weighing the weight of the sample crucible and the weight of the reference crucible after the diaphragm sample is placed, and accurately obtaining the weight of 0.01 mg;

step 3, temperature scanning:

3.1 at room temperature, placing the sample crucible and the reference crucible into a sample chamber, and cleaning with nitrogen for 5min in advance before starting the temperature rise operation, wherein the flow rate is 50mL/min (1 +/-10%);

3.2 starting to heat up and record at the speed of 20 ℃/min, heating the sample crucible to 20-30 ℃ above the estimated melting temperature of the diaphragm so as to eliminate the previous thermal history of the test material, and keeping for a certain time at the temperature;

3.3 cooling the instrument to room temperature, taking out the sample crucible, observing whether the sample crucible is deformed or whether the sample overflows, re-weighing the sample crucible to be accurate to +/-0.01 mg, opening the crucible and checking the sample if the mass loss exists, discarding the experimental result if the sample is degraded, and selecting a lower upper limit temperature for re-testing;

and 4, data processing:

and generating a DSC test curve graph of the test diaphragm sample, then making a first derivative on the DSC test curve to obtain a first derivative curve of the test diaphragm sample, marking the position of the DSC test curve corresponding to the peak value of the first derivative curve, wherein the temperature corresponding to the intersection point of the tangent line at the mark position and the tangent line of the base line is the diaphragm closed pore temperature.

The invention has the advantages and beneficial effects that:

the method comprises the steps of quantitatively detecting the closed pore temperature of the diaphragm by using a differential scanning calorimeter, measuring the heat flow difference between a diaphragm sample and a reference object in the temperature rising process, and making a first derivative on a melting curve to form a first-order curve, wherein the highest point corresponding temperature is the temperature at which heat is absorbed most quickly, the heated contact area of the diaphragm is the largest at the moment, the diaphragm is completely closed, and therefore the corresponding temperature is the completely closed pore temperature of the diaphragm. The method can obtain various experimental results through one-time test, can test the general thermal property of the diaphragm, and can also detect the closed pore temperature of the diaphragm, thereby avoiding the loss of purchasing special instruments, saving the test time and increasing the test efficiency.

Drawings

Fig. 1 is a graph of experimental data for testing a diaphragm sample using a differential scanning calorimeter in example two of the present invention.

For a person skilled in the art, other relevant figures can be obtained from the above figures without inventive effort.

Detailed Description

In order to make the technical solution of the present invention better understood, the technical solution of the present invention is further described below with reference to specific examples.