Device and method for detecting saturated vapor pressure of lithium battery electrolyte

Abstract

The invention belongs to the field of electrochemistry, and particularly relates to a device and a method for detecting saturated vapor pressure of lithium battery electrolyte. According to the technical scheme, the device for detecting the saturated vapor pressure of the lithium battery electrolyte comprises a cavity, a top cover, a polytetrafluoroethylene tube I, a polytetrafluoroethylene tube II, silicone oil, a pressure sensor I, a pressure sensor II, a PID (Proportion Integration Differentiation) control constant-temperature heating system and a data collector, one end of a polytetrafluoroethylene tube I and one end of a polytetrafluoroethylene tube II are inserted into the top cover and are communicated with the cavity, the other end of the polytetrafluoroethylene tube I is connected with a pressure sensor I, the other end of the polytetrafluoroethylene tube II is connected with a pressure sensor II, and silicone oil is added into the polytetrafluoroethylene tube I and the polytetrafluoroethylene tube II; the PID control constant-temperature heating system is arranged at the bottom of the cavity, a wire of a data collector is inserted into the top cover, and a probe of the data collector is arranged above the liquid level of the electrolyte in the cavity.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry, specifically relating to a device and method for detecting the saturated vapor pressure of lithium battery electrolyte. Background Technology

[0002] A typical safety hazard of lithium batteries stems from thermal runaway, a phenomenon characterized by a rapid rise in internal temperature, triggering a continuous thermal release reaction and the generation of large amounts of flammable gases. Therefore, monitoring and testing the saturated vapor pressure of the electrolyte inside lithium batteries is of great significance.

[0003] Monitoring the internal pressure of a battery is crucial for identifying overheating conditions. Thermal runaway involves multiple stages, including performance degradation due to temperature increases, rupture of the solid electrolyte interphase (SEI) film, reactions between the negative electrode material and the electrolyte, separator melting, disintegration of the positive electrode material, electrolyte analysis, and chemical reactions between the negative electrode material and the binder. These reactions generate various gases, such as oxygen, carbon dioxide, ethylene, and hydrogen. At high temperatures, these gases rapidly accumulate within the battery, causing a sharp rise in internal pressure. Once the pressure reaches the explosion limit, the battery may explode. Therefore, effective monitoring of the electrolyte's saturated vapor pressure is essential for ensuring battery safety, and accurate prediction of the electrolyte's saturated vapor pressure is of great significance for accident prevention.

[0004] To mitigate the risk of battery explosions, venting valves are a standard passive safety measure. When the internal pressure of the battery exceeds a set threshold, the venting valve opens to release the pressure, thus ensuring battery safety. However, in the development of lithium battery technology, changes in the positive and negative electrode materials and electrolyte composition can affect characteristics such as gas generation and internal pressure. Different electrolyte compositions often correspond to different gas production rates. Therefore, conducting pre-testing of the saturated vapor pressure for different electrolytes is crucial for preventing battery explosions caused by excessive internal pressure and is also an important step in analyzing the risk of battery thermal runaway.

[0005] The saturated vapor pressure of an electrolyte refers to the vapor pressure in the gas phase at a given temperature when its components evaporate into the gas phase and reach gas-liquid equilibrium. Specifically, it represents the pressure at which volatile molecules on the electrolyte surface evaporate into the air and condense back into the liquid, reaching a dynamic equilibrium. In this dynamic equilibrium state, the evaporation rate equals the condensation rate, and the vapor pressure on the electrolyte surface remains constant. This pressure is the saturated vapor pressure under those conditions, and it depends only on the chemical properties of the electrolyte and the temperature. Vapor pressure is a key concept in thermodynamics, crucial for understanding and predicting phenomena such as liquid evaporation rates, gas-liquid two-phase mass exchange, and evaporative cooling effects. In battery technology, the saturated vapor pressure of the electrolyte significantly impacts the thermal stability and safety of the battery. A high saturated vapor pressure indicates high volatility, potentially leading to significant gas expansion during battery temperature increases or charging / discharging processes, thereby increasing the risk of battery explosion or leakage. Therefore, the saturated vapor pressure must be considered when designing and selecting electrolyte formulations to ensure the overall safety and stability of the battery during operation.

[0006] Patent CN117824911A discloses an experimental device for measuring the saturated vapor pressure of a pure liquid and its pressure measurement method. This method involves reducing the internal pressure of a vacuum chamber to a set value using a vacuum pump, then introducing the liquid to be tested into a polytetrafluoroethylene (PTFE) liquid-blocking and gas-permeable porous membrane until the temperature sensor and heating wire are submerged. After the pressure sensor readings stabilize, the average value of the two pressure sensors is taken as the saturated vapor pressure of the solution at the set temperature. However, this method has the following limitations: in a vacuum environment, due to the extremely low external pressure, the liquid usually requires a certain pressure difference to pass through the porous material. Since the PTFE membrane itself is designed to block liquids, it is difficult for the liquid to enter the vacuum chamber without additional pressure. Patent CN105865968A discloses a device for measuring the saturated vapor pressure of a liquid in a porous medium. This method utilizes the local negative pressure generated by water circulation and is suitable for measuring the saturated vapor pressure of liquids in general large spaces. However, this method does not fully consider the following problem: in a vacuum environment, gas molecules are scarce or nonexistent, which significantly lowers the boiling point of the liquid. During the process of injecting liquid into a vacuum environment, the liquid may boil and evaporate rapidly, and excessively high vapor pressure may cause safety hazards such as rupture of the device casing.

[0007] In addition, a large number of complex experimental devices, such as circulating water pumps and vacuum systems, can lead to cumbersome experimental operations, high prices, and poor universality.

[0008] To address the issue of defining the saturated vapor pressure of different electrolytes in battery cells, existing technologies primarily predict the internal pressure of cell failure by searching for curves showing the vapor pressure of commonly used solvents as a function of temperature and considering the fluctuation range. This is then used as the pressure boundary for that batch of cells. This method has the following limitations: it does not consider the differences in electrolyte type, internal components, and additives during the cell manufacturing process, resulting in poor universality; it requires extensive research into the boiling point and vapor pressure curves of electrolytes with different additive systems to calculate the internal pressure boundary, making the method complex and difficult to implement in some cases.

[0009] Existing technologies for vapor pressure testing apparatus mainly employ U-shaped isobaric tubes, buffer gas storage tanks, and vacuum systems. These apparatuses result in complex overall structures, cumbersome operation, and high costs. Furthermore, during operation, the vacuum environment significantly lowers the boiling point of the test sample, potentially causing rapid boiling and evaporation, or even leading to safety hazards such as apparatus shell rupture due to excessively high vapor pressure. These methods not only fail to ensure the safety of the testing process but also affect the accuracy of saturated vapor pressure measurements. Summary of the Invention

[0010] This invention provides a device and method for detecting the saturated vapor pressure of lithium battery electrolyte. It can pre-detect the vapor pressure of electrolyte inside different test cells and can determine the saturated vapor pressure value of a specific electrolyte under sealed conditions. At the same time, it avoids the interference caused by changes in the boiling point of the electrolyte due to the vacuum environment, thereby solving the problem of the difficulty in accurately determining the saturated vapor pressure of electrolyte inside the cell.

[0011] The technical solution of the present invention is as follows:

[0012] A device for detecting the saturated vapor pressure of lithium battery electrolyte includes a cavity, a top cover, a first polytetrafluoroethylene (PTFE) tube, a second PTFE tube, silicone oil, a first pressure sensor, a second pressure sensor, a PID-controlled constant temperature heating system, and a data acquisition unit. The top cover is sealed to the cavity. One end of each of the first and second PTFE tubes is inserted into the top cover and communicates with the cavity. The other end of the first PTFE tube is connected to the first pressure sensor, and the other end of the second PTFE tube is connected to the second pressure sensor. Silicone oil is added to the first and second PTFE tubes. The PID-controlled constant temperature heating system is located at the bottom of the cavity. The data acquisition unit's wires are inserted into the top cover, and the probe of the data acquisition unit is positioned above the electrolyte surface in the cavity.

[0013] Furthermore, in the lithium battery electrolyte saturated vapor pressure detection device, the upper part of the cavity is equipped with an explosion-proof exhaust valve.

[0014] Furthermore, in the lithium battery electrolyte saturated vapor pressure detection device, a sealing gasket is provided between the top cover and the cavity.

[0015] Furthermore, the lithium battery electrolyte saturated vapor pressure detection device, the PID control constant temperature heating system includes an ultra-thin temperature sensor, a PID controller and a heating wire. The heating wire is evenly arranged at the bottom of the cavity and is completely immersed in the electrolyte during the test. The ultra-thin temperature sensor is set in the cavity and is connected to the PID controller, which is used to control the heating wire.

[0016] Furthermore, in the lithium battery electrolyte saturated vapor pressure detection device, the cavity is made of double-layered glass material.

[0017] Furthermore, in the lithium battery electrolyte saturated vapor pressure detection device, the volume of silicone oil injected is 1 / 3 of the internal volume of polytetrafluoroethylene tube one and polytetrafluoroethylene tube two.

[0018] A method for detecting the saturated vapor pressure of a lithium battery electrolyte, utilizing the aforementioned detection device for the saturated vapor pressure of a lithium battery electrolyte, includes the following steps:

[0019] Step 1: Pour the electrolyte to be tested into the cavity. The electrolyte level should completely submerge the heating wire. Then, seal the top cover to the cavity using a sealing gasket.

[0020] Step 2: Start pressure sensor one, pressure sensor two, and the data acquisition unit to begin recording data;

[0021] Step 3: Start the PID control constant temperature heating system, set the target temperature, and record the real-time data of vapor pressure changes with temperature.

[0022] Step 4: After the data acquisition device displays that the upper gas temperature in the cavity has reached the set temperature, observe and record the values ​​of each pressure sensor.

[0023] Step 5: After the vapor pressure values ​​of pressure sensor 1 and pressure sensor 2 stabilize, record the steady-state data.

[0024] Step 6: After recording the vapor pressure measurements of the electrolyte at different temperatures, calculate the enthalpy of vaporization and the saturated vapor pressure of the electrolyte based on the vapor pressure measurement data.

[0025] Furthermore, in the method for detecting the saturated vapor pressure of the lithium battery electrolyte, step 6 includes the following calculation steps and formulas:

[0026] 1) First, calculate the partial pressure of the air in the cavity at a specific temperature T1, using the following formula:

[0027]

[0028] Where Pα is the partial pressure of air, in Pa; and V is the volume of air, in m³. 3 T1 is temperature, in K; n is the amount of substance of air, in mol; R is the molar gas constant, in J / mol·K.

[0029] 2) Calculate the average value of pressure sensor one and pressure sensor two to obtain the pressure value in the cavity. The formula is:

[0030]

[0031] Among them, P b1 and P b2 These are the measured values ​​of pressure sensor one and pressure sensor two at temperature T1, respectively.

[0032] 3) Calculate the measured vapor pressure of the electrolyte at temperature T1 using the following formula:

[0033] Wherein, P1 is the actual vapor pressure of the electrolyte at temperature T1;

[0034] Similarly, the actual vapor pressure P2 of the electrolyte at temperature T2 and the actual vapor pressure P3 at temperature T3 are calculated respectively.

[0035] 4) Formulas for calculating enthalpy of vaporization and saturated vapor pressure, defining the enthalpy of vaporization of this electrolyte as... The calculation formula is as follows:

[0036]

[0037] Substituting the measured values ​​of P1, T1, P2, and T2, we can obtain the enthalpy coefficient of evaporation for the electrolyte. Substitute the initial vapor pressure P into the equation. n Temperature T n , and the required temperature T n+1 The enthalpy coefficient of evaporation is calculated based on this. It can predict at any target temperature T n+1 The saturated vapor pressure P of the electrolyte n+1 .

[0038] The beneficial effects of this invention are as follows:

[0039] 1. This invention uses a polytetrafluoroethylene tube filled with silicone oil in conjunction with a pressure sensor and a saturated vapor pressure numerical calculation method to directly and accurately measure the saturated vapor pressure of a specific electrolyte, and uses this as a reference to predict the internal pressure of the battery cell. This invention eliminates the need for complex device models and vacuum systems, significantly simplifying the operation process and reducing safety hazards.

[0040] 2. This invention obtains the saturated vapor pressure of the electrolyte at different temperatures by controlling the temperature with a heating wire, which significantly reduces the workload. At the same time, this invention calculates based on measured data and uses silicone oil sealing tubes combined with a high-precision pressure sensor to calculate and measure the saturated vapor pressure, ensuring that the boiling point of the electrolyte is not affected by the measuring device, thus having higher reliability.

[0041] 3. This invention uses a polytetrafluoroethylene (PTFE) tube, pre-filled with silicone oil, and the pressure sensors on both sides are zeroed before testing. The electrolyte is controlled to heat using a heating wire. Once the data acquisition system shows that the temperature above and below the liquid surface is consistent, and the pressure sensor readings stabilize and no longer rise, the average of the two readings is taken, and the partial pressure of air is subtracted to obtain the saturated vapor pressure of the electrolyte at the current temperature. This invention eliminates the need to construct a vacuum environment before testing, thus completely eliminating the interference caused by changes in the liquid's boiling point on the saturated vapor pressure measurement results.

[0042] 4. This invention provides a precise description and implementation of the saturated vapor pressure testing process for liquids at different temperatures, enhancing the applicability and universality of the solution. Furthermore, the saturated vapor pressure of the electrolyte measured by this invention, after calculation, maintains good consistency with the internal pressure during actual cell operation, thus providing a reliable data foundation for in-depth research on the thermal runaway mechanism of lithium batteries.

[0043] 5. This invention, by averaging the data from both pressure gauges and subtracting the initial air partial pressure, effectively reduces the impact of the initial air partial pressure on the calculation results while ensuring data accuracy. This invention provides high accuracy in measuring electrolyte vapor pressure and can be further used to estimate solvent vaporization partial pressure, providing a reliable basis for electrolyte safety assessment and risk warning.

[0044] 6. This invention is applicable to the saturated vapor pressure test of various mixed electrolytes. This method can be used to estimate the solvent vaporization partial pressure for any type of battery cell, enabling early identification and assessment of its thermal safety risks. It has good versatility and engineering applicability. Attached Figure Description

[0045] Figure 1 A schematic diagram of a device for detecting the saturated vapor pressure of lithium battery electrolyte;

[0046] Figure 2 This is a comparison chart of measured and theoretically calculated saturated vapor pressures. Detailed Implementation

[0047] like Figure 1As shown, a device for detecting the saturated vapor pressure of lithium battery electrolyte includes a cavity 5, a top cover 9, a polytetrafluoroethylene (PTFE) tube 1, a polytetrafluoroethylene (PTFE) tube 2, silicone oil, a pressure sensor 3, a pressure sensor 4, a PID-controlled constant temperature heating system 8, and a data acquisition unit 6. The cavity 5 is made of double-layered glass. The top cover 9 is sealed to the cavity 5, and a sealing gasket is provided between the top cover 9 and the cavity 5. One end of the PTFE tube 1 and the PTFE tube 2 are inserted into the top cover 9 and communicate with the cavity 5. The other end of tube 1 is connected to pressure sensor 3, and the other end of PTFE tube 2 is connected to pressure sensor 4. Silicone oil is added to PTFE tube 1 and PTFE tube 2, and the volume of silicone oil injected is 1 / 3 of the internal volume of PTFE tube 1 and PTFE tube 2. PID control constant temperature heating system 8 is set at the bottom of the cavity 5. The wire of data acquisition device 6 is inserted into the top cover 9, and the probe 7 of data acquisition device 6 is placed above the electrolyte surface in the cavity 5. An explosion-proof exhaust valve 10 is provided at the top of the cavity 5.

[0048] The PID-controlled constant temperature heating system 8 includes an ultra-thin temperature sensor, a PID controller, and a heating wire. The heating wire is evenly distributed at the bottom of the cavity 5 and is completely submerged in electrolyte during the test. The ultra-thin temperature sensor is located inside the cavity 5 and is connected to the PID controller, which is used to control the heating wire.

[0049] A method for detecting the saturated vapor pressure of a lithium battery electrolyte, utilizing the aforementioned detection device for the saturated vapor pressure of a lithium battery electrolyte, includes the following steps:

[0050] Step 1: Pour the electrolyte to be tested into the cavity 5. The electrolyte level should completely submerge the heating wire. Then, seal the top cover 9 to the cavity 5 using a sealing gasket.

[0051] Step 2: Start pressure sensor 3, pressure sensor 4, and data acquisition unit 6 to begin recording data;

[0052] Step 3: Start the PID control constant temperature heating system 8, set the target temperature, and record the real-time data of vapor pressure changes with temperature.

[0053] Step 4: After the data acquisition device 6 displays that the upper gas temperature in the cavity 5 has reached the set temperature, observe and record the values ​​of each pressure sensor.

[0054] Step 5: After the vapor pressure values ​​of pressure sensor 3 and pressure sensor 4 stabilize, record the steady-state data.

[0055] Step 6: After recording the vapor pressure measurements of the electrolyte at different temperatures, calculate the enthalpy of vaporization and the saturated vapor pressure of the electrolyte based on the vapor pressure measurement data.

[0056] The calculation steps and formulas are as follows:

[0057] 1) First, calculate the partial pressure of the air in the cavity 5 at a specific temperature T1, using the following formula:

[0058]

[0059] Where Pα is the partial pressure of air, in Pa; and V is the volume of air, in m³. 3 T1 is temperature, in K; n is the amount of substance of air, in mol; R is the molar gas constant, in J / mol·K.

[0060] 2) Calculate the average value of pressure sensor 3 and pressure sensor 4 to obtain the pressure value in the cavity 5. The formula is:

[0061]

[0062] Among them, P b1 and P b2 These are the measured values ​​of pressure sensor 3 and pressure sensor 4 at temperature T1, respectively.

[0063] 3) Calculate the measured vapor pressure of the electrolyte at temperature T1 using the following formula:

[0064] Wherein, P1 is the actual vapor pressure of the electrolyte at temperature T1;

[0065] Similarly, the actual vapor pressure P2 of the electrolyte at temperature T2 and the actual vapor pressure P3 at temperature T3 are calculated respectively.

[0066] 4) Formulas for calculating enthalpy of vaporization and saturated vapor pressure, defining the enthalpy of vaporization of this electrolyte as... The calculation formula is as follows:

[0067]

[0068] Substituting the measured values ​​of P1, T1, P2, and T2, we can obtain the enthalpy coefficient of evaporation for the electrolyte. Substitute the initial vapor pressure P into the equation. n Temperature T n , and the required temperature T n+1 The enthalpy coefficient of evaporation is calculated based on this. It can predict at any target temperature T n+1 The saturated vapor pressure P of the electrolyte n+1 .

[0069] The comparison chart of measured and theoretically calculated saturated vapor pressure is shown below. Figure 2 As shown.

Claims

1. A device for detecting the saturated vapor pressure of lithium battery electrolyte, characterized in that, The device includes a cavity, a top cover, two PTFE tubes (one and two), silicone oil, pressure sensor one and two, a PID-controlled constant-temperature heating system, and a data acquisition unit. The top cover is sealed to the cavity. One end of each PTFE tube is inserted into the top cover and communicates with the cavity. The other end of each PTFE tube is connected to pressure sensor one and pressure sensor two. Silicone oil is added to each PTFE tube. The PID-controlled constant-temperature heating system is located at the bottom of the cavity. The data acquisition unit's wires are inserted into the top cover, and the data acquisition unit's probe is positioned above the electrolyte level in the cavity.

2. The device for detecting the saturated vapor pressure of lithium battery electrolyte according to claim 1, characterized in that, The upper part of the cavity is equipped with an explosion-proof exhaust valve.

3. The device for detecting the saturated vapor pressure of lithium battery electrolyte according to claim 1, characterized in that, A sealing gasket is provided between the top cover and the cavity.

4. The device for detecting the saturated vapor pressure of lithium battery electrolyte according to claim 1, characterized in that, The PID-controlled constant temperature heating system includes an ultra-thin temperature sensor, a PID controller, and a heating wire. The heating wire is evenly distributed at the bottom of the cavity and is completely submerged in electrolyte during the test. The ultra-thin temperature sensor is located inside the cavity and is connected to the PID controller, which controls the heating wire.

5. The device for detecting the saturated vapor pressure of lithium battery electrolyte according to claim 1, characterized in that, The cavity is made of double-layered glass.

6. The device for detecting the saturated vapor pressure of lithium battery electrolyte according to claim 1, characterized in that, The volume of silicone oil injected is 1 / 3 of the internal volume of both PTFE tube 1 and PTFE tube 2.

7. A method for detecting the saturated vapor pressure of a lithium battery electrolyte, characterized in that, The method for detecting the saturated vapor pressure of lithium battery electrolyte as described in any one of claims 1-6 includes the following steps: Step 1: Pour the electrolyte to be tested into the cavity. The electrolyte level should completely submerge the heating wire. Then, seal the top cover to the cavity using a sealing gasket. Step 2: Start pressure sensor one, pressure sensor two, and the data acquisition unit to begin recording data; Step 3: Start the PID control constant temperature heating system, set the target temperature, and record the real-time data of vapor pressure changes with temperature. Step 4: After the data acquisition device displays that the upper gas temperature in the cavity has reached the set temperature, observe and record the values ​​of each pressure sensor. Step 5: After the vapor pressure values ​​of pressure sensor 1 and pressure sensor 2 stabilize, record the steady-state data. Step 6: After recording the vapor pressure measurements of the electrolyte at different temperatures, calculate the enthalpy of vaporization and the saturated vapor pressure of the electrolyte based on the vapor pressure measurement data.

8. The method for detecting the saturated vapor pressure of lithium battery electrolyte according to claim 7, characterized in that, In step 6, the calculation steps and formulas are as follows: 1) First, calculate the partial pressure of the air in the cavity at a specific temperature T1, using the following formula: Where Pα is the partial pressure of air, in Pa; and V is the volume of air, in m³. 3 T1 is temperature, in K; n is the amount of substance of air, in mol; R is the molar gas constant, in J / mol·K. 2) Calculate the average value of pressure sensor one and pressure sensor two to obtain the pressure value in the cavity. The formula is: Among them, P b1 and P b2 These are the measured values ​​of pressure sensor one and pressure sensor two at temperature T1, respectively. 3) Calculate the measured vapor pressure of the electrolyte at temperature T1 using the following formula: Wherein, P1 is the actual vapor pressure of the electrolyte at temperature T1; Similarly, the actual vapor pressure P2 of the electrolyte at temperature T2 and the actual vapor pressure P3 at temperature T3 are calculated respectively. 4) Formulas for calculating enthalpy of vaporization and saturated vapor pressure, defining the enthalpy of vaporization of this electrolyte as... The calculation formula is as follows: Substituting the measured values ​​of P1, T1, P2, and T2, we can obtain the enthalpy coefficient of evaporation for the electrolyte. Substitute the initial vapor pressure P into the equation. n Temperature T n , and the required temperature T n+1 The enthalpy coefficient of evaporation is calculated based on this. It can predict at any target temperature T n+1 The saturated vapor pressure P of the electrolyte n+1 .

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