CN111106399B - Design method, system, safety valve and battery for opening pressure of safety valve of lithium battery - Google Patents

Abstract

The present application relates to a design method, system, safety valve and battery for the opening pressure of a safety valve of a lithium battery. The design method includes measuring the in-situ pressure and temperature of the battery, and fitting to form the temperature-pressure function. By taking the second derivative of the temperature-pressure function, the corresponding pressure value when the second derivative is 0 is calculated, and the opening pressure value of the safety valve is obtained based on the corresponding pressure value when the second derivative is 0. The opening pressure value is the point at which the second derivative of the temperature-pressure function is 0. The opening pressure value represents the transition node of the internal pressure of the battery from the gas production process of the electrolyte solution evaporation to the electrolyte solution decomposition gas production process. The opening pressure value enables the safety valve to release pressure before the electrolyte decomposition stage arrives, effectively preventing the occurrence of thermal runaway of the battery, and improving the safety of the battery.

Description

Design method, system, safety valve and battery for opening pressure of safety valve of lithium battery

technical field

The present application relates to the technical field of batteries, and in particular, to a design method, system, safety valve and battery for the opening pressure of a safety valve of a lithium battery.

Background technique

In the process of thermal runaway, lithium batteries will swell, deflate or even burn. The high temperature flue gas released by the thermal runaway of the single unit spreads in the battery pack, causing the thermal runaway behavior to spread to the adjacent batteries, causing the entire module and even the battery pack to thermally runaway. Thermal runaway of the battery pack can cause combustion or even explosion, resulting in loss of life and property.

The power lithium battery cell is divided into: cylindrical battery, square shell battery and soft pack battery according to different shell mechanisms. Both cylindrical batteries and square case batteries are fitted with safety valves. When the internal pressure of the battery is higher than a certain threshold, the safety valve opens to release the internal pressure of the battery in advance. When the pressure in the pouch battery reaches a certain level, it will be released from the weak part of the aluminum-plastic film, which is the wrapping material of the battery. Relieving the stress will reduce the hazard of thermal runaway of the battery to a certain extent. However, the current design of the discharge pressure of the battery safety valve is not very reasonable, and the discharge of the safety valve cannot completely prevent the occurrence of thermal runaway.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a method, system, safety valve and battery for designing the opening pressure of the safety valve of a lithium battery for the problem of how to reasonably design the discharge pressure of the safety valve of the battery.

A method for designing the opening pressure of a safety valve of a lithium battery, the lithium battery includes a casing and a safety valve, the safety valve is arranged in the casing, the casing surrounds a battery cavity, and the lithium battery is arranged in a gas The design method includes:

The lithium battery is heated or charged, and the pressure in the airtight chamber and the battery chamber of the lithium battery is controlled to be the same.

A plurality of first pressures in the battery cavity and a plurality of first temperatures corresponding to the plurality of first pressures one-to-one are collected.

Fitting a plurality of the first pressures and a plurality of the first temperatures to obtain a temperature-pressure function.

A second derivative is performed on the temperature-pressure function, the corresponding pressure value when the second derivative is 0 is calculated, and the opening pressure value of the safety valve is obtained based on the corresponding pressure value when the second derivative is 0.

In one embodiment, a second derivative is performed on the temperature-pressure function, the corresponding pressure value when the second derivative is 0 is calculated, and the pressure value of the safety valve is obtained based on the corresponding pressure value when the second derivative is 0 The opening pressure values include:

A first derivative of the temperature-pressure function is performed to obtain a pressure rise rate graph.

The pressure rise rate turning plateau is obtained according to the pressure rise rate graph.

A second derivative of the temperature-pressure function is performed, and a graph of the rate of pressure rise is obtained.

Find the pressure value corresponding to the turning platform where the pressure rise rate changes to 0, and the pressure value is the opening pressure value of the safety valve.

In one embodiment, a derivative of the temperature-pressure function is performed to obtain the pressure rise rate curve including:

A first derivative of the temperature-pressure function yields a pressure rise rate function.

The pressure rise rate graph is plotted from the pressure rise rate function and the temperature-pressure function.

In one embodiment, performing a quadratic derivation on the temperature-pressure function, and obtaining the pressure rise rate change curve includes:

A second derivative of the temperature-pressure function is performed to obtain a pressure rise rate change function.

The pressure rise rate change graph is drawn according to the pressure rise rate change function and the temperature-pressure function.

In one embodiment, a Gaussian function is used to fit a plurality of the first pressures and a plurality of the first temperatures to obtain the temperature-pressure function.

A design system for the opening pressure of a lithium battery safety valve. The lithium battery includes a casing and a safety valve. The safety valve is arranged on the casing. The casing surrounds and forms a battery cavity. The lithium battery is arranged in an airtight cavity. The design system includes an in-situ experiment module, a data acquisition module, a data fitting module and a data analysis module. The in-situ experimental module is used to heat or charge the lithium battery, and control the pressure in the airtight chamber to be the same as that in the battery chamber of the lithium battery. The data acquisition module is configured to acquire a plurality of first pressures in the battery cavity and a plurality of first temperatures in one-to-one correspondence with the plurality of first pressures. The data fitting module is used for fitting a plurality of the first pressures and a plurality of the first temperatures to obtain a temperature-pressure function. The data analysis module is used to perform a second derivative of the temperature-pressure function, calculate the corresponding pressure value when the second derivative is 0, and obtain the safety valve based on the corresponding pressure value when the second derivative is 0 the opening pressure value.

In one embodiment, the data analysis module includes a first drawing module, a first searching module, a second drawing module and a second searching module. The first drawing module is configured to perform a derivative of the temperature-pressure function and draw a pressure rise rate curve graph. The first search module is configured to find a pressure rise rate turning platform according to the pressure rise rate graph. The second drawing module is used for performing a quadratic derivation of the temperature-pressure function, and drawing a change curve of the pressure rise rate. The second search module is used to find the pressure value corresponding to the turning platform where the pressure rise rate changes to 0, and the pressure value is the opening pressure value of the safety valve.

In one embodiment, the first drawing module includes a first derivation sub-module and a first drawing sub-module. The first derivation submodule is used to perform a derivative of the temperature-pressure function to obtain a pressure rise rate function. The first drawing sub-module is configured to draw the pressure rise rate curve graph according to the pressure rise rate function and the temperature-pressure function.

In one embodiment, the second drawing module includes a second derivation sub-module and a second drawing sub-module. The second derivation submodule is used to perform a quadratic derivation of the temperature-pressure function to obtain a pressure rise rate change function. The second drawing sub-module is configured to draw the pressure rise rate change curve according to the pressure rise rate change function and the temperature-pressure function.

In one embodiment, the data fitting module is configured to use a Gaussian function to fit a plurality of the first pressures and a plurality of the first temperatures to obtain the temperature-pressure function.

A safety valve, the burst pressure of the safety valve is obtained by implementing the method of any one of the above embodiments.

A battery includes the safety valve described in the above embodiments.

The method for designing the opening pressure of the lithium battery safety valve provided in the embodiments of the present application. The lithium battery includes a casing and a safety valve. The safety valve is arranged on the casing. The casing surrounds and forms a battery cavity. The lithium battery is arranged in an airtight cavity. The lithium battery is heated or charged until thermal runaway of the lithium battery occurs. And during the heating or charging process, the pressure in the airtight cavity is the same as that in the battery cavity of the lithium battery. The design method includes acquiring a plurality of first pressures in the battery cavity and a plurality of first temperatures in a one-to-one correspondence with the plurality of first pressures. Fitting a plurality of the first pressures and a plurality of the first temperatures to obtain a temperature-pressure function. The second derivative is performed on the temperature-pressure function, and the corresponding pressure value when the second derivative is 0 is calculated, and the pressure value is the opening pressure value of the safety valve.

The opening pressure value corresponds to the point where the second derivative of the temperature-pressure function is 0. The opening pressure value represents the transition node of the internal pressure of the battery from the gas production process of the electrolyte solution evaporation to the electrolyte solution decomposition gas production process. The opening pressure value enables the safety valve to release pressure before the electrolyte decomposition stage arrives, effectively preventing the occurrence of thermal runaway of the battery and improving the safety of the battery.

Description of drawings

1 is a flowchart of a method for designing the opening pressure of the lithium battery safety valve provided in an embodiment of the application;

2 is a graph of the temperature-pressure function provided in an embodiment of the present application;

3 is a graph of the pressure rise rate provided in an embodiment of the present application;

FIG. 4 is a graph of the change of the pressure rise rate provided in an embodiment of the present application.

reference number

Turning Platform 20

Detailed ways

In order to make the above objects, features and advantages of the present application more clearly understood, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific implementation disclosed below.

The serial numbers themselves, such as "first", "second", etc., for the components herein are only used to distinguish the described objects, and do not have any order or technical meaning. The "connection" and "connection" mentioned in this application, unless otherwise specified, include both direct and indirect connections (connections). In the description of this application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", The orientation or positional relationship indicated by "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description , rather than indicating or implying that the referred device or element must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as a limitation on the present application.

In this application, unless otherwise expressly stated and defined, a first feature "on" or "under" a second feature may be in direct contact with the first and second features, or the first and second features indirectly through an intermediary touch. Also, the first feature being "above", "over" and "above" the 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 level higher than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower level than the second feature.

Referring to FIG. 1 , an embodiment of the present application provides a method for designing the opening pressure of a safety valve of a lithium battery. The lithium battery includes a casing and a safety valve. The safety valve is arranged on the casing. The casing surrounds and forms a battery cavity. The lithium battery is arranged in an airtight cavity, and the design method includes:

S100, heating or charging the lithium battery, and controlling the pressure in the airtight chamber to be the same as that in the battery chamber of the lithium battery.

S200: Collect a plurality of first pressures in the battery cavity and a plurality of first temperatures in a one-to-one correspondence with the plurality of first pressures.

S300 , fitting a plurality of the first pressures and a plurality of the first temperatures to obtain a temperature-pressure function.

S400. Perform a second derivative of the temperature-pressure function, calculate a pressure value corresponding to when the second derivative is 0, and obtain an opening pressure value of the safety valve based on the corresponding pressure value when the second derivative is 0.

In S100, the lithium battery is heated or charged until thermal runaway occurs in the lithium battery. During the thermal runaway process, the pressures in the airtight chamber and the battery chamber of the lithium battery are controlled to be equal. During the thermal runaway of the lithium battery, the temperature and pressure within the lithium battery increase. The measurement of thermal runaway with equal internal and external pressures is called an in-situ measurement.

In S200, a plurality of the first pressures and a plurality of the first temperatures during the thermal runaway of the battery are collected. A plurality of the first pressures are in a one-to-one correspondence with a plurality of the first temperatures.

The method for designing the opening pressure of the lithium battery safety valve provided in the embodiment of the present application includes measuring the in-situ pressure and temperature of the battery, and fitting to form the temperature-pressure function. By taking the second derivative of the temperature-pressure function, the corresponding pressure value when the second derivative is 0 is calculated, and the opening pressure value of the safety valve is obtained based on the corresponding pressure value when the second derivative is 0. The cracking pressure value is the point at which the second derivative of the temperature-pressure function is zero. The opening pressure value represents the transition node of the internal pressure of the battery from the gas production process of the electrolyte solution evaporation to the electrolyte solution decomposition gas production process. The opening pressure value enables the safety valve to release pressure before the electrolyte decomposition stage arrives, effectively preventing the occurrence of thermal runaway of the battery and improving the safety of the battery.

Referring to FIG. 2 together, a plurality of the first pressures and the plurality of the first temperatures are drawn into a temperature-pressure diagram. In the temperature-pressure graph, the abscissa is temperature, and the ordinate is pressure. As the temperature gradually increases, the pressure gradually increases. When the temperature reaches a certain value, the pressure rises sharply.

In one embodiment, S400 includes:

S410, perform a derivative of the temperature-pressure function to obtain a pressure rise rate curve graph. The abscissa of the pressure rise rate graph is the pressure, and the ordinate is the pressure rise rate.

S420 , obtaining the pressure rise rate turning platform 20 according to the pressure rise rate graph.

S430, perform a second derivative of the temperature-pressure function, and obtain a pressure rise rate change curve.

S440, find a pressure value corresponding to the turning platform 20 where the pressure rise rate changes to 0, and the pressure value is the opening pressure value of the safety valve.

In S420, the turning platform 20 indicates that the pressure increases, and the pressure change rate is basically unchanged.

Please refer to FIG. 3 together, the pressure rise rate graph shows three steps, namely before 165kPa, between 165kPa and 265kPa, and after 265kPa. After the pressure inside the lithium battery reaches 265 kPa, the pressure rise rate inside the lithium battery increases rapidly. The internal pressure of the lithium battery stall increases. The 265 kPa corresponding to the turning platform 20 represents the transition node of the internal pressure of the battery from the gas production process of electrolyte evaporation to the gas production process of electrolyte decomposition. Therefore, the 265kPa is used as the opening pressure value, that is, the pressure of the safety valve is released before the chemical decomposition of the electrolyte in the lithium battery occurs. Using the 265 kPa as the opening pressure value can ensure that the lithium battery can be depressurized in time before thermal runaway, thereby effectively avoiding thermal runaway.

The battery pack for lithium batteries includes a smoke sensor. The flue gas discharged from the battery will be sensed by the flue gas sensor, and the dangerous state of the battery can be sensed in time.

Please refer to FIG. 4 together, the abscissa of the pressure rise rate change curve is the pressure, and the ordinate is the rate of change of the pressure rate. There are multiple pressure points corresponding to the point whose ordinate is 0. The fourth point corresponds to the turning platform 20, that is, the point where 265kPa is located.

Figure 3 is used to find the variation trend of the pressure rise rate, and Figure 4 is used to find the opening pressure value.

In one embodiment, S410 includes:

S411, perform a derivative of the temperature-pressure function to obtain a pressure rise rate function.

S412, draw the pressure rise rate curve graph according to the pressure rise rate function and the temperature-pressure function.

In one embodiment, step S412 is to first draw a temperature-pressure rise rate curve, wherein the abscissa is the temperature and the ordinate is the pressure rise rate. There is a one-to-one correspondence between temperature and pressure. Replacing the temperature on the abscissa in the temperature-pressure rise rate curve with pressure, the pressure rise rate curve graph is obtained.

In one embodiment, S430 includes:

S431 , performing a quadratic derivation on the temperature-pressure function to obtain a pressure rise rate change function.

S432, according to the pressure rise rate change function and the temperature-pressure function, draw the pressure rise rate change curve.

In one embodiment, step S432 is to first draw a temperature-pressure rise rate change curve, wherein the abscissa is the temperature, and the ordinate is the pressure rise rate change. There is a one-to-one correspondence between temperature and pressure. Replacing the temperature on the abscissa in the temperature-pressure rise rate change curve with pressure, the pressure rise rate change curve graph is obtained.

In one embodiment, in S200, a Gaussian function is used to fit a plurality of the first pressures and a plurality of the first temperatures to obtain the temperature-pressure function.

The embodiment of the present application provides a system for designing the opening pressure of a safety valve of a lithium battery. The lithium battery includes a casing and a safety valve. The safety valve is arranged on the casing. The casing surrounds and forms a battery cavity. The lithium battery is arranged in an airtight cavity. The design system includes an in-situ experiment module, a data acquisition module, a data fitting module and a data analysis module. The in-situ experimental module is used to heat or charge the lithium battery, and control the pressure in the airtight chamber to be the same as that in the battery chamber of the lithium battery. The data acquisition module is configured to acquire a plurality of first pressures in the battery cavity and a plurality of first temperatures in one-to-one correspondence with the plurality of first pressures. The data fitting module is used for fitting a plurality of the first pressures and a plurality of the first temperatures to obtain a temperature-pressure function. The data analysis module is used to perform a second derivative of the temperature-pressure function, calculate the corresponding pressure value when the second derivative is 0, and obtain the safety valve based on the corresponding pressure value when the second derivative is 0 the opening pressure value.

The design system for the opening pressure of the lithium battery safety valve provided in the embodiments of the present application. The in-situ pressure and temperature of the battery are measured by the in-situ experiment module and the data acquisition module, and the data fitting module is fitted to form the temperature-pressure function. The second derivative of the temperature-pressure function is performed by the data analysis module, the corresponding pressure value when the second derivative is 0 is calculated, and the pressure value of the safety valve is obtained based on the corresponding pressure value when the second derivative is 0 Opening pressure value. The cracking pressure value is the point at which the second derivative of the temperature-pressure function is zero. The opening pressure value represents the transition node of the internal pressure of the battery from the gas production process of the electrolyte solution evaporation to the electrolyte solution decomposition gas production process. The opening pressure value obtained by the design system of the opening pressure of the lithium battery safety valve enables the safety valve to release pressure before the electrolyte decomposition stage arrives, effectively preventing the occurrence of thermal runaway of the battery and improving the safety of the battery.

In one embodiment, the data analysis module includes a first drawing module, a first searching module, a second drawing module and a second searching module. The first drawing module is configured to perform a derivative of the temperature-pressure function and draw a pressure rise rate curve graph. The first search module is configured to find the pressure rise rate turning platform 20 according to the pressure rise rate graph. The second drawing module is used for performing a quadratic derivation of the temperature-pressure function, and drawing a change curve of the pressure rise rate. The second search module is used to find the pressure value corresponding to the turning platform 20 where the pressure rise rate changes to 0, and the pressure value is the opening pressure value of the safety valve.

In one embodiment, the first drawing module includes a first derivation sub-module and a first drawing sub-module. The first derivation submodule is used to perform a derivative of the temperature-pressure function to obtain a pressure rise rate function. The first drawing sub-module is configured to draw the pressure rise rate curve graph according to the pressure rise rate function and the temperature-pressure function.

In one embodiment, the second drawing module includes a second derivation sub-module and a second drawing sub-module. The second derivation submodule is used to perform a quadratic derivation of the temperature-pressure function to obtain a pressure rise rate change function. The second drawing sub-module is configured to draw the pressure rise rate change curve according to the pressure rise rate change function and the temperature-pressure function.

In one embodiment, the data fitting module is configured to use a Gaussian function to fit a plurality of the first pressures and a plurality of the first temperatures to obtain the temperature-pressure function.

The embodiment of the present application provides the safety valve, and the burst pressure of the safety valve is obtained by implementing the method of any one of the above embodiments. The embodiment of the present application provides the safety valve to release pressure before the electrolyte decomposition stage arrives, which effectively prevents the occurrence of thermal runaway of the battery and improves the safety of the battery.

The embodiments of the present application provide a battery, including the safety valve described in the above embodiments. The embodiments of the present application provide that the safety valve in the battery releases pressure before the electrolyte decomposition stage arrives, which effectively prevents the occurrence of thermal runaway of the battery and improves the safety of the battery.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present application, but should not be construed as limiting the scope of the present application. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims (8)

1. A design method for opening pressure of a safety valve of a lithium battery, wherein the lithium battery comprises a shell and the safety valve, the safety valve is arranged on the shell, the shell surrounds and forms a battery cavity, the lithium battery is arranged in an airtight cavity, and the design method comprises the following steps:

heating or charging the lithium battery, and controlling the pressure in the airtight cavity to be the same as that in the battery cavity of the lithium battery;

collecting a plurality of first pressures in the battery cavity and a plurality of first temperatures in one-to-one correspondence with the first pressures;

fitting the plurality of first pressures and the plurality of first temperatures by adopting a Gaussian function to obtain a temperature-pressure function;

carrying out first derivation on the temperature-pressure function to obtain a pressure rise rate curve chart;

obtaining a turning platform (20) of the pressure rising rate according to the pressure rising rate curve chart, and continuously rising the pressure rising rate after the turning platform (20) is reached;

carrying out secondary derivation on the temperature-pressure function, and obtaining a pressure rise rate change curve chart;

and finding a pressure value with the pressure rising rate change of 0 corresponding to the turning platform (20), wherein the pressure value is the opening pressure value of the safety valve.

2. The method of claim 1, wherein the step of deriving the temperature-pressure function to obtain a pressure rise rate curve comprises:

performing first derivation on the temperature-pressure function to obtain a pressure rise rate function;

and drawing the pressure rise rate curve according to the pressure rise rate function and the temperature-pressure function.

3. The method of claim 1, wherein the step of performing a second derivation on the temperature-pressure function to obtain a pressure rise rate curve comprises:

carrying out secondary derivation on the temperature-pressure function to obtain a pressure rise rate change function;

and drawing a pressure rise rate change curve according to the pressure rise rate change function and the temperature-pressure function.

4. A design system of a lithium battery safety valve opening pressure, the lithium battery comprises a shell and a safety valve, the safety valve is arranged on the shell, the shell surrounds to form a battery cavity, the lithium battery is arranged in an airtight cavity, and the design system comprises:

the in-situ experiment module is used for heating or charging the lithium battery and controlling the pressure in the airtight cavity to be the same as that in the battery cavity of the lithium battery;

the data acquisition module is used for acquiring a plurality of first pressures in the battery cavity and a plurality of first temperatures in one-to-one correspondence with the first pressures;

the data fitting module is used for fitting the plurality of first pressures and the plurality of first temperatures by adopting a Gaussian function to obtain a temperature-pressure function;

a data analysis module, the data analysis module comprising:

the first drawing module is used for carrying out first derivation on the temperature-pressure function and drawing a pressure rise rate curve chart;

the first searching module is used for finding the turning platform (20) of the pressure rising rate according to the pressure rising rate curve graph, and the pressure rising rate continuously rises after the turning platform (20) is reached;

the second drawing module is used for carrying out secondary derivation on the temperature-pressure function and drawing a pressure rise rate change curve chart;

and the second searching module is used for searching a pressure value with the pressure rising rate change of 0 corresponding to the turning platform (20), and the pressure value is the opening pressure value of the safety valve.

5. The system for designing a lithium battery safety valve opening pressure as claimed in claim 4, wherein the first drawing module includes:

the first derivation submodule is used for carrying out primary derivation on the temperature-pressure function to obtain a pressure rise rate function;

and the first drawing submodule is used for drawing the pressure rise rate curve according to the pressure rise rate function and the temperature-pressure function.

6. The system for designing a lithium battery safety valve opening pressure as claimed in claim 4, wherein the second drawing module comprises:

the second derivation submodule is used for carrying out secondary derivation on the temperature-pressure function to obtain a pressure rise rate change function;

and the second drawing submodule is used for drawing the pressure rise rate change curve according to the pressure rise rate change function and the temperature-pressure function.

7. A safety valve, characterized in that the opening pressure of the safety valve is obtained by implementing the design method as set forth in any one of claims 1 to 3.

8. A battery comprising the safety valve according to claim 7.

Images