Diaphragm, preparation method thereof and battery

Abstract

The invention provides a diaphragm, a preparation method thereof and a battery, the diaphragm comprises a porous film, a sensor is embedded in the porous film, and two sides of the porous film are respectively provided with a coating layer; the coating layer is one or both of an oxide and a polymer. The sensor is integrated into the battery diaphragm, so that the detection accuracy of the battery state is higher, the problem can be found at the initial stage of a battery fault, and a hysteresis phenomenon is avoided; the material / structure and the like of the battery cell are not influenced, and the battery cell is not damaged; irreversible damage to the sensor is avoided, and the sensitivity, the accuracy and the stability of the sensor are guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery diaphragms, and in particular relates to a diaphragm and a preparation method thereof, and a battery. Background Art

[0002] Driven by the "dual carbon" goals, countries around the world have increased their investment in renewable energy and clean technologies. As an important and mature energy storage solution, batteries have shown strong market demand and development potential. However, with the rapid development of batteries, fires and explosions caused by battery thermal runaway, pressure runaway, etc. have become increasingly prominent, which seriously threatens the safety of battery-based large-scale energy storage power stations, electric vehicles and electronic equipment. Based on this, in-depth understanding of the causes of thermal runaway and pressure runaway of battery cells, development of battery cell status monitoring technology, and formulation of effective early warning strategies will help to timely discover potential hidden dangers, thereby preventing battery fires and explosions, and ensuring the safe use and promotion of batteries.

[0003] Thermal runaway of a battery refers to a significant increase in the temperature inside the battery during the charging or discharging process, which accelerates chemical reactions and generates more heat. As the temperature continues to rise, the reaction inside the battery will enter a vicious cycle, further exacerbating the heat, leading to electrolyte decomposition, gas generation, and thermal runaway reactions of battery materials, which may cause fires or explosions in extreme cases. Pressure runaway is mainly due to the decomposition of the electrolyte, the intensification of side reactions, and the decomposition of diaphragm and electrode materials, which leads to the rapid generation of a large amount of gas inside the battery, resulting in increased internal pressure. When the internal pressure increases sharply, the internal structure of the electrode changes, which may lead to internal short circuits and other phenomena, further exacerbating side reactions. If the internal pressure exceeds the carrying capacity of the battery casing, the casing may rupture, leading to pressure runaway and a series of other safety issues.

[0004] During the thermal runaway and pressure runaway process, various parameters of the battery, such as current, voltage, internal resistance, surface temperature and internal pressure, will change significantly. The health status of the battery can be estimated by monitoring the battery status parameters (capacitance, etc.), electrical parameters (current, voltage, etc.), temperature and pressure. However, there are many limitations in relying on these signals to evaluate the thermal runaway and pressure runaway of the battery, including: 1) The battery status parameters and electrical parameters are related to the battery environment, energy storage status, load size, etc. There is no clear correlation between the currently detected battery status parameters, electrical parameters and thermal runaway; 2) The traditional temperature sensor of the battery is on the outside of the battery cell. In the early stage of thermal runaway, the battery cell has already overheated / side reactions are obvious, but it takes a certain amount of time (seconds to minutes) for the temperature and pressure to be transmitted to the sensor, resulting in a lag in the detection of the external sensor, making it difficult to effectively achieve early warning.

[0005] The Chinese patent application with publication number CN115663322A discloses a simple method for implanting a temperature sensor in a power battery and a temperature sensor. The temperature sensing material is sprayed on the tab, and the temperature of the temperature sensing material is detected to detect the temperature inside the battery. The Chinese patent application with publication number CN110690505A discloses a method for embedding a lithium battery sensing optical fiber, and the internal state of the battery is monitored by inserting an optical fiber sensor. Although these implantable sensors can effectively provide temperature information and state information inside the battery core, they also have certain defects. First, this type of implantable sensor may interfere with the internal structure of the battery core to a certain extent, thereby affecting the overall performance and safety of the battery. For example, spraying a temperature sensing material on the tab will increase the thickness of the tab, affect the tab welding, and change the internal structure; the optical fiber sensor inside the battery may affect the force of the electrode and the uniform flow of lithium ions during the energy storage process, thereby affecting the performance of the battery; when the battery is hit, the optical fiber sensor may cause internal structural damage, similar to piercing the electrode / diaphragm, etc. Secondly, placing micron to millimeter-scale sensors inside the battery will increase the difficulty of battery preparation and the production cost of the battery, which is not conducive to the development of the entire battery industry, and the high cost makes its commercial application difficult. The Chinese patent application with publication number CN116646528A discloses a temperature sensor placed inside a composite diaphragm to monitor the internal temperature of the battery. Although this method can solve the problem of introducing sensors to change the structure of the battery cell, it still has technical and process defects. For example: during the electrode preparation process, when the electrode slurry is coated, the composite diaphragm needs to withstand a stretch of about 150Mpa, a vacuum bake at 120°C, and immersion in highly soluble organic solvents such as N-methyl-2-pyrrolidone, etc. These will cause irreversible damage to the built-in temperature sensor, seriously affecting the sensitivity, accuracy and stability of the sensor.

[0006] In view of this, it is of great significance to improve battery safety to develop new battery monitoring technologies and solutions that can detect battery cell temperature, pressure, electrical parameters, etc. in real time, so as to continuously monitor the battery operating status with high sensitivity and accuracy without interfering with the internal structure of the battery. Summary of the invention

[0007] In order to solve the above-mentioned problems of the prior art, the present invention provides a diaphragm and a preparation method thereof and a battery, which can continuously monitor the operating status of the battery with high sensitivity and accuracy without interfering with the internal structure of the battery, thereby improving the safety of the battery.

[0008] The present invention is achieved through the following technical solutions: The present invention provides a diaphragm, comprising: a porous film, a sensor is embedded in the porous film, and coating layers are respectively arranged on both sides of the porous film; the coating layers are one or both of oxides and polymers.

[0009] Preferably, the material of the porous film is a polymer material or an inorganic material, the polymer material is one or more of polyethylene, polypropylene, polyvinyl chloride, polyamide, polyvinyl alcohol, polyacrylonitrile, polycarbonate, polyurethane, cellulose and polyimide; the inorganic material is one or more of silicon oxide, aluminum oxide and magnesium oxide.

[0010] Preferably, the sensor is made of a thermosensitive material, a pressure-sensitive material, a gas sensor material or an electrochemical sensor material.

[0011] Furthermore, the thermosensitive material is one or more of silver, platinum, gold, graphene, carbon nanotubes, carbon black, tin oxide, nickel oxide, cobalt oxide, copper oxide, antimony oxide and iron oxide.

[0012] Furthermore, the pressure-sensitive material is one or more of a mixture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) and graphene, graphite, graphene, reduced graphene oxide, carbon nanotubes, MXenes, polyaniline, zinc oxide, silicon carbide, titanium dioxide and strontium titanate.

[0013] Furthermore, the gas sensor material is one or more of silicon oxide, silver oxide, iron oxide, platinum, gold, silver, graphite, graphene and carbon nanotubes.

[0014] Furthermore, the electrochemical sensing material is one or more of platinum, gold, silver, carbon nanotubes, graphite and graphene.

[0015] Preferably, the oxide is one or more of silicon oxide, aluminum oxide, oxidized state, magnesium oxide, boehmite and calcium hydroxide; the polymer is one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyamide and polyimide.

[0016] The present invention provides a method for preparing the above-mentioned diaphragm, comprising: S1, preparing a porous film; S2, on one side surface of the porous film, a sensor is prepared by using 3D printing or screen printing technology, and a wire connected to the sensor is prepared; S3, depositing another layer of porous film on the surface of one side of the film having the sensor, to obtain a porous film in which the sensor is embedded; S4, attaching a coating layer on both sides of the porous film in which the sensor is embedded, to obtain a diaphragm.

[0017] The present invention provides a battery, comprising the above-mentioned diaphragm, and a positive electrode and a negative electrode; the diaphragm is located between the positive electrode and the negative electrode.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The sensor of the present invention is integrated into the battery diaphragm, and the signal can be transmitted to the outside of the battery through a wire. Compared with the temperature and pressure measurement of the battery outside, the solution provided by the present invention has higher accuracy in detecting the battery status, can find problems at the early stage of battery failure, without hysteresis, can obtain information at the moment (milliseconds) of battery failure, and take intervention measures to effectively improve the safety of the battery / battery core. The present invention integrates the sensor into the interior of the porous film in the battery diaphragm, and the porous film completely wraps the sensor. Therefore, compared with the solution of burying the sensor, the present invention will not have any effect on the material / structure of the battery core, and will not cause any damage to the battery core. Since the present invention integrates the sensor into the battery diaphragm, and the preparation of the diaphragm does not involve stretching, high-temperature vacuum baking, organic solvent immersion, etc., therefore, compared with the solution of integrating the sensor into the electrode diaphragm, the present invention will not cause irreversible damage to the sensor, and the sensitivity, accuracy and stability of the sensor are guaranteed. Therefore, the present invention can realize high sensitivity and accuracy monitoring of parameters such as temperature and pressure inside the battery without destroying the battery structure.

[0019] The technologies used in the preparation method of the diaphragm of the present invention are relatively mature, such as silk screen / printing technology, which has been verified in flexible electronics. Therefore, preparing sensors in the diaphragm will not have any impact on the battery manufacturing process and has a high prospect for commercial application.

[0020] By assembling the separator provided by the present invention with the positive electrode and the negative electrode, a new type of battery with a self-monitoring function can be obtained. The obtained battery can quickly and effectively monitor the battery status and provide battery safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 Schematic diagram of the diaphragm designed for the present invention: (a) and (b) are macroscopic photographs of the diaphragm; (c) is a top view of the diaphragm, wherein the central portion is the sensor; (d) is a side view of the diaphragm, wherein the central portion is the sensor.

[0023] Figure 2It is a schematic diagram of the structure of the diaphragm of the present invention.

[0024] Figure 3 The present invention is a flow chart for preparing the diaphragm.

[0025] Figure 4 This is a design drawing of the screen-printed sensor pattern of the present invention.

[0026] Figure 5 This is a real photo of the porous film containing the temperature sensor of the present invention.

[0027] Figure 6 This is a photo of the porous film containing the pressure sensor and the wire of the present invention.

[0028] Figure 7 This is the charge and discharge curve of the graphite / / lithium cobalt oxide battery of the present invention.

[0029] Figure 8 This is the charge and discharge curve of the lithium / / nickel-cobalt-manganese ternary battery of the present invention.

[0030] Fig. 9 This is the charge and discharge curve of the lithium / / lithium iron phosphate battery of the present invention.

[0031] Fig.10 This is a real photo of the lithium metal / / lithium metal symmetrical battery containing the pressure sensor of the present invention.

[0032] Fig.11 This is a design diagram of the electrochemical sensor of the present invention.

[0033] Fig.12 This is the resistance-temperature correspondence of the present invention.

[0034] Fig.13 This is a comparison chart of the temperature calculated by the internal sensor of the lithium-ion battery of the present invention and the actual temperature.

[0035] Fig.14 Electrochemical energy storage and internal temperature diagram of the lithium / / lithium iron phosphate battery of the present invention: (a) 10C charge and discharge curve, (b) battery internal temperature curve.

[0036] Fig.15 The energy storage characteristics and pressure change curves of the lithium symmetrical battery of the present invention are as follows: (a) charge and discharge curve, (b) internal pressure change curve. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0039] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0040] See also Figure 1 The present invention designs a new type of composite diaphragm to realize real-time monitoring of the internal state of the battery (such as temperature and pressure, etc.), thereby building a battery with higher safety.

[0041] See also Figure 2 The diaphragm of the present invention comprises a porous film 1, in which a sensor 2 and a wire 4 connected to the sensor 2 are embedded, and coating layers 3 are provided on both sides of the porous film 1; the coating layers are oxides or polymers. The porous film 1 mainly serves as a supporting structure to separate the positive and negative electrodes, allowing ions to pass through and isolating electrons. The coating layer 3 plays a role in protecting the diaphragm from swelling. The sensor 2 is embedded in the porous film and can effectively transmit signals such as temperature and pressure, making it possible to monitor the internal state of the battery in real time.

[0042] The materials of the porous film of the present invention include but are not limited to: polymer materials, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC), polyurethane (PU), polyimide (PI), etc.; inorganic materials include but are not limited to: silicon oxide, aluminum oxide, magnesium oxide.

[0043] The materials of the sensor of the present invention include but are not limited to: thermosensitive materials, pressure-sensitive materials, gas sensor materials, electrochemical sensing materials, etc. The thermosensitive materials are silver, platinum, gold, graphite, graphene, carbon nanotubes, carbon black, tin oxide, nickel oxide, cobalt oxide, copper oxide, antimony oxide, and iron oxide; the pressure-sensitive materials include but are not limited to: a mixture of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PDOS:PSS) and graphene, graphite, graphene, reduced graphene oxide, carbon nanotubes, MXenes, polyaniline, zinc oxide, silicon carbide, titanium dioxide, and strontium titanate; the gas sensor materials include but are not limited to: silicon oxide, silver oxide, iron oxide, platinum, gold, silver, graphene, and carbon nanotubes; the electrochemical sensing materials include but are not limited to: platinum, gold, silver, carbon nanotubes, and graphene.

[0044] The thickness of the porous film is 1 μm to 1 mm, the thickness of the sensor is 0.1 μm to 50 μm, the thickness of the wire is 0.1 μm to 50 μm, and the thickness of the coating layer is 50 nm to 25 μm.

[0045] See also Figure 3 The method for preparing the diaphragm of the present invention comprises the following steps: S1, preparing a porous film; S2, on one side surface of the porous film, a sensor is prepared by using 3D printing or screen printing technology, and a wire connected to the sensor is prepared; S3, preparing another porous film on the surface of one side of the porous film having the sensor, to obtain a porous film with the sensor embedded therein; S4, depositing a coating layer on both sides of the porous film in which the sensor is embedded, to obtain a diaphragm.

[0046] Based on the diaphragm provided by the present invention, a battery is assembled with a negative electrode and a positive electrode, and the resistance signal of the sensor is led out of the battery through a wire, so that real-time monitoring of the battery cell temperature, pressure, etc. can be achieved, which will greatly improve the battery safety.

[0047] Example 1 This example uses polypropylene as a porous film material, a metal silver paste-printed thermistor as a sensor, and a polyvinylidene fluoride and aluminum oxide composite material as a coating layer material to prepare a lithium-ion battery diaphragm as an example to demonstrate its preparation process: 1) Preparation of polypropylene porous film: Polypropylene (iPP, T38F, 3.8×10 5 g / mol, melt flow rate is 2.9 g / min), β-nucleating agent (NAB83) and nano-alumina are uniformly mixed and extruded into polypropylene casting film through a twin-screw extruder.

[0048] 2) At a certain temperature, the polypropylene cast film is stretched longitudinally and transversely to obtain a polypropylene porous film.

[0049] 3) Printing thermosensitive materials using screen printing technology: Print the thermosensitive conductive silver paste onto the surface of the polypropylene porous film, and print the pattern as follows: Figure 4 As shown in (a), it includes multiple concentric U-shaped structures with a line width of 0.2 mm to form a temperature sensor; the thickness of the temperature sensor is 5 μm. 4) Screen printing technology is used to print high-conductivity silver paste as the paste to obtain a conductor to transmit the signal of the temperature sensor; the thickness of the printed conductor is 5 μm.

[0050] 5) Prepare a polyvinylidene fluoride N-methylpyrrolidone solution, apply it to the temperature sensor and the wire, dry it at 70°C to encapsulate the sensor and the wire, and prepare a polypropylene porous film (thickness 15μm) containing a temperature sensor, such as Figure 5 As shown in (a).

[0051] 6) The two sides of the polypropylene porous film containing the temperature sensor are coated with a water-based composite material of polyvinylidene fluoride and aluminum oxide by a doctor blade method, and then dried to obtain a battery separator.

[0052] Example 2 It is basically the same as Example 1, except that in step 4), the printing pattern is as follows Figure 4 As shown in (e), a polypropylene porous film containing a temperature sensor is prepared, including multiple concentric U-shaped structures with a line width of 0.1 mm. Figure 5 As shown in (d).

[0053] Example 3 It is basically the same as Example 1, except that in step 4), the printing pattern is as follows Figure 4 As shown in (b), it has a serpentine structure with a line width of 0.2 mm. A polypropylene porous film containing a temperature sensor was prepared, as shown in Figure 5 As shown in (c).

[0054] Example 4 It is basically the same as Example 1, except that in step 4), the printing pattern is as follows Figure 4 As shown in (d), it has a serpentine structure with a line width of 0.1 mm. A polypropylene porous film containing a temperature sensor was prepared, as shown in Figure 5 As shown in (d).

[0055] Example 5 The method is basically the same as Example 1, except that the coating layer in step 6) is a magnesium hydroxide micron particle layer, and a polypropylene diaphragm coated with magnesium hydroxide is obtained.

[0056] Example 6 1) Preparation of polypropylene porous film: Polypropylene (iPP, T38F, 3.8×10 5 g / mol, melt flow rate is 2.9 g / min), β-nucleating agent (NAB83) and nano-alumina are uniformly mixed and extruded into polypropylene casting film through a twin-screw extruder.

[0057] 2) At a certain temperature, the polypropylene cast film is stretched longitudinally and transversely to obtain a polypropylene porous film; 3) Printing pressure-sensitive materials using screen printing technology: Print the pressure-sensitive material poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PDOS:PSS) and graphene mixed slurry onto the surface of the polypropylene porous film, and print the pattern as follows Figure 4 As shown in (c), it includes multiple concentric circles to form a pressure sensor; the thickness of the pressure sensor is 1 μm.

[0058] 4) Screen printing technology is used to print wires with high conductivity silver paste as the paste to transmit the signal of the pressure sensor; the thickness of the printed wire is 5 μm.

[0059] 5) Prepare N-methylpyrrolidone solution of polyvinylidene fluoride, apply it on the pressure sensor and the wire, dry it at 70℃, realize the packaging of the pressure sensor and the wire, and prepare a polypropylene porous film containing the pressure sensor, such as Figure 6 shown.

[0060] 6) The two sides of the polypropylene porous film containing the pressure sensor are coated with a water-based polyvinylidene fluoride and aluminum oxide composite material by a doctor blade method, and then dried to obtain a porous polypropylene diaphragm with pressure sensing.

[0061] Example 7 It is basically the same as Example 6, except that the pressure-sensitive material in step 3) is graphene slurry, and a porous polypropylene diaphragm with pressure sensitivity is obtained.

[0062] Example 8 It is basically the same as Example 6, except that the pressure-sensitive material in step 3) is carbon nanotube slurry, and a porous polypropylene diaphragm with pressure sensitivity is obtained.

[0063] Example 9 It is basically the same as Example 6, except that the pressure-sensitive material in step 3) is Ti3 C 2 T x MXenes and carbon nanotubes composite slurry to obtain a porous polypropylene diaphragm with pressure sensing.

[0064] Example 10 It is basically the same as Example 6, except that the pressure-sensitive material in step 3) is a composite slurry of zinc oxide and carbon nanotubes, and a porous polypropylene diaphragm with pressure sensitivity is obtained.

[0065] Embodiment 11 The surface capacity is 2.2 mAh cm -2 The graphite anode has a single-sided capacity of 2 mAh cm -2 The lithium cobalt oxide positive electrode sheet and the separator of Example 6 are assembled into a soft pack battery with a battery size of 10 × 10 cm 2 , the measured total capacity is 187 mAh, such as Figure 7 shown.

[0066] Example 12 A lithium foil with a thickness of 100 μm and a single-sided capacity of 2 mAh cm -2 The nickel-cobalt-manganese ternary positive electrode sheet and the separator of Example 1 are assembled into a soft pack battery with a battery size of 10 × 10 cm 2 , the measured total capacity is 196 mAh, such as Figure 8 shown.

[0067] Embodiment 13 A lithium foil with a thickness of 100 μm and a single-sided capacity of 2 mAh cm -2 The lithium iron phosphate positive electrode sheet and the separator of Example 1 are assembled into a soft pack battery with a battery size of 10 × 10 cm 2 , the measured total capacity is 199 mAh, such as Fig. 9 shown.

[0068] Embodiment 14 Two pieces of lithium foil with a thickness of 100 μm and the separator of Example 6 were assembled into a soft-pack lithium metal symmetric battery with a battery size of 10 × 10 cm 2 The mold is then clamped on both sides of the battery to test the internal pressure of the battery, such as Fig.10 shown.

[0069] Embodiment 15 1) Preparation of polypropylene porous film: Polypropylene (iPP, T38F, 3.8×10 5g / mol, melt flow rate is 2.9 g / min), β-nucleating agent (NAB83) and nano-alumina are uniformly mixed and extruded into polypropylene casting film through a twin-screw extruder.

[0070] 2) At a certain temperature, the polypropylene cast film is stretched longitudinally and transversely to obtain a polypropylene porous film.

[0071] 3) Print electrochemical sensing materials using screen printing technology: Graphene and tin oxide paste are printed on the surface of polypropylene porous film to form graphene-tin oxide electrode, and platinum paste is printed on the surface of polypropylene porous film to form platinum electrode. The printed pattern is as follows: Fig.11 As shown, the electrode width is 0.2 mm, forming an electrochemical sensor; the electrode thickness is 3 μm.

[0072] 4) Screen printing technology is used to print high-conductivity platinum slurry to obtain wires to transmit the signals of the electrochemical sensor; the thickness of the printed wires is 3 μm.

[0073] 5) Prepare a polyvinylidene fluoride N-methylpyrrolidone solution, apply it on the pressure sensor and the wire, dry it at 70°C to achieve the packaging of the sensor and the wire, and prepare a polypropylene porous film containing an electrochemical sensing electrode.

[0074] 6) The two sides of the polypropylene porous film containing the electrochemical sensor are coated with a water-based polyvinylidene fluoride and aluminum oxide composite material by a doctor blade method, and then dried to obtain a porous polypropylene diaphragm with an electrochemical sensor.

[0075] Example 16 Lithium foil with a thickness of 100 μm, copper foil and the separator of Example 15 were assembled into a soft-pack lithium metal||copper half-cell with a cell size of 10 × 10 cm 2 .

[0076] After the preparation of the diaphragm containing the sensor is completed, the temperature sensor and pressure sensor in the diaphragm need to be calibrated. The specific calibration process of the temperature sensor is: place the diaphragm of Example 1-4 in a constant temperature oven, test the resistance value of the temperature sensor every 10°C from 30°C to 80°C, and fit it with the temperature value measured by the commercial temperature measuring equipment to obtain a fitting curve. In this case, the four temperature sensors of Examples 1-4 have certain differences, and the average value is taken to finally obtain the temperature-resistance fitting curve of the temperature sensor in the diaphragm, such as Fig.12As shown. According to the fitting curve, the temperature-resistance fitting equation can be obtained: T=0.124R+51.19. Through this equation, the accurate temperature can be obtained by measuring the resistance value. Using the same method, the correlation between the resistance value and the pressure of the pressure sensor is tested and calibrated to obtain the pressure-resistance value equation. In the present invention, a certain mass is used to replace the force. Since the effective area is constant, the mass and the pressure exerted on the diaphragm can be equivalent. The mass-resistance fitting equation of the diaphragm of Example 6 is: M=56R -1.44 .

[0077] The polypropylene diaphragm containing the temperature sensor obtained in the above Example 1 and the internal temperature of the lithium ion battery obtained in Example 12 were tested: the polypropylene diaphragm and the lithium ion battery were placed in a constant temperature oven, a specific temperature was set and the temperature was kept constant for 30 minutes to ensure that the temperature of each sample was the same as the ambient temperature, the resistance value of the temperature sensor was tested and converted to temperature according to the above temperature-resistance value equation, and it was compared with the temperature value tested by the commercial temperature detection equipment, the error was calculated, and the accuracy of the temperature sensor was evaluated. The specific test results are shown in Table 1 and Fig.13 shown.

[0078] Table 1 Test temperature error of prepared samples

[0079] It can be seen from Table 1 that the temperature errors of the above samples of the present invention obtained by the temperature sensor test are less than 8%, which proves that the sensor design scheme of the present invention is feasible.

[0080] The battery of Example 13 was placed at room temperature for charge and discharge tests, and the resistance change collected by the temperature sensor during the charge and discharge process was collected, and the temperature change inside the battery cell was calculated according to the temperature-resistance fitting equation. Fig.14 As shown in the figure, under the fast charging condition of 10 C, the battery is charged and discharged in about 5 minutes. As the charging and discharging proceeds, the temperature of the battery cell gradually rises from room temperature 25°C to 30.5°C. The temperature sensor in the soft pack battery can accurately measure the internal temperature of the battery cell, proving that the sensor solution of the present invention is feasible.

[0081] The battery of Example 14 was subjected to charge and discharge tests at a current density of 1 mA cm -2 , the charge and discharge capacity is 1 mAhcm -2 , and collect the resistance changes collected by the pressure sensor as the charge and discharge progress, and convert the pressure changes inside the battery cell according to the pressure-resistance fitting equation. Fig.15As shown in the figure, in the lithium metal symmetric battery cycle, as the lithium metal deposition / stripping proceeds, the pressure inside the initial battery changes significantly. This is mainly because the lithium metal is stripped from the dense lithium metal foil and deposited as loose lithium on the counter electrode. The volume of the battery increases and the internal pressure increases. As the deposition / stripping proceeds, the pressure inside the entire battery gradually stabilizes. After 45 hours of cycling, the lithium dendrites increase significantly, resulting in a significant increase in internal pressure, as shown in the figure. Fig.15 As shown in (b), the pressure sensor in the soft pack battery can test the internal pressure of the battery cell, proving that the sensor solution of the present invention is feasible.

[0082] Example 16 was subjected to a charge and discharge test, and lithium metal was first deposited on the surface of the copper foil; as charging proceeded, the lithium deposited on the surface of the copper foil was peeled off from the copper surface and reduced to metallic lithium on the surface of the negative electrode. Since the coulomb efficiency of this process is only about 95%, side reactions are obvious. The decomposition of the electrolyte was calibrated and evaluated by detecting the change in the potential difference on both sides of the platinum electrode and the graphene-tin oxide electrode. Electrolyte decomposition byproducts such as hydrogen fluoride can react chemically with tin oxide, and as the chemical reaction continues, the potential difference between the platinum electrode and the graphene-tin oxide electrode changes significantly. The electrochemical sensor can evaluate and detect the decomposition of the electrolyte, proving that the sensor scheme of the present invention is feasible.

Claims

1. A diaphragm, characterized in that: The invention comprises a porous film in which a sensor is embedded, and coating layers are arranged on both sides of the porous film respectively; the coating layers are one or both of oxides and polymers.

2. The diaphragm according to claim 1, characterized in that The material of the porous film is a polymer material or an inorganic material, the polymer material is one or more of polyethylene, polypropylene, polyvinyl chloride, polyamide, polyvinyl alcohol, polyacrylonitrile, polycarbonate, polyurethane, cellulose and polyimide; the inorganic material is one or more of silicon oxide, aluminum oxide and magnesium oxide.

3. The diaphragm according to claim 1, characterized in that The sensor is made of a thermosensitive material, a pressure-sensitive material, a gas sensor material or an electrochemical sensor material.

4. The diaphragm according to claim 3, characterized in that The thermosensitive material is one or more of silver, platinum, gold, graphene, carbon nanotubes, carbon black, tin oxide, nickel oxide, cobalt oxide, copper oxide, antimony oxide and iron oxide.

5. The diaphragm according to claim 3, characterized in that The pressure-sensitive material is one or more of a mixture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) and graphene, graphite, graphene, reduced graphene oxide, carbon nanotubes, MXenes, polyaniline, zinc oxide, silicon carbide, titanium dioxide and strontium titanate.

6. The diaphragm according to claim 3, characterized in that The gas sensor material is one or more of silicon oxide, silver oxide, iron oxide, platinum, gold, silver, graphite, graphene and carbon nanotubes.

7. The diaphragm according to claim 3, characterized in that The electrochemical sensing material is one or more of platinum, gold, silver, carbon nanotubes, graphite and graphene.

8. The diaphragm according to claim 1, characterized in that The oxide is one or more of silicon oxide, aluminum oxide, oxidized state, magnesium oxide, boehmite and calcium hydroxide; the polymer is one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyamide and polyimide.

9. A method for preparing a diaphragm according to any one of claims 1 to 8, characterized in that: include: S1, preparing a porous film; S2, on one side surface of the porous film, a sensor is prepared by using 3D printing or screen printing technology, and a wire connected to the sensor is prepared; S3, depositing another layer of porous film on the surface of one side of the film having the sensor, to obtain a porous film in which the sensor is embedded; S4, attaching a coating layer on both sides of the porous film in which the sensor is embedded, to obtain a diaphragm.

10. A battery, characterized in that: The invention comprises the separator according to any one of claims 1 to 8, and a positive electrode and a negative electrode; the separator is located between the positive electrode and the negative electrode.

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