A flexible capacitive sensor for lithium battery pressure detection and preparation method thereof

Abstract

The present invention belongs to the field of sensors, and specifically relates to a flexible capacitive sensor for lithium battery pressure detection and a preparation method thereof. The sensor includes: a stacked first electrode plate and a second electrode plate; a dielectric layer, which is stacked between the first electrode plate and the second electrode plate, and a protrusion array is arranged on the side close to the first electrode plate, and a gap is left between the top of the protrusion array and the first electrode plate, and the bottom area of ​​the protrusion is larger than the top area of ​​the protrusion, which is a polymer ionic liquid gel layer with a porous structure; a spacer layer, which is stacked between the first electrode plate and the dielectric layer, and is sleeved on the periphery of the protrusion array, one side of which is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of which is in contact with the first electrode plate, and is a polymer gel layer with a porous structure; the polymer, porosity and average pore size of the spacer layer correspond to the polymer, porosity and average pore size of the dielectric layer; it can improve the sensing sensitivity, linearity and widen the detection range.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular, relates to a flexible capacitive sensor for lithium battery pressure detection and a preparation method thereof. Background Art

[0002] Batteries are an important power source for new energy vehicles. To ensure the safety of batteries throughout their life cycle, regular testing is required during the battery development and use phases to monitor the battery health status to ensure reliable and safe operation of the vehicle.

[0003] During the battery charging and discharging process, internal chemical reactions, material expansion or contraction, etc. cause changes in pressure on the battery surface or inside. This makes battery surface pressure measurement technology promising for use in battery health testing. In order to clarify the health status of the battery, such as internal material loss, changes in electrode surface structure, etc., it is necessary to detect pressure changes on the battery surface or inside with high precision and sensitivity.

[0004] Pressure detection in the form of thin film capacitor sensors is expected to be used to detect pressure on the surface or inside of batteries. The basic principle of thin film capacitor sensors for detecting pressure is that when the sensor is subjected to force or strain, the film thickness is changed, the capacitance is changed, and the capacitance change is converted into an electrical signal, thereby sensing force or strain. However, the unit pressure change of thin film capacitor sensors corresponds to a small change in film thickness and a small change in capacitance, and the detection sensitivity is limited. When used to detect battery surface or internal pressure, it is difficult to determine the health of the battery.

[0005] It should be noted that this part of the present invention only provides background technology related to the present invention and does not necessarily constitute prior art or known technology. Summary of the invention

[0006] The purpose of the present invention is to overcome the defect of existing thin film capacitor sensors, which have limited pressure sensing sensitivity, making it difficult to clearly determine the health status of the battery through pressure sensing. A flexible capacitor sensor for lithium battery pressure detection and a preparation method thereof are provided, which can significantly improve the sensing sensitivity, thereby facilitating the determination of the health status of the battery.

[0007] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a flexible capacitive sensor for lithium battery pressure detection, comprising:

[0008] A plate, comprising a first plate and a second plate stacked together;

[0009] A dielectric layer, which is stacked between the first electrode plate and the second electrode plate, and a protrusion array is arranged on a side of the dielectric layer close to the first electrode plate, the protrusion array is composed of evenly distributed protrusions, a gap is left between the top of the protrusion array and the first electrode plate, the bottom area of ​​the protrusion is larger than the top area of ​​the protrusion, and the dielectric layer is a polymer ion gel layer, which has a porous structure;

[0010] A spacer layer, which is stacked between the first electrode plate and the dielectric layer, and is provided with through holes along the thickness direction. The spacer layer is sleeved on the periphery of the protrusion array through the through holes, and one side of the spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the spacer layer is in contact with the first electrode plate. The spacer layer is a polymer gel layer having a porous structure;

[0011] The composition of the polymer of the Spacer layer corresponds to the composition of the polymer of the dielectric layer, and the porosity and average pore size of the Spacer layer correspond to the porosity and average pore size of the dielectric layer.

[0012] In some preferred embodiments, the porosity of the spacer layer and the dielectric layer are both 18% to 53%.

[0013] Preferably, the polymers of the spacer layer and the dielectric layer include at least one of P (VDF-HFP), PEGDA and PVDF.

[0014] Preferably, when the flexible capacitive sensor is not subjected to pressure, the distance between the side of the Spacer layer in contact with the first electrode plate and the top of the protrusion array is 120 μm to 300 μm.

[0015] In some preferred embodiments, based on the mass of the dielectric layer, the mass of the polymer accounts for 9.1 wt% to 50 wt%.

[0016] In some preferred embodiments, the dielectric layer is a polymer ionic liquid gel layer, the anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation.

[0017] In some preferred embodiments, the protrusion is in the shape of a regular quadrangular pyramid.

[0018] Preferably, the bottom side length of the regular quadrangular pyramid-shaped protrusion is 130 μm to 170 μm, the top side length is 20 μm to 40 μm, and the height is 80 μm to 120 μm;

[0019] And / or, the ratio of the bottom side length, top side length, and height of the regular quadrangular pyramid-shaped protrusion is 1:0.15~0.25:0.55~0.75.

[0020] In a second aspect, the present invention provides a method for preparing the flexible capacitive sensor according to the first aspect, comprising: preparing a polymer solution and a polymer ion mixed solution;

[0021] The polymer ion mixture is spread in a dielectric layer mold with a depression array, and the polymer solution is spread in a spacer layer mold, and after curing, a dielectric layer and a spacer layer are obtained, wherein the depression array is formed by evenly distributed depressions, and the opening area of ​​the depression is larger than the bottom area of ​​the depression, and the dielectric layer has a convex array formed by evenly distributed convexities, and the bottom area of ​​the convexities is larger than the top area of ​​the convexities;

[0022] A first electrode plate and a second electrode plate are prepared, and the first electrode plate, a Spacer layer, a dielectric layer and the second electrode plate are stacked in sequence, and the flexible capacitive sensor is obtained after packaging. The packaging includes: the protrusion array of the dielectric layer faces the first electrode plate, and a gap is left between the top of the protrusion array and the first electrode plate. The Spacer layer is sleeved on the periphery of the protrusion array of the dielectric layer through the through holes thereon, one side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode plate.

[0023] In some preferred embodiments, the polymer solution and the polymer ion mixture both include water, a polymer and a solvent, and the mass ratio of the polymer to the solvent of the polymer solution and the polymer ion mixture is 1:8-12 and the mass ratio of the polymer to water is 1:1-3; the curing conditions include drying at room temperature for 0.25h-0.5h, and then baking in an oven at 60°C-80°C for more than 24h.

[0024] In the flexible capacitive sensor of the present invention, a dielectric layer is stacked between a first electrode plate and a second electrode plate, a protrusion array composed of evenly distributed protrusions is arranged on one side of the dielectric layer close to the first electrode plate, the bottom area of ​​the protrusions is larger than the top area of ​​the protrusions, and the dielectric layer with the protrusion array has a porous structure. When the pressure on the flexible capacitive sensor changes, the contact area between the dielectric layer and the electrode on the first electrode plate is changed, and the capacitance is changed. Since the bottom area of ​​the protrusions is larger than the top area of ​​the protrusions, the dielectric layer with the protrusion array has a porous structure, and the deformation of the protrusion array of the dielectric layer corresponding to a unit pressure change is large, and the dielectric layer The change in the contact area with the electrode on the first electrode plate is large, and the change in capacitance is large. The present invention adjusts the existing pressure changing thickness, thickness changing capacitance, to pressure changing the contact area between the dielectric layer and the electrode, and the contact area changing capacitance. Then, by making the bottom area of ​​the protrusion larger than the top area of ​​the protrusion and the porous structure of the protrusion, the change in the contact area between the dielectric layer and the electrode corresponding to the unit pressure change is amplified, thereby amplifying the capacitance change corresponding to the unit pressure change. The sensing sensitivity of the flexible capacitive sensor can be significantly improved. When it is used for lithium battery pressure detection, pressure detection is helpful to clarify the battery health status.

[0025] If lithium-ion batteries want to become power sources, they need to be structurally packaged and connected in series, and the batteries need to be fixed by pressure during the packaging process. The inventors found that applying appropriate pressure to lithium-ion batteries can reduce the loss of active lithium and slow down the attenuation of battery capacity. Within an appropriate pressure range, as the battery assembly pressure increases, the battery cycle life will increase significantly. A certain pressure is conducive to slowing down battery capacity attenuation, improving battery discharge capacity, and shortening the distance between the positive and negative electrodes. In order to encapsulate and fix the battery and improve the battery performance, a certain pressure will be applied to the battery. The flexible capacitive sensor is attached to the surface of the battery to detect the surface or internal pressure of the battery. When the battery is fixed by pressure encapsulation, the flexible capacitive sensor will also be subjected to a certain pressure. When the battery is fixed and packaged but has not yet started working, the flexible capacitive sensor will be subjected to a certain pressure, for example, it will be subjected to a pressure of 500kpa. During the operation of the battery, due to internal chemical reactions, material expansion and contraction, the flexible capacitive sensor will be subjected to a pressure in the range of, for example, 800kpa. However, the deformation range of the protrusion array of the dielectric layer is limited, and the corresponding pressure sensing range is also limited, for example, it can only sense pressure within the range of 800kpa. At this time, the sum of the pressures brought to the flexible sensor by the encapsulation and fixing of the battery and the working process of the battery exceeds the pressure sensing range of the protrusion array of the dielectric layer, for example, reaching 1300kpa. In the flexible capacitive sensor for lithium battery pressure detection of the present invention, a gap is left between the top of the protrusion array of the dielectric layer and the first electrode plate, a through hole is provided on the Spacer layer along the thickness direction, the Spacer layer is sleeved on the outer periphery of the protrusion array of the dielectric layer through the through hole, one side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode plate. When the sensor is subjected to a small pressure, the first electrode plate is only in contact with the spacer layer, and the protrusion array on the dielectric layer is not deformed. When the sensor is subjected to a large pressure, the spacer layer is compressed so that the first electrode plate is deformed. A plate contacts the protrusion array on the dielectric layer. As the pressure changes, the shape of the protrusion array changes, the contact area between the dielectric layer and the first plate changes, and the capacitance changes. The pressure is sensed by the capacitance change. Compared with the Spacer layer and the dielectric layer that are not provided with a specific structure and positional relationship, when the present invention encapsulates and fixes the battery, the pressure received by the flexible capacitive sensor can not occupy the range of the protrusion array pressure sensing. The range of the protrusion array pressure sensing is only used to sense the pressure change when the lithium-ion battery is working, which can broaden the detection range of the working state of the lithium-ion battery and can better judge the health state of the lithium-ion battery through pressure detection.

[0026] The polymer compositions, porosities and average pore sizes of the dielectric layer and the Spacer layer of the present invention correspond to each other, so that the elastic moduli of the dielectric layer and the Spacer layer can be kept matched. When the pressure is large, when the dielectric layer and the Spacer layer are pressed at the same time, the linearity of the relationship between pressure and capacitance can be improved.

[0027] As the pressure increases, the elastic modulus of the dielectric layer increases. The dielectric layer has a porous structure and is easily compressed. As the pressure increases, the contact area between the dielectric layer and the electrode on the first plate also changes greatly, which compensates for the impact of the change in elastic modulus on the sensor performance and can improve the linearity of the relationship between pressure and capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 This is a stereoscopic diagram of a flexible capacitive sensor for lithium battery pressure detection according to Example 1 of the present invention.

[0030] Figure 2 This is a front view of a flexible capacitive sensor for lithium battery pressure detection according to Example 1 of the present invention.

[0031] Figure 3 This is an exploded stereoscopic diagram of a flexible capacitive sensor for lithium battery pressure detection according to Example 1 of the present invention.

[0032] Figure 4 This is an exploded front view of a flexible capacitive sensor for lithium battery pressure detection according to Example 1 of the present invention.

[0033] Figure 5 This is a scanning electron microscope photograph of the cross section of the dielectric layer of the flexible capacitive sensor according to Example 1 of the present invention.

[0034] Figure 6 This is a pressure-capacitance relationship curve diagram of the flexible capacitive sensor according to Example 1 of the present invention.

[0035] Figure 7 This is a response time diagram of the flexible capacitive sensor according to Example 1 of the present invention.

[0036] Figure 8 This is a pressure-capacitance relationship curve of the flexible capacitive sensor of comparative example 1.

[0037] Description of reference numerals:

[0038] 1. First electrode plate; 2. Spacer layer; 21. Through hole; 3. Dielectric layer; 31. Protrusion array; 4. Second electrode plate. DETAILED DESCRIPTION

[0039] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0040] The inventors of the present invention have found that the existing thin film capacitor sensors have limited pressure sensing sensitivity, which makes it difficult to clearly determine the health status of the battery through pressure sensing.

[0041] In this regard, in a first aspect, the present invention provides a flexible capacitive sensor for lithium battery pressure detection, comprising:

[0042] The electrode plate comprises a first electrode plate 1 and a second electrode plate 4 stacked together;

[0043] The dielectric layer 3 is stacked between the first electrode plate 1 and the second electrode plate 4, and a protrusion array 31 is provided on the side close to the first electrode plate 1. The protrusion array 31 is composed of evenly distributed protrusions. A gap is left between the top of the protrusion array 31 and the first electrode plate 1. The bottom area of ​​the protrusion is larger than the top area of ​​the protrusion. The dielectric layer 3 is a polymer ion gel layer having a porous structure.

[0044] A spacer layer 2, which is stacked between the first electrode plate 1 and the dielectric layer 3, and is provided with a through hole 21 along the thickness direction. The spacer layer 2 is sleeved on the periphery of the protrusion array 31 through the through hole 21, and one side of the spacer layer is in contact with the surface of the edge of the protrusion array 31 of the dielectric layer 3, and the other side of the spacer layer is in contact with the first electrode plate 1. The spacer layer 2 is a polymer gel layer having a porous structure;

[0045] The composition of the polymer of the Spacer layer 2 corresponds to the composition of the polymer of the dielectric layer 3 , and the porosity and average pore size of the Spacer layer 2 correspond to the porosity and average pore size of the dielectric layer 3 .

[0046] The flexible capacitive sensor of the present invention comprises a stacked first electrode plate, a dielectric layer and a second electrode plate, wherein the dielectric layer is a polymer ion gel layer and has a porous structure, a protrusion array is arranged on one side of the dielectric layer close to the first electrode plate, and the bottom area of ​​the protrusion is larger than the top area of ​​the protrusion. When the pressure applied to the flexible sensor changes, the contact area between the dielectric layer and the electrode on the first electrode plate changes greatly relative to the unit pressure change, and the capacitance changes greatly, which can improve the sensing sensitivity of the flexible capacitive sensor. When the flexible capacitive sensor is used for lithium battery pressure detection, pressure detection is helpful to clarify the health status of the battery.

[0047] However, the inventors discovered that in order to encapsulate and fix the battery and improve the battery performance, a certain pressure will be applied to the battery. The flexible capacitive sensor is attached to the surface of the battery to detect the surface or internal pressure of the battery. When the battery is fixed by pressure encapsulation, the flexible capacitive sensor will also be subjected to a certain pressure. When the battery is fixed and packaged but has not yet started working, the flexible capacitive sensor will be subjected to a certain pressure. However, the deformation range of the protrusion array of the dielectric layer is limited, and the corresponding pressure sensing range is also limited. At this time, the sum of the pressures brought to the flexible sensor by the encapsulation and fixing of the battery and the working process of the battery is likely to exceed the pressure sensing range of the protrusion array of the dielectric layer. The flexible capacitive sensor of the present invention, further, has a gap between the top of the protrusion array of the dielectric layer and the first electrode plate, and a through hole is provided on the Spacer layer along the thickness direction. The Spacer layer is sleeved on the periphery of the protrusion array of the dielectric layer through the through hole, and one side of the Spacer layer is connected to the surface of the edge of the protrusion array of the dielectric layer. The other side of the Spacer layer is in contact with the first electrode plate, and the other side of the Spacer layer is in contact with the first electrode plate. When the sensor is subjected to a smaller pressure, the first electrode plate is only in contact with the spacer layer, and the pressure is only transmitted to the spacer layer. The first electrode plate does not contact the protrusion array on the dielectric layer, and the capacitance remains unchanged. When the sensor is subjected to a larger pressure, the spacer layer is compressed so that the first electrode plate contacts the protrusion array on the dielectric layer. As the pressure changes, the shape of the protrusion array changes, the contact area between the dielectric layer and the first electrode plate changes, and the capacitance changes. The pressure is sensed by the capacitance change. Compared with the Spacer layer and the dielectric layer that are not provided with a specific structure and positional relationship, when the present invention encapsulates and fixes the battery, the pressure received by the flexible capacitive sensor can not occupy the range of the protrusion array pressure sensing. The range of the protrusion array pressure sensing is only used to sense the pressure change when the lithium-ion battery is working, which can broaden the detection range of the working state of the lithium-ion battery, and can better judge the health state of the lithium-ion battery through pressure detection.

[0048] The present invention can flexibly adjust the minimum pressure that causes the protrusion array to deform or the capacitance of the flexible capacitive sensor to change by adjusting the spacing between the top of the protrusion array of the dielectric layer and the first electrode plate, the pore structure of the dielectric layer and the Spacer layer, and the polymer composition of the dielectric layer and the Spacer layer.

[0049] The polymer composition, porosity and average pore size of the dielectric layer and the Spacer layer of the present invention correspond to each other, so that the elastic modulus of the dielectric layer and the Spacer layer can be kept matched. When the pressure is large, when the dielectric layer and the Spacer layer are pressed at the same time, the linearity of the relationship between pressure and capacitance can be improved, the pressure and capacitance can be fitted and analyzed, and the pressure can be identified more accurately.

[0050] The preparation method of the flexible capacitive sensor of the present invention is simple, and sensor arrays of different specifications can be prepared according to the shape and size of the battery, which is convenient.

[0051] The composition of the polymer of the Spacer layer of the present invention corresponds to the composition of the polymer of the dielectric layer, which means that the composition of the polymer of the Spacer layer and the polymer of the dielectric layer are close, for example, the polymer of the Spacer layer and the polymer of the dielectric layer are both the first polymer, or one of the polymer of the Spacer layer and the polymer of the dielectric layer includes a very small amount of the second polymer in addition to the first polymer, or the polymer of the Spacer layer and the polymer of the dielectric layer both include the first polymer, the second polymer, etc., and the composition of each polymer is close. The porosity and average pore size of the Spacer layer of the present invention correspond to the porosity and average pore size of the dielectric layer, which means that the porosity of the Spacer layer is close to the porosity of the dielectric layer, and the average pore size of the Spacer layer is close to the average pore size of the dielectric layer, wherein the average pore size is calculated by observing the cross-section direct observation method, and when the pore cross section is irregular, the pore size is represented by an equivalent circle diameter, and the equivalent circle diameter is the diameter of a circle with the same area as the irregular pore cross section.

[0052] It can be understood that the protrusion array of the dielectric layer of the present invention is arranged as a whole, and the electrode on the electrode plate is arranged as a whole, and is arranged correspondingly.

[0053] In some preferred embodiments, the porosity of the spacer layer and the dielectric layer are both 18% to 53%. Under this preferred embodiment, when the pressure on the flexible sensor changes, the contact area between the dielectric layer and the electrode on the first plate changes more with respect to the unit pressure change, and the capacitance changes more, which is more conducive to improving the sensing sensitivity of the flexible capacitive sensor. When it is used for lithium battery pressure detection, it is more conducive to clarifying the battery health status through pressure detection. According to the formula P= Get the porosity, where P represents the porosity, represents the density of the porous material, Indicates the density of a non-porous material. Examples of porosity are 18%, 27%, 35%, 47% and 53%.

[0054] Preferably, the polymers of the Spacer layer 2 and the dielectric layer 3 include at least one of P (VDF-HFP), PEGDA, and PVDF. Under this preferred embodiment, the change in the contact area between the dielectric layer and the electrode on the first plate and the capacitance change corresponding to the unit pressure change can be further increased, which is more conducive to improving the sensing sensitivity of the flexible capacitive sensor, and can further increase the resilience of the dielectric layer and the Spacer layer, which is more conducive to shortening the response time of the flexible capacitive sensor, and can further increase the ability of the dielectric layer and the Spacer layer to recover to their original state after being compressed and deformed, which is more conducive to accurate sensing force. When it is used for lithium battery pressure detection, it is more conducive to accurately judging the health of the battery through pressure detection.

[0055] Further preferably, when the flexible capacitive sensor is not subjected to pressure, a distance between a side of the Spacer layer in contact with the first electrode plate and a top of the protrusion array is 120 μm to 300 μm. Under this preferred embodiment, the porosity of the Spacer layer and the dielectric layer is 18%~53%, and the polymer includes at least one of P (VDF-HFP), PEGDA, and PVDF. When the flexible capacitive sensor is not subjected to pressure, the distance between the side of the Spacer layer in contact with the first electrode plate and the top of the protrusion array is 120μm~300μm, that is, the interval between the top of the protrusion array and the first electrode plate is 120μm~300μm, which is more conducive to making the protrusion array of the dielectric layer begin to deform when the pressure on the flexible capacitive sensor reaches 250kPa~700kpa, so that the flexible capacitive sensor initially has a preload of 250kPa~700kpa. When the battery is encapsulated and fixed, the pressure on the flexible capacitive sensor does not occupy the range of the pressure sensing of the protrusion array, thereby widening the detection range of the working state of the lithium-ion battery, and avoiding the situation that when the pressure on the surface or inside of the battery changes during the working process of the lithium-ion battery, the pressure change during the working process of the lithium-ion battery cannot be sensed by the capacitance change because the protrusion array has not yet deformed. When the flexible capacitive sensor is not subjected to pressure, the distance between the side of the Spacer layer in contact with the first electrode plate and the top of the protrusion array is, for example, 120 μm, 150 μm, 200 μm, 250 μm and 300 μm.

[0056] In some preferred embodiments, based on the mass of the dielectric layer 3, the mass proportion of the polymer is 9.1wt%~50wt%. Under this preferred scheme, it is more conducive to improving the sensing sensitivity of the flexible capacitive sensor, further increasing the resilience of the dielectric layer, shortening the response time of the flexible capacitive sensor, and further increasing the ability of the dielectric layer to recover to its original state after being compressed and deformed, which is more conducive to accurate sensing force. Based on the mass of the dielectric layer, the mass proportion of the polymer is, for example, 9.1wt%, 10wt%, 20wt%, 30wt%, 40wt% and 50wt%. Preferably, based on the mass of the dielectric layer 3, the mass proportion of the polymer is 9.1wt%~30wt%.

[0057] The present invention does not limit the type of polymer ion gel layer. For example, the ions can be ions formed by ionic liquids and ions formed by electrolyte salts. For example, the polymer ion gel layer is a NaCl-PAM layer. In some preferred embodiments, the dielectric layer 3 is a polymer ion liquid gel layer, and the anions of the ionic liquid include at least one of hexafluorophosphate anions, tetrafluoroborate anions, bistrifluoromethanesulfonyl imide anions, trifluoromethanesulfonate anions, acetate anions, dicyanamide anions, bromide anions, ethyl sulfate anions, and hydrogen sulfide anions, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cations, 1-butyl-3-methylimidazolium cations, 1-hexyl-3-methylimidazolium cations, and 1-octyl-3-methylimidazolium cations. Under this preferred embodiment, it is more conducive to improving the sensitivity of the capacitive sensor.

[0058] The present invention does not limit the shape of the protrusion, for example, it can be a truncated cone, an arc, a regular quadrangular cone, etc. In some preferred embodiments, the protrusion is a regular quadrangular cone. Under this preferred scheme, it is more conducive to increasing the resilience of the protrusion array, shortening the response time of the flexible capacitive sensor, increasing the ability of the protrusion array to recover to its original state after being compressed and deformed, accurately sensing force, increasing the change in the contact area of ​​the dielectric layer and the electrode on the first electrode plate corresponding to a unit pressure change and the capacitance change, and improving the sensing sensitivity of the flexible capacitive sensor.

[0059] Preferably, the bottom side length of the regular quadrangular pyramid-shaped protrusion is 130 μm to 170 μm, the top side length is 20 μm to 40 μm, and the height is 80 to 120 μm;

[0060] And / or, the ratio of the bottom side length, top side length, and height of the regular quadrangular pyramid-shaped protrusion is 1:0.15~0.25: 0.55~0.75.

[0061] Under this preferred scheme, it is more conducive to increasing the resilience of the protrusion array, shortening the sensor response time, increasing the ability of the protrusion array to recover to its original state after deformation, accurately sensing force, and improving the sensing sensitivity of the flexible capacitive sensor; increasing the pressure sensing range of the protrusion array deformation, and widening the detection range of the working status of the lithium-ion battery.

[0062] In some preferred embodiments, the linearity of the flexible capacitive sensor of the present invention is above 0.99 and the sensitivity is 0.73 kPa. -1 ~5.43kPa -1 , the initial preload force is 250kPa~700kpa.

[0063] In a second aspect, the present invention provides a method for preparing the flexible capacitive sensor according to the first aspect, comprising: preparing a polymer solution and a polymer ion mixed solution;

[0064] The polymer ion mixture is spread in a dielectric layer mold with a depression array, and the polymer solution is spread in a spacer layer mold, and after curing, a dielectric layer and a spacer layer are obtained, wherein the depression array is formed by evenly distributed depressions, and the opening area of ​​the depression is larger than the bottom area of ​​the depression, and the dielectric layer has a convex array formed by evenly distributed convexities, and the bottom area of ​​the convexities is larger than the top area of ​​the convexities;

[0065] A first electrode plate and a second electrode plate are prepared, and the first electrode plate, a Spacer layer, a dielectric layer and the second electrode plate are stacked in sequence, and the flexible capacitive sensor is obtained after packaging. The packaging includes: the protrusion array of the dielectric layer faces the first electrode plate, and a gap is left between the top of the protrusion array and the first electrode plate. The Spacer layer is sleeved on the periphery of the protrusion array of the dielectric layer through the through holes thereon, one side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode plate.

[0066] The preparation method of the flexible capacitive sensor of the present invention is to spread a polymer solution and a polymer ion mixture with similar composition in a spacer layer mold and a dielectric layer mold respectively, and obtain a dielectric layer and a spacer layer with similar polymer composition, porosity and average pore size after curing under similar or identical conditions, wherein the composition of the polymer solution and the polymer ion mixture is close to that of the polymer, solvent, pore structure regulator, etc. in the polymer solution and the polymer ion mixture, and the composition of the solvent and the composition of the pore structure regulator, etc. are similar. The dielectric layer and the spacer layer of the present invention have a porous structure, and the spacer layer is sticky. When encapsulated, the spacer layer can connect the first plate, the dielectric layer and the second plate together.

[0067] In some preferred embodiments, the polymer solution and the polymer ion mixture both include water, polymer and solvent, the mass ratio of polymer to solvent in the polymer solution and the polymer ion mixture is 1:8-12 and the mass ratio of polymer to water is 1:1-3; the curing conditions include drying at room temperature for 0.25h-0.5h and then baking in an oven at 60°C-80°C for more than 24h. Under this preferred embodiment, it is more conducive to making the porosity of the spacer layer and the dielectric layer 18%-53%.

[0068] Preferably, the polymer includes at least one of P (VDF-HFP), PEGDA, and PVDF, and in the polymer ion mixture, based on the mass of dry matter, the mass of the polymer accounts for 9.1wt% to 50wt%.

[0069] Preferably, the packaging includes making the distance between the top of the protrusion array and the first electrode plate be 120 μm to 300 μm.

[0070] In some preferred embodiments, the polymer ion mixture is a polymer ion liquid mixture, the anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation.

[0071] In some preferred embodiments, the depression is in the shape of a regular quadrangular pyramid, the bottom side length of the depression is 20 μm to 40 μm, the opening side length of the depression is 130 μm to 170 μm, and the depth of the depression is 80 μm to 120 μm; and / or, the ratio of the opening side length, bottom side length, and depth of the regular quadrangular pyramid depression is 1:0.15~0.25:0.55~0.75.

[0072] The present invention is further described in detail below with reference to specific embodiments.

[0073] Example 1

[0074] A method for preparing a flexible capacitive sensor, the steps are as follows:

[0075] Step 1: Prepare a mixed solution of polymer ionic liquid, the mixed solution includes P(VDF-HFP) polymer, [EMIM][TFSI] ionic liquid, deionized water and chloroform. Based on the mass of the mixed solution, the content of P(VDF-HFP) polymer is 6.25wt%, the content of [EMIM][TFSI] ionic liquid is 18.75wt%, the content of chloroform is 62.5%, the content of deionized water is 12.5%, the mass ratio of polymer to solvent (chloroform) in the mixed solution is 1:10, the mass ratio of polymer to water is 1:2, and the content of polymer and ion in the mixed solution is 1:10. The sum of the contents of the sub-liquids is 25wt%, and the mass proportion of the polymer in the mixed solution is 25wt% based on the sum of the content of the polymer and the content of the ionic liquid (dry matter); preparing a polymer solution, the polymer solution includes P(VDF-HFP) polymer, deionized water and chloroform, based on the mass of the polymer solution, the content of P(VDF-HFP) polymer is 7.7wt%, the content of chloroform is 76.9wt%, the content of deionized water is 15.4wt%, the mass ratio of the polymer to the solvent (chloroform) in the polymer solution is 1:10, and the mass ratio of the polymer to water is 1:2;

[0076] Step 2: Use ultra-high precision micro-scale CNC to process a dielectric layer mold with a recess array, the evenly distributed recesses constitute the recess array, the recess is a regular quadrangular pyramid recess, the bottom side length of the recess is 30 μm, the opening side length is 150 μm, the depth is 100 μm, and the ratio of the opening side length, bottom side length, and depth of the regular quadrangular pyramid recess is 1:0.2:0.67. Spread the mixed solution of the polymer ionic liquid obtained in step 1 on the dielectric layer mold, and spread the polymer solution obtained in step 1 on the S in a pacer layer mold, and after curing, a dielectric layer and a spacer layer are obtained, wherein the curing sequentially includes drying at room temperature for 0.5 hours and then baking in an oven at 70° C. for more than 24 hours, wherein one side of the dielectric layer has a protrusion array, and the protrusions evenly distributed constitute the protrusion array, and the protrusions are regular quadrangular pyramid-shaped protrusions, and the top side length of the protrusions is 30 μm, the bottom side length is 150 μm, and the height is 100 μm, and the ratio of the bottom side length, the top side length, and the height of the regular quadrangular pyramid-shaped protrusions is 1:0.2:0.67;

[0077] Step three: Screen-print electrodes on the PI film to obtain the first electrode plate and the second electrode plate, the electrode material is Au, and the first electrode plate, the Spacer layer, the dielectric layer and the second electrode plate are stacked in sequence, and a flexible capacitive sensor is obtained after packaging. The packaging includes: the protrusion array of the dielectric layer faces the first electrode plate, and a gap is left between the top of the protrusion array and the first electrode plate, so that the distance between the top of the protrusion array and the first electrode plate is 200μm, and the Spacer layer is arranged on the periphery of the protrusion array of the dielectric layer through the through holes thereon, and one side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode plate.

[0078] A flexible capacitive sensor comprises a plate, a dielectric layer and a spacer layer; the plate comprises a first plate and a second plate stacked together; the dielectric layer is stacked between the first plate and the second plate, a protrusion array is arranged on one side of the dielectric layer close to the first plate, the protrusions evenly distributed constitute the protrusion array, a gap is left between the top of the protrusion array and the first plate, the protrusion is a regular quadrangular pyramid protrusion, the top side length of the protrusion is 30 μm, the bottom side length is 150 μm, the height is 100 μm, the ratio of the bottom side length, the top side length and the height of the regular quadrangular pyramid protrusion is 1:0.2:0.67, and the dielectric layer is a polymer ion liquid gel layer with a porous structure; the spacer layer is stacked between the first plate and the dielectric layer, the spacer layer is provided with through holes along the thickness direction, and the spacer layer passes through the through holes on the spacer layer. The holes are set on the periphery of the protrusion array of the dielectric layer. One side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode. The Spacer layer is a polymer gel layer with a porous structure. The composition, porosity and pore size distribution of the polymer of the Spacer layer correspond to the composition, porosity and pore size distribution of the polymer of the dielectric layer. The porosity of the Spacer layer and the dielectric layer is about 27%. The dielectric layer includes P (VDF-HFP) polymer and [EMIM] [TFSI] ionic liquid. Based on the mass of the dielectric layer, the mass of the polymer accounts for 25wt%. When the flexible capacitive sensor is not under pressure, the distance between the side of the Spacer layer in contact with the first electrode and the top of the protrusion array is 200μm. The structure of the flexible capacitive sensor can be found in Figure 1~Figure 4 , the morphology of the dielectric layer can be found in Figure 5 .

[0079] Example 2

[0080] Referring to the preparation method of the flexible capacitive sensor of Example 1, the difference is that in step three, the distance between the top of the protrusion array and the first electrode is 100 μm. Referring to a flexible capacitive sensor of Example 1, the difference is that when the flexible capacitive sensor is not subjected to pressure, the distance between the side of the Spacer layer in contact with the first electrode and the top of the protrusion array is 100 μm.

[0081] Example 3

[0082] Referring to the method for preparing the flexible capacitive sensor of Example 1, the difference is that the polymer is PEGDA. Referring to a flexible capacitive sensor of Example 1, the difference is that the polymer is PEGDA.

[0083] Example 4

[0084] Referring to the preparation method of the flexible capacitive sensor and the flexible capacitive sensor of Example 1, the difference is that the bottom side length of the depression is 15 μm, the opening side length is 75 μm, the depth is 80 μm, the top side length of the protrusion is 15 μm, the bottom side length is 75 μm, and the height is 80 μm.

[0085] Example 5

[0086] Referring to the preparation method of the flexible capacitive sensor and the flexible capacitive sensor of Example 1, the difference is that the bottom side length of the depression is 40 μm, the opening side length is 130 μm, the depth is 120 μm, the top side length of the protrusion is 40 μm, the bottom side length is 130 μm, and the height is 120 μm.

[0087] Comparative Example 1

[0088] Referring to the method for preparing the flexible capacitive sensor and the flexible capacitive sensor of Example 1, the difference is that no spacer layer is stacked between the first electrode plate and the dielectric layer, and the protrusion array on the dielectric layer is in contact with the first electrode plate.

[0089] Comparative Example 2

[0090] Referring to the preparation method of the flexible capacitive sensor and the flexible capacitive sensor of Example 1, the difference is that the shape of the depression is a cylinder with a bottom radius of 15 μm and a depth of 100 μm, and the shape of the protrusion is a cylinder with a bottom radius of 15 μm and a height of 100 μm.

[0091] The sensitivity, linearity, initial preload and response time data of the capacitive sensors obtained in the above embodiments and comparative examples were measured using a MARK-10 brand Model F105 advanced tension / compression testing machine with reference to the measurement method in the "Technical Specifications for Distributed Thin Film Pressure Sensors". The results are shown in Table 1. Sensitivity indicates the relative growth rate of capacitance as pressure increases, linearity indicates the degree of linearity of the relationship between capacitance and pressure, and initial preload indicates the minimum pressure applied to the sensor in order to change capacitance. Response time indicates the time interval from when the sensor receives an input signal to when the output is stable. For the pressure-capacitance relationship curve of Example 1, see Figure 6 The response time of the capacitive sensor of Example 1 is shown in Figure 7 The pressure-capacitance relationship curve of comparative example 1 is shown in Figure 8 .

[0092] Table 1

[0093]

[0094] In the comparative example and comparative example 1, the Spacer layer is stacked between the first electrode plate and the dielectric layer, a through hole is provided on the Spacer layer along the thickness direction, the Spacer layer is sleeved on the periphery of the protrusion array of the dielectric layer through the through hole, one side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode plate, and a gap is left between the top of the protrusion array of the dielectric layer and the first electrode plate, so that the sensor has an initial preload force and can expand the detection range of the working state of the lithium-ion battery; in the comparative example and comparative example 2, the bottom area of ​​the protrusion is larger than the top area of ​​the protrusion, which can improve the sensing sensitivity and linearity and shorten the response time.

[0095] Comparing Example 1 and Example 2, when the flexible capacitive sensor is not subjected to pressure, the distance between the side of the Spacer layer in contact with the first electrode plate and the top of the protrusion array is 120μm~300μm, which is more conducive to making the flexible capacitive sensor initially have a preload of 250kPa~700kpa. When the battery is encapsulated and fixed, the pressure exerted on the flexible capacitive sensor does not occupy the range of pressure sensing of the protrusion array, thereby widening the detection range of the working state of the lithium-ion battery; Comparing Example 1 and Example 3, the polymer P (VDF-HFP) is more conducive to improving the detection sensitivity; Comparing Examples 1, 4 and 5, the bottom side length of the regular quadrangular pyramid protrusion is 130μm~170μm, the top side length is 20μm~40μm, and the height is 80~120μm. The ratio of the bottom side length, top side length and height of the regular quadrangular pyramid protrusion is 1:0.15~0.25:0.55~0.75, which is more conducive to improving the detection sensitivity.

[0096] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A flexible capacitive sensor for lithium battery pressure detection, characterized in that: It includes: A polar plate comprising a first polar plate (1) and a second polar plate (4) stacked together; A dielectric layer (3) is stacked between the first electrode plate (1) and the second electrode plate (4), a protrusion array (31) is provided on a side of the dielectric layer close to the first electrode plate (1), the protrusion array (31) is composed of evenly distributed protrusions, a gap is left between the top of the protrusion array (31) and the first electrode plate (1), the bottom area of ​​the protrusion is larger than the top area of ​​the protrusion, and the dielectric layer is a polymer ion gel layer having a porous structure; A spacer layer (2), which is stacked between the first electrode plate (1) and the dielectric layer (3), and is provided with a through hole (21) along the thickness direction. The spacer layer (2) is sleeved on the periphery of the protrusion array (31) through the through hole (21), and one side of the spacer layer is in contact with the surface of the edge of the protrusion array (31) of the dielectric layer (3), and the other side of the spacer layer is in contact with the first electrode plate (1). The spacer layer is a polymer gel layer having a porous structure; The composition of the polymer of the Spacer layer (2) corresponds to the composition of the polymer of the dielectric layer (3), and the porosity and average pore size of the Spacer layer (2) correspond to the porosity and average pore size of the dielectric layer (3); The porosity of the Spacer (2) layer and the dielectric layer (3) are both 18% to 53%; The polymers of the spacer layer (2) and the dielectric layer (3) both include at least one of P (VDF-HFP), PEGDA, and PVDF; When the flexible capacitive sensor is not subjected to pressure, the distance between the side of the Spacer layer (2) in contact with the first electrode plate (1) and the top of the protrusion array (31) is 120 μm to 300 μm.

2. The flexible capacitive sensor according to claim 1, characterized in that: Based on the mass of the dielectric layer (3), the mass proportion of the polymer is 9.1 wt% to 50 wt%.

3. The flexible capacitive sensor according to claim 1, characterized in that: The dielectric layer (3) is a polymer ionic liquid gel layer, wherein the anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation.

4. The flexible capacitive sensor according to claim 1, characterized in that: The protrusion is in the shape of a regular quadrangular pyramid.

5. The flexible capacitive sensor according to claim 4, characterized in that: The bottom side length of the regular quadrangular pyramid-shaped protrusion is 130μm~170μm, the top side length is 20μm~40μm, and the height is 80μm~120μm; And / or, the ratio of the bottom side length, top side length, and height of the regular quadrangular pyramid-shaped protrusion is 1:0.15~0.25:0.55~0.

75.

6. A method for preparing a flexible capacitive sensor according to any one of claims 1 to 5, characterized in that: include: preparing a polymer solution and a polymer ion mixed solution; The polymer ion mixture is spread in a dielectric layer mold with a depression array, and the polymer solution is spread in a spacer layer mold, and after curing, a dielectric layer and a spacer layer are obtained, wherein the depression array is formed by evenly distributed depressions, and the opening area of ​​the depression is larger than the bottom area of ​​the depression, and the dielectric layer has a convex array formed by evenly distributed convexities, and the bottom area of ​​the convexities is larger than the top area of ​​the convexities; A first electrode plate and a second electrode plate are prepared, and the first electrode plate, a Spacer layer, a dielectric layer and the second electrode plate are stacked in sequence, and the flexible capacitive sensor is obtained after packaging. The packaging includes: the protrusion array of the dielectric layer faces the first electrode plate, and a gap is left between the top of the protrusion array and the first electrode plate. The Spacer layer is sleeved on the periphery of the protrusion array of the dielectric layer through the through holes thereon, one side of the Spacer layer is in contact with the surface of the edge of the protrusion array of the dielectric layer, and the other side of the Spacer layer is in contact with the first electrode plate.

7. The preparation method according to claim 6, characterized in that: The polymer solution and the polymer ion mixture both include water, polymer and solvent, the mass ratio of polymer to solvent in the polymer solution and the polymer ion mixture is 1:8-12, and the mass ratio of polymer to water is 1:1-3; the curing conditions include drying at room temperature for 0.25h-0.5h, and then baking in an oven at 60°C-80°C for more than 24h.

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