Method for improving discharge energy density of ferroelectric material and application

Abstract

The invention discloses a method for improving the discharge energy density of a ferroelectric material and application, and belongs to the technical field of functional materials. The method specifically comprises the following steps: heating the ferroelectric material under the condition that an electric field is applied until the temperature reaches a preset temperature T (prognosis), and discharging the ferroelectric material after the electric field is removed. According to the method, the ferroelectric material is heated under the condition that the electric field is applied, and then the ferroelectric material is completely discharged under the condition that the electric field is removed, so that the discharge energy density is greatly improved, and the energy storage performance is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of functional materials, and in particular to a method for improving the discharge energy density of ferroelectric materials and its application. Background Art

[0002] Dielectric capacitors are indispensable energy storage and power regulation components in many important applications such as smart grids and new energy vehicles. Due to their unique polarization properties, ferroelectric materials can produce stronger polarization responses than conventional dielectric materials under the action of electric fields, which provides conditions for high energy density dielectric energy storage. However, due to the large remnant polarization of ferroelectric materials, when the external electric field is removed, only a small amount of stored energy can be released, and most of the energy is still bound inside the material, which leads to the low energy density that ferroelectric materials can produce.

[0003] Therefore, it is necessary to provide a method for improving the discharge energy density of ferroelectric materials. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for improving the discharge energy density of ferroelectric materials. The method can achieve a significant improvement in the discharge energy density of ferroelectric polymers.

[0005] The present invention also provides application of the above method in a dielectric capacitor.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for improving the discharge energy density of a ferroelectric material, the method specifically comprising: heating the ferroelectric material under the condition of applying an electric field until the temperature reaches a predetermined temperature T 预 Then, the ferroelectric material is discharged after the electric field is removed.

[0008] The heating rate is no less than 10°C / s.

[0009] The discharge time is no more than 5RC, where R is the discharge resistance and C is the capacitance of the ferroelectric material.

[0010] Wherein, heating is stopped immediately when the temperature of the ferroelectric material reaches a predetermined temperature.

[0011] Wherein, when the ferroelectric material is applied to a high electric field, T 预 >T C , when the ferroelectric material is applied to a low electric field T 预 <T C , where T C is the Curie temperature of the ferroelectric material;

[0012] The high electric field is higher than the coercive field of the ferroelectric material (or the electric field at which the dipoles in the ferroelectric material are almost completely turned); the low electric field is equal to or lower than the coercive field of the ferroelectric material (or the electric field at which the dipoles in the ferroelectric material are almost not turned).

[0013] The ferroelectric material is heated by various heat sources, electric heating or optical heating.

[0014] Wherein, the ferroelectric material package is a ferroelectric polymer.

[0015] Among them, the ferroelectric material is a composite material, which includes a ferroelectric polymer and a material with thermal effect, and the material with thermal effect is in close contact with the ferroelectric polymer; the material with thermal effect is a metal electrode with photothermal effect, a photothermal inorganic filler, or a photothermal organic filler.

[0016] Wherein, the ferroelectric material is a composite material of P (VDF-TrFE) and nano-gold electrodes; the electric field strength of the high electric field is greater than 70 MV / m; the ferroelectric material is a composite material of P (VDF-TrFE) and nano-gold electrodes, and the electric field strength of the low electric field is not greater than 70 MV / m.

[0017] The above method for improving the discharge energy density of ferroelectric materials is applied in dielectric capacitors.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The present invention first heats the ferroelectric material under the condition of applying an electric field, and then discharges the ferroelectric material under the condition of removing the electric field, thereby greatly increasing the discharge energy density and achieving a significant improvement in energy storage performance.

[0020] (2) The method of increasing the discharge energy density of ferroelectric materials of the present invention is applicable to electric fields of any magnitude, especially to high electric fields (close to the breakdown electric field of the material), and has a wide range of applications.

[0021] (3) The method of increasing the discharge energy density of ferroelectric materials of the present invention can completely release the stored energy within a few milliseconds, thereby ensuring a high discharge power density of the capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the dielectric temperature spectrum of the ferroelectric material of Example 1.

[0023] Figure 2 The ferroelectric material of Example 1 is detected by an infrared thermal imager with a light intensity of 400 mW / cm 2 Schematic diagram of the sample temperature before and after 450nm blue light irradiation.

[0024] Figure 3 The discharge voltage curves and corresponding discharge energy density under different electric fields at room temperature without light.

[0025] Figure 4 1 is the discharge voltage curve and the corresponding discharge energy density of the ferroelectric material of Example 1 under a low electric field.

[0026] Figure 5 1 is the discharge voltage curve and the corresponding discharge energy density of the ferroelectric material of Example 2 under a low electric field.

[0027] Figure 6 1 is the discharge voltage curve and the corresponding discharge energy density of the ferroelectric material of Example 3 under a high electric field.

[0028] Figure 7 1 is the discharge voltage curve and the corresponding discharge energy density of the ferroelectric material of Example 4 under a high electric field.

[0029] Figure 8 1 is the discharge voltage curve and the corresponding discharge energy density of the ferroelectric material of Example 5 under a high electric field.

[0030] Fig. 9 1 is the discharge voltage curve and the corresponding discharge energy density of the ferroelectric material of Example 6 under a high electric field. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] A method for increasing the discharge energy density of a ferroelectric material, comprising: heating the ferroelectric material under an applied electric field until the temperature reaches a predetermined temperature T 预 Then, the ferroelectric material is discharged under the condition of no electric field. Discharging the ferroelectric material under the condition of no electric field can greatly shorten the discharge time and improve the discharge energy density of the ferroelectric material.

[0033] Preferably, the heating rate is not less than 10°C / s. The present invention suggests that the higher the heating rate, the better. The faster the heating rate, the more it can avoid the influence of thermal effects on the dielectric capacitor during the heating process, thereby avoiding affecting the energy storage performance of the capacitor.

[0034] Preferably, the discharge time is not greater than 5RC, where R is the discharge resistance and C is the capacitance of the ferroelectric material. In other words, the discharge time is not greater than the 5RC constant, where C is the capacitance of the ferroelectric material to be treated. This embodiment adopts centralized discharge, which will not damage the discharge speed of the capacitor itself and ensure high power density.

[0035] At the same time, it is preferred to discharge immediately after reaching the predetermined temperature, so as to avoid adverse effects of the thermal effect generated during the heating process on the dielectric capacitor as much as possible.

[0036] Preferably, the heating is stopped immediately when the temperature of the ferroelectric material reaches a predetermined temperature. That is, the method of the present invention is to release the stored energy of the ferroelectric material as much as possible through the heating step, but it does not need to maintain a high temperature for a long time to avoid adverse effects.

[0037] Preferably, when the ferroelectric material is applied to a high electric field, T 预 >T C , when the ferroelectric material is applied to a low electric field T 预 <T C , where T C is the Curie temperature of the ferroelectric material; wherein the high electric field is higher than the coercive field of the ferroelectric material (or the electric field that can make most dipoles in the ferroelectric material turn); the low electric field is the electric field at which the dipoles in the ferroelectric material hardly turn. More preferably, when used in a high electric field, T C <T 预 <T 熔 (T 熔 is the melting temperature of the ferroelectric material); when used in low electric fields, T 当 <T 预 <T C , where T 当 is the current temperature of the ferroelectric material. When controlling the T of the ferroelectric polymer 预 Lower than the material's T C When the material capacitance changes through heat, the discharge energy density is increased; when the T 预 Higher than the material's T C When the ferroelectric polymer is used, the pyroelectric effect is used to further release the energy stored in the material, thereby increasing the discharge energy density.

[0038] Preferably, the ferroelectric material is heated by various heat sources, electric heating or optical heating, wherein the wavelength range of the light source during optical heating can cover the ultraviolet, visible and infrared regions.

[0039] Wherein, the ferroelectric material includes a ferroelectric polymer. The ferroelectric polymer is a polyvinylidene fluoride (PVDF)-based ferroelectric copolymer, such as P(VDF-TrFE) (55 / 45) (molar ratio of vinylidene fluoride to trifluoroethylene monomer is 55:45, the same below), P(VDF-TrFE) (65 / 35) and P(VDF-TrFE) (70 / 30).

[0040] The ferroelectric material may be a composite material formed by a ferroelectric polymer and a material having a thermal effect, and the material having a thermal effect is in close contact with the ferroelectric polymer; the material having a thermal effect is a metal electrode having a photothermal effect, such as gold, a photothermal inorganic filler, or a photothermal organic filler. When performing photothermal heating, the photothermal material may be a gold electrode or a filler having a photothermal effect, such as a Schiff base photothermal agent, polypyrrole, polydopamine, and polyaniline.

[0041] Wherein, the ferroelectric material is a composite material of P (VDF-TrFE) and nano-gold electrodes; the electric field strength of the high electric field is greater than 70 MV / m; the ferroelectric material is a composite material of P (VDF-TrFE) and nano-gold electrodes, and the electric field strength of the low electric field is less than or equal to 70 MV / m.

[0042] Among them, the T C Obtained by testing the dielectric temperature spectrum of the material.

[0043] The invention is further described below through specific examples.

[0044] Example 1

[0045] The ferroelectric material in this embodiment is a composite material of a ferroelectric polymer and a photothermal agent nano-gold electrode.

[0046] 1.1 Preparation of ferroelectric materials: The preparation process of the composite material is as follows: P(VDF-TrFE) (55 / 45) thin film samples were prepared by solution casting: First, a certain amount of P(VDF-TrFE) (55 / 45) powder was weighed and placed in a glass bottle, and an appropriate amount of DMF (dimethylformamide) solution was added and stirred continuously at room temperature overnight to ensure full dissolution. Subsequently, the uniform solution was cast on a pre-cleaned glass plate and heated in an oven at 90 °C for 2 h to completely evaporate the solvent. Subsequently, it was peeled off the glass plate and placed in a vacuum oven for heat treatment at 135 °C for 5 h to optimize the crystallinity of the film. Then, gold electrode layers were prepared on the upper and lower surfaces of the film by magnetron sputtering technology for electrical connection and subsequent performance testing.

[0047] In this embodiment, a light heating method is used to control the temperature of the ferroelectric material, a nano-gold electrode is used as a photothermal agent, and a 450 nm blue light is used as a light source.

[0048] 1.2 Determine T C value: Figure 1 is the dielectric temperature spectrum of the ferroelectric material of Example 1, and it can be obtained that T C is 73 ℃.

[0049] 1.3 The operation steps are as follows: First, at the current temperature (T 当 ) is connected to a high voltage source, a DC voltage of a specific value is applied to the sample by the high voltage source (to put the sample in an electric field), and then the sample is heated to a predetermined temperature T while maintaining this voltage. 预 . Reach T 预 Immediately stop heating and disconnect the high voltage source to start discharging the sample; that is, connect the sample to the discharge resistor (R) to discharge the sample through the resistor, and use an oscilloscope to record the curve of the discharge voltage (U) at both ends of the resistor versus the discharge time (t). Using the formula: The discharge energy density (N) can be calculated by integrating the discharge voltage-discharge time curve, where V refers to the volume of the sample, thereby achieving accurate measurement and performance evaluation of the discharge energy density of ferroelectric polymer films.

[0050] In this embodiment, T 预 The light intensity in this embodiment is 200 mW / cm 2 The average heating rate of the sample is about 35 ℃ / s.

[0051] 1.4 Under different electric field strengths, the sample (ferroelectric material) was directly heated by light, and the discharge energy density under electric fields of 60 MV / m and 70 MV / m was tested. The test results are shown in Figure 4 shown.

[0052] Test comparison

[0053] This test comparative example uses the ferroelectric material prepared in 1.1.

[0054] 1.5 Measure the discharge voltage curve and corresponding discharge energy density under different electric fields at room temperature (26±1℃) without light (no heating). The measurement results are as follows Figure 3 As shown. Figure 3 As shown in Figure 2, at room temperature, the discharge energy density of the sample increases with the increase of the electric field. When the electric field is 60 and 70 MV / m, the discharge energy density is 0.34 and 0.5 J / cm, respectively. 3 When the electric field increases from 100 to 175 MV / m, the discharge energy density increases from 0.82 to 1.88 J / cm 3 .

[0055] contrast Figure 3 and Figure 4 , it can be seen that when the temperature of the sample is controlled to be lower than T C When the discharge energy density of the sample is 0.88 J / cm under an electric field of 60 MV / m, 3 ; The discharge energy density of the sample under an electric field of 70 MV / m is 1.14 J / cm 3 Compared with 0.34 and 0.5 J / cm at room temperature 3 The energy density of the capacitor has been improved by more than 250%. At the same time, it can be seen that the discharge speed of the capacitor is very fast, only a few milliseconds, thus ensuring the high power density of the capacitor.

[0056] Example 2

[0057] The other conditions of this embodiment are the same as those of embodiment 1, except for the applied light intensity (that is, the heating rate is different). The light intensity of this embodiment is 400 mW / cm 2 In this embodiment, T 预 is about 73°C.

[0058] Figure 2 The ferroelectric material of Example 1 was tested by an infrared thermal imager at 400 mW / cm 2 The temperature of the sample before and after illumination is shown in Figure 1. The temperature of the sample is detected by an infrared thermal imager. It can be observed that the temperature of the sample rises significantly during illumination. The temperature change is related to the light intensity. At 400 mW / cm 2 Under 450 nm blue light, its temperature can be raised from room temperature to over 100 °C in a few seconds.

[0059] In this embodiment, light is used to heat the sample under an electric field of 60 and 70 MV / m. The discharge energy density test results are shown in FIG. Figure 5 As shown. Figure 5 It can be seen that the discharge energy density of the sample under the electric field of 60 and 70 MV / m is 1.08 and 1.49 J / cm respectively. 3 Compared with 0.34 and 0.5 J / cm at room temperature 3 The energy density of the capacitor has been increased by 318% to 298%. At the same time, the energy release of the capacitor is still very fast.

[0060] Example 3

[0061] The other conditions of this embodiment are the same as those of embodiment 2, except for the applied electric field strength. 预 About 73-97 ℃ (100-175 MV / m)

[0062] In this embodiment, light is used to heat the device under a high electric field of 100-175 MV / m. The discharge energy density test results are shown in FIG. Figure 6 As shown. Figure 6 It can be seen that the discharge energy density of the sample under the electric field of 100-175 MV / m increases from 2.62 to 4.75 J / cm 3 Compared with 0.83 J / cm 3 to 1.88 J / cm 3 The energy density of the capacitor has been improved by 253% to 315%. At the same time, the energy release of the capacitor is still very fast.

[0063] Example 4

[0064] The other conditions of this embodiment are the same as those of embodiment 1, except that the heating method is hot silicone oil heating and the applied electric field is 100 MV / m. 预 is 80 ℃.

[0065] In this embodiment, the sample is heated by hot silicone oil under an electric field of 100 MV / m, and its discharge energy density is tested and compared with the energy density measured under the same electric field at room temperature. The test results are as follows: Figure 7 As shown. Figure 7 It can be seen that the discharge energy density of the sample under an electric field of 100 MV / m is 2.49 J / cm 3 Compared with 0.83 J / cm at room temperature 3 The energy density of the capacitor has been increased by 300%. At the same time, the energy release of the capacitor is still very fast.

[0066] Example 5

[0067] The other conditions of this embodiment are the same as those of Embodiment 1, except that the material used is P(VDF-TrFE) (65 / 35) and the applied electric field is 100 MV / m.

[0068] The T of the ferroelectric material of this embodiment C is 97°C. In this embodiment, T 预 is 80 ℃.

[0069] In this embodiment, the sample is heated by light under an electric field of 100 MV / m, and its discharge energy density is tested and compared with the energy density measured at room temperature under the same electric field without light. The test results are as follows: Figure 8 As shown. Figure 8 It can be seen that the discharge energy density of the sample under an electric field of 100 MV / m is 2.17 J / cm 3 Compared with 0.76 J / cm at room temperature 3The energy density of the capacitor has been improved by 286%. At the same time, the energy release of the capacitor is still very fast.

[0070] Example 6

[0071] The other conditions of this embodiment are the same as those of Embodiment 1, except that the material used is P(VDF-TrFE) (70 / 30) and the applied electric field is 100 MV / m.

[0072] The T of the ferroelectric material of this embodiment C is 110°C. In this embodiment, T 预 is 80 ℃.

[0073] In this embodiment, the sample is heated by light under an electric field of 100 MV / m, and its discharge energy density is tested and compared with the energy density measured at room temperature under the same electric field without light. The test results are as follows: Fig. 9 As shown. Fig. 9 It can be seen that the discharge energy density of the sample under an electric field of 100 MV / m is 1.96 J / cm 3 Compared with 0.69 J / cm at room temperature 3 The energy density of the capacitor has been improved by 284%. At the same time, the energy release of the capacitor is still very fast.

[0074] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0075] The parts not elaborated in detail in the description of the present invention belong to the known technology in the art. The above embodiments are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A method for improving the discharge energy density of a ferroelectric material, characterized in that: The method specifically comprises: heating the ferroelectric material under the condition of applying an electric field until the temperature reaches a predetermined temperature T 预 Then, the ferroelectric material is discharged after the electric field is removed.

2. The method according to claim 1, characterized in that The heating rate is not less than 10℃ / s.

3. The method according to claim 1, characterized in that The discharge time is no greater than 5RC, where R is the discharge resistance and C is the capacitance of the ferroelectric material.

4. The method according to claim 1, characterized in that When the temperature of the ferroelectric material reaches a predetermined temperature, the heating is stopped immediately.

5. The method according to claim 1, characterized in that When the ferroelectric material is applied to a high electric field, T 预 >T C , when the ferroelectric material is applied to a low electric field T 预 <T C , where T C is the Curie temperature of the ferroelectric material; The high electric field is higher than the coercive field of the ferroelectric material; and the low electric field is equal to or lower than the coercive field of the ferroelectric material.

6. The method according to claim 1, characterized in that The ferroelectric material is heated by various heat sources, electric heating or optical heating.

7. The method according to claim 1, characterized in that The ferroelectric material is a ferroelectric polymer.

8. The method according to claim 1, characterized in that The ferroelectric material is a composite material, which includes a ferroelectric polymer and a material with thermal effect, and the material with thermal effect is in close contact with the ferroelectric polymer; the material with thermal effect is a metal electrode with photothermal effect, a photothermal inorganic filler, or a photothermal organic filler.

9. The method according to claim 8, characterized in that The ferroelectric material is a composite material of P (VDF-TrFE) and nano-gold electrodes; the electric field strength of the high electric field is greater than 70 MV / m; the ferroelectric material is a composite material of P (VDF-TrFE) and nano-gold electrodes, and the electric field strength of the low electric field is not greater than 70 MV / m.

10. Use of the method for improving the discharge energy density of ferroelectric materials according to claims 1 to 9 in dielectric capacitors.

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