CN104505146A - Dielectric composite material with nano core-shell and inner crystal structures, and preparation method of dielectric composite material - Google Patents

Abstract

The invention discloses a dielectric composite material with a nano core-shell and inner crystal structure and a preparation method thereof, belonging to the technical field of dielectric composite materials. The nanoscale Ag metal particles serve as the "core", and the PbO inorganic insulating material constitutes the "shell"; this nano-core-shell structure composed of Ag metal particles and PbO inorganic insulating material is uniformly distributed in the submicron scale as the second phase particles. An intracrystalline structure is formed inside the grains of the PZN-PZT material. The submicron-scale PZN-PZT ceramic powder is used as the base material, and the nano-scale metal Ag particles are used as the filler, and is prepared by wet grinding, drying, calcining, secondary ball milling, compression molding, and sintering. The invention is applied to the energy storage device, can be integrated with the energy collection device, and temporarily stores the energy recovered and reused by the energy collection device, and has significant economic and social value.

Description

A kind of dielectric composite material with nano-core shell and inner crystal structure and its preparation method

technical field

The invention belongs to the technical field of dielectric composite materials, and in particular relates to a percolation type ferroelectric composite material with high dielectric constant and low dielectric loss that can be applied to energy storage devices and a preparation method thereof.

Background technique

Under the background of the energy crisis, how to collect and convert waste energy in the environment into reusable electric energy has attracted the attention of governments, academia and the general public. Among them, the energy harvesting device based on the piezoelectric effect can convert the mechanical energy generated in the environment into electrical energy. It has the characteristics of high electromechanical conversion efficiency, high output voltage, no electromagnetic interference, and no external bias, so it has broad application prospects. . Many scholars at home and abroad are devoted to the research of this work. At present, the piezoelectric material system for energy harvesting widely concerned by researchers is mainly the modified PZN-PZT material system. Through technical means such as doping, in order to obtain high piezoelectric constant and low dielectric constant, improve energy harvesting. Device efficiency. It is worth noting that while the energy harvesting materials are developing rapidly, the research on energy storage materials used to store energy harvesting devices to obtain electrical energy is seriously lagging behind, especially for material systems whose composition is similar to energy harvesting materials, and there is no relevant literature at present. reports. The performance requirements of the energy storage materials: low dielectric loss and high dielectric constant are significantly different from the performance requirements of energy harvesting materials. Designing and preparing this key material is of great significance for promoting the miniaturization and integration of piezoelectric effect-based energy harvesting systems (including energy harvesting units and energy storage units).

At present, among numerous energy storage materials, inorganic-metal composites have attracted extensive attention due to their flexible and adjustable material composition and excellent energy storage performance. It is well known that this type of composite material system has a sudden change in dielectric properties near the percolation threshold, which can be described by formula (1):

ε _r =ε ₀ |(f _c -f)/f _c | ^-q (1)

Among them, ε _r , ε ₀ are the dielectric constants of the composite material and the matrix material, respectively, q is the critical exponential factor of the dielectric constant, f is the volume percentage of metal filling, and f _c is the percolation threshold. According to this theory, it is easy to obtain a high dielectric constant near the percolation threshold. However, many previous researches have found that when a high dielectric constant is obtained near the percolation threshold, the dielectric loss will also increase significantly, making the material impracticable for practical application. Researchers have proposed many solutions, the most effective of which is to use polymer insulating materials to coat the surface of metal filler particles, and then use the coated metal particles as filler particles. However, this method is only applicable when the matrix material is a high molecular polymer, and this method is not applicable to the inorganic-metal composite material system. The main reason is that the synthesis temperature of such composite materials is generally higher than 1000 °C. Therefore, how to reduce the dielectric loss of inorganic-metal composites is still a big challenge.

To sum up, it can be seen that the performance of dielectric composite materials for energy storage is significantly different from that of energy harvesting materials, and they cannot be obtained by the same technical means. Therefore, in order to match the widely studied PZN-PZT-based energy harvesting material system, but also to meet the high dielectric constant and low dielectric loss requirements of energy storage materials.

Contents of the invention

The object of the present invention is to provide a dielectric composite material applicable to energy storage devices and a preparation method thereof. The dielectric composite material of the invention is characterized in that it has a novel nano-core-shell and inner crystal structure.

A dielectric composite material of the present invention is characterized in that the dielectric composite material has a nano-core-shell and inner crystal structure, nanoscale Ag metal particles are used as the "core", and inorganic insulating materials such as PbO form the "shell" ; This nano-core-shell structure composed of Ag metal particles and PbO and other inorganic insulating materials is uniformly distributed in the submicron-scale PZN-PZT material grains as the second phase particles to form an inner crystal structure. The existence of this special structure greatly improves the dielectric properties of the material, specifically manifested as high dielectric constant and low dielectric loss, which can meet the performance requirements of energy storage devices. In order to achieve the above object, the present invention adopts the following technical solutions.

The above-mentioned dielectric composite material with nano core-shell and inner crystal structure, the chemical composition of the composite material is: Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /xAg, The value of x is 10.0 vol.% to 18.0 vol.%. It is further preferred that the volume of the composite matrix material contains 16.6 vol.% of nanometer metal Ag particles.

The dielectric composite material with nano-core shell and inner crystal structure of the present invention can be used as a dielectric composite material applied to energy storage devices.

The method for preparing the above-mentioned dielectric composite material with a novel nano-core-shell and inner crystal structure of the present invention is characterized in that submicron-scale PZN-PZT ceramic powder is selected as the matrix material, and nano-scale metal Ag particles are used as fillers , prepared by a common sintering process, which specifically includes the following steps:

(1) Synthesis of Ag ₂ O precursor, which can be prepared by reacting AgNO ₃ with KOH, the reaction process is as follows:

AgNO ₃ +KOH→AgOH↓+KNO ₃ (2)

AgOH→Ag2O↓+ _H2O ( ₃ )

First, a certain amount of AgNO ₃ powder is dissolved in distilled water. After the AgNO ₃ powder is completely dissolved, an excessive amount of KOH powder is added to the AgNO ₃ solution, and the reaction in (2) above occurs first. AgOH is extremely unstable. The reaction in (3) above occurs rapidly, and a brownish-brown Ag ₂ O precipitate is formed. Using a high-speed centrifuge at 4000 r/min, centrifuge to obtain brown Ag ₂ O powder, and dry at 80°C for use.

(2) Weigh the obtained Ag ₂ O and Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO ₂ according to the stoichiometric ratio, Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO ₂ are all sub-micron scales. Put the weighed raw materials into a ball mill tank, place them in a planetary ball mill for 12 hours with anhydrous ethanol as the medium, and then dry them at 80°C; put the dried powder at 800°C Calcined at -900°C for 2 hours, then cooled with the furnace. It is worth pointing out that during the calcination process, Ag ₂ O will decompose into Ag simple substance and O ₂ , and the reaction process is as follows:

Ag ₂ O→Ag+O ₂ ↑ (4) The obtained powder was ball milled again for 12 hours, and dried at 80°C for later use.

(3) The powders of each component do not need to add a binder, and are directly molded under a pressure of 100MPa, and then sintered at 1000°C-1100°C and kept for 2 hours to obtain the target composite material.

The prepared composite material is first polished on the surface, and the microstructure and thermal properties are tested, and then coated with silver electrodes, and the electrical properties of the sample are tested.

Among them, the best sample composition is: Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /16.6vol.%Ag, its performance can reach: dielectric constant ε _r =16600, dielectric constant Electric loss tanδ=0.056, meeting the requirements of energy storage devices.

In the present invention, submicron-scale PZN-PZT ceramic powder is selected as the matrix material, and nanoscale metal Ag particles are used as fillers to construct a PZN-PZT/Ag dielectric composite material with a novel nano-core-shell structure. In this novel nano-core-shell structure, nanoscale Ag metal particles serve as the "core", and inorganic insulating materials such as PbO form the "shell". And this nano-core-shell structure can be evenly dispersed into the interior of the ceramic grains to form a stable inner crystal structure. The so-called internal crystal structure means that the nano-scale second phase particles enter the interior of the crystal grains of the matrix material. Specific to the patent of the present invention, the nano-core-shell structure composed of Ag metal particles and inorganic insulating materials such as PbO enters the interior of the PZN-PZT material grains as the second phase particles. Due to the existence of this special nanostructure, the interface polarization effect of the composite material is significantly enhanced, and the dielectric constant is greatly increased; more importantly, the inorganic insulating material can effectively reduce the interfacial contact between the Ag particles after wrapping the metal Ag particles. The tunneling current is high, and the purpose of reducing the dielectric loss is achieved. It is a potential dielectric composite material for energy storage devices.

Description of drawings

Figure 1 is a schematic diagram of the structure of the novel nano-core-shell and the inner crystal.

Fig. 2 is a TEM photo of Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /16vol.%Ag in the composition of the present invention.

Fig. 3 is an HRTEM photograph of the composition of the present invention being Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /16vol.%Ag.

detailed description

Further illustrate substantive characteristics and remarkable advantages of the present invention below by embodiment. It should be pointed out that the invention is by no means limited to the examples presented.

Synthesize the Ag ₂ O precursor, which is prepared by the reaction of AgNO ₃ and KOH, and the reaction process is as follows:

AgNO ₃ +KOH→AgOH↓+KNO ₃ (2)

AgOH→Ag2O↓+ _H2O ( ₃ )

First, a certain amount of AgNO ₃ powder is dissolved in distilled water. After the AgNO ₃ powder is completely dissolved, an excessive amount of KOH powder is added to the AgNO ₃ solution, and the reaction in (2) above occurs first. AgOH is extremely unstable. The reaction in (3) above occurs rapidly, and a brownish-brown Ag ₂ O precipitate is formed. Using a high-speed centrifuge at 4000 r/min, centrifuge to obtain brown Ag ₂ O powder, and dry at 80°C for use.

Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO ₂ are all submicron scale.

Example 1:

Weigh Ag ₂ O, Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO according to the chemical formula Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /12vol.%Ag ₂ , and ball milled in ethanol for 12 hours. The mixture was dried and calcined at 850°C for 2 hours, ball milled in ethanol for 12 hours, pressed directly at 100 MPa, and then sintered at 1050°C for 2 hours to obtain a composite material.

Example 2:

Weigh Ag ₂ O, Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO according to the chemical formula Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /16vol.%Ag ₂ , other with embodiment 1.

Example 3:

_{Weigh Ag 2} O, Pb ₃ O ₄ , _ZnO , _{Nb 2} O ₅ , _{ZrO 2} and TiO ₂ , others are the same as in Example 1.

Example 4:

_{Weigh Ag 2} O, Pb ₃ O ₄ , _ZnO , _{Nb 2} O ₅ , _{ZrO 2} and TiO ₂ , others are the same as in Example 1.

Table 1 performance comparison table of the above-mentioned embodiments

Claims (6)

1. A dielectric composite material is characterized in that the dielectric composite material has a nano-core shell and an inner crystal structure, and nanoscale Ag metal particles are used as "core", and PbO inorganic insulating material constitutes a "shell"; A nano-core-shell structure composed of Ag metal particles and PbO inorganic insulating material is uniformly distributed in the submicron-scale PZN-PZT material grains as the second phase particles to form an inner crystal structure. 2. A dielectric composite material according to claim 1, characterized in that the chemical composition of the composite material is: Pb(Zn _1/15 Nb _2/15 Zr _2/5 Ti _2/5 )O ₃ /xAg, The value of x is 10.0 vol.% to 18.0 vol.%. 3. A dielectric composite material according to claim 1, characterized in that the chemical composition of the composite material is: the volume of the composite matrix material contains 16.6 vol.% of nanometer metal Ag particles. 4. The method for preparing any one of the dielectric composite materials of claims 1-3, characterized in that, comprising the following steps: (1) Synthesis of Ag ₂ O precursor; (2) Weigh the obtained Ag ₂ O and Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO ₂ according to the stoichiometric ratio, Pb ₃ O ₄ , ZnO, Nb ₂ O ₅ , ZrO ₂ and TiO ₂ are all sub-micron scales. Put the weighed raw materials into a ball mill tank, place them in a planetary ball mill for 12 hours with anhydrous ethanol as the medium, and then dry them at 80°C; put the dried powder at 800°C Calcined at ‐900°C for 2 hours, then cooled with the furnace; ball milled the obtained powder again for 12 hours, and dried at 80°C for later use; (3) The powders of each component do not need to add a binder, and are directly molded under a pressure of 100MPa, and then sintered at 1000°C-1100°C and kept for 2 hours to obtain the target composite material. 5. according to the method for claim 4, it is characterized in that, synthesize Ag ₂ O precursor, this precursor adopts AgNO ₃ and KOH reaction make, and its reaction process is as follows: AgNO ₃ +KOH→AgOH↓+KNO ₃ (2) AgOH→Ag2O↓+ _H2O ( ₃ ) First, a certain amount of AgNO ₃ powder is dissolved in distilled water. After the AgNO ₃ powder is completely dissolved, an excessive amount of KOH powder is added to the AgNO ₃ solution, and the reaction in (2) above occurs first. AgOH is extremely unstable. The reaction in (3) above occurs rapidly, and a brownish-brown Ag ₂ O precipitate is formed. Using a high-speed centrifuge at 4000 r/min, centrifuge to obtain brown Ag ₂ O powder, and dry at 80°C for use. 6. Use of the dielectric composite material according to claims 1-3 in an energy storage device.