CN110544741A - method for improving service stability of fast ion conductor thermoelectric material - Google Patents
method for improving service stability of fast ion conductor thermoelectric material Download PDFInfo
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/10—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects
- H10N10/17—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects characterised by the structure or configuration of the cell or thermocouple forming the device
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- H10N19/00—Integrated devices, or assemblies of multiple devices, comprising at least one thermoelectric or thermomagnetic element covered by groups H10N10/00 - H10N15/00
- H10N19/101—Multiple thermocouples connected in a cascade arrangement
Abstract
The invention provides a method for improving the service stability of a fast ion conductor thermoelectric material, which is characterized in that at least one ion barrier layer is distributed between any two adjacent sections of the fast ion conductor thermoelectric material in a thermoelectric arm formed by connecting n sections of the fast ion conductor thermoelectric material along the action direction of an external field so as to improve the service stability of the fast ion conductor thermoelectric material, wherein n is more than or equal to 2; the material of the ion barrier layer is at least one of nickel, titanium, molybdenum, platinum, palladium and carbon elements; the fast ion conductor thermoelectric material is made of one of Cu 2-delta S, Cu 2-delta Se, Cu 2-delta Te, Ag2Se, CuAgSe, Cu5FeS4, CuCrSe2, Ag9GaSe6 and Ag8GeSe6, wherein delta is more than 0 and less than 0.1; the length of the fast ion conductor thermoelectric material is 0.1 mm-20 mm.
Description
Technical Field
The invention relates to a method for improving service stability of a fast ion conductor thermoelectric material, in particular to a method for improving service stability of the fast ion conductor thermoelectric material under the action of an external field (an electric field, a temperature field, a magnetic field and the like) and simultaneously maintaining excellent thermoelectric performance, and belongs to the field of thermoelectric materials and devices.
Background
The thermoelectric conversion technology has attracted much attention internationally in recent years as a new renewable clean energy technology. The thermoelectric conversion device directly converts heat energy and electric energy into each other by utilizing the Seebeck effect and the Peltier effect of semiconductor materials, has the characteristics of long service life, high reliability, environmental friendliness, wide application temperature range, capability of effectively utilizing low-density energy and the like, and has remarkable advantages in high and new technical fields of recycling of industrial waste heat and automobile exhaust waste heat, high-precision temperature control devices, military power supplies and the like. Thermoelectric devices are composed of numerous thermoelectric elements. Each thermoelectric element comprises an n-type thermoelectric leg and a p-type thermoelectric leg. Each thermoelectric leg is typically formed from a length of thermoelectric material and a corresponding electrode material.
In recent years, fast ion conductor thermoelectric materials typified by Cu2- δ X (X S, Se or Te, δ representing Cu vacancy content) and Ag2Se have gained wide attention from thermoelectric researchers worldwide. Such materials have very good thermoelectric properties, comparable to conventional thermoelectric materials [1 ]. In addition, the Cu-based material has the characteristics of low cost, rich raw materials, environmental friendliness and the like, so that the compound attracts the important attention of thermoelectric researchers and shows extremely wide application prospects.
The main reason for the excellent thermoelectric performance of fast ion conductor thermoelectric materials is that metal cations (such as Cu ions or Ag ions) are weakly bonded to the anion framework in the crystal structure, and the metal cations can migrate relatively freely in a liquid-like form inside the anion framework. The liquid-like migration behavior of the metal cations can increase the scattering of phonons, obviously inhibit the lattice thermal conductivity of the material and improve the thermoelectric property of the material. However, under the action of an external field (such as an electric field, a thermal field, a magnetic field, etc.), metal cations in these fast ion conductors can directionally migrate along the direction of the external field and gather at one end of the material, and meanwhile, vacancies are left at the other end of the material, so that the internal components of the material are unevenly distributed. In particular, when the external field applied to the material is strong enough, the concentration of the metal cations accumulated at one end of the material reaches the maximum limit that can be accommodated by the crystal structure of the material, resulting in that a part of the metal cations will be precipitated from the crystal structure and converted into a simple metal, such as a simple Cu metal or a simple Ag metal, which is the phenomenon of precipitation of the metal cations of the fast ion conductor thermoelectric material (see fig. 1). Taking Cu 2-deltaS as an example, Dennler et al applied a current of 24A/cm2 to a Cu2S sample at room temperature, and found a significant phenomenon of elemental enrichment of Cu at the current outflow end after a short time [2 ]. For Cu2- Δ Se materials, Brown et al also report a similar phenomenon of Cu ion precipitation under the action of an electric field [3 ].
The metal cation precipitation phenomenon of the fast ion conductor thermoelectric material is extremely unfavorable for the service stability of the fast ion conductor thermoelectric material. The mechanism responsible for the correlation between fast ion conductor thermoelectric material length and service stability is as follows. When an external field is applied to the fast ion conductor thermoelectric material, metal cations migrate directionally inside the material and gather at one end of the material, eventually forming a concentration gradient of metal cations inside the material. This concentration gradient will also exert an opposing force on the metal cations, driving them to migrate in the opposite direction to the external field. If the external field acting force is equal to the counter acting force of the concentration gradient, the movable ions in the material can reach dynamic balance, namely the movable ions do not exist in the material as a whole, and at the moment, the fast ion conductor thermoelectric material can show high service stability similar to that of the traditional thermoelectric material. If the external field force is stronger than the counter force of the concentration gradient, part of movable ions can not stably exist in the crystal structure, and the metal cation precipitation phenomenon can occur. On the one hand, metal cations precipitate from the crystal structure, resulting in a change in the chemical composition of the material, which in turn causes a significant deterioration in the thermoelectric properties. On the other hand, the influence of Cu ion deposition on the thermoelectric device is more significant. A large amount of metal simple substances precipitated on the surface of the material can damage the connection between the surface of the material and the interface of the electrode layer, increase the interface contact resistance and thermal resistance, further deteriorate the thermoelectric conversion efficiency of the thermoelectric device and even cause the complete failure of the material. In the last 60 th century, the U.S. 3M company and NASA jet power laboratory tried to replace the conventional SiGe material with a Cu2 Se-based thermoelectric device to provide power for deep space exploration satellites, but the problem of Cu ion precipitation under the action of an external field still cannot be solved after the research of last decade, and finally the project is forced to be terminated [4 ].
Therefore, to realize the real application of the fast ion conductor thermoelectric material, the service stability of the fast ion conductor thermoelectric material must be improved. Researchers in the field can destroy the original migration channel of Cu ions by introducing immobile 'pinning ions' (such as transition metal elements Cr, Mn, Fe, Co and the like) under the action of an external field into the crystal structure of the fast ion conductor thermoelectric material at the earlier stage, thereby effectively reducing the migration rate of the Cu ions and improving the service stability of the material [5 ]. However, while the service stability is improved, the introduced "pinning ions" may also introduce additional electrons/holes, secondary phases and the like, so as to change the initial thermoelectric properties of the material.
The reference:
[1]H.L.Liu,X.Shi,F.F.Xu,L.L.Zhang,W.Q.Zhang,L.D.Chen,Q.Li,C.Uher,T.Day
and G.J.Snyder,Nat.Mater,2012,11,422–425；Y.He,T.Day,T.S.Zhang,H.L.Liu,X.Shi,
L.D.Chen,G.J.Snyder,Adv.Mater,2014,26,3974–3978.；
[2]Dennler,Gilles,Chmielowski,Radoslaw,Jacob,Stéphane,Capet,Frédéric,
Roussel,Pascal,Zastrow,Sebastian,Nielsch,Kornelius,Opahle,Ingo,Madsen,Georg K
H,Advanced Energy Materials,2014,1301581.；
[3]Brown,David R,Day,Tristan,Caillat,Thierry,Snyder,G Jeffrey,Journal of
Electronic Materials,2013,42,2014-2019.；
[4]Hinderman,J.D.Thermoelectric materials evaluation program annual
technical report for fiscal years1980/1981.U.S.Department of Energy.doi:
10.2172/50492661981.；
[5] Thermoelectric materials capable of inhibiting Cu ion migration and methods for inhibiting Cu ion migration in Cu-based thermoelectric materials, CN104310457A [ P ].2015.
disclosure of Invention
in view of the above problems in the prior art, the present invention aims to provide a simpler method capable of effectively inhibiting the precipitation of metal cations under the action of an external field (such as an electric field, a thermal field, a magnetic field, etc.), while maintaining the original excellent thermoelectric properties without deterioration, so as to promote the real application of fast ion conductor thermoelectric materials.
On one hand, the invention provides a method for improving the service stability of a fast ion conductor thermoelectric material, wherein at least one ion barrier layer is distributed between any two adjacent sections of fast ion conductor thermoelectric materials in a thermoelectric arm formed by connecting n sections of fast ion conductor thermoelectric materials along the action direction of an external field so as to improve the service stability of the fast ion conductor thermoelectric material, wherein n is more than or equal to 2;
The material of the ion barrier layer is at least one of nickel, titanium, molybdenum, platinum, palladium and carbon elements;
The fast ion conductor thermoelectric material is made of one of Cu 2-delta S, Cu 2-delta Se, Cu 2-delta Te, Ag2Se, CuAgSe, Cu5FeS4, CuCrSe2, Ag9GaSe6 and Ag8GeSe6, wherein delta is more than 0 and less than 0.1;
The length of the fast ion conductor thermoelectric material is 0.1 mm-20 mm.
The invention adopts at least one ion barrier layer (at least one of nickel, titanium, molybdenum, platinum, palladium and carbon elements) with excellent heat conduction and electric conduction performance to connect the thermoelectric material with n sections (n is more than or equal to 2) of specific sizes and fast ion conductors (such as Cu 2-delta S, Cu 2-delta Se, Cu 2-delta Te, Ag2Se, CuAgSe, Cu5FeS4, CuCrSe2, Ag9GaSe6, Ag8GeSe6 and the like) into a thermoelectric arm. The ion barrier layer can limit the migration of movable ions to the inside of each section of the fast ion conductor thermoelectric material, but cannot migrate between different sections of the fast ion conductor thermoelectric material for a long distance through the ion barrier layer, namely the ion barrier layer can allow electrons/holes to pass through, but cannot allow Cu ions and Ag ions in the fast ion conductor to pass through. In addition, the length of each section of the fast ion conductor thermoelectric material is independently regulated and controlled (0.1-20 mm), and the maximum external field effect which can be borne by the fast ion conductor thermoelectric material can be effectively improved under the action of the ion barrier layer, so that high service stability is obtained.
Preferably, the length of the fast ion conductor thermoelectric material is 1-10 mm. In practice, the thermoelectric arms of a thermoelectric device are required to have a sufficient length (at least 2mm) so that a corresponding temperature difference can be established across the device. If the length of the fast ion conductor thermoelectric material is too long, ions in the fast ion conductor hot spot material will be separated out from the material, resulting in the change of chemical components and the significant deterioration of thermoelectric properties. If multiple segments of fast ion conductor thermoelectric material are connected such that each segment of material in the thermoelectric legs is too short, the number of ion barriers required from segment to segment increases. On one hand, the difficulty of the preparation of the thermoelectric arm is improved due to the increase of the number of the ion blocking layers; on the other hand, the increase of the number of ion blocking layers also increases the contact resistance and the thermal resistance at the interface, which is not beneficial to maintaining the high thermoelectric performance similar to that of the thermoelectric arm formed by only a single-segment material by the thermoelectric material formed by connecting multiple segments of fast ion conductors.
in addition, when the fast ion conductor thermoelectric material is made of Cu 2-delta S and Cu 2-delta Se, the length of the fast ion conductor thermoelectric material is preferably 2-6 mm. Taking a Cu2- δ S (δ ═ 0.02) compound as an example, fig. 3 shows the critical current density and critical electric field strength corresponding to the precipitation of a simple metal Cu when the length thereof is 10mm, 6mm, and 3mm, respectively, i.e., the maximum current density and electric field strength that can be tolerated. At 750K, the critical current density JC and critical electric field strength EC of Cu2- δ S (δ ═ 0.02) samples with a length of 10mm were 9A/cm2 and 10V/m, respectively. For most thermoelectric materials, the maximum current density experienced in a real application environment is typically 12A/cm 2. When a 10mm long Cu2- δ S (δ ═ 0.02) sample is used to prepare a thermoelectric device, the critical current density is below 12A/cm2, and therefore Cu ion precipitation will occur, resulting in low service stability. However, the present inventors found that when the Cu2- δ S (δ ═ 0.02) sample length was 6mm, its critical current density JC and critical electric field strength EC increased to 15A/cm2 and 19V/m, respectively. The current density is higher than 12A/cm2, so that the Cu ion precipitation phenomenon can not occur, and the material has high service stability. When the length is further shortened to 3mm, the critical current density JC and the critical electric field strength EC thereof are further increased to 23A/cm2 and 32V/m. This indicates that even in an environment where the current density is much higher than 12A/cm2, Cu2- δ S (δ ═ 0.02) still has high service stability, and the Cu ion precipitation phenomenon does not occur. The results are similar for Cu2Se and other fast ion conductor thermoelectric materials.
Preferably, the external field is at least one of an electric field, a temperature field and a magnetic field.
preferably, the ion barrier layer is prepared by brushing, electric arc spraying, magnetron sputtering, thermal evaporation, electric arc ion plating, hot-press sintering or spark plasma sintering.
Preferably, the thickness of the ion blocking layer is 0.001 to 1mm, preferably 0.01 to 0.5 mm.
In another aspect, the invention further provides a thermoelectric arm prepared according to the above method, wherein the length of the thermoelectric arm is at least 2mm, preferably at least 10mm, and more preferably 10-20 mm.
Has the advantages that:
the invention can effectively improve the maximum external field effect which can be borne by the material without metal cation precipitation phenomenon only by changing the length of the material. The invention has very important promotion significance for the practical application of the fast ion conductor thermoelectric material.
Drawings
Fig. 1 shows the distribution of metal cations and vacancies in a fast ion conductor thermoelectric material, wherein (a) the metal cations and vacancies in the fast ion conductor thermoelectric material exist in a disordered distribution without external field, (b) the metal cations are directionally migrated in the material and aggregated at one end and the vacancies are aggregated at the other end under the action of external field (such as electric field, thermal field, magnetic field), (c) the metal cations are precipitated from the material and transformed into metal precipitates when the external field is strong enough;
FIG. 2 is a graph showing the resistance of Cu2S under the action of an external electric field with a current density of 12A/cm2, which is continuously applied at a temperature of 573K, as a function of time, wherein R/R0 represents the relative change of resistance, R0 is the initial resistance of the sample, and R is the resistance of the sample after passing rated time current;
Fig. 3 shows the critical current density JC and critical electric field strength EC that can be tolerated by Cu2- δ S (δ ═ 0.02) materials of different lengths (3mm, 6mm and 10 mm);
FIG. 4 shows a configuration diagram of a thermoelectric leg composed of n segments of fast ion conductor thermoelectric materials connected by an ion barrier layer having excellent electrical and thermal conductivity between adjacent fast ion conductor thermoelectric materials;
Fig. 5 shows the electrical conductivity (a) and seebeck coefficient (b) at different temperatures for a thermoelectric arm composed of a 10mm long piece of Cu2- δ S (δ ═ 0.02) material and a 3.3mm long piece of Cu2- δ S (δ ═ 0.02) material, where the ion barrier layer used for the three-piece material was platinum;
Fig. 6 shows the relative resistance change of a thermoelectric leg composed of a 10mm long piece of Cu2- δ S (δ ═ 0.02) material and a 3.3mm long piece of Cu2- δ S (δ ═ 0.02) material, respectively, under an applied current of 24A/cm2, wherein the ion barrier layer used in the three pieces of material is platinum;
fig. 7 shows the electrical conductivity (a) and seebeck coefficient (b) at different temperatures for a thermoelectric arm composed of one length of 10mm Cu2- δ S (δ ═ 0.02) material and ten lengths of 1mm Cu2- δ S (δ ═ 0.02) material, where the ion barrier used for the ten lengths of material is platinum;
Fig. 8 shows the relative resistance change of a thermoelectric arm composed of a length of 10mm Cu2- δ S (δ ═ 0.02) and a length of ten lengths of 1mm Cu2- δ S (δ ═ 0.02) under an applied current of 24A/cm2, respectively, wherein the ion barrier layer used in the ten lengths of material is platinum;
FIG. 9 shows the electrical conductivity (a) and Seebeck coefficient (b) at different temperatures for a thermoelectric arm constructed from a length of 10mm of Ag9GaSe6 material and a length of 3.3mm of Ag9GaSe6 material, wherein the ion blocking layers used for the three lengths of material are platinum;
FIG. 10 shows the relative resistance change of a thermoelectric leg consisting of a length of 10mm Ag9GaSe6 material and a length of 3.3mm Ag9GaSe6 material under an applied current of 24A/cm2, wherein the ion blocking layers used in the three materials are platinum.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
the invention improves the service stability of the fast ion conductor thermoelectric material by improving the reverse acting force of the concentration gradient. Moreover, for a fast ion conductor thermoelectric material with the same chemical composition, if the metal cation concentrations at both ends of the material are the same, the shorter the length of the material, the larger the concentration gradient, i.e., the larger the external force that the metal cation can bear. Referring to fig. 2, a graph of the relative resistance of the Cu2S material as a function of time under an electric field is shown. When the current density is 12A/cm2, after 5 seconds, obvious Cu ions are separated out from the Cu2S material, so that the resistance is reduced to 45% of the initial resistance; after 2000 seconds of current application, the precipitation of Cu ions is more obvious, and correspondingly, the resistance is reduced to 10% of the initial resistance. This can be used to explain the experimental phenomena that the critical current density and electric field intensity of the Cu2S material increase gradually as the length of the sample is shortened. The results show that the service stability of the fast ion conductor thermoelectric material can be effectively improved by shortening the length of the fast ion conductor thermoelectric material. However, different operating environments require the p-type and n-type thermoelectric legs that make up the thermoelectric device to have a specified length. For example, in an operating environment with a hot side temperature of 800 ℃ and a cold side temperature of 30 ℃, the length of the thermoelectric legs needs to be at least 10mm to establish a sufficient temperature difference to achieve the highest thermoelectric conversion efficiency. At this time, for the Cu2- δ S (δ ═ 0.02) material, although it has high service stability when its length is 3mm and 6mm, it cannot meet the practical application needs; and when the length of the material is 10mm, the material has low service stability, Cu ions are easy to separate out, and the practical application cannot be met.
in one embodiment of the present invention, n (n ≧ 2) segments of fast ion conductor thermoelectric materials with specific dimensions are connected to form a thermoelectric arm with an ion blocking layer with excellent heat and electric conductivity along the external field acting direction, so that mobile ions can keep short-range migration inside each segment of fast ion conductor thermoelectric material, but can not migrate long-range migration between different segments of fast ion conductor thermoelectric materials through the ion blocking layer, and the structure is shown in fig. 4. On the basis, the length of each section of fast ion conductor thermoelectric material is independently regulated, so that the thermoelectric arm formed by connecting n sections of fast ion conductor thermoelectric materials can integrally obtain high service stability, and meanwhile, the original excellent thermoelectric performance is maintained. That is, by changing the length (0.1-20 mm) of each section of the fast ion conductor thermoelectric material, the concentration gradient inside the material can be increased, and the external acting force born by each section of the fast ion conductor thermoelectric material can be further improved. Since the ion blocking layer allows electrons/holes to pass through and has good heat conduction and electric conduction performance, the thermoelectric arm formed by connecting the ion blocking layer with n (more than or equal to 2) sections of fast ion conductor thermoelectric materials has similar electric and heat transport properties to the conventional thermoelectric arm formed by connecting a section of fast ion conductor thermoelectric materials. By the method, the service stability of the fast ion conductor thermoelectric material can be effectively improved. For example, the external field may be an electric field, a temperature field, a magnetic field, or the like.
In an alternative embodiment, the material of each segment of the fast ion conductor thermoelectric material can be one of Cu 2-delta S, Cu 2-delta Se, Cu 2-delta Te, Ag2Se, CuAgSe, Cu5FeS4, CuCrSe2, Ag9GaSe6 and Ag8GeSe6, wherein 0 < delta < 0.1. At this time, the movable ions in the fast ion conductor thermoelectric material are Cu ions or Ag ions.
in an alternative embodiment, the number of n and the length of each segment of fast ion conductor thermoelectric material are determined by the properties of the material itself and the application environment. If the maximum external force that the material itself can bear is small, or the external force applied to the material by the application environment is large, the more the number of segments n of the fast ion conductor thermoelectric material is needed, or the shorter the length of each segment of the fast ion conductor thermoelectric material is. It should be noted that the thermoelectric legs of the present invention have a sufficient length (at least 2mm) to establish a corresponding temperature difference across the device. Generally, the number of stages n constituting the thermoelectric legs is 2 or more. The length of each section of the fast ion conductor thermoelectric material can be 0.1 mm-20 mm, and preferably 1-10 mm. Furthermore, when the fast ion conductor thermoelectric material is made of Cu 2-delta S and Cu 2-delta Se, the length of each section of fast ion conductor thermoelectric material is preferably 2-6 mm.
In alternative embodiments, the selection and fabrication of ion barriers between different segments of fast ion conductor thermoelectric materials is critical to maintaining good thermoelectric performance of the thermoelectric legs formed from the multiple segments of materials. The ion blocking layer must have excellent electrical and thermal conductivity to avoid additional electrical or thermal losses of electrons/holes and phonons through the ion blocking layer. Meanwhile, the ion barrier layer must have certain inertia relative to the fast ion conductor thermoelectric material, and does not react with the fast ion conductor thermoelectric material at high temperature or reacts slowly. Therefore, the ion barrier layer in the present invention may be selected from at least one or more of nickel, titanium, molybdenum, platinum, a target, and a carbon material. Since the seebeck coefficient of these materials is very low, the thickness of the ion blocking layer should be as thin as possible to reduce the deterioration of the overall thermoelectric performance of the thermoelectric legs. Generally, the thickness of the ion blocking layer may be 0.001mm to 1mm, preferably 0.01 to 0.5 mm.
in alternative embodiments, the ion barrier layer can be prepared on the end face of the fast ion conductor thermoelectric material by brushing, arc spraying, magnetron sputtering, thermal evaporation, arc ion plating, hot-press sintering, spark plasma sintering, and the like. Wherein the brush coating method comprises: coating the conductive slurry on the end faces of the two sections of fast ion conductor thermoelectric materials in a brush coating mode, and then heating the conductive slurry to 100-900 ℃ in a vacuum atmosphere furnace to remove the organic solvent in the conductive slurry to obtain the ion barrier layer. In an alternative pilot mode, the conductive paste includes a solute and an organic solvent. Wherein the solute is at least one of nickel, titanium, molybdenum, platinum, palladium and carbon, and the content is 50-90 wt%. The organic solvent may be at least one of epoxy resin, terpineol, butyl carbitol and butyl carbitol acetate.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
The p-type fast ion conductor thermoelectric material Cu 2-delta S (delta is 0.02) is selected, and the method for improving the service stability of the fast ion conductor thermoelectric material is verified. The invention produces two Cu2- δ S (δ ═ 0.02) thermoelectric legs. The first Cu2- δ S (δ ═ 0.02) thermoelectric leg consisted of only one segment of thermoelectric material and was 10mm in length. The second Cu 2-delta S (delta is 0.02) thermoelectric arm is composed of three sections of Cu 2-delta S (delta is 0.02) materials with the length of 3.3mm, and every two adjacent sections of materials are connected through conductive platinum slurry (platinum powder: 78-82 wt%, bisphenol A epoxy resin: 8-12 wt%, and anhydride curing agent: 1-3 wt%). Coating conductive platinum slurry on the end face of the material by a brush coating mode, and then heating the material in a vacuum atmosphere furnace to 800 ℃ to remove the organic solvent in the platinum slurry, thereby obtaining the ion barrier layer (namely the platinum layer, the thickness of each platinum layer is 0.2 mm). In this case, platinum may function to connect adjacent Cu2- δ S (δ 0.02) materials and may also function to conduct electrons/holes but not copper ions. And the high electrical conductivity and high thermal conductivity of platinum can enable the material to maintain the initial excellent thermoelectric performance. As shown in fig. 5, the electrical conductivity of the thermoelectric leg made of three pieces of Cu2- δ S (δ ═ 0.02) material decreased by only 5% compared to the thermoelectric leg made of one piece of Cu2- δ S (δ ═ 0.02) material, while the seebeck coefficient remained almost unchanged. This indicates that the added ion barrier layer (i.e., platinum) has a negligible effect on the thermoelectric properties of the Cu2- δ S (δ ═ 0.02) material. Since Cu ions cannot migrate through the platinum layer from one section of Cu2- δ S (δ ═ 0.02) material to another section of Cu2- δ S (δ ═ 0.02) material, the Cu ion migration inside each section of Cu1.98s material is independent, and therefore it will be able to withstand larger external field forces. As shown in fig. 6, an applied current of 24A/cm2 was applied to each of two Cu2- δ S (δ ═ 0.02) thermoelectric arms to drive long-range migration of Cu ions. After 200 minutes of energization, the resistance of the hot leg made of a single piece of Cu2- δ S (δ 0.02) material was greatly reduced to 76% of the initial value by Cu ion deposition. On the other hand, in the thermoelectric leg made of three-stage Cu2- δ S (δ 0.02), the resistance was almost maintained after 10000 minutes of energization. No metallic Cu deposition was observed on the surface of the material. The method provided by the application is proved to be capable of effectively avoiding the precipitation of Cu ions and improving the service stability of the fast ion conductor thermoelectric material.
Example 2
The invention produces two Cu2- δ S (δ ═ 0.02) thermoelectric legs. The first Cu2- δ S (δ ═ 0.02) thermoelectric leg consisted of only one segment of thermoelectric material and was 10mm in length. The second Cu2- δ S (δ ═ 0.02) thermoelectric leg was composed of ten lengths of Cu2- δ S (δ ═ 0.02) thermoelectric leg material of 1mm, and each of the adjacent lengths was connected by conductive platinum paste (platinum powder: 78-82 wt%, bisphenol a type epoxy resin: 8-12 wt%, acid anhydride type curing agent: 1-3 wt%). Coating the end face of the material with conductive platinum slurry by brush coating, and then heating the material in a vacuum atmosphere furnace to 800 ℃ to remove the organic solvent in the platinum slurry, thereby obtaining the ion barrier layer (namely the platinum layer, the thickness of which is 0.2 mm). As shown in fig. 7, the seebeck coefficient of a thermoelectric arm made of ten sections of Cu2- δ S (δ ═ 0.02) materials is reduced by about 10% compared with that of a thermoelectric arm made of one section of Cu2- δ S (δ ═ 0.02) materials, but the electrical conductivity is reduced by 30%, and the reduction of the electrical conductivity (i.e., the increase of the resistance) in the actual working process will seriously affect the power generation efficiency of the thermoelectric material, so that the number of sections of the material needs to be controlled within a reasonable range to control the influence on the thermoelectric performance to a certain extent while inhibiting the long-range migration of ions inside the material, thereby simultaneously ensuring that the thermoelectric arm made of the multi-section fast ion conductor thermoelectric material has high service stability and high thermoelectric performance.
example 3
The method provided by the invention adopts an N-type fast ion material thermoelectric material Ag9GaSe6 to verify the method for improving the service stability of the fast ion conductor thermoelectric material. The invention prepares two Ag9GaSe6 thermoelectric arms, wherein the first thermoelectric arm is made of thermoelectric materials with only one section and the length of 10mm, the second thermoelectric arm is made of 3 sections of thermoelectric arms with the length of 3.3mm, and the middle parts of the thermoelectric arms are connected by conductive platinum paste. The specific experimental procedure was the same as in example 1, and the results of the thermoelectric properties measurement are shown in FIG. 9. As can be seen from the figure, the thermoelectric legs composed of three pieces of Ag9GaSe6 material have very small changes in electrical conductivity and seebeck coefficient compared to the thermoelectric legs composed of one piece of Ag9GaSe6 material. This indicates that the added ion barrier (i.e., platinum) has little, if any, effect on the thermoelectric properties of the Ag9GaSe6 material. Because Ag ions cannot migrate from one section of Ag9GaSe6 material to another section of Ag9GaSe6 material through the platinum layer, the Ag ion migration is relatively independent inside each section of material, which is equivalent to reducing the length, so that each section can bear larger external field acting force. Similarly, an applied current of 24A/cm2 was applied to two Ag9GaSe6 thermoelectric arms to drive long-range migration of Ag ions, as shown in FIG. 10. After 200 minutes of energization, the resistance of the hot leg, which was composed of a single strand of Ag9GaSe6 material, dropped significantly to 75% of the initial value due to the deposition of Ag ions. In contrast, the resistance of the thermoelectric legs made of three pieces of Ag9GaSe6 material remained almost unchanged after 10000 minutes of energization. No metallic Ag deposition was observed on the surface of the material. Therefore, the method is proved to have universality, has strong inhibiting effect on cation precipitation of the fast ion conductor thermoelectric material, can effectively improve the stability of the material and improve the performance of the material in the service process.
The method provided by the invention can effectively avoid the damage of metal cation precipitation to thermoelectric materials and thermoelectric devices, remarkably improve the service stability of the fast ion conductor thermoelectric materials, and simultaneously maintain the initial excellent thermoelectric performance of the materials. In addition, the method has low cost and simple process, and is convenient for large-scale batch preparation.
Claims (7)
1. A method for improving the service stability of a fast ion conductor thermoelectric material is characterized in that at least one ion barrier layer is distributed between any two adjacent sections of the fast ion conductor thermoelectric material in a thermoelectric arm formed by connecting n sections of the fast ion conductor thermoelectric material along the action direction of an external field so as to improve the service stability of the fast ion conductor thermoelectric material, wherein n is more than or equal to 2;
the material of the ion barrier layer is at least one of nickel, titanium, molybdenum, platinum, palladium and carbon elements;
the fast ion conductor thermoelectric material is made of one of Cu 2-delta S, Cu 2-delta Se, Cu 2-delta Te, Ag2Se, CuAgSe, Cu5FeS4, CuCrSe2, Ag9GaSe6 and Ag8GeSe6, wherein delta is more than 0 and less than 0.1;
The length of the fast ion conductor thermoelectric material is 0.1 mm-20 mm.
2. The method of claim 1, wherein the fast ion conductor thermoelectric material has a length of 1-10 mm.
3. The method according to claim 2, wherein when the fast ion conductor thermoelectric material is Cu2- δ S or Cu2- δ Se, the length of the fast ion conductor thermoelectric material is 2-6 mm.
4. The method of any one of claims 1-3, wherein the external field is at least one of an electric field, a temperature field, and a magnetic field.
5. the method according to any one of claims 1 to 4, wherein the ion barrier layer is prepared by brushing, arc spraying, magnetron sputtering, thermal evaporation, arc ion plating, hot press sintering or spark plasma sintering.
6. the method according to any of claims 1 to 5, wherein the thickness of the ion barrier layer is 0.001 to 1mm, preferably 0.01 to 0.5 mm.
7. A thermoelectric leg produced by the process of any one of claims 1 to 6, having a length of at least 2mm, preferably at least 10mm, more preferably 10 to 20 mm.
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