CN111430660B - Ion-electron mixed conductive metal sodium cathode and preparation method thereof - Google Patents

Ion-electron mixed conductive metal sodium cathode and preparation method thereof Download PDF

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CN111430660B
CN111430660B CN202010194060.7A CN202010194060A CN111430660B CN 111430660 B CN111430660 B CN 111430660B CN 202010194060 A CN202010194060 A CN 202010194060A CN 111430660 B CN111430660 B CN 111430660B
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姜银珠
曹克爽
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Zhejiang University ZJU
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Abstract

The invention discloses an ion-electron mixed conductive metal sodium cathode, which consists of solid electrolyte and metal sodium, and is formed by melting and mixing solid electrolyte powder and metal sodium, wherein the metal sodium forms a matrix of the metal sodium cathode, and Na is constructed in the metal sodium matrix by the solid electrolyte+A conductive network in which the solid electrolyte is coated with SnO2NZSP particles of (1), wherein NZSP means Na3+xZr2Si2+xP1‑xO12. The invention also discloses a preparation method of the sodium cathode, which mainly comprises three processes of synthesizing the solid electrolyte, modifying the surface of the solid electrolyte and preparing the electrode by melting and mixing the solid electrolyte and the metal sodium. The metal sodium cathode prepared by the invention has excellent cycling stability and lower electrochemical impedance, and shows high cycling stability and lower capacity attenuation in a full battery test.

Description

Ion-electron mixed conductive metal sodium cathode and preparation method thereof
Technical Field
The invention relates to a sodium ion battery electrode material and a preparation method thereof, belonging to the field of energy materials.
Background
With the rapid development of the electric energy storage market, research and development of energy storage systems, and the search for advanced methods for improving energy density and reducing production and manufacturing costs have become important issues of global common attention. Among a plurality of novel battery systems, sodium metal batteries have attracted extensive attention because of the similar working principle of lithium ion batteries, high energy density and abundant crust sodium resource reserves, and have become an important development direction in the technical field of electrochemical energy storage. The electrode material is a carrier for charge storage of the secondary battery, and determines the overall performance of the battery. The metallic sodium has high theoretical capacity (1165 mAh g-1) And the advantage of a low electrochemical potential (-2.71V relative to a standard hydrogen electrode), with S, O2Or CO2After the novel positive electrode is matched, the energy density is 3-4 times that of the lithium ion battery commonly used at present, and the novel positive electrode is an indispensable part in the sodium metal battery and is also the key for the research of the sodium metal battery.
However, sodium metal cathodes face several serious challenges during electrochemical cycling, mainly: (1) formation of unstable, easily broken solid electrolyte interface layers (SEI); (2) large volume changes; (3) severe dendrite growth phenomenon. These problems greatly hinder the practical application of metallic sodium cathodes. Therefore, how to stabilize the metal sodium cathode becomes a key problem that needs to be solved urgently in the way of the practicability of the sodium metal battery, and the metal sodium cathode is widely concerned by researchers.
In the prior art, part of the research work is dedicated to modifying the surface of metallic sodium to artificially SEI (such as constructing ALD-Al on the surface of an electrode)2O3Layer of Na3PS4Layer, NaBr layer, Na — Sn alloy layer, etc., or electrolyte modification) to replace the originally spontaneously formed SEI that is heterogeneous, non-uniform and prone to cracking. Another part of research work focuses on the construction of three-dimensional current collectors, such as porous copper, porous aluminum, functional carbon materials, Mxene, etc., which utilize the rich pore structure inside to accommodate the volume change of the electrode.
However, there are some disadvantages in these prior art techniques, mainly: 1. the artificial SEI construction strategy can improve the cycling stability of the sodium metal to a certain extent under the conditions of low current and low capacity charge and discharge. However, since the sodium deposition and dissolution reaction only occur on the surface of the electrode, the lower layer of the artificial SEI undergoes a large volume change during the cycling process, and the discharge capacity in practical use: (>3 mAh cm-2) The interface of the lower electrode cannot be kept stable. 2. Although the higher specific surface area of the three-dimensional current collector is beneficial for reducing local current density, the inside is an open pore structure, which also causes more electrolyte exposure and increases consumption of active sodium and electrolyte. In addition, since the reaction still occurs on the surface of metallic sodium, a dendrite growth phenomenon caused by non-uniform SEI after increasing current density cannot be avoided.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a metal sodium cathode, and the structure of the metal sodium cathode can simultaneously comprise: (1) fast electron and ion conduction pathways; (2) more reaction interfaces are used for electrochemical reactions; (3) less exposure of electrolyte; (4) a rigid, porous skeleton to accommodate volume changes. The invention aims to realize the long cycle stability of the metal sodium cathode under different charging and discharging conditions by constructing the metal sodium cathode with the characteristics, and lays a solid foundation for the practical application of the metal sodium cathode.
In order to construct an ideal sodium negative electrode structure having the above conditions for achieving the above object of the invention, the inventors considered Na+The slow diffusion in the metal sodium is to integrate the ion conduction network into the bulk metal sodium electrode, which is important for realizing the deposition and dissolution of sodium in the whole electrode, and the compact electrode structure can greatly reduce the exposed area of the metal sodium in the electrolyte.
Based on the above consideration, the inventors have provided the following technical solutions in the present application to achieve the object of the invention.
The invention provides an ion-electron mixed conductive metal sodium cathode, which consists of a solid electrolyte and metal sodium, and is formed by melting and mixing solid electrolyte powder and metal sodium, wherein the metal sodium forms a matrix of the metal sodium cathode, and Na is constructed in the metal sodium matrix by the solid electrolyte +A conducting network.
The solid electrolyte has the characteristics of high conductivity of sodium ions and good chemical stability with metal sodium; the high sodium ion conductivity can ensure the rapid conduction of sodium ions, and the good chemical stability with metal sodium can ensure the stable performance of the electrode formed after the solid electrolyte is fused with sodium. Preferably, the sodium ion conductivity of the solid electrolyte is higher than 10 at normal temperature-5 S cm-1(ii) a For example, the solid electrolyte NZSP used in example 1 of the present invention, the inventors have found that the sodium ion conductivity is about 4.8X 10-3S cm-1。
Particularly preferably, the solid electrolyte is coated with SnO2NZSP particles of ZnO, Au or Ag, the NZSP having the formula Na3+xZr2Si2+xP1-xO12Wherein x is more than or equal to 0 and less than or equal to 0.6. More preferably, the NZSP has a chemical formula of Na3.4Zr2Si2.4P0.6O12。
The invention also provides a method for preparing the metal sodium cathode, which mainly comprises the following steps:
1) synthesizing NZSP: synthesizing NZSP powder by a solution-assisted solid phase reaction method;
2) NZSP pretreatment: coating SnO on the surface of NZSP powder2Layer to obtain surface modified NZSP (SnO)2@ NZSP) powder, i.e., powder of the solid electrolyte;
coating SnO on the surface of NZSP powder2The wettability of the powder with the metal sodium can be improved, and the complete mixing of the powder and the molten sodium can be realized in the subsequent mixing process of the solid electrolyte powder and the molten sodium. The inventors believe that SnO2And the chemical reaction with sodium can be carried out under the heating condition, and the wettability is effectively improved. The inventor finds in the research process that the mode of improving the wettability of the solid electrolyte and the metallic sodium is not limited to the surface coating of SnO2Other wettability improvement approaches may also be used, such as: the surface of the solid electrolyte is coated with ZnO, Au, Ag, or the like, and the wettability of the solid electrolyte with metallic sodium can be also significantly improved by the reaction of these substances with molten metallic sodium.
3) Preparing an electrode by melting and mixing metal sodium: and in a closed atmosphere protected by argon, melting and mixing the solid electrolyte powder and metal sodium to obtain the metal sodium cathode electrode.
Further, the step 1) of synthesizing NZSP specifically includes: adding NaNO3And ZrO (NO)3)2Dissolving in distilled water to form a solution, and stirring while adding Si (OCH)2CH3)4And NH4H2PO4Adding into the solution; after drying at 85 ℃, calcining the obtained powder at 900-1200 ℃ for 2-4 hours to obtain NZSP powder.
Particularly preferred, wherein NaNO3And ZrO (NO)3)2And Si (OCH)2CH3)4And NH4H2PO4The amount of the reagent added is strictly in accordance with NZSP, i.e. Na3+xZr2Si2+xP1-xO12Wherein x is more than or equal to 0 and less than or equal to 0.6.
Further, the step 2) of NZSP pretreatment specifically comprises: SnCl2Dissolving in N, N-Dimethylformamide (DMF) to obtain 0.1-0.6 mol L-1SnCl of2A solution; adding a proper amount of NZSP powder synthesized in the step 1) and SnCl in the solution2The quality of the NZSP is controlled to be 5-20% of the quality of the NZSP; after mixing with stirring, the solution was dried in an oven at 80 ℃ overnight. Subsequently, grinding the powder, and then sintering the powder in a tube furnace at 350-500 ℃ for 1-3 hours to obtain the surface-coated SnO2NZSP (SnO)2@ NZSP) solid electrolyte powder, wherein the sintering atmosphere is air, and the heating rate is 5 ℃ for min-1。
Further, the step 3) of preparing the electrode by melting and mixing the metal sodium specifically comprises the following steps: in a glove box filled with argon; coating the surface of the SnO obtained in the step 2) with SnO2Weighing NZSP solid electrolyte powder and sodium metal with a surface oxide layer cut off according to a certain proportion, then putting the powder into a nickel crucible, and heating the powder to 180-250 ℃; stirring to melt sodium and SnO2@ NZSP powder was mixed thoroughly; and after the mixture is cooled, punching the mixture into a wafer electrode to obtain the metal sodium cathode. Wherein the surface is coated with SnO2The mixing ratio of the NZSP solid electrolyte powder to the sodium metal for cutting off the surface oxidation layer is 1:1-5 by mass.
It is noted that the method of the present invention for producing a sodium metal negative electrode is equally applicable to the production of other metal electrodes, such as lithium metal electrodes.
After electrochemical analysis and test are carried out on the prepared metallic sodium cathode, under the same test condition, compared with untreated sodium, the prepared metallic sodium cathode has excellent cycle stability, and the cycle life can be improved by nearly 8 times; in addition, the electrochemical impedance is greatly reduced and is only one tenth of that of an untreated sodium sheet, and the exchange current density on the electrode is improved by 3 times, which shows a faster charge transfer process and a lower sodium ion diffusion barrier in the electrode; and shows high specific capacity (102 mAh g) in full battery test-1) And lower capacity fade.
The inventors believe that the reason why the metallic sodium negative electrode of the present invention exhibits excellent electrochemical performance can be summarized as the following points:
(1) the NZSP network of the solid electrolyte uniformly distributed in the metal sodium cathode can provide rapid Na +Conduction, so that the reaction area for sodium deposition/stripping is expanded throughout the electrode body phase, rather than being concentrated at the electrode surface;
(2) due to the introduction of the NZSP particles, the ceramic electrolyte framework constructed by the NZSP particles greatly inhibits the violent volume change and uneven deposition/stripping behavior of the electrode surface, and the enhanced mechanical strength of the electrode can also effectively inhibit the growth of sodium dendrites.
During the research process of the invention, the inventor finds that other researchers can construct an ion-electron mixed conductive Sodium negative electrode through NZSP, and Yao Lu et al researchers are in the literature (A High-Performance Monolithic Solid-State Sodium Battery with Ca)2+ Doped Na3Zr2Si2PO12In electroyte, adv. Energy mater, 2019, 9, 1901205), Ca is added2+Doped Na3Zr2Si2PO12Mixing with pore-forming agent, pressing into electrode slice, sintering in air to form solid electrolyte with porous structure; SnCl for porous solid electrolyte structure4After treatment and sintering, SnO is obtained2The outer layer increases wettability, and then molten metal sodium is poured into the pores of the solid electrolyte with a porous structure to form an electrode.
Unlike the present invention, Yao Lu et al form electrodes by first constructing a solid electrolyte with a porous structure and then pouring molten sodium into the pores of the solid electrolyte. Therefore, the prepared metal sodium cathode takes the solid electrolyte with the porous structure as a matrix frame of the electrode, a rapid transmission channel of sodium ions is constructed, and the metal sodium is filled into pores of the solid electrolyte with the porous structure to form a transmission channel of electrons.
In the invention, solid electrolyte powder is mixed with molten metal sodium and then pressed into the electrode. The metallic sodium negative electrode prepared by the method of the invention is formed by the metallic sodium to form the electrode matrix, thereby ensuring that high overall electrode capacity is obtained, and solid electrolyte particles are in the metalNa is bound in the sodium matrix +And the conduction network forms an ion conduction path, so that more reaction interfaces are obtained for electrochemical reaction.
Compared with the preparation method of Yao Lu and the like and the prepared sodium electrode, the invention has the advantages that:
1) the method is simpler and more efficient, and has a prospect of large-scale production. NZSP is mixed with a pore-forming agent and then pressed into an electrode plate by Yao Lu and the like, and a porous solid electrolyte structure is formed by high-temperature sintering; the invention directly mixes the solid electrolyte powder with sodium in a melting way without an additional high-temperature sintering step.
2) The metal sodium negative electrode prepared by the invention is formed by metal sodium as a substrate of the electrode, so that the content of sodium is higher (more than 50 percent), and the higher total capacity of the electrode is ensured.
3) The metal sodium cathode prepared by the invention is cooled by molten metal sodium to form an electrode matrix, and then the electrode matrix is pressed into an electrode, so that the electrode microstructure is compact, and the exposure of the metal sodium in electrolyte is greatly reduced by the compact electrode structure.
Drawings
Fig. 1 is a method of preparing a sodium metal anode according to each example.
Fig. 2 is a schematic diagram of the action mechanism of the sodium metal negative electrode prepared by the embodiments of the present invention.
Fig. 3 is a micro-topography of the sodium negative electrode made in example 1.
Fig. 4 is a graph of electrochemical performance in a symmetric cell test for a sodium negative electrode made in example 1.
Fig. 5 is an electrochemical impedance spectrum (left) and a Tafel curve (right) after 10 cycles of charge and discharge in a symmetric cell test with a sodium cathode made in example 1.
FIG. 6 shows Na + negative electrode prepared in example 13V2(PO4)3And the electrochemical performance diagram of the full battery test formed by matching the/C positive electrode.
Detailed Description
The method for preparing the metallic sodium cathode in each embodiment of the invention is to mix solid electrolyte powder with molten metallic sodium and press the mixture into the metallic electrode, and the steps are mainlyThe method comprises three processes of synthesizing solid electrolyte, pretreating the solid electrolyte and preparing the electrode by melting and mixing with metal sodium. The preparation principle can be presented as the attached figure 1, as shown in the figure: the powdered solid electrolyte is mixed with molten metal sodium, and solid electrolyte particles form a skeleton network in the metal sodium to form a rapid sodium ion conduction channel. FIG. 2 is a schematic diagram of the mechanism of the sodium metal negative electrode made according to the embodiments of the present invention, in which the sodium metal negative electrode is composed of sodium metal as the electrode matrix, and solid electrolyte particles are connected in the sodium metal matrix to form Na +A conducting network; referring to fig. 3, which is a micro-topography of a sodium metal negative electrode prepared in the following example 1, it can be seen that, the sodium metal is used as a matrix, solid electrolyte particles are uniformly embedded in the sodium matrix, and it can be seen that the microstructure of the electrode is dense, and the compact microstructure of the electrode greatly reduces the exposure of the sodium metal in the electrolyte.
The present invention will be described in detail below with reference to specific examples.
Example 1
Mainly comprises three processes of synthesizing solid electrolyte, pretreating the solid electrolyte and preparing an electrode by melting and mixing the solid electrolyte with metal sodium.
(1) Synthesis of solid electrolyte Na3.4Zr2Si2.4P0.6O12: adding NaNO3And ZrO (NO)3)2Dissolving in distilled water, and stirring to obtain Si (OCH)2CH3)4And NH4H2PO4Added to the solution in amounts strictly as Na3.4Zr2Si2.4P0.6O12The stoichiometric ratio of (a). After drying at 85 ℃, the obtained powder was calcined at 1100 ℃ for 3 hours to obtain NZSP powder.
(2) Solid electrolyte pretreatment: SnCl2Dissolved in N, N-Dimethylformamide (DMF) to give 0.5 mol L-1SnCl of2And (3) solution. Adding NZSP powder and SnCl in the solution2The mass control of (a) is 15% of the mass of the NZSP. After stirring for 2 hours, the solution was dried overnight in an oven at 80 ℃.Subsequently, the powder was ground in an agate milling dish for 5 minutes and then sintered in a tube furnace at 450 ℃ for 2 hours to obtain SnO2@ NZSP powder, in which the sintering atmosphere is air and the heating rate is 5 ℃ for min-1。
(3) Preparing an electrode by melting and mixing NZSP and sodium metal: the process was carried out in an argon-filled glove box (O)2≤0.1 ppm，H2O is less than or equal to 0.1 ppm). SnO2The @ NZSP powder and an equal mass of sodium metal from which the surface oxide layer was removed were placed in a nickel crucible and heated to 250 ℃. After stirring for about 5 minutes, the sodium and SnO were melted2@ NZSP is fully mixed. And after cooling the mixture, punching the mixture into an electrode plate to obtain the prepared sodium metal cathode.
Example 2
Mainly comprises three processes of synthesizing solid electrolyte, pretreating the solid electrolyte and preparing an electrode by melting and mixing the solid electrolyte with metal sodium.
(1) Synthesis of solid electrolyte Na3.2Zr2Si2.2P0.8O12: adding NaNO3And ZrO (NO)3)2Dissolving in distilled water, and stirring to obtain Si (OCH)2CH3)4And NH4H2PO4Adding into solution in the amount of Na3.2Zr2Si2.2P0.8O12Weighing the components according to the stoichiometric ratio. After drying at 85 ℃, the obtained powder was calcined at 1000 ℃ for 3 hours to obtain NZSP powder.
(2) Solid electrolyte pretreatment: SnCl2Dissolved in N, N-Dimethylformamide (DMF) to give 0.4 mol of L-1SnCl of2And (3) solution. Adding NZSP powder and SnCl in the solution2The mass control of (a) is 10% of the mass of the NZSP. After stirring for 2 hours, the solution was dried overnight in an oven at 80 ℃. Subsequently, the powder was ground in an agate milling dish for 5 minutes and then sintered in a tube furnace at 500 ℃ for 1 hour to obtain SnO2@ NZSP powder, in which the sintering atmosphere is air and the heating rate is 5 ℃ for min-1。
(3) Melt mixing NZSP with metallic sodiumPreparing an electrode: the process was carried out in an argon-filled glove box (O)2≤0.1 ppm，H2O is less than or equal to 0.1 ppm). SnO2The @ NZSP powder and sodium metal with a surface oxide layer removed are placed into a nickel crucible according to a mass ratio of 1 to 3, and heated to 250 ℃. After stirring for about 5 minutes, the sodium and SnO were melted2@ NZSP is fully mixed. After the mixture was cooled, it was punched into an electrode sheet shape and used as a negative electrode.
Example 3
Mainly comprises three processes of synthesizing solid electrolyte, pretreating the solid electrolyte and preparing an electrode by melting and mixing the solid electrolyte with metal sodium.
(1) Synthesis of solid electrolyte Na3Zr2Si2PO12: adding NaNO3And ZrO (NO)3)2Dissolving in distilled water, and stirring to obtain Si (OCH)2CH3)4And NH4H2PO4Adding into solution in the amount of Na3Zr2Si2PO12Weighing the components according to the stoichiometric ratio. After drying at 85 ℃, the obtained powder was calcined at 1100 ℃ for 4 hours to obtain NZSP powder.
(2) Solid electrolyte pretreatment: SnCl2Dissolved in N, N-Dimethylformamide (DMF) to give 0.6 mol of L-1SnCl of2And (3) solution. Adding NZSP powder and SnCl in the solution2The mass control of (a) is 20% of the mass of the NZSP. After stirring for 2 hours, the solution was dried overnight in an oven at 80 ℃. Subsequently, the powder was ground in an agate milling dish for 5 minutes and then sintered in a tube furnace at 500 ℃ for 2 hours to obtain SnO2@ NZSP powder, in which the sintering atmosphere is air and the heating rate is 5 ℃ for min-1。
(3) Preparing an electrode by melting and mixing NZSP and sodium metal: the process was carried out in an argon-filled glove box (O)2≤0.1 ppm，H2O is less than or equal to 0.1 ppm). SnO2The @ NZSP powder and sodium metal with a surface oxide layer removed are placed in a nickel crucible according to a mass ratio of 1 to 5 and heated to 200 ℃. After stirring for about 5 minutes, the sodium and SnO were melted2@NZSPAnd (4) completely mixing. After the mixture was cooled, it was punched into an electrode sheet shape and used as a negative electrode.
Example 4
Mainly comprises three processes of synthesizing solid electrolyte, pretreating the solid electrolyte and preparing an electrode by melting and mixing the solid electrolyte with metal sodium.
(1) Synthesis of solid electrolyte Na3.6Zr2Si2.6P0.4O12: adding NaNO3And ZrO (NO)3)2Dissolving in distilled water, and stirring to obtain Si (OCH)2CH3)4And NH4H2PO4Adding into solution in the amount of Na3.6Zr2Si2.6P0.4O12Weighing the components according to the stoichiometric ratio. After drying at 85 ℃, the obtained powder was calcined at 1200 ℃ for 2 hours to obtain NZSP powder.
(2) Solid electrolyte pretreatment: SnCl2Dissolved in N, N-Dimethylformamide (DMF) to give 0.1 mol of L-1SnCl of2And (3) solution. Adding NZSP powder and SnCl in the solution2The mass control of (a) is 5% of the mass of the NZSP. After stirring for 2 hours, the solution was dried overnight in an oven at 80 ℃. Subsequently, the powder was ground in an agate milling dish for 5 minutes and then sintered in a tube furnace at 350 ℃ for 3 hours to obtain SnO2@ NZSP powder, in which the sintering atmosphere is air and the heating rate is 5 ℃ for min-1。
(3) Preparing an electrode by melting and mixing NZSP and sodium metal: the process was carried out in an argon-filled glove box (O)2≤0.1 ppm，H2O is less than or equal to 0.1 ppm). SnO2The @ NZSP powder and sodium metal with a surface oxide layer removed are put into a nickel crucible according to a mass ratio of 1: 5 and heated to 180 ℃. After stirring for about 5 minutes, the sodium and SnO were melted2@ NZSP is fully mixed. After the mixture was cooled, it was punched into an electrode sheet shape and used as a negative electrode.
After electrochemical analysis tests are performed on the sodium metal negative electrode prepared in each of the above embodiments, the test results are as follows:
(1) in thatIn a symmetrical cell test with a carbonate-based electrolyte, at moderate test conditions (1 mA cm)-2Current density of 1 mAh cm-2Depth of discharge) can maintain a low overpotential, stably circulate for more than 750 hours; under more severe and practical test conditions (1 mA cm)-2Current density of 5 mAh cm-2Depth of discharge) was able to stably cycle for 700 hours. Cycle life was improved by approximately 8-fold compared to untreated sodium. Wherein the test results of example 1 are shown in figure 4.
(2) The electrochemical impedance is greatly reduced and is only one tenth of that of an untreated sodium sheet (12 omega and 126 omega respectively); the exchange current density on the electrode is increased by 3 times (0.52 mA cm each)-2And 0.15 mA cm-2). Indicating a faster charge transfer process in the electrode and a lower sodium diffusion barrier. Referring to fig. 5, electrochemical impedance spectra (left) and Tafel curves (right) are shown after 10 cycles of charging and discharging in a symmetric cell test with a sodium cathode made in example 1.
(3) With Na3V2(PO4)3After the/C positive electrode is assembled into a full cell, the cell is under the high current density of 5C (1C = 117 mA g)-1) Specific capacity of 102 mAh g-1And exhibits a lower capacity fade (capacity fade of only 0.012% per cycle). The results of the full cell test for the sodium negative electrode of example 1 are shown in fig. 6.

Claims (8)

1. An ion-electron mixed conductive metallic sodium cathode, characterized in that: the metal sodium cathode consists of solid electrolyte and metal sodium, and is formed by melting and mixing solid electrolyte powder and metal sodium, wherein the metal sodium forms a matrix of the metal sodium cathode, and Na is constructed in the metal sodium matrix by the solid electrolyte+A conductive network, said solid electrolyte having a sodium ion conductivity higher than 10 at ambient temperature-5 S cm-1(ii) a The solid electrolyte is coated with SnO on the surface2NZSP particles of ZnO, Au or Ag, the NZSP having the formula Na3+xZr2Si2+xP1-xO12Therein is disclosed0 ≤ x ≤ 0.6。
2. The method for preparing the ion-electron mixed conductive metallic sodium cathode of claim 1, which mainly comprises the following steps:
1) synthesizing NZSP: synthesizing NZSP powder by a solution-assisted solid phase reaction method;
2) NZSP pretreatment: coating SnO on the surface of NZSP powder2Layer to obtain surface modified NZSP or SnO2@ NZSP powder, i.e., powder of the solid electrolyte;
3) preparing an electrode by melting and mixing metal sodium: and in a closed atmosphere protected by argon, melting and mixing the solid electrolyte powder and metal sodium to obtain the metal sodium cathode electrode.
3. The method for preparing the ion-electron mixed conductive metallic sodium cathode according to claim 2, wherein the method comprises the following steps: the step 1) of synthesizing NZSP is as follows: adding NaNO3And ZrO (NO)3)2Dissolving in distilled water to form a solution, and stirring while adding Si (OCH)2CH3)4And NH4H2PO4Adding into the solution; after drying, calcining the obtained powder at 900-1200 ℃ for 2-4 hours to obtain NZSP powder.
4. The method for preparing the ion-electron mixed conductive metallic sodium cathode according to claim 3, wherein the method comprises the following steps: wherein NaNO3And ZrO (NO)3)2And Si (OCH)2CH3)4And NH4H2PO4The amount of the reagent added is NZSP (sodium niobate) which is Na3+ xZr2Si2+xP1-xO12Wherein x is more than or equal to 0 and less than or equal to 0.6.
5. The method for preparing the ion-electron mixed conductive metallic sodium cathode according to claim 2, wherein the method comprises the following steps: the step 2) NZSP pretreatment comprises the following steps: SnCl2Dissolving in N, N-dimethylformamide to obtain 0.1-0.6 mol L-1SnCl of2A solution; adding NZSP powder synthesized in the step 1), stirring and mixing, drying the solution in a baking oven to powder, grinding the powder, and sintering the powder in a tubular furnace at 350-500 ℃ for 1-3 hours to obtain the SnO coated on the surface2The NZSP solid electrolyte powder of (1).
6. The method for preparing the ion-electron mixed conductive metallic sodium cathode according to claim 5, wherein the method comprises the following steps: SnCl in step 2)2The mass of the added NZSP powder is 5-20%.
7. The method for preparing the ion-electron mixed conductive metallic sodium cathode according to claim 2, wherein the method comprises the following steps: the step 3) of preparing the electrode by melting and mixing the metal sodium comprises the following steps: in a glove box filled with argon; coating the surface of the SnO obtained in the step 2) with SnO2Weighing NZSP solid electrolyte powder and sodium metal with a surface oxide layer cut off according to a certain proportion, then putting the powder into a nickel crucible, and heating the powder to 180-250 ℃; stirring to melt sodium and SnO2@ NZSP powder was mixed thoroughly; and after the mixture is cooled, punching the mixture into a wafer electrode to obtain the metal sodium cathode.
8. The method for preparing the ion-electron mixed conductive metallic sodium cathode according to claim 7, wherein the method comprises the following steps: wherein SnO2The mixing ratio of the @ NZSP powder to the sodium metal is 1:1-5 by mass.
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