CN111313087A - Electrolyte materials, sodium ion solid electrolytes and their applications and sodium ion solid state batteries - Google Patents

Abstract

The invention relates to the field of solid batteries, in particular to electrolyte materials, sodium ion solid electrolytes and sodium ion solid batteries formed therefrom. The composition of the electrolyte material is Na _3+2x Zr _{2- x} Ca _x Si ₂ PO ₁₂ , wherein x is 0.05-0.3. The sodium ion solid electrolyte includes an at least two-layer structure formed of the above electrolyte material, the at least two-layer structure including a dense layer and a porous layer on at least one side of the dense layer, the porous layer having a natriophilic porous surface. The sodium ion solid battery includes: an integrated metal Na negative electrode; a positive electrode; wherein, the integrated metal Na negative electrode is obtained by integrating the above-mentioned sodium ion solid electrolyte and metal Na, and the metal Na is located in the sodium ion solid in the pores of the electrolyte porous layer.

Description

Electrolyte materials, sodium ion solid electrolytes and their applications and sodium ion solid state batteries

technical field

The invention relates to the field of solid batteries, in particular to electrolyte materials, sodium ion solid electrolytes and sodium ion solid batteries formed therefrom.

Background technique

Compared with lithium-ion batteries that have been successfully commercialized, all-solid-state sodium batteries have attracted worldwide attention due to their excellent safety properties, higher energy density, and abundant sodium resources. In all-solid-state sodium batteries, the use of solid-state sodium-ion electrolytes instead of flammable organic liquid electrolytes greatly improves battery safety. The solid electrolyte also has the characteristics of high hardness, which can block sodium dendrites and avoid puncturing the electrolyte and causing a short circuit of the battery. Therefore, it is possible to use Na metal with high energy density as anode material in batteries.

At present, there are two main factors hindering the development and application of all-solid-state sodium batteries: the ionic conductivity of the solid electrolyte is low; the interface resistance between the solid electrolyte and the metal Na anode is large. Regarding the problem of large interface resistance, the prior art mainly reduces the interface resistance between the electrolyte and the sodium anode material by adding liquid electrolyte at the interface, introducing a polymer interface layer, and applying pressure. Although these methods have a certain effect on improving the interfacial resistance, they still cannot achieve long-term stable operation of all-solid-state batteries. In addition, the existing solid electrolytes are often fabricated into a simple flat-plate configuration, and the assembled full battery is still a three-layer structure.

Therefore, an electrolyte material with high sodium ion conductivity is urgently needed, and a solid electrolyte that can advantageously reduce the interfacial resistance between the electrolyte and the metallic Na anode is urgently needed, and the solid battery formed by the solid electrolyte has excellent battery performance.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to overcome the problem of low ionic conductivity of solid electrolytes in the prior art, and to provide an electrolyte material with high ionic conductivity.

The second purpose of the present invention is to overcome the problems of high interfacial resistance between the solid electrolyte and the metal Na negative electrode in the prior art solid battery and poor battery performance such as cycle performance forming a full battery, and to provide a sodium ion solid electrolyte and a sodium ion solid battery.

In order to achieve the above object, the first aspect of the present invention provides an electrolyte material, the composition of the electrolyte material is Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ , wherein x is 0.05-0.3.

A second aspect of the present invention provides a method for preparing the electrolyte material, the method comprising:

(1) Mix Na source, Zr source, Ca source, silicon source, P source and citric acid in a molar ratio of (3+2x):(2-x):x:2:1:(6-10) In the water-alcohol mixed solution, fully stir and dissolve to obtain mixture I;

(2) heating the mixture 1 until complete evaporation of water and alcohol to form a gel;

(3) drying, grinding and calcining the gel to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ powder.

A third aspect of the present invention provides a sodium ion solid electrolyte, comprising an at least two-layer structure formed of an electrolyte material, the at least two-layer structure comprising a dense layer and a porous layer on at least one side of the dense layer, the porous layer having Sodium-philic porous surface, the electrolyte material is the electrolyte material described in the first aspect of the present invention.

The fourth aspect of the present invention provides a method for preparing the solid electrolyte according to the third aspect of the present invention, comprising:

(a) The base layer is formed from pure electrolyte material; the mixture II is obtained by mixing the electrolyte material and the pore-forming agent in a mass ratio of 1:(0.5-5), and the mixture II is placed on at least one side of the base layer to form an outer layer. The base layer and the outer layer apply pressure to obtain a green body;

(b) sintering the green body in air at 1000-1400° C. for 0.5-30 h to obtain a structure comprising a porous layer and a dense layer;

(c) modifying the porous layer obtained in step (b) with SnO ₂ and/or Bi ₂ O ₃ .

The fifth aspect of the present invention provides the application of the sodium ion solid electrolyte of the third aspect of the present invention in the field of solid batteries.

A sixth aspect of the present invention provides a sodium ion solid state battery, comprising:

Integrated metal Na negative electrode;

positive electrode;

Wherein, the integrated metal Na negative electrode is obtained by integrating a sodium ion solid electrolyte and metal Na, the sodium ion solid electrolyte is the sodium ion solid electrolyte described in the third aspect of the present invention, and the metal Na is located in the sodium ion solid electrolyte. in the pores of the solid electrolyte porous layer.

The seventh aspect of the present invention provides the preparation method of the above-mentioned sodium ion solid state battery, comprising:

(1) metal Na is placed on the surface of the sodium ion solid electrolyte porous layer, heated to melt the metal Na, the molten metal Na penetrates into the porous layer, and is integrated with the sodium ion solid electrolyte to form an integrated metal Na negative electrode;

(2) Assembling the integrated metal Na negative electrode and the positive electrode.

The invention provides an electrolyte material with high ionic conductivity, and uses the electrolyte material to form a sodium ion solid electrolyte (including a dense layer and a porous layer) similar to a "sandwich" structure, which can effectively reduce the amount of electrolyte and metal Na The interface resistance of the solid electrolyte can reach 175Ω·cm ^-2 , and the solid battery formed by this electrolyte can achieve higher specific capacity and good cycle performance.

Description of drawings

FIG. 1 shows the X-ray diffraction (XRD) patterns of the electrolyte materials prepared in Preparation Examples 1-5 and Comparative Preparation Example 4, wherein (2) is a partial enlarged view of 2θ of 5-35 degrees in (1).

FIG. 2 is a graph showing the relationship between the electrical conductivity and temperature of the electrolyte materials prepared in Preparation Examples 1-5 and Comparative Preparation Example 4. FIG.

FIG. 3 is a current-voltage change diagram measured by cyclic voltammetry when the electrolyte material A1 of the present invention is made into a flat-plate electrolyte sheet, and a stainless steel sheet|electrolyte|metal sodium battery is assembled.

FIG. 4 is a graph showing the variation of the voltage of the symmetrical battery E1 with cycle time according to Example 10. FIG.

FIG. 5 is a graph of impedance changes of the symmetrical battery E1 described in Example 10 at different cycle times.

FIG. 6 is a graph showing the change of the specific capacity of charge and discharge with the number of cycles, and the graph of the change of the Coulomb efficiency with the number of cycles, of the full battery C1 prepared by the method described in Example 11.

FIG. 7 is a graph showing the impedance change of the full battery C1 prepared by the method described in Example 11 under different cycle times.

FIG. 8 is a schematic diagram of the fabrication of a sandwich-structure symmetrical battery.

Fig. 9(1) is an optical microscope photo of the sodium ion solid electrolyte S1 according to the present invention when Na is poured into it; Fig. 9(2) is an optical microscope photo of the sodium ion solid electrolyte D4 of the comparative example 4 when Na is poured into it.

Figure 10 shows the element energy spectrum of the porous layer after the metal Na is poured into the porous layer of the sodium ion solid electrolyte S1 of the present invention, wherein (1) is the element distribution of Na; (2) is Zr The element distribution map of ; (3) is the element distribution map of P.

FIG. 11 shows a schematic structural diagram of the sodium ion solid electrolyte of the present invention assembled into an all-solid-state sodium ion battery.

Detailed ways

The endpoints of ranges and any values disclosed herein are not limited to the precise ranges or values, which are to be understood to encompass values proximate to those ranges or values. For ranges of values, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values can be combined with each other to yield one or more new ranges of values that Ranges should be considered as specifically disclosed herein.

A first aspect of the present invention provides an electrolyte material, wherein the composition of the electrolyte material is Na _3+2x Zr _{2- x} Ca _x Si ₂ PO ₁₂ , wherein x is 0.05-0.3.

According to the present invention, the electrolyte material is a Ca-doped NASICON type electrolyte material, and in the composition structure of the electrolyte material, x may be 0.28 or 0.3, and any two of the above values stated as any value in the range. Preferably, x is 0.05-0.25.

A second aspect of the present invention provides a method for preparing the electrolyte material, the method comprising:

(1) Mix Na source, Zr source, Ca source, silicon source, P source and citric acid in a molar ratio of (3+2x):(2-x):x:2:1:(6-10) In the water-alcohol mixed solution, fully stir and dissolve to obtain mixture I;

(2) heating the mixture 1 until complete evaporation of water and alcohol to form a gel;

(3) drying, grinding and calcining the gel to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ powder.

Preferably, the method includes:

(1) Mix Na source, Zr source, Ca source, silicon source, P source and citric acid in a molar ratio of (3+2x):(2-x):x:2:1:(6-10) In the water-alcohol mixed solution, fully stir and dissolve to obtain mixture I;

(2) heating the mixture I to 50-90° C. until the water and alcohol are completely evaporated to form a gel;

(3) drying and grinding the gel, and calcining at 500-700 ℃ for 2-8 hours, and then heating up to 900-1000 ℃ and calcining for 8-16 hours; obtaining Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ powder.

The Na source can be a water-soluble compound of Na, preferably selected from at least one of sodium acetate, sodium nitrate, sodium carbonate and sodium hydroxide; the Zr source can be a water-soluble compound of Zr, preferably selected from At least one of zirconium oxynitrate hydrate, zirconium trichloride, zirconium acetylacetonate and zirconium acetate; the Ca source can be a water-soluble compound of Ca, preferably selected from calcium nitrate, calcium hydroxide, calcium acetate and chloride at least one of calcium. In this context, "water-soluble compounds" are to be understood as compounds which are soluble or sparingly soluble in deionized water. The Si source can be silicate, silicic acid, silicate or silicone oil, preferably the Si source is selected from at least one of ethyl orthosilicate, propyl orthosilicate, silicic acid and silicone oil. The P source may be phosphoric acid and/or phosphate, preferably the P source is selected from at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid.

In step (1), the Na source, Zr source, Ca source, silicon source, P source and citric acid in a molar ratio of (3+2x):(2-x):x:2:1:(6- 10), preferably in a molar ratio of (3+2x): (2-x): x: 2: 1: 8 mixed in a water-alcohol mixed solution, fully stirring and dissolving to obtain mixture I, wherein x is 0.05-0.3 . The water-alcohol mixed solution is a mixture of water and alcohol, and the alcohol is a monohydric or polyhydric alcohol that is miscible with water, such as ethanol, methanol, propanol, and the like. The volume ratio of water and alcohol in the water-alcohol mixed solution may be a ratio known in the prior art, for example, may be 1:1, 1:2, 1:0.5, 1:3, and the like. Preferably, the mixing process is accompanied by agitation, for example, with sufficient stirring for 1-20 h, and stirring for 6-18 h.

In step (2), the mixture I is heated to 50-90°C, preferably 60-90°C, until the water and alcohol are completely evaporated and a gel is formed.

In step (3), the gel is dried, ground, and calcined at 500-700°C for 2-8h, preferably 550-650°C for 4-7h; then heated to 900-1000°C for 8 hours -16h; Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ powder was obtained. Preferably, the drying conditions include: a temperature of 100-150° C. and a time of 8-16 h.

In a preferred embodiment, the method includes:

(1) CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ H ₂ PO ₄ and citric acid in a molar ratio (3+2x): (2-x): x: 2: 1: 8 is dissolved in a mixed solution of ethanol and water, fully stirred for 12h to obtain mixture I;

(2) heating mixture I to 50-90° C. until the deionized water and ethanol are completely evaporated to form a gel;

(3) The gel was dried at 120°C for 12h, fully ground, calcined at 600°C for 6h, and then heated to 950°C for 12h to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ powder.

The particle size of the electrolyte material prepared by this method is smaller, and the distribution of elements is more uniform.

A third aspect of the present invention provides a sodium ion solid electrolyte, comprising an at least two-layer structure formed of an electrolyte material, the at least two-layer structure comprising a dense layer and a porous layer on at least one side of the dense layer, the porous layer having The sodium-philic porous surface, the electrolyte material is the electrolyte material described in the first aspect of the present invention.

According to the sodium ion solid electrolyte of the present invention, the dense layer can effectively separate the positive and negative electrodes, suppress sodium dendrites, and prevent the dendrites from penetrating the electrolyte to cause a short circuit of the battery; the porous layer can be used as a carrier for the sodium negative electrode, and the porous skeleton forms a three-dimensional The ion transport network increases the contact area and leaves a void for the volume change during the deposition/stripping of metallic Na, avoiding the increase in interface resistance caused by interface fracture.

According to the sodium ion solid electrolyte of the present invention, in order to pour metal Na into the porous layer and ensure good contact between the metal Na and the electrolyte, the porous layer has a natriophilic porous surface, and the "natriophilic porous surface" should be It is understood as a porous surface that can be easily combined with metallic Na. The natriophilic porous surface can be obtained by technical means and/or methods known in the art. Preferably, the natriophilic porous surface is prepared by modifying the porous layer with SnO ₂ and/or Bi ₂ O ₃ . The modification method can be a method known in the art, for example, the porous layer can be immersed in a mixed solution of SnCl ₄ aqueous solution and concentrated HCl. If the surface of the porous layer is not provided with a natriophilic porous surface, when metallic Na is poured into the porous layer, the metallic Na cannot enter effectively. As shown in Fig. 9(2), the surface of the porous layer is not modified with sodium affinity, and the metal Na cannot effectively enter the pores of the porous layer. The entry of sodium can be verified by the microscopic morphology and element distribution (SU scanning electron microscope and incidental characteristic X-ray energy dispersive spectrometer) of the cross-section of the porous layer region. As shown in FIG. 10 , it can be seen that a large amount of metallic Na enters the pores of the porous layer by removing the existing regions of Zr and P elements from the existing regions of Na element.

Preferably, in the sodium ion solid electrolyte, the thickness of the dense layer is 1-1000 μm, the thickness of the porous layer is 1-1000 μm, the porosity of the porous layer is 10-80%, and the average pore diameter is 2-50 μm. More preferably, the thickness of the dense layer is 10-300 μm, the thickness of the porous layer is 10-300 μm, the porosity of the porous layer is 40-60%, and the average pore diameter is 5-20 μm.

According to the sodium ion solid electrolyte of the present invention, the at least two-layer structure in the sodium ion solid electrolyte can be prepared by technical means known in the art, for example, by co-pressing technology.

Preferably, the co-pressing technique includes the following steps:

(a) The base layer is formed from pure electrolyte material; Mixture II is obtained by mixing electrolyte material and pore-forming agent in a mass ratio of 1:(0.5-5); Mixture II is placed on at least one side of the base layer to form an outer layer. The base layer and the outer layer apply pressure to obtain a green body;

(b) sintering the green body in air at 1000-1400° C. for 0.5-30 h;

Preferably, the pore-forming agent is selected from at least one of starch, polymethyl methacrylate powder, spherical graphite and polystyrene powder, and the average particle size of the pore-forming agent is 2-50 μm.

In the application process, the interface impedance of the sodium ion solid electrolyte of the present invention and the metal Na and the cycle performance of the sodium ion solid electrolyte of the present invention in the application process can be detected by using a symmetrical battery as a test sample. The symmetric cell is fabricated in a similar manner to the sodium ion solid electrolyte of the present invention, and has a three-layer "sandwich structure", ie, the same two-layer porous layer is formed on both sides of the dense layer. In the test process, a certain current is given to the symmetrical battery, and the voltage and impedance of the symmetrical battery are tested with the time of the cycle (the current direction changes, and the current direction changes once is one cycle) time, so as to reflect the sodium ion solid of the present invention in the application process. Interfacial impedance between electrolyte and metal Na and cycle performance of the sodium ion solid electrolyte of the present invention.

A fourth aspect of the present invention provides a method for preparing the above-mentioned solid electrolyte, comprising the following steps:

(a) The base layer is formed from pure electrolyte material; the mixture II is obtained by mixing the electrolyte material and the pore-forming agent in a mass ratio of 1:(0.5-5), and the mixture II is placed on at least one side of the base layer to form an outer layer. The base layer and the outer layer apply pressure to obtain a green body;

(b) sintering the green body in air at 1000-1400° C. for 0.5-30 h to obtain a structure comprising a porous layer and a dense layer;

(c) modifying the porous layer obtained in step (b) with SnO ₂ and/or Bi ₂ O ₃ .

More preferably, the method includes the following steps:

(a) Mix the electrolyte material and the pore-forming agent in a mass ratio of 1:(0.5-5) to obtain the mixture II, and disperse the mixture II and the pure electrolyte material in the mold in turn, and the mixture II is located in the layer formed by the pure electrolyte material. At least one side, applying pressure to the mold to obtain a green body;

(b) sintering the green body in air at 1000-1400° C. for 0.5-30 h to obtain a structure comprising a porous layer and a dense layer;

(c) modifying the porous layer obtained in step (b) with SnO ₂ and/or Bi ₂ O ₃ .

Preferably, the applied pressure is in the range of 100-140 MPa.

Preferably, the pore-forming agent is selected from at least one of starch, polymethyl methacrylate powder, spherical graphite and polystyrene powder, and the average particle size of the pore-forming agent is 2-50 μm. In the process of preparing sodium ion solid electrolyte, the pore-forming agent with smaller particle size forms pores with smaller pore size, which is beneficial to increase the contact area between the solid electrolyte and metal Na and reduce the interface resistance. However, the average particle size of the pore-forming agent is too small, for example, less than 2 μm, which is not conducive to the preparation of porous networks with continuous pores and electrolyte skeletons, and it is difficult for molten metal Na to penetrate into the pores.

Preferably, the mass ratio of the electrolyte material to the pore-forming agent is 1:(0.5-2), for example, it may be 1:1.5.

According to the sodium ion solid electrolyte of the present invention, in order to improve the wettability of metal Na and the sodium ion solid electrolyte and enhance the interface bonding, preferably, the porous layer is modified to obtain a natriophilic porous surface modified with SnO ₂ . . Preferably, the porous layer is modified by dropwise adding a mixture of _SnCl4 aqueous solution and concentrated HCl to the porous layer and drying.

According to the sodium ion solid electrolyte of the present invention, in step (c), the porous layer is modified with SnO ₂ and/or Bi ₂ O ₃ , and SnO ₂ and/or Bi ₂ O ₃ required for the modification process The amount can be selected as required, as long as the porous layer can have a natriophilic porous surface.

The sodium ion solid electrolyte of the invention not only ensures the close bonding between the metal Na and the surface of the sodium ion solid electrolyte, but also greatly expands the contact area and greatly reduces the interface resistance between the metal Na and the electrolyte in the all-solid-state sodium battery.

The fifth aspect of the present invention provides the application of the sodium ion solid electrolyte of the present invention in the field of solid batteries.

A sixth aspect of the present invention provides a sodium ion solid state battery, comprising:

Integrated metal Na negative electrode;

positive electrode;

Wherein, the integrated metal Na negative electrode is obtained by integrating sodium ion solid electrolyte and metal Na, the sodium ion solid electrolyte is the sodium ion solid electrolyte described in the third aspect of the present invention, and the metal Na is located in the place where the sodium ion solid electrolyte is located. Included in the pores of the porous layer.

According to the sodium ion solid state battery of the present invention, the positive electrode comprises a positive electrode material, and the positive electrode material can be selected according to the prior art, preferably, the positive electrode material is selected from Na ₃ V ₂ (PO ₄ ) ₃ /C , NaMnO ₂ , NaFePO ₄ , Na _{2/ 3} Ni _1/3 Mn _1/3 Ti _1/3 O ₂ and Na ₃ V ₂ (PO ₄ ) ₂ F ₃ and Na ₃ V ₂ (PO ₄ ) ₂ O ₂ F at least one of them.

In one embodiment, the positive electrode is a positive electrode sheet.

The seventh aspect of the present invention provides the preparation method of the above-mentioned sodium ion solid state battery, comprising:

(1) metal Na is placed on the surface of the porous layer included in the sodium ion solid electrolyte and heated, so that the metal Na is melted and penetrated into the porous layer to form the integrated metal Na negative electrode;

(2) Assembling the integrated metal Na negative electrode and the positive electrode.

Preferably, in step (1), heating to 100-300° C. to melt Na metal, and the melting process is carried out in an inert atmosphere.

The electrolyte material of the present invention has high ionic conductivity, for example, can reach 1.67×10 ^-3 S cm ^-1 . The sodium ion solid electrolyte of the present invention can effectively reduce the interface resistance between the sodium ion solid electrolyte and the metal Na negative electrode. The integrated solid battery formed by the sodium ion solid electrolyte of the present invention has high specific capacity and excellent cycle performance.

The present invention will be described in detail below through preparation examples and examples.

Preparation Examples and Comparative Preparation Examples are used to illustrate electrolyte materials.

Preparation Example 1

This example is intended to illustrate the preparation of the electrolyte material of the present invention.

CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ H ₂ PO ₄ and citric acid in molar ratio (3+2x): (2-x ): x: 2: 1: 8 (x=0.1) was dissolved in a mixed solution of 250 mL of ethanol and 250 mL of deionized water, and fully stirred for 12 h. The solution was heated to 80°C with stirring until the deionized water and alcohol were completely evaporated and a gel formed. The gel was dried at 120°C for 12h, fully ground, then calcined at 600°C for 6h in a muffle furnace, and then heated to 950°C for 12h to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A1 (x=0.1).

Preparation Example 2

This example is intended to illustrate the preparation of the electrolyte material of the present invention.

CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ H ₂ PO ₄ and citric acid in molar ratio (3+2x): (2-x ): x: 2: 1: 6 (x=0.05) was dissolved in a mixed solution of 250 mL of ethanol and 250 mL of deionized water, and fully stirred for 6 h. The solution was heated to 90°C with stirring until the deionized water and alcohol were completely evaporated and a gel formed. The gel was dried at 100 °C for 16 h, fully ground, then calcined in a muffle furnace at 550 °C for 7 h, and then heated to 1000 °C for 16 h to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A2(x=0.05).

Preparation Example 3

This example is intended to illustrate the preparation of the electrolyte material of the present invention.

CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ H ₂ PO ₄ and citric acid in molar ratio (3+2x): (2-x ): x: 2: 1: 10 (x=0.25) was dissolved in a mixed solution of 250 mL of ethanol and 250 mL of deionized water, and fully stirred for 18 h. The solution was heated to 60°C with stirring until the deionized water and alcohol were completely evaporated and a gel formed. The gel was dried at 150°C for 8h, fully ground, then calcined at 650°C for 4h in a muffle furnace, and then heated to 950°C for 16h to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A3 (x=0.25).

Preparation Examples 4 and 5

The electrolyte material of the present invention was prepared by referring to the method described in Preparation Example 1, except that CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ were used The molar ratio of H ₂ PO ₄ and citric acid is (3+2x): (2-x): x: 2: 1: 8 (x=0.15, 0.2), and finally Na _3+2x Zr _2-x Ca are obtained respectively _x Si ₂ PO ₁₂ sample powders A4 (x=0.15), A5 (x=0.2).

Preparation Example 6

NaNO ₃ , ZrCl ₃ , calcium hydroxide, silicic acid, phosphoric acid and citric acid were dissolved in 250 mL methanol and 250 mL in molar ratio (3+2x):(2-x):x:2:1:10 (x=0.3) The mixed solution of deionized water was fully stirred for 20h. The solution was heated to 50°C with stirring until the deionized water and alcohol were completely evaporated and a gel formed. The gel was dried at 150 °C for 8 hours, fully ground, then calcined at 700 °C for 2 hours in a muffle furnace, and then heated to 1000 °C for 8 hours to obtain Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A6 (x=0.3).

Comparative Preparation Example 1

Na ₂ CO ₃ , NH ₄ H ₂ PO ₄ , ZrO ₄ , SiO ₂ , and CaO were ball-milled, and kept at 170-900° C. for 4 hours and 1200° C. for 16 hours in an atmosphere of flowing oxygen. Finally, Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder B1 (x=0.1) was obtained.

Comparative Preparation Example 2

Electrolyte materials were prepared according to the method described in Preparation Example 1, except that CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ H ₂ PO ₄ and lemon The molar ratio of acid (3+2x): (2-x): x: 2: 1: 8 (x=0.4), the rest is the same as in Preparation Example 1, and finally Na _3+2x Zr _2-x Ca _x Si ₂ is obtained PO ₁₂ sample powder B2 (x=0.4).

Comparative Preparation Examples 3 and 4

Electrolyte materials were prepared according to the method described in Preparation Example 1, except that CH ₃ COONa, ZrO(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ ·4H ₂ O, ethyl orthosilicate, NH ₄ H ₂ PO ₄ and lemon The molar ratio of acid (3+2x): (2-x): x: 2: 1: 8 (x=0.04, 0), the rest is the same as in Preparation Example 1, and finally Na _3+2x Zr _2-x Ca _{x is} obtained Si ₂ PO ₁₂ sample powders B3 (x=0.04), B4 (x=0).

Examples 1-9 and comparative examples 1-4 are used to illustrate the sodium ion solid electrolyte

Example 1

The Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A1 (x=0.1) prepared in Preparation Example 1 and starch (the average particle size of starch granules is 10 μm) were mixed in a mortar at a mass ratio of 1:1.5. Grind and mix well. 0.025 g of the mixed powder and 0.1 g of pure Na _{3 + 2x} Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder were sequentially and uniformly placed in a stainless steel cylindrical mold to form two layers respectively. Then a pressure of 120 MPa was applied to the two layers of sample powder in the mold to obtain a green body. After sintering at 1230 °C for 5 h in air, two layers of solid electrolytes with a similar "sandwich" structure were obtained, in which the thickness of the dense layer was 240 μm and the thickness of the porous layer was 80 μm. Prepare 50 mL of 0.5M SnCl ₄ aqueous solution, and add 10 mL of concentrated HCl to prevent hydrolysis. The solution was added dropwise to the porous layer, dried, and then treated in air at 500 °C for 1 h to obtain a sodium-ion solid electrolyte S1 (the porous layer has a natriophilic porous surface) whose porous layer was modified by SnO ₂ . The porous layer has a porosity of 60 %, the average pore size is 10 μm.

Example 2

The Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A3 (x=0.25) prepared in Preparation Example 3 and starch (average particle size of starch granules 5 μm) were mixed in a mortar at a mass ratio of 1:1. Grind and mix well. 0.015 g of the mixed powder and 0.08 g of pure Na _{3 + 2x} Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder were uniformly dispersed in a stainless steel cylindrical mold in turn to form two layers respectively. Then a pressure of 120 MPa was applied to the two layers of sample powder in the mold to obtain a green body. After sintering at 1200 °C for 2 h in air, two layers of solid electrolytes similar to "sandwich" structures were obtained, in which the thickness of the dense layer was 200 μm and the thickness of the porous layer was 50 μm. Prepare 50 mL of 0.5M SnCl ₄ aqueous solution, and add 10 mL of concentrated HCl to prevent hydrolysis. The solution was added dropwise to the porous layer, dried, and then treated in air at 500 °C for 1 h to obtain a sodium-ion solid electrolyte S2 modified by SnO ₂ on the surface of the porous layer (the porous layer has a natriophilic porous surface). The porosity of the porous layer is 50%, and the average pore size is 5 μm.

Example 3

The Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A5 (x=0.2) prepared in Preparation Example 5 and spherical graphite (the average particle size of the spherical graphite particles is 50 μm) were prepared in a mass ratio of 1:0.8. Grind in a mortar and mix well. 0.05 g of the mixed powder and 0.2 g of pure Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder were uniformly dispersed in a stainless steel cylindrical mold in turn to form two layers respectively. Then a pressure of 120 MPa was applied to the two layers of sample powder in the mold to obtain a green body. After sintering in air at 1150 °C for 10 h, two layers of solid electrolytes similar to "sandwich" structures were obtained, in which the thickness of the dense layer was 300 μm and the thickness of the porous layer was 100 μm. Prepare 50 mL of 0.5M SnCl ₄ aqueous solution, and add 10 mL of concentrated HCl to prevent hydrolysis. The solution was added dropwise to the porous layer, dried, and treated in air at 500 °C for 1 h to obtain a sodium-ion solid electrolyte S3 (the porous layer has a natriophilic porous surface) whose surface was modified by SnO ₂ . 40%, and the average pore size is 50 μm.

Example 4

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that the mass ratio of Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder to starch was 1:6, and the rest were the same as in Example 1, Finally, the sodium ion solid electrolyte S4 was obtained, the porosity of the porous layer was 80%, and the average pore diameter was 10 μm.

Example 5

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that the electrolyte material used was the sample powder A2 (x=0.05).

Example 6

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that the mass ratio of Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder to starch was 1:0.5, and the rest were the same as in Example 1, Finally, the sodium ion solid electrolyte S6 was obtained, the porosity of the porous layer was 20%, and the average pore diameter was 10 μm.

Example 7

The sodium ion solid electrolyte was prepared according to the method described in Example 1. The difference was that the average particle size of the starch used was 80 μm. %, the average pore size is 80 μm.

Example 8

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that the quality of mixture I and mixture II was adjusted, so that the obtained sodium ion solid electrolyte S8 similar to the "sandwich" structure, in which the thickness of the dense layer was 500 μm, porous The thickness of the layers is 500 μm.

Example 9

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that 50 mL of 0.5M Bi(NO ₃ ) ₃ aqueous solution was prepared, and 10 mL of concentrated HNO ₃ was added to prevent hydrolysis. The solution was added dropwise to the porous layer, dried, and treated in air at 500°C for 1 h, so that the porous layer had a Na-philic porous surface modified by Bi ₂ O ₃ , which was designated as sodium ion solid electrolyte S9.

Comparative Example 1

The Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ powder A1 (x=0.1) prepared in Preparation Example 1 was formed by dry pressing, pressed into a sheet under a pressure of 120MPa, sintered at 1230°C for 5h, and sandpaper was used. It was polished to a thickness of 300 μm to obtain a sodium ion solid electrolyte sheet D1.

Comparative Example 2

The Na _3+2x Zr _2-x Ca _x Si ₂ PO ₁₂ sample powder A1 (x=0.1) prepared in Preparation Example 1 was formed by dry pressing, pressed into a sheet under a pressure of 120MPa, and sintered at 1230°C for 5h , to obtain a solid electrolyte sheet, which was polished with sandpaper to a thickness of 300 μm. Prepare 50 mL of 0.5M SnCl ₄ aqueous solution, and add 10 mL of concentrated HCl to prevent hydrolysis. The solution was added dropwise to the surface of the solid electrolyte, dried, and treated in air at 500 °C for 1 h to obtain the sodium ion solid electrolyte D2 whose surface was modified by SnO ₂ .

Comparative Example 3

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that the electrolyte material used was the sample powder B1 obtained in Comparative Preparation Example 1, and the rest were the same as in Example 1, and finally the sodium ion solid electrolyte D3 was obtained.

Comparative Example 4

The sodium ion solid electrolyte was prepared according to the method described in Example 1, except that the SnO ₂ modification on the surface of the porous layer was not carried out, and finally the sodium ion solid electrolyte D4 was obtained.

Example 10

This example is used to illustrate a symmetrical cell formed from a sodium ion solid electrolyte (for testing the sodium ion solid electrolyte of the present invention).

According to the methods provided in Examples 1-9 and Comparative Example 3, respectively, using the respective mixed powders (the same amount), a porous layer was formed on each side of the dense layer to prepare a three-layer "sandwich structure" (porous layer). /dense layer/porous layer), and then perform sodium-philic modification according to the method described in each, and pour sodium into each porous layer, such as the preparation process shown in FIG. 8 . Afterwards, 2032 button battery shells were used to assemble symmetrical batteries in an Ar gas atmosphere glove box, which were denoted as symmetrical batteries E1-E9 and DE3, respectively.

A flat-plate solid electrolyte was prepared according to the method described in Comparative Example 1, and Na metal was pressed on the surface of the solid electrolyte. Symmetrical cells were assembled in an Ar gas atmosphere glove box using a 2032 coin cell case, denoted as DE1.

The SnO ₂ modified flat solid electrolyte was prepared according to the method described in Comparative Example 2. Metal Na was placed on the surface of the solid electrolyte, heated to 250 ° C to melt the metallic Na, and then combined with the flat solid electrolyte after cooling, using a 2032 button battery shell in Ar gas Symmetric cells were assembled in the atmosphere glove box, denoted as DE2.

According to the method described in Comparative Example 4, a three-layer "sandwich structure" sodium ion solid electrolyte without _SnO modification was prepared. The metallic Na was placed on the surface of the sodium ion solid electrolyte and heated to 250 °C to melt the metallic Na, but the Na could not all enter the porous structure. A 2032 button battery case was used to assemble a symmetrical battery in an Ar gas atmosphere glove box, denoted as DE4.

Example 11

This example is used to illustrate a full cell assembled from a solid electrolyte.

The solid electrolytes prepared in Examples 1-9 and Comparative Examples 1-4 were assembled into a full battery according to the following method:

The preparation method of the integrated metal Na anode: the metal Na is placed on the surface of the solid electrolyte porous layer, heated to 250 ° C, and the molten metal Na automatically penetrates into the porous layer by capillary action, and integrates with the porous electrolyte to form an integrated metal Na negative electrode.

Preparation of Na ₃ V ₂ (PO ₄ ) ₃ /C cathode material: NaH ₂ PO ₄ , NH ₄ VO ₃ and citric acid were dissolved in deionized water in a molar ratio of 3:2:2, and stirred thoroughly for 2 h. The solution was heated to 70°C until the water evaporated completely and a gel formed. The gel was dried at 120 °C for 12 h, and fully ground to obtain a powdery precursor. Then calcined at 800℃ for 8h in Ar gas atmosphere to obtain Na ₃ V ₂ (PO ₄ ) ₃ /C cathode material.

Preparation of positive electrode sheet: Na ₃ V ₂ (PO ₄ ) ₃ /C, SP conductive carbon black (Alfar, 99.9%), succinonitrile (Aladdin, 99%), polyethylene oxide (Aladdin, Mw 100000) and high Sodium chlorate (Aladdin, 99%) was added to acetonitrile according to a mass ratio of 6:1:1.5:0.5:1, stirred well to obtain a uniform slurry, and coated on aluminum foil. Then vacuum-dried at 50° C. for 24 h to obtain a positive electrode sheet.

Full cell assembly: PEO (0.05 g), SCN (0.15 g) and NaClO ₄ (0.1 g) were dissolved in 5 mL of acetonitrile and fully stirred for 12 h to obtain a polymer electrolyte solution. 4 μL of polymer electrolyte solution was dropped on the surface of the positive electrode sheet and dried in vacuum for 4 h to reduce the interface resistance. The positive electrode sheet was attached to one side of the dense layer, and assembled in an Ar gas atmosphere glove box using a 2032 button battery case, wherein the positive electrode sheet was in contact with the solid electrolyte dense layer, and finally the full cells C1-C9, DC1-DC4 were formed , the structure of the full cell is shown in Figure 11.

test case

1. Structural characterization of electrolyte materials

The structures of the electrolyte materials A1-A6 were characterized by X-ray diffraction, and the results are shown in Figure 1. By comparing the XRD patterns of samples x=0, 0.05, 0.1, 0.15, and 0.2, it is found that they are all monoclinic structures without other impurities (including ZrO ₂ ).

2. Test of ionic conductivity

The ionic conductivity of the electrolyte materials A1-A6 and B1-B3 was tested by the AC impedance method. Specifically, the ionic conductivity of the electrolyte material was tested by the following methods:

Through dry pressing, the electrolyte material powder samples were pressed into sheets, and sintered at 1250 °C for 5 h to obtain dense electrolyte sheets (the sizes of various electrolyte materials were the same). The dense electrolyte sheet was used as the blocking electrode, and the AC impedance spectrum was obtained by testing under the bias voltage of 10mV in the frequency range of 1MHz-1Hz. The ohmic impedance R of the solid electrolyte is obtained by fitting, and the ionic conductivity is calculated according to the following formula.

σ=L/(S×R),

where σ is the conductivity, S is the electrolyte cross-sectional area, and L is the electrolyte thickness.

The test results are shown in Figure 2 and Table 1.

Table 1

Electrolyte material Ionic conductivity (S/cm) A6(x=0.3) 6.21×10^-4 B1 (x=0.1 prepared by dry method) 2.09×10^-4 B2(x=0.4) 1.68×10^-4 B3(x=0.04) 5.03×10^-4

3. Electrochemical stability of electrolyte materials

Using metallic Na as the reference electrode and stainless steel sheet as the counter electrode, using x=0.1 electrolyte material to prepare a flat-plate electrolyte sheet, assembling a stainless steel sheet|electrolyte|metal Na battery, using cyclic voltammetry, in the range of -1V to 7V , the scanning speed is 5mV/s, and the electrochemical stability window of the electrolyte material is tested. The test results are shown in Figure 3.

4. Symmetrical battery performance test

The three-layer "sandwich structure" symmetrical battery prepared according to the method described in Example 10 (for example, corresponding to Example 1) was subjected to a constant current charge-discharge test on a battery tester (LAND CT2001A). The test results are shown in Figure 4 . Figure 5 shows the impedance changes of the symmetrical battery after different cycles were tested with an AC impedance meter. Similarly, the three-layer "sandwich structure" symmetrical batteries corresponding to Examples 2-9 and Comparative Examples 1-4 were subjected to constant current charge-discharge test and AC impedance test, and the test results are shown in Table 2.

Table 2

"-" in Table 2 indicates that the interface impedance is too large, so that the battery cannot be cycled or 300 cycles cannot be achieved, so the corresponding data cannot be measured.

5. Full battery performance test

The full battery C1 formed in Example 11 was subjected to a constant current charge-discharge test on a battery tester (LAND CT2001A), and the test results are shown in FIG. 6 . Figure 7 shows the impedance change of the full battery after different cycles were tested with an AC impedance meter. Similarly, the full cells C2-C9 and DC1-DC4 formed in Example 11 were subjected to constant current charge-discharge test and AC impedance test, and the test results are shown in Table 3.

table 3

"-" in Table 3 indicates that the interface impedance is too large, so that the battery cannot be cycled or 300 cycles cannot be achieved, so the corresponding data cannot be measured.

It can be seen from the results in Fig. 2 and Fig. 3 that the electrolyte material of the present invention has high ionic conductivity and is electrochemically stable in a wide voltage range (eg, 0-7V).

The "sandwich structure"-like solid electrolyte formed by the electrolyte material of the present invention effectively reduces the interfacial resistance between the negative electrode metal Na and the electrolyte. The natriophilic surface enhances the binding of metallic Na to the solid electrolyte. The porous structure builds a three-dimensional ion conduction network, increases the contact area between metallic Na and electrolyte, reduces the local current density, and the porous structure reserves space for the volume change during the deposition/stripping of metallic Na, avoiding internal stress damage the battery structure. Corresponding to the symmetric battery of the solid electrolyte described in Examples 1-9, based on the Ca-doped solid electrolyte with x=0.05-0.25, by constructing a three-dimensional porous structure and carrying out sodium-philic surface modification, a lower interface impedance was obtained. Data As shown in Table 2 and Figures 4 and 5. In particular, the symmetric battery with the solid electrolyte described in Example 1 can be cycled for 600 h at a current density of 0.1-0.3 mA·cm ^-2 (as shown in Figure 4), and maintains a stable interfacial impedance of 175 Ω·cm ^-2 (as shown in Figure 4). shown in Figure 5). Symmetric cells corresponding to the electrolytes described in Comparative Examples 1-4 have significantly larger interfacial impedances, for example, corresponding to the electrolytes described in Comparative Example 1, without the three-dimensional porous structure and the natriophilic surface modification, the interfacial impedance reaches 10000 Ω·cm ⁻² . Although the natriophilic surface modification was carried out in Comparative Example 2, there was no three-dimensional porous structure, and the interface impedance was still as high as 906Ω·cm ^-2 . Comparative Example 4, although it has a three-dimensional porous structure, has no sodium-philic surface modification, and the interface impedance reaches 9506Ω·cm ^-2 . In Comparative Example 3, due to the low conductivity of the electrolyte material obtained by the preparation method, as shown in Table 1, the interface impedance reaches 709Ω·cm ⁻² .

The integrated solid-state battery assembled with the "sandwich structure" solid electrolyte has a high specific capacity and excellent cycle performance, and realizes the long-term stable operation of the all-solid-state sodium battery under high current density at room temperature. 500 cycles at 1C (as shown in Figure 6). The solid-state battery can suppress sodium dendrites and realize the application of metal Na anode, which greatly promotes the improvement of the safety and energy density of all-solid-state batteries. Compared with DC1, the electrolyte does not have a porous structure and a natriophilic surface; DC2, the electrolyte does not have a porous structure; DC3, the conductivity of the electrolyte material is low, and DC4, does not have a natriophilic modified surface. Batteries such as C1-C3, C5, C7-C9 exhibit excellent battery performance, such as lower overall impedance, high specific capacity, and long cycle life. In particular, the performance of the full cell C1 is shown in Figures 6 and 7. In Fig. 6, the full cell C1 was cycled under the condition of increasing current density (from 0.1C to 4C), and then returned to 1C, maintaining 1C to continue cycling. It can cycle more than 500 times at a current density of 1C, and the specific capacity remains at 93.7mAh·g ^-1 ; at a current density of 4C, the specific capacity can still reach 80.5mAh·g ^-1 ; the Coulombic efficiency of charge and discharge (here, Coulombic efficiency=discharge capacity/charge capacity) remains above 99.5%. As shown in Fig. 7, the total impedance of the full cell is about 400Ω·cm ^-2 , and there is no significant change after 300 cycles and 500 cycles.

The preferred embodiments of the present invention have been described above in detail, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solutions of the present invention, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed in the present invention. All belong to the protection scope of the present invention.

Claims (10)

1. An electrolyte material, the composition of the electrolyte material being Na_3+2xZr_2-xCa_xSi₂PO₁₂Wherein x is 0.05-0.3.

2. The electrolyte material of claim 1 wherein the electrolyte material is prepared by:

(1) mixing a Na source, a Zr source, a Ca source, a silicon source, a P source and citric acid in a molar ratio of (3+2x) to (2-x): x: 2: 1: (6-10) mixing the mixture in a water-alcohol mixed solution, and fully stirring and dissolving to obtain a mixture I;

(2) heating the mixture I to 50-90 ℃ until complete evaporation of water and alcohol to form a gel;

(3) drying and grinding the gel, calcining for 2-8h at the temperature of 500-700 ℃, and then heating to the temperature of 900-1000 ℃ for calcining for 8-16 h; to obtain Na_3+2xZr_2-xCa_xSi₂PO₁₂And (3) powder.

3. The electrolyte material according to claim 2, wherein the Na source is selected from at least one of sodium acetate, sodium nitrate, sodium carbonate, and sodium hydroxide;

the Zr source is selected from at least one of zirconyl nitrate hydrate, zirconium trichloride, zirconium acetylacetonate and zirconium acetate;

the Ca source is selected from at least one of calcium nitrate, calcium acetate, calcium hydroxide and calcium chloride;

the Si source is selected from at least one of ethyl orthosilicate, propyl orthosilicate, silicic acid and silicone oil;

the P source is selected from at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid.

4. A sodium ion solid electrolyte comprising at least two-layer structure formed of an electrolyte material, the at least two-layer structure comprising a dense layer and a porous layer on at least one side of the dense layer, the porous layer having a sodium-philic porous surface; wherein the electrolyte material is the electrolyte material according to any one of claims 1 to 3.

5. The sodium ion solid electrolyte according to claim 4, wherein the dense layer has a thickness of 1 to 1000 μm, the porous layer has a porosity of 10 to 80%, and the average pore diameter is 2 to 50 μm;

preferably, the thickness of the compact layer is 10-300 μm, the thickness of the porous layer is 10-300 μm, the porosity of the porous layer is 40-60%, and the average pore diameter is 5-20 μm;

preferably, the sodium-philic porous surface is formed by SnO subjecting the porous layer to₂And/or Bi₂O₃And (3) modifying to obtain the modified starch.

6. The sodium ion solid electrolyte of claim 4 or 5, wherein the at least two-layer structure is prepared by a co-compression technique;

preferably, the co-compression technique comprises the steps of:

(a) forming a base layer from a pure electrolyte material; the electrolyte material and the pore-forming agent are mixed according to the mass ratio of 1: (0.5-5) mixing to obtain a mixture II; placing the mixture II on at least one side of the base layer to form an outer layer, and applying pressure to the base layer and the outer layer to obtain a blank body;

(b) sintering the green body in air at the temperature of 1000-1400 ℃ for 0.5-30 h;

preferably, the pore-forming agent is at least one selected from starch, polymethyl methacrylate powder, spherical graphite and polystyrene powder, and the average particle size of the pore-forming agent is 2-50 μm.

7. Use of the sodium ion solid electrolyte of any one of claims 4 to 6 in the field of solid batteries.

8. A sodium-ion solid-state battery comprising:

an integrated metallic Na negative electrode;

a positive electrode;

wherein the integrated metallic Na negative electrode is obtained by integrating a sodium ion solid electrolyte, which is the sodium ion solid electrolyte according to any one of claims 4 to 6, with metallic Na located in pores of a porous layer included in the sodium ion solid electrolyte.

9. The sodium ion solid state battery of claim 8, wherein the integrated metallic Na negative electrode is made by:

and placing metal Na on the surface of the porous layer included in the sodium ion solid electrolyte, and heating the metal Na so as to melt the metal Na and penetrate into the porous layer to form the integrated metal Na negative electrode.

10. The sodium ion solid state battery of claim 8, wherein the positive electrode comprises a positive electrode material selected from Na₃V₂(PO₄)₃/C、NaMnO₂、NaFePO₄、Na_2/3Ni_1/3Mn_1/3Ti_1/3O₂And Na₃V₂(PO₄)₂F₃、Na₃V₂(PO₄)₂O₂F.

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