Sodium ion composite solid electrolyte material and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion solid-state batteries, and particularly discloses a sodium ion composite solid-state electrolyte material as well as a preparation method and application thereof. The sintering temperature of the sodium silicate solid electrolyte is remarkably reduced by adding the sintering aid into the sodium silicate solid electrolyte, and in addition, the growth of electrolyte grains is effectively promoted by introducing the sintering aid, so that pores at the grain boundary are reduced, the material density is improved, the grain boundary resistance is reduced, and the ionic conductivity of the sodium silicate solid electrolyte is remarkably improved. The composite electrolyte provided by the invention is excellent in performance and simple in preparation process, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion solid-state batteries, and in particular to a sodium ion composite solid-state electrolyte material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have good application prospects in large-scale energy storage and other fields due to their advantages such as abundant resource reserves and low preparation costs. However, existing sodium-ion batteries have safety issues such as leakage and combustion due to the use of organic electrolytes, which is not conducive to practical application. Using solid electrolytes to replace organic electrolytes and developing all-solid-state sodium-ion batteries is a fundamental measure to improve battery safety performance and reduce the risk of thermal runaway. Based on this, solid-state batteries are becoming a research hotspot and future development direction in the field of electrochemical energy storage.

[0003] The development of high-performance solid electrolytes is the key to realizing solid-state batteries. Among various solid electrolyte material systems, oxide electrolytes have attracted extensive attention from researchers due to their good mechanical properties and excellent chemical / electrochemical stability. However, their development still faces challenges such as high synthesis temperature, large grain boundary resistance, and poor electrode-electrolyte interface contact: oxide electrolytes are usually prepared by high-temperature solid-phase reaction, and the high sintering temperature greatly increases the energy cost of material synthesis (Energy Environ. Sci., 2018, 11, 1945-1976); in addition, the hard texture of oxide electrolytes leads to poor contact between grains, so the grain boundary resistance dominates the total resistance (Adv. Energy Mater., 2019, 9, 1902373). Eliminating or reducing the grain boundary resistance is the key to improving the ionic conductivity of oxide solid electrolytes.

[0004] Among the reported oxide electrolyte systems, silicate electrolytes composed of RO6 (R = Y, Gd, Sm, etc.) octahedra and SiO4 tetrahedra with open three-dimensional skeleton structures and rich sodium ion transport channels exhibit extremely excellent ion transport properties, thereby showing high bulk ion conductivity. However, its high sintering temperature (usually higher than 1150°C, Energy Technol., 2023, 11, 2201323) and large grain boundary resistance limit the total ion conductivity. Therefore, exploring modification strategies to reduce sintering temperature and improve grain contact, effectively reducing production energy consumption and electrolyte grain boundary resistance, is of great significance for enhancing the application potential of silicate electrolytes and promoting the development of all-solid-state sodium-ion batteries. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a sodium ion composite solid electrolyte material with simple preparation process, low grain boundary resistance and high ionic conductivity, as well as a preparation method and application thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a sodium ion composite solid electrolyte material, which comprises a solid electrolyte and a sintering aid;

[0008] The solid electrolyte includes Na 5-x+3y R 1-y P x Si 4-x O 12 , wherein R is any one of Ho, In, Sc, Y, Yb, Er, Dy, Gd, and Sm;

[0009] Among them, the value ranges of x and y are 0≤x≤0.5 and 0≤y≤0.5 respectively;

[0010] The sintering aid is a sodium salt;

[0011] The sodium salt includes at least one of Na2O, NaF, Na2B4O7, Na3BO3, NaAlO2, and Na3AlF6.

[0012] In view of the high sintering temperature and large grain boundary resistance of silicate electrolytes, the inventors have found through extensive research and experiments that adding the above-mentioned sintering aid with a low melting point to sodium silicate solid electrolytes can effectively promote grain growth, improve grain contact, and thus reduce the pores at the grain boundaries, increase material density and reduce grain boundary resistance, thereby significantly improving the ionic conductivity of oxide electrolytes. For example, by introducing sintering aids, an ionic conductivity of 1.97×10 -3 S cm -1 Composite electrolyte Na5YSi4O 12 ·Prepared with 1.5% Na2B4O7.

[0013] As a preferred embodiment of the sodium ion composite solid electrolyte material of the present invention, the solid electrolyte is Na 5-x+3y Y 1-y P x Si 4-x O 12 、Na 5-x+3y G 1-y P x Si 4-x O 12 Or Na 5-x+3y Sm1-y P x Si 4-x O 12 (x=0, y=0);

[0014] Preferably, the solid electrolyte is Na5YSi4O 12 、Na5SmSi4O 12 or Na5GdSi4O 12 .

[0015] As a preferred embodiment of the sodium ion composite solid electrolyte material of the present invention, the sintering aid is Na2B4O7 or NaAlO2.

[0016] As a preferred embodiment of the sodium ion composite solid electrolyte material of the present invention, the content of the sintering aid is not more than 5wt%.

[0017] The present invention adopts the sintering aid in the above content, which can effectively promote the close bonding between the composite electrolyte grains, significantly reduce the grain boundary resistance, and improve the ion conductivity.

[0018] As a preferred embodiment of the sodium ion composite solid electrolyte material of the present invention, the content of the sintering aid is 0.5-2wt%.

[0019] Preferably, the content of the sintering aid is in the range of one or any two of 0.5wt%, 1wt%, 1.5wt%, and 2wt%.

[0020] When the content of the sintering aid is preferably within the above range, it can more effectively promote the close bonding between the composite electrolyte grains, significantly reduce the grain boundary resistance, and improve the ionic conductivity.

[0021] More preferably, the content of the sintering aid is 1.5 wt %.

[0022] When the content of the sintering aid is 1.5wt%, the ionic conductivity of the prepared sodium ion composite solid electrolyte material is the highest. When the sintering aid is excessive, too much non-sodium ion conductive phase will be introduced, resulting in a significant decrease in the proportion of sodium ion conductors and destroying the continuous ion migration path. The accumulation of non-sodium ion conductive phases may further lead to an increase in grain boundary resistance, ultimately resulting in a decrease in the ionic conductivity of the solid electrolyte ceramic sheet.

[0023] The present invention also provides a method for preparing the above-mentioned sodium ion composite solid electrolyte material, comprising the following steps:

[0024] S1, raw materials Na2CO3, R2O3 and SiO2 are mixed and wet ball milled, and then dried to obtain precursor powder, which is subjected to high temperature heat treatment to obtain solid electrolyte pre-sintered powder;

[0025] S2, adding a sintering aid to the solid electrolyte pre-calcined powder obtained in step S1 and then performing dry ball milling to obtain a composite solid electrolyte powder;

[0026] S3, cold-pressing the composite solid electrolyte to form a green blank, and then sintering it at high temperature to obtain a sodium ion composite solid electrolyte ceramic sheet.

[0027] As a preferred embodiment of the method for preparing the sodium ion composite solid electrolyte material of the present invention, in the step S1, the medium for wet ball milling is anhydrous ethanol or isopropanol, the rotation speed of the ball milling is 200 to 1000 rpm, and the ball milling time is 0.5 to 30 h.

[0028] As a preferred embodiment of the method for preparing the sodium ion composite solid electrolyte material of the present invention, in the step S1, the heat treatment temperature is 600-900° C. and the time is 1-20 h;

[0029] In the step S3, the high temperature sintering is performed at a temperature of 900 to 1100° C. and for a time of 1 to 20 hours.

[0030] The present invention also provides application of the sodium ion composite solid electrolyte material in a sodium ion solid-state battery.

[0031] The sodium ion solid-state battery prepared by using the sodium ion composite solid-state electrolyte material of the present invention has the characteristics of good safety, high charge and discharge specific capacity, excellent cycle stability, etc.

[0032] The present invention also provides a sodium ion solid-state battery, comprising a positive electrode material, a negative electrode material and the sodium ion composite solid-state electrolyte material.

[0033] The sodium ion solid-state battery of the present invention can be further used in large-scale energy storage equipment for solar power generation, wind power generation, smart grid peak regulation, distributed power stations, backup power supplies or communication base stations.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides a sodium ion composite solid electrolyte material and a preparation method and application thereof. By adding a sintering aid to the sodium silicate solid electrolyte, the sintering temperature can be significantly reduced; the sintering aid promotes the growth of grains during the sintering process, thereby increasing the density of the material and effectively reducing the grain boundary resistance. In addition, by further optimizing the type and amount of the sintering aid, the present invention converts the composite electrolyte Na5YSi4O 12The preparation conditions of 1.5wt% Na2B4O7 are reduced to below 1000℃, which improves the material's compactness and significantly improves its ionic conductivity. On this basis, the excellent chemical / electrochemical properties of the solid electrolyte material are achieved, providing a broader possibility for its application in all-solid-state sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 X-ray diffraction spectra of the sodium ion composite solid electrolyte materials of Example 1 and Example 2 and the composite solid electrolytes of Comparative Example 1 and Comparative Example 2;

[0037] Figure 2 The X-ray diffraction spectra of the composite solid electrolytes of Example 3, Example 4 and Comparative Example 1 and Comparative Example 2;

[0038] Figure 3 The AC impedance spectra of the sodium ion composite solid electrolyte material of Example 1 and the composite solid electrolyte of Comparative Example 1;

[0039] Figure 4 The AC impedance spectra of the sodium ion composite solid electrolyte material of Example 2 and the composite solid electrolyte of Comparative Example 2;

[0040] Figure 5 The AC impedance spectra of the sodium ion composite solid electrolyte material of Example 4 and the composite solid electrolyte of Comparative Example 1;

[0041] Figure 6 is a scanning electron microscope image of a cross section of the sodium ion composite solid electrolyte material of Example 3;

[0042] Figure 7 This is a scanning electron microscope image of the cross-section of the composite solid electrolyte of Comparative Example 1. DETAILED DESCRIPTION

[0043] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0044] In the following examples and comparative examples, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified, and the components and raw materials used in each parallel experiment are of the same type.

[0045] Example 1

[0046] This embodiment provides a sodium ion composite solid electrolyte material (Na5YSi4O 12 Na2B4O7), comprising the following steps:

[0047] S1, Na5YSi4O 12 The raw materials of Na2CO3, Y2O3 and SiO2 with a total mass of 4 g were weighed in a stoichiometric ratio, 10 ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400 rpm for 4 h to obtain a mixed slurry. After the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8 h to obtain a sodium silicate solid electrolyte pre-sintered powder (Na5YSi4O 12 );

[0048] S2, weigh 1.5g sodium silicate solid electrolyte pre-sintered powder Na5YSi4O 12 , and adding sintering aid Na2B4O7 at a ratio of 1wt%, putting it into a high-energy ball mill, and ball milling it at 400rpm for 4h to obtain a sodium ion composite solid electrolyte powder;

[0049] S3. Weigh 0.3 g of the sodium ion composite solid electrolyte precursor, put it into a mold, press it into a green billet at a pressure of 6 MPa, and then place the green billet in a muffle furnace and solid-phase sinter it at 1000° C. for 9 hours to obtain a sodium ion composite solid electrolyte ceramic sheet.

[0050] Example 2

[0051] Similar to Example 1, the difference is that in step S3 of Example 2, the solid phase sintering temperature is changed to 1050° C., that is, the green blank is placed in a muffle furnace and sintered at 1050° C. for 9 hours. The rest of the preparation method is the same as Example 1.

[0052] Example 3

[0053] Similar to Example 1, the difference is that in step S2 of Example 3, sintering aid Na2B4O7 is added at a ratio of 1.5wt%, and the rotation speed of the ball mill is 350rpm; the temperature of solid phase sintering in step S3 is 1080℃, and the rest of the preparation method is the same as Example 1.

[0054] Example 4

[0055] Similar to Example 1, the difference is that in step S2 of Example 4, a sintering aid Na2B4O7 is added at a ratio of 1.5wt%, the temperature of solid phase sintering in step S3 is 1000°C, and the rest of the preparation method is the same as Example 1.

[0056] Example 5

[0057] Similar to Example 1, the difference is that in step S2 of Example 5, the sintering aid Na2B4O7 is added at a ratio of 2wt%, and the ball mill speed is 300rpm; the temperature and time of solid phase sintering in step S3 are 1050℃ and 2h respectively, and the rest of the preparation method is the same as Example 1.

[0058] Example 6

[0059] Similar to Example 1, the difference is that in step S1 of Example 6, the calcination temperature is adjusted to 650°C; in step S2, the sintering aid Na2B4O7 is added at a ratio of 2wt%; in step S3, the solid phase sintering temperature is 1080°C, and the rest of the preparation method is the same as Example 1.

[0060] Example 7

[0061] This embodiment provides a sodium ion composite solid electrolyte material (Na5SmSi4O 12 Na2B4O7), comprising the following steps:

[0062] S1, Na5SmSi4O 12 The raw materials of Na2CO3, Sm2O3 and SiO2 with a total mass of 4 g were weighed in a stoichiometric ratio, 10 ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400 rpm for 4 h to obtain a mixed slurry. After the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8 h to obtain a sodium silicate solid electrolyte pre-sintered powder (Na5SmSi4O 12 );

[0063] S2, weigh 1.5g silicate electrolyte Na5 SmSi4 O 12 , and adding sintering aid Na2B4O7 at a ratio of 1wt%, putting it into a high-energy ball mill, and ball milling it at 400rpm for 4 hours to obtain a sodium ion composite solid electrolyte powder;

[0064] S3. Weigh 0.3 g of the sodium ion composite solid electrolyte precursor, put it into a mold, press it into a green blank at a pressure of 6 MPa, and then place the green blank in a muffle furnace for solid-phase sintering at 900° C. for 20 hours to obtain a sodium ion composite solid electrolyte ceramic sheet.

[0065] Example 8

[0066] Similar to Example 7, the difference is that the temperature of solid phase sintering in step S3 of Example 8 is 950° C., and the rest of the preparation method is the same as Example 6.

[0067] Example 9

[0068] Similar to Example 7, the difference is that in step S2 of Example 9, sintering aid Na2B4O7 is added at a ratio of 1.5wt%, and the ball mill speed is 300rpm; the solid phase sintering temperature in step S3 is 980℃, and the rest of the preparation method is the same as Example 6.

[0069] Example 10

[0070] Similar to Example 7, the difference is that in step S2 of Example 10, sintering aid Na2B4O7 is added at a ratio of 1.5wt%, the speed of the ball mill is 350rpm; the temperature of solid phase sintering in step S3 is 1000℃

[0071] Embodiment 11

[0072] Similar to Example 7, the difference is that in step S1 of Example 11, the calcination temperature is adjusted to 700°C; in step S2, the sintering aid Na2B4O7 is added at a ratio of 2wt%; in step S3, the solid phase sintering time is 6h.

[0073] Example 12

[0074] Similar to Example 7, the difference is that in step S2 of Example 12, sintering aid Na2B4O7 is added at a ratio of 2wt%, and the rest of the preparation method is the same as Example 7.

[0075] Embodiment 13

[0076] Similar to Example 1, the difference is that in step S2 of Example 13, sintering aid NaAlO2 is added at a ratio of 1wt%, and the rest of the preparation method is the same as Example 1.

[0077] Embodiment 14

[0078] Similar to Example 7, the difference is that in step S2 of Example 14, sintering aid NaAlO2 is added at a ratio of 1wt%, and the rest of the preparation method is the same as Example 7.

[0079] Embodiment 15

[0080] This embodiment provides a sodium ion composite solid electrolyte material (Na 5.3 Y 0.8 P 0.3 Si 3.7 O 12 Na2B4O7), comprising the following steps:

[0081] S1, Na5YSi4O12 The raw materials of Na2CO3, Y2O3, SiO2, and NH4H2PO4 with a total mass of 4g were weighed in a stoichiometric ratio, 10ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400rpm for 4h to obtain a mixed slurry; after the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8h to obtain a sodium silicate solid electrolyte pre-sintered powder (Na 5.3 Y 0.8 P 0.3 Si 3.7 O 12 );

[0082] S2, weigh 1.5g sodium silicate solid electrolyte pre-burned powder Na 5.3 Y 0.8 P 0.3 Si 3.7 O 12 , and adding sintering aid Na2B4O7 at a ratio of 1wt%, putting it into a high-energy ball mill, and ball milling it at 400rpm for 4h to obtain a sodium ion composite solid electrolyte powder;

[0083] S3. Weigh 0.3 g of the sodium ion composite solid electrolyte precursor, put it into a mold, press it into a green billet at a pressure of 6 MPa, and then place the green billet in a muffle furnace and solid-phase sinter it at 1050° C. for 9 hours to obtain a sodium ion composite solid electrolyte ceramic sheet.

[0084] Example 16

[0085] Similar to Example 1, the difference is that in step S2 of Example 16, sintering aid Na2B4O7 is added at a ratio of 5wt%, and the rest of the preparation method is the same as Example 1.

[0086] Embodiment 17

[0087] This embodiment provides a sodium ion composite solid electrolyte material (Na5GdSi4O 12 Na2B4O7), comprising the following steps:

[0088] S1, Na5GdSi4O 12 The raw materials of Na2CO3, Gd2O3 and SiO2 with a total mass of 4 g were weighed in a stoichiometric ratio, 10 ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400 rpm for 4 h to obtain a mixed slurry. After the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8 h to obtain a sodium silicate solid electrolyte pre-sintered powder (Na5GdSi4O 12);

[0089] S2, weigh 1.5g sodium silicate solid electrolyte pre-sintered powder Na5GdSi4O 12 , and adding sintering aid Na2B4O7 at a ratio of 1wt%, putting it into a high-energy ball mill, and ball milling it at 400rpm for 4h to obtain a sodium ion composite solid electrolyte powder;

[0090] S3. Weigh 0.3 g of the sodium ion composite solid electrolyte precursor, put it into a mold, press it into a green billet at a pressure of 6 MPa, and then place the green billet in a muffle furnace and solid-phase sinter it at 1050° C. for 9 hours to obtain a sodium ion composite solid electrolyte ceramic sheet.

[0091] Embodiment 18

[0092] Similar to Example 17, the difference is that in step S2 of Example 18, the sintering aid Na2B4O7 is added at a ratio of 1.5wt%; the temperature of solid phase sintering in step S3 is 1080°C.

[0093] Comparative Example 1

[0094] Comparative Example 1 provides a solid electrolyte material Na5YSi4O 12 The preparation method comprises the following steps:

[0095] S1: Na5YSi4O 12 4 g of Na2CO3, Y2O3 and SiO2 raw materials were weighed in a stoichiometric ratio, 10 ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400 rpm for 4 h to obtain a mixed slurry; after the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8 h to obtain a sodium silicate solid electrolyte powder;

[0096] S2: Weigh 0.3g of sodium silicate solid electrolyte powder, put it into a mold, and press it into a green blank at a pressure of 6MPa. Then place the green blank in a muffle furnace and solid-phase sinter it at 1000℃ for 9h to obtain a composite solid electrolyte ceramic sheet.

[0097] Comparative Example 2

[0098] Similar to Comparative Example 1, the difference is that in step S2 of Comparative Example 2, the temperature of solid phase sintering is 1050° C., and the rest of the preparation method is the same as Comparative Example 1.

[0099] Comparative Example 3

[0100] This comparative example 3 provides a solid electrolyte material Na5SmSi4O12 The preparation method comprises the following steps:

[0101] S1: Na5SmSi4O 12 4 g of Na2CO3, Sm2O3 and SiO2 raw materials were weighed in a stoichiometric ratio, 10 ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400 rpm for 4 h to obtain a mixed slurry; after the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8 h to obtain a sodium silicate solid electrolyte powder;

[0102] S2: Weigh 0.3g of sodium silicate solid electrolyte powder, put it into a mold, and press it into a green blank at a pressure of 6MPa. Then place the green blank in a muffle furnace and sinter it at 900℃ for 9h to obtain a composite solid electrolyte ceramic sheet.

[0103] Comparative Example 4

[0104] Similar to Comparative Example 3, the difference is that in step S2 of Comparative Example 4, the temperature of solid phase sintering is 950° C., and the rest of the preparation method is the same as Comparative Example 3.

[0105] Comparative Example 5

[0106] Comparative Example 5 provides a solid electrolyte material Na5GdSi4O 12 The preparation method comprises the following steps:

[0107] S1: Na5GdSi4O 12 4 g of Na2CO3, Gd2O3 and SiO2 raw materials were weighed in a stoichiometric ratio, 10 ml of isopropanol was added, and the mixture was placed in a high-energy ball mill for ball milling at a speed of 400 rpm for 4 h to obtain a mixed slurry; after the ball milling, the mixed slurry was transferred to an 80°C forced air drying oven for drying, and then transferred to a muffle furnace for calcination at 800°C for 8 h to obtain a sodium silicate solid electrolyte powder;

[0108] S2: Weigh 0.3g of sodium silicate solid electrolyte powder, put it into a mold, and press it into a green blank at a pressure of 6MPa. Then place the green blank in a muffle furnace and solid-phase sinter it at 1000℃ for 9h to obtain a composite solid electrolyte ceramic sheet.

[0109] Comparative Example 6

[0110] Similar to Example 1, the difference is that in step S2 of Comparative Example 6, sintering aid Na2B4O7 is added at a ratio of 10wt%, and the rest of the preparation method is the same as Example 1.

[0111] Comparative Example 7

[0112] Similar to Example 7, the difference is that in step S2 of Comparative Example 7, sintering aid Na2B4O7 is added at a ratio of 10wt%, and the rest of the preparation method is the same as Example 7.

[0113] Comparative Example 8

[0114] Similar to Example 1, the difference is that in step S2 of Comparative Example 8, sintering aid MgB4O7 is added at a ratio of 1wt%, and the rest of the preparation method is the same as Example 1.

[0115] Test example, test of ionic conductivity and density of composite solid electrolyte materials

[0116] The sodium ion composite solid electrolyte materials or composite solid electrolyte materials prepared in Examples 1 to 18 and Comparative Examples 1 to 8 were subjected to an AC impedance test, which was performed using an electrochemical workstation, and the ionic conductivity was calculated based on the obtained AC impedance spectrum and the formula: σ=L / R·S; wherein σ is the ionic conductivity (S / cm), L is the thickness of the electrolyte membrane (cm), R is the measured impedance (Ω), and S is the area of ​​the electrolyte membrane (cm 2 ).

[0117] The ionic conductivity test and density results of the sodium ion composite solid electrolyte materials or composite solid electrolyte materials prepared in Examples 1 to 18 and Comparative Examples 1 to 8 are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] As shown in Table 1, compared with Comparative Examples 1 to 4, Examples 1 to 18 of the present invention add a sintering aid of no more than 5wt% to the sodium silicate electrolyte, which helps the densification of the composite solid electrolyte sample and makes the sample have a higher ionic conductivity. Among them, adding 1.5wt% of Na2B4O7 sintering aid to the silicate electrolyte can significantly improve the density of the sodium ion composite solid electrolyte, thereby reducing the grain boundary resistance and making the sample have a higher ionic conductivity.

[0122] Example 4: Dense sintering can be achieved at a relatively low temperature (1000°C), and the ionic conductivity can be increased from 0.82 mS·cm -1 Increased to 1.86mS·cm -1, and its ion migration activation energy is 0.27eV. This result shows that by optimizing the addition ratio of sintering aids, the grain boundary resistance can be effectively reduced, thereby effectively improving the ion transport performance of sodium silicate solid electrolytes.

[0123] The addition of an appropriate amount of sodium salt sintering aid to the sodium silicate solid electrolyte of the present invention can effectively promote the close bonding between the composite electrolyte grains, significantly reduce the grain boundary resistance, and thus improve the ionic conductivity; however, in comparative examples 6 to 7, excessive amounts of sintering aid are added. Since the ionic conductivity of the sintering aid itself is not high, when the amount added is too high, the ionic conductivity of the composite electrolyte is reduced.

[0124] Comparative Example 8 uses magnesium salt MgB4O7 as a sintering aid, and its ion conductivity is significantly lower than that of Comparative Example 3, and has no sintering aid effect.

[0125] in, Figure 1 X-ray diffraction spectra of the sodium ion composite solid electrolyte materials of Example 1 and Example 2 and the composite solid electrolytes of Comparative Example 1 and Comparative Example 2; the obtained composite electrolyte has the same diffraction peak as the silicate electrolyte, indicating that the addition of the sintering aid does not change the phase structure of the electrolyte.

[0126] Figure 2 The X-ray diffraction spectra of the composite solid electrolytes of Example 3, Example 4 and Comparative Example 1 and Comparative Example 2 are shown; the obtained composite electrolytes and Na5YSi4O 12 The diffraction peaks of the solid electrolyte are the same, indicating that properly adjusting the preparation conditions of the composite electrolyte will not change the physical phase of the composite electrolyte, and no impurity phase is generated.

[0127] Figure 3 The AC impedance spectra of the sodium ion composite solid electrolyte material of Example 1 and the composite solid electrolyte of Comparative Example 1; According to the formula σ=L / R·S, the ion conductivity of the above electrolytes is 1.38mS·cm -1 、0.82mS·cm -1 .

[0128] Figure 4 The AC impedance spectra of the sodium ion composite solid electrolyte material of Example 2 and the composite solid electrolyte of Comparative Example 2; According to the formula σ=L / R·S, the ion conductivity of the above electrolytes is 1.69mS·cm -1 、0.87mS·cm -1 .

[0129] Figure 5The AC impedance spectra of the sodium ion composite solid electrolyte material of Example 4 and the composite solid electrolyte of Comparative Example 1; According to the formula σ=L / R·S, the ion conductivity of the above electrolytes is 1.86mS·cm -1 、0.82mS·cm -1 .

[0130] Figure 6 This is a scanning electron microscope image of the cross-section of the sodium ion composite solid electrolyte material of Example 3; compared with Comparative Example 1, the density of the composite solid electrolyte is significantly improved and the pores are significantly reduced after adding the sintering aid.

[0131] Figure 7 This is a scanning electron microscope image of the cross-section of the composite solid electrolyte of Comparative Example 1; there are a large number of pores between the silicate electrolyte grains without sintering aids, and the density is low.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the solution of the present invention.

Claims

1. A sodium ion composite solid electrolyte material, characterized in that: The sodium ion composite solid electrolyte material comprises a sodium solid electrolyte and a sintering aid; The solid electrolyte includes Na 5-x+3y R 1-y P x Si 4-x O 12 , wherein R is any one of Ho, In, Sc, Y, Yb, Er, Dy, Gd, and Sm; Among them, the value ranges of x and y are 0≤x≤0.5 and 0≤y≤0.5 respectively; The sintering aid is a sodium salt; The sodium salt includes at least one of Na2O, NaF, Na2B4O7, Na3BO3, NaAlO2, and Na3AlF6.

2. The sodium ion composite solid electrolyte material according to claim 1, characterized in that The solid electrolyte is Na 5-x+3y Y 1-y P x Si 4-x O 12 、Na 5-x+3y G 1-y P x Si 4-x O 12 Or Na 5-x+3y Sm 1-y P x Si 4-x O 12 .

3. The sodium ion composite solid electrolyte material according to claim 1, characterized in that The sintering aid is Na2B4O7 or NaAlO2.

4. The sodium ion composite solid electrolyte material according to claim 1, characterized in that The content of the sintering aid is not more than 5wt%.

5. The sodium ion composite solid electrolyte material according to claim 4, characterized in that: The content of the sintering aid is 0.5-2wt%.

6. The method for preparing the sodium ion composite solid electrolyte material according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: S1, raw materials Na2CO3, R2O3, NH4H2PO4 and SiO2 are mixed and wet ball milled, and then dried to obtain precursor powder, which is subjected to high temperature heat treatment to obtain solid electrolyte pre-sintered powder; S2, adding a sintering aid to the solid electrolyte pre-calcined powder obtained in step S1 and performing secondary ball milling to obtain a composite solid electrolyte powder; S3, cold pressing the composite solid electrolyte powder to form a green billet, and then sintering it at high temperature to obtain a sodium ion composite solid electrolyte material.

7. The method for preparing the sodium ion composite solid electrolyte material according to claim 6, characterized in that: In the step S1, the medium for wet ball milling is anhydrous ethanol or isopropanol, the rotation speed of the ball milling is 200 to 1000 rpm, and the ball milling time is 0.5 to 30 hours.

8. The method for preparing the sodium ion composite solid electrolyte material according to claim 6, characterized in that: In the step S1, the heat treatment temperature is 600-900°C and the time is 1-20h; In the step S3, the high temperature sintering is performed at a temperature of 900 to 1100° C. and for a time of 1 to 20 hours.

9. Use of the sodium ion composite solid electrolyte material according to any one of claims 1 to 5 in a sodium ion solid-state battery.

10. A sodium ion solid-state battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material and a sodium ion composite solid electrolyte material as claimed in any one of claims 1 to 5.

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