NASICON solid electrolyte with local amorphous structure as well as preparation method and application of NASICON solid electrolyte

Abstract

The invention relates to the technical field of solid-state electrolyte, in particular to NASICON solid-state electrolyte with a local amorphous structure and a preparation method and application of the NASICON solid-state electrolyte. The preparation method comprises the following steps: S1, proportioning Na2CO3, ZrO2, SiO2 and NH4H2PO4 according to a molar ratio, and then carrying out ball milling; s2, drying and pre-calcining the raw materials subjected to ball milling in the step S1 to obtain precursor powder; and S3, carrying out ball milling on the precursor powder, drying, pressing into a blank, and calcining to obtain the NASICON solid electrolyte with the local amorphous structure. The solid electrolyte provided by the invention has high ionic conductivity and interface stability to a sodium metal negative electrode, shows higher critical current density, effectively improves the interface compatibility of the solid electrolyte to the sodium metal negative electrode, improves the safety of a solid-state battery in an actual application scene, and prolongs the cycle life of the solid-state sodium metal battery.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular to a NASICON solid electrolyte with a localized amorphous structure and a preparation method and application thereof. Background Art

[0002] The good chemical and electrochemical stability of sodium solid electrolytes reduces the side reactions between electrolytes and electrodes, making it possible to apply metallic sodium negative electrodes, which can further improve their energy density and achieve the dual goals of battery cost and high energy density. It is an ideal choice for large-scale energy storage scenarios in electric vehicles and power grids. However, compared with traditional liquid electrolytes, the hard, non-wettable NZSP solid electrolyte has insufficient contact and poor interface compatibility with the Na metal negative electrode, showing a high interface impedance, which leads to weak cycle stability of solid-state sodium metal batteries. In addition, the large grain boundary resistance in the solid electrolyte is the bottleneck part of the solid electrolyte ion transport. Improving the grain boundary ion conductivity can effectively improve the total ion conductivity of the solid electrolyte. In the prior art, the introduction of low melting point materials such as Na2B4O7 and NaF has improved the ionic conductivity and interface compatibility to a certain extent, but the effect is still difficult to meet the actual needs of solid-state batteries. Summary of the invention

[0003] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide a NASICON solid electrolyte with a localized amorphous structure and a preparation method and application thereof.

[0004] A method for preparing a NASICON solid electrolyte having a localized amorphous structure according to the present invention comprises the following steps:

[0005] S1. Na2CO3, ZrO2, SiO2, and NH4H2PO4 are mixed in a molar ratio and then ball milled;

[0006] S2. The ball-milled raw material in S1 is dried and pre-calcined to obtain a precursor powder;

[0007] S3. The precursor powder is ball-milled, dried, pressed into an embryonic body, and calcined to obtain a NASICON solid electrolyte having a localized amorphous structure.

[0008] Furthermore, the molar ratio of Na2CO3, ZrO2, SiO2, and NH4H2PO4 is 1.71-1.81:2:2.11-2.29:0.71-0.89.

[0009] Furthermore, the molar ratio of Na2CO3, ZrO2, SiO2, and NH4H2PO4 is 1.76:2:2.2:0.8.

[0010] Furthermore, in step S2, the pre-firing temperature is 950-1050°C.

[0011] Furthermore, in step S2, the pre-firing temperature is 1000°C.

[0012] Furthermore, in step S3, the calcination temperature is 1200-1300°C.

[0013] Furthermore, in step S3, the calcination temperature is 1250°C.

[0014] A solid-state sodium metal battery comprises the above-mentioned NASICON solid-state electrolyte.

[0015] A NASICON solid electrolyte with a local amorphous structure prepared by the above-mentioned preparation method. The present invention adjusts the silicon-phosphorus ratio and the pre-firing temperature so that the prepared NASICON solid electrolyte has a local amorphous structure, effectively improves the grain boundary ion conductivity, thereby improving the overall ion conductivity of the solid electrolyte; and effectively improves the interface stability of the solid electrolyte to the sodium metal negative electrode, improves the safety of the solid-state battery in actual application scenarios, and improves the cycle life of the solid-state sodium metal battery.

[0016] The NASICON solid electrolyte with a local amorphous structure prepared by the present invention exhibits a higher critical current density, and effectively improves the interface compatibility of the solid electrolyte with the sodium metal negative electrode.

[0017] The preparation method of the present invention is simple, the process is mature, and it can be prepared on a large scale, and it has a wide range of application scenarios in the field of solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The scanning electron microscope comparison diagrams of the NASICON solid electrolyte (ab) in Comparative Example 1 and the NASICON solid electrolyte (cd) in Example 1;

[0019] Figure 2 is the XRD pattern of the NASICON solid electrolyte in Example 1;

[0020] Figure 3 It is a comparison diagram of electrochemical impedance of NASICON solid electrolyte in comparative example 1 and NASICON solid electrolyte in embodiment 1;

[0021] Figure 4 It is a comparison diagram of the critical current density of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1;

[0022] Figure 5It is a symmetric battery cycle diagram of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1;

[0023] Figure 6 It is a solid-state sodium metal battery cycle diagram of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1. DETAILED DESCRIPTION

[0024] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0025] Example 1

[0026] 1. Mix Na2CO3, ZrO2, SiO2 and NH4H2PO4 in a molar ratio of 1.76:2:2.2:0.8, and then ball mill;

[0027] 2. Dry the raw material after ball milling in 1 and pre-calcine it at 1000°C to obtain a precursor powder;

[0028] 3. The precursor powders in step 2 were ball-milled, dried, pressed into embryos, and calcined at 1250°C. The electrolyte ion conductivity was 4.11 mS cm -1 , CCD is 1.3 mA cm -2 .

[0029] Comparative Example 1

[0030] 1. Mix Na2CO3, ZrO2, SiO2 and NH4H2PO4 in a molar ratio of 1.65:2:2:1, and then ball mill;

[0031] 2. Dry the raw material after ball milling in 1, and pre-calcine it at 1000°C to obtain a precursor powder;

[0032] 3. The precursor powders in step 2 were ball-milled, dried, pressed into embryos, and calcined at 1250°C. The electrolyte ion conductivity was 2.43 mS cm -1 , CCD is 0.4 mA cm -2 .

[0033] Comparative Example 2

[0034] 1. Mix Na2CO3, ZrO2, SiO2 and NH4H2PO4 in a molar ratio of 1.705:2:2.1:0.9, and then ball mill;

[0035] 2. Dry the raw material after ball milling in 1, and pre-calcine it at 1000°C to obtain a precursor powder;

[0036] 3. The precursor powders in step 2 were ball-milled, dried, pressed into embryos, and calcined at 1250°C. The electrolyte ion conductivity was 3.56 mS cm -1 , CCD is 0.6 mA cm -2 .

[0037] Comparative Example 3

[0038] 1. Mix Na2CO3, ZrO2, SiO2 and NH4H2PO4 in a molar ratio of 1.815:2:2.3:0.7, and then ball mill;

[0039] 2. Dry the raw material after ball milling in 1, and pre-calcine it at 1000°C to obtain a precursor powder;

[0040] 3. The precursor powders in step 2 were ball-milled, dried, pressed into embryos, and calcined at 1250°C. The electrolyte ion conductivity was 2.58 mS cm -1 , CCD is 0.7 mA cm -2 .

[0041] Application Examples

[0042] In order to further demonstrate the practical effect of the present invention and to better understand the present invention, the inventors tested the solid electrolyte obtained in Example 1.

[0043] Ionic conductivity was measured using AC impedance analysis (Zahner) with an applied frequency range of 10 MHz to 1 Hz and an amplitude of 10 mV. A thin layer of gold was sputtered on each surface of the electrolyte as a blocking electrode. The ionic conductivity was calculated using the following formula: in, L, S, and R represent ionic conductivity, electrolyte thickness, electrolyte surface area, and resistance, respectively.

[0044] The Na|NASICON|Na symmetric cells were assembled at room temperature using an automated battery testing system (Land, CT-3001A) and tested at 0.05 mA cm -2 The initial current density and 0.05 mA cm -2 The CCD value of the increasing rate cycle test. The sodium metal foil was placed directly on both sides of the solid electrolyte without any post-treatment. When assembling the coin cell, the pressure of the hydraulic press was 800PSI. At 0.1mA cm -2 The constant current electrochemical cycling of the Na|NASICON|Na symmetric cell was recorded at a current density of 1.3-1.5 mg cm-1. The positive electrode was prepared by mixing Na3V2(PO4)3 (70% wt%), Super P (20%) and PVDF (10%) to form a uniformly distributed slurry, which was then coated on aluminum foil. The active material loading was 1.3-1.5 mg cm-1.-2 A solid-state sodium metal battery was assembled using a Na3V2(PO4)3 composite material with a diameter of 8 mm as the positive electrode and a Na foil with a diameter of 9 mm as the negative electrode. To wet the cathode and maintain its nanoflammability, 5 uL of ionic liquid electrolyte (1 M bis(fluorosulfonyl)imide in 1-methyl-1-propylpyridinium bis(fluorosulfonyl)imide) was leached on the electrolyte / cathode interface. The electrolyte / cathode interface was heated to 100 ℃ and then heated to 100 ℃ for 2 h at different rates (1C = 117.6 mA g -1 ) The battery was charged and discharged at a constant current, and the cut-off voltage window was set to 2.2-3.8 V. All assembly processes were carried out in an argon-filled glove box, and all electrochemical tests were performed at room temperature.

[0045] Figure 1 The scanning electron microscope comparison diagrams of the NASICON solid electrolyte (ab) in comparative example 1 and the NASICON solid electrolyte (cd) in example 1 are shown in the figure. As shown in the figure, Example 1 exhibits obvious amorphous grain boundaries, and the amorphous interface phase effectively connects the grains and promotes the transport of ions at the grain boundaries.

[0046] Figure 2 This is the XRD pattern of the NASICON solid electrolyte in Example 1. Figure 2 The XRD pattern shown shows an obvious bulge between 15-25°, further proving the existence of the amorphous phase.

[0047] Figure 3 : is a comparison diagram of the electrochemical impedance of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1. Figure 3 As shown in Figure 1, the solid electrolyte in Example 1 has a lower grain boundary impedance (from 17.9 to 2.0Ω), which is beneficial to the transmission of sodium ions at the grain boundary, so that the ionic conductivity is increased from 2.43 to 4.11 mS cm -1 .

[0048] Figure 4 : This is a comparison chart of the critical current density of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1. As shown in the figure, the critical current density of Comparative Example 1 is 0.4 mA cm -2 , Example 1 is 1.3 mA cm -2 ; After testing, the critical current density of comparative example 2 is 0.6mA cm -2 The critical density of comparative example 3 is 0.7 mA cm -2 By comparison, it can be seen that the solid electrolyte in Example 1 exhibits a higher critical current density, which effectively improves the interfacial compatibility of the solid electrolyte with the sodium metal negative electrode.

[0049] Figure 5The symmetrical battery cycle diagram of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1. As shown in the figure, the cycle life of the solid electrolyte in Comparative Example 1 is 15 hours, and the solid electrolyte in Example 1 shows higher cycle stability for the sodium metal negative electrode, with a cycle life of 4500 hours. This shows that the presence of amorphous grain boundaries improves the stability of the sodium metal negative electrode, not only improves the critical current density, but also shows excellent improvement in the long cycle process.

[0050] Figure 6 The solid-state sodium metal battery cycle diagram of the NASICON solid electrolyte in Comparative Example 1 and the NASICON solid electrolyte in Example 1. As shown in the figure, the coulombic efficiency of the solid-state sodium metal battery assembled with the solid electrolyte in Comparative Example 1 rapidly decays to less than 50% after 30 cycles. Thanks to the stable stability of the sodium metal negative electrode, the solid-state sodium metal battery assembled with the solid electrolyte in Example 1 has a capacity retention rate of 92% after 3000 cycles, and the coulombic efficiency is close to 100%, showing good cycle life and cycle stability, which is much higher than the solid-state sodium metal battery assembled with the solid electrolyte in Comparative Example 1.

[0051] Table 1 is a comparison of ionic conductivity in Example 1 and Comparative Examples 1-3. There is no obvious change in grain conductivity, and the change in total conductivity is mainly due to the change in grain boundary ionic conductivity, especially the grain boundary conductivity in Example 1 is about 7 times that of Comparative Example 1.

[0052] For matters not mentioned above, the prior art applies.

[0053] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a NASICON solid electrolyte having a local amorphous structure, characterized in that: The steps include: S1. Na2CO3, ZrO2, SiO2, and NH4H2PO4 are mixed in a molar ratio and then ball milled; S2. The ball-milled raw material in S1 is dried and pre-calcined to obtain a precursor powder; S3. The precursor powder is ball-milled, dried, pressed into an embryonic body, and calcined to obtain a NASICON solid electrolyte having a localized amorphous structure.

2. The preparation method according to claim 1, characterized in that The molar ratio of Na2CO3, ZrO2, SiO2, and NH4H2PO4 is 1.71-1.81:2:2.11-2.29:0.71-0.

89.

3. The preparation method according to claim 1, characterized in that: The molar ratio of Na2CO3, ZrO2, SiO2, and NH4H2PO4 is 1.76:2:2.2:0.

8.

4. The preparation method according to claim 1, characterized in that: In step S2, the pre-firing temperature is 950-1050°C.

5. The preparation method according to claim 1, characterized in that: In step S2, the pre-firing temperature is 1000°C.

6. The preparation method according to claim 1, characterized in that: In step S3, the calcination temperature is 1200-1300°C.

7. The preparation method according to claim 1, characterized in that: In step S3, the calcination temperature is 1250°C.

8. A NASICON solid electrolyte having a localized amorphous structure prepared by the preparation method according to any one of claims 1 to 7.

9. A solid-state sodium metal battery, characterized in that: Comprising the NASICON solid electrolyte as claimed in claim 8.

Images