CN117276642A - Sodium ion sulfide electrolyte and preparation method and application thereof - Google Patents

Abstract

The invention discloses a sodium ion sulfide electrolyte, a preparation method and application thereof, belonging to the field of sodium ion battery electrolyte materials, wherein the sodium ion sulfide electrolyte is Na with a cubic phase structure ₆ PS ₅ Cl _1‑x (BF ₄ ) _x The preparation method comprises the following steps: raw material Na ₂ S、P ₂ S ₅ NaCl and NaBF ₄ Pouring into a ball milling tank, uniformly mixing, pressing into compact discs under certain pressure, and placing in a vacuum environment for calcination to obtain a product which can be used as a solid electrolyte for sodium ion batteries. The invention is realized by combining BF ₄ ^‑ The anionic groups are introduced into the sodium ion solid electrolyte to partially replace Cl ^‑ The site of the anion enlarges the transmission channel of the sodium ion, improves the solid stateThe ionic conductivity of the electrolyte, the preparation process is simple, and the sodium ion sulfide solid electrolyte with high ionic conductivity is easy to synthesize in large scale, so that the commercialization process of the sodium ion sulfide solid electrolyte is promoted.

Description

A kind of sodium ion sulfide electrolyte and preparation method and application thereof

Technical field

The invention relates to a sodium ion sulfide electrolyte and its preparation method and application, belonging to the field of sodium ion battery electrolyte materials.

Background technique

Lithium-ion batteries have been widely used in portable electronic devices such as mobile phones and computers due to their high energy density, long cycle life, high operating voltage, and no memory effect. As the demand for lithium-ion batteries in power vehicles and energy storage systems gradually increases, the energy storage market requires a large amount of lithium sources. However, the price of lithium sources has been skyrocketing in recent years and my country's lithium resources are extremely limited. Therefore, sodium-ion batteries have become one of the options to replace lithium-ion batteries.

The elements sodium and lithium are in the same main group and have similar physical and chemical properties. Like lithium-ion batteries, sodium-ion batteries also have flammability problems. The reason is that traditional sodium-ion batteries use liquid electrolytes, that is, a mixed solution of ester compounds and sodium salts. This type of electrolyte contains esters and organic compounds, which are easily flammable under high temperature or collision conditions. Therefore, it is urgent to solve the safety problem of power batteries.

Using solid electrolytes instead of liquid electrolytes to prepare all-solid-state batteries is an important way to improve safety performance because the solid electrolytes in all-solid-state batteries will not decompose and burn when exposed to high temperatures. At present, research on sodium ion solid electrolytes mainly focuses on sulfides such as Na ₃ PS ₄ , Na ₁₁ Sn ₂ PS ₁₂ , Na ₁₀ GeP ₂ S ₁₂ and Na ₃ SbS ₄ . Among the above-mentioned sulfide solid electrolytes, Na ₃ PS ₄ has low ionic conductivity, while other solid electrolytes require the use of expensive raw materials such as SnS ₂ , GeS ₂ and Sb ₂ S ₅ , which is not conducive to commercial production and application. Therefore, how to prepare low-cost, high-performance sodium-ion solid-state electrolytes has become the key to the development of next-generation sodium-ion batteries.

Contents of the invention

Li ₆ PS ₅ Cl with a silver sulfide structure is a classic lithium ion sulfide solid-state electrolyte with an ionic conductivity of about 10 ^-3 S/m. However, the literature (doi.org/10.1016/j.jpcs.2021.110269) shows that the ion conductivity of the sodium ion solid electrolyte Na ₆ PS ₅ Cl is low, only about 2×10 ^-5 S/m. The reason may be that Na There are essential differences in the crystal structure between ₆ PS ₅ Cl (cubic phase structure) and Li ₆ PS ₅ Cl (silver germanite structure).

In view of this, the present invention provides a sodium ion sulfide electrolyte and its preparation method and application, which improves the ionic conductivity of the material by expanding the transmission channel of sodium ions in the Na ₆ PS ₅ Cl structure.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A sodium ion sulfide electrolyte with a cubic phase structure and a chemical formula of Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x ,

Where, x=0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3.

The invention also provides a preparation method for the above-mentioned sodium ion sulfide electrolyte, which includes the following steps:

(1) Mix Na ₂ S, P ₂ S ₅ , NaCl and NaBF ₄ in the above proportions and implement solid phase ball milling;

(2) After solid-phase ball milling, the material is pressed into tablets and then calcined in a vacuum environment.

As raw materials for this application, suitable but non-limiting examples are Na ₂ S, P ₂ S ₅ , NaCl and NaBF _4. P ₂ S ₅ can also be replaced by P powder plus S powder according to the metering ratio, and NaBF ₄ can also be used. NaPF ₆ , NaCN, NaBH ₄ , NaNH ₂ , NaSCN, NaBr or NaI can be used instead.

On the basis of the above technical solutions, the present invention can also make the following improvements:

Further, the solid phase ball milling process described in step (1) is carried out in a protective gas environment;

The protective gas is argon, or may be nitrogen, hydrogen and argon mixed atmosphere, or other inert atmosphere.

Further, the ball milling speed described in step (1) is 280 to 400 rpm, and the ball milling time is 8 to 16 hours.

Further, the material after solid phase ball milling described in step (2) is a sheet-shaped material obtained by cold pressing.

Furthermore, the pressure of the cold pressing molding is 10-30MPa.

Furthermore, the calcination process described in step (2) is only carried out in a vacuum environment and cannot be protected by an inert atmosphere, otherwise impurities will be generated.

Further, the calcination temperature is 280-360°C, and the calcination time is 8-16 hours.

The present invention also provides the application of the above-mentioned sodium ion sulfide electrolyte as a solid electrolyte in sodium ion batteries.

The beneficial effects of the present invention are:

This application uses the method of introducing BF ₄ ^-groups to electrochemically modify the electrolyte material Na ₆ PS ₅ Cl. After the BF ₄ ^- anionic group partially replaces the Cl- anion site, the transmission channel of sodium ions will be expanded, the ionic conductivity of the solid electrolyte will be improved, and Na ₆ PS with high ionic conductivity can be prepared in batches at a lower temperature. ₅ Cl _1-x (BF ₄ ) _x (x=0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) solid electrolyte, optimized Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x electrolyte material tested , the ionic conductivity is as high as about 2×10 ^-3 S/m. Compared with the reported unmodified Na ₆ PS ₅ Cl, the ionic conductivity is improved by one to two orders of magnitude, which makes Na ₆ PS ₅ Cl _{1- x} (BF ₄ ) _x Solid electrolyte has great commercial value in terms of electrochemical performance.

Description of the drawings

Figure 1 is an XRD comparison chart of Example 5 and Comparative Example 5 of the present application;

Figure 2 is a comparison chart of ionic conductivity between Example 5 and Comparative Example 5 of the present application;

Figure 3 is a comparison chart of the experimental results of Experimental Example 7 and Comparative Example 7 of the present application.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

To the extent that it does not conflict with the commonly used meanings in the relevant technology, the terms in this application shall be subject to the following interpretations:

As used herein, "ball milling" refers to the method of pulverizing and mixing materials by utilizing the impact of falling grinding bodies (such as steel balls, etc.) and the grinding action of the grinding bodies and the inner wall of the ball mill.

As used herein, "calcining" means heating a raw material such as an inorganic material to a high temperature without melting in order to produce useful physical and chemical changes in order to convert or remove certain undesirable materials contained therein.

Example 1

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.05) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 1.11gNaCl, 0.11gNaBF ₄ into the ball mill tank, set the ball milling speed to 385rpm, and the ball milling time to 10h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 12MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 280°C and the calcination time to 12h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Example 2

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.1) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 1.05gNaCl, 0.22gNaBF ₄ into the ball mill tank, set the ball milling speed to 400rpm, and the ball milling time to 12h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 15MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 300°C and the calcination time to 10h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Example 3

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.15) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 0.994gNaCl, 0.33gNaBF ₄ into the ball mill tank, set the ball milling speed to 380rpm, and the ball milling time to 8h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 20MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 320°C and the calcination time to 8h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Example 4

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.2) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 0.935gNaCl, 0.44gNaBF ₄ into the ball mill tank, set the ball milling speed to 450rpm, and the ball milling time to 16h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 11MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 340°C and the calcination time to 16h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Example 5

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.25) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 0.876gNaCl, 0.55gNaBF ₄ into the ball mill tank, set the ball milling speed to 420rpm, and the ball milling time to 9h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 16MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 360°C and the calcination time to 15h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Example 6

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.3) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 0.818gNaCl, 0.66gNaBF ₄ into the ball mill tank, set the ball milling speed to 410rpm, and the ball milling time to 9h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 15MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 350°C and the calcination time to 14h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Example 7

The preparation method of sodium ion sulfide electrolyte Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.01) is prepared by adopting the following preparation steps:

1) Under an inert atmosphere, add 3.9gNa ₂ S, 2.22gP ₂ S ₅ , 1.157gNaCl, 0.022gNaBF ₄ into the ball mill tank, set the ball milling speed to 400rpm, and the ball milling time to 9h;

2) Under an inert atmosphere, collect the above mixture and perform cold pressing at 16MPa to prepare precursor wafers;

3) Place the precursor wafers in step 2) into the tube furnace, and evacuate the tube furnace. Set the temperature to 320°C and the calcination time to 10h. Finally, the reacted products were collected and subjected to XRD physical phase and electrochemical testing.

Comparative example 1

The only difference from Embodiment 1 is that x=0. That is, put 3.9gNa ₂ S, 2.222gP ₂ S ₅ and 1.17gNaCl into the ball mill tank. The rest of the steps are the same.

Comparative example 2

The only difference from Embodiment 2 is that x=0. That is, put 3.9gNa ₂ S, 2.222gP ₂ S ₅ and 1.17gNaCl into the ball mill tank. The rest of the steps are the same.

Comparative example 3

The only difference from Embodiment 3 is that x=0. That is, put 3.9gNa ₂ S, 2.222gP ₂ S ₅ and 1.17gNaCl into the ball mill tank. The rest of the steps are the same.

Comparative example 4

The only difference from Embodiment 4 is that x=0. That is, put 3.9gNa ₂ S, 2.222gP ₂ S ₅ and 1.17gNaCl into the ball mill tank. The rest of the steps are the same.

Comparative example 5

The only difference from Embodiment 5 is that x=0. That is, put 3.9gNa ₂ S, 2.222gP ₂ S ₅ and 1.17gNaCl into the ball mill tank. The rest of the steps are the same.

Comparative example 6

The only difference from Embodiment 6 is that x=0. That is, put 3.9gNa ₂ S, 2.222gP ₂ S ₅ and 1.17gNaCl into the ball mill tank. The rest of the steps are the same.

Comparative example 7

The only difference from Example 7 is that the tube furnace is not evacuated and pure Ar gas is introduced instead. The rest of the steps are the same.

Experimental example 1

1. Evaluation process

XRD analysis was performed on the solid electrolyte products of all the above examples and comparative examples using a D8 model XRD analyzer produced by Bruker, Germany. The specific operation process is: put the target test sample into a special (air-isolated) sample stage, 0.01°/step, and the test range is 10°-60°.

Conduct conductivity tests on the sodium ion solid electrolyte products of all the above examples and comparative examples. The French Bio-Logic electrochemical workstation was used for AC impedance testing. First, weigh 300 mg of solid electrolyte sample and place it in a mold with a diameter of 10 mm. Use 10 MPa pressure to press the solid electrolyte into a small disc. After applying gold powder slurry on both ends of the disc, place it in the test mold for AC impedance testing. Among them, the AC impedance Hertz setting interval range is 100MHz ~ 10μHz. After measuring the impedance data, calculate the ionic conductivity of the sample.

2. Evaluation results

Figure 1 is a comparison of the XRD diffraction peaks of Example 5 and Comparative Example 5. Compared with Comparative Example 5, the main peak of the sample of Example 5 is sharper, but no new impurity peaks are generated.

Table 1 shows the conductivity results of the sodium ion solid electrolyte products of all examples and all comparative examples. It can be seen from Table 1 that the ion conductivity of the comparative examples is significantly lower than that of the examples of this application, which illustrates the introduction of BF ₄ ^- in this application. The technical contribution of anionic groups to the improvement of ionic conductivity of sodium ion solid electrolytes. The reason may be that the introduction of BF ₄ ^- anionic group expands the transmission channel of sodium ions, thereby increasing the conduction migration rate of sodium ions in the lattice structure.

Table 1

Figure 2 is a comparison of the AC impedance of Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x Example 5 and Comparative Example 5. It can be seen from the figure that the charge transfer resistance of Example 5 is about 300Ω, while the charge transfer resistance of Comparative Example 5 is as high as 3000Ω. This data shows that compared with x=0, the charge transfer resistance of the sample when x=0.25 is lower, so Example 5 has higher ionic conductivity.

In Figure 3, a is the appearance of Comparative Example 7, b is the appearance of Example 7, c is the XRD comparison of the samples of Comparative Example 7 and Example 7, the "#" symbol represents impurity peaks, and "*" represents missing peaks. As can be seen from Figure 3, when Ar inert atmosphere is used to protect the reaction environment, the product fails to maintain its original wafer shape but deforms, and blood-red impurities appear on the surface; when vacuum conditions are used to protect the reaction environment, the product still maintains The original disc shape has been lost, and the color is uniformly yellow. Compared with the vacuum condition, the inert atmosphere has two more peaks at 27° and 56° (positions marked with # in the picture), and many peaks are missing. (The position marked by * in the figure) is related to the blood-red impurities on the surface of the sample in Figure 3(a). It can be seen that although the introduction of inert atmosphere and vacuum conditions is a simple environmental protection mechanism in the field of lithium ion sulfide solid electrolyte synthesis , but in the field of sodium ion sulfide solid electrolyte synthesis, introducing an inert atmosphere will affect the production of products, and even generate other substances.

In addition, during the experiment, it was found that when the temperature increased to 190°, the pressure gauge value of the air pressure valve would rise rapidly, which shows that the precursor of Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.01) is A large amount of gas will be released during the heating process. The gas has a strong rotten egg smell, which is speculated to be related to hydrogen sulfide, and hydrogen sulfide gas contains sulfur sources. In Comparative Example 7, introducing an inert atmosphere into the glass tube will greatly dilute the hydrogen sulfide gas in the glass tube, resulting in insufficient sulfur sources in the reaction system, which will eventually lead to Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x ( x=0.01) The sample is not completely vulcanized, causing the sample to turn into a blood-red substance. The vacuum condition in Example 7 belongs to a closed environment, and the hydrogen sulfide gas released during the heating process of the Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.01) precursor will always be enclosed in the glass tube, as The sulfur source for the sulfidation of the Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x = 0.01) sample makes the Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x = 0.01) sample more completely sulfurized, Finally, a high-purity Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x (x=0.01) sample can be obtained.

Claims (9)

1. A sodium ion sulfide electrolyte, characterized in that the electrolyte has a cubic phase structure and the chemical formula is Na ₆ PS ₅ Cl _1-x (BF ₄ ) _x , Among them, x=0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3. 2. A method for preparing sodium ion sulfide electrolyte, which is characterized by comprising the following steps: (1) Mix Na ₂ S, P ₂ S ₅ , NaCl and NaBF ₄ according to the proportion in claim 1 and implement solid phase ball milling; (2) After solid-phase ball milling, the material is pressed into tablets and then calcined in a vacuum environment. 3. The preparation method of sodium ion sulfide electrolyte according to claim 2, characterized in that the solid-phase ball milling process in step (1) is carried out in a protective gas environment; The protective gas is argon. 4. The preparation method of sodium ion sulfide electrolyte according to claim 2, characterized in that the ball milling speed in step (1) is 280~400rpm, and the ball milling time is 8~16h. 5. The method for preparing sodium ion sulfide electrolyte according to claim 2, characterized in that the solid-phase ball milled material in step (2) is a sheet-shaped material obtained by cold pressing. 6. The preparation method of sodium ion sulfide electrolyte according to claim 5, characterized in that the pressure of the cold pressing molding is 10~30MPa. 7. The method for preparing sodium ion sulfide electrolyte according to claim 2, characterized in that the calcination in step (2) is performed in a vacuum environment. 8. The preparation method of sodium ion sulfide electrolyte according to claim 7, characterized in that the calcination temperature is 280~360°C, and the calcination time is 8~16h. 9. Application of the sodium ion sulfide electrolyte according to any one of claims 1 to 8 as a solid electrolyte in sodium ion batteries.