High-conductivity melt material for sodium salt energy storage batteries and preparation method and application thereof

Abstract

This invention discloses a high-conductivity melt material for sodium salt energy storage batteries, its preparation method, and its application, belonging to the field of battery material technology. The invention involves mixing zinc chloride and sodium chloride under vacuum to obtain a mixture; adding the resulting mixture to a melting vessel, heating, and stirring after complete melting to ensure no molten material splashing; ultimately, a high-conductivity melt material is obtained. This invention proposes binary and ternary molten salt systems based on NaCl-ZnCl2 as a new generation of melt materials. The NaCl-ZnCl2 system exhibits higher electronic conductivity, ionic conductivity, ionic activity, and hydrolysis resistance. Using sodium chloride and zinc chloride as raw materials, and lithium chloride and lithium fluoride as additives, this invention employs a melt-overflow process to prepare a high-purity, hydrolysis-free NaCl-ZnCl2 melt, which can be used for the mass production of sodium salt battery melts.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a high-conductivity melt material for sodium salt energy storage batteries, its preparation method, and its application. Background Technology

[0002] Since the beginning of the 21st century, clean energy has become a focus of attention for countries around the world. New energy sources such as photovoltaics and wind power have rapidly attracted attention due to their pollution-free nature, wide range of applications, and broad development prospects. However, whether it is wind or solar power, direct grid connection requires the support of safe energy storage batteries.

[0003] Sodium-ion batteries, as a novel type of energy storage battery, have broad application prospects due to their numerous advantages, including high safety, maintenance-free operation, high specific energy, strong environmental adaptability, and environmental friendliness. As a key material in sodium-ion batteries with high performance requirements, the melt material faces increasingly stringent demands, requiring higher ionic conductivity, electronic conductivity, ionic activity, and hydrolysis resistance. Currently, the most commonly used melt material is sodium tetrachloroaluminate (NaAlCl4), prepared by the mutual melting of sodium chloride (NaCl) and aluminum chloride (AlCl3). It possesses good Na-ion conductivity and electronic conductivity, and when filled into the positive electrode particles in sodium-ion batteries, it simultaneously transports sodium ions and conducts electrons, playing a crucial role in the internal resistance and discharge performance of sodium-ion batteries, making it one of the core materials. However, with the increasing application of sodium-ion batteries in energy storage, even higher requirements are placed on the melt material performance, namely, higher sodium-ion conductivity, low resistivity, high ionic activity, and hydrolysis resistance. Based on this, the present invention proposes a new melt material and its preparation process. Summary of the Invention

[0004] To address the above technical problems, this invention provides a high-conductivity melt material for sodium-based energy storage batteries, its preparation method, and its applications. Unlike the NaCl-AlCl3 binary molten salt system based on sodium tetrachloroaluminate (NaAlCl4), this invention proposes a new generation of molten salt systems based on NaCl-ZnCl2 as binary and ternary molten salt materials. The NaCl-ZnCl2 system exhibits higher electronic conductivity, ionic conductivity, ionic activity, and hydrolysis resistance. Using sodium chloride and zinc chloride as raw materials, this invention employs a melt-overflow process to prepare a high-purity, hydrolysis-free NaCl-ZnCl2 melt, which can be used for the mass production of sodium-based battery melts. The high-conductivity melt material obtained by this invention is mainly used for preparing sodium-based battery melts and sodium-sulfur battery melts. The preparation process of this invention can also be used for the preparation of solid-state lithium battery cathode materials and high-temperature molten salt materials. The sodium-based battery cathode material of this invention mainly consists of sodium chloride (NaCl), nickel powder, and a melt, i.e., molten salt. The positive electrode material reaction during charging and discharging is as follows: during charging, NaCl + Ni accepts positive charge (i.e., loses electrons) to generate sodium ions and nickel chloride; during discharging, the reaction is reversed. In battery assembly, sodium chloride and nickel powder are filled into the battery as solid particles. Gaps between these particles hinder the transport of sodium ions and electrons. Molten salt, in liquid form, fills these gaps and plays an auxiliary role in the transport of sodium ions and electrons during charging and discharging. Although it does not participate in the electrochemical reaction, it plays a significant role in the transport of sodium ions and electrons and is a key material for reducing battery internal resistance.

[0005] The first objective of this invention is to provide a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, comprising the following steps:

[0006] Zinc chloride and sodium chloride were mixed under vacuum to obtain a mixture;

[0007] The resulting mixture is added to a melting vessel, and heating is started. After it is completely melted, stirring is started to ensure that the melt does not splash. The final product is a melt material with high electrical conductivity.

[0008] In some embodiments of the present invention, the mass ratio of zinc chloride to sodium chloride is (72.2:27.8) to (68.4:31.6).

[0009] In some embodiments of the present invention, the vacuum level of the vacuum environment is <1 Pa.

[0010] In some embodiments of the present invention, the heating temperature is 270~280°C and the heating time is 1~2 hours.

[0011] In some embodiments of the present invention, the stirring rate is <30 rpm.

[0012] In some embodiments of the present invention, additives, namely lithium chloride and lithium fluoride, are added to the mixture.

[0013] In some embodiments of the present invention, the mass ratio of lithium chloride to lithium fluoride is (3:2) to (1:1).

[0014] In some embodiments of the present invention, the mass ratio of the additive to the sum of the mixed masses of zinc chloride and sodium chloride is (0.4~1):100.

[0015] A second objective of this invention is to provide a high-conductivity melt material for sodium salt energy storage batteries, prepared by the aforementioned preparation method.

[0016] The third objective of this invention is to provide a positive electrode material, including the high conductivity melt material for sodium salt energy storage batteries; the high conductivity melt material has high conductivity, low hydrolysis, simple manufacturing process, and can be continuously produced.

[0017] The beneficial effects of this invention are:

[0018] Higher electronic conductivity: The electronic conductivity of the original sodium tetrachloroaluminate (NaAlCl4) melt at 280℃ is 0.78 S / cm, while the electronic conductivity of the NaCl-ZnCl2 melt used in this invention is >1.23 S / cm.

[0019] Higher sodium ion conductivity: Using the internal resistance comparison method after assembly into a battery, the internal resistance of the battery using the NaCl-ZnCl2 melt of the present invention is reduced by 5.4%~6.4% compared with the original sodium tetrachloroaluminate NaAlCl4 internal resistance, which translates to a reduction of 16.4%~18.2% in sodium ion conductivity.

[0020] Superior hydrolysis resistance: Traditional sodium tetrachloroaluminate (NaAlCl4) melts are prone to hydrolysis due to the hygroscopic nature of AlCl3, which generates Al(OH)3 and HCl impurities. This causes turbidity and introduces impurities, affecting the purity and electrical properties of the melt. The ZnCl2 component used in this invention possesses excellent hydrolysis resistance, preventing the introduction of Al(OH)3 and HCl impurities during the preparation process.

[0021] More stable, efficient and continuous production capacity: The original sodium tetrachloroaluminate (NaAlCl4) melt needs to stand and settle for more than 4 hours after heating and melting in the preparation process to settle and absorb moisture and form impurities. This invention does not require settling. It adopts a process of direct overflow of the upper layer solution after heating and melting, which can achieve continuous production of high-quality melt materials. Attached Figure Description

[0022] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0023] Figure 1 This is a process flow diagram of the preparation process of the high conductivity melt material for sodium salt energy storage batteries of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0025] Example 1:

[0026] This embodiment provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0027] (1) Weigh 72.2 parts by weight of zinc chloride ZnCl2 dry powder and 27.8 parts by weight of sodium chloride NaCl dry powder and add them to a vacuum mixing tank with a vacuum degree <1 Pa. Mix thoroughly, then add 0.2 g of lithium chloride and 0.2 g of lithium fluoride to obtain a mixture;

[0028] (2) After mixing, add it to the melting tank, turn on the heating, heat to 275°C, heat for 2 hours, and after it is completely melted, turn on the stirring, stirring speed <30 rpm, stir for 30 minutes, and ensure that the melt splashes during the stirring process.

[0029] (3) After stirring, open the top overflow port and let the clear melt flow out slowly for storage;

[0030] (4) Repeat step (1) to continuously supply material to the melting tank and continue the overflow process in step (2) to prepare molten material.

[0031] (5) The performance of the melt material obtained in step (4) was tested. The direct test results showed that the electronic conductivity of the melt material at 280℃ was 1.28 S / cm. The test was conducted at 280℃ using the high-temperature molten salt ion conductivity test method. The cell was fabricated using the sodium salt battery preparation process. The sodium ion resistivity decreased by 16.4% when the battery was assembled.

[0032] Example 2:

[0033] This embodiment provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0034] (1) Weigh 68.4 parts by weight of zinc chloride ZnCl2 dry powder and 31.6 parts by weight of sodium chloride NaCl dry powder and add them to a vacuum mixing tank with a vacuum degree <1 Pa. Mix thoroughly, then add 0.3 g of lithium chloride and 0.2 g of lithium fluoride to obtain a mixture;

[0035] (2) After mixing, add it to the melting tank, turn on the heating, heat to 275°C, heat for 2 hours, and after it is completely melted, turn on the stirring, stirring speed <30 rpm, stir for 30 minutes, and ensure that the melt splashes during the stirring process.

[0036] (3) After stirring, open the top overflow port and let the clear melt flow out slowly for storage;

[0037] (4) Repeat step (1) to continuously supply material to the melting tank and continue the overflow process in step (1) to prepare molten material.

[0038] (5) The performance of the melt material obtained in step (4) was tested. The direct test results showed that the electronic conductivity of the melt material at 280℃ was 1.31 S / cm. The test was conducted at 280℃ using the high-temperature molten salt ion conductivity test method. The cell was fabricated using the sodium salt battery preparation process. The sodium ion resistivity decreased by 16.9% when the battery was assembled.

[0039] Example 3:

[0040] This embodiment provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0041] (1) Weigh 69.2 parts by weight of zinc chloride ZnCl2 dry powder and 30.8 parts by weight of sodium chloride NaCl dry powder and add them to a vacuum mixing tank with a vacuum degree <1 Pa. Mix thoroughly, then add 0.3 g of lithium chloride and 0.2 g of lithium fluoride to obtain a mixture;

[0042] (2) After mixing, add it to the melting tank, turn on the heating, heat to 275°C, heat for 2 hours, and after it is completely melted, turn on the stirring. The stirring speed is <30 rpm to ensure that the melt does not splash.

[0043] (3) After stirring, open the top overflow port and let the clear melt flow out slowly for storage;

[0044] (4) Repeat step (1) to continuously supply material to the melting tank and continue step (2) to continuously overflow and prepare melt;

[0045] (5) The performance of the melt material obtained in step (4) was tested. The direct test results showed that the electronic conductivity of the melt material at 280℃ was 1.37 S / cm. The test was conducted at 280℃ using the high-temperature molten salt ion conductivity test method. The cell was fabricated using the sodium salt battery preparation process. The sodium ion resistivity decreased by 18.1% when the battery was assembled.

[0046] Example 4:

[0047] This embodiment provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0048] (1) Weigh 69.2 parts by weight of zinc chloride ZnCl2 dry powder, 31.8 parts by weight of sodium chloride NaCl dry powder, 0.3 parts by weight of lithium chloride, and 0.1 parts by weight of lithium fluoride, add them to a vacuum mixing tank with a vacuum degree <1 Pa, mix thoroughly, and then add 0.2 g of lithium chloride and 0.2 g of lithium fluoride to obtain a mixture;

[0049] (2) After mixing, add it to the melting tank, turn on the heating, heat to 275°C, heat for 2 hours, and after it is completely melted, turn on the stirring. The stirring speed is <30 rpm to ensure that the melt does not splash.

[0050] (3) After stirring, open the top overflow port and let the clear melt flow out slowly for storage;

[0051] (4) Repeat step (1) to continuously supply material to the melting tank and continue step (2) to continuously overflow and prepare melt;

[0052] (5) The performance of the melt material obtained in step (4) was tested. The direct test results showed that the electronic conductivity of the melt material at 280℃ was 1.32 S / cm. The test was conducted at 280℃ using the high-temperature molten salt ion conductivity test method. The cell was fabricated using the sodium salt battery preparation process. The sodium ion resistivity decreased by 17.7% when the battery was assembled.

[0053] Example 5:

[0054] This embodiment provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0055] (1) Weigh 69.2 parts by weight of zinc chloride ZnCl2 dry powder, 30.8 parts by weight of sodium chloride NaCl dry powder, 0.2 parts by weight of lithium chloride and 0.2 parts by weight of lithium fluoride, add them to a vacuum mixing tank with a vacuum degree <1 Pa, mix thoroughly to obtain a mixture;

[0056] (2) After mixing, add it to the melting tank, turn on the heating, heat to 275°C, heat for 2 hours, and after it is completely melted, turn on the stirring. The stirring speed is <30 rpm to ensure that the melt does not splash.

[0057] (3) After stirring, open the top overflow port and let the clear melt flow out slowly for storage;

[0058] (4) Repeat step (1) to continuously supply material to the melting tank and continue to overflow to prepare melt in step (3);

[0059] (5) The performance of the melt material obtained in step (4) was tested. The direct test results showed that the electronic conductivity of the melt material at 280℃ was 1.32 S / cm. The test was conducted at 280℃ using the high-temperature molten salt ion conductivity test method. The cell was fabricated using the sodium salt battery preparation process. The sodium ion resistivity decreased by 17.5% when the battery was assembled.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0062] (1) Weigh 72.2.6 parts of anhydrous aluminum chloride AlCl3 dry powder and 27.8 parts of sodium chloride NaCl dry powder and add them to a vacuum mixing tank with a vacuum degree <1 Pa, and mix thoroughly;

[0063] (2) After mixing, add it to the melting tank, turn on the heating, and heat to 275°C;

[0064] (3) Heat and keep warm for 10 hours until sedimentation is completely clear;

[0065] (4) Slowly pour out the clarified melt and store it for later use;

[0066] (5) The properties of the melt material were tested. The direct test results showed that the electronic conductivity at 280℃ was 0.78 S / cm. The test was conducted using the high-temperature molten salt ion conductivity test method at 280℃. The cell was fabricated using the sodium salt battery manufacturing process. The sodium ion resistivity of the assembled battery increased by 1.4%, which was almost no significant improvement.

[0067] Comparative Example 2:

[0068] This comparative example provides a method for preparing a high-conductivity melt material for sodium salt energy storage batteries, as detailed below:

[0069] (1) Weigh 68.2 parts of zinc chloride ZnCl2 dry powder and 31.8 parts of sodium chloride NaCl dry powder, add them to a vacuum mixing tank, vacuum degree <1Pa, and mix thoroughly;

[0070] (2) After mixing, add it to the melting tank, turn on the heating, heat to 275℃, and heat for 2 hours;

[0071] (3) If sediment is found to be produced, the stirring rate is <30 rpm. Turn on the stirring to ensure that the melt does not splash.

[0072] (4) After stirring for 30 minutes, open the top overflow port and let the clear melt flow out slowly. Store it for later use.

[0073] (5) Repeat step (1) to continuously supply material to the melting tank and continue to overflow to prepare melt in step (3);

[0074] (6) The properties of the melt material were tested. The direct test results showed that the electronic conductivity at 280℃ was 0.909 S / cm. The test was conducted using the high-temperature molten salt ion conductivity test method at 280℃. The cell was fabricated using the sodium salt battery manufacturing process. The sodium ion resistivity decreased by 1.5% when the battery was assembled.

[0075] Performance testing

[0076] 1. The changes in electronic conductivity and resistivity of the material melts obtained in the examples and comparative examples were tested at 280°C. The results are shown in Table 1.

[0077] Table 1

[0078] Electron conductivity at 80℃ (S / cm) Resistivity decrease (%) Example 1 1.28 16.4 Example 2 1.31 16.9 Example 3 1.37 18.1 Example 4 1.32 17.7 Example 5 1.32 17.5 Comparative Example 1 0.78 1.4% (almost no improvement) Comparative Example 2 0.909 1.5%

[0079] As shown in the table above, the melt prepared by this invention exhibits excellent electronic conductivity, more than 50% higher than that of the original sodium tetrachloroaluminate. After being assembled into a battery cell, the overall sodium ion internal resistance of the cell decreases by >15%, demonstrating excellent electronic and ion conduction characteristics. Furthermore, the entire process boasts advantages such as simplicity, controllability, continuous production, and high production efficiency. The optimal ratio of ZnCl2 to sodium chloride (NaCl) is 69.2:30.8. Adding lithium chloride (LiCl) and lithium fluoride (LiF) further optimizes the sodium ion resistivity. The resulting optimal formula is ZnCl2:NaCl:Lithium chloride (LiCl):Lithium fluoride (LiF) at a ratio of 69.2:30.8:0.3:0.1.

[0080] 2. Internal resistance test

[0081] Using the sodium salt battery manufacturing process to fabricate the battery cells, and comparing the internal resistance of the assembled batteries, the results show that the internal resistance of the battery using the NaCl-ZnCl2 melt of the present invention is reduced by 5.4% to 6.4% compared with the original sodium tetrachloroaluminate NaAlCl4 (Comparative Example 3), which translates to a reduction of 16.4% to 18.2% in sodium ion conductivity.

[0082] The embodiments described above are merely preferred embodiments for fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a high-conductivity melt material for sodium salt energy storage batteries, characterized in that, Includes the following steps: Zinc chloride and sodium chloride were mixed under vacuum to obtain a mixture; The resulting mixture is added to a melting vessel, and heating is started. After it is completely melted, stirring is started to ensure that the melt does not splash. Finally, a high-conductivity melt material is obtained.

2. The preparation method according to claim 1, characterized in that, The mass ratio of zinc chloride to sodium chloride is (72.2:27.8) to (68.4:31.6).

3. The preparation method according to claim 1, characterized in that, The vacuum level in the vacuum environment is <1 Pa.

4. The preparation method according to claim 1, characterized in that, The heating temperature is 270~280℃, and the heating time is 1~2 hours.

5. The preparation method according to claim 1, characterized in that, The stirring speed is <30 rpm.

6. The preparation method according to claim 1, characterized in that, It also includes adding additives to the mixture, namely lithium chloride and lithium fluoride.

7. The preparation method according to claim 6, characterized in that, The mass ratio of lithium chloride to lithium fluoride is (3:2) to (1:1).

8. The preparation method according to claim 6, characterized in that, The mass ratio of the additive to the mixture is (0.4~1):

100.

9. A high-conductivity melt material for sodium salt energy storage batteries, characterized in that, Prepared by the preparation method described in any one of claims 1 to 8.

10. A positive electrode material, characterized in that, Includes the high conductivity melt material for sodium salt energy storage batteries as described in claim 9.

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