A low temperature sodium-based liquid metal battery and a method of making the same

Abstract

The application belongs to the field of energy storage batteries, and particularly relates to a low-temperature sodium-based liquid metal battery and a preparation method thereof. The battery comprises a negative electrode, an electrolyte and a positive electrode. The negative electrode is sodium or an alloy of sodium. The electrolyte is an inorganic composite molten salt electrolyte, which comprises a cesium halide salt and two or more of a potassium halide salt, a sodium halide salt, a lithium halide salt and a rubidium halide salt. The molar percentage of the cesium halide salt in the electrolyte is 10-30%. By introducing the cesium halide salt into the electrolyte of the liquid metal battery, the melting point of the electrolyte is significantly reduced, so that the liquid metal battery can work at a relatively low temperature of 270-370 DEG C, and the service life of the insulating sealing material of the battery is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of energy storage batteries, specifically relating to a low-temperature sodium-based liquid metal battery and its preparation method. Background Technology

[0002] Traditional lithium-ion batteries face intractable problems in large-scale energy storage, including performance degradation, high cost, and poor safety. Liquid metal batteries are a novel electrochemical energy storage device that uses molten metal / alloy as electrodes and inorganic molten salt as electrolyte. Due to the significant density difference and immiscibility between the electrodes and electrolyte, a unique three-layer liquid structure spontaneously forms inside the battery. The upper layer is a low-density alkali or alkaline earth metal (such as Li, Na, K, Mg, Ca, etc.), the middle layer is an inorganic molten salt electrolyte, and the lower layer is a high-density, high-electrone metal (such as Sb, Pb, Sn, Bi, Te, etc.). This liquid electrode has an amorphous structure, which effectively avoids dendrite growth and can self-heal mechanical damage during cycling, exhibiting "self-healing" characteristics. Therefore, it has an extremely long lifespan and is very suitable for large-scale grid-scale static energy storage. However, to simultaneously meet the melting points of the electrodes and electrolyte, liquid metal batteries need to operate at high temperatures, which has become a major drawback. For example, currently competitive liquid metal battery systems such as Li||Sb-Pb, Li||Sb-Sn, Li||Bi, Li||Sb, Ca-Mg||Bi, and Na||Sb-Sn operate at temperatures of 480–550°C. However, due to the scarcity of Li resources and the severe corrosion caused by the high operating temperatures, the long-term stable operation of large-scale liquid metal batteries still faces significant challenges. Metallic Na has a low melting point (97.8°C) and a low density (0.93 g / cm³). 3 Sodium (Na) exhibits good compatibility with sealing materials such as Al₂O₃, and its abundance in the Earth's crust reaches 2.83% wt, making it a plentiful resource. Sodium-based liquid metal batteries possess significant potential for achieving low operating temperatures, low costs, and long lifespans, and hold broad application prospects in large-scale energy storage. Therefore, developing a low-cost liquid metal battery with a low operating temperature is of significant theoretical and practical importance.

[0003] To enable sodium-based liquid metal batteries to operate at lower temperatures, the negative electrode, positive electrode, and electrolyte must all meet melting point requirements. Typically, metallic sodium (Na) is used as the negative electrode, with a melting point of 98°C, and it remains liquid at the operating temperature, thus not a limiting factor. For the positive electrode, a series of low-melting-point, inexpensive, and high-energy-density materials exist, such as Bi-Sn (eutectic point 141°C), Bi-Pb (eutectic point 125°C), Sb-Pb (252°C), and Sn-Pb (182°C), therefore also not a limiting factor. However, electrolytes with low melting points, strong adaptability, and stable chemical properties are actually very difficult to find. For example, the melting point of Na₂CO₃-NaCl eutectic salt is 637°C, and that of NaF-NaCl-NaI eutectic salt is 501°C. Considering the difficulty in lowering the melting point of a single sodium-ion electrolyte, some researchers have proposed using multi-cation composite electrolytes, such as those with added lithium halides and potassium halides. Zhou et al. reported a liquid metal battery using LiCl-NaCl-KCl (melting point 390℃) as the electrolyte, which can operate at 450℃ (Energy Storage Materials, 2022, 50: 572–579.). However, its operating temperature is still relatively high, so further optimization of the electrolyte is needed to reduce its operating temperature. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-temperature sodium-based liquid metal battery and its preparation method, with the aim of reducing the battery's operating temperature, improving the lifespan of the liquid metal battery, and reducing additional thermal management power consumption.

[0005] According to a first aspect of the present invention, a sodium-based liquid metal battery is provided, comprising a negative electrode, an electrolyte, and a positive electrode; the negative electrode is elemental sodium or a sodium alloy; the electrolyte is an inorganic composite molten salt electrolyte, comprising cesium halide salt, and further comprising two or more salts selected from potassium halide salt, sodium halide salt, lithium halide salt, and rubidium halide salt, wherein the molar percentage of the cesium halide salt in the electrolyte is 10% to 30%.

[0006] Preferably, the potassium halide salt is selected from one or more of KCl, KBr, and KI; the sodium halide salt is selected from one or more of NaCl, NaBr, and NaI; the lithium halide salt is selected from one or more of LiCl, LiBr, and LiI; the cesium halide salt is selected from one or more of CsCl, CsBr, and CsI; and the rubidium halide salt is selected from one or more of RbCl, RbBr, and RbI.

[0007] Preferably, the inorganic composite molten salt electrolyte is a mixture of KCl, NaCl, and CsCl, wherein the molar percentage of KCl is 30-50%, the molar percentage of NaCl is 20-40%, and the molar percentage of CsCl is 10-30%; or the inorganic composite molten salt electrolyte is a mixture of RbCl, KCl, and CsCl, wherein the molar percentage of RbCl is 20-40%, the molar percentage of KCl is 30-50%, and the molar percentage of CsCl is 10-30%; or the inorganic composite molten salt electrolyte is a mixture of NaCl, LiBr, and CsCl, wherein the molar percentage of NaCl is 20-40%, the molar percentage of LiBr is 30-50%, and the molar percentage of CsCl is 10-30%. The inorganic composite molten salt electrolyte is a mixture of LiCl, KI, and CsI, wherein the molar percentage of LiCl is 20-40%, the molar percentage of KI is 30-50%, and the molar percentage of CsI is 10-30%; or the inorganic composite molten salt electrolyte is a mixture of NaCl, KBr, and CsBr, wherein the molar percentage of NaCl is 20-40%, the molar percentage of KBr is 30-50%, and the molar percentage of CsBr is 10-30%; or the inorganic composite molten salt electrolyte is a mixture of KI, LiBr, NaI, and CsCl, wherein the molar percentage of KI is 20-40%, the molar percentage of LiBr is 10-30%, and the molar percentage of CsI is 10-30%. The inorganic composite molten salt electrolyte is a mixture of KI, LiBr, NaBr, and CsCl, wherein the molar percentages of KI, LiBr, NaBr, and CsCl are 20-40%, 20-40%, 10-30%, and 10-30%, respectively; or the inorganic composite molten salt electrolyte is a mixture of KI, LiBr, NaI, and CsI, wherein the molar percentages of KI, LiBr, NaI, and CsI are 20-40%, 20-60%, 10-30%, and 10-30%, respectively. 0–30%; or the inorganic composite molten salt electrolyte is a mixture of KCl, CsCl, NaBr, and RbCl, wherein the molar percentage of KCl is 20–40%, the molar percentage of CsCl is 10–30%, the molar percentage of NaBr is 10–30%, and the molar percentage of RbCl is 10–30%; or the inorganic composite molten salt electrolyte is a mixture of KCl, LiCl, LiBr, NaCl, and CsCl, wherein the molar percentage of KCl is 20–40%, the molar percentage of LiCl is 10–40%, the molar percentage of LiBr is 10–40%, the molar percentage of NaCl is 10–30%, and the molar percentage of CsCl is 10–30%.Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KBr, LiBr, LiI, NaBr, and CsBr, wherein the molar percentages of KBr, LiBr, LiI, NaBr, and CsBr are 20–40%, 10–40%, 10–40%, 10–30%, and 10–30%; or the inorganic composite molten salt electrolyte may be a mixture of KI, LiBr, LiI, NaI, and CsI, wherein the molar percentages of KI, LiBr, LiI, NaI, and CsI are 20–40%, 10–40%, 10–40%, 10–30%, and 10–30%.

[0008] Preferably, the sodium alloy is selected from Na-K, Na-In, Na-Al or Na-Zn, and the molar percentage of sodium in the sodium alloy is greater than 40%-90%.

[0009] Preferably, the material of the positive electrode is selected from an alloy composed of two or more elements selected from Bi, Cd, Sn, and Pb.

[0010] Preferably, the positive electrode is a Bi-Sn alloy, wherein the molar percentage of Bi is 10-90%; or the positive electrode is a Bi-Pb-Cd alloy, wherein the molar percentage of Bi is 50-60%, the molar percentage of Pb is 10-30%, and the molar percentage of Cd is 10-30%; or the positive electrode is a Bi-Pb-Sn alloy, wherein the molar percentage of Bi is 50-60%, the molar percentage of Pb is 20-30%, and the molar percentage of Sn is 10-30%; or the positive electrode is a Bi-Pb-Sn-Cd alloy, wherein the molar percentage of Bi is 50-60%, the molar percentage of Pb is 20-30%, the molar percentage of Sn is 10-20%, and the molar percentage of Cd is 10-20%.

[0011] Preferably, the battery operates at a temperature of 270–370°C, and the negative electrode, electrolyte, and positive electrode are all in a liquid state at the operating temperature.

[0012] According to another aspect of the present invention, a method for preparing the sodium-based liquid metal battery is provided, the specific preparation steps of which are as follows:

[0013] (1) Prepare a positive electrode alloy material by placing the positive electrode alloy material in a shell to obtain a positive electrode;

[0014] (2) Melt the electrolyte and pour it into the positive electrode to make the electrolyte molten;

[0015] (3) The negative electrode current collector adsorbed with elemental sodium or sodium alloy is placed in an electrolyte in a molten state and submerged by the electrolyte;

[0016] (4) Assemble the top cover onto the housing and weld it to obtain a sodium-based liquid metal battery; wherein, steps (1) to (4) are all carried out under the protection of a protective gas.

[0017] Preferably, the negative electrode current collector is selected from foamed iron-nickel or foamed aluminum.

[0018] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0019] (1) This invention innovatively introduces cesium halide salts (such as CsCl, CsBr, CsI) into the electrolyte of a liquid metal battery. By precisely adjusting the molar percentage of cesium halide salts to 10%–30%, the melting point of the electrolyte is significantly reduced without sacrificing electrolyte stability, allowing the liquid metal battery to operate at a lower temperature of 270–370°C. The lower operating temperature not only significantly reduces the power consumption of the thermal management system but also effectively extends the lifespan of the battery's insulating and sealing materials.

[0020] (2) By rationally considering and optimizing the amount of each substance in the electrolyte, the molar percentage of other halides is precisely controlled to ensure that the electrolyte has high ion mobility, excellent fluidity and chemical stability at low temperatures, significantly improving the cycle life and safety of the battery. At the same time, a dynamic multi-component compounding technology is proposed, which allows the formulation to be optimized in real time according to specific application requirements.

[0021] (3) The negative electrode sodium alloy of the present invention includes, but is not limited to, Na-K, Na-In, Na-Al or Na-Zn alloys, and the positive electrode material is selected from alloys composed of two or more elements among Bi, Cd, Sn and Pb. The melting point and electrochemical performance are further optimized by adjusting the alloy ratio.

[0022] (4) The electrolyte system of the present invention has the characteristics of low temperature, high performance, environmental protection, economy and wide applicability, and is suitable for a variety of application scenarios such as large-scale energy storage, low temperature extreme environment and high power output. Attached Figure Description

[0023] Figure 1 This is a DSC (melting point) test conducted before cycling the electrolyte battery described in Example 1.

[0024] Figure 2 This is a DSC (melting point) test conducted before cycling the electrolyte battery described in Example 2.

[0025] Figure 3This is a DSC (melting point) test conducted before cycling the electrolyte battery described in Example 3.

[0026] Figure 4 This is a DSC (melting point) test conducted before cycling the electrolyte battery described in Example 4.

[0027] Figure 5 The discharge curve of the battery described in Example 2 at 350°C is shown.

[0028] Figure 6 The cycling curve of the battery described in Example 2 at 350°C. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Example 1

[0031] A liquid metal battery is produced according to the following steps:

[0032] (1) Under the protection of inert gas, weigh 14.5g of bismuth particles and 13.2g of tin particles and place them in a graphite crucible (inner diameter 56mm);

[0033] (2) Under the protection of inert gas, the graphite crucible was heated to 300°C on a heating plate and held for 2 hours to melt the bismuth and tin metals to form an alloy; then it was naturally cooled to room temperature, and then the graphite crucible was placed in a stainless steel shell of the same size.

[0034] (3) Under the protection of inert gas, 2.7g of liquid metallic Na was absorbed by aluminum foam as the negative electrode;

[0035] (4) Under inert gas protection, 65g of dry KI 27 -LiBr 53 -NaI 10 -CsCl 10 ,Depend on Figure 1 It is known that the electrolyte has a melting point of 313°C. The mixed salt is heated and melted, and then poured into the aforementioned graphite crucible.

[0036] (5) Under the protection of inert gas, the aluminum foam current collector with metal adsorbed and the top cover are assembled onto the shell with molten salt added (not solidified), and then naturally cooled to room temperature.

[0037] (6) The casing and top cover are welded together using laser welding or argon arc welding to obtain the assembled battery;

[0038] (7) Place the battery in the test furnace, heat it to the working temperature and maintain it at a constant temperature, and connect it to the battery test system to perform battery testing.

[0039] Example 2

[0040] A liquid metal battery is produced according to the following steps:

[0041] (1) Under the protection of inert gas, weigh 38.98g of bismuth particles, 5.52g of lead particles and 9.49g of tin particles and place them in a graphite crucible (inner diameter 56mm).

[0042] (2) Under the protection of inert gas, the aforementioned graphite crucible is heated to 400°C on a heating plate and held for 2 hours to melt bismuth, lead and tin to form an alloy; then it is naturally cooled to room temperature, and then the graphite crucible is placed in a stainless steel shell of the same size.

[0043] (3) Under the protection of inert gas, 10.5g of liquid metallic Na was absorbed by nickel foam as the negative electrode;

[0044] (4) Under inert gas protection, 180g of dry KI 27 -LiBr 53 -NaI 10 -CsI 10 ,Depend on Figure 2 It is known that the electrolyte has a melting point of 330°C. The mixed salt is heated and melted, and then poured into the aforementioned graphite crucible.

[0045] (5) Under the protection of inert gas, the aluminum foam current collector with metal adsorbed and the top cover are assembled onto the shell with molten salt added (not solidified), and then naturally cooled to room temperature.

[0046] (6) The casing and top cover are welded together using laser welding or argon arc welding to obtain the assembled battery;

[0047] (7) Place the battery in a test furnace, heat it to the operating temperature and maintain a constant temperature, then connect it to the battery testing system for battery testing. Perform a charge-discharge experiment on the prepared battery at 350℃ to obtain the discharge curve, as shown below. Figure 5 As shown in the figure, the battery can operate stably at this temperature; the prepared battery was subjected to a cycle test at 350℃, and the cycle curve was obtained, as shown in the figure. Figure 6 As shown in the figure, the coulombic efficiency reaches 99% after the battery has run for more than 125 cycles.

[0048] Example 3

[0049] A liquid metal battery is produced according to the following steps:

[0050] (1) Under the protection of inert gas, weigh 14.5g of bismuth particles, 8g of lead particles and 5g of tin particles and place them in a graphite crucible (inner diameter 56mm).

[0051] (2) Under the protection of inert gas, the aforementioned graphite crucible is heated to 400°C on a heating plate and held for 2 hours to melt bismuth, lead and tin to form an alloy; then it is naturally cooled to room temperature, and then the graphite crucible is placed in a stainless steel shell of the same size.

[0052] (3) Under the protection of inert gas, 2.7g of liquid metallic Na was absorbed by aluminum foam as the negative electrode;

[0053] (4) Under inert gas protection, 65g of dry KI 24 -LiBr 28 -NaBr 28 -CsCl 20 ,Depend on Figure 3 It is known that the lowest melting point of this system is 276℃. The mixed salt is heated and melted, and then poured into the aforementioned graphite crucible.

[0054] (5) Under the protection of inert gas, the aluminum foam current collector with metal adsorbed and the top cover are assembled onto the shell with molten salt added (not solidified), and then naturally cooled to room temperature.

[0055] (6) The casing and top cover are welded together using laser welding or argon arc welding to obtain the assembled battery;

[0056] (7) Place the battery in the test furnace, heat it to the working temperature and maintain it at a constant temperature, and connect it to the battery test system to perform battery testing.

[0057] Example 4

[0058] A liquid metal battery is produced according to the following steps:

[0059] (1) Under the protection of inert gas, weigh 5.77g of bismuth particles, 3.08g of lead particles, 0.85g of tin particles and 0.29g of cadmium particles and place them in a graphite crucible (inner diameter 56mm).

[0060] (2) Under the protection of inert gas, the aforementioned graphite crucible is heated to 400°C on a heating plate and held for 2 hours to melt bismuth, lead and tin to form an alloy; then it is naturally cooled to room temperature, and then the graphite crucible is placed in a stainless steel shell of the same size.

[0061] (3) Under the protection of inert gas, 2.7g of liquid metallic Na was absorbed by aluminum foam as the negative electrode;

[0062] (4) Under inert gas protection, 40g of dry KCl 24 -CsCl 28 -NaBr 28 -RbCl 20 ,Depend on Figure 4 It is known that the lowest melting point of this system is 265℃. The mixed salt is heated and melted, and then poured into the aforementioned graphite crucible.

[0063] (5) Under the protection of inert gas, the aluminum foam current collector with metal adsorbed and the top cover are assembled onto the shell with molten salt added (not solidified), and then naturally cooled to room temperature.

[0064] (6) The casing and top cover are welded together using laser welding or argon arc welding to obtain the assembled battery;

[0065] (7) Place the battery in the test furnace, heat it to the working temperature and maintain it at a constant temperature, and connect it to the battery test system to perform battery testing.

[0066] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sodium-based liquid metal battery, characterized in that, The battery comprises a negative electrode, an electrolyte, and a positive electrode; the negative electrode is elemental sodium or a sodium alloy; the electrolyte is an inorganic composite molten salt electrolyte, which includes cesium halide salts, and further includes two or more salts selected from potassium halide salts, sodium halide salts, lithium halide salts, and rubidium halide salts, wherein the molar percentage of the cesium halide salt in the electrolyte is 10% to 30%; the battery operates at a temperature of 270 to 370°C. o C, wherein the negative electrode, electrolyte, and positive electrode are all in a liquid state at the operating temperature; the inorganic composite molten salt electrolyte is a mixture of KCl, NaCl, and CsCl, wherein the molar percentage of KCl is 30-50%, the molar percentage of NaCl is 20-40%, and the molar percentage of CsCl is 10-30%; Alternatively, the inorganic composite molten salt electrolyte may be a mixture of NaCl, LiBr, and CsCl, wherein the molar percentage of NaCl is 20-40%, the molar percentage of LiBr is 30-50%, and the molar percentage of CsCl is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of NaCl, KBr, and CsBr, wherein the molar percentage of NaCl is 20-40%, the molar percentage of KBr is 30-50%, and the molar percentage of CsBr is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KI, LiBr, NaI, and CsCl, wherein the molar percentage of KI is 20-40%, the molar percentage of LiBr is 20-60%, the molar percentage of NaI is 10-30%, and the molar percentage of CsCl is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KI, LiBr, NaBr, and CsCl, wherein the molar percentage of KI is 20-40%, the molar percentage of LiBr is 20-40%, the molar percentage of NaBr is 10-30%, and the molar percentage of CsCl is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KI, LiBr, NaI, and CsI, wherein the molar percentage of KI is 20-40%, the molar percentage of LiBr is 20-60%, the molar percentage of NaI is 10-30%, and the molar percentage of CsI is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KCl, CsCl, NaBr, and RbCl, wherein the molar percentage of KCl is 20-40%, the molar percentage of CsCl is 10-30%, the molar percentage of NaBr is 10-30%, and the molar percentage of RbCl is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KCl, LiCl, LiBr, NaCl, and CsCl, wherein the molar percentage of KCl is 20-40%, the molar percentage of LiCl is 10-40%, the molar percentage of LiBr is 10-40%, the molar percentage of NaCl is 10-30%, and the molar percentage of CsCl is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KBr, LiBr, LiI, NaBr, and CsBr, wherein the molar percentage of KBr is 20-40%, the molar percentage of LiBr is 10-40%, the molar percentage of LiI is 10-40%, the molar percentage of NaBr is 10-30%, and the molar percentage of CsBr is 10-30%. Alternatively, the inorganic composite molten salt electrolyte may be a mixture of KI, LiBr, LiI, NaI, and CsI, wherein the molar percentage of KI is 20-40%, the molar percentage of LiBr is 10-40%, the molar percentage of LiI is 10-40%, the molar percentage of NaI is 10-30%, and the molar percentage of CsI is 10-30%.

2. A sodium-based liquid metal battery according to claim 1, wherein, The sodium alloy is selected from Na-K, Na-In, Na-Al or Na-Zn, and the molar percentage of sodium in the sodium alloy is 40%-90%.

3. The sodium-based liquid metal battery of claim 1, wherein, The positive electrode material is selected from an alloy composed of two or more elements among Bi, Cd, Sn, and Pb.

4. A sodium-based liquid metal battery according to claim 3, wherein, The cathode is a Bi-Sn alloy, wherein the molar percentage of Bi is 10-90%; or the cathode is a Bi-Pb-Cd alloy, wherein the molar percentage of Bi is 50-60%, the molar percentage of Pb is 10-30%, and the molar percentage of Cd is 10-30%; or the cathode is a Bi-Pb-Sn alloy, wherein the molar percentage of Bi is 50-60%, the molar percentage of Pb is 20-30%, and the molar percentage of Sn is 10-30%; or the cathode is a Bi-Pb-Sn-Cd alloy, wherein the molar percentage of Bi is 50-60%, the molar percentage of Pb is 20-30%, the molar percentage of Sn is 10-20%, and the molar percentage of Cd is 10-20%.

5. The method of any one of claims 1-4, wherein the sodium-based liquid metal battery is prepared by the method comprising: providing a sodium metal source; providing a molten salt electrolyte; and providing a cathode material. The specific preparation steps are as follows: (1) Prepare a positive electrode alloy material by placing the positive electrode alloy material in a shell to prepare a positive electrode; (2) Melt the electrolyte and pour it into the positive electrode to make the electrolyte molten; (3) The negative electrode current collector adsorbed with elemental sodium or sodium alloy is placed in an electrolyte in a molten state and submerged by the electrolyte; (4) Assemble the top cover onto the shell and weld it to obtain a sodium-based liquid metal battery; wherein, steps (1) to (4) are all carried out under the protection of protective gas.

6. The method of claim 5, wherein the sodium-based liquid metal battery is prepared by the steps of: The negative electrode current collector is selected from foamed iron-nickel or foamed aluminum.

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