Preparation of molten salt electrolyte and application of molten salt electrolyte in aluminum ion battery

Abstract

The invention belongs to the technical field of aluminum ion batteries, and particularly relates to preparation of a molten salt electrolyte and application of the molten salt electrolyte in an aluminum ion battery. In order to design and develop an electrolyte with higher working voltage and larger storage capacity, a fused salt composed of AlCl3 and NaCl is used as the electrolyte, and a novel non-aqueous rechargeable aluminum ion battery is formed. The aluminum ion battery has high specific capacity and excellent cycling stability, the charging specific capacity and the discharging specific capacity of the second circle are 152 mAh.g <-1 > and 168 mAh.g <-1 > respectively, and the specific capacity of the battery can be maintained at 114 mAh.g <-1 > after 200 circles of circulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum-ion batteries, and particularly relates to the preparation of a molten salt electrolyte and its application in aluminum-ion batteries. Background Art

[0002] In the past few decades, the continuous consumption of fossil fuels, the sharp emission of greenhouse gases, and the sharp rise of PM2.5 have attracted extensive attention to renewable energy storage. For this reason, people have begun to seek and develop renewable green energies, such as wind energy, solar energy, etc. Since these renewable energies are unevenly distributed in time and space, they usually need to be equipped with efficient energy storage devices to be used. Since the 1990s, lithium-ion batteries have achieved unprecedented development and application. However, the lithium resources and cobalt resources necessary for the preparation of lithium-ion batteries are limited in reserves in the earth's crust and are unevenly distributed, which to a certain extent restricts the large-scale application of lithium-ion batteries in smart grids. In the past 10 years, the extensive production and use of lithium-ion batteries have led to a sharp rise in the price of lithium resources. From the strategic height of sustainable development, it is imperative to develop a low-cost, high-safety, and long-cycle-life chemical power supply system using elements with richer reserves on the earth. Thus, low-cost batteries using other metal negative electrode materials (including sodium, potassium, magnesium, calcium, and aluminum, etc.) have attracted the interest of many researchers and are considered candidates for an ideal electrochemical storage system.

[0003] Aluminum ranks first among various metals in the earth's crust (8% aluminum vs 0.0065% lithium), and its annual global extraction volume is more than 1000 times that of lithium. And the theoretical capacitance of metallic aluminum is 2978 mAh·g -1 and 8034 mAh·L -1 , and the volume specific capacity is about four times that of lithium. Therefore, using metallic aluminum as the charge carrier of a secondary battery can greatly reduce the production cost of the battery.

[0004] In the past 30 years, the research on aluminum batteries has never stopped, but the battery performance reported in relevant research is relatively poor. Compared with the widely studied cathode materials, the current research on the electrolytes of aluminum-ion batteries is relatively less. As an important part of aluminum-ion batteries, the performance parameters of electrolytes greatly affect the overall performance of the batteries. Generally speaking, aluminum-ion battery electrolytes can be divided into aqueous electrolytes and non-aqueous electrolytes. Among them, aqueous electrolytes are usually composed of strong acidic aluminum salt aqueous solutions. Although they have the advantage of environmental friendliness, the formation of the surface oxidation passivation film will block the contact between the aluminum negative electrode and the electrolyte, reducing the battery voltage and reaction efficiency. At the same time, aqueous electrolytes will cause hydrogen evolution / oxygen evolution reactions during the charge and discharge process of the battery, affecting the cycle stability of the battery, and generating gas inside the closed battery, which is likely to cause safety problems. Common non-aqueous electrolytes mainly include ionic liquids and inorganic molten salt electrolytes. Compared with the aqueous electrolyte system, ionic liquids have a wider electrochemical window, but the materials used are expensive, with high costs. Moreover, the corrosion of the aluminum negative electrode surface and the formation of aluminum dendrites also affect the cycle stability of the battery. In addition, the dissolution of the cathode material in the ionic liquid electrolyte will also cause battery capacity loss. Molten salt electrolytes have the advantages of high ionic conductivity, fast electrode kinetics, and low polarization. Therefore, designing and developing electrolytes with higher working voltages and larger storage capacities is the key to the development of high-performance aluminum batteries. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention proposes a preparation method of a molten salt electrolyte with high performance and high stability. When used in aluminum-ion batteries, it can endow the aluminum-ion batteries with high specific capacity and excellent cycle stability.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a preparation method of a molten salt electrolyte, and the method includes the following steps:

[0008] S1. Calculate the eutectic molar ratio of AlCl 3 :NaCl according to the phase diagram software Factsage, and then further calculate the masses of AlCl 3 and NaCl required respectively;

[0009] S2. Dry and mix and grind AlCl 3 and NaCl evenly, then heat the mixed powder to form a light yellow liquid, and finally grind it to obtain the molten salt electrolyte.

[0010] Preferably, the eutectic molar ratio of AlCl 3 :NaCl is 1.63:1.

[0011] Preferably, the heating temperature is 110 - 140 °C and the time is 8 - 12 h.

[0012] Preferably, the heating is carried out in a closed container.

[0013] Preferably, the drying temperature is 120 - 160 °C and the time is 20 - 30 h.

[0014] Preferably, after drying AlCl 3 and NaCl, they are quickly put into a glove box for standby. The water and oxygen values of the glove box are ≤ 0.1 ppm, and the required amounts of AlCl 3 and NaCl are weighed out separately in the glove box, and then ground.

[0015] In the second aspect of the present invention, a molten salt electrolyte prepared by the preparation method described in the first aspect is also provided.

[0016] In the third aspect of the present invention, an application of the molten salt electrolyte described in the second aspect in an aluminum-ion battery is also provided. The aluminum-ion battery uses the molten salt described in the second aspect as the electrolyte.

[0017] Preferably, the preparation method of the positive electrode used in the aluminum-ion battery is as follows: an active material, carbon black, and a binder are added to an organic solvent to prepare a slurry, and then the slurry is coated on the surface of carbon paper and dried to obtain the positive electrode.

[0018] Furthermore, the active material includes graphite, graphene, sulfur, metal sulfides, metal oxides, etc.

[0019] Furthermore, the binder includes polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), etc.

[0020] Preferably, the negative electrode used in the aluminum-ion battery includes aluminum foil, aluminum alloy, aluminum powder, etc.

[0021] Preferably, the separator used in the aluminum-ion battery includes a glass fiber separator, a cellulose separator, etc.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] Ionic liquid electrolytes are expensive, highly corrosive, and have poor air stability. Aqueous electrolytes, on the other hand, have a narrow electrochemical window and are prone to hydrogen evolution side reactions and passivation of the aluminum anode. In contrast, the main raw materials of inorganic molten salts are inorganic metal chlorides, which are low-cost, highly safe, and stable. They can achieve reversible aluminum deposition and dissolution. As electrolytes, they have high capacity, high Coulombic efficiency, and good cycle stability (refer to the literature: Song Y, Jiao S, Tu J, et al. A long-life rechargeable Al ion battery based on molten salts[J]. J. Mater. Chem. A, 2017, 5(3): 1282-1291.; J.x.Wang, J.g.Tu, H.d.Jiao, et al. Nanosheet-stacked flake graphite for high-performance Al storage in inorganic molten AlCl 3 -NaCl salt. International Journal of Minerals, Metallurgy and Materials. 27(2020), 1711-1722.), and are strong candidates for aluminum-ion battery electrolytes.

[0024] Therefore, the present invention uses a molten salt composed of AlCl 3 and NaCl as the electrolyte to construct a new type of non-aqueous rechargeable aluminum-ion battery. This aluminum-ion battery has a high specific capacity and excellent cycle stability. The charge and discharge specific capacities in the second cycle are 152 mAh·gˉ 1 and 168 mAh·gˉ 1 respectively. After 200 cycles, the specific capacity of the battery can still be maintained at 114 mAh·gˉ 1 . Brief Description of the Drawings

[0025] Figure 1 is the charge-discharge performance test curve of the rechargeable aluminum-ion battery;

[0026] Figure 2 is the cycle performance test curve of the rechargeable aluminum-ion battery. Detailed Embodiments

[0027] The following further describes the detailed embodiments of the present invention. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0029] Example 1: Preparation of molten salt electrolyte

[0030] (1) Calculate AlCl using the phase diagram calculation software Factsage 3 The eutectic molar ratio of :NaCl is 1.63:1, so the required AlCl 3 The masses of NaCl and MgSO4 are 217.99 g and 58.44 g respectively.

[0031] (2) AlCl 3 and NaCl were placed in a vacuum drying oven at 130 °C and dried for 24 h.

[0032] (3) Dry the AlCl 3 Take out the solution and NaCl, and quickly put it into a glove box (water and oxygen value ≤ 0.1ppm) for later use.

[0033] (4) Use a balance to weigh the required AlCl 3 and NaCl, and put them together in a mortar and grind them evenly.

[0034] (5) The uniformly mixed powder is placed in a sealed container, and then placed in an oil bath and heated to 120° C. for 12 h until a light yellow liquid is formed. After cooling, the powder is ground in a glove box until it is in a powder state without obvious particles, thereby obtaining a molten salt electrolyte.

[0035] Example 2: Preparation of aluminum ion battery

[0036] (1) Redox graphene, carbon black and PVDF binder were mixed in a mass ratio of 8:1:1, ground at room temperature for 1 h, and then NMP organic solvent was added to just immerse the mixture, and the grinding was continued for 0.5 h to obtain a positive electrode material slurry. The slurry was coated on carbon paper, dried, and cut into square pieces with a side length of 1 cm.

[0037] (2) Cut the aluminum foil negative electrode into square pieces with a side length of 1.2 cm.

[0038] (3) Cut the glass fiber into square pieces with a side length of 1.4 cm.

[0039] (4) Cut the molybdenum foil current collector into square pieces with a side length of 1.4 cm.

[0040] (5) In the glove box, attach the positive electrode sheet to the current collector, then attach the separator (glass fiber) to the positive electrode sheet, and perform the same operation on the negative electrode. Then place the positive and negative electrodes into a Teflon electrolytic cell and load the electrolyte powder ground in Example 1, thus forming an aluminum-ion battery.

[0041] Example 3: Battery Performance Test

[0042] Using an aluminum foil as the negative electrode, a glass fiber separator and a redox graphene as the positive electrode, and using the molten salt of Example 1 as the electrolyte to form an aluminum-ion battery. After standing for a period of time, perform a constant current charge-discharge test on a charge-discharge instrument.

[0043] Figure 1 Shows the charge and discharge specific capacities of the second cycle of the aluminum-ion battery, which are 152 mAh·gˉ 1 and 168 mAh·gˉ 1 , indicating its high specific capacity. Figure 2 Shows the performance curve of the aluminum-ion battery after 200 cycles. After cycling, the specific capacity of the battery can still be maintained at 114 mAh·gˉ 1 , indicating its excellent cycle stability.

[0044] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and spirit of the present invention, various changes, modifications, substitutions and variations made to these embodiments still fall within the protection scope of the present invention.

Claims

1. A method for preparing a molten salt electrolyte, characterized in that: The following steps are involved: S1. Calculate the eutectic molar ratio of AlCl3:NaCl according to the phase diagram software Factsage, and further calculate the masses of AlCl3 and NaCl required respectively; S2. Dry AlCl3 and NaCl, mix and grind them evenly, then heat the mixed powder to form a light yellow liquid, and finally grind it to obtain a molten salt electrolyte.

2. The method for preparing a molten salt electrolyte according to claim 1, characterized in that: The eutectic molar ratio of AlCl3:NaCl is 1.63:

1.

3. The method for preparing a molten salt electrolyte according to claim 1, characterized in that: The heating temperature is 110-140° C. and the heating time is 8-12 hours.

4. The method for preparing a molten salt electrolyte according to claim 1, characterized in that: The heating is carried out in a closed container.

5. The method for preparing a molten salt electrolyte according to claim 1, characterized in that: The drying temperature is 120-160°C and the drying time is 20-30h.

6. The method for preparing a molten salt electrolyte according to claim 1, characterized in that: After AlCl3 and NaCl are dried, they are quickly placed in a glove box for use. The water and oxygen values ​​in the glove box are ≤0.1ppm. The required amounts of AlCl3 and NaCl are weighed out in the glove box and then ground.

7. A molten salt electrolyte prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the molten salt electrolyte according to claim 7 in an aluminum ion battery, characterized in that: The aluminum ion battery uses the molten salt described in claim 7 as an electrolyte.

9. The use according to claim 8, characterized in that: The preparation method of the positive electrode used in the aluminum ion battery is: adding active material, carbon black and binder into an organic solvent to prepare slurry, then coating the slurry on the surface of carbon paper, and obtaining the positive electrode after drying.

10. The use according to claim 9, characterized in that: The active material includes graphite, graphene, sulfur, metal sulfide, and metal oxide.

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