Organic ammonium iodide-based electrolyte and its preparation method and application

Abstract

The present invention discloses an organic ammonium iodide-based electrolyte and its preparation method and application. The organic ammonium iodide-based electrolyte is composed of a metal iodide salt, an organic ammonium iodide, and an organic solvent. The organic ammonium iodide-based electrolyte of the present invention has stable properties and is easy to prepare. When applied to secondary batteries, it significantly improves the electrochemical performance. At a current density of 0.02 mA cm ‑2 , the symmetric battery formed by it can stably cycle for more than 400 h, greatly reducing the overpotential, and has broad application prospects in the field of secondary batteries.

Description

Technical Field

[0001] The present invention relates to an organic ammonium iodide-based electrolyte and its preparation method and application, belonging to the field of secondary batteries. Background Art

[0002] High-energy-density rechargeable lithium-ion batteries (LIBs) currently dominate the portable electronics market and the electric vehicle market due to their relatively high energy density, good cycle life, and reliable performance characteristics. However, the growth of the electric vehicle market is limited by the limited driving range achievable with lithium-ion technology, and there is a need to continuously increase the driving range by increasing the battery energy density. In addition, it is generally believed that lithium-ion technology has reached the limit of its energy density capabilities, and new "beyond lithium-ion" technologies need to be developed. However, the scarcity of raw materials, severe dendrite formation, and potential safety hazards have greatly hindered the development of lithium metal batteries (LMBs).

[0003] Studies have shown that compared with lithium, multivalent metals (such as Mg and Ca) can be uniformly deposited from a suitable electrolyte solution with little or no dendritic growth. This discovery makes it possible to use multivalent metal anodes instead of the graphite anodes used in lithium-ion batteries, thus significantly increasing the weight and volume capacity of the anode. Compared with lithium-ion batteries, this is expected to increase the energy density of these multivalent battery systems. The use of multivalent ions may also increase the electrochemical capacity of intercalation electrodes, resulting in a significant increase in the energy density of batteries using these electrodes compared with lithium-ion batteries. For example, if divalent ions (such as Mg 2+ , Ca 2+ ) are used, then only half the number of divalent ions need to be inserted to achieve the same number of electron transfers compared with equivalent monovalent ion intercalation. If the host structure can accommodate these divalent ions, then theoretically this can double the electrochemical capacity of the electrode compared with the same intercalation host with monovalent intercalation substances (such as Li + or Na + ).

[0004] Compared with other multivalent metal ions, alkaline earth metal ions (especially calcium ions and magnesium ions) have received increasing attention due to their natural abundance, low cost, and stable valence states. More specifically, calcium and magnesium are the fifth and eighth most abundant elements in the earth's crust, respectively, with a wide global resource distribution, non-toxicity, and excellent thermal stability. The standard redox potentials of Ca / Ca 2+ and Mg / Mg 2+ are -2.87 V and -2.37 V (vs standard hydrogen electrode), close to Li / Li + , and the volume capacities of the corresponding metals are as high as 2073 mAh cm -3 and 3833 mAh cm-3 , which is conducive to achieving a higher energy density.

[0005] Organic ammonium iodide is an organic iodide, which is usually used as an important material in solar cells, especially in perovskite solar cells. Organic ammonium iodide is one of the key components for preparing perovskite materials and is often used in combination with inorganic halides to form lead halide perovskite materials. By optimizing the content and ratio of organic ammonium iodide, the stability and efficiency of perovskite solar cells can be significantly improved. Currently, there is no literature report on the application of organic ammonium iodide in secondary batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide an organic ammonium iodide-based electrolyte and its preparation method and application. The present invention dissolves organic ammonium iodide and metal iodide salts together in an organic solvent to prepare an electrolyte, obtaining an organic ammonium iodide-based electrolyte, and applying it to secondary batteries, which exhibits excellent electrochemical performance.

[0007] The technical solutions for achieving the purpose of the present invention are as follows:

[0008] The organic ammonium iodide-based electrolyte is composed of a metal iodide salt, organic ammonium iodide, and an organic solvent.

[0009] Further, the metal iodide salt is a metal iodide salt that can be used in secondary batteries, including but not limited to CaI2, MgI2, etc.

[0010] Further, the organic ammonium iodide includes but not limited to methylammonium iodide, ethylammonium iodide, propylammonium iodide, butylammonium iodide, pentylammonium iodide, etc.

[0011] Further, the organic solvent is a commonly used organic solvent in secondary batteries, including but not limited to ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, etc.

[0012] Further, in the organic ammonium iodide-based electrolyte, the concentration of organic ammonium iodide is 0.01 - 0.8 mol L -1 .

[0013] Further, in the organic ammonium iodide-based electrolyte, the concentration of the metal iodide salt is 0.01 - 0.05 mol L -1 .

[0014] In a specific embodiment of the present invention, in the organic ammonium iodide-based electrolyte, the concentration of organic ammonium iodide is 0.1 mol L -1 , and the concentration of the metal iodide salt is 0.05 mol L -1 .

[0015] The preparation method of the above-mentioned organic ammonium iodide-based electrolyte includes the following steps:

[0016] Dissolve metal iodide salts and organic ammonium iodides in an organic solvent, and remove water with molecular sieves to obtain an organic ammonium iodide-based electrolyte solution.

[0017] Furthermore, the time for water removal by molecular sieves is 48 - 72 h.

[0018] The present invention provides the application of the above-mentioned organic ammonium iodide-based electrolyte solution as an electrolyte in secondary batteries.

[0019] Furthermore, the secondary battery is a common secondary battery in the art, including but not limited to calcium metal batteries, magnesium metal batteries, etc.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] By introducing metal iodide salts and organic ammonium iodides into the electrolyte solution, the present invention in-situ forms a nitrogen-containing compound layer on the metal surface due to the decomposition of organic ammonium iodides in the battery, reducing the impedance during the transmission of metal ions. The button battery assembled with the organic ammonium iodide-based electrolyte solution of the present invention exhibits good electrochemical activity. In addition, under the condition of 0.02 mA cm -2 , the symmetrical battery composed of the organic ammonium iodide-based electrolyte solution can stably cycle for more than 400 h and has excellent stable cycling performance. Description of the Drawings

[0022] Figure 1 1H-NMR spectrum of the ethylammonium iodide electrolyte containing CaI2 in Example 1 1 1H-NMR spectrum.

[0023] Figure 2 Confocal Raman spectrum of the ethylammonium iodide electrolyte containing CaI2 in Example 1

[0024] Figure 3 Infrared spectrum of the ethylammonium iodide electrolyte containing CaI2 in Example 1

[0025] Figure 4 UV-Vis spectrum of the ethylammonium iodide electrolyte containing CaI2 in Example 1

[0026] Figure 5 Relative elemental content map of the surface of the electrode of the symmetrical battery with the ethylammonium iodide electrolyte containing CaI2 in Example 1 after 90 s of argon ion sputtering

[0027] Figure 6 Graph of the room temperature cycling test results of the symmetrical battery with the ethylammonium iodide electrolyte containing CaI2 in Example 1 at a current density of 0.02 mA cm -2 Current density.

[0028] Figure 7 Cycling test results of the symmetric cell with ethylammonium iodide electrolyte containing CaI2 at different current densities in Example 1

[0029] Figure 8 Cyclic voltammetry (CV) test spectrum of the 50th cycle of the symmetric cell with ethylammonium iodide electrolyte containing CaI2 in Example 1

[0030] Figure 9 Electrochemical impedance spectroscopy (EIS) test spectrum of the symmetric cell with ethylammonium iodide electrolyte containing CaI2 after 400 cycles in Example 1

[0031] Figure 10 Coulombic efficiency graph of the Ca-Cu asymmetric cell with ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 in Example 1

[0032] Figure 11 Cycling test results at room temperature of the symmetric cell with Ca(TFSI)2 electrolyte at a current density of 0.02 mA cm -2 in Comparative Example 1

[0033] Figure 12 Coulombic efficiency graph of the Ca-Cu asymmetric cell with Ca(TFSI)2 electrolyte at a current density of 0.02 mA cm -2 in Comparative Example 1

[0034] Figure 13 Cycling test results at room temperature of the symmetric cell with CaI2 electrolyte at a current density of 0.02 mA cm -2 in Comparative Example 2

[0035] Figure 14 Coulombic efficiency graph of the Ca-Cu asymmetric cell with CaI2 electrolyte at a current density of 0.02 mA cm -2 in Comparative Example 2

[0036] Figure 15 Cycling test results at room temperature of the symmetric cell with low-concentration ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 in Example 2

[0037] Figure 16 Coulombic efficiency graph of the Ca-Cu asymmetric cell with low-concentration ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 in Example 2

[0038] Figure 17 Cycling test results at room temperature of the symmetric cell with high-concentration ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm-2 Graph of the room-temperature cycling test results at a current density.

[0039] Figure 18 For the calcium-copper asymmetric cell with a high-concentration ethylammonium iodide electrolyte containing CaI2 in Example 3 at 0.02 mAcm -2 Graph of the Coulombic efficiency at a current density.

[0040] Figure 19 For the symmetric cell with an ethylammonium iodide electrolyte containing low-concentration CaI2 in Example 4 at 0.02 mA cm -2 Graph of the room-temperature cycling test results at a current density.

[0041] Figure 20 For the calcium-copper asymmetric cell with an ethylammonium iodide electrolyte containing low-concentration CaI2 in Example 4 at 0.02 mAcm -2 Graph of the Coulombic efficiency at a current density.

[0042] Figure 21 For the symmetric cell with a methylammonium iodide electrolyte containing CaI2 in Example 5 at 0.02 mA cm -2 Graph of the room-temperature cycling test results at a current density.

[0043] Figure 22 For the calcium-copper asymmetric cell with a methylammonium iodide electrolyte containing CaI2 in Example 5 at 0.02 mA cm -2 Graph of the Coulombic efficiency at a current density.

[0044] Figure 23 For the symmetric cell with a propylammonium iodide electrolyte containing CaI2 in Example 6 at 0.02 mA cm -2 Graph of the room-temperature cycling test results at a current density.

[0045] Figure 24 For the calcium-copper asymmetric cell with a propylammonium iodide electrolyte containing CaI2 in Example 6 at 0.02 mA cm -2 Graph of the Coulombic efficiency at a current density.

[0046] Figure 25 For the symmetric cell with a butylammonium iodide electrolyte containing CaI2 in Example 7 at 0.02 mA cm -2 Graph of the room-temperature cycling test results at a current density.

[0047] Figure 26 For the calcium-copper asymmetric cell with a butylammonium iodide electrolyte containing CaI2 in Example 7 at 0.02 mA cm -2 Graph of the Coulombic efficiency at a current density.

[0048] Figure 27Charge-discharge curves of the symmetric cell with the amylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 at room temperature in Example 8.

[0049] Figure 28 Coulombic efficiency of the Ca-Cu asymmetric cell with the amylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 at room temperature in Example 8.

[0050] Figure 29 Charge-discharge curves of the symmetric cell with the diethylammonium iodide diglyme electrolyte containing CaI2 at a current density of 0.02 mA cm -2 at room temperature in Example 9.

[0051] Figure 30 Coulombic efficiency of the Ca-Cu asymmetric cell with the diethylammonium iodide diglyme electrolyte containing CaI2 at a current density of 0.02 mA cm -2 at room temperature in Example 9.

[0052] Figure 31 Charge-discharge curves of the symmetric cell with the diethylammonium iodide tetrahydrofuran electrolyte containing CaI2 at a current density of 0.02 mA cm -2 at room temperature in Example 10.

[0053] Figure 32 Coulombic efficiency of the Ca-Cu asymmetric cell with the diethylammonium iodide tetrahydrofuran electrolyte containing CaI2 at a current density of 0.02 mA cm -2 at room temperature in Example 10.

[0054] Figure 33 Charge-discharge curves of the symmetric cell with the MgI2 electrolyte at a current density of 0.1 mA cm -2 at room temperature in Comparative Example 3.

[0055] Figure 34 Coulombic efficiency of the Ca-Cu asymmetric cell with the MgI2 electrolyte at a current density of 0.1 mA cm -2 at room temperature in Comparative Example 3.

[0056] Figure 35 Charge-discharge curves of the symmetric cell with the diethylammonium iodide electrolyte containing MgI2 at a current density of 0.1 mA cm -2 at room temperature in Example 11.

[0057] Figure 36 Coulombic efficiency of the Ca-Cu asymmetric cell with the diethylammonium iodide electrolyte containing MgI2 at a current density of 0.1 mA cm -2 at room temperature in Example 11. Detailed implementation mode

[0058] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0059] Example 1

[0060] Weigh 147 mg (0.5 mmol) of CaI2 and 173 mg (1 mmol) of ethylammonium iodide, add them to 10 mL of ethylene glycol dimethyl ether, stir and mix evenly at room temperature to dissolve, add molecular sieve and let stand for 48 h to remove excess moisture, and obtain an ethylammonium iodide electrolyte containing CaI2.

[0061] Figure 1 It is the 1 1H-NMR spectrum of the ethylammonium iodide electrolyte containing CaI2. δ = 3.21 ppm belongs to the -CH3 peak of the solvent ethylene glycol dimethyl ether, δ = 3.56 ppm belongs to the -CH2 peak of the solvent ethylene glycol dimethyl ether, and δ = 7.29 ppm belongs to the -NH3 peak of ethylammonium iodide. Figure 2 It is the confocal micro-Raman spectrum of the ethylammonium iodide electrolyte containing CaI2. A group of Raman peaks in the range of 900 - 1100 cm -1 are the C-O stretching vibration peaks of different ethylene glycol dimethyl ethers, and a group of Raman peaks in the range of 800 - 900 cm -1 are the CH2 bending vibration peaks of different ethylene glycol dimethyl ethers, and a group of Raman peaks in the range of 300 - 370 cm -1 are the COC bending vibration peaks of different ethylene glycol dimethyl ethers, and a group of Raman peaks in the range of 390 - 600 cm -1 are the OCC bending vibration peaks of different ethylene glycol dimethyl ethers. Figure 3 It is the infrared spectrum of the ethylammonium iodide electrolyte containing CaI2. A group of infrared absorption peaks in the range of 2800 - 3000 cm -1 are attributed to the stretching vibrations of C-H in ethylene glycol dimethyl ether and N-H in ethylammonium iodide. Figure 4 It is the ultraviolet-visible spectrum of the ethylammonium iodide electrolyte containing CaI2. The near-ultraviolet absorption peaks at 300 nm and 380 nm are attributed to the valence electron transition absorption peaks of I - . This proves that CaI2 and ethylammonium iodide are successfully dissolved in ethylene glycol dimethyl ether. Figure 5It is a diagram of the relative elemental content on the surface of a symmetric battery electrode after 90 s of argon ion sputtering. The relative nitrogen content is 5%, indicating that a nitride is formed on the electrode surface.

[0062] A button battery (CR2032) was assembled from bottom to top in a glove box filled with argon in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" for battery performance testing. The positive and negative electrode sheets used were both calcium metal discs with a diameter of 12 mm or copper foils with a diameter of 19 mm. The calcium metal sheets were polished with sandpaper before use. The separator used was cut into discs with a diameter of 19 mm using a cutter and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte was 0.15 mL.

[0063] Figure 6 It is a diagram of the room-temperature cycle test results of a symmetric battery with an ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 . It can be seen that at 0.02 mA cm -2 and 0.02 mAh cm -2 conditions, it can stably cycle for more than 400 h, and the overpotential is only about 0.5 V. Figure 7 It is a diagram of the cycle test results of a symmetric battery with an ethylammonium iodide electrolyte containing CaI2 at different current densities. It can be seen that it can remain stable at current densities of 0.02 - 0.1 mA cm -2 , indicating that the battery has good cycle life and will not undergo excessive decomposition at high currents.

[0064] Figure 8 It is the 50th CV test spectrum of a symmetric battery with an ethylammonium iodide electrolyte containing CaI2, with a scan rate of 5 mV s -1 and a voltage range of -0.5 - 0.5 V. It can be seen that it can still remain stable after 50 cycle tests. Figure 9 It is the EIS test spectrum of a symmetric battery with an ethylammonium iodide electrolyte containing CaI2 after 400 cycles, with a frequency range of 100 kHz - 10 mHz and an amplitude of 10 mV. It can be seen that it can still remain stable after 400 cycle tests, indicating that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0065] An asymmetric battery was assembled using an ethylammonium iodide electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulombic efficiency after 100 cycles under the test conditions of 0.02 mA cm -2 is as Figure 10 shown. After 100 cycles, its Coulombic efficiency is still 78%, indicating that the electrolyte plays a good role in extending the battery life.

[0066] Comparative Example 1

[0067] Using only Ca(TFSI)2 as the electrolyte salt, prepare the Ca(TFSI)2 electrolyte solution according to the steps in Example 1, and assemble it into a battery for testing. The specific steps are as follows:

[0068] Weigh 600 mg (1 mmol) of Ca(TFSI)2 and add it to 10 mL of ethylene glycol dimethyl ether. Stir and mix evenly at room temperature to dissolve it. Add molecular sieve and let it stand for 48 h to remove excess moisture, obtaining the Ca(TFSI)2 electrolyte solution.

[0069] Assemble a button battery (CR2032) from bottom to top in a glove box filled with argon in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" for battery performance testing. The positive electrode sheet used is a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode sheet used is a calcium metal disc with a diameter of 12 mm. The calcium metal sheet is polished with sandpaper before use. The separator used is cut into a disc with a diameter of 19 mm using a cutting machine and dried in a vacuum dryer at 100 °C for 12 h before use. The injection volume of the electrolyte solution is 0.15 mL.

[0070] Figure 11 Fig. is the room-temperature cycling test result diagram of the symmetric battery with Ca(TFSI)2 electrolyte at a current density of 0.02 mA cm -2 It can be seen that it can only cycle for 9 h under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 , and the overpotential exceeds 2 V.

[0071] An asymmetric battery is assembled using Ca(TFSI)2 electrolyte, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as Figure 12 shown, and the Coulomb efficiency is only 5%.

[0072] Comparative Example 2

[0073] Using only CaI2 as the electrolyte salt, prepare the CaI2 electrolyte solution according to the steps in Example 1, and assemble it into a battery for testing. The specific steps are as follows:

[0074] Weigh 147 mg (0.5 mmol) of CaI2 and add it to 10 mL of ethylene glycol dimethyl ether. Stir and mix evenly at room temperature to dissolve it. Add molecular sieve and let it stand for 48 h to remove excess moisture, obtaining the CaI2 electrolyte solution.

[0075] Assemble a button battery (CR2032) from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used is a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used is a calcium metal disc with a diameter of 12 mm. The calcium metal sheet is polished with sandpaper before use. The separator used is cut into a disc with a diameter of 19 mm by a cutting machine and dried in a vacuum dryer at 100 °C for 12 h before use. The injection volume of the electrolyte is 0.15 mL.

[0076] Figure 13 For the CaI2 electrolyte symmetric cell at 0.02 mA cm -2 Current density at room temperature cycling test results graph. It can be seen that its overpotential rises rapidly during cycling at 0.02 mA cm -2 、0.02 mAh cm -2 Conditions and can only cycle for 60 h.

[0077] Using a CaI2 electrolyte, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode to assemble an asymmetric cell, its Coulombic efficiency under the test conditions of 0.02 mA cm -2 As shown in the test conditions, the Coulombic efficiency is only 8%. Figure 14 As shown, the Coulombic efficiency is only 8%.

[0078] Example 2

[0079] This example is basically the same as Example 1, except that the concentration of ethylammonium iodide is reduced to 0.01 mol L -1 . Refer to the steps in Example 1 to prepare a low-concentration ethylammonium iodide electrolyte containing CaI2, assemble the battery and conduct tests. Specifically as follows:

[0080] Weigh 147 mg (0.5 mmol) of CaI2 and 17 mg (0.1 mmol) of ethylammonium iodide, add them to 10 mL of ethylene glycol dimethyl ether, stir and mix evenly at room temperature to dissolve, add molecular sieves and let stand for 48 h to remove excess moisture, and obtain a low-concentration ethylammonium iodide electrolyte containing CaI2.

[0081] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm using a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte used was 0.15 mL.

[0082] Figure 15 It is the room temperature cycling test result diagram of a symmetrical battery with a low-concentration ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 . It can be seen that its overpotential increases to nearly 1 V under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 , but it can still cycle for more than 40 h and the cycling overpotential remains stable.

[0083] An asymmetric battery was assembled using a low-concentration ethylammonium iodide electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulombic efficiency under the test conditions of 0.02 mA cm -2 is as Figure 16 shown. The Coulombic efficiency is 35%, which is significantly improved compared with CaI2 electrolyte and Ca(TFSI)2 electrolyte.

[0084] Example 3

[0085] This example is basically the same as Example 1, except that the concentration of ethylammonium iodide is only increased to 0.8 molL -1 . Referring to the steps in Example 1, a high-concentration ethylammonium iodide electrolyte containing CaI2 was prepared, and the assembled battery was tested. Specifically as follows:

[0086] Weigh 147 mg (0.5 mmol) of CaI2 and 1384 mg (8 mmol) of ethylammonium iodide and add them to 10 mL of ethylene glycol dimethyl ether. Stir and mix evenly at room temperature to dissolve it, add molecular sieves and let it stand for 48 h to remove excess moisture, obtaining a high-concentration ethylammonium iodide electrolyte containing CaI2.

[0087] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm using a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte used was 0.15 mL.

[0088] Figure 17 Figure of the room temperature cycling test results of a symmetric cell with a high-concentration ethylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 It can be seen that its overpotential increases to nearly 1 V under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 and it can be stably cycled more than 200 times.

[0089] An asymmetric cell was assembled using a high-concentration ethylammonium iodide electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as Figure 18 shown, with a Coulomb efficiency of 40%, which is significantly improved compared to CaI2 electrolyte and Ca(TFSI)2 electrolyte.

[0090] Example 4

[0091] This example is basically the same as Example 1, except that the concentration of CaI2 is only reduced to 0.01 mol L -1 . Referring to the steps in Example 1, an ethylammonium iodide electrolyte containing a low concentration of CaI2 was prepared, and a battery was assembled for testing. Specifically as follows:

[0092] Weigh 29 mg (0.1 mmol) of CaI2 and 173 mg (1 mmol) of ethylammonium iodide, add them to 10 mL of ethylene glycol dimethyl ether, stir and mix evenly at room temperature to dissolve, add molecular sieves, and let it stand for 48 h to remove excess moisture, obtaining an ethylammonium iodide electrolyte containing a low concentration of CaI2.

[0093] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm using a cutting machine and dried in a vacuum dryer at 100 °C for 12 h before use. The injection volume of the electrolyte used was 0.15 mL.

[0094] Figure 19 Figure of the room temperature cycling test results of the symmetric cell with an ethylammonium iodide electrolyte containing low-concentration CaI2 at a current density of 0.02 mA cm -2 It can be seen that it can cycle for 50 h under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 and the cycling overpotential is maintained at 0.5 V within 40 h.

[0095] An asymmetric cell was assembled using an ethylammonium iodide electrolyte containing low-concentration CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulombic efficiency under the test conditions is as -2 shown. The Coulombic efficiency is 20%, which is significantly improved compared to the CaI2 electrolyte and the Ca(TFSI)2 electrolyte. Figure 20

[0096] Example 5

[0097] This example is basically the same as Example 1, except that only the organic ammonium iodide is replaced with methylammonium iodide. Referring to the steps in Example 1, an electrolyte containing CaI2 of methylammonium iodide was prepared and assembled into a battery for testing. Specifically as follows:

[0098] 147 mg (0.5 mmol) of CaI2 and 159 mg (1 mmol) of methylammonium iodide were weighed and added to 10 mL of ethylene glycol dimethyl ether, stirred and mixed evenly at room temperature to dissolve it, and molecular sieves were added and left standing for 48 h to remove excess water, obtaining an electrolyte containing CaI2 of methylammonium iodide.

[0099] ​The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode sheet used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode sheet used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm by a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte used was 0.15 mL.

[0100] Figure 21 Figure of the room temperature cycling test results of the symmetric battery with the methylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 It can be seen that it can stably cycle for 400 h under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 , and the overpotential is only about 0.5 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0101] An asymmetric battery was assembled using the methylammonium iodide electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as shown in Figure 22 , and the Coulomb efficiency is 75%, showing a significant improvement compared with the CaI2 electrolyte and the Ca(TFSI)2 electrolyte, indicating that the electrolyte plays a good role in extending the battery life.

[0102] Example 6

[0103] This example is basically the same as Example 1, except that only the organic ammonium iodide is replaced with propylammonium iodide. Referring to the steps in Example 1, the propylammonium iodide electrolyte containing CaI2 was prepared and assembled into a battery for testing. The details are as follows:

[0104] 147 mg (0.5 mmol) of CaI2 and 187 mg (1 mmol) of propylammonium iodide were weighed and added to 10 mL of ethylene glycol dimethyl ether, stirred and mixed evenly at room temperature to dissolve it, and molecular sieves were added and left standing for 48 h to remove excess water, obtaining the propylammonium iodide electrolyte containing CaI2.

[0105] Assemble a button battery (CR2032) from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → spring piece → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used is a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used is a calcium metal disc with a diameter of 12 mm. The calcium metal sheet is polished with sandpaper before use. The separator used is cut into a disc with a diameter of 19 mm using a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte is 0.15 mL.

[0106] Figure 23 Figure of the room-temperature cycling test results of a symmetric battery with a propylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 It can be seen that it can stably cycle for 400 h at 0.02 mA cm -2 and 0.02 mAh cm -2 conditions, and the overpotential is only about 0.5 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0107] An asymmetric battery is assembled using a propylammonium iodide electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as shown in Figure 24 The Coulomb efficiency is 75%, showing a significant improvement compared to the CaI2 electrolyte and the Ca(TFSI)2 electrolyte, indicating that the electrolyte plays a good role in extending the battery life.

[0108] Example 7

[0109] This example is basically the same as Example 1, except that only the organic ammonium iodide is replaced with butylammonium iodide. Refer to the steps in Example 1 to prepare a butylammonium iodide electrolyte containing CaI2 and assemble the battery for testing. Specifically as follows:

[0110] Weigh 147 mg (0.5 mmol) of CaI2 and 201 mg (1 mmol) of butylammonium iodide and add them to 10 mL of ethylene glycol dimethyl ether respectively. Stir and mix evenly at room temperature to dissolve them, add molecular sieves and let stand for 48 h to remove excess moisture, obtaining a butylammonium iodide electrolyte containing CaI2.

[0111] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm by a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The electrolyte injection volume was 0.15 mL.

[0112] Figure 25 Figure of the room temperature cycling test results of the symmetric battery with a butylammonium iodide electrolyte containing CaI2 at a current density of 0.02 mA cm -2 It can be seen that it can stably cycle for 400 h under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 and the overpotential is only about 0.5 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0113] An asymmetric battery was assembled using a butylammonium iodide electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as Figure 26 shown. The Coulomb efficiency is 75%, which is significantly improved compared to the CaI2 electrolyte and the Ca(TFSI)2 electrolyte, indicating that the electrolyte plays a good role in extending the battery life.

[0114] Example 8

[0115] This example is basically the same as Example 1, except that the organic ammonium iodide is only replaced with pentylammonium iodide. Referring to the steps in Example 1, a pentylammonium iodide electrolyte containing CaI2 was prepared and assembled into a battery for testing. Specifically as follows:

[0116] Weigh 147 mg (0.5 mmol) of CaI2 and 215 mg (1 mmol) of pentylammonium iodide and add them to 10 mL of ethylene glycol dimethyl ether. Stir and mix evenly at room temperature to dissolve it, add molecular sieves and let it stand for 48 h to remove excess moisture, obtaining a pentylammonium iodide electrolyte containing CaI2.

[0117] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode sheet used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode sheet used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm by a cutting machine and dried in a vacuum dryer at 100 °C for 12 h before use. The injection volume of the electrolyte used was 0.15 mL.

[0118] Figure 27 Figure of the room temperature cycling test results of the symmetric battery with an electrolyte containing CaI2 and amylammonium iodide at a current density of 0.02 mA cm -2 It can be seen that it can stably cycle for 400 h under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 , and the overpotential is only about 0.5 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0119] An asymmetric battery was assembled using an electrolyte containing CaI2 and amylammonium iodide, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as shown in Figure 28 , and the Coulomb efficiency is 75%, indicating that the electrolyte plays a good role in extending the battery life.

[0120] Example 9

[0121] This example is basically the same as Example 1, except that the organic solvent is only replaced with diethylene glycol dimethyl ether. Referring to the steps in Example 1, an electrolyte containing CaI2 and ethylammonium iodide in diethylene glycol dimethyl ether was prepared and assembled into a battery for testing. Specifically as follows:

[0122] Weigh 147 mg (0.5 mmol) of CaI2 and 173 mg (1 mmol) of ethylammonium iodide and add them to 10 mL of diethylene glycol dimethyl ether. Stir and mix evenly at room temperature to dissolve it, add molecular sieves and let it stand for 48 h to remove excess moisture, obtaining an electrolyte containing CaI2 and ethylammonium iodide in diethylene glycol dimethyl ether.

[0123] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm using a cutting machine and dried in a vacuum dryer at 100 °C for 12 h before use. The injection volume of the electrolyte was 0.15 mL.

[0124] Figure 29 Figure of the room-temperature cycling test results for a symmetric cell with an ethylammonium iodide diglyme electrolyte containing CaI2 at a current density of 0.02 mA cm -2 It can be seen that it can stably cycle for 150 h under the conditions of 0.02 mA cm -2 and 0.02 mAh cm -2 with an overpotential of only about 0.5 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0125] An asymmetric cell was assembled using an ethylammonium iodide diglyme electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulombic efficiency under the test conditions of 0.02 mA cm -2 is as shown in Figure 30 The Coulombic efficiency is 70%, showing a significant improvement compared to the CaI2 electrolyte and the Ca(TFSI)2 electrolyte, indicating that the electrolyte plays a good role in extending the battery life.

[0126] Example 10

[0127] This example is basically the same as Example 1, except that the organic solvent was only replaced with tetrahydrofuran. Referring to the steps in Example 1, an ethylammonium iodide tetrahydrofuran electrolyte containing CaI2 was prepared and assembled into a battery for testing. Specifically as follows:

[0128] 147 mg (0.5 mmol) of CaI2 and 173 mg (1 mmol) of ethylammonium iodide were weighed and added to 10 mL of tetrahydrofuran, stirred and mixed evenly at room temperature to dissolve it, and molecular sieves were added and left standing for 48 h to remove excess moisture, obtaining an ethylammonium iodide tetrahydrofuran electrolyte containing CaI2.

[0129] The button battery (CR2032) was assembled from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode used was a calcium metal disc with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode used was a calcium metal disc with a diameter of 12 mm. The calcium metal sheet was polished with sandpaper before use. The separator used was cut into a disc with a diameter of 19 mm using a cutting machine and dried in a vacuum dryer at 100 °C for 12 h before use. The injection volume of the electrolyte was 0.15 mL.

[0130] Figure 31 Figure of the room temperature cycle test results of the symmetric cell with the ethylammonium iodide tetrahydrofuran electrolyte containing CaI2 at a current density of 0.02 mA cm -2 It can be seen that it can stably cycle for 200 h under the conditions of 0.02 mA cm -2 , 0.02 mAh cm -2 conditions, and the overpotential is only about 0.7 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0131] An asymmetric cell was assembled using the ethylammonium iodide tetrahydrofuran electrolyte containing CaI2, with a calcium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulomb efficiency under the test conditions of 0.02 mA cm -2 is as shown in Figure 32 The Coulomb efficiency is 55%, which is significantly improved compared with the CaI2 electrolyte and the Ca(TFSI)2 electrolyte, indicating that the electrolyte plays a good role in extending the battery life.

[0132] Comparative Example 3

[0133] Only MgI2 was used as the electrolyte salt, and the MgI2 electrolyte was prepared by referring to the steps in Example 1 and assembled into a battery for testing. Specifically as follows:

[0134] Weighed 139 mg (0.5 mmol) of MgI2 and added it to 10 mL of ethylene glycol dimethyl ether, stirred and mixed evenly at room temperature to dissolve it, added molecular sieves and let it stand for 48 h to remove excess water, and obtained the MgI2 electrolyte.

[0135] Assemble a button battery (CR2032) from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode sheet used is a magnesium metal round sheet with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode sheet used is a magnesium metal round sheet with a diameter of 12 mm. The magnesium metal sheet is polished with sandpaper before use. The separator used is cut into a round sheet with a diameter of 19 mm by a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte used is 0.15 mL.

[0136] Figure 33 For the MgI2 electrolyte symmetric battery at 0.1 mA cm -2 Current density at room temperature cycling test results graph. It can be seen that the battery immediately reaches the safety cut-off voltage of -5V after starting to discharge, proving that it cannot operate under this condition.

[0137] Using MgI2 electrolyte, with a magnesium metal sheet as the negative electrode and a copper foil as the positive electrode to assemble an asymmetric battery, its coulombic efficiency under the test conditions of 0.1 mA cm -2 As shown, it can be seen that the battery immediately reaches the safety cut-off voltage of -5V after starting to discharge, proving that it cannot operate under this condition. Figure 34 As shown, it can be seen that the battery immediately reaches the safety cut-off voltage of -5V after starting to discharge, proving that it cannot operate under this condition.

[0138] Example 11

[0139] This example is basically the same as Example 1, except that the metal iodide salt is replaced with MgI2 and the calcium metal sheet is replaced with a magnesium metal sheet. Refer to the steps in Example 1 to prepare an ethylammonium iodide electrolyte containing MgI2, and assemble a battery for testing. Specifically as follows:

[0140] Weigh 139 mg (0.5 mmol) of CaI2 and 173 mg (1 mmol) of ethylammonium iodide, add them to 10 mL of ethylene glycol dimethyl ether, stir and mix evenly at room temperature to dissolve, add molecular sieves and let stand for 48 h to remove excess moisture, obtaining an ethylammonium iodide tetrahydrofuran electrolyte containing MgI2.

[0141] Assemble a button battery (CR2032) from bottom to top in the order of "positive electrode case → positive electrode → separator → negative electrode → gasket → shrapnel → negative electrode case" in a glove box filled with argon for battery performance testing. The positive electrode sheet used is a magnesium metal round sheet with a diameter of 12 mm or a copper foil with a diameter of 19 mm, and the negative electrode sheet used is a magnesium metal round sheet with a diameter of 12 mm. The magnesium metal sheet is polished with sandpaper before use. The separator used is cut into a round sheet with a diameter of 19 mm by a cutting machine and dried in a 100 °C vacuum dryer for 12 h before use. The injection volume of the electrolyte used is 0.15 mL.

[0142] Figure 35 Cycling test results at room temperature of a symmetric cell with an ethylammonium iodide electrolyte containing MgI2 at a current density of 0.1 mA cm -2 As can be seen from the figure, it can stably cycle for more than 200 h under the conditions of 0.1 mA cm -2 and 0.1 mAh cm -2 , and the initial overpotential is only about 0.5 V, proving that the electrolyte plays a good role in improving the electrochemical activity and stability of the battery.

[0143] An asymmetric cell was assembled using an ethylammonium iodide electrolyte containing MgI2, with a magnesium metal sheet as the negative electrode and a copper foil as the positive electrode. Its Coulombic efficiency under the test conditions of 0.1 mA cm -2 is as shown in Figure 36 the figure, and the Coulombic efficiency is 20%, showing a significant improvement compared to the MgI2 electrolyte.

[0144] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An organic ammonium iodide-based electrolyte suitable for calcium metal batteries or magnesium metal batteries, characterized in that, It consists of a metal iodide salt, an organic ammonium iodide, and an organic solvent. The metal iodide salt is CaI2 or MgI2, the organic ammonium iodide is methylammonium iodide, ethylammonium iodide, propylammonium iodide, butylammonium iodide, or pentylammonium iodide, and the organic solvent is ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, or tetrahydrofuran. In the organic ammonium iodide-based electrolyte, the concentration of the organic ammonium iodide is 0.01 - 0.8 mol L -1 , and the concentration of the metal iodide salt is 0.01 - 0.05 mol L -1 .

2. The organic ammonium iodide-based electrolyte according to claim 1, wherein In the organic ammonium iodide-based electrolyte, the concentration of organic ammonium iodide is 0.1 mol / L -1 , and the concentration of metal iodide salt is 0.05 mol / L -1 .

3. The preparation method of the organic ammonium iodide-based electrolyte according to any one of claims 1 to 2, characterized in that, It includes the following steps: Mix and dissolve a metal iodide salt and an organic ammonium iodide in an organic solvent, and remove water with a molecular sieve to obtain an organic ammonium iodide-based electrolyte.

4. The preparation method according to claim 3, characterized in that, The time for water removal by the molecular sieve is 48 - 72 h.

5. Application of the organic ammonium iodide-based electrolyte according to any one of claims 1 - 2 as an electrolyte in a secondary battery.

6. The application according to claim 5, characterized in that, The secondary battery is a calcium metal battery or a magnesium metal battery.

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