An imidolyl lithium salt, a method for electrochemically reducing nitrogen to prepare the imidolyl lithium salt, and applications thereof

Abstract

The application discloses an imidoyl lithium salt, a method for preparing the imidoyl lithium salt through electrochemical nitrogen reduction, and application of the imidoyl lithium salt. The method for preparing the imidoyl lithium salt comprises the following steps: N2 is electrochemically reduced into Li3N through an electrochemical nitrogen reduction method, and the Li3N is in-situ reacted with a lithium salt precursor in an electrolyte to obtain the imidoyl lithium salt. The preparation method is simple, can effectively fix nitrogen in the air into nitrogen in the imidoyl electrolyte, and can realize one-step production of the imidoyl electrolyte lithium salt, so that the preparation cost of the imidoyl lithium salt electrolyte is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrolyte preparation, specifically to a method for the continuous preparation of an imide-based lithium salt by electrochemical nitrogen reduction and its application. Background Technology

[0002] The electrolyte material of a battery is one of the key materials affecting its quality, and it can be divided into two types: liquid electrolytes and solid electrolytes. Liquid electrolytes are usually a liquid of lithium salt and aprotic organic solvent. Among various lithium battery electrolyte materials, imide-based lithium salts, due to their uniquely structured anions, possess many advantages that other electrolyte materials do not have, making them the primary choice for preparing novel lithium battery materials. Furthermore, imide-based lithium salts also exhibit relatively stable chemical and electrochemical stability. Based on these advantages, imide-based lithium salts can serve as excellent novel lithium battery electrolytes and have become a subject of intense research by chemists worldwide.

[0003] However, conventional imide-based electrolyte lithium salts are prepared through organic chemical synthesis, which involves complex reaction equipment, cumbersome processes, and strict requirements on reaction temperature. Excessive chlorination reagents can form highly toxic and corrosive byproducts, resulting in a high impurity content. Purification is necessary before they can be used as supporting electrolyte salts in lithium batteries, which greatly limits the commercial application of imide-based electrolyte lithium salts.

[0004] Nitrogen is a ubiquitous gas in the atmosphere, with wide-ranging sources and well-established separation methods. Considering that existing imide-based electrolyte lithium salts contain nitrogen, directly fixing nitrogen from nitrogen gas into the electrolyte would not only reduce production costs but also promote the development of artificial nitrogen fixation. However, the utilization of nitrogen in electrolyte preparation is currently rarely reported. Summary of the Invention

[0005] To address the above problems, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing an imide-based lithium salt, the method comprising the following steps: electrochemically reducing N2 to Li3N by an electrochemical nitrogen reduction method, wherein the Li3N reacts in situ with a lithium salt precursor in an electrolyte to obtain the imide-based lithium salt.

[0007] According to an embodiment of the present invention, the preparation method may be carried out using apparatus known in the art, as long as it can provide the required low potential, for example, such as... Figure 1 The apparatus shown.

[0008] According to an embodiment of the present invention, the preparation method specifically includes the following steps:

[0009] In the first step, under discharge conditions, Li and N2 react with an electrocatalyst to form Li3N;

[0010] The second step involves reacting the Li3N obtained in the first step with the lithium salt precursor to generate the imide-based lithium salt.

[0011] According to an embodiment of the present invention, the first step is preferably carried out in an anhydrous and oxygen-free environment.

[0012] According to an embodiment of the present invention, in the first step, the electrocatalyst is selected from a metal catalyst or a metal oxide catalyst.

[0013] Preferably, the metal catalyst is selected from at least one of Au, Mo, Pd and Pt.

[0014] Preferably, the metal oxide catalyst is selected from at least one of TiO2, MnO2 and Al2O3.

[0015] For example, the electrocatalyst is selected from at least one of Au, Mo, Pd and Pt, preferably Pt.

[0016] According to an embodiment of the present invention, in the first step, the reaction for generating Li3N is as shown in Formula 1 below:

[0017]

[0018] According to an embodiment of the present invention, the preparation method of Li3N in the first step specifically includes: in an anhydrous and oxygen-free environment, using the catalyst as the positive electrode and lithium metal as the negative electrode, injecting an electrolyte, introducing N2 into the positive electrode side, and after standing for a period of time, discharging from the open circuit voltage to a low potential at a certain current density to generate Li3N.

[0019] According to an embodiment of the present invention, in the method for preparing Li3N, the standing time refers to a standing time of 0.5-20h, and exemplarily, the standing time is 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h or 20h.

[0020] According to an embodiment of the present invention, the discharge refers to discharging to a discharge voltage of 0.4-0.1V, and exemplarily, the discharge voltage is 0.4V, 0.3V, 0.2V or 0.1V.

[0021] According to an embodiment of the present invention, in the second step, the lithium salt precursor is a lithium salt precursor containing a sulfonyl group.

[0022] Preferably, the lithium salt precursor is selected from one or more lithium salt precursors containing sulfonyl groups.

[0023] According to an embodiment of the present invention, the molecular formula of the lithium salt precursor is as follows:

[0024]

[0025] Wherein, A is selected from at least one of F-, F3C-, F3CF2C-, F2CF2CF2C-, and F3CF2CF2CF2C-, preferably F3C-; B is selected from at least one of OLi-, F-, Cl-, Br-, and I-, preferably OLi-.

[0026] According to an embodiment of the present invention, the second step is carried out in the electrolyte.

[0027] According to an embodiment of the present invention, in the second step, the reaction is carried out at a certain potential. Preferably, the potential refers to the potential during the discharge.

[0028] According to an embodiment of the present invention, the lithium salt precursor is dissolved in an electrolyte.

[0029] According to an embodiment of the present invention, the electrolyte comprises a lithium salt precursor, a lithium salt, and an organic solvent.

[0030] According to an embodiment of the present invention, the concentration of the lithium salt precursor in the electrolyte is 0.1-2.0 mol / L.

[0031] According to an embodiment of the present invention, in the electrolyte, the lithium salt is selected from one or two or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide, preferably lithium trifluoromethanesulfonate.

[0032] According to an embodiment of the present invention, the concentration of the lithium salt in the electrolyte is 0.1-2.0 mol / L.

[0033] According to embodiments of the present invention, the organic solvent is selected from at least one of propylene carbonate, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, sulfolane, 1,3-dioxolane (DOL), dimethyl ethylene glycol (DME), tetraethylene glycol dimethyl ether (TEGDME), 1,4-dioxane, and tetrahydrofuran (THF). Exemplarily, the organic solvent is a mixture of DOL and DME in a volume ratio of 1:1.

[0034] According to an embodiment of the present invention, a separator is further included between the positive electrode and the negative electrode. The separator in this invention may be a separator known in the art, such as a Celgard 2400 microporous membrane.

[0035] According to an embodiment of the present invention, the reaction in the second step is as shown in Equation 2 below:

[0036]

[0037] Wherein, A and B have the meanings described above, A is selected from at least one of F-, F3C-, F3CF2C-, F2CF2CF2C-, and F3CF2CF2CF2C-, preferably F3C-; B is selected from at least one of OLi-, F-, Cl-, Br-, and I-;

[0038] The imide-lithium salt is X and Y are selected from substituents containing acyl groups, and X and Y may be the same or different.

[0039] Preferably, X and Y are independently selected from trifluoromethylsulfonyl, pentafluoroethylsulfonyl, nonafluorobutylsulfonyl, perfluoropropane disulfonyl, and fluorosulfonyl.

[0040] According to an embodiment of the present invention, the preparation method further includes: a third step, after the discharge is completed, continuing to charge to a high potential, whereby the byproducts are electrolyzed on the negative electrode side to generate lithium and on the positive electrode side to generate oxygen or halide elements.

[0041] According to an embodiment of the present invention, the byproduct includes LiB, such as one or more of Li2O, LiF, LiCl, LiBr, and LiI.

[0042] According to an embodiment of the present invention, the halide element includes one or more of F2, Cl2, Br2, and I2.

[0043] Preferably, the high potential refers to 3.7-4.0V, and exemplarily, it is charged to 3.7V, 3.8V, 3.9V, or 4.0V.

[0044] According to an exemplary embodiment of the present invention, the method for preparing the imide-based lithium salt includes the following steps:

[0045] 1) Li and N2 react in the presence of an electrocatalyst to form Li3N;

[0046] 2) In step 1), Li3N and the lithium salt precursor react in situ to generate the imide-based lithium salt and lithium oxide; wherein, the molecular formula of the lithium salt precursor is...

[0047] The present invention also provides an imide-based lithium salt, which is obtained by the above preparation method.

[0048] According to an embodiment of the present invention, the imide-based lithium salt has the following structural formula:

[0049]

[0050] Wherein, X and Y are selected from substituents containing acyl groups, and X and Y may be the same or different.

[0051] Preferably, X and Y are independently selected from at least one of trifluoromethylsulfonyl, pentafluoroethylsulfonyl, nonafluorobutylsulfonyl, perfluoropropane disulfonyl, and fluorosulfonyl.

[0052] According to an embodiment of the present invention, the electrocatalyst is selected from metal catalysts or metal oxide catalysts.

[0053] Preferably, the metal catalyst is selected from at least one of Au, Mo, Pd and Pt.

[0054] Preferably, the metal oxide catalyst is selected from at least one of TiO2, MnO2 and Al2O3.

[0055] According to an embodiment of the present invention, the in-situ reaction includes at least one, two, or more lithium salt precursors.

[0056] According to an embodiment of the present invention, the molecular formula of the lithium salt precursor is as follows:

[0057]

[0058] Wherein, A is selected from at least one of F-, F3C-, F3CF2C-, F2CF2CF2C-, and F3CF2CF2CF2C-, preferably F3C-; B is selected from at least one of OLi-, F-, Cl-, Br-, and I-, preferably OLi-.

[0059] The present invention also provides an electrolyte containing the above-mentioned imide-based lithium salt.

[0060] The present invention also provides an electrolyte containing the above-mentioned imide-based lithium salt and / or electrolyte.

[0061] The present invention also provides the application of the above-mentioned imide-based lithium salt, the above-mentioned electrolyte or the above-mentioned electrolyte solution in secondary batteries.

[0062] Beneficial effects of the present invention

[0063] (1) The present invention rapidly and easily prepares pure Li3N by electrochemical nitrogen reduction.

[0064] (2) The present invention utilizes the in-situ reaction of Li3N with a lithium salt precursor containing an acyl group in an electrolyte to obtain a lithium-ion battery electrolyte containing an imide-based lithium salt as an electrolyte in one step.

[0065] (3) After the preparation method of the present invention obtains an electrolyte containing imide-based lithium salt, it can be further purified by charging. The by-products in the electrolyte decompose during the charging process, thereby achieving product purification.

[0066] (4) The preparation process of traditional imide-based electrolyte lithium salts is complex and costly, while the preparation method of the present invention is simple and cost-effective. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the device used in Example 1.

[0068] Figure 2 This is a scanning electron microscope (SEM) image of the Pt electrocatalyst mesh used in the preparation of Li3N in Example 1 (scale bar is 200 μm).

[0069] Figure 3 This is the X-ray diffraction pattern of Li3N prepared in Example 1.

[0070] Figure 4 This is the XPS image of Li3N prepared in Example 1.

[0071] Figure 5 This is a schematic diagram of Li3N discharge.

[0072] Figure 6 This is the F spectrum of trifluoromethanesulfonyl chloride from Example 1.

[0073] Figure 7 This is the F-spectrum of standard lithium bis(trifluoromethanesulfonyl)imide.

[0074] Figure 8 This is the F spectrum measured during the reaction process in Example 1. Detailed Implementation

[0075] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0076] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0077] Experimental reagents and equipment: high-purity nitrogen, high-purity argon, Pt mesh, lithium foil, electrolyte, precursor of sulfonyl electrolyte lithium salt, electrochemical workstation CHI 660E (Shanghai Chenhua), Blue Battery testing system (CT 2001A).

[0078] In the following examples, the precursors of the sulfonyl electrolyte lithium salts were selected from the following:

[0079] Trifluoromethylsulfonyl chloride precursor;

[0080] Fluorosulfonyl lithium salt precursor;

[0081] Pentafluoroethylsulfonyl lithium salt precursor;

[0082] Trifluoromethanesulfonyl lithium salt precursor;

[0083] Perfluoropropane disulfonyl lithium salt precursor;

[0084] Trifluoromethanesulfonyl fluoride precursor;

[0085] Trifluoromethanesulfonyl bromide precursor;

[0086] Trifluoromethanesulfonyl iodine precursor.

[0087] Example 1

[0088] Electrolytes for preparing imide-based lithium salts:

[0089] 1. Figure 1 This is a schematic diagram of the device in this embodiment, which is a Li-N2 battery. The positive electrode of the battery is a 1*1cm Pt mesh, which serves as both an electrocatalyst for the electrochemical reaction and a positive electrode current collector. The battery also includes a polypropylene separator (Celgard 2400) and a lithium foil negative electrode. In the Li-N2 battery, the concentration of the electrolyte is 0.1mol / L, which is obtained by dissolving a trifluoromethanesulfonyl chloride precursor in tetrahydrofuran.

[0090] 2. In an anhydrous and oxygen-free environment (an anhydrous and oxygen-free environment means that the oxygen content is ≤0.1ppm and the water content is ≤0.1ppm), a certain amount of N2 is introduced into the positive electrode side. After standing for 30 minutes, it is discharged from the open circuit voltage (specifically ~2.8V) to 0.3V with a certain current density to generate Li3N.

[0091] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate bis(trifluoromethanesulfonyl)imine lithium, the reaction mechanism of which is shown in Equation 3:

[0092]

[0093] The electrolyte after discharge also contains the byproduct LiCl. When the battery is charged to 3.8V, the byproduct decomposes, producing lithium on the negative electrode side and chlorine on the positive electrode side.

[0094] The product Li3N from Example 1 was characterized using X-ray diffraction and X-ray electron spectroscopy, and the results showed that Li3N was successfully prepared in Example 1. Figure 3 The X-ray diffraction pattern shown exhibits typical characteristic peaks of Li3N. Figure 4 The XPS plots show that the binding energy is significantly enhanced after battery discharge, further confirming the formation of Li3N. Figure 6 This is the F spectrum of CF3SO2Cl before the reaction. Figure 7 It is the F-spectrum of standard lithium bis(trifluoromethanesulfonyl)imide. Figure 8 It is the F spectrum measured during the reaction process, compared with... Figure 6-8 It is known that lithium bis(trifluoromethanesulfonyl)imide is produced during the reaction.

[0095] Experiments showed that, under constant nitrogen flow rate, current density, and discharge time, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte varied depending on the discharge potential. The nitrogen flow rate was 10 sccm, and the discharge current density was 0.02 mA cm⁻¹. -2 After maintaining the condition for 5 hours, the electrolytes were discharged to different low potentials, and the concentrations of lithium bis(trifluoromethanesulfonyl)imine in the resulting electrolytes are shown in Table 1.

[0096] Table 1: Concentration of lithium bis(trifluoromethanesulfonyl)imine in electrolyte at different low discharge potentials

[0097] Electrolyte concentration / M 0 0.001 0.004 0.009 0.018

[0098] Note: In the table, M refers to mol / L.

[0099] Experiments showed that, while maintaining a constant discharge current density and discharge time to a low potential, different nitrogen flow rates resulted in varying concentrations of lithium bis(trifluoromethanesulfonyl)imide in the obtained electrolyte. When the discharge current density was 0.02 mA cm⁻¹... -2 The battery was discharged to 0.3V and maintained for 5 hours. The concentration of lithium bis(trifluoromethanesulfonyl)imine in the resulting electrolyte was shown in Table 2 when the nitrogen flow rate during the reaction was different.

[0100] Table 2: Concentration of lithium bis(trifluoromethanesulfonyl)imine in electrolyte at different nitrogen flow rates

[0101] Electrolyte concentration / M 0.006 0.01 0.016 0.026 0.034

[0102] Experiments showed that, with a constant nitrogen flow rate during the reaction and a fixed discharge potential maintained at a low level for a certain period, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the obtained electrolyte varied with changes in discharge current density. Table 3 shows the electrolyte concentrations obtained at different discharge current densities when the nitrogen flow rate was 10 sccm, the battery was discharged to 0.3V and maintained for 5 hours.

[0103] Table 3: Concentration of lithium bis(trifluoromethanesulfonyl)imide in electrolyte at different discharge current densities

[0104] Electrolyte concentration / M 0.01 0.018 0.032 0.045 0.058

[0105] Experiments revealed that, with a constant discharge current density and nitrogen flow rate during the reaction, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte varied depending on the time the battery maintained a discharge voltage of 0.3V. When the discharge current density was 0.02 mA cm⁻¹ -2 With a nitrogen flow rate of 10 sccm, the electrolyte concentrations obtained at different battery discharge times are shown in Table 4.

[0106] Table 4: Concentration of lithium bis(trifluoromethanesulfonyl)imide in electrolyte at different battery discharge times

[0107] Electrolyte concentration / M 0.01 0.023 0.035 0.051 0.063

[0108] The above experiments show that when the discharge current density is 0.02-0.1 mA cm⁻¹ -2 When the nitrogen flow rate is 10-25 sccm and the battery discharge time is 5-30 h, the maximum concentration of lithium bis(trifluoromethanesulfonyl)imide is 0.24 mol / L.

[0109] Experiments revealed that after complete discharge, recharging the battery to different cutoff voltages resulted in variations in the purity of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte before and after charging. This was observed when the charging current density was 0.02 mA cm⁻¹. -2 Table 5 shows the purity of lithium bis(trifluoromethanesulfonyl)imide obtained in the electrolyte before and after charging, depending on the battery charging voltage. It can be seen that under charging conditions, the byproduct LiCl in the electrolyte of step 3 decomposes to obtain the purified electrolyte.

[0110] Table 5. Purity of lithium bis(trifluoromethanesulfonyl)imine in the electrolyte before and after charging.

[0111] Purity before charging / % 30.1％ 32.5％ 31.2％ 33.2％ 30.5％ Purity after charging / % 35.7％ 60.8％ 89.5％ 95.6％ 96.7％

[0112] Comparative Example 1

[0113] Electrolytes for preparing imide-based lithium salts:

[0114] This comparative example is basically the same as Example 1, except that in step 2, Ar is introduced into the positive electrode side at a rate of 10 sccm in an anhydrous and oxygen-free environment. After standing for 30 minutes, the open-circuit voltage is measured at a rate of 0.02 mA cm⁻¹. -2 The current density is discharged to 0.3V.

[0115] Depend on Figure 5 The discharge curve of Li3N shows that Li3N cannot be prepared under an Ar atmosphere and can only be synthesized under an N2 atmosphere.

[0116] Example 2

[0117] Electrolytes for preparing imide-based lithium salts:

[0118] 1. The Li-N2 battery consists of a 1*1cm Au mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl chloride precursor dissolved in an organic electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0119] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 Discharging to 0.3V generates Li3N;

[0120] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate lithium bis(trifluoromethanesulfonyl)imine, with a concentration of 0.021 mol / L in the electrolyte.

[0121] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiCl decomposes, and the purity of the product increases from 30.6% before charging to 92.6% after charging.

[0122] Example 3

[0123] Electrolytes for preparing imide-based lithium salts:

[0124] 1. The Li-N2 battery consists of a 1*1cm Mo mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl chloride precursor dissolved in an organic mixed electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0125] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2When discharged to 0.3V, Li3N is generated;

[0126] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate lithium bis(trifluoromethanesulfonyl)imine, with a concentration of 0.015 mol / L in the electrolyte.

[0127] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiCl decomposes, and the purity of the product increases from 31.4% before charging to 93.9% after charging.

[0128] Example 4

[0129] Electrolytes for preparing imide-based lithium salts:

[0130] 1. The Li-N2 battery consists of a 1*1cm Pd mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl chloride precursor dissolved in a tetraethylene glycol dimethyl ether (TEGDME) organic electrolyte.

[0131] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0132] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate lithium bis(trifluoromethanesulfonyl)imine, with a concentration of 0.017 mol / L in the electrolyte.

[0133] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiCl decomposes, and the purity of the product increases from 32.7% before charging to 91.5% after charging.

[0134] Example 5

[0135] Electrolytes for preparing imide-based lithium salts:

[0136] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L fluorosulfonyl lithium salt precursor dissolved in an organic electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0137] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0138] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the fluorosulfonyl lithium salt precursor to generate lithium difluorosulfonylimide, the reaction mechanism of which is shown in Equation 4:

[0139]

[0140] In this embodiment, the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.02 mol / L.

[0141] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct Li2O decomposes, and the purity of the product increases from 31.9% before charging to 94.2% after charging.

[0142] Example 6

[0143] Electrolytes for preparing imide-based lithium salts:

[0144] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L pentafluoroethyl sulfonyl lithium salt precursor dissolved in a tetraethylene glycol dimethyl ether (TEGDME) organic electrolyte.

[0145] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0146] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the pentafluoroethylsulfonyl lithium salt precursor to generate bis(pentafluoroethylsulfonyl)imine lithium, the reaction mechanism of which is shown in Equation 5:

[0147]

[0148] In this embodiment, the concentration of lithium bis(pentafluoroethylsulfonyl)imide is 0.016 mol / L in the electrolyte.

[0149] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct Li2O decomposes, and the purity of the product increases from 33.2% before charging to 94.1% after charging.

[0150] Example 7

[0151] Electrolytes for preparing imide-based lithium salts:

[0152] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and 0.1mol / L trifluoromethanesulfonyl lithium salt precursor and nonafluorobutylsulfonyl lithium salt precursor dissolved in a tetraethylene glycol dimethyl ether (TEGDME) organic electrolyte.

[0153] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0154] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the lithium trifluoromethanesulfonyl salt precursor and the lithium nonafluorobutylsulfonyl salt precursor to generate lithium (trifluoromethanesulfonyl)(nonafluorobutylsulfonyl)imine, the reaction mechanism of which is shown in Equation 6:

[0155]

[0156] In this embodiment, the concentration of lithium (trifluoromethylsulfonyl)(nonafluorobutylsulfonyl)imide is 0.013 mol / L in the electrolyte.

[0157] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct Li2O decomposes, and the purity of the product increases from 30.2% before charging to 91.6% after charging.

[0158] Example 8

[0159] Electrolytes for preparing imide-based lithium salts:

[0160] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L perfluoropropane disulfonyl lithium salt precursor dissolved in an organic mixed electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0161] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0162] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the lithium perfluoropropane disulfonyl salt precursor to generate lithium trifluoropropane disulfonylimide, the reaction mechanism of which is shown in Equation 7:

[0163]

[0164] In this embodiment, the concentration of lithium trifluoropropane disulfonylimide in the electrolyte is 0.016 mol / L.

[0165] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct Li2O decomposes, and the purity of the product increases from 31.9% before charging to 90.8% after charging.

[0166] Example 9

[0167] Electrolytes for preparing imide-based lithium salts:

[0168] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and 0.1mol / L fluorosulfonyl lithium salt precursor and trifluoromethanesulfonyl lithium salt precursor dissolved in an organic mixed electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0169] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0170] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the fluorosulfonyl lithium salt precursor and the trifluoromethanesulfonyl lithium salt precursor to form (fluorosulfonyl)(trifluoromethanesulfonyl)imine lithium, the reaction mechanism of which is shown in Equation 8:

[0171]

[0172] In this embodiment, the concentration of lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide in the electrolyte is 0.011 mol / L.

[0173] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct Li2O decomposes, and the purity of the product increases from 33.2% before charging to 94.1% after charging.

[0174] Example 10-1

[0175] Electrolytes for preparing imide-based lithium salts:

[0176] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl fluoride precursor dissolved in an organic mixed electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0177] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0178] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl fluoride precursor to generate lithium bis(trifluoromethanesulfonyl)imide, the reaction mechanism of which is shown in Equation 8:

[0179]

[0180] In this embodiment, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 0.019 mol / L.

[0181] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiF decomposes, and the purity of the product increases from 31.6% before charging to 94.6% after charging.

[0182] Example 10-2

[0183] Electrolytes for preparing imide-based lithium salts:

[0184] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene membrane (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl bromide precursor dissolved in an organic mixed electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0185] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0186] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl bromide precursor to generate lithium bis(trifluoromethanesulfonyl)imide, the reaction mechanism of which is shown in Equation 8:

[0187]

[0188] In this embodiment, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 0.017 mol / L.

[0189] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiBr decomposes, and the purity of the product increases from 29.7% before charging to 89.6% after charging.

[0190] Example 10-3

[0191] Electrolytes for preparing imide-based lithium salts:

[0192] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl iodide precursor dissolved in an organic mixed electrolyte of tetraethylene glycol dimethyl ether (TEGDME).

[0193] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0194] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl iodide precursor to generate lithium bis(trifluoromethanesulfonyl)imide, the reaction mechanism of which is shown in Equation 8:

[0195]

[0196] In this embodiment, the concentration of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 0.015 mol / L.

[0197] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiI decomposes, and the purity of the product increases from 25.9% before charging to 86.4% after charging.

[0198] Example 11

[0199] Electrolytes for preparing imide-based lithium salts:

[0200] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene membrane (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl chloride precursor dissolved in an organic mixed electrolyte of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (volume ratio 1:1).

[0201] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm.-2 When discharged to 0.3V, Li3N is generated;

[0202] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate lithium bis(trifluoromethanesulfonyl)imine. The concentration of lithium bis(trifluoromethanesulfonyl)imine in the electrolyte is 0.017 mol / L.

[0203] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiCl decomposes, and the purity of the product increases from 33.9% before charging to 94.7% after charging.

[0204] Example 12

[0205] Electrolytes for preparing imide-based lithium salts:

[0206] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene membrane (Celgard 2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl chloride precursor dissolved in an organic mixed electrolyte of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) (volume ratio 1:1:1).

[0207] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0208] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate lithium bis(trifluoromethanesulfonyl)imine, with a concentration of 0.02 mol / L in the electrolyte.

[0209] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiCl decomposes, and the purity of the product increases from 31.5% before charging to 94.7% after charging.

[0210] Example 13

[0211] Electrolytes for preparing imide-based lithium salts:

[0212] 1. The Li-N2 battery consists of a 1*1cm Pt mesh as an electrocatalyst and a positive electrode current collector, a polypropylene separator (Celgard2400) and lithium foil, and a 0.1mol / L trifluoromethanesulfonyl chloride precursor dissolved in an organic mixed electrolyte dissolved in 1,4-dioxane.

[0213] 2. In an anhydrous and oxygen-free environment, introduce 10 sccm of N2 into the positive electrode side. After standing for 30 minutes, introduce N2 at an open-circuit voltage of 0.02 mA / cm. -2 When discharged to 0.3V, Li3N is generated;

[0214] 3. Subsequently, Li3N diffuses into the electrolyte and reacts with the trifluoromethanesulfonyl chloride precursor to generate lithium bis(trifluoromethanesulfonyl)imine. The concentration of lithium bis(trifluoromethanesulfonyl)imine in the electrolyte is 0.016 mol / L.

[0215] 4. After discharge is complete, the battery operates at a current density of 0.02 mA / cm². -2 When charged to 3.8V, the byproduct LiCl decomposes, and the purity of the product increases from 31.2% before charging to 95.1% after charging.

[0216] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an imide-based lithium salt, characterized in that, The preparation method includes the following steps: The first step involves electrochemically reducing N2 to Li3N using an electrochemical nitrogen reduction method: In an anhydrous and oxygen-free environment, an electrocatalyst is used as the positive electrode, and lithium metal is used as the negative electrode. After injecting the electrolyte, N2 is introduced to the positive electrode side. After standing for 0.5-20 hours, the electrolyte is discharged from the open-circuit voltage to a low potential of 0.4-0.1V at a certain current density to generate Li3N. The electrolyte includes a lithium salt precursor, lithium salt, and an organic solvent. The lithium salt precursor is selected from one or more lithium salt precursors containing sulfonyl groups, and the lithium salt precursor containing sulfonyl groups is selected from perfluoropropane disulfonyl lithium salt precursor. Or selected from one of the substances having the following molecular formula: Wherein, A is selected from one of F-, F3C-, F3CF2C-, F2CF2CF2C-, and F3CF2CF2CF2C-; B is selected from one of OLi-, F-, Cl-, Br-, and I-. The second step involves reacting the Li3N obtained in the first step with the lithium salt precursor in situ in the electrolyte under the potential conditions during discharge to generate the imide-based lithium salt. The third step involves charging the battery to a high potential of 3.7-4.0V after the discharge is complete. The byproducts are electrolyzed on the negative electrode side to generate lithium, and on the positive electrode side to generate oxygen or halogen elements.

2. The method for preparing the imide-based lithium salt according to claim 1, characterized in that, In the first step, the electrocatalyst is selected from metal catalysts; The metal catalyst is selected from at least one of Au, Mo, Pd and Pt.

3. The method for preparing the imide-based lithium salt according to claim 1, characterized in that, In the first step, the concentration of the lithium salt precursor in the electrolyte is 0.1-2.0 mol / L; In the electrolyte, the lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide. In the electrolyte, the concentration of the lithium salt is 0.1-2.0 mol / L; The organic solvent is selected from at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, sulfolane, 1,3-dioxolane, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. A diaphragm is also included between the positive and negative electrodes.

4. The method for preparing the imide-based lithium salt according to claim 1, characterized in that, The precursor containing a sulfonyl group is selected from at least one of the following substances: Trifluoromethylsulfonyl chloride precursor; Fluorosulfonyl lithium salt precursor; Pentafluoroethylsulfonyl lithium salt precursor; Trifluoromethanesulfonyl lithium salt precursor; Trifluoromethanesulfonyl fluoride precursor; Trifluoromethanesulfonyl bromide precursor; Trifluoromethanesulfonyl iodine precursor.

5. The method for preparing the imide-based lithium salt according to claim 1, characterized in that, The imide-lithium salt is X and Y are the same or different and independent of each other, selected from one of trifluoromethylsulfonyl, pentafluoroethylsulfonyl, nonafluorobutylsulfonyl, perfluoropropane disulfonyl, and fluorosulfonyl.

6. The method for preparing the imide-based lithium salt according to claim 1, characterized in that, The byproducts are one or more of Li₂O, LiF, LiCl, LiBr, and LiI.

7. The method for preparing the imide-based lithium salt according to claim 1, characterized in that, The halogen element includes one or more of F2, Cl2, Br2, and I2.

8. An imide-based lithium salt, characterized in that, The imide-based lithium salt is obtained by the preparation method according to any one of claims 1-7.

9. The imide-based lithium salt according to claim 8, characterized in that, The imide-based lithium salt has the following structural formula: Wherein, X and Y may be the same or different, and X and Y are independently selected from one of trifluoromethylsulfonyl, pentafluoroethylsulfonyl, nonafluorobutylsulfonyl, perfluoropropane disulfonyl, and fluorosulfonyl.

10. An electrolyte comprising the imide-based lithium salt of claim 8 or 9.

11. The use of the imide-based lithium salt of claim 8 or 9 or the electrolyte of claim 10 in a secondary battery.

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