A functional electrolyte additive for lithium metal-air batteries

Abstract

The present application relates to a kind of functional electrolyte additives for lithium metal air battery, and the electrolyte additive of lithium metal air battery is 5-((4-bromo-2,6-difluorophenyl) difluoromethoxy)-1,2,3-trifluorobenzene (BDTMD). The present application uses BDTMD as electrolyte additive, after being introduced into metal air battery electrolyte, can be constructed on the surface of metal lithium electrode by its reaction with metal electrode structure stable, excellent chemical performance SEI film, at the same time, in some metal air battery, it can also reduce the "high charge potential" generally existing in the field of metal air battery simultaneously.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium metal air batteries, and relates to a lithium metal air battery electrolyte material additive. BACKGROUND

[0002] Due to the combustion of fossil fuels and the emission of a large amount of greenhouse gases, the global ecological environment is destroyed, forcing mankind to develop green energy and low-carbon technology. Metal air batteries represented by lithium-carbon dioxide batteries can capture and convert CO2 and other gases into valuable chemical substances, which can not only be used as a new type of energy storage device, but also can effectively alleviate the greenhouse effect. Compared with traditional lithium ion batteries, metal air batteries often have relatively high discharge voltage and ultra-high theoretical specific energy density, and are considered to be an ideal energy storage device for providing sustainable power output for long-distance transportation, especially in CO2-rich environments, such as underwater operations and Mars exploration.

[0003] However, metal air batteries still face many problems in the charging and discharging and cycling processes. One of the most critical links is the decomposition of the discharge product. For example, the discharge product Li2CO3 in lithium-carbon dioxide batteries, as a wide band gap insulator, is difficult to completely decompose even if the battery charging voltage exceeds 4.0V, which brings great obstacles to the performance and cycle life of the battery. Therefore, solving the decomposition problem of the discharge product Li2CO3 and the like is one of the keys to the practical application of metal air batteries.

[0004] In view of this problem, researchers have devoted themselves to the research of battery positive electrode solid catalysts, but because the soluble electrolyte additive can have better contact with the insoluble product, it undoubtedly has more advantages in promoting the reversibility of the battery. Generally speaking, a suitable electrolyte additive must meet the following standards:

[0005] (1) high solubility in the selected electrolyte;

[0006] (2) appropriate redox potential compared with the carbon dioxide redox potential;

[0007] (3) reversible oxidation / reduction reaction;

[0008] (4) chemical inertness to electrolyte components and active substances, such as superoxide free radicals.

[0009] In recent years, soluble electrolyte additives are widely used as electron hole transfer agents to improve the performance of lithium batteries. Compared with solid catalysts on the electrode, this soluble electrolyte additive realizes a more effective "solid-liquid contact" with the discharge product, the contact site between the catalyst and the discharge product is more, and the catalytic decomposition of the discharge product can be more effectively realized. As a mobile charge carrier, the electrolyte additive, i.e. redox medium (RM), can oxidize insoluble discharge products, promote the decomposition of discharge products on the liquid-solid interface, and effectively reduce the overpotential of the battery.

[0010] CN201810977810.0 patent discloses a method for modifying the electrolyte of a lithium-air battery, a certain amount of beta carotene analogues and a small amount of water are added to the non-aqueous electrolyte, so that the battery has higher specific capacity and better rate performance.

[0011] CN202110497351.8 patent discloses an electrolyte additive for improving the electrochemical performance of a lithium-air battery, which is a metal heterocyclic compound and its derivative, which not only greatly reduces the overpotential of the battery during charging and discharging process, improves the energy efficiency, but also significantly improves the cycle life of the battery.

[0012] CN202110695345.3 patent discloses a lithium-air battery ruthenocene additive with both redox medium and lithium metal protection, which acts as a redox medium in the electrochemical reaction of the battery, and has a positive effect on the stability of the negative electrode metal lithium. SUMMARY

[0013] In order to solve the problem that in a lithium metal-air battery, the discharge products Li2CO3, Li2O2, etc. are not easy to be decomposed during the charging process, resulting in too high overpotential of the battery, which seriously affects the performance and cycle life of the battery, the purpose of the present application is to provide a functional electrolyte additive for a lithium metal-air battery.

[0014] The technical solution to achieve the purpose of the present application is: a functional electrolyte additive for a lithium metal-air battery, the electrolyte additive of the lithium metal-air battery is 5-((4-bromo-2, 6-difluorophenyl) difluoromethoxy)-1, 2, 3-trifluorobenzene.

[0015] Preferably, the lithium metal-air battery is a lithium-oxygen battery or a lithium-carbon dioxide battery.

[0016] Preferably, the electrolyte is a 0.5M lithium salt solution.

[0017] Specifically, the lithium salt in the lithium salt solution is one or a mixture of lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium trifluoromethylsulfonate (LiSO3CF3), and lithium bis(trifluoromethylsulfone)imide (LiTFSI), and preferably LiClO4.

[0018] Preferably, the amount of the electrolyte additive is 0.01-1.5 mol / L, and preferably 0.15 mol / L.

[0019] Preferably, the solvent of the electrolyte is one or a mixture of DME, dimethyl sulfoxide (DMSO), and tetraethylene glycol dimethyl ether (TEGDME), and preferably DMSO.

[0020] Compared with the prior art, the present application has the advantages that: by introducing a soluble electrolyte additive into a lithium metal-air battery, the present application enhances the effective contact between solid and liquid phases, increases the effective reaction contact sites, promotes the decomposition of discharge products, and reduces the battery charging potential. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is the cyclic voltammogram of the 0.5M LiClO4 / DMSO electrolyte with an additive concentration of 0.1 mol / L as described in Example 1 of the present application.

[0022] Figure 2 is the XRD characterization of the discharge product of the Li-CO2 battery of Example 2 of the present application.

[0023] Figure 3 is the XRD characterization of the discharge product of the Li-O2 battery of Example 3 of the present application.

[0024] Figure 4 is the charge-discharge curve of the Li-O2 battery of Example 4 of the present application.

[0025] Figure 5 is the lithium deposition curve of the lithium metal symmetric battery described in Example 5 of the present application. DETAILED DESCRIPTION

[0026] The following examples further illustrate the present application, but should not be construed as limiting the present application. Modifications and substitutions to the methods, steps or conditions described herein are considered to be within the scope of the present application.

[0027] If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art.

[0028] The application effectively enhances the "solid-liquid phase contact", increases the effective reaction contact sites, effectively promotes the decomposition of the discharge product, and further reduces the battery charging potential by introducing the additive 5-((4-bromo-2,6-difluorophenyl) difluoromethoxy)-1,2,3-trifluorobenzene in the electrolyte of the lithium-air battery. At the same time, in the application of the metal lithium electrode, it also has the advancement of stabilizing the SEI structure of the metal lithium surface and improving the cycle life of the metal lithium electrode.

[0029] The application is based on the method for improving the electrochemical performance of a lithium-air battery by using an electrolyte additive, and the specific steps are as follows:

[0030] Step 1: rolling the electrode sheet;

[0031] Step 2: preparing the required electrolyte in a glove box with an argon atmosphere and a water oxygen value less than 0.1 ppm, the solvent of the electrolyte is DMSO, the solute is LiClO4, the electrolyte concentration is 0.5 mol / L, and 0.1-0.5 mol / L of the electrolyte additive 5-((4-bromo-2,6-difluorophenyl) difluoromethoxy)-1,2,3-trifluorobenzene (BDTMD, commercially available, CAS No. 511540-64-0) is added;

[0032] Step 3: assembling the 2032 type button cell in the order of negative electrode shell, spring, gasket, negative electrode sheet, GF series glass fiber, electrolyte, positive electrode sheet, and positive electrode shell with holes by using the various accessories prepared in advance;

[0033] Step 4: blowing the 2032 type button cell assembled in Step 2 in the mold for 30 minutes under a reaction atmosphere, and after standing for 12 hours, performing the charge and discharge test, the test conditions are standing for 12 hours-constant current discharge (capacity mAh / voltage cut-off V)-constant current charging (capacity mAh / voltage cut-off V)-cycle-stop.

[0034] Example 1

[0035] Step 1: rolling the electrode sheet. Mix Super P: PTFE in a mass ratio of 90:10 in a small beaker, drop in an appropriate amount of anhydrous ethanol, stir uniformly, and roll into a thin film, and then vacuum dry at 70 ℃ for 12 h. Use a punch to make a circular electrode sheet (about 1-2 mg) with a diameter of 10 mm, and then press it together with a stainless steel mesh using a tablet press to obtain a positive electrode sheet.

[0036] Step 2: preparing the required electrolyte in a glove box with an argon atmosphere and a water oxygen value less than 0.1 ppm: the solvent of the electrolyte is DMSO, the solute is LiClO4, 500 rpm stirring for 12 h, and according to the total mass of the electrolyte, the electrolyte containing 0.1 mol / L BDTMD is prepared in batches;

[0037] Step 3: Assemble the 2032 button cell in the order of negative shell, spring, gasket, lithium negative electrode (d = 16 mm), GF / A glass fiber (d = 16 mm), electrolyte (70 μL), positive electrode (d = 10 mm), and positive shell with hole.

[0038] Step 4: After the 2032 button cell assembled in Step 3 is purged with CO2 for 30 min in a mold, discharge test is performed after 12 h of standing. The discharge product is tested for its phase composition by XRD, and the test results are shown in Figure 1 As shown in Figure 1 , the CV curve measured in the electrolyte atmosphere containing BDTMD can observe the obvious oxidation peak of the substituent Br, indicating that the reduction of the charging overpotential in the metal-air battery benefits from this electrochemical oxidation process.

[0039] Example 2

[0040] Step 1: Prepare the positive electrode as in Example 1;

[0041] Step 2: Prepare the required electrolyte in a glove box under argon atmosphere and with water and oxygen values both less than 0.1 ppm: the solvent of the electrolyte is DMSO, and the solute is LiClO4, 500 rpm stirring for 12 h, and according to the total mass of the electrolyte, the electrolyte containing 0.5 mol / L BDTMD is prepared;

[0042] Step 3: Prepare and assemble the button cell as in Example 1;

[0043] Step 4: After the 2032 button cell assembled in Step 3 is purged with CO2 for 30 min in a mold, discharge test is performed after 12 h of standing. The discharge product is tested for its phase composition by XRD, and the test results are shown in Figure 2 As shown in Figure 2 , the discharge product of the lithium-carbon dioxide battery can be determined as Li2CO3.

[0044] Example 3

[0045] Step 1: Prepare the positive electrode as in Example 1;

[0046] Step 2: Prepare the electrolyte as in Example 2;

[0047] Step 3: Prepare and assemble the button cell as in Example 1;

[0048] Step 4: After the 2032 button cell assembled in Step 3 is purged with O2 for 30 min in a mold, discharge test is performed after 12 h of standing. The discharge product is tested for its phase composition by XRD, and the test results are shown in Figure 3 As shown in Figure 3As shown, the discharge products of lithium-oxygen batteries can be determined as Li2O2 and a small amount of Li2CO3.

[0049] Example 4

[0050] Step 1: The positive electrode sheet was prepared as in Example 1; the negative electrode sheet was prepared as follows: LiFePO4: Super P: PTFE were mixed in a mass ratio of 70:20:10 in a small beaker, and a proper amount of anhydrous ethanol was added. After stirring, a thin film was rolled, and vacuum drying was performed at 70°C for 12 h. The film was punched into a circular electrode sheet with a diameter of 12 mm, and the negative electrode sheet was obtained by pressing the circular electrode sheet and a stainless steel mesh together using a tablet press.

[0051] Step 2: The electrolyte was prepared as in Example 2;

[0052] Step 3: The various components prepared in advance were assembled into a 2032 button cell in the order of negative electrode shell, spring, gasket, negative electrode sheet (d = 12 mm), GF / A glass fiber (d = 16 mm), electrolyte (70 μL), positive electrode sheet (d = 10 mm), and positive electrode shell with holes.

[0053] Step 4: The 2032 button cell assembled in Step 3 was subjected to O2 purging for 30 min in a mold, and then was left to stand for 12 h before being subjected to charge-discharge tests. Test conditions: constant current 0.1 mA·cm -2 discharge (constant volume for 3 h) - standing for 10 min - constant current 0.1 mA·cm -2 charge (constant volume for 3 h) - standing for 10 min - cycling for 50 times - stop Figure 4 As shown in Figure 4 , the introduction of BDTMD into the electrolyte can effectively reduce the overpotential during charging, and the corresponding reasons are explained in Figure 1 .

[0054] Example 5

[0055] Step 1: The two electrodes (positive electrode sheet and negative electrode sheet) of the battery were both directly purchased metal lithium sheets with a diameter of 16 mm.

[0056] Step 2: The electrolyte was prepared as in Example 2;

[0057] Step 3: The various components prepared in advance were assembled into a 2032 button cell in the order of negative electrode shell, spring, gasket, negative electrode sheet, GF / A glass fiber (d = 16 mm), electrolyte (70 μL), positive electrode sheet, and positive electrode shell with holes.

[0058] Step 4: The 2032 button cell assembled in Step 3 was left to stand for 12 h before being subjected to charge-discharge tests. Test conditions: constant current 0.1 and 0.2 mA·cm -2Discharge (5h at constant volume) - stand for 10min - constant current of 0.1 and 0.2 mA·cm -2 Charge (5 hours at constant capacity) - let stand for 10 minutes - cycle 50 times - stop. Test results are shown below. Figure 5 .

[0059] like Figure 5 As shown in Example 5, the stability of the lithium metal electrode was examined, and the battery... Figure 5 a neutralization Figure 5 b was prepared at concentrations of 0.1 and 0.2 mA / cm², respectively. -2 The current was tested, and it was able to maintain stable cycling for up to 1600 hours and 800 hours respectively.

Claims

1. The use of an additive in a lithium metal-air battery electrolyte, characterized in that, The additive is 5-((4-bromo-2,6-difluorophenyl)difluoromethoxy)-1,2,3-trifluorobenzene.

2. The use as described in claim 1, characterized in that, Lithium metal air batteries are either lithium-oxygen batteries or lithium-carbon dioxide batteries.

3. The use as described in claim 1, characterized in that, The electrolyte is a 0.5M lithium salt solution.

4. The use as described in claim 3, characterized in that, The lithium salt in the lithium salt solution is one or a mixture of lithium perchlorate, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide.

5. The use as described in claim 3, characterized in that, The lithium salt in the lithium salt solution is lithium perchlorate.

6. The use as described in claim 1, characterized in that, The additive content in the electrolyte is 0.01-1.5 mol / L.

7. The use as described in claim 1, characterized in that, The additive concentration in the electrolyte is 0.15 mol / L.

8. The use as described in claim 1, characterized in that, The electrolyte solvent is one or a mixture of DME, DMSO, TEGDME.

9. The use as described in claim 1, characterized in that, The solvent for the electrolyte is DMSO.

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