A wide temperature range deep eutectic electrolyte and its preparation method and application

Abstract

A wide temperature range deep eutectic electrolyte and its preparation method and application belong to the field of chemical power source technology. The scheme is as follows: the wide temperature range deep eutectic electrolyte is composed of ethylene carbonate, succinonitrile and alkali metal ion salt, wherein the mass ratio of succinonitrile to ethylene carbonate is 4:6 to 6:4, and the concentration of alkali metal ion salt is 2.5 to 4 mol / L. The preparation method is as follows: Ethylene carbonate and succinonitrile are melted separately, mixed evenly, and cooled to obtain a deep eutectic solvent; alkali metal ion salt is added to the deep eutectic solvent and stirred until completely dissolved to obtain a wide temperature range deep eutectic electrolyte. The wide temperature range deep eutectic electrolyte is used in alkali metal ion batteries. The present invention prepares a deep eutectic solvent with low viscosity, low freezing point, high boiling point and high electrochemical stability, and then composites a high-concentration alkali metal ion salt to obtain a deep eutectic electrolyte with a wide liquid range to meet the working requirements of wide temperature range alkali metal ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical power sources, and in particular relates to a wide temperature range deep eutectic electrolyte and a preparation method and application thereof. Background Art

[0002] The electrolyte is an important component of alkali metal ion batteries. Commercial electrolytes include carbonate solvents, alkali metal ion salts and additives. Cyclic carbonates such as ethylene carbonate have excellent alkali metal ion salt solubility (dielectric constant ε = 89.6) and thermal stability (boiling point over 240°C), but the high melting point (35-38°C) makes it appear as solid crystals at room temperature. When ethylene carbonate is mixed with alkali metal ion salts to form an electrolyte, the melting point of the electrolyte is lower than that of ethylene carbonate, but the viscosity is large and it is very easy to solidify under low temperature conditions (<-20°C), resulting in poor low temperature performance of the battery. Therefore, cyclic carbonates are often used in combination with linear carbonates with low freezing points and low viscosity; however, linear carbonate solvents generally have low boiling points (such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, the boiling points are 90.2°C, 126.8°C, and 107°C, respectively) and high saturated vapor pressure. For this reason, the stable operating temperature range of commercial electrolytes is usually -30°C to 55°C, and they cannot be used normally under extreme temperature conditions. In summary, it is of great significance to develop new electrolytes to meet wide temperature range application scenarios. Summary of the invention

[0003] In order to solve the problem that traditional alkali metal ion battery electrolytes cannot have both high and low temperature performances, the present invention provides a novel wide temperature range deep eutectic electrolyte and a preparation method and application thereof, wherein the solvent of the electrolyte consists of ethylene carbonate and succinonitrile, and the strong electrostatic interaction between the carbon-oxygen double bond in the ethylene carbonate molecule and the α-H in the succinonitrile molecule is utilized to destroy the ordered arrangement state of the two solvents themselves, thereby obtaining a deep eutectic solvent with low viscosity, low freezing point, high boiling point and high electrochemical stability, and then compounding a high-concentration alkali metal ion salt to obtain a deep eutectic electrolyte with a wide liquid range, thereby meeting the working requirements of wide temperature range alkali metal ion batteries.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A wide temperature range deep eutectic electrolyte consists of ethylene carbonate, succinonitrile and alkali metal ion salt, wherein the mass ratio of succinonitrile to ethylene carbonate is 4:6-6:4, and the concentration of the alkali metal ion salt is 2.5-4 mol / L.

[0006] Furthermore, the alkali metal ion salt includes lithium salt or sodium salt.

[0007] Furthermore, the lithium salt is one or more of LiPF6, LiAsF6, LiBF4, LiClO4, LiTFSI, LiODFB, LiPO4F2, LiBOB, and LiFSI.

[0008] Furthermore, the sodium salt is one or more of NaPF6, NaAsF6, NaBF4, NaClO4, NaTFSI, NaODFB, NaPO4F2, NaBOB, and NaFSI.

[0009] A method for preparing a wide temperature range deep eutectic electrolyte comprises the following steps:

[0010] Step 1: heating and melting ethylene carbonate and succinonitrile respectively, mixing them evenly according to the stoichiometric ratio, and cooling them to room temperature to obtain a deep eutectic solvent;

[0011] Step 2: Add alkali metal ion salt to the deep eutectic solvent and stir until completely dissolved to obtain a wide temperature range deep eutectic electrolyte.

[0012] An application of the wide temperature range deep eutectic electrolyte, wherein the wide temperature range deep eutectic electrolyte is applied in alkali metal ion batteries.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention utilizes the strong electrostatic interaction between the carbon-oxygen double bond in the ethylene carbonate molecule and the α-H in the succinonitrile molecule to destroy the ordered arrangement state of the two solvents themselves, thereby obtaining a deep eutectic solvent with low viscosity, low freezing point, high boiling point and high electrochemical stability. Compared with the traditional electrolyte solvent system, the introduction of low boiling point co-solvents is avoided, and the thermal stability of the electrolyte at high temperature is significantly improved, which can meet the application requirements of ultra-high temperature (>125°C); compared with pure ethylene carbonate or pure succinonitrile solvent (melting point 56-58°C), the freezing point of the deep eutectic solvent is significantly reduced (<-60°C), and the electrochemical performance of the battery in the low temperature range will be significantly improved. As a typical non-ionic plastic crystal material, the alkali metal ion salt of succinonitrile has strong solubility (dielectric constant ε=55), high thermal stability (boiling point exceeds 265°C), and the dicyano functional group (C≡N) makes it have excellent oxidation resistance (>5V). Therefore, the deep eutectic solvent has a higher electrochemical stability window than pure ethylene carbonate; in addition, the present invention adopts a high concentration of alkali metal ion salt and a deep eutectic solvent to prepare a deep eutectic electrolyte. The interaction between the alkali metal ion salt and the solvent can further reduce the freezing point of the deep eutectic electrolyte. The high concentration of alkali metal ion salt can also increase the solvation ratio of succinonitrile solvent molecules, reduce the proportion of free succinonitrile molecules, and improve the interface stability between the succinonitrile solvent and the graphite negative electrode or the lithium / sodium metal negative electrode. In addition, the solvation structure formed by the high concentration of alkali metal ion salt helps to construct an anion-derived solid electrolyte interface (SEI) film on the negative electrode surface, further improving the electrolyte / negative electrode interface stability. DETAILED DESCRIPTION

[0015] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] Example 1

[0017] A preparation method and application of a wide temperature range deep eutectic electrolyte, specifically comprising the following steps:

[0018] Step 1: Heat ethylene carbonate and succinonitrile at 50° C. and 70° C. to melt, respectively, mix them evenly in a mass ratio of 6:4, and cool to room temperature to obtain a deep eutectic solvent.

[0019] Step 2: Take 10 mL of deep eutectic solvent, add 0.025 mol of LiTFSI and 0.005 mol of LiODFB to prepare a wide temperature range deep eutectic electrolyte with a lithium ion concentration of 3 mol / L.

[0020] The wide temperature range deep eutectic electrolyte prepared above was subjected to cold storage test, conductivity test and electrochemical window test, and was applied to button lithium metal batteries with LiCoO2 as positive electrode, and electrochemical tests were performed on lithium metal batteries at different temperatures, and the electrochemical window was 3.0-4.4V. The test results show that the wide temperature range deep eutectic electrolyte can maintain liquid fluidity at -70℃, and the room temperature ionic conductivity is 3×10 -3 S / cm, the ionic conductivity at -50°C is 4×10 - 4 S / cm, the electrochemical oxidation potential at room temperature is 5.5V, the discharge capacity of the lithium metal battery at room temperature is 171mAh / g, and the capacity retention rate after 1000 cycles is 90%, the discharge capacity at -40°C is 100mAh / g, and the capacity retention rate after 1000 cycles is 85%, and the discharge capacity at 120°C is 168mAh / g, and the capacity retention rate after 500 cycles is 90%.

[0021] Example 2

[0022] A preparation method and application of a wide temperature range deep eutectic electrolyte, specifically comprising the following steps:

[0023] Step 1: Heat ethylene carbonate and succinonitrile at 50° C. and 70° C. to melt, respectively, mix them evenly in a mass ratio of 4.5:5.5, and cool to room temperature to obtain a deep eutectic solvent.

[0024] Step 2: Take 10 mL of deep eutectic solvent and add 0.04 mol of LiFSI to prepare a wide temperature range deep eutectic electrolyte with a lithium ion concentration of 4 mol / L.

[0025] The deep eutectic electrolyte prepared above was subjected to cold storage test, conductivity test and electrochemical window test, and applied to LiNi 0.8 Co 0.1 Mn 0.1 The deep eutectic electrolyte was used in a button-type lithium metal battery with O2 as the positive electrode, and the lithium metal battery was electrochemically tested at different temperatures, with an electrochemical window of 3.0-4.3 V. The test results showed that the deep eutectic electrolyte can maintain liquid fluidity at -80 °C, and the room temperature ionic conductivity is 4.5×10 -3 S / cm, the ionic conductivity at -60°C is 2.5×10 - 4 S / cm, the electrochemical oxidation potential at room temperature is 5.25V, the discharge capacity of the lithium metal battery at room temperature is 190mAh / g, and the capacity retention rate after 1000 cycles is 96%. The discharge capacity at -60°C is 100mAh / g, and the capacity retention rate after 1000 cycles is 92%. The discharge capacity at 120°C is 178mAh / g, and the capacity retention rate after 500 cycles is 88%.

[0026] Example 3

[0027] A preparation method and application of a wide temperature range deep eutectic electrolyte, specifically comprising the following steps:

[0028] Step 1: Heat ethylene carbonate and succinonitrile at 50° C. and 70° C. to melt, respectively, mix them evenly in a mass ratio of 4:6, and cool to room temperature to obtain a deep eutectic solvent.

[0029] Step 2: Take 10 mL of deep eutectic solvent and add 0.025 mol NaTFSI to prepare a wide temperature range deep eutectic electrolyte with a sodium ion concentration of 2.5 mol / L.

[0030] The deep eutectic electrolyte prepared above was subjected to cold storage test, conductivity test and electrochemical window test, and was applied to button sodium metal battery with Na3V2(PO4)3 as positive electrode, and electrochemical test was carried out on sodium metal battery at different temperatures, and the electrochemical window was 2.5-3.8V. The test results show that the deep eutectic electrolyte can maintain liquid fluidity at -60℃, and the room temperature ionic conductivity is 6×10 -3 S / cm, the ionic conductivity at -40°C is 3×10 -4 S / cm, the electrochemical oxidation potential at room temperature is 5.45V, the discharge capacity of the sodium metal battery at room temperature is 110mAh / g, and the capacity retention rate after 1000 cycles is 95%. The discharge capacity at -50°C is 80mAh / g, and the capacity retention rate after 1000 cycles is 93%. The discharge capacity at 120°C is 108mAh / g, and the capacity retention rate after 500 cycles is 90%.

[0031] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A wide temperature range deep eutectic electrolyte, characterized in that: The wide temperature range deep eutectic electrolyte consists of ethylene carbonate, succinonitrile and alkali metal ion salt, wherein the mass ratio of succinonitrile to ethylene carbonate is 4:6-6:4, and the concentration of the alkali metal ion salt is 2.5-4 mol / L.

2. The wide temperature range deep eutectic electrolyte according to claim 1, characterized in that: The alkali metal ion salt includes a lithium salt or a sodium salt.

3. The wide temperature range deep eutectic electrolyte according to claim 2, characterized in that: The lithium salt is one or more of LiPF6, LiAsF6, LiBF4, LiClO4, LiTFSI, LiODFB, LiPO4F2, LiBOB, and LiFSI.

4. The wide temperature range deep eutectic electrolyte according to claim 2, characterized in that: The sodium salt is one or more of NaPF6, NaAsF6, NaBF4, NaClO4, NaTFSI, NaODFB, NaPO4F2, NaBOB, and NaFSI.

5. A method for preparing a wide temperature range deep eutectic electrolyte according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: heating and melting ethylene carbonate and succinonitrile respectively, mixing them evenly according to the stoichiometric ratio, and cooling them to room temperature to obtain a deep eutectic solvent; Step 2: Add alkali metal ion salt to the deep eutectic solvent and stir until completely dissolved to obtain a wide temperature range deep eutectic electrolyte.

6. An application of the wide temperature range deep eutectic electrolyte according to any one of claims 1 to 4, characterized in that: The wide temperature range deep eutectic electrolyte is applied to alkali metal ion batteries.