Preparation method and application of solvent-synergistic wide-temperature-range sodium metal battery electrolyte

Abstract

The invention belongs to the technical field of new energy electrochemistry, and relates to a preparation method and application of a solvent-synergetic wide-temperature-range sodium metal battery electrolyte, sodium salt, a first solvent, a second solvent and a third solvent are uniformly mixed according to the volume ratio of X: Y: Z in an environment with the water oxygen content smaller than 0.1 ppm, and the colorless and clear wide-temperature-range sodium metal battery electrolyte is obtained; wherein, 5% lt; xlt; 45%, 5% lt; ylt; 65%, Z = 100%-X-Y; intermolecular repulsive force exists between the first solvent and the second solvent, and intermolecular attractive force exists between the first solvent and the third solvent; according to the invention, a solvent with an intermolecular synergistic effect is introduced into the wide-temperature-range sodium metal battery electrolyte, so that the participation of anions is promoted, a solvation structure with a self-strengthening effect on temperature change is realized, the transmission kinetics and desolvation process of sodium ions are enhanced, the side reaction of an interface is inhibited, and an interface film rich in inorganic compounds is generated; and the working temperature window of the electrolyte is expanded, so that the sodium metal battery can stably circulate at-40 DEG C under the multiplying power condition of 1C.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy electrochemistry, and relates to a preparation method and application of an electrolyte for a wide-temperature sodium metal battery with solvent synergy. Background Art

[0002] In the past two decades, the popularization of mobile portable electronic devices and electric vehicles (EVs) has promoted the rapid development of lithium-ion batteries (LIBs). However, the relatively high desolvation barrier and low ionic conductivity of LIBs result in a sharp decline in their performance below -20 degrees Celsius, which may affect the popularization of EVs in high-altitude and high-latitude regions. Sodium metal anodes have received increasing attention due to their high theoretical capacity and low electrochemical potential. In addition, the abundant sodium resources also make it a promising candidate for the next-generation energy storage system. Compared with Li ions, Na ions have a smaller Stokes radius, which results in higher ionic conductivity and lower desolvation barriers. Moreover, the deposition-stripping cycle of metal anodes is more suitable for low-temperature applications than intercalation-extraction, which endows sodium metal batteries with greater application potential in the low-temperature field.

[0003] In sodium metal batteries, the electrochemical performance at low temperatures is mainly affected by slow reaction kinetics, specifically because the mass transfer process of Na ions is hindered during charge and discharge, and the charge transfer rate decreases. Among them, the mass transfer process is mainly affected by the transport rate of Na ions. The increase and even solidification of the electrolyte viscosity at low temperatures are the main factors hindering the mass transfer process. The charge transfer rate is related to the desolvation step of sodium ions and the process of passing through the SEI, and the former is the main factor affecting the charge transfer rate. In this regard, researchers have proposed strategies such as locally concentrated electrolytes, fluorinated electrolytes, and weakly solvating electrolytes (WSEs) to optimize the low-temperature performance of rechargeable metal batteries. Among them, WSEs are widely used in low-temperature lithium / sodium metal batteries due to their advantages such as simple formulation and high degree of anion participation.

[0004] However, the single formulation of WSEs promotes the formation of a highly locally ordered structure in the electrolyte, which to a certain extent hinders the Na ion transport kinetics and reduces the ionic conductivity. Although adding a solvent with strong coordination with cations to the weakly solvating electrolyte can balance the desolvation barrier and ionic conductivity to a certain extent, the dependence relationship between the solvation structure and temperature is ignored. As is well known, the solvation structure of an electrolyte is determined by the combined action of ion-solvent, ion-ion, and solvent-solvent interactions. When the temperature changes, the solvation ability of the solvent also changes, which will inevitably affect the solvation structure of the electrolyte.

[0005] Therefore, on the basis of adjusting ion-solvent interactions, the regulation of solvent-solvent or ion-ion interactions should be increased to eliminate the influence of temperature changes on the solvation structure. SUMMARY OF THE INVENTION

[0006] The technical solution adopted by the present invention to solve the technical problem is: a preparation method of an electrolyte for a wide-temperature sodium metal battery with solvent synergy, comprising the following steps:

[0007] Mix sodium salt, a first solvent, a second solvent, and a third solvent in a volume ratio of X:Y:Z evenly in an environment with a water and oxygen content of less than 0.1 ppm to obtain a colorless and clear electrolyte for a wide-temperature sodium metal battery; there is an intermolecular repulsive force between the first solvent and the second solvent, and there is an intermolecular attractive force between the first solvent and the third solvent;

[0008] Among them, 5% < X < 45%, 5% < Y < 65%, Z = 100% - X - Y;

[0009] The sodium salt includes: one or more of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide;

[0010] The first solvent includes: cyclopentyl methyl ether, 2-methyltetrahydrofuran;

[0011] The second solvent includes: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether;

[0012] The third solvent includes: tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0013] Preferably, the concentration of the sodium salt is 0.1 to 1.5 mol / L.

[0014] The present invention also discloses a wide-temperature sodium metal battery with solvent synergy. This wide-temperature sodium metal battery uses the above-mentioned electrolyte for a wide-temperature sodium metal battery. The wide-temperature sodium metal battery further includes a positive electrode material, a separator, and a negative electrode material; the temperature range of the wide-temperature sodium metal battery is: -40°C to 45°C.

[0015] Preferably, the charge-discharge window of the wide-temperature sodium metal battery is 2 to 3.8 V.

[0016] Preferably, the conductive agent of the wide-temperature sodium metal battery includes: one or more of acetylene black, conductive carbon black SuperP, and carbon nanotubes.

[0017] Preferably, the positive electrode plate of the wide-temperature sodium metal battery is made by mixing a polyanion-based positive electrode material, a binder, and conductive carbon, adding a solvent to make a slurry, coating it on a current collector, and then drying, rolling, and slicing.

[0018] Preferably, the negative electrode sheet of the wide-temperature sodium metal battery is made of sodium metal and a current collector.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The present invention has the advantages of being free of fluorinated solvents and being environmentally friendly. At the same time, no new molecular design is required, and it can be adapted to existing industrial solvents, having a wide application prospect.

[0021] 2. Through the interaction between solvent molecules, the present invention designs an electrolyte with a temperature self-strengthening effect solvation structure, derives an interfacial film rich in inorganic compounds, and guides the uniform deposition of sodium metal, enabling the sodium metal battery to stably cycle at a rate of 1C at -40°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a digital picture after mixing the first solvent and the second solvent, and the first solvent and the third solvent of the present invention, and a schematic diagram of the binding energy between solvent molecules;

[0023] Figure 2 It is an in-situ variable-temperature Raman spectrogram of the electrolyte solvation structure of the present invention;

[0024] Figure 3 It is a long-term cycling test diagram of the sodium metal symmetric battery assembled with the electrolyte of the present invention at -40°C at a current density of 1 mA cm -2 , 1 mAh cm -2 ;

[0025] Figure 4 It is a cycling performance diagram of the Na||NVP (Na3V2(PO4)3) battery assembled with the electrolyte of the present invention at 45°C;

[0026] Figure 5 It is a cycling performance diagram of the Na||NVP battery assembled with the electrolyte of the present invention at -40°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following will clearly and completely describe the relevant technologies in the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Refer to Figures 1 to 5 As shown, the preparation method of the electrolyte of the solvent-synergistic wide-temperature sodium metal battery in this specific embodiment includes the following steps:

[0029] Step S0: The sodium salt and the solvent are purchased from Duoduo Reagent Network Co., Ltd.;

[0030] Step S1: Place the purchased solvent in a glove box with a water and oxygen content less than 0.1 ppm, and add molecular sieves to it to remove trace water;

[0031] Step S2: In a glove box with a water and oxygen content less than 0.1 ppm, mix the sodium salt, the first solvent, the second solvent, and the third solvent obtained in Step S1 in proportion to obtain an electrolyte for a wide-temperature sodium metal battery;

[0032] Step S3: The sodium salt is composed of one or several of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0033] Step S4: The first solvent is composed of one of cyclopentyl methyl ether and 2-methyltetrahydrofuran.

[0034] Step S5: The second solvent is composed of one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0035] Step S6: The third solvent is composed of one of tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0036] Step S7: The concentration of the sodium salt is 0.1 - 1.5 mol / L.

[0037] Step S8: The volume ratio of the first solvent is X, 5% < X < 45%; the volume ratio of the second solvent is Y, 5% < Y < 65%; the volume ratio of the third solvent is Z, Z = 100% - X - Y.

[0038] Application of an electrolyte for a wide-temperature sodium metal battery with solvent synergy in a sodium metal battery. The specific operation steps are as follows: Fill the prepared electrolyte into the battery, with the positive electrode being NVP and the negative electrode being sodium metal, to obtain a wide-temperature sodium metal battery.

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0040] Example 1

[0041] A preparation method of an electrolyte for a wide-temperature sodium metal battery with solvent synergy, comprising the following steps:

[0042] The purchased solvent was placed in an argon - atmosphere glove box with a water content of < 0.01 ppm and an oxygen content of < 0.01 ppm, and molecular sieves were added thereto, and it was left standing for 48 h to remove trace water therein; sodium hexafluorophosphate with a concentration of 0.5 mol / L was added to a mixed solvent with a volume ratio of cyclopentyl methyl ether:ethylene glycol dimethyl ether:tetrahydrofuran of 1:1:1, a magnetic stir bar was added and it was placed on a magnetic stirrer for 12 h; after complete dissolution, a clear and transparent liquid was obtained and left standing for use as an electrolyte.

[0043] As Figure 2 shown, the Raman spectrum at 735 - 755 cm -1 corresponds to the stretching vibration peak of hexafluorophosphate ion (PF6 - ), and can be used to analyze the solvation structure in the electrolyte. As the temperature decreases, the peak at 742 cm -1 in the prepared electrolyte shows a significant blue - shift. This indicates that as the temperature decreases, the interaction between Na + and PF6 - ions in the electrolyte increases. As is well known, the strong interaction between cations and anions under low - temperature conditions is beneficial to the rapid desolvation of sodium ions, thereby leading to good electrochemical performance. Therefore, this electrolyte has a "temperature - self - enhanced" solvation structure.

[0044] The wide - temperature - range electrolyte prepared in this example was applied to a sodium - metal symmetric battery, and the specific operation steps are as follows:

[0045] The prepared electrolyte was injected into a CR 2032 - type button battery, the electrode was a sodium - metal negative electrode, and the separator was a polypropylene separator, obtaining a sodium - metal symmetric battery filled with the wide - temperature - range electrolyte.

[0046] As Figure 3 can be seen, the wide - temperature - range sodium - metal symmetric battery prepared in this example was stably cycled for 800 h at a very low temperature of - 40 °C at a current density of 1 mA cm -2 , 1 mAh cm -2 without short - circuit phenomenon; thus it is proved that the wide - temperature - range sodium - metal symmetric battery prepared by the present invention has long cycle life during use and exhibits excellent electrochemical performance.

[0047] Example 2

[0048] A preparation method of a solvent - synergistic wide - temperature - range sodium - metal battery electrolyte, comprising the following steps:

[0049] Place the purchased solvent in an argon - atmosphere glove box with water content < 0.01 ppm and oxygen content < 0.01 ppm, add molecular sieves to it, and let it stand for 48 h to remove trace water; add sodium hexafluorophosphate at a concentration of 1 mol / L to a mixed solvent with a volume ratio of 2 - methyltetrahydrofuran:triethylene glycol dimethyl ether:1,3 - dioxolane of 1:3:1, add a magnetic stir bar and place it on a magnetic stirrer for 12 h; after complete dissolution, a clear and transparent liquid is obtained and let it stand for use as the electrolyte.

[0050] The wide - temperature - range electrolyte prepared in this example is applied to a sodium - metal battery, and the specific operation steps are as follows:

[0051] Inject the prepared electrolyte into a CR 2032 coin - type battery. The negative electrode is a sodium - metal negative electrode, the positive electrode is NVP@C, and the separator is a polypropylene separator to obtain a sodium - metal battery equipped with the wide - temperature - range electrolyte. The positive - electrode sheet is prepared by mixing NVP, binder, and conductive carbon, adding NMP to make a slurry, coating it on a current collector, and then drying, rolling, and slicing.

[0052] Perform charge - discharge tests on the assembled battery at 45 °C. Activate the battery for the first two cycles at a rate of 0.1C, and then perform charge - discharge tests on the battery at a rate of 1C. The charge - discharge range is 2 - 3.8 V.

[0053] From Figure 4 it can be seen that after the wide - temperature - range sodium - metal battery prepared in this example is stably cycled 100 times at a current density of 1C at 45 °C, the discharge capacity is 110.35 mAh g -1 .

[0054] Example 3

[0055] A preparation method of a wide - temperature - range sodium - metal battery electrolyte synergized by solvents, comprising the following steps:

[0056] Place the purchased solvent in an argon - atmosphere glove box with water content < 0.01 ppm and oxygen content < 0.01 ppm, add molecular sieves to it, and let it stand for 48 h to remove trace water; add sodium bis(fluorosulfonyl)imide at a concentration of 1.2 mol / L to a mixed solvent with a volume ratio of 2 - methyltetrahydrofuran:tetraethylene glycol dimethyl ether:1,3 - dioxolane of 1:1:3, add a magnetic stir bar and place it on a magnetic stirrer for 12 h; after complete dissolution, a clear and transparent liquid is obtained and let it stand for use as the electrolyte.

[0057] The wide - temperature - range electrolyte prepared in this example is applied to a sodium - metal battery, and the specific operation steps are as follows:

[0058] Inject the prepared electrolyte into a CR 2032 coin cell, with the negative electrode being a sodium metal negative electrode, the positive electrode being NVP@C, and the separator being a polypropylene separator, to obtain a sodium metal battery equipped with an electrolyte with a wide temperature range. The positive electrode sheet is prepared by mixing NVP, a binder, and conductive carbon, adding NMP to make a slurry, coating it on a current collector, and then drying, rolling, and slicing.

[0059] Perform charge-discharge tests on the assembled battery at -40°C. Activate the battery for the first two cycles at a rate of 0.1C, and then perform charge-discharge tests on the battery at a rate of 1C. The charge-discharge range is 2 - 3.8V.

[0060] It can be seen from Figure 5 that after the sodium metal battery with a wide temperature range prepared in this example is stably cycled 200 times at a current density of 1C at -40°C, the discharge capacity is 80.86 mAh g -1 , showing excellent electrochemical performance in the wide temperature range (-40 - 45°C).

[0061] In summary, the present invention introduces a solvent with intermolecular synergistic effects into the electrolyte of a sodium metal battery with a wide temperature range, promotes a solvation structure in which anions participate and has a self-strengthening effect on temperature changes, enhances the sodium ion transport kinetics and desolvation process, inhibits interfacial side reactions and generates an interfacial film rich in inorganic compounds, expands the working temperature window of the electrolyte, and enables the sodium metal battery to be stably cycled at a rate of 1C at -40°C.

[0062] It should be emphasized that the above are only preferred embodiments of the present invention, and there is no limitation in any form to the present invention. Any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. Preparation method of electrolyte for sodium metal battery with wide temperature range synergized by solvent, characterized in that, Comprising the following steps: Mix sodium salt, a first solvent, a second solvent and a third solvent evenly at a volume ratio of X:Y:Z in an environment with water and oxygen content less than 0.1 ppm to obtain a colorless and clear wide-temperature sodium metal battery electrolyte; wherein, 5% < X < 45%, 5% < Y < 65%, Z = 100% - X - Y; The sodium salt includes: one or more of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide; The first solvent includes: cyclopentyl methyl ether, 2-methyltetrahydrofuran; The second solvent includes: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; The third solvent includes: tetrahydrofuran, 1,3-dioxolane and 1,4-dioxane.

2. The preparation method of the electrolyte for a wide-temperature-range sodium metal battery with solvent synergy according to claim 1, characterized in that, The concentration of the sodium salt is 0.1 - 1.5 mol / L.

3. A solvent-synergistic sodium metal battery with a wide temperature range, characterized in that, The wide-temperature sodium metal battery uses the electrolyte prepared by the preparation method of any one of claims 1 or 2. The wide-temperature sodium metal battery further includes a positive electrode material, a separator, and a negative electrode material; the temperature range of the wide-temperature sodium metal battery is: -40°C to 45°C.

4. The wide-temperature sodium metal battery with solvent synergy according to claim 3, characterized in that, The charge-discharge window of the wide-temperature sodium metal battery is 2 - 3.8 V.

5. A wide-temperature sodium metal battery with solvent synergy according to claim 3, characterized in that, The conductive agent of the wide-temperature sodium metal battery includes: one or more of acetylene black, conductive carbon black SuperP, and carbon nanotubes.

6. The wide-temperature sodium metal battery with solvent synergy according to claim 3, wherein The positive electrode plate of the wide-temperature sodium metal battery is made by mixing a polyanion-based positive electrode material, a binder, and conductive carbon, adding a solvent to make a slurry, coating it on a current collector, and then drying, rolling, and slicing.

7. A solvent-synergistic sodium metal battery with a wide temperature range according to claim 3, characterized in that, The negative electrode plate of the wide-temperature sodium metal battery is made of sodium metal and a current collector.

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