A high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries, and its preparation method and application

Abstract

The present invention discloses a high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries, and its preparation method and application. The high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries of the present invention is an electrolyte obtained by mixing a lithium salt, water, and a sulfone organic solvent. Its preparation method comprises the following steps: (1) mixing the sulfone organic solvent with the water in an inert atmosphere to obtain a water-sulfone mixed solvent; (2) mixing the lithium salt with the water-sulfone mixed solvent in the inert atmosphere to obtain a high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries. The preparation process of the aqueous electrolyte of the present invention is simple, the raw materials are easily available, and it is safe and pollution-free, suitable for large-scale batch production; it can effectively expand the electrochemical stability window of the electrolyte, and at the same time, due to the non-flammable characteristics of the sulfone electrolyte, the safety of the lithium-ion battery is significantly improved.

Description

Technical Field

[0001] The present invention relates to a high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries and a preparation method and application thereof, belonging to the technical field of lithium secondary batteries. Background Art

[0002] With the rapid development of the economy and society, people's demand for lithium-ion batteries with efficient and reversible energy storage is increasing. However, most commercial lithium batteries use organic liquid electrolytes, which have problems such as leakage, volatilization, oxidative decomposition and thermal runaway during use. As one of the most popular choices for the new generation of power sources, aqueous rechargeable lithium-ion batteries have solved the following problems of traditional lithium-ion batteries: (1) The ionic conductivity of aqueous electrolytes is about two orders of magnitude higher than that of organic electrolytes. Therefore, even with larger electrode materials, higher energy density and cycle efficiency can be achieved. (2) It fundamentally solves the environmental and safety problems of organic electrolytes such as flammability, leakage, volatility and thermal runaway. (3) The assembly environment of aqueous batteries does not require strict humidity control like organic electrolytes. At the same time, the price of electrolyte solvents is low, which effectively reduces costs. It is a hot topic in the current research field of new battery systems and key materials. However, the inherent narrow electrochemical stability window of water itself (1.23V) limits the operating voltage and energy density of aqueous batteries. Although the precipitation of hydrogen at the negative electrode can be effectively suppressed by adjusting the pH value, it will also affect the positive electrode potential. In addition, since the decomposition products of traditional aqueous battery electrolytes are H2 and O2, they cannot be deposited on the electrode surface in solid form.

[0003] In recent years, some pioneering work has provided new ideas for the design and research of highly concentrated salt-based electrolyte materials by reducing the activity of water and constructing a stable SEI film on the electrode surface, which can effectively increase the electrochemical stability window of aqueous electrolytes to 3-4V. The most representative of these is the "water-in-salt" electrolyte published by Suo et al. in 2015. In this high-concentration salt electrolyte system (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissolved in water with a mass molar concentration of >20m), the main component of the reaction product of the electrolyte on the negative electrode surface is the anion TFSI in the lithium salt. - The reduction-formed SEI film, whose primary component is LiF, allows LiTFSI, which has ultra-high solubility in water, to kinetically extend the electrochemical stability window of water from 1.23V to 3.0V. This result represents a breakthrough in the critical voltage limit of aqueous lithium-ion battery research. Furthermore, since the thermodynamic freezing point of water is 0°C, the addition of solutes or new solvents to disrupt the hydrogen bonds between water molecules and form new intermolecular hydrogen bonds with water molecules can thermodynamically suppress the hydrogen evolution reaction in water, a crucial measure for improving the electrolyte's electrochemical window.

[0004] In response to the above problems, it is indeed necessary to find and synthesize an aqueous electrolyte with both excellent electrochemical properties and safety performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries, as well as a preparation method and application thereof.

[0006] The present invention discloses a high-voltage water-sulfone hybrid electrolyte for aqueous lithium-ion batteries, comprising a mixture of lithium salt, water, and a sulfone organic solvent. The present invention combines water and the sulfone electrolyte, and upon use, the decomposition of the lithium salt and organic solvent components kinetically forms a SEI film capable of protecting the electrodes. Simultaneously, the sulfone electrolyte and water form new intermolecular hydrogen bonds, thermodynamically suppressing the hydrogen evolution reaction. The synergistic effect of these two factors effectively expands the electrochemical stability window of the electrolyte. Furthermore, the non-flammable nature of the sulfone electrolyte significantly improves the safety of the lithium-ion battery.

[0007] The present invention is in aqueous lithium-ion batteries, because the inherent narrow electrochemical stability window (1.23V) of water itself greatly limits its operating voltage and energy density, and sulfone organic solvents have the advantages of high oxidation potential, wide electrochemical window and flame retardancy, and introducing them into aqueous electrolytes can greatly broaden the electrochemical window of the electrolyte, so that the output voltage and stability of the battery are greatly improved. At the same time, as a hydrogen bond acceptor, a stable intermolecular hydrogen bond can be formed between the sulfone organic solvent and the water molecule of the hydrogen bond donor, effectively reducing the freezing point of the electrolyte, and being able to effectively suppress the hydrogen evolution reaction thermodynamically, playing a key role in electrolyte stability. The preparation process of the quasi-aqueous electrolyte of the present invention is simple, and conventional equipment is used, raw materials are easily available, and safe and pollution-free, and suitable for large-scale batch production.

[0008] The present invention provides a high-voltage water-sulfone mixed electrolyte for an aqueous lithium-ion battery. The electrolyte is prepared by mixing lithium salt, water and a sulfone organic solvent.

[0009] In the above-mentioned electrolyte, the mass molar concentration of the lithium salt in the electrolyte may be 0.01 to 15 M (i.e., 0.01 to 15 mol / kg), specifically 7 M, 11 M, 14 M, 7 to 11 M, 11 to 14 M, 7 to 11 M or 5 to 15 M;

[0010] The molar mass ratio of the water to the sulfone organic solvent may be 1:1 to 10, specifically 1:2, 1:4, 1:6.9 or 1:2 to 6.9.

[0011] In the above electrolyte, the lithium salt is selected from at least one of LiN(SO2CF3)2, LiCF3SO3 and LiC(SO2CF3)3.

[0012] In the present invention, the sulfone organic solvent is an organic compound containing a sulfonyl group.

[0013] In the above electrolyte, the sulfone organic solvent is selected from at least one of dimethyl sulfone, diethyl sulfone, phenethyl sulfone, phenylpropyl sulfone, dapsone, diphenyl sulfone and sulfolane.

[0014] The method for preparing the electrolyte provided by the present invention comprises the following steps: (1) mixing the sulfone organic solvent with the water in an inert atmosphere to obtain a water-sulfone mixed solvent;

[0015] (2) In the inert atmosphere, the lithium salt is mixed with the water-sulfone mixed solvent to obtain a high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries.

[0016] In the above preparation method, the inert atmosphere is nitrogen or argon with a purity of not less than 99% (or containing O2 less than 1 ppm).

[0017] The aqueous lithium ion battery of the present invention is based on a high-voltage water-sulfone mixed electrolyte for use in preparing aqueous lithium ion batteries.

[0018] In the above application, the positive electrode active material of the aqueous lithium ion battery is LiCoO2, LiMn2O4, LiFePO4 or LiNi 0.5 Mn 1.5 O4, the negative electrode active material is Li4Ti5O 12 .

[0019] In the above application, the ambient temperature for testing the aqueous lithium-ion battery based on the high-voltage water-sulfone mixed electrolyte and the aqueous lithium-ion battery can be -50°C to 30°C.

[0020] The present invention further provides an aqueous lithium-ion battery, which comprises a positive electrode, a negative electrode and an electrolyte;

[0021] The active material of the positive electrode is LiCoO2, LiMn2O4, LiFePO4 or LiNi 0.5 Mn 1.5 O4, the active material of the negative electrode is Li4Ti5O 12 ;

[0022] The electrolyte is the high-voltage water-sulfone mixed electrolyte for the aqueous lithium-ion battery.

[0023] In the above aqueous lithium-ion battery, the ambient temperature for testing the full cell of the aqueous lithium-ion battery may be -50°C to 30°C.

[0024] In a specific example, the assembly of the full cell of the aqueous lithium-ion battery is as follows: in a glove box filled with argon (O2 <1ppm), the electrode plate, aqueous electrolyte and gasket, and shrapnel are placed in the 2025-type button battery blank in the order of negative electrode shell-shrapnel-gasket-negative electrode plate-electrolyte-diaphragm-positive electrode plate-positive electrode shell to assemble into a full battery, and then the two battery shells are compacted and fastened with a sheet press to obtain a button battery for testing. The thickness of the gasket is 1mm, and the model of the diaphragm is glass fiber GF / F.

[0025] The present invention has the following advantages:

[0026] (1) The electrolyte of the present invention destroys the hydrogen bonds in water molecules by adding a sulfone organic solvent, which forms new hydrogen bonds with water, thereby lowering the freezing point of the aqueous electrolyte, thermodynamically destroying the interaction between water molecules, and inhibiting the occurrence of the hydrogen evolution reaction.

[0027] (2) The electrolyte of the present invention can kinetically form a dense SEI film on the surface of the electrode material, effectively protecting the positive and negative electrodes from corrosion. At the same time, due to the high oxidation potential of sulfone organic solvents, the electrochemical window of the aqueous system is further broadened, providing more selectivity for commonly used commercial electrode materials.

[0028] (3) This electrolyte is non-flammable, ensuring sufficient safety performance of the battery.

[0029] (4) The preparation process of the mixed liquid electrolyte of the present invention is simple, conventional equipment is used, raw materials are readily available, and it is safe and pollution-free, making it suitable for large-scale batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the electrochemical window diagram of the mixed liquid electrolyte prepared in Example 1.

[0031] Figure 2 This is a TEM image of the negative electrode surface after full battery cycling assembled with the mixed liquid electrolyte prepared in Example 1. Figure 3 This is the cyclic voltammetry (CV) diagram of the full battery assembled with the mixed liquid electrolyte prepared in Example 2.

[0032] Figure 4 This is the cyclic voltammetry (CV) diagram of the full battery assembled with the mixed liquid electrolyte prepared in Example 3.

[0033] Figure 5 This is the cycle capacity-efficiency diagram of the full battery assembled with the mixed liquid electrolyte prepared in Example 4 at room temperature.

[0034] Figure 6 This is the cycle capacity-efficiency diagram of the full battery assembled with the mixed liquid electrolyte prepared in Example 5 at low temperature (0°C). DETAILED DESCRIPTION

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0036] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0037] In the following embodiment, the assembly of the aqueous lithium-ion full battery is as follows: in a glove box filled with argon (O2 <1ppm), the electrode plate, aqueous electrolyte and gasket, and spring are placed in a 2025-type button battery blank in the order of negative electrode shell-spring plate-gasket-negative electrode plate-electrolyte-diaphragm-positive electrode plate-positive electrode shell to assemble into a full battery. Then, the two battery shells are compacted and fastened with a sheet press to obtain a button battery for the test. The thickness of the gasket is 1mm, and the model of the diaphragm is glass fiber GF / F.

[0038] After the assembled full battery was allowed to stand at 30°C for 24 hours, the electrochemical performance test was carried out: the AC impedance test was carried out on an electrochemical workstation (CHI660D, Shanghai Chenhua Instrument Co., Ltd.), the test frequency range was 10 Hz to 105 Hz, the AC amplitude was 5 mV, and the test temperature was 30°C; the electrochemical window and cyclic voltammetry tests were carried out on an electrochemical workstation (CHI660D, Shanghai Chenhua Instrument Co., Ltd.), with scan rates of 5 mV / s and 10 mV / s respectively; the room temperature and low temperature battery charge and discharge tests were carried out using a LAND battery testing system (Model CT2001A, Wuhan Jinnuo Electronics Co., Ltd.), and the test rate was 3C.

[0039] Example 1

[0040] (1) In a glove box filled with argon gas of purity greater than or equal to 99%, 3.15 g of sulfolane and 1.05 g of ultrapure water (i.e., the molar ratio of sulfolane to water is 1:2) were dissolved in each other and stirred for 0.5 h to obtain a water-sulfone mixed solvent;

[0041] (2) 16.8 g of LiN(SO2CF3)2 was dissolved in the mixed solvent of step (1) and stirred for 12 h to obtain 14 ml of a water-sulfone-based mixed electrolyte for lithium-ion batteries.

[0042] The mixed liquid electrolyte prepared in this example was subjected to electrochemical window test using a CHI660D electrochemical workstation. A three-electrode system was used, with Pt (positive electrode side) and Al (negative electrode side) as the working electrodes, activated carbon (AC) as the counter electrode, and Ag / AgCl as the reference electrode. The scan rate was 10 mV / s. Figure 1 It can be seen from the figure that the window of the water-sulfone based mixed electrolyte for the lithium ion battery of the present invention is approximately 0.3V to 5.7V.

[0043] The mixed liquid electrolyte prepared in this embodiment is mixed with LiNi 0.5 Mn 1.5 O4-Li4Ti5O 12 The positive electrode and negative electrode active materials (i.e., the same below) were assembled into a full battery and the electrochemical performance test was carried out using the Land electrochemical test system. The ambient temperature was tested at room temperature (25°C). In the battery cycle performance and rate performance test, the charge and discharge current size was based on the Li4Ti5O 12 The mass of the active material of the negative electrode and its theoretical capacity are 175 mAh g -1 Calculate and set. 0.5 Mn 1.5 O4-Li4Ti5O 12 The charge and discharge voltage range of the full battery is 2-3.5V. Through testing, it can be known that the full battery prepared by the lithium-ion battery of the present invention using the mixed electrolyte based on water-sulfone has a first-week charge and discharge capacity of about 144mAh / g at a rate of 3C, and the efficiency is stable at about 96%, with good cycle stability. Figure 2 TEM tests have shown that the SEI film generated by the water-sulfone mixed electrolyte used in the lithium-ion battery of the present invention has the characteristics of being thin and relatively dense, which kinetically expands the electrochemical window of the electrolyte and protects the electrode, thereby giving the battery better cycle stability.

[0044] Example 2

[0045] (1) In a glove box filled with argon gas of purity greater than or equal to 99%, 3.15 g of phenylethyl sulfone and 1.05 g (i.e., the molar ratio of phenylethyl sulfone to water is 1:4) were dissolved in each other and stirred for 0.5 h to obtain a water-sulfone mixed solvent;

[0046] (2) 16.8 g of LiN(SO2CF3)2 was dissolved in the mixed solvent of step (1) and stirred for 12 h to obtain 14 ml of a water-sulfone-based mixed electrolyte for lithium-ion batteries.

[0047] The mixed liquid electrolyte prepared in this example was mixed with LiMn2O4-Li4Ti5O 12The battery was assembled into a full battery and the electrochemical performance test was carried out in the same manner as in Example 1 of the present invention. The battery charge and discharge performance test conditions were: Land electrochemical test system, the ambient temperature was tested at room temperature (25°C), and in the battery cycle performance and rate performance tests, the charge and discharge current size was based on the Li4Ti5O 12 The mass of the active material of the negative electrode and its theoretical capacity are 175 mAh g -1 Calculate and set. LiMn2O4-Li4Ti5O 12 The charge and discharge voltage range of the full battery is 1-2.8V. After testing, it can be seen that the charge and discharge capacity of the full battery in the first week at a 2C rate is about 148mAh / g, and the efficiency is stable at about 98%, which has good stability. Figure 3 It can be seen from the cyclic voltammetry curve that the full cell LiMn2O4-Li4Ti5O prepared by the lithium ion battery of the present invention using the mixed electrolyte based on water-sulfone 12 It can undergo reversible lithium insertion and extraction at a scan rate of 5mV / s, showing good structural stability.

[0048] Example 3

[0049] (1) In a glove box filled with argon gas of purity greater than or equal to 99%, 1.2 g of dapsone and 0.6 g of ultrapure water (i.e., the molar ratio of dapsone to water is 1:6.9) were dissolved and stirred for 0.5 h to obtain a water-sulfone mixed solvent;

[0050] (2) 5.74 g of LiN(SO2CF3)2 was dissolved in the mixed solvent of step (1) and stirred for 12 h to obtain 11 ml of a water-sulfone-based mixed electrolyte for lithium-ion batteries.

[0051] The mixed liquid electrolyte prepared in this embodiment was tested using the same method as in Example 1 of the present invention and found to have a wide electrochemical window, reaching above 3V.

[0052] The mixed liquid electrolyte prepared in this embodiment is mixed with LiNi 0.5 Mn 1.5 O4-Li4Ti5O 12 The whole battery was assembled and the electrochemical performance test was carried out in the same manner as in Example 1 of the present invention: the instrument used was a Shanghai Chenhua CHI660D electrochemical workstation with a scanning speed of 5 mV s –1 , 10mV s –1 , the voltage range is set to 1~3.5V. Figure 4It can be seen from the cyclic voltammetry curve that a pair of redox peaks appear near 2.7V and 3.5V at a scan rate of 5mV / s for the obtained full battery. When the scan rate reaches 10mV / s, the redox peaks of the battery are still quite sharp, which shows that the full battery prepared by the lithium-ion battery of the present invention using a water-sulfone-based mixed electrolyte can maintain the stability of the battery structure even under fast scanning, especially the stability of the electrode / electrolyte interface. The main reason is the formation of the SEI film, which ensures that the battery can operate well under fast charge and discharge conditions and has good stability.

[0053] Example 4

[0054] (1) In a glove box filled with argon gas of purity greater than or equal to 99%, 1.2 g of dapsone and 0.6 g of ultrapure water (i.e., the molar ratio of dapsone to water is 1:6.9) were dissolved and stirred for 0.5 h to obtain a water-sulfone mixed solvent;

[0055] (2) 5.74 g of LiN(SO2CF3)2 was dissolved in the mixed solvent of step (1) and stirred for 12 h to obtain 11 ml of a water-sulfone-based mixed electrolyte for lithium-ion batteries.

[0056] The mixed liquid electrolyte prepared in this embodiment was subjected to an electrochemical window test using the same method as in Example 1 of the present invention. The test revealed that the window of this electrolyte was approximately 1.7V to 4.8V.

[0057] The mixed liquid electrolyte prepared in this example was mixed with LiCoO2-Li4Ti5O 12 The battery was assembled into a full cell and the electrochemical performance test was carried out at room temperature in the same manner as in Example 1 of the present invention. Figure 5 It can be seen that the full battery prepared by the lithium-ion battery of the present invention using the water-sulfone mixed electrolyte has a first-week charge and discharge capacity of approximately 135 mAh / g at a 3C rate, and an efficiency stable at around 97.3%, with good cycle stability.

[0058] Example 5

[0059] (1) In a glove box filled with argon gas of purity greater than or equal to 99%, 2.41 g of dimethyl sulfone and 0.41 g of ultrapure water (i.e., a molar ratio of dimethyl sulfone to water of 1.1:1) were dissolved in each other and stirred for 0.5 h to obtain a water-sulfone mixed solvent;

[0060] (2) 5.74 g of LiN(SO2CF3)2 was dissolved in the mixed solvent of step (1) and stirred for 12 h to obtain 7 ml of a water-sulfone-based mixed electrolyte for lithium-ion batteries.

[0061] The mixed liquid electrolyte prepared in this embodiment was subjected to an electrochemical window test using the same method as in Example 1 of the present invention. The test revealed that the window of this electrolyte was approximately 1.5V to 5V.

[0062] The mixed liquid electrolyte prepared in this embodiment is mixed with LiNi 0.5 Mn 1.5 O4-Li4Ti5O 12 The battery was assembled into a full battery and the low temperature 0°C electrochemical performance test was carried out according to the same method as in Example 1 of the present invention. Figure 6 It can be seen that the full battery prepared by the lithium-ion battery of the present invention using the water-sulfone mixed electrolyte has a first-week charge and discharge capacity of approximately 80 mAh / g at a 3C rate, an efficiency stable at around 98%, and good low-temperature cycle stability.

[0063] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-voltage water-sulfone mixed electrolyte for an aqueous lithium-ion battery, characterized in that: The electrolyte is made of a mixture of lithium salt, water and sulfone organic solvent; In the electrolyte, the mass molar concentration of the lithium salt is 5 to 15m; The lithium salt is LiN(SO2CF3)2; The sulfone organic solvent is selected from at least one of dimethyl sulfone, phenethyl sulfone, dapsone and sulfolane.

2. The electrolyte according to claim 1, wherein: The molar mass ratio of the water to the sulfone organic solvent is 1:1-10.

3. The method for preparing the electrolyte according to claim 1 or 2, comprising the steps of: (1) mixing the sulfone organic solvent with the water in an inert atmosphere to obtain a water-sulfone mixed solvent; (2) In the inert atmosphere, the lithium salt is mixed with the water-sulfone mixed solvent to obtain a high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries.

4. The preparation method according to claim 3, wherein: The inert atmosphere is nitrogen or argon with a purity of not less than 99%.

5. Use of the high-voltage water-sulfone mixed electrolyte for aqueous lithium-ion batteries according to claim 1 or 2 in the preparation of aqueous lithium-ion batteries.

6. The use according to claim 5, characterized in that: The positive electrode active material of the aqueous lithium ion battery is LiCoO2, LiMn2O4, LiFePO4 or LiNi 0.5 Mn 1.5 O4, the negative electrode active material is Li4Ti5O 12 .

7. The use according to claim 5 or 6, characterized in that: The ambient temperature for testing the aqueous lithium-ion battery based on the high-voltage water-sulfone mixed electrolyte and the aqueous lithium-ion battery is -50°C to 30°C.

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