Water-alkylene oxide electrolyte for aqueous lithium ion battery as well as preparation method and application of water-alkylene oxide electrolyte

Abstract

The invention relates to a water-alkylene oxide mixed electrolyte for an aqueous lithium ion battery, and belongs to the technical field of lithium secondary batteries. The electrolyte is obtained by mixing a lithium salt, water and an alkylene oxide organic solvent. The positions of oxygen atoms on the ring of the epoxyalkane are fixed, and the epoxyalkane and water molecules can form hydrogen bonds in a specific direction, so that the water molecules are arranged in a space according to a predetermined mode, and an ordered and stable hydrogen bond network is constructed. On one hand, free movement of solvent molecules such as surrounding water molecules is limited, and the activity of free water molecules is reduced, so that the hydrogen evolution reaction is inhibited; and on the other hand, due to the directional arrangement, water molecules can form a uniform and stable solvation shell layer around the lithium ions, and each lithium ion obtains a similar coordination environment, so that ion transmission is improved, and a uniform and stable SEI is formed on the surface of the electrode. The preparation method of the aqueous electrolyte is simple, easy to operate, environmentally friendly and suitable for industrial application, and raw materials are easy to obtain.

Description

Technical Field

[0001] The present invention relates to a water-alkylene oxide electrolyte for aqueous lithium-ion batteries, a preparation method thereof, and applications thereof, belonging to the technical field of lithium secondary batteries. Background Art

[0002] The development of traditional lithium-ion batteries has revolutionized the fields of portable electronic products and electric vehicles, but it has also been accompanied by huge safety risks. From fires, explosions to catastrophic thermal runaway events, numerous accidents have highlighted the serious risks caused by the use of flammable organic electrolytes and internal short circuits in batteries. For example, overcharging and internal short circuits may trigger rapid exothermic reactions and gas release, ultimately leading to explosion failures. These hazards not only endanger human life and property, but also cause huge economic losses and environmental burdens.

[0003] To address these challenges, the development of aqueous lithium-ion batteries has become a promising research direction. The main purpose of its development is for safer and more environmentally friendly energy storage systems, especially for some special scenarios with high safety requirements. By introducing water as a solvent into the electrolyte, the flammability problems associated with traditional organic systems can be essentially eliminated. In addition, aqueous lithium-ion electrolytes usually have higher ionic conductivity, lower manufacturing costs, and sustainable end-of-life recycling processes. These advantages make aqueous lithium-ion batteries highly attractive for large-scale energy storage applications where safety and cost are crucial.

[0004] Despite many advantages, the inherent gas release problem in aqueous batteries can cause performance degradation and potential safety risks. Trace amounts of water in the electrodes and electrolytes are the root cause of gas production. Under neutral conditions with a pH of 7, the reduction potential of water is approximately 2.6 V (vs. Li + / Li), much higher than the working potential of the negative electrode. To address this challenge, researchers have proposed various improvement strategies. First, adding hydrogen bond acceptors (such as urea, polyethylene glycol, sulfolane, and acetonitrile) to the aqueous electrolyte can form a stable hydrogen bond network with water molecules, thereby reducing the number of free water molecules and inhibiting the hydrogen evolution reaction of water reduction to a certain extent. Second, introducing relatively expensive lithium salt film-forming agents, such as LiBOB, LiDFBOP, LiPO2F2, and LiNO3, can form a dense and stable solid electrolyte interface (SEI) on the electrode surface, which also achieves the purpose of inhibiting hydrogen generation. However, the above measures further weaken the advantages of aqueous lithium-ion batteries in terms of safety and cost due to their flammability or high price defects. Therefore, there is an urgent need to develop new strategies to achieve aqueous lithium-ion electrolytes with a wide voltage window, low cost, and non-flammability to realize high-energy-density aqueous batteries. Summary of the Invention

[0005] The object of the present invention is to provide a water-alkylene oxide electrolyte for aqueous lithium-ion batteries, a preparation method thereof and an application thereof.

[0006] The water-alkylene oxide electrolyte for aqueous lithium-ion batteries of the present invention is an electrolyte obtained by mixing a lithium salt, water and an alkylene oxide organic solvent. The oxygen atom on the ring of the alkylene oxide has a fixed position, and can form a hydrogen bond with water molecules in a specific direction, so that the water molecules are arranged in a predetermined manner in space, thereby constructing an ordered and stable hydrogen bond network. On the one hand, the free movement of solvent molecules such as surrounding water molecules is restricted, and the activity of free water molecules is reduced, thereby inhibiting the occurrence of hydrogen evolution reaction. On the other hand, this directional arrangement enables water molecules to form a uniform and stable solvation shell around lithium ions, and each lithium ion obtains a similar coordination environment, which helps to improve ion transport and form a uniform and stable SEI on the electrode surface. The preparation method of the aqueous electrolyte described in the present invention is simple, easy to operate, environmentally friendly, and the raw materials are easily available, which is suitable for industrial applications.

[0007] The object of the present invention is achieved by the following technical solutions.

[0008] A water-alkylene oxide mixed electrolyte for aqueous lithium-ion batteries provided by the present invention is prepared by mixing a lithium salt, water and an alkylene oxide organic solvent.

[0009] In the above electrolyte, the molality of the lithium salt in the electrolyte can be 0.01-20 mol / kg;

[0010] The molar mass ratio of the water to the alkylene oxide organic solvent can be 0.1:1-2:1.

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

[0012] In the above electrolyte, the alkylene oxide is one or more of ethylene oxide, propylene oxide, 1,2-epoxybutane, 1,2-epoxypentane, 1,3-epoxypentane, 1,4-dioxane and 1,3-dioxane.

[0013] The preparation method of the above electrolyte provided by the present invention includes the following steps:

[0014] (1) In an inert atmosphere, mix the alkylene oxide with ultrapure water to obtain a mixed solvent;

[0015] (2) In the inert atmosphere, mix the lithium salt with the mixed solvent to obtain a 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 the O2 content < 1 ppm).

[0017] The water-epoxy alkane mixed electrolyte for the aqueous lithium-ion battery described in the present invention is applied to the preparation of the aqueous lithium-ion battery.

[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, and the negative electrode active material is NbO2 or Li4Ti5O 12 .

[0019] In the above application, both the water-epoxy alkane electrolyte for the aqueous lithium-ion battery and the ambient temperature for testing the aqueous lithium-ion battery can be 30 °C.

[0020] The present invention further provides an aqueous lithium-ion battery, which includes 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, and the active material of the negative electrode is NbO2 or Li4Ti5O 12 ;

[0022] The electrolyte is the water-epoxy alkane electrolyte for the aqueous lithium-ion battery described above.

[0023] In the above aqueous lithium-ion battery, the ambient temperature for testing the full cell of the aqueous lithium-ion battery can be 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 < 1 ppm), the electrode plate, aqueous electrolyte, gasket and spring piece are sequentially placed into the 2025-type button battery blank in the order of negative electrode shell - spring piece - gasket - negative electrode plate - electrolyte - separator - positive electrode plate - positive electrode shell to assemble the full cell, and then the two battery shells are compacted and fastened with a tablet press to obtain the test button battery. The thickness of the gasket is 1 mm, and the model of the separator is glass fiber GF / F.

[0025] The present invention has the following advantages:

[0026] (1) The oxygen atom on the ring of the epoxy alkane has a fixed position, and can form hydrogen bonds with water molecules in a specific direction, enhancing the directionality of the hydrogen bonds. Each lithium ion obtains a similar coordination environment, realizing a rapid lithium ion desolvation process and improving the battery performance.

[0027] (2) The presence of the alkylene oxide reduces the amount of free water at the negative electrode / electrolyte interface. The oriented arrangement enables water molecules to form a uniform and stable solvation shell around lithium ions, and each lithium ion obtains a similar coordination environment, which helps to improve ion transport and form a uniform and stable SEI on the electrode surface.

[0028] (3) The preparation method of the aqueous electrolyte described in the present invention is simple, easy to operate, environmentally friendly, with easily available raw materials, and is suitable for industrial applications. Description of the Drawings

[0029] Figure 1 It is the rate performance graph of the full cell assembled with the mixed liquid electrolyte prepared in Example 1 at 30°C.

[0030] Figure 2 It is the mass spectrometry graph (DEMS) of the hydrogen and oxygen changes during the first charge and discharge of the full cell assembled with the mixed liquid electrolyte prepared in Example 1, as well as the corresponding charge and discharge curve graph.

[0031] Figure 3 It is the cycle capacity-efficiency graph of the full cell assembled with the mixed liquid electrolyte prepared in Example 2 at 30°C.

[0032] Figure 4 It is the electrochemical window graph of the mixed liquid electrolyte prepared in Example 3. Detailed Embodiments

[0033] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0034] The materials, reagents, etc. used in the following examples are all commercially available unless otherwise specified.

[0035] In the following examples, the assembly of the aqueous lithium-ion full cell: Inside a glove box filled with argon (O2 < 1 ppm), the electrode plates, aqueous electrolyte, gasket, and spring washer are sequentially placed into the blank 2025-type button cell in the order of negative electrode shell - spring washer - gasket - negative electrode plate - electrolyte - separator - positive electrode plate - positive electrode shell to assemble a full cell. Then, a tablet press is used to compact and fasten the two battery shells to obtain a test button cell. The thickness of the gasket is 1 mm, and the model of the separator is glass fiber GF / F.

[0036] After the assembled full cell is left standing for 24 h, electrochemical performance tests are carried out: The electrochemical window is tested on an electrochemical workstation (lvium-Start, lvium-N-Stat, Netherlands), and the scanning rate is 5 mV s -1; The battery charge and discharge tests were carried out using a Neware battery tester (model BTS-5V10mA, Shenzhen Neware Electronic Co., Ltd.); the gas production of the battery was analyzed using an electrochemical mass spectrometer (Hiden PHR20, Beijing Inglehead Analysis Technology Co., Ltd.).

[0037] Example 1:

[0038] (1) In a glove box filled with argon with a purity of greater than or equal to 99%, first dissolve 4 g of 1,4-dioxane and 0.5 g of ultrapure water (i.e., the molar ratio of 1,4-dioxane to water is 1.64:1).

[0039] (2) Dissolve 3 g of LiN(SO2CF3)2 in the mixed solvent of step (1) and stir at room temperature for 12 h to obtain the required mixed electrolyte.

[0040] The mixed liquid electrolyte prepared in this example was assembled into a full cell with LiMn2O4-Li4Ti5O 12 (i.e., the positive and negative electrode active materials, the same below), and tested using a Neware electrochemical test system at 30 °C. In the rate performance test of the battery, the magnitude of the charge and discharge current was calculated and set according to the mass of the active material of the negative electrode plate of Li4Ti5O 12 and its theoretical capacity of 175 mAh g -1 . The charge and discharge voltage range of the LiMn2O4-Li4Ti5O 12 full cell was 1 - 2.8 V. It can be seen from the Figure 1 test that in the rate test from 1C to 10C, the discharge specific capacities of the battery were 143.63 mAh g -1 , 139.11 mAh g -1 , 129.2 mAh g -1 , 119.75 mAh g -1 , 110.86 mAh g -1 , 102.72 mAh g -1 , respectively. Even at a high current density of 10C, the capacity retention rate was still as high as 71.5%, showing excellent fast charge and discharge capabilities. In addition, after the rate test, the capacity of the battery recovered to 142.96 mAh g -1 when it returned to 1C, approaching the initial capacity, indicating excellent rate performance.

[0041] The mixed liquid electrolyte prepared in this example was assembled into a full cell with LiMn2O4 positive electrode plate and Li4Ti5O 12 negative electrode plate in an electrochemical reaction cell and tested using a Hiden PHR20 electrochemical mass spectrometer. It can be seen from the Figure 2It can be seen that the full cell LiMn2O4-Li4Ti5O prepared with the water-1,4-dioxane-based mixed electrolyte for the lithium-ion battery of the present invention 12 During the charge and discharge process in the first week, only trace amounts of hydrogen and oxygen are generated, indicating that the decomposition of H2O on the anode surface in the mixed liquid electrolyte prepared in this example is effectively inhibited.

[0042] Example 2:

[0043] (1) In a glove box filled with argon with a purity of greater than or equal to 99%, first dissolve 4 g of 1,4-dioxane and 0.5 g of ultrapure water (i.e., the molar ratio of 1,4-dioxane to water is 1.64:1);

[0044] (2) Dissolve 1.4 g of LiN(SO2F)2 in the mixed solvent of step (1) and stir at room temperature for 12 h to obtain the required mixed electrolyte.

[0045] The mixed liquid electrolyte prepared in this example and LiMn2O4-Li4Ti5O 12 are assembled into a full cell. Using a Neware electrochemical test system, the test is carried out at an ambient temperature of 30 °C. In the cycle performance test of the battery, the magnitude of the charge and discharge current is calculated and set according to the mass of the active material of the negative electrode sheet of Li4Ti5O 12 and its theoretical capacity of 175 mAh g -1 . The charge and discharge voltage range of the LiMn2O4-Li4Ti5O 12 full cell is 1-2.8 V. It can be known from the Figure 3 test that the full cell prepared with the water-1,4-dioxane-based mixed electrolyte for the lithium-ion battery of the present invention can stably cycle 200 weeks at a high rate of 10C, and the discharge specific capacity in the first week is 104.1 mAh g -1 , and the discharge specific capacity after 200 weeks of charge and discharge cycling is 75.5 mAh g -1 , and the capacity retention rate is 72.5%, showing good cycle stability.

[0046] Example 3:

[0047] (1) In a glove box filled with argon with a purity of greater than or equal to 99%, first dissolve 4 g of 1,4-dioxane and 0.5 g of ultrapure water (i.e., the molar ratio of 1,4-dioxane to water is 1.64:1);

[0048] (2) Dissolve 1.5 g of LiN(SO2CF3)2 and 0.7 g of LiN(SO2F)2 in the mixed solvent of step (1) and stir at room temperature for 12 h to obtain the required mixed electrolyte.

[0049] The mixed liquid electrolyte prepared in this embodiment was subjected to an electrochemical window test. The test was carried out using an lvium-Start electrochemical workstation. A three-electrode system was adopted, with the working electrodes being Pt (positive electrode side) and Al (negative electrode side), the counter electrode being activated carbon (AC), and the reference electrode being an Ag / AgCl electrode. The scanning rate was 5 mV s -1 . It can be known from the test that. From Figure 4 , it can be seen that the water-1,4-dioxane electrolyte for the aqueous lithium-ion battery of the present invention achieved a wide electrochemical window of 1 to 5 V, meeting the requirements of LiMn2O4 (4.0 V vs. Li + / Li) and Li4Ti5O 12 (1.55 V vs. Li + / Li) for reversible lithium deintercalation and intercalation.

[0050] In summary, the above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A water-alkylene oxide mixed electrolyte for an aqueous lithium-ion battery, characterized in that: The water-alkylene oxide mixed electrolyte is an electrolyte obtained by mixing lithium salt, water and alkylene oxide organic solvent, and has a wide electrochemical stability window and excellent cycle stability.

2. The water-alkylene oxide mixed electrolyte for lithium battery according to claim 1, characterized in that: The lithium salt is one or more of LiN(SO2CF3)2, LiCF3SO3, LiC(SO2CF3)3, LiBOB, LiMOB, LiBMB, and LiODFB.

3. The water-alkylene oxide mixed electrolyte for lithium battery according to claim 1, characterized in that: The organic solvent is an alkylene oxide organic solvent.

4. The water-alkylene oxide mixed electrolyte for lithium battery according to claim 3, characterized in that: One or more of ethylene oxide, propylene oxide, 1,2-butylene oxide, 1,2-pentene oxide, 1,3-pentene oxide, 1,4-dioxane and 1,3-dioxane.

5. A method for preparing a water-alkylene oxide mixed electrolyte for a lithium battery according to any one of claims 1 to 4, characterized in that: The method steps are as follows: (1) in a glove box filled with protective gas, dissolving an alkylene oxide solvent and water in a certain proportion and stirring them uniformly to obtain a water-alkylene oxide mixed solvent; (2) in a glove box filled with protective gas, dissolving lithium salts of different concentrations in a water-alkylene oxide solvent, mixing and stirring to obtain a water-alkylene oxide mixed electrolyte; The protective gas is nitrogen or argon with a purity of not less than 99%.

6. The method for preparing a water-alkylene oxide mixed electrolyte for a lithium battery according to claim 5, characterized in that: In the electrolyte, the molar concentration of lithium salt dissolved in the mixed solvent may be 0.01 to 20 mol / kg; and the molar mass ratio of water to alkylene oxide solvent is 0.1:1 to 2:

1.

7. An application of the water-alkylene oxide mixed electrolyte for lithium ion batteries as claimed in claims 1 to 4, characterized in that: The water-alkylene oxide mixed electrolyte is used as an electrolyte in an aqueous lithium-ion battery system.

8. The use of the water-alkylene oxide mixed electrolyte for lithium ion batteries according to claim 7, characterized in that: The aqueous lithium-ion battery system is LiMn2O4-NbO2, LiCoO2-Li4Ti5O 12 、LiMn2O4-Li4Ti5O 12 、LiFePO4-Li4Ti5O 12 or LiNi 0.5 Mn 1.5 O4-Li4Ti5O 12 Lithium-ion battery system.

9. The use of the water-alkylene oxide mixed electrolyte for lithium-ion batteries according to claim 8, the ambient temperature of the electrolyte and full battery testing is: -50°C to 30°C.

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