High-safety single-solvent electrolyte, preparation method thereof and battery

Abstract

The invention relates to a high-safety single-solvent electrolyte, a preparation method thereof and a battery, the high-safety single-solvent electrolyte is a liquid electrolyte composed of a lithium salt, an organic solvent and an initiator, the lithium salt, the organic solvent and the initiator can be subjected to in-situ polymerization at a thermal runaway critical temperature to form a solid polymer electrolyte, and the organic solvent is an ester. Compared with the prior art, the single-solvent electrolyte system provided by the invention is used for the lithium battery, meets the discharge requirement at room temperature, can be thermally polymerized at a thermal runaway critical temperature, and can be quickly solidified; the single-solvent electrolyte has no obvious influence on the normal charge-discharge performance of a lithium battery while improving the safety performance of the battery, and when the high-safety single-solvent electrolyte is used for constructing a lithium metal battery, a lithium ion battery and a silicon negative electrode battery, the cycle performance of the battery can be effectively improved, the safety performance of the battery is improved, and the service life of the battery is prolonged. Good application prospects are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolyte materials and relates to a highly safe single-solvent electrolyte, a preparation method thereof and a battery. Background Art

[0002] Lithium battery electrochemical energy storage technology can meet cross-scale needs from energy storage power stations to consumer electronics; it can also meet diverse application needs such as energy type, power type and wide temperature range. However, to achieve its large-scale application, the key lies in solving challenges such as rapid capacity decay at room temperature, short battery cycle life, and flammable and volatile liquid electrolytes at high temperatures.

[0003] The regulation of electrolytes is crucial to achieving high safety and long cycle life of lithium batteries. Electrolytes can be divided into liquid and solid. Liquid electrolytes have the characteristics of high conductivity and good interface contact, but are flammable, volatile and easy to leak. Intrinsically safe solid electrolytes have the characteristics of poor interface contact and low ion conductivity. Among polymer solid electrolytes, they are usually divided into gel polymer electrolytes and solid polymer electrolytes.

[0004] Gel polymer electrolytes effectively improve the conductivity of the electrolyte system by introducing solvent molecules into the polymer matrix. However, the residual liquid components in gel polymer electrolytes mean that they do not completely eliminate the safety issues brought about by liquid electrolytes.

[0005] Therefore, researchers have proposed a variety of solutions to achieve high-safety electrolytes and their preparation and application:

[0006] For example, Chinese patent CN113675474B introduces a new type of electrolyte containing phosphorus-resistant high-temperature additives, which effectively improves the high-temperature cycle performance of high-nickel ternary lithium-ion batteries and inhibits gas production during the cycle while improving flame retardancy.

[0007] For example, in the literature (eScience 2022, 2(2), 201-208), an in-situ polymer gel electrolyte with thermally induced interfacial ion blocking function was developed. Under thermal abuse conditions, the repolymerization and deposition of residual ethylene carbonate in the electrolyte (1M lithium difluorooxalatoborate / propylene carbonate) led to thermally induced ion blocking at the solid electrolyte interface, thereby achieving better lithium metal battery safety. The developed electrolyte also has excellent cycling performance in the battery.

[0008] For example, the literature (Adv. Energy Mater. 2023, 13(3), 2202529) proposes a new deep eutectic electrolyte (succinonitrile / 1,3,5-trioxane / lithium difluorooxalatoborate) with thermally induced intelligent shutdown function to improve the serious safety problems and uncontrollable dendrite growth of lithium metal batteries. 1,3,5-Trioxane can participate in Li + The first solvation shell of the lithium ion battery forms a unique solvation structure, which is beneficial to improve the interfacial compatibility of the electrode / electrolyte. When the battery is exposed to temperatures exceeding 150°C, 1,3,5-trioxane polymerizes into polyoxymethylene with ultra-low ionic conductivity, terminating the transmission of lithium ions and the subsequent operation of the battery.

[0009] As shown in the literature (Energy Storage Mater. 2023, 58, 123-131), a smart polymer gel electrolyte was developed by introducing cyclic carbonate carbamate methacrylate monomers and isocyanoethyl methacrylate monomers into the liquid electrolyte, which coordinates the trade-off between thermal safety and energy density of lithium batteries.

[0010] For example, the literature (Energy Storage Mater. 2024, 70, 103499) uses lithium-induced polycondensation of tetraethyl orthosilicate at high temperature to form a thermally stable polymer network to passivate the metal lithium negative electrode to ensure the safety of lithium metal batteries. In this electrolyte system, pentafluorocyclotriphosphazene is additionally introduced as a non-flammable component to make the electrolyte flame retardant and cycle stable.

[0011] For example, the literature (Adv. Energy Mater. 2023, 13 (22), 2300143) uses a non-volatile, non-flammable, thermally reversible polymer / ionic liquid gel electrolyte as a built-in safety switch to provide high-precision, reversible thermal protection for lithium batteries. At high temperatures, the gel electrolyte undergoes phase separation and deposits polymers on the electrode surface / diaphragm, preventing lithium ion insertion reactions and thus preventing thermal runaway. When the temperature drops, the gel electrolyte returns to its original properties and the battery performance recovers.

[0012] However, the high-safety electrolytes reported so far that combine the advantages of liquid and solid electrolytes are generally based on thermally responsive gel electrolytes. However, at high temperatures, excessive residual solvents in gel electrolytes may trigger parasitic reactions, thus posing safety risks, which is similar to liquid electrolytes. Summary of the invention

[0013] The purpose of the present invention is to provide a highly safe single-solvent electrolyte, a preparation method thereof and a battery, and to enhance the safety performance of lithium batteries by in-situ curing of the single-solvent electrolyte at high temperature.

[0014] The purpose of the present invention can be achieved by the following technical solutions:

[0015] In the first aspect, the present invention provides a highly safe single-solvent electrolyte, which is a liquid electrolyte composed of a lithium salt, an organic solvent and an initiator, wherein the organic solvent can be polymerized in situ at a critical temperature of thermal runaway to form a solid polymer electrolyte, and the organic solvent is an ester. Here, the initiator is used to promote the polymerization of the solvent at the critical temperature of thermal runaway; if in situ polymerization is possible without an initiator, the initiator may not be added.

[0016] Furthermore, the critical temperature of thermal runaway is 80-120°C.

[0017] Furthermore, the organic solvent is one of vinyl ethylene carbonate, vinylene carbonate, methyl difluoroacetate and tetraethyl silicate.

[0018] Furthermore, the lithium salt is one or a mixture of lithium iodide, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium nitrate, and lithium bis(fluorosulfonyl imide), and the concentration thereof in the liquid electrolyte is 1.0 to 3.0 mol / L.

[0019] Furthermore, the initiator is one of azobisisobutyronitrile, lithium iodide, azobisisoheptanenitrile and dibenzoyl peroxide, and its mass fraction in the liquid electrolyte is 0.02wt.%-1.0wt.%.

[0020] Furthermore, the water content in the liquid electrolyte is less than 20 ppm.

[0021] In a second aspect, the present invention provides a method for preparing a highly safe single-solvent electrolyte, wherein a lithium salt, an organic solvent and an initiator are uniformly mixed in an inert atmosphere to obtain the single-solvent electrolyte. Preferably, the inert atmosphere is an argon atmosphere.

[0022] In a third aspect, the present invention provides a battery, using the highly safe single-solvent electrolyte as described in any one of the above items as an electrolyte.

[0023] Furthermore, the battery is a silicon negative electrode battery, a lithium ion battery or a lithium metal battery.

[0024] Furthermore, the battery cell used in the battery is any one of the systems of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based and sulfur.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The designed single-solvent electrolyte is liquid at room temperature, has high ionic conductivity, and good interface contact. When facing thermal safety risks, the single-solvent electrolyte polymerizes in situ to form a polymer electrolyte, reducing parasitic reactions caused by residual solvents, reducing heat generated by internal battery reactions, and improving battery safety performance.

[0027] (2) The designed highly safe single-solvent electrolyte does not require the introduction of additional fluorine-containing additives. The safety performance of lithium batteries is enhanced by in-situ curing of the single-solvent electrolyte at high temperature.

[0028] (3) The proposed high-safety single-solvent electrolyte can meet the requirements of long cycle life of lithium batteries at room temperature.

[0029] (4) Compared with the existing electrolyte system, the single solvent in the present invention is low-cost, does not require the introduction of additional additives, and has no special requirements for the use environment.

[0030] (5) The battery using the electrolyte system in this application has excellent room temperature cycle life, specifically reliable safety performance, can undergo thermal polymerization at the critical temperature of thermal runaway, the electrolyte system polymerizes rapidly, and the free solvent accounts for less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The electrochemical cycle curve of the lithium metal battery using the highly safe single solvent electrolyte of Example 1;

[0032] Figure 2 This is a flame retardant performance diagram of the highly safe single solvent electrolyte of Example 1 and its comparative example;

[0033] Figure 3 The cycle performance of Comparative Example 3;

[0034] Figure 4 This is an optical photograph of the electrolyte of Comparative Example 4 at the critical temperature of thermal runaway. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0036] In order to enhance the safety performance of lithium batteries, the present invention provides a highly safe single-solvent electrolyte, the preparation method of which is to add a lithium salt and an initiator into an ester organic solvent in an inert argon atmosphere.

[0037] In some specific embodiments, the organic solvent is one of vinyl ethylene carbonate, vinylene carbonate, methyl difluoroacetate and tetraethyl silicate.

[0038] In some specific embodiments, the lithium salt is one or a mixture of lithium iodide, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium nitrate, and lithium bis(fluorosulfonyl imide), and the concentration of the lithium salt is 1.0 to 3.0 mol / L.

[0039] In some specific embodiments, the initiator includes one of azobisisobutyronitrile, lithium iodide, azobisisoheptanenitrile and dibenzoyl peroxide, and the mass fraction of the initiator is 0.02wt.%-1.0wt.%.

[0040] The present invention can be further understood from the following examples, but the present invention is not limited to the following examples.

[0041] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0042] Embodiment 1:

[0043] A 1.0 mol / L lithium salt solution of ethylene carbonate was prepared. The lithium salt was lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate (mass ratio was 10:1) with a concentration of 1.0 mol / L. The mass fraction of the initiator azobisisobutyronitrile introduced into the system was 1.0 wt.%. The electrolyte system was used for lithium metal as the negative electrode, LiNi 0.5 C 0.2 M 0.3 The full battery test with O2 as the positive electrode found that the average coulomb efficiency of the battery can reach 99.6%, the cycle life can reach 152 cycles, the capacity retention rate is >90%, and its cycle performance is as follows Figure 1 shown.

[0044] When the temperature rises to 80°C, the single solvent electrolyte polymerizes into a polymer electrolyte with high safety performance, no fire or explosion, and its flame retardant properties are as follows Figure 2 As shown. Example 2:

[0045] Prepare a 1.0 mol / L vinylene carbonate solution, where the lithium salt is lithium iodide, with a concentration of 1.0 mol / L. In addition to being used as a lithium salt, lithium iodide can also be used as an initiator to initiate anionic polymerization of the polymer monomer vinylene carbonate at 80-120°C. This electrolyte system is used for lithium metal as the negative electrode, LiNi 0.5 C 0.2 M 0.3 Full battery test with O2 as the positive electrode. In addition, the assembled soft pack battery was tested for safety using an accelerating calorimeter.

[0046] When the temperature rises to 80°C, the single solvent electrolyte polymerizes into a polymer electrolyte with high safety performance and no fire or explosion.

[0047] Embodiment 3:

[0048] A vinylene carbonate solution with a concentration of 1.0 mol / L was prepared, and the lithium salt was lithium bis(trifluoromethanesulfonyl)imide and lithium nitrate (mass ratio of 10:1), with a concentration of 1.0 mol / L. The mass fraction of the initiator azobisisobutyronitrile introduced into the system was 0.5 wt.%. The electrolyte system was used for lithium metal as the negative electrode, LiNi 0.5 C 0.2 M 0.3 Full battery testing with O2 as the positive electrode. In addition, the assembled soft pack battery was tested for safety using differential scanning calorimetry and accelerating rate calorimetry.

[0049] Embodiment 4:

[0050] A 3.0 mol / L lithium salt solution of ethylene carbonate was prepared. The lithium salt was lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalatoborate (molar ratio of 8:1). The mass fraction of the initiator azobisisobutyronitrile was 1.0 wt.%. The electrolyte system was used for lithium metal as the negative electrode, LiNi 0.5 C 0.2 M 0.3 Full cell test with O2 as the positive electrode.

[0051] When the temperature rises to 100°C, the single solvent electrolyte polymerizes into a polymer electrolyte with high safety performance and no fire or explosion.

[0052] Embodiment 5:

[0053] A vinylene carbonate solution with a lithium salt concentration of 1.0 mol / L was prepared. The lithium salt was lithium difluorooxalate borate and lithium nitrate (mass ratio of 10:1) with a concentration of 1.0 mol / L. The mass fraction of the initiator dibenzoyl peroxide introduced into the system was 0.02wt.%-0.1wt.%. The electrolyte system was used for full battery testing with lithium metal as the negative electrode and lithium iron phosphate as the positive electrode.

[0054] When the temperature rises to 120°C, the single solvent electrolyte polymerizes into a polymer electrolyte with high safety performance and no fire or explosion.

[0055] Embodiment 6:

[0056] A 1.5 mol / L lithium salt solution of ethylene carbonate was prepared, wherein the lithium salt was lithium bis(trifluoromethanesulfonyl)imide and lithium difluorooxalatoborate (molar ratio of 8:1), and the concentration was 1.5 mol / L. The mass fraction of the initiator azobis(isoheptyl)carbonitrile introduced into the system was 1.0 wt.%. The electrolyte system was used for full battery testing with graphite as the negative electrode and lithium cobalt oxide as the positive electrode.

[0057] When the temperature rises to 80°C, the single solvent electrolyte polymerizes into a polymer electrolyte with high safety performance and no fire or explosion.

[0058] Embodiment 7:

[0059] A tetraethyl silicate solution with a lithium salt concentration of 3 mol / L was prepared, wherein the lithium salt was lithium bis(fluoromethanesulfonyl)imide with a concentration of 3 mol / L. The electrolyte system was used for a full battery test with lithium metal as the negative electrode and a lithium-rich manganese-based as the positive electrode.

[0060] When the temperature rises to 80°C, the single solvent electrolyte polymerizes and transforms into a polymer electrolyte, which has high safety performance and does not catch fire or explode. From Examples 1-7, it can be seen that when the temperature rises to 80-120°C, the liquid electrolyte polymerizes and transforms into a polymer electrolyte, which has high safety performance and does not catch fire or explode.

[0061] Comparative Example 1

[0062] Compared with Example 1, most of the conditions are the same, except that ethylene carbonate is replaced by ethylene carbonate and diethyl carbonate (volume ratio is 1:1) which cannot be polymerized in situ at high temperature. When an ignition source is close, the electrolyte of Comparative Example 1 burns rapidly.

[0063] Comparative Example 2

[0064] Compared with Example 1, most of the above are the same, except that 10% by volume of ethylene carbonate and diethyl carbonate (the volume ratio of the two is 1:1) are introduced into the electrolyte in Example 1. When the temperature rises, the electrolyte in Comparative Example 2 is transformed into a gel polymer electrolyte. Since liquid electrolyte still exists in the gel polymer electrolyte, the electrolyte in Comparative Example 2 burns when the ignition source approaches.

[0065] Comparative Example 3

[0066] Compared with Example 1, the other conditions remain unchanged, but in Comparative Example 3, lithium nitrate is not added. The electrolyte system of Comparative Example 3 is used for lithium metal as the negative electrode, LiNi 0.5 C 0.2 M 0.3 The full battery test with O2 as the positive electrode. After testing, it was found that the cycle life of the battery was shortened, and the capacity retention rate was ~50% after 30 cycles. Its cycle performance is as follows Figure 3shown.

[0067] Comparative Example 4

[0068] Compared with Example 1, other conditions remain unchanged, but in Comparative Example 4 where no initiator is added, when the temperature is raised to 80°C, the single solvent electrolyte cannot be polymerized to transform into a polymer electrolyte. Figure 4 shown.

[0069] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A highly safe single-solvent electrolyte, characterized in that: It is a liquid electrolyte composed of lithium salt and organic solvent. The organic solvent can be polymerized in situ at the critical temperature of thermal runaway to form a solid polymer electrolyte. The organic solvent is an ester.

2. A highly safe single-solvent electrolyte according to claim 1, characterized in that: The thermal runaway critical temperature is 80-120°C.

3. A highly safe single-solvent electrolyte according to claim 1, characterized in that: The organic solvent is one of vinyl ethylene carbonate, vinylene carbonate, methyl difluoroacetate and tetraethyl silicate.

4. A highly safe single-solvent electrolyte according to claim 1, characterized in that: The lithium salt is one or a mixture of lithium iodide, lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), lithium nitrate, and lithium bis(fluorosulfonyl imide), and the concentration of the lithium salt in the liquid electrolyte is 1.0 to 3.0 mol / L.

5. A highly safe single-solvent electrolyte according to claim 1, characterized in that: An initiator is also added to the liquid electrolyte, and the mass fraction of the initiator in the liquid electrolyte is 0.02wt.%-1.0wt.%.

6. A highly safe single-solvent electrolyte according to claim 5, characterized in that: The initiator is one of azobisisobutyronitrile, lithium iodide, azobisisoheptanenitrile and dibenzoyl peroxide.

7. A highly safe single-solvent electrolyte according to claim 1, characterized in that: The water content in the liquid electrolyte is less than 20 ppm.

8. The method for preparing a highly safe single-solvent electrolyte according to any one of claims 1 to 7, characterized in that: In an inert atmosphere, a lithium salt, an organic solvent and an initiator are mixed uniformly to obtain the single-solvent electrolyte.

9. A battery, characterized in that: The highly safe single-solvent electrolyte as described in any one of claims 1 to 6 is used as the electrolyte.

10. The battery according to claim 9, characterized in that The battery is a silicon negative electrode battery, a lithium ion battery or a lithium metal battery; The battery cell used in the battery is any one of the systems of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese base and sulfur.

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