Graphene microcapsule lithium battery electrolyte and preparation method thereof

Abstract

The invention discloses a graphene microcapsule lithium battery electrolyte and a preparation method thereof, the graphene microcapsule lithium battery electrolyte comprises an organic solvent, a lithium salt and an additive, the lithium salt is one or a mixture of several of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI and LiPO2F2, the organic solvent is a carbonic ester organic solvent, and the additive is one or a mixture of several of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI and LiPO2F2. The additive is prepared from FEC (fluoroethylene carbonate), graphene microcapsules and hyperbranched polyglycerol ester in a mass ratio of 10: (3-4): (0.3-0.6). The graphene microcapsule disclosed by the invention has a thermal buffering effect, and FEC disclosed by the invention is chemically modified through an interface, so that the integrity of the microcapsule is guaranteed, and the SEI stability is improved; the HPG depends on a hyperbranched topological structure, the problem of microcapsule dispersion is solved, and the interface wettability is optimized; the three components are synergistically used, so that the electrolyte keeps high performance in a wide temperature range of-40 to 60 DEG C, has a relatively good thermal management function, and provides a core material solution for a next-generation high-safety power battery.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of lithium battery electrolyte, specifically a graphene microcapsule lithium battery electrolyte and a preparation method thereof. Background Art

[0002] Lithium-ion battery electrolytes are the carriers of ion transport within the battery, primarily responsible for conducting conductive ions between the positive and negative electrodes. They guarantee the high voltage and high specific energy of lithium-ion batteries and play a key role in the battery's energy density, cycle life, power density, safety, and wide operating temperature range. Known as the "blood of the battery," these electrolytes are typically composed of sodium chloride and organic solvents. These electrolytes are typically formulated under specific conditions and proportions using high-purity organic solvents, electrolyte salts, and necessary additives. However, existing electrolyte technologies suffer from poor thermal management capabilities and fail to meet market demands. Summary of the Invention

[0003] Based on this, the purpose of the present invention is to provide a graphene microcapsule lithium battery electrolyte with good thermal management function and a preparation method thereof, so as to solve the technical problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions: A graphene microcapsule lithium battery electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the lithium salt is one or a mixture of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI and LiPO2F2; the organic solvent is a carbonate organic solvent; and the additive comprises fluoroethylene carbonate (FEC), graphene microcapsules and hyperbranched polyglycerol ester in a mass ratio of 10:(3-4):(0.3-0.6).

[0005] Fluorinated ethylene carbonate (FEC) is reduced to form a dense LiF layer, which blocks direct contact between the phase change material and the electrolyte, reducing interfacial impedance. The FEC-induced organic-inorganic composite SEI improves microcapsule / electrode interface compatibility. FEC decomposition products (such as LiF) form a thermal conductivity pathway with graphene, improving the thermal diffusion efficiency of the microcapsule shell.

[0006] The hyperbranched backbone of the hyperbranched polyglycerol ester (HPG) forms a nanoscale "molecular cage" that encapsulates the terminal ester groups of the graphene sheets, making them compatible with carbonate solvents. The hydrophobic core anchors the graphene surface through π-π interactions and also improves interfacial wettability, promoting electrolyte penetration into the electrode pores (increasing liquid absorption rate by 50%). The hyperbranched polyglycerol ester HPG of the present invention utilizes hydrophilic hyperbranched polyglycidol (HPG) produced by Xi'an Ruixi Biotechnology Co., Ltd., but can also be synthesized using methods described in the literature.

[0007] The mass proportions of the three raw materials, organic solvent, lithium salt and additives, are 80% to 86%, 10% to 14% and 4% to 6% respectively.

[0008] The particle size of the graphene microcapsules is 1-10 μm.

[0009] The carbonate organic solvent is any one or more of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0010] The carbonate organic solvent uses a combination of EC + DMC + EMC or EC + DMC + DEC. Carbonate organic solvents EC and PC have high dielectric constants, making lithium salts more soluble, and their high viscosity reduces the rate of lithium ion migration. However, DMC, DEC, and EMC have low dielectric constants and weak lithium salt dissolution capabilities, but their low viscosity provides excellent fluidity and facilitates lithium ion migration. The present invention uses a combination of EC + DMC + EMC or EC + DMC + DEC to mix high- and low-viscosity solvents. This system not only has excellent dispersion properties for graphene microcapsules, but also has good solubility for lithium salts. It can also remain liquid over a wide temperature range, has stable chemical properties, and further improves thermal stability.

[0011] The lithium salt is a mixture of LiPF6 and LiODFB in a mass ratio of (3-4):1. This lithium salt combination has a low degree of association and is easily soluble in the organic solvent containing the graphene microcapsules, ensuring high ionic conductivity and excellent chemical stability in the electrolyte. LiODFB is thermally coupled to graphene. The B2O3 generated by the decomposition of LiODFB forms a thermal buffer layer with graphene's high thermal conductivity (5300 W / m·K), raising the onset temperature of thermal runaway.

[0012] A method for preparing a graphene microcapsule lithium battery electrolyte comprises the following steps: Step A: adding a formulated amount of hyperbranched polyglycerol ester to an organic solvent accounting for 15% to 20% of the total mass, stirring for 2 to 3 hours to form a micellar solution; then adding a formulated amount of graphene microcapsules to the micellar solution, sonicating for 20 to 30 minutes, stirring for 40 to 60 minutes, adding the remaining organic solvent, and stirring uniformly to obtain a pre-dispersion solution; Step B: adding the formulated amount of lithium salt to the pre-dispersion obtained in step A, stirring evenly to obtain a lithium salt solution; Step C: adding a formulated amount of fluoroethylene carbonate to the lithium salt solution obtained in step B in several batches at a constant temperature of 25° C. under argon protection, and stirring evenly to obtain a graphene microcapsule lithium battery electrolyte.

[0013] The lithium salt in step B is a mixture of LiPF6 and LiODFB. Specifically, the lithium salt is dissolved in a gradient manner: the formulated amount of LiPF6 is added to the pre-dispersion obtained in step A, the temperature is controlled to ≤10°C, and stirred for 2-4 hours; the remaining LiODFB is slowly added, the temperature is raised to 25°C, and the mixture is kept warm and stirred for 5-7 hours.

[0014] This process effectively resolves the conflict between graphene microcapsule sedimentation and lithium salt thermal decomposition through phased solvent control and a gradient temperature dissolution strategy. Graphene phase-change microcapsules can impart intelligent thermal management capabilities to the electrolyte while maintaining its original conductive and mechanical properties.

[0015] The preparation method of the graphene microcapsules of the present invention is as follows: (1) 8-10 parts by weight of paraffin wax and 100 parts by weight of a graphene oxide aqueous solution with a mass concentration of 2%-3% and an average flake diameter of 1-10 μm are uniformly mixed at 65° C.; (2) 2-4 parts by weight of hydrazine hydrate are added and stirred for 30-40 hours; (3) the solution is atomized into tiny particles at 10° C. using a sprayer, and then sprayed into a blast cavity into which dry cold air at 10° C. is introduced, and the cold air removes moisture on the surface of the particles; (4) finally, reduction is performed at 40-50° C. for 3-5 hours, then at 60-70° C. for 3-5 hours, and finally at 120-130° C. for 6-8 hours to obtain graphene microcapsules.

[0016] The graphene microcapsules of the present invention have a dense graphene shell material that solves the problem of easy leakage of the core material, effectively improving the efficiency of heat storage and release of the phase change capsule. The graphene microcapsules absorb heat during phase change and buffer, and the microcapsule core melts and absorbs heat at 55-65°C, delaying the temperature rise of the battery. The graphene shell accelerates heat diffusion, reducing the temperature difference inside the battery and increasing the thermal runaway trigger temperature.

[0017] In summary, the present invention primarily possesses the following beneficial effects: It comprises an organic solvent, a lithium salt, and an additive. The lithium salt is one or a mixture of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI, and LiPO2F2; the organic solvent is a carbonate-based organic solvent; and the additive comprises fluoroethylene carbonate (FEC), graphene microcapsules, and hyperbranched polyglycerol esters in a mass ratio of 10:(3-4):(0.3-0.6). The graphene microcapsules of the present invention have a thermal buffering effect. The FEC, through interfacial chemical modification, protects microcapsule integrity and enhances SEI stability. The HPG, leveraging its hyperbranched topological structure, addresses microcapsule dispersion challenges and optimizes interfacial wettability. The synergistic use of these three additives enables the electrolyte to maintain high performance over a wide temperature range of -40-60°C, providing excellent thermal management capabilities and providing a core material solution for next-generation, high-safety power batteries. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The following embodiments are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0019] The following describes an embodiment of the present invention based on its overall structure. Example 1

[0020] A graphene microcapsule lithium battery electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the lithium salt is one or a mixture of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI and LiPO2F2; the organic solvent is a carbonate organic solvent; and the additive is fluoroethylene carbonate (FEC), graphene microcapsules and hyperbranched polyglycerol ester in a mass ratio of 10:3:0.3.

[0021] The mass proportions of the three raw materials, organic solvent, lithium salt and additives, are 80%, 14% and 6% respectively.

[0022] The particle size of the graphene microcapsules is 1-10 μm.

[0023] The carbonate organic solvent adopts a combination of EC+DMC+EMC in a volume ratio of 1:1:1.

[0024] The lithium salt is a mixture of LiPF6 and LiODFB in a mass ratio of 3:1.

[0025] A method for preparing a graphene microcapsule lithium battery electrolyte comprises the following steps: Step A: adding a formulated amount of hyperbranched polyglycerol ester to an organic solvent accounting for 15% of the total mass, stirring for 2 hours to form a micellar solution; then adding a formulated amount of graphene microcapsules to the micellar solution, sonicating for 20 minutes, stirring for 40 minutes, adding the remaining organic solvent, and stirring evenly to obtain a pre-dispersion solution; Step B: adding the formulated amount of lithium salt to the pre-dispersion obtained in step A, stirring evenly to obtain a lithium salt solution; Step C: adding a formulated amount of fluoroethylene carbonate to the lithium salt solution obtained in step B in several batches at a constant temperature of 25° C. under argon protection, and stirring evenly to obtain a graphene microcapsule lithium battery electrolyte.

[0026] The lithium salt in step B is a mixture of LiPF6 and LiODFB. Specifically, the lithium salt is dissolved in a gradient manner: the formulated amount of LiPF6 is added to the pre-dispersion obtained in step A, the temperature is controlled to ≤10°C, and stirred for 2 hours; the remaining LiODFB is slowly added, the temperature is raised to 25°C, and the mixture is kept warm and stirred for 5 hours.

[0027] The method for preparing graphene microcapsules according to an embodiment of the present invention is as follows: The preparation method of the graphene microcapsules of the present invention is as follows: (1) 8 parts by weight of paraffin wax and 100 parts by weight of a graphene oxide aqueous solution with a mass concentration of 2% and an average flake diameter of 2 μm are uniformly mixed at 65° C.; (2) 2 parts by weight of hydrazine hydrate are added and stirred for 30 hours; (3) the solution is atomized into tiny particles at 10° C. by a sprayer, and then sprayed into a blast cavity into which dry cold air at 10° C. is introduced, and the cold air removes moisture on the surface of the particles; (3) finally, reduction is performed at 40° C. for 5 hours, then at 60° C. for 5 hours, and finally at 120° C. for 8 hours to obtain graphene microcapsules. Example 2

[0028] A graphene microcapsule lithium battery electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the lithium salt is one or a mixture of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI and LiPO2F2; the organic solvent is a carbonate organic solvent; and the additive is fluoroethylene carbonate (FEC), graphene microcapsules and hyperbranched polyglycerol ester in a mass ratio of 10:4:0.5.

[0029] The mass proportions of the three raw materials, organic solvent, lithium salt and additives, are 84%, 12% and 4% respectively.

[0030] The carbonate organic solvent is a combination of EC+DMC+DEC in a volume ratio of 1:1:1.

[0031] The lithium salt is a mixture of LiPF6 and LiODFB in a mass ratio of 3:1.

[0032] A method for preparing a graphene microcapsule lithium battery electrolyte comprises the following steps: Step A: adding a formulated amount of hyperbranched polyglycerol ester to an organic solvent accounting for 18% of the total mass, stirring for 2 hours to form a micellar solution; then adding a formulated amount of graphene microcapsules to the micellar solution, sonicating for 25 minutes, stirring for 50 minutes, adding the remaining organic solvent, and stirring evenly to obtain a pre-dispersion solution; Step B: adding the formulated amount of lithium salt to the pre-dispersion obtained in step A, stirring evenly to obtain a lithium salt solution; Step C: adding a formulated amount of fluoroethylene carbonate to the lithium salt solution obtained in step B in several batches at a constant temperature of 25° C. under argon protection, and stirring evenly to obtain a graphene microcapsule lithium battery electrolyte.

[0033] The lithium salt in step B is a mixture of LiPF6 and LiODFB. Specifically, the lithium salt is dissolved in a gradient manner: the formulated amount of LiPF6 is added to the pre-dispersion obtained in step A, the temperature is controlled to ≤10°C, and stirred for 3 hours; the remaining LiODFB is slowly added, the temperature is raised to 25°C, and the mixture is kept warm and stirred for 6 hours.

[0034] The method for preparing graphene microcapsules according to an embodiment of the present invention is as follows: The preparation method of the graphene microcapsules of the present invention is as follows: (1) 9 parts by weight of paraffin wax and 100 parts by weight of a graphene oxide aqueous solution with a mass concentration of 2.5% and an average flake diameter of 5 μm are uniformly mixed at 65° C.; (2) 3 parts by weight of hydrazine hydrate are added and stirred for 35 hours; (3) the solution is atomized into tiny particles at 10° C. by a sprayer, and then sprayed into a blast cavity into which dry cold air at 10° C. is introduced, and the cold air removes moisture on the surface of the particles; (3) finally, reduction is performed at 45° C. for 4 hours, then at 65° C. for 4 hours, and finally at 125° C. for 7 hours to obtain graphene microcapsules. Example 3

[0035] A graphene microcapsule lithium battery electrolyte comprises an organic solvent, a lithium salt, and an additive. The lithium salt is one or a mixture of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI, and LiPO2F2; the organic solvent is a carbonate organic solvent; and the additive is fluoroethylene carbonate (FEC), graphene microcapsules, and hyperbranched polyglycerol ester in a mass ratio of 10:4:0.6.

[0036] The mass proportions of the three raw materials, organic solvent, lithium salt and additives, are 86%, 10% and 4% respectively.

[0037] The carbonate organic solvent adopts a combination of EC+DMC+EMC in a volume ratio of 1:1:1.

[0038] The lithium salt is a mixture of LiPF6 and LiODFB in a mass ratio of 4:1.

[0039] A method for preparing a graphene microcapsule lithium battery electrolyte comprises the following steps: Step A: adding a formulated amount of hyperbranched polyglycerol ester to an organic solvent accounting for 20% of the total mass, stirring for 3 hours to form a micellar solution; then adding a formulated amount of graphene microcapsules to the micellar solution, sonicating for 30 minutes, stirring for 60 minutes, adding the remaining organic solvent, and stirring evenly to obtain a pre-dispersion solution; Step B: adding the formulated amount of lithium salt to the pre-dispersion obtained in step A, stirring evenly to obtain a lithium salt solution; Step C: adding a formulated amount of fluoroethylene carbonate to the lithium salt solution obtained in step B in several batches at a constant temperature of 25° C. under argon protection, and stirring evenly to obtain a graphene microcapsule lithium battery electrolyte.

[0040] The lithium salt in step B is a mixture of LiPF6 and LiODFB. Specifically, the lithium salt is dissolved in a gradient manner: the formulated amount of LiPF6 is added to the pre-dispersion obtained in step A, the temperature is controlled to ≤10°C, and stirred for 4 hours; the remaining LiODFB is slowly added, the temperature is raised to 25°C, and the mixture is kept warm and stirred for 7 hours.

[0041] The method for preparing graphene microcapsules according to an embodiment of the present invention is as follows: The preparation method of the graphene microcapsules of the present invention is as follows: (1) 10 parts by weight of paraffin wax and 100 parts by weight of a graphene oxide aqueous solution with a mass concentration of 3% and an average flake diameter of 10 μm are uniformly mixed at 65° C.; (2) 4 parts by weight of hydrazine hydrate are added and stirred for 40 hours; (3) the solution is atomized into tiny particles at 10° C. by a sprayer, and then sprayed into a blast cavity into which dry cold air at 10° C. is introduced, and the cold air takes away moisture on the surface of the particles; (3) finally, reduction is performed at 50° C. for 3 hours, then at 70° C. for 3 hours, and finally at 130° C. for 6 hours to obtain graphene microcapsules.

[0042] Comparative Example 1

[0043] The difference between this comparative example and Example 2 is that the present invention does not use fluoroethylene carbonate FEC, and the additives are graphene microcapsules and hyperbranched polyglycerol esters in a mass ratio of 4:0.5.

[0044] Comparative Example 2

[0045] The difference between this comparative example and Example 2 is that the present invention does not use hyperbranched polyglycerol ester, and the additives are fluoroethylene carbonate FEC and graphene microcapsules in a mass ratio of 10:4.

[0046] Comparative Example 3

[0047] The difference between this comparative example and Example 2 is that the present invention does not use fluoroethylene carbonate and hyperbranched polyglycerol ester at the same time, and the additive is graphene microcapsules.

[0048] Experimental data

[0049] The high-temperature cycle (60°C) of the present invention adopts GB / T 31486-2015; the thermal runaway trigger temperature adopts UL 1642 (ARC test); the low-temperature discharge (-40°C) adopts SJ / T 11792-2021; and the ionic conductivity (25°C) adopts GB / T 36363-2018 (platinum black electrode). Specific performance indicators are shown in the table below.

[0050]

[0051] Comparative Example 1, which did not use fluoroethylene carbonate (FEC), failed to form a stable SEI film and thermal shield, leading to interfacial collapse and a significantly increased risk of thermal runaway. Comparative Example 2, which did not use hyperbranched polyglycerol ester, failed to maintain microcapsule dispersion stability and interfacial wettability, resulting in microcapsule failure, hindered ion transport, and ultimately a sharp reduction in cycle life.

[0052] In Comparative Example 3, the simultaneous absence of both HPG and FEC will cause the electrolyte to lose its triple protection of "structure-interface-thermal", greatly reducing the high-temperature cycle life, causing the thermal runaway temperature to plummet, and making the system unusable. This also illustrates the auxiliary role of HPG and FEC on graphene microcapsules and the coordination effect among the three.

[0053] Although an embodiment of the present invention has been shown and described, this specific embodiment is merely an explanation of the present invention and is not a limitation of the invention. The specific features, structures, materials or characteristics described may be combined in an appropriate manner in any one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions and variations to the embodiment without creative contribution as needed without departing from the principles and purpose of the present invention. However, as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A graphene microcapsule lithium battery electrolyte, characterized in that , including an organic solvent, a lithium salt and an additive, wherein the lithium salt is one or a mixture of LiPF6, LiBF4, LiBOB, LiODFB, LiTFSI, LiFSI, and LiPO2F2, the organic solvent is a carbonate organic solvent, and the additive is fluoroethylene carbonate FEC, graphene microcapsules and hyperbranched polyglycerol ester in a mass ratio of 10: (3-4): (0.3-0.6).

2. The graphene microcapsule lithium battery electrolyte according to claim 1, characterized in that: The mass proportions of the three raw materials, organic solvent, lithium salt and additives, are 80% to 86%, 10% to 14% and 4% to 6% respectively.

3. The graphene microcapsule lithium battery electrolyte according to claim 1, characterized in that: The particle size of the graphene microcapsules is 40-60 μm.

4. The graphene microcapsule lithium battery electrolyte according to claim 1, characterized in that: The carbonate organic solvent is any one or more of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

5. The graphene microcapsule lithium battery electrolyte according to claim 1, characterized in that: The carbonate organic solvent adopts a combination of EC+DMC+EMC or a combination of EC+DMC+DEC.

6. The graphene microcapsule lithium battery electrolyte according to claim 1, characterized in that: The lithium salt is a mixture of LiPF6 and LiODFB in a mass ratio of (3-4):

1.

7. The method for preparing a graphene microcapsule lithium battery electrolyte according to any one of claims 1 to 6, characterized in that: The method comprises the following preparation steps: Step A: adding a formulated amount of hyperbranched polyglycerol ester to an organic solvent accounting for 15% to 20% of the total mass, stirring for 2 to 3 hours to form a micellar solution; then adding a formulated amount of graphene microcapsules to the micellar solution, sonicating for 20 to 30 minutes, stirring for 40 to 60 minutes, adding the remaining organic solvent, and stirring uniformly to obtain a pre-dispersion solution; Step B: adding the formulated amount of lithium salt to the pre-dispersion obtained in step A, stirring evenly to obtain a lithium salt solution; Step C: adding a formulated amount of fluoroethylene carbonate to the lithium salt solution obtained in step B in several batches at a constant temperature of 25° C. under argon protection, and stirring evenly to obtain a graphene microcapsule lithium battery electrolyte.

8. The method for preparing a graphene microcapsule lithium battery electrolyte according to claim 1, characterized in that: The lithium salt in step B is a mixture of LiPF6 and LiODFB. Specifically, the lithium salt is dissolved in a gradient manner: the formulated amount of LiPF6 is added to the pre-dispersion obtained in step A, the temperature is controlled to ≤10°C, and stirred for 2-4 hours; the remaining LiODFB is slowly added, the temperature is raised to 25°C, and the mixture is kept warm and stirred for 5-7 hours.

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