Electrolyte and preparation method thereof, lithium battery and electronic equipment

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte, a preparation method thereof, a lithium battery and electronic equipment. The invention provides a preparation method of an electrolyte, which comprises the following steps: constructing a mixed organic solvent system by using fluoro-ether and fluoro-carbonate, cooling the mixed organic solvent system, adding a lithium salt, adding an additive A and an additive B after the lithium salt is completely dissolved, and mixing to obtain the required electrolyte. By constructing a mixed organic solvent system and adding a novel additive A to regulate and control the composition and structure of an SEI film, a compact, stable and low-impedance SEI film is formed, the obtained electrolyte can effectively prevent an electrode structure from being damaged, the safety of a lithium battery is improved, the service life of the lithium battery is prolonged, and meanwhile, the power performance and the cycle performance of the lithium battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium battery and an electronic device thereof. BACKGROUND

[0002] The research and application of silicon-based negative electrode high-power batteries are derived from the urgent demand for energy storage technology with high energy density and high power performance in global energy transformation. The current commercialized lithium ion battery mainly uses graphite negative electrode, and its theoretical specific capacity is only 372 mAh / g, which has reached the performance limit and is difficult to meet the needs of electric vehicle fast charging, electric tool high-current discharging, portable electronic device long endurance and other scenarios. Silicon-based materials have become the core choice of the next generation of negative electrode materials due to their high theoretical specific capacity of 4200 mAh / g (about 10 times that of graphite), suitable lithium intercalation potential of 0.1-0.4V vs. Li / Li + , and rich reserves of 26.4% of the crustal shell. The energy density of batteries using silicon-based negative electrodes can easily break through 300Wh / kg, and some products have reached more than 350Wh / kg. However, silicon-based materials have two inherent defects that seriously restrict high-power performance: First, the volume expansion rate during charging and discharging is as high as 300%, which is much higher than that of graphite (10%-12%), leading to electrode structure rupture, active material pulverization, and repeated rupture and reconstruction of the solid electrolyte interface (SEI) film, consuming a large amount of lithium ions and increasing internal resistance; Second, the intrinsic electrical conductivity is extremely low, leading to severe polarization and significant rate performance degradation under high current density.

[0003] Silicon-based negative electrodes are considered as the core technology direction of the next generation of high-specific-energy high-power batteries due to their extremely high theoretical energy density, but their commercialization process is limited by short cycle life, poor safety and other bottleneck problems. The current core problems of silicon-based high-power batteries are mainly due to the contradiction between the characteristics of silicon materials and the demand for high-power charging and discharging, including: (1) When lithium ions are rapidly intercalated and deintercalated, the volume expansion rate of silicon is as high as 300%, causing particle pulverization and electrode structure rupture; (2) The intrinsic electrical conductivity is low (10 -6 -10 -4 S / cm), and the lithium ion diffusion is slow, which hinders mass transfer and increases polarization under high power; (3) The volume expansion also causes the SEI film (Solid Electrolyte Interface) formed on the surface of the negative electrode material to repeatedly rupture and reconstruct, continuously consume lithium and generate insulating products, and exacerbate the increase of internal resistance and capacity decay. SUMMARY

[0004] In order to solve the problems of volume expansion, low conductivity and poor rate performance of silicon-based negative electrode, the application provides an electrolyte, a preparation method thereof, a lithium battery and an electronic device.

[0005] To solve the above technical problems, the application provides a preparation method of electrolyte, which comprises the following steps: providing lithium salt, organic solvent and additive, wherein the additive comprises additive A and additive B; mixing the organic solvent under inert atmosphere to construct a mixed organic solvent system; cooling the mixed organic solvent system to 0-10 DEG C, then adding one or more lithium salts to the mixed organic solvent system at a flow rate of 0.1-1 mL / min, after the lithium salt is completely dissolved, adding additive A and additive B, and mixing to obtain the required electrolyte. Wherein, the additive amount of additive A is 0.1%-5% of the total mass of electrolyte, and the additive amount of additive B is 0.1-3% of the total mass of electrolyte. Wherein, the additive A is selected from any one or combination of several compounds represented by formula [I]. Formula [I] Wherein, at least one of R1, R2, R3, R4, R5 and R6 is any one of fluorine or fluorinated alkyl, and the rest is selected from any one of hydrogen, halogen atom except fluorine atom, amino, epoxy, alkyl with carbon atom number of 1-5, unsaturated hydrocarbon group with carbon atom number of 2-50, and phenyl; the additive B comprises one or more of ethylene carbonate, fluorinated ethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, methylene methane disulfonate, lithium difluoro oxalate borate, lithium difluoro oxalate phosphate and propylene sulfonic acid lactone.

[0006] Further, the organic solvent accounts for 60%-85% of the total mass of electrolyte; and / or the organic solvent comprises fluorinated ether solvent and fluorinated carbonate solvent.

[0007] Further, the fluorinated ether solvent comprises one or more of 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, 3-fluorotetrahydrofuran, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane; and / or the partial fluorinated carbonate solvent comprises one or more of methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 4,4-difluoro ethylene carbonate, 4-(trifluoromethyl) ethylene carbonate.

[0008] Further, the organic solvent is fluorinated ether and fluorinated carbonate solvent, and the mass ratio of fluorinated ether solvent to fluorinated carbonate solvent is (2.5-5.5):1.

[0009] Further, the lithium salt comprises one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium borate, lithium perchlorate, lithium bis(pentafluoroethylsulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide); and / or the lithium salt is added in an amount of 15%-25% of the total mass of the electrolyte.

[0010] Further, the additive A further comprises: , ,

[0011] one or more of the following: lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium borate, lithium perchlorate, lithium bis(pentafluoroethylsulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide); and / or the additive A accounts for 0.5-3% of the total mass of the electrolyte; and the additive B is one or more of ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluoro(oxalato)borate (phosphate); and the additive B is added in an amount of 0.5-2% of the total mass of the electrolyte.

[0012] The application also provides an electrolyte prepared by the preparation method of the electrolyte as described above.

[0013] The application also provides a lithium battery, which comprises a positive electrode material, a negative electrode material, a separator, and an electrolyte as described above, wherein the negative electrode material comprises one or more of silicon-oxygen material, silicon-carbon material, nano-silicon material, and graphite material.

[0014] Further, the positive electrode material is any one of lithium cobaltate, lithium manganate, lithium-rich manganese-based, ternary nickel-cobalt-manganese lithium, lithium iron phosphate, lithium manganese iron phosphate; and / or the separator material is any one of polyethylene, polypropylene, or a combination thereof.

[0015] The application also provides an electronic device, which comprises a lithium battery as described above as an energy source.

[0016] Compared with the prior art, the electrolyte and the preparation method thereof, the lithium battery, and the electronic device provided by the application have the following beneficial effects: 1. The application provides a preparation method of an electrolyte, which comprises constructing a mixed organic solvent system by using a fluoroether group and a fluoro carbonate, adding a lithium salt after cooling the mixed organic solvent system, adding an additive A and an additive B after the lithium salt is completely dissolved, and mixing to obtain the required electrolyte. By constructing a mixed organic solvent system and adding a new additive A, which is specifically the additive A of formula [I], the composition and structure of the SEI film are controlled, a dense, stable, and low-impedance SEI film is formed, and the power performance and cycle performance of the lithium ion battery are improved.

[0017] 2. In the technical solution of the application, a mixed organic solvent system is constructed by using fluorinated ether solvent and part of fluorinated carbonate solvent, and the fluorinated ether and fluorinated carbonate solvent are used in combination, which has good reduction stability and lithium salt dissociation capacity, ensures the electrochemical stability of the electrolyte and the high lithium ion transmission capacity, and meanwhile, the combination of the two solvents can adjust the solvation structure of lithium ion and reduce the activation energy of desolvation of lithium ion.

[0018] 3. In the technical solution of the application, a new additive A is used, the silicon-oxygen bond (Si-O-Si) in the new additive A is covalently combined with the silicon surface, and the other end group (amino, epoxy, fluorine, etc.) can improve the compatibility of silicon and the binder, reduce the interface impedance, form a dense SEI film, maintain the long-term stability of the electrode, and also form a dense CEI film on the positive electrode surface to prevent the continuous oxidation and decomposition of the solvent, improve the stability of the electrolyte and the cycle performance of the battery.

[0019] 4. The combination of the new additive A and the conventional additive B used in the application can make the electrolyte have good oxidation stability, can transmit lithium ions at a high speed, and the electrolyte is not easy to be oxidized at high voltage, can prevent the continuous consumption of the electrolyte, and at the same time, ensures the effective dissociation of the electrolyte salt. The mixed use of the new additive and the conventional additive can adjust the solvation structure of lithium ion and reduce the activation energy of desolvation of lithium ion, thereby significantly reducing the charge transfer impedance. The use of the conventional additive can help the new additive to form a more dense and stable SEI film, and the formed SEI film is rich in inorganic elements such as S, F, B and P, which further reduces the film forming impedance.

[0020] 5. The application provides a preparation method of an electrolyte, and a mixed organic solvent system is constructed by using fluorinated ether solvent and fluorinated carbonate solvent in a mass ratio of (2.5-5.5), and the solvent system formed under the mass ratio has good lithium ion conductivity, can effectively transmit lithium ions, and enhances the conductivity of the electrolyte.

[0021] 6. In the technical solution of the application, additives A and B are added to the mixed organic solvent system, wherein the additive A accounts for 0.1%-5% of the total mass of the electrolyte, and the additive B accounts for 0.1-3% of the total mass of the electrolyte, and under the proportion, the two additives can better cooperate to construct a stable SEI film.

[0022] 7. The application provides an electrolyte, which uses fluorinated ether solvent and part of fluorinated carbonate solvent to construct a mixed organic solvent system to improve the lithium ion transmission capacity, and uses two types of additives to construct a dense, stable and low-impedance SEI film. By optimizing the solvation structure and interface chemistry of the electrolyte, the film forming impedance can be effectively reduced and the cycle stability can be improved.

[0023] 8. The electrolyte provided by the present application can be integrated with a positive electrode sheet including a positive electrode material such as lithium cobalt oxide, lithium manganate, lithium-rich manganese-based, ternary nickel-cobalt-manganese lithium, lithium iron phosphate, lithium manganese iron phosphate, etc. to prepare a lithium battery, and the electrolyte has wide applicability.

[0024] 9. The present application also provides a lithium battery including the electrolyte provided by the present application, which can improve the thermal stability and cycle capacity of the lithium battery, and the use of the electrolyte provided by the present application can construct a stable and dense SEI film, thereby effectively avoiding the rupture of the electrode structure and ensuring the safety and service life of the lithium battery.

[0025] 10. The present application also provides an electronic device using the lithium battery provided by the present application as a power supply, which can obtain a power supply module with good rate performance and more excellent cycle stability, thereby making the electronic device itself run more stably and have a longer service life. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0027] Figure 1 The specific step flow chart of the preparation method of the electrolyte provided by the first embodiment of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will further describe the present application in combination with the drawings and experimental examples. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0029] In the embodiments provided by the present application, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that the determination of B according to A does not mean that B is determined only according to A, but B can also be determined according to A and / or other information.

[0030] It should be understood that every feature, structure, or characteristic described in relation to an embodiment is within the scope of the present application, and can be combined with any other feature, structure, or characteristic described in relation to an embodiment, in any suitable manner. It should also be understood that the embodiments described in the specification are exemplary in nature, and are not necessarily laid out in order of importance.

[0031] In various embodiments of the present application, it should be understood that the magnitude of the serial number of the above-mentioned processes does not mean the inevitable sequence of execution order, and the execution order of the processes should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process defined by the present application.

[0032] In the flowcharts and block diagrams in the drawings of the present application, the methods and possible implemented architectures, functions and operations according to various embodiments of the present application are illustrated. In this regard, each block in the flowchart or block diagram can represent a part of a step. It should also be noted that in some alternative implementations, the functions denoted in the blocks can also occur in a different order from that denoted in the drawings. For example, two blocks denoted in succession can actually be executed substantially in parallel, and they can also be executed in reverse order, based on the functions involved.

[0033] Referring to Figure 1 The first embodiment of the present application provides a preparation method of electrolyte, specifically comprising the following steps: Step S1, providing a lithium salt, an organic solvent and an additive, wherein the additive comprises an additive A and an additive B; Step S2, mixing the organic solvent under an inert atmosphere to construct a mixed organic solvent system; and Step S3, cooling the mixed organic solvent system to 0-10℃, then adding the lithium salt to the mixed organic solvent system at a flow rate of 0.1-1 mL / min, after the lithium salt is dissolved, adding the additive A and the additive B, and mixing to obtain the required electrolyte.

[0034] In the above step S1, the lithium salt comprises one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate, lithium borate, lithium perchlorate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide) (LiTFSI), lithium bis(fluorosulfonylimide) (LiFSI).

[0035] Specifically, the organic solvent comprises a fluoroether solvent and a fluorocarbonate solvent, wherein the fluoroether solvent comprises one or more of 1,1,2,2-tetrafluoroethyl ethyl ether (TFEE), bis(2,2,2-trifluoroethyl) ether, 3-fluorotetrahydrofuran (3FTHF), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (OFDEE); the fluorocarbonate solvent comprises one or more of methyl trifluoroethyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (TFEC), 4,4-difluoroethylene carbonate, 4-(trifluoromethyl) ethylene carbonate.

[0036] In the present application, a mixed organic solvent system is constructed by using a fluoroether solvent and a fluorocarbonate solvent, which has good reduction stability and lithium salt dissociation capacity, can improve the conductivity of the electrolyte, ensure the electrochemical stability of the electrolyte and the high-efficiency lithium ion transmission capacity, and meanwhile, the use of the two solvents in combination can adjust the solvation structure of lithium ions and reduce the activation energy of desolvation of lithium ions.

[0037] The additive A is selected from any one or a combination of several of the compounds represented by formula [I]; Formula [I] In formula [I], at least one of R1, R2, R3, R4, R5 and R6 is any one of fluorine or a fluoroalkyl group, and the rest is selected from any one of hydrogen, a halogen atom other than fluorine, an amino group, an epoxy group, an alkyl group with 1-5 carbon atoms, an unsaturated hydrocarbon group with 2-50 carbon atoms, and a phenyl group.

[0038] Specifically, the additive A further comprises: , ,

[0039] one or a combination of several of the compounds represented by formula [I].

[0040] Further, in the embodiments of the present application, the additive B comprises one or more of ethylene carbonate, fluoroethylene carbonate (FEC), vinyl ethylene carbonate, vinyl sulfate (DTD), methylene methane disulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluoro(oxalato)phosphate (LiDFOP), vinylene carbonate (VC) and propenyl sulfonic acid lactone.

[0041] The additive A used in the application is a silane coupling agent additive, which is a new type of additive, and the additive B is a conventional additive. The Si-O-Si bond in the additive A covalently combines with the silicon surface, and the other end group (amino, epoxy, fluorine, etc.) can improve the compatibility of silicon and the binder, reduce the interface impedance, form a dense SEI film, maintain the long-term stability of the electrode, and also form a dense CEI film on the positive electrode surface to prevent the continuous oxidation and decomposition of the solvent, improve the stability of the electrolyte and the cycle performance of the battery. The use of conventional additives can help form a dense and low impedance SEI film, and comprehensively improve the cycle performance of the battery.

[0042] The combination of the new additive A and the conventional additive B can make the electrolyte have good oxidation stability, while being able to conduct lithium ions at high speed, and the electrolyte is not easy to oxidize at high voltage, which can prevent the continuous consumption of the electrolyte, while ensuring the effective dissociation of the electrolyte salt. The mixed use of the new additive A and the conventional additive B can adjust the solvation structure of lithium ions and reduce the activation energy of lithium ion desolvation, thereby significantly reducing the charge transfer impedance.

[0043] In the above step S2, the organic solvents are mixed under an inert atmosphere, and a mixed organic solvent system is constructed, wherein the inert atmosphere can be argon.

[0044] Specifically, the mixing of the organic solvents refers to the mixing of the fluoroether solvent and the fluoro carbonate solvent, wherein the fluoroether solvent includes one or more of 1,1,2,2-tetrafluoroethyl ethyl ether (TFEE), bis(2,2,2-trifluoroethyl) ether, 3-fluorotetrahydrofuran (3FTHF), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (OFDEE); the fluoro carbonate solvent includes one or more of methyl trifluoroethyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (TFEC), 4,4-difluoroethylene carbonate, 4-(trifluoromethyl) ethylene carbonate.

[0045] Specifically, the mass ratio of the fluoroether solvent to the partial fluoro carbonate solvent is (2.5-5.5):1, which can be (2.5-3):1, (2.5-3.5):1, (2.6-3.2):1, (3.0-4.0):1, (3.6-4.6):1, (5-5.5):1, etc., and specifically can be 2.5:1, 3.5:1, 3.6:1, 4:1, 4.5:1, 5:1 or 5.5:1.

[0046] Specifically, the organic solvent accounts for 60%-85% of the total mass of the electrolyte, and in some embodiments of the present application, can be 60%-65%, 62%-66%, 65%-70%, 65%-75%, 75%-80%, 75%-85%, etc., and specifically can be 60%, 62%, 65%, 70%, 75%, or 85%.

[0047] In the above step S3, the mixed organic solvent system is cooled to 0-10℃, and in some specific embodiments of the present application, the mixed organic solvent system can be cooled to 0-5℃, 2-4℃, 4-8℃, 5-10℃, 8-10℃, etc., and specifically, the mixed organic solvent system can be cooled to 0℃, 2℃, 4℃, 5℃, 8℃, or 10℃.

[0048] In the above step S3, the lithium salt is added to the mixed organic solvent system at a flow rate of 0.1-1 mL / min, and in some specific embodiments of the present application, the flow rate of the lithium salt can be 0.1-0.5 mL / min, 0.2-0.4 mL / min, 0.3-0.6 mL / min, 0.6-0.8 mL / min, 0.5-1 mL / min, etc., and specifically can be 0.1 mL / min, 0.2 mL / min, 0.4 mL / min, 0.5 mL / min, 0.8 mL / min, or 1 mL / min. The amount of the lithium salt added is 15%-25% of the total amount of the electrolyte, and in some embodiments of the present application, can be 15%-25%, 16%-18%, 15%-20%, 18%-24%, 20%-25%, etc., and specifically can be 15%, 16%, 18%, 20%, 24%, or 25%.

[0049] Further, in the above step S3, the additive A is added in an amount of 0.1%-5% of the total mass of the electrolyte, and in some embodiments of the present application, can be 0.1%-0.8%, 1%-2%, 1.5%-2.5%, 2.6%-3.6%, 3.5%-4.5%, 4%-5%, etc., and specifically can be 0.1%, 0.8%, 1.5%, 2.6%, 4%, or 5%; the additive B is added in an amount of 0.1-3% of the total mass of the electrolyte, and in some embodiments of the present application, can be 0.1%-0.8%, 0.1%-1%, 1%-1.5%, 1.6%-2.5%, 2.5%-3%, etc., and specifically can be 0.1%, 0.8%, 1%, 1.2%, 2%, or 3%.

[0050] The second embodiment of the present invention provides an electrolyte prepared based on the electrolyte preparation method provided in the first embodiment above. Specifically, a mixed organic solvent system is constructed using fluoroether groups and fluorocarbonates. After cooling the mixed organic solvent system, lithium salt is added. After the lithium salt is completely dissolved, additives A and B are added, and the mixture is then used to obtain the desired electrolyte.

[0051] The electrolyte provided in the second embodiment of the present invention has good oxidation stability and can conduct lithium ions at high speed. The electrolyte is not easily oxidized under high voltage, which can prevent the continuous consumption of the electrolyte and ensure the effective dissociation of electrolyte salt.

[0052] The third embodiment of the present invention provides a lithium battery, specifically including a positive electrode material, a negative electrode material, a separator, and the electrolyte described in the second embodiment above.

[0053] The negative electrode material includes any one or a combination of silicon-oxygen materials, silicon-carbon materials, nano-silicon materials, and graphite materials; the positive electrode material is any one of lithium cobalt oxide, lithium manganese oxide, lithium-rich manganese-based materials, ternary nickel-cobalt-manganese lithium, lithium iron phosphate, and lithium manganese-iron phosphate; the separator material is a coated separator of any one or a combination of polyethylene and polypropylene.

[0054] Specifically, the preparation of the lithium battery according to the third embodiment of the present invention includes the following steps: Preparation of positive electrode sheet using positive electrode material: The positive electrode material, conductive agent and binder are mixed evenly according to the preset mass, and then dispersed in the positive electrode solvent to obtain positive electrode slurry. The slurry is then evenly coated on both sides of aluminum foil, and the positive electrode sheet is obtained after drying, rolling and die cutting. The positive electrode solvent can be any one or any combination of N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), etc.; the mass ratio of positive electrode material: conductive agent: binder is (90-98):(1-5):(1-5), further, the mass ratio of positive electrode material: conductive agent: binder can also be (90-96):(2-5):(2-5), (95-98):(1-3):(1-3), etc.; specifically, the mass ratio of positive electrode material: conductive agent: binder is 96:2:2, 98:1:1, 97:2:1 or 96:3:1, etc.

[0055] Anode material is used to prepare the anode sheet: the anode material, lithium metal, and current collector copper are pressed together to form a lithium foil with a thickness of 50μm~200μm, and then die-cut to obtain the anode sheet. To further improve the stability of the lithium layer on the anode substrate, the electrode sheet can be lightly hot-pressed in an inert environment (temperature 50℃~80℃, pressure 3~5MPa, time 30~60s) to enhance the interfacial bonding between lithium and copper foil.

[0056] In some embodiments of the present invention, the thickness of the lithium foil is 50μm to 200μm, and may further be 50μm to 80μm, 50μm to 100μm, 100μm to 120μm, 120μm to 140μm, 150μm to 200μm, etc., specifically 50μm, 80μm, 100μm, 120μm, 150μm or 200μm.

[0057] An ultra-thin protective layer can be coated on the surface of the electrode, such as aluminum oxide or lithium fluoride. The thickness of the protective layer is 1~5μm, which inhibits the growth of lithium dendrites and is suitable for scenarios with high safety requirements.

[0058] Lithium-ion battery integration: The positive electrode, separator, and negative electrode are stacked in sequence to ensure that the separator separates the positive and negative electrode and that the negative electrode completely covers the positive electrode. The stacked cells are then placed in an aluminum-plastic film packaging bag. The electrolyte prepared above is then injected into the cells. The lithium-ion battery is then manufactured after processes such as sealing, formation, aging, and secondary sealing and capacity testing.

[0059] In some embodiments of the present invention, the capacity of the lithium battery is greater than 20,000 mAh. More specifically, the capacity of the lithium battery is greater than 20,000 mAh, greater than 22,000 mAh, greater than 25,000 mAh, greater than 28,000 mAh, greater than 30,000 mAh, etc. Specifically, the capacity of the lithium battery may be 20,000 mAh, 21,000 mAh, 22,000 mAh, 25,000 mAh, 28,000 mAh, or 30,000 mAh.

[0060] The fourth embodiment of the present invention provides an electronic device that uses the lithium battery provided in the third embodiment of the present invention as a power source, thereby obtaining a power module with good conductivity and better cycle stability, which in turn makes the electronic device itself operate more stably and has a longer service life.

[0061] The lithium battery of the third embodiment of the present invention has advantages such as high energy density and is currently mainly used in electric vehicles, smartphones, unmanned devices, humanoid robots, home energy storage systems, and mobile charging systems.

[0062] The aforementioned lithium battery features high energy density, reaching up to 400Wh / kg, allowing it to store more energy in the same volume, demonstrating a significant advantage in space-constrained applications. Furthermore, the use of a silicon-carbon composite anode enables longer battery life and supports high-rate charging, meeting the needs of various usage scenarios.

[0063] In order to better illustrate the effects of the electrolyte, its preparation method, lithium battery, and electronic device claimed in this invention, the following experimental examples and comparative examples are used for comparison and explanation.

[0064] Experimental Example 1: (1) Preparation of electrolyte: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), 1,1,2,2-tetrafluoroethyl ether (TFEE) and methyl trifluoroethyl carbonate (FEMC) were mixed evenly at 55% and 20% of the total weight of the electrolyte, respectively, to obtain a mixed organic solvent system. The mixed organic solvent system was then placed in an environment of 5°C for cooling. Then, 20% of the total weight of lithium hexafluorophosphate (LiPF6) was slowly added. After complete dissolution, 3% of the total weight of the electrolyte, additive A (molecular formula I as follows) was added. Subsequently, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added (each added at 1% of the total weight of the electrolyte). After stirring evenly and dissolving completely, electrolyte a was obtained.

[0065] (Molecular Formula I) (2) Preparation of lithium batteries Lithium batteries consist of lithium cobalt oxide cathode material, silicon-carbon / graphite anode material, separator, and electrolyte.

[0066] Prepare positive electrode sheet using positive electrode material: Mix lithium cobalt oxide positive electrode material, conductive agent carbon black Super-P and binder polyvinylidene fluoride (PVDF) evenly at a mass ratio of 96:2:2, then disperse them in N-methyl-2-pyrrolidone (NMP) to obtain positive electrode slurry, then coat the slurry evenly on both sides of aluminum foil, and obtain positive electrode sheet after drying and rolling.

[0067] Anode sheet preparation using anode material: A mixture of silicon-carbon / graphite anode material, lithium metal and current collector copper are pressed together to form a lithium foil with a thickness of 150μm, and then die-cut to obtain the anode sheet.

[0068] Lithium battery integration: The positive electrode, separator, and negative electrode are stacked in sequence to obtain a stacked cell, ensuring that the separator separates the positive and negative electrodes and that the negative electrode completely covers the positive electrode. The stacked cell is then placed in an aluminum-plastic film packaging bag, and electrolyte a is injected into the cell. After sealing, formation, aging, and secondary sealing and capacity testing, a lithium-ion battery with a capacity of 20,000 mAh is produced.

[0069] Experimental Example 2: (1) Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen < 0.1 ppm), bis(2,2,2-trifluoroethyl) ether and di(2,2,2-trifluoroethyl) carbonate (TFEC) were mixed evenly at 64% and 16% of the total weight of the electrolyte, respectively, to obtain a mixed organic solvent system. The mixed organic solvent system was then placed in an environment of 5°C for cooling. Then, 18% of the total weight of the electrolyte, lithium bis(fluorosulfonylimide) (LiFSI) was slowly added. After complete dissolution, 1% of the total weight of the electrolyte, additive A (molecular formula II as follows) was added. Then, vinyl sulfate (DTD) and fluoroethylene carbonate (FEC) were added (both at 0.5% of the total weight of the electrolyte). After stirring evenly and dissolving completely, electrolyte b was obtained.

[0070] (Molecular Formula II) (2) Preparation of lithium battery: lithium-rich manganese-based cathode material and electrolyte b were used. The other materials and methods were completely consistent with those in Experiment 1.

[0071] Experimental Example 3: (1) Preparation of electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), 3-fluorotetrahydrofuran (3FTHF) and 4,4-difluoroethylene carbonate were mixed evenly at 58% and 12% of the total weight of the electrolyte, respectively, to obtain a mixed organic solvent system. The mixed organic solvent system was then placed in an environment of 5°C for cooling. Then, 22% of the total weight of the electrolyte, lithium bis(fluorosulfonylimide) (LiFSI) was slowly added. After complete dissolution, 1.5% of the total weight of the electrolyte, additive A (molecular formula III as follows) was added. Subsequently, lithium difluorooxalate borate (LiDFOB) and vinylene carbonate (VC) were added (both at 0.75% of the total weight of the electrolyte). After stirring evenly and dissolving completely, electrolyte c was obtained.

[0072] (Molecular Formula III) (2) Preparation of lithium battery: Ternary nickel-cobalt-manganese lithium (NCM811) cathode material and electrolyte c were used. The other materials and methods were completely consistent with those in Experiment 1.

[0073] Experiment Example 4: (1) Preparation of electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (OFDEE) and 4-(trifluoromethyl)ethylene carbonate were mixed evenly at 56% and 19% of the total weight of the electrolyte, respectively, to obtain a mixed organic solvent system. The mixed organic solvent system was then placed in an environment of 5°C for cooling. Then, 20% of the total weight of the electrolyte, lithium bis(trifluoromethanesulfonylimide) (LiTFSI) was slowly added. After complete dissolution, 2% of the total weight of the electrolyte, additive A (molecular formula IV as follows) was added. Subsequently, lithium difluorooxalate phosphate (LiDFOP) and vinylene carbonate (VC) were added (both at 1.5% of the total weight of the electrolyte). After stirring evenly and dissolving completely, electrolyte d was obtained.

[0074] (Molecular Formula IV) (2) Preparation of lithium battery: Electrolyte d was used, and the other materials and preparation methods were completely consistent with those in Experiment 1.

[0075] Experimental Example 5: (1) Preparation of electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), 1,1,2,2-tetrafluoroethyl ether (TFEE), bis(2,2,2-trifluoroethyl) ether, and methyl trifluoroethyl carbonate (FEMC) were mixed evenly at 22%, 40%, and 13% of the total weight of the electrolyte, respectively, to obtain a mixed organic solvent system. The mixed organic solvent system was then placed in an environment of 5°C for cooling. Then, 20% of the total weight of lithium hexafluorophosphate (LiPF6) was slowly added. After complete dissolution, 2.5% of the total weight of additive A (molecular formula V as follows) was added. Then, vinyl sulfate (DTD) was added (the amount added was 2.5% of the total weight of the electrolyte). After stirring evenly and dissolving completely, electrolyte e was obtained.

[0076] (Molecular formula V) (2) Preparation of lithium battery: lithium-rich manganese-based cathode material and electrolyte e were used. The other materials and methods were completely consistent with those in Experiment 1.

[0077] Comparative Example 1: (1) Preparation of electrolyte: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), 1,1,2,2-tetrafluoroethyl ether (TFEE) and methyl trifluoroethyl carbonate (FEMC) were mixed evenly at 55% and 20% of the total weight of the electrolyte, respectively, to obtain a mixed organic solvent system. The mixed organic solvent system was then placed in an environment of 5°C for cooling. Then, 20% of the total weight of lithium hexafluorophosphate (LiPF6) was slowly added. After complete dissolution, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (both added at 2.5% of the total weight of the electrolyte) were added. After stirring evenly and dissolving completely, electrolyte 1 was obtained.

[0078] (2) Preparation of lithium battery: Electrolyte 1 was used, and the other materials and preparation methods were completely consistent with those in Experiment 1.

[0079] Comparative Example 2: (1) Preparation of electrolyte: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), 75% of the total weight of 1,1,2,2-tetrafluoroethyl ether (TFEE) solvent was placed in an environment of 5°C for cooling. Then, 20% of the total weight of lithium hexafluorophosphate (LiPF6) was slowly added. After complete dissolution, 3% of the total weight of additive A (molecular formula I as follows) was added. Then, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added (each added at 1% of the total weight of electrolyte). After stirring evenly and dissolving completely, electrolyte 2 was obtained.

[0080] (Molecular Formula I) (2) Preparation of lithium battery: Electrolyte 2 was used, and the other materials and preparation methods were completely consistent with those in Experiment 1.

[0081] Comparative Example 3: (1) Preparation of electrolyte: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), 75% of the total weight of the electrolyte, 1,1,2,2-tetrafluoroethyl ether (TFEE) solvent was placed in an environment of 5°C for cooling. Then, 20% of the total weight of the electrolyte, lithium hexafluorophosphate (LiPF6) was slowly added. After complete dissolution, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (each added at 2.5% of the total weight of the electrolyte) were added. After stirring evenly and dissolving completely, electrolyte 3 was obtained.

[0082] (2) Preparation of lithium battery: Electrolyte 3 was used, and the other materials and preparation methods were completely consistent with those in Experiment 1.

[0083] The electrolyte composition of Experimental Examples 1-5 and Comparative Examples 1-3 was compared. The ionic conductivity of the electrolytes obtained in Experimental Examples 1-5 and Comparative Examples 1-3 was measured. The internal resistance and capacity retention of the lithium batteries obtained in Experimental Examples 1-5 and Comparative Examples 1-3 were also measured.

[0084] The ionic conductivity of the electrolyte was tested using a conductivity meter. The lithium batteries, after capacity testing, were subjected to charge-discharge cycles at 1C at room temperature (25℃) and high temperature (45℃), with a cutoff voltage range of 2.7~4.4V. The capacity retention rate and internal resistance of the batteries after 1C / 5C cycles were statistically analyzed.

[0085] Table 1. Electrolyte composition and corresponding lithium battery performance test results of the examples and comparative examples.

[0086] As shown in Table 1, the lithium batteries in Examples 1-5 used electrolytes prepared based on the preparation method provided by the present invention. The ionic conductivity of the electrolytes in Examples 1-5 was greater than 9.8 ms / cm, the internal resistance of the lithium batteries in Examples 1-5 was less than 0.91 mΩ, and the capacity retention rate after 400 cycles was greater than 81.8%.

[0087] The electrolyte obtained in Example 1 had an ionic conductivity of 12.35 ms / cm, an internal resistance of 0.82 mΩ for the lithium battery, and a 400-cycle capacity retention of 83.6%. The electrolyte obtained in Comparative Example 1 had a lower conductivity (9.15 ms / cm) and a lower 400-cycle capacity retention (71.3%) than Example 1, but a higher internal resistance (1.13 mΩ). Compared to Example 1, the electrolyte in Comparative Example 1 did not contain additive A, resulting in a lower lithium battery performance. The lack of additive A leads to a less dense SEI film, higher impedance, and affects the uniform transport of lithium ions within the SEI film, thus weakening the cycle performance of the lithium battery. The electrolyte obtained in Comparative Example 2 had a lower conductivity (8.53 ms / cm) and a lower 400-cycle capacity retention (76.8%) than Example 1, but a higher internal resistance (1.09 mΩ). Compared to Example 1, the electrolyte in Comparative Example 2 contained only a fluoroether solvent (1,1,2,2-tetrafluoroethyl ether (TFEE)) and did not include a fluorocarbonate solvent (methyltrifluoroethyl carbonate (FEMC)). The absence of a mixed organic solvent system resulted in a significantly lower electrolyte conductivity, which also affected the lithium-ion desolvation energy and led to a significant reduction in the cycle performance of the lithium battery. The electrolyte obtained in Comparative Example 3 had a lower conductivity (7.35 ms / cm) and a lower 400-cycle capacity retention (75.2%) than that of Example 1, but a higher internal resistance (1.19 mΩ). Compared to Example 1, the electrolyte in Comparative Example 3 lacked additive A and a mixed organic solvent system, resulting in significantly lower conductivity and reduced cycle performance of the lithium battery.

[0088] The electrolyte, its preparation method, lithium battery, and electronic device disclosed in the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an electrolyte, characterized in that: It includes the following steps: Lithium salts, organic solvents, and additives are provided, wherein the additives include additive A and additive B; Organic solvents are mixed under an inert atmosphere to construct a mixed organic solvent system; After cooling the mixed organic solvent system to 0℃-10℃, one or more lithium salts are added to the mixed organic solvent system at a flow rate of 0.1-1 mL / min. After the lithium salts are completely dissolved, additive A and additive B are added and mixed to obtain the desired electrolyte. Wherein, the amount of additive A added is 0.1%-5% of the total mass of the electrolyte, and the amount of additive B added is 0.1%-3% of the total mass of the electrolyte; Wherein, the additive A is selected from any one or a combination of several compounds represented by formula [I]; Formula [I] Among them, at least one of R1, R2, R3, R4, R5 and R6 is fluorine or any one of fluoroalkyl, and the rest are selected from hydrogen, halogen atoms other than fluorine atoms, amino, epoxy, alkane group with 1 to 5 carbon atoms, unsaturated hydrocarbon group with 2 to 50 carbon atoms, and phenyl. Additive B includes one or more of the following: ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, ethylene sulfate, methane disulfonate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, and propylene sulfonate lactone.

2. The method for preparing an electrolyte as described in claim 1, characterized in that: The organic solvent accounts for 60%-85% of the total mass of the electrolyte; and / or the organic solvent includes fluoroether solvents and fluorocarbonate solvents.

3. The method for preparing an electrolyte as described in claim 2, characterized in that: The fluoroether solvent includes one or more of 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, 3-fluorotetrahydrofuran, and 1,2-bis(1,1,2,2-tetrafluoroethoxy) ethane; and / or the partially fluorocarbonate solvent includes one or more of methyltrifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, 4,4-difluoroethylene carbonate, and 4-(trifluoromethyl)ethylene carbonate.

4. The method for preparing an electrolyte as described in claim 2, characterized in that: The organic solvent is a fluoroether solvent and a fluorocarbonate solvent, and the mass ratio of the fluoroether solvent to the fluorocarbonate solvent is (2.5-5.5):

1.

5. The method for preparing an electrolyte as described in claim 1, characterized in that: The lithium salt includes one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium borate, lithium perchlorate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), and lithium bis(fluorosulfonylimide); and / or the amount of the lithium salt added is 15%-25% of the total mass of the electrolyte.

6. The method for preparing an electrolyte as described in claim 1, characterized in that: The additive A further comprises: 、 、 Any one or more of the above; and / or the amount of additive A added is 0.5-3% of the total mass of the electrolyte; The additive B is one or more of ethylene carbonate, fluoroethylene carbonate, ethylene sulfate, lithium difluorooxalate borate, and lithium difluorooxalate phosphate, and the amount added is 0.5 to 2% of the total mass of the electrolyte.

7. An electrolyte, characterized in that, The electrolyte is prepared using the method described in any one of claims 1-6.

8. A lithium battery, characterized in that: It includes a positive electrode material, a negative electrode material, a separator, and an electrolyte as described in claim 7, wherein the negative electrode material includes any one or more of silicon-oxygen materials, silicon-carbon materials, nano-silicon materials, and graphite materials.

9. The lithium battery as described in claim 8, characterized in that: The cathode material is any one of lithium cobalt oxide, lithium manganese oxide, lithium-rich manganese-based oxide, ternary nickel-cobalt-manganese lithium, lithium iron phosphate, and lithium manganese iron phosphate; and / or the separator material is any one of polyethylene, polypropylene, or a combination thereof.

10. An electronic device, characterized in that: It includes lithium batteries as an energy source as described in any one of claims 8-9.

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