Electrolyte, electrochemical device and vehicle
Patent Information
- Application Number
- CN202410186341.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-02-19
- Publication Date
- 2025-08-26
Smart Images
Figure BDA0004707112830000021 
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Abstract
Description
Technical Field
[0001] The present application belongs to the technical field of secondary batteries, and in particular relates to an electrolyte, an electrochemical device, and a vehicle. Background Art
[0002] With the increasing popularity of electric vehicles, lithium-ion batteries have become one of the most widely used secondary batteries due to their advantages of high voltage, high energy density, and long cycle life. However, with technological advancements, more stringent requirements have been placed on lithium-ion batteries, including energy density and high-temperature cycle performance.
[0003] Among currently known anode materials, silicon has the highest theoretical capacity (4200 mAh / g). This capacity is significantly higher than that of graphite anodes (372 mAh / g). Silicon-doped silicon-carbon anode materials, however, have a theoretical capacity of 400-650 mAh / g, also exceeding that of graphite. Therefore, the application of silicon in lithium-ion batteries has attracted widespread attention in order to increase the energy density.
[0004] In order to maximize the energy density of lithium-ion batteries, the most ideal approach is to use high-nickel ternary cathode materials in combination with silicon anodes. However, while using high-nickel ternary cathode materials in combination with silicon anodes to improve the energy density of lithium-ion batteries also brings some problems: because of the large volume expansion of silicon (up to 300%), the SEI film of the silicon anode is constantly broken during the cycle due to the expansion of silicon, and the exposed new interface re-forms the SEI film, causing the electrolyte to be continuously consumed, eventually leading to electrolyte drying up and rapid cycle decay; at the same time, at high temperatures, the high-nickel ternary cathode material has an increased nickel content, and the cathode interface and electrolyte are unstable. The cathode and electrolyte are very likely to undergo side reactions, which further accelerates the consumption of the electrolyte and deteriorates the high-temperature cycle performance.
[0005] Therefore, for lithium-ion batteries using high-nickel ternary positive electrode materials and silicon systems, how to improve high-temperature cycle performance is an urgent problem that needs to be solved. Summary of the Invention
[0006] The present application aims to solve one of the technical problems in the related art at least to a certain extent.
[0007] In view of this, one object of the present application is to provide an electrolyte containing fluoroethylene carbonate (FEC), an unsaturated silicon compound, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein FEC can form an SEI film to improve the high-temperature cycle performance, and the unsaturated silicon compound can capture HF produced by the reaction of FEC and lithium hexafluorophosphate, which will deteriorate the cycle performance and prevent it from damaging the positive electrode interface, so as to ensure the stability of the high-temperature cycle performance, thereby improving the high-temperature cycle performance of the lithium-ion battery as a whole.
[0008] Another object of the present application is to provide an electrochemical device.
[0009] Yet another object of the present application is to provide a vehicle.
[0010] To achieve the above-mentioned objectives, the first aspect of the present application provides an electrolyte comprising fluoroethylene carbonate, an unsaturated silicon compound and a lithium salt; the lithium salt comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the mass content of the fluoroethylene carbonate in the electrolyte is a%, the mass content of the unsaturated silicon compound in the electrolyte is b%, the mass content of the lithium hexafluorophosphate in the electrolyte is c%, and the mass content of the lithium bis(fluorosulfonyl)imide in the electrolyte is d%, 1≤a≤12, 0.01≤b≤1, 3≤c≤15, and 1≤d≤12.
[0011] In some embodiments, c and d satisfy the following relationship: 8≤c+d≤18.
[0012] In some embodiments, c and d satisfy the following relationship: 0.25≤c / d≤15.
[0013] In some embodiments, a, c, and d satisfy the following relationship: 0.05≤(c / d) / a≤5.
[0014] In some embodiments, a, b, c, and d satisfy the following relationship: 0.01≤b / [(c / d) / a]≤2.
[0015] In some embodiments, the unsaturated silicon compound has a structure shown in Formula I:
[0016]
[0017] Wherein, n is an integer of 0-3, R1, R2, and R3 are each independently selected from at least one of fluorine, alkenyl, alkynyl, alkyl, or substituted alkyl, and the substituent element in the substituted alkyl is fluorine.
[0018] Preferably, the unsaturated silicon compound is selected from at least one of compounds 1-8:
[0019]
[0020] In some embodiments, the electrolyte further includes a non-aqueous organic solvent, and the non-aqueous solvent includes a carbonate compound.
[0021] A second aspect of the present application provides an electrochemical device comprising the electrolyte described in the present application.
[0022] In some embodiments, the electrochemical device further includes a negative electrode, the negative electrode includes a negative electrode active material, and the negative electrode active material includes a silicon material.
[0023] In some embodiments, the silicon material comprises SiO z , of which 0.5 <z<1.5。
[0024] In some embodiments, the negative electrode active material further includes a graphite material.
[0025] In some embodiments, the electrochemical device further includes a positive electrode, the positive electrode includes a positive electrode active material, and the positive electrode active material includes a layered lithium composite oxide.
[0026] In some embodiments, the chemical formula of the layered lithium composite oxide is Li 1+x Ni m Co y Mn (1-m-y) O2, where -0.1≤x≤0.2; 0.5≤m≤1, 0.05≤y≤0.5, 0≤1-my≤0.45.
[0027] A third aspect of the present application provides a vehicle comprising the electrochemical device described in the present application.
[0028] The electrolyte of the present application can at least bring the following beneficial effects:
[0029] The electrolyte contains fluoroethylene carbonate (FEC), unsaturated silicon compounds, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. FEC can form an SEI film to improve high-temperature cycle performance, while the unsaturated silicon compound can capture HF produced by the reaction of FEC and lithium hexafluorophosphate, which will deteriorate the cycle performance, and prevent it from damaging the positive electrode interface, thereby ensuring the stability of high-temperature cycle performance and improving the high-temperature cycle performance of lithium-ion batteries as a whole.
[0030] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. DETAILED DESCRIPTION
[0031] The embodiments of the present application are described in detail below. The embodiments are exemplary and intended to be used to explain the present application, but should not be understood as limiting the present application.
[0032] Throughout this application, the disclosure of numerical ranges includes disclosure of all values within the entire range and further subdivided ranges, including the endpoints and subranges given within those ranges.
[0033] In this application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be obtained through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.
[0034] The electrolyte of an embodiment of the present application includes fluoroethylene carbonate (FEC), an unsaturated silicon compound and a lithium salt; the lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI); the mass content of fluoroethylene carbonate in the electrolyte is a%, the content of the unsaturated silicon compound in the electrolyte is b%, the mass content of lithium hexafluorophosphate in the electrolyte is c%, and the content of lithium bis(fluorosulfonyl)imide in the electrolyte is d%, 1≤a≤12, 0.01≤b≤1, 3≤c≤15, 1≤d≤12.
[0035] The inventors discovered that due to the large volume expansion of silicon (up to 300%), the volume of the silicon anode continuously expands and contracts during cycling, causing the SEI film of the silicon anode to continuously rupture and expose new interfaces. Adding FEC can effectively form an SEI at this fresh interface, thereby preventing the consumption of other electrolyte components on the silicon surface and improving high-temperature cycling performance. Therefore, increasing the silicon content requires more FEC to participate in interface repair. However, at high temperatures, the reaction of FEC with lithium hexafluorophosphate (LiPF6) produces HF, which damages the cathode interface, increasing positive electrode side reactions, consuming active lithium, and ultimately degrading high-temperature cycling performance. The inventors further discovered that unsaturated silicon compounds, due to their silicon base, can capture HF by breaking the silicon-carbon bond. Furthermore, the unsaturated silicon base forms a dense protective film on the cathode, preventing HF from damaging the cathode interface. Therefore, adding unsaturated silicon compounds to silicon-based electrolytes containing FEC and lithium hexafluorophosphate (LiPF6) can ensure the stability of high-temperature cycling performance, ultimately improving the high-temperature performance of lithium-ion batteries. At the same time, when the content ratio of FEC, LiPF6 and unsaturated silicon compound is controlled within the range defined in the embodiments of the present application, optimal high-temperature cycle performance can be obtained.
[0036] As a non-limiting example, the value of a includes but is not limited to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, etc.
[0037] As a non-limiting example, the value of b includes but is not limited to 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc.
[0038] As a non-limiting example, the value of c includes but is not limited to 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, etc.
[0039] As a non-limiting example, the value of d includes but is not limited to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, etc.
[0040] In some embodiments, c and d satisfy the following relationship: 8≤c+d≤18.
[0041] As a non-limiting example, the sum of c and d includes but is not limited to 8, 9, 10, 11, 12, 13, 14, 15, 16 or 17. In the embodiments of the present application, if the total mass content of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte is less than 8%, the lithium ion content is low and sufficient lithium ions cannot be effectively provided, resulting in poor battery cell dynamics; if it is greater than 18%, the lithium salt content is too high, the electrolyte viscosity is high, and lithium ions cannot be effectively migrated, resulting in poor battery cell dynamics.
[0042] In some embodiments, c and d satisfy the following relationship: 0.25≤c / d≤15.
[0043] As a non-limiting example, the ratio of c to d includes but is not limited to 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 8, 10, 11, 12, 13, 14 or 15. In the embodiment of the present application, if the ratio of the mass content of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte is less than 0.2, the LiFSI content is high, causing corrosion of the positive electrode current collector, resulting in an increase in the internal resistance of the battery cell and performance degradation; if it is greater than 15, the LiFSI content is low, which affects the kinetic performance on the one hand, and on the other hand, the high content of LiPF6 decomposes to produce a high content of HF, corrodes silicon and SEI and CEI, resulting in degradation of the battery cell performance.
[0044] In some embodiments, a, c, and d satisfy the following relationship: 0.05≤(c / d) / a≤5.
[0045] As a non-limiting example, the values of (c / d) / a include but are not limited to 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75 or 5, etc. In the embodiments of the present application, if the value of (c / d) / a is less than 0.05, the LiFSI content is high, and the risk of corrosion of the aluminum foil is high. In addition, the high content of FEC can decompose HF, thereby further exacerbating the risk of corrosion of the aluminum shell and causing performance degradation; if it is greater than 1.5, the LiPF6 content is high, and its film-forming effect on the negative electrode is weaker than that of LiFSI, and the content of FEC, a negative electrode SEI film repair additive, is low, resulting in an unstable negative electrode SEI film and poor high-temperature cycle performance of the battery cell.
[0046] In some embodiments, a, b, c, and d satisfy the following relationship: 0.01≤b / [(c / d) / a]≤2.
[0047] As a non-limiting example, the values of b / [(c / d) / a] include, but are not limited to, 0.01, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0, etc. In the embodiment of the present application, if the value of b / [(c / d) / a] is less than 0.01, the LiPF6 content is high, the FEC content is high, the unsaturated silicon compound is small, the LiFSI content is low, the FEC and LiPF6 react at high temperature, and the unsaturated silicon compound is small, HF cannot be effectively captured, and the positive electrode protection is insufficient, resulting in poor high-temperature cycle performance; if it is greater than 2, the LiPF6 content is low, the FEC content is low, the unsaturated silicon compound is high, the reaction degree of FEC and LiPF6 is low, and the use of a high content of unsaturated silicon compound is seriously excessive, resulting in the formation of a thick interface layer at the positive and negative electrode interfaces, which hinders the lithium ion conductivity and thus leads to poor cycle performance.
[0048] In some embodiments, the unsaturated silicon compound has the structure shown in Formula I:
[0049]
[0050] Wherein, n is an integer of 0-3, R1, R2, and R3 are each independently selected from at least one of fluorine, alkenyl, alkynyl, alkyl, or substituted alkyl, and the substituent element in the substituted alkyl is fluorine.
[0051] As a non-limiting example, n is 0, 1, 2 or 3.
[0052] As an optional example, R1, R2, and R3 are each independently selected from fluorine, C 2-5 Alkenyl, C 2-5 Alkynyl, C 1-5 Alkyl or substituted C 1-5 At least one of the alkyl groups, substituted C 1-5 The substituent element in the alkyl group is fluorine.
[0053] It should be noted that, in the embodiments of this application, the prefix "C u-v " indicates that the following group has from u to v carbon atoms. For example, "C 1-5 "Alkyl" means an alkyl group having 1 to 5 carbon atoms.
[0054] As a non-limiting example, the number of carbon atoms in the alkenyl or alkynyl groups in R1, R2, and R3 includes, but is not limited to, 2, 3, 4, or 5.
[0055] As a non-limiting example, the number of carbon atoms in the alkyl or substituted alkyl groups in R1, R2, and R3 includes, but is not limited to, 1, 2, 3, 4, or 5.
[0056] It should be noted that the number of carbon atoms in the alkenyl, alkynyl, alkyl or substituted alkyl groups in R1, R2 and R3 may be the same or different.
[0057] As a preferred embodiment, the unsaturated silicon compound is selected from at least one of compounds 1-8:
[0058]
[0059] In some embodiments, the electrolyte further includes a non-aqueous organic solvent, and the non-aqueous solvent includes a carbonate compound.
[0060] As a non-limiting example, carbonate compounds include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), etc.
[0061] The electrolyte of the embodiment of the present application contains fluoroethylene carbonate (FEC), an unsaturated silicon compound, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Among them, FEC can form an SEI film to improve high-temperature cycling performance, and the unsaturated silicon compound can capture HF generated by the reaction of FEC and lithium hexafluorophosphate, which can degrade the cycling performance and prevent it from damaging the positive electrode interface, thereby ensuring the stability of high-temperature cycling performance and thus improving the overall high-temperature cycling performance of the lithium-ion battery.
[0062] In the embodiments of the present application, there is no limitation on the preparation method of the electrolyte, and it can be any preparation method known in the art.
[0063] As an optional example, the method for preparing the electrolyte of this embodiment includes the following steps:
[0064] Under an inert gas atmosphere, a non-aqueous organic solvent is added, and then fluoroethylene carbonate (FEC), an unsaturated silicon compound, and a lithium salt are added in sequence and mixed evenly to obtain the electrolyte of the embodiment of the present application.
[0065] As a non-limiting example, the inert gas includes but is not limited to at least one of argon, nitrogen, helium, and the like.
[0066] The electrolyte of the embodiment of the present application can be widely used in the fields of energy storage, vehicles, etc.
[0067] The electrochemical device of the embodiment of the present application includes the electrolyte of the present application.
[0068] In some embodiments, the electrochemical device includes but is not limited to secondary batteries such as lithium-ion batteries, capacitors, etc. The secondary battery is not limited to button batteries, soft-pack batteries, etc.
[0069] In some embodiments, the electrochemical device further comprises a negative electrode, the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises a silicon material.
[0070] In some embodiments, the silicon material includes SiO z , of which 0.5 <z<1.5。
[0071] As a non-limiting example, z includes, but is not limited to, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5, etc.
[0072] In some embodiments, the negative electrode active material further includes graphite material, such as artificial graphite, natural graphite, etc.
[0073] In some embodiments, the negative electrode active material may further include at least one of mesophase carbon materials (mesophase carbon microspheres, etc.), soft carbon, hard carbon, elemental silicon, silicon-carbon composite materials (SiNPs-amorphous carbon, SiNPs-graphite, etc.), or metal oxide materials (TiO2-B, MoO, CoO, etc.).
[0074] In some embodiments, the negative electrode further comprises a negative electrode material, which includes at least one of the aforementioned negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode thickener. It should be noted that in the embodiments of the present application, there are no particular limitations on the specific selection of the negative electrode conductive agent and negative electrode binder. As non-limiting examples, the negative electrode conductive agent includes, but is not limited to, at least one of carbon nanotubes, conductive carbon black, conductive graphite, vapor-grown carbon fiber, and graphene; the negative electrode binder includes, but is not limited to, at least one of styrene-butadiene rubber (SBR) or polyacrylic acid (PAA); and the negative electrode thickener includes, but is not limited to, at least one of carboxymethyl cellulose and sodium carboxymethyl cellulose.
[0075] In some embodiments, the negative electrode further comprises a negative electrode current collector, a negative electrode material layer is provided on the surface of the negative electrode current collector, and the material of the negative electrode material layer is the above-mentioned negative electrode material. The negative electrode current collector can be selected to comprise copper or any other suitable conductive metal foil (such as solid or mesh or covered foil) known to those skilled in the art, a metal grid or screen, or a porous metal. In some variations, the surface of the negative electrode current collector may comprise a metal foil that has been surface treated (e.g., carbon coated and / or etched).
[0076] In some embodiments, the electrochemical device further includes a positive electrode, the positive electrode includes a positive electrode active material, and the positive electrode active material includes a layered lithium composite oxide.
[0077] In some embodiments, the layered lithium composite oxide has the chemical formula Li 1+x Ni m Co y Mn (1-m-y) O2, where -0.1≤x≤0.2; 0.5≤m≤1, 0.05≤y≤0.5, 0≤1-my≤0.45.
[0078] As a non-limiting example, the value of x includes but is not limited to -0.1, 0, 0.1 or 0.2.
[0079] As a non-limiting example, the value of m includes but is not limited to 0.5, 0.6, 0.7, 0.8, 0.9 or 1.
[0080] As a non-limiting example, the value of y includes but is not limited to 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.
[0081] As a non-limiting example, the value of 1-my includes but is not limited to 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 or 0.45, etc.
[0082] In some embodiments, the positive electrode further includes a positive electrode material, and the positive electrode material includes the above-mentioned positive electrode active material, a positive electrode conductor and a positive electrode binder. In the embodiments of the present application, there is no particular restriction on the specific selection of the positive electrode conductor and the positive electrode binder. As a non-limiting example, the positive electrode conductor includes but is not limited to one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes; the positive electrode binder includes but is not limited to one or more of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose and polyacrylic acid.
[0083] In some embodiments, the positive electrode further comprises a positive electrode current collector, and a positive electrode material layer is provided on the surface of the positive electrode current collector, and the material of the positive electrode material layer is the above-mentioned positive electrode material. The positive electrode current collector can be selected to comprise aluminum or any other suitable conductive metal foil (such as solid or mesh or covered foil) known to those skilled in the art, a metal grid or screen, or a porous metal. In some variations, the surface of the positive electrode current collector may comprise a metal foil that has been surface treated (e.g., carbon coated and / or etched).
[0084] In some embodiments, the electrochemical device further includes a separator disposed between the positive electrode and the negative electrode.
[0085] In some embodiments, the diaphragm includes but is not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene-based polyolefin (PO) diaphragms, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide films (PI), polyamide films (PA), spandex or aramid films, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, diaphragm paper, rolled membranes or spun membranes, etc.
[0086] It should be noted that in the embodiments of the present application, there is no limitation on the specific technical parameters such as the thickness of the positive electrode, negative electrode, and separator, as long as the purpose of the present application can be achieved.
[0087] The preparation method of the electrochemical device in the embodiment of the present application is not limited and can be any method known to those skilled in the art.
[0088] As a possible example, the electrochemical device of the embodiment of the present application is a lithium-ion battery, and the preparation method thereof includes the following steps:
[0089] (1) Preparation of positive electrode sheets: The positive electrode active material, positive electrode conductive agent, and positive electrode binder are dispersed in a positive electrode solvent to obtain a positive electrode slurry, which is then coated on a positive electrode current collector, followed by baking, and finally cold pressing, cutting, and slitting to obtain positive electrode sheets;
[0090] (2) Preparation of negative electrode sheets: Dispersing the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener in a negative electrode solvent to obtain a negative electrode slurry, then coating the negative electrode slurry on the negative electrode current collector, then baking, and finally cold pressing, cutting and slitting to obtain negative electrode sheets;
[0091] (3) Diaphragm preparation: A polyethylene film is used as the isolation membrane, and a boehmite ceramic layer is coated on its surface to obtain a diaphragm.
[0092] (4) Assembly: The positive electrode sheet, separator and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to serve as an isolation. The side coated with the boehmite ceramic layer is aligned with the positive electrode sheet. The sheets are then stacked and placed in an aluminum-plastic film. After drying, the electrolyte of the embodiment of the present application is injected. After vacuum packaging, standing, forming, shaping and other processes, the preparation of the lithium-ion battery is completed.
[0093] The vehicle of the embodiments of the present application may be any vehicle containing the electrolyte of the embodiments of the present application or any of the electrochemical devices of the embodiments of the present application, including but not limited to automobiles, motorcycles, power-assisted bicycles, bicycles, power tools, etc.
[0094] The electrochemical devices, vehicles, etc. according to the embodiments of the present application all have at least the beneficial effects of the electrolyte according to the embodiments of the present application.
[0095] Certain features of the present technology are further illustrated in the following non-limiting examples.
[0096] Example 1
[0097] (Electrolyte)
[0098] The electrolyte of this embodiment is composed of a non-aqueous organic solvent, fluoroethylene carbonate (FEC), an unsaturated silicide, and an electrolyte salt, wherein:
[0099] The non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a mass ratio of 15:15:70; the unsaturated silicide is compound 1; and the electrolyte salt is lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).
[0100] The mass content of fluoroethylene carbonate in the electrolyte is a%, the mass content of unsaturated silicon compound in the electrolyte is b%, the mass content of lithium hexafluorophosphate (LiPF6) in the electrolyte is c%, and the mass content of lithium bis(fluorosulfonyl)imide (LiFSI) in the electrolyte is d%, wherein: a=12, b=0.1, c=14, d=1; c / d=14, (c / d) / a=1.40, b / [(c / d) / a]=0.07.
[0101] (Method for preparing electrolyte)
[0102] The preparation method of the electrolyte of this embodiment is as follows: under an argon environment, EC, PC, and EMC are mixed, fluoroethylene carbonate (FEC) and unsaturated silicide are added, and LiPF6 and LiFSI are added and mixed to obtain the electrolyte of this embodiment.
[0103] (Electrochemical Device)
[0104] The electrochemical device of this embodiment is a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte.
[0105] The positive electrode includes a positive electrode current collector and a positive electrode material layer provided on the opposite sides of the positive electrode current collector. The positive electrode current collector is an aluminum foil with a thickness of 12 μm. The positive electrode material layer is composed of the following components in parts by weight: LiNi 0.8 Co 0.1 Mn 0.1 (NCM811) 96 parts, conductive carbon black (SP) 1 part, carbon nanotubes (CNTs) 0.5 parts, polyvinylidene fluoride (PVDF) 2.5 parts.
[0106] The negative electrode includes a negative electrode current collector and negative electrode material layers disposed on opposite sides of the current collector. The negative electrode current collector is a 6μm-thick copper foil. The negative electrode material layers are composed of the following components by weight: 95.5 parts negative electrode active material, 1 part conductive carbon black (SP), 2 parts sodium carboxymethyl cellulose, and 1.5 parts styrene-butadiene rubber (SBR). The negative electrode active material is artificial graphite and SiO, with the SiO content of the negative electrode active material being 5% by weight and the artificial graphite content being 95% by weight.
[0107] The separator is arranged between the positive electrode and the negative electrode. The separator is a polyethylene film with a boehmite ceramic layer on the surface. The thickness of the polyethylene film is 7 μm, and the thickness of the boehmite ceramic layer is 2 μm.
[0108] The electrolyte is the electrolyte of this embodiment.
[0109] (Method for preparing electrochemical device)
[0110] The method for preparing the electrochemical device of this embodiment includes the following steps:
[0111] (1) Positive electrode preparation: NCM811, conductive carbon black (SP), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed in a solvent, N-methylpyrrolidone, at a weight ratio of 96:1:0.5:2.5 and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was applied to the opposite sides of the positive electrode current collector. The positive electrode current collector coated with the positive electrode slurry was then baked at 120°C for 1 hour, and then cold pressed, cut, and slit to obtain the positive electrode.
[0112] (2) Preparation of the negative electrode: The negative electrode active material, conductive carbon black (SP), sodium carboxymethyl cellulose, and styrene-butadiene rubber (SBR) were mixed in deionized water at a weight ratio of approximately 95.5:1:2:1.5 and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was applied to the opposite sides of the negative electrode current collector. The negative electrode current collector coated with the negative electrode slurry was then baked at 120°C for 1 hour, and then cold pressed, cut, and slit to obtain the negative electrode.
[0113] (3) Preparation of diaphragm: A polyethylene film was used as the isolation membrane, and a 2 μm thick boehmite ceramic layer was coated on its surface to obtain a diaphragm.
[0114] (4) Assembly of the electrochemical device: The positive electrode, separator, and negative electrode are stacked in order, with the separator positioned between the positive and negative electrodes to serve as an insulator. The side coated with the boehmite ceramic layer is aligned with the positive electrode. The sheets are then stacked and placed in an aluminum-plastic film. After drying at 80°C, the electrolyte of this embodiment is injected. After vacuum packaging, standing, forming, and shaping, the electrochemical device of this embodiment is completed.
[0115] Examples 2-22 and Comparative Examples 1-2 are basically the same as Example 1, except that the selection and dosage of some substances in the electrolyte are different, and the electrolyte corresponding to each example or comparative example is used in the electrochemical device, as shown in Table 1.
[0116] Table 1 Electrolyte components and parameter selection of each embodiment and comparative example
[0117]
[0118]
[0119] Note: When there are two or more unsaturated silicon compounds in Table 1, for the same example, the values in the unsaturated silicon compound content column represent the contents of the compounds in the unsaturated silicon compound type column from left to right.
[0120] The high temperature cycle performance of the electrochemical devices of the embodiments and comparative examples was tested using the following test method:
[0121] High-temperature cycling performance test: The finished electrochemical device (lithium-ion battery) of each embodiment or comparative example was placed in a constant temperature box at 45°C for 30 minutes, charged to 4.25V at a constant charge rate of 2C, then charged at a constant voltage to a charge rate of 0.05C, allowed to stand for 5 minutes, and then discharged to 3.0V at a constant discharge rate of 1.0C. The capacity was recorded as D0. The cycling test was carried out according to the following steps:
[0122] 1) Let it stand for 5 minutes;
[0123] 2) Charge at a constant charge rate of 1C to 4.25V; then charge at a constant voltage to a charge rate of 0.05C;
[0124] 3) Let it stand for 5 minutes;
[0125] 4) Discharge to 3.0V at a constant discharge rate of 1.0C;
[0126] 5) Steps 1) to 4) are repeated 800 times; the recording capacity is D1.
[0127] The cycle capacity retention rate of the electrochemical device at 45°C was calculated according to formula (1):
[0128] Cycle capacity retention rate (%) = (D1-D0) / D0×100% Formula (1).
[0129] The high temperature cycle performance test results of the electrochemical devices of various embodiments and comparative examples are shown in Table 2.
[0130] Table 2 High temperature cycle performance test results of the electrochemical devices of various embodiments and comparative examples
[0131]
[0132]
[0133] From the data in Table 1 and Table 2, it can be seen that when the electrolyte contains fluoroethylene carbonate (FEC) and the content of lithium hexafluorophosphate (LiPF6) is high, the addition of unsaturated silicon compounds can significantly improve the high-temperature cycle performance. This is mainly because the unsaturated silicon compound can capture the HF generated by FEC and high-content hexafluorophosphate at high temperatures, and it can form a protective film at the positive electrode interface to further reduce the damage of HF. By comparing Comparative Example 1, Examples 1-12 and Example 15, when the value of b / [(c / d) / c] is between 0.01 and 2, the high-temperature cycle performance is better; when the ratio is low, the unsaturated silicon compound captures HF and the positive electrode interface protection is insufficient, resulting in no obvious improvement in high-temperature performance; when the ratio is high, the unsaturated silicon compound is excessive, resulting in large positive electrode interface impedance, large polarization, increased side reactions, and the effect of improving high-temperature performance is also affected.
[0134] In this application, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.
[0135] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.
Claims
1. An electrolyte, characterized in that: The invention comprises fluoroethylene carbonate, an unsaturated silicon compound and a lithium salt; the lithium salt comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the mass content of the fluoroethylene carbonate in the electrolyte is a%, the mass content of the unsaturated silicon compound in the electrolyte is b%, the mass content of the lithium hexafluorophosphate in the electrolyte is c%, and the mass content of the lithium bis(fluorosulfonyl)imide in the electrolyte is d%, 1≤a≤12, 0.01≤b≤1, 3≤c≤15, and 1≤d≤12.
2. The electrolyte according to claim 1, characterized in that The c and the d satisfy the following relationship: 8≤c+d≤18; and / or, 0.25≤c / d≤15.
3. The electrolyte according to claim 1, characterized in that The a, the c, and the d satisfy the following relationship: 0.05≤(c / d) / a≤5.
4. The electrolyte according to claim 1, characterized in that The a, b, c, and d satisfy the following relationship: 0.01≤b / [(c / d) / a]≤2.
5. The electrolyte according to any one of claims 1 to 4, characterized in that The unsaturated silicon compound has the structure shown in Formula I: wherein n is an integer of 0-3, R1, R2, and R3 are each independently selected from at least one of fluorine, alkenyl, alkynyl, alkyl, or substituted alkyl, wherein the substituent element in the substituted alkyl is fluorine; And / or, the electrolyte further includes a non-aqueous organic solvent, and the non-aqueous solvent includes a carbonate compound.
6. The electrolyte according to claim 5, characterized in that The unsaturated silicon compound is selected from at least one of compounds 1-8:
7. An electrochemical device, characterized in that Comprising the electrolyte according to any one of claims 1 to 6.
8. The electrochemical device according to claim 7, characterized in that The electrochemical device further comprises a negative electrode, the negative electrode comprising a negative electrode active material, and the negative electrode active material comprises a silicon material; And / or, the electrochemical device further includes a positive electrode, the positive electrode includes a positive electrode active material, and the positive electrode active material includes a layered lithium composite oxide.
9. The electrochemical device according to claim 8, characterized in that The silicon material includes SiO z , of which 0.5 <z<1.5; And / or, the negative electrode active material further comprises a graphite material; And / or, the chemical formula of the layered lithium composite oxide is Li 1+x Ni m Co y Mn (1-m-y) O2, where -0.1≤x≤0.2; 0.5≤m≤1, 0.05≤y≤0.5, 0≤1-my≤0.
45.
10. A vehicle, characterized in that: Comprising the electrochemical device according to any one of claims 7 to 9.