Electrolyte and battery

Abstract

The application provides an electrolyte and a battery, and relates to the technical field of lithium ion batteries. The electrolyte comprises a first additive, a lithium salt and an organic solvent, wherein the structure of the first additive is: wherein R1, R2, R3 and R4 are each independently selected from any one of a hydrogen atom, a halogen atom, an alkyl group, an alkyl group substituted or unsubstituted by a halogen atom, an alkoxy group substituted or unsubstituted by a halogen atom, a phenyl group substituted or unsubstituted by a halogen atom and a cyano group, or CR2R3 is a cyclopropyl group; R5 is selected from any one of a hydrogen atom, an alkyl group, an alkyl group substituted or unsubstituted by a halogen atom and a cyano group; and R6 is selected from a hydrogen atom, or R6 is a carbonyl group and R6 is connected to an ortho-phenyl group relative to an amide group. The first additive is applied to the battery, and the high energy density and cycle performance of the battery can be considered.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and more specifically, to an electrolyte and a battery. Background Technology

[0002] With the development of portable electronic devices and electric vehicles, consumers have placed higher demands on the long service life of lithium-ion batteries. The energy density of a battery directly determines the duration of a single use. High energy density can provide a longer usage time. Currently, most methods increase the energy density of batteries by increasing the compaction density and areal density of the electrode sheets. However, at present, the solvent system of traditional electrolytes (such as carbonate solvents) has a high surface tension in high-density electrode sheets and cannot effectively penetrate into the micropores of the electrode sheets. Insufficient electrolyte wetting in some areas of the electrode sheets affects the formation of SEI and CEI films, which reduces the stability of the electrode-electrolyte interface. An unstable electrode-electrolyte interface will promote the continuous decomposition of the electrolyte on the electrode surface, leading to the thickening of the interface film and an increase in lithium-ion transport resistance. Ultimately, this leads to accelerated battery capacity decay and may even cause safety problems such as thermal runaway. Summary of the Invention

[0003] The main objective of this application is to provide an electrolyte and a battery to solve the problem of battery capacity decay in high-energy-density batteries due to insufficient electrolyte wetting in related technologies.

[0004] To achieve the above objectives, according to one aspect of this application, a first additive is provided, the first additive having the structure shown in general formula (I):

[0005]

[0006] R1 and R4 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, alkyl group with or without halogen atom substituted or unsubstituted, alkoxy group with or without halogen atom substituted or unsubstituted, phenyl group with or without halogen atom substituted or unsubstituted, and cyano group.

[0007] R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, alkyl group with or without halogen atom substitution, alkoxy group with or without halogen atom substitution, phenyl group with or without halogen atom substitution, or CR2R3 is cyclopropyl.

[0008] R5 is selected from any one of hydrogen atom, alkyl group, halogen atom substituted or unsubstituted alkyl group, cyano group;

[0009] R6 is selected from a hydrogen atom, or R6 is a carbonyl group and R6 is attached to an ortho-phenyl group relative to an amide group.

[0010] Furthermore, R1 and R4 are each independently selected from any one of hydrogen atom, halogen atom, C1-C12 alkyl, C1-C12 alkyl with halogen atom substitution or unsubstitution, C1-C12 alkoxy with halogen atom substitution or unsubstitution, C6-C12 phenyl with halogen atom substitution or unsubstitution, and cyano.

[0011] R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, C1-C12 alkyl group substituted or unsubstituted with halogen atom, C1-C12 alkoxy group substituted or unsubstituted with halogen atom, C6-C12 phenyl group substituted or unsubstituted with halogen atom, or CR2R3 is cyclopropyl.

[0012] Furthermore, R1 is selected from any one of hydrogen atoms, C1-C6 alkyl groups, halogen atoms, substituted or unsubstituted C1-C6 alkyl groups;

[0013] R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, C1-C6 alkyl, C1-C6 alkyl with or without halogen atom substitution, and C6-C18 phenyl with or without halogen atom substitution; or CR2R3 is cyclopropyl.

[0014] R4 is selected from any one of hydrogen atom, C1-C6 alkyl group, halogen atom substituted or unsubstituted C1-C6 alkyl group, and cyano group.

[0015] Furthermore, R1 is selected from any one of hydrogen atoms and C1 to C3 alkyl groups;

[0016] R2 and R3 are each independently selected from any one of hydrogen atom, fluorine atom, C1-C3 alkyl, and C6 phenyl; or CR2R3 is cyclopropyl.

[0017] R4 is selected from any one of hydrogen atom, C1 to C4 alkyl group, and cyano group.

[0018] Furthermore, the first additive is selected from any one of formulas A1, A2, A3, A4, and A5:

[0019]

[0020]

[0021] Furthermore, the mass content of the first additive in the electrolyte is 0.5% to 3.0%;

[0022] Preferably, the mass content of the first additive in the electrolyte is 1% to 2.5%.

[0023] Furthermore, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium borate, lithium difluorooxalate borate, and lithium difluorosulfonyl imide.

[0024] Preferably, the lithium salt is lithium hexafluorophosphate or a mixed lithium salt of lithium hexafluorophosphate and lithium difluorosulfonylimide;

[0025] More preferably, the lithium salt is a mixed lithium salt of lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the mass content of lithium hexafluorophosphate in the electrolyte is 11% to 12%, and the mass content of lithium difluorosulfonylimide in the electrolyte is 0.5% to 3%.

[0026] Preferably, the lithium salt content in the electrolyte is 12% to 15% by mass.

[0027] Furthermore, the organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene sulfite, ethyl acetate, diethyl sulfite, and 1,3-propanesulfonate lactone.

[0028] Preferably, the organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0029] More preferably, the organic solvent is a mixture of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, wherein the mass ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate is (3-9):(0.1-4):(6-7):(4-6).

[0030] Furthermore, the electrolyte also includes a second additive;

[0031] The second additive includes at least one of vinylene carbonate and vinyl sulfate.

[0032] Furthermore, the mass ratio of the first additive to the second additive is 1:(0.1-6).

[0033] Furthermore, the mass content of the second additive in the electrolyte is 0.5% to 3%.

[0034] A third aspect of this application provides a battery comprising the electrolyte of the second aspect.

[0035] Furthermore, the battery also includes a negative electrode sheet containing a negative electrode active material; and / or,

[0036] The battery also includes a positive electrode sheet containing positive electrode active material;

[0037] Preferably, the negative electrode active material includes a carbon-based negative electrode material;

[0038] Preferably, the positive electrode active material includes lithium iron phosphate.

[0039] By applying the technical solution of this application, a first additive with a specific general formula is used as an electrolyte additive in a battery. On the one hand, the benzene ring large π bond, ester group, or carboxyl group in the general formula of the first additive can reduce the surface tension of the electrolyte. The reduction in surface tension is beneficial for the electrolyte to better wet the electrode material with high compaction density and high areal density, ensuring the uniform formation of the interfacial film and maintaining the efficient transport of lithium ions. On the other hand, during the first charge and discharge process of the battery, the ester group, carboxyl group, or amide group in the general formula of the first additive will react rapidly to form amine compounds. These amine compounds will polymerize and cover the electrode surface, participating in the formation of the interfacial film and enhancing the structural stability of the interfacial film. In addition, the interfacial film containing nitrogen compounds also has good thermal stability, which helps to mitigate the damage to the interfacial film caused by battery temperature rise. By applying this first additive to the battery, under the synergistic effect of the functional groups in the general formula structure, not only is the wettability enhanced, but the formation of a more stable and denser interfacial film is also promoted, thereby significantly improving the cycle performance and safety of the battery while maintaining its high energy density. Detailed Implementation

[0040] As described in the background section of this application, existing technologies suffer from high-energy-density batteries experiencing capacity degradation due to insufficient electrolyte wetting. To address this problem, a first aspect of this application provides an electrolyte comprising a first additive, a lithium salt, and an organic solvent, wherein the first additive has the structure shown in general formula (I):

[0041]

[0042] R1 and R4 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, alkyl group with or without halogen atom substituted or unsubstituted, alkoxy group with or without halogen atom substituted or unsubstituted, phenyl group with or without halogen atom substituted or unsubstituted, and cyano group.

[0043] R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, alkyl group with or without halogen atom substitution, alkoxy group with or without halogen atom substitution, phenyl group with or without halogen atom substitution, or CR2R3 is cyclopropyl.

[0044] R5 is selected from any one of hydrogen atom, alkyl group, halogen atom substituted or unsubstituted alkyl group, cyano group;

[0045] R6 is selected from a hydrogen atom, or R6 is a carbonyl group and R6 is attached to an ortho-phenyl group relative to an amide group.

[0046] During the initial charge and discharge cycle, carboxyl or ester groups, and amide groups rapidly decompose, generating amine compounds and carbon dioxide (CO2). The nitrogen atoms in the amine compounds possess lone pairs of electrons. Due to the conjugation effect of the benzene ring, these lone pairs are attracted to the vicinity of the benzene ring, promoting the polymerization of the amine compounds. The polymerized amine compounds form a dense and stable interfacial film on the electrode surface, namely the solid electrolyte interphase (SEI) film and the positive electrode electrolyte interphase (CEI) film. The formation of the interfacial film prevents direct contact between the electrode and the electrolyte, effectively inhibiting the continuous decomposition of the electrolyte, reducing the dissolution of metal ions, thereby reducing internal side reactions and improving the battery's cycle performance.

[0047] The interfacial film formed by nitrogen-containing compounds is not only dense but also exhibits excellent thermal stability. During charging and discharging, heat is generated inside the battery, and high thermal stability can mitigate the damage to the SEI film caused by high temperatures, maintaining the integrity and stability of the film. This not only improves battery safety but also reduces the phenomenon of "dead lithium" caused by high temperatures, where lithium ions cannot return to their initial state during charging and discharging, thereby preventing rapid capacity decay and improving battery cycle performance.

[0048] Because of the presence of benzene ring π bonds, carboxyl groups, or ester groups in the general formula (I) structure, the surface tension of the electrolyte is reduced. The reduction in surface tension is beneficial for the electrolyte to better wet the electrode materials with high compaction density and high areal density, especially the surface of graphite anode, which ensures the uniform formation of SEI film, maintains the efficient transport of lithium ions, and further improves the cycle performance of the battery.

[0049] Therefore, the first additive in this application effectively solves the problem of insufficient wetting during cycling in high-energy-density lithium-ion batteries by promoting the formation of SEI and CEI films, improving the thermal stability of the films, and reducing the surface tension of the electrolyte. The introduction of this first additive not only improves the battery's cycle performance but also enhances its safety and stability, enabling the battery to maintain excellent cycle performance even when the electrode sheets meet the requirements of high compaction density and high areal density.

[0050] In some embodiments, R1 and R4 are each independently selected from any one of hydrogen atom, halogen atom, C1-C12 alkyl group, halogen-substituted or unsubstituted C1-C12 alkyl group, halogen-substituted or unsubstituted C1-C12 alkoxy group, halogen-substituted or unsubstituted C6-C12 phenyl group, and cyano group; R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, halogen-substituted or unsubstituted C1-C12 alkyl group, halogen-substituted or unsubstituted C1-C12 alkoxy group, halogen-substituted or unsubstituted C6-C12 phenyl group, or CR2R3 is cyclopropyl. By further limiting the number of carbon atoms in the substituents, the cost and performance of the electrolyte can be balanced.

[0051] In some embodiments, R1 is selected from any one of hydrogen atom, C1-C6 alkyl, halogen-substituted or unsubstituted C1-C6 alkyl; R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, C1-C6 alkyl, halogen-substituted or unsubstituted C1-C6 alkyl, halogen-substituted or unsubstituted C6-C18 phenyl; or CR2R3 is cyclopropyl; R4 is selected from any one of hydrogen atom, C1-C6 alkyl, halogen-substituted or unsubstituted C1-C6 alkyl, and cyano. Further limiting the number and type of substituents can further improve the performance of the electrolyte.

[0052] In some embodiments, R1 is selected from any one of hydrogen atom and C1-C3 alkyl group; R2 and R3 are each independently selected from any one of hydrogen atom, fluorine atom, C1-C3 alkyl group, and C6 phenyl group; or CR2R3 is cyclopropyl; R4 is selected from any one of hydrogen atom, C1-C4 alkyl group, and cyano group. By further defining the type of substituent, the wettability and thermal stability of the electrolyte can be further improved.

[0053] In some embodiments, the first additive is selected from any one of formulas A1, A2, A3, A4, and A5:

[0054]

[0055] By limiting the first additive to any of the above structures, it is possible to further ensure the formation of a denser and more stable interfacial film, further improve the wettability of the electrolyte to the electrode material, and thus further balance high energy density and excellent cycle performance.

[0056] Because it includes the first additive with the specific structural formula described above, when this electrolyte is applied to a battery, the synergistic effect of the components not only enhances wettability but also promotes the formation of a more stable and denser interfacial film. This significantly improves the battery's cycle performance and safety while maintaining its high energy density. This electrolyte is suitable for lithium-ion batteries.

[0057] In some embodiments, the mass content of the first additive in the electrolyte is 0.5% to 3.0%, for example, a range consisting of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any two thereof. By limiting the mass content of the first additive within the above range, it is ensured that the first additive can exert its effective effect in the electrolyte to the maximum extent.

[0058] In some embodiments, the mass content of the first additive in the electrolyte is 1% to 2.5%. By limiting the mass content of the first additive within the above range, in addition to ensuring that the first additive can exert its effective function in the electrolyte to the maximum extent, the side effects that may be caused by excessive addition are also avoided.

[0059] Lithium salts are the primary source of conductive ions in the electrolyte. For example, lithium salts include at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium borate (LiBOB), lithium difluorooxalate borate (LiODFB), and lithium bis(fluorosulfonyl)imide (LiFSI). In some embodiments, the lithium salt is lithium hexafluorophosphate or a mixed lithium salt of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. When the lithium salt is a mixed lithium salt of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the mass content of lithium hexafluorophosphate in the electrolyte is 11% to 12%, for example, 11%, 11.5%, 12%, or any combination thereof, and the mass content of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.5% to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination thereof.

[0060] This application does not limit the specific amount of lithium salt added, and it can be adjusted according to actual needs. In some embodiments, the mass content of lithium salt in the electrolyte is 12% to 15%, for example, a range of 12%, 13%, 14%, 15%, or any combination thereof.

[0061] Organic solvents are a major component of the electrolyte and are responsible for transporting lithium ions. In some embodiments, organic solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene sulfite (PS), ethyl acetate (EP), diethyl sulfite (DES), and 1,3-propanesulfonate lactone (1,3-PS).

[0062] This application does not limit the amount of organic solvent added. As long as the mass content of the above-mentioned additives and lithium salts meets the above requirements, the remaining components can be organic solvents, provided that the sum of the mass content of each component is 100%.

[0063] The organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Limiting the organic solvent to the above range facilitates lithium-ion transport. For example, in some embodiments, the organic solvent is a mixture of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, wherein the mass ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and dimethyl carbonate is (3–9):(0.1–4):(6–7):(4–6). By limiting the specific type and mass ratio of the organic solvent, the chemical stability, wettability, lithium-ion conductivity, battery internal resistance, safety, lifespan, energy density, and cost-performance balance of the electrolyte can be optimized, thereby significantly improving the overall performance of the lithium-ion battery.

[0064] In some embodiments, the electrolyte further includes a third additive. The third additive improves the wettability of the electrolyte to high areal density electrode materials, ensuring that the electrolyte can fully penetrate the electrode materials, thereby improving lithium-ion transport efficiency and helping to maintain good battery performance at high energy densities. Furthermore, the third additive helps form a thin and stable SEI film, reducing ineffective volume expansion of the battery during cycling.

[0065] This application does not limit the specific type of the third additive, which can be a conventional third additive in the art. For example, in some embodiments, the third additive includes vinyl sulfate (ES).

[0066] In some embodiments, the mass content of the third additive in the electrolyte is 0.5% to 3%, for example, a range of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any two of these.

[0067] In some embodiments, the electrolyte further includes a second additive, which includes at least one of vinylene carbonate (VC) and vinyl sulfate (ES). The second additive can promote the formation of an SEI film on the negative electrode surface. The formation of the SEI film can reduce the formation of lithium dendrites and the direct oxidation of the negative electrode material, thereby reducing the risk of battery short circuit and further improving the cycle performance and safety of the battery.

[0068] The second additive possesses a high oxidation potential, good chemical stability, and thermal stability. Adding the second additive optimizes the volatility of the electrolyte, reducing its volatilization at high temperatures or during charge / discharge processes, thus enhancing the battery's thermal stability. This makes it particularly suitable for devices requiring high power output and improves the overall safety of the battery. Therefore, by introducing the second additive, the composition of the electrolyte can be further optimized through the combined action of the lithium salt, the second additive, and the first additive, thereby further improving the battery's cycle performance.

[0069] In some embodiments, the mass ratio of the first additive to the second additive is 1:(0.1 to 6), for example, a range consisting of 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 or any two of these.

[0070] In some embodiments, the mass content of the second additive in the electrolyte is 0.5% to 3%, for example, a range of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any two of these.

[0071] This application does not limit the specific preparation method of the electrolyte, as long as it contains the above-mentioned components. For example, a specific preparation method of the electrolyte includes the following steps: under a protective atmosphere, adding an electrolyte additive, a third additive, and a second additive to an organic solvent, then adding a lithium salt, and stirring and mixing at a first temperature to obtain the electrolyte; wherein, the protective atmosphere can be argon, and the first temperature can be 5-15°C.

[0072] A third aspect of this application provides a battery comprising the electrolyte provided in the second aspect.

[0073] Thanks to the inclusion of the electrolyte mentioned above, this battery exhibits excellent cycle performance, especially maintaining a high capacity retention rate even at high energy densities. Furthermore, this battery can meet the requirements of different temperature scenarios.

[0074] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer formed of negative electrode active material disposed on the surface of the negative electrode current collector.

[0075] In the specific preparation of the negative electrode sheet, the negative electrode active material, the first conductive agent, and the first binder can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained. In one specific embodiment, the negative electrode active layer comprises, by mass percentage, 70%–99% graphite negative electrode material, 0.5%–15% of the first conductive agent, and 0.5%–15% of the first binder.

[0076] The negative electrode current collector can be made of at least one of copper foil, nickel foam, and copper foam; the first conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the first binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0077] This application does not limit the specific type of negative electrode active material in the negative electrode sheet, and it can be a negative electrode active material commonly used in batteries, such as at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, and silicon-based negative electrode materials. In some embodiments, the negative electrode active material includes a carbon-based negative electrode material.

[0078] The positive electrode includes a positive current collector and a positive active layer formed of positive active material disposed on the surface of the positive current collector.

[0079] In the specific preparation of the positive electrode sheet, the positive electrode active material, the second conductive agent, and the second binder can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, rolling, and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70%–99% of the positive electrode active material, 0.5%–15% of the second conductive agent, and 0.5%–15% of the second binder.

[0080] The positive current collector can be made of at least one of aluminum foil and nickel foil; the second conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the second binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0081] This application does not limit the specific type of positive electrode active material in the positive electrode sheet, and it can be a positive electrode active material commonly used in batteries, such as a composite oxide of lithium with at least one of cobalt, nickel, manganese, or combinations thereof. Specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese-based materials. In some embodiments, the positive electrode active material includes lithium iron phosphate.

[0082] The battery also includes a separator. This application does not limit the specific choice of separator material, and it can be separator materials commonly used in batteries, such as polypropylene separators, polyethylene separators, polypropylene / polyethylene double-layer composite separators, polypropylene / polyethylene / polypropylene (PP / PE / PP) triple-layer composite separators, etc.

[0083] In battery manufacturing, positive electrode sheets, separators, and negative electrode sheets are wound or stacked to obtain battery cells. The battery cells are then encapsulated in pre-stamped aluminum-plastic films. After the encapsulated batteries are dried, electrolyte is injected into the dried batteries. The batteries are then aged, formed, and resealed to complete the battery manufacturing process.

[0084] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0085] Example 1

[0086] The electrolyte in this embodiment, based on a 100% mass content, comprises 1.0% of the compound shown in Formula A1 (CAS No. 918409-37-7), 3% of vinylene carbonate (VC), 11.5% of lithium hexafluorophosphate (LiPF6), and 1.0% of lithium bis(fluorosulfonyl)imide (LiFSI), with the balance being an organic solvent; wherein the organic solvent is a mixture of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 5:1:8:6. The specific components of the electrolyte are shown in Table 1.

[0087]

[0088] Example 2

[0089] The difference from Example 1 is that the compound shown in Formula A1 is replaced with an equal mass of the compound shown in Formula A2 (CAS No. 178872-52-1).

[0090]

[0091] Example 3

[0092] The difference from Example 1 is that the compound shown in Formula A1 is replaced with an equal mass of the compound shown in Formula A3 (CAS No. 112979-49-4).

[0093]

[0094] Example 4

[0095] The difference from Example 1 is that the compound shown in Formula A1 is replaced with an equal mass of the compound shown in Formula A4 (CAS No. 915302-77-1).

[0096]

[0097] Example 5

[0098] The difference from Example 1 is that the compound shown in Formula A1 is replaced with an equal mass of the compound shown in Formula A5 (CAS No. 541547-40-4).

[0099]

[0100] Example 6

[0101] The only difference from Example 1 is that LiFSI is not added, but is made up to 100% with an organic solvent, while the contents of other components are the same as in Example 1.

[0102] Example 7

[0103] The only difference from Example 1 is that LiFSI is replaced with LiPO2F2.

[0104] Example 8

[0105] The only difference from Example 1 is that the organic solvent is composed of ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7.

[0106] Example 9

[0107] The difference from Example 1 is that the mass content of the compound shown in Formula A1 is 0.5%, which is made up to 100% with an organic solvent, while the contents of other components are the same as in Example 1.

[0108] Example 10

[0109] The difference from Example 1 is that the mass content of the compound shown in Formula A1 is 2.5%, which is reduced to 100% by organic solvent, while the contents of other components are the same as in Example 1.

[0110] Example 11

[0111] The difference from Example 1 is that the mass content of the compound shown in Formula A1 is 3%, which is reduced to 100% by organic solvent, while the contents of other components are the same as in Example 1.

[0112] Example 12

[0113] The difference from Example 1 is that the mass content of VC is 0.5%, which is made up to 100% with organic solvent, while the contents of other components are the same as in Example 1.

[0114] Example 13

[0115] The difference from Example 1 is that VC is replaced with vinyl sulfate (ES).

[0116] Comparative Example 1

[0117] The only difference from Example 1 is that the compound shown in Formula A1 is not added, and the amount is made up to 100% with an organic solvent, while the contents of other components are the same as in Example 1.

[0118] Comparative Example 2

[0119] The only difference from Example 1 is that the compound shown in Formula A1 is not added, and the VC content is increased to 4.0%, while the contents of other components are the same as in Example 1.

[0120] Comparative Example 3

[0121] The only difference from Example 1 is that the compound shown in Formula A1 is replaced with a mixture of additives shown in Formula B1, Formula B2, and Formula B3; wherein the mass ratio of additives shown in Formula B1, Formula B2, and Formula B3 is 1:1:1.

[0122]

[0123] Comparative Example 4

[0124] The only difference from Example 1 is that the compound shown in Formula A1 is replaced with the additive shown in Formula C (CAS No.: 16118-22-2).

[0125]

[0126] Comparative Example 5

[0127] The only difference from Example 1 is that the compound shown in Formula A1 is replaced with the additive shown in Formula D (CAS: 90914-57-1).

[0128]

[0129] Comparative Example 6

[0130] The only difference from Example 1 is that the compound shown in Formula A1 is replaced with the additive shown in Formula E (CAS: 61402-69-5).

[0131]

[0132] Comparative Example 7

[0133] The only difference from Example 1 is that the compound shown in Formula A1 is replaced with the additive shown in Formula F (CAS: 55577-65-6).

[0134]

[0135] Test case

[0136] I. Battery Preparation

[0137] Preparation of the positive electrode sheet: A gel solution with a solid content of 1.327% was prepared. Lithium iron phosphate, conductive agent Super-P, and N-methylpyrrolidone (NMP) were added, and the mixture was rotated at 25 r / min, dispersed at 500 r / min, and stirred for 10 min. Then, the mixture was rotated at 25 r / min, dispersed at 1000 r / min, and stirred at 45℃ for 90 min. Next, a conductive agent carbon nanotube slurry was added, and the mixture was rotated at 25 r / min, dispersed at 1000 r / min, and stirred at 45℃ for 60 min under a vacuum of 0.080 kPa. Finally, the gel solution was added, and the mixture was rotated at 25 r / min and dispersed at 2500 r / min. The mixture was stirred at 45°C for 90 minutes under a vacuum of 0.080 kPa. NMP was then added to adjust the slurry viscosity. Finally, the mixture was slowly stirred at 15 r / min and dispersed at 500 r / min under a vacuum of 0.080 kPa for 0.5 hours before cooling down to ensure that the positive electrode discharge viscosity was 20000 mPa·s and the fineness was ≤15 μm. At each step, the deposited material on the stirring cylinder wall and stirring rod was scraped off in time. The positive electrode sheet was obtained by sieving, coating, cold pressing and slitting. The mass ratio of lithium iron phosphate, conductive agent Super-P, carbon nanotubes and binder polyvinylidene fluoride was 95.0:2.0:0.5:2.5.

[0138] Preparation of the negative electrode sheet: Prepare a slurry with a solid content of 8%, add graphite and conductive agent Super-P for dry mixing, rotate at 20 r / min, disperse at 1000 r / min, and stir for 1 h; then add 50% of the negative electrode slurry, rotate at 20 r / min, disperse at 1000 r / min, and stir for 1.5 h; then add another 50% of the negative electrode slurry, rotate at 25 r / min, disperse at 2000 r / min, vacuum degree 0.085 kPa, and stir for 1 h; then add deionized water to adjust the slurry viscosity; finally add the aqueous dispersant styrene-butadiene latex, rotate at 25 r / min, disperse at 800 r / min, vacuum degree 0.085 kPa, and stir for 1 h to finish. The negative electrode discharge viscosity is guaranteed to be 4000 mPa·s, and the fineness is ≤20 μm. The deposited material on the stirring tank wall and stirring rod is scraped in time at each step. The negative electrode sheet is obtained by sieving, coating, cold pressing and slitting. The mass ratio of the negative electrode active material graphite, conductive agent Super-P, thickener sodium carboxymethyl cellulose and binder styrene-butadiene latex is 95.5:1.5:1.2:1.8.

[0139] Lithium-ion battery preparation: The prepared positive electrode sheet, negative electrode sheet and separator are stacked to obtain a bare cell. After the cell is packaged in an aluminum-plastic film, the electrolyte of the above-mentioned examples and comparative examples is injected. Then, the process of sealing, standing, hot and cold pressing, formation and capacity testing is carried out to obtain a lithium-ion battery. The lithium-ion battery is a square aluminum shell 105Ah, with a room temperature capacity distribution of 107-110Ah, an energy density of 210-212Wh / kg, a charge and discharge voltage range of 2.5-3.2V, and supports 1C rate continuous cycling.

[0140] 1. Internal resistance test

[0141] Use a multimeter to test and record the internal resistance of a fresh lithium-ion battery.

[0142] 2. Electrochemical testing

[0143] The following electrochemical tests were performed using the Xinwei charge-discharge test cabinet.

[0144] (1) Room temperature cycling performance test:

[0145] At 25°C, the lithium-ion battery is charged at a constant current of 0.5C (nominal capacity) to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current is ≤0.05C. After resting for 10 minutes, it is discharged at a constant current of 1C to a cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The lithium-ion battery is subjected to 1000 charge-discharge cycles under the above conditions.

[0146] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles = (discharge capacity of the 1000th cycle / initial discharge capacity) × 100%.

[0147] Volume expansion rate (%) of lithium-ion battery after 1000 cycles = (Battery thickness at 1000th cycle - Initial battery thickness) / Initial battery thickness × 100%.

[0148] (2) High-temperature cycling performance test

[0149] At 45°C, the lithium-ion battery is charged at a constant current of 1.0C (nominal capacity) to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current is ≤0.05C. After resting for 10 minutes, it is discharged at a constant current of 1C to a cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The lithium-ion battery is subjected to 1000 charge-discharge cycles under the above conditions.

[0150] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles = (discharge capacity of the 1000th cycle / initial discharge capacity) × 100%.

[0151] Volume expansion rate (%) of lithium-ion battery after 1000 cycles = (Battery thickness at 1000th cycle - Initial battery thickness) / Initial battery thickness × 100%.

[0152] The test results are shown in Table 2.

[0153] Table 1

[0154]

[0155]

[0156] Table 2

[0157]

[0158]

[0159] As shown in Tables 1 and 2, compared with Comparative Examples 1-13 and Comparative Examples 1-7, this application can significantly improve the capacity retention rate and reduce the expansion rate after 1000 cycles under normal and high temperature conditions by introducing a first additive with a specific structure.

[0160] As shown in Table 2, Examples 1-5 exhibit similar room temperature and high temperature cycling performance, with minimal battery volume expansion. The battery provided in Example 1 demonstrates the best overall performance, showing a significant improvement over Comparative Example 1. This indicates that the first additive with a specific general formula provided by this invention, when added to the electrolyte, can significantly improve battery performance. This is because the interfacial film formed by the amine compound effectively isolates the reaction between the electrolyte and the electrode interface. Furthermore, this interfacial film possesses good thermal stability, suppressing battery volume expansion during cycling, thereby enhancing the battery's high-temperature cycling performance.

[0161] A comparison of Examples 1, 6, and 7 reveals that, since lithium salt LiPO2F2 can also form a film on the negative electrode surface, its combined use with the first compound of Formula A1 results in a battery that exhibits improved high-temperature cycle performance with minimal impedance increase. A comparison of Examples 1 and 8 shows that the addition of dimethyl carbonate (DMC), a solvent with low viscosity, helps reduce the battery's internal resistance, thereby improving the overall performance of the lithium iron phosphate battery under high-pressure compaction.

[0162] A comparison of Examples 1, 9, 10, and 11 revealed that the optimal dosage of Formula A1 has the best application range, with 1.0% exhibiting the best performance. While a lower dosage helps reduce internal resistance, it fails to form a sufficiently dense interfacial film, leading to continuous reaction between the electrolyte and electrode materials and consequently reduced cycle performance. A higher dosage, on the other hand, results in an excessively thick interfacial film, increasing internal resistance.

[0163] A comparison of Example 1 and Comparative Example 3 shows that the prior art cathode film-forming additives are not suitable for lithium iron phosphate systems. However, the first compound with a specific structure proposed in this invention can more easily form a film on the anode in lithium iron phosphate systems.

[0164] A comparison of Example 1 and Comparative Examples 4, 5, 6, and 7 shows that additives containing only a single benzene ring, amide group, carboxyl group, or ester group cannot achieve the same improvement in battery cycle performance as Formula A1. This is because the multiple groups in Formula A1 have a synergistic effect, not only adapting to batteries with high compaction density designs but also forming a more stable and denser interfacial film, suppressing volume expansion, and exhibiting excellent cycle performance.

[0165] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises a first additive, a lithium salt, and an organic solvent, wherein the first additive has the structure shown in general formula (I): （I） R1 and R4 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, alkyl group with or without halogen atom substituted or unsubstituted, alkoxy group with or without halogen atom substituted or unsubstituted, phenyl group with or without halogen atom substituted or unsubstituted, and cyano group. R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, alkyl group with or without halogen atom substitution, alkoxy group with or without halogen atom substitution, phenyl group with or without halogen atom substitution, or CR2R3 is cyclopropyl. R5 is selected from any one of hydrogen atom, alkyl group, halogen atom substituted or unsubstituted alkyl group, cyano group; R6 is selected from a hydrogen atom, or R6 is a carbonyl group and R6 is attached to an ortho-phenyl group relative to an amide group.

2. The electrolyte according to claim 1, characterized in that, R1 and R4 are each independently selected from any one of hydrogen atom, halogen atom, C1~C12 alkyl, C1~C12 alkyl with halogen atom substitution or unsubstitution, C1~C12 alkoxy with halogen atom substitution or unsubstitution, C6~C12 phenyl with halogen atom substitution or unsubstitution, and cyano. R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, alkyl group, C1-C12 alkyl group substituted or unsubstituted with halogen atom, C1-C12 alkoxy group substituted or unsubstituted with halogen atom, C6-C12 phenyl group substituted or unsubstituted with halogen atom, or CR2R3 is cyclopropyl.

3. The electrolyte according to claim 2, characterized in that, R1 is selected from any one of hydrogen atoms, C1-C6 alkyl groups, halogen atoms, substituted or unsubstituted C1-C6 alkyl groups; R2 and R3 are each independently selected from any one of hydrogen atom, halogen atom, C1-C6 alkyl, C1-C6 alkyl with or without halogen atom substitution, and C6-C18 phenyl with or without halogen atom substitution; or CR2R3 is cyclopropyl. R4 is selected from any one of hydrogen atom, C1-C6 alkyl group, halogen atom substituted or unsubstituted C1-C6 alkyl group, and cyano group.

4. The electrolyte according to claim 3, characterized in that, R1 is selected from any one of hydrogen atoms and C1~C3 alkyl groups; R2 and R3 are each independently selected from any one of hydrogen atom, fluorine atom, C1~C3 alkyl, and C6 phenyl; or CR2R3 is cyclopropyl. R4 is selected from any one of hydrogen atom, C1~C4 alkyl group, or cyano group.

5. The electrolyte according to any one of claims 1 to 4, characterized in that, The first additive is selected from any one of formulas A1, A2, A3, A4, and A5: Formula A1 Formula A2 Formula A3 Formula A4 Formula A5.

6. The electrolyte according to any one of claims 1 to 4, characterized in that, The mass content of the first additive in the electrolyte is 0.5% to 3.0%.

7. The electrolyte according to any one of claims 1 to 4, characterized in that, The mass content of the first additive in the electrolyte is 1% to 2.5%.

8. The electrolyte according to any one of claims 1 to 4, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium borate, lithium difluorooxalate borate, and lithium difluorosulfonylimide.

9. The electrolyte according to any one of claims 1 to 4, characterized in that, The lithium salt is a mixed lithium salt of lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the mass content of lithium hexafluorophosphate in the electrolyte is 11%~12%, and the mass content of lithium difluorosulfonylimide in the electrolyte is 0.5%~3%.

10. The electrolyte according to any one of claims 1 to 4, characterized in that, The lithium salt in the electrolyte has a mass content of 12% to 15%; and / or, The organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene sulfite, ethyl acetate, diethyl sulfite, and 1,3-propanesulfonate lactone.

11. The electrolyte according to any one of claims 1 to 4, characterized in that, The organic solvent includes at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

12. The electrolyte according to any one of claims 1 to 4, characterized in that, The organic solvent is a mixture of ethylene carbonate, propylene carbonate, methyl ethyl carbonate and dimethyl carbonate, wherein the mass ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate and dimethyl carbonate is (3~9):(0.1~4):(6~7):(4~6).

13. The electrolyte according to any one of claims 1 to 4, characterized in that, The electrolyte also includes a second additive; The second additive includes at least one of vinylene carbonate and vinyl sulfate; The mass content of the second additive in the electrolyte is 0.5% to 3%.

14. A battery, characterized in that, The battery comprises the electrolyte according to any one of claims 1 to 13.

15. The battery according to claim 14, characterized in that, The battery also includes a negative electrode sheet containing a negative electrode active material; The battery also includes a positive electrode sheet containing a positive electrode active material; The negative electrode active material includes a carbon-based negative electrode material; The positive electrode active material includes lithium iron phosphate.

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