Lithium ion secondary battery, electric device, and electrolyte solution

Abstract

The invention provides a lithium ion secondary battery, a power utilization device and an electrolyte. The secondary battery comprises a positive pole piece, a negative pole piece, an isolating membrane and the electrolyte, the positive pole piece comprises a positive pole current collector and a positive pole film layer which is located on at least one surface of the positive pole current collector and contains a positive pole active material, the positive pole active material comprises lithium-containing transition metal oxide and / or lithium-containing transition metal phosphate, and the electrolyte comprises an organic solvent, electrolyte salt and an additive; the additive comprises a polyisocyanate compound with a cyclic structure. The secondary battery provided by the invention has improved high-temperature circulation and high-temperature storage performance, and the power performance of the secondary battery is not deteriorated.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium-ion secondary battery, an electrical device, and an electrolyte. Background Technology

[0002] In recent years, as the application scope of secondary batteries has become increasingly wide, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, and aerospace.

[0003] Due to the significant advancements in secondary batteries, higher requirements have been placed on their high-temperature cycle performance, high-temperature storage performance, and power performance. Summary of the Invention

[0004] This application was made in view of the above-mentioned problems, and its purpose is to provide a lithium-ion secondary battery, an electrical device, and an electrolyte. The lithium-ion secondary battery of this application has improved high-temperature cycle performance and high-temperature storage performance, without deteriorating the power performance of the lithium-ion secondary battery.

[0005] To achieve the above objectives, a first aspect of this application provides a lithium-ion secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector and containing a positive active material. The positive active material includes lithium-containing transition metal oxides and / or lithium-containing transition metal phosphates. The electrolyte includes an organic solvent, an electrolyte salt, and additives. The additives include polyisocyanate compounds with cyclic structures. This application achieves acid removal and water suppression by introducing cyclic isocyanate compounds into the electrolyte, which combine with hydrofluoric acid in the electrolyte or active hydrogen in water. Furthermore, the cyclic isocyanate compounds themselves have good stability, further facilitating acid removal and water suppression, and improving high-temperature cycle performance and high-temperature storage performance. The additives can also suppress side reactions in the electrolyte, thereby further improving the battery's lifespan.

[0006] In some embodiments, the additive comprises the compound shown in Formula 1:

[0007]

[0008] In Formula 1, R1, R2, and R3 are each independently one of hydrogen, a C1-C6 alkyl group, a C1-C6 fluoroalkyl group, a silane group, a siloxane group, a sulfonate group, a sulfate group, a borate group, or a phosphate group. This improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of secondary ion batteries. Furthermore, it also helps the electrolyte to have a suitable viscosity, facilitating the transport of active ions.

[0009] In some embodiments, in Formula 1, R1, R2, and R3 are each independently one of a silane group, a siloxane group, a sulfonate group, a sulfate group, a borate group, and a phosphate group. This further improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of the lithium-ion battery. Furthermore, the sulfonate group, sulfate group, borate group, and phosphate group can also participate in the formation of the negative electrode SEI film, further improving the high-temperature cycling and storage performance of the lithium-ion battery.

[0010] In some embodiments, in Equation 1, R1, R2, and R3 are each independently represented by Equation 2 to Equation 3.

[0011] One of the formulas in Formula 7,

[0012]

[0013] Among them, R4 to R21 are each independently a C1 to C6 alkyl or C1 to C6 fluoroalkyl group. This facilitates further water removal and allows for secondary film formation on the electrode surface, which in turn improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of lithium-ion batteries.

[0014] In some implementations, R1, R2, and R3 are the same. This helps to enhance the effect of the substituents in the additive molecule, reduce the amount of additive used, and avoid excessive additive dosage from affecting battery performance.

[0015] In some embodiments, the additive comprises at least one of the compounds shown in Formulas 8 to 11:

[0016]

[0017] Therefore, on the one hand, it helps to improve the stability of the electrolyte at high temperatures, which is beneficial to the high-temperature cycling and high-temperature storage performance of the secondary battery; on the other hand, it can reduce the internal resistance of the secondary battery, which is beneficial to the power performance of the secondary battery.

[0018] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.01% ≤ W ≤ 5%. This effectively removes water from the electrolyte, which is beneficial to the stability of the electrolyte at high temperatures. Furthermore, it keeps the viscosity and conductivity of the electrolyte within a suitable range, which is beneficial to the cycle performance and storage performance of the secondary battery.

[0019] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.1% ≤ W ≤ 3%. This further benefits the electrolyzer by providing suitable viscosity and conductivity, which in turn improves the cycle performance and storage performance of the secondary battery.

[0020] In some embodiments, the electrolyte further includes an electrolyte salt; the electrolyte salt includes one or more of lithium fluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate.

[0021] In some embodiments, the electrolyte further includes an organic solvent, including cyclic esters and linear esters. This allows for the effective dissociation of electrolyte salts in the electrolyte, reduces electrolyte viscosity, increases lithium-ion transport rate, and consequently improves electrolyte conductivity.

[0022] In some embodiments, the electrolyte has a conductivity of 7 mS / cm to 13 mS / cm at 25°C. This is beneficial for improving the discharge and charge efficiency of the secondary battery, reducing its internal resistance, and thus improving its power performance.

[0023] In some embodiments, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate.

[0024] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector and comprising a negative electrode active material.

[0025] The negative electrode active material includes one or more of the following: artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material, and silicon suboxide.

[0026] A second aspect of this application also provides an electrical device including the secondary battery described in the first aspect of this application. Therefore, the electrical device of this application at least possesses the advantages of the secondary battery of this application.

[0027] A third aspect of this application also provides an electrolyte comprising an electrolyte salt, an organic solvent, and additives, wherein the additives include polyisocyanate compounds with cyclic structures. The cyclic isocyanate compounds combine with active hydrogen in the hydrofluoric acid / water in the electrolyte, achieving acid removal and water suppression. Furthermore, the cyclic isocyanate compounds themselves exhibit good stability, further facilitating acid removal and water suppression, and improving high-temperature cycling and storage performance. The additives can also suppress side reactions in the electrolyte, thereby further extending battery life.

[0028] In some embodiments, the additive comprises the compound shown in Formula 1:

[0029]

[0030] In Formula 1, R1, R2, and R3 are each independently one of hydrogen, a C1-C6 alkyl group, a C1-C6 fluoroalkyl group, a silane group, a siloxane group, a sulfonate group, a sulfate group, a borate group, or a phosphate group. This improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of lithium-ion batteries. Furthermore, it also helps the electrolyte to have a suitable viscosity, facilitating the transport of active ions.

[0031] In some embodiments, in Formula 1, R1, R2, and R3 are each independently one of a silane group, a siloxane group, a sulfonate group, a sulfate group, a borate group, and a phosphate group. This further improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of the lithium-ion battery. Furthermore, the sulfonate group, sulfate group, borate group, and phosphate group can also participate in the formation of the negative electrode SEI film, further improving the high-temperature cycling and storage performance of the lithium-ion battery.

[0032] In some embodiments, in Equation 1, R1, R2, and R3 are each independently represented by Equation 2 to Equation 3.

[0033] One of the formulas in Formula 7,

[0034]

[0035] Among them, R4 to R21 are each independently a C1 to C6 alkyl or C1 to C6 fluoroalkyl group. This facilitates further water removal and allows for secondary film formation on the electrode surface, which in turn improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of lithium-ion batteries.

[0036] In some implementations, R1, R2, and R3 are the same. This helps to enhance the effect of the substituents in the additive molecule, reduce the amount of additive used, and avoid excessive additive dosage from affecting battery performance.

[0037] In some embodiments, the additive comprises at least one of the compounds shown in Formulas 8 to 11:

[0038]

[0039] Therefore, on the one hand, it helps to improve the stability of the electrolyte at high temperatures, which is beneficial to the high-temperature cycling and high-temperature storage performance of the secondary battery; on the other hand, it can reduce the internal resistance of the secondary battery, which is beneficial to the power performance of the secondary battery.

[0040] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.01% ≤ W ≤ 5%. This effectively removes water from the electrolyte, which is beneficial to the stability of the electrolyte at high temperatures. Furthermore, it keeps the viscosity and conductivity of the electrolyte within a suitable range, which is beneficial to the cycle performance and storage performance of the secondary battery.

[0041] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.1% ≤ W ≤ 3%.

[0042] In some embodiments, the electrolyte salt includes one or more of lithium fluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate.

[0043] In some embodiments, the electrolyte further includes an organic solvent, including cyclic esters and linear esters. This allows for effective dissociation of lithium salts in the electrolyte, reduces electrolyte viscosity, increases lithium-ion transport rate, and consequently improves electrolyte conductivity.

[0044] In some embodiments, the cyclic ester includes at least one of ethylene carbonate, propylene carbonate, and butene carbonate;

[0045] The linear esters include at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl acetate, ethyl propionate, and ethyl butyrate.

[0046] In some embodiments, the electrolyte has a conductivity of 7 mS / cm to 13 mS / cm at 25°C. This is beneficial for improving the discharge and charge efficiency of the secondary battery, reducing its internal resistance, and thus improving its power performance. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0048] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0049] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0050] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0051] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0052] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0053] Explanation of reference numerals in the attached figures:

[0054] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0055] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium-ion secondary battery, power supply device, and electrolyte of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0056] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0058] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0059] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0061] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0062] Currently, the electrolyte salt in the electrolyte is generally lithium hexafluorophosphate (LiPF6). LiPF6 is prone to reacting with water at high temperatures and decomposing to produce hydrofluoric acid (HF) as a byproduct. Hydrofluoric acid can cause irreversible damage to the positive and negative electrode interface films, affecting the high-temperature cycling and high-temperature storage performance of secondary batteries.

[0063] In related technologies, acid-removing additives containing silane, acid anhydride, isocyanate, or other groups are added to the electrolyte. These additives react chemically with water or hydrofluoric acid to remove free water or hydrofluoric acid from the electrolyte, reducing the irreversible damage of hydrofluoric acid to the positive and negative electrode interfacial films, improving electrolyte stability, and thus enhancing the high-temperature cycling and storage performance of the secondary battery. However, this method of removing acid by adding acid-removing additives generally requires a large amount, which can affect the electrolyte salt content and further impact the electrochemical performance of the secondary battery. Furthermore, acid-removing additives can increase the internal resistance of the secondary battery, deteriorating its power performance.

[0064] Based on this, this application provides a novel secondary battery, electrical device, and electrolyte. The secondary battery of this application has improved high-temperature cycling and high-temperature storage performance without degrading the power performance of the secondary battery.

[0065] Secondary batteries

[0066] The first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector and containing a positive active material, the positive active material including lithium-containing transition metal oxides and / or lithium-containing transition metal phosphates, and the electrolyte includes an organic solvent, an electrolyte salt, and additives, the additives including polyisocyanate compounds having a cyclic structure.

[0067] In this application, the electrolyte includes a polyisocyanate compound with a cyclic structure. Each nitrogen atom in the cyclic polyisocyanate compound has a lone pair of electrons, which attracts active hydrogen from hydrofluoric acid or water in the electrolyte. This enables acid removal and water suppression, mitigating the damage to the cathode or anode interface film caused by hydrofluoric acid and water at high temperatures. This improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of the secondary battery. Furthermore, the polyisocyanate compound also contains a carbonyl group, which has Lewis basicity and can react with byproducts of lithium salt decomposition in the electrolyte system, such as PF5. This inhibits the reaction between PF5 and ethylene carbonate in the organic solvent, reducing the consumption of organic solvent during cycling, further improving the high-temperature cycling and storage performance of the secondary battery. Moreover, compared to straight-chain isocyanate groups, the cyclic polyisocyanate compound itself is more stable and less prone to decomposition, thus remaining stable in the electrolyte and achieving better water removal, further enhancing the high-temperature cycling and storage performance of the secondary battery. Furthermore, the lone pair electrons on the nitrogen atoms in polyisocyanate compounds can complex with high-valence metal ions. On the one hand, this stabilizes the surface structure of the cathode material, thereby improving the impedance of the cathode interface, reducing the internal resistance of the secondary battery, and improving its power performance. On the other hand, it suppresses the dissolution of metal ions at high voltages, reduces the oxidative activity of the cathode material on the electrolyte, and inhibits side reactions in the electrolyte, thus improving the high-temperature cycling and high-temperature storage performance of the secondary battery. Therefore, the secondary battery in this application can improve high-temperature cycling and high-temperature storage performance without degrading power performance.

[0068] In some embodiments, the additive comprises the compound shown in Formula 1:

[0069]

[0070] In Formula 1, R1, R2, and R3 are each independently one of hydrogen, C1-C6 alkyl, C1-C6 fluoroalkyl, silane group, siloxane group, sulfonate group, sulfate group, borate group, and phosphate group; optionally, R1, R2, and R3 are each independently one of silane group, siloxane group, sulfonate group, sulfate group, borate group, and phosphate group. The additive is selected from the compounds of Formula 1 above. On the one hand, it can attract active hydrogen through the lone pair electrons on the nitrogen atom to remove acid and suppress water; on the other hand, it can remove water through hydrolysis of water with the above groups. That is, the compound shown in Formula 1 can achieve dual water removal, which is more conducive to improving the stability of the electrolyte at high temperatures, thus better improving the high-temperature cycling and high-temperature storage performance of the secondary battery. Furthermore, the selection of R1, R2, and R3 from the above groups ensures that the molecular chain of the additive molecule has a suitable length and that the additive has good compatibility with organic solvents, resulting in a suitable viscosity after the additive dissolves in the electrolyte, facilitating the transport of active ions.

[0071] In this application, alkyl refers to the hydrocarbon group remaining after removing one hydrogen atom from an alkane molecule. C1-C6 alkyl refers to a straight-chain or branched alkyl group having 1-6 carbon atoms. Examples of C1-C6 alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, cyclopentyl, n-hexyl, 2-methylpentyl, 2,2-dimethylbutyl, and 2,2-dimethyl-3-pentyl. Alkyl groups are lipophilic, which facilitates the miscibility of additives with organic solvents in the electrolyte, thus minimizing the impact of additive introduction on electrolyte viscosity and preventing deterioration of the secondary battery's kinetic performance.

[0072] In this application, fluoroalkyl refers to a group formed by replacing hydrogen atoms in an alkyl group with fluorine atoms. C1-C6 fluoroalkyl refers to a straight-chain or branched fluoroalkyl group having 1-6 carbon atoms. Examples of C1-C6 fluoroalkyl groups include fluoromethyl, 1-fluoroethyl, 2-fluoroethyl, and 1,1-difluoroethyl. The fluorine atom in a fluoroalkyl group has strong electron-withdrawing properties, thus reducing the symmetry of the molecule and consequently lowering the viscosity of the additive, which is beneficial to the kinetic performance of the secondary battery. Furthermore, fluoroalkyl can increase the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the additive molecule. This not only improves the antioxidant capacity of the organic solvent but also increases its reduction potential, contributing to improved electrolyte stability and enabling the additive to continuously and stably perform its water-removing function in the battery.

[0073] In this application, the basic structure of the silane group consists of one silicon atom connected to four substituents, which can be hydrogen, alkyl, alkenyl, aryl, etc. The silicon-hydrogen bonds in the silane group have strong reactivity, allowing hydrofluoric acid and water molecules to insert and initiate a reaction. This enables dual dehydration together with cyclic polyisocyanate, enhancing the acid removal and water suppression effects of the additive molecules. In this application, R1, R2, and R3 are selected from silane groups, which is beneficial for further improving the stability of the electrolyte at high temperatures, thus better enhancing the high-temperature cycling and high-temperature storage performance of the secondary battery.

[0074] In this application, the siloxane group refers to the chemical bond composed of silicon and oxygen atoms in a siloxane compound. These groups typically exist in the form of Si-O bonds. The silicon-oxygen bonds in the siloxane group have high reactivity and can undergo hydrolysis reactions with hydrofluoric acid and water molecules to remove water from the electrolyte. In this application, R1, R2, and R3 are selected from siloxane groups, which is beneficial for further improving the stability of the electrolyte at high temperatures, thereby improving the high-temperature cycling and high-temperature storage performance of the secondary battery.

[0075] In this application, the sulfonate group is composed of a sulfonic acid group (R-SO3-) and an ester group (-COO-), usually represented as R-SO3-O-R' (where R and R' represent hydrocarbon or organic groups). The sulfate ester group (-OSO2O-) is a functional group in organic compounds, whose structure consists of one sulfur atom and two oxygen atoms. In the sulfate ester group, the sulfur atom undergoes an esterification reaction with a hydroxyl group (-OH) in an organic molecule to form a sulfate ester.

[0076] The oxygen atoms in the sulfate and sulfonate groups can form hydrogen bonds with water molecules, giving them good hydrophilicity. In this application, R1, R2, and R3 are selected from sulfate or sulfonate groups, which further enables water removal and improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of the secondary battery.

[0077] In this application, a borate ester group refers to a group in which boron atoms and oxygen atoms are covalently bonded, while the oxygen atom forms an ester bond with a carbon atom (usually from alcohols). Its general formula can be represented as ROB(OR')2, where R and R' represent hydrocarbon or organic groups. Borate ester groups are sensitive to water and readily undergo hydrolysis. In this application, R1, R2, and R3 are selected from borate ester groups, which further facilitates water removal, improving the stability of the electrolyte at high temperatures and thus enhancing the high-temperature cycling and storage performance of the secondary battery.

[0078] In this application, the phosphate ester group refers to a compound formed by the reaction of phosphoric acid (H3PO4) with an alcohol, which is an esterified derivative of phosphoric acid. Based on the number of substituted hydrocarbon groups, phosphate ester groups can be classified as primary phosphate ester groups, secondary phosphate ester groups, and tertiary phosphate ester groups. The oxygen atom in the phosphate ester group can form hydrogen bonds with water molecules, and under specific conditions, the phosphate ester group can also undergo hydrolysis with water. In this application, R1, R2, and R3 are selected from phosphate ester groups, which further enables water removal, which is beneficial for further improving the stability of the electrolyte at high temperatures, thus better enhancing the high-temperature cycling and high-temperature storage performance of the secondary battery.

[0079] In addition, sulfonate groups, sulfate groups, borate groups, and phosphate groups are easily reduced, which allows the additive molecules to undergo a reduction reaction at the negative electrode and participate in the formation of the negative electrode SEI film, thereby improving the cycle performance and storage performance of the secondary battery.

[0080] In some implementations, R1, R2, and R3 are each independently represented by the following formulas 2 to 7;

[0081]

[0082] Among them, R4 to R21 are independently C1 to C6 alkyl groups and C1 to C6 fluoroalkyl groups.

[0083] Here, C1 to C6 alkyl groups and C1 to C6 fluoroalkyl groups have the same definition as in Formula 1 above, and will not be repeated here.

[0084] In this application, since the groups shown in Formulas 2 to 7 all have a certain degree of hydrophilicity or can react with water, or participate in the formation of the negative electrode SEI film, R1, R2, and R3 are selected from the above groups, which can further achieve water removal, which is beneficial to further improve the stability of the electrolyte at high temperature, and thus is more conducive to the high temperature cycling and high temperature storage performance of the secondary battery.

[0085] In some embodiments, R1, R2, and R3 are the same. This is beneficial for enhancing the effect of the substituents in the additive molecule, reducing the amount of additive used, and avoiding excessive additive dosage from affecting battery performance. For example, when R1, R2, and R3 are all silane groups or siloxane groups, these groups themselves can also react with active hydrogen to convert into products with lower reactivity, achieving a dual acid removal and water suppression effect; when R1, R2, and R3 are all selected from any one of sulfonate groups, sulfate groups, borate groups, and phosphate groups, they can undergo a reduction reaction on the negative electrode surface, participate in SEI film formation, and form a more stable SEI film, which further helps to improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0086] In some implementations, R1, R2, and R3 may be different or not exactly the same.

[0087] In some embodiments, when R1, R2, and R3 are not hydrogen, the compound shown in Formula 1 can undergo redox reactions at the positive or negative electrode interface depending on the different functional groups, that is, participate in the formation of the positive or negative electrode interface film, thereby stabilizing the positive electrode interface, reducing the internal resistance of the secondary battery, and improving the power performance of the secondary battery.

[0088] In some embodiments, the additive includes isocyanuric acid. The three nitrogen atoms in the cyclic structure of isocyanuric acid each have a lone pair of electrons. On one hand, these lone pairs of electrons attract active hydrogen, thereby achieving water removal and improving the stability of the electrolyte at high temperatures, thus benefiting the high-temperature cycling and storage performance of the secondary battery. On the other hand, these lone pairs of electrons can also complex with high-valence metal ions, for example, adsorbing onto the surface of the cathode material, stabilizing the surface structure of the cathode material, thereby improving the impedance of the cathode interface, reducing the internal resistance of the secondary battery, and improving the power performance of the secondary battery.

[0089] In some embodiments, the additive comprises at least one of the compounds shown in Formulas 8 to 11:

[0090]

[0091] The above-mentioned compounds are used as additives in this application. On the one hand, they help improve the stability of the electrolyte at high temperatures, thereby improving the high-temperature cycling and high-temperature storage performance of the secondary battery. On the other hand, they can reduce the internal resistance of the secondary battery, which is beneficial to the power performance of the secondary battery.

[0092] In some embodiments, R1, R2, and R3 can be selected from Formula 2, and R4 to R7 in Formula 2 can be, for example, ethyl.

[0093] In some embodiments, R1, R2, and R3 can be selected from Formula 5, and R14 and R15 in Formula 5 can be, for example, propyl.

[0094] In some embodiments, R1, R2, and R3 can be selected from Formula 6, and R16 to R18 in Formula 6 can be, for example, methyl groups.

[0095] In some embodiments, R1, R2, and R3 can be selected from Formula 7, and R19 to R21 in Formula 7 can be, for example, methyl groups.

[0096] In some embodiments, R1, R2, and R3 may be selected from C1 to C6 haloalkyl groups, such as chloromethyl groups.

[0097] In some implementations, R1, R2, and R3 can be selected from hydrogen.

[0098] In some embodiments, the additive comprises at least one of the compounds shown in Formulas 12 to 18:

[0099]

[0100]

[0101] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.01% ≤ W ≤ 5%; optionally, 0.1% ≤ W ≤ 3%. Exemplarily, W is a value within the range of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two of these values. When the mass percentage of the additive in the electrolyte is within the above range, it can effectively remove water from the electrolyte, which is beneficial to the stability of the electrolyte at high temperatures. Furthermore, it keeps the viscosity and conductivity of the electrolyte within a suitable range, which is beneficial to the cycle performance and storage performance of the secondary battery.

[0102] In some embodiments, the electrolyte salt includes one or more of lithium fluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate.

[0103] In some embodiments, the electrolyte further includes an organic solvent; the organic solvent includes cyclic esters and linear esters. Cyclic esters in the electrolyte can effectively dissociate electrolyte salts, while linear esters can reduce electrolyte viscosity, increase the active ion transport rate, and thus improve electrolyte conductivity.

[0104] In some embodiments, the cyclic ester is selected from at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and γ-butyrolactone. In some embodiments, the linear ester is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl formate, methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl acetate, methyl butyrate, and butyl acetate.

[0105] In some embodiments, the concentration of lithium salt in the electrolyte is 0.8 mol / L to 1.5 mol / L.

[0106] In this application, the composition of the electrolyte can be determined using equipment and methods known in the art. As an example, the organic components (e.g., additives) in the electrolyte can be quantitatively analyzed by gas chromatography, referring to standard GB / T9722-2006. As an example, the inorganic components and lithium salt concentration in the electrolyte can be quantitatively analyzed by ion chromatography, referring to standard JY / T020-1996.

[0107] In this application, the electrolyte can be prepared by the following steps: In a glove box filled with argon (water content < 0.1 ppm, oxygen content < 0.1 ppm), solvent 1 (e.g., ethylene carbonate) and solvent 2 (e.g., ethyl methyl carbonate) are mixed evenly in a mass ratio of (2:8) to (3:7) to form an organic solvent. Then, a certain amount of additive (e.g., isocyanuric acid) is added to the organic solvent, followed by the addition of an appropriate amount of lithium salt (e.g., LiPF6). After the lithium salt is completely dissolved, the electrolyte is obtained.

[0108] In some embodiments, the electrolyte has a conductivity of 7 mS / cm to 13 mS / cm at 25°C. An electrolyte conductivity within this range is beneficial for improving the discharge and charge efficiency of the secondary battery, reducing its internal resistance, and thus improving its power performance. For example, the electrolyte conductivity at 25°C is a value between 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, or any two of these values.

[0109] In this application, the electrical conductivity of the electrolyte refers to the magnitude of the electrolyte's ability to conduct electricity, which can be measured using equipment and methods known in the art. As an example, it can be tested using a conductivity meter in accordance with industry standard HG / T4067-2015. Specifically, two metal plates, i.e., electrodes, are inserted into the electrolyte solution, and the resistivity between the two electrodes is measured to determine the conductivity. Conductivity is the reciprocal of resistivity, and its definition is given by an electrode cross-sectional area of ​​1 cm². 2 The conductivity of the solution when the distance between the two electrodes is 1 cm is expressed in S / cm.

[0110] The term "secondary battery" as used in this application refers to a battery cell, battery module, or battery pack. Typically, a secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0111] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector and containing a positive active material; the positive active material includes one or more of lithium cobalt oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate.

[0112] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the active material region is disposed on either or both of the two opposite surfaces of the positive current collector.

[0113] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0115] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the active material region of the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0117] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector and containing a negative electrode active material; the negative electrode active material includes one or more of artificial graphite, natural graphite, lithium titanate, lithium metal, silicon-carbon composite material, and silicon suboxide.

[0118] In some embodiments, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0119] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0121] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0124] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0125] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0126] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0127] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0128] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0129] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0130] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0131] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0132] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0133] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0134] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0135] Figure 4 and Figure 5This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0136] Electrical appliances

[0137] Furthermore, a second aspect of this application provides an electrical device, which includes the secondary battery provided in the first aspect of this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0138] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0139] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0140] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0141] electrolyte

[0142] A third aspect of this application provides an electrolyte comprising an electrolyte salt, an organic solvent, and additives, wherein the additives include polyisocyanate compounds with cyclic structures. These cyclic isocyanate compounds combine with active hydrogen in the hydrofluoric acid / water of the electrolyte, achieving acid removal and water suppression. Furthermore, the cyclic isocyanate compounds themselves exhibit good stability, further facilitating acid removal and water suppression, and improving high-temperature cycling and storage performance. The additives also inhibit side reactions in the electrolyte, thereby further extending battery life.

[0143] In some embodiments, the additive comprises the compound shown in Formula 1:

[0144]

[0145] In Formula 1, R1, R2, and R3 are each independently one of hydrogen, a C1-C6 alkyl group, a C1-C6 fluoroalkyl group, a silane group, a siloxane group, a sulfonate group, a sulfate group, a borate group, or a phosphate group. This improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of lithium-ion batteries. Furthermore, it also helps the electrolyte to have a suitable viscosity, facilitating the transport of active ions.

[0146] In some embodiments, in Formula 1, R1, R2, and R3 are each independently one of a silane group, a siloxane group, a sulfonate group, a sulfate group, a borate group, and a phosphate group. This further improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of the lithium-ion battery. Furthermore, the sulfonate group, sulfate group, borate group, and phosphate group can also participate in the formation of the negative electrode SEI film, further improving the high-temperature cycling and storage performance of the lithium-ion battery.

[0147] In some embodiments, in Equation 1, R1, R2, and R3 are each independently represented by Equation 2 to Equation 3.

[0148] One of the formulas in Formula 7,

[0149]

[0150] Among them, R4 to R21 are each independently a C1 to C6 alkyl or C1 to C6 fluoroalkyl group. This facilitates further water removal and allows for secondary film formation on the electrode surface, which in turn improves the stability of the electrolyte at high temperatures, thus enhancing the high-temperature cycling and storage performance of lithium-ion secondary batteries.

[0151] In some implementations, R1, R2, and R3 are the same. This helps to enhance the effect of the substituents in the additive molecule, reduce the amount of additive used, and avoid excessive additive dosage from affecting battery performance.

[0152] In some embodiments, the additive comprises at least one of the compounds shown in Formulas 8 to 11:

[0153]

[0154] Therefore, on the one hand, it helps to improve the stability of the electrolyte at high temperatures, which is beneficial to the high-temperature cycling and high-temperature storage performance of the secondary battery; on the other hand, it can reduce the internal resistance of the secondary battery, which is beneficial to the power performance of the secondary battery.

[0155] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.01% ≤ W ≤ 5%. This effectively removes water from the electrolyte, which is beneficial to the stability of the electrolyte at high temperatures. Furthermore, it keeps the viscosity and conductivity of the electrolyte within a suitable range, which is beneficial to the cycle performance and storage performance of the secondary battery.

[0156] In some embodiments, the mass percentage W of the additive in the electrolyte satisfies: 0.1% ≤ W ≤ 3%.

[0157] In some embodiments, the electrolyte salt includes one or more of lithium fluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate.

[0158] In some embodiments, the electrolyte further includes an organic solvent, including cyclic esters and linear esters. This allows for effective dissociation of lithium salts in the electrolyte, reduces electrolyte viscosity, increases lithium-ion transport rate, and consequently improves electrolyte conductivity.

[0159] In some embodiments, the cyclic ester includes at least one of ethylene carbonate, propylene carbonate, and butene carbonate;

[0160] The chain esters include at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, propyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.

[0161] In some embodiments, the electrolyte has a conductivity of 7 mS / cm to 13 mS / cm at 25°C. This is beneficial for improving the discharge and charge efficiency of the secondary battery, reducing its internal resistance, and thus improving its power performance.

[0162] Example

[0163] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0164] Example 1

[0165] 1) Preparation of the positive electrode sheet:

[0166] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1O2, conductive agent carbon black Super P, and binder polyvinylidene fluoride (PVDF) are dissolved in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 80:10:10 and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, a positive electrode sheet is obtained.

[0167] 2) Preparation of the negative electrode sheet:

[0168] Artificial graphite (anode active material), carbon black Super P (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (mass ratio 80:15:2:3) are dissolved in deionized water and mixed evenly to prepare a cathode slurry. The cathode slurry is then uniformly coated onto copper foil (anode current collector), and after drying, cold pressing, slitting, and cutting, a cathode sheet is obtained.

[0169] 3) Preparation of electrolyte:

[0170] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed uniformly at a mass ratio of 30:70 to form an organic solvent. Additives (compounds shown in Formula 8 of Table 1 below) are added to the organic solvent and mixed uniformly. Then, fully dried LiPF6 is dissolved in the above organic solvent to form an electrolyte with a LiPF6 concentration of 1 mol / L. The mass percentage W1 of the additives (compounds shown in Formula 8) in the electrolyte is 0.5%.

[0171] The conductivity of the electrolyte prepared in Example 1 was measured to be 8.7 mS / cm using a conductivity meter according to standard HG / T4067-2015.

[0172] 4) Separating membrane: A 16μm polyethylene film is used as the separating membrane;

[0173] 5) Preparation of secondary batteries:

[0174] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0175] Example 2-10

[0176] The secondary battery was prepared using the same method as in Example 1, except that the types of additives were adjusted according to Tables 1 and 2 below when preparing the electrolyte. Please refer to Tables 1 and 2 below for details.

[0177] Comparative Example 1

[0178] The secondary battery was prepared using the same method as in Example 1, except that the electrolyte did not contain any additives. Please refer to Table 2 below for details.

[0179] Comparative Example 2

[0180] The secondary battery was prepared using the same method as in Example 1, except that isocyanate (HNCO) was used as an additive when preparing the electrolyte, as detailed in Table 2 below.

[0181] Comparative Example 3

[0182] The secondary battery was prepared using the same method as in Example 1, except that trimethoxysilane was used as an additive in the preparation of the electrolyte, as detailed in Table 2 below.

[0183] Comparative Example 4

[0184] The secondary battery was prepared using the same method as in Example 1, except that isocyanate and trimethoxysilane were used as additives when preparing the electrolyte, as detailed in Table 2 below.

[0185] Table 1 below shows the polyisocyanate compounds with cyclic structures used in the embodiments of this application.

[0186] Table 1

[0187]

[0188]

[0189]

[0190] Secondary battery performance test

[0191] 1) High-temperature cycling performance test

[0192] The following steps were performed on the above-mentioned secondary battery at 45°C:

[0193] ① Charge at a constant current of 1C to 4.3V, and then charge at a constant voltage of 4.3V to a current of 0.05C;

[0194] ② Let it sit for 10 minutes;

[0195] ③ Discharge to 2.8V with a constant current of 1C, and record the resulting capacity as the initial capacity C0;

[0196] ④ Let it sit for 5 minutes;

[0197] ⑤ Repeat steps ① to ④ above 600 times, and record the discharge capacity C1 on the 600th cycle;

[0198] Capacity retention rate after 600 cycles = (C1 / C0) * 100%.

[0199] 2) High-temperature storage performance test

[0200] At 25°C, the above-mentioned secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage of 4.3V to the cutoff current of 0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to 2.8V, and the discharge capacity D0 at this time was recorded.

[0201] The secondary battery was stored at 60°C for 80 days. Afterward, the battery was removed and cooled to a surface temperature of 25°C. Then, at 25°C, it was discharged at a constant current of 1C to 2.8V, then charged at a constant current of 1C to 4.3V, and finally charged at a constant voltage of 4.3V to a cutoff current of 0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to 2.8V, yielding the discharge capacity D1 after 80 days of storage at 60°C.

[0202] Capacity retention rate (%) after 80 days of storage at 60℃ = (D1 / D0) × 100%.

[0203] 3) Power performance test

[0204] The DC internal resistance (DCR) of a secondary battery characterizes its power performance. Generally, the lower the DCR, the better the battery's power performance.

[0205] At 25°C, the aforementioned secondary battery was charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V to a cutoff current of 0.05C, allowed to stand for 30 minutes, and then discharged at a constant current of 1C for 0.5 hours, allowed to stand for 30 minutes, and the voltage V1 after standing was recorded. Next, it was discharged at a current of 4C for 30 seconds, with sampling intervals of 0.1 seconds, and the voltage V2 at the end of the discharge was recorded.

[0206] The DCR of a secondary battery is (V1-V2) / I, where I is the current corresponding to a 4C rate.

[0207] The test results of the secondary batteries prepared in Examples 1-10 and Comparative Examples 1-4 are shown in Table 2 below.

[0208] Table 2

[0209]

[0210] As shown in Table 2 above, compared to Comparative Example 1 (without additives), the addition of cyclic polyisocyanate additives to the electrolyte in Examples 1-9 significantly improved the high-temperature cycling and high-temperature storage performance of the secondary batteries, and Examples 1-9 did not worsen the internal resistance and power performance of the secondary batteries. Comparative Examples 2 (with isocyanate as an additive) and 3 (with trimethoxysilane as an additive) showed less improvement in the secondary battery's high-temperature cycling and high-temperature storage performance, and the addition of trimethoxysilane as an additive in Comparative Example 3 significantly worsened the internal resistance and power performance of the secondary battery. Furthermore, in Comparative Example 4 (with cyanuric acid and trimethoxysilane as additives), although there was some improvement in high-temperature cycling and high-temperature storage performance, the internal resistance and power performance of the secondary battery were worsened.

[0211] Examples 10-13

[0212] The secondary battery was prepared using the same method as in Example 1, except that the amount of additives in the electrolyte was different, as detailed in Table 3 below.

[0213] The test results of the secondary batteries prepared in Examples 10-13 above are shown in Table 3 below.

[0214] Table 3

[0215]

[0216] As can be seen from Table 3 above, when the content of the additive W1 satisfies 0.01%≤W1≤5%, it is beneficial to improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery, and will not deteriorate the internal resistance and power performance of the secondary battery.

[0217] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium-ion secondary battery, characterized in that, Includes positive electrode, negative electrode, separator, and electrolyte. The positive electrode sheet includes a positive current collector and a positive electrode film layer containing positive active material located on at least one surface of the positive current collector. The positive electrode active material includes lithium-containing transition metal oxides and / or lithium-containing transition metal phosphates. The electrolyte includes an organic solvent, an electrolyte salt, and additives, the additives including polyisocyanate compounds having a cyclic structure.

2. The secondary battery according to claim 1, characterized in that, The additive comprises the compound shown in Formula 1: In Formula 1, R1, R2, and R3 are each independently one of hydrogen, C1-C6 alkyl, C1-C6 fluoroalkyl, silane group, siloxane group, sulfonate group, sulfate group, borate group, and phosphate group.

3. The secondary battery according to claim 2, characterized in that, In Formula 1, R1, R2, and R3 are each independently one of silane group, siloxane group, sulfonate group, sulfate group, borate group, and phosphate group.

4. The secondary battery according to claim 2 or 3, characterized in that, In Equation 1, R1, R2, and R3 are each independently one of Equations 2 to 7 below. Among them, R4 to R21 are each independently a C1 to C6 alkyl group or a C1 to C6 fluoroalkyl group.

5. The secondary battery according to any one of claims 2 to 4, characterized in that, R1, R2, and R3 are the same.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The additive comprises at least one of the compounds shown in Formulas 8 to 11:

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The mass percentage W of the additive in the electrolyte satisfies: 0.01% ≤ W ≤ 5%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The mass percentage W of the additive in the electrolyte satisfies: 0.1% ≤ W ≤ 3%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The electrolyte salt includes one or more of lithium fluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The electrolyte also includes an organic solvent, which includes cyclic esters and linear esters.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The electrolyte has a conductivity of 7 mS / cm to 13 mS / cm at 25°C.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, ternary nickel-cobalt-manganese lithium, nickel-manganese lithium oxide, lithium iron phosphate, or lithium manganese iron phosphate.

13. The secondary battery according to any one of claims 1 to 12, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer containing a negative electrode active material located on at least one surface of the negative electrode current collector. The negative electrode active material includes one or more of the following: artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material, and silicon suboxide.

14. An electrical appliance, characterized in that, The secondary battery includes any one of claims 1 to 13.

15. An electrolyte, characterized in that, The electrolyte comprises an electrolyte salt, an organic solvent, and additives; the additives include polyisocyanate compounds with a cyclic structure.

16. The electrolyte according to claim 15, characterized in that, The additive comprises the compound shown in Formula 1: In Formula 1, R1, R2, and R3 are each independently one of hydrogen, C1-C6 alkyl, C1-C6 fluoroalkyl, silane group, siloxane group, sulfonate group, sulfate group, borate group, and phosphate group.

17. The electrolyte according to claim 16, characterized in that, In Formula 1, R1, R2, and R3 are each independently one of silane group, siloxane group, sulfonate group, sulfate group, borate group, and phosphate group.

18. The electrolyte according to claim 16 or 17, characterized in that, In Equation 1, R1, R2, and R3 are each independently one of Equations 2 to 7 below. Among them, R4 to R21 are each independently a C1 to C6 alkyl group or a C1 to C6 fluoroalkyl group.

19. The electrolyte according to any one of claims 16 to 18, characterized in that, R1, R2, and R3 are the same.

20. The electrolyte according to any one of claims 15 to 19, characterized in that, The additive comprises at least one of the compounds shown in Formulas 8 to 11:

21. The electrolyte according to any one of claims 15 to 20, characterized in that, The mass percentage W of the additive in the electrolyte satisfies: 0.01% ≤ W ≤ 5%.

22. The electrolyte according to any one of claims 15 to 21, characterized in that, The mass percentage W of the additive in the electrolyte satisfies: 0.1% ≤ W ≤ 3%.

23. The electrolyte according to any one of claims 15 to 22, characterized in that, The electrolyte salt includes one or more of lithium fluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, and lithium difluorophosphate.

24. The electrolyte according to any one of claims 15 to 23, characterized in that, The organic solvents include cyclic esters and linear esters.

25. The electrolyte according to claim 24, characterized in that, The cyclic esters include at least one of ethylene carbonate, propylene carbonate, and butene carbonate; The linear esters include at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl acetate, ethyl propionate, and ethyl butyrate.

26. The electrolyte according to any one of claims 15 to 25, characterized in that, The electrolyte has a conductivity of 7 mS / cm to 13 mS / cm at 25°C.

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