Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a non-aqueous electrolyte, the non-aqueous electrolyte comprises fluoroethyl propionate, the fluoroethyl propionate is selected from one or two of 1-propionic acid-2, 2-difluoroethyl propionate and propionic acid-2, 2, 2-trifluoroethyl propionate, based on the total mass of the non-aqueous electrolyte, the fluoroethyl propionate is selected from one or two of 1-propionic acid-2, 2-difluoroethyl propionate and 1-propionic acid-2, 2, 2-trifluoroethyl propionate, and the fluoroethyl propionate is selected from one or two of 1-propionic acid-2, 2-difluoroethyl propionate and 1-propionic acid-2, 2, 2-trifluoroethyl propionate. The mass percentage content of the fluoroethyl propionate is 5%-65%; based on the total mass of the non-aqueous electrolyte, the sum of the mass percentage content of the ethylene carbonate (EC) and the mass percentage content of the propylene carbonate (PC) is smaller than or equal to 15%. The secondary battery can reduce the heat accumulation of the battery and improve the thermal safety performance of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, especially lithium-ion batteries, are widely used in portable electronic products, electric vehicles, aerospace, energy storage and other fields due to their high energy density, good cycle performance, safety, environmental protection and no memory effect. In order to meet the needs of social development, seeking secondary batteries with higher energy density has become an urgent problem to be solved, which makes the battery design towards large capacity, resulting in battery heat accumulation and poor thermal safety performance.

[0003] Therefore, there is an urgent need to provide a secondary battery that can reduce heat accumulation in large-capacity batteries and improve the thermal safety performance of the secondary battery. Summary of the invention

[0004] In order to solve the above problems, the present application provides a secondary battery and an electronic device.

[0005] According to a first aspect of the present application, a secondary battery is provided, the secondary battery comprising a non-aqueous electrolyte, the non-aqueous electrolyte comprising:

[0006] (1) fluoroethyl propionate, wherein the fluoroethyl propionate is selected from one or both of 2,2-difluoroethyl 1-propionate and 2,2,2-trifluoroethyl propionate, and the mass percentage of the fluoroethyl propionate is 5% to 65% based on the total mass of the non-aqueous electrolyte;

[0007] (2) Ethylene carbonate (EC) and propylene carbonate (PC). Based on the total mass of the non-aqueous electrolyte, the sum of the mass percentages of ethylene carbonate (EC) and propylene carbonate (PC) is ≤ 15%.

[0008] In some embodiments of the present application, the non-aqueous electrolyte of the present application satisfies at least one of the following conditions: (1) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate is 10% to 60%; (2) based on the total mass of the non-aqueous electrolyte, the mass percentage of ethylene carbonate is ≤10%; (3) based on the total mass of the non-aqueous electrolyte, the mass percentage of propylene carbonate is ≤10%.

[0009] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate is 12% to 50%.

[0010] In some embodiments of the present application, the non-aqueous electrolyte of the present application satisfies at least one of the following conditions: (1) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate is 12% to 45%; (2) based on the total mass of the non-aqueous electrolyte, the ratio of the mass percentage of ethylene carbonate to the mass percentage of propylene carbonate is 1:1.

[0011] In some embodiments of the present application, the non-aqueous electrolyte of the present application further includes fluoroethylene carbonate (FEC), and the mass percentage of fluoroethylene carbonate is 3% to 15% based on the total mass of the non-aqueous electrolyte.

[0012] In some embodiments of the present application, the non-aqueous electrolyte of the present application satisfies at least one of the following conditions: (1) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethylene carbonate is 3% to 8%; (2) based on the total mass of the non-aqueous electrolyte, the ratio of the mass percentage of fluoroethyl propionate to the mass percentage of fluoroethylene carbonate is 0.8 to 12.

[0013] In some embodiments of the present application, the non-aqueous electrolyte of the present application further includes a nitrile compound having 2 or more nitrile groups in a single molecule, and the mass percentage of the nitrile compound is 0.5% to 5% based on the total mass of the non-aqueous electrolyte; the nitrile compound is selected from succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methylglutaronitrile, and one or more of the compounds of the following formulas I-1 to I-19:

[0014]

[0015]

[0016]

[0017] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of the nitrile compound is 1.5% to 4%.

[0018] In some embodiments of the present application, in the secondary battery provided by the present application, the non-aqueous electrolyte also includes fluoroethylene carbonate (FEC), and the mass percentage of fluoroethylene carbonate is 3% to 15% based on the total mass of the non-aqueous electrolyte; based on the total mass of the non-aqueous electrolyte, the ratio of the mass percentage of fluoroethylene carbonate to the mass percentage of nitrile compounds is 0.6 to 16.

[0019] In some embodiments of the present application, in the secondary battery provided in the present application, the non-aqueous electrolyte further includes a compound of formula II, and the compound of formula II is selected from one or more of the following compounds of formula II-1 to formula II-14:

[0020]

[0021] In some embodiments of the present application, in the secondary battery provided by the present application, the mass percentage of the compound of formula II is 0.2% to 3% based on the total mass of the non-aqueous electrolyte.

[0022] In some embodiments of the present application, the secondary battery provided in the present application further includes a positive electrode, a negative electrode, a diaphragm, a shell and a tab, the tab extending from the inside of the shell to the outside of the shell, along the direction of extension of the tab, the width of the diaphragm is greater than the width of the negative electrode, and the difference between the width of the diaphragm and the width of the negative electrode is 0.5 mm to 2.8 mm.

[0023] According to a second aspect of the embodiments of this specification, there is provided an electronic device comprising the secondary battery described in any one of the embodiments of the first aspect.

[0024] The technical solution provided by this application may have the following beneficial effects:

[0025] (1) In the secondary battery provided in the embodiment of the present application, fluoroethyl propionate is relatively further away from the positive electrode surface during the flow process, and its reactivity at the positive electrode is reduced, thereby reducing heat generation on the positive electrode side;

[0026] (2) Ethylene carbonate and propylene carbonate, as cyclic carbonates, have good chemical stability and cycle performance, which helps to quickly form the desired solid electrolyte interface (SEI) and reduce heat generation at the negative electrode.

[0027] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present specification. DETAILED DESCRIPTION

[0028] Here, exemplary embodiments will be described in detail, but the exemplary embodiments described below do not represent all embodiments consistent with this specification. Instead, they are only embodiments consistent with some aspects of this specification as detailed in the appended claims.

[0029] The terms used in this specification are only for the purpose of describing specific implementations / embodiments and are not intended to limit this specification. The singular forms of "a", "said" and "the" used in this specification and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0030] It should be noted that in the specific implementation of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0031] The secondary battery provided in the present application includes a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains:

[0032] (1) Fluoroethyl propionate, the fluoroethyl propionate is selected from one or both of 2,2-difluoroethyl 1-propionate (also referred to as difluoroethyl propionate (CAS No. 1133129-90-4)) and 2,2,2-trifluoroethyl propionate (also referred to as trifluoroethyl propionate (CAS No. 82259-34-5)), and the mass percentage of the fluoroethyl propionate is 5% to 65% based on the total mass of the non-aqueous electrolyte;

[0033] (2) Ethylene carbonate (EC) and propylene carbonate (PC). Based on the total mass of the non-aqueous electrolyte, the sum of the mass percentages of ethylene carbonate and propylene carbonate is ≤ 15%.

[0034] In order to meet the needs of social development, secondary batteries are currently designed in the direction of large capacity, and large capacity design will lead to heat accumulation in the battery and poor thermal safety performance. The inventors have found that when fluoroethyl propionate selected from 1-2,2-difluoroethyl propionate and / or 2,2,2-trifluoroethyl propionate is used in a non-aqueous electrolyte, the fluoroethyl propionate is relatively farther away from the positive electrode surface during the flow process, and the reactivity at the positive electrode is reduced, thereby reducing heat generation on the positive electrode side, thereby improving the hot box accumulation effect of the secondary battery and improving thermal performance.

[0035] In particular, the inventors have found that 2,2-difluoroethyl 1-propionate and / or 2,2,2-trifluoroethyl propionate have better thermal performance improvement effects in the secondary battery of the present application than other fluoroethyl propionates, and the non-aqueous electrolyte formed by them and other components in the non-aqueous electrolyte provided by the present application, such as ethylene carbonate and propylene carbonate, fluoroethylene carbonate, nitrile compounds having 2 or more nitrile groups in a single molecule, and compounds of formula II, have even better performance.

[0036] In the present application, the fluoroethyl propionate is one or both selected from 2,2-difluoroethyl 1-propionate and 2,2,2-trifluoroethyl propionate, and there is no particular limitation.

[0037] The study found that when the content of fluoroethyl propionate is too low, the thermal performance of the non-aqueous electrolyte using it is limited, and when the content of fluoroethyl propionate is too high, the stability of the non-aqueous electrolyte using it will be affected.

[0038] In the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 2,2-difluoroethyl 1-propionate and / or 2,2,2-trifluoroethyl propionate is 5% to 65%.

[0039] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 2,2-difluoroethyl 1-propionate and / or 2,2,2-trifluoroethyl propionate is, for example, 5%, 6%, 8%, 9%, 10%, 11%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 61%, 62%, 63%, 64%, 65%, or a range consisting of any two of these values.

[0040] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 2,2-difluoroethyl 1-propionate and / or 2,2,2-trifluoroethyl propionate is 10% to 60%.

[0041] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 1-propionic acid-2,2-difluoroethyl ester and / or propionic acid-2,2,2-trifluoroethyl ester is, for example, 10%, 11%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, or the range of any two of these values. At this point, the thermal performance of the secondary battery provided by the present application is further improved.

[0042] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 2,2-difluoroethyl 1-propionate and / or 2,2,2-trifluoroethyl propionate is 12% to 50%.

[0043] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 1-propionic acid-2,2-difluoroethyl ester and / or propionic acid-2,2,2-trifluoroethyl ester is, for example, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 48%, 50%, or the range of any two of these values. At this point, the thermal performance of the secondary battery provided by the present application is significantly improved.

[0044] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 2,2-difluoroethyl 1-propionate and / or 2,2,2-trifluoroethyl propionate is 12% to 45%.

[0045] In some embodiments of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate selected from 1-propionic acid-2,2-difluoroethyl ester and / or propionic acid-2,2,2-trifluoroethyl ester is, for example, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, or a range consisting of any two of these values. At this point, the thermal performance of the secondary battery provided by the present application is further significantly improved. In the secondary battery provided by the present application, ethylene carbonate and propylene carbonate are also used as important component solvents in the non-aqueous electrolyte. Among them, ethylene carbonate and propylene carbonate, as cyclic carbonates, have good chemical stability and cycle performance, which help to quickly form the desired solid electrolyte interface (SEI).

[0046] In the secondary battery provided in the present application, the sum of the mass percentages of ethylene carbonate and propylene carbonate in the non-aqueous electrolyte is no more than 15%, thereby not only ensuring the cycle performance of the secondary battery but also improving the thermal performance of the obtained secondary battery.

[0047] In some embodiments of the present application, the sum of the mass percentages of ethylene carbonate and propylene carbonate in the non-aqueous electrolyte is, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of these values.

[0048] In some embodiments of the present application, the mass percentage of ethylene carbonate in the non-aqueous electrolyte is ≤10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of these values. In this case, the thermal stability of the secondary battery is better.

[0049] In some embodiments of the present application, the mass percentage of propylene carbonate in the non-aqueous electrolyte is ≤10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of these values. In this case, the thermal stability of the secondary battery is better.

[0050] In some embodiments of the present application, the sum of the mass percentages of ethylene carbonate and propylene carbonate in the non-aqueous electrolyte is ≤10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of these values. In this case, the thermal performance of the secondary battery obtained is further improved.

[0051] In some embodiments of the present application, the non-aqueous electrolyte satisfies at least one of the following conditions: (1) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate is 10% to 60%; (2) based on the total mass of the non-aqueous electrolyte, the mass percentage of ethylene carbonate is ≤10%; (3) based on the total mass of the non-aqueous electrolyte, the mass percentage of propylene carbonate is ≤10%. When the non-aqueous electrolyte satisfies the above conditions, fluoroethyl propionate is relatively further away from the positive electrode surface during the flow process, and the reactivity at the positive electrode is reduced, thereby reducing the heat generation on the positive electrode side; ethylene carbonate and propylene carbonate, as cyclic carbonates, have good chemical stability and cycle performance, which helps to quickly form the desired solid electrolyte interface (SEI) and reduce the heat generation of the negative electrode; thereby reducing the heat accumulation of the battery and improving the thermal safety performance of the secondary battery.

[0052] In some embodiments of the present application, the non-aqueous electrolyte satisfies at least one of the following conditions: (1) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate is 12% to 45%; (2) based on the total mass of the non-aqueous electrolyte, the mass percentage of ethylene carbonate and the mass percentage of propylene carbonate is 1:1. In this case, the obtained secondary battery has not only excellent thermal performance, but also excellent cycle performance.

[0053] In the secondary battery provided in the present application, the non-aqueous electrolyte also includes fluoroethylene carbonate (Fluoroethylene Carbonate, FEC, or fluoroethylene carbonate), which is beneficial to improving the structural stability and thermal stability of the solid electrolyte interface (SEI), thereby improving the cycle performance and thermal performance of the secondary battery.

[0054] When the content of fluoroethylene carbonate in the non-aqueous electrolyte is too low, such as less than 3%, the improvement of the performance of the secondary battery is limited; when the content of fluoroethylene carbonate in the non-aqueous electrolyte is too high, such as more than 15%, the viscosity of the electrolyte increases, affecting the transmission of lithium ions, and the rate performance of the secondary battery will be affected. Therefore, in the embodiment of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethylene carbonate is 3% to 15%.

[0055] In some embodiments of the present application, the content of fluoroethylene carbonate in the non-aqueous electrolyte is, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of these values.

[0056] In some embodiments of the present application, the content of fluoroethylene carbonate in the non-aqueous electrolyte is 3% to 8%, for example, 3%, 4%, 5%, 6%, 7%, 8%, or a range consisting of any two of these values.

[0057] In some embodiments of the present application, the non-aqueous electrolyte satisfies at least one of the following conditions: (1) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethylene carbonate is 3% to 8%; (2) based on the total mass of the non-aqueous electrolyte, the mass percentage of fluoroethyl propionate to the mass percentage of fluoroethylene carbonate is 0.8 to 12, for example, 0.8, 0.9, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11.1, 11.2, 11.3, 11.4, 11.5, 12, or a range consisting of any two of these values. In this case, the secondary battery has more excellent thermal performance and cycle performance.

[0058] In some embodiments of the present application, based on the total mass in the non-aqueous electrolyte, the ratio of the mass percentage of fluoroethyl propionate to the mass percentage of fluoroethylene carbonate is 4 to 10, for example, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of these values. In this case, the secondary battery has particularly excellent thermal performance and cycle performance.

[0059] The inventors have found that in the secondary battery of the present application, the use of nitrile compounds having two or more nitrile groups in a single molecule in the non-aqueous electrolyte can adsorb and complex transition metals on the surface of the positive electrode, reduce the reaction heat generated on the surface of the positive electrode, and improve the interface stability of the positive electrode under high voltage. At the same time, it can reduce the deposition of transition metals on the negative electrode, alleviate the catalytic decomposition heat generated at the solid electrolyte interface (SEI), and improve the hot box performance.

[0060] The nitrile compound having two or more nitrile groups in a single molecule is preferably selected from succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methylglutaronitrile, and one or more compounds of the following formulas I-1 to I-19:

[0061]

[0062]

[0063]

[0064] In the secondary battery of the present application, in the non-aqueous electrolyte, if the mass percentage of the nitrile compound having 2 or more nitrile groups in a single molecule is too low, such as less than 0.5%, the improvement of the hot box performance of the secondary battery is limited; if the content is too high, such as more than 5%, the overall performance of the secondary battery may be affected. Therefore, in the embodiment of the present application, based on the total mass of the non-aqueous electrolyte, the mass percentage of the nitrile compound is 0.5% to 5%.

[0065] In some embodiments of the present application, in a non-aqueous electrolyte, the mass percentage of the nitrile compound having 2 or more nitrile groups in a single molecule is 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values.

[0066] In some embodiments of the present application, the mass percentage of nitrile compounds having 2 or more nitrile groups in a single molecule in a non-aqueous electrolyte is 1.5% to 4%, such as 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a range consisting of any two of these values, and in particular, the mass percentage of nitrile compounds having 2 or more nitrile groups in a single molecule is 2% to 4%, such as 2%, 2.5%, 3%, 3.5%, 4%, or a range consisting of any two of these values. In this case, the secondary battery has better overall performance including thermal performance.

[0067] In some embodiments of the present application, the non-aqueous electrolyte further contains fluoroethylene carbonate (FEC), and the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte is 3% to 15% based on the total mass of the non-aqueous electrolyte; the mass percentage of fluoroethylene carbonate to the mass percentage of nitrile compounds having 2 or more nitrile groups in a single molecule is 0.6 to 16, such as 0.6, 1, 1.6, 2, 4, 6, 8, 10, 12, 14, 16, or the range of any two of these values, more particularly, the mass percentage of fluoroethylene carbonate to the mass percentage of nitrile compounds having 2 or more nitrile groups in a single molecule is 2 to 12, such as 2, 4, 6, 8, 10, 12, or the range of any two of these values. In this case, the secondary battery has extremely excellent thermal performance.

[0068] In a preferred embodiment of the secondary battery of the present application, the non-aqueous electrolyte further comprises a compound of formula II, and the compound of formula II is selected from one or more of the following compounds of formula II-1 to formula II-14:

[0069]

[0070] In the non-aqueous electrolyte of the secondary battery of the present application, the use of a compound selected from Formula II helps to form a stable solid electrolyte interface SEI earlier, reduce heat generation at the negative electrode, and improve hot box performance.

[0071] In some embodiments of the present application, in the non-aqueous electrolyte, if the percentage of the compound selected from Formula II is too low, such as less than 0.2%, the improvement of the thermal performance of the secondary battery is limited; if the percentage of the compound selected from Formula II is too low, such as higher than 3%, it may cause a larger impedance of the solid electrolyte interface SEI, affecting the transmission of lithium ions, and the cycle performance of the secondary battery will be affected. Therefore, in the embodiment of the present application, based on the total mass in the non-aqueous electrolyte, the mass percentage of the compound of Formula II is 0.2% to 3%.

[0072] In some embodiments of the present application, in the non-aqueous electrolyte, the percentage of the compound selected from Formula II is, for example, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or a range consisting of any two of these values.

[0073] In the present application, the non-aqueous electrolyte may further include a lithium salt. In some embodiments, the electrolyte further includes a lithium salt. The lithium salt is, for example, at least one of LiPF6, LiBF4, LiSO3F, LiN(FSO2)2LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2 or LiN(C2F5SO2)2. Preferably, LiPF6 is used.

[0074] In the non-aqueous electrolysis of the present application, the amount of lithium salt such as LiPF6 can be 12.5% ​​or other conventional amount.

[0075] In the present application, the non-aqueous electrolyte may also include other carbonate solvents, such as linear carbonates, for example, diethyl carbonate (DEC), dimethyl carbonate (DMC), etc. There is no particular restriction on their usage, for example, they can be used to supplement the non-aqueous electrolyte.

[0076] In some embodiments of the present application, the secondary battery further includes a positive electrode, a negative electrode, a diaphragm, a shell and a pole ear, the pole ear extends from the inside of the shell to the outside of the shell, along the direction of extension of the pole ear, the width of the diaphragm is greater than the width of the negative electrode, and the difference between the width of the diaphragm and the width of the negative electrode is 0.5mm to 2.8mm, for example, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 1.0mm, 1.2mm, 1.4mm, 1.5mm, 1.8mm, 2.0mm, 2.1mm, 2.3mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, or a range consisting of any two of these values. In this case, the secondary battery can adapt to the shrinkage of the diaphragm at high temperature, reduce the risk of short circuit, and improve the performance of the hot box.

[0077] In the present application, the positive electrode material may be prepared using materials, structures, and manufacturing methods known in the art.

[0078] The positive electrode may include a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes at least one lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material includes a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel.

[0079] In some embodiments, the positive electrode active material is selected from one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0080] In some embodiments, the positive electrode active material may have a coating on its surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound for the coating may be amorphous or crystalline.

[0081] In some embodiments, the coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or any combination thereof. The coating may be applied by any method as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method may include any coating method known in the art, such as spraying, dipping, etc.

[0082] The positive electrode active material layer also includes a binder, and optionally a conductive material. The binder improves the bonding of the positive electrode active material particles to each other and also improves the bonding of the positive electrode active material to the current collector.

[0083] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0084] In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0085] In some embodiments, the current collector may be aluminum, but is not limited thereto.

[0086] The positive electrode can be prepared by a preparation method known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent may include N-methylpyrrolidone, etc., but is not limited thereto.

[0087] In some embodiments, the positive electrode is made by forming a positive electrode material using a positive electrode active material layer including a lithium transition metal compound powder and a binder on a current collector.

[0088] In some embodiments, the positive electrode active material layer can be generally prepared by dry mixing the positive electrode material and the binder (conductive material and thickener used as needed) to form a sheet, pressing the obtained sheet to the positive electrode collector, or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry on the positive electrode collector and drying. In some embodiments, the material in the positive electrode active material layer includes any material known in the art.

[0089] The negative electrode includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material, and the specific types of the negative electrode active materials are not subject to specific restrictions and can be selected according to needs. Specifically, the negative electrode active material can include lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12, Li-Al alloy.

[0090] The negative electrode active material layer may further include a binder. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0091] The negative electrode active material layer may further include a conductive material. In some embodiments, the conductive material includes, but is not limited to: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver or polyphenylene derivatives.

[0092] The negative electrode active material layer may further include conventional thickeners and fillers and the like.

[0093] The negative electrode current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a polymer substrate coated with a conductive metal.

[0094] The negative electrode may further include a conductive layer. The conductive material of the conductive layer may include, but is not limited to: at least one of a carbon-based material (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, etc.), a metal-based material (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), a conductive polymer (e.g., a polyphenylene derivative), and a mixture thereof.

[0095] The secondary battery of the present application is provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the present application are not particularly limited, and it can be any technology disclosed in the prior art. For example, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0096] The present application has no particular restrictions on the isolation membrane, as long as the purpose of the present application can be achieved. For example, the isolation membrane may include a substrate layer and a surface treatment layer. The material of the substrate layer may include, but is not limited to, polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin isolation membranes, polyester films (such as polyethylene terephthalate films), cellulose films, polyimide films, polyamide films, spandex, aramid films, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, diaphragm paper, rolled membranes or spinning membranes. At least one of them is preferably polyethylene. The isolation membrane of the present application may have a porous structure, and the size of the pore size is not particularly limited, as long as the purpose of the present application can be achieved. In the present application, the thickness of the isolation membrane is not particularly limited, as long as the purpose of the present application can be achieved. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The inorganic layer may include, but is not limited to, inorganic particles and inorganic layer binders. The present application has no particular restrictions on inorganic particles, as long as the purpose of the present application can be achieved. For example, it may include, but is not limited to, at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on inorganic layer binders, for example, it may include, but is not limited to, at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0097] The secondary battery of the present application is not particularly limited, and may include any device that undergoes an electrochemical reaction. In some embodiments, the secondary battery may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0098] The preparation process of the secondary battery is well known to those skilled in the art, and there is no particular limitation in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0099] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The secondary battery provided by the present application has good cycle performance and safety performance, so that the electronic device provided by the present application has a long service life.

[0100] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0101] Example

[0102] Next, the embodiments of this specification are described in detail.

[0103] Preparation of electrolytes in Examples 1-1 to 1-24

[0104] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC) and propylene carbonate (PC) are mixed, and then 1-propionic acid-2,2-difluoroethyl ester and / or propionic acid-2,2,2-trifluoroethyl ester are added and mixed evenly, and then fully dried lithium salt LiPF6 is dissolved in the above non-aqueous solvent, fluoroethylene carbonate (FEC) is added, and finally diethyl carbonate (DEC) is added to make up 100% to prepare an electrolyte, wherein the components and amounts used are shown in Table 1 below;

[0105] Examples 2-1 to 2-8 Preparation of electrolyte

[0106] On the basis of the components and amounts of the electrolyte in Examples 1-13, fluoroethylene carbonate (FEC) was added, followed by a nitrile compound, and finally diethyl carbonate (DEC) was added to make up to 100% to prepare an electrolyte, wherein the components and amounts used are shown in Table 2 below.

[0107] Examples 2-9 to 2-11 Preparation of electrolyte

[0108] Based on the electrolyte components and amounts of Examples 1-13, as shown in Table 2, the amount of fluoroethylene carbonate (FEC) was adjusted, and after adding fluoroethylene carbonate (FEC), a nitrile compound was added, and finally diethyl carbonate (DEC) was added to make up 100% to prepare an electrolyte, wherein the components and amounts used are shown in Table 2 below.

[0109] Preparation of electrolytes in Examples 2-12 to 2-15

[0110] On the basis of the components and amounts of the electrolyte in Examples 1-13, fluoroethylene carbonate (FEC) was added, then the compound of formula II was added, and finally diethyl carbonate (DEC) was added to make up to 100% to prepare an electrolyte, wherein the components and amounts used are shown in Table 2 below.

[0111] Preparation of electrolytes in Examples 2-16 to 2-17

[0112] On the basis of the components and amounts of the electrolyte in Examples 1-13, fluoroethylene carbonate (FEC) was added, followed by the nitrile compound and the compound of formula II, and finally diethyl carbonate (DEC) was added to make up to 100% to prepare an electrolyte, wherein the components and amounts used are shown in Table 2 below.

[0113] Comparative Examples 1-6

[0114] A lithium ion secondary battery was prepared in a similar manner to Examples 1-1 to 1-24, except that the components and their mass percentages in the electrolyte were as shown in Table 1 below.

[0115] Example Preparation of Secondary Battery

[0116] (1) Preparation of negative electrode

[0117] The negative electrode active materials graphite, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a proper amount of deionized water solvent at a weight ratio of 97.4:1.2:1.4 to form a uniform negative electrode slurry; the slurry is coated on the negative electrode current collector copper foil, and the copper foil is dried, cold pressed, and the pole ears are welded to obtain the negative electrode.

[0118] (2) Preparation of positive electrode

[0119] The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent acetylene black, and the binder polyvinylidene fluoride are mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) is added. The mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 70wt%. The positive electrode slurry is evenly coated on one surface of the positive electrode current collector aluminum foil and dried to obtain a positive electrode sheet coated with a positive electrode material layer with a thickness of 110μm on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. Then, after cold pressing and cutting, a positive electrode sheet with a specification of 74mm×867mm is obtained.

[0120] (3) Preparation of isolation membrane

[0121] A porous polyethylene film with a thickness of 7 μm (provided by Celgard Company) was used as the separator.

[0122] Example 1-13, Example 3-1, Example 3-2

[0123] Along the width direction of the secondary battery, the separator width exceeds the negative electrode width by 1.5 mm, 0.5 mm, and 2.8 mm, respectively, as shown in Table 3 below.

[0124] Among them, the electrolytes in Example 3-1 and Example 3-2 are consistent with those in Example 1-13, and only the width of the diaphragm super-negative electrode is different.

[0125] In other embodiments in Table 1 & Table 2 of this document, the width of the separator exceeds the width of the negative electrode by 1.5 mm.

[0126] (4) Preparation of lithium-ion secondary batteries

[0127] The positive electrode, separator, and negative electrode prepared above are stacked in order, with the separator placed between the positive electrode and the negative electrode to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, and after drying, the electrolytes obtained in Examples 1-1 to 1-24, 2-1 to 2-17, and Comparative Example 1-6 are respectively injected, and a lithium-ion secondary battery is obtained through vacuum packaging, standing, formation, degassing, trimming, and other processes.

[0128] Test Example 1 Hot Box Test

[0129] 130℃ hot box test:

[0130] The lithium-ion secondary battery was charged at a constant current of 0.5C at 25°C to a voltage of 4.52V, and then charged at a constant voltage of 0.05C at a voltage of 4.52V and then rested for 60 minutes. The lithium-ion battery was then transferred to a high-low temperature box for testing. The high-low temperature box was heated at a rate of 3°C / min, and the temperature was kept at a set temperature of 130°C for 60 minutes. The lithium-ion battery passed the test if it did not catch fire or explode. Ten lithium-ion batteries were tested for each embodiment or comparative example, and the number of batteries that passed the test was recorded.

[0131] 135℃ hot box test:

[0132] Except for changing the set temperature to 135°C, the rest of the steps are the same as the above 130°C hot box test.

[0133] Test Example 2 Cycle Capacity Retention Test

[0134] The lithium-ion secondary battery was placed in a 45°C constant temperature box, charged at a constant current of 1.5C to a voltage of 4.52V, then charged at a constant voltage of 0.05C at a voltage of 4.52V, and then discharged at a constant current of 1.0C to 3.0V. This was a charge and discharge cycle process. The charge and discharge test was performed 500 times in the above manner to monitor the capacity retention rate of the lithium-ion battery, capacity retention rate = 500th discharge capacity / 1st discharge capacity × 100%.

[0135]

[0136]

[0137]

[0138]

[0139] Wherein, (1) the sum of the contents of the components of the electrolyte is 100%, of which the content of LiPF6 is 12.5%, and the remaining components are all DEC (diethyl carbonate);

[0140] (2) “ / ” in the table means that the component was not used or the content was 0.

[0141] Table 3 Width of the separator super anode in Examples 1-13, 3-1 and 3-2 and test results of the obtained secondary batteries

[0142]

[0143] The above description is only a preferred embodiment of this specification and is not intended to limit this specification. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this specification should be included in the scope of protection of this specification.

Claims

1. A secondary battery comprising a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises: (1) fluoroethyl propionate, wherein the fluoroethyl propionate is selected from one or both of 2,2-difluoroethyl 1-propionate and 2,2,2-trifluoroethyl propionate, and the mass percentage of the fluoroethyl propionate is 5% to 65% based on the total mass of the non-aqueous electrolyte; (2) Ethylene carbonate (EC) and propylene carbonate (PC), based on the total mass of the non-aqueous electrolyte, the sum of the mass percentages of ethylene carbonate (EC) and propylene carbonate (PC) is ≤15%.

2. The secondary battery according to claim 1, wherein The non-aqueous electrolyte satisfies at least one of the following conditions: (1) Based on the total mass of the non-aqueous electrolyte, the mass percentage of the fluoroethyl propionate is 10% to 60%; (2) Based on the total mass of the non-aqueous electrolyte, the mass percentage of the ethylene carbonate is ≤10%; (3) Based on the total mass of the non-aqueous electrolyte, the mass percentage of the propylene carbonate is ≤10%.

3. The secondary battery according to claim 1, wherein Based on the total mass of the non-aqueous electrolyte, the mass percentage of the fluoroethyl propionate is 12% to 50%.

4. The secondary battery according to claim 1, wherein The non-aqueous electrolyte satisfies at least one of the following conditions: (1) Based on the total mass of the non-aqueous electrolyte, the mass percentage of the fluoroethyl propionate is 12% to 45%; (2) Based on the total mass of the non-aqueous electrolyte, the ratio of the mass percentage of the ethylene carbonate to the mass percentage of the propylene carbonate is 1:

1.

5. The secondary battery according to claim 1, wherein The non-aqueous electrolyte also includes fluoroethylene carbonate (FEC). Based on the total mass of the non-aqueous electrolyte, the mass percentage of the fluoroethylene carbonate is 3% to 15%.

6. The secondary battery according to claim 5, wherein The non-aqueous electrolyte satisfies at least one of the following conditions: (1) Based on the total mass of the non-aqueous electrolyte, the mass percentage of the fluoroethylene carbonate is 3% to 8%; (2) Based on the total mass of the non-aqueous electrolyte, the ratio of the mass percentage of the fluoroethyl propionate to the mass percentage of the fluoroethylene carbonate is 0.8 to 12.

7. The secondary battery according to claim 1, wherein The non-aqueous electrolyte further comprises a nitrile compound having two or more nitrile groups in a single molecule, and the mass percentage of the nitrile compound is 0.5% to 5% based on the total mass of the non-aqueous electrolyte; The nitrile compound is selected from succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, 2-methylglutaronitrile, and one or more of the following compounds of formula I-1 to formula I-19:

8. The secondary battery according to claim 7, wherein Based on the total mass of the non-aqueous electrolyte, the mass percentage of the nitrile compound is 1.5% to 4%.

9. The secondary battery according to claim 7, wherein The non-aqueous electrolyte further comprises fluoroethylene carbonate (FEC), and the mass percentage of the fluoroethylene carbonate is 3% to 15% based on the total mass of the non-aqueous electrolyte; Based on the total mass of the non-aqueous electrolyte, the ratio of the mass percentage of the fluoroethylene carbonate to the mass percentage of the nitrile compound is 0.6 to 16.

10. The secondary battery according to claim 1, wherein The non-aqueous electrolyte further comprises a compound of formula II, wherein the compound of formula II is selected from one or more of the following compounds of formula II-1 to formula II-14:

11. The secondary battery according to claim 10, wherein Based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound of formula II is 0.2% to 3%.

12. The secondary battery according to any one of claims 1 to 11, wherein: The secondary battery also includes a positive electrode, a negative electrode, a diaphragm, a shell and a tab, wherein the tab extends from the inside of the shell to the outside of the shell, and along the direction in which the tab extends, the width of the diaphragm is greater than the width of the negative electrode, and the difference between the width of the diaphragm and the width of the negative electrode is 0.5 mm to 2.8 mm. 13 . An electronic device comprising the secondary battery according to claim 1 .

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