Electrolyte, secondary battery, battery module, battery pack, and power consumption device

Abstract

The present application provides an electrolyte, a secondary battery, a battery, and a power consuming device. The electrolyte of the present application includes a halogen-substituted C2-C4 olefin and / or a partially halogenated saturated polyolefin. The present application provides an electrolyte that can generate an electrochemical reduction reaction on the surface of the negative electrode active material to generate a solid electrolyte interfacial film by adding a halogen-substituted C2-C4 olefin and / or a partially halogenated saturated polyolefin to the electrolyte, thereby improving low-temperature performance and service life at the same time.

Description

Technical Field

[0001] The present application relates to the field of batteries, and specifically to electrolytes, secondary batteries, battery modules, battery packs, and power consumption devices.

Background Art

[0002] Since secondary batteries have characteristics such as high capacity and long service life, they are widely applied to electronic devices, such as mobile phones, notebook computers, electric scooters, electric vehicles, electric aircraft, electric ships, electric toy cars, electric toy ships, electric toy aircraft, and electric tools. Due to the significant progress in the research of secondary batteries, the requirements for the performance of secondary batteries are increasing. In order to improve the performance of secondary batteries, generally, materials inside the secondary batteries, such as electrolytes, are optimized and improved. As a transmission medium for metal ions in secondary batteries, electrolytes have a non-negligible impact on the performance of secondary batteries.

[0003] However, when currently improved electrolytes are applied to secondary batteries, the secondary batteries still cannot simultaneously improve their low-temperature performance and service life during the use process.

Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide an electrolyte, a secondary battery, a battery module, a battery pack, and a power consumption device.

[0005] The first aspect of the present application provides an electrolyte for a secondary battery, and the electrolyte contains C2-C4 olefins substituted with halogen atoms and / or partially halogenated saturated polyolefins.

[0006] As a result, by providing a C2-C4 olefin substituted with a halogen atom and / or a partially halogenated saturated polyolefin in the electrolyte of the embodiment of the present application, an electrochemical reduction reaction can occur on the surface of the negative electrode active material to form a halogen-containing solid electrolyte interface film. The generated halogen-containing solid electrolyte interface film has a low interface resistance on the one hand, so that the secondary battery has good low-temperature characteristics. On the other hand, it reduces the risk of direct contact between the electrolyte and the negative electrode active material and reduces the risk of occurrence of the reduction reaction of the electrolyte, thereby improving the service life of the secondary battery.

[0007] In the embodiment of the present application, by adding a partially halogenated saturated polyolefin to the electrolyte, an electrochemical reduction reaction can occur on the surface of the negative electrode active material to form a solid electrolyte interface film. In addition, the partially halogenated saturated polyolefin has a certain viscosity, which improves the bonding force between the negative electrode active material and the solid electrolyte interface film, improves the reliability of forming the solid electrolyte interface film during the charge and discharge process of the secondary battery, and further improves the electrochemical performance of the secondary battery, thereby simultaneously improving the low-temperature performance and service life.

[0008] In any embodiment, the C2-C4 olefin substituted with a halogen atom includes one or more of the compounds represented by Formula I.

Chemical formula

[0009] More optionally, R 11 ~R 13 are each independently selected from a hydrogen atom, a fluorine atom or -CF3.

[0010] As a result, the C2-C4 olefin substituted with a halogen atom in the embodiment of the present application is more easily controlled in solubility in the electrolytic solution and helps to cause an electrochemical reaction with the negative electrode active material.

[0011] In any embodiment, the C2-C4 olefin substituted with a halogen atom includes one or more of the compounds represented by formulas (I-1) to (I-5).

Chemical formula

[0012] In any embodiment, based on the mass of the electrolytic solution, the mass percentage a of the C2-C4 olefin substituted with a halogen atom satisfies 0.05% ≤ a ≤ 10%, and optionally, 0.1% ≤ a ≤ 1%.

[0013] As a result, in the embodiment of the present application, by adjusting the mass percentage of the C2-C4 olefin substituted with a halogen atom within the above range, the C2-C4 olefin substituted with a halogen atom can be stably dissolved in the electrolytic solution and a dense protective film can be formed on the surface of the negative electrode active material, thereby being able to exert a good protective effect on the negative electrode sheet.

[0014] In any embodiment, the partially halogenated saturated polyolefin includes one or more of the structural units represented by formula II, and the partially halogenated saturated polyolefin includes at least one partially halogenated olefin structural unit.

Chemical formula

[0015] Thereby, the molecular weight of the partially halogenated saturated polyolefin in the examples of the present application is relatively small, and its solubility with other substances in the electrolyte is relatively high, which helps to control the electrochemical reduction reaction on the surface of the negative electrode active material of the partially halogenated saturated polyolefin.

[0016] In any embodiment, the partially halogenated saturated polyolefin contains one or more of the structural units represented by formulas (II-1) to (II-5), and the partially halogenated saturated polyolefin contains at least one partially fluorinated olefin structural unit.

Chemical formula

[0017] In any embodiment, the weight average molecular weight of the partially halogenated saturated polyolefin is 10000 Da or less, and optionally, the weight average molecular weight of the partially halogenated saturated polyolefin is 200 Da to 10000 Da.

[0018] In any embodiment, based on the mass of the electrolyte, the mass percentage b of the partially halogenated saturated polyolefin satisfies 0.05% ≦ b ≦ 10%, and optionally, 0.1% ≦ b ≦ 1%.

[0019] As a result, the partially halogenated saturated polyolefin in the examples of the present application has a relatively small weight-average molecular weight and is easily dissolved in the electrolyte, thereby generating an electrochemical reaction on the surface of the negative electrode active material to form a solid electrolyte interface film.

[0020] The second aspect of the present application further provides a secondary battery including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The separator is provided between the positive electrode sheet and the negative electrode sheet. The electrolyte employs the electrolyte of any example of the first aspect of the present application. Optionally, the positive electrode sheet contains a lithium element and / or a sodium element.

[0021] The third aspect of the present application further provides a battery module including the secondary battery of the examples of the second aspect of the present application.

[0022] The fourth aspect of the present application further provides a battery pack including the battery module of the examples of the third aspect of the present application.

[0023] The fifth aspect of the present application further provides a power consumption device including the secondary battery of the examples of the second aspect of the present application, the battery module of the examples of the third aspect of the present application, or the battery pack of the examples of the fourth aspect of the present application.

Brief Description of the Drawings

[0024] To more clearly illustrate the technical solutions of the examples of the present application, the following briefly describes the drawings necessary for the examples of the present application. Obviously, the drawings described below are only some examples of the present application, and those skilled in the art can obtain other drawings based on the drawings without creative effort. Here, the description of the reference numerals is as follows. 1. Secondary battery, 11. Exterior, 111. Top cover assembly, 112. Case, 12. Electrode assembly, 10. Battery module, 20. Battery pack, 21. Upper housing, 22. Lower housing, 30. Power consumption device.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0025] Hereinafter, embodiments specifically disclosing the electrolytic solution, secondary battery, battery, and power consumption device of the present application will be described in detail. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. Also, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0026] The "range" disclosed in this application is limited in the form of a lower limit and an upper limit. A predetermined range is limited by selecting one lower limit and one upper limit, and the selected lower limit and upper limit particularly limit the boundary of the range. The range limited in such a manner may or may not include the 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 enumerated for a specific parameter, ranges of 60 - 110 and 80 - 120 are also understood to be expected. Also, if minimum range values 1 and 2, and maximum range values 3, 4, and 5 are enumerated, ranges of 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5 are all expected. In this application, unless otherwise explained, the numerical range "a - b" represents a reduced expression of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" represents all real numbers between "0 - 5" in this specification, and "0 - 5" is a reduced expression of the combination of these numbers. Also, when a certain parameter is expressed as an integer ≧ 2, it corresponds to the disclosure that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and selectable embodiments of this application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and selectable technical features of this application can be combined with each other to form a new technical solution.

[0028] Unless otherwise specified, all steps of the present application can be performed in sequence, can be performed randomly, and preferably are performed in sequence. For example, when it is said that a method includes steps (a) and (b), it means that the method can include steps (a) and (b) performed in sequence, and can also include steps (b) and (a) performed in sequence. For example, when it is said that the method can further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), can also include steps (a), (c) and (b), and can further include steps (c), (a) and (b), etc.

[0029] Unless otherwise specified, the terms "having", "comprising" and "including" referred to in the present application are open-ended and may also be closed-ended. For example, "having", "comprising" and "including" can further have, comprise or include other components not listed, and can also comprise or include only the listed components.

[0030] Unless otherwise specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition of "A or B". A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist). Electrolyte

[0031] In a first aspect, the present application provides an electrolyte for a secondary battery, and the electrolyte includes a C2-C4 olefin substituted with a halogen atom and / or a partially halogenated saturated polyolefin.

[0032] As can be understood, the electrolyte can contain a C2-C4 olefin substituted with a halogen atom. The electrolyte can contain a partially halogenated saturated polyolefin. Or, the electrolyte can contain a C2-C4 olefin substituted with a halogen atom and a partially halogenated saturated polyolefin.

[0033] The C2-C4 olefin substituted with a halogen atom means that one hydrogen atom or two or more hydrogen atoms in the C2-C4 olefin are substituted with a halogen atom. When two or more hydrogen atoms are substituted with a halogen atom, different hydrogen atoms may be substituted with different halogen atoms. For example, one hydrogen atom is substituted with a fluorine atom F, and another hydrogen atom is substituted with a bromine atom Br. Here, the C2-C4 olefin refers to one or more of ethylene, propylene, and butylene. The halogen atom may be a fluorine atom, a chlorine atom, etc. The C2-C4 olefin substituted with a halogen atom may be, for example, one or more of vinyl fluoride, 1,1-difluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, fluoropropene, 1,1-difluoropropene, 1,2,3-trifluoropropene, fluorobutene, vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, perchloroethylene, chloropropene, 1,1-dichloropropene, 1,2,3-trichloropropene, and chlorobutene. It should be noted that the above is only an illustrative description and does not limit the scope of the C2-C4 olefin substituted with a halogen atom.

[0034] C2-C4 olefins substituted with halogen atoms are gaseous. As an additive for forming a film on the negative electrode of the electrolyte, an electrochemical reduction reaction can occur on the surface of the negative electrode active material to generate a solid electrolyte interphase (SEI) film. Also, as a small molecule substance, C2-C4 olefins substituted with halogen atoms have high solubility in the electrolyte and are easily uniformly dispersed inside the electrolyte, thereby improving the uniformity of the thickness of the formed solid electrolyte interphase film and further guaranteeing the uniform performance of the solid electrolyte interphase film. Moreover, C2-C4 olefins substituted with gaseous halogen atoms are used as industrial raw materials and their cost is relatively low. Partially halogenated saturated polyolefins refer to those containing halogen atoms in their constituent repeating units and the polymer still having hydrogen atoms. Exemplarily, the constituent repeating units of partially halogenated saturated polyolefins are one or more of vinyl fluoride, 1,1-difluoroethylene, 1,2-difluoroethylene, fluoropropene, 1,1-difluoropropene, 1,2,3-trifluoropropene, fluorobutene, vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, perchloroethylene, chloropropene, 1,1-dichloropropene, 1,2,3-trichloropropene, and chlorobutene.

[0035] Partially halogenated saturated polyolefins refer to those containing halogen atoms in their constituent repeating units and the polymer containing hydrogen atoms. Exemplarily, the constituent repeating units of partially halogenated saturated polyolefins are one or more of vinyl fluoride, 1,1-difluoroethylene, 1,2-difluoroethylene, fluoropropene, 1,1-difluoropropene, 1,2,3-trifluoropropene, fluorobutene, vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, perchloroethylene, chloropropene, 1,1-dichloropropene, 1,2,3-trichloropropene, and chlorobutene.

[0036] The electrolytic solution of the embodiment of the present application installs C2-C4 olefins substituted with halogen atoms and / or partially halogenated saturated polyolefins, so that the above substances can generate an electrochemical reduction reaction on the surface of the negative electrode active material to form a halogen-containing solid electrolyte interface film. The generated halogen-containing solid electrolyte interface film has, on the one hand, a low interface resistance, whereby the secondary battery has good low-temperature characteristics, and on the other hand, it reduces the risk of direct contact between the electrolytic solution and the negative electrode active material and reduces the risk of occurrence of the reduction reaction of the electrolytic solution, thereby improving the service life of the secondary battery.

[0037] In some embodiments, the C2-C4 olefin substituted with a halogen atom includes one or more of the compounds represented by Formula I.

Chemical formula

[0038] Here, R 11 ~R 13 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C2 alkyl group which may or may not be substituted with a halogen atom, and the sum of the number of carbon atoms in R 11 ~R 13 is 0, 1 or 2.

[0039] Optionally, R 11 ~R 13 are each independently selected from a hydrogen atom, a halogen atom or -CF3.

[0040] The C2-C4 olefin substituted with a halogen atom in the embodiment of the present application is more easily controlled in solubility in the electrolytic solution, and it helps the C2-C4 olefin to generate an electrochemical reaction with the negative electrode active material.

[0041] Optionally, the halogen atom includes a fluorine atom or a chlorine atom. More optionally, the halogen atom includes a fluorine atom. Fluorine atoms and chlorine atoms have relatively high potentials, especially the potential of fluorine atoms is relatively high, and they are useful for participating in electrochemical reactions to form an SEI film. In other words, C2-C4 olefins substituted with fluorine atoms are useful for participating in electrochemical reactions to form an SEI film.

[0042] Exemplarily, C2-C4 olefins substituted with halogen atoms include one or more of the compounds shown in Formula I-1 to Formula I-5.

Chemical formula

[0043] In some embodiments, based on the mass of the electrolytic solution, the mass percentage a of C2-C4 olefins substituted with halogen atoms satisfies 0.05% ≤ a ≤ 10%.

[0044] The inventors have found that when the mass percentage a of C2-C4 olefins substituted with halogen atoms is less than 0.05%, the content of C2-C4 olefins substituted with halogen atoms in the electrolytic solution is too low, and the SEI formed on the negative electrode active material is not dense, and it may not be able to effectively protect the interface of the negative electrode sheet.

[0045] Since C2-C4 olefins substituted with halogen atoms are gaseous at ambient temperature, for example, 25°C, when the mass percentage a of C2-C4 olefins substituted with halogen atoms is greater than 10%, the content of C2-C4 olefins substituted with halogen atoms in the electrolytic solution is too high, which may exceed its own solubility, and some C2-C4 olefins substituted with halogen atoms may volatilize, and the volatilization process affects the storage stability of the electrolytic solution.

[0046] In view of the above problems, the inventors set the mass percentage a of the C2-C4 olefin substituted with a halogen atom to 0.05% ≦ a ≦ 10%, and selectively, 0.1% ≦ a ≦ 1%. The C2-C4 olefin substituted with a halogen atom within the content range can be stably dissolved in the electrolytic solution, and a dense protective film is formed on the surface of the negative electrode active material, thereby being able to exert a good protective effect on the negative electrode sheet.

[0047] In some embodiments, the partially halogenated saturated polyolefin contains one or more of the structural units shown in Formula II, and the partially halogenated saturated polyolefin contains at least one partially halogenated olefin structural unit.

Chemical formula

[0048] Here, R 21 ~R 24 are each independently selected from a hydrogen atom, a halogen atom, or a linear or branched C1-C8 alkyl group which may or may not be substituted with a halogen atom. Further selectively, R 21 ~R 24 are each independently selected from a hydrogen atom, a halogen atom, or -CF3. The total degree of polymerization m of the partially halogenated saturated polyolefin satisfies 1 < m ≦ 220, and m is a positive integer. Selectively, 4 < m ≦ 220.

[0049] The molecular weight of this type of partially halogenated saturated polyolefin is relatively small, and its solubility with other substances in the electrolytic solution is relatively high, which helps to control the electrochemical reduction reaction on the surface of the negative electrode active material of the partially halogenated saturated polyolefin.

[0050] Optionally, the halogen atom includes a fluorine atom or a chlorine atom. More optionally, the halogen atom includes a fluorine atom. Fluorine atoms and chlorine atoms have relatively high potentials, especially the potential of fluorine atoms is relatively high, and they are useful for participating in electrochemical reactions to form an SEI film. In other words, the partially fluorinated saturated polyolefin is further useful for participating in electrochemical reactions to form an SEI film.

[0051] Specifically, the partially halogenated saturated polyolefin contains one or more of the structural units represented by Formulas II-1 to II-5, and the partially halogenated saturated polyolefin has at least one partially fluorinated olefin structural unit.

Chemical formula

[0052] Exemplarily, the partially halogenated saturated polyolefin may be the following polymers.

Chemical formula

[0053] Optionally, the weight average molecular weight of the partially halogenated saturated polyolefin is 10,000 Da or less. More optionally, the weight average molecular weight of the partially halogenated saturated polyolefin is 200 Da to 10,000 Da. The partially halogenated saturated polyolefin has a relatively small molecular weight of its weight average molecular weight, is easily dissolved in the electrolyte, and thereby helps to generate an electrochemical reaction on the surface of the negative electrode active material to form an SEI film.

[0054] In some embodiments, based on the mass of the electrolyte, the mass percentage b of the partially halogenated saturated polyolefin satisfies 0.05% ≤ b ≤ 10%, and optionally, 0.1% ≤ b ≤ 1%.

[0055] The partially halogenated saturated polyolefin within the above content range can, on the one hand, form a dense and stable SEI film on the surface of the negative electrode active material, and on the other hand, can maintain a certain viscosity, with a relatively low viscosity, thereby reducing the adverse effects on the movement of metal ions, ensuring the transmission characteristics of metal ions in the electrolyte, and further ensuring the electrochemical performance of the secondary battery.

[0056] The electrolyte of the embodiment of the present application plays a role in conducting metal ions between the positive electrode sheet and the negative electrode sheet and is in a liquid state.

[0057] In some embodiments, the electrolyte can further include an electrolyte salt and a solvent.

[0058] Optionally, the electrolyte salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroborate oxalate, lithium diborate oxalate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluorooxalate phosphate.

[0059] Optionally, the solvent is at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0060] Optionally, the electrolyte can further contain additives. For example, the additives can include other negative electrode film-forming additives and positive electrode film-forming additives, and additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc. Secondary battery

[0061] In a second aspect, the present application provides a secondary battery. The secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The separator is disposed between the positive electrode sheet and the negative electrode sheet, thereby separating the positive electrode sheet and the negative electrode sheet. The electrolyte can employ the electrolyte of the first aspect of the present application.

[0062] According to the secondary battery of the embodiment of the present application, the electrolyte can form a stable SEI film on the surface of the negative electrode material. The SEI film can effectively protect the negative electrode active material and guarantee the structural stability of the negative electrode active material, thereby improving the low-temperature performance and service life of the secondary battery.

[0063] Optionally, the positive electrode sheet contains a lithium element and / or a sodium element. During the charge and discharge process of the secondary battery, lithium ions and / or sodium ions move stably between the positive electrode sheet and the negative electrode sheet as active ions, thereby guaranteeing the electrochemical performance of the secondary battery. [Positive Electrode Sheet]

[0064] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer contains a positive electrode active material.

[0065] As an example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0066] In some embodiments, the positive electrode current collector can employ a metal foil sheet or a composite current collector. For example, as the metal foil sheet, an aluminum foil can be employed. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] In some embodiments, the positive electrode active material can employ a positive electrode active material used in batteries known in the art. As an example, the positive electrode active material can include at least one of lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and conventional materials used as positive electrode active materials for other batteries can further be used. These positive electrode active materials can be used alone, or two or more of them can be used in combination. Here, examples of lithium transition metal oxides are lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may be abbreviated as NCM 211 ), LiNi 0.6 Co0.2 Mn 0.2 O2 (which may be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (for example, LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc., but not limited thereto. Examples of olivine-structured lithium-containing phosphates include lithium iron phosphate (for example, LiFePO4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (for example, LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon, but not limited thereto.

[0068] In some embodiments, the positive electrode film layer may further contain an adhesive. As an example, the adhesive can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of vinylidene fluoride - tetrafluoroethylene - propylene, a terpolymer of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, a copolymer of tetrafluoroethylene - hexafluoropropylene, and a fluorine-containing acrylate resin.

[0069] In some embodiments, the positive electrode film layer can optionally further contain a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the positive electrode sheet can be fabricated in the following manner. Components for fabricating the positive electrode sheet, such as a positive electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. After the positive electrode slurry is applied to the positive electrode current collector, and processes such as drying and cold pressing are performed, a positive electrode sheet can be obtained. [Negative electrode sheet]

[0071] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the negative electrode film layer contains a negative electrode active material.

[0072] As an example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0073] In some embodiments, the negative electrode current collector can employ a metal foil sheet or a composite current collector. For example, as the metal foil sheet, a copper foil can be employed. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] In some embodiments, the negative electrode active material can adopt a negative electrode active material used in batteries known in the art. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloy. However, the present application is not limited to these materials, and conventional materials used as negative electrode active materials for other batteries can be used. These negative electrode active materials may be used alone or in combination of two or more types.

[0075] In some embodiments, the negative electrode film layer may optionally further include an adhesive. The adhesive may be at least one selected from 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).

[0076] In some embodiments, the negative electrode film layer can optionally further include a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the negative electrode film layer may optionally further include other auxiliaries, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0078] In some embodiments, the negative electrode sheet can be produced in the following manner. Components for producing the negative electrode sheet, such as a negative electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry. After the negative electrode slurry is applied to a negative electrode current collector and subjected to processes such as drying and cold pressing, a negative electrode sheet can be obtained. [Separator]

[0079] In some embodiments, the secondary battery further includes a separator. The present application is not particularly limited to the type of separator, and any known separator having good chemical stability and mechanical stability and a porous structure can be selected.

[0080] In some embodiments, the material of the separator may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0081] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to produce an electrode assembly by a winding process or a lamination process.

[0082] In some embodiments, the secondary battery can include an exterior. The exterior can be used to seal the electrode assembly and the electrolyte.

[0083] In some embodiments, the outer package of the secondary battery may be a hard case, such as a rigid plastic case, an aluminum case, a steel case, etc. The outer package of the secondary battery may also be a soft package, such as a pouch - type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate. The shape of the secondary battery of the present application is not particularly limited and may be cylindrical, rectangular, or any other arbitrary shape. For example, FIGS. 1 and 2 show a secondary battery 1 with an exemplary rectangular structure.

[0084] In some embodiments, the secondary battery 1 includes an outer package 11. The outer package 11 includes a top - cover assembly 111 and a case 112. The positive - electrode sheet, the negative - electrode sheet, and the separator constitute an electrode assembly 12 and are housed in the case 112, and an electrolyte is further housed in the case 112. The positive - electrode sheet or the negative - electrode sheet includes tabs. During the charge - discharge process of the secondary battery 1, active ions repeatedly insert or escape between the positive - electrode sheet and the negative - electrode sheet. The electrolyte serves to conduct ions between the positive - electrode sheet and the negative - electrode sheet. The separator is installed between the positive - electrode sheet and the negative - electrode sheet, mainly serving to prevent short - circuiting between the positive and negative electrodes and at the same time allowing active ions to pass through. Specifically, the secondary battery 1 may be a wound - type or laminated - type battery, such as a lithium - ion battery or a sodium - ion battery, but is not limited thereto.

[0085] Optionally, the case 112 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodation cavity. The case 112 has an opening communicating with the accommodation cavity, and the top cover assembly 111 covers the opening to seal the accommodation cavity. The positive electrode sheet, the negative electrode sheet and the separator form the electrode assembly 12 by a winding process or a lamination process. The electrode assembly 12 is enclosed in the accommodation cavity. The electrolyte is impregnated in the electrode assembly 12. The number of the electrode assemblies 12 included in the secondary battery 1 may be one or more, and those skilled in the art can select according to specific actual needs.

[0086] In some embodiments, the secondary battery 1 can be assembled into a battery. The battery may be a battery module or a battery pack. For example, the number of the secondary batteries 1 included in the battery module may 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.

[0087] FIG. 3 shows a battery module 10 as an example. Referring to FIG. 3, in the battery module 10, a plurality of secondary batteries 1 may be arranged and installed in sequence along the length direction of the battery module 10. Of course, they can be arranged in any other way. Further, the plurality of secondary batteries 1 may be fixed by fasteners. Optionally, the battery module 10 further includes a housing having an accommodation space, and the plurality of secondary batteries 1 are accommodated in the accommodation space.

[0088] In some embodiments, the battery module 10 described above can be further assembled into a battery pack. The number of the battery modules 10 included in the battery pack may 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 pack. Of course, the battery pack may also be directly composed of a plurality of secondary batteries 1.

[0089] Figs. 4 and 5 show a battery pack 20 as an example. Referring to Figs. 4 and 5, the battery pack 20 can include a battery box and a plurality of battery modules 10 installed in the battery box. The battery box includes an upper housing 21 and a lower housing 22. The upper housing 21 is provided to cover the lower housing 22 and can form a sealed space for accommodating the battery modules 10. The plurality of battery modules 10 can be arbitrarily arranged within the battery box.

[0090] The present application further provides a power consumption device including at least one of a secondary battery, a battery module, or a battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or may be used as an energy storage unit of the power consumption device. The power consumption device can include, but is not limited to, mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as battery electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc. As the power consumption device, a secondary battery, a battery module, or a battery pack can be selected according to its usage requirements.

[0091] Fig. 6 shows a power consumption device 30 as an example. The power consumption device 30 is a battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the requirements for high power and high energy density for the secondary battery of the power consumption device 30, a battery pack or a battery module can be adopted. As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is generally required to be thin and can adopt a secondary battery as a power source. Embodiment

[0092] Hereinafter, examples of the present application will be described. The examples described below are illustrative and are used for interpreting the present application, and should not be construed as limiting the present application. When specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature of this field or according to the product specifications. When the reagents or equipment used are not specified by the manufacturer, they are all commercially available conventional products. Examples 1 to 23 and Comparative Example 1 1. Preparation of the positive electrode sheet

[0093] As the positive electrode current collector, an aluminum foil with a thickness of 8 μm is used. The positive electrode active material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM 333 ), conductive carbon black, and polyvinylidene fluoride (PVDF) as an adhesive are sufficiently stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 93:2:5 to form a uniform positive electrode slurry. The positive electrode slurry is applied to the surface of the positive electrode current collector, and after undergoing processes such as drying, a positive electrode sheet is obtained.

[0094] 2. The preparation of the negative electrode sheet is carried out as follows. Graphite as the negative electrode active material, conductive carbon black, sodium carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene emulsion (SBR) as an adhesive are sufficiently stirred and mixed in an appropriate amount of deionized water at a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry. The negative electrode slurry is applied to the negative electrode current collector, and after undergoing processes such as drying, a negative electrode sheet is obtained.

[0095] 3. The preparation of the electrolyte is carried out as follows. Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a volume ratio of 3:7 are uniformly mixed to obtain an organic solvent. Next, a negative electrode film-forming additive and 1 mol / L of LiPF6 are uniformly dissolved in the above organic solvent, where the type and mass percentage of the negative electrode film-forming additive are as shown in Tables 1 and 2. 4. Preparation of the secondary battery

[0096] The positive electrode sheet, separator (PP / PE / PP composite film), and negative electrode sheet are stacked and installed in sequence, then wound around an electric core and placed in an outer housing. The above electrolyte is injected into the electric core, and then sealed, left standing, subjected to processes such as hot and cold pressing, formation, etc., to obtain a secondary battery.

[0097]

Table 1

[0098]

Table 2

[0099] At 45°C, the secondary battery is left standing for 30 minutes, then charged at a constant current of 1C until the voltage reaches 4.2V, and further charged at a constant voltage of 4.2V until the current reaches 0.05C. After leaving it standing for 5 minutes, it is then discharged at a constant current of 1C until the voltage reaches 2.8V. This is one charge-discharge cycle process. The discharge capacity this time is regarded as the initial discharge capacity of the battery. The battery is subjected to 1000 cycle charge-discharge tests according to the above method, and the discharge capacity of the secondary battery after the 1000th cycle is recorded.

[0100] The capacity retention rate (%) of the secondary battery after the 1000th cycle = (discharge capacity at the 1000th cycle / discharge capacity at the first cycle) × 100%. 2. Test method for DC resistance DCR at low temperature

[0101] At room temperature, the state of charge (SOC) of the secondary battery is adjusted to 20% of the capacity, placed in an ultra-low temperature box at -25°C, left standing for 2 hours to allow the temperature of the secondary battery to reach -25°C. At this time, the voltage of the secondary battery is measured and recorded as U1. Then, it is discharged at a rate of 0.3C for 10S, and the voltage of the secondary battery after discharge is measured and recorded as U2.

[0102] The DCR of the secondary battery at low temperature = (U1 - U2) / I, where I represents the current. Test results

[0103] As shown in Table 3, the effect of the electrolyte of the present application on improving the low-temperature characteristics and service life of the secondary battery is as follows.

[0104]

Table 3

[0105] As can be seen from the data in Table 3, compared with Comparative Example 1, the examples of the present application add C2-C4 olefins substituted with halogen atoms and / or partially halogenated saturated polyolefins to the electrolyte, and can significantly improve the capacity retention rate and DCR of the secondary battery.

[0106] As can be seen from Examples 1 to 7, when the mass percentage of C2-C4 olefins substituted with halogen atoms is 0.05% to 10%, especially when the mass percentage of C2-C4 olefins substituted with halogen atoms is 0.1% to 1%, the capacity retention rate of the secondary battery is relatively high, and the DCR is relatively small. In other words, the cycle performance and low-temperature performance of the secondary battery are significantly improved.

[0107] As can be seen from Examples 8 and 9, the cycle performance and low-temperature performance of the secondary battery can also be improved by adopting C2-C4 olefins substituted with multiple types of halogen atoms.

[0108] As can be seen from Examples 10 to 16, when the mass percentage of partially halogenated saturated polyolefins is 0.05% to 10%, especially when the mass percentage of partially halogenated saturated polyolefins is 0.1% to 1%, the capacity retention rate of the secondary battery is relatively high, and the DCR is relatively small. In other words, the cycle performance and low-temperature performance of the secondary battery are significantly improved.

[0109] As can be seen from Examples 17 and 18, the cycle performance and low-temperature performance of the secondary battery can also be improved by adopting multiple types of partially halogenated saturated polyolefins.

[0110] As can be seen from Example 12 and Examples 19 to 22, when the weight-average molecular weight of the partially halogenated saturated polyolefin is less than 10,000 Da, particularly when it is from 200 Da to 10,000 Da, the capacity retention rate of the secondary battery is relatively high and the DCR is relatively small.

[0111] Compared with Example 3 and Example 12, Example 23 simultaneously employs a C2-C4 olefin substituted with a halogen atom and a partially halogenated saturated polyolefin, and all three can significantly improve the performance of the secondary battery.

[0112] The present application has been described with reference to the preferred embodiments, but various improvements can be made and the members thereof can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, any of the technical features mentioned in each embodiment can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An electrolyte for a secondary battery, comprising: a C2-C4 olefin substituted with a halogen atom and a partially halogenated saturated polyolefin; based on the mass of the electrolyte, the mass percentage a of the C2-C4 olefin substituted with the halogen atom satisfies 0.05% ≤ a ≤ 10%; based on the mass of the electrolyte, the mass percentage b of the partially halogenated saturated polyolefin satisfies 0.05% ≤ b ≤ 10%, an electrolyte for a secondary battery.

2. The electrolyte according to Claim 1, wherein the C2-C4 olefin substituted with the halogen atom comprises one or more of the compounds represented by Formula I. 【Chemical 1】 (Here, R １１ ~R １３ are each independently selected from a hydrogen atom, a halogen atom, or a C1-C2 alkyl group which may or may not be substituted with a halogen atom, and the sum of the number of carbon atoms in R １１ ~R １３ is 0, 1 or 2).

3. The electrolyte according to Claim 1 or 2, wherein the C2-C4 olefin substituted with the halogen atom comprises one or more of the compounds represented by Formulas (I-1) to (I-5). [Chemical Formula 2]

4. The electrolyte according to Claim 1 or 2, wherein based on the mass of the electrolyte, the mass percentage a of the C2-C4 olefin substituted with the halogen atom satisfies 0.1% ≤ a ≤ 1%.

5. The partially halogenated saturated polyolefin comprises one or more of the structural units represented by Formula II, and the partially halogenated saturated polyolefin comprises at least one partially halogenated olefin structural unit; the total degree of polymerization m of the partially halogenated saturated polyolefin satisfies 1 < m ≤ 220, and m is a positive integer, the electrolyte according to Claim 1 or 2. 【Chemical 3】 (Here, R ２１ to R ２４ are each independently selected from a hydrogen atom, a halogen atom, or a C1-C8 linear or branched alkyl group which may or may not be substituted with a halogen atom.)

6. The partially halogenated saturated polyolefin comprises one or more of the structural units represented by Formulas (II-1) to (II-5), and the partially halogenated saturated polyolefin comprises at least one partially fluorinated olefin structural unit, the electrolyte according to Claim 1 or 2. 【Chemical Formula 4】

7. The electrolyte according to Claim 1 or 2, wherein the weight average molecular weight of the partially halogenated saturated polyolefin is 10,000 Da or less.

8. The electrolyte according to Claim 1 or 2, wherein based on the mass of the electrolyte, the mass percentage b of the partially halogenated saturated polyolefin satisfies 0.1% ≤ b ≤ 1%.

9. a positive electrode sheet; a negative electrode sheet; a separator disposed between the positive electrode sheet and the negative electrode sheet; and the electrolyte according to Claim 1, a secondary battery.

10. A battery module comprising the secondary battery according to Claim 9.

11. A battery pack comprising the battery module according to Claim 10.

12. An electric power consuming device comprising the secondary battery according to Claim 9, the battery module according to Claim 10, or the battery pack according to Claim 11.

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