Electrolyte, secondary battery, and electrical apparatus

Abstract

An electrolyte, a secondary battery, and an electrical apparatus. The electrolyte includes a first additive having the chemical formula R((CH3)mSi)n, wherein R comprises at least one of a phosphate group, a phosphite group, a borate group, an amine group, an isocyanate group, a fluorine atom, an oxygen atom and a sulfur atom, m is 1, 2 or 3, and n is 1, 2 or 3. The first additive is introduced into the electrolyte so as to improve the conductivity of an SEI film, which helps to improve lithium ion transport performance. In addition, the introduction of the first additive can enable the SEI film to have good stability, so that a battery has good cycle performance.

Description

Electrolyte, secondary battery, and electrical device

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2023112768425, entitled “Electrolyte, Secondary Battery and Electrical Device,” filed on September 28, 2023, the entire text of which is incorporated herein by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] During the battery charging process, the solid electrolyte interface film (SEI film) formed by the electrolyte will affect the battery's cycle performance and lithium ion transmission performance. However, in the traditional battery performance improvement process, it is difficult to effectively take into account both cycle performance and lithium ion transmission performance. For example, in order to improve the battery's cycle performance, it is often necessary to improve the stability of the SEI film to reduce interface side reactions, but this adjustment may reduce the lithium ion transmission kinetics, thereby reducing the battery's charge and discharge speed.

[0006] Summary of the Invention

[0007] The first aspect of the present application provides an electrolyte comprising a chemical formula of R((CH3) m Si) n The first additive, wherein R includes at least one of a phosphate group, a phosphite group, a borate group, an amine group, an isocyanate group, a fluorine atom, an oxygen atom and a sulfur atom, m is 1, 2 or 3, and n is 1, 2 or 3.

[0008] Introducing the first additive into the aforementioned electrolyte improves the conductivity of the SEI film, thereby improving lithium ion transport performance. Simultaneously, the introduction of the first additive enhances the stability of the SEI film, thereby improving the battery's cycle performance. In other words, the introduction of the first additive into the electrolyte allows the battery to achieve both good cycle stability and good lithium ion transport performance.

[0009] In some embodiments, the first additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, trimethylsilyl isocyanate, trimethylfluorosilane, hexamethyldisiloxane, and hexamethyldisilazane.

[0010] In some embodiments, the first additive accounts for 0.01% to 1% by weight of the electrolyte. Within this range, the first additive can better contribute to the formation of a more structurally stable SEI film, resulting in a battery with a lower DCR and better cycling performance. Alternatively, the first additive accounts for 0.05% to 0.5% by weight of the electrolyte.

[0011] In some embodiments, the electrolyte further includes a second additive comprising ethylene carbonate. The introduction of this second additive can effectively promote the dissociation of electrolyte salts in the electrolyte, increase the electrolyte conductivity, and facilitate lithium ion transport. Furthermore, the second additive can participate in the formation of the SEI film, reducing the occurrence of interfacial side reactions and thus improving the battery's cycling performance.

[0012] In some embodiments, the mass percentage of the second additive in the electrolyte is 10% to 40%. The mass percentage of the second additive in the electrolyte within this range can maintain a suitable viscosity of the electrolyte and a high conductivity of the electrolyte.

[0013] In some embodiments, the mass ratio of the first additive to the second additive is 0.0001 to 0.05. When the mass ratio of the first additive to the second additive is within this range, the decomposition products of the first additive and the second additive have a good synergistic effect, which can reduce the DCR of the battery while maintaining good high-temperature cycle performance. Optionally, the mass ratio of the first additive to the second additive is 0.0003 to 0.03.

[0014] In some embodiments, the electrolyte further comprises a third additive, the third additive comprising at least one of difluorophosphate and tetrafluoroborate. Difluorophosphate and tetrafluoroborate can improve the stability of the SEI film, giving the SEI film better toughness, while making the SEI film more uniform and dense. In addition, difluorophosphate and tetrafluoroborate can reduce the decomposition of the electrolyte, which is beneficial to improving the cycle performance of the battery. Alternatively, the difluorophosphate comprises at least one of lithium difluorophosphate, sodium difluorophosphate and potassium difluorophosphate. Alternatively, the tetrafluoroborate comprises at least one of lithium tetrafluoroborate, sodium tetrafluoroborate and potassium tetrafluoroborate.

[0015] In some embodiments, the mass percentage of the third additive in the electrolyte is 0.01% to 1%. The mass percentage of the third additive in the electrolyte within this range can further improve the stability of the SEI film and further improve the cycle performance of the battery.

[0016] In some embodiments, the mass ratio of the first additive to the third additive is 0.1 to 30. Within this range, the mass ratio of the first additive to the third additive can achieve both low impedance and good high-temperature cycle performance. Alternatively, the mass ratio of the first additive to the third additive is 3 to 10.

[0017] In some embodiments, the electrolyte further includes a fourth additive comprising at least one of vinylene carbonate and vinyl ethylene carbonate. The fourth additive can undergo free radical polymerization on the surface of the negative electrode to generate polyalkyl lithium carbonate, which participates in the formation of the SEI film. This can further improve the flexibility of the SEI film and enable the SEI film to change with changes in the volume of the negative electrode. This can reduce the risk of SEI film rupture and exposure of new active sites during cycling, thereby reducing the occurrence of side reactions and thereby improving the cycle life and charge-discharge efficiency of the battery.

[0018] In some embodiments, the mass percentage of the fourth additive in the electrolyte is 1% to 5%. The mass percentage of the fourth additive in the electrolyte within this range can enable the battery to have both low impedance and good high temperature cycle performance.

[0019] In some embodiments, the mass ratio of the total mass of the first additive and the third additive to the mass of the fourth additive is 0.01 to 0.5. Within this range, the mass ratio of the total mass of the first additive and the third additive to the mass of the fourth additive can enable the battery to better balance high-temperature cycling performance and kinetic performance. Alternatively, the mass ratio of the total mass of the first additive and the third additive to the mass of the fourth additive is 0.3 to 0.4.

[0020] A second aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte; the separator is located between the positive electrode sheet and the negative electrode sheet.

[0021] In some embodiments, the separator has a thickness of 10 μm to 30 μm. A separator thickness within this range can provide good stability and resist puncture, while allowing lithium ions to pass through at a faster rate, thereby enabling the battery to maintain good high-temperature cycling performance and good lithium ion transport performance.

[0022] In some embodiments, the separator has a porosity of 20% to 50%. A separator porosity within this range can reduce the risk of metal ions dissolved from the positive electrode plate passing through the separator and reaching the negative electrode plate during cycling, helping to reduce side reactions on the negative electrode plate surface, thereby maintaining good high-temperature cycling performance for the battery. Furthermore, a separator porosity within this range allows lithium ions to pass through more smoothly, helping the battery maintain good lithium ion transport performance.

[0023] A third aspect of the present application provides an electrical device comprising the electrolyte and / or the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0025] FIG1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0026] FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .

[0027] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0028] Explanation of the accompanying symbols: 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electric device. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, 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 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0032] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0035] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, and in some embodiments are performed sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0036] In this application, open technical features or technical solutions described with words such as "contain," "include," and "includes" do not exclude additional members beyond the listed members unless otherwise specified, and can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may or may not include other members unless otherwise specified. This can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0037] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0038] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0039] One embodiment of the present application provides an electrolyte solution comprising a chemical formula of R((CH3) m Si) nA first additive is provided, wherein R comprises at least one of a phosphate group, a phosphite group, a borate group, an amine group, an isocyanate group, a fluorine atom, an oxygen atom, and a sulfur atom, m is 1, 2, or 3, and n is 1, 2, or 3. In this electrolyte, the introduction of the first additive can improve the conductivity of the SEI film, which is beneficial to improving the lithium ion transport performance. At the same time, the introduction of the first additive can make the SEI film have better stability, thereby making the battery have better cycle performance. That is, by introducing the first additive into the electrolyte, the battery can have both good cycle stability and good lithium ion transport performance.

[0040] In some embodiments, m=3. The chemical formula of the first additive is R((CH3)3Si) n During the charging process of the battery, the first additive is more likely to participate in the formation process of the SEI film, reduce the direct current resistance (DCR) of the battery, and further improve the lithium ion transmission performance.

[0041] In some embodiments, R includes at least one of a phosphite group, a borate group, an amine group, an isocyanate group, an oxygen atom, and a sulfur atom. In this case, the corresponding first additive can effectively improve the gas generation problem of the battery during the cycle of the battery, thereby further improving the cycle performance of the battery.

[0042] In some embodiments, the first additive includes tris(trimethylsilyl)phosphate (TMSP, ), tris(trimethylsilyl)phosphite (TMSPi, ), tris(trimethylsilyl)borate (TMSB, ), trimethylsilyl isocyanate Trimethylsilyl fluoride (TMSF, ), hexamethyldisiloxane (HMDSO, ) and hexamethyldisilazane (HDMS, ) at least one of.

[0043] In some embodiments, the first additive includes at least one of tris(trimethylsilyl)phosphate and trimethylfluorosilane. In this case, by selecting the first additive from tris(trimethylsilyl)phosphate and trimethylfluorosilane, the DCR of the battery can be more effectively reduced, thereby improving the initial power performance of the battery.

[0044] In some embodiments, the first additive includes at least one of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, hexamethyldisiloxane, and hexamethyldisilazane. In this case, selecting the first additive from tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, hexamethyldisiloxane, and hexamethyldisilazane can effectively improve gas generation during battery cycling, thereby improving the structural stability of the battery.

[0045] In some embodiments, the mass percentage of the first additive in the electrolyte is 0.01% to 1%. The mass percentage of the first additive in the electrolyte within this range can better participate in the formation of a more structurally stable SEI film, so that the battery has a lower DCR and better cycle performance. Optionally, the mass percentage of the first additive in the electrolyte is 0.05% to 0.5%. Further optionally, the mass percentage of the first additive in the electrolyte can be 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0046] In some embodiments, the electrolyte further includes a second additive comprising ethylene carbonate. The introduction of this second additive can effectively promote the dissociation of electrolyte salts in the electrolyte, increase the electrolyte conductivity, and facilitate lithium ion transport. Furthermore, the second additive can participate in the formation of the SEI film, reducing the occurrence of interfacial side reactions and thus improving the battery's cycling performance.

[0047] Optionally, the second additive accounts for a mass percentage of 10% to 40% of the electrolyte. Within this mass percentage range, the second additive can maintain an appropriate viscosity and a high electrical conductivity. Furthermore, the second additive can account for a mass percentage of 10%, 15%, 20%, 25%, 30%, 35%, 40%, or the like.

[0048] In some embodiments, the mass ratio of the first additive to the second additive is 0.0001 to 0.05. When the mass ratio of the first additive to the second additive is within this range, the decomposition products of the first additive and the second additive have a good synergistic effect, which can reduce the DCR of the battery while maintaining good high-temperature cycle performance of the battery. Alternatively, the mass ratio of the first additive to the second additive is 0.0003 to 0.03. Further optionally, the mass ratio of the first additive to the second additive can be 0.0005, 0.001, 0.005, 0.008, 0.01, 0.02, 0.03, 0.04, etc.

[0049] In some embodiments, the electrolyte further comprises a third additive, the third additive comprising at least one of difluorophosphate and tetrafluoroborate. Difluorophosphate and tetrafluoroborate can improve the stability of the SEI film, giving the SEI film better toughness, while making the SEI film more uniform and dense. In addition, difluorophosphate and tetrafluoroborate can reduce the decomposition of the electrolyte, which is beneficial to improving the cycle performance of the battery. Further optionally, the difluorophosphate comprises at least one of lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate. The tetrafluoroborate comprises at least one of lithium tetrafluoroborate, sodium tetrafluoroborate, and potassium tetrafluoroborate.

[0050] In some embodiments, the mass percentage of the third additive in the electrolyte is 0.01% to 1%. The mass percentage of the third additive in the electrolyte within this range can further improve the stability of the SEI film and further improve the cycle performance of the battery. Alternatively, the mass percentage of the third additive in the electrolyte can be 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0051] In some embodiments, the mass ratio of the first additive to the third additive is 0.1 to 30. Within this range, the mass ratio of the first additive to the third additive can provide a battery with both low impedance and good high-temperature cycling performance. Alternatively, the mass ratio of the first additive to the third additive is 3 to 10. Further, the mass ratio of the first additive to the third additive can be 0.1, 0.5, 0.8, 1, 5, 8, 10, 15, 20, 25, 30, etc.

[0052] In some embodiments, the electrolyte further includes a fourth additive comprising at least one of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). The fourth additive can undergo free radical polymerization on the negative electrode surface to generate polyalkyl lithium carbonate, which participates in the formation of the SEI film. This can further improve the flexibility of the SEI film, allowing the SEI film to change with changes in the negative electrode volume. This can reduce the risk of SEI film rupture during cycling, exposing new active sites, and further reduce the occurrence of side reactions, thereby improving the battery's cycle life and charge / discharge efficiency.

[0053] Optionally, the fourth additive accounts for 1% to 5% by mass of the electrolyte. Within this range, the fourth additive can achieve both low impedance and good high-temperature cycle performance. Optionally, the fourth additive accounts for 1% to 3% by mass of the electrolyte. Further, the fourth additive can account for 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0054] In some embodiments, the mass ratio of the total mass of the first additive and the third additive to the mass ratio of the fourth additive is 0.01 to 0.5. The mass ratio of the total mass of the first additive and the third additive to the mass ratio of the fourth additive within this range can be a better balance between high temperature cycle performance and kinetic performance of the battery. Alternatively, the mass ratio of the total mass of the first additive and the third additive to the mass ratio of the fourth additive is 0.3 to 0.4. Further optionally, the mass ratio of the total mass of the first additive and the third additive to the mass ratio of the fourth additive can be 0.01, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc.

[0055] In some embodiments, the electrolyte further comprises an electrolyte salt and a solvent.

[0056] Alternatively, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0057] Alternatively, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), 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.

[0058] Optionally, the electrolyte may further include other additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0059] Optionally, other additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0060] Another embodiment of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the aforementioned electrolyte; the separator is positioned between the positive and negative electrode sheets. By incorporating the aforementioned electrolyte into the battery, the battery can achieve both good cycle performance and good lithium ion transport performance.

[0061] In some embodiments, the separator has a thickness of 10 micrometers (μm) to 30 μm. A separator thickness within this range can provide good stability and resist puncture, while allowing lithium ions to pass through at a faster rate, thereby maintaining good high-temperature cycling performance and good lithium ion transport performance for the battery. Alternatively, the separator can have a thickness of 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, etc.

[0062] In some embodiments, the separator has a porosity of 20% to 50%. A separator porosity within this range can reduce the risk of metal ions dissolved from the positive electrode plate passing through the separator and reaching the negative electrode plate during cycling, helping to reduce side reactions on the negative electrode plate surface, thereby maintaining good high-temperature cycling performance for the battery. Furthermore, a separator porosity within this range allows lithium ions to pass through more smoothly, helping to maintain good lithium ion transport performance for the battery.

[0063] Another embodiment of the present application provides an electrical device including the above-mentioned electrolyte and / or the above-mentioned secondary battery.

[0064] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0065] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0066] Positive electrode

[0067] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0068] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0069] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0070] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0071] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0072] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from, but not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascals·second (mPa·s) to 25000 mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm2 (mg / cm 2 )~35mg / cm 2 The compacted density of the positive electrode can be 3.0 g / cm3 (g / cm3 )~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0074] Negative electrode

[0075] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0076] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0077] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0078] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0079] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0080] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0082] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 grams per square meter (g / m 2 )~220g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0083] electrolytes

[0084] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0085] In some embodiments, the electrolyte is an electrolyte. Optionally, the electrolyte can be selected from the electrolytes of the present application.

[0086] Isolation film

[0087] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0088] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0089] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may optionally be 12 μm to 20 μm.

[0090] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0091] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0092] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0093] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0094] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0095] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 1 with a square structure as an example.

[0096] In some embodiments, referring to Figure 2, the outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to actual needs.

[0097] The secondary battery may be a battery module or a battery pack.

[0098] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0099] In a battery module, multiple battery cells can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Further, the multiple battery cells can be fixed by fasteners.

[0100] Optionally, the battery module may further include a housing having an accommodation space, wherein the plurality of battery cells are accommodated in the accommodation space.

[0101] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0102] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0103] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0104] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0105] Figure 3 shows an example of an electric device 2. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0106] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0107] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0108] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0109] Example 1

[0110] (1) Preparation of positive electrode sheets.

[0111] Lithium iron phosphate positive electrode material, polyvinylidene fluoride (PVDF), and carbon black (SP) are mixed with NMP solvent in a mass ratio of 97:2:1, and stirred to obtain a uniformly dispersed positive electrode slurry. The positive electrode slurry is evenly coated on both surfaces of the aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0112] (2) Preparation of negative electrode sheets.

[0113] Artificial graphite, carbon black, styrene-butadiene rubber, and sodium hydroxymethyl cellulose are mixed with water in a mass ratio of 97:0.5:1.5:1, and stirred to obtain a uniformly dispersed negative electrode slurry. The negative electrode slurry is evenly coated on both surfaces of the copper foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0114] (3) A polyethylene film was used as the separator. The thickness and porosity of the separator are shown in Table 1.

[0115] (4) The composition of the electrolyte is shown in Table 1.

[0116] (5) Preparation of secondary batteries.

[0117] The positive electrode sheet, negative electrode sheet and separator are made into an electrode assembly through a winding process, placed in a shell made of aluminum shell, aluminum-plastic film, etc., injected with electrolyte, and after high-temperature standing, formation and capacity separation, a secondary battery is obtained.

[0118] The difference between Examples 2 to 20 and Comparative Examples 1 to 4 and Example 1 lies in the different compositions of the electrolytes, as shown in Table 1.

[0119] Test Case

[0120] (1) Determination of high temperature cycle performance at 60 degrees Celsius (℃).

[0121] At 60°C, the batteries of each embodiment and comparative example were charged at a constant current of 0.5C to a voltage upper limit of 3.8 volts (V), and then charged at a constant voltage to a current of 0.05C. The batteries were allowed to rest for 5 minutes and discharged at a constant current of 1 / 3C to 2.0V. This was the first charge and discharge cycle of the battery, and the discharge capacity at this time was recorded as the discharge capacity of the battery in the first cycle, D1. The battery was subjected to a cyclic charge and discharge test according to the above method, and the capacity Dn of the battery at the nth cycle was recorded. The capacity retention rate was Dn / D1. The number of cycles at which the capacity retention rate reached 80% was recorded. The results are shown in Table 1.

[0122] (2)DCR test.

[0123] At 25°C, the batteries from each example and comparative example were charged at a constant current of 0.5C to a voltage upper limit of 3.8V, then charged at a constant voltage to a current of 0.05C. The batteries were then discharged at 0.5C for 1 hour to 50% SOC, with the voltage at this point recorded as U1. They were then discharged at 4C for 30 seconds, with the voltage at this point recorded as U2. DCR = (U1 - U2) / 4C. The results are shown in Table 1. DCR can be used to measure lithium ion transport performance.

[0124] (3) Gas production test.

[0125] The gas production rate of a battery can be expressed as its expansion rate. The batteries of each example and comparative example were charged at a constant current of 0.1C to 3.8V, then charged at a constant voltage of 3.8V to a current ≤ 0.05C. At this point, the battery was fully charged, and the battery volume (V1) was measured using the water displacement method. The fully charged battery was then stored at 60°C. After 30 days, the battery was removed and allowed to stand at 25°C for 2 hours. The battery volume (V2) was then measured using the water displacement method. The battery gas production rate is then calculated as (V2 - V1) / V1 × 100%. The results are shown in Table 1.

[0126] Table 1

[0127] In Table 1, w1 represents the mass percentage of the first additive in the electrolyte. w2 represents the mass percentage of the second additive in the electrolyte. w3 represents the mass percentage of the third additive in the electrolyte. w4 represents the mass percentage of the fourth additive in the electrolyte. w5 represents the mass percentage of the electrolyte salt in the electrolyte. A / C represents the mass ratio of the first additive to the second additive. A / B represents the mass ratio of the first additive to the third additive. (A+B) / D represents the mass ratio of the total mass of the first additive and the third additive to the mass of the fourth additive. The unit of separator thickness is μm. The unit of DCR is mΩ.

[0128] It can be seen from Table 1 that when the electrolyte contains the first additive, the battery can achieve both good cycle performance and good lithium ion transport performance.

[0129] Furthermore, compared with TMSP and TMSF, when TMSB, TMSPi, HMDSO, HDMS and trimethylsilyl isocyanate are used as the first additive, although the battery has a slightly higher DCR, the battery has a lower gas production rate, which is beneficial to improving the structural stability inside the battery.

[0130] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0131] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. An electrolyte comprising a chemical formula of R((CH3) m Si) n A first additive, wherein R includes at least one of a phosphate group, a phosphite group, a borate group, an amine group, an isocyanate group, a fluorine atom, an oxygen atom and a sulfur atom, m is 1, 2 or 3, and n is 1, 2 or 3.

2. The electrolyte according to claim 1, wherein The first additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, trimethylsilyl isocyanate, trimethylfluorosilane, hexamethyldisiloxane and hexamethyldisilazane.

3. The electrolyte according to claim 1 or 2, wherein The mass percentage of the first additive to the electrolyte is 0.01% to 1%, and optionally 0.05% to 0.5%.

4. The electrolyte according to any one of claims 1 to 3, wherein The electrolyte further includes a second additive, and the second additive includes ethylene carbonate.

5. The electrolyte according to claim 4, wherein The mass percentage of the second additive in the electrolyte is 10% to 40%.

6. The electrolyte according to claim 4 or 5, wherein The mass ratio of the first additive to the second additive is 0.0001 to 0.05, and optionally 0.0003 to 0.

03.

7. The electrolyte according to any one of claims 1 to 6, wherein The electrolyte further comprises a third additive, wherein the third additive comprises at least one of difluorophosphate and tetrafluoroborate; Optionally, the difluorophosphate includes at least one of lithium difluorophosphate, sodium difluorophosphate and potassium difluorophosphate; Optionally, the tetrafluoroborate includes at least one of lithium tetrafluoroborate, sodium tetrafluoroborate and potassium tetrafluoroborate; Optionally, the mass percentage of the third additive in the electrolyte is 0.01% to 1%.

8. The electrolyte according to claim 7, wherein The mass ratio of the first additive to the third additive is 0.1-30, and optionally 3-10.

9. The electrolyte according to claim 7 or 8, wherein The electrolyte further includes a fourth additive including at least one of vinylene carbonate and vinyl ethylene carbonate.

10. The electrolyte according to claim 9, wherein The mass percentage of the fourth additive in the electrolyte is 1% to 5%.

11. The electrolyte according to claim 9 or 10, wherein The mass ratio of the total mass of the first additive and the third additive to the mass of the fourth additive is 0.01 to 0.5, and optionally 0.3 to 0.

4. 12 . A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to claim 1 ; the separator is located between the positive electrode sheet and the negative electrode sheet.

13. The secondary battery according to claim 12, wherein: The thickness of the isolation film is 10 μm to 30 μm; and / or the porosity of the isolation film is 20% to 50%.

14. An electrical device comprising the electrolyte according to any one of claims 1 to 11 and / or the secondary battery according to any one of claims 12 to 13.

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