Electrolyte solution, secondary battery, and electric device

Abstract

The invention provides an electrolyte, a secondary battery and an electric device. The electrolyte includes a first additive having a chemical formula of R ((CH3) mSi) n, where R includes at least one of a phosphate group, a phosphite group, a borate group, an amino 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. According to the electrolyte, by introducing the first additive, the conductivity of an SEI film can be improved, and the transmission performance of lithium ions can be improved. And meanwhile, due to the introduction of the first additive, the SEI film has relatively good stability, so that the battery has relatively good cycle performance.

Description

Technical Field

[0001] 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

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] 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 process of improving battery performance, 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 transmission kinetics of lithium ions, causing the battery's charge and discharge speed to slow down. Summary of the invention

[0004] In order to achieve the above-mentioned object, 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.

[0005] In the above electrolyte, the conductivity of the SEI film can be improved by introducing the first additive, which is beneficial to improving the lithium ion transmission 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 better cycle stability and better lithium ion transmission performance.

[0006] 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.

[0007] 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 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%.

[0008] In some embodiments, the electrolyte further comprises a second additive, wherein the second additive comprises ethylene carbonate. The introduction of the second additive can better promote the dissociation of electrolyte salts in the electrolyte, improve the conductivity of the electrolyte, and promote the transmission of lithium ions. At the same time, the second additive can participate in the film formation process of the SEI film, reduce the occurrence of interface side reactions, and help improve the cycle performance of the battery.

[0009] 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 keep the electrolyte with a suitable viscosity and a high conductivity.

[0010] 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. Optionally, the mass ratio of the first additive to the second additive is 0.0003 to 0.03.

[0011] In some embodiments, the electrolyte further comprises a third additive, and the third additive comprises at least one of difluorophosphate and tetrafluoroborate. Difluorophosphate and tetrafluoroborate can improve the stability of the SEI film, make the SEI film have better toughness, and make the SEI film more uniform and dense. In addition, difluorophosphate and tetrafluoroborate can reduce the decomposition of the electrolyte, which is conducive to improving the cycle performance of the battery. Optionally, the difluorophosphate comprises at least one of lithium difluorophosphate, sodium difluorophosphate and potassium difluorophosphate. Optionally, the tetrafluoroborate comprises at least one of lithium tetrafluoroborate, sodium tetrafluoroborate and potassium tetrafluoroborate.

[0012] 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.

[0013] In some embodiments, the mass ratio of the first additive to the third additive is 0.1 to 30. The mass ratio of the first additive to the third additive within this range can enable the battery to have both lower impedance and better high temperature cycle performance. Optionally, the mass ratio of the first additive to the third additive is 3 to 10.

[0014] In some embodiments, the electrolyte further comprises a fourth additive, the fourth additive comprising at least one of vinylene carbonate and vinyl ethylene carbonate. The fourth additive can undergo a free radical polymerization reaction on the surface of the negative electrode to generate polyalkyl lithium carbonate to participate in the formation of the SEI film, which can further improve the flexibility of the SEI film, so that the SEI film can change with the change of the negative electrode volume, thereby reducing the risk of SEI film rupture and exposing new active sites during the cycle, thereby reducing the occurrence of side reactions, thereby improving the cycle life and charge and discharge efficiency of the battery.

[0015] In some embodiments, the mass percentage of the fourth additive in the electrolyte is 1% to 5%. When the mass percentage of the fourth additive in the electrolyte is within this range, the battery can have both lower impedance and better high temperature cycle performance.

[0016] 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 battery that better balances high temperature cycle performance and kinetic performance. Optionally, 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.

[0017] 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.

[0018] In some embodiments, the thickness of the separator is 10 μm to 30 μm. When the separator thickness is within this range, the separator has good stability and is not easily punctured, and lithium ions can pass through at a faster rate, thereby maintaining good high temperature cycle performance and good lithium ion transmission performance of the battery.

[0019] In some embodiments, the porosity of the separator is 20% to 50%. The porosity of the separator within this range can reduce the risk of metal ions dissolved from the positive electrode plate passing through the separator to reach the negative electrode plate during the cycle, which is beneficial to reduce the side reactions on the surface of the negative electrode plate, thereby enabling the battery to maintain good high-temperature cycle performance. At the same time, the porosity of the separator within this range can allow lithium ions to pass more smoothly, which is beneficial for the battery to maintain good lithium ion transmission performance.

[0020] A third aspect of the present application provides an electrical device, comprising the electrolyte and / or the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the 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 of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0022] Figure 1 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0023] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0024] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0025] Description of reference numerals:

[0026] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0029] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and 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 a particular range. The range defined in this way can be inclusive or exclusive of the end values, and 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 a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is 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 can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0030] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Reference to "embodiments" herein means 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 the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0033] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean 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. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0034] In this application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It 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".

[0035] 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.

[0036] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0037] One embodiment of the present application provides an electrolyte solution, comprising a chemical formula of R((CH3) m Si) nThe first additive is 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. In the electrolyte, the conductivity of the SEI film can be improved by introducing the first additive, which is beneficial to improving the lithium ion transmission performance. At the same time, the introduction of the first additive can make the SEI film have better stability, and then the battery has 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 transmission performance.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] In some embodiments, the first additive includes at least one of tris(trimethylsilyl)phosphate and trimethylfluorosilane. At this time, by selecting the first additive from tris(trimethylsilyl)phosphate and trimethylfluorosilane, the DCR of the battery can be more effectively reduced, and the initial power performance of the battery can be improved.

[0042] In some embodiments, the first additive includes at least one of tris(trimethylsilane)phosphite, tris(trimethylsilane)borate, hexamethyldisiloxane and hexamethyldisilazane. At this time, by selecting the first additive from tris(trimethylsilane)phosphite, tris(trimethylsilane)borate, hexamethyldisiloxane and hexamethyldisilazane, the gas generation problem during the battery cycle can be effectively improved, which is beneficial to improving the structural stability inside the battery.

[0043] 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.

[0044] In some embodiments, the electrolyte further comprises a second additive, and the second additive comprises ethylene carbonate. The introduction of the second additive can better promote the dissociation of the electrolyte salt in the electrolyte, improve the conductivity of the electrolyte, and promote the transmission of lithium ions. At the same time, the second additive can participate in the film formation process of the SEI film, reduce the occurrence of interface side reactions, and help improve the cycle performance of the battery.

[0045] Optionally, 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 keep the electrolyte at a suitable viscosity and can keep the electrolyte at a high conductivity. Further optionally, the mass percentage of the second additive in the electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0046] 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. Optionally, 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.

[0047] 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, make the SEI film have better toughness, and make the SEI film more uniform and dense. In addition, difluorophosphate and tetrafluoroborate can reduce the decomposition of the electrolyte, which is conducive to improving the cycle performance of the battery. Further optionally, the difluorophosphate comprises at least one of lithium difluorophosphate, sodium difluorophosphate and potassium difluorophosphate. Tetrafluoroborate comprises at least one of lithium tetrafluoroborate, sodium tetrafluoroborate and potassium tetrafluoroborate.

[0048] 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. Optionally, 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.

[0049] In some embodiments, the mass ratio of the first additive to the third additive is 0.1 to 30. The mass ratio of the first additive to the third additive within this range can allow the battery to have both lower impedance and better high temperature cycle performance. Optionally, the mass ratio of the first additive to the third additive is 3 to 10. Further optionally, 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.

[0050] In some embodiments, the electrolyte further comprises a fourth additive, which comprises at least one of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). The fourth additive can undergo a free radical polymerization reaction on the surface of the negative electrode to generate polyalkyl lithium carbonate to participate in the formation of the SEI film, which can further improve the flexibility of the SEI film, so that the SEI film can change with the change of the volume of the negative electrode, thereby reducing the risk of SEI film rupture and exposing new active sites during the cycle, thereby reducing the occurrence of side reactions, thereby improving the cycle life and charge and discharge efficiency of the battery.

[0051] Optionally, 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 give the battery both lower impedance and better high temperature cycle performance. Optionally, the mass percentage of the fourth additive in the electrolyte is 1% to 3%. Further optionally, the mass percentage of the fourth additive in the electrolyte can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0052] 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 battery that better balances good high temperature cycle performance and kinetic performance. Optionally, 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.

[0053] In some embodiments, the electrolyte further comprises an electrolyte salt and a solvent.

[0054] Optionally, 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).

[0055] 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), ethylene 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0056] Optionally, the electrolyte may further include other additives, such as 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, additives that improve battery high or low temperature performance, etc.

[0057] 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.

[0058] Another embodiment of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the above electrolyte; the separator is located between the positive electrode sheet and the negative electrode sheet. By applying the above electrolyte to the battery, the battery can have both good cycle performance and good lithium ion transmission performance.

[0059] In some embodiments, the thickness of the separator is 10 μm to 30 μm. The separator thickness within this range can make the separator have good stability and not be easily punctured, and at the same time allow lithium ions to pass through at a faster rate, thereby allowing the battery to maintain good high temperature cycle performance and good lithium ion transmission performance. Optionally, the thickness of the separator can be 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, etc.

[0060] In some embodiments, the porosity of the separator is 20% to 50%. The porosity of the separator within this range can reduce the risk of metal ions dissolved from the positive electrode plate passing through the separator to reach the negative electrode plate during the cycle, which is beneficial to reduce the side reactions on the surface of the negative electrode plate, thereby enabling the battery to maintain good high-temperature cycle performance. At the same time, the porosity of the separator within this range can allow lithium ions to pass through more smoothly, which is beneficial for the battery to maintain good lithium ion transmission performance.

[0061] Another embodiment of the present application provides an electrical device, including the above-mentioned electrolyte and / or the above-mentioned secondary battery.

[0062] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0063] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0064] Positive electrode

[0065] 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, wherein the positive electrode film layer includes a positive electrode active material.

[0066] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0067] 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.

[0068] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: a lithium-containing phosphate with an olivine structure, 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 positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, 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 lithium-containing phosphates with an olivine structure 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 0.85 Co 0.15 Al 0.05 O2.

[0069] In some of these embodiments, the positive electrode active material layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0070] 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.

[0071] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: 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 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 one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15-35 mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0072] Negative electrode

[0073] 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.

[0074] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0075] In some of the 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.

[0076] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries 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. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, 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.

[0077] 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).

[0078] 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.

[0079] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0080] In some of the 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 surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode 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 2000-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75-220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0081] Electrolytes

[0082] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0083] In some embodiments, the electrolyte is an electrolyte. Optionally, the electrolyte can be selected from the electrolytes of the present application.

[0084] Isolation film

[0085] 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 stability and mechanical stability can be selected.

[0086] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0087] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may be 12 to 20 μm.

[0088] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0089] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0090] 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 package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0091] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0092] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0093] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 1 is a square structure as an example.

[0094] In some of these embodiments, reference Figure 2 , the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate 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 form 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 battery cell 1 can be one or more, and those skilled in the art can select according to actual needs.

[0095] The secondary battery may be a battery module or a battery pack.

[0096] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0097] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0098] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0099] In some of the 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 a suitable number according to the application and capacity of the battery pack.

[0100] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0101] In addition, the present application also provides an electrical device, which includes a secondary battery provided by 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 may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0102] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0103] Figure 3 The power consumption device 2 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0104] Another example of a device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0105] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0106] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0107] Example 1

[0108] (1) Preparation of positive electrode sheet.

[0109] 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 a uniformly dispersed positive electrode slurry is obtained by stirring. The positive electrode slurry is evenly coated on both surfaces of an aluminum foil, and the positive electrode sheet is obtained by drying, cold pressing, and cutting.

[0110] (2) Preparation of negative electrode sheets.

[0111] 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 dried, cold pressed and cut to obtain a negative electrode sheet.

[0112] (3) A polyethylene film is used as the separator. The thickness and porosity of the separator are shown in Table 1.

[0113] (4) The composition of the electrolyte is shown in Table 1.

[0114] (5) Preparation of secondary batteries.

[0115] The positive electrode sheet, the negative electrode sheet and the isolation film are made into an electrode assembly through a winding process, placed in a casing made of an aluminum shell, an aluminum-plastic film, etc., injected with electrolyte, and after high-temperature standing, formation, and capacity division, a secondary battery is obtained.

[0116] The difference between Examples 2 to 19 and Comparative Examples 1 to 4 and Example 1 is that the composition of the electrolyte is different, as shown in Table 1.

[0117] Test Case

[0118] (1) Determination of 60℃ high temperature cycle performance.

[0119] At 60°C, the batteries of the embodiments and comparative examples were charged at a constant current of 0.5C to an upper voltage limit of 3.8V, and then charged at a constant voltage to a current of 0.05C. The battery was left to stand 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 D1 of the first cycle of the battery. The battery was subjected to a cyclic charge and discharge test according to the above method, and the capacity Dn at the nth cycle of the battery was recorded, and the capacity retention rate was Dn / D1. The number of cycles when the capacity retention rate was 80% was recorded. The results are shown in Table 1.

[0120] (2)DCR test.

[0121] At 25°C, the batteries of each embodiment and comparative example were charged at a constant current of 0.5C to an upper voltage limit of 3.8V, and then charged at a constant voltage to a current of 0.05C. Subsequently, the battery was discharged at 0.5C for 1h to adjust the battery to 50% SOC, and the voltage at this time was recorded as U1. Then, the battery was discharged at 4C for 30s, and the voltage at this time was recorded as U2. DCR = (U1-U2) / 4C. The results are shown in Table 1. The DCR can represent the transport performance of lithium ions.

[0122] (3) Gas production test.

[0123] The gas production rate of the battery can be expressed by the expansion rate of the battery. The batteries of each embodiment and comparative example were charged to 3.8V at a constant current of 0.1C, and then charged at a constant voltage of 3.8V to a current ≤ 0.05C. At this time, the battery was fully charged, and the battery volume V1 was tested by the water discharge method. The fully charged battery was then stored at 60°C, and the battery was taken out after 30 days, and left to stand at 25°C for 2 hours, and the battery volume V2 was tested by the water discharge method. Then the gas production rate of the battery = (V2-V1) / V1×100%. The results are shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127]

[0128] 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 ratio of the fourth additive. The thickness of the isolation membrane is in μm. The unit of DCR is mΩ.

[0129] It can be seen from Table 1 that when the electrolyte contains the first additive, the battery can have both good cycle performance and good lithium ion transmission performance.

[0130] 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 generation rate, which is beneficial to improving the structural stability inside the battery.

[0131] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0132] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An electrolyte, characterized in that: Containing a compound having the chemical formula 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.

2. The electrolyte according to claim 1, characterized in that 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, characterized in that 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, characterized in that The electrolyte further includes a second additive, and the second additive includes ethylene carbonate.

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

6. The electrolyte according to claim 4 or 5, characterized in that 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, characterized in that 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, characterized in that 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, characterized in that 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, characterized in that The mass percentage of the fourth additive in the electrolyte is 1% to 5%.

11. The electrolyte according to claim 9 or 10, characterized in that 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, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 11; the separator is located between the positive electrode sheet and the negative electrode sheet.

13. The secondary battery according to claim 12, characterized in that: 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, characterized in that: A secondary battery comprising the electrolyte according to any one of claims 1 to 11 and / or any one of claims 12 to 13.

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