Electrolyte solution, secondary battery, battery module, battery pack, and electric device

Abstract

The invention relates to an electrolyte. The electrolyte comprises an organic solvent and an electrolyte salt dissolved in the organic solvent, wherein the electrolyte salt comprises alkali metal double salt, and the alkali metal double salt contains lithium ions and at least one kind of other alkali metal ions except the lithium ions. The invention also relates to a corresponding secondary battery, a battery module, a battery pack and an electric device. According to the electrolyte, the alkali metal double salt containing the lithium ions and at least one alkali metal ion except the lithium ions is adopted in the electrolyte salt, so that the cycle performance of the secondary battery can be effectively improved, the cycle life of the secondary battery can be prolonged, additional impurities cannot be introduced, and side reaction cannot be caused.

Description

Electrolyte, secondary battery, battery module, battery pack and power-consuming device Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to an electrolyte, a secondary battery, a battery module, a battery pack, and an electrical device. Background Art

[0002] In recent years, the application of secondary ion batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have made great progress, higher requirements have been placed on the cycle life of secondary ions.

[0003] With the increasing demand for energy density, the demand and design of ternary cathodes have evolved from the earliest low-nickel materials to today's high-nickel materials. However, the overall lifespan of high-nickel materials is relatively poor. This is because, on the one hand, the increase in nickel content will inevitably lead to more lithium-nickel mixing, thereby reducing the battery cycle life; on the other hand, the solid electrolyte interphase (SEI) film formed on the electrode surface by conventional lithium salt electrolytes contains less organic lithium. Low organic lithium content will cause solvent molecules to co-intercalate, thereby destroying the electrode material and reducing the cycle life of the secondary battery.

[0004] The electrolyte is a crucial component of secondary batteries. It determines the composition and structure of the SEI film and significantly impacts the stability of the secondary battery electrode structure and its cycle life. Optimizing the electrolyte design is a primary means of improving the cycle life of secondary batteries. Therefore, the search for electrolytes that can further enhance the cycle life of secondary batteries is a key research area for those skilled in the art.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide an electrolyte, a secondary battery, a battery module, a battery pack and an electrical device, which can enable the secondary battery containing the electrolyte to have a longer cycle life.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present application provides an electrolyte solution comprising an organic solvent and an electrolyte salt dissolved in the organic solvent; the electrolyte salt comprises an alkali metal double salt, and the alkali metal double salt contains lithium ions and at least one other alkali metal ion other than lithium ions.

[0008] In any embodiment, the other alkali metal ions in the alkali metal double salt include sodium ions and potassium ions.

[0009] In any embodiment, the alkali metal double salt contains both sodium ions and potassium ions.

[0010] In any embodiment, the alkali metal double salt includes Li a Na b K c PF6, Li a Na b K c BOB, Li a Na b K c ODFB, Li a Na b K c TFOP, Li a Na b K c PO2F2、Li a Na b K c TFSI、Li a Na b K c FSI and Li a Na b K c One or more of BODFP;

[0011] Among them, a+b+c=1, 0.5≤a<1.

[0012] In any embodiment, the electrolyte salt further contains a basic lithium salt, and the basic lithium salt includes one or more of LiPF6, LiBOB, LiODFB, LiTFOP, LiPO2F2, LiTFSI, LiFSI and LiBODFP.

[0013] In any embodiment, the mass ratio of the basic lithium salt to the alkali metal double salt in the electrolyte salt is X:1;

[0014] Among them, 0.65≤X<1.

[0015] In any embodiment, 0.7≤X<0.9.

[0016] In any embodiment, the base lithium salt and the alkali metal double salt have the same anion type.

[0017] In any embodiment, the molar concentration of the electrolyte salt in the electrolyte solution is 0.5 mol / L to 2 mol / L.

[0018] In any embodiment, the organic solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, ethylene carbonate, propylene carbonate, and diethyl carbonate.

[0019] The second aspect of the present application further provides a secondary battery comprising the electrolyte of the first aspect of the present application.

[0020] In any embodiment, the positive electrode active material in the positive electrode sheet of the secondary battery is a layered structure positive electrode active material.

[0021] A third aspect of the present application further provides a battery module, comprising the secondary battery according to the second aspect of the present application.

[0022] The fourth aspect of the present application also provides a battery pack, comprising the battery module of the third aspect of the present application.

[0023] The fifth aspect of the present application further provides an electrical device comprising at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.

[0024] The electrolyte of the present application adopts an alkali metal complex salt including lithium ions and at least one alkali metal ion other than lithium ions in the electrolyte salt; on the one hand, the radius of the alkali metal ions other than lithium (such as sodium ions and potassium ions) in the alkali metal complex salt is larger than that of lithium, and can be embedded in part of the lithium sites of the layered positive electrode during the first discharge process, thereby improving the stability of the layered structure and preventing the Li / Ni mixed arrangement of the layered positive electrode, thereby improving the cycle performance of the secondary battery; on the other hand, the sodium ions, potassium ions, etc. in the alkali metal complex salt help to increase the organic lithium component in the SEI during the formation of the SEI film for the first charge and discharge, thereby effectively improving the co-embedding of solvent molecules, avoiding damage to the electrode material due to the co-embedding of solvent molecules, and greatly improving the cycle performance of the electrode; on the other hand, some lithium sites in the lithium salt are replaced with sodium salts, potassium salts, etc. with larger ionic radius, and the sodium ions and potassium ions can occupy the same spatial sites and energy levels as the lithium ions, and the structures of the sodium ions and potassium ions occupying the original lithium sites in the lithium salt are more stable. Lithium vacancies provide a stable space for storing sodium and potassium. The failure rate of sodium and potassium ions detaching from and embedding into the corresponding lithium sites is reduced, which is conducive to a longer-lasting effect of sodium and potassium ions. The ions have the same movement trajectory when they are released during charging and discharging, which can quantitatively improve the cycle life of the battery cell without introducing additional impurities or causing side reactions. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0027] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0028] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0029] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0030] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0031] Description of reference numerals:

[0032] 1. Battery pack; 2. Upper case; 3. Lower case; 4. Battery module; 5. Secondary battery; 5. Casing; 5. Electrode assembly; 5. Cover; 6. Electrical device. DETAILED DESCRIPTION

[0033] Below, the embodiments of the electrolyte, secondary battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0034] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the end values ​​and may be combined arbitrarily, i.e., any lower limit may 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 contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "ab" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "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 disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or 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.

[0038] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0039] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0040] Currently, with the rapid development of secondary batteries, higher requirements have been placed on their cycle performance. Secondary batteries with excellent cycle performance place high demands on electrolytes. Therefore, finding electrolytes that can better improve the cycle performance of secondary batteries is a key research focus for those skilled in the art.

[0041] With the increasing demand for energy density in secondary batteries, ternary cathode materials are now mostly high-nickel materials, which generally have a poor overall lifespan. On the one hand, the increase in nickel content inevitably leads to more lithium-nickel intermixing, thereby reducing the cycle life of the secondary battery. On the other hand, the SEI film formed by conventional lithium salt electrolytes contains little organic lithium, which easily causes solvent molecules to co-intercalate, thus damaging the electrode material and further reducing the cycle life of the secondary battery.

[0042] The inventors have discovered an electrolyte solution that uses an alkali metal double salt as its electrolyte salt. The alkali metal double salt contains lithium ions and other alkali metal ions (such as sodium and potassium) in addition to lithium ions. This electrolyte solution can effectively improve the cycle performance of secondary batteries and increase the cycle life of secondary batteries.

[0043] In some embodiments, the first aspect of the present application provides an electrolyte comprising an organic solvent and an electrolyte salt dissolved in the organic solvent; wherein the electrolyte salt comprises an alkali metal double salt, and the alkali metal double salt contains lithium ions and at least one other alkali metal ion other than lithium ions.

[0044] The electrolyte of the present application adopts an alkali metal double salt containing lithium ions and at least one alkali metal ion other than lithium ions in the electrolyte salt; the radius of the alkali metal ions other than lithium in the alkali metal double salt (such as sodium ions and potassium ions) is larger than that of lithium, and can be embedded in part of the lithium sites of the layered positive electrode during the first discharge process, thereby improving the stability of the layered structure, preventing Li / Ni mixing in the layered positive electrode, and thus improving the cycle performance of the secondary battery.

[0045] On the other hand, the sodium ions, potassium ions, etc. in the alkali metal double salt help to increase the organic lithium content in the SEI during the formation of the SEI film during the first charge and discharge, thereby effectively improving the co-embedding of solvent molecules, avoiding damage to the electrode material caused by the co-embedding of solvent molecules, and greatly improving the cycle performance of the electrode.

[0046] If sodium salts, potassium salts, etc. are directly added to lithium salts as electrolyte salts; on the one hand, in the production process of the electrolyte, additional pipelines are needed to add additional introduction and purification steps to introduce sodium salts, potassium salts, etc. This series of processes requires additional equipment introduction support and increased production costs; on the other hand, simply adding sodium salts and potassium salts to lithium salts will cause a large amount of sodium and potassium ions to be free in the electrolyte. These sodium and potassium ions are not bound by ionic bonds, and the ions move irregularly, making it impossible to quantitatively control the improvement of the SEI film. In addition, simply adding sodium salts and potassium salts will introduce additional anions; in the same solvent, the type of metal salt will change the thermodynamic stability and solvation structure of the electrolyte, thereby affecting the decomposition behavior of the electrolyte, and further changing the interface characteristics of the electrode|electrolyte and the electrochemical performance of the electrode; different anions have different electronegativity, and anions will enter the solvation layer and participate in the solvation structure reaction, thereby accelerating the decomposition of the electrolyte and causing irreversible losses.

[0047] The present application replaces some lithium sites in lithium salts with alkali metal complex salts such as sodium salts and potassium salts with larger ionic radius. Compared with the method of directly adding sodium salts and potassium salts to lithium salts, the sodium ions and potassium ions in the alkali metal complex salts can occupy the same spatial position and energy level as lithium ions. The structure of sodium ions and potassium ions occupied by the in-situ lithium sites in the lithium salt is more stable, and the lithium vacancies provide a stable space for sodium and potassium storage. The failure rate of sodium ions and potassium ions detaching from and embedding into the corresponding lithium sites is reduced, which is conducive to a more lasting effect of sodium and potassium ions. The ions have the same motion trajectory when they are released during charging and discharging, which can quantitatively improve the cycle life of the secondary battery without introducing additional impurities or causing side reactions.

[0048] In some embodiments, other alkali metal ions in the alkali metal double salt include sodium ions and potassium ions. It is understood that other alkali metal ions may also include alkali metal ions such as rubidium ions and cesium ions.

[0049] In some embodiments, the alkali metal double salt contains both sodium ions and potassium ions, that is, the alkali metal double salt includes two or more other alkali metal ions, and the two or more other alkali metal ions include sodium ions and potassium ions.

[0050] In some embodiments, the alkali metal double salt comprises Li a Na b K c PF6, Li a Na b K c BOB, Li a Na b K c ODFB, Li a Na b K c TFOP, Li a Na b K c PO2F2、Li a Na b K c TFSI、Li a Na b K c FSI and Li a Na b K c One or more of BODFP; wherein a+b+c=1, 0.5≤a<1. Thus, the other alkali metal ions in the aforementioned alkali metal double salt are sodium and potassium. Using the aforementioned alkali metal double salt as the electrolyte salt can effectively improve the cycle life of the secondary battery. wherein a, b, and c represent the number of lithium, sodium, and potassium atoms in the molecular formula of the aforementioned alkali metal double salt, respectively.

[0051] It can be understood that in the above "0.5≤a<1", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiment and: 0.6, 0.7, 0.8, 0.9.

[0052] In any embodiment, the electrolyte salt further comprises a basic lithium salt, which includes one or more of LiPF6, LiBOB, LiODFB, LiTFOP, LiPO2F2, LiTFSI, LiFSI, and LiBODFP. Thus, the electrolyte salt contains both an alkali metal double salt and a basic lithium salt. It will be appreciated that in other embodiments, the electrolyte salt may include only an alkali metal double salt without the aforementioned basic lithium salt.

[0053] Furthermore, when the electrolyte salt contains both an alkali metal double salt and a basic lithium salt, the anions in the alkali metal double salt are of the same type as those in the basic lithium salt.

[0054] In any embodiment, the mass ratio of the basic lithium salt to the alkali metal double salt in the electrolyte salt is X:1, wherein 0.65≤X<1. It is understood that the mass content of the basic lithium salt in the electrolyte salt is less than the mass content of the alkali metal double salt.

[0055] It can be understood that in the above "0.65≤X<1", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and: 0.68, 0.70, 0.72, 0.75, 0.78, 0.80, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, and 0.98.

[0056] In any embodiment, 0.7≤X<0.9.

[0057] In any embodiment, the molar concentration of the electrolyte salt in the electrolyte solution is 0.5 mol / L to 2 mol / L.

[0058] In any embodiment, the organic solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, ethylene carbonate, propylene carbonate, and diethyl carbonate. That is, the organic solvent in the electrolyte may include any one of the above organic solvents, or may include two or more of the above organic solvents at the same time.

[0059] The second aspect of the present application further provides a secondary battery comprising the electrolyte of the first aspect of the present application, so that the secondary battery has good cycle performance and a long cycle life.

[0060] In any embodiment, the positive electrode active material in the positive electrode sheet of the secondary battery is a layered structure positive electrode active material.

[0061] A third aspect of the present application further provides a battery module, comprising the secondary battery according to the second aspect of the present application.

[0062] The fourth aspect of the present application also provides a battery pack, comprising the battery module of the third aspect of the present application.

[0063] The fifth aspect of the present application further provides an electrical device comprising at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.

[0064] The secondary battery, battery module, battery pack, and electric device of the present application are described below with reference to the accompanying drawings as appropriate.

[0065] In one embodiment of the present application, a secondary battery is provided.

[0066] 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.

[0067] [Positive electrode]

[0068] 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.

[0069] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0070] 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 formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. Polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one 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. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (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 Co 0.25 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 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0072] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100 weight percent based on the total weight of the positive electrode film layer.

[0073] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one 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. The weight ratio of the binder in the positive electrode film layer is 0 to 20 weight%, based on the total weight of the positive electrode film layer.

[0074] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 to 20% by weight, based on the total weight of the positive electrode film layer.

[0075] 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 (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40 to 80 wt %, and the viscosity at room temperature is adjusted to 5000 to 25000 mPa·s, the positive electrode slurry is coated on the surface of the positive electrode current collector, and after drying, the positive electrode sheet is formed by cold rolling; the positive electrode powder coating unit area density is 150 to 350 mg / m 2 The compaction density of the positive electrode is 3.0-3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0076] The calculation formula of the compacted density is:

[0077] Compaction density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0078] [Negative electrode]

[0079] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0080] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0081] 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 formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc., and the polymer material substrate includes but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates.

[0082] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one 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 be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one 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.

[0083] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight, based on the total weight of the negative electrode film layer.

[0084] In some embodiments, the negative electrode film layer may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20% by weight, based on the total weight of the negative electrode film layer.

[0085] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)). The weight ratio of the other additives in the negative electrode film layer is 0 to 15% by weight, based on the total weight of the negative electrode film layer.

[0086] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 (such as deionized water) to form a negative electrode slurry, wherein the negative electrode slurry has a solid content of 30 to 70 wt % and a viscosity at room temperature adjusted to 2000 to 10000 mPa·s; the obtained negative electrode slurry is coated on the negative electrode current collector, and after a drying process, cold pressing, such as a roller, is performed to obtain the negative electrode sheet. The negative electrode powder coating unit area density is 75 to 220 mg / m 2 , the compaction density of the negative electrode is 1.2~2.0g / m 3 .

[0087] [Electrolyte]

[0088] The electrolyte conducts ions between the positive and negative electrodes. The secondary battery of the present application employs the electrolyte of the present application. The electrolyte comprises an electrolyte salt and an organic solvent; the electrolyte salt comprises an alkali metal double salt, which contains lithium ions and at least one alkali metal ion other than lithium ions.

[0089] In some embodiments, the alkali metal double salt comprises Li a Na b K c PF6, Li a Na b K c BOB, Li a Na b K c ODFB, Li a Na b K c TFOP, Li a Na b K c PO2F2、Li a Na b K c TFSI、Li a Na b K c FSI and Li a Na b K c One or more of BODFP; wherein a+b+c=1, 0.5≤a<1.

[0090] In some embodiments, the electrolyte salt further includes a basic lithium salt, and the basic lithium salt includes one or more of LiPF6, LiBOB, LiODFB, LiTFOP, LiPO2F2, LiTFSI, LiFSI, and LiBODFP.

[0091] In some embodiments, the mass ratio of the basic lithium salt to the alkali metal double salt in the electrolyte salt is X:1; wherein 0.65≤X<1.

[0092] In some embodiments, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, and diethyl carbonate.

[0093] In some embodiments, the electrolyte may further include 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.

[0094] [Isolation film]

[0095] 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.

[0096] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0097] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may optionally be 12 to 20 μm.

[0098] 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.

[0099] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0100] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0101] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0102] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 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 51 has an opening connected to the receiving cavity, and the cover plate 53 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 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0103] In some embodiments, referring to FIG. 3 , secondary batteries 5 may be assembled into a battery module 4 . The battery module 4 may contain one or more secondary batteries 5 . The specific number may be selected by those skilled in the art based on the application and capacity of the battery module 4 .

[0104] In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0105] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0106] In some embodiments, referring to Figures 4 and 5, the above-mentioned battery modules 4 can also be assembled into a battery pack 1. The number of battery modules 4 contained in the battery pack 1 can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack 1.

[0107] The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0108] In addition, the present application also provides an electrical device 6, which includes at least one of the secondary battery 5, battery module 4, or battery pack 1 provided in the present application. The secondary battery 5, battery module 4, or battery pack 1 can be used as a power source for the electrical device 6, or as an energy storage unit for the electrical device 6. The electrical device 6 can include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0109] As the power-consuming device 6 , a secondary battery 5 , a battery module 4 or a battery pack 1 may be selected according to its usage requirements.

[0110] FIG4 shows an example of an electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery 5 of the electric device 6, a battery pack 1 or a battery module 4 can be used.

[0111] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and a secondary battery 5 may be used as a power source.

[0112] Example

[0113] 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.

[0114] 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.

[0115] Example 1:

[0116] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 PF6. Prepared into an electrolyte solution with a concentration of 1M. Among them, the electrolyte salt Li 0.5 Na 0.3 K 0.2 PF6 can be prepared by the hydrogen fluoride solvent method, and its reaction process can be expressed as follows:

[0117] (0.5LiF+0.3NaF+0.2KF)+PF5+CH3CN→Li 0.5 Na 0.3 K 0.2 (CH3CN)4PF6→Li0.5 Na 0.3 K 0.2 PF6

[0118] Preparation of secondary battery positive electrode: 1) Polyvinylidene fluoride (PVDF), layered positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 and the conductive agent, carbon black Super P, are mixed in a mass ratio of 90:5:5, using N-methyl-pyrrolidone (NMP) as the solvent. The solvent dosage is adjusted to maintain a slurry viscosity between 100 and 20,000 mPa.s. The slurry is applied to the positive electrode current collector using a coater or sprayer. After drying at 85°C, the slurry is cold-pressed, trimmed, cut, and slit. The slurry is then dried under vacuum at 85°C for 4 hours, and the tabs are welded to produce a secondary battery positive electrode sheet that meets the requirements.

[0119] Preparation of secondary battery negative electrode sheets: Add negative electrode active material graphite, conductive agent Super-P, thickener CMC, and adhesive SBR in a mass ratio of 96.5:1.0:1.0:1.5 to solvent deionized water and mix evenly to form a negative electrode slurry; apply the negative electrode slurry on the current collector copper foil and dry it at 85°C, then trim, cut and strip it, and then dry it at 110°C under vacuum conditions for 4 hours, weld the tabs, and make a secondary battery negative electrode sheet that meets the requirements.

[0120] Preparation of a secondary battery: Using a 12μm polypropylene film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound into a square bare cell. The bare cell is wrapped in aluminum foil, injected with electrolyte, and vacuum-sealed. Repeated charging and discharging cycles complete the secondary battery.

[0121] Example 2:

[0122] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 BOB. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 BOB can be prepared by the hydrogen fluoride solvent method.

[0123] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0124] Example 3:

[0125] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 ODFB. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 ODFB can be prepared by the hydrogen fluoride solvent method.

[0126] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0127] Example 4:

[0128] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 TFOP. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 TFOP can be prepared by the hydrogen fluoride solvent method.

[0129] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0130] Example 5:

[0131] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 PO2F2. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 PO2F2 can be prepared by the hydrogen fluoride solvent method.

[0132] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0133] Example 6:

[0134] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 TFSI. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 TFSI can be prepared by the hydrogen fluoride solvent method.

[0135] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0136] Example 7:

[0137] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 FSI. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 FSI can be prepared by the hydrogen fluoride solvent method.

[0138] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0139] Example 8:

[0140] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.3 K 0.2 BODFP. Prepared into an electrolyte solution with a concentration of 1M. Electrolyte salt Li 0.5 Na 0.3 K 0.2 BODFP can be prepared by the hydrogen fluoride solvent method.

[0141] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0142] Example 9:

[0143] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.7 Na 0.2 K 0.1 PF6. Prepared into an electrolyte solution with a concentration of 1M. Among them, the electrolyte salt Li 0.7 Na 0.2 K 0.1 PF6 can be prepared by the hydrogen fluoride solvent method.

[0144] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0145] Example 10:

[0146] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.8 Na 0.1 K 0.1 PF6. Prepared into an electrolyte solution with a concentration of 1M. Among them, the electrolyte salt Li 0.8 Na 0.1 K 0.1 PF6 can be prepared by the hydrogen fluoride solvent method.

[0147] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0148] Example 11:

[0149] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.9 Na 0.05 K 0.05 PF6. Prepared into an electrolyte solution with a concentration of 1M. Among them, the electrolyte salt Li 0.9 Na 0.05 K 0.05 PF6 can be prepared by the hydrogen fluoride solvent method.

[0150] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0151] Example 12:

[0152] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salts in the electrolyte are LiPF6 and Li 0.5 Na 0.3 K 0.2 PF6. LiPF6 and Li 0.5 Na 0.3 K 0.2 The mass ratio of PF6 is 0.7:1, and the electrolyte concentration is prepared to be 1M.

[0153] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0154] Example 13:

[0155] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) was used as the organic solvent, wherein the mass ratio of each component was EC:PC:DEC=30:30:40. The electrolyte salts in the electrolyte were LiBOB and Li 0.5 Na 0.3 K 0.2 BOB. LiBOB and Li 0.5 Na 0.3 K 0.2 The mass ratio of BOB is 0.8:1, and the electrolyte concentration is prepared to be 1M.

[0156] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0157] Example 14:

[0158] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) was used as the organic solvent, wherein the mass ratio of each component was EC:PC:DEC=30:30:40. The electrolyte salts in the electrolyte were LiODFB and Li 0.5 Na 0.3 K 0.2 ODFB. LiODFB and Li 0.5 Na 0.3 K 0.2 The mass ratio of ODFB is 0.9:1, and the electrolyte concentration is prepared to be 1M.

[0159] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0160] Example 15:

[0161] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.5 PF6. Prepare an electrolyte solution with a concentration of 1M.

[0162] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0163] Example 16:

[0164] Preparation of secondary battery electrolyte: A mixture of dimethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate is used as an organic solvent, wherein the mass ratio of each component is dimethyl carbonate: ethyl methyl carbonate: methyl propyl carbonate = 20:30:40. The electrolyte salt in the electrolyte is Li 0.5 K 0.5 BOB. Prepare an electrolyte solution with a concentration of 0.5M.

[0165] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0166] Example 17:

[0167] Preparation of secondary battery electrolyte: A mixture of methyl formate, methyl acetate and methyl butyrate is used as an organic solvent, wherein the mass ratio of each component is methyl formate: methyl acetate: methyl butyrate = 30:20:30. The electrolyte salt in the electrolyte is Li 0.5 Na 0.5 ODFB. Prepare an electrolyte solution with a concentration of 1.5M.

[0168] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0169] Example 18:

[0170] Preparation of secondary battery electrolyte: A mixture of ethyl propionate, ethylene carbonate and propylene carbonate is used as an organic solvent, wherein the mass ratio of each component is ethyl propionate: ethylene carbonate: propylene carbonate = 30:20:50. The electrolyte salt in the electrolyte is Li 0.5 K 0.5 TFOP. Prepare an electrolyte solution with a concentration of 2M.

[0171] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0172] Example 19:

[0173] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.5 PO2F2. Prepare an electrolyte with a concentration of 0.8M.

[0174] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0175] Example 20:

[0176] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.5 TFSI was prepared into an electrolyte solution with a concentration of 1.2M.

[0177] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0178] Example 21:

[0179] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=20:20:40. The electrolyte salt in the electrolyte is Li 0.5 K 0.5 FSI. Prepare an electrolyte solution with a concentration of 1M.

[0180] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0181] Example 22:

[0182] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=20:20:40. The electrolyte salt in the electrolyte is Li 0.5 Na 0.5 BODFP. Prepare an electrolyte solution with a concentration of 1.8M.

[0183] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0184] Example 23:

[0185] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=20:20:40. The electrolyte salt in the electrolyte is Li 0.7 K 0.3 PF6. Prepare an electrolyte with a concentration of 0.9M.

[0186] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0187] Example 24:

[0188] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.8 Na 0.2 PF6. Prepare an electrolyte solution with a concentration of 1M.

[0189] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0190] Example 25:

[0191] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.9 K 0.1 PF6. Prepare an electrolyte solution with a concentration of 1M.

[0192] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0193] Example 26:

[0194] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salts in the electrolyte are LiPF6 and Li 0.5 Na 0.5 PF6. LiPF6 and Li 0.5 Na 0.5 The mass ratio of PF6 is 0.7:1. The electrolyte concentration is prepared to be 1M.

[0195] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0196] Example 27:

[0197] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) was used as the organic solvent, wherein the mass ratio of each component was EC:PC:DEC=30:30:40. The electrolyte salts in the electrolyte were LiBOB and Li 0.5 K 0.5 BOB. LiBOB and Li 0.5 K 0.5 The mass ratio of BOB is 0.8:1. The electrolyte concentration is prepared to be 1M.

[0198] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0199] Comparative Example 1:

[0200] Preparation of the secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiPF6, and the concentration was 1M.

[0201] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0202] Comparative Example 2:

[0203] Preparation of the secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiBOB, and the concentration was 1M.

[0204] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0205] Comparative Example 3:

[0206] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiODFB. The electrolyte concentration was adjusted to 1 M.

[0207] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0208] Comparative Example 4:

[0209] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiTFOP. The electrolyte concentration was adjusted to 1 M.

[0210] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0211] Comparative Example 5:

[0212] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiPO₂F₂. The electrolyte concentration was prepared to 1 M.

[0213] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0214] Comparative Example 6:

[0215] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiTFSI. The electrolyte concentration was adjusted to 1 M.

[0216] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0217] Comparative Example 7:

[0218] Preparation of the secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiFSI. A 1M concentration was achieved.

[0219] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0220] Comparative Example 8:

[0221] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) was used as the organic solvent, with the mass ratio of EC:PC:DEC being 30:30:40. The electrolyte salt in the electrolyte was LiBODFP. The electrolyte concentration was adjusted to 1 M.

[0222] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0223] Comparative Example 9:

[0224] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is Li 0.4 Na 0.5 K 0.1 PF6, prepared into an electrolyte with a concentration of 1M.

[0225] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0226] Comparative Example 10:

[0227] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salt in the electrolyte is all Li 0.3 Na 0.3 K 0.4 PF6, prepared into an electrolyte with a concentration of 1M.

[0228] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0229] Comparative Example 11:

[0230] Preparation of secondary battery electrolyte: A mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) is used as an organic solvent, wherein the mass ratio of each component is EC:PC:DEC=30:30:40. The electrolyte salts in the electrolyte are LiPF6 and Li 0.5 Na 0.3 K 0.2 PF6. LiPF6 and Li 0.5 Na 0.3 K 0.2 The mass ratio of PF6 is 0.4:1, and the electrolyte concentration is prepared to be 1M.

[0231] The preparation of the positive electrode sheet, the negative electrode sheet and the secondary battery is the same as that in Example 1.

[0232] Cyclic performance test:

[0233] The cycling performance test conditions for secondary batteries are as follows: 1C / 1C cycle charge and discharge tests are performed at 25°C and 45°C, with a charge and discharge voltage range of 2.8V to 4.35V. Testing is terminated when the capacity decays to 80% of the initial discharge capacity (i.e., 80% SOH). SOH stands for battery health, which represents the percentage of a secondary battery's fully charged capacity relative to its rated capacity. The SOH of a new secondary battery is 100%.

[0234] The secondary batteries of the above embodiments and comparative examples were subjected to cycle performance tests, and the test results are shown in Table 1.

[0235] Table 1 Cycling performance test data of secondary batteries of various embodiments and comparative examples

[0236]

[0237]

[0238] It can be seen from the cycle performance test data of the above embodiments and comparative examples that in the electrolytes of different lithium salts, in-situ doping of lithium with a reasonable proportion of sodium or potassium ions can effectively improve the cycle life of the battery. When the total proportion of doped ions in the lithium salt is greater than a coefficient of 0.5, due to the large number of doped ions in the lithium salt, the Li amount is insufficient, which will lead to insufficient lithium consumption in the middle and late stages of the cycle and thus reduce the cycle life of the battery.

[0239] By replacing some lithium sites in lithium salts with sodium and potassium with larger ionic radius, sodium and potassium ions occupy the same spatial positions as lithium ions, have the same energy levels, and have the same motion trajectories when charging and discharging ions are released. The doped sodium or potassium ions can effectively prevent the Li / Ni mixing of the layered positive electrode, thereby improving the cycle performance; on the other hand, the sodium ions and potassium ions in the alkali metal double salt help to increase the organic lithium component in the SEI during the formation of the SEI film during the first charge and discharge.

[0240] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte comprising an organic solvent and an electrolyte salt dissolved in the organic solvent; The electrolyte salt includes an alkali metal double salt containing lithium ions and at least one alkali metal ion other than lithium ions.

2. The electrolyte according to claim 1, characterized in that The other alkali metal ions in the alkali metal double salt include sodium ions and potassium ions.

3. The electrolyte according to claim 1 or 2, characterized in that The alkali metal double salt contains sodium ions and potassium ions at the same time.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The alkali metal double salt includes Li a Na b K c PF6, Li a Na b K c BOB, Li a Na b K c ODFB, Li a Na b K c TFOP, Li a Na b K c PO2F2、Li a Na b K c TFSI、Li a Na b K c FSI and Li a Na b K c One or more of BODFP; Among them, a+b+c=1, 0.5≤a<1.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte salt further contains a basic lithium salt, and the basic lithium salt includes one or more of LiPF6, LiBOB, LiODFB, LiTFOP, LiPO2F2, LiTFSI, LiFSI and LiBODFP.

6. The electrolyte according to claim 5, characterized in that The mass ratio of the basic lithium salt to the alkali metal double salt in the electrolyte salt is X:1; Among them, 0.65≤X<1.

7. The electrolyte according to claim 6, characterized in that 0.7≤X＜0.9。 8. The electrolyte according to any one of claims 5 to 7, characterized in that The basic lithium salt and the alkali metal double salt have the same anion type.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The concentration of the electrolyte salt in the electrolyte solution is 0.5 mol / L to 2 mol / L.

10. The electrolyte according to any one of claims 1 to 9, characterized in that The organic solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, ethylene carbonate, propylene carbonate and diethyl carbonate.

11. A secondary battery, characterized in that: The electrolyte according to any one of claims 1 to 10.

12. The secondary battery according to claim 11, wherein The positive electrode active material in the positive electrode sheet of the secondary battery is a layered structure positive electrode active material.

13. A battery module, characterized in that: The secondary battery according to claim 11 or 12 is included.

14. A battery pack, characterized in that: A battery module comprising the battery module according to claim 13.

15. An electrical device, characterized in that: The battery comprises at least one of the secondary battery according to claim 11 or 12, the battery module according to claim 13, or the battery pack according to claim 14.

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