Secondary battery, battery module, battery pack and power consuming device

Abstract

The present application provides a secondary battery, a battery module, a battery pack, and an electric power consuming device. The secondary battery includes a positive electrode sheet and an electrolytic solution. The positive electrode sheet includes a positive electrode active material. The electrolytic solution includes a boron-containing salt. Let the mass percentage of the boron-containing salt with respect to the total mass of the electrolytic solution be A%, and the upper limit potential of the positive electrode active material with respect to metallic lithium be V1 (V). The secondary battery satisfies 0 < A / (V1 - 4.1) ≤ 4 and V1 > 4.1, and optionally, 0

Description

[Technical field]

[0001] The present application relates to the field of batteries, and in particular to secondary batteries, battery modules, battery packs and power consuming devices. [Background technology]

[0002] 2. Description of the Related Art Secondary batteries have characteristics such as high capacity and long life, and are therefore widely used in electronic devices such as mobile phones, laptops, electric motorcycles, electric cars, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes, and power tools.

[0003] As the range of applications of batteries becomes wider, the requirements for the performance of secondary batteries become more stringent. For example, good cycle capacity retention and low cycle DCR increase rate are required. Therefore, how to improve the cycle capacity retention and cycle DCR increase rate is an issue that needs to be solved as soon as possible. Summary of the Invention

[0004] The present application has been made in view of the above-mentioned problems, and has an object to provide a secondary battery, a battery module, a battery pack, and a power consuming device.

[0005] A first aspect of the present application provides a secondary battery including a positive electrode sheet and an electrolyte, the positive electrode sheet including a positive electrode active material, and the electrolyte including a boron-containing salt, the boron-containing salt including one or more of a compound represented by Formula 1, a compound represented by Formula 2, and a compound represented by Formula 3. JPEG2025502317000002.jpg158146

[0006] In formulas 1 to 3, M is independently selected from Li, Na, or K, the mass percentage of the boron-containing salt relative to the total mass of the electrolyte is A%, and the upper limit potential of the positive electrode active material relative to metallic lithium is V 1 (V), and the secondary battery is 0 1 -4.1)≦4 and V 1 ​>4.1 is met, selectable, 0 1 -4.1)≦3.

[0007] In the above technical proposal, the secondary battery of the present application meets the above formula range, and in a high voltage system, the boron-containing salt can form a dense and stable CEI film on the surface of the positive electrode active material, which plays a good protective role for the positive electrode active material, and can reduce the risk of side reactions occurring due to contact between the positive electrode active material and the electrolyte. This makes it difficult for the transition metal in the positive electrode active material to cause an oxidation-reduction reaction, and difficult for cation mixing to occur in the positive electrode active material, which is favorable for the desorption of metal ions. This ensures the capacity of the positive electrode active material and the stability of its structure, and improves the cycle capacity retention rate of the secondary battery. The positive electrode active material and the electrolyte are unlikely to cause side reactions that generate by-products such as oxygen gas, and the secondary battery can ensure that the voltage in the secondary battery is in a normal state during the charge and discharge cycle, and ensure the safety performance of the secondary battery. It can also improve the cycle DCR increase rate of the secondary battery during the cycle process.

[0008] In any embodiment, 4.1 <V 1 ≦4.6. The upper limit potential V of the positive electrode active material against metallic lithium 1 The positive electrode active material has a relatively high resistance to charge and discharge, and is therefore suitable for charging and discharging in a high-voltage system. In addition, by using the positive electrode active material in combination with a boron-containing salt, the boron-containing salt can adequately protect the surface of the positive electrode active material, thereby ensuring the structural stability of the positive electrode active material in a high-voltage system.

[0009] In any embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material, and a maximum potential of the negative electrode active material relative to metallic lithium is V 2 (V), and the secondary battery is 0 <A×V 2 ≦1.2, selectable, 0 <A×V 2 ​It satisfies ≤1. The boron salt has a relatively high reduction potential and is similarly involved in the formation of the anode film, can form a dense and stable SEI film. Since the SEI film can form sufficient protection on the surface of the negative electrode active material to reduce the risk of side reactions occurring due to the contact between the negative electrode active material and the electrolyte, it can mitigate the risk of reduction of the organic solvent in the electrolyte and further improve the cycle stability of the secondary battery.

[0010] In any embodiment, 0.02 ≤ V 2 ≤ 2.5, and optionally, 0.1 ≤ V 2 ≤ 2. The above negative electrode active material is applied to charge and discharge in a high voltage system, and by using the combination of the above negative electrode active material and the boron-containing salt, the boron-containing salt can sufficiently protect the surface of the positive electrode active material, thus ensuring the structural stability of the positive electrode active material in the high voltage system.

[0011] In any embodiment, the negative electrode active material includes at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

[0012] In any embodiment, 0 < A ≤ 2. When the boron-containing salt is within the above range, a dense and stable CEI film can be formed on the surface of the positive electrode active material, thus sufficiently protecting the positive electrode active material, improving the structural stability of the positive electrode active material, and ensuring the cycle stability of the secondary battery. Also, the boron-containing salt can form an SEI film on the surface of the negative electrode active material and improve the protective effect on the negative electrode active material.

[0013] In any embodiment, the boron-containing salt includes the compound represented by Formula 1, the compound represented by Formula 2, and the compound represented by Formula 3. Optionally, the compound represented by Formula 1 includes lithium difluorosulfoborate and / or sodium difluorosulfoborate, and / or the compound represented by Formula 2 includes lithium tetrafluoroborate and / or sodium tetrafluoroborate, and / or the compound represented by Formula 3 includes lithium disulfoborate and / or sodium disulfoborate.

[0014] In an optional embodiment, the electrolyte is lithium hexafluorophosphate LiPF 6 , Lithium perchlorate LiClO 4 , Lithium hexafluoroarsenate LiAsF 6 , Lithium bisfluorosulfonyl imide LiFSI, Lithium bistrifluoromethanesulfonyl imide LiTFSI, Lithium trifluoromethanesulfonate LiTFS, Lithium difluorophosphate LiPO 2 F 2 , Lithium difluorooxalic acid phosphate LiDFOP, Lithium tetrafluorooxalic acid phosphate LiTFOP, Sodium hexafluorophosphate NaPF 6 , Sodium bisfluorosulfonylimide NaFSI, Sodium difluorophosphate NaPO 2 F 2 , sodium bistrifluoromethanesulfonylimide NaTFSI and sodium fluorosulfonate NaFSO 3 The lithium salt and the boron-containing salt may be used in combination to improve the conductivity of the electrolyte.

[0015] In any embodiment, the electrolyte further comprises a film-forming additive. The film-forming additive comprises one or more of carbonate-based additives, sulfate-based additives, sulfite-based additives, phosphate-based additives, and polynitrile-based additives. Optionally, the mass percentage d of the film-forming additive relative to the total mass of the electrolyte satisfies 0.5%≦d≦10%, and optionally satisfies 1%≦d≦6%. The negative electrode film-forming additive can form an SEI film on the surface of the negative electrode active material, and a plurality of compositions can be formed on the surface of the SEI film together to enrich the SEI film and improve the structural stability of the SEI film.

[0016] In any embodiment, the cyclic carbonate additive comprises a cyclic carbonate additive and / or a linear carbonate additive. Optionally, the cyclic carbonate additive comprises one or more of vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC, and / or the linear carbonate additive comprises one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, methyl allyl carbonate PMC, and vinyl acetate VA.

[0017] In any embodiment, the sulfate additive comprises a cyclic sulfonate additive and / or a hydrocarbyl sulfate additive. Optionally, the cyclic sulfonate additive comprises one or more of 1,3-propane sultone PS, propene sultone PES, and 3-fluoro-1,3-propane sultone FPS.

[0018] In an optional embodiment, the hydrocarbyl sulfate additive comprises one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS, and / or the sulfite additive comprises ethylene sulfite ES and / or vinyl ethylene sulfite VES.

[0019] In an optional embodiment, the phosphate ester additive comprises one or more of tris(trimethylsilyl) phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate.

[0020] In an optional embodiment, the polynitrile additive comprises one or more of toluene diisocyanide, hexamethylene diisocyanide, adiponitrile, tolylene diisocyanate, hexamethylene diisocyanate.

[0021] In any embodiment, the electrolyte further comprises an organic solvent, which may include one or more of ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, dipropyl carbonate DPC, methyl propyl carbonate MPC, ethyl propyl carbonate EPC, butylene carbonate BC, methyl formate MF, methyl acetate MA, ethyl acetate EA, propyl acetate PA, methyl propionate MP, ethyl propionate EP, propyl propionate PP, methyl butyrate MB, ethyl butyrate EB, 1,4-butyrolactone GBL, sulfolane SF, dimethyl sulfone MSM, methyl ethyl sulfone EMS, and diethyl sulfone ESE.

[0022] In an optional embodiment, the positive electrode active material has the molecular formula LiN ix Co y M 1-x-y wherein M represents one or more of Mn, Fe, Mg, Al, Cu, and Ti; and x≧0.5, 0≦y≦0.2, and x+y≦1.

[0023] A second aspect of the present application further provides a battery module including a secondary battery according to any one of the embodiments of the first aspect of the present application.

[0024] A third aspect of the present application further provides a battery pack including a battery module according to an embodiment of the second aspect of the present application.

[0025] A fourth aspect of the present application further provides a power consuming device including a secondary battery according to any one of the embodiments of the first aspect of the present application, a battery module according to an embodiment of the second aspect of the present application, or a battery pack according to an embodiment of the third aspect of the present application. [Brief description of the drawings]

[0026] In order to more clearly explain the technical solutions of the embodiments of the present application, the following will briefly describe the drawings that need to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can also obtain other drawings based on the drawings without creative labor. [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] FIG. 1 is a schematic diagram of an embodiment of a power consumption device including a secondary battery of the present application as a power source. The drawings are not necessarily drawn to scale. The symbols are as follows: 1, battery pack; 2, upper housing; 3, lower housing; 4, battery module; 5, secondary battery; 51, case; 52, electrode assembly; 53, cover plate; 6, power consumption device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, the embodiments specifically disclosing the secondary battery, battery module, battery pack, and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of known matters or duplicate description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0028] The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, when the ranges 60-120 and 80-110 are recited for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. Also, when the minimum range values ​​1 and 2 and the maximum range values ​​3, 4 and 5 are recited, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "a-b" is represented by the abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" refers to all real numbers between "0-5" throughout this specification, with "0-5" being an abbreviation for combinations of these numerical values. Also, expressing a parameter as an integer greater than or equal to 2 (≧2) is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise stated, all embodiments and optional embodiments in this application can be combined with each other to form new technical solutions.Unless otherwise stated, all technical features and optional technical features in this application can be combined with each other to form new technical solutions.

[0030] Unless otherwise stated, all steps in the present application may be performed in sequence or randomly, but are preferably performed in sequence. For example, the method includes steps (a) and (b) and may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated that the method may further include step (c), it means 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.

[0031] Unless otherwise specified, the terms "comprise" and "include" used in this application mean open-ended and may also be closed-ended. For example, the terms "comprise" and "include" can mean "comprise" or "include" other components not listed, or "comprise" or "include" only the listed components.

[0032] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, 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).

[0033] In this application, the terms "plurality" and "plurality" refer to two or more.

[0034] In the present application, the secondary battery may include a lithium ion battery, a lithium sulfur battery, a sodium lithium ion battery, a sodium ion battery, a magnesium ion battery, etc., and the embodiments of the present application are not limited thereto.

[0035] With the application and popularity of secondary batteries, their overall performance has been attracting more and more attention. Taking the secondary battery as an example of a lithium-ion battery, the positive electrode active material provides lithium insertion compounds and active lithium ions, while the stability of its material structure directly affects the overall performance of the lithium-ion battery. At high voltages, the positive electrode active material is expensive because a large amount of lithium is released during charging of the secondary battery, and the expensive transition metals in the positive electrode active material, such as Co, 4+ , Ni 4+ The content of is extremely high. Transition metals in high oxidation states are easily reduced by the electrolyte to produce low-valence transition metals, which can cause cation mixing to occupy lithium sites, and some lithium ions cannot return to the lithium sites during discharge, which can cause the capacity loss of the positive electrode active material. At the same time, the oxygen on the surface of the crystal lattice of the positive electrode active material is unstable and easily taken by the electrolyte, causing side reactions with the electrolyte or being released in the form of oxygen gas. In addition, oxygen reacts with the electrolyte, leaving oxygen vacancies on the crystal lattice surface, which can cause the transition metals to become unstable and move, which can cause the positive electrode active material to undergo a phase transition and the Li on the surface of the cathode to be lost. + The surface phase transition progresses with increasing voltage, the surface activity of the positive electrode active material becomes higher, and the side reaction with the electrolyte becomes more intense, accelerating the capacity loss and seriously deteriorating the cycle capacity retention rate.

[0036] Therefore, the inventors improved the composition of the electrolyte in a high-voltage system and obtained a correlation between the electrolyte and the positive electrode active material, thereby improving the cycle capacity retention rate of the secondary battery and the Li on the negative electrode surface. + The aim of the present invention is to improve the dynamic performance of the battery. Next, a specific embodiment of the secondary battery will be described. secondary battery

[0037] According to a first aspect, the present application provides a secondary battery. A secondary battery is also called a rechargeable battery or a storage battery, and refers to a battery that can be continuously used by activating the active material by charging after the battery is discharged.

[0038] The secondary battery includes a positive electrode sheet and an electrolyte, the positive electrode sheet including a positive electrode active material, the electrolyte including a boron-containing salt, and the boron-containing salt including one or more of a compound represented by Formula 1, a compound represented by Formula 2, and a compound represented by Formula 3. JPEG2025502317000003.jpg159148

[0039] In formulas 1 to 3, M is independently selected from Li, Na, or K, the mass percentage of the boron-containing salt relative to the total mass of the electrolyte is A%, and the upper limit potential of the positive electrode active material relative to metallic lithium is V 1 (V), and the secondary battery is 0 1 -4.1)≦4 and V 1 >4.1 is met, selectable, 0 1 -4.1)≦3.

[0040] Although the mechanism is not clear, the secondary battery according to the present application can simultaneously improve the cycle life, safety performance, and capacity of the secondary battery. The inventors speculate that the reaction principle of the present application is as follows.

[0041] ​​The boron-containing salt is a salt with a B atom as the central atom, and can be coordinated with an alkoxy group, o-diphenol, o-hydroxy group, carboxylic acid, etc. to form an anion complex. The anion complex mainly has a delocalized π bond structure, in which the negative charge distribution of the central ion is relatively dispersed, the charge is delocalized, and the anion radius is large, and the anion is unlikely to form a strong ion pair with a metal ion, such as a lithium ion, a sodium ion, or a potassium ion, in an organic solvent, so that the solubility is relatively good. The more electron-withdrawing groups in the anion complex, the more stable the anion structure becomes, and the higher the solubility of the metal ion in the electrolyte, the more advantageous it is for improving the conductivity of the electrolyte. In addition, the boron-containing salt can form a cathode solid electrolyte interphase (CEI) film with excellent performance on the surface of the cathode active material. The CEI film is insoluble in organic solvents and can stably exist in an organic electrolyte solution, effectively reducing the insertion of solvent molecules in the electrolyte solution into the positive electrode active material, thereby ensuring the structural stability of the positive electrode active material and improving the cycle life of the secondary battery. In addition, the boron-containing salt forms a high-performance solid electrolyte interface (SEI) film on the surface of the negative electrode active material, which can provide good protection for the negative electrode active material, thereby ensuring the structural stability of the negative electrode active material and further improving the cycle performance of the secondary battery.

[0042] For example, if M is lithium, the boron-containing lithium salt is lithium tetrafluoroborate (LiBF 4 ), lithium borate disoxalate (LiB(C 2 O 4 ) 2 , LiBOB) and lithium difluorooxalate borate (LiC 2 O 4 F 2 , LiDFOB) may be used. Furthermore, the boron-containing lithium salt may include lithium tetrafluoroborate LiBF 4, lithium borate disoxalate (LiB(C 2 O 4 ) 2 , LiBOB), and lithium difluorooxalate borate (LiC 2 O 4 F 2 , abbreviated as LiDFOB).

[0043] Either the compound represented by formula 1 or the compound represented by formula 3 has a passivation effect on the positive electrode current collector in the positive electrode sheet, and can reduce the risk of corrosion of the positive electrode current collector due to a side reaction with the positive electrode current collector, thereby improving the structural stability of the positive electrode sheet. In addition, an electrolyte containing either the compound represented by formula 1 or the compound represented by formula 3 is less likely to generate acidic substances and can further reduce the risk of corrosion of the positive electrode current collector, so that it can provide good protection for the entire positive electrode sheet, ensure the cycle stability of the secondary battery, and improve the cycle life of the secondary battery. Either the compound represented by formula 1 or the compound represented by formula 3 has good compatibility with the positive electrode active material, which is favorable for the movement of lithium ions, and therefore it is possible to ensure the capacity of the secondary battery.

[0044] When the compound represented by formula 2 is used in combination with an organic solvent in the electrolyte, such as a carbonate-based solvent or an additive, the system made of the compound represented by formula 2 has a low viscosity, which is favorable for the release of metal ions, and improves the electrical conductivity in the electrolyte. The CEI film formed from the compound represented by formula 2 has a relatively uniform thickness, good kinetic activity, and small charge transfer resistance in the secondary battery, which can significantly improve the low-temperature performance and cycle DCR increase rate of the secondary battery. This improves the kinetic performance of lithium ion transfer on the cathode surface of the secondary battery, and the CEI film is not easily thermally decomposed and its performance at high temperatures is relatively stable, which can significantly improve the high-temperature performance of the secondary battery.

[0045] In some embodiments, the compounds represented by Formulae 1 to 3 are used in combination, and the amount of the components of the CEI film formed by the three is large, so that the structure of the CEI film is more stable. In addition, while ensuring the stability of the structure, the CEI film can provide good protection of the positive electrode active material.

[0046] In the embodiment of the present application, the secondary battery satisfies the above formula range, and in the high voltage system, the boron-containing salt can form a dense and stable CEI film on the surface of the positive electrode active material, which plays a good protective role for the positive electrode active material, and can reduce the risk of side reactions occurring due to contact between the positive electrode active material and the electrolyte, so that the transition metal in the positive electrode active material is less likely to cause oxidation-reduction reactions, and the positive electrode active material is less likely to cause cation mixing, which is favorable for metal ion insertion / extraction, thereby ensuring the capacity and structural stability of the positive electrode active material, and improving the cycle capacity retention rate of the secondary battery. The secondary battery is less likely to cause side reactions between the positive electrode active material and the electrolyte that produce by-products such as oxygen gas, and can ensure that the voltage in the secondary battery is normal during the charge / discharge cycle, thereby ensuring the safety performance of the secondary battery.

[0047] When the secondary battery of the present application is a lithium ion battery, the boron-containing salt may be selected as a boron-containing lithium salt, for example, lithium tetrafluoroborate LiBF 4 , lithium borate disoxalate (LiB(C 2 O 4 ) 2 , LiBOB) and lithium difluorooxalate borate (LiC 2 O 4 F 2 , LiDFOB) may be used. Furthermore, the boron-containing lithium salt may include lithium tetrafluoroborate LiBF 4, lithium dioxalate borate LiBOB, and lithium difluorooxalate borate LiDFOB. Of course, when the secondary battery is a lithium ion battery, the boron-containing salt may be a boron-containing sodium salt, a boron-containing potassium salt, etc. When the secondary battery is a sodium ion battery, the boron-containing salt may be a sodium salt, etc., or a boron-containing lithium salt, a boron-containing potassium salt, etc. may be selected. Selectably, 0 1 -4.1)≦3, for example, 0 1 -4.1)≦0.1, 0 1 -4.1)≦0.2, 0 1 -4.1)≦0.5, 0 1 -4.1)≦1, 0 1 -4.1)≦1.5, 0 1 -4.1)≦2, 0 1 -4.1)≦2.5, 0 1 -4.1)≦3, 0 1 -4.1) ≦ 3.5 or 0 1 -4.1)≦4.

[0048] In some embodiments, V 1 >4.1.

[0049] The upper limit potential V of the positive electrode active material against metallic lithium 1 The positive electrode active material has a relatively high VV, which is suitable for charging and discharging in a high-voltage system. By combining the positive electrode active material with a boron-containing salt, the boron-containing salt can sufficiently protect the surface of the positive electrode active material, thereby ensuring the structural stability of the positive electrode active material in a high-voltage system. 1 ≦4.6, and for example, the upper limit potential V of the positive electrode active material with respect to metallic lithium 1 (V) may be 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, or 4.6V, or may be within a range between any two of the above numerical compositions.

[0050] The upper limit potential V of the positive electrode active material against metallic lithium 1 ​​​​​​​​​​​can be considered as the difference in potential between the positive electrode active material and metallic lithium. The upper limit potential V 1 can be measured using known test methods and equipment in this field. In the specific test process, the positive electrode active material powder is mixed with SP and PVDF in a ratio of 90:5:5, stirred, and uniformly applied to an Al foil with a thickness of 13 μm, and then compressed to obtain a positive electrode membrane sheet with a compressed density of 3.3-3.6 g / cm. 3 The humidity during this process is controlled to <10%. The positive electrode film sheet is then dried in an oven at 100°C for 2h, and before current collection, the positive electrode film sheet is vacuum dried under the conditions of 105°C / 4h / -0.09Mpa. The fabricated positive electrode film sheet is then assembled into a CR2430 type half-coin cell of the film sheet-lithium sheet in a PRS340 / 11-119-11 brown glove box, of which 1M LiPF6 EC / EMC / DEC=3 / 5 / 2 is used as the electrolyte, and the assembled half-coin cell is left to stand for 3h. The test is carried out at 25°C, using 0.5C, first at a voltage section of 2.8-V 1 Charge the battery at 0.1C to remove lithium, and then charge it at 0.1C to the voltage range V 1 The coin cell capacity is then calculated by discharging the battery between -2.8V and -1.5V to insert lithium. The coin cell capacity is then divided by the mass of the positive electrode active material to obtain the gram capacity (capacity per gram) of the charge and discharge. The upper limit potential V of the positive electrode active material against metallic lithium is calculated. 1 is the upper limit potential when the discharge gram capacity is 150 to 220 mAh / g.

[0051] In some embodiments, 0 <A≦2である。

[0052] When the boron-containing salt is within the above range, a dense and stable CEI film can be formed on the surface of the positive electrode active material, so that the positive electrode active material can be sufficiently protected, the structural stability of the positive electrode active material can be improved, and the cycle stability of the secondary battery can be ensured. In addition, the boron-containing salt can also form an SEI film on the surface of the negative electrode active material and improve the protective effect on the negative electrode active material. Optionally, 0 < A ≤ 1.5. Exemplarily, the mass percentage A% of the boron-containing salt may be 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8% or 2%, or may be in the range consisting of any two of the above numerical values.

[0053] In some embodiments, the secondary battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material, and the upper limit potential of the negative electrode active material with respect to metallic lithium is V 2 (V), and the secondary battery further satisfies 0 < A × V 2 ≤ 1.2.

[0054] The boron-containing salt has a high reduction potential and is similarly involved in the formation of the anode film, and can form an SEI film with high density and stability. The SEI film can form sufficient protection on the surface of the negative electrode active material, reduce the risk of side reactions occurring due to the contact between the negative electrode active material and the electrolyte, relieve the risk of reduction of the organic solvent in the electrolyte, and further improve the cycle stability of the secondary battery.

[0055] As the depth of lithium insertion into the negative electrode active material increases, the stronger the activity of the negative electrode active material, the easier it is for the electrolyte to be reduced on the surface of the negative electrode active material. In view of this, when the secondary battery of the present application satisfies the above relationship, the mass percentage of the boron-containing salt increases with the upper limit potential of the negative electrode active material, and a denser and more stable SEI film is formed on the surface of the negative electrode active material with strong activity, strengthening the protection of the negative electrode active material, improving the cycle stability of the secondary battery, and further improving the cycle life of the secondary battery.

[0056] In some embodiments, 0.02 ≤ V 2 ≤ 2.5, and optionally, 0.1 ≤ V2 <= 2.

[0057] The negative electrode active material is applied to charging and discharging in a high voltage system, and by combining the negative electrode active material with a boron-containing salt, the boron-containing salt can sufficiently protect the surface of the positive electrode active material, thereby ensuring the structural stability of the positive electrode active material in a high voltage system.

[0058] The upper limit potential V of the negative electrode active material against metallic lithium 2 can be considered as the difference in potential between the negative electrode active material and metallic lithium. The upper limit potential V 2 can be measured using known test methods and equipment in the art. In the specific test process, the negative active material powder is mixed with SP and PVDF in a ratio of 91.6:1.8:6.6, stirred, and uniformly applied to a Cu foil with a thickness of 8 μm, and then compressed to form a negative film sheet with a compressed density of 1.4-1.6 g / cm. 3 The humidity during this process is controlled to <10%. After that, the negative electrode film sheet is dried in an oven at 100°C for 2h, and before collecting current, the negative electrode film sheet is vacuum dried under the conditions of 105°C / 4h / -0.09Mpa. Then, the negative electrode film sheet is assembled into a CR2430 type half-coin cell of the negative electrode film sheet-lithium sheet in a PRS340 / 11-119-11 brown glove box, of which the electrolyte is 1M LiPF6 EC / EMC / DEC=3 / 5 / 2, and the assembled half-coin cell is left to stand for 5h, and the test is performed at 25°C, 0.05C~0.005V, 50uA DC~0.005V, 5min standing, 10uA DC~0.005V, 5min standing, 0.1C CC~V 2 After standing for 5 minutes, the lithium insertion / extraction of the charge / discharge is performed to obtain the coin cell capacity of the charge / discharge. The coin cell capacity is then divided by the mass of the negative electrode active material to obtain the gram capacity of the charge / discharge. The upper limit potential V of the negative electrode active material with respect to metallic lithium is calculated. 2 is the upper limit potential when the discharge gram capacity is 330 to 380 mAh / g.

[0059] In some embodiments, M can be selected from Li or Na to enable lithium ions or sodium ions to be boosted in the secondary battery system.

[0060] Illustratively, the compound represented by formula (1) includes lithium difluorooxalate borate and / or sodium difluorooxalate borate.

[0061] Illustratively, the compound represented by formula 2 includes lithium tetrafluoroborate and / or sodium tetrafluoroborate.

[0062] Illustratively, the compound represented by formula 3 includes lithium disoxalate borate and / or sodium disoxalate borate.

[0063] Examples of boron-containing lithium salts include lithium difluoroborate (LiDFOB) and lithium tetrafluoroborate (LiBF). 4 and lithium borate disoxalate LiBOB. Lithium tetrafluoroborate LiBF 4 By using lithium dioxalate borate LiBOB and lithium difluorooxalate borate LiDFOB in combination, the three can form a CEI film on the surface of the positive electrode active material, which can effectively reduce the decomposition of the positive electrode active material in the electrolyte; the three can also form an SEI film on the surface of the negative electrode active material, which can improve the transport of lithium ions and reduce the continuous reductive decomposition of the electrolyte, thereby improving the cycle stability of the secondary battery.

[0064] In some embodiments, the electrolyte is lithium hexafluorophosphate LiPF 6 , Lithium perchlorate LiClO 4 , Lithium hexafluoroarsenate LiAsF 6 , Lithium bisfluorosulfonyl imide LiFSI, Lithium bistrifluoromethanesulfonyl imide LiTFSI, Lithium trifluoromethanesulfonate LiTFS, Lithium difluorophosphate LiPO 2F 2 , Lithium difluorooxalic acid phosphate LiDFOP, Lithium tetrafluorooxalic acid phosphate LiTFOP, Sodium hexafluorophosphate NaPF 6 , Sodium bisfluorosulfonylimide NaFSI, Sodium difluorophosphate NaPO 2 F 2 , sodium bistrifluoromethanesulfonylimide NaTFSI and sodium fluorosulfonate NaFSO 3 The lithium salt and the boron-containing salt may be used in combination to improve the conductivity of the electrolyte.

[0065] For example, the electrolyte is lithium hexafluorophosphate (LiPF 6 , Lithium tetrafluoroborate LiBF 4 , Lithium perchlorate LiClO 4 , Lithium hexafluoroarsenate LiAsF 6 , Lithium bisfluorosulfonyl imide LiFSI, Lithium bistrifluoromethanesulfonyl imide LiTFSI, Lithium trifluoromethanesulfonate LiTFS, Lithium difluorooxalyl borate LiDFOB, Lithium disoxalyl borate LiBOB, Sodium hexafluorophosphate NaPF 6 , Sodium bisfluorosulfonylimide NaFSI, Sodium difluorophosphate NaPO 2 F 2 , sodium bistrifluoromethanesulfonylimide NaTFSI and sodium fluorosulfonate NaFSO 3 may include:

[0066] In some embodiments, the electrolyte may further include a Lewis base solvent. The Lewis base can promote dissociation of the boron-containing salt, contribute to the release of lithium ions, and improve the electrical conductivity of the electrolyte. For example, the Lewis base solvent includes a compound that includes one or more of a halogen atom, an alkoxy group, an olefin, and an aromatic hydrocarbon group. For example, the Lewis base may include trimethyl phosphate, etc.

[0067] In some embodiments, the organic solvent may further comprise a combination of one or more of ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, dipropyl carbonate DPC, methyl propyl carbonate MPC, ethyl propyl carbonate EPC, butylene carbonate BC, methyl formate MF, methyl acetate MA, ethyl acetate EA, propyl acetate PA, methyl propionate MP, ethyl propionate EP, propyl propionate PP, methyl butyrate MB, ethyl butyrate EB, 1,4-butyrolactone GBL, sulfolane SF, dimethyl sulfone MSM, methyl ethyl sulfone EMS, and diethyl sulfone ESE.

[0068] In some embodiments, the electrolyte may further include a film-forming additive, such as a negative electrode film-forming additive. The negative electrode film-forming additive includes one or more of a carbonate-based additive, a sulfate-based additive, a sulfite-based additive, a phosphate-based additive, and a polynitrile-based additive. The negative electrode film-forming additive can form an SEI film on the surface of the negative electrode active material, and the SEI film can be abundantly formed on the surface of the SEI film with a plurality of compositions, thereby improving the structural stability of the SEI film. Furthermore, the negative electrode film-forming additive includes at least two of a carbonate-based additive, a sulfate-based additive, a sulfite-based additive, a phosphate-based additive, and a polynitrile-based additive, thereby forming an SEI film with a rich composition and a higher structural stability. Optionally, the mass percentage d of the film-forming additive relative to the total mass of the electrolyte satisfies 0.5%≦d≦10%, and optionally is 1%≦d≦6%.

[0069] For example, the carbonate ester additive includes a cyclic carbonate ester additive and / or a linear carbonate ester additive. Furthermore, the cyclic carbonate ester additive includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinylethylene carbonate (VEC), and dioctyl carbonate (CC). The linear carbonate ester additive includes one or more of ethyl allyl carbonate (AEC), diphenyl carbonate (DPC), methyl allyl carbonate (MAC), and polycarbonate (VA).

[0070] For example, the sulfate additive includes a cyclic sulfonate additive and / or a hydrocarbyl sulfate additive. Further, the cyclic sulfonate additive includes one or more of 1,3-propane sultone PS, propene sultone PES, and 3-fluoro-1,3-propane sultone FPS. The hydrocarbyl sulfate additive includes one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS.

[0071] By way of example, sulfite additives include ethylene sulfite ES and / or vinyl ethylene sulfite VES.

[0072] By way of example, phosphate ester based additives include, for example, one or more of tris(trimethylsilyl) phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate.

[0073] By way of example, polynitrile additives include one or more of toluene diisocyanide, hexamethylene diisocyanide, adiponitrile, tolylene diisocyanate, hexamethylene diisocyanate.

[0074] The electrolyte of the present application can be prepared according to a conventional method in the field. For example, the additive, the solvent, the electrolyte salt, etc. can be mixed uniformly to obtain the electrolyte. The order of addition of each substance is not particularly limited. For example, the additive, the electrolyte salt, etc. can be added to the non-aqueous solvent and mixed uniformly to obtain the non-aqueous electrolyte.

[0075] In the present application, each component and its content in the electrolyte solution can be measured according to a method known in the art, for example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0076] In addition, when testing the electrolyte of the present application, a freshly prepared electrolyte may be directly obtained, or the electrolyte may be obtained from a secondary battery. One exemplary method for obtaining the electrolyte from a secondary battery includes the steps of discharging the secondary battery to a discharge end voltage (for safety reasons, the battery is generally placed in a fully discharged state), centrifuging the secondary battery, and then extracting an appropriate amount of the liquid obtained by the centrifugation as the nonaqueous electrolyte. The nonaqueous electrolyte may be directly obtained from the electrolyte inlet of the secondary battery. [Positive electrode sheet]

[0077] In some embodiments, 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. For example, the positive electrode current collector has two surfaces facing each other in the thickness direction, and the positive electrode film layer is provided on either one or both of the two facing surfaces of the positive electrode current collector.

[0078] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for secondary batteries known in the art. For example, the positive electrode active material may include at least one of lithium transition metal oxide, lithium-containing phosphate with an olivine structure, and modified compounds thereof. Examples of lithium transition metal oxides include at least one of lithium cobalt oxide, 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 modified compounds thereof. Examples of lithium-containing phosphate with an olivine structure include 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 manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and at least one of modified compounds thereof. The present application is not limited to these materials, and other materials known in the art that are used as a positive electrode active material for secondary batteries can be used. These positive electrode active materials may be used alone or in combination of two or more.

[0079] In some embodiments, the positive electrode active material is LiNi x Co y Mn z M 1-x-y-z O 2 Or LiNi a Co b Al c N 1-a-b-c O 2wherein M and N are each independently any one selected from Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≦y≦1, 0≦x<1, 0≦z≦1, x+y+z≦1, 0≦a≦1, 0≦b≦1, 0≦c≦1, a+b+c≦1. By using the positive electrode active material in combination with a boron-containing lithium salt, the B atom in the boron-containing lithium salt is easily bonded to the O atom in the positive electrode active material, thereby reducing the charge transfer resistance of the positive electrode active material and reducing the diffusion resistance of lithium ions in the bulk of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains an appropriate content of lithium tetrafluoroborate and lithium difluorooxalate borate, the low-cobalt or cobalt-free positive electrode active material can have a significantly improved lithium ion diffusion rate, and the lithium ions in the bulk of the low-cobalt or cobalt-free positive electrode active material body can be timely replenished to the surface, avoiding excessive lithium desorption on the surface of the low-cobalt or cobalt-free positive electrode active material, and stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the occurrence probability of problems such as the structural, chemical or electrochemical properties of the positive electrode active material being unstable due to the occurrence of excessive lithium desorption on the surface of the low-cobalt or cobalt-free positive electrode active material, for example, the positive electrode active material being irreversibly distorted and lattice defects increasing, can be greatly reduced.

[0080] LiNi x Co y Mn z M 1-x-y-z O 2 Or LiNi a Co b Al c N 1-a-b-c O 2 can be produced according to a conventional method in the art. An exemplary production method is to mix a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, a precursor of the M element, and a precursor of the N element, and then sinter the mixture. The sintering atmosphere may be an atmosphere containing oxygen, such as an air atmosphere or an oxygen atmosphere. The O atmosphere of the sintering atmosphere may be 0.01 to 0.01. 2The concentration is, for example, 70%-100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0081] For example, the lithium source may be lithium oxide (Li 2 O), lithium phosphate (Li 3 PO 4 ), lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium acetate (CH 3 COOLi), lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ) and lithium nitrate (LiNO 3 ) as examples, the nickel source includes, but is not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As examples, the cobalt source includes, but is not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As examples, the manganese source includes, but is not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As examples, the aluminum source includes, but is not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As examples, the precursor of the M element includes, but is not limited to, at least one of an oxide, a nitrate compound, a carbonate compound, a hydroxide compound, and an acetate compound of the M element. By way of example, precursors of N element include at least one of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium hydrogen sulfate, ammonium hydrogen sulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur, but are not limited thereto.

[0082] In some embodiments, the total mass of the positive electrode layer is a compound having the molecular formula LiNi x Co y Mn z M 1-x-y-z O 2 Or LiNi a Co b Al c N 1-a-b-c O 2 The mass percentage of the layered material is 80%-99%. For example, the molecular formula LiNi x Co y Mn z M 1-x-y-z O 2 Or LiNi a Co b Al c N 1-a-b-c O 2 The weight percentage of the layered material having the molecular formula LiNi may be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range of values ​​greater than or equal to 80%. x Co y Mn z M 1-x-y-z O 2 Or LiNi a Co b Al c N 1-a-b-c O 2 The mass percentage of the layered material that is is 85%-99%, 90%-99%, 95%-99%, 80%-98%, 85%-98%, 90%-98%, 95%-98%, 80%-97%, 85%-97%, 90%-97% or 95%-97%.

[0083] In some embodiments, the positive electrode active material has the molecular formula LiN ix Co y M 1-x-yIn the formula, M represents one or more of Mn, Fe, Mg, Al, Cu, and Ti, and x≧0.5, 0≦y≦0.2, and x+y≦1. The lithium deficiency state on the surface of the positive electrode active material under high voltage is likely to cause phase transition, Li / Ni mixing, oxygen release, etc. on the surface of the positive electrode active material, and the boron-containing salt can inactivate the surface of the positive electrode active material and can also deactivate metal cations, such as Al 3+ and Ni 2+ to improve Li / Ni mixing and to passivate the aluminum foil.

[0084] In some embodiments, the positive electrode membrane layer further comprises a selective positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited. As an example, the positive electrode conductive agent comprises one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent relative to the total mass of the positive electrode membrane layer is 5% or less.

[0085] In some embodiments, the positive electrode membrane layer further includes a selective positive electrode binder. In the present application, the type of the positive electrode binder is not particularly limited. For example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. In some embodiments, the mass percentage of the positive electrode binder relative to the total mass of the positive electrode membrane layer is 5% or less.

[0086] In some embodiments, the positive electrode current collector can be a metal foil sheet or a composite current collector. Examples of the metal foil sheet include aluminum foil and aluminum alloy foil. The composite current collector can include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. As an example, the metal material can include one or more combinations selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the polymeric material base layer can include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0087] The positive electrode membrane layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent, and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). [Negative electrode sheet]

[0088] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer that is provided on at least one surface of the negative electrode current collector and contains a negative electrode active material.

[0089] For example, the negative electrode current collector has two surfaces opposing each other in the thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0090] In some embodiments, the negative electrode active material may be a battery negative electrode active material known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and lithium aluminum alloy. The silicon-based material may be at least one selected from silicon alone, silicon oxygen compound, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from tin alone, tin oxygen compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative electrode active material may be used. These negative electrode active materials may be used alone or in combination of two or more.

[0091] In some embodiments, the negative electrode membrane layer further includes a negative electrode binder, which can be selected. In the present application, the type of the negative electrode binder is not particularly limited. For example, the negative electrode binder may include one or more combinations selected from styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder relative to the total mass of the negative electrode membrane layer is 5% or less.

[0092] In some embodiments, the negative electrode film layer further comprises a selective negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited, and for example, the negative electrode conductive agent may comprise one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent relative to the total mass of the negative electrode film layer is 5% or less.

[0093] In some embodiments, the negative electrode membrane layer may further include other auxiliary agents. For example, the other auxiliary agents may include a thickener, such as sodium carboxymethylcellulose (CMC-Na), a PTC thermistor material, etc. In some embodiments, the mass percentage of the other auxiliary agents relative to the total mass of the negative electrode membrane layer is 2% or less.

[0094] In some embodiments, the negative electrode current collector can be a metal foil sheet or a composite current collector. Examples of the metal foil sheet include copper foil and copper alloy foil. The composite current collector can include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. By way of example, the metal material can include one or more combinations selected from copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the polymeric material base layer can include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0095] The negative electrode membrane layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and optional other auxiliary agents in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0096] The negative electrode sheet does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the negative electrode film layer. [Separator]

[0097] In some embodiments, the secondary battery further includes a separator. In the present application, the type of the separator is not particularly limited, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

[0098] In some embodiments, the material of the separator may be at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and is not particularly limited.

[0099] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be fabricated into an electrode assembly by a winding process or a lamination process.

[0100] In some embodiments, the secondary battery may have an exterior packaging, which is used to seal the electrode assembly and electrolyte.

[0101] In some embodiments, the exterior of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft pack, for example, a bag-shaped soft pack. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0102] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. Figure 1 shows a secondary battery 5 with a rectangular structure as an example.

[0103] In some embodiments, as shown in FIG. 1 and FIG. 2, the exterior may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 covers the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be adjusted as needed.

[0104] The method for manufacturing the secondary battery of the present application is known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, a positive electrode sheet, a separator, and a negative electrode sheet can be formed into an electrode assembly by a winding process or a lamination process, and the electrode assembly can be placed in an outer casing, dried, and then injected with an electrolyte, followed by vacuum sealing, standing, chemical formation, shaping, and other processes to obtain a secondary battery.

[0105] In some embodiments of the present application, the secondary battery of the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0106] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fasteners.

[0107] Optionally, the battery module 4 may further include a housing having an accommodation space in which the multiple secondary batteries 5 are accommodated.

[0108] In some embodiments, the above battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0109] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Fig. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 covers the lower housing 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. power consumption equipment

[0110] In a second aspect, the present application provides a power consuming device including at least one of the secondary battery, the battery module, and the battery pack according to the present application. The secondary battery, the battery module, and the battery pack may be used as a power source for the power consuming device, or may be used as an energy storage means for the power consuming device. The power consuming device may be, but is not limited to, a portable device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., 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.), a train, a ship and a satellite, an energy storage system, etc.

[0111] A power consuming device can select a secondary battery, a battery module or a battery pack according to its usage needs.

[0112] 6 is a schematic diagram of an example power consuming device 6, such as an electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack 1 or a battery module can be employed to meet the high power and high energy density requirements of the power consuming device.

[0113] Other examples of power consuming devices may be mobile phones, tablet computers, notebook computers, etc. Such power consuming devices are generally required to be thin and can use secondary batteries as their power source. Working Example

[0114] The following examples are provided to more specifically illustrate the disclosure of the present application, and are merely illustrative, since it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are by weight. All reagents used in the examples are commercially available or can be synthesized according to conventional methods and can be used directly without further processing. All instruments used in the examples are commercially available. Example 1 1. Manufacturing of positive electrode sheet

[0115] An aluminum foil having a thickness of 13 μm was used as the positive electrode current collector.

[0116] Positive electrode active material LiNi 0.65 Co 0.07 Mn 0.28 The conductive agent, carbon black, and binder, polyvinylidene fluoride (PVDF), were mixed in a weight ratio of 97.5:1.4:1.1 in an appropriate amount of NMP, which was a solvent, and stirred thoroughly to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly applied to the surface of an aluminum foil, which was a positive electrode current collector, and the resulting material was dried and cold-pressed to obtain a positive electrode sheet. 2. Manufacturing of negative electrode sheet

[0117] A copper foil with a thickness of 8 μm was used as the negative electrode current collector.

[0118] The negative electrode active material graphite, the binder styrene butadiene rubber (SBR), the thickener sodium carboxymethylcellulose (CMC-Na), and the conductive agent carbon black (SuperP) were thoroughly mixed in a weight ratio of 96.2:1.8:1.2:0.8 with an appropriate amount of solvent and deionized water to form a uniform negative electrode slurry. The negative electrode slurry was then uniformly applied to the surface of the copper foil, which was the negative electrode current collector, and dried and cold pressed to obtain a negative electrode sheet. 3. Separator

[0119] A porous polyethylene (PE) film was used as the separator. 4. Preparation of Electrolyte Solution

[0120] In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent, and additives were then dissolved in the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L. The specific substances contained in the electrolyte are shown in the table below. 5. Secondary battery manufacturing

[0121] The positive electrode sheet, separator, and negative electrode sheet are stacked in this order, with the separator positioned between the positive electrode sheet and the negative electrode sheet to perform isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an exterior housing, dried, and then an electrolyte is injected. The lithium-ion battery is obtained through processes such as vacuum sealing, standing, chemical formation, and shaping. Example 2 Examples 2-1 to 2-5

[0122] The secondary battery was manufactured in a manner similar to that in Example 1, except that the mass percentage A of the “boron-containing salt” was adjusted. The specific parameters are shown in Table 1. Comparative Example Comparative Example 1 and Comparative Example 2 The secondary battery was manufactured in a similar manner to that in Example 1, except that the mass percentage A1 of the “boron-containing salt additive” was adjusted. The specific parameters are shown in Table 1. Example 3 Example 3-1 to Example 3-3

[0123] Secondary batteries have an upper limit potential V of the positive electrode active material. 1 The specific parameters are shown in Table 1. Example 4 Examples 4-1 to 4-5

[0124] Secondary batteries have an upper limit potential V of the negative electrode active material. 2 The specific parameters are shown in Table 1. Example 5 Example 5-1 The secondary battery was manufactured in a manner similar to that of Example 1, except that the type of “positive electrode active material” was adjusted. The specific parameters are shown in Table 1. Example 5-2

[0125] The secondary battery was manufactured in a manner similar to that of Example 1, except that the type of the "negative electrode active material" was adjusted. The specific parameters are shown in Table 1.

[0126] [Table 1] Testing Part 1. The upper limit potential V of the positive electrode active material against metallic lithium 1 How to measure

[0127] The positive electrode active material powder was mixed with SP and PVDF in a ratio of 90:5:5, stirred, and uniformly applied to an Al foil with a thickness of 13 μm. The mixture was then compressed to obtain a positive electrode membrane sheet with a compressed density of 3.3-3.6 g / cm. 3The humidity during this process is controlled to <10%. After that, the positive electrode film sheet is dried in an oven at 100°C for 2h. Before collecting current, the positive electrode film sheet is vacuum dried under the conditions of 105°C / 4h / -0.09Mpa. Then, the produced positive electrode film sheet is assembled into a CR2430 type half-coin cell of the film sheet-lithium sheet in a PRS340 / 11-119-11 brown glove box, of which the electrolyte is 1M LiPF6 EC / EMC / DEC=3 / 5 / 2. The assembled half-coin cell is left to stand for 3h. The test is performed at 25°C and 0.5C, and the voltage range is 2.8-V. 1 Charge the battery at 0.1C to remove lithium, and then charge it at 0.1C to the voltage range V 1 The coin cell capacity is then divided by the mass of the positive electrode active material to obtain the gram capacity for charging and discharging. The upper limit potential V of the positive electrode active material against metallic lithium is calculated. 1 is the upper limit potential when the discharge gram capacity is 150 to 220 mAh / g. 2. The upper limit of the potential V of the negative electrode active material against metallic lithium 2 How to measure

[0128] The negative electrode active material powder was mixed with SP and PVDF in a ratio of 91.6:1.8:6.6, stirred, and uniformly applied to a Cu foil with a thickness of 8 μm. The mixture was then compressed to form a negative electrode membrane sheet with a compressed density of 1.4-1.6 g / cm. 3 The humidity during this process is controlled to <10%. After that, the negative electrode film sheet is dried in an oven at 100°C for 2h, and before collecting current, the negative electrode film sheet is vacuum dried under the conditions of 105°C / 4h / -0.09Mpa. Then, the negative electrode film sheet is assembled into a CR2430 type half-coin cell of the negative electrode film sheet-lithium sheet in a PRS340 / 11-119-11 brown glove box, of which the electrolyte is 1M LiPF6 EC / EMC / DEC=3 / 5 / 2, and the assembled half-coin cell is left to stand for 5h, and the test is performed at 25°C, 0.05C~0.005V, 50uA DC~0.005V, 5min standing, 10uA DC~0.005V, 5min standing, 0.1C CC~V 2After standing for 5 minutes, the lithium insertion / extraction of the charge / discharge is performed to obtain the coin cell capacity of the charge / discharge. The coin cell capacity is then divided by the mass of the negative electrode active material to obtain the gram capacity of the charge / discharge. The upper limit potential V of the negative electrode active material with respect to metallic lithium is calculated. 2 is the upper limit potential when the discharge gram capacity is 330 to 380 mAh / g. 3. Secondary battery performance testing 3.1 Cycle life measurement

[0129] At 25°C, the secondary battery was charged to 4.35V at a constant current of 0.5C, then charged to a constant voltage of 4.33V until the current became 0.05C, and then discharged to 2.8V at a constant current of 1C, which constituted one charge-discharge cycle. The capacity retention rate of the battery after 500 cycles was calculated by taking the capacity of the first discharge as 100%. Capacity retention rate of the battery after 500 cycles (%) = discharge capacity at 500 cycles / capacity of the first discharge × 100%.

[0130] 3.2 Performance test of DCR increase rate of lithium-ion battery after 500 cycles at 25℃

[0131] DCR test at 25°C before cycling: At 25°C, a freshly manufactured core is charged at 0.5C to 4.35V, then charged at a constant voltage of 0.05C, at which the voltage is V 1 Then, discharge at 4C for 30s. The voltage at the end of discharge is V 2 , sampled every 0.1s, the discharge DCR1 at 100% SOC of the core before the cycle is (V 1 -V 2 ) / I.

[0132] DCR test at 25°C after cycling: At 25°C, the core after the above 25°C cycle is charged at 0.5C to 4.35V, then charged at a constant voltage of 0.05C, at which time the voltage is V3, and then discharged at 4C for 30s, the voltage at the end of discharge is V4, and sampled every 0.1s. The discharge DCR2 at 100% SOC of the core after cycling is (V 3 -V 4 ) / I.

[0133] DCR increase rate: DCR increase rate is (DCR2-DCR1) / DCR1 * It is 100%. Test results

[0134] Table 2 shows the improvement effect of the present application on the cycle life, safety performance, and capacity of secondary batteries.

[0135] [Table 2]

[0136] As can be seen from Table 2, in Comparative Example 1, when no boron-containing salt is added, the positive electrode active material is likely to come into contact with the electrolyte and cause side reactions, which may destroy the positive electrode active material, shorten the cycle life of the secondary battery, and increase the interfacial resistance. In Comparative Example 2, a boron-containing salt is added, but the relationship between the mass percentage of the boron-containing salt and the upper limit potential of the positive electrode active material is A / (V 1 Since −4.1)>4, although the boron-containing salt can protect the surface of the positive electrode active material, the resistance of the CEI film formed by the boron-containing salt is high, and there is a risk that the boron-containing salt system will decompose, making the system unstable.

[0137] In Examples 1 to 2-5, the mass percentage of the boron-containing salt and the upper limit potential of the positive electrode active material are 0 1 -4.1)≦4, in particular, 0 1 By adjusting the content of the positive electrode active material to satisfy -4.1)≦3, the boron-containing salt can form a dense and stable CEI film on the surface of the positive electrode active material, which can provide good protection for the positive electrode active material. As a result, the transition metal in the positive electrode active material is less likely to undergo an oxidation-reduction reaction, cation mixing is less likely to occur in the positive electrode active material, and this is favorable for the desorption of metal ions, thereby improving the cycle life of the secondary battery; in addition, the CEI film formed by the boron-containing salt has a dense and uniform thickness, which reduces the interface resistance, which is favorable for improving the dynamic performance of the secondary battery.

[0138] ​​In Examples 3-1 to 3-3, the upper limit potential V 1 , especially 4.1 <V 1 By adjusting the ratio to ≦4.6, the cycle life and DCR increase rate of the secondary battery can be significantly improved.

[0139] In Examples 4-1 to 4-5, the upper limit potential V 2 , especially 0 <A×V 2 ≦1.2, 0 <A×V 2 By adjusting the ratio to ≦1, the cycle life and DCR increase rate of the secondary battery can be significantly improved.

[0140] As can be seen from the results of adjusting the type of positive electrode active material and the type of negative electrode active material in Examples 5-1 and 5-2, 1 When the condition (-4.1)≦4 is satisfied, the boron-containing lithium salt effectively protects the positive electrode active material and the negative electrode active material, thereby improving the cycle life and DCR increase rate of the secondary battery.

[0141] Although the present application has been described with reference to the preferred embodiments, various improvements may be made without departing from the scope of the present application, or some of the components may be replaced with equivalents. In particular, as long as there is no structural contradiction, the technical features mentioned in each embodiment may be arbitrarily combined. The present application is not limited to the specific embodiments disclosed above, but includes all aspects included in the scope of the claims.​

Claims

1. A secondary battery, A positive electrode sheet including a positive electrode active material; an electrolyte solution containing a boron-containing salt containing one or more of a compound represented by formula 1, a compound represented by formula 2, and a compound represented by formula 3; In formulas 1 to 3, each M is independently selected from Li, Na, or K; The mass percentage of the boron-containing salt with respect to the total mass of the electrolyte is A%, and the upper limit potential of the positive electrode active material with respect to metallic lithium is V １ (V), 0<A / (V １ −4.1)≦4, and V １ >4.1, selectable, 0<A / (V １ -4.1)≦3.

2. 4.1<V １ 2. The secondary battery according to claim 1, wherein the elastic modulus is ≦4.

6.

3. The secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material, and a maximum potential of the negative electrode active material with respect to metallic lithium is V ２ (V), The secondary battery is 0<A×V ２ ≦1.2, selectable, 0<A×V ２ The secondary battery according to claim 1 or 2, wherein the ratio of the total mass of the secondary battery to the total mass of the second battery is 1 or less.

4. 0.02≦V ２ ≦2.5, and optionally, 0.1≦V ２ 4. The secondary battery according to claim 3, wherein the ratio of the ionic liquid to the organic solvent is ≦2.

5. 5. The secondary battery according to claim 3, wherein the negative electrode active material comprises at least one material selected from the group consisting of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

6. The secondary battery according to claim 1 , wherein 0<A≦2.

7. The boron-containing salt includes a compound represented by formula 1, a compound represented by formula 2, and a compound represented by formula 3, Optionally, the compound of formula 1 comprises lithium difluorooxalate borate and / or sodium difluorooxalate borate; and / or The compound represented by formula 2 includes lithium tetrafluoroborate and / or sodium tetrafluoroborate, and / or The compound represented by formula 3 includes lithium disoxalate borate and / or sodium disoxalate borate. The secondary battery according to claim 1 .

8. The electrolyte is lithium hexafluorophosphate LiPF ６ , Lithium perchlorate LiClO ４ , lithium hexafluoroarsenate LiAsF ６ , lithium bisfluorosulfonylimide LiFSI, lithium bistrifluoromethanesulfonylimide LiTFSI, lithium trifluoromethanesulfonate LiTFS, lithium difluorophosphate LiPO ２ F ２ , lithium difluorooxalic acid phosphate LiDFOP, lithium tetrafluorooxalic acid phosphate LiTFOP, sodium hexafluorophosphate NaPF ６ , sodium bisfluorosulfonylimide NaFSI, sodium difluorophosphate NaPO ２ F ２ , sodium bistrifluoromethanesulfonylimide NaTFSI and sodium fluorosulfonate NaFSO ３ The secondary battery according to claim 1 , further comprising one or more of the following:

9. The electrolytic solution further includes a film-forming additive, and the film-forming additive includes one or more of a carbonate-based additive, a sulfate-based additive, a sulfite-based additive, a phosphate-based additive, and a polynitrile-based additive; Optionally, a mass percentage d of the film-forming additive relative to the total mass of the electrolyte satisfies 0.5%≦d≦10%, and optionally 1%≦d≦6%. The secondary battery according to any one of claims 1 to 8.

10. The carbonate ester additive comprises a cyclic carbonate ester additive and / or a linear carbonate ester additive, optionally the cyclic carbonate ester additive comprises one or more of vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC and dioctyl carbonate CC, and / or the linear carbonate ester additive comprises one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, methyl allyl carbonate PMC and vinyl acetate VA, and / or The sulfate additive comprises a cyclic sulfonate additive and / or a hydrocarbyl sulfate additive, and optionally the cyclic sulfonate additive comprises one or more of 1,3-propane sultone PS, propene sultone PES, 3-fluoro-1,3-propane sultone FPS, and / or the hydrocarbyl sulfate additive comprises one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS, and / or The sulfite additive comprises ethylene sulfite ES and / or vinyl ethylene sulfite VES, and / or The phosphate ester additive comprises one or more of tris(trimethylsilyl)phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate; The secondary battery according to claim 9 , wherein the polynitrile-based additive comprises one or more of toluene diisocyanide, hexamethylene diisocyanide, adiponitrile, tolylene diisocyanate, and hexamethylene diisocyanate.

11. The secondary battery according to any one of claims 1 to 10, wherein the electrolytic solution further contains an organic solvent, and the organic solvent includes one or more of ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, dipropyl carbonate DPC, methyl propyl carbonate MPC, ethyl propyl carbonate EPC, butylene carbonate BC, methyl formate MF, methyl acetate MA, ethyl acetate EA, propyl acetate PA, methyl propionate MP, ethyl propionate EP, propyl propionate PP, methyl butyrate MB, ethyl butyrate EB, 1,4-butyrolactone GBL, sulfolane SF, dimethyl sulfone MSM, methyl ethyl sulfone EMS, and diethyl sulfone ESE.

12. The positive electrode active material has the molecular formula LiN ｉｘ Co ｙ M １－ｘ－ｙ wherein M represents one or more of Mn, Fe, Mg, Al, Cu, and Ti, and x≧0.5, 0≦y≦0.2, and x+y≦1.

13. A battery module comprising the secondary battery according to claim 1 .

14. A battery pack comprising the battery module according to claim 13.

15. A power consuming device comprising the secondary battery according to any one of claims 1 to 12, the battery module according to claim 13, or the battery pack according to claim 14.

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