Secondary battery, battery module, battery pack, and power consumption 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] This application relates to the field of batteries, and in particular, to secondary batteries, battery modules, battery packs, and power-consuming devices.

Background Art

[0002] Secondary batteries have characteristics such as high capacity and long life, and thus are widely applied to electronic devices such as mobile phones, notebook computers, electric bicycles, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and electric tools.

[0003] As the application range of batteries becomes increasingly wide, the requirements for the performance of secondary batteries also become increasingly strict. For example, it is required to have a good cycle capacity retention rate and a low cycle DCR increase rate. Therefore, how to improve the cycle capacity retention rate and the cycle DCR increase rate is also an urgent problem to be solved.

Summary of the Invention

[0004] This application is made in view of the above problems, and its purpose is to provide a secondary battery, a battery module, a battery pack, and a power-consuming device.

[0005] The first aspect of this application is a secondary battery including a positive electrode sheet and an electrolytic solution. The positive electrode sheet contains a positive electrode active material, the electrolytic solution contains a boron-containing salt, and the boron-containing salt contains one or more of the compounds represented by Formula 1, the compounds represented by Formula 2, and the compounds represented by Formula 3, and provides a secondary battery. JPEG0007785186000001.jpg158146

[0006] In Formulas 1 to 3, M is independently selected from Li, Na, or K respectively. 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 satisfies 0 < A / (V1 - 4.1) ≤ 3.

[0007] In the above technical solution, the secondary battery of the present application satisfies the range of the above formula. 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, exert a good protective effect on the positive electrode active material, and reduce the risk of side reactions occurring when the positive electrode active material contacts the electrolyte. As a result, it is difficult for the transition metal in the positive electrode active material to undergo an oxidation-reduction reaction, it is difficult for cation mixing to occur in the positive electrode active material, and it is advantageous for the desorption of metal ions. Thereby, the capacity of the positive electrode active material is ensured and the structural stability is maintained, and the cycle capacity retention rate of the secondary battery is improved. The positive electrode active material and the electrolyte are less likely to cause side reactions that generate by-products such as oxygen gas, and the secondary battery can ensure that the voltage inside the secondary battery is in a normal state during the charge-discharge cycle, thereby ensuring the safety performance of the secondary battery. Also, the cycle DCR increase rate of the secondary battery during the cycle process can be improved.

[0008] In any embodiment, 4.1 < V1 ≤ 4.6. The upper limit potential V1 of the positive electrode active material with respect to metallic lithium is relatively high and is applied to charge and discharge in a high-voltage system. Also, by using the combination of the above positive electrode active material and the 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.

[0009] In any embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material, the upper limit potential of the negative electrode active material with respect to metallic lithium is V2 (V), and the secondary battery satisfies 0 < A × V2 ≤ 1.2, and optionally satisfies 0 < A × V2 ≤ 1. The boron salt has a relatively high reduction potential and is similarly involved in forming a film on the anode, and can form a SEI film with high density and stability. The SEI film can form sufficient protection on the surface of the negative electrode active material to reduce the risk of side reactions occurring when the negative electrode active material contacts the electrolyte, so as to 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 ≤ V2 ≤ 2.5, and optionally, 0.1 ≤ V2 ≤ 2. The negative electrode active material is applied to charge and discharge in a high-voltage system, and by using the negative electrode active material in combination with a boron-containing salt, the boron-containing salt can sufficiently protect the surface of the positive electrode active material, so as to ensure the structural stability of the positive electrode active material in the high-voltage system.

[0011] In any embodiment, the negative electrode active material contains 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, so as to sufficiently protect the positive electrode active material, improve the structural stability of the positive electrode active material, and ensure the cycle stability of the secondary battery. 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.

[0013] In any embodiment, the boron-containing salt contains a compound represented by formula 1, a compound represented by formula 2, and a compound represented by formula 3. Optionally, the compound represented by formula 1 contains lithium difluoroborate and / or sodium difluoroborate, and / or the compound represented by formula 2 contains lithium tetrafluoroborate and / or sodium tetrafluoroborate, and / or the compound represented by formula 3 contains lithium diborate and / or sodium diborate.

[0014] In some embodiments, the electrolyte solution further comprises one or more of lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium hexafluoroarsenate LiAsF6, lithium bisfluorosulfonylimide LiFSI, lithium bistrifluoromethanesulfonylimide LiTFSI, lithium trifluoromethanesulfonate LiTFS, lithium difluorophosphate LiPO2F2, lithium difluorodisalophosphate LiDFOP, lithium tetrafluorooxalophosphate LiTFOP, sodium hexafluorophosphate NaPF6, sodium bisfluorosulfonylimide NaFSI, sodium difluorophosphate NaPO2F2, sodium bistrifluoromethanesulfonylimide NaTFSI, and sodium fluorosulfonate NaFSO3. The use of the lithium salt in combination with a boron-containing salt can improve the conductivity of the electrolyte solution.

[0015] In an optional embodiment, the electrolyte solution further includes a film-forming additive. The film-forming additive includes one or more of a carbonate ester-based additive, a sulfate ester-based additive, a sulfite ester-based additive, a phosphate ester-based additive, and a polynitrile-based additive. Optionally, the mass percentage d of the film-forming additive relative to the total mass of the electrolyte solution 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 multiple compositions can form a film on the surface of the SEI film 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), vinylethylene 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 (MCO), and / or methyl allyl carbonate (MCC). To Beauty Polycarbonate PC It includes one or more of the following.

[0017] In any embodiment, the sulfate ester additive comprises a cyclic sulfonate ester additive and / or a hydrocarbon group sulfate ester additive. Optionally, the cyclic sulfonate ester 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 is ,a It contains one or more of diponitrile, tolylene diisocyanate, and hexamethylene diisocyanate.

[0021] In optional embodiments, the electrolyte solution further comprises an organic solvent, such as 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 LiNi x Co y M 1-x-y O 2, 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 consumption device including a secondary battery according to any one of 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 explanation 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 any creative work. [Figure 1] 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Figure 3] 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 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. Reference numerals 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 INVENTION

[0027] Hereinafter, detailed descriptions will be given of embodiments specifically disclosing the secondary battery, battery module, battery pack, and power consumption device of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of known matters or redundant descriptions of substantially identical configurations 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. 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 that 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, if ranges of 60-120 and 80-110 are recited for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are recited, then ranges of 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all contemplated. In this application, unless otherwise specified, a numerical range "a-b" is represented by the abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are included herein, and "0-5" is an abbreviation for combinations of these numbers. 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 specified, all steps in the present application may be performed in order or randomly, but are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or may include steps (b) and (a) performed in order. 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, or a magnesium ion battery, etc., and the embodiments of the present application are not limited thereto.

[0035] With the application and widespread use of secondary batteries, their overall performance has been attracting increasing attention. Taking lithium-ion batteries as an example of secondary batteries, the positive electrode active material provides lithium insertion compounds and active lithium ions, while the stability of the material structure directly affects the overall performance of the lithium-ion battery. At high voltages, the positive electrode active material loses a large amount of lithium during charging of the secondary battery, so the expensive transition metals in the positive electrode active material, such as Co, are used. 4+ , Ni 4+ The content of is extremely high. Highly oxidized transition metals are easily reduced by the electrolyte to produce low-valent transition metals. Such transition metals can cause cation mixing, occupying lithium sites, and some lithium ions cannot return to the lithium sites during discharge, which can cause a loss of capacity in 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 is easily taken by the electrolyte, causing side reactions with the electrolyte or being released in the form of oxygen gas. Furthermore, the reaction of oxygen with the electrolyte leaves oxygen vacancies on the surface of the crystal lattice, which can cause the transition metals to become unstable and move, resulting in a phase transition of the positive electrode active material and the Li on the surface of the cathode. + The surface phase transition progresses with increasing voltage, which increases the surface activity of the positive electrode active material and the side reaction with the electrolyte, accelerating capacity loss and seriously deteriorating the cycle capacity retention rate.

[0036] Therefore, the inventors have 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 was to improve the dynamic performance of the movement. Next, specific embodiments of the secondary battery will be described. secondary battery

[0037] According to a first aspect, the present application provides a secondary battery, also known as a rechargeable battery or storage battery, which can be continuously used by activating the active material through charging after discharging.

[0038] 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. The boron-containing salt includes one or more of the compounds represented by Formula 1, the compounds represented by Formula 2, and the compounds represented by Formula 3. JPEG0007785186000002.jpg159148

[0039] In Formulas 1 to 3, M is independently selected from Li, Na, or K respectively. Let the mass percentage of the boron-containing salt with respect to the total mass of the electrolytic solution be A%. Let 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 satisfies 0 < A / (V1 - 4.1) ≤ 3.

[0040] Although the mechanism is not clear, the secondary battery according to the present application can achieve both improvement of the cycle life, safety performance, and capacity of the secondary battery. The inventors speculated on the reaction principle of the present application as follows.

[0041] Boron-containing salts, as salts with a central B atom, can coordinate with alkoxy groups, o-diphenols, o-hydroxy groups, carboxylic acids, etc. to form anion complexes. The anion complexes typically have a delocalized π-bond structure, with the central ion's negative charge relatively dispersed and delocalized. Furthermore, the anion radius is large, making it difficult for the anion to form strong ion pairs with metal ions, such as lithium ions, sodium ions, or potassium ions, in organic solvents, resulting in relatively good solubility. The more electron-withdrawing groups in the anion complex, the more stable the anion structure becomes, and the higher the solubility of metal ions in the electrolyte, the more advantageous it is for improving the conductivity of the electrolyte. Furthermore, boron-containing salts can form a high-performance cathode solid electrolyte interphase (CEI) film on the surface of the cathode active material. The CEI film is insoluble in organic solvents and can stably exist in organic electrolytes. It effectively prevents solvent molecules in the electrolyte from intercalating into the positive electrode active material, thereby ensuring the structural stability of the positive electrode active material and improving the cycle life of secondary batteries. Furthermore, the boron-containing salt forms a high-performance solid electrolyte interface (SEI) on the surface of the negative electrode active material, providing excellent 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 secondary batteries.

[0042] Taking an example where M is lithium element, the boron-containing lithium salt may include one or more of lithium tetrafluoroborate (LiBF), lithium disoxalate borate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorooxalate borate (LiCOF2, abbreviated as LiDFOB). Further, the boron-containing lithium salt includes compositions of lithium tetrafluoroborate LiBF4, lithium disoxalate borate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorooxalate borate (LiCOF2, abbreviated as LiDFOB).

[0043] Either the compound represented by Formula 1 or the compound represented by Formula 3 has a passivating effect on the positive electrode current collector in the positive electrode sheet, reducing the risk of corrosion of the positive electrode current collector due to side reactions with the positive electrode current collector and improving the structural stability of the positive electrode sheet. Furthermore, an electrolyte containing either the compound represented by Formula 1 or the compound represented by Formula 3 is less likely to generate acidic substances, further reducing the risk of corrosion of the positive electrode current collector, thereby providing good protection for the entire positive electrode sheet, ensuring the cycle stability of the secondary battery and improving 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 lithium ion migration, ensuring the capacity of the secondary battery.

[0044] When the compound represented by Formula 2 is used in combination with an organic solvent, such as a carbonate ester-based solvent or additive, in an electrolyte, the system comprising the compound represented by Formula 2 has low viscosity, favoring the release of metal ions and improving the conductivity of the electrolyte. The CEI film formed from the compound represented by Formula 2 has a relatively uniform thickness, good kinetic activity, and low charge transfer resistance in secondary batteries, thereby significantly improving the low-temperature performance and cycle DCR increase rate of the secondary battery. This improves the kinetic performance of lithium ion migration on the cathode surface of the secondary battery. The CEI film is resistant to thermal decomposition and its performance at high temperatures is relatively stable, significantly improving the high-temperature performance of the secondary battery.

[0045] In some embodiments, the compounds represented by Formulas 1 to 3 are used in combination, and the CEI film formed by the three compounds contains many components, making the structure of the CEI film more stable. Furthermore, while ensuring structural stability, the CEI film can also provide good protection of the positive electrode active material.

[0046] In the embodiments of the present application, the secondary battery satisfies the range of the above formula, 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, exert a good protective effect on the positive electrode active material, and reduce the risk of side reactions occurring due to the contact between the positive electrode active material and the electrolyte. Thereby, it is difficult for the transition metal in the positive electrode active material to undergo an oxidation-reduction reaction, it is difficult for cation mixing to occur in the positive electrode active material, which is advantageous for the insertion / desorption of metal ions. Thereby, the capacity of the positive electrode active material is ensured and the structural stability is ensured, and the cycle capacity retention rate of the secondary battery is improved. The secondary battery is less likely to cause side reactions in which by-products such as oxygen gas are generated between the positive electrode active material and the electrolyte, and it is ensured that the voltage in the secondary battery is in a normal state during the charge-discharge cycle, and the safety performance of the secondary battery can be ensured.

[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, the boron-containing lithium salt may include one or more of lithium tetrafluoroborate LiBF4, lithium diborate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorosulfate (LiC2O4F2, abbreviated as LiDFOB). Further, the boron-containing lithium salt includes a composition of lithium tetrafluoroborate LiBF4, lithium diborate LiBOB, and lithium difluorosulfate 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, a sodium salt or the like may be selected as the boron-containing salt, or a boron-containing lithium salt, a boron-containing potassium salt, etc. may be selected. Optionally, 0 < A / (V1 - 4.1) ≤ 3. Exemplarily, 0 < A / (V1 - 4.1) ≤ 0.1, 0 < A / (V1 - 4.1) ≤ 0.2, 0 < A / (V1 - 4.1) ≤ 0.5, 0 < A / (V1 - 4.1) ≤ 1, 0 < A / (V1 - 4.1) ≤ 1.5, 0 < A / (V1 - 4.1) ≤ 2, 0 < A / (V1 - 4.1) ≤ 2.5, 0 < A / (V1 - 4.1) ≤ 3, 0 < A / (V1 - 4.1) ≤ 3.5 or 0 < A / (V1 - 4.1) ≤ 4.

[0048] In some embodiments, V1>4.1.

[0049] The positive electrode active material has a relatively high upper potential V1 relative to metallic lithium, making it suitable for charging and discharging in a high-voltage system. Furthermore, by combining the positive electrode active material with a boron-containing salt, the boron-containing salt can adequately protect the surface of the positive electrode active material, ensuring the structural stability of the positive electrode active material in a high-voltage system. Alternatively, 4.1≦V1≦4.6. For example, the upper potential V1 (V) of the positive electrode active material relative to metallic lithium may be 4.1 V, 4.2 V, 4.3 V, 4.4 V, 4.5 V, or 4.6 V, or may be within a range between any two of the above numerical values.

[0050] The upper limit potential V1 of the positive electrode active material relative to metallic lithium can be considered as the difference in potential between the positive electrode active material and metallic lithium. The upper limit potential V1 of the positive electrode active material can be measured using test methods and test equipment known in the art. Specifically, the positive electrode active material powder was mixed with SP and PVDF in a 90:5:5 ratio, stirred, and then uniformly coated on a 13 μm thick Al foil. The mixture was then compressed to obtain a positive electrode membrane sheet with a compressed density of 3.3-3.6 g / cm. 3Perform at <10% humidity control during this process. Then, dry the positive electrode membrane sheet in an oven at 100 °C for 2 h. Before current collection, vacuum dry the positive electrode membrane sheet under the conditions of 105 °C / 4 h / -0.09 Mpa. Then, assemble the manufactured positive electrode membrane sheet into a CR2430 type half coin cell of membrane sheet - lithium sheet in a PRS340 / 11 - 119 - 11 brown glove box. Among them, use 1M LiPF6 EC / EMC / DEC = 3 / 5 / 2 as the electrolyte, and let the assembled half coin cell stand for 3 h. Conduct the test at 25 °C. Using 0.5C, first charge in the voltage range of 2.8 - V1 to desorb lithium, and then discharge between the voltage range of V1 - 2.8 using 0.1C to insert lithium to obtain the charge - discharge coin cell capacity. Further, divide the coin cell capacity by the mass of the positive electrode active material to obtain the charge - discharge gram capacity (capacity per gram). The upper limit potential V1 of the positive electrode active material with respect to metallic lithium is the upper limit potential when the discharge gram capacity is 150 - 220 mAh / g.

[0051] In some embodiments, 0 < A ≤ 2.

[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 as to sufficiently protect the positive electrode active material, improve the structural stability of the positive electrode active material, and ensure 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 protection 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 composed 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. Let the upper limit potential of the negative electrode active material with respect to metallic lithium be V2 (V). The secondary battery further satisfies 0 < A × V2 ≤ 1.2.

[0054] The boron-containing salt has a high reduction potential and is also involved in the anode film formation, forming a dense and stable SEI film, which provides sufficient protection to the surface of the negative electrode active material, reducing the risk of side reactions occurring due to contact between the negative electrode active material and the electrolyte, mitigating the risk of reduction of the organic solvent in the electrolyte, and further improving the cycle stability of the secondary battery.

[0055] The deeper the lithium insertion depth of the negative electrode active material, the more active the negative electrode active material, and the more easily the electrolyte is reduced on the surface of the negative electrode active material. In view of this, in the secondary battery of the present application, when the above relationship is satisfied, the mass percentage of the boron-containing salt increases with the upper potential limit of the negative electrode active material, forming a denser and more stable SEI film on the surface of the highly active negative electrode active material, thereby strengthening protection for the negative electrode active material and improving the cycle stability and cycle life of the secondary battery.

[0056] In some embodiments, 0.02≦V2≦2.5, and optionally, 0.1≦V2≦2.

[0057] The negative electrode active material is applicable to charging and discharging in a high-voltage system, and by using the negative electrode active material in combination 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 V2 of the negative electrode active material relative to metallic lithium can be considered as the difference in potential between the negative electrode active material and metallic lithium. The upper limit potential V2 of the negative electrode active material can be measured using test methods and test equipment known in the art. Specifically, the negative electrode active material powder was mixed with SP and PVDF in a ratio of 91.6:1.8:6.6, stirred, and then uniformly coated on an 8 μm-thick Cu foil. The mixture was then compressed to form a negative electrode membrane sheet with a compressed density of 1.4-1.6 g / cm. 3The humidity during this process is controlled to <10%. The negative electrode sheet was then dried in an oven at 100°C for 2 hours. Before collecting current, the negative electrode sheet was vacuum dried at 105°C for 4 hours at -0.09MPa. The negative electrode sheet was then assembled into a CR2430 half coin cell consisting of a negative electrode sheet and a lithium sheet in a PRS340 / 11-119-11 brown glove box. The electrolyte was 1M LiPF6 EC / EMC / DEC=3 / 5 / 2. The assembled half coin cell was left to stand for 5 hours. Tests were conducted at 25°C, with lithium insertion / extraction occurring during charge / discharge: 0.05C~0.005V, 50uA DC~0.005V, 5 minutes of standing, 10uA DC~0.005V, 5 minutes of standing, and 0.1C CC~V2, 5 minutes of standing. The charge / discharge capacity of the coin cell was obtained. Furthermore, the coin cell capacity is divided by the mass of the negative electrode active material to obtain the charge / discharge gram capacity, and the upper limit potential V2 of the negative electrode active material relative to metallic lithium 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 the boosting of lithium ions or sodium ions in secondary battery systems.

[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] For example, the boron-containing lithium salt may include at least one of lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium disoxalate borate (LiBOB). By combining lithium tetrafluoroborate (LiBF4), lithium disoxalate borate (LiBOB), and lithium difluorooxalate borate (LiDFOB), the three can form a CEI film on the surface of the positive electrode active material, which effectively reduces 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 may further include one or more of lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium hexafluoroarsenate LiAsF6, lithium bisfluorosulfonylimide LiFSI, lithium bistrifluoromethanesulfonylimide LiTFSI, lithium trifluoromethanesulfonate LiTFS, lithium difluorophosphate LiPO2F2, lithium difluorodisalophosphate LiDFOP, lithium tetrafluorooxalophosphate LiTFOP, sodium hexafluorophosphate NaPF6, sodium bisfluorosulfonylimide NaFSI, sodium difluorophosphate NaPO2F2, sodium bistrifluoromethanesulfonylimide NaTFSI, and sodium fluorosulfonate NaFSO3. The use of a combination of the lithium salt and a boron-containing salt can improve the conductivity of the electrolyte.

[0065] By way of example, the electrolyte may include lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium perchlorate LiClO4, lithium hexafluoroarsenate LiAsF6, lithium bisfluorosulfonylimide LiFSI, lithium bistrifluoromethanesulfonylimide LiTFSI, lithium trifluoromethanesulfonate LiTFS, lithium difluorooxalate borate LiDFOB, lithium disoxalate borate LiBOB, sodium hexafluorophosphate NaPF6, sodium bisfluorosulfonylimide NaFSI, sodium difluorophosphate NaPO2F2, sodium bistrifluoromethanesulfonylimide NaTFSI, and sodium fluorosulfonate NaFSO3.

[0066] In some embodiments, the electrolyte may further include a Lewis base solvent. The Lewis base promotes dissociation of the boron-containing salt, contributing to the release of lithium ions and improving the conductivity of the electrolyte. For example, the Lewis base solvent may include a compound containing 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 solution may further include a film-forming additive, such as a negative electrode film-forming additive. The negative electrode film-forming additive may include one or more of a carbonate ester-based additive, a sulfate ester-based additive, a sulfite ester-based additive, a phosphate ester-based additive, and a polynitrile-based additive. The negative electrode film-forming additive may form an SEI film on the surface of the negative electrode active material, and multiple additives may be combined to form a rich SEI film on the surface of the SEI film and improve the structural stability of the SEI film. Furthermore, the negative electrode film-forming additive may include at least two additives from a carbonate ester-based additive, a sulfate ester-based additive, a sulfite ester-based additive, a phosphate ester-based additive, and a polynitrile-based additive, thereby forming a rich SEI film and improving its structural stability. Optionally, the mass percentage d of the film-forming additive relative to the total mass of the electrolyte solution satisfies 0.5%≦d≦10%, and optionally 1%≦d≦6%.

[0069] For example, the carbonate ester additive includes a cyclic carbonate ester additive and / or a linear carbonate ester additive. Further, 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 (MCO), and the like. To and polycarbonate PC It includes one or more of the following.

[0070] For example, the sulfate ester additive may include a cyclic sulfonate ester additive and / or a hydrocarbon-based sulfate ester additive. The cyclic sulfonate ester additive may include one or more of 1,3-propane sultone PS, propene sultone PES, and 3-fluoro-1,3-propane sultone FPS. The hydrocarbon-based sulfate ester additive may include 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] For example, the phosphate ester additive may include one or more of tris(trimethylsilyl) phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate.

[0073] For example, polynitrile additives are ,a It contains one or more of diponitrile, tolylene diisocyanate, and hexamethylene diisocyanate.

[0074] The electrolyte solution of the present application can be prepared according to a conventional method in this field. For example, the additive, the solvent, the electrolyte salt, etc. can be uniformly mixed to obtain the electrolyte solution. 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 solution.

[0075] In the present application, the components and their contents in the electrolyte solution can be measured according to methods known in the art, such as 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 solution of the present application, a freshly prepared electrolyte solution may be obtained directly, or the electrolyte solution may be obtained from a secondary battery. One exemplary method for obtaining the electrolyte solution from a secondary battery includes discharging the secondary battery to a discharge end voltage (for safety reasons, the battery is generally fully discharged), then centrifuging the battery, and then extracting an appropriate amount of the liquid obtained by the centrifugation as the nonaqueous electrolyte solution. The nonaqueous electrolyte solution may also be obtained directly from the filling port 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 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, which 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 a lithium transition metal oxide, a lithium-containing phosphate with an olivine structure, and a modified compound 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 a modified compound thereof. Examples of lithium-containing phosphates with an olivine structure include at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and a modified compound thereof. The present application is not limited to these materials, and other materials known in the art for use as positive electrode active materials for secondary batteries can also 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 O2 or LiNi a Co b Al c N 1-a-b-cO2, and 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 a positive electrode active material in combination with a boron-containing lithium salt, B atoms in the boron-containing lithium salt are more likely to bond with O atoms in the positive electrode active material, thereby reducing the charge transfer resistance of the positive electrode active material and the diffusion resistance of lithium ions within the bulk of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains an appropriate amount 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 lithium ions in the bulk of the low-cobalt or cobalt-free positive electrode active material can be promptly replenished to the surface, preventing excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material and stabilizing the crystalline structure of the low-cobalt or cobalt-free positive electrode active material. Because the crystalline structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems occurring, such as unstable structural, chemical, or electrochemical properties of the positive electrode active material due to excessive lithium desorption from the surface of the low-cobalt or cobalt-free positive electrode active material, such as irreversible distortion of the positive electrode active material and an increase in lattice defects, can be significantly reduced.

[0080] LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-cO2 can be produced according to conventional methods in the art. An exemplary production method involves mixing 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, followed by sintering. The sintering atmosphere may be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. The O2 concentration in the sintering atmosphere is, for example, 70%-100%. The sintering temperature and sintering time can be adjusted according to actual conditions.

[0081] Examples of lithium sources include, but are not limited to, at least one of lithium oxide (LiO), lithium phosphate (LiPO), lithium dihydrogen phosphate (LiHPO), lithium acetate (CHCOOLi), lithium hydroxide (LiOH), lithium carbonate (LiCO), and lithium nitrate (LiNO). Examples of nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. Examples of cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. Examples of manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. Examples of aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. By way of example, precursors of the M element include, but are not limited to, at least one of oxides, nitrates, carbonates, hydroxides, and acetates of the M element. By way of example, precursors of the N element include, but are not limited to, at least one of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium hydrogen carbonate, 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.

[0082] In some embodiments, the total mass of the positive electrode layer is x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c The mass percentage of O2 in layered materials is 80%-99%. For example, the molecular formula is LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c The mass percentage of the layered material that is O2 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 O2 or LiNi a Co b Al c N 1-a-b-c The mass percentage of the layered material that is O2 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 LiNi x Co y M 1-x-y O2, where 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. Under high voltage, the lithium deficiency on the surface of the positive electrode active material is likely to cause phase transition, Li / Ni mixing, oxygen release, etc. on the surface of the positive electrode active material. The boron-containing salt can deactivate the surface of the positive electrode active material, and also deactivate metal cations, such as Al. 3+ and Ni 2+ to improve Li / Ni mixing and passivate the aluminum foil.

[0084] In some embodiments, the positive electrode film layer optionally further includes a positive electrode conductive agent. The type of the positive electrode conductive agent is not particularly limited in the present application. For example, the positive electrode conductive agent may include 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 film layer is 5% or less.

[0085] In some embodiments, the positive electrode membrane layer optionally further includes a positive electrode binder. The type of positive electrode binder is not particularly limited in the present application. For example, the positive electrode binder may include one or more combinations selected from 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. 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 may 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 may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may 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 may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0087] The positive electrode film 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 that contains a negative electrode active material.

[0089] For example, the negative electrode current collector has two surfaces that face each other in the thickness direction, and the negative electrode film layer is provided on one or both of the two facing 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 materials, tin-based materials, lithium titanate, and lithium-aluminum alloys. The silicon-based material may be at least one selected from silicon elemental, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from tin elemental, tin-oxygen compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials usable as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination.

[0091] In some embodiments, the negative electrode membrane layer optionally further includes a negative electrode binder. The type of negative electrode binder is not particularly limited in the present application. 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 optionally further includes a negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited. For example, the negative electrode conductive agent may include one or a combination of materials 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 additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC-Na), a PTC thermistor material, etc. In some embodiments, the mass percentage of the other additives relative to the total mass of the negative electrode membrane layer is 2% or less.

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

[0095] The negative electrode film 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, optional conductive agent, optional binder, and optional other additives 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 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 separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the layers may be the same or different, and are 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 outer casing, 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, or a steel case. The exterior of the secondary battery may be a soft pack, such as a bag-shaped soft pack. The soft bag may be made of 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 FIGS. 1 and 2 , the exterior may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, which together form a housing cavity. The case 51 has an opening communicating with the housing cavity, and the cover plate 53 covers the opening to close the housing cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the housing cavity. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted as needed.

[0104] Methods for manufacturing the secondary battery of the present application are well 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, the positive electrode sheet, the separator, and the negative electrode sheet can be wound or stacked to form an electrode assembly, which can then be placed in a housing, dried, and then injected with an electrolyte. The secondary battery can then be obtained by vacuum sealing, standing, forming, shaping, and other processes.

[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 plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed with fasteners.

[0107] Optionally, the battery module 4 may further include a housing having an accommodating space for accommodating a plurality of secondary batteries 5.

[0108] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may 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 FIGS. 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, battery module, and battery pack according to the present application. The secondary battery, battery module, and battery pack may be used as a power source for the power consuming device or 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, 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. 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 include mobile phones, tablet computers, laptop computers, etc. Such power consuming devices are generally required to be thin and can use secondary batteries as their power source. Example

[0114] The following examples are provided to more specifically illustrate the disclosure of the present application, and are for illustrative purposes only, as various modifications and variations within the scope of the disclosure will be apparent to those skilled in the art. 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 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 sheets

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

[0116] LiNi, the positive electrode active material 0.65 Co 0.07 Mn 0.28 O 2. Carbon black, a conductive agent, and polyvinylidene fluoride (PVDF), a binder, were mixed in a weight ratio of 97.5:1.4:1.1 in an appropriate amount of NMP, a solvent, by thorough stirring to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly applied to the surface of aluminum foil, a positive electrode current collector, and after drying and cold pressing, a positive electrode sheet was obtained. 2. Manufacturing of negative electrode sheets

[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 carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (SuperP) were mixed in a weight ratio of 96.2:1.8:1.2:0.8 with an appropriate amount of solvent and deionized water and stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry was then uniformly applied to the surface of copper foil, 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. Electrolyte Preparation

[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 then additives were dissolved in the mixed solvent to prepare an electrolyte solution with a lithium salt concentration of 1 mol / L. The specific substances contained in the electrolyte solution 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 and negative electrode sheets to provide isolation, and then wound up to obtain an electrode assembly. The electrode assembly is placed in an outer housing, dried, and then an electrolyte is injected. After vacuum sealing, standing, chemical formation, and shaping, a lithium-ion battery is obtained. Example 2 Examples 2-1 to 2-5

[0122] The secondary battery was manufactured in a similar manner 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 Examples 1 and 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 Examples 3-1 to 3-3

[0123] The secondary battery was manufactured in a manner similar to that of Example 1, except that the upper limit potential V1 of the "positive electrode active material" was adjusted. Specific parameters are shown in Table 1. Example 4 Examples 4-1 to 4-5

[0124] The secondary battery was manufactured in a manner similar to that of Example 1, except that the upper limit potential V2 of the "negative electrode active material" was adjusted. The specific parameters are shown in Table 1. Example 5 Example 5-1 The secondary battery was manufactured in a similar manner to 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 "negative electrode active material" was adjusted. The specific parameters are shown in Table 1.

[0126] [Table 1] Testing part 1.Method for measuring the upper limit potential V1 of the positive electrode active material relative to metallic lithium

[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 a 13 μm thick Al foil. The mixture was then compressed to obtain a positive electrode membrane sheet with a compressed density of 3.3-3.6 g / cm. 3The process is carried out under controlled humidity of less than 10%. The positive electrode film sheet is then dried in an oven at 100°C for 2 hours. Before current collection, the positive electrode film sheet is vacuum dried at 105°C for 4 hours at -0.09MPa. The resulting positive electrode film sheet is then assembled into a CR2430 half-coin cell consisting of a film sheet and a lithium sheet in a PRS340 / 11-119-11 brown glove box. The electrolyte is 1M LiPF6 EC / EMC / DEC=3 / 5 / 2. The assembled half-coin cell is allowed to stand for 3 hours. The test is carried out at 25°C. At 0.5C, the cell is first charged at a voltage range of 2.8-V1 to remove lithium, and then discharged at 0.1C between the voltage ranges of V1 and V2 to insert lithium, thereby obtaining the charge and discharge capacity of the coin cell. Furthermore, the coin cell capacity is divided by the mass of the positive electrode active material to obtain the charge / discharge gram capacity, and the upper limit potential V1 of the positive electrode active material relative to metallic lithium is the upper limit potential when the discharge gram capacity is 150 to 220 mAh / g. 2.Method for measuring the upper limit potential V2 of the negative electrode active material relative to metallic lithium

[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. 3The humidity during this process is controlled to <10%. The negative electrode sheet was then dried in an oven at 100°C for 2 hours. Before collecting current, the negative electrode sheet was vacuum dried at 105°C for 4 hours at -0.09MPa. The negative electrode sheet was then assembled into a CR2430 half coin cell consisting of a negative electrode sheet and a lithium sheet in a PRS340 / 11-119-11 brown glove box. The electrolyte was 1M LiPF6 EC / EMC / DEC=3 / 5 / 2. The assembled half coin cell was left to stand for 5 hours. Tests were conducted at 25°C, with lithium insertion / extraction occurring during charge / discharge: 0.05C~0.005V, 50uA DC~0.005V, 5 minutes of standing, 10uA DC~0.005V, 5 minutes of standing, and 0.1C CC~V2, 5 minutes of standing. The charge / discharge capacity of the coin cell was obtained. Furthermore, the coin cell capacity is divided by the mass of the negative electrode active material to obtain the charge / discharge gram capacity, and the upper limit potential V2 of the negative electrode active material relative to metallic lithium 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 at a constant voltage of 4.33V until the current reached 0.05C, and then discharged to 2.8V at a constant current of 1C. This constituted one charge-discharge cycle. The capacity retention rate of the battery after 500 cycles was calculated, assuming the capacity at the first discharge as 100%. Capacity retention rate of the battery after 500 cycles (%) = discharge capacity at 500 cycles / capacity at first discharge × 100%.

[0130] 3.2 Performance test of DCR increase rate of lithium-ion battery from 25°C to 500 cycles

[0131] Pre-cycling DCR test at 25°C: At 25°C, a freshly manufactured core was charged at 0.5C to 4.35V, then charged at a constant voltage of 0.05C, at which point the voltage was V1. It was then discharged at 4C for 30s, with the voltage at the end of discharge being V2. Samples were taken every 0.1s, and the pre-cycling core's discharge DCR1 at 100% SOC was (V1-V2) / I.

[0132] DCR test at 25°C after cycling: At 25°C, the core after the 25°C cycle was charged at 0.5C to 4.35V, then charged at a constant voltage of 0.05C, at which point the voltage was V3. It was then discharged at 4C for 30s, with the voltage at the end of discharge being V4. Samples were taken every 0.1s, and the discharge DCR2 at 100% SOC of the core after cycling was (V3-V4) / I.

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

[0134] Table 2 shows the improvements of the present invention 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, without the addition of boron-containing salt, the positive electrode active material is likely to come into contact with the electrolyte, causing side reactions, resulting in destruction of the positive electrode active material, shortening the cycle life of the secondary battery, and possibly increasing the interfacial resistance. In Comparative Example 2, boron-containing salt was added, but the relationship between the mass percentage of boron-containing salt and the upper potential limit of the positive electrode active material was A / (V1-4.1)>4. Therefore, 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 increases, and there is a risk of the boron-containing salt system decomposing, making the system unstable.

[0137] Examples 1 to Example 2-5 are adjusted such that the mass percentage of the boron-containing salt and the upper limit potential of the positive electrode active material satisfy 0 < A / (V1 - 4.1) ≤ 4, and in particular, 0 < A / (V1 - 4.1) ≤ 3. By doing so, the boron-containing salt can form a dense and stable CEI film on the surface of the positive electrode active material, and can exert a good protective effect on the positive electrode active material. As a result, it is difficult for the transition metal in the positive electrode active material to undergo an oxidation-reduction reaction, it is difficult for cation mixing to occur in the positive electrode active material, and it is advantageous for the desorption of metal ions. Therefore, the cycle life of the secondary battery is improved. In addition, the film thickness of the CEI film formed by the boron-containing salt is dense and uniform, its interfacial resistance is low, which is advantageous for improving the kinetic performance of the secondary battery.

[0138] Examples 3-1 to Example 3-3 can significantly improve the cycle life and DCR increase rate of the secondary battery by adjusting the upper limit potential V1 of the positive electrode active material, particularly to 4.1 < V1 ≤ 4.6.

[0139] Examples 4-1 to Example 4-5 can significantly improve the cycle life and DCR increase rate of the secondary battery by adjusting the upper limit potential V2 of the negative electrode active material, particularly to 0 < A × V2 ≤ 1.2, 0 < A × V2 ≤ 1.

[0140] As can be seen from the results of adjusting the types of the positive electrode active material and the negative electrode active material in Examples 5-1 and Example 5-2 respectively, when 0 < A / (V1 - 4.1) ≤ 4 is satisfied, the boron-containing lithium salt can effectively protect the positive electrode active material and the negative electrode active material. Therefore, the cycle life and DCR increase rate of the secondary battery can be improved.

[0141] As described above, the present application has been described with reference to the preferred embodiments. However, various improvements are possible or some of its components may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural contradiction, the technical features mentioned in each embodiment can be arbitrarily combined. The present application is not limited to the specific embodiments disclosed above, but includes all aspects included in 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 including 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 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), 0<A / (V １ -4.1)≦4, and V １ A secondary battery that satisfies the conditions of >4.1 and 0.6≦A≦2.

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

6.

3. The secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material, and an upper limit potential of the negative electrode active material relative to metallic lithium is V ２ (V), The secondary battery has a temperature of 0<A×V ２ 2. The secondary battery according to claim 1, wherein the .lambda. / .lambda. ratio satisfies .ltoreq.1.

2.

4. 0.02≦V ２ 4. The secondary battery according to claim 3, wherein the ρ 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 of claim 1, wherein 0.6≦A≦1.

5.

7. The compound represented by 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:

9. 2. The secondary battery according to claim 1, wherein the electrolytic solution further contains a film-forming additive, and the film-forming additive contains 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.

10. The carbonate ester additive comprises a cyclic carbonate ester additive and / or a linear carbonate ester additive, and / or The sulfate ester additive includes a cyclic sulfonate ester additive and / or a hydrocarbon group sulfate ester additive, and / or The sulfite ester additive comprises ethylene sulfite ES and / or vinyl ethylene sulfite VES, and / or The phosphate ester additive includes 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 includes one or more of adiponitrile, tolylene diisocyanate, and hexamethylene diisocyanate.

11. 2. The secondary battery of claim 1, wherein the electrolytic solution further comprises an organic solvent, and the organic solvent comprises 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 LiNi ｘ Co ｙ M １－ｘ－ｙ 2. The secondary battery of claim 1, comprising a compound represented by the formula: O2, 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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