Secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a secondary battery, a battery module, a battery pack and a power utilization device. The secondary battery comprises a positive electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode active material; the electrolyte comprises a boron-containing salt, the mass percentage of the boron-containing salt in the total mass of the electrolyte is denoted as A%; the upper limit potential of the positive electrode active material relative to metal lithium is denoted as V1 (V); the secondary battery satisfies: 0 < A / (V1-4.1) ≤ 4, and V1 > 4.1; optionally, 0 < A / (V1-4.1) ≤ 3. The application can improve the cycle capacity retention rate and the cycle DCR growth rate of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] Secondary batteries have the characteristics of high capacity and long service life, and are therefore widely used in electronic devices such as mobile phones, notebook computers, electric vehicles, electric cars, electric planes, electric ships, electric toy cars, electric toy ships, electric toy planes and electric tools.

[0003] With the increasingly wide range of applications of batteries, the requirements for the performance of secondary batteries are gradually stringent, such as the requirement for good cycle capacity retention rate and low cycle DCR growth rate, and therefore how to improve the cycle capacity retention rate and the cycle DCR growth rate is also a problem to be solved. SUMMARY

[0004] The present application is made in view of the above-mentioned problem, and aims to provide a secondary battery, a battery module, a battery pack and a power utilization device.

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

[0006]

[0007]

[0008] In Formulas 1 to 3, M is each independently selected from Li, Na or K; the mass percentage content of the boron-containing salt relative to the total mass of the electrolyte is denoted as A%; the upper limit potential of the positive electrode active material relative to metallic lithium is denoted as V1(V); the secondary battery satisfies: 0

[0009] In the technical solution, the secondary battery of the application meets 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 active material, which plays a good protective role on the positive active material, can reduce the risk of contact between the positive active material and the electrolyte and the occurrence of side reactions, so that the transition metal in the positive active material is not easy to undergo redox reaction, and the positive active material is not easy to undergo cation mixing, which is beneficial to the deintercalation of metal ions, thereby ensuring the capacity development and structural stability of the positive active material, so as to improve the cycle capacity retention rate of the secondary battery. The positive active material and the electrolyte are not easy to produce by-products such as oxygen through side reactions, and the secondary battery can ensure that the voltage in the secondary battery is in a normal state during the charging and discharging cycle process, and ensure the safety performance of the secondary battery. In addition, the application can also improve the cycle DCR growth rate of the secondary battery during the cycle process.

[0010] In any embodiment, 4.1 < V1 ≤ 4.6. The upper limit potential V1 of the positive active material relative to metal lithium is relatively high, which is suitable for charging and discharging in a high-voltage system; and the use of the above positive active material and boron-containing salt together, the boron-containing salt can fully protect the surface of the positive active material, thereby ensuring the structural stability of the positive active material in a high-voltage system.

[0011] In any embodiment, the secondary battery further comprises a negative electrode sheet, the negative electrode sheet comprises a negative active material, and the upper limit potential of the negative active material relative to metal lithium is denoted as V2 (V); the secondary battery meets: 0 < A × V2 ≤ 1.2; optionally, 0 < A × V2 ≤ 1. The boron salt has a relatively high reduction potential and can also participate in anode film formation to form a dense and stable SEI film, which can form sufficient protection on the surface of the negative active material, reducing the risk of side reactions between the negative active material and the electrolyte, thereby reducing the risk of reduction of organic solvents in the electrolyte, and further improving the cycle stability of the secondary battery.

[0012] In any embodiment, 0.02 ≤ V2 ≤ 2.5; optionally, 0.1 ≤ V2 ≤ 2. The above negative active material is suitable for charging and discharging in a high-voltage system; and the use of the above negative active material and boron-containing salt together, the boron-containing salt can fully protect the surface of the positive active material, thereby ensuring the structural stability of the positive active material in a high-voltage system.

[0013] In any embodiment, the negative active material comprises at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon and silicon-based materials.

[0014] In any embodiment, 0 < A ≤ 2. When the boron-containing salt is in the above range, a dense and stable CEI film can be formed on the surface of the positive electrode active material, thereby sufficiently protecting the positive electrode active material and improving the structural stability of the positive electrode active material, so as to ensure the cycle stability of the secondary battery. Moreover, the boron-containing salt can also form an SEI film on the surface of the negative electrode active material, thereby improving the protection of the negative electrode active material.

[0015] In any embodiment, 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 represented by Formula 1 includes lithium difluoro(oxalato)borate and / or sodium difluoro(oxalato)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 bis(oxalato)borate and / or sodium bis(oxalato)borate.

[0016] In any embodiment, the electrolyte further includes one or more of lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium hexafluoroarsenate LiAsF6, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium trifluoromethanesulfonate LiTFS, lithium difluorophosphate LiPO2F2, lithium difluorodioxalate phosphate LiDFOP, lithium tetrafluorooxalate phosphate LiTFOP, sodium hexafluorophosphate NaPF6, sodium bis(fluorosulfonyl)imide NaFSI, sodium difluorophosphate NaPO2F2, sodium bis(trifluoromethylsulfonyl)imide NaTFSI, and sodium fluorosulfonate NaFSO3. The above lithium salt and the boron-containing salt are used in combination, which can improve the electrical conductivity of the electrolyte.

[0017] In any embodiment, the electrolyte 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 content d of the film-forming additive satisfies: 0.5% ≤ d ≤ 10%, based on the total mass of the electrolyte; optionally, 1% ≤ d ≤ 6%. The negative electrode film-forming additive can form an SEI film on the surface of the negative electrode active material, and the film-forming of multiple components on the surface of the SEI film can enrich the film layer structure of the SEI film and improve the structural stability of the SEI film.

[0018] In any embodiment, the carbonate-based additive includes a cyclic carbonate-based additive and / or a linear carbonate-based additive; optionally, the cyclic carbonate-based additive includes 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-based additive includes one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, methyl allyl carbonate, and polycarbonate PC.

[0019] In any embodiment, the sulfate ester additives include cyclic sulfonate additives and / or sulfate hydrocarbon ester additives; optionally, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone PS, propenesulfonate lactone PES, and 3-fluoro-1,3-propanesulfonate lactone FPS.

[0020] In any embodiment, the sulfate hydrocarbon ester additives include one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS; and / or the sulfite ester additives include vinyl sulfite ES and / or vinyl vinyl sulfite VES.

[0021] In any embodiment, the phosphate ester additive includes one or more of tris(trimethylsilane) phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate.

[0022] In any embodiment, the polynitrile additive includes one or more of adiponitrile, toluene diisocyanate, and hexamethylene diisocyanate.

[0023] In any embodiment, the electrolyte further includes an organic solvent, which includes one or more of the following: ethylene carbonate EC, propylene carbonate PC, methyl ethyl 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.

[0024] In any embodiment, the positive electrode active material includes LiN ix Co y M 1-x-y The compound is given by the formula, where M represents one or more of Mn, Fe, Mg, Al, Cu and Ti, x≥0.5, 0≤y≤0.2, and x+y≤1.

[0025] A second aspect of this application also provides a battery module including a secondary battery as described in any embodiment of the first aspect of this application.

[0026] A third aspect of this application also provides a battery pack including a battery module as described in the second aspect of this application.

[0027] The fourth aspect of this application also provides an electrical device, including a secondary battery as described in any embodiment of the first aspect of this application, a battery module as described in the second aspect of this application, or a battery pack as described in the third aspect of this application. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0029] FIG. 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0030] FIG. 2 yes FIG. 1 An exploded view of the implementation method of the secondary battery.

[0031] FIG. 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0032] FIG. 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0033] FIG. 5 yes FIG. 4 An exploded view of an embodiment of the battery pack shown.

[0034] FIG. 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0035] The accompanying drawings may not be drawn to scale.

[0036] The annotations in the attached figures are explained as follows:

[0037] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0038] 5. Secondary battery; 51. Housing; 52. Electrode assembly;

[0039] 53. Cover plate;

[0040] 6. Electrical appliances. Detailed Implementation

[0041] The following detailed description discloses embodiments of the secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0046] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0047] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0048] In this application, the secondary battery may include lithium-ion batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries, or magnesium-ion batteries, etc., and the embodiments of this application are not limited to this.

[0049] With the application and promotion of rechargeable batteries, their comprehensive performance has received increasing attention. Taking lithium-ion batteries as an example, the positive electrode active material, as the lithium intercalation compound and the provider of active lithium ions, has a direct impact on the overall performance of the lithium-ion battery due to the stability of its material structure. Under high voltage, a large amount of lithium is released from the positive electrode active material during the charging process of the rechargeable battery, leading to the degradation of high-valence transition metals such as Co in the positive electrode active material. 4+ Ni 4+ The content is extremely high. High-oxidation-state transition metals are easily reduced by the electrolyte, generating low-valence transition metals. These transition metals may undergo cation mixing, occupying lithium sites. This prevents some lithium ions from migrating back to the lithium sites during discharge, resulting in a loss of capacity in the cathode active material. Simultaneously, oxygen on the lattice surface of the cathode active material is unstable and easily captured by the electrolyte, reacting with it or being released as oxygen. Furthermore, the reaction of oxygen with the electrolyte leaves oxygen vacancies on the lattice surface. The unstable transition metals may migrate, causing a phase transition in the cathode active material and affecting the Li on the cathode surface. + Migration is hindered, leading to increased impedance; surface phase transitions intensify with increasing voltage, resulting in higher surface activity of the positive electrode active material, more intense side reactions with the electrolyte, accelerated capacity loss, and severe deterioration of cycle capacity retention.

[0050] In view of the above problems, the inventors considered improving the composition of the electrolyte under high-voltage systems and seeking the correlation between the electrolyte and the positive electrode active material, thereby improving the cycle capacity retention rate of the secondary battery and the kinetic performance of Li+ migration on the cathode surface. The specific scheme for the secondary battery will be described below.

[0051] Secondary battery

[0052] Firstly, this application proposes a secondary battery. A secondary battery, also known as a rechargeable battery or storage battery, refers to a battery that can be recharged after discharge to activate the active materials and continue to be used.

[0053] The secondary battery includes a positive electrode and an electrolyte; the positive electrode includes a positive electrode active material; the electrolyte includes a boron-containing salt, and the boron-containing salt includes one or more of the compounds shown in Formula 1, Formula 2, and Formula 3.

[0054]

[0055] In Equations 1 to 3, M is independently selected from Li, Na or K; the mass percentage of boron salt relative to the total mass of the electrolyte is denoted as A%; the upper limit potential of the positive electrode active material relative to lithium metal is denoted as V1(V); the secondary battery satisfies: 0 < A / (V1-4.1) ≤ 4, and V1 > 4.1; optionally, 0 < A / (V1-4.1) ≤ 3.

[0056] Although the mechanism is not entirely clear, the secondary battery described in this application can simultaneously improve the cycle life, safety performance, and capacity of secondary batteries; the inventors speculate that the reaction principle of this application is as follows:

[0057] Boron-containing salts, as salts with boron atoms as the central atom, can coordinate with alkoxy groups, ortho-diols, ortho-hydroxy groups, and carboxylic acids to form anionic complexes. These anionic complexes primarily exhibit large π-conjugated structures, with a relatively dispersed negative charge distribution of the central ion. The charge is delocalized, and the large radius of the anion makes it difficult for it to form strong ion pairs with metal ions such as lithium, sodium, or potassium ions in organic solvents, resulting in relatively good solubility. The more electron-withdrawing groups in the anionic complex, the more stable the anionic structure, and the higher the solubility of metal ions in the electrolyte, which is beneficial for improving the electrolyte conductivity. Furthermore, boron-containing salts can form a high-performance cathode-electrolyte interphase (CEI) film on the surface of the positive electrode active material. The CEI film is insoluble in organic solvents and can exist stably in organic electrolytes, effectively reducing the embedding of solvent molecules into the positive electrode active material. This ensures the structural stability of the positive electrode active material and thus improves the cycle life of the secondary battery. Furthermore, 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.

[0058] Taking lithium as an example (M being the element), boron-containing lithium salts can include one or more of lithium tetrafluoroborate (LiBF4), lithium bis(C2O4)2 (LiBOB), and lithium bis(FOB)2 (LiBC2O4F2). Further, boron-containing lithium salts can include compositions of lithium tetrafluoroborate (LiBF4), lithium bis(C2O4)2 (LiBOB), and lithium bis(FOB)2 (LiBC2O4F2).

[0059] Either the compound shown in Formula 1 or the compound shown in Formula 3 has a passivating effect on the positive current collector in the positive electrode sheet, which can reduce the risk of side reactions and corrosion of the positive current collector, and improve the structural stability of the positive electrode sheet. Furthermore, the electrolyte containing either the compound shown in Formula 1 or the compound shown in Formula 3 is less likely to produce acidic substances, which can further reduce the risk of corrosion of the positive current collector, thus providing good protection for the overall positive electrode sheet, ensuring the cycle stability of the secondary battery, and improving the cycle life of the secondary battery. Either the compound shown in Formula 1 or the compound shown in Formula 3 has good compatibility with the positive electrode active material, which is beneficial to the migration of lithium ions, thereby ensuring the capacity utilization of the secondary battery.

[0060] When the compound shown in Formula 2 is used in combination with organic solvents such as carbonate solvents or additives in the electrolyte, the system formed by the compound shown in Formula 2 has a relatively low viscosity, which is conducive to the release of metal ions, thereby improving the conductivity in the electrolyte. The CEI film formed by the compound shown in Formula 2 has a more uniform thickness and better kinetic activity, and a lower charge transfer impedance in the secondary battery. This can significantly improve the low-temperature performance and cycle DCR growth rate of the secondary battery, thereby improving the kinetic performance of lithium ion migration on the cathode surface of the secondary battery. The CEI film is not prone to thermal decomposition and its performance is relatively stable at high temperatures, so it can significantly improve the high-temperature performance of the secondary battery.

[0061] In some embodiments, the compounds shown in Formulas 1 to 3 are used together, and the CEI film formed by the three has a larger composition and a more stable structure. Furthermore, while ensuring structural stability, the CEI film can provide good protection for the positive electrode active material.

[0062] In this embodiment, the secondary battery satisfies the range of the above formula. Under high voltage, the boron-containing salt can form a dense and stable CEI film on the surface of the positive electrode active material, providing good protection for the positive electrode active material. This reduces the risk of side reactions occurring when the positive electrode active material and the electrolyte come into contact, thus making it less likely for the transition metals in the positive electrode active material to undergo redox reactions and for cation mixing to occur. This facilitates the intercalation and deintercalation of metal ions, ensuring the capacity utilization and structural stability of the positive electrode active material, thereby improving the cycle capacity retention rate of the secondary battery. The positive electrode active material and the electrolyte are less likely to undergo side reactions producing byproducts such as oxygen. During charge-discharge cycles, the voltage within the secondary battery remains normal, ensuring the safety performance of the secondary battery.

[0063] When the secondary battery in this application is a lithium-ion battery, the boron-containing salt can be selected as a boron-containing lithium salt. For example, the boron-containing lithium salt can include one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalate-borate) (LiB(C2O4)2, abbreviated as LiBOB), and lithium bis(oxalate-borate) (LiBC2O4F2, abbreviated as LiDFOB). Further, the boron-containing lithium salt includes a combination of lithium tetrafluoroborate (LiBF4), lithium bis(oxalate-borate) (LiBOB), and lithium bis(oxalate-borate) (LiDFOB). Of course, when the secondary battery is a lithium-ion battery, the boron-containing salt can also be selected as a boron-containing sodium salt, boron-containing potassium salt, etc. When the secondary battery is a sodium-ion battery, the boron-containing salt can be selected as a sodium salt, and of course, it can also be selected as a boron-containing lithium salt, boron-containing potassium salt, etc. Optionally, 0 < A / (V1-4.1) ≤ 3; exemplaryly, 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.

[0064] In some implementations, V1 > 4.1.

[0065] The positive electrode active material has a relatively high upper limit potential V1 relative to lithium metal, making it suitable for charging and discharging in high-voltage systems. Furthermore, the combined use of the aforementioned positive electrode active material and boron-containing salts allows the boron-containing salts to adequately protect the surface of the positive electrode active material, thereby ensuring its structural stability under high-voltage conditions. Optionally, 4.1 ≤ V1 ≤ 4.6; for example, the upper limit potential V1 (V) of the positive electrode active material relative to lithium metal can be 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, or 4.6V; or within any two of the above values.

[0066] The upper limit potential V1 of the positive electrode active material relative to lithium metal can be considered as the difference between the potentials of the positive electrode active material and lithium metal. The upper limit potential V1 of the positive electrode active material can be determined using test methods and instruments known in the art. The specific test procedure is as follows: The positive electrode active material powder is mixed with SP and PVDF in a 90:5:5 ratio, stirred, and uniformly coated onto an Al foil with a thickness of 13 micrometers. Then, it is compacted to obtain the positive electrode film, with a compaction density of 3.3-3.6 g / cm³. 3The process involves controlling the humidity to <10%, followed by drying the positive electrode film in an oven at 100℃ for 2 hours. Before assembling the coin cell, the positive electrode film is vacuum-dried at 105℃ / 4h / -0.09Mpa. The prepared positive electrode film is then assembled into a CR2430 semi-coin cell (film-lithium sheet) in a PRS340 / 11-119-11 Braun glove box, using 1M LiPF6 as the electrolyte. EC / EMC / DEC = 3 / 5 / 2. The assembled semi-button batteries were left to stand for 3 hours. The test was conducted at 25°C. Lithium was first delithiated at 0.5C in the voltage range of 2.8-V1, and then lithium was intercalated at 0.1C in the voltage range of V1-2.8 to obtain the charge and discharge coin capacity. The coin capacity was then divided by the mass of the positive electrode active material to obtain the charge and discharge specific capacity. The upper limit potential V1 of the positive electrode active material relative to metallic lithium is the upper limit potential when the discharge specific capacity is 150-220mAh / g.

[0067] In some implementations, 0 < A ≤ 2.

[0068] When boron-containing salts are within the aforementioned range, they can form a dense and stable CEI film on the surface of the positive electrode active material, thereby providing sufficient protection for the positive electrode active material, improving its structural stability, and ensuring the cycle stability of the secondary battery. Furthermore, boron-containing salts can also form an SEI film on the surface of the negative electrode active material, enhancing its protective effect. Optionally, 0 < A ≤ 1.5; exemplaryly, the mass percentage A% of the boron-containing salt can 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 any range consisting of two of the above values.

[0069] In some embodiments, the secondary battery further includes a negative electrode sheet comprising a negative electrode active material, the upper limit potential of which relative to lithium metal is denoted as V2 (V); the secondary battery also satisfies 0 < A × V2 ≤ 1.2.

[0070] Boron-containing salts have relatively high reduction potentials and can also participate in anodic film formation to form a dense and stable SEI film. The SEI film can form sufficient protection on the surface of the negative electrode active material, reducing the risk of side reactions occurring when the negative electrode active material and the electrolyte come into contact. This can alleviate the risk of organic solvents in the electrolyte being reduced and further improve the cycle stability of the secondary battery.

[0071] As the lithium insertion depth of the negative electrode active material increases, the activity of the negative electrode active material becomes stronger, and the electrolyte is more easily reduced on the surface of the negative electrode active material. In view of this, when the above relationship is satisfied, the mass percentage of boron salt in the secondary battery of this application increases with the upper limit potential of the negative electrode active material, which can form a denser and more stable SEI film on the surface of the more active negative electrode active material, strengthen the protection of the negative electrode active material, improve the cycle stability of the secondary battery, and thus improve the cycle life of the secondary battery.

[0072] In some implementations, 0.02 ≤ V2 ≤ 2.5; alternatively, 0.1 ≤ V2 ≤ 2.

[0073] The aforementioned negative electrode active material is suitable for charging and discharging under high voltage systems; and the combined use of the aforementioned negative electrode active material and boron-containing salts allows the boron-containing salts to fully protect the surface of the positive electrode active material, thereby ensuring the structural stability of the positive electrode active material under high voltage systems.

[0074] The upper limit potential V2 of the negative electrode active material relative to lithium metal can be considered as the difference between the potentials of the negative electrode active material and lithium metal. The upper limit potential V2 of the negative electrode active material can be determined using test methods and instruments known in the art. The specific test procedure is as follows: The negative electrode active material powder is mixed with SP and PVDF in a formulation of 91.6:1.8:6.6, stirred, and uniformly coated onto a Cu foil with a thickness of 8 micrometers. Then, it is compacted to form a negative electrode film, with a compaction density of 1.4-1.6 g / cm³. 3 The process involves controlling the humidity to <10%, followed by drying the negative electrode film in an oven at 100℃ for 2 hours. Before assembling the coin cell, the negative electrode film is vacuum dried at 105℃ / 4h / -0.09Mpa. The prepared negative electrode film is then assembled into a CR2430 semi-coin cell (negative electrode film-lithium sheet) in a PRS340 / 11-119-11 Braun glove box. The electrolyte used is 1M LiPF6EC / EMC / DEC = 3 / 5 / 2. The assembled semi-coin cells are allowed to stand for 5 hours. Testing is conducted at 25℃ using the following conditions: 0.05C to 0.005V, 50uA DC to 0.005V, rest for 5 minutes, 10uA DC to 0.005V, rest for 5 minutes, and 0.1C CC to... V2, rest for 5 minutes. Perform charge / discharge lithium insertion / extraction to obtain the charge / discharge coin capacity. Then divide the coin capacity by the mass of the negative electrode active material to obtain the charge / discharge specific capacity. The upper limit potential V2 of the negative electrode active material relative to the lithium metal sheet is the upper limit potential when the charge specific capacity is 330-380 mAh / g.

[0075] In some implementations, M can be selected from Li or Na, which can increase the lithium-ion or sodium-ion concentration in a secondary battery system.

[0076] For example, the compounds shown in Formula 1 include lithium difluorooxalate borate and / or sodium difluorooxalate borate.

[0077] For example, the compounds shown in Formula 2 include lithium tetrafluoroborate and / or sodium tetrafluoroborate.

[0078] For example, the compounds shown in Formula 3 include lithium bis(oxalatoborate) and / or sodium bis(oxalatoborate).

[0079] As an example, boron-containing lithium salts include one or more of lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium difluorooxalate borate (LiBOB). When used in combination, these three compounds can form a CEI film on the surface of the positive electrode active material. The CEI film effectively reduces the decomposition of the electrolyte by the positive electrode active material. They can also form an SEI film on the surface of the negative electrode active material. The SEI film improves lithium-ion transport and reduces the continuous reduction and decomposition of the electrolyte, thereby improving the cycle stability of the secondary battery.

[0080] In some embodiments, the electrolyte may further include one or more combinations of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), lithium tetrafluorooxalate phosphate (LiTFOP), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium difluorophosphate (NaPO2F2), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium fluorosulfonate (NaFSO3). The combined use of the above lithium salts and boron-containing salts can improve the conductivity of the electrolyte.

[0081] As an example, the electrolyte can be lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium di(oxalate borate) borate (LiBOB), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium difluorophosphate (NaPO2F2), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium fluorosulfonate (NaFSO3).

[0082] In some embodiments, the electrolyte may also include a Lewis base solvent. Lewis bases can promote the dissociation of boron-containing salts, facilitating the release of lithium ions and thereby increasing the conductivity of the electrolyte. As an example, Lewis base solvents include compounds containing one or more groups selected from halogen atoms, alkoxy groups, olefins, and aromatic hydrocarbons; exemplarily, Lewis bases may include trimethyl phosphate, etc.

[0083] In some embodiments, the organic solvent may also include one or more combinations of ethylene carbonate EC, propylene carbonate PC, methyl ethyl 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.

[0084] In some embodiments, the electrolyte may further include film-forming additives, such as negative electrode film-forming additives; negative electrode film-forming additives include one or more of carbonate additives, sulfate additives, sulfite additives, phosphate additives, and polynitrile additives. Negative electrode film-forming additives can form an SEI film on the surface of the negative electrode active material, and the combined formation of multiple components on the surface of the SEI film can enrich the film layer structure of the SEI film and improve its structural stability. Further, the negative electrode film-forming additive includes at least two of carbonate additives, sulfate additives, sulfite additives, phosphate additives, and polynitrile additives; the SEI film formed by this additive has a richer composition and higher structural stability. Optionally, based on the total mass of the electrolyte, the mass percentage d of the film-forming additive satisfies: 0.5% ≤ d ≤ 10%; optionally, 1% ≤ d ≤ 6%.

[0085] As an example, carbonate additives include cyclic carbonate additives and / or linear carbonate additives. Further, the cyclic carbonate additives include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The linear carbonate additives include one or more of ethyl allyl carbonate (AEC), diphenyl carbonate (DPC), methyl allyl carbonate, and polycarbonate (PC).

[0086] As an example, sulfate ester additives include cyclic sulfonate additives and / or sulfate hydrocarbon ester additives. Further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro-1,3-propanesulfonate lactone (FPS). The sulfate hydrocarbon ester additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS).

[0087] As an example, sulfite additives include vinyl sulfite ES and / or vinyl vinyl sulfite VES.

[0088] As an example, phosphate ester additives include one or more of tris(trimethylsilane) phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate.

[0089] As an example, polynitrile additives include one or more of adiponitrile, toluene diisocyanate, and hexamethylene diisocyanate.

[0090] The electrolyte of this application can be prepared using methods conventional in the art. For example, the additives, solvent, and electrolyte salt can be mixed evenly to obtain the electrolyte. There are no particular restrictions on the order in which the materials are added; for example, the additives and electrolyte salt can be added to the non-aqueous solvent and mixed evenly to obtain a non-aqueous electrolyte.

[0091] In this application, the components and their contents in the electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0092] It should be noted that during the electrolyte testing of this application, freshly prepared electrolyte can be used directly, or electrolyte can be obtained from a secondary battery. An exemplary method for obtaining electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cutoff voltage (for safety, the battery is generally left fully discharged), followed by centrifugation. A suitable amount of the centrifuged liquid is then taken as the non-aqueous electrolyte. Alternatively, the non-aqueous electrolyte can be obtained directly from the secondary battery's filling port.

[0093] [Positive electrode plate]

[0094] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0095] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may 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 their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0096] In some embodiments, the positive electrode active material includes LiNi. x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b- c O2, wherein M and N are each independently selected from any one of 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. When the positive electrode active material is used in conjunction with boron-containing lithium salts, the B atoms in the boron-containing lithium salts readily combine with the O atoms 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 within the bulk phase of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains appropriate amounts of lithium tetrafluoroborate and lithium difluorooxalate borate, low-cobalt or cobalt-free cathode active materials exhibit significantly improved lithium-ion diffusion rates. Lithium ions within the bulk phase of the low-cobalt or cobalt-free cathode active material can be promptly replenished to the surface, preventing excessive delithiation and thus stabilizing the crystal structure. Because the crystal structure of low-cobalt or cobalt-free cathode active materials is more stable, the probability of instability in the structural, chemical, or electrochemical properties of the cathode active material due to excessive delithiation on its surface is greatly reduced. For example, this can lead to irreversible distortion and increased lattice defects.

[0097] LiNi xCo y Mn z M 1-x-y-z O2 or LiNi a Co b Al c N 1-a-b-c O2 can be prepared according to conventional methods in the art. An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M-element precursor, and an N-element precursor are mixed and then sintered. The sintering atmosphere can 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% to 100%. The sintering temperature and sintering time can be adjusted according to actual conditions.

[0098] As examples, lithium sources include, but are not limited to, at least one of lithium oxide (Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate (LiH₂PO₄), lithium acetate (CH₃COOLi), lithium hydroxide (LiOH), lithium carbonate (Li₂CO₃), and lithium nitrate (LiNO₃). As examples, nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As examples, cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As examples, manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As examples, aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As examples, precursors of element M include, but are not limited to, at least one of oxides, nitrate compounds, carbonate compounds, hydroxides, and acetate compounds of element M. As an example, precursors of nitrogen 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 bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0099] In some implementations, based on the total mass of the positive electrode film, 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 layered material containing O2 has a mass percentage of 80% to 99%. For example, the molecular formula LiNi x Co y Mn z M 1-x-y-z O2 or LiNi a Co b Alc N 1-a-b-c The mass percentage of the O2 layered material can be any range consisting of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher. Optionally, 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 layered O2 is 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97%, or 95% to 97%.

[0100] In some embodiments, the positive electrode active material includes LiN ix Co y M 1-x-y The compound, in which M represents one or more of Mn, Fe, Mg, Al, Cu, and Ti, x ≥ 0.5, 0 ≤ y ≤ 0.2, x + y ≤ 1. The lithium-deficient state on the surface of the above-mentioned positive electrode active material under high voltage easily leads to phase transitions, Li / Ni mixing, and oxygen release on the surface of the positive electrode active material. Boron-containing salts can passivate the surface of the positive electrode active material and can react with metal cations such as Al. 3+ and Ni 2+ This combination can improve the mixing of Li / Ni and passivate aluminum foil.

[0101] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent; as an example, the positive electrode conductive agent includes 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 is less than 5% based on the total mass of the positive electrode film layer.

[0102] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode film layer.

[0103] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of the metal material include one or more combinations selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0104] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0105] [Negative electrode plate]

[0106] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0107] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0108] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and lithium-aluminum alloys, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0109] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more combinations selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (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 is less than 5% based on the total mass of the negative electrode film layer.

[0110] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative 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 negative electrode conductive agent is less than 5% based on the total mass of the negative electrode film layer.

[0111] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of other additives is less than 2% based on the total mass of the negative electrode film.

[0112] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil or copper alloy foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more combinations selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymeric material substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0113] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0114] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also includes a protective layer covering the surface of the negative electrode film layer.

[0115] [Isolation membrane]

[0116] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0117] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0118] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0119] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0120] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0121] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. FIG. 1 This is an example of a square-structured secondary battery 5.

[0122] In some embodiments, such as FIG. 1 and FIG. 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0123] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0124] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0125] FIG. 3 This is a schematic diagram of battery module 4 as an example. FIG. 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0126] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0127] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0128] FIG. 4 and FIG. 5 This is a schematic diagram of battery pack 1 as an example. FIG. 4 and FIG. 5As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0129] Power consuming device

[0130] Secondly, this application provides an electrical device, which includes at least one of the secondary battery, battery module, and battery pack described in this application. The secondary battery, battery module, and battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0131] Electrical devices can be equipped with secondary batteries, battery modules, or battery packs depending on their usage requirements.

[0132] FIG. 6 This is a schematic diagram of an example electrical device. The electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or a battery module can be used.

[0133] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0134] Example

[0135] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0136] Example 1

[0137] 1. Preparation of positive electrode sheet

[0138] Aluminum foil with a thickness of 13μm was used as the positive electrode current collector.

[0139] LiNi, the positive electrode active material 0.65 Co 0.07 Mn 0.28 Conductive agent carbon black and binder polyvinylidene fluoride (PVDF) are mixed in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0140] 2. Preparation of negative electrode sheet

[0141] A copper foil with a thickness of 8μm was used as the negative electrode current collector.

[0142] 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 (Super P) are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0143] 3. Separating membrane

[0144] Porous polyethylene (PE) membrane is used as the separator.

[0145] 4. Preparation of electrolyte

[0146] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain the electrolyte solvent. Additives are 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.

[0147] 5. Preparation of secondary batteries

[0148] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0149] Example 2

[0150] Examples 2-1 to 2-5

[0151] The secondary battery was prepared in a similar manner to that in Example 1, except that the mass percentage A of the "boron salt" was adjusted. Specific parameters are detailed in Table 1.

[0152] Comparative Example

[0153] Comparative Example 1 and Comparative Example 2

[0154] The secondary battery was prepared in a similar manner to that in Example 1, except that the mass percentage A1 of the "boron salt additive" was adjusted. Specific parameters are detailed in Table 1.

[0155] Example 3

[0156] Examples 3-1 to 3-3

[0157] The secondary battery was prepared in a similar manner to that in Example 1, except that the upper limit potential V1 of the "positive electrode active material" was adjusted. The specific parameters are detailed in Table 1.

[0158] Example 4

[0159] Examples 4-1 to 4-5

[0160] The secondary battery was prepared in a similar manner to that in Example 1, except that the upper limit potential V2 of the "negative electrode active material" was adjusted. The specific parameters are detailed in Table 1.

[0161] Example 5

[0162] Example 5-1

[0163] The secondary battery was prepared in a similar manner to that in Example 1, except that the type of "positive electrode active material" was adjusted. Specific parameters are detailed in Table 1.

[0164] Example 5-2

[0165] The secondary battery was prepared in a similar manner to that in Example 1, except that the type of "negative electrode active material" was adjusted. Specific parameters are detailed in Table 1.

[0166] Table 1

[0167]

[0168] Test section

[0169] 1. Test method for the upper limit potential V1 of positive electrode active material relative to metallic lithium

[0170] The positive electrode active material powder was mixed with SP and PVDF in a ratio of 90:5:5, and then uniformly coated onto an Al foil with a thickness of 13 micrometers. The mixture was then compacted to obtain the positive electrode film, with a compaction density of 3.3-3.6 g / cm³. 3The process involves controlling the humidity to <10%, followed by drying the positive electrode film in an oven at 100℃ for 2 hours. Before assembling the coin cell, the positive electrode film is vacuum-dried at 105℃ / 4h / -0.09Mpa. The prepared positive electrode film is then assembled into a CR2430 semi-coin cell (film-lithium sheet) in a PRS340 / 11-119-11 Braun glove box. The electrolyte used is 1M... The LiPF6EC / EMC / DEC = 3 / 5 / 2, assembled semi-coin cells were left to stand for 3 hours, and the test was carried out at 25℃. The lithium was first delithiated by charging at 0.5C in the voltage range of 2.8-V1, and then lithium was intercalated by discharging at 0.1C in the voltage range of V1-2.8 to obtain the charge and discharge coin capacity. The coin capacity was then divided by the mass of the positive electrode active material to obtain the charge and discharge specific capacity. The upper limit potential V1 of the positive electrode active material relative to metallic lithium is the upper limit potential when the discharge specific capacity is 150-220mAh / g.

[0171] 2. Test method for the upper limit potential V2 of negative electrode active material relative to metallic lithium

[0172] The negative electrode active material powder was mixed with SP and PVDF in a ratio of 91.6:1.8:6.6, and then uniformly coated onto a Cu foil with a thickness of 8 micrometers. The mixture was then compacted to form a negative electrode film with a compaction density of 1.4-1.6 g / cm³. 3 The process involves controlling the humidity to <10%, followed by drying the negative electrode film in an oven at 100℃ for 2 hours. Before assembling the coin cell, the negative electrode film is vacuum dried at 105℃ / 4h / -0.09Mpa. The prepared negative electrode film is then assembled into a CR2430 semi-coin cell (negative electrode film-lithium sheet) in a PRS340 / 11-119-11 Braun glove box. The electrolyte used is 1M LiPF6 EC / EMC / DEC = 3 / 5 / 2. The assembled semi-coin cells are allowed to stand for 5 hours. Testing is conducted at 25℃ using the following conditions: 0.05C to 0.005V, 50uA DC to 0.005V, rest for 5 minutes, 10uA DC to 0.005V, rest for 5 minutes, 0.1CCC to V2, rest... Perform a charge / discharge process for 5 minutes to obtain the charge / discharge coin capacity. Then, divide the coin capacity by the mass of the negative electrode active material to obtain the charge / discharge specific capacity. The upper limit potential V2 of the negative electrode active material relative to the lithium metal sheet is the upper limit potential when the charge specific capacity is 330-380 mAh / g.

[0173] 3. Performance testing of secondary batteries

[0174] 3.1 Determination of cycle life

[0175] The secondary battery was charged at 25°C with a constant current of 0.5C to 4.35V, then charged at a constant voltage of 4.33V to a current of 0.05C, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. Using the initial discharge capacity as 100%, the capacity retention rate after 500 cycles was calculated. Capacity retention rate (%) after 500 cycles = Discharge capacity of the 500th cycle / Initial discharge capacity × 100%.

[0176] 3.2 Performance test of DCR growth rate of lithium-ion battery at 25℃ up to 500 cycles

[0177] DCR test at 25℃ before cycling: At 25℃, the freshly prepared cell was charged to 4.35V at 0.5C, and then charged to 0.05C at a constant voltage. At this time, the voltage is V1. Then, it was discharged at 4C for 30s. The voltage at the end of the discharge is V2. The point was sampled at 0.1s. The discharge DCR1 of the cell at 100% SOC before cycling is (V1-V2) / I.

[0178] DCR test at 25℃ after cycling: At 25℃, the cell after cycling at 25℃ was charged to 4.35V at 0.5C, and then charged to 0.05C at constant voltage, at which point the voltage was V3; then discharged at 4C for 30s, the voltage at the end of the discharge was V4, and the point was sampled at 0.1s. The discharge DCR2 of the cell at 100% SOC after cycling is (V3-V4) / I.

[0179] DCR growth rate: The DCR growth rate is (DCR2 – DCR1) / DCR1 * 100%

[0180] Test Results

[0181] The role of this application in improving the cycle life, safety performance, and capacity of secondary batteries is shown in Table 2.

[0182] Table 2

[0183] Item 25 °C cycle capacity retention rate @ 500 cycles 25 °C cycle DCR growth rate @ 500 cycles Example 1 92.0％ 50.0％ Example 2-1 88.0％ 80.0％ Example 2-2 90.0％ 62.0％ Example 2-3 91.0％ 55.0％ Example 2-4 93.0％ 45.0％ Example 2-5 87.0％ 85.0％ Comparative Example 1 80.0％ 100.0％ Comparative Example 2 82.0％ 95.0％ Example 3-1 92.0％ 46.0％ Example 3-2 91.0％ 55.0％ Example 3-3 86.0％ 80.0％ Example 4-1 90.0％ 60.0％ Example 4-2 89.0％ 62.0％ Example 4-3 89.5％ 60.0％ Example 4-4 90.5％ 58.0％ Example 4-5 86.0％ 88.0％ Example 5-1 90.0％ 60.0％ Example 5-2 89.0％ 65.0％

[0184] As shown in Table 2, in Comparative Example 1 without the addition of boron salt, the positive electrode active material is prone to side reactions with the electrolyte, which damages the positive electrode active material and results in poor cycle life of the secondary battery; moreover, its interfacial impedance may be high. Although Comparative Example 2 added boron salt, the relationship between the mass percentage of boron salt and the upper limit potential of the positive electrode active material is: A / (V1-4.1)>4. This means that although the boron salt can protect the surface of the positive electrode active material, the CEI film formed by the boron salt has high impedance, and the boron salt system still has the risk of decomposition, leading to system instability.

[0185] In Examples 1 to 2-5, the mass percentage of boron salt and the upper limit potential of the positive electrode active material were adjusted to satisfy 0 < A / (V1-4.1) ≤ 4, and especially 0 < A / (V1-4.1) ≤ 3. This allows the boron salt to form a dense and stable CEI film on the surface of the positive electrode active material, providing good protection for the positive electrode active material. This makes it less likely for the transition metals in the positive electrode active material to undergo redox reactions, and less likely for cation mixing to occur in the positive electrode active material, which is conducive to the intercalation and deintercalation of metal ions, thereby improving the cycle life of the secondary battery. Furthermore, the CEI film formed by the boron salt is dense and uniform in thickness, and has a low interfacial impedance, which is beneficial to improving the kinetic performance of the secondary battery.

[0186] Examples 3-1 to 3-3 show that by adjusting the upper limit potential V1 of the positive electrode active material, especially when 4.1 < V1 ≤ 4.6, the cycle life and DCR growth rate of the secondary battery can be significantly improved.

[0187] Examples 4-1 to 4-5 show that by adjusting the upper limit potential V2 of the negative electrode active material, especially when 0 < A × V2 ≤ 1.2 and 0 < A × V2 ≤ 1, the cycle life and DCR growth rate of the secondary battery can be significantly improved.

[0188] Examples 5-1 and 5-2 adjusted the types of positive and negative active materials, respectively. The results showed that when 0 < A / (V1-4.1) ≤ 4, boron-containing lithium salts can effectively protect both positive and negative active materials, thereby improving the cycle life and DCR growth rate of the secondary battery.

[0189] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, comprising: Positive electrode sheet, which includes positive electrode active material; as well as An electrolyte comprising a boron-containing salt, said boron-containing salt comprising one or more of the compounds shown in Formula 1, Formula 2, and Formula 3. Formula 1 Formula 2 Formula 3, In Equations 1 to 3, M is independently selected from Li, Na, or K; The mass percentage of the boron salt relative to the total mass of the electrolyte is denoted as A; the upper limit potential of the positive electrode active material relative to lithium metal is denoted as V1, where V1 is in V; The secondary battery satisfies: 0 < A / (V1-4.1) ≤ 4, and V1 > 4.

1. The secondary battery also includes a negative electrode sheet, which includes a negative electrode active material. The upper limit potential of the negative electrode active material relative to lithium metal is denoted as V2, where V2 is in V, and 0.1 ≤ V2 ≤ 2. The secondary battery satisfies: 0 < A × V2 ≤ 1.

2. The specific testing process for V1 is as follows: The positive electrode active material powder, SP, and PVDF are mixed and stirred in a 90:5:5 ratio, then uniformly coated onto an Al foil with a thickness of 13 micrometers. The mixture is then compacted to obtain the positive electrode film, with a compaction density of 3.3-3.6 g / cm³. 3 The process involves controlling the humidity to <10%, then drying the positive electrode film in an oven at 100℃ for 2 hours, followed by vacuum drying at 105℃ and -0.09Mpa for 4 hours. The prepared positive electrode film is then assembled into a CR2430 semi-button battery (film-lithium sheet) in a glove box, using 1M LiPF6 EC / EMC / DEC=3 / 5 / 2 electrolyte. The assembled semi-button battery is left to stand for 3 hours, and testing is conducted at 25℃. Lithium removal is performed at 0.5C in the voltage range of 2.8V-V1, followed by lithium insertion at 0.1C in the voltage range of V1-2.8V. The charging and discharging capacities are obtained. The discharge capacity is then divided by the mass of the positive electrode active material to obtain the discharge specific capacity. The upper limit potential V1 of the positive electrode active material relative to metallic lithium is the upper limit potential when the discharge specific capacity is 150-220mAh / g. The specific testing process for V2 is as follows: The negative electrode active material powder, SP, and PVDF are mixed and stirred according to a formula of 91.6:1.8:6.6, and then uniformly coated onto an 8-micron thick Cu foil. The mixture is then compacted to form a negative electrode film, with a compaction density of 1.4-1.6 g / cm³. 3 The process involves controlling the humidity to <10%, followed by drying the negative electrode film in an oven at 100℃ for 2 hours, and then vacuum drying it at 105℃ and -0.09 MPa for 4 hours. Finally, the prepared negative electrode film is assembled into a CR2430 semi-coin cell (negative electrode film-lithium sheet) in a glove box, using 1M LiPF6 as the electrolyte. With EC / EMC / DEC = 3 / 5 / 2, the assembled semi-button battery was left to stand for 5 hours. The test was conducted at 25°C. The battery was charged with a 0.05C current to a voltage of 0.005V, then maintained at a DC current of 50uA to 0.005V for 5 minutes. The battery was then charged with a DC current of 10uA to 0.005V for 5 minutes. The battery was then charged with a constant current of 0.1C to V2 and left to stand for 5 minutes. The battery was then charged and discharged to extract lithium, and the charging and discharging capacities were obtained. The charging capacity was then divided by the mass of the negative electrode active material to obtain the specific capacity. The upper limit potential V2 of the negative electrode active material relative to the lithium metal sheet is the upper limit potential when the specific capacity is 330-380mAh / g.

2. The secondary battery according to claim 1, wherein, 4.1＜V1≤4.6。 3. The secondary battery according to claim 1 or 2, The secondary battery further satisfies 0 < A × V² ≤ 1.

4. The secondary battery according to claim 3, wherein, The negative electrode active material includes at least one selected from artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

5. The secondary battery according to claim 1, wherein, 0＜A≤2。 6. The secondary battery according to claim 1, wherein, The boron-containing salts include the compounds shown in Formula 1, Formula 2, and Formula 3; The compound represented by Formula 1 includes 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 compounds represented by Formula 3 include lithium bis(oxalato)borate and / or sodium bis(oxalato)borate.

7. The secondary battery according to claim 1, wherein, The electrolyte also includes one or more of the following: lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorodioxarate phosphate (LiDFOP), lithium tetrafluorooxarate phosphate (LiTFOP), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium difluorophosphate (NaPO2F2), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium fluorosulfonate (NaFSO3).

8. The secondary battery according to claim 1, wherein, The electrolyte also includes film-forming additives, which include one or more of carbonate additives, sulfate additives, sulfite additives, phosphate additives, and polynitrile additives. Based on the total mass of the electrolyte, the mass percentage d of the film-forming additive satisfies: 0.5% ≤ d ≤ 10%.

9. The secondary battery according to claim 8, wherein, The carbonate additives include cyclic carbonate additives and / or linear carbonate additives; the cyclic carbonate additives include 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 additives include one or more of ethyl allyl carbonate (AEC), diphenyl carbonate (DPC), methyl allyl carbonate (PMC), and vinyl acetate (VA); and / or The sulfate ester additives include cyclic sulfonate additives and / or sulfate hydrocarbon ester additives; the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro-1,3-propanesulfonate lactone (FPS); and / or the sulfate hydrocarbon ester additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS); and / or The sulfite additives include vinyl sulfite ES and / or vinyl vinyl sulfite VES; and / or The phosphate ester additives include one or more of tris(trimethylsilane) phosphate, triallyl phosphate, trimethyl phosphate, and triethyl phosphate; and / or The polynitrile additives include one or more of toluene diisocyanate, hexamethylene diisocyanate, adiponitrile, and toluene diisocyanate.

10. The secondary battery according to claim 1, wherein, The electrolyte further includes an organic solvent, which includes one or more of the following: ethylene carbonate EC, propylene carbonate PC, methyl ethyl 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.

11. The secondary battery according to claim 1, wherein, The positive electrode active material includes LiN ix Co y M 1-x-y The compound is given by the formula, where M represents one or more of Mn, Fe, Mg, Al, Cu and Ti, x≥0.5, 0≤y≤0.2, and x+y≤1.

12. A battery module comprising a secondary battery as claimed in any one of claims 1 to 11.

13. A battery pack comprising the battery module as claimed in claim 12.

14. An electrical device comprising a secondary battery as claimed in any one of claims 1 to 11, a battery module as claimed in claim 12, or a battery pack as claimed in claim 13.

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