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

Abstract

The present application provides a secondary battery, a battery module, a battery pack, and a power consumption device, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the negative electrode sheet including a negative electrode film layer containing a negative electrode active material, the electrolyte including a boron-containing lithium salt, the boron-containing lithium salt being configured to form a solid electrolyte interfacial film on the surface of the negative electrode active material, where the discharge capacity of the secondary battery is A Ah, the mass of the electrolyte is Bg, and the mass percentage of the boron-containing lithium salt relative to the total mass of the electrolyte is C%, the secondary battery has a solid electrolyte interfacial film having a capacity of 1≦B / A≦5, 5×10 -6 The present application improves the film formation stability of the electrolyte on the negative electrode active material, ensures the structural stability of the negative electrode active material, improves the cycle performance of the secondary battery, and makes the electrolyte system relatively stable and not easily decomposed, thereby further improving the high temperature storage performance of the secondary battery.

Description

[Technical field]

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

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

[0003] As the range of applications of batteries becomes wider, the requirements for the performance of secondary batteries are becoming more stringent. For example, secondary batteries are required to have good cycle performance and long high-temperature storage life. Therefore, improvements in the cycle performance and high-temperature storage performance of secondary batteries are also a problem to be solved. Summary of the Invention

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

[0005] A first aspect of the present application is a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the negative electrode sheet comprising a negative electrode film layer containing a negative electrode active material, the electrolyte comprising a boron-containing lithium salt, the boron-containing lithium salt being configured to form a solid electrolyte interfacial film on a surface of the negative electrode active material, wherein the secondary battery has a discharge capacity of A Ah, a mass of the electrolyte is B g, and a mass percentage of the boron-containing lithium salt relative to the total mass of the electrolyte is C%, and the secondary battery has a capacity of 1≦B / A≦5, 5×10 -6 ≦B×C% / A≦0.25, selectable, 1×10 -3 To provide a secondary battery that satisfies ≦B×C% / A≦0.23.

[0006] As a result, the present application satisfies the following conditions: 1≦B / A≦5, 5×10 -6By controlling ≦B×C% / A≦0.25, the mass of the electrolyte, the discharge capacity of the secondary battery, and the mass percentage of the boron-containing lithium salt are coordinated with each other, and the film formation stability of the electrolyte on the negative electrode active material is improved, so that the structural stability of the negative electrode active material is ensured, the cycle performance of the secondary battery is improved, and the capacity of the secondary battery can be fully exerted. In addition, when the discharge capacity of the secondary battery and the mass percentage of the boron-containing lithium salt are coordinated with each other, the electrolyte system is relatively stable and not easily decomposed, and the high-temperature storage performance of the secondary battery can be further improved.

[0007] In any embodiment, the secondary battery satisfies at least one of conditions (1) to (3). (1) 0.01≦A≦1000, and optionally 50≦A≦550; (2) 0.01≦B≦3000, and optionally 0.5≦B≦1500; (3) 1×10 -4 %≦C%≦5%, and optionally 0.01%≦C≦3%.

[0008] In the above technical solution, the secondary battery can meet the needs of different situations, and when the mass percentage of the boron-containing lithium salt is within the above range, a stable SEI film can be formed on the surface of the negative electrode active material, which is also beneficial for ensuring the conductivity of the electrolyte.

[0009] In any embodiment, the electrolyte further comprises a negative electrode film-forming additive, the negative electrode film-forming additive comprises a first class additive and / or a second class additive, the first class additive comprises at least two of a carbonate ester additive, a sulfate ester additive, and a sulfite ester additive, and the second class additive comprises a fluorooxalic acid or phosphate skeleton lithium salt, and a sulfonimide skeleton lithium salt, where the mass percentage of the negative electrode film-forming additive relative to the total mass of the electrolyte is D%, the secondary battery further satisfies 0.1%≦(C+D)%≦20%.

[0010] In the above technical solution, both the negative electrode film-forming additive and the boron-containing lithium salt are components of the SEI film. By adjusting the common usage amount of the negative electrode film-forming additive and the boron-containing lithium salt, the SEI film formed has better film-forming uniformity, a more stable structure, and a reduced interface impedance, thereby improving the battery performance such as the cycle and high-temperature storage of the secondary battery.

[0011] In any embodiment, the secondary battery further satisfies at least one of conditions (4) to (7). (4) If the mass percentage of the carbonate additive to the total mass of the electrolyte is D1%, -4 %≦D1%≦5%, (5) When the mass percentage of the sulfate ester additive and the sulfite ester additive to the total mass of the electrolyte is D2%, 10 -4 %≦D2%≦5%, (6) When the mass percentage of the fluorooxalic acid or phosphate skeleton lithium salt relative to the total mass of the electrolyte is D3%, 10 -4 %≦D3%≦5%, (7) When the mass percentage of the sulfonimide-skeleton lithium salt relative to the total mass of the electrolyte is D4%, -4 %≦D4%≦5%.

[0012] In the present invention, by adjusting the mass percentage of each component in the negative electrode film-forming additive, a stable SEI film is formed on the surface of the negative electrode active material, and the SEI film has good chemical stability and thermal stability.

[0013] In any embodiment, the carbonate ester additive comprises a cyclic carbonate ester additive and / or a linear carbonate ester additive, optionally the cyclic carbonate ester additive comprises one or more of vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC; the linear carbonate ester additive comprises one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, and methyl allyl carbonate MAC, and polycarbonate VA; and / or the sulfate ester additive comprises a cyclic sulfonate ester additive and / or a hydrocarbyl sulfate ester additive, optionally the cyclic sulfonate ester additive comprises 1,3-propane sultone PS, propene sultone PES, 3-fluoro-1,3-propane sultone. and / or the hydrocarbon group sulfate ester additive comprises one or more of vinyl sulfate DTD, diethyl sulfate DES and dimethyl sulfate DMS; and / or the sulfite ester additive comprises ethylene sulfite ES and / or vinyl ethylene sulfite VES; and / or the fluorooxalic acid or phosphate backbone lithium salt comprises one or more of lithium tetrafluorooxalic acid phosphate LiTFOP, lithium difluorophosphate LiPO2F2 and lithium difluorobisoxalatophosphate LiBODFP; and / or the sulfonimide backbone lithium salt comprises one or more of lithium bisfluorosulfonylimide [LiN(SO2F)2], lithium bis(trifluoromethylsulfonyl)imide LiN(CF3SO2)2 and lithium bistrifluoromethanesulfonylimide LiTFSI.

[0014] The present application employs one or more of a carbonate ester additive, a sulfate ester additive, a sulfite ester additive, and a lithium fluorooxalyl phosphate, thereby enabling the formation of an SEI film on the surface of a negative electrode active material, and the formed SEI film has a rich composition and is more structurally stable.

[0015] In any embodiment, the coating weight of the negative electrode film layer is F mg / 1540.25 mm 2 The secondary battery is furthermore 2×10 -5 The relationship ≦B×(C+D)% / F≦1 is satisfied.

[0016] When the secondary battery of the present invention satisfies the above formula, the electrolyte reacts with the surface of the negative electrode active material to form a film, and the SEI film is uniformly formed on the surface of the negative electrode active material, thereby providing good protection for the negative electrode active material. In addition, the conductivity of the electrolyte is relatively high, and after lithium ions are desorbed from the positive electrode sheet, they are smoothly inserted into the negative electrode active material via the electrolyte, thereby ensuring the cycle performance of the secondary battery.

[0017] In any embodiment, 50≦F≦500.

[0018] When the coating weight of the negative electrode film layer of the present invention is within the above range, the capacity of the secondary battery can be ensured.

[0019] In any embodiment, the boron-containing lithium salt has the molecular formula LiBF a O b C c P d and in the molecular formula, 0≦a≦4, 0≦b≦8, 0≦c≦4, and 0≦d≦4.

[0020] The B atom of the present invention can be bonded to an oxygen-containing oxalic acid ligand, and the product after bonding has excellent thermal stability and is easy to form a high-performance SEI film on the surface of the negative electrode active material, ensuring the structural stability of the negative electrode active material and improving the cycle performance of the secondary battery. The boron-containing lithium salt has a large anion group, which promotes the dissociation of lithium ions and allows the electrolyte to have a higher lithium ion mobility, which is advantageous for improving the polarization and rate performance of the secondary battery.

[0021] In any embodiment, the boron-containing lithium salt includes one or more of lithium tetrafluoroborate LiBF4, lithium bis(oxalato)borate LiBOB, and lithium bis(fluorooxalato)borate LiDFOB.

[0022] By using lithium tetrafluoroborate LiBF4, lithium bis(oxalato)borate LiBOB, and lithium bis(fluorooxalato)borate LiDFOB in combination, the SEI film formed by the three has a large compositional component, the structure of the SEI film is more stable, and the stability of the structure is guaranteed, while ensuring a relatively small impedance value of the SEI film and ensuring the low-temperature performance of the secondary battery.

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

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

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

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

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

[0028] The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, when 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. Also, when minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are recited, ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "a-b" is represented by the abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, with "0-5" being an abbreviation for combinations of these numerical values. Furthermore, 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 specified, all the embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution, and such technical solution is considered to be included in the disclosure content of the present application.

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

[0031] Unless otherwise specified, the terms "comprise" and "include" used herein mean open-ended and may also be closed-ended. For example, the terms "comprise" and "include" may refer to further "comprising" or "including" other components not listed, or to "comprising" or "including" only the listed components.

[0032] In this application, unless otherwise stated, 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] As used herein, the terms "plurality" and "plurality" mean two or more than two.

[0034] With the application and popularization of secondary batteries, their overall performance has been attracting more and more attention. Non-aqueous electrolyte is one of the important factors that affect the performance of secondary batteries. At present, the most widely commercialized non-aqueous electrolyte system is a mixed carbonate ester solution of lithium hexafluorophosphate. In view of the poor thermal stability of lithium hexafluorophosphate in high temperature environments, the inventors added a boron-containing lithium salt to the electrolyte system, and the boron-containing lithium salt itself has a high thermal decomposition temperature, so it has excellent performance in secondary batteries. However, after extensive research, the inventors found that although the boron-containing lithium salt has a high thermal decomposition temperature, it has poor thermal stability in the electrolyte system, which deteriorates the high-temperature storage performance of secondary batteries, and the stability of the solid electrolyte interphase (SEI film) formed on the surface of the negative electrode active material is insufficient, making it impossible to effectively protect the negative electrode active material for a long period of time, and side reactions continue to occur between the negative electrode active material and the electrolyte in the later stage, which further deteriorates the cycle performance of the secondary battery.

[0035] The inventors of the present application have conducted extensive studies and have unexpectedly found that when the discharge capacity of the secondary battery, the mass of the electrolyte, and the mass percentage of the boron-containing lithium salt are within specific ranges, the secondary battery can achieve both good cycle performance and high-temperature storage performance. secondary battery

[0036] According to a first aspect, the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the negative electrode sheet comprising a negative electrode film layer containing a negative electrode active material, the electrolyte comprising a boron-containing lithium salt, the boron-containing lithium salt being disposed so as to form a solid electrolyte interfacial film on the surface of the negative electrode active material, wherein the secondary battery has a discharge capacity of A Ah, a mass of the electrolyte is B g, and a mass percentage of the boron-containing lithium salt relative to the total mass of the electrolyte is C%, and the secondary battery has a capacity of 1≦B / A≦5, 5×10 -6 The relationship B × C% / A is 0.25.

[0037] Although the mechanism is unclear, the inventors unexpectedly discovered that the present application can improve the cycle performance and high-temperature storage performance of a secondary battery by controlling the relationship between A, B and C% to satisfy the above range.

[0038] The discharge capacity A Ah of a secondary battery is the capacity value of the secondary battery measured by setting the corresponding current and voltage with a constant current charge / discharge tester at room temperature. Taking a ternary material as an example, the test method for the discharge capacity of a secondary battery is as follows. The secondary battery is placed in a constant current charge / discharge tester, the test temperature is 25°C, and the test flow is first to charge the completed battery to the upper limit voltage (the upper limit voltage of the ternary material is generally 4.2 to 4.5V) at a constant rate of 0.05C (0.05C is the current value at which all the electricity of the secondary battery is discharged in 20h), leave it for 30 minutes, and discharge it to the lower limit voltage (the lower limit voltage of the ternary material is generally 2.5V) at a rate of 0.05C, and the measured discharge capacity is the discharge capacity A Ah of the secondary battery.

[0039] The mass B g of the electrolyte is the mass of the electrolyte in the product secondary battery, and its measurement method is as follows: As an exemplary method for obtaining the electrolyte from the secondary battery, the secondary battery is discharged to the discharge cut-off voltage (for safety, the battery is generally fully discharged), and centrifuged, first, the liberated electrolyte is poured out from the injection hole and collected, and then the remaining bare core parts such as the electrode sheet separator are centrifuged, and the centrifugal collection of the electrolyte is repeated until the centrifugal rotation speed is greater than 10000 rpm and there is no obvious liquid after centrifugation, and the total amount of the collected electrolyte is the electrolyte mass g of the product core.

[0040] The electrolyte is an important component of lithium-ion batteries, and serves to transport lithium ions between the positive and negative electrode sheets of secondary batteries. Boron-containing lithium salts are lithium salts with a B atom as the central atom, and form anion complexes by coordinating with alkoxy groups, o-diphenols, o-hydroxy groups, carboxylic acids, etc. The anion complexes mainly have a delocalized π bond structure, in which the negative charge distribution of the central ion is relatively dispersed and the charge is delocalized. In addition, the anion radius is large, and the anion does not easily form an ion pair with a strong bond with lithium ions in an organic solvent. This can improve the lithium ion mobility of the electrolyte, which is advantageous for improving the polarization and rate performance of secondary batteries. In addition, the boron-containing lithium salt can form a high-performance solid electrolyte interface (SEI) film on the surface of the negative electrode active material in the above-mentioned period. The SEI film is insoluble in organic solvents and can exist stably in an organic electrolyte solution, effectively reducing the occurrence of solvent molecules in the electrolyte solution being reduced and decomposed at the interface of the negative electrode sheet to continue to form an unstable SEI, thereby ensuring the structural stability of the negative electrode active material and ultimately improving the cycle performance of the secondary battery.

[0041] The mass percentage C% of the boron-containing lithium salt can be measured according to a method known in the art, for example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0042] It should be noted that when testing the parameters of the electrolyte, the electrolyte can be obtained from the secondary battery. An exemplary method for obtaining the electrolyte from the secondary battery includes discharging the secondary battery to a discharge cut-off voltage (for safety reasons, the battery is generally fully discharged), centrifuging, and then obtaining an appropriate amount of the centrifugal liquid as the electrolyte. The electrolyte can also be obtained directly from the electrolyte inlet of the secondary battery.

[0043] This application is for 1≦B / A≦5, 5×10 -6 By controlling the ratio B×C% / A to 0.23, the mass of the electrolyte, the discharge capacity of the secondary battery, and the mass percentage of the boron-containing lithium salt are coordinated to improve the film formation stability of the electrolyte on the negative electrode active material, ensure the structural stability of the negative electrode active material, improve the cycle performance of the secondary battery, and allow the capacity of the secondary battery to be fully utilized. In addition, when the discharge capacity of the secondary battery and the mass percentage of the boron-containing lithium salt are coordinated to each other, the electrolyte system is relatively stable and less susceptible to decomposition, and the high-temperature storage performance of the secondary battery can be further improved. Optionally, 10 -4 ≦B×C% / A≦0.2. For example, 5×10 -6 ≦B×C% / A≦0.25, 5×10 -5 ≦B×C% / A≦0.25, 5×10 -4 ≦B×C% / A≦0.25, 3×10 -4 ≦B×C% / A≦0.25, 1×10 -4 ≦B×C% / A≦0.25, 1×10 -4 ≦B×C% / A≦0.2, 5×10 -3 ≦B×C% / A≦0.25, 5×10 -2 ≦B×C% / A≦0.25, 0.5≦B×C% / A≦0.25, 5×10 -6 ≦B×C% / A≦0.2, 5×10 -6 ≦B×C% / A≦0.1, 5×10 -6 ≦B×C% / A≦0.01, or 5×10 -6 ≦B×C% / A≦2×10 -3 And so on.

[0044] In some embodiments, 0.01≦A≦1000. When the discharge capacity of the secondary battery is in the above range, it can meet the use in different situations. Optionally, 50≦A≦550. Exemplarily, the discharge capacity A Ah of the secondary battery may be 0.01 Ah, 0.1 Ah, 0.2 Ah, 0.5 Ah, 1 Ah, 2 Ah, 5 Ah, 10 Ah, 15 Ah, 20 Ah, 50 Ah, 80 Ah, 100 Ah, 200 Ah, 300 Ah, 500 Ah, 600 Ah, 700 Ah, 800 Ah, or 1000 Ah, or may be a range consisting of any two of the above values.

[0045] In some embodiments, 0.01≦B≦3000. When the mass of the electrolyte is in the above range, it can meet the use in different industrial situations. Optionally, 0.5≦B≦1500. Exemplarily, the mass B g of the electrolyte can be 0.01g, 0.05g, 0.1g, 0.2g, 0.5g, 0.6g, 0.8g, 1g, 2g, 5g, 8g, 10g, 15g, 20g, 30g, 50g, 80g, 100g, 200g, 300g, 500g, 700g, 800g, 1000g, 1500g, 2000g, 2500g, 2800g or 3000g, or a range consisting of any two of the above values.

[0046] In some embodiments, 1×10 -4 %≦C%≦5%. When the mass percentage of the boron-containing lithium salt is in the above range, a stable SEI film can be formed on the surface of the negative electrode active material, which is also advantageous in ensuring the conductivity of the electrolyte. Optionally, 0.1%≦C≦3%. Exemplarily, the mass percentage C% of the boron-containing lithium salt is 1×10 -4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2%, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of the above values.

[0047] [Electrolyte]

[0048] The electrolyte serves to conduct metal ions between the positive electrode sheet and the negative electrode sheet, and may be any electrolyte used in secondary batteries known in the art. The electrolyte includes a lithium salt and an organic solvent.

[0049] In some embodiments, the lithium salt comprises a boron-containing lithium salt, the molecular formula of the boron-containing lithium salt being LiBF a O b C c P d and in the molecular formula, 0≦a≦4, 0≦b≦8, 0≦c≦4, and 0≦d≦4.

[0050] B atom can be bonded with oxygen-containing oxalic acid ligand, the product after bonding has excellent thermal stability, and is easy to form a high-performance SEI film on the surface of the negative electrode active material, ensuring the structural stability of the negative electrode active material, and further improving the cycle performance of the secondary battery. Of course, B atom can be bonded with halogen atom, especially fluorine atom, and because of the strong electron-attracting induction effect of fluorine atom, its high thermal stability and chemical stability, and the large-volume anion group, the dissociation of lithium ion is promoted, and the electrolyte has a higher lithium ion mobility, which is favorable for improving the polarization and rate performance of the secondary battery.

[0051] As an example, the boron-containing lithium salt includes one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorooxalatoborate (LiBC2O4F2, abbreviated as LiDFOB). Further, the boron-containing lithium salt includes the lithium tetrafluoroborate LiBF4, lithium bis(oxalato)borate (LiB(C2O4)2, abbreviated as LiBOB), and lithium difluorooxalatoborate (LiBC2O4F2, abbreviated as LiDFOB) compositions.

[0052] When lithium tetrafluoroborate (LiBF4) is used in conjunction with an organic solvent in the electrolyte, such as a carbonate-based solvent or an additive, the viscosity of the system made of lithium tetrafluoroborate is relatively low, which is favorable for the release of lithium ions, thereby improving the electrical conductivity in the electrolyte. The thickness of the SEI film formed by lithium tetrafluoroborate is relatively uniform, the kinetic activity is good, and the impedance of charge transfer in the secondary battery is small, which can significantly improve the low-temperature performance of the secondary battery; the SEI film is not easily thermally decomposed, and the performance at high temperatures is relatively stable, which can significantly improve the high-temperature performance of the secondary battery.

[0053] Either lithium bis(oxalate) borate LiBOB or lithium difluorooxalate borate LiDFOB has a passivation effect on the positive electrode current collector in the positive electrode sheet, and can reduce the risk of corroding the positive electrode current collector by a side reaction with the positive electrode current collector, thereby improving the structural stability of the positive electrode sheet. In addition, an electrolyte containing either lithium bis(oxalate) borate LiBOB or lithium difluorooxalate borate LiDFOB is less likely to generate acidic substances, and can further reduce the risk of corroding the positive electrode current collector. Lithium bis(oxalate) borate LiBOB and lithium difluorooxalate borate LiDFOB have good compatibility with the positive electrode active material, are favorable for the movement of lithium ions, and can form an effective SEI film on the surface of the negative electrode active material, thereby improving the protective performance for the negative electrode active material.

[0054] By using lithium tetrafluoroborate LiBF4, lithium bis(oxalato)borate LiBOB, and lithium difluorooxalatoborate LiDFOB in combination, the SEI film formed by the three has a large compositional component, the structure of the SEI film is more stable, and the stability of the structure is guaranteed, while ensuring a relatively small impedance value of the SEI film and ensuring the low-temperature performance of the secondary battery.

[0055] When the secondary battery of the present application contains the above-mentioned boron-containing lithium salt, an SEI film having a stable structure and a relatively small impedance value can be formed on the surface of the negative electrode active material, thereby improving the high and low temperature performance of the secondary battery.

[0056] In some embodiments, the lithium salt may further include one or more of the following combinations: lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorodisulfophosphate (LiDFOP), and lithium tetrafluorooxalophosphate (LiTFOP). The use of the lithium salt in combination with a boron-containing lithium salt can improve the conductivity of the electrolyte.

[0057] By way of example, the lithium salt may include one or a combination of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), and lithium bisoxalatoborate (LiBOB).

[0058] In some embodiments, the organic solvent may further comprise one or more combinations selected from 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).

[0059] In some embodiments, the electrolyte may further include a film-forming additive, for example, a negative electrode film-forming additive, and the negative electrode film-forming additive includes a first type additive and / or a second type additive, the first type additive includes at least two of a carbonate ester additive, a sulfate ester additive, and a sulfite ester additive, and the second type additive includes a fluorooxalic acid or phosphate backbone lithium salt, and / or a sulfonimide backbone lithium salt.

[0060] The negative electrode film-forming additive is one or more of carbonate ester additives, sulfate ester additives, sulfite ester additives, and lithium fluorooxalate phosphate. The negative electrode film-forming additive can form an SEI film on the surface of the negative electrode active material, and the SEI film formed has a rich composition and is more stable in structure.

[0061] When the mass percentage of the negative electrode film-forming additive relative to the total mass of the electrolyte is D%, and the mass percentage of the boron-containing lithium salt relative to the total mass of the electrolyte is C%, the secondary battery satisfies 0.01%≦(C+D)%≦20%.

[0062] Both the negative electrode film-forming additive and the boron-containing lithium salt constitute the composition of the SEI film, and by adjusting the total amount of the negative electrode film-forming additive and the boron-containing lithium salt, the SEI film formed has better film-forming uniformity, a more stable structure, and reduced interface impedance, thereby improving the cycle and high-temperature storage performance of the secondary battery. Optionally, 0.1%≦(C+D)%≦12%. Exemplarily, (C+D)% may be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 18, or 20, or may be a range consisting of any two of the above values.

[0063] 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 MAC, and polycarbonate VA. The mass percentage of the carbonate ester additive with respect to the total mass of the electrolyte is D1%.

[0064] The mass percentage D1% of the carbonate ester additive is 10 -4By adjusting the mass percentage D1% of the carbonate additive to satisfy the above condition, a stable SEI film is formed on the surface of the negative electrode active material, and the SEI film has good chemical stability and thermal stability. -4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2 %, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of the above values.

[0065] For example, the sulfate additives include cyclic sulfonate additives and / or hydrocarbyl sulfate additives. Further, the cyclic sulfonate additives include one or more of 1,3-propane sultone PS, propene sultone PES, and 3-fluoro-1,3-propane sultone FPS. The hydrocarbyl sulfate additives include one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS.

[0066] By way of example, sulfite additives include ethylene sulfite ES and / or vinyl ethylene sulfite VES.

[0067] The mass percentage of the sulfate ester additive or the sulfite ester additive with respect to the total mass of the electrolyte is defined as D2%.

[0068] The mass percentage D2% of the sulfate ester additive or sulfite ester additive is 10 -4 By adjusting the mass percentage D2% of the sulfate ester additive or sulfite ester additive to satisfy the above condition, a stable SEI film can be formed on the surface of the negative electrode active material, and the SEI film has good chemical stability and thermal stability.-4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2 %, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of the above values.

[0069] For example, the fluorooxalic acid or phosphate framework lithium salt includes one or more of lithium tetrafluorooxalate phosphate LiTFOP, lithium difluorophosphate LiPO2F2, and lithium difluorobisoxalatophosphate LiBODFP. The mass percentage of the fluorooxalic acid or phosphate framework lithium salt with respect to the total mass of the electrolyte is D3%.

[0070] The mass percentage D3% of the fluorooxalic acid or phosphoric acid skeleton lithium salt is 10 -4 By adjusting the mass percentage D3% of the lithium salt with a fluorooxalic acid or phosphate framework to satisfy the above condition, a stable SEI film can be formed on the surface of the negative electrode active material, and the SEI film has good chemical stability and thermal stability. -4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2 %, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of the foregoing values.

[0071] For example, the sulfonimide-based lithium salt includes one or more of bisfluorosulfonylimide lithium [LiN(SO2F)2], bis(trifluoromethylsulfonyl)imide lithium LiN(CF3SO2)2, and bistrifluoromethanesulfonylimide lithium LiTFSI. The mass percentage of the sulfonimide-based lithium salt with respect to the total mass of the electrolyte is D4%.

[0072] The mass percentage D4% of the sulfonimide skeleton lithium salt is 10 -4 By adjusting the mass percentage D4% of the sulfonimide skeleton lithium salt to satisfy the relationship D4%≦D4%≦5%, a stable SEI film is formed on the surface of the negative electrode active material, and the SEI film has good chemical stability and thermal stability. -4 %, 1.5×10 -4 %, 2×10 -4 %, 5×10 -4 %, 1×10 -3 %, 1.5×10 -3 %, 2×10 -3 %, 5×10 -3 %, 1×10 -2 %, 5×10 -2 %, 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4% or 5%, or may be a range consisting of any two of the foregoing values.

[0073] The electrolyte of the present application can be prepared according to a conventional method in the field. For example, additives, solvents, electrolyte salts, etc. can be mixed uniformly to obtain an electrolyte. The order of addition of each material is not particularly limited, and for example, the additives, electrolyte salts, etc. can be added to the non-aqueous solvent and mixed uniformly to obtain a non-aqueous electrolyte.

[0074] In the present application, each component and its content in the electrolyte solution can be measured according to a method known in the art, for example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0075] In the test of the electrolyte solution of the present application, a freshly prepared electrolyte solution may be obtained as it is, or the electrolyte solution may be obtained from a secondary battery. An exemplary method for obtaining the electrolyte solution from a secondary battery includes the steps of discharging the secondary battery to a discharge cut-off voltage (for safety reasons, the battery is generally fully discharged), centrifuging, and then using 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 electrolyte inlet of the secondary battery. [Negative electrode sheet]

[0076] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

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

[0078] In some embodiments, the negative electrode active material may be a negative electrode active material used in batteries known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and lithium aluminum alloy. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloy. However, the present application is not limited to these materials, and conventional materials used as negative electrode active materials in other batteries may be used. These negative electrode active materials may be used alone or in combination of two or more.

[0079] In some embodiments, the coating weight of the negative electrode membrane layer is F mg / 1540.25 mm 2 The secondary battery is furthermore 2×10 -5The negative electrode film layer coating weight satisfies the relationship ≦B×(C+D)% / F≦1. Here, the coating weight of the negative electrode film layer refers to the coating weight of the negative electrode film layer provided on one side of the negative electrode current collector.

[0080] When the secondary battery satisfies the above formula, the electrolyte reacts with the surface of the negative electrode active material to form a film, and the SEI film is uniformly formed on the surface of the negative electrode active material, thereby providing good protection for the negative electrode active material. In addition, the conductivity of the electrolyte is relatively high, and after lithium ions are desorbed from the positive electrode sheet, they are smoothly inserted into the negative electrode active material through the electrolyte, thereby ensuring the cycle performance of the secondary battery. -5 ≦B×(C+D)% / F≦0.5. For example, B×(C+D)% / F is 2×10 -5 , 5×10 -5 , 1×10 -4 , 2×10 -4 , 2×10 -3 , 5×10 -2 , 0.1 or 1, or it may be a range consisting of any two of the above values.

[0081] The coating weight of the negative electrode film layer is a known method in the art and can be measured by the following differential weight method. The negative electrode film layer mass test method is to vacuum-dry the negative electrode sheet of the obtained secondary battery at 105°C for 48 hours, and measure the mass of the negative electrode film layer by 100%. 2 Several small wafers are punched out using a circular press, and the average value is determined to be m0mg by weighing and recording. Then, one side of the negative electrode active material is completely removed, and the negative electrode current collector is wiped with deionized water until no obvious black imprints remain, and dried at 105°C for 5 hours. After that, several wafers are punched out again using the same press, and the average value is determined to be m1mg by weighing and recording. The coating weight of the negative electrode film layer is (m0-m1)mg / 1540.25mm 2 and the m0-m1 value corresponds to F in this specification.

[0082] In some embodiments, 50≦F≦500.

[0083] When the coating weight of the negative electrode film layer is within the above range, the capacity of the secondary battery can be ensured.

[0084] In some embodiments, the negative electrode film layer may further include a negative electrode adhesive. In the present application, the type of the negative electrode adhesive is not particularly limited, but as an example, the negative electrode adhesive may include one or more combinations selected from styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-soluble acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMMA, 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 adhesive is 5% or less based on the total mass of the negative electrode film layer.

[0085] In some embodiments, the negative electrode film layer may further include a selective negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited, but for 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 5% or less based on the total mass of the negative electrode film layer.

[0086] In some embodiments, the negative electrode membrane layer may further include other optional auxiliary agents. For example, the other auxiliary agents may include thickeners such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other auxiliary agents is 2% or less based on the total mass of the negative electrode membrane layer.

[0087] In some embodiments, the negative electrode current collector may be a metal foil piece or a composite current collector. Examples of the metal foil piece 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).

[0088] The negative electrode membrane layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional adhesive, and other optional auxiliary agents in a solvent, and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0089] The negative electrode sheet does not exclude any additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a protective layer coated on the surface of the negative electrode film layer. [Positive electrode sheet]

[0090] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, for example, the positive electrode current collector has two opposing surfaces in a thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0091] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material may be a positive electrode active material used in a secondary battery known in the art. For example, the positive electrode active material may include at least one of lithium transition metal oxide, lithium-containing phosphate having an olivine structure, and modified compounds thereof. Examples of lithium transition metal oxides include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium-containing phosphate having an olivine structure include at least one of lithium iron phosphate, lithium iron phosphate and carbon composite material, lithium manganese phosphate, lithium manganese phosphate and carbon composite material, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composite material, and modified compounds thereof. The present application is not limited to these materials, and other conventionally known materials used as secondary battery positive electrode active materials may be used. These positive electrode active materials may be used alone or in combination of two or more.

[0092] 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, where 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. When the positive electrode active material is combined with a boron-containing lithium salt, the B atom in the boron-containing lithium salt is easily bonded to the O atom in the positive electrode active material, which can reduce the impedance of the charge transfer of the positive electrode active material and reduce the diffusion resistance of lithium ions in the bulk of the positive electrode active material. Therefore, when the non-aqueous electrolyte contains an appropriate content of lithium tetrafluoroborate and lithium difluorooxalate borate, the low-cobalt or cobalt-free positive electrode active material can have a significantly improved lithium ion diffusion rate, and the lithium ions in the bulk of the low-cobalt or cobalt-free positive electrode active material can be timely replenished to the surface, thereby preventing excessive lithium from being desorbed from the surface of the low-cobalt or cobalt-free positive electrode active material, thereby stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Since the crystal structure of the low-cobalt or cobalt-free positive electrode active material is more stable, the probability of problems such as excessive lithium desorption occurring on the surface of the low-cobalt or cobalt-free positive electrode active material causing instability in the structural, chemical or electrochemical properties of the positive electrode active material, for example, the probability of problems such as irreversible distortion and increased lattice defects in the positive electrode active material, can be greatly reduced.

[0093] 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 prepared according to conventional methods in the art. An exemplary preparation method is as follows. It is obtained by mixing a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M element precursor, and an N element precursor and sintering them. The sintering atmosphere can be an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual situation.

[0094] By way of example, the lithium source includes, but is 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). By way of example, the nickel source includes, but is not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. By way of example, the cobalt source includes, but is not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. By way of example, the manganese source includes, but is not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. By way of example, the aluminum source includes, but is not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. By way of example, the M element precursor includes, but is not limited to, at least one of an oxide, a nitrate compound, a carbonate compound, a hydroxide compound, and an acetate compound of the M element. By way of example, the N element precursor includes, but is 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.

[0095] In some embodiments, 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 is 80% to 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 may be 85%-99%, 90%-99%, 95%-99%, 80%-98%, 85%-98%, 90%-98%, 95%-98%, 80%-97%, 85%-97%, 90%-97%, or 95%-97%.

[0096] In some embodiments, the positive electrode film layer may further include a selective positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited, but 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 is 5% or less based on the total mass of the positive electrode film layer.

[0097] In some embodiments, the positive electrode membrane layer may further include a positive electrode adhesive. In the present application, the type of the positive electrode adhesive is not particularly limited, but for example, the positive electrode adhesive may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene ternary copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. In some embodiments, the mass percentage of the positive electrode adhesive is 5% or less based on the total mass of the positive electrode membrane layer.

[0098] In some embodiments, the positive electrode current collector may be a metal foil piece or a composite current collector. Examples of the metal foil piece include aluminum foil or 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).

[0099] The positive electrode membrane layer is usually formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). [Separator]

[0100] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known separator having a porous structure with good chemical stability and mechanical stability can be selected.

[0101] In some embodiments, the separator is 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 multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and is not particularly limited.

[0102] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be prepared into an electrode assembly by a winding process or a lamination process.

[0103] In some embodiments, the secondary battery can include an exterior packaging, which can be used to seal the electrode assembly and electrolyte.

[0104] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft package, such as a bag-type soft package. The material of the soft package may be plastic. Examples of plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. For example, FIG. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0106] In some embodiments, as shown in FIG. 1 and FIG. 2, the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are surrounded to form a receiving chamber. The case 51 has an opening communicating with the receiving chamber, and the cover plate 53 covers the opening to close the receiving chamber. The positive electrode sheet, the negative electrode sheet and the separator may form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed in the receiving chamber. The electrode assembly 52 is infiltrated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted according to needs.

[0107] The method for preparing the secondary battery of the present application is known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, a positive electrode sheet, a separator, and a negative electrode sheet can be formed into an electrode assembly by a winding process or a lamination process, and the electrode assembly can be placed in an outer casing, dried, and then an electrolyte can be injected, and a secondary battery can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0108] 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.

[0109] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by a fastener.

[0110] Optionally, the battery module 4 further includes a housing having an accommodating space, and the multiple secondary batteries 5 are accommodated in the accommodating space.

[0111] 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.

[0112] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Fig. 4 and 5, the battery pack 1 may include a battery housing and a plurality of battery modules 4 provided in the battery housing. The battery housing includes an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by 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 housing in any manner. power consumption equipment

[0113] 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 of the present application. The secondary battery, battery module, and battery pack may be used as a power source for the power consuming device, or may be used as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile 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.), an electric train, a ship and a satellite, an energy storage system, etc.

[0114] A power consuming device can select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0115] 6 is a schematic diagram of an example power consuming device 6, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack 1 or a battery module can be employed to meet the high power and high energy density demands of the power consuming device.

[0116] Other examples of power consuming devices may be mobile phones, tablet computers, notebook computers, etc. Such power consuming devices are usually required to be thin and may employ secondary batteries as their power source. Working Example

[0117] The following examples will more specifically explain the contents of the present disclosure. These examples are merely used for explanatory purposes, and it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the contents of the present disclosure. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass, and all reagents used in the examples can be purchased or synthesized according to conventional methods and can be used directly without the need for further processing. In addition, all devices used in the examples can be purchased.

[0118] Example 1 1. Preparation of Positive Electrode Sheet

[0119] As the positive electrode current collector, an aluminum foil having a thickness of 12 μm is used.

[0120] Positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as an adhesive were thoroughly mixed in a weight ratio of 97.5:1.4:1.1 in an appropriate amount of NMP solvent to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly applied to the surface of an aluminum foil as a positive electrode current collector, and after drying and cold pressing, a positive electrode sheet was obtained. 2. Preparation of Negative Electrode Sheet

[0121] A copper foil with a thickness of 8 μm is used as the negative electrode current collector.

[0122] The negative electrode active material graphite, the adhesive styrene butadiene rubber (SBR), the thickener sodium carboxymethylcellulose (CMC-Na), and the conductive agent carbon black (Super P) were thoroughly mixed in a weight ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water as a solvent to form a uniform negative electrode slurry. The negative electrode slurry was then uniformly applied to the surface of copper foil as the negative electrode current collector, and dried and cold pressed to obtain a negative electrode sheet. 3. Separator

[0123] A porous polyethylene (PE) film is used as the separator. 4. Preparation of Electrolyte Solution

[0124] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC) and diethyl carbonate (DMC) were mixed in a volume ratio of 1:1 to obtain an electrolyte solvent, which was then mixed with a lithium salt to obtain an electrolyte with a lithium salt concentration of 1 mol / L. 5. Preparation of Secondary Batteries

[0125] The positive electrode sheet, separator, and negative electrode sheet are stacked in this order, and the separator is interposed between the positive electrode sheet and the negative electrode sheet to perform an isolating function. Then, the stack is wound to obtain an electrode assembly. The electrode assembly is placed in an outer case, dried, and then an electrolyte is injected. The lithium ion battery is obtained through processes such as vacuum sealing, standing, chemical formation, and shaping. Example 2 Examples 2-1 to 2-10

[0126] The secondary batteries of Examples 2-1 to 2-10 were prepared in a manner similar to that of Example 1, and differed from Example 1 in that the mass percentage C% of the boron-containing lithium salt was adjusted in Examples 2-1 to 2-10. Examples 2-11 and 2-12

[0127] The secondary batteries of Examples 2-11 and 2-12 were prepared in a manner similar to that of Example 1, and differed from Example 1 in that the type of boron-containing lithium salt was adjusted in Examples 2-11 and 2-12. Comparative Example 1

[0128] The secondary battery of Comparative Example 1 was prepared in a manner similar to that of Example 1, except that no boron-containing lithium salt was added, and only LiPF6 was added. Comparative Example 2 and Comparative Example 3

[0129] The secondary batteries of Comparative Example 2 and Comparative Example 3 were prepared in a manner similar to that of Example 1, and differed from Example 1 in that the mass percentage C% of the boron-containing lithium salt was adjusted in Comparative Example 2 and Comparative Example 3. Example 3

[0130] The secondary batteries of Examples 3-1 to 3-7 were prepared in a manner similar to that of Example 1, and differed from Example 1 in that the mass Bg of the electrolyte and the discharge capacity A Ah of the secondary battery were adjusted in Examples 3-1 to 3-7. Example 4

[0131] The secondary batteries of Examples 4-1 to 4-9 were prepared in a manner similar to that of Example 1, and differed from Example 1 in that the type and content of the negative electrode film-forming additive in Example 4-1 to Example 4-9 were adjusted. Example 5

[0132] The secondary batteries of Examples 5-1 to 5-4 were prepared in a manner similar to that of Example 1. In Example 5, the coating weight of the negative electrode film layer F was 0.25 mm 2 has been adjusted.

[0133] The data for Examples 1 to 5 and the Comparative Example are shown in Tables 1 and 2.

[0134] [Table 1]

[0135] [Table 2] Test part (1) Testing the room temperature cycle performance of secondary batteries

[0136] At 25°C, the secondary battery was charged to 4.4V at a constant current of 0.5C, and the constant voltage charging was continued until the current became 0.05C. At this time, the secondary battery was in a fully charged state, and the charge capacity at this time was recorded, which is the first charge capacity. After leaving the secondary battery stationary for 5 minutes, it was discharged to 2.8V at a constant current of 1C, which is one cycle of charge and discharge process, and the discharge capacity at this time was recorded, which is the first discharge capacity. The secondary battery was subjected to a cycle charge and discharge test according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 25°C = discharge capacity after 600 cycles / first discharge capacity × 100%. (2) High-temperature cycle performance test of secondary batteries

[0137] At 45°C, the secondary battery was charged to 4.4V at a constant current of 0.5C, and the constant voltage charging was continued until the current became 0.05C, at which point the secondary battery was fully charged, and the charge capacity at this time was recorded, which is the first charge capacity. After leaving the secondary battery stationary for 5 minutes, it was discharged to 2.8V at a constant current of 1C, which is one cycle of charge and discharge, and the discharge capacity at this time was recorded, which is the first discharge capacity. The secondary battery was subjected to a cycle charge and discharge test according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 45°C = discharge capacity after 600 cycles / first discharge capacity × 100%. (3) Testing the high-temperature storage performance of secondary batteries

[0138] The battery is left at 60°C for 6 hours, first the secondary battery is charged at 0.33C to 4.4V, constant voltage charging is continued until the current is 0.05C, and after leaving it for 5 minutes, it is discharged at a current of 0.33C to 2.8V, and the initial discharge capacity is A0 Ah, then the battery is charged at a current of 0.5C to 4.4V, and then constant voltage charging is continued until the current is 0.05C, and the fully charged battery is left at 60°C for 100 days in a high-temperature furnace, taken out, and discharged at a current of 1C to 2.8V, and the final discharge capacity is A1 Ah. The capacity retention rate (%) after storing the secondary battery at 60°C for 100 days = [(A1-A0) / A0] × 100%.

[0139] The storage volume test method is as follows: leave the battery at 60°C for 6 hours, charge the secondary battery to 4.3V at a constant current of 1C, and continue constant voltage charging until the current reaches 0.05C. At this time, test the volume of the secondary battery using the drainage method and set it as V0. Put the secondary battery into a thermostatic box at 60°C and store it for 30 days, then take it out. At this time, test the volume of the secondary battery using the drainage method and set it as V1. The volume expansion rate (%) of the secondary battery after storing it at 60°C for 30 days = [(V1-V0) / V0] x 100%. Test Results

[0140] The effect of the present invention on improving the cycle performance and storage performance of the secondary battery is shown in Table 3.

[0141] [Table 3]

[0142] As can be seen from the table, when the boron-containing lithium salt is not added to Comparative Example 1, the negative electrode active material cannot be protected, and therefore the structure of the negative electrode active material is easily destroyed during the cycle process of the secondary battery, and both the cycle performance and storage performance of the secondary battery are poor.

[0143] In the present application, the addition of boron-containing lithium salt to the electrolyte provides good protection for the negative electrode active material, and improves the cycle performance and storage performance of the secondary battery. However, in Comparative Examples 2 and 3, the performance of the secondary battery cannot be significantly improved. This is because an excessive amount of boron-containing lithium salt is added, and the stability of the SEI film formed on the negative electrode active material by the boron-containing lithium salt alone is insufficient, so that the negative electrode active material cannot be effectively protected for a long period of time. In contrast, in Examples 1 to 2-12, the amount of boron-containing lithium salt added is 1≦B / A≦5, 5×10 -6 ≦B×C% / A≦0.25, and in particular, 1×10 -3 When the relationship ≦B×C% / A≦0.23 is satisfied, the boron-containing lithium salt, in cooperation with other parameters, can not only form a stable and dense SEI film on the surface of the negative electrode active material, but also provide good and long-term protection for the negative electrode active material.

[0144] In Examples 3-1 to 3-7, the injection amount of the electrolyte and the discharge capacity A Ah of the secondary battery are adjusted, and in particular, the mass B of the electrolyte satisfies 0.01≦B≦3000, optionally 0.5≦B≦1500, so that the boron-containing lithium salt can adjust the thickness of the SEI film formed on the surface of the negative electrode active material, thereby improving the cycle performance and storage performance of the secondary battery.

[0145] In Examples 4-1 to 4-7, by adjusting the type and content of the negative electrode film-forming additive, the active components in the electrolyte can form a stable and composition-rich SEI film on the surface of the negative electrode active material, which further improves the protective effect on the negative electrode active material, thereby further improving the cycle performance and storage performance of the secondary battery.

[0146] In Examples 5-1 to 5-4, by adjusting the coating weight of the negative electrode film layer, the electrolyte can sufficiently protect the surface of the negative electrode active material, and the SEI film can be uniformly formed on the surface of the negative electrode active material, thereby improving the cycle performance and storage performance of the secondary battery.

[0147] Although the present application has been described with reference to the preferred embodiments, various improvements may be made without departing from the scope of the present application, or some of the components may be replaced with equivalents. In particular, as long as there is no structural contradiction, the technical features mentioned in each embodiment may be arbitrarily combined. The present application is not limited to the specific embodiments disclosed above, but includes all aspects included in the scope of the claims.

Claims

1. A positive electrode sheet; a negative electrode sheet including a negative electrode membrane layer containing a negative electrode active material; and an electrolyte solution including a boron-containing lithium salt configured to form a solid electrolyte interfacial film on the surface of the negative electrode active material; When the discharge capacity of the secondary battery is A Ah, the mass of the electrolyte is B g, and the mass percentage of the boron-containing lithium salt with respect to the total mass of the electrolyte is C %, 1≦B / A≦5, 5×10 －６ ≦B×C% / A≦0.25, selectable, 1×10 －３ A secondary battery that satisfies the following: ≦B×C% / A≦0.

23.

2. The secondary battery according to claim 1 , wherein the secondary battery satisfies at least one of conditions (1) to (3). (1) 0.01≦A≦1000, and optionally 50≦A≦550; (2) 0.01≦B≦3000, and optionally 0.5≦B≦1500; (3) 1 x 10 －４ %≦C%≦5%, and optionally 0.01%≦C≦3%.

3. the electrolytic solution further comprises a negative electrode film-forming additive, the negative electrode film-forming additive comprises a first class additive and / or a second class additive, the first class additive comprises at least two of a carbonate ester additive, a sulfate ester additive, and a sulfite ester additive, the second class additive comprises a fluorooxalic acid or phosphate skeleton lithium salt, and a sulfonimide skeleton lithium salt, When the mass percentage of the negative electrode film-forming additive with respect to the total mass of the electrolyte is D%, the secondary battery further satisfies 0.1%≦(C+D)%≦20%, The secondary battery according to claim 1 or 2.

4. The secondary battery according to claim 3 , further satisfying at least one of conditions (4) to (7). (4) When the mass percentage of the carbonate additive with respect to the total mass of the electrolyte is D1%, 10 －４ %≦D1%≦5%, (5) When the mass percentage of the sulfate ester additive and the sulfite ester additive with respect to the total mass of the electrolyte is D2%, －４ %≦D2%≦5%, (6) When the mass percentage of the fluorooxalic acid or phosphate skeleton lithium salt with respect to the total mass of the electrolyte solution is D3%, －４ %≦D3%≦5%, (7) When the mass percentage of the sulfonimide skeleton lithium salt with respect to the total mass of the electrolyte solution is D4%, －４ %≦D4%≦5%.

5. The carbonate ester additives include cyclic carbonate ester additives and / or linear carbonate ester additives, optionally the cyclic carbonate ester additives include one or more of vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC, and the linear carbonate ester additives include one or more of ethyl allyl carbonate AEC, diphenyl carbonate DPC, and methyl allyl carbonate MAC, and polycarbonate VA, and / or The sulfate additive comprises a cyclic sulfonate additive and / or a hydrocarbyl sulfate additive, optionally the cyclic sulfonate additive comprises one or more of 1,3-propane sultone PS, propene sultone PES, 3-fluoro-1,3-propane sultone FPS, and / or the hydrocarbyl sulfate additive comprises one or more of vinyl sulfate DTD, diethyl sulfate DES, and dimethyl sulfate DMS, and / or The sulfite additive comprises ethylene sulfite ES and / or vinyl ethylene sulfite VES, and / or The fluorooxalic acid or phosphate skeleton lithium salt is preferably lithium tetrafluorooxalic acid phosphate (LiTFOP), lithium difluorophosphate (LiPO ２ F ２ and lithium difluorobisoxalatophosphate LiBODFP; and / or The sulfonimide-based lithium salt is lithium bisfluorosulfonylimide [LiN(SO ２ F) ２ ], lithium bis(trifluoromethylsulfonyl)imide LiN(CF ３ SO ２ ) ２ and lithium bistrifluoromethanesulfonylimide LiTFSI; The secondary battery according to claim 3 or 4.

6. The coating weight of the negative electrode film layer is F mg / 1540.25 mm ２ and The secondary battery is 2×10 －５ ≦B×(C+D)% / F≦1 is further satisfied; The secondary battery according to claim 3 .

7. 50≦F≦500; The secondary battery according to claim 1 .

8. The molecular formula of the boron-containing lithium salt is LiBF ａ O ｂ C ｃ P ｄ In the molecular formula, 0≦a≦4, 0≦b≦8, 0≦c≦4, and 0≦d≦4. The secondary battery according to claim 1 .

9. The boron-containing lithium salt is lithium tetrafluoroborate LiBF ４ , lithium bis(oxalato)borate LiBOB and lithium bis(fluorooxalato)borate LiDFOB; The secondary battery according to claim 8.

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

11. A battery pack comprising the battery module according to claim 10.

12. A power consuming device comprising: the secondary battery according to claim 1 ; the battery module according to claim 10 ; or the battery pack according to claim 11 .

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