Lithium-ion secondary battery, battery cell, and electric device

Abstract

This application provides a lithium-ion secondary battery, a battery cell, and an electrical device. The lithium-ion secondary battery comprises a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains a first additive, which includes 1,3-propenesulfonyl lactone. The mass concentration of 1,3-propenesulfonyl lactone in the electrolyte is 0.01% to 3.5%. The positive electrode comprises a positive electrode active material, and the specific surface area of ​​the positive electrode active material is ≤15 m². 2 / g, the negative electrode sheet contains a negative electrode active material, and the specific surface area of ​​the negative electrode active material is ≤1.5m². 2 / g. The lithium-ion secondary battery exhibits good cycle capacity retention and cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a lithium ion secondary battery, an electric core and an electric device. BACKGROUND

[0002] In recent years, the application range of secondary batteries such as lithium ion batteries is more and more extensive, which has been widely applied in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles. Since the secondary battery has achieved great development, higher requirements have been put forward for its energy density, cycle performance and safety performance.

[0003] 1,3-propylene sulfite (PST) is an electrolyte additive of lithium ion battery, which can improve the cycle life of the battery to a certain extent. However, 1,3-propylene sulfite is easy to hydrolyze in the electrolyte when it meets water, and it is difficult to play its own efficacy. At the same time, it is acidic after hydrolysis, which increases the acidity of the electrolyte and the corrosion of the material, so that the cycle life of the battery is difficult to be effectively improved. SUMMARY

[0004] In order to achieve the above purpose, the present application provides a lithium ion secondary battery with good cycle life, an electric core and an electric device.

[0005] The present application provides a lithium ion secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the electrolyte comprises a first additive, the first additive comprises 1,3-propylene sulfite, the mass concentration of 1,3-propylene sulfite in the electrolyte is 0.01%~3.5%, the positive electrode sheet comprises a positive electrode active material, the specific surface area of the positive electrode active material is ≤15m 2 / g, and the negative electrode sheet comprises a negative electrode active material, the specific surface area of the negative electrode active material is ≤1.5m 2 / g.

[0006] The present application researches and finds that in the battery using 1,3-propylene sulfite as an additive (the mass concentration of 1,3-propylene sulfite in the electrolyte is 0.01%~3.5%), by controlling the specific surface area of the positive electrode active material ≤15m 2 / g and the specific surface area of the negative electrode active material ≤1.5m 2 / g, the influence of water in the system on the hydrolysis of 1,3-propylene sulfite can be effectively controlled, the acid production is reduced, the electrolyte acidity is reduced, and the cycle capacity retention rate of the battery is improved, so that the battery has good cycle life.

[0007] Further, by controlling the specific surface area of the positive active material and the negative active material within a suitable range, the hydrolysis of the PST can be reduced, the cycle capacity retention of the battery can be improved, and a higher energy density can be obtained.

[0008] In some embodiments, the specific surface area of the positive active material is 8 m 2 / g~15 m 2 / g.

[0009] In some embodiments, the particle size Dv50 of the positive active material is 0.5 μm~2.5 μm.

[0010] In some embodiments, the specific surface area of the negative active material is 1 m 2 / g~1.5 m 2 / g.

[0011] In some embodiments, the particle size Dv50 of the negative active material is 8 μm~18 μm.

[0012] In some embodiments, the electrolyte further comprises a second additive, and the second additive comprises a silicon-containing acid-removing additive. By using the silicon-containing acid-removing additive as an additive, the proton hydrogen generated by the hydrolysis of 1,3-propanesultone in the electrolyte can be effectively captured, the acidity of the electrolyte can be reduced, and the cycle capacity retention of the battery can be improved in cooperation with the specific surface area of the positive active material and the negative active material.

[0013] In some embodiments, the second additive has one or more of the following characteristics:

[0014] (1) The mass concentration of the second additive in the electrolyte is 0.01%~0.5%;

[0015] (2) The second additive comprises one or more of tris(trimethylsilyl) phosphate, silazane, N-trimethylsilylimidazole, and tris(trimethylsilyl) borate.

[0016] In some embodiments, the electrolyte further comprises a third additive, and the third additive comprises a combination of a fluorine-containing negative electrode film-forming additive and a double-bond-containing negative electrode film-forming additive. The fluorine-containing negative electrode film-forming additive and the double-bond-containing negative electrode film-forming additive can cooperate with 1,3-propanesultone to form a stable composite SEI film on the surface of the negative electrode sheet, reduce the occurrence of side reactions, improve the stability of the negative electrode sheet, and further improve the cycle capacity retention. In addition, the consumption of active lithium during the cycle can be reduced, and the initial capacity of the battery can be improved.

[0017] In some embodiments, the third additive has one or more of the following characteristics:

[0018] (1) the fluorine-containing negative electrode film-forming additive comprises one or more of fluoroethylene carbonate and fluoroalkyl-substituted ethylene carbonate;

[0019] (2) the mass concentration of the fluorine-containing negative electrode film-forming additive in the electrolyte is 0.01% to 3%;

[0020] (3) the double-bond-containing negative electrode film-forming additive comprises one or more of vinylene carbonate, alkyl-substituted vinylene carbonate, and alkenyl-substituted vinylene carbonate;

[0021] (4) the mass concentration of the double-bond-containing negative electrode film-forming additive in the electrolyte is 0.01% to 3%.

[0022] In some embodiments, the positive electrode active material comprises lithium iron phosphate.

[0023] In some embodiments, the negative electrode active material comprises one or both of natural graphite and artificial graphite.

[0024] In a second aspect, the present application provides a battery cell, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the electrolyte comprises a first additive, the first additive comprises 1,3-propene sultone, the mass concentration of the 1,3-propene sultone in the electrolyte is 0.01% to 5%, the positive electrode sheet comprises a positive electrode active material, the specific surface area of the positive electrode active material is ≤15 m 2 / g, and the negative electrode sheet comprises a negative electrode active material, the specific surface area of the negative electrode active material is ≤1.5 m 2 / g.

[0025] In some embodiments, the electrolyte further comprises a second additive, and the second additive comprises a silicon-containing acid-removing additive.

[0026] In some embodiments, the second additive has one or more of the following characteristics:

[0027] (1) the mass concentration of the second additive in the electrolyte is 0.01% to 1%;

[0028] (2) the second additive comprises one or more of tris(trimethylsilyl)phosphate, silazane, N-trimethylsilylimidazole, and tris(trimethylsilyl)borate.

[0029] In some embodiments, the electrolyte further comprises a third additive comprising a combination of a fluorine-containing negative electrode film-forming additive and a double-bond-containing negative electrode film-forming additive.

[0030] In some embodiments, the third additive has one or more of the following characteristics:

[0031] (1) the fluorine-containing negative electrode film-forming additive comprises one or more of fluoroethylene carbonate and fluoroalkyl-substituted ethylene carbonate;

[0032] (2) the mass concentration of the fluorine-containing negative electrode film-forming additive in the electrolyte is 0.01% to 5%;

[0033] (3) the double-bond-containing negative electrode film-forming additive comprises one or more of vinylene carbonate, alkyl-substituted vinylene carbonate, and alkenyl-substituted vinylene carbonate;

[0034] (4) the mass concentration of the double-bond-containing negative electrode film-forming additive in the electrolyte is 0.01% to 5%.

[0035] In a third aspect, the present application provides a power-consuming device comprising the lithium ion secondary battery of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0036] For a better description and illustration of the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any one of the disclosed applications, the presently described embodiments or examples, and the best mode presently understood of these applications. Moreover, in all the drawings, the same reference numbers are used to denote the same components. In the drawings:

[0037] Figure 1 is a schematic view of a secondary battery of an embodiment of the present application.

[0038] Figure 2 is a schematic view of a secondary battery of an embodiment of the present application. Figure 1

[0039] Figure 3 is a schematic view of a power-consuming device using the secondary battery of an embodiment of the present application as a power source.

[0040] BRIEF DESCRIPTION OF DRAWINGS

[0041] 1. Secondary battery; 11, housing; 12, electrode assembly; 13, cover plate; 2, power-consuming device. DETAILED DESCRIPTION

[0042] ​For the purposes of this application, a more complete description of the application will be presented with reference to the associated drawings. The drawings provided herein are for purposes of illustration only and serve to further facilitate understanding of the present application. However, the application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0044] "Ranges" disclosed herein are of the form of a lower limit and an upper limit, a given range is defined by selecting a lower limit and an upper limit, the selected lower limit and upper limit define the boundaries of a particular range. Ranges defined in this manner can be inclusive or exclusive of the end values, either end value can be included or excluded independently, and can be combined in any manner, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Further, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every intervening real number, a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, "0-5" is a shorthand way of listing these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to listing the parameter as, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a parameter is an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0045] In this application, references to "a plurality" "plural" and the like can include two or more unless otherwise stated.

[0046] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not otherwise specified.

[0047] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0048] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. 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) can 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.

[0049] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0050] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0051] One embodiment of this application provides a lithium-ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains a first additive, which includes 1,3-propenesulfonate lactone, wherein the mass concentration of 1,3-propenesulfonate lactone in the electrolyte is 0.01% to 3.5%. The positive electrode comprises a positive electrode active material, wherein the specific surface area of ​​the positive electrode active material is ≤15 m². 2 / g, wherein the negative electrode sheet comprises a negative electrode active material, and the specific surface area of ​​the negative electrode active material is ≤1.5m². 2 / g.

[0052] 1,3-Propylene sulfonate lactone is prone to hydrolysis and acid production under high water content, which deteriorates the cycle life of the battery. Materials with excessively large specific surface areas tend to absorb more water, leading to a higher water content in the system. This study found that in batteries using 1,3-propenesulfonate lactone as an additive (with a mass concentration of 0.01%~3.5% in the electrolyte), controlling the specific surface area of ​​the positive electrode active material to ≤15m² is beneficial. 2 / g, and the specific surface area of ​​the negative electrode active material is ≤1.5m². 2 / g can effectively control the effect of moisture in the system on the hydrolysis of 1,3-propenesulfonate lactone, reduce acid production, lower electrolyte acidity, and thus improve the cycle capacity retention rate of the battery, giving the battery a better cycle life.

[0053] Without limitation, the mass concentration of 1,3-propenesulfonate lactone in the electrolyte can be detected by organic gas chromatography; the specific surface area of ​​the positive electrode active material and the negative electrode active material can be detected by BET.

[0054] Understandably, the specific surface area of ​​both the positive and negative electrode active materials is greater than 0.

[0055] It should be noted that the additives in the electrolyte may change during the formation or cycling process of the battery. For ease of understanding, this application refers to the battery after formation or cycling as a "lithium-ion secondary battery" and the battery before formation and cycling as a "cell". The mass percentage or concentration of the components in the following text will be explained from these two aspects.

[0056] Corresponding to the statement in the lithium-ion secondary battery that "the mass concentration of 1,3-propenesulfonate lactone in the electrolyte is 0.01%~3.5%", the statement in the battery cell that "the mass concentration of 1,3-propenesulfonate lactone in the electrolyte is 0.01%~5%" is correct.

[0057] Specifically, the mass concentration of 1,3-propenesulfonate lactone in the electrolyte includes, but is not limited to, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or any range between the foregoing. Further, the mass concentration of 1,3-propenesulfonate lactone in the electrolyte is 0.1% to 2%. Correspondingly, the mass concentration of 1,3-propenesulfonate lactone in the electrolyte in the battery cell is 0.1% to 3%.

[0058] Furthermore, when the specific surface area of ​​the positive and negative electrode active materials is too small, the battery's kinetic performance will be reduced, leading to increased polarization. This results in a faster attainment of the cutoff voltage during constant current or constant power charging, reducing the provided capacity and lowering the battery's energy density. Therefore, it is necessary to appropriately control the specific surface area of ​​the positive and negative electrode active materials to effectively reduce acid production from PST hydrolysis, improve the battery's cycle capacity retention, and simultaneously achieve a higher energy density.

[0059] In some embodiments, the specific surface area of ​​the positive electrode active material is 8 m². 2 / g~15m 2 / g. Specifically, the specific surface area of ​​the positive electrode active material includes, but is not limited to, 8m². 2 / g, 8.5m 2 / g、9m 2 / g, 9.7m 2 / g, 10m 2 / g, 10.2m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 14.8m 2 / g, 15m 2 / g or a range between the two mentioned above. Further, the specific surface area of ​​the positive electrode active material is 10m². 2 / g~12m 2 / g.

[0060] In some embodiments, the specific surface area of ​​the negative electrode active material is 1 m². 2 / g~1.5m 2 / g. Specifically, the specific surface area of ​​the negative electrode active material includes, but is not limited to, 1m². 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or a range between the two mentioned above. Further, the specific surface area of ​​the negative electrode active material is 1.2m². 2 / g~1.4m 2 / g.

[0061] Furthermore, the particle size Dv50 of the positive and negative active materials is related to the specific surface area. The larger the particle size Dv50, the smaller the specific surface area, which increases polarization. At the same time, the compaction of the positive active layer will also decrease, resulting in a decrease in energy density. The smaller the particle size Dv50, the larger the specific surface area, which makes PST more prone to hydrolysis and acid production, reducing the cycle capacity retention rate of the battery.

[0062] In some embodiments, the particle size Dv50 of the positive electrode active material is 0.5 μm to 2.5 μm. Specifically, the particle size Dv50 of the positive electrode active material includes, but is not limited to: 0.5 μm, 0.8 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, or any range between the foregoing. Further, the particle size Dv50 of the positive electrode active material is 0.5 μm to 1.5 μm. Even further, the particle size Dv50 of the positive electrode active material is 1 μm to 1.3 μm.

[0063] In some embodiments, the particle size Dv50 of the negative electrode active material is 8 μm to 18 μm. Specifically, the particle size Dv50 of the negative electrode active material includes, but is not limited to: 8 μm, 8.9 μm, 9.5 μm, 10.1 μm, 11 μm, 12.2 μm, 12.5 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any range between the foregoing. Further, the particle size Dv50 of the negative electrode active material is 8 μm to 12.5 μm. Even further, the particle size Dv50 of the negative electrode active material is 9.5 μm to 11 μm.

[0064] Without limitation, the particle size Dv50 of the positive electrode active material and the negative electrode active material can be detected by laser particle size distribution.

[0065] In some embodiments, the electrolyte further comprises a second additive, which includes a silicon-containing acid-removing additive. Using a silicon-containing acid-removing additive as an additive can effectively capture protonated hydrogen generated by the hydrolysis of 1,3-propenesulfonate lactone in the electrolyte, reducing the acidity of the electrolyte. This, combined with the specific surface area of ​​the positive and negative electrode active materials, improves the cycle capacity retention rate of the battery.

[0066] In some embodiments, the mass concentration of the second additive in the electrolyte is 0.01% to 0.5%. Correspondingly, in the battery cell, "the mass concentration of the second additive in the electrolyte is 0.01% to 1%". Reasonably controlling the mass concentration of the second additive in the electrolyte can effectively capture protonated hydrogen in the electrolyte while obtaining lower impedance, thus comprehensively improving cycle capacity retention. Specifically, the mass concentration of the second additive in the electrolyte includes, but is not limited to: 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any range between the foregoing. Further, the mass concentration of the second additive in the electrolyte is 0.01% to 0.3%. Correspondingly, in the battery cell, "the mass concentration of the second additive in the electrolyte is 0.05% to 0.5%".

[0067] In some embodiments, the second additive comprises one or more of tris(trimethylsilane) phosphate (TMSP), silazane, N-trimethylsilylimidazolium, and tris(trimethylsilane) borate.

[0068] Without limitation, the mass concentration of the second additive in the electrolyte can be detected by organic gas chromatography.

[0069] In some embodiments, the electrolyte further comprises a third additive, which includes one or more of a fluorinated negative electrode film-forming additive and a double-bonded negative electrode film-forming additive. More specifically, the third additive includes a combination of a fluorinated negative electrode film-forming additive and a double-bonded negative electrode film-forming additive. The fluorinated negative electrode film-forming additive and the double-bonded negative electrode film-forming additive can cooperate with 1,3-propenesulfonate lactone to form a stable composite SEI film on the surface of the negative electrode, reducing the occurrence of side reactions, improving the stability of the negative electrode, and thus improving the cycle capacity retention rate. Additionally, it can reduce the consumption of active lithium during cycling and increase the initial capacity of the battery.

[0070] Without limitation, the fluorinated negative electrode film-forming additive includes one or more of fluoroethylene carbonate and its analogues (e.g., fluoroalkyl-substituted ethylene carbonate). The alkyl group can be a C1-C5 alkyl group. As an example, it can be as follows... (FEC) and One or more of them.

[0071] Without limitation, the double-bonded negative electrode film-forming additive includes one or more of vinylene carbonate and its analogues (e.g., alkyl-substituted vinylene carbonate, alkenyl-substituted vinylene carbonate). The alkyl group can be C1-C5 alkyl; the alkenyl group can be C2-C5 alkenyl. As an example, it can be as follows... (VC) , and One or more of them.

[0072] In some embodiments, the mass concentration of the fluorinated negative electrode film-forming additive in the electrolyte is 0.01% to 3%. Correspondingly, in the battery cell, "the mass concentration of the fluorinated negative electrode film-forming additive in the electrolyte is 0.01% to 5%". Specifically, the mass concentration of the fluorinated negative electrode film-forming additive in the electrolyte includes, but is not limited to: 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range between the foregoing. Further, the mass concentration of the fluorinated negative electrode film-forming additive in the electrolyte is 0.5% to 2%. Correspondingly, in the battery cell, "the mass concentration of the fluorinated negative electrode film-forming additive in the electrolyte is 1% to 3.5%".

[0073] In some embodiments, the mass concentration of the double-bonded negative electrode film-forming additive in the electrolyte is 0.01% to 3%. Correspondingly, in the battery cell, "the mass concentration of the double-bonded negative electrode film-forming additive in the electrolyte is 0.01% to 5%". Specifically, the mass concentration of the double-bonded negative electrode film-forming additive in the electrolyte includes, but is not limited to: 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range between the foregoing. Further, the mass concentration of the double-bonded negative electrode film-forming additive in the electrolyte is 0.5% to 2%. Correspondingly, in the battery cell, "the mass concentration of the double-bonded negative electrode film-forming additive in the electrolyte is 1% to 3.5%".

[0074] Without limitation, the mass concentration of negative electrode film-forming additives containing double bonds in the electrolyte can be detected by organic gas chromatography.

[0075] In some embodiments, the positive electrode active material includes lithium iron phosphate.

[0076] In some embodiments, the negative electrode active material includes one or both of natural graphite and artificial graphite.

[0077] In other embodiments of this application, an electrical device is provided, including the lithium-ion secondary battery described above.

[0078] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0079] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0080] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material.

[0081] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0082] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0083] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0084] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area (dry weight, minus solvent) can be 15 mg / cm³. 2 ~35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0086] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0087] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0088] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0089] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0090] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0092] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, or other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75 g / m². 2 ~220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~ 1.8g / cm 3 .

[0093] The electrolyte has the function of conducting ions between the positive and negative electrode plates.

[0094] In some embodiments, the electrolyte comprises an electrolyte salt and a solvent.

[0095] In some embodiments, the electrolyte salt may include one or more of 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 difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0096] In some embodiments, the solvent may include 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), butene carbonate ( One or more of the following: fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0097] 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.

[0098] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0099] In some embodiments, the thickness of the isolation membrane is 6μm to 40μm, and optionally 12μm to 20μm.

[0100] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0101] 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.

[0102] 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-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0103] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0104] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0105] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0106] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0107] Secondary batteries can be battery modules or battery packs.

[0108] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0109] In a battery module, multiple battery cells can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these battery cells can be secured using fasteners.

[0110] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0111] 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 one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0112] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0113] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0114] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0115] Figure 3 Here is an example of an electrical device 2. This electrical device 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 the secondary battery for this electrical device, a battery pack or battery module can be used.

[0116] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0117] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0118] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0119] The battery performance testing methods in each embodiment and comparative example are as follows:

[0120] (1) HF content:

[0121] Hydrofluoric acid content was analyzed by acid-base titration (SYA); the determination of free acid content in lithium hexafluorophosphate electrolyte 5.10 was performed according to standard HG / T4067-2015; the free acid in the electrolyte was titrated with triethylamine standard solution under dry conditions to calculate the HF content.

[0122] HF(ppm)=(V2-V1) / 1000*C*20 / m*1000000=(V2-V1)*C / m*20000;

[0123] In the formula: C—concentration of SYA standard solution, 0.02 mol / L;

[0124] V1—The volume reading of the burette before the start of titration, in mL;

[0125] V2—The volume reading of the burette, in mL, when the electrolyte sample is added and titration reaches the endpoint;

[0126] 20 — Molar molecular weight of HF, g / mol;

[0127] m — the amount of electrolyte weighed, in grams;

[0128] 20000 — the coefficient for converting to μg / g.

[0129] (2) Cyclic capacity retention:

[0130] At 45℃, the battery cell is charged at a constant current of 1C to 3.65V, then charged at a constant voltage of 3.65V to the cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.5V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as C1 of the lithium-ion battery cell in the first cycle. This cycle is repeated for the same battery cell. After 600 cycles, the discharge capacity C2 of the 600th cycle is recorded. The cycle capacity retention rate of the 600th cycle is calculated as C2 / C1 * 100%.

[0131] (3) Energy density:

[0132] At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a constant current of 0.5C to 3.65V, charged at a constant voltage of 3.65V to a cutoff current of 0.05C, and then discharged at a constant current of 0.5C to 2.5V. After three charge-discharge cycles, the actual discharge energy E0 (Wh) was recorded. Under the same temperature conditions, the lithium-ion battery was weighed using an electronic balance, and the length, width, and height of the lithium-ion battery were measured using a micrometer to obtain the battery volume V (L). The ratio of the actual discharge energy E0 of the lithium-ion battery to the volume V of the lithium-ion battery is the actual volumetric energy density of the lithium-ion battery.

[0133] Example 1

[0134] 1) Preparation of positive electrode sheet

[0135] The positive electrode active material (lithium iron phosphate, specific surface area 10.2 m²) will be prepared. 2 The positive electrode slurry was prepared by uniformly dispersing NMP solvent with a particle size Dv50 of 1.2 μm (g), conductive carbon black SP, and binder PVDF at a weight ratio of 98%:1%:1% to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both sides of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained, with a coating weight per unit area of ​​0.27 g / 1540.25 mm² on both sides. 2 .

[0136] 2) Preparation of negative electrode sheet

[0137] The negative electrode active material (artificial graphite, specific surface area 1.3 m²) 2 The following ingredients were mixed in a mass ratio of 97%:1%:1%:1% (particle size Dv50: 10.1 μm), thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both sides of a copper foil. After the copper foil was dried at room temperature, it was transferred to a 120°C oven and dried for 1 hour. Then, it was cold-pressed and slit to obtain a negative electrode sheet, with a coating amount of 0.17 g / 1540.25 mm² on both sides. 2 .

[0138] 3) Separating membrane

[0139] A 12μm thick polypropylene separator membrane was selected.

[0140] 4) Preparation of electrolyte

[0141] The organic solvent was a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC:20%:20%:60%. In an argon-atmosphere glove box with a water content <10 ppm, PST, TMSP, FEC, VC, and thoroughly dried lithium salt LiPF6 were dissolved in the organic solvent and mixed thoroughly to obtain the electrolyte. The concentrations of the lithium salt and VC were: lithium salt 1 mol / L, PST 5% (mass concentration), TMSP 0.2% (mass concentration), FEC 2.0% (mass concentration), and VC 3.5% (mass concentration).

[0142] 5) Battery manufacturing

[0143] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. They are then wound into a square bare cell, encased in an aluminum-plastic film, and baked at 80°C to remove moisture. Afterward, 10g of the appropriate non-aqueous electrolyte is injected, and the cell is sealed to obtain the battery cell. The cell undergoes processes such as settling, hot and cold pressing, formation, clamping, and capacity testing to obtain the finished battery. The formation process is as follows: constant current charging at 0.02C for 600 minutes at 45°C. After formation, the electrolyte contains 1 mol / L lithium salt, 3.5% PST, 0.1% TMSP, 0.3% FEC, and 1.5% VC.

[0144] The battery preparation methods in Examples 2-4 are the same as in Example 1, the main difference being the use of positive and negative electrode active materials with different specific surface areas and particle sizes (Dv50). See Table 1 below:

[0145] Table 1

[0146]

[0147] The battery preparation method in Example 5 is the same as in Example 1, the main difference being that TMSP was not added to the electrolyte. See Table 2 below:

[0148] Table 2

[0149]

[0150] The battery preparation method in Example 6 is the same as in Example 1, the main difference being that: no vitamin C was added to the electrolyte, and the mass concentration of FEC was adjusted to 5.5% (1.5% after formation). See Table 3 below:

[0151] Table 3

[0152]

[0153] The battery preparation method for Comparative Example 1 is the same as that for Example 1, the main difference being the use of positive electrode active materials with different specific surface areas and particle sizes (Dv50). See Table 4 below:

[0154] Table 4

[0155]

[0156] The battery preparation method for Comparative Example 2 is the same as that for Example 1, the main difference being the use of negative electrode active materials with different specific surface areas and particle sizes (Dv50). See Table 5 below:

[0157] Table 5

[0158]

[0159] A comparison between Examples 1-6 and Comparative Examples 1 and 2 shows that controlling the specific surface area of ​​the positive electrode active material to ≤15m² is effective. 2 / g, and the specific surface area of ​​the negative electrode active material is ≤1.5m². 2 / g, improves the battery's cycle capacity retention rate, giving the battery a better cycle life.

[0160] A comparison of Examples 1-6 shows that by reasonably controlling the range of specific surface areas of the positive and negative electrode active materials, it is possible to achieve a high energy density while ensuring a good cycle life for the battery.

[0161] A comparison between Example 1 and Example 5 shows that adding TMSP as an additive can improve the cycle capacity retention rate of the battery.

[0162] A comparison between Example 1 and Example 6 shows that the combined use of fluorine-containing negative electrode film-forming additives and double-bonded negative electrode film-forming additives can improve the cycle capacity retention rate of the battery.

[0163] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0164] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A lithium-ion secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains a first additive, which includes 1,3-propenesulfonate lactone, wherein the mass concentration of 1,3-propenesulfonate lactone in the electrolyte is 0.01% to 3.5%. The positive electrode sheet contains a positive electrode active material, and the specific surface area of ​​the positive electrode active material is 7.6 m². 2 / g~15m 2 / g, wherein the particle size Dv50 of the positive electrode active material is 0.5μm~2.4μm; The negative electrode sheet contains a negative electrode active material, and the specific surface area of ​​the negative electrode active material is 0.8 m². 2 / g~1.5m 2 / g, the particle size Dv50 of the negative electrode active material is 8μm~18μm.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The specific surface area of ​​the positive electrode active material is 8m². 2 / g~15m 2 / g.

3. The lithium-ion secondary battery according to claim 1, characterized in that, The particle size Dv50 of the positive electrode active material is 0.5μm~1.5μm.

4. The lithium-ion secondary battery according to claim 1, characterized in that, The specific surface area of ​​the negative electrode active material is 1m². 2 / g~1.5m 2 / g.

5. The lithium-ion secondary battery according to claim 1, characterized in that, The particle size Dv50 of the negative electrode active material is 8μm~12.5μm.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The electrolyte also contains a second additive, which includes a silicon-containing acid-removing additive.

7. The lithium-ion secondary battery according to claim 6, characterized in that, The second additive has one or more of the following characteristics: (1) In the electrolyte, the mass concentration of the second additive is 0.01%~0.5%; (2) The second additive includes one or more of tris(trimethylsilane) phosphate, silazane, N-trimethylsilylimidazolium and tris(trimethylsilane) borate.

8. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The electrolyte also contains a third additive, which includes a combination of a fluorine-containing negative electrode film-forming additive and a negative electrode film-forming additive containing double bonds.

9. The lithium-ion secondary battery according to claim 8, characterized in that, The third additive has one or more of the following characteristics: (1) The fluorine-containing negative electrode film-forming additive includes one or more of fluoroethylene carbonate and fluoroalkyl-substituted ethylene carbonate; (2) In the electrolyte, the mass concentration of the fluorine-containing negative electrode film-forming additive is 0.01%~3%; (3) The double-bonded negative electrode film-forming additive includes one or more of vinylene carbonate, alkyl-substituted vinylene carbonate, and alkenyl-substituted vinylene carbonate; (4) In the electrolyte, the mass concentration of the negative electrode film-forming additive containing double bonds is 0.01%~3%.

10. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The positive electrode active material includes lithium iron phosphate.

11. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The negative electrode active material includes one or both of natural graphite and artificial graphite.

12. A battery cell, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte contains a first additive, which includes 1,3-propenesulfonate lactone, wherein the mass concentration of 1,3-propenesulfonate lactone in the electrolyte is 0.01% to 5%. The positive electrode sheet contains a positive electrode active material, and the specific surface area of ​​the positive electrode active material is 7.6 m². 2 / g~15m 2 / g, wherein the particle size Dv50 of the positive electrode active material is 0.5μm~2.4μm; The negative electrode sheet contains a negative electrode active material, and the specific surface area of ​​the negative electrode active material is 0.8 m². 2 / g~1.5m 2 / g, the particle size Dv50 of the negative electrode active material is 8μm~18μm.

13. The battery cell according to claim 12, characterized in that, The electrolyte also contains a second additive, which includes a silicon-containing acid-removing additive.

14. The battery cell according to claim 13, characterized in that, The second additive has one or more of the following characteristics: (1) In the electrolyte, the mass concentration of the second additive is 0.01%~1%; (2) The second additive includes one or more of tris(trimethylsilane) phosphate, silazane, N-trimethylsilylimidazolium and tris(trimethylsilane) borate.

15. The battery cell according to any one of claims 12 to 14, characterized in that, The electrolyte also contains a third additive, which includes a combination of a fluorine-containing negative electrode film-forming additive and a negative electrode film-forming additive containing double bonds.

16. The battery cell according to claim 15, characterized in that, The third additive has one or more of the following characteristics: (1) The fluorine-containing negative electrode film-forming additive includes one or more of fluoroethylene carbonate and fluoroalkyl-substituted ethylene carbonate; (2) In the electrolyte, the mass concentration of the fluorine-containing negative electrode film-forming additive is 0.01%~5%; (3) The double-bonded negative electrode film-forming additive includes one or more of vinylene carbonate, alkyl-substituted vinylene carbonate, and alkenyl-substituted vinylene carbonate; (4) In the electrolyte, the mass concentration of the negative electrode film-forming additive containing double bonds is 0.01%~5%.

17. An electrical appliance, characterized in that, Includes the lithium-ion secondary battery as described in any one of claims 1 to 11.

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