Lithium ion secondary battery and electric equipment

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a lithium ion secondary battery and electric equipment. The lithium ion secondary battery provided by the invention comprises a winding battery cell and an electrolyte, the winding battery cell comprises a positive plate, a diaphragm and a negative plate, and the negative plate comprises a silicon-based negative electrode material; the negative plate comprises straight areas and arc areas which are arranged in a staggered manner; according to the lithium ion secondary battery, the through holes are formed in the arc area of the negative plate, so that the dynamic performance of the lithium ion secondary battery can be improved, lithium precipitation and black spots caused by volume expansion, electrolyte short circuit and the like in the arc area are avoided, and the falling performance degradation caused by balancing the through holes by controlling the ratio of the mass percentage content of the halogenated sulfonamide compound to the aperture of the through holes; the long-cycle performance of the battery is improved. Besides, the halogenated sulfonamide compound has relatively good flame retardant property and relatively good thermal stability, and can isolate continuous side reaction between a positive electrode and a negative electrode and the electrolyte when being used in the electrolyte, so that the safety performance of the lithium ion secondary battery is remarkably improved.

Description

Technical Field

[0001] This application belongs to the technical field of secondary batteries, and particularly relates to a lithium-ion secondary battery and an electrical device. Background Art

[0002] Lithium-ion secondary batteries are widely used in various fields such as portable electronic devices and electric vehicles due to their high energy density, long cycle life, low self-discharge rate, etc. Among them, silicon-based anode materials have become the most potential alternative to graphite anode materials because of their high specific capacity.

[0003] Due to the huge volume change of silicon-based anode materials during charge and discharge, the electrode structure will be damaged. Especially at the arc of the wound battery, the stress is too large due to the expansion of the silicon-based anode material, the compaction density at the arc will increase, the lithium-ion transmission ability will decrease, and the kinetics is insufficient, resulting in lithium deposition at the arc. At the same time, high expansion is prone to interface damage and aggravates the reaction between the electrolyte and the active material, resulting in performance defects such as lithium deposition and black spots at the arc, affecting the cycle performance of the battery.

[0004] In view of this, it is urgent to develop a technology that can alleviate the defects such as lithium deposition and black spots at the arc caused by the volume expansion of silicon-based anode materials and improve the long-cycle stability of silicon anodes. Summary of the Invention

[0005] Therefore, the technical problem to be solved by this application is to overcome the defects of the silicon-based anode material in the prior art, such as easy lithium deposition and black spots at the arc due to volume expansion, which affect the cycle stability of the battery, so as to provide a lithium-ion secondary battery and an electrical device.

[0006] For this reason, this application provides the following technical solutions:

[0007] According to one aspect of this application, a lithium-ion secondary battery is provided, including a wound battery core and an electrolyte. The wound battery core includes a positive electrode sheet, a separator, and a negative electrode sheet, and the negative electrode sheet includes a silicon-based anode material;

[0008] The negative electrode sheet includes a plurality of flat areas and an arc area connecting two adjacent flat areas. Through holes are provided on the arc area, and the diameter of the through holes is X2 mm, where 0.02 ≤ X2 ≤ 0.15;

[0009] The electrolyte includes a halogenated sulfonamide compound. Based on the total mass of the electrolyte, the mass percentage content of the halogenated sulfonamide compound is X1%, where 0.5 ≤ X1 ≤ 50;

[0010] The ratio between X1 and X2 satisfies: 50 ≤ X1 / X2 ≤ 1200.

[0011] In some alternative embodiments, the hole pitch of the through holes is 0.12 mm - 2 mm.

[0012] In some alternative embodiments, the halogenated sulfonamide compound has a structure represented by any of the following general formulas:

[0013]

[0014] Wherein, X is selected from one of halogen or C1-C4 haloalkyl;

[0015] R1 and R2 are each independently selected from one of C1-C3 alkyl and C1-C3 haloalkyl;

[0016] R3 is selected from one of C1-C3 alkylene, C1-C3 alkoxy, and C1-C3 alkenylene.

[0017] In some alternative embodiments, the halogenated sulfonamide compound has a structure represented by any of the following:

[0018]

[0019] In some alternative embodiments, the electrolyte further includes ethylene carbonate, and the ratio of the mass percentage content of the halogenated sulfonamide compound to the mass percentage content of the ethylene carbonate is X3, where 0.05 ≤ X3 ≤ 2;

[0020] Optionally, based on the mass of the electrolyte, the mass percentage content of the ethylene carbonate is 5% - 25%.

[0021] In some alternative embodiments, the adhesion between the separator and the negative electrode sheet is X4 N / m, where 3 ≤ X4 ≤ 10.

[0022] In some alternative embodiments, the separator includes a base film, an adhesive layer on one surface of the base film, and a ceramic layer on the other surface of the base film. The thickness of the adhesive layer is X5 μm, the thickness of the ceramic layer is X6 μm, and X5 and X6 satisfy: 0.7 ≤ X6 / X5 ≤ 3;

[0023] Preferably, the thickness of the separator is 4 μm - 20 μm, the thickness of the base film is 3 μm - 17 μm, 0.5 ≤ X5 ≤ 1.5, and 0.5 ≤ X6 ≤ 1.5.

[0024] In some alternative embodiments, the tap density of the positive electrode sheet is 4.0 g / cm 3 - 4.5 g / cm 3 , and the tap density of the negative electrode sheet is 1.5 g / cm 3 - 1.9 g / cm 3 .

[0025] In some optional embodiments, the sphericity of the silicon-based anode material is

[0026] In some optional embodiments, the silicon-based anode material includes at least one of nano-silicon, silicon-oxygen material, and silicon-carbon material;

[0027] Preferably, the mass percentage of silicon element in the silicon-based anode material is 10%-80%.

[0028] According to another aspect of the present application, there is provided an electrical device including the above-mentioned lithium-ion secondary battery.

[0029] The technical solution of the present application has the following advantages:

[0030] The lithium-ion secondary battery provided by the present application includes a wound battery cell and an electrolyte. The wound battery cell includes a positive electrode sheet, a separator, and a negative electrode sheet. The negative electrode sheet includes a silicon-based anode material; the negative electrode sheet includes a plurality of flat regions and arc regions connecting adjacent two flat regions. Through holes are provided on the arc regions, and the diameter of the through holes is X2 mm, where 0.02 ≤ X2 ≤ 0.15; the electrolyte includes a halogenated sulfonamide compound. Based on the total mass of the electrolyte, the mass percentage content of the halogenated sulfonamide compound is X1%, where 0.5 ≤ X1 ≤ 50; the ratio between X1 and X2 satisfies: 50 ≤ X1 / X2 ≤ 1200. By providing through holes in the arc regions of the negative electrode sheet, the kinetic performance of the lithium-ion secondary battery can be improved, and the lithium deposition and black spots caused by volume expansion and kinetic decline in the arc regions can be avoided. However, the setting of the through holes will deteriorate the drop performance of the battery. Therefore, it is also necessary to cooperate with the regulation of the ratio of the mass percentage content of the halogenated sulfonamide compound to the aperture of the through holes to alleviate the deterioration of the drop performance caused by the setting of the through holes and improve the long cycle performance. In addition, the halogenated sulfonamide compound has good flame retardancy and good thermal stability, and can also isolate the continuous side reactions between the positive and negative electrodes and the electrolyte when used in the electrolyte, significantly improving the safety performance of the lithium-ion secondary battery.

[0031] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or will be explained through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic structural diagram of the arc region of the negative electrode sheet in Embodiment 1 of the present application;

[0034] Reference numerals:

[0035] 1, flat region; 2, arc region; 3, through hole. Specific embodiments

[0036] The following embodiments are provided to better further understand the present application, which is not limited to the described best embodiment, and does not limit the content and protection scope of the present application. Any product that is the same as or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior art features falls within the protection scope of the present application.

[0037] For those embodiments where specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0038] As described in the background art, due to the huge volume change of the silicon-based negative electrode material during the charge and discharge process, problems such as interface damage and kinetic decline are likely to occur at the arc of the wound battery due to high expansion, and then performance defects such as lithium deposition and black spots appear at the arc, affecting the cycle performance of the battery.

[0039] To solve the above problems, the present application provides the following technical solutions:

[0040] According to one aspect of the present application, a lithium-ion secondary battery is provided, including a wound battery core and an electrolyte. The wound battery core includes a positive electrode sheet, a separator, and a negative electrode sheet, and the negative electrode sheet includes a silicon-based negative electrode material;

[0041] The negative electrode sheet includes a plurality of flat regions and an arc region connecting adjacent two flat regions. Through holes are provided on the arc region, and the diameter of the through holes is X2 mm, 0.02 ≤ X2 ≤ 0.15;

[0042] The electrolyte includes a halogenated sulfonamide compound. Based on the total mass of the electrolyte, the mass percentage content of the halogenated sulfonamide compound is X1%, 0.5 ≤ X1 ≤ 50;

[0043] The ratio between X1 and X2 satisfies: 50 ≤ X1 / X2 ≤ 1200.

[0044] As an example, the diameter of the through hole can be 0.02 mm, 0.04 mm, 0.05 mm, 0.07 mm, 0.09 mm, 0.1 mm, 0.12 mm, 0.14 mm, 0.15 mm, or within the range composed of any of the above values; based on the total mass of the electrolyte, the mass percentage of the halogenated sulfonamide compound can be 0.5%, 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or within the range composed of any of the above values; the ratio between X1 and X2 can be 50, 100, 300, 500, 700, 800, 900, 1000, 1200, or within the range composed of any of the above values.

[0045] Those skilled in the art can understand that the through hole refers to a hole that completely penetrates the negative electrode sheet, and the processing methods of the through hole include but are not limited to laser drilling, etc. Specifically in this application, the through hole refers to a hole generated by penetrating the active layer and the negative electrode current collector of the negative electrode sheet.

[0046] In this application, by providing through holes in the arc area of the negative electrode sheet, the kinetic performance of the lithium-ion secondary battery can be improved, and lithium deposition and black spots caused by the volume expansion of the negative electrode in the arc area can be avoided. By controlling the ratio of the mass percentage of the halogenated sulfonamide compound to the aperture of the through hole, the deterioration of the drop performance caused by the through hole can be balanced, and the halogenated sulfonamide compound can improve the interface stability between the positive and negative electrodes and improve the long-cycle performance. In addition, the halogenated sulfonamide compound has good flame retardancy and good thermal stability, and can also isolate the continuous side reactions between the positive and negative electrodes and the electrolyte when used in the electrolyte, significantly improving the safety performance of the lithium-ion secondary battery.

[0047] Specifically, by providing through-holes in the arc region, the present application can effectively improve the problems of lithium deposition and black spots caused by the volume expansion of the silicon-based anode material in the arc region, and enhance the kinetic performance. However, the provision of through-holes will lead to a decrease in the stability of the current collector in the arc region and a decrease in the mechanical strength of the electrode sheet, and it is prone to broken pieces during the drop test, resulting in test failure. By matching the content of the halogenated sulfonamide compound with the aperture of the through-hole, the drop performance can be effectively improved, avoiding the deterioration of the drop performance caused by the provision of through-holes, and the halogenated sulfonamide compound can enhance the interfacial stability between the positive and negative electrodes and improve the long-cycle performance. The fluorine atom and nitrogen atom in the halogenated sulfonamide compound have strong reactivity and can chemically react with the metal substance on the surface of the current collector to form a stable protective film at the position of the through-hole on the current collector, avoiding the decrease in stability or even the occurrence of foil breakage due to the continuous dissolution of the current collector during the long-cycle process, and improving the drop performance. The larger the aperture of the through-hole, the larger the exposed hole edge, and the more halogenated sulfonamide compound is required. Therefore, it is necessary to limit the ratio between the content of the halogenated sulfonamide compound and the aperture of the through-hole. If the aperture is too large, the mechanical strength of the electrode sheet becomes poor, and the drop performance will be significantly deteriorated. If the aperture is too small, the pores are not sufficient to provide electrolyte flow-through, resulting in the still existence of lithium deposition in the arc region. If the mass percentage content of the halogenated sulfonamide compound is too low, the improvement of the drop performance is not obvious, and the flame retardancy of the electrolyte is reduced, and the thermal runaway is significantly advanced during the short-circuit of the safety test. If it is too high, its impedance will be significantly increased and the kinetics will be insufficient. If the ratio between X1 and X2 is too low, it means that the aperture is too large and the halogenated sulfonamide is insufficient, the improvement of the drop performance is not obvious, and the safety performance is significantly deteriorated. If the aperture is too small and the halogenated sulfonamide is too much, the kinetics will be significantly decreased and the lithium deposition will be severely aggravated.

[0048] In some alternative embodiments, the hole pitch of the through-hole is 0.12 mm - 2 mm. As an example, the hole pitch of the through-hole can be 0.12 mm, 0.15 mm, 0.25 mm, 0.5 mm, 0.65 mm, 0.75 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, or within the range composed of any of the above values. By limiting the hole pitch in the present application, it can be ensured that the hole pitch is not too small to ensure that the negative electrode sheet has sufficient mechanical strength, nor too large to result in poor improvement effect on lithium deposition in the arc region. By limiting the hole pitch of the through-hole to the above range in the present application, the balance between mechanical strength and improvement of lithium deposition can be achieved.

[0049] In some alternative embodiments, the halogenated sulfonamide compound has a structure represented by any of the following general formulas:

[0050]

[0051] Wherein, X is selected from one of halogen or C1-C4 haloalkyl;

[0052] R1 and R2 are each independently selected from one of C1-C3 alkyl groups and C1-C3 haloalkyl groups;

[0053] R3 is selected from one of C1-C3 alkylene groups, C1-C3 alkoxy groups, and C1-C3 alkenylene groups.

[0054] As an example, X can be at least one of F, Cl, Br, I, partially fluorinated or perfluorinated methyl, partially fluorinated or perfluorinated ethyl, partially fluorinated or perfluorinated propyl, partially fluorinated or perfluorinated isopropyl, partially brominated or perbrominated methyl, partially brominated or perbrominated ethyl, etc.; R1 and R2 are each independently selected from at least one of methyl, ethyl, propyl, isopropyl, partially fluorinated or perfluorinated methyl, partially fluorinated or perfluorinated ethyl, partially fluorinated or perfluorinated propyl, etc., and R1 and R2 can be the same or different; R3 can be at least one of a linking bond, methylene, ethylene, propylene, methoxy (-CH2O-), ethoxy (-CH2CH2O-), vinyl (-CH=CH-), etc.

[0055] In some alternative embodiments, the halogenated sulfonamide compound has any of the following structures:

[0056]

[0057]

[0058] By further defining the structure of the halogenated sulfonamide compound in this application, the battery drop performance, thermal stability, safety performance, etc. can be better balanced.

[0059] In some alternative embodiments, the electrolyte further includes ethylene carbonate (EC), and the ratio of the mass percentage content of the halogenated sulfonamide compound to the mass percentage content of the ethylene carbonate is X3, where 0.05 ≤ X3 ≤ 2;

[0060] Optionally, based on the mass of the electrolyte, the mass percentage content of the ethylene carbonate is 5%-25%. As an example, the ratio of the mass percentage content of the halogenated sulfonamide compound to the mass percentage content of the ethylene carbonate can be 0.05, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or within the range composed of any of the above values; as an example, the mass percentage content of the ethylene carbonate in the electrolyte can be 5%, 10%, 15%, 20%, 25%, or within the range composed of any of the above values.

[0061] Those skilled in the art can understand that halogenated sulfonamide compounds tend to cause a relatively high viscosity of the electrolyte, deteriorate the kinetic performance, and at the same time have insufficient ability to repair the interface film. Therefore, ethylene carbonate needs to be matched with halogenated sulfonamide compounds to balance the kinetic deterioration and insufficient interface film repair ability brought by halogenated sulfonamide compounds. Ethylene carbonate can improve the film formation stability and the later repair ability, and the synergistic effect of halogenated sulfonamide compounds and ethylene carbonate to form a stable interface film not only has good stability, but also the formed N-rich interface film has high-temperature stability and high lithium-ion transport efficiency, which can further improve the drop performance, kinetic performance and cycle performance. When the amount of halogenated sulfonamide compounds is excessive and the amount of ethylene carbonate is insufficient, the stability and self-repair ability of the interface film will decrease due to the lack of organic components decomposed by ethylene carbonate, deteriorating the cycle performance; when the amount of ethylene carbonate is excessive and the amount of halogenated sulfonamide compounds is insufficient, the organic interface film components formed have low high-temperature stability of SEI, which will cause the battery to generate gas easily at high temperatures; by controlling the dosage ratio of halogenated sulfonamide compounds and ethylene carbonate within the above range, the drop performance, kinetic performance and cycle performance can be improved more effectively.

[0062] In some optional embodiments, the adhesion between the separator and the negative electrode sheet is X4 N / m, where 3 ≤ X4 ≤ 10. As an example, the adhesion between the separator and the negative electrode sheet can be 3 N / m, 4 N / m, 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, or within the range composed of any of the above values. By limiting the adhesion between the separator and the negative electrode sheet within the above range, the tensile strength of the arc area can be effectively improved, further improving the drop performance and reducing the safety risk.

[0063] In this application, methods and equipment known in the art can be used to test the adhesion between the separator and the negative electrode sheet. As an example, the test for the adhesion between the separator and the electrode sheet can include the following steps: After the battery is taken off the sorting table, it is placed in an environment of (25 ± 2) °C and left to stand for 2 h - 3 h. The battery is charged at a constant current of 0.7C, and the cut-off current is 0.05C. When the battery terminal voltage reaches the charging limit voltage, it is changed to constant voltage charging until the charging current ≤ the cut-off current, and then the charging is stopped. After standing for 5 min, the fully charged battery is dissected. Referring to the national standard GB / T 2790-1995, the separator and the positive electrode sheet or the negative electrode sheet are cut into small strips of 15 mm × 54.2 mm, and the adhesion between the separator and the positive electrode sheet or the negative electrode sheet is tested using the 180° peel test standard. In this application, the adhesion can be adjusted by controlling the hot pressing temperature. The higher the hot pressing temperature, the higher the adhesion.

[0064] In some optional embodiments, the diaphragm includes a base film, a glue layer located on one side of the base film, and a ceramic layer located on the other side of the base film, and the thickness of the glue layer is X5 μm and the thickness of the ceramic layer is X6 μm, satisfying: 0.7≤X6 / X5≤3; as an example, the ratio of the thickness of the glue layer to the thickness of the ceramic layer can be 0.7, 1, 1.2, 1.4, 1.5, 1.7, 1.9, 2, 2.2, 2.5, 2.8, 3, or within the range of any of the above indices;

[0065] Preferably, the thickness of the diaphragm is 4 μm-20 μm, the thickness of the base film is 3 μm-17 μm, 0.5≤X5≤1.5, 0.5≤X6≤1.5. As an example, the thickness of the diaphragm can be 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, or within the range of any of the above values; the thickness of the base film can be 3μm, 4μm, 5μm, 6μm, 7μm, 9μm, 10μm, 12μm, 14μm, 15μm, 17μm, or within the range of any of the above values; the thickness of the glue layer can be 0.5μm, 0.7μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, or within the range of any of the above values; the thickness of the ceramic layer can be 0.5μm, 0.7μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, or within the range of any of the above values.

[0066] It can be understood by those skilled in the art that the ceramic layer of the diaphragm can enhance the structural strength of the diaphragm, reduce the risk of internal short circuit caused by mechanical impact when the battery falls, and the diaphragm containing the ceramic layer has better thermal stability. The ceramic layer can better maintain the electrical performance after the battery falls. In addition, the capacity retention rate and internal resistance of the battery containing the ceramic layer diaphragm change less after falling, and the thermal shrinkage rate of the ceramic layer diaphragm is low, which can reduce the increase in internal pressure caused by thermal shrinkage after the battery falls, thereby reducing safety risks. The glue layer can provide adhesion for the diaphragm to prevent the pole piece from detaching during the working process, and improve the cycle stability, drop performance and safety. However, if the ceramic layer is too thick and the glue layer is too thin, the diaphragm and the pole piece will be easily detached, and the pole piece will lose the high toughness support of the diaphragm, resulting in easy failure due to falling; and if the ceramic layer is too thin and the glue layer is too thick, it will affect the thermal stability.

[0067] It should be noted that the compositions of the ceramic layer and the adhesive layer are conventional in the art and may include any prior art disclosed in the art. The present application does not make specific limitations. As an example, the ceramic layer includes at least one of alumina, boehmite (hydrated aluminum hydroxide), magnesium oxide, magnesium hydroxide, BaSO4, CaSiO3, CaSiO4, and TiO2; the adhesive layer includes at least one of polyvinylidene fluoride (PVDF) or polymethyl methacrylate (PMMA), etc.

[0068] In some alternative embodiments, the tap density of the positive electrode sheet is 4.0 g / cm 3 - 4.5 g / cm 3 , and the tap density of the negative electrode sheet is 1.5 g / cm 3 - 1.9 g / cm 3 . As an example, the tap density of the positive electrode sheet can be 4.0 g / cm 3 , 4.05 g / cm 3 , 4.1 g / cm 3 , 4.15 g / cm 3 , 4.2 g / cm 3 , 4.25 g / cm 3 , 4.3 g / cm 3 , 4.5 g / cm 3 , or within the range composed of any of the above values; the tap density of the negative electrode sheet can be 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.9 g / cm 3 , or within the range composed of any of the above values.

[0069] In some alternative embodiments, the sphericity of the silicon-based negative electrode material is As an example, the sphericity of the silicon-based negative electrode material can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.8, 0.9, 0.95, 0.99, or within the range composed of any of the above values.

[0070] Those skilled in the art can understand that sphericity is a parameter characterizing the particle morphology. The closer the particle morphology is to a sphere, the closer its sphericity is to 1. By improving the sphericity of the silicon-based anode material in this application, the abnormal extrusion of the electrode sheet on the current collector during charge and discharge can be effectively reduced, thereby enhancing the strength of the current collector during safety tests and reducing the impact force on the current collector by sharp substances. If the sphericity is too low, the particles are irregular and have sharp edges, which are likely to cause abnormal extrusion of the current collector and reduce the safety performance.

[0071] In this application, methods and equipment known in the art can be used to test the sphericity of the silicon-based anode material. As an example, by using image processing software (such as Image Pro Plus) to analyze the images of each particle in the SEM photo of the composite material at a certain magnification (such as 2500 times), the perimeter and area of each particle are obtained, and the perimeter equivalent radius r1 and area equivalent radius r2 of each particle are calculated respectively. Then the sphericity of each particle Furthermore, the sphericities of each particle are weighted and averaged numerically to obtain the average sphericity of the composite material.

[0072] In some optional embodiments, the silicon-based anode material includes at least one of nano-silicon, silicon-oxygen material (SiO x (0 < x < 2)), and silicon-carbon material;

[0073] As an example, the silicon-carbon material includes a porous carbon skeleton and silicon particles located in the pores of the porous carbon skeleton; further preferably, at least part of the surface of the porous carbon skeleton also includes a carbon coating layer; the silicon-carbon graphite blended anode material can be obtained by physical mixing.

[0074] Preferably, the mass ratio of silicon element in the silicon-based anode material is 10% - 80%. As an example, the mass ratio of silicon element in the silicon-based anode material can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or within the range composed of any of the above values. By limiting the mass ratio of silicon element in the silicon-based anode material in this application, the balance between energy density and volume expansion can be achieved.

[0075] Those skilled in the art can understand that during the charge and discharge process of the battery, lithium ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet, the electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet, and the separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing lithium ions to pass through.

[0076] As an example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector. The materials, compositions, and manufacturing methods of the positive electrode sheet used in the lithium-ion secondary battery of the present application may include any techniques disclosed in the prior art. As an example, the positive electrode active material is selected from layered lithium composite oxides, and its chemical general formula is Li (1+x) Ni y Co z M (1-y-z) O2, where -0.1 ≤ x ≤ 1; 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ y + z ≤ 1; M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0077] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector has two surfaces opposite to 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. The materials, compositions, and manufacturing methods of the negative electrode sheet used in the lithium-ion secondary battery of the present application may include any techniques disclosed in the prior art. In the present application, the negative electrode active material includes a silicon-based negative electrode material.

[0078] There are no particular limitations on the materials and shapes of the separator used in the lithium-ion secondary battery of the present application, and it may include any techniques disclosed in the prior art.

[0079] The organic solvents in the electrolyte of the present application are selected from one or more of carbonates and / or carboxylates;

[0080] Preferably, the carbonate is selected from one or more of the following solvents: propylene carbonate (PC), dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0081] Preferably, the carboxylate is selected from one or more of the following solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-butyl ethyl acetate.

[0082] The additives in the electrolyte are selected from: vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), ethylene sulfate, succinonitrile (SN), glutaronitrile, adiponitrile (ADN), pimelonitrile, suberonitrile, sebaconitrile, 1,3,6-hexanetricarbonitrile, glycerol trinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3-propane sultone (PS), and allyl-1,3-sulfonic acid lactone, etc.

[0083] The lithium salt in the electrolyte of the present application is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, or lithium bis(trifluoromethylsulfonyl)imide.

[0084] In the present application, based on the total mass of the electrolyte, the mass concentration of the lithium salt can be 12% - 18%. As an example, the mass concentration of the lithium salt in the electrolyte can be 12%, 13%, 14%, 15%, 16%, 17%, 18%, or within the range composed of any of the above values.

[0085] In the present application, the preparation method of the lithium ion secondary battery is conventional in the art. As an example, the preparation method may include:

[0086] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, ensure that the separator is between the positive and negative electrode sheets to play an insulating role, and then obtain an un-injected bare battery cell by winding; place the bare battery cell in an outer packaging foil, inject the prepared electrolyte into the dried bare battery cell, and obtain the required lithium ion secondary battery through processes such as vacuum packaging, standing, formation, shaping, and sorting.

[0087] According to another aspect of the present application, there is provided an electrical device including the above-mentioned lithium ion secondary battery.

[0088] In the present application, the lithium ion 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 can be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0089] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0090] In all the embodiments and comparative examples of the present application, the unit % represents mass percentage.

[0091] Example 1

[0092] This example provides a lithium ion secondary battery, and its specific composition and preparation method are as follows:

[0093] Composition of the electrolyte:

[0094] Base organic solvent: The mass ratio of ethylene carbonate (EC): PC: diethyl carbonate is 3:5:4;

[0095] Based on the total mass of the electrolyte, it also includes 30% of halogenated sulfonamide compounds (the structure shown in Formula 1); 15% of ethylene carbonate, 11% of FEC, 0.7% of LiODFB, 1.5% of PS, 1.8% of 1,3,6-hexanetricarbonitrile, 1.4% of ADN, 0.7% of SN, and the balance is the base organic solvent;

[0096] Lithium salt: Based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 14%;

[0097] Composition and preparation of the positive electrode sheet: Mix the positive electrode active material lithium cobaltate, polyvinylidene fluoride (PVDF), conductive carbon black SP (super P), and carbon nanotubes (CNT) according to a mass ratio of 97.2:1:1.3:0.5, add N-methylpyrrolidone (NMP), and stir under a vacuum mixer until the mixed system becomes a homogeneous and fluid positive electrode active paste; uniformly coat the positive electrode active paste on both surfaces of the aluminum foil; dry the coated aluminum foil, and then obtain the required positive electrode sheet through rolling and slitting. The tap density of the positive electrode sheet is 4.2 g / cm 3 。

[0098] Composition and preparation of the negative electrode sheet: Mix the carbon-based negative electrode material (artificial graphite, average particle size Dv50 is 14 μm), silicon-based negative electrode material (silicon-carbon negative electrode material, average particle size Dv50 is 9 μm, and the mass percentage of silicon element is 30%), sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) according to a mass ratio of 79.5:15:2.5:1.5:1:0.5, add deionized water, and obtain the negative electrode paste under the action of a vacuum mixer; uniformly coat it on both surfaces of the copper foil; dry the coated copper foil at room temperature, then transfer it to an 80°C oven for drying for 10 h, and then obtain the negative electrode sheet through cold pressing and slitting. Make perforations by laser at the arc, and the main perforation range is in the arc area. The tap density of the negative electrode sheet is 1.7 g / cm 3 。Among them, the silicon-based negative electrode material is a silicon-carbon negative electrode material, in which the mass percentage of silicon is 30%, and its sphericity is 0.7, as Figure 1 shown. The negative electrode sheet includes a plurality of straight regions 1 and an arc region 2 connecting two adjacent straight regions 1. Through holes 3 are provided on the arc region 2. The diameter of the through holes 3 is 0.06 mm; the hole pitch of the through holes 3 is 0.5 mm; the adhesion between the separator and the negative electrode sheet is 7 N / m 。

[0099] Separator:

[0100] The separator includes a base film with a thickness of 7 μm, a 1-μm-thick adhesive layer (composed of PVDF) on one surface of the base film, and a 1-μm-thick ceramic layer (composition including alumina) on the other surface.

[0101] Battery assembly:

[0102] Stack the prepared positive electrode sheet, separator (with the ceramic layer facing the positive electrode sheet), and negative electrode sheet in sequence, ensuring that the separator is between the positive and negative electrode sheets to play an isolation role, and then obtain an un-injected bare battery cell through winding; place the bare battery cell in an outer packaging foil, inject the prepared electrolyte into the dried bare battery cell, and obtain the required lithium-ion secondary battery through processes such as vacuum packaging, standing, formation, shaping, and sorting.

[0103] Examples 2 - 22

[0104] The differences between Examples 2 - 22 and Example 1 are shown in the following table:

[0105] Table 1

[0106]

[0107] Examples 23 - 35

[0108] The differences between Examples 23 - 35 and Example 1 are shown in the following table:

[0109] Table 2

[0110]

[0111]

[0112] Comparative Example 1

[0113] The difference from Example 9 is that ethyl methanesulfonate with the same mass is used instead of the compound shown in Formula 1.

[0114] Comparative Example 2

[0115] The difference from Example 9 is that the content of the compound shown in Formula 1 is 3%, and the part less than 100% is made up with the base solvent.

[0116] Comparative Example 3

[0117] The difference from Example 9 is that the amount of the base solvent is reduced, and the content of the compound shown in Formula 1 is adjusted to 55%.

[0118] Comparative Example 4

[0119] The difference from Example 9 is that there is no through-hole in the arc area.

[0120] Comparative Example 5

[0121] The difference from Example 9 is that the content of the compound shown in Formula 1 is 50%, and the aperture of the through-hole is 0.02 mm.

[0122] Comparative Example 6

[0123] The difference from Example 9 is that the aperture of the through-hole is 0.3 mm.

[0124] Test Example

[0125] The lithium-ion secondary batteries prepared in each example and comparative example were subjected to performance tests. The specific test methods are as follows:

[0126] 1. Drop performance

[0127] After the battery core was charged at a constant current of 0.2C to 4.5V and then charged at a constant voltage until cut off at 0.02C until fully charged, the test was carried out within 12 - 24h. In this example, the test was carried out within 12h. The battery core was freely dropped from a height of 1m onto a cement floor, and each surface was dropped once, for a total of 6 tests. After the test, a discharge-charge cycle was carried out according to the standard charge-discharge steps. If the battery core did not catch fire, explode, or leak liquid, it was considered to pass the test. Record the number of battery cores passing the test as n, and record it as n / 6 pass.

[0128] 2. Gas generation during storage

[0129] After the battery was charged at a constant current of 0.2C and a constant voltage until cut off at 0.02C until fully charged, the thickness d1 of the battery before high-temperature storage was measured using a PPG battery thickness gauge (PPG with 500g). The battery was placed in an 85°C constant temperature oven for storage. After 6h of storage, the thickness was measured to obtain the thickness expansion rate data.

[0130] 3. High-temperature cycling

[0131] The lithium-ion battery was placed at 45°C, charged at a constant current of 1C to the upper limit voltage (4.5V), then charged at a constant voltage of 4.5V until 0.05C, and left standing for 5 minutes; then discharged at a constant current of 0.5C to 3V and left standing for 5 minutes. This was one charge-discharge cycle. Charge / discharge in this way, and record the discharge capacity retention rate of the lithium-ion battery after 400 cycles.

[0132] 4. Lithium precipitation at 3C

[0133] The batteries obtained in each example and comparative example were placed in a constant temperature environment of 25°C. ① Stand still for 10 min, ② first discharge at 0.2C to 3.0V, ③ stand still for 10 min, ④ charge at a rate of 3C to 4.5V, with a cut-off current of 0.02C, ⑤ stand still for 10 min, ⑥ discharge at 0.2C to 3.0V, ⑦ stand still for 10 min. Steps ④ to ⑦ were cycled 30 times, and the battery was disassembled in a fully charged state to observe the lithium deposition on the negative electrode interface.

[0134] The specific test results are shown in the following table:

[0135] Table 3

[0136]

[0137]

[0138]

[0139] From the data in the above table, it can be seen that the lithium-ion secondary battery provided by the embodiment of the present application can improve the kinetic performance of the lithium-ion secondary battery by setting through holes in the arc area of the negative electrode sheet, avoiding lithium deposition caused by volume expansion in the arc area, and balancing the deterioration of the drop performance caused by the through holes by controlling the ratio of the mass percentage content of the halogenated sulfonamide compound to the aperture of the through hole, thereby improving the long-cycle performance.

[0140] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A lithium ion secondary battery, characterized in that: It comprises a wound battery cell and an electrolyte, wherein the wound battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet, and the negative electrode sheet comprises a silicon-based negative electrode material; The negative electrode sheet includes a plurality of straight areas and an arc area connecting two adjacent straight areas, and the arc area is provided with a through hole, and the diameter of the through hole is X2mm, 0.02≤X2≤0.15; The electrolyte includes a halogenated sulfonamide compound, and the mass percentage of the halogenated sulfonamide compound is X1% based on the total mass of the electrolyte, 0.5≤X1≤50; The ratio between X1 and X2 satisfies: 50≤X1 / X2≤1200.

2. The lithium ion secondary battery according to claim 1, characterized in that: The through holes have a hole spacing of 0.12 mm to 2 mm.

3. The lithium ion secondary battery according to claim 1, characterized in that: The halogenated sulfonamide compound has a structure shown in any of the following general formulas: Wherein, X is selected from one of halogen or C1-C4 haloalkyl; R1, R2 are independently selected from one of C1-C3 alkyl and C1-C3 haloalkyl; R3 is selected from one of C1-C3 alkylene, C1-C3 alkyleneoxy, and C2-C3 alkenylene.

4. The lithium ion secondary battery according to claim 3, characterized in that: The halogenated sulfonamide compound has any of the following structures:

5. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The electrolyte also includes ethylene carbonate, and the ratio of the mass percentage of the halogenated sulfonamide compound to the mass percentage of the ethylene carbonate is X3, 0.05≤X3≤2; Optionally, based on the mass of the electrolyte, the mass percentage of the ethylene carbonate is 5%-25%.

6. The lithium ion secondary battery according to claim 1, characterized in that: The bonding force between the separator and the negative electrode sheet is X4 N / m, 3≤X4≤10.

7. The lithium ion secondary battery according to claim 1, characterized in that: The diaphragm includes a base film, a glue layer located on one side of the base film, and a ceramic layer located on the other side of the base film, the glue layer has a thickness of X5 μm, the ceramic layer has a thickness of X6 μm, and X5 and X6 satisfy: 0.7≤X6 / X5≤3; Preferably, the thickness of the diaphragm is 4 μm-20 μm, the thickness of the base film is 3 μm-17 μm, 0.5≤X5≤5, 0.5≤X6≤5.

8. The lithium ion secondary battery according to claim 1, characterized in that: The compaction density of the positive electrode sheet is 4.0 g / cm 3 -4.5g / cm 3 The compaction density of the negative electrode sheet is 1.5 g / cm 3 -1.9g / cm 3 ; And / or, the sphericity of the silicon-based negative electrode material is 9. The lithium ion secondary battery according to any one of claims 1 to 4 or 6 to 8, characterized in that: The silicon-based negative electrode material includes at least one of nano-silicon, silicon-oxygen material, and silicon-carbon material; Preferably, the mass proportion of silicon element in the silicon-based negative electrode material is 10%-80%.

10. An electrical device, characterized in that: A lithium ion secondary battery comprising the lithium ion secondary battery according to claim 9.

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