Battery

Abstract

The invention provides a battery. The battery comprises an electrolyte, a positive electrode, a negative electrode and a diaphragm, the diaphragm comprises a base film and a first functional coating positioned on at least one side of the base film; the first functional coating comprises nitrogen-containing organic particles, the mass ratio of nitrogen in the first functional coating is awt%, and a is larger than or equal to 10 wt% and smaller than or equal to 60 wt%; the electrolyte comprises a boron-containing additive, the mass ratio of the boron-containing additive in the electrolyte is bwt%, and 0.1 wt% < = b < = 3wt%; the boron-containing additive has a structure as shown in a formula I; the battery provided by the invention has relatively high high-temperature safety and low-temperature discharge performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a battery. Background Technology

[0002] Due to their advantages such as high energy density and long cycle life, rechargeable batteries have been widely used in portable electronic devices (such as smartphones and laptops), electric vehicles, energy storage systems, and aerospace.

[0003] With the expansion of application scenarios, the performance requirements of batteries in extreme temperature environments are becoming increasingly prominent. However, current rechargeable batteries suffer from insufficient safety at high temperatures and poor discharge performance at low temperatures, which limits their development.

[0004] Therefore, there is an urgent need for a method that can improve both the high-temperature safety and low-temperature discharge performance of secondary batteries. Summary of the Invention

[0005] This invention provides a battery that combines high high-temperature safety and low-temperature discharge performance.

[0006] This invention provides a battery comprising an electrolyte, a positive electrode, a negative electrode, and a separator;

[0007] The diaphragm includes a base membrane and a first functional coating located on at least one side of the base membrane;

[0008] The first functional coating comprises nitrogen-containing organic particles, wherein the mass percentage of nitrogen in the first functional coating is awt%, 10wt%≤a≤60wt%;

[0009] The electrolyte includes a boron-containing additive, wherein the boron-containing additive accounts for b% of the electrolyte by mass, and 0.1wt%≤b≤3wt%.

[0010] The boron-containing additive has the structure shown in Formula I:

[0011] Formula I

[0012] R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1 to 12 substituted or unsubstituted carbon atoms, alkenyl groups with 2 to 12 substituted or unsubstituted carbon atoms, alkynyl groups with 2 to 12 substituted or unsubstituted carbon atoms, and aryl groups with 6 to 12 substituted or unsubstituted carbon atoms. When substituted, the substituent is selected from at least one of halogen atoms and cyano groups.

[0013] In some embodiments of the present invention, the boron-containing additive comprises one or more compounds represented by formulas II-1 to II-11:

[0014] II-1 II-2 II-3

[0015] II-4 II-5 II-6

[0016] II-7 II-8 II-9

[0017] II-10 II-11.

[0018] In some embodiments of the present invention, the battery satisfies: 10 ≤ a / b ≤ 500; preferably 15 ≤ a / b ≤ 475;

[0019] And / or, the average particle size e of the nitrogen-containing organic particles is 0.1 μm ≤ e ≤ 1 μm;

[0020] And / or, the nitrogen-containing organic particles include melamine cyanurate, melamine thiocyanate, melamine polyphosphate, 1,3,5-triazine-2,4,6-triamine, 4,6-dimethyl-2-phenylpyrimidine, uracil, 2-amino-4,6-methoxy-1,3,5-triazine, cytosine, 2 At least one of 4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, melamine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, and tris(tribromophenoxy)triazine.

[0021] In some embodiments of the present invention, the separator further includes an adhesive layer located on at least a portion of the surface of the first functional coating opposite to the base film and / or on the surface of the base film, and the battery satisfies at least one of the following conditions:

[0022] 1) The thickness of the base film is c, where 3.5μm≤c≤13μm;

[0023] 2) The thickness of the first functional coating is d, 0.3μm≤d≤5μm;

[0024] 3) The thickness of the adhesive layer is f, where 0.5μm≤f≤5μm;

[0025] 4) The total thickness of the diaphragm is 4.3μm~23μm.

[0026] In some embodiments of the present invention, the electrolyte further includes a fluorinated additive, wherein the mass percentage of the fluorinated additive in the electrolyte is 0.5wt% ≤ g ≤ 30wt%; preferably, the fluorinated additive includes one or more compounds represented by formulas III-1 to III-8:

[0027] III-1 III-2 III-3

[0028] III-4 III-5 III-6

[0029] III-7 III-8;

[0030] And / or, the electrolyte further includes a sulfur-containing additive, wherein the mass percentage p of the sulfur-containing additive in the electrolyte is 0.1wt% ≤ p ≤ 5wt%; preferably, the sulfur-containing additive includes one or more compounds represented by formulas IV-1 to IV-8:

[0031] IV-1 IV-2 IV-3

[0032] IV-4 IV-5 IV-6

[0033] IV-7 IV-8

[0034] IV-9 IV-10.

[0035] In some embodiments of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector;

[0036] The positive electrode current collector and the positive electrode active material layer include a second functional coating. Preferably, the second functional coating includes one or more of alumina, boehmite, titanium dioxide, silicon dioxide, and magnesium oxide.

[0037] Preferably, the battery satisfies: 0.5≤h / b≤50, where h is the thickness of the second functional coating in μm; preferably, 1≤h≤10.

[0038] In some embodiments of the present invention, the positive electrode active material layer comprises a solid electrolyte material;

[0039] Preferably, the solid electrolyte material includes at least one of lithium aluminum titanium phosphate, lithium lanthanum titanate, and lithium lanthanum zirconate.

[0040] In some embodiments of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; wherein the negative electrode active material layer includes a silicon-based material;

[0041] Preferably, the silicon-based material includes a silicon-carbon material, which includes porous carbon and silicon material deposited in the porous carbon channels;

[0042] Preferably, the silicon-based material includes a carbon coating layer, and the thickness m of the carbon coating layer is 0.5 nm ≤ m ≤ 25 nm.

[0043] In some embodiments of the present invention, the negative electrode active material layer comprises carbon nanotubes;

[0044] Preferably, the diameter k of the carbon nanotube is 1 nm ≤ k ≤ 40 nm.

[0045] Preferably, the length l of the carbon nanotube is 0.1 μm ≤ l ≤ 30 μm;

[0046] Preferably, the carbon nanotubes may be distributed inside the silicon-based material and / or at least partially on its surface.

[0047] In some embodiments of the present invention, at least a portion of the surface of the negative electrode active material layer away from the negative electrode current collector is provided with a groove, and the depth n of the groove is 5μm≤n≤40μm;

[0048] And / or, the width w of the groove is 30μm≤w≤500μm;

[0049] And / or, the spacing o between adjacent grooves is 0.5mm ≤ o ≤ 10mm.

[0050] The present invention provides a battery that, by setting a first functional coating including nitrogen-containing organic particles in the separator, adding a boron-containing additive to the electrolyte, and controlling the relationship between the mass ratio of nitrogen in the first functional coating and the mass ratio of the boron-containing additive in the electrolyte, can synergistically improve the battery's performance, enabling the battery to have both high high-temperature safety and low-temperature discharge performance. Attached Figure Description

[0051] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0052] Figure 1 This is a schematic diagram of the structure of a battery according to an embodiment of the present invention.

[0053] Explanation of reference numerals in the attached figures

[0054] 11: Base film; 12: First functional coating; 13: Adhesive layer; 21: Negative electrode current collector; 22: Negative electrode active material layer; 31: Positive electrode current collector; 32: Positive electrode active material layer; 33: Second functional layer.

[0055] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0057] Currently, rechargeable batteries face the dual challenge of simultaneously meeting low-temperature discharge performance and high-temperature safety requirements. Inventors have attempted to improve low-temperature discharge performance by adding low-temperature modifiers (such as ether compounds) to reduce electrolyte viscosity and enhance the transport efficiency of active metal ions. However, the decomposition of ether compounds at high temperatures reduces electrolyte stability and worsens high-temperature safety. Adding flame retardants to the electrolyte to suppress thermal runaway can improve high-temperature safety to some extent, but it significantly reduces the electrolyte's ionic conductivity, making it impossible to meet the required low-temperature discharge performance.

[0058] Therefore, based on the premise of balancing the improvement of the electrolyte's ionic conductivity at low temperatures and the battery's stability at high temperatures, the inventors attempted to improve both the battery's high-temperature safety and low-temperature discharge performance.

[0059] Based on this, embodiments of the present invention provide a battery, the battery comprising an electrolyte, a positive electrode, a negative electrode, and a separator; the separator comprises a base membrane and a first functional coating located on at least one side of the base membrane; the first functional coating comprises nitrogen-containing organic particles, wherein the mass percentage of nitrogen in the first functional coating is awt%, 10wt%≤a≤60wt%; the electrolyte comprises a boron-containing additive, wherein the mass percentage of the boron-containing additive in the electrolyte is bwt%, 0.1wt%≤b≤3wt%; the boron-containing additive has the structure shown in Formula I:

[0060] Formula I

[0061] R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1 to 12 substituted or unsubstituted carbon atoms, alkenyl groups with 2 to 12 substituted or unsubstituted carbon atoms, alkynyl groups with 2 to 12 substituted or unsubstituted carbon atoms, and aryl groups with 6 to 12 substituted or unsubstituted carbon atoms. When substituted, the substituent is selected from at least one of halogen atoms and cyano groups.

[0062] The battery of this invention, when meeting the above conditions, balances high-temperature safety and low-temperature discharge performance.

[0063] The inventors analyzed that the reason why the battery of the present invention has both high high-temperature safety and low-temperature discharge performance is that: First, the separator of the present invention includes a first functional coating, which includes nitrogen-containing organic particles. On the one hand, nitrogen-containing organic particles have high stability and low coefficient of thermal expansion, which can improve the stability of the separator under high-temperature conditions; on the other hand, nitrogen-containing organic particles can consume free radicals in the electrolyte and inhibit free radical chain reactions that occur in the electrolyte, thereby effectively reducing the large amount of heat generated by free radical chain reactions, which is beneficial to improving the high-temperature safety of the battery.

[0064] However, in nitrogen-containing organic particles, the lone pairs of electrons on nitrogen (N) atoms readily adsorb lithium ions, leading to increased resistance to lithium ions passing through the separator, which has a particularly significant impact on the battery's discharge performance at low temperatures.

[0065] The electrolyte of this invention includes a boron-containing additive with the structure shown in Formula I. By controlling the mass percentage of nitrogen in the first functional coating and the mass percentage of the boron-containing additive in the electrolyte to meet the above conditions, the discharge performance of the battery at low temperatures can be improved. Specifically, during battery charging and discharging, the low oxidation potential of the boron-containing additive makes it easily oxidized and decomposed into borate esters and borate compounds. These compounds deposit on the surface and pores of the separator to form a protective layer. This protective layer increases the polarity of the separator surface, which is beneficial for improving the wettability of the electrolyte to the separator, making the interface between the electrolyte and the separator more compact and stable, reducing air gaps and poor contact at the interface, thereby reducing the battery's interface resistance and improving the efficiency of lithium ions passing through the separator. Furthermore, it also forms a shielding effect against the attraction of nitrogen atoms to lithium ions, which is beneficial for lithium ion transport.

[0066] Therefore, when the above conditions are met, the battery of the present invention can synergistically improve the ionic conductivity of the electrolyte at low temperatures and the stability of the battery at high temperatures by combining nitrogen-containing organic particles and boron-containing additives, thereby improving both the high-temperature safety and low-temperature discharge performance of the battery.

[0067] In this embodiment of the invention, the mass percentage of nitrogen in the first functional coating can be detected by conventional testing methods and instruments in the art. For example, the membrane with the first functional coating can be tested by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectrometer) surface scanning to obtain the mass percentage of nitrogen in the first functional coating.

[0068] The mass percentage of boron-containing additives in the electrolyte can be detected by conventional testing methods in the field, such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography (LC).

[0069] The material of the base film of the present invention is selected from, for example, at least one of polyethylene (PE) and polypropylene (PP).

[0070] In this embodiment of the invention, when 10wt%≤a≤60wt%, the high-temperature safety and low-temperature discharge performance of the battery can be further improved. For example, a can be a range of 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, or any combination thereof.

[0071] In this embodiment of the invention, when 0.1wt%≤b≤3wt%, the high-temperature safety and low-temperature discharge performance of the battery can be further improved. For example, b is a range of 0.1wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, or any combination thereof.

[0072] In detail, the boron-containing additive has the structure shown in Formula II:

[0073] Formula I

[0074] R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1 to 12 carbon atoms, alkyl groups with 1 to 12 carbon atoms substituted with halogen atoms or cyano groups, alkenyl groups with 2 to 12 carbon atoms, alkenyl groups with 2 to 12 carbon atoms substituted with halogen atoms or cyano groups, alkynyl groups with 2 to 12 carbon atoms, alkynyl groups with 2 to 12 carbon atoms substituted with halogen atoms or cyano groups, aryl groups with 6 to 12 carbon atoms, and aryl groups with 6 to 12 carbon atoms substituted with halogen atoms or cyano groups. When the boron-containing additive has the structure shown in Formula II, it is beneficial to reduce the interfacial resistance of the battery, thereby improving the transport efficiency of active metal ions and enhancing the low-temperature discharge performance of the battery.

[0075] For example, when R1 is selected from C6 to C12 aryl groups, R1 includes, but is not limited to, phenyl, tolyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl, 1-naphthyl, 2-naphthyl, 1-methyl-2-naphthyl, 2-methyl-1-naphthyl, 1-ethyl-2-naphthyl, 9-phenylanthrayl, etc.

[0076] The choices for R2 and R3 are the same as for R1, and will not be elaborated upon here.

[0077] In some embodiments, preferably, the boron-containing additive comprises one or more compounds represented by formulas II-1 to II-11:

[0078] II-1 II-2 II-3

[0079] II-4 II-5 II-6

[0080] II-7 II-8 II-9

[0081] II-10 II-11.

[0082] In some embodiments of the present invention, 10 ≤ a / b ≤ 500, which further improves the low-temperature discharge performance of the battery. Preferably, 15 ≤ a / b ≤ 475.

[0083] In some embodiments, when the average particle size e of the nitrogen-containing organic particles is 0.1 μm ≤ e ≤ 1 μm, it can provide more active sites for boron-containing additives while also improving the occurrence of electrolyte side reactions, further enhancing the transport efficiency of active metal ions within the battery, and thus better improving the low-temperature discharge performance of the battery. For example, the average particle size e of the nitrogen-containing organic particles can be, for example, a range of 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, or any combination thereof. The average particle size e of the nitrogen-containing organic particles is the volume median particle size and can be obtained using methods known in the art. For example, it can be measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0084] In some embodiments, nitrogen-containing organic particles include melamine cyanurate, melamine thiocyanate, melamine polyphosphate, 1,3,5-triazine-2,4,6-triamine, 4,6-dimethyl-2-phenylpyrimidine, uracil, 2-amino-4,6-methoxy-1,3,5-triazine, cytosine, and 2... At least one of the following: 4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, melamine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, and tris(tribromophenoxy)triazine, is more beneficial for improving the low-temperature discharge performance of the battery. In embodiments of the present invention, nitrogen-containing aromatic substances in nitrogen-containing organic particles can be detected using conventional testing methods and instruments in the art, such as infrared spectroscopy. Specifically, the separator can be separated from the battery, dried, and the nitrogen-containing organic particles on the surface of the separator can be scraped for infrared spectroscopy detection.

[0085] In some embodiments of the present invention, the separator further includes an adhesive layer located on at least a portion of the surface of the first functional coating facing away from the base film and / or on the surface of the base film, and the battery satisfies at least one of the following conditions:

[0086] 1) The thickness of the base film is c, where 3.5μm≤c≤13μm;

[0087] 2) The thickness of the first functional coating is d, 0.3μm≤d≤5μm;

[0088] 3) The thickness of the adhesive layer is f, where 0.5μm≤f≤5μm;

[0089] 4) The total thickness of the diaphragm is 4.3μm~23μm.

[0090] When the battery of the present invention meets the above conditions, it can simultaneously improve the mechanical properties of the separator and the transport efficiency of active metal ions, thereby further enhancing the high-temperature safety and low-temperature discharge performance of the battery.

[0091] In detail, the adhesive layer can be partially disposed on the surface of the first functional coating facing away from the base film. The adhesive layer strengthens the adhesion between the separator and the positive and negative electrodes, which is beneficial to further improve the high-temperature stability of the separator and electrode interface, thereby better improving the high-temperature stability of the battery. In addition, when the first functional coating is not present on one side of the base film, the adhesive layer can also be disposed on the surface of the base film.

[0092] The composition of the adhesive layer is not specifically limited in the embodiments of the present invention and can be selected according to the actual situation. For example, the adhesive layer may include at least one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li) and polyvinylpyrrolidone (PVP).

[0093] In detail, when 3.5μm ≤ c ≤ 13μm, the mechanical properties and ion transport efficiency of the separator can be better balanced, thereby further improving the high-temperature safety and low-temperature discharge performance of the battery. For example, c can be a range of 3.5μm, 5μm, 8μm, 10μm, 13μm, or any combination thereof.

[0094] Specifically, when 0.3μm ≤ d ≤ 5μm, the mechanical properties and ion transport efficiency of the separator can be better balanced, thereby further improving the high-temperature safety and low-temperature discharge performance of the battery. For example, d can be a range of 0.3μm, 1μm, 2μm, 3μm, 4μm, 5μm, or any combination thereof.

[0095] In some embodiments, when 0.5μm≤f≤5μm, the bonding performance between the separator and the positive and negative electrodes and the ionic conductivity of the battery can be further improved, thereby further enhancing the high-temperature safety and low-temperature discharge performance of the battery.

[0096] In some embodiments, the total thickness of the separator is 4.3 μm to 23 μm, which can further improve the mechanical and electrical properties of the separator, and is conducive to better improving the high-temperature safety and low-temperature discharge performance of the battery. The total thickness of the separator is, for example, a range of 4.3 μm, 5 μm, 8 μm, 10 μm, 13 μm, 13.5 μm, 15 μm, 18 μm, 20 μm, 23 μm or any combination thereof.

[0097] In this embodiment of the invention, the thickness c of the base film, the thickness d of the first functional coating, the thickness f of the adhesive layer, and the total thickness of the separator can be tested using conventional testing methods and instruments, such as SEM. It should be noted that when the thicknesses c of the base film, d of the first functional coating, f of the adhesive layer, and the total thickness of the separator are not uniform, the thickness is taken as the average value of the thicknesses in different regions.

[0098] In some embodiments, the electrolyte further includes a fluorinated additive, wherein the mass percentage (g) of the fluorinated additive in the electrolyte is 0.5 wt% ≤ g ≤ 20 wt%. This can further reduce the solvation / desolvation energy of active metal ions, better improve the transport efficiency of active metal ions, and thus better improve the discharge performance of the battery at low temperatures. For example, g may be in the range of 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, or any combination thereof. The fluorinated additive in the electrolyte can be detected using conventional testing methods and instruments in the art, such as liquid chromatography-mass spectrometry.

[0099] In some embodiments, preferably, the fluorinated additive includes one or more compounds represented by Formulas III-1 to III-8, which can further reduce the solvation / desolvation energy of active metal ions, better improve the transport efficiency of active metal ions, and thus better improve the discharge performance of the battery at low temperatures.

[0100] III-1 III-2 III-3

[0101] III-4 III-5 III-6

[0102] III-7 III-8.

[0103] In some embodiments, the electrolyte further includes a sulfur-containing additive, wherein the mass percentage (p) of the sulfur-containing additive in the electrolyte is 0.1 wt% ≤ p ≤ 5 wt%. This allows for better formation of an interfacial film in the battery, which is more conducive to improving the battery's ion transport performance and low-temperature discharge performance. For example, the mass percentage (p) of the sulfur-containing additive in the electrolyte may be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, or any combination thereof. The sulfur-containing additive in the electrolyte can be detected using conventional testing methods and instruments in the art, such as liquid chromatography-mass spectrometry.

[0104] In some embodiments, preferably, the sulfur-containing additive includes one or more compounds represented by formulas IV-1 to IV-8, which can better form an interfacial film in the battery, further improving the battery's ion transport performance and enhancing its low-temperature discharge performance.

[0105] IV-1 IV-2 IV-3

[0106] IV-4 IV-5 IV-6

[0107] IV-7 IV-8

[0108] IV-9 IV-10.

[0109] It should be clarified that the fluorine-containing additives in the embodiments of the present invention are used to optimize the solvation of active metal ions and reduce the desolvation energy, while the sulfur-containing additives are used to improve the formation of the interfacial film in the battery. The classification of fluorine-containing and sulfur-containing additives is mainly based on these functions. For example, formulas III-1 to III-4 include both fluorine and sulfur elements, but the role of these compounds in the battery is to optimize the solvation structure of active metal ions and reduce the desolvation energy; therefore, they are classified as fluorine-containing additives.

[0110] In some embodiments of the present invention, the battery includes a positive electrode sheet, which includes a positive current collector and a positive active material layer located on at least one side of the positive current collector; wherein, a second functional coating is included between the positive current collector and the positive active material layer, and the second functional coating includes one or more of alumina, bauxite, titanium dioxide, silicon oxide, and magnesium oxide; the battery satisfies: 0.5≤h / b≤50, where h is the thickness of the second functional coating in μm. When the positive electrode sheet of the battery in the embodiments of the present invention is provided with a second functional coating, the needle penetration safety of the battery can be further improved. When the battery meets the above conditions, it can further improve both the needle penetration safety and ionic conductivity of the battery, which is beneficial to further improve the high-temperature safety and low-temperature discharge performance of the battery.

[0111] In this embodiment of the invention, the second functional layer can be formed by dissolving one or more of alumina, bauxite, titanium dioxide, silicon dioxide, and magnesium oxide with a conductive agent and a binder in a solvent (e.g., N-methylpyrrolidone) to form a second functional layer slurry. This second functional layer slurry is then coated onto at least one side of the positive electrode current collector and dried to obtain the second functional layer. This embodiment of the invention does not impose any special limitations on the amount of the above materials used; they can be selected according to actual conditions.

[0112] The thickness h of the second functional coating can be tested using conventional testing methods and instruments in the art. For example, scanning electron microscopy (SEM) can be used. When the thickness of the second functional coating is non-uniform, m is taken as the average of the thicknesses of multiple different regions.

[0113] Preferably, when 1≤h≤10, the battery's needle penetration safety and ionic conductivity can be further improved, which is beneficial to further improving the battery's high-temperature safety and low-temperature discharge performance.

[0114] In some embodiments of the present invention, the positive electrode active material layer includes a solid electrolyte material, and the mass percentage i of the solid electrolyte material in the positive electrode active material layer is 0.1wt%≤i≤5wt%, which makes the ionic conductivity of the positive electrode active material layer better and is beneficial to further improve the low-temperature discharge performance of the battery.

[0115] In this embodiment of the invention, the solid electrolyte material in the positive electrode active material layer can be at least one of lithium aluminum titanium phosphorus oxide, lithium lanthanum zirconium tantalum oxide, and lithium lanthanum titanium oxide. For example, at least one of lithium titanium aluminum phosphate, lithium lanthanum titanate, and lithium lanthanum zirconate.

[0116] In this embodiment of the invention, the average particle size j of the solid electrolyte material in the positive electrode active material layer is 0.02 μm ≤ j ≤ 3 μm. This allows for better interfacial contact between the solid electrolyte material and the positive electrode active material in the positive electrode active material layer, further reducing the interfacial transport resistance of lithium ions between the positive electrode active material and the solid electrolyte, and further improving the discharge performance of the battery at low temperatures. The average particle size j of the solid electrolyte material is the volume median particle size and can be obtained using methods known in the art. For example, it can be measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0117] Specifically, a positive electrode active material layer can be provided on one side of the surface of the positive electrode current collector in the thickness direction, or a positive electrode active material layer can be provided on both sides of the surface of the positive electrode current collector in the thickness direction.

[0118] The positive electrode active material layer may include a positive electrode active material, a conductive agent, and a binder. In the positive electrode active material layer, the mass percentage of the positive electrode active material may be 70wt% to 99wt%, for example, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 93wt%, 95wt%, 97wt%, 99wt%, or any two of these ranges. The mass fraction of the binder may be 0.5wt% to 15wt%, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 8wt%, 10wt%, 13wt%, 15wt%, or any two of these ranges.

[0119] The binder for the positive electrode active material layer can be either the polyimide binder provided in the embodiments of the present invention, or a combination of one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc., as the binder for the positive electrode active material layer.

[0120] In some embodiments, the battery is a lithium-ion battery, and the positive electrode active material includes, but is not limited to, LiCoO2, LiNiO2, and LiCo. x Ni 1-x O2 (0≤x≤1), LiCo x Ni 1-x-y Al y O2 (0≤x≤1, 0≤y≤1), LiMn2O4, LiFe x Mn y M zO4 (M is one or more of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn or Mo, 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), Li 1＋ x L 1－y－z M y N z O2 (L, M, N are one or more of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤x≤0.2, 0≤y≤1, 0≤z≤1, 0≤y+z≤1), LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, Li2CuO2, Li5FeO4, and metal sulfides and oxides (such as TiS2, V2S3, FeS, FeS2, LiMS) x (M is at least one of the transition metal elements such as Ti, Fe, Ni, Cu, Mo, etc., 1≤x≤2.5), TiO2, Cr3O8, V2O5, MnO2, etc.

[0121] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0122] In this embodiment of the invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the positive electrode active material layer, such as the positive electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0123] The battery includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector. The negative electrode active material layer includes a silicon-based material, preferably a silicon-carbon material, which includes porous carbon and silicon material deposited in the porous carbon channels. Preferably, the silicon-based material includes a carbon coating layer with a thickness m of 0.5 nm ≤ m ≤ 25 nm. When the battery of this embodiment has the above structure, a conductive network can be better formed in the negative electrode active material layer, further improving the transport efficiency of active metal ions and electrons in the negative electrode active material layer, and further improving the low-temperature discharge performance of the battery.

[0124] like Figure 1 As shown, the battery in some embodiments of the present invention has Figure 1The structure shown includes a separator comprising a base membrane 11 and a first functional coating 12 on one side of the base membrane 11, with an adhesive layer 13 disposed on the surface of the base membrane 11 and the surface of the first functional coating 12; a negative electrode comprising a negative current collector 21 and negative active material layers 22 on both sides of the negative current collector; and a positive electrode comprising a positive current collector 31 and positive active material layers 32 on both sides of the positive current collector, with a second functional layer 33 located between the positive current collector 31 and the positive active material layers 32.

[0125] The present invention does not impose any special limitation on the preparation method of silicon-based materials, and can select according to the actual situation. In one specific embodiment, when the silicon-based material has a carbon coating layer, it can be prepared by the following method: the silicon-based material is carbon coated by chemical vapor deposition with a mixed gas of ethylene and nitrogen (volume ratio of 20%:80%), the gas flow rate is 300 mL / min, the deposition temperature is 800℃, and the deposition time is 1 h, so as to obtain the carbon-coated silicon-based material.

[0126] In one specific embodiment, preferably, the thickness m of the carbon layer distributed on at least a portion of the surface of the silicon-based material is 0.5 nm ≤ m ≤ 25 nm. This can further reduce the volume expansion rate of the silicon-based material, further stabilize the interface film in the battery, and thus improve the low-temperature discharge performance of the battery. For example, the thickness m of the carbon layer distributed on at least a portion of the surface of the silicon-based substrate is, for example, a range of 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, or any combination thereof. Embodiments of the present invention can test the thickness m of the carbon layer distributed on at least a portion of the surface of the silicon-based substrate using conventional testing methods and instruments in the art. For example, scanning electron microscopy (SEM) or transmission electron microscopy (TEM) can be used for testing. When the thickness of the carbon layer distributed on at least a portion of the surface of the silicon-based substrate is non-uniform, m is taken as the average of the thicknesses of multiple different regions.

[0127] In some embodiments, the negative electrode active material layer includes carbon nanotubes. Preferably, the diameter k of the carbon nanotubes is 1 nm ≤ k ≤ 40 nm; preferably, the length l of the carbon nanotubes is 0.1 μm ≤ l ≤ 30 μm; preferably, the carbon nanotubes can be distributed inside the silicon-based material and / or at least partially on its surface. This allows for a better formation of a conductive network in the negative electrode active material layer, thus improving the low-temperature discharge performance of the battery. Specifically, the relationship between the carbon nanotubes and the silicon-based material satisfies at least one of the following conditions:

[0128] 1. Carbon nanotubes are located inside silicon-based materials;

[0129] 2. Carbon nanotubes are located within the carbon coating layer;

[0130] 3. Carbon nanotubes extend from the interior of the silicon-based material into the carbon coating layer;

[0131] 4. Carbon nanotubes extend from the interior of the silicon-based material into the carbon coating layer, and extend out of the carbon coating layer;

[0132] 5. Carbon nanotubes are located within the negative electrode active material layer, between silicon-based material particles.

[0133] In some embodiments, at least a portion of the surface of the negative electrode active material layer away from the negative electrode current collector is provided with grooves, the depth n of which is 5μm≤n≤40μm, the width w of which is 30μm≤w≤500μm, and the spacing o between adjacent grooves is 0.5mm≤o≤10mm. When the battery of the present invention has the above structure, more ion-conducting paths can be formed on the negative electrode surface, further improving the efficiency of lithium ions embedding from the electrolyte into the negative electrode active material layer, reducing the transport distance of active metal ions embedding into the silicon-based material near the negative electrode current collector, and thus better improving the discharge performance of the battery at low temperatures.

[0134] The present invention does not impose any special limitation on the preparation method of the groove. It can be prepared by conventional preparation methods in the art. For example, the groove can be formed on at least a part of the surface of the negative electrode active material layer away from the negative electrode current collector by laser.

[0135] In one specific embodiment, a negative electrode active material layer can be provided on one side surface of the negative electrode current collector in the thickness direction, or negative electrode active material layers can be provided on both opposite sides surface in the thickness direction of the negative electrode current collector.

[0136] In this embodiment of the invention, the binder in the negative electrode active material layer can be either the polyimide binder provided in this embodiment or a combination of any binder suitable for negative electrodes known in the art. For example, at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene-polyethylene glycol block copolymers), polyethers and their copolymers (e.g., polyethylene oxide), polyesters and their copolymers (e.g., polyethylene ester, polyvinyl acetate, polyacrylate, etc.), carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA) can be used together with the polyimide binder provided in this embodiment of the invention in the preparation of the negative electrode active material layer.

[0137] In addition, the negative electrode active material layer also includes a negative electrode active material. Specifically, the negative electrode active material may include graphite, and the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber.

[0138] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0139] In embodiments of the present invention, the negative electrode sheet can be prepared by a dry process (i.e., rolling the material used to form the negative electrode active material layer into a film and then combining it with the negative electrode current collector to obtain the negative electrode sheet), or by a wet process (coating method) (i.e., coating the negative electrode slurry used to form the negative electrode active material layer onto the surface of the negative electrode current collector, and then drying, rolling and other processes to form the negative electrode active material layer on the surface of the negative electrode sheet to obtain the negative electrode sheet).

[0140] Generally, a battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes electrode plates (including positive and negative electrode plates) and a separator located between the positive and negative electrode plates. The battery cell can be a stacked cell, meaning it is composed of positive electrode plates, a separator, and negative electrode plates stacked alternately; or it can be a wound cell, meaning it is composed of positive electrode plates, a separator, and negative electrode plates stacked and then wound together. In practice, a stacked cell can be formed by alternating layers of positive electrode plates, a separator, and negative electrode plates, and then the cell is encapsulated using an aluminum-plastic film.

[0141] The electrolyte in this embodiment of the invention may further include organic solvents, other additives and lithium salts. Organic solvents include, for example, one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and propylene carbonate (PC). Other additives include fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0142] In some embodiments of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), and lithium difluorooxalate borate (LiDFOB), which can better improve the ionic conductivity of the battery, thereby better improving the rate performance and capacity retention of the battery.

[0143] In this embodiment of the invention, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment of the invention, and there are no special limitations on this.

[0144] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0145] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection, encapsulation, formation and capacity testing, a battery is obtained.

[0146] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0147] Example 1

[0148] The battery of this invention is prepared by the following method:

[0149] 1) Preparation of the positive electrode sheet: Boehmite, carbon black, and polyacrylate were mixed in a mass ratio of 90:5:5 and dissolved in the solvent N-methylpyrrolidone (NMP) to obtain a mixture. The solid content of the mixture was adjusted to 40%, and after stirring evenly, a second functional coating slurry was obtained. The second functional coating slurry was then coated onto both surfaces of an aluminum foil using a gravure roller and dried to obtain a second functional coating with a thickness of 5 μm. The positive electrode active materials lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNTs) were mixed in a mass ratio of 94.8:2:1.5:0.5, and N-methylpyrrolidone (NMP) was added. The mixture was stirred under vacuum until a uniform and fluid positive electrode slurry was formed. The positive electrode slurry was uniformly coated onto the surface of the second functional coating, and after drying, rolling, and slitting, the positive electrode sheet was obtained.

[0150] 2) Negative electrode preparation: The negative electrode active material artificial graphite, silicon-based material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 70:24.5:2.5:1.5:1:0.5, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both surfaces of a copper foil. The coated copper foil was dried at room temperature and then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode precursor was obtained. The negative electrode was then prepared by cleaning, drying, and tab welding. The carbon nanotubes were distributed inside and on the surface of the silicon-based material, as well as interspersed between the silicon-based materials. The carbon nanotubes had a diameter of 20 nm and a length of 15 μm. The silicon-based material coating layer (carbon layer) had a thickness of 10 nm.

[0151] 3) Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), and ethyl propionate (EP) were uniformly mixed in a ratio of 1:1:6:2. Then, 10 wt% of a fluorinated additive (including 5 wt% of the fluorinated additive shown in Formula III-1 and 5 wt% of the fluorinated additive shown in Formula III-8) based on the total mass of the electrolyte was added. Next, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI based on the total mass of the electrolyte were added. After dissolution, 1 wt% of compound B (shown in Formula II-1) and 1 wt% of a sulfur-containing compound (shown in Formula IV-1) based on the total mass of the electrolyte were added. After thorough stirring, the electrolyte was obtained after passing tests for moisture and free acid.

[0152] 4) Preparation of the diaphragm: Nitrogen-containing organic particles (melamine cyanurate) and sodium polyacrylate are mixed at a mass ratio of 96:6 to obtain a coating slurry; PVDF, PMMA, CMC, and PVP are mixed at a mass ratio of 40:44:15:1 to obtain an adhesive layer slurry; a base film (PE, 5 μm thick) is prepared and wound up using a wet biaxial stretching process. The wound base film is unwound and fed into the coating area. The coating slurry is applied to one side of the base film using a gravure roller to obtain the first functional coating. After drying in an oven, the adhesive layer slurry is sprayed onto the coating surface and the other surface of the base film to obtain the adhesive layer. Finally, the coating is dried in an oven and wound up to obtain the diaphragm. (The mass percentage of nitrogen in the first functional coating is 47.4 wt%, the thickness of the functional coating is 1 μm, the particle size of its nitrogen-containing organic particles is 0.3 μm, and the thickness of the adhesive layer is 1.5 μm).

[0153] 5) The positive electrode sheet obtained in step 1), the negative electrode sheet obtained in step 2), and the separator obtained in step 4) are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion battery is obtained. The charge / discharge range of the battery of this invention is 3.0-4.55V.

[0154] Example 2

[0155] This embodiment is basically the same as Embodiment 1, except that in step 3) of the electrolyte preparation, the electrolyte is prepared as follows: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, PP, and EP are uniformly mixed in a ratio of 1:1:6:2. Then, 10 wt% of a fluorinated additive (including 5 wt% of the fluorinated additive shown in Formula III-1 and 5 wt% of the fluorinated additive shown in Formula III-8) based on the total mass of the electrolyte is added. Then, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI based on the total mass of the electrolyte are added. After dissolving, 0.2 wt% of compound B (shown in Formula II-4) and 1 wt% of a sulfur-containing compound (shown in Formula IV-2) based on the total mass of the electrolyte are added. After stirring evenly, the electrolyte is obtained after passing the moisture and free acid tests.

[0156] Example 3

[0157] This embodiment is basically the same as Embodiment 1, except that in step 3) of the electrolyte preparation, the electrolyte is prepared as follows: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, PP, and EP are uniformly mixed in a ratio of 1:1:6:2. Then, 10 wt% of a fluorinated additive (including 5 wt% of the fluorinated additive shown in Formula III-3 and 5 wt% of the fluorinated additive shown in Formula III-5) based on the total mass of the electrolyte is added. Then, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI based on the total mass of the electrolyte are added. After dissolving, 3 wt% of compound B (shown in Formula II-8) and 1 wt% of a sulfur-containing compound (shown in Formula IV-6) based on the total mass of the electrolyte are added. After stirring evenly, the electrolyte is obtained after passing the moisture and free acid tests.

[0158] Example 4

[0159] This embodiment is basically the same as Embodiment 1, except that in step 3) of the electrolyte preparation, the electrolyte is prepared as follows: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, PP, and EP are uniformly mixed in a ratio of 1:1:6:2. Then, 10% of a fluorinated additive based on the total mass of the electrolyte (including 5 wt% of the fluorinated additive shown in Formula III-1 and 5 wt% of the fluorinated additive shown in Formula III-8) is added. Then, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI are added based on the total mass of the electrolyte. After dissolving, 0.1 wt% of compound B (shown in Formula II-9) and 1 wt% of a sulfur-containing compound (shown in Formula IV-7) based on the total mass of the electrolyte are added. After stirring evenly, the electrolyte is obtained after passing the moisture and free acid tests.

[0160] In step 4) of this embodiment, the mass percentage of nitrogen in the first functional coating during the preparation of the diaphragm is 10 wt%.

[0161] Example 5

[0162] This embodiment is basically the same as Embodiment 1, except that in step 3) of the electrolyte preparation, the electrolyte is prepared as follows: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, PP, and EP are uniformly mixed in a ratio of 1:1:6:2. Then, 10 wt% of a fluorinated additive (including 5 wt% of the fluorinated additive shown in Formula III-1 and 5 wt% of the fluorinated additive shown in Formula III-8) based on the total mass of the electrolyte is added. Then, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI based on the total mass of the electrolyte are added. After dissolving, 3 wt% of compound B (i.e., boron-containing additive, shown in Formula II-1) and 1 wt% of a sulfur-containing compound (shown in Formula IV-1) based on the total mass of the electrolyte are added. After stirring evenly, the electrolyte is obtained after passing the moisture and free acid tests.

[0163] In step 4) of this embodiment, the mass percentage of nitrogen in the first functional layer is 47.7 wt%.

[0164] The differences between Examples 6-18 and Example 1 lie in the following parameters: the mass percentage of nitrogen in the first functional coating, the mass percentage of boron-containing additives in the electrolyte, the average particle size e of nitrogen-containing organic particles, the thickness c of the base film, the thickness d of the first functional coating, the thickness f of the adhesive layer, the total thickness of the separator, the mass percentage g of fluorine-containing additives in the electrolyte, the mass percentage p of sulfur-containing additives in the electrolyte, the thickness h of the second functional coating, h / b, the thickness m of the carbon layer distributed on at least part of the surface of the silicon-based substrate, the depth n of the groove, the width w of the groove, the spacing o between adjacent grooves, and the size of the carbon nanotubes. See Tables 1, 2, and 3 for details.

[0165] Example 19

[0166] This embodiment is basically the same as Embodiment 1, except that the mass ratio i of the solid electrolyte material in the positive electrode active material layer is different, as detailed in Table 3. In step 1), the positive electrode active materials lithium cobalt oxide (LiCoO2), lithium titanium aluminum phosphate, polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) are mixed in a mass ratio of 94.8:0.1:2:1.5:0.5.

[0167] Example 20

[0168] This embodiment is basically the same as Embodiment 1, except that the mass ratio i of the solid electrolyte material in the positive electrode active material layer is different, as detailed in Table 3. In step 1), the positive electrode active materials lithium cobalt oxide (LiCoO2), lithium titanium aluminum phosphate, polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) are mixed in a mass ratio of 94.8:5:2:1.5:0.5.

[0169] Example 21

[0170] This embodiment is basically the same as embodiment 1, except that in step 2) of this embodiment, the negative electrode slurry does not include single-walled carbon nanotubes.

[0171] Example 22

[0172] This embodiment is basically the same as Embodiment 1, except that the mass ratio i of the solid electrolyte material in the positive electrode active material layer is different, as detailed in Table 3. In step 1), the positive electrode active materials lithium cobalt oxide (LiCoO2), lithium titanium aluminum phosphate, polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNTs) are mixed in a mass ratio of 94.8:1.2:2:1.5:0.5. In step 2) of this embodiment, the negative electrode slurry does not include single-walled carbon nanotubes.

[0173] The negative electrode sheet in Examples 23-25 ​​further includes the following steps: laser-grooving the negative electrode sheet precursor, setting grooves on the entire surface of the negative electrode active material layer, the grooves are matrix grooves, the groove width w, the groove depth n; the groove spacing o is shown in Table 3, and the negative electrode sheet is obtained after cleaning, drying and sheet preparation (tab welding) of the laser-treated negative electrode sheet precursor.

[0174] Comparative Example 1

[0175] The difference between this comparative example and Example 1 is that the separator of this comparative example battery does not contain the first functional coating.

[0176] Comparative Example 2

[0177] The difference between this comparative example and Example 1 is that the electrolyte of this comparative example battery does not contain boron-containing additives.

[0178] Comparative Example 3

[0179] The difference between this comparative example and Example 1 is that the separator of this comparative example battery does not contain a first functional coating, and the electrolyte does not contain boron-containing additives.

[0180] Comparative Example 4

[0181] This embodiment is basically the same as Embodiment 1, except that in step 3) of the electrolyte preparation, the electrolyte is prepared as follows: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, PP, and EP are uniformly mixed in a ratio of 1:1:6:2. Then, 10 wt% of a fluorinated additive (including 5 wt% of the fluorinated additive shown in Formula III-1 and 5 wt% of the fluorinated additive shown in Formula III-8) based on the total mass of the electrolyte is added. Then, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI based on the total mass of the electrolyte are added. After dissolving, 0.01 wt% of compound B (shown in Formula II-1) and 1 wt% of a sulfur-containing compound (shown in Formula IV-1) based on the total mass of the electrolyte are added. After stirring evenly, the electrolyte is obtained after passing the moisture and free acid tests.

[0182] In step 4) of this embodiment, the mass percentage of nitrogen in the first functional layer is 5 wt%.

[0183] Comparative Example 5

[0184] This embodiment is basically the same as Embodiment 1, except that in step 3) of the electrolyte preparation, the electrolyte is prepared as follows: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, PP, and EP are uniformly mixed in a ratio of 1:1:6:2. Then, 10 wt% of a fluorinated additive (including 5 wt% of the fluorinated additive shown in Formula III-1 and 5 wt% of the fluorinated additive shown in Formula III-8) based on the total mass of the electrolyte is added. Then, 13 wt% of fully dried lithium hexafluorophosphate and 7 wt% of fully dried LiTFSI based on the total mass of the electrolyte are added. After dissolving, 3.5 wt% of compound B (shown in Formula II-1) and 1 wt% of a sulfur-containing compound (shown in Formula IV-1) based on the total mass of the electrolyte are added. After stirring evenly, the electrolyte is obtained after passing the moisture and free acid tests.

[0185] In step 4) of this embodiment, the mass percentage of nitrogen in the first functional layer is 65 wt%.

[0186] In the batteries of the examples and comparative examples, the mass percentage of nitrogen in the first functional coating (a), the mass percentage of boron-containing additives in the electrolyte (b), the correlation between a and b, the average particle size of nitrogen-containing organic particles (e), the thickness of the base film (c), the thickness of the first functional coating (d), the thickness of the adhesive layer (f), the total thickness of the separator, the mass percentage of fluorine-containing additives in the electrolyte (g), the mass percentage of sulfur-containing additives in the electrolyte (p), the thickness of the second functional coating (h), h / b, the mass percentage of solid electrolyte material in the positive electrode active material layer (i), the thickness of the carbon layer distributed on at least part of the surface of the silicon-based substrate (m), the depth of the groove (n), the width of the groove (w), the spacing between adjacent grooves (o), and the size of the carbon nanotubes are shown in Tables 1, 2, and 3.

[0187]

[0188]

[0189]

[0190] Test case

[0191] Test of the mass percentage 'a' of nitrogen in the first functional coating: The separators in the cells of the examples and comparative examples were separated from the cells, and the first functional coating in the separators was scraped off for XRD testing.

[0192] Tests on the mass percentage of boron-containing additives in the electrolyte (b), the mass percentage of sulfur-containing additives in the electrolyte (p), and the mass percentage of fluorine-containing additives in the electrolyte (g): The batteries in the examples and comparative examples were disassembled, and 1.5 ml of electrolyte was taken for testing by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography (LC).

[0193] Test methods for the average particle size e of nitrogen-containing organic particles, the thickness c of the base film, the thickness d of the first functional coating, the thickness f of the adhesive layer, and the total thickness of the separator: The separator in the example and comparative battery is separated from the battery, the cross-section of the separator in the example and comparative battery is obtained, and then the above parameters are tested using SEM.

[0194] The thickness h of the second functional layer was tested by disassembling the cells of the examples and comparative examples, separating the positive electrode from the cells, obtaining the cross-section of the positive electrode in the examples and comparative examples, and then using SEM to test the thickness h of the second functional layer.

[0195] Test of the mass percentage of solid electrolyte material in the positive electrode active material layer: The batteries of the examples and comparative examples were disassembled, and the positive electrode sheet was separated from the battery. The positive electrode active material layer was carefully peeled off, and then soaked in DMC (dimethyl carbonate) solvent to obtain a mixture of positive electrode active material and solid electrolyte. XRD test was then performed to confirm that the sample contained only the target positive electrode and solid electrolyte phases and no impurity phases. Then, the content of characteristic elements (such as La, Zr, Ta, P, S, etc.) in the sample was tested by inductively coupled plasma optical emission spectrometry (ICP-OES) to accurately calculate the mass fraction of solid electrolyte.

[0196] Carbon layer thickness m test: The cells of the examples and comparative examples were disassembled, and the negative electrode was separated from the cells. The negative electrode was sliced ​​using a focused ion beam (FIB), and the cross-section of the silicon-based material was observed by a scanning electron microscope. The carbon layer thickness of the silicon-based material was measured. The carbon layer thickness was measured at five different locations of the silicon-based material, and the average value was taken to obtain the carbon layer thickness m.

[0197] Carbon nanotube size testing: The negative electrode sheet was sliced ​​using focused ion beam (FIB), and the cross-section of the silicon-based material was observed using a scanning electron microscope to obtain the size of the carbon nanotubes.

[0198] Testing of the depth n, width w, length y, and spacing o of the grooves in the negative electrode: The batteries of the examples and comparative examples were disassembled, and the negative electrode was separated from the batteries. The depth n, width w, and spacing o of the grooves in the negative electrode were tested using SEM.

[0199] -10℃ Discharge Performance Test: The batteries obtained in the examples and comparative examples were charged at 25℃ with a constant current of 2C to a voltage of 4.55V, then charged at 4.55V with a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 2C to a voltage of 3.0V. This constitutes one charge-discharge cycle, and the discharge capacity of the third cycle is recorded as x mAh. The batteries obtained in the examples and comparative examples were then allowed to stand at 25℃ for 2 hours, charged at a constant current of 2C to a voltage of 4.55V, then charged at 4.55V with a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 2C to a voltage of 3.0V. This constitutes one charge-discharge cycle, and the discharge capacity of the third cycle is recorded as y mAh. The discharge capacity retention rate of the battery at -10℃ is represented by y / x. The test results (-10℃ discharge performance test) are shown in Table 4.

[0200] Needle penetration safety test: The batteries obtained in the examples and comparative examples were discharged to the lower limit voltage at 1C current in an environment of 25°C and left to stand for 10 minutes. They were then charged at a constant current of 0.7C to the upper limit voltage of 4.55V, and then charged at a constant voltage until the current cutoff was 0.02C. After standing for 10 minutes, they were discharged to the lower limit voltage at 1C current. This constitutes one charge-discharge cycle. After 5 charge-discharge cycles, the batteries were charged at a constant current of 0.7C to the upper limit voltage of 4.55V, and then charged at a constant voltage until the current cutoff was 0.02C. After standing for 10 minutes, at 25°C, a 3mm diameter iron nail with a 15mm tip length was inserted through the center of the cell at a needle speed of 30m / s. The nail remained inside the battery for 5 minutes. If the battery did not smoke, catch fire, or explode during the test, the test was considered passed. Twenty batteries from each of the examples and comparative examples were tested, and the pass rate of the needle penetration test was recorded. The test results (pass rate of the needle penetration safety test) are shown in Table 4.

[0201] Furnace temperature safety test: At room temperature, the batteries obtained in the examples and comparative examples were charged to 4.55V at a constant current of 1C, left to stand for 60 minutes, and their appearance was inspected and photographed. Then, the temperature was increased to 132℃±2℃ at a rate of 3℃ / min±2℃ / min and held for 60 minutes. The samples were observed; those that did not leak, smoke, ignite, or explode were considered to have passed the test. Twenty samples were tested for each example or comparative example, and the pass rate of the furnace performance test was recorded. The test results (furnace temperature safety test pass rate) are shown in Table 4.

[0202]

[0203] As shown in Table 4, compared with the comparative example, the embodiments of the present invention, by setting a first functional coating in the separator of the battery, including a nitrogen-containing additive in the electrolyte, and controlling the mass ratio of nitrogen in the first functional coating and the mass ratio of boron-containing additive in the electrolyte, enable the battery to have both high high-temperature safety and low-temperature discharge performance.

[0204] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, The battery includes an electrolyte, a positive electrode, a negative electrode, and a separator; The diaphragm includes a base membrane and a first functional coating located on at least one side of the base membrane; The first functional coating comprises nitrogen-containing organic particles, wherein the mass percentage of nitrogen in the first functional coating is awt%, 10wt%≤a≤60wt%; The electrolyte includes a boron-containing additive, wherein the boron-containing additive accounts for bwt% of the electrolyte by mass, and 0.1wt%≤b≤3wt%. The boron-containing additive has the structure shown in Formula I: Equation I R1, R2, and R3 are each independently selected from halogen atoms, alkyl groups with 1 to 12 substituted or unsubstituted carbon atoms, alkenyl groups with 2 to 12 substituted or unsubstituted carbon atoms, alkynyl groups with 2 to 12 substituted or unsubstituted carbon atoms, and aryl groups with 6 to 12 substituted or unsubstituted carbon atoms. When substituted, the substituent is selected from at least one of halogen atoms and cyano groups.

2. The battery according to claim 1, characterized in that, The boron-containing additive includes one or more of the compounds shown in Formulas II-1 to II-11: II-1 II-2 II-3 II-4 II-5 II-6 II-7 II-8 II-9 II-10 II-11。 3. The battery according to claim 1 or 2, characterized in that, The battery satisfies the following condition: 10 ≤ a / b ≤ 500; preferably 15 ≤ a / b ≤ 475. And / or, the average particle size e of the nitrogen-containing organic particles is 0.1 μm ≤ e ≤ 1 μm; And / or, the nitrogen-containing organic particles include melamine cyanurate, melamine thiocyanate, melamine polyphosphate, 1,3,5-triazine-2,4,6-triamine, 4,6-dimethyl-2-phenylpyrimidine, uracil, 2-amino-4,6-methoxy-1,3,5-triazine, cytosine, 2 At least one of 4-dimercaptopyrimidine, 2,4-dimercapto-5,6-diaminopyrimidine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, melamine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, and tris(tribromophenoxy)triazine.

4. The battery according to any one of claims 1-3, characterized in that, The separator further includes an adhesive layer located on at least a portion of the surface of the first functional coating opposite to the base film and / or on the surface of the base film, and the battery satisfies at least one of the following conditions: 1) The thickness of the base film is c, where 3.5μm≤c≤13μm; 2) The thickness of the first functional coating is d, 0.3μm≤d≤5μm; 3) The thickness of the adhesive layer is f, where 0.5μm≤f≤5μm; 4) The total thickness of the diaphragm is 4.3μm~23μm.

5. The battery according to any one of claims 1-4, characterized in that, The electrolyte further includes a fluorinated additive, wherein the mass percentage of the fluorinated additive in the electrolyte is 0.5wt% ≤ g ≤ 20wt%; preferably, the fluorinated additive includes one or more compounds represented by formulas III-1 to III-8: III-1 III-2 III-3 III-4 III-5 III-6 III-7 III-8; And / or, the electrolyte further includes a sulfur-containing additive, wherein the mass percentage p of the sulfur-containing additive in the electrolyte is 0.1wt% ≤ p ≤ 5wt%; preferably, the sulfur-containing additive includes one or more compounds represented by formulas IV-1 to IV-8: IV-1 IV-2 IV-3 IV-4 IV-5 IV-6 IV-7 IV-8 IV-9 IV-10。 6. The battery according to any one of claims 1-5, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector; The positive electrode current collector and the positive electrode active material layer include a second functional coating. Preferably, the second functional coating includes one or more of alumina, boehmite, titanium dioxide, silicon dioxide, and magnesium oxide. Preferably, the battery satisfies: 0.5≤h / b≤50, where h is the thickness of the second functional coating in μm; preferably, 1≤h≤10.

7. The battery according to any one of claims 1-6, characterized in that, The positive electrode active material layer includes a solid electrolyte material; Preferably, the solid electrolyte material includes at least one of lithium aluminum titanium phosphate, lithium lanthanum titanate, and lithium lanthanum zirconate.

8. The battery according to any one of claims 1-7, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; wherein the negative electrode active material layer includes a silicon-based material; Preferably, the silicon-based material includes a silicon-carbon material, which includes porous carbon and silicon material deposited in the porous carbon channels; Preferably, the silicon-based material includes a carbon coating layer, and the thickness m of the carbon coating layer is 0.5 nm ≤ m ≤ 25 nm.

9. The battery according to claim 8, characterized in that, The negative electrode active material layer includes carbon nanotubes; Preferably, the diameter k of the carbon nanotube is 1 nm ≤ k ≤ 40 nm; Preferably, the length l of the carbon nanotube is 0.1 μm ≤ l ≤ 30 μm; Preferably, the carbon nanotubes may be distributed inside the silicon-based material and / or at least partially on its surface.

10. The battery according to claim 8, characterized in that, At least a portion of the surface of the negative electrode active material layer away from the negative electrode current collector is provided with a groove, and the depth n of the groove is 5μm≤n≤40μm; And / or, the width w of the groove is 30μm≤w≤500μm; And / or, the spacing o between adjacent grooves is 0.5mm ≤ o ≤ 10mm.

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