Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device, and particularly relates to the technical field of batteries. The secondary battery comprises a bipolar pole piece, a diaphragm and electrolyte, wherein the bipolar pole piece and the diaphragm are infiltrated in the electrolyte; the bipolar pole piece comprises a positive active material layer, the positive active material layer comprises LiNi0. 5Mn1. 5O4 or xLi2MnO3. (1-x) LiMO2, x is more than 0 and less than 1, and M comprises one or more of Ni, Co and Mn; the electrolyte comprises a non-aqueous solvent, a lithium salt and an additive, the additive comprises a compound shown in the following formula, and based on the total mass of the electrolyte, the mass percentage of the following compound is 0.1%-3%; r1 and R2 in the # imgabs0 # formula are independently selected from substituents with the carbon atom number of 0-3, the unsaturation degree of 0-4 and the heteroatom number of 0-3, and the heteroatoms comprise nitrogen atoms and / or sulfur atoms. The additive matched with the high-voltage positive electrode materials LRM and LNMO is introduced into the electrolyte, so that the overcharge safety of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] Bipolar batteries refer to multiple batteries that are stacked and adjacent to each other, sharing the same current collector and packaged together. The battery is connected in series, which can greatly increase the output voltage and output power of the battery, and reduce a lot of connecting wires, pole ears, etc., which can greatly improve the energy density of the battery. Therefore, bipolar batteries have broad application prospects in electric vehicles and energy storage.

[0003] Liquid bipolar batteries also have serious safety issues during use. Like conventional lithium-ion batteries, bipolar batteries can cause thermal runaway under extreme conditions such as short circuit, puncture, impact, overheating, and overcharging. Thermal runaway caused by overcharging is particularly serious. Under overcharging conditions, the structure of the positive electrode active material is more unstable, lithium is more easily deposited on the negative electrode surface, and the side reactions between the electrode material and the electrolyte are more intense, resulting in serious battery capacity decay, affecting the battery's cycle performance, and even causing safety accidents such as fire and explosion.

[0004] In order to prevent the occurrence of safety problems caused by overcharging of batteries, the traditional approach is to modify the battery materials or use circuit breaker protection devices, explosion-proof safety devices, and voltage-sensitive membranes inside the battery. These methods cannot fundamentally solve the problem of battery overcharging safety. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention provides a secondary battery and an electrical device, which improves the overcharge safety problem of the bipolar battery by adding a redox shuttle inhibitor matching the high-voltage positive electrode materials LRM and LNMO into the electrolyte.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides a secondary battery in a first aspect, the secondary battery comprising: a bipolar pole piece, a separator and an electrolyte in which the bipolar pole piece and the separator are immersed; the bipolar pole piece comprises a positive electrode active material layer, the positive electrode active material layer comprises LiNi 0.5 Mn 1.5 O4 or xLi2MnO3·(1-x)LiMO2, wherein 0<x<1, and M comprises one or more of Ni, Co, and Mn; the electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive, the additive comprises a compound represented by formula I, and the mass percentage of the compound represented by formula I is 0.1% to 3% based on the total mass of the electrolyte;

[0007]

[0008] In formula I, R1 and R2 are each independently selected from a substituent having 0 to 3 carbon atoms, 0 to 4 unsaturations, and 0 to 3 heteroatoms, wherein the heteroatoms include nitrogen atoms and / or sulfur atoms.

[0009] In one embodiment of the present invention, based on the total mass of the electrolyte, the mass percentage of the compound represented by formula I is 0.1% to 1%.

[0010] In one embodiment of the present invention, R1 and R2 in Formula I are independently selected from any one of an alkyl group, an alkenyl group, and an amino group.

[0011] In one embodiment of the present invention, the bipolar pole piece further includes a bipolar current collector and a negative electrode active material layer, and the positive electrode active material layer and the negative electrode active material layer are respectively arranged on both side surfaces of the bipolar current collector.

[0012] In one embodiment of the present invention, the electrolyte between adjacent bipolar current collectors is sealed by packaging glue.

[0013] In one embodiment of the present invention, the packaging adhesive includes epoxy resin adhesive and epoxy resin curing adhesive, and the epoxy resin adhesive includes bisphenol A epoxy resin adhesive.

[0014] In one embodiment of the present invention, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet and the negative electrode sheet are respectively arranged on both sides of the stack of bipolar electrode sheets, and the diaphragm is arranged between adjacent bipolar electrode sheets, between the bipolar electrode sheet and the positive electrode sheet, and between the bipolar electrode sheet and the negative electrode sheet.

[0015] In one embodiment of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethylsulfonate; based on the total mass of the electrolyte, the mass percentage of the lithium salt is 12% to 16%.

[0016] In one embodiment of the present invention, the non-aqueous solvent includes one or more of carbonates, carboxylates, ethers and nitriles; the carbonate includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, and fluoroethyl methyl carbonate; the carboxylate includes one or more of ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; the ethers include ethylene glycol dimethyl ether and / or diethanol diethyl ether; the nitriles include one or more of acetonitrile, propionitrile, butyronitrile, and valeronitrile.

[0017] The present invention further provides an electric device, wherein the electric device comprises the secondary battery of the present invention.

[0018] The secondary battery of the present invention adds a redox shuttle inhibitor compatible with the high-voltage positive electrode materials LRM and LNMO to the electrolyte. When the battery is overcharged, the additive will be oxidized near the positive electrode to form active free radicals, which will then diffuse to the negative electrode to be reduced to form neutral molecules, and then diffuse to the positive electrode. This cycle is repeated until the overload current in the battery is consumed, thereby avoiding the continuous increase of the positive electrode voltage during overcharging and the continuous and violent reaction with the electrolyte, thereby improving the safety of battery overcharging.

[0019] In addition, the secondary battery of the present invention is a bipolar battery. When packaging the bipolar battery, a mixture of epoxy resin glue and epoxy resin fixing glue is used as packaging glue, which can achieve rapid curing at high temperature and rapid curing time of less than 30 minutes at room temperature, thereby realizing the packaging of the bipolar battery, greatly simplifying the packaging steps and reducing the packaging time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A schematic diagram of the structure of a secondary battery in one embodiment of the present invention;

[0022] Figure 2 A schematic structural diagram of an assembly step S1 of a secondary battery of the present invention in one embodiment;

[0023] Figure 3 A schematic structural diagram of an assembly step S2 of a secondary battery in one embodiment of the present invention;

[0024] Figure 4 A schematic structural diagram of an assembly step S3 of a secondary battery in one embodiment of the present invention;

[0025] Figure 5 FIG. 1 is a schematic structural diagram of an assembly step S5 of a secondary battery in an embodiment of the present invention.

[0026] Component number description:

[0027] 100, negative electrode plate; 200, bipolar electrode plate; 300, positive electrode plate; 10, bipolar current collector; 20, negative electrode active material layer; 30a, first packaging glue; 30b, second packaging glue; 40, separator; 50, positive electrode active material layer. DETAILED DESCRIPTION

[0028] The following is an explanation of the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied by other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and the features in the embodiments can be combined with each other without conflict. The test methods for which specific conditions are not specified in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturers.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0030] In this article, when it comes to numerical ranges, unless otherwise specified, the distribution of optional values ​​within the numerical range is considered continuous and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined.

[0031] In this document, unless otherwise specified, “%” refers to mass percentage.

[0032] In this article, substituents refer to atoms or groups of atoms that replace the main chain or ring in organic compounds. They can replace a hydrogen atom or other atoms in the molecule and affect the chemical and physical properties of the molecule. The type and position of the substituent have an important influence on the reactivity, polarity, solubility and other properties of the molecule.

[0033] Unsaturation, also known as the hydrogen deficiency index or the ring double bond index, is a quantitative indicator of the degree of unsaturation of organic compound molecules. n H m Hydrocarbons with molecular formula C n H m O x If m<2n+2, the hydrocarbon and its hydrocarbon group have a certain degree of unsaturation Ω, that is, compared with open-chain alkanes with the same number of carbon atoms in the organic compound molecule, the unsaturation of the organic compound increases by 1 for every 2 hydrogen atoms reduced.

[0034] Number of heteroatoms: In organic chemistry, non-carbon atoms are collectively referred to as heteroatoms. The most common heteroatoms are nitrogen atoms, sulfur atoms, and oxygen atoms.

[0035] Lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4, referred to as LNMO) and lithium-rich manganese-based layered oxides (xLi2MnO3·(1-x)LiMO2, 0<x<1, M includes one or more of Ni, Co, Mn, referred to as LRM), with high energy density, excellent cycle ability and high discharge platform voltage, are the research hotspots of lithium-ion battery positive electrode materials today. However, as the capacity of energy storage batteries increases, the safety performance of LNMO and LRM system batteries (including short circuit, overcharge, thermal runaway, etc.) also has certain risks, among which the safety problems caused by overcharge are particularly serious. Overcharge means that the charge stored in the battery exceeds the battery design capacity, resulting in excessive voltage of the battery. When a lithium-ion battery is overcharged, the battery voltage rises rapidly with the increase of polarization, which is bound to cause irreversible changes in the structure of the positive electrode active material and oxidative decomposition of the electrolyte, thereby generating a large amount of gas and releasing a large amount of heat, causing the internal pressure and temperature of the battery to rise sharply, and there are unsafe risks such as explosion and combustion. At the same time, the surface of the negative electrode in the overcharged state will also reduce its safety due to the deposition of metallic lithium.

[0036] The present application proposes an electrolyte based on the overcharge safety problem of LNMO and LRM system secondary batteries. By introducing a redox shuttle inhibitor that matches the LNMO and LRM positive electrode materials into the electrolyte, the redox reaction of the additive when the battery is overcharged is utilized to avoid the continuous increase of the positive electrode voltage and the continuous and violent reaction with the electrolyte, thereby improving the overcharge problem of the battery.

[0037] See also Figure 1 The present invention provides a secondary battery, which includes a bipolar pole piece 200, a separator 40, and an electrolyte in which the bipolar pole piece 200 and the separator 40 are immersed, wherein the bipolar pole piece 200 includes a positive electrode active material layer 50, and the positive electrode active material layer 50 includes a positive electrode active material LiNi 0.5 Mn 1.5 O4 or xLi2MnO3·(1-x)LiMO2, wherein 0<x<1, and M comprises one or more of Ni, Co, and Mn. The electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a compound shown in Formula I:

[0038]

[0039] In Formula I, R1 and R2 are each independently selected from a substituent having 0 to 3 carbon atoms, 0 to 4 unsaturations, and 0 to 3 heteroatoms, wherein the heteroatoms include nitrogen atoms and / or sulfur atoms. That is, the types of R1 and R2 in Formula I do not affect each other, and they may be the same substituent or different substituents. The number of carbon atoms in the above-mentioned substituents may be any value in the range of 0 to 3, such as 0, 1, 2 or 3, and the degree of unsaturation may be any value in the range of 0 to 4, such as 0, 1, 3 or 4. Heteroatoms are non-carbon atoms, and heteroatoms are selected from nitrogen (N) atoms and / or sulfur (S) atoms, but are not limited thereto. The number of heteroatoms may be any value in the range of 0 to 3. For example, 0, 1, 2 or 3. When the number of heteroatoms is 1, the heteroatom may be a nitrogen atom or a sulfur atom. When the number of heteroatoms is 2 or 3, the heteroatoms may be all nitrogen atoms or all sulfur atoms, or both nitrogen atoms and sulfur atoms.

[0040] In one embodiment, R1 and R2 in Formula I are independently selected from any one of alkyl, alkenyl, and amino. That is, R1 and R2 can be selected from any one of alkyl, alkenyl, and amino, and can be the same or different. As an example, R1 and R2 are both alkyl; or R1 is alkyl, R2 is alkenyl or amino, and so on.

[0041] The compound shown in Formula I contains a naphthoquinone structure and an electron-withdrawing functional group cyano (-CN), and an edge ring of the naphthoquinone structure is substituted by two S atoms in the opposite position. The cyano group, as a strong electron-withdrawing group, can increase its oxidation potential by reducing the electron density of the molecule, and the edge ring is substituted by two S atoms in the opposite position, which can further improve its voltage resistance, so that it is oxidized above 4.85V, for example, 4.9V, and will not be oxidized below 4.85V, which is similar to the high-voltage positive electrode material LiNi 0.5 Mn 1.5 O4 or xLi2MnO3·(1-x)LiMO2. Therefore, under the normal operating voltage of the LRM and LNMO battery systems, the compound shown in Formula I does not undergo an electrochemical reaction. When the battery is overcharged, the compound shown in Formula I is oxidized near the positive electrode to form active free radicals, which then diffuse to the negative electrode, obtain electrons and are reduced to form neutral molecules that diffuse to the positive electrode. This cycle continues until the overload current in the battery is consumed, thereby achieving the purpose of preventing overcharge. The additive shown in Formula I converts the excess electricity provided by overcharge into heat through a reversible reaction on both sides of the electrode, avoids side reactions between the electrode and the electrolyte, protects the battery components from loss under high voltage, and thus improves the battery's cycle performance.

[0042] The amount of the compound shown in Formula I added has a great influence on the performance of the battery. When the amount of the compound shown in Formula I added to the electrolyte is insufficient, the anti-overcharge effect on the battery is not obvious. When the amount added is too much, a thicker solid electrolyte interface film will be formed on the electrode surface, thereby increasing the internal resistance of the battery and affecting the cycle performance of the battery. In this application, based on the total mass of the electrolyte, the content of the compound shown in Formula I in the electrolyte is 0.1% to 3%, further 0.1% to 1%, and can be specifically listed as 0.1%, 0.5%, 0.8 or 1%, etc.

[0043] The lithium salt in the electrolyte can be selected from any lithium salt suitable for lithium-ion batteries in the art. To obtain a better electrolyte, the lithium salt must have the following characteristics: low dissociation energy and high solubility. Low dissociation energy ensures that the electrolyte formed after the lithium salt dissolves has high conductivity, thereby achieving a high rate of the battery; high solubility ensures that there are enough lithium ions in the electrolyte for transmission; good stability, when the battery works at high voltage and high temperature, the lithium salt will not react with other components; good SEI film-forming performance to ensure that the electrolyte will not be continuously consumed during subsequent cycles.

[0044] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethyl)sulfonyl imide (LiFSI), lithium bis(trifluoromethyl)sulfonyl imide (LiTFSI), lithium acetate (CH3COOLi), lithium methanesulfonate (CH3SO3Li), and lithium trifluoromethylsulfonate (CF3SO3Li). That is, the lithium salt can be a single lithium salt or a mixed lithium salt. Based on the total mass of the electrolyte, the total mass percentage of the lithium salt in the electrolyte is 12% to 16%, which can be specifically listed as 12%, 14% or 16%, etc. Further, the lithium salt adopts a mixed lithium salt with lithium hexafluorophosphate (LiPF6) as the main component and other lithium salts as the auxiliary component, which can improve the comprehensive performance of the electrolyte. For example, a mixed lithium salt of lithium hexafluorophosphate and lithium bis(trifluoromethyl)sulfonyl imide is used, wherein the mass ratio of lithium hexafluorophosphate to lithium bis(trifluoromethyl)sulfonyl imide can be 14:1, 14:2 or 13:2, etc.

[0045] The non-aqueous solvent is used as the main part of the electrolyte to disperse lithium salts and additives. In some embodiments, the non-aqueous solvent includes one or more of carbonates, carboxylates, ether solvents and nitrile solvents. Among them, carbonates include carbonates selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC) and fluoroethyl methyl carbonate (FEMC); carboxylates include one or more of ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; ethers include one or two of ethylene glycol dimethyl ether and diethanol diethyl ether; nitrile solvents include one or more of acetonitrile, propionitrile, butyronitrile, and valeronitrile. That is, the non-aqueous solvent can be selected from any one of the solvents listed above, or any combination of two or more. As an example, the non-aqueous solvent is a combination of ethylene carbonate, dimethyl carbonate and methyl formate, or a combination of ethyl formate and ethylene carbonate, and so on. Those skilled in the art can select a suitable solvent combination according to actual needs.

[0046] Based on the total mass of the electrolyte, the mass percentage of the non-aqueous solvent in the electrolyte is 80% to 90%, for example, 80%, 85% or 90%.

[0047] In other embodiments, other types of additives may be added to the electrolyte, such as vinylene carbonate (VC), diethylene sulfate (DTD), fluoroethylene carbonate (FEC), propenyl-1,3-sultone (PST), tetravinylsilane (TVSI), etc. Those skilled in the art may make a selection according to actual production requirements.

[0048] An example of the preparation method of the electrolyte of the present invention is as follows: in a glove box with an argon atmosphere having a water content of <10 ppm, the non-aqueous solvent is mixed evenly according to a set ratio, and then the fully dried lithium salt and additives are added to the above-mentioned organic solvent, mixed evenly, and prepared into an electrolyte.

[0049] See also Figure 1 In one embodiment, the secondary battery includes at least one bipolar pole piece 200, and at least one bipolar pole piece 200 and a separator 40 are alternately arranged to form a stacked electrode body. Specifically, the bipolar pole piece 200 includes a bipolar current collector 10, a negative electrode active material layer 20, and a positive electrode active material layer 50. Among them, the bipolar current collector 10 adopts a conventional current collector type in the art, such as a copper-aluminum integrated current collector, which has a copper foil surface and an aluminum foil surface, the copper foil surface is used to form the negative electrode active material layer 20 thereon, and the aluminum foil surface is used to form the positive electrode active material layer 50 thereon.

[0050] The positive electrode active material layer 50 is disposed on the aluminum foil surface of the bipolar current collector 10. The positive electrode active material layer 50 includes a positive electrode active material, a positive electrode conductive agent and a positive electrode binder. In this application, the positive electrode active material may be LiNi 0.5 Mn 1.5 O4 (LNMO), LNMO is a spinel structure, and the diffusion channel of lithium ions in the spinel crystal structure is three-dimensional, so it has excellent rate performance. In addition, LNMO has good cycle performance, high energy density and high operating voltage (about 4.7V). The positive electrode active material of the present application can also be xLi2MnO3·(1-x)LiMO2 (LRM), wherein 0<x<1, for example, x is 0.1, 0.3, 0.5 or 0.8, etc., and M includes one or more of Ni, Co, and Mn, for example, M is Ni, Mn or a combination of Co and Mn, etc. LRM has high specific capacity, excellent cycle ability and high operating voltage (about 4.6V). The positive electrode conductive agent can be selected from one of carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or a combination of two or more in any proportion, such as carbon black, or a combination of carbon black and graphene, or a combination of acetylene black, graphene and carbon nanofibers, and the like. The positive electrode binder is, for example, selected from any one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene or styrene butadiene rubber (SBR), such as polyvinylidene fluoride, or a combination of polyamide and polyacrylonitrile, etc. The ratio between the various substances in the positive electrode active material layer 50 can be set according to actual production requirements.

[0051] The negative electrode active material layer 20 is disposed on the copper foil surface of the bipolar current collector 10. The negative electrode active material layer 20 includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and a thickener. The negative electrode active material includes but is not limited to a graphite negative electrode material and / or a silicon-based negative electrode material. The graphite negative electrode material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon. The silicon-based negative electrode material includes silicon element, silicon oxide compound (SiO x, 0<x<2), silicon carbon, etc. One or more. The negative electrode conductive agent is selected from one of carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc., or a combination of two or more mixed in any proportion. The negative electrode conductive agent may be the same as the positive electrode conductive agent or different. The negative electrode binder is selected from one of polyacrylic acid (PAA), lithium acrylate (PAALi), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), or a combination of multiple mixed in any proportion, such as styrene butadiene rubber, a combination of styrene butadiene rubber and polyacrylic acid, etc. The thickener is selected from carboxymethyl cellulose (CMC), such as sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li). The ratio between the substances in the negative electrode active material layer 20 can be set according to actual production requirements.

[0052] The separator 40 between adjacent bipolar pole pieces 200 is made of a porous material that is insulating and allows lithium ions to pass through, such as polyethylene film (PE), polypropylene film (PP), glass fiber film, polyethylene film or composite film.

[0053] See also Figure 1 In some embodiments, the secondary battery further comprises a negative electrode sheet 100 and a positive electrode sheet 300. Along the stacking direction of the bipolar electrode sheet 200, the negative electrode sheet 100 and the positive electrode sheet 300 are respectively arranged on both sides of the stacked electrode body, and the negative electrode sheet 100 is arranged on the side of the stacked electrode body where the positive electrode active material layer 50 is exposed, and the positive electrode sheet 300 is arranged on the side of the stacked electrode body where the negative electrode active material layer 20 is exposed. A separator 40 is provided between the negative electrode sheet 100 and the bipolar electrode sheet 200 and between the positive electrode sheet 300 and the bipolar electrode sheet 200 for insulation separation. The negative electrode sheet 100 comprises a negative current collector and a negative active material layer 20 arranged on one side of the negative current collector. The negative current collector may be copper foil or the above-mentioned bipolar current collector 10. In this embodiment, the bipolar current collector 10 is used, and the negative active material layer 20 is only arranged on the copper foil surface of the bipolar current collector 10. The positive electrode plate 300 includes a positive electrode current collector and a positive electrode active material layer 50 arranged on one side surface of the positive electrode current collector. The positive electrode current collector can be made of aluminum foil or the above-mentioned bipolar current collector 10. In this embodiment, the bipolar current collector 10 is used, and the positive electrode active material layer 50 is only arranged on the aluminum foil surface of the bipolar current collector 10.

[0054] In order to avoid the failure of the bipolar battery due to the short circuit of the liquid junction, it is necessary to inject the electrolyte at the edges of the two adjacent bipolar current collectors 10 and then set an insulating seal for packaging. However, the current packaging method is to use light curing or hot pressing curing to illuminate or heat each unit one by one, and the preparation process is very cumbersome and labor-intensive. Therefore, the present invention proposes a simple curing packaging glue, which can be quickly cured at different speeds at different temperatures to form a sealing layer, thereby simplifying the packaging steps of the bipolar battery. The packaging glue includes a first packaging glue 30a and a second packaging glue 30b, the first packaging glue 30a includes an epoxy resin glue, and the second packaging glue 30b includes an epoxy resin curing glue. The epoxy resin glue and the epoxy resin curing glue have a commonly used epoxy glue component. After the two are mixed, they can be cured at different temperatures and for different times, such as curing for 30 seconds at 80°C, or curing for 30 minutes at room temperature.

[0055] In some embodiments, the epoxy resin glue can be a bisphenol A epoxy resin glue, and the epoxy resin curing glue can be a fatty amine curing agent, including but not limited to ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. The epoxy resin curing glue can be selected from one of them, or any two or more of them can be selected. The ratio of epoxy resin glue to epoxy resin curing glue is not limited, and can be mixed in any proportion. As an example, the mass ratio of epoxy resin glue to epoxy resin curing glue is 10:1. The encapsulation glue of this embodiment can achieve ultra-rapid curing at a slightly higher temperature, as well as rapid curing at room temperature, thereby realizing the encapsulation of secondary batteries, greatly simplifying the encapsulation steps and reducing the encapsulation time.

[0056] The negative electrode sheet 100, the bipolar electrode sheet 200 and the positive electrode sheet 300 can be prepared by referring to conventional processes in the art, as exemplified below:

[0057] Preparation of negative electrode sheet: The negative electrode active material, negative electrode conductive agent, negative electrode binder and thickener are dispersed in deionized water according to a set ratio to form a uniform negative electrode slurry: The negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, a negative electrode sheet 100 is obtained.

[0058] Preparation of positive electrode sheet: The positive electrode active material, positive electrode conductive agent and positive electrode binder are dispersed in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, a positive electrode sheet 300 is obtained.

[0059] Preparation of bipolar pole piece: the above negative electrode slurry is coated on the copper foil surface of the bipolar current collector, dried at room temperature and then transferred to an oven for drying; then the above prepared positive electrode slurry is coated on the aluminum foil surface of the bipolar current collector coated with negative electrode active material on one side, dried at room temperature and then transferred to an oven for drying, and then the bipolar pole piece 200 is obtained after cold pressing and other processes.

[0060] Then, the negative electrode sheet 100, the bipolar electrode sheet 200 and the positive electrode sheet 300 prepared above are assembled into a bipolar battery. The assembly steps are as follows. Figures 1 to 5 , the specific process is as follows:

[0061] S1. Assemble the separator 40 on the surface of the negative electrode plate 100, wherein the bipolar current collector 10 of the negative electrode plate 100 is coated with the negative electrode active material layer 20 on one side, and the separator 40 is assembled on the side of the negative electrode plate 100 coated with the negative electrode active material layer 20 (see Figure 2 );

[0062] S2, the bipolar pole piece 200 is arranged on the diaphragm 40 of step S1, and the side of the bipolar pole piece 200 provided with the positive electrode active material layer 50 faces the diaphragm 40 (see Figure 3 );

[0063] S3, then place the diaphragm 40 on the bipolar pole piece 200 (see Figure 4 );

[0064] S4, repeating steps S2 to S3 several times (determined according to actual production conditions) to reach the preset number of battery cells required;

[0065] S5, assembling the positive electrode sheet 300 on the separator 40 of the previous step, wherein the bipolar current collector 10 of the positive electrode sheet 300 is coated with a positive electrode active material layer 50 on one side, and the positive electrode active material layer 50 faces the separator 40 (see Figure 5 ).

[0066] S6, coating three of the four sides between the adjacent bipolar current collectors 10 with a mixture of a first packaging glue 30a (epoxy resin glue) and a second packaging glue 30b (epoxy resin curing glue), and heating at 80° C. for 30 seconds;

[0067] S7. After the injection, apply a mixture of epoxy resin glue and epoxy resin curing glue on the last surface and leave it at room temperature for half an hour to cure (see Figure 1 ).

[0068] S8, the assembled battery is put through the processes of static, formation, aging, fixture, capacity division, etc. Figure 1 The bipolar battery shown.

[0069] The secondary battery of the present invention adopts a bipolar stacking structure, and a plurality of electrode sheets are stacked to form a connection structure in which a plurality of battery cells are substantially connected in series. A plurality of bipolar current collectors 10 of the bipolar battery are stacked, and a positive electrode active material layer 50, a separator 40 and a negative electrode active material layer 20 are sequentially arranged between adjacent bipolar current collectors 10 to form a battery cell with the bipolar current collectors 10 on both sides. The positive electrode active material layer 50, the separator 40 and the negative electrode active material layer 20 in each battery cell are stacked in a set order. The plurality of battery cells formed in the secondary battery are stacked in series to form a bipolar stacking structure, and are quickly sealed by a packaging glue. Moreover, during packaging, after all the pole pieces are assembled except for the injection, three-sided sealing is first performed, which is time-consuming and more convenient; after the injection, the last side is packaged, and the epoxy resin glue and the epoxy resin curing glue are mixed, and the curing can be completed by only placing at room temperature for less than half an hour, so as to realize the packaging of the battery.

[0070] A second aspect of the present invention provides an electric device, which includes the secondary battery of the present invention. The secondary battery can supply power to the electric device.

[0071] The above-mentioned electrical devices include but are not limited to mobile phones, tablets, laptops, electric toys, battery cars, new energy vehicles, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid vehicles or extended-range vehicles, etc.

[0072] The technical scheme of the present invention is described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0073] Example 1

[0074] See also Figures 1 to 5This embodiment provides a secondary battery, which includes a negative electrode sheet 100, a bipolar electrode sheet 200, a positive electrode sheet 300, a separator 40, an electrolyte and a packaging glue 30. The bipolar electrode sheet 200 includes a bipolar current collector 10, a negative electrode active material layer 20 disposed on the copper foil surface of the bipolar current collector 10, and a positive electrode active material layer 50 disposed on the aluminum foil surface of the bipolar current collector 10; the negative electrode sheet 100 includes a bipolar current collector 10 and a negative electrode active material layer 20 disposed on the copper foil surface of the bipolar current collector 10; the positive electrode sheet 300 includes a bipolar current collector 10 and a positive electrode active material layer 50 disposed on the aluminum foil surface of the bipolar current collector 10. The negative electrode sheet 100, the separator 40, the bipolar electrode sheet 200, the separator 40... the bipolar electrode sheet 200, the separator 40 (repeated 9 times), and the positive electrode sheet 300 are assembled into a stacked electrode body. The electrolyte includes a non-aqueous solvent of battery-grade fluoroethyl methyl carbonate (FEMC) and fluoroethylene carbonate (FEC) mixed in a mass ratio of 7:3, lithium salt LiPF6 and additives Based on the total mass of the electrolyte, the mass percentage of the additive is 1%; the mass percentage of the lithium salt is 13%.

[0075] The specific preparation process is as follows:

[0076] (1) Preparation of positive electrode sheet: LiNi 0.5 Mn 1.5 O4, binder polyvinylidene fluoride and conductive agent Super P are mixed in a weight ratio of 98:1:1, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the aluminum foil surface of the bipolar current collector, and after drying at room temperature, it is transferred to an oven for drying to obtain a positive electrode sheet.

[0077] (2) Preparation of negative electrode sheet: artificial graphite, a negative electrode active material, Super P, a thickener, sodium carboxymethyl cellulose (CMC-Na), and a binder, styrene-butadiene rubber (SBR), are mixed in a mass ratio of 96:1:1:2, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the copper foil surface of the bipolar current collector; after drying at room temperature, the mixture is transferred to an oven for drying to obtain a negative electrode sheet.

[0078] (3) Preparation of bipolar pole pieces: The above-mentioned positive electrode slurry is evenly coated on the aluminum foil surface of the bipolar current collector, and then transferred to an oven for drying after being dried at room temperature; then the above-mentioned negative electrode slurry is evenly coated on the copper foil surface of the bipolar current collector, and then transferred to an oven for drying after being dried at room temperature to obtain bipolar pole pieces.

[0079] (4) Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, battery-grade fluoroethyl methyl carbonate (FEMC) and fluoroethylene carbonate (FEC) were mixed at a mass ratio of 7:3 to form an organic solvent. Additives and lithium salt LiPF6 were then added according to Table 1. The content of each component in the electrolyte, except the solvent, was the weight percentage calculated based on the total weight of the electrolyte, and the content of each component in the solvent was 10% of the total solvent.

[0080] (5) Diaphragm: Polypropylene film is used as the diaphragm.

[0081] (6) Battery assembly: First, assemble the separator on the negative electrode active material layer 20 of the negative electrode plate 100, and then place the bipolar plate 200 on the separator 40, with the positive electrode active material layer 50 of the bipolar plate 200 facing the separator 40; then place the separator 40 on the bipolar plate 200, and place the bipolar plate on the separator 40, etc. Repeat 9 times, and then place the positive electrode plate 300 on the separator 40 of the previous step, with the positive electrode active material layer 50 facing the separator 40, to form a stacked battery. Electrode body; coating packaging glue 30a and 30b (a mixture of epoxy resin glue and epoxy resin curing glue in a ratio of 10:1) on three sides of the surrounding positions between adjacent bipolar current collectors 10 in the stacked electrode body and heating at 80°C for 30s to cure; then injecting electrolyte from the side not coated with packaging glue and applying packaging glue, and placing at room temperature for half an hour to complete the curing; the assembled battery is subjected to standing, formation, aging, clamping, capacity division and other processes to obtain a secondary battery (bipolar battery).

[0082] Example 2

[0083] The difference between this embodiment and embodiment 1 is that the amount of the additive added is 0.1%.

[0084] Example 3

[0085] The difference between this embodiment and embodiment 1 is that the amount of the additive is 0.5%.

[0086] Example 4

[0087] The difference between this embodiment and embodiment 1 is that the amount of the additive is 3%.

[0088] Example 5

[0089] The difference between this embodiment and embodiment 1 is that R1 and R2 of the additive are vinyl groups, and the additive has the following structure:

[0090]

[0091] Example 6

[0092] The difference between this embodiment and embodiment 1 is that R1 of the additive is methyl, R2 is amino, and the additive has the following structure:

[0093]

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is that the amount of the additive added is 0.05%.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that the amount of the additive added is 5%.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that the bipolar battery is not sealed with packaging glue.

[0100] Comparative Example 4

[0101] The difference between this comparative example and Example 1 is that R1 and R2 of the additive are n-butyl groups, and the additive has the following structure:

[0102]

[0103] In order to verify the performance of the secondary battery of the present application, the applicant conducted performance tests on the secondary batteries prepared in Examples 1-6 and Comparative Examples 1-4, respectively. The test results are shown in Table 1. The test method is as follows:

[0104] (1) High temperature cycle test:

[0105] The secondary batteries in the above-mentioned embodiments 1-6 and comparative examples 1-4 were subjected to long-term cycle charge and discharge at 45°C. When the battery capacity reached 80% of the first cycle discharge capacity, the test was stopped. This number of cycles was the cycle number of the battery at 45°C (test ended at 80% SOH state), wherein the voltage range was 3.4V to 4.85V, and the charge and discharge rate was 0.5C / 1C.

[0106] (2) Battery DC resistance (DCR) test

[0107] At 25°C, when the secondary batteries in Examples 1-6 and Comparative Examples 1-4 are discharged to 50% SOC (state of charge, reflecting the remaining capacity of the battery) at 1C current, the current is increased to 4C and maintained for 30s, and the difference between the updated stable voltage and the original platform voltage is detected. The ratio of its value to the 4C current value is the DC resistance DCR of the corresponding secondary battery. The DCR test result after the corresponding secondary battery is fully charged for the first time is the initial DCR of the battery.

[0108] Table 1: Secondary battery performance parameters of Examples 1-6 and Comparative Examples 1-4

[0109]

[0110]

[0111] Referring to Table 1, it can be seen from the comparison of Examples 1-4 and Comparative Examples 1-2 that: based on the total mass of the electrolyte, when the mass percentage of the additive is in the range of 0.1%-3%, the high temperature cycle performance of the battery is better than the cycle performance when the amount added is not within this range. This is because the additive can effectively exert its redox shuttle inhibition ability within the above range, consume the overload current in the battery, avoid the side reaction between the electrode and the electrolyte, and protect the battery components from loss under high voltage, thereby improving the cycle performance and overcharge safety of the battery, and when its addition amount is 1%, it reaches the optimum. When the amount of additive added is less than 0.1% (for example, 0.05% in Comparative Example 1), the redox shuttle ability is insufficient, and the cycle performance and overcharge safety of the battery cannot be effectively improved; when the amount of additive added is higher than 3% (for example, 5% in Comparative Example 2), a thicker solid electrolyte interface film will be formed on the electrode surface, increasing the DC resistance of the battery, thereby increasing irreversible losses and reducing its cycle performance.

[0112] By comparing Example 1 with Comparative Example 3, it can be seen that when the packaging glue is not used for sealing, the secondary battery cannot be cycled. This is because the liquid short circuit occurs in the secondary battery and the battery cannot be cycled.

[0113] By comparing Example 1, Examples 5-6 and Comparative Example 4, it can be seen that when the number of carbon atoms of the substituents R1 and R2 of the additive in the electrolyte exceeds 3, the overcharge safety performance of the battery will be affected to a certain extent. This is because when the number of carbon atoms of R1 and R2 is too large, the redox shuttle inhibition ability of the additive will be affected, and the overload current in the battery cannot be completely consumed to avoid side reactions between the electrode and the electrolyte, thereby affecting the cycle performance and overcharge safety performance of the battery.

[0114] The secondary battery of the present invention adds an additive compatible with the high-voltage positive electrode materials LRM and LNMO to the electrolyte. When the battery is overcharged, the additive will be oxidized near the positive electrode to form active free radicals, and then diffuse to the negative electrode to be reduced to form neutral molecules, and then diffuse to the positive electrode, and repeat the cycle. The internal cyclic redox reaction of the battery is used to avoid the continuous rise of the positive electrode voltage during overcharging and the continuous and violent reaction with the electrolyte, thereby improving the safety of battery overcharging. In addition, the secondary battery adopts a bipolar battery structure design, introduces an encapsulation layer that solidifies at different speeds at different temperatures, simplifies the encapsulation steps, solves the problems of liquid short circuit and cumbersome sealing process in liquid batteries, and improves the overall energy density of the battery. Therefore, the present invention effectively overcomes some practical problems in the prior art and has high utilization value and use significance.

[0115] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A secondary battery, characterized in that: include: A bipolar pole piece, a diaphragm, and an electrolyte in which the bipolar pole piece and the diaphragm are soaked; The bipolar plate includes a positive electrode active material layer, and the positive electrode active material layer includes LiNi 0.5 Mn 1.5 O4 or xLi2MnO3·(1-x)LiMO2, wherein 0<x<1, and M includes one or more of Ni, Co, and Mn; The electrolyte includes a non-aqueous solvent, a lithium salt and an additive, wherein the additive includes a compound represented by formula I, and the mass percentage of the compound represented by formula I is 0.1% to 3% based on the total mass of the electrolyte; In formula I, R1 and R2 are each independently selected from a substituent having 0 to 3 carbon atoms, 0 to 4 unsaturations, and 0 to 3 heteroatoms, wherein the heteroatoms include nitrogen atoms and / or sulfur atoms.

2. The secondary battery according to claim 1, characterized in that: Based on the total mass of the electrolyte, the mass percentage of the compound represented by formula I is 0.1% to 1%.

3. The secondary battery according to claim 1, characterized in that: In formula I, R1 and R2 are each independently selected from any one of an alkyl group, an alkenyl group, and an amino group.

4. The secondary battery according to claim 1, characterized in that: The bipolar pole piece further comprises a bipolar current collector and a negative electrode active material layer. The positive electrode active material layer and the negative electrode active material layer are respectively arranged on both side surfaces of the bipolar current collector.

5. The secondary battery according to claim 4, characterized in that: The electrolyte between adjacent bipolar current collectors is sealed by packaging glue.

6. The secondary battery according to claim 5, characterized in that: The packaging glue includes epoxy resin glue and epoxy resin curing glue, and the epoxy resin glue includes bisphenol A epoxy resin glue.

7. The secondary battery according to claim 1, characterized in that: The secondary battery also includes a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet are respectively arranged on both sides of the stacked electrode body of the bipolar electrode sheet, and the diaphragm is arranged between adjacent bipolar electrode sheets, between the bipolar electrode sheet and the positive electrode sheet, and between the bipolar electrode sheet and the negative electrode sheet.

8. The secondary battery according to claim 1, characterized in that: The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethylsulfonate; based on the total mass of the electrolyte, the mass percentage of the lithium salt is 12% to 16%.

9. The secondary battery according to claim 1, characterized in that: The non-aqueous solvent includes one or more of carbonates, carboxylates, ethers and nitriles; the carbonate includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, and fluoroethyl methyl carbonate; the carboxylates include one or more of ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; the ethers include ethylene glycol dimethyl ether and / or diethanol diethyl ether; the nitriles include one or more of acetonitrile, propionitrile, butyronitrile, and valeronitrile.

10. An electrical device, characterized in that: A secondary battery comprising any one of claims 1 to 9.

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