Secondary battery and electric device

Abstract

The application provides a secondary battery and a power utilization device, and particularly relates to the technical field of batteries. The secondary battery comprises a bipolar electrode sheet, a diaphragm and an electrolyte for impregnating the bipolar electrode sheet and the diaphragm; the bipolar electrode sheet comprises a positive active material layer, and the positive active material layer comprises lithium iron phosphate; the electrolyte comprises a non-aqueous solvent, a lithium salt and an additive, the additive comprises a compound shown in the following formula, and the mass percentage of the compound is 0.1% to 3% based on the total mass of the electrolyte; in the formula, R1 and R2 are each independently selected from a substituent group with 0 to 3 carbon atoms, 0 to 4 unsaturations and 0 to 3 heteroatoms, and the heteroatoms include nitrogen atoms and / or sulfur atoms. The application introduces an additive matched with lithium iron phosphate in the electrolyte, so that the overcharge safety of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a secondary battery and an electrical device. Background Technology

[0002] Bipolar batteries refer to multiple batteries stacked together, where adjacent cells share the same current collector and are packaged together. The batteries use an internal series connection, which significantly increases the battery's output voltage and power while reducing the number of connecting wires and tabs, thus greatly improving energy density. Therefore, bipolar batteries have broad application prospects in electric vehicles and energy storage.

[0003] Liquid bipolar batteries also present serious safety issues during use. Like conventional lithium-ion batteries, bipolar batteries can experience thermal runaway under extreme conditions such as short circuits, punctures, impacts, overheating, and overcharging, with overcharging-induced thermal runaway being particularly severe. Under overcharge conditions, the structure of the positive electrode active material becomes more unstable, lithium plating is more likely to occur on the negative electrode surface, and the side reactions between the electrode material and the electrolyte are more intense. This leads to severe capacity decay, affects the battery's cycle performance, and may even cause safety accidents such as fires and explosions.

[0004] To prevent battery safety issues caused by overcharging, traditional methods include modifying battery materials, using circuit breakers, explosion-proof safety devices, and voltage-sensitive films inside the battery. However, these methods cannot fundamentally solve the battery overcharging safety problem. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a secondary battery and an electrical device that improves the overcharge safety of bipolar batteries by adding a redox shuttle inhibitor that matches the positive electrode active material lithium iron phosphate to the electrolyte.

[0006] To achieve the above and other related objectives, a first aspect of the present invention provides a secondary battery, the secondary battery comprising: a bipolar electrode, a separator, and an electrolyte therein wetting the bipolar electrode and the separator; the bipolar electrode includes a positive active material layer, the positive active material layer comprising lithium iron phosphate; the electrolyte includes a non-aqueous solvent, a lithium salt, and an additive, the additive comprising a compound represented by Formula I, wherein 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 substituents having 0 to 3 carbon atoms, 0 to 4 degrees of unsaturation, and 0 to 3 heteroatoms, wherein the heteroatoms include nitrogen atoms and / or sulfur atoms.

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

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

[0011] In one embodiment of the present invention, the bipolar electrode further includes a bipolar current collector and a negative electrode active material layer, wherein the positive electrode active material layer and the negative electrode active material layer are respectively disposed on both sides of the bipolar current collector.

[0012] In one embodiment of the present invention, the electrolyte between adjacent bipolar current collectors is sealed with encapsulating adhesive.

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

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

[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; the mass percentage of the lithium salt is 12% to 16% based on the total mass of the electrolyte.

[0016] In one embodiment of the present invention, the non-aqueous solvent includes one or more of carbonates, carboxylic esters, ethers, and nitriles; the carbonate includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, and ethyl fluorocarbonate; the carboxylic ester includes one or more of ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; the ether includes ethylene glycol dimethyl ether and / or diethyl glycol diethyl ether; and the nitrile includes one or more of acetonitrile, propionitrile, butyronitrile, and valerate.

[0017] The present invention also provides an electrical device, which includes the secondary battery described above.

[0018] The secondary battery of the present invention adds a redox shuttle inhibitor adapted to the positive electrode active material lithium iron phosphate to the electrolyte. When the battery is overcharged, the additive is oxidized near the positive electrode to form active free radicals, which then diffuse to the negative electrode to be reduced to form neutral molecules, and then diffuse back to the positive electrode. This cycle repeats until the overload current in the battery is completely consumed, thus avoiding the continuous rise of the positive electrode voltage and the continuous violent reaction with the electrolyte during overcharging, thereby improving the safety of battery overcharging.

[0019] Furthermore, the secondary battery of the present invention is a bipolar battery. When encapsulating the bipolar battery, a mixture of epoxy resin adhesive and epoxy resin fixative is used as the encapsulating adhesive, which can achieve rapid curing at high temperature and a curing time of less than 30 minutes at room temperature, thereby realizing the encapsulation of the bipolar battery, greatly simplifying the encapsulation steps and reducing the encapsulation time. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

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

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

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

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

[0025] Figure 5 This is a schematic diagram of the assembly step S5 of the secondary battery of the present invention in one embodiment.

[0026] Component designation explanation:

[0027] 100, Negative electrode; 200, Bipolar electrode; 300, Positive electrode; 10, Bipolar current collector; 20, Negative active material layer; 30a, First encapsulant; 30b, Second encapsulant; 40, Separator; 50, Positive active material layer. Detailed Implementation

[0028] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0031] Unless otherwise specified, "%" in this article refers to the percentage content by mass.

[0032] In this article, substituents refer to atoms or groups of atoms that replace those on the main chain or rings of organic compounds. They can replace a hydrogen atom or other atoms in a molecule, affecting its chemical and physical properties. The type and position of substituents have a significant impact on the reactivity, polarity, solubility, and other properties of a molecule.

[0033] Unsaturation, also known as the hydrogen deficiency index or cycloaddition double bond index, is a quantitative indicator of the degree of unsaturation in organic compound molecules. Its molecular formula is C2. n H m The hydrocarbon and its molecular formula is C n H m O x For hydrocarbon derivatives, if m < 2n + 2, then 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, the degree of unsaturation of the organic compound increases by 1 for every 2 hydrogen atoms removed.

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

[0035] Lithium iron phosphate (LiFePO4, LFP) has a three-dimensional network olivine structure. Due to its high cycle life, good safety, and low price, LFP is one of the most commonly used cathode materials for power batteries. However, as the capacity of LFP energy storage batteries increases, certain safety risks (including short circuits, overcharging, and thermal runaway) also emerge, with overcharging causing particularly serious safety issues. Overcharging refers to the storage of charge within the battery exceeding its design capacity, resulting in excessively high battery voltage. After overcharging, the lithium-ion intercalation reaction at the negative electrode transforms into lithium metal deposition on the negative electrode surface, resulting in needle-like lithium metal crystals that can puncture the separator, causing a short circuit. This can lead to anything from accelerated self-discharge to a severe short circuit, where the short-circuit current causes a rapid increase in battery temperature, potentially leading to fire or explosion. This application proposes an electrolyte to address the overcharge safety issue of LFP-based secondary batteries. By introducing a redox shuttle inhibitor that matches the LiFePO4 cathode material into the electrolyte, the redox reaction during battery overcharging is prevented from causing a continuous rise in cathode voltage and a continuous and violent reaction with the electrolyte, thereby improving the overcharge problem of the battery.

[0036] Please see Figure 1 This invention provides a secondary battery comprising a bipolar electrode 200, a separator 40, and an electrolyte therein wetting the bipolar electrode 200 and the separator 40. The bipolar electrode 200 includes a positive active material layer 50, which comprises the positive active material LiFePO4. The electrolyte includes a non-aqueous solvent, a lithium salt, and additives, wherein the additives include compounds represented by Formula I.

[0037]

[0038] In Formula I, R1 and R2 are each independently selected from substituents with 0-3 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms, including nitrogen and / or sulfur atoms. That is, the types of R1 and R2 in Formula I do not affect each other; they can be the same substituent or different substituents. The number of carbon atoms in the substituents can be any value from 0 to 3, such as 0, 1, 2, or 3, and the degree of unsaturation can be any value from 0 to 4, such as 0, 1, 3, or 4. Heteroatoms are non-carbon atoms, selected from nitrogen (N) atoms and / or sulfur (S) atoms, but not limited to these. The number of heteroatoms can be any value from 0 to 3, such as 0, 1, 2, or 3. When the number of heteroatoms is 1, the heteroatom can be either a nitrogen atom or a sulfur atom. When the number of heteroatoms is 2 or 3, the heteroatoms can all be nitrogen atoms, all be sulfur atoms, or simultaneously contain both nitrogen and sulfur atoms.

[0039] In one embodiment, R1 and R2 in Formula I are each independently selected from any one of alkyl, alkenyl, and amino groups. That is, R1 and R2 can both be selected from any one of alkyl, alkenyl, and amino groups, and can be the same or different. As an example, R1 and R2 can both be alkyl groups; or R1 can be alkyl groups and R2 can be alkenyl or amino groups, etc.

[0040] The compound shown in Formula I contains a naphthoquinone structure and an electron-donating functional group, methoxy (-OCH3). This electron-donating functional group increases the electron density of the molecule, lowering the compound's oxidation potential so that oxidation begins at 3.7-3.8V, and it will not oxidize below this potential, matching the high-voltage resistance of LiFePO4. Therefore, under the normal operating voltage of the LFP battery system, 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, forming active free radicals, which then diffuse to the negative electrode, gain electrons, are reduced, form neutral molecules, and then diffuse back to the positive electrode. This cycle continues until the overload current in the battery is completely consumed, thus achieving the purpose of preventing overcharge. The additive shown in Formula I converts the excess electricity provided by overcharging into heat through a reversible reaction on both sides of the electrode, avoiding side reactions between the electrode and the electrolyte, protecting the battery components from damage under high voltage, and thus improving the battery's cycle performance.

[0041] The amount of compound shown in Formula I added has a significant impact on battery performance. When the amount of compound shown in Formula I added to the electrolyte is insufficient, the overcharge protection effect on the battery is not obvious. However, when the amount added is excessive, a thick solid electrolyte interface film will form on the electrode surface, thereby increasing the internal resistance of the battery and affecting its cycle performance. In this application, based on the total mass of the electrolyte, the content of compound shown in Formula I in the electrolyte is 0.1% to 3%, more specifically 0.1% to 1%, and can be listed as 0.1%, 0.5%, 0.8%, or 1%, etc.

[0042] The lithium salt in the electrolyte can be selected from any lithium salt suitable for lithium-ion batteries in this field. To obtain a better electrolyte, the lithium salt needs to 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 high battery rate; high solubility ensures that there are enough lithium ions in the electrolyte for transport; good stability, so that the lithium salt will not react with other components when the battery is operating at high voltage and high temperature; and good SEI film formation performance to ensure that the electrolyte is not continuously consumed during subsequent cycles.

[0043] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium acetate (CH3COOLi), lithium methanesulfonate (CH3SO3Li), and lithium trifluoromethylsulfonate (CF3SO3Li). That is, a single lithium salt or a mixture of lithium salts can be used. Based on the total mass of the electrolyte, the total mass percentage of lithium salts in the electrolyte is 12% to 16%, specifically 12%, 14%, or 16%, etc. Furthermore, using a mixture of lithium salts with lithium hexafluorophosphate (LiPF6) as the main component and other lithium salts as auxiliary components can improve the overall performance of the electrolyte. For example, a mixture of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide can be used, wherein the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide can be 14:1, 14:2, or 13:2, etc.

[0044] Non-aqueous solvents serve as the main component of the electrolyte, used to disperse lithium salts and additives. In some embodiments, the non-aqueous solvent includes one or more of carbonates, carboxylic esters, ether solvents, and nitrile solvents. Specifically, carbonates include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and ethyl fluorocarbonate (FEMC); carboxylic esters include one or more selected from ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; ethers include one or two selected from ethylene glycol dimethyl ether and diethanolethylene diethyl ether; and nitrile solvents include one or more selected from acetonitrile, propionitrile, butyronitrile, and valerate. That is, the non-aqueous solvent can be selected from any one of the solvents listed above, or any combination of two or more. For example, the non-aqueous solvent may be a combination of ethylene carbonate, dimethyl carbonate, and methyl formate, or a combination of ethyl formate and ethylene carbonate, etc. Those skilled in the art can select appropriate solvent combinations according to actual needs.

[0045] Based on the total mass of the electrolyte, the mass percentage of non-aqueous solvents in the electrolyte is 80% to 90%, for example, 80%, 85%, or 90%.

[0046] In other embodiments, other types of additives may be added to the electrolyte, such as vinylene carbonate (VC), vinyl sulfate (DTD), fluoroethylene carbonate (FEC), propylene-1,3-sulfonyl lactone (PST), tetravinylsilane (TVSI), etc. Those skilled in the art can select according to actual production needs.

[0047] An example of the preparation method of the electrolyte of the present invention is as follows: In a glove box with an argon atmosphere containing less than 10 ppm of water, a non-aqueous solvent is mixed evenly according to a set ratio, and then the fully dried lithium salt and additives are added to the organic solvent and mixed evenly to prepare the electrolyte.

[0048] Please see Figure 1 In one embodiment, the secondary battery includes at least one bipolar electrode 200, and the at least one bipolar electrode 200 and a separator 40 are alternately arranged to form a stacked electrode body. Specifically, the bipolar electrode 200 includes a bipolar current collector 10, a negative electrode active material layer 20, and a positive electrode active material layer 50. The bipolar current collector 10 adopts a current collector type conventional in the art, such as a copper-aluminum integrated current collector, which has a copper foil side and an aluminum foil side. The copper foil side is used to form the negative electrode active material layer 20 thereon, and the aluminum foil side is used to form the positive electrode active material layer 50 thereon.

[0049] A 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 is LiFePO4. The positive electrode conductive agent can be selected from one or more of carbon black, acetylene black, graphene, carbon nanotubes, and carbon nanofibers, or a combination of two or more mixed 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, etc. The positive electrode binder is selected from any one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexanefluoropropylene, or polymerized styrene-butadiene rubber (SBR). For example, polyvinylidene fluoride, or a combination of polyamide and polyacrylonitrile, etc. The proportions of the various substances in the positive electrode active material layer 50 can be set according to actual production needs.

[0050] 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, graphite-based negative electrode materials and / or silicon-based negative electrode materials. Graphite-based negative electrode materials include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Silicon-based negative electrode materials include elemental silicon and silicon oxide compounds (SiO₂). xThe negative electrode conductive agent is selected from one or more of the following: carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc., or a combination of two or more of them mixed in any proportion. The negative electrode conductive agent can be the same as or different from the positive electrode conductive agent. The negative electrode binder is selected from one of the following: polyacrylic acid (PAA), lithium acrylate (PAALi), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), or a combination of multiple substances mixed in any proportion, such as styrene-butadiene rubber, or a combination of styrene-butadiene rubber and polyacrylic acid. The thickener is selected from carboxymethyl cellulose (CMC), such as sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li). The proportions of the various substances in the negative electrode active material layer 20 can be set according to actual production needs.

[0051] The separator 40 between adjacent bipolar electrodes 200 is made of a porous material that is insulating and allows lithium ions to pass through, such as polyethylene (PE), polypropylene (PP), glass fiber membrane, polyethylene membrane or composite membrane, etc.

[0052] Please see Figure 1 In some embodiments, the secondary battery further includes a negative electrode 100 and a positive electrode 300. Along the stacking direction of the bipolar electrode 200, the negative electrode 100 and the positive electrode 300 are respectively disposed on both sides of the stacked electrode body. The negative electrode 100 is disposed on the side of the stacked electrode body exposing the positive active material layer 50, and the positive electrode 300 is disposed on the side of the stacked electrode body exposing the negative active material layer 20. A separator 40 is provided to insulate between the negative electrode 100 and the bipolar electrode 200, and between the positive electrode 300 and the bipolar electrode 200. The negative electrode 100 includes a negative current collector and a negative active material layer 20 disposed on one side of the negative current collector. The negative current collector can be copper foil or the aforementioned bipolar current collector 10. In this embodiment, the bipolar current collector 10 is used, and the negative active material layer 20 is only disposed on the copper foil surface of the bipolar current collector 10. The positive electrode 300 includes a positive current collector and a positive active material layer 50 disposed on one side surface of the positive current collector. The positive current collector can be aluminum foil or the bipolar current collector 10 described above. In this embodiment, the bipolar current collector 10 is used, and the positive active material layer 50 is disposed only on the aluminum foil surface of the bipolar current collector 10.

[0053] To prevent short circuits in the liquid junction of bipolar batteries from causing battery failure, electrolyte needs to be injected at the edges of two adjacent bipolar current collectors 10 before an insulating seal is installed for encapsulation. However, current encapsulation methods involve photocuring or thermoforming each cell individually, resulting in a very cumbersome and labor-intensive manufacturing process. Therefore, this invention proposes a simple-curing encapsulating adhesive that can rapidly cure at different temperatures and speeds to form a sealing layer, simplifying the encapsulation steps for bipolar batteries. The encapsulating adhesive includes a first encapsulating adhesive 30a and a second encapsulating adhesive 30b. The first encapsulating adhesive 30a comprises an epoxy resin adhesive, and the second encapsulating adhesive 30b comprises an epoxy resin curing adhesive. Both the epoxy resin adhesive and the epoxy resin curing adhesive contain commonly used epoxy adhesive components. When mixed, they can achieve curing at different temperatures and times, such as curing at 80°C for 30 seconds or at room temperature for 30 minutes.

[0054] In some embodiments, the epoxy resin adhesive can be a bisphenol A type epoxy resin adhesive, and the epoxy resin curing adhesive can be a fatty amine curing agent, including but not limited to ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. One, two, or more of these epoxy resin curing adhesives can be used. The ratio of epoxy resin adhesive to epoxy resin curing adhesive is not limited and can be mixed in any proportion. As an example, the mass ratio of epoxy resin adhesive to epoxy resin curing adhesive is 10:1. The encapsulating adhesive of this embodiment can achieve ultra-rapid curing at slightly higher temperatures and rapid curing at room temperature, thereby enabling the encapsulation of secondary batteries, greatly simplifying the encapsulation steps and reducing the encapsulation time.

[0055] The aforementioned negative electrode 100, bipolar electrode 200, and positive electrode 300 can be prepared using conventional processes in the art, as illustrated below:

[0056] Negative electrode preparation: The above-mentioned negative electrode active material, negative electrode conductive agent, negative electrode binder and thickener are dispersed in deionized water according to the set ratio to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, negative electrode 100 is obtained.

[0057] Positive electrode preparation: The above-mentioned positive active material, positive conductive agent and positive binder are dispersed in a solvent (e.g. N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive slurry; the positive slurry is coated on the positive current collector, and after drying, cold pressing and other processes, positive electrode 300 is obtained.

[0058] Bipolar electrode preparation: The above-mentioned 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 that has been coated with negative electrode active material on one side, dried at room temperature, and then transferred to an oven for drying. After cold pressing and other processes, bipolar electrode 200 is obtained.

[0059] The negative electrode 100, bipolar electrode 200, and positive electrode 300 prepared above are then assembled into a bipolar battery. The assembly steps are described below. Figures 1 to 5 The specific process is as follows:

[0060] S1. Assemble the separator 40 on the surface of the negative electrode 100, wherein the bipolar current collector 10 of the negative electrode 100 is coated with a negative electrode active material layer 20 on one side, and the separator 40 is assembled on the side of the negative electrode 100 coated with the negative electrode active material layer 20 (see...). Figure 2 );

[0061] S2. The bipolar electrode 200 is disposed on the separator 40 in step S1, with the side of the bipolar electrode 200 having the positive electrode active material layer 50 facing the separator 40 (see...). Figure 3 );

[0062] S3. Next, a diaphragm 40 is disposed on the bipolar electrode 200 (see...). Figure 4 );

[0063] S4. Repeat steps S2 to S3 several times (determined according to actual production conditions) to reach the preset required number of battery cells;

[0064] S5. Assemble the positive electrode 300 onto the separator 40 from the previous step, wherein the bipolar current collector 10 of the positive electrode 300 is coated with a positive active material layer 50 on one side, and the positive active material layer 50 faces the separator 40 (see...). Figure 5 ).

[0065] S6. Apply an encapsulating adhesive, consisting of a mixture of a first encapsulating adhesive 30a (epoxy resin adhesive) and a second encapsulating adhesive 30b (epoxy resin curing adhesive), to three of the four sides of the adjacent bipolar current collectors 10, and heat at 80°C for 30 seconds.

[0066] S7. After injection, apply a sealing adhesive consisting of a mixture of epoxy resin and epoxy resin curing adhesive to the last side. Let it cure at room temperature for half an hour (see [link]). Figure 1 ).

[0067] S8. The assembled batteries undergo processes such as settling, formation, aging, clamping, and capacity testing to obtain... Figure 1 The bipolar battery shown.

[0068] The secondary battery of this invention adopts a bipolar stacked structure. Multiple electrode sheets are stacked to form a substantially series-connected structure of multiple battery cells. Multiple bipolar current collectors 10 are stacked, with a positive electrode active material layer 50, a separator 40, and a negative electrode active material layer 20 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, separator 40, and negative electrode active material layer 20 in each battery cell are stacked in a predetermined order. Multiple battery cells formed in the secondary battery are stacked in series to form a bipolar stacked structure and quickly sealed with encapsulating adhesive. Furthermore, during encapsulation, except for the portion where electrolyte is injected, after all electrode sheets are assembled, three sides are sealed first, which is time-saving and more convenient; after electrolyte injection, the final side is encapsulated. Epoxy resin adhesive and epoxy resin curing adhesive are mixed, and curing is completed within half an hour at room temperature, thus achieving battery encapsulation.

[0069] A second aspect of the present invention provides an electrical device comprising the secondary battery described above, wherein the secondary battery can supply power to the electrical device.

[0070] The aforementioned electrical devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Electric toys can include stationary 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 electric vehicles, or range-extended electric vehicles, etc.

[0071] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0072] Example 1

[0073] This embodiment provides a secondary battery, which includes a negative electrode 100, a bipolar electrode 200, a positive electrode 300, a separator 40, an electrolyte, and an encapsulating adhesive 30. The bipolar electrode 200 includes a bipolar current collector 10, a negative active material layer 20 disposed on the copper foil surface of the bipolar current collector 10, and a positive active material layer 50 disposed on the aluminum foil surface of the bipolar current collector 10. The negative electrode 100 includes the bipolar current collector 10 and the negative active material layer 20 disposed on the copper foil surface of the bipolar current collector 10. The positive electrode 300 includes the bipolar current collector 10 and the positive active material layer 50 disposed on the aluminum foil surface of the bipolar current collector 10. The negative electrode 100, separator 40, bipolar electrode 200, separator 40... bipolar electrode 200, separator 40 (repeated 9 times), and positive electrode 300 are assembled into a stacked electrode body. The electrolyte consists of a non-aqueous solvent, a mixture of battery-grade ethyl fluorocarbonate (FEMC) and ethylene fluorocarbonate (FEC) in a 7:3 mass ratio, lithium salt LiPF6, and additives.

[0074] Based on the total mass of the electrolyte, the additive accounts for 1% by mass; the lithium salt accounts for 13% by mass.

[0075] The specific preparation process is as follows:

[0076] (1) Preparation of positive electrode sheet: The positive active material LiFePO4, the binder polyvinylidene fluoride and the 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 stirrer to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on the aluminum foil surface of the bipolar current collector, dried at room temperature and then transferred to an oven to dry to obtain a positive electrode sheet.

[0077] (2) Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC-Na) and 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 stirrer; the negative electrode slurry is uniformly coated on the copper foil surface of the bipolar current collector; after drying at room temperature, it is transferred to an oven for drying to obtain the negative electrode sheet.

[0078] (3) Preparation of bipolar electrode: The above positive electrode slurry is uniformly coated on the aluminum foil surface of the bipolar current collector, dried at room temperature and then transferred to an oven for drying; the above negative electrode slurry is then uniformly coated on the copper foil surface of the bipolar current collector, dried at room temperature and then transferred to an oven for drying, thus obtaining the bipolar electrode.

[0079] (4) Electrolyte preparation: In an argon atmosphere glove box with a water content of <10ppm, battery-grade ethyl fluorocarbonate (FEMC) and ethylene fluorocarbonate (FEC) were mixed at a mass ratio of 7:3 to form an organic solvent. Then, additives and lithium salt LiPF6 were added according to Table 1. The content of each component in the electrolyte, except for the solvent, is the weight percentage calculated based on the total weight of the electrolyte, and the content of each component in the solvent is ten percent of the total solvent content.

[0080] (5) Separator: Polypropylene membrane is used as the separator.

[0081] (6) Battery assembly: First, assemble the separator onto the negative electrode active material layer 20 of the negative electrode 100, then place the bipolar electrode 200 onto the separator 40, with the positive electrode active material layer 50 of the bipolar electrode 200 facing the separator 40; then place the separator 40 on the bipolar electrode 200, place the bipolar electrode on the separator 40... repeat 9 times, then place the positive electrode 300 onto the separator 40 of the previous step, with the positive electrode active material layer 50 facing the separator 40, forming a stack. Electrode body; three sides of the perimeter between adjacent bipolar current collectors 10 within the stacked electrode body are coated with encapsulating adhesive 30a and 30b (a mixture of epoxy resin adhesive and epoxy resin curing adhesive in a 10:1 ratio) and cured at 80°C for 30 seconds; then, electrolyte is injected into the side without encapsulating adhesive and encapsulating adhesive is applied, and the side is left at room temperature for half an hour to cure; the assembled battery is subjected to processes such as settling, formation, aging, clamping, and capacity testing to obtain a secondary battery (bipolar battery).

[0082] Example 2

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

[0084] Example 3

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

[0086] Example 4

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

[0088] Example 5

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

[0090]

[0091] Example 6

[0092] The difference between this embodiment and Example 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 additive added is 0.05%.

[0096] Comparative Example 2

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

[0098] Comparative Example 3

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

[0100] Comparative Example 4

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

[0102]

[0103] To verify the performance of the secondary battery of this 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, and the test methods are as follows:

[0104] (1) High-temperature cycle count test:

[0105] The secondary batteries in Examples 1-6 and Comparative Examples 1-4 were subjected to long-term cyclic charge-discharge at 45°C. The test was stopped when the battery capacity reached 80% of the discharge capacity of the first cycle. This number of cycles is the number of cycles of the battery at 45°C (the test ends at 80% SOH state). The voltage range is 2.5V to 3.8V, and the charge-discharge rate is 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 a 1C current, the current is increased to 4C and maintained for 30 seconds. The difference between the updated stable voltage and the original platform voltage is measured, and the ratio of this difference to the 4C current value is the DC resistance (DCR) of the corresponding secondary battery. The DCR test result performed after the first full charge of the corresponding secondary battery is the initial DCR of the battery.

[0108] Table 1: Performance parameters of secondary batteries in Examples 1-6 and Comparative Examples 1-4

[0109]

[0110]

[0111]

[0112] Referring to Table 1, comparing Examples 1-4 and Comparative Examples 1-2, it can be seen 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 that of the battery with an additive amount outside this range. This is because, within this range, the additive can effectively exert its redox shuttle suppression capability, consume the overload current in the battery, avoid side reactions between the electrode and the electrolyte, and protect the battery components from damage under high voltage, thereby improving the battery's cycle performance and overcharge safety. The optimal addition amount is 1%. When the additive addition amount is less than 0.1% (e.g., 0.05% in Comparative Example 1), the redox shuttle capability is insufficient, and it cannot effectively improve the battery's cycle performance and overcharge safety. When the additive addition amount is higher than 3% (e.g., 5% in Comparative Example 2), a thicker solid electrolyte interface film will form on the electrode surface, increasing the battery's DC resistance, thereby increasing irreversible losses and reducing its cycle performance.

[0113] Comparing Example 1 and Comparative Example 3, it can be seen that the secondary battery cannot cycle when it is not sealed with encapsulant because the liquid connection in the secondary battery is short-circuited, preventing it from cycling.

[0114] Comparing Examples 1, 5-6 and Comparative Example 4, it can be seen that when the number of carbon atoms of the substituents R1 and R2 in the electrolyte exceeds 3, it will affect the overcharge safety performance of the battery to a certain extent. This is because when the number of carbon atoms of R1 and R2 is too large, it will affect the redox shuttle suppression ability of the additive, and cannot completely consume the overload current in the battery, thus avoiding the side reaction between the electrode and the electrolyte, thereby affecting the cycle performance and overcharge safety performance of the battery.

[0115] The secondary battery of this invention incorporates an additive compatible with the positive electrode active material LiFePO4 into the electrolyte. When the battery is overcharged, this additive is oxidized near the positive electrode to form active free radicals, which then diffuse to the negative electrode, are reduced to form neutral molecules, and then diffuse back to the positive electrode. This cycle repeats continuously, utilizing the internal cyclic redox reaction within the battery to prevent a continuous rise in the positive electrode voltage and a sustained, violent reaction with the electrolyte during overcharging, thereby improving the battery's overcharge safety. Furthermore, this secondary battery employs a bipolar battery structure design, introducing an encapsulation layer that solidifies at different rates at different temperatures. This simplifies the encapsulation process, solves the problems of liquid-liquid short circuits and cumbersome sealing processes in liquid batteries, and improves the overall energy density of the battery. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0116] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can 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 those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A secondary battery, characterized in that, include: Bipolar electrode, diaphragm, and electrolyte therein for wetting the bipolar electrode and diaphragm; The bipolar electrode includes a positive active material layer, which includes lithium iron phosphate. 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 substituents having 0 to 3 carbon atoms, 0 to 4 degrees of unsaturation, 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 alkyl, alkenyl, and amino groups.

4. The secondary battery according to claim 1, characterized in that, The bipolar electrode also includes a bipolar current collector and a negative electrode active material layer, wherein the positive electrode active material layer and the negative electrode active material layer are respectively disposed on the two sides 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 with encapsulating adhesive.

6. The secondary battery according to claim 5, characterized in that, The encapsulating adhesive includes epoxy resin adhesive and epoxy resin curing adhesive, and the epoxy resin adhesive includes bisphenol A type epoxy resin adhesive.

7. The secondary battery according to claim 1, characterized in that, The secondary battery further includes a positive electrode and a negative electrode, the positive electrode and the negative electrode are respectively disposed on both sides of the stacked electrode body of the bipolar electrode, and the separator is disposed between adjacent bipolar electrodes, between the bipolar electrode and the positive electrode, and between the bipolar electrode and the negative electrode.

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; the mass percentage of the lithium salt is 12% to 16% based on the total mass of the electrolyte.

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

10. An electrical device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 9.

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