Secondary battery and electronic equipment

Abstract

The invention provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, the diaphragm comprises a porous base material and an insulating layer formed on the porous base material, the insulating layer comprises polymer particles with the melting point of 75-138 DEG C, and the polymer particles can be melted when the temperature of the battery reaches the melting point and fill pores of the porous base material to block ion conduction; the electrolyte comprises a component A and a component B, wherein the component A comprises at least one of lithium difluorophosphate, lithium bis (trifluoromethanesulfonyl) imide and lithium bis (fluorosulfonyl) imide; and the component B comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate and 1, 4-butyrolactone. The secondary battery provided by the invention has excellent low-temperature output performance, lithium precipitation inhibition characteristic and safety characteristic.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a secondary battery and electronic device. Background Technology

[0002] With the emergence of high-energy batteries, on the one hand, the capacity of lithium-ion batteries has increased and the energy density has generally improved; on the other hand, higher requirements have been placed on the safety of lithium-ion batteries, especially on the performance of lithium-ion battery separators.

[0003] Lithium-ion batteries release a significant amount of heat during charging, discharging, or short circuits, causing localized heat buildup and temperature increases, which can lead to explosions in severe cases. The lithium-ion battery separator, as a crucial material for isolating the positive and negative electrodes, must first and foremost function to thermally shut off in the event of thermal runaway, preventing further ion exchange between the electrodes. Secondly, it must remain intact at high temperatures to maintain its insulating properties and prevent short circuits caused by electrode deformation due to temperature increases.

[0004] Traditional polyolefin separators have a low heat distortion temperature, and the separator melts or deforms at around 160°C, which affects the safety of battery use. Existing ceramic-coated separators, due to the surface coating of inorganic materials such as alumina, can only increase the membrane breaking temperature to 170°C~180°C, which still cannot meet the needs of the rapid development of lithium-ion battery technology. Summary of the Invention

[0005] One aspect of the present invention provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the separator comprises a porous substrate and an insulating layer formed on the porous substrate, the insulating layer comprising polymer particles with a melting point of 75°C to 138°C, the polymer particles being capable of melting and filling the pores of the porous substrate when the battery temperature reaches their melting point to block ion conduction; the electrolyte comprises component A and component B, component A comprising at least one of lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide; component B comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, and 1,4-butyrolactone. The secondary battery provided by the present invention exhibits excellent low-temperature output performance, lithium deposition suppression characteristics, and safety characteristics.

[0006] In some embodiments, the polymer particles are made of at least one of the following: homopolymers of non-fluorinated alkenyl monomers, homopolymers of olefin monomers, homopolymers of unsaturated nitrile monomers, homopolymers of acrylate monomers, and homopolymers of ester monomers.

[0007] In some preferred embodiments, the polymer particles are made of polyethylene and / or polypropylene.

[0008] In some embodiments, the average particle size of the polymer particles is less than 2µm, preferably 0.2µm to 2µm, and more preferably 0.5µm to 1.5µm.

[0009] In some embodiments, the melting point of the polymer particles is 85°C to 128°C.

[0010] In some embodiments, based on 100 parts by mass of the electrolyte, the content of component A is 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass.

[0011] In some embodiments, based on 100 parts by mass of the electrolyte, the content of component B is 5 to 68 parts by mass, preferably 11 to 55 parts by mass.

[0012] In some embodiments, component B comprises ethyl propionate and propyl propionate, or component B comprises ethyl propionate and 1,4-butyrolactone.

[0013] In some embodiments, the electrolyte further includes additive C, which includes at least one of succinic anion, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, glyceryl trionitrile, lithium 1-ethyl-3-methylimidazolium tetrafluoroborate, lithium 1-butyl-3-methylimidazolium hexafluorophosphate, and lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonylimide).

[0014] In some embodiments, based on 100 parts by mass of the electrolyte, the content of succinic anion is 0.7-3.5 parts by mass, and / or the content of adiponitrile is 0.6-4 parts by mass, and / or the content of ethylene glycol bis(propionitrile) ether is 0.2-2 parts by mass, and / or the content of 1,3,6-hexanetrionitrile is 0.1-3 parts by mass, and / or the content of glycerol trionitrile is 0.1-4 parts by mass, and / or the content of lithium 1-ethyl-3-methylimidazolium tetrafluoroborate is 0.01-2 parts by mass, and / or the content of lithium 1-butyl-3-methylimidazolium hexafluorophosphate is 0.01-2 parts by mass, and / or the content of lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide is 0.01-2 parts by mass.

[0015] In some embodiments, the insulating layer further includes an adhesive and / or inorganic particles.

[0016] In some embodiments, the inorganic particles are made of at least one of strontium titanate, barium titanate, silicon dioxide, aluminum oxide, boehmite, magnesium oxide, magnesium hydroxide, and barium sulfate.

[0017] In some embodiments, the thickness of the insulating layer is 0.1µm to 5µm.

[0018] Another aspect of the present invention provides an electronic device comprising the aforementioned secondary battery. Attached Figure Description

[0019] 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 recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the diaphragm structure in one embodiment of the present invention; 1-Porous substrate; 2-Insulating layer. Detailed Implementation

[0021] The invention will now be described in more detail to allow for a clearer understanding. In this context, it will be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in common dictionaries, and it will be further understood that, based on the principle that the inventors may appropriately define the meanings of terms or words to best interpret the invention, these terms or words should be interpreted as having meanings consistent with the technical concept of the invention and the context of related art.

[0022] This invention provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The separator comprises a porous substrate and an insulating layer formed on the porous substrate. The insulating layer comprises polymer particles with a melting point of 75°C to 138°C. The polymer particles are capable of melting and filling the pores of the porous substrate when the battery temperature reaches their melting point to block ion conduction. The electrolyte comprises component A and component B. Component A comprises at least one of lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide. Component B comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, and 1,4-butyrolactone. The secondary battery provided by this invention exhibits excellent low-temperature output performance, lithium deposition suppression performance, and safety characteristics.

[0023] The components of the secondary battery of the present invention will be described below.

[0024] positive electrode

[0025] The positive electrode may include a positive electrode current collector and a positive electrode additive layer containing positive electrode active material formed on the positive electrode current collector.

[0026] The positive electrode of this exemplary embodiment includes a positive electrode current collector formed of, for example, a metal foil, etc., and a positive electrode mixture layer formed on one surface or both surfaces of the positive electrode current collector. The positive electrode mixture layer is formed such that the positive electrode current collector is covered with a positive electrode binder. Here, in this specification, the "positive electrode mixture layer" refers to the part of the components constituting the positive electrode other than the positive electrode current collector, and includes a positive electrode active material and a positive electrode binder, and if necessary, may include additives such as conductive aids, etc. The positive electrode active material is a material capable of absorbing and desorbing lithium. In this specification, substances that do not absorb and desorb lithium, such as binders, are not included in the positive electrode active material.

[0027] There is no particular limitation on the positive electrode active material as long as the material can absorb and desorb lithium, and it can be selected according to some viewpoints. From the viewpoint of achieving a higher energy density, it is preferable to contain a high-capacity compound. Examples of high-capacity compounds include: Li-rich layered positive electrodes; lithium nickelate (LiNiO2); and lithium nickel composite oxides, where a part of Ni in lithium nickelate is replaced by other metal elements, and the Li-rich layered positive electrode represented by Formula A1 and the layered lithium nickel composite oxide represented by Formula A2 are preferable.

[0028] Formula A1: Li(Li γ ,

[0030] , α , β ,

[0029] , (1-x) , x , , δ , , y , β , β , γ , δ , α M 1-x-z Mn z )O2; where 0.1 ≤ x < 0.3, 0.4 ≤ z ≤ 0.8, and M includes at least one of Ni, Co, Fe, Ti, Al, and Mg.

[0029] Formula A2: Li y Ni (1-x) M x O2; where 0 ≤ x < 1, 0 < y ≤ 1, and M includes at least one of Li, Co, Al, Mn, Fe, Ti, and B.

[0030] From the viewpoint of high capacity, it is preferable that the content of Ni is high, that is, x in Formula A2 is less than 0.5, preferably 0.4 or less. Examples of such compounds include Li α Ni β Co<00000{9}>Mn<{0000010}>O2(0 < α ≤ 1.2, preferably 1 ≤ α ≤ 1.2, α + β + γ + δ = 2, β ≥ 0.7 and γ ≤ 0.2) and Li α Ni β Co γ Al δ [[ID= {40}]]O2(0 < α ≤ 1.2, preferably 1 ≤ α ≤ 1.2, α + β + γ + δ = 2, β ≥ 0.6, preferably β ≥ 0.7, and γ ≤ 0.2), particularly including LiNi β Coγ Mn δ O2 (0.75≤β≤0.85, 0.05≤γ≤0.15, and 0.10≤δ≤0.20, β+γ+δ=1). More specifically, LiNi, for example, can be preferred. 0.8 Co 0.05 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Al 0.1 One or more of the following: O2, etc.

[0031] From a thermal stability perspective, it is preferable that the Ni content does not exceed 0.5%, i.e., x in formula A2 is 0.5 or more. Furthermore, it is also preferable that specific transition metals do not exceed half. Examples of such compounds include Li. α Ni β Co γ Mn δ O2 (0 < α ≤ 1.2, preferably 1 ≤ α ≤ 1.2, α + β + γ + δ = 2, 0.2 ≤ β ≤ 0.5, 0.1 ≤ γ ≤ 0.4 and 0.1 ≤ δ ≤ 0.4). More specific examples may include LiNi. 0.4 Co 0.3 Mn 0.3 O2 (abbreviated as NCM433), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523) and LiNi 0.5 Co 0.3 Mn 0.2 O2 (abbreviated as NCM532) also includes compounds in which the content of various transition metals varies by about 10%.

[0032] Furthermore, two or more compounds represented by Formula A2 can be mixed and used. For example, it is also preferable to mix and use NCM532 or NCM523 and NCM433 in the range of 9:1 to 1:9. In addition, by mixing materials in which the Ni content in Formula A2 is high (x is 0.4 or less) and materials in which the Ni content in Formula A2 is no more than 0.5 (x is 0.5 or more, such as NCM433), it is also possible to form a battery with high capacity and high thermal stability.

[0033] Examples of the above positive electrode active material include, for example, lithium manganate having a layered structure or a spinel structure, such as LiMnO2, Li x Mn2O4 (0 < x < 2), Li2MnO3, and Li x Mn 1.5 Ni 0.5 O4 (0 < x < 2); LiCoO2 or a material in which a part of such transition metals is replaced by other metals; a material in which Li is in excess compared to the stoichiometric composition among these lithium transition metal oxides; and a material having an olivine structure such as LiFePO4. In addition, materials obtained by partially replacing these metal oxides with the following elements can also be used: Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. The above positive electrode active materials can be used alone or in combination of two or more of them.

[0034] Examples of the positive electrode binder include, but are not limited to, polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene copolymer, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide, polyacrylic acid, etc. Styrene - butadiene rubber (SBR), etc. can be used. When using an aqueous binder such as an SBR emulsion, a thickener such as carboxymethyl cellulose (CMC) can also be used. By mixing two or more, the positive electrode binder can be used. From the viewpoint of the trade - off relationship between "sufficient binding force" and "high energy density", based on 100 parts by mass of the positive electrode active material, the amount of the positive electrode binder is preferably 2 to 10 parts by mass.

[0035] For the purpose of reducing impedance, a conductive additive can be added to the coating containing the positive electrode active material. Examples of the conductive additive include flaky or fibrous carbonaceous fine particles such as graphite, carbon black, acetylene black, and vapor - grown carbon fiber.

[0036] As the positive electrode current collector, from the viewpoint of electrochemical stability, aluminum, nickel, copper, silver, iron, chromium, manganese, molybdenum, titanium, niobium, and their alloys are preferred. Examples of its shape include foil, flat plate shape, and mesh shape. Particularly, it is preferred to use a current collector of aluminum, aluminum alloy, or Fe - Ni - Cr - Mo type stainless steel.

[0037] The positive electrode can be prepared by forming a positive electrode mixture layer containing the positive electrode active material and the positive electrode binder on the positive electrode current collector. Examples of the method for forming the positive electrode mixture layer include: doctor blade method, die coating method, CVD method, sputtering method, etc. After pre - forming the positive electrode mixture layer, a thin film of aluminum, nickel, or their alloy can also be formed thereon as the positive electrode current collector by methods such as vapor deposition or sputtering.

[0038] From the viewpoint of improving the adhesion between the binder layer and the current collector, the binder layer may include a primer layer and an active material layer, with the primer layer disposed on the current collector and the active material layer disposed on the primer layer. The primer layer includes a conductive agent and a binder, optionally inorganic or polymeric particles.

[0039] In this exemplary embodiment, in some cases, it is preferable that the capacity ratio (capacity per unit area of ​​the negative electrode / capacity per unit area of ​​the positive electrode) in the configuration of the negative and positive electrodes arranged facing each other with a separator between them is preferably greater than 1:1, and preferably less than 2. When the capacity ratio is within the above range, a secondary battery with excellent cycle characteristics can be obtained.

[0040] negative electrode

[0041] The negative electrode of the present invention includes a negative electrode current collector and a negative electrode mixture layer formed on the current collector, wherein the negative electrode mixture layer includes a negative electrode active material.

[0042] In this specification, "negative electrode composite layer" refers to the portion of the negative electrode constituent elements other than the negative electrode current collector, and includes a negative electrode active material and a negative electrode conductive agent composition, and may include additives such as conductive aids as needed. The negative electrode active material is a material capable of absorbing and desorbing lithium. In this specification, substances that do not absorb and desorb lithium, such as conductive agent compositions, are not included in the negative electrode active material.

[0043] The negative electrode current collector can be copper foil, iron foil, or stainless steel foil. The negative electrode active material can be a material that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloy, a material capable of doping and dedoping lithium, and / or a transition metal oxide.

[0044] Materials that can reversibly insert / deintercalate lithium ions include carbon materials. Carbon materials can be any suitable carbon-based anode active material commonly used in rechargeable lithium batteries. Examples of carbon materials include crystalline carbon, amorphous carbon, and combinations thereof. Crystalline carbon can be amorphous natural graphite and / or synthetic graphite, such as flake, sheet, spherical, and / or fibrous natural graphite and / or synthetic graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0045] Lithium metal alloys include, for example, lithium, and also include one or more metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0046] Materials capable of doping and dedoping lithium include Si and SiO. x(0 < x < 2), Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements other than Si, Group 15 elements, Group 16 elements, transition metals, rare earth elements or combinations thereof), Sn, SnO2, Sn-R alloy (where R is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements other than Sn, Group 15 elements, Group 16 elements, transition metals, rare earth elements or combinations thereof), etc. At least one of them can be mixed with SiO2.

[0047] Elements Q and R can further be independently selected from one or more of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn (element R does not include Sn), In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po.

[0048] The transition metal oxide can be vanadium oxide, lithium vanadium oxide, etc. [[ID=T7]]

[0049] In some exemplary embodiments, the negative electrode active material can be selected from at least one of graphite and Si composite.

[0050] The Si composite includes Si particles and amorphous carbon. And for example, the Si particles can be selected from at least one of Si-C composite, SiO k (0 < k ≤ 2) and Si alloy.

[0051] For example, the Si-C composite can include Si particles and amorphous carbon. The amorphous carbon has a porous structure, and the Si particles are disposed in the porous structure. <000016]. The Si particles can have a median particle size of 10 nm to 200 nm.

[0053] As used herein, the median particle size (D50) can be the particle size at a volume ratio of 50% in the cumulative size distribution curve.

[0054] When the median particle size of the Si particles is within the above range, the volume expansion occurring during charging and discharging can be suppressed or reduced, and the disconnection of the conduction path due to particle pulverization during charging and discharging can be prevented or reduced.

[0055] Based on the total weight of the Si composite, the amount of Si particles included can be 1 wt% to 60 wt%, for example 3 wt% to 60 wt%.

[0056] Amorphous carbon can be one or a combination of soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke.

[0057] The negative electrode active material may further include crystalline carbon.

[0058] When the negative electrode active material includes both Si complex and crystalline carbon, it can be a mixture of Si complex and crystalline carbon, and in some embodiments, the weight ratio of Si complex and crystalline carbon can be 1:99 to 50:50. In some embodiments, the weight ratio of Si complex and crystalline carbon can be 3:97 to 20:80 or 5:95 to 20:80.

[0059] Crystalline carbon can be, for example, graphite, such as natural graphite, artificial graphite, or mixtures thereof.

[0060] Crystalline carbon can have a median particle size of 5µm to 30µm.

[0061] Amorphous carbon precursors may include coal pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil and / or polymer resins (such as phenolic resins, furan resins and / or polyimide resins).

[0062] In the negative electrode mixture layer, the amount of negative electrode active material included, based on the total weight of the negative electrode mixture layer, can be 95wt%~99wt%.

[0063] In some example embodiments, the negative electrode binder layer may further include a binder and optionally include a conductive material (e.g., an electrically conductive material). In the negative electrode binder layer, the amount of binder may be 1 wt% to 5 wt% based on the total weight of the negative electrode binder layer. When the negative electrode binder layer further includes a conductive material, the negative electrode binder layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0064] The binder improves the bonding characteristics between the negative electrode active material particles and the bonding characteristics between the negative electrode active material and the current collector. The binder may include one or more of the following: polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, and polyimide. The binder may also include rubber-based binders and / or polymer resin binders. Rubber-based binders may be selected from one or more of the following: styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, and fluororubber. Polymer resin binders may be selected from one or more of the following: polytetrafluoroethylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, and polyvinyl alcohol.

[0065] Conductive materials provide electrode conductivity (e.g., electrical conductivity), and any suitable conductive material can be used as a conductive material (e.g., an electrical conductive material) unless it causes undesirable chemical changes (e.g., unless it causes undesirable changes in a rechargeable lithium battery). Conductive materials can be carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metallic materials (such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.), conductive polymers (such as polyphenylene derivatives, etc.), or mixtures thereof.

[0066] diaphragm

[0067] The separator for secondary batteries of the present invention has a porous substrate and an insulating layer disposed on at least one surface of the porous substrate.

[0068] Porous substrates can be porous components made of organic materials. Examples of porous substrates include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, aromatic polyamide resins, etc. Due to their excellent strength, microporous membranes containing polyethylene are preferred.

[0069] In some embodiments, the insulating layer comprises polymer particles with a melting point of 75°C to 138°C and an average particle size of less than 2 micrometers, a binder, and optional inorganic particles. The polymer particles can melt into the pores of the porous substrate during thermal runaway of the battery to block ion conduction, thereby preventing internal short circuits and significantly improving the battery's safety performance.

[0070] Examples of polymer particles include non-conductive thermoplastic resin particles. The polymer particles may be made of at least one of the following: homopolymers of non-fluorinated alkenyl monomers, homopolymers of olefin monomers, homopolymers of unsaturated nitrile monomers, homopolymers of acrylic acid monomers, and homopolymers of ester monomers. Preferably, the polymer particles are made of polyethylene and / or polypropylene. For example, the polymer particles may include at least one of polyethylene wax, oxidized polyethylene wax, polypropylene wax, oxidized polypropylene wax, Fischer-Tropsch wax, paraffin wax, modified paraffin wax, high-density polyethylene (HDPE), and oxidized high-density polyethylene.

[0071] Polymer particles can be used alone or in combination of two or more as needed.

[0072] From the viewpoint of improving battery performance, the average particle size of the polymer particles is preferably 0.2 to 2 micrometers, more preferably 0.5 to 1.5 micrometers. Within this range, the insulating layer can be uniformly formed on the porous substrate. If the average particle size of the polymer particles is too large, it will be difficult to embed them into the porous substrate.

[0073] From the perspective of improving battery safety, the melting point of polymer particles is 75℃~138℃, preferably 85℃~128℃. If the melting point of the polymer particles is too low, it will affect the battery's high-temperature performance. For example, during charging and discharging, the particles may melt and embed into the substrate, blocking pores and hindering lithium-ion conduction. If the melting point of the polymer particles is too high, it will affect the battery's safety performance. For example, if the internal temperature of the battery reaches above 138℃, the separator substrate may shrink, causing an internal short circuit. At this point, the polymer has not yet melted and cannot play its blocking role.

[0074] Examples of binders include carboxymethyl cellulose, carboxymethyl cellulose derivatives such as sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble alginate derivatives, gelatin, carrageenan, glucomannan, pectin, gellan gum, gellan gum, polyacrylic acid, and polyacrylic acid derivatives. Among these, carboxymethyl cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid are particularly preferred, and carboxymethyl cellulose derivatives are even more preferred. The mass ratio of polymer particles to binder can be (1~5):1, preferably (1.2~4):1. In this invention, the binder preferably has a weight-average molecular weight greater than or equal to 1000 Da. From the viewpoint of improving dispersibility, the weight-average molecular weight of the binder is more preferably greater than or equal to 5000 Da, further preferably greater than or equal to 10000 Da, and particularly preferably greater than or equal to 50000 Da.

[0075] Examples of inorganic particles include at least one of strontium titanate, barium titanate, silicon dioxide, aluminum oxide, boehmite, magnesium oxide, magnesium hydroxide, and barium sulfate. Introducing inorganic particles into the insulating layer can further prevent internal short circuits caused by thermal runaway. In embodiments containing both polymer particles and inorganic particles, the mass ratio of polymer particles to inorganic particles can be (2~8):1, preferably (3~7):1.

[0076] An insulating layer can be formed, for example, by applying an insulating layer paste onto a porous substrate, drying it, and then calendering it as needed.

[0077] Furthermore, in one embodiment, from the viewpoint of balancing battery characteristics and safety, the thickness of the insulating layer is preferably 0.1 to 5 µm, more preferably 0.5 to 3 µm, even more preferably 0.8 to 2.5 µm, and particularly preferably 1.2 to 2 µm.

[0078] Furthermore, from the viewpoint of discharge rate, the thickness of the porous substrate is preferably 4 to 20 µm, more preferably 5 to 10 µm, and even more preferably 6 to 8 µm.

[0079] Figure 1 This is a schematic diagram of the diaphragm structure in one embodiment, which includes a porous substrate 1 and an insulating layer 2 formed on one surface of the porous substrate. In other embodiments, insulating layers may be formed on multiple surfaces of the porous substrate, such as on two opposing surfaces of the porous substrate.

[0080] electrolyte

[0081] As an electrolyte, an organic electrolyte in which the supporting electrolyte is dissolved in an organic solvent is typically used. As a supporting electrolyte, lithium salts can be used, for example, in lithium-ion secondary batteries. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, and LiClO4. A single electrolyte can be used, or two or more can be used in combination. Since there is a general tendency for using a supporting electrolyte with a higher degree of dissociation to result in higher lithium-ion conductivity, the lithium-ion conductivity can be adjusted according to the type of supporting electrolyte.

[0082] As for the organic solvent used in the electrolyte, there are no particular limitations as long as it can dissolve and support the electrolyte. For example, in lithium-ion secondary batteries, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), and ethyl methyl carbonate (EMC) are preferred; esters such as γ-butyrolactone, methyl formate, ethyl acetate, propyl propionate, and ethyl propionate are preferred; ethers such as 1,2-dimethoxyethane and tetrahydrofuran are preferred; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are preferred. Mixtures of these solvents can also be used. Among these, carbonates and carboxylic acid esters are preferred because they have high dielectric constants and wide stable potential ranges. Since there is a general tendency for lower viscosity solvents to have higher lithium-ion conductivity, the lithium-ion conductivity can be adjusted according to the type of solvent.

[0083] The electrolyte of the secondary battery provided by the present invention includes component A and component B. Component A includes at least one of lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide; and component B includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, and 1,4-butyrolactone.

[0084] The use of polymer particles in the insulating layer significantly improves the adhesion between the insulating layer and the porous substrate. However, under low-temperature conditions, the insulating layer is prone to cracking in an electrolyte system containing component B. Through systematic research, this invention has discovered that when component A is included in the electrolyte, the secondary battery unexpectedly suppresses insulating layer cracking, thereby improving not only the low-temperature output and lithium deposition suppression performance of the secondary battery but also significantly enhancing safety.

[0085] Based on 100 parts by mass of the electrolyte, the content of component A is 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass.

[0086] Based on 100 parts by mass of the electrolyte, the content of component B is 5 to 68 parts by mass, preferably 11 to 55 parts by mass.

[0087] Components A and / or B, when within the above range, can further suppress insulation layer cracking, improve the low-temperature output and lithium deposition suppression performance of secondary batteries, and significantly improve safety.

[0088] The electrolyte further includes additive C, which comprises at least one of succinic anionyl nitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, glycerol trionitrile, lithium 1-ethyl-3-methylimidazolium tetrafluoroborate, lithium 1-butyl-3-methylimidazolium hexafluorophosphate, and lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. This invention has found that component B causes instability in the positive electrode film formation under high-temperature conditions, leading to excessively rapid lithium ion release. Systematic research has shown that additive C can inhibit the excessively rapid lithium ion release caused by the instability of the positive electrode film formation under high-temperature conditions, thereby further improving the low-temperature output and lithium deposition suppression performance of the secondary battery, and significantly improving safety.

[0089] Based on 100 parts by mass of the electrolyte, the content of the succinic anion is 0.7-3.5 parts by mass, and / or the content of the adiponitrile is 0.6-4 parts by mass, and / or the content of the ethylene glycol bis(propionitrile) ether is 0.2-2 parts by mass, and / or the content of the 1,3,6-hexanetrionitrile is 0.1-3 parts by mass, and / or the content of the glycerol trionitrile is 0.1-4 parts by mass, and / or the content of the lithium 1-ethyl-3-methylimidazolium tetrafluoroborate is 0.01-2 parts by mass, and / or the content of the lithium 1-butyl-3-methylimidazolium hexafluorophosphate is 0.01-2 parts by mass, and / or the content of the lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide is 0.01-2 parts by mass. When additive C meets the above ranges, it can further improve the low-temperature output and lithium deposition suppression performance of the secondary battery, and significantly improve safety.

[0090] Manufacturing method of secondary batteries

[0091] Secondary batteries can be manufactured by, for example, overlapping the positive and negative electrodes with a separator, winding or folding them according to the battery shape as needed, placing them in a battery container, injecting electrolyte into the battery container, and sealing it. To prevent internal pressure rise, overcharging, and over-discharging from occurring, overcurrent protection components such as fuses and PTC elements, porous metal mesh, and conductive plates can also be added as needed.

[0092] The secondary battery of the present invention can be a wound battery structure or a stacked battery structure.

[0093] The shape of the lithium secondary battery of the present invention is not particularly limited, and can be cylindrical, prismatic, pouch or coin-shaped.

[0094] Another aspect of the present invention provides an electronic device comprising the secondary battery described in any of the technical solutions of the present invention.

[0095] The secondary battery of the present invention can be used in electronic devices such as laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, but is not limited thereto.

[0096] Example

[0097] The following examples and comparative examples illustrate the present invention in more detail, but the present invention is not limited to the following examples.

[0098] 1. Preparation of the diaphragm

[0099] Example 1-1

[0100] Polymer particles (polyethylene particles, melting point 75°C, average particle size 1µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60°C to produce a membrane with a 2µm thick insulating layer.

[0101] Examples 1-2

[0102] Polymer particles (polyethylene particles, melting point 138℃, average particle size 1.5µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60℃ to produce a membrane with a 2µm thick insulating layer.

[0103] Examples 1-3

[0104] Polymer particles (polyethylene particles, melting point 82°C, average particle size 1.2µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60°C to produce a membrane with a 2µm thick insulating layer.

[0105] Examples 1-4

[0106] Polymer particles (polyethylene particles, melting point 95°C, average particle size 1.1µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60°C to produce a membrane with a 2µm thick insulating layer.

[0107] Examples 1-5

[0108] Polymer particles (polyethylene particles, melting point 116℃, average particle size 1.1µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60℃ to produce a membrane with a 2µm thick insulating layer.

[0109] Examples 1-6

[0110] Polymer particles (polyethylene particles, melting point 126℃, average particle size 1.5µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60℃ to produce a membrane with a 2µm thick insulating layer.

[0111] Examples 1-7

[0112] Polymer particles (polypropylene particles, melting point 132℃, average particle size 1.6µm) and polyacrylic acid were mixed at a solids content mass ratio (polymer particles:PAA) of 60:40 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated onto both sides of a 5µm thick porous polyethylene substrate and dried at 60℃ to produce a membrane with a 2µm thick insulating layer.

[0113] Examples 1-8

[0114] Polymer particles (polypropylene particles, melting point 132℃, average particle size 1.6µm), barium titanate, and polyacrylic acid were mixed at a solid content mass ratio (polymer particles: barium titanate: PAA) of 60:10:30 and uniformly dispersed. Water was added to the resulting mixture to prepare an insulating slurry. This insulating slurry was coated on both sides of a 5µm thick porous polyethylene substrate and dried at 60℃ to produce a membrane with a 2µm thick insulating layer.

[0115] Comparative Example 1-1

[0116] The only difference between Comparative Example 1-1 and Example 1-1 is that the polyethylene particles used in Comparative Example 1-1 have a melting point of 70°C. The rest of the procedures are the same as in Example 1-1 and will not be repeated here.

[0117] Comparative Examples 1-2

[0118] The only difference between Comparative Examples 1-2 and Examples 1-7 is that the polypropylene particles used in Comparative Examples 1-2 have a melting point of 145°C and an average particle size of 3µm. The rest of the procedures are the same as in Examples 1-2 and will not be repeated here.

[0119] 2. Construction of secondary batteries

[0120] Lithium cobalt oxide (Shanghai Shanshan, 4.5V lithium cobalt oxide) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5, and N-methyl-2-pyrrolidone (NMP) was added to prepare a slurry for forming the positive electrode binder layer. The slurry was coated onto aluminum foil, dried, and then pressed to produce a positive electrode sheet.

[0121] A slurry for forming the negative electrode mixture was prepared by mixing natural graphite and silicon carbon (as the negative electrode active material), styrene-butadiene rubber and polyacrylate (as the binder), and carboxymethyl cellulose (as the tackifier) ​​with deionized water in a mass ratio of 85:10:2:1.5:1.5. This slurry was then coated onto copper foil, dried, and pressed to produce a negative electrode sheet.

[0122] The diaphragm used is the diaphragm prepared according to the above embodiments and comparative examples.

[0123] Electrolyte preparation: In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and propylene carbonate (PC) were mixed uniformly at a mass ratio of 1:2. Based on 100 parts by mass of the total electrolyte, 10 parts by mass of LiPF6 lithium salt dissolved in the organic solvent were added, followed by 5 parts by mass of fluoroethylene carbonate, component A, component B, and optional additive C, to obtain the electrolyte. Partial compositions of the electrolytes in each embodiment and comparative example are shown in Table 1.

[0124] In Table 1, the abbreviations for component A represent: lithium difluorophosphate (A1), lithium bis(trifluoromethanesulfonyl)imide (A2), and lithium bis(fluorosulfonyl)imide (A3).

[0125] In Table 1, the abbreviations for component B represent: dimethyl carbonate (B1), diethyl carbonate (B2), methyl ethyl carbonate (B3), ethyl propionate (B4), propyl propionate (B5), and 1,4-butyrolactone (B6).

[0126] In Table 1, the abbreviations for additive C represent: succinic anion (C1), adiponitrile (C2), ethylene glycol bis(propionitrile) ether (C3), 1,3,6-hexanetrionitrile (C4), glyceryl trionitrile (C5), lithium 1-ethyl-3-methylimidazolium tetrafluoroborate (C6), lithium 1-butyl-3-methylimidazolium hexafluorophosphate (C7), and lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (C8).

[0127] Table 1

[0128] Note: The numbers in parentheses corresponding to the electrolyte components in Table 1 represent the mass fractions of the relevant components based on a mass of 100 parts by mass of electrolyte.

[0129] Fabrication of wound-type battery cells: The negative electrode sheet obtained above is wound together with the positive electrode sheet and the separator to form a battery cell. Fabrication of stacked-type battery cells: The negative electrode sheet obtained above is stacked together with the positive electrode sheet and the separator to form a battery cell.

[0130] Preparation of secondary batteries: After the prepared cells are hot-pressed and shaped, they are packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte to obtain secondary batteries.

[0131] The relevant performance of the assembled secondary battery was tested using the following methods: (1) Low temperature output characteristics The manufactured lithium-ion battery was left to stand at 25°C for 24 hours, then charged at 25°C with a 0.2C CC-CV charge rate (terminating at 0.02C) to 4.6V. It was then discharged at 0.2C CC to 3.0V. This discharged capacity was taken as the initial capacity. It was then charged until the capacity reached 50% of the initial capacity, at which point the voltage was V0. Next, it was discharged at -10°C with a 1C discharge rate, and the voltage V1 was measured 0.1 seconds after the start of discharge. The low-temperature output characteristics were then evaluated using the voltage change ΔV, expressed as ΔV = V0 - V1. A smaller ΔV value indicates better low-temperature performance. The letters in the "Low-Temperature Output Characteristics" column represent: A++: The voltage change ΔV is less than 0.1V; A+: Voltage change ΔV is greater than 0.1V and less than 0.2V; A: Voltage change ΔV is greater than 0.2V and less than 0.3V; B: Voltage change ΔV is greater than 0.3V and less than 0.5V; C: Voltage change ΔV is greater than 0.5V and less than 0.8V; D: Voltage change ΔV is greater than 0.8V and less than 1.0V; E: Voltage change ΔV is greater than 1.0V.

[0132] (2) Lithium deposition suppression characteristics

[0133] The fabricated battery was charged to 100% depth of charge (SOC) at a constant current of 1C at -10°C. Then, the battery was disassembled, the negative electrode was removed, and the area of ​​lithium deposited on the surface of the negative electrode binder layer was calculated. The lithium deposition area ratio was calculated as (area of ​​deposited lithium / surface area of ​​the negative electrode binder layer) × 100%. The battery was then evaluated according to the following criteria. The letters in the "Lithium Deposition Inhibition Characteristics" column represent: A++: The lithium deposition area ratio is less than 0.5%; A+: Lithium deposition area ratio is 0.5% or more but less than 1%; A: The lithium deposition area ratio is more than 1% and less than 3%; B: The lithium deposition area ratio is 3% or more but less than 5%; C: The lithium deposition area ratio is 5% or more but less than 8%; D: The lithium deposition area ratio is 8% or more but less than 10%; E: The lithium deposition area ratio is above 10%.

[0134] (3) Safety test

[0135] After the secondary batteries manufactured in the examples and comparative examples were left to stand for 24 hours, they were charged to 4.5V and discharged to 3.0V at a charge-discharge rate of 0.2C. Then, they were charged to 4.5V at 25°C at a charging rate of 0.2C. A voltage measurement terminal was connected to the secondary battery, and it was placed inside a heating test apparatus. The temperature was then increased to 150°C at a rate of 5°C / min and held at 150°C. The elapsed time from reaching 150°C until a short circuit occurred was measured. This elapsed time was evaluated using the following criteria, and the results are shown in Table 1. A longer elapsed time indicates higher battery safety. The letters in the "Safety" column represent: A++: 35 minutes or more; A+: 30 minutes or more but less than 35 minutes; A: More than 25 minutes but less than 30 minutes; B: More than 20 minutes but less than 25 minutes; C: More than 15 minutes but less than 20 minutes; D: More than 10 minutes but less than 15 minutes; E: Less than 10 minutes.

[0136] Examples 2-1 to 2-8

[0137] Examples 2-1 to 2-8 used the separators and electrolytes prepared in Examples 1-1 to 1-8 respectively to prepare secondary batteries. The battery performance test results are shown in Table 2.

[0138] Comparative Examples 2-1 to 2-6

[0139] Comparative Examples 2-1 to 2-2 used the separators and electrolytes prepared in Comparative Examples 1-1 to 1-2, respectively, to prepare secondary batteries; Comparative Examples 2-3 to 2-4 used the separators and electrolytes prepared in Comparative Examples 1-1 to 1-2, respectively, to prepare secondary batteries; Comparative Examples 2-5 to 2-6 used the separators and electrolytes prepared in Example 1-1, respectively, to prepare secondary batteries using E0-1 and E0-2. The battery performance test results are shown in Table 2.

[0140] Table 2

[0141] Examples 3-1 to 3-37

[0142] Examples 3-1 to 3-37 used the separators prepared in Examples 1-1 to 1-8 and the electrolytes E1-2 to E1-38 to prepare secondary batteries. The battery performance test results are shown in Table 3.

[0143] Table 3

[0144] Examples 4-1 to 4-12

[0145] Examples 4-1 to 4-12 used the separators prepared in Examples 1-6 and 1-7, and the electrolytes E2-1 to E2-9, respectively, to prepare secondary batteries. The battery performance test results are shown in Table 4.

[0146] Table 4

[0147] Examples 5-1 to 5-20

[0148] Examples 5-1 to 5-20 used the separators prepared in Examples 1-6 and 1-7, and the electrolytes used were E2-10 to E2-24, respectively, to prepare secondary batteries. The battery performance test results are shown in Table 5.

[0149] Table 5

[0150] The separator of the secondary battery provided by the present invention has an insulating layer formed on a porous substrate. The insulating layer includes polymer particles with a melting point of 75°C to 138°C, a binder, and optional inorganic particles. When the battery experiences thermal runaway, the insulating layer can melt and fill the pores of the porous substrate to block ion conduction and avoid internal short circuits, thereby significantly improving the safety performance of the battery.

[0151] This invention has discovered that using the polymer particles of this invention in the insulating layer significantly improves the adhesion between the insulating layer and the porous substrate. However, under low-temperature conditions, the insulating layer is prone to cracking in an electrolyte system containing component B described in this invention. To address this, this invention, through systematic research, has found that when the secondary battery contains component A described in this invention in the electrolyte, it unexpectedly suppresses the cracking of the insulating layer, thereby improving not only the low-temperature output and lithium deposition suppression performance of the secondary battery, but also further enhancing its safety.

[0152] This invention also discovered that component B, as described in this invention, causes instability in the positive electrode film formation under high-temperature conditions, leading to the problem of excessively rapid lithium ion release. Through systematic research, this invention found that when the electrolyte also includes additive C as described in this invention, additive C can suppress the excessively rapid lithium ion release caused by the instability of the positive electrode film formation of component B under high-temperature conditions, further improving the low-temperature output and lithium deposition suppression performance of the secondary battery, and significantly improving safety.

[0153] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The membrane includes a porous substrate and an insulating layer formed on the porous substrate. The insulating layer includes polymer particles with a melting point of 75°C to 138°C. The polymer particles are able to melt and fill the pores of the porous substrate when the battery temperature reaches their melting point to block ion conduction. The electrolyte comprises component A and component B. Component A comprises at least one of lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide. Component B comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, and 1,4-butyrolactone.

2. The secondary battery according to claim 1, wherein the polymer particles are made of at least one of the following: homopolymers of non-fluorinated alkenyl monomers, homopolymers of olefin monomers, homopolymers of unsaturated nitrile monomers, homopolymers of olefinic monomers, and homopolymers of ester monomers; preferably, the polymer particles are made of polyethylene and / or polypropylene.

3. The secondary battery according to claim 1, wherein the average particle size of the polymer particles is less than 2µm, preferably 0.2µm to 2µm, and more preferably 0.5µm to 1.5µm; And / or, the melting point of the polymer particles is 85°C to 128°C.

4. The secondary battery according to claim 1, wherein the content of component A is 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the electrolyte; And / or, based on 100 parts by mass of the electrolyte, the content of component B is 5 to 68 parts by mass, preferably 11 to 55 parts by mass.

5. The secondary battery according to claim 1, wherein component B comprises ethyl propionate and propyl propionate, or wherein component B comprises ethyl propionate and 1,4-butyrolactone.

6. The secondary battery according to claim 1, characterized in that: The electrolyte further includes additive C, which includes at least one of succinic acid, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, glycerol trionitrile, lithium 1-ethyl-3-methylimidazolium tetrafluoroborate, lithium 1-butyl-3-methylimidazolium hexafluorophosphate, and lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonylimide).

7. The secondary battery according to claim 1, characterized in that: Based on 100 parts by mass of the electrolyte, the content of succinic anion is 0.7-3.5 parts by mass, and / or the content of adiponitrile is 0.6-4 parts by mass, and / or the content of ethylene glycol bis(propionitrile) ether is 0.2-2 parts by mass, and / or the content of 1,3,6-hexanetrionitrile is 0.1-3 parts by mass, and / or the content of glycerol trionitrile is 0.1-4 parts by mass, and / or the content of lithium 1-ethyl-3-methylimidazolium tetrafluoroborate is 0.01-2 parts by mass, and / or the content of lithium 1-butyl-3-methylimidazolium hexafluorophosphate is 0.01-2 parts by mass, and / or the content of lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide is 0.01-2 parts by mass.

8. The secondary battery according to claim 1, characterized in that: The insulating layer also includes an adhesive and / or inorganic particles; And / or, the thickness of the insulating layer is 0.1µm to 5µm.

9. The secondary battery according to claim 8, characterized in that: The inorganic particles are made of at least one of the following materials: strontium titanate, barium titanate, silicon dioxide, aluminum oxide, boehmite, magnesium oxide, magnesium hydroxide, and barium sulfate.

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

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