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, wherein the positive electrode comprises a current collector, and a positive electrode mixture layer and an organic matter insulating layer which are arranged in contact with the current collector; the organic matter insulating layer comprises an organic insulating material and an adhesive, the organic insulating material comprises polyolefin, and the electrolyte comprises lithium difluorophosphate and boron-containing lithium salt. The secondary battery has good low-temperature cycling performance, low-temperature voltage drop and good safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy, and particularly relates to a secondary battery and an electronic device. Background Art

[0002] With the development of technology and the increasing demand for mobile devices, the demand for secondary batteries has grown rapidly. Therefore, many studies on batteries that can meet various requirements have been conducted. Representatively, in terms of battery shape, there is a high demand for square batteries and pouch batteries that can be applied in thinner products (such as mobile phones, etc.), and in terms of materials, there is a high demand for lithium secondary batteries (such as lithium cobalt polymer batteries, etc.) with high energy density, high discharge voltage, and stable voltage drop.

[0003] One of the main research projects for these secondary batteries is to improve safety. The main cause of accidents related to battery safety is an abnormal low-temperature state caused by a short circuit between the positive electrode and the negative electrode. In the prior art, in order to solve the internal short circuit of the battery, a method of forming an insulating layer on the non-coated part of the electrode has been proposed. For example, the insulating paste for forming the insulating layer contains polyvinylidene fluoride (PVDF) binder, as well as inorganic particles and colorants mixed therein. The insulating layer containing a PVDF-based binder has excellent electrical safety and coating processability, but when the insulating layer containing a PVDF-based binder is wetted by the electrolyte, the adhesion strength decreases, and the insulating layer may be detached from the current collector or the electrode mixture layer, affecting the cycle life of the battery and becoming an obstacle to battery safety. Summary of the Invention

[0004] The present invention conducts research and finds that there are the following problems in the above prior art: The above-mentioned prior insulating layer containing a PVDF-based binder or an insulating layer containing inorganic particles is easily cracked or detached after being infiltrated by the electrolyte and with the expansion and contraction of the electrode during charge and discharge cycles, especially when charging and discharging repeatedly at low temperatures, the battery performance deteriorates, so there is room for improvement in this regard.

[0005] One aspect of the present invention is to provide a secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a current collector, and a positive electrode mixture layer and an organic insulating layer in contact with the current collector; the organic insulating layer includes an organic insulating material and a binder, the organic insulating material includes polyolefin, and the electrolyte includes lithium difluorophosphate and a lithium borate salt. According to such a configuration, not only can the low-temperature cycle performance and voltage drop of the secondary battery be improved, but also the safety can be enhanced.

[0006] In some embodiments, the polyolefin includes at least one of polyethylene, polypropylene, polybutene, polystyrene, or polytetrafluoroethylene.

[0007] In some embodiments, based on the mass of the organic insulating layer being 100%, the content of the polyolefin is 60 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0008] In some embodiments, the polyolefin is polyolefin particles, and the average particle size of the polyolefin particles is 5 to 20 μm, preferably 6 to 15 μm.

[0009] In some embodiments, the binder includes at least one of polyvinylidene fluoride, polyimide, polyacrylic acid, polymethyl acrylate, nitrile rubber, hydrogenated nitrile rubber, or polyacrylonitrile.

[0010] In some embodiments, based on the mass of the organic insulating layer being 100%, the content of the binder is 5 wt% to 40 wt%, preferably 10 wt% to 30 wt%.

[0011] In some embodiments, the thickness of the organic insulating layer is 20% to 70% of the thickness of the positive electrode mixture layer, preferably 35% to 65%.

[0012] In some embodiments, the thickness of the organic insulating layer is 0.1 - 100 μm.

[0013] In some embodiments, the organic insulating layer is disposed at the edge of at least one side of the current collector and / or at the connection between the current collector and the tab.

[0014] In some embodiments, the organic insulating layer further includes an organic dye.

[0015] In some embodiments, the organic dye includes at least one of anthraquinone - based dyes, aniline - based azo dyes, triphenylmethane - based dyes, pyrazole azo dyes, pyridone azo dyes, methylpyridone - based dyes, oxyphenol - based dyes, benzylidene dyes, xanthene dyes. Preferably, it includes benzylidene dyes and / or azo dyes, and more preferably includes benzylidene dyes.

[0016] In some embodiments, the organic insulating layer does not contain inorganic particles. The organic insulating layer can be formed, for example, by the organic insulating material and the binder, or by the organic insulating material, the binder, and the organic dye.

[0017] In some embodiments, the boron - containing lithium salt includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium tricyanomethyl borate, lithium tricyanoethyl borate, lithium tricyanopropyl borate.

[0018] In some embodiments, based on the mass of the electrolyte being 100 parts by mass, the content of the boron - containing lithium salt is 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass.

[0019] In some embodiments, based on 100 parts by mass of the electrolyte, the content of lithium difluorophosphate is 0.01 to 2 parts by mass, preferably 0.05 to 1.2 parts by mass.

[0020] In some embodiments, the electrolyte further includes additive A, and additive A includes at least one of succinonitrile, adiponitrile, vinylene carbonate, 1,3 - propylene sulfonic acid lactone, ethylene sulfate, and 1,3 - propanediol cyclic sulfate.

[0021] In some embodiments, based on 100 parts by mass of the electrolyte, the content of succinonitrile is 0.7 to 3.5 parts by mass, and / or the content of adiponitrile is 0.6 to 4 parts by mass, and / or the content of vinylene carbonate is 0.2 to 2 parts by mass, and / or the content of 1,3 - propylene sulfonic acid lactone is 0.01 to 2 parts by mass, and / or the content of ethylene sulfate is 0.01 to 2 parts by mass, and / or the content of 1,3 - propanediol cyclic sulfate is 0.01 to 2 parts by mass.

[0022] Another aspect of the present invention is to provide an electronic device, and the electronic device includes the secondary battery described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention; Figure 2 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention; Figure 3 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention; Figure 4 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention; Figure 5 It is a schematic structural diagram of the positive electrode of the laminated battery structure of the present invention; Figure 6 It is a schematic structural diagram of the positive electrode of the laminated battery structure of the present invention; 1 - current collector; 2 - positive electrode tab; 3 - positive electrode mixture layer; 4 - organic insulating layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In the following, the present invention will be described in more detail to allow for a clearer understanding of the present invention. In this case, it will be understood that the terms or words used in the specification and claims of the present invention should not be construed as having the meanings defined in a common dictionary, and it will further be understood that based on the principle that the inventor can appropriately define the meanings of the terms or words to best explain the present application, these terms or words should be construed as having meanings consistent with the technical concept of the present application and the background of the related art.

[0026] The present invention provides a secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a current collector, a positive electrode mixture layer in contact with the current collector, and an organic insulating layer in contact with the current collector. The organic insulating layer includes an organic insulating material and a binder. The organic insulating material includes polyolefin. The electrolyte includes lithium difluorophosphate and a lithium borate salt. This design can not only improve the low-temperature cycle and voltage drop performance of the secondary battery, but also enhance the safety.

[0027] The components of the secondary battery of the present invention will be described below.

[0028] Positive electrode The positive electrode in the secondary battery of the present invention includes a current collector, a positive electrode mixture layer in contact with the current collector, and an organic insulating layer in contact with the current collector. The organic insulating layer includes an organic insulating material and a binder. The organic insulating material includes polyolefin.

[0029] 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 conductive agent composition, and if necessary, may include additives such as conductive aids. 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 the conductive agent composition, are not included in the positive electrode active material. From the viewpoint of improving the adhesion between the mixture layer and the current collector, the mixture layer may include a primer layer and an active material layer. The primer layer is provided on the current collector, and the active material layer is provided on the primer layer. The primer layer includes a conductive agent and a binder, and optional inorganic particles or polymer particles.

[0030] The current collector is not particularly limited as long as it has high electrical conductivity without causing chemical changes in the battery. For example, it can be stainless steel, aluminum, nickel, titanium, calcined carbon, or stainless steel or aluminum cadmium alloy treated with carbon, nickel, titanium, or silver on the surface. In addition, the current collector usually can have a thickness of 3 μm to 30 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion strength with the electrode active material. For example, the current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a non-woven fabric, etc.

[0031] In the present invention, from the perspective of improving the safety of secondary batteries, an insulating layer is provided at the edge of at least one side of the current collector and / or at the connection between the current collector and the tab, which can reduce the risk of short circuit. In the prior art, an insulating layer containing PVDF or an insulating layer containing inorganic particles is used, and film peeling is likely to occur. The inventors of the present invention surprisingly found that after using polyolefin in the organic insulating layer, the adhesion between the organic insulating layer and the current collector is significantly improved, and film peeling is significantly improved. However, at low temperatures, polyolefin is prone to brittle fracture in a conventional carbonate electrolyte system. The inventors found that when a lithium salt containing boron is included in the electrolyte, brittle fracture of polyolefin is unexpectedly inhibited, and cracking and peeling on the surface of the organic insulating layer are reduced, but this will cause a voltage drop problem at low temperatures. The inventors further found that when lithium difluorophosphate is also included in the electrolyte, the low-temperature voltage drop can be effectively inhibited, thereby improving the low-temperature cycle and voltage drop of the secondary battery, and significantly improving the safety.

[0032] In the present invention, from the perspective of improving the safety of secondary batteries, the organic insulating layer can be provided at the edge of at least one side of the current collector and / or at the connection between the current collector and the tab. For example, the organic insulating layer can be provided at the edge of one or more long sides of the current collector (as shown in Figure 1 and 2 ), at the edge of one or more short sides of the current collector (as shown in Figure 4 ), at the four peripheral edges of the current collector (as shown in Figure 5 ), at the end of the positive tab connected to the current collector (as shown in Figure 2 , Figure 3 and Figure 6 ), or at least one of these positions. The organic insulating layer can be provided at the edge of at least one side of the current collector and at the end of the positive tab connected to the current collector simultaneously (as shown in Figure 2 ). In the solution where the organic insulating layer is provided at the edge of at least one side of the current collector, for example, the organic insulating layer can be provided in the edge area of the current collector not covered by the positive electrode mixture layer.

[0033] In the present invention, the organic insulating layer can be an insulating film or a coating applied to the current collector and / or the connection between the current collector and the tab.

[0034] If the organic insulating layer is an insulating film, the insulating film can be a thermoplastic polymer film. If the insulating film is a thermoplastic polymer film, the thermoplastic polymer thereof includes polyolefin and an adhesive. For example, the thermoplastic polymer film can include a polyolefin layer and an adhesive layer arranged in a laminated manner, and the adhesive layer is used for attaching the thermoplastic polymer film to the edge of at least one side of the current collector and / or the connection part between the current collector and the tab. The polyolefin is preferably at least one of polyethylene, polypropylene, polybutene, polystyrene or polytetrafluoroethylene. The adhesive of the adhesive layer is preferably at least one of polyvinylidene fluoride, polyimide, polyacrylic acid, methyl polyacrylate, nitrile rubber, hydrogenated nitrile rubber or polyacrylonitrile, which is beneficial to improving the mechanical properties of the final organic insulating layer.

[0035] If the organic insulating layer is a coating applied to the current collector and / or the connection part between the current collector and the tab, it is formed by coating a slurry containing polyolefin and an adhesive at a preset position and drying.

[0036] In the present invention, from the perspective of reducing brittle fracture and film peeling of the organic insulating layer, the organic insulating layer includes polyolefin and an adhesive, wherein the polyolefin includes at least one of polyethylene, polypropylene, polybutene, polystyrene or polytetrafluoroethylene, and preferably includes polypropylene. The weight average molecular weight of the polyolefin can be 50,000 - 5,000,000, especially 100,000 - 800,000, and more especially 150,000 - 350,000. Within the above-defined range, swelling and film peeling of the organic insulating layer can be reduced.

[0037] In the present invention, the polyolefin can be polyolefin particles, the particle size of the polyolefin particles can be in the micron size, and the average particle size of the polyolefin particles can be 5 - 20 microns, preferably 6 - 15 microns. When the average particle size of the polyolefin particles is greater than 20 microns, the defect of battery swelling will increase. In particular, when the average particle size of the polyolefin particles is in the range of 5 - 20 microns, the low-temperature cycle life characteristics and the effect of suppressing swelling are improved.

[0038] The average particle size of the polyolefin particles is obtained in the following manner. First, an SEM image of the particles is taken using an SEM manufactured by Hitachi High-Technologies Corporation. Then, using image analysis software, 10 polyolefin particles are randomly selected from the SET image, and the area of each of these polyolefin particles (the area when observing the polyolefin particles from one direction in the SEM image) is obtained. Next, assuming that the polyolefin particles are spherical, the particle size is obtained through the following formula: R = 2×(S / π) 1 / 2 , where S is the area when observing the polyolefin particles from one direction. The process of obtaining the particle size of the above polyolefin particles is performed on 10 SEM images, and the particle sizes of the obtained (10×10) polyolefin particles are simply averaged (arithmetic average), thereby obtaining the average particle size of the polyolefin particles.

[0039] Based on the mass of the organic insulating layer being 100%, the content of the polyolefin is 60 wt% - 95 wt%, preferably 70 wt% - 90 wt%.

[0040] In terms of improving the adhesion strength and cohesive strength, the binder in the organic insulating layer includes at least one of polyvinylidene fluoride, polyimide, polyacrylic acid, polymethyl acrylate, nitrile rubber, hydrogenated nitrile rubber, or polyacrylonitrile. Among these binder polymers, in terms of adhesiveness, chemical resistance, and electrochemical stability, the binder preferably includes polyacrylonitrile.

[0041] Based on the mass of the organic insulating layer being 100%, the content of the binder is 5 wt% - 40 wt%, preferably 10 wt% - 30 wt%.

[0042] The organic insulating layer may further include a colorant to facilitate the detector to determine the formation and / or orientation position of the organic insulating layer. The colorant may be an organic dye, and the organic dye may include, for example, at least one of anthraquinone-based dyes, aniline-based azo dyes, triphenylmethane-based dyes, pyrazole azo dyes, pyridone azo dyes, methylpyridone-based dyes, oxyphenol-based dyes, benzylidene dyes, and xanthene dyes. Preferably, it includes at least one of benzylidene dyes and azo dyes, and more preferably includes benzylidene dyes to improve the slurry stability and prevent phase separation.

[0043] Based on the mass of the organic insulating layer being 100%, the content of the organic dye is 0.1 - 3 wt%.

[0044] The thickness of the organic insulating layer can be, for example, 0.1 - 100 μm, specifically 10 μm or more, 20 μm or more, or 30 μm or more, and can be 90 μm or less, 80 μm or less, or 70 μm or less.

[0045] The thickness of the organic insulating layer can be 20% - 70% of the thickness of the positive electrode mixture layer, preferably 35% - 65%. If the thickness of the organic insulating layer is too low and less than 20% of the thickness of the positive electrode mixture layer, the effect of preventing short circuit may not be obtained. If the thickness of the organic insulating layer is too high and more than 70% of the thickness of the positive electrode mixture layer, the overall volume of the electrode becomes large and the mobility of lithium ions becomes poor, so it is not preferred.

[0046] The positive electrode mixture layer includes a positive electrode active material, and the positive electrode active material includes, for example, a lithiated insertion compound that can reversibly insert and extract lithium ions. For example, at least one composite oxide of lithium and at least one of cobalt, manganese, nickel, or a combination thereof can be used.

[0047] A composite oxide having a coating on its surface may be used, or a mixture of a composite oxide and a composite oxide having a coating may be used. The coating may include a coating element compound selected from the following: an oxide of the coating element, a hydroxide of the coating element, a hydroxyoxide of the coating element, an oxycarbonate of the coating element, or a basic carbonate of the coating element. The compound used for the coating may be amorphous or crystalline. The coating element included in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, W, La, Y, Ce, or a mixture thereof. The coating process may include any suitable process commonly used in the art, as long as it does not (or substantially does not) cause any side effects (e.g., any undesired side effects) on the properties of the positive electrode active material (e.g., spraying, dipping), which will be obvious to those of ordinary skill in the art after reading the present invention, and thus need not be described in detail herein.

[0048] For example, the positive electrode active material may include lithium cobalt oxide.

[0049] In some embodiments, the positive electrode active material may include a lithium cobalt oxide represented by Chemical Formula 1: Chemical Formula 1: Li a11 Co x11 M 11 y11 O2.

[0050] In Chemical Formula 1, 0.9 ≤ a11 ≤ 1.8, 0.9 ≤ x11 ≤ 1, 0 ≤ y11 ≤ 0.1, x11 + y11 = 1, and M 11 is at least one of Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, and Zr.

[0051] For example, the positive electrode active material may be LiCoO2.

[0052] In some embodiments, the positive electrode active material may include a lithium nickel-based composite oxide represented by Chemical Formula 2: Chemical Formula 2: Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 .

[0053] In Chemical Formula 2, 0.9 ≤ a1 ≤ 1.2, 0.7 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1; M 1 and M2 each independently selected from one or more elements of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr; and X is selected from one or more elements of F, P, and S.

[0054] In Chemical Formula 2, 0.75 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.18, and 0 ≤ z1 ≤ 0.18; 0.85 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.15, and 0 ≤ z1 ≤ 0.15; or 0.9 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.1, and 0 ≤ z1 ≤ 0.1.

[0055] For example, the positive electrode active material may include a lithium nickel-based composite oxide represented by Chemical Formula 3. The compound represented by Chemical Formula 3 may be referred to as a lithium nickel cobalt-based composite oxide: Chemical Formula 3: Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2 .

[0056] In Chemical Formula 3, 0.9 ≤ a2 ≤ 1.8, 0.7 ≤ x2 < 1, 0 < y2 ≤ 0.2, 0 ≤ z2 ≤ 0.2, 0.9 ≤ x2 + y2 + z2 ≤ 1.1, and 0 ≤ b2 ≤ 0.1, M 3 is selected from one or more elements of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is selected from one or more elements of F, P, and S.

[0057] In Chemical Formula 3, 0.75 ≤ x2 ≤ 0.99, 0 ≤ y2 ≤ 0.15, and 0 ≤ z2 ≤ 0.15; 0.85 ≤ x2 ≤ 0.99, 0.01 ≤ y2 ≤ 0.15, and 0.01 ≤ z2 ≤ 0.15; or 0.9 ≤ x2 ≤ 0.99, 0.01 ≤ y2 ≤ 0.1, and 0.01 ≤ z2 ≤ 0.1.

[0058] For example, the positive electrode active material may include a lithium nickel-based composite oxide represented by Chemical Formula 4. The compound represented by Chemical Formula 4 may be referred to as a lithium nickel cobalt aluminum oxide or a lithium nickel cobalt manganese oxide.

[0059] Chemical Formula 4: Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O2-b3 X b3 In Chemical Formula 4, 0.9 ≤ a3 ≤ 1.8, 0.7 ≤ x3 ≤ 0.98, 0.01 ≤ y3 ≤ 0.19, 0.01 ≤ z3 ≤ 0.19, 0 ≤ w3 ≤ 0.19, 0.9 ≤ x3 + y3 + z3 + w3 ≤ 1.1, and 0 ≤ b3 ≤ 0.1, M 4 is one or more elements selected from Al and Mn, M 5 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0060] In Chemical Formula 4, 0.75 ≤ x3 ≤ 0.98, 0 ≤ y3 ≤ 0.16, 0 ≤ z3 ≤ 0.16, and 0 ≤ w3 ≤ 0.16; 0.85 ≤ x3 ≤ 0.98, 0.01 ≤ y3 ≤ 0.14, 0.01 ≤ z3 ≤ 0.14, and 0 ≤ w3 ≤ 0.14; or 0.9 ≤ x3 ≤ 0.98, 0.01 ≤ y3 ≤ 0.09, 0.01 ≤ z3 ≤ 0.09, and 0 ≤ w3 ≤ 0.09.

[0061] For example, the positive electrode active material may include a lithium nickel-based composite oxide represented by Chemical Formula 5. The compound represented by Chemical Formula 5 may be referred to as a cobalt-free lithium nickel manganese oxide.

[0062] Chemical Formula 5: Li a4 Ni x4 Mn y4 M 6 z4 O 2-b4 X b4 In Chemical Formula 5, 0.9 ≤ a4 ≤ 1.8, 0.7 ≤ x4 < 1, 0 < y4 ≤ 0.2, 0 ≤ z4 ≤ 0.2, 0.9 ≤ x4 + y4 + z4 ≤ 1.1, and 0 ≤ b4 ≤ 0.1, M 6 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0063] In some exemplary embodiments of the positive electrode, based on the total weight of the positive electrode binder layer, the content of the positive electrode active material may be 90 wt% - 98 wt%, 50 wt% - 99 wt%, 60 wt% - 99 wt%, 70 wt% - 99 wt%, 80 wt% - 99 wt%, or 90 wt% - 99 wt%.

[0064] In some embodiments of the present invention, the positive electrode mixture layer may further include a conductive material (e.g., a conductivity material) and a binder. In some embodiments, based on the total weight of the positive electrode mixture layer, the respective contents of the conductive material and the binder may be 1.0 wt% to 5.0 wt%.

[0065] The conductive material is used to impart conductivity (e.g., electrical conductivity) to the electrode, and any suitable conductivity material can be used as the conductive material (e.g., a conductivity material), unless it causes chemical changes in the battery (e.g., undesired changes in a rechargeable lithium battery). Examples of the conductive material may include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.), conductive polymers (such as polyphenylene derivatives), or a mixture of these.

[0066] The binder in the positive electrode mixture layer improves the bonding characteristics between the positive electrode active material particles and the bonding characteristics between the positive electrode active material particles and the positive electrode current collector. The binder may be, for example, one or a combination of more than one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but is not limited thereto.

[0067] The method for preparing the positive electrode includes the following steps: Forming an undried electrode mixture layer by coating an active material slurry composite on the electrode current collector; forming an undried organic insulating layer by coating a composite for forming the organic insulating layer, and simultaneously drying the undried positive electrode mixture layer and the undried organic insulating layer.

[0068] Negative electrode The negative electrode of the present invention includes a negative electrode current collector and a negative electrode mixture layer formed on the current collector, and the negative electrode mixture layer includes a negative electrode active material.

[0069] Here, in this specification, the "negative electrode mixture layer" refers to the part of the components of the negative electrode other than the negative electrode current collector, and includes a negative electrode active material and a negative electrode conductive agent composition, and may optionally include additives such as a conductive aid. 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 the conductive agent composition, are not included in the negative electrode active material. From the viewpoint of improving the adhesion between the mixture layer and the current collector, the mixture layer may include a base coating and an active material layer. The base coating is provided on the current collector, and the active material layer is provided on the base coating. The base coating includes a conductive agent, a binder, and optionally inorganic particles or polymer particles.

[0070] The negative electrode current collector can be a copper foil, an iron foil, or a stainless steel foil. The negative electrode active material can be a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, and / or a transition metal oxide.

[0071] Materials capable of reversibly inserting / extracting lithium ions include carbon materials. The carbon materials can be any suitable carbon-based negative electrode active materials commonly used in rechargeable lithium batteries. Examples of the carbon materials include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon can be amorphous natural graphite and / or artificial graphite, such as flaky, sheet-like, spherical, and / or fibrous natural graphite and / or artificial graphite. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, etc.

[0072] 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.

[0073] Materials capable of doping and dedoping lithium may include Si, SiO x (0 < x < 2), Si-Q alloys (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 alloys (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.

[0074] Element Q and element 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.

[0075] The transition metal oxide can be vanadium oxide, lithium vanadium oxide, etc.

[0076] In some exemplary embodiments, the negative electrode active material can be selected from at least one of graphite and Si composites.

[0077] 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 composites, SiO k (0 < k ≤ 2) and Si alloys.

[0078] 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.

[0079] The Si particles can have a median particle size of 10 nm to 200 nm.

[0080] As used herein, the median particle size (D50) can be the particle size at which the volume ratio is 50% in the cumulative size distribution curve.

[0081] When the median particle size of the Si particles is within the above range, volume expansion occurring during charging and discharging can be suppressed or reduced, and disconnection of the conduction path due to particle pulverization during charging and discharging can be prevented or reduced.

[0082] 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%.

[0083] The amorphous carbon can be a combination of one or more of soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke.

[0084] The negative electrode active material can further include crystalline carbon.

[0085] When the negative electrode active material includes both the Si composite and crystalline carbon, it may include the Si composite and crystalline carbon in the form of a mixture, and in some embodiments, may include the Si composite and crystalline carbon in a weight ratio of 1:99 to 50:50. In some embodiments, it may include the Si composite and crystalline carbon in a weight ratio of 3:97 to 20:80 or 5:95 to 20:80.

[0086] The crystalline carbon can be, for example, graphite, such as natural graphite, artificial graphite, or a mixture thereof.

[0087] The crystalline carbon may have a median particle size of 5 μm to 30 μm.

[0088] The amorphous carbon precursor may include coal tar pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, and / or polymer resins (such as phenolic resin, furan resin, and / or polyimide resin).

[0089] In the negative electrode binder layer, based on the total weight of the negative electrode binder layer, the amount of the negative electrode active material included may be 95 wt% to 99 wt%.

[0090] In some exemplary embodiments, the negative electrode binder layer may further include a binder, and optionally may include a conductive material (e.g., a conductivity material). In the negative electrode binder layer, based on the total weight of the negative electrode binder layer, the amount of the binder may be 1 wt% to 5 wt%. 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.

[0091] 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 a combination of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide. The binder may also include a rubber-based binder and / or a polymer resin binder. The rubber-based binder may be selected from one or a combination of styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber. The polymer resin binder may be selected from one or a combination of polytetrafluoroethylene, ethylene-propylene copolymer, poly(ethylene oxide), polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol.

[0092] The conductive material provides electrode conductivity (e.g., electrical conductivity), and any suitable conductive material can be used as the conductive material (e.g., conductive material), unless it causes undesirable chemical changes (e.g., unless it causes undesirable changes in a rechargeable lithium battery). The conductive material can be a carbon-based material (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), a metal-based material (such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.), a conductive polymer (such as polyphenylene derivatives, etc.), or a mixture thereof.

[0093] Electrolyte As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent can generally be used. As the supporting electrolyte, for example, a lithium salt can be used in a lithium-ion secondary battery. Examples of the lithium salt include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, etc. The electrolytes can be used individually or in combination of two or more. Since there is generally a tendency that the higher the dissociation degree of the supporting electrolyte, the higher the lithium-ion conductivity, the lithium-ion conductivity can be adjusted according to the type of the supporting electrolyte.

[0094] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in a lithium-ion secondary battery, carbonate esters such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC) can be preferably used; esters such as γ-butyrolactone, methyl formate, ethyl acetate, propyl propionate, and ethyl propionate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compound classes such as sulfolane and dimethyl sulfoxide, etc. In addition, a mixture of these solvents can also be used. Among them, carbonate esters are preferred because of their high dielectric constant and wide stable potential region. Since there is generally a tendency that the lower the viscosity of the solvent used, the higher the lithium-ion conductivity, the lithium-ion conductivity can be adjusted according to the type of the solvent.

[0095] Particularly, after using polyolefin in the organic insulating layer, the adhesion between the organic insulating layer and the current collector is significantly improved. However, under low-temperature conditions, polyolefin is prone to brittle fracture in a conventional carbonate electrolyte system. The inventors found that when a boron-containing lithium salt is included in the electrolyte, unexpectedly, the brittle fracture of polyolefin is inhibited, and the cracking and peeling on the surface of the organic insulating layer are reduced, but it will cause an increase in voltage drop under low-temperature conditions. The inventors further found that when lithium difluorophosphate is also included in the electrolyte, the low-temperature voltage drop can be effectively inhibited, thereby improving the low-temperature cycle and voltage drop of the secondary battery, and significantly improving the safety.

[0096] The above-mentioned boron-containing lithium salts include at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium tricyanomethyl borate, lithium tricyanoethyl borate, and lithium tricyanopropyl borate.

[0097] Based on 100 parts by mass of the electrolyte, the content of the boron-containing lithium salt is 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass. Meeting the above range can further inhibit the brittle fracture of polyolefins and reduce the cracking and peeling on the surface of the organic insulating layer.

[0098] Based on 100 parts by mass of the electrolyte, the content of lithium difluorophosphate is 0.01 to 2 parts by mass, preferably 0.05 to 1.2 parts by mass. Meeting the above range can effectively inhibit the low-temperature voltage drop.

[0099] The electrolyte may further include additive A, and additive A includes at least one of succinonitrile, adiponitrile, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, and 1,3-propylene glycol cyclic sulfate. When the electrolyte contains additive A, it can further inhibit the brittle fracture of polyolefins and reduce the cracking and peeling on the surface of the organic insulating layer.

[0100] Based on 100 parts by mass of the electrolyte, the content of succinonitrile is 0.7 to 3.5 parts by mass, and / or the content of adiponitrile is 0.6 to 4 parts by mass, and / or the content of vinylene carbonate is 0.2 to 2 parts by mass, and / or the content of 1,3-propane sultone is 0.01 to 2 parts by mass, and / or the content of ethylene sulfate is 0.01 to 2 parts by mass, and / or the content of 1,3-propylene glycol cyclic sulfate is 0.01 to 2 parts by mass. Meeting the above range can further inhibit the brittle fracture of polyolefins and reduce the cracking and peeling on the surface of the organic insulating layer.

[0101] Separator A separator can use a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, etc. As the material of the separator, it can be an olefin resin such as polyethylene and polypropylene, cellulose, etc. The separator can be either a single-layer structure or a laminated structure. On the surface of the separator, a heat-resistant layer containing a heat-resistant material can be formed. Examples of the heat-resistant material include polyamide resins such as aliphatic polyamides and aromatic polyamides (aramids), polyamide-imides, polyimide resins such as polyimides, etc.

[0102] Manufacturing method of secondary battery A secondary battery can be manufactured, for example, by overlapping a positive electrode and a negative electrode with a separator interposed therebetween, winding, folding, etc. them as required corresponding to the battery shape, placing them in a battery container, injecting an electrolyte into the battery container, and sealing it. In order to prevent an increase in the internal pressure of the secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse, a PTC element, etc., a porous metal mesh, a guide plate, etc. may be provided as required.

[0103] The secondary battery of the present invention can have a wound battery structure or a laminated battery structure. Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 The structure schematic diagrams of the positive electrodes of four wound battery structures are shown. Figure 5 、 Figure 6 The structure schematic diagrams of the positive electrodes of the laminated battery structures are shown.

[0104] The shape of the lithium secondary battery of the present invention is not particularly limited, and a cylindrical shape, a prismatic shape, a pouch shape, or a coin shape using a can can be used.

[0105] The present invention also provides an electronic device including the secondary battery of the present invention.

[0106] The secondary battery of the present invention can be used for a notebook computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo earphone, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a voltage drop card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an assist bicycle, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flash, a camera, a large household storage battery, a lithium ion capacitor, etc., but is not limited thereto.

[0107] Examples Examples and comparative examples are listed below to illustrate the present invention more specifically, but the present invention is not limited to the following examples.

[0108] 1. Preparation of positive electrode

[0109] Example 1-1A

[0110] Layered lithium cobaltate (LCO) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming a positive electrode mixture layer.

[0111] Polyethylene (PE) as a polymer and polyacrylic acid as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 60:40 to prepare a slurry for forming an organic insulating layer.

[0112] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. Among them, the average particle size of polyethylene is 5 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 20% of the thickness of the positive electrode mixture layer.

[0113] Example 1-1B Layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0114] Polyethylene (PE) as a polymer and polyacrylic acid as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 50:50 to prepare a slurry for forming an organic insulating layer.

[0115] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. Among them, the average particle size of polyethylene is 5 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 20% of the thickness of the positive electrode mixture layer.

[0116] Example 1-1C Layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0117] Polyethylene (PE) as a polymer and polyacrylic acid as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 60:40 to prepare a slurry for forming an organic insulating layer.

[0118] Using an aluminum foil as the positive current collector, a slurry for forming a positive electrode mixture layer was coated on the aluminum foil, and a slurry for forming an organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was performed to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 1 shown. The average particle size of polyethylene is 25 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 75% of the thickness of the positive electrode mixture layer.

[0119] Example 1-1D The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming a positive electrode mixture layer.

[0120] Polyethylene (PE) and polyvinylidene fluoride as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 60:40 to prepare a slurry for forming an insulating layer.

[0121] Using an aluminum foil as the positive current collector, a slurry for forming a positive electrode mixture layer was coated on the aluminum foil, and a slurry for forming an insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was performed to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 1 shown. The average particle size of polyethylene (PE) is 5 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the insulating layer is 20% of the thickness of the mixture layer.

[0122] Example 1-2 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming a positive electrode mixture layer.

[0123] Polyethylene (PE) as the polymer and polyacrylic acid as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 95:5 to prepare a slurry for forming an organic insulating layer.

[0124] Using an aluminum foil as the positive current collector, a slurry for forming a positive electrode mixture layer was coated on the aluminum foil, and a slurry for forming an organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was performed to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 1 shown. The average particle size of polyethylene is 5 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 20% of the thickness of the positive electrode mixture layer.

[0125] Examples 1 - 3 The layered lithium cobalt oxide (LCO) as the cathode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the cathode mixture layer.

[0126] Polyethylene (PE) as the polymer and polyacrylic acid as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 95:5 to prepare a slurry for forming the organic insulating layer.

[0127] Using aluminum foil as the cathode current collector, the slurry for forming the cathode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a cathode sheet. The structural schematic diagram of the cathode is as Figure 1 shown. The average particle size of the polyethylene is 20 microns, the thickness of the cathode mixture layer is 60 microns, and the thickness of the organic insulating layer is 70% of the thickness of the cathode mixture layer.

[0128] Examples 1 - 4 The layered lithium cobalt oxide (LCO) as the cathode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the cathode mixture layer.

[0129] Polypropylene (PP) as the polymer and polyvinylidene fluoride as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 70:30 to prepare a slurry for forming the organic insulating layer.

[0130] Using aluminum foil as the cathode current collector, the slurry for forming the cathode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a cathode sheet. The structural schematic diagram of the cathode is as Figure 1 shown. The average particle size of the polypropylene is 6 microns, the thickness of the cathode mixture layer is 60 microns, and the thickness of the organic insulating layer is 20% of the thickness of the mixture layer.

[0131] Examples 1 - 5 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0132] Polybutene (PB) as the polymer and polyimide as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 75:25 to prepare a slurry for forming the organic insulating layer.

[0133] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil and the end of the tab. After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 2 shown. The average particle size of polybutene is 10 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 40% of the thickness of the mixture layer.

[0134] Examples 1-6 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0135] Polystyrene as the polymer and nitrile rubber amine as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:20 to prepare a slurry for forming the organic insulating layer.

[0136] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. The average particle size of polystyrene is 12 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 60% of the thickness of the mixture layer.

[0137] Examples 1-7 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0138] Polytetrafluoroethylene as a polymer and hydrogenated nitrile rubber amine as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 85:15 to prepare a slurry for forming an organic insulating layer.

[0139] Using aluminum foil as the positive current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. Among them, the average particle size of polytetrafluoroethylene is 15 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0140] Examples 1-8 Layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0141] Polypropylene as a polymer and polyvinylidene fluoride as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:20 to prepare a slurry for forming an organic insulating layer.

[0142] Using aluminum foil as the positive current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. Among them, the average particle size of polypropylene is 12 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0143] Examples 1-9 Layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0144] Polypropylene as a polymer and polymethyl acrylate as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:20 to prepare a slurry for forming an organic insulating layer.

[0145] Using aluminum foil as the positive electrode current collector, a slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and a slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The schematic structural diagram of the positive electrode is as shown in Figure 1 shown. Among them, the average particle size of polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0146] Examples 1 - 10 The layered lithium cobaltate (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0147] Polypropylene as the polymer and polyacrylonitrile as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 80:20 to prepare a slurry for forming the organic insulating layer.

[0148] Using aluminum foil as the positive electrode current collector, a slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and a slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The schematic structural diagram of the positive electrode is as shown in Figure 1 shown. Among them, the average particle size of polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0149] Examples 1 - 11 The layered lithium cobaltate (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0150] Polypropylene as the polymer and polyacrylonitrile as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 80:20 to prepare a slurry for forming the organic insulating layer.

[0151] Using aluminum foil as the positive electrode current collector, a slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and a slurry for forming the organic insulating layer was coated on the edge of one short side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The schematic structural diagram of the positive electrode is as shown in Figure 4 shown. Among them, the average particle size of polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0152] Examples 1 - 12 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0153] Polypropylene as the polymer and polyacrylonitrile as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:20 to prepare a slurry for forming the organic insulating layer.

[0154] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the four peripheral edges of the aluminum foil. After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 5 shown. Among them, the average particle size of polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0155] Examples 1 - 13 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0156] Polypropylene as the polymer and polyacrylonitrile as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:20 to prepare a slurry for forming the organic insulating layer.

[0157] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated at the end position of the tab (i.e., the connection between the tab and the current collector). After drying, a pressing treatment was carried out to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 6 shown. Among them, the average particle size of polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0158] Examples 1 - 14 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0159] Polypropylene as the polymer, polyacrylonitrile as the binder, and anthraquinone-based dye Disperse Red 60 as the colorant were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:17:3 to prepare a slurry for forming the organic insulating layer.

[0160] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. The average particle size of the polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0161] Example 1-15 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0162] Polypropylene as the polymer, polyacrylonitrile as the binder, and benzylidene dye Yellow 081 as the colorant were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:17:3 to prepare a slurry for forming the organic insulating layer.

[0163] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the organic insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. The average particle size of the polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0164] Example 1-16 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0165] The organic insulating layer uses a polypropylene tape, which has an adhesive layer and a polypropylene layer arranged in a laminated manner. The material of the polypropylene layer is polypropylene, and the material of the adhesive layer is polyacrylonitrile, with a mass ratio of polypropylene to polyacrylonitrile of 80:20.

[0166] Using an aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the polypropylene tape was attached to the edge of one long side of the aluminum foil to form an organic insulating layer. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 1 shown. Among them, the average particle size of the polypropylene is 12 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 50% of the thickness of the mixture layer.

[0167] Comparative Example 1-1 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0168] Aluminum oxide and polyvinylidene fluoride as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 60:40 to prepare a slurry for forming the insulating layer.

[0169] Using an aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming the insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is similar to Figure 1 shown. Among them, the average particle size of the aluminum oxide is 5 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the insulating layer is 20% of the thickness of the mixture layer.

[0170] Comparative Example 1-2 The layered lithium cobalt oxide (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0171] A slurry for forming an insulating layer was prepared by mixing polyvinylidene fluoride and polyacrylic acid as an adhesive in a mass ratio of 80:20 with N-methyl-2-pyrrolidone (NMP).

[0172] Using aluminum foil as the positive current collector, a slurry for forming a positive electrode mixture layer was coated on the aluminum foil, and the slurry for forming an insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was carried out to fabricate a positive electrode sheet. The schematic structural diagram of the positive electrode is similar to Figure 1 that shown. Among them, the average particle size of polyvinylidene fluoride is 5 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the insulating layer is 20% of the thickness of the mixture layer.

[0173] 2. Fabrication of the secondary battery Natural graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as the adhesive, and carboxymethyl cellulose (CMC) as the tackifier were mixed with ion-exchanged water in a mass ratio of C:SBR:CMC = 98:1:1 to prepare a slurry for forming a negative electrode mixture layer. The slurry for forming the negative electrode mixture layer was coated on copper foil, and after drying, a pressing treatment was carried out to fabricate a negative electrode sheet.

[0174] A polypropylene film was used as the separator.

[0175] Preparation of the electrolyte: In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) / propylene carbonate (PC) / dimethyl carbonate (DMC) were mixed evenly in a mass ratio of 1:1.2:2. 10.5 mass% of LiPF6 lithium salt was added and dissolved in the organic solvent, and then 3 mass% of fluoroethylene carbonate, 3% mass of 1,3-propane sultone, lithium difluorophosphate, lithium boron-containing salt, and optional additive A were added to obtain the electrolyte. Refer to Table 1.

[0176] The codes of the relevant components of the electrolyte in Table 1 represent: lithium difluorophosphate (P1); lithium tetrafluoroborate (B1), lithium difluorooxalate borate (B2), lithium bis(oxalato)borate (B3), lithium tricyanomethyl borate (B4), lithium tricyanoethyl borate (B5), lithium tricyanopropyl borate (B6); succinonitrile (A1), adiponitrile (A2), vinylene carbonate (A3), 1,3-propane sultone (A4), ethylene sulfate (A5), 1,3-propanediol cyclic sulfate (A6).

[0177] Table 1 Relevant components and contents of the electrolyte ;

[0178] Note: The "parts" of the relevant components in Table 1 refer to the mass parts of the corresponding components when the mass of the electrolyte is 100 mass parts.

[0179] Preparation of the wound-type battery cell: The negative electrode sheet, the positive electrode sheet, and the separator prepared above are wound together to form a battery cell. Preparation of the stacked-type battery cell: The negative electrode sheet, the positive electrode sheet, and the separator prepared above are stacked together to form a battery cell.

[0180] Preparation of the secondary battery: After hot-pressing and shaping the prepared battery cell, it is packaged with an aluminum-plastic film, baked to remove moisture, and then filled with an electrolyte to obtain a secondary battery.

[0181] 3. Battery performance test (1) Evaluation test of low-temperature cycle characteristics After the secondary batteries manufactured through the examples and comparative examples are left standing in an environment at 25 °C for 24 hours, the following charge and discharge operations are performed: In an environment at 25 °C, charge at a charging rate of 1C to 4.5V and discharge at a discharge rate of 1C to 3.0V, and measure the initial capacity C0. Then, in an environment at -20 °C, repeat the same charge and discharge operations, and measure the capacity C1 after 100 cycles. Then, the capacity retention rate is evaluated by the capacity retention rate ΔC shown by ΔC = (C1 / C0) × 100 (%). The higher this capacity retention rate ΔC is, the more excellent the low-temperature characteristics are. In the column of "low-temperature cycle" in Table 2-5, A++, A+, A, B, C, D, and E respectively represent: A++: The capacity retention rate ΔC is 75% or more; A+: The capacity retention rate ΔC is more than 70% and less than 75%; A: The capacity retention rate ΔC is more than 65% and less than 70%; B: The capacity retention rate ΔC is more than 60% and less than 65%; C: The capacity retention rate ΔC is more than 55% and less than 60%; D: The capacity retention rate ΔC is more than 50% and less than 55%; E: The capacity retention rate ΔC is less than 50%.

[0182] (2) Evaluation test of voltage drop Under the condition of 25 °C, charge the secondary battery at a constant current of 1C to 4.5V, then charge at a constant voltage until the current is 0.05C, and then discharge at a constant current of 1C to 3.2V, and leave it standing for 5 minutes to measure the voltage before storage. Then, after storing the secondary battery at -15 °C for 24 hours, measure the voltage after storage. The voltage drop of the secondary battery is calculated according to the following formula: Voltage drop = Voltage before storage - Voltage after storage. In the column of "low-temperature voltage drop" in Table 2-5, A++, A+, A, B, C, D, and E respectively represent: A++: The voltage drop is below 0.25 V; A+: The voltage drop is 0.25 - 0.30 V; A: The voltage drop is 0.30 - 0.35 V; B: The voltage drop is 0.30 - 0.35 V; C: The voltage drop is 0.30 - 0.35 V; D: The voltage drop is 0.30 - 0.35 V; E: The voltage drop is 0.30 - 0.35 V.

[0183] (3) Safety test Heat release suppression during internal short circuit (forced internal short circuit test) safety test: The secondary batteries fabricated in the examples and comparative examples are charged by the constant current method of 0.2C (the upper limit cell voltage is 4.5 V) in the CC - CV charging mode, and discharged by the constant current method of 0.2C to 3.0 V in the CC mode. This 0.2C charge - discharge process is repeated 3 times. Then, in an atmosphere of 25°C, it is charged to 4.5 V by the constant voltage and constant current (CC - CV) method at a charging rate of 0.2C (termination condition: 0.02C). Then, near the center of the secondary battery, a 3 - mm - diameter and 10 - cm - long iron nail is penetrated at a speed of 5 m / min to force a short circuit. This forced short - circuit operation is performed on 10 secondary batteries fabricated by the same operation respectively. According to the number of test specimens that do not rupture and do not catch fire, the evaluation is carried out according to the following criteria. The larger the number of test specimens that do not rupture and do not catch fire, the better the heat release suppression performance of the secondary battery during internal short circuit. In the "Safety" column of Table 2 - 5, A++, A+, A, B, C, D, and E represent respectively: A++: The number of test specimens that do not rupture and do not catch fire is 10; A+: The number of test specimens that do not rupture and do not catch fire is 9; A: The number of test specimens that do not rupture and do not catch fire is 8; B: The number of test specimens that do not rupture and do not catch fire is 7; C: The number of test specimens that do not rupture and do not catch fire is 5 - 6; D: The number of test specimens that do not rupture and do not catch fire is 2 - 4; E: The number of test specimens that do not rupture and do not catch fire is 0 - 1.

[0184] Examples 2 - 1 to 2 - 16 Examples 2-1 to 2-16 respectively used the positive electrodes prepared in Examples 1-1 to 1-16, and used E1-1 as the electrolyte to fabricate secondary batteries. The relevant performance of the batteries in Examples 2-1 to 2-16 is shown in Table 2.

[0185] Comparative Examples 2-1 to 2-6 Comparative Examples 2-1 to 2-2 respectively used the positive electrodes prepared in Comparative Examples 1-1 to 1-2, and used E1-1 as the electrolyte to fabricate secondary batteries; Comparative Examples 2-3 to 2-4 respectively used the positive electrodes prepared in Comparative Examples 1-1 to 1-2, and used E0-1 as the electrolyte to fabricate secondary batteries; Comparative Examples 2-5 to 2-6 respectively used the positive electrode prepared in Example 1-1, and used E0-1 and E0-2 as the electrolytes to fabricate secondary batteries.

[0186] The relevant performance of the batteries in Comparative Examples 2-1 to 2-6 is shown in Table 2.

[0187] Table 2

[0188] Examples 3-1 to 3-16 Examples 3-1 to 3-16 respectively used the positive electrodes prepared in Examples 1-1 to 1-16, and used E1-1 to E1-12 as the electrolytes to fabricate secondary batteries. The relevant performance of the batteries in Examples 3-1 to 3-16 is shown in Table 3.

[0189] Table 3

[0190] Examples 4-1 to 4-12 Examples 4-1 to 4-12 respectively used the positive electrodes prepared in Examples 1-8 to 1-16, and used E2-1 to E2-12 as the electrolytes to fabricate secondary batteries. The relevant performance of the batteries in Examples 4-1 to 4-12 is shown in Table 4.

[0191] Table 4

[0192] Examples 5-1 to 5-12 Examples 5-1 to 5-12 respectively used the positive electrodes prepared in Examples 1-8 to 1-16, and used E2-13 to E2-24 as the electrolytes to fabricate secondary batteries. The relevant performance of the batteries in Examples 5-1 to 5-12 is shown in Table 5.

[0193] Table 5

[0194] In summary, the positive electrode of the secondary battery provided by the present invention is provided with an organic insulating layer, and the organic insulating layer includes polyolefin and a binder. In a chemical system where the electrolyte includes lithium difluorophosphate and a lithium salt containing boron, it can not only improve the low-temperature cycle and low-temperature voltage drop of the secondary battery, but also enhance safety.

[0195] The inventors also found that: When the polyolefin is selected from polypropylene, the battery safety is further improved, and a further improved effect is obtained.

[0196] When the content of the polyolefin is 60 wt% to 95 wt%, it can further improve the low-temperature cycle and low-temperature voltage drop of the secondary battery, and can also enhance safety; When the organic insulating layer further includes a colorant, it can facilitate the detector to determine the formation and / or orientation position of the organic insulating layer, and can further improve the low-temperature cycle and low-temperature voltage drop of the secondary battery, and can also enhance safety.

[0197] When at least one of additive A is included in the electrolyte system, it can further inhibit the brittle fracture of the polyolefin, reduce the cracking and peeling on the surface of the organic insulating layer, and can further improve the low-temperature cycle and low-temperature voltage drop of the secondary battery, and can also enhance safety.

[0198] It should be noted that the present invention is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure and the same function and effect as the technical idea within the technical solution scope of the present invention are all included in the technical scope of the present invention. In addition, within the scope not departing from the gist of the present invention, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining a part of the constituent elements in the embodiments are also included in 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 positive electrode includes a current collector, a positive electrode mixture layer and an organic insulating layer which are arranged in contact with the current collector; the organic insulating layer includes an organic insulating material and an adhesive, the organic insulating material includes polyolefin, and the electrolyte includes lithium difluorophosphate and a boron-containing lithium salt.

2. The secondary battery according to claim 1, wherein: The polyolefin includes at least one of polyethylene, polypropylene, polybutene, polystyrene or polytetrafluoroethylene, and preferably includes polypropylene; And / or, based on the mass of the organic insulating layer being 100%, the content of the polyolefin is 60wt% - 95wt%, preferably 70wt% - 90wt%; And / or, the polyolefin is polyolefin particles, and the average particle size of the polyolefin particles is 5 - 20μm, preferably 6 - 15μm.

3. The secondary battery according to claim 1, wherein: The adhesive includes at least one of polyvinylidene fluoride, polyimide, polyacrylic acid, methyl polyacrylate, nitrile rubber, hydrogenated nitrile rubber or polyacrylonitrile; And / or, based on the mass of the organic insulating layer being 100%, the content of the adhesive is 5wt% - 40wt%, preferably 10wt% - 30wt%.

4. The secondary battery according to claim 1, wherein: The thickness of the organic insulating layer is 20% - 70% of the thickness of the positive electrode mixture layer, preferably 35% - 65%.

5. The secondary battery according to claim 1, wherein: The organic insulating layer is arranged at the edge of at least one side of the current collector and / or at the connection between the current collector and the tab.

6. The secondary battery according to claim 1, characterized in that: The organic insulating layer further includes an organic dye; preferably, the organic dye includes at least one of anthraquinone-based dyes, aniline-based azo dyes, triphenylmethane-based dyes, pyrazole azo dyes, pyridone azo dyes, methylpyridone-based dyes, oxyphenol-based dyes, benzylidene dyes, xanthene dyes, more preferably includes benzylidene dyes and / or azo dyes, and further preferably includes benzylidene dyes; And / or, the organic insulating layer does not contain inorganic particles.

7. The secondary battery according to claim 1, characterized in that: The boron-containing lithium salt includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate)borate, lithium tricyanomethyl borate, lithium tricyanoethyl borate, lithium tricyanopropyl borate; And / or, based on the mass of the electrolyte being 100 parts by mass, the content of the boron-containing lithium salt is 0.01 - 5 parts by mass, preferably 0.1 - 3 parts by mass; And / or, based on the mass of the electrolyte being 100 parts by mass, the content of lithium difluorophosphate is 0.01 - 2 parts by mass, preferably 0.05 - 1.2 parts by mass.

8. The secondary battery according to claim 1, wherein: The electrolyte further includes additive A, and additive A includes at least one of succinonitrile, adiponitrile, vinylene carbonate, 1,3 - propylene sulfonic acid lactone, ethylene sulfate, 1,3 - propanediol cyclic sulfate.

9. The secondary battery according to claim 8, wherein: Based on the mass of the electrolyte being 100 parts by mass, the content of succinonitrile 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 vinylene carbonate is 0.2 - 2 parts by mass, and / or the content of 1,3 - propylene sulfonic acid lactone is 0.01 - 2 parts by mass, and / or the content of ethylene sulfate is 0.01 - 2 parts by mass, and / or the content of 1,3 - propanediol cyclic sulfate is 0.01 - 2 parts by mass.

10. An electronic device, characterized in that it includes the secondary battery according to any one of claims 1 to 9.

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