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 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 polyolefin and an adhesive, and the electrolyte comprises carboxylic ester and a trinitrile compound. The secondary battery provided by the invention has good high-temperature cycling performance, storage performance and 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. Thus, 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 output.

[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 high-temperature state caused by a short circuit between the positive electrode and the negative electrode. In the prior art, to solve the internal short circuit of the battery, a method of forming an insulating layer on the non-coated portion 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 PVDF-based binder has good electrical safety and coating processability, but when the insulating layer containing 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 has conducted research and found that the above prior art has the following problems: The above existing insulating layer containing PVDF-based binder or the 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 repeatedly charged and discharged under high-temperature conditions, the battery performance deteriorates, so there is room for improvement in this regard.

[0005] One aspect of 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, the organic insulating layer includes an organic insulating material and a binder, the organic insulating material includes polyolefin, and the electrolyte includes a carboxylic ester and a trinitrile compound. According to such a configuration, not only can the high-temperature cycle and storage performance 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, poly(methyl 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 30% to 65%.

[0012] 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.

[0013] In some embodiments, the organic insulating layer further includes an organic dye.

[0014] 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, or xanthene dyes.

[0015] 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.

[0016] In some embodiments, the carboxylic ester includes at least one of ethyl acetate, 2,2-difluoroethyl acetate, methyl propionate, ethyl propionate, propyl propionate, the compound shown in formula (1), the compound shown in formula (2), the compound shown in formula (3), and the compound shown in formula (4);

[0017]

[0018] In some embodiments, based on the mass of the electrolyte being 100 parts by mass, the content of the carboxylic ester is 5 to 60 parts by mass, preferably 10 to 50 parts by mass.

[0019] In some embodiments, the trinitrile compound includes at least one of 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, and 1,2,4-tris(2-cyanoethoxy)butane.

[0020] In some embodiments, based on 100 parts by mass of the electrolyte, the content of the trinitrile compound is 0.5 to 6 parts by mass, preferably 0.8 to 5 parts by mass.

[0021] In some embodiments, the electrolyte further includes additive A, and additive A includes at least one of succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 15-crown-5, 18-crown-6, and 21-crown-7.

[0022] 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 ethylene glycol bis(propionitrile) ether is 0.2 to 2 parts by mass, and / or the content of 15-crown-5 is 0.01 to 2 parts by mass, and / or the content of 18-crown-6 is 0.01 to 2 parts by mass, and / or the content of 21-crown-7 is 0.01 to 2 parts by mass.

[0023] Another aspect of the present invention provides an electronic device, and the electronic device includes the secondary battery described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 1 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention;

[0026] Figure 2 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention;

[0027] Figure 3 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention;

[0028] Figure 4 It is a schematic structural diagram of the positive electrode of the wound battery structure of the present invention;

[0029] Figure 5It is a schematic structural view of the positive electrode of the laminated battery structure of the present invention;

[0030] Figure 6 It is a schematic structural view of the positive electrode of the laminated battery structure of the present invention;

[0031] 1 - Current collector; 2 - Positive electrode tab; 3 - Positive electrode mixture layer; 4 - Organic insulating layer. Detailed implementation mode

[0032] In the following, the present invention will be described in more detail to allow a clearer understanding of the present invention. In this case, it will be understood that the terms or words used in this specification and the claims should not be construed as having the meanings defined in a common dictionary, and it will be further understood that based on the principle that the inventor can appropriately define the meanings of the terms or words to best explain the present invention, these terms or words should be construed as having meanings consistent with the technical concept of the present invention and the background of the related art.

[0033] 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 provided on the surface of the current collector, and an organic insulating layer in contact with the current collector. The organic insulating layer includes polyolefin and a binder, and the electrolyte includes a carboxylic acid ester and a trinitrile compound. This secondary battery has good high-temperature cycle performance, storage performance, and safety.

[0034] The components of the secondary battery of the present invention will be described below.

[0035] Positive electrode

[0036] The positive electrode of the present invention includes a current collector, and a positive electrode mixture layer and an organic insulating layer in contact with the current collector. The above-mentioned organic insulating layer includes an organic insulating material and a binder, and the organic insulating material includes polyolefin.

[0037] 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.

[0038] In the present invention, 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. Additionally, the current collector generally 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 bonding strength with the electrode active material. For example, the current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0039] In the present invention, from the perspective of improving the safety of the secondary battery, 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, insulating layers containing PVDF or insulating layers containing inorganic particles have been used, but film peeling is likely to occur. The inventors of the present invention unexpectedly found that after using polyolefin in the insulating layer, the adhesion between the organic insulating layer and the current collector is significantly improved, thereby significantly improving film peeling; however, under high-temperature conditions, polyolefin is likely to swell in the carboxylic acid ester electrolyte system. The inventors further found that when the secondary battery electrolyte contains a trinitrile compound, the swelling of polyolefin is unexpectedly suppressed, reducing cracking and peeling on the surface of the organic insulating layer, which can not only improve the high-temperature cycle and storage performance of the secondary battery, but also significantly improve safety.

[0040] In the present invention, from the perspective of improving the safety of the secondary battery, 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 Figure 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 ), in 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.

[0041] 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.

[0042] 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 stacked manner, and the adhesive layer is used to attach the thermoplastic polymer film to the edge of at least one side of the current collector and / or the connection between the current collector and the tab. The polyolefin is preferably at least one of polyethylene, polypropylene, polybutene, polystyrene or polytetrafluoroethylene. The adhesive 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.

[0043] If the organic insulating layer is a coating applied to the current collector and / or the connection 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.

[0044] In the present invention, from the perspective of reducing the swelling and film peeling of the organic insulating layer, the organic insulating layer includes polyolefin and an adhesive; the polyolefin includes at least one of polyethylene, polypropylene, polybutene, polystyrene or polytetrafluoroethylene, and preferably includes polypropylene. The polyolefin can have a weight average molecular weight of 50,000 - 5,000,000, particularly 100,000 - 800,000, and more particularly 150,000 - 350,000. Within the above-defined range, the swelling and film peeling of the organic insulating layer can be reduced.

[0045] In the present invention, the polyolefin is polyolefin particles, and the particle size of the polyolefin particles can be in the micron size, for example, the average particle size is 5 microns to 20 microns, preferably 6 microns to 15 microns. When the average particle size of the polyolefin particles is greater than 20 microns, the defect of battery swelling may increase. In particular, when the average particle size of the polyolefin particles is in the range of 5 microns to 20 microns, improved high-temperature cycle life characteristics and an improved effect of suppressing swelling can be obtained.

[0046] 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 above-mentioned process of obtaining the particle size of the polyolefin particles is performed on 10 SEM images, and the obtained (10×10) particle sizes of the polyolefin particles are simply averaged (arithmetic average) to obtain the average particle size of the polyolefin particles.

[0047] In the present invention, taking the mass of the organic insulating layer as 100%, the content of the polyolefin is 60 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0048] In the present invention, in terms of improving the adhesion strength and cohesion strength, the binder in the organic insulating layer is preferably 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 adhesion, chemical resistance and electrochemical stability, the binder polymer is preferably polyacrylonitrile.

[0049] In the present invention, taking the mass of the organic insulating layer as 100%, the content of the binder is 5 wt% to 40 wt%, preferably 10 wt% to 30 wt%.

[0050] In the present invention, the organic insulating layer may further include a colorant to enable the detector to determine the formation or orientation position of the organic insulating layer. The colorant may be an organic dye, and the organic dye may, for example, include one or a combination of more 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. It is preferably to include at least one of benzylidene dyes and azo dyes, and more preferably benzylidene dyes, in order to improve the slurry stability and the effect of preventing phase separation.

[0051] Taking the mass of the organic insulating layer as 100%, the content of the colorant, such as the organic dye, is 0.1 to 3 wt%.

[0052] In the present invention, the thickness of the formed organic insulating layer may, for example, be 0.1 - 100 μm, specifically 10 μm or more, 20 μm or more, or 30 μm or more, and may be 90 μm or less, 80 μm or less, or 70 μm or less.

[0053] In the present invention, the thickness of the organic insulating layer is 20% - 70% of the thickness of the positive electrode mixture layer, preferably 30% - 65%. If the thickness of the organic insulating layer is too low and lower 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 higher than 70% of the thickness of the positive electrode mixture layer, the overall volume of the electrode becomes larger, resulting in a poor mobility of lithium ions.

[0054] In the present invention, 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.

[0055] A composite oxide having a coating on its surface can be used, or a mixture of a composite oxide and a composite oxide having a coating can be used. The coating can include a coating element compound selected from the following: oxides of coating elements, hydroxides of coating elements, hydroxyoxides of coating elements, oxycarbonates of coating elements, or basic carbonates of coating elements. The compound used for the coating can be amorphous or crystalline. The coating elements included in the coating can 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 can 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 undesirable 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.

[0056] For example, the positive electrode active material can include lithium cobalt oxide.

[0057] In some embodiments, the positive electrode active material can include a lithium cobalt oxide represented by Chemical Formula 1:

[0058] Chemical Formula 1: Li a11 Co x11 M 11 y11 O2.

[0059] 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.

[0060] For example, the positive electrode active material can be LiCoO2.

[0061] In some embodiments, the positive electrode active material can include a lithium nickel-based composite oxide represented by Chemical Formula 2:

[0062] Chemical Formula 2: Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 .

[0063] 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 M 2 are 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.

[0064] 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.

[0065] 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:

[0066] Chemical Formula 3: Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2 .

[0067] 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.

[0068] 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.

[0069] 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.

[0070] Chemical Formula 4: Lia3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0071] 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.

[0072] 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.

[0073] 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-based oxide.

[0074] Chemical Formula 5: Li a4 Ni x4 Mn y4 M 6 z4 O 2-b4 X b4

[0075] 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.

[0076] In some exemplary embodiments of the positive electrode, based on the total weight of the positive electrode mixture layer, the content of the positive electrode active material may be 90 wt% to 98 wt%, 50 wt% to 99 wt%, 60 wt% to 99 wt%, 70 wt% to 99 wt%, 80 wt% to 99 wt%, or 90 wt% to 99 wt%.

[0077] In some embodiments of the present invention, the positive electrode mixture layer further includes 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%.

[0078] 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.), conductive polymers (such as polyphenylene derivatives), or a mixture of these.

[0079] The binder improves the binding characteristics between the positive electrode active material particles and the binding characteristics between the positive electrode active material particles and the positive electrode current collector. The binder may, for example, be one or a combination of more 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.

[0080] The method for preparing the positive electrode includes the following steps:

[0081] Forming an undried positive electrode mixture layer by coating an active material slurry composite on the positive 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.

[0082] Negative electrode

[0083] 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.

[0084] 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 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, a binder, and optionally inorganic particles or polymer particles.

[0085] 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 that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, and / or a transition metal oxide.

[0086] Materials that reversibly intercalate / deintercalate 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 carbonization products, calcined coke, etc.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] The transition metal oxide can be vanadium oxide, lithium vanadium oxide, etc.

[0091] In some exemplary embodiments, the negative electrode active material can be selected from at least one of graphite and Si composite.

[0092] 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.

[0093] 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.

[0094] The Si particles can have a median particle size of 10 nm to 200 nm.

[0095] 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.

[0096] 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.

[0097] 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%.

[0098] The amorphous carbon can be a combination of one or more of soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke.

[0099] The negative electrode active material can further include crystalline carbon.

[0100] When the negative electrode active material includes both the Si composite and crystalline carbon, the Si composite and crystalline carbon may be included in the form of a mixture, and in some embodiments, the Si composite and crystalline carbon may be included in a weight ratio of 1:99 to 50:50. In some embodiments, the Si composite and crystalline carbon may be included in a weight ratio of 3:97 to 20:80 or 5:95 to 20:80.

[0101] The crystalline carbon can be, for example, graphite, such as natural graphite, artificial graphite, or a mixture thereof.

[0102] The crystalline carbon may have a median particle size of 5 μm to 30 μm.

[0103] 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).

[0104] 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%.

[0105] 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.

[0106] 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, epichlorohydrin polymer, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol.

[0107] The conductive material provides electrical conductivity (e.g., conductance) for the electrode. Any suitable conductive material can be used as the conductive material (e.g., the 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.

[0108] Separator

[0109] A separator can use a porous sheet having ion permeability and insulation. Specific examples of the porous sheet can include microporous films, woven fabrics, non-woven fabrics, etc. As the material of the separator, it can include olefin resins 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. As the heat-resistant material, polyamide resins such as aliphatic polyamides and aromatic polyamides (aramids), polyamide-imides, polyimide resins such as polyimides, etc. can be exemplified.

[0110] Electrolyte

[0111] As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt can be used in a lithium-ion secondary battery. As the lithium salt, for example, LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, etc. can be cited. The electrolytes can be used alone 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.

[0112] As the organic solvent used in the electrolyte, as long as it can dissolve the supporting electrolyte, there is no particular limitation. 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), ethyl methyl carbonate (EMC), etc.; esters such as γ-butyrolactone, methyl formate, ethyl acetate, propyl propionate, ethyl propionate, etc.; ethers such as 1,2-dimethoxyethane, tetrahydrofuran, etc.; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, etc. can be preferably used. In addition, a mixture of these solvents can also be used. Among them, carbonate esters and carboxylic 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.

[0113] In particular, after using polyolefin in the organic insulating layer, the adhesion between the organic insulating layer and the current collector is significantly improved. However, at high temperatures, polyolefin is prone to swelling in an electrolyte system containing carboxylic acid esters. The inventors found that when the secondary battery contains a trinitrile compound in the electrolyte, the swelling of the polyolefin is unexpectedly inhibited, and the cracking and peeling on the surface of the organic insulating layer are reduced. This can not only improve the high-temperature cycle and storage performance of the secondary battery, but also significantly improve the safety performance.

[0114] The above-mentioned carboxylic acid esters include at least one of ethyl acetate (EA), ethyl 2,2-difluoroacetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), the compound represented by formula (1), the compound represented by formula (2), the compound represented by formula (3), and the compound represented by formula (4):

[0115]

[0116] Based on 100 parts by mass of the electrolyte, the content of the carboxylic acid ester is 5 to 60 parts by mass, preferably 10 to 50 parts by mass.

[0117] The trinitrile compound includes at least one of 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile (HTCN), 1,2,3-tris(2-cyanoethoxy)propane (TCEP), and 1,2,4-tris(2-cyanoethoxy)butane.

[0118] Based on 100 parts by mass of the electrolyte, the content of the trinitrile compound is 0.5 to 6 parts by mass, preferably 0.8 to 5 parts by mass.

[0119] The electrolyte may further include additive A. Additive A includes at least one of succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EDN), 15-crown-5, 18-crown-6, and 21-crown-7, which can further inhibit the swelling of polyolefin and reduce the cracking and peeling on the surface of the organic insulating layer.

[0120] 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 ethylene glycol bis(propionitrile) ether is 0.2 to 2 parts by mass, and / or the content of 15-crown-5 is 0.01 to 2 parts by mass, and / or the content of 18-crown-6 is 0.01 to 2 parts by mass, and / or the content of 21-crown-7 is 0.01 to 2 parts by mass. When additive A meets the above range, it can further inhibit the swelling of polyolefin and reduce the cracking and peeling on the surface of the organic insulating layer.

[0121] Manufacturing method of secondary battery

[0122] 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 electrolytic solution into the battery container, and sealing it. In order to prevent an increase in the internal pressure of the secondary battery, occurrence of 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.

[0123] 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 Shown are schematic structural views of the positive electrodes of four wound battery structures. Figure 5 , Figure 6 Shown are schematic structural views of the positive electrodes of the laminated battery structure.

[0124] 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.

[0125] The present invention further provides an electronic device including the secondary battery according to the present invention.

[0126] The secondary battery of the present invention can be used, for example, in a notebook computer, a pen input type computer, a mobile computer, an e-book player, a portable phone, a portable facsimile 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 memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flash, a camera, a large household storage battery, and a lithium ion capacitor, etc., but is not limited thereto.

[0127] Examples

[0128] 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.

[0129] 1. Preparation of positive electrode

[0130] Example 1-1A

[0131] The 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 form a slurry for forming a positive electrode mixture layer.

[0132] 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 form a slurry for forming an 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. 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 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.

[0134] Example 1-1B

[0135] 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 form a slurry for forming the positive electrode mixture layer.

[0136] 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 form a slurry for forming an organic insulating layer.

[0137] 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 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.

[0138] Example 1-1C

[0139] 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.

[0140] 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.

[0141] 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 performed to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 1 Figure. 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.

[0142] Example 1-1D

[0143] 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 the slurry for forming the positive electrode mixture layer.

[0144] Polyethylene (PE) and polyvinylidene fluoride as the binder were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 60:40 to prepare the slurry for forming the insulating layer.

[0145] 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 insulating layer was coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment was performed to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 1 Figure. 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.

[0146] Example 1-2

[0147] 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 form the slurry for forming the positive electrode mixture layer.

[0148] 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 form the slurry for forming the organic insulating layer.

[0149] 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 performed to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as shown in Figure 1As shown. The average particle size of the polyethylene is 5 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 20% of the thickness of the positive electrode mixture layer.

[0150] Examples 1 - 3

[0151] 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) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0152] The 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 form a slurry for forming the organic insulating layer.

[0153] 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 schematic structural diagram of the positive electrode is as Figure 1 shown. The average particle size of the polyethylene is 20 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 70% of the thickness of the positive electrode mixture layer.

[0154] Examples 1 - 4

[0155] 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) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0156] The 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 form 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 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 as Figure 1 shown. The average particle size of the polypropylene is 6 μm, the thickness of the positive electrode mixture layer is 60 μm, and the thickness of the organic insulating layer is 30% of the thickness of the mixture layer.

[0158] Examples 1 - 5

[0159] 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 are mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0160] Polybutene (PB) as the polymer and polyimide as the binder are mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 75:25 to form a slurry for forming the organic insulating layer.

[0161] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer is coated on the aluminum foil, and the slurry for forming the organic insulating layer is coated on the edge of one long side of the aluminum foil and the end of the tab. After drying, a pressing treatment is 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 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 40% of the thickness of the mixture layer.

[0162] Examples 1-6

[0163] 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 are mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0164] Polystyrene as the polymer and acrylonitrile-butadiene rubber amine as the binder are mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:20 to form a slurry for forming the organic insulating layer.

[0165] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer is coated on the aluminum foil, and the slurry for forming the organic insulating layer is coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment is 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 microns, the thickness of the positive electrode mixture layer is 60 microns, and the thickness of the organic insulating layer is 60% of the thickness of the mixture layer.

[0166] Examples 1-7

[0167] 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 are mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0168] Polytetrafluoroethylene as a polymer and hydrogenated nitrile rubber amine as an adhesive are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 85:15 to form a slurry for forming an organic insulating layer.

[0169] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer is coated on the aluminum foil, and the slurry for forming the organic insulating layer is coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment is 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 polytetrafluoroethylene is 15 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.

[0170] Examples 1-8

[0171] Layered lithium cobaltate (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the adhesive are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0172] Polypropylene as a polymer and polyvinylidene fluoride amine as an adhesive are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 80:20 to form a slurry for forming an organic insulating layer.

[0173] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer is coated on the aluminum foil, and the slurry for forming the organic insulating layer is coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment is 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 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.

[0174] Examples 1-9

[0175] Layered lithium cobaltate (LCO) as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the adhesive are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0176] Polypropylene as a polymer and polymethyl acrylate as an adhesive are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 80:20 to form a slurry for forming an organic insulating layer.

[0177] Using an aluminum foil as the positive electrode 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 the figure. 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.

[0178] Examples 1 - 10

[0179] 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) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming a positive electrode mixture layer.

[0180] The 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 form a slurry for forming an organic insulating layer.

[0181] Using an aluminum foil as the positive electrode 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 the figure. 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.

[0182] Examples 1 - 11

[0183] 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) at a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming a positive electrode mixture layer.

[0184] The 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 form a slurry for forming an organic insulating layer.

[0185] Using an aluminum foil as the positive electrode 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 short 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 4As 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.

[0186] Examples 1 - 12

[0187] 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) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0188] The 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 form a slurry for forming the organic insulating layer.

[0189] 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 organic insulating layer was coated on the four peripheral edges 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 Figure 5 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.

[0190] Examples 1 - 13

[0191] 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) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to prepare a slurry for forming the positive electrode mixture layer.

[0192] The 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.

[0193] 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 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 performed to fabricate a positive electrode sheet. The structural schematic diagram of the positive electrode is as Figure 6 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.

[0194] Examples 1 - 14

[0195] 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 form a slurry for forming the positive electrode mixture layer.

[0196] The 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 form a slurry for forming the organic insulating layer.

[0197] 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 performed to fabricate the 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.

[0198] Example 1-15

[0199] 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 form a slurry for forming the positive electrode mixture layer.

[0200] The polypropylene as the polymer, polyacrylonitrile as the binder, and benzylidene dye Yellow081 as the colorant were mixed with N-methyl-2-pyrrolidone (NMP) at a mass ratio of 80:17:3 to form a slurry for forming the organic insulating layer.

[0201] 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 performed to fabricate the 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.

[0202] Example 1-16

[0203] 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 are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0204] 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. The mass ratio of polypropylene to polyacrylonitrile is 80:20.

[0205] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer is coated on the aluminum foil, and the polypropylene tape is attached to the edge of one long side of the aluminum foil to form an organic insulating layer. After drying, a pressing treatment is performed to fabricate the 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.

[0206] Comparative Example 1-1

[0207] 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 are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0208] Aluminum oxide and polyvinylidene fluoride as the binder are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 60:40 to form a slurry for forming the insulating layer.

[0209] Using aluminum foil as the positive electrode current collector, the slurry for forming the positive electrode mixture layer is coated on the aluminum foil, and the slurry for forming the insulating layer is coated on the edge of one long side of the aluminum foil. After drying, a pressing treatment is performed to fabricate the positive electrode sheet. The structural schematic diagram of the positive electrode is as 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.

[0210] Comparative Example 1-2

[0211] 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 are mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of LCO:AB:PVdF = 97:1.5:1.5 to form a slurry for forming the positive electrode mixture layer.

[0212] Polyvinylidene fluoride and polyacrylic acid as an adhesive were mixed with N-methyl-2-pyrrolidone (NMP) in a mass ratio of 80:20 to form a slurry for forming an insulating layer.

[0213] 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 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 Figure 1 shown. The average particle size of the 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.

[0214] 2. Fabrication of the secondary battery

[0215] 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 performed to fabricate a negative electrode sheet.

[0216] Using a polypropylene film as the separator.

[0217] Preparation of the electrolyte: In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / propylene carbonate (PC) as organic solvents were mixed evenly in a mass ratio of 1:1.2. 10.5 wt% of LiPF6 lithium salt was added and dissolved in the organic solvent. Then, 4 wt% of fluoroethylene carbonate, 1 wt% of 1,3-propane sultone, and carboxylic acid esters, trinitrile compounds, and optional additive A were added to obtain the electrolyte. The partial compositions of the electrolytes in each example and comparative example are shown in Table 1.

[0218] Table 1

[0219]

[0220]

[0221] Note: The "parts" of the relevant components in the electrolyte in Table 1 refer to the mass parts of the corresponding relevant components when the mass of the electrolyte is 100 mass parts.

[0222] Preparation of the wound-type battery cell: The negative electrode sheet, positive electrode sheet, and separator prepared above were wound together to form a battery cell. Preparation of the stacked-type battery cell: The negative electrode sheet, positive electrode sheet, and separator prepared above were stacked together to form a battery cell.

[0223] Preparation of 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 electrolyte is injected to obtain the secondary battery.

[0224] The relevant performance of the assembled secondary battery was tested, and the test methods are as follows:

[0225] (1) Evaluation test of high-temperature cycling characteristics

[0226] After the secondary battery is left standing in an environment of 25 °C for 24 hours, charge and discharge operations are performed at a charge-discharge rate of 4.5 V and 0.1 C to measure the initial capacity C0. Then, the charge and discharge of charging to 4.5 V at a charge-discharge rate of 0.1 C and discharging to 3.0 V in an environment of 60 °C are repeated, and the capacity C1 after 500 cycles is measured. The high-temperature cycling characteristics were evaluated using the capacity retention rate shown by ΔC = C1 / C0 × 100 (%). The higher this value, the less the discharge capacity decreases, and the more excellent the cycling characteristics. In Tables 2 - 5, A++, A+, A, B, C, D, and E in the "High-temperature cycling" column represent:

[0227] A++: Above 95%;

[0228] A+: Above 90% and below 95%;

[0229] A: Above 85% and below 90%;

[0230] B: Above 80% and below 85%;

[0231] C: Above 75% and below 80%;

[0232] D: Above 70% and below 75%;

[0233] E: Below 70%.

[0234] (2) Evaluation test of high-temperature storage characteristics

[0235] For the fabricated lithium-ion secondary battery, in an environment of 25 °C, it is charged to 4.5 V by a constant current method of 0.1 C and then stored at 80 °C for 100 hours. The open circuit voltage (Open circuit voltage, hereinafter marked as "OCV") before the start of storage at 80 °C and the OCV of the cell after storage at 80 °C for 100 hours are measured, and the ratio of the OCV after storage at 80 °C for 100 hours to the OCV before the start of storage at 80 °C is calculated as the OCV retention rate and evaluated using the following criteria. The larger the OCV retention rate, the more excellent the high-temperature storage characteristics, that is, the more excellent the life characteristics. In Tables 2 - 5, A++, A+, A, B, C, D, and E in the "High-temperature storage" column represent:

[0236] A++: The OCV retention rate is 99.5% or more;

[0237] A+: The OCV retention rate is 99.2% or more and less than 99.5%;

[0238] A: The OCV retention rate is 99.0% or more and less than 99.2%;

[0239] B: The OCV retention rate is 98.5% or more and less than 99.0%;

[0240] C: The OCV retention rate is 98.0% or more and less than 98.5%;

[0241] D: The OCV retention rate is 97.5% or more and less than 98.0%;

[0242] E: The OCV retention rate is less than 97.5%.

[0243] (3) Safety test

[0244] Exothermic suppression during internal short circuit (forced internal short circuit test) safety test:

[0245] The secondary batteries prepared in the examples and comparative examples are charged by the constant current method of 0.2C in CC-CV (the upper limit cell voltage is 4.5V), and discharged by the constant current method of 0.2C in CC to 3.0V. This 0.2C charge and discharge is repeated 3 times. Then, in an atmosphere of 25°C, it is charged to 4.5V 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 it to short circuit. This forced short circuit is performed on 10 secondary batteries prepared by the same operation, and according to the number of test bodies that did not crack and did not catch fire, the evaluation is carried out according to the following criteria. The larger the number of test bodies that did not crack and did not catch fire, the better the exothermic suppression performance of the secondary battery during internal short circuit. In Tables 2 - 5, A++, A+, A, B, C, D, and E in the "Safety" column represent:

[0246] A++: The number of test bodies that did not crack and did not catch fire is 10;

[0247] A+: The number of test bodies that did not crack and did not catch fire is 9;

[0248] A: The number of test bodies that did not crack and did not catch fire is 8;

[0249] B: The number of test bodies that did not crack and did not catch fire is 7;

[0250] C: The number of test specimens without rupture or ignition is 5 to 6;

[0251] D: The number of test specimens without rupture or ignition is 2 to 4;

[0252] E: The number of test specimens without rupture or ignition is 0 to 1.

[0253] Examples 2-1 to 2-16

[0254] For Examples 2-1 to 2-16, the positive electrodes prepared in Examples 1-1 to 1-16 were used, and electrolyte E1-1 was used to fabricate secondary batteries. The battery performance test results are shown in Table 2.

[0255] Comparative Examples 2-1 to 2-6

[0256] For Comparative Examples 2-1 to 2-2, the positive electrodes prepared in Comparative Examples 1-1 to 1-2 were used, and electrolyte E1-1 was used to fabricate secondary batteries; for Comparative Examples 2-3 to 2-4, the positive electrodes prepared in Comparative Examples 1-1 to 1-2 were used, and electrolyte E0-1 was used to fabricate secondary batteries; for Comparative Examples 2-5 to 2-6, the positive electrode prepared in Example 1-1 was used, and electrolytes E0-1 and E0-2 were used to fabricate secondary batteries. The battery performance test results are shown in Table 2.

[0257] Table 2

[0258]

[0259]

[0260] Examples 3-1 to 3-16

[0261] For Examples 3-1 to 3-16, the positive electrodes prepared in Examples 1-1 to 1-16 were used, and electrolytes E1-1 to E1-12 were used to fabricate secondary batteries. The battery performance test results are shown in Table 3.

[0262] Table 3

[0263] Group Positive Electrode Electrolyte High-Temperature Cycling High-Temperature Storage Safety Example 3-1 Example 1-1A E1-2 B B B Example 3-2 Example 1-2 E1-3 B B B Example 3-3 Example 1-3 E1-4 B B B Example 3-4 Example 1-4 E1-5 A A A Example 3-5 Example 1-5 E1-6 A A A Example 3-6 Example 1-6 E1-7 A A A Example 3-7 Example 1-7 E1-8 A A A Example 3-8 Example 1-8 E1-9 A A A Example 3-9 Example 1-9 E1-10 A A A Example 3-10 Example 1-10 E1-11 A A A Example 3-11 Example 1-11 E1-12 A A A Example 3-12 Example 1-12 E1-12 A A A Example 3-13 Example 1-13 E1-12 A A A Example 3-14 Example 1-14 E1-12 A A A Example 3-15 Example 1-15 E1-12 A A A Example 3-16 Example 1-16 E1-12 A A A

[0264] Examples 4-1 to 4-12

[0265] For Examples 4-1 to 4-12, the positive electrodes prepared in Examples 1-8 to 1-16 were used, and electrolytes E2-1 to E2-12 were used to fabricate secondary batteries. The battery performance test results are shown in Table 4.

[0266] Table 4

[0267] Group Positive Electrode Electrolyte High-Temperature Cycling High-Temperature Storage Safety Example 4-1 Example 1-8 E2-1 A+ A+ A+ Example 4-2 Example 1-9 E2-2 A+ A+ A+ Example 4-3 Example 1-10 E2-3 A+ A+ A+ Example 4-4 Example 1-11 E2-4 A+ A+ A+ Example 4-5 Example 1-12 E2-5 A+ A+ A+ Example 4-6 Example 1-13 E2-6 A+ A+ A+ Example 4-7 Example 1-14 E2-7 A+ A+ A+ Example 4-8 Example 1-15 E2-8 A+ A+ A+ Example 4-9 Example 1-16 E2-9 A+ A+ A+ Example 4-10 Example 1-10 E2-10 A+ A+ A+ Example 4-11 Example 1-10 E2-11 A+ A+ A+ Example 4-12 Example 1-10 E2-12 A+ A+ A+

[0268] Examples 5-1 to 5-12

[0269] For Examples 5-1 to 5-12, the positive electrodes prepared in Examples 1-8 to 1-16 were used, and electrolytes E2-13 to E2-24 were used to fabricate secondary batteries. The battery performance test results are shown in Table 5.

[0270] Table 5

[0271] Group Positive Electrode Electrolyte High-Temperature Cycling High-Temperature Storage Safety Example 5-1 Example 1-8 E2-13 A++ A++ A++ Example 5-2 Example 1-9 E2-14 A++ A++ A++ Example 5-3 Example 1-10 E2-15 A++ A++ A++ Example 5-4 Example 1-11 E2-16 A++ A++ A++ Example 5-5 Example 1-12 E2-17 A++ A++ A++ Example 5-6 Example 1-13 E2-18 A++ A++ A++ Example 5-7 Example 1-14 E2-19 A++ A++ A++ Example 5-8 Example 1-15 E2-20 A++ A++ A++ Example 5-9 Example 1-16 E2-21 A++ A++ A++ Example 5-10 Example 1-10 E2-22 A++ A++ A++ Example 5-11 Example 1-10 E2-23 A++ A++ A++ Example 5-12 Example 1-10 E2-24 A++ A++ A++

[0272] The positive electrode 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 carboxylic ester and trinitrile compound, it can not only improve the high-temperature cycle and storage performance of the secondary battery, but also enhance the safety.

[0273] The present invention also found that:

[0274] When the polyolefin is selected from polypropylene, the high-temperature storage property and safety of the secondary battery are further improved, and a further improved effect is obtained.

[0275] When the content of the polyolefin is 60% to 95%, the high-temperature cycle and storage performance of the secondary battery can be further improved, and the safety can also be enhanced.

[0276] When the organic insulating layer further includes a colorant, it can facilitate the detector to confirm the formation or orientation position of the organic insulating layer, and a further improved effect is obtained.

[0277] When the carboxylic ester includes at least one of EP or PP, or the trinitrile compound includes at least one of HTCN or TCEP, the high-temperature cycle and storage performance of the secondary battery can be further improved, and the safety can also be enhanced.

[0278] When at least one of additive A is included in the electrolyte system, the swelling of the polyolefin can be further inhibited, and the cracking and peeling on the surface of the organic insulating layer can be reduced, and a further improved effect is obtained.

[0279] 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 constitution as the technical idea and exhibiting the same effect within the technical 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 conceived by those skilled in the art to the embodiments and other forms constructed by combining some constituent elements of 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 that are 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 a carboxylic acid ester and a trinitrile compound.

2. The secondary battery according to claim 1, wherein: The polyolefin includes at least one of polyethylene, polypropylene, polybutene, polystyrene or polytetrafluoroethylene; and / or, 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%; and / or, the polyolefin is polyolefin particles, and the average particle size of the polyolefin particles is 5 to 20 μm, preferably 6 to 15 μm.

3. The secondary battery according to claim 1, wherein: The binder 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 binder is 5 wt% to 40 wt%, preferably 10 wt% to 30 wt%.

4. The secondary battery according to claim 1, wherein: The thickness of the organic insulating layer is 20% to 70% of the thickness of the positive electrode mixture layer, preferably 30% to 65%; and / or, 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.

5. 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 an anthraquinone-based dye, an aniline-based azo dye, a triphenylmethane-based dye, a pyrazole azo dye, a pyridone azo dye, a methylpyridone-based dye, an oxyphenol-based dye, a benzylidene dye or an oxanthene dye; and / or, the organic insulating layer does not contain inorganic particles.

6. The secondary battery according to claim 1, characterized in that: The carboxylic acid ester includes at least one of ethyl acetate, 2,2-difluoroethyl acetate, methyl propionate, ethyl propionate, propyl propionate, the compound shown in formula (1), the compound shown in formula (2), the compound shown in formula (3), the compound shown in formula (4); and / or, based on 100 parts by mass of the electrolyte, the content of the carboxylic acid ester is 5 to 60 parts by mass, preferably 10 to 50 parts by mass.

7. The secondary battery according to claim 1, wherein: The trinitrile compound includes at least one of 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane; and / or, based on 100 parts by mass of the electrolyte, the content of the trinitrile compound is 0.5 to 6 parts by mass, preferably 0.8 to 5 parts by mass.

8. The secondary battery according to claim 1, characterized in that: The electrolyte further includes additive A, and additive A includes at least one of succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 15-crown-5, 18-crown-6, 21-crown-7.

9. The secondary battery according to claim 8, wherein: 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 ethylene glycol bis(propionitrile) ether is 0.2 to 2 parts by mass, and / or the content of 15-crown-5 is 0.01 to 2 parts by mass, and / or the content of 18-crown-6 is 0.01 to 2 parts by mass, and / or the content of 21-crown-7 is 0.01 to 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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