Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. A positive electrode sheet in the secondary battery comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab, wherein the positive electrode active material layer is arranged on at least one surface of the positive electrode current collector; a first recess exposing the positive electrode current collector is disposed in the positive electrode active material layer; the positive electrode tab is arranged in the first recess and is connected to the positive electrode current collector; and an insulating tape is arranged on the surface of the positive electrode tab and is arranged in a region, corresponding to the first recess, in the surface of the positive electrode sheet that is away from the positive electrode tab, the melting point of the insulating tape being 250-450°C. An electrolyte comprises carbonic ester and carboxylic ester; and on the basis of the mass of the electrolyte, the mass percentage content of the carbonic ester is A, the mass percentage content of the carboxylic ester is B, and A and B satisfy: 75%≤A+B≤88% and 1<A / B. By means of the above arrangement, the secondary battery has good reliability.

Description

Secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on September 7, 2023, with application number 202311150807.9 and invention name “A Secondary Battery and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0003] Secondary batteries generally include a positive electrode, a negative electrode, a separator, an electrolyte, and a packaging bag. Due to their high energy density, high power density, light weight, small size, and long cycle life, they are widely used in consumer electronics (3C) products. However, when secondary batteries encounter extreme environmental conditions, they may catch fire and explode, posing a threat to consumer safety. Therefore, ensuring the reliability of secondary batteries is particularly important. High-temperature short circuits are a key component of secondary battery reliability testing. When an external short circuit occurs, excessive heat generation can cause a sudden rise in the secondary battery temperature, leading to a local short circuit and safety issues. Therefore, how to improve the high-temperature short circuit pass rate of secondary batteries, thereby improving their reliability, has become a technical problem that needs to be solved urgently by those skilled in the art.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and an electronic device to improve the reliability of the secondary battery.

[0006] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides a secondary battery, which includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode collector, a positive electrode active material layer and a positive electrode tab, the positive electrode active material layer is arranged on at least one surface of the positive electrode collector, a first groove exposing the positive electrode collector is provided in the positive electrode active material layer, the positive electrode tab is arranged in the first groove and connected to the positive electrode collector, and insulating tape is provided on the surface of the positive electrode tab and in the area corresponding to the first groove on the surface of the positive electrode sheet away from the positive electrode tab; the melting point of the insulating tape is 250°C to 450°C; the electrolyte includes carbonate and carboxylate; based on the mass of the electrolyte, the mass percentage of the carbonate is A, the mass percentage of the carboxylate is B, and A and B satisfy: 75%≤A+B≤88% and 1<A / B. The present invention provides insulating tape within the melting point range of the present invention on the surface of the positive electrode tab and in the area corresponding to the first groove on the surface of the positive electrode current collector away from the positive electrode tab, and controls the total content of carbonate and carboxylate in the electrolyte and the carbonate to carboxylate content ratio A / B within the above range. When the secondary battery undergoes a high-temperature short-circuit test, the internal temperature of the secondary battery rises rapidly, generating a large amount of heat in the secondary battery. The insulating tape has good high-temperature stability and low thermal shrinkage, maintaining its intact state when attached, providing good protection for the positive electrode tab. This reduces the possibility of the positive electrode tab contacting the negative electrode tab after being exposed, thereby reducing the risk of a short circuit. The electrolyte has good stability at high temperatures, few side reactions, and low gas production, reducing the risk of secondary battery deformation. The positive and negative electrode tabs can maintain their original relative positions, thereby reducing the risk of internal short circuits caused by contact between the positive and negative electrode tabs. As a result, the insulating tape and the electrolyte work synergistically, improving the high-temperature short-circuit pass rate of the secondary battery and improving the reliability of the secondary battery.

[0008] In one embodiment of the present application, the melting point of the insulating tape is 250° C. to 400° C. By controlling the melting point of the insulating tape within the above range, the high-temperature short-circuit pass rate of the secondary battery can be improved, thereby reducing the production cost of the secondary battery.

[0009] In one embodiment of the present application, the negative electrode plate includes a negative electrode current collector, a negative electrode active material layer, and a negative electrode tab. The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. A second groove exposing the negative electrode current collector is disposed in the negative electrode active material layer. The negative electrode tab is disposed in the second groove and is connected to the negative electrode current collector. The surface of the negative electrode plate away from the negative electrode tab is provided with tab protection tape in an area corresponding to the second groove. The area on the surface of the positive electrode plate opposite to the second groove and the area on the surface of the positive electrode plate opposite to the aforementioned tab protection tape are each provided with insulating tape. By providing insulating tape in the area on the surface of the positive electrode plate opposite to the second groove and the area on the surface of the positive electrode plate opposite to the tab protection tape, the risk of internal short circuit at high temperature of the secondary battery can be further reduced.

[0010] In one embodiment of the present application, the insulating tape includes a substrate and an adhesive layer disposed on one surface of the substrate; the substrate comprises at least one of polyethylene terephthalate, polyethylene, polytetrafluoroethylene, polyvinyl chloride, polyimide, or polypropylene. These substrates have high melting points and good thermal stability, and their use is beneficial in improving the high-temperature short-circuit pass rate of secondary batteries.

[0011] In one embodiment of the present application, the length of the insulating tape applied to the surface of the positive electrode tab along the length direction of the positive electrode tab is 3 to 4 times the width of the positive electrode tab; and the width of the insulating tape applied to the surface of the positive electrode tab along the width direction of the positive electrode tab is 0.25 to 0.4 times the width of the positive electrode tab. Controlling the length and width of the insulating tape covering the positive electrode tab within the above ranges helps improve the coverage of the insulating tape on the positive electrode tab, thereby improving the high-temperature short-circuit pass rate of the secondary battery.

[0012] In one embodiment of the present application, the thermal shrinkage of the insulating tape at 300°C is less than or equal to 1% along both the length and width directions of the insulating tape, indicating that the insulating tape has good high-temperature stability at 300°C.

[0013] In one embodiment of the present application, the carbonate includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, dioctyl carbonate, diamyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate or propyl carbonate; the carboxylic acid ester includes at least one of ethyl acetate, propyl propionate, butyl acetate, ethyl propionate, propyl acetate or butyl propionate.

[0014] In one embodiment of the present application, the carbonate comprises at least one of ethylene carbonate, propylene carbonate, or diethyl carbonate, and the carboxylate comprises at least one of propyl acetate or propyl propionate; 75% ≤ A + B ≤ 88% and 2% ≤ AB ≤ 5%. Selecting the aforementioned carbonates and carboxylates, and regulating the total mass A + B of the carbonate and carboxylate in the electrolyte, as well as the difference AB between the carbonate and carboxylate contents, within the aforementioned ranges, can further reduce the probability of explosion caused by excessive gas production within the secondary battery, thereby further improving the reliability of the secondary battery.

[0015] In one embodiment of the present application, a secondary battery includes a packaging bag containing an electrode assembly and an electrolyte. The positive and negative electrode tabs extend from the packaging bag. Sealants are provided on each of the positive and negative electrode tabs, sealing the sealants to the packaging bag. The melting point of the sealant is between 130°C and 150°C. Controlling the melting point of the sealant within this range further improves the reliability of the secondary battery.

[0016] In one embodiment of the present application, the sealant includes at least one of polypropylene, polyethylene, polyethylene terephthalate or polyethylene naphthalate.

[0017] A second aspect of the present application provides an electronic device comprising the secondary battery according to any one of the aforementioned embodiments.

[0018] Beneficial effects of this application:

[0019] The present application provides a secondary battery and an electronic device, wherein the secondary battery is provided with insulating tape within the melting point range of the present application on the surface of the positive electrode tab and in an area corresponding to the first groove on the surface of the positive electrode tab away from the positive electrode tab, and the total content of carbonate and carboxylate in the electrolyte and the content ratio A / B of carbonate and carboxylate are controlled within the above range. When the secondary battery undergoes a high-temperature short-circuit test, the internal temperature of the secondary battery rises rapidly, and a large amount of heat is generated in the secondary battery. The insulating tape has good high-temperature stability and low thermal shrinkage, and can maintain its intact state when attached, providing good protection for the positive electrode tab, thereby reducing the possibility of the positive electrode tab contacting the negative electrode tab after being exposed and causing a short circuit. The electrolyte has good stability at high temperatures, has few side reactions and low gas production, reduces the risk of secondary battery deformation, and can maintain the original relative position of the electrode sheets, thereby reducing the risk of internal short circuit caused by contact between the positive and negative electrode sheets. As a result, the insulating tape and the electrolyte work synergistically, improving the high-temperature short-circuit pass rate of the secondary battery and improving the reliability of the secondary battery.

[0020] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0022] FIG1 is a schematic diagram of the pasting position of the insulating tape in one embodiment of the present application;

[0023] FIG2 is a schematic diagram of the pasting position of the insulating tape on the surface of the positive electrode tab according to an embodiment of the present application;

[0024] FIG3 is a schematic diagram of the pasting position of the insulating tape in FIG2 on the surface of the positive electrode current collector away from the positive electrode tab and corresponding to the first groove;

[0025] FIG4 is a schematic diagram of the pasting position of the insulating tape in another embodiment of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0028] When the secondary battery is abused and produces too much heat, it is exposed to high temperatures (temperature ≥ 150 ° C). The diaphragm is prone to shrinkage, which can easily cause the positive and negative pole pieces to contact and form an internal short circuit. Since the temperature of the positive pole ear, especially the aluminum pole ear, is often the highest, the pole ear protective glue and the exposed sealant will melt, causing the positive pole ear at the weld to contact the large area of ​​the negative pole piece. The area of ​​the internal short circuit of the secondary battery is expanded. At the same time, the side reaction of the electrolyte at high temperature will intensify and generate a large amount of gas. The migration of gas inside the secondary battery will cause the separation of the positive pole piece, diaphragm, and negative pole piece, which will cause the lithium ions to be unable to be normally deintercalated during the charge and discharge process of the secondary battery, resulting in capacity loss, or the positive and negative pole pieces short-circuit and fire, causing the secondary battery to explode. In addition, the gas cannot be discharged in time, which will cause the secondary battery to burn and explode. Based on this, the present application provides a secondary battery and an electronic device.

[0029] The first aspect of the present application provides a secondary battery, which includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode collector, a positive electrode active material layer and a positive electrode tab, the positive electrode active material layer is arranged on at least one surface of the positive electrode collector, a first groove exposing the positive electrode collector is provided in the positive electrode active material layer, the positive electrode tab is arranged in the first groove and connected to the positive electrode collector, and insulating tape is provided on the surface of the positive electrode tab and in the area corresponding to the first groove on the surface of the positive electrode sheet away from the positive electrode tab; the melting point of the insulating tape is 250°C to 450°C; the electrolyte includes carbonate and carboxylate; based on the mass of the electrolyte, the mass percentage of the carbonate is A, the mass percentage of the carboxylate is B, and A and B satisfy: 75%≤A+B≤88% and 1<A / B.

[0030] As shown in Figures 1 to 4, for ease of understanding, a three-dimensional rectangular coordinate system is established with the length direction of the positive electrode sheet 10 itself as the X direction, the width direction of the positive electrode sheet 10 itself as the Y direction, and the thickness direction of the positive electrode sheet 10 itself as the Z direction. It can be understood that the length direction, width direction, and thickness direction of the positive electrode current collector 11, the positive electrode active material layer 12, the negative electrode sheet 20, and the separator are the same as those of the positive electrode sheet. The above-mentioned "positive electrode active material layer is provided on at least one surface of the positive electrode current collector" means that the positive electrode active material layer is provided on one surface or both surfaces of the positive electrode current collector, wherein the above-mentioned "surface" can be a partial surface of the positive electrode current collector or the entire surface of the positive electrode current collector. For example, in some embodiments, as shown in Figure 1, the positive electrode current collector 11 includes a first surface 11a and a second surface 11b, and the positive electrode active material layer 12 is provided on both surfaces of the positive electrode current collector 11, namely, the first surface 11a and the second surface 11b. In other embodiments, the positive electrode active material layer 12 is disposed on one surface of the positive electrode current collector 11, which may be the first surface 11a or the second surface 11b. As shown in Figures 1 and 2, a first groove 16 is provided in the positive electrode active material layer 12, exposing the positive electrode current collector 11. The positive electrode tab 13 is disposed in the first groove 16 and connected to the positive electrode current collector 11. The positive electrode tab 13 is connected to the first surface 11a of the positive electrode current collector 11. Insulating tape 14 is provided on the surface of the positive electrode tab 13. As shown in Figures 1 and 3, the insulating tape 14 is provided on the surface of the positive electrode sheet 10 away from the positive electrode tab 13 in the area corresponding to the first groove 16.

[0031] For example, the melting point of the insulating tape is 250°C, 300°C, 350°C, 400°C, 450°C, or any value between any two of the above numerical ranges. When the melting point of the insulating tape is less than 250°C, the melting point of the insulating tape is too low. When a large amount of heat is generated in the secondary battery, the insulating tape is prone to thermal shrinkage, and the probability of maintaining its intact state when pasted is reduced. It will fall off the surface of the positive electrode tab, and the positive electrode tab will be easily exposed, thereby contacting the negative electrode tab, expanding the area of ​​the internal short circuit of the secondary battery, causing a short circuit in the secondary battery, and increasing the probability of the tab causing a safety risk. Insulating tape with a melting point greater than 450°C is difficult to produce and has a high cost, which will increase the production cost of the secondary battery and is not conducive to industrial mass production.

[0032] For example, the value of A+B is 75%, 76%, 78%, 80%, 80%, 82%, 84%, 86%, 88%, or any value between any two of the above numerical ranges. For example, the value of A / B is 1.01, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.49, or any value between any two of the above numerical ranges. When the total carbonate and carboxylate content (A+B) in the electrolyte exceeds 88%, the lithium salt and additive content in the electrolyte is too low. Insufficient lithium salt content will affect the charge and discharge performance of the secondary battery. Insufficient additive content will hinder the additive's inherent function, affecting the performance of the secondary battery and the additive. For example, film-forming additives can decompose before the carbonate and carboxylate in the electrolyte during the initial charge and discharge, forming a stable solid electrolyte interface film on the negative electrode surface, thereby protecting the electrode from damage by carbonate and carboxylate, and improving the battery's lifespan and safety. However, if the film-forming additive content is too low, the battery's lifespan and safety will be affected. When the total carbonate and carboxylate content (A+B) in the electrolyte is less than 75%, the electrolyte's ability to dissolve lithium salt is limited, reducing the lithium ions available to the secondary battery during charge and discharge, which will affect the battery's charge and discharge performance and cycle life. Carbonates offer excellent stability at high temperatures and generate low gassing, while carboxylates have low viscosity, facilitate lithium ion transport, and contribute to high electrolyte kinetics. When the value of A / B is less than or equal to 1, the relative content of carbonate in the solvent is too small, which will affect the high-temperature stability of the electrolyte, is not conducive to reducing the gas production of the electrolyte at high temperature, and thus increases the risk of explosion of the secondary battery due to increased gas production.

[0033] The present invention provides insulating tape within the melting point range of the present invention on the surface of the positive electrode tab and on the surface of the positive electrode sheet away from the positive electrode tab in an area corresponding to the first groove, and controls the total content of carbonate and carboxylate in the electrolyte and the carbonate to carboxylate content ratio A / B within the above range. When the secondary battery undergoes a high-temperature short-circuit test, the internal temperature of the secondary battery rises rapidly, generating a large amount of heat in the secondary battery. The insulating tape has good high-temperature stability and low thermal shrinkage, maintaining its intact state at the time of attachment, and providing good protection for the positive electrode tab. This reduces the possibility of the positive electrode tab contacting the negative electrode sheet after being exposed, thereby reducing the risk of a short circuit. The electrolyte has good stability at high temperatures, with few side reactions and low gas production, reducing the risk of secondary battery deformation, and allowing the electrodes to maintain their original relative positions, thereby reducing the risk of internal short circuits caused by contact between the positive and negative electrode sheets. As a result, the insulating tape and the electrolyte work synergistically, improving the high-temperature short-circuit pass rate of the secondary battery and improving the reliability of the secondary battery.

[0034] In one embodiment of the present application, the melting point of the insulating tape is between 250°C and 400°C. For example, the melting point of the insulating tape is 250°C, 300°C, 350°C, 400°C, or any value between any two of the above ranges. Insulating tape with a melting point within the above range is easier to produce. By regulating the melting point of the insulating tape within the above range, the high-temperature short-circuit pass rate of the secondary battery can be improved, thereby reducing the production cost of the secondary battery.

[0035] In one embodiment of the present application, the positive electrode tab includes any one of an aluminum tab or an aluminum alloy tab.

[0036] In one embodiment of the present application, the negative electrode plate includes a negative electrode current collector, a negative electrode active material layer and a negative electrode tab, and the negative electrode active material layer is arranged on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer is arranged on at least one surface of the negative electrode current collector" means that the negative electrode active material layer is arranged on one surface or two surfaces of the negative electrode current collector, wherein the above-mentioned "surface" can be a partial surface of the negative electrode current collector or the entire surface of the negative electrode current collector. A second groove is provided in the negative electrode active material layer to expose the negative electrode current collector, and the negative electrode tab is arranged in the second groove and connected to the negative electrode current collector. The area of ​​the surface of the negative electrode plate away from the negative electrode tab corresponding to the second groove is provided with tab protection tape. The area of ​​the positive electrode plate surface opposite to the second groove and the area of ​​the positive electrode plate surface opposite to the tab protection tape are each provided with insulating tape. It should be noted that the positive electrode sheet in the "area where the surface of the positive electrode sheet is opposite to the second groove" and the positive electrode sheet in the "area where the surface of the positive electrode sheet is opposite to the tab protective tape" are not the same layer of positive electrode sheets, but two layers of positive electrode sheets adjacent to the negative electrode sheets respectively. The above-mentioned "two layers of positive electrode sheets" can be two positive electrode sheets, or two layers formed by winding a positive electrode sheet. As shown in Figure 4, the negative electrode sheet 20 includes a negative electrode collector 21, a negative electrode active material layer 22 and a negative electrode tab 23. The negative electrode collector 21 includes a third surface 21a and a fourth surface 21b. The negative electrode active material layer 22 is arranged on the third surface 21a and the fourth surface 21b of the negative electrode collector 21. A second groove 26 exposing the negative electrode collector 21 is provided in the negative electrode active material layer 22. The negative electrode tab 23 is arranged in the second groove 26 and is connected to the negative electrode collector 21. The negative electrode tab 23 Connected to the third surface 21a of the negative electrode current collector 21, the surface of the negative electrode tab 23 is provided with tab protection tape 17, the surface of the negative electrode plate 20 away from the negative electrode tab 23 is provided with tab protection tape 17, the area of ​​the positive electrode plate 10 surface opposite to the second groove 26 is provided with insulating tape 14, and the area of ​​the positive electrode plate 10 surface opposite to the tab protection tape 17 provided in the area corresponding to the second groove 26 on the surface of the negative electrode plate 20 away from the negative electrode tab 23 is also provided with insulating tape 14. By providing insulating tape on the area of ​​the positive electrode plate surface opposite to the second groove, and on the area of ​​the positive electrode plate surface opposite to the tab protection tape provided on the surface of the negative electrode plate away from the second groove, the risk of internal short circuit occurring in the secondary battery at high temperature can be further reduced. As a result, the high-temperature short circuit pass rate of the secondary battery is improved, thereby improving the reliability of the secondary battery.

[0037] In one embodiment of the present application, the negative electrode tab includes any one of a nickel tab and a copper-plated nickel tab.

[0038] The present application does not particularly limit the type of tab protection tape. Those skilled in the art can select tab protection tape known in the art according to actual needs, as long as the purpose of the present application can be achieved.

[0039] In one embodiment of the present application, the insulating tape includes a substrate and an adhesive layer provided on one surface of the substrate; the substrate includes at least one of polyethylene terephthalate, polyimide, or polypropylene. The aforementioned types of substrates have a high melting point and good thermal stability. Selecting the aforementioned types of substrates is conducive to making the insulating tape have a high melting point. In this way, when the secondary battery is in a high temperature state, the insulating tape has a small thermal shrinkage rate and good thermal stability, and can maintain its finished state when pasted, thereby protecting the positive electrode tab by the insulating tape, reducing the possibility of contact with the negative electrode tab, reducing the area of ​​internal short circuit in the secondary battery, thereby reducing the probability of internal short circuit in the secondary battery, and improving the high-temperature short circuit pass rate of the secondary battery.

[0040] The present application does not particularly limit the type of material for the adhesive layer. Persons skilled in the art may select materials known in the art based on actual needs, as long as they can achieve the objectives of the present application. For example, the adhesive layer material includes at least one of acrylate, rubber, or silicone. Furthermore, the acrylate includes at least one of methyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, or octyl methacrylate. The rubber includes at least one of isoprene or styrene.

[0041] In one embodiment of the present application, as shown in FIG2 , along the longitudinal direction X of the positive electrode sheet 10 , the length L of the insulating tape 14 provided on the surface of the positive electrode tab is 141 The width W of the positive electrode tab 13 13 3 to 4 times of the width of the positive electrode tab. For example, the length of the insulating tape provided on the surface of the positive electrode tab is 3 times, 3.2 times, 3.4 times, 3.6 times, 3.8 times, 4 times the width of the positive electrode tab or any value between any two of the above numerical ranges. It should be noted that the width direction of the positive electrode tab is the same as the length direction of the positive electrode sheet, and the length direction of the positive electrode tab is the same as the width direction of the positive electrode sheet. The length of the insulating tape provided on the surface of the positive electrode tab is regulated within the above range. When the secondary battery is in a high temperature state, the insulating tape can cover the surface of the positive electrode tab, so that the positive electrode tab is protected by the insulating tape, reducing the possibility of contact with the negative electrode sheet, reducing the area of ​​internal short circuit of the secondary battery, thereby reducing the probability of internal short circuit of the secondary battery, and improving the high-temperature short circuit pass rate of the secondary battery.

[0042] In one embodiment of the present application, as shown in FIG2 , along the width direction Y of the positive electrode sheet 10 , the width W of the insulating tape 14 provided on the surface of the positive electrode tab is 141 is the width W of the positive electrode 1010 0.25 to 0.4 times of the width of the positive electrode tab. For example, the width of the insulating tape provided on the surface of the positive electrode tab is 0.25 times, 0.28 times, 0.31 times, 0.34 times, 0.37 times, 0.4 times, or any value between any two of the above numerical ranges, of the width of the positive electrode tab. By regulating the width of the insulating tape provided on the surface of the positive electrode tab within the above range, when the secondary battery is in a high temperature state, the insulating tape can cover the surface of the positive electrode tab, so that the positive electrode tab is protected by the insulating tape, reducing the possibility of contact with the negative electrode tab, reducing the area of ​​the internal short circuit of the secondary battery, thereby reducing the probability of internal short circuit of the secondary battery, and improving the high-temperature short circuit pass rate of the secondary battery.

[0043] In the present application, there is no particular restriction on the size of the insulating tape provided at locations other than the surface of the positive electrode tab, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved.

[0044] In one embodiment of the present application, the thermal shrinkage of the insulating tape at a temperature of 300°C is less than or equal to 1% along both the length and width directions of the insulating tape. For example, along the length direction of the insulating tape, the thermal shrinkage at a temperature of 300°C is 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, or any value between any two of the aforementioned numerical ranges. For example, along the width direction of the insulating tape, the thermal shrinkage at a temperature of 300°C is 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, or any value between any two of the aforementioned numerical ranges. This indicates that the insulating tape has good high-temperature stability at a temperature of 300°C.

[0045] In one embodiment of the present application, a secondary battery includes a packaging bag, an electrode assembly and an electrolyte are contained in the packaging bag, a positive electrode tab and a negative electrode tab extend from the packaging bag, and a sealant is provided on each of the positive electrode tab and the negative electrode tab, and the sealant is sealed to the packaging bag; the melting point of the sealant is 130°C to 150°C. For example, the melting point of the sealant is 130°C, 135°C, 140°C, 145°C, 150°C, or any value between any two of the above numerical ranges. For example, as shown in FIG2 , a sealant 15 is provided on the positive electrode tab 13. The melting point of the sealant is controlled within the above range. When the internal temperature of the secondary battery reaches the melting point range of the sealant, the sealant will melt to reduce the packaging strength of the connection area between the sealant and the packaging bag, allowing the gas generated by the high temperature to rush out of the connection area between the sealant and the packaging bag, reducing the heat accumulation and deformation degree inside the secondary battery, thereby further improving the reliability of the secondary battery.

[0046] In one embodiment of the present application, the sealant comprises at least one of polypropylene (PP), polyethylene, polyethylene terephthalate (PET), or polyethylene naphthalate (PEN). The present application does not particularly limit the structure of the sealant, as long as it can achieve the objectives of the present application. For example, the sealant can have a single-layer structure or a multi-layer structure, where multi-layer can refer to two, three, or four layers. For example, multi-layer sealants include, but are not limited to, PP / PET / PP and PP / PEN / PP.

[0047] In one embodiment of the present application, the carbonate includes at least one of ethylene carbonate (EC, also known as ethylene carbonate), propylene carbonate (PC, also known as propylene carbonate), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), dioctyl carbonate, dipentyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate or propyl carbonate; the carboxylic acid ester includes at least one of ethyl acetate, propyl propionate, butyl acetate, ethyl propionate, propyl acetate (EP) or butyl propionate.

[0048] In one embodiment of the present application, carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC) or diethyl carbonate (DEC), and carboxylate includes at least one of propyl acetate (EP) or propyl propionate. In certain embodiments, carbonate includes EC, PC and DEC, and carboxylate includes EP and propyl propionate. 75%≤A+B≤88% and 2%≤AB≤5%. For example, A+B is 75%, 76%, 78%, 80%, 82%, 83%, 84%, 85%, 86%, 87%, 88% or any numerical value between any two numerical ranges. For example, the value of AB is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any numerical value between any two numerical ranges. By selecting the above-mentioned types of carbonates and carboxylates, and regulating the total mass A+B of the carbonates and carboxylates, as well as the content difference AB of the carbonates and carboxylates within the above-mentioned ranges, the gas production of the electrolyte at high temperatures can be further reduced, thereby further reducing the probability of explosion caused by large gas production inside the secondary battery, and further improving the reliability of the secondary battery.

[0049] Furthermore, based on the mass of the electrolyte, the mass percentage of DEC is 5% to 10%, the mass percentage of EC is 10% to 20%, the mass percentage of PC is 20% to 25%, the mass percentage of EP is 10% to 20%, and the mass percentage of propyl propionate is 20% to 25%.

[0050] In one embodiment of the present application, the electrolyte includes a carbonate, a carboxylate, and a lithium salt. The present application does not particularly limit the content of the lithium salt, as long as the purpose of the present application can be achieved. In one embodiment of the present application, the mass percentage of the lithium salt is 8% to 15% based on the mass of the electrolyte. For example, the mass percentage of the lithium salt is 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value between any two of the above numerical ranges.

[0051] The present application does not particularly limit the type of lithium salt, as long as it can achieve the purpose of this application. For example, the lithium salt includes but is not limited to at least one of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or LiDFOB.

[0052] In one embodiment of the present application, the electrolyte includes a carbonate, a carboxylate, a lithium salt, and an additive. The present application does not particularly limit the content of the additive, as long as it can achieve the purpose of the present application. For example, based on the mass of the electrolyte, the weight percentage of the additive is 4% to 15%. For example, the weight percentage of the additive is 4%, 6%, 8%, 10%, 12%, 14%, 15%, or any value between any two of the above ranges.

[0053] The application is not particularly limited to the type of additive, as long as the purpose of the application can be achieved. Exemplarily, in some embodiments, the additive includes but is not limited to succinonitrile, adiponitrile, pimelonitrile, suberonitrile, 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,6-dicyano-2-methyl-5-methyl-3-hexene, ethylene glycol diethyl cyanide, 1,3,6-hexanetricarbonitrile or at least one of 1,2,3-tris(2-cyano)propane. In other embodiments, the additive includes but is not limited to at least one of succinonitrile, adiponitrile, or 1,3,6-hexanetricarboxylic acid nitrile.

[0054] The present application does not particularly limit the type of positive electrode current collector, as long as it can achieve the purpose of the present application. For example, the positive electrode current collector can include aluminum foil, aluminum alloy foil, etc.

[0055] The present application has no special restrictions on the positive electrode active material layer, as long as the purpose of the present application can be achieved. In one embodiment of the present application, the positive electrode active material layer includes a positive electrode active material. The present application has no special restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. Optionally, the positive electrode active material layer also includes a positive electrode conductor and a positive electrode binder. The present application has no special restrictions on the types of positive electrode conductors and positive electrode binders in the positive electrode active material layer, as long as the purpose of the present application can be achieved. The present application has no special restrictions on the mass ratio of the positive electrode active material, positive electrode conductor and positive electrode binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer is (97.5-97.9):(0.9-1.7):(1.0-2.0).

[0056] The thickness of the positive electrode current collector and the positive electrode active material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0057] The present application has no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam.

[0058] The present application has no particular restrictions on the negative electrode active material layer, as long as the purpose of the present application can be achieved. In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material. The present application has no particular restrictions on the type of negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microbeads, tin-based materials, silicon-based materials, lithium titanate, transition metal nitrides or natural flake graphite. Optionally, the negative electrode active material layer also includes at least one of a negative electrode conductor, a thickener, and a negative electrode binder. The present application has no particular restrictions on the types of negative electrode conductors, thickeners and negative electrode binders in the negative electrode active material layer, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the mass ratio of the negative electrode active material, negative electrode conductor, thickener and negative electrode binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the mass ratio of the negative electrode active material, the negative electrode conductor, the thickener, and the negative electrode binder in the negative electrode active material layer is (97-98):(0-1.5):(0.5-1.5):(1.0-1.9).

[0059] The thickness of the negative electrode current collector and the negative electrode active material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 5 μm to 20 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

[0060] The present application does not particularly limit the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0061] The present application has no particular limitation on packaging bags. Those skilled in the art may select packaging bags known in the art according to actual conditions, as long as the purpose of the present application can be achieved.

[0062] The present application does not particularly limit the type of secondary battery, which may include any device that undergoes an electrochemical reaction. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), sodium ion secondary batteries (sodium ion batteries), lithium polymer secondary batteries, and lithium ion polymer secondary batteries.

[0063] This application does not impose any particular restrictions on the preparation method of a secondary battery, and any preparation method known in the art may be selected as long as the purpose of this application can be achieved. For example, the preparation method of a secondary battery includes but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, affixing insulating tape thereto, and then winding, folding, and other operations as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain a secondary battery; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, affixing insulating tape thereto, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain a secondary battery.

[0064] A second aspect of the present application provides an electronic device comprising the secondary battery according to any one of the aforementioned embodiments.

[0065] The electronic devices of the present application are not particularly limited and may include, but are not limited to, the following types: laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0066] Example

[0067] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0068] Test methods and equipment:

[0069] 1. Thermal shrinkage test:

[0070] Take an insulating tape sample, measure the length and width as A and B; put it into a 300℃ oven for 1 hour; and measure the length and width after high-temperature baking again as A' and B'.

[0071] Thermal shrinkage in the longitudinal direction S L (%) = [1 - (A` / A)] × 100%;

[0072] Thermal shrinkage in width direction S W (%) = [1-(B` / B)] × 100%.

[0073] 2. High temperature short circuit pass rate test:

[0074] (1) Pretreatment: The lithium-ion battery was fully charged at room temperature (25°C ± 2°C) to prepare the sample. The full charging step was to charge the battery to 4.5V at a constant current of 0.2C, and then charge the battery to 0.25C at a constant voltage of 4.5V.

[0075] (2) Place the sample in a test environment at 55±2℃, use a 60±20mΩ load resistor to short-circuit the positive and negative electrodes of the sample, and test until the voltage is lower than 0.1V;

[0076] (3) The test ends when one of the following conditions is met:

[0077] 1) Stop when the sample voltage is lower than 0.1V and the surface temperature of the main body area drops to the test ambient temperature ±10℃;

[0078] 2) If the voltage cannot be reduced to 0.1V, the surface temperature of the main body area is allowed to drop to the test environment temperature;

[0079] The main body area refers to the area where the positive electrode sheet, the negative electrode sheet and the separator of the electrode assembly contained in the lithium-ion battery are all in a flat state.

[0080] 3. Measurement frequency:

[0081] The voltage internal resistance measurement uses the 1KHz specification and is measured once after the pretreatment in step (1) and after the test in step (3);

[0082] Judgment criteria: no explosion, sample surface temperature does not exceed 150℃, and no fire.

[0083] 100 lithium-ion batteries were tested in each embodiment and comparative example, and the high-temperature short-circuit pass rate (%) = the number of passed batteries / 100×100%.

[0084] Example 1-1

[0085] <Preparation of Insulating Tape>

[0086] The insulating adhesive tape comprises a base material and an adhesive layer. The adhesive layer is arranged on one surface of the base material. The base material is polyimide and the material of the adhesive layer is styrene.

[0087] The melting point of insulating tape is 400℃.

[0088] <Preparation of sealant>

[0089] The sealant has a single-layer structure and includes polypropylene and polyethylene, and the mass ratio of polypropylene to polyethylene is 2:1.

[0090] The melting point of the sealant is 140°C.

[0091] <Preparation of Electrolyte>

[0092] In a dry argon atmosphere glove box, diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), propyl acetate (EP), and propyl propionate were mixed to obtain a solvent. Then, additives such as succinonitrile, adiponitrile, and 1,3,6-hexanetricarbonitrile were added to the solvent, and lithium salt LiBF4 was dissolved and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of DEC is N DEC =8%, PC mass percentage N PC =23%, EC mass percentage N EC =13%, mass percentage of EP N EP =18%, mass percentage of propyl propionate N PP=23%, the mass percentage of succinonitrile is 2%, the mass percentage of adiponitrile is 3%, the mass percentage of 1,3,6-hexanetricarbonitrile is 3%, the mass percentage of LiBF4 is N L =7%.

[0093] <Preparation of positive electrode sheet>

[0094] The positive electrode active material LiCoO2, the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder PVDF were mixed in a mass ratio of 97.5:1:1.5. NMP was added as a solvent and stirred in a vacuum mixer until a solid content of 75wt% and a uniform positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a 10μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a positive electrode sheet coated with a single-sided positive electrode active material layer (50μm thick). The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a double-sided positive electrode active material layer. The positive electrode tab was then cold pressed, cut, and welded to the aluminum tab to obtain a 96mm×851mm positive electrode sheet for use. The positive tab was provided with the aforementioned sealant.

[0095] <Preparation of negative electrode sheet>

[0096] The negative electrode active material graphite, the negative electrode conductive agent Super P, the thickener carboxymethyl cellulose, and the negative electrode binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97.5:1:0.5:1. Deionized water was then added as a solvent and stirred in a vacuum mixer until a uniform negative electrode slurry with a solids content of 50 wt% was obtained. The negative electrode slurry was evenly coated on one surface of an 8 μm thick negative electrode current collector copper foil and dried at 85°C to obtain a negative electrode sheet coated on one side with a negative electrode active material layer (60 μm thick). The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode active material layer. The negative electrode sheet was then cold pressed, cut, and welded to a nickel tab, resulting in a 98 mm x 867 mm negative electrode sheet for later use. The negative electrode tab was coated with the aforementioned sealant.

[0097] <Preparation of Separator>

[0098] A polyethylene film with a thickness of 15 μm (manufacturer: Hunan Zhongli New Materials Co., Ltd.) was used.

[0099] <Preparation of lithium-ion batteries>

[0100] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The lithium-ion battery is produced through vacuum packaging, static standing, formation, capacity measurement, degassing, and trimming.

[0101] Among them, as shown in Figure 1, the surface of the positive electrode tab is pasted with insulating tape, and the area of ​​the surface of the positive electrode sheet away from the positive electrode tab corresponding to the first groove is pasted with insulating tape; as shown in Figure 4, the area of ​​the surface of the positive electrode sheet opposite to the second groove is pasted with insulating tape, and the area of ​​the surface of the positive electrode sheet opposite to the tab protection tape set on the surface of the negative electrode sheet away from the second groove is pasted with insulating tape.

[0102] Along the length direction of the positive electrode sheet, the length of the insulating tape provided on the surface of the positive electrode tab is 3.5 times the width of the positive electrode tab. 13 =6mm, length of insulating tape L 141 = 21mm; along the width direction of the positive electrode sheet, the width of the insulating tape provided on the surface of the positive electrode tab is 0.3 times the width of the positive electrode sheet, wherein the width W of the positive electrode sheet 10 =96mm, width of insulating tape W 141 =29mm.

[0103] Example 1-2

[0104] The preparation method was the same as that of Example 1-1, except that the base material in the preparation of insulating tape was changed to polyethylene terephthalate so that the melting point of the insulating tape was 250°C.

[0105] Example 1-3 to Example 1-11

[0106] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0107] When the mass percentages of carbonate and carboxylate change, the mass percentage of lithium salt changes accordingly, while the mass percentage of additives remains unchanged. The sum of the mass percentages of carbonate, carboxylate, lithium salt and additives is 100%.

[0108] Example 2-1 to Example 2-8

[0109] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0110] Among them, when the length of the insulating tape set on the surface of the positive electrode tab changes as a multiple of the width of the positive electrode tab, the width of the positive electrode tab remains unchanged and the length of the insulating tape changes; when the width of the insulating tape set on the surface of the positive electrode tab changes as a multiple of the width of the positive electrode sheet, the width of the positive electrode sheet remains unchanged and the width of the insulating tape changes.

[0111] Examples 2-9

[0112] The preparation process was the same as that of Example 1-1, except that the mass ratio of polypropylene to polyethylene in the preparation of sealant was adjusted to 1:3 so that the melting point of the sealant was 130°C.

[0113] Example 2-10

[0114] The preparation process was the same as that of Example 1-1, except that the mass ratio of polypropylene to polyethylene in the preparation of sealant was adjusted to 4:1 so that the melting point of the sealant was 150°C.

[0115] Example 2-11

[0116] The preparation process was the same as that of Example 1-1, except that the mass ratio of polypropylene to polyethylene in the preparation of sealant was adjusted to 1:4 so that the melting point of the sealant was 120°C.

[0117] Example 2-12

[0118] The preparation process was the same as that of Example 1-1, except that the mass ratio of polypropylene to polyethylene in the preparation of sealant was adjusted to 6:1 so that the melting point of the sealant was 160°C.

[0119] Comparative Example 1

[0120] The preparation method was the same as that of Example 1-1 except that the substrate in the preparation of insulating tape was changed to a biaxially oriented polypropylene (BOPP) film so that the melting point of the insulating tape was 200°C.

[0121] Comparative Examples 2 to 5

[0122] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0123] When the mass percentages of carbonate and carboxylate change, the mass percentage of lithium salt changes accordingly, while the mass percentage of additives remains unchanged. The sum of the mass percentages of carbonate, carboxylate, lithium salt and additives is 100%.

[0124] Comparative Example 6 and Comparative Example 7

[0125] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Comparative Example 1.

[0126] When the mass percentages of carbonate and carboxylate change, the mass percentage of lithium salt changes accordingly, while the mass percentage of additives remains unchanged. The sum of the mass percentages of carbonate, carboxylate, lithium salt and additives is 100%.

[0127] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1 and Table 2.

[0128] Table 1

[0129] As can be seen from Examples 1-1 to 1-11 and Comparative Examples 1 to 7, the secondary batteries in the embodiments of the present application have insulating tape within the melting point range of the present application disposed on the surface of the positive electrode tab and in the area corresponding to the first groove on the surface of the positive electrode sheet away from the positive electrode tab, respectively. Furthermore, the total mass A+B of the carbonate and carboxylate esters in the electrolyte and the carbonate and carboxylate content ratio A / B are within the ranges of the present application. The insulating tape has low thermal shrinkage along the length and width directions, and the secondary battery has a higher high-temperature short-circuit pass rate, indicating greater reliability. In contrast, the secondary battery in the comparative example has at least one of the insulating tape disposed on the surface of the positive electrode tab and in the area corresponding to the first groove on the surface of the positive electrode sheet away from the positive electrode tab, the total mass A+B of the carbonate and carboxylate esters in the electrolyte, and the carbonate and carboxylate content ratio A / B outside the ranges of the present application, resulting in a lower high-temperature short-circuit pass rate, indicating poor reliability of the secondary battery in the comparative example.

[0130] The melting point of insulating tape generally affects the reliability of secondary batteries. As can be seen from Examples 1-1, 1-2, and Comparative Example 1, secondary batteries using insulating tape with a melting point within the range of this application exhibit low thermal shrinkage along both the length and width directions, and high high-temperature short-circuit resistance, demonstrating good secondary battery reliability.

[0131] The total mass A+B of carbonate and carboxylate in the electrolyte, the content ratio A / B of carbonate and carboxylate, and the content difference AB of carbonate and carboxylate generally affect the reliability of secondary batteries. As can be seen from Examples 1-1, 1-3 to 1-11, and Comparative Examples 2 to 7, secondary batteries with a total mass A+B of carbonate and carboxylate in the electrolyte and a content ratio A / B of carbonate and carboxylate within the ranges of this application exhibit low thermal shrinkage of the insulating tape along the length and width directions, and high high-temperature short-circuit pass rates for the secondary batteries, indicating good reliability.

[0132] Table 2

[0133] The ratio of the length of the insulating tape provided on the surface of the positive electrode tab to the width of the positive electrode tab, and the ratio of the width of the insulating tape to the width of the positive electrode tab generally affect the reliability of the secondary battery. From Examples 1-1, 2-1 to 2-8, it can be seen that for secondary batteries in which the ratio of the length of the insulating tape provided on the surface of the positive electrode tab to the width of the positive electrode tab, and the ratio of the width of the insulating tape to the width of the positive electrode tab are within the scope of this application, the thermal shrinkage of the insulating tape along the length and width directions is low, and the high-temperature short-circuit pass rate of the secondary battery is high, indicating that the secondary battery has good reliability. Among them, the secondary battery of Example 2-4, although the high-temperature short-circuit pass rate is the same as that of Examples 1-1, 2-1 and 2-2, the length of the insulating tape is longer, which will affect the production cost of the secondary battery, and the capacity loss will be caused by the increase in the volume of the secondary battery, thereby affecting the capacity of the secondary battery. Although the high-temperature short-circuit pass rate of the secondary battery of Example 2-8 is the same as that of Example 1-1, Example 2-5 and Example 2-6, the width of the insulating tape is relatively wide, which will affect the production cost of the secondary battery. In addition, the capacity loss will be caused by the increase in the volume of the secondary battery, thereby affecting the capacity of the secondary battery.

[0134] The melting point of a sealant generally affects the reliability of a secondary battery. As can be seen from Examples 1-1, 2-9, and 2-12, secondary batteries using sealants with melting points within the range of this application exhibit low thermal shrinkage along the length and width of the insulating tape, and high high-temperature short-circuit resistance, demonstrating good secondary battery reliability. Compared with Example 1-1, Example 2-10 and Example 2-11, Example 2-11 uses a secondary battery with a sealant melting point of 120°C. The melting point of the sealant is low, the sealing is relatively biased, and the probability of leakage in the secondary battery is relatively high. Therefore, the high-temperature short-circuit pass rate is lower than that of Example 1-1, Example 2-10 and Example 2-11; Compared with Example 1-1, Example 2-10 and Example 2-11, Example 2-12 uses a secondary battery with a sealant melting point of 160°C. The melting point of the sealant is high. When the internal temperature of the secondary battery rises, the gas generated inside the secondary battery rushes out of the packaging bag relatively slowly, and the secondary battery dissipates heat relatively slowly, resulting in an increased probability of thermal runaway. Therefore, the high-temperature short-circuit pass rate is lower than that of Example 1-1, Example 2-10 and Example 2-11.

[0135] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0136] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0137] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; The positive electrode plate comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab, wherein the positive electrode active material layer is disposed on at least one surface of the positive electrode current collector, a first groove exposing the positive electrode current collector is disposed in the positive electrode active material layer, the positive electrode tab is disposed in the first groove and connected to the positive electrode current collector, and insulating tape is disposed on the surface of the positive electrode tab and in an area corresponding to the first groove in the surface of the positive electrode plate away from the positive electrode tab; The melting point of the insulating tape is 250°C to 450°C; The electrolyte includes carbonate ester and carboxylate ester; Based on the mass of the electrolyte, the mass percentage of the carbonate is A, the mass percentage of the carboxylate is B, and A and B satisfy: 75%≤A+B≤88% and 1<A / B.

2. The secondary battery according to claim 1, wherein The melting point of the insulating tape is 250°C to 400°C.

3. The secondary battery according to claim 1, wherein The negative electrode plate comprises a negative electrode current collector, a negative electrode active material layer and a negative electrode tab, wherein the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector, a second groove exposing the negative electrode current collector is disposed in the negative electrode active material layer, the negative electrode tab is disposed in the second groove and connected to the negative electrode current collector, and a tab protective adhesive tape is disposed in an area corresponding to the second groove on the surface of the negative electrode plate away from the negative electrode tab; The insulating tape is respectively provided on the area on the surface of the positive electrode sheet opposite to the second groove and the area on the surface of the positive electrode sheet opposite to the tab protection tape.

4. The secondary battery according to any one of claims 1 to 3, wherein The insulating adhesive tape comprises a base material and an adhesive layer disposed on one surface of the base material; The substrate includes at least one of polyethylene terephthalate, polyethylene, polytetrafluoroethylene, polyvinyl chloride, polyimide or polypropylene.

5. The secondary battery according to any one of claims 1 to 3, wherein Along the length direction of the positive electrode sheet, the length of the insulating tape disposed on the surface of the positive electrode tab is 3 to 4 times the width of the positive electrode tab; Along the width direction of the positive electrode plate, the width of the insulating tape disposed on the surface of the positive electrode tab is 0.25 to 0.4 times the width of the positive electrode plate.

6. The secondary battery according to any one of claims 1 to 3, wherein Along the length direction and the width direction of the insulating tape, the thermal shrinkage rate of the insulating tape at a temperature of 300° C. is less than or equal to 1%.

7. The secondary battery according to any one of claims 1 to 3, wherein The carbonate comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dioctyl carbonate, diamyl carbonate, ethyl isobutyl carbonate, isopropyl methyl carbonate, di-n-butyl carbonate, diisopropyl carbonate or propyl carbonate; The carboxylic acid ester includes at least one of ethyl acetate, propyl propionate, butyl acetate, ethyl propionate, propyl acetate or butyl propionate.

8. The secondary battery according to claim 7, wherein The carbonate comprises at least one of ethylene carbonate, propylene carbonate or diethyl carbonate, and the carboxylate comprises at least one of propyl acetate or propyl propionate; And 2%≤AB≤5%.

9. The secondary battery according to any one of claims 1 to 3, wherein The secondary battery comprises a packaging bag, the electrode assembly and the electrolyte are contained in the packaging bag, the positive electrode tab and the negative electrode tab extend from the packaging bag, the positive electrode tab and the negative electrode tab are respectively provided with a sealant, and the sealant is sealed and connected to the packaging bag; The melting point of the sealant is 130°C to 150°C.

10. The secondary battery according to claim 9, wherein The sealant includes at least one of polypropylene, polyethylene, polyethylene terephthalate or polyethylene naphthalate.

11. An electronic device, wherein: The electronic device includes the secondary battery according to any one of claims 1 to 10.

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