A secondary battery and electronic device

Abstract

This application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material and a positive additive. The positive active material includes a transition metal element, comprising at least one of Co, Ni, Mn, Fe, or V. The positive additive is a nitrile-containing organic compound with a carbon-to-nitrogen atom ratio of m, where 1 ≤ m ≤ 6, and a weight-average molecular weight of M. w 300≤M w ≤800000; Based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode additive is x%, 0.01≤x≤0.50. The above settings can improve the thermal performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, possess advantages such as environmental friendliness, high energy density, high open-circuit voltage, low self-discharge rate, and long cycle life, and are widely used in various fields such as energy storage, mobile electronic devices, electric vehicles, and aerospace equipment. With the widespread application of lithium-ion batteries, the market is placing increasingly higher demands on their performance. However, in current lithium-ion battery systems, thermal performance has become a bottleneck issue for some projects, severely limiting the application of lithium-ion batteries. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and an electronic device to improve the thermal performance of the secondary battery.

[0004] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0005] This application provides a secondary battery comprising an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material and a positive additive. The positive active material includes a transition metal element, which includes at least one of Co, Ni, Mn, Fe, or V. The positive additive is a nitrile-containing organic compound with a carbon-to-nitrogen atom ratio of m, where 1 ≤ m ≤ 6, and a weight-average molecular weight of M. w 300≤M w ≤800000; Based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode additive is x%, 0.01≤x≤0.50. This is determined by the carbon-nitrogen atom ratio m and the weight-average molecular weight M of the positive electrode additive. w The mass percentage of the positive electrode additive is controlled within the range of this application. The positive electrode additive gives the positive electrode sheet good stability and low oxidation ability to the electrolyte. The content of gas generated by the oxidation of the electrolyte is reduced, and the pass rate of the hot box test of the secondary battery is improved, thereby improving the hot box performance of the secondary battery.

[0006] In some embodiments of this application, the secondary battery satisfies at least one of the following conditions: (1) 3 ≤ m ≤ 4; (2) 300000 ≤ Mw ≤500000; (3)0.30≤x≤0.50. When a secondary battery meets at least one of the above conditions (1) to (3), it is beneficial to further improve the thermal performance of the secondary battery.

[0007] In some embodiments of this application, the positive electrode additive includes at least one selected from polyacrylonitrile, polybutadiene nitrile, poly(5-hexene nitrile), or polyisobutylene nitrile. Using the above-mentioned types of positive electrode additives is beneficial for improving the thermal performance of the secondary battery.

[0008] In some embodiments of this application, 0.1 ≤ xM w / 1000≤300. Preferably, 90≤xM w / 1000≤175. xM w Adjusting the value of / 1000 within the above range is beneficial to improving the thermal performance of the secondary battery.

[0009] In some embodiments of this application, the secondary battery further includes an electrolyte comprising nitrile additives, including at least one selected from butadienenitrile, adiponitrile, ethylene glycol di(2-acrylonitrile ethyl) ether, or 1,2,3-tris(2-acrylonitrile ethoxy)propane. Based on the mass of the electrolyte, the mass percentage of the nitrile additives is z%, 0.1 ≤ z < 4.2. Selecting the above-mentioned types of nitrile additives and controlling the mass percentage z% of the nitrile additives in the electrolyte within the above range is beneficial for improving the thermal performance and room temperature storage performance of the secondary battery.

[0010] In some embodiments of this application, 2.0 ≤ z + x ≤ 4.5, preferably 3.0 ≤ z + x ≤ 4.0. By controlling the sum of the mass percentage x% of the positive electrode additive in the positive electrode active material layer and the mass percentage z% of the nitrile additive in the electrolyte, z + x is controlled within the above range, the positive electrode additive and the nitrile additive have a synergistic effect, which is beneficial to improving the thermal performance and room temperature storage performance of the secondary battery.

[0011] In some embodiments of this application, the upper limit voltage of the secondary battery is U / x, where 3.0 ≤ U ≤ 5.0 and 8.0 ≤ U / x ≤ 440.0. Preferably, 10.0 ≤ U / x ≤ 100.0, and more preferably, 20.0 ≤ U / x ≤ 80.0. Controlling the ratio of the upper limit voltage of the secondary battery to the mass percentage of the positive electrode additive in the positive electrode active material layer, U / x, within the above range is beneficial for improving the thermal performance of the secondary battery.

[0012] In some embodiments of this application, the working capacity of the secondary battery is C Ah, 1≤C≤20, 2.2≤C / x≤200.0. Preferably, 5.0≤C / x≤50.0. Controlling the ratio C / x of the working capacity of the secondary battery to the mass percentage of the positive electrode additive in the positive electrode active material layer within the above range is beneficial to improving the thermal performance of the secondary battery.

[0013] In some embodiments of this application, the transition metal element includes Ni, and the mass percentage of Ni is n% based on the total mass of the transition metal element, with 18 ≤ n ≤ 64, 0.4 ≤ n / (100x) ≤ 33.0, preferably 2.0 ≤ n / (100x) ≤ 20.0. Controlling the mass percentage of Ni in the transition metal element (n%) and the value of n / (100x) within the above ranges is beneficial for improving the thermal performance of the secondary battery.

[0014] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. Therefore, it offers good safety performance and a long service life.

[0015] Technical effects of this application:

[0016] This application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material and a positive additive. The positive active material includes a transition metal element, which includes at least one of Co, Ni, Mn, Fe, or V. The positive additive is a nitrile-containing organic compound with a carbon-to-nitrogen atom ratio of m, where 1 ≤ m ≤ 6, and a weight-average molecular weight of M. w 300≤M w ≤800000; Based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode additive is x%, 0.01≤x≤0.50. This is determined by the carbon-nitrogen atom ratio m and the weight-average molecular weight M of the positive electrode additive. w The mass percentage (x%) of the positive electrode additive is simultaneously controlled within the range specified in this application. The positive electrode additive imparts good stability to the positive electrode sheet and exhibits low oxidation resistance to the electrolyte. This reduces the content of gases generated by electrolyte oxidation, thereby improving the pass rate of the secondary battery's thermal chamber test and ultimately enhancing the secondary battery's thermal chamber performance. Furthermore, the secondary battery demonstrates good room temperature cycle performance, high production efficiency, and low production cost. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application are within the scope of protection of this application.

[0018] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0019] In current lithium-ion battery systems, thermal performance has become a bottleneck for some projects, severely limiting the development of lithium-ion batteries. The main failure mode in thermal testing is as follows: severe gas production at high temperatures leads to lithium-ion battery damage, and then, under further high temperatures, the negative electrode and electrolyte combust, resulting in thermal test failure. The amount of gas produced is primarily related to the redox reaction between the positive electrode and the electrolyte. In existing lithium-ion batteries, the positive electrode has a strong oxidizing ability on the electrolyte at high temperatures, causing the electrolyte to produce a large amount of gas, thus reducing the thermal performance of the lithium-ion battery.

[0020] Adding additives to the electrolyte can reduce the oxidation capacity of the positive electrode. However, these additives typically employ functional groups with strong electronegativity (such as nitrile groups). The electronegativity of these polar functional groups interacts with the high-valence transition metal ions (TM) at the fully charged positive electrode. + Complexation, reducing TM + The addition of polar functional groups improves the oxidation capacity of secondary batteries and enhances their high-temperature performance. However, the introduction of polar functional groups often introduces reactive α-H, which is easily reduced on the negative electrode side, accelerating the consumption of negative electrode additives and causing deterioration in room-temperature cycling performance. Balancing the high-temperature performance and room-temperature cycling performance of secondary batteries is crucial for improving their thermal performance. Based on this, this application provides a secondary battery and an electronic device.

[0021] This application provides a secondary battery comprising an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material and a positive additive. The positive active material includes a transition metal element, comprising at least one of Co, Ni, Mn, Fe, or V. The positive additive is a nitrile-containing (-CN) organic compound, and the carbon-to-nitrogen atom ratio of the positive additive is m, where 1 ≤ m ≤ 6, preferably 3 ≤ m ≤ 4. The weight-average molecular weight of the positive additive is M. w 300≤M w≤800000. Preferably, 300000≤M w ≤500000. Based on the mass of the positive electrode active material layer, the mass percentage content of the positive electrode additive is x%, 0.01≤x≤0.50. Preferably, 0.30≤x≤0.50. For example, the carbon-nitrogen atom ratio m of the positive electrode additive is 1, 2, 3, 4, 5, 6 or any value between any two of the above ranges. For example, the weight-average molecular weight M of the positive electrode additive... w The value can be 300, 1000, 10000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, or any value within any two of the above ranges. For example, based on the mass of the positive electrode active material layer, the mass percentage (x%) of the positive electrode additive can be 0.01%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or any value within any two of the above ranges. It should be understood that, for ease of reference, this application defines the positive electrode additive as a nitrile-containing organic compound, but the positive electrode active material layer may also include other additives, such as a first positive electrode additive.

[0022] When the carbon-to-nitrogen ratio m of the positive electrode additive is less than 1, the content of polar functional groups (such as -CN) in the positive electrode additive is too low, which is insufficient to form complexes with the transition metal elements in the positive electrode active material. The transition metals that have not undergone complexation have a strong oxidizing ability on the electrolyte, causing the electrolyte to generate a large amount of gas, thereby affecting the high-temperature performance of the secondary battery and reducing the thermal conductivity of the secondary battery. When the carbon-to-nitrogen ratio m of the positive electrode additive is greater than 6, the content of polar functional groups in the positive electrode additive is too high, which will introduce a large amount of active α-H. α-H is easily reduced on the negative electrode side, accelerating the consumption of the negative electrode additive and causing deterioration of the room temperature cycling performance.

[0023] The weight-average molecular weight M of the positive electrode additive w When the molecular weight is less than 300, the positive electrode additive is easily soluble in the electrolyte; the weight-average molecular weight M of the positive electrode additive... w When the value is greater than 800,000, during the preparation of positive electrode slurry by adding positive electrode additives, the positive electrode additives and positive electrode active materials are not easily mixed evenly, which will affect the respective roles of the positive electrode active materials and positive electrode additives in the secondary battery cycle process, and affect the performance of the secondary battery, such as room temperature cycle performance, thermal performance, energy density, etc.

[0024] Based on the quality of the positive electrode active material layer, when the mass percentage of the positive electrode additive (x%) is less than 0.01%, the content of the positive electrode additive is too low, which reduces the possibility of inhibiting the oxidation ability of transition metal elements in the positive electrode active material on the electrolyte, and the improvement effect on the thermal performance of the secondary battery is not obvious. When the mass percentage of the positive electrode additive (x%) is greater than 0.50%, the brittleness of the positive electrode sheet increases, and abnormalities are prone to occur in its manufacturing process, such as cold pressing breakage or winding breakage, which will increase the production cost of the secondary battery and reduce its production efficiency.

[0025] Overall, by adjusting the carbon-to-nitrogen atom ratio m of the cathode additive and the weight-average molecular weight M of the cathode additive... w The mass percentage (x%) of the positive electrode additive is simultaneously controlled within the range of this application. The positive electrode additive imparts good stability to the positive electrode sheet and exhibits low oxidation resistance to the electrolyte. This reduces the content of gases generated by electrolyte oxidation, thereby improving the pass rate of the secondary battery's hot-box test and ultimately enhancing the secondary battery's hot-box performance. Furthermore, the secondary battery demonstrates good room-temperature cycle performance, high production efficiency, and low production cost. The carbon-to-nitrogen atom ratio (m) and weight-average molecular weight (M) of the positive electrode additive are controlled accordingly. w By controlling at least one of the following within the preferred range of this application—or the mass percentage of the positive electrode additive (x%)—the thermal performance of the secondary battery is improved.

[0026] The aforementioned "positive electrode active material layer disposed on at least one surface of the positive electrode current collector" refers to a positive electrode active material layer disposed on one surface of the positive electrode current collector, or a positive electrode active material layer disposed on two surfaces of the positive electrode current collector. Here, "surface" can be part or all of the surface of the positive electrode current collector. In some embodiments of this application, other material layers, such as adhesive layers, safety layers, and other active material layers, may also be disposed between the positive electrode active material layer and the positive electrode current collector.

[0027] This application addresses the weight-average molecular weight M of the cathode additive. w There are no particular restrictions on the control method, as long as it can achieve the purpose of this application. For example, the weight-average molecular weight M of the cathode additive can be adjusted by controlling the reaction temperature or the amount of monomer added. w Things have changed.

[0028] In some embodiments of this application, the positive electrode additive includes polyacrylonitrile (molecular formula: (C3H3N)). n Polybutadiene acrylonitrile (molecular formula: (C4H5N)) n Poly(5-hexenonitrile) (Molecular formula: (C6H9N) n ) or polyisobutylene nitrile (molecular formula: (C4H5N) nAt least one of the above-mentioned positive electrode additives. By selecting the above-mentioned positive electrode additives, the polar functional groups in the positive electrode active additives can undergo a sufficient complexation reaction with the transition metal elements in the positive electrode active material, so that the positive electrode sheet has good stability, has a low oxidation capacity to the electrolyte, and the content of gas generated by the oxidation of the electrolyte is reduced, thereby improving the pass rate of the hot box test of the secondary battery and thus improving the hot box performance of the secondary battery.

[0029] In some embodiments of this application, 0.1 ≤ xM w / 1000≤300. Preferably, 90≤xM w / 1000≤175. For example, xM w / 1000 is 0.1, 5, 30, 60, 90, 150, 200, 300, or any value between any two of the above ranges. xM w When the / 1000 value is controlled within the above range, the positive electrode sheet exhibits good stability while maintaining a good manufacturing yield. It also has a low oxidation capacity on the electrolyte, reducing the content of gases generated by electrolyte oxidation. This improves the pass rate of the secondary battery's thermal chamber test, thereby enhancing the secondary battery's thermal chamber performance. Furthermore, the secondary battery demonstrates good room temperature cycling performance, high production efficiency, and low production cost.

[0030] In some embodiments of this application, the electrolyte includes nitrile additives, which include at least one selected from butadionitrile, adiponitrile, ethylene glycol di(2-acrylonitrile ethyl) ether, or 1,2,3-tris(2-acrylonitrile ethoxy)propane. Based on the mass of the electrolyte, the mass percentage of the nitrile additive is z%, 0.1 ≤ z < 4.2. For example, the mass percentage z% of the nitrile additive is 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.15%, or any value between any two of the above ranges. By selecting the above-mentioned types of nitrile additives and controlling the mass percentage z% of the nitrile additives in the electrolyte within the above range, it is possible to reduce the corrosion rate of the negative electrode current collector (such as copper foil), slow down the self-discharge of the secondary battery, and reduce the risk of secondary battery failure during room temperature storage, thereby enabling the secondary battery to have good room temperature storage performance, while maintaining good thermal performance.

[0031] In some embodiments of this application, 2.0 ≤ z + x ≤ 4.5, preferably 3.0 ≤ z + x ≤ 4.0. For example, the value of z + x is 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or any value between any two of the above ranges. By controlling the sum of z + x (the mass percentage x% of the positive electrode additive in the positive electrode active material layer and the mass percentage z% of the nitrile additive in the electrolyte) within the above range, the positive electrode additive and the nitrile additive work synergistically, resulting in a suitable positive electrode active material loading on the positive electrode sheet and good lithium-ion transport capability in the electrolyte. The positive electrode additive gives the positive electrode sheet good stability and low oxidation capacity in the electrolyte. The content of gases generated by oxidation in the electrolyte is reduced, the corrosion rate of the negative electrode current collector (such as copper foil) is lowered, the self-discharge of the secondary battery is slowed down, and the risk of secondary battery failure during room temperature storage is reduced. Therefore, the secondary battery has high thermal performance and room temperature storage performance. When the value of z+x is controlled within the above-mentioned preferred range, the thermal performance and room temperature storage performance of the secondary battery are better.

[0032] In some embodiments of this application, the upper limit voltage of the secondary battery is U / x, where 3.0 ≤ U ≤ 5.0 and 8.0 ≤ U / x ≤ 440.0. Preferably, 10.0 ≤ U / x ≤ 100.0, and more preferably, 20.0 ≤ U / x ≤ 80.0. For example, the value of U is 3.0, 3.5, 4.0, 4.5, 5.0, or any value between any two of the above ranges. The value of U / x is 8.0, 9.0, 10.0, 15.0, 20.0, 40.0, 60.0, 80.0, 100.0, 150.0, 200.0, 250.0, 300.0, 350.0, 400.0, 440.0, or any value between any two of the above ranges. When the upper limit voltage of the secondary battery is increased, the oxidation capacity of the positive electrode plate to the electrolyte will be enhanced, thereby affecting the thermal performance of the secondary battery. By controlling the ratio U / x of the upper limit voltage of the secondary battery to the mass percentage of the positive electrode additive in the positive electrode active material layer within the aforementioned range, as the upper limit voltage of the secondary battery increases, the mass percentage x% of the positive electrode additive in the positive electrode active material layer also increases. This allows the positive electrode additive to complex with the transition metal elements in the positive electrode active material, resulting in good stability of the positive electrode sheet and a lower oxidation capacity towards the electrolyte. The content of gases generated by electrolyte oxidation is reduced, thus improving the pass rate of the secondary battery's thermal chamber test and enhancing its thermal chamber performance, leading to good safety performance. Furthermore, by controlling the content of the positive electrode additive and the loading of the positive electrode active material on the positive electrode sheet within appropriate ranges, the impact on the energy density of the secondary battery is reduced.

[0033] This application does not impose any particular restrictions on the method of controlling the upper limit voltage of the secondary battery, as long as the purpose of this application can be achieved. For example, the upper limit voltage of the secondary battery can be controlled by adjusting the ratio of the coating weight of the positive and negative electrodes (the coating weight of the active material layer).

[0034] In some embodiments of this application, the operating capacity of the secondary battery is CAh, where 1 ≤ C ≤ 20 and 2.2 ≤ C / x ≤ 200.0. Preferably, 5.0 ≤ C / x ≤ 50.0. For example, the value of C is 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, or any value within any two of the above ranges. The value of C / x is 2.2, 3.0, 5.0, 20.0, 40.0, 50.0, 80.0, 100.0, 150.0, 200.0, or any value within any two of the above ranges. When the operating capacity of the secondary battery increases, the reaction sites between the positive electrode and the electrolyte increase, the risk of side reactions in the electrolyte increases, and the heat generated by the reaction leads to heat accumulation, which will affect the thermal performance of the secondary battery. By controlling the ratio C / x of the working capacity of the secondary battery to the mass percentage of the positive electrode additive in the positive electrode active material layer within the aforementioned range, the mass percentage x% of the positive electrode additive in the positive electrode active material layer increases as the working capacity of the secondary battery increases. This reduces the degree of side reactions in the electrolyte, slows down heat accumulation caused by reaction heat generation, thereby reducing the risk of thermal box failure, improving the thermal box performance of the secondary battery, and giving the secondary battery good safety performance. Furthermore, by controlling the content of the positive electrode additive and the loading of the positive electrode active material on the positive electrode sheet within an appropriate range, the impact on the energy density of the secondary battery is reduced.

[0035] This application does not impose any particular restrictions on the method of adjusting the working capacity of the secondary battery, as long as the purpose of this application can be achieved. For example, the working capacity of the secondary battery can be adjusted by regulating the coating amount of the positive and negative electrodes (the coating weight of the active material layer).

[0036] In some embodiments of this application, the transition metal element includes Ni, and the mass percentage of Ni is n% based on the total mass of the transition metal elements, with 18 ≤ n ≤ 64, 0.4 ≤ n / (100x) ≤ 33.0, preferably 2.0 ≤ n / (100x) ≤ 20.0. For example, the value of n is 18, 24, 30, 36, 42, 48, 54, 60, 64, or any value between any two of the above ranges. The value of n / (100x) is 0.4, 1.0, 2.0, 11.0, 20.0, 24.0, 28.0, 32.0, 33.0, or any value between any two of the above ranges. Ni 4+ The oxidizing power is greater than that of Co. 4+ Mn 4+Therefore, increasing the Ni content leads to more side reactions in the positive electrode and electrolyte of the entire secondary battery system, further affecting the thermal performance of the secondary battery. By controlling the mass percentage of Ni in the transition metal elements (n%) and the value of n / (100x) within the above range, without affecting the energy density of the secondary battery, the content of the positive electrode additive increases with the increase of Ni content. This allows for timely complexation with Ni, resulting in good stability of the positive electrode sheet, lower oxidation capacity of the electrolyte, and reduced content of gases generated by electrolyte oxidation. This improves the thermal performance of the secondary battery and enhances its safety performance. Furthermore, by controlling the content of the positive electrode additive and the loading of the positive electrode active material on the positive electrode sheet within appropriate ranges, the impact on the energy density of the secondary battery is reduced.

[0037] This application does not impose any particular restrictions on the method of controlling the mass percentage (n%) of Ni in the transition metal element, as long as it achieves the purpose of this application. For example, the mass percentage (n%) of Ni in the transition metal element can be controlled by adjusting the type of positive electrode active material and the ratio of different positive electrode active materials (such as the ratio of LCO and NCM).

[0038] This application does not impose any particular limitation on the type of positive electrode current collector, as long as it achieves the purpose of this application. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, etc. The type of positive electrode active material in this application only needs to include the transition metal elements described in this application to achieve the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may also include non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur, which can further improve the stability of the positive electrode active material. In this application, there is no particular limitation on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0039] Optionally, the positive electrode active material layer may further include a conductive agent and a binder. There are no particular limitations on the types of the conductive agent and the binder in the positive electrode active material layer in the present application, as long as the objectives of the present application can be achieved. There are no particular limitations on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer in the present application, and those skilled in the art can select according to actual needs, as long as the objectives of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the positive electrode additive, the conductive agent, and the binder in the positive electrode active material layer is (90.00 - 99.00):(0.01 - 0.50):(0.495 - 4.75):(0.495 - 4.75).

[0040] There are no particular limitations on the negative electrode sheet in the present application, as long as the objectives of the present application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. There are no particular limitations on the negative electrode current collector in the present application, as long as the objectives of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam or copper foam, etc. The negative electrode active material layer of the present application includes a negative electrode active material. There are no particular limitations on the type of the negative electrode active material in the present application, as long as the objectives of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy or metallic lithium, etc. At least one. In the present application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the objectives of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 130 μm. Optionally, the negative electrode active material layer may further include at least one of a conductive agent, a stabilizer, and a binder. There are no particular limitations on the types of the conductive agent, the stabilizer, and the binder in the negative electrode active material layer in the present application, as long as the objectives of the present application can be achieved. There are no particular limitations on the mass ratio of the negative electrode active material, the conductive agent, the stabilizer, and the binder in the negative electrode active material layer in the present application, as long as the objectives of the present application can be achieved. For example, the mass ratio of the negative electrode active material, the conductive agent, the stabilizer, and the binder in the negative electrode active material layer is (97 - 98):(0.5 - 1.5):(0.5 - 1.5):(1.0 - 1.9).

[0041] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0042] For example, the diaphragm may include a diaphragm substrate layer and a surface treatment layer. The diaphragm substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the diaphragm substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, at least one surface of the diaphragm substrate layer is provided with a surface treatment layer, which may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited, as long as it can achieve the purpose of this application. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0043] The electrolyte of this application also includes lithium salts and non-aqueous solvents. The lithium salts may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not have particular limitations on non-aqueous solvents, as long as they achieve the purpose of this application; for example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of lithium salt and non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.For example, based on the mass of the electrolyte, the mass percentage of lithium salt can be 2% to 20%, exemplarily 2%, 5%, 10%, 15%, 20%, or any value between any two of the above ranges, and the mass percentage of non-aqueous solvent can be 15% to 80%, exemplarily 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value between any two of the above ranges.

[0044] The secondary battery of this application also includes a packaging bag, in which the electrolyte and electrode assembly are contained. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application.

[0045] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. 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.

[0046] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. Therefore, it offers good safety performance and a long service life.

[0047] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0048] Example

[0049] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0050] Test methods and equipment:

[0051] Methods for detecting the carbon-to-nitrogen atom ratio:

[0052] Disassemble the lithium-ion batteries of each embodiment and comparative example, and take the positive electrode portion. Wash it three times with dimethyl carbonate (DMC) to remove free lithium salts and soluble components in the solid electrolyte interphase (SEI) film. Place the positive electrode in an appropriate amount of N-methylpyrrolidone to submerge it, and stir for 5 hours. Filter and collect the supernatant. Separate the supernatant by chromatography to obtain a pure-phase N-methylpyrrolidone solution as the positive electrode additive.

[0053] The obtained N-methylpyrrolidone solution of the cathode additive was dried to obtain a pure-phase cathode additive. Then, the carbon-to-nitrogen ratio of the cathode additive was determined using an organic elemental analyzer.

[0054] Weight-average molecular weight M w Detection method:

[0055] The weight-average molecular weight M was determined using a laser light scattering instrument. W .

[0056] Transition metal element content testing methods:

[0057] The lithium-ion batteries of each embodiment and comparative example were disassembled, and their positive electrode portions were taken. After calcining at 600°C for 2 hours in air, the positive electrode active material layer was scraped off from the positive electrode current collector, digested with hydrochloric acid, filtered, and the supernatant was obtained. After being fully diluted with ultrapure water, the content of each transition metal element was obtained by inductively coupled plasma mass spectrometry (ICP-MS).

[0058] Negative electrode specific capacity testing method:

[0059] Take a fully discharged lithium-ion battery, disassemble the negative electrode, clean and dry it, then use a lithium sheet as the positive electrode to assemble it into a coin cell for testing. The coin cell is discharged to 5.0mV at 0.05C, discharged to 5.0mV at 50μA, discharged to 5.0mV at 10μA, and charged to 2.0V at 0.1C. The capacity of the coin cell at these times is recorded as its specific capacity. 0.05C refers to the current value at 0.05 times the designed specific capacity, and 0.1C refers to the current value at 0.1 times the designed specific capacity.

[0060] CB testing method:

[0061] Take a fully discharged lithium-ion battery, disassemble each one, and separate the positive and negative electrodes. Clean and dry them. Using a 14mm diameter die, punch five complete electrode sheets from the flat single-sided area of ​​each electrode. Use lithium sheets as the counter electrode and assemble them into coin cells for testing. Test according to the specific capacity method, measure the capacity of the positive electrode, and record it as C1, C2, C3, C4, and C5. Calculate the average capacity C of the punched positive electrode sheets. 正Similarly, measure the capacities of the negative electrodes, denoted as A1, A2, A3, A4, and A5, and calculate the average capacity A of the negative electrode punching electrode sheets. 负 , CB = A 负 / C 正 .

[0062] In this application, the above "CB" refers to Cell balance, the battery balance value; the CB value can represent the capacity ratio of the negative electrode and the positive electrode in the battery.

[0063] Working capacity C test method:

[0064] (1) Discharge the lithium-ion batteries of each embodiment and comparative example at a current density of 0.2C until 3.0V.

[0065] (2) Disassemble the lithium-ion battery, take the negative electrode sheet, record the length of the coating area (the length of the front and back sides, L1 + L2, unit: cm) and width (W d , unit: cm), take the negative electrode sheet (double-sided area, 2cm × 2cm), wash it twice with DMC, and then dry it.

[0066] (3) Weigh it and record as W1.

[0067] (4) Wash the negative electrode sheet with distilled water to remove the coating layer on the current collector, dry it and then weigh it, record as W2.

[0068] (5) Working capacity C = 1 / 4 (W1 - W2) × W d (L1 + L2) × A 负 / CB.

[0069] Upper limit voltage U test method:

[0070] (1) First, fully discharge the lithium-ion batteries of each embodiment and comparative example. The discharge process is: discharge at a constant current of 0.2C until 3.0V, and stand for 30 min; then discharge at a constant current of 0.2C until 3.0V (C is the working capacity of the lithium-ion battery).

[0071] (2) Charge with a current of 0.05C for 20h, and then record the voltage V at this time, which is the upper limit voltage.

[0072] Hot box performance test:

[0073] For each embodiment and comparative example, take 5 lithium-ion batteries, charge them to the upper limit voltage at 0.2C (C is the working capacity of the lithium-ion battery), and then keep charging at the upper limit voltage (constant voltage charging) until the current ≤ 0.02C, and stop charging; after full charge, place the lithium-ion batteries in an environment with the test temperature (such as 130°C) for 60 min. The judgment condition "not burning, not exploding" is considered to pass.

[0074] The highest temperature that passes the test when "number of passes / number of tests = 5 / 5" is determined to be the hot chamber test temperature of the corresponding embodiment or comparative example.

[0075] With Comparative Example 1 as the control group, the excess hot chamber test temperature = the hot chamber test temperature of each embodiment or comparative example - the hot chamber test temperature of Comparative Example 1. 0℃ < excess hot chamber test temperature < 2℃ indicates that the hot chamber performance has improved; when the excess hot chamber test temperature is ≥ 2℃, it indicates that the hot chamber performance has improved significantly.

[0076] Method for testing capacity retention at room temperature:

[0077] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 1C to a voltage of 4.4V, followed by a constant voltage charge of 4.4V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V. This initial capacity was then measured. The battery was then charged at a constant current of 1C to 3.85V, followed by a constant voltage charge of 3.85V to a current of 0.05C (approximately 50% State of Charge (SOC)). After 6 months of storage at 25°C, the battery was discharged at a constant current of 1C to a voltage of 3.0V, then charged at a constant current of 1C to a voltage of 4.4V, then charged at a constant voltage of 4.4V to a current of 0.05C, and finally discharged at a constant current of 1C to a voltage of 3.0V. The final discharge capacity was called the reversible capacity after storage.

[0078] Capacity retention rate (%) of lithium-ion batteries after room temperature storage = reversible capacity after storage / initial capacity × 100%.

[0079] Example 1-1

[0080] <Preparation of the positive electrode>

[0081] LiNi, the positive electrode active material 0.33 Co 0.33 Mn 0.33 O2 (where n% = 33%), positive electrode additive polyacrylonitrile (m = 3, M) w=300), conductive agent acetylene black, and binder PVDF were mixed in a mass ratio of 97:0.5:0.8:1.7, with N-methylpyrrolidone (NMP) added as a solvent. The mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75wt% was obtained. The positive electrode slurry was uniformly coated onto one surface of a 10μm thick aluminum foil for the positive electrode current collector and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive active material layer (110μm thick). The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material layer. After drying at 90°C, the sheet was cold-pressed, cut, and had tabs welded to obtain a positive electrode sheet with a size of 74mm×867mm for later use.

[0082] <Preparation of Negative Electrode Sheets>

[0083] Graphite (negative electrode active material), conductive carbon (Super P) (conductive agent), and styrene-butadiene rubber (SBR, weight average molecular weight 500,000) (batch agent) were mixed in a mass ratio of 97.8:0.7:1.5. Deionized water was then added as a solvent, and the mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 70 wt% was obtained. The negative electrode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector and dried at 90°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer (130 μm thick). The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After drying at 90°C, the sheet was cold-pressed, cut, and had tabs welded to obtain a negative electrode sheet with dimensions of 76 mm × 851 mm for later use.

[0084] <Preparation of Electrolyte>

[0085] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a mass ratio of 20:30:20:28:2. Lithium hexafluorophosphate (LiPF6) was then added to the non-aqueous organic solvents, dissolved, and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the non-aqueous organic solvents comprised 87% by mass, and the lithium salts comprised 13% by mass.

[0086] <Preparation of the diaphragm>

[0087] A porous polyethylene film with a thickness of 7μm is used (manufacturer: Nitto).

[0088] <Preparation of Lithium-ion Batteries>

[0089] The negative electrode, separator, and positive electrode prepared above are stacked and wound in sequence to obtain a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, degassing, and edge trimming, a lithium-ion battery is obtained. The upper limit of the formation voltage is 4.15V, the formation temperature is 70℃, and the formation standing time is 2h.

[0090] Examples 1-2 to Examples 1-15

[0091] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0092] Examples 2-1 to 2-18

[0093] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-10.

[0094] Example 3-1

[0095] Except for the addition of nitrile additive succinate (z% = 0.1%) in the <Preparation of Electrolyte>, the content of non-aqueous organic solvent varies with the content of nitrile additive, and the sum of the mass percentages of non-aqueous organic solvent, lithium salt and nitrile additive is 100% based on the mass of electrolyte, the rest is the same as in Examples 1-2.

[0096] Examples 3-2 to 3-8

[0097] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Example 3-1.

[0098] Comparative Example 1

[0099] Except for the fact that no positive electrode additives are added in the <Preparation of Positive Electrode Sheet> and the mass ratio of positive electrode active material, conductive agent and binder is adjusted to 97.5:0.8:1.7, the rest is the same as in Example 1-1.

[0100] Comparative Examples 2 to 5

[0101] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0102] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0103] Table 1

[0104]

[0105] Note: "\" in Table 1 indicates that there are no corresponding preparation parameters.

[0106] As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1 to 5, this application achieves its effect by adding a positive electrode additive to the positive electrode active material layer, and by adjusting the carbon-nitrogen atom ratio m and the weight-average molecular weight M of the positive electrode additive. w By simultaneously controlling the mass percentage (x%) of the positive electrode additive within the range specified in this application, the hot box test temperature of the secondary battery is increased. The temperature exceeds 0°C, indicating improved hot box performance of the secondary battery. In Comparative Examples 1 to 5, the positive electrode active material layer did not contain any positive electrode additive, or the carbon-to-nitrogen atom ratio (m) and weight-average molecular weight (M) of the positive electrode additive were... w If at least one of the following secondary batteries, namely the positive electrode additive mass percentage x%, is not within the scope of this application, and its hot box test temperature fails to increase, or the hot box test temperature exceeds 0°C, or, as in Comparative Examples 2 and 4, the positive electrode sheet shows manufacturing abnormalities and cannot be used normally, it indicates that the hot box performance of the secondary battery has not been improved.

[0107] xM w The value of / 1000 typically affects the thermal performance of secondary batteries. As can be seen from Examples 1-1 to 1-11, 1-14, 1-15, Comparative Example 3, and Comparative Example 4, selecting xM... w The value of / 1000 indicates that the secondary battery within the scope of this application has a higher thermal chamber test temperature, exceeding the thermal chamber test temperature by more than 0°C, indicating that the thermal chamber performance of the secondary battery has been improved.

[0108] Table 2

[0109]

[0110] The values ​​of the upper limit voltage U and U / x, the working capacity C and C / x, and the mass percentage of Ni in the transition metal elements n% and n / (100x) of the secondary battery also typically affect the thermal performance of the secondary battery. As can be seen from Examples 1-11, 2-1 to 2-18, the secondary batteries within the scope of this application that use the values ​​of the upper limit voltage U and U / x, the working capacity C and C / x, and the mass percentage of Ni in the transition metal elements n% and n / (100x) exhibit higher thermal test temperatures, exceeding 0°C, indicating that the secondary batteries possess good thermal performance.

[0111] Table 3

[0112]

[0113] Note: "\" in Table 3 indicates that there are no corresponding preparation parameters.

[0114] As can be seen from Examples 1-2 and Examples 3-1 to 3-8, when the electrolyte contains nitrile additives, it can improve the room temperature storage performance of the secondary battery while maintaining its good thermal performance.

[0115] The content z% of nitrile additives typically affects the thermal performance and room temperature storage performance of secondary batteries. As can be seen from Examples 1-2, 3-1 to 3-7, secondary batteries with a nitrile additive content of z% within the scope of this application exhibit higher thermal test temperatures, exceeding the thermal test temperature by more than 0°C, indicating improved thermal performance. Furthermore, they demonstrate higher room temperature storage capacity retention, indicating improved room temperature storage performance.

[0116] When the electrolyte contains nitrile additives, the value of z+x typically affects the thermal performance and room temperature storage performance of the secondary battery. As can be seen from Examples 3-1 to 3-7, the secondary batteries using z+x values ​​within the scope of this application exhibit higher thermal test temperatures, exceeding 0°C, indicating improved thermal performance. Furthermore, they demonstrate higher room temperature storage capacity retention, indicating improved room temperature storage performance.

[0117] When the electrolyte contains nitrile additives, the type of nitrile additive usually affects the thermal performance and room temperature storage performance of the secondary battery. As can be seen from Examples 3-1 to 3-8, the secondary batteries using nitrile additives within the scope of this application exhibit higher thermal test temperatures, exceeding the thermal test temperature by more than 0°C, indicating improved thermal performance. Furthermore, they exhibit higher room temperature storage capacity retention, indicating improved room temperature storage performance.

[0118] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0119] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0120] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode tab, a negative electrode tab, and a separator, the separator being disposed between the positive electrode tab and the negative electrode tab, the positive electrode tab comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; the positive electrode active material layer comprising a positive electrode active material and a positive electrode additive; the positive electrode active material comprising a transition metal element, the transition metal element comprising at least one of Co, Ni, Mn, Fe, or V; The positive electrode additive is a nitrile group-containing organic compound, the carbon-nitrogen atom number ratio of the positive electrode additive is m, 1≤m≤6, the weight average molecular weight of the positive electrode additive is M w , 300≤M w ≤800000; the mass percentage content of the positive electrode additive is x%, 0.01≤x≤0.50, based on the mass of the positive electrode active material layer; 90≤ xM w / 1000≤ 175.

2. The secondary battery according to claim 1, wherein the secondary battery satisfying at least one of conditions (1) to (3) below: （1）3≤m≤4； （2）300000≤M w ≤500000； （3）0.30≤x≤0.50。 3. The secondary battery according to claim 1, wherein the positive electrode additive comprising at least one of polyacrylonitrile, polybutylenenitrile, poly(5-hexenenitrile), or polyisobutylenenitrile.

4. The secondary battery according to claim 1, wherein the electrolyte comprising a nitrile-based additive, the nitrile-based additive comprising at least one of succinonitrile, adiponitrile, ethyleneglycol bis(2-cyanoethylether), or 1,2,3-tris(2-cyanoethoxy)propane; a mass percentage content of the nitrile-based additive is z% based on a mass of the electrolyte, 0.1≤z<4.

2.

5. The secondary battery according to claim 4, wherein 2.0≤z+x≤4.

5.

6. The secondary battery according to claim 5, wherein 3.0≤z+x≤4.

0.

7. The secondary battery according to claim 1, wherein an upper limit voltage of the secondary battery is U V, 8.0≤U / x≤440.0, 3.0≤U≤5.

0.

8. The secondary battery according to claim 7, wherein 10.0≤U / x≤100.

0.

9. The secondary battery according to claim 8, wherein 20.0≤U / x≤80.

0.

10. The secondary battery according to claim 1, wherein a working capacity of the secondary battery is C Ah, 1≤C≤20, 2.2≤C / x≤200.

0.

11. The secondary battery according to claim 10, wherein 5.0≤C / x≤50.

0.

12. The secondary battery according to claim 1, wherein the transition metal element comprises Ni, a mass percentage content of Ni is n% based on a total mass of the transition metal, 18≤n≤64, 0.4≤n / (100x)≤33.

0.

13. The secondary battery according to claim 12, wherein 2.0≤n / (100x)≤20.

0. 14.An electronic device comprising the secondary battery of any one of claims 1 to 13.

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