A positive electrode sheet, a secondary battery, and an electronic device

Abstract

The application provides a positive electrode sheet, a secondary battery and an electronic device, comprising a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode active material and a first compound, the first compound comprising at least one of ethylene phosphate, allyl phosphate, vinylidene phosphate, diallyl phosphate, phenylethylene phosphate, diphenyl phosphate or diphenyl ethylene phosphate, and the infrared spectrum of the positive electrode material layer has infrared characteristic peaks at any two of 1150 cm ‑1 ±10 cm ‑1 , 1085 cm ‑1 ±10 cm ‑1 , 1600 cm ‑1 ±10 cm ‑1 , 1640 cm ‑1 ±10 cm ‑1 or 1500 cm ‑1 ±10 cm ‑1 . Through the above setting, the high-temperature cycle performance and thermal safety performance of the secondary battery are improved, and the low-temperature and impedance performance are considered.

Description

Technical Field

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

[0002] Lithium-ion batteries have significant advantages such as high energy density, miniaturization, and lightweight, and are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, and power storage systems.

[0003] Lithium-ion batteries often use ternary materials such as lithium nickel cobalt manganese oxide as positive electrode active materials. However, when ternary materials are used as positive electrode active materials, the production process of ternary materials can easily lead to excessive residual alkali content in the positive electrode material layer. During cycling, the lithium-ion battery generates gas at high temperature, and interfacial adhesion occurs between the positive electrode sheet and the separator, which reduces the initial efficiency of the lithium-ion battery and thus leads to a decrease in cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode sheet, a secondary battery, and an electronic device to reduce the residual alkali content on the surface of the positive electrode material layer, improve high-temperature gas generation, thereby enhancing the high-temperature cycle performance of the secondary battery, while taking into account low-temperature and impedance performance, and improving the thermal safety performance of the secondary battery.

[0005] 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:

[0006] A first aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The positive electrode material layer comprises a positive electrode active material and a first compound, wherein the first compound comprises at least one selected from vinyl phosphate, allyl phosphate, vinylidene phosphate, diallyl phosphate, styrene phosphate, diphenyl phosphate, or stilbene phosphate. The infrared spectrum of the positive electrode material layer is at 1150 cm⁻¹. -1 ±10cm -1 And, 1085cm -1 ±10cm -1 1600cm -1 ±10cm -1 1640cm -1 ±10cm -1 Or 1500cm -1 ±10cm -1Infrared characteristic peaks are present at any two locations within the cathode material layer. This configuration neutralizes residual alkali, reducing its content on the surface of the cathode material layer and improving high-temperature gas generation. Furthermore, the first compound has a low oxidation potential of approximately 3.7V, promoting cathode film formation and reducing the risk of transition metal dissolution and electrolyte oxidation. Additionally, the C=C unsaturated bonds in the first compound facilitate anode film formation, reducing side reactions between the cathode and electrolyte and improving the cycle performance of the secondary battery. Including the first compound in the cathode material layer enhances the high-temperature cycle performance of the secondary battery, while also considering low-temperature performance and impedance performance, effectively improving the thermal stability of the cathode interface and enhancing the thermal safety performance of the secondary battery.

[0007] In some embodiments of this application, based on the mass of the cathode material layer, the mass percentage content of the first compound is B, where 0.1% ≤ B ≤ 3%; preferably, 0.1% ≤ B ≤ 1%. By controlling the mass percentage content B of the first compound within the above range, it is beneficial to improve the high-temperature cycle performance of the secondary battery, while taking into account low-temperature performance and impedance performance, and effectively improving the thermal stability of the cathode interface, thereby improving the thermal safety performance of the secondary battery.

[0008] In some embodiments of this application, the positive electrode active material includes LiNi. x Co y M 1-x-y O2, 0.6≤x≤1.0, 0≤y≤0.4, M is Al or Mn. In some embodiments of this application, the positive electrode active material includes lithium nickel cobalt manganese oxide, which includes metal element M1, and metal element M1 includes at least one selected from Al, Zr, Mg, Ba, or Ti. In some embodiments of this application, the positive electrode active material includes lithium nickel cobalt aluminum oxide, which includes metal element M2, and metal element M2 includes at least one selected from Zr, Mg, Ba, or Ti. In some embodiments of this application, the positive electrode active material includes both lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. Lithium nickel cobalt manganese oxide includes metal element M1, and metal element M1 includes at least one selected from Al, Zr, Mg, Ba, or Ti; lithium nickel cobalt aluminum oxide includes metal element M2, and metal element M2 includes at least one selected from Zr, Mg, Ba, or Ti. By selecting positive electrode active materials within the above-mentioned range, it is beneficial to further improve the thermal stability and electrochemical performance of the positive electrode active materials. The positive electrode active materials within the scope of this application, when used in combination with the first compound, are beneficial to improve the high-temperature cycle performance of the secondary battery, while taking into account the low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thereby improving the thermal safety performance of the secondary battery.

[0009] In some embodiments of this application, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is A; the mass percentage of the first compound is B, and A, x, and B satisfy: B = k × A × x, 93% ≤ A ≤ 95.9%, 0.6 ≤ x ≤ 0.9, 0.001792 ≤ k ≤ 0.03475. When A, x, and B satisfy the above relationship, and the values ​​of A, x, and k are adjusted within the above range, it is beneficial to improve the high-temperature cycle performance of the secondary battery, while taking into account low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thereby improving the thermal safety performance of the secondary battery. While maintaining the high energy density of the secondary battery, the structural stability of the positive electrode sheet is further improved.

[0010] A second aspect of this application provides a secondary battery comprising a negative electrode, a separator, an electrolyte, and a positive electrode as described in any of the foregoing embodiments. The secondary battery of this application exhibits excellent high-temperature cycle performance and thermal safety performance, while also considering low-temperature performance and impedance performance.

[0011] In some embodiments of this application, the electrolyte includes a second compound, which includes at least one of a cyclic sulfate compound or a cyclic carbonate compound. The cyclic sulfate compound includes at least one of vinyl sulfate, propylene sulfate, or methyl vinyl sulfate, and the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, or fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of the second compound is C, where 0.05% ≤ C ≤ 3%. By adding the above-mentioned types of second compounds to the electrolyte and controlling the mass percentage C of the second compound within the above range, the first compound and the second compound work synergistically to further improve the high-temperature storage and cycle performance of the secondary battery.

[0012] In some embodiments of this application, the electrolyte includes a third compound, which includes at least one of methylene methane disulfonate, vinylene carbonate, ethyl methyl carbonate, or propyl methyl carbonate. Based on the mass of the electrolyte, the mass percentage of the third compound is D, where 0.05% ≤ D ≤ 2%. By adding the aforementioned third compound to the electrolyte and controlling the mass percentage D of the third compound within the above range, the high-temperature cycle performance of the secondary battery is further improved, while maintaining low-temperature and impedance performance, and the thermal safety performance of the secondary battery is also improved.

[0013] A third aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0014] The beneficial effects of this application are:

[0015] This application provides a positive electrode sheet, a secondary battery, and an electronic device, including a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material and a first compound, wherein the first compound includes at least one selected from vinyl phosphate, allyl phosphate, vinylidene phosphate, diallyl phosphate, styrene phosphate, diphenyl phosphate, or stilbene phosphate. The infrared spectrum of the positive electrode material layer is at 1150 cm⁻¹. -1 ±10cm -1 And, 1085cm -1 ±10cm -1 1600cm -1 ±10cm -1 1640cm -1 ±10cm -1 Or 1500cm -1 ±10cm -1 Infrared characteristic peaks are present at any two locations within the cathode material layer. This configuration neutralizes residual alkali, reducing its content on the surface of the cathode material layer and improving high-temperature gas generation. Furthermore, the first compound has a low oxidation potential of approximately 3.7V, promoting cathode film formation and reducing the risk of transition metal dissolution and electrolyte oxidation. Additionally, the C=C unsaturated bonds in the first compound facilitate anode film formation, reducing side reactions between the cathode and electrolyte and improving the cycle performance of the secondary battery. Including the first compound in the cathode material layer enhances the high-temperature cycle performance of the secondary battery, while also considering low-temperature performance and impedance performance, effectively improving the thermal stability of the cathode interface and enhancing the thermal safety performance of the secondary battery.

[0016] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0018] Figure 1 This is the infrared spectrum of diphenyl phosphate. Detailed Implementation

[0019] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0020] 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.

[0021] Nickel-cobalt-manganese ternary cathode materials are widely used in the fields of computer, communication, and consumer electronics (3C electronic products) batteries and power batteries due to their advantages such as low cost, high specific capacity, and stable cycle performance. In lithium-ion battery cathode materials, replacing high-voltage lithium cobalt oxide with some high-voltage ternary materials can reduce the cost of lithium battery cathodes. However, ternary materials have a high pH and high residual alkali on the material surface, which makes lithium-ion batteries prone to swelling, placing high demands on manufacturing processes and environmental conditions, and making processing difficult. Furthermore, cycle stability deteriorates at voltages above 4.4V. Therefore, a solution that can solve the above technical problems is urgently needed. Based on this, this application provides a cathode sheet, a secondary battery, and an electronic device that can effectively improve the high-temperature cycle performance and thermal safety performance of secondary batteries, especially ternary cathode material systems, while also considering low-temperature performance and impedance performance. The specific technical solution is as follows:

[0022] A first aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector. The positive electrode material layer comprises a positive electrode active material and a first compound, wherein the first compound comprises at least one selected from vinyl phosphate, allyl phosphate, vinylidene phosphate, diallyl phosphate, styrene phosphate, diphenyl phosphate, or stilbene phosphate. The infrared spectrum of the positive electrode material layer is at 1150 cm⁻¹. -1 ±10cm -1 And, 1085cm -1 ±10cm -1 1600cm -1 ±10cm -1 1640cm -1 ±10cm -1 Or 1500cm -1 ±10cm -1 There are infrared characteristic peaks at any two locations in the image.

[0023] The inventors discovered that when the first compound of this application is added to the cathode material layer, the infrared spectrum of the cathode material layer at 1150 cm⁻¹... -1 ±10cm -1 And, 1085cm -1 ±10cm -1 1600cm -1 ±10cm -1 1640cm -1 ±10cm -1 Or 1500cm -1±10cm -1 Infrared characteristic peaks are present at any two locations. For example, Figure 1 This is the infrared spectrum of diphenyl phosphate; this substance is at 1150 cm⁻¹. -1 1600cm -1 And 1490cm -1 The presence of infrared characteristic peaks corresponds to phosphate groups and C=C groups. When the first compound of this application is added to the positive electrode material layer, the positive electrode material layer includes phosphate groups and C=C groups, which can neutralize residual alkali to reduce the residual alkali content on the surface of the positive electrode material layer and improve high-temperature gas generation. Furthermore, the oxidation potential of the first compound is low, around 3.7V, which can promote positive electrode film formation and reduce the risk of transition metal dissolution and electrolyte oxidation. In addition, the C=C unsaturated bonds in the first compound can form a film on the negative electrode, reducing side reactions between the negative electrode and the electrolyte, improving the cycle performance of the secondary battery, and increasing the initial efficiency of the secondary battery. Including the first compound in the positive electrode material layer can improve the high-temperature cycle performance of the secondary battery, while also considering low-temperature performance and impedance performance, and effectively improve the thermal stability of the positive electrode interface, thus improving the thermal safety performance of the secondary battery.

[0024] The aforementioned "negative electrode material layer located on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or it can be located on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a part of the surface of the positive electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0025] In some embodiments of this application, based on the mass of the positive electrode material layer, the mass percentage content of the first compound is B, where 0.1% ≤ B ≤ 3%; preferably, 0.1% ≤ B ≤ 1%. For example, the value of B can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or a range of any two of these values. By controlling the mass percentage content B of the first compound within the above range, it is beneficial to neutralize residual alkali to reduce the residual alkali content on the surface of the positive electrode material layer and improve high-temperature gas generation; moreover, the oxidation potential of the first compound is relatively low, around 3.7V, which can promote positive electrode film formation and reduce the risk of transition metal dissolution and electrolyte oxidation; in addition, the C=C unsaturation in the first compound can form a film on the negative electrode, reducing side reactions between the negative electrode sheet and the electrolyte and improving the cycle performance of the secondary battery. Adding the first compound within the above-mentioned content range to the cathode material layer is beneficial to improving the high-temperature cycle performance of the secondary battery, while taking into account the low-temperature performance and impedance performance, and effectively improving the thermal stability of the cathode interface and improving the thermal safety performance of the secondary battery.

[0026] In some embodiments of this application, the positive electrode active material includes LiNi. x Co y M 1-x-y O2, 0.6≤x≤1.0, 0≤y≤0.4, M is Al or Mn. For example, the value of x can be 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, or any two of these values; the value of y can be 0, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, or any two of these values. When a positive electrode active material within the above range is selected, the positive electrode active material has a high theoretical specific capacity and good structural and thermal stability during charge-discharge cycles. The positive electrode active material within the scope of this application, when used in combination with the first compound, is beneficial to improving the high-temperature cycle performance of the secondary battery, while taking into account the low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thereby improving the thermal safety performance of the secondary battery.

[0027] In some embodiments of this application, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is A, and the mass percentage of the first compound is B; A, x, and B satisfy: B = k × A × x, 93% ≤ A ≤ 95.9%, 0.6 ≤ x ≤ 0.9, 0.001792 ≤ k ≤ 0.03475. For example, the value of A can be 93%, 93.2%, 93.5%, 93.8%, 94%, 94.2%, 94.5%, 94.8%, 95%, 95.2%, 95.5%, 95.8%, 95.9%, or a range of any two of these values; the value of x can be 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0. The values ​​of k can be 85, 0.88, 0.9, or any two of these values; the values ​​of k can be 0.001792, 0.0018, 0.002, 0.005, 0.008, 0.01, 0.012, 0.015, 0.018, 0.02, 0.022, 0.025, 0.028, 0.03, 0.032, 0.34, 0.03475, or any two of these values. When A, x, and B satisfy the above relationship, and the values ​​of A, x, and k are adjusted within the above range, the positive electrode material layer includes a positive electrode active material with a high Ni content. The combination of the first compound and the positive electrode active material with a high Ni content can neutralize residual alkali to reduce the residual alkali content on the surface of the positive electrode material layer, improving high-temperature gas generation. Furthermore, the first compound has a low oxidation potential of around 3.7V, which can promote positive electrode film formation and reduce the risk of transition metal dissolution and electrolyte oxidation. In addition, the C=C unsaturation in the first compound can form a film on the negative electrode, reducing side reactions between the negative electrode and the electrolyte, and improving the cycle performance of the secondary battery. Adding the first compound within the above content range to the positive electrode material layer is beneficial for improving the high-temperature cycle performance of the secondary battery, while also considering low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thus improving the thermal safety performance of the secondary battery. While maintaining the high energy density of the secondary battery, it further improves the structural stability of the positive electrode.

[0028] In some embodiments of this application, the positive electrode active material includes lithium nickel cobalt manganese oxide, which includes a metal element M1, and the metal element M1 includes at least one selected from Al, Zr, Mg, Ba, or Ti. By controlling the type of M1 within the above-mentioned range, it is beneficial to further improve the thermal stability and electrochemical performance of the positive electrode active material. The positive electrode active material within the scope of this application, when used in combination with the first compound, is beneficial to improve the high-temperature cycle performance of the secondary battery, while taking into account low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thereby improving the thermal safety performance of the secondary battery.

[0029] In some embodiments of this application, the positive electrode active material includes lithium nickel cobalt aluminum oxide, which includes the metal element M2, and the metal element M2 includes at least one selected from Zr, Mg, Ba, or Ti. By controlling the type of M2 within the above-mentioned range, it is beneficial to further improve the thermal stability and electrochemical performance of the positive electrode active material. The positive electrode active material within the scope of this application, when used in combination with the first compound, is beneficial to improve the high-temperature cycle performance of the secondary battery, while taking into account low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thereby improving the thermal safety performance of the secondary battery.

[0030] In some embodiments of this application, the positive electrode active material includes lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. Lithium nickel cobalt manganese oxide includes metal element M1, which includes at least one of Al, Zr, Mg, Ba, or Ti. Lithium nickel cobalt aluminum oxide includes metal element M2, which includes at least one of Zr, Mg, Ba, or Ti. By controlling the types of M1 and M2 within the aforementioned range, it is beneficial to further improve the thermal stability and electrochemical performance of the positive electrode active material. The positive electrode active material within the scope of this application, when used in combination with the first compound, is beneficial to improve the high-temperature cycle performance of the secondary battery, while also considering low-temperature performance and impedance performance, and effectively improving the thermal stability of the positive electrode interface, thereby improving the thermal safety performance of the secondary battery.

[0031] In this application, lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide with different Ni content can be purchased, and the required Ni content of lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide can be selected by combining the test methods of "A, B and x" in this application.

[0032] This application does not impose any particular limitation on the doping amount of metal element M1, as long as the purpose of this application can be achieved. For example, based on lithium nickel cobalt manganese oxide, the remaining mass of metal element M1 after removing metal element M1 is 0.002% to 0.028%, that is, the doping amount of metal element M1 is 0.002% to 0.028%. This application does not impose any particular limitation on the doping amount of metal element M2, as long as the purpose of this application can be achieved. For example, based on lithium nickel cobalt aluminum oxide, the remaining mass of metal element M2 after removing metal element M2 is 0.001% to 0.02%, that is, the doping amount of metal element M2 is 0.001% to 0.02%.

[0033] This application does not impose any particular limitation on the 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, or composite current collectors (such as aluminum-carbon composite current collectors). In this application, the positive electrode material layer also includes a positive electrode binder and a conductive agent. This application does not impose any particular limitation on the type of positive electrode binder in the positive electrode material layer, as long as it achieves the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it achieves the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, or graphene. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers.

[0034] This application does not impose any particular restrictions on the preparation method of the positive electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the positive electrode sheet includes, but is not limited to, the following steps: (1) mixing the positive active material, the first compound, the positive binder and the conductive agent in a certain mass ratio and then adding a solvent to prepare a positive electrode slurry; (2) coating the positive electrode slurry on one surface of the positive current collector, and drying it to obtain a positive electrode sheet with a single-sided coating of positive electrode material layer; (3) repeating the above steps on the other surface of the positive current collector to obtain a positive electrode sheet with a double-sided coating of positive electrode material layer; (4) obtaining the positive electrode sheet after cold pressing, cutting and slitting.

[0035] In this application, the mass percentage B of the first compound and the mass percentage A of the positive electrode active material in the positive electrode material layer can be controlled by adjusting the mass ratio of the positive electrode active material, the first compound, the positive electrode binder, and the conductive agent. This application does not impose any particular restrictions on the solvent and solid content used in the positive electrode slurry in step (1) above, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the drying temperature and time in step (2) above; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the process parameters of cold pressing, cutting, and slitting in step (4) above; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application does not impose any particular restrictions on the size of the positive electrode sheet above, as long as the purpose of this application can be achieved.

[0036] A second aspect of this application provides a secondary battery comprising a negative electrode, a separator, an electrolyte, and a positive electrode as described in any of the foregoing embodiments. The secondary battery of this application exhibits excellent high-temperature cycle performance and thermal safety performance, while also considering low-temperature performance and impedance performance.

[0037] In some embodiments of this application, the electrolyte includes a second compound, which includes at least one of a cyclic sulfate compound or a cyclic carbonate compound. The cyclic sulfate compound includes at least one of vinyl sulfate, propylene sulfate, or methyl vinyl sulfate, and the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, or fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of the second compound is C, where 0.05% ≤ C ≤ 3%. For example, the value of C can be 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or a range of any two of these values. By adding the aforementioned second compounds to the electrolyte and adjusting the mass percentage C of the second compound within the above range, the first and second compounds work synergistically to improve the thermal stability of the electrolyte, reduce the risk of electrolyte decomposition and gas generation under high temperature conditions, improve the stability of the solid electrolyte interphase (SEI) film, further enhance the high-temperature storage and cycle performance of the secondary battery, take into account both low-temperature performance and impedance performance, effectively improve the thermal stability of the positive electrode interface, and improve the thermal safety performance of the secondary battery.

[0038] In some embodiments of this application, the electrolyte includes a third compound, which includes at least one of methylene methane disulfonate, vinylene carbonate, ethyl methyl carbonate, or propyl methyl carbonate. Based on the mass of the electrolyte, the mass percentage of the third compound is D, where 0.05% ≤ D ≤ 2%. For example, the value of D can be 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values. By adding the aforementioned third compound to the electrolyte and controlling the mass percentage D of the third compound within the above range, it is beneficial to form a more stable SEI film during the charge and discharge process of the secondary battery. The first and third compounds work synergistically, and the third compound exhibits good electrochemical stability, thereby further improving the high-temperature cycle performance of the secondary battery, while also considering low-temperature and impedance performance, and improving the thermal safety performance of the secondary battery.

[0039] In this application, the electrolyte also includes lithium salts and non-aqueous solvents. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, 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 impose any particular limitation on the content of lithium salts in the electrolyte, as long as it achieves the purpose of this application. For example, based on the mass of the electrolyte, the mass percentage of lithium salts may be 1% to 15%.

[0040] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0041] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain 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), and ethyl propyl carbonate (EPC). Fluorocarbonate compounds may include, but are not limited to, at least one of 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. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 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 non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the content of 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 non-aqueous solvents may be 80% to 99%.

[0042] This application places no particular restrictions on the negative electrode sheet, as long as the objectives of this application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along its thickness direction, or can be provided on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector or a partial area of the surface of the negative electrode current collector. This application places no particular restrictions, as long as the objectives of this application can be achieved. This application places no particular restrictions on the negative electrode current collector, as long as the objectives of this application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). The negative electrode material layer of this application includes a negative electrode active material. This application places no particular restrictions on the type of the negative electrode active material, as long as the objectives of this application can be achieved. For example, the negative electrode active material can 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, lithium titanate with a spinel structure Li4Ti5O 12 , Li-Al alloy, or at least one of metallic lithium. In this application, there are no particular restrictions on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm, and the thickness of the negative electrode material layer is 30 μm to 130 μm. Optionally, the negative electrode material layer can further include a conductive agent and a negative electrode binder. This application places no particular restrictions on the type of the conductive agent in the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the conductive agent can be of the same type as the conductive agent in the above positive electrode material layer. This application places no particular restrictions on the type of the negative electrode binder in the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the negative electrode binder can be of the same type as the positive electrode binder in the above positive electrode material layer. Optionally, the negative electrode material layer further includes a thickening agent. This application places no particular restrictions on the type of the thickening agent, as long as the objectives of this application can be achieved. For example, the thickening agent can include at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose. This application places no particular restrictions on the mass ratio of the negative electrode active material, conductive agent, binder, and thickening agent in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the objectives of this application can be achieved.

[0043] 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), polyolefins (PO) mainly composed of 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.

[0044] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven membrane or composite membrane with a porous structure, and the material of the 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.

[0045] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0046] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from 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. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0047] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0048] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0049] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0050] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0051] A third aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0052] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0053] Example

[0054] 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. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0055] Test methods and equipment:

[0056] Infrared spectroscopy test:

[0057] The lithium-ion battery was discharged at a constant current of 0.1C to 3.0V. The electrolyte was collected by centrifugation, and the lithium-ion battery was disassembled to obtain the positive electrode sheet. The positive electrode sheet was soaked in 10 mL of dimethyl carbonate (DMC) for 30 min and then mixed with the collected electrolyte. The positive electrode sheet was then baked at 100℃ for 2 h before use. The positive electrode material layer on the positive electrode sheet was scraped off, and the powder of the positive electrode material layer was collected.

[0058] Using an infrared spectrometer (Nicolet iS50), the collected liquid and solid samples were tested using the potassium bromide (KBr) pellet method and the liquid film method to obtain the infrared spectra of the cathode material layer. 500 mg of KBr and 10 mg of cathode material powder were ground in a mortar to obtain a mixture. This mixture was placed in a pressure mold and pressurized to 20 MPa, held for 10 seconds, and then depressurized to obtain a disc. The disc was then removed, and the infrared spectrum of the solid sample was tested using the infrared spectrometer. The window was cleaned with acetone, and the collected liquid sample was evenly coated onto the window for testing. The infrared spectrum of the liquid sample was then measured using the infrared spectrometer. The original spectra of the solid and liquid samples were preprocessed and then combined to obtain the infrared spectrum of the cathode material layer.

[0059] Tests of A, B, and x:

[0060] A's test:

[0061] (1) Take the positive electrode sheet after cleaning with DMC, and use a 1540.25mm diameter plate. 2 The die punches and cuts the double-sided material layer area of ​​the positive electrode sheet and the aluminum foil for the positive current collector; the number of double-sided material layer area discs is 3, and the number of aluminum foil is 1;

[0062] (2) Weigh the mass of weighing bottle A and filter membrane B, and record it as M0; weigh the weight of a single aluminum foil, and record it as M1; use a 250mL conical flask to tare and weigh the weight of 3 punched positive electrode sheets, and record it as M2;

[0063] (3) Add about 50 mL of concentrated hydrochloric acid to the conical flask;

[0064] (4) Place the conical flask on a flat plate heater to heat and digest. When it is almost dry, add an appropriate amount of water to continue heating. Stop heating after boiling for 15 minutes and remove it to cool.

[0065] (5) Filter the digested solution portion using a vacuum filter, and rinse the filter residue retained in the conical flask with deionized water 3 to 4 times until colorless;

[0066] (6) Add another 50 mL of concentrated hydrochloric acid to the conical flask containing the filter residue and continue digestion;

[0067] (7) Vacuum filter and rinse the filter residue with deionized water 3 to 4 times. Add a small amount of concentrated hydrochloric acid to the conical flask containing the filter residue. If it is colorless and transparent, it means that the positive electrode active material has been completely digested and there is no need to continue digestion. Otherwise, repeat steps (4) to (5) until the filtrate is transparent.

[0068] (8) Transfer the filter residue and filter membrane B to weighing bottle A. At this time, be careful not to lose the mass of the filter residue. Place it in a vacuum drying oven at 85°C for more than 4 hours to ensure thorough drying. Then take out the weighing bottle and transfer it to a desiccator to cool for half an hour. Weigh the dried filter residue, filter membrane and weighing bottle to obtain the mass M3.

[0069] (9) The mass percentage of the positive electrode active material A = (M3-M0) / (M2-M1×3).

[0070] Test B:

[0071] Following the same infrared spectroscopy testing steps as described above, the content of the first compound in the liquid and solid samples collected after centrifugation was tested.

[0072] Test of x:

[0073] The mass percentage of each metal element in the cathode material layer is measured using energy-dispersive X-ray spectroscopy (EDS). Based on the mass percentage of the cathode active material in the cathode material layer obtained above, the molar percentage of Ni in the cathode active material can be obtained, and then x can be calculated.

[0074] Electrolyte component content test:

[0075] The lithium-ion battery was discharged to 2.8V at a constant current of 0.5C and then disassembled. The electrolyte was collected, and the disassembled positive electrode, negative electrode, and separator were centrifuged. The liquid obtained after centrifugation was mixed evenly with the electrolyte. Then, gas chromatography-mass spectrometry (Agilent 8890 instrument) and ion chromatography (AQUION ion chromatograph) were used to test the components in the electrolyte and determine their content.

[0076] Initial efficiency test:

[0077] The lithium-ion batteries in the examples and comparative examples were subjected to formation and capacity tests to compare their initial efficiency. Test conditions: The lithium-ion batteries were first formed, and then charged at 80°C and 1.2 MPa with a constant current of 0.3C for 300s, followed by a constant current of 1C for 270s, and then a constant current of 1.5C for 1980s. The charging capacity C1 was recorded. Then, at 45°C, the batteries were charged with a constant current of 0.5C to 4.4V, followed by a constant voltage charge to 0.05C. After resting for 5 minutes, the batteries were discharged at 0.5C to 3.0V. The charging capacity C2 and the initial discharge capacity D' of the lithium-ion batteries were recorded.

[0078] The initial efficiency (%) of a lithium-ion battery = initial discharge capacity / initial charge capacity × 100% = D' / (C1 + C2) × 100%.

[0079] 85℃, 4-hour high-temperature storage test:

[0080] The lithium-ion batteries in the examples and comparative examples were subjected to a high-temperature storage test at 85°C for 4 hours. At room temperature (25°C), the lithium-ion batteries were charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage of 0.05C, and left to stand for 1 hour. The thickness, voltage, and internal resistance of the lithium-ion batteries were measured. Then, the batteries were charged at a constant current of 0.2C to 4.4V, then charged at a constant voltage of 0.05C, left to stand for 5 minutes, and then discharged at 0.2C to 3.0V. The discharge capacity before storage was recorded. The lithium-ion batteries were then placed in an 85°C constant-temperature chamber and left to stand for 4 hours. The thickness, voltage, and internal resistance of the lithium-ion batteries were measured at the high temperature of 85°C. After cooling to room temperature (25°C), the batteries were charged at a constant current of 0.2C to 4.4V, then charged at a constant voltage of 0.05C, left to stand for 5 minutes, and then discharged at 0.2C to 3.0V. The discharge capacity after storage was recorded.

[0081] Thickness expansion rate (%) at 85℃ for 4 hours = (thickness after storage - thickness before storage) / thickness before storage × 100%;

[0082] Capacity retention rate (%) at 85℃ for 4 hours = Discharge capacity after storage / Discharge capacity before storage × 100%.

[0083] 60℃, 30-day high-temperature storage test:

[0084] The lithium-ion batteries in the examples and comparative examples were subjected to a 30-day high-temperature storage test at 60°C. At room temperature (25°C), the lithium-ion batteries were charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage of 0.05C, and left to stand for 1 hour. The thickness, voltage, and internal resistance of the lithium-ion batteries were measured. They were then charged at a constant current of 0.2C to 4.4V, then charged at a constant voltage of 0.05C, left to stand for 5 minutes, and then discharged at 0.2C to 3.0V. The discharge capacity before storage was recorded. The lithium-ion batteries were then placed in a 60°C constant-temperature chamber and left to stand for 30 days. At a high temperature of 60°C, the thickness, voltage, and internal resistance of the lithium-ion batteries were measured. After cooling to room temperature (25°C), they were charged at a constant current of 0.2C to 4.4V, then charged at a constant voltage of 0.05C, left to stand for 5 minutes, and then discharged at 0.2C to 3.0V. The discharge capacity after storage was recorded.

[0085] Thickness expansion rate (%) at 60℃ for 30 days = (thickness after storage - thickness before storage) / thickness before storage × 100%;

[0086] Capacity retention rate at 60℃ for 30 days (%) = Discharge capacity after storage / Discharge capacity before storage × 100%.

[0087] Hot box pass rate test for lithium-ion batteries:

[0088] The hot box testing procedure is as follows:

[0089] (1) Adjust the furnace temperature to 25℃ and let it stand for 5 minutes; (2) Charge the furnace with 0.2C DC to 3.0V; (3) Let it stand for 10 minutes; (4) Charge the furnace with 0.7C constant current to 4.4V, and charge it with 4.4V constant voltage to 0.05C; (5) Let it stand for 10 minutes.

[0090] Before testing, photographs were taken, and the voltage and internal resistance of the lithium-ion batteries were measured. A temperature sensing wire was attached to the surface of the lithium-ion batteries. The lithium-ion battery samples were placed in the heating furnace chamber, and the temperature was increased to 130±2℃ at a rate of 5±2℃ / min and held for 60 minutes. After the test, photographs were taken, and the voltage and internal resistance of the lithium-ion batteries were measured again. Ten lithium-ion batteries were tested in each group. If the lithium-ion batteries did not catch fire or explode, they were considered to have passed the hot chamber test.

[0091] Gas generation test:

[0092] The online voltage was tested using a Xinwei machine, and the online thickness of the lithium-ion battery was tested using a Yuaneng Technology CBS1300. At 25°C, the lithium-ion batteries from the examples and comparative examples were discharged at a constant current of 0.05C to 3.0V and then allowed to stand for 5 minutes. They were then discharged at a constant current of 10mA to 0.1C and allowed to stand for 30 minutes, followed by a constant current of 1mA to 0.1C and a stand for 30 minutes. During this process, online voltage and thickness (Tx) measurements were taken every 30 seconds, with the initial thickness recorded as T0. The thickness expansion rate (Tx / T0) of the lithium-ion battery was then calculated. A smaller thickness expansion rate at the same voltage level indicates better uniformity of the SEI film formation in the secondary battery.

[0093] DC Impedance (DCR) Test:

[0094] At 10°C, the lithium-ion batteries in the examples and comparative examples were charged at a constant current of 0.5C to 4.4V, and then charged at a constant voltage of 4.4V to 0.05C; they were then left to stand for 30 minutes. Next, they were discharged at 0.1C for 10 seconds (taking a sample every 0.1 seconds and recording the corresponding voltage value U1), and then discharged at 1C for 360 seconds (taking a sample every 0.1 seconds and recording the corresponding voltage value U2). This charging and discharging process was repeated 5 times. Here, "1C" refers to the current value required to completely discharge the lithium-ion battery within 1 hour.

[0095] The DCR of a lithium-ion battery is calculated using the following formula:

[0096] DCR (mΩ)=(U2-U1) / (1C-0.1C).

[0097] In this application, DCR is the value at 50% state of charge (SOC).

[0098] Example 1-1

[0099] <Preparation of the positive electrode>

[0100] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1O2), conductive carbon black (Super P), conductive carbon nanotubes (CNTs), positive electrode binder polyvinylidene fluoride (PVDF), and the first compound, vinyl phosphate, were mixed in a mass ratio of 95.4:2:0.8:1.2:0.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was thoroughly stirred to form a uniform positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil current collector and dried at 85°C to obtain a single-sided coated positive electrode sheet. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm. The coating weight of the positive electrode material layer during coating was 0.2419 g / 1540.25 mm. 2 The compaction density of the cathode material layer after cold pressing is 3.4 g / cm³. 3 Among them, based on the mass of the positive electrode material layer, the mass percentage content A of the positive electrode active material is 95.4%, and the mass percentage content B of the first compound is 0.6%.

[0101] <Preparation of Negative Electrode Sheets>

[0102] Artificial graphite, used as the negative electrode active material, was mixed with styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) at a mass ratio of 97.7:1.2:1.1, and then deionized water was added. The mixture was thoroughly stirred to form a homogeneous negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was coated onto one surface of a 6 μm thick copper foil current collector and dried at 85°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material. This process was repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material. After drying under vacuum at 120°C for 12 hours, the sheet was cold-pressed, cut, and slit to obtain a negative electrode sheet with dimensions of 78 mm × 875 mm. The coating weight of the negative electrode material layer was 0.14 g / 1540.25 mm. 2 The compaction density of the negative electrode material layer after cold pressing is 1.75 g / cm³. 3 .

[0103] <Preparation of Electrolyte>

[0104] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1:1 to obtain the base solvent. Then, ethylene sulfate (the second compound) and methylene methane disulfonate (MMDS) were added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 1.15%, the mass percentage of ethylene sulfate (C) was 0.1%, the mass percentage of methylene methane disulfonate (D) was 0.1%, and the remainder was the base solvent.

[0105] <Septum>

[0106] A 5μm thick porous polyethylene (PE) polymer film was used as the separator.

[0107] <Preparation of Lithium-ion Batteries>

[0108] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, the electrodes are wound, the tabs are welded, and the battery is placed in an outer packaging foil aluminum-plastic film. Electrolyte is injected, and the battery undergoes vacuum sealing, settling, formation, shaping, and capacity testing to obtain a soft-pack lithium-ion battery.

[0109] Examples 1-2 to Examples 1-15

[0110] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, when the mass percentage B of the first compound changes, the mass percentage A of the positive electrode active material changes accordingly, while the mass percentages of the two conductive agents and the positive electrode binder remain unchanged.

[0111] Examples 1-16

[0112] In addition to lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 The O2) is doped with the metal element Mg. Based on the remaining mass of lithium nickel cobalt manganese oxide after removing the metal element Mg, the mass percentage of the metal element Mg is 0.015%, that is, the doping amount of the metal element Mg is 0.015%. And based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material remains unchanged, and the rest is the same as in Example 1-1.

[0113] Examples 1-17

[0114] In addition to lithium nickel cobalt aluminum oxide (LiNi 0.8 Co 0.1 Al 0.1In the O2) doping, the metal element Zr is based on the remaining mass of lithium nickel cobalt aluminum oxide after removing the metal element Zr. The mass percentage of metal element Zr is 0.01%, that is, the doping amount of metal element Zr is 0.01%. And based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material remains unchanged. The rest is the same as in Example 1-1.

[0115] Examples 1-18

[0116] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0117] Example 2-1

[0118] Except for the preparation of the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0119] <Preparation of Electrolyte>

[0120] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1:1 to obtain the base solvent. Then, vinyl sulfate (a second compound) was added, dissolved, and thoroughly stirred before lithium salt LiPF6 was added and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 1.15%, the mass percentage of vinyl sulfate (C) was 0.05%, and the remainder was the base solvent.

[0121] Examples 2-2 to 2-6

[0122] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Example 2-1. Specifically, when the mass percentage of the second compound changes, the mass percentage of the base solvent changes accordingly, while the mass ratio of each substance in the base solvent remains unchanged, and the mass percentage of lithium salt LiPF6 remains unchanged.

[0123] Examples 2-7

[0124] Except for the preparation of the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0125] <Preparation of Electrolyte>

[0126] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1:1 to obtain the base solvent. Then, a third compound, methylene disulfonate (MMDS), was added, dissolved, and thoroughly stirred. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 1.15%, the mass percentage of the third compound methylene disulfonate (D) was 0.05%, and the remainder was the base solvent.

[0127] Examples 2-8 to Examples 2-12

[0128] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 2-7. Specifically, when the mass percentage of the second compound changes, the mass percentage of the base solvent changes accordingly, while the mass ratio of each substance in the base solvent remains unchanged, and the mass percentage of lithium salt LiPF6 remains unchanged.

[0129] Example 2-13

[0130] Except for the preparation of the electrolyte according to the following steps, the rest is the same as in Example 1-1.

[0131] <Preparation of Electrolyte>

[0132] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1:1 to obtain a base solvent. After thorough stirring, lithium salt LiPF6 was added and mixed evenly to obtain the electrolyte. The mass percentage of LiPF6 in the electrolyte was 1.15%, with the remainder being the base solvent.

[0133] Comparative Example 1

[0134] Except that the first compound is not added in the <Preparation of Positive Electrode Sheet>, the mass percentage A of the positive electrode active material changes accordingly, and the mass percentages of the two conductive agents and the positive electrode binder remain unchanged, the rest is the same as in Example 1-1.

[0135] Comparative Example 2

[0136] Except for replacing the first compound ethylene phosphate with methyl phosphate in the <Preparation of the positive electrode sheet>, the rest is the same as in Example 1-1.

[0137] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0138] Table 1

[0139]

[0140] Note: " / " in Table 1 indicates that there are no relevant preparation parameters.

[0141] As can be seen from Examples 1-1 to 1-18 and Comparative Examples 1 to 2, by adding the first compound to the positive electrode material layer, the positive electrode material layer at 1150 cm⁻¹ can achieve the desired effect. -1 ±10cm -1 And, 1085cm -1 ±10cm -1 1600cm -1 ±10cm -1 1640cm -1 ±10cm -1 Or 1500cm -1 ±10cm -1 The presence of infrared characteristic peaks at any two locations in Comparative Example 1 indicates that the lithium-ion battery exhibits high initial efficiency, low thickness expansion at high temperatures, low DCR value at 50% state of charge, high capacity retention at high temperatures, and high hot box pass rate. This demonstrates that the lithium-ion battery possesses good high-temperature cycling performance, while also maintaining low-temperature performance and impedance performance. Furthermore, the SEI film of the lithium-ion battery exhibits high uniformity and stability. In Comparative Example 1, no characteristic peaks within the scope of this application are present in the positive electrode material layer during infrared testing. In Comparative Example 2, only one characteristic peak within the scope of this application is present in the positive electrode material layer during infrared testing. In these cases, the lithium-ion batteries in Comparative Examples 1 and 2 exhibit lower initial efficiency, higher thickness expansion at high temperatures, higher DCR value at 50% state of charge, lower capacity retention at high temperatures, and lower hot box pass rate. This indicates that the lithium-ion battery cannot simultaneously achieve high-temperature cycling performance, low-temperature performance, and impedance performance. Additionally, the SEI film of the lithium-ion battery exhibits poor uniformity and stability, resulting in lower thermal safety performance. The lithium-ion batteries in Examples 1-1 to 1-18 have good high-temperature cycle performance, while also taking into account low-temperature performance and impedance performance, and the lithium-ion batteries have good thermal safety performance.

[0142] The content of the first compound B typically affects the high-temperature cycle performance, low-temperature performance, impedance performance, and thermal safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-5 to 1-9, when the content of the first compound B is controlled within the scope of this application, the lithium-ion battery exhibits high initial efficiency, low thickness expansion at high temperatures, low DCR value at 50% state of charge, high capacity retention at high temperatures, and high thermal conductivity. This indicates that the lithium-ion battery possesses good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance. Furthermore, the high uniformity and stability of the SEI film in the lithium-ion battery demonstrate that it exhibits good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance, and that the lithium-ion battery has good thermal safety performance.

[0143] The type of positive electrode active material typically affects the high-temperature cycle performance, low-temperature performance, impedance performance, and thermal safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-10 to 1-15, when the positive electrode active material within the scope of this application is used, the lithium-ion battery exhibits higher initial efficiency, lower thickness expansion at high temperatures, lower DCR value at 50% state of charge, higher capacity retention at high temperatures, and higher thermal conductivity. This indicates that the lithium-ion battery possesses good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance. Furthermore, the high uniformity and stability of the SEI film in the lithium-ion battery demonstrate its excellent high-temperature cycle performance, while also maintaining good low-temperature and impedance performance, and its relatively good thermal safety performance.

[0144] The relationship between A, x, and B typically affects the high-temperature cycle performance, low-temperature performance, impedance performance, and thermal safety performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-15, when the relationship between A, x, and B satisfies the requirements of this application, the lithium-ion battery exhibits higher initial efficiency, lower thickness expansion at high temperatures, lower DCR value at 50% state of charge, higher capacity retention at high temperatures, and higher thermal conductivity. This indicates that the lithium-ion battery possesses good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance. Furthermore, the uniformity and stability of the SEI film in the lithium-ion battery are high, demonstrating good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance, and good thermal safety performance.

[0145] The type of M1 or M2 typically affects the high-temperature cycle performance, low-temperature performance, impedance performance, and thermal safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-16, and 1-17, when M1 or M2 within the scope of this application is used, the lithium-ion battery exhibits higher initial efficiency, lower thickness expansion at high temperatures, lower DCR value at 50% state of charge, higher capacity retention at high temperatures, and higher thermal box throughput. This indicates that the lithium-ion battery possesses good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance. Furthermore, the uniformity and stability of the SEI film in the lithium-ion battery are high, demonstrating good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance, and good thermal safety performance.

[0146] Table 2

[0147]

[0148] In Table 2, “ / ” indicates that no relevant preparation parameters are available.

[0149] The type and content of the second compound typically affect the high-temperature cycle performance, low-temperature performance, impedance performance, and thermal safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-6, and 2-13, when the electrolyte includes the second compound and its content is within the range specified in this application, the lithium-ion battery exhibits higher initial efficiency, lower thickness expansion at high temperatures, lower DCR value at 50% state of charge, higher capacity retention at high temperatures, and higher thermal conductivity. This indicates that the lithium-ion battery possesses good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance. Furthermore, the high uniformity and stability of the SEI film in the lithium-ion battery demonstrate its excellent high-temperature cycle performance, while also maintaining good low-temperature and impedance performance, and exhibiting good thermal safety performance.

[0150] The type and content of the third compound typically affect the high-temperature cycle performance, low-temperature performance, impedance performance, and thermal safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-7 to 2-13, when the electrolyte includes the third compound and its content is within the scope of this application, the lithium-ion battery exhibits higher initial efficiency, lower thickness expansion at high temperatures, lower DCR value at 50% state of charge, higher capacity retention at high temperatures, and higher thermal conductivity. This indicates that the lithium-ion battery has good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance. Furthermore, the high uniformity and stability of the SEI film in the lithium-ion battery demonstrate that it possesses good high-temperature cycle performance, while also maintaining good low-temperature and impedance performance, and exhibits good thermal safety performance.

[0151] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0152] 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.

[0153] 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 positive electrode sheet comprising a positive current collector and a positive electrode material layer located on at least one surface of the positive current collector, the positive electrode material layer comprising a positive electrode active material and a first compound, the first compound comprising at least one selected from vinyl phosphate, allyl phosphate, vinylene phosphate, diallyl phosphate, styrene phosphate, diphenyl phosphate, or stilbene phosphate, wherein the infrared spectrum of the positive electrode material layer is at 1150 cm⁻¹. -1 ±10cm -1 And, 1085cm -1 ±10cm -1 1600cm -1 ±10cm -1 1640cm -1 ±10cm -1 Or 1500cm -1 ±10cm -1 There are infrared characteristic peaks at any two locations in the image.

2. The cathode sheet of claim 1, wherein, The mass percentage of the first compound is B based on the mass of the positive electrode material layer, and 0.1%≤B≤3%.

3. The cathode sheet of claim 2, wherein, 0.1%≤B≤1%。 4. The cathode sheet of claim 1, wherein, The positive electrode active material includes LiNi x Co y M 1-x-y O2, 0.6≤x≤1.0, 0≤y≤0.4, M is Al or Mn.

5. The cathode sheet of claim 4, wherein, The mass percentage of the positive electrode active material is A, and the mass percentage of the first compound is B based on the mass of the positive electrode material layer; A, x, and B satisfy: B=k×A×x, 93%≤A≤95.9%, 0.6≤x≤0.9, and 0.001792≤k≤0.03475.

6. The positive electrode sheet according to claim 4, which satisfies at least one of the following characteristics: (1) the positive electrode active material includes lithium nickel cobalt manganese oxide, and the lithium nickel cobalt manganese oxide includes a metal element M1, the metal element M1 including at least one of Al, Zr, Mg, Ba, or Ti; (2) the positive electrode active material includes lithium nickel cobalt aluminum oxide, and the lithium nickel cobalt aluminum oxide includes a metal element M2, the metal element M2 including at least one of Zr, Mg, Ba, or Ti.

7. A secondary battery including a negative electrode sheet, a separator, an electrolyte, and the positive electrode sheet according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, wherein The electrolyte includes a second compound, the second compound including at least one of a cyclic sulfate compound or a cyclic carbonate compound, the cyclic sulfate compound including at least one of vinyl sulfate, propylene sulfate, or methyl vinyl sulfate, and the cyclic carbonate compound including at least one of vinylene carbonate, vinyl ethylene carbonate, or fluoro vinyl carbonate; the mass percentage of the second compound is C based on the mass of the electrolyte, and 0.05%≤C≤3%.

9. The secondary battery according to claim 7, wherein The electrolyte includes a third compound, the third compound including at least one of methylene methane disulfonate, vinylene carbonate, methyl ethyl carbonate, or methyl propyl carbonate; the mass percentage of the third compound is D based on the mass of the electrolyte, and 0.05%≤D≤2%.

10. An electronic device including the secondary battery according to any one of claims 7 to 9.

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