Secondary battery and electronic device

Abstract

A secondary battery and an electronic device, the secondary battery comprising a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector, as well as a first material layer and a second material layer disposed on a surface of the positive electrode current collector, the first material layer being located between the positive electrode current collector and the second material layer; the peel strength F between the first material layer and the positive electrode current collector is 50 N / m to 130 N / m; the electrolyte comprises an additive, the additive containing at least one of a difluorophosphate anion and a tetrafluorooxalatophosphate anion; and on the basis of the mass of the electrolyte, the mass percentage W of the additive is 0.5% to 10%. The secondary battery has good nail penetration safety performance.

Description

A secondary battery and electronic device

[0001] This application claims priority to Chinese Patent Application No. 202510378055.4, filed on March 27, 2025, entitled "A Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0003] Secondary batteries, such as lithium-ion batteries, have become a core power source for portable electronic devices, electric vehicles, and renewable energy systems since their commercialization in the 1990s, serving as efficient, rechargeable energy storage devices. Their high energy density, long cycle life, and low self-discharge rate set them apart from other battery technologies.

[0004] However, during use or transportation, secondary batteries may experience internal short circuits due to mechanical damage, leading to thermal runaway and potentially causing fires or even explosions, posing a safety hazard. Therefore, improving the needle penetration safety performance of secondary batteries remains a pressing issue. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device to improve the needle penetration safety performance of the secondary battery.

[0006] 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:

[0007] The first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, with the first material layer located between the positive current collector and the second material layer. The peel strength F between the first material layer and the positive current collector is 50 N / m to 130 N / m; in some embodiments of this application, 70 N / m ≤ F ≤ 100 N / m. The electrolyte includes an additive containing at least one of difluorophosphate anion and tetrafluorooxalate phosphate anion; based on the mass of the electrolyte, the mass percentage W of the additive is 0.5% to 10%. In some embodiments of this application, 2% ≤ W ≤ 7%. In some embodiments of this application, 3% ≤ W ≤ 5%. With the above configuration, the peel strength between the first material layer and the positive current collector is moderate. Combined with the above-mentioned amount of additive, this facilitates the maintenance of active ion transport channels and improves the thermal stability of the electrolyte, thereby improving the needle penetration safety performance of the secondary battery while also considering its kinetic performance.

[0008] In some embodiments of this application, the additive includes at least one selected from lithium difluorophosphate, lithium tetrafluorooxalate phosphate, fluoroalkyl difluorophosphate, and trimethyl hexafluorophosphate, wherein the alkyl group in the fluoroalkyl difluorophosphate has 1 to 10 carbon atoms. By selecting the above-mentioned additives, the thermal stability of the electrolyte can be further improved, thereby enhancing the needle penetration safety performance of the secondary battery. Simultaneously, the above-mentioned additives also facilitate the transport of active ions, thereby improving the kinetic performance of the secondary battery.

[0009] In some embodiments of this application, the first material layer includes a first binder, which includes at least one of carboxylated polyvinylidene fluoride, sulfonated polyvinylidene fluoride, carboxylated polyimide, sulfonated polyimide, or sulfonated polyether ether ketone. The aforementioned types of first binders help reduce the probability of the first material layer peeling off from the positive electrode current collector during puncture testing, thereby improving the puncture safety performance of the secondary battery.

[0010] Based on the mass of the first material layer, the mass percentage m1 of the first adhesive is 0.1% to 4%. In some embodiments of this application, 0.2% ≤ m1 ≤ 2.5%. In some embodiments of this application, 0.8% ≤ m1 ≤ 2%. By adjusting m1 within the above range, it is beneficial to increase the number of punctures the secondary battery passes in the puncture test. At the same time, a suitable m1 also helps to reduce the impedance of the secondary battery, thereby balancing the puncture safety performance and kinetic performance of the secondary battery.

[0011] In some embodiments of this application, 0.5% ≤ m2 ≤ 2.5%. By adjusting m2 within the above range, the second adhesive layer has good adhesion while maintaining suitable conductivity, which is beneficial for further improving the needle penetration safety performance and kinetic performance of the secondary battery.

[0012] In some embodiments of this application, the second material layer includes a second adhesive, and the mass percentage (m2) of the second adhesive, based on the mass of the second material layer, is 0% ≤ m1-m2 ≤ 3%. In some embodiments of this application, it is 0.5% ≤ m1-m2 ≤ 2%. By adjusting m1-m2 within the above range, it is beneficial to increase the number of punctures the secondary battery passes in the puncture test, while reducing the impedance of the secondary battery. Therefore, adjusting m1-m2 within the above range is beneficial to further improve the needle penetration safety performance and kinetic performance of the secondary battery.

[0013] In some embodiments of this application, the second binder includes at least one selected from polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. By selecting the above-mentioned second binder, and using the first material layer of the second binder in conjunction with the first material layer of this application, it is beneficial to further improve the needle penetration safety performance and kinetic performance of the secondary battery.

[0014] In some embodiments of this application, the coating mass per unit area of ​​the first material layer is CW1, and the coating mass per unit area of ​​the second material layer is CW2. In some embodiments of this application, 1% ≤ CW1 / (CW1+CW2)×100% ≤ 15%; in some embodiments of this application, 3% ≤ CW1 / (CW1+CW2)×100% ≤ 10%; in some embodiments of this application, 85% ≤ CW2 / (CW1+CW2)×100% ≤ 99%; in some embodiments of this application, 90% ≤ CW2 / (CW1+CW2)×100% ≤ 97%. By adjusting CW1 / (CW1+CW2)×100% and CW2 / (CW1+CW2)×100% ≤ 99% within the above ranges, the first and second adhesive layers cooperate effectively, which helps to better balance the needle penetration safety performance, energy density, and kinetic performance of the secondary battery.

[0015] In some embodiments of this application, 150mg / 1540.24mm 2 ≤CW1+CW2≤350mg / 1540.24mm 2 In some embodiments of this application, 200 mg / 1540.24 mm 2 ≤CW1+CW2≤300mg / 1540.24mm2 By adjusting CW1+CW2 within the aforementioned range, it is beneficial to balance the mechanical properties, energy density, and active ion transport of the positive electrode, thereby further improving the needle penetration safety performance, energy density, and kinetic performance of the secondary battery.

[0016] In some embodiments of this application, the first material layer includes a first material, which includes at least one of alumina, lithium iron phosphate, boehmite, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganese oxide. In some embodiments of this application, the first material includes at least one of lithium nickel cobalt aluminum oxide or lithium nickel cobalt manganese oxide. In some embodiments of this application, the second material layer includes a second positive electrode material, which includes at least one of lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron phosphate. By selecting the above materials, it is beneficial to further improve the energy density of the secondary battery.

[0017] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments.

[0018] The beneficial effects of this application are:

[0019] This application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, with the first material layer located between the positive current collector and the second material layer. The peel strength F between the first material layer and the positive current collector is 50 N / m to 130 N / m. The electrolyte includes an additive containing at least one of difluorophosphate anion and tetrafluorooxalate phosphate anion. Based on the mass of the electrolyte, the mass percentage W of the additive is 0.5% to 10%. With the above configuration, the peel strength between the first material layer and the positive current collector is moderate. Combined with the above-mentioned amount of additive, this facilitates the maintenance of channels for active ion transport, thereby improving the needle penetration safety performance of the secondary battery while also considering its kinetic performance.

[0020] 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. Detailed Implementation

[0021] The technical solutions of this application will be clearly and completely described below with reference to the embodiments of this application. 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.

[0022] 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.

[0023] Lithium iron phosphate cathode active materials exhibit good thermal stability and high resistivity, resulting in a high pass rate in nail penetration tests of secondary batteries. This helps reduce the occurrence of thermal runaway, leading to high nail penetration safety performance in secondary batteries. However, the nail penetration capability of secondary batteries using other cathode materials still needs improvement. Based on these issues, this application provides a secondary battery and electronic device that can improve the nail penetration safety performance of secondary batteries using various cathode materials.

[0024] The first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, the first material layer being located between the positive current collector and the second material layer; the peel strength F between the first material layer and the positive current collector is 50 N / m to 130 N / m. In some embodiments of this application, 70 N / m ≤ F ≤ 100 N / m. For example, F can be 50 N / m, 55 N / m, 60 N / m, 65 N / m, 70 N / m, 75 N / m, 80 N / m, 85 N / m, 90 N / m, 95 N / m, 100 N / m, 105 N / m, 110 N / m, 115 N / m, 120 N / m, 125 N / m, 130 N / m, or a range consisting of any two of these values. When F is less than 50 N / m, the peel strength between the first material layer and the positive electrode current collector is too low. During the nail penetration test, the first material layer easily peels off from the positive electrode current collector, and the metal needle used in the test is prone to contact with the positive electrode current collector, causing a short circuit and potentially leading to thermal runaway. When F is greater than 130 N / m, the peel strength between the first material layer and the positive electrode current collector is too high, which can easily affect the transport of active ions in the positive electrode of the secondary battery, increase internal resistance, affect the rate performance of the secondary battery, and thus affect the kinetic performance. Therefore, the peel strength F between the first material layer and the positive electrode current collector is within the range of this application, which is beneficial for increasing the number of needle penetrations passed by the secondary battery while maintaining kinetic performance.

[0025] In some embodiments of this application, the electrolyte includes an additive containing at least one of difluorophosphate anion and tetrafluorooxalate phosphate anion. Adding the above-mentioned additive to the electrolyte improves its thermal stability, thereby reducing the risk of combustion and explosion of the secondary battery due to thermal runaway during puncture testing, and thus enhancing the puncture safety performance of the secondary battery.

[0026] In some embodiments of this application, the mass percentage W of the additive is 0.5% to 10% based on the mass of the electrolyte. In some embodiments of this application, 2% ≤ W ≤ 7%. In some embodiments of this application, 3% ≤ W ≤ 5%. For example, W can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range of any two of these values. When W is less than 0.5%, the additive does not sufficiently improve the thermal stability of the electrolyte, resulting in a higher risk of thermal runaway in the secondary battery during puncture testing and poor needle penetration safety performance. Simultaneously, if the additive content is too low, its improvement on the active ion transport performance is insufficient, which also affects the kinetic performance of the secondary battery. When W exceeds 10%, excessive additives reduce the high-voltage withstand performance of the secondary battery, thereby reducing its needle penetration safety performance. Furthermore, excessively high additive content also affects the transport rate of active ions, thus impacting the kinetic performance of the secondary battery. Therefore, by adjusting W within the scope of this application, it is beneficial to balance the high-voltage withstand performance and thermal stability of the secondary battery while maintaining good active ion transport, thereby improving the needle penetration safety performance and kinetic performance of the secondary battery.

[0027] Thus, through the above configuration, the peel strength between the first material layer and the positive electrode current collector is moderate. Combined with the above-mentioned amount of additives, it is beneficial to maintain a channel for the transport of active ions, thereby improving the needle penetration safety performance of the secondary battery while taking into account the kinetic performance.

[0028] In some embodiments of this application, the additive includes at least one selected from lithium difluorophosphate, lithium tetrafluorooxalate phosphate, fluoroalkyl difluorophosphate, and trimethyl hexafluorophosphate, wherein the alkyl group in the fluoroalkyl difluorophosphate has 1 to 10 carbon atoms. For example, the fluoroalkyl difluorophosphate can be at least one selected from trifluoromethyl difluorophosphate, pentafluoroethyl difluorophosphate, or perfluoropropyl difluorophosphate. By selecting the above-mentioned additives, it is beneficial to further improve the thermal stability of the electrolyte and improve the transport of active ions such as lithium ions, thereby improving the needle penetration safety performance of the secondary battery while also considering the kinetic performance.

[0029] In some embodiments of this application, the first material layer includes a first binder, which includes at least one of carboxylated polyvinylidene fluoride, sulfonated polyvinylidene fluoride, carboxylated polyimide, sulfonated polyimide, or sulfonated polyether ether ketone. The aforementioned types of first binders include carboxyl or sulfonic acid groups, and hydrogen bonds are easily formed between and within the molecules of the first binder. The resulting first binder exhibits higher peel strength compared to currently used binders, reducing the probability of the first material layer peeling off from the positive electrode current collector during puncture testing, thereby improving the needle penetration safety performance of the secondary battery. This application does not impose any particular limitation on the molecular weight of the first binder, as long as it achieves the purpose of this application. For example, the weight-average molecular weight of carboxylated polyvinylidene fluoride and carboxylated polyimide can be from 100,000 to 2,000,000 (g / mol); the weight-average molecular weight of sulfonated polyvinylidene fluoride, sulfonated polyimide, and sulfonated polyether ether ketone can range from 100,000 to 2,500,000 (g / mol).

[0030] In some embodiments of this application, the mass percentage m1 of the first binder is 0.1% to 4% based on the mass of the first material layer. In some embodiments of this application, 0.2% ≤ m1 ≤ 2.5%. In some embodiments of this application, 0.8% ≤ m1 ≤ 2%. For example, m1 can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, or a range of any two of these values. By adjusting m1 within the above range, the first material layer has good peel strength with the positive electrode current collector, which also facilitates the transport of active ions, thereby improving the pass rate of the secondary battery in the puncture test and taking into account rate performance, thus improving the needle penetration safety performance and kinetic performance of the secondary battery.

[0031] In some embodiments of this application, the second material layer includes a second adhesive. Based on the mass of the second material layer, the mass percentage m2 of the second adhesive is 0.5% ≤ m2 ≤ 2.5%. For example, m2 can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or a range consisting of any two of these values. By adjusting m2 within the above range, the second adhesive layer exhibits good adhesion while maintaining suitable conductivity, which is beneficial for further improving the needle penetration safety performance and kinetic performance of the secondary battery.

[0032] In some embodiments of this application, 0% ≤ m1-m2 ≤ 3%. In some embodiments of this application, 0.5% ≤ m1-m2 ≤ 2%. For example, m1-m2 can be 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or a range of any two of these values. By adjusting m1-m2 within the above range, the first material layer, which is relatively closer to the positive electrode current collector, has a higher binder mass percentage than the second material layer, which is relatively farther away from the positive electrode current collector. This results in stronger first binder adhesion, which is beneficial for increasing the number of punctures passed in the secondary battery test. At the same time, the relatively lower second peel strength is beneficial for the transport of active ions in the positive electrode sheet of the secondary battery, reducing the impedance of the secondary battery. Therefore, adjusting m1-m2 within the above range is beneficial for further improving the needle penetration safety performance and kinetic performance of the secondary battery.

[0033] In some embodiments of this application, the second binder includes at least one selected from polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. By selecting the above-mentioned second binder, and using the first material layer of the second binder in conjunction with the first material layer of this application, it is beneficial to further improve the needle penetration safety performance and kinetic performance of the secondary battery.

[0034] In some embodiments of this application, the coating mass per unit area of ​​the first material layer is CW1, and the coating mass per unit area of ​​the second material layer is CW2, where 1% ≤ CW1 / (CW1+CW2)×100% ≤ 15%. In some embodiments of this application, 3% ≤ CW1 / (CW1+CW2)×100% ≤ 10%. For example, CW1 / (CW1+CW2)×100% can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range of any two of these values. In some embodiments of this application, 85% ≤ CW2 / (CW1+CW2)×100% ≤ 99%. In some embodiments of this application, 90% ≤ CW2 / (CW1+CW2)×100% ≤ 97%. For example, CW2 / (CW1+CW2)×100% can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any combination of two of these values. The first material layer has good adhesion, which helps it bond more firmly to the surface of the positive electrode current collector, thus reducing the possibility of a short circuit between the test needle and the positive electrode sheet during puncture testing. The second material layer has lower internal resistance, which helps improve the energy density and kinetic performance of the secondary battery. Therefore, by controlling CW1 / (CW1+CW2)×100% and CW2 / (CW1+CW2)×100% ≤ 99% within the above ranges, the first and second adhesive layers work together to better balance the needle penetration safety performance, energy density, and kinetic performance of the secondary battery.

[0035] In some embodiments of this application, 150mg / 1540.24mm 2 ≤CW1+CW2≤350mg / 1540.24mm 2 In some embodiments of this application, 200 mg / 1540.24 mm 2 ≤CW1+CW2≤300mg / 1540.24mm 2 For example, CW1+CW2 can be 150mg / 1540.24mm. 2 160mg / 1540.24mm 2 170mg / 1540.24mm 2 180mg / 1540.24mm 2 190mg / 1540.24mm 2 200mg / 1540.24mm 2 210mg / 1540.24mm 2220mg / 1540.24mm 2 230mg / 1540.24mm 2 240mg / 1540.24mm 2 250mg / 1540.24mm 2 260mg / 1540.24mm 2 270mg / 1540.24mm 2 280mg / 1540.24mm 2 290mg / 1540.24mm 2 300mg / 1540.24mm 2 310mg / 1540.24mm 2 320mg / 1540.24mm 2 330mg / 1540.24mm 2 340mg / 1540.24mm 2 350mg / 1540.24mm 2 It can be any range consisting of two of these values. By adjusting CW1+CW2 within the above range, it is beneficial to balance the mechanical properties, energy density, and active ion transport of the positive electrode, thereby further improving the needle penetration safety performance, energy density, and kinetic performance of the secondary battery.

[0036] In some embodiments of this application, the first material layer includes a first material, which includes at least one selected from alumina, boehmite, lithium iron phosphate, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganese oxide. By selecting the above materials, the mechanical properties of the first material layer are further enhanced, thereby improving the needle penetration safety performance of the secondary battery. In some embodiments of this application, the first material includes at least one selected from lithium cobalt oxide, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganese oxide. By selecting the above materials, the first material layer has suitable peel strength, which further improves the safety performance of the secondary battery.

[0037] The second material layer includes a second positive electrode material, which includes at least one of lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron phosphate.

[0038] This application does not impose any special restrictions on the content of the first material in the first material layer. For example, based on the mass of the first material layer, the mass percentage of the first material in the first material layer can be 80% to 98%. This application does not impose any special restrictions on the content of the positive electrode active material in the second material layer. For example, based on the mass of the second material layer, the mass percentage of the positive electrode active material in the second material layer can be 85% to 99%.

[0039] The first and second material layers in this application may each independently include a conductive agent. This application does not particularly limit the type of conductive agent, 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, graphene, metallic materials, or conductive polymers. Conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. 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. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0040] This application does not impose any particular limitation on the content of the conductive agent, as long as it achieves the purpose of this application. For example, based on the mass of the first material layer, the mass percentage of the conductive agent in the first material layer can be from 0.2% to 5%; based on the mass of the second material layer, the mass percentage of the conductive agent in the second material layer can be from 0.2% to 4%.

[0041] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 8 μm to 20 μm, and the thickness of the positive electrode material layer can be 30 μm to 120 μm.

[0042] This application does not impose any particular limitation 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 may include, but is not limited to, the following steps:

[0043] A first material layer slurry and a second material layer slurry are prepared. The first material layer slurry is then deposited on one surface of the positive electrode current collector and dried. The second material layer slurry is then deposited on the surface of the first material layer and dried, resulting in a positive electrode sheet with a material layer on one side. The above steps are then repeated on the other surface of the positive electrode current collector to obtain a positive electrode sheet with a material layer on both sides.

[0044] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0045] In this application, the secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0046] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0047] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0048] In some embodiments of this application, the negative electrode material layer may also include a conductive agent. This application does not have any particular limitation on the type of conductive agent, as long as it can achieve the purpose of this application. For example, it may be at least one of the conductive agents mentioned above.

[0049] In some embodiments of this application, the negative electrode material layer may further include a negative electrode binder. This application does not have any particular limitation on the type of negative electrode binder, as long as it can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0050] This application does not impose any particular restrictions on the mass ratio of negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0051] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0052] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0053] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0054] 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 fabric, 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.

[0055] 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.

[0056] In this application, the electrolyte also includes lithium salts and non-aqueous solvents.

[0057] 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 the lithium salt 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 the lithium salt may be 8% to 15%. For example, the mass percentage of the lithium salt may be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or a range consisting of any two of these values.

[0058] This application does not impose any particular limitation 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. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate 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). Fluorocarbonate 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. The aforementioned 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.

[0059] 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 can be 75% to 91.5%. For example, the mass percentage of non-aqueous solvents can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 91.5%, or a range of any two of these values.

[0060] 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.

[0061] 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.

[0062] A second 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.

[0063] 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.

[0064] Example

[0065] 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.

[0066] Test methods and equipment:

[0067] Test on the types and percentage content of additives:

[0068] First, discharge the lithium-ion battery to 3V at a constant current of 0.5C under 25℃ conditions. Then, remove the packaging bag, cut off the tabs, wind up the remaining electrode assembly and put it into a centrifuge tube, and centrifuge the electrolyte in a centrifuge.

[0069] The content of electrolyte salts in the electrolyte was determined by ion chromatography (IC), and the content of each component in the organic solvent was determined by gas chromatography-mass spectrometry (GC-MS).

[0070] Positive electrode sampling:

[0071] The lithium-ion battery was disassembled at an ambient temperature of 25°C, the positive electrode was removed, cleaned with dimethyl carbonate, and then placed in an oven and dried at 80°C for 12 hours to obtain a positive electrode sample.

[0072] Unless otherwise specified, the above samples were used for testing.

[0073] Peel strength F:

[0074] Take the positive electrode sheet and attach the tape to the side of the positive electrode sheet where the first material layer is located. Cut the tape and the positive electrode sheet together into a strip with a size of 100mm×20mm. Clamp one end of the positive electrode sheet and one end of the tape onto the tensile testing machine fixture, stretch it 180°, turn on the tensile testing machine, and pull it at a uniform speed of 50mm / min until the positive electrode sheet peels off from the tape. After the test is completed, the peel strength F between the first material layer and the separator is obtained.

[0075] Coating quality test per unit area:

[0076] A piece with an area of ​​1540.24 mm was cut out. 2 For the positive electrode sample, the entire positive electrode material layer was scraped off, and its mass was measured as mg using an analytical balance. If the positive electrode material layer is applied to only one side of the positive electrode current collector, then the coating mass per unit area of ​​the positive electrode material layer is mg / 1540.24 mm. 2 If the positive electrode current collector has positive electrode material layers on both sides, then the coating mass per unit area of ​​the positive electrode material layer is m / 2mg / 1540.24mm. 2 .

[0077] The cross-section of the positive electrode sheet along its thickness direction is ion-polished. The resulting cross-section is then observed under a scanning electron microscope (SEM) and combined with energy dispersive spectroscopy (EDS). Based on the different elemental distribution ranges and concentrations, the first and second material layers can be distinguished. The material layer closer to the positive current collector is the first material layer, and the material layer farther away is the second material layer. The thickness of the first material layer is measured and recorded as h1, and the thickness of the second material layer as h2. Based on the measured thickness h1, the second material layer is scraped off, and its mass is measured using an analytical balance as n2 mg. Then, the first material layer is scraped off, and its mass is measured using an analytical balance as n1 mg. If the positive current collector has both the first and second material layers on one side, the coating mass per unit area of ​​the first material layer, CW1, is n1 mg / 1540.24 mm. 2 The coating mass per unit area of ​​the second material layer, CW1, is n1-n2 mg / 1540.24mm. 2 If a first material layer and a second material layer are disposed on both sides of the positive electrode current collector, then the coating mass per unit area of ​​the first material layer is n1 / 2mg / 1540.24mm. 2 The coating mass per unit area of ​​the second material layer is (n1-n2) / 2mg / 1540.24mm. 2 Then, CW1+CW2, CW1 / (CW1+CW2)×100%, and CW2 / (CW1+CW2)×100% are calculated.

[0078] Tests on the mass percentage of the first adhesive (m1) and the mass percentage of the second adhesive (m2):

[0079] Take the positive electrode sheet, and scrape off the first material layer and the second material layer in sequence according to the thickness h1 of the first material layer and the thickness h2 of the second material layer in the unit area coating quality test.

[0080] Take n3 mg of the first material layer and test it using a thermogravimetric-mass spectrometer (TGA-MS). Set the starting temperature to 25℃ and the ending temperature to 600℃, with a heating rate of 5℃ / min. The test is conducted in an N2 atmosphere, and the mass change curve with temperature is recorded. The mass loss n4 between 400℃ and 500℃ is the mass of the first binder in the first material layer, and m1 = n4 / n3 × 100%.

[0081] Then, take n5 mg of the second material layer and test it using a thermogravimetric-mass spectrometer (TGA-MS). Set the starting temperature to 25℃ and the ending temperature to 600℃, with a heating rate of 5℃ / min. The test is conducted in an N2 atmosphere, and the mass change curve with temperature is recorded. The mass loss n6 between 400℃ and 500℃ is the mass of the second binder in the second material layer, and m2 = n6 / n5 × 100%.

[0082] Needle prick test:

[0083] The lithium-ion battery was charged to 4.45V at a 0.5C rate, then charged to 0.05C at a constant voltage. A 3mm steel needle was used to completely penetrate the lithium-ion battery from a direction perpendicular to its maximum surface area at a speed of 10cm / s. The battery was considered passed if it did not ignite, explode, or emit smoke. Ten lithium-ion batteries were tested in each embodiment or comparative example, and the number of passing batteries was recorded as: number of passing batteries / number of tests. For example, 9 / 10 means 9 out of 10 lithium-ion batteries were tested and passed.

[0084] 1C Rate Performance Test:

[0085] The lithium-ion battery is charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage of 4.45V to 0.05C, and then discharged at a constant voltage of 0.2C to obtain the capacity Cap1. The battery is then charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage of 4.45V to 0.05C, and then discharged at a constant current of 1C to 3.0V to obtain the capacity Cap2. The 1C rate discharge retention rate = Cap2 / Cap1 × 100%.

[0086] Example 1-1

[0087] <Preparation of the positive electrode>

[0088] First material layer slurry: The positive electrode active material lithium nickel cobalt manganese oxide (LiNi) is then applied. 1 / 3 Co 1 / 3 Mn 1 / 3 O2), conductive agent conductive carbon black Super P, binder hydroxylated polyvinylidene fluoride CH3-[CH(COOH)CF2] n -CH3) were mixed at a mass ratio of 97:1.5:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the first material layer slurry was obtained. The weight average molecular weight of the above binder is 500,000, and the unit is g / mol.

[0089] Second material layer slurry: The positive electrode active material lithium nickel cobalt manganese oxide (Ni...) 0.6 Co 0.2 Mn 0.2 Conductive agent Super P conductive carbon black and binder polyvinylidene fluoride are mixed in a mass ratio of 97.5:1.5:1, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is prepared into a slurry with a solid content of 75wt%. After vacuum stirring, the second material layer slurry is obtained.

[0090] The first material layer slurry was uniformly coated onto one surface of a 10 μm thick positive electrode current collector aluminum foil and dried at 120°C. Then, the second material layer slurry was uniformly coated onto the surface of the first material layer to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The coating weight CW1 of the first material layer was 20 mg / 1540 mm. 2 The coating weight (CW2) of the second material layer is 200 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material layers. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with a size of 74mm×867mm for use. The thickness of the first material layer on one side is 8μm, and the thickness of the second material layer on one side is 80μm.

[0091] <Preparation of Negative Electrode Sheets>

[0092] Artificial graphite (negative electrode active material), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector and dried at 120 °C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a negative electrode sheet with a size of 78mm×875mm for use. The thickness of the single-sided negative electrode material layer is 54.5μm.

[0093] <Preparation of Electrolyte>

[0094] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, the electrolyte salt LiPF6 was added to the organic solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the electrolyte salt comprised 12.5% ​​by mass, with the remainder being the organic solvent.

[0095] <Septum>

[0096] A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.

[0097] <Preparation of Lithium-ion Batteries>

[0098] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The electrolyte prepared above is then injected, and the battery undergoes vacuum sealing, settling, formation, degassing, and edge trimming to obtain a lithium-ion battery. The formation upper limit voltage is 4.15V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0099] Examples 1-2 to 1-24

[0100] Except for adjusting the relevant preparation parameters according to the table, everything else is the same as in Examples 1-1. The fluoroalkyl difluorophosphate in Examples 1-9 is trifluoromethyl difluorophosphate; the sulfonated polyvinylidene fluoride in Examples 1-22 is -[CH(SO3H)CF2] n - The weight-average molecular weight is 700,000, and the unit is g / mol.

[0101] Examples 2-1 to 2-10

[0102] Except for adjusting the relevant preparation parameters according to the table, everything else is the same as in Example 1-1.

[0103] Comparative Examples 1 to 6

[0104] Except for adjusting the relevant preparation parameters according to the table, everything else is the same as in Example 1-1.

[0105] Table 1

[0106] In Table 1, “ / ” indicates that the relevant preparation parameters are not present.

[0107] As can be seen from Examples 1-1 to 1-24 and Comparative Examples 1 to 6, the peel strength F between the first material layer and the positive electrode current collector, and the mass percentage W of the additive in the electrolyte, are within the range of this application. The resulting lithium-ion batteries exhibit a high number of passes in the nail penetration test and good 1C rate performance. However, in Comparative Example 1, the additive content in the electrolyte is too low, resulting in a low number of passes in the nail penetration test and poor 1C rate performance. In Comparative Example 2, the additive content in the electrolyte is too high, resulting in poor 1C rate performance. In Comparative Example 3, no additive was added to the electrolyte, resulting in a low number of passes in the nail penetration test and poor 1C rate performance. In Comparative Example 4, the peel strength F between the second material layer and the positive electrode current collector is outside the range of this application, resulting in a low number of passes in the nail penetration test and poor 1C rate performance. In Comparative Examples 5 and 6, the peel strength F between the second material layer and the positive electrode current collector is outside the range of this application. The resulting lithium-ion batteries exhibited a low number of passes in the nail penetration test and poor 1C rate performance. This demonstrates that the lithium-ion battery meeting the requirements of this application possesses better nail penetration safety performance and better kinetic performance.

[0108] The mass percentage m1 of the first binder typically affects the nail penetration safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11 to 1-16, and Comparative Example 6, when m1 is within the scope of this application, the peel strength F between the first material layer and the positive electrode current collector is larger, resulting in a higher number of successful nail penetration tests and better 1C rate performance in the lithium-ion battery. This demonstrates that when m1 is within the scope of this application, the resulting lithium-ion battery exhibits good nail penetration safety and good kinetic performance.

[0109] The mass percentage m2 of the second binder and the type of the second binder typically affect the nail penetration safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-17 to 1-19, when m2 and the type of the second binder are within the scope of this application, a larger peel strength F between the first material layer and the positive electrode current collector results in a higher number of successful nail penetration tests and better 1C rate performance. This demonstrates that when m2 and the type of the second binder are within the scope of this application, the resulting lithium-ion battery exhibits good nail penetration safety and good kinetic performance.

[0110] The difference between the mass percentage of the first binder (m1) and the mass percentage of the second binder (m2) typically affects the needle penetration safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11 to 1-21, and Comparative Example 6, when m1-m2 are within the scope of this application, the peel strength F between the first material layer and the positive electrode current collector is relatively large, resulting in a higher number of successful needle penetration tests and better 1C rate performance in the lithium-ion battery. This demonstrates that when m1-m2 are within the scope of this application, the resulting lithium-ion battery exhibits good needle penetration safety and good kinetic performance.

[0111] The type of electrolyte additive affects the nail penetration safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1 and 1-8 to 1-10, when the type of electrolyte additive is within the scope of this application, the resulting lithium-ion batteries have a higher number of passes in the nail penetration test and better 1C rate performance. This demonstrates that when the type of electrolyte additive is within the scope of this application, the resulting lithium-ion batteries exhibit good nail penetration safety and good kinetic performance.

[0112] The type of the first binder typically affects the nail penetration safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1 and 1-22, when the type of the first binder is within the scope of this application, the peel strength F between the first material layer and the positive electrode current collector is greater, resulting in a higher number of successful nail penetration tests and better 1C rate performance in the lithium-ion battery. This demonstrates that when the type of the first binder is within the scope of this application, the resulting lithium-ion battery exhibits good nail penetration safety and good kinetic performance.

[0113] The types of the first and second cathode materials typically affect the nail penetration safety and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-23, and 1-24, when the types of the first and second cathode materials are within the scope of this application, the resulting lithium-ion batteries exhibit a higher number of passes in the nail penetration test and better 1C rate performance. This demonstrates that when the types of the first and second cathode materials are within the scope of this application, the resulting lithium-ion batteries possess both good nail penetration safety and good kinetic performance.

[0114] Table 2

[0115] The coating quality of the first material layer and the sum of the coating quality of the second material layer, CW1+CW2, typically affect the needle penetration safety performance and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-7 to 2-10, when CW1+CW2 is within the scope of this application, the peel strength F between the first material layer and the positive electrode current collector is larger, resulting in a higher number of successful needle penetration tests and better 1C rate performance in the lithium-ion battery. This indicates that when CW1+CW2 is within the scope of this application, the resulting lithium-ion battery exhibits good needle penetration safety performance and good kinetic performance.

[0116] The coating mass ratio of the first material layer (CW1 / (CW1+CW2)×100%) and the coating mass ratio of the second material layer (CW2 / (CW1+CW2)×100%) typically affect the needle penetration safety performance and kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-6, when CW1 / (CW1+CW2)×100% and CW2 / (CW1+CW2)×100% are within the scope of this application, the peel strength F between the first material layer and the positive electrode current collector is larger, resulting in a higher number of successful needle penetration tests and better 1C rate performance in the lithium-ion battery. This indicates that when CW1 / (CW1+CW2)×100% and CW2 / (CW1+CW2)×100% are within the scope of this application, the resulting lithium-ion battery exhibits good needle penetration safety performance and good kinetic performance.

[0117] The various embodiments in this specification are described in a related manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0118] 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.

[0119] 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.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a first material layer and a second material layer disposed on the surface of the positive current collector, the first material layer being located between the positive current collector and the second material layer; The peel strength F between the first material layer and the positive electrode current collector is 50 N / m to 130 N / m; The electrolyte includes an additive containing one or more of difluorophosphate anions and tetrafluorooxalate phosphate anions; the mass percentage W of the additive is 0.5% to 10% based on the mass of the electrolyte.

2. The secondary battery according to claim 1, wherein, 70N / m≤F≤100N / m.

3. The secondary battery according to claim 1, wherein, 2％≤W≤7％。 4. The secondary battery according to claim 1, wherein, 3％≤W≤5％。 5. The secondary battery according to claim 1, wherein, The additive includes at least one of lithium difluorophosphate, lithium tetrafluorooxalate phosphate, fluoroalkyl difluorophosphate, and trimethyl hexafluorophosphate, wherein the alkyl group in the fluoroalkyl difluorophosphate has 1 to 10 carbon atoms.

6. The secondary battery according to claim 1, wherein, The first material layer includes a first adhesive, which includes at least one of carboxylated polyvinylidene fluoride, sulfonated polyvinylidene fluoride, carboxylated polyimide, sulfonated polyimide, or sulfonated polyether ether ketone; based on the mass of the first material layer, the mass percentage m1 of the first adhesive is 0.1% to 4%.

7. The secondary battery according to claim 6, wherein, m1 ranges from 0.2% to 2.5%.

8. The secondary battery according to claim 7, wherein, 0.8％≤m1≤2％。 9. The secondary battery according to claim 6, wherein, The second material layer includes a second adhesive, and based on the mass of the second material layer, the mass percentage of the second adhesive m2 is 0% ≤ m1 - m2 ≤ 3%.

10. The secondary battery according to claim 9, wherein it satisfies at least one of the following characteristics: (1)0.5％≤m2≤2.5％； (2) 0.5% ≤ m1 - m2 ≤ 2%; (3) The second adhesive includes at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride.

11. The secondary battery according to any one of claims 1 to 10, wherein, The coating mass per unit area of ​​the first material layer is CW1, and the coating mass per unit area of ​​the second material layer is CW2, where 1% ≤ CW1 / (CW1+CW2)×100% ≤ 15%, and 85% ≤ CW2 / (CW1+CW2)×100% ≤ 99%.

12. The secondary battery according to claim 11, wherein, 3% ≤ CW1 / (CW1+CW2)×100% ≤ 10%, and / or, 90% ≤ CW2 / (CW1+CW2)×100% ≤ 97%.

13. The secondary battery according to claim 11, wherein, 150mg / 1540.24mm 2 ≤CW1+CW2≤350mg / 1540.24mm 2 。 14. The secondary battery according to claim 13, wherein, 200mg / 1540.24mm 2 ≤CW1+CW2≤300mg / 1540.24mm 2 。 15. The secondary battery according to any one of claims 1 to 10, wherein, The first material layer includes a first material, which includes at least one of alumina, lithium iron phosphate, boehmite, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganese oxide. The second material layer includes a second positive electrode material, which includes at least one of lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron phosphate.

16. The secondary battery according to claim 15, wherein, The first material includes at least one of lithium iron phosphate, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganese oxide.

17. An electronic device comprising a secondary battery as claimed in any one of claims 1 to 16.

Images