Secondary battery and electronic device
Patent Information
- Application Number
- PCT/CN2026/070936
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-28
- Filing Date
- 2026-01-06
- Publication Date
- 2026-10-01
Smart Images
Figure PCTCN2026070936-FTAPPB-I100001 
Figure PCTCN2026070936-FTAPPB-I100002
Abstract
Description
A secondary battery and electronic device
[0001] This application claims priority to Chinese Patent Application No. 202510382880.1, filed on March 28, 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 been widely used in many fields, including portable electronic devices, due to their outstanding advantages such as high energy density, long cycle life, and safety. In practical applications, lithium-ion batteries typically face various operating environments. However, at high temperatures, the surface activity of the positive electrode material in lithium-ion batteries increases, and the decomposition of the electrolyte in direct contact with the positive electrode active material intensifies, resulting in poor high-temperature cycle performance of lithium-ion batteries and hindering their further development and application.
[0004] In existing technologies, the high-temperature cycle performance of lithium-ion batteries is usually improved by adding protective additives to the electrolyte or by adding element coating to the positive electrode active material. However, these methods have problems such as reduced lithium-ion battery kinetics and severely reduced rate performance. Summary of the Invention
[0005] The purpose of this application is to provide a secondary battery and electronic device to improve the high-temperature cycle performance of the secondary battery, while also providing good kinetic and rate performance.
[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 sheet, the positive electrode sheet including a positive electrode material layer, the positive electrode material layer including a positive electrode active material, an additive, and a fluoride; the positive electrode material layer including a first metal element, the first metal element being at least one selected from strontium, calcium, magnesium, and sodium, and the mass percentage M of the first metal element being 0.01% to 0.3% based on the mass of the positive electrode material layer; the additive including at least one selected from strontium carbonate, calcium carbonate, magnesium carbonate, sodium carbonate, calcium silicate, or magnesium silicate; and the fluoride including at least one selected from calcium fluoride, strontium fluoride, magnesium fluoride, or sodium fluoride. The inclusion of the above-mentioned additives in the positive electrode material layer and the control of the mass percentage of the first metal element within the scope of this application facilitates the full reaction of the additives with HF in the electrolyte, generating the above-mentioned fluoride in situ to coat the surface of the positive electrode active material particles, reducing the direct contact area between the electrolyte and the positive electrode active material, thereby reducing electrolyte decomposition at high temperatures and improving the high-temperature cycle performance of the secondary battery. Furthermore, due to the low content of remaining unreacted additives and the good conductivity of the generated fluorides, the secondary battery also exhibits good kinetic and rate performance.
[0008] In some embodiments of this application, the additive includes at least one of strontium carbonate or sodium carbonate; the fluoride includes at least one of strontium fluoride or sodium fluoride. By adjusting the cathode material layer to include the above-mentioned additives and fluorides, the high-temperature cycle performance of the secondary battery can be further improved, and the secondary battery also has better kinetic performance and rate performance.
[0009] In some embodiments of this application, in the X-ray photoelectron spectroscopy (XPS) spectrum of the positive electrode material layer, a first characteristic peak exists between 531 eV and 535 eV, and a second characteristic peak exists between 683 eV and 687 eV. The peak area ratio of the first characteristic peak to the second characteristic peak is 0.1:1 to 0.5:1. The fact that the peak area ratio of the first characteristic peak to the second characteristic peak is within the above range indicates that most of the additives react with HF to generate fluorides coated on the surface of the positive electrode active material. This reduces the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery. Furthermore, since the content of remaining unreacted additives is relatively small, and the generated fluorides have good conductivity, the secondary battery also exhibits good kinetic performance and rate performance.
[0010] In some embodiments of this application, the mass percentage M of the first metal element is 0.1% to 0.2% based on the mass of the positive electrode material layer. By controlling the mass percentage of the first metal element within the above range, the high-temperature cycle performance of the secondary battery can be further improved, and the secondary battery also has better kinetic performance and rate performance.
[0011] In some embodiments of this application, the average particle size of the additive is D μm, where 0.1 ≤ D ≤ 3. By controlling the average particle size D of the additive within the above range, agglomeration between additive particles can be reduced, allowing the additive to be more uniformly dispersed in the positive electrode material layer. This facilitates the full reaction between the additive and HF, resulting in a higher coating degree of fluoride on the surface of the positive electrode active material particles. This reduces the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery. Furthermore, due to the good conductivity of the generated fluoride, the secondary battery also exhibits better kinetic and rate performance.
[0012] In some embodiments of this application, the specific surface area of the positive electrode active material is S m 2 / g, 0.1≤S≤1, D×S≤1. By controlling the specific surface area S of the positive electrode active material within the above range and adjusting D and S to satisfy the above relationship, the positive electrode active material has a suitable particle size, the aggregation between particles is weak, the distribution of additives in the positive electrode active material is more reasonable, and the generated fluoride has a high coating degree on the surface of the positive electrode active material particles, which is beneficial to reducing the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery.
[0013] In some embodiments of this application, 0.1 ≤ S ≤ 0.5. By controlling the specific surface area S of the positive electrode active material within the above range, it is beneficial to further reduce the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery.
[0014] In some embodiments of this application, the positive electrode material layer further includes at least one of the second metallic elements lithium, cobalt, and manganese, and the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, or a ternary positive electrode active material. By adjusting the type of positive electrode active material within the above-mentioned range, the secondary battery exhibits better kinetic performance and rate performance.
[0015] In some embodiments of this application, the film resistance of the positive electrode is R, where 0.1Ω ≤ R ≤ 0.5Ω. Having the film resistance R of the positive electrode within this range reduces energy loss caused by excessive resistance, thereby improving the efficiency of insertion and extraction of active ions such as lithium ions during charging and discharging. This improves the high-temperature cycle performance of the secondary battery, and the secondary battery also exhibits better kinetic and rate performance.
[0016] 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.
[0017] The beneficial effects of this application are:
[0018] This application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, which includes a positive electrode material layer. The positive electrode material layer includes a positive electrode active material, additives, and a fluoride. The positive electrode material layer includes a first metal element, which is at least one selected from strontium, calcium, magnesium, and sodium. Based on the mass of the positive electrode material layer, the mass percentage of the first metal element is 0.01% to 0.3%. The additives include at least one selected from strontium carbonate, calcium carbonate, magnesium carbonate, sodium carbonate, calcium silicate, or magnesium silicate. The fluoride includes at least one selected from calcium fluoride, strontium fluoride, magnesium fluoride, or sodium fluoride. The additives in the positive electrode material layer can react with HF in the electrolyte to generate the fluoride in situ, coating the surface of the positive electrode active material. This reduces the direct contact area between the electrolyte and the positive electrode active material, thereby reducing electrolyte decomposition at high temperatures and improving the high-temperature cycle performance of the secondary battery. Furthermore, since the generated fluoride has good conductivity and has little impact on lithium-ion transport inside the positive electrode active material, the secondary battery also has good kinetic performance and rate performance. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following embodiments are provided to further illustrate this application in detail. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on 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] A first aspect of this application provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet including a positive electrode material layer, the positive electrode material layer including a positive electrode active material, an additive, and a fluoride. The positive electrode material layer includes a first metal element, which is at least one selected from strontium, calcium, magnesium, and sodium. Based on the mass of the positive electrode material layer, the mass percentage M of the first metal element is 0.01% to 0.3%. In some embodiments of this application, the mass percentage M of the first metal element is 0.1% to 0.2%. For example, the mass percentage M of the first metal element can be 0.01%, 0.03%, 0.07%, 0.1%, 0.13%, 0.16%, 0.2%, 0.25%, 0.3%, or a range consisting of any two of these values. The additive includes at least one selected from strontium carbonate, calcium carbonate, magnesium carbonate, sodium carbonate, calcium silicate, or magnesium silicate; the fluoride includes at least one selected from calcium fluoride, strontium fluoride, magnesium fluoride, or sodium fluoride. In some embodiments of this application, the additive includes at least one of strontium carbonate or sodium carbonate; the fluoride includes at least one of strontium fluoride or sodium fluoride.
[0022] Under high-temperature conditions, the surface activity of the positive electrode active material particles in a secondary battery increases, making it easier for the electrolyte in contact with them to oxidize and decompose, thus affecting the high-temperature cycle performance of the secondary battery. When the positive electrode material layer includes the aforementioned additives, these additives can react with HF in the electrolyte to generate fluorides in situ, coating the surface of the positive electrode active material particles. This reduces the direct contact area between the electrolyte and the positive electrode active material, thereby reducing electrolyte decomposition and improving the high-temperature cycle performance of the secondary battery. Furthermore, since the aforementioned fluorides have good conductivity and minimal impact on lithium-ion transport within the positive electrode active material, the secondary battery also exhibits better kinetic and rate performance. In this application, the aforementioned high temperature refers to a temperature greater than or equal to 35°C.
[0023] The inventors discovered that when the mass percentage M of the first metal element is too small, for example, less than 0.01%, the additive content is too low, resulting in insufficient fluoride formation. This leads to low coating of the positive electrode active material particles with fluoride, and at high temperatures, most of the positive electrode active material can still react with the electrolyte, exacerbating electrolyte decomposition and thus affecting the improvement of the high-temperature cycle performance of the secondary battery. When the mass percentage M of the first metal element is too large, for example, greater than 0.3%, the additive content is too high, and most of the remaining additive cannot react with HF. Furthermore, the additive has poor conductivity, which is detrimental to the transport of active ions such as lithium ions and electrons. This not only hinders the improvement of the high-temperature cycle performance of the secondary battery but also affects its kinetic and rate performance. Therefore, within the scope of this application, the mass percentage of the first metal element helps the additive react fully with HF in the electrolyte to generate fluoride coating on the surface of the positive electrode active material particles, reducing the direct contact area between the electrolyte and the positive electrode active material, thereby reducing electrolyte decomposition and improving the high-temperature cycle performance of the secondary battery. Furthermore, due to the low content of remaining unreacted additives and the good conductivity of the generated fluorides, the secondary battery also exhibits good kinetic and rate performance.
[0024] The inventors also discovered that the enrichment of elements such as strontium and sodium at the grain boundaries on the surface of the positive electrode active material particles helps maintain the surface stability of the positive electrode active material particles, reduces side reactions between the positive electrode material layer and the electrolyte, thereby reducing electrolyte decomposition and improving the high-temperature cycle performance of the secondary battery. Furthermore, strontium fluoride and sodium fluoride have better conductivity than calcium fluoride and magnesium fluoride; therefore, the secondary battery also exhibits better kinetic and rate performance. When the additive includes at least one of strontium carbonate or sodium carbonate, the high-temperature cycle performance of the secondary battery can be further improved, and the secondary battery also exhibits better kinetic and rate performance.
[0025] In this application, the positive electrode material layer may further include a second metal element. This application does not impose any particular limitation on the type of the second metal element, as long as it achieves the purpose of this application. The second metal element can be any metal element other than the first metal element. For example, the second metal element can be at least one of lithium, cobalt, and manganese.
[0026] In some embodiments of this application, in the X-ray photoelectron spectroscopy (XPS) spectrum of the cathode material layer, a first characteristic peak exists between 531 eV and 535 eV, and a second characteristic peak exists between 683 eV and 687 eV, with a peak area ratio P between the first and second characteristic peaks ranging from 0.1:1 to 0.5:1. For example, the peak area ratio P between the first and second characteristic peaks may be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, or a range consisting of any two of these values. In this application, the first characteristic peak refers to the characteristic peak corresponding to the additive, and the second characteristic peak refers to the characteristic peak corresponding to the fluoride. The peak area ratio P corresponding to the first characteristic peak and the second characteristic peak, which is also the peak area ratio of the additive to the fluoride, is within the above range. This indicates that the additive can react with HF to generate fluoride. Furthermore, the content of additive in the positive electrode material layer is less than that of fluoride, suggesting that most of the additive reacted with HF to generate fluoride coating the surface of the positive electrode active material. This reduces the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery. In addition, due to the low content of unreacted additive and the good conductivity of the generated fluoride, the secondary battery also exhibits good kinetic and rate performance.
[0027] In some embodiments of this application, the average particle size of the additive is D μm, where 0.1 ≤ D ≤ 3. For example, D can be 0.1, 0.3, 0.6, 1, 1.5, 1.8, 2, 2.5, 3, or a range of any two of these values. By controlling the average particle size D of the additive within the above range, agglomeration between additive particles can be reduced, allowing the additive to be more uniformly dispersed in the positive electrode material layer. This facilitates the full reaction of the additive with HF, resulting in a higher coating degree of fluoride on the surface of the positive electrode active material particles. This helps reduce the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery. Furthermore, due to the good conductivity of the generated fluoride, the secondary battery also exhibits better kinetic and rate performance. In this application, the above-mentioned additives with different average particle sizes can be purchased, and their average particle size can be tested using scanning electron microscopy to select the additive with the desired particle size.
[0028] In some embodiments of this application, the specific surface area of the positive electrode active material is S m 2 / g, 0.1≤S≤1, D×S≤1. In some embodiments of this application, 0.1≤S≤0.5. For example, S can be 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1, or a range of any two values therein; D×S can be 0.01, 0.02, 0.06, 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, 1.0, or a range of any two values therein. By controlling the specific surface area S of the positive electrode active material within the above range and adjusting D and S to satisfy the above relationship, when S is within the above range, the positive electrode active material has a suitable particle size, and the aggregation between the positive electrode active material particles is weak, which is beneficial to the dispersion of additives. Under normal circumstances, the positive electrode active material has a large specific surface area and a small particle size. When D and S satisfy the above relationship, the particle size of the positive electrode active material particles matches the average particle size D of the additives, which can make the distribution of additives in the positive electrode active material more reasonable. The generated fluoride has a high coating degree on the surface of the positive electrode active material particles, which is beneficial to reduce the direct contact area between the electrolyte and the positive electrode active material, thereby improving the high-temperature cycle performance of the secondary battery.
[0029] In some embodiments of this application, the cathode material layer further includes at least one of the second metal elements lithium, cobalt, and manganese, and the cathode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, and ternary cathode active materials. Lithium cobalt oxide and ternary cathode active materials have layered structures, while lithium manganese oxide cathode active materials have spinel structures. Therefore, during the charging and discharging process of the secondary battery, active ions such as lithium ions migrate rapidly in the crystal lattice, enabling rapid insertion and extraction, thus giving the secondary battery better kinetic and rate performance.
[0030] This application does not impose any particular restrictions on the ternary cathode active material, as long as it can achieve the purpose of this application. For example, the ternary cathode active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. The chemical formula of lithium nickel cobalt manganese oxide is LiNi. x Co y Mn z M m O2, x+y+z+m=1, 0.3≤x≤0.95, 0.1≤y≤0.4, 0.1≤z≤0.5, 0≤m≤0.2. M is a dopant element, selected from at least one of Ag, Sn, Zn, Al, Mg, Mo, Cu, B, Ti, W, Zr, Ir, V, and Fe. For example, lithium nickel cobalt manganese oxide may include, but is not limited to, LiNi. 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111).
[0031] In some embodiments of this application, the film resistance of the positive electrode is R, which is 0.1Ω ≤ R ≤ 0.5Ω. For example, R can be 0.1Ω, 0.15Ω, 0.2Ω, 0.26Ω, 0.33Ω, 0.4Ω, 0.45Ω, 0.5Ω, or a range of any two of these values. When the film resistance R of the positive electrode is within the above range, a smaller R reduces energy loss caused by excessive resistance, thereby improving the efficiency of insertion and extraction of active ions such as lithium ions during charging and discharging. This improves the high-temperature cycle performance of the secondary battery, and the secondary battery also exhibits better kinetic and rate performance.
[0032] The positive electrode material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they can achieve 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. The 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 polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The 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. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved. For example, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material may be 96% to 98%, the mass percentage of the conductive agent may be 0.5% to 1.5%, and the mass percentage of the binder may be 0.8% to 2.5%.
[0033] This application does not impose any particular limitation on the thickness of the cathode material layer, as long as it achieves the purpose of this application. For example, the thickness of the cathode material layer can be from 30 μm to 120 μm.
[0034] In this application, the positive electrode sheet further includes a positive current collector, and the positive electrode material layer is disposed on at least one surface of the positive current collector. The phrase "disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of the positive current collector, or only a portion of it; this application has no particular limitation, as long as the purpose of this application is achieved.
[0035] 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, it may include aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors). This application also does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector may be from 5 μm to 20 μm.
[0036] 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:
[0037] A positive electrode active material, additives, conductive agents, and binders are mixed, and a solvent is added to prepare a positive electrode slurry. The positive electrode slurry is coated onto one surface of a positive electrode current collector, and after drying, a positive electrode sheet with a single-sided coating of positive electrode material is obtained. The above operation is repeated on the other surface of the positive electrode current collector to obtain a positive electrode sheet with a double-sided coating of positive electrode material. Based on the total mass of the positive electrode active material, additives, conductive agents, and binders, the mass percentage content of the positive electrode active material is 96% to 98%, the mass percentage content of the additives is 0.05% to 0.5%, the mass percentage content of the conductive agent is 0.5% to 1.5%, and the mass percentage content of the binder is 0.8% to 2.5%. There is no particular limitation on the solid content of the positive electrode slurry in this application, as long as it achieves the purpose of this application; for example, the solid content of the positive electrode slurry is 70 wt% to 80 wt%.
[0038] During the production of secondary batteries, despite strict drying measures, trace amounts of moisture are difficult to completely remove. Fluorinated electrolytes (such as lithium hexafluorophosphate) in the electrolyte readily react with water to produce HF. Some fluorinated non-aqueous solvents may decompose in the complex electrochemical environment inside the secondary battery, producing fluorinated active intermediates. These fluorinated active intermediates may also react with water to produce HF. Therefore, the electrolyte contains a small amount of HF. Adding the aforementioned additives that react with HF during the preparation of the positive electrode allows for the in-situ formation of fluorides that coat the surface of the positive electrode active material particles. This reduces the direct contact area between the electrolyte and the positive electrode active material, improving the high-temperature cycle performance of the secondary battery. Since the reaction between the additives and HF is incomplete, a certain amount of additives remains in the positive electrode material layer.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] The negative electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.
[0043] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode material layer can be from 30 μm to 120 μm. This application also does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 15 μm.
[0044] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.
[0045] 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.
[0046] 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.
[0047] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). 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. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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).
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] Example
[0058] 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.
[0059] Test methods and equipment:
[0060] Sampling of the positive electrode sheet:
[0061] At 25°C, the lithium-ion battery was discharged at a constant current of 0.5C until the discharge cutoff voltage of 3.0V. The lithium-ion battery was then disassembled, and the residual electrolyte on the surface of the positive electrode was wiped off with lint-free paper to obtain the positive electrode.
[0062] Unless otherwise specified, the following test methods shall use the positive electrode obtained by the above method for testing.
[0063] First metal element content test:
[0064] 1) The surface of the positive electrode material layer of the positive electrode sheet was observed under a scanning electron microscope (SEM) in backscatter mode at a magnification of 5000x.
[0065] 2) The surface of the above cathode material layer was scanned using an energy dispersive spectroscopy (EDS) instrument to obtain the type and content of the first metallic element;
[0066] 3) Repeat steps 1) and 2) 10 times and take the average value as the content of the first metallic element.
[0067] Five parallel samples were tested for each embodiment or comparative example, and the average value was taken as the final result.
[0068] It is understandable that although the additives have good dispersibility in the cathode material layer, since the additives are solid powder particles, there will be micro-enrichment in the cathode active material, which may cause the tested mass percentage M value of the first metal element to be higher than the theoretical value.
[0069] Peak area ratio test of additives and fluorides:
[0070] The cathode material layer was tested using X-ray photoelectron spectroscopy (XPS), obtaining its full-scan XPS spectrum. The second characteristic peak (F1s) and the first characteristic peak (O1s) detected in the XPS full-scan spectrum were then subjected to peak fitting. The peak area of the F1s peak plot represents the peak area corresponding to the fluoride, and the peak area of the O1s peak plot represents the peak area corresponding to the additive. The ratio of the peak area corresponding to the additive to that corresponding to the fluoride is calculated as: peak area corresponding to the additive / peak area corresponding to the fluoride. Peak area refers to the integral area of the peak.
[0071] Additive average particle size D test:
[0072] The surface of the positive electrode material layer of the positive electrode sheet was observed using SEM at a magnification of 5000x. Fifty additive particles were randomly selected, and the diameter of each particle was measured. The average particle size D of the additives was obtained by averaging the measurements. Particles with high contrast and a diameter much smaller than the positive electrode active material in the SEM image were identified as additive particles.
[0073] Specific surface area test of positive electrode active material:
[0074] According to the national standard "Determination of Specific Surface Area of Solid Substances by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of the positive electrode active material was tested by nitrogen adsorption using a specific surface area analyzer (model TristarⅡ3020M).
[0075] Positive electrode diaphragm resistance R test:
[0076] The test was conducted using a Yuaneng Technology BER2500 diaphragm resistance meter, with a holding time of 10 seconds, a pressure of 0.4 tons, and a test area of 153.9 mm². 2 After testing 12 values, a test report is output. The average value of the 12 membrane resistances is taken to obtain the membrane resistance R of the positive electrode.
[0077] High-temperature cycling performance test:
[0078] The high-temperature cycle performance of lithium-ion batteries is evaluated by capacity retention rate; a higher capacity retention rate indicates better high-temperature cycle performance. At a test temperature of 45°C, the lithium-ion battery is charged at a constant current of 0.5C to 4.53V, then charged at a constant voltage of 4.53V to a current of 0.025C, and then fully discharged at a current of 0.5C with a cutoff voltage of 3.0V. This charge-discharge cycle is repeated 500 times, and the discharge capacity after the first cycle and after the 500th cycle is recorded. Cycle capacity retention rate = (Discharge capacity after 500 cycles / First discharge capacity) × 100%.
[0079] Ratio performance test:
[0080] The lithium-ion battery was placed at a test temperature of 25°C for 5 minutes, then charged at a constant current of 0.7C to 4.53V, and then charged at a constant voltage of 4.53V to the cutoff current of 0.05C. After placing it at a resting temperature of 5 minutes, it was discharged at a constant current of 0.2C to 3.0V at the test temperature of 25°C, and the 0.2C discharge capacity was recorded. This process was repeated after placing it at a resting temperature of 5 minutes. Once fully charged, it was discharged at a constant current of 2C at the test temperature of 25°C, and the 2C discharge capacity was recorded. Rate performance = 2C discharge capacity / 0.2C discharge capacity × 100%. Rate performance can also be used to evaluate the kinetic performance of lithium-ion batteries.
[0081] Example 1
[0082] <Preparation of the positive electrode>
[0083] LiCoO2 (positive electrode active material), magnesium carbonate (additive), Super P (conductive agent), and polyvinylidene fluoride (binder) were mixed in a mass ratio of 96.9:0.2:1.0:1.9. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was then vacuum-stirred to obtain the positive electrode slurry. This slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector. The foil was then dried at 120°C to obtain a single-sided coated positive electrode sheet with a coating weight of 267.8 mg / 1540 mm². 2After drying at 120℃ and cold pressing, the material is then cut and welded with tabs to obtain a positive electrode sheet with a size of 74mm×867mm for later use. The average particle size D of the additives is 1.5μm, and the thickness of the single-sided positive electrode material layer is 42μm.
[0084] <Preparation of Negative Electrode Sheets>
[0085] 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 After drying at 120℃ and cold pressing, the material is then cut and welded with tabs to obtain a negative electrode sheet with dimensions of 78mm×875mm for later use. The thickness of the single-sided negative electrode material layer is 54.5μm.
[0086] <Preparation of Electrolyte>
[0087] 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.
[0088] <Preparation of the diaphragm>
[0089] A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.
[0090] <Preparation of Lithium-ion Batteries>
[0091] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to act as a separator. 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.
[0092] Examples 2 to 23
[0093] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1. Specifically, when the mass percentage of additives in the positive electrode material layer changes, the mass percentage of the positive electrode active material LiCoO2 changes accordingly, while the mass percentages of the conductive agent Super and the binder polyvinylidene fluoride remain unchanged.
[0094] In Example 11, the mass ratio of the additives magnesium carbonate and strontium carbonate was 1:1.
[0095] Comparative Examples 1 to 5
[0096] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1. Specifically, when the mass percentage of additives in the positive electrode material layer changes, the mass percentage of the positive electrode active material LiCoO2 changes accordingly, while the mass percentages of the conductive agent Super and the binder polyvinylidene fluoride remain unchanged.
[0097] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Table 1.
[0098] As can be seen from Examples 1 to 23 and Comparative Examples 1 to 5, the positive electrode material layer of the examples includes additives, fluorides, and a first metal element within the scope of this application, and the mass percentage M of the first metal element is within the scope of this application. Comparative Example 1 does not include additives, fluorides, and the first metal element. The mass percentage M of the first metal element in Comparative Examples 2 and 3 is not within the scope of this application. The additives and fluorides in Comparative Examples 4 and 5 are not within the scope of this application. Compared with the comparative examples, the lithium-ion batteries obtained in the examples have a higher high-temperature cycle capacity retention rate, indicating that the high-temperature cycle performance of the lithium-ion battery is improved. Furthermore, the obtained lithium-ion batteries also have better rate performance and kinetic performance.
[0099] As can be seen from Examples 1 to 5, Comparative Examples 2 and 3, increasing the mass percentage M of the first metal element can improve the high-temperature cycle capacity retention rate and the high-temperature cycle performance of the lithium-ion battery. However, with the continuous increase of the mass percentage M of the first metal element, the high-temperature cycle capacity retention rate of the lithium-ion battery decreases, affecting the high-temperature cycle performance of the lithium-ion battery. The rate performance and kinetic performance of the lithium-ion battery also decrease with the increase of the mass percentage M of the first metal element.
[0100] When the type of additive changes, the type of fluoride generated also changes, which affects the high-temperature cycle performance and rate performance of the lithium-ion battery. As can be seen from Examples 1, 6 to 11, when the types of additives and fluorides are within the scope of this application, the lithium-ion battery exhibits a higher high-temperature cycle capacity retention rate, indicating that the high-temperature cycle performance of the lithium-ion battery is improved. Furthermore, the lithium-ion battery also exhibits good rate performance and kinetic performance.
[0101] The peak area ratio P corresponding to the first characteristic peak and the second characteristic peak varies with the mass percentage content M of the first metal element, the type of additive, the average particle size D of the additive, the specific surface area S and D×S of the positive electrode active material. When the above parameters are within the range of this application, the peak area ratio P corresponding to the first characteristic peak and the second characteristic peak is also within the range of this application. The lithium-ion battery has good high-temperature cycle performance, rate performance and kinetic performance.
[0102] The average particle size D of the additive affects the high-temperature cycle performance and rate performance of the lithium-ion battery. As can be seen from Examples 1, 12 to 15, when the average particle size D of the additive is within the range of this application, the lithium-ion battery has better high-temperature cycle performance, rate performance and kinetic performance.
[0103] The specific surface area S and D×S of the positive electrode active material affect the high-temperature cycle performance and rate performance of lithium-ion batteries. As can be seen from Examples 1, 16 to 21, when the specific surface area S and D×S of the positive electrode active material are within the range of this application, the lithium-ion battery has better high-temperature cycle performance, rate performance and kinetic performance.
[0104] The type of positive electrode active material affects the high-temperature cycle performance and rate performance of lithium-ion batteries. As can be seen from Examples 1, 22 to 23, when the type of positive electrode active material is within the scope of this application, the lithium-ion battery has better high-temperature cycle performance, rate performance and kinetic performance.
[0105] The film resistance R of the positive electrode varies with the mass percentage M of the first metal element and the type of additive. When the mass percentage M of the first metal element and the type of additive are within the scope of this application, the obtained film resistance R is also within the scope of this application, and the obtained lithium-ion battery has good high-temperature cycle performance, rate performance and kinetic performance.
[0106] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.
Claims
1. A secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, an additive, and a fluoride; The positive electrode material layer includes a first metal element, which is at least one of strontium, calcium, magnesium and sodium. Based on the mass of the positive electrode material layer, the mass percentage M of the first metal element is 0.01% to 0.3%. The additives include at least one of strontium carbonate, calcium carbonate, magnesium carbonate, sodium carbonate, calcium silicate, or magnesium silicate. The fluoride includes at least one of calcium fluoride, strontium fluoride, magnesium fluoride, or sodium fluoride.
2. The secondary battery according to claim 1, wherein The additive includes at least one of strontium carbonate or sodium carbonate; The fluoride includes at least one of strontium fluoride or sodium fluoride.
3. The secondary battery according to claim 1, wherein In the X-ray photoelectron spectroscopy test spectrum of the cathode material layer, there is a first characteristic peak between 531eV and 535eV, and a second characteristic peak between 683eV and 687eV. The peak area ratio between the first characteristic peak and the second characteristic peak is 0.1:1 to 0.5:
1.
4. The secondary battery according to claim 1, wherein M is 0.1% to 0.2%.
5. The secondary battery according to any one of claims 1 to 4, wherein The average particle size of the additive is D μm, where 0.1 ≤ D ≤ 3.
6. The secondary battery according to claim 5, wherein The specific surface area of the positive electrode active material is Sm 2 / g, 0.1≤S≤1, D×S≤1.
7. The secondary battery according to claim 6, wherein 0.1≤S≤0.5。 8. The secondary battery according to any one of claims 1 to 4, wherein The cathode material layer further includes at least one of the second metal elements lithium, cobalt, and manganese, and the cathode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, or ternary cathode active material.
9. The secondary battery according to any one of claims 1 to 4, wherein The film resistance of the positive electrode is R, where 0.1Ω≤R≤0.5Ω.
10. An electronic device comprising a secondary battery according to any one of claims 1 to 9.