Secondary batteries and electronic devices

Abstract

The application discloses a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the negative electrode sheet comprises a first material layer, a second material layer and a negative electrode current collector; the first material layer comprises silicon-based particles and first particles, the first particles comprise at least four of lithium, lanthanum, aluminum, titanium, phosphorus and oxygen; the second material layer comprises carbon-based particles and second particles, the second particles comprise lithium, lanthanum, zirconium and oxygen; and the second material layer is arranged between the negative electrode current collector and the first material layer. The secondary battery provided by the application has relatively optimal electrochemical performance, in particular, a relatively low expansion rate and relatively optimal rate discharge performance and cycle performance.

Description

Technical Field

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

[0002] With societal development, rechargeable batteries have become indispensable energy storage and supply units. From smartphones and wearable devices in people's daily lives to large-scale electric vehicles and distributed energy storage systems, the application scope of rechargeable batteries continues to expand and penetrate deeper. In these diverse application scenarios, the requirements for their performance are becoming increasingly stringent, among which rate discharge performance and cycle performance are some key indicators for measuring the quality and practicality of rechargeable batteries. Summary of the Invention

[0003] This application provides a secondary battery and electronic device that achieves superior rate discharge performance and low expansion rate while also improving cycle performance.

[0004] In a first aspect, embodiments of this application provide a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode comprises a first material layer, a second material layer, and a negative current collector; the first material layer comprises silicon-based particles and first particles, the first particles comprising at least four elements selected from lithium, lanthanum, aluminum, titanium, phosphorus, or oxygen; the second material layer comprises carbon-based particles and second particles, the second particles comprising lithium, lanthanum, zirconium, and oxygen; the second material layer is disposed between the negative current collector and the first material layer.

[0005] Based on the secondary battery embodiments of this application, a double-layer negative electrode design is adopted. The first material layer is a silicon-based material, and the second material layer is a carbon-based material, which can improve the electron transport rate and control the volume expansion of the upper silicon material. Furthermore, the inventors discovered that the first material layer further includes solid electrolyte particles containing the aforementioned elements, which have reversible lithium insertion / extraction capacity and can react with the surface of the active material during charging and discharging to form a stable electron-ion conductor, suppressing side reactions between silicon and the electrolyte, and simultaneously improving the volume expansion of the silicon material. The second material layer further includes solid electrolyte particles containing the aforementioned elements, which have excellent stability and can improve the ion conduction efficiency of the second material layer, synergistically constructing an ion conduction network with the first material layer and enhancing electrode dynamics. By optimizing the double-layer negative electrode structure and the selection of the electrolyte material in the above manner, electrode expansion can be suppressed while simultaneously improving rate discharge performance and cycle performance.

[0006] In some embodiments, the circumcircle of the cross-section of the silicon-based particle is a first circumcircle with a diameter of R1 nm. A circular region concentric with the first circumcircle and having a radius of R1+500 nm is defined as a first region. The number of first particles in the first region is M, where 10≤M≤119. Based on the secondary battery of this application embodiment, by controlling the relationship between the number of silicon-based particles and the number of first particles in the first material layer within the aforementioned range, a suitable number of first particles are distributed on the surface of the silicon-based particles. This allows for the construction of efficient ion conduction channels, reducing the solvation energy of the silicon material surface, and the formation of an in-situ protective layer to protect the reactivity of the silicon surface. This further slows down the expansion rate of the silicon-based material, improves electrode kinetics, and thus, while suppressing electrode expansion, simultaneously improves rate discharge performance and cycle performance.

[0007] In some embodiments, the circumcircle of the cross-section of the carbon-based particle is a second circumcircle, and the diameter of the second circumcircle is R2 nm. A circular region concentric with the second circumcircle and with a radius of R2+500 nm is a second region, and the number of second particles in the second region is N, where 4≤N≤88, preferably 11≤N≤38. Based on the secondary battery of this application embodiment, by controlling the relationship between the number of carbon-based particles and second particles in the second material layer within the above range, and distributing an appropriate number of second particles on the surface of the carbon-based particles, the ion conduction efficiency of the second material layer can be further improved. It can also synergistically construct an ion conduction network with the first material layer, enhance electrode dynamics, and thus further suppress electrode expansion while improving rate discharge performance and cycle performance.

[0008] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) the carbon-based particles include at least one of graphite or hard carbon; (2) the first particles include Li 1+x Al x Ti 2-x (PO4)3 or Li x La (2-x) / 3 TiO3, where 0.1≤x≤0.3; (3) The second particle includes Li7La3Zr2O2. Based on the secondary battery of the present application embodiment, the first particle includes lithium aluminum titanium phosphate with NASICON structure or lithium lanthanum titanate with perovskite structure, which has reversible lithium insertion and extraction capacity, and can react on the surface of the active material during charging and discharging to form a stable electron-ion conductor, reduce the side reaction between silicon and electrolyte, and suppress the volume expansion of silicon material; the second particle includes lithium lanthanum zirconate with garnet structure, which has excellent stability, can improve the ion conduction efficiency of the second material layer, and cooperate with the first material layer to construct an ion conduction network, improve the electrode dynamics, thereby suppressing electrode expansion while improving rate discharge performance and cycle performance.

[0009] In some embodiments, the first particle and / or the second particle further includes a doping element, which includes at least one selected from niobium, zirconium, germanium, tantalum, lanthanum, sulfur, silicon, or fluorine. Further addition of the aforementioned doping element to the solid electrolyte can suppress electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0010] In some embodiments, the mass percentage of titanium element is T%, or 2.12 × 10⁻⁶, based on the mass of the first material layer. -3 The mass ratio of titanium in the first material layer is ≤T≤1.36, preferably 0.14≤T≤0.54. Based on the secondary battery of this application embodiment, by controlling the mass ratio of titanium in the first material layer within the above range, it is possible to further suppress electrode expansion while improving rate discharge performance and cycle performance.

[0011] In some embodiments, based on the mass of the first material layer, the mass ratio of silicon is a%, the mass ratio of phosphorus is b%, and the first material layer satisfies at least one of the following conditions: (1) 5 ≤ a ≤ 98.6; (2) 0.04 ≤ b ≤ 2.43; (3) 2.06 ≤ a / b ≤ 2465. Based on the secondary battery of this application embodiment, by controlling the mass relationship between silicon and phosphorus in the first material layer within the above range, it is possible to further suppress electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0012] In some embodiments, the thickness of the first material layer is H1 μm, the thickness of the second material layer is H2 μm, p = H1 / (H1 + H2), and 0.08 ≤ p ≤ 0.86. Based on the secondary battery of this application embodiment, by controlling the thickness relationship between the first and second material layers within the above range, the thicknesses of the first and second material layers are at a relative equilibrium point, which effectively controls volume expansion without significantly affecting rate discharge performance and cycle performance.

[0013] In some embodiments, both the first and second material layers include a binder. Based on the mass of the negative electrode sheet, the mass percentage of the binder in the first material layer is 1.2% to 12.8%, and the mass percentage of the binder in the second material layer is 0.5% to 2.2%. Based on the mass of the negative electrode sheet, the mass percentage of the binder in the first material layer is K%, and the mass percentage of the binder in the second material layer is J%, with a ratio of 0.55 ≤ K / J ≤ 25.6, preferably 1.5 ≤ K / J ≤ 16. Based on the secondary battery of this application embodiment, by controlling the mass ratio of the binder in the first and second material layers within the above ranges, the amount of binder in the first and second material layers can be kept within a suitable range, which can alleviate the volume expansion of silicon material during cycling, while also improving rate discharge performance and cycle life.

[0014] In some embodiments, the electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is E%, 2.2 ≤ E ≤ 13.5, preferably 5.5 ≤ E ≤ 11.5, based on the mass of the electrolyte. In the secondary battery based on the embodiments of this application, the inclusion of fluoroethylene carbonate in the electrolyte allows for the formation of a LiF-rich SEI during cell cycling. This can improve the ion transport rate in the electrode and reduce side reactions during electrode cycling, thereby further suppressing electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0015] In some embodiments, the electrolyte includes lithium nitrate. Based on the mass of the electrolyte, the mass percentage of lithium nitrate is F%, 0.1 ≤ F ≤ 8.8. In the secondary battery based on the embodiments of this application, the inclusion of lithium nitrate in the electrolyte can form a Li3N-rich SEI during cell cycling. Li3N possesses extremely high ion conductivity, which can accelerate lithium-ion conduction, thereby further suppressing electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0016] In some embodiments, tabs are provided on both the positive and negative electrode sheets; the positive electrode sheet, separator, and negative electrode sheet are sequentially stacked and wound to form an electrode assembly, with the thickness direction of the electrode assembly as the first direction; a first adhesive tape and a second adhesive tape are provided on the negative electrode sheet, and a third adhesive tape is provided on the positive electrode sheet; the first adhesive tape is provided on at least a portion of the surface of the negative electrode tab, and the third adhesive tape is provided on at least a portion of the surface of the positive electrode tab; the projection of the second adhesive tape along the first direction at least partially overlaps with the projection of the positive electrode tab along the first direction. Based on the secondary battery of this application embodiment, by providing the aforementioned second adhesive tape, on the one hand, short circuits caused by the positive electrode tab piercing the separator can be prevented; on the other hand, the problem of reduced electrode cohesion caused by the large difference in specific surface area of ​​material particles in the negative electrode material layer and uneven adhesion of the binder can be improved, thereby further suppressing electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0017] In some embodiments, the area of ​​the second adhesive tape is S1 cm. 2 The area of ​​the first material layer is S² cm. 2 S = S1 / S2, 0.3 ≤ S ≤ 6. Based on the secondary battery of this application embodiment, by controlling the ratio of the area of ​​the second adhesive paper to the area of ​​the first material layer within the above range, the problem of reduced electrode cohesion caused by the large specific surface area of ​​the particles added in the negative electrode material layer and the strong adsorption force on the binder can be further improved, thereby further suppressing electrode expansion while improving rate discharge performance and cycle performance.

[0018] In some embodiments, the capacitance-voltage characteristic curves of the aforementioned negative electrode have reduction peaks at 0 to 0.8V, 1.5V to 1.8V, and 2.3V to 2.5V, respectively. Based on the secondary battery embodiments of this application, when its capacitance-voltage characteristic curve contains characteristic peaks in a specific voltage range, the secondary battery exhibits a lower electrode expansion rate and superior rate discharge performance and cycle performance.

[0019] Secondly, embodiments of this application provide an electronic device that includes the aforementioned secondary battery. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] The first aspect of this application provides a secondary battery, including a negative electrode, a positive electrode, an electrolyte, and a separator.

[0022] negative electrode

[0023] The negative electrode includes a negative electrode sheet, which comprises a first material layer, a second material layer, and a negative electrode current collector. The first material layer includes silicon-based particles and a first particle, the first particle comprising at least four elements selected from lithium, lanthanum, aluminum, titanium, phosphorus, or oxygen. The second material layer includes carbon-based particles and a second particle, the second particle comprising lithium, lanthanum, zirconium, titanium, and oxygen. The second material layer is disposed between the negative electrode current collector and the first material layer. In some embodiments, the second material layer completely overlaps the first material layer. In some embodiments, the second material layer and the first material layer partially overlap; for example, the edge of the second material layer may extend beyond the first material layer, or the edge of the first material layer may extend beyond the second material layer. The first and second material layers of the dual-layer negative electrode design each comprise solid electrolyte particles containing the aforementioned elements, which can improve electrode kinetics and mitigate the volume expansion of the silicon material, thereby suppressing electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0024] In some embodiments, the circumcircle of the cross-section of the silicon-based particle is a first circumcircle with a diameter of R1 nm. A circular region concentric with the first circumcircle and with a radius of R1 + 500 nm is defined as a first region. The number of first particles in the first region is M, where 10 ≤ M ≤ 119. For example, the number of first particles in the first region can be 10, 27, 53, 58, 94, 111, 119, or any value within the range of any two of these values. By controlling the relationship between the number of silicon-based particles and the number of first particles in the first material layer within the above range, an efficient ion conduction channel can be constructed, reducing the solvation energy of the silicon material surface. It can also form an in-situ protective layer to protect the reactivity of the silicon surface, thereby further suppressing electrode expansion while improving rate discharge performance and cycle performance.

[0025] In some embodiments, the circumcircle of the cross-section of the carbon-based particle is a second circumcircle with a diameter of R2 nm. A circular region concentric with the second circumcircle and with a radius of R2 + 500 nm is designated as a second region. The number of second particles in the second region is N, where 4 ≤ N ≤ 88, preferably 11 ≤ N ≤ 38. For example, the number of second particles in the second region can be 4, 11, 17, 32, 35, 48, 67, 88, or any combination of these values. By controlling the relationship between the number of carbon-based particles and the number of second particles in the second material layer within the aforementioned range, and by distributing an appropriate number of second particles on the surface of the carbon-based particles, the ion conduction efficiency of the second material layer can be further improved. This allows the second material layer to synergistically construct an ion conduction network with the first material layer, enhancing electrode dynamics and thereby further suppressing electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0026] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) the carbon-based particles include at least one of graphite or hard carbon; (2) the first particles include Li 1+x Al x Ti 2-x (PO4)3 or Li x La (2-x) / 3 TiO3, where 0.1≤x≤0.3; (3) The second particle includes Li7La3Zr2O2. The first particle includes lithium aluminum titanium phosphate with NASICON structure or lithium lanthanum titanate with perovskite structure, and the second particle includes lithium lanthanum zirconate with garnet structure, which can suppress electrode expansion while improving rate discharge performance and cycle performance.

[0027] In some embodiments, the first particle and / or the second particle further includes a dopant element, which includes at least one selected from niobium, zirconium, germanium, tantalum, lanthanum, sulfur, silicon, or fluorine. Further addition of dopant elements to the solid electrolyte can suppress electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0028] In some embodiments, the mass percentage of titanium is T%, or 2.12 × 10⁻⁶, based on the mass of the first material layer. -3 The mass percentage of titanium in the first material layer can be ≤T≤1.36, preferably 0.14≤T≤0.54. For example, the mass percentage of titanium in the first material layer can be 0.00212, 0.14, 0.35, 0.45, 0.54, 0.58, 0.62, 0.78, 1.36, or any combination of these values. Controlling the mass percentage of titanium in the first material layer within the above range can further suppress electrode expansion while improving rate discharge performance and cycle performance.

[0029] In some embodiments, based on the mass of the first material layer, the mass percentage of silicon is a%, the mass percentage of phosphorus is b%, and the first material layer satisfies at least one of the following conditions: (1) 5 ≤ a ≤ 98.6; (2) 0.04 ≤ b ≤ 2.43; (3) 2.06 ≤ a / b ≤ 2465. For example, the mass percentage of silicon in the first material layer can be 5, 12.3, 37.6, 50.7, 55.0, 67.6, 87.7, 98.6, or any two of these values. For example, the mass percentage of phosphorus in the first material layer can be 0.04, 0.05, 0.76, 1.39, 1.55, 1.60, 1.66, 2.36, 2.43, or any two of these values. For example, the mass ratio of silicon to phosphorus in the first material layer can be 2.06, 23.50, 32.71, 48.63, 160.73, 671.04, 1012.29, 1425.59, 1624.76, 1989.97, 2465, or any value within a range of these values. Controlling the mass ratio of silicon to phosphorus in the first material layer within the aforementioned range can further suppress electrode expansion while simultaneously improving rate discharge performance and cycle performance.

[0030] In some embodiments, the thickness of the first material layer is H1 μm, the thickness of the second material layer is H2 μm, p = H1 / (H1+H2), and 0.08 ≤ p ≤ 0.86. For example, the value of p can be 0.08, 0.21, 0.34, 0.48, 0.50, 0.67, 0.77, 0.86, or any value within the range of any two of these values. The thickness relationship between the first and second material layers is controlled within the above range, so that the thicknesses of the first and second material layers are at a relative equilibrium point, which effectively controls volume expansion without significantly affecting rate discharge performance and cycle performance.

[0031] In some embodiments, both the first and second material layers include a binder. Based on the mass of the negative electrode sheet, the mass percentage of the binder in the first material layer is 1.2% to 12.8%. For example, the mass percentage of the binder in the first material layer can be 1.2%, 2.1%, 3.5%, 5.4%, 7.6%, 12.8%, or any value within the range of any two of these values. The mass percentage of the binder in the second material layer is 0.5% to 2.2%. For example, the mass percentage of the binder in the second material layer can be 0.5%, 0.71%, 1.2%, 1.4%, 1.5%, 1.7%, 2.2%, or any value within the range of any two of these values. Based on the mass of the negative electrode sheet, the mass percentage of the binder in the first material layer is K%, and the mass percentage of the binder in the second material layer is J%, where 0.55 ≤ K / J ≤ 25.6, preferably 1.5 ≤ K / J ≤ 16. For example, based on the mass of the negative electrode sheet, the ratio of the mass percentage of the binder in the first material layer to the mass percentage of the binder in the second material layer can be 0.55, 0.76, 1.50, 7.0, 8.40, 10.50, 11.20, 12.30, 13.50, 16.00, 18.14, 25.60, or a value within any two of these ranges. In some embodiments, the binder in the first material layer includes polyacrylic acid, and the binder in the second material layer includes styrene-butadiene rubber or carboxymethyl cellulose. Controlling the mass ratio of the binder in the first and second material layers within the above range ensures that the amount of binder in both layers is within a suitable range, which can alleviate the volume expansion of the silicon material during cycling while simultaneously improving rate discharge performance and cycle life.

[0032] The negative electrode material layer of this application also includes a conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent, as long as it can achieve the purpose of this application. For example, the negative electrode conductive agent can be at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene, etc., and the aforementioned carbon nanotubes can include, but are not limited to, at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0033] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. The conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalate). In this application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 160 μm. In this application, the negative electrode mixture layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a part of it. This application has no particular restrictions, as long as the purpose of this application can be achieved.

[0034] This application does not impose any particular limitation on the compaction density of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 Up to 1.85 g / cm 3 This application does not impose any particular limitation on the cold pressing pressure of the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the cold pressing pressure of the negative electrode sheet can be from 3 tons to 30 tons.

[0035] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer, and it can be at least one of the aforementioned conductive agents and binders. This application does not impose any particular limitation on the mass ratio of the conductive agent to the binder in the conductive layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the thickness of the conductive layer, as long as the purpose of this application is achieved; for example, the thickness of the conductive layer is 1 μm to 10 μm.

[0036] positive electrode

[0037] The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a lithium-containing transition metal composite oxide, which includes Li... w Na z Co 1-y A yO2, where 0.6 < w < 0.95, 0 ≤ y < 0.15, 0 < z ≤ 0.03, and A is selected from at least one of the groups consisting of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, and Zr. For example, the above subscripts can be 0.6 < w < 0.7, 0 ≤ y < 0.10, and 0 < z < 0.01; 0.7 < w < 0.8, 0.05 < y < 0.10, and 0 < z < 0.02; 0.8 < w < 0.9, 0.06 < y < 0.09, and 0 < z ≤ 0.03; 0.9 < w < 0.95, 0.07 < y < 0.08, and 0.01 < z < 0.02; 0.6 < w < 0.9, 0.08 < y < 0.15, and 0.01 < z ≤ 0.03. By adding the aforementioned lithium-containing transition metal composite oxide to the cathode material layer in an electrochemical device, and controlling the content ratio of each metal atom in the lithium-containing transition metal composite oxide, especially the content ratio of sodium atoms, to meet the above-mentioned range, it is possible to improve both the high-temperature storage performance and the low-temperature discharge performance of the electrochemical device.

[0038] In some embodiments, the positive electrode material layer includes a positive electrode conductive material. There is no limitation on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, acetylene black, Super-P carbon black, etc.; amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0039] In some embodiments, the positive electrode material layer includes a positive electrode binder. There are no particular limitations on the type of positive electrode binder; in the case of a coating method, any material that is soluble or dispersible in the liquid medium used during electrode manufacturing is acceptable. Examples of positive electrode adhesives may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with alkali metal ion conductivity. The above-mentioned positive electrode adhesives may be used alone or in any combination.

[0040] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry can include any of aqueous and organic solvents. Examples of aqueous media can include, but are not limited to, mixtures of alcohol and water or water. Examples of organic media can include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0041] Thickeners are typically used to adjust the viscosity of slurries. In the case of aqueous media, thickeners and styrene-butadiene rubber latex can be used for slurry preparation. There are no particular limitations on the types of thickeners; examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The above-mentioned thickeners can be used alone or in any combination.

[0042] There are no particular limitations on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0043] To reduce the electronic contact resistance between the positive current collector and the positive electrode material layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0044] electrolyte

[0045] The electrolyte used in the secondary battery of this application includes an electrolyte and a non-aqueous solvent for dissolving the electrolyte.

[0046] In some embodiments, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is E%, 2.2 ≤ E ≤ 13.5, preferably 5.5 ≤ E ≤ 11.5. For example, the mass percentage of fluoroethylene carbonate in the electrolyte can be 2.2, 3.7, 5.5, 6.1, 7.8, 8.3, 9.9, 11.5, 13.5, or any combination of these values. The inclusion of fluoroethylene carbonate in the electrolyte allows for the formation of a LiF-rich SEI during cell cycling. This improves ion transport speed in the electrodes and reduces side reactions during electrode cycling, thereby improving both rate discharge performance and cycle performance.

[0047] In some embodiments, the electrolyte includes lithium nitrate. The mass percentage of lithium nitrate is F%, ranging from 0.1 ≤ F ≤ 8.8, based on the mass of the electrolyte. For example, the mass percentage of lithium nitrate in the electrolyte can be 0.1, 0.7, 1.6, 3.4, 4.6, 7.3, 8.8, or any combination of these values. The inclusion of lithium nitrate in the electrolyte can form a Li3N-rich SEI during cell cycling. Li3N possesses extremely high ion conductivity, which can accelerate lithium-ion conduction, thereby further improving both rate discharge performance and cycle performance.

[0048] This application does not impose any particular limitation on the type of 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 lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalateborate)borate (LiBOB), or lithium difluorooxalateborate (LiDFOB). 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%, 9%, 10%, 11%, 12.5%, 13%, 15%, or a range consisting of any two of these values. This application does not impose any particular limitation on the type of non-aqueous solvent mentioned above, as long as it achieves the purpose of this application. For example, it may include, but is 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 or cyclic carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate, butylene carbonate, or ethylene ethylene 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 ethylene glycol dimethyl ether, 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 other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0049] diaphragm

[0050] This application typically includes a separator between the positive and negative electrodes. The separator is used to separate the positive and negative electrode plates, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process.

[0051] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the diaphragm type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0052] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0053] In this application, the pore size of the separator is from 0.01 μm to 1 μm, and the thickness is from 5 μm to 50 μm. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0054] In some embodiments, tabs are provided on both the positive and negative electrode sheets. The positive electrode sheet, separator, and negative electrode sheet are sequentially stacked and wound to form an electrode assembly, with the thickness direction of the electrode assembly as the first direction. A first adhesive tape and a second adhesive tape are provided on the negative electrode sheet, and a third adhesive tape is provided on the positive electrode sheet. The first adhesive tape is disposed on at least a portion of the surface of the negative electrode tab, and the third adhesive tape is disposed on at least a portion of the surface of the positive electrode tab. The projection of the second adhesive tape along the first direction at least partially overlaps with the projection of the positive electrode tab along the first direction. The second adhesive tape can, on the one hand, protect against short circuits caused by the positive electrode tab piercing the separator, and on the other hand, improve the problem of reduced cohesion of the electrode sheet caused by the large difference in specific surface area of ​​the material particles in the negative electrode material layer and the uneven adsorption force of the binder, thereby further suppressing electrode expansion while improving rate discharge performance and cycle performance.

[0055] In some embodiments, the area of ​​the second adhesive tape is S1 cm. 2 The area of ​​the first material layer is S² cm. 2 S = S1 / S2, 0.3 ≤ S ≤ 6. For example, the ratio of the area of ​​the second adhesive tape to the area of ​​the first material layer can be 0.3, 0.5, 1.3, 2.8, 3.5, 4.9, 6.0, or any value within the range of any two of these values. Controlling the ratio of the area of ​​the second adhesive tape to the area of ​​the first material layer within the above range can further improve the problem of reduced electrode cohesion caused by the large specific surface area of ​​the particles added in the negative electrode material layer and their strong adsorption force on the binder. This further suppresses electrode expansion while improving rate discharge performance and cycle performance.

[0056] In some embodiments, the capacitance-voltage characteristic curves of the aforementioned negative electrode sheet exhibit reduction peaks at 0 to 0.8V, 1.5V to 1.8V, and 2.3V to 2.5V, respectively. When the capacitance-voltage characteristic curve of the secondary battery contains the aforementioned characteristic peaks within a specific voltage range, the secondary battery exhibits a lower electrode expansion rate and superior rate discharge performance and cycle performance.

[0057] This application also provides an electronic device, which includes the secondary battery described in this application. Electronic devices include, but are not limited to, laptops, pen-based 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.

[0058] Example

[0059] The following examples, using lithium-ion batteries as an example, provide more specific illustrations of the implementation methods of the secondary battery of this application. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" refer to mass measurements.

[0060] Example 1-1

[0061] 1. Preparation of the positive electrode

[0062] Lithium cobalt oxide (CCO), conductive carbon black (CCO), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a CCO slurry with a solid content of 70 wt%. The CCO slurry was uniformly coated onto one surface of a 9 μm thick aluminum foil current collector and dried to obtain a single-sided coated CCO electrode sheet. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated CCO electrode sheet. By adjusting the cold pressing pressure, CCO electrodes with different compaction densities and surface roughness could be obtained. After cold pressing, slitting, and welding of tabs, a third adhesive tape was applied to the tab surface, and the mixture was dried to obtain a CCO electrode sheet with dimensions of 74 mm × 867 mm.

[0063] 2. Preparation of electrolyte

[0064] In a dry argon atmosphere glove box, diethyl carbonate was used as the base solvent. Lithium hexafluorophosphate (LiPF6) was then dissolved in the base solvent, and vinylene carbonate and fluoroethylene carbonate were added to obtain the electrolyte. Based on the total mass of the electrolyte, LiPF6 accounted for 12.5% ​​by mass, vinylene carbonate accounted for 2% by mass, and fluoroethylene carbonate accounted for 7% by mass.

[0065] 3. Preparation of the negative electrode

[0066] <Preparation of Negative Electrode Sheets>

[0067] (1) Silicon-carbon material (mass ratio silicon:carbon = 65:35) and graphite are mixed at a mass ratio of 8:92 to obtain the second negative electrode active material; the second negative electrode active material, polyacrylonitrile (PAA), carbon nanotubes (CNTs), and second particles Li7La3Zr2O2 are mixed at a mass ratio of 97.99:1.2:0.8:0.01, and then deionized water is added and stirred evenly to prepare a second slurry with a solid content of 45wt%. The second slurry is uniformly coated on one surface of a 10μm thick negative electrode current collector copper foil to obtain a negative electrode sheet with a single-sided coating of the second material layer; the above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a double-sided coating of the second material layer;

[0068] (2) Silicon-carbon material (mass ratio silicon:carbon = 65:35) and graphite are mixed at a mass ratio of 8:92 to obtain negative electrode active material one; negative electrode active material one, polyacrylonitrile (PAA), carbon nanotubes (CNTs), and first particle Li 1.1 Al 0.1 Ti 1.9 (PO4)3 is mixed in a mass ratio of 97.99:1.2:0.8:0.01, and then deionized water is added and stirred evenly to prepare a first slurry with a solid content of 45wt%. The first slurry is uniformly coated on one surface of the negative electrode sheet obtained in step (1); the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a first material layer and a second material layer coated on both sides.

[0069] (3) After cold pressing, slitting and welding of the tabs, the first adhesive paper is attached to the surface of the tabs and dried to obtain a negative electrode sheet with a specification of 76.6mm×875mm.

[0070] 4. Preparation of the diaphragm

[0071] A porous polyethylene film with a thickness of 15μm was used as the diaphragm.

[0072] 5. Preparation of lithium-ion batteries

[0073] The positive electrode, negative electrode, and separator are stacked sequentially, with the separator positioned between the positive and negative electrodes for isolation. A second adhesive tape is applied to the negative electrode, and the assembly is then wound to form the electrode assembly. After winding, the projection of the second adhesive tape along the thickness direction of the electrode assembly overlaps with the projection of the positive electrode tab along the thickness direction of the electrode assembly. The electrode assembly is placed in a packaging bag, dehydrated at 80°C, injected with the electrolyte, and sealed. After formation, hot pressing, degassing, and edge trimming processes, a lithium-ion battery is obtained.

[0074] 6. Testing Methods

[0075] (1) Particle count measurement

[0076] Take a lithium-ion battery, polish the negative electrode sheet with argon ions, and then cut it open to expose the cross-section along the thickness direction. Then, observe the cross-section of the material particles in the electrode cross-section using a scanning electron microscope. The circumcircle of the particle is defined by a circle with diameters equal to the two farthest points on its cross-section, and its radius is R nm. A circular region concentric with the circumcircle and with a radius of R + 500 nm is designated as the counting region. During counting, if only part of the cross-section of a particle is located within the counting region, it is counted as one particle. The arithmetic mean of the counts from 20 counting regions is taken as the number of the first particle in the first region or the number of the second particle in the second region.

[0077] (2) Element content test

[0078] A lithium-ion battery was discharged at a constant current of 0.5C to 2.8V to obtain a fully discharged battery. The negative electrode was removed, and the cross-section of the electrode along the thickness direction was analyzed by energy dispersive X-ray diffraction. The mass percentages of titanium, silicon, and phosphorus in the first material layer were measured respectively.

[0079] (3) Test method for adhesive mass ratio

[0080] Take a lithium-ion battery, and cut the negative electrode sheet after ion polishing to expose the entire cross-section of the electrode sheet along the thickness direction. Then, use an infrared spectrometer (ATR IR spectroscopy) to test the absorption spectrum of the cross-section. Analyze the binder distribution pattern along the electrode thickness direction to obtain the relative content of binder in the first material layer and the relative content of binder in the second material layer. Divide the two relative contents to obtain the mass ratio of binder.

[0081] (4) Capacitor voltage characteristic curve test

[0082] For the initial first particle, the first particle is uniformly mixed with PVDF and carbon in a mass ratio of 8:1:1, and then coated onto a current collector to prepare an electrode. The prepared electrode is then assembled with a Li sheet to form a coin cell. The cell is charged and discharged at 0.2C, and the QV curve is integrated to obtain the dQ / dV-V image. For the secondary battery, a lithium-ion battery is used, and the cell is charged and discharged at 0.2C. The QV curve is integrated to obtain the dQ / dV-V image.

[0083] (5) Thickness expansion performance test

[0084] Take a lithium-ion battery and place it in a constant temperature environment of 25℃ for 30 minutes to allow it to reach a constant temperature. Charge it at a constant current of 0.5C to 4.5V, then charge it at a constant voltage of 4.5V to a current of 0.025C. Use a PPG soft-pack battery thickness gauge to test the battery thickness under a pressure of 700g. Select 5 different points outside the tabs to measure the thickness and record the thickness of the lithium-ion battery in 5 measurements. Record the average of the 5 test values ​​as the initial thickness. After measurement, discharge it at a constant current of 0.5C to 3.0V, let it stand for 5 minutes, charge it at a constant current of 0.5C to 4.5V, and then charge it at a constant voltage of 4.5V to a current of 0.025C. Repeat this process 100 times. Remove the battery, select 5 different points outside the tabs, and use a PPG soft-pack battery thickness gauge to test the battery thickness under a pressure of 700g. Record the thickness of the battery after the cycle and record the average of the 5 test values ​​as the final thickness. Cyclic thickness expansion rate % = (final thickness - initial thickness) / initial thickness × 100%.

[0085] (6) 4C rate discharge test

[0086] A lithium-ion battery was charged at 25°C with a constant current rate of 0.2C to 4.5V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 30 minutes, it was discharged at a constant current rate of 0.2C to 2.8V. The 0.2C discharge capacity of the lithium-ion battery at 25°C was measured. Similarly, at 25°C, the lithium-ion battery was charged at a constant current rate of 0.2C to 4.5V, then charged at a constant voltage rate until the current was less than or equal to 0.05C, and finally discharged at a constant current rate of 4C to 2.8V. The 4C discharge capacity retention rate % = 4C discharge capacity / 0.2C discharge capacity × 100%.

[0087] (7) Room temperature cycling performance test

[0088] Take a lithium-ion battery and place it in a 25°C constant temperature test chamber. Let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge it at a constant current of 0.5C to 4.5V, then charge it at a constant voltage of 4.5V to a current of 0.025C. Let it stand for 5 minutes, then discharge it at a constant current of 0.5C to 2.8V. Record this as the initial discharge capacity C0. Repeat this process 500 times, and record the discharge capacity C1 after 100 cycles. Calculate the cycle capacity retention rate of the lithium-ion battery. Cycle capacity retention rate % = C1 / C0 × 100%.

[0089] The lithium-ion batteries in the following embodiments or comparative examples differ from those in Examples 1-1 only in that the amounts of silicon-based particles and first particles in the first material layer, the amounts of carbon-based particles and second particles in the second material layer, and the elemental ratios in the first particles are adjusted according to Table 1. The performance test results of the lithium-ion batteries in each embodiment and comparative example are shown in Table 1 below.

[0090] Table 1

[0091]

[0092]

[0093] *In the table above, the calculation result of a / b is rounded to two decimal places.

[0094] As shown in Table 1, the lithium-ion batteries prepared in the embodiments of this application have significantly improved energy density compared to Comparative Example 1 (without a first material layer), from Examples 1-1 to 1-26. Compared to Comparative Example 2 (without the first particle in the first material layer), the lithium-ion batteries of Examples 1-1 to 1-26 have significantly improved energy density. Compared to Comparative Example 3 (without a second material layer), the lithium-ion batteries of Examples 1-1 to 1-26 exhibit significantly improved rate discharge capacity retention, room temperature cycle capacity retention, and cycle thickness expansion performance. Compared to Comparative Example 4 (without the second particle in the second material layer), the lithium-ion batteries of Examples 1-1 to 1-26 exhibit significantly improved rate discharge capacity retention, room temperature cycle capacity retention, and cycle thickness expansion performance.

[0095] Specifically, the lithium-ion battery prepared in the embodiments of this application exhibits excellent performance in rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density when the number of first particles in the first region satisfies 10 ≤ M ≤ 119. Similarly, when the number of second particles N in the second region satisfies 4 ≤ N ≤ 88, especially 11 ≤ N ≤ 38, the lithium-ion battery also exhibits excellent performance in rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density. Furthermore, when the mass percentage of titanium in the first material layer satisfies 2.12 × 10⁻⁶, the lithium-ion battery also demonstrates superior performance. -3 When T ≤ 1.36, especially when T ≤ 0.14 ≤ T ≤ 0.54, lithium-ion batteries exhibit excellent performance in rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density. When the mass percentage of silicon in the first material layer satisfies 5 ≤ ​​a ≤ 98.6, or the mass percentage of phosphorus in the first material layer satisfies 0.04 ≤ b ≤ 2.43, or the relationship between a and b satisfies 2.06 ≤ a / b ≤ 2465, lithium-ion batteries also exhibit excellent performance in rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density.

[0096] The lithium-ion batteries in Examples 2-1 to 2-30 differ from those in Examples 1-24 only in that the thickness of the first material layer and the second material layer, the mass ratio of the binder in the first material layer and the second material layer, the area ratio of the first adhesive paper and the second adhesive paper to the first material layer, and the mass ratio of fluoroethylene carbonate and lithium nitrate in the electrolyte are adjusted according to Table 2.

[0097] Table 2

[0098]

[0099]

[0100] *In the table above, the calculation results of p and K / J are rounded to two decimal places; the calculation result of S is rounded to one decimal place.

[0101] As shown in Table 2, the lithium-ion batteries prepared in the embodiments of this application exhibit better performance in terms of rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density when the relationship between the thickness of the first material layer and the thickness of the second material layer is adjusted to satisfy 0.08≤p≤0.86. Furthermore, when the mass ratio of the binder in the first material layer to the mass ratio of the binder in the second material layer is adjusted to satisfy 0.55≤K / J≤25.6, especially 1.5≤K / J≤16, the lithium-ion batteries exhibit even better performance in terms of rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density. Finally, when the relationship between the area of ​​the first adhesive paper, the area of ​​the second adhesive paper, and the area of ​​the first material layer is adjusted to satisfy 0.3≤S≤6, the lithium-ion batteries exhibit even better performance in terms of rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density. When the mass percentage of fluoroethylene carbonate in the electrolyte is adjusted to meet the requirements of 2.2 ≤ E ≤ 13.5, especially 5.5 ≤ E ≤ 11.5, the lithium-ion battery exhibits better performance in rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density. Similarly, when the mass percentage of lithium nitrate in the electrolyte is adjusted to meet the requirements of 0.1 ≤ F ≤ 8.8, the lithium-ion battery demonstrates even better performance in rate discharge capacity retention, room temperature cycle capacity retention, cycle thickness expansion, and energy density.

[0102] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, characterized by, The negative electrode sheet comprises a first material layer, a second material layer and a negative electrode current collector; The first material layer comprises silicon-based particles and first particles, the first particles comprising at least four of lithium element, lanthanum element, aluminum element, titanium element, phosphorus element or oxygen element; The second material layer comprises carbon-based particles and second particles, the second particles comprising lithium element, lanthanum element, zirconium element and oxygen element; The second material layer is arranged between the negative electrode current collector and the first material layer.

2. The secondary battery according to claim 1, characterized by A circumscribed circle of a transverse section of the silicon-based particles is a first circumscribed circle, a diameter of the first circumscribed circle is R1 nm; A circular region concentric with the first circumscribed circle and having a radius of R1+500 nm is a first region, a number of the first particles in the first region is M, 10≤M≤119.

3. The secondary battery according to claim 1, characterized by A circumscribed circle of a transverse section of the carbon-based particles is a second circumscribed circle, a diameter of the second circumscribed circle is R2 nm; A circular region concentric with the second circumscribed circle and having a radius of R2+500 nm is a second region, a number of the second particles in the second region is N, 4≤N≤88.

4. The secondary battery according to claim 3, characterized by 11≤N≤38。 5. The secondary battery according to any one of claims 1 to 4, characterized by The secondary battery satisfies at least one of the following conditions: (1) The carbon-based particles comprise at least one of graphite or hard carbon; (2) the first particles comprise Li 1+x Al x Ti 2-x (PO4)3or Li x La (2-x) / 3 TiO3, wherein 0.1 < x < 0.3; (3) The second particles comprise Li7La3Zr2O2.

6. The secondary battery according to claim 1, characterized by Based on the mass of the first material layer, the mass proportion of titanium element is T%, 2.12x10 -3 ≤T≤1.

36.

7. The secondary battery according to claim 6, characterized by 0.14≤T≤0.54。 8. The secondary battery according to claim 1, characterized by Based on a mass of the first material layer, a mass proportion of silicon element is a%, a mass proportion of phosphorus element is b%, the first material layer satisfies at least one of the following conditions: （1）5≤a≤98.6； （2）0.04≤b≤2.43； (3) 2.06≤a / b≤2465.

9. The secondary battery according to claim 1, characterized by A thickness of the first material layer is H1 μm, a thickness of the second material layer is H2 μm, p=H1 / (H1+H2), 0.08≤p≤0.

86.

10. The secondary battery according to claim 1, characterized by The first material layer and the second material layer both comprise a binder; Based on a mass of the negative electrode sheet, a mass proportion of the binder in the first material layer is K%, a mass proportion of the binder in the second material layer is J%, 0.55≤K / J≤25.

6.

11. The secondary battery according to claim 10, characterized by 1.5≤K / J≤16.

12. The secondary battery according to claim 1, characterized by The electrolyte comprises fluoroethylene carbonate, based on a mass of the electrolyte, a mass proportion of the fluoroethylene carbonate is E%, 2.2≤E≤13.

5.

13. The secondary battery according to claim 12, characterized by 5.5≤E≤11.5。 14. The secondary battery according to claim 12, characterized by The electrolyte comprises lithium nitrate; Based on a mass of the electrolyte, a mass proportion of the lithium nitrate is F%, 0.1≤F≤8.

8.

15. The secondary battery according to claim 1, characterized by Both the positive electrode sheet and the negative electrode sheet are provided with tabs; the positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and wound to form an electrode assembly, a thickness direction of the electrode assembly is a first direction; the negative electrode sheet is provided with first adhesive paper and second adhesive paper, and the positive electrode sheet is provided with third adhesive paper; The first adhesive paper is arranged on at least part of a surface of a negative electrode tab, and the third adhesive paper is arranged on at least part of a surface of a positive electrode tab; A projection of the second adhesive paper along the first direction at least partially overlaps a projection of the positive electrode tab along the first direction.

16. The secondary battery according to claim 15, characterized by The sum of the areas of the first and second adhesive papers is S1 cm 2 The area of the first material layer is S2 cm 2 S = 100 x S1 / S2, 0.3 ≤ S ≤ 6.

17. The secondary battery according to claim 15, characterized by The negative electrode sheet has a reduction peak at 0-0.8 V, 1.5 V-1.8 V and 2.3 V-2.5 V, respectively, in a capacitive voltage characteristic curve.

18. An electronic device, comprising: The secondary battery according to any one of claims 1 to 17.

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