Secondary battery and electronic apparatus

Abstract

Disclosed in the present application are a secondary battery and an electronic apparatus. The secondary battery comprises a positive electrode sheet, and the positive electrode sheet comprises a positive electrode mixture layer. A dQ / dV-V image of the discharge of the secondary battery comprises a first peak and a second peak, the peak position of the first peak being 4.05 V to 4.25 V, and the peak position of the second peak being 3.88 V to 4.08 V. The present application can improve the high-temperature storage expansion phenomenon of secondary batteries, reduce the high-temperature storage thickness expansion rate, and improve both the high-temperature cycle capacity retention rate and the normal-temperature rate discharge retention rate of secondary batteries.

Description

Secondary batteries and electronic devices 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 the increasing demand for electronic products such as mobile phones, laptops, and cameras, electrochemical devices are playing an increasingly important role in our daily lives as power sources for these devices. This has driven the need to improve the performance of electrochemical devices in diverse scenarios. Ternary lithium batteries, as a widely used cathode material, are prone to releasing oxygen during high-temperature charging and discharging. This oxygen may further react with the electrolyte, leading to a degradation of the high-temperature performance of the secondary battery. Therefore, providing secondary batteries with good high-temperature performance has become a top priority. Summary of the Invention

[0003] This application provides a secondary battery and electronic device that achieves superior high-temperature cycling performance while also improving room-temperature rate performance.

[0004] In a first aspect, embodiments of this application provide a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode flux layer disposed on at least one surface of the positive current collector; the dQ / dV-V image of the secondary battery discharge includes a first peak and a second peak, the peak position of the first peak being 4.05V to 4.25V, and the peak position of the second peak being 3.88V to 4.08V.

[0005] Based on the secondary battery embodiments of this application, the positive electrode layer of this application includes a specific positive electrode material. This material exhibits a characteristic peak in the high-voltage region of the capacity-voltage differential dQ / dV versus voltage V curve during secondary battery discharge. This peak represents a significant elemental redox reaction occurring in the positive electrode material at this voltage, corresponding to the voltage point where a significant phase transition occurs in the material structure. The potential of the characteristic peak indicates the redox activity of the positive electrode material, which is reflected by the electronic density of states of the positive electrode material. The electronic density of states is directly related to the elemental composition and proportions. The dQ / dV characteristic peak reflects the intrinsic structure and compositional characteristics of the positive electrode material. This phase transition structure is difficult to define using structural formulas and conventional phase transition types, and the redox activity is also difficult to reflect using simple material chemical formulas and material structures. The aforementioned characteristic peaks indicate that the positive electrode material of this application possesses unique physicochemical properties, which can improve the high-temperature storage expansion phenomenon of the secondary battery and reduce the high-temperature storage thickness expansion rate. Simultaneously, it has good thermal stability, which can improve both the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate while simultaneously improving the high-temperature storage thickness expansion rate of the secondary battery.

[0006] In some embodiments, the peak position of the first peak is 4.1V to 4.2V; and / or, the peak position of the second peak is 3.93V to 4.03V. Based on the above embodiments, when the characteristic peaks in the curve of the capacity-voltage differential dQ / dV versus voltage V of the secondary battery discharge are further located within the above range, it indicates that the cathode material has unique physicochemical properties, which can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0007] In some embodiments, the peak area of ​​the first peak is S1 mAh, the peak area of ​​the second peak is S2 mAh, and 0.18 ≤ S1 / S2 ≤ 3.7. Based on the above embodiments, when the peak area in the curve of the capacity-voltage differential dQ / dV versus voltage V of the secondary battery discharge is within the above range, it indicates that the elements in the cathode material have a suitable proportion, which can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0008] In some embodiments, under full-discharge conditions, the XRD image of the positive electrode sheet includes at least a first diffraction peak and a second diffraction peak at angles between 35.5° and 37°; the diffraction angle 2θ of the first diffraction peak is smaller than the diffraction angle 2θ of the second diffraction peak; the intensity of the first diffraction peak is IA, and the intensity of the second diffraction peak is IB, where 1.5 ≤ IB / IA ≤ 4. Based on the above embodiments, when the XRD image of the positive electrode sheet of the secondary battery includes a first diffraction peak and a second diffraction peak, and the peak intensity ratio of the first diffraction peak and the second diffraction peak is within the above range, it indicates that the elements in the positive electrode material have a suitable proportion, which can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0009] In some embodiments, 1.8 ≤ IB / IA ≤ 3.5. Based on the above embodiments, when the peak intensity ratio of the XRD image of the positive electrode sheet of the secondary battery is further within the above range, it indicates that the elements in the positive electrode material have a more suitable ratio, which can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room temperature rate discharge retention rate.

[0010] In some embodiments, the aforementioned positive electrode composite layer includes a first material and a second material. The first material has an R3-m type layered structure, and the second material has an Fd3m type spinel structure. Based on the above embodiments, the positive electrode material in this embodiment includes a first material with an R3-m type layered structure and a second material with an Fd3m type spinel structure. The synergistic use of these two materials can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0011] In some embodiments, the aforementioned positive electrode mixture layer includes a first material and a second material. The first material consists of nearly spherical secondary particles composed of primary particles, with a diameter of 8 μm to 12 μm, and the second material has a diameter of 0.1 μm to 1 μm. Based on the above embodiments, the positive electrode material in this embodiment includes a first material with a larger particle size and a second material with a smaller particle size. When the particle diameters are distributed within the aforementioned ranges, the material has a larger active surface area, which is beneficial for the rapid migration of lithium ions. This further improves the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0012] In some embodiments, the positive electrode mixture layer comprises a first material and a second material, wherein the first material comprises LiNi. x Co y Mn (1-x-y) O2, where 0.4≤x≤0.6, 0≤y≤0.2; the second material includes LiMnO2. Based on the above embodiments, when the positive electrode mixture layer includes nickel-manganese materials and lithium manganese oxide materials, the dense manganese-oxygen framework of lithium manganese oxide materials can capture the oxygen released by nickel-manganese materials during high-temperature operation, reduce the gas generation reaction between oxygen and electrolyte, improve the high-temperature storage expansion phenomenon of secondary batteries, and reduce the high-temperature storage thickness expansion rate; at the same time, lithium manganese oxide materials themselves have good thermal stability, and when mixed with nickel-manganese materials as positive electrode active materials, it can improve the high-temperature storage thickness expansion rate of secondary batteries while also improving the high-temperature cycle capacity retention rate and the room temperature rate discharge retention rate.

[0013] In some embodiments, under full discharge conditions, the above-mentioned positive electrode additive layer satisfies at least one of the following conditions: (1) based on the molar amount of metal elements other than lithium, the molar percentage content of nickel is a%, 14≤a≤34; (2) based on the molar amount of metal elements other than lithium, the molar percentage content of manganese is b%, 66≤b≤86. Based on the above embodiments, this embodiment limits the content of nickel and manganese in the positive electrode additive layer to the above range, which can efficiently utilize the three-dimensional diffusion channels of lithium manganese oxide material, allowing lithium ions to pass through quickly, thereby improving the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room temperature rate discharge retention rate.

[0014] In some embodiments, the positive electrode additive layer satisfies at least one of the following conditions: (1) 19 ≤ a ≤ 29; (2) 71 ≤ b ≤ 81; (3) 0.25 ≤ a / b ≤ 0.42. Based on the above embodiments, this embodiment, by further limiting the content of nickel and manganese elements in the positive electrode additive layer to the above range, can improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0015] Secondly, embodiments of this application provide an electronic device including the aforementioned secondary battery. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 is a capacity-voltage differential dQ / dV-V graph of the lithium-ion batteries in Examples 1-3 of this application. The vertical axis is in mAh / V, and the horizontal axis is in V. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] The first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, an electrolyte, and a separator.

[0020] positive electrode

[0021] The positive electrode of this application embodiment includes a positive electrode sheet, which includes a positive current collector and a positive electrode flux layer disposed on at least one surface of the positive current collector. The dQ / dV-V image of the secondary battery discharge includes a first peak and a second peak. The peak position of the first peak is 4.05V to 4.25V. Preferably, the peak position of the first peak is 4.1V to 4.2V. For example, the peak position of the first peak can be 4.05, 4.10, 4.14, 4.15, 4.20, 4.25, or a value within the range of any two of these values. The peak position of the second peak is 3.88V to 4.08V. Preferably, the peak position of the second peak is 3.93V to 4.03V. For example, the peak position of the second peak can be 3.88, 3.93, 3.97, 3.98, 4.03, 4.08, or a value within the range of any two of these values. The positive electrode compound layer includes a positive electrode material with a specific structure, which has a characteristic peak in the high-voltage region of the relationship curve between the capacity-voltage differential dQ / dV and voltage V during secondary battery discharge. This can improve the thickness expansion rate of the secondary battery during high-temperature storage, while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0022] In some embodiments, the peak area of ​​the first peak is S1 mAh, the peak area of ​​the second peak is S2 mAh, and 0.18 ≤ S1 / S2 ≤ 3.7. For example, the ratio of the peak area S1 of the first peak to the peak area S2 of the second peak can be 0.18, 0.56, 1.33, 1.69, 2.01, 2.85, 3.7, or any value within the range of any two of these values. When the peak area in the curve of the capacity-voltage differential dQ / dV versus voltage V of the secondary battery discharge is within the above range, it indicates that the elements in the cathode material have a suitable proportion, which can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0023] In some embodiments, under full discharge conditions, the XRD image of the positive electrode includes at least a low-angle first diffraction peak and a high-angle second diffraction peak in the range of 35.5° to 37°; the diffraction peak intensity of the first diffraction peak is IA, and the diffraction peak intensity of the second diffraction peak is IB, with 1.5 ≤ IB / IA ≤ 4. Preferably, 1.8 ≤ IB / IA ≤ 3.5. For example, the ratio of the diffraction peak intensity IB of the second diffraction peak to the diffraction peak intensity IA of the first diffraction peak can be a value within the range of 1.5, 1.8, 2.5, 3.2, 3.5, 4, or any two of these values. When the XRD image of the positive electrode of the secondary battery includes the first diffraction peak and the second diffraction peak, and the peak intensity ratio of the first diffraction peak and the second diffraction peak is within the above range, it indicates that the elements in the positive electrode material have a suitable proportion, which can further improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0024] In some embodiments, the positive electrode composite layer includes a first material and a second material. The first material has an R3-m type layered structure, and the second material has an Fd3m type spinel structure. The positive electrode material comprising the first material with an R3-m type layered structure and the second material with an Fd3m type spinel structure, used synergistically, can further improve the high-temperature storage thickness expansion rate of the secondary battery while simultaneously improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0025] In some embodiments, the positive electrode layer includes a first material and a second material. The first material consists of spherical secondary particles composed of primary particles, with a diameter of 8 μm to 12 μm. For example, the diameter of the first material can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value within the range of any two of these values. The diameter of the second material is 0.1 μm to 1 μm. For example, the diameter of the second material can be 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, or any value within the range of any two of these values. The positive electrode material includes a first material with a larger particle size and a second material with a smaller particle size. When the particle diameters are distributed within the aforementioned ranges, the material has a larger active surface area, which facilitates rapid lithium-ion migration. This further improves the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0026] In some embodiments, the positive electrode mixture layer includes a first material and a second material, wherein the first material includes LiNi. x Co y Mn (1-x-y)O2, where 0.4 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.2. For example, in the first material, the value of x can be 0.4, 0.5, 0.6, or any value within a range of two of these values. For example, the first material can be LiNi. 0.5 Mn 0.5 O2, LiNi 0.4 Mn 0.6 O2 or LiNi 0.5 Co 0.2 Mn 0.3 O2. The second material includes LiMnO2. When the positive electrode mixture layer includes nickel-manganese materials and lithium manganese oxide materials, the dense manganese-oxygen framework of lithium manganese oxide materials can capture the oxygen released by nickel-manganese materials during high-temperature operation, reduce the gas generation reaction between oxygen and electrolyte, improve the high-temperature storage expansion phenomenon of secondary batteries, and reduce the high-temperature storage thickness expansion rate; at the same time, lithium manganese oxide materials themselves have good thermal stability, and when mixed with nickel-manganese materials as positive electrode active materials, it can improve the high-temperature storage thickness expansion rate of secondary batteries while also improving the high-temperature cycle capacity retention rate and the room temperature rate discharge retention rate.

[0027] In some embodiments, in the fully charged state, the positive electrode binder layer satisfies at least one of the following conditions: (1) the molar percentage of nickel is a% based on the molar amount of metal elements other than lithium, 14≤a≤34; (2) the molar percentage of manganese is b% based on the molar amount of metal elements other than lithium, 66≤b≤86; (3) 0.25≤a / b≤0.35. Preferably, 19≤a≤29. For example, the value of a can be 14, 19, 23, 29, 31, 34, or any value within the range of any two of these values. Preferably, 71≤b≤81. For example, the value of b can be 66, 71, 73, 77, 81, 86, or any value within the range of any two of these values. For example, the value of a / b can be 0.25, 0.27, 0.28, 0.30, 0.33, 0.35, or any value within the range of any two of these values. By limiting the content of nickel and manganese in the positive electrode additive layer to a specific range, it is possible to improve the high-temperature storage thickness expansion rate of the secondary battery while also improving the high-temperature cycle capacity retention rate and the room-temperature rate discharge retention rate.

[0028] The positive electrode mixture layer of this application also includes a positive electrode conductive material; there is no limitation on the type of positive electrode conductive material, and 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 materials such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0029] The positive electrode mixture layer of this application also includes a positive electrode binder; there are no particular restrictions on the type of positive electrode binder, and in the case of coating method, any material that can be dissolved or dispersed in the liquid medium used in 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.

[0030] The application does not limit the type of solvent used to form the positive electrode slurry, as long as it is a solvent 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 include any of aqueous solvents and organic solvents. Examples of aqueous media include, but are not limited to, mixtures of alcohol and water or water. Examples of organic media 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.

[0031] This application does not impose any particular limitation on the type of thickener, and examples may 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 may be used alone or in any combination.

[0032] The type of positive electrode current collector in this application is not particularly limited, and 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.

[0033] To reduce the electronic contact resistance between the positive current collector and the positive electrode binder layer, the surface of the positive current collector in this application may include a conductive additive or a conductive coating. Examples of conductive additives may 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.

[0034] negative electrode

[0035] The negative electrode includes a negative electrode current collector and a negative electrode additive layer disposed on at least one surface of the negative electrode current collector, the negative electrode additive layer containing a negative electrode active material. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0036] Negative electrode active materials may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), silicon, silicon-carbon composites, and SiO2. z (0.5 < z < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 At least one of Li-Al alloys or metallic lithium. Optionally, the negative electrode active material may further include amorphous carbon materials, which may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, or calcined coke, etc.

[0037] The negative electrode mixture layer of this application also includes a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When preparing the negative electrode mixture slurry using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0038] The negative electrode 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.

[0039] 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 binder layer, as long as they achieve 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 binder layer is 30 μm to 160 μm. In this application, the negative electrode binder 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.

[0040] 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.

[0041] The negative electrode sheet of this application may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode binder 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 and 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.

[0042] electrolyte

[0043] The electrolyte used in the secondary battery of this application includes an electrolyte and a solvent for dissolving the electrolyte. The electrolyte may also include lithium salts and non-aqueous solvents. This application does not particularly limit 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(oxalatoborate)borate (LiBOB), or lithium difluorooxalatoborate (LiDFOB). Based on the mass of the electrolyte, the mass percentage of lithium salt may be from 8% to 15%, for example, the mass percentage of 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 particularly limit the type of the aforementioned non-aqueous solvent, 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.

[0044] diaphragm

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] A second aspect of this application provides an electronic device including a secondary battery as described in this application. The electronic device includes, but is 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.

[0050] Example

[0051] 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.

[0052] Example 1-1

[0053] 1. Preparation of the positive electrode

[0054] <Preparation of Positive Electrode Active Material 1>

[0055] (1) A mixed solution containing NiSO4 and MnSO4 was prepared according to the element molar ratio Ni:Mn=50:50. The solution was then mixed with a precipitant (NaOH solution) and a complexing agent (ammonia water) and reacted. By controlling the reaction time, ammonia water concentration and pH value, a nickel-manganese precursor TM(OH)2 (TM=Ni / Mn) with an average particle size Dv50 of 11μm was obtained.

[0056] (2) Grind and mix the nickel-manganese precursor and sodium chloride from the above steps at a Na:(Ni+Mn) molar ratio of 1.1:1 until homogeneous. Calcinate at 800℃ in air for 20 h to obtain a reaction product with a Ni:Mn molar ratio of 50:50. Then, after crushing, sieving, and demagnetizing, obtain the product precursor NaNi. 0.5 Mn 0.5 O2;

[0057] (3) The product precursor was mixed with lithium nitrate at a Na:Li molar ratio of 1.15:1, heated to 400°C at a rate of 10°C / min and held for 6 hours, and then quenched to room temperature in air at a certain cooling rate of 50°C / min.

[0058] (4) Wash and soak the reaction product in deionized water and then dry it;

[0059] (5) The positive electrode active material 1, namely the first material LiNi, is obtained by crushing and sieving. 0.5 Mn 0.5 O2.

[0060] <Preparation of Positive Electrode Active Material II>

[0061] The second positive electrode active material is commercially available lithium manganese oxide (LiMnO2).

[0062] <Preparation of the positive electrode>

[0063] The positive electrode active material (including the first and second materials, with a mixing mass ratio as shown in Table 1), conductive carbon black, and polyvinylidene fluoride (PVDF) prepared in the above steps were mixed at a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 9 μm thick positive electrode current collector aluminum foil and dried to obtain a positive electrode sheet with a single-sided coating of positive electrode additive layer. The above steps were repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode additive layer. After cold pressing, slitting, welding of electrode tabs, and drying, a positive electrode sheet with a size of 74 mm × 867 mm was obtained.

[0064] 2. Preparation of electrolyte

[0065] In a dry argon atmosphere glove box, diethyl carbonate was used as the base solvent, and lithium hexafluorophosphate (LiPF6) was dissolved in the base solvent. Ethylene carbonate was added as an additive to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of vinylene carbonate was 2%.

[0066] 3. Preparation of the negative electrode

[0067] Using artificial graphite as the negative electrode active material, a mixture of the negative electrode active material, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNTs), and carboxymethyl cellulose (CMC) was prepared in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and the mixture was stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector, and then dried to obtain a negative electrode sheet with a single-sided coating of the negative electrode mixture layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode mixture layer. By adjusting the cold pressing pressure, negative electrode sheets with different compaction densities and surface roughness could be obtained. After cold pressing, slitting, welding of electrode tabs, and drying, a negative electrode sheet with a specification of 76.6 mm × 875 mm was obtained.

[0068] 4. Preparation of the diaphragm

[0069] A porous polyethylene film with a thickness of 15μm was used as the diaphragm.

[0070] 5. Preparation of lithium-ion batteries

[0071] The positive electrode, negative electrode, and separator are stacked sequentially, with the separator positioned between the positive and negative electrodes for isolation. The electrode assembly is then wound to form the electrode assembly. The electrode assembly is placed in a packaging bag, injected with electrolyte, and sealed. After processes including formation hot pressing (at 80℃ / 1~2.5Mpa for 0.5h~2h), degassing, edge trimming, and capacity testing, a lithium-ion battery is obtained.

[0072] 6. Testing Methods

[0073] (1) dQ / dV-V image testing method (peak position and peak area testing and calculation method)

[0074] The lithium-ion battery prepared in the above steps was charged and discharged at 0.2C, and the QV curve was integrated to obtain the dQ / dV-V image. The discharge capacity in the voltage range of ±0.13V at the peak position of the first peak was calculated, and the peak area of ​​the first peak S1 mAh was obtained. The discharge capacity in the voltage range of ±0.085V at the peak position of the second peak was calculated, and the peak area of ​​the second peak S2 mAh was obtained.

[0075] (2) XRD image testing method (diffraction peak intensity testing method)

[0076] The lithium-ion battery prepared in the above steps was discharged at a constant current of 0.5C to 2.8V to obtain a fully discharged battery. X-ray diffraction analysis was then performed on the positive electrode to obtain an XRD image. Instrument model: Bruker D8 ADVANCE; target material: Cu Kα; scanning angle: 5° to 80°.

[0077] (3) Structural observation methods

[0078] The lithium-ion battery prepared in the above steps was used. The positive electrode sheet was ion-polished and then cut open. The crystal structure of the material in the electrode sheet was then observed and the particle size was measured using a scanning electron microscope. Instrument model: ZEISS SEM, accelerating voltage: 0.1KV~30KV.

[0079] (4) Test methods for the mass content of nickel and manganese in metallic elements other than lithium

[0080] Take the lithium-ion battery prepared in the above steps, discharge it at a constant current of 0.5C to 2.8V to obtain a fully discharged battery. Disassemble the positive electrode and dissolve it in a mixed solvent (for example, use a mixed solvent of 5 ml aqua regia and 5 ml deionized water for 0.4 g of positive electrode). Make up the volume to 100 mL, and then use an ICP analyzer to test the mass percentage content of elements such as Ni, Co, Mn, Na and Mg in the solution. Mole percentage = mass percentage / relative molecular mass.

[0081] (5) High-temperature cycling performance test

[0082] First, in an environment of 45℃, the first charge and discharge were performed. Constant current charging was performed using a current of 0.5C until the voltage reached 4.35V, and then constant voltage charging was performed. Then, constant current discharging was performed using a current of 0.5C until the voltage reached 2.8V. The discharge capacity of the third cycle was recorded. Then, 500 charge and discharge cycles were performed, and the discharge capacity of the 500th cycle was recorded.

[0083] 45℃ cycle capacity retention % = (discharge capacity of the 500th cycle / discharge capacity of the 3rd cycle) × 100%.

[0084] (6) High-temperature storage performance test

[0085] First, the lithium-ion secondary battery is charged at 25°C to 4.35V. Then, the battery is clamped with two metal plates, and the thickness of the cell is measured with a micrometer. The initial thickness of the cell at this point is defined as H0. After that, the cell is stored in a constant temperature chamber at 85°C for 24 hours, and the thickness of the cell is measured in the same way. The thickness of the cell after storage is defined as H1.

[0086] Thickness expansion rate % at 85℃ = (H1 - H0) / H0 × 100%

[0087] (7) Room temperature rate discharge retention performance test

[0088] The battery was placed in a constant temperature chamber at 25°C for charging and discharging. Charging was done at 0.2C, and after charging to 4.35V, discharging was done at 0.1C, 0.2C, 0.5C, 1C, and 2C in sequence.

[0089] 25℃ rate capability = 2C discharge capacity / 0.2C discharge capacity

[0090] The lithium-ion batteries in the following embodiments or comparative examples differ from those in Examples 1-1 only in that the mixing ratio of the first and second materials is adjusted according to Table 1, and the molar amounts of nickel and manganese in the positive electrode binder layer are adjusted. The performance test results of the lithium-ion batteries in each embodiment and comparative example are shown in Table 1 below.

[0091] Table 1 *In the table above, "First Material: Second Material" represents the weight percentage of the first material and the second material in 100 parts of positive electrode active material; the calculation result of S1 / S2 is rounded to two decimal places; the calculation result of IB / IA is rounded to one decimal place; and the calculation result of a / b is rounded to two decimal places.

[0092] As shown in Table 1, compared with Comparative Example 1 which used only the first material, the lithium-ion batteries prepared in the embodiments of this application exhibit significantly improved high-temperature cycle capacity retention and significantly reduced high-temperature storage thickness expansion rate. Compared with Comparative Example 2 which used only the second material, the lithium-ion batteries in Examples 1 to 18 exhibit significantly improved discharge capacity.

[0093] Specifically, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent discharge specific capacity, high-temperature storage thickness expansion rate, high-temperature cycle capacity retention rate, and room-temperature rate discharge retention rate when 0.18 ≤ S1 / S2 ≤ 3.7. When 1.5 ≤ IB / IA ≤ 4, and especially 1.8 ≤ IB / IA ≤ 3.5, the lithium-ion batteries exhibit excellent discharge specific capacity, high-temperature storage thickness expansion rate, high-temperature cycle capacity retention rate, and room-temperature rate discharge retention rate. In particular, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent discharge specific capacity, high-temperature storage thickness expansion rate, high-temperature cycle capacity retention rate, and room-temperature rate discharge retention rate when the diameter of the first cathode material is between 8 μm and 12 μm and the diameter of the second cathode material is between 0.1 μm and 1 μm. In particular, the lithium-ion batteries prepared in the embodiments of this application exhibit excellent discharge specific capacity, high-temperature storage thickness expansion rate, high-temperature cycle capacity retention rate, and room-temperature rate discharge retention rate when satisfying 14≤a≤34 or 66≤b≤86, especially when satisfying 19≤a≤29 or 71≤b≤81 or 0.25≤a / b≤0.42.

[0094] 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 characterized by comprising: The positive electrode sheet includes a positive electrode current collector and a positive electrode mixture layer provided on at least one surface of the positive electrode current collector. The capacity-voltage differential dQ / dV-V image of the secondary battery in discharge includes a first peak and a second peak, the peak position of the first peak is 4.05V to 4.25V, and the peak position of the second peak is 3.88V to 4.08V.

2. The secondary battery according to claim 1, characterized by The peak position of the first peak is 4.1V to 4.2V; and / or, the peak position of the second peak is 3.93V to 4.03V.

3. The secondary battery according to claim 1 or 2, characterized by The peak area of the first peak is S1 mAh, and the peak area of the second peak is S2 mAh, 0.18≤S1 / S2≤3.

7.

4. The secondary battery according to claim 1 or 2, characterized by In a full discharge state, the XRD image of the positive electrode sheet includes at least a first diffraction peak and a second diffraction peak at 35.5° to 37°; the diffraction angle 2θ of the first diffraction peak is smaller than the diffraction angle 2θ of the second diffraction peak. The diffraction peak intensity of the first diffraction peak is IA, and the diffraction peak intensity of the second diffraction peak is IB, 1.5≤IB / IA≤4.

5. The secondary battery according to claim 4, characterized by 1.8≤IB / IA≤3.

5.

6. The secondary battery according to claim 1 or 2, characterized by The positive electrode mixture layer includes a first material and a second material, the first material has an R3-m type layered structure, and the second material has an Fd3m type spinel structure.

7. The secondary battery according to claim 1 or 2, characterized by The positive electrode mixture layer includes a first material and a second material, the first material is a near-spherical secondary particle composed of primary particles, the diameter of the first material is 8μm to 12μm, and the diameter of the second material is 0.1μm to 1μm.

8. The secondary battery according to claim 1 or 2, characterized by The positive electrode mixture layer includes a first material and a second material; The first material includes LiNi x Co y Mn (1-x-y) O2, wherein 0.4≤x≤0.6, 0≤y≤0.2; The second material includes LiMnO2.

9. The secondary battery according to claim 8, characterized by In a full discharge state, the positive electrode mixture layer satisfies at least one of the following conditions: (1) The molar percentage content of nickel element is a%, 14≤a≤34, based on the molar amount of metal elements other than lithium element; (2) The molar percentage content of manganese element is b%, 66≤b≤86, based on the molar amount of metal elements other than lithium element.

10. The secondary battery according to claim 9, characterized by The positive electrode mixture layer satisfies at least one of the following conditions: (1)19≤a≤29； (2)71≤b≤81； (3) 0.25≤a / b≤0.

42.

11. An electronic device, comprising: The secondary battery includes the secondary battery according to any one of claims 1 to 10.

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