Secondary battery and electric device

Abstract

The embodiment of the present application provides a secondary battery and an electric equipment, wherein the secondary battery provided by the embodiment of the present application controls the thickness Hc of a battery positive electrode diaphragm layer, the contact angle theta of electrolyte on the positive electrode current collector, the weighted value a of the dielectric constant of the organic solvent in the electrolyte and the total lithium ion concentration M in the electrolyte, and satisfies the following relationship: 0.450 <= (cos theta * a) / (M * Hc) <= 0.792, so that the prepared secondary battery has smaller self-discharge performance, better kinetic performance and cycle performance under the condition of meeting high energy density.

Description

Technical Field

[0001] This application relates to the field of battery manufacturing technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] Currently, lithium-ion batteries are widely used in portable electronic products and new energy vehicles due to their advantages such as high operating voltage, long cycle life, high energy density, low self-discharge, and no memory effect.

[0003] In the existing technology, in order to obtain high energy density, lithium-ion battery electrodes need to be set with a large coating weight or compaction density, but this also brings problems such as the electrode being difficult to wet with electrolyte, increased battery polarization, and deterioration of kinetic performance. On the other hand, in order to obtain better kinetic performance, the electrode is set with a smaller coating weight or compaction density, which leads to an increase in side reactions, resulting in increased self-discharge and rapid degradation of cycle performance.

[0004] Therefore, existing lithium-ion batteries cannot effectively balance high energy density and good kinetic performance. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a secondary battery and electrical device to solve the problem that existing lithium-ion batteries cannot effectively balance high energy density and good dynamic performance.

[0006] To solve the above problems, this application provides the following technical solution:

[0007] This application proposes a secondary battery, comprising a positive electrode and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the electrolyte comprises a lithium salt, an organic solvent, and an additive; the secondary battery satisfies the following formula (1):

[0008] 0.450≤(cosθ×a) / (M×Hc)≤0.792 Formula (1)

[0009] In the formula, θ is the contact angle of the electrolyte on the positive electrode current collector; a is the weighted value of the dielectric constant of the organic solvent in the electrolyte, which satisfies formula (2); M mol / L is the total lithium ion concentration in the electrolyte; Hcμm is the thickness of the positive electrode film layer on one surface of the positive electrode current collector;

[0010]

[0011] In the formula, n is the amount of organic solvent in the electrolyte; x i Let y be the ratio of the mass of the i-th organic solvent to the total mass of all organic solvents;i Let be the dielectric constant of the i-th organic solvent.

[0012] Furthermore, the secondary battery satisfies at least one of the following conditions: 1) 26.0° < θ < 48.0°; 2) 21.0°. <a<38.0;3)0.8≤M≤1.3;4)36.5≤Hc≤54.0。

[0013] Furthermore, in the secondary battery, the lithium salt includes lithium hexafluorophosphate, and at least one of lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorophosphate, lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium difluorodioxalate phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0014] Furthermore, in the secondary battery, the organic solvent includes acetonitrile, and at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, ethyl difluoroacetate, 2,2-difluoroethyl acetate, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0015] Furthermore, in the secondary battery, the organic solvent includes acetonitrile, and at least one of fluoroethylene carbonate and sulfolane.

[0016] Furthermore, in the secondary battery, the organic solvent includes fluoroethylene carbonate, acetonitrile, and sulfolane, wherein, based on the total mass of the organic solvent, fluoroethylene carbonate accounts for 2% to 15%, acetonitrile accounts for 2% to 20%, and sulfolane accounts for 2% to 10%.

[0017] Furthermore, in the secondary battery, the additive includes at least one of the following: vinylene carbonate, erythritol bis(carbonate), ethylene sulfate, pentaerythritol bicyclic sulfate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methanedisulfonate methylene ester, 1-propene-1,3-sulfonate lactone, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, and triargyl phosphate.

[0018] Furthermore, in the secondary battery, the additive includes vinylene carbonate, and at least one of erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol dicyclic sulfate.

[0019] Furthermore, in the secondary battery, the electrolyte additives include vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol dicyclic sulfate.

[0020] Further, in the secondary battery, based on the total mass of the electrolyte, vinylene carbonate accounts for 0.01% to 1.5%, erythritol bis(carbonate) accounts for 0.01% to 1%, 1,3-propane sultone accounts for 0.1% to 2%, and pentaerythritol bicyclic sulfate accounts for 0.1% to 2%.

[0021] Further, in the secondary battery, the positive electrode current collector includes a polymer substrate layer and metal layers provided on two surfaces of the polymer substrate layer, and the positive electrode film layer is provided on the metal layer.

[0022] Further, in the secondary battery, the positive electrode film layer contains a positive electrode active material; the positive electrode active material includes Li x Ni a1 Co b M c A d O2, where M includes one or both of Mn and Al, A includes at least one of W, B, Mg, Y, V, F, P, Zr, Bi, and Ti, 0.95 ≤ x ≤ 1.2, 0.8 < a1 ≤ 0.95, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d < 0.1 and a1 + b + c + d = 1.

[0023] The present application also provides an electrical device, characterized in that it includes the lithium-ion secondary battery described in any one of the foregoing, and the lithium-ion secondary battery serves as the power supply of the electrical device.

[0024] Compared with the prior art, the embodiments of the present application have the following advantages:

[0025] In the embodiments of the present application, the thickness Hc of the battery positive electrode film layer, the contact angle θ of the electrolyte on the positive electrode current collector, the weighted value a of the dielectric constant of the organic solvent in the electrolyte, and the total lithium ion concentration M in the electrolyte are controlled to satisfy the following relationship: 0.450 ≤ (cosθ × a) / (M × Hc) ≤ 0.792, so that the prepared secondary battery has smaller self-discharge performance, better kinetic performance, and cycling performance while meeting high energy density.

[0026] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a comparison diagram of the 45°C cycling performance of the lithium-ion secondary batteries prepared in Comparative Example 1, Example 1, and Example 2 of the present application.

[0028] Description of the reference numerals:

[0029] 1- Cycle-capacity curve of the lithium-ion battery prepared in Comparative Example 1; 2- Cycle-capacity curve of the lithium-ion battery prepared in Example 1; 3- Cycle-capacity curve of the lithium-ion battery prepared in Example 2. Detailed Implementation

[0030] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The applicant of this application has discovered that existing battery design technologies are unable to fabricate lithium-ion batteries that simultaneously achieve high energy density, low self-discharge, good kinetic performance, and good cycle performance.

[0032] To address the aforementioned problems, this application provides a secondary battery comprising a positive electrode and an electrolyte. The positive electrode comprises a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The electrolyte comprises a lithium salt, an organic solvent, and additives. The secondary battery satisfies the following formula (1):

[0033] 0.450≤(cosθ×a) / (M×Hc)≤0.792 Formula (1)

[0034] In the formula, θ is the contact angle of the electrolyte on the positive electrode current collector; a is the weighted value of the dielectric constant of the organic solvent in the electrolyte, which satisfies formula (2); M mol / L is the total lithium ion concentration in the electrolyte; Hcμm is the thickness of the positive electrode film layer on one surface of the positive electrode current collector.

[0035]

[0036] In the formula, n is the amount of organic solvent in the electrolyte; x i Let y be the ratio of the mass of the i-th organic solvent to the total mass of all organic solvents; i Let be the dielectric constant of the i-th organic solvent.

[0037] In this application, the amount of organic solvent in the electrolyte refers to the number of different types of organic solvent present in the electrolyte. The quantitative relationship between electrolyte parameters and positive electrode parameters is established through the above formulas (1) and (2), enabling the prepared secondary battery to achieve high energy density while exhibiting lower self-discharge, better kinetic performance, and better cycle performance. Optionally, the value of formula (1) can be any one or any two of the following: 0.45, 0.48, 0.56, 0.68, 0.72, 0.75, 0.78, and 0.792.

[0038] Optionally, the positive electrode current collector includes a polymer substrate layer and a metal layer disposed on two surfaces of the polymer substrate layer, with the positive electrode film layer disposed on the metal layer.

[0039] Optionally, the polymer substrate layer comprises an organic polymer material, including at least one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, or polycarbonate.

[0040] Optionally, the metal layer can be an aluminum layer.

[0041] Optionally, the polymer substrate layer has a thickness of 6–10 μm, and the aluminum layer has a thickness of 0.5–1.5 μm. Using composite aluminum foil improves the flexibility of the positive electrode current collector. The surface of the positive electrode current collector is stable and uniform, minimizing its impact on the liquid. The contact angle θ of the electrolyte on the aluminum foil is an important parameter for evaluating the wetting performance of the electrolyte. Good wetting performance of the electrolyte can effectively improve the ion transport rate, reduce battery impedance, and enhance the battery rate performance.

[0042] Optionally, in one embodiment, the contact angle θ of the electrolyte on the positive electrode current collector satisfies 26.0° < θ < 48.0°, which can effectively ensure the high kinetic performance and long-cycle stability of the electrolyte. The contact angle θ can be one of 27°, 30°, 35°, 40°, 45°, 47° or any combination thereof.

[0043] The contact angle of the electrolyte on the positive current collector can be determined as follows: 4 μL of electrolyte is dropped onto the surface of the positive current collector with a thickness of 8 μm, and the contact angle of the electrolyte on the surface of the positive current collector is measured using a contact angle meter. The value with a contact time of 10 s is taken as the test result of the contact angle.

[0044] Optionally, in one embodiment, the weighted value 'a' of the dielectric constant of the organic solvent in the electrolyte satisfies: 21.0 <a<38.0。

[0045] The weighted average of the dielectric constants of organic solvents in an electrolyte can comprehensively reflect the dielectric constant level of the electrolyte. By controlling the weighted average of the dielectric constants of organic solvents within the aforementioned range, both electrolyte viscosity and solvent stability can be effectively balanced, thereby ensuring low self-discharge, high kinetic performance, and long-cycle stability of the electrolyte.

[0046] Optionally, in some embodiments, the weighted value α of the dielectric constant of the organic solvent in the electrolyte can be a range of one or any two of 21.1, 22, 25, 27, 30, 32, 35, 37.9.

[0047] The weighted value of the dielectric constant can be determined in the following way:

[0048] The obtained electrolyte is first filtered through an organic needle filter with a pore size of 0.22 μm, and then directly tested on a gas chromatograph-mass spectrometer (GC-MS). Based on the peak position of the substance, the corresponding substance structure is matched in the mass spectrometer to determine the composition of the organic solvent.

[0049] Once the composition of the organic solvent is determined, the dielectric constant (γ) of the corresponding organic solvent can be found in publicly available literature or books. i The dielectric constant of the i-th organic solvent can be obtained from sources such as Lang's Handbook of Chemistry and Solvents and Solutes for Lithium-ion Batteries. Furthermore, the mass fraction of each organic solvent in the electrolyte can be determined using a standard curve method based on the intensity of the peaks.

[0050] First, calculate the ratio of the mass fraction of the i-th organic solvent to the sum of the mass fractions of all organic solvents; this ratio is the mass fraction percentage of the i-th organic solvent (x). i Then calculate the weighted value of the dielectric constant of the organic solvent in the electrolyte: a = x1×y1 + x2×y2 + x3×y3 + ... + x i ×y i .

[0051] Optionally, in one embodiment, the total lithium-ion concentration M in the electrolyte satisfies 0.8 ≤ M ≤ 1.3 mol / L. This ensures the formation of an interfacial film with sufficient inorganic components, resulting in more stable long-cycle performance of the battery. It also ensures sufficient charge transfer capacity in the electrolyte, guaranteeing its ion-conducting properties and effectively suppressing self-discharge. Furthermore, it prevents excessive electrolyte viscosity from deteriorating the battery's kinetic performance. Optionally, in some embodiments, the lithium-ion concentration M can be any combination of 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, and 1.3 mol / L.

[0052] Optionally, in one embodiment, the thickness Hc of the positive electrode film layer on one surface of the positive electrode current collector satisfies 36.5≤Hc≤54.0, in μm. The thickness of the positive electrode film layer within the above range is suitable for electrolyte wetting, thereby ensuring the dynamic performance of the battery and enabling the battery to have a high energy density.

[0053] In some embodiments, the thickness Hc of the positive electrode film layer is the thickness of the positive electrode film layer on either the upper or lower surface of the positive electrode current collector.

[0054] In some embodiments, the thickness Hc of the above-mentioned positive electrode film layer can be one or any two of the following: 36.5 μm, 37.5 μm, 40 μm, 42 μm, 46.5 μm, 48.5 μm, 50 μm, 52.5 μm, and 54 μm.

[0055] The thickness of the positive electrode film can be measured as follows: Take a small piece of the positive electrode sheet, use argon ion polishing technology to obtain a flat cross-section of the positive electrode sheet perpendicular to its surface, and then take an image of the cross-section using a scanning electron microscope (SEM) to measure the thickness of the positive electrode film. Alternatively, after the battery is fully discharged to 0% SOC and the cell is disassembled, the thickness of the positive electrode sheet at this point can also be considered as Hc.

[0056] Optionally, the energy density of the secondary battery in this application is 230 to 330 Wh / kg. Within the above energy density range, by systematically optimizing the thickness of the positive electrode film, the concentration of lithium ions in the electrolyte, the dielectric constant of the organic solvent, and the contact angle of the electrolyte, the lithium-ion secondary battery can have low self-discharge, high dynamic performance, and long cycle stability while meeting the requirements of high energy density.

[0057] Optionally, in one embodiment, the lithium salt includes lithium hexafluorophosphate (LiPF6), and at least one of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (LiOF), lithium trifluoromethanesulfonate (LiOTF), lithium difluorodioxalatophosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0058] Optionally, in one embodiment, the aforementioned organic solvent includes acetonitrile (AN) and at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), methyltrifluoroethyl carbonate, ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), ethyl difluoroacetate, 2,2-difluoroethyl acetate, sulfolane (TMS), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). Acetonitrile has a low viscosity, resulting in a faster lithium-ion transport rate in the electrolyte, thereby reducing battery internal resistance and improving kinetic performance.

[0059] Optionally, in some embodiments, the organic solvent includes acetonitrile, and at least one of fluoroethylene carbonate and sulfolane. That is, in the embodiments of this application, the organic solvent of the electrolyte is composed of acetonitrile, fluoroethylene carbonate, and / or sulfolane, resulting in a high oxidation potential of the electrolyte, making it less susceptible to oxidation and decomposition, thereby improving the electrolyte's oxidation resistance and the battery's cycle performance.

[0060] Optionally, in some embodiments, the organic solvents mentioned above include acetonitrile, fluoroethylene carbonate, and sulfolane, that is, the organic solvents in the electrolyte are composed of acetonitrile, fluoroethylene carbonate, and sulfolane.

[0061] Optionally, in some embodiments, based on the total mass of the organic solvent, 2% to 15% fluoroethylene carbonate, 2% to 20% acetonitrile, and 2% to 10% sulfolane can more significantly improve the oxidation resistance of the electrolyte and the cycle performance of the battery.

[0062] Optionally, in one embodiment, the additive includes at least one of vinylene carbonate (VC), erythritol bis(carbonate) (EBC), ethylene sulfate (DTD), pentaerythritol bicyclic sulfate, 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone (BS), methanedisulfonate methylene ester (MMDS), 1-propene-1,3-sulfonate lactone (PST), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate ester (TMSB), and tripropargyl phosphate (TPP).

[0063] Optionally, in some embodiments, the above-mentioned additives include vinylene carbonate, and at least one of erythritol bis(carbonate), 1,3-propanesulfonate lactone and pentaerythritol bicyclic sulfate, which not only utilizes the positive and negative electrodes to form films, but also the above-mentioned additive components are stable at high temperatures and are not easily decomposed to produce acidic substances, thereby improving the high-temperature stability of the electrolyte, battery cycle performance and high-temperature storage performance.

[0064] Optionally, in some embodiments, the additives specifically include vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol bicyclic sulfate.

[0065] Optionally, in some embodiments, based on the total mass of the electrolyte, vinylene carbonate accounts for 0.01% to 1.5%, erythritol bis(carbonate) accounts for 0.01% to 1%, 1,3-propanesulfonate lactone accounts for 0.1% to 2%, and pentaerythritol dicyclic sulfate accounts for 0.1% to 2%, which can more significantly improve the high-temperature stability, battery cycle performance, and high-temperature storage performance of the electrolyte.

[0066] Optionally, in one embodiment, the above-mentioned positive electrode film layer contains a positive electrode active material; the positive electrode active material includes Li x Ni a1 Co b M c A d O2, where M includes one or both of Mn and Al, A includes at least one of W, B, Mg, Y, V, F, P, Zr, Bi, and Ti, 0.95 ≤ x ≤ 1.2, 0.8 < a1 ≤ 0.95, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d < 0.1, and a1 + b + c + d = 1.

[0067] In this embodiment, the positive electrode active material can be obtained by doping and modifying lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide with at least one of W, B, Mg, V, F, P, Zr, Bi, and Ti. The above elements are beneficial to improving the stability and energy density of the positive electrode material. Moreover, the nickel content of the positive electrode active material used in this application is greater than 80% and less than or equal to 95%, which can further improve the energy density. Using this positive electrode active material to make the positive electrode film layer in the embodiments of this application can further improve the energy density, kinetic performance, and cycle performance of the secondary battery.

[0068] Optionally, in one embodiment, 0.9 ≤ a1 ≤ 0.95. When the content of Ni is within the above range, the energy density of the secondary battery can be further improved.

[0069] Optionally, in one embodiment, the positive electrode active material contains first particles and second particles, and the nickel contents in the first particles and the second particles are different.

[0070] Optionally, in one embodiment, the positive electrode active material contains first particles and second particles, and the particle sizes of the first particles and the second particles are different. Mixing particles of different sizes can optimize the distribution of the positive electrode active material particles in the positive electrode film, and can further improve the energy density, kinetic performance, and cycle performance of the secondary battery. Optionally, in one embodiment, the above-mentioned positive electrode sheet further includes a conductive agent, and the conductive agent can include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0071] In some embodiments, the preparation method of the positive electrode sheet is as follows: Disperse the components for preparing the positive electrode sheet, such as the positive electrode active material including the above-mentioned positive electrode material, the binder, and the conductive agent, in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; coat the positive electrode slurry on a positive electrode current collector such as aluminum foil; after processes such as drying, rolling, and die-cutting, the positive electrode sheet can be obtained.

[0072] The secondary battery provided in this application embodiment also includes a negative electrode sheet and a separator.

[0073] Optionally, in one embodiment, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector, wherein the negative active material layer includes a negative active material.

[0074] Optionally, in one specific embodiment, the above-mentioned negative electrode active material includes at least one of silicon-oxygen materials, silicon-carbon materials, metal silicides, or elemental silicon.

[0075] Optionally, in one specific embodiment, the above-mentioned negative electrode active material comprises silicon oxide material and graphite.

[0076] Optionally, in one embodiment, the silicon-oxygen material comprises SiO2. x (1 <x<2)。

[0077] In the secondary battery provided in this embodiment of the invention, the negative electrode sheet further includes a conductive agent and a binder; optionally, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes carboxymethyl cellulose-based binders and resin-based binders.

[0078] Optionally, in one embodiment, the carboxymethyl cellulose-based adhesive includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based adhesive includes one or more of styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.

[0079] In some embodiments, the negative electrode sheet is prepared as follows: the components used to prepare the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0080] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0081] In practical applications, the negative electrode sheet, positive electrode sheet, and separator are wound together to obtain a core, the core is packaged to obtain a dry cell, and the dry cell is baked and then injected with electrolyte, formed, resealed, and sorted to obtain the above-mentioned secondary battery.

[0082] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the electrical device.

[0083] The above-described electrical equipment embodiment includes the aforementioned secondary battery and achieves the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the secondary battery embodiment.

[0084] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0085] The present application will be described in detail below through embodiments.

[0086] Test methods: (The lower cutoff voltage mentioned below is 2.8V, and the upper cutoff voltage is 4.2V) (1) Electrolyte contact angle test:

[0087] 4 μL of electrolyte was dropped onto the surface of an 8 μm thick aluminum foil (the aluminum foil structure is: 1 μm aluminum layer + 6 μm polymer substrate layer + 1 μm aluminum layer). The contact angle of the electrolyte on the aluminum foil surface was measured using a contact angle meter, and the value of the contact angle test result was taken as the contact time of 10 s.

[0088] (2) Weighted value test of dielectric constant:

[0089] The obtained electrolyte is first filtered through an organic needle filter with a pore size of 0.22 μm, and then directly tested on a gas chromatograph-mass spectrometer (GC-MS). Based on the peak position of the substance, the corresponding substance structure is matched in the mass spectrometer to determine the composition of the organic solvent.

[0090] After determining the composition of the organic solvent, the dielectric constant (γ) of the corresponding organic solvent was found in Lang's Handbook of Chemistry. i : the dielectric constant of the i-th organic solvent); at the same time, the mass fraction of each organic solvent in the electrolyte can be determined by the intensity of the peak using the standard curve method;

[0091] First, calculate the ratio of the mass fraction of the i-th organic solvent to the sum of the mass fractions of all organic solvents; this ratio is the mass fraction percentage of the i-th organic solvent (x). i Then calculate the weighted value of the dielectric constant of the organic solvent in the electrolyte: a = x1×y1 + x2×y2 + x3×y3 + ... + x i ×y i .

[0092] (3) Positive electrode film thickness test

[0093] The battery is fully discharged to 0% SOC, and then the cell is disassembled. The positive electrode, separator, and negative electrode are taken out and placed separately. A small piece of the positive electrode is taken, and an argon ion polishing technique is used to obtain a flat cross-section of the positive electrode that is perpendicular to the surface of the positive electrode. The cross-section of the positive electrode is then photographed with a scanning electron microscope (SEM) to measure the thickness of the positive electrode film layer.

[0094] (4) Energy density test

[0095] a. At 25±2℃, discharge the secondary battery at a constant current of 1C to the lower limit cutoff voltage, and then let it stand for 30 minutes.

[0096] b. Charge at a constant current and constant voltage of 1C to the upper limit cutoff voltage. The cutoff condition for constant voltage charging is that the current drops to less than or equal to 0.05C, and then let it stand for 30 minutes.

[0097] c. Repeat step a and measure the discharge energy E (unit: Wh).

[0098] d. Repeat steps b to c twice, and take the average value Ea of the three discharge energies.

[0099] e. If the mass M (in kg) of a single battery is weighed using a balance, then the energy density of the secondary battery is the ratio of the average energy of the three discharges, Ea, to the mass of the single battery (in Wh / kg).

[0100] (5) Fast charging cycle performance test

[0101] a. Let the secondary battery stand for 5 minutes at 45±2℃.

[0102] b. Charge at a constant current rate of 1.2C until the upper limit cutoff voltage is reached, then charge at a constant voltage until the current is less than or equal to 0.05C.

[0103] c. Let stand for 5 minutes, then discharge at a constant current rate of 1C until the lower cutoff voltage is reached, and record the discharge capacity C1.

[0104] d. Repeat steps a to c until the discharge capacity is less than or equal to 80% of the initial discharge capacity. Record the number of cycles to characterize the battery's cycle performance, with the unit being cycles.

[0105] (6) Room temperature DCR test

[0106] At 25±2℃, the secondary battery was charged to the upper limit cutoff voltage at 1C constant current and constant voltage, then discharged at 1C constant current for 30 minutes. After adjusting to 50% SOC, it was left to stand for 30 minutes. Then, it was pulsed discharged at 5C constant current for 10 seconds. The voltage values ​​before and after the pulse were recorded. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current * 100%.

[0107] (7) Self-discharge test (storage performance test)

[0108] a. At 25±2℃, charge the secondary battery with 1C constant current and constant voltage to the upper limit cutoff voltage. The constant voltage charging cutoff condition is that the current drops to less than or equal to 0.05C. Then let it stand for 10 minutes, and then discharge it with 1C constant current to the lower limit cutoff voltage. Record the initial discharge capacity C0.

[0109] b. At 25±2℃, let stand for 10 minutes, then charge at a constant current and constant voltage rate of 1C to the upper limit cutoff voltage. The cutoff condition for constant voltage charging is that the current drops to less than or equal to 0.05C.

[0110] c. Store the fully charged lithium-ion secondary batteries in an environment of 60±2℃ for 15 days.

[0111] d. After 15 days, remove the battery and allow it to cool naturally to 25±2℃. Then, let it stand for 10 minutes and discharge it at a constant current of 1C to the lower limit cutoff voltage. Record the discharge capacity Cs and calculate the residual capacity retention rate (%), which is equal to the ratio of Cs to C0. This is used to characterize the self-discharge of the secondary battery.

[0112] Example 1

[0113] (1) Preparation of the positive electrode sheet:

[0114] LiNi, the positive electrode active material 0.92 Co 0.07 Mn 0.01 O2, conductive agent SP, and binder polyvinylidene fluoride (PVDF) are uniformly dispersed in solvent N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 to obtain positive electrode slurry;

[0115] The positive electrode slurry is uniformly coated on the upper and lower surfaces of an 8μm aluminum foil (the aluminum foil structure is: 1μm aluminum layer + 6μm polymer substrate layer + 1μm aluminum layer) to form a positive electrode film layer with a thickness of 40.8μm, thus obtaining the positive electrode sheet.

[0116] (2) Preparation of negative electrode sheet:

[0117] The negative electrode active material graphite, conductive agent SP, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene latex (SBR) were dispersed in deionized water at a mass ratio of 96.5:1:1:1.5 and mixed evenly to obtain the negative electrode slurry.

[0118] The negative electrode slurry is evenly coated on the upper and lower surfaces of the negative electrode current collector copper foil, and then dried, cold-pressed, slit, and cut into sheets to obtain the negative electrode sheet.

[0119] (3) Preparation of electrolyte:

[0120] EC, EMC, and DEC are mixed evenly in a mass ratio of 30:50:20 to obtain a mixed solvent. Then, the temperature is controlled at ≤20℃, and the fully dried lithium salts LiPF6 and LiBF4 are dissolved in the mixed organic solvent. The mixture is stirred evenly and fully dissolved. The temperature is then controlled at ≤20℃, and the additives vinylene carbonate and ethylene sulfate are added. The final electrolyte has a lithium ion concentration M of 0.8 mol / L and contains 2% ethylene sulfate and 0.5% vinylene carbonate by mass.

[0121] (4) Preparation of lithium-ion batteries:

[0122] The positive electrode, separator, and negative electrode are stacked in sequence, so that each positive electrode layer and negative electrode layer are covered with a separator. Then they are stacked into a cell, hot-pressed, and the tabs are welded and placed in an outer packaging shell. After baking and drying, the electrolyte is injected. Then, after standing, formation, aging, and capacity testing, a lithium-ion battery is made.

[0123] Example 2

[0124] The difference between Example 2 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiPF6 added is adjusted, and the total lithium ion concentration M in the final electrolyte is 1.0 mol / L.

[0125] Example 3

[0126] The difference between Example 3 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiPF6 added is adjusted, and the total lithium ion concentration M in the final electrolyte is 1.3 mol / L.

[0127] Example 4

[0128] The difference between Example 4 and Example 2 is that in the electrolyte preparation step (3), EC and EMC are mixed evenly at a mass ratio of 35:65 to obtain a mixed solvent, and the lithium salt is adjusted to consist of 11.5 parts LiPF6 and 1.5 parts LiFSI by mass, so that the total lithium ion concentration M in the final electrolyte is 1.0 mol / L.

[0129] Example 5

[0130] The difference between Example 5 and Example 4 is that in the electrolyte preparation step (3), EC and EMC are mixed evenly at a mass ratio of 40:60 to obtain a mixed solvent.

[0131] Example 6

[0132] The difference between Example 6 and Example 2 is that in the electrolyte preparation step (1), the thickness Hc of the positive electrode film is adjusted to 54.0 μm.

[0133] Example 7

[0134] The difference between Example 7 and Example 1 is that in the electrolyte preparation step (3), EC, EMC and EDC are mixed evenly in a mass ratio of 30:30:40 to obtain a mixed solvent, and the lithium salt is adjusted to consist of 12.7 parts LiPF6 and 0.9 parts LiPO2F2 by mass, and the total lithium ion concentration M in the final electrolyte is 1.1 mol / L.

[0135] Example 8

[0136] The difference between Example 8 and Example 7 is that in the electrolyte preparation step (3), EC and EMC are mixed evenly at a mass ratio of 30:70 to obtain a mixed solvent.

[0137] Example 9

[0138] The difference between Example 9 and Example 7 is that, in the electrolyte preparation step (3), ethylene carbonate, methyl ethyl carbonate, acetonitrile, fluoroethylene carbonate and sulfolane are mixed evenly in a mass ratio of 10:45:20:15:10 to obtain a mixed solvent, and in the negative electrode preparation step (2), the negative electrode active material is adjusted to be a composite material of silicon oxide (SiO) and graphite, wherein the mass ratio of silicon oxide (SiO) to graphite is 5:95.

[0139] Example 10

[0140] The difference between Example 10 and Example 9 is that in the electrolyte preparation step (3), ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, fluoroethylene carbonate and sulfolane are mixed evenly in a mass ratio of 20:35:20:15:10 to obtain a mixed solvent.

[0141] Example 11

[0142] The difference between Example 11 and Example 10 is that in the electrolyte preparation step (3), the additives are adjusted to vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone and pentaerythritol bicyclic sulfate. The final electrolyte contains 0.2% erythritol bis(carbonate), 0.5% 1,3-propanesulfonate lactone, 1.0% pentaerythritol bicyclic sulfate and 0.5% vinylene carbonate by mass.

[0143] Example 12

[0144] The difference between Example 12 and Example 10 is that in the electrolyte preparation step (3), the additives are adjusted to vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol dicyclic sulfate. The final electrolyte contains 0.01% erythritol bis(carbonate), 0.1% 1,3-propanesulfonate lactone, 0.1% pentaerythritol dicyclic sulfate, and 0.01% vinylene carbonate by mass. In the positive electrode preparation step (1), the positive electrode active material is adjusted to LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0145] Example 13

[0146] The difference between Example 13 and Example 10 is that in the electrolyte preparation step (3), the additives are adjusted to vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol dicyclic sulfate. The final electrolyte contains 1.0% erythritol bis(carbonate), 2.0% 1,3-propanesulfonate lactone, 2.0% pentaerythritol dicyclic sulfate, and 1.5% vinylene carbonate by mass. In the positive electrode preparation step (1), the positive electrode active material is adjusted to LiNi. 0.85 Co 0.1 Mn 0.05 O2.

[0147] Example 14

[0148] The difference between Example 14 and Example 11 is that in step (1) of preparing the positive electrode sheet, the positive electrode active material is adjusted to LiNi. 0.9 Co 0.08 Mn 0.01 Zr 0.01 O2.

[0149] Example 15

[0150] The difference between Example 15 and Example 11 is that in step (1) of preparing the positive electrode sheet, the positive electrode active material is adjusted to LiNi. 0.9 Co 0.08 Mn 0.01 Ti 0.01 O2.

[0151] Example 16

[0152] The difference between Example 16 and Example 11 is that in step (1) of preparing the positive electrode sheet, the positive electrode active material is adjusted to LiNi. 0.95 Co 0.02 Al0.02 Ti 0.01 O2.

[0153] Example 17

[0154] The difference between Example 17 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiBF4 added is adjusted, and the total lithium ion concentration M in the final electrolyte is 0.79 mol / L, and the thickness Hc of the positive electrode film is adjusted to 40.3 μm.

[0155] Comparative Example 1

[0156] The difference between Comparative Example 1 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiPF6 added was adjusted, and the total lithium ion concentration M in the final electrolyte was 0.7 mol / L.

[0157] Comparative Example 2

[0158] The difference between Comparative Example 2 and Example 4 is that in the electrolyte preparation step (3), EC and EMC are mixed evenly at a mass ratio of 20:80 to obtain a mixed solvent.

[0159] Comparative Example 3

[0160] The difference between Comparative Example 3 and Example 9 is that in the electrolyte preparation step (3), EC, EMC, EDC and FEC are mixed evenly in a mass ratio of 10:60:20:10 to obtain a mixed solvent.

[0161] The contact angle of the electrolyte and the weighted value α of the dielectric constant of the organic solvent in each embodiment were measured to obtain the composition and parameters of the battery structure in each embodiment, as shown in Table 1.

[0162] Table 1

[0163]

[0164]

[0165]

[0166] According to Table 1, the Y value corresponding to the battery in each embodiment is calculated according to formula (1): Y=(cosθ×a) / (M×Hc). The batteries prepared in each embodiment are subjected to energy density test, 45℃ fast charge cycle performance test, room temperature DCR test and self-discharge test. The test results are shown in Table 2.

[0167] Table 2

[0168]

[0169] As can be seen from Table 2, the batteries prepared in Examples 1 to 17 of this application can all meet the requirements of normal temperature DCR ≤ 14.5 mOhm, cycle number at 45°C ≥ 1000 cls, and residual capacity retention rate ≥ 82.0% after storage at 60°C for 15 days.

[0170] Specifically, by comparing Examples 1 to 3 and Comparative Example 1 in Table 2, it can be seen that by adjusting the mass fraction of lithium salt LiPF6 in the electrolyte to change the total lithium ion concentration M in the electrolyte, the electrolyte composition changes, and the contact angle θ of the electrolyte also changes accordingly. As Figure 1 shown in the comparison diagram of the 45°C cycle performance of the lithium-ion secondary batteries prepared in Examples 1 to 3 and Comparative Example 1, the lithium-ion secondary battery prepared in Example 3 has the most cycle number at 45°C, and the lithium-ion secondary battery prepared in Comparative Example 1 has the least cycle number at 45°C. In Comparative Example 1, the total lithium ion concentration M in the electrolyte < 0.8 mol / L, and (cosθ × a) / (M × Hc) > 0.792. The normal temperature DCR of the prepared lithium-ion secondary battery is significantly greater than that of Examples 1 to 3, and the 45°C cycle performance deteriorates significantly.

[0171] Therefore, the total lithium ion concentration M in the electrolyte should be controlled within a suitable range. By adjusting the lithium ion concentration in the electrolyte within the range of 0.8 ≤ M ≤ 1.3 in this application and satisfying formula (1), the prepared lithium-ion secondary battery can have small self-discharge, high kinetic performance, and stable long-cycle performance simultaneously.

[0172] By comparing Examples 2, Examples 4 to 5 and Comparative Example 2 in Table 2, it can be seen that by adjusting the composition and content ratio of the organic solvent, the weighted value a of the dielectric constant of the organic solvent is changed; the contact angle θ of the electrolyte also changes accordingly. Specifically, the weighted value a of the dielectric constant of the organic solvent in Comparative Example 2 < 21.0, and (cosθ × a) / (M × Hc) < 0.450. Although the prepared lithium-ion secondary battery has a lower normal temperature DCR, the cycle number at 45°C and the residual capacity retention rate after storage at 60°C for 15 days are significantly lower than those of Examples 2, Example 4, and Example 5.

[0173] Therefore, the weighted value a of the dielectric constant of the organic solvent in the electrolyte should be controlled within a suitable range. By adjusting the weighted value of the dielectric constant of the organic solvent in the electrolyte within the range of 21.0 < a < 38.0 in this application and satisfying formula (1), the prepared lithium-ion secondary battery has more excellent comprehensive performance.

[0174] According to Table 2, comparing Examples 2 and 6, the thickness Hc of the positive electrode film layer on one surface of the positive electrode current collector in the prepared lithium-ion secondary battery was adjusted. Specifically, the positive electrode film layer thickness Hc of the lithium-ion secondary battery prepared in Example 6 was 54.0 μm, (cosθ×a) / (M×Hc) = 0.462, and the battery energy density was increased from 276 Wh / kg to 282 Wh / kg. At the same time, the battery's cycle performance at 45°C and the residual capacity retention rate after 15 days of storage at 60°C remained at a high level.

[0175] Therefore, the thickness Hc of the positive electrode film of the prepared lithium-ion secondary battery is within the range of 36.5≤Hc≤54.0 in this application and satisfies formula (1), which enables the prepared lithium-ion secondary battery to obtain high energy density and excellent comprehensive performance.

[0176] According to Table 2, comparing Examples 7-8 and Comparative Example 3, the contact angle of the electrolyte can be changed by adjusting the composition of the organic solvent, and the weighted value α of the dielectric constant of the organic solvent in the electrolyte will also change accordingly. Specifically, the contact angle θ of the electrolyte in Comparative Example 3 is <26.0°, (cosθ×a) / (M×Hc)<0.450, the stability of the electrolyte deteriorates, and the cycling performance of the prepared lithium-ion secondary battery at 45°C and the residual capacity retention rate after storage at 60°C for 15 days are significantly worse.

[0177] Therefore, the contact angle θ of the electrolyte should be controlled within a suitable range. Adjusting the contact angle θ of the electrolyte within the range of 26.0° < θ < 48.0° in this application, and satisfying formula (1), results in a lithium-ion secondary battery with superior overall performance.

[0178] According to Table 2, comparing Example 9 and Example 8, Example 9 used a mixed solvent of acetonitrile, fluoroethylene carbonate, and sulfolane, which had the lowest DCR at room temperature, indicating that it had excellent kinetic performance. At the same time, the battery energy density was increased from 275Wh / kg to 302Wh / kg, and it still achieved stable cycle performance and storage performance, indicating that the solvent combination of Example 9 had good electrochemical stability.

[0179] According to Table 2 comparing Example 10 and Example 7, the battery energy density of Example 10 is increased from 274Wh / kg to 305Wh / kg. Because a mixed solvent of fluoroethylene carbonate and sulfolane is used, it has excellent storage performance and cycle performance, but the DCR at room temperature is relatively large.

[0180] According to Table 2 comparing Example 9 and Example 10, the addition of acetonitrile in Example 9 can improve the problem of high DCR at room temperature in Example 10, while also ensuring good storage performance and cycling performance.

[0181] According to Table 2 comparing Examples 11-13 and Example 10, the additives used in Example 11, namely vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol dicyclic sulfate, improved the battery's room temperature DCR, cycle performance, and storage performance. Meanwhile, Examples 11-13 show that adding 0.01%-1.5% vinylene carbonate, 0.01%-1% erythritol bis(carbonate), 0.1%-2% 1,3-propanesulfonate lactone, and 0.1%-2% pentaerythritol dicyclic sulfate to the electrolyte resulted in good room temperature DCR, cycle performance, and storage performance.

[0182] As shown in Table 2, comparing Examples 14-16 with Example 11, the use of Zr or Ti in the positive electrode active material of Examples 14-16 enhances the ion diffusion capability of the active material, resulting in a lower DCR at room temperature. Simultaneously, it improves the stability of the positive electrode active material structure, thereby enhancing cycle performance and storage performance.

[0183] In summary, in this embodiment, by adjusting the electrolyte contact angle θ, the total lithium-ion concentration M in the electrolyte, the weighted value a of the dielectric constant of the organic solvent in the electrolyte, and the thickness Hc of the positive electrode film layer on one surface of the positive electrode current collector to satisfy a specific relationship, the lithium-ion secondary battery can achieve high energy density while exhibiting low self-discharge, better kinetic performance, and long cycle performance. This solves the problem that existing lithium-ion batteries cannot effectively balance high energy density and good kinetic performance.

[0184] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0185] The above provides a detailed description of a secondary battery and electrical device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A secondary battery, comprising a positive electrode and an electrolyte, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the electrolyte includes lithium salt, organic solvent and additives; the secondary battery satisfies formula (1): 0.450≤(cosθ×a) / (M×Hc)≤0.792 Formula (1) In the formula, θ is the contact angle of the electrolyte on the positive electrode current collector; a is the weighted value of the dielectric constant of the organic solvent in the electrolyte, which satisfies formula (2); M mol / L is the total lithium ion concentration in the electrolyte; Hcμm is the thickness of the positive electrode film layer on one surface of the positive electrode current collector; In the formula, n is the amount of organic solvent in the electrolyte; x i Let y be the ratio of the mass of the i-th organic solvent to the total mass of all organic solvents; i Let be the dielectric constant of the i-th organic solvent; The secondary battery meets the following conditions: 1) 26.0° < θ < 48.0°; 2)21.0<a<38.0； 3)0.8≤M≤1.3； 4) 36.5≤Hc≤54.

0.

2. The secondary battery according to claim 1, characterized in that, The lithium salt includes lithium hexafluorophosphate, and at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium difluorodioxalatophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

3. The secondary battery according to claim 1, characterized in that, The organic solvent includes acetonitrile, and at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, ethyl difluoroacetate, 2,2-difluoroethyl acetate, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

4. The secondary battery according to claim 3, characterized in that, The organic solvent includes acetonitrile, and at least one of fluoroethylene carbonate and sulfolane.

5. The secondary battery according to claim 4, characterized in that, The organic solvent includes fluoroethylene carbonate, acetonitrile, and sulfolane, wherein, based on the total mass of the organic solvent, fluoroethylene carbonate accounts for 2% to 15%, acetonitrile accounts for 2% to 20%, and sulfolane accounts for 2% to 10%.

6. The secondary battery according to claim 1, characterized in that, The additives include at least one of the following: vinylene carbonate, erythritol bis(carbonate), ethylene sulfate, pentaerythritol bicyclic sulfate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methanedisulfonate methylene ester, 1-propene-1,3-sulfonate lactone, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, and triargyl phosphate.

7. The secondary battery according to claim 6, characterized in that, The additives include vinylene carbonate, and at least one of erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol bicyclic sulfate.

8. The secondary battery according to claim 6, characterized in that, The additives include vinylene carbonate, erythritol bis(carbonate), 1,3-propanesulfonate lactone, and pentaerythritol bicyclic sulfate.

9. The secondary battery according to claim 7, characterized in that, Based on the total mass of the electrolyte, vinylene carbonate accounts for 0.01% to 1.5%, erythritol bis(carbonate) accounts for 0.01% to 1%, 1,3-propanesulfonate lactone accounts for 0.1% to 2%, and pentaerythritol bicyclic sulfate accounts for 0.1% to 2%.

10. The secondary battery according to claim 1, characterized in that, The positive electrode current collector includes a polymer substrate layer and a metal layer disposed on two surfaces of the polymer substrate layer, and the positive electrode film layer is disposed on the metal layer.

11. The secondary battery according to claim 1, characterized in that, The positive electrode film layer contains a positive electrode active material; the positive electrode active material includes Li x Ni a1 Co b M c A d O2, where M includes one or both of Mn and Al, A includes at least one of W, B, Mg, Y, V, F, P, Zr, Bi, and Ti, 0.95 ≤ x ≤ 1.2, 0.8 < a1 ≤ 0.95, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d < 0.1, and a1 + b + c + d = 1.

12. An electrical appliance, characterized in that, Includes a secondary battery as described in any one of claims 1 to 11, wherein the secondary battery serves as the power supply for the electrical equipment.

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