A secondary battery and an electric device

Abstract

The application discloses a secondary battery and a power utilization device, and belongs to the technical field of batteries. The secondary battery provided by the application introduces a lithium supplement into a positive active material layer, and adds a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound into an electrolyte. Meanwhile, the non-faradic capacitance of the positive electrode sheet, the mass percentage of the lithium supplement in the positive active material layer, the mass percentage of the silane compound containing the carbon-carbon double bond in the electrolyte and the mass percentage of the cyclic lithium borate compound in the electrolyte are reasonably controlled, so that the secondary battery satisfies a specific relationship: (Cdl-0.1) 2 × (A+B+1) × 100 / N 2 ≥ 10, thereby simultaneously achieving excellent cycle performance, rate performance and safety performance of the secondary battery.

Description

Technical Field

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

[0002] Lithium-ion batteries have high energy density and low self-discharge rate, but the cycle life of lithium-ion batteries needs to be improved. Taking lithium iron phosphate batteries as an example, the cycle life of a single cell is generally less than 8,000 cycles, which is difficult to meet the requirements of some high-demand application scenarios for a service life of 20 to 30 years (more than 12,000 cycles).

[0003] All existing methods for improving the cycle life of lithium-ion batteries inevitably suffer from problems such as increased risk of gas generation, intensified lithium plating leading to reduced safety, or increased internal resistance resulting in decreased rate performance. Summary of the Invention

[0004] The purpose of this application is to solve the problem that existing technologies cannot simultaneously achieve excellent cycle performance, rate performance and safety performance of secondary batteries, and to provide a secondary battery and electrical device with excellent rate performance, cycle performance and good safety.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer comprises a positive active material and a lithium replenishing agent. The electrolyte comprises a silane compound containing carbon-carbon double bonds and a cyclic lithium borate compound.

[0006] The secondary battery satisfies: Y≥10;

[0007] Where Y = (Cdl - 0.1) 2 ×(A+B+1)×100 / N 2 ;

[0008] Cdl nF is the non-Radal capacitance of the positive electrode;

[0009] N% is the mass percentage of lithium supplementer in the positive electrode active material layer;

[0010] A% represents the mass percentage of silane compounds containing carbon-carbon double bonds in the electrolyte;

[0011] B% represents the mass percentage of cyclic lithium borate compounds in the electrolyte.

[0012] As an embodiment of this application, the non-Radal capacitance Cdl nF of the positive electrode is 0.6nF to 1.4nF.

[0013] As an embodiment of this application, the mass percentage N% of the lithium replenishing agent in the positive electrode active material layer is 1% to 5%.

[0014] As an embodiment of this application, the mass percentage A% of the silane compound containing carbon-carbon double bonds in the electrolyte is 0.05% to 3%.

[0015] As an embodiment of this application, the mass percentage (B%) of the cyclic lithium borate compound in the electrolyte is 0.05% to 3%.

[0016] As an implementation scheme of this application, 0.1≤M≤5, where M=A+B.

[0017] As an embodiment of this application, the silane compound containing carbon-carbon double bonds includes at least one of tetravinylsilane, tetrapropenylsilane, trivinylethylsilane, and tripropenylmethylsilane.

[0018] As an embodiment of this application, the cyclic lithium borate compound includes at least one of lithium difluorooxalate borate, lithium difluoroborate fluoromalonic acid, and lithium difluoroborate oxalate.

[0019] As an embodiment of this application, the electrolyte further includes fluoroethylene carbonate and vinylene carbonate.

[0020] As an embodiment of this application, the electrolyte contains 0.5% to 1.5% by mass of fluoroethylene carbonate.

[0021] As an embodiment of this application, the electrolyte contains 0.5% to 1.5% by mass of vinylene carbonate.

[0022] As an embodiment of this application, the lithium supplement includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2.

[0023] As an embodiment of this application, the lithium replenishing agent has a Dv99 ≤ 25 μm.

[0024] As an embodiment of this application, at least a portion of the surface of the positive electrode active material is provided with a carbon layer, the thickness C of which is 5 nm to 200 nm.

[0025] In a second aspect of this application, an electrical device is provided, including the aforementioned secondary battery.

[0026] Compared with the prior art, the beneficial effects of this application are:

[0027] The secondary battery provided in this application introduces a lithium replenishing agent into the positive electrode active material layer and adds silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds to the electrolyte. Simultaneously, by rationally controlling the non-Radicacious capacitance of the positive electrode, the mass percentage of the lithium replenishing agent in the positive electrode active material layer, the mass percentage of the silane compounds containing carbon-carbon double bonds in the electrolyte, and the mass percentage of the cyclic lithium borate compounds in the electrolyte, the secondary battery satisfies a specific relationship: (Cdl-0.1). 2 ×(A+B+1)×100 / N 2 ≥10, thus enabling the secondary battery to simultaneously achieve excellent cycle performance, rate performance and safety performance. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of this application, the following will provide further explanation of this application in conjunction with specific embodiments.

[0029] Unless otherwise specified, the reagents, methods and equipment used in this application are all conventional reagents, methods and equipment in the field.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0032] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0033] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0034] In one embodiment of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material and a lithium replenishing agent. The electrolyte includes silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds.

[0035] The secondary battery satisfies: Y≥10;

[0036] Where Y = (Cdl - 0.1) 2 ×(A+B+1)×100 / N 2 ;

[0037] Cdl nF is the non-Radal capacitance of the positive electrode;

[0038] N% is the mass percentage of lithium supplementer in the positive electrode active material layer;

[0039] A% represents the mass percentage of silane compounds containing carbon-carbon double bonds in the electrolyte;

[0040] B% represents the mass percentage of cyclic lithium borate compounds in the electrolyte.

[0041] The secondary battery provided in this application introduces a lithium replenishing agent into the positive electrode active material layer and adds silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds to the electrolyte. Simultaneously, by rationally controlling the non-Radicacious capacitance of the positive electrode, the mass percentage of the lithium replenishing agent in the positive electrode active material layer, the mass percentage of the silane compounds containing carbon-carbon double bonds in the electrolyte, and the mass percentage of the cyclic lithium borate compounds in the electrolyte, the secondary battery satisfies a specific relationship: (Cdl-0.1). 2 ×(A+B+1)×100 / N 2 ≥10, thus enabling the secondary battery to simultaneously achieve excellent cycle performance, rate performance and safety performance.

[0042] Specifically, the secondary battery provided in this application introduces a lithium replenishing agent into the positive electrode active material layer, and adds silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds to the electrolyte, thereby enabling the secondary battery to satisfy a specific relationship: (Cdl-0.1). 2 ×(A+B+1)×100 / N 2A concentration of ≥10 can achieve significant effects. Firstly, the introduction of lithium replenishing agents can compensate for the loss of active lithium without compromising the stability of the SEI layer (solid electrolyte interface), thereby improving the energy density and cycle life of the secondary battery and ensuring its safety performance. Secondly, the addition of silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds as additives to the electrolyte can promote the formation of the SEI film, effectively improving its flexibility and stability, thus enhancing the cycle stability and safety performance of the secondary battery. Thirdly, the combined effect of the above factors can reduce gas generation and lithium plating during the cycling process of the secondary battery, improve its rate performance and fast charge / discharge performance, thereby significantly increasing the lithium plating window during cycling, reducing the occurrence of lithium plating, and further improving the cycle performance and rate performance of the secondary battery.

[0043] For example, the secondary battery satisfies: Y≥10, where Y can be any point value or any two-point range value of Y≥10, such as one or any two range values ​​of 10, 12, 14, 16, 18, 20, 25, 30, 40, 50, 80, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000.

[0044] In one embodiment, the secondary battery satisfies: 28 ≤ Y ≤ 64. For example, Y can be a value within the range of one or any two of the following: 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, and 64. This application research has found that when the secondary battery is further selected to satisfy the above range, the overall performance of the resulting secondary battery is superior.

[0045] In one embodiment, the non-Radal capacitance Cdl nF of the positive electrode is 0.6nF to 1.4nF.

[0046] It should be noted that the test method for the non-Radal capacitance Cdl of the positive electrode includes the following steps:

[0047] S1: Clean the surface of the positive electrode sheet with electrolyte to remove surface impurities, dry it, cut it into round pieces, weigh it and transfer it to a vacuum oven, dry it at 90-105℃ for 6 hours, and then assemble the symmetrical battery in a glove box.

[0048] S2: The assembled battery was tested using cyclic voltammetry (CV) to obtain the non-Radida potential range of the corresponding battery. The test voltage range was 0.05–3.0V, and the scan rate was 0.1–1mV / s.

[0049] S3: Select the flat potential range from the second step for cyclic voltammetry (CV) testing and collect voltage-current curves. The potential range is 2.5 to 2.7 V, and the scan rate is 1 to 20 mV / s.

[0050] S4: Obtain the median value U of the potential range for five specific scan rates V1 (the specific scan rate can be 0.1mV / s, 1mV / s, 5mV / s, 10mV / s, and 20mV / s, etc.) in the third step, and obtain the corresponding current value. Obtain the scan rate-current scatter plot, and fit it to obtain a linear function. The slope of the linear function is the non-Radal capacitance value Cdl of the positive electrode plate.

[0051] Non-Faraday capacitance refers to the ability of an electrode material to store charge in an electrolyte through physical adsorption or intercalation of ions. In secondary batteries, the magnitude of non-Faraday capacitance affects the instantaneous charging rate and instantaneous power output. Non-Faraday capacitance can be altered by modifying the positive electrode active material, such as through nano-sizing or surface modification. This application's research found that, under the technical solution provided in this application, non-Faraday capacitance in the range of 0.4 nF to 1.6 nF can better achieve excellent cycle performance and rate performance in secondary batteries.

[0052] For example, Cdl nF can be any point value or any two-point range value between 0.6nF and 1.4nF. For instance, Cdl nF can be one or any two of the following: 0.6nF, 0.7nF, 0.8nF, 0.9nF, 1.0nF, 1.1nF, 1.2nF, 1.3nF, and 1.4nF.

[0053] In one embodiment, the non-Radical capacitance Cdl nF of the positive electrode is 0.9nF to 1.2nF. For example, Cdl can be one or any two of the following values: 0.9nF, 0.93nF, 0.95nF, 0.98nF, 1nF, 1.03nF, 1.05nF, 1.08nF, 1.1nF, 1.13nF, 1.15nF, 1.18nF, and 1.2nF. This application has found that when the non-Radical capacitance Cdl nF of the positive electrode is further selected to be 0.9nF to 1.2nF, the rate performance and cycle performance of the resulting secondary battery are superior.

[0054] In one embodiment, the mass percentage (N%) of the lithium replenishing agent in the positive electrode active material layer is 1% to 5%.

[0055] It should be noted that the mass percentage of lithium replenishing agent in the positive electrode active material layer was obtained by inductively coupled plasma atomic emission spectroscopy (ICP).

[0056] Lithium replenishers can improve the energy density and cycle life of rechargeable batteries by compensating for the loss of active lithium. Specifically, during the initial charge formation of a rechargeable battery, the lithium replenisher undergoes a decomposition reaction, releasing a large number of active lithium ions to compensate for the irreversible loss of active lithium caused by the formation of the SEI layer on the negative electrode. The formation of the SEI layer is an unavoidable phenomenon during the first charge of a lithium-ion battery. This layer protects the negative electrode material and prevents further electrolyte decomposition, but it also consumes some active lithium, leading to a loss of initial battery capacity. By adding a lithium replenisher to the positive electrode active material layer, this loss of active lithium can be effectively compensated, thereby improving the battery's initial capacity and energy density. However, during the release of lithium ions, the lithium replenisher often involves the breaking and recombination of the crystal structure. This structural change may generate small molecule gases, leading to an increase in internal battery pressure and drastic changes in material volume. These factors can have toxic side effects on the SEI layer, potentially reducing its stability and thus affecting the battery's cycle life and safety. This application research found that, under the technical solution provided in this application, by further selecting the mass percentage N% of the lithium replenishing agent in the positive electrode active material layer to be 1% to 5%, it is possible to simultaneously achieve good cycle performance, rate performance and safety performance of the secondary battery.

[0057] For example, the mass percentage N% of the lithium replenishing agent in the positive electrode active material layer can be any point value or any two points between 1% and 5%. For example, N can be one or any two of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0058] In one embodiment, the mass percentage N% of the lithium supplement in the positive electrode active material layer is 2% to 3%. For example, it can be a range of one or both of 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, and 3.0%. This application has found that when the mass percentage N% of the lithium supplement in the positive electrode active material layer is further selected to be 2% to 3%, the overall performance of the resulting secondary battery is superior.

[0059] In one embodiment, the mass percentage A% of the silane compound containing carbon-carbon double bonds in the electrolyte is 0.05% to 3%.

[0060] In one embodiment, the mass percentage (B%) of the cyclic lithium borate compound in the electrolyte is 0.05% to 3%.

[0061] It should be noted that the method for testing the mass percentage of silane compounds containing carbon-carbon double bonds in the electrolyte is as follows: Take a certain mass m1 of battery electrolyte sample, and use matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to quantitatively test the mass m2 of silane compounds containing carbon-carbon double bonds. Then, the mass percentage A% of silane compounds containing carbon-carbon double bonds is calculated as follows: A% = m2 / m1 * 100%.

[0062] It should be noted that the test method for the mass percentage of cyclic lithium borate compounds in the electrolyte is as follows: take a certain mass m1 of battery electrolyte sample, and use ion chromatography to quantitatively test the mass m3 of cyclic lithium borate compounds. Then the mass percentage B% of cyclic lithium borate compounds is calculated as m3 / m1*100%.

[0063] This study found that silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds, when added to the electrolyte as additives, can synergistically improve the stability and flexibility of the SEI film, thereby reducing gas generation and lithium deposition during the cycling process of the secondary battery, and improving the cycle performance and safety performance of the secondary battery. Specifically, silane compounds containing carbon-carbon double bonds can not only inhibit the reductive decomposition of the electrolyte, but also effectively form polymer components in the SEI film, thereby improving the flexibility of the SEI film; cyclic lithium borate compounds can serve as lithium salt-rich components of the SEI film, improving the thermal stability of the SEI film.

[0064] For example, the mass percentage A% of silane compounds containing carbon-carbon double bonds in the electrolyte can be any point value or any two points range between 0.05% and 3%, such as one or any two of the following: 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, and 3.0%.

[0065] For example, the mass percentage B% of the cyclic lithium borate compound in the electrolyte can be any point value or any two points between 0.05% and 3%, such as one or any two of 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, and 3.0%.

[0066] In one embodiment, the mass percentage A% of the silane compound containing carbon-carbon double bonds in the electrolyte is 1% to 2%. For example, it can be one or any two of the following values: 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%. This application has found that when the mass percentage A% of the silane compound containing carbon-carbon double bonds in the electrolyte is further selected to be 1% to 2%, the overall performance of the resulting secondary battery is superior.

[0067] In one embodiment, the mass percentage B% of the cyclic lithium borate compound in the electrolyte is 1% to 2%. For example, it can be one or any two of the following values: 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%. This application has found that when the mass percentage B% of the cyclic lithium borate compound in the electrolyte is further selected to be 1% to 2%, the overall performance of the resulting secondary battery is superior.

[0068] In one embodiment, 0.1 ≤ M ≤ 5, where M = A + B.

[0069] This study found that there is a synergistic effect between silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds added to the electrolyte. When the sum of the amounts of the two added is further selected to be 0.1 to 5, the cycle performance and safety performance of the secondary battery are even better.

[0070] For example, M can be any point value or any two-point range value between 0.1 and 5. For instance, M can be one or any two of the following: 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0.

[0071] In one embodiment, 3 ≤ M ≤ 4. This application research found that when M is further selected as 3 to 4, the overall performance of the resulting secondary battery is even better.

[0072] In one embodiment, the silane compound containing carbon-carbon double bonds includes at least one of tetravinylsilane, tetrapropenylsilane, trivinylethylsilane, and tripropenylmethylsilane.

[0073] In one embodiment, the cyclic lithium borate compound includes at least one of lithium difluorooxalate borate, lithium difluoroborate fluoromalonic acid, and lithium difluoroborate oxalate.

[0074] This study found that when silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds are selected as the aforementioned types of substances, the overall performance of the resulting secondary battery is even better.

[0075] In one embodiment, the electrolyte further includes fluoroethylene carbonate and vinylene carbonate.

[0076] In one embodiment, the electrolyte contains 0.5% to 1.5% fluoroethylene carbonate by mass.

[0077] For example, the mass percentage of fluoroethylene carbonate in the electrolyte can be any point value or any two points between 0.5% and 1.5%, such as one or any two of 0.5%, 0.8%, 1.0%, 1.2%, and 1.5%.

[0078] In one embodiment, the electrolyte contains 0.5% to 1.5% by mass of vinylene carbonate.

[0079] For example, the mass percentage of vinylene carbonate in the electrolyte can be any point value or any two points between 0.5% and 1.5%, such as one or any two of 0.5%, 0.8%, 1.0%, 1.2%, and 1.5%.

[0080] This study found that adding fluoroethylene carbonate and vinylene carbonate as additives to the electrolyte allows them to better interact with silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds, forming a more stable and elastic SEI film during the first charge of the secondary battery. This effectively mitigates electrolyte decomposition and corrosion of the negative electrode metal, thereby enhancing the safety and cycle performance of the secondary battery. In particular, when the amounts of fluoroethylene carbonate and vinylene carbonate added are further selected within the range given in this application, the overall performance of the resulting secondary battery is even better.

[0081] In one embodiment, the lithium supplement includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2.

[0082] In one embodiment, the lithium replenishing agent has a Dv99 ≤ 25 μm.

[0083] It should be noted that Dv99 is the particle size corresponding to a cumulative volume percentage of lithium supplementation reaching 99%, obtained by testing with a dynamic image particle analyzer.

[0084] For example, the Dv99 of the lithium replenishing agent is any point value or any two-point range value of ≤25μm. For example, Dv99 can be one or any two of the following: 25μm, 23μm, 20μm, 18μm, 15μm, 13μm, 10μm, 8μm, 6μm, 4μm, 2μm, 1μm.

[0085] In one embodiment, the lithium replenishing agent has a Dv99 of 1 μm to 20 μm.

[0086] This study found that when the lithium replenishing agent is further selected with a Dv99 ≤ 25 μm, especially when the Dv99 is 1 μm to 20 μm, it can provide a larger surface area for contact with the electrolyte to improve energy density. It can also avoid recrystallization caused by excessively small lithium replenishing agent particles, which would affect the cycle performance and safety performance of the secondary battery.

[0087] In one embodiment, at least a portion of the surface of the positive electrode active material is provided with a carbon layer, the thickness C of which is 5 nm to 200 nm.

[0088] It should be noted that the thickness of the carbon layer was obtained by transmission electron microscopy.

[0089] For example, the thickness C of the carbon layer can be any point value or any two-point range value between 5nm and 200nm, such as one or any two of the following: 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, and 200nm.

[0090] This application does not limit the positive electrode active material; any known positive electrode active material can be used. As an example, the positive electrode active material can be a lithium phosphate with an olivine structure.

[0091] In one embodiment, the positive electrode active material layer further includes a binder. This application does not limit the binder; any known binder can be used. As an example, the binder may be polyvinylidene fluoride (PVDF).

[0092] In one embodiment, the positive electrode current collector can be made of a material with good conductivity and mechanical strength, serving both as a conductor and a current collector. In another embodiment, the positive electrode current collector can be a metal foil or a composite current collector (a composite current collector can be formed by depositing metal material on a polymer substrate). As an example, the positive electrode current collector is made of aluminum foil or carbon-coated aluminum foil.

[0093] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector; the negative active material layer includes a negative active material. This application does not limit the negative active material; any known negative active material can be used. As an example, the negative active material can be at least one of artificial graphite, natural graphite, silicon-carbon composite material, elemental silicon, silicon suboxide, and hard carbon.

[0094] In one embodiment, the negative electrode current collector can be made of a material with good conductivity and mechanical strength, serving both as a conductor and a current collector. In another embodiment, the negative electrode current collector can be a metal foil or a composite current collector (a composite current collector can be formed by depositing a metal material on a polymer substrate). As an example, copper foil is used as the negative electrode current collector.

[0095] In one embodiment, the electrolyte further includes an organic solvent and a lithium salt. This application does not limit the use of organic solvents and lithium salts in the electrolyte; any known organic solvent and lithium salt can be used.

[0096] For example, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0097] In one embodiment, the separator of the secondary battery is disposed between the positive and negative electrodes.

[0098] In one embodiment of this application, an electrical device is provided, which includes the secondary battery described in this application.

[0099] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0100] Example 1

[0101] This application provides a secondary battery, the preparation method of which includes the following steps:

[0102] (1) Preparation of positive electrode sheet

[0103] Lithium iron phosphate (carbon layer thickness of 60nm), lithium supplementer Li5FeO5 (Dv99 of 20μm), conductive carbon black (SP), and PVDF were mixed in a weight ratio of 94:3:0.9:2.1. Then NMP was added and thoroughly mixed. After uniform mixing, the mixture was coated on both sides of a (12+1+1)μm carbon-coated aluminum foil. The electrode was then dried, rolled, slit, and cut to obtain the positive electrode.

[0104] The non-Radical capacitance of the positive electrode is 0.9 nF;

[0105] (2) Preparation of negative electrode sheet

[0106] Artificial graphite, conductive carbon black (SP), binder (carboxymethyl cellulose), and styrene-butadiene rubber are mixed evenly in a mass ratio of 96:1:1.8:1.2. Then, water is added to the mixture in batches and the mixture is stirred and mixed thoroughly to prepare a negative electrode slurry. The homogeneous negative electrode slurry is then evenly coated on both sides of a 6μm copper foil. After drying, rolling, slitting, and cutting, a negative electrode sheet is obtained.

[0107] (3) Preparation of electrolyte

[0108] In an argon-atmospheric glove box (H2O content <1ppm, O2 content <1ppm), ethylene carbonate and ethyl methyl carbonate were mixed, and 1.2 mol / L LiPF6 lithium salt was dissolved. Then, tetravinylsilane (first additive), lithium difluorooxalate borate (second additive), and other additives (fluoroethylene carbonate and vinylene carbonate) were added. The mixture was stirred evenly and aged for 72 hours to prepare the lithium-replenished electrolyte. Based on the total mass of the lithium-replenished electrolyte, the mass content of the first additive (A%) was 1%, the mass content of the second additive (B%) was 2%, the mass content of fluoroethylene carbonate was 1%, and the mass content of vinylene carbonate was 1%.

[0109] (4) Preparation of secondary batteries

[0110] The prepared positive electrode, negative electrode, separator and other battery components are assembled and then processed through shaping, baking, packaging, liquid injection, formation and capacity testing to obtain a secondary battery.

[0111] Examples 2-4

[0112] This application provides a secondary battery, which differs from Embodiment 1 in that the non-Radica capacitance of the positive electrode is changed by adjusting the content ratio of the positive electrode active material in the positive electrode sheet, the particle size distribution of the positive electrode active material, the powder compaction density of the positive electrode material, as well as the porosity and compaction density of the positive electrode sheet, and the positive electrode formulation (such as the content of conductive agent and the content of positive electrode active material).

[0113] Examples 5-7

[0114] This application provides a secondary battery, which differs from Embodiment 1 in that the mass percentage of lithium supplementation in the positive electrode active material layer is changed by adjusting the amount of lithium supplementation added to the positive electrode active material layer.

[0115] Examples 8-10

[0116] This application provides a secondary battery, which differs from Example 1 in that the mass percentage of silane compounds containing carbon-carbon double bonds in the electrolyte is changed by adjusting the amount of silane compounds containing carbon-carbon double bonds added to the electrolyte.

[0117] Examples 11-13

[0118] This application provides a secondary battery, which differs from the one in Example 1 in that the mass percentage of the cyclic lithium borate compound in the electrolyte is changed by adjusting the amount of the added cyclic lithium borate compound.

[0119] Example 14

[0120] This application provides a secondary battery, which differs from Example 1 in that the mass percentage of cyclic lithium borate compounds in the electrolyte is changed by adjusting the amount of cyclic lithium borate compounds added, and the mass percentage of lithium supplementer in the positive electrode active material layer is changed by adjusting the amount of lithium supplementer added.

[0121] Examples 15-16

[0122] This application provides a secondary battery, which differs from the one in Example 1 in that the amount of M is changed by adjusting the amount of silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds added to the electrolyte.

[0123] Example 17

[0124] This application provides a secondary battery, which differs from Example 1 in that the parameters in Table 1 are achieved by adjusting the content ratio of positive electrode active material in the positive electrode sheet, the particle size distribution of the positive electrode active material, the powder compaction density of the positive electrode material, the porosity and compaction density of the positive electrode sheet, the positive electrode formulation (such as the content of conductive agent and the content of positive electrode active material), the amount of lithium supplementer added, and the amount of silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds added to the electrolyte.

[0125] Examples 18-21

[0126] This application provides a secondary battery, which differs from Example 1 in that the parameters in Table 1 are achieved by adjusting the amount of fluoroethylene carbonate and vinylene carbonate added.

[0127] Example 22

[0128] This application provides a secondary battery, which differs from Example 1 in that the type of silane compound containing carbon-carbon double bonds is changed.

[0129] Example 23

[0130] This application provides a secondary battery, which differs from Example 1 in that the type of cyclic lithium borate compound is changed.

[0131] Example 24

[0132] This application provides a secondary battery, which differs from the one in embodiment 1 in that the type of lithium replenishing agent is changed.

[0133] Examples 25-26

[0134] This application provides a secondary battery, which differs from the one in Example 1 in that the lithium replenishing agent Dv99 is changed by adjusting the preparation method of the lithium replenishing agent.

[0135] Examples 27-28

[0136] This application provides a secondary battery, which differs from Embodiment 1 in that the thickness of the carbon layer is changed by adjusting the positive electrode active material.

[0137] Comparative Example 1

[0138] This application provides a secondary battery in comparison. The difference between the secondary battery and Example 1 is that the parameters in Table 1 are achieved by adjusting the content ratio of positive electrode active material in the positive electrode sheet, the particle size distribution of the positive electrode active material, the powder compaction density of the positive electrode material, the porosity and compaction density of the positive electrode sheet, the positive electrode formulation (such as the content of conductive agent and the content of positive electrode active material), the amount of lithium supplement added, and the amount of silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds added to the electrolyte.

[0139] Comparative Example 2

[0140] This application provides a secondary battery in comparison, the difference between the secondary battery and Example 1 is that the electrolyte does not contain silane compounds containing carbon-carbon double bonds, but is supplemented by cyclic lithium borate compounds.

[0141] Comparative Example 3

[0142] This application provides a secondary battery in comparison, which differs from Example 1 in that it does not contain cyclic lithium borate compounds, but is supplemented by silane compounds containing carbon-carbon double bonds.

[0143] Comparative Example 4

[0144] This application provides a secondary battery in comparison, which differs from Example 1 in that it does not contain silane compounds with carbon-carbon double bonds or cyclic lithium borate compounds.

[0145] Comparative Example 5

[0146] This application provides a secondary battery in comparison, which differs from Example 1 in that it does not contain a lithium replenishing agent.

[0147] The non-Radical capacitance Cdl of the positive electrode in the examples and comparative examples, the mass percentage N of the lithium replenishing agent in the positive electrode active material layer, the mass percentage A of the silane compound containing carbon-carbon double bonds in the electrolyte, the mass percentage B and M of the cyclic lithium borate compound in the electrolyte, the type of the silane compound containing carbon-carbon double bonds, the type of the cyclic lithium borate compound, the mass percentage E of the fluoroethylene carbonate in the electrolyte, the mass percentage F of the vinylene carbonate in the electrolyte, the type of lithium replenishing agent, the Dv99 of the lithium replenishing agent, and the thickness C of the carbon layer of the positive electrode active material are shown in Tables 1-2.

[0148] Table 1. Parameters of Secondary Batteries

[0149]

[0150]

[0151] Table 2 Parameter Table of Secondary Batteries

[0152]

[0153]

[0154] The cycle performance, rate performance, and lithium plating of the secondary batteries prepared in the examples and comparative examples are shown in Table 3; the test methods include the following steps:

[0155] 1) Cycle capacity retention rate: The nominal capacity of the battery is C0. Under the condition of 25℃, the discharge capacity C is obtained by 3000 cycles of 0.5C / 0.5C. The capacity retention rate = C / C0×100%;

[0156] 2) 1C Lithium Plaque Status: After the battery underwent three 0.5C rate charge-discharge cycles and ten 1C rate charge-discharge cycles at 25℃, it was disassembled and the lithium plaque status at the negative electrode interface was observed. Based on the degree of lithium plaque, it was divided into four levels: no lithium plaque, slight lithium plaque, moderate lithium plaque, and severe lithium plaque. Among them, no lithium plaque means the lithium plaque area is less than 2%, slight lithium plaque means 2-10%, moderate lithium plaque means 10-30%, and severe lithium plaque means more than 30%.

[0157] 3) 2C Lithium Plaque Status: After the battery underwent three 0.5C rate charge-discharge cycles and ten 2C rate charge-discharge cycles at 25℃, it was disassembled and the lithium plaque status at the negative electrode interface was observed. Based on the degree of lithium plaque, it was divided into four levels: no lithium plaque, slight lithium plaque, moderate lithium plaque, and severe lithium plaque. Among them, no lithium plaque means that the lithium plaque area is less than 5%, slight lithium plaque means 5-20%, moderate lithium plaque means 20-50%, and severe lithium plaque means more than 50%.

[0158] Table 3 Performance Test Table for Secondary Batteries

[0159]

[0160]

[0161] As can be seen from Table 3, this application achieves the desired result by controlling the secondary battery to meet (Cdl-0.1). 2 ×(A+B+1)×100 / N 2 When the value is ≥10, the obtained secondary battery has good cycle performance, rate performance and safety performance; specifically, the obtained secondary battery retains more than 89.06% of the cycle capacity after 6000 cycles at 0.5C / 0.5C under 25℃ conditions, and does not exhibit lithium plating in 1C / 2C lithium plating tests.

[0162] The results of Examples 1-28 and Comparative Example 1 of this application also show that when Y satisfies Y≥10, the secondary battery can be guaranteed to have excellent cycle performance, rate performance and good lithium plating. The results of Examples 1-28 and Comparative Examples 2-4 of this application also show that when no silane compounds containing carbon-carbon double bonds and / or cyclic lithium borate compounds are added to the electrolyte, the overall performance of the obtained secondary battery cannot achieve the purpose of this application. The results of Examples 1-28 and Comparative Example 5 of this application also show that when no lithium replenishing agent is introduced, the overall performance of the obtained secondary battery deteriorates significantly.

[0163] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, characterized in that, The positive electrode active material layer includes a positive electrode active material and a lithium supplement agent, and the electrolyte includes silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds; The secondary battery satisfies: Y≥10; Where Y = (Cdl - 0.1) 2 ×(A+B+1)×100 / N 2 ; CdlnF is the non-Radal capacitance of the positive electrode, and the non-Radal capacitance CdlnF of the positive electrode is 0.6nF~1.4nF; N% represents the mass percentage of the lithium supplement agent in the positive electrode active material layer, and the mass percentage N% of the lithium supplement agent in the positive electrode active material layer is 1%~5%; A% represents the mass percentage of silane compounds containing carbon-carbon double bonds in the electrolyte, and the mass percentage A% of the silane compounds containing carbon-carbon double bonds in the electrolyte is 0.05% to 3%. B% represents the mass percentage of cyclic lithium borate compounds in the electrolyte, and the mass percentage B% of cyclic lithium borate compounds in the electrolyte is 0.05% to 3%.

2. The secondary battery according to claim 1, characterized in that, 0.1≤M≤5, where M=A+B.

3. The secondary battery according to claim 1, characterized in that, The silane compounds containing carbon-carbon double bonds include at least one of tetravinylsilane, tetrapropenylsilane, trivinylethylsilane, and tripropenylmethylsilane.

4. The secondary battery according to claim 1, characterized in that, The cyclic lithium borate compounds include at least one of lithium difluorooxalate borate and lithium difluoroborate difluoromalonic acid.

5. The secondary battery according to claim 1, characterized in that, The electrolyte also includes fluoroethylene carbonate and vinylene carbonate.

6. The secondary battery according to claim 5, characterized in that, The electrolyte contains 0.5% to 1.5% fluoroethylene carbonate by mass. And / or, the electrolyte contains 0.5% to 1.5% by mass of vinylene carbonate.

7. The secondary battery according to claim 1, characterized in that, The lithium supplementer includes at least one of Li5FeO5, Li6CoO4, and Li2NiO2; And / or, the lithium supplement has a Dv99 ≤ 25 μm.

8. The secondary battery according to claim 1, characterized in that, At least a portion of the surface of the positive electrode active material is provided with a carbon layer, the thickness C of which is 5 nm to 200 nm.

9. An electrical device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 8.

Images