Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, the lithium supplement agent is introduced into the positive electrode active material layer, and the silane compound containing carbon-carbon double bonds and the cyclic lithium borate compound are added into the electrolyte; the non-Faraday capacitance of the positive pole piece, the mass percentage of the lithium supplement agent 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 meets the specific relational expression: (Cdl-0. 1) 2 * (A + B + 1) * 100 / N2 is greater than or equal to 10; therefore, excellent cycle performance, rate capability and safety performance of the secondary battery can be realized at the same time.

Description

Technical Field

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

[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 their single cells is generally less than 8,000 times, which is difficult to meet the requirements of 20 to 30 years of service life (more than 12,000 cycles) in certain high-demand application scenarios.

[0003] A series of methods proposed in the prior art to improve the cycle life of lithium-ion batteries inevitably have the problem of increased gas production risk, aggravated lithium precipitation resulting in reduced safety, or increased internal resistance resulting in reduced rate performance. Summary of the invention

[0004] The purpose of the present application is to solve the problem in the prior art that it is impossible to simultaneously achieve excellent cycle performance, rate performance and safety performance of secondary batteries, and to provide a secondary battery and an electrical device with excellent rate performance, cycle performance and good safety.

[0005] To achieve the above-mentioned object, in a first aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material and a lithium supplement, and wherein the electrolyte comprises a silane compound containing a carbon-carbon double bond 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-Faraday capacitance of the positive electrode;

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

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

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

[0012] As an implementation scheme of the present application, the non-Faraday capacitance Cdl nF of the positive electrode plate is 0.6nF to 1.4nF.

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

[0014] As an embodiment of the present 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 the present application, the mass percentage B% of the cyclic lithium borate compounds in the electrolyte is 0.05% to 3%.

[0016] As an implementation scheme of the present application, 0.1≤M≤5, wherein M=A+B.

[0017] As an embodiment of the present application, the silane compound containing a carbon-carbon double bond includes at least one of tetravinylsilane, tetrapropylenesilane, trivinylethylsilane, and tripropylenemethylsilane.

[0018] As an embodiment of the present application, the cyclic lithium borate compound includes at least one of lithium difluorooxalatoborate, lithium difluoromalonateborate, and lithium difluorooxalatoborate.

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

[0020] As an embodiment of the present application, in the electrolyte, the mass percentage of fluoroethylene carbonate is 0.5% to 1.5%.

[0021] As an embodiment of the present application, in the electrolyte, the mass percentage of vinylene carbonate is 0.5% to 1.5%.

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

[0023] As an embodiment of the present application, the Dv99 of the lithium supplement agent is ≤25 μm.

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

[0025] In a second aspect of the present application, an electrical device is provided, comprising the secondary battery described above.

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

[0027] The secondary battery provided by the present application introduces a lithium supplement agent into the positive electrode active material layer, and adds a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound to the electrolyte. At the same time, the non-Faraday capacitance of the positive electrode plate, the mass percentage of the lithium supplement agent in the positive electrode active material layer, the mass percentage of the silane compound containing a 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 achieving excellent cycle performance, rate performance and safety performance of the secondary battery. DETAILED DESCRIPTION

[0028] In order to better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific embodiments.

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

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0031] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0032] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0033] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0034] In one embodiment of the present application, the present application proposes a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material and a lithium supplement, and the electrolyte comprises a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound;

[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-Faraday capacitance of the positive electrode;

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

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

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

[0041] The secondary battery provided by the present application introduces a lithium supplement agent into the positive electrode active material layer, and adds a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound to the electrolyte. At the same time, the non-Faraday capacitance of the positive electrode plate, the mass percentage of the lithium supplement agent in the positive electrode active material layer, the mass percentage of the silane compound containing a 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 achieving excellent cycle performance, rate performance and safety performance of the secondary battery.

[0042] Specifically, the secondary battery provided by the present application introduces a lithium supplement agent into the positive electrode active material layer, and adds a silane compound containing a carbon-carbon double bond and a cyclic lithium borate compound to the electrolyte, and the secondary battery satisfies a specific relationship: (Cdl-0.1) 2 ×(A+B+1)×100 / N 2≥10 can achieve significant effects; firstly, the introduction of lithium supplement can compensate for the loss of active lithium without damaging the stability of SEI layer (solid electrolyte interface), thereby improving the energy density and cycle life of secondary batteries, and ensuring the safety performance of secondary batteries; secondly, silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds are added to the electrolyte as additives to promote the formation of SEI film, effectively improve the flexibility and stability of SEI film, thereby improving the cycle stability and safety performance of secondary batteries; thirdly, the combined effect of the above factors can reduce the gas production and lithium precipitation during the cycle of secondary batteries, improve the rate performance and fast charge and discharge performance of secondary batteries, thereby greatly improving the lithium precipitation window during the cycle, reducing the occurrence of lithium precipitation, and further improving the cycle performance and rate performance of secondary batteries.

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

[0044] In one embodiment, the secondary battery satisfies: 28≤Y≤64. For example, Y can be a range value of one or any two of 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 64. The present application has found that when the secondary battery is further selected to meet the above range, the comprehensive performance of the secondary battery obtained is better.

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

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

[0047] S1: Clean the surface of the positive electrode with electrolyte to remove surface impurities, dry, cut into discs, transfer to a vacuum oven after weighing, dry at 90-105°C for 6h, and assemble symmetrical batteries in a glove box;

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

[0049] S3: Select the flat potential interval in the second step to perform cyclic voltammetry (CV) test and collect voltage-current curves, wherein the potential range is 2.5-2.7 V and the scan rate is 1-20 mV / s;

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

[0051] Non-Faradaic capacitance refers to the ability of an electrode material to store charge in an electrolyte by physical adsorption of charge or intercalation of ions. In a secondary battery, the size of the non-Faradaic capacitance affects the instantaneous charging rate and instantaneous power output of the secondary battery. The change of the non-Faradaic capacitance can be achieved by modifying the positive electrode active material, such as nano-sizing, surface modification, etc. This application study found that under the technical solution provided by this application, the non-Faradaic capacitance in the range of 0.4nF to 1.6nF can better achieve the excellent cycle performance and rate performance of the secondary battery.

[0052] Exemplarily, the Cdl nF may be any point value or any two point range values ​​between 0.6nF and 1.4nF, for example, Cdl nF may be one or any two range values ​​of 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-Faraday capacitance Cdl nF of the positive electrode plate is 0.9nF to 1.2nF. For example, Cdl can be a range of one or any two of 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. The present application has found that when the non-Faraday capacitance Cdl nF of the positive electrode plate is further selected to be 0.9nF to 1.2nF, the rate performance and cycle performance of the secondary battery obtained are better.

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

[0055] It should be noted that the mass percentage of the lithium supplement in the positive electrode active material layer is obtained through inductively coupled plasma emission spectroscopy (ICP) testing.

[0056] Lithium supplements can improve the energy density and cycle life of secondary batteries by compensating for the loss of active lithium. Specifically, lithium supplements will undergo a decomposition reaction during the first charging and formation process of the secondary battery, releasing a large amount of active lithium ions to compensate for the irreversible loss of active lithium caused by the formation of the negative electrode SEI layer. The formation of the SEI layer is an inevitable phenomenon in the first charging process of lithium-ion batteries. This layer can protect the negative electrode material and prevent further decomposition of the electrolyte, but it will also consume part of the active lithium, resulting in the loss of the initial capacity of the battery. By adding lithium supplements to the positive electrode active material layer, the loss of this part of active lithium can be effectively compensated, thereby improving the initial capacity and energy density of the battery. However, in the process of releasing lithium ions, the lithium supplement is often accompanied by the rupture and reorganization of the crystal structure. This structural change may produce small molecular gases, resulting in an increase in the internal pressure of the battery, and also cause a drastic change in the volume of the material. These factors will have toxic side effects on the SEI layer of the battery, which may cause the stability of the SEI layer to decrease, thereby affecting the cycle life and safety of the battery. The present application has found that under the technical solution provided in the present application, by further selecting the mass percentage N% of the lithium supplement in the positive electrode active material layer to be 1% to 5%, good cycle performance, rate performance and safety performance of the secondary battery can be achieved at the same time.

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

[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 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0% or any two of them. The present application 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 comprehensive performance of the secondary battery obtained is better.

[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 test method for the mass percentage of silane compounds containing carbon-carbon double bonds in the electrolyte is: take a battery electrolyte sample of a certain mass m1, 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 of silane compounds containing carbon-carbon double bonds 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: take a battery electrolyte sample of a certain mass m1, and use ion chromatography to quantitatively test the mass m3 of the cyclic lithium borate compounds, then the mass percentage of the cyclic lithium borate compounds B% = m3 / m1*100%.

[0063] The present application has found that silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds added as additives into the electrolyte can work together to effectively improve the stability and flexibility of the SEI film, thereby reducing the gas production and lithium precipitation of the secondary battery during the cycle process, and improving the cycle performance and safety performance of the secondary battery. Specifically, silane compounds containing carbon-carbon double bonds can effectively form polymer components in the SEI film on the basis of being able to inhibit the reduction and decomposition of the electrolyte, thereby improving the flexibility of the SEI film; cyclic lithium borate compounds can serve as lithium salt-rich components of the SEI film to improve the thermal stability of the SEI film.

[0064] Exemplarily, the mass percentage A% of the silane compound containing carbon-carbon double bonds in the electrolyte can be any point value between 0.05% and 3% or any two point range values, for example, it can be one 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%, 3.0% or any two range values.

[0065] Exemplarily, the mass percentage B% of the cyclic lithium borate compound in the electrolyte can be any point value between 0.05% and 3% or any two point range values, for example, it can be 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%, 3.0% or any two of the range values.

[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 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or any two of them. The present application 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 comprehensive performance of the secondary battery obtained is better.

[0067] In one embodiment, the mass percentage B% of the cyclic borate lithium compound in the electrolyte is 1% to 2%. For example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or any two of them. The present application found that when the mass percentage B% of the cyclic borate lithium compound in the electrolyte is further selected to be 1% to 2%, the comprehensive performance of the secondary battery obtained is better.

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

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

[0070] Exemplarily, the M may be any point value or any two point range values ​​between 0.1 and 5, for example, M may be one or any two range values ​​of 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. The present application has found that when M is further selected to be 3-4, the comprehensive performance of the secondary battery obtained is better.

[0072] In one embodiment, the silane compound containing a carbon-carbon double bond includes at least one of tetravinylsilane, tetrapropylenesilane, trivinylethylsilane, and tripropylenemethylsilane.

[0073] In one embodiment, the cyclic lithium borate compound includes at least one of lithium difluorooxalatoborate, lithium difluoromalonateborate, and lithium difluorooxalatoborate.

[0074] The present application has found that when silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds are further selected as the above-mentioned types of substances, the comprehensive performance of the secondary battery obtained is better.

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

[0076] In one embodiment, in the electrolyte, the mass percentage of fluoroethylene carbonate is 0.5% to 1.5%.

[0077] Exemplarily, in the electrolyte, the mass percentage of fluoroethylene carbonate can be any point value or any two point range values ​​between 0.5% and 1.5%, for example, it can be one of 0.5%, 0.8%, 1.0%, 1.2%, 1.5% or any two range values.

[0078] In one embodiment, in the electrolyte, the mass percentage of vinylene carbonate is 0.5% to 1.5%.

[0079] Exemplarily, in the electrolyte, the mass percentage of vinylene carbonate can be any point value or any two point range values ​​between 0.5% and 1.5%, for example, it can be one of 0.5%, 0.8%, 1.0%, 1.2%, 1.5% or any two range values.

[0080] The present application has found that further adding fluoroethylene carbonate and vinylene carbonate as additives to the electrolyte can better cooperate with silane compounds and cyclic lithium borate compounds containing carbon-carbon double bonds to form a more stable and elastic SEI film during the first charging of the secondary battery, thereby effectively alleviating the decomposition of the electrolyte and the corrosion of the negative electrode metal, thereby enhancing the safety performance of the secondary battery and improving the cycle performance of the secondary battery. In particular, when the addition amount of fluoroethylene carbonate and vinylene carbonate is further selected within the range given in the present application, the comprehensive performance of the secondary battery obtained is better.

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

[0082] In one embodiment, the Dv99 of the lithium supplement is ≤25 μm.

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

[0084] Exemplarily, the Dv99 of the lithium supplement is any point value ≤ 25 μm or any two point range values, for example, Dv99 may be one of 25 μm, 23 μm, 20 μm, 18 μm, 15 μm, 13 μm, 10 μm, 8 μm, 6 μm, 4 μm, 2 μm, 1 μm or any two range values.

[0085] In one embodiment, the Dv99 of the lithium supplement is 1 μm to 20 μm.

[0086] The present application study found that when the Dv99 of the lithium supplement agent is further selected to be ≤25μm, especially when Dv99 is 1μm to 20μm, it can provide a larger surface area for contact with the electrolyte to improve energy density, and can also avoid the recrystallization phenomenon caused by the lithium supplement agent particles being too small, which affects the cycle performance and safety performance of the secondary battery.

[0087] In one embodiment, a carbon layer is disposed on at least part of the surface of the positive electrode active material, and the thickness C of the carbon layer is 5 nm to 200 nm.

[0088] It should be noted that the thickness of the carbon layer is obtained by testing with a transmission electron microscope.

[0089] Exemplarily, the thickness C of the carbon layer may be any point value or any two point range values ​​between 5nm and 200nm, for example, it may be one or any two range values ​​of 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, and 200nm.

[0090] The present application has no limitation on the positive electrode active material, and any known positive electrode active material may be used. As an example, the positive electrode active material may be a lithium-containing phosphate having an olivine structure.

[0091] In one embodiment, the positive electrode active material layer further includes a binder, and the present application has no limitation on the binder, and any known binder can be used. As an example, the binder can be polyvinylidene fluoride.

[0092] In one embodiment, the positive electrode current collector may be made of a material with good electrical conductivity and mechanical strength to perform the functions of electrical conduction and current collection. In one embodiment, the positive electrode current collector may be made of a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). 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 plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. The present application has no limitation on the negative electrode active material, and any known negative electrode active material can be used. As an example, the negative electrode active material can be at least one of artificial graphite, natural graphite, silicon-carbon composite material, silicon alone, silicon oxide, and hard carbon.

[0094] In one embodiment, the negative electrode current collector may be made of a material with good electrical conductivity and mechanical strength to perform the functions of conducting electricity and collecting current. In one embodiment, the negative electrode current collector may be made of a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector is made of copper foil.

[0095] In one embodiment, the electrolyte further comprises an organic solvent and a lithium salt. The present application has no limitation on the organic solvent and the lithium salt in the electrolyte, and any known organic solvent and lithium salt can be used.

[0096] Exemplarily, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl 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 electrode and the negative electrode.

[0098] In one embodiment of the present application, the present application proposes an electrical device, and the electrical device includes the secondary battery described in the present application.

[0099] Exemplarily, the above-mentioned 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] The present invention provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0102] (1) Preparation of positive electrode sheet

[0103] Lithium iron phosphate (carbon layer thickness of 60nm), lithium supplement Li5FeO5 (Dv99 of 20μm), conductive carbon black (SP), and PVDF are mixed in a weight ratio of 94:3:0.9:2.1, then added into NMP for thorough mixing, and after mixing evenly, coated on both sides on a (12+1+1)μm carbon-coated aluminum foil, and then the electrode is dried, rolled, slit and cut to obtain a positive electrode;

[0104] Among them, the non-Faraday capacitance of the positive electrode is 0.9nF;

[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, and then water is added to the above mixture in batches and continued to be fully mixed and stirred to prepare a negative electrode slurry, and then the homogeneous negative electrode slurry is evenly coated on both sides of a 6μm copper foil, and after drying, rolling, slitting and cutting, a negative electrode sheet is obtained;

[0107] (3) Preparation of electrolyte

[0108] In an argon atmosphere glove box (H2O content <1ppm, O2 content <1ppm), ethylene carbonate and ethyl methyl carbonate are mixed, and 1.2mol / L LiPF6 lithium salt is dissolved, and then the first additive tetravinylsilane, the second additive lithium difluorooxalate borate and other additives (fluoroethylene carbonate and vinylene carbonate) are added, stirred evenly, aged for 72h, and a lithium supplement electrolyte is prepared. Based on the total mass of the lithium supplement electrolyte, the mass content A% of the first additive is 1%, the mass content B% of the second additive is 2%, the mass content of fluoroethylene carbonate is 1%, and the mass content of vinylene carbonate is 1%;

[0109] (4) Preparation of secondary batteries

[0110] The prepared positive electrode sheet, negative electrode sheet, separator and other battery components are assembled, and a secondary battery is obtained through processes such as shaping, baking, packaging, liquid injection, formation, and capacity division.

[0111] Embodiments 2 to 4

[0112] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the non-Faraday capacitance of the positive electrode sheet 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, and the porosity and compaction density of the positive electrode sheet, as well as the positive electrode formulation (such as the conductive agent content, the positive electrode active material content).

[0113] Embodiments 5 to 7

[0114] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the lithium replenisher in the positive electrode active material layer is changed by adjusting the amount of the lithium replenisher added in the positive electrode active material layer.

[0115] Embodiments 8 to 10

[0116] The embodiment of the present application provides a secondary battery, which differs from the embodiment 1 in that the mass percentage of the silane compound containing carbon-carbon double bonds in the electrolyte is changed by adjusting the addition amount of the silane compound containing carbon-carbon double bonds in the electrolyte.

[0117] Examples 11 to 13

[0118] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the mass percentage of the cyclic lithium borate compound in the electrolyte is changed by adjusting the addition amount of the cyclic lithium borate compound in the electrolyte.

[0119] Embodiment 14

[0120] The embodiment of the present application provides a secondary battery, which is different from Example 1 in that the mass percentage of the cyclic lithium borate compound in the electrolyte is changed by adjusting the addition amount of the cyclic lithium borate compound in the electrolyte, and the mass percentage of the lithium supplement agent in the positive electrode active material layer is changed by adjusting the addition amount of the lithium supplement agent.

[0121] Embodiments 15-16

[0122] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the change of M is achieved by adjusting the addition amount of silane compounds containing carbon-carbon double bonds and cyclic lithium borate compounds in the electrolyte.

[0123] Embodiment 17

[0124] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the parameters in Table 1 are achieved by adjusting the content ratio of the positive electrode active material in the positive electrode plate, 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 plate, the positive electrode formula (such as the conductive agent content, the positive electrode active material content), the addition amount of the lithium supplement agent, and the addition amount of the silane compound containing carbon-carbon double bonds and the cyclic lithium borate compound in the electrolyte.

[0125] Examples 18 to 21

[0126] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the parameters in Table 1 are achieved by adjusting the addition amounts of fluoroethylene carbonate and vinylene carbonate.

[0127] Embodiment 22

[0128] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the type of the silane compound containing a carbon-carbon double bond is changed.

[0129] Embodiment 23

[0130] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the type of the cyclic lithium borate compound is changed.

[0131] Embodiment 24

[0132] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the type of lithium supplement is changed.

[0133] Embodiments 25-26

[0134] The embodiment of the present application provides a secondary battery, which is different from the embodiment 1 in that the change of the lithium supplement Dv99 is achieved by adjusting the lithium supplement preparation method.

[0135] Examples 27-28

[0136] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the thickness of the carbon layer is changed by adjusting the positive electrode active material.

[0137] Comparative Example 1

[0138] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that the parameters in Table 1 are achieved by adjusting the content ratio of the positive electrode active material in the positive electrode plate, 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 plate, the positive electrode formula (such as the conductive agent content, the positive electrode active material content), the addition amount of the lithium supplement agent, and the addition amount of the silane compound containing carbon-carbon double bonds and the cyclic lithium borate compound in the electrolyte.

[0139] Comparative Example 2

[0140] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that no silane compound containing a carbon-carbon double bond is added to the electrolyte, and the amount thereof is supplemented by a cyclic lithium borate compound.

[0141] Comparative Example 3

[0142] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that no cyclic lithium borate compound is added, and the amount thereof is supplemented by a silane compound containing a carbon-carbon double bond.

[0143] Comparative Example 4

[0144] The comparative example of the present application provides a secondary battery, which is different from Example 1 in that the silane compound containing a carbon-carbon double bond and the cyclic lithium borate compound are not added.

[0145] Comparative Example 5

[0146] The comparative example of the present application provides a secondary battery, which is different from the embodiment 1 in that no lithium supplement agent is added.

[0147] The non-Faraday capacitance Cdl of the positive electrode plate, the mass percentage N of the lithium supplement in the positive electrode active material layer, the mass percentage A of the silane compound containing a carbon-carbon double bond in the electrolyte, the mass percentage B, M of the cyclic lithium borate compound in the electrolyte, the type of the silane compound containing a carbon-carbon double bond, the type of the cyclic lithium borate compound, the mass percentage E of fluoroethylene carbonate in the electrolyte, the mass percentage F of vinylene carbonate in the electrolyte, the type of the lithium supplement, the Dv99 of the lithium supplement, and the thickness C of the carbon layer of the positive electrode active material are shown in Tables 1 to 2 in the embodiments and comparative examples;

[0148] Table 1 Parameters of secondary batteries

[0149]

[0150]

[0151] Table 2 Parameters of secondary batteries

[0152]

[0153]

[0154] The cycle performance, rate performance and lithium deposition of the secondary batteries prepared in the examples and comparative examples are shown in Table 3; wherein the test method comprises the following steps:

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

[0156] 2) 1C lithium deposition: At 25°C, the battery was disassembled after 3 cycles of charge and discharge at a rate of 0.5C and 10 cycles of charge and discharge at a rate of 1C to observe the lithium deposition at the interface of the negative electrode. According to the degree of lithium deposition, it was divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition and severe lithium deposition; among them, no lithium deposition means that the lithium deposition area is less than 2%, slight lithium deposition means 2-10%, moderate lithium deposition means 10-30%, and severe lithium deposition means more than 30%;

[0157] 3) 2C lithium deposition: At 25°C, the battery was disassembled after 3 cycles of charge and discharge at a rate of 0.5C and 10 cycles of charge and discharge at a rate of 2C to observe the lithium deposition at the interface of the negative electrode. According to the degree of lithium deposition, the battery was divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition and severe lithium deposition; among them, no lithium deposition means that the lithium deposition area is less than 5%, slight lithium deposition means 5-20%, moderate lithium deposition means 20-50%, and severe lithium deposition means more than 50%;

[0158] Table 3 Performance test table of secondary batteries

[0159]

[0160]

[0161] As can be seen from Table 3, the present application satisfies (Cdl-0.1) by controlling the secondary battery 2 ×(A+B+1)×100 / N 2 ≥10, the obtained secondary battery has good cycle performance, rate performance and safety performance; specifically, the obtained secondary battery has a cycle capacity retention rate of more than 89.06% after 6000 cycles at 0.5C / 0.5C at 25°C, and no lithium deposition is shown in 1C / 2C lithium deposition tests;

[0162] The results of Examples 1 to 28 of the present application and Comparative Example 1 also show that when Y satisfies Y ≥ 10, it is possible to ensure that the secondary battery has excellent cycle performance, rate performance and good lithium deposition conditions; the results of Examples 1 to 28 of the present application and Comparative Examples 2 to 4 also show that when silane compounds and / or cyclic lithium borate compounds containing carbon-carbon double bonds are not added to the electrolyte, the comprehensive performance of the obtained secondary battery cannot achieve the purpose of the present application; the results of Examples 1 to 28 of the present application and Comparative Example 5 also show that when the lithium supplement agent is not introduced, the comprehensive performance of the obtained secondary battery is significantly deteriorated.

[0163] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

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

2. The secondary battery according to claim 1, characterized in that: At least one of the following is met: a. The non-Faraday capacitance Cdl nF of the positive electrode plate is 0.6nF to 1.4nF; b. The mass percentage N% of the lithium supplement in the positive electrode active material layer is 1% to 5%; c. The mass percentage A% of the silane compound containing carbon-carbon double bonds in the electrolyte is 0.05% to 3%; d. The mass percentage B% of the cyclic lithium borate compounds in the electrolyte is 0.05% to 3%.

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

4. The secondary battery according to claim 1, characterized in that: The silane compound containing a carbon-carbon double bond includes at least one of tetravinylsilane, tetrapropylenesilane, trivinylethylsilane and tripropylenemethylsilane.

5. The secondary battery according to claim 1, characterized in that: The cyclic lithium borate compound includes at least one of lithium difluorooxalatoborate, lithium difluoromalonateborate, and lithium difluorooxalatoborate.

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

7. The secondary battery according to claim 6, characterized in that: In the electrolyte, the mass percentage of fluoroethylene carbonate is 0.5% to 1.5%; And / or, in the electrolyte, the mass percentage of vinylene carbonate is 0.5% to 1.5%.

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

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

10. An electrical device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 9.

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