Secondary battery and electric device

Abstract

This application discloses a secondary battery and an electrical device, belonging to the field of battery technology. By controlling the total content of silicon-containing compounds and fluorocarbonates in the electrolyte, the single-sided areal density and number of layers of the positive electrode sheet, and the height and width of the stacked battery cell to meet certain relationships, this application can effectively improve the wetting speed, increase the utilization rate of the positive and negative active materials, reduce gas production in the secondary battery, effectively reduce the interface impedance, and improve the energy efficiency of the secondary battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries have significant advantages in the field of energy storage, but there are still some problems in practical applications. For example, the energy efficiency of secondary batteries is a key parameter affecting battery use and returns, as it determines the battery's ability to convert charge and discharge energy. Currently, the energy efficiency of secondary batteries, mainly lithium iron phosphate batteries, still needs to be improved.

[0003] Therefore, this application is submitted. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a secondary battery and power device that effectively reduces interface impedance and improves the energy efficiency of the secondary battery.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a stacked cell and an electrolyte. The stacked cell includes a positive electrode, a negative electrode, and a separator stacked together. The electrolyte includes a first additive, which includes a silicon-containing compound and a fluorinated carbonate.

[0006] The secondary battery satisfies: 0.277≤Y≤11.076;

[0007]

[0008] Wherein, a% is the mass percentage of the first additive in the electrolyte;

[0009] b mg / mm 2 The surface density of one side of the positive electrode sheet;

[0010] cm is the height of the stacked battery cell;

[0011] dm is the width of the stacked battery cell;

[0012] e-layer refers to the number of layers stacked on the positive electrode sheet.

[0013] As an implementation scheme of this application, at least one of the following (1) to (5) is satisfied:

[0014] (1) 0.1 ≤ a ≤ 4;

[0015] (2) 0.08 ≤ b ≤ 0.3;

[0016] (3) 0.18 ≤ c ≤ 0.26;

[0017] (4) 0.16 ≤ d ≤ 0.5;

[0018] (5)66≤e≤125.

[0019] As an implementation scheme of this application, at least one of the following (1) to (5) is satisfied:

[0020] (1) 1 ≤ a ≤ 3;

[0021] (2) 0.15 ≤ b ≤ 0.26;

[0022] (3) 0.207 ≤ c ≤ 0.215;

[0023] (4) 0.17≤d≤0.4;

[0024] (5)76≤e≤120.

[0025] As an embodiment of this application, the first additive includes a silicon-containing compound and a fluorocarbonate, wherein the mass ratio of the silicon-containing compound to the fluorocarbonate is (0.5-2):1.

[0026] As an embodiment of this application, the silicon-containing compound includes at least one of tris(trimethylsilane) phosphate and tris(trimethylsilane) borate.

[0027] As an embodiment of this application, the fluorocarbonate comprises at least one of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate.

[0028] As an embodiment of this application, the electrolyte further includes a second additive and a third additive;

[0029] The second additive includes at least one of vinyl sulfate, 1,3-propane sulpholactone, methylene disulfonate, propenyl-1,3-sulfonate lactone, N,N'-thiodiimidazole, triphenyl phosphonite, n-butyric anhydride, hexanetrionitrile, succinate, and tetrafluoroterephthalonitrile.

[0030] The third additive includes at least one of lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl-imidazolium lithium, and lithium trifluoromethanesulfonate.

[0031] As an embodiment of this application, the second additive accounts for 0.1% to 1% of the mass percentage of the electrolyte.

[0032] As an embodiment of this application, the third additive accounts for 0.05% to 0.5% of the mass percentage of the electrolyte.

[0033] As an embodiment of this application, the second additive comprises vinyl sulfate, the third additive comprises lithium difluorooxalate borate, the vinyl sulfate accounts for F% of the mass percentage of the electrolyte, and the lithium difluorooxalate borate accounts for G% of the mass percentage of the electrolyte, satisfying: 0.1 <F<1,1≤F / G≤10。

[0034] As an embodiment of this application, the electrolyte further includes a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate; the concentration of the lithium salt in the electrolyte is 0.5 to 1.3 M.

[0035] A second aspect of this application provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0036] The beneficial effects of this invention are as follows: By controlling the total content of silicon-containing compounds and fluorocarbonates in the electrolyte, the single-sided areal density and number of layers of the positive electrode sheet, and the height and width of the stacked cell to meet certain relationships, this application can construct an SEI and CEI interface layer with lower reactivity, reduce side reactions of the electrolyte, enhance the low-temperature and high-temperature stability of the SEI interface layer, inhibit the oxidative decomposition of the electrolyte, optimize the ionic conductivity of the interface film, improve the wettability of the electrolyte, effectively increase the wetting rate, improve the utilization rate of positive and negative electrode active materials, reduce gas production in the secondary battery, effectively reduce interface impedance, and improve the energy efficiency of the secondary battery. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] 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.

[0040] This application provides a secondary battery, including a stacked cell and an electrolyte. The stacked cell includes a positive electrode, a negative electrode, and a separator stacked together. The electrolyte includes a first additive, which includes a silicon-containing compound and a fluorinated carbonate.

[0041] The secondary battery satisfies: 0.277≤Y≤11.076, for example, it can be 0.277, 0.28, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11.076 or any two of these values.

[0042]

[0043] Wherein, a% is the mass percentage of the first additive in the electrolyte;

[0044] b mg / mm 2 The surface density of one side of the positive electrode sheet;

[0045] cm is the height of the stacked battery cell;

[0046] dm is the width of the stacked battery cell;

[0047] e-layer refers to the number of layers stacked on the positive electrode sheet.

[0048] The inventors of this application have discovered that the electrochemical performance of a secondary battery is significantly correlated with the additives in the electrolyte, the areal density of the positive electrode, the number of layers, and the height and width of the stacked cell. By controlling the total content of silicon-containing compounds and fluorocarbonates in the electrolyte, the areal density and number of layers of the positive electrode, and the height and width of the stacked cell to satisfy the relationships described in this application, it is possible to construct a SEI and CEI interface layer with lower reactivity, reduce side reactions in the electrolyte, enhance the low-temperature and high-temperature stability of the SEI interface layer, inhibit the oxidative decomposition of the electrolyte, optimize the ionic conductivity of the interface film, improve electrolyte wettability, effectively increase the wetting rate, improve the utilization rate of positive and negative electrode active materials, reduce gas production in the secondary battery, effectively reduce interfacial impedance, and improve the energy efficiency of the secondary battery.

[0049] In one embodiment, 1.948≤Y≤8.307, especially when the value of Y is controlled within this range, can further reduce the interface impedance and improve the energy efficiency of the secondary battery.

[0050] In one embodiment, 0.1 ≤ a ≤ 4, for example, it can be a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4 or any two of these values. By controlling the mass percentage of the first additive in the electrolyte within this range, this application can improve the thermal stability of the electrolyte, promote the formation of a more stable and less reactive SEI and CEI interface layer, reduce side reactions and electrolyte consumption, suppress side reactions initiated by metal ions in the positive electrode active material, improve the ionic conductivity of the SEI and CEI interface layer, increase the migration rate of lithium ions, improve high and low temperature performance, further reduce interface impedance, and improve the energy efficiency of the secondary battery.

[0051] In one embodiment, 0.08 ≤ b ≤ 0.3, for example, it can be a range of 0.08, 0.1, 0.12, 0.15, 0.2, 0.22, 0.25, 0.3 or any two of these values. By controlling the single-sided areal density of the positive electrode sheet within this range, it is possible to promote the uniform distribution of the positive electrode active material on the positive electrode sheet, reduce the migration and diffusion paths of active ions in the positive electrode active material, effectively reduce the internal resistance of the secondary battery, further reduce gas production in the secondary battery, reduce interface impedance, and improve the energy efficiency of the secondary battery.

[0052] In this application, the method for testing the areal density of the positive electrode sheet is to cut the positive electrode sheet into pieces with an area of ​​1540.25 mm². 2 The mass of the small circular sheet is measured using a high-precision balance. After deducting the mass of the current collector, the mass is divided by the area of ​​the circular sheet and then by 2 to calculate the surface density of the positive electrode sheet.

[0053] In one embodiment, 0.18≤c≤0.26, for example, can be a range of 0.18, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26 or any two of these values. By controlling the height of the stacked cell within this range, it is beneficial to increase the electrolyte wetting rate of the electrode and improve the dynamic performance of the secondary battery.

[0054] In one embodiment, 0.16 ≤ d ≤ 0.5, for example, it can be a range of 0.16, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5 or any two of these values. By controlling the width of the laminated cell within this range, it is beneficial to reduce the electrode transmission impedance and improve energy efficiency.

[0055] In one embodiment, 66≤e≤125, for example, can be a range of 66, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125 or any two of these values. By controlling the number of layers of the positive electrode sheet within this range, the capacity of the secondary battery can be effectively guaranteed and the energy density improved.

[0056] In one implementation, 1≤a≤3, for example, it can be 1, 1.2, 1.5, 2, 2.5, 2.8, 3 or a range of any two of these values.

[0057] In one implementation, 0.15 ≤ b ≤ 0.26, for example, it can be 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26 or a range of any two of these values.

[0058] In one implementation, 0.207 ≤ c ≤ 0.215, for example, it can be 0.207, 0.208, 0.209, 0.21, 0.211, 0.212, 0.213, 0.214, 0.215 or a range of any two of these values.

[0059] In one implementation, 0.17 ≤ d ≤ 0.4, for example, it can be a range of 0.17, 0.18, 0.2, 0.22, 0.25, 0.3, 0.32, 0.35, 0.38, 0.4 or any two of these values.

[0060] In one implementation, 76≤e≤120, for example, can be a range of 76, 78, 80, 85, 90, 95, 100, 105, 110, 115, 120 or any two of these values.

[0061] In one embodiment, the first additive comprises a silicon-containing compound and a fluorocarbonate, wherein the mass ratio of the silicon-containing compound to the fluorocarbonate is (0.5-2):1. This application uses a combination of a silicon-containing compound and a fluorocarbonate with a mass ratio of (0.5-2):1 as the first additive, which can more effectively improve the stability of the electrolyte, promote the formation of a more uniform and dense interface film, suppress electrolyte decomposition and side reactions under high voltage, further reduce interface impedance, and improve the energy efficiency of the secondary battery.

[0062] In one embodiment, the silicon-containing compound includes at least one of tris(trimethylsilane) phosphate and tris(trimethylsilane) borate.

[0063] In one embodiment, the fluorocarbonate comprises at least one of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate.

[0064] In one embodiment, the electrolyte further includes a second additive and a third additive.

[0065] In one embodiment, the second additive comprises at least one of vinyl sulfate, 1,3-propane sulpholactone, methylene disulfonate, propenyl-1,3-sulfonyl lactone, N,N'-thiodiimidazole, triphenyl phosphonite, n-butyric anhydride, hexanetrionitrile, succinate, and tetrafluoroterephthalonitrile.

[0066] In one embodiment, the third additive includes at least one of lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl-imidazolium lithium, and lithium trifluoromethanesulfonate.

[0067] This application employs a combination of the three types of additives mentioned above. The first additive effectively improves the stability of the initial interface film formation of the negative electrode and reduces internal resistance. The second additive improves the stability of the high-temperature interface film formation of the initial interface between the positive and negative electrodes. The third additive effectively ensures the interface state of the initial SEI inorganic layer of the secondary battery, forming a structure with low impedance, high temperature resistance, dense film formation, and high electronic insulation. After thermal runaway, the reactivity of polymers such as binders containing CF bonds on the active surface of the negative electrode and the positive electrode sheet is reduced, thereby reducing H2 generation, effectively reducing interface impedance, and improving the energy efficiency of the secondary battery.

[0068] In one embodiment, the second additive accounts for 0.1% to 1% of the mass percentage of the electrolyte, for example, it can be 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, 1%, or any two of these values. In particular, when the mass percentage of the second additive in the electrolyte is controlled within this range, a protective interface film with high temperature resistance and chemical stability is formed at the positive and negative electrode interfaces, effectively reducing side reactions at high temperatures and mitigating corrosion of the positive and negative electrodes.

[0069] In one embodiment, the third additive accounts for 0.05% to 0.5% of the mass percentage of the electrolyte, for example, it can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any two of these values. In particular, when the mass percentage of the third additive in the electrolyte is controlled within this range, the film-forming interface state of the initial SEI inorganic layer of the secondary battery can be more effectively guaranteed, forming a structure with low impedance, high temperature resistance, dense film formation, and high electronic insulation, thereby reducing interface impedance and improving the energy efficiency of the secondary battery.

[0070] In one embodiment, the second additive comprises vinyl sulfate, and the third additive comprises lithium difluorooxalate borate, wherein the vinyl sulfate accounts for F% of the mass percentage of the electrolyte, and the lithium difluorooxalate borate accounts for G% of the mass percentage of the electrolyte, satisfying: 0.1 <F<1,1≤F / G≤10。

[0071] In one embodiment, the electrolyte further includes a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate; the concentration of the lithium salt in the electrolyte is 0.5 to 1.3 M, for example, it can be 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1 M, 1.1 M, 1.2 M, 1.3 M or any two of these values.

[0072] In one embodiment, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates.

[0073] In one embodiment, the cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, and propylene carbonate.

[0074] In one embodiment, the chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0075] In one embodiment, the cyclic carbonate accounts for 30-40% of the organic solvent by mass, for example, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any combination of two of these values.

[0076] In one embodiment, the chain carbonate accounts for 60-70% of the organic solvent by mass, for example, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, or any combination of two of these values.

[0077] In one embodiment, the positive electrode sheet 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 including a positive active material.

[0078] In one embodiment, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate.

[0079] In one embodiment, the positive electrode active material comprises Li a Fe 1-b M b Compounds of PO4, wherein 0.8 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.9, and M is selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Ti, V, Mg, and Al.

[0080] In one embodiment, the type of positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0081] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0082] In one embodiment, the positive electrode active material layer further includes a conductive agent and a binder.

[0083] In one embodiment, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including 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 including a negative active material.

[0084] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0085] In one embodiment, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12At least one of Li-Al alloys and metallic lithium.

[0086] In one embodiment, the negative electrode active material layer further includes a conductive agent and a binder.

[0087] In one embodiment, there is no limitation on the type of conductive agent mentioned in this application, and any known conductive agent may be used.

[0088] In one embodiment, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0089] In one embodiment, there is no limitation on the type of adhesive mentioned in this application, and any known adhesive may be used.

[0090] In one embodiment, the adhesive includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydrogenation, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0091] In the secondary battery mentioned in this application, a separator is usually provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0092] In the secondary battery mentioned in this application, a separator is usually provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0093] In one embodiment, the diaphragm comprises a porous sheet-like or nonwoven material with excellent liquid retention properties. Materials for resin or glass fiber diaphragms include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone.

[0094] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the diaphragm described above can be used alone or in any combination.

[0095] In one embodiment, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0096] In one embodiment, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0097] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0098] One embodiment of this application provides an electrical device including the secondary battery described above.

[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] The present application is further illustrated below with specific embodiments:

[0101] Example 1

[0102] Example 1 provides a secondary battery, including a stacked cell with a height of 207 mm, a width of 352 mm, and a thickness of 71.5 mm. The preparation method of this secondary battery includes the following steps:

[0103] (1) Preparation of positive electrode sheet

[0104] Lithium iron phosphate (LiFePO4), acetylene black (Super P), polyvinylidene fluoride (PVDF), and polyether phosphate were mixed uniformly at a mass ratio of 97.55:1.8:0.5:0.15, and then uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a homogeneous positive electrode slurry. The mixed positive electrode slurry was coated on both sides of an aluminum foil, then baked, rolled, and cut into sheets to obtain the positive electrode sheet. The density (PD) of the positive electrode active material layer was 2.6 g / cm³. 3 .

[0105] (2) Preparation of negative electrode sheet

[0106] Graphite, acetylene black (Super P), CMC (sodium carboxymethyl cellulose), SBR (styrene-butadiene rubber), and PAA (polyacrylic acid) were mixed evenly in a mass ratio of 96.7:0.7:0.6:1.5:0.5, and then uniformly dispersed in deionized water to form a homogeneous black slurry. This slurry was coated onto both sides of a copper foil, and after baking, rolling, and cutting, a negative electrode sheet was obtained. The density (PD) of the negative electrode active material layer was 1.6 g / cm³. 3 .

[0107] (3) Preparation of electrolyte

[0108] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), DMC, EMC, and EC were mixed thoroughly at a volume ratio of 30:30:40. Molecular sieve dehydration is performed. 6% LiFSI and 6% LiPF6 by mass are added sequentially to the resulting mixed solvent. The mixture is continuously stirred and cooled. When the electrolyte temperature rises by no more than 2°C, lithium salt can be added further, ultimately yielding a colorless and transparent liquid. Then, 0.50 wt% of tris(trimethylsilane)phosphate (TMSP), 0.50 wt% of ethylene sulfate (DTD), 0.50 wt% of fluoroethylene carbonate (FEC), and 0.2 wt% of lithium difluorooxalate borate (LiODFB) are added and stirred until homogeneous to obtain the electrolyte described in this application.

[0109] (4) Assembly of secondary batteries:

[0110] The positive electrode, separator (made of Xingyuan material PE (9μm) + ceramic (2μm) + adhesive layer (5μm) + adhesive layer (5μm), total thickness 21μm) and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode. After stacking, a battery cell is obtained. The battery cell is then encapsulated in a square aluminum shell, dried, and injected with 2400g of electrolyte. After wetting, formation, sealing, and capacity testing, a secondary battery is obtained.

[0111] The parameters of Example 1 are shown in Table 1.

[0112] Examples 2-8, Comparative Examples 1-3

[0113] The difference between Examples 2-8 and Comparative Examples 1-3 and Example 1 is that the amounts of FEC and TMSP were adjusted in Examples 2-8 and Comparative Examples 1-3, thereby adjusting the value of a, as shown in Table 1.

[0114] Examples 9-13, Comparative Examples 4-5

[0115] The difference between Examples 9-13 and Comparative Examples 4-5 and Example 1 is that in Examples 9-13 and Comparative Examples 4-5, b and e are adjusted by adjusting the amount of positive electrode slurry coated on the current collector and the number of layers of the positive electrode sheet, as shown in Table 1.

[0116] Examples 14-17

[0117] The difference between Examples 14-17 and Example 1 is that the value of c is adjusted in Examples 14-17, as shown in Table 1.

[0118] Examples 18-22

[0119] The difference between Examples 18-22 and Example 1 is that the value of d is adjusted in Examples 18-22, as shown in Table 1.

[0120] Comparative Examples 6-7

[0121] The difference between Comparative Examples 6 and 7 and Example 1 is that the values ​​of c and d are adjusted in Comparative Examples 6 and 7, as shown in Table 1.

[0122] Table 1

[0123]

[0124] Examples 23-27

[0125] The difference between Examples 23-27 and Example 1 is that the contents of DTD and LiODFB in the electrolyte of the secondary batteries described in Examples 23-27 are different, as shown in Table 2.

[0126] Table 2

[0127]

[0128] Test case

[0129] Room temperature DCR test method: At 25±2℃, the secondary batteries of the examples and comparative examples were charged to 3.65V at 0.5C, then discharged at 0.5C capacity for 60min. After adjusting to 50% SOC, they were pulsed discharged at 1C constant current for 10s. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current. The test results are shown in Table 3.

[0130] Energy efficiency test method: At 25±2℃, the secondary batteries of the examples and comparative examples were charged to 3.65V with a charging power of 0.5P, and then discharged to 2.5V with a discharging power of 0.5P. The energy efficiency was calculated as (discharge energy / charging energy) * 100%. The test results are shown in Table 3.

[0131] High and low temperature performance test method (high and low temperature energy efficiency): At 5±2℃ and 45±2℃, the secondary batteries of the examples and comparative examples were charged to 3.65V with a charging power of 0.5P and then discharged to 2.5V with a discharging power of 0.5P. The energy efficiency was calculated as (discharge energy / charging energy) * 100%. The test results are shown in Table 3.

[0132] Table 3

[0133]

[0134]

[0135] As can be seen from Table 3, this application, by controlling the total content of silicon-containing compounds and fluorocarbonates in the electrolyte, the single-sided areal density and number of layers of the positive electrode sheet, and the height and width of the stacked cell to satisfy certain relationships, can construct an SEI and CEI interface layer with lower reactivity, reduce side reactions of the electrolyte, enhance the low-temperature and high-temperature stability of the SEI interface layer, inhibit the oxidative decomposition of the electrolyte, optimize the ionic conductivity of the interface film, improve the wettability of the electrolyte, effectively increase the wetting rate, improve the utilization rate of positive and negative electrode active materials, reduce gas production in the secondary battery, effectively reduce the interface impedance, and improve the energy efficiency of the secondary battery.

[0136] Comparing Examples 1 to 4, it can be seen that by controlling the mass percentage of the first additive in the electrolyte to be 1% to 3%, the interfacial impedance can be further reduced and the energy efficiency of the secondary battery can be improved.

[0137] Comparing Examples 1 and 5-8, it can be seen that by using a silicon-containing compound and fluorinated carbonate in a mass ratio of (0.5-2):1 as the first additive, the present invention can further reduce the interfacial impedance and improve the energy efficiency of the secondary battery.

[0138] Comparing Examples 1 and 9-13, it can be seen that by controlling 0.15≤b≤0.26 and 76≤e≤120, the interface impedance can be further reduced and the energy efficiency of the secondary battery can be improved.

[0139] Comparing Examples 1 and 14-17, it can be seen that by controlling 0.207≤c≤0.215, the interface impedance can be further reduced and the energy efficiency of the secondary battery can be improved.

[0140] Comparing Examples 1 and 18-22, it can be seen that by controlling 0.17≤d≤0.4, the interface impedance can be further reduced and the energy efficiency of the secondary battery can be improved.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention 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 the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery, comprising a stacked battery cell and an electrolyte, wherein the stacked battery cell comprises a positive electrode, a negative electrode, and a separator stacked together, characterized in that, The electrolyte includes a first additive, which includes a silicon-containing compound and a fluorocarbonate. The secondary battery satisfies: 0.277≤Y≤11.076; Wherein, a% is the mass percentage of the first additive in the electrolyte, and 0.1≤a≤4; b mg / mm 2 The areal density of one side of the positive electrode sheet is 0.08 ≤ b ≤ 0.3; cm is the height of the stacked battery cell, 0.18≤c≤0.26; dm is the width of the stacked battery cell, 0.16≤d≤0.5; e is the number of stacked layers of the positive electrode sheet, where 66≤e≤125; The silicon-containing compound includes at least one of tris(trimethylsilane) phosphate and tris(trimethylsilane) borate; the fluorocarbonate includes at least one of fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, and 4-trifluoromethylethylene carbonate.

2. The secondary battery according to claim 1, characterized in that, Satisfy at least one of the following (1) to (5): （1）1≤a≤3； （2）0.15≤b≤0.26； （3）0.207≤c≤0.215； （4）0.17≤d≤0.4； （5）76≤e≤120。 3. The secondary battery according to claim 1, characterized in that, The first additive comprises a silicon-containing compound and a fluorocarbonate, wherein the mass ratio of the silicon-containing compound to the fluorocarbonate is (0.5~2):

1.

4. The secondary battery according to claim 1, characterized in that, The electrolyte also includes a second additive and a third additive; The second additive includes at least one of vinyl sulfate, 1,3-propane sulpholactone, methylene disulfonate, propenyl-1,3-sulfonate lactone, N,N'-thiodiimidazole, triphenyl phosphonite, n-butyric anhydride, hexanetrionitrile, succinate, and tetrafluoroterephthalonitrile. The third additive includes at least one of lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium difluorodi(oxalato)phosphate, lithium difluorophosphate, lithium 4,5-dicyano-2-trifluoromethyl-imidazolium lithium, and lithium trifluoromethanesulfonate.

5. The secondary battery according to claim 4, characterized in that, The second additive accounts for 0.1% to 1% of the mass of the electrolyte; And / or, the third additive accounts for 0.05~0.5% of the mass percentage of the electrolyte.

6. The secondary battery according to claim 4, characterized in that, The second additive comprises vinyl sulfate, and the third additive comprises lithium difluorooxalate borate, wherein the vinyl sulfate accounts for F% of the mass percentage of the electrolyte, and the lithium difluorooxalate borate accounts for G% of the mass percentage of the electrolyte, satisfying: 0.1 <F<1,1≤F / G≤10。 7. The secondary battery according to claim 1, characterized in that, The electrolyte also includes a lithium salt, which includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate; the concentration of the lithium salt in the electrolyte is 0.5~1.3M.

8. An electrical device, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 7, wherein the secondary battery serves as the power supply for the electrical device.

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