Cylindrical battery

Abstract

The invention relates to the technical field of batteries, and particularly provides a cylindrical battery which comprises an electrode assembly, a shell and a top cover assembly, the top cover assembly comprises a cover body and a flow collecting disc, the cover body covers the opening of the shell and is provided with an anti-explosion valve, the flow collecting disc is provided with an air guide hole, the air guide hole and the anti-explosion valve are at least partially overlapped, and the area proportion A of the overlapped area in the anti-explosion valve is 8%-30%; the electrode assembly comprises a positive plate, the positive plate comprises a positive active layer, the positive active layer comprises a ternary material, the electrolyte comprises ethylene carbonate (EC) and propylene carbonate (PC), the mass contents of the EC and the PC in the electrolyte are a and b respectively, and a / b is more than or equal to 0.17 and less than or equal to 3. In the invention, the oxidation stability of EC is lower than that of PC, and the EC is easier to oxidize and produce gas on the positive plate, the high-temperature gas production performance of the battery is improved by controlling the content of EC and PC, and the gas is discharged in time and the risk of thermal runaway is prevented by matching with the gas guide hole and the explosion-proof valve.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and specifically provides a cylindrical battery. BACKGROUND

[0002] With the rapid development of new energy vehicles and energy storage systems, cylindrical batteries are widely used due to their stable structure and mature manufacturing process. A cylindrical battery is usually composed of an electrode assembly, a shell and a top cover assembly. As an important part of the battery, the top cover assembly not only bears the electrical connection function, but also needs to have a safety protection function. At present, the top cover assembly of the cylindrical battery usually includes a top cover sheet, a current collector plate and a pressure relief valve.

[0003] However, there are still some technical problems in the design of the existing cylindrical battery. First, during the charging and discharging process, the decomposition of electrolyte or the side reaction of the positive electrode material can cause gas to be generated. If the gas cannot be discharged in time, it may cause the internal pressure to rise, and even lead to thermal runaway. Second, in the existing top cover assembly of the cylindrical battery, the current collector plate often blocks the exhaust path of the pressure relief valve, causing the gas to be discharged to be blocked, and reducing the pressure relief efficiency of the pressure relief valve. In addition, the structural design of the pressure relief valve and the current collector plate does not fully consider the optimization of the gas flow path, and there is a risk of gas retention. SUMMARY

[0004] The purpose of the present application is to solve at least part of the technical problems mentioned in the above content, and the purpose is achieved by the following technical scheme: The present application provides a cylindrical battery, which includes an electrode assembly, a shell and a top cover assembly. The electrode assembly includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the separator and the negative electrode sheet are wound to form a roll core; the shell is in a cylindrical shape and is provided with an opening at least at one end, and the roll core is accommodated in the shell; the top cover assembly includes a cover body and a current collector plate, the cover body covers the opening and is provided with a pressure relief valve, the current collector plate is arranged on the side of the cover body facing the electrode assembly, and the current collector plate is electrically connected with the electrode assembly; the current collector plate is provided with a gas guide hole, the projection of the gas guide hole on the cover body at least partially overlaps the pressure relief valve, and the area ratio A of the overlapping area in the pressure relief valve is 8% to 30%; the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes a ternary material, the electrolyte includes an organic solvent, the organic solvent includes ethylene carbonate and propylene carbonate, the mass content of ethylene carbonate in the electrolyte is a, the mass content of propylene carbonate in the electrolyte is b, and 0.17≤a / b≤3 is satisfied.

[0005] In some embodiments, the mass content a of ethylene carbonate in the electrolyte satisfies 5%≤a≤30%, and / or the mass content b of propylene carbonate in the electrolyte satisfies 5%≤b≤30%.

[0006] In some embodiments, the gas guide holes are provided in at least two, and the diameter of the gas guide holes is d1, the distance between the adjacent two gas guide holes is d2, and 1.5mm≤d1≤4mm, and / or 3mm≤d2≤6.3mm, and / or 1:3.8≤d1 / d2≤1:1.2 are satisfied.

[0007] In some embodiments, the sum of the areas of the gas guide holes is S1, the area of the current collector is S2, and 1.77mm 2 ≤S1≤25.12mm 2 , and / or 227mm 2 ≤S2≤1590mm 2 , and / or 0.5%≤S1 / S2≤12% are satisfied.

[0008] In some embodiments, the area of the explosion-proof valve is S3, the area of the cover is S4, and 20mm 2 ≤S3≤64mm 2 , and / or 254mm 2 ≤S4≤1662mm 2 , and / or 2%≤S3 / S4≤22% are satisfied.

[0009] In some embodiments, the chemical formula of the ternary material in the positive active layer is LiNi x Co y Mn z O2, wherein x+y+z=1, 0.5≤x≤0.98, 0.02≤y≤0.3, 0.02≤z≤0.2; the ternary material is a single crystal structure; the ternary material further comprises a doping element, the doping element is selected from one or more of Zr and W; the average particle size of the ternary material is d4, and 0.3μm≤d4≤4μm are satisfied.

[0010] In some embodiments, the thickness of the positive current collector is d5, the thickness of the positive active layer is d6, and 6μm≤d5≤25μm, and / or 40μm≤d6≤150μm, and / or 1:15≤d5 / d6≤1:1.6 are satisfied.

[0011] In some embodiments, the organic solvent further comprises fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate in the electrolyte is c, and 0.1%≤c≤10% are satisfied.

[0012] In some embodiments, the electrolyte further comprises a sulfur-containing compound, the sulfur-containing compound comprises one or more of 1,3-propane sultone, propylene-1,3-sulfonic acid lactone, ethylene sulfate, ethylene sulfite, thiophene; the mass content e of the sulfur-containing compound in the electrolyte is 0.5% to 5%; and / or, the positive active layer contains Ni element, the ratio of the content of the sulfur-containing compound to the content of the Ni element in the positive active layer is 1:50 to 1:4; and / or, the electrolyte further comprises a lithium salt, the lithium salt comprises lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide, and the total mass content of the two is 10% to 20% of the electrolyte.

[0013] In some embodiments, the separator comprises a base film and a coating layer arranged on the surface of the base film; the base film is one of polyethylene, polypropylene, and polypropylene / polyethylene composite film, and / or the coating layer comprises ceramic particles, the ceramic particles are one of alumina, boehmite, and magnesium oxide; and / or, the thickness of the base film is d7, the thickness of the coating layer is d8, and 6um≤d7≤25um and / or 2um≤d8≤15um are satisfied.

[0014] The technical scheme provided in the present application has at least the following technical effects: In the present application, the electrolyte solvent comprises cyclic carbonates, i.e. ethylene carbonate (EC) and propylene carbonate (PC), which can well dissociate lithium salt, but EC in the two cyclic carbonates is more likely to be oxidized at the ternary positive electrode, because EC forms a solvated structure by coordinating with Li+ and migrates to the positive electrode surface active site together with Li+, so that EC contacts the positive electrode surface, and the H on the two methylene groups is oxidized by the TM-O2 (transition metal oxide) on the positive electrode surface, causing EC to decompose. The molecular structure of PC is -CH3 instead of H in EC, so that when PC contacts the positive electrode surface, the TM-O2 on the positive electrode surface cannot contact the H on the methylene group due to the steric hindance of -CH3, so PC cannot be oxidized to decompose. Therefore, the oxidation stability of EC is not as good as that of PC, and EC is more likely to be oxidized to produce gas at the positive electrode. By controlling the contents of the two within a specific range, the high-temperature gas production performance of the battery is improved. In addition, the gas guide hole is arranged on the current collector plate, and the projection of the gas guide hole on the cover at least partially overlaps the explosion-proof valve, and the area ratio of the overlapping area in the explosion-proof valve is within a specific range, so that the gas produced by the battery in the case of thermal runaway can be more directly discharged through the gas guide hole and the explosion-proof valve, improving the exhaust efficiency. Even in the case of excessive gas production, the gas can be discharged in time by matching the area of the gas guide hole and the explosion-proof valve, avoiding the aggravation of the accumulation of gas in the battery, preventing the risk of thermal runaway, and improving the safety performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to better combine the content shown in the drawings of the specification with the content described in the specific embodiments, the drawings of the specification are briefly introduced as follows. It can be understood that the drawings of the specification mentioned below only show some embodiments of the related technical solutions and the technical solutions of the present application, and one skilled in the art can also make drawings showing other embodiments without creative labor.

[0016] Specifically, the annotations of the drawings of the specification are as follows: Figure 1 The schematic diagram of the explosion of the cylindrical battery described in some embodiments of the present application; Figure 2 The schematic diagram of the structure of the top cover assembly described in some embodiments of the present application.

[0017] Specifically, the annotations of the drawings of the specification are as follows: 10, electrode assembly; 20, shell; 30, cover; 301, explosion-proof valve; 40, current collector plate; 401, air guide hole. Specific embodiments

[0018] In order to make the content of the embodiments of the present application more clear, the following will be described in conjunction with the drawings of the specification. It can be understood that the content mentioned below is only part of the embodiments of the present application, and all the embodiments are not exhaustively listed. Therefore, other embodiments obtained based on the following embodiments fall within the protection scope of the present application without creative labor.

[0019] It should be understood that the terms used herein are only for the purpose of describing specific embodiments and are not intended to strictly limit the technical solutions, unless the context clearly indicates otherwise. For example, the terms "one", "a" and "said" used herein to modify a feature do not exclude the possibility that the feature can be plural in other embodiments.

[0020] It should be understood that the terms "include", "contain" and "have" are open, which indicates the presence of the stated features, but does not exclude the possibility that other features also exist in the embodiments. Similarly, the terms "first", "second" and the like are used herein to describe multiple features, which only indicate that one feature is distinguished from another feature, and unless the context clearly indicates otherwise, such terms do not imply order or sequence.

[0021] It should be understood that unless the context clearly indicates otherwise, the terms "set", "connect", "mount" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through a medium. For one skilled in the art, the specific meaning of the above terms in the text can be understood according to the specific circumstances.

[0022] In addition, for the convenience of description, the spatial relative terms are used to describe the position of one feature relative to another feature, such as "inner", "outer", "end", "side", "upper", "middle", "lower", "high", "low", "axial", "circumferential", "radial", "horizontal", "vertical", "first direction", "second direction", and the like. It can be understood that the spatial relative relationship between two features should include other specific conditions other than those shown in the drawings.

[0023] The embodiments of the present application are described below in conjunction with the drawings. It can be understood that the technical features involved in the different embodiments described below can be combined with each other as long as they do not conflict with each other.

[0024] The present application provides a cylindrical battery, referring to Figure 1 and Figure 2 , which comprises an electrode assembly 10, a shell 20 and a top cover assembly. The electrode assembly 10 comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the separator and the negative electrode sheet are wound to form a roll core; the shell 20 is cylindrical and at least one end is provided with an opening, and the roll core is accommodated in the shell 20; the top cover assembly comprises a cover body 30 and a current collector plate 40, the cover body 30 seals the opening and is provided with a pressure relief valve 301, the current collector plate 40 is arranged on the side of the cover body 30 facing the electrode assembly 10, and the current collector plate 40 is electrically connected with the electrode assembly 10; the current collector plate 40 is provided with a gas guide hole 401, the projection of the gas guide hole 401 on the cover body 30 at least partially overlaps the pressure relief valve 301, and the area ratio A of the overlapping area in the pressure relief valve 301 is 8% to 30%; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises a ternary material, the electrolyte comprises an organic solvent, the organic solvent comprises ethylene carbonate and propylene carbonate, the mass content of ethylene carbonate in the electrolyte is a, the mass content of propylene carbonate in the electrolyte is b, and 0.17≤a / b≤3 is satisfied.

[0025] In the present embodiment, the electrolyte solvent comprises cyclic carbonates, i.e. ethylene carbonate (EC) and propylene carbonate (PC), which can well dissociate lithium salt, but EC in the two cyclic carbonates is more prone to oxidation at the ternary positive electrode. This is because EC and Li + form a coordination structure to form a solvated structure, and the solvated structure is more prone to oxidation. +The EC is migrated to the positive electrode surface active site together, so that the EC contacts the positive electrode surface, and the H on the two methylene groups is oxidized by the TM-O2 (transition metal oxide) on the positive electrode surface, causing the EC to decompose. The molecular structure of the PC is -CH3 instead of H in the EC, so that when the PC contacts the positive electrode surface, the TM-O2 on the positive electrode surface cannot contact the H on the methylene group due to the steric hindrance of -CH3, and thus cannot oxidize the PC to cause decomposition. Therefore, the oxidation stability of EC is not as good as that of PC, and EC is more prone to oxidation to produce gas at the positive electrode. By controlling the contents of the two within a specific range, the high-temperature gas production performance of the battery is improved. In addition, the gas guide hole is arranged on the current collector plate, and the projection of the gas guide hole on the cover body at least partially overlaps the explosion-proof valve, and the area ratio of the overlapping area in the explosion-proof valve is within a specific range, so that the battery can more directly discharge the generated gas through the gas guide hole and the explosion-proof valve in the case of thermal runaway, thereby improving the exhaust efficiency. Even in the case of excessive gas production, the area of the gas guide hole 401 and the explosion-proof valve 301 can timely discharge the gas, avoid aggravating the accumulation of gas in the battery, prevent the risk of thermal runaway, and improve the safety performance of the battery.

[0026] Further, the ratio of the mass content a of ethylene carbonate in the electrolyte to the mass content b of propylene carbonate in the electrolyte satisfies the condition 0.17≤a / b≤3, which ensures a reasonable ratio of the easy-gas-producing components in the electrolyte. This ratio range effectively reduces the gas production of the battery under high-temperature or overcharge conditions, improving the safety performance of the battery. When the a / b ratio is too low, the content of ethylene carbonate is relatively insufficient, making it difficult to form a stable SEI film, leading to continuous decomposition of the electrolyte; when the a / b ratio is too high, the content of ethylene carbonate is too high, which is prone to decomposition and gas production under high-temperature conditions, aggravating the accumulation of gas in the battery and increasing the risk of thermal runaway.

[0027] Specifically, a / b can take any one of 0.17, 0.5, 1, 1.5, 2, 2.5, and 3 or a range between any two of them.

[0028] In addition, it should be understood that the area ratio A of the projection overlap area of the gas guide hole 401 and the explosion-proof valve 301 in the explosion-proof valve 301 satisfies 8% to 30%; if A is too small, the exhaust path will be limited, affecting the exhaust efficiency and there is a risk of thermal runaway; if A is too large, the area of the gas guide hole 401 is too large, forming a stress concentration point, reducing the overall mechanical resistance of the battery, and easily causing the current collector plate 40 to break during the cycling process, affecting the cycling ability.

[0029] In some embodiments, the mass content a of ethylene carbonate in the electrolyte satisfies 5%≤a≤30%, and / or the mass content b of propylene carbonate in the electrolyte satisfies 5%≤b≤30%.

[0030] In the present embodiment, the mass content a of ethylene carbonate in the electrolyte can take any of 5%, 10%, 15%, 20%, 25%, and 30% or a range between any two of them; the mass content b of propylene carbonate in the electrolyte can take any of 5%, 10%, 15%, 20%, 25%, and 30% or a range between any two of them.

[0031] In some embodiments, at least two gas guide holes 401 are provided, and the diameter of the gas guide hole 401 is d1, the distance between adjacent two gas guide holes 401 is d2, and satisfy 1.5mm≤d1≤4mm, and / or 3mm≤d2≤6.3mm, and / or 1:3.8≤d1 / d2≤1:1.2.

[0032] In the present embodiment, the diameter d1 of the gas guide hole 401 satisfies 1.5mm≤d1≤4mm, the distance d2 between adjacent gas guide holes 401 satisfies 3mm≤d2≤6.3mm, and the ratio d1 / d2 satisfies 1:3.8≤d1 / d2≤1:1.2. This parameter range ensures that the gas can be effectively discharged while maintaining the integrity of the battery structure. When the ratio of the hole diameter to the hole spacing is less than 1:3.8, the too small hole diameter limits the gas release speed, causing the internal pressure to continue to rise, and the too large hole spacing also reduces the area of the gas guide hole overlapping with the explosion-proof valve, affecting the gas discharge rate; when the ratio of the two is greater than 1:1.2, the too large hole diameter will cause the mechanical strength of the current collector plate to decrease, causing deformation or rupture under external force, increasing the safety risk, in addition, the too large hole diameter will also affect the welding area of the current collector plate and the tab, reducing the overcurrent area of the cell.

[0033] Further, d1 can take any of 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, and 4mm or a range between any two of them; d2 can take any of 3mm, 4mm, 5mm, 6mm, and 6.3mm or a range between any two of them.

[0034] In some embodiments, the sum of the areas of the gas guide holes 401 is S1, the area of the current collector plate 40 is S2, and satisfy 1.77mm 2 ≤S1≤25.12mm 2 , and / or 227mm 2 ≤S2≤1590mm 2 , and / or 0.5%≤S1 / S2≤12%.

[0035] In the present embodiment, the sum of the areas of the gas guide holes 401 S1 satisfies 1.77mm 2 ≤S1≤25.12mm 2 , and the area S2 of the current collector plate 40 satisfies 227mm 2 ≤S2≤1590mm2 , and the ratio of S1 / S2 satisfies 0.5%≤S1 / S2≤12%. The ratio range ensures sufficient exhaust passage while not affecting the mechanical strength and electrical conductivity of the current collector plate 40. When the ratio of S1 / S2 is lower than 0.5%, the total area of the gas guide hole 401 is insufficient, the gas release rate is lower than the gas production rate, and the internal pressure continuously rises; when the ratio of S1 / S2 is higher than 12%, the excessive area of the gas guide hole 401 reduces the mechanical strength of the current collector plate, which deforms or breaks when subjected to external force, increasing the safety risk.

[0036] Further, the number of the gas guide hole 401 is not limited, for example, it can be one or two, etc. Specifically, the sum of the areas S1 of the gas guide hole 401 can be any one of 1.77mm 2 , 2mm 2 , 3mm 2 , 4mm 2 , 5mm 2 , 6mm 2 , 7mm 2 , 8mm 2 , 9mm 2 , 10mm 2 , 11mm 2 , 12mm 2 , 15mm 2 , 20mm 2 , 25mm 2 , and 25.12mm 2 , or a range between any two of them; S2 can be any one of 227mm 2 , 300mm 2 , 400mm 2 , 500mm 2 , 600mm 2 , 700mm 2 , 800mm 2 , 900mm 2 , 1000mm 2 , 1100mm 2 , 1200mm 2 , 1300mm 2 , 1400mm 2 , 1500mm 2 , and 1590mm 2 , or a range between any two of them; S1 / S2 can be any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, and 12%, or a range between any two of them.

[0037] In some embodiments, the area of the explosion-proof valve 301 is S3, the area of the cover 30 is S4, and the following conditions are satisfied: 20mm 2 ≤ S3≤ 64mm 2 , and / or 254mm 2 ≤ S4≤ 1662mm 2 , and / or 2%≤ S3 / S4≤ 22%.

[0038] In the present embodiment, the area S3 of the explosion-proof valve 301 satisfies 20mm 2 ≤ S3≤ 64mm 2 , the area S4 of the cover 30 satisfies 254mm 2 ≤ S4≤ 1662mm 2 , and the ratio S3 / S4 satisfies 2%≤ S3 / S4≤ 22%. The ratio range ensures that the explosion-proof valve 301 can work effectively, neither too early nor too late. When the ratio S3 / S4 is less than 2%, the area of the explosion-proof valve 301 is too small, and high pressure is required to trigger the rupture, resulting in prolonged dangerous pressure accumulation time; when the ratio is greater than 22%, the area of the explosion-proof valve 301 is too large, and the valve breaking threshold is too low and breaks prematurely, causing electrolyte leakage, leading to battery failure or short circuit, and a large-area explosion-proof valve also weakens the structural strength of the cover, making it more prone to deformation or damage under external impact.

[0039] Further, in some embodiments, the area S3 of the explosion-proof valve 301 can refer to the area selected by the circular dashed line frame as shown in Figure 2 . Specifically, S3 can take any one of 20mm 2 , 30mm 2 , 40mm 2 , 50mm 2 , 60mm 2 , and 64mm 2 , or a range between any two of them; S4 can take any one of 254mm 2 , 300mm 2 , 400mm 2 , 500mm 2 , 600mm 2 , 700mm 2 , 800mm 2 , 900mm 2 , 1000mm 2 , 1100mm 2 , 1200mm 2 , 1300mm 2 , 1400mm 2 , 1500mm 2 , 1600mm 2 , and 1662mm 2Any one of the values or a range between any two of the values; S3 / S4 can take any one of the values 2%, 5%, 10%, 15%, 20%, and 22% or a range between any two of the values.

[0040] In some embodiments, the chemical formula of the ternary material in the positive electrode active layer is LiNi x Co y Mn z O2, wherein x+y+z=1, 0.5≤x≤0.98, 0.02≤y≤0.3, 0.02≤z≤0.2; the ternary material is a single crystal structure; the ternary material further comprises a doping element selected from one or more of Zr and W; the average particle size of the ternary material is d4, and satisfies 0.3 μm≤d4≤4 μm.

[0041] In the present embodiment, the positive electrode active material is a ternary material LiNi x Co y Mn z O2 (x+y+z=1, 0.5≤x≤0.98, 0.02≤y≤0.3, 0.02≤z≤0.2), adopts a single crystal structure and is doped with Zr or W elements, and the average particle size d4 satisfies 0.3 μm≤d4≤4 μm. The positive electrode ternary material adopts a single crystal particle, the single crystal particle has high structural integrity, the material has higher thermal stability, has fewer side reactions with the electrolyte, and has lower heat production, which makes the battery exhibit better safety in a high temperature environment. Doping the ternary positive electrode material with one or more of Zr or W effectively inhibits the lattice distortion, phase transition and particle cracking of the ternary material caused by lithium ion deintercalation during charging and discharging, reduces the direct contact of the active material with the electrolyte, inhibits the dissolution of transition metals, reduces the side reactions of electrolyte decomposition to generate gas, thereby reducing gas production and improving the safety performance of the battery.

[0042] Further, the average particle size d4 of the ternary material can take any one of the values 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm and 4 μm or a range between any two of the values. The average particle size of the above-mentioned ternary material can be tested according to the following process: in a scanning electron microscope field with a magnification of 10,000 times, the particle size of the ternary positive electrode active material particle is tested, and then an average value is taken to obtain the average particle size of the ternary positive electrode active material.

[0043] In some embodiments, the thickness of the positive electrode current collector is d5, the thickness of the positive electrode active layer is d6, and satisfies 6 μm≤d5≤25 μm, and / or 40 μm≤d6≤150 μm, and / or 1:15≤d5 / d6≤1:1.6.

[0044] In the present embodiment, the positive electrode current collector thickness d5 satisfies 6 pm≤d5≤25 pm, the positive electrode active layer thickness d6 satisfies 40 pm≤d6≤150 pm, and the d5 / d6 ratio satisfies 1:15≤d5 / d6≤1:1.6. The ratio range ensures good electrical conductivity and electrode performance while avoiding unnecessary increases in volume and weight. When the d5 / d6 ratio is less than 1:15, the excessively thin aluminum foil results in a large resistance, increased ohmic polarization, intensified heat generation during charging and discharging, and decomposition of the electrolyte; an excessively thick positive electrode active layer thickness prolongs the lithium ion diffusion path, reduces the lithium ion transport efficiency, increases the lithium ion diffusion resistance, reduces the rate performance while intensifying the polarization, and affects the battery life. When the ratio is greater than 1:1.6, the excessively thick aluminum foil increases the overall thickness of the battery, affecting the winding process and reducing the battery energy density, and the excessively thin active layer thickness may result in insufficient adhesion of the active material to the current collector, which is prone to active material shedding or electrode pulverization during the cyclic charging and discharging process.

[0045] Further, d5 can take any one of 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, 19 pm, 20 pm, 21 pm, 22 pm, 23 pm, 24 pm, and 25 pm or a range between any two of them; d6 can take any one of 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, 100 pm, 110 pm, 120 pm, 130 pm, 140 pm, and 150 pm or a range between any two of them.

[0046] In some embodiments, the organic solvent further includes fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate in the electrolyte is c, and satisfies 0.1%≤c≤10%.

[0047] In the present embodiment, fluoroethylene carbonate (FEC) is used as an electrolyte additive, has a high reduction activity, and can be reduced and decomposed on the negative electrode surface before PC intercalation to form a dense SEI film rich in LiF. The interface film has a high mechanical modulus and can effectively resist solvent intercalation, which is beneficial to the protection of the negative electrode and prevents PC from intercalating into the graphite negative electrode; moreover, the interface film has a unique ion sieving property, which builds a fast lithium ion transport channel, and the high bond energy of the C-F bond can also endow the SEI with excellent thermodynamic stability. However, when the weight percentage of FEC in the electrolyte is too high, it will cause the battery to produce HF etching interface at high temperature, leading to intensified battery outgassing, and the fluoro-additive has a large molecular weight and a large density, so too much FEC in the electrolyte will cause the viscosity of the electrolyte to decrease, affecting the transport of lithium ions. Therefore, in order to balance the battery outgassing and high-temperature cycling performance, the mass content of FEC in the electrolyte is controlled within the above range.

[0048] Further, the mass content of the FEC in the electrolyte is c, which can be any one of 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%, or within a range between any two of them.

[0049] In some embodiments, the electrolyte further comprises a sulfur-containing compound, the sulfur-containing compound comprises one or more of 1,3-propane sultone, propenyl-1,3-sulfonic acid lactone, ethylene sulfate, ethylene sulfite, thiophene; the mass content of the sulfur-containing compound in the electrolyte is e, which is 0.5% to 5%; and / or, the positive electrode active layer contains Ni element, the ratio of the content of the sulfur-containing compound to the content of the Ni element in the positive electrode active layer is 1:50 to 1:4; and / or, the electrolyte further comprises a lithium salt, the lithium salt comprises lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide, and the total mass content of the two is 10% to 20% of the electrolyte.

[0050] In the present embodiment, the mass content of the sulfur-containing compound in the electrolyte is e, which is 0.5% to 5%, and the ratio of the content of the sulfur-containing compound to the content of the Ni element in the positive electrode active layer is 1:50 to 1:4. By controlling the mass content of the sulfur-containing compound in the electrolyte and the ratio of the content of the sulfur-containing compound to the content of the Ni element in the positive electrode active layer, the risk of ethylene carbonate (EC) being oxidized to produce gas at the positive electrode side is further reduced, and the high-temperature cycle performance and safety performance of the battery are improved. The addition of the sulfur-containing additive in the electrolyte can form a protective layer on the positive electrode through a preferential oxidation mechanism, reduce the contact between ethylene carbonate and oxygen atoms in the positive electrode material, and reduce the risk of ethylene carbonate being oxidized to produce gas. Specifically, the sulfur-containing additive can generate a CEI film rich in Li2SO3 / Li2SO4 during charging and discharging, the CEI film has an electron tunneling potential barrier of >1.2 eV to form a high-efficiency electron insulation layer, and can reduce the release and oxidation of oxygen at the positive electrode. However, too much addition of the sulfur-containing additive can cause the positive electrode interface to be too thick, resulting in a decrease in the kinetics of the positive electrode due to too large impedance. In addition, when the weight percentage of Ni in the positive electrode active material increases, the concentration of oxygen vacancies on the surface of the positive electrode active material also increases, and the lattice of the positive electrode active material is more likely to release oxygen, which is more likely to react with ethylene carbonate to produce gas. In order to reduce the risk of oxygen release in the lattice, the sulfur-containing additive needs to form a sufficient CEI film on the surface of the ternary material, thereby reducing the release of oxygen, further improving the high-temperature cycle performance of the battery, controlling the ratio of the content of the sulfur-containing compound in the electrolyte to the content of the Ni element in the positive electrode active layer, and improving the matching degree of the sulfur-containing additive and the content of Ni in the ternary material, thereby reducing the release of oxygen and the risk of ethylene carbonate gas production, and further improving the high-temperature cycle performance and safety performance of the battery.

[0051] In the embodiment, the electrolyte lithium salt includes lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide, and the total mass content of the two is 10% to 20% of the electrolyte. Lithium bis(trifluoromethylsulfonyl)imide is introduced into the electrolyte, the lithium salt has high thermal stability, can significantly reduce the relative content of lithium hexafluorophosphate which is sensitive to heat in the electrolyte, effectively inhibit the side reaction of hydrolysis of lithium hexafluorophosphate to generate HF, fundamentally reduce the etching of HF to the positive electrode material, significantly reduce the dissolution of metal ions, and thus improve the high-temperature cycle performance and cycle life of the battery.

[0052] In some embodiments, the separator includes a base film and a coating layer disposed on the surface of the base film; the base film is one of polyethylene, polypropylene, and polypropylene / polyethylene composite film, and / or the coating layer includes ceramic particles, the ceramic particles are one or more of alumina, boehmite, magnesium oxide, zirconium oxide, titanium oxide, and silicon oxide; and / or the thickness of the base film is d7, the thickness of the coating layer is d8, and 6 μm≤d7≤25 μm and / or 2 μm≤d8≤15 μm are satisfied.

[0053] In the embodiment, the thickness d7 of the base film satisfies 6 μm≤d7≤25 μm, and the thickness d8 of the coating layer satisfies 2 μm≤d8≤15 μm. The parameter range improves the thermal stability and mechanical strength of the separator, and reduces the risk of short circuit in the battery.

[0054] Further, d7 can take any one of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, and 25 μm or a range between any two of them; d8 can take any one of 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm or a range between any two of them.

[0055] In some examples, the coating layer further includes a first binder, and the first binder includes one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol, styrene butadiene rubber, ethylene-vinyl acetate copolymer, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, polyurethane polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, or a copolymer system derived from the above polymers.

[0056] In some examples, the ceramic particles have a weight percentage of 92-97% (e.g., 92%, 93%, 94%, 95%, 96%, or 97%) and the first binder has a weight percentage of 3-8% (e.g., 3%, 4%, 5%, 6%, 7%, or 8%) based on the total weight of the coating.

[0057] In some embodiments, the separator film includes a glue layer on the surface of the coating layer or on the other side surface of the substrate layer. The glue layer on the separator film can well bond the positive and negative electrode sheets, so that the bonding between the separator and the electrode sheet is more compact. The glue layer includes one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid resin, polyacrylate, butyl acrylate-acrylonitrile copolymer, polyacrylonitrile, ethylene-acrylic acid copolymer, polyacrylate, and sodium carboxymethyl cellulose.

[0058] Some detailed examples and comparative examples are listed below to illustrate the present application: I. Preparation of the battery Example 1 1. Preparation of the positive electrode sheet: The positive electrode active material ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2), binder PVDF, and conductive carbon black D1 are mixed by stirring to form a uniform and stable mixture. In the mixture, the solid components include 93wt% of the positive electrode active material L1, 2wt% of the binder PVDF, and 5wt% of the conductive carbon black D1. The ternary material (LiNi 0.8 Co 0.1 Mn 0.1 O2) is a single crystal particle with an average particle size of 2.5μm, and the ternary material contains Zr and W as doping elements. NMP is used as the solvent to prepare a positive electrode active material slurry with a solid content of 52wt%. The slurry is uniformly coated on both sides of the carbon-coated aluminum foil with a thickness of 12μm, and then dried and rolled to control the thickness of the positive electrode active layer to 65μm, cut into strips, and punched to obtain the positive electrode sheet P1. 2. Preparation of the negative electrode sheet: The negative electrode active material graphite G1, the binder SBR, and the conductive agent E1 are mixed by stirring to form a uniform and stable mixture. In the mixture, the solid components include 95wt% of the graphite G1, 3wt% of the binder SBR, and 2wt% of the conductive agent E1. Water is used as the solvent to prepare a negative electrode active material slurry with a solid content of 46wt%. The slurry is uniformly coated on both sides of a copper foil with a thickness of 6μm, and then dried and rolled to compact, to obtain the negative electrode sheet N1. 3. Preparation of the separator: the base film is polypropylene (PP); the coating layer includes a ceramic layer and a glue layer, the ceramic layer is located on one side of the base film, and the glue layer is located on the other side of the base film and the surface of the ceramic layer. In the ceramic layer, the composition of the inorganic particles is aluminum oxide, the first binder is PVDF, and the weight ratio of the inorganic particles to the first binder is 95:5; the glue layer is butyl acrylate-acrylonitrile copolymer; the thickness of the base film d7 is 7 μm, the thickness of the single ceramic layer is 3 μm, the thickness of the glue layer is 2 μm, that is, the thickness of the coating layer d8 is 5 μm.

[0059] 4. Preparation of the electrolyte: the electrolysis is carried out in an argon glove box with water content ≤0.1 ppm and oxygen content ≤0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (EMC) and methyl ethyl carbonate (EMC) are mixed uniformly according to the mass ratio of 2:1:3:4, and fully dried lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide salt (LiTFSI) are added and stirred to dissolve, the mass of LiPF6 and LiTFSI added is 3% and 12% of the total mass of the electrolyte, 3% of the total mass of the electrolyte based on fluoroethylene carbonate (FEC) is added, 3% of the total mass of the electrolyte based on 1,3-propane sultone is added, 0.5% of the total mass of the electrolyte based on lithium difluorophosphate (LiPO2F2) is added, and stirring is uniform to obtain the electrolyte.

[0060] 5. After the positive electrode sheet P1, the negative electrode sheet N1 and the separator are wound to form a bare battery cell, the current collecting disc 40 is welded, the shell is entered and the pole is welded, and the battery is baked at 95°C for 24 hours in a high-temperature vacuum oven. After the electrolyte is injected, the battery is formed, sealed, sorted, OCV tested, and a cylindrical battery is obtained.

[0061] II. Test method: 1. The battery cycle test method is as follows: at 45°C, discharge at 3C standard constant current to the discharge termination voltage 2.7V, stand for 30min; then charge at 3C standard constant current and constant voltage to the charge limit voltage 4.2V, the cutoff current is 0.05C, stand for 30min; discharge at 3C standard constant current to the discharge termination voltage 2.7V, stand for 30min; repeat the above full charge and full discharge steps until the capacity decays to 80%, the number of repeated cycles is the cycle number, which is used to evaluate the cycle performance of the battery after aging.

[0062] For example, according to the table below, the high-temperature cycle number of Example 1 is 2315, that is, the battery in Example 1 has undergone 2315 repeated charge and discharge cycles, and its capacity has decayed from 100% to 80%.

[0063] It can be understood that the higher the value in the column of high-temperature cycle number in the table, the less likely the capacity of the battery is to decay, and the better the performance of the battery.

[0064] 2. The hot box test method is as follows: 10 fully charged 100% SOC batteries are placed in a hot box, the temperature is set to 85°C, and the temperature is kept constant for 24 hours. During the test, the battery status is monitored to observe whether it catches fire, smokes, explodes, and whether the shell swells, leaks, etc. After the test, the appearance of the battery is checked. If there is no abnormality, it is considered to pass the test.

[0065] For example, according to the table below, the hot box pass rate in Example 1 is 10 / 10, which means that none of the 10 batteries tested in Example 1 had any abnormalities and all passed the test.

[0066] Specifically, in addition to the data listed in the table and the data involved in the above preparation method, the other conditions of the battery tested in Example 1 are as follows: the current collector 40 is provided with 2 air guide holes 401, the distance d2 between the 2 air guide holes 401 is 4mm, according to the d1 in the table, which is 3mm, i.e. d1 / d2 is 1:1.33; the area S2 of the current collector 40 is 240mm², according to the S1 in the table, which is 14.13mm², i.e. S1 / S2 is 5.89%; the area S4 of the cover body 30 is 280mm², according to the S3 in the table, which is 40mm², i.e. S3 / S4 is 14.29%; the average particle size d4 of the ternary material contained in the positive active layer is 2μm; the thickness d5 of the positive current collector is 10μm, the thickness d6 of the positive active layer is 50μm, i.e. d5 / d6 is 1:5; In Examples 2 to 15 and Comparative Examples 1 to 4, except that the data in the table are changed, and in Example 11, the current collector 40 is provided with 1 air guide hole 401, the other conditions are the same as those of the battery in Example 1.

[0067] The specific table is shown below, where f refers to the mass content of Ni element in the positive active layer.

[0068] Table I

[0069] Table II

[0070] With reference to Table 1 and Table 2, with emphasis on Table 1, further in combination with Examples 1 to 3 and Comparative Examples 1 and 2, it can be seen that when the area ratio A of the projection overlap area of the air guide hole 401 and the explosion-proof valve 301 satisfies 8% to 30%, the battery high-temperature cycle number is larger, and the hot box passing rate is higher; with reference to Comparative Example 1, when A is 5%, that is, A is less than 8%, the battery high-temperature cycle number is 1738, and the capacity decreases from 100% to 80% in a smaller number of cycles, that is, when the overlap between the air guide hole 401 and the explosion-proof valve 301 is smaller, the exhaust path is limited, which affects the exhaust efficiency, the battery internal temperature is easy to be out of control, and the battery is also more likely to have thermal runaway, even explosion, which also shows that the hot box passing rate in Comparative Example 1 is only 3 / 10; with reference to Comparative Example 2, when A is 40%, that is, A is greater than 30%, the battery high-temperature cycle number is 1625, and the hot box passing rate is 7 / 10, which shows that A is too large, the area of the air guide hole 401 is too large, a stress concentration point is formed, the overall mechanical resistance of the battery is reduced, the current collector plate 40 is easy to break during the cycle process, the cycle capacity is affected, and at the same time, the appearance of the battery is also easy to be abnormal, which reduces the hot box passing rate.

[0071] With reference to Table 1 and Table 2, with emphasis on Table 1, further in combination with Examples 1 to 3 and Comparative Examples 1 and 2, it can be seen that when the area ratio A of the projection overlap area of the air guide hole 401 and the explosion-proof valve 301 satisfies 8% to 30%, the battery high-temperature cycle number is larger, and the hot box passing rate is higher; with reference to Comparative Example 1, when A is 5%, that is, A is less than 8%, the battery high-temperature cycle number is 1738, and the capacity decreases from 100% to 80% in a smaller number of cycles, that is, when the overlap between the air guide hole 401 and the explosion-proof valve 301 is smaller, the exhaust path is limited, which affects the exhaust efficiency, the battery internal temperature is easy to be out of control, and the battery is also more likely to have thermal runaway, even explosion, which also shows that the hot box passing rate in Comparative Example 1 is only 3 / 10; with reference to Comparative Example 2, when A is 40%, that is, A is greater than 30%, the battery high-temperature cycle number is 1625, and the hot box passing rate is 7 / 10, which shows that A is too large, the area of the air guide hole 401 is too large, a stress concentration point is formed, the overall mechanical resistance of the battery is reduced, the current collector plate 40 is easy to break during the cycle process, the cycle capacity is affected, and at the same time, the appearance of the battery is also easy to be abnormal, which reduces the hot box passing rate.

[0072] With reference to Table 1 and Table 2, with emphasis on Table 2, further in combination with Examples 2, 7 and 8, it can be seen that when the mass content c of fluoroethylene carbonate in the electrolyte satisfies 0.1%≤c≤10%, the battery high-temperature cycle number is larger, and the hot box passing rate is higher; in combination with Examples 9 to 13, it can be seen that the pore diameter d1 of the air guide hole 401 satisfies 1.5mm≤d1≤4mm, and the total area S1 of the air guide hole 401 satisfies 1.77mm 2 ≤S1≤25.12mm 2The area S3 of the explosion-proof valve 301 satisfies 20mm 2 ≤S3≤64mm 2 When the mass content e of the sulfur compound in the electrolyte is 0.5% to 5% and the ratio of the content of the sulfur compound to the content of the Ni element in the positive active layer is 1:50 to 1:4, the high-temperature cycle number of the battery is larger, and the hot box pass rate is higher.

[0073] In particular, the term "and / or" in this application should be understood as follows: In the first case, the term "and / or" between the first subject and the second subject includes any of the following meanings: (1) only the first subject; (2) only the second subject; and (3) the first subject and the second subject.

[0074] In the second case, the term "and / or" between the last two subjects among three or more subjects means that at least any one of the plurality of subjects is included. For example, "the first subject, the second subject and / or the third subject" has the same meaning as "the first subject and / or the second subject and / or the third subject", and specifically includes the following combinations: (1) only the first subject; (2) only the second subject; (3) only the third subject; (4) the first subject and the second subject without the third subject; (5) the first subject and the third subject without the second subject; (6) the second subject and the third subject without the first subject; and (7) the first subject, the second subject and the third subject; In addition, the character " / " in this application means that the associated objects before and after it are in an "or" relationship.

[0075] Finally, although the above describes the embodiments of the application in conjunction with the drawings, those skilled in the art can also make various modifications and variations without departing from the concept of the application, and such modifications and variations also fall within the scope of protection of the application.

Claims

1. A cylindrical battery, characterized in that, include: The electrode assembly (10) includes a positive electrode, a separator, a negative electrode and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode, and the positive electrode, the separator and the negative electrode are wound together to form a core; The housing (20) is cylindrical and has an opening at at least one end, and the winding core is accommodated inside it; The top cover assembly includes a cover body (30) and a manifold (40). The cover body (30) seals the opening and is provided with an explosion-proof valve (301). The manifold (40) is located on the side of the cover body (30) facing the electrode assembly (10) and is electrically connected to the electrode assembly (10). The manifold (40) is provided with a vent hole (401). The projection of the vent hole (401) on the cover body (30) at least partially overlaps with the explosion-proof valve (301), and the area of ​​the overlapping region in the explosion-proof valve (301) accounts for 8% to 30% of the area A. The positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector. The positive active layer includes a positive active material, which includes a ternary material. The electrolyte includes an organic solvent, which includes ethylene carbonate and propylene carbonate. The mass content of ethylene carbonate in the electrolyte is a, and the mass content of propylene carbonate in the electrolyte is b, and the condition 0.17 ≤ a / b ≤ 3 is met.

2. The cylindrical battery according to claim 1, characterized in that, The ethylene carbonate content (a) of the electrolyte is 5% ≤ a ≤ 30%, and / or the propylene carbonate content (b) of the electrolyte is 5% ≤ b ≤ 30%.

3. The cylindrical battery according to claim 1, characterized in that, The air guide hole (401) is provided with at least two, and the diameter of the air guide hole (401) is d1, the distance between two adjacent air guide holes (401) is d2, and satisfies 1.5mm≤d1≤4mm, and / or 3mm≤d2≤6.3mm, and / or 1:3.8≤d1 / d2≤1:1.

2.

4. The cylindrical battery according to claim 1, characterized in that, The sum of the areas of the air guide holes (401) is S1, and the area of ​​the collector plate (40) is S2, and both satisfy 1.77mm. 2 ≤S1≤25.12mm 2 and / or 227mm 2 ≤S2≤1590mm 2 And / or 0.5%≤S1 / S2≤12%.

5. The cylindrical battery according to claim 1, characterized in that, The explosion-proof valve (301) has an area of ​​S3, and the cover (30) has an area of ​​S4, both satisfying a 20mm... 2 ≤S3≤64mm 2 and / or 254mm 2 ≤S4≤1662mm 2 And / or 2%≤S3 / S4≤22%.

6. The cylindrical battery according to claim 1, characterized in that, The chemical formula of the ternary material in the positive electrode active layer is LiNi. x Co y Mn z O2, where x+y+z=1, 0.5≤x≤0.98, 0.02≤y≤0.3, 0.02≤z≤0.2; The ternary material has a single crystal structure; the ternary material also includes a doping element, which is selected from one or more of Zr and W; The average particle size of the ternary material is d4, and it satisfies 0.3μm≤d4≤4μm.

7. The cylindrical battery according to claim 1, characterized in that, The thickness of the positive electrode current collector is d5, and the thickness of the positive electrode active layer is d6, satisfying 6μm≤d5≤25μm, and / or 40μm≤d6≤150μm, and / or 1:15≤d5 / d6≤1:1.

6.

8. The cylindrical battery according to claim 1, characterized in that, The organic solvent also includes fluoroethylene carbonate, wherein the fluoroethylene carbonate accounts for c% of the mass content of the electrolyte and satisfies 0.1% ≤ c ≤ 10%.

9. The cylindrical battery according to claim 1, characterized in that, The electrolyte also includes sulfur-containing compounds, including one or more of 1,3-propanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, vinyl sulfite, and thiophene. The mass content e of the sulfur-containing compound in the electrolyte is 0.5% to 5%; And / or, the positive electrode active layer contains Ni element, and the ratio of the content of the sulfur-containing compound to the content of Ni element in the positive electrode active layer is 1:50 to 1:4; And / or, the electrolyte further includes a lithium salt, which includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide, and the total mass content of the two accounts for 10% to 20% of the mass of the electrolyte.

10. The cylindrical battery according to any one of claims 1 to 9, characterized in that, The diaphragm includes a base membrane and a coating disposed on the surface of the base membrane; The base film is one of polyethylene, polypropylene, or polypropylene / polyethylene composite film, and / or the coating includes ceramic particles, wherein the ceramic particles are one or more of alumina, boehmite, magnesium oxide, zirconium oxide, titanium oxide, and silicon oxide. And / or, the thickness of the base film is d7, the thickness of the coating is d8, and the conditions are met: 6μm≤d7≤25μm, and / or 2μm≤d8≤15μm.

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