Electrochemical device and electronic device comprising same

Abstract

The invention provides an electrochemical device and an electronic device comprising the same, the electrochemical device comprises a positive electrode, a negative electrode, an isolating membrane and an electrolyte, and the electrolyte comprises an additive; the liquid retention coefficient of the electrochemical device is a g / Ah, and a is more than or equal to 0.5 and less than or equal to 3.5; based on the total mass of the electrolyte, the mass percentage content of the additive is b%, and b is more than or equal to 0.005 and less than or equal to 3; wherein the additive comprises at least one of lithium bis (oxalato) borate, vinylethylene carbonate, methylene methanedisulfonate, triallyl phosphate, trifluoromethyl ethylene carbonate or allyl-1, 3-sultone, and the additive comprises at least one of lithium bis (oxalato) borate, vinylethylene carbonate, methylene methanedisulfonate, triallyl phosphate, trifluoromethyl ethylene carbonate and allyl-1, 3-sultone. According to the electrochemical device, the low-temperature discharge performance and the safety performance of the electrochemical device can be effectively improved by adopting a proper electrolyte preservation amount and adding a proper amount of the additive into the electrolyte. The electronic device comprising the electrochemical device also has good low-temperature discharge performance and safety performance.

Description

[0001] This invention is a divisional application with application number 202180031243.X, application date December 28, 2021, and invention name “An electrochemical device and an electronic device comprising the same”. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device comprising the same. Background Art

[0003] As a new type of mobile energy storage device, secondary batteries (such as lithium-ion batteries) have been widely used in portable electronic devices such as mobile phones, laptops, and cameras due to their high energy density, high operating voltage, long cycle life, no memory effect, and green environmental protection. Their scope of use is also expanding from small portable electronic devices to large electric transportation tools and renewable energy storage. With the widespread application of lithium-ion batteries in the above fields, people have put forward higher development requirements for the performance of lithium-ion batteries, such as improving energy density, improving safety performance, and reducing costs. Summary of the invention

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device comprising the same, so as to improve the low-temperature discharge performance and safety performance of the electrochemical device.

[0005] In a first aspect, the present application provides an electrochemical device, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises an additive; the liquid retention coefficient of the electrochemical device is ag / Ah, satisfying 0.5≤a≤3.5; based on the total mass of the electrolyte, the mass percentage of the additive is b%, satisfying 0.005≤b≤3; wherein the additive comprises at least one of lithium bis(oxalatoborate), ethylene carbonate, methylene disulfonate, triallyl phosphate, trifluoromethylethylene carbonate or propenyl-1,3-sultone.

[0006] In some embodiments of the first aspect of the present application, the liquid retention coefficient ag / Ah of the electrochemical device is 1 g / Ah to 2.5 g / Ah; and satisfies: -1.6≤ln(a×b)≤1.8.

[0007] In some embodiments of the first aspect of the present application, the tortuosity d of the isolation membrane is 1.5 to 3, satisfying: 0.6≤d / a≤3.

[0008] In some embodiments of the first aspect of the present application, the electrolyte further comprises vinylene carbonate; based on the total mass of the electrolyte, the mass percentage of the vinylene carbonate is c%, satisfying: 0.005≤c≤3, 0.003≤c / a≤3.

[0009] In some embodiments of the first aspect of the present application, the electrolyte further comprises a sulfonate compound; the sulfonate compound comprises at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propane disulfonic anhydride or 2,4-butane sultone; based on the total mass of the electrolyte, the mass percentage of the sulfonate compound is e%, satisfying: 0.01≤e≤5.

[0010] In some embodiments of the first aspect of the present application, the electrolyte comprises a first fluorine-containing lithium salt additive; the first fluorine-containing lithium salt additive comprises at least one of lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide, and based on the total mass of the electrolyte, the mass percentage of the first fluorine-containing lithium salt additive is f1%, satisfying: 0.08≤f1≤6;

[0011] And / or, the electrolyte contains a second fluorine-containing lithium salt additive; the second fluorine-containing lithium salt additive includes at least one of lithium difluorooxalatoborate, lithium difluorooxalatophosphate or lithium tetrafluoroborate, and based on the total mass of the electrolyte, the mass percentage of the second fluorine-containing lithium salt additive is f2%, satisfying: 0.01≤f2≤3.

[0012] In some embodiments of the first aspect of the present application, the electrolyte further comprises a polynitrile compound; the polynitrile compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyano-2-butene, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetrinitrile or 1,2,3-tris(2-cyanoethoxy)propane; based on the total mass of the electrolyte, the mass percentage of the polynitrile compound is g%, satisfying: 0.08≤g≤3.

[0013] In some embodiments of the first aspect of the present application, the electrolyte further contains aromatic compounds; the aromatic compounds include at least one of biphenyl, cyclohexylbenzene, fluorobenzene or difluorobiphenyl; based on the total mass of the electrolyte, the mass percentage of the aromatic compounds is h%, satisfying: 0.008≤h≤7.

[0014] In some embodiments of the first aspect of the present application, the positive electrode comprises a positive electrode active material layer, and the compaction density j of the positive electrode active material layer is 1 g / cm 3 Up to 4g / cm 3 .

[0015] In some embodiments of the first aspect of the present application, the positive electrode active material layer contains a positive electrode active material, the positive electrode active material Dv50 is k, k is 2μm to 40μm; the thickness of the isolation membrane is i, satisfying: i is 3μm to 20μm, 5μm≤i+k≤60μm.

[0016] A second aspect of the present application provides an electronic device, which includes the electrochemical device provided in the first aspect of the present application.

[0017] The present application provides an electrochemical device and an electronic device containing the same, wherein the electrochemical device comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises an additive; the electrochemical device has a liquid retention coefficient of ag / Ah, satisfying 0.5≤a≤3.5; based on the total mass of the electrolyte, the mass percentage of the additive is b%, satisfying 0.005≤b≤3; wherein the additive comprises at least one of lithium bis(oxalatoborate), ethylene carbonate, methylene disulfonate, triallyl phosphate, trifluoromethylethylene carbonate or propenyl-1,3-sultone. The electrochemical device of the present application can effectively improve the low-temperature discharge performance and safety performance of the electrochemical device by adopting an appropriate electrolyte retention amount and adding an appropriate amount of the above-mentioned additives to the electrolyte. The electronic device containing the electrochemical device also has good low-temperature discharge performance and safety performance. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme, and advantages of the present application more clearly understood, the present application is further described in detail with reference to the following embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application belong to the scope of protection of the present application.

[0019] It should be noted that, in this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. Those skilled in the art should understand that the following description is only for illustrative purposes and does not limit the scope of protection of this application.

[0020] In the first aspect of the present application, an electrochemical device is provided, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises an additive; the electrochemical device has a liquid retention coefficient of ag / Ah, which satisfies 0.5≤a≤3.5; based on the total mass of the electrolyte, the mass percentage of the additive is b%, which satisfies 0.005≤b≤3; wherein the additive comprises at least one of lithium bis(oxalatoborate), ethylene carbonate, methylene disulfonate, triallyl phosphate, trifluoromethylethylene carbonate or propenyl-1,3-sultone. For example, the value of a may be 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.2, 3.5 or any range therebetween; the value of b may be 0.005, 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 2.8, 3 or any range therebetween. Without being limited to any theory, the inventors have found that the electrochemical device of the present application can effectively improve the low-temperature discharge performance and safety performance of the electrochemical device by adopting an appropriate electrolyte retention amount and adding an appropriate amount of the above-mentioned additives to the electrolyte.

[0021] Without being limited to any theory, the inventors have found that when the value of the liquid retention coefficient a is too low, for example, less than 0.5g / Ah, the active material is not fully wetted during the formation process, and it is difficult for the additives in the electrolyte to form an effective synergy with the active material, and it is impossible to improve the low-temperature discharge performance of the electrochemical device by forming a functional interface; when the value of the liquid retention coefficient a is too high, for example, higher than 3.5g / Ah, the protective effect of the electrode interface on the active material is weakened, which will cause the active lithium component in the lithium-ion battery to be continuously consumed, thereby causing the accelerated decay of the capacity of the lithium-ion battery. Adding the additive to an electrochemical system with a specific electrolyte retention amount can form an interface protection film at the positive and negative electrodes, but when the additive is too much, for example, more than 3%, the interface impedance will increase, affecting the low-temperature discharge performance and discharge temperature rise. Without being limited to any theory, by selecting the above-mentioned additives and controlling a and b within the above range, it is beneficial to improve the low-temperature discharge performance and safety performance of the electrochemical device.

[0022] In some embodiments of the first aspect of the present application, the liquid retention coefficient ag / Ah of the electrochemical device is 1g / Ah to 2.5g / Ah; and satisfies: -1.6≤ln(a×b)≤1.8. For example, the value of a can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5 or any range therebetween; the value of ln(a×b) can be -1.6, -1.3, -1.0, -0.5, 0, 0.05, 0.1, 0.2, 0.5, 0.7, 1, 1.2, 1.5, 1.8 or any range therebetween. The inventors of the present application have found that controlling the values ​​of a and ln(a×b) within the above range can further improve the low-temperature discharge performance and safety performance of the electrochemical device.

[0023] In some embodiments of the first aspect of the present application, the tortuosity d of the isolation membrane is 1.5 to 3, satisfying: 0.6≤d / a≤3. For example, the value of d can be 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or any range therebetween; the value of d / a can be 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or any range therebetween. The inventors have found that by controlling the values ​​of d and d / a within the above ranges, the electrochemical device can have excellent low-temperature discharge performance and safety performance.

[0024] The inventors found that increasing the tortuosity d of the isolation membrane is beneficial to improving the isolation membrane's barrier effect on burrs and lithium dendrites, thereby improving the safety performance of the electrochemical device; when the tortuosity d is too low, for example, lower than 1.5, it cannot provide a good protective effect on the electrochemical device; when the tortuosity d is too high, for example, higher than 3, it will affect the ion permeability and thus affect the low-temperature discharge performance of the electrochemical device; by controlling d and d / a within the above range, the electrochemical device can have excellent low-temperature discharge performance and safety performance.

[0025] In some embodiments of the first aspect of the present application, the electrolyte further comprises vinylene carbonate; based on the total mass of the electrolyte, the mass percentage of the vinylene carbonate is c%, satisfying: 0.005≤c≤3, 0.003≤c / a≤3. For example, the value of c can be 0.005, 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 2.8, 3 or any range therebetween; the value of c / a can be 0.003, 0.005, 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 2.8, 3 or any range therebetween. By controlling the values ​​of c and c / a within the above ranges, the electrochemical device can have excellent performance.

[0026] Adding vinylene carbonate (VC) to the electrolyte can further modify the solid electrolyte interface (SEI) film of the negative electrode, so that the formed SEI film has a tighter structure. The SEI film with better performance can prevent the electrolyte from further decomposing, thereby further improving the performance of the electrochemical device. However, when the content of vinylene carbonate is too much, for example, more than 3%, it will cause the impedance to rise and the trend of lithium precipitation at the interface, which is not conducive to the safety performance of the electrochemical device. Therefore, the values ​​of c and c / a are controlled within the above range.

[0027] In some embodiments of the first aspect of the present application, the electrolyte further comprises a sulfonate compound; the present application has no particular restrictions on the type of the sulfonate compound, as long as the purpose of the present application can be achieved, for example, the sulfonate compound may include at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propane disulfonic anhydride or 2,4-butane sultone; based on the total mass of the electrolyte, the mass percentage of the sulfonate compound is e%, satisfying: 0.01≤e≤5. For example, the value of e can be 0.01, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any range therebetween. Adding sulfonate compounds to the electrolyte can significantly improve the low-temperature discharge performance of the electrochemical device, and the improvement effect becomes more obvious as the content of the sulfonate compounds increases; however, when the amount of sulfonate compounds is too high, for example, higher than 5%, the low-temperature discharge performance of the electrochemical device will no longer be improved. By controlling the value of e within the above range, the low-temperature discharge performance and safety performance of the electrochemical device can be further improved.

[0028] In some embodiments of the first aspect of the present application, the electrolyte further comprises a fluorine-containing lithium salt additive; the present application has no particular restrictions on the type of the fluorine-containing lithium salt additive, as long as the purpose of the present application can be achieved. For example, the electrolyte comprises a first fluorine-containing lithium salt additive; the first fluorine-containing lithium salt additive comprises at least one of lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide, and based on the total mass of the electrolyte, the mass percentage of the first fluorine-containing lithium salt additive is f1%, satisfying: 0.08≤f1≤6;

[0029] And / or, the electrolyte contains a second fluorine-containing lithium salt additive; the second fluorine-containing lithium salt additive includes at least one of lithium difluorooxalatoborate, lithium difluorooxalatophosphate or lithium tetrafluoroborate, and based on the total mass of the electrolyte, the mass percentage of the second fluorine-containing lithium salt additive is f2%, satisfying: 0.01≤f2≤3.

[0030] In the present application, the value of f1 can be 0.08, 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 or any range therebetween; the value of f2 can be 0.01, 0.1, 0.2, 0.5, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or any range therebetween. Fluorine-containing lithium salt additives can form a film on the negative electrode, and a good SEI film can protect the negative electrode and improve the low-temperature discharge performance of the electrochemical device; however, when the content of the fluorine-containing lithium salt additive is high, the formed SEI film will be too thick, resulting in increased impedance.

[0031] When the first fluorine-containing lithium salt additive is added to the electrolyte, the f1 is controlled within the range of 0.08% to 6%, which can improve the low-temperature discharge performance and safety performance of the electrochemical device; when the second fluorine-containing lithium salt additive is added to the electrolyte, the f2 is controlled within the range of 0.01% to 3%, which can improve the low-temperature discharge performance and safety performance of the electrochemical device; the first fluorine-containing lithium salt additive and the second lithium salt additive can be used alone or in combination.

[0032] In some embodiments of the first aspect of the present application, the electrolyte further comprises a polynitrile compound; the present application has no particular restrictions on the type of the polynitrile compound, as long as the purpose of the present application can be achieved. For example, the polynitrile compound may include at least one of succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyano-2-butene, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetrinitrile or 1,2,3-tri(2-cyanoethoxy)propane; based on the total mass of the electrolyte, the mass percentage of the polynitrile compound is g%, satisfying: 0.08≤g≤3. For example, the value of g can be 0.08, 0.1, 0.2, 0.5, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3 or any range therebetween. The polynitrile compound can form a polymer film on the positive electrode, which can better protect the positive electrode. By adjusting the mass percentage of the polynitrile compound within the above range, the low-temperature discharge performance and safety performance of the electrochemical device can be effectively improved. By selecting the above polynitrile compound, the low-temperature discharge performance and safety performance of the electrochemical device can be further improved.

[0033] In some embodiments of the first aspect of the present application, the electrolyte further comprises an aromatic compound; the present application has no particular restrictions on the type of the aromatic compound, as long as the purpose of the present application can be achieved. For example, the aromatic compound may include at least one of biphenyl, cyclohexylbenzene, fluorobenzene or difluorobiphenyl; based on the total mass of the electrolyte, the mass percentage of the aromatic compound is h%, satisfying: 0.008≤h≤7. For example, the value of h can be 0.008, 0.01, 0.02, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 4, 4.5, 5, 5.5, 6, 6.5, 7 or any range therebetween, such as 1 to 5. The present application adds an aromatic compound to the electrolyte, because the aromatic compound can undergo an electropolymerization reaction, and the generated polymer film can prevent thermal runaway, thereby significantly improving the hot box performance of the electrochemical device, so that the electrochemical device has better safety performance; preferably, when the value of h satisfies 1≤h≤5, the electrochemical device has better safety performance.

[0034] In the present application, the electrolyte may also contain other non-aqueous solvents. The present application has no particular restrictions on other non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of carboxylic acid ester compounds, ether compounds or other organic solvents. The above-mentioned carboxylic acid ester compounds may include but are not limited to methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, 2,2-difluoroethyl acetate, valerolactone, butyrolactone, 2-fluoroethyl acetate, 2,2-difluoroethyl acetate or trifluoroethyl acetate. The above-mentioned ether compounds may include but are not limited to at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, bis (2,2,2-trifluoroethyl) ether, 1,3-dioxane or 1,4-dioxane. The above-mentioned other organic solvents may include, but are not limited to, at least one of ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, cyclopentane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and di(2,2,2-trifluoroethyl) carbonate. Based on the total mass of the electrolyte, the total content of the above-mentioned other non-aqueous solvents is 5% to 90%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or any range therebetween.

[0035] In some embodiments of the first aspect of the present application, the positive electrode comprises a positive electrode active material layer, and the compaction density j of the positive electrode active material layer is 1 g / cm 3 Up to 4g / cm 3 For example, the value of j can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.7, 3, 3.2, 3.5, 3.7, 4 or any range therebetween. Increasing the compaction density of the positive electrode active material layer can increase the energy density of the electrochemical device, but when the compaction density is too large, for example, greater than 4 g / cm 3 , which will lead to poor electrode wetting and poor dynamics of the electrochemical device. The inventors have found that by controlling the value of j within the above range, the electrochemical device can have better low-temperature discharge performance.

[0036] In some embodiments of the first aspect of the present application, the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material Dv50 is k, k is 2μm to 40μm; the thickness of the isolation film is i, satisfying: i is 3μm to 20μm, 5μm≤i+k≤60μm. For example, the value of k can be 2, 3, 5, 8, 10, 13, 15, 18, 20, 22, 25, 27, 30, 32, 35, 37, 40 or any range therebetween; the value of i can be 3, 5, 7, 8, 10, 12, 15, 16, 18, 20 or any range therebetween; the value of i+k can be 5, 10, 13, 15, 18, 20, 22, 25, 27, 30, 35, 40, 45, 48, 50, 53, 55, 60 or any range therebetween. Without being limited to any theory, the inventors of the present application have found that by controlling the values ​​of k, i and i+k within the above ranges, the energy density of the electrochemical device can be increased and the low-temperature discharge performance of the electrochemical device can be improved.

[0037] In this application, the term "Dv50" means the particle size at which the cumulative distribution of particles is 50%; that is, the volume content of particles smaller than this particle size accounts for 50% of all particles. The particle size is measured using a laser particle size analyzer.

[0038] The positive electrode of the present application may also include a positive electrode current collector. The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector. The positive electrode active material layer of the present application includes a positive electrode active material. The present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. In the present application, the positive electrode active material may also include non-metallic elements, such as non-metallic elements including at least one of fluorine, phosphorus, boron, chlorine, silicon, sulfur, etc., which can further improve the stability of the positive electrode active material. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode collector is 5μm to 20μm, preferably 6μm to 18μm. The thickness of the single-sided positive electrode active material layer is 30μm to 120μm. In the present application, the positive electrode active material layer can be arranged on one surface in the thickness direction of the positive electrode collector, or on two surfaces in the thickness direction of the positive electrode collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode collector or a partial area of ​​the positive electrode collector. This application is not particularly limited as long as the purpose of this application can be achieved. Optionally, the positive electrode may also include a conductive layer, which is located between the positive electrode collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited, and it may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0039] There is no special limitation on the negative electrode of the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode comprises a negative electrode current collector and a negative electrode material layer. There is no special limitation on the negative electrode current collector of the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may comprise copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or a composite current collector, etc. The negative electrode material layer of the present application comprises a negative electrode material. There is no special limitation on the type of negative electrode material of the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode material may comprise natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO xAt least one of (0 < x < 2), metallic lithium, etc. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 150 μm. In this application, the negative electrode material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no particular limitation in this application, as long as the purpose of this application can be achieved. Optionally, the negative electrode may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder.

[0040] There is no particular limitation on the above-mentioned conductive agent, as long as the purpose of this application can be achieved. For example, the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, flake graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, or graphene. There is no particular limitation on the above-mentioned binder, as long as the purpose of this application can be achieved. For example, the binder may include at least one of polyvinyl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamideimide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na), etc.

[0041] The isolation membrane of the present application may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example, they may be selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is not particularly limited, and for example, it can be selected from at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene, etc. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene), etc.

[0042] The electrochemical device of the present application is not particularly limited, and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0043] The preparation process of the electrochemical device is well known to those skilled in the art, and the present application has no particular limitation. For example, it may include but is not limited to the following steps: stacking the positive electrode, the separator and the negative electrode in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain an electrochemical device; or stacking the positive electrode, the separator and the negative electrode in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent pressure rise and overcharge and discharge inside the electrochemical device.

[0044] The second aspect of the present application provides an electronic device, which includes the electrochemical device provided in the first aspect of the present application. The electronic device has good low-temperature discharge performance and safety performance.

[0045] The electronic devices of the present application are not particularly limited, and may include but are not limited to the following types: laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, and large household batteries, etc.

[0046] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0047] Test methods and equipment:

[0048] Low temperature discharge test:

[0049] Place the lithium-ion battery in a high and low temperature box, adjust the temperature to 25°C, and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Discharge the lithium-ion battery that has reached a constant temperature to 2.8V at a current of 0.5C, then charge it to 4.2V at a current of 0.5C, and then charge it at a constant voltage of 4.2V until the current is less than or equal to 0.05C. Also at a temperature of 25°C, discharge it to 3.0V at a current of 0.5C, and record the discharge capacity as the initial discharge capacity. At a temperature of 25°C, charge it to 4.2V at a current of 0.5C, and then charge it at a constant voltage of 4.2V until the current is less than or equal to 0.05C. After that, place the lithium-ion battery at a temperature of -20°C and let it stand for 30 minutes to keep the temperature of the lithium-ion battery consistent with the outside temperature. At -20°C, discharge it to 3.0V at a current of 0.5C, and record the discharge capacity as the low-temperature discharge capacity.

[0050] -20℃ low temperature discharge capacity retention rate = (low temperature discharge capacity / initial discharge capacity) × 100%.

[0051] Temperature rise test:

[0052] The lithium-ion battery is kept at rest at 45°C for 5 minutes, discharged at a current of 0.5C to 2.8V, and left to rest for 60 minutes; then, it is charged at a constant current of 0.5C to 4.2V, and then charged at a constant voltage to a current less than or equal to 0.05C, and left to rest for 60 minutes; the lithium-ion battery is discharged at a constant current of 5C to 2.8V, and the highest temperature during the 5C current discharge process is obtained. The highest temperature is subtracted from the test temperature of 45°C to obtain the temperature rise value (referred to as temperature rise) during 5C discharge.

[0053] Overcharge test:

[0054] The lithium-ion battery was placed at room temperature for 5 minutes, discharged to 2.8V at a constant current rate of 1C, then charged to 4.2V at a constant current rate of 1C, and charged at a constant voltage until the current was less than or equal to 0.05C, and then placed for 30 minutes. The lithium-ion battery was then transferred to the overcharge area for testing, charged to 5V at a constant current rate of 1C, and charged at a constant voltage for 3 hours at 5V. The passing standard is that the lithium-ion battery does not burn or explode. Ten lithium-ion batteries prepared in each embodiment or comparative example were tested, and the number of batteries that passed the test was recorded.

[0055] High temperature storage performance test:

[0056] Fully charged storage: Place the lithium-ion battery in a 25°C constant temperature box for 5 minutes, charge to 4.2V at a constant current rate of 1C, then charge at a constant voltage until the current is less than or equal to 0.05C, then place it for 5 minutes, discharge to 2.8V at a constant current rate of 1C, record the discharge capacity at this time as the initial discharge capacity, then charge to 4.2V at a constant current rate of 1C, charge at a constant voltage until the current is less than or equal to 0.05C, then place the fully charged lithium-ion battery in a 60°C oven for 30 days, after 30 days of storage, take out the lithium-ion battery and place it in a 25°C constant temperature box for 3 hours. And test the capacity recovery according to the following process: discharge to 2.8V at a constant current rate of 1C, then charge to 4.2V at a constant current rate of 1C, charge at a constant voltage until the current is less than or equal to 0.05C, then discharge to 2.8V at a constant current rate of 1C, and record the discharge capacity at this time as the discharge capacity after storage.

[0057] Capacity recovery rate = discharge capacity after storage / initial discharge capacity × 100%.

[0058] Hot box test:

[0059] Place the lithium-ion battery in a 25°C thermostat and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge to 4.2V at a constant current of 0.5C, and charge to a current of 0.05C at a constant voltage. Then transfer the lithium-ion battery to a hot box, heat it to 140°C at a rate of 2°C / min, and keep it for 30 minutes. The passing standard is that the lithium-ion battery does not burn or explode. Ten lithium-ion batteries prepared in each embodiment or comparative example are tested, and the number of batteries that pass the test is recorded.

[0060] Liquid retention coefficient test:

[0061] The liquid retention coefficient of lithium-ion batteries is calculated according to the following expression:

[0062] Liquid retention coefficient = electrolyte retention / lithium-ion battery first-cycle discharge capacity.

[0063] Electrolyte content test: Take a lithium-ion battery and weigh it as m 0 Then, the lithium-ion battery is disassembled, the electrolyte is separated by centrifugation, and the disassembled aluminum-plastic film, separator, positive electrode sheet, negative electrode sheet, and tab are placed in an acetonitrile solution. Then, the aluminum-plastic film, separator, positive electrode sheet, negative electrode sheet, and tab are taken out, dried, and weighed to record as m 1 , the electrolyte content is m 0 -m 1 .

[0064] Isolation film tortuosity test:

[0065] The McMullin formula is used to calculate the tortuosity of the isolation membrane: (tortuosity d) 2 =N M ×ε.

[0066] Among them, N M represents the McMullin number, which is σ s Divide by σ e The value of σ s represents the resistivity of the isolation film, σ e represents the conductivity value of the electrolyte, and ε represents the porosity of the separator.

[0067] Positive electrode active material layer compaction density test:

[0068] Take the positive double-sided electrode sheet and make it into an area of ​​1540.25mm 2 Take 20 small discs for weighing and thickness measurement, compaction density = (weight of small disc - weight of substrate) / (1540.25 × (double-sided thickness of small disc - thickness of substrate)) × 1000, and the test average value is the positive electrode compaction in the embodiment.

[0069] Weight and thickness of substrate (copper foil): obtained by weighing and measuring the area without active material;

[0070] The weight of the small disc and the weight of the substrate: unit (mg),

[0071] Double-sided thickness of the wafer and substrate thickness: unit (µm).

[0072] Positive electrode active material particle size test:

[0073] MasterSizer 2000 was used to test the particle size distribution of the positive electrode active material.

[0074] Isolation film thickness test:

[0075] Use a micrometer to test the thickness of the isolation film.

[0076] Example 1-1

[0077] <Preparation of Electrolyte>

[0078] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC) and lithium hexafluorophosphate (LiPF 6 ), lithium bis(oxalatoborate) (LiBOB) and diethyl carbonate (DEC) were mixed evenly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of EC was 26%, and the mass percentage of LiPF 6 The mass percentage of is 11%, the mass percentage of LiBOB is 0.005%, and the balance is the mass percentage of DEC.

[0079] <Preparation of positive electrode sheet>

[0080] The positive electrode material is lithium nickel cobalt manganese oxide (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96:2:2, and then N-methylpyrrolidone (NMP) is added as a solvent, stirred evenly, and a positive electrode slurry with a solid content of 75wt% is prepared; the positive electrode slurry is evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 10μm, dried at 90°C, and cold pressed to obtain a positive electrode sheet with a positive electrode active material layer thickness of 100μm, and the positive electrode sheet is cut into a specification of 74mm×867mm and welded with a pole ear for standby use.

[0081] <Preparation of negative electrode sheet>

[0082] The negative electrode material artificial graphite, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC), and binder styrene butadiene rubber (SBR) are mixed in a weight ratio of 95:2:2:1, and then deionized water is added as a solvent, stirred evenly, and a negative electrode slurry with a solid content of 70wt% is prepared; the negative electrode slurry is evenly coated on both surfaces of a negative electrode current collector copper foil with a thickness of 8μm, dried at 90°C, and cold pressed to obtain a negative electrode sheet with a negative electrode active material layer thickness of 150μm, and the negative electrode sheet is cut into a specification of 74mm×867mm and welded to the pole ear for standby use.

[0083] <Preparation of Separator Film>

[0084] A polyethylene (PE) porous film with a thickness of 5 μm was used as the isolation membrane.

[0085] <Preparation of lithium-ion batteries>

[0086] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound to obtain a bare cell; the bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried battery. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, the preparation of the lithium-ion battery is completed.

[0087] Example 1-2 to Example 1-17

[0088] Except for the changes in relevant preparation parameters and performance parameters as shown in Table 1, the rest is the same as Example 1-1.

[0089] Comparative Example 1-1 to Comparative Example 1-4

[0090] Except for the changes in relevant preparation parameters and performance parameters as shown in Table 1, the rest is the same as Example 1-1.

[0091] Table 1

[0092] “ / ” means that the substance or component is not contained.

[0093] It can be seen from Examples 1-1 to 1-17 and Comparative Examples 1-1 to 1-4 that when the value of the liquid retention coefficient a is between 0.5 and 3.5, and the value of the mass percentage content b of the additive is between 0.005 and 3, the lithium ion battery has good low-temperature discharge performance and safety performance; when the values ​​of a and b satisfy 1≤a≤2.5, -1.6≤ln(a×b)≤1.8, the low-temperature discharge performance and safety performance of the lithium ion battery can be further improved.

[0094] Example 2-1 to Example 2-10

[0095] Except for the changes in relevant preparation parameters and performance parameters as shown in Table 2, the rest is the same as Example 1-16.

[0096] Table 2

[0097] It can be seen from Examples 1-16 and 2-1 to 2-10 that when the values ​​of the liquid retention coefficient a and the isolation membrane tortuosity d satisfy 1.5≤d≤3 and 0.6≤d / a≤3, the lithium-ion battery has good low-temperature discharge performance and safety performance.

[0098] Example 3-1 to Example 3-8

[0099] <Preparation of Electrolyte>

[0100] Except for adding vinylene carbonate to the electrolyte according to the proportion in Table 3 and reducing the mass percentage of DEC accordingly so that the total mass of the electrolyte is 100%, the rest is the same as Example 1-16. The changes in relevant preparation parameters and performance parameters are shown in Table 3.

[0101] The preparation of <Preparation of Positive Electrode Plate>, <Preparation of Negative Electrode Plate>, <Preparation of Separator> and <Preparation of Lithium-ion Battery> are the same as those in Example 1-16.

[0102] Embodiment 3-9

[0103] <Preparation of Electrolyte>

[0104] Except for adding vinylene carbonate to the electrolyte according to the proportion in Table 3 and reducing the mass percentage of DEC accordingly so that the total mass of the electrolyte is 100%, the rest is the same as Example 1-2. The changes in relevant preparation parameters and performance parameters are shown in Table 3.

[0105] The preparation of <Preparation of Positive Electrode Piece>, <Preparation of Negative Electrode Piece>, <Preparation of Separator> and <Preparation of Lithium Ion Battery> are the same as those in Example 1-2.

[0106] Table 3

[0107] “ / ” means that the substance or component is not contained.

[0108] It can be seen from Examples 1-16 and 3-1 to 3-9 that when the values ​​of the liquid retention coefficient a and the vinylene carbonate content c satisfy 0.005≤c≤3, 0.003≤c / a≤3, the lithium-ion battery has good high-temperature storage performance.

[0109] Example 4-1 to Example 4-30

[0110] <Preparation of Electrolyte>

[0111] Except that at least one of the sulfonate compound, the first fluorine-containing lithium salt additive, the second fluorine-containing lithium salt additive, the polynitrile compound or the aromatic compound is added to the electrolyte according to the proportion in Table 4, and the mass percentage of DEC is reduced accordingly so that the total mass of the electrolyte is 100%, the rest is the same as Example 1-16. The changes in relevant preparation parameters and performance parameters are shown in Table 4.

[0112] The preparation of <Preparation of Positive Electrode Plate>, <Preparation of Negative Electrode Plate>, <Preparation of Separator> and <Preparation of Lithium-ion Battery> are the same as those in Example 1-16.

[0113] Table 4

[0114] “ / ” means that the substance or component is not contained.

[0115] According to Examples 1-16, 4-1 and 4-5, it can be seen that adding sulfonate compounds to the electrolyte can improve the low-temperature discharge performance of the lithium-ion battery, and the improvement effect is more obvious as the content of the sulfonate compounds increases; when the content of the sulfonate compounds is higher than 5%, the low-temperature discharge performance will not be improved. When the mass percentage e of the sulfonate compounds satisfies 0.01≤e≤5, the lithium-ion battery has good low-temperature discharge performance and safety performance.

[0116] According to Examples 1-16, 4-6 to 4-15, it can be seen that adding the first fluorine-containing lithium salt additive and / or the second fluorine-containing lithium salt additive to the electrolyte can improve the low-temperature discharge performance and hot box performance of the lithium-ion battery. According to Examples 1-16, 4-1 to 4-30, it can be seen that adding at least one of a sulfonate compound, a first fluorine-containing lithium salt additive, a second fluorine-containing lithium salt additive, a polynitrile compound and an aromatic compound to the electrolyte of the present application can further improve the low-temperature discharge performance and hot box performance of the lithium-ion battery.

[0117] Example 5-1 to Example 5-14

[0118] Except for the changes in relevant preparation parameters and performance parameters as shown in Table 5, the rest is the same as Examples 1-16.

[0119] Table 5

[0120] It can be seen from Examples 1-16 and 5-1 to 5-14 that the compaction density j of the positive electrode active material layer is 1 g / cm3 Up to 4g / cm 3 When the thickness i of the isolation film is between 3μm and 20μm, the Dv50 k of the positive electrode active material is between 2μm and 40μm, and 5μm≤i+k≤60μm is satisfied, the lithium-ion battery has good low-temperature discharge performance.

[0121] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises an additive; the electrochemical device has a liquid retention coefficient of ag / Ah, which satisfies 0.5≤a≤3.5; based on the total mass of the electrolyte, the mass percentage of the additive is b%, which satisfies 0.005≤b≤3; in, The additive includes at least one of lithium bis(oxalatoborate), ethylene carbonate, methylene disulfonate, triallyl phosphate, trifluoromethylethylene carbonate or propenyl-1,3-sultone; The electrolyte further comprises a polynitrile compound, which includes at least one of succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyano-2-butene, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetrinitrile or 1,2,3-tris(2-cyanoethoxy)propane; based on the total mass of the electrolyte, the mass percentage of the polynitrile compound is g%, satisfying: 0.08≤g≤3.

2. The electrochemical device according to claim 1, in, The electrochemical device has a liquid retention coefficient ag / Ah of 1 g / Ah to 2.5 g / Ah; Satisfies: -1.6≤ln(a×b)≤1.

8.

3. The electrochemical device according to claim 1, in, The tortuosity d of the isolation film is 1.5 to 3, satisfying: 0.6≤d / a≤3.

4. The electrochemical device according to claim 1, in, The electrolyte further comprises vinylene carbonate; based on the total mass of the electrolyte, the mass percentage of the vinylene carbonate is c%, satisfying: 0.005≤c≤3, 0.003≤c / a≤3.

5. The electrochemical device according to claim 1, in, The electrolyte further comprises a sulfonate compound; the sulfonate compound comprises at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propane disulfonic anhydride or 2,4-butane sultone; based on the total mass of the electrolyte, the mass percentage of the sulfonate compound is e%, satisfying: 0.01≤e≤5.

6. The electrochemical device according to claim 1, in, The electrolyte comprises a first fluorine-containing lithium salt additive; the first fluorine-containing lithium salt additive comprises at least one of lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide, and based on the total mass of the electrolyte, the mass percentage of the first fluorine-containing lithium salt additive is f1%, satisfying: 0.08≤f1≤6; And / or, the electrolyte contains a second fluorine-containing lithium salt additive; the second fluorine-containing lithium salt additive includes at least one of lithium difluorooxalatoborate, lithium difluorooxalatophosphate or lithium tetrafluoroborate, and based on the total mass of the electrolyte, the mass percentage of the second fluorine-containing lithium salt additive is f2%, satisfying: 0.01≤f2≤3.

7. The electrochemical device according to claim 1, in, The electrolyte further contains aromatic compounds; the aromatic compounds include at least one of biphenyl, cyclohexylbenzene, fluorobenzene or difluorobiphenyl; based on the total mass of the electrolyte, the mass percentage of the aromatic compounds is h%, satisfying: 0.008≤h≤7.

8. The electrochemical device according to claim 1, in, The positive electrode comprises a positive electrode active material layer, and the compaction density j of the positive electrode active material layer is 1 g / cm 3 Up to 4g / cm 3 .

9. The electrochemical device according to claim 8, in, The positive electrode active material layer contains a positive electrode active material, wherein Dv50 of the positive electrode active material is k, and k is 2 μm to 40 μm; the thickness of the isolation film is i, and the following conditions are satisfied: i is 3 μm to 20 μm, and 5 μm≤i+k≤60 μm. 10 . An electronic device comprising the electrochemical device according to claim 1 .

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