Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device, and belongs to the technical field of energy storage. The electrochemical device comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer located on at least part of the surface of the positive electrode current collector; the positive electrode mixture layer comprises a boron-containing additive, and the boron-containing additive comprises a boron element; based on the mass of the positive electrode mixture layer, the mass ratio of the boron element is a%; the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer located on at least part of the surface of the negative electrode current collector; the negative electrode mixture layer comprises an iodine-containing additive, and the iodine-containing additive comprises an iodine element; based on the mass of the negative electrode mixture layer, the mass ratio of the iodine element is b%; 0.1 < = a < = 1; 0.04 < = a / b < = 10. According to the invention, the charging temperature rise and thermal safety performance of the electrochemical device can be improved, and the dynamics, low-temperature discharge and high-temperature storage performance can also be improved.

Description

Technical Field

[0001] The present application belongs to the field of energy storage technology, and specifically relates to an electrochemical device and an electronic device. Background Art

[0002] Electrochemical devices refer to devices that convert electrical energy into chemical energy. Starting from the earliest voltaic pile, the technology of electrochemical devices has gone through several stages of development from lead-acid batteries to nickel-metal hydride batteries, and then to the lithium-ion batteries that are widely used today. Among them, lithium-ion batteries have become the mainstream choice of energy storage systems due to their high energy density, long cycle life and light weight, and are widely used in portable electronic devices, electric vehicles and large-scale energy storage systems.

[0003] Although electrochemical devices have many advantages in energy storage systems, they still face some technical challenges, especially in terms of overcharge temperature rise and thermal safety. Since the battery generates heat during the charging process, if the heat is not properly controlled, it may cause the battery to overheat or even catch fire, especially under overcharge conditions, which will greatly accelerate the rate of temperature rise. In order to expand the application scenarios of electrochemical devices, improve the thermal safety performance of electrochemical devices, and ensure the safety of batteries during the charging and discharging process, it is an issue that needs special attention in this field. Summary of the invention

[0004] In view of this, the present application provides an electrochemical device and an electronic device, which can not only improve the charging temperature rise and thermal safety performance of the electrochemical device, but also improve the kinetics, low-temperature discharge and high-temperature storage performance.

[0005] In a first aspect, the present application provides an electrochemical device comprising a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer located on at least a portion of the surface of the positive electrode current collector; the positive electrode mixture layer comprises a boron-containing additive, the boron-containing additive comprises a boron element; based on the mass of the positive electrode mixture layer, the mass proportion of the boron element is a%; the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer located on at least a portion of the surface of the negative electrode current collector; the negative electrode mixture layer comprises an iodine-containing additive, the iodine-containing additive comprises an iodine element; based on the mass of the negative electrode mixture layer, the mass proportion of the iodine element is b%; 0.1≤a≤1; 0.04≤a / b≤10.

[0006] Based on the above scheme, the present application adds a boron-containing additive to the positive electrode and controls the mass proportion of the boron element in the positive electrode mixture layer to meet the above range. The boron element can improve the thermal conductivity of the positive electrode mixture layer, improve the thermal management of the positive electrode, enhance the thermal safety of the battery cell, and improve the electrochemical performance and safety of the electrochemical device under high temperature and overcharge conditions; secondly, the boron element can also provide more active particles (such as lithium ions) diffusion channels for the positive electrode, promote the transmission dynamics of active particles, and improve ion conductivity. However, the addition of boron will lose the energy density (ED) of the positive electrode, and the high transmission rate of active particles at the positive electrode will also cause the problem of mismatch between the transmission dynamics of active particles at the positive and negative electrodes, resulting in excess active particles on the negative electrode surface, resulting in uneven distribution or precipitation of active particles at the negative electrode. This application adds an iodine-containing additive to the negative electrode and controls the mass ratio of the iodine element in the negative electrode mixture layer and the boron content to meet the above relationship. It can construct a solid electrolyte interface (SEI) layer rich in LiI on the surface of the negative electrode active material, which can not only improve the ionic conductivity of the negative electrode, but also match the active particle transmission dynamics of the positive electrode, balance the active particle transmission dynamics between the positive and negative electrodes, and help to improve the mechanical strength and ionic conductivity of the SEI layer formed on the negative electrode, reduce the occurrence of side reactions and gas production, and the iodine-containing additive can provide gram capacity, which is conducive to improving the energy density of the negative electrode and compensating for the ED loss caused by the positive boron-containing additive. Therefore, this application realizes the improvement of the kinetic performance of the electrochemical device under high capacity density conditions through the coordination of boron-containing additives and iodine-containing additives, and takes into account the improvement of the high temperature performance, overcharge temperature rise and thermal safety performance of the electrochemical device.

[0007] In some embodiments, the electrochemical device satisfies at least one of the following conditions: (1) 0.1≤a / b≤5; (2) 0.2≤a≤0.5; (3) 0.1≤b≤2.5. Regulating the mass ratio of boron and iodine to meet the above relationship can promote better coordination between the two and further improve the kinetics, high temperature performance, overcharge temperature rise and thermal safety performance of the electrochemical device.

[0008] In some embodiments, the boron-containing additive includes boron nitride, and the boron-containing additive has a multilayer sheet structure; the number of layers of the boron-containing additive is 2 to 20 layers, and the sheet diameter of the boron-containing additive is 0.2 μm to 0.5 μm; and / or, the iodine-containing additive includes iodinated polyacrylonitrile. The present application controls the multilayer sheet structure of boron nitride to meet the above conditions, which can provide more heat conduction and heat dissipation space and active particle diffusion channels, and further improve the kinetics, high temperature performance, overcharge temperature rise and thermal safety performance of the electrochemical device.

[0009] In some embodiments, the positive electrode mixture layer includes titanium; based on the mass of the positive electrode mixture layer, the mass proportion of titanium is c%; 0.1≤c≤0.5. Doping titanium into the positive electrode active material can optimize the electronic structure of the positive electrode material and form a new ion transmission channel. In combination with the above-mentioned boron and iodine elements, it can further improve the kinetics, high temperature performance, overcharge temperature rise and thermal safety performance of the electrochemical device.

[0010] In some embodiments, the electrolyte includes a first substance, the electrolyte includes a first substance, the first substance includes a compound of Formula 1, cesium hexafluorophosphate (CsPF6), or a combination thereof;

[0011]

[0012] In formula 1, R 1 and R 2 Each is independently selected from a fluorine group or a C1-C4 fluoroalkyl group substituted by at least one fluorine group. The compound represented by Chemical Formula 1 may be referred to as a cesium sulfonimide salt or a fluorinated cesium sulfonimide salt. The present application uses the first substance to form a uniform and dense SEI film on the surface of the negative electrode in combination with the iodine element, thereby reducing side reactions, reducing gas production and capacity attenuation during the cycle, thereby improving the kinetics, high temperature performance, overcharge temperature rise and thermal safety performance of the electrochemical device.

[0013] In some embodiments, the compound of Formula 1 includes at least one of the following compounds:

[0014]

[0015] In some embodiments, based on the mass of the electrolyte, the mass proportion of the first substance is m%, and 0.01≤m≤3.

[0016] In some embodiments, the electrolyte includes lithium difluorophosphate; based on the mass of the electrolyte, the mass proportion of lithium difluorophosphate is n%; 0.05≤m / n≤1; 0.02≤n≤2. In the present application, lithium difluorophosphate can be combined with boron and iodine elements to participate in the formation of a uniform and stable electrolyte membrane at the positive and negative electrodes, and can also improve the ionic conductivity of the electrochemical device by combining with the above-mentioned first substance, thereby further improving the kinetics, high temperature performance, overcharge temperature rise and thermal safety performance of the electrochemical device.

[0017] In some embodiments, 0.1≤m≤2; and / or, 0.08≤m / n≤0.1.

[0018] In a second aspect, the present application provides an electronic device comprising the electrochemical device according to any one of claims 1 to 9. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is a SEM image of boron nitride provided for a specific embodiment of the present application. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0021] The electrochemical device of the present application is not particularly limited, and may include any device in which an electrochemical reaction occurs, such as a secondary battery. The present application is described below using a secondary battery as an example in conjunction with the embodiments of the present application. In some embodiments of the present application, the secondary battery may include, but is not limited to: a lithium-ion secondary battery (lithium-ion battery) or a sodium-ion battery. It should be noted that in the specific embodiments of the present application, the present application is explained using a secondary battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a secondary battery.

[0022] Further improvement of the coating weight of lithium-ion batteries is of great significance and is the most direct and effective way to increase energy density and reduce costs. However, as the electrode thickness increases, the electrode tortuosity increases, the lithium ion conduction inside the porous electrode pores is hindered, the electrode concentration polarization becomes larger, and the battery performance deteriorates. As the electrode thickness increases, lithium ion transmission gradually becomes the rate-controlling step of lithium battery dynamics. In order to improve the performance of thick electrodes, it is necessary to improve battery dynamics from many aspects, the core of which is to build an efficient lithium ion transmission network.

[0023] In order to solve the problems existing in the prior art, the present application provides an electrochemical device, including a positive electrode, a negative electrode and an electrolyte; the positive electrode includes a positive electrode current collector and a positive electrode mixture layer located on at least part of the surface of the positive electrode current collector; the positive electrode mixture layer includes a boron-containing additive, the boron-containing additive includes a boron element; based on the mass of the positive electrode mixture layer, the mass proportion of the boron element is a%; the negative electrode includes a negative electrode current collector and a negative electrode mixture layer located on at least part of the surface of the negative electrode current collector; the negative electrode mixture layer includes an iodine-containing additive, the iodine-containing additive includes an iodine element; based on the mass of the negative electrode mixture layer, the mass proportion of the iodine element is b%; 0.1≤a≤1; 0.04≤a / b≤10. The present application adds a boron-containing additive to the positive electrode, which can improve the overcharge temperature rise and thermal safety performance of the secondary battery. The use of an iodine-containing additive in the negative electrode in combination with the positive electrode can balance the lithium ion transfer kinetics of the positive and negative electrodes, improve the kinetic performance of the secondary battery, and take into account the improvement of the high temperature performance of the secondary battery.

[0024] In some embodiments, 0.04≤a / b≤10, preferably, 0.1≤a / b≤5; for example, the value of a / b is 0.04, 0.1, 0.4, 1.6, 3.2, 3.4, 5.3, 5.8, 6.9, 7.9, 9, 10 or a value in the range of any two thereof. When the mass ratio of the boron element and the iodine element meets the above relationship, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery can be further improved.

[0025] In some embodiments, 0.1≤a≤1; preferably, 0.2≤a≤0.5; for example, a may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value in the range of any two thereof. Regulating the mass ratio of the boron element to meet the above range can further improve the dynamics, high temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0026] In some embodiments, 0.1≤b≤2.5. For example, b may be 0.1, 0.2, 0.6, 0.8, 1.0, 1.3, 1.6, 1.9, 2.1, 2.4, 2.5, or a value in the range of any two thereof. Regulating the mass ratio of the iodine element to conform to the above range can further improve the dynamics, high temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0027] In some embodiments, the boron-containing additive includes boron nitride (BN), and the boron-containing additive has a multilayer sheet structure; the number of layers of the boron-containing additive is 2 to 20 layers, such as 2 layers, 3 layers, 5 layers, 6 layers, 9 layers, 11 layers, 13 layers, 15 layers, 17 layers, 20 layers, or a value in the range of any two thereof; the sheet diameter of the boron-containing additive is 0.2 μm to 0.5 μm, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or a value in the range of any two thereof. The polar bonds of boron nitride can couple lithium ions, and combined with its multilayer sheet structure, more lithium ion migration and transmission channels can be established on the surface of the positive electrode active material, thereby improving ion conductivity and the kinetics of the secondary battery; and boron nitride can also improve the thermal conductivity of the positive electrode, and improve the electrochemical performance and safety performance of the secondary battery under high temperature and overcharge conditions.

[0028] In the present application, the number of layers and the diameter of the boron nitride flakes can be tested by methods known in the art, and the present application does not make any special restrictions. For example, a cp sample of the positive electrode mixture layer can be obtained, and the morphology of the boron nitride in the cp sample can be observed by a scanning electron microscope (SEM). Ten multilayer flaky boron nitrides with the sides exposed to the field of view can be randomly selected, and the number of layers can be counted and the arithmetic mean can be calculated as the number of layers of the boron nitride (it can be understood that the boron nitride can also include single-layer boron nitride, as long as the arithmetic mean of the number of layers counted reaches 2 or more); ten multilayer flaky boron nitrides with the front side exposed to the field of view can be randomly selected, and the longest distance (longest diameter) between any two points on the circumference can be counted and the arithmetic mean can be calculated as the diameter of the boron nitride flakes. See. Figure 1 SEM image of boron nitride. The diameter of a single boron nitride sheet is shown by the red line segment in the figure.

[0029] In some embodiments, the iodine-containing additive includes iodinated polyacrylonitrile (I-PAN). I-PAN can promote the formation of a solid electrolyte interface layer rich in LiF / LiI, and improve the bulk / interphase diffusion kinetics of lithium ions, expand ion transport channels, balance the lithium ion transport kinetics of positive and negative electrodes, and improve the overall kinetics of the secondary battery; it also helps to reduce side reactions and gas production, and improve the high temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0030] In some embodiments, the positive electrode mixture layer includes titanium; based on the mass of the positive electrode mixture layer, the mass percentage of the titanium element is c%; 0.1≤c≤0.5. For example, c can be a value in the range of 0.1, 0.2, 0.3, 0.4, 0.5 or any two thereof. By regulating the mass percentage of the titanium element within the above range, in combination with the above-mentioned boron-containing additive and iodine-containing additive, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery can be further improved.

[0031] The positive electrode sheet in the present application also includes a positive current collector. The present application has no particular restrictions on the positive current collector, as long as the purpose of the present application can be achieved. For example, the positive current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The present application has no particular restrictions on the thickness of the positive current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 5μm to 20μm.

[0032] In the present application, the positive electrode mixture layer can be arranged on one side surface in the thickness direction of the positive electrode current collector, or on both side surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" can be the entire area of ​​the positive electrode current collector, or it can be a partial area of ​​the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0033] In the present application, the positive electrode mixture layer includes a positive electrode active material, and the positive electrode active material is any substance that can reversibly embed and de-embed alkali metal ions (such as lithium ions).

[0034] Alternatively, the positive electrode active material includes a lithium transition metal oxide containing nickel and other transition metals. In the lithium transition metal oxide including nickel and other transition metals, the amount of nickel relative to the total molar number of the transition metal may be 60 mol% or more, for example, 75 mol% or more, for example, 80 mol% or more, for example, 85 mol% or more, or for example, 90 mol% or more.

[0035] For example, the lithium transition metal oxide may be a compound represented by the following formula α:

[0036] Formula α: Li a Ni x Co y M z O 2-b A b ,

[0037] Wherein, in formula α, 0.9≤a≤1.2, 0≤b≤0.2, 0.6≤x<1, 0<y≤0.3, 0<z≤0.3, and x+y+z=1, M is at least one selected from manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al) or boron (B), and A is F, S, Cl, Br or a combination thereof. For example, the above subscripts may be 0.7≤x<1, 0<y≤0.3, and 0<z≤0.3; 0.8≤x<1, 0<y≤0.3, and 0<z≤0.3; 0.8≤x<1, 0<y≤0.2, and 0<z≤0.2; 0.83≤x<0.97, 0<y≤0.15, and 0<z≤0.15; or 0.85≤x<0.95, 0<y≤0.1, and 0<z≤0.1.

[0038] For example, the lithium transition metal oxide may be at least one compound represented by the following formula β or formula γ:

[0039] Formula β: LiNi x Co y Mn z O2,

[0040] Wherein, in formula β, 0.6≤x≤0.95, 0<y≤0.2, and 0<z≤0.1, for example, 0.7≤x≤0.95, 0<y≤0.3, and 0<z≤0.3.

[0041] Formula γ: LiNi xCo y Al z O2,

[0042] Wherein, in formula γ, 0.6≤x≤0.95, 0<y≤0.2, and 0<z≤0.1, for example, 0.7≤x≤0.95, 0<y≤0.3, and 0<z≤0.3, for example, 0.8≤x≤0.95, 0<y≤0.3, and 0<z≤0.3, for example, 0.82≤x≤0.95, 0<y≤0.15, and 0<z≤0.15, for example, 0.85≤x≤0.95, 0<y≤0.1, and 0<z≤0.1.

[0043] For example, the lithium transition metal oxide may be LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.88 Co 0.08 Mn 0.04 O2、LiNi 0.8 Co 0.15 Mn 0.05 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.88 Co 0.1 Mn 0.02 O2、LiNi 0.8 Co 0.15 Al 0.05 O2 or LiNi 0.88 Co 0.1 Al 0.02 O2.

[0044] According to another embodiment, the positive electrode active material includes at least one active material selected from the group consisting of Li-Ni-Co-Al (NCA), Li-Ni-Co-Mn (NCM), lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2) and lithium iron phosphate (LiFePO4).

[0045] In the present application, the positive electrode mixture layer also includes a positive electrode conductive agent. The present application has no special restrictions on the positive electrode conductive agent, 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 conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0046] In the present application, the positive electrode mixture layer also includes a positive electrode binder. The present application has no special restrictions on the positive electrode binder 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 polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polystyrene butadiene copolymer, sodium alginate, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose.

[0047] The negative electrode sheet of the present application also includes a negative electrode current collector. In the present application, the negative electrode mixture layer can be arranged on the surface on one side in the thickness direction of the negative electrode current collector, or on the surfaces on both sides 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 it can be a partial area of ​​the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the thickness of the negative electrode mixture layer, as long as the purpose of this application can be achieved. For example, the thickness of a single-sided negative electrode mixture layer can be 30μm to 160μm.

[0048] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector), etc. The present application has no particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 10μm.

[0049] The negative electrode mixture layer of the present application includes a negative electrode active material. The present application has no particular restrictions on the negative electrode active material, as long as it can reversibly embed and deintercalate electron transport materials such as lithium. For example, the negative electrode active material may include but is not limited to carbon materials such as graphite (artificial graphite, natural graphite or graphitized carbon fiber) or amorphous carbon; metals such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys that can be alloyed with lithium or alloys formed with lithium; SiO β (0<β≤2), metal oxides that can be doped or dedoped with lithium, such as SnO, SnO2, vanadium oxide, lithium vanadium oxide, or alloys thereof with lithium; or composites containing metal and carbon materials, such as Si-C composites or Sn-C composites; or lithium titanate with spinel structure TiO2-Li4Ti5O 12 , and any one of them or a mixture of two or more thereof can be used. In addition, a metallic lithium film can also be used as the negative electrode active material. Specifically, the carbon material can use low-crystalline carbon and high-crystalline carbon, etc. Representative low-crystalline carbons are soft carbon and hard carbon. Examples of high-crystalline carbon can be amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, primary graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, carbon microspheres (mesophase carbon microspheres), mesophase pitch, and high-temperature calcined carbon such as petroleum and coal-based coke (coke derived from petroleum or coal tar pitch).

[0050] In the present application, the negative electrode mixture layer may also include a negative electrode binder. The present application has no particular limitation on the negative electrode binder 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 polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon.

[0051] In some embodiments, the electrolyte includes a first substance, the electrolyte includes a first substance, the first substance includes a compound of Formula 1, cesium hexafluorophosphate, or a combination thereof;

[0052]

[0053] In formula 1, R 1 and R 2Each is independently selected from a fluorine group or a C1-C4 fluoroalkyl group substituted by at least one fluorine group. The compound represented by Chemical Formula 1 may be referred to as a cesium sulfonimide salt or a fluorinated cesium sulfonimide salt. The first substance can be combined with an iodine-containing additive to promote the formation of a solid electrolyte interface (SEI) layer rich in LiI, improve the ionic conductivity of the negative electrode and the film-forming quality of the surface SEI film, thereby further improving the kinetics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery.

[0054] In some embodiments, the compound of Formula 1 includes at least one of the following compounds:

[0055]

[0056] The compound of formula 1 can further improve the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery.

[0057] In some embodiments, based on the mass of the electrolyte, the mass proportion of the first substance is m%; 0.01≤m≤3, preferably 0.1≤m≤2. Exemplarily, the value of m can be 0.01, 0.05, 0.1, 0.2, 0.5, 1.0, 1.2, 1.5, 1.7, 2.3, 2.4, 2.7, 3 or a value in the range of any two thereof. When the mass proportion of the first substance in the electrolyte is regulated to meet the above range, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery can be further improved.

[0058] In some embodiments, the electrolyte includes lithium difluorophosphate, and the mass proportion of lithium difluorophosphate is n% based on the mass of the electrolyte; 0.05≤m / n≤1, preferably, 0.08≤m / n≤0.1; for example, the value of m / n is 0.05, 0.07, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a value in the range of any two thereof. When the mass proportion of lithium difluorophosphate and the first substance is regulated to meet the above relationship, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery can be further improved.

[0059] In some embodiments, 0.02≤n≤2. For example, the value of n can be 0.02, 0.19, 0.43, 0.48, 0.80, 0.92, 1.12, 1.49, 1.58, 1.80, 2, or a value in the range of any two thereof. When the mass ratio of lithium difluorophosphate is regulated within the above range, the dynamics, high temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery can be further improved.

[0060] In the present application, the electrolyte may also include other lithium salts and non-aqueous solvents. Other lithium salts may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, and lithium bis(oxalatoborate) (LiBOB). The present application does not particularly limit the concentration of other lithium salts in the electrolyte, as long as the purpose of the present application can be achieved.

[0061] The present application has no particular restrictions on 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 carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. The above-mentioned linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0062] The secondary battery of the present application also includes a separator. The present application has no special restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene-based polyolefin (PO) separators, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide films (PI), polyamide films (PA), spandex or aramid films, etc. At least one of the types of separators may include but is not limited to woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, rolled membranes or spinning membranes, etc. The separator of the present application may have a porous structure, and the size of the pore size is not particularly limited, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01 μm to 1 μm. In the present application, the thickness of the separator is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness can be 5 μm to 500 μm.

[0063] The secondary battery of the present application also includes a packaging bag for containing a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in the secondary battery, and the present application does not limit the above other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0064] The secondary battery of the present application is not particularly limited, and may include any device that undergoes an electrochemical reaction. In one embodiment of the present application, the secondary battery may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium metal secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In one embodiment, the structure of the electrode assembly includes a winding structure or a laminated structure.

[0065] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application has no special restrictions. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0066] The present application has no limitation on the packaging bag, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved. For example, an aluminum-plastic film packaging bag can be used.

[0067] In a second aspect, the present application further provides an electronic device, comprising the electrochemical device provided in the first aspect of the present application.

[0068] The electronic device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used for, but not limited to, 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-discs, 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, large household batteries and lithium-ion capacitors, etc.

[0069] The following uses lithium-ion batteries as an example to illustrate the solution of the present application in combination with the following specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from common commercial products, and the devices or equipment used are all purchased from conventional market sales channels.

[0070] Performance testing method:

[0071] Dynamics (low temperature rate performance) test:

[0072] At -20℃, the lithium-ion battery was discharged to 3.0V at 0.2C constant current, left standing for 5 minutes, then charged to 4.5V at 0.5C constant current, then charged to 0.05C constant voltage and left standing for 5 minutes. Then, constant current discharge tests were performed at 0.2C and 2.0C respectively to obtain discharge capacity 1 and discharge capacity 2. The rate of the lithium-ion battery was calculated by the following formula:

[0073] Rate discharge capacity retention ratio (%)=(discharge capacity 2 / discharge capacity 1)×100%.

[0074] High temperature performance (cell gas generation) test:

[0075] The lithium-ion battery was left to stand at 25°C for 24 hours. Then, it was charged to 4.5V at 0.1C constant current at 25°C, and then discharged to 3.0V at 0.1C constant current. The battery cell of the battery was immersed in liquid paraffin, and the volume X0 of the battery cell was measured. Then, the battery was repeatedly cycled 100 times under the same charge and discharge conditions as above at 85°C. The battery cell of the battery after 100 cycles was immersed in liquid paraffin, and the volume X1 of the battery cell was measured. The battery cell volume change rate (%) before and after the high-temperature cycle test of repeated 100 cycles of charge and discharge = (X1-X0) / X0×100. The smaller the value of the battery cell volume change rate, the less gas is generated from the electrode, and the better the ability of the electrode to suppress gas generation.

[0076] Overcharge temperature rise test:

[0077] At 25°C, the lithium-ion battery is charged by CC-CV at a constant current of 0.7C for 8 hours (upper limit battery cell voltage is 5.05V), and then left to stand until the surface temperature of the battery returns to the ambient temperature ±10°C before stopping the test. The surface temperature of the battery is monitored during the process. The lower the temperature rise, the better the heat release suppression performance of the secondary battery during overcharge.

[0078] Thermal safety (heat suppression safety during internal short circuit) test:

[0079] The battery was charged by constant current constant voltage (CC-CV) at a constant current method of 0.2C (the upper limit of the battery cell voltage was 4.5V), and CC discharged to 3.0V at a constant current method of 0.2C. This charge and discharge process was repeated 3 times. Then, at 25°C, it was charged to 4.5V by constant current constant voltage (CC-CV) at a charging rate of 0.2C (termination condition: 0.05C). Then, an iron nail with a diameter of 3mm and a length of 10cm was penetrated near the center of the secondary battery at a speed of 5m / min to force it to short-circuit. The surface temperature of the battery cell was monitored during the process. The lower the temperature rise, the better the heat release suppression performance of the secondary battery during internal short circuit.

[0080] Example 1-1

[0081] 1) Positive electrode

[0082] The positive electrode active material lithium cobalt oxide, the conductive agent Super P and carbon nanotubes, the binder polyvinylidene fluoride (PVDF), and boron nitride (BN) are mixed in a weight ratio of 97.0:0.8:0.5:1.3:0.4, and all the materials are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent to form a uniform positive electrode slurry, wherein the solid content of the positive electrode slurry is 72wt%. The slurry is coated on the positive electrode current collector aluminum foil, dried at 85°C, and then the above steps are repeated on the other surface of the aluminum foil. After cold pressing, cutting, and slitting, it is dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.

[0083] 2) Negative electrode

[0084] Graphite and IPAN materials were mixed together in a weight ratio of 99.9:0.1 as negative electrode active materials, and mixed with styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a weight ratio of 97.6:1.2:1.2 in an appropriate amount of deionized water to form a uniform negative electrode slurry, wherein the solid content of the negative electrode slurry was 50wt%. The slurry was coated on the negative electrode collector (copper foil), dried at 85°C, and then the above steps were repeated on the other surface of the copper foil. After cold pressing, cutting, and slitting, it was dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode sheet.

[0085] 3) Electrolyte

[0086] In a dry argon environment, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and propyl propionate (PP) are mixed in a mass ratio of 1:1:1:1, and then lithium salt LiPF6 is added. After mixing evenly, an electrolyte is obtained, in which the mass percentage of LiPF6 based on the mass of the electrolyte is 12.1%.

[0087] 4) Isolation film

[0088] A 5 μm thick polyethylene (PE) porous polymer film was used as the isolation membrane.

[0089] 5) Lithium-ion battery

[0090] The positive electrode sheet after welding the tabs, the separator, and the negative electrode sheet after welding the tabs are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role, and then wound and placed in the outer packaging foil aluminum-plastic film, and the electrolyte is injected. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a soft-pack lithium-ion battery is obtained.

[0091] Examples 1-2 to 1-9, Comparative Examples 1-1 to 1-4

[0092] Except for adjusting the parameters shown in Table 1, the rest is the same as Example 1-1. In Comparative Example 1-1, iodinated polyacrylonitrile is not added, and pure graphite is used as the negative electrode active material; and in Comparative Example 1-2, boron nitride is not added.

[0093] The boron nitride used in Examples 1-6 is all single-layer boron nitride.

[0094] Table 1

[0095]

[0096]

[0097] As can be seen from Table 1, the present application adds a boron-containing additive to the positive electrode and controls the mass proportion of the boron element in the positive electrode mixture layer to meet the following conditions: 0.1≤a≤1, and adds an iodine-containing additive to the negative electrode, controls the mass proportion of the iodine element in the negative electrode mixture layer to meet the following conditions: 0.04≤a / b≤10, thereby improving the kinetics, high temperature performance, overcharge temperature rise, and thermal safety performance of the lithium-ion battery. In particular, when 0.2≤a≤0.5 is met, the kinetics, high temperature performance, overcharge temperature rise, and thermal safety performance of the lithium-ion battery can be further improved. And, when 0.1≤a / b≤5 is met, the kinetics, high temperature performance, overcharge temperature rise, and thermal safety performance of the lithium-ion battery can be more significantly improved.

[0098] In particular, when 0.1≤b≤2.5 is met, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery can be further improved.

[0099] In particular, when the number of boron nitride layers is 2 to 20, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of lithium-ion batteries can be further improved. In particular, when the boron nitride sheet diameter is adjusted to 0.2 μm to 0.5 μm, lithium-ion batteries can exhibit better dynamics, high temperature performance, overcharge temperature rise and thermal safety performance.

[0100] Examples 2-1 to 2-12

[0101] Except for adjusting the parameters shown in Table 2, the rest is the same as Example 1-8. Among them, commercially available lithium cobalt oxide doped with titanium element is used as the positive electrode active material; when the substances in Table 2 are added to the electrolyte, the mass of ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate is correspondingly reduced, and the mass ratio of the four is controlled to be the same.

[0102] Table 2

[0103]

[0104] As can be seen from Table 2, by regulating the inclusion of titanium in the positive electrode mixture layer, when its mass proportion c% satisfies: 0.1≤c≤0.5, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery can be further improved.

[0105] In particular, when the first substance is included in the regulating electrolyte and its mass proportion m% satisfies 0.01≤m≤3, in combination with the positive and negative electrode systems of the present application, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery can be further improved. In particular, when 0.1≤m≤2 is satisfied, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the secondary battery can be more significantly improved. More preferably, when the first substance includes both the compound of formula 1 and cesium hexafluorophosphate, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery can be further improved.

[0106] In particular, when the electrolyte includes lithium difluorophosphate, and its mass proportion n% satisfies the relationship of 0.05≤m / n≤1 with the first substance, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery can be further improved. In particular, when 0.08≤m / n≤0.1 is satisfied, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery are more significantly improved. In particular, when 0.02≤n≤2 is satisfied, the dynamics, high temperature performance, overcharge temperature rise and thermal safety performance of the lithium-ion battery can be further improved.

[0107] 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 and improvements made within the principles of the present application should be included in the protection scope of the present application.

Claims

1. An electrochemical device, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte; the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer located on at least a part of the surface of the positive electrode current collector; the positive electrode mixture layer comprises a boron-containing additive, and the boron-containing additive comprises a boron element; based on the mass of the positive electrode mixture layer, the mass proportion of the boron element is a%; The negative electrode comprises a negative electrode current collector and a negative electrode mixture layer located on at least a portion of the surface of the negative electrode current collector; the negative electrode mixture layer comprises an iodine-containing additive, and the iodine-containing additive comprises iodine element; based on the mass of the negative electrode mixture layer, the mass proportion of the iodine element is b%; 0.1≤a≤1; 0.04≤a / b≤10.

2. The electrochemical device according to claim 1, characterized in that The electrochemical device satisfies at least one of the following conditions: (1) 0.1≤a / b≤5; (2)0.2≤a≤0.5； (3)0.1≤b≤2.5。 3. The electrochemical device according to claim 1, characterized in that The boron-containing additive comprises boron nitride, and the boron-containing additive has a multi-layered sheet structure; the number of layers of the boron-containing additive is 2 to 20, and the sheet diameter of the boron-containing additive is 0.2 μm to 0.5 μm; and / or, The iodine-containing additive includes iodinated polyacrylonitrile.

4. The electrochemical device according to any one of claims 1 to 3, characterized in that The positive electrode mixture layer includes titanium element; based on the mass of the positive electrode mixture layer, the mass proportion of the titanium element is c%; 0.1≤c≤0.

5.

5. The electrochemical device according to any one of claims 1 to 3, characterized in that: The electrolyte includes a first substance, wherein the first substance includes a compound of formula 1, cesium hexafluorophosphate, or a combination thereof; In formula 1, R 1 and R 2 Each is independently selected from a fluoro group or a C1-C4 fluoroalkyl group substituted by at least one fluoro group.

6. The electrochemical device according to claim 5, characterized in that The compound of formula 1 includes at least one of the following compounds:

7. The electrochemical device according to claim 5, characterized in that Based on the mass of the electrolyte, the mass proportion of the first substance is m%, and 0.01≤m≤3.

8. The electrochemical device according to claim 7, characterized in that The electrolyte includes lithium difluorophosphate; based on the mass of the electrolyte, the mass proportion of the lithium difluorophosphate is n%; 0.05≤m / n≤1; 0.02≤n≤2。 9. The electrochemical device according to claim 8, characterized in that 0.1≤m≤2; and / or, 0.08≤m / n≤0.

1.

10. An electronic device, characterized in that: An electrochemical device comprising any one of claims 1 to 9.

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