Electrochemical devices and electronic devices

Abstract

The application 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; the mass percentage of the boron element is a% based on the mass of the positive electrode mixture layer; 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; the mass percentage of the iodine element is b% based on the mass of the negative electrode mixture layer; 0.1<=a<=1; 0.04<=a / b<=10. The application 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.

Description

Technical Field

[0001] This application belongs to the field of energy storage technology, specifically relating to an electrochemical device and an electronic device. Background Technology

[0002] Electrochemical devices are devices that convert electrical energy into chemical energy. Starting with the earliest voltaic stacks, electrochemical device technology has undergone several development stages, from lead-acid batteries to nickel-metal hydride batteries, and now to the widely used lithium-ion batteries. Among these, lithium-ion batteries, with their high energy density, long cycle life, and light weight, have become the mainstream choice for energy storage systems, widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems.

[0003] Despite the numerous advantages of electrochemical devices in energy storage systems, several technical challenges remain, particularly regarding overcharge temperature rise and thermal safety. Batteries generate heat during charging, and improper heat management can lead to overheating and even fire, especially under overcharge conditions, which significantly accelerate the temperature rise rate. Expanding the application scenarios of electrochemical devices, improving their thermal safety performance, and ensuring battery safety during charging and discharging are issues that require special attention in this field. Summary of the Invention

[0004] In view of this, this application provides an electrochemical device and an electronic device that 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, this 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 additive layer located on at least a portion of the surface of the positive electrode current collector; the positive electrode additive layer includes a boron-containing additive, which includes boron element; based on the mass of the positive electrode additive layer, the mass percentage of boron element is a%; the negative electrode includes a negative electrode current collector and a negative electrode additive layer located on at least a portion of the surface of the negative electrode current collector; the negative electrode additive layer includes an iodine-containing additive, which includes iodine element; based on the mass of the negative electrode additive layer, the mass percentage of iodine element is b%; 0.1≤a≤1; 0.04≤a / b≤10.

[0006] Based on the above scheme, this application, by adding boron-containing additives to the positive electrode and controlling the mass ratio of boron in the positive electrode additive layer to meet the aforementioned range, can improve the thermal conductivity of the positive electrode additive layer, improve the thermal management of the positive electrode, enhance the thermal safety performance of the battery cell, and improve the electrochemical performance and safety performance of the electrochemical device under high temperature and overcharge conditions. Secondly, boron can also provide more diffusion channels for active particles (such as lithium ions) in the positive electrode, promote the transport kinetics of active particles, and improve ionic conductivity. However, the addition of boron will reduce the energy density (ED) of the positive electrode, and the high transport rate of active particles in the positive electrode will also cause a mismatch in the transport kinetics of active particles between the positive and negative electrodes, resulting in an excess of active particles on the surface of the negative electrode, leading to uneven distribution or precipitation of active particles in the negative electrode. This application, by adding an iodine-containing additive to the negative electrode and controlling the mass ratio of iodine in the negative electrode additive layer to satisfy the aforementioned relationship with the boron content, enables the construction of a LiI-rich solid electrolyte interface (SEI) layer on the surface of the negative electrode active material. This not only improves the ionic conductivity of the negative electrode, matching it with the active particle transport kinetics of the positive electrode and balancing the active particle transport kinetics between the two electrodes, but also helps to improve the mechanical strength and ionic conductivity of the SEI layer formed on the negative electrode, reducing side reactions and gas generation. Furthermore, the iodine-containing additive provides specific capacity, thereby improving the energy density of the negative electrode and compensating for the ED loss caused by the boron-containing additive in the positive electrode. Therefore, this application, through the synergistic effect of the boron-containing and iodine-containing additives, achieves improved kinetic performance of the electrochemical device under high capacity density conditions, while also improving 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. Adjusting the mass ratio of boron and iodine to conform to the above relationship can promote better cooperation 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-like 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 polyacrylonitrile iodide. This application satisfies the above conditions by controlling the multilayer sheet-like structure of boron nitride, which can provide more space for heat conduction and dissipation and active particle diffusion channels, further improving the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the electrochemical device.

[0009] In some embodiments, the positive electrode additive layer includes titanium; the mass percentage of titanium is c% based on the mass of the positive electrode additive layer; 0.1 ≤ c ≤ 0.5. Doping titanium into the positive electrode active material can optimize the electronic structure of the positive electrode material, forming new ion transport channels. Combined with the aforementioned 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, which includes a compound of formula 1, cesium hexafluorophosphate (CsPF6), or a combination thereof.

[0011]

[0012] In Equation 1, R 1 and R 2 Each compound is independently selected from fluorinated or C1-C4 fluoroalkyl groups substituted with at least one fluorinated group. Compounds represented by Formula 1 may be called cesium sulfonamide salts or fluorinated cesium sulfonamide salts. This application utilizes the first substance to form a uniform and dense SEI film on the negative electrode surface in combination with iodine, reducing side reactions, reducing gas generation and capacity decay during cycling, 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 implementations, the mass percentage of the first substance is m%, based on the mass of the electrolyte, and 0.01 ≤ m ≤ 3.

[0016] In some embodiments, the electrolyte includes lithium difluorophosphate; the mass percentage of lithium difluorophosphate is n% based on the mass of the electrolyte; 0.05 ≤ m / n ≤ 1; 0.02 ≤ n ≤ 2. This application demonstrates that lithium difluorophosphate can combine with boron and iodine elements to participate in the formation of a uniform and stable electrolyte film at the positive and negative electrodes. Combined with the aforementioned first substance, it can also improve the ionic conductivity of the electrochemical device, thereby further improving the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the electrochemical device.

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

[0018] Secondly, this application provides an electronic device, including an electrochemical device. Attached Figure Description

[0019] Figure 1A SEM image of boron nitride provided for a specific embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] The electrochemical device described in this application is not particularly limited and can include any device in which an electrochemical reaction occurs, such as a secondary battery. The following description uses a secondary battery as an example in conjunction with embodiments of this application. In some embodiments of this application, the secondary battery may include, but is not limited to, lithium-ion secondary batteries (lithium-ion batteries) or sodium-ion batteries. It should be noted that in the specific embodiments of this application, a secondary battery is used as an example of an electrochemical device to explain the application; however, the electrochemical device of this application is not limited to a secondary battery.

[0022] Further improvements in the coating weight of lithium-ion batteries are significant, representing the most direct and effective way to increase energy density and reduce costs. However, as electrode thickness and tortuosity increase, lithium-ion conduction within the porous electrode pores is hindered, leading to greater concentration polarization and deterioration of battery performance. With increasing electrode thickness, lithium-ion transport gradually becomes the rate-controlling step in lithium battery kinetics. To improve the performance of thick electrodes, it is necessary to enhance battery kinetics from multiple aspects, with the core being the construction of an efficient lithium-ion transport network.

[0023] To address the problems existing in the prior art, this 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 additive layer located on at least a portion of the surface of the positive electrode current collector. The positive electrode additive layer includes a boron-containing additive, which includes boron element. Based on the mass of the positive electrode additive layer, the mass percentage of boron element is a%. The negative electrode includes a negative electrode current collector and a negative electrode additive layer located on at least a portion of the surface of the negative electrode current collector. The negative electrode additive layer includes an iodine-containing additive, which includes iodine element. Based on the mass of the negative electrode additive layer, the mass percentage of iodine element is b%. 0.1≤a≤1; 0.04≤a / b≤10. This 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 conjunction with the boron-containing additive, can balance the lithium-ion transport kinetics of the positive and negative electrodes, improve the kinetic performance of the secondary battery, and also improve 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 within the range of 0.04, 0.1, 0.4, 1.6, 3.2, 3.4, 5.3, 5.8, 6.9, 7.9, 9, 10, or any two of these ranges. When the mass ratio of boron to iodine conforms to the above relationship, the kinetics, 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 can be a value within the range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any two of these. Adjusting the mass ratio of boron within the above range can further improve the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0026] In some embodiments, 0.1 ≤ b ≤ 2.5. Exemplarily, b can be a value within the range of 0.1, 0.2, 0.6, 0.8, 1.0, 1.3, 1.6, 1.9, 2.1, 2.4, 2.5, or any two of these. Adjusting the mass percentage of iodine within the above range can further improve the kinetics, 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), which has a multilayer sheet-like structure. The number of layers in the boron-containing additive is 2 to 20, for example, values ​​within the range of 2, 3, 5, 6, 9, 11, 13, 15, 17, 20 layers, or any combination thereof. The sheet diameter of the boron-containing additive is 0.2 μm to 0.5 μm, for example, values ​​within the range of 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or any combination thereof. The polar bonds of boron nitride can couple lithium ions, and combined with its multilayer sheet-like structure, more lithium ion migration and transport channels can be established on the surface of the positive electrode active material, improving ionic conductivity and enhancing the kinetics of the secondary battery. Furthermore, boron nitride can also improve the thermal conductivity of the positive electrode, enhancing the electrochemical performance and safety performance of the secondary battery under high temperature and overcharge conditions.

[0028] In this application, the number of boron nitride layers and the sheet diameter can be tested using methods known in the art, and this application does not impose any special limitations. For example, a CP sample of the positive electrode mixture layer can be obtained, and the morphology of boron nitride in the CP sample can be observed using a scanning electron microscope (SEM). Ten multilayer sheet-like boron nitride layers with their sides exposed in the field of view can be randomly selected, and the number of layers can be counted and the arithmetic mean calculated as the number of boron nitride layers (understandably, boron nitride can also include single-layer boron nitride, as long as the arithmetic mean of the counted number of layers is greater than 2); ten multilayer sheet-like boron nitride layers with their front exposed in the field of view can be randomly selected, and the longest distance (longest diameter) between any two points on the perimeter can be counted and the arithmetic mean calculated as the sheet diameter of the boron nitride. See also Figure 1 The SEM image of boron nitride shows the diameter of a single boron nitride flake as indicated 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 LiF / LiI-rich solid electrolyte interface layer, improve the bulk / phase diffusion kinetics of lithium ions, expand ion transport channels, balance the lithium ion transport kinetics of the positive and negative electrodes, and improve the overall kinetics of the secondary battery; it also helps to reduce side reactions and gas generation, and improve the high-temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0030] In some embodiments, the positive electrode additive layer includes titanium; the mass percentage of titanium is c% based on the mass of the positive electrode additive layer; 0.1 ≤ c ≤ 0.5. For example, c can be a value within the range of 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these. Adjusting the mass percentage of titanium within the above range, in conjunction with the aforementioned boron-containing and iodine-containing additives, can further improve the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0031] The positive electrode in this application also includes a positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may comprise aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). This application does not impose any particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive current collector may be from 5 μm to 20 μm.

[0032] In this application, the positive electrode mixture layer can be disposed on one side surface in the thickness direction of the positive electrode current collector, or on both sides surface in the thickness direction of the positive electrode current collector. It should be noted that "surface" can be the entire area of ​​the positive electrode current collector or a part of the positive electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0033] In this application, the positive electrode mixture layer includes a positive electrode active material, which is any substance capable of reversibly inserting and deintercalating alkali metal ions (e.g., lithium ions).

[0034] Optionally, the positive electrode active material comprises a lithium transition metal oxide containing nickel and other transition metals. In the lithium transition metal oxide comprising nickel and other transition metals, the amount of nickel 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, relative to the total moles of the transition metals.

[0035] For example, lithium transition metal oxides can be compounds represented by the following formula α:

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

[0037] 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 can 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, lithium transition metal oxides can 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] In equation 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] In the 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, lithium transition metal oxides can 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 substance 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 this application, the positive electrode mixture layer also includes a positive electrode conductive agent. This application does not impose any particular limitation on the positive electrode conductive agent, as long as it can achieve the purpose of this application. 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, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic 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 aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0046] In this application, the positive electrode binder is also included in the positive electrode mixture layer. This application does not have any particular limitation on the positive electrode binder, as long as it can achieve the purpose of this application. For example, it can include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylonitrile, polystyrene-butadiene copolymer, sodium alginate, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose.

[0047] The negative electrode sheet of this application also includes a negative electrode current collector. In this application, the negative electrode flux layer can be disposed on one surface in the thickness direction of the negative electrode current collector, or on both 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 part of the negative electrode current collector; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the thickness of the negative electrode flux layer, as long as the purpose of this application is achieved. For example, the thickness of a single-sided negative electrode flux layer can be from 30 μm to 160 μm.

[0048] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. 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 collectors (e.g., carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector), etc. This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector may be from 4 μm to 10 μm.

[0049] The negative electrode additive layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it enables reversible insertion and extraction of 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 that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys, or their alloys with lithium; SiO... β (0<β≤2), SnO, SnO2, vanadium oxide, lithium vanadium oxide, and other lithium-doped or de-doped metal oxides or their alloys with lithium; or Si-C composites or Sn-C composites containing metals and carbon materials; or spinel-structured lithium titanate lithiation TiO2-Li4Ti5O 12 Furthermore, any one or a mixture of two or more of them can be used. Additionally, lithium metal thin films can also be used as the negative electrode active material. Specifically, carbon materials can include low-crystallinity carbon and high-crystallinity carbon. Representative low-crystallinity carbons are soft carbon and hard carbon. Examples of high-crystallinity carbon include amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, primary graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, carbon microspheres (mesophase carbon microspheres), mesophase pitch, and high-temperature calcined carbons such as petroleum and coal-based coke (coke derived from petroleum or coal tar pitch).

[0050] In this application, the negative electrode binder may also be included in the negative electrode binder layer. This application does not have any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. 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, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

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

[0052]

[0053] In Equation 1, R 1 and R 2Each compound is independently selected from fluorinated or C1-C4 fluoroalkyl groups substituted with at least one fluorinated group. Compounds represented by Formula 1 may be called cesium sulfonamide salts or fluorinated cesium sulfonamide salts. The first substance can combine with iodine-containing additives to promote the formation of a LiI-rich solid electrolyte interphase (SEI) layer, improve the ionic conductivity of the negative electrode and the 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 kinetics, high-temperature performance, overcharge temperature rise and thermal safety performance of secondary batteries.

[0057] In some embodiments, the mass percentage of the first substance in the electrolyte is m%, based on the mass of the electrolyte; 0.01 ≤ m ≤ 3, preferably 0.1 ≤ m ≤ 2. Exemplarily, the value of m can be within the range of 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 any two of these. When the mass percentage of the first substance in the electrolyte is controlled within the above range, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery can be further improved.

[0058] In some embodiments, the electrolyte comprises lithium difluorophosphate, and the mass percentage 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 a value within the range of 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 any two of these. When the mass ratio of lithium difluorophosphate to the first substance is adjusted to meet the above relationship, the kinetics, 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 any combination thereof. Adjusting the mass ratio of lithium difluorophosphate within the above range can further improve the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery.

[0060] In this application, the electrolyte may also include other lithium salts and non-aqueous solvents. Other lithium salts may include at least one selected from LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, and lithium bis(oxalatoborate) (LiBOB). This application does not impose any particular limitation on the concentration of other lithium salts in the electrolyte, as long as the purpose of this application is achieved.

[0061] This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain 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 methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are 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 aforementioned carboxylic acid ester compounds may include, but are 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, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are 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 aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0062] The secondary battery of this application also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester films (e.g., polyethylene terephthalate (PET) films), cellulose films, polyimide films (PI), polyamide films (PA), spandex, or aramid films. The type of separator can include, but is not limited to, at least one of woven films, nonwoven films (non-woven fabrics), microporous films, composite films, rolled films, or spun films. The separator of this application can have a porous structure, and the pore size is not particularly limited, as long as it achieves the purpose of this application. For example, the pore size can be from 0.01 μm to 1 μm. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application. For example, the thickness can be from 5 μm to 500 μm.

[0063] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0064] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion secondary batteries, lithium metal secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries. In one embodiment, the electrode assembly structure includes a wound structure or a stacked structure.

[0065] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0066] This application does not limit the packaging bags used; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, aluminum-plastic film packaging bags can be used.

[0067] In a second aspect, this application also provides an electronic device, including the electrochemical device provided in the first aspect of this application.

[0068] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electrochemical device described in this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0069] The following uses a lithium-ion battery as an example to illustrate the solution of this application with reference to the specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0070] Performance testing methods:

[0071] Kinetic (low-temperature rate performance) test:

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

[0073] Rate discharge capacity retention rate (%) = (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 at a constant current of 0.1C to 4.5V at 25°C, and then discharged at a constant current of 0.1C to 3.0V. The battery cells were immersed in flowing paraffin, and the cell volume X0 was measured. The battery was then cycled 100 times at 85°C under the same charge-discharge conditions. After 100 cycles, the battery cells were immersed in flowing paraffin, and the cell volume X1 was measured. The cell volume change rate (%) before and after the 100-cycle high-temperature charge-discharge test is calculated as (X1-X0) / X0×100. A smaller cell volume change rate indicates less gas generation from the electrodes and a better ability of the electrodes to suppress gas generation.

[0076] Overcharge temperature rise test:

[0077] At 25℃, the lithium-ion battery was subjected to CC-CV charging at a constant current of 0.7C for 8 hours (upper limit of cell voltage: 5.05V). The battery was then allowed to stand until the cell surface temperature returned to within ±10℃ of ambient temperature, at which point the test was stopped. The cell surface temperature was monitored throughout the process. A lower temperature rise indicates better heat dissipation suppression performance of the secondary battery during overcharging.

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

[0079] The battery was charged at a constant current rate of 0.2C using constant current-constant voltage (CC-CV) charging (upper limit of 4.5V for battery cell voltage), and then discharged at a constant current rate of 0.2C to 3.0V. This charge-discharge process was repeated three times. Then, at 25°C, it was charged at a charge rate of 0.2C using constant current-constant voltage (CC-CV) charging to 4.5V (termination condition: 0.05C). Next, a 3mm diameter, 10cm long iron nail was driven through the vicinity of the center of the secondary battery at a speed of 5m / min, forcibly short-circuiting it. The cell surface temperature was monitored during the process; a lower temperature rise indicated better heat dissipation suppression performance during internal short circuits.

[0080] Example 1-1

[0081] 1) Positive electrode

[0082] Lithium cobalt oxide (CCO), a positive electrode active material, Super P (a conductive agent), carbon nanotubes, polyvinylidene fluoride (PVDF), and boron nitride (BN) were mixed in a weight ratio of 97.0:0.8:0.5:1.3:0.4. All materials were thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent to form a uniform positive electrode slurry with a solid content of 72 wt%. This slurry was coated onto an aluminum foil current collector and dried at 85°C. The above steps were repeated on another surface of the aluminum foil. After cold pressing, cutting, and slitting, the foil was dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0083] 2) Negative electrode

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

[0085] 3) Electrolyte

[0086] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1:1. Then, lithium salt LiPF6 was added and mixed thoroughly to obtain an electrolyte. The mass percentage of LiPF6 was 12.1% based on the mass of the electrolyte.

[0087] 4) Separating membrane

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

[0089] 5) Lithium-ion batteries

[0090] The positive electrode sheet after welding the tabs, the separator, and the negative electrode sheet after welding the tabs are stacked in sequence so that the separator is positioned between the positive and negative electrodes to provide isolation. Then, they are wound and placed in the outer packaging foil aluminum-plastic film, and electrolyte is injected. After vacuum sealing, 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 in Example 1-1. Among them, Comparative Example 1-1 does not add polyacrylonitrile iodide and uses pure graphite as the negative electrode active material; Comparative Example 1-2 does not add boron nitride.

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

[0094] Table 1

[0095]

[0096]

[0097] As shown in Table 1, this application achieves a balance between improving the kinetic performance, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries by adding boron-containing additives to the positive electrode and controlling the mass percentage (a%) of boron in the positive electrode mixture layer to meet the condition of 0.1 ≤ a ≤ 1, and by adding iodine-containing additives to the negative electrode and controlling the mass percentage (b%) of iodine in the negative electrode mixture layer to meet the relationship of 0.04 ≤ a / b ≤ 10. In particular, when the condition of 0.2 ≤ a ≤ 0.5 is met, the kinetic performance, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries can be further improved. Furthermore, when the condition of 0.1 ≤ a / b ≤ 5 is met, the kinetic performance, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries can be improved even more significantly.

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

[0099] In particular, when the number of boron nitride layers is 2 to 20, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries can be further improved. Especially, when the boron nitride sheet diameter is controlled to be between 0.2 μm and 0.5 μm, lithium-ion batteries can exhibit even better kinetics, 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 in Examples 1-8. Specifically, commercially available titanium-doped lithium cobalt oxide is used as the positive electrode active material; when adjusting the addition of substances from Table 2 to the electrolyte, the masses of ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate are reduced accordingly to maintain the same mass ratio among the four.

[0102] Table 2

[0103]

[0104] As shown in Table 2, when the mass percentage (c%) of titanium in the positive electrode additive layer meets the condition that 0.1 ≤ c ≤ 0.5, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries can be further improved.

[0105] Specifically, when the electrolyte includes the first substance and its mass percentage (m%) satisfies 0.01 ≤ m ≤ 3, it can further improve the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the lithium-ion battery when combined with the positive and negative electrode systems of this application. In particular, when 0.1 ≤ m ≤ 2 is satisfied, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the secondary battery can be improved more significantly. More preferably, when the first substance simultaneously includes the compound of Formula 1 and cesium hexafluorophosphate, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of the lithium-ion battery can be further improved.

[0106] Specifically, adjusting the electrolyte to include lithium difluorophosphate, so that its mass percentage (n%) satisfies the relationship of 0.05 ≤ m / n ≤ 1 with the first substance, can further improve the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries. In particular, when 0.08 ≤ m / n ≤ 0.1 is satisfied, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries are improved even more significantly. Especially, when 0.02 ≤ n ≤ 2 is satisfied, the kinetics, high-temperature performance, overcharge temperature rise, and thermal safety performance of lithium-ion batteries can be further improved.

[0107] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. An electrochemical device, characterized by, 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; the mass percentage of the boron element in the positive electrode mixture layer is a%; 0.1≤a≤1; 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; the mass percentage of the iodine element in the negative electrode mixture layer is b%; 0.04≤a / b≤10. 0.1≤a≤1; 0.04≤a / b≤10.

2. The electrochemical device of claim 1, wherein 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 of claim 1, wherein The boron-containing additive comprises boron nitride, and the boron-containing additive has a multi-layer sheet structure; the number of layers of the boron-containing additive is 2-20, and the sheet diameter of the boron-containing additive is 0.2-0.5 μm; and / or, The iodine-containing additive comprises iodized polyacrylonitrile.

4. The electrochemical device according to any one of claims 1 to 3, wherein The positive electrode mixture layer comprises a titanium element; the mass percentage of the titanium element in the positive electrode mixture layer is c%; 0.1≤c≤0.

5.

5. The electrochemical device according to any one of claims 1 to 3, wherein The electrolyte comprises a first substance, and the first substance comprises a compound of Formula 1, cesium hexafluorophosphate, or a combination thereof; In formula 1, R 1 and R 2 are each independently selected from fluoro or C1-C4 fluoroalkyl substituted with at least one fluoro.

6. The electrochemical device of claim 5, wherein, The compound of Formula 1 comprises at least one of the following compounds:

7. The electrochemical device of claim 5, wherein The mass percentage of the first substance in the electrolyte is m%; 0.01≤m≤3.

8. The electrochemical device of claim 7, wherein The electrolyte comprises lithium difluorophosphate; the mass percentage of lithium difluorophosphate in the electrolyte is n%; 0.05≤m / n≤1; 0.02≤n≤2。 9. The electrochemical device of claim 8, wherein, 0.1≤m≤2; and / or, 0.08≤m / n≤0.

1.

10. An electronic device, comprising: The electrochemical device comprises any one of claims 1-9.

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