Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device. The electrochemical device comprises a positive pole piece, a negative pole piece and an electrolyte, wherein the electrolyte comprises a compound shown in a formula I and a compound shown in a formula II; wherein the compound in the formula I is # imgabs 0, and the compound in the formula II is # imgabs 1, based on the total mass of the electrolyte, the mass percentage content of the compound in the formula I is 1%-50%, and the ratio of the mass percentage content of the compound in the formula I to the mass percentage content of the compound in the formula II is within the range of 0.5-500. According to the electrochemical device, the cycle performance, the safety performance and the low-temperature discharge performance of the electrochemical device can be improved by controlling the components of the electrolyte in the electrochemical device and the content of the components.

Description

Technical Field

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

[0002] Electrochemical devices such as lithium-ion batteries are widely used in portable electronic products, electric vehicles, aerospace, energy storage and other fields due to their high energy density, good cycle performance, safety, environmental protection and no memory effect. However, during the charging and discharging process of lithium-ion batteries, the electrolyte easily reacts at the positive and negative electrodes of the battery, which is not conducive to the cycle performance, safety performance and low-temperature discharge performance of lithium-ion batteries. Summary of the invention

[0003] The present application provides an electrochemical device and an electronic device. The positive and negative electrode sheets in the electrochemical device of the present application have high film-forming quality, which can greatly improve the cycle performance, safety performance and low-temperature discharge performance of the electrochemical device.

[0004] In a first aspect, the present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte includes a compound of formula I and a compound of formula II. The compound of formula I is: R is selected from any one of fluorine-substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorine-substituted or unsubstituted C6-C12 aryl group; the compound of formula II is: Wherein R1 is selected from O or -CH(R a )-, and R a Any one selected from H, F, C1-C5 alkyl, C1-C5 alkoxy; R2, R3 are each independently selected from any one selected from H, F, C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl; R4 is selected from any one selected from H, F, fluorine-substituted or unsubstituted C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of the compound of formula II is b%, 1≤a≤50, 0.5≤a / b≤500.

[0005] In the above technical scheme, the sulfonyl fluoride group of the compound of formula I makes it have good antioxidant ability, and its viscosity is also low. When the content of the compound of formula I in the electrolyte is above 1wt%, the viscosity of the electrolyte is significantly reduced, and the stability can also be improved, which is beneficial to improve the low-temperature discharge performance and cycle performance of the electrochemical device; however, the inventors found that when there are too many compounds of formula I in the electrolyte, not only a thicker SEI film (i.e., solid electrolyte interface film) will be formed on the surface of the negative electrode plate, but also the electrolyte will have a reduced solubility for lithium salts, which will not only reduce the safety performance of the electrochemical device, but also be detrimental to the discharge performance of the electrochemical device. The inventors also found that the compound of formula II in the electrolyte can generate a polymer containing a heterocyclic ring, which can form a tough protective film on the negative electrode plate. The protective film can inhibit the continuous reaction of the compound of formula I, thereby improving the safety performance of the electrochemical device, and also improving the discharge performance of the electrochemical device; but the content of the compound of formula II should not be too high, otherwise the impedance of the protective film will increase, which is detrimental to the cycle performance and low-temperature discharge performance of the electrochemical device. In addition, the inventors also found that the mass percentage ratio of the compound of formula I and the compound of formula II in the electrolyte needs to be in the range of 0.5 to 500; if the mass ratio is too low, the protective performance of the protective film formed by the compound of formula II is insufficient, which is not conducive to the safety performance of the electrochemical device; if the mass ratio is too high, the impedance of the protective film is too large, which is not conducive to the cycle performance of the electrochemical device.

[0006] In a possible implementation, the electrolyte satisfies at least one of the following conditions: (1) 2≤a≤10; (2) 0.1≤b≤1; (3) 4≤a / b≤50.

[0007] In the above technical solution, the cycle performance, safety performance and low-temperature discharge performance of the electrochemical device that meets the above conditions can be further improved.

[0008] In one possible implementation, the compound of formula I includes at least one of the following compounds:

[0009]

[0010] In the above technical solution, when the electrolyte contains at least one compound of formula I, the cycle performance and low-temperature discharge performance of the electrochemical device can be further improved.

[0011] In one possible implementation, the compound of formula II includes at least one of the following compounds:

[0012]

[0013] In the above technical solution, when the electrolyte contains at least one compound of formula II, the safety performance of the electrochemical device can be further improved.

[0014] In one possible implementation, the electrolyte also includes a second component, which includes at least one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, and lithium tetrafluoroborate; based on the total mass of the electrolyte, the mass percentage of the second component is c%, where 0.01≤c≤3, and 0.011≤(c+b) / a≤3.

[0015] In the above technical solution, the second component can act synergistically with the compound of formula I and the compound of formula II to further improve the cycle performance of the electrochemical device.

[0016] In one possible implementation, the electrolyte further includes a third component, the third component including at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide; based on the total mass of the electrolyte, the mass percentage of the third component is d%, wherein 0.1≤d≤10, and 0.1≤d / b≤100.

[0017] In the above technical solution, the third component can further reduce the impedance of the interface film in the electrochemical device and improve the stability of the interface film after synergistic action with the compound of formula II, thereby improving the cycle performance and low-temperature discharge performance of the electrochemical device.

[0018] In a possible implementation, the electrolyte also includes a fourth component, which includes at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methane disulfonic acid methylene ester, vinyl sulfate, and glyoxal disulfate; based on the total mass of the electrolyte, the mass percentage of the fourth component is e%, where 0.1≤e≤6.

[0019] In the above technical solution, the fourth component can enhance the stability of the compound of formula I on the negative electrode sheet and improve the cycle performance of the electrochemical device.

[0020] In a possible implementation, the electrolyte further includes fluoroethylene carbonate; based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is f%, where 1≤f≤20.

[0021] In the above technical solution, fluoroethylene carbonate is beneficial to further improve the cycle performance of the electrochemical device.

[0022] In one possible implementation, 3≤f≤15.

[0023] In the above technical solution, the electrolyte that meets the above conditions is conducive to further improving the cycle performance and safety performance of the electrochemical device.

[0024] In a second aspect, an embodiment of the present application provides an electronic device, which includes the above-mentioned electrochemical device. Therefore, the electronic device provided by the present application has good performance.

[0025] Beneficial effects of this application:

[0026] The present application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte comprises a compound of formula I and a compound of formula II. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, the mass percentage of the compound of formula II is b%, 1≤a≤50, 0.5≤a / b≤500. By regulating the electrolyte to include a compound of formula I and a compound of formula II, and the types and mass percentages of the compound of formula I and the compound of formula II within the scope of the present application, the cycle performance, safety performance and low-temperature discharge performance of the electrochemical device can be improved. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conditions recommended by the normal conditions or manufacturers are carried out. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0028] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0029] The present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte includes a compound of formula I and a compound of formula II. The compound of formula I is as follows:

[0030]

[0031] Wherein, R is selected from any one of fluorine-substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorine-substituted or unsubstituted C6-C12 aryl;

[0032] The compound of formula II is as follows:

[0033]

[0034] Wherein, R1 is selected from O or -CH(R a )-, and R aAny one selected from H, F, C1-C5 alkyl, C1-C5 alkoxy; R2, R3 are each independently selected from any one selected from H, F, C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl; R4 is selected from any one selected from H, F, fluorine-substituted or unsubstituted C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, and the mass percentage of the compound of formula II is b%, 1≤a≤50, 0.5≤a / b≤500. Preferably, 2≤a≤10; for example, a can be 5, 7.3, 8.6, 10, 13, 24, 30, 34, 39.7, 43.2, 50, etc. or a range consisting of any two of the above values. Preferably, 0.1≤b≤1; for example, b can be 0.01, 0.03, 0.07, 0.1, 0.4, 0.94, 1, 1.2, 1.76, 1.85, 2, etc., or a range consisting of any two of the above values. Preferably, 25≤a / b≤100; for example, a / b can be 2.5, 22.5, 23.3, 25, 28.3, 30, 32.5, 72.5, 100, 122.8, 243.3, 500, etc., or a range consisting of any two of the above values.

[0035] The inventors found that the compound of formula I not only has a low viscosity, but also has a good antioxidant capacity due to the sulfonyl fluoride group it contains. When the content of the compound of formula I in the electrolyte is above 1wt%, the viscosity of the electrolyte can be significantly reduced, and the stability can also be improved, which is beneficial to improve the low-temperature discharge performance and cycle performance of the electrochemical device. However, the inventors found that when there are too many compounds of formula I in the electrolyte, not only a thicker SEI film will be formed on the surface of the negative electrode plate, but also the electrolyte's ability to dissolve lithium salts will decrease, which is not conducive to the safety performance of the electrochemical device, nor to the discharge performance of the electrochemical device. The inventors also found that the compound of formula II in the electrolyte can generate a polymer containing a heterocyclic ring, which can form a tough protective film on the negative electrode plate. The protective film can inhibit the continuous reaction of the compound of formula I on the surface of the negative electrode plate, thereby improving the safety performance of the electrochemical device, and also improving the discharge performance of the electrochemical device; but the content of the compound of formula II should not be too high, otherwise the impedance of the protective film will increase, which is not conducive to the cycle performance and low-temperature discharge performance of the electrochemical device. In addition, the inventors also found that the mass percentage ratio of the compound of formula I and the compound of formula II in the electrolyte needs to be in the range of 0.5 to 500; if the mass ratio is too low, the protective performance of the protective film formed by the compound of formula II is insufficient, which is not conducive to the safety performance of the electrochemical device; if the mass ratio is too high, the impedance of the protective film is too large, which is not conducive to the cycle performance of the electrochemical device.

[0036] In some embodiments of the present application, in order to further improve the cycle performance and low-temperature discharge performance of the electrochemical device, the compound of formula I may be at least one of the following compounds:

[0037]

[0038] In some embodiments of the present application, in order to further improve the safety performance of the electrochemical device, the compound of formula II includes at least one of the following compounds:

[0039]

[0040] In some embodiments of the present application, the electrolyte further includes a second component, the second component includes at least one of lithium bis(oxalate borate), lithium difluoro(oxalate borate), and lithium tetrafluoroborate, and the second component can synergize with the compound of formula I and the compound of formula II to further improve the cycle performance of the electrochemical device. Based on the total mass of the electrolyte, the mass percentage of the second component is c%, 0.01≤c≤3, and 0.011≤(c+b) / a≤3. For example, c can be 0.01, 0.08, 0.24, 0.95, 1.36, 2.45, 2.9, 3, etc. or a range consisting of any two of the above values, (c+b) / a can be 0.011, 0.055, 0.09, 0.17, 0.525, 0.73, 1.275, 1.55, 3, etc. or a range consisting of any two of the above values.

[0041] In some embodiments of the present application, the electrolyte further includes a third component, and the third component includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide; the third component can synergize with the compound of formula II to further reduce the impedance of the interface film in the electrochemical device, improve the stability of the interface film, and thus improve the cycle performance and low-temperature discharge performance of the electrochemical device. Based on the total mass of the electrolyte, the mass percentage of the third component is d%, 0.1≤d≤10, and 0.1≤d / b≤100. For example, d can be 0.1, 2.4, 3.6, 5.5, 7.2, 8.6, 10, etc., or a range consisting of any two of the above values; d / b can be 0.1, 1, 24, 36, 55, 72, 86, 100, etc., or a range consisting of any two of the above values.

[0042] In some embodiments of the present application, the electrolyte further includes a fourth component, which includes at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methane disulfonic acid methylene ester, vinyl sulfate, and glyoxal disulfate; the fourth component can enhance the stability of the compound of formula I on the negative electrode sheet and improve the cycle performance of the electrochemical device. Based on the total mass of the electrolyte, the mass percentage of the fourth component is e%, 0.1≤e≤6. For example, e can be 0.1, 1, 2, 3, 4, 5, 6, etc. or a range consisting of any two of the above values.

[0043] In a possible implementation, the electrolyte further includes fluoroethylene carbonate; the fluoroethylene carbonate in the electrolyte is beneficial to further improve the cycle performance of the electrochemical device. Based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate is f%, where 1≤f≤20; for example, f can be 1, 3, 6, 10, 14, 17, 20, etc. or a range consisting of any two of the above values; preferably, 3≤f≤15.

[0044] In the electrochemical device of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. "The positive electrode material layer arranged on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along the thickness direction of itself, or it can be arranged on two surfaces of the positive electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or 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. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0045] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance that can reversibly embed and extract active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in the multilayer positive electrode material layer can contain the same or different positive electrode active materials. The present application has no particular restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. At least one of the positive electrode material layer of the present application also includes a conductive agent and a binder. The present application has no particular restrictions on the conductive agent and the binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers. The above-mentioned conductive carbon black may include but is not limited to Super P, acetylene black or Ketjen black. 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 nanocarbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers, and 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. The binder may include but is not limited to polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose (CMC-Na), potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose. The present application does not particularly limit the mass ratio of the positive active material, the conductive agent and the binder in the positive electrode material layer, and those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0046] The present application has no particular restrictions on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The present application has no particular restrictions on the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0047] Optionally, the positive electrode plate may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The present application has no particular restrictions on the composition of the conductive layer, which may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application has no particular restrictions on the conductive agent and the binder in the conductive layer, which may be at least one of the above conductive agent and the above binder. The present application has no particular restrictions on the mass ratio of the conductive agent and the binder in the conductive layer, and those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0048] In the present application, the electrochemical device also includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. 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 negative electrode current collector, as long as the purpose of this application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector, etc.

[0049] The negative electrode material layer of the present application includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0.5<x<1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O 12 , Li-Al alloy or metallic lithium, etc. The negative electrode material layer of the present application also includes a binder. The present application has no special restrictions on the binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the binder can be at least one of the above binders. The negative electrode material layer of the present application also includes a conductive agent. The present application has no special restrictions on the conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent can be at least one of the above conductive agents. The present application has no special restrictions on the mass ratio of the negative electrode active material, the binder and the conductive agent in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0050] The present application has no particular limitation 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 5 μm to 16 μm. The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm.

[0051] Optionally, the negative electrode plate may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular restrictions on the composition of the conductive layer, which may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application has no particular restrictions on the conductive agent and the binder in the conductive layer, which may be at least one of the above conductive agent and the above binder. The present application has no particular restrictions on the mass ratio of the conductive agent and the binder in the conductive layer, and those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the thickness of the conductive layer, as long as the purpose of the present application can be achieved, for example, the thickness of the conductive layer is 1 μm to 10 μm. In the present application, the electrochemical device also includes a diaphragm, which is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuits in the electrochemical device, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the diaphragm, 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)-based polyolefin (PO), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of the separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. The present application has no particular limitation on the thickness of the separator, as long as the purpose of the present application can be achieved, for example, the thickness of the separator is 3 μm to 30 μm.

[0052] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, the thickness of the base film is 3 μm to 25 μm. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the present application has no particular restrictions on the above-mentioned inorganic particles, for example, it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the above-mentioned binder, for example, it can be at least one of the aforementioned binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene). Optionally, the thickness of the surface treatment layer is 1 μm to 10 μm.

[0053] The electrochemical device 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 electrochemical device, 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.

[0054] The present application does not particularly limit the type of electrochemical device, which may include any device that undergoes an electrochemical reaction. In the present application, the electrochemical device may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery (lithium ion polymer battery), etc.

[0055] The preparation process of the electrochemical device of the present application is well known to those skilled in the art, and the present application has no particular limitation. For example, it may include but is not limited to the following steps: stacking the positive electrode 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 an electrochemical device; 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 an electrochemical device. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent pressure rise and overcharge and discharge inside the electrochemical device.

[0056] The second aspect of the present application provides an electronic device, which includes the electrochemical device in any of the above embodiments. Therefore, the electronic device provided by the present application has good performance.

[0057] The present application does not particularly limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0058] Example

[0059] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0060] Test methods and equipment:

[0061] Cycle performance test:

[0062] The cycle performance of the electrochemical device is evaluated by the capacity retention rate after 400 cycles at 45° C. The greater the capacity retention rate after 400 cycles at 45° C., the better the cycle performance of the electrochemical device.

[0063] The electrochemical device was placed in a 45°C thermostat and allowed to stand for 30 minutes to allow the electrochemical device to reach a constant temperature. The electrochemical device that reached a constant temperature was charged to 4.5V at 0.2C constant current at 45°C, charged to 0.05C at 4.5V, allowed to stand for 5 minutes, and then discharged to 3.0V at 0.2C constant current, allowed to stand for 5 minutes, and the initial discharge capacity C0 of the electrochemical device was tested; then charged to 4.15V at 1.8C constant current, and charged to 1C at 4.15V constant voltage; then charged to 4.25V at 1C constant current, and then charged to 0.8C at 4.25V constant voltage; then charged to 4.5V at 0.8C constant current, and then charged to 0.05C at 4.5V constant voltage; left for 5 minutes; then discharged to 3.0V at 1C constant current, and allowed to stand for 5 minutes. This is one charge and discharge cycle. The electrochemical device was cycled 400 times according to the above charge / discharge cycle steps, and the discharge capacity C1 of the electrochemical device after 400 cycles was measured.

[0064] The capacity retention rate after 400 cycles at 45°C = C1 / C0×100%.

[0065] Safety performance test:

[0066] The electrochemical device is discharged at 0.2C constant current to 3.0V at 25℃, then charged at 0.5C constant current to 4.5V, and then charged at 4.5V to 0.05C constant voltage. Place it in a high temperature furnace at 130℃, 131℃, 132℃, 133℃, 134℃ or 135℃ for 1 hour. After 1 hour, observe whether the electrochemical device catches fire. If it does not catch fire, it is judged to have passed. The pass rate is recorded as N / 10, which means that N of the 10 electrochemical devices tested passed the test.

[0067] Hot box performance judgment standard: Under different temperatures, the higher the temperature without ignition, the better the hot box performance and the better the thermal safety performance; under the same temperature, the higher the pass rate, the better the hot box performance and the better the thermal safety performance. For example, the test results of 5 / 10 at 133°C are better than the test results of 3 / 10 at 133°C, and the test results of 3 / 10 at 133°C are better than the test results of 5 / 10 at 132°C. The specific data of the hot box test of the electrochemical device in each embodiment and comparative example are shown in the table.

[0068] Low temperature discharge performance test:

[0069] The electrochemical device was charged to 4.5V at 0.2C at 25°C, then charged to a cut-off current of 0.02C at a constant voltage of 4.5V, and then discharged at a constant current of 0.2C for 4h. The temperature was adjusted to -20°C, and after keeping warm for 30min, 0.4C was discharged for 1s, 0.1C was discharged for 2s, and this step (0.4C discharge for 1s, 0.1C discharge for 2s) was repeated until the voltage was lower than 3V. The number of cycles at this time was recorded, which was the number of low-temperature pull-load cycles. The higher the number of low-temperature pull-load cycles, the better the low-temperature discharge performance.

[0070] Example 1-1

[0071] <Preparation of Electrolyte>

[0072] In an argon atmosphere glove box with a water content of less than 10ppm, ethylene carbonate, propylene carbonate and propyl propionate were mixed in a mass percentage of 1:1:2 to prepare a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) and the components in Table 1 were added. Based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate (LiPF6) was 12.5%, the contents of the compound of formula I and the compound of formula II were shown in Table 1, and the remainder was the base solvent.

[0073] <Preparation of positive electrode sheet>

[0074] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2:3, N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry was evenly coated on the upper and lower surfaces of a positive electrode current collector aluminum foil with a thickness of 9μm, and a positive electrode material layer with a thickness of 110μm was formed on the surface of the aluminum foil after drying. After pressure treatment, the positive electrode was sheared into a specified size to obtain a positive electrode sheet.

[0075] <Preparation of negative electrode sheet>

[0076] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8, and then deionized water was added as a solvent and stirred evenly to prepare a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry was evenly coated on the upper and lower surfaces of a negative electrode current collector copper foil with a thickness of 6μm, and a negative electrode material layer with a thickness of 100μm was formed on the surface of the copper foil after drying. After pressure treatment, it was sheared into a specified size to obtain a negative electrode sheet.

[0077] <Isolation film>

[0078] A porous polyethylene film with a thickness of 15 μm was used as the separator.

[0079] <Preparation of electrochemical device>

[0080] The prepared positive electrode sheet, separator, negative electrode sheet and separator are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. After welding the pole ears, the electrode assembly is placed in an aluminum-plastic film packaging bag, placed in a vacuum oven at 85°C for 12 hours to remove moisture, and the prepared electrolyte is injected. After vacuum packaging, standing, formation, shaping, and capacity testing, a lithium-ion battery (i.e., an electrochemical device) is obtained.

[0081] Example 1-2 to Example 1-4

[0082] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Wherein, when the content of the compound of formula I and / or the compound of formula II changes, the mass percentage of LiPF6 remains unchanged.

[0083] Example 1-5 to Example 1-11

[0084] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-4. Wherein, when the content of the compound of formula I changes, the mass percentage of LiPF6 remains unchanged.

[0085] Example 1-12 to Example 1-19

[0086] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-6.

[0087] Table 1

[0088]

[0089]

[0090] Example 2-1 to Example 2-9

[0091] Except for further adding the second component in <Preparation of Electrolyte> and adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-5. When the mass percentage of the second component changes, the mass percentage of LiPF6 remains unchanged.

[0092] Example 2-10 to Example 2-11

[0093] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 2-3.

[0094] Table 2

[0095]

[0096] Example 3-1 to Example 3-8

[0097] Except for further adding the third component in <Preparation of Electrolyte> and adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 1-5. Wherein, when the mass percentage of the third component changes, the mass percentage of LiPF6 remains unchanged.

[0098] Embodiment 3-9

[0099] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 3-3.

[0100] Table 3

[0101]

[0102] Example 4-1 to Example 4-7

[0103] Except for further adding the fourth component in <Preparation of Electrolyte> and adjusting the relevant preparation parameters according to Table 4, the rest is the same as Example 1-5. Wherein, when the mass percentage of the fourth component changes, the mass percentage of LiPF6 remains unchanged.

[0104] Example 4-8 to Example 4-12

[0105] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as Example 4-4.

[0106] Table 4

[0107]

[0108] Example 5-1 to Example 5-7

[0109] Except for further adding fluoroethylene carbonate in <Preparation of Electrolyte> and adjusting relevant preparation parameters according to Table 5, the rest is the same as Example 1-5. Among them, when the mass percentage of fluoroethylene carbonate changes, the mass percentage of LiPF6 remains unchanged.

[0110] Table 5

[0111]

[0112]

[0113] Comparative Example 1 and Comparative Example 2

[0114] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-5. Wherein, when the mass percentage of the compound of formula I changes, the mass percentage of LiPF6 remains unchanged.

[0115] Comparative Example 3

[0116] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. When the mass percentage of the compound of formula I changes, the mass percentage of LiPF6 remains unchanged.

[0117] As can be seen from Table 1, in the electrochemical device of the present application, when the electrolyte contains no more than 2% of the compound of formula II and 5% to 50% of the compound of formula I, the electrochemical device has excellent cycle performance, safety performance and low-temperature discharge performance.

[0118] As can be seen from Table 2, the combination of the second component with the compound of formula I and the compound of formula II can better improve the cycle performance of the electrochemical device.

[0119] It can be seen from Table 3 that the third component can further reduce the impedance of the interface film in the electrochemical device and improve the stability of the interface film after synergistic action with the compound of formula II, thereby improving the cycle performance and low-temperature discharge performance of the electrochemical device.

[0120] It can be seen from Table 4 that the combination of the fourth component and the compound of formula I can further improve the cycle performance of the electrochemical device.

[0121] It can be seen from Table 5 that fluoroethylene carbonate is beneficial to further improve the cycle performance of the electrochemical device; especially when the content of fluoroethylene carbonate is in the range of 3% to 15%, the cycle performance of the electrochemical device can be further improved.

[0122] The above are only embodiments of the present application and are not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The components of the electrolyte include a compound of formula I and a compound of formula II, wherein the compound of formula I is: Wherein R is selected from any one of fluorine-substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclic group, and fluorine-substituted or unsubstituted C6-C12 aryl group; the compound of formula II is: Wherein R1 is selected from O or -CH(R a )-, and R a is selected from any one of H, F, C1-C5 alkyl, C1-C5 alkoxy; R2 and R3 are each independently selected from any one of H, F, C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl; R4 is selected from any one of H, F, fluorine-substituted or unsubstituted C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl; Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is a%, the mass percentage of the compound of formula II is b%, 1≤a≤50, 0.5≤a / b≤500.

2. The electrochemical device according to claim 1, characterized in that The electrolyte satisfies at least one of the following conditions: (1)2≤a≤10； (2)0.1≤b≤1； (3)4≤a / b≤50.

3. The electrochemical device according to claim 1, characterized in that The compound of formula I comprises at least one of the following compounds:

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

5. The electrochemical device according to claim 1, characterized in that The electrolyte also includes a second component, which includes at least one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, and lithium tetrafluoroborate; based on the total mass of the electrolyte, the mass percentage of the second component is c%, where 0.01≤c≤3, and 0.011≤(c+b) / a≤3.

6. The electrochemical device according to claim 1, characterized in that The electrolyte also includes a third component, which includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide; based on the total mass of the electrolyte, the mass percentage of the third component is d%, wherein 0.1≤d≤10, and 0.1≤d / b≤100.

7. The electrochemical device according to claim 1, characterized in that The electrolyte also includes a fourth component, which includes at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methane disulfonic acid methylene ester, vinyl sulfate, and glyoxal disulfate; based on the total mass of the electrolyte, the mass percentage of the fourth component is e%, and 0.1≤e≤6.

8. The electrochemical device according to claim 1, characterized in that The electrolyte also includes fluoroethylene carbonate; based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is f%, where 1≤f≤20.

9. The electrochemical device according to claim 8, characterized in that 3≤f≤15。 10. An electronic device, characterized in that: The device comprises the electrochemical device according to any one of claims 1 to 9.

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