An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, and the electrolyte comprises a compound of formula I and a compound of formula II; wherein the compound of formula I is: the compound of formula II is: the mass percentage of the compound of formula I is 1-50% based on the total mass of the electrolyte, and the mass percentage ratio of the compound of formula I and the compound of formula II is in the range of 0.5-500. In the application, by controlling the components and the content of the components of the electrolyte in the electrochemical device, the cycle performance, the safety performance and the low-temperature discharge performance of the electrochemical device can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular, to an electrochemical device and an electronic device. BACKGROUND

[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 is prone to react 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

[0003] The present application provides an electrochemical device and an electronic device, the positive and negative electrode sheets in the electrochemical device in the present application have high film forming quality, which can well 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 comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the electrolyte comprising 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, fluorine-substituted or unsubstituted C6-C12 aryl; and 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, 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. The mass percentage content of the compound of formula I is a%, and the mass percentage content of the compound of formula II is b%, based on the total mass of the electrolyte, 1≤a≤50, 0.5≤a / b≤500.

[0005] In the technical solution, the sulfuryl fluoride group of the compound of formula I has good antioxidant capacity, and the viscosity is also low. When the content of the compound of formula I in the electrolyte is more than 1wt%, the viscosity of the electrolyte is obviously reduced, and the stability is improved, which is beneficial to improve the low-temperature discharge performance and cycle performance of the electrochemical device. However, the inventors found that when the content of the compound of formula I in the electrolyte is too much, not only a relatively thick SEI film (solid electrolyte interface film) is formed on the surface of the negative electrode sheet, but also the solubility of the electrolyte to lithium salt is reduced, which reduces the safety performance of the electrochemical device and is not conducive 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 sheet. 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. However, 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 to the compound of formula II in the electrolyte needs to be in the range of 0.5-500. 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 manner, 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 technical solution, the cycle performance, safety performance, and low-temperature discharge performance of the electrochemical device can be further improved.

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

[0009]

[0010] In the 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 a possible implementation manner, the compound of formula II includes at least one of the following compounds:

[0012]

[0013] In the 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 a possible implementation, the electrolyte further comprises a second component, the second component comprises at least one of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate; the mass percentage content of the second component is c% based on the total mass of the electrolyte, where 0.01≤c≤3, and 0.011≤(c+b) / a≤3.

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

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

[0017] In the technical solution, the third component can synergize with the compound of formula II, 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.

[0018] In a possible implementation, the electrolyte further comprises a fourth component, the fourth component comprises at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methanedisulfonate methylene, ethylene sulfate, and glyoxal disulfate; the mass percentage content of the fourth component is e% based on the total mass of the electrolyte, where 0.1≤e≤6.

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

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

[0021] In the technical solution, the fluoroethylene carbonate is conducive to further improving the cycle performance of the electrochemical device.

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

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

[0024] In a second aspect, the embodiments of the present application provide an electronic device comprising the above-mentioned electrochemical device. Therefore, the electronic device provided by the present application has good use performance.

[0025] Advantages of the present application:

[0026] The present application provides an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The electrolyte comprises a compound of Formula I and a compound of Formula II. The mass percentage of the compound of Formula I is a%, and the mass percentage of the compound of Formula II is b%, based on the total mass of the electrolyte, 1≤a≤50, and 0.5≤a / b≤500. By adjusting the electrolyte to comprise the compound of Formula I and the compound of Formula II, the types and mass percentages of the compound of Formula I and the compound of Formula II are within the scope of the present application, which can improve the cycle performance, safety performance and low-temperature discharge performance of the electrochemical device. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturers are used. If the reagents or instruments used are not specified by the manufacturers, they are all conventional products that can be purchased in the market. Obviously, the described embodiments are only some of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0028] It should be noted that in the specific embodiments of the present application, lithium ion batteries are used as examples of electrochemical devices to explain the present application, but the electrochemical devices of the present application are not limited to lithium ion batteries.

[0029] The present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet and an electrolyte. The electrolyte comprises 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, 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 aR1is selected from any one of H, F, C1-C5alkyl, C1-C5alkoxy; R2, R3are each independently selected from any one of H, F, C1-C5alkyl, C1-C5alkoxy, C2-C5alkenyl, C2-C5alkynyl; R4is selected from any one of H, F, fluorine-substituted or unsubstituted C1-C5alkyl, C1-C5alkoxy, C2-C5alkenyl, C2-C5alkynyl. The mass percentage of the compound of Formula I is a%, and the mass percentage of the compound of Formula II is b%, based on the total mass of the electrolyte, 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, or a range between any two of the foregoing. 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, or a range between any two of the foregoing. 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, or a range between any two of the foregoing.

[0035] The inventors have 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 contained therein. When the content of the compound of Formula I in the electrolyte is greater than 1 wt%, the viscosity of the electrolyte can be significantly reduced, and the stability can also be improved, which is conducive to improving the low-temperature discharge performance and cycle performance of the electrochemical device. However, the inventors have found that when the content of the compound of Formula I in the electrolyte is too high, not only a relatively thick SEI film is formed on the surface of the negative electrode sheet, but also the solubility of the electrolyte for lithium salt is reduced, which is not conducive to the safety performance and discharge performance of the electrochemical device. The inventors have also found that the compound of Formula II in the electrolyte can generate a polymer containing a heterocycle, and a tough protective film can be formed on the negative electrode sheet, which can inhibit the continuous reaction of the compound of Formula I on the surface of the negative electrode sheet, thereby improving the safety performance of the electrochemical device, and also improving the discharge performance of the electrochemical device. However, 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 have also found that the mass percentage ratio of the compound of Formula I to the compound of Formula II in the electrolyte needs to be in the range of 0.5-500; 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, and 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, to further improve the cycle performance and low-temperature discharge performance of the electrochemical device, the compound of Formula I can be at least one of the following compounds:

[0037]

[0038] In some embodiments of the present application, 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 bisoxalate borate, lithium difluoro oxalate borate, lithium tetrafluoroborate, the second component can synergistically act with the compound of Formula I and the compound of Formula II to further improve the cycle performance of the electrochemical device. The mass percentage content of the second component is c% based on the total mass of the electrolyte, 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, or a range consisting of any two of the foregoing, and (c+b) / a can be 0.011, 0.055, 0.09, 0.17, 0.525, 0.73, 1.275, 1.55, 3, or a range consisting of any two of the foregoing.

[0041] In some embodiments of the present application, the electrolyte further includes a third component, the third component includes at least one of lithium bisfluorosulfonylimide and lithium bistrifluoromethylsulfonylimide; the third component can synergistically act with the compound of Formula II to further reduce the impedance of the interfacial film in the electrochemical device, improve the stability of the interfacial film, and thus improve the cycle performance and low-temperature discharge performance of the electrochemical device. The mass percentage content of the third component is d% based on the total mass of the electrolyte, 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, or a range consisting of any two of the foregoing, and d / b can be 0.1, 1, 24, 36, 55, 72, 86, 100, or a range consisting of any two of the foregoing.

[0042] In some embodiments of the present application, the electrolyte further comprises a fourth component, the fourth component comprising at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methylene methane disulfonate, ethylene sulfate, and glyoxal disulfate; the fourth component can improve the stability of the compound of Formula I on the negative electrode tab and improve the cycle performance of the electrochemical device. The mass percentage content of the fourth component in the electrolyte is e%, 0.1≤e≤6, based on the total mass of the electrolyte. For example, e can be 0.1, 1, 2, 3, 4, 5, 6, or a range defined by any two of the above values.

[0043] In one possible implementation, the electrolyte further comprises fluoroethylene carbonate; the fluoroethylene carbonate in the electrolyte is conducive to further improving the cycle performance of the electrochemical device. The mass percentage content of the fluoroethylene carbonate in the electrolyte is f%, 1≤f≤20, based on the total mass of the electrolyte; for example, f can be 1, 3, 6, 10, 14, 17, 20, or a range defined by any two of the above values; preferably, 3≤f≤15.

[0044] In the electrochemical device of the present application, the positive electrode tab comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or can be disposed on two surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The positive electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can comprise an aluminum foil, an 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, which includes a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive electrode material layer can be one layer or multiple layers, and each layer of the multiple layers of the positive electrode material layer can include the same or different positive electrode active material. The positive electrode active material of the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the positive electrode active material can include, but is not limited to, at least one of nickel cobalt manganese lithium acid (e.g., NCM811, NCM622, NCM523, NCM111), nickel cobalt aluminum lithium acid, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate. The positive electrode material layer of the present application also includes a conductive agent and a binder, and the conductive agent and the binder in the positive electrode material layer of the present application are not particularly limited as long as the purpose of the present application can be achieved. For example, the conductive agent can 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 can include, but is not limited to, Super P, acetylene black, or Ketjen black. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal materials can include, but are not limited to, metal powder and / or metal fibers, and in particular, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder can include, but is not limited to, at least one of 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 mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer of the present application is not particularly limited, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0046] The thickness of the positive electrode current collector of the present application is not particularly limited 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 thickness of the positive electrode material layer of the present application is not particularly limited 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 sheet can further include an electrically conductive layer between the positive current collector and the positive material layer. The composition of the electrically conductive layer is not particularly limited in the present application and can be an electrically conductive layer commonly used in the art. The electrically conductive layer includes an electrically conductive agent and a binder. The electrically conductive agent and the binder in the electrically conductive layer are not particularly limited in the present application and can be at least one of the electrically conductive agents and the binders described above. The mass ratio of the electrically conductive agent and the binder in the electrically conductive layer is not particularly limited in the present application and can be selected by a person skilled in the art as needed, as long as the purpose of the present application can be achieved.

[0048] In the present application, the electrochemical device further includes a negative electrode sheet including a negative current collector and a negative material layer disposed on at least one surface of the negative current collector. The "negative material layer disposed on at least one surface of the negative current collector" means that the negative material layer can be disposed on one surface of the negative current collector in the thickness direction of the negative current collector, or can be disposed on both surfaces of the negative current collector in the thickness direction of the negative current collector. It should be noted that the "surface" herein can be the entire area of the negative current collector or a partial area of the negative current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The negative current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, etc.

[0049] The negative material layer of the present application includes a negative active material. The negative active material is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the negative active material can include at least one of natural graphite, artificial graphite, mesocarbon microbeads (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, lithium titanate Li4Ti5O 12 with a spinel structure, Li-Al alloy, or metallic lithium, etc. The negative material layer of the present application further includes a binder. The binder in the negative material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the binder can be at least one of the binders described above. The negative material layer of the present application further includes an electrically conductive agent. The electrically conductive agent in the negative material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the electrically conductive agent can be at least one of the electrically conductive agents described above. The mass ratio of the negative active material, the binder, and the electrically conductive agent in the negative material layer is not particularly limited in the present application and can be selected by a person skilled in the art as needed, as long as the purpose of the present application can be achieved.

[0050] The thickness of the negative current collector is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the negative current collector is 5 pm to 16 pm. The thickness of the negative material layer is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the single-sided negative material layer is 30 pm to 120 pm.

[0051] Optionally, the negative electrode sheet can further comprise a conductive layer, which is located between the negative current collector and the negative material layer. The composition of the conductive layer is not particularly limited in the present application, and can be a commonly used conductive layer in the art. The conductive layer comprises a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The mass ratio of the conductive agent and the binder in the conductive layer is not particularly limited in the present application, and can be selected by a person skilled in the art according to actual needs, as long as the object of the present application can be achieved. The thickness of the conductive layer is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the conductive layer is 1 pm to 10 pm. In the present application, the electrochemical device further comprises a separator, which is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the electrochemical device, allow free passage of electrolyte ions, and not affect the electrochemical charging and discharging process. The separator is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) mainly including polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film or spunlaced film. The thickness of the separator is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the separator is 3 pm to 30 pm.

[0052] In the present application, the separator can include a base material and a surface treatment layer. The base material can be a nonwoven fabric or a composite film having a porous structure, and the material of the base material can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can 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 base material, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited in the present application, and for example, can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited in the present application, and for example, can be at least one of the aforementioned binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, 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 further includes a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art in the electrochemical device, and the present application does not limit the other components. The packaging bag is not particularly limited in the present application, and can be a packaging bag known in the art, as long as the purpose of the present application can be achieved.

[0054] The kind of the electrochemical device is not particularly limited in the present application, and can include any device in which an electrochemical reaction occurs. In the present application, the electrochemical device can 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 is not particularly limited, for example, can 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, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly into a packaging bag, injecting an 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, then fixing the four corners of the entire stack structure with tape to obtain a stack structure electrode assembly, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, a current protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the internal pressure of the electrochemical device from rising and overcharging and discharging.

[0056] The second aspect of the present application provides an electronic device comprising the electrochemical device of any of the preceding embodiments. Therefore, the electronic device provided by the present application has good use performance.

[0057] The present application does not have a particular limitation on 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 notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0058] Embodiments

[0059] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0060] Test methods and apparatus:

[0061] Cycling performance test:

[0062] The cycling performance of the electrochemical device was 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 cycling performance of the electrochemical device.

[0063] The electrochemical device was placed in a 45 °C constant temperature oven for 30 minutes to allow the electrochemical device to reach a constant temperature. The electrochemical device that reached a constant temperature was charged at 0.2 C to 4.5 V at 45 °C, charged at 4.5 V to 0.05 C, left for 5 minutes, discharged at 0.2 C to 3.0 V, left for 5 minutes, and the initial discharge capacity C0of the electrochemical device was tested; then charged at 1.8 C to 4.15 V, charged at 4.15 V to 1 C, charged at 1 C to 4.25 V, then charged at 4.25 V to 0.8 C, charged at 0.8 C to 4.5 V, then charged at 4.5 V to 0.05 C, left for 5 minutes, and then discharged at 1 C to 3.0 V, left for 5 minutes, which was one charge-discharge cycle. According to the above charge-discharge cycle steps, 400 cycles were cycled, and the discharge capacity C1of the electrochemical device after 400 cycles was measured.

[0064] Capacity retention rate after 45 °C cycling for 400 cycles = C1 / C0x 100%.

[0065] Safety performance test:

[0066] The electrochemical device was discharged at 0.2 C to 3.0 V at 25 °C, then charged at 0.5 C to 4.5 V, and charged at 4.5 V to 0.05 C. It was stored in a high-temperature oven at 130 °C, 131 °C, 132 °C, 133 °C, 134 °C or 135 °C for 1 hour, and after 1 hour, whether the electrochemical device caught fire was observed, and if it did not catch fire, it was determined to pass. The pass rate was recorded as N / 10, indicating that 10 electrochemical devices were tested, and N passed the test.

[0067] Hot box performance judgment standard: At different temperatures, the higher the temperature at which it does not catch fire, the better the hot box performance, and the better the thermal safety performance; at the same temperature, the higher the pass rate, the better the hot box performance, and the better the thermal safety performance. For example, 133 °C, 5 / 10 test results are better than 133 °C, 3 / 10 test results, 133 °C, 3 / 10 test results are better than 132 °C, 5 / 10 test results. The specific data of the hot box test of the electrochemical device in each example and comparative example is shown in the table.

[0068] Low-temperature discharge performance test:

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

[0070] Example 1-1

[0071] Preparation of electrolyte

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

[0073] Preparation of positive electrode sheet

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

[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 uniformly to prepare a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated on the upper and lower surfaces of a negative electrode current collector copper foil with a thickness of 6 μm, and after drying, a negative electrode material layer with a thickness of 100 μm was formed on the surface of the copper foil. After pressure treatment, the negative electrode sheet was cut to a specified size.

[0077] Separator film

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

[0079] Preparation of the electrochemical device

[0080] The positive electrode sheet, the separator, the negative electrode sheet and the separator prepared above are stacked in order with the separator in 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 tab, the electrode assembly is put into an aluminum plastic film packaging bag, placed in a vacuum oven at 85°C for 12h to remove water, injected with the electrolyte prepared above, and subjected to vacuum packaging, standing, formation, shaping, capacity test procedures to obtain a lithium ion battery (i.e. an electrochemical device).

[0081] Examples 1-2 to 1-4

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

[0083] Examples 1-5 to 1-11

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

[0085] Examples 1-12 to 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] Examples 2-1 to 2-9

[0091] Except for further adding a second component in the preparation of the electrolyte and adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-5. Among them, when the mass percentage content of the second component changes, the mass percentage content of LiPF6 remains unchanged.

[0092] Examples 2-10 to 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] The rest is the same as Example 1-5 except that the third component is further added in the preparation of electrolyte and the relevant preparation parameters are adjusted according to Table 3. Among them, when the mass percentage of the third component changes, the mass percentage of LiPF6 remains unchanged.

[0098] Example 3-9

[0099] The rest is the same as Example 3-3 except that the relevant preparation parameters are adjusted according to Table 3.

[0100] Table 3

[0101]

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

[0103] The rest is the same as Example 1-5 except that the fourth component is further added in the preparation of electrolyte and the relevant preparation parameters are adjusted according to Table 4. Among them, 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] The rest is the same as Example 4-4 except that the relevant preparation parameters are adjusted according to Table 4.

[0106] Table 4

[0107]

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

[0109] The rest is the same as Example 1-5 except that fluoroethylene carbonate is further added in the preparation of electrolyte and the relevant preparation parameters are adjusted according to Table 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] The rest is the same as Example 1-5 except that the relevant preparation parameters are adjusted according to Table 1. Among them, when the mass percentage of the compound of formula I changes, the mass percentage of LiPF6 remains unchanged.

[0115] Comparative Example 3

[0116] The rest was the same as Example 1-1 except that the relevant preparation parameters were adjusted according to Table 1. Among them, when the mass percentage of the compound of formula I changed, the mass percentage of LiPF6 remained unchanged.

[0117] As can be seen from Table 1, when the electrolyte contains not 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 second component combined with the compound of formula I and the compound of formula II can better improve the cycle performance of the electrochemical device.

[0119] As can be seen from Table 3, the third component synergizes 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.

[0120] As can be seen from Table 4, the fourth component combined with the compound of formula I can further improve the cycle performance of the electrochemical device.

[0121] As can be seen from Table 5, fluoroethylene carbonate is conducive to further improving 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 is only an embodiment of the present application and does not limit the protection scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, characterized by, The components of the electrolyte include a compound of Formula I: wherein R is selected from any of a fluorine-substituted or unsubstituted C2-C6 alkyl, C6-C12 nitrogen-containing heterocyclyl, fluorine-substituted or unsubstituted C6-C12 aryl; and a compound of Formula II: wherein R1is selected from O or -CH(R a )-, and R a is selected from any of H, F, C1-C5 alkyl, C1-C5 alkoxy; R2, R3are each independently selected from any of H, F, C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl; R4is selected from any of H, F, fluorine-substituted or unsubstituted C1-C5 alkyl, C1-C5 alkoxy, C2-C5 alkenyl, C2-C5 alkynyl. The mass percentage content of the compound of Formula I is a%, and the mass percentage content of the compound of Formula II is b%, based on the total mass of the electrolyte, 1≤a≤50, and 0.5≤a / b≤500.

2. The electrochemical device of claim 1, wherein 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 of claim 1, wherein The compound of Formula I includes at least one of the following compounds:

4. The electrochemical device of claim 1, wherein The compound of Formula II includes at least one of the following compounds:

5. The electrochemical device of claim 1, wherein The electrolyte further includes a second component, the second component including at least one of lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate; the mass percentage content of the second component is c%, based on the total mass of the electrolyte, wherein 0.01≤c≤3, and 0.011≤(c+b) / a≤3.

6. The electrochemical device of claim 1, wherein The electrolyte further includes a third component, the third component including at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide; the mass percentage content of the third component is d%, based on the total mass of the electrolyte, wherein 0.1≤d≤10, and 0.1≤d / b≤100.

7. The electrochemical device of claim 1, wherein The electrolyte further includes a fourth component, the fourth component including at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methanediyl dimethanesulfonate, ethylene sulfate, glyoxal disulfate; the mass percentage content of the fourth component is e%, based on the total mass of the electrolyte, 0.1≤e≤6.

8. The electrochemical device of claim 1, wherein The electrolyte further includes fluoroethylene carbonate; the mass percentage content of the fluoroethylene carbonate is f%, based on the total mass of the electrolyte, wherein 1≤f≤20.

9. The electrochemical device of claim 8, wherein, 3≤f≤15。 10. An electronic device, comprising: The electrochemical device includes the electrolyte of any one of claims 1-9. The electrochemical device includes the electrolyte of any one of claims 1-9.

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