Electrochemical device and electronic device

Abstract

Provided in the present application are an electrochemical device and an electronic device. The electrochemical device comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material and a negative electrode binder, the negative electrode binder comprises an ester substance and a non-ester substance, and based on the mass of the negative electrode binder, the mass percentage content of the ester substance is x; the electrolyte comprises fluoroethylene carbonate and a high-kinetics solvent, the high-kinetics solvent comprises at least one of ethyl propionate, propyl propionate or diethyl carbonate, and the ratio of the mass percentage content of the fluoroethylene carbonate in the electrolyte to that of the high-kinetics solvent is y; the electrochemical device satisfies 17%≤x+y≤53%, and y is in the range of 0.4% to 14%; and based on the mass of the electrolyte, the mass percentage content of the fluoroethylene carbonate is 0.1-10%. In the present application, by means of the coordinated regulation of x and y, the volume expansion and capacity fading of a fast charge system during cycling are enhanced, and the cycle performance is improved.

Description

Electrochemical device and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 27, 2023, with application number 202310768103.1 and invention name “An electrochemical device and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

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

[0003] Electrochemical devices, such as lithium-ion secondary batteries, are widely used in fields such as smartphones, portable wearable devices, and electric vehicles due to their advantages such as high energy density, high operating voltage, stable cycle, and environmental friendliness. With the continuous iterative development of consumer devices, the market requires ever-increasing charging speeds, and therefore the demand for fast-charging lithium-ion secondary batteries has increased accordingly. However, compared with traditional non-fast-charging systems, the volume expansion and capacity attenuation of fast-charging systems during the cycle are more obvious. In view of this, improving the above-mentioned problems of the fast-charging system and improving the cycle performance have become technical problems that need to be urgently solved by those skilled in the art.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide an electrochemical device and an electronic device that improves the volume expansion and capacity decay problems of a fast-charging system during cycling and enhances cycling performance. The specific technical solution is as follows:

[0006] A first aspect of the present application provides an electrochemical device comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material and a negative electrode binder, the negative electrode binder comprises an ester substance and a non-ester substance, and the mass percentage of the ester substance is x based on the mass of the negative electrode binder; the electrolyte comprises fluoroethylene carbonate (FEC) and a high kinetic solvent, the high kinetic solvent comprises at least one of ethyl propionate (EP), propyl propionate (PP) or diethyl carbonate (DEC), and the ratio of the mass percentage of FEC in the electrolyte to the mass percentage of the high kinetic solvent is y; the electrochemical device satisfies: 17%≤x+y≤53%, and y is 0.4% to 14%, and the mass percentage of FEC is 0.1% to 10% based on the mass of the electrolyte. Through in-depth research, the inventors of this application found that when the combination of negative electrode plates and electrolyte formulas is optimized and x and y are coordinated to meet the above relationship, the volume expansion and capacity attenuation problems during the fast charging system cycle can be improved, thereby improving the cycle performance.

[0007] In some embodiments of the present application, the ester substance includes at least one of isooctyl acrylate, isooctyl methacrylate, 1,3-propane sultone, diisocyanate, polyethylene glycol dimethyl ether acetate, methyl methacrylate, 2-ethylhexyl methyl acrylate, butyl acrylate or phenolphthalein containing an ester group; the non-ester substance includes at least one of butadiene, acrylonitrile, styrene, acrylic acid, hydroxymethyl cellulose, polyacrylic acid or adiponitrile.

[0008] In some embodiments of the present application, the negative electrode binder comprises an propylene-based substance, and the propylene-based substance includes at least one of acrylic acid, acrylonitrile, isooctyl acrylate, isooctyl methacrylate, or butyl acrylate.

[0009] In some embodiments of the present application, x is 3% to 48%. By controlling the mass percentage of the ester substance in the negative electrode binder within the above range, the volume expansion and capacity decay problems during the fast charging system cycle can be further improved, thereby improving the cycle performance.

[0010] In some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions: a) x is 10% to 35%; b) y is 3% to 13%; c) based on the mass of the electrolyte, the mass percentage of DEC in the electrolyte is 0% to 30%; d) based on the mass of the negative electrode active material layer, the mass percentage of the negative electrode binder is 0.5% to 5%; e) the conductivity of the electrolyte is 7mS / cm to 11mS / cm; f) 17%≤x+y≤30%. By regulating the above parameters, the volume expansion and capacity attenuation problems during the fast charging system cycle can be further improved, thereby improving the cycle performance.

[0011] In some embodiments of the present application, the electrolyte further comprises at least one of ethyl difluoroacetate, ethylene carbonate (EC), propylene carbonate (PC), 1,3-propane sultone (PS), ethylene glycol diethyl cyanide, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, δ-valerolactone, acetonitrile, succinonitrile, adiponitrile, glutaronitrile, 1,3,6-hexanetrionitrile, trans-hexenedinitrile, ethylene glycol bis(propionitrile) ether or hexafluorocyclotriphosphazene.

[0012] In some embodiments of the present application, the negative electrode binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyvinyl vinyl ester, or polyvinyl alcohol.

[0013] In some embodiments of the present application, the negative electrode active material layer further comprises a negative electrode conductive agent and a dispersant. Based on the mass of the negative electrode active material layer, the mass percentage of the negative electrode active material is 88% to 99%, the mass percentage of the negative electrode conductive agent is 0% to 2%, and the mass percentage of the dispersant is 0.5% to 5%.

[0014] In some embodiments of the present application, the negative electrode active material includes at least one of natural graphite, artificial graphite, lithium titanate, hard carbon, nano-silicon, silicon carbon or silicon oxygen; the negative electrode conductive agent includes at least one of conductive carbon balls, acetylene black, conductive carbon black, Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, nano-carbon fibers, graphene or conductive graphite sheets; the dispersant includes at least one of lithium hydroxymethyl cellulose, sodium hydroxymethyl cellulose or hydroxymethyl cellulose modifications.

[0015] In some embodiments of the present application, the negative electrode active material includes artificial graphite, and the D peak intensity / G peak intensity ratio of the artificial graphite measured by Raman testing is 0.1 to 0.6.

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

[0017] Beneficial effects of this application:

[0018] The present application provides an electrochemical device and an electronic device. The electrochemical device includes an electrode assembly and an electrolyte, wherein the electrode assembly includes a negative electrode plate, the negative electrode plate includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a negative electrode binder, the negative electrode binder includes an ester substance and a non-ester substance, and the mass percentage of the ester substance is x based on the mass of the negative electrode binder; the electrolyte includes FEC and a high kinetic solvent, the high kinetic solvent includes at least one of EP, PP, or DEC, and the ratio of the mass percentage of FEC in the electrolyte to the mass percentage of the high kinetic solvent is y; the electrochemical device satisfies the following conditions: 17% ≤ x + y ≤ 53%, y is 0.4% to 14%, and the mass percentage of FEC is 0.1% to 10% based on the mass of the electrolyte. This application optimizes the ratio of ester components and electrolyte solvent components in the negative electrode binder, synergistically regulates x and y to satisfy the above relationship, improves the volume expansion and capacity attenuation problems during the fast charging system cycle, improves the cycle performance, and has good high-temperature storage performance.

[0019] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only 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 this application are within the scope of protection of this application.

[0021] It should be noted that, in the specific embodiments of the present application, a lithium-ion secondary 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 secondary battery.

[0022] In a first aspect, the present application provides an electrochemical device comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material and a negative electrode binder, the negative electrode binder comprises an ester substance and a non-ester substance, and the mass percentage of the ester substance is x based on the mass of the negative electrode binder; the electrolyte comprises FEC and a high kinetic solvent, the high kinetic solvent comprises at least one of EP, PP, or DEC, and the ratio of the mass percentage of FEC in the electrolyte to the mass percentage of the high kinetic solvent is y; and the electrochemical device satisfies: 17% ≤ x + y ≤ 53%, and y is 0.4% to 14%, and the mass percentage of FEC is 0.1% to 10% based on the mass of the electrolyte. In some embodiments, 17% ≤ x + y ≤ 30%. In some embodiments, y is 3% to 13%. For example, x+y can be 17%, 20%, 25%, 30%, 35%, 40%, 50%, 53% or any range therebetween; y can be 0.4%, 1%, 4%, 7%, 10%, 14% or any range therebetween, and the mass percentage of FEC can be 0.1%, 2%, 4%, 6%, 8%, 10% or any range therebetween. The inventors of this application have found through research that when y is too low, for example, less than 0.4%, the electrochemical device swells after cycling, resulting in poor cycle performance; when y is too high, for example, greater than 14%, the electrochemical device experiences severe high-temperature storage expansion, resulting in bloating, and the storage expansion rate exceeds the required 10%, deteriorating high-temperature storage performance. Regulating the y value within the range of this application is beneficial to improving the volume expansion and capacity attenuation problems during the cycling of the fast charging system, improving the cycle performance and achieving good high-temperature storage performance. In the present application, the contents of the above-mentioned ester substances and non-ester substances were tested by pyrolysis gas chromatography mass spectrometry (PY-GCMS).

[0023] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of the high kinetic solvent is 35% to 55%. For example, the mass percentage of the high kinetic solvent can be 35%, 40%, 45%, 50%, 55% or any range therebetween. The electrolyte includes a high kinetic solvent within the above range and regulates its content within the above range. The electrolyte has a lower viscosity and a higher conductivity, which is beneficial to the migration of ions in the electrolyte, so that the electrochemical device has a stable positive electrode interface and a negative electrode interface, which is beneficial to improve the volume expansion and capacity attenuation problems during the cycle of the fast charging system and improve the cycle performance.

[0024] In some embodiments of the present application, the ester substance includes at least one of isooctyl acrylate, isooctyl methacrylate, 1,3-propane sultone, diisocyanate, polyethylene glycol dimethyl ether acetate, methyl methacrylate, 2-ethylhexyl methyl acrylate, butyl acrylate, or phenolphthalein alcohol containing an ester group. The above-mentioned ester substance can be produced by cracking the negative electrode binder during the cracking gas chromatography-mass spectrometry test, or can be introduced during the preparation of the negative electrode binder. The non-ester substance includes at least one of butadiene, acrylonitrile, styrene, acrylic acid, hydroxymethyl cellulose, polyacrylic acid, or adiponitrile.

[0025] In fast-charging electrochemical device systems, low-viscosity, high-dielectric-constant solvents are often used to improve kinetic behavior, and at the same time, styrene-acrylic negative electrode binders with better kinetic behavior are introduced to improve the high-rate charge and discharge performance of the electrochemical device. However, in this case, the film formation consistency of the electrolyte at the solid electrolyte interface (SEI) on the negative electrode graphite surface is poor, and the affinity and adhesion with the negative electrode binder are insufficient, resulting in deterioration of the adhesion and conductive network in the SEI film during the cycle, which in turn leads to more obvious expansion of the electrochemical device and more serious cycle capacity attenuation. In this application, a fast-charging electrochemical device refers to an electrochemical device that can be quickly charged to a state of charge of ≥60% within 30 minutes.

[0026] The inventors of the present application have found through research that when the negative electrode binder in the fast-charging electrochemical system is combined with a certain amount of ester substances, it is easier to produce weak bonds and overlapping effects with the organic components on the surface of the SEI film, thereby maintaining an intact conductive network inside the negative electrode plate during the cycle. At the same time, increasing the ratio of FEC solvent to fast-charging solvent in the electrolyte can improve the film-forming stability of the graphite surface, ensure that the weak bond effect with the negative electrode binder can be maintained on the negative electrode surface for a long time, and avoid repeated breakage and generation due to the instability of the SEI film, resulting in the good negative electrode plate structure initially formed by the negative electrode binder disappearing due to damage to the overlapping matrix (SEI film on the graphite surface) during the cycle. The synergistic effect of the above two increases the affinity between the negative electrode binder and the SEI interface on the graphite surface, thereby improving the volume expansion and capacity attenuation problems during the cycle of the fast-charging system and improving the cycle performance.

[0027] The presence of esters in the negative electrode binder is due to the fact that during the preparation process, in addition to mixing the main raw materials (styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyacrylic acid (PAA), etc.) and the lithium source (lithium carbonate, etc.) in a certain proportion, additional solvents, crosslinkers, and other modifying additives are added. These modifying additives include conductive agents, nanofillers, surfactants, antioxidants, and flexibility additives, and their types include inorganic substances, metal oxides, organic polymers, and polymer-metal compounds. The function of the crosslinker is to induce a crosslinking reaction upon heating to form a crosslinked network, thereby forming the negative electrode binder. The modifying additives function to improve the specific properties of the negative electrode binder. During the addition of the crosslinker and modifying monomer, a certain proportion of esters as required by the present invention can be introduced, including at least one of isooctyl acrylate, isooctyl methacrylate, 1,3-propane sultone, butyl acrylate, diisocyanate, polyethylene glycol dimethyl ether acetate, methyl methacrylate, 2-ethylhexyl methyl acrylate, or phenolphthalein containing an ester group. The above-mentioned ester substances can be added during the preparation process of the negative electrode binder, or can be produced by cracking the negative electrode binder.

[0028] In some embodiments of the present application, the negative electrode binder includes an propylene-based substance, wherein the propylene-based substance includes at least one of acrylic acid, acrylonitrile, isooctyl acrylate, isooctyl methacrylate, or butyl acrylate. In the present application, the content of the propylene-based substance is measured by pyrolysis gas chromatography-mass spectrometry.

[0029] In the present application, the preparation method of the negative electrode binder is not particularly limited, as long as the purpose of the present invention can be achieved. For example, the negative electrode binder of the present application can be prepared by methods such as emulsion polymerization and solution polymerization.

[0030] In some embodiments of the present application, x is 3% to 48%. For example, x can be 3%, 10%, 20%, 30%, 40%, 48%, or any range therebetween. By regulating x within the scope of the present application, the electrochemical device can reduce the occurrence of flatulence after cycling, and on the other hand, the substance can effectively complete the cross-linking reaction during the synthesis of the negative electrode binder. This is conducive to improving the volume expansion and capacity attenuation problems during the cycling of the fast charging system and improving the cycle performance. x is preferably 10% to 35%.

[0031] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of DEC in the electrolyte is 0% to 30%. For example, the mass percentage of DEC can be 0%, 5%, 10%, 15%, 20%, 25%, 30% or any range therebetween. By regulating the content of DEC in the electrolyte within the above range, the electrolyte has a lower viscosity and a higher conductivity, which is beneficial to the migration of ions in the electrolyte, so that the electrochemical device has a stable positive electrode interface and a negative electrode interface, which is beneficial to improving the volume expansion and capacity attenuation problems during the cycle of the fast charging system and improving the cycle performance.

[0032] In some embodiments of the present application, the mass percentage of the negative electrode binder is 0.5% to 5% based on the mass of the negative electrode active material layer. For example, the mass percentage of the negative electrode binder can be 0.5%, 1%, 2%, 3%, 4%, 5%, or any range therebetween.

[0033] In some embodiments of the present application, the conductivity of the electrolyte is 7mS / cm to 11mS / cm. For example, the conductivity can be 7mS / cm, 8mS / cm, 9mS / cm, 10mS / cm, 11mS / cm, or any range therebetween. By regulating the conductivity within the above range, it is beneficial to the migration of ions in the electrolyte, which in turn helps to improve the volume expansion and capacity attenuation problems during the fast charging system cycle and improve the cycle performance.

[0034] In some embodiments of the present application, the electrolyte further comprises other compounds, including at least one of ethyl difluoroacetate, ethylene carbonate (EC), propylene carbonate (PC), 1,3-propane sultone (PS), ethylene glycol diethyl cyanide, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, δ-valerolactone, acetonitrile, succinonitrile, adiponitrile, glutaronitrile, 1,3,6-hexanetrinitrile, trans-hexenedinitrile, ethylene glycol bis(propionitrile) ether or hexafluorocyclotriphosphazene. Based on the mass of the electrolyte, the mass percentage of the other compounds in the electrolyte is 30% to 50%. For example, the mass percentage of the above-mentioned other compounds can be 30%, 35%, 40%, 45%, 50% or any range therebetween. The electrolyte includes the above-mentioned other compounds and their content is regulated within the above-mentioned range. The electrolyte has a lower viscosity and a higher conductivity, which is beneficial to the migration of ions in the electrolyte, so that the electrochemical device has a stable positive electrode interface and a negative electrode interface, which is beneficial to improving the volume expansion and capacity attenuation problems during the cycle of the fast charging system and improving the cycle performance.

[0035] In the present application, the electrolyte also includes a lithium salt. The present application does not particularly limit the type of lithium salt, as long as it can achieve the purpose of the present application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(oxalatoborate), or lithium difluoroborate. Preferably, the lithium salt includes LiPF6.

[0036] In some embodiments of the present application, the mass percentage of the lithium salt is 10% to 20% based on the mass of the electrolyte. For example, the mass percentage of the lithium salt can be 10%, 12%, 14%, 16%, 18%, 20%, or any range therebetween.

[0037] In some embodiments of the present application, the negative electrode binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyvinyl vinyl ester, or polyvinyl alcohol.

[0038] In some embodiments of the present application, the negative electrode active material layer further comprises a negative electrode conductive agent and a dispersant. Based on the mass of the negative electrode active material layer, the mass percentage of the negative electrode active material is 88% to 99%, for example, the mass percentage of the negative electrode active material can be 88%, 90%, 92%, 94%, 96%, 99%, or any range therebetween. The mass percentage of the negative electrode conductive agent is 0% to 2%, for example, the mass percentage of the negative electrode conductive agent can be 0%, 0.4%, 0.8%, 1.2%, 1.6%, 2%, or any range therebetween. The mass percentage of the dispersant is 0.5% to 5%, for example, the mass percentage of the dispersant can be 0.5%, 1%, 2%, 3%, 4%, 5%, or any range therebetween.

[0039] In some embodiments of the present application, the negative electrode active material includes at least one of natural graphite, artificial graphite, lithium titanate, hard carbon, nano-silicon, silicon carbon or silicon oxygen; the negative electrode conductive agent includes at least one of conductive carbon balls, acetylene black, conductive carbon black, Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, nano-carbon fibers, graphene or conductive graphite sheets; the dispersant includes at least one of lithium hydroxymethyl cellulose, sodium hydroxymethyl cellulose or hydroxymethyl cellulose modifications.

[0040] In some embodiments of the present application, the negative electrode active material includes artificial graphite, and the artificial graphite has a D peak intensity / G peak intensity ratio of 0.1 to 0.6 as measured by Raman spectroscopy. For example, the D peak intensity / G peak intensity ratio can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or any range therebetween.

[0041] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.). In the present application, there is no particular restriction on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, a thickness of 4 μm to 12 μm.

[0042] Optionally, the negative electrode may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode active material layer. The present application has no particular limitation on the composition of the conductive layer, which may be a conductive layer commonly used in the art.

[0043] There are no special restrictions on the positive electrode sheets in this application, as long as the purpose of this application can be achieved. The positive electrode sheet generally comprises a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer comprises a positive electrode active material. The above-mentioned positive electrode current collector is not particularly limited and may be any positive electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collector (such as aluminum-carbon composite current collector). The above-mentioned positive electrode active material is not particularly limited and may be any positive electrode active material in the prior art. 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 at least one of lithium titanate.

[0044] In this application, the thickness of the positive electrode current collector and the positive electrode active material layer is not particularly limited, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0045] In the present application, the positive electrode active material layer may also include a positive electrode conductive agent. The present application has no particular restrictions on the positive electrode conductive agent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0046] In the present application, the positive electrode active material layer may also include a positive electrode binder. The present application has no particular limitation on the positive electrode binder, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin, nylon, etc.

[0047] Optionally, the positive electrode may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode active material layer. The present application does not particularly limit the composition of the conductive layer, and it can be a conductive layer commonly used in the art, for example, it can include but is not limited to the above-mentioned positive electrode conductive agent and the above-mentioned positive electrode binder.

[0048] There is no special limitation on the isolation membrane in the present application, as long as the purpose of the present application can be achieved. The isolation membrane may include a substrate layer and a surface treatment layer. The present application has no special limitation on the substrate layer. For example, the material of the isolation membrane may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of isolation membrane 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 isolation membrane of the present application may have a porous structure, and the size of the pore size is not particularly limited, as long as the purpose of the present application can be achieved. For example, the size of the pore size can be 0.01μm to 1μm. In the present application, there is no special limitation on the thickness of the isolation membrane, as long as the purpose of the present application can be achieved. For example, the thickness can be 3μm to 16μm.

[0049] In the present application, a surface treatment layer may also be provided on at least one surface of the substrate layer. The present application has no particular restrictions on the surface treatment layer, and may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer may include, but is not limited to, inorganic particles and an inorganic layer binder. The present application has no particular restrictions on the inorganic particles, and for example, may include but is not limited to 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 inorganic layer binder, and for example, may include but is not limited to at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material may include but is not limited to at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0050] The preparation process of an electrochemical device is well known to those skilled in the art and is not particularly limited in this application. For example, it may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and winding, folding, and other operations as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the packaging bag to obtain the electrochemical device; or stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then securing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the packaging bag to obtain the electrochemical device. In addition, as needed, overcurrent protection components, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharging and discharging within the electrochemical device.

[0051] A second aspect of the present application provides an electronic device comprising the electrochemical device of any of the foregoing embodiments of the present application. The electrochemical device provided herein can improve the volume expansion and capacity decay problems during the cycling of a fast-charging system, thereby improving cycling performance, thereby providing the electronic device provided herein with a long service life and good performance.

[0052] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a 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, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0053] Example

[0054] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0055] Test methods and equipment:

[0056] Negative electrode binder material composition test:

[0057] The lithium-ion secondary battery was discharged at a current of 0.2C to 3.0V, and this step was repeated three times to prevent voltage rebound. The lithium-ion secondary battery was disassembled in a dry room (water content <2%), and the negative electrode was removed. The negative electrode was soaked in dimethyl carbonate (DMC) solvent for 12 hours (completely submerged in the liquid), and the solvent was discarded. The negative electrode was soaked in DMC solvent for another 12 hours (completely submerged in the liquid), and the solvent was discarded. After the soaking operation, the negative electrode was placed in a 60°C oven to dry. The dried negative electrode was sampled and tested on a pyrolysis gas chromatography-mass spectrometer. The instrument parameters were Agilent 7890B / 5977B, a mass selective detector (MSD), a pyrolysis gas EGA / PY-3030D injector, a column oven temperature of 40°C to 320°C, and a pyrolysis temperature of 40°C to 1000°C.

[0058] Electrolyte material composition test:

[0059] The lithium-ion secondary battery was discharged at a current of 0.2C to 3.0V, and this step was repeated three times to prevent voltage rebound. The lithium-ion secondary battery was disassembled in a dry room (water content <2%), and the electrode assembly and electrolyte were removed and quickly placed in a centrifuge tube. After centrifugation at 3200 rpm for 20 to 30 minutes, the centrifuge was opened, the centrifuge tube was removed, and the electrolyte obtained by centrifugation was transferred to a sample injection bottle using a syringe. The sample was injected into a pyrolysis gas chromatography-mass spectrometer for testing. The instrument parameters were Agilent 8890-5977B, the detector was a mass selective detector (MSD), the injector was an Agilent G4513A autosampler, and the column oven temperature was 40°C to 270°C.

[0060] 25℃ Lithium-ion secondary battery expansion and cycle test method:

[0061] 1) The lithium-ion secondary battery was placed in a 25° C. environment for 10 minutes, and the initial thickness of the lithium-ion secondary battery was measured using a 600 g flat plate thickness gauge (PPG) and defined as the 25° C. cyclic expansion reference value (0%).

[0062] 2) Charging process: Charge to 4.2V at 2.6C constant current, then charge to 2.35C constant voltage; charge to 4.25V at 2.35C constant current, then charge to 2C constant voltage; charge to 4.3V at 2C constant current, then charge to 1.5C constant voltage; charge to 4.38V at 1.5C constant current, then charge to 1.2C constant voltage; charge to 4.45V at 1.2C constant current, then charge to 1C constant voltage; charge to 4.48V at 1C constant current, then charge to 0.1C constant voltage.

[0063] 3) Let it sit for 10 minutes.

[0064] 4) Discharge process: During the first cycle and every 50 cycles thereafter (1, 51, 101, 151, ..., 1001), discharge to 3 V at a constant current of 0.2 C; during the other cycles, discharge to 3 V at a constant current of 1 C.

[0065] 5) Let the battery rest for 10 minutes. Repeat the charging and discharging process of the lithium-ion secondary battery from steps 2) to 5) 1001 times. Record the discharge capacity of each cycle.

[0066] 6) After the cycle is completed, charge the lithium-ion secondary battery according to step 2) until it is fully charged, and then measure the thickness of the 600g PPG. Record it as the fully charged thickness of the lithium-ion secondary battery at the 1001st cycle.

[0067] The 25°C cycle expansion rate, 25°C 0.2C capacity retention rate, 25°C 1C capacity retention rate and 25°C cycle capacity loss of the lithium-ion secondary battery are calculated using the following expressions: 25°C cycle expansion rate = ((full charge thickness of the lithium-ion secondary battery at the 1001st cycle / 25°C cycle expansion reference value) - 1) × 100%; 25°C 0.2C capacity retention rate = (discharge capacity at the 1001st cycle / discharge capacity at the 1st cycle) × 100%; 25°C 1C capacity retention rate = (discharge capacity at the 1000th cycle / discharge capacity at the 1st cycle) × 100%; 25°C cycle capacity loss = 25°C 0.2C capacity retention rate - 25°C 1C capacity retention rate.

[0068] 80℃ storage expansion test method:

[0069] 1) Place the lithium-ion secondary battery in a 25°C environment for 1 hour.

[0070] 2) Charging process: Charge at a constant current of 2.6C to 4.2V, then charge at a constant voltage of 2.35C; charge at a constant current of 2.35C to 4.25V, then charge at a constant voltage of 2C; charge at a constant current of 2C to 4.3V, then charge at a constant voltage of 1.5C; charge at a constant current of 1.5C to 4.38V, then charge at a constant voltage of 1.2C; charge at a constant current of 1.2C to 4.45V, then charge at a constant voltage of 1C; charge at a constant current of 1C to 4.48V, then charge at a constant voltage of 0.1C. The thickness of the 600g PPG of the lithium-ion secondary battery was measured and defined as the expansion reference value (0%).

[0071] 3) The lithium-ion secondary battery was placed in an 80°C environment for 7 hours, and then immediately taken out to measure the thickness of 600g of PPG, which was recorded as the thickness of the lithium-ion secondary battery after storage at 80°C.

[0072] The 80° C. high-temperature storage expansion ratio was calculated using the following expression: 80° C. high-temperature storage expansion ratio=((lithium ion secondary battery thickness after 80° C. storage / expansion reference value)−1)×100%.

[0073] Electrolyte conductivity test:

[0074] Discharge the lithium-ion secondary battery at a current of 0.2C to 3.0V. Repeat this step three times to prevent voltage rebound. In a dry room (moisture content <2%), cut open the outer packaging bag of the lithium-ion secondary battery and place the bag with the opening facing downward into a centrifuge tube. Centrifuge at 3200 rpm for 20 to 30 minutes. Open the centrifuge, remove the tube, and transfer the resulting electrolyte to a sample bottle using a syringe. Measure the electrolyte conductivity using a Leici conductivity meter.

[0075] Example 1

[0076] <Preparation of Negative Electrode Binder>

[0077] The solutes acrylonitrile, phenolphthalein, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 3:17:25:55, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0078] <Preparation of negative electrode sheet>

[0079] Artificial graphite (D peak intensity / G peak intensity ratio of 0.5 as measured by Raman spectroscopy) as the negative electrode active material, a negative electrode binder, and lithium hydroxymethyl cellulose as the dispersant were mixed in a mass ratio of 97.5:1.4:1.1. Deionized water was added as the solvent to prepare a slurry with a solid content of 70 wt%, and stirred evenly. The slurry was evenly coated on one surface of an 8 μm thick copper foil, dried at 110°C, and cold pressed to obtain a negative electrode sheet with a single-sided negative electrode active material layer of 110 μm thickness. The above coating steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode active material layer. The negative electrode sheet was cut into a size of 75.5 mm x 867 mm and the tabs were welded before use.

[0080] <Preparation of positive electrode sheet>

[0081] Lithium cobalt oxide (LiCoO2), the positive electrode active material, acetylene black, the positive electrode conductive agent, and polyvinylidene fluoride (PVDF), the positive electrode binder, were mixed in a mass ratio of 97:1.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent and stirred in a vacuum mixer until a uniform positive electrode slurry with a solids content of 75 wt% was formed. The positive electrode slurry was evenly coated on a 9 μm thick positive electrode current collector aluminum foil, dried at 85°C, and cold pressed to obtain a positive electrode sheet with an 88 μm thick positive electrode active material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. The positive electrode sheet was cut into 74 mm x 867 mm dimensions and welded to the tabs before use.

[0082] <Preparation of Electrolyte>

[0083] In an argon atmosphere glove box with a water content of less than 10 ppm, FEC, a high-kinetic solvent, and other compounds were mixed to form a base solvent. The high-kinetic solvent consisted of EP, PP, and DEC. The other compounds included PC, EC, PS, succinonitrile, adiponitrile, ethylene glycol diethyl cyanide, and 1,3,6-hexanetricarbonitrile. The mass ratio of FEC, EP, PP, DEC, PC, EC, PS, succinonitrile, adiponitrile, ethylene glycol diethyl cyanide, and 1,3,6-hexanetricarbonitrile was 0.3:15.8:23.6:7.9:18.4:9.6:2.6:1.1:1.9:0.4:5.9. Lithium salt LiPF6 was then added to the base solvent and mixed to form an electrolyte. The mass percentage of LiPF6 was 12.5%, with the remainder being the base solvent.

[0084] <Preparation of Separator>

[0085] A polyethylene (PE) porous polymer film with a thickness of 7 μm was used as the separator.

[0086] <Preparation of Lithium-ion Secondary Battery>

[0087] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain a bare lithium-ion secondary battery; the bare lithium-ion secondary battery is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried lithium-ion secondary battery. After vacuum packaging, standing, formation, shaping and other processes, the preparation of the lithium-ion secondary battery is completed.

[0088] Example 2

[0089] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1.

[0090] Example 3

[0091] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0092] <Preparation of Negative Electrode Binder>

[0093] The solutes acrylonitrile, 1,3-propane sultone, styrene, and butadiene were added to a cyclohexane solvent in a mass ratio of 3:17:25:55, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0094] Example 4

[0095] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0096] <Preparation of Negative Electrode Binder>

[0097] The solutes acrylonitrile, diisocyanate, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 3:17:25:55, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solution, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0098] Example 5

[0099] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0100] <Preparation of Negative Electrode Binder>

[0101] The solutes acrylonitrile, polyethylene glycol dimethyl ether acetate, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 3:17:25:55, resulting in a solute to solvent mass ratio of 1:9. Based on the total mass of the solute and solution, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0102] Example 6

[0103] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0104] <Preparation of Negative Electrode Binder>

[0105] The solutes acrylonitrile, 2-ethylhexyl methyl acrylate, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 3:17:25:55, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solution, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0106] Example 7 to Example 12

[0107] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1.

[0108] Example 13

[0109] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0110] <Preparation of Negative Electrode Binder>

[0111] The solutes acrylonitrile, phenolphthalein, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 2.5:17.5:25:55, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0112] Example 14

[0113] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0114] <Preparation of Negative Electrode Binder>

[0115] The solutes acrylonitrile, phenolphthalein, styrene, and butadiene were added to a cyclohexane solvent in a mass ratio of 2:18:25:55, resulting in a solute to solvent mass ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0116] Example 15

[0117] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0118] <Preparation of Negative Electrode Binder>

[0119] The solutes acrylonitrile, isooctyl acrylate, styrene, and butadiene were added to a cyclohexane solvent in a mass ratio of 3:22:23:52, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0120] Example 16

[0121] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0122] <Preparation of Negative Electrode Binder>

[0123] The solutes phenolphthalein, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 35:20:45, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0124] Example 17

[0125] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 15.

[0126] Example 18

[0127] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 16.

[0128] Example 19

[0129] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0130] <Preparation of Negative Electrode Binder>

[0131] The solutes phenolphthalein, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 50:15:35, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0132] Example 20

[0133] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0134] <Preparation of Negative Electrode Binder>

[0135] The solutes phenolphthalein, styrene, and butadiene were added to a cyclohexane solvent at a mass ratio of 7:28:65, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0136] Example 21

[0137] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1.

[0138] Example 22

[0139] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0140] <Preparation of Negative Electrode Binder>

[0141] The solutes acrylonitrile, methyl methacrylate, butyl acrylate, styrene, and butadiene were added to a cyclohexane solvent in a mass ratio of 1.5:2.0:1.0:86.6:8.9, resulting in a solute to solvent mass ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0142] Example 23 to Example 24

[0143] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 14.

[0144] Comparative Examples 1 to 3

[0145] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1.

[0146] Comparative Example 4

[0147] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of lithium salt remains unchanged, the rest is the same as Example 20.

[0148] Comparative Example 5

[0149] The preparation process was the same as in Example 1 except that the mass percentage of each substance in the electrolyte base solvent was adjusted as shown in Table 1 and the mass percentage of the lithium salt remained unchanged in <Preparation of Negative Electrode Binder> and <Preparation of Electrolyte>.

[0150] <Preparation of Negative Electrode Binder>

[0151] The solutes acrylonitrile, methyl methacrylate, butyl acrylate, styrene, and butadiene were added to a cyclohexane solvent in a mass ratio of 1.5:2.0:1.2:86.4:8.9, resulting in a solute to solvent mass ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0152] Comparative Example 6

[0153] The preparation process was the same as in Example 1 except that the type of negative electrode binder and the mass percentage of each substance in the electrolyte base solvent were adjusted as shown in Table 1, and the mass percentage of the lithium salt remained unchanged in the preparation of the negative electrode binder and the electrolyte base solvent.

[0154] <Preparation of Negative Electrode Binder>

[0155] The solutes acrylonitrile, methyl methacrylate, butyl acrylate, styrene, and butadiene were added to a cyclohexane solvent in a mass ratio of 1.7:1.8:1.0:86.6:8.9, resulting in a solute to solvent ratio of 1:9. Based on the total mass of the solute and solvent, 0.5% of the initiator ammonium persulfate and 1% of the cationic emulsifier amide sulfonate were added. Emulsion polymerization was performed at a stirring speed of 500 rpm, a reaction temperature of 60°C, and a reaction time of 14 hours to produce a styrene-butadiene rubber (SBR) emulsion. Gel separation was then performed to obtain the negative electrode binder.

[0156] Comparative Examples 7 to 8

[0157] Except that in <Preparation of Electrolyte>, the mass percentage of each substance in the electrolyte base solvent is adjusted as shown in Table 1, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 14.

[0158] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Table 1.

[0159] Note: 1. Taking the data of Example 1 in Table 1 as an example, the high kinetic solvent is EP+PP+DEC, and the mass percentage (%) of the high kinetic solvent is 15.8+23.6+7.9, which means that based on the mass of the electrolyte, the mass percentage of EP is 15.8%, the mass percentage of PP is 23.6%, and the mass percentage of DEC is 7.9%. The other compounds are PC+EC+PS+succinonitrile+adiponitrile+ethylene glycol diethyl cyanide+1,3,6-hexanetricarbonitrile, and the mass percentage (%) of the other compounds is 18.4+9.6+2.6+1.1+1.9+0.4+5.9, which means that based on the mass of the electrolyte, the mass percentage of PC is 18.4%, the mass percentage of EC is 9.6%, the mass percentage of PS is 2.6%, the mass percentage of succinonitrile is 1.1%, the mass percentage of adiponitrile is 1.9%, the mass percentage of ethylene glycol diethyl cyanide is 0.4%, and the mass percentage of 1,3,6-hexanetricarbonitrile is 5.9%. The negative electrode binder's cracking composition after PY-GCMS testing was acrylonitrile / styrene / isooctyl acrylate / isooctyl methacrylate = 3.4% / 80.1% / 15.0% / 1.5%. This means that based on the mass of the negative electrode binder, the mass percentage of acrylonitrile was 3.4%, the mass percentage of styrene was 80.1%, the mass percentage of isooctyl acrylate was 15.0%, and the mass percentage of isooctyl methacrylate was 1.5%. Examples 2 to 24 and Comparative Examples 1 to 8 should be understood with reference to Example 1.

[0160] 2. The “flatulence” in Table 1 refers to the flatulence of lithium-ion secondary batteries after undergoing the 25°C expansion and cycle test or the 80°C storage expansion test.

[0161] It can be seen from Examples 1 to 20 and Comparative Examples 1 to 5 that when x and y simultaneously satisfy: 17% ≤ x + y ≤ 53%, and y is 0.4% to 14%, the electrolyte has a high conductivity, and the electrochemical device also has a low 25°C cycle expansion rate, 25°C cycle capacity loss, 80°C high-temperature storage expansion rate, and a high 25°C 0.2C capacity retention rate and 25°C 1C capacity retention rate. This indicates that the volume expansion and capacity attenuation of the electrochemical device during the fast charging system cycle are small, the cycle performance is good, and the high-temperature storage performance is good.

[0162] From Example 14, Example 23 to Example 24, and Comparative Examples 7 to 8, it can be seen that when x and y satisfy: 17% ≤ x + y ≤ 53%, the electrolyte has a high electrical conductivity, but when y < 0.4%, the electrochemical device exhibits flatulence after cycling at 25°C, indicating that when y is too small, the cycling performance of the electrochemical device deteriorates; when y > 14%, the electrochemical device exhibits flatulence after high-temperature storage at 80°C, indicating that when y is too large, the high-temperature storage performance of the electrochemical device deteriorates. When y is between 0.4% and 14%, the electrochemical device has a low 25°C cycling expansion rate, 25°C cycling capacity loss, 80°C high-temperature storage expansion rate, and a high 25°C 0.2C capacity retention rate and 25°C 1C capacity retention rate. This indicates that the volume expansion and capacity attenuation during the cycling process of the electrochemical device fast-charging system are small, the cycling performance is good, and the high-temperature storage performance is good, so that both cycling performance and high-temperature storage performance can be taken into account.

[0163] The mass percentage x of the ester substance in the negative electrode binder generally affects the cycling performance of the electrochemical device. As can be seen from Examples 1 to 24, when the value of x is within the range of this application, the electrochemical device does not experience flatulence after cycling at 25°C, and has a low 25°C cycling expansion rate, 25°C cycling capacity loss, 80°C high-temperature storage expansion rate, and high 25°C 0.2C capacity retention rate and 25°C 1C capacity retention rate. This indicates that the volume expansion and capacity attenuation of the electrochemical device during the fast-charging system cycle are small, the cycling performance is good, and the high-temperature storage performance is good.

[0164] The types of ester and non-ester substances in the negative electrode binder generally affect the cycling performance of the electrochemical device. As can be seen from Examples 1 to 24, when the ester and non-ester substances in the negative electrode binder are within the scope of this application, the electrochemical device simultaneously has a low 25°C cycling expansion rate, 25°C cycling capacity loss, and 80°C high-temperature storage expansion rate, as well as a high 25°C 0.2C capacity retention rate and 25°C 1C capacity retention rate. This indicates that the electrochemical device has small volume expansion and capacity decay during the fast-charging system cycle, good cycling performance, and good high-temperature storage performance.

[0165] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising an electrode assembly and an electrolyte, wherein: The electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material and a negative electrode binder, the negative electrode binder comprises an ester substance and a non-ester substance, and the mass percentage of the ester substance is x based on the mass of the negative electrode binder; The electrolyte comprises fluoroethylene carbonate and a high kinetic solvent, the high kinetic solvent comprises at least one of ethyl propionate, propyl propionate or diethyl carbonate, and the ratio of the mass percentage of fluoroethylene carbonate in the electrolyte to the mass percentage of the high kinetic solvent is y; The electrochemical device satisfies: 17%≤x+y≤53%, and y is 0.4% to 14%. Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 0.1% to 10%.

2. The electrochemical device according to claim 1, wherein: The ester substance includes at least one of isooctyl acrylate, isooctyl methacrylate, 1,3-propane sultone, diisocyanate, polyethylene glycol dimethyl ether acetate, methyl methacrylate, 2-ethylhexyl methyl acrylate, butyl acrylate or phenolphthalein containing an ester group; the non-ester substance includes at least one of butadiene, acrylonitrile, styrene, acrylic acid, hydroxymethyl cellulose, polyacrylic acid or adiponitrile.

3. The electrochemical device according to claim 1, wherein The negative electrode binder comprises an propylene-based substance, and the propylene-based substance comprises at least one of acrylic acid, acrylonitrile, isooctyl acrylate, isooctyl methacrylate or butyl acrylate.

4. The electrochemical device according to claim 1, wherein x ranges from 3% to 48%.

5. The electrochemical device according to claim 1, wherein The electrochemical device satisfies at least one of the following: a) x is between 10% and 35%; b) y is between 3% and 13%; c) based on the mass of the electrolyte, the mass percentage of diethyl carbonate in the electrolyte is 0% to 30%; d) based on the mass of the negative electrode active material layer, the mass percentage of the negative electrode binder is 0.5% to 5%; e) the conductivity of the electrolyte is 7mS / cm to 11mS / cm; f)17%≤x+y≤30%.

6. The electrochemical device according to claim 1, wherein The electrolyte further comprises at least one of ethyl difluoroacetate, ethylene carbonate, propylene carbonate, 1,3-propane sultone, ethylene glycol diethyl cyanide, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, δ-valerolactone, acetonitrile, succinonitrile, adiponitrile, glutaronitrile, 1,3,6-hexanetrinitrile, trans-hexenedinitrile, ethylene glycol bis(propionitrile) ether or hexafluorocyclotriphosphazene.

7. The electrochemical device according to claim 1, wherein: The negative electrode binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyvinyl vinyl ester or polyvinyl alcohol.

8. The electrochemical device according to claim 1, wherein The negative electrode active material layer further comprises a negative electrode conductor and a dispersant. Based on the mass of the negative electrode active material layer, the mass percentage of the negative electrode active material is 88% to 99%, the mass percentage of the negative electrode conductor is 0% to 2%, and the mass percentage of the dispersant is 0.5% to 5%.

9. The electrochemical device according to claim 8, wherein: The negative electrode active material includes at least one of natural graphite, artificial graphite, lithium titanate, hard carbon, nano-silicon, silicon carbon or silicon oxygen; the negative electrode conductive agent includes at least one of conductive carbon balls, acetylene black, conductive carbon black, Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, nano-carbon fibers, graphene or conductive graphite sheets; the dispersant includes at least one of lithium hydroxymethyl cellulose, sodium hydroxymethyl cellulose or modified hydroxymethyl cellulose.

10. The electrochemical device according to claim 1, wherein The negative electrode active material includes artificial graphite, and the D peak intensity / G peak intensity ratio of the artificial graphite measured by Raman testing is 0.1 to 0.

6.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

Images