An electrochemical device and an electronic device

Abstract

The application provides an electrochemical device and an electronic device, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer, the negative electrode material layer comprising a silicon-based composite material, the silicon-based composite material comprising silicon-based particles, the strength of the negative electrode current collector being A MPa, the difference between the maximum value and the minimum value of the relative percentage content of silicon atoms in the silicon-based particles being B%, and the mass content of silicon in the negative electrode material layer being C%, which satisfies: the lithium ion battery obtained by synergistically adjusting A, B and C to satisfy the above conditions has good cycle performance and expansion performance.

Description

[0001] This application is a divisional application of the Chinese patent application No. 202180030502.7, filed on December 27, 2021, and entitled "An Electrochemical Device and Electronic Device". TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to an electrochemical device and electronic device. BACKGROUND

[0003] Lithium ion batteries have many advantages such as large volume and mass energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, light weight, etc., and have been widely used in consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, people have higher and higher demands on the energy density, safety, cycle performance, etc. of the battery, and expect the emergence of new lithium ion batteries with comprehensive performance.

[0004] Silicon material has high specific capacity and can significantly improve the energy density of lithium ion batteries as a negative electrode material. However, it has a large volume expansion and contraction during lithium extraction and insertion, which causes the repeated destruction and formation of the solid electrolyte interface film (SEI) in the cycle, consumes reversible lithium, and affects the cycle performance and swelling performance of the lithium ion battery. SUMMARY

[0005] The purpose of the present application is to provide an electrochemical device and electronic device to improve the cycle performance and swelling performance of lithium ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer comprises a silicon-based composite material, the silicon-based composite material comprises silicon-based particles, the strength of the negative electrode current collector is A MPa, the difference between the maximum value and the minimum value of the relative percentage content of silicon atoms in the silicon-based particles is B%, and the mass content of silicon element in the negative electrode material layer is C%, satisfying:

[0007]

[0008] The present application can obtain a lithium ion battery with good cycle performance and swelling performance by cooperatively adjusting A, B and C to satisfy the above conditions.

[0009] In an embodiment of the present application, B satisfies: 10≤B≤16. By adjusting B within the above range, silicon-based particles with good uniformity of silicon element distribution can be obtained, which is beneficial to reduce the stress generated by the swelling of the lithium ion battery, thereby obtaining a lithium ion battery with good cycle performance and swelling performance.

[0010] In an embodiment of the present application, C satisfies: 1≤C≤20. By adjusting C within the above range, the expansion performance and energy density of the lithium ion battery can be balanced.

[0011] In an embodiment of the present application, A satisfies: 370≤A≤800. By adjusting A within the above range, the expansion performance and production cost of the lithium ion battery can be balanced.

[0012] In an embodiment of the present application, the single-side thickness of the negative electrode material layer is H, and the maximum particle size of the silicon-based particles is Dmax, which satisfy: H≥3×Dmax. By adjusting H and Dmax to satisfy the above relationship, the cycle performance and expansion performance of the lithium ion battery can be improved.

[0013] In an embodiment of the present application, Dmax of the silicon-based particles satisfies: 10μm≤Dmax≤25μm. By adjusting Dmax within the above range, the processing performance, expansion performance and energy density of the lithium ion battery can be balanced.

[0014] In an embodiment of the present application, the single-side thickness H of the negative electrode material layer satisfies: 30μm≤H≤90μm. By adjusting the single-side thickness H of the negative electrode material layer within the above range, the strength and toughness of the negative electrode material layer can be balanced, thereby improving the performance of the lithium ion battery.

[0015] In an embodiment of the present application, the porosity of the negative electrode sheet is P%, and P and C satisfy: P>15×C 1 / 4 . By adjusting P and C to satisfy the above relationship, the expansion performance and kinetic performance of the lithium ion battery are improved.

[0016] In an embodiment of the present application, P satisfies: 18≤P≤40. By adjusting P within the above range, the negative electrode sheet can be effectively infiltrated in the electrolyte, and the negative electrode sheet has good strength, thereby improving the expansion performance and kinetic performance of the lithium ion battery.

[0017] In an embodiment of the present application, the electrolyte comprises fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate in the electrolyte is Q%, and Q and C satisfy: 0.3≤C / Q≤3. By adjusting Q and C to satisfy the above relationship, the lithium ion battery with good expansion performance and kinetic performance can be obtained.

[0018] In an embodiment of the present application, Q satisfies: 1≤Q≤20. By adjusting Q within the above range, the cycle performance of the lithium ion battery can be improved.

[0019] In one embodiment of the present application, the silicon-based particles include silicon and carbon elements, and the atomic ratio of silicon to carbon in the silicon-based particles is 1:1 to 2.5. The negative electrode tab of the present application includes the silicon-based particles having the above element atomic ratio, and a lithium ion battery having good expansion performance and cycle performance can be obtained.

[0020] The second aspect of the present application provides an electronic device including the electrochemical device of the above first aspect.

[0021] The present application provides an electrochemical device and an electronic device, including a positive electrode tab, a negative electrode tab, and an electrolyte, the negative electrode tab including a negative electrode current collector and a negative electrode material layer, the negative electrode material layer including a silicon-based composite material, the silicon-based composite material including silicon-based particles, the strength of the negative electrode current collector being A MPa, the difference between the maximum value and the minimum value of the relative percentage content of silicon atoms in the silicon-based particles being B%, the mass content of silicon elements in the negative electrode material layer being C%, and satisfying:

[0022]

[0023] By synergistically adjusting A, B, and C to satisfy the above conditions, the lithium ion battery obtained has good cycle performance and expansion performance. Of course, implementing any embodiment of the present application does not necessarily require all the advantages described above to be achieved at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the present application and the prior art, the following briefly introduces the drawings needed to be used in the embodiments and the prior art. Obviously, the drawings described below are only some of the embodiments of the present application.

[0025] Figure 1a The figure is a scanning electron microscope (SEM) image of the cross section of the silicon-based particles.

[0026] Figure 1b The figure is a fluctuation curve of the relative percentage content of silicon atoms in the X-ray energy dispersive spectrometer (EDS) line scan. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions, and advantages of the present application more clear and apparent, the following further describes the present application in detail with reference to the drawings and embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other technical solutions obtained by those skilled in the art belong to the scope of protection of the present application.

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

[0029] In the prior art, in order to improve the lithium intercalation expansion problem of the silicon negative electrode, mainly through nanometerization and compounding of silicon. For example, by reducing the particle size of the silicon material to the nanometer level, the stress generated when the silicon material intercalates lithium is relieved, and the material is reduced. The rupture; or by compounding with other carbonaceous materials, reducing the contact with the electrolyte, and reducing the generation of the solid electrolyte interface (SEI). However, the nanometerization method of silicon has the problems of complex preparation process and high energy consumption, and the high specific surface area of nanometer silicon material makes it extremely easy to agglomerate, which affects the electrical performance of the lithium ion battery. The existing compounding method only improves the carbonaceous composite material, and ignores the overall influence of other factors on the expansion of the lithium ion battery, so it has limitations on the improvement of the expansion performance and cycle performance of the lithium ion battery. In addition, the volume expansion caused by lithium intercalation is an intrinsic property of silicon-based materials. Although these solutions can improve the expansion of the silicon negative electrode to some extent, they are not enough to meet the application of industrial products.

[0030] Therefore, the present application provides an electrochemical device and an electronic device to improve the cycle performance and expansion performance of the lithium ion battery.

[0031] The first aspect of the present application provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer comprises a silicon-based composite material, the silicon-based composite material comprises silicon-based particles, the strength of the negative electrode current collector is A MPa, the difference between the maximum value and the minimum value of the relative percentage content of silicon atoms in the silicon-based particles is B%, and the mass content of silicon elements in the negative electrode material layer is C%, satisfying:

[0032]

[0033] The present inventors have found that the difference B% between the maximum and minimum relative percentage content of silicon atoms in the silicon-based particles is a fluctuation value, which can represent the uniformity of the distribution of silicon elements in the silicon-based particles. The greater the fluctuation value, the poorer the uniformity of the distribution of silicon elements. During the lithium intercalation of silicon, volume expansion occurs in multiple directions (e.g., along the length, width, and height directions of the lithium ion battery), and thus the negative current collector needs to have a certain strength to resist the stress caused by the expansion, thereby inhibiting the deformation of the lithium ion battery. The present inventors have also found that the more uniform the distribution of silicon elements in the silicon-based particles, the smaller the stress caused by the expansion; the greater the content of silicon elements in the negative material layer, the greater the expansion trend during the cycling of the lithium ion battery; and the greater the fluctuation degree of the distribution of silicon elements in the silicon-based particles and the mass content of silicon elements in the negative material layer, the higher the demand for the strength of the negative current collector, but when the negative current collector exceeds a certain strength, the improvement in the cycling and expansion performance will be greatly reduced. Based on the above findings, the present application can obtain a lithium ion battery with good cycling and expansion performance by synergistically adjusting A, B, and C to satisfy the above conditions.

[0034] In an embodiment of the present application, B satisfies: 10≤B≤16. By adjusting B within the above range, silicon-based particles with good uniformity of the distribution of silicon elements can be obtained, which is beneficial to reducing the stress caused by the expansion of the lithium ion battery, thereby obtaining a lithium ion battery with good cycling and expansion performance.

[0035] In an embodiment of the present application, C satisfies: 1≤C≤20. By adjusting C within the above range, the following situations can be avoided: the content of silicon elements in the negative material layer is too low, which may affect the energy density of the lithium ion battery; and the content of silicon elements in the negative material layer is too high, which may exacerbate the expansion trend of the lithium ion battery. Thus, by adjusting C within the above range, the energy density and expansion performance of the lithium ion battery can be balanced.

[0036] In an embodiment of the present application, A satisfies: 370≤A≤800. By adjusting A within the above range, the following situations can be avoided: the strength of the negative current collector is too low, which affects the expansion performance of the lithium ion battery; and the strength of the negative current collector is too high, which on the one hand does not improve the cycling and expansion performance, and on the other hand greatly increases the production cost of the current collector. Thus, by adjusting A within the above range, the expansion performance and production cost of the lithium ion battery can be balanced.

[0037] In one embodiment of this application, the single-sided thickness of the negative electrode material layer is H, and the maximum particle size of the silicon-based particles is Dmax, satisfying: H ≥ 3 × Dmax. By adjusting the relationship between H and Dmax to satisfy the above, the cycle performance and expansion performance of the lithium-ion battery can be improved. It is speculated that this is because the lithium intercalation of silicon material causes significant expansion. When the thickness of the negative electrode sheet is constant, an excessively large Dmax of the silicon-based particles can easily lead to uneven expansion of the electrode sheet, resulting in excessive local expansion of the negative electrode sheet. Furthermore, since the dispersion of the negative electrode material slurry is not an ideal situation of completely uniform dispersion, some silicon-based particles may be unevenly dispersed in the negative electrode sheet. If the Dmax of the silicon-based particles is too large, it can easily lead to bumps on the negative electrode sheet, affecting the appearance and performance of the negative electrode sheet, thereby affecting the cycle performance and expansion performance of lithium-ion batteries. Therefore, by adjusting the relationship between H and Dmax to satisfy the above, a lithium-ion battery with good cycle performance and expansion performance can be obtained.

[0038] It is understandable that the negative electrode material layer can be set on one side of the negative electrode current collector (i.e., single-sided coating) or on both sides of the negative electrode current collector (i.e., double-sided coating). In one example, assuming the overall thickness of the negative electrode sheet is h and the thickness of the negative electrode current collector is h1, when it is double-sided coating, then H is: H = (h - h1) / 2; when it is single-sided coating, then H is: H = h - h1.

[0039] In one embodiment of this application, the Dmax of the silicon-based particles satisfies: 10μm ≤ Dmax ≤ 25μm. By adjusting Dmax within this range, the following situations can be avoided: An excessively large Dmax of the silicon-based particles can easily lead to uneven electrode expansion and generate bumps during processing, affecting the interface and expansion performance of the lithium-ion battery; an excessively small Dmax of the silicon-based particles results in an excessively large specific surface area, leading to more SEI film accumulation on the negative electrode surface, increasing the expansion tendency, and requiring more binder to achieve the bonding effect during processing, thus reducing the energy density of the lithium-ion battery. Therefore, by adjusting Dmax within the above range, this application helps to balance the processing performance, expansion performance, and energy density of the lithium-ion battery.

[0040] In one embodiment of this application, the single-sided thickness H of the negative electrode material layer satisfies: 30μm ≤ H ≤ 90μm. By adjusting the single-sided thickness H of the negative electrode material layer within the above range, the strength and toughness of the negative electrode material layer can be balanced, thereby improving the performance of the lithium-ion battery.

[0041] In one embodiment of this application, the porosity of the negative electrode sheet is P%, where P and C satisfy: P > 15 × C 1 / 4By adjusting P and C to satisfy the above relationship, the expansion performance and dynamic performance of the lithium ion battery are improved. It is speculated that this may be due to the fact that the volume expansion of the silicon-based material after lithium intercalation is very large (about 300%), and the huge volume effect is easy to cause the negative electrode sheet to be prone to demolding and powder falling, etc. The negative electrode sheet with a certain porosity can effectively alleviate the volume expansion of the silicon-based material. However, when the porosity of the negative electrode sheet is too low, the electrolyte is difficult to fully infiltrate the negative electrode sheet, increasing the transmission distance of lithium ions, affecting the dynamic performance of the lithium ion battery. Therefore, by adjusting P and C to satisfy the above relationship, a lithium ion battery with good expansion performance and dynamic performance can be obtained.

[0042] In an embodiment of the present application, P satisfies: 18≤P≤40. By adjusting P within the above range, the negative electrode sheet can be effectively infiltrated in the electrolyte, and the negative electrode sheet has good strength, so that the expansion performance and dynamic performance of the lithium ion battery are improved.

[0043] In an embodiment of the present application, the electrolyte includes fluoroethylene carbonate (FEC), and the mass percentage of fluoroethylene carbonate in the electrolyte is Q%, based on the mass of the electrolyte. The Q and the C satisfy: 0.3≤C / Q≤3. By adjusting Q and C to satisfy the above relationship, the following situations can be avoided: when C / Q is too high, the expansion trend of the lithium ion battery during the cycle process increases, and when C / Q is too low, the addition of FEC will reduce the migration rate of lithium ions in the electrolyte, affecting the rate performance of the lithium ion battery. Therefore, by adjusting Q and C to satisfy the above relationship, a lithium ion battery with good expansion performance and dynamic performance can be obtained.

[0044] In an embodiment of the present application, Q satisfies: 1≤Q≤20. Fluoroethylene carbonate (FEC) is an important film-forming additive in the electrolyte, which produces a SEI film during the cycle process of the lithium ion battery to isolate the material and the electrolyte, reducing the consumption of lithium ions. By adjusting Q within the above range, the cycle performance of the lithium ion battery is improved.

[0045] In an embodiment of the present application, the silicon-based particles include silicon elements and carbon elements, and the atomic ratio of silicon to carbon in the silicon-based particles is 1:1 to 2.5. The negative electrode sheet of the present application includes silicon-based particles with the above element atomic ratio, and a lithium ion battery with good expansion performance and cycle performance can be obtained.

[0046] The preparation method of the silicon-based composite material in the present application is not limited, as long as the purpose of the present application can be achieved. For example, an organic matter is carbonized to obtain a porous carbon matrix, and then the porous carbon matrix is placed in a silicon-containing gas atmosphere, and then heat treated to obtain a silicon-based composite material. In an example, the following preparation method can be used:

[0047] The porous carbon matrix is placed in a rotary furnace, the furnace tube is purged with nitrogen at room temperature for 20 to 40 minutes, and then the temperature of the porous carbon matrix sample is raised to 450 to 500°C. The nitrogen flow rate is adjusted so that the residence time of the gas in the rotary furnace is at least 90 seconds, and maintained at this flow rate for about 30 minutes. The gas supply is then switched from nitrogen to a mixed gas containing silicon-containing gas and nitrogen (the volume fraction of the silicon-containing gas in the mixed gas is 5% to 30%). After deposition at a gas flow rate of 200 to 400 seem for 8 to 16 hours, the nitrogen gas is continuously supplied to the rotary furnace to blow out the silicon-containing gas from the furnace, and the rotary furnace is purged with nitrogen for 30 minutes. Then the nitrogen gas in the rotary furnace is gradually converted to air from a compressed air source by switching the gas flow from nitrogen to air in 1 to 2 hours, to obtain a silicon-based composite material.

[0048] In the present application, the type of the porous carbon matrix is not particularly limited as long as the purpose of the present application can be achieved, for example, the porous carbon matrix can be selected from at least one of hard carbon, soft carbon, and graphite. Exemplarily, the above-mentioned hard carbon can include resin carbon, carbon black, organic polymer pyrolytic carbon, and combinations thereof. The above-mentioned soft carbon can include carbon fibers, carbon microspheres, and combinations thereof. The particle size of the porous carbon matrix is not limited as long as the purpose of the present application can be achieved. For example, the particle size of the porous carbon matrix ranges from 3 μm < Dv50 < 15 μm, 15 μm < Dv99 < 30 μm.

[0049] The difference B% between the maximum value and the minimum value of the relative percentage content of silicon atoms in the silicon-based particles is related to the uniformity of the pore distribution and the pore size in the carbon matrix, for example, the more uniform the pore distribution in the carbon matrix, the smaller the B%. Based on this, the B% can be adjusted by adjusting the pore distribution and the pore size.

[0050] The mass content C% of silicon elements in the negative electrode material layer is related to the addition amount of the silicon-based composite material, wherein the content of silicon deposited in the silicon-based composite material can be adjusted by adjusting the deposition temperature, the deposition time, and the concentration of the silicon-containing gas, for example, C% generally increases with the increase of the deposition temperature, C% generally increases with the increase of the deposition time, and C% generally increases with the increase of the concentration of the silicon-containing gas. Based on this, the adjustment of the mass content C% of silicon elements in the negative electrode material layer can be carried out.

[0051] The particle size maximum Dmax of the silicon-based particles is positively correlated with the particle size of the porous carbon matrix, based on which the particle size maximum Dmax of the silicon-based particles can be adjusted by performing particle size screening on the porous carbon matrix.

[0052] The porosity of the negative electrode sheet generally decreases as the compaction density of the negative electrode sheet increases. Based on this, the porosity of the negative electrode sheet can be adjusted by adjusting the cold-pressing pressure of the negative electrode sheet to adjust the compaction density of the negative electrode sheet.

[0053] The atomic ratio of silicon element to carbon element in the silicon-based particles can be adjusted by adjusting the ratio of the silicon-containing gas to the nitrogen gas in the mixed gas. Generally, as the ratio of the silicon-containing gas in the mixed gas increases, more silicon element is deposited in the porous carbon matrix, increasing the atomic ratio of silicon element to carbon element in the silicon-based particles.

[0054] In the present application, the negative electrode sheet includes a negative electrode current collector, and the negative electrode material layer can be disposed on one surface or both surfaces along the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector, or can be a partial area of the negative 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 negative 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 include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc. In the present application, the thickness of the negative electrode current collector is not particularly limited as long as the purpose of the present application can be achieved, for example, the thickness is 4 μm to 12 μm. The thickness of the negative electrode material layer of the present application can be 70 μm to 120 μm.

[0055] In the present application, in addition to the above-mentioned silicon-based composite material, the negative electrode material layer can also include other negative electrode active materials known in the art, for example, it can include but is not limited to at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 or Li-Al alloy.

[0056] In the present application, the negative electrode material layer can also include a negative electrode conductive agent, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can include but is not limited to at least one of carbon-based material, metal-based material, or conductive polymer. The above-mentioned carbon-based material is selected from at least one of natural graphite, artificial graphite, conductive carbon black, acetylene black, ketjen black, or carbon fiber. The above-mentioned metal-based material can include but is not limited to metal powder and / or metal fiber, specifically, the metal can include but is not limited to at least one of copper, nickel, aluminum, or silver. The conductive polymer can include but is not limited to at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0057] In the present application, the negative electrode material layer can further include a negative electrode binder, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, and can include, for example, but is not limited to, at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon.

[0058] Optionally, the negative electrode tab can further include a conductive layer between the negative electrode current collector and the negative electrode 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, which can include, but is not limited to, the above-mentioned negative electrode conductive agent and the above-mentioned negative electrode binder.

[0059] The electrolyte of the present application can further include a lithium salt and other non-aqueous solvents, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, and can include, for example, 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, LiBOB, or lithium difluoroborate. Preferably, the lithium salt includes LiPF6.

[0060] The other non-aqueous solvent is not particularly limited as long as the object of the present application can be achieved, and for example, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents can be included, but is not limited thereto. The above-mentioned carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The above-mentioned chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above-mentioned cyclic carbonate can include, but is not limited to, at least one of butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of 1,2-difluoro ethylene carbonate, 1,1-difluoro ethylene carbonate, 1,1,2-trifluoro ethylene carbonate, 1,1,2,2-tetrafluoro ethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The above-mentioned carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or hexanolactone. The above-mentioned ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, 1-ethoxy-1-methoxy ethane, 2-methyl tetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the other non-aqueous solvent is not particularly limited as long as the object of the present application can be achieved, and for example, the mass percentage content of the above-mentioned other non-aqueous solvent can be 67% to 87%, for example, 67%, 67.5%, 70%, 75%, 80%, 83%, 85%, 86.5%, 87%, or any range therebetween.

[0061] The electrochemical device of the present application can further include a positive electrode tab, and the present application does not particularly limit the positive electrode tab as long as the purpose of the present application can be achieved, for example, the positive electrode tab generally includes a positive electrode current collector and a positive electrode material layer. The positive electrode material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector, and the present application does not particularly limit it as long as the purpose of the present application can be achieved. In the present application, the positive electrode current collector is not particularly limited as long as the purpose of the present application can be achieved, for example, it can include but is not limited to an aluminum foil, an aluminum alloy foil, or a composite current collector, etc. In the present application, the thickness of the positive electrode current collector is not particularly limited as long as the purpose of the present application can be achieved, for example, the thickness is 8 μm to 12 μm.

[0062] In the present application, the positive electrode material layer includes a positive electrode active material, and the present application does not particularly limit the positive electrode active material as long as the purpose of the present application can be achieved, for example, it can include at least one of a composite oxide of lithium or a transition metal element. The present application does not particularly limit the above-mentioned transition metal element as long as the purpose of the present application can be achieved, for example, it can include at least one of nickel, manganese, cobalt, or iron. Specifically, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, lithium manganese iron phosphate, or lithium titanate.

[0063] In the present application, the positive electrode material layer can further include a positive electrode conductive agent, and the present application does not particularly limit the positive electrode conductive agent as long as the purpose of the present application can be achieved, for example, it can include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, acetylene black, flake graphite, ketjen black, graphene, a metal material, or a conductive polymer, preferably, the positive electrode conductive agent includes conductive carbon black and carbon nanotubes. 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 nano carbon fibers. The above-mentioned metal material can include but is not limited to metal powder and / or metal fibers, and specifically, 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. In the present application, the positive electrode material layer can further include a positive electrode binder, and the present application does not particularly limit the positive electrode binder as long as the purpose of the present application can be achieved, for example, it can include but is not limited to at least one of fluorine-containing resin, polypropylene resin, fiber type binder, rubber type binder, or polyimide type binder.

[0064] Optionally, the positive electrode sheet can further include a conductive layer between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited in the present application and can be a conventional conductive layer used in the art, for example, can include but is not limited to the above-mentioned positive electrode conductive agent and the above-mentioned positive electrode binder.

[0065] The electrochemical device of the present application can further include a separator film, which is not particularly limited in the present application as long as the object of the present application can be achieved. The above-mentioned separator film can include a substrate layer and a surface treatment layer, and the substrate layer is not particularly limited in the present application, for example, can include but is not limited to at least one of polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin-based separator film, polyester film (e.g., polyethylene terephthalate film), cellulose film, polyimide film, polyamide film, spandex, aramid film, woven film, nonwoven film (nonwoven fabric), microporous film, composite film, separator paper, calendered film, or spunlaced film, preferably polyethylene or polypropylene, which has a good effect on preventing short circuit and can improve the stability of the electrochemical device by shutdown effect. The separator film of the present application can have a porous structure, and the size of the pore diameter is not particularly limited in the present application as long as the object of the present application can be achieved, for example, the size of the pore diameter can be 0.01 μm to 1 μm. In the present application, the thickness of the separator film is not particularly limited as long as the object of the present application can be achieved, for example, the thickness can be 5 μm to 500 μm.

[0066] In the present application, the surface treatment layer is provided on at least one surface of the above-mentioned substrate layer, and the surface treatment layer is not particularly limited in the present application and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer can include but is not limited to inorganic particles and an inorganic layer binder, and the inorganic particles are not particularly limited in the present application, for example, can include but are not limited to 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 inorganic layer binder is not particularly limited in the present application, for example, can include but is not limited to at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer is not particularly limited in the present application, and the material of the polymer can 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).

[0067] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, a lithium-ion battery.

[0068] The preparation process of electrochemical devices is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0069] A second aspect of this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments. The electrochemical device provided by this application has good expansion and cycling performance, thereby providing a long service life.

[0070] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0071] Example

[0072] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0073] Test method and equipment:

[0074] Porosity test of negative electrode sheet:

[0075] The porosity of the negative electrode sheet is tested by gas replacement method: 50 pieces of negative electrode sheets with radius d are punched out by using the same mold, the thickness h of each negative electrode sheet is measured, and the 50 pieces of negative electrode sheets are loaded into the sample cup of the test equipment (AccuPycП1340), and the negative electrode sheets are filled with helium in a closed sample chamber, so as to measure the true volume V of the negative electrode sheet, and then the porosity of the negative electrode sheet is calculated by the following formula: P = (1-V / πd 2 ×50×h)×100%.

[0076] Strength test of the current collector:

[0077] The current collector is punched into a test sample with a width of 15 mm and a length of 70 mm by a punching machine. The tensile strength of the test sample is tested by fixing the test sample to the test fixture of a high-iron tension machine, the tensile speed is 5 mm / min, and the standard distance between the two fixtures of the tension machine is 50 mm. The tensile strength and displacement curve are recorded, and the point of sudden drop of the tensile strength is the strength of resisting external force damage.

[0078] Test of the content of silicon element in the negative electrode material layer:

[0079] The negative electrode sheet is dried in a vacuum oven at 100°C for 24 hours, part of the active material on the negative electrode sheet is scraped off by a blade and weighed to obtain a mass M1, and then the scraped active material is heat-treated at 800°C in a continuous air atmosphere to remove carbonaceous material, and the remaining material is weighed to obtain a mass M2. Then the content of silicon element in the negative electrode material layer is calculated by the following formula: C = 0.467M2 / M1x100%.

[0080] Determination of the difference between the maximum value and the minimum value of the relative percentage content of silicon atoms in the silicon-based particles:

[0081] The negative electrode sheet is dried in a vacuum oven at 100°C for 24 hours, and the silicon-based particles in the sheet are processed into thin slices of 50-100 nm under a protective atmosphere (such as nitrogen) by using a focused ion beam (FIB), and the SEM image is as shown in Figure 1a Then, the relative percentage content of silicon atoms in the silicon-based particles is tested by using the X-ray energy spectrum (EDS) line scanning in the transmission electron microscope (TEM) equipment, and the test results are as shown in Figure 1b The line scanning position is selected at any position inside the silicon-based particles, for example, Figure 1b The starting point and the ending point of the line scanning data of Figure 1a correspond to the starting point and the ending point of the black arrow line in Figure 1b The line scanning data of Figure 1a is the data corresponding to the position of the black arrow line in

[0082] Determination of the maximum particle size Dmax of silicon-based particles:

[0083] The negative electrode sheet is vertically cut using an ion polishing machine, and more than 20 silicon-based particles in the sheet are randomly selected under an electron microscope. The particle size of the silicon-based particles is tested, and the maximum particle size of the randomly selected particles is taken as Dmax.

[0084] Determination of the content of fluoroethylene carbonate (FEC) in the electrolyte:

[0085] After the lithium ion battery is discharged to 0% state of charge (SOC) and centrifuged, the liquid obtained after centrifugation is tested by GC-MS (gas chromatography mass spectrometry) to detect the mass content percentage of the FEC component in the electrolyte.

[0086] Normal temperature cycle performance test of lithium ion battery:

[0087] The test temperature is 25°C. The lithium ion battery is charged to 4.45V at a rate of 0.7C (C), then charged at a constant voltage to 0.025C, and then discharged to 3.0V at a rate of 0.5C after 5 minutes of standing. The capacity obtained in this step is the initial discharge capacity, and the cycle test of 0.7C charging / 0.5C discharging is carried out for 400 cycles, and the discharge capacity of the 400th cycle is recorded. Cycle capacity retention rate = (discharge capacity of the 400th cycle / initial discharge capacity) x 100%.

[0088] Low temperature cycle performance test of lithium ion battery:

[0089] At 25°C, the lithium ion battery after formation is charged to 4.45V at a rate of 0.2C (C), then charged at a constant voltage to a current less than or equal to 0.05C, then left to stand for 30 minutes, then discharged to 3.0V at a rate of 0.2C, and the 25°C 0.2C discharge capacity of the lithium ion battery is tested.

[0090] At 25°C, the lithium ion battery is charged to 4.45V at a rate of 0.2C (C), then charged at a constant voltage to a current less than or equal to 0.05C; then the cell is placed in a-10°C environment and left to stand for 60 minutes, then discharged to 3.0V at a rate of 0.2C, and the-10°C 0.2C discharge capacity of the lithium ion battery is tested.

[0091] Lithium ion battery-10°C discharge capacity retention rate (%) = discharge capacity at-10°C / discharge capacity at 25°C x 100%.

[0092] Swelling rate test of lithium ion battery:

[0093] The thickness of the lithium ion battery at 50% SOC was tested at a test temperature of 25°C with a screw micrometer, denoted as H0, and then the thickness of the lithium ion battery at 100% SOC was tested after the steps in the cycle performance test were followed to 400 cycles, denoted as H1. The 25°C cycle expansion rate = (H1-H0) / H0 x 100%.

[0094] Example 1-1

[0095] Preparation of silicon-based composite

[0096] A porous carbon substrate with a Dmax of 25 pm was placed in a rotary furnace, and the furnace tube was purged with nitrogen for 30 minutes at room temperature. The heating temperature of the porous carbon sample was then increased to 450°C. The nitrogen flow rate was adjusted so that the residence time of the gas in the rotary furnace was at least 90 seconds, and the flow rate was maintained for 30 minutes. The gas supply was then switched from nitrogen to a mixed gas containing a silicon-containing gas (e.g., silane) and nitrogen, with a volume ratio of the silicon-containing gas to nitrogen in the mixed gas being 5:95. After 8 hours of deposition at a gas flow rate of 200 seem, the nitrogen gas was continuously supplied to the rotary furnace to blow out the silicon-containing gas from the furnace, and the rotary furnace was purged with nitrogen for 30 minutes. The nitrogen gas in the rotary furnace was then gradually converted to air from a compressed air source over 2 hours by switching the gas flow from nitrogen to air, to obtain a silicon-based composite, i.e., a silicon-based particle. The difference B% between the maximum and minimum relative percentage contents of silicon atoms in the silicon-based particle was determined, as shown in Table 1.

[0097] Preparation of negative electrode sheet

[0098] The silicon-based composite, graphite particles, and nano-conductive carbon black prepared above were mixed in a mass ratio of 3:94:3 to obtain a first mixture; the first mixture and a binder polyacrylic acid (PAA) were added to deionized water in a mass ratio of 95:5, and the mixture was adjusted to a solid content of 70 wt% to obtain a first mixed slurry.

[0099] The first mixed slurry was uniformly coated on one surface of a negative current collector copper foil with a thickness of 8 pm, and was dried at a vacuum drying temperature of 85°C for 12 hours to obtain a negative electrode sheet coated with negative electrode active material on one side; then, the above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with negative electrode active material on both sides; and then the negative electrode sheet obtained above was cold-pressed, slitted, and cut to obtain a negative electrode sheet with a size of 76 mm x 867 mm. The thickness of the negative electrode sheet was 90 mm, and the porosity was 33%.

[0100] Preparation of positive electrode sheet

[0101] The positive active material lithium cobaltate, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5, NMP was added as a solvent, a slurry with a solid content of 75 wt% was prepared, and the slurry was stirred uniformly. The slurry was uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 10 μm, dried at 90°C, and a positive electrode sheet with a coating thickness of 110 μm was obtained. After the above steps were completed, the single-sided coating of the positive electrode sheet was completed. Then, the above steps were repeated on the other surface of the positive electrode sheet, and a positive electrode sheet coated with a positive active material on both sides was obtained. Then, after cold pressing and cutting, a positive electrode sheet with a size of 74 mm x 851 mm was obtained.

[0102] <Preparation of electrolyte>

[0103] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 1:1:1 as a base solvent, LiPF6 was added, and the mixture was stirred uniformly to obtain an electrolyte, wherein the mass percentage of LiPF6 was 12.5 wt%.

[0104] <Preparation of separator>

[0105] A polyethylene (PE) film with a thickness of 15 μm (provided by Celgard) was used.

[0106] <Preparation of lithium ion battery>

[0107] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were stacked in order, with the separator between the positive electrode and the negative electrode to play a role of isolation, and an electrode assembly was obtained by winding. The electrode assembly was placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, degassing, and edge cutting, a lithium ion battery was obtained.

[0108] Examples 1-2 to 1-14

[0109] Except for adjusting the strength A of the negative current collector, the difference B% between the maximum and minimum relative percentage contents of silicon atoms in the silicon-based particles, and the mass content C% of silicon elements in the negative material layer as shown in Table 1, the rest was the same as in Example 1-1.

[0110] Examples 2-1 to 2-9

[0111] Except for adjusting the single-sided thickness H of the negative material layer and the maximum particle size Dmax of the silicon-based particles as shown in Table 2, the rest was the same as in Example 1-6.

[0112] Examples 3-1 to 3-9

[0113] The rest is the same as Example 2-3 except that the porosity P% of the negative electrode tab is adjusted as shown in Table 3, and the mass content C% of silicon element in the negative electrode material layer is adjusted.

[0114] Example 4-1

[0115] The rest is the same as Example 1-1 except that the preparation of the electrolyte is different from Example 1-1.

[0116] Preparation of electrolyte

[0117] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 1:1:1 as a base solvent, LiPF6 and fluoroethylene carbonate were added, and stirred uniformly to obtain an electrolyte, wherein the mass percentage content of LiPF6 was 12.5 wt%, and the mass percentage content of fluoroethylene carbonate was shown in Table 4.

[0118] Examples 4-2 to 4-4

[0119] The rest is the same as Example 4-1 except that the mass percentage content Q% of fluoroethylene carbonate is adjusted as shown in Table 4.

[0120] Comparative Examples 1-1 to 1-4

[0121] The rest is the same as Example 1-1 except that the strength A of the negative current collector, the difference B% between the maximum and minimum values of the relative percentage content of silicon atoms in the silicon-based particles, and the mass content C% of silicon element in the negative electrode material layer are adjusted as shown in Table 1.

[0122] Table 1

[0123]

[0124]

[0125] It can be seen from Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-4 that when the strength A of the negative current collector, the difference B% between the maximum and minimum values of the relative percentage content of silicon atoms in the silicon-based particles, and the mass content C% of silicon element in the negative electrode material layer satisfy:

[0126] The cycle performance and swelling performance of the lithium ion battery are improved.

[0127] Table 2

[0128]

[0129] The single-face thickness H of the negative electrode material layer, the maximum particle size Dmax of the silicon-based particles also affect the performance of the lithium ion battery. As can be seen from Examples 1-6, Examples 2-1 to 2-9, when H and Dmax satisfy H≥3×Dmax, the lithium ion battery has good cycle performance and expansion performance.

[0130] Table 3

[0131]

[0132]

[0133] The porosity P% of the negative electrode sheet, the mass content C% of silicon element in the negative electrode material layer also affect the performance of the lithium ion battery. As can be seen from Examples 2-3, Examples 3-1 to 3-9, when P and C satisfy: P>15×C 1 / 4 , the lithium ion battery has good room temperature cycle performance, expansion performance and low temperature cycle performance.

[0134] Table 4

[0135]

[0136] The mass content C% of silicon element in the negative electrode material layer, the content Q% of fluoroethylene carbonate in the electrolyte also affect the performance of the lithium ion battery. As can be seen from Examples 3-5, Examples 4-1 to 4-4, when Q and C satisfy: 0.3≤C / Q≤3, the lithium ion battery has good room temperature cycle performance, expansion performance and low temperature cycle performance.

[0137] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative current collector and a negative electrode material layer. in, The negative electrode material layer comprises a silicon-based composite material, which includes silicon-based particles. The strength of the negative electrode current collector is A MPa. A line scan test is performed on the silicon-based composite material. The difference between the maximum and minimum percentage of silicon atoms in the silicon-based particles within the line scan test interval is B%. The mass content of silicon in the negative electrode material layer is C%, satisfying the following: ； The condition A satisfies: 375≤A≤800; The condition C satisfies: 1 ≤ C ≤ 20; The electrolyte includes fluoroethylene carbonate, and based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is Q%, where Q and C satisfy: 0.3≤C / Q≤3; The thickness of the negative electrode material layer on one side is H, and the maximum particle size of the silicon-based particles is Dmax, satisfying: H≥3×Dmax.

2. The electrochemical device according to claim 1, wherein, The condition B satisfies: 10 ≤ B ≤ 16.

3. The electrochemical device according to claim 1, wherein, The Dmax satisfies: 10μm≤Dmax≤25μm.

4. The electrochemical device according to claim 1, wherein, The H satisfies: 30μm≤H≤90μm.

5. The electrochemical device according to any one of claims 1 to 4, wherein, The porosity of the negative electrode sheet is P%, and P and C satisfy: P > 15 × C 1 / 4 .

6. The electrochemical device according to claim 5, wherein, The condition P satisfies: 18 ≤ P ≤ 40.

7. The electrochemical device according to any one of claims 1 to 4, wherein, The condition C satisfies: 1 ≤ C ≤ 10.

8. The electrochemical device according to any one of claims 1 to 4, wherein, The condition Q satisfies: 1≤Q≤20.

9. The electrochemical device according to any one of claims 1 to 4, wherein, The condition Q satisfies: 2≤Q≤10.

10. The electrochemical device according to any one of claims 1 to 4, wherein, The silicon-based particles include silicon and carbon elements, and the atomic ratio of silicon to carbon in the silicon-based particles is 1:1 to 2.

5.

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

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