Electrochemical apparatus and electronic apparatus

Abstract

An electrochemical apparatus and an electronic apparatus. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet and a separator; the negative electrode sheet comprises a negative electrode current collector, a surface of the negative electrode current collector being provided with a first negative electrode active material layer containing a silicon-based material; the separator is disposed between the negative electrode sheet and the positive electrode sheet, a polymer particle layer being disposed on a surface of the separator adjacent to the first negative electrode active material layer. By means of matching separators coated with polymer particle layers of different thicknesses based on differences in silicon content of the negative electrode active material layer coated on the surface of the negative electrode current collector in the negative electrode sheet, it is possible to reserve corner space to buffer electrode sheet extrusion and fracture, overcome the problems of electrode sheet fracture and cycle lithium deposition caused by silicon-based expansion, and maximize energy density.

Description

Electrochemical devices and electronic devices Technical Field

[0001] This application relates to the field of energy storage technology, and more particularly to electrochemical devices and electronic devices. Background Technology

[0002] Due to silicon's high reversible capacity of up to 4200 mAh / g, silicon-based anode materials are considered one of the effective strategies for improving the energy density of lithium-ion batteries. However, during the insertion and extraction of lithium ions during charging and discharging, silicon particles undergo a volume expansion of over 300%, which brings a series of problems. First, the excessive volume expansion damages the solid electrolyte interphase (SEI) film, causing electrolyte to penetrate into the anode electrode and triggering a series of unstable reactions, such as electrolyte decomposition and repeated SEI formation, leading to capacity decay and performance instability in the lithium-ion battery. Second, the volume expansion of silicon can also cause corner electrode breakage. Corner electrodes must remain stable throughout the charge-discharge cycle of the lithium-ion battery, but the volume expansion of silicon can cause stress concentration at the corner electrodes, ultimately leading to breakage and reducing the lifespan and reliability of the lithium-ion battery.

[0003] Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, this application proposes an electrochemical device and an electronic device, which, by configuring and designing the silicon content of the negative electrode sheet and the polymer particle layer on the separator surface, reserves space in the corner area to buffer the compression, aiming to solve the corner breakage and interface problems of the negative electrode sheet caused by silicon-based expansion, while improving the energy density of lithium-ion batteries.

[0005] In a first aspect, this application provides an electrochemical device, including a positive electrode, a negative electrode, and a separator; the negative electrode includes a negative current collector, and a first negative electrode active material layer containing silicon-based material is disposed on the surface of the negative current collector; the separator is disposed between the negative electrode and the positive electrode; a polymer particle layer is disposed on the surface of the separator adjacent to the first negative electrode active material layer.

[0006] Based on the mass of the first negative electrode active material layer, the mass percentage of silicon is X; the thickness of the polymer particle layer is H. In some embodiments, 0 < X ​​< 2%, 0 < H < 1 μm. In some embodiments, 2% ≤ X < 10%, 1 μm ≤ H < 2.8 μm. In some embodiments, 10% ≤ X < 25%, 2.8 μm ≤ H < 4 μm. In some embodiments, 25% ≤ X ≤ 30%, 4 μm ≤ H ≤ 5 μm. The thickness of the polymer particle layer is the thickness of the flat region. The thickness of the polymer particle layer in the corner region is greater than that in the flat region. This is because during the battery fabrication process, after winding, formation, and hot pressing, the polymer particle layer in the flat region is flattened due to the effect of hot pressing, while the thickness of the polymer layer in the corner region does not change much. When the polymer particle layer after hot pressing satisfies this relationship, it can ensure that the space reserved in the corner region is sufficient to withstand the stress generated by the expansion in the corner region. Depending on the silicon content in the negative electrode active material layer coated on the surface of the negative electrode current collector, a separator with a polymer particle layer of different thickness is matched. This can reserve corner space to buffer the extrusion and breakage of the electrode, overcome the problems of electrode breakage and cycle lithium plating caused by silicon-based expansion, and maximize energy density.

[0007] In some embodiments, 2% ≤ X < 5%, 1.5 μm ≤ H < 2.5 μm. In some embodiments, 5% ≤ X < 10%, 2.5 μm ≤ H < 2.8 μm. In some embodiments, 10% ≤ X < 15%, 2.8 μm ≤ H < 3.5 μm. In some embodiments, 15% ≤ X ≤ 20%, 3.5 μm ≤ H < 4 μm. When the silicon content in the negative electrode active material layer coated on the negative electrode current collector side of the negative electrode sheet and the thickness of the polymer particle layer on the matching separator satisfy this rule, the problem of lithium plating during cycling is further optimized and improved.

[0008] In some embodiments, the separator adjacent to the first negative electrode active material layer has a polymer particle layer on its surface away from the first negative electrode active material layer.

[0009] In some embodiments, the separator adjacent to the first negative electrode active material layer has an adhesive layer on its surface facing the first negative electrode active material layer, and the thickness of the adhesive layer is preferably 0 to 1 μm.

[0010] In some embodiments, the adhesive layer may be selected from at least one material selected from homopolymers or copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, methacrylonitrile, and maleic acid. In some embodiments, the adhesive layer is preferably a polymer of acrylic acid, acrylate, styrene, isobutyl acrylate, or acrylonitrile.

[0011] In some embodiments, the first negative electrode active material layer includes a negative electrode active material, which includes a silicon-based active material selected from at least one of silicon, silicon oxides, silicon carbide compounds, or silicon alloys. In some embodiments, the silicon-based active material is preferably silicon carbide particles.

[0012] In some embodiments, the negative electrode active material includes a carbon active material selected from at least one of graphite or hard carbon. In some embodiments, the carbon active material is preferably graphite.

[0013] In some embodiments, the mass percentage X of silicon element is preferably satisfied to be 2% ≤ X ≤ 5%, based on the mass of the first negative electrode active material layer. When the silicon element meets this range, the expansion of silicon can be better controlled, and the lithium plating problem can be improved.

[0014] In some embodiments, a second negative electrode active material layer is disposed on the other surface of the negative electrode current collector; the second negative electrode active material layer does not contain silicon. In this case, silicon is distributed in the active material layer on one side of the negative electrode current collector surface.

[0015] In some embodiments, the second negative electrode active material layer does not contain silicon, and there is no polymer particle layer on the surface of the separator adjacent to the second negative electrode active material layer.

[0016] In some embodiments, the second negative electrode active material layer does not contain silicon, and the separator adjacent to the second negative electrode active material layer includes a substrate, an inorganic coating applied to one side of the substrate, and an adhesive layer applied to the surface of the inorganic coating. In some embodiments, an adhesive layer is applied to the other side of the substrate of the separator.

[0017] In some embodiments, the adhesive layer may be selected from at least one material selected from homopolymers or copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, methacrylonitrile, and maleic acid. In some embodiments, the adhesive layer is preferably a polymer of acrylic acid, acrylate, styrene, isobutyl acrylate, or acrylonitrile.

[0018] In some embodiments, the thickness of the adhesive layer is preferably 0 to 1 μm.

[0019] In some embodiments, a second negative electrode active material layer is disposed on the other surface of the negative electrode current collector; the second negative electrode active material layer contains silicon. The mass percentage of silicon is also X, based on the mass of the second negative electrode active material layer. In this case, the silicon is uniformly distributed in the active material layers on both surfaces of the negative electrode current collector.

[0020] In some embodiments, the second negative electrode active material layer comprises silicon, and a polymer particle layer is disposed on one surface of the separator adjacent to the second negative electrode active material layer.

[0021] In some embodiments, the second negative electrode active material layer comprises silicon, and the separator adjacent to the second negative electrode active material layer has a polymer particle layer disposed on its surface away from the second negative electrode active material layer.

[0022] In some embodiments, the second negative electrode active material layer comprises silicon, and the separator adjacent to the second negative electrode active material layer does not have a polymer particle layer on its surface facing the second negative electrode active material layer.

[0023] In some embodiments, the polymer particle layer is selected from at least one homopolymer or copolymer of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, propylene chloride, acrylic acid, acrylate, styrene, butadiene, and acrylonitrile. In some embodiments, the polymer particle layer is preferably polyvinylidene fluoride.

[0024] In some embodiments, the separator adjacent to the first negative electrode active material layer includes a substrate and an inorganic coating disposed between the substrate and the polymer particle layer.

[0025] In some embodiments, an adhesive layer is coated on the other side surface of the substrate of the separator adjacent to the first negative electrode active material layer.

[0026] In some embodiments, the inorganic coating is selected from at least one material selected from boehmite, magnesium hydroxide, aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, or silicon nitride.

[0027] In some embodiments, the inorganic coating is preferably boehmite. In some embodiments, the thickness of the inorganic coating is preferably from 0.5 μm to 6 μm.

[0028] In some embodiments, the substrate is selected from at least one material selected from polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane.

[0029] In some embodiments, the substrate is preferably a porous polyethylene (PE) polymer film. In some embodiments, the thickness of the substrate is preferably 3 μm to 6 μm.

[0030] Secondly, this application provides an electronic device that includes the electrochemical device of the first aspect. Beneficial effects:

[0031] Based on the characteristic of easy expansion of silicon-based anodes, this application proposes a matching design scheme for silicon-based anode plates and separators. By matching the separator with polymer particle layers of different thicknesses according to the different silicon contents in the anode active material layer coated on the surface of the anode current collector side of the anode plate, corner space can be reserved to buffer the extrusion and breakage of the anode plate, overcome the problems of anode plate breakage and cycle lithium plating caused by silicon expansion, and maximize energy density. Attached Figure Description

[0032] The accompanying drawings, necessary for describing embodiments of this application or the prior art, will be briefly described below to facilitate the depiction of embodiments of this application. It is obvious that the drawings described below represent only a portion of the embodiments in this application. Those skilled in the art can still derive other embodiments based on the structures illustrated in these drawings.

[0033] Figure 1 is a schematic diagram of the design of the negative electrode sheet in Embodiment 1 of this application.

[0034] Figure 2 is a schematic diagram of the design of the separator matched with the first negative electrode active material layer in Embodiment 1 of this application.

[0035] Figure 3 is a schematic diagram of the battery design of Embodiment 1 of this application.

[0036] Figure 4 is a schematic diagram of the winding effect of the battery before compression in Embodiment 1 of this application.

[0037] Figure 5 is a schematic diagram of the winding effect of the battery after compression in Embodiment 1 of this application.

[0038] Figure 6 is a surface image of the diaphragm before compression, which is matched with the first negative electrode active material layer of Embodiment 1 of this application.

[0039] Figure 7 is a side view of the membrane after compression, which is matched with the first negative electrode active material layer of Embodiment 1 of this application.

[0040] Figure 8 is a schematic diagram of the design of the negative electrode sheet in Embodiment 22 of this application.

[0041] Figure 9 is a schematic diagram of the battery design of Embodiment 22 of this application.

[0042] Figure 10 is a schematic diagram of the winding effect of the battery before compression in Embodiment 22 of this application.

[0043] Figure numbers: 1-Silicon carbon particles, 2-Graphite, 3-Negative electrode current collector, 4-Substrate, 5-Polymer particles, 6-Inorganic coating, 7-Positive electrode sheet, 8-First negative electrode active material layer, 9-Second negative electrode active material layer, 10-Negative electrode sheet, 11-Separator. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0045] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0046] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0047] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0048] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0049] In the detailed description and claims, a list of items connected by the terms "one of," "one of," "one of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A; or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; or only B; or only C.

[0050] In the description of this article, it should also be noted that the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0051] In a first aspect, this application provides an electrochemical device, including a positive electrode, a negative electrode, and a separator; the negative electrode includes a negative current collector, and a first negative electrode active material layer containing silicon-based material is disposed on the surface of the negative current collector; the separator is disposed between the negative electrode and the positive electrode; a polymer particle layer is disposed on the surface of the separator adjacent to the first negative electrode active material layer. Based on the mass of the first negative electrode active material layer, the mass percentage of silicon is X; the thickness of the polymer particle layer is H. In some embodiments, 0 < X ​​< 2%, 0 < H < 1 μm. In some embodiments, 2% ≤ X < 10%, 1 μm ≤ H < 2.8 μm. In some embodiments, 10% ≤ X < 25%, 2.8 μm ≤ H < 4 μm. In some embodiments, 25% ≤ X ≤ 30%, 4 μm ≤ H ≤ 5 μm.

[0052] This application provides a separator with polymer particle layers of different thicknesses that are matched to the different silicon contents in the negative electrode active material layer coated on the surface of the negative electrode current collector in the negative electrode sheet. This can reserve corner space to buffer the extrusion and breakage of the electrode sheet, overcome the electrode sheet breakage and lithium plating at the cycle corner caused by silicon-based expansion, and maximize the energy density.

[0053] In some embodiments, 2% ≤ X < 5%, 1.5 μm ≤ H < 2.5 μm. In some embodiments, 5% ≤ X < 10%, 2.5 μm ≤ H < 2.8 μm. In some embodiments, 10% ≤ X < 15%, 2.8 μm ≤ H < 3.5 μm. In some embodiments, 15% ≤ X ≤ 20%, 3.5 μm ≤ H < 4 μm. When the silicon content in the negative electrode active material layer coated on the negative electrode current collector side of the negative electrode sheet and the thickness of the polymer particle layer on the matching separator satisfy this rule, the lithium plating problem at the cycle corner is further improved.

[0054] In some embodiments, the separator adjacent to the first negative electrode active material layer has a polymer particle layer on its surface away from the first negative electrode active material layer.

[0055] In some embodiments, the separator adjacent to the first negative electrode active material layer has an adhesive layer on its surface facing the first negative electrode active material layer. Since the polymer particle layer has weak adhesion, while the adhesive layer has strong adhesion, in order to avoid separation between the electrode and the separator caused by the large expansion of the first negative electrode active material layer, it is preferable to place the side of the separator with the adhesive layer closer to the side of the first negative electrode active material layer to ensure good adhesion between the first negative electrode active layer and the separator.

[0056] In some embodiments, the first negative electrode active material layer includes a negative electrode active material, which includes a silicon-based active material selected from at least one of silicon, silicon oxides, silicon carbide compounds, or silicon alloys. In some embodiments, the silicon-based active material is preferably silicon carbide particles.

[0057] In some embodiments, the negative electrode active material includes a carbon active material selected from at least one of graphite or hard carbon. In some embodiments, the carbon active material is preferably graphite.

[0058] In some embodiments, the mass percentage of silicon, X, is preferably 2% ≤ X < 5%, based on the mass of the first negative electrode active material layer. When the silicon content meets this range, silicon expansion can be better controlled, thus improving the lithium plating problem.

[0059] In some embodiments, a second negative electrode active material layer is disposed on the other surface of the negative electrode current collector; the second negative electrode active material layer does not contain silicon. In this case, silicon is distributed in the active material layer on one side of the negative electrode current collector surface.

[0060] In some embodiments, when the second negative electrode active material layer does not contain silicon, there is no polymer particle layer on the surface of the separator adjacent to the second negative electrode active material layer.

[0061] In some embodiments, the second negative electrode active material layer does not contain silicon, and the separator adjacent to the second negative electrode active material layer includes a substrate, an inorganic coating applied to one side of the substrate, and an adhesive layer applied to the surface of the inorganic coating. In some embodiments, an adhesive layer is applied to the other side of the substrate of the separator.

[0062] In some embodiments, the adhesive layer may be selected from at least one material selected from homopolymers or copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, methacrylonitrile, and maleic acid. In some embodiments, the adhesive layer is preferably a polymer of acrylic acid, acrylate, styrene, isobutyl acrylate, or acrylonitrile.

[0063] In some embodiments, the thickness of the adhesive layer is preferably 0 to 1 μm. In some embodiments, a second negative electrode active material layer is disposed on the other surface of the negative electrode current collector; the second negative electrode active material layer contains silicon. Based on the mass of the second negative electrode active material layer, the mass percentage of silicon is also X. In this case, the silicon is uniformly distributed in the active material layers on both sides of the negative electrode current collector.

[0064] In some embodiments, the second negative electrode active material layer comprises silicon, and a polymer particle layer is disposed on one surface of the separator adjacent to the second negative electrode active material layer.

[0065] In some embodiments, the second negative electrode active material layer comprises silicon, and the separator adjacent to the second negative electrode active material layer has a polymer particle layer disposed on its surface away from the second negative electrode active material layer.

[0066] In some embodiments, the second negative electrode active material layer comprises silicon, and the separator adjacent to the second negative electrode active material layer does not have a polymer particle layer on its surface facing the second negative electrode active material layer.

[0067] In some embodiments, the polymer particle layer is selected from at least one homopolymer or copolymer of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, propylene chloride, acrylic acid, acrylate, styrene, butadiene, and acrylonitrile. In some embodiments, the polymer particle layer is preferably polyvinylidene fluoride.

[0068] In some embodiments, the separator adjacent to the first negative electrode active material layer includes a substrate and an inorganic coating, the inorganic coating being disposed between the substrate and the polymer particle layer. This application does not impose any particular limitation on the inorganic coating; for example, the inorganic coating may be selected from at least one material chosen from boehmite, magnesium hydroxide, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, or silicon nitride.

[0069] In some embodiments, an adhesive layer is coated on the other side surface of the substrate of the separator adjacent to the first negative electrode active material layer.

[0070] In some embodiments, the inorganic coating is preferably boehmite. In some embodiments, the thickness of the inorganic coating is preferably from 0.5 μm to 6 μm.

[0071] In some embodiments, the substrate is selected from at least one material selected from polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane.

[0072] In some embodiments, the substrate is preferably a porous polyethylene (PE) polymer film. In some embodiments, the thickness of the substrate is preferably 3 μm to 6 μm.

[0073] In some embodiments, the negative current collector may be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0074] In some embodiments, the first negative electrode active material layer further includes a conductive agent and a binder. The binder includes, but is not limited to, at least one of: polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, or styrene-butadiene rubber. In some embodiments, the conductive agent can be any conductive material, as long as it does not cause a chemical change. In some embodiments, the conductive agent includes at least one of: conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, carbon fiber, or graphene.

[0075] In some embodiments, the positive electrode includes a positive active material layer and a positive current collector.

[0076] In some embodiments, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive electrode active material includes at least one of a nickel-cobalt ternary material and a phosphate-based material. In some embodiments, the nickel-cobalt ternary material includes LiNi. x Co y M (1-x-y) At least one of the O2 materials, M including at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5≤x≤1, 0≤y≤0.5, x+y≤1. In some embodiments, the phosphate-based material includes LiMn. k B (1-k) At least one of PO4, 0 ≤ k ≤ 1, and element B includes at least one of iron, cobalt, magnesium, calcium, zinc, chromium, or lead. In some preferred embodiments, the positive electrode active material is selected from nickel-cobalt ternary materials. In some embodiments, the positive electrode active material may have a coating on its surface, or may be mixed with another compound having a coating. In some embodiments, the coating may include at least one coating element compound selected from oxides of the coating element, hydroxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compound used for the coating may be amorphous or crystalline. The coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating may be applied by any method, as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method may include any coating method well known to those skilled in the art, such as spraying, dipping, etc.

[0077] In some embodiments, the positive electrode active material layer further includes a conductive agent and a binder. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber, etc. In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, graphene, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0078] In some embodiments, the positive electrode sheet further includes a positive current collector, which can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0079] In some embodiments, the electrochemical device also includes an electrolyte comprising a lithium salt and a non-aqueous solvent.

[0080] In some embodiments, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, LiPF6 can be selected as the lithium salt.

[0081] In some embodiments, the non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

[0082] The aforementioned carbonate compounds may be chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof.

[0083] Examples of the aforementioned chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

[0084] Examples of the above-mentioned carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, and combinations thereof.

[0085] Examples of the above-mentioned ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0086] Examples of other organic solvents mentioned above include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

[0087] According to some embodiments of this application, the electrochemical device of this application includes, but is not limited to, all types of primary or secondary batteries. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0088] Secondly, the electronic device of this application can be any device that uses the electrochemical device of the first aspect of this application.

[0089] In some embodiments, the electronic device includes, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0090] Examples and Comparative Examples

[0091] The present application will be further described in detail below with examples and comparative examples, but the present application is not limited to these examples as long as it does not depart from its spirit.

[0092] Preparation of lithium-ion batteries

[0093] Example 1

[0094] (1) Preparation of negative electrode sheet

[0095] Using copper foil as the negative electrode current collector, 87.84 wt% artificial graphite, 9.76 wt% silicon carbide, 0.5 wt% carboxymethyl cellulose (CMC), 1.7 wt% polyacrylic acid (PAA), and 0.2% carbon nanotubes were thoroughly mixed in an appropriate amount of deionized water to form the first negative electrode slurry. The first negative electrode slurry was uniformly coated on one side of the copper foil (i.e., side A). 97.6 wt% artificial graphite, 1.3 wt% carboxymethyl cellulose (CMC), and 1.1 wt% styrene-butadiene rubber (SBR) were thoroughly mixed in an appropriate amount of deionized water to form the second negative electrode slurry. The second negative electrode slurry was uniformly coated on the other side of the copper foil (i.e., side B, the opposite side of side A). The mixture was then dried, cold-pressed, cut, and had tabs welded to obtain the negative electrode sheet. The active material layer on the A side of the negative electrode current collector is the first negative electrode active material layer, in which the mass percentage of silicon is 4.3%; the active material layer on the B side of the negative electrode current collector is the second negative electrode active material layer, in which the mass percentage of silicon is 0 (a silicon percentage of no more than 0.5% can be considered as not containing silicon).

[0096] (2) Preparation of positive electrode sheet

[0097] Aluminum foil is used as the positive electrode current collector. 97.8 wt% lithium cobalt oxide (LCO), 0.8 wt% polyvinylidene fluoride (PVDF) and 1.4 wt% conductive carbon black are thoroughly mixed in an appropriate amount of N-methylpyrrolidone solvent to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of the aluminum foil, and then dried, cold-pressed, cut and welded to obtain the positive electrode sheet.

[0098] (3) Preparation of electrolyte

[0099] In a dry argon atmosphere, LiPF6 was added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1, and mixed thoroughly to obtain an electrolyte with a concentration of 1.15 mol / L.

[0100] (4) Preparation of the diaphragm

[0101] The separator (first separator) matched with the first negative electrode active material layer includes a substrate, an inorganic coating applied to one side of the substrate, and a polymer particle layer applied to the surface of the inorganic coating. The substrate is a 4.5 μm thick porous polyethylene (PE) polymer film, the inorganic coating is a 2 μm thick boehmite, and the polymer particle layer is a 2 μm thick polyvinylidene fluoride (PVDF). An adhesive layer, made of acrylic acid or acrylate polymer, is coated on the other side of the substrate of the first separator. The separator (second separator) matched with the second negative electrode active material layer includes a substrate, an inorganic coating applied to one side of the substrate, and an adhesive layer applied to the surface of the inorganic coating. An adhesive layer, also made of acrylic acid or acrylate polymer, is coated on the other side of the substrate of the second separator. The substrate is a 4.5 μm thick porous polyethylene (PE) polymer film, the inorganic coating is a 2 μm thick boehmite, and the adhesive layer is made of acrylic acid or acrylate polymer.

[0102] (5) Preparation of lithium-ion batteries

[0103] The positive and negative electrode sheets are slit and then wound together. A separator separates the positive and negative electrode sheets. The first negative electrode active material layer is matched with a separator coated with a polymer particle layer on one side, with the polymer particle layer on the separator facing the positive electrode sheet. The second negative electrode active material layer is matched with a separator without a polymer particle layer. These are stacked sequentially, allowing the separator to act as a separator, and the resulting winding produces a bare cell. The bare cell undergoes hot pressing, top-side sealing, inkjet printing, vacuum drying, electrolyte injection, high-temperature settling, and pressure formation and capacity testing to obtain the finished lithium-ion battery.

[0104] Example 2-19

[0105] The method for preparing the lithium-ion battery provided in Examples 2-19 can be referred to Example 1, with the difference being:

[0106] Adjust the mass percentage of silicon in the active material layer (first negative electrode active material layer) on the A side of the negative electrode current collector and the thickness of the polymer particle layer of the matching separator (first separator). Adaptively adjust the mass percentage of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer. See Table 1 below for specific data.

[0107] Example 20

[0108] The method for preparing the lithium-ion battery provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0109] The silicon-based material in the active material layer (first negative electrode active material layer) on the A side of the negative electrode current collector is a silicon-oxygen material. By adjusting the mass percentage of silicon element and the thickness of the polymer particle layer of the matching separator (first separator), the mass percentage of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer are also adjusted. Please see Table 1 below for specific data.

[0110] Example 21

[0111] The method for preparing the lithium-ion battery provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0112] The silicon-based material in the active material layer (first negative electrode active material layer) on the A side of the negative electrode current collector is silicon. The mass percentage content of silicon element and the thickness of the polymer particle layer of the matching separator (first separator) are adjusted to adaptively adjust the mass percentage content of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer. Please see Table 1 below for specific data.

[0113] Comparative Examples 1-6

[0114] The preparation methods of the lithium-ion batteries provided in Comparative Examples 1-6 can be referred to in Examples 1-19, with the difference being:

[0115] Adjust the mass percentage of silicon in the active material layer (first negative electrode active material layer) on the A side of the negative electrode current collector and the thickness of the polymer particle layer of the matching separator (first separator). Adaptively adjust the mass percentage of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer. See Table 1 below for specific data.

[0116] Example 22

[0117] The method for preparing the lithium-ion battery provided in this embodiment can be referred to in Embodiment 1, with the difference being:

[0118] (1) Preparation of negative electrode sheet

[0119] Copper foil was used as the negative electrode current collector. 92.2 wt% artificial graphite, 5.6 wt% silicon carbide, 0.5 wt% carboxymethyl cellulose (CMC), 1.5 wt% polyacrylic acid (PAA), and 0.2% conductive carbon nanotubes were thoroughly mixed in an appropriate amount of deionized water to form a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of the copper foil (i.e., side A and side B), followed by drying and cold pressing. After cutting and welding the tabs, the negative electrode sheet was prepared. The active material layer on side A of the negative electrode current collector is the first negative electrode active material layer, in which the mass percentage of silicon is 2.5%. The active material layer on side B of the negative electrode current collector is the second negative electrode active material layer, in which the mass percentage of silicon is 2.5%.

[0120] (4) Preparation of the diaphragm

[0121] Both the first separator (matched to the first negative electrode active material layer) and the second separator (matched to the second negative electrode active material layer) comprise a substrate, an inorganic coating applied to one side of the substrate, and a polymer particle layer applied to the surface of the inorganic coating. The substrate is a 4.5 μm thick porous polyethylene (PE) polymer film, the inorganic coating is a 1.8 μm thick boehmite, and the polymer particle layer is a 1.8 μm thick polyvinylidene fluoride (PVDF).

[0122] (5) Preparation of lithium-ion batteries

[0123] The positive and negative electrode sheets are slit and then wound together, separated by a separator. The polymer particles on the separator are all positioned facing the positive electrode. These are stacked sequentially, allowing the separator to act as a separator, and wound to obtain a bare cell. The bare cell undergoes hot pressing, top-side sealing, inkjet printing, vacuum drying, electrolyte injection, and high-temperature settling, followed by pressure formation and capacity testing to obtain the finished lithium-ion battery.

[0124] Examples 23-33

[0125] The preparation method of the lithium-ion battery provided in Examples 23-33 can refer to Example 22, except that: the mass percentage of silicon in the active material layer (first negative electrode active material layer) of the negative electrode current collector A side is adjusted and the thickness of the polymer particle layer of the matching separator (first separator) is adjusted accordingly. The mass percentage data of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer and the inorganic coating thickness of the first separator and the second separator are also adjusted accordingly. For specific data, please see Table 2 below.

[0126] Comparative Examples 7-12

[0127] The preparation method of the lithium-ion battery provided in Comparative Examples 7-12 can be referred to in Example 22, the difference being:

[0128] Adjust the mass percentage of silicon in the active material layer (first negative electrode active material layer) on the A side of the negative electrode current collector and the thickness of the polymer particle layer of the matching separator (first separator). Adaptively adjust the mass percentage of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer and the thickness of the inorganic coating of the first separator and the second separator. See Table 2 below for specific data.

[0129] Test methods

[0130] 1. Silicon element test

[0131] In this invention, the silicon content refers to the percentage of silicon by mass in the silicon-containing negative electrode active material layer. The testing method involves taking a negative electrode from a finished battery cell, using SEM / EDS to identify the silicon-containing active material layer, and then performing an ICP test on the active material layer to obtain the percentage of silicon by mass.

[0132] 2. Test of membrane polymer particle layer thickness

[0133] In the planar region of the battery cell, the position of the separator matching the silicon-containing negative electrode active material layer and the positive electrode sheet was determined. A 6×6 mm sample was obtained by ion cutting, and a side view of the separator was obtained by SEM / EDS scanning, as shown in Figure 7. Combining SEM and EDS, the separator substrate PP / PE, inorganic coating, and polymer particle layer can be distinguished. The thickness of the polymer particle layer was measured, and 10 sets of data were taken from both the flat area and the protrusion area. The average thickness was calculated as the thickness of the polymer particle layer (the flat area here is roughly flat relative to the protrusion area).

[0134] 3. Corner lithium plating area percentage test after 1000 cycles at 25℃

[0135] CCD imaging technology is used to acquire images of the electrode surface. By processing and detecting the images, the lithium plating area at the corner can be identified, and the proportion of the lithium plating area at the corner to the total area can be calculated.

[0136] Test Results

[0137] Table 1

[0138] A comparison of the data from Examples 1-21 and Comparative Examples 1-6 in Table 1 shows that in the negative electrode sheet of this application, silicon is concentrated in the active material layer on the surface of the negative electrode current collector. This application uses a separator with polymer particle layers of different thicknesses coated on the surface of the negative electrode active material layer coated on the negative electrode current collector side to match the silicon content. When the matching relationship between the mass percentage of silicon X and the thickness H of the polymer particle layer meets the conditions defined in this application, the electrochemical device can reserve corner space to buffer electrode extrusion and breakage, overcome electrode breakage and cycle lithium plating problems caused by silicon-based expansion, and maximize energy density. A comparison of data from Examples 5-6, 7-8, 9-11, 12-13, and 14-15 shows that when the mass percentage of silicon (X) and the thickness (H) of the polymer particle layer further satisfy one of the conditions specified in this application: 2% ≤ X < 5% and 1.5 μm ≤ H < 2.5 μm, 5% ≤ X < 10% and 2.5 μm ≤ H < 2.8 μm, 10% ≤ X < 15% and 2.8 μm ≤ H < 3.5 μm, or 15% ≤ X ≤ 20% and 3.5 μm ≤ H < 4 μm, the problem of lithium plating during cycling in the electrochemical device is further optimized and improved. Data from Comparative Examples 1-6 shows that when the thickness (H) of the polymer particle layer is lower than the conditions specified in this application, the problems caused by silicon-based expansion cannot be effectively overcome, especially the electrode extrusion and breakage at the corners of the electrochemical device, accompanied by severe lithium plating during cycling. When the thickness (H) of the polymer particle layer is higher than the conditions specified in this application, the energy density of the electrochemical device is significantly reduced.

[0139] Table 2

[0140] A comparison of the data from Examples 22-33 and Comparative Examples 7-12 in Table 2 shows that in the negative electrode sheet of this application, silicon is uniformly distributed in the active material layer on both sides of the negative electrode current collector. This application uses polymer particle layers of different thicknesses to match the silicon content in the negative electrode active material layer coated on one side of the negative electrode current collector. When the matching relationship between the mass percentage X of silicon and the thickness H of the polymer particle layer meets the conditions defined in this application, the electrochemical device can reserve corner space to buffer electrode extrusion and breakage, overcoming electrode breakage and cycle lithium plating problems caused by silicon-based expansion, while maximizing energy density. A comparison of the data from Examples 22-23, 24-25, 26-27, 28-29, 30-31, and 32-33 shows that when the mass percentage of silicon X and the thickness H of the polymer particle layer further satisfy one of the conditions specified in this application—2% ≤ X < 5% and 1.5 μm ≤ H < 2.5 μm, 5% ≤ X < 10% and 2.5 μm ≤ H < 2.8 μm, 10% ≤ X < 15% and 2.8 μm ≤ H < 3.5 μm, or 15% ≤ X ≤ 20% and 3.5 μm ≤ H < 4 μm—the problem of cyclic lithium plating in the electrochemical device is further optimized and improved. The data shown in Comparative Examples 7-12 demonstrate that when the thickness H of the polymer particle layer is less than the conditions defined in this application, the problems caused by silicon-based expansion cannot be effectively overcome. In particular, the electrochemical device will experience electrode compression and breakage at the corners, accompanied by severe lithium plating problems during cycling. When the thickness H of the polymer particle layer is greater than the conditions defined in this application, the energy density of the electrochemical device will be severely reduced.

[0141] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device, comprising a positive electrode, a negative electrode, and a separator; wherein the negative electrode includes a negative current collector, and a first negative electrode active material layer containing silicon-based material is disposed on the surface of the negative current collector; The diaphragm is disposed between the negative electrode and the positive electrode; A polymer particle layer is disposed on the surface of the separator adjacent to the first negative electrode active material layer; Based on the mass of the first negative electrode active material layer, the mass percentage of silicon is X; the thickness of the polymer particle layer is H; and the electrochemical device satisfies one of the following conditions: 0<X<2%, 0<H<1μm; 2%≤X<10%, 1μm≤H<2.8μm; 10%≤X<25%, 2.8μm≤H<4μm; 25% ≤ X ≤ 30%, 4μm ≤ H ≤ 5μm.

2. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies one of the following conditions: 2% ≤ X < 5%, 1.5 μm ≤ H < 2.5 μm; 5% ≤ X < 10%, 2.5 μm ≤ H < 2.8 μm; 10% ≤ X < 15%, 2.8 μm ≤ H < 3.5 μm; 15% ≤ X ≤ 20%, 3.5 μm ≤ H < 4 μm.

3. The electrochemical device according to claim 1, wherein, The separator adjacent to the first negative electrode active material layer has a polymer particle layer disposed on its surface away from the first negative electrode active material layer.

4. The electrochemical device according to claim 1, wherein, The first negative electrode active material layer includes a negative electrode active material, which includes silicon-based active material and carbon active material; The silicon-based material is selected from at least one of silicon, silicon oxides, silicon carbide, or silicon alloys; and / or The carbon-active material is selected from at least one of graphite or hard carbon.

5. The electrochemical device according to claim 4, wherein, The silicon-based active material is silicon-carbon particles, and the carbon-based active material is graphite.

6. The electrochemical device according to claim 1, wherein, Based on the mass of the first negative electrode active material layer, the mass percentage of silicon element X satisfies 2% ≤ X ≤ 5%.

7. The electrochemical device according to any one of claims 1 to 5, wherein, A second negative electrode active material layer is provided on the other surface of the negative electrode current collector; The second negative electrode active material layer does not contain silicon. Alternatively, the second negative electrode active material layer contains silicon.

8. The electrochemical device according to claim 7, wherein, The second negative electrode active material layer does not contain silicon, and there is no polymer particle layer on the surface of the separator adjacent to the second negative electrode active material layer.

9. The electrochemical device according to claim 1, wherein, The polymer particle layer is selected from at least one homopolymer or copolymer of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, propylene chloride, acrylic acid, acrylate, styrene, butadiene, and acrylonitrile.

10. The electrochemical device according to claim 1, wherein, The separator adjacent to the first negative electrode active material layer includes a substrate and an inorganic coating, wherein the inorganic coating is disposed between the substrate and the polymer particle layer; the inorganic coating is selected from at least one material selected from boehmite, magnesium hydroxide, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, or silicon nitride. The substrate is selected from at least one material selected from polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane.

11. The electrochemical device according to claim 1, wherein, The separator adjacent to the first negative electrode active material layer has an adhesive layer on its surface facing the first negative electrode active material layer.

12. The electrochemical device according to claim 11, wherein, The adhesive layer is a polymer formed from at least one of acrylic acid, acrylate, styrene, isobutyl acrylate or acrylonitrile.

13. An electronic device comprising the electrochemical device according to any one of claims 1 to 12.

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