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] The present application relates to the field of energy storage technology, and in particular to electrochemical devices and electronic devices. Background Art

[0002] Since silicon has a reversible capacity of up to 4200mAh / g, silicon-based negative electrode materials are considered to be one of the effective strategies to improve the energy density of lithium-ion batteries. However, when lithium ions are inserted and removed during the charge and discharge process, silicon particles will undergo a volume expansion of more than 300%. The extremely high volume expansion will bring a series of problems. First, the extremely high volume expansion will damage the solid electrolyte interface (SEI) film, causing the electrolyte to penetrate into the interior of the negative electrode plate, triggering a series of unstable reactions, such as the decomposition of the electrolyte and the repeated formation of SEI, which will lead to the attenuation of the capacity of the lithium-ion battery and the instability of the performance; secondly, the volume expansion of silicon may also cause the problem of corner pole piece fracture. The corner pole piece must remain stable during the charge and discharge cycle of the lithium-ion battery, and the volume expansion of silicon may cause stress concentration in the corner pole piece, eventually leading to fracture, thereby reducing the life and reliability of the lithium-ion battery.

[0003] Summary of the Invention

[0004] In view of the above-mentioned problems existing in the prior art, the present application proposes an electrochemical device and an electronic device, which configures and designs the silicon content of the negative electrode plate and the polymer particle layer on the surface of the diaphragm, and reserves space in the corner area to buffer extrusion, aiming to solve the corner fracture and interface problems of the negative electrode plate caused by silicon-based expansion, while improving the energy density of lithium-ion batteries.

[0005] In a first aspect, the present application provides an electrochemical device comprising a positive electrode sheet, a negative electrode sheet and a separator; the negative electrode sheet comprises a negative electrode current collector, and a first negative electrode active material layer containing a silicon-based material is provided on the surface of the negative electrode current collector; the separator is provided between the negative electrode sheet and the positive electrode sheet; a polymer particle layer is provided 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 element is X; the thickness of the polymer particle layer is H. In some embodiments, 0<X<2%, and 0<H<1μm. In some embodiments, 2%≤X<10%, and 1μm≤H<2.8μm. In some embodiments, 10%≤X<25%, and 2.8μm≤H<4μm. In some embodiments, 25%≤X≤30%, and 4μm≤H≤5μm. The thickness of the polymer particle layer is the thickness of the straight area. The thickness of the polymer particle layer in the corner area is greater than the thickness of the polymer particles in the straight area. This is because during the battery preparation process, after winding, formation, and hot pressing, the polymer particle layer in the straight area is flattened due to the influence of hot pressing, while the thickness of the polymer layer in the corner area does not change much. When the polymer particle layer after hot pressing satisfies this relationship, it is necessary to ensure that the space reserved in the corner area is sufficient to withstand the stress generated by the expansion of the corner area. The diaphragm coated with polymer particle layers of different thicknesses according to the different silicon contents in the negative active material layer coated on the surface of one side of the negative current collector in the negative electrode plate can reserve corner space to buffer the extrusion and fracture of the plate, overcome the problems of plate fracture and cyclic lithium deposition 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 surface of the negative electrode current collector side of the negative electrode sheet and the thickness of the polymer particle layer on the matching separator meet 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 is provided with 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 is provided with 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, an acrylate, styrene, isobutyl acrylate, or acrylonitrile.

[0011] In some embodiments, the first negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based active material, and the silicon-based material is selected from at least one of silicon, a silicon oxide, a silicon carbon compound, or a silicon alloy. In some embodiments, the silicon-based active material is preferably silicon carbon particles.

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

[0013] In some embodiments, based on the mass of the first negative electrode active material layer, the mass percentage X of silicon preferably satisfies 2%≤X≤5%. When silicon satisfies this range, silicon expansion can be better controlled and lithium plating 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 surface of the negative electrode current collector.

[0015] In some embodiments, the second negative electrode active material layer does not contain silicon, and no polymer particle layer exists 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 layer coated on one surface of the substrate, and an adhesive layer coated on a surface of the inorganic coating layer. In some embodiments, the adhesive layer is coated on the other surface 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, an 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, silicon is evenly distributed in the active material layer on both sides of the negative electrode current collector.

[0020] In some embodiments, the second negative electrode active material layer includes 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 includes silicon, and the separator adjacent to the second negative electrode active material layer is provided with a polymer particle layer on a surface away from the second negative electrode active material layer.

[0022] In some embodiments, the second negative electrode active material layer includes 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 of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, allyl 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 active material layer includes a substrate and an inorganic coating layer disposed between the substrate and the polymer particle layer.

[0025] In some embodiments, an adhesive layer is coated on the other surface of the substrate of the separator adjacent to the first negative 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 0.5 μm to 6 μm.

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

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

[0030] In a second aspect, the present application provides an electronic device comprising the electrochemical device of the first aspect. Beneficial effects:

[0031] Based on the characteristic of easy expansion of silicon-based negative electrodes, this application proposes a matching design scheme for silicon-based negative electrode plates and diaphragms. By matching the diaphragms coated with polymer particle layers of different thicknesses according to the different silicon contents in the negative electrode active material layer coated on the surface of one side of the negative electrode current collector in the negative electrode plate, corner space can be reserved to buffer the plate extrusion and fracture, overcoming the problems of plate fracture and cyclic lithium deposition caused by silicon-based expansion, while maximizing energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following briefly describes the drawings necessary to describe the embodiments of the present application or the prior art to facilitate the description of the embodiments of the present application. Obviously, the drawings described below only represent some of the embodiments of the present application. Those skilled in the art can still derive drawings for other embodiments based on the structures illustrated in these drawings.

[0033] FIG1 is a schematic diagram of the design of the negative electrode plate of Example 1 of the present application.

[0034] FIG2 is a schematic diagram of the design of the separator matched with the first negative electrode active material layer of Example 1 of the present application.

[0035] FIG3 is a schematic diagram of the design of the battery of Example 1 of the present application.

[0036] FIG4 is a schematic diagram of the winding effect of the battery before compression according to Example 1 of the present application.

[0037] FIG5 is a schematic diagram of the winding effect of the battery after compression in Example 1 of the present application.

[0038] FIG6 is a surface image of the separator matched with the first negative electrode active material layer of Example 1 of the present application before compression.

[0039] FIG7 is a side view of the separator matched with the first negative electrode active material layer of Example 1 of the present application after compression.

[0040] Figure 8 is a schematic diagram of the design of the negative electrode plate of Example 22 of the present application.

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

[0042] Figure 10 is a schematic diagram of the winding effect of the battery before compression in Example 22 of the present 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 plate, 8-first negative electrode active material layer, 9-second negative electrode active material layer, 10-negative electrode plate, 11-diaphragm. DETAILED DESCRIPTION

[0044] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of this application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of this application. The embodiments of this application should not be interpreted as limiting this application.

[0045] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0046] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0047] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples 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, 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, 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 linked by the terms "one of," "one of," "one of," or other similar terms may mean any one of the listed items. For example, if items A and B are listed, the phrase "one of A and B" means only A; or only B. In another example, if items A, B, and C are listed, 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 only used to distinguish the description and cannot be understood as indicating or implying relative importance.

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

[0052] The present application is a diaphragm coated with polymer particle layers of different thicknesses according 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 plate. It can reserve corner space to buffer the extrusion and fracture of the plate, overcome the problems of plate fracture and lithium deposition in the cycle corner caused by silicon-based expansion, and maximize 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 surface of the negative electrode current collector side of the negative electrode sheet and the thickness of the polymer particle layer on the matching separator meet this rule, the problem of lithium plating in the cycle corner is further improved.

[0054] In some embodiments, the separator adjacent to the first negative electrode active material layer is provided with 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 is provided with an adhesive layer on its surface facing the first negative electrode active material layer. Because the polymer particle layer has weaker adhesion and the adhesive layer has stronger adhesion, to prevent separation between the electrode sheet and the separator caused by significant expansion of the first negative electrode active material layer, the side of the separator with the adhesive layer is preferably positioned closer to the side facing 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, the negative electrode active material includes a silicon-based active material, and the silicon-based material is selected from at least one of silicon, a silicon oxide, a silicon carbon compound, or a silicon alloy. In some embodiments, the silicon-based active material is preferably silicon carbon particles.

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

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

[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 surface of the negative electrode current collector.

[0060] In some embodiments, when the second negative electrode active material layer does not include silicon, no polymer particle layer exists 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 layer coated on one surface of the substrate, and an adhesive layer coated on a surface of the inorganic coating layer. In some embodiments, the adhesive layer is coated on the other surface 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, an 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 provided 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, silicon is evenly distributed in the active material layer on both sides of the negative electrode current collector.

[0064] In some embodiments, the second negative electrode active material layer includes 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 includes silicon, and a polymer particle layer is provided on a surface of the separator adjacent to the second negative electrode active material layer away from the second negative electrode active material layer.

[0066] In some embodiments, the second negative electrode active material layer includes 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 of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, allyl 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, wherein the inorganic coating is disposed between the substrate and the polymer particle layer. The inorganic coating is not particularly limited herein. For example, the inorganic coating may be selected from at least one of 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.

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

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

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

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

[0073] In some embodiments, the negative electrode 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, polyvinyl pyrrolidone, polyvinyl ether, or styrene-butadiene rubber. In some embodiments, the conductive agent can be any conductive material as long as it does not cause chemical changes. 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 sheet 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 includes 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, B element includes at least one of iron, cobalt, magnesium, calcium, zinc, chromium or lead. In some preferred embodiments, the positive active material is selected from nickel-cobalt ternary materials. In some embodiments, the positive active material may have a coating on the 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 an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating may be amorphous or crystalline. The coating elements contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating may be applied by any method as long as the method does not adversely affect the performance of the positive active material. For example, the method may include any coating method well known to those of ordinary skill in the art, such as spraying, dipping, and the like.

[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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber or acrylic (ester) 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 fiber, 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 electrode 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 metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0079] In some embodiments, the electrochemical device further 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, the lithium salt can be LiPF6.

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

[0082] The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof.

[0083] Examples of the above-mentioned linear carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), and combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2-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 carboxylic acid ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.

[0085] Examples of the above-mentioned ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

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

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

[0088] In a second aspect, the electronic device of the present application may be any device using the electrochemical device of the first aspect of the present application.

[0089] In some embodiments, the electronic device includes, but is not limited to: a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0090] Examples and Comparative Examples

[0091] Hereinafter, the present application will be described in more detail with reference to Examples and Comparative Examples. However, the present application is not limited to these Examples unless departing from the gist of the present application.

[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, 87.84wt% artificial graphite, 9.76wt% silicon carbon, 0.5wt% carboxymethyl cellulose (CMC), 1.7wt% polyacrylic acid (PAA), and 0.2% carbon nanotubes were thoroughly stirred in an appropriate amount of deionized water to form a first negative electrode slurry. The first negative electrode slurry was evenly coated on one surface of the copper foil (i.e., side A). 97.6wt% artificial graphite, 1.3wt% carboxymethyl cellulose (CMC), and 1.1wt% styrene-butadiene rubber (SBR) were thoroughly stirred in an appropriate amount of deionized water to form a second negative electrode slurry. The second negative electrode slurry was evenly coated on the other surface of the copper foil (i.e., side B, opposite side A). The mixture was then dried, cold pressed, cut into pieces, and welded to the tabs to produce a negative electrode sheet. The active material layer on the surface of the negative electrode collector A is the first negative electrode active material layer, in which the mass percentage of silicon element is 4.3%; the active material layer on the surface of the negative electrode collector B is the second negative electrode active material layer, in which the mass percentage of silicon element is 0 (the silicon element percentage is not greater than 0.5% and it can be considered that there is no silicon element).

[0096] (2) Preparation of positive electrode sheet

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

[0098] (3) Preparation of electrolyte

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

[0100] (4) Preparation of diaphragm

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

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

[0103] The positive and negative electrode sheets are stripped and then wound. The positive and negative electrode sheets are separated by a separator. The first negative electrode active material layer matches the 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 matches the separator without a polymer particle layer. Stacking them in order, allowing the separator to act as an insulator, and winding to obtain a bare cell. The bare cell undergoes hot pressing, top and side sealing, inkjet printing, vacuum drying, electrolyte injection, and high-temperature stabilization before pressure formation and capacity measurement to obtain a finished lithium-ion battery.

[0104] Example 2-19

[0105] The preparation methods of the lithium-ion batteries provided in Examples 2-19 can refer to Example 1, except that:

[0106] Adjust the mass percentage of silicon element in the surface active material layer of the negative electrode current collector A (first negative electrode active material layer) and the thickness of the polymer particle layer of the matching diaphragm (first diaphragm), and adaptively adjust the mass percentage data of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer. For specific data, please see Table 1 below.

[0107] Example 20

[0108] The preparation method of the lithium ion battery provided in this embodiment can refer to Example 1, except that:

[0109] The silicon-based material in the active material layer (first negative electrode active material layer) of the negative electrode current collector A is a silicon oxide material. The mass percentage of the silicon element and the thickness of the polymer particle layer of the matching diaphragm (first diaphragm) are adjusted, and the mass percentage data of the artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer are adaptively adjusted. For specific data, please see Table 1 below.

[0110] Example 21

[0111] The preparation method of the lithium ion battery provided in this embodiment can refer to Example 1, except that:

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

[0113] Comparative Examples 1-6

[0114] The preparation method of the lithium ion battery provided in Comparative Examples 1-6 can refer to Examples 1-19, except that:

[0115] Adjust the mass percentage of silicon element in the surface active material layer of the negative electrode current collector A (first negative electrode active material layer) and the thickness of the polymer particle layer of the matching diaphragm (first diaphragm), and adaptively adjust the mass percentage data of artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in the first negative electrode active material layer. For specific data, please see Table 1 below.

[0116] Example 22

[0117] The preparation method of the lithium ion battery provided in this embodiment can refer to Example 1, except that:

[0118] (1) Preparation of negative electrode sheet

[0119] Copper foil is used as the negative electrode current collector, and 92.2wt% artificial graphite, 5.6wt% silicon carbon, 0.5wt% carboxymethyl cellulose (CMC), 1.5wt% polyacrylic acid (PAA) and 0.2% conductive carbon nanotubes are fully mixed in an appropriate amount of deionized water to form a negative electrode slurry. The negative electrode slurry is evenly coated on both sides of the copper foil (i.e., side A and side B), and then dried and cold pressed. After cutting and welding the pole ears, a negative electrode sheet is prepared. The active material layer on the negative electrode current collector A side is the first negative electrode active material layer, in which the mass percentage of silicon element is 2.5%, and the active material layer on the negative electrode current collector B side is the second negative electrode active material layer, in which the mass percentage of silicon element is 2.5%.

[0120] (4) Preparation of diaphragm

[0121] The separator (first separator) used with the first negative electrode active material layer and the separator (second separator) used with the second negative electrode active material layer each comprise a substrate, an inorganic coating applied to one surface of the substrate, and a polymer particle layer applied to the surface of the inorganic coating. The substrate is a 4.5 μm thick polyethylene (PE) porous 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.

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

[0123] The positive and negative electrode sheets are slit and then wound. A separator separates the positive and negative electrodes, with the polymer particles on the separator facing the positive electrode. The cells are stacked sequentially, allowing the separator to act as an insulator, and wound to form a bare cell. The bare cell undergoes hot pressing, top and side sealing, inkjet printing, vacuum drying, electrolyte injection, and high-temperature stabilization before pressure formation and capacity measurement to create a 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, with the following differences: adjusting the mass percentage of the silicon element in the active material layer (first negative electrode active material layer) of the negative electrode current collector A and the thickness of the polymer particle layer of the matching diaphragm (first diaphragm), adaptively adjusting 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 thickness of the inorganic coating of the first diaphragm and the second diaphragm. For specific data, please see Table 2 below.

[0126] Comparative Examples 7-12

[0127] The preparation methods of the lithium-ion batteries provided in Comparative Examples 7-12 can refer to Example 22, except that:

[0128] Adjust the mass percentage of silicon element in the active material layer (first negative electrode active material layer) of the negative electrode collector A and the thickness of the polymer particle layer of the matching diaphragm (first diaphragm), and adaptively adjust 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 thickness of the inorganic coating of the first diaphragm and the second diaphragm. For specific data, please see Table 2 below.

[0129] Test Method

[0130] 1. Silicon element test

[0131] As used herein, silicon content refers to the mass percentage of silicon based on the mass of the silicon-containing negative electrode active material layer. The testing method involves taking a negative electrode sheet from a finished battery cell, identifying the silicon-containing active material layer using SEM / EDS, and then performing an ICP test on the material from this active material layer to determine the silicon mass percentage.

[0132] 2. Diaphragm polymer particle layer thickness test

[0133] In the flat area of ​​the cell, the position of the separator between the silicon-containing negative electrode active material layer and the positive electrode plate was determined. Ion sectioning was performed to obtain a 6×6 mm sample, and then SEM / EDS scanning was used to obtain a side view of the separator, as shown in Figure 7. Combining SEM and EDS, the separator substrate PP / PE, the inorganic coating, and the polymer particle layer can be distinguished. The thickness of the polymer particle layer was measured, and 10 sets of data were collected in the flat area and 10 sets of data in the protrusions. The average thickness was calculated as the thickness of the polymer particle layer (the flat area here is roughly flat relative to the protrusions).

[0134] 3. Test of the ratio of corner lithium deposition area after 1000 cycles at 25°C

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

[0136] Test results

[0137] Table 1

[0138] Comparing the data of Examples 1-21 and Comparative Examples 1-6 in Table 1, it can be seen that in the negative electrode plates of the present application, silicon is concentrated in the active material layer on the surface of one side of the negative electrode current collector. The present application provides separators coated with polymer particle layers of varying thicknesses, based on the silicon content in the negative electrode active material layer coated on the surface of the negative electrode current collector in the negative electrode plates. 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 the present application, the electrochemical device can reserve corner space to buffer against plate extrusion and fracture, overcoming the problems of plate fracture and cyclic lithium deposition caused by silicon-based expansion, while maximizing energy density. By comparing the data of Examples 5-6, 7-8, 9-11, 12-13, and 14-15, it can be seen that when the mass percentage X of the silicon element and the thickness H of the polymer particle layer further meet the conditions of 2%≤X<5% and 1.5μm≤H<2.5μm, 5%≤X<10% and 2.5μm≤H<2.8μm, 10%≤X<15% and 2.8μm≤H<3.5μm, 15%≤X≤20% and 3.5μm≤H<4μm as defined in this application, the problem of cyclic lithium deposition in the electrochemical device is further optimized and improved. It can be seen from the data shown in Examples 1-6 that when the thickness H of the polymer particle layer is lower than the conditions defined in this application, the problems caused by silicon-based expansion cannot be effectively overcome, especially the electrode extrusion and fracture of the electrochemical device will occur at the corners, accompanied by serious cyclic lithium deposition problems; when the thickness H of the polymer particle layer is higher than the conditions defined in this application, the energy density of the electrochemical device will be seriously reduced.

[0139] Table 2

[0140] Comparing the data of Examples 22-33 and Comparative Examples 7-12 in Table 2, it can be seen that in the negative electrode plates of the present application, silicon is evenly distributed in the active material layer on both sides of the negative electrode current collector. The present application provides a separator coated with polymer particle layers of varying thicknesses, based on the silicon content in the negative electrode active material layer coated on one side of the negative electrode current collector in the negative electrode plates. 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 the present application, the electrochemical device can reserve corner space to buffer the extrusion and fracture of the plate, overcoming the problems of plate fracture and cyclic lithium deposition caused by silicon-based expansion, while maximizing energy density. By comparing the data of Examples 22-23, 24-25, 26-27, 28-29, 30-31, and 32-33, it can be seen that when the mass percentage X of the silicon element and the thickness H of the polymer particle layer further meet one of the conditions defined in this application of 2%≤X<5% and 1.5μm≤H<2.5μm, 5%≤X<10% and 2.5μm≤H<2.8μm, 10%≤X<15% and 2.8μm≤H<3.5μm, 15%≤X≤20% and 3.5μm≤H<4μm, the problem of cyclic lithium deposition in the electrochemical device is further optimized and improved. It can be seen from the data shown in Comparative Examples 7-12 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 will occur, accompanied by serious cyclic lithium deposition problems; 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 will be seriously reduced.

[0141] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may 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 plate, a negative electrode plate, and a separator; the negative electrode plate includes a negative current collector, and a first negative active material layer containing a silicon-based material is provided on the surface of the negative current collector; The separator is disposed between the negative electrode plate and the positive electrode plate; A polymer particle layer is provided on the surface of the separator adjacent to the first negative active material layer; Based on the mass of the first negative active material layer, the mass percentage content of silicon element 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 < 1 μm; 2% ≤ X < 10%, 1 μm ≤ H < 2.8 μm; 10% ≤ X < 25%, 2.8 μm ≤ H < 4 μm; 25% ≤ X ≤ 30%, 4 μm ≤ H ≤ 5 μm.

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, A polymer particle layer is provided on the surface of the separator adjacent to the first negative active material layer, on the side away from the first negative active material layer.

4. The electrochemical device according to claim 1, wherein, The first negative active material layer includes a negative active material, and the negative active material includes a silicon-based active material and a carbon active material; The silicon-based material is selected from at least one of silicon, silicon oxide compounds, silicon carbide compounds, 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 carbide particles, and the carbon active material is graphite.

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

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

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

9. The electrochemical device according to claim 1, wherein, The polymer particle layer is selected from at least one of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropylene, acrylic acid, acrylate, styrene, butadiene, 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, and the inorganic coating is disposed between the substrate and the polymer particle layer; the inorganic coating is selected from at least one material of 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; The substrate is selected from at least one material of a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a 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 is provided with 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, which includes the electrochemical device according to any one of claims 1 to 12.

Images