Electrochemical devices and electronic devices

Abstract

The application provides an electrochemical device and an electronic device, the 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 arranged on the surface of the negative electrode current collector; the separator is arranged between the negative electrode sheet and the positive electrode sheet; and a polymer particle layer is arranged on the surface of the separator adjacent to the first negative electrode active material layer. According to the application, the thickness of the polymer particle layer is matched with the content of silicon in the negative electrode active material layer coated on the surface of the negative electrode current collector of the negative electrode sheet, so that a corner space is reserved to buffer the extrusion and fracture of the electrode sheet, the problems of electrode sheet fracture and lithium precipitation in the cycle caused by the expansion of the silicon-based material are overcome, and the energy density is maximized.

Description

TECHNICAL FIELD

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

[0002] Due to the high reversible capacity of silicon of up to 4200 mAh / 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, during the embedding and de-embedding of lithium ions in the charging and discharging process, the silicon particles will undergo more than 300% volume expansion, which will cause a series of problems. First, the ultra-high volume expansion will cause damage to the solid electrolyte interface (SEI) film, causing the electrolyte to penetrate into the negative electrode sheet, triggering a series of unstable reactions, such as decomposition of the electrolyte and repeated formation of the SEI, which in turn leads to capacity attenuation and performance instability of the lithium ion battery; second, the volume expansion of silicon can also cause the problem of corner sheet fracture. The corner sheet must remain stable during the charging and discharging cycle of the lithium ion battery, while the volume expansion of silicon can cause stress concentration in the corner sheet, eventually leading to fracture, thereby reducing the service life and reliability of the lithium ion battery. SUMMARY

[0003] In view of the above problems existing in the prior art, the present application provides an electrochemical device and an electronic device, which are configured and designed by configuring the silicon content of the negative electrode sheet and the polymer particle layer on the surface of the separator, and reserving space in the corner area to buffer the extrusion, aiming to solve the problems of negative electrode sheet corner fracture and interface caused by silicon-based expansion, and at the same time improve the energy density of the lithium ion battery.

[0004] 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 arranged on the surface of the negative electrode current collector; the separator is arranged between the negative electrode sheet and the positive electrode sheet; a polymer particle layer is arranged on the surface of the separator adjacent to the first negative electrode active material layer.

[0005] 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, in some embodiments, 0 < X < 2%, 0 < H < 1 µm. In some embodiments, 2%≤X<10%, 1 µm≤H<2.8µm. In some embodiments, 10%≤X<25%, 2.8µm≤H<4µm. In some embodiments, 25%≤X≤30%, 4µm≤H≤5µm. The thickness of the polymer particle layer is the thickness of the flat area, the thickness of the polymer particle layer in the corner area is greater than that in the flat area, because during the battery preparation process, after winding, formation and hot pressing, the polymer particle layer in the flat area is flattened due to the influence of hot pressing, and the thickness of the polymer layer in the corner area changes little, when the polymer particle layer after hot pressing meets this relationship, it can be ensured that the space reserved in the corner area is sufficient to withstand the stress generated by the expansion of the corner area. According to the matching of the different thicknesses of the polymer particle layer on the separator coated with the negative electrode active material layer on the surface of the negative electrode current collector side of the negative electrode sheet, the corner space is reserved to buffer the extrusion and fracture of the sheet, and the problems of sheet fracture and cycle lithium precipitation caused by silicon-based expansion are overcome, while the energy density is maximized.

[0006] In some embodiments, 2%≤X<5%, 1.5µm≤H<2.5µm. In some embodiments, 5%≤X<10%, 2.5µm≤H<2.8µm. In some embodiments, 10%≤X<15%, 2.8µm≤H<3.5µm. In some embodiments, 15%≤X≤20%, 3.5µm≤H<4µm. 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 separator matched therewith meet this rule, the problem of cycle lithium precipitation is further optimized and improved.

[0007] In some embodiments, the separator adjacent to the first negative electrode active material layer is provided with a polymer particle layer on the surface thereof away from the first negative electrode active material layer.

[0008] In some embodiments, the separator adjacent to the first negative electrode active material layer is provided with an adhesive layer on the surface thereof facing the first negative electrode active material layer, and the thickness of the adhesive layer is preferably 0 to 1 µm.

[0009] In some embodiments, the adhesive layer can be selected from at least one material of a homopolymer or copolymer 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.

[0010] In some embodiments, the first negative active material layer comprises a negative active material, the negative active material comprises a silicon-based active material, and the silicon-based material is selected from at least one of silicon, silicon oxide, silicon carbide, or silicon alloy. In some embodiments, the silicon-based active material is preferably silicon-carbon particles.

[0011] In some embodiments, the negative active material comprises a carbon active material, and the carbon active material is selected from at least one of graphite or hard carbon. In some embodiments, the carbon active material is preferably graphite.

[0012] In some embodiments, the mass percentage content X of silicon element is preferably 2%≤X≤5% based on the mass of the first negative active material layer. When the silicon element satisfies this range, the expansion of silicon can be better controlled, and the problem of lithium precipitation can be improved.

[0013] In some embodiments, the other surface of the negative current collector is provided with a second negative active material layer; and the second negative active material layer does not contain silicon element. At this time, the silicon element is distributed in the active material layer on one side surface of the negative current collector.

[0014] In some embodiments, 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.

[0015] In some embodiments, the second negative active material layer does not contain silicon element, and the separator adjacent to the second negative active material layer comprises a substrate, an inorganic coating layer coated on one side surface of the substrate, and a bonding layer coated on the surface of the inorganic coating layer. In some embodiments, the other side surface of the substrate of the separator is coated with a bonding layer.

[0016] In some embodiments, the bonding layer can be selected from at least one material of 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 bonding layer is preferably a polymer of acrylic acid, acrylate, styrene, isobutyl acrylate, or acrylonitrile.

[0017] In some embodiments, the thickness of the bonding layer is preferably 0 to 1 µm.

[0018] In some embodiments, the other surface of the negative current collector is provided with a second negative active material layer; and the second negative active material layer contains silicon element. The mass percentage content of silicon element is also X based on the mass of the second negative active material layer. At this time, the silicon element is uniformly distributed in the active material layers on both side surfaces of the negative current collector.

[0019] In some embodiments, the second negative electrode active material layer contains silicon element, and the separator adjacent to the second negative electrode active material layer is provided with a polymer particle layer on one surface thereof.

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

[0021] In some embodiments, the second negative electrode active material layer contains silicon element, and the separator adjacent to the second negative electrode active material layer is provided with a polymer particle layer on one surface thereof.

[0022] 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, chloropropylene, acrylic acid, acrylate, styrene, butadiene, acrylonitrile. In some embodiments, the polymer particle layer is preferably polyvinylidene fluoride.

[0023] In some embodiments, the separator adjacent to the first negative electrode active material layer comprises a substrate and an inorganic coating layer, and the inorganic coating layer is disposed between the substrate and the polymer particle layer.

[0024] In some embodiments, the other side surface of the substrate of the separator adjacent to the first negative electrode active material layer is coated with an adhesive layer.

[0025] In some embodiments, the inorganic coating layer 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.

[0026] In some embodiments, the inorganic coating layer is preferably boehmite. In some embodiments, the thickness of the inorganic coating layer is preferably 0.5 µm to 6 µm.

[0027] In some embodiments, the substrate is selected from at least one material of polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film.

[0028] 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.

[0029] In a second aspect, the present application provides an electronic device comprising the electrochemical device of the first aspect.

[0030] Advantages:

[0031] Based on the characteristics of easy expansion of silicon-based negative electrode, a matching design scheme of silicon-based negative electrode sheet and separator is proposed. By matching the separator coated with different thickness of polymer particle layer according to the different silicon content in the negative active material layer coated on the surface of the negative electrode current collector side of the negative electrode sheet, the corner space can be reserved to buffer the extrusion and fracture of the sheet, overcome the sheet fracture and cycle lithium precipitation problem caused by silicon-based expansion, and maximize the energy density. BRIEF DESCRIPTION OF DRAWINGS

[0032] In the following, the drawings necessary for describing the embodiments of the present application or the prior art will be briefly described in order to facilitate the description of the embodiments of the present application. Obviously, the drawings in the following description are only part of the embodiments in the present application. Other embodiments of the drawings can still be obtained by those skilled in the art according to the structures illustrated in the drawings.

[0033] Figure 1 Design schematic diagram of the negative electrode sheet of embodiment 1 of the present application.

[0034] Figure 2 Design schematic diagram of the separator matched with the first negative active material layer of embodiment 1 of the present application.

[0035] Figure 3 Design schematic diagram of the battery of embodiment 1 of the present application.

[0036] Figure 4 Winding effect schematic diagram of the battery of embodiment 1 of the present application before compression.

[0037] Figure 5 Winding effect schematic diagram of the battery of embodiment 1 of the present application after compression.

[0038] Figure 6 Surface picture of the separator matched with the first negative active material layer of embodiment 1 of the present application before compression.

[0039] Figure 7 Side picture of the separator matched with the first negative active material layer of embodiment 1 of the present application after compression.

[0040] Figure 8 Design schematic diagram of the negative electrode sheet of embodiment 22 of the present application.

[0041] Figure 9 Design schematic diagram of the battery of embodiment 22 of the present application.

[0042] Figure 10 Winding effect schematic diagram of the battery of embodiment 22 of the present application before compression.

[0043] FIG. 1 - silicon-carbon particles, 2 - graphite, 3 - negative current collector, 4 - substrate, 5 - polymer particles, 6 - inorganic coating, 7 - positive electrode sheet, 8 - first negative active material layer, 9 - second negative active material layer, 10 - negative electrode sheet, 11 - separator. DETAILED DESCRIPTION

[0044] For the purpose of clarity, technical solutions and advantages of the present application will be described below in detail with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as a limitation of the present application.

[0045] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, as can any upper limit with any other upper limit to form a range not explicitly recited. Further, each individual disclosed point or singular number can be combined as a lower limit or an upper limit with any other point or singular number or with other lower limits or upper limits to form a range not explicitly recited.

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

[0047] Unless otherwise defined, the terms used in the present application have the meanings commonly understood by those skilled in the art. Unless otherwise stated, the values of each parameter mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the method given in the examples of the present application).

[0048] In the detailed description and in the claims, a list of items joined by the term "at least one of" or "one or more of" can mean any combination of the items in the list. For example, if the items in a list are A and B, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if the items in a list are A, B, and C, the phrase "at least one of A, B, and C" means A alone; B alone; C alone; A and B (not C); A and C (not B); B and C (not A); or A, B, and C.

[0049] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "one of" or "one of each" or other similar term means any one of the listed items. For example, if a list of items A and B is provided, the phrase "one of A and B" means only A; or, only B. In another example, if a list of items A, B, and C is provided, the phrase "one of A, B, and C" means only A; or, only B; or, only C.

[0050] In the description of the present document, it should also be noted that the terms "first", "second" and the like are used only to distinguish descriptions, 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 electrode current collector, and a first negative electrode active material layer containing a silicon-based material is arranged on the surface of the negative electrode current collector; the separator is arranged between the negative electrode sheet and the positive electrode sheet; a polymer particle layer is arranged on the surface of the separator adjacent to the first negative electrode active material layer. The mass percentage of silicon element in the first negative electrode active material layer 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%, 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] The present application matches the separator coated with the polymer particle layer of different thickness according to the different silicon content in the negative electrode active material layer coated on the surface of the negative electrode current collector in the negative electrode sheet, which can reserve the corner space to buffer the extrusion and fracture of the electrode sheet, overcome the fracture of the electrode sheet and the problem of lithium precipitation at the corner in the cycle caused by the expansion of the silicon-based material, 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 one side of the surface of the negative electrode current collector in the negative electrode sheet and the thickness of the polymer particle layer on the separator matched therewith satisfy the rule, the problem of lithium precipitation at the corner in the cycle 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 the surface thereof away from the first negative electrode active material layer.

[0055] In some embodiments, the separator adjacent to the first negative active material layer is provided with an adhesive layer on the surface thereof facing the first negative active material layer. Since the polymer particle layer is weakly adhesive, the adhesive layer has stronger adhesive capacity, and in order to avoid separation between the electrode sheet and the separator caused by large expansion of the first negative active material layer, the side of the separator with the adhesive layer is preferably close to the first negative active material layer to ensure good adhesion between the first negative active material layer and the separator.

[0056] In some embodiments, the first negative active material layer comprises a negative active material, and the negative active material comprises a silicon-based active material selected from at least one of silicon, a silicon oxide compound, 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 active material comprises 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 content X of silicon element is preferably 2%≤X<5% based on the mass of the first negative active material layer. When the silicon element satisfies this range, the expansion of silicon can be better controlled, and the problem of lithium precipitation can be improved.

[0059] In some embodiments, the other surface of the negative current collector is provided with a second negative active material layer; and the second negative active material layer does not contain silicon element. At this time, the silicon element is distributed in the active material layer on the surface of the side of the negative current collector.

[0060] In some embodiments, when the second negative active material layer does not contain silicon element, the surface of the separator adjacent to the second negative active material layer is free of the polymer particle layer.

[0061] In some embodiments, when the second negative active material layer does not contain silicon element, the separator adjacent to the second negative active material layer comprises a substrate, an inorganic coating layer coated on one side surface of the substrate, and an adhesive layer coated on the surface of the inorganic coating layer. In some embodiments, the other side surface of the substrate of the separator is coated with an adhesive layer.

[0062] In some embodiments, the adhesive layer can be selected from at least one material of a homopolymer or copolymer of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, methacrylonitrile, or 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, the other surface of the negative electrode current collector is provided with a second negative electrode active material layer; the second negative electrode active material layer contains silicon element. The mass percentage content of silicon element is also X based on the mass of the second negative electrode active material layer. At this time, the silicon element is uniformly distributed in the active material layers on both side surfaces of the negative electrode current collector.

[0064] In some embodiments, the second negative electrode active material layer contains silicon element, and the one surface of the separator adjacent to the second negative electrode active material layer is provided with a polymer particle layer.

[0065] In some embodiments, the second negative electrode active material layer contains silicon element, and the one surface of the separator adjacent to the second negative electrode active material layer is provided with a polymer particle layer.

[0066] In some embodiments, the second negative electrode active material layer contains silicon element, and the one surface of the separator adjacent to the second negative electrode active material layer is provided with a polymer particle 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, chloropropylene, acrylic acid, acrylate, styrene, butadiene, 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 comprises a substrate and an inorganic coating layer, and the inorganic coating layer is disposed between the substrate and the polymer particle layer. The present application does not have a particular limitation on the inorganic coating layer, for example, the inorganic coating layer can be 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.

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

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

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

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

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

[0074] In some embodiments, the first negative 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, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, or styrene butadiene rubber. In some embodiments, the conductive agent can use 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 nanotube, ketjen black, carbon fiber, or graphene.

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

[0076] In some embodiments, the positive active material layer includes a positive active material. In some embodiments, the positive active material includes at least one of a nickel-cobalt-based ternary material and a phosphate-based material. In some embodiments, the nickel-cobalt-based ternary material includes LiNi x Co y M (1-x-y) O2 material, 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 P04, 0 < k < 1, and 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-based ternary materials. In some embodiments, the positive active material can have a coating on the surface, or can be mixed with another compound having a coating. In some embodiments, the coating can include at least one coating element compound selected from oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compound used for the coating can be amorphous or crystalline. The coating element contained in the coating can include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating can 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 can include any coating method well known to one of ordinary skill in the art, such as spraying, dipping, etc.

[0077] In some embodiments, the positive 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 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, an 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, and silver alloy, etc.) on a polymer substrate.

[0079] In some embodiments, the electrochemical device further includes an electrolyte, which includes 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 can be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

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

[0083] Examples of the chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and a combination thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and a combination thereof. Examples of the fluorinated carbonate compound 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-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, and a combination thereof.

[0084] Examples of the carboxylic acid ester compound are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, methylvaleronolactone, caprolactone, and a combination thereof.

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

[0086] Examples of the other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphates, and a combination thereof.

[0087] According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to, all kinds 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, 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 can 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 notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, an electric power tool, a flashlight, a camera, a household large storage battery, or a lithium ion capacitor, etc.

[0090] Examples and Comparative Examples

[0091] Hereinafter, the present application is further specifically explained by citing examples and comparative examples, but the present application is not limited to these examples as long as the gist of the present application is not deviated.

[0092] Preparation of lithium ion battery

[0093] Example 1

[0094] (1) Preparation of negative electrode sheet

[0095] The copper foil is used as the negative 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 are fully stirred and mixed in a proper amount of deionized water to form a first negative electrode slurry. The first negative electrode slurry is uniformly coated on one side surface (i.e. A surface) of the copper foil. 97.6wt% artificial graphite, 1.3wt% carboxymethyl cellulose (CMC), and 1.1wt% butadiene-styrene rubber (SBR) are fully stirred in a proper amount of deionized water to form a second negative electrode slurry. The second negative electrode slurry is uniformly coated on the other side surface (i.e. B surface, the opposite surface of the A surface) of the copper foil, and then dried, cold-pressed, cut, and welded to prepare a negative electrode sheet. The active material layer on the A surface of the negative current collector is the first negative electrode active material layer, and the mass percentage of silicon element in the first negative electrode active material layer is 4.3%. The active material layer on the B surface of the negative current collector is the second negative electrode active material layer, and the mass percentage of silicon element in the second negative electrode active material layer is 0 (the percentage of silicon element is not greater than 0.5% and it can be considered that the second negative electrode active material layer does not contain silicon element).

[0096] (2) Preparation of the positive electrode sheet

[0097] The aluminum foil is used as the positive 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 a proper amount of N-methyl pyrrolidone 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 prepare a positive electrode sheet.

[0098] (3) Preparation of the electrolyte

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

[0100] (4) Preparation of the separator

[0101] The separator (first separator) matched with the first negative electrode active material layer includes a base material, an inorganic coating layer coated on one side surface of the base material, and a polymer particle layer coated on the surface of the inorganic coating layer. The base material is a 4.5 pm thick polyethylene (PE) porous polymer film, the inorganic coating layer is 2 pm thick boehmite, and the polymer particle layer is 2 pm thick polyvinylidene fluoride. The other side surface of the base material of the first separator is coated with a bonding layer, which is an acrylic or acrylate polymer. The separator (second separator) matched with the second negative electrode active material layer includes a base material, an inorganic coating layer coated on one side surface of the base material, and a bonding layer coated on the surface of the inorganic coating layer. The other side surface of the base material of the second separator is coated with a bonding layer. The base material is a 4.5 pm thick polyethylene (PE) porous polymer film, the inorganic coating layer is 2 pm thick boehmite, and the bonding layer is an acrylic or acrylate polymer.

[0102] (5) Preparation of a lithium ion battery

[0103] The positive electrode sheet and the negative electrode sheet are wound after slitting, and the positive electrode sheet and the negative electrode sheet are separated by the separator. The first negative electrode active material layer matches the separator coated with a polymer particle layer on one side, and the polymer particle layer on the separator is placed towards the side of the positive electrode sheet. The second negative electrode active material layer matches the separator without a polymer particle layer. Stack in order to make the separator play a role of isolation, and roll to obtain a bare battery. The bare battery is subjected to hot pressing, top side sealing, code spraying, vacuum drying, injection of electrolyte, high temperature standing, pressure formation and capacity, and a finished lithium ion battery is obtained.

[0104] Example 2-19

[0105] The preparation method of the lithium ion battery provided in Example 2-19 can refer to Example 1, and the difference lies in that:

[0106] The mass percentage content of silicon element in the negative electrode active material layer (first negative electrode active material layer) on the A surface of the negative electrode current collector and the thickness of the polymer particle layer of the separator (first separator) matched therewith are adjusted, and the mass percentage content data of artificial graphite, carboxymethyl cellulose, butadiene rubber and conductive carbon black in the first negative electrode active material layer are adaptively adjusted. The specific data are shown in Table 1 below.

[0107] Example 20

[0108] The preparation method of the lithium ion battery provided in this example can refer to Example 1, and the difference lies in that:

[0109] The silicon-based material in the active material layer on the A surface of the negative current collector (the first negative active material layer) is a silicon-oxygen material. The mass percentage of silicon element and the thickness of the polymer particle layer of the matched separator (the first separator) are adjusted. The mass percentage data of artificial graphite, carboxymethyl cellulose, butadiene rubber, and conductive carbon black in the first negative active material layer are adaptively adjusted. The specific data can be seen in Table 1.

[0110] Example 21

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

[0112] The silicon-based material in the active material layer on the A surface of the negative current collector (the first negative active material layer) is a silicon material. The mass percentage of silicon element and the thickness of the polymer particle layer of the matched separator (the first separator) are adjusted. The mass percentage data of artificial graphite, carboxymethyl cellulose, butadiene rubber, and conductive carbon black in the first negative active material layer are adaptively adjusted. The specific data can be seen in Table 1.

[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] The mass percentage of silicon element in the active material layer on the A surface of the negative current collector (the first negative active material layer) and the thickness of the polymer particle layer of the matched separator (the first separator) are adjusted. The mass percentage data of artificial graphite, carboxymethyl cellulose, butadiene rubber, and conductive carbon black in the first negative active material layer are adaptively adjusted. The specific data can be seen in Table 1.

[0116] Example 22

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

[0118] (1) Preparation of the negative electrode sheet

[0119] A copper foil is used as the negative current collector. 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 uniformly coated on both sides of the copper foil surface (i.e. the A surface and the B surface), and then dried, cold-pressed, and then cut and welded to prepare a negative electrode sheet. The active material layer on the A surface of the negative current collector is the first negative active material layer, and the mass percentage of silicon element is 2.5%. The active material layer on the B surface of the negative current collector is the second negative active material layer, and the mass percentage of silicon element is 2.5%.

[0120] (4) Preparation of the separator

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

[0122] (5) Preparation of the lithium ion battery

[0123] The positive electrode sheet and the negative electrode sheet are wound after slitting, and the positive electrode sheet and the negative electrode sheet are separated by the separator, wherein the polymer particle layer on the separator is placed towards the side of the positive electrode sheet. Stack in order, so that the separator plays a role of isolation, and the bare battery is obtained by winding. The bare battery is subjected to hot pressing, top side sealing, code spraying, vacuum drying, injection of electrolyte, high temperature standing, and then pressure formation and capacity, and the finished lithium ion battery is obtained.

[0124] Examples 23-33

[0125] The preparation method of the lithium ion battery provided in Examples 23-33 can refer to Example 22, and the difference lies in that:

[0126] The mass percentage content of silicon element in the negative electrode current collector A-side active material layer (first negative electrode active material layer) and the thickness of the polymer particle layer of the matched separator (first separator) are adjusted, and the mass percentage content data of artificial graphite, carboxymethyl cellulose, butadiene rubber and conductive carbon black in the first negative electrode active material layer and the thickness of the inorganic coating layer of the first separator and the second separator are adaptively adjusted. See Table 2 below for specific data.

[0127] Comparative Examples 7-12

[0128] The preparation method of the lithium ion battery provided in Comparative Examples 7-12 can refer to Example 22, and the difference lies in that:

[0129] The mass percentage content of silicon element in the negative electrode current collector A-side active material layer (first negative electrode active material layer) and the thickness of the polymer particle layer of the matched separator (first separator) are adjusted, and the mass percentage content data of artificial graphite, carboxymethyl cellulose, butadiene rubber and conductive carbon black in the first negative electrode active material layer and the thickness of the inorganic coating layer of the first separator and the second separator are adaptively adjusted. See Table 2 below for specific data.

[0130] Test method

[0131] 1. Silicon element test

[0132] The silicon element content in the present application refers to the mass percentage of silicon element based on the mass of the negative active material layer containing silicon element. The test method is to take the negative electrode sheet in the finished product battery cell, identify the active material layer containing silicon element by SEM / EDS, take the material of the active material layer to test ICP to obtain the mass percentage of silicon element.

[0133] 2. Separator polymer particle layer thickness test

[0134] In the plane area of the battery cell, the position of the matching separator between the negative active material layer containing silicon element and the positive electrode sheet is determined, 6x6mm samples are obtained by ion cutting, and the side view of the separator is obtained by SEM / EDS scanning, as shown in Figure 7 The SEM and EDS can distinguish the separator substrate PP / PE, inorganic coating and polymer particle layer. The thickness of the polymer particle layer is measured, and 10 groups of data are taken at the flat area and the protrusion, and the average thickness is calculated as the thickness of the polymer particle layer (here, the flat area is relative to the protrusion, and is roughly flat).

[0135] 3. Corner lithium precipitation area ratio test after 1000 cycles at 25℃

[0136] CCD imaging technology is used to obtain the image of the surface of the electrode sheet, and the corner lithium precipitation area is identified by processing and detecting the image, and the proportion of the corner lithium precipitation area to the total area can be calculated.

[0137] Test results

[0138] Table 1

[0139]

[0140] As can be seen from the data comparison of Examples 1-21 and Comparative Examples 1-6 in Table 1, in the negative electrode tab of the present application, the silicon element is concentrated in the active material layer on the surface of the negative electrode current collector side. According to the present application, the separator coated with a polymer particle layer of different thickness is matched according to the different silicon content in the negative electrode active material layer coated on the surface of the negative electrode current collector side. When the matching relationship between the mass percentage content X of silicon element and the thickness H of the polymer particle layer meets the conditions defined in the present application, the electrochemical device can reserve a corner space to buffer the tab extrusion and fracture, overcome the tab fracture and cycle lithium precipitation problem caused by silicon-based expansion, and maximize the energy density. As can be seen from the data comparison of Examples 5-6, 7-8, 9-11, 12-13, 14-15, when the mass percentage content X of silicon element and the thickness H of the polymer particle layer further meet one of the conditions defined in the present 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, 15%≤X≤20% and 3.5 µm≤H<4 µm, the cycle lithium precipitation problem of the electrochemical device is further optimized and improved. As can be seen from the data shown in Comparative Examples 1-6, when the thickness H of the polymer particle layer is lower than the conditions defined in the present application, the problems caused by silicon-based expansion cannot be effectively overcome, especially the tab extrusion and fracture of the electrochemical device at the corner, accompanied by serious cycle lithium precipitation problem; when the thickness H of the polymer particle layer is higher than the conditions defined in the present application, the energy density of the electrochemical device will be seriously reduced.

[0141] Table 2

[0142]

[0143] As can be seen from the data comparison of Examples 22-33 and Comparative Examples 7-12 in Table 2, in the negative electrode sheet of the present application, the silicon element is uniformly distributed in the active material layer on both sides of the negative current collector. According to the present application, the separator coated with a polymer particle layer of different thickness is matched according to the different silicon content in the negative active material layer coated on the single side surface of the negative current collector of the negative electrode sheet. When the matching relationship between the mass percentage content X of silicon element and the thickness H of the polymer particle layer meets the conditions defined in the present application, the electrochemical device can reserve a corner space to buffer the extrusion and fracture of the electrode sheet, overcome the electrode sheet fracture and cycle lithium precipitation problem caused by silicon-based expansion, and maximize the energy density. As can be seen from the data comparison of Examples 22-23, 24-25, 26-27, 28-29, 30-31, 32-33, when the mass percentage content X of silicon element and the thickness H of the polymer particle layer further meet one of the conditions defined in the present application, i.e. 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, 15%≤X≤20% and 3.5 µm≤H<4 µm, the cycle lithium precipitation problem of the electrochemical device is further optimized and improved. As can be seen from the data shown in Comparative Examples 7-12, when the thickness H of the polymer particle layer is lower than the conditions defined in the present application, the problems caused by silicon-based expansion cannot be effectively overcome, especially the electrode sheet extrusion and fracture at the corner of the electrochemical device, accompanied by serious cycle lithium precipitation problem; when the thickness H of the polymer particle layer is higher than the conditions defined in the present application, the energy density of the electrochemical device will be seriously reduced.

[0144] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be interpreted as a limitation of the present application, and 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 jelly-roll type battery cell, the jelly-roll type battery cell comprising a positive electrode tab, a negative electrode tab, and a separator; the negative electrode tab comprising a negative electrode current collector, a surface of the negative electrode current collector being provided with a first negative electrode active material layer comprising a silicon-based material; the separator being disposed between the negative electrode tab and the positive electrode tab; the separator adjacent to the first negative electrode active material layer being provided with a polymer particle layer on a surface thereof distal to the first negative electrode active material layer; the separator adjacent to the first negative electrode active material layer being provided with an adhesive layer on a surface thereof facing the first negative electrode active material layer; a mass percentage of silicon element in the first negative electrode active material layer is X based on the mass of the first negative electrode active material layer; a thickness of the polymer particle layer is H, the electrochemical device satisfying one of the following conditions: 0<X<2%, 0<H<1 µm; 2%≤X<5%, 1 µm≤H<2.5 µm; 5%≤X<10%, 2.5 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 of claim 1, wherein, the electrochemical device satisfying one of the following conditions: 2%≤X<5%, 1.5 µm≤H<2.5 µm; 10%≤X<15%, 2.8 µm≤H<3.5 µm; 15%≤X≤20%, 3.5 µm≤H<4 µm.

3. The electrochemical device of claim 1, wherein, the first negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-based active material and a carbon active material; the silicon-based material being selected from at least one of silicon, a silicon oxide compound, a silicon carbon compound, or a silicon alloy; and / or the carbon active material being selected from at least one of graphite or hard carbon.

4. The electrochemical device of claim 3, wherein, the silicon-based active material is a silicon carbon particle, and the carbon active material is graphite.

5. The electrochemical device of claim 1, wherein, a mass percentage of silicon element X in the first negative electrode active material layer satisfies 2%≤X≤5% based on the mass of the first negative electrode active material layer.

6. The electrochemical device according to any one of claims 1 to 4, wherein another surface of the negative electrode current collector is provided with a second negative electrode active material layer; the second negative electrode active material layer does not contain silicon element; or, the second negative electrode active material layer contains silicon element.

7. The electrochemical device of claim 6, wherein, the second negative electrode active material layer does not contain silicon element, and there is no polymer particle layer on a surface of the separator adjacent to the second negative electrode active material layer.

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

9. The electrochemical device of claim 1, wherein, the separator adjacent to the first negative electrode active material layer comprises a substrate and an inorganic coating layer, the inorganic coating layer being disposed between the substrate and the polymer particle layer; the inorganic coating layer 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.

10. The electrochemical device of claim 1, wherein, The adhesive layer is a polymer formed from at least one of acrylic acid, acrylate, styrene, isobutyl acrylate, or acrylonitrile.

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

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