Negative pole piece, secondary battery and electronic device

Abstract

The invention relates to the technical field of electrochemistry, in particular to a negative pole piece, a secondary battery and an electronic device. The negative pole piece comprises a porous current collector and a negative active compound filled in pores of the porous current collector, the negative active compound is formed by curing negative slurry, the negative pole piece meets the conditions that S * theta * epsilon ' / epsilon is smaller than or equal to 0.18, D50 is smaller than or equal to 60 / S, epsilon is larger than or equal to 70% + 0.002 (d-20), S is the percentage of the mass of silicon-containing particles in the negative pole piece to the total mass of the negative active material, and D50 is smaller than or equal to 60 / S. Theta is the filling rate of the negative electrode slurry, epsilon'is the porosity of the negative electrode plate, epsilon is the porosity of the porous current collector, D50 is the median particle size of silicon-containing particles in the negative electrode plate, and d is the pore size of the porous current collector. The negative pole piece provides enough buffer space for volume expansion of silicon particles, effectively inhibits damage of an electrode structure and falling of active substances, enables the battery to have excellent performance in the aspects of energy density, 800cls capacity retention rate and expansion rate, and maximizes the performance of the battery.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technology, and in particular to a negative electrode sheet, a secondary battery and an electronic device. Background Art

[0002] With the continuous development of lithium-ion battery technology, its application in fields such as electric vehicles, energy storage systems, and portable electronic devices is becoming increasingly widespread. However, traditional lithium-ion battery anode materials, such as graphite, are gradually failing to meet market demand in terms of energy density and cycle life. Silicon-based anode materials have attracted much attention due to their high theoretical specific capacity. However, silicon anodes suffer from severe volume expansion during charge and discharge, which leads to a decline in battery cycle performance and limits their practical application. Summary of the Invention

[0003] The present invention provides a negative electrode plate to solve the technical problem of volume expansion of the existing silicon negative electrode during the charging and discharging process.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A negative electrode plate comprises a porous current collector and a negative electrode active composite filled in the pores of the porous current collector, wherein the negative electrode active composite is formed by solidifying a negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material, wherein the negative electrode active material comprises silicon-containing particles, and wherein the negative electrode plate satisfies the following relationship:

[0006] S×θ×ε' / ε≤0.18, D50≤60 / S, ε≥70%+0.002(d-20);

[0007] Wherein, S is the percentage of the mass of silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material;

[0008] θ is the negative electrode slurry filling rate, which represents the percentage of the actual filling volume of the negative electrode slurry in the pores of the porous current collector to the pore volume that can be filled by the porous current collector;

[0009] ε' is the porosity of the negative electrode sheet;

[0010] ε is the porosity of the porous current collector;

[0011] D50 is the median particle size of the silicon-containing particles in the negative electrode sheet, in nm;

[0012] d is the pore size of the porous current collector, in μm.

[0013] Furthermore, the percentage S of the mass of the silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material is 1%-40%.

[0014] Furthermore, the negative electrode slurry filling rate θ is 40%-90%.

[0015] Furthermore, the porosity ε' of the negative electrode plate is 45%-85%.

[0016] Furthermore, the porosity ε of the porous current collector is 80%-99%.

[0017] Furthermore, the median particle size D50 of the silicon-containing particles in the negative electrode plate is 50-8000 nm.

[0018] Furthermore, the pore size d of the porous current collector is 10-200 μm.

[0019] Furthermore, the porous current collector is at least one of porous copper foil, porous copper alloy foil, porous nickel foil, porous stainless steel foil, and porous titanium foil.

[0020] The present invention also discloses a secondary battery, which comprises the above-mentioned negative electrode plate.

[0021] The present invention also discloses an electronic device comprising the secondary battery.

[0022] Beneficial effects of the present invention:

[0023] The present invention constructs a relationship between the negative electrode slurry filling rate, the silicon content in the negative electrode pole piece, the porosity of the porous current collector, the porosity of the negative electrode pole piece after drying and roller pressing, the median particle size of the silicon-containing particles, and the pore size of the porous current collector. Through reasonable matching between them, sufficient buffer space is provided for the volume expansion of the silicon negative electrode, effectively suppressing the destruction of the electrode structure and the shedding of the active material, while making the battery perform excellently in terms of liquid retention, energy density, 800cls capacity retention rate and expansion rate, thereby maximizing the battery performance. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and technical effect of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention is clearly and completely described. The embodiments described below are part of the embodiments of the present invention, rather than all the embodiments. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer; if the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0025] In the present description, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0026] In the description of the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0027] It should be understood that the weights of the relevant components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally increased or decreased according to the embodiments of the present invention, it is within the scope of the present invention. Specifically, the weights described in the embodiments of the present invention may be mass units known in the chemical industry, such as μg, mg, g, and kg.

[0028] In addition, unless the context clearly requires otherwise, expressions in the singular form of a word should be understood to include the plural form of the word. The terms "include" or "have" are intended to specify the presence of a feature, number, step, operation, element, part, or combination thereof, but are not used to exclude the presence or possibility of adding one or more other features, numbers, steps, operations, elements, parts, or combinations thereof.

[0029] An embodiment of the present invention provides a negative electrode plate, which includes a porous current collector and a negative electrode active composite filled in the pores of the porous current collector, wherein the negative electrode active composite is formed by solidifying a negative electrode slurry, wherein the negative electrode slurry includes a negative electrode active material, wherein the negative electrode active material includes silicon-containing particles, and wherein the negative electrode plate satisfies the following relationship:

[0030] S×θ×ε' / ε≤0.18, D50≤60 / S, ε≥70%+0.002(d-20);

[0031] Wherein, S is the percentage of the mass of silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material;

[0032] θ is the negative electrode slurry filling rate, which represents the percentage of the actual filling volume of the negative electrode slurry in the pores of the porous current collector to the pore volume that can be filled by the porous current collector;

[0033] ε' is the porosity of the negative electrode sheet;

[0034] ε is the porosity of the porous current collector;

[0035] D50 is the median particle size of the silicon-containing particles in the negative electrode sheet, in nm;

[0036] d is the pore size of the porous current collector, in μm.

[0037] Specifically, the porosity ε of the porous current collector is the percentage of the pore volume in the porous current collector to the total volume of the porous current collector, and the calculation formula is, ε = (1-ρ1 / ρ0) × 100%;

[0038] Wherein, ρ1 is the apparent density (mass per unit volume) of the porous current collector, and ρ0 is the theoretical density of the raw material of the porous current collector. For example, if the porous current collector is a porous copper foil, ρ0 is the theoretical density of pure copper.

[0039] The negative electrode slurry filling rate θ is the percentage of the actual filling volume of the negative electrode slurry in the pores of the porous current collector to the pore volume that can be filled by the porous current collector, that is, θ = (m 浆料 / ρ 浆料 ) / V 孔 × 100%, V 孔 =V 总 ·ε;

[0040] Among them, m 浆料 is the mass of the negative electrode slurry, ρ 浆料 is the density of the negative electrode slurry (measured by the specific gravity cup method), V 孔 is the pore volume of the porous current collector, V 总 is the total volume of the porous current collector.

[0041] The porosity ε' of the negative electrode sheet is the porosity of the negative electrode sheet after drying and roller pressing, and the porosity ε' of the negative electrode sheet is measured using a true density meter.

[0042] Among them, the percentage S of the mass of silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material can be obtained by adjusting the mass ratio of silicon-containing particles in the negative electrode active material, or can be obtained by back-calculating the gram capacity method, that is, the calculation formula of the percentage S of the mass of silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material is: S=(C 综合 -C C ) / (C Si -C C );

[0043] Among them, C 综合 is the gram capacity of the negative electrode, in mAh / g; C Siis the gram capacity of silicon-containing particles, in mAh / g; C C It is the gram capacity of carbon, and the unit is mAh / g.

[0044] Traditional lithium-ion battery anode current collectors primarily use copper foil. However, due to its rigidity and planar structure, copper foil is unable to effectively buffer the volume changes of the silicon anode during cycling, exacerbating electrode structural damage and battery performance degradation. The present invention utilizes a porous current collector as a novel battery structure for lithium-ion battery silicon-doped anode current collectors. This structure significantly improves the expansion problem of the silicon-doped anode during cycling, thereby improving the battery's cycling stability and energy density.

[0045] The present invention adopts a porous current collector, whose porous structure provides sufficient buffer space for the volume expansion of the silicon negative electrode, effectively suppresses the destruction of the electrode structure and the shedding of the active material, thereby improving the cycle stability of the battery. The porous structure of the porous current collector of the present invention increases the contact area between the electrode material and the current collector, strengthens the bonding force between them, helps to reduce the shedding of the electrode material during the cycle, and improves the cycle life of the battery. On the other hand, the present invention constructs a relationship between the negative electrode slurry filling rate, the silicon content in the negative electrode pole piece, the porosity of the porous current collector, the porosity of the negative electrode pole piece after drying and rolling, the median particle size of the silicon-containing particles, and the pore size of the porous current collector. Through the reasonable combination of them, sufficient buffer space is provided for the volume expansion of the silicon negative electrode, effectively suppresses the destruction of the electrode structure and the shedding of the active material, so that the battery performs excellently in terms of liquid retention, energy density, 800cls capacity retention rate and expansion rate, and maximizes the performance of the battery.

[0046] When S×θ×ε′ / ε≤0.18, D50≤60 / S, and ε≥70%+0.002(d-20) are not simultaneously met, insufficient space is reserved for silicon particle expansion in the negative electrode, resulting in poor battery performance in terms of energy density, 800-cycle life, and cycle expansion rate. When S×θ×ε′ / ε>0.18, the slurry filling rate is too high and the pore buffering is insufficient, leading to silicon particle expansion stress concentration, causing electrode cracking and active material delamination. When D50>60 / S, silicon particle agglomeration prevents effective electrolyte infiltration, SEI film thickening uncontrollably, and lithium ion transport is hindered. When ε<70%+0.002(d-20), the silicon-based negative electrode material cannot effectively buffer volume expansion during cycling, causing silicon particle expansion stress concentration, poor electrolyte infiltration, electrode structure damage, reduced energy density, and increased manufacturing costs.

[0047] In some embodiments, the value of (S×θ×ε′ / ε) is, but is not limited to, 0.031-0.047, 0.031-0.060, 0.031-0.075, 0.031-0.086, 0.031-0.170, 0.031-0.18, 0.047-0.060, 0.047-0.075, 0.047-0.086 , 0.047-0.170, 0.047-0.18, 0.060-0.075, 0.060-0.086, 0.060-0.170, 0.060-0.18, 0.075-0.086, 0.075-0.170, 0.086-0.170, 0.086-0.18, or 0.075-0.18.

[0048] Furthermore, the mass percentage S of the silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material is 1%-40%. In some embodiments, S may be, but is not limited to, 1%-5%, 1%-7.5%, 1%-10%, 1%-12.5%, 1%-15%, 1%-30%, 5%-7.5%, 5%-10%, 5%-12.5%, 5%-15%, 5%-30%, 5% -40%, 7.5%-10%, 7.5%-13%, 7.5%-15%, 7.5%-30%, 7.5%-40%, 10%-12.5%, 10%-15%, 10%-30%, 10%-40%, 12.5%-15%, 12.5%-30%, 12.5%-40%, 15%-30%, 15%-40%, or any value between 30% and 40%.

[0049] When the silicon content is too high, the volume of silicon particles expands severely, causing local stress concentration, leading to cracking of the negative electrode active composite filled in the porous current collector, and then destroying the electrode structure, reducing the battery's energy density and cycle life, and increasing the cycle expansion rate. If the silicon content is too low, the battery's energy density will be affected, resulting in a decline in battery performance.

[0050] Further, the negative electrode slurry filling rate θ is 40%-90%. In some embodiments, θ can be, but is not limited to, any value of 40%-65%, 40%-71%, 40%-75%, 40%-78, 40%-82%, 40%-85%, 65%-71%, 65%-75%, 65%-78%, 65%-82%, 65%-85%, 65%-90%, 71%-75%, 71%-78%, 71%-82%, 71%-85%, 71%-90%, 75%-78%, 75%-82%, 75%-85%, 75%-90%, 78%-82%, 78%-85%, 78%-90%, 82%-85%, 82%-90%, or 85%-90%.

[0051] When the slurry filling rate is too high, the expansion space reserved for silicon particles is too small, resulting in excessive silicon loading on the porous current collector and causing local stress concentration, which in turn leads to cracking and delamination of the active material, reduced energy density and cycle life, and increased cycle expansion rate. When the slurry filling rate is too low, the negative electrode active material content is too low, and the negative electrode active material has difficulty in effective contact with the negative electrode current collector, resulting in a decrease in battery capacity and poor cycle stability.

[0052] Furthermore, the porosity ε' of the negative electrode sheet is 45%-85%. In some embodiments, ε' may be, but is not limited to, 45%-60%, 45%-62%, 45%-65%, 45%-68%, 45%-70%, 45%-80%, 60%-62%, 60%-65%, 60%-68%, 60%-70%, 60 ... Any value between 0%-85%, 62%-65%, 62%-68%, 62%-70%, 62%-80%, 62%-85%, 65%-68%, 65%-70%, 65%-80%, 65%-85%, 68%-70%, 68%-80%, 68%-85%, 70%-80%, 70%-85% or 80%-85%.

[0053] This application regulates the porosity of the negative electrode sheet to reserve space for silicon particle expansion in advance, thereby alleviating the silicon expansion problem and improving battery energy density and cycle stability. When the porosity of the negative electrode sheet is too low, the expansion space reserved for silicon particles is insufficient, resulting in excessive silicon loading and causing local stress concentration, leading to cracking and peeling of active materials, reduced energy density and cycle life, and increased cycle expansion rate. When the porosity of the negative electrode sheet is too large, the active material contained in the negative electrode sheet is insufficient, resulting in a decrease in battery energy density and affecting battery performance.

[0054] Furthermore, the porosity ε of the porous current collector is 80%-99%. In some embodiments, ε can be, but is not limited to, any value of 80%-82%, 80%-85%, 80%-87%, 80%-92%, 82%-85%, 82%-87%, 82%-92%, 82%-99%, 85%-87%, 85%-92%, 85%-99%, 87%-92%, 87%-99% or 92%-99%.

[0055] The application uses a high-porosity porous current collector as the negative electrode current collector, which can alleviate the effect of silicon particle expansion on the thickness of the battery cell to a certain extent. When the porosity of the porous current collector is too small, the expansion space reserved for the silicon particles is insufficient, resulting in excessive silicon loading and triggering local stress concentration, leading to cracking and peeling of the active material, reduced energy density and cycle life, and increased cycle expansion rate. When the porosity of the porous current collector is too high, the current collector is not strong enough and is prone to breakage, which in turn affects the cycle stability of the battery.

[0056] Furthermore, the median particle size D50 of the silicon-containing particles in the negative electrode plate is 50nm-8000nm. In some embodiments, D50 may be, but is not limited to, 50nm-200nm, 50nm-400nm, 50nm-480nm, 50nm-600nm, 50nm-800nm, 50nm-1200nm, 200nm-400nm, 200nm-480nm, 200nm-600nm, 200nm-800nm, 200nm-1200nm, 200nm-8000nm, 400nm-480nm, 400nm- Any value among 600nm, 400nm-800nm, 400nm-1200nm, 400nm-8000nm, 480nm-600nm, 480nm-800nm, 480nm-1200nm, 480nm-8000nm, 600nm-800nm, 600nm-1200nm, 600nm-8000nm, 800nm-1200nm, 800nm-8000nm or 1200nm-8000nm.

[0057] When the median particle size D50 of silicon-containing particles is too large, the silicon particles expand significantly and the cycle expansion rate increases. When D50 is too small, silicon particles are prone to agglomeration, resulting in ineffective electrolyte infiltration, uncontrolled SEI film thickening, and obstructed lithium ion transmission.

[0058] Furthermore, the porous current collector has a pore size d of 10-200 μm. In some embodiments, d may be, but is not limited to, any value in the range of 10 μm-25 μm, 10 μm-30 μm, 10 μm-35 μm, 10 μm-37 μm, 10 μm-40 μm, 25 μm-30 μm, 25 μm-35 μm, 25 μm-37 μm, 25 μm-40 μm, 25 μm-200 μm, 30 μm-35 μm, 30 μm-37 μm, 30 μm-40 μm, 30 μm-200 μm, 35 μm-37 μm, 35 μm-40 μm, 35 μm-200 μm, 37 μm-40 μm, 37 μm-200 μm, or 40 μm-200 μm.

[0059] When the pore size of the porous current collector is too small, the expansion space reserved for silicon particles is insufficient, resulting in concentrated stress on the silicon particles, causing cracking of the pole pieces and peeling of the active material, which in turn leads to poor battery performance in terms of energy density, 800-cycle life, and cycle expansion rate. When the pore size of the porous current collector is too large, the bonding force between the negative electrode slurry and the current collector is insufficient, and the negative electrode slurry or negative electrode active material is easily separated from the pores, affecting battery performance. In addition, an excessively large pore size will lead to insufficient mechanical strength of the porous current collector, causing the current collector to easily break, affecting battery cycle performance.

[0060] In an embodiment, the porous current collector is at least one of porous copper foil, porous copper alloy foil, porous nickel foil, porous stainless steel foil, and porous titanium foil, preferably porous copper foil.

[0061] In an embodiment, the negative electrode slurry includes a negative electrode active material, a binder and a solvent, the negative electrode active material includes silicon-containing particles and graphite, the silicon-containing particles include at least one of elemental silicon, silicon carbon, silicon oxide, and a silicon-metal alloy composite, preferably, the silicon-containing particles are silicon carbon particles. The binder can use any binder known in the art, and the binder can include at least one of polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamide-imide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride, polytetrafluoroethylene (PTFE), carboxymethyl cellulose or sodium carboxymethyl cellulose (CMC-Na). For example, the binder can be styrene-butadiene rubber (SBR). The solvent is deionized water or NMP.

[0062] In some embodiments, the negative electrode slurry may further include at least one of a thickener and a conductive agent. In this embodiment, the thickener is sodium carboxymethyl cellulose, and the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black or graphene.

[0063] The present invention also discloses a secondary battery comprising a positive electrode sheet, a separator, and the aforementioned negative electrode sheet. Specifically, the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, degassed, and trimmed to produce the secondary battery.

[0064] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may include but is not limited to a chemical formula of Li a Ni x Co y Mz O 2-b N b A combination of one or more of the compounds shown, wherein 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from a combination of one or more of Mn and Al, N is selected from a combination of one or more of F, P, and S, and the positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 A combination of one or more of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc.

[0065] The positive electrode active material may also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, the positive electrode active material may be modified by coating, doping, or the like. The materials used for the modification may include, but are not limited to, a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0066] The positive electrode active material layer may further include a conductive agent, and the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, or graphene.

[0067] The positive electrode active material layer may further include a binder. The binder may use any binder known in the art. The binder may include at least one of polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamide-imide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose, or sodium carboxymethyl cellulose (CMC-Na). For example, the binder may be polyvinylidene fluoride (PVDF).

[0068] The positive electrode current collector is usually a structure or part that collects current. The positive electrode current collector can be any material in the art that is suitable for use as a positive electrode current collector for lithium-ion batteries. For example, the positive electrode current collector can include but is not limited to metal foil, and more specifically can include but is not limited to aluminum foil.

[0069] The isolation membrane can be any material suitable for lithium-ion battery isolation membranes in the art, for example, it can be a combination of one or more materials including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0070] The electrolyte includes a lithium salt and a solvent. The lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, LiTFSI, or lithium difluoroborate. The solvent may be at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents. The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorocarbon compound, or a combination thereof. The linear carbonate compound may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. The cyclic carbonate compound may be ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), and combinations thereof. The fluorinated carbonate compound may be fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof. The carboxylate compound may be 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. The ether compound may be dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof. The other organic solvent may be at least one of 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, or a phosphate ester.

[0071] An embodiment of the present invention further discloses an electronic device comprising the aforementioned secondary battery.

[0072] The electronic device of the present application can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a mobile phone, 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 headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0073] In order to enable those skilled in the art to clearly understand the implementation details and operations of the present invention, and to significantly demonstrate the improved performance of the embodiments of the present invention, the above technical solutions are illustrated below through multiple embodiments.

[0074] Example 1

[0075] Preparation of negative electrode sheet:

[0076] The negative electrode active material, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were dispersed in deionized water at a mass ratio of 97.8:1.1:1.1. After thorough stirring and mixing, the negative electrode slurry was applied to the three-dimensional porous framework of porous copper by coating. After drying, roller pressing, and stripping, the negative electrode sheet was obtained. The negative electrode active material is a mixture of graphite and silicon-carbon particles in a mass ratio of 95:5. The silicon-carbon particles were purchased from Jiangxi Zichen Technology Co., Ltd.

[0077] Preparation of positive electrode:

[0078] The positive electrode material lithium cobalt oxide, carbon nanotube conductive agent, and PVDF binder are dispersed in an N-methylpyrrolidone solvent system in a mass ratio of 98:1:1. After being fully stirred and mixed, a positive electrode slurry is prepared. The slurry is coated on both surfaces of the Al foil, and the positive electrode sheet is obtained after drying, rolling, and slitting.

[0079] Preparation of electrolyte:

[0080] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0081] Battery assembly:

[0082] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound and placed in an aluminum-plastic film packaging bag. After drying, the electrolyte is injected and the secondary battery is produced through vacuum packaging, resting, formation, degassing, and trimming.

[0083] Among them, the preparation methods of Examples 2-6 and Comparative Examples 1-4 are the same as the preparation method of Example 1, the difference lies in the parameters of the negative electrode sheets. The parameters of the negative electrode sheets of Examples 1-6 and Comparative Examples 1-4 are shown in Table 1 below.

[0084] Comparative Example 5

[0085] The difference between Comparative Example 5 and Example 1 is that the preparation method of the negative electrode sheet is as follows:

[0086] The negative electrode active material, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dispersed in deionized water at a mass ratio of 97.8:1.1:1.1. After being fully stirred and mixed, the negative electrode slurry is coated on the surface of the copper foil by coating. After drying, rolling, and slitting, the negative electrode sheet is obtained.

[0087] The other preparation methods of Comparative Example 5 are the same as those of Example 1 and are not described in detail here.

[0088] Table 1: Negative electrode parameters of Examples 1-6 and Comparative Examples 1-5

[0089]

[0090]

[0091] Note: The changes in the parameters in the examples and comparative examples in Table 1 were obtained by adjusting the following methods.

[0092] The percentage S of the mass of silicon-containing particles to the total mass of the negative electrode active material is achieved by adjusting the mass ratio of graphite to silicon and carbon;

[0093] The negative electrode slurry filling rate θ is controlled by adjusting the amount of deionized water (solvent) added to the negative electrode slurry to control the mass m of the negative electrode slurry. 浆料 and the density of the negative electrode slurry ρ 浆料 , thereby obtaining the corresponding θ value;

[0094] The different porosities and pore sizes of porous copper are obtained by purchasing porous copper with corresponding porosity coefficients and corresponding pore sizes from the market;

[0095] The porosity ε′ of the negative electrode sheet changes with the slurry filling rate;

[0096] Silicon-containing particles with different D50 were obtained by purchasing materials with corresponding particle sizes from the market.

[0097] Performance test: The batteries obtained in the examples and comparative examples were subjected to the following tests, and the test results are shown in Table 2.

[0098] (1) Energy density test

[0099] The battery cell was fully charged at a constant current of 0.5C, and then discharged at a constant current of 0.2C to 3.0V. The current and voltage during the discharge process were recorded to calculate the total discharge capacity of the battery (unit: ampere-hour, Ah).

[0100] Energy density (Wh / L) = (capacity × platform voltage) / (cell length × cell width × cell thickness)

[0101] (2) Cyclic performance test

[0102] The cycle test process is as follows:

[0103] 1. Charge the cell to 4.2V at 1.2C constant current and constant voltage, with a cut-off rate of 0.7C;

[0104] 2. Charge the cell to 4.53V at 0.7C constant current and constant voltage, with a cut-off rate of 0.05C;

[0105] 3. Shelf time: 10 minutes;

[0106] 4. Discharge at a constant current of 0.5C, with a cut-off voltage of 3.0V;

[0107] 5. Shelf time: 10 minutes;

[0108] 6. Cycle 800 times to test the battery capacity attenuation.

[0109] Capacity retention rate = capacity after 800 cycles / initial capacity × 100%.

[0110] (3) Battery cell expansion rate test

[0111] The initial thickness of the battery cell was tested at a pressure of 600ppg.

[0112] The cycle test process is as follows:

[0113] 1. Charge to 4.2V at 1.2C constant current and constant voltage, with a cut-off rate of 0.7C;

[0114] 2. Charge to 4.53V at 0.7C constant current and constant voltage, with a cut-off rate of 0.05C;

[0115] 3. Shelf time: 10 minutes;

[0116] 4. Discharge at a constant current of 0.5C, with a cut-off voltage of 3.0V;

[0117] 5. Shelf time: 10 minutes;

[0118] 6. Repeat 800 times.

[0119] The thickness of the battery cell is tested under a pressure of 600ppg in the fully charged state and RT cycled for 800cls. The battery cell expansion rate = the thickness of the battery cell after full charge cycle / the initial thickness of the battery cell × 100% - 1.

[0120] Table 2: Test results of Examples 1-6 and Comparative Examples 1-5

[0121]

[0122]

[0123] The above test results are analyzed as follows:

[0124] As can be seen from the table, the negative electrode sheets of Examples 1-6 of the present application all satisfy the following relationship: S×θ×ε′ / ε≤0.18, D50≤60 / S, and ε≥70%+0.002(d-20). The present invention constructs a relationship by regulating the relationship between the silicon content of the negative electrode sheet, the filling rate of the negative electrode slurry on the porous current collector, the porosity of the negative electrode sheet, the median particle size of the silicon-containing particles, and the pore size of the porous current collector, so that the prepared silicon-based negative electrode sheet can effectively alleviate the volume expansion problem of silicon particles, thereby making the battery using the negative electrode sheet perform well in energy density, 800cls cycle capacity retention rate and expansion rate. The energy density of the battery using the negative electrode sheet of the present application is 910-1060Wh / L, the capacity retention rate after 800 cycles is 84.1%-85.7%, and the cell expansion rate after 800 cycles of the cell RT is 9.0%-9.4%.

[0125] It can be seen from the test results of Comparative Examples 1-4 and Example 1 that the energy density, cycle life and cell expansion rate of the battery can be effectively improved only when the negative electrode plate satisfies the following relationships at the same time: S×θ×ε′ / ε≤0.18, D50≤60 / S, and ε≥70%+0.002(d-20).

[0126] By comparing Examples 1-6 of the present application with Comparative Example 5, it can be seen that the present application addresses the problem of silicon particle expansion during the cycle by using a porous current collector with high porosity as the negative electrode current collector, which can alleviate the effect of silicon particle expansion on the thickness of the battery cell to a certain extent. By using a porous current collector, the energy density of the battery and the cycle life of 800 cycles can be improved, and the expansion rate of the battery cell can be reduced.

[0127] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a porous current collector and a negative electrode active composite filled in the pores of the porous current collector, wherein the negative electrode active composite is formed by solidifying a negative electrode slurry, the negative electrode slurry comprises a negative electrode active material, the negative electrode active material comprises silicon-containing particles, and the negative electrode sheet satisfies the following relationship: S×θ×ε' / ε≤0.18, D50≤60 / S, ε≥70%+0.002(d-20); Wherein, S is the percentage of the mass of silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material; θ is the negative electrode slurry filling rate, which represents the percentage of the actual filling volume of the negative electrode slurry in the pores of the porous current collector to the pore volume that can be filled by the porous current collector; ε' is the porosity of the negative electrode sheet; ε is the porosity of the porous current collector; D50 is the median particle size of the silicon-containing particles in the negative electrode sheet, in nm; d is the pore size of the porous current collector, in μm.

2. The negative electrode sheet according to claim 1, characterized in that: The percentage S of the mass of the silicon-containing particles in the negative electrode plate to the total mass of the negative electrode active material is 1%-40%.

3. The negative electrode sheet according to claim 1, characterized in that: The negative electrode slurry filling rate θ is 40%-90%.

4. The negative electrode sheet according to claim 1, characterized in that: The porosity ε' of the negative electrode plate is 45%-85%.

5. The negative electrode sheet according to claim 1, characterized in that: The porosity ε of the porous current collector is 80%-99%.

6. The negative electrode sheet according to claim 1, characterized in that: The median particle size D50 of the silicon-containing particles in the negative electrode plate is 50-8000 nm.

7. The negative electrode according to claim 1, characterized in that: The pore size d of the porous current collector is 10-200 μm.

8. A negative electrode according to any one of claims 1 to 7, characterized in that: The porous current collector is at least one of porous copper foil, porous copper alloy foil, porous nickel foil, porous stainless steel foil, and porous titanium foil.

9. A secondary battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 8.

10. An electronic device, characterized in that: A secondary battery according to claim 9 is included.

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