Composite additive and preparation method thereof, silicon-based negative electrode, electrochemical device and electronic equipment

Abstract

The invention discloses a composite additive and a preparation method thereof, a silicon-based negative electrode, an electrochemical device and electronic equipment, the composite additive comprises a carbon nanotube and a crown ether compound, and the carbon nanotube and the crown ether compound are connected through a C-N bond. The electrochemical device adopting the silicon-based negative electrode containing the composite additive has excellent coulombic efficiency and cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite additive and a preparation method thereof, a silicon-based negative electrode, an electrochemical device and an electronic equipment. BACKGROUND

[0002] Lithium ion batteries, as a mainstream chemical energy, have been widely used in energy storage systems, electric vehicles and portable electronic devices due to their high energy density, low self-discharge rate and long cycle life. As one of the most critical components of the battery, the negative electrode plays a key role in the electrochemical performance of the battery, especially the energy density. Graphite is widely used in commercial lithium ion batteries due to its high electrical conductivity, good reversibility and low cost. However, the specific capacity of graphite is relatively low, with a theoretical specific capacity of only 372 mAh / g, which cannot meet the application scenarios of high energy density and high performance batteries. Therefore, it is urgent to develop new negative electrode materials for the next generation of lithium ion batteries. Silicon, as the second most abundant element in the earth's crust, has a theoretical specific capacity of about 4200 mAh / g, which is more than ten times higher than that of graphite. In addition, the lithiation voltage platform of the silicon negative electrode (~0.4V vs. Li + / Li) is higher than that of the graphite negative electrode (~0.05V vs. Li + / Li), which can effectively avoid unnecessary lithium deposition and potential dendrite formation, reduce safety hazards, and effectively balance the high energy density and safety performance of the battery, and is considered as one of the most promising negative electrode materials.

[0003] Unlike the lithium storage behavior of graphite intercalation / deintercalation, the lithium storage process of silicon is completed through alloying reaction. Silicon will undergo structural transformation during charging and discharging, crystalline silicon evolves into amorphous Li-Si alloy, and then evolves into amorphous silicon. The dramatic structural change causes a large volume change (>300%) of the silicon negative electrode during lithiation / delithiation, which makes the silicon unable to withstand excessive stress during charging and discharging, leading to particle breakage and shedding, and the volume expansion also causes the continuous damage-repair of the SEI film, consuming a large amount of active lithium, resulting in low coulombic efficiency. In addition, silicon is a semiconductor material with low electrical conductivity, which leads to poor electron and ion transport performance during long-term cycling, resulting in poor battery cycle performance. SUMMARY

[0004] In order to solve the defects of low coulombic efficiency and poor cycle performance of the existing lithium ion battery using silicon negative electrode material, the present application provides a composite additive and a preparation method thereof, a silicon-based negative electrode, an electrochemical device and an electronic equipment. The electrochemical device using the silicon-based negative electrode containing the composite additive pair has excellent coulombic efficiency and cycle performance.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows.

[0006] In a first aspect, the present application provides a composite additive, which comprises carbon nanotubes and crown ether compounds, and the carbon nanotubes and the crown ether compounds are connected through C-N bonds.

[0007] In a second aspect, the present application provides a preparation method of the composite additive as described above, which comprises the following steps:

[0008] S1, performing a grafting reaction on a mixture to obtain an intermediate; the mixture comprises carbon nanotubes containing amino groups and crown ether compounds containing aldehyde groups;

[0009] S2, performing a reduction reaction on the intermediate under the action of a reducing agent to obtain the composite additive.

[0010] In a third aspect, the present application provides a silicon-based negative electrode, which comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises a silicon-based material, a binder, a conductive agent, and the composite additive as described above.

[0011] In a fourth aspect, the present application provides an electrochemical device, which comprises the silicon-based negative electrode as described above.

[0012] In a fifth aspect, the present application provides an electronic device, which comprises the electrochemical device as described above.

[0013] The positive progress effect of the present application is that:

[0014] The present application provides a composite additive suitable for a silicon-based negative electrode, which comprises carbon nanotubes and crown ether compounds connected through C-N bonds, and the carbon nanotubes and the crown ether compounds jointly play a role, so that the electrochemical device using the silicon-based negative electrode has excellent coulombic efficiency and cycle performance at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The flowchart of preparing the composite additive for the embodiments of the present application is shown. DETAILED DESCRIPTION

[0016] The present application will be further described in the following embodiments, but the present application is not limited in the scope of the embodiments. The experimental methods not specified in the following embodiments are selected according to the conventional methods and conditions, or according to the instructions of the goods.

[0017] Composite additive

[0018] In the composite additive provided in the first aspect of the present application, it comprises carbon nanotubes and crown ether compounds, and the carbon nanotubes and the crown ether compounds are connected through C-N bonds.

[0019] In the present application, the C-N bond (i.e. carbon-nitrogen single bond) between the carbon nanotube and the crown ether compound can exist stably under high temperature and high pressure conditions, and is not prone to breakage compared with C=N bond (i.e. carbon-nitrogen double bond) under high temperature and high pressure conditions. When the crown ether compound is applied in a battery, it can effectively avoid the dissolution of the crown ether compound in the electrolyte.

[0020] In the present application, the C-N bond in the composite additive can be tested by SPS or infrared.

[0021] In the present application, the content of the C-N bond in the composite additive is related to the content of the crown ether compound. Generally, the more the content of the crown ether compound, the more the content of the C-N bond.

[0022] In some optional embodiments, the crown ether compound comprises one or more of crown ether and crown ether derivatives.

[0023] Preferably, the crown ether derivative is one or more of benzo crown ether, azacrown ether and thiacrown ether.

[0024] Preferably, the benzo crown ether is, for example, benzo 12-crown-4 (structural formula as shown in formula-1), benzo 15-crown-5 (structural formula as shown in formula-2) or benzo 18-crown-6 (structural formula as shown in formula-3).

[0025]

[0026] Preferably, the azacrown ether is, for example, a compound as shown in formula-4.

[0027]

[0028] Preferably, the thiacrown ether is, for example, a compound as shown in formula I-5.

[0029]

[0030] In some optional embodiments, the carbon nanotube comprises one or more of single-walled carbon nanotube, double-walled carbon nanotube and multi-walled carbon nanotube.

[0031] In some optional embodiments, the mass content of the carbon nanotube in the composite additive is 10%-35%.

[0032] In some specific embodiments, the mass content of the carbon nanotube in the composite additive is 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 84% or 87%.

[0033] In some alternative embodiments, the mass content of the crown ether compound in the composite additive is 65% to 90%.

[0034] In some specific embodiments, the mass content of the crown ether compound in the composite additive is 13%, 16%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, or 28%.

[0035] In the present application, the mass content of the crown ether compound and the mass content of the carbon nanotube in the composite additive can be determined by thermogravimetric analysis (TGA). Generally, the thermal decomposition temperature of the crown ether compound is 100-300°C, and the thermal decomposition temperature of the carbon nanotube is 500-700°C, and the content is determined by using the difference in thermal decomposition behavior. For example, a specific test method includes the following steps:

[0036] 1) The composite additive is dried at 60°C under vacuum for 24 h to remove adsorbed water (to avoid weight loss interference near 100°C), and then a certain mass of sample is weighed, denoted as M0, and uniformly laid in an alumina crucible;

[0037] 2) The crucible is placed in a thermogravimetric analyzer, and the temperature is raised to 950°C at a rate of 5°C / min under air atmosphere, and the mass change during the whole process is recorded to obtain the thermogravimetric curve of the composite additive;

[0038] 3) The crown ether compound used alone is weighed, and the thermogravimetric curve is determined by the same method as step 2) to obtain its decomposition temperature range T CE ;

[0039] In the thermogravimetric curve of the composite additive, the mass loss of the crown ether compound in the decomposition temperature range T CE is M1, and the weight loss mass fraction W of the crown ether compound in the temperature range T CE is calculated by the following formula:

[0040]

[0041] 4) The carbon nanotube is weighed alone, and the mass is M a , and the thermogravimetric curve of the carbon nanotube is determined by the same method as step 2);

[0042] In the thermogravimetric curve of the carbon nanotube, the mass loss M b of the carbon nanotube in the decomposition temperature range T CE of the crown ether compound is recorded, and the weight loss mass fraction W' of the carbon nanotube in the temperature range T CE is calculated by the following formula:

[0043]

[0044] 5) The mass content W of the crown ether compound in the composite additive can be obtained by the following formula CE and the mass content W of the carbon nanotube CNT :

[0045]

[0046] W CNT = 1-W CE

[0047] The mass content of the carbon nanotube and the mass content of the crown ether compound in the composite additive can be obtained by the above method.

[0048] Method for preparing the composite additive

[0049] In the method for preparing the composite additive provided in the second aspect of the present application, the method comprises the following steps:

[0050] S1, performing grafting reaction on a mixture to obtain an intermediate; the mixture comprises carbon nanotubes containing amino groups and crown ether compounds containing aldehyde groups;

[0051] S2, performing reduction reaction on the intermediate under the action of a reducing agent to obtain the composite additive.

[0052] In some optional embodiments, in step S1, the ratio of the mass (g) of the carbon nanotubes containing amino groups to the molar amount (mmol) of the crown ether compounds containing aldehyde groups is 1:(2-5).

[0053] In some specific embodiments, in step S1, the ratio of the mass (g) of the carbon nanotubes containing amino groups to the molar amount (mmol) of the crown ether compounds containing aldehyde groups is 1:2, 1:3 or 1:5.

[0054] In some optional embodiments, in step S1, the mixture further comprises acetic acid; wherein the ratio of the mass (g) of the carbon nanotubes containing amino groups to the molar amount (mmol) of the acetic acid is preferably 1:(0.1-0.5).

[0055] In some specific embodiments, in step S1, the mixture further comprises acetic acid; wherein the ratio of the mass (g) of the carbon nanotubes containing amino groups to the molar amount (mmol) of the acetic acid is 1:0.25.

[0056] In some optional embodiments, in step S1, the mixture further comprises a solvent.

[0057] The solvent is optionally one or more of anhydrous ethanol, toluene, tetrahydrofuran, acetonitrile, dichloromethane, chloroform, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and ethyl acetate.

[0058] The ratio of the mass (g) of the amino-containing carbon nanotubes to the volume (mL) of the solvent is optionally 1:(100-200).

[0059] In some embodiments, the ratio of the mass (g) of the amino-containing carbon nanotubes to the volume (mL) of the solvent is 1:150.

[0060] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0061] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0062] In some embodiments, the time of the grafting reaction in step S1 is 18h.

[0063] In some embodiments, the time of the grafting reaction in step S1 is 18h.

[0064] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0065] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0066] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0067] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0068] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0069] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0070] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0071] In some embodiments, the temperature of the grafting reaction in step S1 is 70°C.

[0072] Carbon nanotubes containing amino groups

[0073] In some alternative embodiments, the carbon nanotubes containing amino groups include one or more of single-walled carbon nanotubes containing amino groups, double-walled carbon nanotubes containing amino groups, and multi-walled carbon nanotubes containing amino groups.

[0074] In the present application, the carbon nanotubes containing amino groups can be prepared by amination of carbon nanotubes using methods conventional in the art.

[0075] In some preferred embodiments, the method for preparing the carbon nanotubes containing amino groups comprises the following steps:

[0076] (1) acidizing carbon nanotubes to obtain carbon nanotubes containing carboxyl groups;

[0077] (2) aminating the carbon nanotubes containing carboxyl groups to obtain the carbon nanotubes containing amino groups.

[0078] In step (1), the acidizing treatment can optionally be performed using an acid mixture; wherein the acid mixture can optionally include nitric acid and sulfuric acid, or nitric acid and potassium permanganate.

[0079] In a specific embodiment, the acid mixture includes a nitric acid solution and a sulfuric acid solution, the volume ratio of the nitric acid solution to the sulfuric acid solution is 3:1, the mass concentration of the nitric acid solution is 68%, and the mass concentration of the sulfuric acid solution is 98%.

[0080] In step (1), the ratio of the mass (g) of the carbon nanotubes to the volume (mL) of the acid mixture can optionally be 1:(30-200).

[0081] In some specific embodiments, the ratio of the mass (g) of the carbon nanotubes to the volume (mL) of the acid mixture is, for example, 1:100.

[0082] In step (1), the temperature of the acidizing treatment can optionally be 80-110°C.

[0083] In some specific embodiments, the temperature of the acidizing treatment is, for example, 90°C.

[0084] In step (1), the time of the acidizing treatment can optionally be 8-12h.

[0085] In some specific embodiments, the time of the acidizing treatment is, for example, 10h.

[0086] In step (2), the amination treatment can optionally be performed using acyl chloride or silane coupling agent.

[0087] The silane coupling agent optionally includes one or more of γ-aminopropyl triethoxysilane, γ-ureidophenyl triethoxysilane, γ-aminopropyl trimethoxysilane, phenyl triethoxysilane, and benzyl triethoxysilane.

[0088] The ratio of the mass (g) of the carboxyl-containing carbon nanotube to the volume (mL) of the silane coupling agent is optionally 1:(20-120).

[0089] In some embodiments, the ratio of the mass (g) of the carboxyl-containing carbon nanotube to the volume (mL) of the silane coupling agent is, for example, 1:50.

[0090] In step (2), the temperature of the amination treatment is optionally 100-130°C.

[0091] In some embodiments, the temperature of the amination treatment is, for example, 120°C.

[0092] In step (2), the time of the amination treatment is optionally 6-10h.

[0093] In some embodiments, the time of the amination treatment is, for example, 9h.

[0094] Aldehyde group-containing crown ether compound

[0095] In certain optional embodiments, the aldehyde group-containing crown ether compound has a molar ratio of aldehyde group to crown ether compound of 1:1 or more.

[0096] In some embodiments, the aldehyde group-containing crown ether compound has a molar ratio of aldehyde group to crown ether compound of 1:1.

[0097] In certain optional embodiments, the aldehyde group-containing crown ether compound includes one or more of an aldehyde group-containing crown ether and an aldehyde group-containing crown ether derivative.

[0098] The aldehyde group-containing crown ether derivative is preferably one or more of an aldehyde group-containing benzo crown ether, an aldehyde group-containing azacrown ether, and an aldehyde group-containing thiacrown ether.

[0099] The aldehyde group-containing benzo crown ether is, for example, aldehyde- functionalized benzo 12-crown-4 (structural formula as shown in Formula-1'), aldehyde- functionalized benzo 15-crown-5 (structural formula as shown in Formula-2'), or aldehyde- functionalized benzo 18-crown-6 (structural formula as shown in Formula-3').

[0100]

[0101] The azacrown ether is, for example, the compound shown in Formula-4.

[0102]

[0103] wherein the thiacrown ether is, for example, a compound represented by formula I-5.

[0104]

[0105] In the present application, the aldehyde group-containing crown ether compound can be prepared by aldehyde groupification of a crown ether compound using a method conventional in the art.

[0106] In some alternative embodiments, the aldehyde group-containing crown ether compound can be prepared by Vilsmeier-Haack reaction.

[0107] In some specific embodiments, the preparation of the aldehyde group-containing crown ether compound by Vilsmeier-Haack reaction comprises the following steps:

[0108] The phosphorus oxychloride (POCl3) is added dropwise to the solution of the crown ether compound, and the reaction is carried out at a temperature of 80-95°C; after the reaction is completed, cooling, extraction and recrystallization are carried out in sequence to obtain the aldehyde group-containing crown ether compound.

[0109] In the process of dropwise addition, the temperature is optionally less than 5°C.

[0110] The reaction time is optionally 6-10h.

[0111] The solvent of the solution of the crown ether compound is optionally anhydrous DMF.

[0112] In some alternative embodiments, the aldehyde group-containing crown ether compound can be prepared by Blanc chloromethylation reaction and Duff reaction.

[0113] In some specific embodiments, the preparation of the aldehyde group-containing crown ether compound by Blanc chloromethylation reaction and Duff reaction comprises the following steps:

[0114] (1) the solution of the crown ether compound and the chloromethylation reagent are subjected to Blanc chloromethylation reaction in the presence of a first catalyst to obtain a chloromethyl-containing crown ether compound;

[0115] (2) the mixture is subjected to Duff reaction in the presence of a second catalyst, and after the Duff reaction is completed, hydrolysis reaction, extraction and purification are carried out in sequence to obtain the aldehyde group-containing crown ether compound; wherein the mixture comprises urotropine and the chloromethyl-containing crown ether compound.

[0116] The temperature of the Blanc chloromethylation reaction is 60-90°C.

[0117] wherein the chloromethylation reagent is optionally HCHO and HCl.

[0118] wherein the first catalyst is optionally ZnCl2.

[0119] wherein the time of the Blanc chloromethylation reaction is optionally 4-8 h.

[0120] wherein the Blanc chloromethylation reaction is further optionally followed by a filtration step.

[0121] wherein the temperature of the Duff reaction is 20-50 °C.

[0122] wherein the mixture is optionally further comprising ethanol.

[0123] wherein the second catalyst is optionally trifluoroacetic acid.

[0124] wherein the time of the Duff reaction is optionally 3-6 h.

[0125] wherein the Duff reaction is further optionally followed by a filtration and washing step.

[0126] wherein the hydrolysis agent of the hydrolysis reaction is optionally HCl solution.

[0127] wherein the temperature of the hydrolysis reaction is optionally 90 °C.

[0128] wherein the time of the hydrolysis reaction is optionally 2-4 h.

[0129] Silicon-based negative electrode

[0130] In the silicon-based negative electrode provided in the third aspect of the present application, it comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a silicon-based material, a binder, a conductive agent, and the composite additive as described above.

[0131] In certain optional embodiments, the silicon-based material comprises elemental silicon and / or silicon oxide. Wherein the chemical formula of the silicon oxide can be SiOx, x satisfying: 0 < x < 2.

[0132] In some specific embodiments, the chemical formula of the silicon oxide is SiO.

[0133] In certain optional embodiments, the binder comprises one or more of polyacrylic acid, lithiumated polyacrylic acid, sodium carboxymethyl cellulose, styrene butadiene rubber, polyvinyl alcohol, sodium alginate, polyvinyl amine, and polyacrylamide.

[0134] In some alternative embodiments, the mass content of the binder in the silicon-based negative electrode is 5%-15%.

[0135] In some specific embodiments, the mass content of the binder in the silicon-based negative electrode is 5%, 10% or 13%.

[0136] In some alternative embodiments, the conductive agent comprises conductive carbon black and / or graphene.

[0137] In some specific embodiments, the conductive agent is conductive carbon black.

[0138] In some alternative embodiments, the mass content of the conductive agent in the silicon-based negative electrode is 0.5%-2%.

[0139] In some specific embodiments, the mass content of the conductive agent in the silicon-based negative electrode is 2%.

[0140] In some alternative embodiments, the mass content of the silicon-based material in the silicon-based negative electrode is 75%-88%.

[0141] In some specific embodiments, the mass content of the silicon-based material in the silicon-based negative electrode is 75%, 80% or 88%.

[0142] In some alternative embodiments, the mass content of the composite additive in the silicon-based negative electrode is 0.5%-10%.

[0143] In some specific embodiments, the mass content of the composite additive in the silicon-based negative electrode is 5%, 8% or 10%.

[0144] Method for preparing a silicon-based negative electrode

[0145] The silicon-based negative electrode slurry is coated on at least one surface of the negative electrode current collector by rolling; the silicon-based negative electrode slurry comprises the silicon-based material, the binder, the conductive agent and the composite additive.

[0146] In some alternative embodiments, the solid content of the silicon-based negative electrode slurry is 47%-57%. The solid content refers to the mass percentage of the solid in the silicon-based negative electrode slurry.

[0147] In some alternative embodiments, the silicon-based negative electrode slurry can be prepared by conventional methods in the art, for example, by the following steps: the silicon-based material, the binder, the conductive agent and the composite additive are sequentially subjected to stirring, dispersion, kneading, defoaming and temperature reduction to form the silicon-based negative electrode slurry.

[0148] In some alternative embodiments, the negative current collector can be a conventional negative current collector in the art. The negative current collector serves as a substrate to support the negative material layer, and is typically a metal foil having a thickness of 3-500 μm. The material is not particularly limited as long as it has high electrical conductivity and does not chemically react in the system of the secondary battery. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative current collector is typically smooth, but can have fine lines or the like formed on its surface to improve the adhesion between the negative material layer and the negative current collector. In addition to the foil, the negative current collector can also take any one or a combination of multiple forms of a film, a mesh, a porous material, a foam, or a non-woven fabric. Generally, the negative current collector is a copper foil.

[0149] Electrochemical device

[0150] In the electrochemical device provided in the fourth aspect of the present application, the electrochemical device comprises the silicon-based negative electrode as described above.

[0151] In the present application, the electrochemical device is preferably a battery.

[0152] In an alternative embodiment, the electrochemical device is a lithium ion battery; the lithium ion battery comprises a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte, and the negative electrode sheet is the silicon-based negative electrode as described above.

[0153] Positive electrode sheet

[0154] In the present application, the positive electrode sheet can comprise a positive current collector and a positive material layer disposed on at least one surface of the positive current collector.

[0155] In the present application, the positive active material in the positive material layer can be a conventional positive active material used in the art, such as one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

[0156] In some alternative embodiments, the positive material layer further comprises a binder.

[0157] The type of the binder is not particularly limited and can be optionally selected from polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and sulfonated products thereof, styrene butadiene rubber (SBR), fluororubber, and various copolymers.

[0158] In some alternative embodiments, the positive material layer further comprises a conductive agent.

[0159] The type of conductive agent is not particularly limited; it is a reagent used to ensure that the electrode has good charge and discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as SP, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber and metal fiber; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; and conductive metal oxides or polyphenylene derivatives such as titanium dioxide.

[0160] In this invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. As a substrate supporting the positive electrode material layer, the positive electrode current collector is typically a metal foil with a thickness of 3-500 μm. There are no particular limitations on the material, as long as it has high conductivity and will not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The positive electrode current collector usually has a smooth surface, but fine textures can also be formed on its surface to improve the adhesion between the positive electrode material layer and the positive electrode current collector. Besides foil, the positive electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. Generally, the positive electrode current collector is aluminum foil.

[0161] In some embodiments, the method for preparing the positive electrode sheet includes: coating a positive electrode slurry obtained by thoroughly mixing the components of the positive electrode material layer in a solvent onto at least one surface of the positive electrode current collector, drying, and rolling to compact it, thereby obtaining the positive electrode sheet.

[0162] diaphragm

[0163] In this invention, the diaphragm can be a diaphragm conventionally used in the art.

[0164] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0165] In one specific embodiment, the diaphragm is a polyethylene film; the thickness of the diaphragm is 11 μm.

[0166] electrolyte

[0167] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries in the art, generally including non-aqueous solvents, lithium salts, and additives.

[0168] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0169] In some embodiments, the non-aqueous solvent preferably comprises ester solvents, more preferably carbonate solvents. The carbonate solvent may optionally be one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0170] In this invention, the lithium salt can be a conventional lithium salt in the art, such as LiPF6.

[0171] In this invention, the additive may be a conventional additive in the art, such as fluoroethylene carbonate (FEC).

[0172] In some embodiments, the electrolyte includes LiPF6, dimethyl carbonate (FEC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC).

[0173] The volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) is, for example, 1:1.

[0174] The concentration of LiPF6 is, for example, 1 mol / L.

[0175] The fluoroethylene carbonate (FEC) has a mass concentration of 5 wt%, which is the mass percentage of the total mass of the electrolyte.

[0176] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: mixing the various non-aqueous solvents and additives in proportion in an argon atmosphere glove box with a water content of <10ppm, and then adding a fully dried lithium salt and mixing evenly to obtain the electrolyte.

[0177] In some embodiments, the method for preparing the lithium-ion battery includes the following steps: in a high-purity argon glove box, the positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator; then an aluminum-plastic film is wrapped around the electrode, dried, and the electrolyte is injected; after encapsulation, settling, and formation processes, a soft-pack battery is finally prepared.

[0178] electronic devices

[0179] The electronic device provided in the fifth aspect of the present invention includes the electrochemical device described above.

[0180] For example, the electronic device described in this invention may be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0181] Example 1

[0182] The single-walled carbon nanotubes used in the following examples were purchased from OCSiAl, model TUBALL. TM BATT H2O and multi-walled carbon nanotubes were purchased from Aladdin Reagent, model: C313046. Schematic diagrams of the preparation processes for the composite additives in each embodiment are shown below. Figure 1 As shown.

[0183] 1. Preparation of composite additives

[0184] The preparation method of amino-containing carbon nanotubes includes the following steps:

[0185] (1) Acid treatment of single-walled carbon nanotubes was carried out using an acid mixture (temperature 90℃, time 10h) to obtain carbon nanotubes containing carboxyl groups.

[0186] The acid mixture consists of a nitric acid solution (68% by mass) and a sulfuric acid solution (98% by mass) in a volume ratio of 3:1; the ratio of the mass (g) of carbon nanotubes to the volume (mL) of the acid mixture is 1:100.

[0187] (2) The prepared carbon nanotubes containing carboxyl groups were amination treatment (at a temperature of 120°C for 9 hours) to obtain carbon nanotubes containing amino groups; wherein, the amination treatment was carried out using γ-aminopropyltriethoxysilane.

[0188] The ratio of the mass (g) of the carboxyl-containing carbon nanotubes to the volume (mL) of the silane coupling agent is 1:50.

[0189] Crown ether compounds containing aldehyde groups:

[0190] The crown ether compound containing an aldehyde group is aldehyde-modified benzo12-crown-4 (structural formula shown in Formula-1'), wherein the molar ratio of the aldehyde group to benzo12-crown-4 is 1:1.

[0191]

[0192] The preparation method of the composite additive includes the following steps:

[0193] S1. Disperse amino-containing carbon nanotubes in DMF solvent, then add crown ether compounds containing aldehyde groups, then add acetic acid to obtain a mixture; subject the mixture to a grafting reaction (temperature 70℃, time 18h) to obtain an intermediate.

[0194] The ratio of the mass (g) of amino-containing carbon nanotubes to the molar amount (mmol) of crown ether compounds containing aldehyde groups is 1:3; the ratio of the mass (g) of amino-containing carbon nanotubes to the molar amount (mmol) of acetic acid is 1:0.25; and the ratio of the mass (g) of amino-containing carbon nanotubes to the volume (mL) of solvent is 1:150.

[0195] S2. The intermediate is reduced in the presence of a reducing agent (NaBH3CN) (temperature 25℃, time 4h) to obtain a composite additive; wherein the mass ratio of the intermediate to the reducing agent is 1:0.6.

[0196] The composite additive obtained by the above preparation method includes carbon nanotubes and crown ether compounds, which are linked by CN bonds. The composite additive contains 79% carbon nanotubes and 21% crown ether compounds. The mass content of carbon nanotubes and crown ether compounds in the composite additive can be determined by thermogravimetric analysis (TGA).

[0197] 2. Preparation of silicon-based anodes

[0198] A silicon-based anode paste with a solid content of 47%-57% is coated onto one surface of the anode current collector and rolled. The effect of the solid content of 47%-57% on the final result is negligible. The coating and rolling process parameters are conventional process parameters in the field. The silicon-based anode paste includes silicon-based material (elemental silicon), binder (PAA), conductive agent (conductive carbon black), and composite additives prepared as above.

[0199] The silicon-based anode contains 80% silicon-based material by mass, 8% composite additives by mass, 10% binder by mass, and 2% conductive agent by mass.

[0200] The silicon-based anode was prepared using the above method.

[0201] Some of the process parameters for the preparation process are listed in Table 1.

[0202] Example 2-17

[0203] The different parameters in the preparation process of Examples 2-17 compared to Example 1 are listed in Table 1, while the other conditions are the same as in Example 1.

[0204] The structural formula of the aldehyde-modified benzo15-crown-5 in Example 6 is as follows:

[0205]

[0206] The structural formula of benzo-18-crown-6 in Example 11 is as follows:

[0207]

[0208]

[0209] The structural formula of the azacrown ether in Example 12 is as follows:

[0210]

[0211] The structural formula of the thiocrown ether in Example 13 is as follows:

[0212]

[0213] Among them, the multi-walled carbon nanotubes of Example 15.

[0214] Comparative Examples 1-3

[0215] The parameters of the preparation processes of Comparative Examples 1-3 that differ from those of Example 1 are listed in Table 1, while the other conditions are the same as those of Example 1.

[0216] Comparative Example 1 does not contain any compound additives;

[0217] In Comparative Example 2, untreated single-walled carbon nanotubes from Example 1 were used to replace the composite additives in Example 1.

[0218] In Comparative Example 3, the same relative amounts of carbon nanotubes and crown ether compounds were simply physically mixed to replace the composite additives in Example 1.

[0219] Table 1

[0220]

[0221]

[0222]

[0223] Example 1

[0224] The mass content of crown ether compounds and carbon nanotubes in the composite additives obtained in each example and comparative example was determined by thermogravimetric analysis (TGA, Mettler Toledo TGA / DSC 3+, Switzerland). The test methods are as follows:

[0225] 1) The composite additive was vacuum dried at 60℃ for 24h to remove adsorbed water (to avoid interference from weight loss near 100℃). Then, a certain mass of sample was weighed and recorded as M0, and evenly spread in an alumina crucible.

[0226] 2) Place the crucible in a thermogravimetric analyzer and heat it to 950°C at a rate of 5°C / min in an air atmosphere. Record the mass change throughout the process to obtain the thermogravimetric curve of the composite additive.

[0227] 3) Weigh out the crown ether compound used separately and determine its thermogravimetric curve using the same method as in step 2) to obtain its decomposition temperature range T. CE ;

[0228] In the thermogravimetric curve of the composite additive, record the decomposition temperature range T of the crown ether compound. CE The mass loss is M1. The following formula is used to calculate the mass loss of crown ether compounds at T. CE Weight loss fraction W in the temperature range:

[0229]

[0230] 4) Weigh out the carbon nanotubes separately; the mass is M. a The thermogravimetric curves of carbon nanotubes were determined using the same method as in step 2).

[0231] The thermogravimetric analysis (TGA) curves of carbon nanotubes were used to record the decomposition temperature range T of crown ether compounds. CE mass loss M b The following formula is used to calculate the T value of carbon nanotubes. CE Weight loss fraction W' in the temperature range:

[0232]

[0233] 5) The mass content W of crown ether compounds in the composite additive can be obtained using the following formula. CE And the mass content of carbon nanotubes W CNT :

[0234]

[0235] W CNT =1-W CE

[0236] The test results are shown in Table 1.

[0237] Example 2

[0238] Lithium-ion battery assembly:

[0239] The silicon-based negative electrode obtained in the examples and comparative examples is the negative electrode, the lithium sheet is the counter electrode, the polyethylene film (11 μm thick) is the separator, the electrolyte is an EC / DMC (1:1) solution containing 1 mol / L LiPF6 and 5 wt% FEC additive, and it is packaged into a lithium-ion battery (CR2032 type) in a high-purity argon glove box.

[0240] The lithium-ion battery assembled as described above was subjected to the following tests:

[0241] 1. Initial coulombic efficiency test: A complete charge-discharge cycle was performed at 25℃ with a current density of 0.1A / g. The charging cutoff voltage was 1.5V and the discharging cutoff voltage was 0.01V. The first discharge capacity (before activation) and the first charge capacity (before activation) were recorded.

[0242] Initial coulombic efficiency = initial discharge capacity (before activation) / initial charge capacity (before activation) × 100%.

[0243] 2. Capacity retention after 500 cycles:

[0244] At room temperature of 25°C, within the test voltage range of 0.01V (discharge cutoff voltage) to 1.5V (charge cutoff voltage), the system was first activated for 3 cycles at a current density of 0.05A / g; then, it was charged and discharged at a current density of 0.5A / g, and the capacity retention rate was tested after 500 cycles.

[0245] Capacity retention rate after 500 cycles = discharge capacity after 500 cycles / initial discharge capacity (after activation) × 100%.

[0246] The test results are listed in Table 2.

[0247] Table 2

[0248] Initial coulombic efficiency Capacity retention after 500 cycles Example 1 89.5％ 81.4％ Example 2 85.2％ 78.3％ Example 3 89.9％ 82.5％ Example 4 83.7％ 76.0％ Example 5 90.0％ 82.3％ Example 6 88.6％ 80.2％ Example 7 90.7％ 84.7％ Example 8 90.0％ 82.8％ Example 9 84.8％ 79.7％ Example 10 91.0％ 88.6％ Example 11 87.5％ 80.0％ Example 12 90.2％ 81.9％ Example 13 90.5％ 82.4％ Example 14 88.3％ 82.0％ Example 15 87.9％ 82.5％ Example 16 89.0％ 80.7％ Example 17 89.8％ 81.5％ Comparative Example 1 65.40％ ＜50％ Comparative Example 2 78.30％ 67.50％ Comparative Example 3 84.20％ 70.60％

[0249] As shown in Table 2, when the composite additive provided in the examples is applied to the fabrication of batteries using silicon-based anodes, it enables the battery to achieve an initial coulombic efficiency of over 83.7% and a capacity retention of over 76% after 500 cycles, indicating excellent electrical performance. This is likely because the composite additive provided in the examples effectively immobilizes the crown ether and carbon nanotubes through a Schiff base condensation-reduction reaction, and the crown ether and lithium ions form a crown ether-Li bond under electrostatic interaction. + The complex subsequently releases / captures Li during charge and discharge. + Reduce Li +The crown ether cavity prevents solvent molecules from contacting the silicon surface and inhibits electrolyte reduction and decomposition, thereby improving coulombic efficiency. Secondly, the crown ether complex can effectively reduce lithium-ion transport impedance, and when combined with the three-dimensional conductive framework formed by CNTs, it can achieve synergistic effect between selective lithium-ion transport and conductive network. Finally, the flexible macrocyclic structure of the crown ether buffers the volume change of silicon particles through the stretching and contraction of the molecular chain.

[0250] According to the results of Examples 1-3, the initial coulombic efficiency and capacity retention after 500 cycles of the silicon-based anode with the same amount of composite additives vary with the ratio of the mass of the carboxyl-containing carbon nanotubes to the volume of the silane coupling agent. When the volume of the silane coupling agent increases, the initial coulombic efficiency and capacity retention after 500 cycles increase accordingly. This may be because the increase of the silane coupling agent increases the amylation groups of the carbon nanotubes, thereby increasing the active sites grafted with crown ethers.

[0251] Based on the results of Examples 1 and 4-5, it can be seen that the amount of crown ether compounds containing aldehyde groups added affects the final electrical properties, which may be because it affects the grafting rate of crown ether compounds containing aldehyde groups to carbon nanotubes.

[0252] Based on the results of Examples 1, 6, and 11-13, it can be seen that composite additives obtained from different crown ether types affect the electrochemical performance of silicon-based anodes; selecting nitrogen crown ethers and thio crown ethers can further improve the initial coulombic efficiency and capacity retention after 500 cycles.

[0253] Based on the results of Examples 1 and 7, it can be seen that Example 7, which uses lithium-ionized polyacrylic acid (PAA-Li), can further improve the initial coulombic efficiency and the capacity retention rate after 500 cycles. This may be because the lithium ions of PAA-Li can compensate for the irreversible lithium loss during the first charge and discharge, further improving the initial coulombic efficiency and the capacity retention rate after 500 cycles. This shows that the combination of pre-lithiated binder and composite additives may bring unexpected effects.

[0254] Based on the results of Examples and Comparative Examples 1-2, it is evident that if no composite additive is used or only untreated CNTs are used to replace the composite additive, the initial coulombic efficiency and capacity retention after 500 cycles will be significantly reduced. Based on the results of Examples and Comparative Example 3, it is evident that if carbon nanotubes and crown ethers are simply physically mixed without grafting, although a certain initial coulombic efficiency can be guaranteed, the capacity retention after 500 cycles will be significantly reduced. This may be because without grafting, carbon nanotubes and crown ether compounds cannot be connected through CN bonds, causing the crown ethers to easily dissolve in the electrolyte and fail to play a better role, thus affecting their electrical performance.

[0255] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A complex additive characterized in that, It comprises carbon nanotubes and crown ether compounds, and the carbon nanotubes and the crown ether compounds are connected by C-N bonds.

2. The composite additive of claim 1, wherein It meets one or more of the following conditions: (a) the crown ether compounds comprise one or more of crown ethers and crown ether derivatives; (b) the carbon nanotubes comprise one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; (c) the mass content of the carbon nanotubes in the composite additive is 65%-90%; (d) the mass content of the crown ether compounds in the composite additive is 10%-35%.

3. The composite additive of claim 2, wherein The crown ether derivatives are one or more of benzocrown ethers, azacrown ethers, and thiacrown ethers.

4. A method of preparing a composite additive as claimed in any one of claims 1 to 3, characterised in that, It comprises the following steps: S1, grafting reaction of a mixture to obtain an intermediate; the mixture comprises carbon nanotubes containing amino groups and crown ether compounds containing aldehyde groups; S2, reduction reaction of the intermediate under the action of a reducing agent to obtain the composite additive.

5. The method of claim 4, wherein the composite additive is prepared by mixing the above-mentioned components in a weight ratio of 1 : 1 : 1 to 1 : 2 :

1. It meets one or more of the following conditions: (a) in step S1, the ratio of the mass (g) of the carbon nanotubes containing amino groups to the molar amount (mmol) of the crown ether compounds containing aldehyde groups is 1:(2-5); (b) in step S1, the mixture further comprises acetic acid; wherein the ratio of the mass (g) of the carbon nanotubes containing amino groups to the molar amount (mmol) of the acetic acid is 1:(0.1-0.5); (c) in step S1, the mixture further comprises a solvent; (d) in step S1, the temperature of the grafting reaction is 60-80°C; (e) in step S1, the time of the grafting reaction is 12-24h; (f) in step S2, the reducing agent comprises one or more of NaBH4, NaBH3CN, and NaBH(OAc)3; (g) in step S2, the mass ratio of the intermediate to the reducing agent is 1:(0.3-1.5); (h) in step S2, the temperature of the reduction reaction is 20-30°C; (i) in step S2, the time of the reduction reaction is 2-6h; (j) in the crown ether compounds containing aldehyde groups, the molar ratio of aldehyde groups to crown ether compounds is 1:1 or more.

6. The method of claim 4, wherein the composite additive is prepared by mixing the above-mentioned components in a weight ratio of 1 : 1 : 1 to 1 : 2 :

1. The preparation method of the carbon nanotubes containing amino groups comprises the following steps: (1) acidizing treatment of carbon nanotubes to obtain carbon nanotubes containing carboxyl groups; (2) amination treatment of the carbon nanotubes containing carboxyl groups to obtain the carbon nanotubes containing amino groups.

7. A silicon-based negative electrode, characterized by, It comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, and the negative electrode material layer comprises a silicon-based material, a binder, a conductive agent, and a composite additive as claimed in any one of claims 1-3.

8. The silicon-based anode of claim 7, wherein, It meets one or more of the following conditions: (a) the silicon-based material comprises elemental silicon and / or silicon oxide; (b) the binder comprises one or more of polyacrylic acid, lithiumated polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, sodium alginate, polyvinylamine, and polyacrylamide; (c) the conductive agent comprises conductive carbon black and / or graphene; (d) the mass content of the silicon-based material in the silicon-based negative electrode is 75%-88%; (f) the mass content of the composite additive in the silicon-based negative electrode is 0.5%-10%.

9. An electrochemical device, characterized by, The electrochemical device comprises the silicon-based negative electrode as claimed in claim 7 or 8.

10. An electronic device, comprising: The electronic device comprises the electrochemical device as claimed in claim 9.

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