CN111129436B

CN111129436B - Negative electrode and method for producing same

Info

Publication number: CN111129436B
Application number: CN201911358618.4A
Authority: CN
Inventors: 王可飞
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2019-12-25
Filing date: 2019-12-25
Publication date: 2022-11-04
Anticipated expiration: 2039-12-25
Also published as: CN111129436A

Abstract

The application relates to a negative electrode and a preparation method thereof. Specifically, the present application provides a method of producing an anode, which includes a step of adding an auxiliary having Si-C and Si-O bonds. The method for preparing the cathode can reduce the defects on the surface of the cathode and produce the cathode with high quality.

Description

Negative electrode and method for producing same

Technical Field

The application relates to the field of energy storage, in particular to a negative electrode and a preparation method thereof.

Background

As technology develops and the demand for mobile devices increases, the demand for electrochemical devices (e.g., lithium ion batteries) has increased significantly. An electrochemical device having high safety and excellent life is one of research directions.

In the preparation process of a negative electrode of an electrochemical device, a negative electrode active material, a dispersant, a binder, a conductive agent, and the like are dissolved in a solvent to form a negative electrode slurry. However, it is generally difficult to uniformly disperse the anode active material, the dispersant, the binder, the conductive agent, and the like, thereby causing the surface tension of the anode slurry to be non-uniform. The difference in surface tension may cause a shrinkage cavity, a pit or a shrink edge phenomenon, which has an adverse effect on the apparent performance of the negative electrode and the performance of the electrochemical device, affecting the safety and yield of the product, and further increasing the production cost.

In view of the above, it is necessary to provide an improved negative electrode and a method for preparing the same.

Disclosure of Invention

Embodiments of the present application address at least one of the problems presented in the related art to at least some extent by providing an anode and a method of preparing the same.

In one aspect of the present application, there is provided a method of manufacturing an anode including the step of adding an assistant having Si-C and Si-O bonds.

According to some embodiments of the application, the adjuvant having Si-C and Si-O bonds is mixed with a solvent.

According to some embodiments of the present application, the auxiliary agent having Si-C and Si-O bonds is added after the binder is added.

According to some embodiments of the application, the method comprises the steps of:

s1: a material mixing step, wherein a negative electrode active material, a dispersing agent, a binder, a solvent and the auxiliary agent with Si-C and Si-O bonds are uniformly mixed to obtain negative electrode slurry;

s2: coating, namely coating the negative electrode slurry prepared in the step S1 on a negative electrode current collector at a coating speed of 10-100 m/min to obtain an initial pole piece;

s3: and a drying step, namely placing the initial pole piece obtained in the step S2 in vacuum drying equipment for drying, wherein the drying temperature is 80-150 ℃, and the negative electrode is obtained.

According to some embodiments of the application, the auxiliary agent having Si-C and Si-O bonds has at least one of the following characteristics:

(a) The oxidation potential is not less than 4.5V, and the reduction potential is not more than 0.5V; and

(b) The surface tension of an aqueous solution containing 0.1% of the assistant having Si-C and Si-O bonds is not more than 30mN/m.

According to some embodiments of the present application, the coagent having Si-C and Si-O bonds includes a polyether siloxane.

According to some embodiments of the present application, the co-agent having Si-C and Si-O bonds comprises at least one of a complex silicone polyether complex, a polyether modified trisiloxane, or a polyether modified silicone polyether siloxane.

According to some embodiments of the present application, the negative active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon oxygen, silicon carbon, a silicon alloy, or a tin alloy.

According to some embodiments of the present application, the solvent is deionized water or N-methylpyrrolidone.

According to some embodiments of the application, the vibration treatment is performed simultaneously in any of the steps S1, S2 or S3, the vibration treatment being at least one of mechanical vibration or ultrasonic vibration.

According to some embodiments of the present application, any step of S1, S2 or S3 is followed by a vibration treatment, the vibration treatment being at least one of mechanical vibration or ultrasonic vibration.

According to some embodiments of the present application, the vibration process has a vibration frequency of 100Hz to 800Hz, an amplitude of 0.01 mm to 0.5 mm, and a vibration time of 1 minute to 5 minutes.

According to some embodiments of the application, the vibration treatment is performed a plurality of times, and a vibration frequency of at least one of the vibration treatments is lower than a vibration frequency of a previous vibration treatment.

In another aspect of the present application, there is provided an anode obtained by the method of preparing an anode according to the present application.

According to some embodiments of the present application, the content of the auxiliary having Si-C and Si-O bonds in the anode is 500ppm or less, preferably 300ppm or less.

According to some embodiments of the present application, a contact angle of a surface of the anode with respect to diethyl carbonate is reduced by 10% or more, compared to an anode prepared without adding an auxiliary agent having Si-C and Si-O bonds.

In another aspect of the present application, there is provided an electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the negative electrode is obtained according to the method of preparing a negative electrode of the present application or the negative electrode is the negative electrode of the present application.

In another aspect of the present application, the present application provides an electronic device comprising an electrochemical device according to the present application.

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the drawings can be obtained from the structures illustrated in these drawings without the need for inventive work.

Fig. 1 shows a surface appearance of the negative electrode of comparative example 1.

Fig. 2 shows a surface appearance of the negative electrode of example 2.

Detailed Description

Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

In the detailed description and claims, a list of items linked by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items a, B, and C are listed, the phrase "at least one of a, B, and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or all of A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements. At least one of the terms has the same meaning as at least one of the terms.

In the preparation process of the negative electrode, a negative electrode active material, a dispersant, a binder, a conductive agent and the like are generally dissolved in a solvent to form a negative electrode slurry, and then the negative electrode slurry is coated on a negative electrode current collector and dried to form the negative electrode. Since the negative electrode active material has poor compatibility with a solvent, it is generally difficult for the dispersant to sufficiently function, and it is often difficult for the negative electrode active material, the dispersant, the binder, the conductive agent, and the like to be uniformly dispersed in the solvent, so that the negative electrode slurry is not uniform enough. Non-uniform anode slurry can cause non-uniform surface tension. The difference in surface tension may cause a shrinkage cavity, a pit, or a beading phenomenon (as shown in fig. 1), which may adversely affect the apparent performance of the negative electrode and the performance of the electrochemical device, affect the safety and yield of the product, and thus increase the production cost.

The preparation method improves the compatibility between the negative active material and the solvent, further improves the surface tension of the negative slurry, and reduces the phenomena of shrinkage cavity, pit or edge shrinkage on the surface of the negative electrode (as shown in figure 2), thereby improving the quality of the negative electrode and improving the performance of the electrochemical device.

1. Method for preparing negative electrode

In one embodiment, the present application provides a method of preparing an anode including the step of adding an assistant having Si-C and Si-O bonds.

s1: mixing step

In the step, a negative electrode active material, a dispersant, a binder, a solvent and the auxiliary agent having Si-C and Si-O bonds are uniformly mixed to obtain a negative electrode slurry.

According to some embodiments of the present application, the dispersant comprises at least one of carboxymethyl cellulose, carboxymethyl cellulose derivatives, alginic acid derivatives, polyacrylic acid derivatives, polyamic acid derivatives, polyvinyl alcohol derivatives, starch derivatives, hydroxypropyl cellulose, or hydroxypropyl cellulose derivatives.

According to some embodiments of the present application, the binder comprises at least one of styrene-butadiene rubber, polyacrylate, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, hexafluoropropylene-tetrafluoroethylene copolymer, or vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer.

(c) The oxidation potential is not less than 4.5V, and the reduction potential is not more than 0.5V; and

(d) The surface tension of an aqueous solution containing 0.1% of the auxiliary having Si-C and Si-O bonds is not more than 30mN/m.

In some embodiments, the adjuvant having Si-C and Si-O bonds has an oxidation potential of not less than 4.5V and a reduction potential of not more than 0.5V. In some embodiments, the adjuvant having Si-C and Si-O bonds has an oxidation potential of not less than 5V and a reduction potential of not more than 0.3V. The auxiliary having the above oxidation/reduction potential is stable in electrochemical properties, and contributes to improvement of cycle and high-temperature storage properties of an electrochemical device.

In some embodiments, an aqueous solution containing 0.1wt% of the adjuvant having Si-C and Si-O bonds has a surface tension of not more than 30mN/m. In some embodiments, an aqueous solution containing 0.1wt% of the aid having Si-C and Si-O bonds has a surface tension of not more than 25mN/m. In some embodiments, an aqueous solution containing 0.1wt% of the adjuvant having Si-C and Si-O bonds has a surface tension of not more than 20mN/m. In some embodiments, an aqueous solution containing 0.1wt% of the adjuvant having Si-C and Si-O bonds has a surface tension of not more than 15mN/m. In some embodiments, an aqueous solution containing 0.1wt% of the adjuvant having Si-C and Si-O bonds has a surface tension of not more than 10mN/m. When the surface tension of the aqueous solution containing the auxiliary agent having Si — C and Si — O bonds is within the above range, the interface of the negative electrode mixture layer is good.

The surface tension of the aqueous solution containing the assistant having Si-C and Si-O bonds can be measured by the following method: and (3) testing the auxiliary agent aqueous solution with the solid content of 0.1% by using a JC2000D3E type contact angle measuring instrument, testing each sample at least 3 times, selecting at least 3 data, and averaging to obtain the surface tension of the auxiliary agent-containing aqueous solution.

According to some embodiments of the present application, the additive having Si-C and Si-O bonds is added in an amount of 3000ppm or less. In some embodiments, the coagent having Si-C and Si-O bonds is added in an amount of 2500ppm or less. In some embodiments, the coagent having Si-C and Si-O bonds is added in an amount of 2000ppm or less. In some embodiments, the addition amount of the auxiliary having Si-C and Si-O bonds is 1500ppm or less. In some embodiments, the addition amount of the auxiliary having Si-C and Si-O bonds is 1000ppm or less. In some embodiments, the coagent having Si-C and Si-O bonds is added in an amount of 500ppm or less. When the addition amount of the auxiliary agent having Si-C and Si-O bonds is within the above range, the surface tension of the anode slurry can be effectively reduced.

The proportions of the anode active material, the dispersant, the binder, the solvent and the auxiliary having Si — C and Si — O bonds added in this step are not particularly limited as long as they are known to be employable in the preparation process of the anode slurry.

S2: coating step

In this step, the negative electrode slurry prepared in S1 is coated on a negative electrode current collector at a coating speed of 10 m/min to 100 m/min, to obtain an initial pole piece.

S3: drying step

In the step, the initial pole piece obtained in the step S2 is placed in vacuum drying equipment for drying, and the drying temperature is 80-150 ℃, so that the negative electrode is obtained.

According to some embodiments of the application, the vibration treatment is performed simultaneously in any of the steps S1, S2 or S3, the vibration treatment being at least one of mechanical vibration or ultrasonic vibration. According to some embodiments of the application, any of the steps S1, S2 or S3 is followed by a vibration treatment, the vibration treatment being at least one of a mechanical vibration or an ultrasonic vibration. The vibration treatment can effectively prevent the anode slurry from being non-uniform due to the density difference.

2. Negative electrode

In another embodiment, the present application provides an anode obtained by a method of making an anode according to the present application.

According to some embodiments of the present application, a content of the auxiliary having Si — C and Si — O bonds in the anode is 500ppm or less. In some embodiments, the content of the auxiliary having Si — C and Si — O bonds in the anode is 400ppm or less. In some embodiments, the content of the assistant having Si — C and Si — O bonds in the anode is 300ppm or less. In some embodiments, the content of the assistant having Si — C and Si — O bonds in the anode is 200ppm or less.

According to some embodiments of the present application, a contact angle of a surface of the negative electrode with respect to diethyl carbonate is reduced by 10% or more, compared to a negative electrode (contact angle greater than 70 °) prepared without adding an auxiliary having Si-C and Si-O bonds.

The contact angle refers to a contact angle measured within 10 seconds after a droplet of diethyl carbonate was dropped on the negative electrode mixture layer. Diethyl carbonate is a commonly used electrolyte solvent. The wettability of the electrolyte into the negative electrode mixture layer can be checked by using diethyl carbonate as a test index of the contact angle. The smaller contact angle of the surface of the negative electrode with respect to diethyl carbonate indicates that the impregnation of the electrolyte into the negative electrode mixture layer is improved and the liquid holding property of the negative electrode mixture layer is enhanced.

The contact angle can be measured by an automatic contact angle meter or the like prepared by Kyowa Interface Science co. The contact angle θ can be determined by, for example, θ/2 method, that is, in the case where the angle between the droplet base line and the line exceeding the droplet apex is defined as θ ', the contact angle θ =2 θ' holds. From this, the contact angle θ can be calculated by measuring θ' using the distance 2r from the baseline of the droplet and the height h of the droplet. At this time, it is necessary to drop the droplets in such an amount as not to be affected by gravity. The non-aqueous solvent used in the contact angle test may be selected from common electrolyte solvents such as diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl propyl carbonate or methyl isopropyl carbonate.

According to some embodiments of the present application, a contact angle of the anode active material layer with respect to a nonaqueous solvent is not more than 60 °. In some embodiments, the contact angle of the anode active material layer with respect to a nonaqueous solvent is not more than 50 ° as measured by a contact angle measuring method. In some embodiments, the contact angle of the anode active material layer with respect to a nonaqueous solvent is not more than 30 ° as measured by a contact angle measuring method. When the negative electrode active material layer has the contact angle with respect to the nonaqueous solvent as described above, the negative electrode active material layer has less defects at the interface, and is excellent in stability during charge and discharge cycles of the electrochemical device, and can ensure the cycle performance of the electrochemical device.

3. Positive electrode

The positive electrode, the separator, and the electrolyte are not particularly limited as long as the positive electrode, the separator, and the electrolyte are known to be useful for electrochemical devices (e.g., lithium ion batteries).

The positive electrode that can be used in the embodiments of the present application includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The kind of the positive electrode active material is not particularly limited as long as it is a known positive electrode active material that can be used in an electrochemical device (e.g., a lithium ion battery), such as a lithium-containing compound, which can provide a high energy density to the electrochemical device. The lithium-containing compound includes one or more of a lithium transition metal composite oxide and a lithium transition metal phosphate compound. The lithium transition metal composite oxide includes lithium and an oxide having one or more transition metal elements. The lithium transition metal phosphate compound is a phosphate compound comprising lithium and one or more transition metal elements. The transition metal element includes one or more of Co, ni, mn, and Fe, which can allow the electrochemical device to obtain higher voltage. The lithium-containing compound has the chemical formula LixM1O ₂ Or LiyM2PO ₄ Wherein M1 and M2 represent one or more transition metal elements, and the values of x and y are dependent on charge/dischargeThe state, and typically in the following ranges: x is more than or equal to 0.05 and less than or equal to 1.10, and y is more than or equal to 0.05 and less than or equal to 1.10. In some embodiments, the lithium transition metal composite oxide includes, but is not limited to, liCoO ₂ 、LiNiO ₂ And from the formula LiNi _1- _z MzO ₂ The lithium-nickel-based transition metal composite oxide represented by (1), wherein M is one or more selected from the group consisting of Co, mn, fe, al, V, sn, mg, ti, sr, ca, zr, mo, tc, ru, ta, W, re, yb, cu, zn, ba, B, cr, si, ga, P, sb and Nb, and z satisfies 0.005<z<0.5. In some embodiments, the lithium transition metal phosphate compound includes, but is not limited to, liFePO ₄ And from the formula LiFe _1-u Mn _u PO ₄ A compound of formula (I) wherein u<1. By using these compounds as an active material for a positive electrode, an electrochemical device having a high battery capacity and excellent cycle characteristics can be obtained.

4. Electrolyte solution

The kind of the electrolyte is not particularly limited as long as it is known to be useful for electrochemical devices (e.g., lithium ion batteries).

The electrolyte comprises any non-aqueous solvent known in the art that can act as a solvent for the electrolyte. The non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, cyclic ether, chain ether, phosphorus-containing organic solvent, sulfur-containing organic solvent, and aromatic fluorine-containing solvent.

Examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene Carbonate (EC), propylene Carbonate (PC) and butylene carbonate. In some embodiments, the cyclic carbonate has 3 to 6 carbon atoms.

Examples of the chain carbonate may include, but are not limited to, one or more of the following: and chain carbonates such as dimethyl carbonate, methylethyl carbonate, diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate. Examples of chain carbonates substituted with fluorine may include, but are not limited to, one or more of the following: bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, bis (2-fluoroethyl) carbonate, bis (2, 2-difluoroethyl) carbonate, bis (2, 2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2-difluoroethyl methyl carbonate, and 2, 2-trifluoroethyl methyl carbonate, and the like.

Examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: one or more of gamma-butyrolactone and gamma-valerolactone. In some embodiments, a portion of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

Examples of the chain carboxylic acid ester may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate, and the like. In some embodiments, a part of hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of the fluorine-substituted chain carboxylic acid ester may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, 2-trifluoroethyl trifluoroacetate, and the like.

Examples of the cyclic ether may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 2-methyl-1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 3-dioxane, 1, 4-dioxane and dimethoxypropane.

Examples of the chain ether may include, but are not limited to, one or more of the following: dimethoxymethane, 1-dimethoxyethane, 1, 2-dimethoxyethane, diethoxymethane, 1-diethoxyethane, 1, 2-diethoxyethane, ethoxymethoxymethane, 1-ethoxymethoxyethane, 1, 2-ethoxymethoxyethane, and the like.

Examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, methyldiethyl phosphate, ethylenemethyl phosphate, ethyleneethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphate, tris (2, 2-trifluoroethyl) phosphate, and tris (2, 3-pentafluoropropyl) phosphate, and the like.

Examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, ethylmethylsulfone, methylpropylsulfone, dimethylsulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, a portion of the hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

The aromatic fluorine-containing solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene and trifluoromethylbenzene.

In some embodiments, the solvent used in the electrolyte of the present application includes at least one of a cyclic carbonate, a chain carbonate, a cyclic carboxylic ester, or a chain carboxylic ester. In some embodiments, the solvent used in the electrolyte of the present application comprises at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, or ethyl acetate. In some embodiments, the solvent used in the electrolyte of the present application includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, or γ -butyrolactone.

Electrolytes that may be used in the electrolytes of embodiments of the present application include, but are not limited to: inorganic lithium salts, e.g. LiClO ₄ 、LiAsF ₆ 、LiPF ₆ 、LiBF ₄ 、LiSbF ₆ 、LiSO ₃ F、LiN(FSO ₂ ) ₂ Etc.; organic lithium salts containing fluorine, e.g. LiCF ₃ SO ₃ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Ring 1, 3-hexaLithium fluoropropane disulfonimide, lithium cyclic 1, 2-tetrafluoroethane disulfonimide, liN (CF) ₃ SO ₂ )(C ₄ F ₉ SO ₂ )、LiC(CF ₃ SO ₂ ) ₃ 、LiPF ₄ (CF ₃ ) ₂ 、LiPF ₄ (C ₂ F ₅ ) ₂ 、LiPF ₄ (CF ₃ SO ₂ ) ₂ 、LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ 、LiBF ₂ (CF ₃ ) ₂ 、LiBF ₂ (C ₂ F ₅ ) ₂ 、LiBF ₂ (CF ₃ SO ₂ ) ₂ 、LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ (ii) a The dicarboxylic acid complex-containing lithium salt may, for example, be lithium bis (oxalato) borate, lithium difluorooxalato borate, lithium tris (oxalato) phosphate, lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, or the like. The electrolyte may be used alone or in combination of two or more. For example, in some embodiments, the electrolyte comprises LiPF ₆ And LiBF ₄ A combination of (a) and (b). In some embodiments, the electrolyte comprises LiPF ₆ Or LiBF ₄ An inorganic lithium salt and LiCF ₃ SO ₃ 、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ And the like, a combination of fluorine-containing organic lithium salts. In some embodiments, the concentration of the electrolyte is in the range of 0.8 to 3mol/L, such as in the range of 0.8 to 2.5mol/L, in the range of 0.8 to 2mol/L, in the range of 1 to 2mol/L, again such as 1mol/L, 1.15mol/L, 1.2mol/L, 1.5mol/L, 2mol/L, or 2.5mol/L.

5. Isolation film

The kind of the separator is not particularly limited as long as it is a known separator that can be used in an electrochemical device (e.g., a lithium ion battery).

The separator that can be used in the embodiments of the present application includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application, and the like. For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

The inorganic layer comprises inorganic particles and a binder, and the inorganic particles comprise one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder comprises one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.

The polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

6. Electrochemical device

The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device of the present application includes a positive electrode sheet having a positive active material capable of occluding and releasing metal ions; a negative electrode sheet according to an embodiment of the present application; an electrolyte; and a separator disposed between the positive electrode tab and the negative electrode tab.

7. Electronic device with a detachable cover

The use of the electrochemical device of the present application is not particularly limited, and it may be used for any electronic device known in the art. In one embodiment, the electrochemical device of the present application can be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game machines, clocks, power tools, flashlights, cameras, household large batteries, lithium ion capacitors, and the like.

Taking a lithium ion battery as an example and describing the preparation of the lithium ion battery with reference to specific examples, those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

Examples

Embodiments of the present application will be described more specifically below with reference to examples and comparative examples. However, the embodiments of the present application are not limited to only these examples.

1. Preparation of lithium ion battery

1. Preparation of the negative electrode

S1: mixing step

Mixing artificial graphite, styrene butadiene rubber and carboxymethyl cellulose with deionized water according to the mass ratio of 96% to 3% to 1%, wherein the adding sequence is as follows:

1. artificial graphite and carboxymethyl cellulose

2. Deionized water

3. Carboxymethyl cellulose

4. Styrene butadiene rubber

2000ppm of an auxiliary having Si-C and Si-O bonds was added according to the following examples, and a comparative example was made without an auxiliary or with 2000ppm of an auxiliary having no Si-C and Si-O bonds. The auxiliaries having Si-C and Si-O bonds used in the examples of the present application are shown in the following table:

auxiliary agent	Name (trade name)
		Auxiliary agent 1	Trisiloxane surfactant (CAS No.3390-61-2
Auxiliary agent 2	Silicone surfactants (Sylgard 309)
		Auxiliary 3	Dihydroxy polydimethylsiloxane (PMX-0156)
Auxiliary agent 4	N-beta-aminoethyl-Y-aminopropyldimethoxymethylsilane (KH-602)
		Auxiliary 5	Polydimethylsiloxane methyl silicone oil (CAS No. 63148-62-9)

And uniformly mixing the components to obtain the cathode slurry.

S2: coating step

And (3) coating the negative electrode slurry prepared in the step (S1) on a copper foil with the thickness of 12 microns at the coating speed of 10-100 m/min to obtain an initial pole piece.

S3: drying step

And (3) drying the initial pole piece obtained in the step (S2) in vacuum drying equipment at the drying temperature of 80-150 ℃ to obtain the negative pole.

2. Preparation of the Positive electrode

Mixing lithium cobaltate (LiCoO) ₂ ) Mixing the conductive material (Super-P) and polyvinylidene fluoride (PVDF) with N-methyl pyrrolidone (NMP) according to the mass ratio of 95% to 2% to 3%, and uniformly stirring to obtain the anode slurry. And coating the anode slurry on an aluminum foil with the thickness of 12 mu m, drying, cold pressing, cutting into pieces, and welding a tab to obtain the anode.

3. Preparation of the electrolyte

EC, PC and DEC (1 in weight ratio 1 ₆ Mixing uniformly to obtain electrolyte, wherein LiPF ₆ The concentration of (2) is 1.15mol/L.

4. Preparation of the separator

Polyethylene (PE) porous polymer film is used as a separation film.

5. Preparation of lithium ion battery

The obtained positive electrode, separator and negative electrode were wound in order and placed in an outer packaging foil, leaving a liquid inlet. And (4) pouring electrolyte from the electrolyte injection port, packaging, and performing formation, capacity and other processes to obtain the lithium ion battery.

2. Method for testing surface defects of negative electrode of lithium ion battery

Scanning and shooting the cold-pressed pole piece by using a CCD scanner, and identifying the defect by using the gray difference of different positions to obtain a picture with the thickness of 0.2mm ² And (5) judging the defects of the pole piece when the area and the gray difference are larger than 10, and counting the number of the defects.

3. Test results

Table 1 shows the effect of the adjuvants and their order of addition on the negative electrode surface defects of lithium ion batteries.

TABLE 1

	Auxiliary agent and adding sequence thereof	Number of negative electrode surface defects/10 m ²
			Comparative example 1	Without addition of auxiliary agents	20
Example 1	Mixing auxiliary 1 with carboxymethylcellulose in sequence 1	10
			Example 2	Mixing of auxiliary 1 with deionized water in sequence 2	1
Example 3	Addition of auxiliary 1 between sequences 3 and 4	11
			Example 4	Mixing of auxiliary 1 with Binder in sequence 4	2
Example 5	Addition of auxiliary 1 after sequence 4	1

As shown in comparative example 1, the number of surface defects of the obtained negative electrode was large without adding an auxiliary agent when preparing the negative electrode. As shown in examples 1 to 5, addition of an auxiliary agent having Si — C and Si — O bonds when preparing an anode can significantly improve the surface tension of anode slurry, thereby significantly reducing the number of anode surface defects. When the auxiliary agent is added in the preparation of the negative electrode, the auxiliary agent with Si-C and Si-O bonds is mixed with the solvent, the auxiliary agent with Si-C and Si-O bonds is mixed with the binder, or the auxiliary agent with Si-C and Si-O bonds is added after the binder is added, and the number of defects on the surface of the negative electrode is very small. Fig. 1 and 2 show the pole pieces obtained in comparative example 1 and example 2, respectively, where the position where the chromatic aberration is evident in fig. 1 (for example, the position marked by the black circle in fig. 1) is the pole piece defect, and almost no chromatic aberration spot is seen in fig. 2.

Table 2 shows the effect of different adjuvants on the negative electrode surface defects of lithium ion batteries. In the examples of table 2, the auxiliaries are mixed with deionized water in sequence 2.

TABLE 2

	Auxiliary agent	Number of negative electrode surface defects/10 m ²
			Comparative example 2	Ethanol	18
Comparative example 3	Acetone (II)	16
			Comparative example 4	Ethylene carbonate	15
Example 2	Auxiliary agent 1	1
			Example 6	Auxiliary 2	1.2
Example 7	Auxiliary 3	1.1
			Example 8	Auxiliary agent 4	0.9
Example 9	Auxiliary 5	0.8

As shown in comparative examples 2 to 4, the number of surface defects of the negative electrode was not significantly improved by adding a common organic solvent (e.g., ethanol, acetone, or ethylene carbonate, which does not have Si — C and Si — O bonds) as an auxiliary agent in the preparation of the negative electrode. As shown in examples 2 and 6 to 9, addition of an auxiliary agent having Si — C and Si — O bonds when preparing a negative electrode can significantly reduce the surface tension of the negative electrode slurry and significantly reduce the number of negative electrode surface defects.

Table 3 shows the effect of coating speed, drying temperature and vibration treatment on the negative electrode surface defects of the lithium ion battery. In the examples of table 3, adjuvant 1 was mixed with deionized water in sequence 2. The vibration processing is ultrasonic processing after step S2.

TABLE 3

The results show that the number of surface defects of the negative electrode can be further reduced when the coating speed is 10 to 100 m/min and the drying temperature is 80 to 150 ℃. The number of surface defects of the negative electrode can be further reduced at a coating speed of 20 m/min to 100 m/min and a drying temperature of 80 ℃ to 150 ℃. Especially after the vibration treatment is added, better effect can be obtained.

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that at least one embodiment or example in this application includes a particular feature, structure, material, or characteristic described in the embodiment or example. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. A method of making an anode, the method comprising the steps of:

s1: a material mixing step, wherein the artificial graphite, the carboxymethyl cellulose, the styrene butadiene rubber, the deionized water and the auxiliary agent with Si-C and Si-O bonds are added in the following sequence to obtain the cathode slurry:

(1) The artificial graphite and the carboxymethyl cellulose are mixed,

(2) The deionized water is added into the reaction kettle,

(3) The carboxymethyl cellulose is a cellulose derivative having a carboxyl group,

(4) The styrene-butadiene rubber is characterized in that,

wherein the auxiliary agent with Si-C and Si-O bonds is mixed with the deionized water for addition; or the auxiliary agent with Si-C and Si-O bonds is added after the styrene butadiene rubber is added;

s2: coating, namely coating the negative electrode slurry prepared in the step S1 on a negative electrode current collector at a coating speed of 50-100 m/min to obtain an initial pole piece;

s3: a drying step, namely placing the initial pole piece obtained in the step S2 in vacuum drying equipment for drying, wherein the drying temperature is 130-150 ℃, so as to obtain the negative pole,

wherein the step S2 is followed by a vibration treatment, the vibration treatment being at least one of mechanical vibration or ultrasonic vibration.

2. The method of producing an anode according to claim 1, wherein the auxiliary having Si-C and Si-O bonds has at least one of the following characteristics:

(b) The surface tension of an aqueous solution containing 0.1% of the auxiliary having Si-C and Si-O bonds is not more than 30mN/m.

3. The method of preparing an anode of claim 1, wherein the promoter having Si-C and Si-O bonds comprises a polyether siloxane comprising at least one of a complex silicone polyether complex, a polyether modified trisiloxane, or a polyether modified silicone polyether siloxane.

4. The method for producing an anode according to claim 1, wherein an addition amount of the auxiliary having Si-C and Si-O bonds is 3000ppm or less.

5. The method for producing an anode according to claim 1, wherein the vibration treatment has a vibration frequency of 100Hz to 800Hz, an amplitude of 0.01 mm to 0.5 mm, and a vibration time of 1 minute to 5 minutes.

6. The method for producing an anode according to claim 1, wherein the vibration treatment is performed a plurality of times, and a vibration frequency of at least one of the vibration treatments is smaller than a vibration frequency of a previous vibration treatment.

7. An anode obtained by the method for producing an anode according to any one of claims 1 to 6.

8. The anode according to claim 7, wherein a content of the auxiliary having Si-C and Si-O bonds in the anode is 500ppm or less.

9. The anode according to claim 7, wherein a content of the auxiliary having Si-C and Si-O bonds in the anode is 300ppm or less.

10. The anode according to claim 7, wherein a contact angle of a surface of the anode with respect to diethyl carbonate is reduced by 10% or more compared to an anode prepared without adding an auxiliary having Si-C and Si-O bonds.

11. An electrochemical device comprising a cathode, an anode, a separator and an electrolyte, wherein the anode is obtained by the method for producing an anode according to any one of claims 1 to 6 or the anode is the anode according to any one of claims 7 to 10.

12. An electronic device comprising the electrochemical device of claim 11.