KR20210031563A - Silicon-containing anode material for lithium-ion secondary battery and preparation method thereof - Google Patents

Abstract

In a negative electrode material for a lithium-ion secondary battery according to the present invention, silicon-based particles and conductive carbon-based materials are effectively combined by a silane coupling agent, thereby reducing the volume change in a lithium adsorption/desorption process, and improving cycle characteristics. Accordingly, the negative electrode material is applied to a negative electrode of a lithium-ion secondary battery, and can improve the energy density while maintaining good cycle characteristics compared to the conventional carbon-based negative electrode material.

Description

Silicon-containing anode material for lithium-ion secondary battery and its manufacturing method {SILICON-CONTAINING ANODE MATERIAL FOR LITHIUM-ION SECONDARY BATTERY AND PREPARATION METHOD THEREOF}

The present invention relates to a silicon-containing negative electrode material for a lithium ion secondary battery and a method of manufacturing the same. More specifically, the present invention relates to a composite negative electrode material containing silicon and a carbon-based material, a method for manufacturing the same, and a negative electrode and a lithium ion secondary battery including the same.

With the progress of miniaturization and weight reduction of electronic devices, a light and high energy density secondary battery for use as a power source is required. In addition, in order to be used in an electric vehicle or a hybrid vehicle, a secondary battery having a high charging/discharging speed and a safe secondary battery is required. The secondary battery discharges chemical energy of the positive electrode active material and the negative electrode active material as electrical energy to the outside by a chemical reaction through an electrolyte.

Among these secondary batteries, a lithium-ion secondary battery having a high energy density and being put into practical use is a non-aqueous lithium-ion secondary battery (hereinafter simply referred to as a'lithium-ion secondary battery') being actively used.

As the positive electrode active material of the lithium ion secondary battery, a lithium-containing metal composite oxide having a spinel structure, such as a lithium cobalt composite oxide, is mainly used, and as a negative electrode active material, a multi-layer structure capable of intercalation of lithium metal (inserted into a crystal of lithium) Carbon-based materials, such as graphite, are mainly used, and improvements are being made.

On the other hand, a battery using a carbon-based material as a negative electrode active material is implemented as a high-density negative electrode film under conditions of about 360 mAh/g to close to the theoretical capacity (370 mAh/g), and is used as an energy source for future high-function portable devices or electric vehicles. In order to achieve higher capacity, a negative electrode active material having a capacity of more than carbon is required.

Among these, a variety of studies have been made on practical use, while receiving attention so far, is a negative electrode active material using an alloy-based material containing elements such as silicon and tin. That is, since some metal elements such as silicon and tin can form metallic lithium at low temperatures, lithium can be electrochemically occluded and lithium ions can be released. In particular, a significantly larger charge/discharge capacity is possible compared to carbon-based materials. (The theoretical discharge capacity of silicon is known to be about 4200 mAh/g). However, alloy-based materials containing elements such as silicon and tin cause very large expansion and contraction when occluding and releasing lithium, resulting in poor current collection due to various factors such as pulverization and pulverization of the active material, and peeling of the anode film. As a result, there is a problem of lowering the cycle characteristics.

In order to solve this problem, there are attempts to improve various components such as the anode material itself, binder polymer, and current collector, and in particular, for the anode material, capacity reduction (reduction in volume change due to charge/discharge) by microstructuring or complexing of the active material has been made. Through this, some improvement is being made. However, it has not been reached yet to be put into practical use by being optimized in terms of capacity, life, and initial efficiency of the negative electrode material.

For example, Japanese Laid-Open Patent Publication Nos. 2006-260944 and 2007-087796 use silicon (Si) and SiM _x (M = Ti, Ni, Cu, Co, Fe, x = positive integer) as active materials. Although an electrode configuration has been disclosed, since such an electrode uses a transition metal (M), there is a problem of high density and heavy weight. In addition, PCT Publication No. WO 2013/141104 is a negative electrode material that improves cycle characteristics by carbon coating on silicon oxide (SiO) at a high temperature to improve the cycle characteristics by microstructure of silicon and conduction on the surface of the negative electrode material particles due to silicon non-uniformity. Is disclosed, but it cannot be considered sufficient in terms of initial efficiency and speed characteristics. In addition, Japanese Laid-Open Patent Publication No. 2004-047404 discloses a conductive silicon composite negative electrode material with improved initial efficiency, but there is a problem in that the life and stability of a battery using the same are insufficient.

Japanese Laid-Open Patent Publication No. 2006-260944 Japanese Unexamined Patent Publication No. 2007-087796 PCT Patent Publication No. WO 2013/141104 Japanese Laid-Open Patent Publication No. 2004-047404

The conventional silicon or alloy-based active material containing a silicon compound has the advantage of having a large charge/discharge capacity, but there is a problem that the performance of the electrode is deteriorated due to a large change in volume, so to improve this, the electrode or the active material itself has a porous structure, Various attempts have been made, such as adding an inert substance. As one of them, it is conceivable to combine a carbon-based material such as graphite used as an anode active material for a lithium-ion secondary battery with silicon or a silicon compound, but simply mixing them is difficult to obtain the effect expected in terms of cycle characteristics.

Accordingly, the present inventors have noted that the surface properties of the alloy-based negative electrode material and the carbon-based material are significantly different, so that an effective composite cannot be achieved simply by mixing. Accordingly, as a result of further research by the present inventors, it was found that bonding between constituent materials can be effectively improved by surface treatment of the negative electrode active material and addition of an appropriate silane coupling agent. In addition, when an alloy-based active material having a large volume change is used, the performance of the electrode due to charge and discharge can be suppressed by increasing adhesion to both the negative electrode material and the current collector.

Accordingly, the present invention effectively combines an alloy-based negative electrode material containing silicon, etc., which has a large charge and discharge capacity, with a carbon-based negative electrode material having a small charge and discharge capacity but good cycle characteristics, and has excellent cycle characteristics, a high charge and discharge speed, and a capacity An object of the present invention is to provide a controllable negative electrode material for lithium ion secondary batteries and a method of manufacturing the same.

According to the above object, the present invention provides a composite comprising silicon particles or silicon compound particles including microcrystalline silicon, and a conductive carbon-based material; And it provides a negative electrode material for a lithium ion secondary battery comprising a silane coupling agent coated on the surface of the composite.

In addition, the present invention comprises the steps of forming a composite by mixing silicon particles or silicon compound particles including microcrystalline silicon, and a conductive carbon-based material under high shear force; And it provides a method for producing a negative electrode material for a lithium ion secondary battery comprising the step of adding and kneading an aqueous solution of a silane coupling agent to the composite.

In addition, the present invention provides a method for producing a negative electrode material for a lithium ion secondary battery, comprising mixing a silicon particle or a silicon compound particle including microcrystalline silicon, a conductive carbon-based material, and an aqueous solution of a silane coupling agent under high shear force. .

In addition, the present invention provides a negative electrode for a lithium ion secondary battery including the negative electrode material and a current collector for the lithium ion secondary battery.

In addition, the present invention provides a lithium ion secondary battery comprising the negative electrode, a positive electrode and an electrolyte for the lithium ion secondary battery.

In the negative electrode material for a lithium ion secondary battery according to the present invention, a silicon-based particle and a conductive carbon-based material are effectively combined with a silane coupling agent, and cycle characteristics can be improved by mitigating a volume change in a lithium adsorption/desorption process. Accordingly, the negative electrode material has solved the difficulties that hindered the practical use of the alloy-based negative electrode material containing silicon, and it is also very useful in terms of battery design because the charge/discharge capacity can be adjusted. Accordingly, the negative electrode material according to the present invention is applied to the negative electrode of a lithium-ion secondary battery, so that the energy density can be improved while maintaining good cycle characteristics compared to the existing negative electrode material.

The present invention is not limited to the contents disclosed below, and may be modified in various forms unless the gist of the invention is changed.

In the present specification, a description that a certain object "includes" a predetermined component is not limited to these components, unless otherwise specified, and should be interpreted as being capable of further including additional components.

The negative electrode material for a lithium ion secondary battery according to the present invention includes a composite comprising silicon particles or silicon compound particles including microcrystalline silicon, and a conductive carbon-based material; And a silane coupling agent coated on the surface of the composite.

Hereinafter, each component of the negative electrode material for a lithium ion secondary battery will be described in detail.

Silicon particles or silicon compound particles

The silicon particles or silicon compound particles containing microcrystalline silicon can be obtained by milling silicon powders such as nano silicon, silicon compound, metallic silicon, etc. obtained by CVD or plasma deposition from a silane-based compound by a jet mill or a bead mill. , There is no particular limitation on the type and manufacturing method thereof.

Specifically, the silicon compound particles may contain at least one of a compound of the following formula (1) and a compound of the following formula (2).

SiO _x ... (1) M _y SiO _z ... (2)

In the above formula

x is 0 <x <2, 0.02 <y <0.2, and 0.8 <z <1.2,

M is selected from the group consisting of Mg, Li, Na, K, B and Al.

Specifically, the range of x in Equation (1) may be 0.5 <x <1.5, or 0.8 ≤ x ≤ 1.2. If it is within the above range, it is possible to easily prepare the compound of Formula (1) while suppressing a decrease in charge/discharge capacity in a lithium ion secondary battery due to the generation of _{inert SiO 2.}

For example, a compound having x greater than 1 in the above formula (1) can be easily obtained by cooling and depositing a silicon monoxide gas generated by heating a mixture of silicon dioxide and silicon metal. At this time, the temperature of the evaporation plate for cooling and depositing the silicon monoxide gas by heating the mixture of silicon dioxide and silicon particles is preferably maintained at 1,050°C or less in terms of suppressing deterioration of cycle characteristics due to an increase in silicon crystallite size.

In addition, y and z in Equation (2) may be appropriately determined according to the oxidation value of M.

The silicon compound particles may include a silicon compound capable of reacting with lithium. Alternatively, the silicon compound particles may include a silicon compound reacted with lithium or magnesium, specifically Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ Si ₃ O ₇ , Li ₂ Si ₂ O ₅ , Li ₈ SiO ₆ , Li ₆ Si ₂ O ₇ , MgSiO ₃ , Mg ₂ SiO ₄ , and may include at least one or more of _{Mg 2} Si ₂ O _6. This may be a compound in which y and z are 2 to 10, respectively, in the above formula (2), where y and z may be appropriately determined according to the oxidation value of M. These compounds are used as negative active materials for lithium ion secondary batteries. At the time, it is possible to improve the cycle characteristics and initial charge/discharge characteristics.

The silicon particles or the silicon compound particles may have a surface coated with a conductive carbon-based material in advance, and in this case, conductivity is imparted to the particles, thereby improving the conductivity of lithium ions and battery performance.

The method of coating the conductive carbon-based material is not particularly limited, but may be coated by a gas phase reaction or pyrolysis method at 600 to 1200°C using a carbon precursor, and specifically, may be coated by a vapor phase chemical heat treatment method (CVD). .

The conductive carbon-based material may include pyrolytic carbons, coke, glassy carbon fibers, sintered organic polymer compounds, carbon black, and the like. Alternatively, the conductive carbon-based material may include at least one or more of graphene, reduced graphene oxide, and carbon nanofibers.

The carbon precursor may be formed from a reaction gas containing at least one or more of the compounds represented by the following formulas (3) and (4).

C _n H _2n+2-a OH _a ... (3)

In the above formula, n is an integer from 1 to 20, and a is 0 or 1.

C _n H _2n ... (4)

In the above formula, n is an integer of 2 to 6.

The compound represented by the formula (3) or (4) may be methane, ethane, propane, ethylene, propylene, methanol, ethanol, propanol, and the like.

The reaction gas may further include a compound represented by the following formula (5).

C _x H _y O _z ... (5)

In the above formula, x is 0 or an integer of 1 to 20, y is 0 or an integer of 1 to 20, and z is an integer of 0 to 2.

The compound represented by the above formula (5) may be water vapor, carbon dioxide gas, acetylene, butadiene, benzene, toluene, xylene, pitch, and the like.

As an example, when the reaction gas contains water vapor or carbon dioxide gas, since a carbon layer having a higher crystallinity is coated, the conductivity of the particles may be improved even if the coating amount is small. In this case, the content of the water vapor or carbon dioxide gas may be, for example, 0.01% to 30% by volume based on the total volume of the reaction gas, but is not limited thereto.

As another example, the reaction gas may include a carbon source gas, for example, the carbon source gas is _{a mixed gas including methane (CH 4} ) and an inert gas, a mixed gas including methane and oxygen, and methane ( It _{may be a mixed gas including CH 4} ) and carbon dioxide (CO ₂ ), or a mixed gas including methane (CH ₄ ), carbon dioxide (CO ₂ ) and water vapor (H ₂ O). In this case, the inert gas may be argon, hydrogen, nitrogen, or helium.

The gas phase reaction may be performed by heat treatment at a temperature of 600°C to 1200°C, and specifically, the heat treatment temperature may be 700°C to 1100°C, or 700 to 1000°C.

The pressure during the heat treatment may be controlled by adjusting the amount of the reaction gas introduced and the amount of the reaction gas flowing out. For example, the pressure during the heat treatment may be 1 atm, 2 atm or more, 3 atm or more, 4 atm or more, or 5 atm or more, but is not limited thereto.

The time for performing the heat treatment may be appropriately adjusted according to the heat treatment temperature, heat treatment pressure, composition of the gas mixture, and the amount of carbon coating. For example, the heat treatment time may be 10 minutes to 100 hours, 30 minutes to 90 hours, or 50 minutes to 40 hours, but is not limited thereto. In addition, the thickness of the conductive carbon coating layer may be adjusted by adjusting the heat treatment time. For example, the longer the heat treatment time is, the thicker the conductive carbon coating layer is formed, thereby improving electrical properties.

The average particle diameter of the silicon particles or the silicon compound particles may be 0.01 µm to 20 µm, 0.01 µm to 10 µm, 0.01 µm to 5 µm, 0.01 µm to 3 µm, 0.1 µm to 10 µm, or 0.5 µm to 10 µm have.

Preferably, the average particle diameter of the silicon particles or silicon compound particles may be 2 µm to 10 µm, and when it is within the above range, the bulk density is sufficient to improve the charge/discharge capacity per unit volume, and the electrode film formation is excellent. Peeling can be suppressed from the current collector. More preferably, the average particle diameter of the silicon particles or silicon compound particles may be 2 µm to 5 µm, and when it is within the above range, cracks (cracks) occurring in the composite are reduced, and the matrix is reinforced to reduce destruction. have.

The average particle diameter of the silicon particles or silicon compound particles may be calculated as _{D 50} , which is a cumulative 50% particle diameter in a volume-based distribution measured by a laser diffraction method.

_{In addition, D min} of the silicon particles or silicon compound particles may be 0.3 µm or less, and D _max may be 10 µm to 15 µm. When it is within the above range, the specific surface area of the composite decreases, so that initial efficiency and cycle characteristics may be further improved.

The crystallite size of the microcrystalline silicon may be 0.1 nm to 300 nm, 0.1 nm to 200 nm, 0.5 nm to 100 nm, 0.1 nm to 50 nm, 2 nm to 50 nm, or 50 nm to 100 nm.

Preferably, the microcrystalline silicon may have a crystallite size of 2 nm to 20 nm. When it is within the above range, it has a specific surface area suitable for formation of a lithium alloy, while suppressing the expansion and contraction of the electrode during the charging and discharging process, thereby improving the cycle characteristics, and coulomb efficiency indicating the ratio of the charging capacity and the discharging capacity, that is, charging and discharging. Efficiency can be improved.

The crystallite size of the microcrystalline silicon can be obtained by Scherrer's equation based on the diffusion of diffraction lines attributed to Si 220 centered around 2θ = 47.5° in X-ray diffraction (Cu-Kα).

In addition, the silicon particles may include amorphous silicon. Specifically, the silicon particles may be a mixture of an amorphous form and a crystalline form. For example, when the amorphous ratio in the silicon particles is 50% or more, it may be advantageous to alleviate damage to volume expansion during initial charging and discharging.

The content of the silicon particles or silicon compound particles is 1% to 90% by weight, 1% to 80% by weight, 1% to 60% by weight, 3% by weight based on the total weight of the negative electrode material for the lithium ion secondary battery. It may be 80% by weight, 3% by weight to 50% by weight, or 3% by weight to 30% by weight.

Alternatively, the silicon particles or silicon compound particles may be included in an amount of 30% to 80% by weight based on the total weight of the negative electrode material for the lithium ion secondary battery. When it is within the above range, the amount of the active material in which lithium is inserted and released is sufficient to increase the charge/discharge capacity of the lithium ion secondary battery, while suppressing the expansion and contraction of the electrode during the charging/discharging process due to the precipitation of silicon, thereby improving the cycle characteristics. Can be improved. Specifically, the silicon particles or silicon compound particles may be included in an amount of 40% by weight to 70% by weight based on the total weight of the negative electrode material for the lithium ion secondary battery.

The negative electrode material according to the present invention may adjust the charge/discharge capacity by changing the content of silicon capable of reacting with lithium to form a lithium alloy by adjusting the content of silicon particles or silicon compound particles.

Conductive carbon-based material

The conductive carbon-based material may be a conventional conductive carbon-based material used as a negative electrode material of a lithium ion secondary battery.

By blending such a conductive carbon-based material into the negative electrode material, it is possible to reduce the electrical resistance of the negative electrode active material and at the same time alleviate the expansion stress caused by charging.

For example, the conductive carbon-based material is natural graphite (imposed graphite, earth graphite, etc.), artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, graphene, reduced graphene, carbon nanotubes, carbon It may be one or more selected from the group consisting of nanofibers and conductive carbon black, but is not particularly limited.

The conductive carbon-based material may have a particle shape, and an average particle diameter thereof may be 0.01 µm to 20 µm, or 0.5 µm to 15 µm.

The content of the conductive carbon-based material particles is 20% to 97% by weight, 30% to 95% by weight, 40% to 95% by weight, or 50% by weight based on the total weight of the negative electrode material for the lithium ion secondary battery. 85% by weight.

The silicon particles or silicon compound particles and the conductive carbon-based material form a composite. The composite shape may be spherical, and is not particularly limited.

Silane coupling agent

The silane coupling agent improves adhesion and fine dispersion between the interface between the silicon particles or silicon compound particles and the conductive carbon-based material.

The silane coupling agent may be a silane compound and may be selected to optimize its performance according to the type of binder.

In addition, the silane coupling agent may include at least one of a hydrolyzate and a dehydration condensate of a silane compound.

As a specific example, the silane coupling agent may include a silane compound represented by the following formula (6) or a hydrolyzate thereof.

Ra _(4-mn) Si (R') _m (Y) _n ... (6)

In the above formula, Ra is an organic group having a functional group, R'is a non-hydrolyzable hydrocarbon group, Y is a monovalent hydrolyzable group, m is 0 or 1, and n + m is an integer of 1 to 3.

In the formula (6), Ra may be, for example, a hydrocarbon group having 1 to 12 carbon atoms, specifically 1 to 10 carbon atoms having a functional group. More specifically, Ra may be a C _1-10 alkyl group, a C _3-10 cycloalkyl group, a C _2-10 alkenyl group, a C _6-10 aryl group, or a C _7-10 aralkyl group having a functional group. The functional group may be one or more selected from the group consisting of (meth)acrylic group, (meth)acryloxy group, acryloyl group, methacryloyl group, mercapto group, amino group, amide group, ureido group, epoxy group, and cyano group. have. In addition, some or all of the hydrogen atoms present in the hydrocarbon group may be unsubstituted or substituted with a halogen atom such as F, Cl, or Br, an oxyalkylene group such as an oxyethylene group, or a polyoxyalkylene group such as a polyoxyethylene group. have. In addition, a -O-, -NH-, -N(-CH ₃ )- or -N(-C ₆ H ₅ )- group may be inserted in the chain of the hydrocarbon group.

Examples of R'in the above formula (6) include an alkyl group such as _{CH 3} -, CH ₃ CH ₂ -and CH ₃ CH ₂ CH _{2 -, CH 2} =CH- and CH ₂ =CHCH ₂ -CH ₂ =C(CH ₃ ) Alkenyl group such as -, aryl group such as _{C 6} H _{5 -, ClCH 2} -, ClCH ₂ CH ₂ CH ₂ -, CF ₃ CH ₂ CH ₂ -, CNCH ₂ CH ₂ -, CH ₃ -(CH ₂ CH ₂ O) _n -CH ₂ CH ₂ CH ₂ -, CH ₂ (O)CHCH ₂ OCH ₂ CH ₂ CH ₂ -(where CH ₂ (O)CHCH ₂ represents a glycidyl group), CH ₂ =CHCOOCH ₂ -, HSCH ₂ CH ₂ CH ₂ -, NH ₂ CH ₂ CH ₂ CH ₂ -, NH ₂ CH ₂ CH ₂ NHCH ₂ CH ₂ CH ₂ -, NH ₂ CONHCH ₂ H ₂ CH ₂ -.

Preferably, Ra is a γ-glycidyloxypropyl group, β-(3,4-epoxycyclohexyl)ethyl group, γ-aminopropyl group, γ-cyanopropyl group, γ-acryloxypropyl group, γ -Methacryloxypropyl group, γ-ureidopropyl group, or N-β-(aminoethyl)-γ-aminopropyl group, and R'is a methyl group, a vinyl group, or a phenyl group.

In addition, in the formula (6), Y is, for example, an alkoxy group such as _{-OCH 3} and -OCH ₂ CH _{3 , an amino group such as -N(CH 3} ) ₂ , -ON=C(CH ₃ )CH ₂ CH ₃ and such oxime group, -ON (CH ₃₎ aminooxy group such as a _2, a carboxyl group, such as _{-OCOCH 3, -OC (CH 3)} = alkenyloxy group such as _{CH 2, -CH 2 COOCH 3,} -CH (CH 3 )COOCH _3, etc. are mentioned. When two or more Y are included in the above formula (6), they may all be the same group or different groups. Preferably, Y is a methoxy group, an ethoxy group, or an isopropenyloxy group.

In addition, in the above formula (6), m may be 0 or 1, and n may be an integer of 1 to 3.

Specific examples of the silane coupling agent include vinyltrimethoxysilane, methylvinyldiethoxysilane, γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-cyanopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, β-(3,4-epoxycyclo Hexyl) ethyl trimethoxysilane, γ-ureidopropyl trimethoxysilane, etc. are mentioned.

The silane coupling agent may be used singly or in combination of two or more. Further, the silane coupling agent may be partially condensed and oligomerized.

The content of the silane coupling agent may be 0.01 wt% to 20 wt%, 0.05 wt% to 10 wt%, or 0.05 wt% to 5 wt% based on the total weight of the negative electrode material for the lithium ion secondary battery.

Preferably, the silane coupling agent may be included in an amount of 0.05% to 10% by weight based on the total weight of the negative electrode material for the lithium ion secondary battery. When it is within the above preferred content range, it may be more advantageous in terms of initial efficiency and cycle characteristics. More preferably, the silane coupling agent may be included in an amount of 1% to 5% by weight based on the total weight of the negative electrode material for the lithium ion secondary battery.

The content range of the silane coupling agent varies depending on the type of the silane coupling agent and the specific surface area of the active material (silicon particles or a composite of a silicon compound particle and a carbon-based material). The larger the specific surface area, the more the silane coupling agent needs to be used.

Manufacturing method of negative electrode material for lithium ion secondary battery

The negative electrode material for a lithium ion secondary battery may include forming a composite by mixing silicon particles or silicon compound particles including microcrystalline silicon, and a conductive carbon-based material under high shear force; And adding and kneading an aqueous solution of a silane coupling agent to the composite.

In the method of manufacturing the negative electrode material, prior to the step of forming the composite, a step of hydrophilizing the surface of the conductive carbon-based material under high shear force in air may be further included.

Alternatively, the negative electrode material for a lithium ion secondary battery may be prepared by a method comprising mixing silicon particles or silicon compound particles including microcrystalline silicon, a conductive carbon-based material, and an aqueous solution of a silane coupling agent under high shear force.

The device for mixing the raw materials is not particularly limited as long as it is a powder mixing device capable of applying a shearing force by combining functions (impact, compression, friction, etc.) such as a pulverizer capable of overcoming a strong cohesive force. A mixing device such as a mixer or a planetary ball mill may be used.

Further, as an example of a device for mixing while applying the shearing force, a high-speed stirrer may be mentioned. The high-speed stirrer is not particularly limited as long as it has a container capable of accommodating silicon particles or silicon compound particles and a conductive carbon-based material, and a rotating blade in the container.

The rotational angular speed of the blades of the high-speed stirrer may be calculated by the following equation, and may be, for example, 15 m/s or more.

Rotation angular velocity (m/s) = number of revolutions (rpm) × blade diameter (m) × π / 60

Preferably, the rotational angular speed of the blades of the high-speed stirrer may be 15 m/s to 90 m/s, and when it is within the above range, it is easy to implement in a conventional device and the effect of hydrophilizing the surface may be sufficient. More preferably, the rotational angular speed of the blades of the high-speed stirrer may be 30 m/s to 70 m/s, and when it is within the above range, the required processing time may be further shortened and the cost may be further lowered.

In addition, the mixing time under the high shear force may preferably be 1 minute to 60 minutes, and when it is within the above range, the mixing effect is sufficient and a decrease in productivity due to an excessive amount of time can be prevented. More preferably, the mixing time under the high shear force may be 5 minutes to 60 minutes, and when it is within the above range, the effect of surface hydrophilization can be obtained more stably.

In addition, a well-known grinder or classifier may be used in order to control the particle diameter of the particles in a predetermined range during the manufacturing process.

The pulverizer may include, for example, a ball mill for pulverizing an object using an impact force, frictional force, or compression force by the kinetic energy by moving a pulverizing medium such as balls and beads, a roller mill pulverizing using a compression force by a roller, A jet mill for rapidly colliding an object and crushing it by its impact force, a hammer mill for crushing an object by colliding with a fixed hammer by rotating a rotor, and a colloid mill using shear force are used. Grinding can be either wet grinding or dry grinding.

In addition, in order to control the particle size distribution after pulverization, dry classification, wet classification, or classification by sieve may be performed. Dry classification is a process of dispersing, separating (separating fine particles and coarse particles), collecting (separating solids and gases), and discharging sequentially or simultaneously using airflow. At this time, pre-treatment (moisture, dispersion, humidity control) is performed before classification so that classification efficiency is not lowered due to interference between particles, particle shape, airflow confusion, velocity distribution, and static electricity effects, and moisture or oxygen concentration in the airflow. Can be adjusted. In addition, a type in which a dry classifier such as a cyclone is integrated can be pulverized and classified at a time to achieve a desired particle size distribution.

Anode for lithium ion secondary battery

The present invention also provides a negative electrode for a lithium ion secondary battery including the negative electrode material and a current collector for the lithium ion secondary battery.

The negative electrode material for a lithium ion secondary battery uses the negative electrode material of the present invention as described above, and the other current collector may be a conventional metal thin film used for a negative electrode for a lithium ion secondary battery.

The negative electrode for a lithium ion secondary battery may be obtained by applying a negative electrode material to the current collector and drying it.

At this time, the negative electrode material may be formed in a paste form and then applied to the current collector.

The negative electrode material paste may be prepared by mixing the negative electrode material with a binder polymer and a solvent. At this time, the blending amount of the solvent may be adjusted so that the negative electrode material paste has high viscosity. In addition, the mixing is preferably carried out under a high shear force, and for this purpose, a kneading device such as a kneading roll, a kneader having a single or double shaft, a Henschel mixer, a dispenser, a mixing device such as a rotation/revolution mixer, a planetary mill, or the like can be used. Thereafter, a solvent, a diluent, or the like may be further added as necessary to obtain a paste suitable for film formation.

After coating and drying such a negative electrode material paste on a current collector such as a metal foil, it may be pressed with a roll or the like to improve adhesion.

In addition, heat treatment may be performed at high temperature under an inert atmosphere or vacuum in order to increase initial efficiency. At this time, the heat treatment temperature varies depending on the heat resistance of the binder polymer, but the polyamic acid-type polyimide and polyamideimide is preferably 250°C or higher, and for other imidized polymers, 200°C or higher is preferable. The treatment conditions for it can be appropriately adjusted.

Lithium ion secondary battery

The present invention also provides a lithium ion secondary battery comprising the negative electrode, a positive electrode and an electrolyte for the lithium ion secondary battery. The negative electrode for a lithium ion secondary battery uses the negative electrode of the present invention as described above, and other conventional positive electrodes, electrolytes, separators, etc. used in lithium ion secondary batteries may be used.

[Example]

The above will be described in more detail by the following examples. However, the following examples are for illustrative purposes only, and the scope of the examples is not limited thereto.

Example 1

Microcrystalline silicon powder (crystallite size 10 nm by XRD, specific gravity 2.01) of 0.1-100 μm obtained as a by-product in the process of pyrolyzing monosilane (SiH _{4) in a fluidized bed reactor (FBR) to produce polycrystalline silicon is bead milled.} Pulverized at, to prepare a microcrystalline silicon powder having an average particle diameter of 0.9 µm. 10 g of the silicon powder and 90 g of natural graphite (PAS-C1, POSCO Chemtech Co., Ltd.) having an average particle diameter of 5 µm were ^{mixed for 10 minutes in an air atmosphere with a dry particle complexing device (MekanoFusion TM} , Hosokawa Micron Co., Ltd.) to obtain a composite. . 50 g of a 1% by weight aqueous solution of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (Z-6020, DowCorning) as a silane coupling agent was added thereto, stirred sufficiently, and dried to obtain a negative electrode material. .

Polyamic acid type polyimide (U-varnish A, Ubekosan) was added to 100 parts by weight of the negative electrode material so as to be 15 parts by weight based on solid content, and sufficiently mixed through mechanical stirring for 1 hour.

Thereafter, the viscosity was adjusted with a small amount of solvent (N-methylpyrrolidone, NMP) to prepare a negative electrode material paste. The negative electrode material paste was applied to the copper foil so that the thickness after drying was about 20 μm using a doctor blade, and dried in a vacuum dryer at 100°C. Then, it was compressed with a pressure roll and heat-treated in a vacuum dryer at 200° C. for 4 hours to obtain a silicon-graphite composite electrode.

Example 2

After evaporating the metal silicon powder in a thermal plasma device, it is deposited on a deposition plate controlled at 800°C to obtain a polycrystalline silicon mass (crystallite size of 15 nm by XRD, specific gravity 2.10), pulverized with a jaw crusher, and then jet mill Pulverized at, to prepare a microcrystalline silicon powder having an average particle diameter of 0.5 µm. 30 g of the silicon powder and 70 g of natural graphite (PAS-C1, POSCO Chemtech) having an average particle diameter of 5 μm were mixed with a planetary ball mill while applying high shearing force for 10 minutes in an air atmosphere to obtain a composite. Add 100 g of a 1% by weight acetic acid aqueous solution (1% by weight of acetic acid concentration) of 3-glycidyloxypropyltrimethoxysilane (A-187, Momentive Performance Materials) as a silane coupling agent, and dry sufficiently. A negative electrode material was obtained.

An acrylic binder (Aquacharge, Sumitomo Seika) was added to 100 parts by weight of the negative electrode material so as to be 5 parts by weight based on solid content, and mechanically stirred for 1 hour to sufficiently mix. Thereafter, the viscosity was adjusted with a small amount of ion-exchanged water to prepare a negative electrode material paste. The negative electrode material paste was applied to copper foil so that the thickness after drying was about 20 μm using a doctor blade, and dried in a vacuum dryer at 100°C. Thereafter, it was compressed with a pressure roll and heat-treated in a vacuum dryer at 80° C. for 12 hours to obtain a silicon-graphite composite electrode.

Example 3

The silicon metal powder was evaporated in a thermal plasma apparatus and deposited on a vapor deposition plate controlled at 800°C to obtain a polycrystalline silicon mass (crystallite size of 15 nm by XRD, specific gravity 2.10), pulverized with a jaw crusher, and then in a jet mill. By pulverizing, microcrystalline silicon powder having an average particle diameter of 5.1 µm was prepared. The silicon powder was placed inside a tube-type electric furnace and reacted at 1100° C. for 1 hour while flowing methane gas and carbon dioxide gas at 1 L/min, respectively, to prepare silicon powder coated with 5% by weight of carbon on the surface.

30 g of the carbon-coated silicon powder and 70 g of natural graphite (PAS-C1, POSCO Chemtech) having an average particle diameter of 9 μm were added 2 g of methylvinyl diethoxysilane (Sigma Aldrich) as a silane coupling agent, and dry A negative electrode material was obtained by mixing and drying while applying high shearing force for 10 minutes in an air atmosphere with a particle complexing device (MekanoFusion ^{TM, Hosokawa Micron Corporation).} Using the negative electrode material, a silicon-graphite composite electrode was obtained in the same manner as in Example 2.

Example 4

Monosilane was pyrolyzed at 800° C. in a tube furnace under a hydrogen atmosphere to prepare microcrystalline silicon powder (crystallite size of 20 nm) having an average particle diameter of 25 nm. 10 parts by weight of the silicon powder and 90 parts by weight of natural graphite (PAS-C1, POSCO Chemtech Co., Ltd.) having an average particle diameter of 5 µm are mixed for 10 minutes in an air atmosphere using a ^{dry particle complexing device (MekanoFusion TM, Hosokawa Micron Co., Ltd.).} Got it. 300 g of 3-glycidyloxypropyltrimethoxysilane (A-187, Momentive Performance Materials, Inc.) of 1% by weight acetic acid solution (1% by weight of acetic acid concentration) was added thereto, followed by drying sufficiently to obtain a negative electrode material. . Thereafter, a silicon-graphite composite electrode was obtained in the same manner as in Example 2.

Example 5

Crystalline silicon oxide (DSO, Daeju Electronics Co., Ltd.) obtained from silicon and silicon dioxide by gas phase synthesis (average particle diameter 5 µm, crystallite size 5 nm, carbon content 5 wt%) 15 parts by weight and natural graphite (PAS) having an average particle diameter of 5 µm -C1, POSCO Chemtech Co., Ltd.) 83 parts by weight, carbon black (Super P, Imeri Co.) 2 parts by weight of the Henschel Mixer (Henschel Mixer) was mixed for 20 minutes at 5000 rpm in an air atmosphere to obtain a composite. After adding 50 g of 3-glycidyloxypropyltrimethoxysilane (A-187, Momentive Performance Materials, Inc.) of 1% by weight acetic acid solution (1% by weight of acetic acid concentration) and mixing at 2000 rpm for 10 minutes , Sufficiently dried to obtain a negative electrode material. Thereafter, a silicon-graphite composite electrode was obtained in the same manner as in Example 2.

Example 6

Carbon-silicon composite oxide (DMSO, Daejoo Electronic Materials Co., Ltd.) obtained by carbon coating silicon oxide obtained by gas phase synthesis from magnesium, silicon and silicon dioxide (average particle diameter 5 µm, silicon crystallite size 10 nm, magnesium content 10% by weight, carbon) Content 5% by weight) was prepared as a silicon powder. 20 parts by weight of the silicon powder and 77.5 parts by weight of natural graphite (PAS-C1, POSCO Chemtech) having an average particle diameter of 5 µm, 2 parts by weight of carbon black (Super P, Imeri), 0.5 parts by weight of carbon nanotubes, dry particle composite A composite was obtained by mixing for 10 minutes in an air atmosphere with an apparatus (MechanoFusion ^{™ AMS, Hosokawa Micron Corporation).} To this was added 500 g of a 1% by weight aqueous acetic acid solution (1% by weight acetic acid concentration) of 3-glycidyloxypropyltrimethoxysilane (A-187, Momentive Performance Materials), and sufficiently dried to obtain a negative electrode material. . Thereafter, a silicon-graphite composite electrode was obtained in the same manner as in Example 2.

Comparative Example 1

The procedure of Example 1 was repeated, but without adding a silane coupling agent, a silicon-graphite composite electrode was prepared.

Comparative Example 2

The procedure of Example 1 was repeated, but instead of the microcrystalline silicon powder as the silicon powder, a fine powder obtained by further grinding Elkem's industrial metal silicon powder (Silgrain HQ 10 µm series product, crystallite size: more than 300 nm) in a bead mill (average A silicon-graphite composite electrode was prepared using a particle diameter of 0.88 µm).

Comparative Example 3

The silicon metal powder was evaporated in a thermal plasma apparatus and deposited on a vapor deposition plate controlled at 800°C to obtain a polycrystalline silicon mass (crystallite size of 15 nm by XRD, specific gravity 2.10), pulverized with a jaw crusher, and then in a jet mill. By pulverizing, microcrystalline silicon powder having an average particle diameter of 5.1 µm was prepared. 30 g of the silicon powder and 70 g of natural graphite (PAS-C1, POSCO Chemtech Co., Ltd.) having an average particle diameter of 9 µm were mixed in an air atmosphere with a dry particle complexing device (MekanoFusionTM, Hosokawa Micron Co., Ltd.) for 10 minutes to obtain a composite. . This was used as a negative electrode material without being coated with a silane coupling agent on the surface, and a silicon-graphite composite electrode was obtained in the same manner as in Example 2.

Comparative Example 4

The procedure of Example 4 was repeated, but as silicon powder, 10 parts by weight of OCI's rod-shaped polycrystalline silicon pulverized powder (average particle diameter 5.5 µm) and 90 parts by weight of natural graphite (PAS-C1, POSCO Chemtech) having an average particle diameter of 5 µm A composite was obtained by mixing in a planetary ball mill for 10 minutes, and a silicon-graphite composite electrode was prepared using an emulsion-type SBR-based binder (RD2001, JSR) as a binder.

The configurations of the Examples and Comparative Examples prepared above are summarized in Table 1 below.

Test example

A lithium ion secondary battery including a silicon-graphite composite electrode manufactured using the negative electrode materials of the above Examples and Comparative Examples was fabricated and evaluated. The silicon-graphite composite electrode was punched into a circle having a diameter of 14 mm to prepare a negative electrode, and a lithium thin film having a thickness of 0.3 mm was used as a counter electrode. _{In addition, a porous polyethylene sheet having a thickness of 0.1 mm was used as a separator, and LiPF 6} having a concentration of 1 M was dissolved in a solution in which ethylene carbonate (EC) and diethylene carbonate (DEC) were mixed at a volume ratio of 1:1 as an electrolyte. Using these components, a lithium ion secondary battery having a thickness of 2 mm and a diameter of 32 mm (so-called CR2032 type coin cell) was manufactured.

The lithium ion secondary battery was allowed to stand at room temperature overnight, and then a charge/discharge test was performed. Before the test, the open circuit voltage was 4.0 V, and lithium was inserted (charged) in the electrode at a constant current of 0.1 mA until the voltage became 0.00 V, and then lithium ions at the electrode at a constant current of 0.1 mA until the voltage became 3.0 V. Was discharged (discharged) to evaluate an electrode containing silicon-containing amorphous carbon powder. The results of charging and discharging evaluation converted into capacity per 1 g of negative electrode material are summarized in Table 1 below.

division Example 1 Example 2 Example 3 Example 4 Example 5 silicon
powder Kinds FBR by-product
smash
Microcrystalline powder plasma
Evaporation crushing
Microcrystalline powder Carbon coated
Microcrystalline silicon
powder Silane low temperature
Pyrolysis generation
Microcrystalline powder Crystalline
silicon
oxide Crystallite size 10 nm 15 nm 15 nm 20 nm 5 nm Average particle diameter 0.9 μm 0.5 μm 6.0 μm 25 nm 5 μm Blending amount
(Part by weight) 10 30 30 10 15 carbon
matter Kinds Natural graphite Natural graphite Natural graphite Natural graphite Natural graphite, etc. Blending amount
(Part by weight) 90 70 70 90 85 mix Device Mechano Fusion Planetary ball mill Mechano Fusion Mechano Fusion Hensel mixer Silane coupling agent Kinds Aminosilane Glycidyl
Oxysilane Vinyl silane Glycidyl
Oxysilane Glycidyl
Oxysilane Added amount
(Part by weight) 0.5 1.0 2.0 3.0 0.5 coating bookbinder
Blending amount U-varnish A
15% by weight Aquacharge
5.0% by weight Aquacharge
5.0% by weight Aquacharge
5.0% by weight Aquacharge
5.0% by weight Charge and discharge
evaluation Initial efficiency (%) 91 89 90 90 87 Initial discharge capacity (mAh/g) 750 1530 1620 750 530 Retention rate (%)
(@50 cycles) 92 85 86 89 91

division Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 silicon
powder Kinds Carbon-silicon composite oxide FBR by-product
smash
Microcrystalline powder Industrial
Metal silicon
Crushed powder plasma
Evaporation crushing
Microcrystalline powder OCI's
Polycrystalline silicon
Crushed powder Crystallite size 10 nm 10 nm >300 nm 15 nm >300 nm Particle size 5 μm 0.9 μm 0.88 μm 5.1 μm 5.5 μm Blending amount
(Part by weight) 20 10 10 30 10 carbon
matter Kinds Natural graphite, etc. Natural graphite Natural graphite Natural graphite Natural graphite Blending amount
(Part by weight) 80 90 90 70 90 mix Device Mechano Fusion Mechano Fusion Mechano Fusion Mechano Fusion Planetary ball mill Silane
Coupling agent Kinds Glycidyl
Oxysilane - Aminosilane - Glycidyl
Oxysilane Added amount
(Part by weight) 5 - 0.5 - 3.0 coating bookbinder
Blending amount Aquacharge
5.0% by weight U-varnish A
15% by weight U-varnish A
15% by weight Aquacharge
5.0% by weight SBR
5.0% by weight Charge and discharge
evaluation Initial efficiency (%) 88 91 90 89 88 Initial discharge capacity (mAh/g) 550 740 730 1510 730 Retention rate (%)
(@50 cycles) 88 80 76 73 65

As shown in Tables 1 and 2, in the negative electrode materials of Examples 1 to 6, silicon-based particles and conductive carbon-based materials are effectively combined with a silane coupling agent, thereby reducing the volume change in the lithium adsorption and desorption process, thereby improving cycle characteristics. On the other hand, the negative electrode materials of Comparative Examples 1 to 4 were evaluated poorly in cycle characteristics.

Claims (15)

A composite composed of silicon particles or silicon compound particles containing microcrystalline silicon, and a conductive carbon-based material; And
A negative electrode material for a lithium ion secondary battery comprising a silane coupling agent coated on the surface of the composite.
The method of claim 1,
The microcrystalline silicon has a crystallite size of 2 nm to 20 nm, a negative electrode material for a lithium ion secondary battery.
The method of claim 1,
A negative electrode material for a lithium ion secondary battery, wherein the silicon compound particles contain at least one of a compound of the following formula (1) and a compound of the following formula (2):
SiO _x ... (1) M _y SiO _z ... (2)
In the above formula, x is 0 <x <2, 0.02 <y <0.2, and 0.8 <z <1.2, and M is selected from the group consisting of Mg, Li, Na, K, B, and Al.
The method of claim 3,
A negative electrode material for a lithium ion secondary battery, wherein the silicon compound particles contain the compound of the formula (1).
The method of claim 1,
A negative electrode material for a lithium ion secondary battery, wherein the silicon compound particles contain a silicon compound capable of reacting with lithium.
The method of claim 1,
The silicon particles or the silicon compound particles are contained in an amount of 30% by weight to 80% by weight based on the total weight of the negative electrode material for a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery.
The method of claim 1,
The conductive carbon-based material is one selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, graphene, reduced graphene, carbon nanotubes, carbon fibers, and conductive carbon black. Above, a negative electrode material for lithium ion secondary batteries.
The method of claim 1,
The negative electrode material for a lithium ion secondary battery, wherein the silane coupling agent contains at least one of a hydrolyzate and a dehydration condensate of a silane compound.
The method of claim 1,
A negative electrode material for a lithium ion secondary battery, wherein the silane coupling agent contains a silane compound represented by the following formula (6) or a hydrolyzate thereof:
Ra _(4-mn) Si (R') _m (Y) _n ... (6)
In the above formula, Ra is an organic group having a functional group, R'is a non-hydrolyzable hydrocarbon group, Y is a monovalent hydrolyzable group, m is 0 or 1, and n + m is an integer of 1 to 3.
The method of claim 1,
The negative electrode material for a lithium ion secondary battery, wherein the silane coupling agent is contained in an amount of 0.05% to 10% by weight based on the total weight of the negative electrode material for a lithium ion secondary battery.
Mixing silicon particles or silicon compound particles including microcrystalline silicon, and a conductive carbon-based material under a high shear force to form a composite; And
A method for producing a negative electrode material for a lithium ion secondary battery comprising the step of adding and kneading an aqueous solution of a silane coupling agent to the composite.
The method of claim 11,
Before the step of forming the composite, the method of manufacturing a negative electrode material for a lithium ion secondary battery further comprising the step of hydrophilizing the surface of the conductive carbon-based material under high shear force in air.
A method for producing a negative electrode material for a lithium ion secondary battery, comprising mixing a silicon particle or a silicon compound particle including microcrystalline silicon, a conductive carbon-based material, and an aqueous solution of a silane coupling agent under high shear force.
A negative electrode for a lithium-ion secondary battery comprising the negative electrode material for a lithium-ion secondary battery of claim 1 and a current collector.
A lithium ion secondary battery comprising a negative electrode, a positive electrode, and an electrolyte for a lithium ion secondary battery of claim 14.