KR20240077458A - Anode composite materials for lithium secondary battery and method producing the same - Google Patents

Abstract

The present invention relates to a negative active material composite material for lithium secondary batteries and a method of manufacturing the same. Specifically, the surface of silicon-based particles is coated with fluorine-based resin in a certain content range to reduce contact loss, side reactions with electrolyte, and increase resistance. It relates to a negative electrode active material composite material that can prevent deterioration caused by a composite material and a method of manufacturing the same.

Description

Negative active material composite material for lithium secondary batteries and method for manufacturing the same {ANODE COMPOSITE MATERIALS FOR LITHIUM SECONDARY BATTERY AND METHOD PRODUCING THE SAME}

The present invention relates to a negative active material composite material for lithium secondary batteries and a method of manufacturing the same. Specifically, the surface of silicon-based particles is coated with a certain amount of fluorine-based resin to cause contact loss, side reactions, and deterioration due to increased resistance. It relates to a negative active material composite material that can prevent and a method of manufacturing the same.

Metal oxides such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ or LiCrO ₂ are used as the positive electrode active materials that make up the positive electrode of a lithium secondary battery, and metal lithium and graphite are used as the negative electrode active materials that make up the negative electrode. ) or carbon-based materials such as soft carbon (non-graphitizable carbon) and hard carbon (non-graphitizable carbon), or materials such as silicon oxide (SiO _x ) are used. Among the negative electrode active materials, metallic lithium was initially mainly used, but as the charge and discharge cycle progressed, lithium atoms grew on the surface of metallic lithium, damaging the separator and damaging the battery. Recently, carbon-based materials have been mainly used. However, in the case of carbon-based materials, the theoretical capacity is only about 400 mAh/g, which has the disadvantage of being small in capacity.

Accordingly, various studies have been conducted to replace the carbon-based material using silicon (Si), which has a high theoretical capacity (4,200 mAh/g) as a negative electrode active material.

When a silicon-based anode material reacts with lithium, a volume expansion phenomenon (swelling) occurs that is close to 3 to 4 times compared to before the reaction. This causes the particles to break due to pulverization of the active material, resulting in electrical contact loss. In addition, there is a problem of rapid deterioration of the lifespan of the secondary battery due to an increase in resistance due to the electrolyte decomposition reaction as a new interface is formed.

The internal environment of a lithium secondary battery is an environment where the chemical stability of the polymer can be weakened due to side reactions of the electrolyte solution, which is an organic solvent, the voltage environment during charging or discharging, and hydrofluoric acid (HF) generated from the side reactions. Silicon containing polymers When particles are used as a lithium secondary battery material, the destruction of the polymer layer is accelerated due to dissolution of the polymer layer by the electrolyte and excessive volume expansion (swelling), which may weaken its function as a coating film in the anode material.

If a voltage of 4V or more is passed through a base electrolyte containing hydrofluoric acid (HF) or an organic solvent, problems may occur due to electrolyte decomposition on the surface of the silicon-based anode material. In this case, a side reaction may occur between active chemical species and lithium ions, which are generated by-products, and irreversible loss of secondary battery capacity may occur, and the output of the secondary battery decreases and its lifespan as the resistance inside the electrode increases excessively due to the side reaction product. Performance deterioration may occur.

In order to solve the above problems, methods for manufacturing silicon particles containing polymers are being studied, and the conventional manufacturing method is described as follows.

An example of a conventional manufacturing method is a method of mixing silicon particles and polymer monomers in a solvent to polymerize them, then washing and drying them to produce a polymer containing silicon particles. This method does not allow control of particle size due to agglomeration between particles. It is difficult, and excessive environmental costs due to water treatment during flushing and excessive energy costs may occur when drying.

Another example of a conventional manufacturing method is a method of melting and mixing polymers and silicon particles, curing them, and then pulverizing them. Since a lump of mixture created through curing is pulverized, if the grain boundary between the particles and the polymer or the silicon particles themselves are broken, the silicon particles are broken. It is inevitable that there will be cases of exposure.

In addition, the high energy applied to crush the silicon/polymer may make the interface unstable and weaken the adhesion between the polymer and silicon. In this case, the exposed silicon particles come into direct contact with the electrolyte, causing an electrolyte decomposition reaction, which causes an initial decomposition reaction. The increase in irreversible capacity causes the problem of lower battery utilization capacity, and the weakened silicon/polymer interface causes the polymer layer to easily peel off due to expansion of the silicon during charging or discharging, causing the silicon particles to fall out, causing a sharp drop in lifespan. There is a possibility that it may result in

In the case of the above grinding process, due to the ductility of the polymer and the high strength characteristics of the silicon particles, phenomena such as crushing and stretching, rather than breaking, occur, so not only is the grinding process itself not suitable, but it is also unsuitable for the implementation of polymer coating and the matrix structure itself. don't do it

As described above, in the case of polymers containing conventional silicon particles, it is difficult to maintain chemical stability in a secondary battery environment where voltage is applied to a base electrolyte containing hydrofluoric acid (HF) and an organic solvent, resulting in battery deterioration due to side reactions. has occurred.

In addition, a method of coating carbon was used to suppress swelling, but this method has the disadvantage that the coating layer is easily broken due to the brittleness of carbon, making it difficult to achieve the above objective.

Therefore, there is a need for research and development of new silicon-based active material particles and manufacturing methods that can prevent deterioration due to contact loss, side reactions, and increased resistance of the negative electrode of lithium secondary batteries.

The purpose of the present invention is to provide a negative electrode active material and a method of manufacturing the same that can prevent contact loss, side reactions with electrolyte solutions, and deterioration due to increased resistance.

In order to achieve the above object, the lithium secondary battery negative active material composite material of one embodiment of the present invention includes a silicon-based compound; A fluorine-based resin coating the surface of the silicon-based compound; and conductive particles, including a primer, wherein the conductive particles are contained in an amount of 0.1 to 5% by weight based on the total weight of the lithium secondary battery negative active material composite material, and the average particle diameter (D ₅₀ ) of the conductive particles is 0.1 to 20um. It can be.

The silicon-based compound included in the lithium secondary battery negative active material composite material of one embodiment of the present invention includes silicon, silicon oxide particles (SiO _x , 0<x≤2), silicon-metal alloy, and silicon oxide particles (SiO _x , 0< x≤2) may be at least one selected from the group consisting of metal alloys and silicon-carbon composites.

The conductive particles included in the lithium secondary battery negative active material composite material of one embodiment of the present invention may be one or more selected from the group consisting of graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), and carbon black. You can.

The content range of silicon contained in the silicon-based compound contained in the lithium secondary battery negative active material composite material of one embodiment of the present invention is 20 to 70% based on the total weight of the lithium secondary battery negative active material composite material. It may be weight percent.

The fluorine-based resin contained in the lithium secondary battery negative active material composite material of one embodiment of the present invention may be included in an amount of 0.1 to 20 parts by weight compared to 100 parts by weight of the silicon-based compound.

The lithium secondary battery negative active material composite material of one embodiment of the present invention includes a first step of preparing a resin solution by dissolving a fluorine-based resin in a solvent; A second step of preparing a lithium secondary battery negative active material composite mixture by kneading the silicon-based compound powder and the resin solution at a solid concentration of 70% or more; and a third step of preparing a mixed solution with a diluted concentration by adding additional solvent to the mixture; A fourth step of manufacturing a lithium secondary battery negative electrode active material composite material powder by drying the mixed solution using a spray dryer at a temperature of 120 to 180 ° C.; It may be manufactured including a fifth step of classifying the lithium secondary battery negative active material composite material powder and controlling the average particle diameter (D ₅₀ ).

“Lithium secondary battery negative active material composite material” as a component of the primer used in this specification contains reactive groups (amino group, vinyl group, epoxy group, alkoxy group, It is a compound that has one or more halogen groups. Specifically, dimethoxydiphenylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, disyltrimethoxysilane, methyltrimethoxysilane, methyltrithoxysilane, vinyltrimethoxysilane, octadicyltritoxysilane, jade Tyltriethoxysilane, teraethoxysilane, trifluopropyltrithoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, hexamethyldisilazane, hexyltrimethoxysilane, 3-acroxylpropyltrimethoxysilane , 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-hexyltriethoxysilane, p-sti. It may be selected from liltrimethoxysilane and combinations thereof, but is not limited thereto.

In one embodiment of the present invention, conductive particles may be further added to the mixed solution in the first step.

In one embodiment of the present invention, the silicon-based compound of the first step may have a surface modified with an organic compound.

In one embodiment of the present invention, the second step may include kneading at a speed of 30 to 250 rpm for 5 to 60 minutes.

The anode material for lithium secondary batteries and its manufacturing method of the present invention coat and composite a fluorine-based resin with excellent mechanical and chemical stability on a silicon-based compound, resulting in the phenomenon of silicon-based compounds being detached from the electrode and excessive decomposition products (SEI) on the surface of the silicon-based compound. It is possible to improve the lifespan characteristics of secondary batteries by preventing increases in irreversible capacity and resistance caused by excessive accumulation.

In addition, the coated fluorine-based resin maintains mechanical strength and contains an electrolyte, thereby improving the ionic conductivity of the anode material and improving the C-rate performance of the secondary battery.

Figure 1 is a diagram showing an anode material for a lithium secondary battery and a method of manufacturing the same.
Figure 2(a) is a diagram showing the results of scanning electron microscopy (FE-SEM) analysis of the material of Comparative Example 1, and Figure 2(b) is a diagram showing the results of scanning electron microscopy (FE-SEM) analysis of the material of Example 1.
Figure 3 shows a mapping image through energy dispersive spectrometry (EDS).
Figure 4(a) shows the results of scanning electron microscopy (FE-SEM) analysis and energy dispersive spectrometry (EDS) of the material of Comparative Example 1, and Figure 4(b) shows the results of scanning electron microscopy (FE-SEM) analysis of the material of Experimental Example 2-2. This is a diagram showing a mapping image.
Figure 5 is a coin cell first cycle charge/discharge curve data of a negative electrode active material composite material (silicon-based compound + primer + fluorine-based resin) that does not contain graphite, and Example 3 in Figure 5A is a negative electrode material coated with an appropriate amount of PVDF, Figure 5B. Comparative Example 3 in Figure 5C is a negative electrode material without PVDF coating, and Comparative Example 4 in Figure 5c is a coin cell first cycle charge/discharge curve using a negative electrode material with excessive PVDF coating.

The anode material for lithium secondary batteries and its manufacturing method of the present invention coat and composite a fluorine-based resin with excellent mechanical and chemical stability on a silicon-based compound, resulting in the phenomenon of silicon-based compounds being detached from the electrode and excessive decomposition products (SEI) on the surface of the silicon-based compound. It has the effect of improving the lifespan characteristics of secondary batteries by preventing increases in irreversible capacity and resistance caused by excessive accumulation.

In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various changes can be made. However, the description of the present embodiments is provided to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the present invention of the scope of the invention.

The average particle size (D ₅₀ ) in the present invention can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve.

The lithium secondary battery negative active material composite material of the present invention includes a silicon-based compound; A fluorine-based resin coating the surface of the silicon-based compound; and conductive particles, wherein the conductive particles are included in an amount of 0.1 to 5% by weight based on the total weight of the lithium secondary battery negative active material composite material, and the average particle diameter (D ₅₀ ) of the conductive particles may be 0.1 to 20 um.

The silicon-based compound contained in the lithium secondary battery negative active material composite material of the present invention is silicon, silicon oxide particles (SiO _x , 0<x≤2), silicon-metal alloy, and silicon oxide particles (SiOx, 0<x≤2). It may be one or more selected from the group consisting of metal alloys and silicon-carbon composites. At this time, the silicon oxide particles (SiO _x , 0<x≤2) may be a composite composed of crystalline SiO ₂ , amorphous SiO ₂ , crystalline Si, and amorphous Si.

In the silicon-metal alloy or metal alloy of silicon oxide particles (SiO _x , 0<x≤2), the metal may be a transition metal, Al, Cu, Zr, Ni, Ti, Co, Cr, V, Mn And it may be at least one of Fe. At this time, silicon-metal alloy or metal alloy of silicon oxide particles ( _SiO

The content range of silicon contained in the silicon-based compound of the present invention may be 20 to 70% by weight relative to the total weight of the lithium secondary battery negative active material composite material, but if contained in less than 20% by weight, the capacity of the manufactured lithium secondary battery may be reduced. If it is included in more than 70% by weight, cracking of particles may occur due to excessive volume expansion due to alloying reaction with lithium ions, and the efficiency and capacity maintenance rate of the battery may be significantly reduced due to side reactions with the electrolyte solution. Problems may arise.

The fluorine-based resin included in the lithium secondary battery negative active material composite material of the present invention can be used without limitation as long as it can exhibit ionic conductivity by retaining the electrolyte solution (absorbing and retaining the electrolyte solution), but polyvinylidene fluoride ( It may be one or more selected from PVDF), polytetrafluoroethylene (PTFE), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP).

The polyvinylidene fluoride (PVDF) is not excessively swollen in the electrolyte solution, so it can properly maintain the mechanical strength of the negative electrode active material composite material for lithium secondary batteries, and has excellent ion conduction performance because it can be impregnated with the electrolyte solution, so it is poly among the fluorine-based resins. It is most preferred that vinylidene fluoride (PVDF) is included.

The weight average molecular weight (M _w ) of the fluorine-based resin included in the lithium secondary battery negative active material composite material of the present invention is not particularly limited, but is preferably 100,000 to 1,000,000. If it is less than 100,000, the resin has strong hardness but is not ductile. , there may be a problem as long as it cannot flexibly accommodate the volume expansion of the active material, and if it exceeds 1,000,000, there may be a problem as the viscosity of the solution is high and the adhesive strength of the resin is strong, making it difficult to form particles during the process.

The fluorine-based resin contained in the lithium secondary battery negative active material composite material of the present invention may be included in an amount of 0.1 to 20 parts by weight compared to 100 parts by weight of the silicon-based compound. If it is included in less than 0.1 parts by weight, the amount of fluorine-based resin is too small and silicon-based particles are formed. It is difficult to provide sufficient mechanical strength for expansion, and the effect of reinforcing the adhesion between the binder and particles is significantly reduced, which may lead to a decrease in lifespan due to the particles falling off. In addition, the surface of the silicon-based particles cannot be sufficiently coated, causing side reactions with the electrolyte. It can be difficult to block it effectively. If it is included in excess of 20 parts by weight, the proportion of polymers that do not contribute to the capacity increases, the expansion rate increases due to the swelling of the electrolyte of the polymer, and the plasticity of the polymer causes the pores of the electrode to become clogged during electrode rolling, increasing resistance and lowering the specific energy density. There is.

The fluorine-based resin is chemically stable and has excellent mechanical properties, forming a shell structure and network skeleton surrounding the surface of the silicon-based compound, thereby suppressing the breaking phenomenon of the silicon-based particles when they react with lithium and expand in volume. Even if the particles are broken, loss due to falling off of the silicon-based particles can be prevented by confining them inside the shell structure and network skeleton formed of fluorine-based resin.

The shell structure and network skeleton formed by the fluorine-based resin can improve the conductivity of electrons or lithium ions by maintaining mechanical contact with adjacent particles, for example, conductive particles, which will be described below.

The lithium secondary battery negative active material composite material of the present invention may include conductive particles in the structure of the fluorine-based resin and silicon-based compound to improve electronic conductivity. The conductive particles may have the form of granular, plate-shaped, or linear particles, It may be metal and carbon or a mixture of any one or more of these.

The conductive particles contained in the lithium secondary battery negative active material composite material of the present invention are not particularly limited as long as they have conductivity without causing chemical changes in the lithium secondary battery, and include, for example, graphite such as natural graphite or artificial graphite; This graphitizable carbon (soft carbon); non-graphitizable carbon (hard carbon); Carbon black such as acetylene black, Ketjen black, channel black, Paneth black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

Among the conductive particle materials, the lithium secondary battery negative active material composite material of the present invention may preferably include one or more selected from the group consisting of graphite, carbon fiber, carbon nanotubes, and carbon black, and has excellent conductivity and chemical It is stable and has low reactivity with lithium ions, so electrolyte decomposition reaction is small. Therefore, it is possible to prevent deterioration of battery life characteristics.

The conductive particles may be included in an amount of 0.1 to 5% by weight based on the total weight of the lithium secondary battery negative active material composite material, but if included in less than 0.1% by weight, it may be difficult to form a network that can secure sufficient conductivity, If it is contained in excess of 5% by weight, the capacity of the battery will decrease and the proportion of conductive particles exposed to the outside of the fluorine resin polymer shell structure will be high, causing an increase in electrolyte side reactions, or due to the nature of the high specific surface conductivity particles, the fluorine polymer Problems with reduced adhesion and mechanical strength may occur.

The average particle diameter (D ₅₀ ) of the conductive particles may be 0.1 to 20 um. If it is less than 0.1 um, there may be problems with dispersion due to excessive agglomeration, and if it exceeds 20 um, the number of particles required to form a sufficient conductive network is There may be a problem with insufficient .

The average particle diameter (D ₅₀ ) of the silicon-based compound of the present invention may be 0.05 to 15 um. If it is less than 0.05 um, the specific surface area of the particle and the ratio of the oxide layer on the surface of the silicon-based compound are high, resulting in lower side reactivity and specific capacity, which may lower the utilization capacity of the battery. If it exceeds 15um, the diffusion rate of lithium ions slows down and the expansion force of the silicon-based compound particles increases, which may cause the lithium secondary battery anode active material composite particles to be destroyed and the lifespan of the battery to be deteriorated.

The average particle diameter (D ₅₀ ) of the lithium secondary battery negative active material composite material of the present invention may be 1 to 20 um. If it is less than 1 um, the particles are too small and may block the pores of the negative electrode, reducing the output performance of the lithium secondary battery. If it exceeds 20 um, the resistance increases due to an increase in the lithium ion diffusion distance, which reduces the output performance of the lithium secondary battery. As a significant proportion of the electrode thickness direction is composed of silicon-based materials, excessive expansion stress is concentrated when the silicon-based composite particles expand in volume. This may result in a sharp decrease in battery life due to detachment and destruction of the electrode compound.

The "primer" of the present invention can serve as a buffer coating layer that improves adhesion by coating at a nano thickness between the base material and the functional coating layer.

The lithium secondary battery negative active material composite material of the present invention includes the first step of preparing a resin solution by dissolving a fluorine-based resin in a solvent; A second step of kneading the silicone compound powder and the resin solution to a solids concentration of 70% or more to create a mixture in which the surface of the silicone compound powder and the resin solution are mixed with high affinity; A third step of preparing a mixed solution at a concentration suitable for spray drying by adding and mixing a solvent to the mixture; A fourth step of producing composite material powder by spray drying the mixed solution; And a fifth step of classifying the negative active material composite material powder for lithium secondary batteries to control the average particle diameter (D ₅₀ ).

The fluorine-based resin can be used without limitation as long as it can retain electrolyte and exhibit ionic conductivity, but polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) ) may be used.

The polyvinylidene fluoride (PVDF) is not excessively swollen in the electrolyte solution, so it can properly maintain the mechanical strength of the negative electrode active material composite material for lithium secondary batteries, and has excellent ion conduction performance because it can be impregnated with the electrolyte solution, so it is poly among the fluorine-based resins. It is most preferable to use vinylidene fluoride (PVDF).

Solvents that dissolve the fluorine resin include acetone, tetrahydrofuran, acetonitrile, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, NMP (N-methyl pyrrolidone), water, etc., and two or more of these solvents are mixed. You can also use it.

The first step of preparing a resin solution by dissolving a fluorine-based resin in a solvent for the lithium secondary battery negative active material composite material of the present invention is to mix the fluorine-based resin in the solvent in a mixing tank at a speed of 500-1500 rpm at 40-80°C for 30 minutes. This may be a step of preparing a mixed solution by stirring for minutes to 2 hours.

Conductive particles may be further added to the mixed solution in the first step. The conductive particles may have the form of granular, plate-shaped, or linear particles, and may be a mixture of metal and carbon or one or more of these. .

Specifically, the conductive particles are not particularly limited as long as they have conductivity without causing chemical changes in the lithium secondary battery, and include, for example, graphite such as natural graphite or artificial graphite; This graphitizable carbon (soft carbon); non-graphitizable carbon (hard carbon); Carbon black such as acetylene black, Ketjen black, channel black, Paneth black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

Among the conductive particle materials, the lithium secondary battery negative active material composite material of the present invention may preferably include one or more selected from the group consisting of graphite, carbon fiber, carbon nanotubes, and carbon black, and has excellent conductivity and chemical It is stable and has low reactivity with lithium ions, so electrolyte decomposition reaction is small. Therefore, it is possible to prevent deterioration of battery life characteristics.

The fluorine-based resin in the mixed solution is preferably included in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the silicone-based compound.

The method for producing a lithium secondary battery negative active material composite material of the present invention may include a second step of producing a lithium secondary battery negative active material composite mixture by kneading the mixed solution with a solid content of 70% or more.

In the second step, the step must be performed with the solids concentration of the mixed solution being 70% or more. However, if the solids concentration is less than 70%, the kneading energy is not sufficient and the resin solution is sufficiently electrowetted on the surface of the silicone compound particles ( Problems such as electrowetting or insufficient dispersion of fine conductive particles may occur.

The second step may include kneading at a speed of 30 to 250 rpm for 5 to 60 minutes. When kneading for less than 5 minutes in the kneading process, the resin solution is sufficiently electrowetting the surface of the silicon-based particles. ) or the conductive particles are not sufficiently dispersed and mixed, and if kneaded for more than 60 minutes, problems such as fine powder or increased surface energy may occur due to damage to the particle surface of the silicon-based compound due to excessive friction. It can happen.

If kneading is performed at a speed of less than 30 rpm in the kneading process, problems may occur in which the resin solution is not sufficiently wetted on the surface of the silicon-based particles or the conductive particles are not sufficiently dispersed and mixed due to insufficient kneading energy. When kneading at an excessive speed, the movement speed of the powder increases, so the milling phenomenon in which the solvent and powder move separately rather than the kneading phenomenon in which the powder and solution move together becomes the dominant environment, so the particle surface of the silicon-based compound becomes Problems may arise where differentiation occurs due to damage.

The manufacturing method of the lithium secondary battery negative active material composite material of the present invention may include a mixed solution preparation step of adding and mixing a solvent to dilute the composite mixture to a concentration that is easy to spray dry, where the solid content concentration is 3%. to 30% is preferred. A solid concentration of less than 3% causes problems with reduced process yield and process energy efficiency, and a concentration of more than 30% causes problems such as reduced flowability and increased nozzle pressure within the spray drying process equipment due to viscosity.

The method for manufacturing a lithium secondary battery negative active material composite material of the present invention may include a fourth step of drying the mixed solution using a spray dryer in a temperature range of 120 to 150 ℃, under temperature conditions of less than 120 ℃. If this is done, the solvent may not dry sufficiently, which may cause the particles to clump together. If the process is performed at a temperature exceeding 150°C, the fluorine resin may melt, causing particles to stick together, and thermal polymerization of the resin. , problems with physical property changes due to thermal denaturation such as decomposition may occur.

The spray dryer can be an explosion-proof type or a general spray dryer.

Here, the temperature of the injection part of the mixed solution, which is the subject of spray drying, may be 120 to 180°C, and the temperature of the discharge part may be 70 to 110°C. The injection speed of the liquid and the amount of compressed air can be changed depending on the capacity of the spray dryer, the amount of evaporation, the size of the droplet, and the viscosity of the liquid. After spray drying, the lithium secondary battery negative active material composite material coated with fluorine resin can be recovered. .

If the temperature of the injection part during spray drying is less than 120°C, it is difficult to manufacture dry powder due to residual moisture, and if it exceeds 180°C, there may be a problem of oxidation of silicon.

If the discharge temperature is less than 70°C, it is difficult to recover the composite particles due to wetness, and if it exceeds 110°C, there are problems such as narrow selection of recovery containers due to heat deformation problems and oxidation of silicon.

The manufacturing method of the lithium secondary battery negative active material composite material of the present invention may include a fifth step of classifying the lithium secondary battery negative active material composite powder to control the average particle diameter (D ₅₀ ).

Any method for classifying the lithium secondary battery negative active material composite powder can be used as long as it can be separated, but classification can be performed using a sieve classifier or air flow classifier, and the average particle diameter (D ₅₀ ) or particle size distribution can be controlled.

Below, specific examples are presented to aid understanding of the present invention. However, the following examples are provided only to make the present invention easier to understand, and the content of the present invention is not limited by the examples.

Example 0: Manufacturing of lithium secondary battery negative active material composite material

<Surface modification of the SiOx particle surface to improve the adhesion (bondability) between fluorine resin and SiOx (primer introduction step)>

(One). After dispersing 2 kg of silicon oxide (SiOx) in 4 L of ethanol in the reactor, 20 mL of hexyltrimethoxysilane (HTMS), a primer, was slowly added dropwise while stirring at 600 rpm at room temperature. 40 mL of ammonia water (NH4OH, ~30%) was sequentially added and reacted at 40°C for 4 hours. After the reaction was completed, SiOx modified with HTMS (SiOx-HTMS) and residual HTMS and NH4OH were separated through a centrifuge, and washing and centrifugation were repeated three times with ethanol. The washed SiOx-HTMS was dried under reduced pressure at 60°C.

(2). In a mixing tank, 200 g of polyvinylidene fluoride (PVDF) resin was completely dissolved in 850 mL of NMP (N-methyl pyrrolidone) solvent by stirring at 40°C for 1 hour at a speed of 800 rpm, and SiOx (SiOx() modified with HTMS primer was added thereto. A mixture was prepared by adding 1800 g of SiOx-HTMS) and kneading at 100 rpm.

<Spray drying method>

(3-1). In the reaction vessel, 17.15 L of NMP was added to the mixture and stirred for 1 hour at a speed of 1200 rpm to prepare a mixed solution diluted to a solid content concentration of 10%. Then, the mixed solution was dried at 190° C. using a Yamato Spray Dryer (spray dryer). It was dried using ADL311SA). Here, the temperature of the injection part of the spray dryer was set to 170°C and the temperature of the discharge part was 100°C to obtain about 1800 g of silicon-based negative active material composite material powder surface-coated with polyvinylidene fluoride (PVDF).

<Water casting method>

(3-2). In a reaction vessel, 17.15 L of NMP was added to the mixture and stirred for 1 hour at a speed of 1200 rpm to prepare a mixed solution diluted to a solid content concentration of 10%, and then added to 600 L of distilled water stirred at 400 rpm at a speed of 100 mL/min. The mixed solution was added dropwise to solidify, separated from the solvent by centrifugation, and dried at 60 ^o C to obtain about 1600 g of silicon-based negative active material composite powder surface-coated with polyvinylidene fluoride (PVDF).

(4). The lithium secondary battery negative electrode active material composite powder was classified to prepare about 1500 g of silicon-based negative electrode active material composite powder with an average particle diameter (D50) of 10 um surface-coated with polyvinylidene fluoride (PVDF).

Example 1: Preparation of lithium secondary battery negative active material coated with 10% fluorine resin using spray drying method

A silicon-based negative electrode active material material coated with 3% fluorine-based resin was manufactured in the same manner as the process (3-1) of Example 0.

Example 2: Preparation of lithium secondary battery negative electrode active material coated with 10% fluorine resin using water casting method

A silicon-based negative active material material coated with 10% fluorine-based resin was manufactured in the same manner as the process (3-2) of Example 0.

Comparative Example 1: Manufacturing of lithium secondary battery negative active material whose surface is not coated with fluorine resin

The same SiOx used in the process of (1) of Example 0 was used, but the difference was that it was not coated with polyvinylidene fluoride (PVDF) resin.

Comparative Example 2: Preparation of a negative electrode active material with an overcoating of 50% fluorine-based resin on the surface

Produced in the same manner, except that 1000 g of polyvinylidene resin was dissolved in 4.5 L of NMP in step (1) of Example 0 and diluted with 34 L of NMP in steps (3-1) to (3-2). did.

Experimental Example 1 : EDS analysis of silicon oxide (SiOx) into which primers were introduced

In order to confirm that silicon oxide (SiOx) was modified with a primer (HTMS) in Example 0, SiOx and The surface elemental composition of SiOx-HTMS material is shown.

It was confirmed that the ratio of C increased and the ratio of Si and O decreased, confirming that a hydrophobic C ₆ H ₁₃ - hydrocarbon film was formed through modification of HTMS on the SiOx surface.

Element At.No. Mass
[%] Mass Norm.
[%] Atom
[%] abs. error[%]
(3 sigma) _SiO C 6 9.52 11.61 19.19 2.99 O 8 28.15 34.33 42.60 8.70 Si 14 44.31 54.05 38.20 6.15 Pt 78 0.00 0.00 0.00 0.00 81.98 100.00 100.00 SiOx-HTMS C 6 9.89 12.71 20.85 3.13 O 8 26.30 33.80 41.63 8.20 Si 14 41.63 53.49 37.53 5.78 Pt 78 0.00 0.00 0.00 0.00 77.82 100.00 100.00

Experimental Example 2-1: Scanning electron microscope (FE-SEM) analysis of anode active material manufactured by spray drying method

Scanning electron microscopy (FE-SEM) analysis was performed on the silicon-based anode active material prepared in Example 1 and Comparative Example 1 to confirm the shape and internal microstructure of the structural particles. The results are shown in Figure 2.

Figure 2(a) is a diagram showing the results of scanning electron microscopy (FE-SEM) analysis of the material of Comparative Example 1, and Figure 2(b) is a diagram showing the results of scanning electron microscopy (FE-SEM) analysis of the material of Example 1.

In Figure 2(a), it was shown that polyvinylidene fluoride (PVDF) was not formed on the surface of silicon dioxide (SiO ₂ ), and in Figure 2(b), polyvinylidene fluoride (PVDF) was formed on the surface of silicon dioxide (SiO 2 ). ₂ ) was confirmed to have formed amorphously on the surface.

Figure 3 shows a mapping image through energy dispersive spectrometry (EDS), with Figure 3(a) showing the material of Comparative Example 1 and Figure 3(b) showing the material of Example 0. This is a drawing showing the analysis results. Through this, it was confirmed that the amorphous portion (dark green) formed in the material of Example 0 in FIG. 3(b) was PVDF resin.

Table 2 below shows the composition of the materials of Example 1 and Comparative Example 1 calculated based on the results of quantitative analysis through energy dispersive spectrometry (EDS). In Comparative Example 1, no fluorine (F) was present on the surface of the material, but in Preparation Example 1, it was confirmed that about 0.84% of fluorine (F) was present.

Element At.No. Mass
[%] Mass Norm.
[%] Atom
[%] Example 1 C 6 30.61 20.88 45.06 O 8 21.85 14.91 24.15 Si 14 41.33 28.20 26.02 F 9 1.23 0.84 1.15 Comparative Example 1 C 6 21.38 14.76 33.36 O 8 26.96 18.60 31.57 Si 14 45.73 31.55 30.50

Experimental Example 2-2: Scanning electron microscope of anode active material manufactured by water casting method (FE-SEM) analyze

Scanning electron microscopy (FE-SEM) analysis was performed on the silicon-based anode active material prepared in Example 2 and Comparative Example 1 to confirm the shape and internal microstructure of the structural particles. The results are shown in Figure 4.

Figure 4(a) shows the results of scanning electron microscopy (FE-SEM) analysis and energy dispersive spectrometry (EDS) of the material of Comparative Preparation Example 1, and Figure 4(b) shows the results of scanning electron microscopy (FE-SEM) analysis of the material of Experimental Example 2-2. This is a diagram showing a mapping image through .

In Figure 4(a), it was shown that polyvinylidene fluoride (PVDF) was not formed on the surface of silicon dioxide (SiO ₂ ), and in Figure 4(b), polyvinylidene fluoride (PVDF) magnets with a size of about 100 nm were observed. It was confirmed that the assembled nanostructure formed an assembled film on the surface of silicon oxide (SiOx). Additionally, as a result of EDS confirmation, the nanostructure was confirmed to be polyvinylidene fluoride (PVDF) (green).

Table 3 below shows the composition of the materials of Example 2 and Comparative Example 2 calculated based on the results of quantitative analysis through energy dispersive spectrometer (EDS). In Comparative Example 1, fluorine (F) was not present on the surface of the material, but in Example 2, it was confirmed that fluorine (F) was present in an amount of about 4.864%.

Element At.No. Mass
[%] Mass Norm.
[%] Atom
[%] abs. error[%]
(3 sigma) Example 2 C 6 18.88 23.77 35.78 6.00 O 8 22.16 27.89 31.53 7.09 F 9 4.06 5.11 4.86 1.42 Si 14 34.35 43.23 27.84 4.77 Pt 78 0.00 0.00 0.00 0.00 79.45 100.00 100.00 comparison
Example 2 C 6 10.40 13.78 22.62 3.31 O 8 23.96 31.77 39.14 7.51 F 9 0.06 0.08 0.08 0.03 Si 14 41.0 54.38 38.17 5.70 Pt 78 0.00 0.00 0.00 0.00 75.44 100.00 100.00

Experiment example 3: Specific surface area and pore volume analysis

In order to analyze the specific surface area and pore volume of 2g of the negative active material composite powder prepared according to Example 1 and Comparative Example 1, a nitrogen adsorption and desorption experiment was performed.

The nitrogen adsorption and desorption experiment was performed using a BET specific surface area analyzer (BET, Brunauer Emmett Teller), and N2 adsorption was performed under a temperature of 77K to obtain an adsorption isotherm curve.

At this time, the specific surface area ( _{as, BET} ) was calculated using the BET equation (Brunauer-Emmett-Teller equation), and the total pore volume was calculated from the amount of nitrogen adsorbed under the above conditions.

Table 4 below shows the results of the BET specific surface area analysis, and the meaning of each item is as follows.

V _m : Adsorption amount required to form a monomolecular layer on the sample surface (㎤/g)

a _{s, BET} : Specific surface area of sample (m ² g ^-1 )

C: BET constant

total pore volume: total pore volume (cm ³ g ^-1 )

item Example 1 Comparative Example 1 V _m 0.99cm ² (STP)g ^-1 1.027cm ² (STP)g ^-1 _as,BET 4.309m ² g ^-1 4.47 m ² g ^-1 C 59.426 132.59 total pore volume
(Under the condition of P/P ₀ = 0.99) 0.032258cm ³ g ^-1 0.01724cm ³ g ^-1

Experimental Example 4 : Pore size analysis

The pore size of the material manufactured according to Example 1 and Comparative Example 1 was measured using a Surface area analyzer (ASAP-2420) manufactured by Micromeritics. Specifically, the maximum peak position of the Barrett-Joyner-Halenda (BJH) pore size distribution curve obtained from the nitrogen gas sorption isotherm of the samples obtained from Example 1 and Comparative Example 1 was measured to determine the powder particle size. The pore size was measured.

Table 5 below shows the Barrett-Joyner-Halenda (BJH) pore size analysis results, and the meaning of each item is as follows.

V _p : Pore volume (cm ³ g ^-1 )

d _{p, peak} (Vol):

a _p : Specific surface area of pores

average pore diameter: average pore diameter

median pore diameter: median pore diameter

item Example 1 Comparative Example 1 V _p 0.031452cm ³ g ^-1 0.016656cm ³ g ^-1 d _{p, peak} (Vol) 103.54nm 90.216nm a _p 4.8915 m ² g ^-1 4.5296m ² g ^-1 Average pore diameter 25.72 nm 14.709 nm Median pore diameter 54.246nm 24.057 nm

As described above, Example 1 has a larger average pore diameter and median pore diameter compared to Comparative Example 1, thereby minimizing structural changes in the silicon used as the cathode material and Cycle stability can be improved by alleviating volume expansion during discharge electrochemical reactions.

Experimental Example 5 : charging capacity , discharge capacity and evaluation of coulombic efficiency.

To prepare the powder of Example 0 in slurry form, the powder of Example 0 was mixed with water at a ratio of 19.2 wt.%, 76.8% artificial graphite, 1 wt.% Super P, 1.3 wt.% CMC, and 1.7 wt.% SBR. It was mixed and prepared at a solid content concentration of 50%. The slurry was applied to a copper (Cu) metal thin film at a loading of 160 mg/25 cm ² (6 mg/cm ² ) and dried. At this time, the temperature of the circulating air was 70°C.

Next, the slurry applied and dried negative electrode current collector was rolled and dried in a vacuum oven at 120°C for 8 hours to prepare a negative electrode.

The cathodes were each cut into circular shapes of 1.13 cm ² to be used as working electrodes, and Li-metal was used as the counter electrode.

A porous polyethylene separator was interposed between the counter electrode and the working electrode, and ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC) were mixed at a concentration of 1M in a mixed solution with a mixing volume of 4:3:3. Five coin-half-cells containing one sheet of Li-metal and one cathode were manufactured by injecting an electrolyte solution containing dissolved LiPF6. The values of the three cells were averaged by excluding the highest and lowest values. .

An experiment was conducted to evaluate the charge capacity, discharge capacity, and coulombic efficiency of the coin-half-cell at a temperature of 25 degrees under the conditions shown in Table 6 below.

cycle Current density conditions Charging cut-off voltage Discharge cut-off voltage pause time 1~3 0.3mA/ ^cm2 0.01V 1.5V 10 minutes 4~50 0.5 mA/ ^cm2

In the above 1 to 3 cycles, the battery is charged with a constant current of 0.3 mA/cm ² , cut-off when the voltage reaches 0.01 V, then left in OCV state for 10 minutes, then discharged with a constant current of 0.3 mA/cm ² and then the voltage drops to 1.5 V. Each cycle was charged and discharged by setting the cut-off when reaching .

In the above 4 to 50 cycles, the battery is charged with a constant current of 0.5 mA/cm ² , cut-off when the voltage reaches 0.01 V, then left in OCV state for 10 minutes, then discharged with a constant current of 0.5 mA/cm ² and then the voltage drops to 1.5 V. Each cycle was charged and discharged by setting the cut-off when reaching .

The results of evaluating the first cycle charge capacity, discharge capacity, initial irreversible capacity, Coulombic efficiency, 50 cycle capacity retention rate, and electrode adhesion of the coin-half-cell under the conditions of Table 6 are as follows. It was the same as Table 7 in .

In Example 1, the 50 cycle capacity maintenance rate was 91.3, which was higher than Comparative Examples 1 and 2.

Example 1 Comparative Example 1 Comparative example 2 First cycle charging capacity
(mAh/g) 617.4 711.68 492.8 First cycle discharge capacity (mAh/g) 528.6 602.2 425.9 Initial irreversible capacity (mAh/g) 88.9 109.4 66.9 Initial efficiency (%) 85.6 84.6 86.4 50 cycle capacity maintenance rate 91.3 52.3 87.8 Electrode adhesion (N) 0.42 0.23 0.43

In addition, in order to prepare the powder of Example 0 in the form of a slurry, the powder of Example 0 was mixed at a ratio of 96%, Super P 1wt.%, CMC 1.3wt.%, and SBR 1.7wt.% with water to obtain a solid concentration of 50%. It was manufactured as is. The slurry was applied to a copper (Cu) metal thin film at a loading of 160 mg/25 cm2 (6 mg/cm2) and dried. At this time, the temperature of the circulating air was 70°C. First cycle charge capacity, discharge capacity, initial irreversible capacity, Coulombic efficiency, 50 cycle capacity maintenance rate, and electrode adhesion were evaluated under the conditions of Table 6 above, and the evaluation results are shown in Table 8 below.

In Example 3, it was confirmed that the 50-cycle capacity maintenance rate was 69.5, which was higher than Comparative Examples 3 and 4.

In Table 8 and Figures 5-1, 5-2, and 5-3, Example 3 is a cathode material with an appropriate amount of PVDF coating, Comparative Example 3 is a cathode material without PVDF coating, and Comparative Example 4 is a cathode material with excessive PVDF coating. It is a material.

Example 3 Comparative Example 3 Comparative example 4 First cycle charging capacity
(mAh/g) 2095.7 2263.5 1034.6 First cycle discharge capacity (mAh/g) 1467.3 1630.7 744.9 Initial irreversible capacity (mAh/g) 628.4 632.8 289.7 Initial efficiency (%) 70 72 72 50 cycle capacity maintenance rate 69.5 36.2 60.3

The cathode materials of each Example and Comparative Example showed the same level of initial efficiency, but it can be seen that the charging resistance level is different through the voltage curve during initial charging. The voltage curve graph during initial charging is shown in Figure 5.

In the case of Example 3, when comparing the charging curve voltage, the charging voltage was formed higher than that of Comparative Example 3, and considering that the CV charging rate starting at 0.01 V was significantly lower than that of Comparative Example 3, the low voltage expected by the present inventors by PVDF coating It can be seen that surface resistance has been realized. On the other hand, in the case of Comparative Example 4, it can be seen that the CV charge ratio is very high at about 40% of the total, which can be seen as because PVDF, an initial insulator, exists in excess on the surface and acts as resistance.

Claims (6)

In the lithium secondary battery negative active material composite material,
Silicone-based compounds;
A fluorine-based resin coating the surface of the silicon-based compound; and
Contains conductive particles,
Contains a primer,
The conductive particles are contained in an amount of 0.1 to 5% by weight based on the total weight of the lithium secondary battery negative active material composite material,
A lithium secondary battery negative active material composite material where the average particle diameter (D ₅₀ ) of the conductive particles is 0.1 to 20 um.
According to paragraph 1,
The silicon-based compound is selected from the group consisting of silicon, silicon oxide particles (SiO _x , 0<x≤2), silicon-metal alloys, metal alloys of silicon oxide particles (SiO _x , 0<x≤2), and silicon-carbon composites. One or more selected lithium secondary battery negative active material composite materials.
According to paragraph 1,
A lithium secondary battery negative active material composite material wherein the conductive particles are one or more selected from the group consisting of graphite, carbon fiber, carbon nanotubes, and carbon black.
According to paragraph 1,
A lithium secondary battery negative electrode active material composite material in which the content range of silicon contained in the silicon-based compound is 20 to 70% by weight based on the total weight of the lithium secondary battery negative electrode active material composite material.
According to paragraph 1,
A lithium secondary battery negative active material composite material containing the fluorine-based resin in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the silicon-based compound.
According to claim 1,
The primers include dimethoxydiphenylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, disyltrimethoxysilane, methyltrimethoxysilane, methyltritoxysilane, vinyltrimethoxysilane, octadicyltritoxysilane, and jade. Tyltriethoxysilane, teraethoxysilane, trifluopropyltrithoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, hexamethyldisilazane, hexyltrimethoxysilane, 3-acroxylpropyltrimethoxysilane , 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-hexyltriethoxysilane, p-sti. A lithium secondary battery negative electrode active material composite material that is at least one selected from the group consisting of liltrimethoxysilane.