KR102661927B1 - Negative active material and negative electrode comprising the same - Google Patents

Abstract

The present invention provides a negative electrode active material including a recessed portion and first silicon-based particles including a skeleton portion disposed around the recessed portion and partitioning each of the recessed portions, and a negative electrode including the same.

Description

Negative active material and negative electrode containing the same {NEGATIVE ACTIVE MATERIAL AND NEGATIVE ELECTRODE COMPRISING THE SAME}

The present invention relates to a negative electrode active material and a negative electrode containing the same.

As the electronics, communications, and space industries develop, the demand for secondary batteries as an energy power source is rapidly increasing. In particular, as the importance of global eco-friendly policies is emphasized, the electric vehicle market is growing rapidly, and research and development on secondary batteries is being actively conducted at home and abroad.

Secondary batteries generally consist of a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and an electrolyte. In particular, lithium secondary batteries have high energy density and can exhibit high capacity, so they are applied in various fields.

As the negative electrode active material constituting the negative electrode, materials such as carbon-based materials or silicon oxide are used. However, in the case of carbon-based materials, the theoretical capacity is only about 400 mAh/g, which has the disadvantage of having a small capacity.

Therefore, research has been conducted to replace carbon-based materials using silicon, which has a high theoretical capacity, as a negative electrode active material. However, the volume of the silicon material expands by about 300% due to lithium insertion, which causes the cathode to be destroyed and the cycle characteristics to deteriorate. In addition, as the cycle continues, volume expansion continues to occur due to the lithium insertion, causing problems such as loss of contact with the conductive material and the current collector or the formation of an unstable solid electrolyte interphase (SEI).

The present invention provides a negative electrode active material that suppresses volume expansion of a silicon-based active material and has improved lifespan characteristics, and a negative electrode containing the same.

The negative electrode active material according to the present invention includes first silicon-based particles that include a recessed portion and a skeleton portion disposed around the recessed portion and dividing each of the recessed portions.

In one embodiment of the present invention, the first silicon-based particles may have a diameter of 3 ㎛ to 15 ㎛.

In one embodiment of the present invention, the depth of the concave portion in the direction toward the center of the first silicon-based particle: The diameter of the first silicon-based particle may have a ratio of 0.01:1 to 0.80:1.

In one embodiment of the present invention, the ratio of the opening area of the concave portion to the area of the first silicon-based particle may be 20% to 95%.

In one embodiment of the present invention, the volume ratio of the concave portion to the volume of the first silicon-based particle may be 5% to 80%.

In one embodiment of the present invention, the skeleton portion may include a branched structure.

In one embodiment of the present invention, the first silicon-based active material may satisfy the following general formula 1.

[General Formula 1]

1 ≤ Y/X ≤ 80

In General Formula 1,

In one embodiment of the present invention, it includes the concave portion and the skeleton portion, and may further include second silicon-based particles having a diameter of 0.1 ㎛ to less than 3 ㎛.

In one embodiment of the present invention, the second silicon-based particle may be disposed in at least a portion of the concave portion of the first silicon-based particle.

In one embodiment of the present invention, the first silicon-based particles may include silicon particles and silicon oxide in which the surface of the silicon particles is oxidized.

In one embodiment of the present invention, the silicon particles may have a diameter of 1 nm to 500 nm.

In one embodiment of the present invention, the silicon oxide may be represented by the following formula (1).

[Formula 1]

SiO _x (0<x≤0.9)

In one embodiment of the present invention, the first silicon-based particle may have a carbon layer formed on at least a portion of the surface of the silicon oxide.

A negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a concave portion and a surrounding portion of the concave portion. It is disposed in and includes first silicon-based particles including a skeleton portion that partitions each of the concave portions.

The present invention includes silicon-based particles with concave portions formed as a negative electrode active material, so that the influence of volume expansion of the silicon-based particles due to insertion of lithium ions can be reduced. As a result, the destruction behavior of silicon-based particles is reduced, and the phenomenon of silicon-based particles being pulverized as the cycle increases is minimized, thereby improving the lifespan characteristics of a secondary battery containing the negative electrode active material.

In addition, the silicon-based particles of the present invention have a plurality of concave structures, so that the surface area of the silicon-based particles can be increased, thereby improving the charging and discharging performance of the secondary battery, and reducing the volume expansion of the silicon-based particles that can occur in various directions. It can be reduced more efficiently.

In addition, the silicon-based particles of the present invention have a branched skeletal structure, thereby improving mechanical properties and minimizing the phenomenon of silicon-based particles breaking due to the manufacturing process of a secondary battery or external impact.

In addition, the silicon-based particles of the present invention have a composite form containing nano-sized silicon particles, silicon oxide, and a carbon-based coating layer, and thus have superior electrical conductivity compared to conventional silicon oxide and exhibit a high silicon ratio, increasing the capacity of secondary batteries. can be increased.

Figure 1 schematically shows a first silicon-based particle according to an embodiment of the present invention.
Figure 2 schematically shows first silicon-based particles and second silicon-based particles according to another embodiment of the present invention.
Figure 3 shows an SEM photograph of the negative electrode active material particles of Preparation Example 1.
Figure 4 shows an SEM photograph of the negative electrode active material particles of Comparative Example 1.
Figure 5 shows an SEM photograph of the negative electrode active material particles of Comparative Example 2.

The structural or functional descriptions of the embodiments disclosed in the present specification or application are merely illustrative for the purpose of explaining embodiments according to the technical idea of the present invention, and the embodiments according to the technical idea of the present invention are described in this specification. Alternatively, it may be implemented in various forms other than the embodiments disclosed in the application, and the technical idea of the present invention is not to be construed as being limited to the embodiments described in this specification or application.

In addition, when it is said that a certain element is 'included' in this specification or application, this does not mean excluding other elements, but may further include other elements, unless specifically stated to the contrary. In addition, all numerical ranges representing physical property values, dimensions, etc. of components described in this specification or application should be understood as modified by the term 'about' in all cases unless otherwise specified.

In addition, in this specification or application, “silicon-based” means containing about 50% by weight or more of silicon.

Below, a negative electrode active material according to the present invention and a negative electrode containing the same will be described.

<Anode active material>

The negative electrode active material according to the present invention includes first silicon-based particles. Figure 1 schematically shows a first silicon-based particle according to an embodiment of the present invention. Referring to FIG. 1, the first silicon-based particles 100 are disposed around the concave portion 10 and the concave portion 10, and include a skeleton portion 20 that partitions each of the concave portions 10. do.

The concave portion 10 is 100 nm to 5 ㎛, 100 nm to 4 ㎛, 100 nm to 3 ㎛, 100 nm to 2 ㎛, 100 nm to 1 ㎛, or It may have a depth of 100 nm to 900 nm. The first silicon-based particle 100 includes a concave portion 10 having the depth, so that the volume expansion of the silicon particle due to insertion of lithium ions can be absorbed as much as the space of the concave portion 10. By significantly suppressing the volume expansion of the particles themselves, the phenomenon of micronization of the silicon-based particles as the cycle increases can be minimized.

The first silicon-based particles 100 may have a diameter of 3 ㎛ to 15 ㎛, 3 ㎛ to 12 ㎛, 3 ㎛ to 10 ㎛, 3 ㎛ to 9 ㎛, 3 ㎛ to 8 ㎛, or 3 ㎛ to 7.5 ㎛. there is. The diameter can be defined as a diameter corresponding to 50% of the volume accumulation in the diameter distribution curve. For example, the diameter can be measured using a laser diffraction method. When the above range is satisfied, the content of the first silicon-based particles can be increased, and the phenomenon of pulverizing the first silicon-based particles during electrode rolling can be minimized.

The depth of the concave portion 10 in the direction toward the center of the first silicon-based particle: The diameter of the first silicon-based particle 100 may have a ratio of 0.01:1 to 0.80:1. Preferably, the depth of the concave portion 10: The diameter of the first silicon-based particle 100 is 0.10:1 to 0.80:1, 0.10:1 to 0.75:1, 0.20:1 to 0.75:1, 0.20:1. It may have a ratio of from 0.60:1 to 0.20:1 to 0.50:1. When the above range is satisfied, the volume expansion of the silicon-based particles themselves can be significantly suppressed without reducing mechanical strength.

The concave portion 10 may include a first concave portion 11 and a second concave portion 12 adjacent to the first concave portion 11 . The first silicon-based particles 100 are formed with a plurality of concave parts such as the first concave part 11 and the second concave part 12, thereby more effectively suppressing volume expansion of the silicon-based particles that may occur in various directions. can do.

The ratio of the opening area of the concave portion 10 to the area of the first silicon-based particle 100 is 20% to 95%, 25% to 95%, 30% to 95%, 35% to 95%, 35%. It may be from 40% to 90%, or from 40% to 90%. The ratio of the opening area of the concave portion 10 means the ratio of the opening area of the flat surface portion 10 to the area of the first silicon-based particle 100 on a plane. The opening area ratio of the concave portion 10 is determined by observing a portion of the surface of the first silicon-based particle 100 using a scanning electron microscope (SEM), and then determining the ratio of the opening area of the concave portion 10 in the surface area. It can be obtained by calculating the ratio of the opening area of .

The volume ratio of the concave portion 10 to the volume of the first silicon-based particle 100 is 5% to 80%, 7% to 80%, 10% to 80%, 15% to 80%, and 18% to 80%. %, 20% to 80%, or 25% to 80%. The volume ratio of the concave portion 10 refers to the ratio of the volume of the concave portion 10 to the volume of the virtual outline of the first silicon-based particle 100. The volume of the virtual outline of the first silicon-based particle 100 refers to the volume when the concave portion 10 does not exist, that is, assuming that the space of the concave portion 10 is filled. The volume of the concave portion 10 can be obtained by calculating the increased weight of the first silicon-based particle 100 when immersed in a solvent and the density of the solvent.

When the above range is satisfied, the volume expansion of the silicon-based particles due to insertion of lithium ions can be significantly suppressed, and the surface area of the silicon-based particles can be increased to improve the lifespan characteristics and charge/discharge performance of the secondary battery.

The skeleton portion 20 may include a branched structure. The skeleton portion 20 may include a structure branched in a first direction, a second direction, a third direction, or a fourth direction. The skeleton portion 20 may include a structure extending in any one of the first to fourth directions with the branch point as the center. As the skeleton portion 20 has a branched structure, mechanical properties are improved and the phenomenon of silicon-based material being broken due to the manufacturing process of a secondary battery or external shock can be minimized.

The first silicon-based particles 100 may satisfy the following general formula 1.

[General Formula 1]

1 ≤ X/Y ≤ 80

In the general formula 1, Length (A, nm). The depth of the concave portion 10 refers to the maximum depth among the plurality of concave portions 10, and the length A of the skeleton portion 20 refers to the minimum length between adjacent concave portions 10 in the width direction. do.

X/Y in the general formula 1 is 2 ≤ X/Y ≤ 80, 2 ≤ X/Y ≤ 75, 2 ≤ X/Y ≤ 70, 5 ≤ can be satisfied. When the above range is satisfied, mechanical properties can be improved, and volume expansion of silicon-based particles due to insertion of lithium ions can be significantly suppressed.

Figure 2 schematically shows first silicon-based particles 100 and second silicon-based particles 200 according to another embodiment of the present invention. Referring to FIG. 2, the negative electrode active material according to the present invention includes the concave portion and the skeleton portion, and may further include second silicon-based particles 200 having a diameter of 0.1 ㎛ to less than 3 ㎛. Preferably, the second silicon-based particles 200 may have a diameter of 0.2 ㎛ to less than 3 ㎛, 0.2 ㎛ to 2 ㎛, 0.2 ㎛ to 1 ㎛, or 0.3 ㎛ to 1 ㎛. The diameter may be measured by the same method as the diameter measurement method of the first silicon-based particle.

The second silicon-based particles 200 may be disposed in at least a portion of the concave portion 10 of the first silicon-based particles 100. The second silicon-based particles 200 having a diameter smaller than the diameter of the first silicon-based particles 100 are included in the concave portion 10 of the first silicon-based particles 100, so that the second silicon-based particles 200 are formed during charging and discharging of lithium. Even if volume expansion of (200) occurs, it is possible to suppress volume expansion within the space of the concave portion 10 of the first silicon-based particle 100, thereby preventing structural collapse of the second silicon-based particle. In addition, when the second silicon-based particle 200 is included in the concave portion 10 of the first silicon-based particle 100, it can have a high silicon content compared to the same volume, thereby increasing the capacity of the secondary battery. .

The first silicon-based particles 100 may include silicon particles and silicon oxide in which the surface of the silicon particles is oxidized. The first silicon particles 100 may be in the form of primary particles in which the silicon particles and the surfaces of the silicon particles are oxidized, or secondary particles in which the primary particles are aggregated.

Conventionally, as silicon-based active materials are manufactured by mixing silicon particles and silicon oxide physically or chemically, cracks occur at the boundary between the silicon particles and the silicon oxide during charging and discharging of a secondary battery. The first silicon-based particle according to the present invention includes the silicon oxide oxidized from the silicon particle, so that a boundary between the silicon particle and the silicon oxide is not formed, but the silicon is directed from the surface portion of the silicon oxide toward the center. Since the concentration of the oxide can decrease, the occurrence of cracks at the boundary between the silicon particles and the silicon oxide can be reduced during charging and discharging.

The silicon particles may be spherical silicon nanoparticles. The silicon particles are 1 nm to 500 nm, 1 nm to 400 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 250 nm, 10 nm to 200 nm, or 10 nm to 10 nm. It may have a diameter of 150 nm. The diameter may be measured by the same method as the diameter measurement method of the first silicon-based particle. When the above range is satisfied, manufacturing costs are not significantly increased, and battery capacity and lifespan characteristics can be improved.

The silicon oxide may be represented by the following formula (1).

[Formula 1]

SiO _x (0<x≤0.9)

In Formula 1, when x satisfies the above range, the generation of irreversible products such as Li ₂ O and Li-silicate (Li _x Si _y O _z ) by reacting lithium ions with oxygen can be minimized, thereby , it is possible to minimize the problem of capacity reduction due to lithium ions reacting with the negative electrode active material being trapped inside the negative electrode rather than returning to the electrolyte or positive electrode. The second silicon particles 200 may also include the above-described silicon particles and silicon oxide in which the surface of the silicon particles is oxidized.

The first silicon-based particle 100 may have a carbon layer formed on at least a portion of the surface of the silicon oxide. The carbon layer may improve electrical conductivity of the first silicon-based particles 100. The carbon layer may also be formed on the second silicon-based particles 200, and may improve electrical conductivity of the second silicon-based particles 200.

A carbonaceous conductive material may be used to form the carbon layer. The carbonaceous conductive material may be one or more selected from natural graphite, artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, graphene, carbon nanotubes, and conductive polymers. .

The carbonaceous conductive material may be amorphous carbon. The amorphous carbon may mean an amorphous structure in which carbon corresponding to a diamond structure and carbon corresponding to a graphite structure are irregularly mixed. The proportion of carbon atoms corresponding to the diamond structure among the amorphous carbon is 5% to 70%, 10% to 70%, 15% to 70%, 18% to 70%, 20% to 70%, or 30% to 70%. It can be. When the above range is satisfied, the volume expansion of the silicon-based particles can be partially suppressed while the electrical conductivity can be improved, and the capacity and lifespan characteristics of the secondary battery can be improved. The ratio of carbon atoms corresponding to the diamond structure and carbon atoms corresponding to the graphite structure can be calculated by Electron Energy-Loss Spectroscopy using a TEM (Transmission electron microscope).

The carbon layer may be formed by carbonization of a carbon precursor such as saccharide. The saccharide may be a compound containing a C _n H _2n cycloalkane ring having 3 to 6 carbon atoms. For example, the saccharide may be any one or more selected from the group consisting of glucose, fructose, galactose, sucrose, maltose, and lactose.

The thickness of the carbon layer may be 1 nm to 10 nm, 1 nm to 9 nm, 1 nm to 8 nm, 2 nm to 8 nm, 2 nm to 7 nm, or 2 nm to 6 nm. Additionally, the carbon layer coating layer may be formed to cover 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more of the surface area of the silicon-based particles. When the above range is satisfied, the movement of lithium ions is not hindered and the electrical conductivity can be increased.

The negative active material according to the present invention may further include natural graphite particles. The natural graphite particles may include a carbon layer formed on the natural graphite particles. The carbon layer can reduce micropores of the natural graphite particles, reduce side reactions with the electrolyte solution, and improve structural stability.

The carbon layer is 1% to 10% by weight, 1% to 9% by weight, 2% to 9% by weight, 2% to 8% by weight, or 3% to 8% by weight of the natural graphite particles. may be included. When the above range is satisfied, the structural stability of the natural graphite particles can be improved while excessive lithium insertion and desorption phenomenon can be prevented.

The carbon layer may include amorphous carbon. For example, the carbon layer may be formed by providing at least one carbon layer precursor selected from the group consisting of pitch, rayon, and polyacrylonitrile-based resin to the natural graphite particles, and then heat-treating the natural graphite particles.

The BET specific surface area of the natural graphite particles is 1.0 m ² /g to 5.0 m ² /g, 1.2 m ² /g to 5.0 m ² /g, 1.2 m ² /g to 4.8 m ² /g, 1.5 m ² /g It may be from 4.8 m ² /g, or from 1.5 m ² /g to 4.5 m ² /g. When the above range is satisfied, side reactions with the electrolyte can be prevented, the lifespan characteristics of the secondary battery can be improved, and high output characteristics can be realized.

The degree of sphericity of the natural graphite particles may be 0.6 to 1, 0.7 to 1, 0.8 to 1, 0.9 to 1, or 0.95 to 1. The degree of sphericity can be measured using a known sphericity measurement method. When the above range is satisfied, packing between particles can be smooth, and the stress on particles during production of an anode can be alleviated, thereby reducing the swelling phenomenon.

The negative electrode active material according to the present invention may further include artificial graphite particles. The artificial graphite particles may be primary particles, secondary particles, or a mixture of primary particles and secondary particles. The primary particle may refer to a single, non-agglomerated particle. The secondary particles may refer to aggregates of the primary particles.

The carbon layer is 1% to 10% by weight, 1% to 9% by weight, 2% to 9% by weight, 2% to 8% by weight, or 3% to 8% by weight of the artificial graphite particles. may be included. When the above range is satisfied, the structural stability of the artificial graphite particles can be improved while excessive lithium insertion and desorption phenomenon can be prevented.

The carbon layer may include amorphous carbon. For example, the carbon layer may be formed by providing at least one carbon layer precursor selected from the group consisting of pitch, rayon, and polyacrylonitrile-based resin to the natural graphite particles, and then heat-treating the natural graphite particles.

The BET specific surface area of the natural graphite particles is 0.5 m ² /g to 3.0 m ² /g, 0.5 m ² /g to 2.5 m ² /g, 0.5 m ² /g to 2.0 m ² /g, 0.5 m ² /g It may be from 1.8 m ² /g, or from 0.5 m ² /g to 1.5 m ² /g. When the above range is satisfied, side reactions with the electrolyte can be prevented, the lifespan characteristics of the secondary battery can be improved, and high output characteristics can be realized.

The degree of sphericity of the natural graphite particles may be 0.65 to 1, 0.68 to 1, 0.7 to 1, 0.8 to 1, or 0.9 to 1. The degree of sphericity can be measured using a known sphericity measurement method. When the above range is satisfied, packing between particles can be smooth, and the stress on particles during production of an anode can be alleviated, thereby reducing the swelling phenomenon.

<Method for manufacturing negative electrode active material>

The method for producing a negative electrode active material according to the present invention includes the steps of (a) adding silicon particles and beads to a solvent and milling them to produce a first silicon slurry, (b) adding the first silicon slurry to a carbon-based polymer solution and stirring it. It may include preparing a second silicon slurry, and (c) heat treating the second silicon slurry in a temperature range of 1,000°C to 1,500°C and in an inert atmosphere.

In step (a), the silicon particles may be spherical silicon nanoparticles. The silicon particles are 0.5 nm to 500 nm, 1 nm to 400 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 250 nm, 10 nm to 200 nm, or 10 nm to 10 nm. It may have a diameter of 150 nm. The diameter can be defined as a diameter corresponding to 50% of the volume accumulation in the diameter distribution curve. For example, the diameter can be measured using a laser diffraction method. When the above range is satisfied, battery capacity and life characteristics can be improved.

The beads may be zirconium oxide balls (YTZ). The zirconium oxide ball may have a diameter of 0.01 mm to 1 mm, 0.05 mm to 1 mm, 0.05 mm to 0.5 mm, or 0.05 mm to 0.3 mm. The solvent is not particularly limited, but may be isopropyl alcohol. The silicon particles and beads are included in an amount of 10% to 50% by weight, 10% to 40% by weight, 10% to 35% by weight, or 15% to 35% by weight based on the total weight of the solvent, so that the milling process is performed. You can.

In step (a), the milling process may be performed under temperature conditions of 45°C or lower. By satisfying the above temperature conditions, a silicon-based active material with suppressed oxidation reaction can be manufactured. If necessary, the solvent may be additionally added in the milling process.

In step (b), a carbon layer may be formed on the surface of the silicon-based active material by the carbon-based polymer solution.

After step (b), (b-1) may include the step of homogenizing the second silicon slurry under pressure conditions of 800 bar to 1,200 bar. The homogenization step may improve kneading between the second silicon slurry and the carbon-based polymer solution.

Additionally, after step (b-1), (b-2) may include spray drying the second silicon slurry. A silicon-based carbon polymer precursor can be manufactured through the spray drying step, and the density of the negative electrode active material can be improved by manufacturing the precursor.

A carbon coating layer may be formed on the surface of the silicon oxide by the heat treatment in step (c). Additionally, the solvent may be evaporated in step (c), and a concave portion may be formed in the space where the solvent is evaporated from the silicon-based particles.

<Cathode>

A negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a concave portion and a surrounding portion of the concave portion. It is disposed in and includes first silicon-based particles including a skeleton portion that partitions each of the concave portions.

The negative electrode active material and the first silicon-based particles may be the same as the negative electrode active material and the first silicon-based particles described above.

The negative electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the secondary battery. For example, it can be used on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding power of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The negative electrode active material layer may further include a binder. The binder may be used to maintain the molded body by binding particles included in the negative electrode active material. The binder may be a non-aqueous binder or an aqueous binder. For example, the non-aqueous binders such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), and polyvinylidene fluoride. (PVdF), polyethylene, or polypropylene can be used, and any one selected from the group consisting of acrylonitrile-butadiene rubber, styrene-butadiene rubber, and acrylic rubber, which are water-based binders, or a mixture of two or more of these can be used. You can. The aqueous binder is more economical and environmentally friendly than the non-aqueous binder, is harmless to the health of workers, and has a superior binding effect compared to the non-aqueous binder, so the ratio of active materials per same volume can be increased, enabling high capacity. Specifically, styrene-butadiene rubber may be used.

The binder is present in an amount of 0.1% to 10% by weight, 0.1% to 8% by weight, 0.1% to 7% by weight, 0.1% to 6% by weight, or 0.1% to 5% by weight, based on the total weight of the slurry for producing the negative electrode active material layer. It can be included as a %. When the above range is satisfied, the effect as a binder can be excellent without a decrease in capacity per volume due to a decrease in the relative content of the negative electrode active material.

The negative electrode active material layer may further include a conductive material. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the secondary battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, conductive materials such as polyphenylene derivatives may be mentioned. The conductive material is used in an amount of 0.1% to 10% by weight, 0.1% to 8% by weight, 0.1% to 7% by weight, 0.1% to 6% by weight, or 0.1% to 5% by weight, based on the total weight of the slurry for producing the negative electrode active material layer. It can be included as a %. When the above range is satisfied, electrical conductivity can be improved without a decrease in capacity per volume due to a decrease in the relative content of the active material.

<Secondary battery>

The secondary battery according to the present invention may include a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode.

The cathode may be the same as the cathode described above.

The anode can be manufactured by general methods known in the art. For example, a positive electrode can be manufactured by mixing and stirring a positive electrode active material with a solvent, binder, conductive material, and dispersant to prepare a slurry, which is then applied to a positive electrode current collector, compressed, and dried.

The positive electrode current collector is a highly conductive metal to which the slurry of the positive electrode active material can easily adhere, and is not particularly limited as long as it has high conductivity without causing chemical changes in the secondary battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or the surface of aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc. can be used. Additionally, the adhesion of the positive electrode active material can be increased by forming fine irregularities on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics, and may have a thickness of 3 ㎛ to 500 ㎛.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. there is.

Specifically, the lithium composite metal oxide is lithium-manganese-based oxide (for example, LiMnO ₂ , LiMn ₂ O ₄ , etc.), lithium-cobalt-based oxide (for example, LiCoO ₂ , etc.), lithium-nickel-based oxide (for example, For example, LiNiO ₂ etc.), lithium-nickel-manganese oxide (for example, LiNi _1-Y Mn _Y O ₂ (here, 0<Y<1), LiMn _2-z Ni _z O ₄ (here , 0<Z<2), etc.), lithium-nickel-cobalt-based oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (where 0<Y1<1), etc.), lithium-manganese-cobalt-based Oxides (for example, LiCo _1-Y2 Mn _Y2 O ₂ (where 0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (where 0<Z1<2), etc.), lithium-nickel- Manganese-cobalt oxide (for example, Li(Ni _p Co _q Mn _r1 )O ₂ (where 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1 ) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium-nickel -Cobalt-transition metal (M) oxide (e.g., Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (where M is composed of Al, Fe, V, Cr, Ti, Ta, Mg and Mo) selected from the group, and p2, q2, r3 and s2 are each independent atomic fractions of elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2+ r3+s2=1), etc., and any one or two or more of these compounds may be included. Among these, in that the capacity characteristics and stability of the battery can be improved, the lithium composite metal oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (for example, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ etc.), or lithium nickel cobalt aluminum oxide (for example, Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ etc.), etc., and considering the remarkable improvement effect due to control of the type and content ratio of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , etc., and any one or a mixture of two or more of these may be used. there is.

The solvent includes organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide, or water, and these solvents can be used alone or in a mixture of two or more types. . The amount of the solvent used is sufficient to dissolve and disperse the positive electrode active material, the binder, and the conductive material in consideration of the slurry application thickness and manufacturing yield.

The binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, poly Vinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), alcohol Various types of binder polymers can be used, such as ponified EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, polymers whose hydrogen is substituted with Li, Na, or Ca, or various copolymers. there is.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the secondary battery. For example, graphite such as natural graphite or artificial graphite; 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. The conductive material may be used in an amount of 1% to 20% by weight based on the total weight of the positive electrode slurry.

The dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The separator may be interposed between the cathode and the anode. The separator is configured to prevent electrical short-circuiting between the cathode and the anode and to generate a flow of ions. The separator may include a porous polymer film or a porous non-woven fabric. Here, the porous polymer film is ethylene polymer, propylene polymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate. ) It may be composed of a single layer or multiple layers containing polyolefin-based polymers such as copolymers. The porous nonwoven fabric may include high melting point glass fibers and polyethylene terephthalate fibers. However, it is not limited to this, and depending on the embodiment, the separator may be a highly heat-resistant separator (CCS; Ceramic Coated Separator) containing ceramic.

The anode, the cathode, and the separator may be manufactured into an electrode assembly by a winding, lamination, folding, or zigzag stacking process. Additionally, the electrode assembly can be provided with an electrolyte solution and manufactured into a secondary battery according to the present invention. The secondary battery may be any one of a cylindrical, prismatic, pouch, or coin type using a can, but is not limited thereto.

The electrolyte may be a non-aqueous electrolyte. The electrolyte solution may include lithium salt and an organic solvent. The organic solvent includes propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), dipropyl carbonate (DPC), Vinylene carbonate (VC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone ), propylene sulfide, or tetrahydrofuran.

The present invention can provide a battery module including the secondary battery as a unit cell. The battery module can be used as a power source for medium to large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

For example, the medium to large-sized device includes a power tool that is powered by an omni-electric motor and moves; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; Electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf cart; Examples include, but are not limited to, power storage systems.

Below, the present invention will be described in more detail based on examples and comparative examples. However, the following examples and comparative examples are only examples to explain the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

Manufacturing Example - Preparation of negative electrode active material

Manufacturing Example 1

Silicon with a particle size of approximately 800 nm and zirconia beads (YTZ) with a particle size of approximately 0.1 mm were added to an isopropyl alcohol solvent. Thereafter, the mixture was milled for 9 hours while maintaining the temperature below 45°C to prepare a first silicon slurry having a solid content of 30% by weight of metallic silicon with a particle size of approximately 100 nm.

After stirring the first silicon slurry for 10 minutes in a homogenization reactor (2,500 rpm), polyvinyl pyrrolidone (PVP) was added, and the second silicon slurry was prepared by stirring again in the homogenization reactor for 10 minutes.

The second silicon slurry was subjected to a homogenization process twice under a pressure of 1,000 bar in a high pressure homogenizer. Thereafter, the second silicon slurry was spray-dried at a temperature of 100°C, a pressure of 0.5Mpa, and a flow rate of 3 L/h. Afterwards, a negative electrode active material was manufactured by heat treatment at 1,200°C under nitrogen conditions.

Production example 2

A negative electrode active material was prepared through the same process as Preparation Example 1, except that instead of using metallic silicon with a particle size of about 100 nm, it was made of metallic silicon with a particle size of about 80 nm.

Production example 3

A negative electrode active material was prepared through the same process as Preparation Example 1, except that instead of spray drying at a flow rate of 3 L/h in Preparation Example 1, it was spray-dried at a flow rate of 2 L/h.

Production example 4

A negative electrode active material was prepared through the same process as Preparation Example 1, except that instead of spray drying at a flow rate of 3 L/h in Preparation Example 1, it was spray-dried at a flow rate of 4 L/h.

Example

Example 1

<Cathode manufacturing>

A slurry was prepared by mixing the negative electrode active material of Preparation Example 1: conductive material (Super-P): binder (SBR-CMC) in N-methyl pyrrolidone solvent at a weight ratio of 8:1:1. Afterwards, the slurry was applied to a copper thin film and dried in a vacuum oven at 80°C for 8 hours to prepare a cathode.

<Coin type half cell manufacturing>

Metal lithium foil with a thickness of 0.3 mm was used as a counter electrode (anode) to the cathode prepared above, and a polypropylene sheet with a thickness of 0.1 mm was used as a separator. A coin-type half-cell was manufactured using 1M LiPF ₆ dissolved in a solvent mixed with ethylene carbonate and ethylmethyl carbonate at a volume ratio of 3:7 as an electrolyte.

Example 2

A coin-type half-cell was manufactured through the same process as Example 1, except that the negative electrode active material of Preparation Example 2 was used instead of the negative electrode active material of Preparation Example 1.

Example 3

A coin-type half-cell was manufactured through the same process as Example 1, except that the negative electrode active material of Preparation Example 3 was used instead of the negative electrode active material of Preparation Example 1.

Example 4

A coin-type half-cell was manufactured through the same process as Example 1, except that the negative electrode active material of Preparation Example 4 was used instead of the negative electrode active material of Preparation Example 1.

Comparative Example 1

In Example 1, a coin-type half-cell was manufactured through the same process as Example 1, except that Daejoo Electronic Materials' DMSO-H85 silicon oxide composite (shown in FIG. 4) was used as the negative electrode active material instead of the negative electrode active material of Preparation Example 1. was manufactured.

Comparative Example 2

A coin-type half-cell was manufactured in the same process as Example 1, except that BTR's silicon carbide composite (shown in FIG. 5) was used as the negative electrode active material instead of the negative electrode active material of Preparation Example 1.

Experiment example

Experimental Example 1 - SEM Analysis

The results of scanning electron microscopy (SEM) analysis on the negative electrode active material of Preparation Example 1 are shown in FIG. 3. In addition, the results of scanning electron microscopy (SEM) analysis on the negative electrode active materials of Comparative Examples 1 and 2 are shown in Figures 4 and 5, respectively.

Referring to Figures 3 to 5, it was confirmed that the negative electrode active material of Preparation Example 1 had a concave portion and a skeleton portion dividing each of the concave portions. In contrast, no concave portion could be confirmed in the negative electrode active materials of Comparative Examples 1 and 2.

Experimental Example 2 - Discharge capacity maintenance rate

Each of the coin-type half cells manufactured in Examples 1 to 4 and Comparative Examples 1 to 2 were charged at a constant current of 0.1C until the voltage reached 0.01V, and then charged at a constant current of 0.1C until the voltage reached 1.5V. The discharging process was performed three times to proceed with the battery stabilization process.

Afterwards, each coin-type half cell was charged at a constant current of 0.5C until the voltage reached 0.01V, and discharged at a constant current of 0.5C until the voltage reached 1.0V. The process was performed 50 times, and the 50th The maintenance rate of discharge capacity compared to the first time after charging and discharging was measured, and the results are shown in Table 1 below.

Experimental Example 3 - Swelling Ratio

The swelling ratio during the charging and discharging process according to Experimental Example 2 was measured and calculated according to Equation 1 below, and the results are shown in Table 1 below.

[Equation 1]

Swelling ratio (%) = [(t2-t1)/t1] × 100

(In Equation 1 above, t1 is the thickness of the cathode before the 1st charge and discharge, and t2 is the thickness of the cathode after the 50th charge and discharge.)

Discharge capacity maintenance rate swelling ratio Example 1 96.8% 20% Example 2 96.5% 21% Example 3 96.3% 20% Example 4 96.4% 20% Comparative Example 1 88.4% 28% Comparative Example 2 87.9% 29%

As can be seen in Table 1, Examples 1 to 4 showed a higher discharge capacity maintenance rate than Comparative Examples 1 to 2, and it was confirmed that the change in the thickness of the cathode after cycling was significantly reduced. This is because the silicon-based particles according to the present invention include concave portions, the volume expansion of the silicon-based particles due to insertion of lithium ions can be suppressed, and the phenomenon of silicon-based particles being finely divided as the cycle increases is minimized, thereby reducing the discharge of the secondary battery. By increasing the capacity retention rate, the swelling rate of the cathode can be reduced.

10: recess
11: first concave portion
12: second concave portion
20: skeleton part
100: first silicon-based particle
200: second silicon-based particle

Claims (14)

recess; and
It is disposed around the concave portions and includes first silicon-based particles including a skeleton portion that partitions each of the concave portions,
A negative electrode active material including the concave portion and the skeleton portion, and further comprising second silicon-based particles having a diameter of 0.1 ㎛ to less than 3 ㎛. According to paragraph 1,
A negative electrode active material wherein the first silicon-based particles have a diameter of 3 ㎛ to 15 ㎛. According to paragraph 1,
A negative electrode active material wherein the depth of the concave portion in the direction toward the center of the first silicon-based particle:the diameter of the first silicon-based particle has a ratio of 0.01:1 to 0.80:1. According to paragraph 1,
A negative electrode active material wherein the ratio of the opening area of the concave portion to the area of the first silicon-based particle is 20% to 95%. According to paragraph 1,
A negative electrode active material wherein the volume ratio of the concave portion to the volume of the first silicon-based particle is 5% to 80%. According to paragraph 1,
A negative electrode active material wherein the skeleton portion includes a branched structure. According to paragraph 1,
The first silicon-based particle is a negative electrode active material that satisfies the following general formula 1:
[General Formula 1]
1 ≤ X/Y ≤ 80
In General Formula 1, delete According to paragraph 1,
The second silicon-based particle is a negative electrode active material disposed in at least a portion of the concave portion of the first silicon-based particle. According to paragraph 1,
A negative electrode active material wherein the first silicon-based particles include silicon particles and silicon oxide in which the surface of the silicon particles is oxidized. According to clause 10,
A negative electrode active material wherein the silicon particles have a diameter of 1 nm to 500 nm. According to clause 10,
The silicon oxide is a negative electrode active material represented by the following formula (1):
[Formula 1]
SiO _x (0<x≤0.9) According to clause 10,
The first silicon-based particle is a negative electrode active material in which a carbon layer is formed on at least a portion of the surface of the silicon oxide. negative electrode current collector; and
It includes a negative electrode active material layer formed on at least one surface of the negative electrode current collector,
The negative electrode active material layer includes a negative electrode active material,
The negative electrode active material includes a first silicon-based particle including a concave portion and a framework disposed around the concave portion and dividing each of the concave portions, and includes the concave portion and the framework portion, and has a thickness of 0.1 ㎛ to 3 ㎛. A negative electrode further comprising second silicon-based particles having a diameter of less than 20%.

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