WO2017099456A1 - Negative electrode active material for lithium secondary battery comprising core composed of carbon, manufacturing method therefor, and lithium secondary battery including same - Google Patents

Abstract

A negative electrode active material for a lithium secondary battery, a manufacturing method therefor, and a lithium secondary battery including the same are provided, the negative electrode active material comprising: core particles that include one or more selected from hard carbon, soft carbon and spherical natural graphite; and shell layers located on surfaces of the core particles, wherein the shell layer comprises i) a first shell layer that includes silicon (Si)/carbon black/carbon composite particles, and amorphous or semi-crystalline carbon, and ii) a second shell layer that has a structure in which the amorphous or semi-crystalline carbon is dispersed between flake graphite fragment particles, and the flake graphite fragment particles are stacked and structured in a concentric circle direction, and that is formed on the first shell layer.

Description

Anode active material for lithium secondary battery comprising a core made of carbon, a manufacturing method thereof and a lithium secondary battery comprising the same

The present disclosure provides a negative electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

Recently, as the application of lithium secondary batteries to medium and large-sized lithium secondary batteries such as electric vehicles as well as portable electronic devices, high capacity and charge / discharge output characteristics are required to be improved.

However, graphite as a commercially available negative active material is limited to a theoretical capacity of about 372 mAh / g, so it is urgent to develop a new high capacity negative active material.

As a material which can replace graphite, silicon (Si) or its compound has been studied conventionally. Silicon reversibly occludes and releases lithium through compound formation reaction with lithium and is promising as a high capacity cathode material because its theoretical maximum capacity is about 4200 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much larger than graphite.

However, during charging and discharging, a volume change occurs due to reaction with lithium, which causes micronization of the silicon active material powder and poor electrical contact between the silicon active material powder and the current collector. As a result, as the charge and discharge cycles of the battery proceed, the battery capacity is drastically reduced, which causes the cycle life to be shortened.

Accordingly, in order to improve charge and discharge cycle characteristics, a method of forming silicon (Si) or a compound particle thereof or using a composite active material of these compound particles and carbon has been studied. However, there is still not enough improvement in capacity, cycle characteristics, and output characteristics for use as a negative electrode active material for lithium secondary batteries. In addition, in the case of Si and Si-based compounds exposed to the surface of the composite particles, the reaction with the electrolyte may occur during charging and discharging, and thus the cycle characteristics may be lowered, and thermal stability may decrease due to an increase in temperature.

One embodiment of the present invention is to provide a negative active material for a lithium secondary battery having a large charge and discharge capacity, excellent cycle life characteristics, excellent charge and discharge output characteristics at high current density and improved thermal stability.

Another embodiment of the present invention is to provide a method of manufacturing the negative electrode active material for the lithium secondary battery.

Another embodiment of the present invention is to provide a lithium secondary battery comprising the negative electrode active material for the lithium secondary battery.

One embodiment of the present invention includes a core particle including at least one selected from hard carbon, soft carbon, and spherical natural graphite, and a shell layer on the surface of the core particle,

The shell layer may comprise: i) a first shell layer comprising silicon (Si) / carbon black / carbon composite particles, and amorphous or semi-crystalline carbon; And ii) a structure in which amorphous or quasi-crystalline carbon is distributed between the flaky graphite fragment particles, and the flaky graphite fragment particles are stacked in a concentric manner and formed, and a second shell layer formed on the first shell layer. Provided is a negative active material for a secondary battery.

The average particle diameter (D50) of the core particles may be 2 to 20 ㎛.

The core particles may be included in 5 to 85% by weight based on the total amount of the negative electrode active material.

The average particle diameter (D50) of the composite particles included in the first shell layer may be 0.05 μm to 2 μm.

The composite particles included in the first shell layer may include silicon particles having an average particle diameter of 5 to 200 nm, and may include mesopores having an average size of 2.0 to 50 nm.

The composite particles included in the first shell layer may include silicon particles and carbon black particles in a weight ratio of 1: 9 to 9: 1.

The composite particles included in the first shell layer may include 0.1 to 70% by weight of amorphous or semicrystalline carbon.

The first shell layer may include the composite particles and amorphous or semicrystalline carbon in a weight ratio of 1: 9 to 9: 1.

The total weight of the first shell layer may be 10 to 94% by weight based on the total weight of the negative electrode active material.

An average thickness of the flaky graphite fragment particles included in the second shell layer may be 100 nm or less.

The flaky graphite fragment particles included in the second shell layer may be included in an amount of 1 to 40 wt% based on the total weight of the negative electrode active material.

The amorphous or semicrystalline carbon may be sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, polyyi It may be formed from a carbon precursor including at least one selected from the group consisting of mid, epoxy resin, vinyl chloride resin, coal-based pitch, petroleum-based pitch, mesoface pitch, tar and low molecular weight heavy oil.

The ratio of the average particle diameter (D50) of the core particles and the thickness of the shell layer may be 17 to 95: 5 to 83.

The ratio of the thickness of the first shell layer and the second shell layer may be 5 to 95:95 to 5.

The anode active material may further include a coating layer disposed on the surface of the shell layer and including the amorphous or semicrystalline carbon, and the thickness of the coating layer may be 0.01 to 5 μm.

The average particle diameter (D50) of the negative electrode active material may be 2 to 40 ㎛.

Another embodiment of the present invention provides a surface of a core particle comprising at least one selected from hard carbon, soft carbon, and spherical natural graphite, a mixture of silicon / carbon black / carbon composite particles, and an amorphous or semicrystalline carbon precursor. Coating to form a first shell layer, and coating the surface of the first shell layer with a mixture of flaky graphite fragment particles and an amorphous or semi-crystalline carbon precursor to form a second shell layer to obtain anode active material precursor particles; And it provides a method for producing a negative electrode active material for a lithium secondary battery comprising the step of heat-treating the negative electrode active material precursor particles.

The method of manufacturing the negative active material may further include coating the surface of the negative electrode active material precursor particles with an amorphous or semi-crystalline carbon precursor before the heat treatment of the negative electrode active material precursor particles.

The heat treatment may be performed under an atmosphere containing nitrogen, argon, hydrogen or a mixed gas thereof, or under vacuum, and may be performed at a temperature of 700 to 1300 ° C.

Another embodiment of the invention the negative electrode including the negative electrode active material; anode; And it provides a lithium secondary battery comprising an electrolyte solution.

Other specific details of embodiments of the present invention are included in the following detailed description.

A lithium secondary battery having a large charge and discharge capacity, excellent cycle life characteristics, excellent charge and discharge output characteristics at a high current density, and greatly improved thermal stability can be implemented.

1 is a schematic cross-sectional view of a negative electrode active material according to an embodiment.

2 is a conceptual diagram of a cross section of a silicon (Si) / carbon black / carbon composite particle included in a core of a negative active material for a lithium secondary battery according to the present invention.

3 is a schematic cross-sectional view of a negative electrode active material according to another embodiment.

4 is a scanning electron microscope (SEM) photograph of the core particles used in Example 1 and Comparative Example 1. FIG.

5 is a scanning electron microscope (SEM) photograph of the core particles used in Example 2 and Comparative Example 2.

6 is a scanning electron microscope (SEM) photograph of the negative electrode active material prepared in Example 1. FIG.

7 is a scanning electron microscope (SEM) photograph of the negative electrode active material prepared in Comparative Example 1. FIG.

8 is a scanning electron microscope (SEM) photograph of the anode active material prepared in Example 2. FIG.

9 is a scanning electron microscope (SEM) photograph of the negative electrode active material prepared in Comparative Example 2. FIG.

10 is a particle size distribution of negative electrode active materials prepared in Example 1 and Comparative Example 1. FIG.

11 is a particle size distribution of the negative electrode active materials prepared in Example 2 and Comparative Example 2. FIG.

12 is a charge and discharge curve of one and two cycles for the lithium secondary battery prepared using the negative electrode active material prepared in Example 1.

13 is a charge and discharge curve of one and two cycles for the lithium secondary battery prepared in Comparative Example 1.

14 is a charge and discharge curve of one and two cycles for the lithium secondary battery prepared using the negative electrode active material prepared in Example 2.

15 is a charge and discharge curve of one and two cycles for the lithium secondary battery prepared in Comparative Example 2.

 16 is a cycle curve for the lithium secondary battery prepared in Example 1 and Comparative Example 1.

 17 is a cycle curve for the lithium secondary battery prepared in Example 2 and Comparative Example 2.

FIG. 18 shows the results of differential scanning thermal analysis (DSC) of electrodes prepared using the negative electrode active materials of Example 1 and Comparative Example 1. FIG.

19 is a result of differential scanning thermal analysis (DSC) of electrodes prepared using the negative electrode active materials of Example 2 and Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The negative electrode active material according to one embodiment may be described with reference to FIG. 1.

1 is a schematic cross-sectional view of a negative electrode active material according to an embodiment.

Referring to FIG. 1, the negative electrode active material 1 according to an embodiment may include a core particle 11 and a shell layer located on the surface of the core particle 11. In detail, the shell layer may have a shape surrounding the core particle 11.

The core particle 11 may include at least one selected from hard carbon, soft carbon, and spherical natural graphite. Specifically, the hard carbon may be amorphous hard carbon, and the soft carbon may be specifically semicrystalline or low crystalline soft carbon. In addition, the spherical natural graphite particles are formed by flakes of natural graphite fragments in the cabbage or random phase.

The shell layer comprises: i) a first shell layer comprising silicon (Si) / carbon black / carbon composite particles (12), and amorphous or semi-crystalline carbon (13); And ii) amorphous or quasi-crystalline carbon 15 is distributed between the flaky graphite fragment particles 14, and the flaky graphite fragment particles are laminated in a concentric direction and formed and formed on the first shell layer. It may comprise two shell layers.

Hard carbon or soft carbon used as the core particles has good output characteristics of the battery when used as a negative electrode material, but has low initial efficiency and low storage capacity of lithium ions.

The spheronized natural graphite used as the core particles has a limit of theoretical capacity of 372 mAh / g of lithium ions, which has a need for increasing capacity.

In addition, when the silicon or silicon alloy fine particles are used as the negative electrode material, the capacity of the battery is high, but the initial efficiency is low, and the volume change occurs, which causes micronization of the silicon active material powder and poor electrical contact between the silicon active material powder and the current collector. Can be. As a result, as the charge and discharge cycle of the battery proceeds, the battery capacity is drastically reduced, which causes the cycle life to be shortened. In addition, when the silicon or silicon alloy fine particles are used as the negative electrode material, the thermal recognition property may be lowered by directly contacting and reacting with the electrolyte.

According to one embodiment, hard carbon, soft carbon, and spherical natural graphite are used as core particles, and the surface of the core particles is i) silicon (Si) / carbon black / carbon composite particles 12, and amorphous ( a first shell layer comprising amorphous or semi-crystalline carbon 13; And ii) amorphous or quasi-crystalline carbon 15 is distributed between the flaky graphite fragment particles 14, and the flaky graphite fragment particles are laminated in a concentric direction and formed and formed on the first shell layer. It has a structure of coating with 2 shell layers, which has a large lithium storage capacity, high capacity retention rate, improved initial efficiency, easy movement of lithium ions during charge and discharge, and excellent output characteristics and high charge and discharge efficiency. have. In addition, the thermal stability of the negative electrode active material is greatly improved by preventing contact between the silicon (Si) / carbon black / carbon composite particles 12 and the electrolyte solution.

The average particle diameter (D50) of the core particles may be 2 to 20 ㎛, specifically 5 to 15 ㎛. When the core particles have an average particle diameter (D50) in the above range, the coating for forming the shell layer with the carbon fine particles is well made, and thus can be usefully applied to a lithium secondary battery having a high capacity and excellent output characteristics. At this time, the average particle diameter (D50) refers to the diameter of the particles corresponding to the cumulative volume 50% by volume in the particle size distribution.

The hard carbon may be sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, polyimide, epoxy resin. ), Cellulose, styrene, citric acid, stearic acid, polyvinylidene fluoride, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene At least one carbonaceous material selected from ethylene-propylene-diene monomer (EPDM), sulfonated ethylene-propylene-diene monomer (EPDM), starch, glucose, gelatin and saccharides may be used.

The soft carbon may be formed by carbonizing at least one carbonaceous material selected from polyvinyl alcohol, polyvinyl chloride, coal-based pitch, petroleum-based pitch, mesoface pitch, and low molecular weight heavy oil.

The core particles may be included in 5 to 85% by weight, specifically, 20 to 80% by weight based on the total amount of the negative electrode active material. When the core particles are included in the above range, the shell layer may be formed at an appropriate ratio around the core particles to exhibit excellent output characteristics and to improve capacity.

Silicon / carbon black / carbon composite particles (hereinafter referred to as “composite particles”) included in the first shell layer And amorphous or semicrystalline carbon in the core in a weight ratio of 1: 9 to 9: 1. If the weight ratio of the multiparticulates and amorphous or semicrystalline carbon is less than 1: 9, the effect of increasing the capacity may not be sufficient. If the weight ratio of the multiparticulates and the amorphous or semicrystalline carbon is less than 9: 1, it is difficult to uniformly mix and disperse the multiparticulates and the amorphous or semicrystalline carbon. Properties as the negative electrode active material may be lowered.

Further, the total weight of the first shell layer including the composite particles and amorphous or semi-crystalline carbon is preferably included in 10 to 94% by weight based on the total weight of the negative electrode active material.

As shown in FIG. 2, the composite particles 12 have a structure in which silicon particles 21 and carbon black particles 22 are uniformly mixed and bonded by amorphous or semi-crystalline carbon 23.

D ₅₀ (50% volume cumulative particle diameter measured by laser diffraction scattering particle size distribution measurement) of the composite particles is preferably from 0.05 ㎛ to 2 ㎛, which is dispersed during the preparation of the negative electrode active material when D ₅₀ is less than 0.05 ㎛ This may not be sufficient, and when it exceeds 2 μm, it may be difficult to form the first shell layer in the negative electrode active material.

In addition, the composite particle provides a negative active material for a lithium secondary battery, characterized in that the silicon particles and carbon black particles in a weight ratio of 1: 9 to 9: 1. When the weight ratio of the silicon particles and the carbon black particles is less than 1: 9, when the amount of the silicon particles is small, the high capacity effect by silicon may not be sufficient, and the weight ratio of the silicon particles and the carbon black particles is 9: 1. When the amount of the silicon particles is larger, the dispersion effect of the silicon particles by the carbon black may not be sufficient.

In addition, the composite particles may include 0.1 to 70% by weight of amorphous or semicrystalline carbon relative to the total weight of the composite particles for the purpose of bonding and coating the silicon particles and the carbon black particles. When the amorphous or semi-crystalline carbon of the composite particles is less than 0.1% by weight, the effect of bonding and coating the silicon particles and the carbon black particles is not sufficient, and the capacity by silicon when the amorphous or semi-crystalline carbon is 70% by weight or more It is difficult to expect an increase effect.

Carbon black included in the composite particles may be exemplified by acetylene black, Caten black, channel black, furnace black, summer black, super P, but not limited thereto. Can be.

Carbon black particles generally have an average particle size of 10 nm to 100 nm, but several of these carbon black particles may be present in agglomerated particles such as grape clusters.

The carbon in the composite particles may be prepared using the same precursor as the precursor for forming amorphous or semicrystalline carbon, which will be described later as amorphous or semicrystalline carbon.

For reference, amorphous carbon refers to hard carbon that does not change into crystalline graphite even when the temperature is raised in a state in which carbon atoms are randomly arranged. The semicrystalline carbon is crystalline graphite having low crystallinity when heated to a temperature of 2000 ° C. or less It means a low crystalline carbon is changed to.

In addition, the composite particles may include silicon particles having an average particle diameter of 5 to 200 nm, more preferably silicon particles having an average particle diameter of 20 to 100 nm. When the size of the silicon particles is less than 5 nm, it is easy to form a compound such as SiC during heat treatment at 1000 ° C. or higher during the preparation of the negative electrode active material, and thus it is difficult to expect a high capacity effect by silicon. In addition, when the size of the silicon particles exceeds 200 nm, it is difficult to control the volume expansion of the negative electrode active material particles due to the large volume expansion when forming a lithium compound by reacting with lithium.

On the other hand, the composite particles may comprise a mesopore (24) having an average size of 2.0 to 50 nm, thereby preventing the volume expansion by the reaction of the silicon particles in the composite particles with lithium during charge and discharge A buffering effect can be expected.

The amorphous or semi-crystalline carbon included in the first shell layer may be sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin And those formed from carbon precursors including at least one selected from cellulose, styrene, polyimide, epoxy resins, vinyl chloride resins, coal-based pitches, petroleum-based pitches, mesophase pitches, tars, and low molecular weight heavy oils.

The flaky graphite fragment particles 14 included in the second shell layer may be obtained by peeling flaky graphite to have an average thickness of 100 nm or less.

The flaky graphite fragment particles included in the second shell layer are preferably included in an amount of 1 to 40% by weight based on the total weight of the negative electrode active material, which is less than 1% by weight based on the total amount of the negative electrode active material. This is because the buffering effect on the volume expansion of the composite particles is not sufficient, and when the content exceeds 40% by weight, the charge / discharge output characteristics of the negative electrode active material may decrease and the capacity increase effect is insufficient.

In addition, the amorphous or quasicrystalline carbon 16 between the flaky graphite segments in the second shell layer may be made of the same material as the amorphous or quasicrystalline carbon of the first shell layer, and may exist in the form of the particles or the matrix. When the amorphous or semicrystalline carbon is present in the form of particles, pores may be included between the flaky graphite fragments.

The thickness of the shell layer including the first shell layer and the second shell layer is preferably 1 to 15 µm, more preferably 2 to 10 µm. When the thickness of the shell layer is less than 1 μm, the capacity increase and structural stability improvement effect of the negative electrode active material by the shell layer are insufficient, and when the thickness of the shell layer exceeds 15 μm, the reaction of the composite particles with lithium during charge and discharge may occur. It is suppressed, so it is difficult to expect high capacity at high rate charge and discharge.

On the other hand, the ratio of the average particle diameter (D50) of the core particles and the thickness of the shell layer may be 17 to 95: 5 to 83, specifically 30 to 90: 70 to 10. The negative electrode active material having a ratio in the above range may have a high capacity and exhibit excellent high rate output characteristics.

Furthermore, it is preferable that the ratio of the thickness of a said 1st shell layer and a said 2nd shell layer is 5-95: 95-5.

The negative electrode active material 1 may be manufactured according to the following two methods, but is not necessarily limited thereto, and any method capable of finally obtaining the negative electrode active material according to the present invention may be used without limitation.

First, the surface of the core particles is coated with a mixture of silicon / carbon black / carbon composite particles and an amorphous or semicrystalline carbon precursor to form a first shell layer, and the surface of the first shell layer is flaky graphite fragment particles and amorphous particles. Alternatively, the negative electrode active material may be prepared by coating a mixture of semi-crystalline carbon precursors to form a second shell layer to prepare negative electrode active material precursor particles and heat treating the same.

Alternatively, after coating with a mixture of silicon / carbon black / carbon composite particles and an amorphous or semi-crystalline carbon precursor to form a first shell layer and performing a first heat treatment, the surface of the first shell layer is flake graphite fragment particles and amorphous particles. Alternatively, the negative electrode active material may be prepared by coating a mixture of semi-crystalline carbon precursors to form a second shell layer to prepare negative electrode active material precursor particles, and to perform a second heat treatment.

The amorphous or semi-crystalline carbon precursor may be sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, At least one selected from polyimide, epoxy resin, vinyl chloride resin, coal pitch, petroleum pitch, mesoface pitch, tar and low molecular weight heavy oil can be used.

As the coating method of the first shell layer or the second shell layer, a mechanochemical method such as a blade, mechano-fusion, etc., which can give a shear force, may be used, and a spray dry method or an emulsion method may also be used. (emulsion) may be used, but is not limited thereto.

For example, the core particles, the silicon / carbon black / carbon composite particles, and the amorphous or semi-crystalline carbon precursor are introduced into a rotor blade mill, and thus, at a temperature higher than the softening point of the amorphous or semi-crystalline carbon precursor. The first shell layer may be coated by imparting a strong mechanical shear force.

The composite particle including the first shell layer, the flaky graphite fragment particles, and the amorphous or quasi-crystalline carbon precursor are introduced into a rotor blade mill, whereby the temperature above the softening point of the amorphous or quasi-crystalline carbon precursor. In order to give a strong mechanical shear force in the second shell layer can be coated.

All heat treatments including the first heat treatment and the second heat treatment may be performed under an atmosphere containing nitrogen, argon, hydrogen, or a mixed gas thereof, or under vacuum.

In addition, the heat treatment may be performed at a temperature of 700 to 1300 ℃, more preferably may be carried out at a temperature of 800 to 1200 ℃. When the heat treatment is performed in the temperature range, the silicon of the silicon / carbon black / carbon composite particles is suppressed from forming a silicon compound (eg, SiC), so that the capacity increase effect is excellent, and the amorphous or quasi-crystalline carbon precursor Carbonization can take place sufficiently.

The negative electrode active material according to another embodiment may be described with reference to FIG. 3.

3 is a schematic cross-sectional view of a negative electrode active material according to another embodiment.

Referring to FIG. 3, the negative electrode active material 2 may further include a coating layer 16 positioned on the shell layer of the negative electrode active material particles having the structure shown in FIG. 1. Specifically, the shell layer may be in the form of surrounding the core particles, the coating layer may be in the form of surrounding the shell layer.

Details of the core particles and the shell layer are as described above.

The coating layer 16 may include amorphous or semicrystalline carbon, and the amorphous or semicrystalline carbon is as described above.

When the amorphous or semi-crystalline carbon is further coated on the shell layer, the exposure of the graphite edge surface may be reduced, thereby improving initial charge and discharge efficiency, and appropriately buffering the volume expansion of silicon in the composite particles to provide cycle life characteristics and thermal properties. Stability can be further improved.

The thickness of the coating layer may be 0.01 to 5 ㎛, specifically 0.1 to 3 ㎛. When the thickness of the coating layer is formed in the above range, the exposure of the graphite edge surface is reduced, thereby increasing the initial charge and discharge efficiency, excellent output characteristics, and can implement a lithium secondary battery having improved high capacity and thermal stability.

The negative electrode active material 1 may be manufactured according to the following two methods, but is not necessarily limited thereto, and any method capable of finally obtaining the negative electrode active material according to the present invention may be used without limitation. .

First, the surface of the core particles is coated with a mixture of silicon / carbon black / carbon composite particles and an amorphous or semicrystalline carbon precursor to form a first shell layer, and the surface of the first shell layer is flaky graphite fragment particles and amorphous particles. Or by coating with a mixture of semi-crystalline carbon precursors to form a second shell layer to prepare negative electrode active material precursor particles, and after coating the surface of the negative electrode active material precursor particles with the amorphous or semi-crystalline carbon precursor, the coated negative electrode active material precursor The negative electrode active material may be prepared by heat treating the particles.

Alternatively, after coating with a mixture of silicon / carbon black / carbon composite particles and an amorphous or semi-crystalline carbon precursor to form a first shell layer and performing a first heat treatment, the surface of the first shell layer is flake graphite fragment particles and amorphous particles. Or by coating with a mixture of semi-crystalline carbon precursors to form a second shell layer to prepare negative electrode active material precursor particles, and after coating the surface of the negative electrode active material precursor particles with the amorphous or semi-crystalline carbon precursor, the coated negative electrode active material precursor The negative electrode active material may be prepared by subjecting the particles to a second heat treatment.

The silicon / carbon black / carbon composite particles, flaky graphite fragment particles, and amorphous or semicrystalline carbon precursors are as described above, and the atmosphere and temperature of the heat treatment are also as described above.

The shape of the negative active material according to the exemplary embodiment illustrated through FIGS. 1 and 3 may be spherical, but is not limited thereto.

The average particle diameter (D50) of the negative electrode active material may be 2 to 40 ㎛, specifically, may be 5 to 30 ㎛. When the negative electrode active material has an average particle diameter (D50) in the above range it can be obtained an excellent electrode manufacturing process efficiency and electrode density.

According to another embodiment of the present invention, a cathode including a cathode active material capable of intercalating and deintercalating lithium ions, a cathode including the anode active material, and a lithium secondary battery including an electrolyte is provided. .

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, etc., Depending on the size, it can be divided into bulk type and thin film type. Since the structure and manufacturing method of these batteries are well known in the art, detailed description thereof will be omitted.

The negative electrode may be prepared by mixing the above-described negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then coating the negative electrode current collector.

The binder may be polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinylchloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or Polypropylene may be used, but is not limited thereto.

The binder may be mixed in an amount of 1 to 30 wt% based on the total amount of the composition for forming the negative electrode active material layer.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes to the battery. Specifically, graphite such as natural graphite and artificial graphite; Carbon blacks 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 powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The conductive material may be mixed in an amount of 0.1 to 30 wt% based on the total amount of the composition for forming the negative electrode active material layer.

The negative electrode current collector may have a thickness of 3 to 500 μm. Examples of the negative electrode current collector may include stainless steel, aluminum, nickel, titanium, calcined carbon, or a surface treated with carbon, nickel, titanium, silver, or the like on the surface of aluminum or stainless steel. The negative electrode current collector may increase the adhesion of the negative electrode active material by forming fine irregularities on its surface, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The positive electrode includes a positive electrode active material, and as the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used. Specifically, at least one selected from cobalt, manganese and nickel and at least one of complex oxides of lithium can be used.

Like the negative electrode, the positive electrode may also be prepared by mixing the positive electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum.

The electrolyte solution is a lithium salt; And non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like.

The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carbonate, lithium tetraphenylborate, imide and the like can be used.

The non-aqueous organic solvent is N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrate Roxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate Esters, trimethoxy methane, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrionate, ethyl propionate And the like can be used.

The organic solid electrolyte may include a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly etchation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, and an ionic dissociation group. To the polymer can be used.

The inorganic solid electrolyte may be Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ − Nitrides, halides, sulfates, and the like of Li, such as LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ , may be used.

For the purpose of improving the charge and discharge characteristics, flame retardancy and the like, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexa phosphate triamide, nitrobenzene Derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like can be added.

In addition, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included to impart nonflammability, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The separator may exist between the positive electrode and the negative electrode according to the type of the lithium secondary battery. As the separator, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may have a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm.

Specifically, the separator may include an olefin polymer such as polypropylene having chemical resistance and hydrophobicity; Sheets or nonwovens made of glass fibers, polyethylene, and the like can be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

Manufacture of negative electrode active material

< Example  1> Hard carbon  Used as core particle Cathode active material  Produce

1. Manufacture of Silicon (Si) / Carbon Black / Carbon Composite Particles

100 parts by weight of a mixture of silicon having an average particle diameter (D50) of 50 nm and carbon black having an average particle diameter (D50) of 30 nm in a 60:40 weight ratio was added to 8 parts by weight of polyacrylic acid and 1000 parts by weight of water, followed by stirring. It was prepared and spray dried at a hot air temperature of 160 ℃ to obtain granulated particles. After heat-treating the granulated particles at a temperature of 1000 ° C. under argon atmosphere, silicon (Si) / carbon black / carbon composite particles having an average particle diameter (D50) of 170 nm through a ball milling process and an ultrasonic treatment process. Was prepared.

2. Manufacturing process of flaky graphite fragment particles

A graphite fragment having an average particle diameter (D50) of 200 μm was added to an ethyl alcohol solution, mixed using a magnetic stirrer, and then a flaky graphite fragment having an average thickness of 30 nm using a high shear mixer. Particles were prepared.

3. Anode Active Material Manufacturing Process

35% by weight of hard carbon having an average particle diameter (D50) of 9 μm, 35% by weight of silicon (Si) / carbon black / carbon composite particles having an average particle diameter (D50) of 170 nm, and 30% by weight of a petroleum pitch of the rotor blade mill. Into a rotor blade mill (rotated at 5000 to 20000 rpm in a few seconds to several minutes), the surface of the hard carbon was coated with a mixture of the silicon (Si) / carbon black / carbon composite particles and the petroleum pitch The composite particle powder was obtained. The obtained composite particle powder was mixed with flaky graphite fragment particles having a thickness of 30 nm and a petroleum pitch and introduced into a rotor blade mill, and the surface of the composite particle was coated with a shell layer composed of flaky graphite fragments and a petroleum pitch. Obtained composite particles. The obtained composite particle powder was heat-treated at 1000 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter (D50) of 15 μm.

< Example  2> Spherical natural graphite  Used as core particle Cathode active material  Produce

1. Manufacture of Silicon (Si) / Carbon Black / Carbon Composite Particles

100 parts by weight of a mixture of silicon and ketjen black having a mean particle diameter (D50) of 50 nm in a 70:30 weight ratio was added to 40 parts by weight of petroleum pitch in 100 parts by weight of tetrahydrofuran to prepare a suspension, which was then ball milled (ball Through milling and drying, silicon (Si) / carbon black / carbon composite particles having an average particle diameter (D50) of 1.6 μm were prepared.

2. Manufacturing process of flaky graphite fragment particles

 A graphite fragment having an average particle diameter (D50) of 200 μm was added to an ethyl alcohol solution, mixed using a magnetic stirrer, and then a flaky graphite fragment having an average thickness of 30 nm using a high shear mixer. Particles were prepared.

3. Anode Active Material Manufacturing Process

35 wt% of spherical natural graphite with an average particle diameter (D50) of 10 μm, 35 wt% of silicon (Si) / carbon black / carbon composite particles with an average particle diameter (D50) of 170 nm, and 30 wt% of petroleum pitch Into a rotor blade mill (rotated at 5000 to 20000 rpm in seconds to minutes), the surface of the hard carbon is coated with a mixture of the silicon (Si) / carbon black / carbon composite particles and the petroleum pitch Composite particle powder was obtained. The obtained composite particle powder was mixed with flaky graphite fragment particles having a thickness of 30 nm and a petroleum pitch and introduced into a rotor blade mill, and the surface of the composite particle was coated with a shell layer composed of flaky graphite fragments and a petroleum pitch. Obtained composite particles. The obtained composite particle powder was heat-treated at 1000 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter (D50) of 15 μm.

Comparative Example 1

35% by weight of hard carbon having an average particle diameter (D50) of 9 μm, 35% by weight of silicon (Si) / carbon black / carbon composite particles having an average particle diameter (D50) of 170 nm, and 30% by weight of a petroleum pitch of the rotor blade mill. Into a rotor blade mill (rotated at 5000 to 20000 rpm in a few seconds to several minutes), the surface of the hard carbon was coated with a mixture of the silicon (Si) / carbon black / carbon composite particles and the petroleum pitch The composite particle powder was obtained. The obtained composite particle powder was heat-treated at 1000 ° C. for 1 hour at an elevated temperature rate of 5 ° C./min in argon atmosphere, and then cooled to prepare a negative electrode active material having an average particle diameter (D50) of 13 μm.

Comparative Example 2

A negative electrode active material was prepared in the same manner as in Comparative Example 1 except that the average particle diameter (D50) of 10 µm population type natural graphite was used in Comparative Example 1.

Evaluation 1: Scanning Electron Microscopy (SEM) Analysis of Cathode Active Material

Scanning electron microscope (SEM) photographs of the core particles used in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. 4 and 5.

FIG. 4 is a scanning electron microscope (SEM) photograph of hard carbon particles as core particles used in Example 1 and Comparative Example 1, and FIG. 5 is spherical natural graphite particles as core particles used in Example 2 and Comparative Example 2. FIG. Scanning electron microscope (SEM) photographs.

 4 and 5, it can be seen that the hard carbon particles, which are the core particles used in Example 1 and Comparative Example 1, have a sharp shape, and are spherical natural particles of the core particles used in Examples 2 and Comparative Example 2. In the case of graphite, it can be confirmed that spherical natural graphite fragments are spherical.

Scanning electron microscope (SEM) photographs of the negative electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. 6 to 9.

 6 is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Comparative Example 1, and FIG. 7 is a scanning electron microscope (SEM) photograph of the negative electrode active material according to Example 1. FIG.

 Referring to FIGS. 6 and 7, in Example 1, a semi-crystalline material obtained by carbonizing carbon fine particles, silicon (Si) / carbon black / carbon composite particles, and petroleum pitch on the surface of core particles that are hard carbon or soft carbon It can be confirmed that the core particles made of carbon have a core-shell structure forming a shell layer, and in Comparative Example 1, only core particles were present without the coated shell layer.

 8 is a scanning electron microscope (SEM) picture of the negative electrode active material according to Comparative Example 2, Figure 9 is a scanning electron microscope (SEM) picture of the negative electrode active material according to Example 2.

 Referring to FIGS. 8 and 9, in Example 2, carbon particles, silicon (Si) / carbon black / carbon composite particles, and semicrystalline carbon obtained by carbonizing petroleum pitch on the surface of spherical natural graphite core particles It can be confirmed that the core particles have a core-shell structure forming a shell layer, and in Comparative Example 2, only core particles were present without the coated shell layer.

Evaluation 2: Of cathode active material Particle size distribution  analysis

The particle size distributions of the negative electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIGS. 10 and 11 even when measured by laser diffraction scattering particle size distribution measurement (PSA).

 10 is a particle size distribution of the negative electrode active material according to Example 1 and Comparative Example 1, Figure 11 is a particle size distribution of the negative electrode active material according to Example 2 and Comparative Example 2.

 Referring to FIG. 10, it can be seen that the particle size distribution of the negative electrode active material of Example 1 increases as compared with the case of the negative electrode active material of Comparative Example 1. This is due to the fact that the negative electrode active material prepared in Example 1 had a shell layer composed of flaky graphite and semi-crystalline carbon on the surface of the negative electrode active material particles of Comparative Example 1.

 Referring to FIG. 11, in comparison with the case of the negative electrode active material of Comparative Example 2, it can be seen that the particle size distribution of the negative electrode active material of Example 2 increases. This is due to the fact that the negative electrode active material prepared in Example 2 had a shell layer composed of flaky graphite and semi-crystalline carbon on the surface of the negative electrode active material particles of Comparative Example 2.

(Lithium Secondary Battery)

The negative electrode active material, carbon black, and CMC / SBR (carboxymethyl cellulose / styrene-butadiene rubber) prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were mixed in distilled water at a weight ratio of 80: 5: 15. A negative electrode slurry was prepared. The negative electrode slurry was coated on a copper foil, followed by drying and pressing to prepare a negative electrode.

Each of the negative electrode and the lithium metal was used as the positive electrode, and the electrode assembly was manufactured by laminating the negative electrode and the positive electrode through a cell guard as a separator. Then, a lithium secondary battery cell was prepared by adding an electrolyte solution in which 1 M LiPF ₆ was dissolved in a mixed solvent (DEC: EC = 1: 1) of diethyl carbonate (DEC) and ethylene carbonate (EC).

Evaluation 3: Cycle Electrochemical Characteristics of a Lithium Secondary Battery

The lifespan characteristics of the lithium secondary batteries manufactured using the negative electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated in the following manner.

For one and two cycles, charging was performed in CC / CV mode, the termination voltage was maintained at 0.02V, and charging was terminated when the current was 0.02mA. Discharge was performed in CC mode, and the termination voltage was kept at 2.0V. Charging was performed in CC mode from three cycles thereafter, and the termination voltage was maintained at 0.02V. Discharge was performed in CC mode, and the termination voltage was kept at 2.0V.

12 and 13 are charge and discharge curves of one (1st) and two (2nd) cycles of the lithium secondary battery manufactured using the negative electrode active materials prepared in Example 1 and Comparative Example 1, respectively. 15 is a charge and discharge curve of one and two cycles for the lithium secondary battery prepared using the negative electrode active material prepared in Example 2 and Comparative Example 2, respectively, from which the lithium secondary including the negative electrode active material according to the present invention It was found that the battery can obtain better initial efficiency characteristics.

16 and 17 are cycle curves for the lithium secondary battery manufactured by using the negative electrode active materials prepared in Example 1, Comparative Example 1, Example 2, and Comparative Example 2, respectively. It was found that the included lithium secondary battery can obtain better life characteristics.

Evaluation 4: Anode Active Material Differential Scanning Sequence Analysis ( DSC )

18 and 19 show the results of differential scanning sequence analysis of the electrodes prepared using the negative electrode active materials of Example 1, Comparative Example 1, Example 2, and Comparative Example 2, respectively. It can be seen that the calorific values of Examples 1 and 2 are lower than those of Comparative Examples 1 and 2 in the low temperature (250 ° C. or lower) range, and the exothermic peaks of Examples 1 and 2 in the high temperature (250 ° C. or higher) range. It turned out that was higher than the comparative example 1 and the comparative example 2.

[Description of the code]

1 and 2: negative electrode active material

11: core particle

12: silicon (Si) / carbon black / carbon composite particles

13, 15: amorphous carbon or semicrystalline carbon

14: flaky graphite fragment particle

16: coating layer

21: silicon particles

22: carbon black particles

23: amorphous carbon or semicrystalline carbon

24: pore

Claims (22)

1. A core particle comprising at least one selected from hard carbon, soft carbon, and spheroidized natural graphite, and a shell layer located on the surface of the core particle,

   The shell layer may comprise: i) a first shell layer comprising silicon (Si) / carbon black / carbon composite particles, and amorphous or semi-crystalline carbon; And ii) an amorphous or semi-crystalline carbon is distributed between the flaky graphite fragment particles, and the scaly graphite fragment particles are laminated in a concentric direction and formed by the second shell layer formed on the first shell layer. The negative electrode active material for lithium secondary batteries characterized by the above-mentioned.
2. The method of claim 1,

   The average particle diameter (D50) of the core particles is 2 to 20 ㎛ negative electrode active material for a secondary battery.
3. The method of claim 1,

   The core particle is a lithium secondary battery negative electrode active material is contained in 5 to 85% by weight based on the total amount of the negative electrode active material.
4. The method of claim 1,

   The average particle diameter (D50) of the composite particles contained in the first shell layer is a lithium secondary battery negative electrode active material, characterized in that 0.05 to 2 ㎛.
5. The method of claim 1,

   The composite particle included in the first shell layer includes silicon particles having an average particle diameter of 5 to 200 nm and a mesopore having a mean size of 2.0 to 50 nm.
6. The method of claim 1,

   The composite particles included in the first shell layer include silicon particles and carbon black particles in a weight ratio of 1: 9 to 9: 1.
7. The method of claim 1,

   The composite particle included in the first shell layer is a negative active material for a lithium secondary battery, characterized in that containing 0.1 to 70% by weight of amorphous or semicrystalline carbon.
8. The method of claim 1,

   The first shell layer is a negative active material for a lithium secondary battery, characterized in that the composite particles and the amorphous or semi-crystalline carbon in a weight ratio of 1: 9 to 9: 1.
9. The method of claim 1,

   The total weight of the first shell layer is a lithium secondary battery negative electrode active material, characterized in that 10 to 94% by weight based on the total weight of the negative electrode active material.
10. The method of claim 1,

    An average thickness of the flaky graphite fragment particles contained in the second shell layer is 100 nm or less, the negative electrode active material for lithium secondary batteries.
11. The method of claim 1,

    The scaly graphite fragment particles included in the second shell layer are included in an amount of 1 to 40 wt% based on the total weight of the negative electrode active material.
12. The method of claim 1,

    The amorphous or semicrystalline carbon may be sucrose, phenol resin, naphthalene resin, polyvinyl alcohol, polyvinyl chloride, furfuryl alcohol, polyacrylonitrile, polyamide, furan resin, cellulose, styrene, polyyi A negative electrode active material for a lithium secondary battery formed from a carbon precursor comprising at least one selected from mead, epoxy resin, vinyl chloride resin, coal-based pitch, petroleum-based pitch, mesophase pitch, tar, and low molecular weight heavy oil.
13. The method of claim 1,

    The ratio of the average particle diameter (D50) of the core particles and the thickness of the shell layer is 17 to 95: 5 to 83 negative electrode active material for lithium secondary batteries.
14. The method of claim 1,

    The ratio of the thickness of the said 1st shell layer and the said 2nd shell layer is 5-95: 95-5 the negative electrode active material for lithium secondary batteries.
15. The method of claim 1,

    The negative active material is

    The negative active material for a rechargeable lithium battery further comprising a coating layer on the surface of the shell layer and containing the amorphous or semi-crystalline carbon.
16. The method of claim 15,

    The thickness of the coating layer is a negative active material for a lithium secondary battery of 0.01 to 5 ㎛.
17. The method of claim 1,

    An average particle diameter (D50) of the negative electrode active material is a negative active material for a lithium secondary battery having a 2 to 40 ㎛.
18. The surface of the core particle comprising at least one selected from hard carbon, soft carbon and spherical natural graphite is coated with a mixture of silicon / carbon black / carbon composite particles and amorphous or semicrystalline carbon precursors to form a first shell layer. Let's

    Coating the surface of the first shell layer with a mixture of flake graphite fragment particles and an amorphous or semi-crystalline carbon precursor to form a second shell layer to obtain anode active material precursor particles; And

    Heat treating the anode active material precursor particles;

    Method for producing a negative electrode active material for a lithium secondary battery comprising a.
19. The method of claim 18,

    Before the heat treatment of the negative electrode active material precursor particles,

    The method of manufacturing a negative active material for a lithium secondary battery further comprising the step of coating the surface of the negative electrode active material precursor particles with an amorphous or semi-crystalline carbon precursor.
20. The method of claim 18,

    The heat treatment is a method for producing a negative electrode active material for a lithium secondary battery is carried out under an atmosphere containing nitrogen, argon, hydrogen or a mixed gas thereof, or under a vacuum.
21. The method of claim 18,

    The heat treatment is a method of manufacturing a negative electrode active material for a lithium secondary battery is carried out at a temperature of 700 to 1300 ℃.
22. A negative electrode comprising the negative electrode active material of any one of claims 1 to 17; anode; And a lithium secondary battery comprising an electrolyte solution.

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