KR20230057314A - Negative active material for lithium secondary battery, method of manufacturing the same, and lithium secondary battery including the same - Google Patents

Abstract

The present invention provides a negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same which comprise carbon-based particles, a composite layer located on the carbon-based particles, wherein silicon particles are dispersed in a carbon matrix in the composite layer, and a carbon coating layer located on the composite layer. A carbonization degree of the carbon matrix in the composite layer is 94% or more and 98% or less.

Description

Negative active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery including the same

The present invention relates to a lithium secondary battery, and more particularly, to a negative electrode active material for a lithium secondary battery, a manufacturing method thereof, and a secondary battery including the same.

BACKGROUND OF THE INVENTION Recently, as demand for electronic devices such as mobile devices increases, technology development for mobile devices is expanding. Demand for lithium secondary batteries, such as lithium batteries, lithium ion batteries, and lithium ion polymer batteries, as power sources for driving these electronic devices is greatly increasing. In addition, the growth of the electric vehicle market is accelerating as regulations on vehicle fuel efficiency and exhaust gas are being strengthened worldwide. Demand for batteries is expected to soar.

Meanwhile, as an anode material for a secondary battery, a carbon-based anode material having excellent cycle characteristics and a theoretical capacity of 372 mAh/g has been generally used. However, as high-capacity secondary batteries such as medium and large-sized secondary batteries are gradually required, silicon (Si), germanium (Ge), tin (Sn) or antimony having a capacity of 500 mAh / g or more that can replace the theoretical capacity of carbon-based anode materials Inorganic anode materials such as (Sb) are attracting attention. Among these inorganic anode materials, silicon-based anode materials exhibit a very large amount of lithium bonds. However, the silicon-based negative electrode material may cause pulverization due to intercalation/desorption of lithium, that is, large volume change during charge/discharge of the battery. As a result, a phenomenon of aggregation of pulverized particles may occur, and the negative electrode active material may be electrically detached from the current collector, which may result in a loss of reversible capacity under a long cycle. For this reason, the silicon-based negative electrode material and the secondary battery including the same have disadvantages of low cycle life characteristics and capacity retention despite the advantage of high charge capacity, and thus have barriers to practical use.

In order to solve the problems of such silicon-based anode materials, research on silicon-based composite anode materials such as carbon/silicon composites is being actively conducted. However, even in this composite anode material, as the amount of silicon increases, more extreme volume expansion occurs during charging and discharging of the secondary battery. As a result, the new surface of silicon in the composite anode material is continuously exposed to the electrolyte, constantly creating a solid electrolyte interface (SEI) layer to form a thick side reaction layer, resulting in electrolyte depletion and increased battery resistance. In addition, such a thick side reaction layer affects not only silicon but also graphite, and causes an electrical short circuit (peel off) between negative electrode active material particles or from the current collector, thereby rapidly degrading the performance of the secondary battery such as cycle life characteristics. There is a problem.

Therefore, for practical use of a high-capacity silicon-based composite anode material, the content of silicon is increased for higher capacity, and at the same time, volume expansion generated by charging and discharging of the secondary battery is mitigated to prevent deterioration in the performance of the secondary battery. technology needs to be developed.

One aspect of the present invention is to provide a negative electrode active material for a secondary battery having a long lifespan characteristic by mitigating volume expansion due to charging and discharging of the secondary battery while having a high capacity.

One aspect of the present invention is to provide a manufacturing method capable of economically mass-producing an anode active material having the above-described advantages through a simple process.

One aspect of the present invention is to provide a secondary battery including a negative electrode active material having the above-described advantages.

One aspect of the present invention includes carbon-based particles, a composite layer in which silicon particles are dispersed in a carbon matrix located on the carbon-based particles, and a carbon coating layer located on the composite layer, and a carbon matrix in the composite layer A degree of carbonization of 94% or more and 98% or less, provides a negative electrode active material for a lithium secondary battery.

The silicon particles in the composite layer may have a mixed form of an amorphous portion and a crystalline portion.

Crystallinity of the silicon particles in the composite layer may be 5% or more and 85% or less.

In the negative active material for a lithium secondary battery according to one aspect of the present invention, 10% by weight or more and 90% by weight or less, 5% by weight or more and 50% by weight or less of a composite layer, and a carbon coating layer 5, based on the total weight of the negative electrode active material. It may include more than 40% by weight or less by weight.

The negative active material for a lithium secondary battery according to one aspect of the present invention may contain silicon particles in an amount of 0.5% by weight or more and 30% by weight or less based on the total weight of the negative electrode active material.

The thickness of the composite layer may be 0.01 μm or more and 10 μm or less.

In another aspect of the present invention, a mixture of carbon-based particles, silicon particles, and a first carbon precursor is stirred, and the silicon particles are located on the carbon-based particles in a dispersed form in the first carbon precursor. Obtaining a composite precursor, stirring a mixture of the first composite precursor and the second carbon precursor to obtain a second composite precursor in which the second carbon precursor is positioned on the first composite precursor, and Calcining the second composite precursor at a temperature of 600 ° C. or more and 800 ° C. or less to obtain an anode active material, wherein the anode active material is carbon-based particles, located on the carbon-based particles, and silicon particles dispersed in a carbon matrix. It provides a method for producing a negative active material for a lithium secondary battery, including a composite layer and a carbon coating layer disposed on the composite layer, wherein the degree of carbonization of the carbon matrix in the composite layer is 94% or more and 98% or less.

The silicon particles may be amorphous silicon particles.

During stirring in the step of obtaining the first composite precursor and/or the step of obtaining the second composite precursor, a solvent may be sprayed.

In the method for producing a negative electrode active material for a lithium secondary battery according to an aspect of the present invention, 10% by weight or more 90% by weight of carbon-based particles with respect to the total mixing amount of carbon-based particles, silicon particles, first carbon precursor, and second carbon precursor % or less, the total amount of the silicon particles and the first carbon precursor may be 5% by weight or more and 50% by weight or less, and 5% by weight or more and 40% by weight or less of the second carbon precursor.

In the manufacturing method of the negative electrode active material for a lithium secondary battery according to one aspect of the present invention, silicon particles are added in an amount of 0.5% by weight or more to 30% by weight based on the total mixing amount of the carbon-based particles, the silicon particles, the first carbon precursor, and the second carbon precursor % or less may be mixed.

A sintering temperature in the step of sintering the second composite precursor to obtain an anode active material may be 600°C or more and 700°C or less.

One aspect of the present invention provides a negative electrode including the negative electrode active material according to one aspect of the present invention.

One aspect of the present invention provides a lithium secondary battery including a negative electrode including the negative electrode active material according to one aspect of the present invention.

The negative active material for a lithium secondary battery according to one embodiment of the present invention has a high silicon content and thus has high capacity characteristics, and can effectively prevent electrical isolation and peeling caused by volume expansion of silicon. In addition, by blocking direct exposure of the silicon interface to the electrolyte, occurrence of a side reaction with the electrolyte and depletion of the electrolyte may be suppressed. Thus, excellent lifespan characteristics of the secondary battery can be implemented.

In addition, a manufacturing method capable of economically mass-producing the negative electrode active material having the above advantages through a simple process is provided.

In addition, a secondary battery including an anode active material having the above-described advantages is provided.

1 is a scanning electron microscope (SEM) photograph of a silicon-carbon composite negative electrode active material prepared in Example 1.
FIG. 2 a) is a cross-sectional scanning electron microscope image of the silicon-carbon composite anode active material prepared in Example 1, and FIG. 2 b) is a cross-sectional scanning electron microscope image of a more enlarged portion of the coating layer.
3 is a scanning electron micrograph of the silicon-carbon composite anode active material prepared in Comparative Example 4.
4 is a scanning electron micrograph of the silicon-carbon composite anode active material prepared in Comparative Example 5.
5 is a transmission electron microscope (TEM) and fast Fourier transform (FFT) pattern of the silicon-carbon composite anode active material prepared in Example 1.
6 is a graph showing the correlation between the weight change of the pitch and the degree of carbonization according to the firing temperature.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used in a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, singular forms also include plural forms unless specifically stated in the text.

In this specification, when a part such as a layer, film, region, plate, etc. is said to be “on” or “on” another part, this includes not only the case where it is “directly on” the other part, but also the case where there is another part in the middle. do.

In addition, in the present specification, “on” and “on” mean to be located above or below the target part, and do not necessarily mean to be located on the upper side with respect to the direction of gravity.

In this specification, “ratio (ratio) of B to A” means B/A.

As described above, it is expected that the demand for medium and large-sized secondary batteries such as secondary batteries for electric vehicles (EV) and secondary batteries for energy storage systems (ESS) will soar. Accordingly, the need to develop high-capacity secondary batteries is increasing, and as part of this, in order to put into practical use a silicon-based composite anode material that exhibits high-capacity characteristics, the content of silicon is increased for high capacity, and at the same time, according to the charging and discharging of the secondary battery There is a demand for the development of a technology capable of preventing performance deterioration of a secondary battery by alleviating the volume expansion that occurs.

The present invention realizes high capacity by increasing the content of silicon than conventionally known negative electrode active materials for secondary batteries, effectively prevents electrical isolation and peeling phenomena caused by volume expansion of silicon that occurs during charging and discharging of secondary batteries, and silicon The present invention relates to an anode active material for a lithium secondary battery capable of realizing excellent lifespan characteristics of a secondary battery by suppressing side reactions with the electrolyte and depletion of the electrolyte by blocking direct exposure of the interface to the electrolyte.

Specifically, one aspect of the present invention includes carbon-based particles, a composite layer located on the carbon-based particles and in which silicon particles are dispersed in a carbon matrix, and a carbon coating layer located on the composite layer, the carbon in the composite layer A carbonization degree of the matrix is 94% or more and 98% or less to provide an anode active material for a lithium secondary battery.

In the negative electrode active material according to one aspect of the present invention, since silicon particles are dispersed and positioned in a carbon matrix on carbon-based particles, direct exposure of silicon to an electrolyte can be minimized to reduce side reactions in the electrolyte, and during charging and discharging of a secondary battery Since volume expansion can be alleviated, problems such as occurrence of an electrical short between silicon particles or from a current collector can be alleviated. Also, lifespan characteristics of the secondary battery may be improved. In addition, since a large amount of silicon can be contained relative to the total amount of the negative electrode active material, high capacity can be realized. In addition, since the silicon particles are dispersed in the carbon matrix on the carbon-based particles rather than attached to the surface of the carbon-based particles, lifespan characteristics of the secondary battery may be improved.

In addition, by further including a carbon coating layer on the composite layer, it is possible to additionally cover the silicon particles exposed on the surface of the composite layer to further prevent external exposure of the silicon particles, and to enhance the effect of suppressing the volume expansion of silicon.

In the negative electrode active material according to one aspect of the present invention, the carbon coating layer on the composite layer may have silicon particles intermittently located in the carbon coating layer that are inevitably diffused during the preparation of the negative electrode active material, and this form is also included in the scope of the present invention. do. The silicon particles intermittently located in the carbon coating layer are distinguished from the silicon particles dispersed in the composite layer, and the composite layer and the carbon coating layer of this type can be confirmed through scanning electron micrographs.

An anode active material in the form of a silicon-carbon composite of one aspect of the present invention has a high capacity and exhibits excellent lifespan characteristics compared to conventionally known anode materials.

In the negative active material according to one aspect of the present invention, the degree of carbonization of the carbon matrix in the composite layer may be 94% or more and 98% or less.

The degree of carbonization of the carbon matrix in the composite layer is calculated from the degree of carbonization of the carbon matrix prepared by firing the same carbon precursor as the carbon precursor used for the formation of the composite layer in the manufacture of the negative electrode active material under the same conditions as in the manufacture of the negative electrode active material and its weight change rate. It can be.

Specifically, the degree of carbonization of the carbon matrix in the composite layer is determined by putting the same amount of carbon precursor used in the preparation of the negative electrode active material into a tube furnace and firing under the same conditions as in the preparation of the negative electrode active material, including the firing temperature. After manufacturing the carbon matrix, the weight change rate is measured, and after establishing the correlation between the degree of carbonization and the weight change rate calculated using an element analyzer (Element analyzer, model name: Flash2000, manufacturer: Thermo), The degree of carbonization of the carbon matrix in the composite layer can be calculated by substituting the weight change ratio before and after firing of the composite precursor in which silicon particles are dispersed and located in the carbon precursor.

If the degree of carbonization of the carbon matrix in the composite layer is too small, the matrix acts as a resistance during the charging/discharging reaction of the battery and causes a side reaction with lithium ions, which can reduce the performance of the battery and also effectively alleviate the volume expansion of the silicon particles. Therefore, the degree of carbonization of the carbon matrix in the composite layer may be greater than or equal to 94%.

More specifically, the degree of carbonization of the carbon matrix in the composite layer may be 94% or more and 96% or less, 94% or more and 95.2% or less, 94.1% or more and 95.2% or less, or 94.1% or more and 94.8% or less. However, the present invention is not necessarily limited to some of these.

As an example, the upper limit of the degree of carbonization of the carbon matrix in the composite layer may be 96% or less. This is because, in one process of manufacturing the negative electrode active material of one aspect of the present invention, when the heat treatment temperature is too high in the heat treatment sintering step for carbonization of the carbon precursor, the degree of carbonization and the crystallinity of the silicon particles may rapidly increase. At this time, carbon This is because when the degree of carbonization of the matrix exceeds 96%, the crystallization of the silicon particles also increases too much, and thus, when the volume of the silicon expands due to charging and discharging of the battery, more stress is received, which can degrade the characteristics of the battery.

In the negative active material according to one aspect of the present invention, the silicon particles in the composite layer may have a mixed form of an amorphous silicon portion and a crystalline silicon portion.

Most of the silicon of the conventionally known silicon-carbon composite negative electrode active material has crystallinity, and the crystallinity of this silicon induces a selective reaction in a specific crystal plane when silicon reacts with lithium to form an alloy in a battery. Such a selective reaction causes anisotropic expansion of silicon, and crystalline silicon is subjected to great stress during an alloying reaction with lithium. This leads to deterioration of the negative electrode active material and deterioration of battery characteristics.

On the other hand, amorphous silicon shows a non-selective alloying reaction with lithium and isotropic expansion, and accordingly, less stress is received when amorphous silicon alloys with lithium.

Accordingly, when the silicon particles in the composite layer have an amorphous portion and a crystalline portion in a mixed form, they have better material properties than crystalline silicon, and excellent battery characteristics can be implemented.

On the other hand, not only when each silicon particle in the composite layer has a mixed form of an amorphous part and a crystalline part, but also when the silicon particle in the composite layer is a physically mixed form of crystalline silicon particle and amorphous silicon particle, etc. All forms in which the and crystalline parts are mixed are included in the scope of the present invention.

In the present invention, that the amorphous portion and the crystalline portion are mixed may mean that the crystallinity of the entire silicon particle in the composite layer is less than 95%. More specifically, it may mean that the crystallinity is greater than 0% and less than 95%. The degree of crystallinity can be calculated from the Raman spectrum of the silicon in the composite layer, and specifically, it can be calculated by dividing the area of the Raman peak representing crystalline silicon in the composite layer by the area of the Raman peak representing the entire silicon including crystalline and amorphous phases in the composite layer. there is.

Since the crystallinity of the silicon particles in the composite layer is less than 95%, the composite layer receives less stress during alloying reaction with lithium (ie, during charging and discharging of the secondary battery), and volume expansion can be alleviated. As a result, it is possible to prevent deterioration of battery characteristics such as deterioration of the negative electrode and life characteristics.

In the negative electrode active material of one aspect of the present invention, the composite layer on the carbon-based material may be formed by, for example, mechanically mixing carbon-based particles, amorphous silicon particles, and carbon precursors such as pitch and then firing, as described below. there is. At this time, some crystallization occurs in the amorphous silicon during the firing process, which may vary depending on the firing temperature, and crystallinity tends to increase as the firing temperature increases.

The lower the crystallinity of the composite layer may be preferable in terms of volume expansion, but considering the appropriate carbonization temperature of the carbon precursor such as pitch, the upper limit of the crystallinity of the composite layer is less than 91%, 90% or less, 85% or less, 80 % or less, 75% or less, 74.9% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 15% or less, specifically, 85% or less may be preferable, and more Specifically, it may be good to be 75% or less, or 74.9% or less. The lower limit of the crystallinity of the composite layer may be, for example, 0% or more (0% means amorphous), 5% or more, 10% or more, 20% or more, or 30% or more. More specifically, as supported by the examples described later, when the carbonization temperature of the carbon precursor, such as pitch, is too low, the crystallinity of the composite layer is lowered, but sufficient carbonization of the carbon precursor is not achieved, resulting in initial efficiency and lifespan characteristics of the secondary battery. Considering this relatively lowering, 5% or more may be good.

The negative electrode active material of one embodiment of the present invention is not particularly limited, but based on the total amount of the negative electrode active material, 10% by weight or more and 90% by weight or less of carbon-based particles, 5% by weight or more and 50% by weight or less of a composite layer, and 5% by weight of a carbon coating layer It may contain more than 40% by weight or less by weight. More specifically, it may include 30% by weight or more and 90% by weight or less of carbon-based particles, 5% by weight or more and 40% by weight or less of a composite layer, and 5% by weight or more and 30% by weight or less of a carbon coating layer.

In addition, although not particularly limited, silicon particles are contained in an amount of 0.5% by weight or more and 30% by weight or less, preferably 5% by weight or more and 20% by weight or less, more preferably 8% by weight or more and 20% by weight, based on the total amount of the negative electrode active material. Or less, 10 wt% or more and 20 wt% or less, 11 wt% or more and 20 wt% or less, or 11 wt% or more and 15 wt% or less may be included. When silicon is included in this range, high-capacity characteristics may be implemented compared to conventionally known silicon-carbon composite anode active materials.

In addition, in the negative electrode active material of one aspect of the present invention, satisfying both the carbonization degree of the carbon matrix and the crystallinity of the silicon particles in the composite layer described above may be good in terms of improving lifespan characteristics.

The thickness of the composite layer of the negative electrode active material of one aspect of the present invention is not particularly limited, but may be 0.01 μm or more and 10 μm or less. However, if the thickness of the composite layer is too thick, the stress applied to the composite layer increases due to the volume expansion of silicon during charging and discharging of the secondary battery as the composite layer becomes thick, resulting in deterioration of the negative electrode, thereby reducing the lifespan of the secondary battery. Since properties may deteriorate, it may be preferable to be 0.1 μm or more and 4 μm or less.

Meanwhile, the boundary between the carbon-based particles, the composite layer, and the carbon coating layer can be confirmed through cross-sectional scanning electron micrographs, from which the thickness of each layer can be measured.

The thickness of the carbon coating layer located on the composite layer of the negative electrode active material of one aspect of the present invention is not particularly limited, but is 0.01 μm or more and 10 μm or less, preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm. It may be more than 1 μm or less. By positioning the carbon coating layer in this thickness range, it is possible to prevent the surface exposure of the silicon particles by covering the silicon particles exposed on the surface of the composite layer. Accordingly, problems due to volume expansion of the silicon particles can be alleviated.

The carbon-based particles of the negative electrode active material of one aspect of the present invention are not limited thereto, but may be, for example, crystalline carbon-based particles, and more specifically, graphite particles.

The average particle diameter of the carbon-based particles of the negative electrode active material of one aspect of the present invention is not particularly limited, but is 1 μm or more and 100 μm or less, preferably 3 μm or more and 40 μm or less, more preferably 5 μm or more and 20 μm or less. can

The average particle diameter of the silicon particles of one aspect of the present invention is not particularly limited, but may be 1 nm or more and 500 nm or less, preferably 5 nm or more and 200 nm or less, and more preferably 10 nm or more and 100 nm or less.

Excellent capacity characteristics and lifespan characteristics may be implemented in the average particle diameter range of the carbon-based particles and the silicon particles.

On the other hand, in the present specification, the average particle diameter means a value measured as a volume average value D50 (ie, particle diameter when the cumulative volume becomes 50%) in particle size distribution measurement by laser beam diffraction method.

In another aspect of the present invention, a mixture of carbon-based particles, silicon particles, and a first carbon precursor is stirred, and the silicon particles are located on the carbon-based particles in a dispersed form in the first carbon precursor. Obtaining a composite precursor, stirring a mixture of the first composite precursor and the second carbon precursor to obtain a second composite precursor in which the second carbon precursor is positioned on the first composite precursor, and Calcining the second composite precursor at a temperature of 600 ° C. or more and 800 ° C. or less to obtain an anode active material, wherein the anode active material is carbon-based particles, located on the carbon-based particles, and silicon particles dispersed in a carbon matrix. It provides a method for producing a negative electrode active material for a lithium secondary battery, including a composite layer and a carbon coating layer disposed on the composite layer, wherein the degree of carbonization of the carbon matrix in the composite layer is 94% or more and 98% or less.

This is a method for preparing the negative electrode active material according to one aspect of the present invention described above. In addition, there is an advantage in that the negative electrode active material of the present invention can be mass-produced in a very simple process by mixing and stirring carbon-based particles, silicon particles, and carbon precursors.

Hereinafter, the manufacturing method will be described in more detail. The previously described materials, such as the type and average particle diameter of carbon-based particles and the average particle diameter of silicon particles, are omitted.

First, a mixture of carbon-based particles, silicon particles, and the first carbon precursor is stirred to obtain a first composite precursor in which the silicon particles are dispersed in the first carbon precursor on the carbon-based particles.

At this time, the silicon particles may be amorphous silicon particles. By using the amorphous silicon particles, silicon may be formed in a form in which an amorphous portion and a crystalline portion are mixed in the final composite layer of the negative active material. Accordingly, as described above, as the composite layer includes amorphous silicon, volume expansion due to charging and discharging is alleviated, and battery characteristics such as life characteristics may be improved. On the other hand, not only when each silicon particle in the composite layer has a mixed form of an amorphous part and a crystalline part, but also when the silicon particle in the composite layer is a physically mixed form of crystalline silicon particle and amorphous silicon particle, etc. Various types of composite layers in which the and crystalline portions are mixed may be formed.

In addition, by placing the silicon particles and the first carbon precursor on the carbon-based particles through stirring, the silicon particles may be dispersed in the first carbon precursor and a large amount of silicon may be placed on the carbon-based particles. Accordingly, it is possible to manufacture a high-capacity silicon-carbon composite negative electrode active material.

Meanwhile, during stirring, an organic solvent may be sprayed for better dispersion of the carbon-based particles, the silicon particles, and the first carbon precursor. By spraying a small amount of organic solvent, stirring can be performed in a high-viscosity solution state to obtain a first composite precursor. In this case, as the dispersibility is improved, the silicon particles may be further dispersed and located in the first carbon precursor, so that an increase in silicon content in the negative electrode active material and improvement in battery characteristics may be expected. The organic solvent may be, for example, tetrahydrofuran (THF), but is not limited thereto.

The stirring method may be mechanical stirring, and may be performed through a particle mixer. The particle mixer is not particularly limited, but may be performed through a rotating stirrer, an orbital stirrer, a blade mixer, or a particle fuser.

The first carbon precursor may be a carbon precursor selected from the group including pitch-based, PAN-based, rayon-based, or combinations thereof, but is not limited thereto.

Thereafter, the obtained mixture of the first composite precursor and the second carbon precursor is stirred to place the second carbon precursor on the first composite precursor. Through this step, surface exposure may be reduced by covering the silicon particles exposed on the surface of the first composite precursor with the second carbon precursor. Thus, by minimizing the number of silicon particles exposed on the surface of the finally prepared negative electrode active material, direct exposure of silicon to the electrolyte may be blocked, thereby improving lifespan characteristics.

The stirring method in this step may be mechanical stirring or may be performed through a particle mixer. The particle mixer is not particularly limited, but may be performed through a rotating stirrer, an orbital stirrer, a blade mixer, or a particle fuser.

The second carbon precursor may be a carbon precursor selected from the group including pitch-based, PAN-based, rayon-based, or combinations thereof, but is not limited thereto.

Also, it goes without saying that the first carbon precursor and the second carbon precursor may be the same material or different materials.

During stirring in this step, an organic solvent may be sprayed for better dispersion of the first composite precursor and the second carbon precursor. In this case, the density of the carbon coating layer formed from the second carbon precursor is improved through more smooth dispersion, and battery characteristics can be improved.

On the other hand, in the manufacturing method of the negative electrode active material of one aspect of the present invention, although not particularly limited, 10 weight of carbon-based particles relative to the total mixing amount of carbon-based particles, silicon particles, first carbon precursor, and second carbon precursor % or more and 90% by weight or less, the total amount of the silicon particles and the first carbon precursor is 5% by weight or more and 50% by weight or less, and the second carbon precursor is 5% by weight or more and 40% by weight or less. More specifically, 30% by weight or more and 90% by weight or less of carbon-based particles, 5% by weight or more and 40% by weight or less based on the total amount of silicon particles and the first carbon precursor, and 5% by weight or more and 30% by weight or less of the second carbon precursor. can do.

In addition, although not particularly limited, the amount of silicon particles is 0.5% by weight or more and 30% by weight or less, preferably 5% by weight or more, based on the total mixing amount of the carbon-based particles, silicon particles, the first carbon precursor, and the second carbon precursor. 20 wt% or less, more preferably 8 wt% or more and 15 wt% or less, 10 wt% or more and 20 wt% or less, 11 wt% or more and 20 wt% or less, or 11 wt% or more and 15 wt% or less. When silicon is included in this range, high-capacity characteristics may be implemented compared to conventionally known silicon-carbon composite anode active materials.

Meanwhile, an exemplary mixing ratio of the first carbon precursor and the second carbon precursor to the mixing amount of the silicon particles may be 0.6/1 or more by weight.

In addition, when the mixing ratio of the first carbon precursor and the second carbon precursor to the mixing amount of the silicon particles is too small, the composite layer and the carbon coating layer on the composite layer are not sufficiently formed, so that the surface of the graphite is exposed to the outside, or a large amount of silicon particles are formed. Exposure to the surface may cause a problem that the structure of the negative electrode active material according to one aspect of the present invention cannot be formed. The upper limit of the mixing ratio of the first carbon precursor and the second carbon precursor to the mixing amount of the silicon particles is not particularly limited, but may be less than 2/1, more preferably 1.5/1 or less.

Hereinafter, the firing step will be described.

This step heat-treats the material in which the second carbon precursor is located on the first precursor obtained through the above-described manufacturing step, and carbonizes the first and second carbon precursors, and finally the carbon-based particles and the carbon-based particle phase. This is a step of preparing an anode active material including a composite layer in which silicon particles are dispersed in a carbon matrix, and a carbon coating layer positioned on the composite layer.

Firing in this step may be performed under an inert atmosphere, for example, in an argon (Ar), helium (He), or nitrogen (N ₂ ) atmosphere. However, it is not limited thereto.

The firing temperature in this step is not particularly limited, but may be 600 ° C or more and 800 ° C or less. More specifically, it may be 600 ° C. or more and 700 ° C. or less. If the calcination temperature is too low, carbonization of the carbon precursor is not sufficiently progressed, and thus initial efficiency or lifespan characteristics of a secondary battery employing the prepared anode active material may be relatively deteriorated compared to the case of calcination within the above range. If the sintering temperature is too high, excessive crystallization of amorphous silicon may occur, and lifespan characteristics of a secondary battery including the negative electrode active material may be relatively deteriorated compared to the case of sintering within the above range.

The pressure and firing time of the firing step are not limited to a specific range.

Another aspect of the present invention provides a lithium secondary battery including a negative electrode including the negative electrode active material according to one aspect of the present invention described above.

This is a lithium secondary battery with improved battery characteristics such as high-capacity and lifespan characteristics of a lithium secondary battery, as well as ensuring stability even after repeated charging and discharging, mitigating volume expansion, by including an anode active material having the above-described characteristics. .

In this case, the lithium secondary battery may further include a positive electrode and an electrolyte, and may further include a separator between the positive electrode and the negative electrode.

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 cylindrical, prismatic, coin, pouch, etc. according to the shape, According to the size, it can be divided into bulk type and thin film type. Since the structures and manufacturing methods of these batteries are well known in the art, a minimal description will be added.

First, the negative electrode includes a current collector and a negative active material layer formed on the current collector, and the negative active material layer may include the negative active material according to one aspect of the present invention described above. Since the description of the negative active material is the same as described above, it will be omitted.

The negative electrode active material layer also includes an anode binder, and may optionally further include a conductive material.

The anode binder serves to well attach the anode active material particles to each other and also to well attach the anode active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and an olefin copolymer having 2 to 8 carbon atoms, (meth)acrylic acid and (meth)acrylic acid alkyl ester. copolymers or combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, at least one of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof may be used in combination. As the alkali metal, Na, K or Li may be used. The content of the thickener may be 0.1 to 3 parts by weight based on 100 parts by weight of the binder.

In addition, the conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and conducts electrons can be used, such as natural graphite, artificial graphite, carbon black, and acetylene black , carbon-based materials such as ketjen black and carbon fiber; metal-based materials such as metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

In addition, as the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used. can

Meanwhile, the cathode includes a current collector and a cathode active material layer formed on the current collector. As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used. Specifically, at least one of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. As a more specific example, a compound represented by any one of the following formulas may be used.

Li _a A _1-b X _b D ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); Li _a A _1-b X _b O _2-c D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _1-b X _b O _2-c D _c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b X _b O _4-c D _c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b X _c O _{2 - α} T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b X _c O _{2 - α} T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _{b E c} G _d O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b PO ₄ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); LiFePO ₄

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Of course, one having a coating layer on the surface of this compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include at least one coating element compound selected from the group consisting of oxides, hydroxides, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. Compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. In the coating layer forming process, any coating method may be used as long as the compound can be coated with a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (eg, spray coating, dipping method, etc.). Since it is a content that can be well understood by those working in the field, detailed explanations will be omitted.

The positive electrode active material layer also includes a positive electrode binder and a conductive material.

The binder serves to well attach the cathode active material particles to each other and to well attach the cathode active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and conducts electrons can be used, such as natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. Black, carbon fibers, metal powders such as copper, nickel, aluminum, and silver, metal fibers, and the like may be used, and conductive materials such as polyphenylene derivatives may be used alone or in combination of one or more.

In addition, Al may be used as the current collector, but is not limited thereto.

The negative electrode and the positive electrode may be prepared by preparing an active material composition by mixing an active material, a conductive material, and a binder in a solvent, and applying the composition to a current collector, respectively. Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted herein. As the solvent, N-methylpyrrolidone or the like may be used, but is not limited thereto.

On the other hand, the lithium secondary battery may be a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte in this case may include a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

Also, as mentioned above, a separator may be present between the positive electrode and the negative electrode. As the separator, polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more layers thereof may be used, and a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and a polypropylene/polyethylene/polyethylene It goes without saying that a mixed multilayer film such as a propylene three-layer separator or the like can be used.

Preferred examples and comparative examples of the present invention are described below. However, the following example is only a preferred embodiment of the present invention, but the present invention is not limited to the following example.

Assessment Methods

(1) Measurement of initial discharge capacity

A constant current was applied until the battery voltage reached 0.01V (vs. Li) at a current of 0.1C rate at 25 ° C. When the battery voltage reached 0.01V, a constant voltage was applied until the current reached a 0.01C rate to charge. During discharge, it was discharged with a constant current of 0.1C rate until the voltage reached 1.5V (vs. Li).

(2) Evaluation of life characteristics

At 25°C, a constant current was applied at a current of 0.5C rate until the battery voltage reached 0.01V (vs. Li), and when the battery voltage reached 0.01V (vs. Li), the current was charged until the current reached 0.01C rate. It was charged by applying a constant voltage. The cycle of discharging with a constant current at a rate of 0.5C was repeated 50 times until the voltage reached 1.5V during discharging.

[Example 1]

After dispersing 11% by weight of amorphous silicon (Si) particles with an average particle diameter of 200 nm, 76% by weight of graphite particles with an average particle diameter of 20㎛ and 6.5% by weight of pitch (viscosity at 25 ° C: ≥ 10 ⁵ cP) without a solvent, mechanical Through stirring, a first composite precursor in which the silicon particles are located on the graphite particles in a dispersed form in the pitch was obtained.

After adding 6.5% by weight of pitch to the first composite precursor, the pitch was placed on the first composite precursor through mechanical stirring to obtain a second composite precursor.

Thereafter, it was calcined for 1 hour under a nitrogen (N ₂ ) atmosphere at 700° C. to prepare a silicon-carbon composite negative electrode active material. The anode active material has a structure in which a composite layer in which silicon particles are dispersed in a carbon matrix is positioned on graphite particles and a carbon coating layer surrounds the composite layer.

1 is a scanning electron micrograph (model name: Verios 460, manufacturer: FEI) of a prepared silicon-carbon composite negative electrode active material. It can be confirmed that the composite layer is coated by the outermost carbon coating layer, and thus no silicon particles are exposed on the surface of the negative electrode active material.

FIG. 2 a) is a cross-sectional scanning electron microscope image of the prepared silicon-carbon composite anode active material, and FIG. 2 b) is a cross-sectional scanning electron microscope image of a more enlarged portion of the coating layer. It can be seen that a composite layer in which silicon particles are uniformly dispersed in a carbon matrix is formed on the graphite particles, and a carbon coating layer is formed on the composite layer. The thickness of the composite layer was observed to be about 0.2 μm or more and 3 μm or less, and the thickness of the outermost carbon coating layer was observed to be about 200 nm or more and 1 μm or less.

[Example 2]

A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1, except that the firing temperature of the second composite precursor was set to 600°C .

[Example 3]

A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1, except that the firing temperature of the second composite precursor was set to 650°C .

[Example 4]

A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1, except that the firing temperature of the second composite precursor was set to 800°C .

[Comparative Example 1]

A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1, except that the firing temperature of the second composite precursor was set to 300°C .

[Comparative Example 2]

A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1, except that the firing temperature of the second composite precursor was set to 500°C .

[Comparative Example 3]

A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1, except that the firing temperature of the second composite precursor was set to 850°C .

[Comparative Example 4]

Except for using 11% by weight of amorphous silicon particles, 83% by weight of graphite particles, and 3% by weight of pitch in the first composite precursor obtaining step, and using 3% by weight of pitch in the second composite precursor synthesis step, the above embodiment A silicon-carbon composite negative electrode active material was prepared in the same manner as in Example 1.

3 is a scanning electron micrograph of the prepared silicon-carbon composite anode active material. Since the content of total pitch is small compared to the content of silicon particles, it can be confirmed that the composite layer and the carbon coating layer on the composite layer are not formed on the surface of the graphite particles, and the graphite particles are exposed to the surface or the silicon particles are exposed to the surface. .

[Comparative Example 5]

A silicon-carbon composite negative electrode active material was prepared without forming a carbon coating layer on the composite layer. That is, after obtaining the first composite precursor in Example 1, without performing the step of positioning the second carbon precursor on the first composite precursor, the first composite precursor was directly calcined in the same manner as in Example 1 to obtain graphite particles. An anode active material was prepared in which only a composite layer in which silicon particles were uniformly dispersed in a carbon matrix was positioned on the surface.

4 is a scanning electron micrograph of the prepared silicon-carbon composite anode active material. Since the carbon coating layer is not formed on the first composite layer, it can be confirmed that the silicon particles are exposed on the surface of the negative electrode active material.

[Comparative Example 6]

Carbon coating was performed on graphite particles having an average particle diameter of 20 μm through chemical vapor deposition. Specifically, 50 g of the graphite particles were heated from room temperature at a rate of 5 ° C per minute in an inert atmosphere (N ₂ ) to 900 ° C, and when the temperature reached 900 ° C, ethylene (C ₂ H ₂ ) gas was flowed at 1.5 L / min for 30 minutes. .

Thereafter, SiH ₄ (g) was chemically deposited at a rate of 50 sccm/60 min to form a silicon coating layer on the coated carbon layer through a chemical vapor deposition method.

Next, under a temperature condition of 900 °C, C ₂ H ₂ (g) was thermally decomposed at a rate of 1.5 L/min to prepare a negative electrode active material coated with a carbon layer on the silicon coating layer.

With respect to the total amount of the negative electrode active material prepared, components were identified as 86.5 wt% of graphite, 3.0 wt% of a carbon coating layer on graphite, 8.5 wt% of silicon, and 2.0 wt% of an outermost carbon coating layer.

[Comparative Example 7]

Carbon coating was performed on graphite particles having an average particle diameter of 20 μm through a sol-gel method. Specifically, sucrose was used as a carbon precursor, and 5 g of sucrose was dissolved by mixing water and ethanol at a ratio of 9:1.

When sucrose is subsequently carbonized in a high-temperature inert atmosphere, only about 30% of the total added amount remains as carbon, so 5g of sucrose was added to 50g of graphite to leave only about 3.0wt% of carbon based on the total weight of 50g of graphite + carbon.

Thereafter, 50 g of the graphite particles were added to the solution in which the sucrose was dissolved, and the solvent was evaporated at 100° C. while continuously stirring. The solid thus obtained was charged into a furnace under an inert atmosphere (N ₂ ), carbonized at 900° C. for 10 minutes, and the obtained powder was filtered through a micro sieve.

Thereafter, SiH ₄ (g) was chemically deposited at a rate of 50 sccm/60 min to form a silicon coating layer on the coated carbon layer through a sol-gel method.

Next, under a temperature condition of 900 °C, C ₂ H ₂ (g) was thermally decomposed at a rate of 1.5 L/min to prepare a negative electrode active material coated with a carbon layer on the silicon coating layer.

With respect to the total amount of the negative electrode active material prepared, components were identified as 86.5 wt% of graphite, 1.5 wt% of a carbon coating layer on graphite, 8.5 wt% of silicon, and 3.5 wt% of an outermost carbon coating layer.

5 is a transmission electron microscope (TEM, model name: JEM-2100F, manufacturer: FEI) and fast Fourier transform (FFT, model name: Aztec, manufacturer: Oxford) pattern of the silicon-carbon composite negative electrode active material prepared in Example 1.

In FIG. 5 , the crystalline silicon pattern of the portion indicated by the circle along with the amorphous silicon pattern can be confirmed. From this, it can be seen that the silicon in the composite layer of Example 1 has a mixture of crystalline and amorphous portions.

Table 1 shows the crystallinity of silicon and the degree of carbonization of the carbon matrix in the composite layer of the silicon-carbon composite anode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3.

The crystallinity of silicon is calculated by dividing the peak area of crystalline silicon in the composite layer by the peak area of all crystalline and amorphous silicon in the composite layer in the Raman spectra (model name: NRS-5100, manufacturer: JASCO) of each Example and Comparative Example. did

The degree of carbonization of the carbon matrix of each Example and Comparative Example was measured as follows.

First, the same amount of pitch as in each Example and Comparative Example is fired for each temperature, and the degree of carbonization is obtained using a weight change rate and an element analyzer to establish a correlation between the two.

The carbonization degree calculated using an element analyzer (model name: Flash2000, manufacturer: Thermo) is calculated as the weight percent of carbon atoms relative to the total weight of nitrogen, oxygen, hydrogen, and carbon atoms included in the sample.

The degree of carbonization of the carbon matrix in the composite layer of each Example and Comparative Example was obtained by substituting the weight change before and after firing of the first composite precursor of each Example and Comparative Example to the correlation between the weight change rate and the degree of carbonization established above.

6 is a graph showing the correlation between the weight change of the pitch and the degree of carbonization according to the firing temperature.

division Crystallinity of Si in the composite layer (%) Weight change after firing of the composite layer in the composite (%) Degree of carbonization (%) of the carbon matrix in the composite layer Example 1 74.9 61.3 94.8 Example 2 5.0 63.3 94.1 Example 3 14.0 62.4 94.3 Example 4 85.0 59.5 95.2 Comparative Example 1 0.0 91.9 93.2 Comparative Example 2 0.0 69.9 93.9 Comparative Example 3 91.0 57.6 98.1

[Example 5]

A slurry was prepared by mixing the silicon-carbon composite anode active material:conductive material:binder prepared in Example 1 in distilled water at a ratio of 95:1:4. At this time, carbon black (super-P) was used as the conductive material, and sodium carboxymethyl celluose and styrene butadiene rubber were used as the binder in a ratio of 1:1.

The slurry was uniformly coated on copper foil, dried in an oven at 80° C. for about 2 hours, then roll-pressed to a thickness of 50 μm and further dried in a vacuum oven at 110° C. for about 12 hours to prepare a negative electrode plate.

The prepared negative plate, lithium foil as a counter electrode, a porous polyethylene film as a separator, and LiPF 6 in a solvent mixed with ethylene carbonate and diethyl carbonate (DEC) at a volume ratio of 3:7, LiPF ₆ is 1.3 A CR2016 coin-type half-cell was manufactured using a liquid electrolyte dissolved in M concentration and containing 10% by weight of fluoro-ethylene carbonate (FEC) according to a commonly known manufacturing process.

[Examples 6 to 8]

A half cell was prepared in the same manner as in Example 5, except that the negative active material prepared in Examples 2 to 4 was used.

[Comparative Examples 8 to 14]

Half cells were prepared in the same manner as in Example 5, except that the negative electrode active materials prepared in Comparative Examples 1 to 7 were used in order.

Table 2 shows the results of measuring the initial charge and discharge capacities of the half cells of Examples 5 to 8 and Comparative Examples 13 and 14. As can be seen from Table 2, it can be seen that the silicon carbon negative electrode active material of the present invention exhibits a discharge capacity of 600 mAh / g or more and an initial efficiency of 85% or more, and has excellent initial discharge capacity characteristics and initial efficiency compared to Comparative Examples 13 and 14. know what you have

division Initial discharge capacity (mAh/g) Initial Efficiency (%) Example 5 655 87.6 Example 6 658 86.2 Example 7 649 86.1 Example 8 641 85.2 Comparative Example 13 575 81.7 Comparative Example 14 553 82.2

Table 3 is life characteristic evaluation data for the half cells of Examples 5 to 8 and Comparative Examples 8 to 12.

division Capacity retention rate after 50 cycles (%) Example 5 91.5 Example 6 92.2 Example 7 91.6 Example 8 88.9 Comparative Example 8 83.0 Comparative Example 9 83.6 Comparative Example 10 84.7 Comparative Example 11 71.2 Comparative Example 12 39.2

Referring to this, in the case of Examples 5 to 8, even if the battery is repeatedly charged and discharged, it can be seen that the decrease in capacity is small and the improved lifespan characteristics are exhibited.

In the case of Comparative Example 11 in which the composite layer and the carbon coating layer were not formed on the graphite particles or Comparative Example 12 in which the carbon coating layer was not formed on the composite layer, it could be confirmed that the lifespan characteristics were very poor.

On the other hand, in the case of Comparative Example 10 employing an anode active material having a high crystallinity of silicon in the composite layer with a sintering temperature of over 800 ° C for the second composite precursor, it showed lower lifespan characteristics than Examples 5 to 8.

In addition, in the case of Comparative Examples 8 and 9 employing an anode active material having a sintering temperature lower than 600° C. for the second composite precursor, lower lifespan characteristics were exhibited than Examples 5 to 8. This is a result of not sufficiently carbonizing the pitch compared to Examples 5 to 8.

Furthermore, Examples 5 to 7, which simultaneously satisfied that the crystallinity of silicon in the composite layer was 75% or less and the degree of carbonization of the carbon matrix was 94% or more and 98% or less, showed the best lifespan characteristics of 90% or more.

1: carbon coating layer
2: composite layer
3 : Graphite

Claims (12)

A carbon-based particle, a composite layer positioned on the carbon-based particle and in which silicon particles are dispersed in a carbon matrix, and a carbon coating layer positioned on the composite layer,
The degree of carbonization of the carbon matrix in the composite layer is 94% or more and 98% or less,
The silicon particles in the composite layer are in the form of a mixture of amorphous and crystalline portions,
The crystallinity of the silicon particles in the composite layer is 5% or more and 85% or less, a negative electrode active material for a lithium secondary battery.
In claim 1,
A negative electrode for a lithium secondary battery comprising 10% by weight or more and 90% by weight or less of carbon-based particles, 5% by weight or more and 50% by weight or less of a composite layer, and 5% by weight or more and 40% by weight or less of a carbon coating layer, based on the total weight of the negative electrode active material. active material.
In paragraph 2,
A negative electrode active material for a lithium secondary battery comprising 0.5% by weight or more and 30% by weight or less of silicon particles based on the total weight of the negative electrode active material.
In claim 1,
The thickness of the composite layer is 0.01 μm or more and 10 μm or less,
Negative active material for lithium secondary batteries.
Stirring a mixture of carbon-based particles, silicon particles, and a first carbon precursor to obtain a first composite precursor in which the silicon particles are located on the carbon-based particles in a dispersed form in the first carbon precursor;
stirring a mixture of the first composite precursor and the second carbon precursor to obtain a second composite precursor in which the second carbon precursor is positioned on the first composite precursor; and
Calcining the second composite precursor at a temperature of 600 ° C. or more and 800 ° C. or less to obtain a negative electrode active material,
The anode active material includes carbon-based particles, a composite layer positioned on the carbon-based particles and in which silicon particles are dispersed in a carbon matrix, and a carbon coating layer positioned on the composite layer, and the degree of carbonization of the carbon matrix in the composite layer is 94% or more and 98% or less,
The silicon particles in the composite layer are in the form of a mixture of amorphous and crystalline portions,
The crystallinity of the silicon particles in the composite layer is 5% or more and 85% or less, a method for producing a negative electrode active material for a lithium secondary battery.
In paragraph 5,
The silicon particles are amorphous silicon particles,
Manufacturing method of negative electrode active material for lithium secondary battery.
In paragraph 5,
During the stirring of the step of obtaining the first composite precursor and / or the step of obtaining the second composite precursor, spraying a solvent,
Manufacturing method of negative electrode active material for lithium secondary battery.
In paragraph 5,
10% by weight or more and 90% by weight or less, 5% by weight or more in the total amount of the silicon particles and the first carbon precursor, based on the total mixing amount of the carbon-based particles, silicon particles, the first carbon precursor, and the second carbon precursor 50 A method for producing a negative electrode active material for a lithium secondary battery, which is mixed at 5% by weight or more and 40% by weight or less of the second carbon precursor.
In paragraph 5,
Method for producing a negative electrode active material for a lithium secondary battery, wherein the silicon particles are mixed in an amount of 0.5% by weight or more and 30% by weight or less based on the total mixing amount of the carbon-based particles, the silicon particles, the first carbon precursor, and the second carbon precursor.
In paragraph 5,
The firing temperature in the step of sintering the second composite precursor to obtain a negative electrode active material is 600 ° C. or more and 700 ° C. or less.
An anode for a lithium secondary battery comprising the anode active material of any one of claims 1 to 4.
A lithium secondary battery comprising the negative electrode for a lithium secondary battery of claim 11 .

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