WO2017099523A1 - Method for preparing anode active material for lithium secondary battery and lithium secondary battery to which method is applied - Google Patents

Abstract

The present invention relates to: a method for preparing an anode active material for a secondary battery, the anode active material being capable of preventing oxidation during the preparation of nano-sized silicon particles; an anode active material for a secondary battery, prepared by the method; an anode for a secondary battery, comprising the anode active material for a secondary battery; and a lithium secondary battery.

Description

Manufacturing method of negative electrode active material for lithium secondary battery and lithium secondary battery using same

Cross Citation with Related Application (s)

The present application is filed with Korean Patent Application Nos. 10-2015-0176259, 10-2015-0176263, and 10-2015-0176265, issued Dec. 10, 2015, and Korean Patent Application No. 10-Dec. 8, 2016. Claiming the benefit of priority based on 2016-0166995, all the contents disclosed in the literature of that Korean patent application are incorporated as part of this specification.

Technical Field

The present invention relates to a method for producing a negative electrode active material for a lithium secondary battery, and a lithium secondary battery using the same.

In recent years, as the electronic devices become smaller, lighter, thinner, and portable with the development of the information and communication industry, the demand for high energy density of batteries used as power sources for such electronic devices is increasing.

Lithium secondary batteries are chargeable and dischargeable batteries that can best meet these requirements, and are currently used in portable electronic devices and communication devices such as small video cameras, mobile phones, and notebook computers.

In general, a lithium secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte, and lithium ions from the positive electrode active material are inserted into the negative electrode active material, that is, carbon particles, and desorbed again when discharged. Since it plays a role of transferring energy while reciprocating, charge and discharge are possible.

Meanwhile, as high-capacity batteries continue to be required due to the development of portable electronic devices, high-capacity non-carbon-based negative electrode active materials having a much higher capacity per unit weight than carbon used as conventional negative electrode active materials have been actively studied. Among these, the silicon-based negative electrode active material is known as a high capacity negative electrode active material having a low price and high capacity, for example, a discharge capacity (about 4200 mAh / g) of about 10 times that of graphite, which is a commercial negative electrode active material.

However, the silicon-based negative electrode active material is a nonconductor, and due to the rapid volume change that occurs during the charging and discharging process, the accompanying side reactions, for example, pulverization of the negative electrode active material particles, or form an unstable solid electrolyte interface (SEI) layer. In addition, battery performance is deteriorated, such as a decrease in capacity due to electrical contact, and there is a significant limitation in commercialization.

Recently, in order to minimize the pulverization of the silicon-based negative electrode active material due to charging and discharging, a technique for preparing a silicon-based negative electrode active material of nano size has been proposed.

However, in order to manufacture nano-sized silicon-based anode active material, a silicon-based material mass must be made and then crushed to nano-sized, but there is a disadvantage that it is difficult to control the crystallinity of nano-sized silicon-based particles. . In addition, as the silicon-based negative active material is oxidized in the crushing process, there is a problem in that the initial efficiency of the secondary battery is reduced.

Therefore, in order to solve this problem, the development of a method capable of preventing oxidation in the production of nano-sized silicon-based anode active material is required.

Prior art literature

Republic of Korea Patent Publication No. 10-2015-0109056

Republic of Korea Patent Publication No. 10-2014-0094676

In order to solve the above problems, the first technical problem of the present invention is to provide a method for producing a negative electrode active material for secondary batteries that can prevent oxidation during the production of nano-sized silicon particles.

A second object of the present invention is to provide a negative electrode active material for a secondary battery manufactured by the method for producing a negative electrode active material.

A third object of the present invention is to provide a negative electrode for a secondary battery including the negative electrode active material of the present invention.

In addition, a fourth technical object of the present invention is to provide a lithium secondary battery having improved discharge capacity, initial efficiency and output characteristics by providing the negative electrode of the present invention.

In order to solve the above problems, in one embodiment of the present invention

Depositing an amorphous silicon layer on the surface of the organic substrate by chemical vapor deposition (CVD) using a silane (SiH ₄ ) gas as a source (S1);

Ultrasonically grinding the amorphous silicon layer to prepare amorphous silicon particles (S2);

Dispersing the amorphous silicon particles in a carbon-based precursor solution to prepare a dispersion solution (S3);

Spray drying the dispersion solution to prepare a silicon-based composite precursor (S4); And

The heat treatment of the silicon-based composite precursor, to form a silicon-based composite comprising an amorphous carbon coating layer containing one or more amorphous silicon particles therein (S5); provides a method for producing a negative electrode active material for a lithium secondary battery comprising a. .

The amorphous silicon layer deposition step (S1) is 10 sccm / 60min silane gas at a temperature of 500 ℃ to 700 ℃ and 10 ^-8 Torr to 760 Torr (1 atmosphere), specifically 10 ^-2 Torr to 760 Torr It can be carried out while adding at a rate of from 50 sccm / 60 min.

At this time, the thickness of the deposited amorphous silicon layer is 20nm to 500nm.

In addition, the amorphous silicon layer crushing step (S2) is immersed in the acetone solution a glass substrate on which an amorphous silicon layer is deposited, and then pulverized for 10 minutes to 20 minutes at room temperature with an output between 50W and 200W using an ultrasonic grinder. It can be carried out.

The method of the present invention may further include preparing the amorphous silicon particles, and then collecting the pulverized amorphous silicon particles by volatilizing an acetone solvent.

The average particle diameter (D50) of the pulverized amorphous silicon particles is 5nm to 500nm.

In addition, the dispersion solution manufacturing step (S3) may be carried out by mixing carbonizable carbon-based materials in distilled water at a temperature of 1000 ° C. or less to prepare a carbon-based precursor solution, and then dispersing amorphous silicon particles.

The carbon-based precursor solution may be used from 25 parts by weight to 4,000 parts by weight based on 100 parts by weight of amorphous silicon particles.

In the method of the present invention, at the time of dispersing the amorphous silicon particles, at least one conductive carbon-based material selected from the group consisting of crystalline and amorphous carbon may be dispersed together.

The conductive carbonaceous material may be used in an amount of 0.99 parts by weight to 1900 parts by weight based on 100 parts by weight of amorphous silicon particles.

In the spray drying step (S4), the precursor solution may be supplied into a spray device to form a droplet by spraying, and then the drying of the droplet may be simultaneously performed.

At this time, the spray drying step may be carried out at a rate of 10 mL / min to 50 mL / min at about 50 ℃ to 300 ℃.

In addition, the step (S5) of the heat treatment of the silicon-based composite precursor may be performed at 400 ℃ to 1000 ℃ temperature, for about 10 minutes to 1 hour.

In addition, in one embodiment of the present invention

As a negative electrode active material for a lithium secondary battery produced by the method of the present invention,

Amorphous carbon coating layer; And it provides a negative electrode active material for a lithium secondary battery comprising a silicon composite consisting of one or more amorphous silicon particles contained in the amorphous carbon coating layer.

The amorphous silicon particles may include single amorphous particles or secondary amorphous silicon particles formed by aggregation of primary amorphous silicon particles formed of the single particles. The amorphous silicon particles may be uniformly dispersed in the amorphous carbon coating layer.

The amorphous silicon particles may be included in an amount of 1 to 95% by weight, and specifically 5 to 90% by weight, based on the total weight of the negative electrode active material.

The weight ratio of the amorphous silicon particles to the amorphous carbon coating layer may be 1:99 to 95: 5, specifically 5:95 to 90:10.

The anode active material may further include at least one conductive carbon-based material selected from the group consisting of crystalline or amorphous carbon different from the amorphous carbon layer forming material in the amorphous carbon coating layer.

Specifically, the negative electrode active material is an amorphous carbon coating layer; And it may include a silicon composite consisting of one or more amorphous silicon particles and amorphous carbon contained in the amorphous carbon coating layer.

In addition, the negative electrode active material is an amorphous carbon coating layer; And one or more amorphous silicon particles and crystalline carbon contained in the amorphous carbon coating layer, and the silicon composite may include the one or more amorphous silicon particles distributed on the surface of the crystalline carbon.

The conductive carbon-based material may be included in an amount of 0.1 wt% to 90 wt% based on the total weight of the negative electrode active material. Specifically, when the conductive carbon-based material is amorphous carbon, it may be included in an amount of 0.1% to 50% by weight based on the total weight of the negative electrode active material, and when the conductive carbon-based material is crystalline carbon, based on the total weight of the negative electrode active material 10 wt% to 90 wt% may be included.

In another embodiment of the present invention,

Provided is a negative electrode comprising a current collector and a negative electrode active material produced by the method of the present invention formed on at least one surface of the current collector.

In addition, an embodiment of the present invention provides a lithium secondary battery having the negative electrode.

According to the method of the present invention, it is possible to produce amorphous silicon particles for the negative electrode active material in which oxidation is prevented and crystallinity is controlled during the production of the nano silicon particles. In addition, by including such amorphous silicon particles, it is possible to manufacture a negative electrode active material and a negative electrode including the same, the electrode thickness expansion phenomenon is reduced than when using the crystalline silicon particles. Furthermore, by providing the negative electrode, a lithium secondary battery having improved initial efficiency, reversible capacity, and lifetime characteristics can be manufactured.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is a schematic diagram of a negative electrode active material for a lithium secondary battery including the silicon composite prepared in Example 1 of the present invention.

2 is a schematic view of a negative electrode active material for a lithium secondary battery including the silicon composite prepared in Example 2 of the present invention.

3 is a schematic diagram of a negative electrode active material for a lithium secondary battery including the silicon composite prepared in Example 3 of the present invention.

Explanation of the sign

1, 11, 111: amorphous silicon particles

13: amorphous carbon

5, 15, 115: amorphous carbon coating layer

10, 50, 100: negative electrode active material

117: crystalline carbon

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Recently, a silicon-based negative electrode active material has been proposed as a negative electrode active material for a lithium secondary battery, but the silicon-based negative electrode active material is a nonconductor, and due to the rapid volume change that occurs during the charging and discharging process, crushing of the negative electrode active material particles occurs or an unstable SEI. (Solid Electrolyte Interface) has a disadvantage in that the battery performance is reduced by forming a layer. In particular, in the case of Si / C composites developed to impart high electrical conductivity to silicon, the brittle carbon has a problem of being broken by volume expansion of silicon generated during charge and discharge. In order to improve this, a method for preparing a nano-sized silicon-based powder has been developed, but as the silicon-based material is oxidized during the grinding process, another problem may occur that the initial efficiency is reduced.

Thus, in the present invention, by depositing an amorphous silicon layer, and then performing an ultrasonic grinding, it is possible to provide a method for producing a negative electrode active material that can be used to prepare amorphous silicon particles that can easily control the crystallinity and prevent oxidation during the manufacturing process. Can be. In addition, by using this as a negative electrode active material, it is possible to manufacture a lithium secondary battery with improved initial efficiency, life characteristics and electrode thickness expansion characteristics.

Specifically, the present invention in one embodiment

Depositing an amorphous silicon layer on the surface of the organic substrate by chemical vapor deposition (CVD) using a silane (SiH ₄ ) gas as a source (S1);

Ultrasonically grinding the amorphous silicon layer to prepare amorphous silicon particles (S2);

Dispersing the amorphous silicon particles in a carbon-based precursor solution to prepare a dispersion solution (S3);

Spray drying the dispersion solution to prepare a silicon-based composite precursor (S4); And

The heat treatment of the silicon-based composite precursor, to form a silicon composite comprising an amorphous carbon coating layer including one or more amorphous silicon particles therein (S5); provides a method for producing a negative electrode active material for a lithium secondary battery comprising a.

At this time, in the method of the present invention, the amorphous silicon layer deposition step (S1) is 700 ℃ or less, specifically 500 ℃ to 700 ℃ temperature and 10 ^-8 Torr to 760 Torr (1 atm), specifically 10 ^-2 Torr The silane gas may be carried out at a rate of 10 sccm / 60 min to 50 sccm / 60 min under a pressure condition of 760 Torr.

As described above, in the method of the present invention, by performing the chemical vapor deposition method in the temperature range of 500 ° C to 700 ° C, the bonding force between the silicon elements is weak, and thin enough to be easily broken in the ultrasonic grinding step described later. A thick amorphous silicon layer can be deposited. If the silane gas is added at a temperature below 500 ° C., an amorphous silicon layer may not be deposited. On the other hand, when silane gas is added at a temperature above 700 ° C., crystal growth of silicon-based particles may be increased to form a crystalline silicon layer.

As described above, in the method of the present invention, by performing a chemical vapor deposition method in a low temperature range, crystal growth of silicon particles can be suppressed to form an amorphous silicon layer. In the case of the amorphous silicon layer formed by the chemical vapor deposition method of the present invention, the nanoparticles have an advantage of excellent life characteristics and small volume expansion compared to the crystalline silicon layer.

The amorphous silicon layer may be deposited to a thickness of about 20nm to 500nm.

If the deposition thickness of the amorphous silicon layer is less than 20 nm, when the subsequent ultrasonic grinding process is performed, the particle size of the collected silicon particles is very small, and the specific surface area is increased, thereby decreasing initial efficiency. On the other hand, when the deposition thickness of the amorphous silicon layer exceeds 500nm, it may be difficult to proceed with the subsequent ultrasonic grinding process stable.

In addition, in the method of the present invention, the amorphous silicon layer grinding step (S2) is impregnated in the beaker containing acetone, the glass substrate on which the amorphous silicon layer is deposited, and then outputs 50 W to 200 W using an ultrasonic grinder. Ultrasonic grinding may be performed at room temperature for 10 to 20 minutes. At this time, even if it is possible to grind | pulverize amorphous silicon particle of the nanoparticle size of a desired size even if it is an ultrasonic output other than the above and processing time, it can use sufficiently.

The amount of acetone used may be largely independent of the thickness ratio of the silicon layer, but may be used to the extent that the glass substrate on which the amorphous silicon layer is deposited is completely impregnated with acetone.

On the other hand, in the case of amorphous silicon particles having a very low crystallinity produced by the method of the present invention, when heat is applied at a high temperature in the drying process after grinding, the crystallinity of the crushed amorphous silicon particles increases to increase the crystalline silicon particles Can be formed. Therefore, the drying process should proceed at the lowest possible temperature, for this purpose, it is preferable to use a solvent that is highly volatile even at low temperatures such as acetone during the ultrasonic grinding process. In this case, in addition to the acetone, an organic solvent having high volatility may be used even at a low temperature such as ethanol or methanol.

In the conventional general mechanical grinding process, the processing time is long, and the temperature may increase due to the friction between the particles during the grinding process. As a result, the oxidation of the silicon particles may occur due to the reaction of surrounding oxygen or moisture with silicon particles. However, in the method of the present invention, by depositing an amorphous silicon layer and then performing an ultrasonic grinding, not only can the amorphous silicon layer be ground in a short time at low temperature, but also the ultrasonically pulverized amorphous silicon particles Since the process of collecting is carried out, it is possible to prevent the problem that silicon grains grow or silicon particles are oxidized during the grinding process.

In addition, the method of the present invention may include the step of collecting the pulverized amorphous silicon particles by volatilizing acetone solvent after the completion of the ultrasonic grinding process.

The average particle diameter (D50) of the amorphous silicon particles obtained by the method of the present invention may be 5nm to 500nm, specifically 20nm to 200nm.

If the average particle diameter of the amorphous silicon particles is less than 5 nm, the specific surface area may be too large, resulting in loss of reversible capacity. If the average particle diameter is larger than 500 nm, the particle size is large and the volume expansion becomes severe when reacting with lithium ions. The efficiency of buffering the volume expansion of the negative electrode active material is inferior.

That is, in general, the negative electrode active material reacts with the electrolyte during filling to form a protective film called an SEI film on the surface of the particle. In theory, the SEI film does not decompose well once produced. However, the SEI film may be broken by the volume change or crack of the negative electrode active material, or by heat or impact applied externally. In this case, when the electrode surface is exposed to the electrolyte, the SEI film may be regenerated. If the average particle diameter (D50) of the single silicon particles exceeds 500 nm, since cracks are repeatedly generated due to charge and discharge, the volume increases as the SEI film is repeatedly generated. As such, an increase in the volume of the silicon particles will soon lead to an increase in the volume of the final anode active material particles.

In addition, in the method of the present invention, in the dispersion solution preparation step (S3) to prepare a carbon-based precursor solution by mixing a carbonaceous carbon material at a temperature of 1000 ℃ or less in distilled water, and then to disperse amorphous silicon particles Can be carried out in stages.

It can be prepared by mixing the distilled water: carbon-based material in a weight ratio of approximately 1: 2 to 10: 1.

The carbonaceous material which can be carbonized even at a low temperature of 1000 ° C. or lower may include a single substance or a mixture of two or more selected from the group consisting of sucrose, glucose, fructose, galactose, maltose, and lactose. Sucrose may be carbonized at a relatively low temperature.

In the method of the present invention, the carbon-based precursor solution may be used from 25 parts by weight to 4,000 parts by weight based on 100 parts by weight of amorphous silicon particles. If the amount of the carbon-based precursor solution is less than 25 parts by weight, the viscosity of the amorphous silicon particles / carbon-based precursor solution is not easy to perform a spray process, when the amount of the carbon-based precursor solution exceeds 4,000 parts by weight, The content of amorphous silicon particles in the dispersion solution is so low that the role as a high capacity negative electrode material can be reduced.

In addition, in the method of the present invention, when preparing the dispersion solution by dispersing the amorphous silicon particles, at least one conductive carbon-based material selected from the group consisting of crystalline carbon and amorphous carbon may be dispersed together. In this case, the amorphous carbon is preferably a material different from the amorphous carbon layer forming material as described above.

That is, the negative electrode active material of the present invention may further include a conductive carbon-based material to supplement the low conductivity of the silicon particles or to implement the role of the structural support when secondary particles are formed.

The conductive carbonaceous material may be dispersed in a range of 0.99 parts by weight to 1,900 parts by weight based on 100 parts by weight of amorphous silicon particles.

If the amount of the conductive carbonaceous material is less than 0.99 parts by weight, the conductivity does not improve or serve as a structural support, and if the amount exceeds 1,900 parts by weight, the silicon-based active material content is reduced, the discharge capacity per weight (mAh / g Since) decreases, there is no advantage in terms of discharge capacity of the final active material.

The conductive carbon-based material is not particularly limited as long as it is a crystalline or amorphous carbon having conductivity without causing chemical change in the battery. Specifically, the crystalline carbon may include natural graphite, artificial graphite, graphene, or the like. As the amorphous carbon, a single material or a mixture of two or more selected from the group consisting of hard carbon, soft carbon, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon nanofibers may be used. have.

In this case, the average particle diameter (D50) of the natural graphite or artificial graphite particles of the crystalline carbon may be 300nm to 30㎛. When the average particle diameter of the natural or artificial graphite particles is less than 300 nm, the role as a structural support may be reduced. When the average particle diameter of the natural or artificial graphite particles is greater than 30 μm, the average particle diameter of the final negative electrode active material is increased, making the coating process difficult in manufacturing a secondary battery. The disadvantage is that you can.

In addition to the conductive carbonaceous material, the negative electrode active material of the present invention may optionally add a single material selected from the group consisting of metal fibers, metal powders, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, or two or more of these conductive materials. It can be included as.

In addition, in the method of the present invention, the spray drying step (S4) for preparing a silicon-based composite precursor is supplied to the precursor solution into a spray device to form a droplet by spraying, and then the step of drying the droplet simultaneously Can be performed.

The spraying step may be carried out using a drying method including rotary spraying, nozzle spraying, ultrasonic spraying, or a combination thereof, from 10 mL / min to 50 mL / min at a temperature of about 50 ° C to 300 ° C, specifically 80 ° C to 250 ° C. Can be done at speed.

At this time, the liquid crystal state and drying of the solvent is stably made when the spray drying within the temperature and speed range.

Meanwhile, the average particle diameter (D50) of the amorphous silicon particles included in the present invention is 5 nm to 500 nm, the average particle diameter (D50) of the amorphous carbon particles is about 100 nm to 300 nm, and the average particle diameter (D50) of the crystalline carbon particles is 300 nm. The above is specifically several micrometers-30 micrometers. Therefore, in the spraying step, when the amorphous silicon particles and the amorphous carbon particles are sprayed together and complexed, the two particles do not have a large difference in average particle diameter, so that the amorphous silicon particles and the amorphous carbon particles are formed inside the final active material as shown in FIG. 2. It is produced in a form of even distribution. On the other hand, in the spraying step, when the amorphous silicon particles and the crystalline carbon particles are dispersed together in the composite, due to the difference in the average particle diameter of the two particles, that is, because the average particle diameter of the crystalline carbon is larger than the average particle diameter of the amorphous silicon particles, Figure 3 As shown in the figure, the surface of the crystalline carbon particles may be prepared in a shape such that amorphous silicon particles are coated.

Further, in the method of the present invention, the step (S5) of heat treating the silicon-based composite precursor is at a temperature of 400 ℃ to 1000 ℃, preferably 500 ℃ to 800 ℃, about 10 minutes to 1 hour, preferably 20 It may be from minutes to 1 hour.

If the heat treatment temperature is less than 400 ° C., the temperature is so low that the carbonization process does not occur sufficiently, making it difficult to form an amorphous carbon coating layer. If the temperature exceeds 1000 ° C., the crystallinity of the amorphous carbon coating layer included in the precursor is increased. There is a problem.

The heat treatment step is preferably performed in an inert atmosphere in which nitrogen gas, argon gas, helium gas, krypton gas, or xenon gas is present.

In addition, in one embodiment of the present invention

As a negative electrode active material for a lithium secondary battery produced by the method of the present invention,

An amorphous carbon coating layer 5; And

Provided is an anode active material 10 for a lithium secondary battery including a silicon composite including one or more amorphous silicon particles 1 included in the amorphous carbon coating layer 5 (see FIG. 1).

In this case, the amorphous silicon particles included in the amorphous carbon coating layer may include secondary amorphous silicon particles formed by agglomeration of the single particles or primary amorphous silicon particles formed of the single particles. The amorphous silicon particles may be uniformly dispersed in the amorphous carbon coating layer.

Specifically, the average particle diameter of the amorphous silicon particles may be 5nm to 500nm, specifically 20nm to 200nm. The amorphous silicon particles may be included in an amount of 1 to 95% by weight, and specifically 5 to 90% by weight, based on the total weight of the negative electrode active material.

In addition, the weight ratio of the at least one amorphous silicon particle: amorphous carbon coating layer may be in the range of 5:90 to 90:10, specifically 10:90 to 80:20.

In addition, the negative electrode active material may further include at least one conductive carbon-based material selected from the group consisting of crystalline or amorphous carbon different from forming the amorphous carbon coating layer inside the amorphous carbon coating layer.

The conductive carbon-based material may be included in an amount of 0.1 wt% to 90 wt% based on the total weight of the negative electrode active material.

Specifically, in one embodiment of the present invention

As a negative electrode active material for a lithium secondary battery produced by the method of the present invention,

An amorphous carbon coating layer 15; And it provides a negative electrode active material 50 for a lithium secondary battery comprising a silicon composite consisting of one or more amorphous silicon particles 11 and amorphous carbon 13 contained in the amorphous carbon coating layer (see FIG. 2).

The amorphous carbon may be included in 0.1 to 50% by weight based on the total weight of the negative electrode active material. When the content of the amorphous carbon is less than 0.1% by weight, it is difficult to describe the effect of improving the electrical conductivity by adding the conductive carbonaceous material, and when the content exceeds 50% by weight, the reversible capacity of the final negative electrode active material is lowered.

In addition, in one embodiment of the present invention

As a negative electrode active material for a lithium secondary battery produced by the method of the present invention,

An amorphous carbon coating layer 115; And at least one amorphous silicon particle 111 and crystalline carbon 117 included in the amorphous carbon coating layer, wherein the at least one amorphous silicon particle 111 includes a silicon composite distributed in the crystalline carbon 117. To provide a negative electrode active material 100 for a lithium secondary battery (see Figure 3).

The crystalline carbon may include spherical / plate-shaped natural graphite or artificial graphite particles.

The average particle diameter (D50) of the crystalline carbon is 300 nm to 30 μm.

If the average particle diameter of the crystalline carbon is less than 300 nm, the role as a structural support may be reduced, and if the average particle diameter exceeds 30 μm, the average particle size of the final negative electrode active material is increased to perform a uniform coating process in manufacturing a secondary battery. It can be difficult.

The crystalline carbon may be included in 10 to 90% by weight based on the total weight of the negative electrode active material. When the content of the crystalline carbon is less than 10% by weight, it is difficult to expect the effect of improving the electrical conductivity and the role of the structural support by adding crystalline carbon, when the content of the crystalline carbon exceeds 90% by weight of the reversible capacity of the final negative electrode active material There is a problem of being lowered.

In addition, the average particle diameter (D50) of the negative electrode active material of the present invention is 50nm to 35㎛.

Specifically, when the negative electrode active material of the present invention includes amorphous carbon particles, or amorphous carbon particles and amorphous carbon (see FIGS. 1 and 2), the average particle diameter (D50) of the negative electrode active material is 50 nm to 30 μm, and When the negative electrode active material contains amorphous carbon particles and crystalline carbon (see FIG. 3), the average particle diameter (D50) of the negative electrode active material is 500 nm to 35 μm.

When the average particle diameter of the negative electrode active material is within the above range, it is possible to reduce the stress of the silicon due to volume expansion generated during charging and discharging of the negative electrode active material, to increase the reversible capacity, and to inhibit the volume expansion during reaction with lithium, thereby improving cycle life. Characteristics are improved. If the average particle diameter of the negative electrode active material is less than 50 nm, the specific surface area is too large to cause a loss of reversible capacity. If the average particle diameter exceeds 35 μm, cracking and crushing of the negative electrode active material itself occurs very easily due to the stress caused by volume expansion. As the particle size is large, the volume expansion becomes severe upon reaction with lithium, thereby decreasing efficiency in buffering the volume expansion of the whole spherical particles.

In addition, the specific surface area (BET) of the negative electrode active material of the present invention may be 0.5 m 2 / g to 20 m 2 / g. In this case, when the specific surface area exceeds 20 m 2 / g, an irreversible reaction between the electrolyte and lithium ions occurs on the surface of the active material during charge and discharge, thereby causing consumption of lithium ions, which may cause initial efficiency reduction.

As described above, the negative electrode active material made of the composite including the amorphous silicon particle-amorphous carbon coating layer prepared by the method of the present invention can lower the overall process temperature to prevent the crystalline growth and oxidation of the silicon particles, the conventional crystalline Compared to the silicon-based nanoparticle-carbon composites, there is an advantage in that the life and volume expansion characteristics are excellent, and the initial efficiency is superior to the general crystalline silicon-based nanoparticle-carbon composites. In addition, by preventing the oxidation of the silicon-based active material during the grinding process, the initial efficiency is superior to the conventional crystalline silicon-based nanoparticles-carbon composites, the discharge capacity (mAh / g) compared to the conventional crystalline silicon-based nanoparticles-carbon composites There is a big advantage. In particular, when graphite is used as a negative electrode active material, the discharge capacity of the graphite itself is 360 mAh / g, which is not large compared to silicon, and when the amount of silicon compounded to increase the discharge capacity is increased, silicon particles are concentrated on the graphite surface. It may cause deterioration of lifespan characteristics.

However, the composite produced by the method of the present invention can evenly distribute the silicon particles in the carbon matrix to prevent degradation of life characteristics.

Furthermore, the negative electrode active material produced by the method of the present invention further includes a conductive material such as graphite particles or a conductive material therein, thereby further realizing a conductivity improving effect.

In addition, in the method of the present invention

Current collector, and

It provides a negative electrode comprising the negative electrode active material of the present invention formed on at least one surface of the current collector.

At this time, the negative electrode according to an embodiment of the present invention can be prepared by a conventional method known in the art. For example, a slurry is prepared by selectively mixing and stirring a solvent, a binder, and a conductive material in the negative electrode active material, if necessary, and then applying (coating) to a current collector of a metal material, compressing, and drying to prepare a negative electrode. Can be.

According to one embodiment of the present invention, the binder is used to bind the negative electrode active material particles to maintain the molded body, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), styrene butadiene rubber Binders) are used.

According to one embodiment of the invention, the conductive material is natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon nanotube, fullerene, carbon fiber, metal Fiber, carbon fluoride, aluminum, nickel powder, zinc oxide, potassium titanate, titanium oxide and polyphenylene derivatives may be any one selected from the group consisting of, or a mixture of two or more thereof, preferably carbon black.

In one embodiment of the present invention, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, Surface treated with carbon, nickel, titanium, silver, or the like on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of about 3 to 500 μm, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In addition, in one embodiment of the present invention

By using the negative electrode, there is provided a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode and a non-aqueous electrolyte in which lithium salt is dissolved.

In this case, in the lithium secondary battery of the present invention, the positive electrode and the electrolyte used may be a material commonly used in the art, but is not limited thereto.

Specifically, the positive electrode may be prepared by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material, a solvent, and the like on a positive electrode current collector, followed by drying and rolling.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may specifically include a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. have. More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), lithium-cobalt oxide (eg, LiCoO _2, etc.), lithium-nickel oxide (for example, LiNiO ₂ and the like), lithium-nickel-manganese-based oxide (for example, LiNi _1-Y Mn _Y O ₂ (where, 0 <Y <1), LiMn _2-z Ni _z O ₄ ( here, 0 <Z <2) and the like), lithium-nickel-cobalt oxide (e.g., LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1) and the like), lithium-manganese-cobalt oxide (e. g., LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn 2 - z1 Co z1 O 4 ( here, 0 <z1 <2) and the like), lithium-nickel Manganese-cobalt-based oxides (e.g., Li (Ni _p Co _q Mn _r1 ) O ₂ , where 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co _q1 Mn _r2 ) O ₄ (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2, etc.), or lithium- Nickel-cobalt-transition metal (M) oxide (e.g. Li (Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (excitation Where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of the independent elements, respectively, 0 <p2 <1, 0 <Q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds may be included. Among the lithium composite metal oxides, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and lithium nickel manganese cobalt oxides (eg, Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ may be improved in capacity and stability of the battery. , Li (Ni _0.5 Mn _0.3 Co _0.2) O ₂ or _{Li (Ni 0.8 Mn 0.1 Co 0.1} ) O 2 ), or lithium nickel cobalt aluminum oxide _{(e.g., Li (Ni 0. 8 Co} 0. 15 Al 0 _{. 05} O _2, etc.) and the like, considering the remarkable also in the improvement according to the kind and content ratio control of constituent elements forming the lithium composite metal oxide, wherein the lithium composite metal oxide is _{Li (Ni 0.6 Mn 0.2 Co 0.2} ) O ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O _2, or Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ , and the like, and any one or a mixture of two or more thereof may be used. have.

The cathode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the cathode slurry.

The conductive material is typically added at 1 to 30% by weight based on the total weight of the positive electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; 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. Specific examples of commercially available conductive materials include Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack and EC, which are acetylene black series. Family (Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by Timcal).

The binder is a component that assists in bonding the active material and the conductive material and bonding to the current collector, and is generally added in an amount of 1 to 30 wt% based on the total weight of the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers, and the like.

The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that becomes a desirable viscosity when including the cathode active material, and optionally a binder and a conductive material. For example, the concentration of the positive electrode active material and, optionally, the solid content including the binder and the conductive material may be included in an amount of 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

The electrolyte is commonly used in manufacturing a lithium secondary battery, and includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent is not particularly limited as long as it can minimize decomposition by an oxidation reaction or the like in the process of charging and discharging a battery, and can exhibit desired properties with an additive. Examples thereof include a carbonate-based compound or propio. Nate type compounds etc. can be used individually, or can mix and use 2 or more types.

Examples of such carbonate compounds include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC), any one selected from the group consisting of, or a mixture of two or more thereof.

In addition, the propionate-based compound may be ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, iso-propyl propionate, n-butyl propionate, iso One or a mixture of two or more selected from the group consisting of -butyl propionate and tert-butyl propionate.

In addition, as the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2 Dimethoxy ethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester , Trimethoxy methane, dioxorone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate and the like Can be.

Further, as the anion wherein the lithium salt comprises a Li ⁺ cation, are ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, AlO 4 _{^{-, AlCl 4 -, PF 6}} -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, ^{_{(CF 3) 4 PF 2 -}} , (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 ^{_{SO 2) 2 N -, (}} F 2 SO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, CF 3 (CF 2) 7 SO 3 -, _{^{CF 3 CO 2 -, CH 3}} CO 2 -, SCN - can include at least one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N. The said lithium salt can also be used 1 type or in mixture of 2 or more types as needed. The lithium salt may be appropriately changed within a range generally available, but may be included in an electrolyte solution at a concentration of 0.8 M to 1.5 M in order to obtain an effect of forming an anti-corrosion coating on the surface of the electrode.

The lithium secondary battery according to the exemplary embodiment of the present invention may include all conventional lithium secondary batteries, such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

In addition, the external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, square, pouch type or coin type using a can.

The lithium secondary battery of the present invention can be used as a power source for various electronic products. For example, the present invention may be used in a portable telephone, a mobile phone, a game console, a portable television, a laptop computer, a calculator, and the like, but is not limited thereto.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

<Production of Anode Active Material>

Example 1

Silane gas was added at a rate of 25 sccm / 60 min under a pressure condition of 500 ° C. and 760 Torr to deposit an amorphous silicon layer having a thickness of 100 nm on the surface of the glass substrate.

Subsequently, the glass substrate on which the amorphous silicon layer is deposited is impregnated in a beaker containing acetone, and then subjected to ultrasonic grinding for 10 minutes at room temperature at 100W output using an ultrasonic mill, thereby obtaining amorphous silicon particles having an average particle diameter (D50) of 100 nm. Was prepared. Then, acetone was volatilized in a convection oven at 60 ° C. to collect the pulverized amorphous silicon particles.

Next, 120 g of sucrose was dissolved in 1 L of distilled water to prepare a carbon-based precursor solution, and then 50 g of the pulverized amorphous silicon particles were dispersed to prepare a dispersion solution.

The dispersion solution was spray dried at a rate of 20 mL / min at 220 ° C. to prepare a silicon-based composite precursor.

Subsequently, the silicon-based composite precursor was heat-treated at 600 ° C. for 15 minutes, and the average particle diameter (D5) including amorphous silicon particles 1 (50% by weight) inside the amorphous carbon coating layer 5 (50% by weight). A 5 μm lithium secondary battery negative electrode active material 10 was prepared (see FIG. 1).

Example 2

When dispersing the pulverized amorphous silicon particles in the carbon-based precursor solution in Example 1, in the same manner as in Example 1, except that 2g of carbon black which is amorphous carbon is dispersed together to prepare a dispersion solution, amorphous Cathode active material for lithium secondary battery having an average particle diameter (D5) of 5 μm including amorphous silicon particles 11 (49 wt%) and conductive material 13 (2 wt%) in the carbon coating layer 15 (49 wt%). 50 was prepared (see FIG. 2).

Example 3

When dispersing the pulverized amorphous silicon particles in the carbon-based precursor solution in Example 1, in the same manner as in Example 1 except for dispersing the artificial graphite particles of crystalline carbon together to prepare a dispersion solution, A lithium secondary battery having an average particle diameter (D5) of 21 μm including amorphous silicon particles 111 (17 wt%) and graphite particle core 117 (66 wt%) inside an amorphous carbon coating layer 115 (17 wt%). A negative electrode active material 100 was prepared.

Comparative Example 1

Nano-size crystalline silicon particles were prepared by pulverizing silicon powder (Sigma-aldrich) having an average particle diameter of 44 μm using a ball mill method. At this time, a zirconia ball having a diameter of 3mm was used as the milling media, and the ratio of the ball and the silicon powder was mixed in a 1: 1 mass ratio and pulverized for 2 hours. The average particle diameter of the crystalline silicon particles after grinding was 150 nm.

Subsequently, 120 g of sucrose was dissolved in 1 L of distilled water to prepare a carbon-based precursor solution, and then 50 g of the pulverized crystalline silicon particles were dispersed to prepare a dispersion solution.

The dispersion solution was spray dried at a rate of 20 mL / min at 220 ° C. to prepare a silicon-based composite precursor.

Subsequently, the silicon-based composite precursor was heat-treated at 600 ° C. for 15 minutes to have an average particle diameter (D5) of 5 μm including amorphous silicon particles (50%) inside the amorphous carbon coating layer (50%) inside the amorphous carbon coating layer (50%). A negative electrode active material for a lithium secondary battery was prepared.

Comparative Example 2.

When dispersing the pulverized crystalline silicon particles in the carbon-based precursor solution in Comparative Example 1, except for preparing a dispersion solution by dispersing 2g of carbon black, the amorphous carbon coating layer ( 49%) to prepare a negative active material for a lithium secondary battery having an average particle diameter (D5) of 5 μm including amorphous silicon particles (49%) and carbon black (2%).

Comparative Example 3

When dispersing the pulverized crystalline silicon particles in the carbon-based precursor solution in Comparative Example 1, except for preparing a dispersion solution by dispersing 200g of graphite particles together, in the same manner as in Comparative Example 1, the amorphous carbon coating layer ( 17%) to prepare a negative active material for a lithium secondary battery having an average particle diameter (D5) of 21 μm including amorphous silicon particles (17%) and graphite particles (66%).

<Production of Lithium Secondary Battery>

Example 4

(Cathode production)

The negative electrode active material prepared in Example 1 as a negative electrode active material, acetylene black as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96: 1: 2: 1. And, these were mixed with water (H ₂ O) as a solvent to prepare a uniform negative electrode active material slurry.

The prepared negative electrode active material slurry was coated on one surface of a copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a predetermined size to prepare a negative electrode.

(Manufacture of Lithium Secondary Battery)

Lithium metal foil was used as a counter electrode for the negative electrode.

After interposing a polyolefin separator between the lithium metal foil and the negative electrode, an electrolyte containing 1 M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70 was injected to form a coin. A lithium secondary battery was prepared.

Example 5

A lithium secondary battery was manufactured in the same manner as in Example 4, except that the negative electrode active material prepared in Example 2 was used instead of the negative electrode active material prepared in Example 1 as the negative electrode active material.

Example 6

A lithium secondary battery was manufactured in the same manner as in Example 4, except that the anode active material prepared in Example 3 was used instead of the anode active material prepared in Example 1 as the anode active material.

Comparative Example 4

A lithium secondary battery was manufactured in the same manner as in Example 4, except that the negative electrode active material prepared in Comparative Example 1 was used as the negative electrode active material.

Comparative Example 5

A lithium secondary battery was manufactured by the same method as Comparative Example 4, except that the negative electrode active material prepared in Comparative Example 2 was used as the negative electrode active material.

Comparative Example 6

A lithium secondary battery was manufactured by the same method as Comparative Example 4, except that the negative electrode active material prepared in Comparative Example 3 was used as the negative electrode active material.

Experimental Example

Experimental Example 1 Measurement of Physical Properties of Anode Active Material

Oxygen analysis was performed on the negative electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 using the CS-800 equipment of ELTRA, and the specific surface area was measured using the BELSORP-max equipment of BEL JAPAN. It was. In addition, the silicon grain size present in the negative electrode active materials of Examples 1 to 3 and the silicon grain size present in the negative electrode active materials of Comparative Examples 1 to 3 were measured through Bruker's D4 Endeavor XRD equipment. The results are shown in Table 1.

As shown in Table 1, in the negative electrode active material of Examples 1 to 3 including amorphous silicon particles prepared by ultrasonic pulverization, no oxygen element was detected, while silicon particles pulverized bulk silicon powder by a ball mill process. About 5% or more of oxygen elements were detected in the negative electrode active materials of Comparative Examples 1 to 3 containing.

On the other hand, when the silicon grain size contained in the negative electrode active material is small, it is known that the electrode volume expansion rate is low. At this time, in the case of the negative electrode active material of Comparative Examples 1 to 3 including silicon particles obtained by grinding a commercially available bulk silicon powder by a ball mill process, as shown in Table 1 after grinding according to the silicon grain size of the bulk silicon powder, Silicon grains of about 17 nm to 19 nm in size. On the other hand, in the case of the negative electrode active material of Examples 1 to 3 including amorphous silicon particles prepared by ultrasonic grinding, compared to the negative electrode active material of Comparative Examples 1 to 3, the silicon grains of 4.3 nm or less are included. Therefore, in the case of the electrode including the negative electrode active material of Examples 1 to 3 of the present invention, it can be predicted that the volume expansion ratio is reduced.

Experimental Example 2: Measurement of initial efficiency and charge / discharge capacity of lithium secondary battery

After charging the lithium secondary battery (coin-type half-cell) prepared in Examples 4 to 6 and Comparative Examples 4 to 6 with a constant current (CC) of 0.1C at constant current / constant voltage (CC / CV) until 5mV The charge capacity of the 1st cycle was measured by charging with constant voltage (CV) until the electric current of 0.005 C was reached. Thereafter, the mixture was left for 20 minutes and then discharged to 1.5 V at a constant current of 0.1 C to measure initial efficiency and discharge capacity. The charging and discharging results of the lithium secondary batteries of Examples 4 to 6 and Comparative Examples 4 to 6 are shown in Table 2 below.

As shown in Table 2, the secondary battery of Example 4 increased the initial efficiency by 10% and the discharge capacity by about 210 mAh / g, compared to the secondary battery of Comparative Example 4. In addition, compared with the secondary battery of Comparative Example 5, the secondary battery of Example 5 had an initial efficiency of 9% and a discharge capacity of about 210 mAh / g. In addition, compared with the secondary battery of Comparative Example 6, the secondary battery of Example 6 increased the initial efficiency by 9% and the discharge capacity by about 80 mAh / g.

That is, the negative electrode active materials of Comparative Examples 4 to 6 including silicon particles prepared by pulverizing the bulk silicon powder are oxidized by frictional heat during grinding, and irreversible phase during initial charging as oxygen is bonded to the silicon particles. Since a phase formed by an irreversible reaction, which is produced during the discharge but is not decomposed again during discharge, is formed, the initial efficiency is lowered and the amount of silicon atoms that can participate in the reversible reaction is reduced. Therefore, as shown in Table 2, the charge and discharge reversible capacity of the secondary batteries of Comparative Examples 4 to 6 including the negative electrode active materials of Comparative Examples 1 to 3 is reduced.

On the other hand, in the secondary battery of Example 6, since the content of the amorphous silicon particles 111 in the negative electrode active material is lower than the secondary batteries of Comparative Examples 4 and 5, it can be seen that the charge and discharge capacity is relatively reduced.

Experimental Example 3: Lifetime Characteristics and Electrode Thickness Expansion Characteristics of a Lithium Secondary Battery

After charging the lithium secondary battery (coin-type half-cell) prepared in Examples 4 to 6 and Comparative Examples 4 to 6 with a constant current (CC) of 0.1C at constant current / constant voltage (CC / CV) until 5mV The charge capacity of the 1st cycle was measured by charging with constant voltage (CV) until the electric current of 0.005 C was reached. Thereafter, the mixture was left for 20 minutes and then discharged to 1.5 V at a constant current of 0.1 C to measure initial efficiency and discharge capacity. Thereafter, after 20 minutes, 0.5C constant current (CC / CV) charging in the same voltage range, and then repeated 0.5C constant current (CC) cycle 50 times to measure the life characteristics. After 50 cycles, the battery was charged at 0.5C again and the coin-type lithium secondary battery was disassembled to measure the negative electrode thickness expansion rate in a fully charged state. The life characteristics and electrode thickness expansion results are shown in Table 3 below.

-Life characteristics (%): 50th cycle discharge capacity ÷ 1st cycle discharge capacity × 100 electrode thickness

-Electrode thickness expansion rate (%): (51th cycle charge negative electrode thickness-initial negative electrode thickness before battery assembly) ÷ (initial negative electrode thickness before battery assembly-current collector thickness) × 100

As shown in Table 3, in the case of the secondary battery of Example 4 of the present invention it can be seen that the life characteristics are about 8% superior to the secondary battery life characteristics of Comparative Example 4. In addition, it can be seen that the life characteristics of the secondary battery of Example 5 of the present invention are about 9% superior to those of the secondary battery of Comparative Example 5. In addition, it can be seen that the life characteristics of the secondary battery of Example 6 of the present invention are about 6% superior to those of the secondary battery of Comparative Example 6.

In addition, it can be seen that the electrode thickness expansion ratio of the 51st cycle charged state of the secondary batteries of Examples 4 to 6 is significantly lower than that of each of the secondary batteries of Comparative Examples 4 to 6.

On the other hand, in the secondary batteries of Examples 4 and 5, since the content of the amorphous silicon particles (1, 11) in the negative electrode active material is higher than that of the secondary battery of Comparative Example 6, the life characteristics are high and the electrode thickness expansion rate is also high It is confirmed. That is, since the secondary battery of Comparative Example 6 contains a negative electrode active material containing silicon particles and crystalline carbon, compared with the secondary batteries of Examples 4 and 5, the life characteristics are high and the expansion rate is low.

Claims (30)

1. Depositing an amorphous silicon layer on the surface of the organic substrate by chemical vapor deposition (CVD) using a silane (SiH ₄ ) gas as a source (S1);

   Ultrasonically grinding the amorphous silicon layer to prepare amorphous silicon particles (S2);

   Dispersing the amorphous silicon particles in a carbon-based precursor solution to prepare a dispersion solution (S3);

   Spray drying the dispersion solution to prepare a silicon-based composite precursor (S4); And

   Heat-treating the silicon-based composite precursor to form a silicon-based composite including an amorphous carbon coating layer including at least one amorphous silicon particle therein (S5); manufacturing method of a negative electrode active material for a lithium secondary battery.
2. The method according to claim 1,

   The amorphous silicon layer deposition step (S1) is carried out while applying the silane gas at a rate of 10 sccm / 60min to 50 sccm / 60min under a temperature of 500 ° C to 700 ° C and a pressure condition of 10 ^-8 Torr to 760 Torr. Method for producing a negative electrode active material for a lithium secondary battery.
3. The method according to claim 1,

   The thickness of the deposited amorphous silicon layer is 20nm to 500nm manufacturing method of the negative electrode active material for a lithium secondary battery.
4. The method according to claim 1,

   In the amorphous silicon layer grinding step (S2), the glass substrate on which the amorphous silicon layer is deposited is immersed in an acetone solution, and then subjected to ultrasonic grinding for 10 to 20 minutes at room temperature with an output of 50 W to 200 W using an ultrasonic mill. Method for producing a negative electrode active material for a lithium secondary battery.
5. The method according to claim 1,

   The method further includes the step of collecting the pulverized amorphous silicon particles by volatilizing the acetone solvent after the amorphous silicon particle manufacturing step (S2), before the dispersion solution manufacturing step (S3). .
6. The method according to claim 1,

   The average particle diameter (D50) of the pulverized amorphous silicon particles is 5nm to 500nm manufacturing method of the negative electrode active material for a lithium secondary battery.
7. The method according to claim 1,

   The dispersing solution manufacturing step (S3) is to prepare a carbon-based precursor solution by mixing a carbonizable carbon-based material in distilled water, at a temperature of 1000 ℃ or less, and then to disperse amorphous silicon particles to the lithium secondary battery negative electrode active material Method of preparation.
8. The method according to claim 7,

   The carbonaceous material is a single material or a mixture of two or more selected from the group consisting of sucrose, glucose, fructose, galactose, maltose, and lactose, a method for producing a negative electrode active material for a lithium secondary battery.
9. The method according to claim 1,

   The carbon-based precursor solution is 25 to 4,000 parts by weight based on 100 parts by weight of the amorphous silicon particles to prepare a negative electrode active material for a lithium secondary battery.
10. The method according to claim 1,

    At the time of dispersing the amorphous silicon particles, at least one conductive carbon-based material selected from the group consisting of crystalline and amorphous carbon further dispersing a negative electrode active material for a lithium secondary battery.
11. The method according to claim 10,

    The conductive carbon-based material is dispersed in 0.99 part by weight to 1,900 parts by weight based on 100 parts by weight of amorphous silicon particles.
12. The method according to claim 1,

    The spray drying step (S4) of the dispersion solution is to supply the precursor solution into a spray device to form a droplet by spraying, and then drying the droplet is a method of manufacturing a negative electrode active material for a lithium secondary battery .
13. The method according to claim 1,

    The spray drying step is a method for producing a negative electrode active material for a lithium secondary battery that is carried out at a rate of 10 mL / min to 50 mL / min at about 50 ℃ to 300 ℃.
14. The method according to claim 1,

    The step (S5) of the heat treatment of the silicon-based composite precursor is performed for about 10 minutes to 1 hour at 400 ℃ to 1000 ℃ temperature method for producing a negative electrode active material for a lithium secondary battery.
15. As a negative electrode active material for a lithium secondary battery produced by the method of claim 1,

    Amorphous carbon coating layer; And

    A negative electrode active material for a lithium secondary battery comprising a silicon composite made of one or more amorphous silicon particles contained in the amorphous carbon coating layer.
16. The method according to claim 15,

    The amorphous silicon particle is a negative electrode active material for a lithium secondary battery comprising a single particle or secondary amorphous silicon particles formed by agglomeration of primary amorphous silicon particles consisting of the single particle.
17. The method according to claim 15,

    The amorphous silicon particles are uniformly dispersed in the amorphous carbon coating layer negative electrode active material for a lithium secondary battery.
18. The method according to claim 15,

    The amorphous silicon particles are contained in 1 to 95% by weight based on the total weight of the negative electrode active material negative electrode active material for a lithium secondary battery.
19. The method according to claim 15,

    The amorphous silicon particle: the weight ratio of the amorphous carbon coating layer is 1:99 to 95: 5 negative electrode active material for a lithium secondary battery.
20. The method according to claim 19,

    The weight ratio of the amorphous silicon particles: amorphous carbon coating layer is 5:95 to 90:10, the negative electrode active material for a lithium secondary battery.
21. The method according to claim 15,

    The negative electrode active material further comprises at least one conductive carbon-based material selected from the group consisting of crystalline carbon and amorphous carbon inside the amorphous carbon coating layer.
22. The method according to claim 21,

    The negative electrode active material is an amorphous carbon coating layer; And a silicon composite including at least one amorphous silicon particle and amorphous carbon included in the amorphous carbon coating layer.
23. The method according to claim 22,

    The amorphous carbon is a negative active material for a lithium secondary battery that is contained in 0.1 to 50% by weight based on the total weight of the negative electrode active material.
24. The method according to claim 21,

    The negative electrode active material is an amorphous carbon coating layer; And one or more amorphous silicon particles and crystalline carbon contained in the amorphous carbon coating layer, wherein the one or more amorphous silicon particles are distributed on the surface of the crystalline carbon.
25. The method of claim 24,

    The average particle diameter (D50) of the crystalline carbon is 300nm to 30㎛ negative electrode active material for a lithium secondary battery.
26. The method of claim 24,

    The crystalline carbon is 10% by weight to 90% by weight based on the total weight of the negative electrode active material negative electrode active material for a lithium secondary battery.
27. The method according to claim 15,

    An average particle diameter (D50) of the negative electrode active material is a lithium secondary battery negative electrode active material is 50nm to 35㎛.
28. The method according to claim 15,

    Specific surface area (BET) of the negative electrode active material is 0.5 m 2 / g to 20 m 2 / g negative electrode active material for a lithium secondary battery.
29. Current collector, and

    A negative electrode comprising the negative electrode active material of claim 15 formed on at least one surface of the current collector.
30. Lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the negative electrode is the negative electrode of claim 29.

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