KR20200023870A - AN ANODE ACTIVE MATERIAL CONTAINING Si FOR LITHIUM SECONDARY BATTERY AND A METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

The present invention relates to a silicon-based negative electrode active material for a lithium secondary battery and a manufacturing method thereof. After forming a composite by coating microscale silicon particles on graphite particles, the composite is subjected to wet crushing and redispersion, and it is possible to produce a negative electrode active material for a lithium secondary battery having excellent efficiency and charge and discharge capacity, and a secondary battery including the negative electrode active material.

Description

Silicon-based negative electrode active material for lithium secondary battery and manufacturing method thereof {AN ANODE ACTIVE MATERIAL CONTAINING Si FOR LITHIUM SECONDARY BATTERY AND A METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a silicon-based negative electrode active material for a lithium secondary battery and a method of manufacturing the same, wherein the charge-discharge capacity and efficiency are improved by (wet) crushing and redispersing the silicon-graphite composite coated with micrometer-sized silicon particles on the graphite particles. Provided is a silicon-based composite anode active material for a lithium secondary battery, which is an excellent silicon / graphite / carbon composite, and a method of manufacturing the same.

In the case of conventional commercialized graphite, lithium storage capacity is about 372mAh / g, and the storage capacity is relatively low, and thus it does not sufficiently satisfy the long operation time due to the light weight, miniaturization and multifunctionality of the next-generation portable devices.

Therefore, researches on silicon-based composites have been actively conducted as an alternative to the negative electrode active material having a lithium storage capacity larger than graphite. In the case of the silicon-based negative active material, the theoretical storage capacity is about 4200 mAh / g, which has a high capacity since Si atoms can react with up to 4.4 lithium, but the lithium reacts while alloying with the metal, occupying a gap between the metal atoms and lattice. As the constant increases, volume expansion necessarily occurs.

This volume expansion can be up to about 400%. When alloying occurs due to the reaction between metal and lithium, the bond between lithium and metal has the property of weak brittle ionic bond, which causes stress and easily breaks due to volume expansion. Cracking of the material occurs.

Since the volume expansion of the silicon-based negative active material can be said to be a major cause of inhibiting the actual application of lithium secondary batteries, it is necessary to minimize the stress due to volume expansion and contraction by dispersing mechanical stress generated when alloying lithium ions. .

Patent Registration No. 10-1749505

The present invention is to solve the problems of the prior art, by forming a micrometer-sized silicon on the surface of the graphite to produce a silicon-graphite composite, and then (wet) pulverization and redispersion process is more uniform and It is possible to alleviate the volume expansion phenomenon by manufacturing a small size silicon, and additionally by mixing the carbon precursor to form a silicon / graphite / carbon composite, not only the simple expansion of the volume expansion, but also silicon based lithium secondary battery having high efficiency and long life characteristics It is an object to provide a negative electrode active material.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery prepared through such a manufacturing method, and another object is to provide a lithium secondary battery including a negative electrode active material for a lithium secondary battery prepared by such a manufacturing method.

The problem and effects to be solved of the present invention will be more clearly understood through the preferred embodiments described below.

In order to achieve the problems of the prior art and the object of the present invention described above, the lithium secondary battery silicon-based composite negative electrode active material proposed by the present invention, the average particle diameter of the secondary particles is 20㎛ or less, the specific surface area 1 ~ 20㎡ / g composite particles of carbon-silicon-graphite.

The carbon-silicon-graphite composite particles may be obtained by pulverizing a silicon-graphite composite having silicon formed on the surface and internal pores of graphite, followed by carbonization by adding a carbon precursor.

In this case, the average particle diameter of the graphite used as the base material before the grinding step is 20㎛ or less, the specific surface area is 1 ~ 10㎡ / g, and the silicon formed by coating on such a substrate is 1 ~ 3㎛ thickness desirable.

Silicon formed in the silicon-graphite composite may be formed through a pyrolysis reaction using a silane-based gas of SiH ₄ , SiHCl ₃ , Si ₂ H _6, or SiH ₂ Cl ₂ .

It is preferable that 20 to 70 parts by weight of silicon and 3 to 50 parts by weight of graphite are included based on 100 parts by weight of the carbon-silicon-graphite composite particles.

Another embodiment of the present invention includes a method for producing a negative electrode active material for a lithium secondary battery, comprising: preparing graphite as a base material; Coating silicon on the surface and internal pores of the graphite to form a silicon-graphite composite; Grinding the silicon-graphite composite; Redispersing the milled silicon-graphite composite; And mixing the carbon precursor with the redispersed mixture, followed by carbonization to produce composite particles of carbon-silicon-graphite.

Since the silicon-based composite negative electrode active material for a lithium secondary battery in the form of a silicon / graphite / carbon composite obtained by using the method for preparing a silicon-based negative electrode active material according to the present invention can effectively alleviate the volume expansion and is a composite including graphite and carbon, There is an advantage that can secure the characteristics of high efficiency long life,

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description.

1 is a silicon based graphite (a), a silicon-graphite composite (b) formed in a micrometer size, a silicon-graphite composite (c) subjected to wet grinding and redispersion, and a silicon / graphite / carbon composite used as a coating base material. A scanning electron microscope (SEM) photograph of the negative electrode active material (d).
2 is a result of measuring the particle size distribution of Experimental Examples 1 to 3.
Figure 3 is a result showing the one-time charge and discharge curve of the half-cell evaluation of Experimental Example 1 and Experimental Example 3.
4 is a result showing the life results of 10 times of charge and discharge of the half-cell evaluation of Experimental Example 1 and Experimental Example 3.
Figure 5 is a result showing the life results of 100 charge / discharge of the pouch full cell evaluation of Experimental Example 1 and Experimental Example 3.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to ordinary or dictionary meanings, but should be construed as meanings and concepts consistent with the technical spirit of the present invention.

Throughout this specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding the other components unless otherwise stated.

Each of the steps may be performed out of the stated order unless the context clearly dictates the specific order. That is, each step may be performed in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

In order to achieve the problems and the objects and effects of the prior art described above, it is preferable that the negative electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is manufactured through the following process.

First, after preparing the graphite as a coating base material, the silicon-graphite composite is formed by thermally decomposing a silane-based gas to form a silicon coating layer on the surface and inside of the thus prepared graphite. The silicon coating layer constituting the silicon-graphite composite is present on the surface and inside of the graphite in the form of a micrometer-thick film to form the silicon-graphite composite.

At this time, the average particle diameter of the graphite used as the base material is 20 ㎛ or less, the surface area is preferably about 1 ~ 10 m 2 / g. The silicon constituting the micrometer-thick silicon coating layer may be included in a range of about 20 to 70 parts by weight based on 100 parts by weight of the total weight of the silicon-graphite composite, and is preferably formed to a thickness of 1 to 3 μm.

In the step of forming the micrometer-sized silicon coating layer, the silicon coating layer coated on the surface of the graphite as the base material and the internal pores, may be formed by chemical vapor deposition or pyrolysis reaction in the temperature range of 400 ℃ to less than 800 ℃. In this case, a silane-based gas such as SiH ₄ , SiHCl ₃ , Si ₂ H _6, or SiH ₂ Cl ₂ may be used as a raw material.

The silicon-graphite composite thus prepared is subjected to a pulverization process, preferably a wet pulverization process, so that the silicon is reduced to a nanometer size, for example, an average particle diameter of 500 nm or less, more preferably 200 nm or less. In the case of graphite, the micrometer size, for example, the average particle diameter can be ground to a size of about 3㎛.

Silicon and graphite may be pulverized to nanometer and micrometer sizes or less through wet grinding, respectively, and the wet grinding may be performed to crush silicon to nanometer size, thereby alleviating volume expansion due to agglomeration of silicon. It is preferable that the silicon pulverized more uniformly through wet grinding has an average particle diameter of at least about 500 nm or less.

The carbon precursor is further mixed with the pulverized nanometer-sized silicon and micrometer-sized graphite mixture, followed by a wet dispersion step, wherein the mixed carbon precursors include pitch and citric acid. ), Sucrose (sucrose) or glucose (glucose) at least one or more may be selected.

The additionally mixed carbon precursor is subjected to carbonization after forming a composite particle of carbon-silicon-graphite through sol-gel reaction with pulverized silicon and graphite in the dispersion process, and the carbonization process is about 600 It is preferably carried out in the temperature range of ~ 1,100 ℃.

The present invention includes a lithium ion secondary battery comprising a silicon-based negative electrode active material prepared by this method.

The silicon-based negative active material including the carbon-silicon-graphite composite particles according to the present invention has a shape in which graphite and silicon, which have been pulverized and dispersed, are evenly mixed with carbon, and the silicon-based negative active material is silicon when the battery is charged or discharged. The volume expansion of the structure effectively solves the problem of fragile structure.

That is, the carbon-silicon-graphite composite particles prepared according to one embodiment of the present invention may be formed by coating the silicon and graphite on the surface of the base material and the inner pores by using porous graphite containing internal pores as a base material. By manufacturing the composite, it is possible to reduce the thickness of the silicon coating layer to be coated compared to the thickness of the silicon coating layer of the same content, it is possible to increase the dispersibility of nanometer-sized silicon particles through wet grinding and wet dispersion process.

In addition, by using graphite and carbon, the electrical conductivity can be improved while the binding degree can be increased at the same time. As a result, as the charge and discharge cycle of the secondary battery progresses, it may play a very important role in mechanically stabilizing the electrode.

In more detail describing the manufacturing process of the silicon-based negative active material according to the present invention, the graphite (an average particle diameter is 20㎛ or less, specific surface area of 1 ~ 10㎡ / g) used as the base material and on the surface of the internal pore . A silicon-graphite composite is first prepared by forming a silicon coating layer having a micrometer size (thickness of 1 to 3 μm) in a film structure.

After the silicon-graphite composite thus prepared was pulverized to a nanometer size (500 nm or less, more preferably 200 nm or less) silicon and micrometer size graphite (average particle size of about 3㎛) through a wet grinding process, The carbon precursor is further mixed with the pulverized silicon and graphite, and the wet dispersion equipment is used to redistribute the silicon and graphite more uniformly.

By drying the mixture, which has undergone such redispersion, and then carbonizing it, a negative electrode active material having a silicon-graphite-carbon composite structure having an average particle diameter of 20 µm or less and a specific surface area of 1 to 20 m 2 / g is produced. can do.

The method for preparing a silicon-based negative electrode active material having a silicon-graphite-carbon composite structure according to the present invention includes a dispersion process of silicon, graphite, and carbon, and a composite form in which graphite and silicon layers are evenly mixed with a carbon layer. Has

Hereinafter will be described in more detail with respect to the silicon-based negative electrode active material and a method for manufacturing the same according to the present invention through specific examples.

[ Example  One]

Graphite having an average particle diameter of 18 µm and a specific surface area of 9 m ² / g (see FIG. 1 (a)) was charged into a rotary kiln, and monosilane (SiH ₄ ) gas was pyrolyzed at 500 ° C. for 10 hours to allow the surface and the interior of the graphite to The silicon-graphite composite was formed by forming a silicon coating layer having a thickness of 4 μm (see FIG. 1 (b)).

[ Example  2]

The silicon-graphite composite formed in Example 1 was ground to nanometer sized silicon using a wet grinding equipment. Wet grinding was performed for about 5 hours at 2,000-3,000 rpm using horizontal or vertical wet ball milling equipment to reduce the size to about 500 nm of silicon with an average particle diameter. At this time, the graphite particles also had an average particle diameter reduced to about 3 μm (see FIGS. 1C and 1D).

In this wet grinding process, the internal temperature of the wet ball milling equipment was controlled not to exceed 60 ° C., and the zirconia balls used in the wet grinding process were used with a diameter of 0.1 to 0.5 mm.

[ Example  3]

The pitch was mixed with the wet pulverized silicon and graphite prepared in Example 2 with a carbon precursor, and then uniformly redispersed through a dispersion process.

The dispersion process for this redispersion was performed using the same horizontal or vertical wet ball milling equipment as in Example 2 above, followed by wet grinding for about 1 hour in the 2,000-3,000 rpm range. In addition, the internal temperature of the wet ball milling equipment was controlled not to exceed 70 ℃, in the case of zirconia balls (Zirconia beads) used a diameter of 0.3 ~ 0.65mm.

Through this redispersion, the carbon precursor can form a composite particle of carbon-silicon-graphite through sol-gel reaction with the pulverized silicon and graphite. Heat treatment was performed in an inert atmosphere at 2 ° C. for 2 hours, and finally, composite particles of carbon-silicon-graphite were obtained (see (e) to (g) of FIG. 1).

[ Experimental Example  1] electron microscope observation

The results obtained in each of Examples 1 to 3 were observed using a scanning electron microscope (SEM), and the results are summarized in (a) to (g) of FIG. 1.

In the case of Example 1 (Fig. 1 (b)) it can be seen that the silicon covers the entire graphite surface, it can be confirmed that the thickness is about 1-3㎛.

In the case of Example 2 (Fig. 1 (c), (d)) it can be seen that the silicon-graphite composite is effectively pulverized through a wet grinding process to reduce the average size of the silicon to about 500nm.

In the case of Example 3 (Figs. 1 (e), (f), and (g)), after the carbon precursor is further mixed with the pulverized silicon and graphite, the silicon, graphite, and carbon are evenly distributed through a wet redispersion process. It can be seen that it is implemented in the form of redispersed secondary particles.

As a result of confirming the composition of the composite particles of carbon-silicon-graphite obtained through Example 3, it was confirmed that 20 to 70 parts by weight of silicon and 3 to 50 parts by weight of graphite were included based on 100 parts by weight of the composite particles. It was confirmed that the average particle diameter of the composite particles of silicon-graphite was about 200 nm.

[ Experimental Example  2] particle size analysis

Particle size analysis of the samples obtained in Examples 1, 2, and 3 was performed, and the results are summarized in FIG. 2.

As a result of measuring the particle size distribution, the particle size distribution of the silicon-graphite composite before wet grinding was about 3-5 µm in size and about 20 µm in graphite (see Example 1 of FIG. 2). ), The particle size after the wet grinding was observed as silicon particles of about 200 nm level and graphite particles of 3 μm level (see Example 2 of FIG. 2).

In view of this change in particle size distribution, it can be seen that the wet-grinding significantly reduced the particle size of silicon and graphite of the silicon-graphite composite.

In the case of Example 3, the carbon-silicon-graphite composite particles were effectively formed by further mixing, redispersing, and carbonizing the carbon precursor, and thus, the average particle diameter was about 10 μm.

[ Experimental Example  3] Of lithium secondary battery  Capacity characteristics (coin half cell)

A slurry was prepared by mixing the negative electrode active material including the carbon-silicon-graphite composite particles obtained in Example 3, the conductive material (Super-P), and the binder in a weight ratio of 8: 1: 1. The slurry thus prepared was applied to a copper foil and firstly dried at a temperature of about 80 ° C. for about 2 hours, and further dried for 12 hours in a vacuum oven at about 110 ° C. to prepare a plate.

Formation of CR2032 coin half cell was charged and discharged at 0.1C in a 0.005 ~ 1.5V section (see Figure 3), the initial efficiency and capacity retention was calculated by the following equation.

Initial Efficiency (%) = 1 charge capacity / 1 discharge capacity x 100

Capacity retention rate (%) = 50th cycle discharge capacity / 1st cycle discharge capacity x 100

As a result of confirming the results of one time charge and discharge evaluation, when the silicon-graphite composite of Example 1 was used, reversible capacity [mAh / g] and efficiency [%] were confirmed to be 1015 mAh / g and 62.9%, respectively. In the case of the carbon-silicon-graphite composite anode active material of 1351mAh / g, it was measured as 86.1%.

These results suggest that capacity and efficiency are increased by reducing side size during charge / discharge by reducing the size of silicon and increasing the degree of dispersion through wet grinding and redispersion. It is interpreted that the capacity and efficiency are increased due to the increase of the contact surface of graphite and the volume expansion and the electrical conductivity.

[ Experimental Example  4] Lithium secondary battery  Life Characteristics (Coin Half Cell)

In order to confirm the life characteristics of the negative electrode active material for the same sample as in Experimental Example 3, the life characteristics were evaluated using an electrode manufactured at 500 mAh / g class.

A negative electrode active material of Example 1 or Example 3: conductive material (SFG6L): binder (SBR): thickener (CMC) 92: 5: 1.5: 1.5 by mixing in a weight ratio of a slurry was prepared.

The slurry thus prepared was applied to a copper foil, and then dried first at a temperature of about 80 ° C. for about 2 hours, and then secondarily dried at 110 ° C. in a vacuum oven for about 12 hours to prepare a plate.

The CR2032 coin half cell is charged and discharged twice at 0.1C in the range of 0.005 ~ 1.5V, and the charge and discharge is performed 10 times at 0.5C at 0.005 ~ 1.0V for 10 hours. It evaluated, and the result is shown in FIG.

Capacity retention rate (%) = 10th cycle discharge capacity / 1st cycle discharge capacity x 100

In Example 1, the lifetime characteristics were 86.02% and 99.32% in Example 3, and the carbon-silicon-graphite composite anode active material of Example 3 was significantly improved compared to the silicon-graphite composite of Example 1. The results are shown.

[ Experimental Example  5] Of lithium secondary battery Volume expansion rate  Characteristics (coin half cell)

Under the same conditions as in Experimental Example 4, 10 charge and discharge cycles were performed to measure the volume expansion rate, and after 11 full charge cycles (100% SOC), the electrode was dismantled after dismantling the electrode in a dry controlled room (DRY ROOM). After washing the negative electrode plate in DMC for about 2 minutes, the thickness of the negative electrode was measured by using a micrometer, and the volume expansion rate was confirmed.

In Example 1, the volume expansion rate was 64%, and in Example 3, it was confirmed as 42% .In the case of using the carbon-silicon-graphite composite anode active material of Example 3 compared to the silicon-graphite composite of Example 1, The result was a marked decrease in volume expansion.

Volume expansion rate (%) = (electrode thickness at initial charge-initial electrode thickness) / initial electrode thickness x 100

[ Experimental Example  6] Of lithium secondary battery  Capacity characteristics (pouch Full Cell )

After confirming the pouch full cell life characteristics of the carbon-silicon-graphite composite anode active material according to the present invention, using the samples of Example 1 and Example 3 to prepare the electrode produced at 500mAh / g class, life characteristics Evaluation was conducted.

A negative electrode active material of Example 1 or Example 3: conductive material (SFG6L): binder (SBR): thickener (CMC) 92: 5: 1.5: 1.5 by mixing in a weight ratio to prepare a slurry. The slurry thus prepared was applied to a copper foil and first dried at a temperature of 80 ° C. for about 2 hours, and further dried for 12 hours in a vacuum oven at 110 ° C. to prepare a plate.

The 30mAh pouch square full cell was evaluated for life at 1C at 2.7 to 4.35V, and the results are shown in FIG. 5.

Capacity retention rate (%) = 100th cycle discharge capacity / 1st cycle discharge capacity x 100

In Example 1, the lifespan was 36.32%, and in Example 3, 74.23%, and the carbon-silicon-graphite of Example 3 was compared to the silicon-graphite composite of Example 1 similarly to the previous Experimental Example 4. The composite anode active material showed significantly improved results.

Claims (10)

Silicon-based negative electrode active material for lithium secondary batteries containing carbon-silicon-graphite composite particles having an average particle diameter of secondary particles of 20 µm or less and a specific surface area of 1 to 20 m 2 / g. The method of claim 1,
The composite particles of carbon-silicon-graphite are
A silicon-based composite anode active material for a lithium secondary battery, characterized in that obtained by carbonizing a silicon-graphite composite having silicon formed on the surface and internal pores of graphite after a pulverization step, and then adding a carbon precursor. The method of claim 2,
An average particle diameter of graphite before the grinding step is 20 μm or less, and the specific surface area is 1 to 10 m 2 / g, wherein the silicon-based composite negative electrode active material for a lithium secondary battery. The method of claim 2,
The silicon coating layer formed on the silicon-graphite composite prior to the grinding and redispersion has a thickness of 1 to 3 μm, wherein the silicon-based composite negative electrode active material for a lithium secondary battery. The method of claim 2,
20 to 70 parts by weight of silicon and 3 to 50 parts by weight of graphite, based on 100 parts by weight of the composite particles of carbon-silicon-graphite, the silicon-based composite negative electrode active material for a lithium secondary battery. In the manufacturing method of the negative electrode active material for lithium secondary batteries,
Preparing graphite as a substrate;
Coating silicon on the surface and internal pores of the graphite to form a silicon-graphite composite;
Grinding the silicon-graphite composite;
Mixing the carbon precursor with a mixture of the ground silicon and graphite, and then redispersing; And
Carbonizing step of sintering the redispersed mixture; through the carbon-silicon-graphite composite to produce a composite particle, a method for producing a silicon-based composite negative electrode active material for a lithium secondary battery. The method of claim 5,
The silicon coated on the silicon-graphite composite is formed through a thermal decomposition reaction using a silane gas of SiH ₄ , SiHCl ₃ , Si ₂ H _6, or SiH ₂ Cl _2, the silicon-based composite for lithium secondary battery Method for producing a negative electrode active material. The method of claim 5,
In the step of forming the silicon-graphite composite, the silicon coating layer formed on the silicon-graphite composite, characterized in that the thickness of 1 ~ 3㎛, method for producing a silicon-based composite negative active material for a lithium secondary battery. The method of claim 5,
3 to 50 parts by weight of graphite and 20 to 70 parts by weight of silicon, based on 100 parts by weight of the carbon-silicon-graphite composite particles, the method of manufacturing a silicon-based composite negative electrode active material for a lithium secondary battery. The method of claim 5,
Method for producing a silicon-based composite negative active material for a lithium secondary battery, characterized in that the silicon particles contained in the carbon-silicon-graphite composite particles have an average particle size of about 200nm.

Images