KR20150067627A - Method for synthesis of Silicon/Carbon composite as the lithium secondary battery anode material - Google Patents

Abstract

In the present invention, disclosed is a manufacturing method of silicon and carbon composite materials for negative electrode materials of secondary batteries, comprising the steps of manufacturing mesoporous silica by using surfactant and tetraethyl orthosilicate (TEOS); manufacturing mesoporous silicon with use of the mesoporous silica; and mixing the mesoporous silicon with carbon precursor.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a silicon and carbon composite material for a secondary battery anode material,

The present invention relates to a method for manufacturing a silicon and carbon composite material for a secondary battery anode material, and more particularly, to a method for manufacturing a silicon and a carbon composite material for a secondary battery anode material, which more suitably compensates for volume expansion, which is one of the biggest disadvantages of high- And a method for manufacturing a silicon and carbon composite material for a secondary battery negative electrode material.

As IT (Information Technology) technology develops, a variety of portable information communication devices such as smart phones, digital cameras, notebooks, and tablet PCs are in the spotlight, and miniaturization and high energy density of such portable information communication devices are required. [0003] Lithium secondary batteries commercialized in the early 1990s occupy a very important position as a main power source device of such portable electronic devices.

Recent data Lithium secondary batteries have higher operating voltages and energy densities than other secondary batteries and have excellent properties that can meet various requirements of devices because they can be used for a long time. Efforts are being actively made to expand the application field of the vehicle to a transportation device, a power storage device, a medical device, and a defense device.

Despite the relatively high theoretical capacity of 372 mAh / g in the case of Graphite, which is widely used as a negative electrode material for lithium secondary batteries, the theoretical capacity is limited in various applications of lithium secondary batteries.

In addition, since the low reversibility capacity after the first cycle and the problem of low rate characteristic arise, it is difficult to apply various devices of the lithium secondary battery, and research on other new anode materials is under way.

As one of the materials that is newly attracted to the cathode material of lithium secondary battery, silicon has a theoretical capacity of 4200 mAh / g, which has a significantly higher capacity than conventional negative electrode materials, has many reserves on the earth, Which is a suitable material for application of various devices and the like.

These silicones have a high theoretical capacity, while the decomposition of silicon particles due to the large volume expansion occurring during charging / discharging, and thus the storage space of Li ions are lost, It has a fatal disadvantage that decay occurs very quickly.

Silicon Nano Tube and Silicon Nano Wire have been studied to induce rapid insertion / desorption at the time of charging / discharging by shortening the Li diffusion distance by nanoizing the silicon particles to suppress the volume expansion of the silicon having a high capacity.

In addition, there is a method of coating an inactive carbon layer on the silicon surface to make the carbon layer serve as a buffer for volume expansion of the silicon. By making the porous silicon, it is possible to increase the contact area with the electrolyte, .

1. Korean Patent No. 10-0441513 2. Korean Patent No. 10-0830612 3. Korean Patent No. 10-1253494

It is an object of the present invention to provide a method for manufacturing a silicon and carbon composite material for a secondary battery anode material, which can prevent the volume of a high-capacity silicon as an anode material of a lithium secondary battery from being expanded. .

In order to accomplish the above object, the present invention provides a method for preparing a silicon and carbon composite material for a secondary battery anode material, comprising the steps of: preparing a mesoporous silica using a surfactant and tetraethyl orthosilicate (TEOS); Preparing mesoporous silicon using the mesoporous silica; And mixing the mesoporous silicon and the carbon precursor.

A step of producing the mesoporous silica, (a) P123 (polyethylene glycol -block-polypropylene glycol-block-polyethylene glycol) with hydrochloric acid comprising: stirring until completely dissolved by the addition of (HCl) and water (H ₂ O) ; (b) adding tetraethyl orthosilicate (TEOS) to the solution and agitating the solution together by ultrasonic waves; (c) heating at 100 占 폚 for 12 to 24 hours; (d) filtration, washing with ethanol and drying at 100 < 0 >C; And (e) firing at 550 DEG C to remove P123.

(A) mixing the mesoporous silica and MgO in a molar ratio of 1: 2 and stirring the mesoporous silica; (b) firing at 650 DEG C at a heating rate of 3 DEG C / min under an argon gas atmosphere; (c) acid treatment with hydrochloric acid to remove MgO, followed by filtering with ethanol; And (d) drying in an oven at a temperature of 100 ° C. The method of claim 1, further comprising the step of removing silica by using hydrogen fluoride.

The step of mixing the mesoporous silicon and the carbon precursor comprises: (a) preparing mesoporous silicon and a carbon precursor at a weight ratio of 1: 3 to 7; (b) dissolving the carbon precursor in acetone to prepare a solution; (c) adding mesoporous silicon to the solution and uniformly mixing the solution; (d) drying the mixture in an oven at a temperature of 100 DEG C for evaporation of acetone; And (e) calcining the mixture at 700 to 900 占 폚 for 7 hours while flowing argon (Ar) gas.

In the (a) mixing step, the carbon precursor is characterized by using phenol resin or sucrose.

In the step (e), the calcination is performed while adjusting the reaction atmosphere by injecting argon and / or nitrogen gas at a rate of 300 to 500 cc / min.

According to the present invention, the reversible capacity of the produced silicon and carbon composite material exhibited a high capacity of 1300 mAh / g, and the cyclic test showed a stable and excellent cycle storage capacity of 76%.

The mesoporous silicon is produced from the hydrophilic and hydrophobic block copolymer of the present invention as a template material and carbonized to produce a silicon / carbon composite material, thereby producing a cathode material having an excellent electrochemical charge / discharge characteristic of the battery.

According to the present invention, the capacity of a battery is greatly improved, electrode loss due to volume expansion, which is a disadvantage of silicon, is complemented, and the stability of charging and discharging cycles is excellent. Thus, Thereby improving the performance of the battery together with various anode materials. In the present invention, it is possible to realize an energy storage device (secondary battery) using such an electrode material and having excellent electrical stability according to an electrolyte solution and improved characteristics of the battery.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing a manufacturing process of a silicon and carbon composite material for a secondary battery anode material. FIG.
FIG. 2 is a view showing a process for manufacturing a negative electrode and a half-cell of a secondary battery of a silicon and carbon composite material.
FIG. 3 shows XRD analysis results to confirm the crystal structure of the silicon and carbon composite material.
FIG. 4 is a cross- It is the result of analyzing the surface SEM photograph of the composite material.
FIG. 5 is a cross- This is the result of analyzing the isotherm curves of composite materials.
FIG. 6 is a cross- It is the analysis result of the thermal analysis of the composite material.
7 is a graph showing the charging / discharging characteristics of a secondary battery using various ratios of silicon and carbon as the negative electrode active material.
8 is a graph showing rate characteristics of a secondary battery using a silicon and carbon composite material as a negative electrode active material.
9 is a graph showing impedance characteristics of a secondary battery using a silicon and carbon composite material as a negative electrode active material.

Hereinafter, a method of manufacturing a silicon and carbon composite material for a secondary battery negative electrode material according to the present invention will be described in detail with reference to the accompanying drawings.

The present invention solves the volumetric expansion of a high-capacity silicon to produce a negative electrode material excellent in cycle stability and is used for a secondary battery. First, silicon having mesopores of nanoparticles is synthesized and carbonized, In order to solve the problem of volume expansion, we synthesized silicon and carbon composites coated with carbon. Silicon and carbon composites coated with a carbon material with cyclic stability due to volume expansion, which is a disadvantage of silicon particles, are manufactured to produce a composite material that complements the high capacity of silicon and the stability of the carbon material.

By using the silicon / carbon composite thus prepared as an anode material for a secondary battery, the performance and stability of the battery according to the organic electrolyte can be improved.

In the present invention, mesoporous silicon is synthesized using TEOS and a surfactant, and carbonized using phenol resin or sucrose to produce a silicon and carbon composite material.

The method for producing a silicon and carbon composite material for an anode material for a secondary battery according to the present invention comprises (1) a step of producing mesoporous silica, (2) a step of producing mesoporous silicon (Si) using the mesoporous silica, and (3) mixing the mesoporous silicon and the carbon precursor.

The three processes of the present invention will now be described in more detail.

1. Mesoporous silica manufacturing process

(a) The surfactant is added with hydrochloric acid (HCl) and water (H ₂ O) and aged at 15 ° C for 24 hours with stirring until completely dissolved. At this time, P123 (polyethylene glycol-block-polypropylene glycol-block-polyethylene glycol) may be used as the surfactant.

(b) The solution is slowly dispersed in a solution of tetraethyl orthosilicate (TEOS) and stirred for 12 hours by ultrasonic waves.

(c) Heat at 100 占 폚 for 12 to 24 hours.

(d) After filtration, washing with ethanol and drying at 100 ° C for 50 minutes.

(e) Firing at 550 ° C for 10 hours to remove P123.

At this time, the temperature was raised to 550 DEG C for 5 hours and then maintained at 550 DEG C for 5 hours.

2. Manufacturing process of mesoporous silicon (Si)

(a) The mesoporous silica and MgO are mixed in a molar ratio of 1: 2 and stirred.

(b) Sintering is carried out at a temperature of 650 ° C under an argon (Ar) gas atmosphere at a heating rate of 3 ° C / min for 5 hours.

(c) acid treatment with hydrochloric acid followed by filtering with ethanol.

After the calcination, MgO is removed by acid treatment with 1 mol / L hydrochloric acid and then filtered using ethanol.

(d) Drying in an oven at a temperature of 100 캜 for 12 hours.

3. Process of mixing mesoporous silicon and carbon precursor

(a) Mesoporous silicon and a carbon precursor are prepared in a weight ratio of 1: 3 to 7.

Phenol resin or sucrose is used as the carbon precursor.

(b) The carbon precursor is dissolved in acetone to prepare a solution.

(c) Mesoporous silicon is added to the solution and mixed uniformly.

(d) Drying in an oven at a temperature of 100 DEG C for evaporation of acetone.

(e) Sintering is carried out for 7 hours while flowing argon (Ar) gas at 700 to 900 占 폚.

The firing can be performed while controlling the reaction atmosphere by injecting argon and / or nitrogen gas at a rate of 300 to 500 cc / min.

Also, the firing step may be performed by raising the temperature to 0.1 to 10 ° C / min, maintaining the temperature at the activation temperature for 300 to 420 minutes, and then slowly cooling.

The silicon and carbon composite material can be finally manufactured through the above-described processes, and the composite material can be used as a negative electrode material of a secondary battery.

Hereinafter, various embodiments using the above-described silicon and carbon composite material will be described, and various experimental data measured through these embodiments will be described.

Example 1 Production of Silicon and Carbon Composite Material

P123, a surfactant, is dissolved in HCl. TEOS is slowly dispersed and stirred for 12 hours or more, followed by heating at 100 ° C for 24 hours using a cooler. After heating, it is filtered using ethanol and dried in an oven at 100 ° C for 50 minutes. Then, to remove P123, it is baked at 550 DEG C under an argon atmosphere at a heating rate of 5 DEG C / min for 5 hours. The prepared SBA-15 and Mg (Sigma Aldrich) were mixed at a molar ratio of 1: 2 and then calcined at 650 ° C for 5 hours at a heating rate of 3 ° C / min under an argon gas atmosphere. After firing, Mg and by-products are removed to produce mesoporous silicon. The phenolic resin was used as the carbon precursor, and the weight ratio of the mesoporous silicone to the phenol resin was 1: 3, 1: 5, 1: 7. The mixture was uniformly mixed and then dried in an oven at 100 ° C to evaporate acetone. Thereafter, firing was performed at 800 DEG C for 7 hours in an argon gas atmosphere to prepare a silicon / carbon composite. XRD, SEM, BET and TGA were measured in order to investigate the crystallinity and crystal shape of the prepared composites.

≪ Example 2 > Secondary battery cathode and cell manufacturing

A coin - type half - cell was fabricated to confirm the electrochemical properties of the fabricated silicon and carbon / silicon composites. The slurry was prepared by controlling the viscosity with NMP using silicon / carbon (40 wt%) as the active material, Super P (40 wt%) as the conductive material and PVDF (20 wt%) as the binder, Coated on a foil and dried in an oven at 100 ° C for 12 hours. In order to fabricate a 2032-type half-cell using the prepared electrode, a counter electrode was made of Li metal in a glove box filled with Ar gas and a cell guard 2400 was used as a separator. LiPF ₆ (EC / DMC = 1: ) Was used. Electrochemical tests were conducted for charge / discharge test, cycle test, rate test, cyclic voltammetric test, and impedance test. The test voltage range was 0 ~ 1.5V and the cyclic voltammetry test was performed under various C-rate conditions of 0.5mV / s, 1mV / s, 1.5mV / s and 2mV / Hz. ≪ / RTI >

The physical properties of the silicon / carbon composite prepared according to Example 1 are shown in the following tables and figures.

XRD analysis characteristics

Figure 3 shows the XRD pattern of SBA-15, silicon, and silicon / carbon. In FIG. 3, SBA-15 has a broad peak at around 23 °, which is amorphous SiO ₂ and coincides with JCPDS # 38-0448. XRD analysis of Silion prepared by magnesium thermal reduction of SBA-15 revealed that the major peaks of Silicon were 2θ = 28.4 °, 47.3 °, 56.1 °, 69.1 °, 76.4 ° and 88.1 °, and JCPDS # 27-1402 Respectively. Further, each of the peaks showed crystal planes of (111), (220), (311), (400), (331) and (442). The XRD analysis of the silicon / carbon composite showed similar trends to the results of the silicon analysis, and no peak corresponding to carbon was observed. Therefore, the crystal structure of carbon was not formed in the pyrolysis process, The wide peak showed that the carbon structure was amorphous and was consistent with JCPDS # 74-2328.

The reaction scheme in which the silica material is reduced to silicon by the magnesium thermal reduction method is as follows.

2 Mg (s) + SiO ₂ (s) -> 2 MgO (s) + Si (s)

When Mg and silicon remaining after reduction react, MgO and Mg ₂ Si can be produced as by-products. The reaction formula is as follows. These by-products can be removed with HCl.

Mg (g) + Si (s ) -> Mg 2 Si (s)

FE-SEM analysis characteristics

SBA-15 in FIG. 4 had a triangular prismatic crystal structure, and the particle size was approximately 1 μm. The silicon produced by the magnesium thermal reduction of SBA-15 has a triangular columnar crystal structure similar to SBA-15. When the surface is enlarged, it can be confirmed that it has a pore structure. The silicon / carbon composite of (e) has a crystal structure similar to that of SBA-15 and silicon, but it is confirmed that the surface of silicon having the pore structure of (d) is coated with a carbon material there was.

BET analysis characteristics

As shown in Table 1, the specific surface area of the SBA-15, silicon and silicon / carbon composite was 608 m 2 / g, 40 m 2 / g and 323 m 2 / g, respectively. And the pore size of SBA-15 and silicon was 7 nm and 17 nm, respectively, as shown in FIG. 5 and Table 1. As a result, it was confirmed that mesopores were formed in the two materials.

Specific surface area and pore size of composites SBA-15 silicon Silicon / carbon Specific surface area (m < 2 > / g) 608 40 323 Pore size (nm) 7 17 13

TGA analysis characteristics

In order to investigate the carbon content in the silicon / carbon composite, TGA was measured while heating from 5 ° C to 1,000 ° C in an Ar atmosphere. Silicone: The content of phenol resin was about 80% when the synthesis ratio of silicone: phenolic resin was 1: 5, and the weight change was 75% at about 400 ~ 600 ℃ by TGA analysis. It was confirmed in FIG. 6 that the amount of phenol resin was almost the same as that of phenol resin.

In order to evaluate the electrochemical characteristics of the produced secondary battery, a charge / discharge test was performed using a WBCS 3000 Battery Cycler (Won A Tech). The cell was aged for at least 24 hours after the cell assembly to reach the electrochemical equilibrium, and then the charge and discharge test was carried out using the constant current method. At this time, the constant current method is a method of evaluating the performance of the battery active material most accurately when an actual battery is constituted, and can show the results depending on the reaction characteristics of materials used in the case of a lithium secondary battery. The cut-off voltage of the charge / discharge test was set from 0.01V to 2.5V, and the C-rate was set based on the theoretical capacity of 4,200 mAh / g of silicon. In order to evaluate the rate characteristics, 40 cycles were tested at various C-rates of 0.1C, 0.2C, 0.3C and 0.4C, respectively. Cyclic Voltammetric Test For electrochemical experiments, the scan voltage was set to 0 to 2.5 V and the scan rate was 0.5, 1, 1.5, and 2 mV / sec, and measured using ZIVE LAB MP2 (Won A Tech). Periodic voltage was applied to the interface between the electrode and the electrolyte through the cyclic voltammetric test to observe the current change at that time and predict the reaction in the cell. The impedance test was performed using ZIVE LAB MP2 (Won A Tech) in the range of 100 KHz to 0.01 Hz. R _s is the transfer resistance of the lithium ion in the electrolyte, and R _ct is the resistance at the interface between the electrode and the electrolyte. The interface resistance and the electrolyte resistance of the electrode were measured by impedance test.

The composition ratio of silicon and phenol resin was varied from 1: 3, 1: 5, 1: 7 for the Siliocn / carbon composite electrode material. As shown in FIG. 7, the charge / discharge capacity at 1: 3 exhibited a low capacity of 316 mAh / g in the first cycle and decreased to 133 mAh / g after the second cycle, indicating a 42% lower capacity retention rate. The charge / discharge capacity at 1: 5 showed a high capacity of 1,348 mAh / g in the first cycle and the capacity of 1,334 mAh / g in the second cycle. The capacity retention rate was also stable at 98%. The charge / discharge capacity at 1: 7 was similar to 1: 3, showing a low capacity of 414 mAh / g in the first cycle and a drastic decrease in capacity at 180 mAh / g in the second cycle. After 50th cycle, 1: 3 and 1: 7 had a low capacity retention rate of 63% and 50%, respectively, whereas the ratio of 1: 5 showed the most stable cycle characteristic of 76%.

Capacity and capacity retention of silicon and carbon composites Silicone: phenol resin 1: 3 1: 5 1: 7 1st cycle capacity (mAh / g) 316 1,348 414 Second cycle capacity (mAh / g) 133 1,334 180 50th cycle capacity (mAh / g) 201 932 208 Capacity retention after the second cycle (%) 42 98 43 Capacity retention after the 50th cycle (%) 63 69 50

In the case of a lithium secondary battery manufactured using a silicon / carbon composite material as an electrode material, the ratio of silicon to phenilic resin was 1: 5, which showed the best capacity and cycle stability. Therefore, the capacity and cycle characteristics at various C- The rateer characteristics test was performed. As shown in FIG. 8, the capacities were 932 mAh / g at 5 C, 570 mAh / g at 0.2 C, 350 mAh / g at 0.3 C and 190 mAh / g at 0.4 C after the 50th cycle. As the rate increased, the capacity tended to decrease relatively, but the cycle stability at each rate was stable at over 80%. This is because it acts as a buffer layer for the volumetric expansion that occurs during the charging and discharging of the silicon / carbon composite of pore structure, and the electric conductivity of the composite is improved by synthesizing carbon in silicon.

Figure 9 shows the results of the impedance measurements performed to analyze the improved electrochemical properties of a silicon / carbon composite. R _s is the transfer resistance of the lithium ion in the electrolyte, and R _ct is the resistance at the interface between the electrode and the electrolyte. If you compare the two figures in the figure, you can see that the size of the second semicircle is small. The R _s and R _ct values of the silicon electrode cell were measured to be 0.9 ohm and 235 ohm, respectively. It was found that R _s and R _ct values after synthesizing phenolic resin in silicon were significantly decreased to 0.7 ohm and 30 ohm, Synthesis of phenol resin in silicon increased the structural stability and the electrochemical conductivity and the diffusion rate of lithium due to the increase in the resistivity. It was confirmed that the resistance value was significantly lower when graphite, which is more conductive than silicon, was added to silicon. I could.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined by the appended claims. .

Claims (6)

Preparing mesoporous silica using a surfactant and tetraethyl orthosilicate (TEOS);
Preparing mesoporous silicon using the mesoporous silica; And
And mixing the mesoporous silicon and the carbon precursor. The method of manufacturing a silicon and carbon composite material for a secondary battery negative electrode material according to claim 1, The method according to claim 1,
Wherein the step of preparing the mesoporous silica comprises:
(a) to the (polyethylene block-glycol-polypropylene glycol-block-polyethylene glycol) P123 was added to hydrochloric acid (HCl) and water (H ₂ O) the steps of stirring until completely dissolved;
(b) adding tetraethyl orthosilicate (TEOS) to the solution and agitating the solution together by ultrasonic waves;
(c) heating at 100 占 폚 for 12 to 24 hours;
(d) filtration, washing with ethanol and drying at 100 < 0 >C; And
(e) firing at 550 [deg.] C to remove P123. < / RTI > The method according to claim 1,
Wherein the step of preparing the mesoporous silicon comprises:
(a) mixing and agitating the mesoporous silica and MgO in a molar ratio of 1: 2;
(b) firing at 650 DEG C at a heating rate of 3 DEG C / min under an argon gas atmosphere;
(c) acid treatment with hydrochloric acid to remove MgO, followed by filtering with ethanol; And
(d) drying in an oven at a temperature of 100 ° C. [Claim 10] The method according to claim 1, Gt; The method according to claim 1,
Wherein mixing the mesoporous silicon and the carbon precursor comprises:
(a) preparing mesoporous silicon and a carbon precursor at a weight ratio of 1: 3 to 7;
(b) dissolving the carbon precursor in acetone to prepare a solution;
(c) adding mesoporous silicon to the solution and uniformly mixing the solution;
(d) drying the mixture in an oven at a temperature of 100 DEG C for evaporation of acetone; And
(e) firing the silicon nitride film for 7 hours while flowing argon (Ar) gas at 700 to 900 ° C. 5. The method according to claim 4, wherein in the mixing step (a)
Wherein the carbon precursor is phenol resin or sucrose. The method of claim 1, wherein the carbon precursor is phenol resin or sucrose. 5. The method according to claim 4, wherein in the step (e)
Wherein the firing is performed while injecting argon and / or nitrogen gas at a rate of 300 to 500 cc / min to adjust the reaction atmosphere.

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