KR101501804B1 - Silicon based negative active material and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a silicon-based anode active material and a lithium secondary battery using the same. SiO _x (0 < x < 2) phase; And a silicon dioxide-based negative electrode active material, and a positive electrode comprising a positive electrode active material, a negative electrode including a negative electrode active material, and a separator, wherein the negative electrode active material is a silicon phase; SiO _x (0 < x < 2) phase; And a silicon-based negative electrode active material containing a silicon dioxide phase.

Description

[0001] Silicon based negative active materials and secondary batteries comprising same [0002]

The present invention relates to a silicon-based negative electrode active material and a secondary battery comprising the same.

Since the discovery of electricity in the 1800s, it has evolved from a primary cell to a secondary cell with a high operating voltage in batteries with low operating voltages. Lithium secondary batteries among various batteries are leading the 21st century battery technology and have attracted attention as an energy storage system from various portable devices to electric vehicles.

A lithium secondary battery is an energy storage device in which lithium moves from a cathode to an anode during a discharge process and lithium ions move from an anode to a cathode during charging to store electric energy in the battery. Compared to other cells, the degree of self-discharge with a high energy density is small, and it is used in various projects.

The components of the lithium secondary battery can be divided into an anode, a cathode, an electrolyte, and a separator. In the early lithium secondary battery, lithium metal was used as an anode active material. However, lithium metal was replaced with a carbon-based material such as graphite due to repeated safety of charging and discharging. The carbon-based negative electrode active material has a similar electrochemical reaction potential with lithium metal, and the change of the crystal structure during continuous lithium ion intercalation / deintercalation process can be continuously performed, enabling continuous charge / discharge. I had.

However, as the market has recently expanded from small lithium secondary batteries used in portable devices to large secondary batteries used in automobiles, high capacity and high output of negative electrode active materials have been demanded. Therefore, non-carbon anode active materials are being developed centering on silicon, tin, germanium, zinc, and lead, which have higher theoretical capacities than carbon-based anode active materials.

Among them, the silicon-based material has a capacity (4190 mAh / g) 11 times higher than the theoretical capacity (372 mAh / g) of the carbonaceous anode active material, . However, when only silicon is used, since the volume expansion of the material is three times or more when the lithium ion is inserted, the battery capacity tends to decrease as the charging and discharging progresses, and safety problems occur. do.

Therefore, studies on silicon-based composites are actively underway. Among them, the study of using the silicon-based material and the carbon-based material at the same time has been developed to simultaneously increase the capacity and the charge / discharge life by minimizing the volume expansion of the silicon-based material. The most basic composite synthesis method is to use carbon-coated silicon-based materials. This leads to an improvement in the electrical conductivity between the active material particles and the electrolyte and the increase in the battery life by reducing the volume expansion of the silicon-based particles. However, due to the formation of the irreversible phase by the silicon- Is lowered.

The present invention provides a silicon-based anode active material capable of improving initial charging / discharging efficiency while using a silicon-based material as a negative electrode active material of a secondary battery.

The present invention relates to a silicon phase; SiO _x (0 < x < 2) phase; And a silicon dioxide phase.

The present invention also relates to a positive electrode comprising a positive electrode active material, a negative electrode including a negative electrode active material, and a separator, wherein the negative electrode active material is a silicon phase; SiO _x (0 < x < 2) phase; And a silicon-based negative electrode active material containing a silicon dioxide phase.

Further, the present invention relates to a process for producing a polyimide precursor, which comprises dissolving an alkali hydroxide in a polar solvent and then mixing with SiO _x (0 < x < 2) And evaporating the polar solvent in the mixture prepared in the step and then heat-treating the mixture.

The present invention increases the initial coulombic efficiency of the conventional silicon-based anode active material and enables silicon-based anode active material to be mass-produced by a simple process, and thus can be usefully used as a negative electrode active material of a lithium secondary battery.

1 is a schematic view showing a method of manufacturing a silicon-based anode active material particle according to an embodiment of the present invention.
FIG. 2 is a scanning electron microscope (SEM) photograph of the silicon-based anode active material particles (SiO 2, SiO 2, b): heat treatment time 30 minutes, : Heat treatment time 60 minutes, (d): heat treatment time 120 minutes).
FIG. 3 is a transmission electron microscope (TEM) photograph of a silicon-based anode active material particle according to an embodiment of the present invention ((a): heat treatment time 30 minutes, (b) heat treatment time 60 minutes, 120 minutes).
FIG. 4 is an X-ray diffraction spectrum of the silicon-based anode active material particles according to whether or not NaOH is used and the heat treatment time.
5 is an X-ray diffraction analysis spectrum of the silicon-based anode active material particles according to the heat treatment temperature.

The present invention relates to a silicon phase; SiO _x (0 < x < 2) phase; And a silicon dioxide phase.

In the silicon-based negative active material according to an embodiment of the present invention, the silicon dioxide phase may be dispersed on SiO _x (0 <x <2), and the silicon dioxide phase may be crystalline.

In the silicon-based negative active material according to an embodiment of the present invention, the SiO _x may be commercially available silicon monoxide (SiO 2), and the silicon dioxide may include cristoballite have.

The silicon dioxide phase may be present in an amount of from 2 to 50% by weight of the negative electrode active material. When the silicon dioxide phase is less than 2% by weight, there is a problem that the initial efficiency is insignificantly increased. When the silicon dioxide phase is more than 50% by weight, the initial efficiency is greatly increased but the discharge capacity is decreased.

In addition, the silicon phase has a higher concentration in the interior of the silicon-based anode active material than the outside, and the silicon dioxide phase has a greater concentration at the outside than inside of the silicon-based anode active material. The silicon phase and the silicon dioxide phase can be formed by disproportionation of SiO _x . The interior of the silicon-based negative electrode active material in the present invention is defined as follows. The maximum value of the length of the negative electrode active material in the direction perpendicular to the tangent line of the negative electrode active material is obtained on the cross section of the negative electrode active material, the portion inside the line 50% The outside of the line refers to the outside. In addition, the greater the concentration in the interior of the negative active material than in the negative active material means that the average concentration inside the negative active material is higher than the average concentration outside the negative active material in the cross-section of the negative active material having a diameter of 50%.

The above content will be described in more detail in the heat treatment step of the method for producing a silicon-based negative electrode active material described later.

In addition, SiO _x (0 < x < 2) phase; And a silicon-based negative active material further comprising a carbon coating material.

The particle size of the silicon-based anode active material may vary from several tens of nanometers to several tens of micrometers, but may range from 100 nm to 50 micrometers.

In addition, the silicon-based anode active material has a crystal phase in a nanometer size in the active material particle, a crystal size of 1 to 1000 nm in the silicon phase, and a crystal size of 1 to 1000 nm in the silicon dioxide phase. The silicon phase, the SiO _x phase, and the silicon dioxide phase contained in the silicon-based negative electrode active material can insert and desorb lithium.

The present invention also provides a secondary battery including a cathode including a cathode active material, a cathode including the anode active material, and a separator, wherein the anode active material comprises a silicon phase; SiO _x (0 < x < 2) phase; And a silicon-based negative electrode active material containing a silicon dioxide phase.

The secondary battery according to an embodiment of the present invention can be manufactured as follows.

The negative electrode may be prepared by applying the siliceous anode active material according to the present invention on a negative electrode collector and drying the same, and may include components such as a conductive material, a binder, and a filler.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The positive electrode may be prepared by preparing a positive electrode active material composition by mixing a positive electrode active material, a conductive material, a binder and a solvent, coating the positive electrode active material composition directly on the metal current collector, and drying the positive electrode active material composition.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _{2 - y} O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1 - y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The positive electrode current collector is made to have a thickness of 3 to 500 mu m like the negative electrode current collector. Such a positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid , Ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butylene rubber (SBR), fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 - 10 탆, and the thickness is generally 5 - 300 탆. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Further, the present invention relates to a process for producing a polyimide precursor, which comprises dissolving an alkali hydroxide in a polar solvent and then mixing with SiO _x (0 < x < 2) And

And evaporating the polar solvent in the mixture prepared in the step and then heat-treating the mixture.

In order to produce the silicon-based anode active material according to an embodiment of the present invention, the alkali hydroxide is first dissolved in a polar solvent and then mixed with SiO _x .

The SiO _x may be commercially available silicon monoxide.

The alkaline hydroxide may be at least one selected from the group consisting of LiOH, NaOH, KOH, Be (OH) ₂ , Mg (OH), Ca (OH) ₂ and hydrates thereof.

The solvent for dissolving the alkaline hydroxide is not limited to the solvent which can dissolve the alkali hydroxide and is easy to remove, but water or an alcohol solvent can be used, and the alcohol solvent can be ethanol or methanol.

The mixing of the alkaline hydroxide and SiO _x may be 0.01 to 30% by weight of the alkaline hydroxide based on the total weight of the mixture. SiO _x is 0.01 weight%, less amount of the silicon phase and the silicon dioxide formed after the heat treatment to be described later (SiO _x is some Si-SiO ₂ as there is due to the low content of SiO _x Si-SiO _x -SiO through heat treatment of less than when the _second of the Si-SiO ₂ ratio Less) is low, the initial coulombic efficiency problems, and more than 30 wt%, there is a problem that the amount of the Si-SiO ₂ is formed after the heat treatment increases significantly decrease capacity.

The method for producing a silicon-based anode active material according to an embodiment of the present invention includes a step of evaporating a polar solvent present in the mixture and heat-treating the mixture.

The polar solvent evaporation may be performed at 80-120 ° C. and may be performed with an alumina boat preheated at 80-120 ° C. However, the temperature is not limited to the temperature at which the polar solvent can be evaporated. On the other hand, despite the evaporation of the polar solvent, the alkaline hydroxide remains on the surface of the SiO _x particles.

The mixture, in which the polar solvent is evaporated, can then be heat treated at 750 - 1000 ° C for 5 - 120 minutes. When the heat treatment is less than 750 캜, crystalline silicon dioxide is not formed. When the temperature exceeds 1000 캜, a large amount of crystalline silicon is generated to lower the lifetime characteristics of the secondary battery and excess energy is consumed in terms of energy efficiency There is a problem. When the reaction time is less than 5 minutes, crystalline silicon dioxide is not formed well, and when it exceeds 120 minutes, sufficient time has elapsed to form crystalline silicon dioxide, which is not preferable in terms of energy efficiency.

When heat treatment is performed, SiO _x is disproportionated to silicon and silicon dioxide. That is, in the SiO _x particles, oxygen moves to the outside (surface) to form amorphous SiO ₂ , and the silicon separated from oxygen is combined with another silicon separated from oxygen to be present on SiO _x as silicon crystal, SiO ₂ is mainly formed on the outside (surface) rather than inside the SiO _x grains. The amorphous SiO _x gradually decreases as the annealing temperature or time increases, and conversely, the crystalline Si and the crystalline SiO ₂ increase.

In the present invention, when the alkali hydroxide is SiO _x The heat treatment is carried out in the state of being present on the surface of the particle to promote the formation of crystalline SiO ₂ . As can be seen from FIG. 4, even when heat treatment is carried out at the same temperature, no crystalline peak of SiO ₂ is formed at all when an alkaline hydroxide is not used. However, when an alkali hydroxide is used, determining a peak of _divalent is rapidly growing (2 Theta = 21 Fig vicinity). That is, in the case of forming a composite of SiO and carbon as in the prior art, or in the case of heat-treating SiO to coat a carbon precursor or carbon, only Si causes crystal growth (2 theta = 28.5 degrees on the XRD) , SiO ₂ grows in the form of crystalline when an alkali hydroxide is present on the surface of SiO _x , and the initial Coulomb efficiency (discharge capacity / charge capacity × 100) The ratio of the amount of lithium initially released) increases. SiO ₂ grown in crystalline form is electrochemically inactive (non-reactive with lithium), SiO _x is divided into electrochemically active moieties (reacting with lithium) and electrochemically inactive moieties, and the electrochemically active moieties in SiO _x It is considered that the initial coulombic efficiency is increased because the molar concentration of oxygen is decreased compared with that of SiO.

The method of manufacturing a silicon-based anode active material according to an embodiment of the present invention may further include a step of immersing the mixture prepared in the above-described manner in distilled water, followed by filtration. This is a step for removing the alkali hydroxide attached to the SiO _x particle surface. The alkaline hydroxide attached to the surface of the silicon-based anode active material may be left in the distilled water for a sufficient time to be removed.

Further, the present invention relates to a method for producing a polyimide resin, which comprises dissolving an alkaline hydroxide in a polar solvent and then mixing with SiO _x ;

Evaporating the polar solvent in the mixture prepared in the step and then performing heat treatment; And

And a step of coating carbon on the mixture heat-treated in the above step.

In the production of the silicon-based anode active material, the carbon coating may include covering the carbon to further increase the electrical conductivity of the secondary battery, and the carbon coating may be 1-30 wt% of the total amount of the silicon-based anode active material. When the amount of carbon is less than 1% by weight, a uniform coating layer is not formed and electrical conductivity is lowered. When the amount of carbon is more than 30% by weight, an additional irreversible reaction occurs due to the conductive coating layer, There is a problem of decrease.

In addition, the starting material SiO _x may be coated with carbon, and in this case, the step of coating carbon with the silicon-based negative active material may be omitted. Such carbon coating can be achieved by dispersing the carbon precursor in a solvent such as tetrahydrofuran (THF), alcohol, etc., adding the resultant to the silicon oxide, followed by drying and heat treatment, and may be performed by supplying acetylene gas , And is not limited to a method capable of covering the electrode active material with carbon.

The present invention improves the initial coulombic efficiency of the conventional silicon-based anode active material, and can produce a silicon-based anode active material in a simple process. Therefore, the present invention can be effectively used as an anode active material of an electrochemical cell such as a lithium secondary battery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. It should be noted, however, that the scope of the invention is not limited by these embodiments, but is merely given as an example.

&Lt; Example 1 > Preparation of silicon-based negative electrode active material 1

Alkaline system  Mixture of hydroxide and silicon-based material

50 mg of sodium hydroxide was dissolved in ethanol, and 1 g of silicon monoxide was added to the prepared sodium hydroxide solution, followed by stirring for 10 minutes or more.

Solvent evaporation and heat treatment

A solution of silicon monoxide and sodium hydroxide in an alumina boat heated at 80 to 120 ° C was added and the ethanol was evaporated. After the evaporation of the solvent was completed, an alumina boat containing a mixture of silicon monoxide and sodium hydroxide was placed in a quartz tube furnace, heat-treated at a temperature of 800 ° C for 5 minutes while flowing argon gas, and the quartz tube furnace was cooled to room temperature Followed by cooling to prepare a silicon-based anode active material.

After soaking in solvent

The silicon-based anode active material contained in the alumina boat was recovered, immersed in distilled water for 2 hours, and filtered to remove sodium hydroxide attached to the surface of the silicon-based negative active material (see FIG. 1).

&Lt; Example 2 > Preparation of silicon-based anode active material 2

The silicon anode active material was prepared in the same manner as in Example 1 except that the heat treatment time was 10 minutes.

&Lt; Example 3 > Preparation of silicon-based anode active material 3

A silicon anode active material was prepared in the same manner as in Example 1, except that the heat treatment time was 30 minutes.

<Example 4> Production of silicon-based anode active material 4

The silicon anode active material was prepared in the same manner as in Example 1, except that the heat treatment time was 60 minutes.

&Lt; Example 5 > Preparation of silicon-based anode active material 5

A silicon anode active material was prepared in the same manner as in Example 1 except that the heat treatment time was 120 minutes.

&Lt; Example 6 > Preparation of silicon-based negative electrode active material having conductive carbon coating layer 1

20 g of the silicon anode active material prepared in Example 1 was charged into a rotating tubular furnace, and argon gas was flowed at 0.5 L / min., And then the temperature was raised to 800 ° C at a rate of 5 ° C / min. The silicon anode active material having a conductive carbon coating layer formed by spinning the rotary tubular furnace at a rate of 10 rpm / minute while flowing argon gas at 1.8 L / min and acetylene gas at 0.3 L / min for 5 hours. The carbon content of the conductive carbon coating layer at this time was 10 wt% with respect to the negative electrode active material.

&Lt; Example 7 > Production of silicon-based anode active material having conductive carbon coating layer 2

A silicon anode active material having a conductive carbon coating layer formed thereon was prepared in the same manner as in Example 6, except that 20 g of the silicon anode active material prepared in Example 2 was charged into a rotating tubular furnace. The carbon content of the conductive carbon coating layer at this time was 10 wt% with respect to the negative electrode active material.

&Lt; Example 8 > Preparation of silicon-based anode active material having conductive carbon coating layer 3

A silicon anode active material having a conductive carbon coating layer formed thereon was prepared in the same manner as in Example 6, except that 20 g of the silicon anode active material prepared in Example 3 was charged into a rotating tubular furnace. The carbon content of the conductive carbon coating layer at this time was 10 wt% with respect to the negative electrode active material.

<Example 9> Production of silicon-based anode active material having conductive carbon coating layer 4

A silicon anode active material having a conductive carbon coating layer formed thereon was prepared in the same manner as in Example 6, except that 20 g of the silicon anode active material prepared in Example 4 was charged into a rotating tubular furnace. The carbon content of the conductive carbon coating layer at this time was 10 wt% with respect to the negative electrode active material.

&Lt; Example 10 > Production of silicon-based anode active material having conductive carbon coating layer 5

A silicon anode active material having a conductive carbon coating layer formed thereon was prepared in the same manner as in Example 6, except that 20 g of the silicon anode active material prepared in Example 5 was charged into a rotating tubular furnace. The carbon content of the conductive carbon coating layer at this time was 10 wt% with respect to the negative electrode active material.

&Lt; Comparative Example 1 > Preparation of negative electrode active material consisting solely of silicon monoxide

The anode active material was prepared using only silicon monoxide.

&Lt; Comparative Example 2 > Preparation of negative active material coated with carbon on silicon monoxide

Silicon monoxide was coated in the same manner as in Example 6 to prepare an anode active material.

The raw materials and processes of Examples 1 to 10 and Comparative Examples 1 and 2 are shown in Table 1 below.

Yes Initial material Content of SiO ₂
(weight%) Heat treatment time
And temperature Carbon content
(weight%) Coating process
Example 1 SiO + NaOH 5.5 800 ° C, 5 minutes - - Example 2 SiO + NaOH 8.9 800 ° C, 10 minutes - Example 3 SiO + NaOH 17.3 800 ° C, 30 minutes - Example 4 SiO + NaOH 32.4 800 ° C, 60 minutes - Example 5 SiO + NaOH 35.5 800 캜, 120 minutes - Example 6 SiO + NaOH 4.5 800 ° C, 5 minutes 10 800 ° C, 5 hours Example 7 SiO + NaOH 8.2 800 ° C, 10 minutes 10 800 ° C, 5 hours Example 8 SiO + NaOH 16.7 800 ° C, 30 minutes 10 800 ° C, 5 hours Example 9 SiO + NaOH 28.6 800 ° C, 60 minutes 10 800 ° C, 5 hours Example 10 SiO + NaOH 33.2 800 캜, 120 minutes 10 800 ° C, 5 hours Comparative Example 1 SiO - - - - Comparative Example 2 SiO - - 10 800 ° C, 5 hours

Each of the negative electrode active materials of Examples 1 to 10 and Comparative Examples 1 and 2 described above was produced by the method described below.

Manufacture of batteries

The negative electrode active materials of Examples 1 to 10 and Comparative Examples 1 and 2 were mixed with acetylene black as a conductive material and polyvinylidene fluoride (PVdF) as a binder at a weight ratio of 88: 2: 10, N-methyl-2-pyrrolidone (NMP) to prepare a uniform electrode slurry. The prepared electrode slurry was coated on one surface of the copper current collector to a thickness of 65 μm, dried and rolled, and then punched to a required size to prepare an electrode.

Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70, and LiPF ₆ was added to the non-aqueous electrolyte solvent to prepare a 1 M LiPF ₆ non-aqueous electrolyte.

A coin-type battery was prepared by using the above-prepared electrode as a cathode, using a lithium metal foil as an anode electrode, interposing a polyolefin separator between both electrodes, and injecting the electrolyte solution.

Surface, structure and composition analysis of silicon-based anode active material

(SEM), transmission electron microscope (TEM) and X-ray diffraction analysis (XRD) to examine the surface, structure and components of the silicon-based anode active material according to an embodiment of the present invention. Are shown in Figs. 2 to 5.

FIG. 2 is a scanning electron microscope (SEM) photograph of the silicon-based anode active material particles with the passage of time of SiO and (a): SiO, (b): heat treatment time 30 minutes, (c) (d): heat treatment time 120 minutes). As shown in Fig. 2, the silicon dioxide phase was heat treated at 800 &lt; 0 & As shown in Fig.

FIG. 3 is a transmission electron microscope (TEM) photograph of the silicon-based anode active material particles prepared in Examples of the present invention ((a): heat treatment time 30 minutes, (b): heat treatment time 60 minutes, Time 120 minutes). As shown in FIG. 3, it can be seen that as the heat treatment time increases, the silicon crystal increases.

FIG. 4 is an X-ray diffraction spectrum of the silicon-based anode active material particles according to whether or not NaOH is used and the heat treatment time. As shown in FIG. 4, the peak intensity increased at 800 ° C for 5 minutes or longer, and the peak of SiO ₂ rapidly increased as the annealing time increased (2 Theta = 21 degrees). It can also be seen that crystalline Si is grown near 2 Theta = 28.5 degrees. Also, it was found from the XRD quantitative analysis that the crystalline SiO ₂ formed was present in the weight percentages as shown in Table 1 for the total weight of the negative electrode active material. As a result, it can be seen that the silicon-based anode active material according to the present invention is formed by using an alkaline hydroxide.

5 is an X-ray diffraction analysis spectrum of the silicon-based anode active material particles according to the heat treatment temperature. As shown in FIG. 5, it was found that the peak was similar to silicon monoxide at 700 ° C or less, and peak intensity was observed at 750 ° C, and a similar peak was observed at 800 ° C and 900 ° C.

Table 2 shows discharge capacity, charging capacity and initial coulombic efficiency of the secondary battery manufactured using the negative electrode active material prepared in Examples 1 to 10 and Comparative Examples 1 and 2.

Yes Discharge capacity (mAh / g) Charging capacity (mAh / g) Initial coulomb efficiency (%) Example 1 1575.3 2022.2 77.9 Example 2 1518.6 1944.4 78.1 Example 3 1376.8 1762.9 78.1 Example 4 1128.6 1441.4 78.3 Example 5 1081.1 1377.2 78.5 Example 6 1528.2 1854.6 82.4 Example 7 1451.8 1764.0 82.3 Example 8 1308.4 1584.0 82.6 Example 9 1135.8 1370.1 82.9 Example 10 1047.2 1261.7 83.0 Comparative Example 1 1653.8 2355.8 70.2 Comparative Example 2 1575.0 2114.1 74.5

As shown in Table 2, the secondary battery including the negative electrode active material prepared in Examples 1 to 5 had a slightly reduced discharge capacity due to the formation of crystalline SiO ₂ as compared with the secondary battery comprising the negative electrode active material of Comparative Example 1 , But the initial efficiency increased by about 8% or more. In addition, it can be seen that the secondary battery comprising the negative active material prepared in Examples 6 to 10 has an initial coulombic efficiency of about 8% or more as compared with the secondary battery comprising the negative active material of Comparative Example 2. [ On the other hand, in Comparative Example 2 in which carbon monoxide was coated on the surface of silicon monoxide, the initial irreversible reaction was reduced by controlling the surface reaction, and the initial coulombic efficiency was increased by about 4%. This indicates that silicon monoxide is coated with carbon to increase the initial coulombic efficiency and can be confirmed through Examples 6 to 10 in which carbon is coated. Thus, it can be seen that the negative electrode active material produced from the heat treatment of silicon monoxide using an alkaline hydroxide has an excellent initial coulombic efficiency.

Claims (19)

Silicon phase; SiO _x (0 < x < 2) phase; And a silicon dioxide phase comprising cristoballite; And a conductive carbon coating layer.
The method according to claim 1,
The silicon dioxide phase may be any of the SiO _x Wherein the silicon-based negative electrode active material is dispersed in the silicon-based negative electrode active material.
The method according to claim 1,
Wherein the silicon dioxide phase is crystalline.
The method according to claim 1,
Wherein the SiO _x is silicon monoxide.
delete The method according to claim 1,
Wherein the silicon dioxide phase is 2-50 wt% based on the negative electrode active material.
The method according to claim 1,
Wherein the silicon phase has a higher concentration in the interior than the outside of the silicon-based anode active material.
The method according to claim 1,
Wherein the silicon dioxide phase has a higher concentration on the outside than inside of the silicon-based electrode active material.
The method according to claim 1,
Wherein the silicon phase and the silicon dioxide phase are formed by disproportionation of SiO _x (0 < x < 2).
delete A cathode including a cathode active material, a cathode including a cathode active material, and a separator,
Wherein the negative electrode active material comprises the silicon based negative active material according to any one of claims 1 to 4 and 6 to 9.
As alkali hydroxides, NaOH, KOH, was dissolved in _{Be (OH) 2, Mg (} OH), Ca (OH) 2 and those of the first polarity or more solvents selected from the group consisting of hydrate SiO _x (0 _<x &Lt;2); And
Wherein the polar solvent is evaporated from the mixture prepared in the step (a), and the heat treatment is performed at 750 to 1000 ° C for 5 to 120 minutes.
delete The method of claim 12,
Wherein the polar solvent in the mixing step is water or an alcohol.
The method of claim 12,
Wherein the alkaline hydroxide in the mixing step is 0.01 to 30 wt% based on the total weight of the mixture.
delete The method of claim 12,
And filtering the heat-treated mixture. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;
The method of claim 12,
Further comprising the step of coating carbon on the heat-treated mixture.
19. The method of claim 18,
Wherein the carbon is present in an amount of 1 to 30% by weight based on the total weight of the negative electrode active material.

Images