KR102237949B1 - Negative electrode active material particle and method of preparing for the same - Google Patents

Abstract

The present invention provides a method for producing a negative electrode active material including a silicon-based composite with reduced volume expansion, a negative electrode active material particle prepared by the method, and a negative electrode and a secondary battery including the same.

Description

NEGATIVE ELECTRODE ACTIVE MATERIAL PARTICLE AND METHOD OF PREPARING FOR THE SAME}

The present invention relates to negative electrode active material particles and a method of manufacturing the same.

Recently, lithium secondary batteries, which have been in the spotlight as power sources for portable small electronic devices, use an organic electrolyte, and thus exhibit a discharge voltage and high energy density that are twice or more times higher than those of batteries using an aqueous alkaline solution.

As the positive electrode active material of such a lithium secondary battery, an oxide composed of lithium and a transition metal capable of intercalating lithium such as _{LiCoO 2} , LiMn ₂ O ₄ , LiNi _{1 -x} Co _x O _{2 (0<x<1), etc.} It is mainly used, and as a negative electrode active material, various types of carbon-based materials including artificial or natural graphite and hard carbon capable of inserting and desorbing lithium have been applied.

However, the carbon-based material such as graphite has a small capacity per unit mass of 372 mAh/g, so it is difficult to increase the capacity.

Accordingly, as a negative electrode material capable of realizing a higher capacity than the graphite, non-carbon-based metal compounds such as Si, Sn, Al, and oxides thereof have been proposed.

However, these materials have a problem in that when lithium is absorbed and stored during charge/discharge, volume expansion occurs due to a change in crystal structure, and cycle characteristics are deteriorated.

For example, in the case of Si, while absorbing lithium, Li _{4 . By} converting to 4 Si, volume expansion is achieved, and this volume expansion rate can expand up to about 4.12 times compared to the volume of silicon before volume expansion.

Therefore, in order to increase the capacity of a non-carbon-based negative electrode material such as Si, studies are being conducted to reduce the volume expansion rate through alloying of Si or the like.

For example, in the case of a material such as SiO, a lot of research has been conducted because it has the advantage that it is possible to suppress the volume expansion compared to Si and high capacity characteristics compared to the carbon-based material. However, in this case, there is a disadvantage in that the by-product generated by the reaction of lithium and oxygen causes an irreversible reaction, and the initial efficiency is lowered.

Japanese Laid-Open Patent Publication No. 2004-327190

In order to solve the above problems, an object of the present invention is to provide a method for producing negative electrode active material particles including a silicon-based composite with reduced volume expansion.

In addition, another object of the present invention is to provide a negative electrode active material particle that can improve initial efficiency and life characteristics of a secondary battery manufactured by the above method.

In addition, a third technical problem of the present invention is to provide a negative electrode and a secondary battery including the negative active material particles.

In order to achieve the above task to be solved,

In one embodiment of the present invention

Mixing SiO ₂ and aluminum powder in a molar ratio of 1:1.3 to 1:1.5, and ball milling _{to prepare a precursor in which SiO 2} and aluminum are complexed (step 1);

Raising the temperature of the precursor (step 2); And

It provides a method for producing a negative electrode active material particle comprising; heat-treating the heated precursor to prepare a silicon-based composite (Step 3).

The ball milling step (step 1) may be performed for 30 minutes to 3 hours at a rotational speed of 600 times per minute.

The temperature raising step (step 2) may be performed at a temperature increase rate of 0.5° C./min to 3° C./min.

The heat treatment step (step 3) may be performed at 700°C to 1100°C for 3 to 12 hours.

In addition, in an embodiment of the present invention

Si, SiO _x (0.5<x<1.5), aluminum oxide (Al ₂ O ₃ ) and a silicon-based composite including mullite,

The ratio of (weight of Si): (total weight of aluminum oxide and mullite) in the silicon-based composite is 1:3.27 to 1:5.7 to provide negative active material particles.

The mullite may include at least one selected from the group consisting _{of 3Al 2} O ₃ ㆍ2SiO ₂ , and 2Al ₂ O ₃ ㆍ2SiO _2.

The negative electrode active material particles of the present invention may further include a carbon coating layer on the surface.

The carbon coating layer may be included in an amount of 1% to 50% by weight based on the total weight of the negative active material particles.

The negative active material particles may have an average particle diameter (D50) of 0.1 μm to 20 μm.

In addition, in an embodiment of the present invention

It provides a secondary battery including a negative electrode, a positive electrode including the negative electrode active material particles of the present invention, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

According to the method of the present invention, when SiO ₂ and aluminum are compounded, a ball milling process is performed to uniformly attach aluminum powder, which is a reducing metal, to the surface of _{SiO 2, thereby enhancing a reduction effect.} In particular, _{by using aluminum as a reactive metal for SiO 2} reduction, aluminum oxide and mullite are generated, thereby reducing the volume expansion of Si or preventing the volume expansion of Si during charging and discharging, thereby implementing a buffer layer effect. Therefore, it is possible to manufacture a secondary battery with improved capacity and lifespan characteristics.

1 is an XRD graph of components of a silicon-based composite prepared according to Example 1 of the present invention.

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

A silicon-based material with a capacity (3600 mAh/g) that is about 10 times higher than the theoretical capacity (372 mAh/g) of a carbon-based negative active material as a substitute for a carbon-based material as a lithium secondary battery is a high-capacity lithium It is in the spotlight as a material for secondary batteries.

However, silicon-based materials easily cause particle cracking and chemical pulverization due to a large volume change (swelling) that occurs during charging and discharging, so that the silicon-based material is a negative electrode of a secondary battery. When used as a material, there is a problem that the battery life characteristics are rapidly reduced.

To solve this problem, a silicon-based composite has been developed in _{which Si and SiO 2} are present in a state where Si and SiO 2 are partitioned in particles, not a silicon-based negative active material containing Si alone. However, since a typical silicon-based composite is a composite containing _{Si and amorphous SiO 2 , by-products such as Li 2} O are generated due to _{the reaction between amorphous SiO 2} and lithium contained in the electrolyte, and the initial discharge capacity and There was a problem such as a decrease in initial efficiency.

In order to solve this problem, research has been conducted to remove oxygen in _{amorphous SiO 2 or SiO reacting with lithium.}

However, when oxygen is removed by reducing amorphous SiO ₂ or SiO, as the reduction by-products increase compared to the reduced reduction product of Si, the capacity per weight of the negative electrode active material decreases, or the silicon-based composite due to the removal of the reduction by-products. There was a problem of a decrease in yield and a decrease in life characteristics due to structural collapse.

On the other hand, in one embodiment of the present invention, a method of manufacturing a negative electrode active material capable of increasing the reduction effect from _{SiO 2 to Si using aluminum particles, and a negative electrode active material prepared by this method are provided.}

Specifically, in one embodiment of the present invention

Mixing SiO ₂ and aluminum powder at a molar ratio of 1:1.3 to 1:1.5, and then ball milling _{to prepare a precursor in which SiO 2} and aluminum are complexed (step 1);

Raising the temperature of the precursor (step 2); And

It provides a method for producing a negative electrode active material particle comprising; heat-treating the heated precursor to prepare a silicon-based composite (step 3).

According to the method for producing a negative electrode active material of the present invention, _{since SiO 2 is reduced using aluminum particles, oxygen of SiO 2} can be reduced with higher efficiency. That is, in _{the case of reducing SiO 2} using aluminum, it is possible to bring 3 oxygen atoms to 2 Al atoms, so that the reduction efficiency is high. Therefore, even if a relatively small amount of aluminum is used _{, efficient reduction from SiO 2} to Si is performed, so that a reduction product (Si) is large, while a reduction reaction by-product may be formed due to a small amount of aluminum. Therefore, as the Si content increases, there is an effect of securing a large capacity per unit weight.

In the method of manufacturing the negative electrode active material of the present invention, step 1 is a step of preparing a precursor in which _{SiO 2 and aluminum are composited by mixing SiO 2} and aluminum particles and then ball milling.

The complexation of step 1 is on the surface of _{SiO 2} This means that aluminum particles are attached in advance.When aluminum particles and SiO ₂ are not evenly mixed and are agglomerated, _{only SiO 2 in the} area where aluminum particles are relatively agglomerated causes excessive reduction, resulting in non-uniform reduction between _{SiO 2 particles.} This can happen.

Accordingly, in the present invention, this disadvantage can be improved by ball milling.

Specifically, in the step 1, a mixture of stainless balls having a diameter of 3 mm, SiO ₂ and aluminum powder in a molar ratio of 1:1.3 to 1:1.5 is added to the reactor, and a high energy ball mill device By using a rotation speed of 600 times per minute for 30 minutes to 3 hours by performing mechanical alloying (Mechanical alloying), it can be carried out by a method of manufacturing a precursor in which _{SiO 2 and aluminum are composited.}

_{By mixing SiO 2} and aluminum powder in the molar ratio as described above, it is possible to provide an aluminum oxide and mullite buffer layer having a degree of not causing a problem in occlusion and desorption of lithium particles, and a capacity of Si can be secured. At this time, when the molar ratio of the aluminum powder is less than 1.3 _{, the reduction effect from SiO 2} to Si is insignificant, and when the molar ratio of the aluminum powder exceeds 1.5, the capacity increase effect can be realized due to the large amount of Si reduction, There is a disadvantage that the characteristics are deteriorated.

_{In addition, in the case of ball milling SiO 2} and aluminum powder in less than 30 minutes during the ball mill process, _{there is a disadvantage that the aluminum powder cannot be uniformly adhered to the surface of a plurality of SiO 2} , and if it exceeds 3 hours, the ball mill process is performed. During the process, the negative electrode active material particles are greatly deformed and thus the specific surface area may increase.

As described above, when conventional aluminum particles and SiO ₂ are mixed, when the two components are not uniformly mixed and aggregated, _{excessive reduction occurs only in SiO 2} where the aluminum particles are located, and the swelling characteristics of Si grains become excessive during heat treatment. There is a problem with this getting worse. On the other hand, in the method of the present invention, since the aluminum particles _{can be uniformly attached to SiO 2} by using the ball mill process, the disadvantage of excessive Si grains can be improved.

_{Meanwhile, in the method of the present invention, at least a part of SiO 2} may be reduced to Si by heat generated during the ball milling process in step 1, and thus some aluminum may be oxidized to aluminum oxide and mullite.

In the method of manufacturing the negative electrode active material particles of the present invention, SiO _{2 as a} raw material may be crystalline or amorphous, and specifically, crystalline SiO ₂ may be used.

The crystalline SiO ₂ may be one or more selected from the group consisting of quartz, cristobalite, or tridymite.

In addition, in the method for producing the negative electrode active material particles of the present invention, step 2 is a step of raising the temperature of the precursor.

In step 2, the temperature increase rate may be 0.5 °C/min to 3 °C/min. The aluminum of the aluminum particles adhere to the surface of SiO ₂ under the temperature rising rate of, and may be uniformly diffused into SiO ₂ inside. If, performing a heating at a heating rate of 3 ℃ / min exceeded, because the aluminum was present on the surface of the precursor filled micheo not diffuse into the precursor, the reduction reaction of the SiO ₂ of the aluminum to the inside of the SiO ₂ particles It may not occur evenly. Therefore, it may be difficult to obtain a silicon-based composite in which Si and SiO _{2 are uniformly distributed.}

In addition, in the method of manufacturing the negative electrode active material particles of the present invention, step 3 is a step of heat-treating the heated precursor. _{Specifically, reduction of SiO 2} due to aluminum in the precursor may be performed by heat-treating the heated precursor.

Specifically, a _{stoichiometric reaction between SiO 2} and aluminum particles is as follows (see Scheme 1 below):

[Scheme 1]

4Al + 3SiO ₂ → 3Si + 2Al ₂ O ₃

Further, the chemical reaction formula between the aluminum oxide (2Al ₂ O ₃ ) and SiO ₂ is as follows (see Reaction Formula 2 below);

[Scheme 2]

2Al ₂ O ₃ + 2SiO ₂ → 2Al ₂ O ₃ ㆍ2SiO ₂

3Al ₂ O ₃ + 2SiO ₂ → 3Al ₂ O ₃ ㆍ2SiO ₂

In the heat treatment step, SiO ₂ may be thermally reduced by using aluminum particles in an inert atmosphere. Due to the thermal reduction, _{oxygen of SiO 2} is locally escaped, thereby causing local reduction. That is, _{the portion from which oxygen escapes from SiO 2} is reduced to Si, resulting in a silicon-based composite in which Si, SiO ₂ remaining unreduced, and aluminum oxide and mullite, which are byproducts of reduction, form a complex with each other. There is. At this time, since aluminum is _{diffused to the inside of SiO 2} through step 2, as a result, Si from the inside to the surface of the silicon-based composite prepared in step 3, SiO ₂ remaining unreduced, aluminum oxide as a reduction by-product And it is possible to obtain a silicon-based composite in which mullite is uniformly distributed.

In the method of the present invention, the heat treatment process of step 3 may be performed in a reaction furnace, for example, a rotary kiln.

In addition, the heat treatment may be performed at 700° C. to 1100° C. for 3 to 12 hours. If the temperature of thermal reduction is less than 700°C, the temperature is low and the reduction reaction may be difficult to occur. If the temperature exceeds 1100°C, Si crystal grains may become large, resulting in a decrease in lifespan due to volume expansion. In addition, if the heat treatment time is less than 3 hours, the reduction reaction may not be completely terminated or the reduction reaction may _{occur only on the surface of SiO 2} , and if it exceeds 12 hours, the efficiency of the manufacturing process may decrease.

In addition, the heat treatment may be performed while flowing an inert gas, and the inert gas that may be used may be one or two or more mixed gases from the group consisting _{of Ar, N 2, Ne, He, and Kr.}

In addition, the method of the present invention may further include a step (step 4) of forming a carbon coating layer by adding a carbon precursor solution to the prepared silicon-based composite, followed by drying and heat treatment.

In this case, when the carbon precursor solution is added, dried, and heat treated, it may be performed while supplying an acetylene gas, and any method for forming a carbon coating layer that is commonly used may be used without limitation.

The carbon precursor solution may be prepared by dispersing a carbon precursor in a solvent such as tetrahydrofuran (THF), alcohol, or the like.

The carbon precursor may include one or two or more selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fiber, and carbon black.

In addition, in an embodiment of the present invention

Si, SiO _x (0.5<x<1.5), aluminum oxide (Al ₂ O ₃ ) and a silicon-based composite including mullite,

The ratio of (weight of Si): (total weight of aluminum oxide and mullite) in the silicon-based composite is 1:3.27 to 1:5.7 to provide negative active material particles.

When the total weight ratio of aluminum oxide and mullite in the negative electrode active material of the present invention is less than 3.27 _{, it means that SiO 2} cannot be reduced in a large amount, and thus a reduction by-product is formed less. Therefore, there is a problem in that the capacity is reduced due to a small content of Si, which is a reduction product, in the silicon-based composite (SiO _{x ).} In addition, the initial efficiency may be reduced due _{to SiO 2 remaining without reduction.} On the other hand, when the mixed weight ratio of aluminum oxide and mullite in the silicon-based composite exceeds 5.7, a reduction by-product that hinders the occlusion and desorption of lithium ions in the negative electrode active material increases, and the capacity may decrease.

_{Specifically, the weight ratio of Si:SiO x} (0.5<x<1.5): aluminum oxide: mullite in the silicon-based composite may be 1:0.71 to 6.42: 1.21: 2.06 to 4.49.

At this time, the presence and content of aluminum oxide and mullite in the silicon-based composite can be measured with an X-ray diffractometer (XRD) measuring device. In addition, it can be measured by high-resolution TEM (High-Resolution TEM) (see Fig. 1).

In the negative electrode active material of the present invention, the Si is _{a reduction product of SiO 2} , and the SiO _x (0.5<x<1.5) includes both SiO and SiO ₂ remaining without reduction, and the aluminum oxide (Al ₂ O ₃ ) and mullite may be reduction by-products _{of SiO 2.}

In the Si, lithium ions desorbed from the positive electrode active material are occluded and released to substantially cause an electrochemical reaction. The Si may be crystalline or amorphous. For example, when SiO ₂ is crystalline, Si generated by reduction using aluminum particles may be crystalline Si, and when SiO ₂ is amorphous, it may be reduced to amorphous Si.

When the Si is amorphous, the amorphous may be interpreted as including not only the case where there is no crystallinity, but also all cases outside the meaning of the theoretical'crystallinity'.

When the Si is crystalline, the size of Si grains may appear uniformly within the range of 1 nm to 100 nm in diameter. This crystal size can be determined by general X-ray diffraction (XRD) analysis or electron microscopy (SEM, TEM).

In addition, in the negative electrode active material of the present invention, the SiO _x (0.5<x<1.5) may be crystalline or amorphous, and the remaining SiO _x (0.5<x<1.5) included in the silicon-based composite is the crystalline or amorphous SiO ₂ may be formed by remaining without reduction. Specifically, when the SiO _x (0.5<x<1.5) is crystalline, there is _{an effect that the reaction between the lithium ions contained in the electrolyte and the crystalline SiO x} (0.5<x<1.5) is excluded.

The crystalline SiO _x (0.5<x<1.5) may be quartz, cristobalite, or tridymite. _{This is the same component as crystalline SiO 2} before reduction using aluminum particles, which will be described later, and corresponds to _{the remaining SiO 2} remaining without being reduced by reduction contained in the silicon-based composite.

In addition, in the negative electrode active material of the present invention, the mullite refers to an aluminum silicate mineral having _{an Al 2} O ₃ component combined as a solid solution with a _{SiO 2 phase, and the aluminum oxide is SiO 2} It is formed by reacting with, and representative examples thereof may include at least one mixture selected from the group consisting of _{3Al 2} O ₃ ㆍ2SiO ₂ , and 2Al ₂ O ₃ ㆍ2SiO _2.

The negative electrode active material of the present invention may additionally remove _{SiO 2} in the silicon-based composite by including mullite produced by the reaction of _{aluminum oxide and SiO 2.} That is, by including Li and there due to the reaction problem that may cause a problem is the irreversible capacity of the battery increased, in the case of the negative electrode active material of the present invention, aluminum oxide is formed by reaction with the SiO ₂ mullite in the case of SiO ₂ is amorphous electrolyte, The above problems can be solved.

For example, commonly used Si particles involve very complex crystal changes in a reaction of electrochemically occluding and releasing lithium atoms. As the reaction of electrochemically occluding and releasing lithium atoms proceeds, the composition and crystal structure of Si particles are Si (crystal structure: Fd3m), LiSi (crystal structure: I41/a), Li ₂ Si (crystal structure: C2/ m), Li ₇ Si ₂ (Pbam), Li ₂₂ Si ₅ (F23), etc. In addition, the volume of the Si particles may expand by about 4 times according to the change of the complex crystal structure.

However, when the silicon-based composite and the lithium atom react in the negative electrode active material prepared by the method of the present invention, mullite relieves the volume expansion of Si or implements a buffer layer effect of preventing the volume expansion of Si, thereby reducing the volume expansion rate of Si. As a result, the silicon-based composite can proceed while maintaining the crystal structure.

That is, the negative electrode active material of the present invention includes _{Si and SiO x} (0.5<x<1.5), which are reduction products of _{SiO 2} , so that a high capacity effect can be implemented by Si, and SiO _x (0.5<x <1.5), by the buffer layer effect due to aluminum oxide and mullite, it is possible to simultaneously improve the capacity and life characteristics of the secondary battery.

Meanwhile, in the negative electrode active material according to an embodiment of the present invention, _{crystal grains of Si and residual SiO x} (0.5<x<1.5) may be included in a ratio of 1-(x/2):(x/2). That is, the x is a ratio of the number of O (oxygen) elements to the Si element contained in the silicon-based composite, and may be 0.5<x<1.5.

_{At this time, when x} of SiO x in the negative electrode active material of the present invention exceeds 1.5, the swelling phenomenon of the negative electrode active material may be reduced to some extent, but the initial discharge capacity of the lithium secondary battery may decrease. .

In addition, according to an embodiment of the present invention, the negative active material may further include a carbon coating layer on the surface of the negative active material. By imparting conductivity of the silicon-based composite by the carbon coating layer, initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including the silicon-based composite may be improved.

The carbon coating layer may be included in an amount of 1% to 50% by weight based on the total weight of the negative active material. When the carbon coating layer is coated with less than 1% by weight, a uniform coating layer may not be formed, so that the conductivity may decrease, and when it exceeds 50% by weight, the carbon coating layer may become too thick and the size of the negative electrode active material may be too large. , Rather, capacity reduction and initial efficiency may decrease.

The thickness of the carbon coating layer may be 0.003 μm to 3.0 μm. When the thickness of the carbon coating layer is less than 0.003 µm, the carbon coating layer is too thin to reduce conductivity, and when it exceeds 3.0 µm, the carbon coating layer is too thick to increase the size of the negative electrode active material, but rather, capacity reduction and Initial efficiency can be reduced.

The carbon coating layer may include one or two or more selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fiber, and carbon black. Since the carbon coating layer is formed on the surface of the silicon-based composite, conductivity is imparted to the silicon-based composite, and initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including the silicon-based composite may be improved.

The average particle diameter of the negative electrode active material according to an embodiment of the present invention may be 0.1 μm to 20 μm, and specifically 0.5 μm to 10 μm. If the particle diameter of the negative electrode active material is less than 0.1 μm, the electrode plate density may decrease, and if it exceeds 20 μm, the rate characteristics may decrease or the life characteristics may decrease due to volume expansion.

In another embodiment of the present invention,

It provides a secondary battery including a negative electrode including the negative active material particles, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

The secondary battery may exhibit high initial efficiency, life characteristics, and capacity characteristics by including the negative active material particles.

The negative electrode may be prepared by dissolving the negative electrode active material particles, optionally a conductive material, and a binder in a solvent to prepare a negative electrode active material slurry, and then coating the negative electrode active material slurry on a negative electrode current collector, followed by drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a 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, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. may be used on the surface. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

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

The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the negative electrode active material slurry. Examples of such a binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro. Ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative active material, and may be added in an amount of 1 to 20% by weight based on the total weight of the negative active material slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as 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, 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 may be used.

The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount having a desirable viscosity when the negative active material and optionally a binder and a conductive material are included. . For example, it may be included so that the concentration of the negative active material and, optionally, the solid content including the binder and the conductive material is 50% by weight to 95% by weight, preferably 70% by weight to 90% by weight.

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

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , Nickel, titanium, silver, or the like may be used.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include at least one metal such as cobalt, manganese, nickel, or aluminum, and a lithium composite metal oxide containing lithium. have. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (eg, LiMnO ₂ , LiMn ₂ O _4, etc.), a lithium-cobalt-based oxide (eg, LiCoO _2, etc.), and a lithium-nickel-based 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 oxide (e.g., Li(Ni _p Co _q Mn _r1 )O ₂ (here, 0<p<1, 0<q<1, 0<r1<1, p+q+r1= 1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (here, 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 (where M is Al, Fe, V, Cr, Ti, Ta, Mg and Mo) Is selected from the group consisting of, and p2, q2, r3, and s2 are atomic fractions of each independent element, 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 compounds of these may be included. _{Among these, the lithium composite metal oxide is LiCoO 2} , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (e.g., Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ ) in that it can increase the capacity characteristics 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, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni _0.8 Co _0.15 Al _0.05 ) O ₂ etc. ), etc., in consideration of the remarkable improvement effect according to the type and content ratio control of the constituent elements forming the lithium composite metal oxide, 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, etc., any one or a mixture of two or more of them may be used. have.

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

The binder is a component that aids in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material slurry. Examples of such a binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber Various kinds of binder polymers such as (SBR), fluororubber, polyacrylic acid and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers may be used.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material slurry.

Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite; Carbon-based substances 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, 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 may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC The group (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (Timcal).

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

As the separator, a conventional porous polymer film conventionally used as a separator, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, etc. A porous polymer film made of a polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is limited thereto. no.

The electrolyte may include a non-aqueous organic solvent and a metal salt.

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-dime Oxyethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, Methyl acetate, phosphoric acid tryester, trimethoxy methane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate , An aprotic organic solvent such as ethyl propionate may be used.

The metal salt may be a lithium salt, and those commonly used in an electrolyte for a lithium secondary battery may be used without limitation. For example, Li ⁺ is included as a cation of the lithium salt, and F ^- as an anion, ^{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 -, (FSO 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 - , and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- It may include at least any one selected from the group consisting of. The lithium salt may be used alone or in combination of two or more as necessary. The lithium salt may be appropriately changed within a range that is generally usable, but may be included in the electrolyte at a concentration of 0.8 M to 1.5 M in order to obtain an optimum effect of forming an anti-corrosion film on the electrode surface.

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include the secondary battery having high capacity, long life, and high initial efficiency characteristics, a mid- to large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system It can be used as a power source.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to aid understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

Example

Example One.

(Step 1: Attachment of aluminum particles to _{SiO 2)}

_{A stainless steel ball of 3 mm, 100 g of crystalline SiO 2} having an average diameter (D50) of 10 μm, and 49 g of aluminum powder having an average diameter (D50) of 2 μm (1:1.3 molar ratio) were added to the mixing reactor, and 600 times per minute Ball milling was performed at a rotational speed for 3 hours to prepare a composite precursor by attaching aluminum particles to the surface of _{amorphous SiO 2.}

(Step 2: Raising the temperature of the precursor)

The precursor prepared in step 1 was accommodated in a reaction vessel of a thermal reduction chamber, and the temperature of the chamber was then raised to 800° C. at a rate of 1° C./min. Thereafter, Ar was used as an inert gas, and it was supplied at a flow rate of about 800 sccm to prepare a heated precursor.

(Step 3: Preparation of silicon-based composite)

The reaction vessel containing the precursor heated in step 2 was subjected to a thermal reduction reaction using a rotary tube furnace.

A thermal reduction reaction was performed at 800° C. for 12 hours, and after 12 hours, the chamber temperature was reduced to room temperature, and the product in the reaction vessel was collected to prepare a silicon-based composite. Then, using an X-ray diffractometer (XRD) measuring equipment, it was measured whether or not aluminum oxide and mullite were produced in the silicon-based composite (see FIG. 1).

Referring to FIG. 1, it was confirmed that the silicon-based composite of the present invention contained Si: SiO _x (x=1.0): aluminum oxide: mullite in a weight ratio of 1: 2.139: 1.21: 2.06.

(Step 4: Preparation of negative electrode)

The silicon-based composite prepared in step 3, acetylene black as a conductive material, and PVDF as a binder were used, and they were mixed in a weight ratio of 95:1:4, and these were mixed in N-methyl-2-pyrrolidone as a solvent. A negative active material slurry was prepared. The prepared slurry was coated on one surface of a copper current collector to a thickness of 30 μm, dried and rolled, and then punched to a predetermined size to prepare a negative electrode.

(Step 5: manufacture of secondary battery)

A coin-type half cell (2016 R-type half cell) was prepared in a helium-filled glove box using the negative electrode, lithium counter electrode, microporous polyethylene separator, and electrolyte. _{As the electrolyte, 1 M LiPF 6} was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed in a volume ratio of 50:50.

Comparative example One.

In Step 1 of Example 1, a half secondary battery was manufactured in the same manner as in Example 1, except that magnesium powder was used instead of aluminum in the same molar ratio.

Experimental example

Experimental example 1. Measurement of initial discharge capacity, initial efficiency and life characteristics

In order to determine the initial discharge capacity of the coin-type half-cells manufactured in Example 1 and Comparative Example 1, the half-cells manufactured at 25°C were charged and discharged once at 0 V to 1.5 V at 0.1 C. , Initial discharge capacity, initial charge capacity, and Coulomb efficiency were measured.

The measurement results of the initial discharge capacity, initial efficiency and life characteristics measured by the above method are shown in Table 1 below.

Initial discharge capacity (mAh/g) Initial efficiency (%) Life characteristics (%) Example 1 1700 84 70 Comparative Example 1 1300 80 40

-Initial efficiency (%): (first cycle discharge capacity/first cycle charge capacity) × 100

-Life characteristics (%): (49th cycle discharge capacity/first cycle discharge capacity) × 100

As shown in Table 1, in the case of the secondary battery of Example 1 in which reduction was performed using aluminum powder, the initial discharge capacity, initial efficiency, and life characteristics were 21.4 compared to the secondary battery of Comparative Example 1 using magnesium powder, respectively. It can be seen that there is an improvement of %, 5%, and 75%.

Through this, in the case of using aluminum powder, since the aluminum oxide and SiO ₂ are combined and reduced to mullite, _{the reduction efficiency of SiO 2} is higher, so that the initial efficiency and discharge capacity characteristics are excellent, as well as the lifespan due to the residue. It can be seen that the properties can also be excellent.

As described above in connection with a preferred embodiment for illustrating the technical idea of the present invention, the present invention is not limited to the configuration and operation as described as described above, without departing from the scope of the technical idea for the present invention It will be well understood by those of ordinary skill in the art that a number of suitable modifications and modifications are possible. Therefore, all such suitable modifications, modifications and equivalents should be considered to be within the scope of the present invention.

Claims (18)

Mixing SiO ₂ and aluminum powder at a molar ratio of 1:1.3 to 1:1.5, and then ball milling _{to prepare a precursor in which SiO 2} and aluminum are complexed (step 1);
Raising the temperature of the precursor at a heating rate of 0.5° C./min to 3° C./min (step 2); And
To prepare a silicon-based composite comprising _{Si, SiO x} (0.5<x<1.5), aluminum oxide (Al ₂ O ₃ ) and mullite by heat treating the heated precursor at 700°C to 1100°C for 3 to 12 hours Step (Step 3); Method for producing a negative electrode active material particles comprising a.
The method according to claim 1,
The ball milling step is a method for producing negative active material particles that are performed for 30 minutes to 3 hours at a rotational speed of 600 times per minute.
delete delete The method according to claim 1,
The method further comprises a step (step 4) of forming a carbon coating layer by preparing a silicon-based composite (step 3), and then adding a carbon precursor solution to the prepared silicon-based composite, followed by drying and heat treatment. Method for producing active material particles.
Si, SiO _x (0.5<x<1.5), aluminum oxide (Al ₂ O ₃ ) and a silicon-based composite including mullite,
The ratio of (weight of Si): (sum of weight of aluminum oxide and mullite) in the silicon-based composite is 1:3.27 to 1:5.7.
The method of claim 6,
_{The weight ratio of Si:SiO x} (0.5<x<1.5): aluminum oxide: mullite in the silicon-based composite is 1:0.71 to 6.42: 1.21: 2.06 to 4.49.
The method of claim 6,
Si is a reduction product _{of SiO 2,}
The SiO _x (0.5<x<1.5) includes SiO and remaining unreduced SiO ₂ ,
The aluminum oxide and mullite are negative active material particles that are by-products of reduction _{of SiO 2.}
The method of claim 6,
The Si is a crystalline or amorphous negative active material particles.
The method of claim 9,
When the Si is crystalline, the size of the Si grains is 1 nm to 100 nm in diameter of the negative active material particles.
The method of claim 6,
The SiO _x (0.5<x<1.5) is a crystalline or amorphous negative active material particle.
The method of claim 11,
The crystalline SiO _x (0.5<x<1.5) is one or more selected from the group consisting of quartz, cristobalite, and tridymite.
The method of claim 6,
The mullite is a negative active material particle comprising at least one selected from the group consisting _{of 3Al 2} O ₃ ㆍ2SiO ₂ and 2Al ₂ O ₃ ㆍ2SiO _2.
The method of claim 6,
The negative electrode active material particle further comprises a carbon coating layer on the surface of the negative electrode active material particle.
The method of claim 14,
The negative electrode active material particles, wherein the carbon coating layer is contained in an amount of 1% to 50% by weight based on the total weight of the negative electrode active material particles.
The method of claim 14,
The carbon coating layer is a negative active material particle comprising one or more selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fiber, and carbon black.
The method of claim 6,
The negative active material particles have an average particle diameter (D50) of 0.1 µm to 20 µm.
A secondary battery comprising a negative electrode including the negative electrode active material particles of claim 6, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

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