KR102320977B1 - Anode Active Material including Silicon Composite and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a core comprising: a core including secondary particles formed by arranging pulverized polycrystalline silicon particles and pulverized single crystal silicon particles that are primary particles and have different aspect ratios; and a shell surrounding the core and including a first conductive carbon; a high-capacity negative active material having excellent conductivity including a silicon composite in which the second conductive carbon is positioned on all or part of the shell surface, and lifespan including the same A lithium secondary battery having excellent characteristics, output characteristics and safety is provided.

Description

Anode Active Material including Silicon Composite and Lithium Secondary Battery Comprising the Same

The present invention relates to an anode active material including a high-capacity silicon composite having excellent conductivity, and a lithium secondary battery having excellent lifespan characteristics, output characteristics and safety including the same.

Lithium secondary batteries are widely used as power sources for mobile electronic devices, including mobile phones, and their application fields are expanding as demand for large devices such as electric vehicles increases.

Meanwhile, most of the currently commercialized lithium secondary batteries use a carbon-based material as an anode active material. In particular, graphite shows a very reversible charge/discharge behavior due to the uniaxial orientation of the graphite layer, showing excellent lifespan characteristics, and exhibiting a potential almost similar to that of lithium metal. It has the advantage of being able to obtain high energy. However, despite these advantages, the low theoretical capacity (372 mAh/g) of graphite acts as a limit at the present time when a high-capacity battery is required.

Accordingly, there is an attempt to use a metal material such as Si, Sn, Al, etc., which exhibits a relatively high capacity, as a material that can replace the carbon-based negative electrode active material. However, these metal materials cause large volume expansion and contraction during the insertion and desorption of lithium, which may cause micronization and loss of conduction paths, thereby reducing overall battery performance, such as deterioration of lifespan characteristics.

In order to solve this problem, various carbon materials are simply mixed with Si, fine powdered Si is chemically fixed on the carbon surface using a silane coupling agent, etc., or amorphous carbon is fixed on the Si surface through CVD, etc. There is this.

However, in the case of a material in which a carbon material is simply mixed with Si, carbon is liberated from Si in a process where Si undergoes large volume expansion and contraction as charging and discharging proceed, which leads to a significant decrease in lifespan characteristics due to deterioration of electrical conductivity. there is a problem.

In addition, the material in which fine powder of Si is chemically fixed to the carbon surface using a silane coupling agent or CVD does not have a long bonding duration by the silane coupling agent or CVD, so as the charge/discharge cycle progresses, the lifespan characteristics may decrease. Moreover, there is a problem in that it is difficult to obtain a negative electrode material of stable quality by uniformly performing the physicochemical adhesion.

Despite these various attempts, the problem of electrode damage due to expansion of Si during the discharge process was still raised.

Therefore, there is a high need for a high-capacity anode active material having excellent conductivity and a lithium secondary battery having excellent lifespan characteristics and output characteristics, including the same, and high safety.

An object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, it is an object of the present invention to provide an anode active material including a high-capacity silicon composite having excellent conductivity.

Another object of the present invention is to provide a lithium secondary battery having excellent safety while having excellent lifespan characteristics and output characteristics, including the anode active material.

The present invention is

a core including primary particles and secondary particles formed by arranging pulverized polycrystalline silicon particles and pulverized single crystal silicon particles having different aspect ratios; and

A shell surrounding the core and including a first conductive carbon; as a negative active material including a silicon composite in which the second conductive carbon is positioned on all or a part of the shell surface.

The shape of the pulverized polycrystalline silicon particles may be needle-like, and the shape of the pulverized single-crystal silicon particles may be plate-like.

The aspect ratio of the pulverized polycrystalline silicon particles may be greater than 4.0 and less than or equal to 10, and the aspect ratio of the pulverized single crystal silicon particles may be greater than or equal to 1.0 and less than or equal to 4.0.

The weight ratio of the pulverized polycrystalline silicon particles to the pulverized single crystal silicon particles may be 30:70 to 70:30.

The content of the first conductive carbon may be 5 to 30 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles and the pulverized single crystal silicon particles.

The average thickness of the first conductive carbon may be 10 nm to 3 μm.

The content of the second conductive carbon may be 1 to 10 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles and the pulverized single crystal silicon particles.

The average thickness of the second conductive carbon may be 10 to 50 nm.

The first conductive carbon may be amorphous carbon, and the second conductive carbon may be crystalline carbon.

The average particle diameter of the silicon composite may be 3 to 20 μm.

The present invention is

It includes a secondary silicon composite formed by gathering a primary silicon composite on an amorphous carbon matrix, wherein the primary silicon composite is

a core including primary particles and secondary particles formed by arranging pulverized polycrystalline silicon particles and pulverized single crystal silicon particles having different aspect ratios; and

A shell surrounding the core and including a first conductive carbon; as a second conductive carbon may be located on all or part of the shell surface.

The content of the amorphous carbon matrix may be 10 to 30 parts by weight based on 100 parts by weight of the primary silicon composite.

The secondary silicon composite may have an average particle diameter of 5 to 50 μm.

The present invention provides a lithium secondary battery including the negative active material.

The anode active material according to the present invention is a primary particle and includes secondary particles formed by arranging polycrystalline silicon pulverized particles and single crystalline silicon pulverized particles having different aspect ratios, so that voids in the secondary particles are minimized to maximize capacity per unit volume. Accordingly, the lifespan characteristics of the lithium secondary battery may be improved.

In addition, according to the present invention, the pores remaining fine inside the secondary particles increase the passage of lithium ions in the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

In addition, according to the present invention, in the core-shell structure, the shell is made of a first conductive carbon, and the second conductive carbon is located on all or a part of the shell surface, so that insertion and Even if the shrinkage and expansion of the silicon particles are repeated due to desorption, the first conductive carbon and the second conductive carbon act as a buffer to suppress volume expansion and damage of the core, thereby minimizing damage to the electrode because it has excellent durability. can

In addition, according to the present invention, since it has the form of a secondary silicon composite formed by gathering a primary silicon composite on an amorphous carbon matrix, it is possible to minimize particle disintegration in the repeated charging and discharging process, and at the same time, contact between the silicon particles and the electrolyte can be suppressed, thereby ensuring the safety of the lithium secondary battery.

1 is a schematic diagram schematically showing a cross-section of an anode active material according to an embodiment of the present invention; and
2 is a schematic diagram schematically showing a cross-section of an anode active material according to an embodiment of the present invention;
3 is an SEM photograph of the silicon composite in Experimental Example 1;
4 is data showing the average particle diameter of the silicon composite in Experimental Example 2;
5 is a photograph of the surface shape of a lithium-charged negative electrode in Experimental Example 3;
6 is a graph showing the capacity retention rate according to the cycle progress in Experimental Example 3; and
7 is a graph showing the capacity retention rate according to the cycle progress in Experimental Example 4;

Negative electrode active material (silicon composite 100)

1 is a schematic diagram schematically showing a cross-section of a negative active material according to an embodiment of the present invention, but the present invention is not limited to the above form.

Referring to FIG. 1 , the anode active material includes: a core including secondary particles formed by arranging pulverized polycrystalline silicon particles 111 and pulverized single crystal silicon particles 112 that are primary particles and have different aspect ratios; and

The shell surrounds the core and includes the first conductive carbon 120; and includes the silicon composite 100 in which the second conductive carbon 130 is positioned on all or part of the shell surface.

In the present invention, "aspect ratio" means a value of the long side/short side of the primary particle.

In the present invention, "pulverized polycrystalline silicon particles 111" refers to particles obtained by pulverizing polycrystalline silicon having an unstable silicon atomic arrangement.

In the present invention, "single-crystal silicon pulverized particles 112" refers to particles obtained by pulverizing single-crystal silicon in which the atomic arrangement of silicon is regular and the arrangement direction is constant.

In the present invention, "arrangement" means that primary particles having different aspect ratios are gathered to form secondary particles so that the voids formed inside the secondary particles are minimized.

In the present invention, the term "primary particle" refers to each of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 having different aspect ratios.

In the present invention, the "secondary particle" is a particle formed by gathering primary particles, that is, the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 having different aspect ratios.

Silicon has a theoretical capacity of about 3,600 mA/g, indicating a relatively high capacity compared to conventional carbon-based anode materials, but it causes large volume expansion and contraction during insertion and desorption of lithium ions, resulting in micronization and conduction. There is a problem in that life characteristics are deteriorated due to loss of path, etc.

The anode active material according to the present invention includes secondary particles formed by arranging polycrystalline silicon pulverized particles 111 and single crystalline silicon pulverized particles 112, which are primary particles and have different aspect ratios, so that voids in the secondary particles are minimized. Since the capacity per unit volume is maximized, the lifespan characteristics of the lithium secondary battery may be improved accordingly.

At the same time, due to the structural characteristics of the pores remaining inside the secondary particles, the passage of lithium ions is increased in the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

Polycrystalline silicon and single-crystal silicon exhibit a certain shape when pulverized using physical and chemical methods as a characteristic according to the crystal structure, for example,

The shapes of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 may be plate-like, needle-like, rectangular parallelepiped, prismatic, ellipsoidal, columnar, or the like.

Preferably, the shape of the pulverized polycrystalline silicon particles 111 may be a needle shape, and the shape of the pulverized single crystal silicon particles 112 may be a plate shape. Here, "acicular" or "plate-shaped" has an approximate shape even if it is not a complete needle or plate, and irregularities may be formed on the surface.

The shapes of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 may be expressed by an aspect ratio.

In the present invention, the aspect ratio of the pulverized polycrystalline silicon particles 111 may be greater than 4.0 and less than or equal to 10, and the aspect ratio of the pulverized single crystal silicon particles 112 may be greater than or equal to 1.0 and less than or equal to 4.0. If it is out of the above range, the intended effect of the present invention according to the minimization of voids through the arrangement of the particles cannot be obtained, and the bond between the primary particles is weakened and cycle characteristics may be deteriorated, which is not preferable. In detail, the aspect ratio of the pulverized polycrystalline silicon particles 111 may be 5.0 or more and 9.0 or less, and the aspect ratio of the pulverized single crystal silicon particles 112 may be 1.5 or more and 3.5 or less.

The size of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 as the primary particles is nano-sized, for example, by pulverizing polycrystalline silicon and single-crystal silicon having a crystal size of 1 nm to 30 nm, respectively. can be formed. It is possible to implement a high capacity within the above range and minimize the voids of the secondary particles while improving the initial efficiency.

The mixing ratio of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 as the primary particles may be 30:70 to 70:30 by weight. When the amount of the single-crystal silicon pulverized particles 112 is too large, economic feasibility is lowered in terms of cost, and when the amount of the polycrystalline silicon pulverized particles 111 is too large, there is a risk of severe micronization in the charging/discharging process of the battery. In addition, when it is outside the above range, it is not preferable because the intended effect of the present invention according to the minimization of voids cannot be obtained through the arrangement of the pulverized silicon particles having different aspect ratios. In detail, the mixing ratio of the pulverized polycrystalline silicon particles 111 to the pulverized single crystal silicon particles 112 may be 40:60 to 60:40 by weight.

As mentioned above, due to the structural characteristics of the micropores remaining inside the secondary particles, the lithium ion movement path increases during the charging/discharging process of the battery, thereby improving the output characteristics of the lithium secondary battery.

Accordingly, the porosity of the secondary particles may be 0.1 to 1%. Here, the porosity means "(pore volume per unit mass)/(specific volume + pore volume per unit mass)", and can be measured by mercury porosimerty or Bruanuer-Emmett-Teller (BET) measurement method. .

That is, the present invention forms secondary particles with primary particles having different aspect ratios, so that the capacity per unit volume can be maximized by minimizing the voids present inside the secondary particles, while the finely formed voids are the lithium ions. As it serves as a movement passage, output characteristics may be improved. Therefore, when the porosity is out of the defined range, the effect of increasing capacity and output characteristics cannot be obtained at the same time.

The anode active material according to the present invention has a core-shell structure in which the secondary particles formed by arranging polycrystalline silicon pulverized particles 111 and single crystalline silicon pulverized particles 112, which are the primary particles and have different aspect ratios, are arranged as a core, and the core is A shell including the first conductive carbon 120 surrounds, and the second conductive carbon 130 is positioned on all or part of the shell surface.

Therefore, even if the shrinkage and expansion of silicon particles are repeated due to the insertion and desorption of lithium ions during the charging and discharging process of the battery, the first conductive carbon 120 and the second conductive carbon 130 act as a buffer to increase the volume of the core and increase the volume of the core. Damage can be suppressed, and since it has excellent durability due to excellent mechanical strength, damage to the electrode can be minimized.

The first conductive carbon 120 may form a film on the entire surface of the secondary particles, and in some cases, the first conductive carbon 120 may be positioned between the primary particles.

The content of the first conductive carbon 120 may be 5 to 30 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 . If the content of the first conductive carbon 120 is small beyond the above range, the core may not be sufficiently wrapped and the reactivity with the electrolyte may be increased, thereby reducing cycle characteristics. it is not preferable to have In detail, the content of the first conductive carbon 120 may be 5 to 20 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 .

The average thickness of the shell including the first conductive carbon 120 may be appropriately adjusted according to the content of the first conductive carbon 120 as defined above, and may be, for example, 10 nm to 3 μm. If the thickness of the shell is too small, there is a fear that electrical conductivity may be lowered, and if the thickness is too thick, it is difficult to disperse during the preparation of the negative electrode mixture, which is not preferable because it may cause problems in the process. Specifically, it may be 30 nm to 1 μm.

The second conductive carbon 130 may form a film on all or part of the shell including the first conductive carbon 120 . In detail, the first conductive carbon 120 may form a film of 60 to 100% based on the total volume of the surface, and the average thickness may be 10 to 50 nm. If the film formation range is too small or the thickness is too small outside the above range, there is a fear that electrical conductivity may be reduced. Specifically, it is 20-40 nm.

The amount of the second conductive carbon 130 may be 1 to 10 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 . If the content of the second conductive carbon 130 is small beyond the above range, the shell cannot be sufficiently wrapped and the reactivity with the electrolyte may be increased, thereby reducing cycle characteristics. may not be preferable. In detail, the content of the second conductive carbon 130 may be 3 to 8 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles 111 and the pulverized single crystal silicon particles 112 .

The first conductive carbon 120 and the second conductive carbon 130 may have different crystallinity. As an example, the first conductive carbon 120 may be amorphous carbon, and the second conductive carbon 130 may be crystalline carbon.

The amorphous carbon may suppress expansion of the core by appropriately imparting strength to maintain the shape of the core shell. The amorphous carbon is not limited as long as it is known in the art, but for example, it may be one or a combination of two or more selected from the group consisting of soft carbon, hard carbon, pitch carbide, mesophase pitch carbide, and calcined coke. And specifically, it may be pitch carbide. More specifically, it may be pitch carbide derived from petroleum pitch. The petroleum pitch may be obtained by refining the impurity component from the high boiling point residue remaining after rectifying crude oil.

The crystalline carbon may further improve electrical conductivity while forming a conductive passage. The conductive carbon is not limited as long as it is known in the art, but, for example, one or more selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene soot. It may be a combination, but is not limited thereto. Specifically, it may be graphene, which is a single layer of graphite.

The average particle diameter of the silicon composite 100 is not particularly limited, but may be, for example, 3 to 20 μm. If the average particle diameter of the silicon composite 100 out of the above range is too small, the cycle characteristics may be deteriorated due to high reactivity with the electrolyte. . Specifically, it may be 5 to 10 μm.

In the present specification, the average particle diameter (D50) may be defined as a particle diameter based on 50% of the particle size distribution of particles, and may be measured using a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of several millimeters from a submicron region, and high reproducibility and high resolution results can be obtained.

Anode active material (secondary silicon composite 300)

2 is a schematic diagram schematically showing a cross-section of a negative active material according to an embodiment of the present invention, but is not limited thereto.

Referring to FIG. 2 , the present invention provides an anode active material including a secondary silicon composite 300 formed by gathering a primary silicon composite 200 on an amorphous carbon matrix 310 . That is, the secondary silicon composite 300 formed by gathering the silicon composite 200 is positioned on the amorphous carbon matrix 310 .

The primary silicon composite 200 is the same as the configuration of the silicon composite 100 described above, and a detailed description thereof will be omitted.

In the present invention, "amorphous carbon matrix 310" means that the amorphous carbon is positioned to form a continuous phase.

The amorphous carbon may be one or a combination of two or more selected from the group consisting of soft carbon, hard carbon, pitch carbide, mesophase pitch carbide, and calcined coke, and specifically may be pitch carbide. In particular, it may be pitch carbide derived from coal-based pitch.

The content of the amorphous carbon matrix 310 may be 10 to 30 parts by weight based on 100 parts by weight of the primary silicon composite 200 . When the content of the amorphous carbon matrix is large or small outside the above range, it is difficult to form an amorphous matrix, and it is difficult to exert the intended effect of the present invention.

The secondary silicon composite 300 according to the present invention is formed as if one or more primary silicon composites 200 are gathered on the amorphous carbon matrix 310 to form one particle, so that the primary silicon composite 200 ), so that more appropriate strength can be given, so particle morphology can be minimized during repeated charging and discharging, and conductivity can be improved. In addition, due to the buffer action of the amorphous carbon matrix 310, damage to the electrode can be minimized, and at the same time, the contact between the silicon particles and the electrolyte can be suppressed, thereby ensuring the safety of the lithium secondary battery.

The average particle diameter of the secondary silicon composite 100 is not particularly limited, but may be, for example, 5 to 50 μm. If the average particle diameter of the silicon composite 100 out of the above range is too small, the cycle characteristics may be deteriorated due to high reactivity with the electrolyte. . Specifically, it may be 10 to 30 μm.

lithium secondary battery

The present invention also provides a lithium secondary battery including the negative active material.

The lithium secondary battery may include a positive electrode including a positive electrode active material; and an anode including the anode active material, and an electrolyte.

The positive electrode is formed by applying a positive electrode mixture including a positive electrode active material to a current collector, and the positive electrode mixture may further include a binder and a conductive material, if necessary.

The positive active material is, for example, LiNi _0.8-x Co _0.2 AlxO ₂ , LiCo _x Mn _y O ₂ , LiNi _x Co _y O ₂ , LiNi _x Mn _y O ₂ , LiNi _x Co _y Mn _z O ₂ , LiCoO ₂ , lithium metal oxides such as LiNiO ₂ , LiMnO ₂ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and Li ₄ Ti ₅ O ₁₂ (0<x<1, 0<y<1); Chalcogenides such as Cu ₂ Mo ₆ S ₈ , FeS, CoS and MiS, oxides, sulfides, or halides such as scandium, ruthenium, titanium, vanadium, molybdenum, chromium, manganese, iron, cobalt, nickel, copper, zinc, etc. may be used, and more specifically, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , TiS ₂ , ZrS ₂ , RuO ₂ , Co ₃ O ₄ , Mo ₆ S ₈ , V ₂ O ₅ and the like may be used, but are not limited thereto.

The shape of the positive active material is not particularly limited, and may be a particle shape, such as a spherical shape, an oval shape, or a rectangular parallelepiped shape. The average particle diameter of the positive electrode active material may be in the range of 1 to 50 μm, but is not limited thereto. The average particle diameter of the positive electrode active material may be obtained by, for example, measuring the particle diameter of the active material observed with a scanning electron microscope and calculating an average value thereof.

The binder is not particularly limited, and a fluorine-containing binder such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) may be used, but is not limited thereto.

The content of the binder is not particularly limited as long as it can fix the positive active material, and may be in the range of 0 to 10 wt % based on the total weight of the positive electrode.

The conductive material is not particularly limited as long as the conductivity of the positive electrode can be improved, and nickel powder, cobalt oxide, titanium oxide, carbon, and the like can be exemplified. The carbon, specifically, may be any one selected from the group consisting of Ketjen black, acetylene black, furnace black, graphite, carbon fiber and fullerene, or at least one of them.

The content of the conductive material may be selected in consideration of other battery conditions such as the type of the conductive material, for example, may be in the range of 1 to 10% by weight based on the entire positive electrode.

A thickness of the positive electrode mixture layer in which the positive electrode mixture including the positive electrode active material, the binder, and the conductive material is applied to the current collector may be, for example, 0.1 micrometers to 1000 micrometers.

The positive electrode mixture may include, in some cases, 0.1 wt% to 60 wt%, specifically 10 wt% to 50 wt%, of the solid electrolyte according to the present invention based on the total weight of the cathode mixture.

The thickness of the positive electrode mixture layer may be, for example, 0.1 micrometers to 1000 micrometers.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel; Those surface-treated with nickel, titanium, silver, etc. may be used. In addition, various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body having fine irregularities formed on the surface may be used.

The negative electrode may be used in which the negative electrode mixture including the negative electrode active material according to the present invention is applied on the negative electrode current collector. The negative electrode mixture may further include a binder and a conductive material having the configuration as described above, if necessary.

At this time, the negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the lithium secondary battery, for example, on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Carbon, nickel, titanium, a surface treated with silver, etc., an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, non-woven body, etc. having fine irregularities formed on the surface, like the positive electrode current collector.

The electrolyte is composed of an organic solvent and an electrolyte.

The organic solvent is not limited as long as it is commonly used, for example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxy At least one selected from the group consisting of ethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran may be used.

There is no limitation as long as a lithium salt that can be included as the electrolyte is commonly used. For example, as an anion of the lithium salt ^{, F -} , Cl ^- , I ^- , NO ³ - , N(CN) ^{2 -} , BF ^{4 -} , ClO ^4- , PF ^6- , (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- , 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 ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ^{3 -} , CF ₃ CO ^{2 -} , CH ₃ CO ^{2 -} , SCN - and (CF ₃ CF ₂ SO ₂ ) One selected from the group consisting of ₂ N ^{− may be used.}

A battery structure is formed by arranging a separator between the positive electrode and the negative electrode, and the battery structure is wound or folded and placed in a cylindrical battery case or a prismatic battery case, and then electrolyte is injected to complete a secondary battery. Alternatively, the lithium secondary battery is completed by stacking the battery structure in a bi-cell structure, impregnating it with an electrolyte, and sealing the obtained result in a pouch.

Although described with reference to the following examples, the following examples are for the purpose of illustrating the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

After mixing polycrystalline silicon and single crystal silicon in a ratio of 50:50 based on weight, 200 parts by weight of ethanol and 50 parts by weight of N-methyl-2-pyrrolidone were added based on 100 parts by weight of the mixture. After the above formulation, a silicon slurry containing nano silicon was prepared by pulverizing using a zirconia ball mill, and ethanol was evaporated through a spray drying process using this to prepare a core. The pulverized polycrystalline silicon particles formed through the above process were needle-shaped with an aspect ratio of 5.0 or more and 9.0 or less, and the pulverized single-crystal silicon particles had a plate shape with an aspect ratio of 1.5 or more and 3.5 or less.

10 parts by weight of petroleum pitch and 90 parts by weight of N-methyl-2-pyrrolidone were added to the core and heat-treated in an inert atmosphere at 200° C. to surround the core to prepare a shell containing carbides of pitch. The average thickness of the shell was 50 nm.

After that, 5 parts by weight of graphene was added and oven dried at 200° C. to prepare a silicon composite in which a graphene film was formed on the entire surface of the core-shell structure. The average thickness of the graphene film was 30 nm. The average particle diameter of the silicon composite is 7.5 to 8.5 μm.

<Example 2>

Using the silicon composite according to Example 1 as a primary silicone composite, 20 parts by weight of a coal-based pitch based on 100 parts by weight of the first silicon composite was mixed, then compressed at a high temperature at 200° C., and calcined at 900° C. in a non-oxygen atmosphere. A secondary silicon composite including carbides of pitch surrounding the secondary silicon composite was prepared. The average particle diameter of the secondary silicon composite is 11.6 μm.

<Comparative Example 1>

A silicon-carbon composite (Si/C) having a D50 of 12.2 μm was prepared as an anode active material.

<Experimental Example 1>

The SEM photograph of the silicon composite prepared in Example 1 is shown in FIG. 3 below.

<Experimental Example 2>

The average particle size data of the silicon composite prepared in Example 1 is shown in FIG. 4 below.

According to FIG. 4, the D50 of the silicon composite was confirmed to be 8.173 μm.

<Experimental Example 3>

A negative electrode plate prepared by using the negative active material according to Example 1 and Comparative Example 1, respectively, was cut in a circular shape of ^{1.4875 cm 2 as} a negative electrode, and a lithium (Li) metal thin film cut in a circular shape of ^{1.4875 cm 2 was used as a positive electrode.} . Here, in the design of the negative electrode plate, the rolling density was 1.55 g/cc, the current density was 2.95 mA/cm ² , and the electrode plate capacity was 510 mAh/g. A separator of porous polyethylene is interposed between the positive electrode and the negative electrode, and 0.5 wt% of vinylene carbonate is dissolved in a mixed solution having a mixing volume ratio of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) of 7: 3, A lithium coin half-cell was prepared by injecting an electrolyte in which 1M concentration of LiPF _{6 was dissolved.}

The thickness change rate, discharge capacity, initial efficiency, capacity retention rate, and discharge capacity and initial efficiency of Comparative Example 1 were measured using the lithium coin half cell and are shown in Table 1 below. In addition, the capacity retention ratio (CRR) of Example 1 is shown in FIG. 5, and the surface shape of the negative electrode charged with lithium after one cycle is shown in FIG. 6 below.

The first cycle (Hwaseong cycle) and the second cycle were charged and discharged at 0.1C (standard cycle), and from the 3rd cycle to the 49th cycle, charge and discharge were performed at 0.5C/1.0C for discharge. After 50 cycles, the battery is disassembled and the thickness is measured, and the thickness of the electrode after 50 cycles is compared to the average charge thickness (average value of 5 samples) in the initial charge. The rate of change was calculated.

The basic charging and discharging conditions are as follows.

- Charging condition: CC (constant current)/CV (constant voltage) (0.01V/0.01C, current cut-off)

- Discharge condition: CC (constant current) condition 1.5Vcut off

Discharge capacity (mAh/g) and initial efficiency (%) were derived from the results of one charge and discharge. Specifically, the initial efficiency (%) was derived by the following calculation.

- Initial efficiency (%) = (discharge capacity after one discharge / one charge capacity) × 100

The capacity retention rate and the electrode thickness change rate were respectively derived by the following calculations.

- Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

- Electrode thickness change rate (%) = (electrode thickness change after 50 cycles/2 electrode thickness after charging cycles) × 100

Electrode thickness change rate (%, 1 cycle) Electrode thickness change rate (%) discharge capacity
(mAh/g) Initial efficiency
(%) Volume
retention rate
(%, 50 cycles) Example 1 23.5% 0.8% 1350 87.2% 92.3% Comparative Example 1 - - 1210 86.4 -

<Experimental Example 4>

A negative electrode using each of the negative active material including the secondary silicon composite prepared in Example 2 and the negative active material according to Comparative Example 1 was prepared, and NCM 111 was used as a positive active material to prepare a positive electrode. Here, the negative electrode has a rolling density of 1.53 g/cc, a current density of 2.95 mA/cm ² , and a plate capacity of 510 mAh/g. The current density of the anode is 2.65 mA/cm ² and N/P is 1.11. A binder containing 1.5 wt% of SBR and CMC was used, and a porous polyethylene separator was interposed between the positive electrode and the negative electrode, and the mixing volume ratio of methylethyl carbonate (EMC) and ethylene carbonate (EC) was 7: 3 A lithium secondary battery having a capacity of 0.45Ah was prepared by dissolving vinylene carbonate dissolved in 0.5% by weight in the mixed solution, _{and injecting an electrolyte in which LiPF 6 of 1M concentration was dissolved.}

The charging conditions of the lithium secondary battery were CC/CV, 0.5C charging, 4.2V/0.05C cutoff, and the discharging conditions were CC, 1.0C discharge, and 2.85V cutoff to measure capacity retention, and are shown in Tables 2 and 4 below. .

1st. Efficiency
(%) Retention
(%, @100cycles) Example 2 89.9 89.6 Comparative Example 1 87.7 86.3

Referring to Table 2 and FIG. 6 , it can be seen that the difference in the initial efficiency values is very large as the cycle progresses. The higher the initial efficiency, the greater the amount of cathode material used when manufacturing a secondary battery of the same capacity, which greatly affects the cost increase, so it is essential to use a high-efficiency anode material. Accordingly, it can be confirmed that the negative active material made of the secondary silicon composite according to the present invention has high efficiency and excellent lifespan characteristics.

(100) silicon composite
(111) single crystal silicon pulverized particles
(112) polycrystalline silicon pulverized particles
(120) first conductive carbon
(130) second conductive carbon
(200) first silicon composite
(211) single crystal silicon pulverized particles
(212) polycrystalline silicon pulverized particles
(220) first conductive carbon
(230) second conductive carbon
(300) second silicon composite
(310) amorphous carbon matrix
Those of ordinary skill in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention based on the above contents.

Claims (14)

A core comprising secondary particles formed by arranging needle-shaped polycrystalline silicon pulverized particles having an aspect ratio of 5.0 or more and 9.0 or less and plate-shaped single crystalline silicon pulverized particles having an aspect ratio of 1.5 or more to 3.5 or less in a weight ratio of 40: 60 to 60: 40 as primary particles; and
A shell surrounding the core and comprising amorphous carbon having an average thickness of 30 nm to 1 μm;
An anode active material comprising a silicon composite in which crystalline carbon having an average thickness of 20 to 40 nm is positioned on all or part of the shell surface. delete delete delete The negative active material according to claim 1, wherein the content of the amorphous carbon is 5 to 30 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles and the pulverized single crystal silicon particles. delete The negative active material according to claim 1, wherein the content of the crystalline carbon is 1 to 10 parts by weight based on 100 parts by weight of the pulverized polycrystalline silicon particles and the pulverized single crystal silicon particles. delete delete The negative active material according to claim 1, wherein the silicon composite has an average particle diameter of 3 to 20 μm. The method of claim 1,
It includes a secondary silicon composite formed by gathering the primary silicon composite, which is the silicon composite, on an amorphous carbon matrix,
The content of the amorphous carbon matrix is an anode active material, characterized in that 10 to 30 parts by weight based on 100 parts by weight of the primary silicon composite. delete The negative active material of claim 11 , wherein the secondary silicon composite has an average particle diameter of 5 to 50 μm. A lithium secondary battery comprising the negative active material according to claim 1 .

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