KR101511694B1 - Anode active material of lithium rechargeable battery and process for preparing the same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery and to a method for manufacturing the same. Particularly, the present invention provides the negative electrode active material for a lithium secondary battery which is a silicon oxide complex including a carbon core layer in the fibrous shape formed by processes of formation of a carbon core material in a metal silicate material having nanopores in the fibrous shape, acid treatment, heat treatment, and reduction firing.

Description

[0001] The present invention relates to an anode active material for a lithium secondary battery,

The present invention relates to a negative electrode active material for a lithium secondary battery and a method for producing the same, and more particularly, to a negative electrode active material for a lithium secondary battery, which is a rod-shaped silicon oxide composite including a fibrous carbon core layer and a method for producing the same.

Recently, with regard to the tendency to miniaturize and lighten portable electronic devices, there is an increasing need for high performance and large capacity of batteries used as power sources for these devices.

The battery is a material that generates electricity by using a material capable of electrochemically reacting with the positive electrode and the negative electrode. A representative example of such a battery is a lithium secondary battery that generates electrical energy by a change in chemical potential when the lithium ions are intercalated / deintercalated in the positive electrode and the negative electrode. The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as an active material for the positive electrode and the negative electrode, and filling an organic electrolyte solution or a polymer electrolyte between the positive electrode and the negative electrode. As the cathode active material of the lithium secondary battery, a lithium composite metal compound is used. Examples of the lithium composite metal compound include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1), LiMnO ₂ Metal oxides are being studied.

Various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting and desorbing lithium have been used as the negative electrode active material. However, when an electrode plate made of artificial graphite such as artificial graphite or natural graphite is used as an active material in the carbon-based material, the density of the electrode plate is lowered and the capacity is low in terms of energy density per unit volume of the electrode plate. Accordingly, metal or intermetallic compounds have been actively studied as an anode active material at present. Japanese Unexamined Patent Application Publication No. 10-223221 discloses a lithium secondary battery using a lower crystal of an element selected from Al, Ge, Pb, Si, Sn, and Zn or an amorphous intermetallic compound as an anode. It is described that the battery is excellent in high capacity and cycle characteristics. However, in practice, the lower crystallization or amorphization of such an intermetallic compound is very difficult. For this reason, it is difficult to realize a lithium secondary battery having a long cycle life with a high capacity from the technical content described in the above publication. In particular, the conventional SnO ₂ or SnO ₂ -based anode active material has a disadvantage that the irreversible capacity accounts for not less than 65% of the total capacity, and the life characteristics are also very poor.

In order to solve the problems of the prior art as described above, the present invention relates to a method of forming carbon nanofibers in a sepiolite (palygorskite) material having shape nano pores, And a negative electrode active material for a lithium secondary battery, which is a silicon oxide composite, and a method for producing the same.

In order to achieve the above object, the present invention provides a negative electrode active material for a lithium secondary battery, which is a silicon oxide composite including a fibrous carbon core layer.

The anode active material for a lithium secondary battery according to the present invention is characterized in that a fibrous carbon core layer is formed in a membrane-like porous inorganic oxide pore containing a silicate component, a metal component other than silicate is removed through an acid treatment, Core silicon oxide complex. Particularly, the carbon core existing in the silicon oxide nanopores imparts excellent electrical conductivity to the oxide and also functions to buffer the volume expansion of the silicon oxide upon reaction with lithium ions, thereby imparting high output and long life characteristics of the anode active material . Thereby providing a silicon oxide / carbon composite anode active material including a silicate having a high capacity, high output, and long life characteristics.

The present invention also provides a method for producing a porous metal oxide, comprising the steps of: mixing a porous metal oxide having fibrous pores and containing a silicate component with an organic compound comprising a hydrocarbon functional group having 1 to 18 carbon atoms; Subjecting the mixture to a first heat treatment at 300 ° C or higher to form a carbon core; Acid treatment of the composite on which the carbon core is formed; And subjecting the acid-treated carbon core composite to a secondary heat treatment at 500 ° C. or higher.

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

The negative active material for a lithium secondary battery of the present invention has excellent capacity, high rate characteristics, and long life characteristics. In addition, the use of natural porous inorganic oxide has the advantage of economical efficiency and mass production at low cost.

1 is a schematic diagram of a carbon core silicon oxide composite prepared according to the present invention. The carbon core is formed inside the pores of the rod-shaped silicon oxide, and the primary particles form a secondary particle.
(B) a silicon oxide composite (Example 1) obtained by heat-treating a carbon core silicon oxide composite at 900 degrees after acid treatment, (c) a carbon core The silicon oxide composite is heat treated at a temperature of 1,100 ° C. after the silicon oxide complex is subjected to the acid treatment (Example 2). (D) In the carbon core silicon oxide composite, the silicon oxide is completely removed using HF, The results are as follows.
FIG. 3 shows the XRD crystal analysis results of the carbon core silicon oxide prepared in Example 1. FIG. Sepiolite crystallinity is not visible in the complex, and exhibits a very amorphous crystal structure and a small crystalline peak at 2θ = 26.6, 27.6.
Figure 4 shows the composition analysis of the carbon core silicon oxide complex using SEM-EDX before and after the acid treatment. A large amount of Mg and Al components were detected before the acid treatment, but most of the metal components were removed after the acid treatment except for Si.
FIG. 5 shows electrochemical charge / discharge evaluation results using a coin cell. Comparative Example (a) shows the charge / discharge results of graphite. Graphite shows a reversible capacity of 320 mAh / g, whereas in (b), the carbon core silicon oxide (Example 1) calcined at 900 ° C after the acid treatment has a calcining temperature of approximately 540 mAh / g, One carbon core silicon oxide (Example 2) shows a high reversible capacity of 620 mAh / g or more.
6 shows the evaluation results of the characteristics of the carbon core silicon oxide produced through the 900-degree calcination (Example 1) and the 1,100-degree calcination (Example 2) (900-DCH: 900- CH: Charging capacity of 900 degree fired product, 1100-DCH: 1,100 degree fired product discharge capacity, 1100-CH: 1,100 degree fired product charging capacity. Here, when the charge / discharge rate is increased from 0.05 C to 1 C, the charging and discharging capacity of the 1,100-degree fired product is higher than that of the 900-degree fired product at the angular rate. In addition, the 1 C reversible capacity of the 1,100-degree fired product showed a capacity retention ratio of more than 92% as compared with the 0.1 C reversible capacity at 580 mAh / g.

In the present invention, the terms first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

Moreover, the terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the present invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprising," "comprising," or "having ", and the like are intended to specify the presence of stated features, But do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

Also in the present invention, when referring to each layer or element being "on" or "on" each layer or element, it is meant that each layer or element is formed directly on each layer or element, Layer or element may be additionally formed between each layer, the object, and the substrate.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an anode active material for a lithium secondary battery of the present invention, a method for producing the same, and a lithium secondary battery including the anode active material will be described in detail.

According to one embodiment of the present invention, there is provided a negative electrode active material for a lithium secondary battery excellent in high capacity, high rate characteristics, and cycle life characteristics. The negative electrode active material for a lithium secondary battery of the present invention is a silicon oxide composite including a fibrous carbon core layer.

In particular, in order to accomplish the above object, the present invention provides a carbon nanofiber comprising fibrous carbon nanofibers formed in a sepiolite (palygorskite) containing a silicate component and having fibrous nanopores to impart excellent electrical conductivity, Is removed through acid treatment and the carbon core silicon oxide complex is produced through the high-temperature reduction and firing of the first and second heat treatment steps to increase the electrochemical reaction activity with lithium, . It also alleviates the volumetric expansion of the silicon oxide by reaction with lithium through the carbon core material, which gives improved life characteristics.

In general, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of lithium intercalation / deintercalation have been applied to the anode active material. The carbon-based graphite has a discharge voltage as low as -0.2 V compared to lithium, and the battery using the negative electrode active material exhibits a high discharge voltage of 3.6 V, thereby providing an advantage in terms of energy density of the lithium battery, And it is most widely used because it guarantees the long life of the battery. However, the graphite active material has a low density (theoretical density of 2.2 g / cc) of graphite in the production of electrode plates, and thus has a low capacity in terms of energy density per unit volume of the electrode plate, and a side reaction with an organic electrolyte used at high discharge voltage tends to occur, There is a risk of ignition or explosion due to malfunction or overcharge of the battery. Therefore, metal-based active materials such as Si have been studied. The Si metal anode active material is known to exhibit a high lithium capacity of about 4,200 mAh / g by forming Li _4.4 Si. However, it causes a volume change of more than 300% before and after the reaction with lithium, that is, during charging and discharging. As a result, pulverization of the negative electrode active material occurs and agglomeration of the undifferentiated particles occurs, causing the negative active material to be electrically removed from the current collector. Such electrical decoupling remarkably reduces the capacity retention rate of the battery. Accordingly, there have been many studies for preparing carbon and Si nanoparticle composites for use as negative electrode active materials in order to suppress the volume change of the metal-based negative electrode active material. In the carbon and Si nanoparticle composites, since the carbon acts as an electrical conductor, the capacity retention ratio can be improved.

However, in order to obtain a relatively good capacity retention rate, there is a problem that the carbon content of the composite should be over 50% by weight and the capacity is lowered. Even if the carbon content is excessively contained, the capacity after 50 cycles is as low as 1,500 mAh / g There was a problem. As another method for suppressing the volume change, there is a part of research on one-dimensional shape silicon nanowires as an anode active material. Morales, A. M .; Lieber, C.M. The Si nanowires fabricated by the laser ablation system described in Science, 1998, 279, 208 have wire diameters of about 10-30 nm. However, the discharge and charge capacities of the nanowires are about 1,300 mAh / g and 900 mAh / g, respectively, and the capacity is somewhat low. As another method, Si nanowires having a diameter of less than 50 nm grown by vapor solid-free template (VS) have been reported. The Si nanowires showed a reversible capacity of about 2,000 mAh / g at 2 V to 0 V and 0.2 C, and no capacity reduction until 10 cycles. Semiconductor nanowires grown by vapor-liquid-solid (VLS), liquid-liquid-solid (SLS) and template-free synthetic methods have been reported. However, the nanowires produced by this method were not able to exhibit sufficient capacity retention.

The negative electrode active material for a lithium secondary battery of the present invention is a silicon oxide composite including a fibrous carbon core layer, and the carbon core silicon oxide composite has a rod-like shape. In this case, the rod-like shape means a shape having a longer length in the axial direction than the particle diameter. This is advantageous in increasing the surface area of silicon oxide for reaction with lithium ions and increasing the particle filling density. In addition, the fibrous carbon core material present in the silicon oxide particles imparts excellent electrical conductivity and functions to buffer the volume expansion of the silicon oxide in the reaction with lithium, thereby improving the lifetime and high-rate characteristics.

The average diameter of the carbon core silicon oxide complex may be 5 to 100 nm, preferably 10 to 50 nm, more preferably 20 to 40 nm. Further, the length of the carbon core silicon oxide composite may be 100 nm to 20 탆, preferably 1 탆 to 10 탆, more preferably 3 탆 to 8 탆.

In the negative electrode active material for a lithium secondary battery of the present invention, the silicon oxide composite may include a component represented by SiO _x (0? _X ? 2).

Further, as shown in FIG. 3, the crystallinity of the carbon core silicon oxide composite has a crystal peak at 2 theta = 26-27 and 27-28 in XRD crystal analysis, and 2 theta = 21-22, and 35-36, which have broad crystal form SiO _2- related crystal peaks.

In the negative electrode active material for a lithium secondary battery of the present invention, the carbon core layer has an average diameter of 2 nm or less or 0.01 nm to 2 nm and a length of 10 nm to 10 mu m.

In the negative electrode active material for a lithium secondary battery according to the present invention, the carbon content may be 1 to 10 wt%, preferably 1.5 to 8 wt%, more preferably 2 to 5 wt%, based on the total weight.

The negative electrode active material for a lithium secondary battery of the present invention has excellent cycle life characteristics and high rate characteristics. In particular, the anode active material for a lithium secondary battery according to the present invention has a high lithium charge capacity characteristic of silicon oxide, excellent electrical conductivity through a carbon core material existing in silicon oxide pores, and volume expansion of silicon oxide upon lithium charging, And has the function of buffering the physical impact of the silicon oxide due to the volume expansion. As a result, it has excellent charge / discharge capacity and excellent characteristics and life characteristics compared to the conventional graphite negative electrode active material.

According to another embodiment of the present invention, there is provided a method of manufacturing the negative electrode active material for a lithium secondary battery as described above. The method for manufacturing a negative electrode active material for a lithium secondary battery according to the present invention comprises the steps of mixing a porous metal oxide having fibrous pores and containing a silicate component with an organic compound containing a hydrocarbon functional group having 1 to 18 carbon atoms; Subjecting the mixture to a first heat treatment at 300 ° C or higher to form a carbon core; Acid treatment of the composite on which the carbon core is formed; And subjecting the acid-treated carbon core composite to a secondary heat treatment at 500 ° C or higher.

In the present invention, an anode active material for a lithium secondary battery having excellent cycle life characteristics can be produced through formation of a carbon core material in a metal silicate material having fibrous nano pores, acid treatment, heat treatment, and reduction and firing.

The porous metal oxide includes a silicate component having fibrous nanopores, and may include at least one metal component selected from the group consisting of Si, Mg, Sn, and Al. Also, the porous metal oxide is selected from the group consisting of SiO _x (0 <x ≦ 2), SnO _{x '} (0 ≦ _x ≦ 2), MgO _{x "} (0 ≦ _x" ≦ 2) .

In the method for preparing an anode active material for a lithium secondary battery according to the present invention, the porous metal oxide may be a material having a composition represented by the following Chemical Formula 1

[Chemical Formula 1]

Mg _a M _b Si _c O _d

In Formula 1,

M is selected from the group consisting of Al, K, Ca, Be, and combinations thereof,

a, b, c, and d satisfy the following conditions: 0.1 <a? 6, 0.01 <b <0.5, 0.1 <c? 10 and d? 2c, < c? 6, d? 2c.

The porous metal oxide comprising a silicate component having fibrous nanopores is selected from the group consisting of sepiolite, palygorskite, and mixtures thereof. In particular, the sepiolite composition is Mg ₄ Si ₆ O ₁₅ (OH) ₂ .6H ₂ O and the material structure is Orthorhombic 2 / m 2 / m 2 / m. For example, sepiolite has a rod-like shape, nano-sized pores are formed along the axis inside the particle, pore size is about 3.6 占 占 10.6 占 and the sepiolite particle diameter is 5 to 100 nm, preferably 10 to 50 nm, more preferably 20 to 40 nm, and the length is 100 nm to 20 탆, preferably 1 탆 to 10 탆, more preferably 3 탆 to 8 탆.

The porous metal oxide may have a specific surface area of 30 to 500 m ² / g, preferably 100 to 400 m ² / g, more preferably 200 to 300 m ² / g.

In addition, the crystallinity of the porous metal oxide shows a unique pattern of sepiolite, palygorskite, and the like, and a large number of crystal peaks can be exhibited depending on the complex crystal form. As shown in FIG. 3, the crystallinity of the porous metal oxide was determined by XRD crystal analysis at two theta = 10-11, 13-15, 27-28, 30-31, 34.5-35.5, 36.5-37.5, 40 &lt; / RTI &gt;

In one embodiment of the present invention, a carbon core material may be formed by mixing the porous metal oxide with an organic compound containing a hydrocarbon functional group having 1 to 18 carbon atoms. Here, the hydrocarbon functional group in the organic compound may be selected from the group consisting of a methyl group, an ethyl group, a butyl group, and a combination thereof. Examples of the organic compound include sucrose, starch, ascorbic acid, and the like.

The organic compound may be added in an amount of 10 to 400 parts by weight, preferably 50 to 200 parts by weight, more preferably 60 to 150 parts by weight based on 100 parts by weight of the porous metal oxide.

In an embodiment of the present invention, in order to form a carbon nanocom material on the porous metal oxide, an organic compound containing a hydrocarbon functional group having 1 to 18 carbon atoms is mixed in an aqueous solution or a vapor phase and then subjected to a first heat treatment High-temperature reduction firing can be performed. The carbon nanofibers can be formed in the core layer of the porous metal oxide through the first heat treatment process. However, in the primary heat treatment step, it is preferable to sinter at 950 ° C or lower in order to prevent formation of silicon magnesium (MgSiO ₃ ). In addition, an organic gas such as methane, ethane, or propane may be passed through the porous metal oxide and may be produced through a high-temperature reduction-firing process. The primary heat treatment may be performed at a temperature of 300 ° C or higher or 300 ° C to 950 ° C, preferably 400 ° C or higher and 900 ° C or lower.

The fired material obtained after the first heat treatment process, that is, the composite having formed the carbon core, includes a step of removing metal components such as Mg, Al, Ti, and Fe through an acid treatment process. In particular, the composite having the carbon core formed thereon can be impregnated with an acid solution or the like to remove metal components such as Mg and Al. At this time, one or more of hydrochloric acid (HCl), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), perchloric acid (HClO ₄ ) and the like may be used as the acid solution.

In one embodiment of the present invention, the acid-treated carbon core composite may be subjected to high-temperature firing in a second heat treatment process at 500 ° C or higher. Through the second heat treatment process, the crystallinity of the entire carbon fiber itself and the carbon core silicon oxide complex can be increased. The high-temperature reduction calcination temperature in the second heat treatment step may be 500 ° C or higher, or 500 ° C to 2,000 ° C, preferably 700 ° C or higher to 1,500 ° C or lower.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the negative electrode active material as described above. The lithium secondary battery of the present invention includes a cathode including a cathode active material, a cathode including the anode active material, and an electrolyte.

The negative electrode is prepared by preparing the negative electrode active material composition by mixing the negative active material according to the present invention, the conductive material, the binder and the solvent, and then directly coating and drying the copper negative electrode active material on the copper current collector. Or by casting the negative electrode active material composition on a separate support, then peeling the support from the support, and laminating the resulting film on an aluminum current collector. The conductive material may be carbon black, graphite, metal powder, and the binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. Further, N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like are used as the solvent. At this time, the content of the cathode active material, the conductive material, the binder and the solvent is used at a level normally used in a lithium secondary battery.

The positive electrode is prepared by mixing a positive electrode active material, a binder and a solvent in the same manner as the negative electrode to produce an anode active material composition. The positive electrode active material film is directly coated on the aluminum current collector or cast on a separate support, Laminated. At this time, the cathode active material composition may further contain a conductive material if necessary. As the cathode active material, a material capable of intercalating / deintercalating lithium is used. Typically, metal oxides, lithium composite metal oxides, lithium composite metal sulfides, and lithium composite metal nitrides are used as the cathode active material do.

The separator may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene double-layer separator, It is needless to say that a mixed multilayer film such as a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged into the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used. The solvent of the non-aqueous electrolyte is not particularly limited, but cyclic carbonate dimethyl carbonate such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like, chain carbonate such as methyl ethyl carbonate and diethyl carbonate, methyl acetate, Esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and? -Butyrolactone; alcohols such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Ethers such as furane; nitriles such as acetonitrile; amides such as dimethylformamide; and the like. These may be used singly or in combination. Particularly, a mixed solvent of cyclic carbonate and chain carbonate can be preferably used. As the electrolyte, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolytic solution, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used. Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and LiI.

Best Mode for Carrying Out the Invention Hereinafter, the function and effect of the present invention will be described in more detail through specific examples of the present invention. It is to be understood, however, that these embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention.

<Examples>

Example 1

Carbon core silicon oxide composites were prepared by forming carbon nanocores in sepiolite pores, which are porous inorganic metal oxides having fibrous nanopores, followed by acid treatment and high temperature reduction calcination.

First, sepiolite was dispersed in water and sucrose, an organic functional group, was mixed. The sepiolite composition has Mg ₄ Si ₆ O ₁₅ (OH) ₂ .6H ₂ O and Orthorhombic 2 / m 2 / m 2 / m structure. The sepiolite has a rod-like shape, and fibrous nanopores are formed along the particle axis within the particle, and the pore size is about 3.6 Å × 10.6 Å, the particle size is 20 nm to 40 nm in average diameter, To 8 mu m. At this time, the sepiolite particle shape is as shown in Fig. 2 (a).

Here, the weight of the sucrose was 60 wt% based on the weight of the sepiolite. The mixed sepiolite / sucrose mixed solution was dried in an oven and reduced and sintered in a N ₂ atmosphere at 700 ° C. for 5 hours through a first heat treatment process. The sintered carbon / sepiolite composite was impregnated with acid solution to remove Mg and Al components and then sintered at 900 ° C for 5 hours in a secondary heat treatment process.

Example 2

A silicon oxide / carbon core composite was prepared in the same manner as in Example 1, except that the second heat treatment step was sintered at 1,100 ° C.

Comparative Example 1

A sepiolite product, which is a porous inorganic metal oxide which is not subjected to a separate sintering process without forming a carbon core layer using sucrose, was prepared.

Comparative Example 2

A graphite product (graphite), which has been used as an anode active material for a lithium secondary battery, was prepared.

<Test Example>

The properties of the silicon oxide / carbon core composite of Examples 1 and 2, the sepiolite of Comparative Example 1 and the graphite product of Comparative Example 2 were evaluated as follows.

Transmission Electron Microscope (TEM) analysis

In order to identify carbon nanofibers present in the silicon oxide / carbon core composite material prepared in Example 1, all metal components other than carbon were removed through treatment with HCl and HF solutions, The shape analysis is shown in Fig. 2 (c). The carbon nanofibers present in the silicon oxide / carbon core composite have a shape having a thickness of 1 nm or less and aggregated along the texture.

X-ray diffraction (XRD, X-ray diffraction) analysis

The results of crystal analysis of the silicon oxide / carbon core composite prepared in Example 1 through XRD are shown in FIG. 3, and the results of sepiolite analysis of Comparative Example 1 are also shown. Here, unlike the sepiolite of Comparative Example 1, the carbon core silicon oxide composite of Example 1 has an amorphous structure in general and a crystal peak related to SiO ₂ exists at ₂ ? = 26-27 and 27-28 .

Electrochemical charge / discharge evaluation

Using the negative electrode active material prepared according to Example 1 and Comparative Example 2, electrochemical characteristics were evaluated by charging and discharging evaluation as a lithium secondary battery negative electrode active material in the following manner.

The slurry was prepared by using the prepared anode active material (Graphite, Sepiolite / C_700 ° C, Sepiolite / C_900 ° C), a conductive agent, a binder and NMP, casting the Cu current collector, Respectively.

The electrode composition was 75: 5: 20 in the order of the negative electrode active material: conductive agent: binder, using carbon black as the conductive agent and PVdF as the binder. Lithium was used as the counter electrode, and the electrolyte used was 1.2M LiPF6 EC / DMC = 5/5 (by volume) composition.

Stacking of a lithium counter electrode, a cathode electrode, and a PE separator, a coin cell containing an electrolytic solution was prepared, and charging and discharging were evaluated.

The charge / discharge evaluation was 0.01V - 1.5V vs. 3 times at each rate from 0.05 C to 1 C based on 600 mAh / g. Li / Li &lt; ⁺ &gt;

On the other hand, electrochemical charge / discharge evaluation results of the carbon core silicon oxide composites prepared in Examples 1 and 2 are shown in FIGS. 5 and 6. The charge / discharge evaluation of the graphite negative electrode active material of Comparative Example 2 proceeded in the same potential region and is shown in Fig. 5 (a). As shown in Figs. 5 (b) and 5 (c), the 0.05 C reversible capacities of the carbon core silicon oxide composite negative electrode active materials of Examples 1 and 2 were 540 mAh / g and 620 mAh / 2 graphite anode active material is about twice as high as the reversible capacity of 320 mAh / g. In FIG. 6, the reversible capacity of the silicon oxide composite of Example 2 is shown, and the reversible capacity at 1 C is 580 mAh / g or more, which is excellent at 93% or more of the reversible capacity at 0.05 C . In addition, the rate of reversible capacity retention according to cycles at each rate is also seen to be very good.

Therefore, it can be seen that the silicon oxide / carbon composite anode active material of Example 1 has a high capacity characteristic higher than the reversible capacity of the graphite anode active material of Comparative Example 2 used in the prior art. In particular, from the results of the XRD analysis of FIG. 3, it can be seen that amorphous silicon oxide of carbon core was produced by high-temperature reduction calcination and removal of dissimilar metals, thereby increasing electrochemical activity and increasing charge / discharge capacity.

Claims (20)

A negative electrode active material for a lithium secondary battery, which is a silicon oxide composite comprising a fibrous carbon core layer. The method according to claim 1,
Wherein the silicon oxide composite has a rod-like shape. The method according to claim 1,
Wherein the silicon oxide composite has an average diameter of 5 to 100 nm and a length of 100 nm to 20 占 퐉 for a negative electrode active material for a lithium secondary battery. The method according to claim 1,
Wherein the silicon oxide composite comprises a component represented by SiO _x (where 0 <x? 2). The method according to claim 1,
The silicon oxide has a crystal peak at a crystal peak at 2? = 26-27 and 27-28 and a crystal peak at 2? (Two theta) = 21-22 and 35-36 in the analysis of XRD crystal by the anode active material for a lithium secondary battery . The method of claim 1, wherein
Wherein the carbon core layer has an average diameter of 2 nm or less. The method of claim 1, wherein
Wherein the negative electrode active material comprises carbon in an amount of 1 to 10 wt% based on the total weight of the negative electrode active material. Mixing a porous metal oxide having fibrous pores and containing a silicate component with an organic compound containing a hydrocarbon functional group having 1 to 18 carbon atoms;
Subjecting the mixture to a first heat treatment at 300 ° C or higher to form a carbon core;
Acid treatment of the composite on which the carbon core is formed; And
Subjecting the acid-treated carbon core composite to a secondary heat treatment at 500 ° C or higher;
And a negative electrode active material for a lithium secondary battery. 9. The method of claim 8,
Wherein the porous metal oxide comprises at least one metal component selected from the group consisting of Si, Mg, Sn, and Al. 9. The method of claim 8,
Wherein the porous metal oxide is selected from the group consisting of SiO _x (0 <x ≦ 2), SnO _{x '} (0 ≦ _x ≦ 2), MgO _{x "} (0 ≦ _x" ≦ 2) By weight based on the weight of the negative electrode active material. 9. The method of claim 8,
Wherein the porous metal oxide has a composition represented by the following formula (1): < EMI ID =
[Chemical Formula 1]
Mg _a M _b Si _c O _d
In Formula 1,
M is selected from the group consisting of Al, K, Ca, Be, and combinations thereof,
a, b, c, and d satisfy 0.1 <a≤4 0.01 <b <0.5, 0.1 <c≤10, and d≥2c. 9. The method of claim 8,
Wherein the porous metal oxide is selected from the group consisting of sepiolite, palygorskite, and mixtures thereof. 9. The method of claim 8,
Wherein the porous metal oxide has an average diameter of 5 to 100 nm and a length of 100 nm to 20 탆. 9. The method of claim 8,
Wherein the porous metal oxide has a specific surface area of 30 to 500 m ² / g. 9. The method of claim 8,
The porous metal oxide has a main peak between 2? = 10-11, 13-15, 27-28, 30-31, 34.5-35.5, 36.5-37.5, and 39-40 in the XRD crystal analysis A method for producing an anode active material for lithium secondary batteries. 9. The method of claim 8,
Wherein the hydrocarbon functional group is selected from the group consisting of a methyl group, an ethyl group, a butyl group, and combinations thereof. 9. The method of claim 8,
Wherein the organic compound is added in an amount of 10 to 400 parts by weight based on 100 parts by weight of the porous metal oxide. 9. The method of claim 8,
Wherein the first heat treatment step is performed at a temperature of 400 ° C to 900 ° C. 9. The method of claim 8,
Wherein the second heat treatment step is performed at 700 ° C to 1,500 ° C. A lithium secondary battery comprising: a cathode including a cathode active material; a cathode including the anode active material; and an electrolyte, wherein the anode active material is the anode active material according to any one of claims 1 to 7.

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