KR20100035372A - Negative active material for rechargeable lithium battery, method of preparing same and rechargeable lithium battery comprising same - Google Patents

Abstract

PURPOSE: A negative active material for a rechargeable lithium battery containing mesopores is provided to ensure excellent cycle lifetime characteristic and high efficiency. CONSTITUTION: A negative active material for a rechargeable lithium battery comprises a core including metal and a carbon layer formed on the core, and includes nanowire having mesopores. The mesopores are the space arranged between nanowires in a constant interval. A method for preparing the negative active material comprises the steps of: mixing inorganic oxide template and metal precursors; heat-treating the mixture; and removing the inorganic oxide template.

Description

A negative electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same.

The present invention relates to a negative electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. More particularly, the negative electrode active material for a lithium secondary battery having excellent cycle life characteristics and high rate characteristics, a method for preparing the same, and a lithium secondary including the same It relates to a battery.

A battery generates power by using a material capable of electrochemical reactions at a positive electrode and a negative electrode. A typical example of such a battery is a lithium secondary battery that generates electric energy by a change in chemical potential when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

A lithium composite metal compound is used as a positive electrode active material of a lithium secondary battery, and examples thereof include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1), and LiMnO ₂ . Composite metal oxides are being studied.

As the negative electrode active material, various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of inserting / desorbing lithium have been applied. The graphite of the carbon series has a low discharge voltage of -0.2V compared to lithium, and the battery using this negative electrode active material exhibits a high discharge voltage of 3.6V, which provides an advantage in terms of energy density of the lithium battery and also has excellent reversibility in lithium secondary. It is most widely used to ensure the long life of the battery. However, the graphite active material has a problem of low capacity in terms of energy density per unit volume of the electrode plate due to the low graphite density (theoretical density of 2.2 g / cc) in the production of the electrode plate, and side reaction with the organic electrolyte used at high discharge voltage is likely to occur. Risk of fire or explosion due to battery malfunction or overcharging.

Accordingly, metal-based active materials such as Si have been studied. Si metal-based negative active materials are known to form Li _4.4 Si to exhibit a high lithium capacity of about 4200 mAh / g. However, before and after the reaction with lithium, that is, when the charge and discharge causes a volume change of more than 300%. As a result, pulverization of the negative electrode active material occurs, a phenomenon in which the finely divided particles are aggregated, and a phenomenon in which the negative electrode active material is detached from the current collector is caused. This electrical dropout significantly reduces the capacity retention of the cell. Therefore, in order to suppress the volume change of the metal-based negative electrode active material, there have been many studies for preparing carbon and Si nanoparticle composites and using them as negative electrode active materials. Since carbon acts as an electrical conductor in the carbon and Si nanoparticle composites, capacity retention was improved. However, in order to obtain a relatively good capacity retention rate, there is a problem in that the capacity is reduced as the carbon content in the composite must be over 50% by weight, and thus the capacity after 50 cycles is lower than 1500mAh / g even when carbon is included in an excessive amount. There was.

As another method for suppressing the volume change, there have been some studies on the one-dimensional shape silicon nanowires as the negative electrode active material. Morales, A. M .; Lieber, C.M. Si nanowires produced by the laser ablation system described in Science, 1998, 279, 208 have a wire diameter of about 10-30 nm. However, the one-time discharge and charge capacity of the nanowires is about 1300 mAh / g and 900 mAh / g, respectively.

Another method reported Si nanowires with a diameter of less than 50 nm grown without vapor solid template-free (VS) template (Ref. 12). This Si nanowire exhibited a reversible capacity of about 2000 mAh / g at 2 V to 0 V and 0.2 C with no capacity reduction up to 10 cycles. Semiconductor nanowires grown by synthesis without vapor-liquid-solid (VLS), solution-liquid solid (SLS) and no template have been reported (Ref. 13-21). .

However, even nanowires produced in this way have been difficult to exhibit sufficient capacity retention.

An object of the present invention for solving the above problems is to provide an anode active material for a lithium secondary battery excellent in cycle life characteristics.

Another object of the present invention is to provide a method for producing the negative electrode active material.

Still another object of the present invention is to provide a lithium secondary battery including the negative electrode active material.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A first embodiment of the present invention for achieving the above object comprises a core including a metal and a surface layer comprising a carbon-based material formed on the core, a negative electrode active material for a lithium secondary battery comprising nanowires having mesopores to provide.

A second embodiment of the present invention comprises the steps of mixing the inorganic oxide template and the precursor material of the metal; It provides a method for producing a negative electrode active material for a lithium secondary battery comprising the step of performing the step of heat-treating the mixture and the step of removing the inorganic oxide template three or more times.

A third embodiment of the present invention provides a lithium secondary battery including a cathode including the cathode active material, an anode including an anode active material, and an electrolyte.

The negative electrode active material of the present invention is excellent in cycle life characteristics and high rate characteristics.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The negative electrode active material for a lithium secondary battery according to the first embodiment of the present invention includes a core including a metal and a carbon layer formed on the core, and include nanowires having mesopores.

In the present specification, mesopores refer to a space in which nanowires and nanowires are arranged at random intervals, that is, an empty space channel formed between nanowires and nanowires. This arbitrary spacing is also referred to as pore diameter.

These mesopores can act as a buffer layer to the volume change generated during the charge and discharge of the negative electrode active material, thereby suppressing the volume change. In addition, in the present invention, the mesopores are preferably arranged so that the electrolyte is more uniformly diffused on the surface in contact with the surface of the cathode. The "constantly arranged" means that the nanowires and mesopores are regularly arranged.

More preferably, the cathode may include a nanowire having mesopores in which the space between the nanowire and the nanowire is arranged very regularly.

The mesopores of the present invention are schematically shown in FIG. 1. As shown in FIG. 1, the mesopores 1 refer to a space between the first nanowires a and the second nanowires b arranged at random intervals, that is, adjacent to each other.

It is preferable that the mesopores have an average pore diameter of 2 to 20 nm, and more preferably have an average pore diameter of 2 to 5 nm. If the mesopores have an average pore diameter of less than 2 nm, the buffering effect at the time of volume expansion / contraction of the active material is not preferable, and if it exceeds 20 nm, the synthesis is not easy and not preferable.

In the core including the metal, the metal may be preferably selected from the group consisting of Si, Sn, and combinations thereof.

The thickness of the carbon layer is preferably 0.5 to 5 nm, more preferably 0.5 to 2 nm. When the thickness of the carbon layer is thinner than 0.5 nm, there is a problem that the high rate characteristic is lowered, and when the thickness of the carbon layer is thicker than 5 nm, there is a problem in capacity reduction, which is not preferable.

The carbon layer preferably contains irregular carbon, so that suitable electrical conductivity can be obtained. Particularly, the Raman integral intensity D / G (I (1357) / I (1582)) is 0.1. To 1.5 is preferable, and it is more preferable that it is 1 to 1.5. When the D / G value which is the Raman integral strength ratio of a carbon layer is contained in the said range, desired electrical conductivity can be obtained and it is preferable.

In the negative electrode active material of the present invention, the content of carbon was 5 to 10% by weight based on the total weight of the negative electrode active material. If the carbon content is included in this range, it is preferable to obtain the desired capacity and high rate properties.

It is preferable that the said nanowire has a diameter of 3-20 nm, and it is more preferable to have a diameter of 5-10 nm. When the diameter of the nanowire is within the above range, there is no fear that the shape of the nanowire may be destroyed even when the active material is expanded or contracted in volume.

The nanowires preferably have as large a specific surface area as possible, preferably having a specific surface area of 30 to 200 m ² / g, and more preferably having a specific surface area of 70 to 180 m ² / g. If the specific surface area of the negative electrode active material of the nanowire is less than 30 m ² / g, the high rate characteristic is deteriorated, and it is not preferable. If the specific surface area is more than 200 m ² / g, the irreversible capacity is increased due to side reaction with excessive electrolyte, which is undesirable.

A second embodiment of the present invention relates to a method of manufacturing the negative electrode active material, which method comprises mixing an inorganic oxide mold and a precursor material of a metal, heat treating the mixture and removing the inorganic oxide mold. It includes a step of performing three or more times, preferably three to five times a process containing. Hereinafter, a manufacturing method will be described in detail with reference to FIG. 2.

Mixing the inorganic oxide template and the precursor material of the metal (S1: mixing step)

As the inorganic oxide mold, a mold made of silica, alumina, titania, ceria, or the like may be used. Among them, a mold made of silica, which can be easily dissolved and removed by a weakly acidic solution, is more preferable. The inorganic oxide template is preferably two-dimensional, has a hexagonal symmetry (hexagonal symmetry), it is preferable to have a p6mm symmetry of the structure in which the cylindrical pores are arranged in a systematically parallel.

Generally the said inorganic oxide mold may use a commercially available thing, and may be manufactured and used by the following process.

Preparing a mixed solution by adding an acid to a polymer-containing solution and heating and then adding an alcohol, or preparing an mixed solution by adding an acid to a mixture containing a polymer and an alcohol and heating the inorganic oxide to the mixed solution. It can be prepared by a manufacturing method comprising the step of adding a raw material to react and then drying.

As the polymer, a block copolymer of ethylene oxide (EO) and propylene oxide (PO) may be used, and specifically, a triple block copolymer of PEO-PPO-PEO (Pluronic polymer, manufactured by Aldrich) may be used. .

The acid may be selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, and mixtures thereof.

In addition, when the acid is added, a solvent may be added together, and water is generally used as a solvent, but is not limited thereto. In addition, the solvent in the polymer-containing solution is also generally used, but is not limited thereto.

The acid is preferably used in 20 to 60 parts by weight, more preferably 30 to 50 parts by weight based on 100 parts by weight of the polymer. When the acid is used within the range, the inorganic oxide mold according to the present invention can be easily formed.

It is preferable that the said heating process is performed at 40-200 degreeC, More preferably, it is performed at 40-150 degreeC. Within the above temperature range, the inorganic oxide mold according to the present invention can be easily formed.

The alcohol serves as a solvent, and as the alcohol, lower alcohols having 1 to 6 carbon atoms may be used, and n-butanol may be preferably used.

Subsequently, an inorganic oxide raw material is added to the mixed solution, followed by reaction, followed by drying to prepare an inorganic oxide mold. The reaction process is preferably carried out by a hydrothermal treatment process. The inorganic oxide raw material may be used a metal nitrate, a metal chloride, a metal acetate, a metal hydroxide or a mixture of one or more thereof. Representative examples of the inorganic oxide raw material may include, but are not limited to, tetraethoxysilane. Examples of the metal include Si, Sn, and combinations thereof.

It is preferable to use a precursor material of the metal selected from the group consisting of Si, Sn, or a combination thereof which is organic functional group-capped. As said organic functional group, a methyl group, an ethyl group, a butyl group, or a combination thereof is preferable. Since the process of protecting the organic functional group is a well known process in the art, a detailed description thereof will be omitted, but it can be easily understood by those skilled in the art.

The precursor material of the metal is preferably used in an amount of 50 to 100 parts by weight, more preferably 80 to 100 parts by weight based on 100 parts by weight of the inorganic oxide mold. Using the precursor material of the metal in the above range can more easily prepare the negative electrode active material according to the present invention.

The mixture of the obtained inorganic oxide mold and the precursor material of the metal is heat treated (heat treatment step), and then the inorganic oxide mold is removed (S2: mold removing step). It is preferable to perform the said heat processing process at 700-1000 degreeC, and it is more preferable to carry out at 800-900 degreeC. If the temperature at the time of heat treatment is less than 700 ℃ there is a problem of low crystallinity of the carbon layer is not preferable, and if it exceeds 1000 ℃ it is not preferable because the pores collapse. This heat treatment step is preferably performed in a vacuum atmosphere because it can prevent side reactions from occurring. According to the heat treatment process, the organic functional group in the precursor material of the metal is decomposed to leave only carbon, thereby forming a carbon layer on the metal surface. As the carbon layer is formed, direct reaction of the metal core and the inorganic oxide can be suppressed, and high temperature heat treatment is possible, and an inorganic oxide, which is generally difficult to use as a mold at a high temperature, can be used as a mold.

The step of removing the inorganic oxide template is preferably performed by adding a heat-treated product to a basic material such as sodium hydroxide, potassium hydroxide or the like or an acidic material such as HF. The addition process is suitably carried out for a suitable time, for example 2 to 3 hours, during which the inorganic oxide template can be removed. The inorganic oxide template is removed from the heat treated product in this way.

The process including the mixing step, heat treatment step and mold removal step described above is carried out three or more times, preferably three to five times. When the mixing step, the heat treatment step and the mold removing step are performed less than three times, the negative electrode active material having the desired nanowire-shaped mesopores cannot be obtained. In addition, since the desired negative electrode active material is obtained by performing the above-mentioned process five times, it is not necessary to carry out any more. When the mixing step, the heat treatment step and the mold removing step are performed three or more times, preferably three to five times, nanowires including a core including a metal and a carbon layer formed on the core and having mesopores are formed. A negative electrode active material of the present invention containing is prepared.

The negative electrode active material of the present invention can be usefully used for the negative electrode of an electrochemical cell such as a lithium secondary battery. The lithium secondary battery includes a cathode and an electrolyte including a cathode active material together with the anode.

The negative electrode is prepared by mixing a negative electrode active material according to the present invention, a conductive material, a binder and a solvent to prepare a negative electrode active material composition, and then coating and drying the copper active material directly on a current collector. Alternatively, the negative electrode active material composition may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on an aluminum current collector.

The conductive material is carbon black, graphite, metal powder, the binder is vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. In addition, N-methylpyrrolidone, acetone, tetrahydrofuran, decane, etc. are used as a solvent. In this case, the content of the positive electrode active material, the conductive material, the binder, and the solvent is used at a level commonly used in a lithium secondary battery.

Like the negative electrode, the positive electrode is mixed with a positive electrode active material, a binder, and a solvent to prepare an anode active material composition, which is directly coated on an aluminum current collector or cast on a separate support and peeled from the support to a copper current collector. It is prepared by lamination. At this time, the positive electrode 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, the cathode active material is a metal oxide, a lithium composite metal oxide, a lithium composite metal sulfide, a lithium composite metal nitride, or the like. do.

The separator may be used as long as it is commonly used in lithium secondary batteries. For example, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used, and a polyethylene / polypropylene two-layer separator, It goes without saying that a mixed multilayer film such as polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt is used.

Although the solvent of the said non-aqueous electrolyte is not specifically limited, Chain carbonate methyl acetate, acetic acid, such as cyclic carbonate dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, such as ethylene carbonate, a propylene carbonate, butylene carbonate, vinylene carbonate Esters such as ethyl, propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyl Amides, such as nitriles, dimethylformamide, such as ethers, acetonitrile, such as tetrahydrofuran, etc. can be used. These can be used individually or in combination of two or more. In particular, a mixed solvent of a cyclic carbonate and a linear carbonate can be preferably used.

As the electrolyte, a gel polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

The lithium salt is 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 , One selected from the group consisting of LiCl and LiI is possible.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are preferred examples of the present invention, and the present invention is not limited by the following examples.

(Example 1)

* Preparation of Si precursor protected with butyl group

40 ml of SiCl ₄ (purity 99.99%, Aldrich) and hexane (purity 99.9%, Aldrich) were thoroughly mixed in an inert atmosphere, and the mixture was stirred at room temperature for 4 hours. Subsequently, 60 ml of n-butyllithium, a Grignard reagent, was added to the obtained liquid mixture. At this time, n-butyllithium, which is a Grignard reagent, reacted with SiCl ₄ as in Scheme 1 to form a Si precursor (Si-C ₄ H ₉ ) protected with a butyl group. Subsequently, the obtained Si liquid protected with a butyl group was washed six times with water to remove LiCl to obtain only a Si precursor (Si-C ₄ H ₉ ) protected with a butyl group.

Scheme 1

LiC ₄ H ₉ + SiCl ₄ → Si-C ₄ H ₉ + LiCl

* Silica Mold Manufacturing

30 g of Pluronic 123 (EO ₂₀ PO ₇₀ EO ₂₀ , weight average molecular weight 5800, Aldrich) and n-butanol (purity 99.9%, Aldrich) were dissolved in 2000 g of distilled water and 60 g of 30 wt% HCl aqueous solution with stirring at 40 ° C. It was. 45 g of tetraethoxysilane was added to the liquid mixture while stirring the liquid mixture at 40 ° C. The resulting mixture was left stirring at 40 ° C. for 24 hours and then hydrothermal treated at 100 ° C. for 24 hours. The resulting product was then calcined at 500 ° C. for 3 hours to prepare a hexagonal p6mm SBA-15 silica template.

* Manufacture of negative electrode active material

Using the butyl group-protected Si precursor and SBA-15 silica template prepared according to the above process to prepare a negative electrode active material in the following process.

2 g of Si precursor protected with butyl group were mixed with 0.5 g of SBA-15 silica template. The mixture was calcined at 900 ° C. and the calcined product was immersed in HF for 2 hours to remove the silica template.

Using the obtained product, the process of mixing with the said silica mold, baking at 900 degreeC, and removing a silica template with HF was further performed 3 times, and the negative electrode active material was manufactured. The prepared negative active material includes a Si core and a carbon layer formed on the core, and exhibited a nanowire shape including mesopores. At this time, the mesopores have an average pore diameter of 2.3nm, the thickness of the carbon layer was 0.5nm. In addition, the nanowires had a diameter of 6.5 nm and a specific surface area of 154 m ² / g.

(Reference Example 1)

The negative electrode active material was manufactured by the following process using the Si precursor protected by the butyl group used in Example 1 and the SBA-15 silica template.

2 g of Si precursor protected with butyl group were mixed with 0.5 g of SBA-15 silica template. The mixture was calcined at 900 ° C. and the silica template was removed using HF to prepare a negative electrode active material. The prepared negative active material was in the form of a nanorod.

(Comparative Example 1)

Si powder (Sigma Aldrich, 20 micron) and natural graphite were reacted at 800 rpm for 8 hours using a ball milling process to prepare carbon coated Si nanoparticles, which were used as a negative electrode active material. At this time, the mixing ratio of carbon and Si was 44:56 weight%.

* TEM photo

The negative active material prepared according to the Reference Example 1 and Example 1 was deposited on a carbon-coated copper grid to prepare TEM samples, respectively, and measured TEM photographs.

A TEM image of the negative active material prepared according to Reference Example 1 is shown in FIG. 3A, and a magnification thereof 100,000 times is shown in FIG. 3B.

In addition, the TEM photograph of the negative electrode active material prepared according to Example 1 is shown in Figure 3d.

As shown in Figure 3a, it can be seen that the negative electrode active material of Reference Example 1 is not a complete nanowire form, but a nanorod form. In addition, since the shape of the (111) lattice fringe in FIG. 3B is shown, and the selected area diffraction pattern (SADP) result shown in FIG. 3C shows the formation of the diamond cubic Si phase, it can be seen that it is not a perfect nanowire. have. From this result, it can be seen that the nanorods are obtained in the case where the mixing with the silica mold, firing at 900 ° C., and removing the silica mold using HF is performed only once.

On the other hand, in Example 1 in which the silica mold was mixed with the silica mold, calcined at 900 ° C., and the silica mold was removed four times, as shown in FIG. 4A, the fully grown nanowire was observed. It became. In FIG. 4A the bright lines represent the spacings (channels), or mesopores, between the nanowires and the nanowires, and the dark lines represent the nanowires comprising the Si core and the carbon layer formed thereon. As shown in FIG. 4B, which is an enlarged view of 100,000 times of FIG. 4A, a very thin irregular carbon layer was observed on the surface of the negative electrode active material, and the carbon content of the negative electrode active material was 6 wt% based on CHS analysis. It was.

In addition, in Example 1, surface enhanced Raman spectral analysis was measured to determine the degree of irregularity and crystallite of the formed carbon layer. Lamax spectrum analysis was measured using a JASCO, NRS-3000 instrument and 633 nm laser excitation, using a 20x optical lens with low laser power density and 30 seconds exposure time to avoid laser thermal effects. Moreover, the laser spot diameter which reached the sample was about 2 micrometers, and the laser output was 1 mW. Spectra were recorded at 2 cm ⁻¹ resolution from 3000 to 50 cm ⁻¹ . The results are shown in Figure 4c. The peak mode at 1582 cm ⁻¹ , which corresponds to the G mode, is due to the in-plane of carbon displacement strongly coupled to the hexagonal sheet, which means that the layers are regularly well arranged. . When a disorder is introduced into the carbon material, the band appearing in the Raman spectrum is broadened, and a band called 'disorder-induced' or 'D mode' is generated near 1357 cm ⁻¹ . Raman integral intensity ratio D / G (I (1357) / I (1582)) represents the degree of carbonization, and the lower the intensity ratio, the higher the degree of carbonization.

As a result of the measurement, the value of G (I (1357) / I (1582)) of the carbon layer formed on the Si nanowire was 1.45, which is much larger than the value of 0.09 for ordered graphite, indicating that an irregular carbon layer was formed. Can be.

* X-ray diffraction measurement

5A shows a low angle XRD pattern of the negative active material prepared in Example 1, and a high angle XRD pattern is shown in FIG. 5B. The two crystal peaks labeled (100) and (111) shown in the bottom angle of FIG. 5A represent a well-aligned, hexagonal mesoporous structure with a space group of p6 mm . In addition, the strong (100) peak at the elevation corresponds to a d-spacing of 8.8 ± 0.1 nm, indicating the presence of Si nanocrystals. In addition, the crystal size of the negative electrode active material including the Si core calculated using the Scherrer equation and the carbon layer formed on the core was about 6.5 nm.

* BET surface area

In order to determine the surface area of the negative electrode active material prepared in Example 1, a nitrogen isothermal adsorption experiment was performed, and the results are shown in FIG. 6, which was calculated using the BET equation (Brunauer-Emmett-Teller). The BET surface area was 74 m ² / g. The nitrogen adsorption-desorption isotherm of the negative electrode active material shown in FIG. 6 was type IV with a sharp capillary condensation step with an H1 hysteresis loop at high relative pressures. This result indicates that the negative electrode active material prepared in Example 1 has pores having a uniform size, and that the mesopores are formed between the nanowires and the nanowires.

In addition, the pore size of the anode active material prepared according to Example 1 was measured using the BarrettJoynerHalenda method at 77K using a Micrometrics ASAP 2020 system device, and the results are shown in FIG. 7. As shown in Figure 7, it can be seen that the mesopores formed in the negative electrode active material are mostly about 3nm.

(Example 2)

A negative electrode active material slurry was prepared by mixing the negative electrode active material, the super P conductive material, and the polyvinylidene fluoride binder prepared according to Example 1 in an N-methyl pyrrolidone solvent at a weight ratio of 80:10:10. The negative electrode active material slurry was coated on a 50 μm thick copper foil, dried at 150 ° C. for 20 minutes, and then roll-pressed to prepare a negative electrode.

At this time, the loading amount of the nanowire negative electrode active material in the prepared negative electrode was 17mg per area of the negative electrode 1cm2.

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

(Comparative Example 2)

Except for using the negative electrode active material prepared according to Comparative Example 1 was carried out in the same manner as in Example 2.

* Charging / discharging characteristics

The half-cell prepared in Example 2 was charged and discharged at 80 ° C. at 1.5 to 0 V at 0.2 C (= 600 mAh / g), thereby showing charge and discharge characteristics at 1, 30, 60 and 80 times. Shown in In Figure 8, 1, 30, 60 and 80 means the number of cycles. As a result, in one cycle, the discharge and charge capacities were 3664 mAh / g and 3163 mAh / g, respectively, and the initial coulombic efficiency was 86%. In addition, 15% of the irreversible capacity calculated from the result shown in FIG.

Coulomb efficiency and cycle life characteristics

The half-cells prepared in Example 2 and Comparative Example 2 were charged and discharged at 0.2 C (= 600 mAh / g) 80 times at 1.5 to 0 V, and the charging capacity and the coulomb efficiency according to the charging and discharging are shown in FIG. 9. . As shown in FIG. 9, after one charge and discharge, the coulombic efficiency remained relatively stable for almost 80 cycles (almost 100%), indicating that the surface layer formed remained intact. After 80 cycles, the capacity was 2738 mAh / g and the capacity retention was 87%.

Rate property

In FIG. 10, the half-cell of Example 2 was charged and discharged at 0.2C, 0.5C, 1C, and 2C at 1.5 to 0V, respectively, to show measured characteristic results for each rate. As shown in FIG. 10, the charging capacities were 0.5C 2954 mAh / g, 1C 2757 mAh / g, and 2C 2462 mAh / g, respectively, and the ratio of 2C charging capacity to 0.2C charging capacity was 78%.

The half cell of Comparative Example 2 was charged and discharged at 0.05C, 0.2C and 1C once at 1.5 to 0V, respectively, and the characteristics for each rate were measured. As a result, the charging capacity at 0.05C was 3124mAh / g, but the charging capacity was rather high, but it was about 2500mAh / g at 0.2C and about 2000mAh / g at 1C. have.

These results indicate that the negative electrode active material of Example 1 used in Example 2 contains mesopores, and as the electrolyte is filled in the mesopores, the area of contact with the electrolyte is large, so that lithium can be actively inserted and removed. I think because. In addition, regularly ordered mesopores enable the electrolyte to be uniformly diffused, and a thin wall of uniform dimensions is thought to shorten the lithium ion and electron paths during charge and discharge and thus improve high rate characteristics.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

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1 is a view for explaining the mesopores of the present invention.

2 is a schematic view showing a step of producing a negative electrode active material for a lithium secondary battery of the present invention.

Figure 3a is a TEM photograph of the nanorods obtained after performing a single mixing, firing and mold removal process of the metal precursor material and the mold in Reference Example 1.

3B is a 100,000 times magnification of FIG. 3A.

3C is a graph showing the SADP results of FIG. 3B.

4A is a TEM photograph of a nanowire negative electrode active material obtained after four times of mixing, firing, and removing a mold of a metal precursor material and a mold in Example 1 of the present invention.

4B is a 100,000 times magnification of FIG. 4B.

Figure 4c is a graph showing the Raman spectrum results of the negative electrode active material prepared according to Example 1 of the present invention.

Figure 5a is a graph showing the X-ray diffraction pattern at the low angle of the negative electrode active material prepared in Example 1 of the present invention.

Figure 5b is a graph showing the X-ray diffraction pattern at the elevation of the negative electrode active material prepared in Example 1 of the present invention.

Figure 6 is a graph showing the nitrogen isothermal adsorption experiment results of the negative electrode active material prepared in Example 1 of the present invention.

Figure 7 is a graph showing the pore size distribution of the negative electrode active material prepared in Example 1 of the present invention.

8 is a graph showing charge and discharge characteristics of the cycle number of a coin-type half battery manufactured using the negative electrode active material prepared in Example 1 of the present invention.

FIG. 9 is a graph showing charge capacity and coulombic efficiency versus cycle number of a coin-type half battery manufactured using the negative electrode active material prepared in Example 1 of the present invention. FIG.

10 is a graph showing charge and discharge characteristics at 0.2C, 0.5C, 1C and 2C of the coin-type half-cell prepared using the negative electrode active material prepared in Example 1 of the present invention.

Claims (20)

A nanowire comprising a core comprising a metal and a carbon layer formed on the core, the nanowires having mesopores Anode active material for lithium secondary battery. The method of claim 1, The mesopores are spaces arranged at random intervals between the nanowires and the nanowires. The method of claim 1, The negative active material for a lithium secondary battery, wherein the mesopores are regularly arranged. The method of claim 1, Mesopores are negative active material for a lithium secondary battery having an average pore diameter of 2 to 20nm. The method of claim 1, The metal is Si, Sn and a negative electrode active material for a lithium secondary battery is selected from the group consisting of a combination thereof. The method of claim 1, The carbon layer is a lithium secondary battery negative electrode active material containing irregular carbon (disordered carbon). The method of claim 6, A cathode active material for a lithium secondary battery, wherein D / G (I (1357) / I (1582)), which is a Raman integral strength ratio of the carbon layer, is 0.1 to 1.5. The method of claim 1, The thickness of the carbon layer is 0.5 to 5nm negative electrode active material for a lithium secondary battery. The method of claim 1, The negative electrode active material is a lithium secondary battery negative electrode active material containing 5 to 10% by weight relative to the total weight. The method of claim 1, The nanowire is a negative active material for a lithium secondary battery having a diameter of 3 to 20nm. The method of claim 1, The nanowires have a specific surface area of 30 to 200m ² / g negative electrode active material for a lithium secondary battery. Mixing the inorganic oxide template with the precursor material of the metal Heat treating the mixture and Removing the inorganic oxide template The manufacturing method of the negative electrode active material for lithium secondary batteries which performs the process containing 3 times or more. The method of claim 12, A method of manufacturing a negative active material for a lithium secondary battery, which performs the tablet three to five times including the mixing, heat treatment, and removing the mold. The method of claim 12, The inorganic oxide is silica, alumina, titania, ceria and a method for producing a negative active material for a lithium secondary battery that is selected from the group consisting of a mixture thereof. The method of claim 12, The precursor material of the metal is a method of producing a negative electrode active material for a lithium secondary battery is selected from the group consisting of Si, Sn or a combination thereof protected with an organic functional group. The method of claim 15, The organic functional group is a method for producing a negative electrode active material for a lithium secondary battery that is selected from the group consisting of methyl group, ethyl group, butyl group and combinations thereof. The method of claim 12, The precursor material of the metal is added to 50 to 100 parts by weight with respect to 100 parts by weight of the inorganic oxide mold manufacturing method of a negative electrode active material for a lithium secondary battery. The method of claim 12, The heat treatment step is to be carried out at 700 to 1000 ℃ manufacturing method of the negative electrode active material for lithium secondary batteries. The method of claim 12, The process of removing the inorganic oxide template is a method for producing a negative electrode active material for a lithium secondary battery that is carried out using a basic or acidic material. A positive electrode containing a positive electrode active material A negative electrode comprising a negative electrode active material and Contains an electrolyte, The negative electrode active material is a lithium secondary battery that is the negative electrode active material according to any one of claims 1 to 11.

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