KR20190059884A - An anode active material for lithium secondary battery and a method for manufacturing the same - Google Patents

Abstract

An embodiment of the present invention provides a method for manufacturing a negative electrode active material for a lithium secondary battery, which comprises following steps of: (a) dissolving a titanium precursor in a solvent and then adding a zero-valent metal powder to prepare a suspension; (b) subjecting the suspension to heat treatment at 100 to 300°C for 1 to 10 hours to produce titanium oxide containing oxygen vacancies; and (c) adding an acid to the suspension to remove the zero-valent metal powder. According to an aspect of the present invention, it is possible to improve electrochemical characteristics of the lithium secondary battery.

Description

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery and a method for manufacturing the negative active material for a lithium secondary battery,

The present invention relates to an anode active material for a lithium secondary battery and a method for preparing the same, and more particularly, to an electrochemical device which improves the electrochemical characteristics of a lithium secondary battery by imparting oxygen vacancy to titanium dioxide, which is one kind of anode active material for a lithium secondary battery. To a negative electrode active material for a lithium secondary battery and a method of manufacturing the same.

As the application fields of lithium secondary batteries such as portable electronic devices and electric vehicles are expanded, demand for high power, large capacity, and long life lithium secondary batteries is increasing. This leads to research and development of lithium secondary battery materials that satisfy high efficiency, low cost, and productivity.

The metal oxide used as a negative electrode active material for a lithium secondary battery has a high theoretical capacity and is environmentally friendly, but has a problem in that the capacity is rapidly reduced as the charge and discharge are repeated.

One of the most widely studied of these metal oxides, anatase titanium dioxide, has a problem of low electron conductivity because it forms a high band gap.

In order to solve this problem, there has been proposed a method of replacing oxygen atoms in titanium dioxide with other atoms, or a method of adjusting the electronic structure of titanium dioxide by adding oxygen atom vacancies. However, the method of replacing oxygen atoms in titanium dioxide with other atoms requires a high temperature of 500 ° C or higher and a high pressure of 20 bar or more, and it takes more than one day to synthesize, resulting in a very low synthesis efficiency.

It is an object of the present invention to provide an anode for a lithium secondary battery capable of improving the electrochemical characteristics of a lithium secondary battery by giving an oxygen atom blank to titanium oxide in an efficient manner in a short time, And a method for producing the active material.

An aspect of the present invention relates to a method for producing a suspension, comprising: (a) dissolving a titanium precursor in a solvent and adding a zero-valence metal powder to prepare a suspension; (b) subjecting the suspension to heat treatment at 100 to 300 ° C for 1 to 10 hours to produce titanium oxide containing oxygen vacancies; And (c) adding an acid to the suspension to remove the zero-valent metal powder. The present invention also provides a method for manufacturing a negative active material for a lithium secondary battery.

In one embodiment, the titanium precursor may be a trivalent titanium compound.

In one embodiment, the trivalent titanium compounds are _{TiCl 3, TiBr 3, Ti (} OH) Cl 2, Ti 2 (SO 4) 3, Ti (OAc) 3, Ti (3+) oxylate, Ti (NO ₃ ) ₃ , Ti (3+) lactate, and mixtures of two or more thereof.

In one embodiment, the solvent may be an alcohol.

In one embodiment, the alcohol may be selected from the group consisting of methanol, ethanol, isopropanol, n-butanol, amyl alcohol, cyclohexanol, and mixtures of two or more thereof.

In one embodiment, the standard reduction potential of the zero valent metal powder may be less than -0.56V.

In one embodiment, the zero-valent metal powder may be selected from the group consisting of zinc, magnesium, aluminum, and mixtures of two or more thereof.

In one embodiment, the titanium oxide may be represented by the following formula (1).

≪ Formula 1 >

TiO _2-x

In the above formula, 0 < x < 0.5.

Another aspect of the present invention provides a negative active material for a lithium secondary battery, which is produced by the above method.

Another aspect of the present invention provides a negative electrode for a lithium secondary battery, wherein the slurry including the negative electrode active material for a lithium secondary battery, a binder, and a conductive material is applied to a current collector.

In one embodiment, the binder is selected from the group consisting of polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene , Ethylene-propylene (EPDM) rubber, styrene-butylene rubber, fluorine rubber, and mixtures of two or more thereof.

In one embodiment, the content of the negative electrode active material for the lithium secondary battery may be 70 to 95% by weight based on the total weight of the slurry.

According to an aspect of the present invention, an oxygen vacancy can be imparted to titanium oxide synthesized by using a zero-valent metal powder having a standard reduction potential in a certain range during solvent thermo-synthesis of titanium oxide, The electrochemical characteristics of the lithium secondary battery can be improved when the negative active material is applied to the secondary battery.

It should be understood that the effects of the present invention are not limited to the effects described above, but include all effects that can be deduced from the description of the invention or the composition of the invention set forth in the claims.

FIG. 1 is a graph showing X-ray diffraction (XRD) analysis results of an anode active material for a lithium secondary battery according to an embodiment of the present invention and a comparative example (a), HR-Raman spectrum (b), X-ray photoelectron spectroscopy , X-ray photoelectron spectroscopy) analysis results ((c), (d));
FIG. 2 is a graph showing the FE-TEM, selected area electron diffraction (SAED), energy dispersive spectrometry (FEM), and the like of the negative electrode active material for a lithium secondary battery according to one embodiment of the present invention and one comparative example. EDS) results;
FIGS. 3 to 5 show the electrochemical characteristics of the negative electrode for a lithium secondary battery according to one embodiment of the present invention and one comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as " comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

An aspect of the present invention relates to a method for producing a suspension, comprising: (a) dissolving a titanium precursor in a solvent and adding a zero-valent metal powder to prepare a suspension; (b) subjecting the suspension to heat treatment at 100 to 300 ° C for 1 to 10 hours to produce titanium oxide containing oxygen vacancies; And (c) adding an acid to the suspension to remove the zero-valent metal powder. The present invention also provides a method for manufacturing a negative active material for a lithium secondary battery.

In the steps (a) and (b), a suspension is prepared by dissolving a titanium precursor in a solvent and adding a zero-valent metal powder, and the suspension is heat-treated at 100 to 300 ° C for 1 to 10 hours to remove oxygen atoms oxygen vacancy can be produced.

The titanium precursor may be a trivalent titanium compound, i.e., any compound containing trivalent titanium (Ti ³⁺ ), and the trivalent titanium compound may be dissolved in a solvent to release Ti ³⁺ ions into the solution May be any compound.

The trivalent titanium compound is, for _{example, TiCl 3, TiBr 3, Ti} (OH) Cl 2, Ti 2 (SO 4) 3, Ti (OAc) 3, Ti (3+) oxylate, Ti (NO ₃ ) ₃ , Ti (3+) lactate, and mixtures of two or more thereof, preferably TiCl ₃ or TiBr ₃ , but is not limited thereto.

The solvent may be alcohol and may be selected from the group consisting of methanol, ethanol, isopropanol, n-butanol, amyl alcohol, cyclohexanol and mixtures of two or more thereof, preferably isopropanol But is not limited thereto.

Anatase-type titanium oxide, for example, titanium dioxide synthesized from an arbitrary titanium precursor by conventional solvent thermal synthesis has a problem of low electron conductivity due to high band gap. On the other hand, the zero-valent metal powder used together with the titanium precursor in the step (a) may be obtained by adding oxygen vacancy to the titanium dioxide synthesized in the subsequent step (b) By switching to a sheet type, the electronic conductivity of titanium dioxide can be remarkably improved.

In general, the Ti ³⁺ released from the trivalent titanium compound is converted to tetravalent titanium (Ti ⁴⁺ ) upon solvent thermo-synthesis, that is, oxidized to produce anatase-type titanium dioxide, wherein Ti ³⁺ The standard reduction potential is -0.56V.

<Expression>

Ti ⁴⁺ + e - &gt; Ti ³⁺

On the other hand, in the step (a), a zero-valent metal powder having a standard reduction potential of less than -0.56 V is used together with the titanium precursor to prevent complete oxidation of Ti ³⁺ during solvent thermal synthesis in the step (b) Blank can be given. Titanium dioxide to which oxygen atom vacancies are imparted may be one in which some or all of its structure has been converted from an anatase form to a rutile form.

The zero-valent metal powder may be one selected from the group consisting of zinc, magnesium, aluminum, and a mixture of two or more thereof, preferably zinc, but is not limited thereto.

Further, the titanium oxide to which oxygen atom space is imparted, that is, titanium dioxide can be represented by the following formula (1).

&Lt; Formula 1 >

TiO _2-x

In the above formula, 0 < x < 0.5.

Conventionally, in order to improve the electron conductivity of titanium oxide, a high temperature of about 500 ° C or more and a high pressure of about 20 bar or more are required to replace oxygen atoms in titanium oxide with other atoms or to dope other atoms in a lattice constituting titanium oxide , Synthesis takes more than one day and synthesis efficiency is very low.

On the other hand, in the step (b), the suspension may be thermally treated under mild conditions, for example, at 100 to 300 ° C for 1 to 10 hours, oxygen vacancy can be imparted, thereby improving the electron conductivity of the titanium oxide to a level similar to that of the case where other atoms are substituted or doped.

In the step (c), an acid may be added to the suspension to remove the zero-valent metal powder. The zero-valent metal powder used in the step (a) is easily dissolved due to its high oxidation tendency and is dissolved in an acid. The acid may be selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and a mixture of two or more thereof, preferably hydrochloric acid, but is not limited thereto. The acid may be used in a small amount in concentrated form, or it may be diluted with an aqueous solution of a certain concentration.

The zero-valent metal powder added to the suspension in the step (a) acts as an inhibitor which inhibits the complete oxidation of Ti ^{3+ in} the step (b), and then is completely removed in the step (c) In the obtained titanium oxide, the zero-valent metal powder is no longer present.

Another aspect of the present invention provides a negative electrode for a lithium secondary battery, wherein the slurry containing the negative electrode active material for a lithium secondary battery, the binder and the conductive material prepared by the above method is applied to a current collector.

The binder may be selected from the group consisting of polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ) Rubber, styrene-butylene rubber, fluorine rubber, and a mixture of two or more thereof, preferably polyvinylidene fluoride, but is not limited thereto. The content of the binder may be 1 to 15% by weight, preferably 5 to 13% by weight, based on the total weight of the slurry.

The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, the conductive material may be graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives, and the like. The content of the conductive material may be 1 to 30 wt%, preferably 5 to 20 wt%, based on the total weight of the slurry.

The content of the negative electrode active material for a lithium secondary battery may be 70 to 95% by weight based on the total weight of the slurry. If the content of the negative electrode active material for a lithium secondary battery is less than 70% by weight, the life characteristics and conductivity of the battery may be deteriorated. If the content is more than 95% by weight, the content of the binder and the conductive material may be decreased.

The current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, the current collector may be a surface treated with carbon, nickel, titanium, silver or the like on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel, aluminum-cadmium alloy, . In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material and can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric. The current collector may have a thickness of 3 탆 to 500 탆.

The lithium secondary battery may have a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a separator interposed between an anode and a cathode.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength can be used. The pore diameter of the separator is generally 0.01 탆 to 10 탆, and the thickness may be 5 탆 to 300 탆. For example, the separator may be an olefinic polymer such as a chemical resistant and hydrophobic polypropylene; A sheet or a nonwoven fabric made of glass fiber, polyethylene, or the like. In addition, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may serve as a separator.

The lithium salt-containing electrolytic solution is composed of an electrolytic solution and a lithium salt, and the electrolytic solution may be water, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like, but is not limited thereto.

Wherein the non-aqueous organic solvent is at least one selected from the group consisting of N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -butylolactone, 1,2-dimethoxyethane, The organic solvent is selected from the group consisting of franc, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, , Trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate But may not be limited to, non-magnetic organic solvents.

Wherein the organic solid electrolyte is selected from the group consisting of a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene, But it is not limited thereto.

Wherein the inorganic solid electrolyte is selected from the group consisting of Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI -LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like, but the present invention is not limited thereto.

The lithium salt is a substance which can be dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , _{LiAsF 6, LiSbF 6, LiAlCl 4} , CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate, but already the like de, but are not limited to .

The electrolytic solution may contain at least one selected from the group consisting of pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexametriacetamide, nitrobenzene derivative, sulfur, quinoneimine Dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added. Further, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride can be further added to impart nonflammability to the electrolyte solution, and carbon dioxide gas, FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone ) May be further added.

Hereinafter, embodiments of the present invention will be described in detail.

Example

2 ml of a 15% to 20% aqueous solution of titanium chloride and 60 ml of isopropyl alcohol were mixed, zinc powder was added, and the mixture was stirred for 30 minutes to prepare a suspension. The suspension was poured into a Teflon-coated stainless steel autoclave and heat-treated at 180 ° C for 6 hours and then cooled to room temperature. After the cooled product was washed three times, 100 ml of 4M hydrochloric acid aqueous solution was used to remove the added zinc powder, and the mixture was dried at 60 ° C for one day to obtain TiO _{2 -x} particles having a blue oxygen vacancy .

Comparative Example

2 ml of a 15% to 20% aqueous solution of titanium chloride and 60 ml of isopropyl alcohol were stirred for 30 minutes to prepare a suspension. The suspension was poured into a Teflon-coated stainless steel autoclave and heat-treated at 180 ° C for 6 hours and then cooled to room temperature. After washing three times, the cooled product is dried at between 60 ℃ 1 il was prepared anatase type TiO ₂ particles in white.

Experimental Example 1: Structural Analysis

FIG. 1 shows X-ray diffraction (XRD) analysis results of the TiO _2-x and TiO ₂ particles as a result of HR-Raman spectrum (b) and X-ray photoelectron spectroscopy (XPS) ((c), (d)).

1 (a), all the peaks of the TiO ₂ particles correspond to the anatase form (JCPDS No. 21-1272), and all peaks of the TiO _{2 -x} particles correspond to the rutile form (JCPDS No. 04-0551) Corresponding. The zinc powder added during the heat treatment (solvent thermo-synthesis) converts white anatase-type particles to blue rutile-type particles. Since zinc was washed and removed with a hydrochloric acid solution after thermolysis of the solvent, no peak for zinc was observed.

When reference to Fig. 1 (b), if the TiO ₂ particles, 143cm ^-1, 396cm ^-1, when the four band at a wavenumber of 516cm ^-1 and 640cm ^-1. Rutile TiO ₂ particles and the TiO _2-x In the case of particles to 143cm ^-1, 230cm ^-1, shows that four peaks at the wave number of 440cm ^-1 and 610cm ^-1, both rutile particles having a typical combination of TiO ₂ . However, the peak intensity of TiO _2-x particles is lower than that of rutile-type TiO ₂ particles.

Ti ³⁺ and / or oxygen atom vacancies are known to cause lattice distortion, and a decrease in peak intensity means that binding is inhibited by the removal of oxygen atoms. Therefore, it is necessary to confirm the surface oxidation state of TiO _2-x particles and TiO ₂ particles through XPS analysis.

When reference to Fig. 1 (c), of the TiO ₂ particles Ti 2p peak is observed at a Ti ⁴⁺ 464.91eV and 459.37eV, the TiO _2-x particles Ti 2p peak, Ti ⁴⁺ or Ti at 458eV and 463.54eV ³⁺ , indicating that the Ti 2p peak of the TiO _2-x particles migrated with lower binding energy than the TiO ₂ particles, indicating that the TiO _2-x particles have a relatively lower Ti oxidation state than the TiO ₂ particles do.

Referring to FIG. 1 (d), the O 1s peak of the TiO _2-x particles migrates at a low binding energy and shows a somewhat asymmetrical shape at about 530 eV, which is due to an increase in oxygen atom vacancies. This asymmetric point is also observed above the peak of the TiO ₂ particle, which means that the concentration of vacancy of oxygen atoms is higher.

Thus, the blue color of the TiO _2-x particles is not due to the presence of zinc powder, but to the presence of Ti ³⁺ and / or oxygen atom vacancies in the TiO _2-x particles.

Experimental Example 2: Morphology analysis

Figure 2 shows the FE-TEM, selected area electron diffraction (SAED), and TiO _2-x particles ((a) to (e)) and TiO ₂ particles (f) Energy dispersive spectrometry (EDS).

Figure 2 (a) and With reference to 2 (f), a rectangle with a uniform size of the TiO _2-x particles and TiO ₂ particles about 30nm both. As shown in Figure 2 (b) to 2 (e), and 2 (g) to Refer to 2 (j), it does not have both the particles of Ti and O, and zinc are present, O in the TiO _2-x particles Peak strength and content are lower than that of TiO ₂ particles, and oxygen vacancies are present in TiO _2-x particles.

Manufacturing example

A mixture of TiO _2-x particles, polyvinylidene difluoride (PVDF, binder), and Super P (conductive material) in a weight ratio of 80: 10: 10 was mixed with N-methylpyrrolidone to prepare a slurry (Hereinafter, referred to as " TiO _2-x cathode (hereinafter referred to as " TiO _{2 -x} cathode &quot;) was prepared by coating a copper foil on a copper foil and drying it sequentially in an oven (80 ° C, 12 hours) &Quot;).

Comparative Manufacturing Example

A slurry was prepared by mixing a mixture of TiO ₂ particles, polyvinylidene difluoride (PVDF, binder), and Super P (conductive material) at a weight ratio of 80:10:10, respectively, with N-methylpyrrolidone (Hereinafter, referred to as " TiO ₂ cathode &quot;) was prepared by coating the copper foil on a copper foil and drying it sequentially in an oven (80 ° C, 12 hours) and a vacuum (80 ° C, 5 hours) Respectively.

An electrode assembly was prepared using the negative electrode prepared in the above Production Examples and Comparative Production Examples, a positive electrode made of a lithium foil (Li foil), and a porous separator (Celgard 2400). The electrode assembly was inserted into a pouch and lead wires were connected. Then, a 1: 1 volume ratio of ethylene carbonate (EC) and diethylene carbonate (DEC) solution containing 1 M of LiPF ₆ salt was injected into the electrolyte and sealed, .

Experimental Example 3: Evaluation of lithium secondary battery performance

Each lithium _secondary battery including a TiO _{2 -x} negative electrode and a TiO ₂ negative electrode was subjected to a constant current charge / discharge cycle at a current density of 100 mA / g in a voltage range of 1.0 V to 3.0 V, 3.

Referring to FIG. 3 (a), the TiO ₂ cathode exhibits a potential plateau at 1.68 V, while the TiO _{2 -x} cathode exhibits a potential plateau above 2.0 V and below 2 V A potential flat area appears. The discharge capacities of the TiO _{2 -x} cathode and the TiO ₂ cathode are shown in Table 1 below.

division 1st cycle 2nd cycle 20th cycle 50th cycle Comparative Manufacturing Example 179.4 152.8 105.4 81.1 Manufacturing example 551.1 348.5 279.9 253.8

(Unit: mAh / g) The discharge capacity of the TiO _{2 -x} cathode is higher than that of the TiO ₂ cathode because the oxygen vacancies formed in TiO _{2 -x} are filled with lithium ions. Therefore, even after the 50th cycle, the TiO _{2 -x} cathode has a discharge capacity about three times higher than that of the TiO ₂ cathode.

On the other hand, FIG. 3 (c) and 3 (d) Note that the first cycle, when TiO ₂ is inserted into the negative electrode of the Li ⁺ ions to 0.53mol, TiO _2-x has a negative electrode is inserted into the Li ⁺ ions of 1.64mol, 420.9 1.3mol of Li ^& lt ^{; + &} gt ^; ions can be reversibly extracted from a specific capacity of mAh / g. Since the insertion of Li ⁺ ions is also done in oxygen atom vacancies, the TiO _{2 -x} cathode carries a higher discharge capacity than the TiO ₂ cathode, but has a higher irreversible capacity of 130 mAh / g.

3 (e) and 3 (f) show electrochemical characteristics of the TiO ₂ cathode and the TiO _{2 -x} cathode measured by cyclic voltammetry, respectively. Measurements were made over five cycles at a voltage of 1.0 V to 3.0 V and a scan rate of 0.1 mV / s. Referring to Figure 3 (e), reduction / oxidation peaks at the TiO ₂ cathode appear at about 1.68 V and about 2.2 V, respectively, corresponding to the anatase form. On the other hand, referring to FIG. 3 (f), a reduction peak is observed at about 1.8 V and 1.25 V in the TiO _{2 -x} cathode, which is due to the irreversible deformation of TiO ₂ to LiTiO ₂ . Lithium ions are trapped in oxygen vacancies of TiO _2-x . The reduction peak after the first cycle is observed at about 1.47 V, which is due to the insertion of lithium ions in LiTiO ₂ . The intensity of the reduction peak at the cycle has increased, which means relatively better reactivity. The TiO _{2 -x} cathodes carry higher capacities compared to TiO ₂ cathodes despite irreversible phase deformation, which has a higher capacity loss in the first cycle.

4 (a) shows the cycling characteristics and the Coulomb efficiency of the TiO _{2 -x} cathode and the TiO ₂ cathode. The measurements were made over 50 cycles at a voltage of 1.0 V to 3.0 V, at a current density of 100 mA / g. Referring to FIG. 4 (a), the TiO _{2 -x} cathode transmits a higher discharge capacity than the TiO ₂ cathode. Coulomb efficiencies of the TiO _{2 -x} cathode and TiO ₂ cathode during the first cycle are 76.4% and 93.8%, respectively, but the Coulomb efficiency of the TiO _{2 -x} cathode continuously increases while cycling is repeated, reaching about 100% Meaning that cycling characteristics after the initial cycle are stable and reversible. It is analyzed that the irreversible lithium ion insertion site in TiO _2-x is continuously filled with inter-cycle lithium ions, and the remaining lithium in TiO _2-x improves the electrical conductivity. Oxygen atom vacancies are continuously expanded, which promotes the insertion and desorption of lithium ions to improve Coulomb efficiency and reduce irreversible capacity.

The rate capability of each lithium secondary battery including the TiO ₂ negative electrode and the TiO _{2 -x} negative electrode was measured in the range of 100 to 300 mA / g, and the result is shown in FIG. 4 (b). Referring to Fig. 4 (b), as the overall current density increases, the capacitance decreases. At a current density of 100 mA / g, the TiO ₂ cathode has a discharge capacity of 134.1 mAh / g after six cycles, and the discharge capacity decreases when the current density increases. For example, the discharge capacities of TiO ₂ cathodes at current densities of 200 mA / g and 300 mA / g are 59.9 mAh / g and 41.9 mAh / g, respectively, which are 44.7% of the measured values at current densities of 100 mA / 31.2%. On the other hand, the TiO _{2 -x} cathodes exhibit very good rate characteristics, and specifically, discharge capacities of 239.4 mAh / g and 220.4 mAh / g are maintained even at current densities of 200 mA / g and 300 mA / g. This corresponds to 84.6% and 77.9% of the 283.1 mAh / g measured after 6 cycles, respectively, at a current density of 100 mA / g. As the current density increases, the difference in capacitance between the TiO ₂ cathode and the TiO _{2 -x} cathode becomes larger.

The electrons are localized within the oxygen atom vacancies, and the ubiquitous electrons form donor levels that generally decrease from 0.75 eV to 1.18 eV from the conduction band. This means that TiO _2-x has higher electrical conductivity than TiO ₂ . Therefore, the TiO _{2 -x} cathode exhibits a relatively better rate characteristic over the TiO ₂ cathode over 36 cycles.

5 (a) and 5 (b) show electrochemical impedance spectra before and after 50 cycles of TiO ₂ cathode and TiO _{2 -x} cathode, respectively, and the values are shown in Table 2 below.

division R _s (Ω) R _s (Ω) R _ct (Ω) R _ct (Ω) Cycle Cycle I After 50 cycles Cycle I After 50 cycles Comparative Manufacturing Example 4.78 5.35 43.5 1,296.7 Manufacturing example 4.82 5.49 34.4 682.9

Referring to Figures 5 (a) and 5 (b), the spectrum consists of two regions. The semicircle at high frequency corresponds to the charge transfer resistance (R _ct ) and the line at low frequency is related to the solid state diffusion and migration of Li ⁺ ions from the electrolyte to the electrode surface, Impedance (Warburg impedance, R _w ) behavior. Semicircles at high frequencies at each cathode are observed one at a time, which means that there is no solid electrolyte interface (SEI) layer at the electrode and electrolyte good contact, specifically at the surface of the positive electrode. The R _ct value of the TiO _{2 -x} cathode is 5.49 Ω and 682.9 Ω before the cycle and after 50 cycles, respectively, while the R _ct value of the TiO ₂ cathode is greatly increased to 1,296.7 Ω after 50 cycles. In addition, TiO _2-x has a larger bug impedance (R _w ) after 50 cycles than TiO ₂ . The low frequency region of the impedance spectrum corresponds to the limited diffusion of ions within the particle. The structure of nanoparticles can affect these limited diffusion impedances. Specifically, the vacancy of oxygen atoms in TiO _2-x facilitates ion diffusion compared to TiO ₂ during electrochemical charging and discharging, and can improve the storage stability of such electrochemical energy.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (12)

(a) dissolving a titanium precursor in a solvent and adding a zero-valent metal powder to prepare a suspension;
(b) subjecting the suspension to heat treatment at 100 to 300 ° C for 1 to 10 hours to produce titanium oxide containing oxygen vacancies; And
(c) adding an acid to the suspension to remove the zero-valent metal powder. The method according to claim 1,
Wherein the titanium precursor is a trivalent titanium compound. 2. The method of claim 1, wherein the titanium precursor is a trivalent titanium compound. 3. The method of claim 2,
The trivalent titanium compounds are _{TiCl 3, TiBr 3, Ti (} OH) Cl 2, Ti 2 (SO 4) 3, Ti (OAc) 3, Ti (3+) _{oxylate, Ti (NO 3) 3,} Ti ( 3+) lactate, and a mixture of at least two of the foregoing. 2. The method for producing a negative active material for a lithium secondary battery according to claim 1, The method according to claim 1,
Wherein the solvent is an alcohol. 5. The method of claim 4,
Wherein the alcohol is selected from the group consisting of methanol, ethanol, isopropanol, n-butanol, amyl alcohol, cyclohexanol, and mixtures of two or more thereof. The method according to claim 1,
Wherein the standard reduction potential of the zero-valent metal powder is less than -0.56 V. &lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 6,
Wherein the zero-valent metal powder is one selected from the group consisting of zinc, magnesium, aluminum, and a mixture of two or more thereof. The method according to claim 1,
Wherein the titanium oxide is represented by the following formula (1): < EMI ID =
&Lt; Formula 1 &gt;
TiO _2-x
In the above formula, 0 < x &lt; 0.5. 9. A negative electrode active material for a lithium secondary battery, which is produced by the method of any one of claims 1 to 8. A negative electrode for a lithium secondary battery according to claim 9, wherein a slurry including a negative electrode active material for a lithium secondary battery, a binder and a conductive material is applied to the current collector. 11. The method of claim 10,
The binder may be selected from the group consisting of polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ) Rubber, styrene-butylene rubber, fluorine rubber, and mixtures of two or more thereof. 11. The method of claim 10,
Wherein the content of the negative electrode active material for a lithium secondary battery is 70 to 95% by weight based on the total weight of the slurry.

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