KR101627781B1 - Method of preparing negative active material for lithium secondary battery - Google Patents

Abstract

The present invention relates to a method of preparing a negative electrode active material for a lithium secondary battery, comprising the steps of: preparing a core material capable of doping and dedoping lithium; Activating a surface of the core material; Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment; And obtaining a negative electrode active material on which a coating layer containing lithium titanium oxide and lithium silicate is formed, wherein the step of hydrophilizing the surface of the core material comprises: Wherein the step of hydrophilizing the surface of the core material using hydrogen peroxide water, nitric acid, sulfuric acid, alcohol series, or a combination thereof is provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a negative active material for a lithium secondary battery,

And more particularly, to a method of manufacturing an anode active material of a lithium secondary battery.

2. Description of the Related Art [0002] Recently, miniaturization, light weight, and wirelessization of electronic devices have rapidly progressed, and as technology development and demand for mobile devices have increased, secondary batteries have attracted attention as a driving power source for such electronic devices. Among secondary batteries, lithium secondary batteries have high energy density and voltage, and have been subjected to a lot of researches since they can be charged rapidly, and they are now widely used in commercial applications.

As an anode active material of such a lithium secondary battery, much research has been made initially due to the capacity of the lithium metal-rich battery. Lithium metal has very high energy density and can realize a high capacity. However, when repeated charge / discharge, many dendritic lithium precipitates on the surface of lithium, which may result in reduction of charging / discharging efficiency, shorting to positive electrode and instability of lithium itself Due to its high reactivity, it is sensitive to heat or shock, and has a safety problem such as explosion hazard and short cycle life, which is a hindrance to commercialization.

In lithium secondary batteries, the conditions of the anode active material should be high capacity, high cycle characteristics, and good electrical conductivity. Silicon anode active materials have the advantage of achieving high capacity (over 3500 mAh / g) when reacting with lithium ions. However, due to the uniformity of the silicon particles due to the volume change of more than 300% during charging / discharging, The cycle performance is drastically reduced. In order to overcome these disadvantages, various studies are under way. Among them, researches are actively conducted to overcome the disadvantages of silicon by coating silicon surface with materials that do not react with carbon or lithium.

It is possible to provide a method for producing a negative electrode active material for a lithium secondary battery that can achieve improved battery characteristics.

In one embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery comprising: preparing a core material capable of doping and dedoping lithium; Activating a surface of the core material; Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment; And a negative electrode active material on which a coating layer comprising lithium titanium oxide and lithium silicate is formed. The present invention also provides a method for producing a lithium secondary battery.

Activating the surface of the core material may be a step of hydrophilizing the surface of the core material.

The step of hydrophilizing the surface of the core material may be a step of hydrophilizing the surface of the core material using a hydrogen peroxide solution, nitric acid, sulfuric acid, alcohol series, water, or a combination thereof. have.

The solvent used in the step of mixing the activated core material, the lithium precursor, and the titanium precursor with the activated surface may be an ethylene glycol, an alcohol solvent, water, a polar solvent, or a combination thereof.

The surface of the core material, the lithium precursor, and the titanium precursor are mixed and then heat-treated, the heat treatment temperature may be 450 to 1100 ° C.

Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment, may be an atmospheric atmosphere or an inert atmosphere.

The titanium precursor may be titanium tetrabutoxide _{(Ti (OCH 2 CH 2 CH} 2 CH 3) 4), titanium tetraisopropoxide (Titanium tetraisopropoxide), titanium tetrachloride (TiCl ₄₎ or a combination thereof.

The lithium precursor may be lithium acetate, lithium nitrate, lithium sulphate, lithium perchlorate, lithium chloride (LiCl), or a combination thereof.

The titanium precursor may be added in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the activated core material in the activated core material, the lithium precursor, and the titanium precursor.

It is possible to provide a negative electrode active material for a lithium secondary battery capable of achieving improved battery characteristics, thereby providing a lithium secondary battery capable of improving the charge / discharge life of the charge / discharge cycle and rapidly charging / discharging.

1 is a schematic view of a lithium secondary battery according to an embodiment of the present invention.
2 is a schematic view of a lithium-titanium oxide and lithium silicate coating layer compound formed on a silicon core and a surface thereof.
3 is an electron transmission microscope (TEM) image of a lithium niobate anode active material coated with lithium silicate and lithium titanium oxide prepared in Example 2. Fig.
FIG. 4 is a graph showing an X-ray diffraction pattern of a lithium niobate anode active material coated with lithium silicate and lithium titanium oxide prepared in Example 2 by X-ray diffraction analysis.
5 is a graph showing voltage change curves of the coin cells prepared in Example 3 and Comparative Example 1 according to the capacity of one cycle.
6 is a graph showing lifetime characteristics of the coin battery manufactured in Example 3 and Comparative Example 1. Fig.
FIG. 7 is a graph of charge / discharge life characteristics according to C-rate of the coin battery manufactured in Example 3 and Comparative Example 1. FIG.
8 is an electron transmission microscope (TEM) image of a silicon nano-powder anode active material coated with lithium silicate and lithium titanium oxide after evaluation of charge / discharge life characteristics according to the C-rate of the coin battery prepared in Example 3. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In one embodiment of the present invention, a core material capable of doping and dedoping lithium; And a coating layer disposed on a surface of the core material, wherein the coating layer comprises lithium titanium oxide and lithium silicate.

The anode active material according to an embodiment of the present invention may include a coating layer containing lithium titanium oxide and lithium silicate.

More specifically, due to the coating layer which simultaneously contains lithium titanium oxide capable of serving as a channel of active material and lithium ion and lithium silicate capable of forming a stable film, charging / discharging can be performed faster than existing silicon negative electrode active material, A negative electrode active material capable of ensuring stable cycle characteristics can be obtained.

More specifically, the core material capable of doping and dedoping lithium can be silicon (Si), silicon monoxide (SiO), silica (SiO ₂ ), silicon based materials, or combinations thereof. Specific examples include, but are not limited to, silicon.

The lithium titanium oxide may include Li ₄ Si ₅ O ₁₂ , Li ₂ TiO ₃ , Li ₂ Ti ₃ O ₇ , or a combination thereof. However, the present invention is not limited thereto.

The lithium silicate may include Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ , Li ₄ SiO ₄ , or a combination thereof. However, the present invention is not limited thereto.

The content of the lithium titanium oxide may be 0.1 to 10 parts by weight based on 100 parts by weight of the core material capable of doping and dedoping lithium. More specifically, it may be 0.1 to 3 parts by weight.

The desired effect may vary depending on the weight ratio of the coating material and the core material in the negative electrode active material.

Specifically, when the content of the core material is large, the capacity characteristics can be improved. Further, when the content of the coating layer is large, the cycle characteristics can be improved.

The weight ratio of the coating layer to the total active material may be 0.1 to 70 wt%, and more specifically, 0.1 to 50 wt%, 0.1 to 30 wt%, or 0.1 to 20 wt%.

In another embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery comprising: preparing a core material capable of doping and dedoping lithium; Activating a surface of the core material, mixing the activated core material, the lithium precursor, and the titanium precursor, followed by heat treatment; And a negative electrode active material on which a coating layer comprising lithium titanium oxide and lithium silicate is formed. The present invention also provides a method for producing a lithium secondary battery.

Activating the surface of the core material may be a step of hydrophilizing the surface of the core material.

More specifically, the step of hydrophilizing the surface of the core material may comprise hydrophilizing the surface of the core material using a hydrogen peroxide solution, nitric acid, sulfuric acid, alcohol, water, or a combination thereof. Lt; / RTI >

Through these steps, the core can be well dispersed in a solvent such as water or ethanol.

The solvent used in the step of mixing the activated core material, the lithium precursor, and the titanium precursor with the activated surface may be an ethylene glycol, an alcohol solvent, water, a polar solvent, or a combination thereof. However, the present invention is not limited thereto.

The surface of the core material, the lithium precursor, and the titanium precursor are mixed and then heat-treated, the heat treatment temperature may be 450 to 1100 ° C. When this range is satisfied, the desired coating layer can be introduced.

Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment, may be an atmospheric atmosphere or an inert atmosphere.

The titanium precursor may be titanium tetrabutoxide _{(Ti (OCH 2 CH 2 CH} 2 CH 3) 4), titanium tetraisopropoxide (Titanium tetraisopropoxide), titanium tetrachloride (TiCl _4), and combinations thereof. However, the present invention is not limited thereto.

The lithium precursor may be lithium acetate, lithium nitrate, lithium sulphate, lithium perchlorate, lithium chloride (LiCl), or a combination thereof. However, the present invention is not limited thereto.

The titanium precursor may be added in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the activated core material in the activated core material, the lithium precursor, and the titanium precursor. More specifically, it may be 0.1 to 3 parts by weight.

In another embodiment of the present invention, there is provided a positive electrode comprising: a positive electrode comprising a positive electrode active material; And an anode active material according to an embodiment of the present invention; And a lithium secondary battery comprising the electrolyte. The lithium secondary battery may have an initial capacity of 500 to 2000 mAh / g. The lithium secondary battery may have a coulombic efficiency of 80% or more after the first cycle.

The construction of a specific lithium secondary battery will be described in detail below.

1 is an exploded perspective view of a lithium secondary battery according to one embodiment. 1, the lithium secondary battery 100 has a cylindrical shape and includes a cathode 112, a cathode 114, a separator 113 disposed between the cathode 112 and the anode 114, An electrolyte 114 (not shown), an electrolyte (not shown) impregnated into the separator 113, a battery container 120, and a sealing member 140 for sealing the battery container 120. The lithium secondary battery 100 is constructed by laminating a cathode 112, a separator 113 and an anode 114 in this order and then winding them in a spiral wound state in the battery container 120.

The negative electrode includes a current collector and a negative active material layer formed on the current collector, and the negative active material layer includes a negative active material.

The negative electrode active material is as described above.

The negative electrode active material layer also includes a binder, and may further include a conductive material.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any material can be used as long as it does not cause any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, , Carbon-based materials such as carbon fibers; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The current collector may be a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, a polymer substrate coated with a conductive metal, or a combination thereof.

The anode includes a current collector and a cathode active material layer formed on the current collector.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Concretely, it is possible to use at least one of complex oxides of cobalt, manganese, nickel or a combination of metals and lithium, and specific examples thereof include compounds represented by any one of the following formulas. Li _a A _{1 - b} R _b D ₂ wherein, in the formula, 0.90? A? 1.8 and 0? B? 0.5; Li _a E _{1 - b} R _b O _{2 - c} D _c , wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05; LiE _{2 - b} R _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -b- c} Co _b R _c D _{α where} 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2; Li _a Ni _{1 -b- c} Co _b R _c O _{2 - ?} Z _{? Where} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Co _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, and 0 <? Li _a Ni _1-bc Mn _b R _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z _{? Where} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -b- c} Mn _b R _c O _{2 - ?} Z ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1.8 and 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise, as a coating element compound, an oxide, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, or a hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be carried out by any of coating methods such as spray coating, dipping, and the like without adversely affecting the physical properties of the cathode active material by using these elements in the above compound. It is a content that can be well understood by people engaged in the field, so detailed explanation will be omitted.

The cathode active material layer also includes a binder and a conductive material.

The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl Polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-acrylonitrile, styrene-butadiene rubber, Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive material is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used alone or in combination.

As the current collector, Al may be used, but the present invention is not limited thereto.

The negative electrode and the positive electrode are prepared by mixing an active material, a conductive material and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein. As the solvent, N-methylpyrrolidone or the like can be used, but it is not limited thereto.

The electrolyte includes a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) EC), propylene carbonate (PC), and butylene carbonate (BC) may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl ethyl acetate, methyl propionate , Ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like can be used. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. As the ketone solvent, cyclohexanone may be used have. As the alcoholic solvent, ethyl alcohol, isopropyl alcohol and the like can be used. As the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, An amide such as nitriles such as dimethylformamide, and dioxolanes such as 1,3-dioxolane, sulfolanes, and the like can be used.

The non-aqueous organic solvent may be used alone or in admixture of one or more. If the non-aqueous organic solvent is used in combination, the mixing ratio may be appropriately adjusted according to the desired cell performance. .

In the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to about 1: 9, the performance of the electrolytic solution may be excellent.

The non-aqueous organic solvent may further include the aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

The aromatic hydrocarbon-based organic solvent may be an aromatic hydrocarbon-based compound represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, R ₁ to R ₆ are each independently hydrogen, halogen, a C1 to C10 alkyl group, a C1 to C10 haloalkyl group, or a combination thereof.

The aromatic hydrocarbon-based organic solvent is selected from the group consisting of benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3- , 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4 - triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4 - trichlorotoluene, iodotoluene, 1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotol Ene, 1,2,3-tree-iodo toluene, 1,2,4-iodo toluene, xylene, or may be a combination thereof.

The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by the following formula (2) to improve battery life.

(2)

Wherein R ₇ and R ₈ are each independently hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ) or a C1 to C5 fluoroalkyl group, and at least one of R ₇ and R ₈ Is a halogen group, a cyano group (CN), a nitro group (NO ₂ ) or a C1 to C5 fluoroalkyl group.

Representative examples of the ethylene carbonate-based compound include, for example, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, . When the vinylene carbonate or the ethylene carbonate compound is further used, the amount of the vinylene carbonate or the ethylene carbonate compound can be appropriately controlled to improve the life.

The lithium salt is dissolved in the non-aqueous organic solvent to act as a source of lithium ions in the battery to enable operation of a basic lithium secondary battery, and a material capable of promoting the movement of lithium ions between the positive electrode and the negative electrode to be. The lithium salt Representative examples are _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2, LiAlCl 4, LiN (C x F 2x + 1 SO 2) (C y F 2y ₊₁ SO ₂₎ (where, x and y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2 ( lithium bis oxalate reyito borate (lithium bis (oxalato) borate; LiBOB) , or in a combination thereof The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity Can exhibit excellent electrolyte performance, and lithium ions can effectively migrate.

The separator 113 separates the cathode 112 and the anode 114 and provides a passage for lithium ions. Any separator 113 may be used as long as it is commonly used in a lithium battery. That is, it is possible to use an electrolyte having a low resistance to ion movement and an excellent ability to impregnate an electrolyte. For example, selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be nonwoven fabric or woven fabric. For example, a polyolefin-based polymer separator such as polyethylene, polypropylene and the like is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer substance may be used for heat resistance or mechanical strength, Structure.

Hereinafter, examples and comparative examples of the present invention will be described. The following embodiments are only examples of the present invention, and the present invention is not limited to the following embodiments.

Example  1: Hydrophilic surface modification of silicon with hydrogen peroxide

2 is a schematic view of a lithium-titanium oxide and lithium silicate coating layer compound formed on a silicon core and a surface thereof according to an embodiment of the present invention.

Lithium titanium oxide or lithium silicate coatings are applicable to various types of silicon-based materials such as silicon wafers, silicon powders, and porous silicon. Silicon nano powder was coated with lithium titanium oxide or lithium silicate for use as an anode active material.

More specifically, in one embodiment of the present invention, silicon nano powder was used. Before the lithium titanium oxide and lithium silicate were coated on the surface of the silicon nano powder, the surface of the silicon nano powder was modified to have a hydrophilic surface so that the reaction of the surface was smooth.

5 g of the silicon powder was placed in a 70 ml glass container, 50 ml of hydrogen peroxide was added, and the mixture was stirred at 50 캜 for about 1 hour. After stirring, the modified silicone and hydrogen peroxide were separated using a centrifuge (3500 rpm, 30 to 1 hour, 2 to 3 times) and washed with distilled water or ethanol to remove residual hydrogen peroxide. More specifically, a plurality of centrifuging methods are repeated in which a supernatant is separated after one centrifugation, and then centrifuged again by adding water and ethanol.

After this process, it was dried in a 70 ° C convection oven to remove moisture from the modified silicone surface. More specifically, it was dried for 2 hours or more using a convection oven at 60 ° C or higher.

Example  2: Preparation of negative electrode active material for lithium secondary battery

Lithium and a titanium precursor were used to form a coating layer on the surface of the above-mentioned silicon nano powder.

More specifically, lithium acetate and titanium tetraisopropoxide were used as coating raw materials.

8 mmol of lithium acetate was dissolved in 10 ml of ethanol and stirred for a sufficient time. The lithium acetate solution prepared by the above method was mixed with 0.5 g of the silicon nano powder prepared by the method of Example 1. And reacted with stirring to form a uniform coating layer on the silicon surface. After sufficient stirring, 5 mmol of titanium tetraisopropoxide was added to a lithium acetate solution in which silicon was dispersed.

The lithium precursor and the titanium precursor were stirred for 2 hours or more to be evenly mixed, and the ethanol was dried in a 70 ° C convection oven. After drying, the material dried by using a mortar bowl was mixed again for uniform dispersion of silicon, lithium and titanium precursors, and heat treated in a nitrogen atmosphere to convert the silicon nano powder surface to lithium silicate and lithium titanium oxide The reaction was carried out in the apparatus for 12 hours at a rate of 5 ° C per minute up to 600 ° C.

In order to control the amount of synthesized lithium silicate and lithium titanium oxide, the molar ratio of lithium in the lithium precursor and titanium in the titanium precursor was fixed at 8: 5, and the molar amount of the titanium precursor and the content of the lithium precursor were adjusted to prepare the titanium precursor amount : 0.83, 1.25, 2.5, 3.75, 5 mmol).

The surface shape of the negative electrode active material prepared by the above method was confirmed and confirmed by a transmission electron microscope (TEM). 3 is a transmission electron micrograph of silicon which is an anode active material before and after surface coating.

In order to confirm the lithium silicate and lithium titanium oxide on the surface of the silicon nano powder produced by the above method, X-ray diffraction (XRD) analysis capable of qualitative / quantitative analysis was performed. 4 is an X-ray diffraction pattern analyzed by X-ray diffraction analysis.

Example  3: The negative active material  Manufacture of Coin Cell Used

A coin battery was prepared using the powder prepared in Example 2 as an anode active material

More specifically, the negative active material prepared in Example 2, super P (super P) as a conductive material, and polyacrylic acid (PAA) as a binder were mixed together with water used as a solvent Thereby preparing a negative electrode active material slurry.

(Weight ratio: anode active material: conductive material: binder = 6: 2: 2)

The prepared slurry was uniformly coated on a copper foil, and vacuum dried in a convection oven at 90 캜 for 10 minutes and a vacuum oven at 150 캜 for 2 hours to prepare a negative electrode. Argon atmosphere with a water content of 2 ppm or less A lithium metal foil was used as a counter electrode in a glove box, and polypropylene (PP) was used as a separation membrane. A coin cell was prepared using 1.3 mol LiPF ₆ / EC: DEC (volume ratio 3: 7) containing 5 wt% of additive FEC (fluoroethylene carbonate) as an electrolyte and 10 wt% of additive FEC.

Comparative Example  1: Manufacture of coin battery using silicon nano powder

A coin cell was manufactured using the same method as in Example 3, except that silicon nano powder not coated with lithium silicate and lithium titanium oxide was used as a negative electrode active material.

Experimental Example  1. Identification of charge / discharge life characteristics of battery

The constant current test was performed on the coin battery manufactured in Example 3 and Comparative Example 1 using a charge / discharge device capable of constant current / constant potential control at 25 占 폚.

More specifically, a constant current corresponding to the C / 5 (lithiation, charge) - C / 2 (Delithiation, discharge) rate of the capacity of each coin cell was applied and the delithiation termination voltage was 2.5 V (vs. Li / Li ⁺ ), and the termination voltage of the lithiation was fixed to 0.01 V (vs. Li / Li ⁺ ), respectively.

5 is a graph showing voltage change curves of the coin cells manufactured in Example 3 and Comparative Example 1 according to the capacity of one cycle.

The material coated with lithium silicate and lithium titanium oxide on the surface confirmed that lithium was removed / inserted into Li ₄ Ti ₅ O ₁₂ (LTO) at 1.5 V or higher as well as the reaction to be released / inserted into silicon Respectively.

In addition, it was confirmed that the cycle capacity decreased by one cycle as compared with the silicon which had no treatment. This is because silicon realizes a capacitance of 10 times or more (1700 mAh / g, at 0.1 C) compared to lithium titanium oxide.

6 is a graph showing lifetime characteristics of the coin battery manufactured in Example 3 and Comparative Example 1. FIG.

FIG. 6 is a graph of capacity retention ratios of silicon nano powders coated with lithium silicate and lithium titanium oxide at a rate of 95% or more, .

Experimental Example  2: Depending on the C-rate of the battery Charging and discharging  Life characteristics

Experiments were conducted by varying the constant current rate of the coin cell manufactured in Example 3 and Comparative Example 1 using a charge / discharge device capable of constant current / constant potential control at 25 ° C.

More specifically, the experimental conditions were a constant current of 0.1 - 0.2 - 0.5 - 1 - 3 - 5 - 7 - 10 C based on the capacity of each coin cell, and the delithiation termination voltage was 2.5 V (vs. Li / Li ⁺ ), and the termination of the lithiation was fixed to 0.01 V (vs. Li / Li ⁺ ), respectively.

7 is a graph of charge-discharge lifetime characteristics according to C-rate of the coin battery manufactured in Example 3 and Comparative Example 1. FIG. In the case of the uncoated solution, the performance of 50% of the silicon core / lithium titanium oxide / lithium silicate cell compound was maintained at 50% at 10 C compared with 0.1 C. % Performance.

8 is a graph showing the results of evaluation of charge / discharge life characteristics according to the C-rate of the coin battery manufactured in Example 3, and after the evaluation of the lifetime of lithium / silicon oxide / lithium silicate cells Compound Electron transmission microscope (TEM) image.

It was confirmed that lithium silicate and lithium titanium oxide retained the crystal on the surface of the silicon nano powder even after evaluating the charge and inversion lifetime characteristics.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

100: lithium secondary battery 112: cathode
113: separator 114: positive electrode
120: battery container 140: sealing member

Claims (7)

Preparing a core material capable of doping and dedoping lithium;
Activating a surface of the core material;
Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment; And
Obtaining a negative electrode active material on which a coating layer containing lithium titanium oxide and lithium silicate is formed;
A method for producing a lithium secondary battery,
Activating a surface of the core material,
Wherein the surface of the core material is hydrophilized on the surface of the core material using aqueous hydrogen peroxide, nitric acid, sulfuric acid, an alcohol series, or a combination thereof.
The method according to claim 1,
Wherein the solvent used in the step of mixing the surface active core material, the lithium precursor, and the titanium precursor and then heat-treating is an ethylene glycol, an alcohol solvent, water, a polar solvent, or a combination thereof. A method for producing an active material.
The method according to claim 1,
Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment,
And the heat treatment temperature is 450 to 1100 ° C.
The method according to claim 1,
And mixing the surface active core material, the lithium precursor, and the titanium precursor with each other, followed by heat treatment, in an air atmosphere or an inert atmosphere.
The method according to claim 1,
The titanium precursor is titanium tetrabutoxide _{(Ti (OCH 2 CH 2 CH} 2 CH 3) 4), titanium tetraisopropoxide (Titanium tetraisopropoxide), titanium tetrachloride (TiCl ₄₎ or a lithium secondary battery that is a combination thereof A method for producing an anode active material.
The method according to claim 1,
Wherein the lithium precursor is lithium acetate, lithium nitrate, lithium sulphate, lithium perchlorate, lithium chloride (LiCl), or a combination thereof. &Lt; / RTI &gt;
The method according to claim 1,
Mixing the surface active core material, the lithium precursor, and the titanium precursor, followed by heat treatment,
Wherein the amount of the titanium precursor is 0.1 to 10 parts by weight based on 100 parts by weight of the surface of the activated core material.

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