KR101504698B1 - Negative active material for secondary battery and secondary battery including the same - Google Patents

Abstract

The present invention relates to a method for producing sodium titanium oxide (Na ₄ Ti ₅ O ₁₂ ) for a negative electrode active material for a secondary battery, a negative electrode active material containing the same, and a secondary battery. Specifically, the manufacturing method includes the steps of coating the (a) titanium dioxide (TiO ₂₎ particles of a carbon material; And (b) mixing the titanium dioxide particles coated with the carbon material with a sodium salt, and heat treating the mixture.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative electrode active material for a secondary battery, and a secondary battery including the negative electrode active material.

The present invention relates to a method for producing sodium titanium oxide (Na ₄ Ti ₅ O ₁₂ ) for a secondary battery anode active material, a negative electrode active material containing the same and a secondary battery.

Conventionally, titanium-based oxides for lithium secondary batteries have been widely used as cathode materials. Examples of such titanium-based oxides include TiO ₂ anatase, TiO ₂ rutile, TiO ₂ (B), Li ₄ Ti ₅ O ₁₂ spinel, Li ₂ Ti ₃ O ₇ ramsdellite, Have been studied as lithium secondary battery cathodes. In recent years, layered Na ₂ Ti ₃ O ₇ has been introduced as an anode material for sodium secondary batteries. However, when the titanium oxide is introduced into the negative electrode material, the performance of the battery is not satisfactory. In particular, the titanium-based oxide-based material has an advantage of being free from the problem of generation of lithium dendrite of graphite due to a reaction voltage higher than that of graphite, but has sufficient battery characteristics (such as cycle characteristics) sufficient for commercialization as an anode material of a secondary battery not. Therefore, new material is needed for this.

One embodiment of the present invention provides sodium titanium oxide having a novel composition and crystal structure and a method for producing the same.

Another embodiment of the present invention is to provide an anode active material for a secondary battery using the sodium titanium oxide produced by the above-described method.

Another embodiment of the present invention is to provide a secondary battery having improved reversibility capacity and cycle characteristics by using the negative electrode active material.

In one embodiment of the present invention comprises the steps of: coating the (a) titanium dioxide (TiO ₂₎ particles of a carbon material; (b) it provides a process for the preparation of Na ₄ Ti ₅ O _12, comprising the step of mixing the sodium salt of the titanium dioxide particles coated with the carbon material, and heating the mixture.

The above titanium dioxide The size of the particles may be between 2 and 100 nm.

The carbon material may be selected from graphite, hard carbon, soft carbon, and combinations thereof.

The carbon material may be coated on titanium dioxide particles by one of the methods selected from spray coating, dipping, sol-gel, chemical vapor deposition, and combinations thereof.

The carbon material may be coated on the surface of the titanium dioxide particles to a thickness of 1 to 20 nm.

The titanium dioxide particles and the sodium salt coated with the carbon material may be mixed so that the atomic ratio of Ti: Na is 5: 4.

The sodium salt may be selected from sodium carbonate, sodium hydroxide, sodium acetate, sodium nitrate, and combinations thereof.

The heat treatment step may be performed at a temperature of 500 to 700 ° C.

The heat treatment step may be performed for 1 to 10 hours.

Another embodiment of the present invention provides Na ₄ Ti ₅ O ₁₂ produced by the process described above.

Another embodiment of the present invention provides a negative electrode active material for a secondary battery comprising Na ₄ Ti ₅ O ₁₂ .

The particle size of Na ₄ Ti ₅ O ₁₂ may be 2 to 100 nm.

The BET surface area of the negative electrode active material may be 10 to 500 m ² / mg.

The Na ₄ Ti ₅ O ₁₂ may include a coating layer containing a carbon material.

The coating layer may be 1 to 20 nm.

The content of the carbon material may be 1 to 30 wt%.

Another embodiment of the present invention provides a secondary battery comprising the above-mentioned negative electrode active material for a secondary battery.

According to the manufacturing method of the embodiment of the present invention, it is possible to easily manufacture nano-sized Na ₄ Ti ₅ O ₁₂ and to produce a negative electrode active material for a lithium secondary battery comprising Na ₄ Ti ₅ O ₁₂ obtained by the above- Improves the deintercalation rate of lithium ions upon charging and discharging, improves the reversible capacity of the secondary battery and improves cycle characteristics.

FIG. 1 shows crystal structures of (100), (010) and (001) planes of Na ₄ Ti ₅ O ₁₂ .
2 is an exploded perspective view of a lithium secondary battery according to one embodiment
3 shows a TGA (thermo gravimetric analyzer) test result of Na ₄ Ti ₅ O ₁₂ according to Production Example 1.
Figures 4a to 4c shows the SEM picture of the Na ₄ Ti ₅ O ₁₂ according to Na ₄ Ti ₅ O _12, prepared according to Example 1, TiO _2, Comparative Production Example 1, respectively.
Figure 5 shows the XRD pattern of Na ₄ Ti ₅ O ₁₂ according to Na ₄ Ti ₅ O _12, prepared according to Example 1 TiO _2, Comparative Production Example 1.
6A shows charging characteristics of a lithium secondary battery according to Example 1, Comparative Example 1, and Comparative Example 2. Fig.
6B shows the discharge characteristics of the lithium secondary battery according to Example 1, Comparative Example 1, and Comparative Example 2. Fig.
7A to 7C show charge / discharge graphs of lithium secondary batteries according to Example 1, Comparative Example 1 and Comparative Example 2, respectively.

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.

Herein, the term 'secondary battery' refers to a secondary battery which can use a titanium oxide as a negative electrode active material, such as a lithium secondary battery sodium secondary battery, and is not limited to a lithium secondary battery.

In one embodiment of the present invention, (a) titanium dioxide (TiO ₂₎ the method comprising the steps of coating the particles of the carbon material and (b) mixing the sodium salt of the titanium dioxide particles coated with the carbon material, and heating the mixture a it provides a process for the preparation of Na ₄ Ti ₅ O ₁₂ containing. Hereinafter, the manufacturing method will be described in more detail.

(a)

In the step (a), the titanium dioxide (TiO ₂ ) particles are coated with a carbon material.

The titanium dioxide may have different crystal phases and physicochemical characteristics depending on the manner of bonding with oxygen atoms. In one embodiment of the present invention, the titanium dioxide may have an antase crystal phase. However, the crystal structure of titanium dioxide is not limited thereto, and may have a crystalline phase of rutile or brookite rutile.

The anatase and ruta titanium dioxide on the daily basis are bonded with oxygen in the symmetrical structure and show stable structure and stable at high temperature while the metastable brookite phase has a metastable structure by bonding with oxygen atoms of asymmetric structure, And exhibits stable characteristics.

The size of the particles of titanium dioxide can be, in one embodiment, from 2 to 100 nm, and preferably from 10 to 30 nm. If the particles of titanium dioxide exceeds 100 nm, the final size of Na ₄ Ti ₅ O ₁₂ is made of is not desirable is more than 100 nm, if a particle of the titanium dioxide is less than 2 nm Na ₄ Ti ₅ O ₁₂ is difficult to grow into a crystal having a trigonal phase structure, and consequently there is a problem that the reversible capacity of the secondary battery is not greatly improved

On the other hand, it is preferable that the particle size of the generated Na ₄ Ti ₅ O ₁₂ finally produced after the heat treatment is several tens nanometers. When the particle size of Na ₄ Ti ₅ O ₁₂ is several tens of nanometers in size, lithium ions diffused in the crystal structure can reduce the migration distance, thereby improving the reversible capacity of the secondary battery. Thus, for the purpose of keeping the particle size of Na ₄ Ti ₅ O ₁₂ small, before the heat treatment, the titanium dioxide is coated with the carbon material.

When the carbon material reacts with the sodium salt of titanium dioxide to form a crystal structure in a subsequent heat treatment step, the crystal structure constituting Na ₄ Ti ₅ O ₁₂ is prevented from continuing to grow, and ultimately Na ₄ Ti ₅ O ₁₂ Prevents the particle size from growing to several hundred nanometers.

If the titanium dioxide is not coated with the carbon material, the size of the finally formed Na ₄ Ti ₅ O ₁₂ particles becomes several hundreds of nm, which is undesirable. In this case, the particles of titanium dioxide, which is the starting material, To 50 nm, the final product, Na ₄ Ti ₅ O _12, is very bulk, and in the case of bulk Na ₄ Ti ₅ O ₁₂ , diffusion of lithium ions is not easy, so that the reversibility of lithium secondary batteries The capacity is small and the charging / discharging efficiency is deteriorated.

On the other hand, when titanium dioxide is coated with a carbon material, Na ₄ Ti ₅ O ₁₂ having a size of several tens of nanometers, for example, 10 to 50 mn can be easily obtained, so that the diffusion rate of lithium ions to be intercalated and deintercalated And the reversible capacity of the secondary battery is remarkably improved.

As the carbon material, graphite, hard carbon, soft carbon, or a combination thereof may be used. As the precursor of the carbon material, hard carbon using phthalocyanine, sucrose, and resorcinol precursor may be used. have.

As a method of coating the titanium dioxide with the carbon material, known methods such as spray coating, dipping, sol-gel, chemical vapor deposition, solid phase method, and combinations thereof can be used. In one embodiment, the titanium dioxide may be coated with a carbon material by a chemical vapor deposition method and a solid phase method. For example, the following method may be used to coat titanium dioxide with a carbon material.

The carbon precursor such as titanium dioxide and phthalocyanine may be mixed at a weight ratio of 10: 1 to 1: 1 and heat-treated at 800 to 1000 ° C for 1 to 3 hours under an inert gas. At this time, the phthalocyanine is decomposed and coated on the titanium dioxide surface.

The coating method is well understood by those skilled in the art, so further explanation will be omitted.

The thickness of the coating layer comprising the carbon material coated by any one of the above coating methods may be from 1 to 20 nm.

The content of the carbon material may be 1 to 30 wt%, for example, 5 to 15 wt%, based on the total amount of the coated Na ₄ Ti ₅ O ₁₂ to be produced. When the coating layer and the carbon material satisfy the numerical ranges as described above, the electric conductivity is improved and the energy density is not significantly lowered, which is preferable

In order to be coated with the carbon material in the numerical range, titanium dioxide and carbon precursor may be used in a weight ratio of 10: 1 to 1: 1.

(b)

In the step (b), the titanium dioxide disodium salt coated with the carbon material obtained in the step (a) is mixed with the sodium salt and heat-treated to form Na ₄ Ti ₅ O ₁₂ .

The titanium dioxide particles coated with the carbon material may be mixed with the sodium salt such that the atomic ratio of Ti: Na in the resulting crystal structure is 5: 4. For example, when sodium carbonate is used as sodium, Sodium carbonate may be mixed in a weight ratio of 1: 1 to 1: 1.1.

The sodium salt can be used without limitation as long as it is a salt capable of providing sodium. For example, the sodium salt may be selected from sodium carbonate, sodium hydroxide, sodium acetate, sodium nitrate, and combinations thereof.

At this time, the heat treatment temperature may be performed at a temperature of 500 to 700 ° C, for example, at a temperature of 550 to 650 ° C. If the temperature range does not satisfy the above numerical range, impurities such as Na ₂ Ti ₃ O ₇ can be generated. If the temperature is too high, crystal growth accelerates and particle size control becomes difficult.

Further, the heat treatment may be performed at the above temperature for 1 to 10 hours.

In one embodiment, 7.9 to 8.1 g of the titanium dioxide coated with the carbon material is added to the agitator, 8.4 to 8.6 g of sodium carbonate is added to the agitator, the mixture is mixed at 100 to 300 rpm for 1 hour, The mixture is heat-treated at 600 ° C for 10 hours to prepare Na ₄ Ti ₅ O ₁₂ .

Figure 1 is a graphical representation of Na ₄ Ti ₅ O ₁₂ Crystal structure. The crystal structure is not limited to the layer structure of the Li ₄ Ti ₅ O ₁₂ spinel structure or the Na ₄ Ti ₅ O ₁₂ homogeneous polymorphism studied in the lithium secondary battery, And have a three-dimensional framework that belongs to the same. Specifically, the O and Na atoms forming the crystal structure form a distorted close-packed structure, and Ti is located at the octahedral site. Also, as shown in FIG. 1, it has a tunnel structure in the [100] and [010] directions, and lithium ions can be diffused into such a tunnel. The unit cell dimension has 0.532 nm in the a-axis and 0.956 nm in the b-axis.

Another embodiment of the present invention provides Na ₄ Ti ₅ O ₁₂ produced by the process described above.

Another embodiment of the present invention provides a negative electrode active material for a secondary battery comprising Na ₄ Ti ₅ O ₁₂ .

The size of the Na ₄ Ti ₅ O ₁₂ particle size may be from 2 to 100 nm, for example from 10 to 30 nm. When the particle size of Na ₄ Ti ₅ O ₁₂ exceeds the above-mentioned range, the diffusion of lithium ions is slowed during charging and discharging, and the reversible capacity is reduced, which is not preferable.

The BET surface area of the Na ₄ Ti ₅ O ₁₂ may be between 10 and 500 m ² / mg. When the numerical value is satisfied, the response surface area is large and the diffusion distance is short, so that the output characteristic is excellent.

The Na ₄ Ti ₅ O ₁₂ may be coated with a carbon material, and the thickness of the coating layer containing carbon may be 1 to 20 nm. In addition, the carbon material may be a coating of Na ₄ Ti ₅ O ₁₂ By weight based on the total amount of the composition.

Another embodiment of the present invention provides a secondary battery comprising the above-mentioned negative electrode active material. The secondary battery includes a lithium secondary battery, a sodium secondary battery, and the like. Hereinafter, in one embodiment, a lithium secondary battery is described, but the present invention is not limited thereto.

2 is an exploded perspective view of a lithium secondary battery according to one embodiment. 2, 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, an anode 114 and a separator 113 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 the negative active material.

The negative electrode active material layer also includes a binder, and may optionally 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.

In an embodiment of the present invention, a compound capable of reversibly intercalating and deintercalating lithium (lithium intercalation compound) can be used as the cathode active material. 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 _{? Wherein} 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05 and 0 <? Li _a Ni _{1 -bc} Co _b R _c O _2-α Z ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 <α <2; Li _a Ni _{1 -b- c} 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 the} 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 wherein, 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.

( Manufacturing example  1: Nano-sized Na ₄ Ti ₅ O ₁₂  of  Manufacturing method)

TiO ₂ having a particle diameter of about 50 nm and phthalocyanine (Aldrich) as a carbon precursor were prepared. 10 g of TiO ₂ and 5 g of phthalocyanine were placed in a stirrer and mixed at 100 rpm for 1 hour. The resulting mixture was heat-treated at 900 ° C. for 3 hours to obtain carbon-coated TiO ₂ . This from TiO ₂ 8 g and Na ₂ CO ₃ to 8.5 g were placed in the agitator to 100 rpm 1 hour while agitating, and the mixture for 10 hours, sodium titanium oxide particle diameter of about 50nm by heating for at 600 ℃ obtained therefrom obtained (Na ₄ Ti ₅ O ₁₂ ).

As a result of TGA (thermo gravimetric analyzer) test for Na ₄ Ti ₅ O ₁₂ obtained in the present example, it was confirmed that the carbon-coated sodium titanium oxide (Na ₄ Ti ₅ O ₁₂ ) contained 10 wt% (Fig. 3).

(compare Manufacturing example  One)

Sodium titanium oxide (Na ₄ Ti ₅ O ₁₂ ) was obtained in the same manner as in Preparation Example 1, except that the carbon material was coated. The obtained Na ₄ Ti ₅ O ₁₂ was bulked and the particle size of the bulk Na ₄ Ti ₅ O ₁₂ was about 500 nm.

SEM  Picture

4A to 4C are SEM photographs of TiO ₂ , Na ₄ Ti ₅ O ₁₂ according to Production Example 1 and Na ₄ Ti ₅ O ₁₂ according to Comparative Production Example 1, respectively. As shown in FIG. 4B, the particle size of Na ₄ Ti ₅ O ₁₂ according to Preparation Example 1 is as small as several tens of nanometers, while Na ₄ Ti ₅ O ₁₂ according to Comparative Preparation Example 1 shown in FIG. The particles were very bulk and the crystal structure was very large.

XRD  Pattern measurement

5 is a graph showing XRD patterns of TiO ₂ and Na ₄ Ti ₅ O ₁₂ according to Production Example 1 and Comparative Production Example 1. As shown in Figure 5, the generation of Na ₄ Ti ₅ O ₁₂ from Na ₄ Ti ₅ O is ₁₂ 2O shown in the XRD of 21, 33, 34, 49, 51 degrees peak according to Preparation Example 1 and Comparative Preparation Example 1 Can be confirmed.

( Example  One)

Manufacture of lithium secondary battery

Na ₄ Ti ₅ O ₁₂ prepared in Preparation Example 1 was mixed with a polyvinylidene fluoride binder and a carbon black conductive material in an N-methylpyrrolidone solvent in an amount of 8: 1: 1 by weight to prepare a negative electrode active material slurry . This negative electrode active material slurry was applied to a Cu-foil current collector to prepare a negative electrode.

As the non-aqueous electrolyte, a mixed solvent (volume ratio = 3/3/4) of EC / DEC / EMC (ethylene carbonate / diethylene carbonate / ethyl methyl carbonate) in which 1 M of LiPF ₆ was dissolved was used.

A coin-type half cell was prepared using the negative electrode, the non-aqueous electrolyte, and the lithium metal as counter electrodes.

( Comparative Example  One)

A lithium secondary battery was produced in the same manner as described in Example 1, except that TiO ₂ having a size of 50 nm was used as a negative electrode active material.

( Comparative Example  2)

Synthesized according to Comparative Preparation Example 1 A lithium secondary battery was produced in the same manner as described in Example 1, except that Na ₄ Ti ₅ O ₁₂ was used as a negative electrode active material.

Evaluation test of cell characteristics

The cells prepared according to Example 1, Comparative Example 1 and Comparative Example 2 were evaluated for battery characteristics by the following methods. Specific experimental methods and experimental results are as follows.

(1) Evaluation of cycle characteristics

The cycle life characteristics were evaluated for 100 coin-type half cells manufactured according to Example 1, Comparative Example 1, and Comparative Example 2 at 30 ° C with 0.1 C charge and discharge, The specific capacity for each cycle was measured and is shown in FIG.

As shown in FIG. 6, the capacity of Comparative Example 1 significantly decreased as the cycle progressed, compared with the initial capacity, whereas the capacity of Example 1 and Comparative Example 2 tended to be maintained even when the cycle proceeded . On the other hand, Example 1 exhibited remarkably superior initial capacity as compared with Comparative Example 2, and the capacity was remarkably superior to Comparative Example 2 even when the cycle proceeded. This indicates that the cycle characteristics of the lithium secondary battery are improved by using the anode active material containing the Na ₄ Ti ₅ O ₁₂ particles having a size of several tens of nanometers.

(2) Charging and discharging  Character rating

The charge / discharge characteristics of the lithium secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 were evaluated by the following methods.

Charging was performed at a constant current (CC) at 0.1 C rate up to 3.0 V. The discharge was performed at the same rate as the charging rate, and cut off at a voltage of 0.43 V. Subsequently, charging and discharging after the cycle were performed at the same rate as the charging rate, and the charging and discharging operations were carried out in the same manner as in Example 1, Comparative Example 1, and Comparative Example 2 at 1 time, 2 times, 5 times, 10 times, 7A, 7B and 7C show the results of charging and discharging the lithium secondary battery according to the present invention.

Figure 7a, 7b, 7c show respectively the first embodiment of the nano-sized Na ₄ Ti ₅ O _12, Comparative Example 1, nano-sized TiO _2, and Comparative Example 2, the bulk size of the charge and discharge curve of Na ₄ Ti ₅ O ₁₂ of the . As shown in FIG. 7B, the nano-sized TiO ₂ of Comparative Example 1 had a flat curve near about 1.7 V, whereas the Na ₄ Ti ₅ O ₁₂ of FIG. 7 a was found to have a flat curve between 2 and 1.5 _V. The nano-sized Na ₄ Ti ₅ O ₁₂ of Example 1 also had a reversible capacity of about 100 mAh / g while the bulk-sized Na ₄ Ti ₅ O ₁₂ of Comparative Example 2 had a small capacity of about 40 mAh / g Respectively. When the particles of Na ₄ Ti ₅ O ₁₂ of Example 1 were used, the diffusion distance of lithium ions was significantly shorter than that of bulk-sized Na ₄ Ti ₅ O ₁₂ , thereby reducing the resistance of the battery and increasing the capacity thereof .

As the cycle progresses, the charging / discharging curve of Na ₄ Ti ₅ O ₁₂ changes from the slope to the flat curve, which results in ion exchange with Na in the Na ₄ Ti ₅ O ₁₂ structure and Li present in the electrolyte. The structure is changed to Na _{4 - x} Li _x Ti ₅ O ₁₂ .

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.

Claims (17)

delete delete delete delete delete delete delete delete delete comprising the steps of: (a) coating a titanium dioxide (TiO ₂₎ particles of a carbon material; And
(b) mixing the carbon dioxide-coated titanium dioxide particles with a sodium salt, and heat-treating the mixture, wherein the Na ₄ Ti ₅ O ₁₂ is produced according to the process for producing Na ₄ Ti ₅ O _12. Na ₄ Ti ₅ O ₁₂ . 12. The method of claim 11,
And the Na ₄ Ti ₅ O ₁₂ particle size is 2 to 100 nm. 12. The method of claim 11,
And a BET surface area of 10 to 500 m ² / mg. 12. The method of claim 11,
Wherein the Na ₄ Ti ₅ O ₁₂ comprises a coating layer containing a carbon material. 15. The method of claim 14,
Wherein the coating layer has a thickness of 1 to 20 nm. 15. The method of claim 14,
Wherein the content of the carbon material is 1 to 30 wt%. 16. A secondary battery comprising a negative electrode active material for a secondary battery according to any one of claims 11 to 16.

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