KR101223556B1 - Negative active material for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

A negative active material for a lithium secondary battery and a lithium secondary battery including the same, the active material includes a metal-based active material and a solid electrolyte having an ionic conductivity of 1.0 × 10 ⁻⁴ S / cm or more.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative active material for a lithium secondary battery, and a lithium secondary battery comprising the negative active material and a lithium secondary battery including the same. BACKGROUND ART [0002]

The present disclosure relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

BACKGROUND ART Lithium secondary batteries, which are in the spotlight as power sources for portable small electronic devices, exhibit high energy densities by showing discharge voltages two times or more higher than those using conventional aqueous alkali solutions using organic electrolyte solutions.

As a cathode active material of a lithium secondary battery, an oxide made of lithium and a transition metal having a structure capable of intercalating lithium, such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNi _{1- x} Co _x O ₂ (0 <X <1) This is mainly used.

As the negative electrode active material, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting / desorbing lithium have been applied, and graphite-based materials such as artificial graphite and natural graphite have been most widely used. Since the graphite-based negative electrode active material does not precipitate metal lithium, internal short circuit caused by dendrites does not occur and thus additional disadvantages do not occur.

However, the graphite-based active material has a theoretical lithium occlusion capacity of 372 mAh / g, and has a limit of very small capacity corresponding to 10% of the lithium metal theoretical capacity. Therefore, research on lithium metal and metal alloy negative electrode active materials, which have been proposed in the early stages of secondary batteries, in which a high capacity is required, has been actively studied again.

The biggest problem of lithium metal and metal alloy negative electrode active materials is that dendrite is formed during recharging, and as the charge and discharge are repeated, the formed dendrite penetrates the separator, causing internal short circuit. In addition, the dendrite formation increases the specific surface area of the negative electrode, thereby rapidly increasing the reactivity, and as a result, an irreversible reaction with the electrolytic solution occurs actively, resulting in a rapid deterioration of cycle life characteristics.

In order to improve this problem, a structural method of minimizing the growth of dendrites is proposed by coating the surface of the lithium metal anode active material or by using lithium metal in the form of powder such as lithium metal powder surface-coated with carbon or polymer. It became.

Another approach is to use lithium alloys or metal materials such as Sn, Si, etc. to minimize lithium metal precipitation. When forming such a structure and metal alloy or compound, the theoretical capacity of Li 3862 mAh / g, Si about 4200 mAh / g, and Sn 994 mAh / g is shown in terms of electrochemical capacity, so that if only electrochemical reversibility is secured, It is possible to secure an extremely high discharge capacity.

However, in the case of the metal-based active material, there are still problems such as electrochemical reversibility, consequent charge and discharge efficiency, and sudden drop in electrochemical cycling charge and discharge capacity. Particularly, in the case of the metal active material, cracks are generated in the metal powder as the lattice volume of the metal is rapidly increased and contracted, which causes the micronization of particles to trigger the growth of the solid electrolyte interface layer. And one of the most fundamental causes of this problem is that the deposition of Li ions during recharging is uneven as the cycle is repeated.

One embodiment of the present invention to provide a negative active material for a lithium secondary battery excellent in cycle life characteristics.

Another embodiment of the present invention is to provide a lithium secondary battery including the negative electrode active material.

One embodiment of the present invention provides a negative electrode active material for a lithium secondary battery including a metal-based active material and a solid electrolyte having an ionic conductivity of 1.0 X 10 ^-4 S / cm or more.

The ionic conductivity of the solid electrolyte may be 1.0 X 10 ^-4 S / cm to 4.0 X 10 ^-3 S / cm.

The solid electrolyte may be at least one represented by the following Chemical Formulas 1 to 3.

[Formula 1]

Li _a X _b Y _c Z _d (PO ₄ ) ₃

(In the formula 1,

X is Zn, Sr, La, Pr, Nd, Eu, Sm, Ta, Ba, Ca or a combination thereof,

Y is Sr, Sb, Nb, Ti, Al, Mg, La, F, Si, B, Ge, O or a combination thereof

Z is In, Mg, W, Al, V, P, Si or a combination thereof,

a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0)

[Formula 2]

Li _a X _b Y _c

(In Formula 2,

X is N, β-Al ₂ O ₃ , Cd, I, P or a combination thereof,

Y is Cl, Br, N or a combination thereof,

a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0, e is an integer from 0 to 5.0)

The metal-based active material is Si, Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements and combinations thereof, not Si) ), Sn, Sn-R (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and not Sn) or their May be a combination.

The solid electrolyte may be mixed with the metal-based active material or coated on the surface of the metal-based active material.

The average particle size of the metal-based active material may be 100 nm to 15 μm, and the average particle size of the solid electrolyte may be 100 nm to 500 nm.

The mixing ratio of the metal-based active material and the solid electrolyte may be 99.99: 0.01 wt% to 70: 30 wt%.

Another embodiment of the present invention provides a lithium secondary battery including a negative electrode including the negative electrode active material, a positive electrode including a positive electrode active material, and a nonaqueous electrolyte.

Other specific details of embodiments of the present invention are included in the following detailed description.

The negative active material for a rechargeable lithium battery according to one embodiment of the present invention may provide a battery exhibiting high capacity and excellent cycle life characteristics.

1 is a schematic diagram showing a charge and discharge state of a negative electrode including a metal-based active material.
Figure 2 is a schematic diagram showing the charge and discharge state of the negative electrode including a metal-based active material and a solid electrolyte according to an embodiment of the present invention.
Figure 3 is a schematic view showing the structure of a lithium secondary battery according to an embodiment of the present invention.
Figure 4 is a graph showing the XRD of the solid electrolyte prepared in Example 1.
FIG. 5 is a graph showing cycle life characteristics of a half cell manufactured using the negative electrode active materials of Examples 1 and 2 and Comparative Examples 1 and 2. FIG.

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

One embodiment of the present invention provides a negative electrode active material for a lithium secondary battery including a metal-based active material and a solid electrolyte having an ionic conductivity of 1.0 X 10 ^-4 S / cm or more.

The metal-based active material is Si, Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements and combinations thereof, not Si) ), Sn, Sn-R (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and not Sn) or their May be a combination.

The metal-based active material is present in the form of particles, the average particle size may be about 100nm to about 15㎛. Metal-based active materials having an average particle size in this range can be easily obtained economically and can exhibit excellent output characteristics.

The solid electrolyte may be present in a mixed state with the metal-based active material or as a coating layer on the surface of the metal-based active material. Whatever the state of the solid electrolyte, when present in the vicinity of the metal-based active material, the volumetric expansion, dendrite formation and irreversible reactions generated during the charge / discharge of the metal-based active material can be reduced, resulting in improved cycle life characteristics. have. That is, since the solid electrolyte should be present around the metal active material, if the active material layer of the metal active material is formed in the current collector, and the solid electrolyte is present as a separate layer on the active material layer, the metal active material as a whole of the active material layer Since there is no solid electrolyte around the material, there is little effect of helping to diffuse ions inside the metal-based active material to suppress the formation of dendrite, to reduce the volume expansion and irreversible reaction generated during charging and discharging.

This will be described in more detail with reference to FIGS. 1 and 2.

FIG. 1 is a view showing a diagram in which dendrites are formed when a negative electrode including only a metal-based active material is repeatedly charged and discharged. As shown in FIG. 1, as re-deposition of lithium ions generated during charging occurs locally and intensively in the metal-based active material, as the dendrites are formed, volume expansion may occur. In addition, cracks are generated due to dendrite formation and volume expansion, and the surface area is increased to increase the irreversible reaction with the electrolyte.

On the contrary, as shown in FIG. 2, when a solid electrolyte is present around the metal-based active material, redeposition of lithium ions occurs evenly on the metal-based active material, and thus, dendrite formation and volume expansion may occur less. It is possible to prevent cracking and to reduce the irreversible reaction with the electrolyte because there is no surface area increase.

Such a solid electrolyte may suitably have an ionic conductivity of at least 1.0 × 10 ⁻⁴ S / cm, and more preferably, have a conductivity of 1.0 × 10 ⁻⁴ S / cm to 4.0 × 10 ⁻³ S / cm. . If the ionic conductivity is less than 1.0 X 10 ^-4 S / cm, there may be a problem that it is difficult to see the effect of using a solid electrolyte. That is, even when the solid electrolyte is used together with the metal-based active material, when the solid electrolyte (eg, polyethylene oxide, etc.) having an ionic conductivity of less than 1.0 X 10 ^-4 S / cm is used, the metal-based active material is generated during charge and discharge. By reducing the volume expansion, dendrite formation and irreversible reaction that results, the effect of improving cycle life characteristics can not be expected as a result.

The ion conductivity is a result obtained by pressing a solid electrolyte in the form of pellets by using electrochemical impedance spectroscopy (EIS), placing the Pt electrode on both sides of the pellet, and then measuring the impedance.

The solid electrolyte may be at least one represented by the following Chemical Formulas 1 to 3.

[Formula 1]

Li _a X _b Y _c Z _d (PO ₄ ) ₃

(In the formula 1,

X is Zn, Sr, La, Pr, Nd, Eu, Sm, Ta, Ba, Ca or a combination thereof,

Y is Sr, Sb, Nb, Ti, Al, Mg, La, F, Si, B, Ge, O or a combination thereof

Z is In, Mg, W, Al, V, P, Si or a combination thereof,

a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0)

[Formula 2]

Li _a X _b Y _c

(In Formula 2,

X is N, β-Al ₂ O ₃ , Cd, I, P or a combination thereof,

Y is Cl, Br, N or a combination thereof,

a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0, e is an integer from 0 to 5.0)

The average particle size of the solid electrolyte may be about 100 nm to about 500 nm. When the particle size of the solid electrolyte is included in the above range, there is no aggregation of the solid electrolyte particles according to an embodiment of the present invention, coating is easy, and ionic conductivity may be properly maintained.

In addition, by using a solid electrolyte having excellent ion conductivity in the negative electrode, lithium ions can be diffused well, and as a result, it is possible to suppress the dendrite phenomenon caused by uneven deposition of lithium ions on the negative electrode active material, resulting in cycle life characteristics. Can improve.

The mixing ratio of the metal-based active material and the solid electrolyte may be 99.99: 0.01 wt% to 70: 30 wt%. When the content of the solid electrolyte is in the above range, the initial capacity is greatly increased, in particular, the initial capacity is more than two times better than when using a crystalline anode active material such as graphite, and the effect of improving the cycle life characteristics more You can get it.

As described above, the negative electrode active material according to the exemplary embodiment of the present invention may exist in a state in which the solid electrolyte is mixed with the metal-based active material or as a coating layer on the surface of the metal-based active material. When present in a mixed state, the solid electrolyte and the metal-based active material may be prepared by physically dry mixing. In addition, when present as a coating layer may be prepared by adding a solid electrolyte to the solvent to prepare a coating solution, and then coating the surface of the metal-based active material with the coating solution. In this case, the coating method may be performed by any coating method such as spray coating or dipping. In addition, ethanol, anhydrous ethanol, isopropyl alcohol may be used as the solvent. The concentration of the coating liquid may be 10 wt% to 40 wt%, and the thickness of the coating layer may be 100 nm to 5 μm.

Another embodiment of the present invention relates to a lithium secondary battery.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, and the like, Depending on the size, it can be divided into bulk type and thin film type. The structure and the manufacturing method of these cells are well known in the art, and detailed description thereof will be omitted.

A lithium secondary battery according to another embodiment of the present invention includes a negative electrode including a negative electrode active material according to an embodiment of the present invention, a positive electrode including a positive electrode active material, and a nonaqueous electrolyte.

The negative electrode includes a negative electrode active material layer including a negative electrode active material and a current collector.

Content of the negative electrode active material in the negative electrode active material layer may be 95 to 99% by weight based on the total weight of the negative electrode active material layer.

The negative electrode active material layer also includes a binder, and optionally may further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 to 5% by weight based on the total weight of the negative electrode active material layer. When the conductive material is further included, the negative electrode active material may be used in an amount of 90 to 98 wt%, the binder may be used in an amount of 1 to 5 wt%, and the conductive material may be used in an amount of 1 to 5 wt%.

The binder adheres the anode active material particles to each other well, and also serves to adhere the anode active material to the current collector well. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

The water-insoluble binder includes polyvinyl chloride, carboxylated polyvinylchloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and olefin copolymers having 2 to 8 carbon atoms, (meth) acrylic acid and (meth) Copolymers or combinations thereof.

When using the water-soluble binder as the negative electrode binder, it may further include a cellulose-based compound capable of imparting viscosity. As the cellulose-based compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, alkali metal salts thereof or the like may be used in combination. Na, K or Li may be used as the alkali metal. The amount of such thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the binder.

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Carbon-based materials such as black and 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.

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

The anode includes a current collector and a cathode active material layer formed on the current collector. As the cathode active material, a compound (lithiated intercalation compound) capable of reversible intercalation and deintercalation of lithium may be used. Concretely, at least one of complex oxides of metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used. More specific examples of the positive electrode active material may be a compound represented by any one of the following formula. Li _a A _{1 -b} X _b D ₂ (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5); Li _a E _{1 - b} X _b O _{2 - c} D _c (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05); _{Li a E 2 - b X b} O 4 - c D c (0 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _{1 -b- c} Co _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <?? 2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 -α} T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 - ?} T ₂ (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? <2); Li _a Ni _{1 -b- c} Mn _b X _c D _? (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <?? 2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2- α} T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2 - ?} T ₂ (0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? <2); Li _a Ni _b E _c G _d O ₂ (0.90? A? 1.8, 0? B? 0.9, 0? C? 0.5, 0.001? D? 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1) Li _a CoG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a MnG _b O ₂ (0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (0.90? A? 1.8, 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO 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); LiFePO ₄

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations 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 at least one coating element compound selected from the group consisting of oxides, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. 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 process may be any coating method as long as it can be coated with the above compounds using a method that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating or dipping). Detailed descriptions thereof will be omitted since they can be understood by those skilled in the art.

The amount of the cathode active material in the cathode active material layer may be 90 to 98 wt% based on the total weight of the cathode active material layer.

The cathode active material layer also includes a binder and a conductive material. At this time, the content of the binder and the conductive material may be 1 to 5% by weight based on the total weight of the positive electrode active material layer, respectively.

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

The binder serves to adhere the positive electrode active materials to each other and to adhere the positive electrode active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinyl pyrrolidone But are not limited to, water, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon .

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Carbon-based materials such as black and 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.

Al foil may be used as the current collector, but 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. N-methylpyrrolidone may be used as the solvent, but is not limited thereto. When a water-soluble binder is used for the negative electrode, water may be used as a solvent used in preparing the negative electrode active material composition.

The nonaqueous electrolyte includes a nonaqueous 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, dimethyl acetate, methyl propionate, ethyl propionate , gamma -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. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent, and the aprotic solvent may be R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms. Amides such as nitriles, dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like.

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, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of 1: 1 to 1: 9, so that the performance of the electrolyte may be excellent.

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

As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound of the following Formula 5 may be used.

[Chemical Formula 5]

(In Formula 5, R ₁ to R ₆ are each independently selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group having 1 to 10 carbon atoms, and a combination thereof.)

Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 , 2,4-trichlorobenzene, iodobenzene, 1,2-dioodobenzene, 1,3-dioiobenzene, 1,4-dioiobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-dioodotoluene, 2,4-diaodotoluene, 2 , 5-diaodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The non-aqueous electrolyte may further include vinylene carbonate or an ethylene carbonate compound represented by Chemical Formula 6 to improve battery life.

[Formula 6]

(In Formula 6, R ₇ and R ₈ are each independently selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and a fluorinated C1-5 alkyl group, wherein R At least one of ₇ and R ₈ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that both R ₇ and R ₈ are not hydrogen; .)

Representative examples of the ethylene carbonate-based compound include diethylene carbonate, diethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and the like, such as difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, . When such a life improving additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the cell to enable operation of a basic lithium secondary battery and to promote the movement of lithium ions between the anode and the cathode. Representative examples of such lithium salts are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiN (SO ₃ C ₂ F ₅ ) ₂ , 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, One or more selected from the group consisting of LiI and LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB)) are included as supporting electrolytic salts. It is preferable to use in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can be effectively moved.

3 schematically shows a typical structure of a lithium secondary battery according to an embodiment of the present invention. 3, the lithium secondary battery 1 includes a battery 3 including an anode 3, a cathode 2, and an electrolyte solution impregnated in the separator 4 existing between the anode 3 and the cathode 2, And a sealing member (6) for sealing the battery container (5).

Depending on the type of the lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. The separator may be a polyethylene / polypropylene double layer separator, a polyethylene / polypropylene / polyethylene triple layer separator, a polypropylene / polyethylene / poly It is needless to say that a mixed multilayer film such as a propylene three-layer separator and the like can be used.

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

(Example 1)

1) Solid Electrolyte Preparation

Li ₂ CO ₃ , Al ₂ O ₃ , TiO ₂ and (NH ₄ ) ₂ HPO ₄ were stirred in an ethanol solvent at a rate of 120 rpm for 2 hours. At this time, the mixing ratio of Li ₂ CO ₃ , Al ₂ O ₃ , TiO ₂ and (NH ₄ ) ₂ HPO ₄ was 1.8791: 0.5984: 5.3118: 15.4992 by weight.

The mixture was calcined at 700 ° C. for 2 hours, and the calcined product was first stirred for 6 hours at a speed of 120 rpm in ethanol solvent and then stirred for 2 hours at a speed of 50 rpm.

The resulting stirred product was dried in air at a temperature of 120 ° C. for 3 hours and then sintered in air at a temperature of 920 ° C. for 8 hours.

By sintering for 2 hours and then pressing the resulting sintered product to a pressure of 4.5ton, the product to a temperature of 1000 ℃ in air _{Li 1 .3 Ti 1 .7 Al 0} .3 (PO 4) 3 Solid electrolytes were prepared. Manufactured _{Li 1 .3 Ti 1 .7 Al 0} .3 (PO 4) 3 X-ray diffraction measurement of the solid electrolyte using CuKα showed a structure similar to that of the LiTi ₂ (PO ₄ ) ₃ reference material, as shown in FIG. 4. The results, it can be seen that as the amount of the Al write down LiTi ₂ (PO _{4) 3} is slightly shifted peak is obtained, the main structure is LiTi ₂ (PO ₄₎ having a structure similar to the _three reference materials.

In addition, the manufactured _{Li 1 .3 Ti 1 .7 Al 0} .3 (PO 4) 3 After preparing the solid electrolyte in pellet form, after placing the Pt electrode on both sides of the pellet, the ion conductivity was measured by an EIS measuring impedance, and 1.19 X 10 ^-4 S / cm was obtained.

2) electrode manufacturing

80 wt% of Sn powder (Aldrich, average particle size: less than 10 μm, particle purity: 99% or more) and 20 wt% of the prepared LiTi ₂ (PO ₄ ) ₃ solid electrolyte were dry mixed to obtain a negative electrode active material.

The negative electrode active material, the super-P conductive material, and the polyvinylidene fluoride binder were mixed in an N-methylpyrrolidone solvent at a ratio of 94: 3: 3% by weight to prepare a negative electrode active material slurry.

The negative electrode active material slurry was applied, dried, and rolled onto a 10 μm thick copper current collector to prepare a negative electrode having an average thickness of about 60 μm and a negative electrode loading level of 10 mg / cm 2.

(Example 2)

90 wt% of Sn powder (Aldrich, 99% or more of particle purity of less than 10 μm) and 10 wt% of the LiTi ₂ (PO ₄ ) ₃ solid electrolyte prepared in Example 1 were dry mixed to obtain a negative electrode active material.

The negative electrode was prepared in the same manner as in Example 1 using the negative electrode active material.

(Comparative Example 1)

Sn powder (Aldrich, 99% by weight particle content of less than 10 μm) The negative electrode active material, the super-P conductive material, and the polyvinylidene fluoride binder were mixed in an N-methylpyrrolidone solvent at a ratio of 94: 3: 3% by weight. To prepare a negative electrode active material slurry.

The negative electrode active material slurry was applied, dried, and rolled onto a 10 μm thick copper current collector to prepare a negative electrode having an average thickness of about 60 μm and a negative electrode loading level of 10 mg / cm 2.

(Comparative Example 2)

LiTi ₂ (PO ₄ ) ₃ with 90% by weight of Sn powder (Aldrich, 99% or more of particle purity less than 10 μm) and ionic conductivity of 1.50 X 10 ^-5 S / cm 10 wt% of the solid electrolyte was dry mixed to obtain a negative electrode active material. LiTi ₂ (PO ₄ ) ₃ The ionic conductivity of the solid electrolyte was obtained by preparing the solid electrolyte in pellet form, and then placing the Pt electrode on both sides of the pellet, and then measuring the ion conductivity by EIS measuring impedance.

The negative electrode was prepared in the same manner as in Example 1 using the negative electrode active material.

Coin-type half cells were manufactured using the negative electrodes and lithium metals prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 as counter electrodes. At this time, a mixed solvent (3: 3: 4 volume ratio) of ethylene carbonate, ethylmethyl carbonate and diethyl carbonate in which 1.15M LiPF ₆ was dissolved was used.

The prepared half cell was charged and discharged 50 times with 0.1C constant current charge (cutoff voltage: 0.01V) and 0.1C constant current discharge (cutoff voltage: 1.5V), and the discharge capacity retention rate according to the number of cycles is shown in FIG. 5. . As shown in FIG. 5, in Comparative Example 1 in which a solid electrolyte was not used, the discharge capacity retention ratio dropped to 80% or less after about 15 cycles, but dropped to less than about 60% after 30 cycles, and after 60 cycles. It can be seen that the cycle life characteristics are markedly degraded as only 24%. In contrast, in Examples 1 and 2 using Sn and a solid electrolyte, it can be seen that even after 50 cycles, capacity retention rates of 60% and 47% were obtained.

In addition, even in the case of using a solid electrolyte, in Comparative Example 2 using a solid electrolyte having a low ionic conductivity of 1.50 × 10 ⁻⁵ S / cm, the discharge capacity retention rate rapidly decreased after about 20 cycles. A result was obtained in which the discharge capacity was hardly obtained.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And it goes without saying that the invention belongs to the scope of the invention.

Claims (6)

Metal-based active materials and
A solid electrolyte having an ionic conductivity of 1.0 × 10 ⁻⁴ S / cm to 4.0 × 10 ⁻³ S / cm, wherein the solid electrolyte is coated on the surface of the metal-based active material,
The solid electrolyte is a negative active material for a lithium secondary battery, which is at least one of the following formulas 1 to 3.
[Formula 1]
Li _a X _b Y _c Z _d (PO ₄ ) ₃
(In Formula 1,
X is Zn, Sr, La, Pr, Nd, Eu, Sm, Ta, Ba, Ca or a combination thereof,
Y is Sr, Sb, Nb, Ti, Al, Mg, La, F, Si, B, Ge, O or a combination thereof
Z is In, Mg, W, Al, V, P, Si or a combination thereof,
a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0)
(2)
Li _a X _b Y _c
(In the formula (2)
X is N, β-Al ₂ O ₃ , Cd, I, P or a combination thereof,
Y is Cl, Br, N or a combination thereof,
a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0, e is an integer from 0 to 5.0)
(3)
N _a X _b Y _c Z _d O _e
(In Chemical Formula 3,
X is Zn, Sr, La, Pr, Nd, Eu, Sm, Ta, Ba, Ca or a combination thereof,
Y is Sr, Sb, Nb, Ti, Al, Mg, La, F, Si, B, Ge, O or a combination thereof,
Z is In, Mg, W, Al, V, P, Si or a combination thereof,
a is an integer from 0.1 to 6.0, b is an integer from 0 to 3.0, c is an integer from 0 to 3.0, d is an integer from 0 to 3.0, e is an integer from 0 to 5.0) The method of claim 1,
The metal-based active material is Si, Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements and combinations thereof, not Si) ), Sn, Sn-R (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and not Sn) or their The negative electrode active material for lithium secondary batteries which is a combination. The method of claim 1,
The metal-based active material is a negative active material for a lithium secondary battery having an average particle size of 100nm to 15㎛. The method of claim 1,
The solid electrolyte is a negative active material for a lithium secondary battery having an average particle size of 100nm to 500nm. The method of claim 1,
The mixing ratio of the metal-based active material and the solid electrolyte is 99.99: 0.01 wt% to 70: 30 wt% of a negative active material for a lithium secondary battery. A negative electrode comprising the negative electrode active material of any one of claims 1 to 5;
A positive electrode including a positive electrode active material; And
Nonaqueous electrolyte
&Lt; / RTI &gt;

Images