KR101780777B1 - Method for charging and discharging lithium secondary battery - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery comprising a positive electrode including a positive electrode active material; cathode; And a charge / discharge method for a lithium secondary battery including an electrolyte, wherein when the reaction capacity is 60-140 mAh / g in the voltage range in which the following Reaction 1 proceeds, the lithium secondary battery Thereby providing a charging / discharging method of the battery.
[Reaction Scheme 1]
Li _{1 + y} Mn _{2 - y - z} M _z O _{4 - x} Q _x + Li ⁺ + e ^- Li _{2 + y} Mn _{2 - y - z} M _z O _{4 - x} Q _x

Description

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

And a charging / discharging method of the lithium secondary battery.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, . Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage. As a negative electrode active material of such a lithium secondary battery, a carbon material is mainly used, and the use of lithium metal, a sulfur compound and the like are also considered. In addition, lithium-containing cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode active material, and a lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure and a lithium- ₂ ) are used.

Among these lithium manganese oxides, the spinel-based LiMn ₂ O ₄ exhibits relatively flat potentials in the ₄ V region (3.7 to 4.3 V) and the 3 V region (2.7 to 3.1 V). However, in the 3V region, cycle and storage characteristics are very poor, and it is known that it is difficult to utilize. The reason for this is the existence of a single phase of the cubic phase in the 4V region due to the phase transition of Jahn-Teller distortion, and a combination of the cubic phase and the tetragonal phase in the 3V region Phase to two-phase, and a phenomenon of elution of manganese into an electrolyte solution.

For this reason, the actual capacity is generally lower than the theoretical capacity and the C-rate characteristic is low when the 3V region of the spinel type lithium manganese oxide is utilized.

Accordingly, various studies have been conducted to improve cycle and storage characteristics in the 3V region.

The present invention provides a lithium secondary battery charging / discharging method capable of realizing a high capacity and an improved life characteristic of the lithium secondary battery.

One embodiment of the present invention relates to a positive electrode comprising a positive electrode active material; cathode; And a charge / discharge method for a lithium secondary battery including an electrolyte, wherein when the reaction capacity is 60-140 mAh / g in the voltage range in which the following Reaction 1 proceeds, the lithium secondary battery Thereby providing a charging / discharging method of the battery.

[Reaction Scheme 1]

Li_2+yMn_2-ｙ-zM_zO_4-xQ_x Li _{1 + y} Mn _{2 - y - z} M _z O _{4 - x} Q _x + Li ⁺ + e ^-

_{Li 2 + y Mn 2-y} -z M z O 4-x Q x

(Wherein M is at least one element selected from the group consisting of Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr and Zn, and Q is one or more elements selected from the group consisting of N, F, S and Cl.

In the charge / discharge method, the charge / discharge may be performed under the condition of 0.1C to 2C.

Wherein the charge / discharge method is a charging / discharging method of a lithium secondary battery in which a first voltage plateau and a second voltage plateau appear, wherein the first voltage plateau is at least 2.80V , And 2.90 V or less.

The charge / discharge method is a charging / discharging method of a lithium secondary battery in which a first voltage plateau and a second voltage plateau appear, and the second voltage plateau is at least 2.15V , And 2.30 V or less.

In the charge / discharge method, the initial cut-off voltage is less than 2.3 V at 0.1 C,

Off voltage may be increased by 0.1 V or more at the time when the reaction capacity in the first voltage plateau is 90 mAh / g or more and 140 mAh / g or less.

The initial cut-off voltage may be 2.0V or more, and less than 2.3V.

The cut-off voltage may be increased to a range of 2.4 V to 2.8 V when the reaction capacity in the first voltage plateau is 90 mAh / g or more and 140 mAh / g mAh / g.

The average capacity fade rate according to the charge / discharge cycle may be 0.50 mAh / (g · cycle) or less.

The positive electrode active material may include a spinel type positive electrode active material represented by the following formula (1); And graphite. ≪ / RTI >

???????? Li _{1 + y} Mn _{2 -y-z} M _z O _{4 -x} Q _x

1, 0? Y? 0.34, 0? Z? 1, M is at least one element selected from the group consisting of Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr and Zn, and Q is one or more elements selected from the group consisting of N, F, S and Cl.

The positive electrode active material may include a spinel type positive electrode active material represented by Formula 1; And graphite. ≪ RTI ID = 0.0 >

The cathode active material may be LiMn ₂ O ₄ .

The above Reaction Scheme 1 may be the Reaction Scheme 2 below.

[Reaction Scheme 2]

Li₂Mn₂O₄ LiMn ₂ O ₄ + Li ⁺ + e ^-

Li ₂ Mn ₂ O ₄

The electrolyte may be a non-aqueous organic solvent, and a lithium salt.

The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, aprotic solvent or a combination thereof.

The lithium _{salt, 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 ) wherein x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB) .

An embodiment of the present invention provides a method for charging and discharging a lithium secondary battery capable of realizing a high capacity and an improved life characteristic of the lithium secondary battery.

1 is a voltage-capacity profile according to the charge-discharge method of the first embodiment of the present invention.
2 is a cycle-capacity profile according to the charge-discharge method of the first embodiment of the present invention.
3 is a voltage-capacitance profile according to the charge-discharge method of Comparative Example 1 of the present invention.
4 is a cycle-capacity profile according to the charge-discharge method of Comparative Example 1 of the present invention.
5 is a voltage-capacitance profile according to the charge-discharge method of Comparative Example 2 of the present invention.
6 is a cycle-capacity profile according to the charge-discharge method of Comparative Example 2 of the present invention.

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

Whenever a component is referred to as " comprising ", it is to be understood that the component may include other components as well, without departing from the scope of the present invention.

In the present specification, "A to B" means not less than A and not more than B, unless otherwise defined.

An embodiment of the present invention provides a charging / discharging method of a lithium secondary battery for obtaining a high capacity and a high battery performance.

Specifically, one embodiment of the present invention is a positive electrode comprising: a positive electrode comprising a positive electrode active material; cathode; And an electrolyte, wherein the lithium secondary battery is a charge / discharge method for a lithium secondary battery, wherein when the reaction capacity is 60-140 mAh / g in a voltage range in which the following Reaction Formula 1 proceeds, A method for charging and discharging a secondary battery is provided.

[Reaction Scheme 1]

Li_2+yMn_2-ｙ-zM_zO_4-xQ_x Li _{1 + y} Mn _{2 - y - z} M _z O _{4 - x} Q _x + Li ⁺ + e ^-

_{Li 2 + y Mn 2-y} -z M z O 4-x Q x

In the above Reaction Scheme 1, 0? X? 1, 0? Y? 0.34, 0? Z? 1, and M is Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr , Sb, W, B, Ti, V, Zr and Zn, and Q is one or more elements selected from the group consisting of N, F, S and Cl.

When a spinel-based lithium manganese oxide is used as a cathode active material, a voltage plateau appears in a voltage range of 3 V or less during charging and discharging of a battery. 1V, which is a voltage-capacity profile according to the charge / discharge method of the embodiment of the present invention, the first voltage plateau part is formed at about 2.9V, And a second voltage flat portion appears at about 2.3 V or so.

Of these, the second voltage flat part appearing at about 2.3 V is presumed to appear at a low voltage due to an over-potential generated for some reason in the material synthesis process. In the initial cycle charging / discharging process, .

When the lithium secondary battery is charged and discharged, a high capacity of about 200 mAh / g or more can be obtained by utilizing the 3V region and the 4V region compared to lithium. However, improvement is required in order to obtain high capacity and excellent lifetime characteristics at the same time.

Accordingly, the inventors of the present invention have found that when the reaction capacity is 60-140 mAh / g in the voltage range of the 3V-region in which the reaction formula 1 proceeds, the cut-off voltage is increased by 0.1V or more to maintain a high capacity, Discharge method of a lithium secondary battery showing life characteristics.

As the initial charge / discharge progresses (about 1 to 15 cycles), the reaction capacity of the first voltage smoothing portion, which appears in the voltage range of about 2.9 V, increases and the overvoltage in the 3 V region increases to about 2.3 V And the second voltage flat portion within and around the voltage is switched to the first voltage flat portion. In view of this point, in order to activate the reaction of the second voltage flat part having a large overvoltage in the 3V-region to the reaction of the first voltage flat part during the early part of the cycle (about 1 to 15 cycles) The charge and discharge method of lowering the voltage to less than 2.3 V and increasing the cut-off voltage by 0.1 V or more in the subsequent cycles can be carried out to maintain a high capacity and to secure high lifetime characteristics.

Specifically, during the early part of the cycle (about 1 to 15 cycles), in order to activate the reaction of the second voltage flat part having a large overvoltage in the 3V-region to the reaction of the first voltage flat part, the initial charge- , The high capacity can be secured. Further, in the subsequent cycles, a charge / discharge method of raising the cut-off voltage by 0.1 V or more is performed, thereby ensuring high lifetime characteristics.

This can be seen also in FIG. 1, which is a voltage-capacity profile of an embodiment of the invention described below, and FIG. 2, which is a cycle-capacity profile.

As can be seen from FIG. 1, the initial cycle results (1 to 14 cycles), the 2.9V voltage plateau in the 3V region, and the 2.3V voltage flatness The plateau appears. Also, as the cycle progresses, the 2.9V voltage plateau increases, while the 2.3V voltage plateau decreases, and the 2.9V voltage plateau increases slowly We can see that the increase almost stopped in about the 15th cycle. Further, as can be seen from FIG. 2, it can be seen that the capacity is almost maintained in this initial cycle, and both the 4V capacity and the 3V capacity are maintained.

The charging and discharging method of such a lithium secondary battery can be carried out under various speed-rates, specifically, under the condition of 0.01C to 5C. Specifically, it may be carried out under 0.1C to 5C conditions. Generally, the reaction capacity of the first voltage flat part appearing at about 2.9 V decreases at a higher rate. For example, the reaction capacity of the first voltage flat part at 0.1C may be about 140 mAh / g, and the reaction capacity of the first voltage flat part at 2C may be about 60 mAh / g.

Also, the voltage at which the first voltage leveling portion and the second voltage leveling portion appear may vary depending on the change in the rate.

Generally, the higher the rate is, the lower the voltage at which the first voltage flat part appears at the discharge, for example, at 0.1 C, the voltage of the first voltage flat part may be about 2.90 V at discharge, The negative voltage may be about 2.80V.

Generally, the higher the rate, the lower the voltage at which the second voltage flat part appears at the discharge. For example, at 0.1 C, the voltage of the second voltage flat part may be about 2.30 V at discharge, This may be about 2.15V.

More specifically, the charging / discharging method of a lithium secondary battery according to an embodiment of the present invention is characterized in that the initial cut-off voltage is less than 2.3 V and the reaction at the first voltage plateau (plateau) It is possible to increase the cut-off voltage by 0.1 V or more at the time when the capacity is 90 mAh / g or more and 140 mAh / g or less. More specifically, the cut-off voltage may be increased by 0.1 V or more at the time when the reaction capacity in the first voltage plateau portion is 100 mAh / g or more and 120 mAh / g or less.

When charging / discharging is performed in this manner, the overvoltage occurring at the second voltage flat portion appearing at the voltage of about 2.3 V at the point where the reaction capacity at the first voltage flat portion at the voltage of about 2.9 V is 90 to 140 mAh / g A large part of the reaction that takes much time can be activated to the first voltage flat part reaction. At this point, by raising the cut-off voltage to a voltage higher than the voltage of the second voltage flat part by raising the cut-off voltage by 0.1 V or more, the high capacity can be maintained and high lifetime characteristics can be ensured. With respect to the lifetime characteristics, the average capacity fade rate according to the charging / discharging cycle during charging and discharging by this method may be 0.50 mAh / (g · cycle) or less. More specifically 0.10 mAh / (g · cycle) or more, and 0.40 mAh / (g · cycle) or less.

More specifically, the initial cut-off voltage may be 2.0V or more, and less than 2.3V. This is in a range similar to or below the voltage of the second voltage smoothing portion appearing under the condition of 0.1 C, and when the initial cut-off voltage is too low, the lifetime characteristic may be deteriorated. On the other hand, if the initial cut-off voltage is too high, activation may not be sufficient, that is, the capacity of the first voltage flat portion may not sufficiently increase. The initial cut-off voltage is more specifically 2.0 V or more, and 2.3 V or less; 2.1 V or higher, and 2.3 V or lower; Or 2.2 V or higher, and 2.3 V or lower;

More specifically, when the reaction capacity in the first voltage plateau is from 90 to 140 mAh / g at 0.1 C, the cut-off voltage is raised to a range of 2.4 V to 2.8 V Lt; / RTI > If the cut-off voltage is increased too little, the cycle (lifetime) characteristic improvement may be insignificant. If the cut-off voltage is increased too much, the capacity may decrease. More specifically, 2.4 V or more and 2.7 V or less; 2.4 V or higher, and 2.6 V or lower; 2.4 V or more, and 2.5 V or less; 2.5 V or higher, and 2.8 V or lower; Or 2.6 V or more, and 2.8 V or less.

In the charge / discharge method of the lithium secondary battery, the positive electrode active material of the lithium secondary battery may be a spinel type positive electrode active material represented by the following formula (1); And graphite. ≪ / RTI >

???????? Li _{1 + y} Mn _{2 -y-z} M _z O _{4 -x} Q _x

Wherein M is at least one element selected from the group consisting of Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, S, W, B, Ti, V, Zr and Zn, and Q is one or more elements selected from the group consisting of N, F, S and Cl.

In general, the spinel-type lithium manganese oxide exists in a single phase of a cubic phase in a 4V region (3.7 to 4.3 V), and Mn ^{3 +} is excessively present in a ³ V region (2.5 to 3.5 V) The charge and discharge characteristics are greatly reduced due to the phase transition from the cubic phase to the tetragonal phase due to the teller distortion effect.

The oxidation-reduction reaction of LiMn ₂ O ₄ , which is one of typical spinel-type lithium manganese oxides, at each voltage band is as follows.

LiMn₂O₄ Redox reaction in the 4V region: Mn ₂ O ₄ + Li ⁺ + e ^-

LiMn ₂ O ₄

Li₂Mn₂O₄ Redox reaction in the 3V region: LiMn ₂ O ₄ + Li ⁺ + e ^-

Li ₂ Mn ₂ O ₄

On the other hand, in the present invention, graphite is simultaneously milled to the spinel-based lithium manganese oxide, whereby the graphite or water-based graphene is coated on the surface of the pulverized spinel-type lithium manganese oxide particle, whereby the reaction capacity in the 3V region can be greatly improved .

More specifically, the cathode active material comprises the spinel-based cathode active material represented by Formula 1; And graphite. ≪ RTI ID = 0.0 >

The graphite does not limit natural graphite or artificial graphite.

Among the methods for forming the composite, there may be a variety of methods for coating graphite on the surface of lithium manganese oxide particles by a method such as milling. In one preferred example, a mixture of graphite and spinel- And can be accomplished by a dry process with oxide and high energy milling or mixing.

As another example, the coating may be performed by a wet process in which the lithium manganese oxide is dispersed in a solvent, the graphite is surface-coated, and then the solvent is recovered by drying.

More specifically, the cathode active material may be LiMn ₂ O ₄ , where Reaction Scheme 1 may be Reaction Scheme 2.

Li₂Mn₂O₄ [Reaction Scheme 2] LiMn ₂ O ₄ + Li ⁺ + e ^-

Li ₂ Mn ₂ O ₄

The positive electrode of the lithium secondary battery may further include a current collector to which the positive electrode active material is applied in addition to the positive electrode active material. As the current collector, Al may be used, but the present invention is not limited thereto.

In addition, the cathode active material layer may further include 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.

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.

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

Manufacturing example

5 g of lithium manganese oxide (LiMn ₂ O _{4 ,} Aldrich), 0.4375 g of graphite (KS6 from TIMCAL) and 6 balls (diameter = 5 mm) were placed in a stainless steel vial and the atmosphere inside the vial was replaced with argon , And ball milling for 6 hours using a high energy ball mill (SPEX8000D). The resulting material was a complex of several layers of graphene coated with nano-sized lithium manganese oxide.

Then, 0.348 g of the composite, 0.028 g of carbon black (Super P), 0.024 g of PVDF binder, and 1 g of NMP (solvent) were mixed to obtain an electrode slurry. An electrode slurry obtained on an aluminum foil was coated to a thickness of about 100 μm and dried to prepare a positive electrode.

Lithium foil was used as a counter electrode, the prepared anode was used as a working electrode, the porous polypropylene membrane was used as a separator, 1.0M LiPF ₆ was dissolved in ethylene carbonate / ethyl methyl carbonate (EC: EMC = 33: 67 , volume%) was used as an electrolyte to prepare a 2032-type half cell.

Examples and Comparative Examples

Example 1

Charging and discharging were repeatedly performed on the prepared half-papers. The charge was discharged at 0.1 C at 4.2-2.2 V for 1 to 15 cycles and at 4.2 to 2.4 V for subsequent cycles. The 1C rate corresponds to 220 mA / g. The first cycle was charged and discharged at a rate of 0.05C.

The voltage-capacity profile of Example 1 is shown in Fig. 1 and the cycle-capacity profile is shown in Fig. After 15 cycles, the cut-off voltage was increased to 2.4V, and the lifetime characteristics were clearly improved (average capacity fade rate: < 0.33 mAh / (gcycle)) and the capacity was also maintained at a high capacity of 220 mA / g . It can be seen from this that the charging and discharging method according to one embodiment of the present invention can simultaneously realize a high capacity and a high life as compared with the comparative example.

Comparative Example 1

The experiment was carried out in the same manner as in Example 1 except that the whole cycle was turned to 4.2-2.2V.

The voltage-capacity profile of Comparative Example 1 is shown in Fig. 3, and the cycle-capacity profile is shown in Fig. It can be seen that capacity is reduced at a fairly fast rate (average capacity fade rate: about 0.5 mAh / (gcycle)).

From this, it was found that the life characteristics were poor compared with Example 1.

Comparative Example 2

The experiment was carried out in the same manner as in Example 1 except that the whole cycle was turned to 4.2-2.0V.

The voltage-capacity profile of Comparative Example 2 is shown in Fig. 5, and the cycle-capacity profile is shown in Fig. As in Comparative Example 1, the capacity decreases with an average capacity fade rate (about 0.66 mAh / (gcycle)).

From this, it was found that the life characteristics were poor compared with Example 1.

If the cut-off voltage is as low as 2.0 to 2.2V, the average capacity fade rate> 0.5 mAh / (gcycle) is known, which means that the over-potential 2.3 V reaction area . When the cut-off voltage is too low, it is presumed that the life characteristics are deteriorated due to other causes such as side reactions.

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 (15)

A cathode comprising a cathode active material;
cathode; And
A method of charging and discharging a lithium secondary battery including an electrolyte,
Wherein a cut-off voltage at the time of discharge is raised in a range of 0.1 V to 0.8 V relative to a cut-off voltage at the time of discharge when the reaction capacity is 60-140 mAh / g in a voltage section in which the following Reaction Scheme 1 proceeds, A method for charging and discharging a battery.
[Reaction Scheme 1]
Li _{1 + y} Mn _{2 -y-z} M _z O _4-x Q _x + Li ⁺ + e ^-

_{Li 2 + y Mn 2-y} -z M z O 4-x Q x
(Wherein M is at least one element selected from the group consisting of Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr and Zn, and Q is one or more elements selected from the group consisting of N, F, S and Cl. The method of claim 1,
In the charge / discharge method, the charge /
0.0 &gt; 0.1C &lt; / RTI &gt; to 2C.
Charging / discharging method of lithium secondary battery. 3. The method of claim 2,
In the charge / discharge method,
Discharging method of a lithium secondary battery in which a first voltage plateau and a second voltage plateau appear at the time of discharging,
Wherein the first voltage plateau (Plateau) appears at 2.80 V or higher and 2.90 V or lower.
Charging / discharging method of lithium secondary battery. 4. The method of claim 3,
In the charge / discharge method,
Discharging method of a lithium secondary battery in which a first voltage plateau and a second voltage plateau appear at the time of discharging,
And the second voltage plateau (Plateau) appears at 2.15 V or higher and 2.30 V or lower.
Charging / discharging method of lithium secondary battery. 5. The method of claim 4,
In the charge / discharge method,
At the 0.1C condition,
The initial discharge cut-off voltage is less than 2.3V,
The cut-off voltage at the time of discharge is in the range of 0.1 V to 0.8 V than the initial discharge cut-off voltage at the time when the reaction capacity in the first voltage plateau is 90 mAh / g or more and 140 mAh / g or less That is,
Charging / discharging method of lithium secondary battery. The method of claim 5,
Wherein the initial discharge cut-off voltage is greater than or equal to 2.0V and less than 2.3V.
Charging / discharging method of lithium secondary battery. The method of claim 5,
Wherein the cut-off voltage during the discharge is raised to a range of 2.4 V to 2.8 V when the reaction capacity in the first voltage plateau is 90 mAh / g or more and 140 mAh / g or less,
Charging / discharging method of lithium secondary battery. The method of claim 1,
Wherein an average capacity fade rate according to a charge / discharge cycle is 0.50 mAh / (g · cycle) or less,
Charging / discharging method of lithium secondary battery. The method of claim 1,
The positive electrode active material may include a spinel type positive electrode active material represented by the following formula (1); And graphite. &Lt; RTI ID = 0.0 &gt;
Charging / discharging method of lithium secondary battery.
???????? Li _{1 + y} Mn _{2 -y-z} M _z O _{4 -x} Q _x
1, 0? Y? 0.34, 0? Z? 1, M is at least one element selected from the group consisting of Mg, Al, Ni, Co, Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr and Zn, and Q is one or more elements selected from the group consisting of N, F, S and Cl. The method of claim 9,
The positive electrode active material,
A spinel-based positive electrode active material represented by Formula 1; And graphite. &Lt; RTI ID = 0.0 &gt;
Charging / discharging method of lithium secondary battery. 11. The method of claim 10,
The positive electrode active material,
LiMn ₂ O ₄ .
Charging / discharging method of lithium secondary battery. 12. The method of claim 11,
Scheme 1 &lt; / RTI &gt;
Charging / discharging method of lithium secondary battery.
[Reaction Scheme 2]
LiMn ₂ O ₄ + Li ⁺ + e ^-

Li ₂ Mn ₂ O ₄ The method of claim 1,
The electrolyte,
A non-aqueous organic solvent, and a lithium salt.
Charging / discharging method of lithium secondary battery. The method of claim 13,
The non-aqueous organic solvent may contain,
A carbonate, an ester, an ether, a ketone, an alcohol, an aprotic solvent, or a combination thereof.
Charging / discharging method of lithium secondary battery. The method of claim 13,
The lithium salt may be,
_{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) ( the, or to a combination thereof; wherein, x and y are natural numbers), LiCl, LiI, LiB ( LiBOB C 2 O 4) 2 ( lithium bis oxalate reyito borate (lithium bis (oxalato) borate)
Charging / discharging method of lithium secondary battery.

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