KR101747496B1 - Electrochemical device - Google Patents

Abstract

The electrochemical device of the present invention includes a case, an electrode assembly disposed inside the case, the electrode assembly including an anode and a cathode, and a separator interposed between the anode and the cathode, and an electrolyte injected into the case, The volume EV of the free space according to Equation 2 is 0 to 45% by volume with respect to the entire volume CV of the empty space inside the case. The contents of the above Equations 1 and 2 are the same as those described in the specification.
The electrochemical device can solve the problem that the gas generated by the oxidation reaction of the electrolyte due to the high voltage reduces the reaction area of the electrode surface, further increases the side reaction and accelerates the capacity degradation.

Description

ELECTROCHEMICAL DEVICE

The present invention relates to an electrochemical device, and more particularly, to an electrochemical device capable of solving the problem of gas generated by an oxidation reaction of an electrolyte due to a high voltage to reduce the reaction area of the electrode surface, And to provide a chemical device.

2. Description of the Related Art Lithium secondary batteries (for example, lithium ion batteries), nickel metal hydride batteries, and other secondary batteries are becoming increasingly important as power sources for vehicle-mounted power supplies and portable terminals such as notebook computers. In particular, a lithium secondary battery capable of obtaining a light energy with a high energy density can be preferably used as a high output power source for in-vehicle use, and it is expected that the demand for lithium secondary batteries will continue to increase in the future.

However, in the case of the high output lithium secondary battery, there is a problem that a large amount of gas is generated due to the oxidation reaction of the electrolyte as it operates under a high voltage. In order to prevent the cell from expanding due to the generated gas, U.S. Patent No. 7223502 discloses a technique of reducing gas generation by using an electrolyte including a compound of a carboxylic acid ester having an unsaturated bond and a sulfone group have.

Korean Patent Laid-Open Publication No. 2011-0083970 also discloses a technique using an electrolyte having a compound containing difluorotoluene having a low oxidation potential so as to improve the phenomenon that the electrolyte is decomposed at a high voltage .

Korean Patent Registration No. 0760763 relates to an electrolyte for a high-voltage lithium secondary battery, wherein an additive having an oxidation reaction potential in the range of 4.6 to 5.0 V in order to ensure stability upon overcharging of a lithium secondary battery includes a biphenyl halide and a dihalogenated toluene A technique for preventing electrolyte decomposition by using an electrolyte is proposed.

Japanese Patent Application Laid-Open No. 2005-135906 discloses a lithium secondary battery including a nonaqueous electrolyte having excellent charge and discharge characteristics, and proposes a technique of adding an overcharge inhibitor to stabilize the performance of the battery at a high voltage.

However, the above technologies do not recognize that the gas generated by the oxidation reaction of the electrolyte due to the high voltage may reduce the reaction area of the electrode surface, increase the side reaction further, and accelerate the capacity degradation. There is also no solution.

US Patent No. 7223502 (Registered on May 29, 2007) Korean Patent Publication No. 2011-0083970 (published on July 21, 2011) Korea Patent No. 0760763 (Registered on September 14, 2007) Japanese Patent Application Laid-Open No. 2005-135906 (published on May 26, 2005).

An object of the present invention is to provide an electrochemical device capable of solving the problem of a gas generated by an oxidation reaction of an electrolyte due to a high voltage, a reaction area of the electrode surface being reduced, a side reaction being further increased, and acceleration of capacity degradation being accelerated.

An electrochemical device according to an embodiment of the present invention includes a case, an electrode assembly disposed inside the case, including an anode and a cathode, and a separator interposed between the anode and the cathode, and an electrolyte injected into the case Wherein the negative electrode comprises lithium titanium oxide (LTO) as a negative electrode active material, and the volume of the free space according to the following formula (2) (EV) is 0 to 45% by volume.

[Equation 1]

The volume (CV) of the empty space inside the case = the total volume (AV) inside the case - the volume of the electrode assembly (BV)

&Quot; (2) "

Volume of free space (EV) = volume of empty space in case (CV) - volume of electrolyte (DV).

The electrochemical device may be a cylindrical electrochemical device.

The volume (EV) of the free space with respect to the entire volume CV of the case hollow space may be 5 to 30% by volume.

The volume (DV) of the electrolyte may be 55 to 100% by volume with respect to the entire volume CV of the cavity inside the case.

The volume (DV) of the electrolyte may be between 0.5 and 10 cm < ³ >.

The electrochemical device is charged at 1C at 25 DEG C, discharged at 1C, and the charge (EV) is 0 to 45% by volume in a state where the charging and discharging are repeated as one cycle and 100 cycles are repeated. The pressure inside the case may be 1.5 to 15 times the pressure inside the case when the volume EV of the free space exceeds 45 vol%.

The pressure inside the case may be 1 to 15 atm in a state where the electrochemical device is charged at 1C at 25 DEG C, discharged at 1C, and the charging and discharging are repeated as one cycle and 100 cycles are repeated.

The positive electrode may be any one selected from the group consisting of LiNi _{1 -y} Mn _y O ₂ (O <y <1), LiMn _{2 -z} Ni _z O ₄ (0 <z <2) .

The electrochemical device may be a high voltage electrochemical device of 3V or more.

The electrochemical device may be a lithium secondary battery.

The electrochemical device of the present invention can solve the problem that the gas generated by the oxidation reaction of the electrolyte due to the high voltage reduces the reaction area of the electrode surface and further increases the side reaction and accelerates the capacity degradation.

1 is an exploded perspective view of a lithium secondary battery according to another embodiment of the present invention.
2 is a diagram schematically showing a capacity degradation due to gas generation in a conventional lithium secondary battery.
FIG. 3 is a diagram illustrating the principle of decreasing the capacity degradation rate in the present invention.
4 is a graph showing lifetime characteristics of a lithium secondary battery manufactured in Examples and Comparative Examples of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as "comprises" or "having" are used to designate the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

An electrochemical device according to an embodiment of the present invention includes a case, an electrode assembly disposed inside the case, including an anode and a cathode, and a separator interposed between the anode and the cathode, and an electrolyte injected into the case do.

The electrochemical device includes all devices that perform an electrochemical reaction. Specific examples of the electrochemical device include capacitors such as all kinds of primary cells, secondary cells, fuel cells, solar cells, and super capacitors.

Hereinafter, the case where the electrochemical device is a lithium secondary battery will be described in detail. 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 the separator and electrolyte used. The lithium secondary battery may be classified into a cylindrical shape, a square shape, a coin shape, Depending on the size, it can be divided into bulk type and thin type.

1 is an exploded perspective view of a lithium secondary battery 1 according to another embodiment of the present invention. 1, the lithium secondary battery 1 includes a separator 7 disposed between a cathode 3, an anode 5, the cathode 3, and an anode 5 to form an electrode assembly 9 The negative electrode 3, the positive electrode 5 and the separator 7 are impregnated with the electrolyte by placing an electrolyte (not shown) in the case 15 and injecting an electrolyte (not shown).

Conductive lead members 10 and 13 for collecting a current generated during a battery operation can be attached to the cathode 3 and the anode 5 respectively and the lead members 10 and 13 are respectively connected to the anode 5, And the current generated in the cathode (3) can be led to the positive electrode terminal and the negative electrode terminal.

The negative electrode 3 may be prepared by preparing a composition for forming a negative electrode active material layer by mixing a negative electrode active material, a binder and an optional conductive agent, and then applying the composition to a negative electrode current collector such as a copper foil.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon. Further, in addition to the carbonaceous material, a compound including a metallic compound capable of alloying with lithium or a metallic compound and a carbonaceous material may be used as the negative electrode active material.

At least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys and Al alloys may be used as the metal capable of being alloyed with lithium. Further, a metal lithium thin film may be used as the negative electrode active material. As the negative electrode active material, any one selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite, lithium metal, lithium-containing alloy, and mixtures thereof may be used in view of high stability.

Lithium titan oxide (LTO) may be used as the negative electrode active material. Recently, the use frequency of the lithium titanium oxide has been increasing. As compared with the carbon material such as graphite as the negative electrode active material, the lithium titanium oxide can be rapidly charged and discharged by virtue of excellent lithium ion mobility, has almost no irreversible reaction (95% of the initial efficiency) It has the advantage of being excellent.

Nonlimiting examples of the lithium titanium oxide include Li _{0 .8} Ti _{2 .2} O ₄ , Li _{2 .67} Ti _{1 .33} O ₄ , LiTi ₂ O ₄ , Li _{1 .33} Ti _{1 .67} O ₄ , Li _{1 .} would at least one member selected from Ti _{14 1 .71} O ₄ is not limited thereto.

The binder serves to attach the electrode active material particles to each other and to adhere the electrode active material to the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC) , Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber , Fluorine rubber, various copolymers thereof, and the like.

In addition, preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone or water.

The current collector may be any metal selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be carbon, nickel, The aluminum alloy may be an aluminum-cadmium alloy. Alternatively, a non-conductive polymer surface-treated with a conductive material, a conductive polymer, or the like may be used.

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 method of applying the current collector composition for forming the anode active material layer may be selected from known methods in consideration of the characteristics of materials and the like or may be carried out by a new suitable method. For example, it is preferable that the composition for forming the anode active material layer is dispersed on a current collector and then uniformly dispersed using a doctor blade or the like. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, methods such as die casting, comma coating, and screen printing may be used.

The positive electrode 5 is prepared by mixing a positive electrode active material, a conductive agent and a binder in the same manner as the negative electrode 3 to prepare a composition for forming a positive electrode active material layer. The composition for forming the positive electrode active material layer is then applied to a positive electrode current collector Followed by rolling.

As the cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used. Specifically, a lithium-containing transition metal oxide may be preferably used. For example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 < LiNi _{1 - y} Mn _y O ₂ , LiNi _{1- y} Mn _y O ₂ (where 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _{1 -y} Co _y O ₂ , y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O ₄ , LiMn _{2 -z} Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more thereof. In addition to these oxides, sulfide, selenide and halide may be used.

If the lithium titanium oxide is used as the negative electrode active material, the lithium titanium oxide has an operating voltage in the range of 1.3 to 1.6 V (vs. Li / Li ⁺ ). Therefore, in order to manufacture a high voltage battery, .

The high-potential positive electrode usable for the lithium-titanium oxide negative electrode active material in the present invention is not particularly limited, but it is preferable that the electrochemical device exhibits a nominal voltage of 2.0 to 3.5 V for the lithium-titanium oxide negative electrode active material If the cathode material may be used without any restriction would, as such a positive electrode active material _{LiNi 1-y Mn y O 2} (O <y <1), LiMn 2 -z Ni z O 4 (0 <z <2) , and mixtures thereof Can be preferably used as the positive electrode active material.

The electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be any organic solvent that can act as a medium through which ions involved in an electrochemical reaction of a battery can move. Specifically, examples of the organic solvent include an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a carbonate solvent, etc. These solvents may be used singly or in combination of two or more.

Specific examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, But are not limited to, ethyl propionate,? -Butyrolactone, decanolide,? -Valerolactone, mevalonolactone,? -Caprolactone (? -caprolactone, 隆 -valerolactone, 竜 -caprolactone, and the like.

Specific examples of the ether solvent include dibutyl ether, tetraglyme, 2-methyltetrahydrofuran, tetrahydrofuran, and the like.

Specific examples of the ketone-based solvents include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, xylene, (xylene), and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane and diethoxy ethane.

Specific examples of the carbonate solvent include dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate (EPC) , Methyl ethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC) And fluoroethylene carbonate (FEC).

Among them, a carbonate-based solvent is preferably used as the organic solvent. Among the carbonate-based solvents, a carbonate-based organic solvent having a high ionic conductivity having a high ion conductivity capable of enhancing the charge / discharge performance of the battery, It may be preferable to use a mixture of a carbonate-based organic solvent having a low viscosity which can appropriately control the viscosity of the organic solvent having a high electrical conductivity. Specifically, an organic solvent having a high dielectric constant selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof, and an organic solvent having a low viscosity selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, Can be mixed and used. More preferably, the organic solvent having a high dielectric constant and the organic solvent having a low viscosity are mixed at a volume ratio of 2: 8 to 8: 2, and more specifically, ethylene carbonate or propylene carbonate; Ethyl methyl carbonate; And dimethyl carbonate or diethyl carbonate in a volume ratio of 5: 1: 1 to 2: 5: 3, preferably 3: 5: 2.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in the lithium secondary battery 1. Specifically, the lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) _{2 , LiN (C 2 F 5 SO} 2) 2, LiN (CF 3 SO 2) 2. _{LiN (C a F 2a +1 SO} 2) (C b F 2b +1 SO 2) ( However, a and b is a natural number, preferably 1≤a≤20, 1≤b≤20 and Im), LiCl, LiI, LiB (C ₂ O ₄ ) _2, and mixtures thereof. It is preferable to use lithium hexafluorophosphate (LiPF ₆ ).

When the lithium salt is dissolved in the electrolyte, the lithium salt functions as a source of lithium ions in the lithium secondary battery 1 and can accelerate the movement of lithium ions between the anode 5 and the cathode 3. Accordingly, the lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%. If the concentration of the lithium salt is less than 0.6 mol%, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. If the concentration exceeds 2 mol%, the viscosity of the electrolyte may increase and the mobility of the lithium ion may be lowered. Considering the conductivity of the electrolyte and the mobility of lithium ions, it is more preferable that the lithium salt is controlled to be approximately 0.7 mol% to 1.6 mol% in the electrolyte.

The electrolyte further includes an additive (hereinafter, referred to as "other additive") which can be generally used for an electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing the decrease of battery capacity, and improving the discharge capacity of the battery in addition to the electrolyte components can do.

Examples of the other additives include vinylene carbonate (vinylenecarbonate, VC), metal fluoride (metal fluoride, for example, LiF, RbF, TiF, AgF , AgF2, BaF 2, CaF 2, CdF 2, FeF 2, HgF ₂ , Hg ₂ F ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF _{3, GdF 3, FeF 3,} HoF 3, InF 3, LaF 3, LuF 3, MnF 3, NdF 3, PrF 3, SbF 3, ScF 3, SmF 3, TbF 3, TiF 3, TmF 3, YF 3, _{YbF 3, TIF 3, CeF 4} , GeF 4, HfF 4, SiF 4, SnF 4, TiF 4, VF 4, ZrF4 4, NbF 5, SbF 5, TaF 5, BiF 5, MoF 6, ReF 6, SF 6 , WF ₆ , CoF ₂ , CoF ₃ , CrF ₂ , CsF, ErF ₃ , PF ₃ , PbF ₃ , PbF ₄ , ThF ₄ , TaF ₅ and SeF ₆ ), glutaronitrile Succinonitrile (SN), adiponitrile (AN), 3,3'-thiodipropionitrile (TPN), vinylethylene carbonate (VEC) Fluoroethylene carbo Fluoroethylene carbonate (FEC), difluoroethylenecarbonate, fluorodimethylcarbonate, fluoroethylmethylcarbonate, lithium bis (oxalato) borate, LiBOB ), Lithium difluoro (oxalate) borate, LiDFOB, lithium (malonato oxalato) borate, LiMOB) and the like. Of these, 1 Or a mixture of two or more species. The other additives may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As the separator 7, a conventional porous polymer film conventionally used as a separator, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer The porous polymer film made of a polyolefin-based polymer may be used alone or in a laminate thereof, or a nonwoven fabric made of a conventional porous nonwoven fabric, for example, a glass fiber of high melting point, polyethylene terephthalate fiber or the like may be used. It is not.

Meanwhile, the lithium secondary battery 1 has a volume (EV) of 0 to 45 volume% of the total volume CV of the inner space of the case 15 according to Equation (1) , Preferably from 5 to 30% by volume, and more preferably from 5 to 25% by volume.

[Equation 1]

The volume (CV) of the empty space inside the case = the total volume (AV) inside the case - the volume of the electrode assembly (BV)

&Quot; (2) &quot;

Volume of free space (EV) = Volume of empty space in case (CV) - Volume of electrolyte (DV)

The volume CV of the inner space of the case 15 in Equation 1 is the volume excluding the volume BV occupied by the electrode assembly 9 in the entire volume AV of the case 15, Means the volume of space that can be injected. The volume CV of the hollow space in the case 15 may be not only the volume BV of the electrode assembly 9 but also the volume of the structure occupying a certain space in the case 15, The volume CV of the inner space 15 may be excluded from the volume of the structure occupying a certain space inside the case 15. [ The volume (DV) of the electrolyte can be known through the amount of electrolyte injected. However, for an already prepared battery, the weight of the electrolyte extracted through centrifugation or the electrolyte is evaporated by heating, and the weight difference between before and after heating is converted into volume Can be measured.

The volume EV of the free space is the volume excluding the volume DV of the electrolyte at the volume CV of the empty space inside the case 15, that is, the void space in which the electrolyte is injected.

The volume DV of the electrolyte may be 55 to 100% by volume, preferably 70 to 95% by volume, more preferably 75 to 95% by volume with respect to the entire volume CV of the void space in the case 15 Vol.%. More specifically, the volume (DV) of the electrolyte may be between 0.5 and 10 cm &lt; ³ &gt;.

Since the lithium secondary battery 1 has the volume EV of the free space or the volume EV of the free space as described above, the gas generated by the oxidation reaction of the electrolyte due to the high voltage reduces the reaction area of the electrode surface, It is possible to solve the problem of further increasing the side reaction and accelerating the capacity degradation.

More specifically, when a pressure is applied while the volume is fixed, when the gas is generated inside, the volume of the gas becomes inversely proportional to the pressure. For example, if 10 ml of gas is generated under 1 atm, assuming that the same mass of gas has been generated, the volume of gas will be ½ times 5 ml under 2 atmospheres. The lithium secondary battery 1 is based on this principle.

That is, in the case of the lithium secondary battery 1, the volume EV of the free space inside the case 15 changes depending on the amount of the main liquid of the electrolyte. When the main liquid amount of the electrolyte is large, the volume EV of the free space is reduced, and when the main liquid amount of the electrolyte is small, the volume EV of the free space becomes large.

The lithium secondary battery 1 has no problem in exerting the performance of the lithium secondary battery 1 even if the electrolyte is injected only to the extent that the positive electrode 5 and the negative electrode 3 are locked, . Therefore, in the case of the high-voltage lithium secondary battery 1, when the electrolyte is injected only to the extent that the anode 5 and the cathode 3 are locked, and when the electrolyte is injected to such an extent that the volume (EV) The mass of the gas produced by the electrolytic oxidation is the same.

Therefore, when the volume of the free space EV is large (the volume DV of the electrolyte is small), the increase in the pressure due to gas generation is small, if the mass of gas generated between charge and discharge is the same. On the other hand, when the volume (EV) of the free space is small (the volume (DV) of the electrolyte is large), the pressure increase due to gas generation becomes large.

Accordingly, the gas generated due to the oxidation reaction at the high voltage is pressurized as the main liquid amount of the electrolyte is increased, and the volume of the generated gas becomes small. This means that the rate at which the reaction area of the surface of the anode 5 or the surface of the cathode 3 is reduced is smaller than that before the pressurization, thereby reducing the rate of capacity degradation.

FIG. 2 is a diagram schematically illustrating the capacity degradation due to gas generation in a conventional lithium secondary battery. FIG. 3 is a graph showing the principle of decreasing the capacity degradation rate when the volume EV of the free space is small as in the present invention It is a picture shown. 2 and 3, LNMO represents an anode 5, Graphite represents a cathode 3, and electrolyte represents an electrolyte.

2, HF gas is generated in the conventional lithium secondary battery, and the generated gas has a large volume so that it does not affect the reaction surface of the cathode 3. The surface coating layer (LiF ) Is formed unevenly and thickly, it is known that the capacity degradation occurs.

More specifically, as the electrolyte is oxidized by the lithium secondary battery operated, such as _{H 2, CO, CO 2,} C 3 H 8, C 3 H 6, C 2 H 6, C 2 H 2, CH 4 gas HF _gas may be generated by reacting with water and lithium salts such as LiPF ₆ contained in the electrolytic solution due to moisture generated or generated in the battery. Particularly, the HF precipitates LiF on the surfaces of the anode and the cathode, particularly on the surface of the cathode, thereby accelerating the aging of the electrode surface, leading to deterioration of battery performance. If the charging voltage exceeds about 4 V depending on the kinds of the negative electrode and the positive electrode active material used in the lithium secondary battery, oxidation of the electrolyte accelerates and deterioration of the battery performance may be intensified.

The inventors of the present invention have focused on the fact that by controlling the volume of the gas by increasing the pressure inside the cell, the area of the gas affecting the reaction site on the electrode surface can be reduced. That is, referring to FIG. 3, since the gas generated due to the small volume EV of the free space is pressurized and the volume thereof is small, the gas does not affect the surface of the cathode 3, (LiF) is formed uniformly and thinly so that the rate of capacity degradation is reduced.

The lithium secondary battery 1 was charged at 1C at 25 DEG C and discharged at 1C, and the charging and discharging cycles were repeated for 100 cycles. The gas generated inside the lithium secondary battery 1 was maintained at 25 DEG C And the volume (GV) occupied under the atmospheric pressure condition may be 1.5 to 15 times, preferably 2 to 10 times, and more preferably 3 to 10 times the volume (EV) of the free space. If the volume of the gas (GV) occupied by the gas at 25 ° C. and 1 atm is within the above range of the volume (EV) of the free space, the generated gas does not affect the surface of the cathode (3) Can be formed uniformly and thinly so that the rate of capacity degradation can be reduced.

The volume (EV) of the free space is 0 to 45% by volume in a state where the lithium secondary battery 1 is charged at 1C at 25 DEG C, discharged at 1C, , The pressure inside the case 15 may be 1.5 to 15 times the pressure inside the case 15 when the volume EV of the free space exceeds 45 vol.%, Preferably 2 to 12 times And more preferably 3 to 10 times. That is, when the volume (EV) of the free space is 0 to 45% by volume, the generated gas is not pressurized so that the surface of the cathode 3 is not affected and the surface coating layer is formed uniformly and thinly, Can be reduced.

The internal pressure of the case 15 is 1 to 15 atm in a state where the lithium secondary battery 1 is charged at 1 DEG C at 25 DEG C and discharged at 1 DEG C and the charging and discharging are repeated one cycle, Preferably between 5 and 15 atmospheres, and more preferably between 7 and 15 atmospheres. When the pressure inside the case 15 is within the above range, the gas generated in the case 15 is pressurized and does not affect the surface of the cathode 3. On the surface of the cathode 3, It can be formed uniformly and thinly so that the rate of capacity degradation can be reduced.

The anode 5 may be any one selected from the group consisting of LiNi _{1 -y} Mn _y O ₂ (O <y <1), LiMn _{2 -z} Ni _z O ₄ (0 <z <2) LNMO based cathode active material, and the cathode 3 may include a lithium titanium oxide based anode active material. Also, the lithium secondary battery 1 may be a high-voltage lithium secondary battery 1 having a voltage of 3 V or more, preferably 5 V or more. When the anode 5 includes the LMNO-based cathode active material and the cathode 3 includes the lithium-titanium oxide-based anode active material, when the lithium secondary battery 1 operates at a high voltage, the effect of the present invention is maximized .

The lithium secondary battery 1 can be manufactured by a conventional method, and a detailed description thereof will be omitted herein. Although the cylindrical lithium secondary battery 1 has been described as an example in the present embodiment, the present invention is not limited to the cylindrical lithium secondary battery 1, and any shape can be used as long as it can operate as a battery.

[ Manufacturing example : Cathode  Preparation of cathode using protection]

( Example  One)

Lithium titanium oxide, a carbon black conductive material and a PVdF binder were mixed in an N-methyl pyrrolidone solvent to prepare a composition for forming an anode active material layer, which was then applied to a copper current collector to form a negative electrode active material layer.

LNMO cathode active material, carbon black conductive material and PVdF binder were mixed in N-methylpyrrolidone solvent to prepare a composition for forming a cathode active material layer, which was then applied to an aluminum current collector to form a cathode active material layer.

The electrode assembly is manufactured through the separation membrane of porous polyethylene between the positive electrode and the graphite negative electrode manufactured as described above, and the electrode assembly is placed inside the case. Then, a free space (EV) of 20% by volume was injected to prepare a lithium secondary battery.

( Comparative Example  One)

Except that the electrolyte was injected such that the volume (EV) of the free space with respect to the entire volume CV of the void space inside the case was 46 vol% To prepare a lithium secondary battery.

[ Experimental Example : Measurement of performance of manufactured lithium secondary battery]

( Experimental Example  1: Measurement of physical properties of the produced lithium secondary battery)

The volume of the free space EV of the lithium secondary battery manufactured in the embodiment was 20 vol% with respect to the entire volume CV of the empty space inside the case, and the volume CV of the inside space of the case was 80 volts %, And the lithium secondary battery was charged at 1C at 25 DEG C, discharged at 1C, and the charging and discharging were repeated one cycle, and 100 cycles were repeated, and the gas generated in the lithium secondary battery was discharged at 25 DEG C and 1 atmosphere The volume (GV) occupied by the condition was 6 times the volume (EV) of the free space, and the pressure inside the case was 6 atm.

The volume of the free space (EV) of the lithium secondary battery manufactured in the comparative example was 46 volume% with respect to the total volume CV of the space inside the case, and the volume CV of the volume inside the case was 56 volume %, And the lithium secondary battery was charged at 1C at 25 DEG C and discharged at 1C, and the charging and discharging were repeated for 100 cycles with one cycle, the gas generated inside the lithium secondary battery was discharged at 25 DEG C and 1 atmosphere The volume (GV) occupied by the condition was 10 times as large as the volume (EV) of 100 parts of the free space, and the pressure inside the case was 10 atm.

( Experimental Example  2: Measurement of lifetime characteristics)

The life characteristics of the lithium secondary batteries prepared in the above Examples and Comparative Examples were measured. Charging / discharging was carried out at 25 ° C under the condition of 1 C / 1 C charging / discharging, and each cycle was measured twice. The results are shown in FIG. In FIG. 4, the embodiment is large when the electrolyte content is large, and the comparative example is small when the electrolyte content is low.

Referring to FIG. 4, it can be seen that the capacity of the lithium secondary battery manufactured in the example is reduced compared to the lithium secondary battery manufactured in the comparative example, and the lifetime characteristics are improved.

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, Of the right.

1: Lithium secondary battery
3: cathode
5: anode
7: Separator
9: Electrode assembly
10, 13: lead member
15: Case

Claims (10)

In an electrochemical device,
case,
An electrode assembly disposed in the case and including a positive electrode and a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
And an electrolyte injected into the case,
The negative electrode includes lithium titanium oxide (LTO) as an anode active material,
The volume EV of the free space according to Equation (2) is 5 to 30% by volume with respect to the entire volume CV of the case hollow space according to Equation (1)
Wherein the electrochemical device is charged at 1C at 25 DEG C and discharged at 1C and the pressure inside the case is 1 to 15 atmospheric pressure in a state where charging and discharging are repeated as one cycle and 100 cycles are repeated,
[Equation 1]
The volume (CV) of the empty space inside the case = the total volume (AV) inside the case - the volume of the electrode assembly (BV)
&Quot; (2) &quot;
Volume of free space (EV) = volume of empty space in case (CV) - volume of electrolyte (DV). The method according to claim 1,
Wherein the electrochemical device is a cylindrical electrochemical device. delete The method according to claim 1,
And the volume (DV) of the electrolyte is 55 to 100% by volume with respect to the entire volume CV of the cavity inside the case. The method according to claim 1,
And the volume (DV) of the electrolyte is 0.5 to 10 cm &lt; ^{3 &} gt ;. delete delete The method according to claim 1,
The positive electrode may be any one selected from the group consisting of LiNi _{1 -y} Mn _y O ₂ (O <y <1), LiMn _{2 -z} Ni _z O ₄ (0 <z <2) And an electrochemical device. The method according to claim 1,
Wherein the electrochemical device is a high-voltage electrochemical device of 3V or more. The method according to claim 1,
Wherein the electrochemical device is a lithium secondary battery.

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