KR20140087771A - Electrolyte for secondary battery and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a secondary battery comprising (a) electrolyte salt; (b) an electrolyte solvent; and (c) a saturated cyclic hydrocarbon compound with a carbon number of six to 12 including a plurality of double bonds; and a secondary battery including the electrolyte for an improved long-term life performance. The electrolyte is capable of forming a firm and uniform solid electrolyte interface (SEI) film and rapidly consuming gas generated during initial charging.

Description

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

The present invention relates to an electrolyte for a secondary battery including an additive capable of forming a firm and uniform SEI film and capable of rapidly consuming gas generated at the time of initial charging and a secondary battery having improved long- .

Recently, miniaturization and lighter weight of electronic equipment have been realized and use of portable electronic devices has become common, so researches on lithium secondary batteries having high energy density have been actively conducted.

The lithium secondary battery generates electrical energy by oxidation and reduction reactions when lithium ions are inserted and removed from the positive and negative electrodes. The lithium secondary battery is manufactured by using a material capable of inserting and desorbing lithium ions as a cathode and an anode, and filling an organic electrolytic solution or a polymer electrolyte between the anode and the cathode.

Further, when the lithium secondary battery is initially charged, the lithium ions from the lithium metal oxide, which is an anode, migrate to the carbon electrode, which is the cathode, and are intercalated into carbon. At this time, lithium reacts strongly with the surface of the carbon particles, which are the negative electrode active material, to form a film called a solid electrolyte interface (SEI) film on the surface of the negative electrode.

The performance of the lithium secondary battery largely depends on the basic electrolyte composition and the SEI film formed by the reaction between the electrolyte and the electrode.

That is, the formed SEI film suppresses the side reaction between the carbon material and the electrolyte solvent, for example, the decomposition of the electrolyte solution on the surface of the carbon particles as the negative electrode, and prevents collapse of the negative electrode material due to co- intercalation of the electrolyte solution into the negative electrode material But also minimizes performance degradation of the battery by faithfully performing its role as a conventional lithium ion tunnel.

However, as the battery is repeatedly charged and discharged, shrinking and expansion of the electrode active material, and subsequent collapse and generation of the SEI film formed on the electrode surface are repeated, so that the stability of the electrode interface is deteriorated. Further, when the SEI film is formed, various kinds of gases are generated by the reduction reaction and the water reduction reaction contained in the electrode. When the gas is excessively generated, the pressure inside the cell is increased, , The resistance is increased in the portion where the gas is collected, and eventually the lithium precipitation is increased. Thus, the life of the battery is reduced.

Accordingly, it is urgent to develop a lithium secondary battery having a new structure capable of solving the problems of the prior art and improving the long-term life characteristics of the battery.

It is an object of the present invention to provide an electrolyte for a secondary battery comprising an additive capable of forming a firm and uniform SEI film on an electrode surface and rapidly consuming gas generated at the time of initial charging.

In addition, the present invention provides a lithium secondary battery having improved long-life performance by including the electrolyte for the secondary battery.

Hereinafter, the present invention will be described in detail.

The present invention

(a) an electrolyte salt;

(b) an electrolyte solvent; And

(c) a saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms and containing a plurality of double bonds.

Specifically, in one embodiment of the present invention, the saturated cyclic hydrocarbon compound having 6-12 carbon atoms containing a plurality of double bonds has a reduction voltage (Li / Li ⁺ ) lower than that of the mixed solvent of the electrolyte (The reduction voltage is high in the half-cell), SEI coating can be easily formed.

Examples of the saturated cyclic hydrocarbon compound having 6-12 carbon atoms and containing a plurality of double bonds include 1,3-cyclohexadiene, 1,4-cycloheptadiene, 1,5-cyclooctadiene or 1,5,9- Cyclodecatriene, and the like, but are not limited thereto. The saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms of the present invention is particularly preferably 1,5-cyclooctadiene.

In addition, the saturated cyclic hydrocarbon compound having 6-12 carbon atoms containing a plurality of double bonds can appropriately control the content thereof in accordance with the goal of improving various performances. Specifically, the content is about 2 wt% based on the total weight of the electrolytic solution %, Preferably from about 0.1% to about 2%, by weight of the composition. If the content of the saturated cyclic hydrocarbon compound having 6-12 carbon atoms containing multiple double bonds is more than 2% by weight, excessive film formation is caused to increase the thickness of the coating film, The capacity of the battery decreases, and the performance and the like are deteriorated. When the content of the saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms is less than 0.1% by weight, the effect of improving the life characteristics of the secondary battery is insufficient.

In the case of the electrolyte for a secondary battery of the present invention, since it contains a saturated cyclic hydrocarbon compound having 6-12 carbon atoms and contains a plurality of double bonds having a low reduction voltage, it is excellent in firmness and thermal stability on the surface of the negative electrode at the time of initial charging, It is possible to form an SEI film which functions as a passivation layer having a low chemical reactivity for selectively intercalating and deintercalating only lithium ions (Li ^< ^{+ &} gt ^; ). As a result, it is possible to prevent the side reaction in which the conventional carbonate solvent is co-intercalated into the active material layer of the layered structure or the solvent is decomposed, and it is possible to exhibit high stability even in cycle repetition, Long-life characteristics can be achieved.

Particularly, the saturated cyclic hydrocarbon compound having 6-12 carbon atoms containing a plurality of double bonds rapidly consumes a gas (for example, hydrogen gas) generated at the time of initial charging by hydrogenation of a double bond, Not only the pressure can be lowered but also the resistance of the cell can be lowered to bring about a long life characteristic of the battery.

Further, in the secondary battery, the electrolytic solution of the present invention, wherein (a) an electrolyte salt is Li ^+, Na ^+, K ^+, and alkali metal cations consisting of a combination thereof _{^{and, PF 6 -, BF 4 -}} , Cl -, Br - , Anion consisting of I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N (CF ₃ SO ₂ ) ₂ ^- , C (CF ₂ SO ₂ ) ₃ ^- Lt; / RTI > Specifically, the electrolyte salt is and lithium salts are preferred, and non-limiting examples include _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _6, there may be mentioned _{LiSbF 6, LiAlCl 4, CH 3} SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, or 4-phenyl lithium borate and the like.

The electrolyte salt may be contained in an amount of about 0.5 to 1.5 M based on the total weight of the electrolytic solution.

In the electrolytic solution for a secondary battery of the present invention, the solvent (b) may be a conventional solvent such as cyclic carbonate and / or linear carbonate. Examples thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, Organic solvents such as methyl, ethyl propionate, ethyl propionate, butyl propionate or mixtures thereof may be used alone or in combination of two or more. At this time, a halogen derivative compound may also be used as the organic solvent.

In addition, the electrolyte of the present invention has a reduction voltage (Li / Li ^< ^{+ &} gt ^; ) lower than that of a mixed electrolyte solution for a battery in order to give a battery with swelling- Compound (having a high reduction voltage in a half-cell), and the like.

Examples of the other additives include vinylene carbonate, propane sultone, and propene sultone. These other additives may be included in the range of 0.01 to 10 parts by weight based on 100 parts by weight of the electrolytic solution.

Further, in the present invention, the SEI film containing the chemical reaction product of the electrolytic solution containing the secondary battery electrolyte of the present invention, that is, the saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms containing a plurality of double bonds, .

Also, the present invention provides a secondary battery comprising a positive electrode, a negative electrode and a separator, and an electrolyte solution for the secondary battery of the present invention.

At this time, the anode, cathode, or both electrodes are preferably electrodes in which a SEI film containing a chemical reaction product of a saturated cyclic hydrocarbon compound containing a plurality of double bonds and having 6 to 12 carbon atoms is formed on a part or all of the surface . That is, when the electrode is charged and discharged by using the above-described electrolyte, a saturated cyclic hydrocarbon compound having 6-12 carbon atoms and containing a plurality of double bonds contained in the electrolyte is automatically formed on the surface of the electrode active material together with reversible lithium ions Or the compound may be coated on the surface of the electrode active material, or may be used in combination with the electrode material, or may be coated on the surface of the produced electrode.

Specifically, the method for producing the electrode according to the present invention is not particularly limited, but it is possible to use a conventional method known in the art, that is, a method in which an active material slurry including a cathode active material or a negative electrode active material is applied on an electrode current collector , ≪ / RTI > and drying.

As the cathode active material, a conventional cathode active material that can be used for a cathode of a conventional secondary battery can be used, and examples thereof include LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) Lithium manganese complex oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and manganese, nickel, and cobalt of these oxides, A vanadium oxide containing lithium, etc.) or a chalcogen compound (e.g., manganese dioxide, titanium disulfide, molybdenum disulfide, etc.), and the like. Preferably, the cathode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b < 1, a + b + c = 1), LiNi 1 - Y Co Y O 2, LiCo 1 - Y Mn Y O 2, LiNi 1 - Y Mn Y O 2 ( where, 0 = 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 (where 0 <Z <2), LiCoPO ₄ , LiFePO _4, or a mixture thereof. Further, lithium manganese-based oxides such as Li _{1 + a} Mn _{2 - a} O ₄ (Where a is an integer from 0 to _{0.33.), LiMnO 3, LiMn} 2 O 3, LiMnO 2, LiMn 2-a M a O 2 ( where, and M = Co, Ni, Fe, Cr, Zn or Ta , a = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu or Zn).

The negative electrode active material may be a conventional negative electrode active material that can be used for a negative electrode of a secondary battery. Examples of the negative electrode active material include lithium metal or lithium alloy, carbon, petroleum coke, activated carbon ), Graphite or other carbon-based materials, and the like. In the present invention, graphite is preferably used as the negative electrode active material.

In addition, examples of the positive electrode current collector include aluminum, nickel, or a combination thereof, and examples of the negative electrode current collector include copper, gold, nickel, or a copper alloy, And a foil produced by a combination of these.

Further, a small amount of a conductive agent and / or a binder may be optionally added to the electrode slurry.

At this time, the conductive agent may be a conventional conductive agent, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

As the binder, a conventional binder can be used. Non-limiting examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, Polymethyl methacrylate, and the like can be used.

The separation membrane used in the present invention is not particularly limited, but a polypropylene-based, polyethylene-based or polyolefin-based porous separation membrane can be used as a non-limiting example, and a porous separation membrane into which inorganic particles are introduced can also be used.

In addition, the secondary battery of the present invention can be manufactured by putting a porous separator between an anode and a cathode by a conventional method known in the art and injecting the electrolyte.

The secondary battery is preferably a lithium secondary battery. Non-limiting examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

The outer shape of the secondary battery manufactured by the above method is not limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The secondary battery according to the present invention can be preferably used as a power source for a vehicle, particularly, a power source for a hybrid electric vehicle, considering excellent low temperature output characteristics, high temperature storage characteristics, rate characteristics, and the like. However, the present invention is not limited thereto.

In the present invention, by including an electrolyte solution containing a saturated cyclic hydrocarbon compound having 6-12 carbon atoms and containing a plurality of double bonds, a firm and uniform SEI film is formed on the electrode surface, and the gas generated during the initial charging is quickly consumed Thus, by reducing the resistance of the battery, it is possible to manufacture a lithium secondary battery having improved long-term service life.

1 is a graph showing a capacity retention rate of a secondary battery according to the present invention after charging and discharging.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the following examples serve to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example

Example  One.

(Anode manufacture)

LiCoO ₂ as a cathode active material, artificial graphite as a conductive agent, and polyvinylidene fluoride as a binder were mixed in a weight ratio of 94: 3: 3, followed by addition of N-methylpyrrolidone to prepare a slurry. The slurry thus prepared was applied to an aluminum foil and dried at 130 DEG C for 2 hours to prepare a positive electrode.

(Cathode manufacture)

Artificial graphite, a conductive material, and a binder were mixed in a weight ratio of 94: 3: 3 as an anode active material, and N-methylpyrrolidone was added to prepare a slurry. The prepared slurry was applied to a copper foil and dried at 130 캜 for 2 hours to prepare a negative electrode.

(Electrolytic solution)

1M LiPF ₆ was added to 0.2% by weight of 1,5-cyclooctadiene in an EC / EMC / DEC system solution (3/2/5) to prepare an electrolytic solution of the present invention.

(Battery manufacturing)

A polyolefin-based separator was interposed between the prepared anode and cathode, and the electrolyte solution was injected to prepare a secondary battery of the present invention.

Example  2.

An electrolytic solution and a secondary battery including the electrolytic solution were prepared in the same manner as in Example 1, except that 1 wt% of vinylene carbonate and 0.5 wt% of 1,5-cyclooctadiene were added as electrolyte components.

Comparative Example  One.

An electrolytic solution and a secondary battery including the electrolytic solution were prepared in the same manner as in Example 2, except that 1,5-cyclooctadiene was not included as an electrolyte component.

Comparative Example  2.

The electrolytic solution and the secondary battery including the electrolytic solution were prepared in the same manner as in Example 1, except that 5 wt% of 1,5-cyclooctadiene was contained as an electrolytic solution component.

Experimental Example

(Experimental Example 1. Comparison of Battery Thickness and Lifetime Performance after First Charging and discharging)

The following experiment was conducted to confirm whether the SEI film on the negative electrode was formed by the battery electrolyte according to the present invention.

The full cell of Examples 1 and 2 and Comparative Example 1 was used, and as a control group thereof, the battery of Comparative Example 2 containing no additive in the electrolyte solution was used.

The thickness increase (nm) of the cell after initial charging and discharging of each cell and the retention ratio (%) of capacity after 250 cycles were measured, and the results are shown in Table 1 below.

1 ^st Battery thickness after charge / discharge Capacity retention after 250 ^th cycle (%) Example 1 + 0.02 mm 91.00 Example 2 + 0.02 mm 88.90 Comparative Example 1 +0.05 mm 86.90 Comparative Example 2 + 0.06 mm 80.94 * 1 ^st also describes the thickness difference between the cell thickness after the 1 ^st charge and discharge of the charge / discharge after the battery thickness = difference after the electrolyte is injected cells.
* Capacity retention rate (%) = the ratio of capacity after 25 ^o C to 250 ^th cycle compared to capacity after the first cycle

As can be seen from the above table, in the case of using 1, 5-cyclooctadiene, the increase in thickness after 1 charge is smaller than that in Comparative Example 2 in which 1,5-cyclooctadiene is not used . That is, it can be seen that the additive included in the electrolyte solution of the present invention actively participates in the formation of the film and the gas consumption generated at the initial charging. As in Comparative Examples 1 and 2, when the thickness increase width is large after activation, the adhesion between the electrodes is lowered, which ultimately affects the long life performance of the battery. Compared with Comparative Example 1 in which 1,5-cyclooctadiene was not used, the capacity retention rate after 250 cycles was low in Comparative Example 2 using an excessive amount of 1,5-cyclooctadiene. In addition, as the battery resistance is increased due to excessive film formation due to excessive additives, the capacity retention rate after 250 cycles is lower than that in Examples 1 and 2.

Claims (14)

(a) an electrolyte salt;
(b) an electrolyte solvent; And
(c) a saturated cyclic hydrocarbon compound having 6-12 carbon atoms containing a plurality of double bonds. The method according to claim 1,
Wherein the saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms is a substance having a reduction voltage (Li / Li ^&lt; ^{+ &} gt ^; ) lower than that of the mixed solvent of the electrolyte solution. The method according to claim 1,
The saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms is selected from the group consisting of 1,3-cyclohexadiene, 1,4-cycloheptadiene, 1,5-cyclooctadiene and 1,5,9-cyclodecatriene Wherein the electrolytic solution for the secondary battery is a lithium secondary battery. The method according to claim 1,
Wherein the saturated cyclic hydrocarbon compound having 6 to 12 carbon atoms is contained in an amount of 0.1 to 2% by weight based on the total weight of the electrolytic solution. The method according to claim 1,
The electrolyte salt (a)
Li ⁺ , Na ⁺ , K ^+, and combinations thereof, and an alkali metal cation selected from the group consisting of Li ⁺ , Na ⁺ , K ^{+
_{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF ₂ SO ₂ ) ₃ ^-, and combinations thereof. 2. The electrolyte solution for a secondary battery according to claim 1, wherein the anion is selected from the group consisting of: The method according to claim 1,
Wherein (a) an electrolyte salt is _{LiCl, LiBr, LiI, LiClO 4} , LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, CH 3 SO 3 _{Li, CF 3 SO 3 Li,} (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, and 4-secondary battery of boric acid, wherein one or two or more kinds of salts selected from the group consisting of lithium Electrolytic solution. The method according to claim 1,
The solvent of the electrolyte (b) is at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, formic acid Wherein the electrolytic solution is one or more mixed organic solvents selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate and butyl propionate. The method according to claim 1,
Wherein the electrolyte for the secondary battery further comprises an additive having a reduction voltage (Li / Li ^&lt; ^{+ &} gt ^; ) lower than that of the mixed electrolyte solvent. The method of claim 8,
Wherein the additive is vinylene carbonate, propane sultone or propene sultone. The method of claim 8,
Wherein the additive is contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the electrolyte solution. An electrode for a secondary battery, wherein an SEI film containing a chemical reaction product of an electrolyte solution for a secondary battery according to claim 1 is formed on part or all of the surface. An anode, a cathode, and a separator,
A secondary battery comprising the electrolyte for a secondary battery according to claim 1. The method of claim 12,
Wherein the separation membrane is a polypropylene-based, polyethylene-based, polyolefin-based porous separation membrane or a porous separation membrane into which inorganic particles are introduced. The method of claim 12,
Wherein the secondary battery is a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

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