KR102195735B1 - Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery having the same, and more specifically, an electrolyte for a lithium secondary battery capable of reducing the interface resistance of an electrode by including an ammonium nitrate as an electrolyte additive, and a lithium secondary battery having the same. It is about the battery. According to the present invention, it is possible to suppress a change in average voltage during charge/discharge caused by an increase in the interface resistance of the electrode, and thereby provide a lithium secondary battery with improved charge/discharge efficiency and high rate characteristics.

Description

Electrolyte for lithium secondary battery and lithium secondary battery equipped with the same {NON-AQUEOUS ELECTROLYTE SOLUTION FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery having the same, and more particularly, an electrolyte for a lithium secondary battery capable of reducing the interface resistance of an electrode by including an ammonium nitrate as an electrolyte additive, and a lithium secondary battery having the same It is about the battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries exhibit high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries are commercialized and widely used.

The lithium secondary battery has a structure in which an electrolyte solution including a lithium salt is impregnated into an electrode assembly in which a porous separator is interposed between a positive electrode and a negative electrode, each of which is coated with an active material on an electrode current collector. During charging, lithium ions of the positive electrode active material are released and inserted into the active material layer of the negative electrode, and during discharge, lithium ions from the active material layer are released and inserted into the positive electrode active material, and the electrolyte acts as a medium to move lithium ions between the negative electrode and the positive electrode. Do it.

The electrolytic solution generally contains an organic solvent and an electrolyte salt, for example, in a mixed solvent of a highly dielectric cyclic carbonate such as propylene carbonate and ethylene carbonate, and a low-viscosity linear carbonate such as diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. , LiPF ₆ , LiBF ₄ , LiClO ₄ What added a lithium salt, such as, is widely used.

Lithium-containing halogen salts such as lithium-containing fluoride salts and lithium-containing chloride salts, which are mainly used as electrolyte salts, react very sensitively to moisture, so HX, a kind of strong acid, reacts with moisture present in the battery or during the manufacturing process of the battery. (X=F, Cl, Br, I) is produced. In particular, since LiPF ₆ lithium salt is unstable at high temperatures, anions may be thermally decomposed to generate acidic substances such as hydrofluoric acid (HF). When these acidic substances are present in the battery, undesirable side reactions are essentially accompanied.

For example, the solid electrolyte interface (SEI) film present on the negative electrode surface can be easily destroyed due to the strong reactivity of the HX (X=F, Cl, Br, I), and thus the continuous regeneration of the SEI film is possible. This may lead to an increase in the interface resistance of the negative electrode due to an increase in the film amount of the negative electrode. In addition, the anode interface resistance may increase due to adsorption of lithium fluoride (LiF), which is a by-product of the formation of hydrofluoric acid (HF), to the anode surface. In addition, the HX can cause a rapid oxidation reaction in the battery to dissolve and degenerate the positive electrode active material, and in particular, the transition metal cations contained in the lithium metal oxide used as the positive electrode active material will be eluted. In this case, as these cations are electrodeposited on the negative electrode, an additional negative electrode film is formed to further increase the negative electrode resistance.

Meanwhile, the SEI film is formed on the negative electrode surface by reacting a carbonate-based polar non-aqueous solvent with lithium ions in the electrolyte during initial charging of the lithium secondary battery, and is a protective film that stabilizes the battery by inhibiting decomposition of the carbonate-based electrolyte on the negative electrode surface. It plays a role as However, the SEI film produced only by the organic solvent and the lithium salt is somewhat insufficient to perform the role as a continuous protective film, so that the charging and discharging of the battery continuously proceeds, especially when the battery is stored at high temperature in a fully charged state, increased electrochemical energy. And can be slowly decayed by thermal energy. Due to the collapse of the SEI film, a side reaction in which the exposed surface of the negative electrode active material and the electrolyte solution react and decompose continuously occurs, which may cause an increase in the resistance of the negative electrode.

In addition to the above causes, the interface resistance between the electrode and the electrolyte can be increased due to various causes, and when the interface resistance is increased in this way, the overall performance of the battery such as output characteristics is deteriorated. For example, an increase in the resistance of a battery may cause a change in the average voltage during charging and discharging, that is, a phenomenon in which the average voltage increases during charging and the average voltage decreases during discharging, and as a result, charging during charging and discharging with a constant current Charging/discharging efficiency indicating discharge capacity relative to capacity may decrease.

In order to solve this problem, Patent Document 1 (Japanese Patent Laid-Open Publication No. Hei 5-13088) describes a method of improving the resistance of a lithium secondary battery by including vinylene carbonate (VC) in an electrolyte. However, since the film formed by this method still exhibits high resistance, it did not exhibit a sufficient effect in terms of suppressing an increase in the resistance of the battery.

In addition, Patent Document 2 (Korean Patent Publication No. 2012-0011209) discloses an electrolyte for a lithium secondary battery containing an alkylene sulfate having a specific structure, an ammonium compound having a specific structure, and vinylene carbonate. However, since the SEI film produced by the sulfate-based compound has the advantage of requiring less resistance, it is possible to improve the low-temperature output characteristics of the battery, but does not show improvement in terms of initial efficiency or high rate characteristics, and further improvement is required. .

As described above, when a specific compound is added to an electrolyte to suppress an increase in battery resistance, the performance of some items is improved, but the performance of other items is reduced, or only some items are improved.

Japanese Patent Laid-Open Publication No. Hei 5-13088 KR 2012-0011209 A

The problem to be solved by the present invention is to provide an electrolyte solution for a lithium secondary battery capable of reducing the interfacial resistance of the electrode to suppress the change in the average voltage generated during charging and discharging, and improving charging/discharging efficiency and high rate characteristics. .

Another problem to be solved by the present invention is to provide a lithium secondary battery including the electrolyte.

In order to solve these problems, the present invention provides an electrolyte for a lithium secondary battery, characterized in that in the electrolyte for a lithium secondary battery containing a lithium salt and an organic solvent, the electrolyte further comprises a nitrate represented by the following formula (1). .

[Formula 1]

In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.

Preferably, the content of the nitrate may be 0.01 to 5 parts by weight based on 100 parts by weight of the total of the lithium salt and the organic solvent.

The compounds represented by Formula 1 according to the present invention include ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate, One selected from the group consisting of monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate, and dibutyldimethylammonium nitrate It can be more than that.

In addition, the present invention provides a lithium secondary battery comprising the electrolyte.

According to the present invention, it is possible to reduce the interface resistance of an electrode by providing an electrolyte for a lithium secondary battery containing the nitrate as an additive.

Therefore, it is possible to suppress a change in the average voltage during charging and discharging that occurs due to an increase in the interface resistance of the electrode, that is, it is possible to reduce the difference between the average voltage during charging and the average voltage during discharging, thereby charging and discharging with a constant current. It is possible to provide a lithium secondary battery with improved charging/discharging efficiency and high rate characteristics.

1 is 0.5C, 1.0C compared to the 0.5C-rate discharge capacity of a coin cell manufactured according to Examples and Comparative Examples. It is a graph showing the comparison of the ratio of discharge capacity at 1.5C and 2.0C rate.

The present invention relates to an electrolyte for a lithium secondary battery comprising a lithium salt and an organic solvent, wherein the electrolyte further comprises a nitrate represented by the following formula (1).

[Formula 1]

In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.

As described above, it is difficult to maintain continuous performance of the SEI film formed with organic solvents or additives known to date. In particular, the resistance of the electrode increases due to the interfacial reaction between the electrode and the electrolyte, which is insufficient to simultaneously achieve various performances such as output characteristics at an effective level. There was a point.

However, when the nitrate is used as an electrolyte solution additive according to the present invention, the interfacial resistance of the electrode is reduced, thereby reducing the amount of change in the average voltage generated during charging and discharging, improving charging/discharging efficiency, and remarkably improving high rate characteristics. can do.

The content of the nitrate is preferably 0.01 to 5.0 parts by weight, and more preferably 0.1 to 3.0 parts by weight based on 100 parts by weight of the total of the lithium salt and the organic solvent. When the content is less than 0.01 parts by weight, it may be difficult to obtain the effect of lowering the interface resistance of the electrode, whereas when it exceeds 5.0 parts by weight, it may cause a decrease in charge/discharge efficiency.

Preferred examples of the compound represented by Formula 1 according to the present invention include ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, and tetrabutylammonium nitrate. ), monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate, dibutyldimethylammonium nitrate, selected from the group consisting of One or more may be mentioned, but is not limited thereto.

The performance of the battery is greatly influenced by the basic electrolyte composition and a solid electrolyte interface (SEI) film formed by reacting the electrolyte and the electrode.

In the lithium secondary battery, during the first charging process, the surface of carbon particles, which is a negative electrode active material, and the electrolyte react at the negative electrode of the battery to form an SEI film. The SEI film formed in this way not only prevents the collapse of the negative electrode material due to side reactions between the carbon material and the electrolyte solvent and co-intercalation of the electrolyte solvent into the negative electrode material, but also faithfully performs the role of a conventional lithium ion tunnel. Minimize degradation. However, the conventional SEI film formed by a carbonate-based organic solvent, a fluorine salt or other inorganic salt is weak, porous, and not dense, so that lithium ions do not move smoothly, resulting in a decrease in the amount of reversible lithium. As a result, an irreversible reaction according to the progress of charging and discharging was increased, and as a result, the capacity and charging/discharging efficiency of the battery were decreased.

In contrast, the ammonium-based nitrate represented by Formula 1, which is included as an additive in the electrolyte solution of the present invention, is reduced on the surface of the negative electrode material before other components during the initial charging of the battery, thereby forming a solid, dense, and excellent SEI film. Formed. Therefore, by preventing side reactions in which the conventional carbonate solvent is intercalated into the layered active material layer or the solvent is decomposed, not only the initial efficiency of the battery is increased, but also the collapse and regeneration of the SEI film is suppressed to prevent the interfacial resistance of the electrode. Can suppress the increase.

On the other hand, the lithium salt contained as an electrolyte in the electrolyte solution of the present invention may be used within a concentration range of 0.6 to 2.0M, more preferably 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte may be lowered and the electrolyte performance may be deteriorated. On the other hand, if the concentration of the lithium salt is more than 2.0M, the viscosity of the electrolyte may increase, thereby reducing the mobility of lithium ions. As the lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example the lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 _{^{-, BF 4 -, ClO 4}} -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, ( ^{_{CF 3) 6 P -, CF}} 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO - _{, (CF 3 SO 2) 2} CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^-It may be any one selected from the group consisting of.

As the organic solvent contained in the electrolyte, those commonly used in the electrolyte for lithium secondary batteries can be used without limitation. For example, ether, ester, amide, linear carbonate, cyclic carbonate, etc. can be used alone or in combination of two or more. Can be used.

Among them, representatively, a cyclic carbonate, a linear carbonate, or a carbonate compound that is a mixture thereof may be included. Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Any one selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, and halides thereof, or a mixture of two or more thereof. In addition, specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate. Any one selected or a mixture of two or more of them may be representatively used, but is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents and can be preferably used because they dissociate lithium salts in the electrolyte well because of their high dielectric constant. If the same low viscosity, low dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte solution having a high electrical conductivity can be prepared, and thus it can be used more preferably.

In addition, as the ether of the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more of them may be used. , But is not limited thereto.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ -Any one selected from the group consisting of valerolactone and ε-caprolactone, or a mixture of two or more of them may be used, but the present invention is not limited thereto.

The electrolyte solution for a lithium secondary battery of the present invention may further include a conventionally known additive for forming an SEI film within a range not departing from the object of the present invention. As an additive for forming an SEI film that can be used in the present invention, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sultone, unsaturated sultone, acyclic sulfone, etc. can be used alone or in combination of two or more. However, it is not limited thereto.

Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, and 4,5-dimethyl propylene sulfite. Pyrite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, and the like, and the saturated sultone 1,3-propane sultone, 1,4-butane sultone, and the like. Unsaturated sultones include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, and 1-methyl-1,3-pro. Phen sultone and the like, and examples of the acyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone.

The additive for forming the SEI film may be included in an appropriate amount according to the specific type of the additive, for example, 0.01 to 10 parts by weight based on 100 parts by weight of the electrolyte.

On the other hand, the present invention provides a lithium secondary battery containing the non-aqueous electrolyte.

The lithium secondary battery is manufactured by injecting the electrolyte prepared according to the present invention into an electrode structure comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. In addition, the positive electrode and the negative electrode may be prepared by mixing an active material, a binder, and a conductive agent with a solvent to prepare a slurry, and coating the slurry on a current collector such as aluminum, followed by drying and pressing.

Lithium-containing transition metal oxide may be preferably used as the positive electrode active material, for example, Li _x CoO ₂ (0.5<x<1.3), Li _x NiO ₂ (0.5<x<1.3), Li _x MnO ₂ (0.5 <x<1.3), Li _x Mn ₂ O ₄ (0.5<x<1.3), Li _x (Ni _a Co _b Mn _c )O ₂ (0.5<x<1.3, 0<a<1, 0<b<1) , 0<c<1, a+b+c=1), Li _x Ni _1-y Co _y O ₂ (0.5<x<1.3, 0<y<1), Li _x Co _{1 -y} Mn _y O ₂ (0.5<x<1.3, 0≤y<1), Li _x Ni _{1 -y} Mn _y O ₂ (0.5<x<1.3, O≤y<1), Li _x (Ni _a Co _b Mn _c )O ₄ (0.5<x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2), Li _x Mn _{2 -z} Ni _z O ₄ (0.5<x<1.3 , 0<z<2), Li _x Mn _{2 -z} Co _z O ₄ (0.5<x<1.3, 0<z<2), Li _x CoPO ₄ (0.5<x<1.3) and Li _x FePO ₄ (0.5 Any one selected from the group consisting of <x<1.3) or a mixture of two or more of them may be used, and the lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition, in addition to the lithium-containing transition metal oxide, sulfide, selenide, and halide may be used.

As the negative electrode active material, a carbon material, lithium metal, silicon, or tin, etc., which may contain and release lithium ions, may be used, and metal oxides such as TiO ₂ and SnO ₂ having a potential for lithium of less than 2V may be used. Preferably, a carbon material may be used, and both low crystalline carbon and high crystalline carbon may be used as the carbon material. As low crystalline carbon, soft carbon and hard carbon are typical, and high crystalline carbon is natural graphite, artificial graphite, Kishgraphite, pyrolytic carbon, liquid crystal pitch system High-temperature calcined carbons such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes are typical.

The binder binds the active material and the conductive agent and fixes it to the current collector. Polyvinylidene fluoride, polypropylene, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polyvinyl alcohol, styrene butadiene Those commonly used in lithium ion secondary batteries such as rubber may be used.

Conductive agents include artificial graphite, natural graphite, acetylene black, Ketjen black, channel black, lamp black, thermal black, conductive fiber such as carbon fiber or metal fiber, conductive metal oxide such as titanium oxide, and metal powder such as aluminum and nickel. Can be used.

In addition, as a separator, a composite of a single olefin or olefin such as polyethylene (PE) and polypropylene (PP), polyamide (PA), polyacrylonitrile (PAN), polyethylene oxide (PEO), polypropylene oxide (PPO) , Polyethylene glycol diacrylate (PEGA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and the like may be used.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch type, or a coin type.

Hereinafter, examples will be described in detail to illustrate the present invention in detail.

Example One

<Preparation of electrolyte solution>

An organic solvent was prepared by mixing ethylene carbonate and ethylmethyl carbonate in a weight ratio of 3:7. Next, LiPF ₆ as a lithium salt was dissolved in the organic solvent to prepare a LiPF ₆ mixed solution having a lithium salt concentration of 1M. Next, ammonium nitrate was added to the mixed solution in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution to prepare an electrolyte.

Example 2

An electrolyte solution was prepared in the same manner as in Example 1, except that tetramethylammonium nitrate was added in an amount of 0.5 parts by weight relative to 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 3

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 4

An electrolyte solution was prepared in the same manner as in Example 1 except that tetrabutylammonium nitrate was added in an amount of 0.5 parts by weight relative to 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 5

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 0.1 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 6

An electrolyte solution was prepared in the same manner as in Example 1 except that tetraethylammonium nitrate was added in an amount of 1.0 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 7

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 2.0 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 8

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 3.0 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Comparative example One

In Example 1 above, ammonium nitrate was not added, and the remaining electrolyte was prepared in the same manner.

Comparative example 2

An electrolyte solution was prepared in the same manner as in Example 1 except that lithium difluorophosphate was added in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

<Manufacture of battery>

As a cathode active material LiNi _{0 .5 Co 0 .2 Mn 0 .3 O} 2, the carbon black, polyvinylidene fluoride (PVdF) as a binder and a conductive material 91.5: 4.4: 4.1 were mixed in a weight ratio of, N- methyl A positive electrode slurry was prepared by dispersing in -2-pyrrolidone, and the slurry was coated on an aluminum current collector, followed by drying and rolling to prepare a positive electrode.

In addition, lithium metal (manufactured by CHEM METAl) having a thickness of 1 mm was used as the negative electrode.

Thereafter, a porous polyethylene membrane (manufactured by Tonen Corporation) was used as a separator together with the prepared positive and negative electrodes, and the prepared electrolyte was injected to prepare a coin cell.

<Evaluation method>

(1) Charge and discharge efficiency

After leaving the prepared coin cell at a constant temperature of 25° C. for 24 hours, using a lithium secondary battery charger and discharger (Toyo-System Co., LTD, TOSCAT-3600), the condition of constant current up to 4.2V at 0.1C and 0.05 Charged under a constant voltage condition with C as the end current, and discharged under a constant current condition to 3.0V at 0.1C to measure the charge/discharge capacity of the first cycle, and the charge/discharge efficiency was calculated according to the following equation, and the charge/discharge capacity in Table 1 And efficiency.

Charge/discharge efficiency (%) = discharge capacity/ charge capacity

(2) Average voltage

The manufactured coin cell is charged and discharged at a rate of 0.2C in the range of 3.0 to 4.2V, and the voltage at the 50% charge state (depth of discharge, DOC) (the average charging voltage) and the 50% discharge state (depth of discharge) , DOD) voltage (discharge average voltage) was measured and shown in Table 1 below. Then, the difference between the average charging voltage and the average discharge voltage was calculated and expressed as a voltage difference.

(3) Rate characteristics

Table 1 shows the discharge capacity according to each c-rate after charging and discharging in the 3.0-4.2V range at 0.5C, 1.0C, 1.5C and 2.0C for the manufactured coin cell. In addition, the ratio of the discharge capacity at 0.5C, 1.0C, 1.5C and 2.0C to the discharge capacity at the c-rate of 0.5C is shown in FIG. 1.

0.1C/0.1C ( mAh ) 0.2C/0.2C (V) Rate characteristics ( mAh ) Charging capacity Discharge capacity Charge and discharge efficiency Average charging voltage Discharge average voltage Voltage difference 0.5C discharge 1.0C discharge 1.5C discharge 2.0C discharge Example 1 4.844 4.261 87.96% 3.802 3.772 0.030 4.120 3.989 3.017 1.320 Example 2 4.849 4.263 87.92% 3.794 3.769 0.025 4.126 3.994 3.053 1.246 Example 3 4.844 4.259 87.92% 3.793 3.770 0.023 4.126 3.975 3.062 1.221 Example 4 4.851 4.264 87.90% 3.791 3.769 0.022 4.127 3.995 3.075 1.236 Example 5 4.866 4.263 87.61% 3.799 3.769 0.030 4.131 4.002 3.011 1.202 Example 6 4.836 4.253 87.94% 3.793 3.769 0.024 4.125 4.001 3.089 1.233 Example 7 4.838 4.250 87.85% 3.797 3.770 0.027 4.109 3.974 3.045 1.134 Example 8 4.841 4.250 87.79% 3.799 3.771 0.028 4.106 3.965 2.927 1.032 Comparative Example 1 4.883 4.241 86.86% 3.811 3.746 0.065 4.114 3.669 1.502 0.499 Comparative Example 2 5.596 4.301 76.86% 3.800 3.723 0.077 4.119 2.863 0.482 0.194

* 0.1C/0.1C, 0.2C/0.2C: 0.1C/0.1C means charged and discharged at 0.1C, and 0.2C/0.2C means charged and discharged at 0.2C.

Looking at Table 1, it can be seen that in the case of the coin cells of Examples 1 to 8 in which the additive according to the present invention was used in the electrolyte, the difference in the average voltage generated during charging and discharging was significantly reduced compared to Comparative Examples 1 to 2. And, it can be seen that the resistance in the battery is reduced by this. As the resistance is reduced in this way, it can be confirmed that the charging/discharging efficiency is improved when charging and discharging with a constant current.

In addition, referring to Tables 1 and 1 showing the results of high rate discharge characteristics of coin cells to which the electrolytes prepared according to Examples 1 to 8 and Comparative Examples 1 to 2 were applied, Examples 1 to 8 prepared according to the present invention In the case of the coin cell, it can be seen that the high rate characteristics are improved compared to the coin cells of Comparative Examples 1 to 2.

As described above, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto. Is to be construed as being included in the scope of the present invention.

Claims (7)

In the lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte for a lithium secondary battery containing a lithium salt and an organic solvent,
The positive electrode comprises a lithium transition metal oxide,
The electrolyte solution includes at least one selected from linear carbonate and cyclic carbonate,
The electrolyte solution is a lithium secondary battery, characterized in that it further comprises a nitrate represented by the following formula (1):
[Formula 1]

In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms. The method of claim 1,
The compounds represented by Formula 1 are ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate, and monoethyltrimethylammonium It is characterized in that it is at least one selected from the group consisting of nitrate (Monoethyltrimethylammonium nitrate), monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate, and dibutyldimethylammonium nitrate. Lithium secondary battery. The method of claim 1,
Lithium secondary battery, characterized in that the content of the nitrate is 0.01 to 5 parts by weight based on 100 parts by weight of the total of the lithium salt and the organic solvent. The method of claim 1,
The lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, ( ^{_{CF 3) 3 PF 3 -,}} (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 ^{_{SO 2) 2 N -, (}} FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2 ^{_{) 3 C -, CF 3 (}} CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - is any one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N Lithium secondary battery, characterized in that. delete The method of claim 1,
The electrolyte solution is a lithium secondary battery, characterized in that it further comprises at least one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate. delete

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