KR20010082428A - Electrolyte for Lithium Rechargeable Batteries - Google Patents

Abstract

PURPOSE: An electrolytic solution for the lithium secondary battery is provided, to improve the internal resistance of a battery in high speed discharging at low temperature and to reduce the expansion of thickness at high temperature. CONSTITUTION: The electrolytic solution is used in the lithium secondary battery comprising an anode made of LiCoO2, LiMnO2, LiMN2O4, LiNiO2 or complex compound (LiM1xM2yO2) and a cathode made of crystalline or amorphous carbon or metal lithium, wherein M1 and M2 are a metal element and x and y are a rational number of 0-2. The electrolytic solution comprises ethylene carbonate; γ-butyrolactone; a lithium salt selected from LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2CF2CF3)2 and their mixtures; and additives selected from phosphates of the formula 1, sulfones, sulfites, sulfates, sultones and their mixtures. Also the electrolytic solution comprises ethylene carbonate; esters of the formula 2, wherein R8-R13 are a saturated or unsaturated hydrocarbon group of C1-C12, and R14 is a saturated or unsaturated hydrocarbon group of C1-C6; lithium salt selected from LiPF6, LiBF4, LiClO4, LiN(SO2CF3)2, LiN(SO2CF2CF3)2 and their mixtures; and additives selected from phosphates, sulfones, sulfites, sulfates, sultones and their mixtures.

Description

Electrolyte for Lithium Secondary Battery {Electrolyte for Lithium Rechargeable Batteries}

A battery is a device that converts chemical energy generated during electrochemical oxidation-reduction reaction of a chemical substance contained therein into electrical energy. The primary battery that should be discarded when energy in the battery is depleted according to its usage characteristics. battery) and a rechargeable battery that can be reused many times while being continuously charged.

In recent years, thanks to the rapid development of the electronics, telecommunications, and computer industries, the use of portable electronic products such as camcorders, mobile phones, notebook PCs, etc. as well as the miniaturization, light weight, and high functionality of the devices are becoming common. 'S small batteries are desperately required, and lithium secondary batteries are attracting much attention and attention in response to such demand.

Lithium is the lightest metal on the planet, and therefore has the highest electric capacity per unit mass. Since lithium has a large thermodynamic oxidation potential, it can produce a high voltage battery. It is a positive electrode material which is the most preferred in the battery which should be able to make it, especially the secondary battery.

The present invention relates to an electrolyte solution and an electrolyte additive of such a lithium secondary battery, and more particularly, to an electrolyte solution and an additive for a lithium secondary battery capable of improving charge / discharge characteristics, lifetime characteristics, and temperature characteristics of a battery.

Recently, the miniaturized and slimmed lithium secondary battery, which is most commonly used in notebook computers, camcorders, mobile phones, and the like, is made of a lithium metal mixed oxide capable of deintercalation and intercalation of lithium ions as a cathode active material, and a carbon material or metal lithium. The anode is used as the cathode, and an appropriate amount of lithium salt dissolved in a mixed organic solvent is used as an electrolyte, and it is classified into a lithium ion battery and a lithium polymer battery by the characteristics of the solvent used as the electrolyte.

In such a lithium secondary battery, the ion conductivity of the electrolyte has a high value because it greatly affects the charge / discharge performance and the rapid discharge performance of the battery. For this purpose, the electrolyte must have a high dielectric constant and transfer lithium ions in solution. It should be easy and should have a low viscosity.

In addition, when a solidification phenomenon of the electrolyte occurs at low temperatures, the movement of ions is restricted and thus the charging and discharging of the battery is impossible, so that the solidification point should be low. (Makoto Ue, Solution Chemistry of Organic Electrolytes, Progress in Battery Materials , Vol. 16 (1997))

Therefore, in the battery industry related to lithium secondary batteries, experiments have been widely conducted to improve the electrochemical characteristics of batteries by mixing a high dielectric constant solvent and a low viscosity solvent in order to increase the ionic conductivity of the electrolyte. Tests to improve the performance at low temperatures of batteries by mixing low solvents have been widely conducted. (USP 5639575 (97, Sony), USP 5525443 (96, Matsushita)

In addition, researches to improve the performance of the electrolyte by mixing high boiling point solvents in order to improve high temperature stability have been widely conducted. (Japanese Patent Laid-Open No. 11-111306)

3.6-3.7V, which is a general average discharge voltage of a lithium secondary battery, is one of the biggest advantages of obtaining high power compared to other alkaline batteries or Ni-MH or Ni-Cd batteries.

In order to achieve such a high driving voltage, an electrolyte having an electrochemically stable composition is required at 2.75-4.2V, which is a charge / discharge voltage range of a lithium secondary battery.Ethylene carbonate (EC) and PC (Propylene) are used to meet these requirements. It is a so-called non-aqueous mixture solvent composed of a combination of carbonates such as carbonate, dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC).

However, the electrolyte solution having such a composition generally has a disadvantage in that it is disadvantageous for high rate charge and discharge because the ion conductivity is significantly lower than the so-called aqueous electrolyte solution used in Ni-MH or Ni-Cd batteries.

For example, in the case of EC, the freezing point is 36 ° C, which has a disadvantage in low temperature characteristics, but it is a solvent that is necessarily used for the electrical performance of a battery. In the case of DMC, the freezing point is 3 ° C. and the boiling point is about 90 ° C., which lowers the low temperature characteristics like the EC, and the high temperature standing characteristics are particularly disadvantageous. In case of DEC, the freezing point is below -40 ℃ and the boiling point is about 126 ℃, but it has the disadvantage of poor compatibility with other solvents. EMC also has many unsatisfactory aspects such as temperature characteristics.

As these solvents have their own advantages and disadvantages, and there is a big difference in battery performance depending on how they are combined in actual use, the battery industry is constantly conducting tests to find more improved combinations. In general, EC / DMC / EMC, EC / EMC / DEC, EC / DMC / EMC / PC are frequently used.

The electrolyte of the lithium secondary battery described above should be stable in the temperature range of -20 ° C-60 ° C, and should be able to maintain stable characteristics even at a voltage of 4V region.

In order to improve the electrochemical characteristics at low temperatures in the lithium secondary battery, an electrolyte having high ionic conductivity is required at low temperatures, and an electrolyte and an electrolyte salt having high boiling point and low reactivity with the battery negative electrode are required to improve high temperature storage characteristics. Shall be.

Therefore, in order to improve the battery performance at low temperatures by mixing a high dielectric constant solvent and a low viscosity solvent and a low freezing solvent in order to have a high ionic conductivity of the electrolyte solution, it is common to use a lithium secondary battery. It can be said that it is a composition of a battery electrolyte solution.

However, since the mobility of lithium ions is significantly lowered at low temperatures, particularly at temperatures of about -20 ° C., it is difficult to prevent the rapid deterioration of the discharge characteristics due to the rapid increase in internal resistance during high rate (1C) discharges only by changing the conventional solvent composition. You still have the disadvantages.

On the other hand, the characteristics of the lithium secondary battery at high temperatures are highly dependent on the electrolytic salt, and LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) _2, and LiN (SO) which are commonly used as solutes for lithium secondary battery electrolytes. Materials such as ₂ CF ₂ CF ₃ ) ₂ act as a lithium ion source in a battery cell to enable the operation of a basic lithium secondary battery. In general, LiBF ₄ among electrolytic salts is used at high temperatures. Is best known for its thermal stability.

As described above, in order to improve the high-rate discharge characteristics at low temperatures of the lithium secondary battery, not only a high dielectric constant and a low viscosity electrolyte having high ion conductivity are required, but also a battery when lithium ions move to the electrode during high-rate discharge at low temperatures. It can be said that an additional low solidification electrolyte which can reduce the internal resistance must be added, and in order to improve the discharge characteristics at high temperature, a solvent and an electrolyte salt which can reduce the decomposition and vaporization of the electrolyte after filling should be used. Can be.

The electrolyte for a lithium secondary battery composed of a solvent and an electrolyte reacts with the carbon constituting the negative electrode to form a thin film called SEI (Solid Electrolyte Interface) on the surface of the negative electrode, which affects ion and charge transfer, thereby affecting battery performance. It is one of the main factors causing change, and the properties of the formed film are known to vary greatly depending on the type of the solvent used as the electrolyte, the properties of the additives, and the like. (Shoichiro Mori, Chemical properties of various organic electrolytes for lithium rechargeable batteries, J. Power Source 68 (1997))

In relation to such SEI membranes, research has been continuously conducted to further improve the physicochemical properties by adding additives to the electrolyte to change the SEI formation reaction. For example, a technique of adding CO ₂ to the electrolyte Japanese Patent Laid-Open Publication No. 95-176323A, Japanese Patent Laid-Open Publication No. 95-320779A, and the like, in which a technique of suppressing decomposition of an electrolyte by adding a sulfide compound to an electrolyte is proposed.

Hereinafter, the SEI film generated on the surface of the cathode by reacting carbon and the electrolyte constituting the cathode will be described in more detail.

During the initial charging of the lithium secondary battery, lithium ions from the lithium metal oxide used as the positive electrode move to the carbon (crystalline or amorphous) electrode used as the negative electrode and are inserted into the carbon of the negative electrode. And react to form Li ₂ CO ₃ , Li ₂ O, LiOH, etc. These form a film on the surface of the negative electrode. This film is an SEI film.

Once formed, the SEI membrane prevents the reaction between lithium ions and carbon negative electrodes or other materials during repeated charging and discharging by using a battery, and passes only lithium ions between the electrolyte and the negative electrode (Ion Tunnel). It will serve as).

This ion tunnel effect blocks the migration of organic solvents of large molecular weight electrolytes, such as EC, DMC, DEC, etc., that dissolve and move lithium ions together, so that they are accompanied by lithium ions in the carbon negative electrode. It is cointercalated to prevent the structure of the carbon negative electrode from collapsing. Once this film is formed, the lithium ions do not react sideways with the carbon negative electrode or other materials, and thus the lithium ion is not charged during the charge and discharge of the battery. The amount will be reversible.

In other words, the carbon material of the negative electrode reacts with the electrolyte during supercharge to form a passivation layer on the surface of the cathode, thereby maintaining stable charge and discharge without further decomposition of the electrolyte (J. Power Sources, 51). (1994) 79-104), in which the amount of charge consumed to form the passivation layer on the negative electrode surface is an irreversible capacity, which is characterized by not reversibly reacting at the time of discharge. It is possible to maintain a stable life cycle without exhibiting an irreversible reaction.

As described above, the formation of such SEI is greatly influenced by not only the type of electrolyte but also the properties of the additive. When the non-uniform SEI is formed due to the use of an additive or an additive having poor properties, the SEI is formed in the active material. The electrons are leaked to reduce the electrolyte by causing the electrolyte to decompose, which increases the irreversible capacity of the battery active material, which in turn leads to the reduction of the capacity and life of the battery and thus the weight reduction of the battery.

In summary, the lithium secondary battery has characteristics of high dielectric constant, low viscosity and low solidification point to improve high rate discharge characteristics at low temperatures, and high boiling point characteristics to improve high rate discharge characteristics at high temperatures. At the same time that the electrolyte is required, additives capable of forming high-performance uniform SEIs that allow lithium ions to pass through but do not allow other materials to pass through will be required.

The present invention is to solve the problems and requirements of the prior art as described above, the object of the charge and discharge characteristics as compared to the conventional electrolyte solution, the life characteristics, temperature characteristics, especially high rate discharge characteristics at low temperatures are improved, It is an object of the present invention to provide an electrolyte and additive for a lithium secondary battery capable of reducing thickness expandability.

To this end, the present invention provides the wettability of cyclic esters without significantly affecting the performance of the battery in an electrolyte solution containing gamma-butyrolactone (GBL), which is a cyclic ester having a high boiling point, and lithium salt as the solute of the electrolyte. It provides an electrolyte solution with an additive which can increase the wetting property.

1 is a structural formula showing the molecular structure of a phosphate compound used as an additive in the present invention. Wherein R and R ₁ are hydrocarbons having 1-12 carbon atoms and are 1 °, 2 ° or 3 ° saturated hydrocarbons, aryl, esters or ethers

Figure 2 is a structural formula showing the molecular structure of sulfone (Sulfone), sulfite (Sulfite), sulfate (sulfate) and Sultone (Sultone) used as an additive in the present invention. Wherein R ₂ -R ₇ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms, n is an integer of 2-5

Figure 3 is a structural formula showing the molecular structure of the esters used in the present invention. Wherein R ₈ -R ₁₃ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms, and R ₁₄ is saturated or unsaturated hydrocarbons having 1-6 carbon atoms)

Figure 4 is a structural formula showing the molecular structure of the linear carbonate used in the present invention. Wherein R ₁₅ -R ₁₆ are hydrocarbons having 1-4 carbon atoms

The present invention provides a battery in an electrolyte solution containing ethylene carbonate (hereinafter referred to as EC), a high boiling point cyclic ester, and a lithium salt in order to reduce the internal resistance of the battery during high rate discharge at low temperature and to reduce the thickness expansion at high temperature. The present invention relates to an electrolyte for a lithium secondary battery with an additive added to increase the wettability of the cyclic ester without significantly affecting the performance of the present invention.

The lithium secondary battery to which the present invention is applied uses any one of LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ or a composite compound (LiM _1x M _2y O ₂ ) as a cathode active material, and is crystalline or amorphous as an anode active material. A lithium ion battery and a lithium polymer battery using carbon or metal lithium, wherein M ₁ and M ₂ are metal elements, and x and y are free numbers of 0-2.

In the present invention, the cyclic ester solvent is gamma-butyrolactone (γ-butyrolactone, hereinafter referred to as GBL), and as an additive, a phosphate-based compound, sulfones, sulfites, and sulfates sulfates and Sultones were used.

In the present invention, the EC is used in an amount of 5-50 vol%, GBL is used in an amount of 50-95 vol%, and the structure of the additives is shown in FIGS. 1 and 2.

In the electrolyte solution of the present invention, at least one of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) _2, and LiN (SO ₂ CF ₂ CF ₃ ) ₂ , which is commonly used as a solute of a lithium ion battery electrolyte, Used at a concentration of 0.5-2.0M.

GBL used in the present invention has a characteristic that can be very preferred as the electrolyte, freezing point -45 ℃ or less, boiling point 204 ℃ or more, but is known to be poor compatibility with other solvents and poor wetting (wetting) .

However, in the present invention, the above problems can be overcome by adding an additive which can increase its compatibility and wettability together with GBL.

Originally, it is not common to include additives in battery manufacturing, especially in the case of improving the characteristics of each sector, for example, life characteristics, low temperature high rate discharge characteristics, high temperature safety, overcharge prevention, and high temperature swelling. As added according to the present invention, the above additives have been used in the present invention to improve the wettability of the solvent and increase the compatibility with other solvents of the GBL, and thus the above-mentioned life characteristics, low temperature high rate discharge, high temperature stability, The safety and high temperature swelling effect has been improved.

That is, since the electrolyte using GBL has poor wettability with respect to the positive electrode, the negative electrode, and the separator, lithium ions cannot be reversibly moved, and thus the battery performance cannot be properly exhibited. By developing an additive that can apply the electrolyte of the GBL system to the lithium secondary battery, the performance of the lithium secondary battery can be significantly improved.

In particular, in the case of the additives shown in Figure 2 of the additives, the first charge in the EC / GBL electrolyte system before the decomposition of the electrolyte is characterized in that it firstly decomposes at the negative electrode to form the SEI, which prevents the decomposition of the electrolyte High rate charge and discharge characteristics, life characteristics, temperature characteristics of the secondary battery can be significantly improved, especially high rate discharge characteristics and high temperature storage stability at low temperatures.

In the electrolyte solution of the present invention, such additives are used in an amount of 0.1-10.0% by weight.

On the other hand, in the present invention, based on the electrolytic solution system in which the additive is mixed in the EC / GBL, other linear carbonates or esters generally used in lithium secondary batteries are 5% by volume to 50% by volume relative to the total electrolyte as a solvent. It can also be mixed and used.

The structures of esters and linear carbonates that can be used as solvents in the present invention are shown in FIGS. 3 and 4, respectively.

When the general linear carbonate or ester organic solvent is added to the EC / GBL electrolyte system together with the additives shown in FIGS. 1 and 2, the surface tension of the EC / GBL mixed solvent electrolyte is lowered through emulsification. As the wettability of the electrolyte to the separator is further improved, the internal resistance of the lithium secondary battery is drastically reduced, thereby greatly improving the high rate charge / discharge characteristics, life characteristics, temperature characteristics, particularly high rate discharge characteristics and high temperature storage stability at low temperatures. Can be.

In addition, in the present invention, based on the general electrolyte solution system of the lithium secondary battery containing EC, the esters shown in FIG. 3 are mixed in a content of 5 vol% -50 vol% with respect to the total electrolyte as solvent, respectively, and additives Phosphate-based compounds, sulfones, sulfites, sulfates, and sultones may be added in an amount of 0.1-10.0% by weight.

Hereinafter, one or more embodiments of the present invention as examples and test examples, but the present invention is not intended to be limited thereto.

Example 1-2

A lithium ion battery was produced by the following procedure.

First, a positive electrode slurry is prepared by mixing LiCoO ₂ as a positive electrode active material, PVDF as a binder and carbon as a conductive agent at a predetermined weight ratio, and dispersing it using N-methyl-2-pyrrolidone. Prepared. The slurry was coated on an aluminum foil having a thickness of 15 μm, dried, and rolled to prepare a positive electrode.

Next, a negative electrode slurry was prepared by mixing crystalline artificial graphite, which is a negative electrode active material, and PVDF, which is a binder, in a predetermined weight ratio and dispersing the mixture using N-methyl-2-pyrrolidinone. The slurry was coated on a copper foil having a thickness of 12 μm, dried, and rolled to prepare a negative electrode.

The positive electrode and the negative electrode and 20 μm-thick PE separator were wound and compressed to assemble a 34 mm x 48 mm x 4.2 mm aluminum laminated Li-ion battery.

Next, LiBF ₄ was dissolved in a solvent having a composition of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte solution, and 1.0 wt% of Tris (2-ethylhexyl) phosphate was added to the electrolyte solution as an additive. The battery of Examples 1 and 2 was produced by adding in the ratio of 2.0 weight%, respectively.

Example 3-4

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. Diethyl carbonate (Diethyl Carbonate) was added as a general linear carbonate at a ratio of 5.0 vol% and 10.0 vol%, to obtain Examples 3 and 4.

Example 5-6

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. In addition, vinylene carbonate (Vinylene Carbonate) was added as a general linear carbonate at a ratio of 1.0 vol% and 2.0 vol%, respectively, to prepare Examples 5 and 6.

Example 7-8

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. 1,3-Propane sultone was added in the ratio of 2.0% by weight and 3.0% by weight, respectively, to obtain Examples 7 and 8.

Example 9-10

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. And vinyl sulfone was added in the ratio of 1.0% by weight and 2.0% by weight, respectively, to obtain Examples 9 and 10.

Example 11

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. Then, Dimethyl Sulfite was added in a ratio of 1.0% by weight to make Example 11.

Example 12

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. Then, Dimethyl Sulfate was added in a ratio of 1.0% by weight to make Example 12.

Example 13-14

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte solution, and tris (2-butoxyethyl) phosphate was added to the electrolyte solution as an additive in an amount of 2.0% by weight and 3.0% by weight. It added in the ratio of respectively and set as Example 13 and 14.

Example 15-16

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte solution, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight relative to the total electrolyte solution. As the esters, dimethyl diethylmalonate (Dimethyl diethylmalonate) was added at 10.0 vol% and 20.0 vol% to obtain Examples 15 and 16, respectively.

Example 17

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte solution, and tris (2-ethylhexyl) phosphate was added to this electrolyte as an additive in a ratio of 2.0% by weight relative to the total electrolyte solution. Example 17 was prepared by adding 10.0 vol% of dimethyl diethylmalonate as ester and 1.0 vol% of vinylene carbonate as general linear carbonate.

Example 18-19

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiBF ₄ was dissolved in a solvent of EC: GBL = 3: 7 vol% to 1.5M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight based on the total electrolyte. As the esters, methyl caproate was added at a ratio of 2.0 vol% and 3.0 vol%, to give Examples 18 and 19, respectively.

Example 20

A battery was manufactured in the same manner as in Example 1, except for the following part.

LiPF ₆ was dissolved in a solvent of EC: EMC = 5: 5 vol% to 1.0M to prepare an electrolyte, and tris (2-ethylhexyl) phosphate was added to the electrolyte as an additive at a ratio of 2.0% by weight relative to the total electrolyte. It was set as Example 20.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, except for the following part.

An electrolyte solution was prepared by dissolving LiPF ₆ to 1.0 M in a solvent having an EC: EMC = 5: 5 vol% composition. No additives were added.

Comparative Example 2

A battery was manufactured in the same manner as in Example 1, except for the following part.

An electrolytic solution was prepared by dissolving LiBF ₄ in a solvent of EC: GBL = 3: 7 vol% to 1.5M. No additives were added.

The batteries produced in the above examples and comparative examples were initially charged under conditions of 120 mA, charging voltage 4.2 V, and constant current-constant voltage (CC-CV) for 1 hour, then discharged to 2.75 V with a current of 120 mA and again. It was left for 1 hour.

The battery subjected to this process twice was charged with a current of 300 mA and a charging voltage of 4.2 V for 2 hours and 30 minutes, and placed in a -20 ° C oven for 5 hours. This was again discharged to 2.75V at a current of 120mA to measure its capacity, and the results are shown in Table 1 below.

-20 ℃, 120mA discharge capacity comparison Examples and Comparative Examples Discharge capacity (%) Examples and Comparative Examples Discharge capacity (%) Comparative Example 1 79.2 Example 10 85.1 Comparative Example 2 13.2 Example 11 86.1 Example 1 78.4 Example 12 81.5 Example 2 87.1 Example 13 89.1 Example 3 90.5 Example 14 86.3 Example 4 88.3 Example 15 85.9 Example 5 82.1 Example 16 86.1 Example 6 83.0 Example 17 84.6 Example 7 79.1 Example 18 83.1 Example 8 75.3 Example 19 85.2 Example 9 93.3 Example 20 85.6

The battery was again charged at room temperature with a current of 120 mA, a charging voltage of 4.2 V, and CC-CV, and then placed in an oven at -20 ° C. for 5 hours. This was again discharged to 2.75V at a current of 600mA to measure its capacity and the results are shown in Table 2 below.

-20 ℃, 600mA discharge capacity comparison Examples and Comparative Examples Discharge capacity (%) Examples and Comparative Examples Discharge capacity (%) Comparative Example 1 20.3 Example 10 43.9 Comparative Example 2 6.5 Example 11 38.3 Example 1 25.3 Example 12 31.7 Example 2 35.7 Example 13 39.5 Example 3 40.2 Example 14 43.5 Example 4 47.8 Example 15 41.8 Example 5 35.1 Example 16 38.6 Example 6 36.8 Example 17 40.8 Example 7 41.6 Example 18 36.1 Example 8 43.2 Example 19 38.3 Example 9 45.2 Example 20 25.6

In view of the results shown in Tables 1 and 2, the discharge characteristics at -20 ° C were significantly improved in Examples 1-19 of the present invention, in which the additives were added, compared to Comparative Examples 1 and 2, in which the additives were not added. You can see that. In particular, Examples 4, 9, 10 and 14 showed the best low temperature discharge performance.

The batteries prepared in Examples and Comparative Examples were initially charged under a current of 120 mA, a charging voltage of 4.2 V, and CC-CV conditions and left for 1 hour, then discharged to 2.5 V with a current of 120 mA, and then left for 1 hour.

The battery subjected to this process twice was charged with a current of 300 mA and a charging voltage of 4.2 V for 2 hours and 30 minutes, and the thickness change of the battery prepared before charging was measured and shown in Table 3 below.

In addition, the battery thus charged was placed in an 85 ° C. oven and left for 4 hours and 4 days (96 hours), respectively, and the change in thickness thereof was measured and shown in Table 4 below. The battery, which was left for one day, was discharged to 2.75 V at a current of 600 mA at room temperature, and its capacity was measured. The results are shown in Table 5 below.

Thickness change after filling Examples and Comparative Examples Thickness change (%) Examples and Comparative Examples Thickness change (%) Comparative Example 1 7.9 Example 10 1.7 Comparative Example 2 3.1 Example 11 2.3 Example 1 2.9 Example 12 2.2 Example 2 2.6 Example 13 2.3 Example 3 3.1 Example 14 1.9 Example 4 3.5 Example 15 3.6 Example 5 3.2 Example 16 3.8 Example 6 3.2 Example 17 3.1 Example 7 3.6 Example 18 2.6 Example 8 3.8 Example 19 2.9 Example 9 2.1 Example 20 4.6

Battery thickness change at 85 ℃ after charging Examples and Comparative Examples 4 hours (%) 96 hours (%) Comparative Example 1 12.5 35.5 Comparative Example 2 3.1 7.1 Example 1 3.2 6.9 Example 2 3.4 7.1 Example 3 4.5 7.3 Example 4 5.1 7.9 Example 5 4.3 12.6 Example 6 26.4 42.3 Example 7 2.9 7.6 Example 8 3.2 7.3 Example 9 2.6 5.3 Example 10 2.3 3.9 Example 11 4.6 8.8 Example 12 3.9 7.1 Example 13 3.2 6.8 Example 14 3.5 7.3 Example 15 4.1 7.9 Example 16 4.3 8.9 Example 17 4.6 10.5 Example 18 3.8 7.6 Example 19 4.0 7.3 Example 20 7.5 17.5

Residual discharge capacity when left at 85 ℃ for 4 days after charging Examples and Comparative Examples Discharge capacity (%) Examples and Comparative Examples Discharge capacity (%) Comparative Example 1 70.1 Example 10 78.5 Comparative Example 2 53.2 Example 11 72.1 Example 1 73.1 Example 12 77.2 Example 2 72.6 Example 13 76.6 Example 3 79.1 Example 14 75.2 Example 4 77.3 Example 15 72.4 Example 5 76.1 Example 16 72.9 Example 6 78.2 Example 17 75.4 Example 7 75.9 Example 18 73.6 Example 8 73.4 Example 19 72.8 Example 9 80.1 Example 20 77.4

In view of the results of Tables 3 and 4, compared to Comparative Examples 1 and 2 in which no additives were added, Examples 1-20 of the present invention, in which the additives were added, significantly reduced the thickness expansion at full charge and the thickness expansion at high temperature. It can be confirmed that the reduction. In addition, it can be seen from the results of Table 5 that there is a significant improvement in terms of capacity recovery after high temperature standing.

Next, the batteries produced in Examples and Comparative Examples were initially charged with a current of 120 mA, a charging voltage of 4.2 V, and CC-CV conditions and left for 1 hour, then discharged to 2.5 V with a current of 120 mA, and left for another hour.

After performing this process twice, the battery life was measured by measuring the battery capacity after carrying out 300 charge / discharge tests which repeat charging to 4.2V and discharging to 2.75V at a current of 600mA. The results are shown in Table 6 below.

Battery capacity after 300 charges / discharges Examples and Comparative Examples Discharge capacity (%) Examples and Comparative Examples Discharge capacity (%) Comparative Example 1 85.9 Example 10 87.6 Comparative Example 2 43.2 Example 11 85.8 Example 1 75.3 Example 12 88.2 Example 2 86.2 Example 13 93.2 Example 3 91.2 Example 14 89.6 Example 4 93.6 Example 15 89.2 Example 5 92.1 Example 16 86.7 Example 6 89.2 Example 17 89.2 Example 7 92.3 Example 18 86.1 Example 8 90.2 Example 19 83.6 Example 9 94.2 Example 20 87.2

In view of the results in Table 6, the present invention Examples 1-20, in which the additive is added as compared to Comparative Examples 1 and 2 without the addition of the additive, maintain the discharge capacity close to the original discharge capacity even after long-term use. It can be seen that the characteristics are greatly improved.

As the present invention is completed as described above, GBL is added to the electrolyte solution, and an electrolyte solution for a lithium ion battery to which an additive is further added in order to increase its wettability can be provided.

Accordingly, it is possible to provide a lithium ion battery having improved charge and discharge characteristics, life characteristics, temperature characteristics, particularly high rate discharge characteristics at low temperatures, and reduced thickness expandability at high temperatures, compared to conventional electrolyte solutions.

Claims (15)

LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ or a composite compound (LiM _1x M _2y O ₂ ) is used as the cathode active material, where M ₁ and M ₂ are metal elements, and x and y are 0 In a lithium ion battery and a lithium polymer battery having a free number of -2 and using crystalline or amorphous carbon or metal lithium as a negative electrode active material, Ethylene carbonate; Gamma-butyrolactone; Lithium salts of at least one of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ CF ₂ CF ₃ ) ₂ ; And Phosphate compounds, sulfone compounds, sulfite compounds, sulfate compounds and sulftone compounds Made, Electrolyte solution. The method of claim 1, Phosphate compounds have the following structure, Electrolyte solution. Wherein R and R ₁ are hydrocarbons having 1-12 carbon atoms and are 1 °, 2 ° or 3 ° saturated hydrocarbons, aryl, esters or ethers The method of claim 1, The sulfone compounds have the following structure, Electrolyte solution. Wherein R ₂ and R ₃ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms The method of claim 1, The sulfite compounds have the following structure, Electrolyte. Wherein R ₄ and R ₅ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms The method of claim 1, Sulfate compounds are characterized by having the structure Electrolyte solution. Wherein R ₆ and R ₇ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms The method of claim 1, Sulton compounds are characterized by having the following structure, Electrolyte solution. Where n is an integer from 2-5 The method of claim 1, The content of ethylene carbonate in the electrolyte is characterized in that 5-50vol%, Electrolyte solution. The method of claim 1, Characterized in that the content of gamma-butyrolactone in the electrolyte is 50-95vol%, Electrolyte solution. The method of claim 1, Characterized in that the concentration of lithium salt in the electrolyte is 0.5-2.0M, Electrolyte solution. The method of claim 1, The content of the additive in the electrolyte is characterized in that 0.1-10.0% by weight, Electrolyte solution. The method of claim 1, Characterized in that it further comprises a ester having the structure Electrolyte solution. Wherein R ₈ -R ₁₃ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms, and R ₁₄ is saturated or unsaturated hydrocarbons having 1-6 carbon atoms) The method of claim 1, Characterized in that further comprises a linear carbonate having the following structure, Electrolyte solution. Wherein R ₁₅ -R ₁₆ are hydrocarbons having 1-4 carbon atoms LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ or a composite compound (LiM _1x M _2y O ₂ ) is used as the positive electrode active material, where M1 and M2 are metal elements, and x and y are 0-2. In a lithium ion secondary battery and a lithium polymer battery, which is a free number and uses crystalline or amorphous carbon or metal lithium as a negative electrode active material, Ethylene carbonate; Esters having the following structure; Wherein R ₈ -R ₁₃ are 1 °, 2 ° or 3 ° saturated or unsaturated hydrocarbons having 1-12 carbon atoms, and R ₁₄ is saturated or unsaturated hydrocarbons having 1-6 carbon atoms) Lithium salts of at least one of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ CF ₂ CF ₃ ) ₂ ; And Phosphate compounds, sulfone compounds, sulfite compounds, sulfate compounds and sulftone compounds Made, Electrolyte solution. The method of claim 13, Ester content of the electrolyte is characterized in that 5-50vol%, Electrolyte solution. The method of claim 13, The content of the additive in the electrolyte is characterized in that 0.1-10.0% by weight, Electrolyte solution.