KR101023374B1 - Additive for non-aqueous electrolyte and secondary battery using the same - Google Patents

Abstract

The present invention provides a secondary battery electrolyte comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte is an electrolyte comprising a compound having a pentahalophenyl group and a sulfonate group at the same time; And it provides a secondary battery having the electrolyte solution.

The electrolyte of the present invention can ensure overcharge safety without degrading the performance of the battery, and can be usefully applied to high voltage batteries.

The present invention also provides novel compounds.

Electrolyte Additive, Secondary Battery, Overcharge

Description

Non-aqueous electrolyte additive and secondary battery using same {ADDITIVE FOR NON-AQUEOUS ELECTROLYTE AND SECONDARY BATTERY USING THE SAME}

The present invention is a non-aqueous electrolyte; And it relates to a secondary battery comprising the same. More specifically, the present invention is a non-aqueous electrolyte containing a compound that can ensure the safety of overcharging without deterioration of the battery; And it relates to a secondary battery comprising the same.

In recent years, with the trend of miniaturization and weight reduction of electronic devices, miniaturization and weight reduction of batteries serving as power sources are also required. BACKGROUND ART Secondary batteries have been put to practical use as small-sized, light-weight, high-capacitance rechargeable batteries, and are used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers.

As such a battery, a secondary battery using a nonaqueous electrolyte has been put to practical use. In particular, a lithium secondary battery developed in the early 1990s among the secondary batteries currently applied is Ni-MH, Ni-Cd, sulfuric acid using an aqueous solution electrolyte. -Compared with conventional batteries such as lead batteries, they have a high operating voltage and a much higher energy density.

However, the secondary battery has a safety problem according to the use of the nonaqueous electrolyte, and one of them may include problems such as ignition and rupture when the battery is overcharged. That is, when the battery is overcharged, lithium is excessively released from the positive electrode and excessively inserted into the negative electrode, so that both the negative electrode and the positive electrode may be deformed into a thermally unstable structure. The positive electrode or the negative electrode may react with the electrolyte to generate a large amount of reaction heat, which may lead to a series of exothermic reactions, resulting in ignition or rupture of the battery due to thermal runway.

The present invention uses a compound having a pentahalophenyl group and a sulfonate group at the same time as an electrolyte component to secure overcharge safety without degrading the performance of the battery.

The present invention provides a secondary battery electrolyte comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte is an electrolyte comprising a compound having a pentahalophenyl group and a sulfonate group at the same time; And it provides a secondary battery having the electrolyte solution.

In addition, the present invention provides a compound having a structure of Formula 1 below.

[Formula 1]

In Formula 1, X is a halogen element; R is hydrogen, C ₁ ~ C ₂₀ linear alkyl group, C ₃ ~ C ₈ cyclic alkyl group, C ₂ ~ C ₂₀ linear alkenyl group, C ₃ ~ C ₈ cyclic alkenyl group, C ₁ substituted with one or more halogen An alkyl group, a phenyl group, and a benzyl group of ˜C ₂₀ ; n is an integer of 1-3.

In the present invention, a compound having a pentahalophenyl group and a sulfonate group at the same time can be used as a component of an electrolyte solution to ensure overcharge safety without deteriorating the performance of a battery.

In particular, the electrolyte additive of the present invention can not only sufficiently secure overcharge safety even in a high voltage battery, but also can form a more robust passivation film on the surface of the negative electrode, thereby improving cycle characteristics of the battery.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In order to solve the overcharge safety problem of the battery described above, various methods have been proposed. For example, there is a method of using a conductive polymer monomer, such as biphenyl, as a electrolyte additive, which can block current flow by increasing battery resistance through a polymerization reaction or the like during overcharging. However, in this case, a large amount of additive is required, and there is a problem that the capacity, performance, and the like of the battery are lowered.

Another example is to mechanically block the flow of current through the cell during overcharging. For example, by using a compound that can rapidly increase the battery temperature during overcharging as an electrolyte additive, the separator may be shut down by heat generation of the electrolyte additive before ignition and rupture due to thermal runaway, or as a safety measure. By operating (e.g., CID-reverse, etc.), the safety of the battery can be ensured. However, such an electrolyte additive may be easily decomposed by reacting with a negative electrode during charging and discharging of a battery, thereby degrading battery performance such as cycle characteristics.

The present invention is characterized in that a compound having a pentahalophenyl group and a sulfonate group at the same time is used as a component of an electrolyte solution to ensure overcharge safety without deterioration of a battery. This action can be estimated as follows, but is not limited thereto.

Since the pentahalophenyl group may cause an oxidative exothermic reaction at 4.6 V or more, the pentahalophenyl group may oxidize when the battery is overcharged, thereby rapidly increasing the internal temperature of the battery. Accordingly, in a battery in which safety means for detecting a pressure / temperature inside the battery and blocking a current flow through the battery is introduced, the electrolyte temperature rises as described above, and as a result of the gas generated while the electrolyte component is burned or decomposed, As the safety means are operated, the safety of the battery can be ensured.

In addition, sulfonate groups can be electrically reduced during initial charging, forming a passivation film on the cathode surface. In this case, the passivation film is not only firm, but also includes a halogen in addition to the sulfonate group, and thus is electrochemically stable, thereby minimizing decomposition of the electrolyte component due to reaction with the cathode. In addition, the passivation film has a low material resistance, so that insertion / desorption of lithium ions may occur more easily. For this reason, in the present invention, performance degradation of the battery during charge and discharge may be minimized.

On the other hand, the pentahalophenyl group and sulfonate group include F, O, S having a high electronegativity. Accordingly, in the present invention, the functional groups may have an electron withdrawing effect on each other, thereby making it possible to secure the overcharge safety of the battery and to form the passivation film on the negative electrode. That is, the pentahalophenyl group acts as an electron withdrawing device of the sulfonate group, thereby lowering the reduction potential of the sulfonate group, thereby enabling the electrolyte additive of the present invention to generate or regenerate a passivation film on the negative electrode surface before the electrolyte solvent. Can be. In addition, the sulfonate group may act as an electron withdrawing group of the pentahalophenyl group, thereby increasing the oxidation potential of the pentasulfonate group. For this reason, the said compound can fully exhibit the overcharge safety ensuring effect also in a high voltage battery.

Compounds having a pentahalophenyl group and a sulfonate group at the same time of the present invention can be represented by the following formula (1).

In Formula 1, X is a halogen element; R is hydrogen, C ₁ ~ C ₂₀ linear alkyl group, C ₃ ~ C ₈ cyclic alkyl group, C ₂ ~ C ₂₀ linear alkenyl group, C ₃ ~ C ₈ cyclic alkenyl group, C ₁ substituted with one or more halogen An alkyl group, a phenyl group, and a benzyl group of ˜C ₂₀ ; n is an integer of 1-3.

Non-limiting examples of the compound include pentafluorophenoxymethyl methylsulfonate, pentafluorophenoxymethyl ethylsulfonate, pentafluorophenoxymethyl allylsulfonate, Pentafluorophenoxymethyl phenylsulfonate, pentafluorophenoxymethyl benzylsulfonate, pentafluorophenoxyethyl methylsulfonate, pentafluorophenoxyethyl methylsulfonate, pentafluorophenoxyethyl methylsulfonate Pentafluorophenoxyethyl ethylsulfonate, pentafluorophenoxyethyl allylsulfonate, pentafluorophenoxyethyl phenylsulfonate, pentafluorophenoxyethyl benzylsulfonate Pentafluorophenoxypropyl methylsulfonate, pentafluorophenoxypropyl ethylsulfonate, pentafluorophenoxypropyl allylsulfonate, pentafluorophenoxypropyl allylsulfonate, pentafluorophenoxypropyl methylsulfonate Pentafluorophenoxypropyl phenylsulfonate, pentafluorophenoxypropyl benzylsulfonate, pentachlorophenoxymethyl methylsulfonate, pentachlorophenoxymethyl ethylsulfonate, pentachlorophenoxy Pentachlorophenoxymethyl allylsulfonate, pentachlorophenoxymethyl phenylsulfonate, pentachlorophenoxymethyl benzylsulfonate, pentachlorophenoxyethyl Pentachlorophenoxyethyl methylsulfonate, pentachlorophenoxyethyl ethylsulfonate, pentachlorophenoxyethyl allylsulfonate, pentachlorophenoxyethyl phenylsulfonate, pentachlorophenoxy Pentachlorophenoxypropyl benzylsulfonate, pentachlorophenoxypropyl methylsulfonate, pentachlorophenoxypropyl ethylsulfonate, pentachlorophenoxypropyl allylsulfonate, pentachlorophenoxypropyl allylsulfonate Chlorophenoxypropyl phenylsulfonate, pentachlorophenoxypropyl benzylsulfonate, and the like.

In the electrolyte solution for secondary batteries of the present invention, the content of a compound having a pentahalophenyl group and a sulfonate group at the same time can be adjusted according to the goal of improving the performance of the battery, but preferably 0.1 to 10 parts by weight per 100 parts by weight of the electrolyte. When less than 0.1 part by weight, the desired overcharge safety and the effect of improving cycle performance is insignificant, and when it exceeds 10 parts by weight, the resistance of the battery may increase.

In addition, it is preferable that the electrolyte solution for secondary batteries of the present invention further includes a compound (hereinafter, a redox shuttle agent) that performs a redox shuttle reaction.

The redox shuttle agent can secure battery safety by consuming an overcharge current through a cycle of oxidation-reduction reaction at a relatively small overcharge current. However, these redox shuttles have a disadvantage in that they easily react with the negative electrode during battery operation, and thus do not last long. In the present invention, the reaction between the redox shuttle agent and the negative electrode can be suppressed by the passivation film formed on the negative electrode surface, and as a result, the life of the redox shuttle agent can be sufficiently exhibited.

In addition, the electrolyte solution for a secondary battery of the present invention may include conventional electrolyte components known in the art, such as electrolyte salts and electrolyte solvents.

The electrolyte salt is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+,, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ⁺ B ^- is 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 ^- is a salt containing an anion ion or a combination thereof, such as. In particular, lithium salts such as LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , or Li (CF ₃ SO ₂ ) ₂ are preferred.

In addition, the electrolyte solvent may be used conventional organic solvents known in the art, such as cyclic carbonate and / or linear carbonate. In particular, in order to increase the dissociation and transfer ability of lithium ions of the electrolyte, it is preferable to use a cyclic carbonate having a high polarity, and to mix the cyclic carbonate and linear carbonate in order to prevent a decrease in the lithium ion conductivity due to the viscosity increase of the electrolyte. It is more preferable to improve the lifespan characteristics of the battery. Non-limiting examples of the solvent solvent is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxy Ethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate Propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate or halogen derivatives thereof. These electrolyte solvents may be used alone or in combination of two or more thereof. For example, ethylene carbonate and propylene carbonate may be mixed to solve the problem of lowering the low temperature performance of ethylene carbonate.

In addition, the present invention (a) anode; (b) a cathode; (c) an electrolyte containing a compound having a pentahalophenyl group and a sulfonate group at the same time; And (d) provides a secondary battery having a separator.

Non-limiting examples of the secondary battery includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

The secondary battery of the present invention may be manufactured according to a conventional method known in the art, for example, after assembling a separator between the positive electrode and the negative electrode, and pentahalo according to the present invention It can be prepared by injecting an electrolyte solution containing a compound having a phenyl group and a sulfonate group at the same time.

The electrode to be applied to the secondary battery of the present invention is not particularly limited and may be prepared according to conventional methods known in the art. For example, the electrode may be prepared by mixing and stirring a solvent, a binder, a conductive agent, and a dispersant in an electrode active material, if necessary, and then applying the coating (coating) to a current collector, compressing, and drying the electrode.

The electrode active material may be a positive electrode active material or a negative electrode active material.

The positive electrode active material may be a conventional positive electrode active material that can be used in the positive electrode of a conventional secondary battery, non-limiting examples of lithium such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) Transition metal composite oxides (for example, lithium manganese composite oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and some of the manganese, nickel and cobalt oxides of these oxides And the like, or a vanadium oxide containing lithium) or a chalcogen compound (for example, manganese dioxide, titanium disulfide, molybdenum disulfide, and the like). Preferably 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, 0 <c <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 ( here, 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 ( Here, 0 <Z <2), LiCoPO ₄ , LiFePO _4, or a mixture thereof is mentioned. Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof.

As the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of a conventional secondary battery can be used. Non-limiting examples thereof include lithium adsorbents such as lithium metal or lithium alloy carbon, petroleum coke, activated carbon, graphite, graphite, graphitized carbon or other carbons. It is preferable to use graphitized carbon having a crystal surface distance constant d002 of a carbonaceous material measured by X-ray diffraction method up to 0.338 nm and a specific surface area measured by BET method up to 10 m ² / g. Non-limiting examples of cathode current collectors include foils made by copper, gold, nickel or copper alloys or combinations thereof.

The separator is not particularly limited, but a porous separator may be used, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator.

In addition, the secondary battery may be a high voltage battery having a charge voltage of up to 4.35 V (˜4.35 V) as well as a general secondary battery having a charge / discharge region of 0 to 4.2 V.

The secondary battery may further include: (a) first safety means for stopping a charging of a battery or switching a charging state to a discharge state by detecting a change in pressure, temperature, or both inside the battery; And (b) second safety means for dissipating heat or gas inside the battery to the outside.

Non-limiting examples of the first safety means that can be used include conventional pressure sensitive elements such as CID or temperature sensitive elements such as PTC, and the like, which can be used alone or in combination. The pressure / temperature sensitive element may be integral, or (i) a pressure / temperature sensitive element; (ii) conducting wires carrying current delivered from the pressure / temperature sensitive element; And (iii) a member for stopping charging of the device or switching the charging state to a discharge state in response to a current transmitted through the conductive wire.

At this time, the pressure / temperature sensitive element detects the pressure / temperature change in the sealed element, i.e., the pressure / temperature rise and itself blocks or discharges the current, or generates an electric current toward the external or control circuit. It refers to a device that is not to proceed the charging or discharge of, as long as it performs the above-described operation in a specific pressure / temperature range, these types or methods are not particularly limited.

The pressure / temperature range in which the pressure / temperature sensitive element operates is not particularly limited as long as it is outside the normal pressure / temperature inside the battery and does not cause rupture, but preferably a pressure range of 9 to 13 kg / cm 2 or , 60 to 80 ℃ temperature range.

Examples of the pressure sensitive element include a crystal having piezoelectricity that senses a pressure change and generates a current, and an example of the temperature sensitive element is a ceramic material whose resistance changes with temperature.

In addition, the second safety means is not particularly limited so long as it functions to dissipate heat or gas (eg, flammable gas, etc.) inside the device by detecting pressure and / or temperature change inside the device, and a non-limiting example thereof is a vent. pressure release valves such as vents and the like.

The secondary battery having the above safety means includes a temperature increase in the battery caused by heat of oxidation generated from a compound having a pentahalophenyl group and a sulfonate group at the same time, a volume expansion caused by the gas ejection pressure of an electrolyte component, and an increase in the battery pressure, Alternatively, the first safety means, the second safety means, or the first safety means and the second safety means may be operated by these combinations, thereby preventing ignition and / or rupture of the battery.

Furthermore, the present invention provides a compound having a structure represented by the following formula (1).

[Formula 1]

In Formula 1, X is a halogen element; R is hydrogen, C ₁ ~ C ₂₀ linear alkyl group, C ₃ ~ C ₈ cyclic alkyl group, C ₂ ~ C ₂₀ linear alkenyl group, C ₃ ~ C ₈ cyclic alkenyl group, C ₁ substituted with one or more halogen An alkyl group, a phenyl group, and a benzyl group of ˜C ₂₀ ; n is an integer of 1-3.

The compound of Formula 1 may be prepared by (i) reacting hexahalobenzene with diol to prepare pentahalophenoxyalcohol (pentahalophenoxyalcohol); And (ii) reacting the pentahalophenoxyalcohol and the sulfonyl halide compound (see Scheme 1 below).

In Scheme 1, X is a halogen element; R is hydrogen, C ₁ ~ C ₂₀ linear alkyl group, C ₃ ~ C ₈ cyclic alkyl group, C ₂ ~ C ₂₀ linear alkenyl group, C ₃ ~ C ₈ cyclic alkenyl group, C ₁ substituted with one or more halogen An alkyl group, a phenyl group, and a benzyl group of ˜C ₂₀ ; n is an integer of 1-3.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

< Example  1>

Example  1-1 Pentafluorophenoxyethyl Of allylsulfonate  Produce

20 g (0.01 mol) of hexafluorobenzene, 48 mL (0.08 mol) of ethyleneglycol, and 51 g (0.012 mol) of sodium hydroxide are mixed and stirred at 80 ° C. for 3 hours. The reaction was carried out. After diluting the reaction mixture with water, the organic layer was extracted with diethyl ether, and sodium sulfate (Na ₂ SO ₄ ) was added thereto to remove excess water. Thereafter, the reaction mixture obtained by concentration using a rotary evaporator was purified by distillation (70 DEG C, 1 mmHg). 17.1 g (75% yield) of pentafluorophenoxyethanol was obtained from the above (see Scheme 2 below).

To 100 mL of acetonitrile (CH ₃ CN), 15 g (0.066 mol) of pentafluorophenoxyethanol prepared above and 9.2 g (0.066 mol) of allylsulfonyl chloride were added thereto. To this, 6.7 g (0.066 mol) of triethylamine was slowly added dropwise at 0 ° C., followed by stirring for 2 hours (see Scheme 3 below). After diluting the reaction mixture with 100 mL of water, the organic layer was extracted with ethyl acetate (EtOAc), and sodium sulfate (Na ₂ SO ₄ ) was added thereto to remove excess water. Thereafter, the reaction mixture obtained by concentration using a rotary evaporator was purified by silica gel chromatography.

17.5 g (80% yield) of pentafluorophenoxyethyl allylsulfonate was obtained from the above, and confirmed by NMR and Mass Spectroscopy.

¹ H NMR (400 MHz, CDCl 3): 5.93 (m, 1H), 5.49 (m, 2H), 4.55 (m, 2H), 4.41 (m, 2H), 3.9 (d, J = 6.5 Hz, 2H).

MS (EI): calcd. for C ₁₁ H ₉ F ₅ O ₄ S, 332; Found: 332.

Example  1-2. Preparation of Electrolyte

An electrolyte solution was prepared by adding 2 parts by weight of pentafluorophenoxyethyl allylsulfonate prepared in Example 1-1 to 100 parts of 1M LiPF ₆ solution in an ethylene carbonate, propylene carbonate, and diethyl carbonate ratio of 1: 1: 2. It was.

Example  1-3. Manufacture of batteries

The negative electrode was mixed with 93 parts by weight of graphitized carbon active material and 7 parts by weight of polyvinylidene difluoride (PVDF) as a solvent, N-methyl-2-pyrrolidone, and mixed in a mixer for 2 hours. It was prepared by coating a copper foil current collector and drying at 130 ° C.

The positive electrode was coated with an aluminum foil current collector after mixing for 2 hours in a mixer using N-methyl-2-pyrrolidone as a solvent with 91 parts by weight of LiCoO ₂ , 3 parts by weight of PVDF, and 6 parts by weight of conductive carbon, and at 130 ° C. Dried and prepared.

A separator made of a polyethylene porous film was disposed between the positive electrode and the negative electrode, wound, inserted into a can, and the electrolyte solution prepared in Example 1-2 was injected, and insulating plates were disposed on upper and lower surfaces of the electrode element. Then, the negative electrode lead made of nickel was drawn from the current collector and welded to the battery can. The positive electrode lead made of aluminum was drawn from the positive electrode current collector, and welded to the aluminum pressure release valve and the CID (Current Interrupt Device) mounted on the battery cover. The battery was prepared.

< Example  2>

An electrolyte solution was prepared in the same manner as in Examples 1-2 and 1-3, except that 0.5 parts by weight of pentafluorophenoxyethyl allylsulfonate was added instead of 2 parts by weight; And a secondary battery.

< Example  3>

An electrolyte solution was prepared in the same manner as in Examples 1-2 and 1-3, except that 6.0 parts by weight of pentafluorophenoxyethyl allylsulfonate was added instead of 2 parts by weight; And a secondary battery.

< Example  4>

An electrolyte solution was prepared in the same manner as in Examples 1-2 and 1-3, except that 2 parts by weight of pentafluorophenoxyethyl methylsulfonate was added instead of pentafluorophenoxyethyl allylsulfonate to prepare an electrolyte solution. And a secondary battery.

< Example  5>

An electrolyte solution was prepared in the same manner as in Examples 1-2 and 1-3, except that 2 parts by weight of pentachlorophenoxyethyl methylsulfonate was added instead of pentafluorophenoxyethyl allylsulfonate to prepare an electrolyte solution. And a secondary battery.

< Comparative example  1>

An electrolyte solution was prepared in the same manner as in Examples 1-2 and 1-3, except that 2 parts by weight of pentafluoroanisole was added instead of pentafluorophenoxyethyl allylsulfonate; And a secondary battery.

< Comparative example  2>

An electrolyte solution was prepared in the same manner as in Examples 1-2 and 1-3, except that 2 parts by weight of ethyl allylsulfonate was added instead of pentafluorophenoxyethyl allylsulfonate to prepare an electrolyte solution. And a secondary battery.

< Comparative example  3>

In the same manner as in Examples 1-2 and 1-3, except that 2 parts by weight of pentafluoroanisole and ethyl allylsulfonate were added instead of pentafluorophenoxyethyl allylsulfonate. Electrolyte solution; And a secondary battery.

< Comparative example  4>

Electrolyte solution in the same manner as in Examples 1-2 and 1-3, except that no compound was added to the LiPF ₆ solution; And a secondary battery.

Experimental Example  1. Oxidation / Reduction Potential Measurement

Measurement of Oxidation Potential

For the electrolyte solution prepared in Example 1 and Comparative Example 1, respectively, linear sweep voltammetry was performed, and the measured oxidation start voltages are shown in Table 1 below. At this time, the oxidation start voltage was defined as the voltage when the oxidation current reached 0.1 mA / cm ² . The working electrode was a Pt disc electrode, the reference electrode was lithium metal, and the auxiliary electrode was a Pt wire electrode, and the scanning speed was 20 mV / s. Measurements were carried out in a glove box in an argon (Ar) atmosphere with moisture and oxygen concentrations of less than 10 ppm.

<Measurement of reduction potential>

Each of the electrolyte solutions of Example 1 and Comparative Example 2, artificial graphite as a positive electrode, and a lithium foil as a negative electrode were manufactured in a coin-type half cell in a conventional manner. The prepared coin half cell was subjected to cyclic voltammetry at a scanning speed of 0.1 mV / sec between 1.5 V and 1 mV, and the reduced peak voltage measured therefrom is shown in Table 1 below. For reference, the value of the reduction potential is shown in the reverse order of the experimental results when the full cell as a reference.

Electrolyte additives Oxidation potential Reduction potential Example 1 Pentafluorophenoxyethyl allylsulfonate 4.7 V 2.4V Comparative Example 1 Pentafluoroanisole 4.6 V - Comparative Example 2 Ethylallyl sulfonate - 1.8 V

As a result of the experiment, a compound having a pentahalophenyl group and a sulfonate group (pentafluorophenoxyethyl allylsulfonate) has a higher oxidation potential than a compound having only a pentahalophenyl group (pentafluoroanisole) and sulfonate It showed a lower reduction potential compared to the compound having only a group (ethylallylsulfonate) (full-cell basis).

From this, it was confirmed that the pentahalophenyl group and the sulfonate group each had an electron attraction effect to each other to increase the oxidation potential of the compound and lower the reduction potential.

Experimental Example  2. Overcharge safety evaluation

After the secondary battery prepared in Examples 1 to 5, and Comparative Examples 1 to 4 overcharged for 25 hours at 25 ℃ under 1C, 12 V constant current / constant voltage conditions in a charged state, the internal temperature and the battery state of the battery is confirmed The results are shown in Table 2 below.

Experimental Example  3. Battery Performance Evaluation

The secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were charged at 25 ° C. to 4.2 V at a rate of 0.5 C, and charged at 4.2 V until the current became 0.05 mA or less, and 0.5 to 3 V. Charge and discharge experiments were conducted by discharging at a rate of C. The results are shown in Table 2 below. At this time, the discharge capacity retention rate (%) was expressed by percentage ratio of the discharge capacity and the initial discharge capacity after 300 cycles.

Electrolyte additives Addition amount
(Parts by weight) Internal battery temperature ( ^oC ) After overcharge
Battery status Discharge capacity
% Retention Example 1 Pentafluorophenoxyethyl allylsulfonate 2.0 78 PASS 85.7 Example 2 Pentafluorophenoxyethyl allylsulfonate 0.5 80 PASS 80.2 Example 3 Pentafluorophenoxyethyl allylsulfonate 6.0 75 PASS 84.9 Example 4 Pentafluorophenoxyethyl methylsulfonate 2.0 78 PASS 82.4 Example 5 Pentachlorophenoxyethyl methylsulfonate 2.0 80 PASS 81.2 Comparative Example 1 Pentafluoroanisole 2.0 88 PASS 52.8 Comparative Example 2 Ethylallyl sulfonate 2.0 160 FIRE 79.3 Comparative Example 3 Pentafluoroanisole
Ethylallyl sulfonate 2.0
2.0 88 PASS 77.4 Comparative Example 4 - - 170 FIRE 65.7

1) As a result of the experiment, the batteries of Examples 1 to 5 did not have a high internal temperature of about 75 to 80 ℃ during overcharging, and did not ignite or explode the battery.

On the other hand, the batteries of Comparative Examples 1 to 4 had a high internal temperature of 88 ° C to 170 ° C during overcharging. In particular, the batteries of Comparative Example 2 (using ethyl allylsulfonate as a compound having only sulfonate groups as electrolyte additives) and the batteries of Comparative Example 4 (not using electrolyte additives) each had an internal temperature of about 160 ° C. and 170 ° C. when overcharged. This was a temperature range far beyond the normal operating range of the cell. In addition, the batteries of Comparative Examples 2 and 4 all caused ignition of the batteries.

From this, in the case of a battery using the electrolytic solution containing the compound according to the present invention, the internal temperature of the battery is rapidly increased due to the oxidative heat due to the oxidative heating reaction of the compound during overcharging, and due to the increase in the internal temperature As a large amount of gas is generated as the electrolyte component is burned or decomposed, it was found that the safety means (ex. CID) is operated early before the battery is ignited or exploded, thereby ensuring the safety of the battery.

2) The battery of Comparative Example 1 using a compound having only pentahalophenyl group (pentafluoroanisole) was safe when overcharged, whereas the discharge capacity retention rate was lower than that of Comparative Example 4, in which no electrolyte additive was used. Showed.

In addition, the battery of Comparative Example 2 using a compound having only a sulfonate group (ethylallylsulfonate) as an electrolyte solution component showed a higher discharge capacity retention rate than Comparative Example 1, but did not pass the overcharge safety test. On the other hand, according to the present invention, the battery of Examples 1 to 5 using a compound having a pentahalophenyl group and a sulfonate group simultaneously as an electrolyte constituent showed safe results when overcharged and exhibited a higher discharge capacity retention rate than Comparative Example 1. It was.

From this, when the compound which has a pentahalophenyl group and a sulfonate group simultaneously as an electrolyte solution component is used, it turned out that overcharge safety can be ensured, improving battery performance.

Various modifications may be made without departing from the spirit and scope of the invention as set forth in the claims.

Claims (14)

An electrolyte solution for a secondary battery comprising an electrolyte salt and an electrolyte solvent, wherein the electrolyte solution has a pentahalophenyl group and a sulfonate group at the same time and includes a compound represented by Formula 1 below: [Formula 1]

In Formula 1, X is a halogen element; R is hydrogen, C ₁ ~ C ₂₀ linear alkyl group, C ₃ ~ C ₈ cyclic alkyl group, C ₂ ~ C ₂₀ linear alkenyl group, C ₃ ~ C ₈ cyclic alkenyl group, C ₁ substituted with one or more halogen An alkyl group, a phenyl group, and a benzyl group of ˜C ₂₀ ; n is an integer of 1-3. delete The method of claim 1, wherein the compound is pentafluorophenoxymethyl methylsulfonate, pentafluorophenoxymethyl ethylsulfonate, pentafluorophenoxymethyl allylsulfonate Pentafluorophenoxymethyl phenylsulfonate, pentafluorophenoxymethyl benzylsulfonate, pentafluorophenoxyethyl methylsulfonate, pentafluorophenoxyethyl methylsulfonate, pentafluorophenoxyethyl methylsulfonate Pentafluorophenoxyethyl ethylsulfonate, pentafluorophenoxyethyl allylsulfonate, pentafluorophenoxyethyl phenylsulfonate, pentafluorophenoxyethyl benzylsulfonate Penta Penafluorophenoxypropyl methylsulfonate, pentafluorophenoxypropyl ethylsulfonate, pentafluorophenoxypropyl allylsulfonate, pentafluorophenoxypropyl phenylsulfonate (pentafluorophenoxypropyl phenylsulfonate), pentafluorophenoxypropyl benzylsulfonate, pentachlorophenoxymethyl methylsulfonate, pentachlorophenoxymethyl ethylsulfonate, pentachlorophenoxymethyl Allylsulfonate (pentachlorophenoxymethyl allylsulfonate), pentachlorophenoxymethyl phenylsulfonate, pentachlorophenoxymethyl benzylsulfonate, pentachlorophenoxyethyl methyl Pentachlorophenoxyethyl methylsulfonate, pentachlorophenoxyethyl ethylsulfonate, pentachlorophenoxyethyl allylsulfonate, pentachlorophenoxyethyl phenylsulfonate, pentachlorophenoxyethyl phenylsulfonate Pentachlorophenoxypropyl benzylsulfonate, pentachlorophenoxypropyl methylsulfonate, pentachlorophenoxypropyl ethylsulfonate, pentachlorophenoxypropyl allylsulfonate, pentachlorophenoxypropyl allylsulfonate An electrolytic solution, characterized in that selected from the group consisting of chlorophenoxypropyl phenylsulfonate and pentachlorophenoxypropyl benzylsulfonate. The electrolyte of claim 1, wherein the amount of the compound is 0.1 to 10 parts by weight per 100 parts by weight of the electrolyte. (a) an anode; (b) a cathode; (c) the electrolyte solution according to any one of claims 1, 3, and 4; And (d) Secondary battery provided with a separator. The secondary battery according to claim 5, wherein the charge / discharge voltage is in the range of 4.35 V. 6. The method of claim 5, wherein the secondary battery includes: (a) first safety means for detecting a change in pressure, temperature, or both inside the battery to stop charging the battery or to switch the charging state to a discharge state; And (b) at least one selected from the group consisting of second safety means for dissipating heat or gas inside the battery to the outside. 8. The secondary battery of claim 7, wherein the first safety means comprises a pressure sensitive element, a temperature sensitive element, or both. The method of claim 7, wherein the first safety means (a) a pressure sensitive element; or (b) (i) a pressure sensitive element; (ii) conducting wires carrying current delivered from the pressure sensitive element; And (iii) a member for stopping charging of the device or switching the charging state to a discharge state in response to a current transmitted through the conductive wire. The method of claim 7, wherein the first safety means (a) a temperature sensitive element; or (b) (i) a temperature sensitive device; (ii) conducting wires carrying current delivered from said temperature sensitive element; And (iii) a member for stopping charging of the device or switching the charging state to a discharge state in response to a current transmitted through the conductive wire. 8. The secondary battery of claim 7, wherein the second safety means is a pressure release valve. The method of claim 7, wherein the secondary battery is a temperature increase inside the battery by the heat of oxidation generated from a compound having a pentahalophenyl group and a sulfonate group at the same time, the volume expansion due to the gas ejection pressure of the electrolyte components, increase in the battery pressure, Or a combination of the first safety means, the second safety means, or the first safety means and the second safety means. A compound having a structure represented by the following formula (1): [Formula 1]

In Formula 1, X is a halogen element; R is hydrogen, C ₁ ~ C ₂₀ linear alkyl group, C ₃ ~ C ₈ cyclic alkyl group, C ₂ ~ C ₂₀ linear alkenyl group, C ₃ ~ C ₈ cyclic alkenyl group, C ₁ substituted with one or more halogen An alkyl group, a phenyl group, and a benzyl group of ˜C ₂₀ ; n is an integer of 1-3. The method of claim 13, wherein pentafluorophenoxymethyl methylsulfonate, pentafluorophenoxymethyl ethylsulfonate, pentafluorophenoxymethyl allylsulfonate, pentafluorophenoxymethyl allylsulfonate Lofenoxymethyl phenylsulfonate, pentafluorophenoxymethyl benzylsulfonate, pentafluorophenoxyethyl methylsulfonate, pentafluorophenoxyethyl methylsulfonate (pentafluorophenoxyethyl methylsulfonate) pentafluorophenoxyethyl ethylsulfonate, pentafluorophenoxyethyl allylsulfonate, pentafluorophenoxyethyl phenylsulfonate, pentafluorophenoxyethyl benzylsulfonate, pentafluorophenoxyethyl benzylsulfonate city Pentafluorophenoxypropyl methylsulfonate, pentafluorophenoxypropyl ethylsulfonate, pentafluorophenoxypropyl allylsulfonate, pentafluorophenoxypropyl phenylsulfonate , Pentafluorophenoxypropyl benzylsulfonate, pentachlorophenoxymethyl methylsulfonate, pentachlorophenoxymethyl ethylsulfonate, pentachlorophenoxymethyl allylsulfonate (pentachlorophenoxymethyl allylsulfonate), pentachlorophenoxymethyl phenylsulfonate, pentachlorophenoxymethyl benzylsulfonate, pentachlorophenoxyethyl methylsulfonate (p entachlorophenoxyethyl methylsulfonate, pentachlorophenoxyethyl ethylsulfonate, pentachlorophenoxyethyl allylsulfonate, pentachlorophenoxyethyl phenylsulfonate, pentachlorosulfonoxyethyl benzyl Pentachlorophenoxypropyl allylsulfonate, pentachlorophenoxypropyl allylsulfonate, pentachlorophenoxypropyl allylsulfonate, pentachlorophenoxypropyl methylsulfonate, pentachlorophenoxypropyl methylsulfonate, pentachlorophenoxypropyl allylsulfonate A compound characterized by being selected from the group consisting of pentachlorophenoxypropyl phenylsulfonate and pentachlorophenoxypropyl benzylsulfonate.