KR101177952B1 - Non-aqueous electrolyte and electrochemical device comprising the same - Google Patents

Abstract

The present invention provides a composition comprising (i) carbonyl bislactam; (ii) organic solvents comprising cyclic carbonates and / or linear carbonates; And (iii) an electrolyte salt. The present invention also relates to an electrochemical device comprising the nonaqueous electrolyte. In addition, the present invention is an electrode comprising an electrode active material formed on a part or all of the surface of the coating film containing a reducing agent of carbonyl bislactam; And it relates to an electrochemical device comprising the electrode.

Electrochemical device, secondary battery, nonaqueous electrolyte, carbonyl bislactam, carbonate

Description

Non-aqueous electrolyte and electrochemical device including same {NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE COMPRISING THE SAME}

1 is a graph showing the differential capacity according to the voltage of the lithium secondary battery prepared according to Example 1 and Comparative Example 2.

The present invention relates to a nonaqueous electrolyte containing carbonyl bislactam and an electrochemical device comprising the nonaqueous electrolyte capable of improving the life characteristics of the device.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. Electrochemical devices are the most attention in this regard, and among them, the development of secondary batteries capable of charging and discharging has become a focus of attention. Recently, in developing such a battery, research and development on the design of a new electrode and a battery have been conducted to improve capacity density and specific energy.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

In general, a lithium secondary battery may include a cathode including a lithium metal composite oxide or sulfur capable of intercalation and disintercalation of lithium ions; An anode comprising a carbon material or metallic lithium; And an electrolyte solution in which a lithium salt is dissolved in an appropriate amount in a carbonate solvent.

During the initial charging of a lithium secondary battery, lithium ions derived from a cathode active material such as lithium metal oxide move to an anode active material such as graphite and are inserted between the layers of the anode active material. At this time, since lithium has a high reactivity, the electrolyte and the carbon constituting the anode active material react on the surface of the anode active material such as graphite to generate compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of SEI (Solid Electrolyte Interface) film on the surface of the anode active material such as graphite.

The SEI film acts as an ion tunnel to pass only lithium ions. The SEI film is an effect of this ion tunnel, and prevents the structure of the anode from being destroyed by intercalation of the organic solvent molecules having a large molecular weight moving together with lithium ions in the electrolyte between the layers of the anode active material. Therefore, by preventing contact between the electrolyte solution and the anode active material, decomposition of the electrolyte solution does not occur, and the amount of lithium ions in the electrolyte solution is reversibly maintained to maintain stable charge and discharge.

However, due to the gases such as CO, CO ₂ , CH ₄ , C ₂ H ₆ generated from decomposition of the carbonate solvent during the SEI formation reaction described above, there is a problem that the battery thickness is expanded during charging. In addition, as time elapses at high temperature in a full charge state, the SEI film gradually collapses due to increased electrochemical energy and thermal energy, so that side reactions in which the exposed anode surface reacts with the surrounding electrolyte continuously occur. Due to the continuous gas generation at this time, the internal pressure of the battery is increased, and the thickness of the battery is increased, causing problems in sets such as mobile phones and laptops. That is, high temperature leaving safety is bad.

In order to suppress such an increase in the internal pressure of the battery, studies have been conducted to change the aspect of the SEI film formation reaction by adding an additive to the electrolyte. However, as far as is known, when certain compounds are added to the electrolyte to improve battery performance, the performance of some items is improved, but the performance of other items is reduced.

When the carbonyl bislactam is used as an electrolyte additive for an electrochemical device, for example, a lithium secondary battery, the present inventors have a reduction property of the film before the carbonate organic solvent causes a reduction decomposition reaction to form a film having excellent properties. Formed.

Accordingly, the present invention is a non-aqueous electrolyte containing a carbonyl bislactam and a carbonate organic solvent; And to provide an electrochemical device comprising the non-aqueous electrolyte.

The present invention provides a composition comprising (i) carbonyl bislactam; (ii) an organic solvent comprising a cyclic carbonate, or a linear carbonate, or both; And (iii) an electrolyte salt.

In addition, the present invention provides an electrode comprising an electrode active material formed on a part or all of the surface of the coating film containing a reducing agent of carbonyl bislactam.

The present invention also provides an electrochemical device comprising an anode, a cathode and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is a nonaqueous electrolyte according to the present invention.

In addition, the present invention provides an electrochemical device comprising an anode, a cathode, and a nonaqueous electrolyte, wherein the anode, or the cathode, or both the anode and the cathode are electrodes according to the present invention.

Hereinafter, the present invention will be described in detail.

The nonaqueous electrolyte solution of this invention contains the carbonyl bislactam with a carbonate organic solvent as an electrolyte solution additive.

In the initial charging of an electrochemical device including the nonaqueous electrolyte of the present invention, for example, a secondary battery, the carbonyl bislactam may be subjected to a reduction decomposition reaction at a lower potential than the carbonate organic solvent. This is because the carbonyl group acts as an electron withdrawing group (EWG) on the structure of carbonyl bislactam, resulting in ring-opening polymerization at a low reduction potential. In addition, carbonyl bislactam reacts at a lower reduction potential compared to lactam without an existing substituent or lactam substituted with an EDG (electron donating group), and is more dense because there are two functional groups capable of reacting. And a stable film can be formed.

Therefore, when carbonyl bislactam is used as an electrolyte additive, the carbonyl bislactam reacts at a low reduction potential, and is highly stable and dense, for example, due to a complex reaction with a cyclic carbonate occurring at a high potential after the reaction. A solid electrolyte interface (SEI) film can be formed. In addition, the coating is less decomposition at high temperature can minimize the generation of gas. Therefore, the shelf life and high temperature life characteristics of the electrochemical device can be improved by the above mechanism.

In the nonaqueous electrolyte of the present invention, the carbonyl bislactam may be a carbonyl bislactam of the following formula (1).

[Formula 1]

In Formula 1, R ¹ to R ¹² are each independently hydrogen, halogen, C ₁ ~ C ₆ alkyl, or C ₁ ~ C ₆ haloalkyl,

m and n are each independently an integer of 0-13.

Carbonyl bislactam can be obtained by a simple method through the reaction of lactam with phosgene (COCl ₂ ).

Carbonyl bislactam may be included in the nonaqueous electrolyte at 0.05 to 10 parts by weight based on 100 parts by weight of the organic solvent. If the carbonyl bislactam is less than 0.05 parts by weight based on 100 parts by weight of the organic solvent, the effect of improving the cycle characteristics of the battery is insufficient. If the carbonyl bislactam is more than 10 parts by weight, the performance of the battery is reduced due to gas generation and impedance increase during initial charging. there is a problem.

The nonaqueous electrolyte of the present invention includes an organic solvent containing cyclic carbonate and / or linear carbonate. The cyclic carbonate and / or linear carbonate is not particularly limited as long as it is normally used for nonaqueous electrolyte.

Non-limiting examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), pentylene carbonate, fluoroethylene carbonate (FEC), and halogen derivatives thereof may be used. . In addition, these cyclic carbonates can be used individually or in mixture of 2 or more types.

Non-limiting examples of the linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dibutyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl Carbonate, methyl butyl carbonate, ethyl propyl carbonate, and the like, and halogen derivatives thereof can also be used. In addition, these linear carbonates can be used individually or in mixture of 2 or more types.

The linear carbonate is preferably included in 40 to 80% by volume of the nonaqueous electrolyte. If the linear carbonate in the non-aqueous electrolyte is less than 40% by volume, the viscosity of the electrolyte itself is increased to decrease the ionic conductivity. If it is more than 80% by volume, the dielectric constant is decreased to dissociate a larger amount of the electrolyte salt. Causes deterioration.

In the nonaqueous electrolyte of the present invention, the organic solvent may further include other organic solvents in addition to the cyclic carbonate and / or linear carbonate.

The organic solvent that can be additionally used is not particularly limited as long as it is usually used as an organic solvent for nonaqueous electrolyte, and lactone, ether, ester, acetonitrile, and / or ketone can be used.

Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane and the like. Examples of the esters include methyl formate, ethyl formate, propyl formate, and the like. Examples of the ketones include polymethylvinyl ketone. Moreover, the halogen derivative of the said organic solvent can also be used. These organic solvents can be used individually or in mixture of 2 or more types.

The nonaqueous electrolyte of the present invention contains an electrolyte salt, and the electrolyte salt is not particularly limited as long as it is usually used as an electrolyte salt for nonaqueous electrolyte.

The electrolyte salt is ^{(i) Li +, Na +} , a cation and (ii) selected from the group consisting of _{^{K + PF 6 -, BF 4}} -, Cl -, Br -, I -, ClO 4 -, AsF 6 -, _{^{CH 3 CO 2 -, CF 3}} SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 - , but can be configured with a combination of an anion selected from the group consisting of, but not always limited thereto. These electrolyte salts can be used individually or in mixture of 2 or more types. In particular, the electrolyte salt is preferably a lithium salt.

The electrode of the present invention is an electrode comprising an electrode active material having a film, for example, a solid electrolyte interface (SEI) film formed on part or all of the surface, wherein the film contains a reducing agent of carbonyl bislactam It features.

The coating, for example, a solid electrolyte interface (SEI) membrane may be formed during initial charging or subsequent charge / discharge of the electrochemical device. The electrode of the present invention can be prepared by reducing the electrode prepared according to a conventional method known in the art one or more times in a non-aqueous electrolyte containing carbonyl bislactam. In addition, the electrode of the present invention can be prepared by putting a porous separator between the positive electrode and the negative electrode prepared by a conventional method known in the art, and after charging a non-aqueous electrolyte containing carbonyl bislactam once or more times. have.

In the electrode of the present invention, the carbonyl bislactam may be a carbonyl bislactam of the formula (1). Therefore, the reduced substance of the carbonyl bislactam may be produced by reduction of the carbonyl bislactam of the formula (1).

Meanwhile, the electrochemical device of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the nonaqueous electrolyte is a nonaqueous electrolyte according to the present invention.

In addition, the electrochemical device according to the present invention comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, the electrode is characterized in that the electrode according to the present invention. In this case, the nonaqueous electrolyte may be used together with the nonaqueous electrolyte according to the present invention.

The electrochemical device of the present invention includes all devices that undergo an electrochemical reaction. Specific examples thereof include all kinds of primary cells, secondary batteries, fuel cells, solar cells, or capacitors. The electrochemical device is preferably a secondary battery, and a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable.

The electrochemical device of the present invention can be prepared according to conventional methods known in the art. For example, a porous separator may be placed between the positive electrode and the negative electrode, and then, the nonaqueous electrolyte solution according to the present invention may be added to the negative electrode. In addition, a porous separator may be placed between the positive electrode and the negative electrode according to the present invention, and a normal nonaqueous electrolyte may be added to prepare the same.

In addition, the electrode can be prepared by conventional methods known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant in an electrode active material, and then applying the coating (coating) to a current collector of a metal material, compressing, and drying the electrode to prepare an electrode. Can be.

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 lithium transition metal composite oxide such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, lithium manganese composite oxide such as LiMn ₂ O ₄ , LiNiO _2, etc.). Lithium cobalt oxides such as lithium nickel oxide, LiCoO ₂ , and manganese, nickel, and cobalt in which some of these oxides are substituted with other transition metals, or lithium-containing vanadium oxide, or a chalcogenide compound (for example, manganese dioxide) , Titanium disulfide, molybdenum disulfide, etc.) may be used, but is not limited thereto.

The negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, non-limiting examples thereof lithium metal, lithium alloy, carbon, petroleum coke that can occlude and release lithium ions ), Activated carbon, graphite, carbon fiber, and the like. In addition, lithium oxide may be occluded and released, and metal oxides such as TiO ₂ , SnO _2, and the like with respect to lithium may be used, but are not limited thereto. In particular, carbon materials such as graphite, carbon fiber and activated carbon are preferable.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the slurry of the electrode active material can be easily adhered and is not reactive in the voltage range of the battery. Non-limiting examples of the positive electrode current collector is a foil produced by aluminum, nickel or a combination thereof, and non-limiting examples of the negative electrode current collector is produced by copper, gold, nickel or copper alloy or a combination thereof Foil and the like.

The electrochemical device of the present invention may include a separator. The separator is not particularly limited, but it is preferable to use a porous separator, and non-limiting examples include a polypropylene-based, polyethylene-based, or polyolefin-based porous separator.

The electrochemical device of the present invention is not limited in appearance, but may be cylindrical, square, pouch or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to the following Examples. However, the following examples are merely to illustrate the present invention and the present invention is not limited by the following examples.

(Example 1)

Ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 2: 1: 7 (v: v: v), the solution of 100 was dissolved to a 1M concentration of LiPF ₆ in an organic solvent having a composition of 0.5 parts by weight of carbonyl biscaprolactam (formula 2) was added to parts by weight to prepare a nonaqueous electrolyte.

[Formula 2]

LiCoO ₂ was used as the positive electrode active material, PVDF as the binder and acetylene black as the conductive material were added to NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry, and then coated on the aluminum (Al) collector. A positive electrode was prepared.

Artificial negative electrode was used as a negative electrode active material, PVDF as a binder and acetylene black as a conductive material were added to NMP to prepare a negative electrode slurry, and then coated on a copper (Cu) current collector to prepare a negative electrode.

After interposing a polyolefin-based separator between the prepared positive electrode and the negative electrode, a non-aqueous electrolyte was prepared to prepare a coin-type battery (MCMB battery).

(Example 2)

A nonaqueous electrolyte solution and a battery were manufactured in the same manner as in Example 1, except that 1 part by weight of carbonyl biscaprolactam (Formula 2) was used.

(Comparative Example 1)

A nonaqueous electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 1 part by weight of vinylene carbonate was used instead of carbonyl biscaprolactam.

(Comparative Example 2)

A nonaqueous electrolyte solution and a battery were prepared in the same manner as in Example 1, except that carbonyl biscaprolactam was not added.

(Comparative Example 3)

A nonaqueous electrolyte and a battery were prepared in the same manner as in Example 1, except that 0.5 parts by weight of epsilon caprolactam (formula 3) was used.

(3)

(Experiment 1: Capacity Measurement with Voltage )

Differential capacity according to voltage was measured using lithium secondary batteries prepared according to Example 1 and Comparative Example 2, and the results are shown in FIG. 1.

According to FIG. 1, since the battery of Example 1 shows the same capacity value at a lower potential than that of Comparative Example 2, the electrolyte solution containing carbonyl bislactam (Example 1) does not contain an electrolyte solution (Comparative Example). 2) It was found that a reduction decomposition reaction occurred at a lower potential to form an electrode coating.

(Experiment 2: Measurement of discharge capacity and capacity retention rate )

The lithium secondary batteries prepared according to Examples 1 to 2 and Comparative Examples 1 to 3 were charged and discharged at 1 ° C. at 60 ° C. to maximize discrimination by experimenting under severe conditions, and the discharge capacities and capacity retention rates are shown in Table 1 below. . In Table 1, the discharge capacity represents discharge capacity after 100 cycles, and the capacity retention ratio represents a% value with respect to the standard discharge amount of the capacity value measured after 100 cycles.

Discharge Capacity (mAh) Capacity retention rate (%)
Example 1
4.4 88 4.32 86.4 4.42 88.4
Example 2
4.23 84.6 4.18 83.6 4.19 83.8
Comparative Example 1
4.38 87.6 4.35 87 4.39 87.8
Comparative Example 2
2.48 49.6 2.33 46.6 2.41 48.2
Comparative Example 3
4.22 84.4 4.18 83.6 4.17 83.4

As shown in Table 1, the batteries of Examples 1 and 2 were equivalent or almost similar to those of Comparative Examples 1 and 3, and showed better results than the batteries of Comparative Example 2.

Experiment 3: Gas Generation Measurement

After the lithium secondary batteries prepared according to Examples 1 to 2 and Comparative Examples 1 to 3 were left at 90 ° C. for 4 hours, the initial internal pressure before leaving and the final internal pressure after leaving were measured to determine the effect of inhibiting gas generation. The results are shown in Table 2 below.

Initial Torr Final Torr Increasing pressure resistance (Torr) Example 1 0.3 0.9 0.6 Example 2 0.4 1.1 0.7 Comparative Example 1 0.4 1.6 1.2 Comparative Example 2 0.5 1.3 0.8 Comparative Example 3 0.4 1.8 1.4

As shown in Table 2, the battery of Example 1 and Example 2 was reduced compared to the batteries of Comparative Examples 1 to 3, the increase in withstand pressure was reduced, and thus it was found that the gas generation inhibiting effect.

The carbonyl bislactam contained in the nonaqueous electrolyte of the present invention may be subjected to a reduction decomposition reaction at a potential lower than that of the carbonate organic solvent during initial charging. Accordingly, the carbonyl bislactam is reduced and decomposed to form a highly stable film on the surface of the electrode active material, and the film is less decomposed at high temperature, thereby minimizing gas generation. High temperature life characteristics can be improved.

Claims (11)

(i) carbonyl bislactam; (ii) an organic solvent comprising a cyclic carbonate, or a linear carbonate, or both; And (iii) an electrolyte salt. The nonaqueous electrolyte of claim 1, wherein the carbonyl bislactam is a carbonyl bislactam of the following Chemical Formula 1. [Formula 1]

In Formula 1, R ¹ to R ¹² are each independently hydrogen, halogen, C ₁ ~ C ₆ alkyl, or C ₁ ~ C ₆ haloalkyl, m and n are each independently an integer of 0-13. The nonaqueous electrolyte of claim 1, wherein the carbonyl bislactam is contained in an amount of 0.05 to 10 parts by weight based on 100 parts by weight of the organic solvent. According to claim 1, wherein the cyclic carbonate is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), pentylene carbonate, fluoroethylene carbonate (FEC) and halogen derivatives thereof A nonaqueous electrolytic solution characterized by being at least a species. The method of claim 1, wherein the linear carbonate is diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dibutyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl iso Non-aqueous electrolyte, characterized in that at least one selected from the group consisting of propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate and halogen derivatives thereof. The nonaqueous electrolyte of claim 1, wherein the linear carbonate is contained in an amount of 40 to 80% by volume in the nonaqueous electrolyte. The method of claim 1, wherein the electrolyte salt is (i) Li ⁺ , Na ⁺ , K ⁺ and a cation selected from the group consisting of ^{_{(ii) 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 characterized by the non-aqueous electrolytic solution which is a combination of an anion selected from the group consisting of. The electrode containing the electrode active material in which the film | membrane containing the reducing substance of carbonyl bislactam was formed in part or all of the surface. The electrode of claim 8, wherein the carbonyl bislactam is a carbonyl bislactam of Formula 1 below. [Formula 1]

In Formula 1, R ¹ to R ¹² are each independently hydrogen, halogen, C ₁ ~ C ₆ alkyl, or C ₁ ~ C ₆ haloalkyl, m and n are each independently an integer of 0-5. An electrochemical device comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the electrolyte is an electrochemical device according to any one of claims 1 to 7. An electrochemical device comprising an anode, a cathode, and a nonaqueous electrolyte, wherein the anode, or the cathode, or both the anode and the cathode are the electrodes of claim 8 or 9.

Images