KR102023678B1 - Electrolyte for Secondary Battery and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a secondary battery electrolyte and a secondary battery comprising the same. More specifically, the resistance during high temperature storage is increased by adding lithium difluorophosphate, vinylene carbonate and trialkylsilyl oxalate compounds to the secondary battery electrolyte. The present invention relates to a secondary battery electrolyte and a secondary battery including the same, wherein the secondary battery electrolyte has an effect of suppressing and improving capacity retention and normal temperature and high temperature lifetime characteristics.

Description

Electrolyte for secondary battery and secondary battery comprising same {Electrolyte for Secondary Battery and Secondary Battery Comprising the Same}

The present invention relates to a secondary battery electrolyte and a secondary battery comprising the same. More specifically, the resistance during high temperature storage is increased by adding lithium difluorophosphate, vinylene carbonate and trialkylsilyl oxalate compounds to the secondary battery electrolyte. The present invention relates to a secondary battery electrolyte and a secondary battery including the same, wherein the secondary battery electrolyte has an effect of suppressing and improving capacity retention and normal temperature and high temperature lifetime characteristics.

Secondary batteries have been applied to small and medium-sized devices such as electric vehicles (EVs) and energy storage systems (ESS) as well as small devices such as mobile phones, camcorders and notebook PCs. Efforts to develop are becoming more and more specific. Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s are charge and discharge cycles as lithium ions are inserted and desorbed from the positive and negative electrodes, and can convert chemical energy into electrical energy through a redox reaction. have.

Lithium secondary batteries using a non-aqueous electrolyte are coated with a lithium metal mixed oxide capable of detaching and inserting lithium ions as a positive electrode active material on a metal as a positive electrode, and a carbon material or a metal lithium as a negative electrode active material on a metal as a negative electrode. The coating is used, and an electrolyte solution in which lithium salt is suitably dissolved in an organic solvent is disposed between the anode and the cathode. The organic solvent of the electrolyte may decompose on the surface of the electrode during charge and discharge of the battery, or may be co-intercalated between the carbon material negative electrode layers to collapse the negative electrode structure, thereby inhibiting battery stability.

However, it is known that a solid electrolyte interface (SEI) film formed on the surface of the negative electrode by reducing the electrolyte solvent during initial charging of the battery can solve these problems.

Nevertheless, the SEI film collapses due to the repeated repetition of charge and discharge, and the life and performance of the secondary battery, especially at high temperatures, are degraded due to the low thermal stability of the SEI film.

In the prior art, Japanese Patent No. 3439085 discloses only the effect of improving storage characteristics after filling with an electrolyte solution containing lithium monofluoro phosphate and / or lithium difluoro phosphate, and Japanese Laid-Open Patent No. 1996-045545. Discloses a method of using vinylene carbonate as an electrolyte additive capable of forming an SEI film on a negative electrode surface, but both of the inventions inhibit the increase in resistance during high temperature storage by adding a trialkylsilyl oxalate compound. However, there is no disclosure about the effect of improving the life characteristics at room temperature and high temperature. In particular, vinylene carbonate has a problem in that it degrades performance and safety of the battery by easily decomposing at the anode during high temperature cycle or high temperature storage to generate gas. Korean Patent Publication No. 10-2010-0041028 discloses only the effect of improving cycle life (room temperature) characteristics and low temperature discharge capacity characteristics with an electrolyte solution containing a trialkylsilyl oxalate compound.

In addition, Japanese Patent No. 4952186 discloses the effect of suppressing the repetitive charge / discharge characteristics (cycle characteristics) of the battery with a non-aqueous electrolyte solution for secondary batteries containing vinylene carbonate and difluorophosphate and improving low temperature discharge characteristics. have. However, by adding the trialkylsilyl oxalate compound to the non-aqueous electrolyte solution for secondary batteries containing the vinylene carbonate and difluorophosphate, it is possible to suppress the increase in resistance during high temperature storage or to improve the life characteristics at high temperature (70 ° C.). There is no disclosure of the effect of improvement. Therefore, there is a need for a study on an electrolyte solution containing an optimal additive composition capable of simultaneously satisfying an improved capacity retention rate and lifetime retention rate while suppressing an increase in resistance during high temperature storage.

Accordingly, the present inventors have made diligent efforts to solve the above problems, and as a result, by adding lithium difluorophosphate, vinylene carbonate and trialkylsilyl oxalate compound to the secondary battery electrolyte, it is possible to suppress the increase in resistance during high temperature storage, The present invention was completed by confirming the improvement of the retention rate and the normal temperature and high temperature life characteristics.

An object of the present invention is to suppress the increase in resistance during high temperature storage, to provide a secondary battery electrolyte excellent in capacity retention rate, room temperature and high temperature life characteristics.

Another object of the present invention is to suppress the increase in resistance during high temperature storage, and to provide a secondary battery having excellent capacity retention ratio, room temperature, and high temperature lifetime characteristics.

In order to achieve the above object, the present invention (A) lithium salt; (B) a non-aqueous organic solvent; (C) lithium difluorophosphate; (D) vinylene carbonate; And (E) provides a secondary battery electrolyte comprising a trialkylsilyl oxalate compound represented by the formula (1).

[Formula 1]

In the above formula, R ₁ to R ₆ are each independently an unsubstituted C ₁ to C ₆ alkyl group or a C ₁ to C ₆ alkyl group substituted with a halogen atom.

The present invention also provides a secondary battery including the positive electrode, the negative electrode, and the electrolyte.

The secondary battery electrolyte according to the present invention is to suppress the increase in resistance during high temperature storage by adding lithium difluoro phosphate, vinylene carbonate and trialkylsilyl oxalate compound, and to improve the capacity retention rate and room temperature and high temperature life characteristics There is.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

Japanese Patent No. 4952186 discloses a secondary battery electrolyte containing vinylene carbonate and difluorophosphate, and Korean Patent Publication No. 10-2010-0041028 discloses an electrolyte solution containing a trialkylsilyl oxalate compound. However, both inventions are known only for the effect of improving the life characteristics and low temperature discharge capacity characteristics at room temperature. In the present invention, by adding a trialkylsilyl oxalate compound to an electrolyte solution containing lithium difluorophosphate and vinylene carbonate, it is confirmed that the resistance during the high temperature storage is not increased, and the capacity retention rate and the room temperature and high temperature life characteristics are improved. It was.

Accordingly, the present invention provides in one aspect: (A) a lithium salt; (B) a non-aqueous organic solvent; (C) lithium difluorophosphate; (D) vinylene carbonate; And (E) relates to a secondary battery electrolyte comprising a trialkylsilyl oxalate compound represented by the formula (1).

[Formula 1]

In the above formula, R ₁ to R ₆ are each independently an unsubstituted C ₁ to C ₆ alkyl group or a C ₁ to C ₆ alkyl group substituted with a halogen atom.

In another aspect, the present invention provides a secondary battery including the positive electrode, the negative electrode, and the electrolyte.

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

In the present invention, the lithium difluorophosphate (lithium difluorophosphate, LiPO ₂ F ₂ ) is a compound represented by the following formula (a).

[Formula a]

In the present invention, the vinylene carbonate (VC) is a compound represented by the following formula (b).

[Formula b]

In the present invention, the trialkylsilyl oxalate compound represented by Chemical Formula 1 is bis (trimethylsilyl) oxalate or bis (triethylsilyl) oxalate, and bis (trimethylsilyl) oxalate is more preferable.

In the present invention, the lithium salt used as the solute of the electrolyte solution is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ It may be at least one selected from the group consisting of F ₅ SO ₂ ) ₂ , CF ₃ SO ₃ Li and LiC (CF ₃ SO ₂ ) ₃ . The concentration of the lithium salt is preferably used in the range of 0.1M to 2.0M, more preferably 0.7M to 1.6M, when less than 0.1M, the conductivity of the electrolyte is reduced, the electrolyte performance is lowered, 2.0M If it exceeds, there is a problem in that the viscosity of the electrolyte is increased to reduce the mobility of lithium ions. These lithium salts act as a source of lithium ions in the battery to enable operation of the basic lithium secondary battery.

In the present invention, the non-aqueous organic solvent may be at least one selected from the group consisting of cyclic carbonate, chain carbonate and propionate, wherein the cyclic carbonate is ethylene carbonate (ethyl carbonate, EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone and mixtures thereof It may be at least one carbonate selected from the group, the chain carbonate is dimethyl carbonate (dimethyl carbonate, DMC), diethyl carbonate (diethyl carbonate, DEC), dipropyl carbonate (DPC), methylpropyl carbonate (methylpropyl carbonate, MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), and mixtures thereof At least one carbonate selected from the group consisting of combinations. In addition, the propionate is methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl propionate (BP) And one or more propion esters selected from the group consisting of mixtures thereof.

In the electrolyte according to an embodiment of the present invention, the non-aqueous organic solvent is a mixed solvent of a cyclic carbonate solvent and a linear carbonate solvent, and a mixing volume ratio of linear carbonate solvent: cyclic carbonate solvent is 1: 1 to 9: It may be 1, and may be preferably used by mixing in a volume ratio of 1.5: 1 to 4: 1.

In the present invention, the content of the lithium difluorophosphate is preferably from 0.05 to 5% by weight, more preferably from 0.05 to 3% by weight, and less than 0.05% by weight relative to the total amount of the electrolyte. The effect of improving the retention rate, capacity retention rate and capacity recovery rate is insignificant, and when it exceeds 5% by weight, the resistance of the battery is increased and the output is reduced, and secondary battery characteristics such as deterioration of room temperature and high temperature life and high temperature storage characteristics are deteriorated. There is a problem.

In the present invention, the content of the vinylene carbonate is preferably 0.05 to 5% by weight based on the total amount of the electrolyte, more preferably 0.05 to 3% by weight, when less than 0.05% by weight at room temperature and high temperature life characteristics When the effect of improving is insignificant and exceeds 5% by weight, the resistance of the battery is increased, so that the output is lowered, and secondary battery characteristics such as normal temperature and high temperature life, and high temperature storage characteristics are deteriorated.

In the present invention, the content of the trialkylsilyl oxalate compound is preferably from 0.05 to 5% by weight, more preferably from 0.05 to 3% by weight, and less than 0.05% by weight based on the total amount of the electrolyte. When the effect of improving the life characteristics is insignificant, and when it exceeds 5% by weight, the resistance of the battery is increased, thereby deteriorating secondary battery characteristics such as deterioration of lifetime and output, and high temperature storage characteristics.

In the present invention, lithium difluorobis (oxalato) phosphate, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate ( lithium difluoro (oxalato) borate), lithium bis (fluorosulfonyl) imide, ethylene sulfate, 1,3-propane sultone, 1 1,3-propene-1,3-sultone, vinyl ethylene carbonate, fluoroethylene carbonate, succinonitrile, With diponitrile, 1,3,6-hexanetricarbonitrile, pentaerythritol disulfate, and bis (triethylsilyl) sulfate It may further comprise one or more additives selected from the group consisting of, In it not limited.

In the present invention, the secondary battery electrolyte is a lithium salt; Organic solvents; It is preferably composed of an additive, and further contains 1 to 10% by weight of the additive based on 100% by weight of the organic solvent in which the lithium salt is dissolved.

The electrolyte solution for secondary batteries of this invention maintains the stable characteristic in the temperature range of -20-50 degreeC normally. The electrolyte solution of the present invention can be applied to a lithium ion secondary battery, a lithium ion polymer battery and the like.

In the present invention, the cathode material of the secondary battery is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or LiNi _1-xy Co _x M _y O ₂ (0 ≦ x ≦ 1, 0 ≦ _y ≦ 1, 0 ≦ x + y ≦ 1, M uses a lithium metal oxide such as Al, Sr, Mg, La, and the like, and as the negative electrode material, crystalline or amorphous carbon, carbon composite, lithium metal, or lithium alloy is used. . The active material is applied to a current collector of a thin plate with a suitable thickness and length, or the active material itself is applied in a film form, wound or laminated with a separator as an insulator to make an electrode group, and then placed in a can or a similar container, followed by lithium di A secondary battery is prepared by injecting an electrolyte solution to which fluorophosphate, vinylene carbonate, and trialkylsilyl oxalate compound are added. As the separator, a resin such as polyethylene or polypropylene may be used.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

Example 1

1.0 M LiPF ₆ was added to a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at 2: 4: 4 (v / v / v). 1.0% by weight of fluorophosphate, 1.5% by weight of vinylene carbonate and 0.2% by weight of trimethylsilyl oxalate compound represented by Chemical Formula 1a were added to prepare an electrolyte solution for a secondary battery.

[Formula 1a]

Example 2

An electrolyte for a secondary battery was prepared in the same manner as in Example 1, except that 0.5 wt% of a trialkylsilyl oxalate compound of Formula 1 was added.

Example 3

An electrolyte solution for a secondary battery was prepared in the same manner as in Example 1, except that 1.0% by weight of the trialkylsilyl oxalate compound of Formula 1 was added.

Comparative Example 1

1.0 M LiPF ₆ was added to a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed at 2: 4: 4 (v / v / v). Was prepared.

Comparative Example 2

An electrolyte solution for a secondary battery was prepared in the same manner as in Comparative Example 1 except that 1.0 wt% of lithium difluorophosphate was added.

Comparative Example 3

An electrolyte solution for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1.5 wt% of vinylene carbonate was added.

Comparative Example 4

An electrolyte solution for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1.0% by weight of the trialkylsilyl oxalate compound of Formula 1a was added.

[Formula 1]

Comparative Example 5

An electrolyte solution for a secondary battery was prepared in the same manner as in Comparative Example 1 except that 1.0 wt% of lithium difluorophosphate and 1.5 wt% of vinylene carbonate were added.

Comparative Example 6

An electrolyte solution for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1.0% by weight of lithium difluorophosphate and 1.0% by weight of trialkylsilyl oxalate compound represented by Chemical Formula 1a were added.

[Formula 1]

Comparative Example 7

An electrolyte solution for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1.5 wt% of vinylene carbonate and 1.0 wt% of a trialkylsilyl oxalate compound represented by Chemical Formula 1a were added thereto.

[Formula 1]

Experimental Example 1

In the present experimental example, the characteristics of the secondary battery containing the electrolyte solution prepared in Examples 1 to 3 and Comparative Examples 1 to 7 were measured according to the following method, and the results are shown in Table 1.

Thickness / internal resistance

A digital caliper is used to measure the thickness change of the manufactured cell. The measurement measures the thickness of the part where the acrylic plate is directly in contact with the surface of the cell after attaching an acrylic plate to each end of the vernier caliper. The measurement is made three times in total, and the average value is recorded.

Use a battery high tester to measure the internal resistance of the battery. The measuring method presses the lead measured on both ends of the battery, and measures the resistance value displayed at that time. At this time, the measurement position of the battery is kept the same each time. Record the value at the point where the resistance value displayed on the instrument remains steady.

DC-IR (direct current-internal resistance)

Measure the capacity retention rate of the manufactured battery, discharge it at 0.5C, discharge 0.5C, 1C, 2C, and 4C for 10 seconds, and charge the battery at 4.2V 1C for 1 week at high temperature (70 ℃), and then measure the capacity retention. After discharging at 0.5C, 0.5C, 1C, 2C, and 4C were discharged for 10 seconds, respectively.

Pulse Power

Pulse power was calculated from the DC-IR measurements.

Capacity retention rate (%) and recovery rate (%)

1C charge to 4.2V at room temperature (25 ℃), 2.75V 1C discharge, 0.5C charge to 4.2V, then 1C charge to 4.2V after 1 week at high temperature (70 ℃), 2.75V 1C discharge 2 Cycle progressed, the discharged capacity of the second cycle was measured and compared. The charge / discharge tester used TOYO SYSTEM.

-Low temperature discharge rate (%)

Measurement was started after the battery was stored for 1 hour in a low temperature chamber maintained at -20 ° C. Measurement conditions were discharged to 2.75V at 1C, and the discharged capacity was measured and compared.

-Normal temperature and high temperature life retention rate (%)

The prepared battery was charged with 1C up to 4.2V and then discharged with 2C up to 2.75V. This process was repeated 500 times to measure the life retention rate. The life retention rate was evaluated at room temperature (25 ° C.) and high temperature (70 ° C.), and the discharge capacity at 500 cycles, the percentage of initial capacity, and the percentage of initial capacity increased compared to Comparative Example 5 were measured.

(Before): Before high temperature storage (25 ℃)

After: After high temperature storage (measured after 1 week storage at 70 ° C)

As shown in Table 1, it was confirmed that the electrolyte solution prepared according to Examples 1 to 3 of the present invention suppressed the increase in resistance during the high temperature life and excellent capacity retention rate compared to Comparative Examples 1 to 7. In particular, in the case of Example 1 containing 0.2% of trialkylsilyl oxalate compound, DC-IR (after) 55.56 Ω, Comparative Example 1 (62.66 Ω) containing no additives, lithium difluorophosphate and vinylene carbonate It was confirmed that the resistance during the high temperature life was increased compared with Comparative Example 5 (64.20 Ω). In addition, also in the capacity retention rate of Comparative Example 1 and Comparative Example 5 was 62.9% and 79.3%, while Example 1 of the present invention was confirmed to have an excellent capacity retention rate of 86.9%.

In addition, it was confirmed that the electrolyte solution prepared according to Examples 1 to 3 of the present invention was also significantly superior in life characteristics at room temperature and high temperature compared to Comparative Examples 1 to 7. In the case of room temperature life efficiency, Comparative Example 1 and Comparative Example 5 was 70.4% and 86.6%, respectively, Example 1 of the present invention was confirmed that it has a remarkably excellent room temperature life characteristics, 91.6%, high temperature life efficiency In the case of Comparative Example 1 and Comparative Example 5 was 65.2% and 85.8%, respectively, Example 1 of the present invention was confirmed that it has excellent high temperature life characteristics of 86.7%.

From these results, the secondary battery electrolyte containing the lithium difluorophosphate, vinylene carbonate and trialkylsilyl oxalate compound of the present invention suppresses the increase in resistance during high temperature storage, and has excellent capacity retention and life characteristics. You can see that.

Having described the specific parts of the present invention in detail, it will be apparent to those skilled in the art that these specific descriptions are merely preferred embodiments, and thus the scope of the present invention is not limited thereto. will be. Thus, the substantial scope of the present invention will be defined by the claims and their equivalents.

Claims (11)

Electrolyte for secondary battery containing:
(A) lithium salts;
(B) a non-aqueous organic solvent which is a mixture of cyclic carbonate and chain carbonate;
(C) lithium difluorophosphate;
(D) vinylene carbonate; And
(E) The trialkylsilyl oxalate compound represented by following formula (1).
[Formula 1]

(Wherein, R ₁ to R ₆ are each independently a methyl group or an ethyl group.)
The electrolyte solution for a secondary battery according to claim 1, wherein the trialkylsilyl oxalate compound is bis (trimethylsilyl) oxalate or bis (triethylsilyl) oxalate.
The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , CF ₃ SO ₃ Li and LiC (CF ₃ SO ₂ ) _{3 The} secondary battery electrolyte, characterized in that at least one selected from the group consisting of.
The electrolyte of claim 1, wherein the non-aqueous organic solvent further comprises propionate.
According to claim 1, wherein the cyclic carbonate is at least one carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone and mixtures thereof, the chain carbonate is dimethyl Electrolyte for secondary batteries, characterized in that at least one carbonate selected from the group consisting of carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethylmethyl carbonate and mixtures thereof.
The method of claim 4, wherein the propionate is methyl propionate, ethyl propionate, propyl propionate, butyl propionate and mixtures thereof. Electrolyte for a secondary battery, characterized in that at least one propion ester selected from the group consisting of.
The method of claim 1, wherein the lithium difluoro phosphate content of the secondary battery electrolyte, characterized in that 0.05 to 5% by weight relative to the total amount of the electrolyte.
The method of claim 1, wherein the content of the vinylene carbonate is a secondary battery electrolyte, characterized in that 0.05 to 5% by weight relative to the total amount of the electrolyte.
The secondary battery electrolyte of claim 1, wherein the trialkylsilyl oxalate compound is present in an amount of 0.05 to 5 wt% based on the total amount of the electrolyte.
According to claim 1, Lithium difluorobis (oxalato) phosphate (lithium difluorobis (oxalato) phosphate), Lithium bis (oxalato) borate, Lithium difluoro (oxalato) borate (lithium difluoro (oxalato) borate), lithium bis (fluorosulfonyl) imide, ethylene sulfate, 1,3-propane sultone, 1,3-propene-1,3-sultone, vinylethylene carbonate, fluoroethylene carbonate, succinonitrile, Adiponitrile, 1,3,6-hexanetricarbonitrile, pentaerythritol disulfate and biethyltriyl sulfate (bis) triethylsilyl sulfate Secondary battery further comprising at least one additive selected from the group consisting of Haeaek.
A secondary battery comprising a positive electrode, a negative electrode and the electrolyte of any one of claims 1 to 10.