KR20190078770A - 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 particularly, the present invention relates to a secondary battery electrolyte having an effect of enhancing room-temperature and high-temperature life characteristics at high voltage as well as general voltage (4.2 V) by adding a cyclic sulfate compound and a trialkylsilyl compound to the secondary battery electrolyte, and to a secondary battery comprising the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrolyte for a secondary battery,

The present invention relates to an electrolyte solution for a secondary battery and a secondary battery comprising the electrolyte solution. More particularly, the present invention relates to an electrolyte solution for a secondary battery, in which a cyclic sulfate compound and a trialkylsilyl compound are added to an electrolyte solution for a secondary battery, To an electrolyte for a secondary battery and an secondary battery including the same.

The rechargeable battery has been applied not only to small-sized devices such as mobile phones, camcorders and notebook PCs but also to medium and large-sized devices such as electric vehicles (EV) and energy storage systems (ESS) Efforts to develop are becoming more and more concrete. Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s is a battery in which charging and discharging are repeated as lithium ions are inserted and removed from the positive electrode and the negative electrode, and the chemical energy can be converted into electrical energy through the oxidation- have.

In order to apply lithium secondary batteries to medium- and large-sized devices such as electric vehicles and energy storage systems, it is essential to develop materials having excellent lifetime characteristics, high output and energy density. In order to increase the charging voltage for increasing energy density, In addition, studies are underway to develop electrochemically stable electrolytes and electrolytic solution additives in a high-voltage environment.

However, in the high voltage battery, the anode material charging voltage is improved and the oxidative decomposition phenomenon of the electrolyte deteriorates, so that the performance of the battery deteriorates. In addition, the high voltage battery generally has a disadvantage that the anode metal ion release phenomenon occurs during use, and particularly when the battery is stored at a high temperature for a long time, the discharge of the anode metal ion becomes worse and the capacity retention rate of the battery also becomes lower.

Korean Patent Laid-Open No. 10-2017-0039369 discloses only an effect of improving the output characteristics and the high-temperature storage characteristics with an electrolytic solution containing a cyclic sulfate compound, and Korean Patent Publication No. 10-2016-0144123 (4.2 V) as an electrolytic solution containing a cyclic sulfate compound, the effects of improving the lifetime characteristics at high voltage by adding a cyclic sulfate compound to both of the inventions There is no disclosure at all. In addition, the applicant of the present invention has found that the lifetime characteristics and high-temperature storage characteristics at room temperature and high temperature of the electrolytic solution containing the cyclic sulfate compound are remarkably improved, but the improvement effect on the lifetime characteristics at high voltage is insufficient, The new electrolytic solution composition was continuously studied.

Korean Patent Laid-Open No. 10-2012-0109407 discloses an electrolytic solution containing a trialkylsilyl compound (first additive), but the first additive has a low temperature characteristic and an output characteristic In order to improve the water content. Korean Patent Laid-Open No. 10-2017-0067663 discloses a non-aqueous electrolyte for a lithium secondary battery containing four kinds of additives including 1,3-propane sultone and tris (trimethylsilyl) borate. However, It can be confirmed that the side reaction between the solvent and the cathode and the anode is lowered to reduce the amount of gas generated at the time of high-temperature storage.

Korean Patent No. 10-1777917 discloses a secondary battery including a polyimide (PI) and a cathode active material surface-coated with a nanocapsule including conductive nanoparticles. However, in the case of a cathode material in which such an organic / inorganic coating layer is introduced It is possible to prevent the metal from leaching in a high voltage environment, but there is still a need for improvement in suppressing side reactions with the electrolytic solution.

As a result of intensive efforts to solve the above problems, the present inventors have found that the addition of a cyclic sulfate compound and a trialkylsilyl compound to an electrolyte for a secondary battery improves the room temperature and high temperature lifetime characteristics not only at a normal voltage (4.2 V) And completed the present invention.

An object of the present invention is to provide an electrolyte for a secondary battery which is excellent not only in the normal voltage (4.2 V) but also in high temperature and high temperature life characteristics at high voltage.

Another object of the present invention is to provide a secondary battery having excellent normal temperature and high temperature lifetime characteristics at a high voltage as well as a normal voltage (4.2 V).

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

[Chemical Formula 1]

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

The electrolyte for a secondary battery according to the present invention has an effect of improving the room temperature and high temperature lifetime characteristics not only at a normal voltage (4.2 V) but also at a high voltage by adding a cyclic sulfate compound and a trialkylsilyl compound.

FIG. 1 shows lifetime characteristics at high voltage and high temperature according to an embodiment of the present invention.

Unless otherwise defined, 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.

The applicant of the present invention has confirmed that the life characteristics and high temperature storage characteristics at a room temperature and a high temperature of the electrolytic solution containing the cyclic sulfate compound are remarkably improved. However, the problem that the lifetime at high voltage is reduced in the secondary battery including the electrolytic solution is solved I can not. However, in the present invention, it was confirmed that the trialkylsilyl compound was added to the electrolyte for the secondary battery including the cyclic sulfate compound, thereby remarkably improving the room temperature and high temperature lifetime characteristics not only at the normal voltage (4.2 V) but also at the high voltage.

Accordingly, the present invention provides, in one aspect, (A) a lithium salt; (B) a non-aqueous organic solvent; (C) a cyclic sulfate compound represented by the following formula (1); And (D) a trialkylsilyl compound.

[Chemical Formula 1]

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

Hereinafter, the present invention will be described in detail.

In the present invention, the cyclic sulfate compound represented by Formula 1 is pentaerythritol disulfate.

In the present invention, the trialkylsilyl compound may be in the form of a borate, phosphate, phosphite or sulfate.

In the present invention, the trialkylsilyl compound is preferably selected from the group consisting of tris (trimethylsilyl) borate, tris (trimethylsilyl) phosphite, tris (trimethylsilyl) phosphate ) phosphate, bis (trimethylsilyl) sulfate, tris (triethylsilyl) borate, tris (triethylsilyl) phosphite, tris (Trimethylsilyl) phosphate (tris (triethylsilyl) phosphate) and bis (triethylsilyl) sulfate, and more preferably at least one selected from the group consisting of tris (trimethylsilyl) borate trimethylsilyl) borate, TMSB), tris (trimethylsilyl) phosphite, TMSPi, tris (trimethylsilyl) phosphate, TMSPa and bis (triethylsilyl) It is more preferably at least one selected from the group consisting of (bis (triethylsilyl) sulfate, TESS).

In the present invention, the lithium salt used as a solute of the electrolyte 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 concentration of the lithium salt is preferably in the range of 0.1 M to 2.0 M, more preferably in the range of 0.7 M to 1.6 M, and in the case of less than 0.1 M, the conductivity of the electrolyte decreases, There is a problem that the viscosity of the electrolytic solution increases and the mobility of the lithium ion decreases. These lithium salts act as a source of lithium ions in the cell to enable operation of a 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 carbonates, chain carbonates, and propionates, and the cyclic carbonates include ethylene carbonate (ethyl carbonate, EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone, And the chain carbonate may be one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate carbonate, MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC) And one or more of carbonates selected from the group consisting of a mixture of two or more carbonates. The propionate may be selected from the group consisting of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl propionate (BP) And mixtures thereof. ≪ / RTI >

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

In the present invention, the content of the cyclic sulfate compound is preferably 0.05 to 5% by weight, more preferably 0.05 to 3% by weight based on the total weight of the electrolytic solution. When the amount is less than 0.05% by weight, The effect of improving the lifetime characteristics is insignificant. When the content is more than 5% by weight, the resistance of the battery is increased and the characteristics of the secondary battery such as the lifetime and the output decrease and the high temperature storage characteristics are lowered.

In the present invention, the content of the trialkylsilyl compound is preferably 0.05 to 5% by weight, more preferably 0.05 to 3% by weight based on the total weight of the electrolytic solution. When the amount is less than 0.05% by weight, The effect of improving the lifetime characteristics is insignificant. When the content is more than 5% by weight, the resistance of the battery is increased and the characteristics of the secondary battery such as the lifetime and the output decrease and the high temperature storage characteristics are lowered.

In the present invention, lithium difluorophosphate, lithium difluorobis (oxalato) phosphate, lithium bis (oxalato) borate, Lithium difluoro (oxalato) borate, lithium bis (fluorosulfonyl) imide, ethylene sulfate, 1,3-propane sultone (1,3-propane sultone), 1,3-propene-1,3-sultone, vinylene carbonate, vinylethylene carbonate, 1, selected from the group consisting of fluoroethylene carbonate, succinonitrile, adiponitrile, and 1,3,6-hexanetricarbonitrile. But may additionally include more than one kind of additive, No.

The electrolyte for a secondary battery of the present invention generally maintains stable characteristics in a temperature range of -20 to 50 캜. The electrolyte solution of the present invention can be applied to a lithium ion secondary battery, a lithium ion polymer battery, and the like.

As the cathode material of the secondary battery in the present invention, 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, x + y? 1, and M is a metal such as Al, Sr, Mg, or La), and a crystalline or amorphous carbon, carbon composite, lithium metal, or lithium alloy is used as the cathode material . The active material is applied to a current collector of a thin plate having an appropriate thickness and length, or the active material itself is coated in a film form and rolled or laminated with a separator as an insulator to form an electrode group. The electrode group is then placed in a can or a similar container, A sulfate compound and a trialkylsilyl compound are injected into the battery to prepare a secondary battery. 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. It is to be understood by those skilled in the art that these embodiments are for illustrative purposes only and that the scope of the present invention is not limited by these embodiments.

Example 1

1.0 M LiPF ₆ was added to a nonaqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 3: 7 (v / v), and 1 wt% of a cyclic sulfate compound of the following formula 1% by weight of tris (trimethylsilyl) borate was added to prepare an electrolyte solution for a secondary battery.

[Chemical Formula 1]

Example 2

An electrolyte for a secondary battery was prepared in the same manner as in Example 1, except that 1 wt% of tris (trimethylsilyl) phosphite was added instead of 1 wt% of tris (trimethylsilyl) borate.

Example 3

An electrolyte for a secondary battery was prepared in the same manner as in Example 1, except that 1 wt% of tris (trimethylsilyl) phosphate was used instead of 1 wt% of tris (trimethylsilyl) borate.

Example 4

An electrolyte for a secondary battery was prepared in the same manner as in Example 1, except that 1 wt% of bis (triethylsilyl) sulfate was added instead of 1 wt% of tris (trimethylsilyl) borate.

Comparative Example 1

1.0 M LiPF ₆ was added to a nonaqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 3: 7 (v / v) to prepare an electrolyte for a secondary battery.

Comparative Example 2

An electrolyte for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1 wt% of tris (trimethylsilyl) borate was added.

Comparative Example 3

An electrolyte for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1 wt% of tris (trimethylsilyl) phosphite was added.

Comparative Example 4

An electrolyte for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1 wt% of tris (trimethylsilyl) phosphate was added.

Comparative Example 5

An electrolyte for a secondary battery was prepared in the same manner as in Comparative Example 1 except that 1 wt% of bis (triethylsilyl) sulfate was added.

Comparative Example 6

An electrolytic solution for a secondary battery was prepared in the same manner as in Comparative Example 1, except that 1 wt% of a cyclic sulfate compound represented by the following formula (1) was added.

[Chemical Formula 1]

Experimental Example 1: Evaluation of life characteristics of secondary batteries

In this experiment, the secondary batteries charged with the electrolytic solutions prepared in Examples 1 to 4 and Comparative Examples 1 to 6, respectively, were formed, and then charged to 4.2 V or 4.35 V until 1 C and then discharged to 3 V at 2 C. This process was repeated 500 times to measure the lifetime characteristics (cycle performance). The cycle performance was evaluated at room temperature (25 캜) and high temperature (45 캜), and the discharge capacity at 500 cycles, the percentage relative to the initial capacity, and the percentage of initial capacity increased relative to Comparative Example 1 were measured. Respectively.

4.2V Cycle Condition 4.35V Cycle Condition Charge (CC / CV) 4.2V / 1C, 0.1C cut-off
(rest time = 10 min) 4.35V / 1C, 0.1C cut-off
(rest time = 10 min) Discharge (CC) 2C / 3V cut-off
(rest time = 10 min) 2C / 3V cut-off
(rest time = 10 min)

Tables 2 to 5 below show the results of evaluating the life characteristics of the electrolytic solution prepared according to Examples 1 to 4 and Comparative Examples 1 to 6 of the present invention under the conditions of 4.2 V and 4.35 V, will be.

As shown in Tables 2 and 3, the electrolyte prepared according to Examples 1 to 4 of the present invention had a life characteristic at 4.2 V and a room temperature (25 ° C) (Trimethylsilyl) borate and bis (triethylsilyl) sulfate as the trialkylsilyl compound, the life characteristics of Examples 1 and 4 (improvement ratio of 3.07 compared to Comparative Example 1) % And 3.19%, respectively). The lifespan characteristics at 4.2 V and high temperature (45 캜) also showed improved lifespan characteristics as compared with those of Comparative Examples 1 to 6 as in the case of room temperature, and the lifetime characteristics of Example 2 containing tris (trimethylsilyl) phosphite as the trialkylsilyl compound It can be confirmed that the life characteristics (5.83% as compared with Comparative Example 1) are the most excellent.

From the above results, it can be seen that the electrolyte for a secondary battery according to the present invention includes the cyclic sulfate compound represented by Chemical Formula 1 and the trialkylsilyl compound to improve the lifetime characteristics under the condition of 4.2 V, I was able to confirm that it was excellent.

As shown in Tables 4 and 5, the electrolyte prepared according to Examples 1 to 4 of the present invention had a life characteristic at 4.35 V and a room temperature (25 ° C) (Trimethylsilyl) phosphite and bis (triethylsilyl) sulfate as the trialkylsilyl compound, the life characteristics of Examples 2 and 4 (the improvement rate of Comparative Example 1: 6.81 %) Is the most excellent. The lifetime characteristics at 4.35 V and high temperature (45 ° C) also showed improved lifetime characteristics as compared with those of Comparative Examples 1 to 6 as in the case of the room temperature, and it was confirmed that the improvement rates of Examples 1 to 4 were 37.16% to 44.23 .

FIG. 1 shows lifetime characteristics of a secondary battery charged with electrolytes prepared in Examples 1 to 4 and Comparative Examples 1 to 6 of the present invention at a temperature of 4.35 V and a high temperature (45 ° C.). As a result, it was confirmed that the initial 100 to 200 cycles exhibited similar behaviors, while the cycle life of Comparative Examples 1 to 6 was remarkably reduced after repeating 350 to 450 cycles. However, in Examples 1 to 4 including the cyclic sulfate compound and the trialkylsilyl compound according to the present invention, the lifetime efficiency after 500 cycles was maintained in the range of 65.77% to 72.85%, which was significantly superior to Comparative Example 1 (28.61%) Life characteristics.

From the above results, it can be seen that the electrolyte for a secondary battery according to the present invention includes the cyclic sulfate compound represented by Chemical Formula 1 and the trialkylsilyl compound to improve the lifetime characteristics under the condition of 4.35 V, It was confirmed that the lifespan characteristics were remarkably excellent.

From these results, it was confirmed that the electrolyte for the secondary battery comprising the cyclic sulfate compound and the trialkylsilyl compound of the present invention had excellent lifespan characteristics under the conditions of 4.2 V and 4.35 V, room temperature (25 캜) and high temperature (45 캜) .

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereto will be. Accordingly, the actual scope of the invention will be defined by the claims and their equivalents.

Claims (11)

Electrolyte for secondary battery comprising:
(A) a lithium salt;
(B) a non-aqueous organic solvent;
(C) a cyclic sulfate compound represented by the following formula (1); And
[Chemical Formula 1]

(D) a trialkylsilyl compound.
The electrolyte solution for a secondary battery according to claim 1, wherein the trialkylsilyl compound is in the form of a borate, a phosphate, a phosphite or a sulfate.
The method of claim 1, wherein the trialkylsilyl compound is selected from the group consisting of tris (trimethylsilyl) borate, tris (trimethylsilyl) phosphite, tris (trimethylsilyl) trimethylsilyl phosphate, bis (trimethylsilyl) sulfate, tris (triethylsilyl) borate, tris (triethylsilyl) phosphite, Wherein the electrolyte is at least one selected from the group consisting of tris (triethylsilyl) phosphate and bis (triethylsilyl) sulfate.
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 electrolyte solution for a secondary battery according to claim 1, wherein the organic solvent is at least one selected from the group consisting of cyclic carbonates, chain carbonates, and propionates.
The method according to claim 5, wherein the cyclic carbonate is at least one carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate,? -Butyrolactone, and mixtures thereof, Wherein the electrolyte is at least one carbonate selected from the group consisting of carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethyl methyl carbonate, and mixtures thereof.
The method of claim 5, wherein the propionate is selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ≪ / RTI > wherein the electrolyte is at least one propionate selected from the group consisting of: < RTI ID = 0.0 >
The electrolyte solution for a secondary battery according to claim 1, wherein the content of the cyclic sulfate compound is 0.05 to 5% by weight based on the total weight of the electrolytic solution.
The electrolyte solution for a secondary battery according to claim 1, wherein the content of the trialkylsilyl compound is 0.05 to 5% by weight based on the total weight of the electrolytic solution.
The lithium secondary battery according to claim 1, wherein the lithium difluorophosphate, lithium difluorobis (oxalato) phosphate, lithium bis (oxalato) borate, , Lithium difluoro (oxalato) borate, lithium bis (fluorosulfonyl) imide, ethylene sulfate, 1,3-propane 1,3-propane sultone, 1,3-propene-1,3-sultone, vinylene carbonate, vinylethylene carbonate ), Fluoroethylene carbonate, succinonitrile, adiponitrile, and 1,3,6-hexanetricarbonitrile. The term " hydroxycarbonyl " An electrolyte solution for a secondary battery, further comprising at least one additive.
A secondary battery comprising an anode, a cathode, and an electrolyte solution according to any one of claims 1 to 10.

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