KR20180136655A - Electrolyte for secondary battery and secondary battery comprising same - Google Patents

Abstract

The present invention relates to an electrolyte solution for a secondary battery and a secondary battery comprising the electrolyte solution. The electrolyte solution for the secondary battery can exhibit stable characteristics over a long period of time under a low temperature and a high temperature, It can be effectively used as an electrolytic solution of a battery.

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 same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among secondary batteries, lithium secondary batteries having high energy density, excellent lifetime characteristics, and low self discharge rate are commercially available and widely used.

In recent years, interest in environmental problems has led to a great deal of research on electric vehicles and hybrid electric vehicles that can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution . For example, studies are underway to use lithium secondary batteries as a power source for electric vehicles and hybrid electric vehicles. Specifically, researches for development of batteries having properties such as high energy density, high discharge voltage, and output stability are actively conducted And some are commercialized.

The lithium secondary battery is composed of a negative electrode made of a carbonaceous material or the like, which stores and releases lithium ions, a positive electrode made of a lithium-containing oxide, or the like, and a nonaqueous electrolyte solution in which a suitable amount of lithium salt is dissolved in a mixed organic solvent. At this time, the non-aqueous liquid electrolyte may further include an additive for improving the performance of the battery, and a lot of techniques for an electrolyte composition including such an additive are well known.

For example, in Japanese Patent No. 3760540, ethylene sulfate is added to an electrolytic solution to form a coating having a high lithium ion permeability on a negative electrode of a lithium battery, thereby suppressing decomposition of the electrolyte, thereby improving lifetime characteristics. Further, U.S. Patent No. 2011/0223476 improves battery high temperature performance by using an electrolyte solution containing a phosphate compound containing lithium difluorobis (oxalato) phosphate and lithium tetrafluoro (oxalato) phosphate . In addition, International Patent No. 2013-031551 improves battery life and performance at high and low temperatures by an electrolyte solution. Japanese Patent No. 3439085 discloses that a secondary battery additive comprising lithium fluorophosphate or lithium difluorophosphate reacts with lithium to form a high-quality coating on the interface between the positive and negative electrodes, and the coating inhibits decomposition of the non-aqueous electrolyte It is disclosed that the self-discharge of the battery can be suppressed during storage for a certain period of time after the secondary battery is charged to improve the storage characteristics. Furthermore, Japanese Laid-Open Patent Application No. 2003-151623 and Korean Laid-Open Patent Application No. 2013-0043221 disclose techniques for increasing the storage characteristics of a battery by forming a dense coating film on a cathode using cyclic sulfate.

However, all of the above additives have shown an improvement in the lifetime characteristics of the battery at room temperature and low temperature, but the effect on battery life characteristics, capacity and resistance for high temperature and / or long term use is not specified or improved It was necessary level.

Therefore, it is necessary to research and develop an electrolyte capable of improving the characteristics of the battery at low temperature and high temperature, particularly, improving the characteristics of the secondary battery at high output and high voltage.

Thus, the present inventors have found a composition of an electrolyte solution for a secondary battery having stable characteristics for a long period of time in an environment of not only low temperature but also high temperature, and completed the present invention.

Japanese Patent No. 3760540 US Patent No. 2011/0223476 International Patent No. 2013-031551 Japanese Patent No. 3439085 Japanese Patent Laid-Open No. 2003-151623 Korean Patent Publication No. 2013-0043221

An object of the present invention is to provide an electrolyte solution for a secondary battery that stably operates even at a low temperature and at a high temperature for a long period of time.

In order to achieve the above object,

(a-1) an electrolyte additive for a secondary battery comprising at least one compound selected from compounds represented by the following general formulas (1) to (4) and (a-2) (b) a non-aqueous solvent and (c) a lithium salt.

 [Chemical Formula 1] < EMI ID =

[Chemical Formula 6] [Chemical Formula 7] [Chemical Formula 8] [Chemical Formula 9]

The present invention also provides a secondary battery comprising the electrolyte for the secondary battery.

The electrolyte for a secondary battery of the present invention can be used as an electrolyte of a secondary battery used at a low temperature and at a high temperature because the electrolyte for a secondary battery can exhibit stable characteristics over a long period of time under a low temperature and a high temperature.

Hereinafter, the present invention will be described in detail.

The electrolyte for a secondary battery according to the present invention comprises

(a-1) an electrolyte additive for a secondary battery comprising at least one compound selected from compounds represented by the following general formulas (1) to (4) and (a-2) (b) a non-aqueous solvent and (c) a lithium salt.

 [Chemical Formula 1] < EMI ID =

[Chemical Formula 6] [Chemical Formula 7] [Chemical Formula 8] [Chemical Formula 9]

The electrolytic solution for the secondary battery can maintain a high ionic conductivity at the surfaces of the negative electrode and the positive electrode by mixing the compounds 1 to 4 and the at least one selected from the compounds 5 to 9 as an additive. Thereby forming a stable film on the positive electrode.

In particular, the compounds of the formulas (1) to (4) can improve lifetime characteristics, capacity and resistance characteristics (low resistance maintenance) at low temperature. In addition, by using one or more compounds of the above formulas But also maintain excellent long life characteristics, capacity retention rate and low resistance even at high temperature.

The compounds of the above formulas (1) to (9) are commercially available as known compounds or can be prepared by a known synthesis method.

Specifically, the compound of Formula 1 is selected from the group consisting of ethylene sulfate, the compound of Formula 2 is lithium difluorobis (oxalato) phosphate, the compound of Formula 3 is lithium tetrafluoro (oxalato) phosphate, the compound of Formula 4 is di Lithium fluorophosphate and the compounds of formulas 5 to 9 may be cyclic sulfates or cyclic sulfites.

More specifically, the compound of Chemical Formula 1 is CAS No. 1. 1072-53-3, the compound of formula (2) is CAS No. 1. 678966-16-0, the compound of Formula 3 is CAS No. 1. 521065-36-1, the compound of formula (IV) is CAS No. < RTI ID = 0.0 > 845910-47-6, the compound of the formula (5) is Cas No. 2. 201419-80-9, the compound of the formula (6) is CAS No. 1. 1591626-61-7, the compound of formula (7) is CAS No. < / RTI > 1431298-10-0, the compound of formula 8 is CAS No. < RTI ID = 0.0 > 3670-93-7 and the compound of formula (9) are CAS No. < / RTI > 92175-74-1. ≪ / RTI >

At least one compound selected from the compounds of the formulas 1 to 4 and at least one compound selected from the compounds of the formulas 5 to 9 may be mixed at a weight ratio of 5: 1, 3: 1 or 2: 1. Within the above range, there is an advantage that the synergistic effect obtained by using both compounds together is maximized

The electrolytic solution may contain 0.1 to 10% by weight, 0.1 to 8% by weight, 0.5 to 8% by weight, 1 to 5% by weight or 1 to 3% by weight of the electrolyte additive based on the total weight of the electrolytic solution. When it is included in the above content range, it is possible to suppress the increase of the resistance of the battery in a high temperature environment, to prevent an excessive increase in initial resistance at room temperature, and to form a film having a high ionic conductivity , And the viscosity of the electrolytic solution can be maintained at an appropriate level.

The non-aqueous solvent preferably has a high solubility in the lithium salt and the compounds of the formulas (1) to (9).

Specifically, the non-aqueous solvent may be selected from the group consisting of diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) (MPC), ethylpropyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and gamma- Gamma-butyrolactone, and the like.

More specifically, the non-aqueous solvent is at least one linear carbonate solvent selected from the group consisting of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, and at least one solvent selected from the group consisting of ethylene carbonate, propylene carbonate , Butylene carbonate, and gamma-butyrolactone. These solvents may be used alone or in combination of two or more.

The lithium salt is not particularly limited as long as it is usually used for an electrolyte solution for a secondary battery.

Specifically, the lithium salt is _{LiPF 6, LiBF 4, LiBF 6} , LiSO 3 CF 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (SO 2 F) 2, LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (SO ₂ F) ₂ and LiC (CF ₃ SO ₂ ) ₃ , And the like.

The electrolytic solution may contain 0.05 to 5.0 moles, 0.05 to 3.0 moles, or 0.05 to 2.5 moles of the lithium salt based on 1 liter of the non-aqueous solvent. When the lithium salt is contained in the above content range, ionic conductivity of the electrolytic solution is appropriately secured, and the ionic conductivity of the electrolytic solution, which can be obtained with respect to the concentration of the added lithium salt, is high, which is economical.

The electrolyte for a secondary battery according to the present invention can be prepared by simply mixing and stirring at least one compound selected from the compounds represented by Chemical Formulas 1 to 4 and the compounds represented by Chemical Formulas 5 to 9 with a non-aqueous solvent and a lithium salt.

The present invention provides a secondary battery comprising the electrolyte for the secondary battery. Specifically, the secondary battery includes: a positive electrode including a positive electrode active material; A negative electrode comprising a negative electrode active material; A separation membrane disposed between the anode and the cathode; And an electrolyte for the secondary battery.

The positive electrode includes a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions. Wherein the cathode active material comprises at least one metal selected from the group consisting of cobalt, manganese, and nickel; And a composite metal oxide including lithium. The positive electrode active material may be composed of at least one metal selected from the group consisting of magnesium (Mg), aluminum (Al), cobalt (Co), potassium (K), sodium (Na) (Ti), tin (Sn), vanadium (V), germanium (Ge), gallium (Ga), boron (B), arsenic (As), zirconium (Zr) (Cr), iron (Fe), strontium (Sr), and rare earth elements.

The negative electrode includes a negative electrode active material capable of intercalating and deintercalating lithium ions. The negative electrode active material may be a carbonaceous anode active material (thermally decomposed carbon, coke, graphite) of a crystalline or amorphous carbon or carbon composite; Burned organic polymer compounds; Carbon fiber; Tin oxide compounds; Lithium metal; Or a lithium alloy.

For example, the amorphous carbon may be hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500 ° C. or lower, mesophase pitch-based carbon fiber (MPCF), or the like. The crystalline carbon may be a graphite based material, for example, natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. Among the lithium alloys, other elements constituting the lithium and the alloy include aluminum (Al), zinc (Zn), bismuth (Bi), cadmium (Cd), antimony (Sb), silicon (Si), lead (Pb) ), Gallium (Ga), or indium (In).

The separator is for preventing a short circuit due to a direct contact between the anode and the cathode. For example, the separator may be a polymer membrane such as polyolefin, polypropylene, or polyethylene, or a multi-layer thereof; Microporous film; web; And nonwoven fabrics. The separation membrane may have a metal oxide or the like coated on one or both sides thereof.

Hereinafter, the present invention will be described in more detail by way of specific examples and comparative examples. The following examples are intended to further illustrate the present invention and are not intended to limit the scope of the present invention.

[ Example ]

The compounds of formulas (1) and (2) used in the following examples and comparative examples are all known compounds, and their structural formulas, chemical names and CAS No. are as follows.

constitutional formula Chemical name CAS No. (1)
compound

Ethylene sulfate 1072-53-3 2
compound

Lithium difluorobis (oxalato) phosphate 678966-16-0 (3)
compound

Lithium tetrafluoro
(Oxalato) phosphate 521065-36-1 4
compound

Lithium difluorophosphate 845910-47-6 5
compound

Cyclic sulfate 201419-80-9 6
compound

1591626-61-7 (7)
compound

1431298-10-0 The compound of formula 8

Cyclic sulfite 3670-93-7 9
compound

92175-74-1

Example  1. Preparation of electrolytic solution

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 30:40:30 to prepare a mixed solution. LiPF ₆ was dissolved in the mixed solution at a concentration of 1 mol / 0.5% by weight of the compound of Formula 1, 0.2% by weight of the compound of Formula 2, 0.3% by weight of the compound of Formula 3, 1% by weight of the compound of Formula 4 and 1% by weight of the compound of Formula 5 were added to the total weight of the electrolytic solution And mixed to prepare an electrolyte solution (electrolyte solution) for a secondary battery.

Example  2 to 20 and Comparative Example  1 to 2. Preparation of electrolytic solution

Except that the composition and the content of at least one selected from the compounds of the following formulas (1) to (4) and the compounds of the formulas (5) to (9) were used as the electrolyte additive as shown in the following formula The electrolyte solution was prepared in the same manner as in Example 1.

Electrolyte additive Formula 1 (2) (3) Formula 4 Formula 5 6 Formula 7 8 Formula 9 Example 1 0.5% 0.2% 0.3% One% One% - - - - Example 2 0.5% 0.2% 0.3% One% - One% - - - Example 3 0.5% 0.2% 0.3% One% - - One% - - Example 4 0.5% 0.2% 0.3% One% - - - One% - Example 5 0.5% 0.2% 0.3% One% - - - - One% Example 6 2% - - - One% - - - - Example 7 - One% One% - One% - - - - Example 8 - - - 2% One% - - - - Example 9 2% - - - - One% - - - Example 10 - One% One% - - One% - - - Example 11 - - - 2% - One% - - - Example 12 2% - - - - - One% - - Example 13 - One% One% - - - One% - - Example 14 - - - 2% - - One% - - Example 15 2% - - - - - - One% - Example 16 - One% One% - - - - One% - Example 17 - - - 2% - - - One% - Example 18 2% - - - - - - - One% Example 19 - One% One% - - - - - One% Example 20 - - - 2% - - - - One% Comparative Example 1 - - - - - - - - - Comparative Example 2 One% 0.5% 0.5% One% - - - - -

Experimental Example  1. Low temperature characteristics of lithium secondary battery

And assembling the 1Ah pouch cell by an ordinary method using the anode material used to 1 weight ratio of positive electrode active material of _{LiNi 1/3 Co 1/3} Mn 1 / with ₃ positive electrode material and negative electrode active material of artificial graphite and natural graphite 1 , Each of the electrolytic solutions prepared in Examples 1 to 20 and Comparative Examples 1 and 2 was injected in an amount of 6 g each, to complete a secondary battery.

The 1Ah pouch battery obtained through the above described battery charging process was charged at a constant current (C-rate) of 4.2 V / 140 mA at a constant current / constant voltage (CC / CV) condition at 25 ° C, The initial capacity was measured with a PNE-0506 charge / discharge device (manufacturer: PNE solution, Inc.) while discharging. The same cell was charged at 1 C to 4.2 V / 100 mA at a constant current / constant voltage (CC / CV) condition at -10 ° C. and then discharged at 1 C up to 3 V under a constant current (CC) condition at which discharge capacity and output value were measured . This procedure was repeated 10 times. The capacity retention ratio and the output retention ratio with respect to the initial value were calculated from the measured discharge capacity and the output value, and the results are shown in Table 3 below (equipment: PNE-0506 charge / discharge unit).

Experimental Example  2. High Temperature Life Characteristics of Lithium Secondary Battery

The discharge capacity and the output value at the initial capacity and the high temperature were measured in the same manner as in Experimental Example 1, except that the discharge capacity and the output value were measured by repeating the secondary battery manufactured in Experimental Example 1 at 45 ° C for 500 times, Based on the values, the capacity retention ratio and the output retention ratio with respect to the initial value are calculated and shown in Table 3 below.

Experimental Example  3. High Temperature Storage Characteristics of Lithium Secondary Battery

A secondary battery was completed in the same manner as in Experimental Example 1. [

The initial capacity of the secondary battery was measured in the same manner as in Experimental Example 1. Then, the secondary battery was charged with SOC (charge depth) of 100%, and stored in an oven at 60 캜 for 8 weeks. The capacity and output value after 8 weeks were measured. The capacity maintenance rate and the output retention rate in relation to the initial value of the battery (initial design capacity of 1 Ah) were calculated from the measured capacities and are shown in Table 3 below (equipment: PNE-0506 charge / discharge unit).

Experimental Example 1
(-10 [deg.] C / 10 times) Experimental Example 2
(45 DEG C / 500 times repeated) Experimental Example 3
(60 占 폚 / 8 weeks) Capacity retention rate Output retention rate Capacity retention rate Output retention rate Capacity retention rate Output retention rate Example 1 78% 66% 93% 84% 87% 80% Example 2 78% 65% 91% 82% 84% 77% Example 3 79% 66% 92% 82% 85% 77% Example 4 77% 65% 88% 79% 80% 72% Example 5 77% 64% 90% 80% 83% 74% Example 6 75% 62% 86% 80% 76% 71% Example 7 73% 62% 86% 78% 78% 72% Example 8 76% 60% 84% 73% 78% 70% Example 9 73% 61% 84% 75% 74% 69% Example 10 74% 60% 83% 74% 75% 68% Example 11 74% 61% 83% 75% 73% 69% Example 12 76% 63% 86% 80% 77% 71% Example 13 75% 63% 86% 79% 76% 70% Example 14 75% 63% 85% 80% 77% 70% Example 15 75% 62% 84% 76% 77% 72% Example 16 74% 61% 82% 77% 75% 69% Example 17 76% 62% 83% 77% 77% 71% Example 18 74% 60% 83% 76% 75% 67% Example 19 73% 60% 84% 76% 74% 66% Example 20 75% 61% 84% 77% 76% 68% Comparative Example 1 60% 63% 53% 44% 45% 39% Comparative Example 2 69% 63% 83% 77% 72% 66%

As shown in Table 3, the secondary batteries including the electrolyte additives of Examples 1 to 20 exhibited excellent capacity and output retention at low temperature and high temperature as compared with the case of containing the electrolyte additives of Comparative Examples 1 and 2 , It was confirmed that the capacity and the output retention ratio remained excellent even after 8 weeks at high temperature. In particular, the case where all of the compounds represented by the formulas (1) to (4) were included was more excellent than the case where all of them were not included.

Further, it was confirmed that the characteristics of the battery at low temperature and high temperature were simultaneously improved when one or more compounds of the general formulas (1) to (4) and one or more compounds of the general formulas (5) to (9) .

In particular, Examples 1 to 5 (when all the compounds of Formulas 1 to 4 were included and cyclic sulfate or cyclic sulfite was added) and Comparative Example 2 (including all the compounds of Formulas 1 to 4, Sulfate and cyclic sulfite were not added), the performance of Examples 1 to 5 was excellent at low temperature and high temperature. Thus, it can be seen that cyclic sulfates or cyclic sulfites can improve performance at low and high temperatures without deteriorating the properties of the compounds of formulas (1) to (4).

Claims (7)

(a-1) at least one compound selected from compounds represented by the following general formulas (1) to (4); And
(a-2) an electrolyte additive for a secondary battery comprising at least one compound selected from compounds represented by the following formulas (5) to (9);
(b) non-aqueous solvent; And
(c) an electrolytic solution for a secondary battery comprising a lithium salt:
[Chemical Formula 1] < EMI ID =

[Chemical Formula 6] [Chemical Formula 7] [Chemical Formula 8] [Chemical Formula 9]

The method according to claim 1,
The non-aqueous solvent may be selected from the group consisting of diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and gamma-butyrolactone -butyrolactone). < / RTI > 3. The method of claim 2,
Wherein the non-aqueous solvent is at least one linear carbonate solvent selected from the group consisting of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, and
And at least one cyclic carbonate-based solvent selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, and gamma-butyrolactone. The method according to claim 1,
The lithium salt _{LiPF 6, LiBF 4, LiBF 6} , LiSO 3 CF 3, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (SO 2 F) 2, LiSbF 6, LiAsF ₆ , LiClO ₄ , LiN (SO ₂ F) _2, and LiC (CF ₃ SO ₂ ) ₃ . The method according to claim 1,
Wherein the electrolytic solution contains the electrolyte additive in an amount of 0.1 to 10 wt% based on the total weight of the electrolytic solution. The method according to claim 1,
Wherein the electrolyte contains 0.05 to 5.0 moles of the lithium salt based on 1 liter of the non-aqueous solvent. A secondary battery comprising an electrolyte solution for a secondary battery according to any one of claims 1 to 6.