WO2021033986A1 - Electrolytic solution for secondary battery, and secondary battery comprising same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolytic solution for a secondary battery, and a secondary battery comprising same. Adding a compound represented by chemical formula 1 and a phosphate-based lithium salt to the non-aqueous electrolytic solution for a secondary battery according to the present invention has the effect of enhancing lifespan characteristics and output characteristics.

Description

Electrolyte for secondary battery and secondary battery containing the same

The present invention relates to an electrolyte for a secondary battery and a secondary battery including the same, and more particularly, to improve the room temperature life and output characteristics by adding a compound represented by Chemical Formula 1 or a phosphate-based lithium salt to a non-aqueous electrolyte for a lithium ion secondary battery. It relates to an effective non-aqueous electrolyte for a secondary battery and a secondary battery including the same.

Recently, as portable electronic devices have become thinner, smaller, and lighter, the secondary battery used as a power source can be charged and discharged for a long time with a small size and light weight, and efforts to improve high rate characteristics are being concentrated.

Secondary batteries include lead-acid batteries, nickel-cadmium (Ni-Cd) batteries, nickel-hydrogen (Ni-MH) batteries, lithium batteries, etc., depending on the anode material or the cathode material. The potential and energy density are determined by Among these, lithium secondary batteries are widely used as driving power supplies for portable electronic devices such as notebook computers, camcorders, and mobile phones because of their high energy density due to the low oxidation/reduction potential and molecular weight of lithium.

A lithium secondary battery using a non-aqueous electrolyte is used as a positive electrode coated with a lithium metal mixed oxide capable of desorbing and intercalating lithium ions as a positive electrode active material on a metal, and a carbon material or metal lithium as a negative electrode active material on the metal as a negative electrode. It is coated and used, and an electrolyte solution in which a lithium salt is suitably dissolved in an organic solvent is placed between the positive electrode and the negative electrode. The organic solvent of the electrolyte may decompose on the electrode surface during charging and discharging of the battery, or co-intercalation between the carbon material negative electrode layers to collapse the negative electrode structure, thereby impairing the stability of the battery.

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

Nevertheless, due to continuous repetition of charging and discharging, the SEI film collapses, and the life and performance of the secondary battery especially under high temperature are deteriorated due to the low thermal stability of the SEI film.

Therefore, as a conventional technology for solving the above problems, Korean Patent Registration No. 10-1492686 discloses lithium oxalyldifluoroborate (LiODFB), vinylidene carbonate-based compound, sulfate-based compound, and sultone-based compound. Although an additive and a non-aqueous electrolyte containing the same are disclosed, the capacity recovery and retention rate at high temperature storage are not described, and the mentioned composition has a limitation in improving discharge efficiency at a high C-rate.

In addition, Korean Patent Registration No. 10-1538485 discloses a non-aqueous electrolyte solution for secondary batteries containing alkylene sulfate, ammonium compound and vinylene carbonate of a specific formula, but the stability of the positive electrode at a high rate is lowered due to the absence of the positive electrode additive. It is difficult to implement a capacity, and there is a problem in that long-term life efficiency is deteriorated because it is not possible to form a stable anode film and elute transition metals.

U.S. Patent Publication 2017/0301952 A1 discloses a non-aqueous electrolyte for a secondary battery containing a cyclic sultonate, a cyclic sulfate, a silane phosphate and/or a silane borate compound and a fluorophosphate salt, and Korean Patent Laid-Open No. 2016-0144123 Is an electrolyte containing vinylene carbonate and a cyclic sulfate compound, and is known for its effects on high temperature stability, low temperature discharge capacity, and room temperature life characteristics, but the addition of lithium difluorophosphate suppresses the increase in resistance during high temperature storage or , There is no disclosure of the effect of improving the life characteristics at high temperature (70°C).

Accordingly, there is a demand for an electrolyte solution containing an optimal additive composition capable of simultaneously satisfying an improved capacity retention rate and a 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 problem, and as a result of adding a compound represented by Formula 1 and a phosphate-based lithium salt to an electrolyte for a secondary battery, it has been confirmed that the normal temperature, high temperature life, and output characteristics before and after high temperature are improved. And completed the present invention.

An object of the present invention is to provide a non-aqueous electrolyte for a secondary battery with improved life characteristics at room temperature and high temperature and output characteristics before and after high temperature.

Another object of the present invention is to provide a secondary battery having excellent life characteristics at room temperature and high temperature at high temperature and output characteristics before and after high temperature.

In order to achieve the above object, (A) lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; And (D) a phosphate-based lithium salt additive.

[Formula 1]

,

또는

이고, 여기서 n은 1 내지 4의 정수이고; Z는 6A족 원소이다.In Formula 1, R ¹ to R ⁶ are each independently an unsubstituted C ₁ to C ₉ alkyl group or a C ₁ to C ₉ alkyl group substituted with a halogen atom, an unsubstituted C ₂ to C _{9 alkenyl group or C 1} substituted with a halogen atom ~C _{9 is an} alkenyl group, X is

,

or

Where n is an integer from 1 to 4; Z is a group 6A element.

The present invention also includes (a) a positive electrode comprising a positive electrode active material capable of occluding and releasing lithium; (b) a negative electrode including a negative electrode active material capable of storing and releasing lithium; (c) the electrolyte for the secondary battery; And (d) a separator to provide a lithium secondary battery.

The non-aqueous electrolyte according to the present invention has the effect of improving the life characteristics at room temperature and high temperature and output characteristics before and after high temperature by adding the compound represented by Formula 1 and a phosphate-based lithium salt.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by an expert skilled in the art to which the present invention belongs. In general, the nomenclature used in this specification is well known and commonly used in the art.

In the present invention, by adding a lithium salt, a non-aqueous organic solvent, a compound represented by Formula 1, and a phosphate-based lithium salt additive to the non-aqueous electrolyte solution of a secondary battery, it was confirmed that the life characteristics and output characteristics at high temperature of the secondary battery were significantly increased. I did.

Accordingly, the present invention, in one aspect, (A) lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; And (D) a phosphate-based lithium salt additive.

[Formula 1]

,

또는

이고, 여기서 n은 1 내지 4의 정수이고; Z는 6A족 원소이다.In Formula 1, R ¹ to R ⁶ are each independently an unsubstituted C ₁ to C ₉ alkyl group or a C ₁ to C ₉ alkyl group substituted with a halogen atom, an unsubstituted C ₂ to C _{9 alkenyl group or C 1} substituted with a halogen atom ~C _{9 is an} alkenyl group, X is

,

or

Where n is an integer from 1 to 4; Z is a group 6A element.

In another aspect, the present invention includes: (a) a positive electrode including a positive electrode active material capable of storing and releasing lithium; (b) a negative electrode including a negative electrode active material capable of storing and releasing lithium; (c) the electrolyte for the secondary battery; And (d) the separator relates to a lithium secondary battery.

Hereinafter, the present invention will be described in detail.

The electrolyte for a secondary battery according to the present invention includes (A) a lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; And (D) a phosphate-based lithium salt additive.

[Formula 1]

,

또는

이고, 여기서 n은 1 내지 4의 정수이고; Z는 6A족 원소이다.In Formula 1, R ¹ to R ⁶ are each independently an unsubstituted C ₁ to C ₉ alkyl group or a C ₁ to C ₉ alkyl group substituted with a halogen atom, an unsubstituted C ₂ to C _{9 alkenyl group or C 1} substituted with a halogen atom ~C _{9 is an} alkenyl group, X is

,

or

Where n is an integer from 1 to 4; Z is a group 6A element.

In the present invention, each component contained in the electrolyte solution for a secondary battery will be described in detail.

(A) Lithium salt

The electrolyte for a secondary battery according to the present invention contains lithium salt as a solute of the electrolyte. Lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li and LiC(CF ₃ SO ₂ ) It may be one or more selected from the group consisting of _3. The concentration of the lithium salt is preferably used within the range of 0.6M to 2.0M, more preferably 0.7M to 1.6M, and if it is less than 0.6M, the conductivity of the electrolyte decreases, resulting in poor electrolyte performance, and 2.0M If it is exceeded, there is a problem in that the viscosity of the electrolyte solution increases and the mobility of lithium ions decreases. These lithium salts act as a source of lithium ions in the battery, thereby enabling the operation of a basic lithium secondary battery.

(B) Non-aqueous Organic solvent

The electrolyte for a secondary battery according to the present invention includes a non-aqueous organic solvent. The non-aqueous organic solvent may be at least one selected from the group consisting of linear carbonates, cyclic carbonates, linear esters and cyclic esters.

Here, the linear carbonate may be one or more carbonates selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethyl methyl carbonate, and mixtures thereof, but is not limited thereto.

The cyclic carbonates are ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and It may be one or more carbonates selected from the group consisting of fluoroethylene carbonate, but is not limited thereto.

The linear ester may be one or more esters selected from the group consisting of methyl propionate, ethyl propionate, propyl acetate, butyl acetate, and ethyl acetate, but is not limited thereto.

The cyclic ester may be one or more esters selected from the group consisting of gamma butyrolactone, caprolactone, and valerolactone, but is not limited thereto.

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

(C) a compound represented by Formula 1

The electrolyte solution for a secondary battery according to the present invention includes a compound represented by Formula 1.

[Formula 1]

,

또는

이고, 여기서 n은 1 내지 4의 정수이고; Z는 6A족 원소이다.In Formula 1, R ¹ to R ⁶ are each independently an unsubstituted C ₁ to C ₉ alkyl group or a C ₁ to C ₉ alkyl group substituted with a halogen atom, an unsubstituted C ₂ to C _{9 alkenyl group or C 1} substituted with a halogen atom ~C _{9 is an} alkenyl group, X is

,

or

Where n is an integer from 1 to 4; Z is a group 6A element.

In the present invention, the compound represented by Formula 1 is bis(trimethylsilyl) fumarate (BTMSF), which is a compound represented by Formula 2, and bis(trimethylsilyl) 2 which is a compound represented by Formula 3 ,2'-thiodiacetate (bis(trimethylsilyl) 2,2'-thiodiacetate, BTMSTDA) or a mixture of a compound represented by Formula 2 and a compound represented by Formula 3.

[Formula 2]

[Formula 3]

In the present invention, the content of the compound represented by Formula 1 may be added in an amount of 0.05 to 10% by weight, preferably 0.1 to 5% by weight, more preferably 0.2 to 3% by weight, based on the electrolyte solution for secondary batteries. If it is less than 0.05% by weight, the effect of forming a stable SEI film on the electrode is insignificant and it is insufficient to suppress the deterioration of the battery.If it exceeds 10% by weight, the electrode film is formed too thick to increase the electrode interface resistance. There is a problem that characteristics are deteriorated.

(D) phosphoric acid Lithium salt

The electrolyte for a secondary battery according to the present invention includes a phosphate-based lithium salt. The phosphoric acid-based lithium salt is lithium difluorophosphate (LFP), lithium tetrafluoro oxalate phosphate (LTFOP), and lithium difluoro bisoxalato phosphate. ) phosphate, LDFBOP) may be one or more selected from the group consisting of.

In the present invention, the content of the phosphate-based lithium salt additive may be added in an amount of 0.05 to 10% by weight, preferably 0.05 to 5% by weight, more preferably 0.05 to 3% by weight, based on the electrolyte solution for a secondary battery, If it is less than 0.05% by weight, there is a problem that it is insufficient to transform the structure of the SEI film into a high ion permeable SEI layer, and if it exceeds 10% by weight, it causes resistance due to an increase in the viscosity of the electrolyte, and the life and output characteristics of the secondary battery There is a problem of this deterioration.

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

In the present invention, the cathode material of the lithium secondary battery is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or LiNi _{1 -x- y} Co _x M _y O ₂ (0≤x≤1, 0≤y≤1 , 0≤x+y≤1, M is a metal such as Al, Sr, Mg, La, etc.), and a lithium metal oxide such as crystalline or amorphous carbon, carbon composite, lithium metal, or lithium alloy Use. The active material is applied to the current collector of a thin plate with an appropriate thickness and length, or the active material itself is applied in the form of a film to form an electrode group by winding or laminating together with a separator, which is an insulator, and then put in a can or similar container, and then trialkyl. A lithium ion secondary battery is prepared by injecting a non-aqueous electrolyte solution to which silyl sulfate and a phosphite stabilizer are added. Resins such as polyethylene and polypropylene may be used as the separator.

Hereinafter, the present invention will be described in more detail through examples. These examples are for illustrative purposes only, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by these examples.

[Example]

Example One

_{Li (Ni 0.6} Co _0.2 Mn _0.2 ) O ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material were mixed in a weight ratio of 92:4:4, and then N-methyl-2- Disperse in pyrrolidone to prepare a positive electrode slurry. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode.

Negative active material slurry by mixing crystalline artificial graphite as an anode active material, acetylene black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 92:1:7 and dispersing in N-methyl-2-pyrrolidone Was prepared. The slurry was coated on a 15 μm-thick copper foil, dried and rolled to prepare a negative electrode.

20㎛ thickness between the prepared electrodes Film made of polyethylene (PE) The separator was stacked, wound, and compressed to form a cell using a pouch having a thickness of 6 mm x 35 mm x 60 mm in length, and a lithium secondary battery was manufactured by injecting the following non-aqueous electrolyte.

_{1.0 M of LiPF 6} was added to a non-aqueous organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at 3:7 (v/v), and 1% by weight of BTMSF and 1% by weight of LiPO ₂ F ₂ Was added to prepare an electrolyte for a secondary battery.

Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1% by weight of BTMSTDA was added instead of 1% by weight of BTMSF in the electrolyte for a secondary battery.

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1 except for adding 0.25% by weight of BTMSF and 0.25% by weight of BTMSTDA instead of 1% by weight of BTMSF in the electrolyte solution for a secondary battery of Example 1.

Example 4

A lithium secondary battery was manufactured in the same manner as in Example 1 except for adding 1% by weight of LTFOP instead of 1% by weight _{of LiPO 2} F ₂ in the electrolyte for a secondary battery.

Example 5

A lithium secondary battery was manufactured in the same manner as in Example 2, except that 1% by weight of LTFOP was added instead of 1% by weight _{of LiPO 2} F ₂ in the electrolyte for a secondary battery.

Example 6

A lithium secondary battery was manufactured in the same manner as in Example 3 except for adding 1% by weight of LTFOP instead of 1% by weight _{of LiPO 2} F ₂ in the electrolyte for a secondary battery of Example 3.

Example 7

A lithium secondary battery was manufactured in the same manner as in Example 1 except that 1% by weight of LDFBOP was added instead of 1% by weight _{of LiPO 2} F ₂ in the electrolyte for a secondary battery.

Example 8

_{A lithium secondary battery was manufactured in the same manner as in Example 2} except for adding 1% by weight of LDFBOP instead of 1% by weight of LiPO 2 F ₂ in the electrolyte for a secondary battery of Example 2.

Example 9

A lithium secondary battery was manufactured in the same manner as in Example 3 except that 1% by weight of LDFBOP was added instead of 1% by weight _{of LiPO 2} F ₂ in the electrolyte for a secondary battery.

Comparative example One

A lithium secondary battery was manufactured in the same manner as in Example 1 except that BTMSF and LiPO ₂ F _{2 were not added to the electrolyte solution for a secondary battery.}

Comparative example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, _{except that LiPO 2} F _{2 was not added to the electrolyte for a secondary battery.}

Comparative example 3

A lithium secondary battery was manufactured in the same manner as in Example 2 _{except that LiPO 2} F _{2 was not added to the electrolyte for a secondary battery.}

Comparative example 4

A lithium secondary battery was manufactured in the same manner, except _{that LiPO 2} F ₂ was not added to the electrolyte solution for a secondary battery of Example 3.

Comparative example 5

A lithium secondary battery was manufactured in the same manner except that BTMSF was not added to the electrolyte solution for a secondary battery of Example 1.

Comparative example 6

A lithium secondary battery was manufactured in the same manner as in Example 4 except that BTMSF was not added to the electrolyte for a secondary battery.

Comparative example 7

A lithium secondary battery was manufactured in the same manner as in Example 7 except that BTMSF was not added to the electrolyte for a secondary battery.

The compositions of the electrolyte solutions of Examples 1 to 9 and Comparative Examples 1 to 7 are shown in Table 1.

Examples/comparative examples Electrolyte composition (100wt%) Example 1 BTMSF 1% + LiPO ₂ F ₂ 1% Example 2 BTMSTDA 1% + LiPO ₂ F ₂ One% Example 3 BTMSF 0.25% + BTMSTDA 0.25% + LiPO ₂ F ₂ 1% Example 4 BTMSF 1% + LTFOP 1% Example 5 BTMSTDA 1% + LTFOP 1% Example 6 BTMSF 0.25% + BTMSTDA 0.25% + LTFOP 1% Example 7 BTMSF 1% + LDFBOP 1% Example 8 BTMSTDA 1% + LDFBOP 1% Example 9 BTMSF 0.25% + BTMSTDA 0.25% + LDFBOP 1% Comparative Example 1 - Comparative Example 2 BTMSF 1% Comparative Example 3 BTMSTDA 1% Comparative Example 4 BTMSF 0.5% + BTMSTDA 0.5% Comparative Example 5 LiPO ₂ F ₂ 1% Comparative Example 6 LTFOP 1% Comparative Example 7 LDFBOP 1%

[Physical property evaluation]

Physical property evaluation 1: 4.2V cycle life characteristics evaluation at room temperature (25℃)

Each of the secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was charged at 1C to 4.2V and then the discharge capacity in 300 cycles of discharging at 1C was measured, and the measured discharge capacity and the percentage of the initial capacity were measured in Table 2 below. Shown in.

Initial capacity (mAh) Capacity after 300 times (mAh) percentage(%) Improvement rate (% for Comparative Example 1) Example 1 861.64 758.46 88.03 5.25 Example 2 862.77 760.66 88.16 5.39 Example 3 867.55 779.51 89.85 7.08 Comparative Example 1 847.24 701.31 82.78 - Comparative Example 2 851.01 710.58 83.50 0.72 Comparative Example 3 852.56 712.99 83.63 0.85 Comparative Example 4 854.27 719.54 84.23 1.45 Comparative Example 5 860.44 740.18 86.02 3.25

As shown in Table 2, the electrolytic solutions of Examples 1 to 3 of the present invention at room temperature (25° C.) exhibited better life performance than those of Comparative Examples 1 to 5 in the ratio of initial capacity to cycle capacity at 4.2V 300 cycles.

Among them, the electrolytic solution of Example 3 in which 0.25% by weight of bis(trimethylsilyl) fumarate, 0.25% by weight of bis(trimethylsilyl) 2,2'-thiodiacetate, and 1% by weight of lithium difluorophosphate was added was Comparative Example 5. It showed about 3% improved life characteristics than that of Examples 1 to 2, about 1.5%.

Physical property evaluation 2: 4.2V cycle life characteristics evaluation at high temperature (45℃)

Each of the secondary batteries prepared in Examples 4 to 9 and Comparative Examples 1 to 4 and Comparative Examples 6 to 7 was charged to 4.2V at 1C and then discharged at 300 cycles of 1C discharge, and the measured discharge capacity and initial capacity It is shown in Table 3 below as a contrast percentage.

Initial capacity (mAh) Capacity after 300 times (mAh) percentage(%) Improvement rate (% for Comparative Example 1) Example 4 913.47 846.66 92.69 4.13 Example 5 913.83 847.79 92.77 4.22 Example 6 914.22 856.51 93.69 5.13 Example 7 914.11 855.49 93.59 5.03 Example 8 914.69 857.25 93.72 5.16 Example 9 915.82 867.17 94.69 6.13 Comparative Example 1 894.94 792.54 88.56 - Comparative Example 2 903.19 803.67 88.98 0.42 Comparative Example 3 904.45 805.13 89.02 0.46 Comparative Example 4 904.88 807.81 89.27 0.71 Comparative Example 6 910.56 820.71 90.13 1.57 Comparative Example 7 911.76 826.44 90.64 2.08

As shown in Table 2, the electrolyte solution of Examples 4 to 9 of the present invention at a high temperature (45° C.) has a cycle capacity ratio of 4.2 V to 300 cycles compared to Comparative Examples 1 to 4 and Comparative Examples 6 to 7 Showed.

Among them, Example 6 and lithium in which 1% by weight of lithium tetrafluorooxalate phosphate was added to 0.25% by weight of bis(trimethylsilyl) fumarate and 0.25% by weight of bis(trimethylsilyl) 2,2'-thiodiacetate, respectively. Example 9 electrolytic solution to which 1% by weight of difluoro bis (oxalato) phosphate was added showed improved lifespan characteristics of about 4% or more compared to Comparative Examples 2 to 4.

Physical property evaluation 3: Evaluation of output characteristics before and after storage at high temperature (70℃)

Each of the secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 7 was charged to 4.2V at 1C and then discharged to 475mA at a constant current of 2C, and then the charge/discharge rates were 0.5C, 1C, 2C, 4C. The initial discharge output was measured by discharging each for 10 seconds.After charging 1C to 4.2V, storing at high temperature (70℃) for 7 days, charging 1C to 4.2V and performing 1C discharge twice in the same way as the initial output measurement method. The output was measured after storage at high temperature (70° C.), and the measured output values are shown in Table 4 below.

Output(W) Output difference value (W for Comparative Example 1) Before storage at high temperature (70℃) After storage at high temperature (70℃) Before storage at high temperature (70℃) After storage at high temperature (70℃) Example 1 76.12 41.86 13.09 12.75 Example 2 76.48 42.68 13.45 13.57 Example 3 79.95 43.17 16.92 14.06 Example 4 70.49 43.30 7.46 14.19 Example 5 70.53 44.09 7.50 14.98 Example 6 72.41 45.59 9.38 16.48 Example 7 72.99 46.00 9.96 16.89 Example 8 72.86 46.28 9.83 17.17 Example 9 74.73 48.49 11.70 19.38 Comparative Example 1 63.03 29.11 - - Comparative Example 2 63.16 29.44 0.13 0.33 Comparative Example 3 63.76 29.52 0.73 0.41 Comparative Example 4 64.54 31.06 1.51 1.95 Comparative Example 5 74.31 35.55 11.28 6.44 Comparative Example 6 68.36 37.73 5.33 8.62 Comparative Example 7 70.57 40.87 7.54 11.76

As shown in Table 3, the electrolytic solutions of Examples 1 to 9 of the present invention before and after storage at high temperature (70° C.) showed better output performance than Comparative Examples 1 to 7 at 4.2V.

In particular, Examples 1 to 3 had excellent initial output characteristics before storage at high temperature (70°C), and among them, 0.25% by weight of bis(trimethylsilyl) fumarate and 0.25% by weight of bis(trimethylsilyl) 2,2'-thiodiacetate , The secondary battery of Example 3 to which 1% by weight of lithium difluorophosphate was added showed the best initial output characteristics with an output value of 79.95W.

Examples 4 to 9 were excellent in output characteristics after storage at high temperature (70°C), and among them, 0.25% by weight of bis(trimethylsilyl) fumarate, 0.25% by weight of bis(trimethylsilyl) 2,2'-thiodiacetate, lithium The secondary battery of Example 9 to which 1% by weight of difluorobis(oxalato) phosphate was added showed the best output characteristics after storage at high temperature (70°C) with an output value of 48.49W.

As described above, the secondary battery electrolyte according to the present invention provides a solid electrolyte interface (SEI) film on the electrode surface formed of the compound represented by Formula 1, rather than the secondary battery electrolyte in which the compound represented by Formula 1 or a phosphate-based lithium salt is added alone. It can be seen that the phosphate-based lithium salt transforms the structure of the SEI film into a highly ion-permeable SEI layer, thereby further improving the output characteristics at room temperature and high temperature life and before and after high temperature.

As described above, specific parts of the present invention have been described in detail, and it will be apparent to those of ordinary skill in the art that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. will be. Accordingly, it will be said that the substantial scope of the present invention is defined by the claims and their equivalents.

Claims (11)

Electrolyte for secondary batteries, including: (A) lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; And (D) phosphoric acid-based lithium salt additive, [Formula 1]

In Formula 1, R ¹ to R ⁶ are each independently an unsubstituted C ₁ to C ₉ alkyl group or a C ₁ to C ₉ alkyl group substituted with a halogen atom, an unsubstituted C ₂ to C _{9 alkenyl group or C 1} substituted with a halogen atom ~C _{9 is an} alkenyl group, X is

,

or

Where n is an integer from 1 to 4; Z is a group 6A element. The secondary according to claim 1, wherein the compound represented by Formula 1 is a compound represented by Formula 2, a compound represented by Formula 3, or a mixture of a compound represented by Formula 2 and a compound represented by Formula 3 Battery electrolyte. [Formula 2]

[Formula 3]

The method of claim 1, wherein the phosphate-based lithium salt is at least one selected from the group consisting of lithium difluorophosphate, lithium tetrafluoro oxalate phosphate, and lithium difluoro bisoxalato phosphate. Electrolyte. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li And LiC(CF ₃ SO ₂ ) ₃ Electrolyte for a secondary battery, characterized in that at least one selected from the group consisting of. The electrolyte of claim 4, wherein the lithium salt is contained in the non-aqueous organic solvent at a concentration of 0.6 to 2.0 M. The electrolyte for a secondary battery according to claim 1, wherein the non-aqueous organic solvent is at least one selected from the group consisting of linear carbonates, cyclic carbonates, linear esters and cyclic esters. The method of claim 6, wherein the linear carbonate is at least one carbonate selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate, and mixtures thereof, The cyclic carbonates are ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and It is at least one carbonate selected from the group consisting of fluoroethylene carbonate, The linear ester is at least one ester selected from the group consisting of methyl propionate, ethyl propionate, propyl acetate, butyl acetate and ethyl acetate, The cyclic ester is at least one ester selected from the group consisting of gamma butyrolactone, caprolactone, and valerolactone. The electrolyte for a secondary battery according to claim 6, wherein the non-aqueous organic solvent is a linear carbonate: cyclic carbonate in a volume ratio of 1:9 to 9:1. The electrolyte solution for secondary batteries according to claim 1, wherein the content of the compound represented by Formula 1 is 0.05 to 10% by weight based on the electrolyte solution for secondary batteries. The electrolyte solution for secondary batteries according to claim 1, wherein the content of the phosphate-based lithium salt additive is 0.05 to 10% by weight based on the electrolyte solution for a secondary battery. Lithium secondary battery including: (a) a positive electrode including a positive electrode active material capable of occluding and releasing lithium; (b) a negative electrode including a negative electrode active material capable of storing and releasing lithium; (c) the electrolyte for a secondary battery according to any one of claims 1 to 10; And (d) a separator.