KR102264048B1 - Electrolyte Solution for Secondary Battery and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for a secondary battery and a secondary battery comprising the same, wherein the compound represented by Formula 1 and a phosphate-based lithium salt are added to the non-aqueous electrolyte for a secondary battery according to the present invention to improve lifespan characteristics and output characteristics It works.

Description

Electrolyte solution for secondary battery and secondary battery including same {Electrolyte Solution for Secondary Battery and Secondary Battery Comprising the Same}

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

Recently, as portable electronic devices become thinner, smaller and lighter, secondary batteries used as power sources are also small and lightweight, can be charged and discharged for a long time, 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, and lithium batteries, depending on the material of the anode or cathode. The potential and energy density are determined by Among them, lithium secondary batteries have high energy density due to the low oxidation/reduction potential and molecular weight of lithium, and thus are widely used as driving power sources for portable electronic devices such as notebook computers, camcorders, or mobile phones.

A lithium secondary battery using a non-aqueous electrolyte is used as a positive electrode coated with a lithium metal mixed oxide capable of desorption and insertion of lithium ions as a positive electrode active material on a metal as a positive electrode, and carbon material or metallic lithium as a negative electrode active material on a metal as a negative electrode It is used by coating, and an electrolyte solution in which lithium salt is appropriately dissolved in an organic solvent is placed with the positive electrode and the negative electrode interposed therebetween. The organic solvent of the electrolyte may be decomposed on the electrode surface during charging and discharging of the battery or co-intercalated between the carbon material anode layers to collapse the anode structure, thereby impairing the stability of the battery.

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

Nevertheless, the SEI film collapses due to repeated charging and discharging, and the lifespan 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 prior art for solving the above problems, Korean Patent Registration No. 10-1492686 discloses lithium oxalyl difluoroborate (LiODFB), a vinylidene carbonate-based compound, a sulfate-based compound, and an electrolyte containing a sultone-based compound. Although the additive and the non-aqueous electrolyte containing the same are disclosed, the capacity recovery and retention rate during high-temperature storage are not described, and there is a limit in improving the discharge efficiency at high C-rate with the mentioned composition.

In addition, Korean Patent No. 10-1538485 discloses a non-aqueous electrolyte for secondary batteries containing alkylene sulfate, ammonium compound, and vinylene carbonate of a specific chemical formula, but due to the absence of a positive electrode additive, the stability of the positive electrode at a high rate is reduced. It is difficult to realize the capacity, and there is a problem in that the long-term life efficiency is lowered because the stable anode film formation and the transition metal elution cannot be prevented.

U.S. Patent Application Laid-Open No. 2017/0301952 A1 discloses a non-aqueous electrolyte for a secondary battery comprising a cyclic sultonate, cyclic sulfate, silane phosphate and/or 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 lifespan characteristics, but by adding lithium difluorophosphate, it suppresses the increase in resistance during high-temperature storage or , there is no disclosure about the effect of improving the lifespan characteristics at high temperature (70°C).

Therefore, there is a demand for development of an electrolyte solution containing an optimal additive composition capable of simultaneously satisfying an improved capacity retention ratio and a life retention ratio 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 of adding the compound represented by Formula 1 and the phosphoric acid-based lithium salt to the electrolyte for a secondary battery, it is confirmed that the output characteristics at room temperature, high temperature life and before and after high temperature are improved. and completed the present invention.

It is an object of the present invention to provide a non-aqueous electrolyte for a secondary battery having improved lifespan 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 lifespan 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) a lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; And (D) provides an electrolyte for a secondary battery comprising a phosphoric acid-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 halogen atom-substituted C ₁ to C ₉ alkyl group, an unsubstituted C ₂ to C ₉ alkenyl group, or a halogen atom-substituted C ₁ ~C _{9 is an} alkenyl group, and X is

,

or

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

The present invention also provides (a) a positive electrode comprising a positive electrode active material capable of intercalating and discharging lithium; (b) an anode comprising an anode active material capable of occluding and releasing lithium; (c) the electrolyte solution for the secondary battery; and (d) a separator for a lithium secondary battery.

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

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 those well known and commonly used in the art.

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

Accordingly, the present invention in one aspect, (A) a lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; And (D) relates to an electrolyte for a secondary battery comprising a phosphoric acid-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 halogen atom-substituted C ₁ to C ₉ alkyl group, an unsubstituted C ₂ to C ₉ alkenyl group, or a halogen atom-substituted C ₁ ~C _{9 is an} alkenyl group, and X is

,

or

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

In another aspect, the present invention, (a) a positive electrode comprising a positive electrode active material capable of occluding and discharging lithium; (b) an anode comprising an anode active material capable of occluding and releasing lithium; (c) the electrolyte solution 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 is (A) a lithium salt; (B) a non-aqueous organic solvent; (C) a compound represented by Formula 1; and (D) a phosphoric acid-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 halogen atom-substituted C ₁ to C ₉ alkyl group, an unsubstituted C ₂ to C ₉ alkenyl group, or a halogen atom-substituted C ₁ ~C _{9 is an} alkenyl group, and X is

,

or

, wherein 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 a 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 at least one 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 from 0.7M to 1.6M, and when it is less than 0.6M, the conductivity of the electrolyte decreases and the electrolyte performance decreases, When it exceeds, the viscosity of the electrolyte increases and there is a problem in that mobility of lithium ions is reduced. These lithium salts act as a source of lithium ions in the battery to enable 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, methyl propyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate, and mixtures thereof, but is not limited thereto.

The cyclic carbonate is ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene 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, a mixing volume ratio of the linear carbonate solvent: the cyclic carbonate solvent is 1:9 to 9:1 days It may be used, preferably mixed in a volume ratio of 1.5:1 to 4:1.

(C) a compound represented by formula (1)

The electrolyte for a secondary battery according to the present invention includes a compound represented by Chemical 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 halogen atom-substituted C ₁ to C ₉ alkyl group, an unsubstituted C ₂ to C ₉ alkenyl group, or a halogen atom-substituted C ₁ ~C _{9 is an} alkenyl group, and X is

,

or

, wherein 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 the compound represented by Formula 2 and the compound represented by Formula 3 may be used.

[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 for a secondary battery. , when it is less than 0.05% by weight, the effect of forming a stable SEI film on the electrode is insignificant, so it is insufficient to suppress the deterioration of the battery. When it exceeds 10% by weight, the electrode film is formed too thickly and the electrode interface resistance increases, so the secondary battery There is a problem in that the characteristics are deteriorated.

(D) phosphate lithium salt

The electrolyte for a secondary battery according to the present invention includes a phosphoric acid-based lithium salt. The phosphoric acid-based lithium salt is lithium difluorophosphate (LFP), lithium tetrafluoro (oxalate) phosphate (LTFOP) and lithium difluoro bisoxalato phosphate (lithium difluoro (bisoxalato) phosphate). ) phosphate, LDFBOP) may be at least one 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 for a secondary battery, If it is less than 0.05% by weight, there is a problem insufficient to transform the SEI film structure into a highly ion-permeable SEI layer. If it exceeds 10% by weight, it causes resistance due to an increase in the viscosity of the electrolyte, resulting in the lifespan and output characteristics of the secondary battery. There is a problem of this deterioration.

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

In the present invention, as the cathode material of the lithium secondary battery, 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, etc.), and crystalline or amorphous carbon, carbon composite, lithium metal, or lithium alloy is used as the anode material. do. 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 and wound or laminated together with a separator, which is an insulator, to make an electrode group, and then placed in a can or similar container, followed by trialkyl A lithium ion secondary battery is manufactured by injecting a non-aqueous electrolyte containing silyl sulfate and a phosphite-based stabilizer. As the separator, a resin such as polyethylene or polypropylene may be used.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, 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 1

_{Li(Ni 0.6} Co _0.2 Mn _0.2 )O ₂ as a cathode 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- A positive electrode slurry was prepared by dispersing in pyrrolidone. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried and rolled to prepare a positive electrode.

A 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. This slurry was coated on a copper foil having a thickness of 15 μm, dried and rolled to prepare a negative electrode.

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

_{1.0M LiPF 6} was added to a non-aqueous organic solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed at 3:7 (v/v), 1 wt% of BTMSF and 1 wt% 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 wt% of BTMSTDA was added instead of 1 wt% of BTMSF in the electrolyte solution for a secondary battery.

Example 3

A lithium secondary battery was prepared in the same manner as in Example 1, except that 0.25% by weight of BTMSF and 0.25% by weight of BTMSTDA were added instead of 1% by weight of BTMSF in the electrolyte for secondary battery of Example 1.

Example 4

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

Example 5

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

Example 6

A lithium secondary battery was prepared in the same manner as in Example 3, except that 1 wt% of LTFOP was added instead of 1 wt% _{of LiPO 2} F ₂ in the electrolyte for a secondary battery.

Example 7

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

Example 8

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

Example 9

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

Comparative Example 1

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 solution 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 solution for a secondary battery.

Comparative Example 4

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

Comparative Example 5

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

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 solution 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 solution for a secondary battery.

The electrolyte compositions 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 1% 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%

[Evaluation of physical properties]

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

The secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were each measured for discharging capacity at 300 cycles of 1C charging to 4.2V and 1C discharging. shown in

Initial capacity (mAh) After 300 servings
(mAh) percentage(%) rate of improvement
(% 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 electrolytes of Examples 1 to 3 of the present invention at room temperature (25° C.) exhibited better life performance than Comparative Examples 1 to 5 in the cycle capacity ratio to the initial capacity at 4.2V 300 cycles.

Among them, the electrolyte 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 prepared in Comparative Example 5 More about 3%, it showed improved life characteristics by about 1.5% compared to Examples 1 and 2.

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

The secondary batteries prepared in Examples 4 to 9, Comparative Examples 1 to 4, and Comparative Examples 6 to 7 were each charged at 1C to 4.2V and then discharged at 300 cycles of 1C discharge. The measured discharge capacity and initial capacity were measured. Table 3 shows the contrast percentage.

Initial capacity (mAh) After 300 servings
(mAh) percentage(%) rate of improvement
(% 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 3, the electrolytes of Examples 4 to 9 of the present invention at a high temperature (45° C.) had better life performance than Comparative Examples 1 to 4 and Comparative Examples 6 to 7 in the initial capacity to cycle capacity ratio at 4.2V 300 cycles. showed

Among them, Example 6 in which 1 wt% of lithium tetrafluorooxalate phosphate was added to 0.25 wt% of bis(trimethylsilyl) fumarate and 0.25 wt% of bis(trimethylsilyl) 2,2'-thiodiacetate, respectively, and lithium The electrolyte solution of Example 9 in which 1 wt% of difluorobis(oxalato)phosphate was added showed improved lifespan characteristics by 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 at 1C up to 4.2V, then discharged at a constant current of 2C up to 475mA, and then the charge/discharge rate (C-rate) was set to 0.5C, 1C, 2C, 4C. were discharged for 10 seconds each to measure the initial discharge output. After 1C charge to 4.2V, store at high temperature (70℃) for 7 days, then charge 1C to 4.2V and discharge 1C twice, in the same manner as in the initial output measurement method. The output was measured after storage at a high temperature (70° C.), and the measured output values are shown in Table 4 below.

Output (W) output difference
(W for Comparative Example 1) high temperature (70℃)
before storage high temperature (70℃)
after storage high temperature (70℃)
before storage high temperature (70℃)
after storage 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 4, the electrolytes of Examples 1 to 9 of the present invention before and after storage at a 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, bis(trimethylsilyl) fumarate 0.25% by weight, bis(trimethylsilyl)2,2'-thiodiacetate 0.25% by weight , the secondary battery of Example 3 to which 1 wt% of lithium difluorophosphate was added showed the best initial output characteristics with an output value of 79.95W.

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

As described above, the secondary battery electrolyte according to the present invention has 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 phosphate-based lithium salt is added alone. It can be seen that the phosphoric acid-based lithium salt transforms the SEI film structure into a highly ion-permeable SEI layer, so that the lifespan at room temperature and high temperature and the output characteristics before and after high temperature are further improved.

As the specific parts of the present invention have been described in detail above, it will be clear to those of ordinary skill in the art that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. will be. Accordingly, it is intended that the substantial scope of the invention be defined by the claims and their equivalents.

Claims (11)

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

In Formula 1, R ¹ to R ⁶ are each independently a methyl group or an ethyl group, and X is

,

or

, wherein n is an integer from 1 to 4; Z is a group 6A element.
The secondary compound of 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 Electrolyte for batteries.
[Formula 2]

[Formula 3]

The secondary battery according to claim 1, wherein the phosphoric acid-based lithium salt is at least one selected from the group consisting of lithium difluorophosphate, lithium tetrafluorooxalate phosphate, and lithium difluorobisoxalatophosphate. electrolyte.
According to 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 solution for a secondary battery according to claim 4, wherein the lithium salt is contained in the non-aqueous organic solvent at a concentration of 0.6 to 2.0M.
The electrolyte solution 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 carbonate is ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate and At least one carbonate selected from the group consisting of fluoroethylene carbonate,
wherein 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 an electrolyte for a secondary battery, characterized in that at least one ester selected from the group consisting of gamma butyrolactone, caprolactone and valerolactone.
The electrolyte solution for a secondary battery according to claim 6, wherein the non-aqueous organic solvent is a mixture of linear carbonate: cyclic carbonate in a volume ratio of 1:9 to 9:1.
The electrolyte for a secondary battery 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 for a secondary battery.
The electrolyte for a secondary battery 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 for a secondary battery.
A lithium secondary battery comprising:
(a) a positive electrode comprising a positive electrode active material capable of occluding and discharging lithium;
(b) an anode comprising an anode active material capable of intercalating and releasing lithium;
(c) the electrolyte for a secondary battery of any one of claims 1 to 10; and
(d) Membrane.