KR101901886B1 - Electrolyte for secondary battery and secondary battery containing the same - Google Patents

Abstract

The present invention relates to a secondary battery electrolyte and a secondary battery comprising the secondary battery electrolyte. The secondary battery electrolyte of the present invention contains a cyclic sulfate compound, thereby remarkably improving the room temperature and high temperature life characteristics, high temperature storage characteristics and long term storage stability.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for a secondary battery,

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 including a cyclic sulfate compound as an additive and a secondary battery comprising the same.

[0002] Recently, portable electronic devices have been widely used, and these portable electronic devices are becoming thinner, smaller, and lighter.

As a result, efforts have been focused on improving the high-rate characteristics of the secondary battery used as the power source so that the secondary battery can be miniaturized and lightweight and can be charged and discharged for a long time.

 The secondary battery is classified into a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen (Ni-MH) battery and a lithium battery according to an anode material and a cathode material. The potential and the energy density are determined. Among them, lithium secondary batteries are widely used as driving power sources 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.

In general, a non-aqueous electrolyte used in a lithium secondary battery includes an electrolyte solvent and an electrolyte salt. The electrolyte solvent is decomposed on the surface of the electrode during charging and discharging of the battery, co-intercalated between the carbonaceous cathode layers, The structure can be collapsed and the stability of the battery can be impaired.

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

Nevertheless, the SEI film is collapsed due to repeated repetition of charging and discharging, and the lifetime and performance of the secondary battery, especially at high temperature, are lowered due to the low thermal stability of the SEI film.

To solve these problems, Korean Patent No. 10-0412522 discloses a secondary battery electrolyte employing a sulfate compound as an additive. However, the sulfate compound disclosed in Korean Patent No. 10-0412522 has a large amount of gas at a high temperature Resulting in deterioration of high-temperature storage performance.

Therefore, there is a demand for research on secondary battery electrolyte having superior high-temperature storage characteristics and life characteristics.

Korean Patent No. 10-0412522

The present invention provides a secondary battery electrolyte and a secondary battery comprising the same, wherein the characteristics at room temperature and high temperature, life cycle characteristics and high temperature storage characteristics are remarkably improved.

The present invention provides a secondary battery electrolyte having extremely improved life characteristics and storage characteristics not only at room temperature but also at a high temperature, and the secondary battery electrolyte according to the present invention comprises a lithium salt; Non-aqueous organic solvent; And a cyclic sulfate compound represented by the following formula (1).

[Chemical Formula 1]

(In the formula 1,

또는

이다.)Z ₁ and Z ₂ are independently of each other

or

to be.)

또는

일 수 있다.Preferably, Z ₁ and Z ₂ in the formula (1) according to an embodiment of the present invention are the same

or

Lt; / RTI >

The cyclic sulfate compound according to an embodiment of the present invention may be contained in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution.

The electrolyte according to an embodiment of the present invention may further include lithium difluorophosphate, and lithium difluorophosphate may be included in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution.

The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent, or a mixture thereof. The non-aqueous organic solvent may be a linear carbonate solvent : The cyclic carbonate-based solvent may have a mixing volume ratio of 1: 1 to 9: 1.

Lithium salt, according to one embodiment of the present invention is _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . _{LiN (C x F 2x + 1} SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y is 0 or a natural number), LiCl, LiI, LiSCN, LiB (C 2 O 4) 2, LiF 2 BC may be _{2 O 4, LiPF 4 (C} 2 O 4), LiPF 2 (C 2 O 4) 2, and LiP (C ₂ O _{4) 3} of one or a mixture of two or more selected from the group consisting of 0.1 to ≪ / RTI > 2.0M.

The present invention also provides a secondary battery comprising the secondary battery electrolyte according to the present invention, wherein the secondary battery comprises: a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium ions; b) a negative electrode comprising a negative active material capable of intercalating and deintercalating lithium ions; c) a secondary battery electrolyte of the present invention; And d) a separator.

The electrolyte of the secondary battery of the present invention contains a cyclic sulfate compound as a specific additive, so that the life characteristics at room temperature and high temperature are excellent.

Furthermore, the secondary battery electrolyte of the present invention has excellent storage stability at a high temperature as well as long-term storage stability.

The present invention provides a secondary battery electrolyte having excellent long-term storage stability as well as normal temperature and high-temperature life characteristics and high-temperature storage characteristics, and the secondary battery electrolyte according to the present invention comprises a lithium salt; Non-aqueous organic solvent; And a cyclic sulfate compound represented by the following formula (1).

[Chemical Formula 1]

(In the formula 1,

또는

이다.)Z ₁ and Z ₂ are independently of each other

or

to be.)

The secondary battery electrolyte of the present invention is excellent in life characteristics at room temperature as well as life characteristics and storage characteristics at high temperatures by incorporating the cyclic sulfate compound represented by Formula 1 as an additive, and has high storage stability even after storage for a long period of time.

또는

일 수 있다.It is preferable that Z ₁ and Z ₂ in the formula (1) according to an embodiment of the present invention are the same as each other in view of having excellent lifetime characteristics at room temperature and high temperature and excellent high-

or

Lt; / RTI >

The cyclic sulfate compound according to an embodiment of the present invention may be contained in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution, and may be included in an amount of 0.05 to 5% by weight in order to achieve improved properties.

The electrolyte according to an embodiment of the present invention may further include lithium difluorophosphate as an additive.

The electrolytic solution according to an embodiment of the present invention includes the cyclic sulfate compound represented by the formula (1) and lithium difluorophosphate in combination, thereby improving the room temperature lifetime characteristics, especially the high temperature lifetime characteristics and the high temperature storage characteristics.

In the secondary battery electrolyte according to an embodiment of the present invention, although the content of the lithium difluorophosphate is not limited, in order to improve battery life characteristics, high temperature storage characteristics and long-term storage stability in the secondary battery electrolyte, May be contained in an amount of 0.05 to 10% by weight, more preferably 0.1 to 3% by weight based on the weight of the composition.

The non-aqueous organic solvent according to an embodiment of the present invention may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent or a mixture thereof. However, the non-aqueous organic solvent may be a cyclic carbonate solvent, And a mixed solvent thereof. It is most preferable to use a mixture of a cyclic carbonate-based solvent and a linear carbonate-based solvent. The cyclic carbonate solvent has a large polarity, which can sufficiently dissociate lithium ions, but has a disadvantage in that the ion conductivity is low due to the high viscosity. Therefore, the characteristics of the secondary battery can be optimized by mixing the cyclic carbonate solvent with a linear carbonate solvent having a low polarity but a low viscosity.

The cyclic carbonate solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluorethylene carbonate, and mixtures thereof. The linear carbonate solvent may be selected from the group consisting of dimethyl carbonate, Diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof.

In the electrolyte for a secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent is a mixed solvent of a cyclic carbonate solvent and a linear carbonate solvent, 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.

Lithium salt, according to one embodiment of the present invention is _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . _{LiN (C x F 2x + 1} SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y is 0 or a natural number), LiCl, LiI, LiSCN, LiB (C 2 O 4) 2, LiF 2 BC ₂ O ₄ , LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , and LiP (C ₂ O ₄ ) ₃ .

The lithium salt concentration according to one embodiment of the present invention may be 0.1 to 2.0 M, preferably 0.4 to 2.0 M, and preferably, it is used in the range of 0.7 to 1.6 M. If the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte is lowered to deteriorate the performance of the electrolyte. If the concentration exceeds 2.0 M, the viscosity of the electrolyte increases and the lithium ion mobility decreases. The lithium salt acts as a source of lithium ions in the battery, thereby enabling operation of the basic secondary battery.

The present invention also provides a secondary battery comprising the secondary battery electrolyte according to the present invention, wherein the secondary battery comprises: a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium ions; b) a negative electrode comprising a negative active material capable of intercalating and deintercalating lithium ions; c) a secondary battery electrolyte of the present invention; And d) a separator.

The secondary battery of the present invention includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The secondary battery comprising the secondary battery electrolyte according to the present invention is manufactured by a conventional method and the battery manufactured using the secondary battery electrolyte containing the cyclic sulfate compound represented by Formula 1, High temperature life characteristics and high temperature storage characteristics are excellent.

An anode according to an embodiment of the present invention includes a current collector and a cathode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material capable of absorbing and desorbing lithium, a binder, a conductive material, and the like. The positive electrode active material is preferably a composite metal oxide of lithium and at least one element selected from cobalt, manganese, and nickel. In addition to these metals, the employment rate of the metals may be varied. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Sr, V, and a rare earth element. Specific examples of the positive electrode active material may include a compound represented by any one of the following formulas:

Li _a A _1-b B _b D ₂ wherein, in the formula, 0.90? A? 1.8, and 0? B? 0.5; Li _a E _1-b B _b O _{2 -c} D _c wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1); Li _a CoG _b O ₂ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); _{Li (3-f) Fe 2} (PO 4) 3 (0≤ f ≤ 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

The negative electrode according to an embodiment of the present invention includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer may include a negative electrode active material capable of intercalating and deintercalating lithium, a binder, a conductive material, and the like. As the negative electrode active material, a carbon material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber, a lithium metal, an alloy of lithium and other elements, and the like can be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500 ° C. or lower, and mesophase pitch-based carbon fiber (MPCF). The crystalline carbon is a graphite-based material, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbonaceous material is preferably a material having an interplanar distance of 3.35 to 3.38 angstroms and a crystallite size (Lc) of at least 20 nm by X-ray diffraction. Other elements constituting the alloy with lithium may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

The anode and / or the cathode according to an embodiment of the present invention may be manufactured by dispersing an electrode active material, a binder and a conductive material, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector have. As the positive electrode current collector, aluminum or an aluminum alloy may be commonly used, and copper or a copper alloy may be used as the negative electrode current collector. The anode current collector and the anode current collector may be in the form of a foil or a mesh.

The binder according to one embodiment of the present invention acts as a paste for the active material, mutual adhesion of the active material, adhesion to the current collector, buffering effect on expansion and contraction of the active material, and the like. Anything is possible. For example, there may be mentioned polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, Polyvinylidene fluoride (PVdF), copolymer of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP)), poly (vinyl acetate), alkylated polyethylene oxide, polyvinyl Butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, polyacrylonitrile, , Epoxy resin, nylon, and the like can be used, but the present invention is not limited thereto. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesive force between the electrode active material and the current collector is insufficient. If the content of the binder is too large, the adhesive force is improved but the content of the electrode active material is reduced accordingly.

The conductive material according to one embodiment of the present invention is used for imparting conductivity to an electrode, and any material can be used as an electron conductive material without causing any chemical change in the battery. As the conductive material, at least one selected from the group consisting of a graphite-based conductive material, a carbon black-based conductive material, and a metal or metal compound-based conductive material may be used. Examples of the black graphite conductive material include artificial graphite and natural graphite. Examples of the carbon black conductive material include acetylene black, ketjen black, denkablack, thermal black, channel black black or the like. Examples of metal or metal compound conductive agents include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ and LaSrMnO ₃ have. However, the present invention is not limited to the above-mentioned conductive materials. The content of the conductive material is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive material is less than 0.1% by weight, the electrochemical characteristics are deteriorated, and when it exceeds 10% by weight, the energy density per weight is decreased.

The thickening agent according to an embodiment of the present invention is not particularly limited as long as it can control the viscosity of the active material slurry. For example, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and the like are used .

As the solvent in which the electrode active material, the binder, the conductive material and the like are dispersed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The secondary battery of the present invention may include a separator to prevent a short circuit between the positive electrode and the negative electrode and to provide a path for the lithium ion. The separator may be a polypropylene, a polyethylene, a polyethylene / polypropylene, a polyethylene / polypropylene / , Polyolefin-based polymer membranes such as polypropylene / polyethylene / polypropylene, or multi-membranes thereof, microporous films, woven fabrics and nonwoven fabrics. Further, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

The lithium secondary battery of the present invention may have other shapes such as a cylindrical shape, a pouch shape, and the like.

The present invention will be described in detail with reference to the following examples. However, the following examples are merely examples of the present invention, and the claims of the present invention are not limited thereto.

The following compounds 1 to 3 of the present invention, lithium difluorophosphate, ethylene sulfate and ethylene sulfite, were used without purification using the Lychee product.

[Example 1]

LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material were mixed at a weight ratio of 92: 4: 4 and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry . This slurry was coated on an aluminum foil having a thickness of 20 mu m, followed by drying and rolling to prepare a positive electrode.

Acetylene black as a conductive material and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 92: 1: 7 and dispersed in N-methyl-2-pyrrolidone as an anode active material to obtain an anode active material slurry . This slurry was coated on a copper foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode.

A thickness of 20 mu m Polyethylene (PE) film A separator was stacked and wound and compressed to form a cell using a pouch having a size of 6 mm x 35 mm x 60 mm and a non-aqueous electrolyte was injected to prepare a lithium secondary battery .

The electrolytic solution was prepared by dissolving LiPF ₆ to 1.0 M in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3: 7 by volume) and then adding 0.5 wt% of the following compound 1.

[Compound 1]

[Example 2]

A secondary battery was prepared in the same manner as in Example 1, except that 0.5 weight% of Compound 1 was added instead of 0.5 weight% of Compound 2 below.

[Compound 2]

[Example 3]

A secondary battery was prepared in the same manner as in Example 1 except that 0.5% by weight of Compound 3 was added instead of 0.5% by weight of Compound 1.

[Compound 3]

[Example 4]

A secondary battery was prepared in the same manner as in Example 1, except that 0.5 wt% of Compound 1 was added and 1 wt% of lithium difluorophosphate (LiPO ₂ F ₂ ) was added.

[Example 5]

A secondary battery was prepared in the same manner as in Example 1 except that 0.5 weight% of Compound 2 was added and 1 weight% of lithium difluorophosphate was added.

[Example 6]

A secondary battery was prepared in the same manner as in Example 1, except that 0.5 weight% of Compound 3 was added and 1 weight% of lithium difluorophosphate was added.

[Comparative Example 1]

A secondary battery was prepared in the same manner as in Example 1, except that 0.5 wt% of ethylene sulfate was added instead of 0.5 wt% of Compound 1.

[Comparative Example 2]

A secondary battery was prepared in the same manner as in Example 1, except that 0.5 wt% of ethylene sulfite was added instead of 0.5 wt% of Compound 1.

[Comparative Example 3]

A secondary battery was prepared in the same manner as in Example 1, except that 1 weight% of lithium difluorophosphate was added instead of 0.5 weight% of Compound 1.

[Comparative Example 4]

A secondary battery was produced in the same manner as in Example 1 except that Compound 1 was not added.

[Evaluation of physical properties 1: Evaluation of cycle life characteristics at room temperature (25 占 폚)

Each of the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 4 was charged at 1 C to 4.2 V and then discharged at 2C. This process was repeated 300 times to measure lifetime characteristics (cycle performance). The initial discharge capacity, the discharge capacity at 300 cycles, the percentage relative to the initial capacity, and the initial capacity percentage increased relative to Comparative Example 4 are shown in Table 1 below.

Initial 2C discharge capacity (mAh) Discharge capacity after 300 cycles (mAh) life span(%) Improvement rate
(% In comparison with Comparative Example 4) Example 1 882 822.2 93.2 8.4 Example 2 880.4 820.3 93.2 8.4 Example 3 881.2 824.3 93.5 8.8 Example 4 885.4 838 94.6 10.1 Example 5 885.2 835.2 94.4 9.7 Example 6 885.4 834.7 94.3 9.6 Comparative Example 1 880.2 806.2 91.6 6.5 Comparative Example 2 880.6 807.1 91.7 6.6 Comparative Example 3 878.5 810.5 92.3 7.3 Comparative Example 4 875 752.3 86.0 -

As shown in Table 1, even when the electrolytic solution of Examples 1 to 3 of the present invention had 300 cycles, the cycle capacity ratio to the initial capacity was improved as compared with Comparative Example 4, and compared with Comparative Examples 1 to 4 Excellent lifetime performance can be seen. In addition, since the lifetime of the electrolytes of Examples 4 to 6 is remarkably superior to that of Comparative Examples 1, 2 and 3, it can be seen that there is a synergistic action by the combination of the additive of the present patent and lithium difluorophosphate. , The non-aqueous electrolyte solution for a secondary battery according to the present invention contains at least one additive selected from the general formulas (1) to (3), thereby showing improved cycle life characteristics at room temperature.

[Property evaluation 2: Evaluation of cycle life characteristics at high temperature (45 캜)] [

Each of the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 4 was charged at 1 C to 4.2 V and then discharged at 2C. This process was repeated 300 times to measure lifetime characteristics (cycle performance). The cycle performance evaluation was performed at a high temperature (45 DEG C). Table 2 shows the initial discharge capacity, the discharge capacity at 300 cycles, the percentage relative to the initial capacity, and the percentage of initial capacity increased relative to Comparative Example 4.

Initial 2C discharge capacity (mAh) Discharge capacity after 300 cycles (mAh) life span(%) Improvement rate
(% In comparison with Comparative Example 4) Example 1 890.5 824.5 92.6 9.7 Example 2 891 822.9 92.4 9.4 Example 3 891 824 92.5 9.5 Example 4 893.4 836 93.6 10.8 Example 5 894.2 837.1 93.6 10.9 Example 6 893.9 832.6 93.1 10.3 Comparative Example 1 890.7 812.6 91.2 8.1 Comparative Example 2 892.3 815 91.3 8.2 Comparative Example 3 891.7 817.3 91.7 8.6 Comparative Example 4 886.2 748.2 84.4 -

As shown in Table 2, even when the electrolytic solution of Examples 1 to 3 of the present invention had 300 cycles, the cycle capacity ratio to the initial capacity was improved as compared with Comparative Example 4, and in comparison with Comparative Examples 1 to 3, Show performance. The lifetimes of the electrolytes of Examples 4 to 6 are superior to those of Comparative Examples 1 to 3, indicating that there is a synergistic effect due to the combination of the additive of the present patent and Lithium difluorophosphate.

As shown in Evaluation 2, the non-aqueous electrolyte solution for a secondary battery according to the present invention includes at least one additive selected from the general formulas (1) to (3), thereby showing improved cycle life characteristics at high temperatures.

[Property evaluation 3: Evaluation of cell preservation property at high temperature (70 DEG C)] [

Using the secondary batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 4, after changing to a standard charge / discharge cycle and a standard charge / discharge cycle, the battery was stored at 70 ° C for 1 week. Table 3 shows the results.

Thickness increase rate (%) Storage capacity after high temperature storage (mAh) percentage(%) Example 1 9.1 768.2 87.1 Example 2 9.6 763.5 86.7 Example 3 9.3 765.3 86.8 Example 4 8 789 89.1 Example 5 8.3 788 89.0 Example 6 8.2 787.5 88.9 Comparative Example 1 17.6 759 86.2 Comparative Example 2 15.4 757 86.0 Comparative Example 3 9.9 756.4 86.1 Comparative Example 4 18.4 663.3 75.8

As shown in Table 3, the storage capacities of the electrolytic solutions of Examples 1 to 6 of the present invention after storage at high temperature were greatly improved as compared with those of Comparative Example 4, and the thickness increase was suppressed in comparison with Comparative Examples 1 to 4, Indicating the preservation performance.

Thus, as shown in Evaluation 3, the nonaqueous electrolyte for a secondary battery according to the present invention includes at least one additive selected from the formulas (1) to (3), and it can be seen that the storage capacity and the thickness increase after high temperature storage are improved.

[Property evaluation 4: Evaluation of properties of electrolyte after storage of electrolyte]

80 g of electrolytes were prepared from the compositions of Examples 1 to 6 and Comparative Examples 1 to 4, and stored in a 100 ml SUS container at 25 캜 for 3 months. The acidity and hue of the electrolytic solution before and after storage were measured. The measurement results are shown in Table 4 below.

Initial pH (ppm) Initial chromaticity (APHA) PH after storage Color after storage (APHA) Example 1 25 20 35 26 Example 2 24 22 39 25 Example 3 26 23 40 25 Example 4 28 25 44 27 Example 5 29 26 46 28 Example 6 28 25 42 29 Comparative Example 1 28 34 102 68 Comparative Example 2 27 32 56 52 Comparative Example 3 25 22 48 35 Comparative Example 4 20 18 35 23

As shown in Table 4, it was found that the stability of the additive was significantly improved as compared with Comparative Examples 1 and 2 in which the acidity increase and discoloration of the electrolytic solution were suppressed after storage at room temperature in the single additive electrolytic solution of Examples 1 to 3 of the present invention, .

Claims (10)

Lithium salts;
Non-aqueous organic solvent;
Lithium difluorophosphate; And
1. A secondary battery electrolyte comprising a cyclic sulfate compound represented by the following formula (1).
[Chemical Formula 1]

(In the formula 1,
Z ₁ and Z ₂ are independently of each other

or

to be.) The method according to claim 1,
In the above formula (1), Z ₁ and Z ₂ are the same

or

Secondary battery electrolyte. The method according to claim 1,
Wherein the cyclic sulfate compound is contained in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution. delete The method according to claim 1,
And the lithium difluorophosphate is contained in an amount of 0.05 to 10% by weight. The method according to claim 1,
The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent or a mixed solvent thereof. The method according to claim 6,
Wherein the non-aqueous organic solvent has a mixing ratio by volume of a linear carbonate solvent: a cyclic carbonate solvent of 1: 1 to 9: 1. The method according to claim 1,
The lithium salt is _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2, LiN ( C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . _{LiN (C x F 2x + 1} SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y is 0 or a natural number), LiCl, LiI, LiSCN, LiB (C 2 O 4) 2, LiF 2 _{BC 2 O 4, LiPF 4 (} C 2 O 4), LiPF 2 (C 2 O 4) 2, and LiP (C ₂ O ₄₎ one or a mixture of two or more secondary battery electrolyte is selected from the group consisting of _3. The method according to claim 1,
Wherein the lithium salt is present in a concentration of 0.1 to 2.0 M. a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium ions;
b) a negative electrode comprising a negative active material capable of intercalating and deintercalating lithium ions;
c) a secondary battery electrolyte according to any one of claims 1 to 3 and 5 to 9; And
d) a separator;
And a secondary battery.