KR20090006691A - Non-aqueous electrolyte solution for lithium secondary batteries and lithium secondary battery containing same - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same. The nonaqueous electrolyte solution for lithium secondary batteries of the present invention, in a nonaqueous electrolyte solution for lithium secondary batteries containing a lithium salt and an organic solvent, contains a sultone compound having a carbon-carbon unsaturated bond in a ring and a cyclic carbonate compound having a vinyl group. The nonaqueous electrolyte solution for a lithium secondary battery of the present invention can improve the high temperature stability of the solid electrolyte interfacial film formed on the surface of the negative electrode, thereby improving the battery life characteristics and high temperature performance.

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery containing same {NON-AQUEOUS ELECTROLYTE SOLUTION FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a nonaqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery containing the same.

As electronic devices are miniaturized, reduced in weight, thinned, and portable in recent years with the development of the information and communication industry, demand for high energy density of batteries used as power sources for such electronic devices is increasing. Lithium secondary batteries are the batteries that can best meet these demands, and research on these is being actively conducted. A lithium secondary battery is composed of a cathode, an anode, and an electrolyte and a separator that provide a migration path of lithium ions between the cathode and the anode, and are used for oxidation and reduction reactions when lithium ions are inserted / deinserted from the cathode and the anode. Thereby generating electrical energy.

The nonaqueous electrolyte used in the lithium secondary battery generally contains an electrolyte solvent and an electrolyte salt. However, the electrolyte solvent may decompose at the electrode surface during charge and discharge of the battery, or may be co-intercalated between the carbon material negative electrode layers to collapse the negative electrode structure, thereby inhibiting battery stability.

It is known that the above problems can be solved by a solid electrolyte interface (SEI) film formed on the surface of the negative electrode by reduction of the electrolyte solvent during initial charging of the battery. However, in general, the SEI film is insufficient to serve as a continuous protective film of the negative electrode, and as a result, when the battery repeats charging and discharging, the lifespan and performance decrease. In particular, the SEI film of the conventional lithium secondary battery is not thermally stable, and when the battery is operated or left at a high temperature, it is susceptible to collapse due to increased electrochemical energy and thermal energy over time. Therefore, under high temperature, the battery performance is further deteriorated, and in particular, gases such as CO ₂ are continuously generated due to collapse of the SEI film, decomposition of the electrolyte, and the like, thereby increasing the internal pressure and thickness of the battery.

In order to solve the above problems, Japanese Patent Application Laid-Open No. 1996-45545 has proposed a method of using vinylene carbonate (VC) as an electrolyte additive capable of forming an SEI film on a negative electrode surface. However, VC has a problem in that it degrades performance and safety of a battery by easily decomposing at an anode during high temperature cycle or high temperature storage to generate gas. In addition, Japanese Patent Application Laid-Open No. 2002-329528 uses an unsaturated sultone compound to suppress the generation of gas at a high temperature. In Japanese Patent Laid-Open No. 2001-006729, attempts have been made to improve the high temperature storage characteristics by using a carbonate-based compound containing a vinyl group, but the SEI film is still not robust and does not sufficiently solve the conventional problem.

Therefore, the problem to be solved by the present invention is to provide a non-aqueous electrolyte for lithium secondary battery that can improve the high temperature stability of the solid electrolyte interfacial film formed on the surface of the negative electrode, thereby improving the life characteristics and high temperature performance of the battery.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, the nonaqueous electrolyte solution for lithium secondary batteries of this invention WHEREIN: The nonaqueous electrolyte solution for lithium secondary batteries containing a lithium salt and an organic solvent WHEREIN: A cyclic compound which has a sultone type compound and a vinyl group which have a carbon-carbon unsaturated bond in a cyclic | annular form. It contains a carbonate compound. The nonaqueous electrolyte solution for lithium secondary batteries of the present invention exhibits a significant synergistic effect by simultaneously containing a sultone compound having a carbon-carbon unsaturated bond and a cyclic carbonate compound having a vinyl group in the ring.

That is, the nonaqueous electrolyte of the present invention provides better high temperature stability of the SEI film than the nonaqueous electrolyte of the conventional lithium secondary battery, which also significantly improves the battery life and high temperature performance.

In the nonaqueous electrolyte solution for a lithium secondary battery of the present invention, the sultone compound having a carbon-carbon unsaturated bond in the above-mentioned annular may be any one selected from the group consisting of compounds represented by the following structural formulas, or a mixture of two or more thereof. , But not limited to:

Moreover, in the nonaqueous electrolyte solution for lithium secondary batteries of this invention, the specific example of the above-mentioned cyclic carbonate compound which has a vinyl group is 4-ethenyl- 1, 3- dioxoran-2-one (vinyl ethylene carbonate) (4-ethenyl -1,3-dioxolane-2-on), 4-ethenyl-4-methyl-1,3-dioxoran-2-one (4-ethenyl-4-methyl-1,3-dioxolane-2-on ), 4-ethenyl-4-ethyl-1,3-dioxolan-2-one (4-ethenyl-4-ethyl-1,3-dioxolane-2-on), 4-ethenyl-4-n 4-ethenyl-4-n-propyl-1,3-dioxolane-2-on, 4-ethenyl-5-methyl-1,3-di Oxoran-2-one (4-ethenyl-5-methyl-1,3-dioxolane-2-on), 4-ethenyl-5-ethyl-1,3-dioxoran-2-one (4-ethenyl -5-ethyl-1,3-dioxolane-2-on) and 4-ethenyl-5-n-propyl-1,3-dioxoran-2-one (4-ethenyl-5-n-propyl-1 , 3-dioxolane-2-on), but may be any one selected from the group consisting of, or a mixture of two or more thereof.

In the nonaqueous electrolyte of the present invention, the content of a sultone compound having a carbon-carbon unsaturated bond and a cyclic carbonate compound having a vinyl group in the annular ring is 0.1 to 5 parts by weight and 0.1 to 5 parts by weight based on 100 parts by weight of the nonaqueous electrolyte, respectively. In this case, the present invention can exhibit the desired optimum effect.

The non-aqueous electrolyte solution for lithium secondary batteries described above can be used for the production of lithium secondary batteries.

Hereinafter, the present invention will be described in detail. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

As described above, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention may contain a sultone compound having a carbon-carbon unsaturated bond and a cyclic carbonate compound having a vinyl group together in the ring to exhibit the desired effect of the present invention.

Specifically, the inventors of the present invention, in the case of a lithium secondary battery containing a conventional non-aqueous electrolyte using a vinylene carbonate, an unsaturated sultone compound or a carbonate compound containing a vinyl group, respectively, SEI formed on the negative electrode surface It was found that the membrane was porous and not dense, so it collapsed easily during repeated charge and discharge processes, resulting in deterioration of cell performance, especially at high temperatures, which accelerated the collapse of the SEI membrane.

Accordingly, in order to solve the above problems, the present invention provides a nonaqueous electrolyte solution containing a sultone compound having a carbon-carbon unsaturated bond in a ring and a cyclic carbonate compound having a vinyl group. Sultone-based compounds having carbon-carbon unsaturated bonds and cyclic carbonate compounds having vinyl groups in the cyclic rings contained in the non-aqueous electrolyte solution of the present invention can be cross-linked and / or repeated polymerization while electrically reducing faster than the electrolyte solvent to form a more robust SEI film. Can be. Through this process, the SEI film formed on the surface of the cathode is firm and dense so that it is not easily collapsed and thermally stable even after repeated charging and discharging. Therefore, even when stored at high temperature, the generation of CO ₂ which is a by-product due to side reactions at the anode is suppressed, thereby improving the high temperature storage characteristics.

The sultone compound having a carbon-carbon unsaturated bond in the cyclic ring according to the present invention can exhibit the desired effect as long as it is a sultone compound having a double bond in the ring structure. Examples of the sultone compound having a carbon-carbon unsaturated bond in a ring included in the nonaqueous electrolyte solution for a lithium secondary battery of the present invention may be any one selected from the group consisting of compounds represented by the following structural formulas, or a mixture of two or more thereof. , But not limited to:

A more preferable example of the sultone compound having a carbon-carbon unsaturated bond in the ring according to the present invention described above may be 1,3- (1-propene) sultone, but is not limited thereto.

In addition, the nonaqueous electrolyte solution for lithium secondary batteries of the present invention contains a cyclic carbonate compound having a vinyl group together with a sultone compound having a carbon-carbon unsaturated bond in the aforementioned ring. In the cyclic carbonate compound having a vinyl group according to the present invention, there is no particular limitation on the cyclic carbonate, but ethylene carbonate or propylene carbonate may be a preferred example.

Specific examples of the cyclic carbonate compound having a vinyl group according to the present invention is 4-ethenyl-1,3-dioxolan-2-one (or vinylethylene carbonate) (4-ethenyl-1,3-dioxolane-2-on ), 4-ethenyl-4-methyl-1,3-dioxolan-2-one (4-ethenyl-4-methyl-1,3-dioxolane-2-on), 4-ethenyl-4-ethyl -1,3-dioxolane-2-one (4-ethenyl-4-ethyl-1,3-dioxolane-2-on), 4-ethenyl-4-n-propyl-1,3-dioxolane 2-one (4-ethenyl-4-n-propyl-1,3-dioxolane-2-on), 4-ethenyl-5-methyl-1,3-dioxoran-2-one (4-ethenyl -5-methyl-1,3-dioxolane-2-on), 4-ethenyl-5-ethyl-1,3-dioxolan-2-one (4-ethenyl-5-ethyl-1,3-dioxolane -2-on) and 4-ethenyl-5-n-propyl-1,3-dioxolane-2-one (4-ethenyl-5-n-propyl-1,3-dioxolane-2-on) It may be any one selected from the group consisting of or a mixture of two or more thereof, but is not limited thereto.

The nonaqueous electrolyte solution for lithium secondary batteries of the present invention contains 0.1 to 5 parts by weight of a sultone compound having a carbon-carbon unsaturated bond and 0.1 to 5 parts by weight of a cyclic carbonate compound having a vinyl group based on 100 parts by weight of the nonaqueous electrolyte. This may be a preferred example. A sultone compound having a carbon-carbon unsaturated bond in a ring exhibits the best effect of improving battery performance while maximally preventing irreversible reaction in the above content range. In addition, the cyclic carbonate compound having a vinyl group also exhibits a battery performance improvement effect, which is an effect desired by the present invention, while preventing gas generation and an increase in impedance in the above content range.

Lithium salt included as an electrolyte in the non-aqueous electrolyte of the present invention described above may be used without limitation those conventionally used in the electrolyte for lithium secondary batteries, representative examples of 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 or any one or a mixture of two or more thereof Have a back

As the organic solvent included in the nonaqueous electrolyte of the present invention described above, those conventionally used in the lithium secondary battery electrolyte may be used without limitation, and typically, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methylethyl carbonate, di Any one selected from the group consisting of propyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, ethylene sulfite, propylene sulfite and tetrahydrofuran Or a mixture of two or more of them may be representatively used. In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are highly viscous organic solvents, and thus have high dielectric constant, which may dissociate lithium salts in the electrolyte, and thus may be preferably used. When a low viscosity, low dielectric constant linear carbonate, such as dimethyl carbonate and diethyl carbonate, is mixed with a suitable carbonate in an appropriate ratio, an electrolyte having high electrical conductivity can be used, and thus it can be used more preferably. .

The non-aqueous electrolyte solution for a lithium secondary battery of the present invention described above is manufactured into a lithium secondary battery by injecting an electrode structure composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. As the positive electrode, the negative electrode, and the separator constituting the electrode structure, all those conventionally used for manufacturing a lithium secondary battery may be used.

As a specific example, a lithium-containing transition metal oxide may be preferably used as the cathode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 < a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _1-y Co _y O ₂ , LiCo _1-y Mn _y O ₂ , LiNi _1-y Mn _y O ₂ (O ≦ y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn ₂ Any one selected from the group consisting of _-z Ni _z O ₄ , LiMn _2-z Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ or a mixture of two or more thereof may be used. In addition to these oxides, sulfides, selenides, and halides may also be used.

As the negative electrode active material, a carbon material, lithium metal, silicon, tin, or the like, into which lithium ions may be inserted / deinserted, may be used. Preferably, a carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, Mesophase pitches and petroleum or coal tar pitch derived cokes. In this case, the negative electrode may include a binder, and the binder may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, Various kinds of binder polymers, such as polymethylmethacrylate, may be used.

In addition, as the separator, conventional porous polymer films conventionally used as separators, for example, polyolefins such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, square, pouch type, or coin type using a can.

Compared with the conventional nonaqueous electrolyte, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention does not easily collapse even when repeated charging and discharging, and forms a thermally stable and robust SEI film. In addition, even when stored at a high temperature, the generation of CO ₂ which is a by-product due to side reactions at the anode is suppressed, thus exhibiting a remarkable effect of improving the high temperature storage characteristics.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1

Ethylene carbonate (EC): diethyl carbonate (DEC) = 3: 7 by adding LiPF ₆ to the solvent mixed in a volume ratio of 1M LiPF ₆ solution to prepare a 100 parts by weight of the solution A nonaqueous electrolyte was prepared by mixing 2 parts by weight of 1,3- (1-propene) sultone (PRS) and 2 parts by weight of vinylethylene carbonate (VEC).

Example 2

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 1 part by weight of PRS and 3 parts by weight of VEC were used.

Example 3

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 3 parts by weight of PRS and 1 part by weight of VEC were used.

Comparative Example 1

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 1 part by weight of PRS was used without adding VEC.

Comparative Example 2

A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 4 parts by weight of PRS was not added.

Comparative Example 3

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 4 parts by weight of VEC was used without adding PRS.

Comparative Example 4

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 2 parts by weight of 1,3-propanesultone (PS) and 2 parts by weight of VEC were used.

Comparative Example 5

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 2 parts by weight of 1,4-butanesultone (BS) and 2 parts by weight of VEC were used.

Comparative Example 6

A nonaqueous electrolyte was prepared in the same manner as in Example 1, except that 2 parts by weight of PRS and 2 parts by weight of vinylene carbonate (VC) were used.

Comparative Example 7

A nonaqueous electrolyte was prepared in the same manner as in Example 1 except that PRS and VEC were not added.

Lithium secondary batteries were manufactured in a cylindrical manner by using a nonaqueous electrolyte prepared according to Examples 1 to 3 and Comparative Examples 1 to 7 and using LiCoO ₂ as an anode and artificial graphite as a cathode. The manufactured battery was measured for life characteristics and high temperature performance in the following manner.

Life characteristic measurement

After the batteries were charged and discharged 300 times at 1 C / 1C at 55 ° C., the capacity retention ratios compared to the initial capacity are shown in Table 1.

High Temperature Performance Measurement

After the cells were fully charged and allowed to stand at 75 ° C. for 3 days, the ratio of the remaining capacity and the recovery capacity to the capacity before storage is shown in Table 1. In addition, the CID short time of each battery is also shown in Table 1. The CID short circuit is caused by an increase in pressure due to gas generation inside the battery. Therefore, the better the high temperature characteristic, the longer the CID short circuit time.

TABLE 1

additive Capacity retention rate after 300 charge / discharge cycles (%) Remaining capacity (%) Recovery capacity (%) CID short time (h) Kinds Addition amount (part by weight) Example 1 PRS / VEC 2/2 89 72 79 148 Example 2 PRS / VEC 1/3 87 70 76 136 Example 3 PRS / VEC 3/1 90 75 81 154 Comparative Example 1 PRS One 56 54 59 100 Comparative Example 2 PRS 4 65 60 66 112 Comparative Example 3 VEC 4 58 58 64 100 Comparative Example 4 PS / VEC 2/2 78 66 72 84 Comparative Example 5 BS / VEC 2/2 69 63 70 84 Comparative Example 6 PRS / VC 2/2 83 (122 times; CID paragraph in 123) CID paragraph CID paragraph 72 Comparative Example 7 - - 49 CID paragraph CID paragraph 48

As can be seen in Table 1, the cells of the examples using a non-aqueous electrolyte containing PRS, which is a sultone compound compound having a carbon-carbon unsaturated bond in a ring, and VEC, which is a cyclic carbonate compound compound having a vinyl group, are cells of Comparative Examples. It can be seen that it shows more excellent life characteristics, higher remaining capacity and recovery capacity, and a relatively longer CID short time.

Claims (8)

In the nonaqueous electrolyte solution for lithium secondary batteries containing a lithium salt and an organic solvent, A nonaqueous electrolyte solution for lithium secondary batteries containing a sultone compound having a carbon-carbon unsaturated bond in a ring and a cyclic carbonate compound having a vinyl group. The method of claim 1, A sultone compound having a carbon-carbon unsaturated bond in the ring is any one selected from the group consisting of compounds represented by the following structural formulas, or a mixture of two or more thereof.

The method of claim 1, A sultone compound having a carbon-carbon unsaturated bond in the ring is (1,3- (1-propene) sultone). The method of claim 1, The cyclic carbonate compound having a vinyl group is 4-ethenyl-1,3-dioxolan-2-one, 4-ethenyl-4-methyl-1,3-dioxoran-2-one, 4-ethenyl -4-ethyl-1,3-dioxolan-2-one, 4-ethenyl-4-n-propyl-1,3-dioxoran-2-one, 4-ethenyl-5-methyl-1 , 3-dioxoran-2-one, 4-ethenyl-5-ethyl-1,3-dioxoran-2-one and 4-ethenyl-5-n-propyl-1,3-dioxolane Non-aqueous electrolyte solution for lithium secondary batteries, characterized in that any one selected from the group consisting of 2-one or a mixture of two or more thereof. The method of claim 1, The content of the sultone compound having a carbon-carbon unsaturated bond and the cyclic carbonate compound having a vinyl group in the annular is 0.1 to 5 parts by weight and 0.1 to 5 parts by weight with respect to 100 parts by weight of the nonaqueous electrolyte, respectively. Electrolyte solution. The method of claim 1, 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 ) A non-aqueous electrolyte solution for lithium secondary batteries, characterized in that any one selected from the group consisting of ₃ or a mixture of two or more thereof. The method of claim 1, The organic solvent is propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-buty Rolactone, ethylene sulfite, propylene sulfite, tetrahydrofuran any one selected from the group consisting of, or a mixture of two or more thereof. An electrode structure comprising an anode, a cathode, and a separator interposed between the anode and the cathode; And a nonaqueous electrolyte solution injected into the electrode structure. The nonaqueous electrolyte is a lithium secondary battery, characterized in that the nonaqueous electrolyte for lithium secondary battery of any one of claims 1 to 7.