阅读说明：本技术 用于锂二次电池的电解液和包含该电解液的锂二次电池 (Electrolyte for lithium secondary battery and lithium secondary battery comprising the same ) 是由 李尹圣 吕悦梅 吴承旼 金益圭 李智殷 金南亨 金东俊 宋丞婉 郑京俊 于 2020-06-17 设计创作，主要内容包括：本发明公开一种用于锂二次电池的电解液。该电解液包括锂盐、溶剂以及功能性添加剂,其中功能性添加剂包括高电压添加剂,并且高电压添加剂包括由以下式表示的1-氟乙基甲基碳酸酯(FEMC),(Disclosed is an electrolyte for a lithium secondary battery. The electrolyte includes a lithium salt, a solvent, and a functional additive, wherein the functional additive includes a high voltage additive, and the high voltage additive includes 1-fluoroethyl methyl carbonate (FEMC) represented by the following formula,)

1. An electrolyte for a lithium secondary battery, comprising:

a lithium salt;

a solvent; and

a functional additive comprising a high voltage additive comprising 1-fluoroethyl methyl carbonate (FEMC) represented by the following [ formula 1],

2. the electrolyte of claim 1,

adding 1 to 3 wt% of the high voltage additive based on the weight of the electrolyte.

3. The electrolyte of claim 1,

the functional additive further comprises a negative electrode film additive, and the negative electrode film additive comprises Vinylene Carbonate (VC).

4. The electrolyte of claim 3,

0.5 to 3.0 wt% of the anode film additive is added based on the weight of the electrolyte.

5. The electrolyte of claim 1,

the lithium salt is selected from the group consisting of LiPF₆、LiBF₄、LiClO₄、LiCl、LiBr，LiI、LiB₁₀Cl₁₀、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiAlCl₄、CH₃SO₃Li、CF₃SO₃Li、LiN(SO₂C₂F₅)₂、Li(CF₃SO₂)₂N、LiC₄F₉SO₃、LiB(C₆H₅)₄、Li(SO₂F)₂N (LiFSI) and (CF)₃SO₂)₂Any one or a mixture of two or more of NLi's.

6. The electrolyte of claim 1,

the solvent is any one or a mixture of two or more selected from the group consisting of carbonate solvents, ester solvents, ether solvents, and ketone solvents.

7. A lithium secondary battery comprising an electrolyte comprising a lithium salt, a solvent, and a functional additive comprising a high voltage additive comprising 1-fluoroethyl methyl carbonate (FEMC) represented by the following formula [ formula 1],

8. the lithium secondary battery according to claim 7, further comprising:

a positive electrode containing an NCM-based positive electrode active material composed of Ni, Co, and Mn;

an anode including one or more anode active materials selected from carbon (C) and silicon (Si) anode active materials; and

a separator interposed between the positive electrode and the negative electrode.

9. The lithium secondary battery according to claim 8,

the Ni content in the positive electrode is 60 wt% or more.

10. A lithium secondary battery comprising:

a battery case;

a positive electrode, a portion of which is within the battery case;

a negative electrode, a portion of which is within the battery case;

a separator interposed between the positive electrode and the negative electrode; and

an electrolyte containing a lithium salt, a solvent, and a functional additive containing a high voltage additive represented by the following [ formula 1] within the battery case,

11. the lithium secondary battery according to claim 10,

the positive electrode contains an NCM-based positive electrode active material composed of Ni, Co, and Mn.

12. The lithium secondary battery according to claim 11,

the NCM-based positive electrode active material contains 60 wt% or more of Ni.

13. The lithium secondary battery according to claim 10,

the negative electrode includes one or more negative electrode active materials, and the negative electrode active material is a carbon-based negative electrode active material or a silicon-based negative electrode active material.

14. The lithium secondary battery according to claim 13,

the carbon-based negative active material includes at least one of artificial graphite, natural graphite, graphitized carbon fiber, graphitized medium-carbon microbeads, fullerene, and amorphous carbon, and the silicon-based negative active material includes silicon oxide, silicon particles, or silicon alloy particles.

15. The lithium secondary battery according to claim 10,

the separator includes a polyolefin-based polymer film, a multilayer film, a microporous film, a woven fabric or a non-woven fabric.

16. The lithium secondary battery according to claim 10,

the high voltage additive includes 1-fluoroethyl methyl carbonate, FEMC.

17. The lithium secondary battery according to claim 10,

the functional additive includes a negative electrode film additive, the high voltage additive being added in an amount of 1 to 3 wt% based on the weight of the electrolyte, and the negative electrode film additive being added in an amount of 0.5 to 3.0 wt% based on the weight of the electrolyte.

18. The lithium secondary battery according to claim 17,

the negative electrode film additive comprises Vinylene Carbonate (VC).

19. The lithium secondary battery according to claim 10,

the lithium salt is selected from the group consisting of LiPF₆、LiBF₄、LiClO₄、LiCl、LiBr，LiI、LiB₁₀Cl₁₀、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiAlCl₄、CH₃SO₃Li、CF₃SO₃Li、LiN(SO₂C₂F₅)₂、Li(CF₃SO₂)₂N、LiC₄F₉SO₃、LiB(C₆H₅)₄、Li(SO₂F)₂N (LiFSI) and (CF)₃SO₂)₂Any one or a mixture of two or more of NLi's.

20. The lithium secondary battery according to claim 10,

the solvent is any one or a mixture of two or more selected from the group consisting of carbonate solvents, ester solvents, ether solvents, and ketone solvents.

Technical Field

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

Background

A lithium secondary battery is an energy storage device including a positive electrode (positive electrode) that supplies lithium at the time of charging, a negative electrode (negative electrode) that receives lithium at the time of charging, an electrolyte that serves as a lithium ion transfer medium, and a separator that separates the positive electrode and the negative electrode from each other. When lithium ions are intercalated/deintercalated on the positive electrode and the negative electrode, electric energy is generated and stored by a change in chemical potential (chemical potential).

Lithium secondary batteries are mainly used for portable electronic devices. However, in recent years, with the commercialization of Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV), lithium secondary batteries have been used as energy storage devices for electric vehicles and hybrid electric vehicles.

Meanwhile, research is being conducted to increase the energy density of the lithium secondary battery to increase the travel distance of the electric vehicle. The energy density of the lithium secondary battery can be increased by increasing the capacity of the positive electrode.

The high capacity of the positive electrode can be achieved by a nickel-rich (Ni-rich) method, which is a method of increasing the Ni content of the Ni-Co-Mn-based oxide forming the positive electrode active material, or by increasing the positive electrode charge voltage.

However, the Ni — Co — Mn-based oxide in a nickel-rich state has an unstable crystal structure while exhibiting high interfacial reactivity, thereby accelerating degradation during cycling, and thus it is difficult to ensure long-term performance of the lithium secondary battery.

The statements disclosed in this background section are only for enhancement of understanding of the general background of the invention and are not to be construed as admissions of prior art or suggestions in any form known to those skilled in the art.

Disclosure of Invention

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same. Embodiments of the present invention address the above problems. Certain embodiments of the present invention provide an electrolyte for a lithium secondary battery capable of improving the lifespan and output characteristics of the lithium secondary battery, and a lithium secondary battery including the same.

In accordance with an embodiment of the present invention, the above and other objects can be accomplished by the provision of an electrolyte for a lithium secondary battery, comprising a lithium salt, a solvent, and a functional additive, wherein the functional additive comprises a high voltage additive 1-fluoroethyl methyl carbonate (FEMC) represented by the following [ formula 1],

the high voltage additive may be added in an amount of 1 to 3 wt% based on the weight of the electrolyte.

The functional additive may further comprise a negative electrode film additive, such as Vinylene Carbonate (VC).

The negative electrode film additive may be added in an amount of 0.5 to 3.0 wt% based on the weight of the electrolyte.

The lithium salt may be selected from the group consisting of LiPF₆、LiBF₄、LiClO₄、LiCl、LiBr，LiI、LiB₁₀Cl₁₀、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiAlCl₄、CH₃SO₃Li、CF₃SO₃Li、LiN(SO₂C₂F₅)₂、Li(CF₃SO₂)₂N、LiC₄F₉SO₃、LiB(C₆H₅)₄、Li(SO₂F)₂N (LiFSI) and (CF)₃SO₂)₂Any one or a mixture of two or more of NLi's.

The solvent may be any one or a mixture of two or more selected from the group consisting of carbonate solvents, ester solvents, ether solvents, and ketone solvents.

According to another embodiment of the present invention, there is provided a lithium secondary battery including an electrolyte. The lithium secondary battery may further include: a positive electrode containing an NCM-based positive electrode active material composed of Ni, Co, and Mn; an anode including one or more anode active materials selected from carbon (C) and silicon (Si) anode active materials; and a separator interposed between the positive electrode and the negative electrode.

The Ni content in the positive electrode may be 60 wt% or more.

Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

fig. 1 to 3 are graphs showing charge and discharge results of the examples and comparative examples;

fig. 4 is a photograph showing the surfaces of the positive electrodes before and after charging and discharging of the examples and comparative examples; and

fig. 5 is a schematic view illustrating a lithium secondary battery according to an embodiment of the present invention.

Detailed Description

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various different forms, and the embodiments herein are provided to complete the disclosure of the present invention and fully convey the scope of the present invention to those skilled in the art.

The electrolyte for a lithium secondary battery according to an embodiment of the present invention is a substance forming an electrolyte applied to a lithium secondary battery, and includes a lithium salt, a solvent, and a functional additive.

The lithium salt may be selected from the group consisting of LiPF₆、LiBF₄、LiClO₄、LiCl、LiBr，LiI、LiB₁₀Cl₁₀、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiAlCl₄、CH₃SO₃Li、CF₃SO₃Li、LiN(SO₂C₂F₅)₂、Li(CF₃SO₂)₂N、LiC₄F₉SO₃、LiB(C₆H₅)₄、Li(SO₂F)₂N (LiFSI) and (CF)₃SO₂)₂Any one or a mixture of two or more of NLi's.

The total amount of lithium salt in the electrolyte may be present in a concentration of 0.1 to 1.2 molar.

The solvent may use any one or a mixture of two or more selected from the group consisting of carbonate solvents, ester solvents, ether solvents, and ketone solvents.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (EMC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), fluoroethylene carbonate (FEC), and Vinylene Carbonate (VC). As the ester solvent, gamma-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, n-propyl acetate, etc. can be used. As the ether solvent, dibutyl ether and the like can be used. However, the present invention is not limited thereto.

In addition, the solvent may further include an aromatic hydrocarbon organic solvent. Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, and the like, which may be used alone or in combination of two or more.

Meanwhile, according to an embodiment of the present invention, a high voltage additive represented by the following [ formula 1], for example, 1-Fluoroethyl methyl carbonate (FEMC) may be used as a functional additive added to the electrolyte.

FEMC is used to improve oxidation stability of the electrolyte and stabilize the interface between the electrolyte and the positive electrode, and 1 wt% to 3 wt% of FEMC may be preferably added based on the weight of the electrolyte.

When the addition amount of the high voltage additive is less than 1 wt%, it is difficult to sufficiently form a surface protective layer, and there is a problem that the intended effect is insufficient. When the addition amount of the high voltage additive is more than 3 wt%, a surface protection layer is excessively formed, and the battery resistance is increased, thereby decreasing the battery output.

Meanwhile, an anode film additive for forming a film on the anode may be further added as a functional additive. For example, Vinylene Carbonate (VC) may be used as an anode film additive.

The negative electrode film additive may be preferably added in an amount of 0.5 to 3.0 wt%, more preferably 1.5 to 2.5 wt%, based on the weight of the electrolyte.

When the additive amount of the anode film additive is less than 0.5 wt%, the long-term life characteristics of the battery are deteriorated. When the additive amount of the negative electrode film additive is more than 3.0 wt%, a surface protection layer is excessively formed, and the battery resistance increases, thereby decreasing the battery output.

As shown in fig. 5, a lithium secondary battery 100 according to an embodiment of the present invention includes: a battery case 102; a positive electrode 104, a portion of which is within the battery case 102; a negative electrode 106, a portion of which is within the battery case 102; a separator 108 interposed between the positive electrode 104 and the negative electrode 106; and an electrolyte as described herein, within the battery case 102.

The positive electrode 104 contains an NCM-based positive electrode active material composed of Ni, Co, and Mn. In particular, in the present embodiment, the positive electrode active material included in the positive electrode 104 may preferably include only an NCM-based positive electrode active material containing 60 wt% or more of Ni.

The anode 106 contains one or more anode active materials selected from carbon (C) -based and silicon (Si) -based anode active materials.

The carbon (C) -based negative electrode active material may use at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fibers, graphitized medium carbon microbeads, fullerene, and amorphous carbon.

The silicon (Si) -based negative electrode active material includes silicon oxide, silicon particles, silicon alloy particles, and the like.

Meanwhile, each of the positive electrode 104 and the negative electrode 106 is prepared by mixing a conductive agent, a binder, and a solvent with its active material to prepare an electrode slurry, and then directly coating the electrode slurry on a current collector and drying. Aluminum (Al) may be used as a current collector. However, embodiments of the present invention are not limited thereto. The method of preparing the electrode is well known in the art to which the present invention pertains, and thus a detailed description thereof will be omitted in this specification.

The binder is used to well attach the active material particles to each other or to the current collector, and examples of the binder may use polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin, nylon, or the like, but the present invention is not limited thereto.

In addition, a conductive agent is used to impart conductivity to the electrode, and any conductive agent may be used as long as the conductive agent does not cause chemical changes in the battery and is made of a conductive material. For example, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black (Ketjen black), carbon fiber, and metal powder or metal fiber such as copper, nickel, aluminum, silver may be used as the conductive agent. In addition, a conductive material such as a polyphenylene derivative may be used alone or in a mixture of two or more.

The separator 108 prevents a short circuit between the positive electrode 104 and the negative electrode 106 and provides a moving path of lithium ions. The separator 108 may use a polyolefin-based polymer film such as polypropylene, polyethylene/polypropylene/polyethylene, polypropylene/polyethylene/polypropylene, or a multilayer film, a microporous film, a woven fabric, or a nonwoven fabric. In addition, a film in which a resin having excellent stability is coated on a porous polyolefin film may be used.

Hereinafter, the present invention will be described based on examples and comparative examples.

< experiment 1> experiment on relationship between voltage characteristics at room temperature (25 ℃) and half cell voltage based on the kind of functional additive

In order to understand the characteristics by voltage based on the kind of the functional additive added to the electrolyte, as shown in table 1 below, the initial capacity and the capacity retention ratio were measured at room temperature (25 ℃) while changing the kind and voltage of the functional additive, and the results thereof are shown in table 1, fig. 1, and fig. 2.

In this case, 0.5M LiPF was used as the lithium salt in the preparation of the electrolyte₆And 0.5M LiFSI, and the solvent used Ethylene Carbonate (EC): ethyl Methyl Carbonate (EMC): diethyl carbonate (DEC) in a weight ratio of 25:45: 30.

NCM622 serves as the positive electrode, and Li metal serves as the negative electrode.

[ Table 1]

From table 1, fig. 1 and fig. 2, it can be confirmed that the case of using FEMC according to the example as a functional additive increases the initial capacity compared to the case of VC using only a conventional general functional additive under the same voltage conditions.

In addition, it was confirmed that in the range of 4.2V to 4.5V, the battery capacity increased by the initial high capacity expression with an increase in voltage while maintaining a high capacity retention ratio in the case of using the same functional additive.

< experiment 2> Charge and discharge characteristics (half cell) experiment at high temperature (45 deg.C) based on the kind and addition amount of functional additive

In order to understand the charge and discharge characteristics based on the kind and addition amount of the functional additive added to the electrolyte, as shown in table 2 below, the initial capacity and the capacity retention rate were measured at a high temperature (45 ℃) while changing the kind and addition amount of the functional additive, and the results thereof are shown in table 2 and fig. 3.

[ Table 2]

From table 2 and fig. 3, it can be confirmed that when VC of a conventional general functional additive is used while FEMC functional additives according to examples are used and the addition amounts thereof are changed, the initial capacity increases as the FEMC addition amount increases.

In addition, it was confirmed that in the case of using FEMC according to the example as a functional additive, a high capacity retention rate was maintained as compared with the case of VC using only a conventional general functional additive.

< experiment 3> analysis experiment of positive electrode surface before and after charging and discharging according to kind of functional additive

In the case of using the electrolytic solutions according to Nos. 11 and 13, the surfaces before and after the charge and discharge experiments at high temperature (45 ℃ C.) were observed, and the results thereof are shown in FIG. 4.

From fig. 4, it was confirmed that in the case of No.11 using only the conventional general functional additive VC as the functional additive, cracks were generated in the positive electrode.

However, it was confirmed that in the case of No.13 using the functional additive FEMC according to the present invention as a functional additive, no cracks were generated in the positive electrode.

As apparent from the above description, according to embodiments of the present invention, long-term life characteristics of a lithium secondary battery may be improved by using an electrolyte containing a high-voltage additive.

In addition, in the case of using an electrolyte containing a high-voltage additive, the battery resistance of the lithium secondary battery is reduced, so that the output characteristics of the lithium secondary battery can be improved.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it will be understood by those skilled in the art that the present invention may be implemented in various other embodiments without changing the technical idea or features of the present invention.