Non-degradable electrolyte additive, electrolyte for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention relates to a non-degradable electrolyte additive, an electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery. The present invention provides a non-degradable electrolyte additive for a lithium secondary battery represented by the following chemical formula 1. The non-degradable electrolyte additive is adsorbed onto the electrode surface during the charging process of the battery and suppresses side reactions between the electrode and the electrolyte, thereby improving the durability of the battery and improving the lifespan characteristics of the battery. [Chemical Formula 1]

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery, and more specifically, to a non-degradable electrolyte additive that can be adsorbed onto the electrode surface during the charging process to suppress side reactions between the electrode and the electrolyte, an electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery. Background Technology

[0002] With the development of the information society and the expansion of mobile devices and ubiquitous computing networks, the demand for energy storage technology capable of supplying power to these electronic devices is increasing unprecedentedly. Among such energy storage devices, secondary battery technology holds technical importance as it is the most suitable for various energy storage and utilization applications. Its ability to be miniaturized allows for its application in personal IT devices, while its versatility enables its use in large-scale devices such as electric vehicles and power storage systems.

[0003] Among the relevant secondary battery technologies, lithium-ion batteries, which can theoretically be designed to possess high operating voltage and capacity, are receiving attention because they can be designed to have the highest energy density per weight and volume among commercially available secondary batteries. Generally, such lithium-ion batteries consist of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte that serves as a medium for transferring lithium ions, and a separator.

[0004] Since the electrolyte of a lithium-ion battery is a component that significantly affects the battery's stability and safety, extensive research is being conducted on materials and compositions to improve these critical performance aspects. Generally, it is desirable to use an electrolyte composed of a mixture of a lithium salt and an organic solvent that possesses high thermal and chemical stability while maintaining electrochemical stability within the operating voltage range of the positive and negative electrodes.

[0005] However, since the reduction voltage of conventional organic solvents is higher than the operating potential of the anode, such as graphite or silicon, reductive decomposition reactions occur on the surface of the anode during initial charging to form an organic / inorganic composite film, while a surface film is formed through oxidative decomposition reactions on the anode surface where the electrolyte is exposed to high voltage. Therefore, controlling these decomposition reactions and surface film formation reactions is a critical factor in improving battery performance.

[0006] The film formed by these decomposition reactions is specifically referred to as a Solid Electrolyte Interphase (SEI) when formed on the cathode surface and a Passivating Film when formed on the anode. Since the film formed on the electrode surface possesses the characteristic of allowing lithium ion movement while suppressing further decomposition reactions of the electrolyte, the proper formation of such a film is considered crucial for battery operation. For instance, if the SEI formed on the cathode surface is destroyed during the battery's charging and discharging process, the electrode interface becomes directly exposed to the electrolyte, which can lead to significant side reactions. These side reactions significantly degrade the battery's lifespan and resistance characteristics.

[0007] As such, the lifespan and resistance characteristics of a battery are largely determined by the characteristics of the film formed on the electrode surface; therefore, there is an urgent need for research on processes to form a film with more robust and superior characteristics during the first charging reaction, as well as research on electrolytes and electrolyte additives that enable efficient film formation. The process of forming such a surface film is called the activation process, and during this activation process, the formation of a suitable film on the surface of the positive and negative active materials is essential for improving various electrochemical performances, such as the battery's lifespan characteristics. Prior art literature

[0008] Published Patent Application No. 2022-0136524 (October 11, 2022) The problem to be solved

[0009] Therefore, the objective of the present invention is to provide a non-degradable electrolyte additive capable of suppressing side reactions caused by contact between the electrode and the electrolyte that may occur on the electrode surface during the charging and discharging process of the battery, an electrolyte for a lithium secondary battery containing the same, and a lithium secondary battery.

[0010] Meanwhile, the objectives of the present invention are not limited to the above objectives, and other unmentioned objectives will be clearly understood from the description below. means of solving the problem

[0011] To achieve the above objective, the present invention provides a non-degradable electrolyte additive for a lithium secondary battery represented by the following chemical formula 1.

[0012] [Chemical Formula 1]

[0013]

[0014] The above electrolyte additive may be tetrabutylammonium nonafluorobutanesulfonate represented by the following chemical formula 2.

[0015] [Chemical Formula 2]

[0016]

[0017] The present invention also provides an electrolyte for a lithium secondary battery comprising a lithium salt; and a non-degradable electrolyte additive represented by Formula 1.

[0018] The above electrolyte contains 0.01 to 10 wt% of the above non-degradable electrolyte additive.

[0019] The above lithium salt may include at least one of LiPF6, LiFSI, LiPO2F2, LiODFB, lithium nonafluoro-1-butanesulfonate(C4F9LiO3S), LiTFSI, LiBETI, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, and LiPF3(CF3)3.

[0020] The above electrolyte may further include at least one solvent selected from FEC, EC, DMC, DEC, DME, and EMC.

[0021] The present invention also provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator; and an electrolyte containing a lithium salt and a non-degradable electrolyte additive represented by Formula 1.

[0022] And the above-mentioned non-degradable electrolyte additive is adsorbed onto the surfaces of the positive and negative electrodes during the charging process of the battery, and is separated from the surfaces of the positive and negative electrodes during the discharging process of the battery. Effects of the invention

[0023] According to the present invention, a non-degradable electrolyte additive included in the electrolyte is adsorbed onto the surface of the electrode during the charging process, thereby suppressing direct contact between the electrode and the electrolyte even if the film formed on the electrode surface is damaged during the charging and discharging process. As a result, by suppressing adverse reactions between the electrode and the electrolyte, the durability and lifespan characteristics of the lithium secondary battery can be improved.

[0024] Meanwhile, the effects of the present invention are not limited to those described above, and other unmentioned effects may be disclosed directly or implicitly in the detailed description according to the embodiments of the present invention to be described below. Brief explanation of the drawing

[0025] FIG. 1 is a drawing showing a lithium secondary battery according to the present invention. Figure 2 is a graph showing the lifespan characteristics of a lithium secondary battery according to an example and a comparative example. Specific details for implementing the invention

[0026] It should be noted that in the following description, only the parts necessary for understanding the embodiments of the present invention are explained, and the description of other parts will be omitted to the extent that it does not deviate from the gist of the present invention.

[0027] The terms and words used in the specification and claims described below should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Accordingly, the embodiments described in this specification and the configurations illustrated in the drawings are merely preferred embodiments of the invention and do not represent all aspects of the technical spirit of the invention; therefore, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0028] Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings.

[0029] FIG. 1 is a drawing showing a lithium secondary battery according to the present invention.

[0030] Referring to FIG. 1, a lithium secondary battery (100) according to the present invention includes a positive electrode (10), a negative electrode (20), a separator (40), and an electrolyte (30).

[0031] The anode (10) comprises a lithium-transition metal oxide or a lithium-transition metal phosphate and may be a material containing 1M of lithium per 1M. The lithium-transition metal oxide may be a composite oxide of lithium and at least one transition metal selected from the group consisting of cobalt, manganese, nickel, and aluminum. For example, the lithium-transition metal oxide is Li(Ni 1-x-yCo x Mn y )O2(0≤x≤1, 0≤y≤1, 0≤x+y≤1), Li(Ni 1-x-y Co x Al y )O2(0≤x≤1, 0 <y≤1, 0<x+y≤1), 또는 Li(Ni 1-x-y Co x Mn y It may be )2O4(0≤x≤1, 0≤y≤1, 0≤x+y≤1). The lithium-transition metal phosphate may be a complex phosphate of lithium with at least one transition metal selected from the group consisting of iron, cobalt, and nickel. For example, as an example, the lithium-transition metal phosphate is Li(Ni 1-x-y Co x Fe y )PO4(0≤x≤1, 0≤y≤1, 0≤x+y≤1) may be possible.

[0032] The cathode (20) may include a carbon-based material, a silicon-based material, or a lithium-based material. For example, the cathode (20) may include one of graphite, lithium, a lithium alloy, a lithium titanate, silicon, a lithium / silicon alloy, a tin oxide, a lithium intermetallic compound, or a mixture thereof, but is not limited thereto.

[0033] A film (11, 21) is formed on each of the positive electrode (10) and the negative electrode (20). On the surface of the negative electrode (20), SEI is formed as the film (21). On the surface of the positive electrode (10), a passivating film is formed as the film (11).

[0034] The separator (40) separates the negative electrode (20) and the positive electrode (10) and provides a passage for the movement of lithium ions. Generally, any separator (40) used in a lithium secondary battery can be used without any special limitations. It is preferable that the separator (40) has low resistance to the movement of ions of the electrolyte (30) and excellent moisture retention of the electrolyte. For example, the separator (40) may include polyethylene, polypropylene, or a copolymer of polyethylene and polypropylene, and a multilayer film of two or more layers thereof may be used, but is not limited thereto.

[0035] And the electrolyte (30) impregnates the negative electrode (20), the positive electrode (10), and the separator (40), and serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0036] This electrolyte (30) includes a lithium salt (31) and a non-degradable electrolyte additive (33), and further includes a solvent.

[0037] As the lithium salt (31), at least one of LiPF6, LiFSI, LiPO2F2, LiODFB, lithium nonafluoro-1-butanesulfonate (C4F9LiO3S), LiTFSI, LiBETI, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, and LiPF3(CF3)3 may be used. The lithium salt (31) may be included in the electrolyte (30) at a concentration of 0.1M to 3M.

[0038] Carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, protic, or aprotic solvents may be used. Carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester-based solvents that may be used include n-methyl acetate (MA), n-ethyl acetate (EA), n-propyl acetate (PA), dimethyl acetate (DME), methylpropionate (MP), ethylpropionate (EP), γ-butyrolactone (GBL), decanolide, valerolactone, mevalonolactone, and caprolactone. Ether-based solvents that may be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, while ketone-based solvents that may be used include cyclohexanone. Additionally, alcohol-based solvents that may be used include ethyl alcohol and isopropyl alcohol, and protic solvents that may be used include diglyme (DGM) and tetraglyme (TGM). For example, at least one selected from FEC, EC, DMC, DEC, DME, and EMC may be used as a solvent.

[0039] And as a non-degradable electrolyte additive (33), an electrolyte additive represented by the following chemical formula 1 is used.

[0040] [Chemical Formula 1]

[0041]

[0042] For example, the non-degradable electrolyte additive (33) may be tetrabutylammonium nonafluorobutanesulfonate represented by the following chemical formula 2.

[0043] [Chemical Formula 2]

[0044]

[0045] The electrolyte (30) according to the present invention may contain 0.01 to 10 wt.% of a non-degradable electrolyte additive (33). If the non-degradable electrolyte additive (33) according to the present invention is not used, or if the content is less than 0.01 wt.% even when used, the improvement in the electrochemical characteristics of the battery due to the use of the non-degradable electrolyte additive (33) may be negligible. Conversely, if the content of the non-degradable electrolyte additive (33) exceeds 10 wt%, the content of the lithium salt (31) in the electrolyte (30) decreases, and a problem may occur in which the inherent function of the electrolyte (30) is degraded. Preferably, in the electrolyte (30), the content of the non-degradable electrolyte additive (33) may be 0.1 to 7 wt.%.

[0046] The non-degradable electrolyte additive (33) according to the present invention is adsorbed on the surface of the electrodes (10, 20), that is, on the surface of the positive electrode (10) and the negative electrode (20), during the charging process. That is, the non-degradable electrolyte additive (33) is adsorbed on the film (11, 21) formed on the surface of the electrodes (10, 20) during the charging process. The non-degradable electrolyte additive (33) adsorbed on the surface of the electrodes (10, 20) suppresses side reactions caused by contact between the electrodes (10, 20) and the electrolyte (30) that may occur on the surface of the electrodes (10, 20) during the charging process of the battery. In FIG. 1, the solid line arrow indicates that the non-degradable electrolyte additive (33) within the electrolyte (30) moves to the surface of the negative electrode (20) during the charging process.

[0047] During the discharge process, the non-degradable electrolyte additive (33) adsorbed on the surface of the electrode (10, 20) is separated from the surface of the electrode (10, 20). In FIG. 1, the dotted arrow indicates that the non-degradable electrolyte additive (33) adsorbed on the surface of the cathode (20) during the discharge process is separated and moves into the electrolyte (30).

[0048] In this way, the non-degradable electrolyte additive (33) included in the electrolyte (30) is adsorbed onto the surface of the electrode (10, 20) during the charging process, thereby suppressing direct contact between the electrode (10, 20) and the electrolyte (30) even if the film (11, 21) formed on the surface of the electrode (10, 20) is damaged during the charging and discharging process. As a result, by suppressing side reactions between the electrode (10, 20) and the electrolyte (30), the durability and lifespan characteristics of the lithium secondary battery (100) can be improved.

[0049] [Examples and Comparative Examples]

[0050] In order to confirm the electrochemical characteristics of the non-degradable electrolyte additive for a lithium secondary battery according to the present invention, the electrolytes according to Example 1, Comparative Example 1, and Comparative Example 2, and a lithium secondary battery containing the electrolytes were prepared.

[0051] The electrolytes according to Comparative Example 1, Comparative Example 2, and Example 1 are as follows.

[0052] Comparative Example 1: 1.0 M LiPF6, EC / EMC (3:7 =v / v) 2.0 wt.% VC

[0053] Comparative Example 2: 1.0 M LiPF6, EC / EMC (3:7 =v / v) 2.0 wt.% VC + 0.5 wt.% VEC

[0054] Example 1: 1.0 M LiPF6, EC / EMC (3:7 =v / v) 2.0 wt.% VC + 0.5 wt.% Tetrabutylammonium nonafluorobutanesulfonate

[0055] In Comparative Example 1, an electrolyte without an electrolyte additive was used. In Comparative Example 2, an electrolyte containing vinyl ethylene carbonate (VEC) as an electrolyte additive was used. And in Example 1, an electrolyte containing the non-degradable electrolyte tetrabutylammonium nonafluorobutanesulfonate as an electrolyte additive was used.

[0056] Then, pouch cell type lithium secondary batteries according to Comparative Example 1, Comparative Example 2, and Example 1 were manufactured using graphite / NCM811 as the cathode / anode.

[0057] The lifespan characteristics of the lithium secondary batteries according to Comparative Example 1, Comparative Example 2, and Example 1 manufactured as described above were evaluated, and the results are shown in FIG. 2. FIG. 2 is a graph showing the lifespan characteristics of the lithium secondary batteries according to the Example and Comparative Example. Here, the lifespan characteristics evaluation was performed under conditions of 0.1C, 45°C, and 2.5~4.35V.

[0058] Referring to FIG. 2, it can be seen that Example 1 has improved lifespan characteristics compared to Comparative Example 1 and Comparative Example 2.

[0059] The improvement in the lifespan characteristics of the lithium secondary battery according to Example 1 is attributed to the use of a non-degradable electrolyte, which leads to improved durability of the battery by suppressing side reactions between the electrode and the electrolyte.

[0060] Meanwhile, the embodiments disclosed in this specification and drawings are merely specific examples provided to aid understanding and are not intended to limit the scope of the invention. It is obvious to those skilled in the art that other variations based on the technical concept of the invention are possible in addition to the embodiments disclosed herein. Explanation of the symbols

[0061] 10 : Anode 20: Cathode 11, 21: membrane 30: Electrolytes 31: Lithium salt 33: Non-degradable electrolyte additive 40 : Separator 100 : Lithium-ion battery

Claims

Claim 1 An electrolyte for a lithium secondary battery comprising: a lithium salt; and a non-degradable electrolyte additive represented by the chemical formula 1 below; wherein the non-degradable electrolyte additive is included in an amount of 0.01 to 10 wt% based on the total weight of the electrolyte, and wherein the non-degradable electrolyte additive is adsorbed onto the surfaces of the positive and negative electrodes during the charging process of the lithium secondary battery to form a protective film that suppresses electrolyte decomposition side reactions, and exhibits reversible adsorption-desorption behavior by separating from the surfaces of the positive and negative electrodes during the discharging process of the lithium secondary battery, thereby improving the lifespan characteristics of the lithium secondary battery. [Chemical Formula 1] Claim 2 delete Claim 3 delete Claim 4 An electrolyte for a lithium secondary battery according to claim 1, characterized in that the non-degradable electrolyte additive is tetrabutylammonium nonafluorobutanesulfonate represented by the following chemical formula 2. [Chemical Formula 2] Claim 5 An electrolyte for a lithium secondary battery according to claim 4, characterized in that the non-degradable electrolyte additive is included in an amount of 0.1 to 7 wt% based on the total weight of the electrolyte. Claim 6 The electrolyte for a lithium secondary battery according to claim 1, wherein the lithium salt comprises at least one of LiPF6, LiFSI, LiPO2F2, LiODFB, lithium nonafluoro-1-butanesulfonate(C4F9LiO3S), LiTFSI, LiBETI, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, and LiPF3(CF3)3. Claim 7 An electrolyte for a lithium secondary battery according to claim 1, wherein the electrolyte further comprises at least one solvent selected from FEC, EC, DMC, DEC, DME, and EMC. Claim 8 A lithium secondary battery comprising: a positive electrode; a negative electrode; a separator; and an electrolyte containing a lithium salt and a non-degradable electrolyte additive represented by the following chemical formula 1; wherein the non-degradable electrolyte additive is included in an amount of 0.01 to 10 wt% based on the total weight of the electrolyte, and wherein the non-degradable electrolyte additive is adsorbed onto the surfaces of the positive electrode and the negative electrode during the charging process of the lithium secondary battery to form a protective film that suppresses electrolyte decomposition side reactions, and exhibits reversible adsorption-desorption behavior by being separated from the surfaces of the positive electrode and the negative electrode during the discharging process of the lithium secondary battery, thereby improving the lifespan characteristics of the lithium secondary battery. [Chemical Formula 1] Claim 9 A lithium secondary battery according to claim 8, characterized in that the non-degradable electrolyte additive is tetrabutylammonium nonafluorobutanesulfonate represented by the following chemical formula 2. [Chemical Formula 2] Claim 10 A lithium secondary battery according to claim 9, characterized in that the non-degradable electrolyte additive is included in an amount of 0.1 to 7 wt% based on the total weight of the electrolyte. Claim 11 A lithium secondary battery according to claim 8, wherein the lithium salt comprises at least one of LiPF6, LiFSI, LiPO2F2, LiODFB, lithium nonafluoro-1-butanesulfonate(C4F9LiO3S), LiTFSI, LiBETI, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, and LiPF3(CF3)3. Claim 12 A lithium secondary battery according to claim 8, wherein the electrolyte further comprises at least one solvent selected from FEC, EC, DMC, DEC, DME, and EMC. Claim 13 delete

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