Electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same

Abstract

The present invention relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same. The electrolyte solution for a lithium secondary battery includes a lithium salt, a solvent, and an anode additive including 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-carbonitrile represented by the following Chemical Formula 1: [Chemical Formula 1]

Description

Technical Field

[0001] The present invention relates to an electrolyte solution for lithium secondary battery packs and a lithium secondary battery pack including the electrolyte solution. Background Technology

[0002] The statements in this section are provided only as background information in relation to the present invention and may not constitute prior art.

[0003] Lithium-ion battery packs are used as power sources for smartphones, laptops, hybrid vehicles, and electric vehicles. Lithium-ion battery packs are rechargeable and offer advantages over traditional lead-acid and nickel / metal hydride battery packs due to their high energy density, high power output, and fast charging speed.

[0004] A lithium-ion secondary battery pack is constructed to include a cathode that provides lithium during charging, an anode that receives lithium, an electrolyte that serves as a channel for lithium-ion movement, and a separator that prevents contact between the cathode and anode. The lithium-ion secondary battery pack generates electrical energy by utilizing changes in chemical potential when lithium ions stored in the anode are deintercalated and intercalated into the cathode.

[0005] When lithium-ion battery packs are repeatedly charged and discharged, the structures of the cathode and anode change from their initial state due to the insertion and extraction of lithium ions, resulting in a decrease in the battery pack's capacity and power output. Therefore, protecting the cathode and anode to increase battery pack life and suppress the decrease in power output is a major challenge facing the industry.

[0006] During the initial charging of a lithium-ion secondary battery pack, an irreversible reaction of excess charge occurs between the anode / cathode and the electrolyte solution. This irreversible reaction forms a solid electrolyte interface (SEI) on the anode surface and a cathode protective film on the cathode surface. These films serve as channels for lithium ions and simultaneously inhibit deformation of the anode and cathode active materials and suppress electrolyte solution decomposition during charging and discharging.

[0007] Therefore, when a SEI and a cathode protection film with high stability and low resistance are formed, the lifespan of the lithium secondary battery pack can be increased and the reduction in power output can be suppressed.

[0008] Detailed information is provided as background art to better understand the background of the present invention, and the described details should not be regarded as corresponding to conventional art already known to those skilled in the art. Summary of the Invention

[0009] The present invention provides an electrolyte solution for lithium secondary battery packs and a lithium secondary battery pack including the electrolyte solution, wherein the electrolyte solution can increase the lifespan of the lithium secondary battery pack.

[0010] One embodiment of the present invention provides an electrolyte solution for a lithium secondary battery pack, comprising a lithium salt, a solvent, and an additive, wherein the additive comprises 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-nitrile represented by the following chemical formula 1:

[0011] [Chemical Formula 1]

[0012]

[0013] Based on the total weight of the electrolyte solution, the amount of the compound represented by Formula 1 can be from 0.5% by weight to 1.5% by weight.

[0014] Based on the total weight of the electrolyte solution, the electrolyte solution may further include 0.5% to 3.0% by weight of vinyl chloride (VC) as an additive.

[0015] The lithium salt can be any single compound or a mixture of two or more compounds, wherein the compound is selected from LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N(LiFSI), and (CF3SO2)2NLi.

[0016] The solvent can be any single substance or a mixture of two or more substances, and the substance is selected from carbonate solvents, ester solvents, ether solvents and ketone solvents.

[0017] Another embodiment of the present invention provides a lithium secondary battery pack comprising the above-described electrolyte solution, cathode, anode, and separator, wherein the cathode comprises a cathode active material containing Ni, Co, and Mn, the anode comprises a carbon (C) based anode active material, and the separator is inserted between the cathode and the anode.

[0018] During charging and discharging, with a discharge terminal voltage of 2.5V, a charging terminal voltage of 4.2V, a temperature of 45℃, and a C-rate of 1C, the lithium secondary battery pack can have a discharge retention rate of 84.6% or more after 50 cycles.

[0019] According to the present invention, additives that form CEI (cathode electrolyte interface) on the cathode and SEI (solid electrolyte interface) on the anode are added to the electrolyte solution, thereby increasing the high-temperature life of the lithium secondary battery pack.

[0020] Other areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0021] To better understand the present invention, various embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0022] Figure 1 and Figure 2 A graph illustrating the measurement results of the performance depending on the additives present in the embodiments and comparative examples according to the present invention.

[0023] The figures described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Detailed Implementation

[0024] The following description is merely exemplary and is not intended to limit the invention, application, or use. It should be understood that throughout the figures, corresponding reference numerals denote the same or corresponding parts and features.

[0025] In the following detailed description of various embodiments of the invention with reference to the accompanying drawings, however, the invention is not limited to the following embodiments and can be modified to have various different embodiments. These embodiments are provided to complete the disclosure of the invention and to fully describe the invention to those skilled in the art.

[0026] According to one embodiment of the present invention, the electrolyte solution for a lithium secondary battery pack is a material used to form an electrolyte applied to the lithium secondary battery pack, and includes a lithium salt, a solvent, and an anode additive.

[0027] The lithium salt can be any single compound or a mixture of two or more compounds, wherein the compound is selected from LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N(LiFSI), and (CF3SO2)2NLi.

[0028] The solvent can be any single substance or a mixture of two or more substances, and the substance is selected from carbonate solvents, ester solvents, ether solvents and ketone solvents.

[0029] Examples of carbonate solvents may include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), fluoroethyl ester carbonate (FEC), and vinylene carbonate (VC). Examples of ester solvents may include, but are not limited to, γ-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, and n-propyl acetate. Examples of ether solvents may include, but are not limited to, dibutyl ether.

[0030] The solvent may further include aromatic hydrocarbon organic solvents. Specific examples of the aromatic hydrocarbon organic solvents include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, etc., which can be used alone or in combination.

[0031] Meanwhile, the additive added to the electrolyte solution according to one embodiment of the present invention may include 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-nitrile represented by the following chemical formula 1:

[0032] [Chemical Formula 1]

[0033]

[0034] The additive is used to form an SEI (solid electrolyte interface) on the anode and an CEI (cathode electrolyte interface) on the cathode, thereby increasing the battery pack's lifespan. The additive is preferably used in an amount of 1.5% by weight or less, more preferably 0.5% to 1.0% by weight, based on the total weight of the electrolyte solution.

[0035] If the amount of additive exceeds 1.5% by weight, excessive formation of the CEI and SEI films may occur, increasing battery resistance and potentially reducing battery power output. On the other hand, if the amount of anode additive is less than 0.5% by weight, insufficient formation of the CEI and SEI films may occur, which could significantly reduce battery life.

[0036] Specifically, when the additive contains polar or unsaturated functional groups (e.g., double or triple bonds at the ends of the additive molecule), it can exhibit a strong ability to accept electrons from the anode compared to using polar solvents, and thus can be reduced at low voltages. Therefore, the additive can form bonds on the anode surface through direct reaction with the carbon anode, through reaction with functional groups present on the anode surface, or by adsorption onto the anode surface, thereby forming an SEI on the anode surface.

[0037] In addition, when the additive contains polar functional groups such as nitrile groups, it can form bonds with transition metals (such as cobalt) at the cathode to obtain complex structures.

[0038] It was confirmed that the additive represented by chemical formula 1, namely the benzyl nitrile (cyanophenyl group) moiety, is involved in the formation of SEI, and the 1,2,3-triazol-4-nitrile moiety is involved in the formation of CEI.

[0039] The resulting SEI formed on the anode thus becomes a channel for lithium-ion movement, suppressing chemical reactions between the electrolyte solution and the electrode, and inhibiting anode degradation during charging and discharging, thereby improving the lifespan and high-temperature stability of the lithium secondary battery pack. The CEI formed on the cathode inhibits the dissolution of transition metal ions (e.g., Ni, CO, Mn, etc.) from the cathode active material into the electrolyte solution, thereby suppressing rapid capacity reduction and reduced battery life. Furthermore, it allows the use of transition metals that are not yet routinely used in cathode active materials due to dissolution.

[0040] In addition to the electrolyte solution described above, a lithium secondary battery pack according to one embodiment of the present invention is configured to include a cathode, an anode, and a separator.

[0041] The cathode comprises an NCM-based cathode active material containing Ni, Co, and Mn. Specifically, in this embodiment, the cathode active material included in the cathode preferably consists only of an NCM-based cathode active material containing 60% by weight or more Ni.

[0042] The anode preferably comprises a carbon (C) based anode active material.

[0043] Carbon (C)-based anode active materials may include at least one material selected from the following: artificial graphite, natural graphite, graphitized carbon fibers, graphitized mesophase carbon microspheres, fullerenes, and amorphous carbon.

[0044] Simultaneously, an electrode slurry is prepared by mixing the corresponding active material with a conductive material, a binder, and a solvent. This slurry is then applied directly to a current collector and dried to manufacture each of the cathode and anode. Here, the current collector used can be aluminum (Al), but is not limited to it. Since this method of manufacturing electrodes is well known in the art, its detailed description will be omitted herein.

[0045] Adhesives are used to adhere active material particles to each other or to adhere active material particles to a current collector. Examples of adhesives include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0046] Furthermore, conductive materials are used to impart conductivity to the electrodes, and any material can be used as long as it does not cause any chemical changes in the constructed battery pack and is conductive. Examples of conductive materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, etc., with examples of metals such as copper, nickel, aluminum, and silver in metal powders or metal fibers, as well as conductive materials such as polyphenylene derivatives, which can be used alone or in combination of two or more.

[0047] The separator suppresses short circuits between the cathode and anode and provides a channel for lithium-ion movement. Examples of separators may include those known in the art, including polyolefin polymer membranes such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, polypropylene / polypropylene / polypropylene, etc., their multilayer, microporous membranes, woven fabrics and nonwoven fabrics. Furthermore, membranes obtained by coating porous polyolefin membranes with a resin having excellent stability can be used.

[0048] A better understanding of the present invention can be obtained through the following embodiments and comparative examples.

[0049] <Test 1> Performance test depending on the type of additive

[0050] To evaluate the high-temperature lifetime, which depends on the type of additive added to the electrolyte solution, different types of additives were used to measure the high-temperature lifetime, as shown in Table 1 below. The results are shown in Table 1 and... Figure 1 As shown in the image.

[0051] In the preparation of the electrolyte solution, the lithium salt used is 0.5M LiPF60.5LiFSI, and the solvent used is a solvent mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a weight ratio of 25:45:30.

[0052] The cathode used was NCM811, and the anode used was graphite.

[0053] Cut-off: 2.5-4.2V

[0054] C-rate: 1C

[0055] Temperature: 45℃ (high temperature)

[0056] [Table 1]

[0057]

[0058] From Table 1 and Figure 1 It is evident that using 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazol-4-nitrile (represented by Formula 1) and VC as additives (Example 1) resulted in a longer measured high-temperature lifetime compared to using VC alone as an additive (Comparative Example 1). Furthermore, the high-temperature lifetime was equivalent to that achieved using LiPO2F2 (Comparative Example 2). Based on the weight of the electrolyte solution, the additive VC can typically be used in amounts ranging from 0.5% to 3.0% by weight.

[0059] <Test 2> Performance test depending on the weight ratio of the anode additive

[0060] In Test 2, to evaluate the high-temperature lifetime depending on the weight ratio of additives of Formula 1, the high-temperature lifetime was measured using additives of Formula 1 at different weight ratios as shown in Table 2 below. The results are shown in Table 2 and... Figure 2 As shown in the image.

[0061] In the preparation of the electrolyte solution, the lithium salt used is 0.5M LiPF60.5LiFSI, and the solvent used is a solvent mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a weight ratio of 25:45:30.

[0062] The cathode used was NCM811, and the anode used was graphite.

[0063] Cut-off: 2.5-4.2V

[0064] C-rate: 1C

[0065] Temperature: 45℃ (high temperature)

[0066] [Table 2]

[0067]

[0068]

[0069] From Table 2 and Figure 2 It is evident that the high-temperature life increases when the additive of Formula 1 is used. Specifically, the high-temperature life is longest when the amount of additive of Formula 1 is 1.0% by weight (Example 2), and the high-temperature life is longer when the amount of additive is 0.5% by weight (Example 1) than when the amount of additive is 1.5% by weight (Example 3).

[0070] Although preferred embodiments of the invention have been disclosed for illustrative purposes with reference to the accompanying drawings, the invention is not limited thereto but is defined by the appended claims. Therefore, those skilled in the art will understand that various modifications, additions, and substitutions can be made without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims

1. An electrolyte solution for a lithium secondary battery pack, the electrolyte solution comprising: Electrolyte salts; Organic solvents; and The additive comprises 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-nitrile represented by the following chemical formula 1: [Chemical Formula 1] ； The additive further comprises, based on the total weight of the electrolyte solution, 0.5% to 3.0% by weight of vinyl chloride; and based on the total weight of the electrolyte solution, 0.5% to 1.5% by weight of 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-onitrile.

2. The electrolyte solution for lithium secondary battery packs according to claim 1, wherein, Based on the total weight of the electrolyte solution, the amount of 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-nitrile is 0.5% to 1.0% by weight.

3. The electrolyte solution for lithium secondary battery packs according to claim 1, wherein, The electrolyte salt is any single compound or a mixture of two or more compounds, wherein the compound is selected from LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N(LiFSI), and (CF3SO2)2NLi.

4. The electrolyte solution for lithium secondary battery packs according to claim 1, wherein, The organic solvent is any one substance or a mixture of two or more substances, and the substance is selected from carbonate solvents, ether solvents and ketone solvents.

5. A lithium secondary battery pack comprising an electrolyte solution, wherein the electrolyte solution comprises: Electrolyte salts; Organic solvents, and The additive comprises 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-nitrile, represented by the following chemical formula 1. [Chemical Formula 1] ； The additive further comprises, based on the total weight of the electrolyte solution, 0.5% to 3.0% by weight of vinyl chloride; and based on the total weight of the electrolyte solution, 0.5% to 1.5% by weight of 5-(4-cyanophenyl)-1-(4-fluorobenzyl)-1H-1,2,3-triazole-4-onitrile.

6. The lithium secondary battery pack according to claim 5, further comprising: The cathode comprises a cathode active material containing Ni, Co, and Mn; Anode, which includes carbon-based anodic active materials; A diaphragm is inserted between the cathode and the anode.

7. The lithium secondary battery pack according to claim 6, wherein, The lithium secondary battery pack is configured to have a discharge retention rate of 84.6% or more after 50 cycles under the conditions of a discharge terminal voltage of 2.5 V, a charging terminal voltage of 4.2 V, a temperature of 45°C, and a C-rate of 1C during charging and discharging.

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