Electrolyte solution for lithium secondary batteries and lithium secondary batteries containing the electrolyte solution

Abstract

This invention relates to an electrolyte solution for lithium secondary batteries and a lithium secondary battery comprising the electrolyte solution. It discloses an electrolyte solution for lithium secondary batteries capable of increasing the lifespan of lithium secondary batteries and a lithium secondary battery comprising the electrolyte solution. An electrolyte solution for lithium secondary batteries is also provided, comprising a lithium salt, a solvent, and an allyl (4-nitrophenyl) carbonate represented by Formula 1, [Formula 1]

Description

Technical Field

[0001] This invention relates to an electrolyte solution for lithium secondary batteries and a lithium secondary battery containing the electrolyte solution. In particular, the electrolyte solution for lithium secondary batteries can increase the lifespan of lithium secondary batteries. Background Technology

[0002] A lithium-ion secondary battery is an energy storage device comprising: a positive electrode for supplying lithium, a negative electrode for receiving lithium during charging, an electrolyte that acts as a medium for transferring lithium ions, and a separator for separating the positive and negative electrodes from each other. When lithium ions are inserted into or extracted at the positive or negative electrode, the lithium-ion secondary battery generates electrical energy and stores this energy through changes in chemical potential.

[0003] These lithium-ion batteries have been primarily used in portable electronic devices, but with the recent commercialization of electric vehicles (EVs) and hybrid electric vehicles (HEVs), they have recently been used as energy storage devices for these vehicles.

[0004] Meanwhile, research has been conducted on increasing the energy density of lithium secondary batteries to increase the driving range of electric vehicles, and the energy density of lithium secondary batteries can be increased by increasing the capacity of the positive electrode.

[0005] The increase in positive electrode capacity can be achieved by Ni enrichment, which is a method of increasing the Ni content of Ni-Co-Mn-based oxides that constitute the positive electrode active material, or by increasing the positive electrode charging voltage.

[0006] However, Ni-enriched Ni-Co-Mn-based oxides have high interfacial reactivity and unstable crystal structures, which adversely accelerate degradation during cycling and make it difficult to ensure long-life performance.

[0007] The information disclosed in the background section is intended only to enhance the understanding of the background technology of this invention, and therefore the information it may contain does not constitute prior art known to those skilled in the art in this country. Summary of the Invention

[0008] In particular, an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the electrolyte are provided, which can increase the life of the lithium secondary battery.

[0009] On one hand, an electrolyte solution for lithium secondary batteries is provided, comprising a lithium salt, a solvent, and an allyl (4-nitrophenyl) carbonate represented by Formula 1 below.

[0010] [Formula 1]

[0011]

[0012] The electrolyte solution may suitably include an amount of less than 3.0% by weight of allyl (4-nitrophenyl) carbonate based on the total weight of the electrolyte solution.

[0013] Preferably, the electrolyte solution may include about 0.5 to 2.0% by weight of allyl (4-nitrophenyl) carbonate based on the total weight of the electrolyte solution.

[0014] Lithium salts may suitably include those selected from LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 One or more of the following: LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N(LiFSI), and (CF3SO2)2NLi.

[0015] The solvent may suitably include one or more selected from carbonate solvents, ester solvents, ether solvents and ketone solvents.

[0016] The electrolyte solution for lithium secondary batteries may further contain a positive electrode additive, wherein the positive electrode additive is LiPO2F2.

[0017] On the other hand, a lithium secondary battery is provided, which includes the electrolyte solution as described above. Furthermore, the lithium secondary battery may further include: a positive electrode comprising a positive electrode active material containing Ni, Co, and Mn; a negative electrode comprising a carbon (C)-based negative electrode active material; and a separator situated between the positive and negative electrodes.

[0018] Lithium-ion rechargeable batteries can have a discharge retention rate of over 94% after 200 cycles, each cycle consisting of a 0.5C cc / cv charge and a 0.5C cc / cv discharge at 45°C and 2.5 to 4.2V (cutoff) conditions.

[0019] A vehicle is also provided that includes the lithium secondary battery disclosed herein.

[0020] Other aspects of the invention are disclosed below. Attached Figure Description

[0021] The above and other objects, features, and advantages of the invention will become clearer from the following detailed description presented in conjunction with the accompanying drawings, in which:

[0022] Figure 1A graph illustrating the evaluation results of the properties after the addition of the additive in Experiment 1 according to an exemplary embodiment of the present invention.

[0023] Figure 2 A graph illustrating the evaluation results of the properties after the addition of the additive in Experiment 2 according to an exemplary embodiment of the present invention.

[0024] Figure 3 A graph illustrating the evaluation results of the properties after the addition of the additive in Experiment 3 according to an exemplary embodiment of the present invention. Detailed Implementation

[0025] Reference will now be made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. However, the invention is not limited to these embodiments and may be implemented in various different forms. These embodiments are provided merely to fully illustrate the invention and to enable those skilled in the art to fully understand its scope.

[0026] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of the stated features, values, steps, operations, elements, and / or components, but do not exclude the presence or inclusion of one or more other features, values, steps, operations, elements, components, and / or groups thereof. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0027] Unless otherwise stated or obvious from the context, the term "about" as used herein is understood to mean within the normal tolerance range in the field, such as within 2 standard deviations of the mean. "About" can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the specified value. All numerical values ​​provided herein are modified by the term "about" unless clearly stated from the context.

[0028] It should be understood that the term “vehicle” or “of a vehicle” or other similar terms used herein generally include motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, vessels including various boats and ships, aircraft, etc., and also include hybrid vehicles, electric vehicles, fuel vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources).

[0029] It should also be understood that the term "solution" as used in this article includes not only actual solutions but also dispersions and other fluid mixtures.

[0030] On one hand, the electrolyte solution for lithium secondary batteries can be the material constituting an electrolyte suitable for lithium secondary batteries, and includes lithium salts, solvents, and negative electrode additives. On the other hand, the electrolyte solution may further contain positive electrode additives.

[0031] Lithium salts may suitably include those selected from LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, and LiB. 10 Cl 10 One or more of the following: LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N(LiFSI), and (CF3SO2)2NLi.

[0032] Lithium salts can exist in electrolyte solutions at concentrations of approximately 0.1 to 1.2 M.

[0033] The solvent may suitably include one or more selected from carbonate solvents, ester solvents, ether solvents and ketone solvents.

[0034] For example, carbonate solvents may suitably include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), etc. Additionally, solvents may suitably include ester solvents (e.g., γ-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, or n-propyl acetate), or ether solvents (e.g., dibutyl ether), but are not limited thereto.

[0035] In addition, the solvent may further include aromatic hydrocarbon-based organic solvents. Aromatic hydrocarbon-based organic solvents may include: benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, mesitylene, etc., and the solvent may be used alone or in combination.

[0036] In addition, LiPO2F2 can be used as a positive electrode additive.

[0037] Meanwhile, allyl (4-nitrophenyl) carbonate, represented by Formula 1 below, can be used as a negative electrode additive added to the electrolyte solution according to an embodiment of the present invention.

[0038] [Formula 1]

[0039]

[0040] Negative electrode additives can improve low resistance characteristics and extend service life by forming a solid electrolyte interphase (SEI) on the negative electrode. The negative electrode additive can be appropriately added in an amount of less than about 3.0% by weight relative to the total weight of the electrolyte solution, or particularly in an amount of about 0.5 to 2.0% by weight.

[0041] When the amount of negative electrode additive exceeds approximately 3.0% by weight, the coating on the negative electrode may over-form, adversely leading to high battery resistance and thus reduced battery power. Specifically, when the amount of negative electrode additive is less than approximately 0.5% by weight, the SEI (Self-Intercepting Intake) acting as a protective film for the negative electrode may not form sufficiently, resulting in a significantly shortened battery life. When the amount of negative electrode additive exceeds approximately 2.0% by weight, the battery power required by the vehicle may decrease.

[0042] In addition to the electrolyte solution mentioned above, lithium secondary batteries also include a positive electrode, a negative electrode, and a separator.

[0043] The positive electrode may suitably include an NCM-type positive electrode active material containing Ni, Co, and Mn. In particular, the positive electrode active material included in the positive electrode in this embodiment preferably comprises only an NCM-type positive electrode active material, which contains more than 60% by weight of Ni based on the total weight of the NCM-type positive electrode active material.

[0044] In addition, the negative electrode may appropriately contain only carbon (C) type negative electrode active materials, or may contain carbon (C) type negative electrode active materials.

[0045] Carbon (C) type anode active materials may include at least one material selected from artificial graphite, natural graphite, graphitized carbon fiber, graphitized carbon microspheres, fullerene and amorphous carbon.

[0046] Simultaneously, by mixing each active material with a conductive material, a binder, and a solvent to prepare an electrode slurry, and then directly coating the current collector with the electrode slurry followed by drying, positive and negative electrodes can be manufactured. In this case, aluminum (Al) can be used as the current collector, but the invention is not limited thereto. Since this method of manufacturing electrodes is well known in the art, its detailed description will be omitted.

[0047] Adhesives can promote adhesion between particles of each active material or adhesion of particles of the active material to the current collector. For example, adhesives may suitably 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, styrene-butadiene rubber, epoxy resin, nylon, etc.

[0048] Furthermore, conductive materials can impart conductivity to the electrodes, and any conductive material can be used as long as it does not cause any chemical changes in the battery to be manufactured. Examples of conductive materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powders (such as copper, nickel, aluminum, and silver powders), metal fibers, etc. Additionally, conductive materials (such as polyphenylene derivatives) can be used alone or in combination.

[0049] The separator prevents short circuits between the positive and negative electrodes and provides a channel for lithium ions. Such separators may suitably include one or more of the following: polyolefin-based polymer membranes (e.g., polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, and polypropylene / polyethylene / polypropylene), as well as their multilayer membranes, microporous membranes, woven fabrics, and nonwoven fabrics. Alternatively, porous polyolefin membranes coated with resins exhibiting excellent stability can be used.

[0050] Example

[0051] In the following description, the invention will be described with reference to embodiments and comparative examples according to the invention.

[0052] Experiment 1: Characteristics depending on the type of negative electrode additive

[0053] To determine various properties depending on the type of negative electrode additive added to the electrolyte solution, ionic conductivity, initial cell resistance, high-temperature durability, and high-rate characteristics were measured when the type of negative electrode additive was varied as shown in Table 1 below, and the results are shown in Table 2 and... Figure 1 .

[0054] At this point, the lithium salts used to prepare the electrolyte solution are 0.5M LiPF6 and 0.5M LiFSI, and the solvent used is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 25:45:30. Furthermore, LiPO2F2 is used as the positive electrode additive.

[0055] NCM811 was used as the positive electrode, and graphite was used as the negative electrode.

[0056] At this point, the measurement conditions for ionic conductivity, initial battery resistance, high-temperature durability, and high-rate characteristics are as follows.

[0057] - Ionic conductivity: measured at room temperature (25°C)

[0058] - Initial cell resistance: Cell DC-IR measured after formation

[0059] - High-temperature durability: During each cycle, at a temperature of 45°C and under conditions of 2.5 to 4.2V (cutoff), it is charged at 0.5C cc / cv and then discharged at 0.5C cc / cv.

[0060] - High rate capability: Capacity values ​​determined during discharge after charging only 0.1C cc / cv in each cycle.

[0061] Table 1

[0062]

[0063] Table 2

[0064]

[0065] As shown in Table 2 and Figure 1 As shown, when allyl (4-nitrophenyl) carbonate as represented by Formula 1 is used as a negative electrode additive, improved ionic conductivity, high-temperature durability, and high-rate characteristics are obtained compared to a comparative example using conventional general-purpose additive VC as a negative electrode additive under the same conditions. In particular, the improved high-rate characteristics and excellent lifespan at the same content meet the performance requirements suitable for vehicle batteries.

[0066] Experiment 2: High-rate characteristics of negative electrode additives

[0067] In Comparative Examples and Example 1 of Experiment 1, charging and discharging were performed at 0.5C, 1.0C, 2.0C, and 0.1C, respectively, to determine the corresponding capacity values, and the results are shown in... Figure 2 .

[0068] like Figure 2 As shown, compared to a comparative example using the conventional additive VC as the negative electrode additive under the same conditions, the use of allyl (4-nitrophenyl) carbonate represented by Formula 1 as the negative electrode additive exhibits improved high-rate characteristics. This implies that the improved high-rate characteristics can be based on excellent ionic conductivity.

[0069] Experiment 3: Characteristics depending on the content of the negative electrode additive

[0070] To determine various properties depending on the type of negative electrode additive added to the electrolyte solution, as shown in Table 3 below, ionic conductivity, initial battery resistance, high-temperature durability, and high-rate characteristics were measured when the type of negative electrode additive was changed. The results are shown in Table 4 and below. Figure 3 In this case, all other conditions and measurement methods are the same as in Experiment 1.

[0071] Table 3

[0072]

[0073] Table 4

[0074]

[0075] As shown in Table 4 and Figure 2 As shown, compared with the comparative example which used the conventional general-purpose additive VC as the negative electrode additive under the same conditions, Examples 1 to 5 which used allyl (4-nitrophenyl) carbonate as the negative electrode additive as shown in Formula 1 have improved ionic conductivity, high temperature durability and high rate performance.

[0076] Specifically, Example 2, which added allyl (4-nitrophenyl) carbonate in an amount of 0.2% by weight, exhibited similar high-temperature durability compared to a comparative example using conventional general-purpose additive VC as the negative electrode additive under the same conditions. However, as the amount of negative electrode additive increased, the high-temperature durability (e.g., at 45°C) improved.

[0077] Therefore, the amount of negative electrode additive added is preferably about 0.5 to 2.0% by weight relative to the total weight of the electrolyte solution.

[0078] According to various exemplary embodiments of the present invention, by adding additives for forming an SEI film on the negative electrode to the electrolyte solution, it is expected to increase the long-term service life of lithium secondary batteries.

[0079] Although exemplary embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various modifications, additions, and deletions are possible without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims

1. A vehicle comprising a lithium secondary battery, the lithium secondary battery comprising an electrolyte solution, the electrolyte solution comprising: a lithium salt; a solvent; a positive electrode additive, and a negative electrode additive, wherein the positive electrode additive comprises LiPO2F2, and wherein the negative electrode additive comprises allyl (4-nitrophenyl) carbonate of Formula 1 [Formula 1] wherein the electrolyte solution comprises the negative electrode additive in an amount of 0.5 to 2.0 wt% based on the total weight of the electrolyte solution. The solvent comprises one or more selected from a carbonate solvent, an ester solvent, an ether solvent, and a ketone solvent. 4.The vehicle comprising a lithium secondary battery according to claim 1, the lithium secondary battery further comprising: a positive electrode comprising a positive electrode active material comprising Ni, Co, and Mn; a negative electrode comprising a carbon-based negative electrode active material; and a separator interposed between the positive electrode and the negative electrode. The lithium secondary battery has a discharge retention rate of 94% or more measured after 200 cycles, each cycle comprising 0.5 C cc / cv charging and 0.5 C cc / cv discharging at a temperature of 45 °C and under conditions of 2.5 to 4.2 V. ​ ​ ​ ​ ， ​ 2. The vehicle comprising a lithium secondary battery according to claim 1, wherein, The lithium salt includes one or more selected from the group consisting of LiPF6, LiBF4, LiClO4, LiCl, LiBr, LiI, LiB 10 Cl 10 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiC4F9SO3, LiB(C6H5)4, Li(SO2F)2N, and (CF3SO2)2NLi.

3. The vehicle comprising a lithium secondary battery according to claim 1, wherein, ​ ​ ​ ​ ​ 5. The vehicle comprising a lithium secondary battery according to claim 1, wherein, ​

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