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, and discloses an electrolyte solution for a lithium secondary battery capable of increasing the lifespan of the lithium secondary battery and a lithium secondary battery including the same. An electrolyte solution for a lithium secondary battery including a lithium salt, a solvent, and a negative electrode additive is also provided. The negative electrode additive preferably includes bis(4-(trifluoromethoxy)phenyl)oxalate [Formula 1] represented by the following 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 and stores electrical 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 it has become possible to increase the energy density of lithium secondary batteries by increasing the capacity of the positive electrode.

[0005] Increased capacity of the cathode can be achieved through nickel enrichment. For example, this method may include increasing the Ni content of the Ni-Co-Mn-based oxide constituting the cathode active material, or it may be achieved by increasing the cathode 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 lithium secondary batteries and a lithium secondary battery including the electrolyte are provided, which can increase the life of lithium secondary batteries.

[0009] On one hand, an electrolyte composition or solution for lithium secondary batteries is provided, comprising a lithium salt, a solvent, and bis(4-(trifluoromethoxy)phenyl)oxalate ester represented by Formula 1.

[0010] [Formula 1]

[0011]

[0012] In some respects, the electrolyte composition comprises a negative electrode additive, which includes bis(4-(trifluoromethoxy)phenyl)oxalate.

[0013] Bis(4-(trifluoromethoxy)phenyl)oxalate may be added appropriately in an amount of less than about 3.0% by weight relative to the total weight of the electrolyte solution.

[0014] Bis(4-(trifluoromethoxy)phenyl)oxalate may be added appropriately in an amount of about 0.2 to 2.0% by weight relative to the total weight of the electrolyte solution.

[0015] 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.

[0016] The solvent may suitably include one or more selected from carbonate solvents, ester solvents, ether solvents, and ketone solvents. Other solvents may also be used.

[0017] The electrolyte solution for lithium secondary batteries may further contain a positive electrode additive. Preferably, the positive electrode additive may include LiPO2F2.

[0018] On one hand, a lithium secondary battery is provided, comprising the electrolyte solution described herein. The lithium secondary battery may further comprise: 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.

[0019] Lithium-ion rechargeable batteries can have a discharge retention rate of over 94% as measured after 200 cycles, each cycle consisting of a 0.5C cc / cv charge and a 0.5C cc / cv discharge at a temperature of 45°C and at a cutoff condition of 2.5V to 4.2V.

[0020] Vehicles that include the lithium secondary batteries disclosed herein are also provided.

[0021] Other aspects of the invention are disclosed below. Attached Figure Description

[0022] 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:

[0023] Figure 1 The graph shows the evaluation results of the properties after the addition of the additives in Experiment 1 and Table 2 of the exemplary embodiment of the present invention, compared to the comparative example.

[0024] Figure 2 This is a graph showing the evaluation results of the properties of the additives added in Experiment 2 of the exemplary embodiment of the present invention, compared to the comparative example.

[0025] Figure 3 This is a graph showing the evaluation results of the properties after the addition of the additive in Experiment 3 according to an exemplary embodiment of the present invention, compared to the comparative example. Detailed Implementation

[0026] 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, gasoline vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources).

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application. 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,” “including,” “having,” etc., are used in this specification, they indicate the presence of the said feature, region, integral, step, operation, element, and / or component, but do not exclude the presence or addition of one or more other features, regions, integrals, steps, operations, elements, components, and / or combinations thereof.

[0028] Furthermore, 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 an average of 2 standard deviations. "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.

[0029] Reference will now be made in detail to preferred exemplary 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 forms. These embodiments are provided merely to fully illustrate the invention and to enable those skilled in the art to fully understand its scope.

[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] Preferably, the lithium salt can be 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 be appropriately present in electrolyte solutions at a concentration of about 0.2 to 1.2 moles.

[0033] Preferably, the solvent may be selected from one or more of carbonate solvents, ester solvents, ether solvents and ketone solvents.

[0034] 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 be 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. For example, aromatic hydrocarbon-based organic solvents may suitably 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 appropriately used as a positive electrode additive.

[0037] Meanwhile, bis(4-(trifluoromethoxy)phenyl)oxalate, 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] In this case, the negative electrode additive 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 0.2 to 2.0% by weight.

[0041] When the amount of negative electrode additive exceeds approximately 3.0% by weight, the coating may over-form, adversely leading to high battery resistance and thus reduced battery power. More precisely, when the amount of negative electrode additive is less than approximately 0.2% by weight, the problem is that the SEI, 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 problem is that the battery power required by the vehicle may be reduced.

[0042] In addition to the electrolyte solution described above, the lithium secondary battery according to embodiments of the present invention also includes a positive electrode, a negative electrode, and a separator.

[0043] The positive electrode includes an NCM-type positive electrode active material containing Ni, Co, and Mn. In particular, the positive electrode active material contained in the positive electrode may preferably consist only of an NCM-type positive electrode active material, which contains about 60% by weight or more of Ni based on the total weight of the NCM-type positive electrode active material.

[0044] In addition, the negative electrode may 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 one or more materials selected from artificial graphite, natural graphite, graphitized carbon fiber, graphitized carbon microspheres, fullerenes and amorphous carbon.

[0046] For example, positive and negative electrodes are manufactured by mixing each active material with a conductive material, a binder, and a solvent to prepare an electrode slurry, then directly coating the electrode slurry onto a current collector, and finally drying it. In this case, aluminum (Al) can be used as the current collector, but the invention is not limited thereto. Since such methods of manufacturing electrodes are well known in the art, their 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] Additionally, conductive materials can be used to impart conductivity to the electrodes. 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 (e.g., copper, nickel, aluminum, and silver powders), metal fibers, etc. Furthermore, conductive materials (e.g., 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 a separator may suitably include known separators selected from 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, the vehicle was charged at 0.5C cc / cv at a high temperature of 45°C and at a voltage of 2.5V to 4.2V (cutoff), followed by discharging 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 bis(4-(trifluoromethoxy)phenyl)oxalate, represented by Formula 1 in this embodiment, is used as the negative electrode additive, improved ionic conductivity, high-temperature durability, and high-rate characteristics are obtained compared to a comparative example using the conventional general-purpose additive VC as the 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, when bis(4-(trifluoromethoxy)phenyl)oxalate, represented by Formula 1 according to this embodiment, is used as the negative electrode additive, improved high-rate characteristics can be obtained compared to a comparative example using the conventional general-purpose additive VC as the negative electrode additive under the same conditions. This means 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 characteristics depending on the type of negative electrode additive added to the electrolyte solution, ionic conductivity, initial battery resistance, high-temperature durability, and high-rate characteristics were measured when the type of negative electrode additive was varied as shown in Table 3 below. The results are shown in Table 4 and... 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 a comparative example using conventional general-purpose additive VC as a negative electrode additive under the same conditions, Examples 1 to 5 using bis(4-(trifluoromethoxy)phenyl)oxalate as a negative electrode additive according to Formula 1 of this example showed improved ionic conductivity, high-temperature durability and high-rate characteristics.

[0076] In particular, as shown in Examples 1 to 5, the ionic conductivity and initial cell resistance gradually increased with the increase of the amount of bis(4-(trifluoromethoxy)phenyl)oxalate added.

[0077] However, as shown in Example 2 (where the amount of bis(4-(trifluoromethoxy)phenyl)oxalate added is 0.2% by weight) and Example 1 (where the amount of bis(4-(trifluoromethoxy)phenyl)oxalate added is 2.0% by weight), the degree of improvement in high-temperature durability remains constant even when the amount of negative electrode additive is changed.

[0078] Therefore, when the amount of bis(4-(trifluoromethoxy)phenyl)oxalate added is greater than about 2.0% by weight, the ionic conductivity and initial battery resistance can be further improved. However, the improvement in high-temperature durability may be insufficient, and its usage is greater than that of VC used as a conventional negative electrode additive. Therefore, the upper limit of the amount of bis(4-(trifluoromethoxy)phenyl)oxalate added is preferably about 2.0% by weight.

[0079] Therefore, the amount of negative electrode additive added is preferably 0.2 to 2.0% by weight relative to the total weight of the electrolyte solution.

[0080] 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.

[0081] In addition, by using an electrolyte solution containing high-voltage additives, it is expected that the battery resistance of the lithium secondary battery can be reduced, thereby improving the power characteristics.

[0082] 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 including an electrolyte solution, the electrolyte solution comprising: Lithium salts, of which, The lithium salt includes 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, and (CF3SO2)2NLi; Solvent; as well as The bis(4-(trifluoromethoxy)phenyl)oxalate ester shown in Formula 1 below, [Formula 1] The bis(4-(trifluoromethoxy)phenyl)oxalate ester accounts for 0.2 to 2.0% by weight relative to the total weight of the electrolyte solution. The electrolyte solution further comprises a positive electrode additive, wherein the positive electrode additive is LiPO2F2.

2. The vehicle according to claim 1, wherein, The solvent includes one or a mixture of two or more selected from carbonate solvents, ester solvents, ether solvents and ketone solvents.

3. The vehicle according to claim 1, wherein the lithium secondary battery further comprises: The positive electrode includes positive electrode active materials containing Ni, Co, and Mn; Anodes, including carbon-based anode active materials; and A diaphragm is located between the positive and negative electrodes.

4. The vehicle according to claim 1, wherein, The lithium secondary battery has a discharge retention rate of over 94% measured after 200 cycles, each cycle comprising a 0.5C cc / cv charge and a 0.5C cc / cv discharge at a temperature of 45°C and a cutoff condition of 2.5V to 4.2V.

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