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

Abstract

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same. The electrolyte for a lithium secondary battery includes: a lithium salt; a solvent; and a functional additive, wherein the functional additive includes a naphthalen-1-ylsulfonyl fluoride represented by the following Formula 1:

Description

Technical Field

[0001] This invention relates to an electrolyte for lithium secondary battery packs and a lithium secondary battery pack including the electrolyte. 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] A lithium-ion battery pack is an energy storage system that includes a positive electrode that provides lithium ions during charging, a negative electrode that receives lithium ions, an electrolyte that serves as a lithium ion transport medium, and a separator for separating the positive and negative electrodes, wherein electrical energy is generated and stored as the chemical potential changes with the insertion / deintercalation of the positive and negative electrodes.

[0004] This type of lithium-ion battery pack has been primarily used in mobile electronic devices, and its use as an energy storage system is now rapidly expanding to commercially successful electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0005] To increase the driving range of electric vehicles, research has focused on increasing the energy density of lithium-ion battery packs. Improving the capacity of the cathode allows for an increase in the energy density of the lithium-ion battery pack.

[0006] In particular, the energy density of a battery pack largely depends on the characteristics of the positive and negative electrodes. Therefore, a suitable electrolyte is needed to enable the electrodes to exhibit excellent electrochemical performance.

[0007] When layered nickel-rich (Ni) LiNi 1-x-y Co x Mn y When O2 (NCM; 1-xy≥0.6) oxides are used as high-capacity cathode active materials, the cathode capacity can be increased by increasing the Ni content or raising the charging voltage. However, the residual lithium components (Li2CO3 and LiOH) on the cathode promote electrolyte degradation and increase interfacial reactivity with the electrolyte, thereby accelerating the degradation rate and causing a rapid decline in charge-discharge performance.

[0008] Therefore, positive-negative electrode and interface control technology are very important.

[0009] The descriptions in the related art are for understanding the background of the present invention only and should not be regarded as prior art known to those skilled in the art. Summary of the Invention

[0010] The present invention provides an electrolyte for lithium secondary battery packs and a lithium secondary battery pack including the electrolyte, wherein the electrolyte can improve the high-temperature life characteristics of the lithium secondary battery pack.

[0011] An electrolyte for a lithium secondary battery pack according to one embodiment of the present invention comprises a lithium salt, a solvent, and a functional additive, wherein the functional additive comprises a naphthyl-1-ylsulfonyl fluoride represented by Formula 1 as a first negative electrode film additive:

[0012]

[0013] Based on the weight of the electrolyte, the first negative electrode film additive can be used in a total amount of 0.5% to 1.0% by weight.

[0014] The functional additive may further include lithium difluoro(oxalate-based)borate, represented by Formula 2, as a positive electrode film additive:

[0015]

[0016] Based on the total weight of the electrolyte, the positive electrode film additive can be used in an amount of 0.5% to 1.0% by weight.

[0017] The functional additive may further include vinylene carbonate (VC) as a second negative electrode film additive.

[0018] Based on the total weight of the electrolyte, the second negative electrode film additive can be used in amounts ranging from 0.5% to 3.0% by weight.

[0019] The lithium salt can be at least one compound selected from the following: 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(LiFSI), and (CF3SO2)2NLi.

[0020] The solvent may be at least one of the following: carbonate solvents, ester solvents and ketone solvents.

[0021] A lithium secondary battery pack according to one embodiment of the present invention includes the above-described electrolyte. The lithium secondary battery pack may further include: a positive electrode containing a positive electrode active material composed of Ni, Co and Mn; a negative electrode containing at least one negative electrode active material selected from carbon (C) based materials and silicon (Si) based materials; and a separator inserted between the positive and negative electrodes.

[0022] The cathode may contain 80% by weight or more Ni.

[0023] 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

[0024] To better understand the present invention, different embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0025] Figure 1 To illustrate the events occurring in the electrolyte, a first negative electrode film additive and a positive electrode film additive according to an embodiment of the present invention are added together to the electrolyte; and

[0026] Figure 2 and Figure 3 The figures show the charge-discharge test results of the embodiments and comparative examples, respectively.

[0027] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Detailed Implementation

[0028] The following description is merely exemplary and is not intended to limit the invention, application, or use. It should be understood that throughout the drawings, corresponding reference numerals denote the same or corresponding parts and features.

[0029] An electrolyte for a lithium secondary battery pack according to one embodiment of the present invention comprises a lithium salt, a solvent, and a functional additive.

[0030] The lithium salt can be at least one compound selected from the following: 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(LiFSI), and (CF3SO2)2NLi.

[0031] Lithium salts can exist in the electrolyte at a total concentration of 0.1 mol to 1.2 mol.

[0032] The solvent may be at least one of the following: carbonate solvents, ester solvents, ether solvents, and ketone solvents.

[0033] Examples of carbonate solvents in this regard include 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 include γ-butyrolactone (GBL), n-methyl acetate, n-ethyl acetate, and n-propyl acetate. Dibutyl ethers can be used as ether solvents, but are not limited to these.

[0034] Furthermore, the solvent may further include aromatic hydrocarbon solvents. Examples of aromatic carbohydrate solvents include benzene, fluorobenzene, bromobenzene, chlorobenzene, cyclohexylbenzene, isopropylbenzene, n-butylbenzene, octylbenzene, toluene, xylene, and mesitylene, which may be used alone or in combination.

[0035] The functional additive used in the electrolyte according to one embodiment of the present invention may be a naphthalene-1-ylsulfonyl fluoride (hereinafter referred to as "S3") represented by Formula 1 as the first negative electrode film additive.

[0036]

[0037] In this regard, the naphthalene-1-yl sulfonyl fluoride (S3) used as the first negative electrode film additive stabilizes the negative electrode by forming a protective film on the surface of the negative electrode material, and can preferably be added in an amount of 0.5% to 1.0% by weight based on the total weight of the electrolyte.

[0038] When added in amounts less than 0.5% by weight, the first negative electrode film additive has little effect because it cannot adequately form a surface protective film on the surface of the negative electrode active material. Adding more than 1.0% by weight of the first negative electrode film additive leads to over-formation of the surface protective layer, increasing battery resistance and thus reducing battery life.

[0039] Simultaneously, the functional additives may further include positive electrode film additives, whose function is to form a film on the positive electrode active material. As a positive electrode film additive, lithium difluoro(oxalate-based)borate (hereinafter referred to as "LiFOB") represented by the following formula 2 can be used:

[0040]

[0041] The positive electrode film additive, lithium difluoro(oxalate-based)borate (LiFOB), stabilizes the positive electrode by forming a protective film on the surface of the positive electrode active material. Furthermore, the positive electrode film additive inhibits the oxidative degradation of S3, which serves as the first negative electrode film additive, contributing to the formation of a film with excellent thermal stability.

[0042] Based on the total weight of the electrolyte, the positive electrode film additive can preferably be added in an amount of 0.5% to 1.0% by weight.

[0043] When added in amounts less than 0.5% by weight, the positive electrode film additive has little effect because it cannot adequately form a surface protective film on the surface of the positive electrode active material. Additions exceeding 1.0% by weight lead to over-formation of the surface protective layer, increasing battery resistance and consequently reducing battery life.

[0044] Figure 1 A diagram illustrating events occurring in the electrolyte is provided, wherein a first negative electrode film additive and a positive electrode film additive are added together to the electrolyte according to an embodiment of the invention.

[0045] The first negative electrode film additive S3 can undergo oxidative degradation on the positive electrode to produce sulfuric acid, leading to continuous battery degradation. However, as... Figure 1 As shown, when added together with the first negative electrode film additive, the positive electrode film additive decomposes on the surface of the positive electrode before the first negative electrode film additive S3 to form a stable CEI, thereby suppressing battery degradation.

[0046] In addition to the first negative electrode film additive, the functional additives may further include a second negative electrode film additive for forming a film on the negative electrode. For example, vinylene carbonate (hereinafter referred to as "VC") can be used as the second negative electrode film additive.

[0047] Based on the weight of the electrolyte, the second negative electrode film additive can preferably be added in an amount of 0.5% to 3.0% by weight. More preferably, the second negative electrode film additive can be added in an amount of 1.5% to 2.5% by weight.

[0048] Less than 0.5% by weight of the second negative electrode film additive reduces the long-term lifespan characteristics of the battery. When it exceeds 3.0% by weight, the amount of the second negative electrode film additive excessively forms a surface protective layer, leading to increased battery resistance and reduced battery pack output.

[0049] According to one embodiment of the present invention, a lithium secondary battery pack is provided, which includes the above-mentioned electrolyte, positive electrode, negative electrode and separator.

[0050] The positive electrode comprises an NCM-based positive electrode active material composed of Ni, Co, and Mn. In particular, according to one embodiment, the positive electrode active material in the positive electrode consists only of an NCM-based positive electrode active material containing 80% by weight or more Ni.

[0051] The negative electrode includes at least one material selected from carbon (C)-based and silicon (Si)-based negative electrode active materials.

[0052] Carbon (C)-based anode active materials can be at least one of the following substances: artificial graphite, natural graphite, graphitized carbon fibers, graphitized mesophase carbon microspheres, fullerenes, and amorphous carbon.

[0053] Silicon (Si)-based anode active materials may include silicon oxide, silicon particles, and silicon alloy particles.

[0054] For both the positive and negative electrodes, the corresponding active materials are mixed with conductive materials, binders, and solvents to prepare electrode slurries. These electrode slurries are then applied directly to a current collector and dried to fabricate the positive or negative electrode. In this regard, the current collector may be formed of aluminum (Al), but is not limited to this. This electrode fabrication method is well known in the art and therefore will not be described in detail.

[0055] Adhesives are used to aggregate active material particles well together or to firmly adhere them 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 resins, and nylon.

[0056] Conductive materials are used to impart conductivity to the electrodes. Any conductive material can be used as long as it possesses electronic conductivity without causing chemical changes in the battery pack. Examples of conductive materials include natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, and metal particles or fibers (such as copper, nickel, aluminum, and silver). Furthermore, at least one conductive material, such as a polyphenylene derivative, can be further used.

[0057] The separator provides a migration channel for lithium ions while suppressing the formation of short circuits between the positive and negative electrodes. This separator can be a well-known type, such as a polyolefin membrane, for example, polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, polypropylene / polyethylene / polypropylene, etc., or multilayer membranes, microporous membranes, woven fabrics, or nonwoven fabrics thereof. Alternatively, porous polyolefin membranes coated with a highly stable resin can be used.

[0058] The present invention will be explained below with reference to embodiments and comparative examples.

[0059] <Experiment 1> Testing of battery resistance and high-temperature life characteristics at high temperature (45°C) depending on the type and amount of functional additives.

[0060] To examine battery resistance and high-temperature life characteristics depending on the amount and type of functional additives used in the electrolyte, the initial battery resistance and discharge retention rate after 100 cycles at high temperature (45°C) were measured while varying the type of functional additives as shown in Table 1 below. The results are summarized in Table 1 and plotted in... Figure 1 and Figure 2 middle.

[0061] In this regard, cycling was performed under the following conditions: cutoff voltage 2.7–4.35 V, C-rate 1 C, and temperature 45 °C. To prepare the electrolyte, 0.5 M LiPF6 + 0.5 LiFSI was used as the lithium salt, along with a mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 25:45:30.

[0062] The positive electrode is NCM811, and the negative electrode is a graphite electrode.

[0063] Table 1

[0064]

[0065] First, as shown in Table 1 and Figure 2 As shown, compared with No. 1 using the usual functional additive VC, improved high-temperature lifetimes were observed in Nos. 3 and 4, wherein the negative electrode film additive according to the invention was added within the amount range recommended herein.

[0066] Meanwhile, compared to No. 1, No. 2, which is added in an amount less than the lower limit of the range recommended herein for the first negative electrode film additive according to the present invention, has a worse high-temperature life.

[0067] From Table 1 and Figure 3 As can be understood from the data, compared with No. 6, which contains the usual functional additive VC and the conventional negative electrode film additive LiPO2F2 (in the same amount as No. 7), the high-temperature lifetime of No. 7, which contains the usual functional additive VC and the first negative electrode film additive according to the present invention, is further improved.

[0068] In particular, the greatest improvement in high-temperature lifetime was detected in number 8, where the usual functional additive VC was used in combination with the first negative electrode film additive and the positive electrode film additive.

[0069] As described above, according to various embodiments of the present invention, the electrolyte can form a CEI on the surface of the negative electrode active material to suppress battery degradation, thereby improving the lifespan of the lithium secondary battery pack.

[0070] In addition, the electrolyte ensures lifespan stability under high temperature and high pressure, which helps to improve the commercial value of the battery pack.

[0071] Those skilled in the art will understand that the invention can be implemented in other specific embodiments without altering its technical spirit and essential characteristics. Therefore, it should be understood that the above embodiments are exemplary in all respects and not restrictive. The scope of the invention is defined by the scope of the appended claims, not by a detailed description. It should be understood that all variations and modifications derived from the scope of the claims and their equivalents are included within the scope of the invention.

Claims

1. An electrolyte for lithium secondary battery packs, the electrolyte comprising: Lithium salts; Solvent; and Functional additives, wherein the functional additives comprise naphthalene-1-ylsulfonyl fluoride represented by Formula 1: [Equation 1] 2. The electrolyte for lithium secondary battery packs according to claim 1, wherein, Naphthalene-1-ylsulfonyl fluoride is added in an amount of 0.5% to 1.0% by weight based on the total weight of the electrolyte.

3. The electrolyte for lithium secondary battery packs according to claim 1, wherein, The functional additive further comprises lithium difluoro(oxalate-based)borate represented by Formula 2: [Equation 2].

4. The electrolyte for lithium secondary battery packs according to claim 3, wherein, Lithium difluoro(oxalate)borate is added in an amount of 0.5% to 1.0% by weight, based on the total weight of the electrolyte.

5. The electrolyte for lithium secondary battery packs according to claim 1, wherein, The functional additive further includes vinylene carbonate.

6. The electrolyte for lithium secondary battery packs according to claim 5, wherein, Based on the total weight of the electrolyte, add vinylene carbonate in an amount of 0.5% to 3.0% by weight.

7. The electrolyte for lithium secondary battery packs according to claim 1, wherein, The lithium salt is at least one compound selected from the following: 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(LiFSI), and (CF3SO2)2NLi.

8. The electrolyte for lithium secondary battery packs according to claim 1, wherein, The solvent is at least one of the following: carbonate solvents, ester solvents, ether solvents and ketone solvents.

9. A lithium secondary battery pack, comprising an electrolyte, said electrolyte comprising: Lithium salts; Solvent; and Functional additives, wherein the functional additives comprise naphthalene-1-ylsulfonyl fluoride represented by Formula 1: [Equation 1] 10. The lithium secondary battery pack according to claim 9, further comprising: The positive electrode contains an NCM-based positive electrode active material; A negative electrode containing at least one negative electrode active material, said negative electrode active material being selected from carbon-based materials and silicon-based materials; and A diaphragm is inserted between the positive and negative electrodes.

11. The lithium secondary battery pack according to claim 10, wherein, The positive electrode contains 80% by weight or more Ni.

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