Electrolyte composition for secondary battery and secondary battery including the same

Abstract

To provide a secondary battery electrolyte composition which reduces the risk of fire and facilitates the temperature control of a battery.SOLUTION: The secondary battery electrolyte composition contains an amphiphilic solvent and a lithium salt electrolyte.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a secondary battery electrolyte composition and a secondary battery containing the same. [Background technology]

[0002] The electrolyte of a secondary battery generally consists of various types of lithium salts (a typical example is lithium hexafluorophosphate (LiPF6)) and a solvent. The solvent used must have a high solubility for the lithium salt, a large dielectric constant, and a high flash point. Ethylene carbonate (EC) is the main material that fulfills this role. However, despite its excellent solvent properties, EC exists as a solid at room temperature and has high viscosity, so it is used by mixing it with other solvents (substances with low viscosity).

[0003] The electrolyte components in secondary batteries are primarily composed of substances with low boiling and flash points, which can easily lead to thermal runaway when subjected to a temporary temperature rise or impact, such as a collision. This risk of fire exists during charging, travel, and transportation, posing a serious threat to the stability of electric vehicles. Furthermore, as the use of secondary batteries expands beyond electric vehicles to include robotics and other fields, the risk of fire-related injuries and property damage is increasing. These fire accidents and the possibility of fires are a major obstacle to the technological development of secondary batteries and their associated products.

[0004] Currently, the technical elements of secondary batteries are divided into performance factors such as charge speed, discharge speed, and charge capacity, and safety factors such as the possibility of fire and overheating. Performance factors are extremely important because they determine the driving range and charging time of electric vehicles. However, safety issues such as fire and difficulty in extinguishing fires are the biggest psychological barrier to consumer awareness in expanding the electric vehicle market. Of the components that threaten the safety of secondary batteries, the solvent component in the electrolyte causes the greatest problem.

[0005] The solvent components in conventional electrolytes must have high solubility in the electrolyte and maintain a low viscosity to allow cations, such as lithium ions, to freely move between the positive and negative electrodes through the separator. To achieve this, electrolyte solvents are composed of mixtures to meet the physicochemical properties required for secondary batteries. Ethylene carbonate (EC) has high solubility in lithium salts and excellent thermal stability, with a boiling point (BP) of 243°C and a flash point (FP) of 150°C. However, because its melting point (MP) is 34°C, it exists as a solid at room temperature and cannot be used as a solvent alone. Therefore, EC is typically mixed with other solvents that can exist in a dissolved state to form an electrolyte.

[0006] The fire risk of conventional electrolytes is due to the addition of organic solvents other than EC, such as dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC). These substances have low viscosity and low freezing points, improving the drawback of EC, which has high solid-state viscosity at room temperature, without compromising the advantages of EC, such as high lithium salt solubility and high thermal conductivity. Therefore, in conventional secondary battery manufacturing, these substances are mixed with EC in various ratios to form the electrolyte. However, these substances have the disadvantage of being easily flammable due to their low flash point or boiling point. Concerns about fires in secondary batteries and electric vehicles, such as the intense firepower upon ignition and the difficulty of extinguishing the fire, are due to the characteristics of these flammable / volatile co-solvents. In particular, these solvents do not dissolve well in water or conventional fire extinguishing solutions, making secondary battery fires difficult to extinguish.

[0007] When using an electrolyte with a low flash point, the battery system requires a strict Battery Management System (BMS) to ensure that the temperature does not rise above the flash point during charging and discharging. If a solvent with a sufficiently high flash point is used as the electrolyte, it can operate comfortably over a wider temperature range. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 2466388 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a secondary battery electrolyte composition that reduces the risk of fire and facilitates temperature control of the battery.

[0010] Another object of the present invention is to provide a secondary battery containing the secondary battery electrolyte composition. [Means for solving the problem]

[0011] 1. A secondary battery electrolyte composition comprising an amphiphilic solvent and a lithium salt electrolyte.

[0012] 2. The secondary battery electrolyte composition according to item 1 above, wherein the amphiphilic solvent is ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate.

[0013] 3. The secondary battery electrolyte composition according to item 2 above, further comprising ethylene carbonate.

[0014] 4. The secondary battery electrolyte composition according to 3 above, comprising ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate and ethylene carbonate in a volume ratio of 1:0.5 to 2.

[0015] 5. A secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the secondary battery electrolyte solution according to any one of 1 to 4 above. [Effects of the Invention]

[0016] The electrolyte composition of the present invention is a non-flammable substance that reduces the vapor pressure of the electrolyte while significantly increasing the flash point, and can therefore suppress the ignition and growth of fire in secondary batteries.

[0017] The electrolyte composition of the present invention and the secondary battery containing it can suppress the ignition and growth of fire.

[0018] Despite the fire suppression effect, the electrolyte solution composition of the present invention and the secondary battery including the same contain an electrolyte solvent composition that can serve as fuel in the event of a fire, and is composed of an environmentally friendly amphipathic solvent that dissolves well in water, making it easy to dissolve and extinguish the fire with water.

[0019] In the case of a battery system employing the electrolyte composition of the present invention and a secondary battery including the same, a non-flammable solvent component having a flash point much higher than 93°C, the flammable standard in the U.S. OSHA fire standard, is used as the electrolyte, making it possible to operate at much higher temperatures or maintain safety and battery condition even in the event of a temporary shock. [Brief explanation of the drawings]

[0020] [Figure 1] This shows the results of measuring the electrical conductivity after dissolving lithium hexafluorophosphate in EHP from 0.5M to 3M. [Figure 2] The electrical conductivity was measured by dissolving lithium hexafluorophosphate in a mixed solvent prepared by dissolving ethylene carbonate (EC) in a 1:1 ratio into EHP, and then dissolving lithium hexafluorophosphate in concentrations ranging from 0.5M to 3M. [Figure 3]The electrical conductivity of two conventionally used lithium ion electrolytes (electrolyte I and II) and EHP / EC electrolyte was measured over a wide temperature range. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below.

[0022] The present invention relates to a secondary battery electrolyte composition.

[0023] The secondary battery electrolyte composition of the present invention comprises an amphiphilic solvent and an electrolyte.

[0024] An amphiphilic solvent has both hydrophobic and hydrophilic properties and can dissolve both hydrophobic and hydrophilic substances.

[0025] Typically, solvents used in secondary battery electrolytes are ethylene carbonate, which is solid at room temperature, and solvents that can dissolve it, such as dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC). However, these solvents have low flash points and boiling points, making them easily flammable and volatile, which can exacerbate fires in the event of a fire.

[0026] However, the electrolyte composition of the present invention can avoid this problem by using an amphiphilic solvent.

[0027] Amphiphilic solvents include, for example, ethyl 3-hydroxypropanoate (CH 10 O3, ethyl-3-hydroxypropanoate (EHP), or methyl 3-hydroxypropanoate (C4H8O3, Methyl-3-hydroxypropanoate (MHP).

[0028] The amphiphilic solvent may be non-volatile or non-flammable.

[0029] The composition of the present invention may further comprise ethylene carbonate, which may be used as a solvent together with the amphiphilic solvent.

[0030] The mixing ratio of the amphipathic solvent and ethylene carbonate is not particularly limited, and may be, for example, 1:0.5-2 by volume.

[0031] The electrolyte may be any electrolyte commonly used in secondary batteries.

[0032] The electrolyte may be, for example, a lithium salt.

[0033] Lithium salts act as a medium for transferring ions, and lithium cations (Li + ), including F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , ClO4 - , BF4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3- , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The anion may contain at least one anion selected from the group consisting of, but is not limited to, the anion.

[0034] The lithium salt may be contained at a concentration of, for example, 0.1 to 3M.

[0035] The present invention also relates to a secondary battery containing the electrolyte solution.

[0036] The secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and the above-described electrolyte solution.

[0037] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0038] Non-limiting examples of the positive electrode current collector include a foil made of aluminum, nickel, or a combination thereof. The positive electrode active material layer may include a positive electrode active material, and optionally a binder, a conductive material, a dispersant, etc.

[0039] As the positive electrode active material, a normal positive electrode active material may be used, for example, lithium cobalt oxide composite oxide (LiCoO2), spinel crystal type lithium manganese oxide composite oxide (LiMn2O4), lithium manganese oxide composite oxide (LiMnO2), lithium nickel oxide composite oxide (LiNiO2), lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (iron pyrophosphate (Li2FeP2O7), lithium niobate composite oxide (LiNbO2), lithium ferrate composite oxide (LiFeO2), lithium magnesium oxide composite oxide (LiMgO2), lithium cuprate composite oxide (LiCuO2), lithium zincate composite oxide (LiZnO2), lithium molybdate composite oxide (LiMoO2), lithium tantalate composite oxide (LiTaO2), lithium tungstate composite oxide (LiWO2), perlithium permanganate nickel cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, and the like, but are not limited to these.

[0040] Examples of conductive materials that can be used include carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. However, there are no particular limitations on the conductive material as long as it is conductive and does not induce chemical changes in the battery.

[0041] The binder polymer may include any one or more selected from the group consisting of nitrile butadiene rubber, polybutadiene rubber, polyethylene glycol, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, polypropylene oxide, polydimethylsiloxane, polyvinylidene fluoride, polyvinylidene carbonate, and polyvinylpyrrolidinone.

[0042] The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

[0043] Non-limiting examples of the negative electrode current collector may be selected from foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0044] The negative electrode active material layer may be any one or more selected from the group consisting of soft carbon, hard carbon, artificial graphite, natural graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, acetylene black, ketjen black, graphene, fullerene, activated carbon, and mesocarbon microbeads; any one metal selected from silicon, tin, lithium, aluminum, silver, bismuth, indium, germanium, lead, platinum, titanium, zinc, manganese, cadmium, cerium, copper, cobalt, nickel, and iron; an alloy containing two or more of the above metals; and an oxide of one or more of the above metals, but is not limited thereto.

[0045] The present invention will be explained in more detail below with reference to examples.

[0046] Example 1. Measurement of electrical conductivity based on electrolyte concentration (1) The electrical conductivity of the electrolyte was measured by adding the electrolyte lithium hexafluorophosphate to the amphiphilic solvent ethyl 3-hydroxypropanoate in concentrations from 0.5M to 3M.

[0047] The experiment was conducted using a temperature-controllable device, and the operating temperature was -20 to 100°C.

[0048] The measurement results are shown in Figure 1.

[0049] As the temperature rises from low to high, ion migration becomes more active, which shows a tendency for electrical conductivity to increase. Electrical conductivity also increases as the lithium salt concentration increases. The 1M and 2M lithium salt concentration conditions showed relatively high electrical conductivity. What is noteworthy from these results is that stable electrical conductivity was observed even at temperatures (30-100°C) that are much higher than the flash points (<30°C) of DMC and DEC, which are used in conventional electrolytes.

[0050] (2) The electrical conductivity of the electrolyte was measured while adding the electrolyte lithium hexafluorophosphate from 0.5M to 3M to a solvent made by mixing the amphiphilic solvent ethyl 3-hydroxypropanoate and ethylene carbonate in a 1:1 volume ratio.

[0051] Ethylene carbonate is a solid at room temperature, but when dissolved in ethyl 3-hydroxypropanoate, it remains stable in a liquid state. It remains liquid even at -20°C, demonstrating its potential as a substitute for conventional volatile solvents.

[0052] The measurement results are shown in Figure 2.

[0053] Similarly, high electrical conductivity was observed up to 100°C without any problems. This is consistent with previous research results showing that the addition of EC is very important for electrical conductivity. Both EHP and EC have high boiling points and flash points, making them very advantageous electrolyte solvents in terms of thermal stability and fire resistance.

[0054] 2. Comparison of electrical conductivity with conventional electrolytes as a function of temperature The electrical conductivity of two conventionally used lithium ion electrolytes (electrolyte I and II) and EHP / EC electrolyte was measured over a wide temperature range. The concentration of lithium hexafluorophosphate was fixed at 1 M. The temperature range was -20 to 100°C.

[0055] The components of conventional commercially available electrolytes are the same as those of electrolyte I; LiPF61M in EC:DEC = 1:1 (v / v) (LiPF61M dissolved in the same volume of EC and DEC at a 1:1 ratio), and electrolyte II; LiPF61M in EC:DEC:EMC = 1:1:1 (v / v) (LiPF61M dissolved in the same volume of EC, DEC, and EMC at a 1:1:1 ratio).

[0056] The measurement results are shown in Figure 3.

[0057] The two conventional electrolytes were highly flammable and could only be operated up to 40°C. The conventional electrolytes had slightly high conductivity up to 40°C, but their stability decreased at higher temperatures, so no further experiments were conducted. However, in the case of EHP+EC or EHP alone proposed in this invention, measurements were possible up to high temperatures.

[0058] For reference, the flash points for each solvent are shown in Table 1 below.

[0059] [Table 1]

[0060] 3.Comparison of electrical conductivity depending on solvent Methyl 3-hydroxypropanoate or ethyl 3-hydroxypropanoate was mixed with ethylene carbonate, and the electrical conductivity was measured as a function of temperature.

[0061] The results are shown in Table 2 below.

[0062] [Table 2]

[0063] It can be seen that MHP has a 20% higher electrical conductivity than EHP within a certain temperature range. This is thought to be because MHP has a smaller molecular weight than EHP, resulting in lower viscosity and better ion mobility. However, unlike EHP, the combination of MHP and EC showed a decrease in electrical conductivity above 90°C, indicating that its thermal stability at high temperatures is slightly lower than EHP's.

Claims

1. A secondary battery electrolyte composition comprising an amphiphilic solvent and a lithium salt electrolyte.

2. 2. The secondary battery electrolyte composition according to claim 1, wherein the amphiphilic solvent is ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate.

3. 3. The secondary battery electrolyte composition of claim 2, further comprising ethylene carbonate.

4. 4. The secondary battery electrolyte composition according to claim 3, comprising ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate and ethylene carbonate in a weight ratio of 1:0.5 to 2.

5. A secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the secondary battery electrolyte solution according to any one of claims 1 to 4.

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