Secondary battery electrolyte composition and secondary battery containing 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] This invention relates to a secondary battery electrolyte composition and a secondary battery containing the same. [Background technology]

[0002] The electrolyte in secondary batteries generally consists of various types of lithium salts (typically lithium hexafluorophosphate (LiPF6)) and a solvent. The solvent used must have high solubility for lithium salts, a large dielectric constant, and a high flash point. Ethylene carbonate (EC) primarily fulfills this role. However, despite its excellent solvent properties, EC exists as a solid at room temperature, has high viscosity, and is therefore used in mixture with other solvents (substances with low viscosity).

[0003] The electrolyte components in secondary batteries are mainly composed of substances with low boiling and flash points, making them susceptible to thermal runaway during temporary temperature increases or impacts such as collisions. This risk of fire exists during charging, movement, and transportation, and acts as a significant defect in the stability of electric vehicles. Furthermore, as the use of secondary batteries expands beyond electric vehicles to various fields such as robotics, personal injury and property damage due to fires are increasing. Such fire incidents and their potential are major obstacles to the technological development of secondary batteries and the applications that use them.

[0004] Currently, the technical elements of secondary batteries can be divided into performance elements such as charging speed, discharging speed, and charging capacity, and safety elements such as the possibility of ignition and overheating. Performance-related elements are extremely important as they determine the driving range and charging time of electric vehicles. However, safety issues such as ignition and difficulty in extinguishing fires are the biggest psychological barrier to consumer awareness for the expansion of the electric vehicle market. Among the components that threaten the safety of such secondary batteries, the solvent component in the electrolyte causes the biggest problem.

[0005] In conventional electrolytes, the solvent component must have high solubility in the electrolyte and maintain a low viscosity below a certain level, in order for cations such as lithium ions to freely move between the positive and negative electrodes via a separation membrane. For this reason, the solvent in the electrolyte is a mixture that satisfies the physicochemical properties required for secondary batteries. Ethylene carbonate (EC) has high solubility in lithium salts, a boiling point (BP) of 243°C, and a flash point (FP) of 150°C, making it very thermally stable. 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 generally mixed with other solvents that can exist in a soluble state to be used as an electrolyte.

[0006] The fire hazard of conventional electrolytes stems from additives other than EC, such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). These substances possess low viscosity and low freezing point properties without compromising the advantages of EC, such as high lithium salt solubility and a high genetic constant, thus improving upon the drawbacks of EC, which is highly viscous in its solid state at room temperature. Therefore, in the manufacture of conventional secondary batteries, these substances are mixed with EC in various proportions to be used as the electrolyte. However, these substances have the disadvantage of having low flash points or boiling points and being easily ignited. Concerns about fires in secondary batteries and electric vehicles, namely the intense heat at ignition and the difficulty of extinguishing fires, are due to the properties of these flammable / volatile cosolvents. In particular, these solvents do not dissolve well in water or conventional fire extinguishing liquids, posing a problem in the event of a secondary battery fire, as they are not easily extinguished.

[0007] When using an electrolyte with a low flash point, the battery system requires a strict battery management system (BMS) to prevent the temperature from rising above the flash point during charging and discharging. If a solvent with a sufficiently high flash point is used as the electrolyte, the battery can operate with a margin over a wider temperature range.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems 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 management of the battery.

[0010] Another object of the present invention is to provide a secondary battery including the secondary battery electrolyte composition.

Means for Solving the Problems

[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 1, wherein the amphiphilic solvent is ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate.

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

[0014] 4. The secondary battery electrolyte composition according to 3, comprising ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate and ethylene carbonate in a volume ratio of 1:0.5 to 2. [[ID=D47]]

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

Advantages of the Invention

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

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

[0018] The electrolyte composition of the present invention and the secondary battery containing the same are composed of an amphiphilic solvent that is environmentally friendly and in which the electrolyte solvent composition that can serve as fuel even in the event of a fire is highly soluble in water, despite the fire suppression effect. Thus, it can be easily dissolved and extinguished by water.

[0019] In the case of a battery system adopting the electrolyte composition of the present invention and the secondary battery containing the same, a non-flammable solvent component with a flash point much higher than 93°C, which is the flammable standard of the US OSHA fire standard, is used as the electrolyte. Therefore, operation at a much higher temperature is possible, or it is safe against a temporary shock and the battery state can be maintained.

Brief Description of the Drawings

[0020] [Figure 1] This is the result of measuring the electrical conductivity after dissolving lithium hexafluorophosphate in EHP from 0.5M to 3M. [Figure 2] This is the result of measuring the electrical conductivity after dissolving lithium hexafluorophosphate from 0.5M to 3M in a mixed solvent prepared by dissolving ethylene carbonate (EC) in EHP at a ratio of 1:1. [Figure 3]This shows the results of measuring the electrical conductivity of two conventionally used lithium-ion electrolytes (electrolyte I and II) and an EHP / EC electrolyte over a wide temperature range. [Modes for carrying out the invention]

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

[0022] This invention relates to an electrolyte composition for secondary batteries.

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

[0024] Amphiphilic solvents possess both hydrophobic and hydrophilic properties simultaneously and can dissolve both hydrophobic and hydrophilic substances.

[0025] Typically, solvents used in the electrolytes of secondary batteries include ethylene carbonate, which is solid at room temperature, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), which can dissolve it. However, these solvents have low flash points and boiling points, making them highly flammable and volatile, which can further intensify a fire if one occurs.

[0026] However, the electrolyte composition of the present invention uses an amphiphilic solvent, which can prevent the aforementioned problems.

[0027] Amphiphilic solvents include, for example, ethyl 3-hydroxypropanoate (C5H 10 It may also be O3, ethyl-3-hydroxypropanoate (EHP). Alternatively, it may be 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 contain ethylene carbonate. This may be used as a solvent together with an amphiphilic solvent.

[0030] The mixing ratio of the amphiphilic solvent and ethylene carbonate is not particularly limited, and may be contained, for example, in a volume ratio of 1:0.5 to 2.

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

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

[0033] The lithium salt contains lithium cations (Li + ) as a mediator for transmitting ions, and 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 - It may, but is not limited to, include at least one anion selected from the group consisting of .

[0034] Lithium salts may be included at concentrations of, for example, 0.1 to 3 M.

[0035] Furthermore, the present invention relates to a secondary battery containing the aforementioned electrolyte.

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

[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 positive electrode current collectors include foils made from aluminum, nickel, or combinations thereof, and the positive electrode active material layer may include positive electrode active material, and optionally a binder, conductive material, dispersant, etc.

[0039] As the positive electrode active material, ordinary positive electrode active materials may be used, for example, lithium cobalt oxide composite oxide (LiCoO2), spinel crystal lithium manganate composite oxide (LiMn2O4), lithium manganate composite oxide (LiMnO2), lithium nickelate composite oxide (LiNiO2), lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (iron Examples include, but are not limited to, pyrophosphate (Li2FeP2O7), lithium niobate composite oxide (LiNbO2), lithium ironate composite oxide (LiFeO2), lithium magnesiumate composite oxide (LiMgO2), lithium copperate composite oxide (LiCuO2), lithium zincate composite oxide (LiZnO2), lithium molybdate composite oxide (LiMoO2), lithium tantalate composite oxide (LiTaO2), lithium tungstate composite oxide (LiWO2), perlithium permanganese nickel cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium nickel cobalt manganese composite oxide.

[0040] As conductive materials, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskey such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used, but there are no particular limitations as long as they are conductive without inducing chemical changes in the battery.

[0041] The binder polymer may include 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 negative electrode current collectors may be selected from foils made of copper, gold, nickel, or copper alloys or combinations thereof.

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

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

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

[0047] The experiment was conducted using a temperature-controlled device, with operating temperatures ranging from -20 to 100°C.

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

[0049] As the temperature increased from low to high, ion movement became more active, resulting in a tendency for electrical conductivity to increase. Electrical conductivity also increased with increasing lithium salt concentration. Relatively high electrical conductivity was observed under lithium salt concentration conditions of 1M and 2M. Notably, these results indicate that stable electrical conductivity was observed even under temperature conditions (30-100°C) far higher than the flash points (<30°C) of conventional electrolytes such as DMC and DEC.

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

[0051] Although ethylene carbonate is a solid at room temperature, it remained stable in a liquid state when dissolved in ethyl 3-hydroxypropanoate. It also remained liquid at -20°C, demonstrating its potential as a replacement for conventional volatile solvents.

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

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

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

[0055] Conventional commercially available electrolyte components are the same as electrolyte I; LiPF61M in EC:DEC = 1:1 (v / v) (dissolved at a concentration of LiPF61M in equal volumes of EC and DEC in a 1:1 ratio) and electrolyte II; LiPF61M in EC:DEC:EMC = 1:1:1 (v / v) (dissolved at a concentration of LiPF61M in equal volumes of EC, DEC, and EMC in 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. While the conventional electrolytes showed slightly higher conductivity up to 40°C, their stability decreased at higher temperatures, preventing further experiments. In contrast, the EHP+EC or EHP alone solutions presented in this invention allowed measurements 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 by solvent Ethylene carbonate was mixed with methyl 3-hydroxypropanoate or ethyl 3-hydroxypropanoate, and the electrical conductivity was measured with respect to temperature.

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

[0062] [Table 2]

[0063] It was found that MHP has approximately 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 thus more favorable ion mobility. However, unlike EHP, the MHP+EC combination showed a decrease in electrical conductivity above 90°C, indicating that its thermal stability at high temperatures is slightly lower than that of EHP.

Claims

1. A secondary battery electrolyte composition comprising an amphiphilic solvent and a lithium salt electrolyte, wherein the amphiphilic solvent is ethyl 3-hydroxypropanoate or methyl 3-hydroxypropanoate.

2. The secondary battery electrolyte composition according to claim 1, further comprising ethylene carbonate.

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

4. A secondary battery comprising a positive electrode, a negative electrode, a separation membrane located between the positive electrode and the negative electrode, and a secondary battery electrolyte according to any one of claims 1 to 3.

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