Electrolyte composition for secondary battery and secondary battery comprising same

Abstract

The present invention relates to a secondary battery electrolyte composition and a secondary battery comprising the same, the secondary battery electrolyte composition comprising an amphiphilic solvent and a lithium salt electrolyte, thereby reducing the risk of fire and facilitating the temperature management of the battery.

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 typically consists of various types of lithium salts (a representative example being lithium hexafluorophosphate (LiPF6)) and solvents. The solvent used is a substance with high solubility, high dielectric constant, and high flash point for lithium salts. Ethylene carbonate (EC) is primarily used for this purpose. However, despite its excellent solvent properties, EC exists as a solid at room temperature and has high viscosity; therefore, it must be mixed with other solvents (substances with lower viscosity).

[0003] The electrolyte in secondary batteries is primarily composed of substances with low boiling or flash points, making them susceptible to thermal runaway when subjected to temporary temperature increases or impacts such as collisions. This fire risk also exists during charging, movement, and transportation, posing a serious deficiency to the stability of electric vehicles. Furthermore, as the use of secondary batteries expands beyond electric vehicles to various fields such as robotics, the number of personal injuries and property losses due to fires is increasing. The occurrence and likelihood of these fire accidents pose a significant obstacle to the technological development of secondary batteries and related applications.

[0004] Currently, the technical elements of rechargeable batteries are divided into performance factors such as charging speed, discharging speed, and charging capacity, and safety factors such as the possibility of fire and overheating. Performance-related factors determine the driving range or charging time of electric vehicles and are therefore very important. However, safety issues such as fire and difficulty in extinguishing batteries are considered the biggest psychological barriers by consumers aiming to expand the electric vehicle market. Among the components threatening the safety of these rechargeable batteries, the solvent component in the electrolyte is the most problematic.

[0005] In existing electrolytes, the solvent composition must exhibit high solubility for the electrolyte, and its viscosity must be kept low to below a specified level to allow cations such as lithium ions to move freely between the positive and negative electrodes through the membrane. Therefore, the electrolyte solvent is composed of a mixture to meet the physicochemical properties required for secondary batteries. Ethylene carbonate (EC) has high solubility for lithium salts, a boiling point (BP) of 243°C, a flash point (FP) of 150°C, and excellent thermal stability. However, because its melting point (MP) is 34°C and it exists as a solid at room temperature, it cannot be used as a solvent alone. Therefore, EC is usually mixed with other solvents that can exist in a dissolved state and used as the electrolyte.

[0006] The fire risk of existing electrolytes is caused by additives such as dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC), which are organic solvents other than electrolytes (EC). These substances do not impair the high lithium salt solubility and high dielectric constant of EC, and have low viscosity and low freezing point characteristics, thus mitigating the disadvantages of EC being solid and highly viscous at room temperature. Therefore, in existing secondary battery preparation, these substances are mixed with EC in various proportions and used as electrolytes. However, the disadvantage of these substances is their flammability due to their low flash point or boiling point. Concerns about fires in secondary batteries or electric vehicles, namely the intense flames upon ignition and the difficulty in extinguishing fires, are due to the characteristics of these flammable / volatile co-solvents. In particular, these solvents are not easily soluble in water or existing inactivators, thus posing a problem of difficulty in extinguishing fires in secondary batteries.

[0007] When using electrolytes with low flash points, the battery system requires a robust Battery Management System (BMS) to prevent temperatures from rising above the flash point during charging and discharging. Using solvents with sufficiently high flash points as electrolytes allows for more efficient operation over a wider temperature range.

[0008] Existing technical documents

[0009] Patent documents

[0010] Korean Patent No. 2466388 Summary of the Invention

[0011] Technical issues

[0012] The purpose of this invention is to provide a secondary battery electrolyte composition that reduces the risk of fire and facilitates battery temperature management.

[0013] The purpose of this invention is to provide a secondary battery comprising the aforementioned secondary battery electrolyte composition.

[0014] Technical solution

[0015] 1. A secondary battery electrolyte composition comprising an amphiphilic solvent and a lithium salt electrolyte.

[0016] 2. In the secondary battery electrolyte composition as described in 1 above, the amphiphilic solvent is ethyl 3-hydroxypropionate or methyl 3-hydroxypropionate.

[0017] 3. The secondary battery electrolyte composition as described in 2 above further comprises ethylene carbonate.

[0018] 4. The secondary battery electrolyte composition as described in 3 above contains ethyl 3-hydroxypropionate or methyl 3-hydroxypropionate and ethylene carbonate in a volume ratio of 1:0.5 to 2.

[0019] 5. A secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and a secondary battery electrolyte as described in any one of 1 to 4 above.

[0020] The effects of the invention

[0021] The electrolyte composition of the present invention can suppress the ignition and spread of fire in secondary batteries. As a non-flammable substance, it reduces the vapor pressure of the electrolyte and significantly increases the flash point.

[0022] The electrolyte composition of the present invention and the secondary battery containing it can suppress ignition and fire spread.

[0023] The electrolyte composition of the present invention and the electrolyte solvent composition of the secondary battery comprising the present invention are composed of an environmentally friendly amphiphilic solvent that is easily soluble in water. The electrolyte solvent composition may become fuel for fires. Therefore, although it has a fire extinguishing effect, if a fire still occurs, the electrolyte solvent composition can be easily dissolved in water and used to extinguish the fire.

[0024] In the case of a battery system employing the electrolyte composition of the present invention and a secondary battery containing the present invention, a non-flammable solvent is used as the electrolyte, with a flash point much higher than 93°C, which is the flammable standard in the US OSHA fire protection standard. Therefore, it can operate at higher temperatures or remain safe and maintain battery status even under temporary shocks. Attached Figure Description

[0025] Figure 1 The results of conductivity measurements are shown after dissolving 0.5 M to 3 M lithium hexafluorophosphate in EHP.

[0026] Figure 2 The results show the conductivity of dissolving 0.5 M to 3 M lithium hexafluorophosphate in a mixed solvent prepared by dissolving ethylene carbonate (EC) in EHP at a 1:1 ratio.

[0027] Figure 3 The results show the conductivity of two lithium-ion electrolytes (electrolyte I, II) and EHP / EC electrolyte used prior to the determination over a wide temperature range. Detailed Implementation

[0028] The present invention will now be described in detail.

[0029] This invention relates to a secondary battery electrolyte composition.

[0030] The secondary battery electrolyte composition of the present invention comprises an amphiphilic solvent and an electrolyte.

[0031] Amphiphilic solvents possess both hydrophobic and hydrophilic properties, thus they can dissolve both hydrophobic and hydrophilic substances simultaneously.

[0032] Typically, solvents used in secondary battery electrolytes include ethylene carbonate, which is solid at room temperature, and dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC), which can dissolve it. However, these solvents have low flash points or boiling points, are easily flammable, and are volatile, thus further intensifying a fire in the event of one.

[0033] However, the electrolyte composition of the present invention uses an amphiphilic solvent, thus preventing the above-mentioned problems.

[0034] For example, an amphiphilic solvent could be ethyl 3-hydroxypropionate (C5H 10 O3, ethyl-3-hydroxypropanoate (EHP). It can also be methyl 3-hydroxypropanoate (C4H8O3, Methyl 3-hydroxypropanoate, MHP).

[0035] Amphiphilic solvents can be non-volatile or non-flammable.

[0036] The compositions of the present invention may also contain ethylene carbonate. It can be used as a solvent in conjunction with amphiphilic solvents.

[0037] There are no particular limitations on the mixing ratio of the amphiphilic solvent and ethylene carbonate; for example, the content can be a volume ratio of 1:0.5 to 2.

[0038] The electrolyte can be the type commonly used in secondary batteries.

[0039] For example, the electrolyte can be a lithium salt.

[0040] Lithium salts contain lithium cations (Li + As a medium for transporting ions, it may also contain elements selected from 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 group consists of one or more anions, but is not limited to them.

[0041] For example, the lithium salt concentration can be from 0.1M to 3M.

[0042] Furthermore, the present invention relates to a secondary battery comprising the electrolyte.

[0043] The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0044] The positive electrode may include a positive current collector and a layer of positive active material formed on the positive current collector.

[0045] Non-limiting examples of positive current collectors may include foils made of aluminum, nickel, or combinations thereof, wherein the positive active material layer may contain a positive active material and, as required, may contain binders, conductive materials, dispersants, etc.

[0046] Common positive electrode active materials can be used as positive electrode active materials, such as lithium cobalt oxide composite oxide (LiCoO2), spinel-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 (Li2FeP2O7), lithium niobate composite oxide (LiNbO2), lithium ferrite composite oxide (LiFeO2), lithium magnesium oxide composite oxide (LiMgO2), lithium copper oxide composite oxide (LiCuO2), lithium zinc oxide composite oxide (LiZnO2), lithium molybdate composite oxide (LiMoO2), lithium tantalate composite oxide (LiTaO2), lithium tungstate composite oxide (LiWO2), lithium permanganate nickel cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, etc., but not limited to these.

[0047] Carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp smoke black, and thermal cracking black can be used as conductive materials. Conductive fibers such as carbon fiber and metal fiber can also be used. Metal powders such as fluorinated carbon, aluminum, and nickel powder can also be used. Conductive whiskers such as zinc oxide and potassium titanate can also be used. Conductive metal oxides such as titanium oxide can also be used. Conductive materials such as polyphenylene derivatives can also be used. However, there are no special restrictions as long as the material does not cause chemical changes in the battery and is conductive.

[0048] The adhesive polymer may include one or more selected from the group consisting of nitrile rubber, polybutadiene rubber, polyethylene glycol, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, polypropylene oxide, polydimethylsiloxane, polyvinylidene fluoride, polyvinylidene carbonate, and polyvinylpyrrolidone.

[0049] The negative electrode may include a negative current collector and a layer of negative active material formed on the negative current collector.

[0050] Non-limiting examples of negative current collectors may be selected from foils made of copper, gold, nickel or copper alloys or combinations thereof.

[0051] The negative electrode active material layer may be any one of the following carbons selected from soft carbon, hard carbon, artificial graphite, natural graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, acetylene black, Ketjen black, graphene, fullerene, activated carbon, and secondary carbon microspheres; any one of the following metals 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 aforementioned metals; and an oxide of one or more of the aforementioned metals; or one or more of the following groups of materials, but not limited thereto.

[0052] The present invention will now be described in more detail through examples.

[0053] Example

[0054] 1. Determine the conductivity based on electrolyte concentration.

[0055] (1) Add 0.5M to 3M of lithium hexafluorophosphate electrolyte to the amphiphilic solvent ethyl 3-hydroxypropionate and measure the conductivity of the electrolyte.

[0056] The experiment was conducted in a temperature-adjustable device with an operating temperature of -20 to 100°C.

[0057] The measurement results are shown in Figure 1 middle.

[0058] As the temperature rises from low to high, ion movement becomes more active, thus exhibiting a trend of increasing conductivity. Conductivity also increases with increasing lithium salt concentration. The conductivity is relatively high at lithium salt concentrations of 1M and 2M. Notably, this result shows stable conductivity even at temperatures (30–100°C) higher than the flash points (<30°C) of DMC or DEC used in existing electrolytes.

[0059] (2) Add 0.5M to 3M of lithium hexafluorophosphate electrolyte to a solvent in which the amphiphilic solvents ethyl 3-hydroxypropionate and ethylene carbonate are mixed in a volume ratio of 1:1, and measure the conductivity of the electrolyte.

[0060] Ethylene carbonate is a solid at room temperature, but it remains stably liquid when dissolved in ethyl 3-hydroxypropionate. It retains its liquid form even at -20°C, thus demonstrating its potential as a substitute for existing volatile solvents.

[0061] The measurement results are shown in Figure 2 middle.

[0062] Similarly, it exhibits high conductivity even at temperatures up to 100°C without any issues. This contradicts previous findings, indicating that the addition of EC is crucial for conductivity. Both EHP and EC have high boiling and flash points, making them highly advantageous electrolyte solvents in terms of thermal stability and fire resistance.

[0063] 2. Comparison with existing electrolytes based on conductivity at temperature

[0064] The conductivity of the two previously used lithium-ion electrolytes (electrolyte I and II) and the EHP / EC electrolyte was measured over a wide temperature range. Under these conditions, the concentration of lithium hexafluorophosphate was fixed at 1 M. The temperature range was set to -20 to 100 °C.

[0065] The existing commercially available electrolytes have the following compositions: Electrolyte I: LiPF6 1M in EC:DEC = 1:1 (v / v) (LiPF6 is dissolved at a concentration of 1M in an equal volume of EC and DEC solutions at a 1:1 ratio), Electrolyte II: LiPF6 1M in EC:DEC:EMC = 1:1:1 (v / v) (LiPF6 is dissolved at a concentration of 1M in an equal volume of EC, DEC, and EMC solutions at a 1:1:1 ratio).

[0066] The measurement results are shown in Figure 3 middle.

[0067] The two existing electrolytes are highly flammable, thus limiting their operation to 40°C. While existing electrolytes exhibit slightly higher conductivity up to 40°C, their stability decreases at higher temperatures, preventing further experiments. The EHP+EC or EHP alone proposed in this invention can be used to measure conductivity up to higher temperatures.

[0068] For reference, the flash points of each solvent are shown in Table 1 below.

[0069] Table 1

[0070] condition Flash point (°C) - Closed cup EHP 112 EC 150 EHP:EC = 1:1 124 EHP:EC = 2:1 117 EHP:EC = 1:2 139 MHP 78

[0071] 3. Compare the conductivity based on the solvent.

[0072] Methyl 3-hydroxypropionate or ethyl 3-hydroxypropionate was mixed with ethylene carbonate, and the conductivity was measured according to temperature.

[0073] The results are shown in Table 2 below.

[0074] Table 2

[0075]

[0076] It is known that, within the specified temperature range, the conductivity of MHP is about 20% higher than that of EHP. This is likely because MHP has a lower molecular weight than EHP, resulting in lower viscosity and thus an advantage in ion mobility. However, unlike EHP, the conductivity of the MHP+EC combination decreases at temperatures 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, characterized in that, It contains amphiphilic solvents and lithium salt electrolytes.

2. The secondary battery electrolyte composition according to claim 1, characterized in that, The amphiphilic solvent is ethyl 3-hydroxypropionate or methyl 3-hydroxypropionate.

3. The secondary battery electrolyte composition according to claim 2, characterized in that, It also contains ethylene carbonate.

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

5. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and a secondary battery electrolyte according to any one of claims 1 to 4.

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