Electrolyte for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

To provide an electrolyte solution for a lithium secondary battery with excellent safety against overcharging and under high temperature, and a lithium secondary battery including the same.SOLUTION: An electrolyte solution for a lithium secondary battery in an embodiment includes a nonaqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound expressed by Chemical Formula 1, and a second compound expressed by Chemical Formula 2. (R1 and R2 independently represent a substituted or non-substituted aryl group with 6 to 30 carbons, and X1 to X3 independently represent a halogen or -O-La-Ra.)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. [Background technology]

[0002] In recent years, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for rechargeable batteries with high energy density and high capacity has been rapidly increasing. Therefore, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0003] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material that allows for the insertion and deintercalation of lithium ions, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated at the positive and negative electrodes.

[0004] Recently, lithium-ion secondary batteries that offer high capacity, high energy density, and high safety are being actively researched for use as power sources for hybrid and electric vehicles, or as power storage devices.

[0005] In lithium-ion batteries, the electrolyte plays a crucial role in transporting lithium ions. It contains organic solvents and lithium salts and exhibits very high ionic conductivity. Such electrolytes play a vital role in determining the safety and performance of lithium-ion batteries.

[0006] When lithium-ion secondary batteries are subjected to overcharging or high temperatures, they can rapidly overheat, generating gas and potentially leading to cell explosions, raising concerns about battery safety.

[0007] Therefore, there is a need to develop electrolytes that provide superior safety even under overcharging and high temperatures. [Overview of the Initiative]

Problems to be Solved by the Invention

[0008] One embodiment of the present invention is an electrolyte for a lithium secondary battery that is excellent in overcharge and high-temperature safety.

[0009] Another embodiment of the present invention is a lithium secondary battery containing the above electrolyte.

Means for Solving the Problems

[0010] One embodiment of the present invention is an electrolyte for a lithium secondary battery, which contains a non-aqueous organic solvent, a lithium salt, and an additive, and the additive contains a first compound represented by the following chemical formula 1 and a second compound represented by the following chemical formula 2.

[0011]

Chem.

[0012] In Chemical Formula 1, R a and R 2 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and any one or more of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms. In Chemical Formula 2, X 1 to X 3 are each independently a halogen or -O-L a -R a and at least one of X 1 to X 3 is -O-L a -R a where L a is a single bond or a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms. R aThese are cyano groups (-CN), difluorophosphate groups (-OPF2), substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 alkenyl groups, substituted or unsubstituted C2-C10 alkynyl groups, substituted or unsubstituted C3-C10 cycloalkyl groups, substituted or unsubstituted C3-C10 cycloalkenyl groups, substituted or unsubstituted C3-C10 cycloalkynyl groups, or substituted or unsubstituted C6-C20 aryl groups.

[0013] R a If is an alkyl group, alkenyl group, alkynyl group, cycloalkyl group, cycloalkenyl group, cycloalkynyl group, or aryl group, at least two carbons may be linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.

[0014] Another embodiment of the present invention is a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator located between the positive electrode and the negative electrode, and the electrolyte described above. [Effects of the Invention]

[0015] An electrolyte for lithium secondary batteries according to one embodiment of the present invention can realize a battery with excellent safety under overcharging and high-temperature conditions. [Brief explanation of the drawing]

[0016] [Figure 1] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 2] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 3] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 4] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 5]This graph shows the overcharge evaluation results for lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 1-4. [Figure 6] This graph shows the evaluation results at high temperatures for lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 1-4. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described in detail below. However, these are presented as examples only and do not limit the present invention, which is defined solely by the scope of the claims described below.

[0018] Unless otherwise specified herein, when a part such as a layer, film, region, or plate is said to be "on top of" another part, this includes not only the case where it is "directly on top of" another part, but also the case where there is yet another part in between.

[0019] Unless otherwise specified herein, singular nouns may also include plural nouns. Similarly, unless otherwise specified, "A or B" may mean "containing A, or containing B, or containing both A and B."

[0020] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0021] Unless otherwise defined herein, particle size may refer to average particle size. Furthermore, particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. Average particle size (D50) can be measured by methods widely known to those skilled in the art. For example, average particle size (D50) can be measured using a particle size analyzer, or by using a transmission electron microscope or scanning electron microscope. Alternatively, a measurement device using dynamic light-scattering can be used, and the average particle size (D50) can be calculated after data analysis and counting of the number of particles for each particle size range. Alternatively, it can be measured using the laser diffraction method. When measuring using laser diffraction, more specifically, the particles to be measured are dispersed in a dispersion medium, the dispersion is introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac's MT3000), and ultrasound at approximately 28 kHz is irradiated at an output of 60 W. Then, the average particle size (D50) at the 50% reference level of the particle size distribution in the analyzer is calculated.

[0022] Here, "substitution" means that, unless otherwise defined, a substituent or at least one hydrogen atom in a compound is substituted with deuterium, halogen, hydroxyl group, amino group, C1-C30 amine group, nitro group, C1-C40 silyl group, C1-C30 alkyl group, C1-C10 alkylsilyl group, C6-C30 arylsilyl group, C3-C30 cycloalkyl group, C3-C30 heterocycloalkyl group, C6-C30 aryl group, C2-C30 heteroaryl group, C1-C20 alkoxy group, C1-C10 fluoroalkyl group, cyano group, or a combination thereof.

[0023] Specifically, "substitution" can mean that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. For example, "substitution" can mean that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. Alternatively, "substitution" can mean that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. For example, "substitution" can mean that a substituent or at least one hydrogen atom in a compound is substituted with deuterium, a cyano group, a halogen, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0024] An electrolyte for a lithium secondary battery according to one embodiment of the present invention comprises a non-aqueous organic solvent, a lithium salt, and an additive, the additive comprising a first compound and a second compound. The first and second compounds are described in detail below.

[0025] When the first and second compounds are used in combination, both battery stability under overcharging conditions and battery safety under high temperatures can be effectively achieved.

[0026] 1.First compound The first compound is a sulfoxide-based compound that effectively suppresses the heat generated by the battery under overcharge driving conditions. The first compound is represented by the following chemical formula 1.

[0027] [ka]

[0028] In chemical formula 1, R 1 and R 2 Each of these is independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, R 1 and R 2 One or more of these are substituted or unsubstituted aryl groups with 6 to 30 carbon atoms.

[0029] In one embodiment, chemical formula 1 can be represented by the following chemical formula 1-1 or chemical formula 1-2. As a most specific example, chemical formula 1 can be represented by the following chemical formula 1-1.

[0030] [ka]

[0031] In chemical formula 1-1, R 1a H is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. a ~H e Each of these may independently be hydrogen, halogen, hydroxyl group, cyano group, nitro group, substituted or unsubstituted C1-C20 alkyl group, substituted or unsubstituted C1-C20 alkoxy group, substituted or unsubstituted C2-C20 alkenyl group, substituted or unsubstituted C2-C20 alkynyl group, substituted or unsubstituted C3-C20 cycloalkyl group, substituted or unsubstituted C6-C20 aryl group, or substituted or unsubstituted C2-C20 heteroaryl group.

[0032] As a specific example, H a ~H e Each of these may independently be hydrogen, a halogen, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0033] [ka]

[0034] In chemical formula 1-2, H a ~H j Each of these may independently be hydrogen, a halogen, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group.

[0035] As a specific example, H a ~H j Each of these may independently be hydrogen, a halogen, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0036] For example, the first compound may be one or more compounds selected from the compounds listed in Group 1 below.

[0037] [ka]

[0038] In one embodiment, the first compound may be present in an amount exceeding 0.05% by weight or 0.1% by weight or more relative to the total weight of the electrolyte for the lithium secondary battery, and may also be present in an amount less than 6% by weight or 5% by weight or less.

[0039] As a specific example, the first compound may be included in an amount exceeding 0.05% by weight but less than 6% by weight of the total weight of the electrolyte for lithium secondary batteries, for example, exceeding 0.05% by weight but not exceeding 5% by weight, 0.1% by weight or more but less than 6% by weight, or 0.1% by weight to 5% by weight.

[0040] When the first compound is present in an amount of 0.05% by weight or less relative to the total weight of the electrolyte for lithium secondary batteries, the effect of improving battery safety during overcharging is low, and when it is present in an amount of 6% by weight or more, there is a problem that the battery resistance increases excessively.

[0041] 2.Second compound The second compound plays a role in stabilizing the lithium salt in the electrolyte, thereby suppressing the decomposition of the electrolyte at high temperatures. This effectively suppresses gas generation inside the battery at high temperatures, simultaneously improving battery safety and lifespan characteristics at high temperatures.

[0042] The second compound is represented by the following chemical formula 2.

[0043] [ka]

[0044] In chemical formula 2, X 1 ~X 3 Each is independently halogen or -OL a -R a X 1 ~X 3 At least one of them is -OL a -R a And, L a R is a single-bonded, substituted, or unsubstituted alkylene group having 1 to 10 carbon atoms, a These are cyano groups (-CN), difluorophosphate groups (-OPF2), substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 alkenyl groups, substituted or unsubstituted C2-C10 alkynyl groups, substituted or unsubstituted C3-C10 cycloalkyl groups, substituted or unsubstituted C3-C10 cycloalkenyl groups, substituted or unsubstituted C3-C10 cycloalkynyl groups, or substituted or unsubstituted C6-C20 aryl groups. aIf is an alkyl group, alkenyl group, alkynyl group, cycloalkyl group, cycloalkenyl group, cycloalkynyl group, or aryl group, at least two carbons may be linked to form a substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle, or a substituted or unsubstituted monocyclic or polycyclic aromatic heterocycle.

[0045] Here, the substituted or unsubstituted monocyclic or polycyclic aliphatic heterocycle may be a C1-C8 heterocycloalkyl group containing a heteroatom of N, O, S, P, or Si within the ring, and the substituted or unsubstituted aromatic heterocycle may be a C3-C8 heteroaryl group containing a heteroatom of N, O, S, P, or Si within the ring.

[0046] In one embodiment, chemical formula 2 can be represented by any one of the following chemical formulas 2-1 to 2-3.

[0047] [ka]

[0048] In chemical formula 2-1, m is one of the integers from 1 to 5, and R 10 This may be a cyano group (-CN) or a difluorophosphate group (-OPF2).

[0049] [ka]

[0050] In chemical formula 2-2, L a1 ~L a3 Each of these is independently a single-bonded, substituted, or unsubstituted alkylene group having 1 to 5 carbon atoms, and R a1 ~R a3Each of these may independently be a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C3-C10 cycloalkenyl group, a substituted or unsubstituted C3-C10 cycloalkynyl group, or a substituted or unsubstituted C6-C20 aryl group.

[0051] [ka]

[0052] In chemical formula 2-3, X 1 is halogen or -OL a4 -R a4 And L a4 R is a single-bonded, substituted, or unsubstituted alkylene group having 1 to 5 carbon atoms, a4 L is a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C3-C10 cycloalkyl group, a substituted or unsubstituted C3-C10 cycloalkenyl group, a substituted or unsubstituted C3-C10 cycloalkynyl group, or a substituted or unsubstituted C6-C20 aryl group. 1 This may be a substituted or unsubstituted alkylene group having 2 to 5 carbon atoms.

[0053] For example, the second compound may be one or more compounds selected from the compounds listed in Group 2 below.

[0054] [ka]

[0055] In one of the most specific embodiments, the additive contained in the electrolyte for a lithium secondary battery may be a composition comprising at least one of the compounds listed in Group 1 as the first compound and at least one of the compounds listed in Group 2 as the second compound.

[0056] As an example, the additive contained in the electrolyte for lithium secondary batteries may be a composition comprising compound 1-a of group 1 as the first compound, and compound 2-a or compound 2-d as the second compound.

[0057] In one embodiment, the second compound may be present in an amount exceeding 0.05% by weight or 0.1% by weight or more relative to the total weight of the electrolyte for the lithium secondary battery, and may also be present in an amount less than 5% by weight, less than 4% by weight, or 3% by weight or less.

[0058] As a specific example, the second compound may be included in an amount greater than 0.05% by weight but less than 4% by weight, or between 0.1% and 3% by weight, relative to the total weight of the electrolyte for the lithium secondary battery.

[0059] When the second compound is present in an amount of 0.05% by weight or less relative to the total weight of the electrolyte for lithium secondary batteries, the effect of improving battery safety at high temperatures is low, and when it is present in an amount of 4% by weight or more, there is a problem that the battery resistance increases excessively.

[0060] In one embodiment, the first compound and the second compound may be included in a weight ratio of 0.01:1 to 100:1, for example, in a weight ratio of 0.05:1 to 100:1, 0.01:1 to 40:1, 0.05:1 to 40:1, 0.05:1 to 20:1, or 0.1:1 to 20:1.

[0061] When the weight ratio of the first compound and the second compound satisfies the above numerical range, a battery with excellent safety in both overcharging and high-temperature conditions can be realized.

[0062] The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0063] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of batteries can move.

[0064] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0065] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles represented as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes can be used.

[0066] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0067] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0068] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium-ion secondary batteries. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 One or more of the following are selected: SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0069] A lithium secondary battery according to another embodiment includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator located between the positive electrode and the negative electrode, and the aforementioned electrolyte.

[0070] 3.Cathode active material As the active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more composite oxides of lithium with a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0071] The composite oxide may be a lithium transition metal composite oxide. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0072] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05), Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05), Li a Ni 1-b-c Co b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2), Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2), Li a Ni b Co c L 1 d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1), Li a NiG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a CoG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn 1-b G b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1), Li a Mn2Gb O4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1), Li a Mn 1-g G g PO4 (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5), Li (3-f) Fe2(PO4)3 (0 ≤ f ≤ 2), Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0073] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof, X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof, D is O, F, S, P, or a combination thereof, G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof, and L 1 is Mn, Al or a combination thereof.

[0074] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the content of nickel with respect to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel positive electrode active material can achieve a high capacity and can be applied to a high-capacity, high-density lithium secondary battery.

[0075] 4. Positive Electrode The positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer contains a positive electrode active material and may further contain a binder and / or a conductive material.

[0076] As an example, the positive electrode may further contain an additive that can serve as a sacrificial positive electrode.

[0077] The content of the positive electrode active material is 90 wt% - 99.5 wt% with respect to 100 wt% of the positive electrode active material layer, and the contents of the binder and the conductive material may be 0.5 wt% - 5 wt% respectively with respect to 100 wt% of the positive electrode active material layer.

[0078] The binder plays a role in firmly adhering the positive electrode active material particles to each other and firmly adhering the positive electrode active material to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0079] Conductive materials are used to impart conductivity to electrodes, and any material can be used as long as it does not cause chemical changes in the battery that is constructed and is an electronically conductive material. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0080] Al can be used as a current collector, but it is not the only option.

[0081] 5.Negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a lithium-doped and dedoped material, or a transition metal oxide.

[0082] Examples of substances that can reversibly intercalate / deintercalate lithium ions include carbon-based negative electrode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0083] As alloys of lithium metal, alloys of lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0084] As substances that can be doped and undoped with lithium, Si-based negative electrode active materials or Sn-based negative electrode active materials can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or combinations thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0085] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may have a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon is also located between the primary silicon particles, for example, the primary silicon particles are coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0086] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of this core.

[0087] Si-based or Sn-based anode active materials can be used in combination with carbon-based anode active materials.

[0088] 6.Negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or conductive material.

[0089] For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0090] The binder plays the role of firmly adhering the negative electrode active material particles to each other and firmly adhering the negative electrode active material to the current collector. Non-aqueous binders, aqueous binders, dry binders, or combinations thereof can be used as binders.

[0091] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0092] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0093] When using an aqueous binder as the negative electrode binder, it may further contain a cellulose series compound that can impart viscosity. This cellulose series compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or their alkali metal salts. Na, K, or Li can be used as the alkali metal.

[0094] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0095] Conductive materials are used to impart conductivity to electrodes, and any material can be used as long as it does not cause chemical changes in the battery that is constructed and is an electronically conductive material. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0096] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, and combinations thereof can be selected.

[0097] 7. Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0098] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0099] The porous substrate may be a polymer film formed from any one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from a copolymer or mixture of two or more of these polymers.

[0100] The organic material may include polyvinylidene fluoride polymers or (meth)acrylic polymers.

[0101] Inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0102] Organic and inorganic materials may be mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are laminated together.

[0103] 8. Lithium-ion batteries Lithium-ion batteries are classified into cylindrical, prismatic, pouch-type, and coin-type depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium-ion battery according to one embodiment, where Figure 1 is cylindrical, Figure 2 is prismatic, and Figures 3 and 4 are pouch-type batteries. Referring to Figures 1 to 4, the lithium-ion battery 100 may include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium-ion battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, as shown in Figure 2, the lithium-ion battery 100 may include a positive electrode lead tap 11 and a positive electrode terminal 12, a negative electrode lead tap 21, and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode taps 70, namely a positive electrode tap 71 and a negative electrode tap 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0104] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, and the present invention is not limited thereto. [Examples]

[0105] Examples and comparative examples of the present invention are described below. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to these examples.

[0106] Example 1 A basic electrolyte was prepared by dissolving 1.5 M lithium LiPF6 salt in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) in a volume ratio of 20:10:70 in order. Compounds 1-a and 2-a were added to the basic electrolyte to prepare further electrolytes.

[0107] [ka]

[0108] At this time, the first compound was present in a 2% by weight and the second compound in a 1% by weight relative to the total electrolyte.

[0109] LiNi 0.91 Co 0.07 Al 0.02 O2, polyvinylidene fluoride as a binder, and Ketjenblack as a conductive material were mixed in a weight ratio of 97:2:1, and this mixture was dispersed in N-methylpyrrolidone to prepare a cathode active material slurry.

[0110] A cathode active material slurry was coated onto a 14 μm thick aluminum foil, dried at 110°C, and then rolled (pressed) to produce the cathode.

[0111] A negative electrode active material slurry was prepared by mixing artificial graphite as the negative electrode active material, styrene-butadiene rubber as the binder, and carboxymethylcellulose as the thickener in a weight ratio of 97:1:2, and dispersing this mixture in distilled water. The negative electrode active material slurry was coated onto a 10 μm thick copper foil current collector, dried at 100°C, and then rolled to produce a negative electrode.

[0112] An electrode assembly was fabricated by placing a 25 μm thick polyethylene-polypropylene multilayer separator between the fabricated positive and negative electrodes. This assembly was then inserted into a circular battery case, and the prepared electrolyte was injected to produce the lithium secondary battery of Example 1.

[0113] Example 2 A lithium secondary battery was prepared in the same manner as in Example 1, except that compound 2-d was used as the second compound during electrolyte preparation.

[0114] [ka]

[0115] Examples 3 to 6 Lithium secondary batteries were prepared in the same manner as in Example 1, except that the content of the first compound relative to the total electrolyte was 0.05% by weight, 0.1% by weight, 5% by weight, and 6% by weight, respectively.

[0116] Examples 7 to 10 Lithium secondary batteries were prepared in the same manner as in Example 2, except that the content of the first compound relative to the total electrolyte was 0.05% by weight, 0.1% by weight, 5% by weight, and 6% by weight, respectively.

[0117] Examples 11-14 Lithium secondary batteries were prepared in the same manner as in Example 1, except that the content of the second compound relative to the total electrolyte was 0.05% by weight, 0.1% by weight, 3% by weight, and 4% by weight, respectively.

[0118] Examples 15-18 Lithium secondary batteries were prepared in the same manner as in Example 2, except that the content of the second compound relative to the total electrolyte was 0.05% by weight, 0.1% by weight, 3% by weight, and 4% by weight, respectively.

[0119] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first and second compounds were not added to the electrolyte.

[0120] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the second compound was not added during the electrolyte preparation.

[0121] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the first compound was not added during the electrolyte preparation.

[0122] Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 2, except that the first compound was not added during the electrolyte preparation.

[0123] Table 1 below shows the types and contents of the first and second compounds contained in the electrolytes of Examples 1 to 18 and Comparative Examples 1 to 4.

[0124] [Table 1]

[0125] Evaluation example Evaluation Example 1: Overcharge Safety Evaluation Overcharge evaluations were performed on the lithium secondary batteries prepared in Examples 1 to 18 and Comparative Examples 1 to 4, and the results are shown in Table 2 and Figure 5 below.

[0126] A safety protection element was welded to the negative electrode of the lithium secondary battery cell, a tap was welded to the positive electrode, and a thermocouple was attached to the center of the cell and fixed in place to allow for temperature measurement. The cell was then charged to 10V at a charging speed of 2.0C, and the maximum temperature (°C) of the cell during overcharging was measured.

[0127] Referring to Table 2, it can be confirmed that in Comparative Examples 1, 3, and 4, where the first compound was not added to the electrolyte, the maximum cell temperature during overcharging was very high.

[0128] Furthermore, referring to Figure 5, it can be seen that in Examples 1 and 2, the maximum cell temperature reached approximately 70°C before approximately 10 minutes had elapsed, while in Comparative Examples 1, 3, and 4, the maximum cell temperature reached approximately 88°C or higher after 10 minutes had elapsed.

[0129] Evaluation Example 2: High Temperature Safety Evaluation The lithium secondary batteries manufactured in Examples 1 to 18 and Comparative Examples 1 to 4 were charged with a constant current at a charge rate of 0.5C and a cutoff condition of 4.2V / 3hr while discharged at 2.8V. After charging, they were charged to 0.05C while maintaining a constant voltage of 4.2V. After charging, high-temperature safety evaluations were performed using cells that were fully charged to SOC100.

[0130] After placing the lithium secondary batteries prepared in Examples 1 to 18 and Comparative Examples 1 to 4 into a chamber, the temperature was increased from room temperature (25°C) to 139°C, 140°C, 141°C, 142°C, 143°C, and 144°C at a heating rate of 5°C / min. The changes in the lithium secondary batteries were observed while maintaining these temperatures for about one hour.

[0131] The results of a total of three experiments are shown in Table 2. In Table 2, "P (Pass)" is displayed if thermal runaway did not occur while the temperature was maintained, and "F (Fail)" is displayed if rapid thermal runaway occurred.

[0132] Furthermore, Figure 6 shows the high-temperature safety evaluation results for the lithium secondary batteries prepared in Examples 1-2 and Comparative Examples 1-4. In Figure 6, the relatively thicker lines indicate voltage changes over time, and the relatively thinner lines indicate temperature changes over time.

[0133] Referring to Table 2, it can be confirmed that thermal runaway was observed at a temperature of 140°C in Comparative Examples 1 and 2, in which the second compound was not added to the electrolyte.

[0134] Referring to Figure 6, a sharp voltage drop was observed in the lithium secondary batteries of Examples 1-2 and Comparative Examples 1-4. When cylindrical batteries are rapidly exposed to high temperatures, gas is generated, increasing the internal pressure, which activates the battery protection circuit (CID) and causes a sharp voltage drop. The occurrence of a sharp voltage drop indicates that the protection circuits of the lithium secondary batteries in Examples 1-2 and Comparative Examples 1-4 were activated due to gas generation caused by high temperatures.

[0135] Specifically, in Comparative Examples 1 and 2, the lithium secondary batteries showed complete opening of the battery vents and a voltage of 0V after approximately 55 minutes. On the other hand, in the case of the lithium secondary batteries of Examples 1-2 and Comparative Examples 3-4, which contained both the first and second compounds, the protection circuit (CID) activated, but the battery vents did not open.

[0136] Referring to Figure 6, it was confirmed that the lithium secondary batteries of Example 1 and Example 2 did not experience thermal runaway even when exposed to a temperature of 142°C.

[0137] On the other hand, in Comparative Example 1, it was confirmed that a rapid thermal runaway occurred, reaching approximately 500°C at around 55 minutes, and in Comparative Example 2, it was confirmed that a rapid thermal runaway occurred, reaching over 600°C at around 56 minutes.

[0138] Evaluation Example 3: DC-IR Resistance Evaluation The DC-IR (direct current-to-internal resistance) of the lithium secondary batteries prepared in Examples 1 to 18 and Comparative Examples 1 to 4 was measured at the state of charge (SOC, state of charge = 100%), and the results are shown in Table 2 below.

[0139] Referring to Table 2, it can be confirmed that the lithium secondary batteries of Examples 1 to 18 maintain a DC-internal resistance at a level equivalent to that of the comparative examples, while exhibiting excellent safety against overcharging and high temperatures, as described above.

[0140] [Table 2]

[0141] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention. [Explanation of Symbols]

[0142] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tap 12: Positive terminal 20: Negative electrode 21: Negative lead tap 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode Tap 71: Positive Tap 72: Negative electrode tap

Claims

1. It comprises a non-aqueous organic solvent, a lithium salt, and additives. The additive comprises a first compound represented by the following chemical formula 1-1 or 1-2, and a second compound represented by any one of the following chemical formulas 2-1 to 2-3. 【Chemistry 1】 【Chemistry 2】 In the aforementioned chemical formula 1-1, R1a is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. H a to H e are each independently hydrogen, halogen, substituted or unsubstituted C1 to C20 alkyl, or substituted or unsubstituted C1 to C20 alkoxy group. In the above chemical formula 1-2, H a to H j are each independently hydrogen, halogen, substituted or unsubstituted C1 to C20 alkyl, or substituted or unsubstituted C1 to C20 alkoxy group. In the aforementioned chemical formula 2-1, m is one of the integers from 1 to 5. R 10 is a cyano group (-CN) or a difluorophosphate group (-OPF 2), In the aforementioned chemical formula 2-2, L a1 to L a3 are each independently single-bonded, substituted, or unsubstituted alkylene groups having 1 to 5 carbon atoms. R a1 to R a3 are each independently a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C2-C10 alkenyl group, or a substituted or unsubstituted C2-C10 alkynyl group. In the above chemical formula 2-3, X1 is a halogen, L1 is a substituted or unsubstituted alkylene group having 2 to 5 carbon atoms. An electrolyte for a lithium secondary battery, comprising the first compound and the second compound in a weight ratio of 0.01:1 to 100:

1.

2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is one or more of the compounds listed in Group 1 below. 【Transformation 3】

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound is one or more of the compounds listed in Group 2 below. 【Chemistry 4】

4. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is contained in an amount greater than 0.05% by weight and less than 6% by weight of the total weight of the electrolyte for the lithium secondary battery.

5. The electrolyte for lithium secondary batteries according to claim 1, wherein the second compound is contained in an amount greater than 0.05% by weight and less than 4% by weight of the total weight of the electrolyte for lithium secondary batteries.

6. Positive electrode containing positive electrode active material, A negative electrode containing negative electrode active material, A separator located between the positive electrode and the negative electrode, and A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to any one of claims 1 to 5.

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