Electrolyte additives for lithium secondary batteries and electrolytes for lithium secondary batteries and lithium secondary batteries each comprising the same

Abstract

Electrolyte additives for lithium secondary batteries, electrolytes for lithium secondary batteries including the same, and lithium secondary batteries including the electrolytes are disclosed. The electrolyte additives include compounds represented by the following chemical formula 1: <Formula 1> In chemical formula 1, R1 to R6 are as defined in the detailed description.

Description

Technical Field

[0001] This disclosure relates to electrolyte additives for lithium secondary batteries, electrolytes for lithium secondary batteries containing the same, and lithium secondary batteries including the electrolyte. Background Art

[0002] Lithium-ion batteries are used to power portable electronic devices such as video cameras, mobile phones, and laptops. Rechargeable lithium-ion batteries have a higher energy density per unit weight than known lead-acid, nickel-cadmium, nickel-metal hydride, and nickel-zinc batteries, and can be charged at high speeds.

[0003] Because lithium-ion batteries operate at high driving voltages, aqueous electrolytes, which are highly reactive with lithium, cannot be used. Organic electrolytes are typically used as electrolytes for lithium-ion batteries. Organic electrolytes are prepared by dissolving lithium salts in organic solvents. Preferably, the organic solvent is stable at high voltages, has high ionic conductivity and a high dielectric constant, and has low viscosity.

[0004] However, when organic electrolytes containing lithium salts are used as electrolytes for lithium secondary batteries, the battery's lifespan and high-temperature stability can be degraded due to side reactions between the anode / cathode and the electrolyte. Therefore, there is a need for an electrolyte that can provide lithium secondary batteries with improved lifespan and high-temperature stability. Summary of the Invention

[0005] Technical issues

[0006] On the one hand, it provides electrolyte additives for lithium secondary batteries.

[0007] On the other hand, it provides electrolytes for lithium secondary batteries that contain electrolyte additives.

[0008] On the other hand, it also provides lithium secondary batteries that include an electrolyte for lithium secondary batteries.

[0009] Solution to the problem

[0010] According to one aspect, an electrolyte additive for lithium secondary batteries is provided, the electrolyte additive comprising a compound represented by Formula 1 below:

[0011] <Formula 1>

[0012]

[0013] In Equation 1, R1 to R3 are each independently hydrogen, substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatics, and

[0014] R4 through R6 are each independently substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatic compounds.

[0015] According to another aspect, an electrolyte is provided, comprising:

[0016] Lithium salts;

[0017] Organic solvents; and

[0018] The above-mentioned additives.

[0019] According to another aspect, a lithium secondary battery is provided, comprising:

[0020] A cathode containing cathode active material;

[0021] An anode containing an anodic active material; and

[0022] Provide electrolyte between the cathode and anode,

[0023] The electrolytes include the additives mentioned above.

[0024] Advantages of this disclosure

[0025] When an electrolyte for lithium secondary batteries containing electrolyte additives according to the embodiments is used, lithium secondary batteries with improved high-temperature characteristics and resistance characteristics can be manufactured. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a lithium secondary battery according to an embodiment.

[0027] Figure 2 This is a graph showing the high-temperature storage resistance characteristics of lithium secondary batteries according to Examples 1 to 4 and Comparative Examples 1 to 3.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1: Lithium secondary battery 2: Anode

[0030] 3: Cathode 4: Partition

[0031] 5: Battery casing 6: Cover assembly Detailed Implementation

[0032] The following will describe in more detail the electrolyte additive for a lithium secondary battery according to embodiments, the electrolyte for a lithium secondary battery comprising the additive, and the lithium secondary battery comprising the electrolyte.

[0033] The electrolyte additive for lithium secondary batteries according to the embodiments includes a compound represented by the following formula 1:

[0034] <Formula 1>

[0035]

[0036] In Equation 1, R1 to R3 are each independently hydrogen, substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatics, and

[0037] R4 through R6 are each independently substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatic compounds.

[0038] In Equation 1, the substituted C1-C 30 Alkyl, substituted C4-C 30 Carbocyclic groups, substituted C6-C 30 Aryl, substituted C2-C 30 Alkenyl, substituted C2-C 30 alkynyl or substituted C2-C 30 The substituents of the heteroaryl group are, for example, selected from at least one of the following groups: C1-C 20 Alkyl, C2-C 20 alkenyl, C2-C 20 Alkyne group, C1-C 20Alkoxy, halogen, cyano, hydroxy, and nitro.

[0039] High-power and high-capacity lithium-ion secondary batteries can be manufactured using lithium transition metal oxides as the cathode active material. These oxides contain nickel and one or more other transition metals, with a nickel content of 80 mol% or more relative to the total molar amount of the transition metals. However, in general, lithium transition metal oxides with high nickel content in lithium-ion secondary batteries have an unstable surface structure, leading to increased gas generation due to side reactions during charging and discharging, and further intensified elution of transition metals such as nickel. Consequently, the lifespan characteristics of the lithium-ion secondary battery deteriorate. Furthermore, because the resistance of lithium-ion secondary batteries increases at high temperatures, it is necessary to improve their high-temperature stability.

[0040] When electrolyte additives containing compounds of Formula 1 are used, lithium secondary batteries with improved life characteristics and high-temperature stability can be manufactured due to their excellent resistance suppression effect at high temperatures.

[0041] In Equation 1, R1 to R3 are each independently hydrogen; substituted or unsubstituted C1-C 30 Alkyl; a C1-C group selected from one or more substituted groups of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkyl; or one or more substituted C2-C groups selected from the group consisting of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkenyl group.

[0042] In Equation 1, R4 to R6 are each independently C1-C 30 Alkyl; a C1-C group selected from one or more substituted groups of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkyl; or one or more substituted C2-C groups selected from the group consisting of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkenyl group.

[0043] In Equation 1, R1 to R3 are each independently, for example, hydrogen or C1-C. 10 Alkyl, specifically C1-C5 alkyl.

[0044] According to the embodiments, the compound of Formula 1 may be a compound of Formula 2.

[0045] <Formula 2>

[0046]

[0047] In Equation 2, R4 to R6 are each independently substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatic compounds.

[0048] In Equation 2, the substituted C1-C 30 Alkyl, substituted C4-C 30 Carbocyclic groups, substituted C6-C 30 Aryl, substituted C2-C 30 Alkenyl, substituted C2-C 30 alkynyl or substituted C2-C 30 The substituents of the heteroaryl group are selected from at least one of the following groups: C1-C 20 Alkyl, C2-C 20 alkenyl, C2-C 20 Alkyne group, C1-C 20 Alkoxy, halogen, cyano, hydroxy, and nitro.

[0049] In Equation 2, R4 to R6 are each independently unsubstituted C1-C. 10 Alkyl; a C1-C group substituted with at least one of the groups selected from methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxyl, and nitro. 10 Alkyl; unsubstituted C2-C 10 alkenyl; a C2-C group substituted with at least one of the following groups: methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxyl, and nitro. 10 alkenyl; unsubstituted C4-C 10 The carbocyclic group; a C4-C group substituted with at least one of the following groups: methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxyl, and nitro. 10 Carbocyclic group; unsubstituted C6-C 10 aryl; or a C6-C group substituted with at least one of the groups selected from methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxyl, and nitro. 10 Aryl.

[0050] The reasons for adding the compound of Formula 1 to the electrolyte to improve the performance of lithium secondary batteries will be described in more detail below, but this is for the purpose of understanding the present disclosure, and the scope of the present disclosure is not limited to the scope described below.

[0051] Although LiPF6 is commonly used as a lithium salt in electrolytes, its problem lies in its lack of thermal stability and its susceptibility to hydrolysis by water. However, when additives comprising compounds represented by Formula 1 are added to the electrolyte, the nitrogen in the imidazole ring of the compound of Formula 1 captures the PF produced by water (H2O) molecules and the decomposition of LiPF6. 5- The ions can suppress the hydrolysis reaction of LiPF6 caused by moisture. As a result, gas generation inside the lithium secondary battery is suppressed, thereby improving the battery's cycle life characteristics. Furthermore, it can prevent battery swelling caused by suppressing gas generation.

[0052] Furthermore, since the compound represented by Formula 1 contains nitrogen, the decomposition of organic solvents such as ethylene carbonate (EC) is suppressed to reduce gas generation, resulting in a lower rate of resistance increase. Additionally, because the compound represented by Formula 1 has an SO2 moiety, a stable thin film can be formed on the cathode. This film formation suppresses additional metal leaching from the substrate, thereby suppressing over-discharge of the lithium secondary battery during placement and improving its characteristics.

[0053] During the initial charging of a lithium-ion secondary battery, the electrolyte decomposition reaction occurs at the anode surface because the reduction potential of the electrolyte is relatively higher than that of lithium. This electrolyte decomposition reaction forms a solid electrolyte interface (SEI) on the electrode surface to suppress the electron movement required for the reaction between the anode and the electrolyte, thereby preventing further electrolyte decomposition. Consequently, the battery performance largely depends on the characteristics of the film formed on the anode surface. Given this fact, by introducing electrolyte additives that can decompose before the electrolyte during the charging reaction, a more robust SEI layer with superior electrical properties is needed.

[0054] The electrolyte additive for lithium secondary batteries, represented by Formula 1, includes silyl groups -Si(R4)(R5)(R6) at its ends, thus forming an SEI film with a high concentration of silyl groups, resulting in a chemically stable, highly polar film. Correspondingly, the resistance at the interface between the electrolyte and the anode decreases, improving lithium-ion conductivity and thereby increasing the low-temperature discharge voltage.

[0055] The compound represented by Formula 1 can be selected from the compounds represented by Formulas 3 to 6 below.

[0056] <Formula 3>

[0057]

[0058] <Formula 4>

[0059]

[0060] In equation 4, Ph represents a phenyl group.

[0061] <Formula 5>

[0062]

[0063] <Formula 6>

[0064]

[0065] The above compounds are used as salt byproduct (PF5) stabilizers and HF scavengers via imidazole functional groups, and are oxidized and decomposed at the cathode to form a sulfite film, thereby suppressing side reactions (solvent decomposition) at high temperatures at the cathode.

[0066] The electrolyte for a lithium secondary battery according to the embodiments includes a lithium salt, an organic solvent, and additives. The content of the additives can range from 0.1 wt% to 10 wt% based on the total weight of the electrolyte for the lithium secondary battery, but is not limited thereto, and can be appropriately selected within a range that does not impair battery characteristics. For example, the content of the additives can range from 0.5 wt% to 5 wt% based on the total weight of the electrolyte for the lithium secondary battery. When the content of the additives is within the above range, a lithium secondary battery with improved high-temperature characteristics and resistivity characteristics can be manufactured without compromising battery life.

[0067] The electrolyte for lithium secondary batteries according to the embodiments may be an electrolyte comprising 0.1 wt% to 2 wt% of at least one compound selected from Formulas 3 to 6 below, wherein the organic solvent comprises a mixed solvent of 50 vol% to 95 vol% of chain carbonates and 5 vol% to 50 vol% of cyclic carbonates.

[0068] <Formula 3>

[0069]

[0070] <Formula 4>

[0071]

[0072] <Formula 5>

[0073]

[0074] <Formula 6>

[0075]

[0076] According to embodiments, the lithium salt may include at least one selected from LiPF6, LiBF4, LiCF3SO3, Li(CF3SO2)2N, LiC2F5SO3, Li(FSO2)2N, LiC4F9SO3, LiN(SO2CF2CF3)2 and compounds represented by Formulas 10 to 13 below, but is not limited thereto, and any lithium salt may be used as long as it is used in the art.

[0077] [Formula 10]

[0078]

[0079] [Equation 11]

[0080]

[0081] [Equation 12]

[0082]

[0083] [Equation 13]

[0084]

[0085] The concentration of lithium salt in the electrolyte is 0.01M to 5.0M, for example, 0.05M to 5.0M, for example, 0.1M to 5.0M, for example, 0.1M to 2.0M. When the concentration of lithium salt is within the above range, further improved characteristics of the lithium secondary battery can be obtained.

[0086] The organic solvent may be at least one selected from carbonate solvents, ester solvents, ether solvents and ketone solvents.

[0087] As carbonate solvents, methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), propylene carbonate (PC), ethylene carbonate (EC), or butyl carbonate (BC) can be used; as ester solvents, methyl propionate, ethyl propionate, ethyl butyrate, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, γ-butyrolactone, decanoic acid lactone, γ-valerolactone, mevalonate lactone, or caprolactone can be used; as ether solvents, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran can be used; as ketone solvents, cyclohexanone can be used; and as nitrile solvents, acetonitrile (AN), succinic acid (SN), or adiponitrile can be used. Other solvents may include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, or tetrahydrofuran, but are not limited to these, and any solvent that can be used as an organic solvent in the art may be used. For example, the organic solvent may be a mixture of 50 vol% to 95 vol% of linear carbonates and 5 vol% to 50 vol% of cyclic carbonates, such as a mixture of 70 vol% to 95 vol% of linear carbonates and 5 vol% to 30 vol% of cyclic carbonates. For example, the organic solvent may be a mixture of three or more organic solvents.

[0088] According to embodiments, the organic solvent may include at least one selected from the group consisting of: ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), butylene carbonate, ethyl propionate, ethyl butyrate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone, and tetrahydrofuran, but is not limited thereto, and any organic solvent that can be used in the art may be used.

[0089] According to embodiments, the electrolyte for lithium secondary batteries may further comprise an aliphatic nitrile compound. For example, the aliphatic nitrile compound may include, but is not limited to, acetonitrile (AN) or succinic anionyl (SN), and any nitrile group may be used, as long as a nitrile group is included at the end of the hydrocarbon. For example, based on the total weight of the electrolyte for lithium secondary batteries, the content of the aliphatic nitrile compound may range from 0.1% to 10% by weight, but is not limited thereto, and may be suitably selected within a range that does not impair the metal elution inhibition effect.

[0090] Electrolytes can be in liquid or gel state.

[0091] A lithium secondary battery according to another embodiment includes: a cathode including a cathode active material; an anode including an anode active material; and an electrolyte provided between the cathode and the anode, wherein the electrolyte includes the above additives.

[0092] Since the lithium secondary battery includes the above additives, an increase in the initial resistance of the lithium secondary battery is suppressed, gas generated due to side reactions is suppressed, and the life characteristics of the lithium secondary battery are improved. The cathode active material includes a lithium transition metal oxide containing nickel and other transition metals. In the lithium transition metal oxide containing nickel and other transition metals, the content of nickel may be 60 mol% or more, for example, 75 mol% or more, for example, 80 mol% or more, for example, 85 mol% or more, for example, 90 mol% or more, relative to the total number of moles of transition metals.

[0093] For example, the lithium transition metal oxide may be represented by the following formula 7:

[0094] <Formula 7>

[0095] Li a Ni x Co y M z O 2-b A b

[0096] In formula 7, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.6 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.3, x + y + z = 1, M is at least one selected from the group consisting of: manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), and boron (B), and A is F, S, Cl, Br, or a combination thereof. For example, 0.7 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.3; 0.8 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.3; 0.8 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2; 0.83 ≤ x < 0.97, 0 < y ≤ 0.15, 0 < z ≤ 0.15; or 0.85 ≤ x < 0.95, 0 < y ≤ 0.1, 0 < z ≤ 0.1.

[0097] For example, the lithium transition metal oxide may be a compound represented by formula 8 or formula 9:

[0098] <Formula 8>

[0099] LiNi x Co y Mn z O2

[0100] In Formula 8, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, 0 < z ≤ 0.1. For example, 0.7 ≤ x ≤ 0.95, 0 < y ≤ 0.3, 0 < z ≤ 0.3

[0101] <Formula 9>

[0102] LiNi x Co y Al z O2

[0103] In Formula 9, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, 0 < z ≤ 0.1. For example, 0.7 ≤ x ≤ 0.95, 0 < y ≤ 0.3, 0 < z ≤ 0.3. For example, 0.8 ≤ x ≤ 0.95, 0 < y ≤ 0.3, 0 < z ≤ 0.3. For example, 0.82 ≤ x ≤ 0.95, 0 < y ≤ 0.15, 0 < z ≤ 0.15. And for example, 0.85 ≤ x ≤ 0.95, 0 < y ≤ 0.1, 0 < z ≤ 0.1.

[0104] For example, the lithium transition metal oxide can be LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.2 O2 or LiNi 0.88 Co 0.1 Al 0.02 O2.

[0105] According to another embodiment, the cathode active material includes at least one active material selected from the group consisting of: Li-Ni-Co-Al (NCA), Li-Ni-Co-Mn (NCM), lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), and lithium iron phosphate (LiFePO4).

[0106] The anode active material may include at least one selected from silicon-based compounds, carbon-based materials, composites of silicon-based compounds and carbon-based compounds, and silicon oxides (SiOx, 0 < x < 2). The silicon-based compound may be silicon particles or silicon alloy particles, etc.

[0107] The size of the silicon-based compound is less than 200 nm, for example, 10 nm to 150 nm. The term "size" may indicate the average particle diameter when the silicon-based compound is spherical, and may indicate the average major axis length when the silicon particles are non-spherical.

[0108] When the size of the silicon-based compound is within the above range, the life characteristics are excellent, and when using the electrolyte according to the embodiment, the life of the lithium secondary battery is further improved.

[0109] The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, plate-shaped, flaky, spherical, or fibrous graphite, such as natural graphite or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, or calcined coke, etc.

[0110] The composite of the silicon-based compound and the carbon-based compound may be a composite having a structure in which silicon nanoparticles are arranged on the carbon-based compound, a composite in which silicon particles are included on and inside the surface of the carbon-based compound, or a composite in which the silicon particles are coated with the carbon-based compound and arranged in the carbon-based compound. In the composite of the silicon-based compound and the carbon-based compound, the carbon-based compound may be graphite, graphene, graphene oxide, or a combination thereof.

[0111] The composite of the silicon-based compound and the carbon-based compound may be an active material obtained by dispersing silicon nanoparticles having an average particle diameter of about 200 nm or less on carbon-based compound particles and then performing carbon coating, or an active material in which silicon (Si) particles are present on and inside graphite, etc. The average particle diameter of the secondary particles of the composite of the silicon-based compound and the carbon-based compound may be 5 μm to 20 μm. The average particle diameter of the silicon nanoparticles may be 5 nm or more, for example 10 nm or more, for example 20 nm or more, for example 50 nm or more, for example 70 nm or more. The average particle diameter of the silicon nanoparticles may be 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, or 10 nm or less. For example, the average particle diameter of the silicon nanoparticles may be 100 nm to 150 nm.

[0112] The average particle diameter of the secondary particles of the composite of the silicon-based compound and the carbon-based compound may be 5 μm to 18 μm, for example, 7 μm to 15 μm, for example, 10 μm to 13 μm.

[0113] The composite material of a silicon-based compound and a carbon-based compound according to an embodiment is a porous silicon composite cluster, which includes a porous core containing porous silicon composite secondary particles and a shell disposed on the porous core and containing a second graphene. The porous silicon composite secondary particles include aggregates of two or more kinds of silicon composite primary particles, and the silicon composite primary particles can be porous silicon composite clusters, and the porous silicon composite clusters include silicon, silicon oxide (SiOx) (O < x < 2) disposed on the silicon, and a first graphene disposed on the silicon oxide.

[0114] The composite material of a silicon-based compound and a carbon-based compound according to another embodiment can be a porous silicon composite cluster structure. The porous silicon composite cluster structure includes a porous silicon composite cluster and a carbon-based coating film containing amorphous carbon and disposed on the porous silicon composite cluster. The porous silicon composite cluster includes porous silicon composite secondary particles and a second carbon sheet on at least one surface of the porous silicon composite secondary particles. The porous silicon composite secondary particles include aggregates of two or more kinds of silicon composite primary particles. The silicon composite primary particles include silicon; silicon oxide (SiOx) (O < x < 2) on at least one surface of the silicon, and a first carbon sheet on at least one surface of the silicon oxide, and the silicon oxide can exist in the state of a film, a matrix, or a combination thereof.

[0115] Each of the first carbon sheet and the second carbon sheet can exist in the form of a film, particles, a matrix, or a combination thereof. In addition, each of the first carbon sheet and the second carbon sheet can be graphene, graphite, carbon fiber, graphene oxide, or the like.

[0116] The composite material of a silicon-based compound and a carbon-based compound can be an active material obtained by dispersing silicon nanoparticles with an average particle size of about 200 nm or less on carbon-based compound particles and then performing carbon coating, or an active material in which silicon (Si) particles are present on and inside graphite, etc. The average particle size of the secondary particles of the composite material of a silicon-based compound and a carbon-based compound can be 5 μm to 20 μm. The average particle size of the silicon nanoparticles can be 5 nm or more, such as 10 nm or more, such as 20 nm or more, such as 50 nm or more, such as 70 nm or more. The average particle size of the silicon nanoparticles can be 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, or 10 nm or less. For example, the average particle size of the silicon nanoparticles can be 100 nm to 150 nm.

[0117] The average particle size of the secondary particles of the composite material of a silicon-based compound and a carbon-based compound can be 5 μm to 18 μm, for example, 7 μm to 15 μm, for example, 10 μm to 13 μm.

[0118] The composite material of a silicon-based compound and a carbon-based compound according to an embodiment is a porous silicon composite cluster, which includes a porous core containing porous silicon composite secondary particles and a shell disposed on the porous core and containing a second graphene. The porous silicon composite secondary particles include an aggregate of two or more kinds of silicon composite primary particles, and the silicon composite primary particles can be a porous silicon composite cluster, which includes silicon, silicon oxide (SiOx) (O < x < 2) disposed on the silicon, and a first graphene disposed on the silicon oxide. The composite material of a silicon-based compound and a carbon-based compound according to another embodiment can be a porous silicon composite cluster structure. The porous silicon composite cluster structure includes a porous silicon composite cluster and a carbon-based coating film containing amorphous carbon and disposed on the porous silicon composite cluster. The porous silicon composite cluster includes porous silicon composite secondary particles and a second carbon sheet on at least one surface of the porous silicon composite secondary particles. The porous silicon composite secondary particles include an aggregate of two or more kinds of silicon composite primary particles. The silicon composite primary particles include silicon; silicon oxide (SiOx) (O < x < 2) on at least one surface of the silicon, and a first carbon sheet on at least one surface of the silicon oxide, and the silicon oxide can exist in a state of a film, a matrix, or a combination thereof.

[0119] Each of the first carbon sheet and the second carbon sheet can exist in the form of a film, a particle, a matrix, or a combination thereof. In addition, each of the first carbon sheet and the second carbon sheet can be graphene, graphite, carbon fiber, graphene oxide, or the like.

[0120] The composite material of a silicon-based compound and a carbon-based compound can be, for example, an active material in which Si particles are dispersed on graphite particles and then coated with a carbon-based compound, an active material in which Si particles are present on and inside graphite, or a composite material in which silicon particles are coated with a carbon-based compound.

[0121] The average particle diameter of the Si particles is 50 nm to 200 nm, for example, 100 nm to 180 nm, for example, about 150 nm. The composite material of a silicon-based compound and a carbon-based compound can include, for example, the porous silicon composite cluster disclosed in Korean Patent Publication No. 10-2018-0031585 and the porous silicon composite cluster structure disclosed in Korean Patent Publication No. 10-2018-0056395.

[0122] After forming a lithium secondary battery and then storing the lithium secondary battery at a high temperature (60 °C) for 30 days, the increase rate of the DC internal resistance of the lithium secondary battery can be 155% or less, for example, 150% or less, for example, 135% to 155%. The formation of the lithium secondary battery can be carried out during 3 cycles.

[0123] There are no particular restrictions on the form of lithium secondary batteries, and they include lithium-ion batteries, lithium-ion polymer batteries, and lithium-sulfur batteries, etc.

[0124] Lithium secondary batteries can be manufactured by the following methods.

[0125] First, the cathode is prepared.

[0126] For example, a cathode active material composition is prepared in which cathode active material, conductive material, binder, and solvent are mixed. The cathode plate is prepared by coating a metal current collector with the cathode active material composition. Alternatively, the cathode plate can be prepared by casting the cathode active material composition onto a separate carrier, separating the film from the carrier, and then laminating the separated film onto the metal current collector. The cathode is not limited to the above-described forms but can have forms different from those described above.

[0127] The cathode active material as a lithium-containing metal oxide can be used without restriction, provided it is commonly used in the art. For example, as a lithium-containing metal oxide, at least one of lithium and a composite oxide of a metal selected from cobalt, manganese, nickel, and combinations thereof can be used. Specifically, compounds represented by any of the following formulas can be used: Li a A 1-b B 1 b D 1 2 (where 0.90≤a≤1.8 and 0≤b≤0.5); Li a E 1-b B 1 b O 2-c D 1 c (Where, 0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05 are satisfied); LiE 2-b B 1 b O 4-c D 1 c (Where, 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05 are satisfied); Li a Ni 1-b-c Co b B 1 c D 1 α (Where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2 are satisfied); Li a Ni 1-b-c Co b B 1 c O 2-α F1 α (Where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2 are satisfied); Li a Ni 1-b-c Co b B 1 c O 2-α F 1 2 (wherein, satisfying 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li a Ni 1-b-c Mn b B 1 c D 1 α (Where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2 are satisfied); Li a Ni 1-b-c Mn b B 1 c O 2-α F 1 α (Where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2 are satisfied); Li a Ni 1-b-c Mn b B 1 c O 2-α F 1 2 (wherein, satisfying 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein, satisfying 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO2 (wherein, satisfying 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1); Li a NiG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG bO2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a MnG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn2G b O4 (wherein, 0.90≤a≤1.8 and 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI 1 O2; LiNiVO4; Li (3-f) J2(PO4)3 (0≤f≤2); Li (3-f) Fe2(PO4)3 (0≤f≤2); and LiFePO4.

[0128] In the above formula, A represents Ni, Co, Mn, or a combination thereof; B 1 It is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof; D 1 O, F, S, P or combinations thereof; E is Co, Mn or combinations thereof; F 1 F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0129] For example, lithium-containing metal oxides can be LiCoO2 or LiMn. g O 2g (g = 1 or 2), LiNi 1-g Mn g O 2g (0 <g<1)、LiNi 1-g-k Co g Mn k O2 (0≤g≤0.5, 0≤k≤0.5) or LiFePO4.

[0130] Specifically, the cathode may include a cathode active material having a layered structure.

[0131] For example, the cathode active material includes lithium transition metal oxide, which contains nickel and one or more other transition metals, and the nickel content is 60 mol% or more, for example, 75 mol% or more, for example, 80 mol% or more, for example, 85 mol% or more, for example, 90 mol% or more, based on the total number of moles of transition metals.

[0132] For example, the cathode active material can be LiNi. 0.33Co 0.33 Mn 0.33 O2, LiNi 0.33 Co 0.33 Al 0.33 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Al 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.8 Co 0.1S Al 0.1 O2, but not limited to this.

[0133] Furthermore, compounds having a coating on the surface of the compound can be used, or mixtures of the compound and compounds having a coating can be used. The coating may include oxides, hydroxides, hydroxy oxides, oxycarbonates, or basic carbonates of the coating element. The compound constituting the coating may be amorphous or crystalline. Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used as coating elements included in the coating. During the coating formation process, any coating method may be used, provided that the compound can be coated with these elements by methods that do not adversely affect the physical properties of the cathode active material (e.g., spraying, dipping, etc.). Those skilled in the art will understand these coating methods, and therefore their detailed descriptions will be omitted.

[0134] As a conductive material, examples such as carbon black or fine graphite particles can be used, but it is not limited to these. Any conductive material can be used, as long as it is suitable for use in this field.

[0135] As a binder, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and mixtures thereof, or styrene-butadiene rubber polymers may be used. Any binder may be used, provided it is suitable for use in this field.

[0136] N-methylpyrrolidone, acetone, or water, etc., can be used as solvents, but this disclosure is not limited thereto. Any solvent can be used, as long as it is suitable for use in this field.

[0137] The content of cathode active material, conductive material, binder, and solvent are commonly used levels in lithium secondary batteries. Depending on the use and configuration of the lithium battery, at least one of the conductive material, binder, and solvent may be omitted.

[0138] Next, prepare the anode.

[0139] For example, prepare an anode active material composition in which an anode active material, a conductive material, a binder, and a solvent are mixed. The anode plate is prepared by coating a metal current collector with the anode active material composition. Optionally, the cathode plate can be prepared by casting the anode active material composition onto a separate carrier, separating the film from the carrier, and then laminating the separated film onto a metal current collector.

[0140] The anode active material can be, for example, at least one selected from the group consisting of silicon-based compounds, carbon-based materials, silicon oxides (SiOx (0 < x < 2)), and composites of silicon-based compounds and carbon-based compounds.

[0141] As the anode active material, any anode active material can be used as long as it is used as an anode active material for a lithium secondary battery in the art. For example, the anode active material can include at least one selected from the group consisting of lithium metal, metals that can form alloys with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0142] As the anode active material, in addition to the above anode active materials, any anode active material can be used together as long as it is used as an anode active material for a lithium secondary battery in the art. For example, the metal that can form an alloy with lithium can be Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si) or Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a combination thereof, and is not Sn), etc. The element Y can be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, or Te.

[0143] For example, the anode active material can be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0144] In the anode active material composition, the conductive material and the binder can be the same as those in the cathode active material composition.

[0145] However, water can be used as a solvent in the anolyte composition. For example, water can be used as a solvent, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), acrylate polymers or methacrylate polymers can be used as binders, and carbon black, acetylene black or graphite can be used as conductive materials.

[0146] The content of anode active material, conductive material, binder, and solvent are commonly used levels in lithium secondary batteries. Depending on the application and configuration of the lithium battery, at least one of the conductive material, binder, and solvent may be omitted.

[0147] For example, the anode can be prepared by mixing 94 wt% of anode active material, 3 wt% of binder and 3 wt% of conductive material in powder form, adding water to about 70 wt% of solids content to make a slurry, and then coating, drying and rolling the slurry.

[0148] Composite materials of silicon and carbon compounds can be used as anode active materials.

[0149] In the anodic active material composition, the conductive material, binder, and solvent may be the same as those in the cathodic active material composition.

[0150] The content of anode active material, conductive material, binder, and solvent are commonly used levels in lithium secondary batteries. Depending on the application and configuration of the lithium battery, at least one of the conductive material, binder, and solvent may be omitted. Next, a separator to be inserted between the anode and cathode is prepared. Any separator can be used as the separator, as long as it is commonly used in lithium batteries. A separator with low resistance to the movement of ions in the electrolyte and excellent electrolyte wettability can be used. For example, the separator may comprise any of glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), and combinations thereof, and may be made in the form of non-woven or woven fabric. For example, wound separators, including polyethylene or polypropylene, can be used in lithium-ion batteries, and separators with good electrolyte impregnation capabilities can be used in lithium-ion polymer batteries. For example, the separator can be manufactured by the following method.

[0151] A polymer resin, filler, and solvent are mixed to prepare a separator composition. The separator composition is applied directly to an electrode and dried to form a separator. Alternatively, the separator composition is cast onto a carrier and dried, a separation membrane is separated from the carrier, and then the separation membrane is laminated onto the electrode to form a separator.

[0152] There are no restrictions on the polymer resin used to manufacture the separator, and any material can be used as long as it can be used as an adhesive for the electrode plates. For example, as polymer resins, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof can be used.

[0153] The loading level of the anolyte composition is set according to the loading level of the cathode active material composition. Based on the capacity of each gram of anolyte composition, the loading level of the anolyte composition is 12 mg / cm³. 2 Or higher, for example, 15 mg / cm³ 2 Or higher. The electrode density can be at least 1.5 g / cc, for example at least 1.6 g / cc. For designs that emphasize energy density, a density of 1.65 g / cc or greater and 1.9 g / cc or less is preferred.

[0154] Next, the above-mentioned electrolyte is prepared.

[0155] According to the embodiments, in addition to the electrolytes mentioned above, the electrolytes may further include non-aqueous electrolytes, organic solid electrolytes, and inorganic solid electrolytes.

[0156] As organic solid electrolytes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfides, polyvinyl alcohol, or polyvinylidene fluoride can be used.

[0157] As inorganic solid electrolytes, for example, Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH or Li3PO4-Li2S-SiS2 can be used.

[0158] like Figure 1 As shown, the lithium secondary battery 1 includes a cathode 3, an anode 2, and a separator 4. The cathode 3, anode 2, and separator 4 are wound or folded and housed in a battery casing 5. An electrolyte according to an embodiment of the present disclosure is then injected into the battery casing 5, and the battery casing 5 is sealed with a capping assembly 6 to complete the manufacture of the lithium secondary battery 1. The battery casing 5 may have a cylindrical shape, a rectangular shape, or a thin-film shape. For example, the lithium secondary battery 1 may be a large thin-film battery. The lithium secondary battery 1 may be a lithium-ion battery.

[0159] A separator 4 can be positioned between the cathode 3 and the anode 2 to form a battery structure. The battery structure is laminated into a dual-cell structure, then impregnated with an electrolyte, and the resulting product is contained in a bag and sealed to complete the lithium-ion polymer battery.

[0160] Furthermore, multiple battery structures are laminated to form a battery pack, which can be used in all electrical appliances requiring high capacity and high power. For example, the battery pack can be used in laptops, smartphones, electric vehicles, etc.

[0161] In the lithium secondary battery according to the embodiment, compared with the lithium secondary battery that uses a general nickel-rich lithium-nickel composite oxide as the cathode active material, the DCIR increase rate is significantly reduced, thus exhibiting superior battery characteristics.

[0162] Lithium-ion secondary batteries that utilize a cathode, anode, and electrolyte have an operating voltage with a lower limit of 2.5V to 2.8V and an upper limit of 4.1V or higher, for example, 4.1V to 4.45V.

[0163] Lithium-ion batteries can be used in power tools powered by electric motors; electric vehicles (EVs) such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs); electric two-wheelers such as electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and energy storage systems, etc.; but this disclosure is not limited thereto.

[0164] As used herein, the term "alkyl" refers to a branched or unbranched aliphatic hydrocarbon group. In embodiments, the alkyl group may be substituted or unsubstituted. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, cyclopropyl, cyclopentyl, cyclohexyl, and cycloheptyl, each of which may optionally be substituted in other embodiments. In another embodiment, the alkyl group may have 1 to 6 carbon atoms. Examples of alkyl groups with 1 to 6 carbon atoms include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, pentyl, 3-pentyl, and hexyl.

[0165] At least one hydrogen atom in the alkyl group may be substituted with: a halogen atom, a halogen-substituted C1-C20 alkyl atom (e.g., CF3, CHF2, CH2F or CCl3, etc.), a C1-C20 alkoxy group, a C2-C20 alkoxyalkyl group, a hydroxyl group, a nitro group, a cyano group, an amino group, an amido group, a hydrazine group, a hydrazone group, a carboxyl group or a salt thereof, a sulfonyl group, an aminosulfonyl group, a sulfonic acid group or a salt thereof, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C1-C20 heteroalkyl group, a C6-C20 aryl group, a C7-C20 arylalkyl group, a C6-C20 heteroaryl group, a C7-C20 heteroarylalkyl group, a C6-C20 heteroaryloxy group, or a C6-C20 heteroaryloxyalkyl group.

[0166] As used herein, "alkenyl" includes, but is not limited to, vinyl, 1-propenyl, 2-propenyl, 2-methyl-1-propenyl, 1-butenyl, 2-butenyl, cyclopropenyl, cyclopentenyl, cyclohexenyl, and cyclopentenyl, as hydrocarbon groups having 2 to 20 carbon atoms having at least one carbon-carbon double bond. In another embodiment, the alkenyl group may be substituted or unsubstituted. In another embodiment, the alkenyl group may have 2 to 40 carbon atoms.

[0167] As used herein, the term "alkynyl" includes, but is not limited to, ethynyl, 1-propynyl, 1-butynyl, and 2-butynyl, as a hydrocarbon group having 2 to 20 carbon atoms having at least one carbon-carbon triple bond. In another embodiment, the alkynyl group may be substituted or unsubstituted. In another embodiment, the alkynyl group may have 2 to 40 carbon atoms.

[0168] As used herein, a substituent originates from an unsubstituted parent group, wherein at least one hydrogen atom is substituted by another atom or functional group. Unless otherwise indicated, when a functional group is considered “substituted,” it means that the functional group is substituted by at least one substituent independently selected from the group consisting of: C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkoxy, halogen, cyano, hydroxy, and nitro. When a functional group is described as being “optionally substituted,” the functional group may be substituted by one of the aforementioned substituents.

[0169] The term "halogen" includes fluorine, bromine, chlorine, and iodine.

[0170] "Alkoxy" refers to "alkyl-O-", where alkyl is as defined above. Examples of alkoxy groups may include methoxy, ethoxy, 2-propoxy, butoxy, tert-butoxy, pentoxy, and hexoxy. At least one hydrogen atom of an alkoxy group may be substituted with a substituent as in the cases of alkyl groups described above.

[0171] "Heteroaryl" refers to a monocyclic or bicyclic organic group containing one or more heteroatoms selected from N, O, P, or S, with the remaining ring atoms being carbon. A heteroaryl group may include, for example, 1 to 5 heteroatoms and may include 5 to 10 ring members. S or N may be oxidized to have various oxidation states.

[0172] Examples of heteroaryl groups may include thienyl, furanyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,3-thiazolyl, 1,2,4-thiazolyl, 1,2,5-thiazolyl, 1,3,4-thiazolyl, isothiazol-3-yl, isothiazol-4-yl, isothiazol-5-yl, oxazol-2-yl, Oxazol-4-yl, oxazol-5-yl, isoxazol-3-yl, isoxazol-4-yl, isoxazol-5-yl, 1,2,4-triazol-3-yl, 1,2,4-triazol-5-yl, 1,2,3-triazol-4-yl, 1,2,3-triazol-5-yl, tetrazolyl, pyridin-2-yl, pyridin-3-yl, 2-pyrazin-2-yl, pyrazin-4-yl, pyrazin-5-yl, 2-pyrimidin-2-yl, 4-pyrimidin-2-yl, and 5-pyrimidin-2-yl.

[0173] The term "heteroaryl" includes cases in which the heteroaryl ring is optionally fused with one or more of an aryl, alicyclic, and heterocyclic group.

[0174] The term "carbocyclic ring" refers to a saturated or partially unsaturated non-aromatic monocyclic, bicyclic, or tricyclic hydrocarbon group.

[0175] Examples of monocyclic hydrocarbon groups include cyclopentyl, cyclopentenyl, cyclohexyl, and cyclohexenyl.

[0176] Examples of bicyclic hydrocarbon groups may include borneol, decahydronaphthyl, bicyclic [2.1.1]hexyl, bicyclic [2.1.1]heptyl (bicyclic) [2.2.1]heptyl), bicyclic [2.2.1]heptenyl and bicyclic [2.2.2]octyl.

[0177] Examples of tricyclic hydrocarbon groups may include adamantyl groups.

[0178] One or more hydrogen atoms in the carbon ring can be substituted with the same substituents as in the case of alkyl groups described above.

[0179] The present disclosure will be described in more detail through the following embodiments and comparative examples. However, these embodiments are provided to illustrate the present disclosure, and the scope of the present disclosure is not limited thereto.

[0180] Preparative Example 1: Preparation of Compound 3

[0181] At 0°C, 10 ml of anhydrous dichloromethane solution of trimethylsilyl imidazole (TCI) (0.05 mol, 9.44 g) was added dropwise to anhydrous dichloromethane solution of trimethylsilyl chlorosulfonate (Sigma-Aldrich) (0.05 mol, 7.01 g) to obtain a reaction mixture.

[0182] The reaction mixture was stirred at room temperature (25°C) for 1 hour. Then, a portion of the liquid in the reaction mixture was evaporated under reduced pressure to reduce the volume of the reaction product to approximately one-third of the initial volume of the reaction mixture. The remaining suspension was filtered to obtain a white precipitate, which was washed twice with anhydrous dichloromethane and once with 5 ml of anhydrous hexane. The resulting product was dried under vacuum for 24 hours to remove residual solvent, yielding compound 3 as a white powder.

[0183] Yield: 8.59g (88%)

[0184] 1 H NMR (400MHz, CDCl3), δ0.63 (s, 9H), 7.08 (s, 1 H), 7.71(s, 1 H), 8.63(s, 1 H).

[0185] 13 C NMR (100MHz, CDCl3), δ-0.70(s), 121.94(s), 122.67(s), 137.08(s).

[0186] 29 Si NMR (80MHz, CDCl3), δ26.86 (s).

[0187] Preparation Example 1: Preparation of Electrolytes

[0188] 1.5 M LiPF6 was added to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 2:1:7, and then the compound of formula 3 obtained according to pre-preparation example 1 was added to prepare an electrolyte for lithium secondary batteries.

[0189] Based on the total weight of the electrolyte, the content of compound 3 is approximately 0.1 wt%.

[0190] <Formula 3>

[0191]

[0192] Preparation Example 2: Preparation of Electrolytes

[0193] The electrolyte for the lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the content of the compound of Formula 3 was changed to about 0.5 wt% based on the total weight of the electrolyte.

[0194] Preparation Example 3: Preparation of Electrolytes

[0195] The electrolyte for the lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the content of the compound of Formula 3 was changed to about 1 wt% based on the total weight of the electrolyte.

[0196] Preparation Example 4: Preparation of Electrolytes

[0197] The electrolyte for the lithium secondary battery was prepared in the same manner as in Preparation Example 1, except that the content of the compound of Formula 3 was changed to about 2 wt% based on the total weight of the electrolyte.

[0198] Comparative Preparation Example 1: Preparation of Electrolytes

[0199] The electrolyte for lithium secondary batteries was prepared in the same manner as in Preparation Example 1, except that the compound of Formula 3 was not added.

[0200] Comparative Preparation Example 2: Preparation of Electrolytes

[0201] The electrolyte for lithium secondary batteries was prepared in the same manner as in Preparation Example 1, except that 1-(trimethylsilyl)imidazole was used instead of compound 3.

[0202] Comparative Preparation Example 3: Preparation of Electrolytes

[0203] The electrolyte for lithium secondary batteries was prepared in the same manner as in Preparation Example 1, except that 1H-pyrazole-1-sulfonic acid was used instead of compound 3.

[0204] Example 1: Manufacturing of Lithium Secondary Batteries

[0205] A mixture of 87 wt% graphite, 11 wt% silicon-carbon compound composite, 1 wt% styrene-butadiene rubber (SBR) (ZEON), and 1.0 wt% carboxymethyl cellulose (CMC, NIPPON A&L) was introduced into distilled water and then stirred using a mechanical stirrer for 60 minutes to prepare an anode active material slurry. The slurry was applied to a 10 μm thick copper current collector using a doctor blade, dried in a hot air dryer at 100 °C for 0.5 hours, and then dried again under vacuum at 120 °C for 4 hours. Finally, the mixture was rolled to prepare the anode.

[0206] As a silicon-carbon compound composite material, a carbon-silicon composite material (manufactured by BTR) including carbon-coated silicon particles is used.

[0207] 97wt% LiNi 0.8 Co 0.1 Al 0.1O2 (NCA), 0.5 wt% artificial graphite (SFG6, Timcal) powder as a conductive material, 0.8 wt% carbon black (Kejtien Black, ECP), 0.2 wt% modified acrylonitrile rubber (BM-720H, Zeon Corporation), 1.2 wt% polyvinylidene fluoride (PVdF, S6020, Solvay), and 0.3 wt% polyvinylidene fluoride (PVdF, S5130, Solvay) were mixed and introduced into N-methyl-2-pyrrolidone, and then stirred with a mechanical stirrer for 30 minutes to prepare a cathode active material slurry. The slurry was applied to an aluminum current collector with a thickness of about 60 μm using a doctor blade, dried in a hot air dryer at 100 °C for 0.5 hours, and then dried again under vacuum and 120 °C for 4 hours, and then rolled to prepare the cathode.

[0208] A cylindrical lithium secondary battery was fabricated using a polyethylene separator with a thickness of 14 μm, wherein a ceramic was applied to the cathode as a separator, and the electrolyte prepared in Preparation Example 1 was used as the electrolyte.

[0209] Examples 2 to 4: Manufacturing of Lithium Secondary Batteries

[0210] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared according to Preparation Examples 2 to 4 was used instead of the electrolyte prepared in Preparation Example 1.

[0211] Comparative Examples 1 to 3: Manufacturing of Lithium-ion Secondary Batteries

[0212] The lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte prepared according to Comparative Preparation Examples 1 to 3 was used instead of the electrolyte prepared in Preparation Example 1.

[0213] Evaluation Example 1: Initial DC resistance (DC-IR) at room temperature (25°C) and the rate of increase in DC resistance after high-temperature storage. Test

[0214] The lithium secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were tested at 25°C under a 1C / 10-second discharge condition (SOC 100), and the initial DC resistance (DCIR) of the lithium secondary batteries was measured as ΔV / ΔI (voltage change / current change) values ​​before storing them in a high-temperature oven at 60°C. Some results are shown in Table 1 below. Figure 2 Then, after measuring the initial DC resistance (DCIR), the DC resistance after 30 days of storage at high temperature (60°C) was measured, and the DCIR increase rate (%) was calculated according to Equation 1 below.

[0215] [Equation 1]

[0216] DCIR increase rate=[DCIR(30d.)-DCIR(0d.) / DCIR(0d.)]×100%

[0217] When the DCIR 1C / 10-second discharge is performed, the voltage (V1) and current (I1) are measured at the start point, and the voltage (V2) and current (I2) are measured at the 10-second point. The DCIR increase rate (%) is calculated by the equation (V1-V2) / (I2-I1).

[0218] The measurement results of the DC resistance increase rate are shown in Table 1 below and Figure 2 middle.

[0219] [Table 1]

[0220]

[0221] As shown in Table 1 and Figure 2 As shown, it can be observed that, compared with the lithium secondary battery of Comparative Example 1 which does not contain the compound of Formula 3 and the lithium secondary batteries of Comparative Examples 2 and 3 which contain other additives, the lithium secondary batteries of Examples 1 to 4 exhibit a very low rate of increase in high-temperature resistance even when stored at high temperatures for extended periods. This is because the compound of Formula 3 effectively acts as a scavenger of PF5 to stabilize the lithium salt and forms a stable film on the surface of the cathode to effectively suppress side reactions between the cathode and the electrolyte. In Example 1, the compound of Formula 3 is used as an additive to the electrolyte, wherein the compound of Formula 3 has an imidazole-SO3-Si(CH3)3 structure and wherein the SO3 moiety is directly bonded to the nitrogen (N) of the imidazole.

[0222] In contrast, in Comparative Example 2, 1-(trimethylsilyl)imidazolium, having a structure in which Si(CH3)3 is directly bonded to the nitrogen of imidazolium, was used as an additive for the electrolyte, and 1-(trimethylsilyl)imidazolium had a structure in which Si(CH3)3 was directly bonded to the nitrogen (N) of imidazolium.

[0223] In Comparative Example 3, 1H-pyrazole-1-sulfonic acid was used as an electrolyte additive, and 1H-pyrazole-1-sulfonic acid had a structure in which the nitrogen (N) of the pyrazole was attached to SO3H, and unlike the compound of Formula 3 in Example 1, it did not contain Si.

[0224] As mentioned above, since 1-(trimethylsilyl)imidazolium, which is the electrolyte additive of Comparative Example 2, and 1Hpyrazole-1-sulfonic acid, which is the electrolyte additive of Comparative Example 3, have structures that are very different from those of the compound of Formula 3 used in Example 1, the effect of using the electrolyte additive of Example 1 cannot be obtained by using the electrolyte additive of Comparative Example 2 or Comparative Example 3 alone.

Claims

1. An electrolyte for lithium secondary batteries, comprising: Lithium salts; Non-aqueous organic solvents; and Electrolyte additives including the following compounds represented by Formula 1: <Formula 1> In Equation 1, R1 to R3 are each independently hydrogen, substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatics, and R4 through R6 are each independently substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatic compounds.

2. The electrolyte as claimed in claim 1, wherein, In Equation 1, R1 to R3 are each independently: hydrogen; substituted or unsubstituted C1-C 30 Alkyl; a C1-C group selected from one or more substituted groups of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkyl; or one or more substituted C2-C groups selected from the group consisting of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkenyl group.

3. The electrolyte as described in claim 1, wherein, In Equation 1, R4 to R6 are each independently: C1-C 30 Alkyl; a C1-C group selected from one or more substituted groups of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkyl; or one or more substituted C2-C groups selected from the group consisting of methyl, ethyl, propyl, butyl, -F, -Cl, -Br, -I, cyano, hydroxy, and nitro. 30 Alkenyl group.

4. The electrolyte as claimed in claim 1, wherein, The compound represented by Formula 1 described above is the same as the compound represented by Formula 2 below: <Formula 2> In Equation 2, R4 to R6 are each independently substituted or unsubstituted C1-C. 30 Alkyl, substituted or unsubstituted C4-C 30 Carbocyclic groups, substituted or unsubstituted C6-C 30 Aryl, substituted or unsubstituted C2-C 30 Alkenyl, substituted or unsubstituted C2-C 30 Alkyne group or substituted or unsubstituted C2-C 30 Mixed aromatics, and In Equation 2, the substituted C1-C 30 Alkyl groups, the substituted C4-C 30 Carbocyclic groups, the substituted C6-C 30 Aryl, the substituted C2-C 30 alkenyl, the substituted C2-C 30 Alkyne group or the substituted C2-C 30 At least one substituent in the heteroaryl group is selected from C1-C. 20 Alkyl, C2-C 20 alkenyl, C2-C 20 alkynyl group, C1-C 20 At least one of the group consisting of alkoxy, halogen, cyano, hydroxy, and nitro.

5. The electrolyte as described in claim 4, wherein, In Formula 2, R4 to R6 are each independently a C1-C5 alkyl, C2-C5 alkenyl, or a C2-C5 alkenyl substituted with a halogen.

6. The electrolyte as claimed in claim 1, wherein, The compound represented by Formula 1 is selected from the compounds represented by Formulas 3 to 6 below: <Formula 3> <Formula 4> In equation 4, Ph represents a phenyl group. <Formula 5> <Formula 6> 7. The electrolyte of claim 1, wherein, The content of the additive is in the range of 0.1 wt% to 10 wt% based on the total weight of the electrolyte.

8. The electrolyte as claimed in claim 1, wherein, The content of the additive is in the range of 0.5 wt% to 5 wt% based on the total weight of the electrolyte.

9. The electrolyte of claim 1, wherein, The lithium salt is selected from at least one of LiPF6, LiBF4, LiCF3SO3, Li(CF3SO2)2N, LiC2F5SO3, Li(FSO2)2N, LiC4F9SO3, LiN(SO2CF2CF3)2, and compounds represented by formulas 10 to 13 below: [Formula 10] [Equation 11] [Equation 12] [Equation 13] 10. The electrolyte of claim 1, wherein, The organic solvent comprises at least one selected from the group consisting of: ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), butylene carbonate, ethyl propionate, ethyl butyrate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone, and tetrahydrofuran.

11. A lithium secondary battery, comprising: A cathode containing cathode active material; An anode containing anodic active material; as well as An electrolyte according to any one of claims 1 to 10, disposed between the cathode and the anode.

12. The lithium secondary battery of claim 11, wherein the cathode comprises a lithium transition metal oxide represented by formula 7: <Formula 7> Li a Ni x Co y M z O 2-b A b in, In Formula 7, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.6 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.3, x + y + z = 1, M is at least one selected from the group consisting of: manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), and boron (B), and A is F, S, Cl, Br, or a combination thereof.

13. The lithium secondary battery according to claim 11, wherein the cathode comprises a lithium transition metal oxide represented by the following Formula 8 or Formula 9: <Formula 8> LiNi x Co y Mr z O2 In Formula 8, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, and 0 < z ≤ 0.

1. <Formula 9> LiNi x Co y Al z O2 In Formula 9, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, and 0 < z ≤ 0.1.

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