Additive, electrolyte for lithium secondary battery including the same, and lithium secondary battery

Abstract

Provided are an additive represented by Chemical Formula 1, an electrolyte for a lithium secondary battery including the additive, and a lithium secondary battery. Details of Chemical Formula 1 are as described in the specification.

Description

Technical Field

[0001] Disclosed are an additive, an electrolyte for a lithium secondary battery including the additive, and a lithium secondary battery. Background Art

[0002] Lithium secondary batteries can be recharged and have an energy density per unit weight that is three times or more higher than that of conventional lead batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and nickel-zinc batteries, and can also be charged at a high rate, so they are commercially manufactured for use in laptop computers, cellular phones, power tools, electric bicycles, etc., and research on improving the additional energy density has been actively conducted.

[0003] Such a lithium secondary battery is manufactured by injecting an electrolyte into a battery cell including a positive electrode including a positive active material capable of intercalating / deintercalating lithium ions and a negative electrode including a negative active material capable of intercalating / deintercalating lithium ions.

[0004] In particular, the electrolyte uses an organic solvent that dissolves a lithium salt and is important in determining the stability and performance of a lithium secondary battery.

[0005] LiPF6, the most commonly used lithium salt for electrolytes, reacts with electrolyte solvents to deplete the solvent and generate large amounts of gas. When LiPF6 decomposes, it generates LiF and PF5, leading to electrolyte depletion in the battery, deterioration of high-temperature performance, and poor safety.

[0006] There is a need for an electrolyte that suppresses the side reactions of such lithium salts and improves the performance of batteries. Summary of the Invention

[0007] Technical issues

[0008] Embodiments provide additives capable of improving battery performance by ensuring high-temperature stability.

[0009] Another embodiment provides an electrolyte for a lithium secondary battery including the additive.

[0010] Another embodiment provides a lithium secondary battery including the electrolyte for a lithium secondary battery.

[0011] Technical Solution

[0012] An embodiment of the present invention provides an additive represented by Chemical Formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] In Chemical Formula 1,

[0016] L is a single bond, C n (R a ) 2n -OC m (R b ) 2m or C1 to C10 alkylene,

[0017] R a and R b are each independently hydrogen, substituted or unsubstituted C1 to C5 alkyl, or substituted or unsubstituted C3 to C10 cycloalkyl, and

[0018] n and m are each independently an integer from 0 to 3.

[0019] R 1 and R 2 are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a substituted or unsubstituted C6 to C20 aryl group, and

[0020] R 3 is a substituted or unsubstituted C1 to C10 alkyl group.

[0021] For example, Chemical Formula 1 may be represented by Chemical Formula 1A.

[0022] [Chemical Formula 1A]

[0023]

[0024] In Chemical Formula 1A,

[0025] R 1 to R 3 The definition is the same as above.

[0026] For example, in Chemical Formula 1, R 1 may be a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group, and

[0027] R 3 It may be a substituted or unsubstituted C1 to C5 alkyl group.

[0028] For example, in Chemical Formula 1, R 1 to R 3 Each independently may be a substituted or unsubstituted C1 to C10 alkyl group.

[0029] Another embodiment of the present invention provides an electrolyte for a lithium secondary battery, the electrolyte for a lithium secondary battery including a non-aqueous organic solvent, a lithium salt, and the aforementioned additives.

[0030] The additive may be included in an amount of 0.05 wt % to 5.0 wt % based on the total weight of the electrolyte for a lithium secondary battery.

[0031] The additive may be included in an amount of 0.1 wt % to 3.0 wt % based on the total weight of the electrolyte for a lithium secondary battery.

[0032] Another embodiment of the present invention provides a lithium secondary battery including: a positive electrode including a positive active material; a negative electrode including a negative active material; and the aforementioned electrolyte.

[0033] The positive electrode active material can be represented by Chemical Formula 4.

[0034] [Chemical Formula 4]

[0035] Li x1 M 1 1-y1-z1 M 2 y1 M 3 z1 O2

[0036] In Chemical Formula 4,

[0037] 0.9≤x1≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1,

[0038] M 1 、M 2 and M 3 Each is independently selected from Ni, Co, Mn, Al, Sr, Mg, La and combinations thereof.

[0039] The positive electrode active material can be represented by Chemical Formula 5.

[0040] [Chemical Formula 5]

[0041] Li x2 Ni y2 Co z2 Al 1-y2-z2 O2

[0042] In Chemical Formula 5,

[0043] 1≤x2≤1.2, 0.6≤y2≤1 and 0≤z2≤0.5.

[0044] Beneficial effects

[0045] A lithium secondary battery having improved high temperature stability and cycle-life characteristics may be implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention.

[0047] Figure 2 dQ / dV results of lithium secondary battery cells according to Example 1 are shown in FIG.

[0048] Figure 3 Graphs showing the results of negative electrode cyclic voltammetry (CV) of the electrolytes according to Example 1 and Comparative Example 1 at room temperature.

[0049] Figure 4 Graphs showing cycle-life characteristics of lithium secondary battery cells according to Examples 1 and 2 and Comparative Examples 1 to 4 at high temperature (45° C.) are shown.

[0050] Figure 5 Graph showing the internal resistance increase rate of the lithium secondary battery cells according to Examples 1 and 2 and Comparative Examples 1 to 4 when left at rest at a high temperature (60° C.).

[0051] <symbol description>

[0052] 100: Lithium secondary battery

[0053] 112: Negative electrode

[0054] 113: Partition

[0055] 114: Positive electrode

[0056] 120: Battery housing

[0057] 140: Sealing component DETAILED DESCRIPTION

[0058] Hereinafter, embodiments of the present invention will be described in detail. However, these embodiments are exemplary and the present invention is not limited thereto and is defined by the scope of the claims.

[0059] In the present specification, when no definition is otherwise provided, “substituted” means that a hydrogen atom of the compound is replaced by a substituent selected from the group consisting of a halogen atom (F, Br, Cl or I), a hydroxyl group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group, a hydrazine group, a hydrazone group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphate group or a salt thereof, a C1 to C20 alkyl group, a C2 to C20 alkenyl group, a C2 to C20 alkynyl group, a C6 to C30 aryl group, a C7 to C30 aralkyl group, a C1 to C4 alkoxy group, a C1 to C20 heteroalkyl group, a C3 to C20 heteroaralkyl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C15 cycloalkynyl group, a C2 to C20 heterocycloalkyl group and combinations thereof.

[0060] Hereinafter, additives according to embodiments are described.

[0061] The additive according to an embodiment of the present invention is represented by Chemical Formula 1.

[0062] [Chemical Formula 1]

[0063]

[0064] In Chemical Formula 1,

[0065] L is a single bond, C n (R a ) 2n -OC m (R b ) 2m or C1 to C10 alkylene,

[0066] R a and R b are each independently hydrogen, substituted or unsubstituted C1 to C5 alkyl, or substituted or unsubstituted C3 to C10 cycloalkyl, and

[0067] n and m are each independently an integer from 0 to 3.

[0068] R 1 and R 2 are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a substituted or unsubstituted C6 to C20 aryl group, and

[0069] R 3 is a substituted or unsubstituted C1 to C10 alkyl group.

[0070] The additive represented by Chemical Formula 1 includes a sulfone functional group (—SO 2 —) and a (meth)acryloyl group in one molecule.

[0071] They decompose into lithium salts in the electrolyte to form a solid electrolyte interface (SEI) film with strong and excellent ion conductivity on the surface of the negative electrode, thereby suppressing the decomposition of the surface of the negative electrode that may occur during high-temperature cycle operation and preventing oxidation reactions of the electrolyte.

[0072] Specifically, due to the (meth)acryloyl group, the compound has an increased self-reduction voltage and is easily reduced and decomposed at a higher starting voltage than before, and thus exhibits high reactivity with the negative electrode. Therefore, the compound can decompose during the initial charge and thus form a solid electrolyte interface (SEI) with excellent ion conductivity and a strong SEI on the surface of the negative electrode, thereby suppressing the decomposition of the negative electrode surface and preventing the oxidation of the electrolyte, thereby reducing the resistance increase rate in the lithium secondary battery.

[0073] In addition, by forming a stable CEI (positive electrode-electrolyte interface) on the initial surface of the positive electrode, stable high-temperature storage characteristics and cycle-life characteristics for a long period of time can be ensured.

[0074] For example, Chemical Formula 1 may be represented by Chemical Formula 1A.

[0075] [Chemical Formula 1A]

[0076]

[0077] In Chemical Formula 1A,

[0078] R 1 to R 3 The definition is the same as above.

[0079] As shown in Chemical Formula 1A, when L is a single bond and the sulfonamide group and the (meth)acryloyl group are directly connected to each other, the effects of improving formation efficiency and initial resistance are more improved.

[0080] For example, in Chemical Formula 1, R 1 may be a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group, and

[0081] R 3 It may be a substituted or unsubstituted C1 to C5 alkyl group.

[0082] For example, in Chemical Formula 1, R 1 to R 3 Each independently may be a substituted or unsubstituted C1 to C10 alkyl group.

[0083] In the most specific embodiment, R of Chemical Formula 1 1 to R 3 Each of them can be independently methyl, ethyl, n-propyl or isopropyl, but is not limited thereto.

[0084] An electrolyte for a lithium secondary battery according to another embodiment of the present invention includes a nonaqueous organic solvent, a lithium salt, and the aforementioned additives.

[0085] The additive may be included in an amount of 0.05 wt % to 5.0 wt %, or specifically, 0.1 wt % to 3.0 wt %, based on the total weight of the electrolyte for a lithium secondary battery.

[0086] When the amount of the additive is within the range described above, a lithium secondary battery having improved cycle-life characteristics may be implemented by preventing an increase in resistance at high temperatures.

[0087] That is, when the amount of the additive represented by Chemical Formula 1 is less than 0.05 wt %, high temperature storage characteristics may be reduced, and when it exceeds 5.0 wt %, cycle life may be reduced due to an increase in interface resistance.

[0088] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0089] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent.

[0090] Carbonate solvents can be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC). Ester solvents can be methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanoic acid lactone, mevalonolactone and caprolactone. Ether solvents can be dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran and tetrahydrofuran. In addition, ketone solvents can be cyclohexanone. In addition, the alcohol solvent may be ethanol and isopropanol, etc., and the aprotic solvent may be a nitrile such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group and may include a double bond aromatic ring or an ether bond), an amide such as dimethylformamide, a dioxolane such as 1,3-dioxolane, and cyclopentane, etc.

[0091] The non-aqueous organic solvents may be used alone or in a mixture. When the organic solvents are used in a mixture, the mixture ratio may be controlled according to the desired battery performance.

[0092] The carbonate-based solvent is prepared by mixing a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte can be improved.

[0093] In addition to the carbonate-based solvent, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0094] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by Chemical Formula 2 may be used.

[0095] [Chemical Formula 2]

[0096]

[0097] In chemical formula 2, R 4 to R 9 are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl, and combinations thereof.

[0098] Specific examples of aromatic hydrocarbon solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, , 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene and combinations thereof.

[0099] The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by Chemical Formula 3 as a cycle-life improving additive in order to improve the battery cycle life.

[0100] [Chemical Formula 3]

[0101]

[0102] In chemical formula 3, R 10 and R 11 are the same or different and are selected from hydrogen, halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, provided that R 10 and R 11 At least one of is halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, and R 13 and R 14 Not all are hydrogen.

[0103] Examples of the ethylene carbonate compound may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive for improving cycle life may be used within an appropriate range.

[0104] Lithium salts are dissolved in non-aqueous organic solvents to supply lithium ions to the battery, allowing the basic operation of the lithium secondary battery and improving the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include one or more selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are natural numbers, for example, integers of 1 to 20), LiCl, LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB). The lithium salt may be used at a concentration ranging from 0.1 M to 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0105] Another embodiment of the present invention provides a lithium secondary battery including: a positive electrode including a positive active material; a negative electrode including a negative active material; and the aforementioned electrolyte.

[0106] The positive electrode may include a current collector and a positive active material layer including a positive active material formed on the current collector.

[0107] The positive active material may include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions.

[0108] Specifically, at least one composite oxide of lithium and a metal of cobalt, manganese, nickel, and a combination thereof may be used.

[0109] Specific examples thereof may include compounds represented by one of the following chemical formulae.

[0110] Li a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c Dc (0.90≤a≤1.8,

[0111] 0≤b≤0.5,0≤c≤0.05);Li a HAVE BEEN 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a HAVE BEEN 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 D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2);Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α≤2);Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mr b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni b HAVE BEEN c Gd O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li a Ni b Co c Mn d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤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 Mn2G b 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); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2);Li (3-f) Fe2(PO4)3(0≤f≤2);Li a FePO4(0.90≤a≤1.8).

[0112] In the chemical formula, A is selected from Ni, Co, Mn, and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from O, F, S, P, and combinations thereof; E is selected from Co, Mn, and combinations thereof; T is selected from F, S, P, and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from Ti, Mo, Mn, and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y, and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0113] The positive electrode active material may include a positive electrode active material having a coating, or a compound of a positive electrode active material and a positive electrode active material coated with a coating. The coating may include the following coating element compounds: oxides or hydroxides of coating elements, hydroxide oxides of coating elements, oxycarbonates of coating elements, or basic carbonates of coating elements. The compound used for the coating may be amorphous or crystalline. The coating element included in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating process may include any conventional process (e.g., spraying, dipping), as long as it does not cause any side effects on the properties of the positive electrode active material, which is something that can be well understood by those skilled in the relevant art, and therefore a detailed description will be omitted.

[0114] Specific examples of the positive active material may include a compound represented by Chemical Formula 4.

[0115] [Chemical Formula 4]

[0116] Li x1 M 1 1-y1-z1 M 2 y1 M 3 z1 O2

[0117] In Chemical Formula 4,

[0118] 0.9≤x1≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, and M 1 、M 2 and M 3 Each is independently selected from any one of Ni, Co, Mn, Al, Sr, Mg, La and combinations thereof.

[0119] For example, the positive active material may be one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, aluminum, and combinations thereof, and the most specific example of the positive active material according to the embodiment of the present invention may include a compound of Chemical Formula 5.

[0120] [Chemical Formula 5]

[0121] Li x2 Ni y2 Co z2 Al 1-y2-z2 O2

[0122] In Chemical Formula 5, 1≤x2≤1.2, 0.6≤y2≤1, and 0≤z2≤0.5.

[0123] The amount of the positive active material may be 90 wt % to 98 wt % based on the total weight of the positive active material layer.

[0124] In an embodiment, the positive active material layer may include a binder and a conductive material. Here, the binder and the conductive material may be included in an amount of 1 wt % to 5 wt % based on the total weight of the positive active material layer.

[0125] The binder improves the binding properties between the positive electrode active material particles and the binding properties between the positive electrode active material particles and the current collector, and examples thereof may include, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon, but are not limited thereto.

[0126] A conductive material is included to improve the conductivity of the electrode, and any conductive material can be used as the conductive material unless it causes chemical changes. Examples of the conductive material include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metal materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0127] The current collector may be Al, but is not limited thereto.

[0128] The negative electrode includes a current collector and a negative active material layer formed on the current collector.

[0129] The negative electrode active material may be a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0130] The material that reversibly intercalates / deintercalates lithium ions includes a carbon material. The carbon material can be any commonly used carbon-based negative electrode active material in lithium-ion secondary batteries, and examples of the carbon material include crystalline carbon, amorphous carbon, and combinations thereof. Crystalline carbon can be natural graphite or artificial graphite in a shapeless, flaky, spherical, or fibrous form. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, and fired coke, etc.

[0131] The lithium metal alloy may include lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0132] Materials that can be doped and dedoped with lithium may include Si, SiO x(0 < x < 2), Si-Q alloys (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, and Sn-R alloys (where R is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition element, rare earth element, or combination thereof, and is not Sn), etc., and at least one of them can be mixed with SiO2. The elements Q and R can be selected from 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, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0133] The transition metal oxides can be vanadium oxide, lithium vanadium oxide, etc.

[0134] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 95 wt% to 99 wt%.

[0135] In an embodiment, the negative electrode active material layer can include a binder and optionally a conductive material. In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the amount of the binder can be 1 wt% to 5 wt%. When it further includes a conductive material, it can include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0136] The binder improves the binding properties between the negative electrode active material particles and the binding properties between the negative electrode active material particles and the current collector. The binder can be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0137] The water-insoluble binder can be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0138] The water-soluble binder can be a rubber-based binder or a polymer resin binder. The rubber-based binder can be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber and a combination thereof. The polymer resin binder can be selected from polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and a combination thereof.

[0139] When a water-soluble binder is used as the negative electrode binder, a cellulose compound may be further used to provide viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts. The alkali metal may be sodium, potassium, or lithium. The thickener may be present in an amount of 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0140] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it undergoes chemical changes. Examples thereof include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metal materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0141] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0142] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may include polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, and a polypropylene / polyethylene / polypropylene three-layer separator.

[0143] refer to Figure 1 According to an embodiment, a lithium secondary battery 100 includes: a battery cell, the battery cell including a negative electrode 112, a positive electrode 114 facing the negative electrode 112, a separator 113 inserted between the negative electrode 112 and the positive electrode 114, and an electrolyte (not shown) impregnating the negative electrode 112, the positive electrode 114 and the separator 113; a battery case 120 configured to accommodate the battery cell; and a sealing member 140 that seals the battery case 120.

[0144] Invention

[0145] Hereinafter, examples of the present invention and comparative examples are described. However, these examples are by no means construed to limit the scope of the present invention.

[0146] Manufacturing of lithium secondary battery cells

[0147] Preparation Example 1: Synthesis of the additive represented by Chemical Formula 1a

[0148] [Chemical Formula 1a]

[0149]

[0150] According to Scheme 1, the compound of Chemical Formula 1a is obtained.

[0151] [Reaction Scheme 1]

[0152]

[0153] Under a nitrogen atmosphere, N-methylmethanesulfonamide and methacryloyl chloride were fully dissolved in a dichloromethane solvent at a 1:1 ratio at 0°C. Subsequently, small amounts of triethylamine and 4-dimethylaminopyridine were slowly added to the mixed solution and fully dissolved therein, followed by stirring at room temperature for 12 hours. After the reaction, the solid produced was filtered to obtain the compound represented by Chemical Formula 1a as a white powder (yield: 89%).

[0154] 1 H NMR (400MHz, CDCl3): δ5.45, 5.35, 3.27, 3.26, 2.01; 13 C NMR: δ172.8,140.0,119.2,41.6,34.4,19.2.

[0155] Preparation Example 2: Synthesis of the additive represented by Chemical Formula 2a

[0156] [Chemical Formula 2a]

[0157]

[0158] The compound represented by Chemical Formula 2a was prepared by changing methacryloyl chloride in Preparation Example 1 to 1-chloro-3-methylbut-3-en-2-one.

[0159] 1 H NMR (400MHz, CDCl3): δ6.03,5.54,4.56,3.11,2.98,1.88; 13 C NMR: δ201.9,144.0,124.0,61.5,32.1,27.1.

[0160] Preparation Example 3: Synthesis of the additive represented by Chemical Formula 3a

[0161] [Chemical Formula 3a]

[0162]

[0163] The compound represented by Chemical Formula 3a was prepared by changing methacryloyl chloride in Preparation Example 1 to 5-chloro-2-methylpent-1-en-3-one.

[0164] 1 H NMR (400MHz, CDCl3): δ5.99,5.52,3.69,3.07,3.07,2.81,1.83; 13 C NMR: δ201.9,144.0,124.0,121.5,55.0,42.1,39.0,27.1,21.1

[0165] Preparation Example 4: Synthesis of the additive represented by Chemical Formula 4a

[0166] [Chemical Formula 4a]

[0167]

[0168] The compound represented by Chemical Formula 4a was prepared by changing methacryloyl chloride in Preparation Example 1 to 6-chloro-2-methylhex-1-en-3-one.

[0169] 1 H NMR (400MHz, CDCl3): δ5.99,5.52,3.43,3.05,2.98,2.56,1.90,1.83; 13 C NMR: δ201.9,144.0,124.0,121.5,60.0,42.1,39.0,27.1,22.5,21.1

[0170] Comparative Preparation Example 1: Synthesis of the Additive Represented by Chemical Formula 1b

[0171] [Chemical Formula 1b]

[0172]

[0173] Under a nitrogen atmosphere, N-methylmethanesulfonamide was dissolved in N,N-dimethylformamide to prepare a solution, and 2-acryloyl bromide and anhydrous potassium carbonate were slowly added thereto in an equal volume ratio of 1:1, followed by stirring at room temperature for 18 hours. After the reaction, the compound represented by Chemical Formula 1b was obtained in liquid form by using a column.

[0174] Comparative Preparation Example 2: Synthesis of the Additive Represented by Chemical Formula 1c

[0175] [Chemical Formula 1c]

[0176]

[0177] In Comparative Preparation Example 1, 2-acryloyl bromide was changed to vinyl bromide to obtain a compound represented by Chemical Formula 1c in liquid form.

[0178] Comparative Preparation Example 3: Synthesis of the Additive Represented by Chemical Formula 1d

[0179] [Chemical Formula 1d]

[0180]

[0181] In Comparative Preparation Example 1, 2-acryloyl bromide was changed to 3-bromo-1-propene to obtain the compound represented by Chemical Formula 1d in liquid form.

[0182] Example 1

[0183] LiNi as the positive electrode active material 0.88 Co 0.105 Al 0.015 O2, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed at a weight ratio of 98:1:1, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0184] The positive electrode active material slurry was coated on a 20 μm thick Al foil, dried at 100° C., and pressed to produce a positive electrode.

[0185] Graphite as a negative electrode active material, a styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed at a weight ratio of 98:1:1, and then dispersed in N-methylpyrrolidone to prepare a negative electrode active material slurry.

[0186] The negative electrode active material slurry was coated on a 10 μm thick Cu foil, dried at 100° C., and pressed to produce a negative electrode.

[0187] The fabricated positive and negative electrodes, a 25 μm thick polyethylene separator, and an electrolyte were used to fabricate a lithium secondary battery cell.

[0188] The composition of the electrolyte is as follows.

[0189] (Electrolyte composition)

[0190] Salt: LiPF6 1.15M

[0191] Solvent: Ethylene carbonate: Ethyl methyl carbonate: Dimethyl carbonate (EC: EMC: DMC = 2:4:4 volume ratio)

[0192] Additive: 0.5 wt% of the compound represented by Chemical Formula 1a

[0193] (Herein, the composition of the electrolyte, "wt%" is based on the total amount of the electrolyte (lithium salt + non-aqueous organic solvent + additives))

[0194] Example 2

[0195] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the amount of the additive was changed to 3.0 wt %.

[0196] Examples 3 to 5

[0197] Lithium secondary battery cells were manufactured in the same manner as in Example 1, except that the compound represented by Chemical Formula 2a, the compound represented by Chemical Formula 3a, and the compound represented by Chemical Formula 4a were used as additives instead of the compound represented by Chemical Formula 1a.

[0198] Comparative Example 1

[0199] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that no additive was used.

[0200] Comparative Example 2

[0201] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the additive was changed to the compound represented by Chemical Formula 1b according to Comparative Preparation Example 1.

[0202] Comparative Example 3

[0203] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the additive was changed to the compound represented by Chemical Formula 1c according to Comparative Preparation Example 2.

[0204] Comparative Example 4

[0205] A lithium secondary battery cell was manufactured in the same manner as in Example 1, except that the additive was changed to the compound represented by Chemical Formula 1d according to Comparative Preparation Example 3.

[0206] Evaluation of battery cell characteristics

[0207] Assessment 1: Measurement of reduction voltage

[0208] At 25° C., the lithium secondary battery cell according to Example 1 was charged at 4.3 V and a 0.1C rate and discharged to 3.5 V at a 0.1C rate, and then the potential (V) and discharge capacity (mAh) after the first cycle were measured, and dQ / dV was calculated to determine the reduction potential.

[0209] The aforementioned dQ / dV result graph is shown in Figure 2 middle.

[0210] Figure 2 A graph showing dQ / dV results of a lithium secondary battery cell according to Example 1 is shown.

[0211] refer to Figure 2 , it was confirmed that the reactivity of the lithium secondary battery cell according to Example 1 was in the range of about 2.0 V to 2.2 V and about 2.5 V to 2.7 V, which means that the additive according to the example embodiment was reduced and a SEI film was formed.

[0212] Evaluation 2: Evaluation of CV characteristics

[0213] In order to evaluate the electrochemical stability of the electrolytes according to Comparative Example 1 and Example 1, cyclic voltammetry (CV) was measured, and the results are shown in FIG. Figure 3 middle.

[0214] A three-electrode electrochemical cell using a graphite negative electrode as the working electrode and Li metal as the reference electrode and counter electrode was used to measure negative electrode cyclic voltammetry (CV). Herein, three cycles were scanned from 3 V to 0 V and from 0 V to 3 V at a scan rate of 0.1 mV / s.

[0215] Figure 3 Graphs showing negative electrode cyclic voltammetry (CV) results of the electrolytes according to Example 1 and Comparative Example 1 at room temperature.

[0216] like Figure 3 As shown in , the electrolyte of Example 1 including the additive according to the present invention exhibits reduction decomposition peaks around about 1.3 V to 1.6 V and about 0.9 V to 1.2 V.

[0217] In contrast, the electrolyte according to Comparative Example 1, which does not include the additive, exhibits a reductive decomposition peak at a lower potential.

[0218] This confirms that the electrolyte including the additive according to the exemplary embodiment of the present invention interacts with the solvent at a relatively high reduction potential, and therefore, the electrolyte according to Example 1 is expected to form an initial SEI film on the negative electrode over a wide voltage range before the solvent decomposes during charging in which lithium ions are inserted into the negative electrode. Therefore, compared to the lithium secondary battery cell using the electrolyte of Comparative Example 1 in which no initial SEI film is formed, the lithium secondary battery cell using the electrolyte of Example 1 is expected to exhibit superior battery performance.

[0219] Evaluation 3: Evaluation of high temperature cycle life characteristics

[0220] At 45° C., under the charge cut-off conditions of 0.5 C, 4.3 V, and 0.05 C, the lithium secondary battery cells according to Examples 1 and 2 and Comparative Examples 1 to 4 were charged 200 times at a constant current-constant voltage, and discharged at a constant current under the discharge cut-off conditions of 0.5 C and 2.8 V, and then the discharge capacity was measured to calculate the capacity retention rate of the discharge capacity at the 200th cycle relative to the discharge capacity at the 1st cycle, and the results are shown in Tables 1 and 2. Figure 4 middle.

[0221] (Table 1)

[0222]

[0223]

[0224] Figure 4 Graphs showing cycle-life characteristics of lithium secondary battery cells according to Examples 1 and 2 and Comparative Examples 1 to 4 at high temperature (45° C.) are shown.

[0225] refer to Figure 4 , Examples 1 and 2 including the additive according to the present invention exhibited excellent high temperature cycle characteristics compared to Comparative Example 1 including no additive and Comparative Examples 2 to 4 including other types of additives.

[0226] Assessment 4: Evaluation of high temperature storage characteristics

[0227] Each of the lithium secondary battery cells according to Examples 1 and 2 and Comparative Examples 1 to 4 was left standing at 60° C. for 30 days in a state of charge (SOC=100%), and then, when the internal resistance increase rate when left standing at high temperature (60° C.) was evaluated, and the results are shown in Tables 2 and 4. Figure 5 middle.

[0228] DC-IR is measured in the following manner.

[0229] The cells according to Examples 1 and 2 and Comparative Examples 1 to 4 were charged at 4 A and 4.3 V at room temperature (25°C) and cut off at 100 mA, followed by a 30-minute pause. Subsequently, the cells were charged at 10 A for 10 seconds, 1 A for 10 seconds, and 10 A for 4 seconds, respectively. The current and voltage were measured at 18 seconds and 23 seconds, and the initial resistance (the difference between the resistance at 18 seconds and the resistance at 23 seconds) was calculated according to ΔR = ΔV / ΔI.

[0230] The single cell was left at 60°C for 30 days under the charging condition of 0.2C and 4.3V, and DC-IR was measured, and the results showed that Figure 5 , and the resistance increase rate thereof before and after standing was calculated, and the results are shown in Table 2.

[0231] <Equation 1>

[0232] Resistance increase rate (%) = [(DC-IR after 30 days of standing - DC-IR before standing) / DC-IR before standing] × 100

[0233] (Table 2)

[0234]

[0235] Figure 5 Graph showing the internal resistance increase rate of the lithium secondary battery cells according to Examples 1 and 2 and Comparative Examples 1 to 4 when left at rest at a high temperature (60° C.).

[0236] refer to Figure 5 and Table 2, the cells of Examples 1 and 2 exhibited reduced resistance increase rates before and after standing compared to Comparative Examples 1 to 4. Therefore, the cells of Examples 1 and 2 exhibited improved high-temperature stability compared to the cells of Comparative Examples 1 to 4.

[0237] Evaluation 5: Evaluation of formation efficiency

[0238] The initial resistances of Example 1, Examples 3 to 5, and Comparative Examples 1 to 4 were calculated in the same manner as in Evaluation 4 and then provided in Table 3.

[0239] The formation efficiency was evaluated as follows: after formation, charging and discharging were performed once at 25°C under the cut-off charge conditions of 0.2C, 4.3V and 0.02C with constant current-constant voltage, and under the cut-off discharge conditions of 0.2C and 2.8V with constant current, respectively. Then, the ratio of the discharge capacity to the charge capacity was calculated, and the results are shown in Table 3.

[0240] (Table 3)

[0241] Formation efficiency (%) Initial resistance (milliohms) Example 1 83.0 2.29 Example 3 82.9 2.29 Example 4 82.8 2.30 Example 5 82.8 2.30 Comparative Example 1 81.5 2.40 Comparative Example 2 81.5 2.39 Comparative Example 3 81.7 2.40 Comparative Example 4 81.5 2.40

[0242] Referring to Table 3, compared with the cells of Comparative Examples 1 to 4, the cells of Example 1 and Examples 3 to 5 included the additive within the scope of the present invention and thus exhibited reduced initial resistance and improved formation efficiency.

[0243] While the invention has been described in connection with what are presently considered to be practical example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An electrolyte for a lithium secondary battery, comprising: non-aqueous organic solvents, lithium salts, and The additive represented by Chemical Formula 1: [Chemical Formula 1] Wherein, in Chemical Formula 1, L is a single bond or a C1 to C10 alkylene group, R 1 and R 2 are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a substituted or unsubstituted C6 to C20 aryl group, and R 3 is a substituted or unsubstituted C1 to C10 alkyl group, Wherein "substituted" means that a hydrogen atom of the compound is replaced by a substituent selected from the group consisting of a hydroxyl group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group, a hydrazine group, a hydrazone group, a carbonyl group, a carbamoyl group, a thiol group, an ester group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphate group or a salt thereof, a C1 to C20 alkyl group, a C2 to C20 alkenyl group, a C2 to C20 alkynyl group, a C6 to C30 aryl group, a C7 to C30 aralkyl group, a C1 to C4 alkoxy group, a C1 to C20 heteroalkyl group, a C3 to C20 heteroaralkyl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C15 cycloalkynyl group, a C2 to C20 heterocycloalkyl group, and combinations thereof.

2. The electrolyte for a lithium secondary battery according to claim 1, wherein Chemical Formula 1 is represented by Chemical Formula 1A: [Chemical Formula 1A] in, In Chemical Formula 1A, R 1 to R 3 The definitions are the same as those in claim 1.

3. The electrolyte for a lithium secondary battery according to claim 1, wherein: In Chemical Formula 1, R 1 is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group, and R 3 is a substituted or unsubstituted C1 to C5 alkyl group.

4. The electrolyte for a lithium secondary battery according to claim 1, wherein: In Chemical Formula 1, R 1 to R 3 Each is independently a substituted or unsubstituted C1 to C10 alkyl group. 5 . The electrolyte for a lithium secondary battery according to claim 1 , wherein the additive is present in an amount of 0.05 wt % to 5.0 wt % based on the total weight of the electrolyte for a lithium secondary battery. 6 . The electrolyte for a lithium secondary battery according to claim 1 , wherein the additive is present in an amount of 0.1 wt % to 3.0 wt % based on the total weight of the electrolyte for a lithium secondary battery.

7. A lithium secondary battery comprising: a positive electrode comprising a positive active material; a negative electrode comprising a negative active material; and The electrolyte according to any one of claims 1 to 4.

8. The lithium secondary battery according to claim 7, wherein the positive electrode active material is represented by Chemical Formula 4: [Chemical Formula 4] Li x1 M 1 1-y1-z1 M 2 y1 M 3 z1 O2 in, In Chemical Formula 4, 0.9≤x1≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1<1, and M 1 、M 2 and M 3 Each is independently selected from Ni, Co, Mn, Al, Sr, Mg, La and combinations thereof.

9. The lithium secondary battery according to claim 7, wherein the positive electrode active material is represented by Chemical Formula 5: [Chemical Formula 5] Li x2 Ni y2 Co z2 Al 1-y2-z2 O2 in, In Chemical Formula 5, 1≤x2≤1.2, 0.6≤y2≤1, and 0≤z2≤0.5.

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