Lithium-ion rechargeable battery

Abstract

To provide a lithium secondary battery that suppresses the collapse of a positive electrode structure, thereby improving the high voltage and high temperature characteristics of a battery by using a positive electrode containing cobalt-free lithium nickel manganese oxide, and combining cobalt-free lithium nickel manganese oxide with an electrolyte that can effectively protect the positive electrode to reduce the elution of transition metals under high voltage and high temperature conditions.SOLUTION: A lithium secondary battery includes an electrolyte containing a non-aqueous organic solvent and a lithium salt, a positive electrode including a positive electrode active material, and a negative electrode including a negative electrode active material, the non-aqueous organic solvent contains less than 5% by weight of ethylene carbonate, and the positive electrode active material includes cobalt-free lithium nickel manganese oxide.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This description relates to a lithium secondary battery.

Background Art

[0002] Lithium secondary batteries are rechargeable and have an energy density per unit weight that is more than three times higher than that of conventional lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, etc., and can be rapidly charged. Therefore, they have been commercialized for use in notebook computers, mobile phones, power tools, and electric bicycles, and research and development for further improving the energy density is actively underway.

[0003] In particular, as IT devices are gradually becoming more high-performance, there is a situation where high-capacity batteries are required. Although the energy density can be increased by realizing high capacity through expanding the voltage range, there is a problem that the electrolyte is oxidized in the high-voltage range, deteriorating the cathode performance.

[0004] In particular, cobalt-free lithium nickel manganese-based oxide as a cathode active material is a cathode active material mainly composed of nickel, manganese, etc. without containing cobalt in the cathode active material composition. The cathode containing this is economical and can achieve a high energy density, so it has been attracting attention as a next-generation cathode active material.

[0005] However, when a cathode containing cobalt-free lithium nickel manganese-based oxide is used in a high-voltage environment, dissolution of transition metals may occur due to the collapse of the cathode structure, which may cause problems such as gas generation inside the cell and capacity reduction. Such a phenomenon of transition metal dissolution tends to become more intense in a high-temperature environment, and the dissolved transition metal may be deposited on the surface of the anode, inducing side reactions, which causes an increase in the resistance of the battery, a decrease in the battery life, and a decrease in the output characteristics.

[0006] Therefore, when using a positive electrode containing a cobalt-free lithium nickel manganese oxide, an electrolyte applicable even under high voltage and high temperature conditions is required.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of one embodiment is to provide a lithium secondary battery in which a positive electrode containing a cobalt-free lithium nickel manganese oxide is combined with an electrolyte capable of effectively protecting the positive electrode containing the cobalt-free lithium nickel manganese oxide, suppressing the collapse of the positive electrode structure by reducing the elution of transition metals under high voltage and high temperature conditions, and thereby improving the high voltage characteristics and high temperature characteristics of the battery.

Means for Solving the Problems

[0008] One embodiment of the present invention includes an electrolyte containing a non-aqueous organic solvent and a lithium salt; a positive electrode containing a positive electrode active material; and a negative electrode containing a negative electrode active material. The non-aqueous organic solvent contains less than 5% by weight of ethylene carbonate. The positive electrode active material contains a cobalt-free lithium nickel manganese oxide, providing a lithium secondary battery. The non-aqueous organic solvent may be composed only of chain carbonates.

[0009] The chain carbonate may be represented by the following Chemical Formula 1.

Chemical Formula

[0010] The non-aqueous organic solvent can be at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC).

[0011] The non-aqueous organic solvent can contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 10:90 to 50:50.

[0012] The electrolytic solution can further contain at least one additive of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinyl ethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP).

[0013] The cobalt-free lithium nickel manganese-based oxide can contain a lithium composite oxide represented by the following Chemical Formula 3. [Chemical Formula 3] Li a Ni x Mn y M 1 z M 2 w O 2±b X c In the Chemical Formula 3, 0.5 ≦ a < 1.8, 0 ≦ b ≦ 0.1, 0 ≦ c ≦ 0.1, 0 ≦ w < 0.1, 0.6 ≦ x < 1.0, 0 < y < 0.4, 0 < z < 0.1, and w + x + y + z = 1, M1 and M 2 Each of the elements is independently selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0014] The aforementioned chemical formula 3 can also be represented by the following chemical formula 3-1. [Chemical formula 3-1] Li a Ni x1 Mn y1 Al z1 M 2 w1 O 2±b X c In the aforementioned chemical formula 3-1, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w1<0.1, 0.6≦x1<1.0, 0 <y1<0.4、0<z1<0.1、w1+x1+y1+z1=1であり、 M 2 Each of the elements is independently selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0015] In the aforementioned chemical formula 3-1, x1 may be 0.6 ≤ x1 ≤ 0.79, y1 may be 0.2 ≤ y1 ≤ 0.39, and z1 may be 0.01 ≤ z1 < 0.1.

[0016] The negative electrode active material may include at least one of graphite and a Si composite.

[0017] The lithium secondary battery may have a maximum charging voltage of 4.35V or higher. [Effects of the Invention]

[0018] One embodiment involves using an electrolyte that effectively protects the positive electrode containing a cobalt-free lithium nickel manganese oxide. This ensures the safety of the positive electrode's phase transition even in high-temperature, high-voltage environments. By suppressing electrolyte decomposition and side reactions with the electrode, gas generation is reduced, and the increase in internal battery resistance is suppressed, thereby realizing a lithium secondary battery with improved battery stability and lifespan characteristics. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram showing a lithium secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0020] A lithium secondary battery according to one embodiment of the present invention will be described in detail below with reference to the attached drawings. However, this is presented as an example and does not limit the present invention, which is defined only within the scope of the claims described below.

[0021] In this specification, "substituted" means, unless otherwise defined, that at least one hydrogen atom of a substituent or compound is substituted with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted C1-C30 amine group, a nitro group, a substituted or unsubstituted C1-C40 silyl group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C20 alkoxy group, a C1-C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0022] In one example of the present invention, "substitution" means that at least one hydrogen atom of the substituent or compound is substituted with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. In another specific example of the present invention, "substitution" means that at least one hydrogen atom of the substituent or compound is substituted with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. In yet another specific example of the present invention, "substitution" means that at least one hydrogen atom of the substituent or compound is substituted with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. Furthermore, in a specific example of the present invention, "substitution" means that at least one hydrogen atom in the substituent or compound is substituted with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0023] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries depending on the type of separator membrane and electrolyte used. They can also be classified by shape into cylindrical, prismatic, coin-type, and pouch-type batteries, and by size into bulk type and thin-film type batteries. Since the structure and manufacturing methods of these batteries are widely known in the field, a detailed explanation will be omitted.

[0024] Here, a cylindrical lithium secondary battery will be used as an example to explain lithium secondary batteries. Figure 1 schematically shows the structure of a lithium secondary battery according to one embodiment. Referring to Figure 1, the lithium secondary battery 100 according to one embodiment includes a battery cell containing a positive electrode 114, a negative electrode 112 positioned opposite the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and an electrolyte (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 housing the battery cell, and a sealing member 140 sealing the battery container 120.

[0025] The following describes a more detailed configuration of the lithium secondary battery 100 according to one embodiment of the present invention.

[0026] A lithium secondary battery according to one embodiment of the present invention includes an electrolyte, a positive electrode, and a negative electrode.

[0027] The electrolyte comprises a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent may contain less than 5% by weight of ethylene carbonate.

[0028] The positive electrode may include a positive electrode active material containing a cobalt-free lithium nickel manganese oxide.

[0029] In the case of positive electrode active materials containing cobalt-free lithium nickel manganese oxides, strong structural instability occurs under high voltage conditions, leading to solvent decomposition and the elution of transition metals, particularly Ni.

[0030] This leaching phenomenon of transition metals leads to degradation and short circuits, reducing the battery's lifespan and capacity, and causing a sudden increase in resistance.

[0031] However, when using an electrolyte solution that combines the aforementioned non-aqueous organic solvent and lithium salt, it is possible to mitigate the decrease in battery life capacity and the phenomenon of a sudden increase in resistance.

[0032] In particular, by using a positive electrode containing cobalt-free lithium nickel manganese oxide in an electrolyte containing less than 5% by weight of ethylene carbonate, the leaching of transition metals under high voltage and high temperature conditions can be effectively reduced, thereby suppressing the collapse of the positive electrode structure and potentially improving the high-voltage and high-temperature characteristics of the battery.

[0033] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0034] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0035] As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., can be used. Furthermore, cyclohexanone and the like can be used as the ketone solvent. Ethyl alcohol and isopropyl alcohol can be used as the alcohol solvent, and nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bond oriented ring or ether bond) can be used as the aprotic solvent, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes can be used.

[0036] The aforementioned non-aqueous organic solvents can be used individually or in combination of one or more. When used in combination of one or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is generally understood by those working in this field.

[0037] As an example, the non-aqueous organic solvent may contain less than 5% by weight of ethylene carbonate.

[0038] When the ethylene carbonate content exceeds 5% by weight within the aforementioned range, the activity of Ni increases during high-voltage operation, and the oxidation state of Ni tends to be reduced from tetravalent to divalent. As a result, ethylene carbonate, which has low oxidation stability, undergoes oxidative decomposition, and Ni is eluted and deposited on the negative electrode.

[0039] As a specific example, the non-aqueous organic solvent may consist solely of chain carbonates. In this case, excellent high-temperature storage characteristics can be achieved by significantly mitigating the rate of resistance increase during high-temperature storage.

[0040] In this specification, "composed solely of linear carbonates" means that it contains, alone or in combination with organic solvents belonging to the category of linear carbonates, without being mixed with cyclic carbonates or the like.

[0041] In one embodiment, the chain-like carbonate may be represented by the following chemical formula 1. [ka] In the above chemical formula 1 R 1 and R 2 These are each independently substituted or unsubstituted C1-C20 alkyl groups.

[0042] As an example, R in the chemical formula 1 above 1 and R 2 Each of these can be independently a substituted or unsubstituted C1-C10 alkyl group, for example, the R 1 and R 2 Each of these can independently be a substituted or unsubstituted C1-C5 alkyl group.

[0043] In one embodiment, R of chemical formula 1 1 and R 2These can each be independently a substituted or unsubstituted methyl group, a substituted or unsubstituted ethyl group, a substituted or unsubstituted n-propyl group, a substituted or unsubstituted n-butyl group, a substituted or unsubstituted n-pentyl group, a substituted or unsubstituted iso-butyl group, or a substituted or unsubstituted neo-pentyl group.

[0044] For example, a specific example of a non-aqueous organic solvent could be at least two of the following: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC).

[0045] In one of the most specific examples, the non-aqueous organic solvent may be a mixed solvent of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0046] The non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 10:90 to 50:50.

[0047] The aforementioned non-aqueous organic solvent may be more advantageous in terms of improving battery characteristics if it contains more than 50% by volume of dimethyl carbonate (DMC).

[0048] For example, the non-aqueous organic solvent may contain ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 10:90 to 40:60, or 10:90 to 30:70.

[0049] The non-aqueous organic solvent may further contain an aromatic hydrocarbon organic solvent in addition to the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon solvent can be mixed in a volume ratio of 1:1 to 30:1.

[0050] As the aforementioned aromatic hydrocarbon solvent, an aromatic hydrocarbon compound of the following chemical formula 2 can be used. [ka] In the aforementioned chemical formula 2, R 9 ~R 14 These elements are either the same as or different from each other, and are selected from the group consisting of hydrogen, halogens, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups having 1 to 10 carbon atoms, and combinations thereof.

[0051] Specific examples of the aromatic hydrocarbon solvents include 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, and The substances are selected from the group consisting of chlorotoluene, 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.

[0052] The aforementioned lithium salts are substances that dissolve in non-aqueous organic solvents and act as a source of lithium ions within the battery, enabling the operation of basic lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Typical examples of such lithium salts include LiPF6, LiBF4, lithium difluoro(oxalate)borate (LiDFOB), LiPO2F2, LiSbF6, LiAsF6, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiN(C x F 2x+1 SO2)(C y F 2y+1 One or more of the following can be selected from the group consisting of SO2) (where x is an integer from 1 to 20 and y is an integer from 0 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB).

[0053] The lithium salt concentration is preferably used within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and effective lithium ion movement.

[0054] On the other hand, the electrolyte may additionally contain at least one additive from among vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propensultone (PST), propanesultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP).

[0055] By further including the aforementioned additives, the lifespan can be improved, and the gases generated at the positive and negative electrodes during high-temperature storage can be effectively controlled.

[0056] The additive may be included in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the total electrolyte for the lithium secondary battery, specifically in an amount of 0.2 to 15 parts by weight, for example, 0.2 to 10 parts by weight.

[0057] When the additive content is as described above, it is possible to minimize the increase in film resistance and contribute to improving battery performance.

[0058] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0059] The positive electrode active material may include a cobalt-free lithium nickel manganese oxide.

[0060] In this specification, a cobalt-free lithium nickel-manganese oxide as a positive electrode active material means a positive electrode active material that does not contain cobalt in its composition and is mainly composed of nickel, manganese, etc.

[0061] As an example, the cobalt-free lithium nickel manganese oxide may contain at least one of the lithium composite oxides represented by the following chemical formula 3. [Chemical formula 3] Li a Ni x Mn y M 1 z M 2 w O 2±b X c In the aforementioned chemical formula 3, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w<0.1, 0.6≦x<1.0, 0 <y<0.4、0<z<0.1、w+x+y+z=1であり、 M 1 and M 2 Each of the elements is independently selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0062] Of course, a lithium composite oxide having a coating layer on its surface can also be used, or a mixture of the lithium composite oxide and a compound having a coating layer can be used. This coating layer may contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxys of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. These compounds forming the coating layer may be amorphous or crystalline. As the coating elements included in the coating layer, Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof can be used. The coating layer formation step may use any coating method (e.g., spray coating, immersion method, etc.) that does not adversely affect the physical properties of the positive electrode active material by using such elements in the compound, and since this is well understood by those engaged in the field, a detailed explanation will be omitted.

[0063] As an example, the aforementioned chemical formula 3 can be represented by the following chemical formula 3-1. [Chemical formula 3-1] Li a Ni x1 Mn y1 Al z1 M 2 w1 O 2±b X c In the aforementioned chemical formula 3-1, 0.5≦a<1.8, 0≦b≦0.1, 0≦c≦0.1, 0≦w1<0.1, 0.6≦x1<1.0, 0 <y1<0.4、0<z1<0.1、w1+x1+y1+z1=1であり、 M 2 Each of the elements is independently selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0064] In one embodiment, in Chemical Formula 3-1, 0.6 ≦ x1 ≦ 0.9, 0.1 ≦ y1 < 0.4, and 0 < z1 < 0.1, and it can be 0.6 ≦ x1 ≦ 0.8, 0.2 ≦ y1 < 0.4, and 0 < z1 < 0.1.

[0065] For example, x1 in Chemical Formula 3-1 can be 0.6 ≦ x1 ≦ 0.79, y1 can be 0.2 ≦ y1 ≦ 0.39, and z1 can be 0.01 ≦ z1 < 0.1.

[0066] The content of the positive electrode active material can be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

[0067] In one embodiment of the present invention, the positive electrode active material layer can include a binder. At this time, the content of the binder can be 1% to 5% by weight based on the total weight of the positive electrode active material layer.

[0068] The binder serves to make the positive electrode active material particles adhere well to each other and also make the positive electrode active material adhere well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0069] As the positive electrode current collector, Al can be used, but is not limited thereto.

[0070] The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector and containing a negative electrode active material.

[0071] The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0072] As the material capable of reversibly inserting / desorbing the lithium ions, a carbon material can be used, and any carbon-based negative electrode active material generally used in a lithium secondary battery can be used. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0073] As the alloy of lithium metal, an alloy of 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 can be used.

[0074] As the material capable of doping and undoping lithium, Si, Si-C composite, SiOx (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element excluding Si, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof), Sn, SnO2, Sn-R 11 (where R 11 is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element excluding Sn, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof), and the like can be mentioned. Also, at least one of these can be mixed with SiO2 and used.

[0075] The elements Q and R 11Examples include those selected from the group consisting of 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.

[0076] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0077] In a specific embodiment, the negative electrode active material can include at least one of graphite and a Si composite.

[0078] The Si composite includes a core containing Si-based particles and an amorphous carbon coating layer. For example, the Si-based particles can include one or more of silicon particles, Si-C composites, SiO x (0 < x ≤ 2), and Si alloys.

[0079] As an example, the core containing the Si-based particles includes voids at the center, the radius of the center corresponds to 30% - 50% of the radius of the Si composite, the average particle size of the Si composite is 5 μm - 20 μm, and the average particle size of the Si-based particles can be 10 nm - 200 nm.

[0080] In this specification, the average particle size can be the particle size (D50) at 50% in volume ratio in the cumulative size-distribution curve.

[0081] When the average particle size of the Si-based particles is within the above range, the volume expansion generated during charge and discharge can be suppressed, and the disconnection of the conductive path due to particle crushing during charge and discharge can be prevented.

[0082] The core containing the Si-based particles further contains amorphous carbon, in which case the central part does not contain amorphous carbon, and amorphous carbon can be present only on the surface of the Si composite.

[0083] In this context, the surface region refers to the area from the outermost surface of the central part to the outermost surface of the Si composite.

[0084] Furthermore, the Si-based particles are distributed substantially uniformly throughout the negative electrode active material, meaning they can be present in substantially uniform concentrations in the central and surface regions.

[0085] The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof.

[0086] For example, the Si-C composite may contain silicon particles and crystalline carbon.

[0087] The silicon particles may be present in an amount of 1% to 60% by weight relative to the total weight of the Si-C composite, for example, 3% to 60% by weight.

[0088] The crystalline carbon may be, for example, graphite, specifically natural graphite, artificial graphite, or a combination thereof.

[0089] The average particle size of the crystalline carbon can be 5 μm to 30 μm.

[0090] When the negative electrode active material contains both graphite and a Si composite, the graphite and Si composite may be present in the form of a mixture, in which case the graphite and Si composite may be present in a weight ratio of 99:1 to 50:50.

[0091] More specifically, the graphite and Si composite may be included in weight ratios of 97:3 to 80:20 and 95:5 to 80:20.

[0092] As the amorphous carbon precursor, coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or polymer resins such as phenolic resin, furan resin, or polyimide resin can be used.

[0093] The content of the negative electrode active material in the negative electrode active material layer may be 95% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0094] In one embodiment of the present invention, the negative electrode active material layer includes a binder and may further optionally include a conductive material. The binder content in the negative electrode active material layer may be 1% to 5% by weight relative to the total weight of the negative electrode active material layer. When a conductive material is further included, the negative electrode active material may be 90% to 98% by weight, the binder 1% to 5% by weight, and the conductive material 1% to 5% by weight.

[0095] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector. As the binder, a non-water-soluble binder, a water-soluble binder, or a combination thereof can be used.

[0096] Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0097] Examples of the water-soluble binder include rubber-based binders and polymer resin binders. The rubber-based binder may be selected from styrene-butadiene rubber, acrylic styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polytetrafluoroethylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0098] When a water-soluble binder is used as the negative electrode binder, a cellulosic compound that can impart viscosity may be further included as a thickening agent. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li. The amount of such thickening agent used may be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0099] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, and carbon fibers; metallic materials such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0100] As the negative electrode current collector, one can be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0101] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, or polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0102] The lithium secondary battery may have a maximum charging voltage of 4.35V or higher. For example, the maximum charging voltage may be between 4.35V and 4.55V.

[0103] Examples and comparative examples of the present invention are described below. These examples are merely one embodiment of the present invention, and the present invention is not limited to these examples.

[0104] Manufacturing of lithium secondary batteries Example 1 LiNi 0.75 Mn 0.23 Al 0.02 A cathode active material slurry was prepared by mixing O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material in a weight ratio of 96:3:1, and dispersing the mixture in N-methylpyrrolidone.

[0105] The cathode active material slurry was coated onto a 15 μm thick aluminum foil, dried at 100°C, and then rolled (pressed) to produce the cathode.

[0106] A mixture of artificial graphite and Si composite in a weight ratio of 93:7 was used as the negative electrode active material. The negative electrode active material was then mixed with styrene-butadiene rubber binder and carboxymethylcellulose in weight ratios of 98:1:1, and dispersed in distilled water to produce a negative electrode active material slurry.

[0107] The Si composite used consisted of a core containing artificial graphite and silicon particles, and a surface of the core coated with coal-based pitch.

[0108] The aforementioned negative electrode active material slurry was coated onto a 10 μm thick copper foil, dried at 100°C, and then rolled (pressed) to produce the negative electrode.

[0109] An electrode assembly was manufactured by assembling the manufactured positive and negative electrodes with a 10 μm thick polyethylene separator, and an electrolyte was injected to manufacture a lithium secondary battery.

[0110] The electrolyte composition is as follows: (Electrolyte composition) Lithium salt: LiPF61.5M Non-aqueous organic solvent: Ethyl methyl carbonate: Dimethyl carbonate (EMC:DMC = 20:80 volume ratio) Additives: Fluoroethylene carbonate (FEC) 10 parts by weight / Succinonitrile (SN) 0.5 parts by weight (However, in the above electrolyte composition, "parts by weight" refers to the relative weight of the additive to 100 parts by weight of the entire electrolyte (lithium salt + non-aqueous organic solvent) excluding the additive.)

[0111] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 5% by weight of ethylene carbonate was added relative to the total weight of the non-aqueous organic solvent in the electrolyte composition.

[0112] Comparative Examples 2 and 3 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that ethylene carbonate was added in amounts of 10% and 20% by weight, respectively.

[0113] Comparative Examples 4-7 Lithium secondary batteries were fabricated in the same manner as in Example 1 and Comparative Examples 1-3, except that the positive electrode active material was changed to LiCoO2.

[0114] Comparative Examples 8-11 The positive electrode active material is LiNi 0.5 Co 0.2 Al 0.3 Lithium secondary batteries were fabricated in the same manner as in Example 1 and Comparative Examples 1-3, except that the oxygen was changed to O2.

[0115] Comparative Examples 12-15 The positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 Lithium secondary batteries were fabricated in the same manner as in Example 1 and Comparative Examples 1-3, except that the oxygen was changed to O2.

[0116] Examples 2 to 4 Lithium secondary batteries were fabricated in the same manner as in Example 1, except that the volume ratio of ethyl methyl carbonate and dimethyl carbonate was changed to 30:70 (Example 2), 40:60 (Example 3), and 70:30 (Example 4), respectively.

[0117] Evaluation 1: Evaluation of high-temperature storage characteristics For the lithium secondary batteries prepared according to Examples 1 to 4 and Comparative Examples 1 to 15, the initial DC resistance (DCIR) was measured using the ΔV / ΔI (voltage change / current change) value. Then, the maximum energy state inside the battery was brought to a fully charged state (SOC 100%), and after being stored at a high temperature (60°C) for 30 days in this state, the DC resistance was measured again, and the DCIR increase rate (%) was calculated using the following formula 1. The results are shown in Tables 1, 2, and 5 below. [Formula 1] DCIR growth rate = {(DCIR after 30 days) / (initial DCIR)} x 100%

[0118] Evaluation 2: Evaluation of high-temperature life characteristics The lithium secondary batteries prepared in Example 1 and Comparative Examples 1-3 were subjected to a single charge-discharge cycle at 0.2C, and their charge-discharge capacities were measured.

[0119] Furthermore, the lithium secondary batteries prepared in Example 1 and Comparative Examples 1-3 were charged at the upper limit charging voltage (4.25V-4.45V), and then discharged to 2.5V at 0.2C under constant current conditions. The initial discharge capacity for each charging voltage was then measured.

[0120] The discharge capacity was measured while performing 200 charge-discharge cycles at 45°C under conditions of 0.33C charging (CC / CV, 4.25V~4.45V, 0.025C cut-off) / 1.0C discharge (CC, 2.5V cut-off). The ratio of the discharge capacity to the initial discharge capacity is shown in Table 4 below as the capacity recovery rate (%).

[0121] Evaluation 3: Measurement of gas generation after high-temperature storage For lithium secondary batteries prepared in Example 1 and Comparative Examples 1-3, the amount of gas generated (ml) on day 1 and day 7 was measured using a refinery gas analyzer (RGA) after being left at 60°C for 7 days, and the results are shown in Table 3 below.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] [Table 4]

[0126] [Table 5]

[0127] Referring to Tables 1 to 5, it can be seen that in the composition combining the lithium salt, non-aqueous organic solvent, and Co-free cathode active material according to this application, the DC-IR increase rate decreased, and both the high-temperature storage characteristics and high-temperature charge-discharge characteristics were improved.

[0128] In particular, as can be seen from Table 2, the reduction in the rate of resistance increase due to the presence of less than 5% by weight of EC is more pronounced in positive electrode active materials containing cobalt-free lithium nickel manganese oxides.

[0129] Furthermore, it can be seen that the lithium secondary battery in the example showed a significant decrease in gas generation after high-temperature storage.

[0130] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. It can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and these variations naturally also fall within the scope of the present invention. [Explanation of Symbols]

[0131] 100: Lithium-ion rechargeable battery 112: Negative electrode 113: Separator 114: Positive electrode 120:Battery container 140: Encapsulation material

Claims

1. An electrolyte containing a non-aqueous organic solvent and a lithium salt; A positive electrode containing a positive electrode active material; and Includes a negative electrode containing a negative electrode active material, The aforementioned non-aqueous organic solvent contains a chain-like carbonate but does not contain ethylene carbonate. The positive electrode active material is a lithium secondary battery containing a cobalt-free lithium nickel manganese oxide, A lithium secondary battery comprising the aforementioned cobalt-free lithium nickel manganese oxide, which contains a lithium composite oxide represented by the following chemical formula 3. [Chemical formula 3] Li a Ni x Mny M 1 z M 2 w O 2±b X c (In the above chemical formula 3, 0.5 ≤ a < 1.8, 0 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.1, 0 ≤ w < 0.1, 0.6 ≤ x < 1.0, 0 < y < 0.4, 0 < z < 0.1, and w + x + y + z = 1. M1 and M2 are each independently one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

2. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is composed solely of a chain-like carbonate.

3. The lithium secondary battery according to claim 2, wherein the chain-like carbonate is represented by the following chemical formula 1. 【Chemistry 1】 (In the above chemical formula 1) R １ and R ２ These are each independently substituted or unsubstituted C1-C20 alkyl groups.

4. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and ethyl methyl carbonate (EMC).

5. The lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent contains ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 10:90 to 50:

50.

6. The electrolyte is vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propensultone (PST), propanesultone (PS), lithium tetrafluoroborate (LiBF) ４ ), lithium difluorophosphate (LiPO ２ F ２ The lithium secondary battery according to claim 1, further comprising at least one additive selected from ) and 2-fluorobiphenyl (2-FBP).

7. The lithium secondary battery according to claim 1, wherein the aforementioned chemical formula 3 is represented by the following chemical formula 3-1. [Chemical formula 3-1] Li ａ Ni ｘ１ Mn ｙ１ Al ｚ１ M ２ ｗ１ O ２±ｂ X ｃ (In the above chemical formula 3-1, 0.5 ≤ a < 1.8, 0 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.1, 0 ≤ w1 < 0.1, 0.6 ≤ x1 < 1.0, 0 < y1 < 0.4, 0 < z1 < 0.1, and w1 + x1 + y1 + z1 = 1. M ２ (Each element is independently selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Si, Ba, Ca, Ce, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.)

8. The lithium secondary battery according to claim 7, wherein x1 in the chemical formula 3-1 is 0.6 ≤ x1 ≤ 0.79, y1 is 0.2 ≤ y1 ≤ 0.39, and z1 is 0.01 ≤ z1 < 0.

1.

9. The lithium secondary battery according to claim 1, wherein the negative electrode active material comprises at least one of graphite and a Si composite.

10. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a maximum charging voltage of 4.35V or higher.

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