Lithium secondary battery

Abstract

To provide a lithium secondary battery capable of suppressing an avalanche of a positive electrode containing a cobalt-free lithium nickel manganese system oxide even under a high voltage and a high temperature condition.SOLUTION: A lithium secondary battery according to an embodiment, contains: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; and an electrolyte containing a non-aqueous organic solvent, a lithium salt, and an additive agent. The positive electrode active material contains a cobalt-free lithium nickel manganese system oxide, the non-aqueous organic solvent contains an ethylene carbonate that is less than 5 wt.%, and the additive agent contains a phosphorus system chemical compound containing a trialkylsilyl group.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This relates to lithium secondary batteries. [Background technology]

[0002] Recently, with the rapid spread of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries with high energy density and capacity is rapidly increasing. As a result, research and development to improve the performance of lithium secondary batteries is being actively conducted.

[0003] A lithium secondary battery is a battery that contains positive and negative electrodes, which include active materials capable of intercalating and deintercalating lithium ions, and an electrolyte. It produces electrical energy through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the positive and negative electrodes.

[0004] In particular, as IT devices become increasingly sophisticated, there is a demand for higher-capacity batteries. By expanding the voltage range to achieve higher capacity, the energy density can be increased. However, there is a problem in that the electrolyte is oxidized in the high-voltage range, deteriorating the performance of the positive electrode.

[0005] In particular, cobalt-free lithium nickel manganese oxide, which is used as a positive electrode active material, does not contain cobalt in the composition of the positive electrode active material, and is composed mainly of nickel, manganese, etc., and positive electrodes containing this are economical and can achieve high energy density, so they are in the spotlight as next-generation positive electrode active materials.

[0006] However, when a positive electrode containing cobalt-free lithium nickel manganese oxide is used in a high voltage environment, the structure of the positive electrode collapses, causing transition metal elution, which can lead to problems such as gas generation inside the cell and capacity reduction. This transition metal elution phenomenon tends to intensify in high temperature environments, and the eluted transition metals can precipitate on the surface of the negative electrode, inducing side reactions, which can lead to an increase in battery resistance and a decrease in battery life and output characteristics.

[0007] This has created a demand for technology that can suppress the structural collapse of positive electrodes containing cobalt-free lithium nickel manganese oxides even under high voltage and high temperature conditions. Summary of the Invention [Problem to be solved by the invention]

[0008] One embodiment is directed to providing a lithium secondary battery that suppresses structural collapse of a positive electrode containing a cobalt-free lithium nickel manganese oxide even under high voltage and high temperature conditions. [Means for solving the problem]

[0009] One embodiment provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte including a lithium salt, a non-aqueous organic solvent, and an additive, wherein the positive electrode active material includes a cobalt-free lithium nickel manganese-based oxide, the non-aqueous organic solvent includes 5 wt % or less of ethylene carbonate, and the additive includes a phosphorus-based compound including a trialkylsilyl group. Effect of the Invention

[0010] According to an embodiment, a lithium secondary battery uses a positive electrode including a cobalt-free lithium nickel manganese-based oxide, and the structure of the positive electrode is prevented from collapsing even under high voltage and high temperature conditions, thereby improving stability and life characteristics. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail, but they are given by way of example only and are not intended to limit the present invention, which is defined only by the scope of the following claims.

[0013] Unless otherwise specified in this specification, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0014] Unless otherwise specified herein, the singular can also include the plural. At the same time, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B."

[0015] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0016] In this specification, unless otherwise defined, the term "substituted" means that at least one hydrogen atom in a substituent or a compound is replaced with deuterium, a halogen group, a hydroxyl group, an amino group, a substituted or unsubstituted amine group having 1 to 30 carbon atoms, a nitro group, a substituted or unsubstituted silyl group having 1 to 40 carbon atoms, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a cyano group, or a combination thereof.

[0017] In one embodiment of the present invention, "substitution" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 30 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an arylsilyl group having 6 to 30 carbon atoms, a cycloalkyl group having 3 to 30 carbon atoms, a heterocycloalkyl group having 3 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, a heteroaryl group having 2 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. In one specific embodiment of the present invention, "substitution" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 30 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, or a cyano group. In one specific embodiment of the present invention, "substitution" means that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen group, an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 18 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, or a cyano group. In addition, in a specific example of the present invention, "substituted" means that at least one hydrogen atom in a substituent or compound is replaced 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.

[0018] (lithium secondary battery) One embodiment provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte including a lithium salt, a non-aqueous organic solvent, and an additive, wherein the positive electrode active material includes a cobalt-free lithium nickel manganese-based oxide, the non-aqueous organic solvent includes 5 wt % or less of ethylene carbonate, and the additive includes a phosphorus-based compound including a trialkylsilyl group.

[0019] In general, cobalt-free lithium nickel manganese oxides have strong structural instability, and under high voltage conditions, the transition metal (especially Ni) dissolution phenomenon occurs, which may lead to a rapid increase in the stability and lifespan of the lithium secondary battery.

[0020] However, the lithium secondary battery according to an embodiment of the present invention uses a positive electrode including a cobalt-free lithium nickel manganese-based oxide, and the structure of the positive electrode is prevented from collapsing even under high voltage and high temperature conditions, thereby improving stability and life characteristics.

[0021] Such an effect is due to the combination of a non-aqueous organic solvent containing 5% by weight or less of ethylene carbonate and a phosphorus-based compound additive containing a trialkylsilyl group.

[0022] The components constituting the lithium secondary battery will now be described in more detail.

[0023] Additives The additive includes a phosphorus-based compound containing a trialkylsilyl group.

[0024] The phosphorus-based compound containing a trialkylsilyl group effectively reduces the elution of transition metals from the cobalt-free lithium nickel manganese oxide under high voltage and high temperature conditions and inhibits the collapse of the positive electrode structure, thereby improving the stability and life characteristics of the lithium secondary battery.

[0025] The additive may include a phosphate-based compound containing a trialkylsilyl group, a phosphite-based compound containing a trialkylsilyl group, or a combination thereof.

[0026] Specifically, the additive may include a compound represented by the following Chemical Formula 1, a compound represented by the following Chemical Formula 2, or a combination thereof:

[0027] [ka]

[0028] [ka]

[0029] In the above chemical formulas 1 and 2, R 1 ~R 6 are each independently the same or different and are a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

[0030] More specifically, in the above formulas 1 and 2, R 1 ~R 6 may all be methyl groups. For example, the additive may include trimethyl phosphate (TMSPa), trimethyl phosphite (TMSPi), or a combination thereof.

[0031] The additive may be included in an amount of 0.1 to 10.0 wt %, specifically 0.5 to 8.0 wt %, for example 0.1 to 5.0 wt %, based on the total amount of the electrolyte, in which case the life of the lithium secondary battery can be further improved or gas generated from the positive and negative electrodes during high-temperature storage can be effectively controlled.

[0032] Meanwhile, the additive may further include at least one additive selected from 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), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), and 2-fluorobiphenyl (2-FBP). The additional additive may be combined with the phosphorus-based compound containing a trialkylsilyl group to exert an increasing effect.

[0033] The additional additive may be included in an amount of 0.1 to 5.0 wt % based on the total weight of the lithium secondary battery electrolyte, specifically, 0.1 to 3.0 parts by weight, for example, 0.1 to 1.0 wt %.

[0034] When the content of the additive is within the above range, the increase in the film resistance can be minimized, thereby contributing to improved battery performance.

[0035] Non-aqueous organic solvents The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0036] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0037] Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester-based solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0038] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0039] Specifically, the non-aqueous organic solvent may contain 5% by weight or less of ethylene carbonate.

[0040] If the content of ethylene carbonate exceeds the above range, the activity of Ni increases during high voltage operation, and Ni oxidation number tends to be reduced from 4 to 2, and ethylene carbonate with low oxidation stability is oxidized and decomposed, resulting in Ni elution and deposition on the negative electrode.

[0041] More specifically, the non-aqueous organic solvent may be composed of only a chain carbonate, in which case the resistance increase rate during high temperature storage is significantly reduced, thereby achieving excellent high temperature storage characteristics.

[0042] In this specification, the term "composed only of chain carbonate" means that it includes an organic solvent that is not mixed with a cyclic carbonate or the like and that belongs to the category of chain carbonate, either alone or in combination.

[0043] The chain carbonate can be represented by the following chemical formula 3.

[0044] [ka]

[0045] In the above chemical formula 3, R 7 and R 8 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

[0046] Specifically, R 7 and R 8 may each independently be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. For example, 7 and R 8 may each independently be a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms.

[0047] More specifically, R 7 and R 8may each independently be 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.

[0048] More specifically, the non-aqueous organic solvent may 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).

[0049] For example, the non-aqueous organic solvent may be a mixed solvent of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0050] 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.

[0051] It may be more advantageous in terms of improving battery characteristics if the non-aqueous organic solvent contains more than 50 volume % dimethyl carbonate (DMC).

[0052] 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.

[0053] Lithium salts The lithium salt is a material that is dissolved in a non-aqueous organic solvent and acts as a source of lithium ions in a battery to enable basic lithium secondary battery operation and promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C p F 2p+1 SO2)(C q F 2q+1 SO2) (wherein p and q are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0054] positive electrode active material The positive electrode active material may include a cobalt-free lithium nickel manganese oxide.

[0055] In this specification, the cobalt-free lithium nickel manganese oxide as a positive electrode active material means a positive electrode active material composed mainly of nickel, manganese, etc. without including cobalt in the composition of the positive electrode active material.

[0056] The cobalt-free lithium nickel manganese oxide may include at least one of lithium composite oxides represented by the following Chemical Formula 4.

[0057] [Chemical formula 4] Li a Ni x Mn y M 1 z M 2 w O 2±b X c In the above chemical formula 4, 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 are each independently one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0058] Specifically, the formula 4 can be represented by the following formula 4-1.

[0059] [Chemical formula 4-1] Li a Ni x1 Mn y1 Al z1 M 2 w1 O 2±b X c In the above chemical formula 4-1, 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 are each independently one or more elements selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

[0060] In the formula 4-1, 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.

[0061] positive electrode The positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material, and may further include a binder and / or a conductive material.

[0062] For example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0063] The content of the positive electrode active material may be 90% by weight to 99.5% by weight based on 100% by weight of the positive electrode active material layer, and the contents of the binder and the conductive material may be 0.5% by weight to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0064] The binder serves to adhere the positive electrode active material particles to each other and to adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0065] The conductive material is used to impart electrical conductivity to the electrodes, and any material that does not cause chemical changes in the battery that is constructed and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, and the like in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0066] As the current collector, Al can be used, but it is not limited thereto.

[0067] negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material dopable and dedopable with lithium, or a transition metal oxide.

[0068] Examples of the material capable of reversibly intercalating / deintercalating the lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0069] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0070] As the material dopable and dedopable with lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (wherein Q is selected from 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), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, an Sn-based alloy, or a combination thereof.

[0071] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to an embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0072] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles and an amorphous carbon coating layer located on the core.

[0073] The Si-based or Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0074] negative electrode The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material, and may further include a binder and / or a conductive material.

[0075] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0076] The binder serves to adhere the negative active material particles to each other and to the current collector well. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0077] The non-aqueous binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0078] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0079] When the negative electrode binder is an aqueous binder, it may further contain a cellulose-based compound capable of imparting viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li.

[0080] The dry binder is a polymeric material that can be fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0081] The conductive material is used to impart conductivity to the electrodes, and any material that does not cause a chemical change in the battery and is electronically conductive can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0082] The negative electrode current collector may 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.

[0083] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be polyethylene, polypropylene, polyvinylidene fluoride, or multi-layered films of two or more of these, and of course mixed multi-layered films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0084] The separator may include a porous substrate and a coating layer, including an organic material, an inorganic material, or a combination thereof, located on one or both sides of the porous substrate.

[0085] The porous substrate may be a polymer membrane formed from any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0086] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0087] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0088] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be laminated.

[0089] Lithium secondary battery FIG 1 shows an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. Referring to FIG 1, the lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50 as shown in FIG 1.

[0090] The lithium secondary battery according to an embodiment may be applied to batteries of various shapes, such as a cylindrical type, a square type, a pouch type, etc., and the present invention is not limited thereto.

[0091] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electric devices, but the present invention is not limited thereto.

[0092] Charging voltage limit The lithium secondary battery may have an upper charge voltage limit of 4.35V or more, specifically 4.35V to 4.55V, for example 4.35V to 4.75V.

[0093] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples. EXAMPLES

[0094] (Production Examples / Comparative Production Examples) Manufacturing Example 1 LiPF6 was dissolved at a concentration of 1.5M in a non-aqueous organic solvent in which ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:80, and 0.1 wt% trimethylsilyl phosphate (TMSPa) was added to prepare an electrolyte.

[0095] In the above electrolyte composition, "wt %" refers to the relative weight of the additive to the weight of the entire electrolyte (lithium salt + non-aqueous organic solvent + additive) including the additive. The same applies hereinafter.

[0096] Manufacturing Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.0 wt % of trimethylsilyl phosphate was added.

[0097] Production Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 5.0 wt % of trimethylsilyl phosphate was added.

[0098] Production Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.1 wt % of trimethyl phosphite (TMSPi) was added.

[0099] Production Example 5 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1.0 wt % of trimethylsilyl phosphite was added.

[0100] Production Example 6 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 5.0 wt % of trimethylsilyl phosphite was added.

[0101] Comparative Manufacturing Example 1 LiPF6 was dissolved at a concentration of 1.5 M in a non-aqueous organic solvent in which ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:80, and 20 wt% ethylene carbonate (EC) was added to prepare an electrolyte.

[0102] Comparative Production Example 2 An electrolyte was prepared by dissolving LiPF6 at a concentration of 1.5 M in a non-aqueous organic solvent in which ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:80.

[0103] (LiNi as positive electrode active material) 0.75 Mn 0.23 Al 0.02 (Example using O2) Example 1-1 LiNi as the positive electrode active material 0.75 Mn 0.23 Al 0.02O2, polyvinylidene fluoride as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96:3:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0104] The positive electrode active material slurry was coated on an aluminum foil having a thickness of 15 μm, dried at 100° C., and pressed to prepare a positive electrode.

[0105] A mixture of artificial graphite and Si-C composite in a weight ratio of 93:7 was used as the negative active material, and the negative active material was mixed with a styrene-butadiene rubber binder and carboxymethyl cellulose in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative active material slurry.

[0106] The Si-C composite used had a core containing artificial graphite and silicon particles, and the surface of the core was coated with coal-based pitch.

[0107] The negative electrode active material slurry was coated on a copper foil having a thickness of 10 μm, dried at 100° C., and pressed to prepare a negative electrode.

[0108] The positive and negative electrodes thus prepared were assembled with a 10 μm thick polyethylene separator to prepare an electrode assembly, and the electrolyte solution of Preparation Example 1 was injected into the electrode assembly to prepare a lithium secondary battery.

[0109] Example 1-2 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte of Preparation Example 2 was used.

[0110] Examples 1-3 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte solution of Preparation Example 3 was used.

[0111] Examples 1-4 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte solution of Preparation Example 4 was used.

[0112] Examples 1-5 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte of Preparation Example 5 was used.

[0113] Examples 1-6 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte of Preparation Example 6 was used.

[0114] Comparative Example 1-1 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte of Comparative Preparation Example 1 was used.

[0115] Comparative Example 1-2 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that the electrolyte of Comparative Preparation Example 2 was used.

[0116] (An example of using LiCoO2 as the positive electrode active material) Comparative Example 2-1 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-1, except that LiCoO2 was used as the positive electrode active material.

[0117] Comparative Example 2-2 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-2, except that LiCoO2 was used as the positive electrode active material.

[0118] Comparative Example 2-3 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that LiCoO2 was used as the positive electrode active material.

[0119] Comparative Example 2-4 A lithium secondary battery was manufactured in the same manner as in Example 1-2, except that LiCoO2 was used as the positive electrode active material.

[0120] Comparative Example 2-5 A lithium secondary battery was manufactured in the same manner as in Example 1-3, except that LiCoO2 was used as the positive electrode active material.

[0121] Comparative Example 2-6 A lithium secondary battery was manufactured in the same manner as in Examples 1-4, except that LiCoO2 was used as the positive electrode active material.

[0122] Comparative Example 2-7 A lithium secondary battery was manufactured in the same manner as in Examples 1-5, except that LiCoO2 was used as the positive electrode active material.

[0123] Comparative Example 2-8 A lithium secondary battery was manufactured in the same manner as in Examples 1-6, except that LiCoO2 was used as the positive electrode active material.

[0124] (LiNi as positive electrode active material) 0.94 Co 0.03 Al 0.03 Comparison example using O2) Comparative Example 3-1 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-1, except that O2 was used.

[0125] Comparative Example 3-2 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Comparative Example 1-2, except that O2 was used.

[0126] Comparative Example 3-3 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Example 1-1, except that O2 was used.

[0127] Comparative Example 3-4 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Example 1-2, except that O2 was used.

[0128] Comparative Example 3-5 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Example 1-3, except that O2 was used.

[0129] Comparative Example 3-6 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Examples 1-4, except that O2 was used.

[0130] Comparative Example 3-7 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Examples 1-5, except that O2 was used.

[0131] Comparative Example 3-8 LiNi as the positive electrode active material 0.94 Co 0.03 Al 0.03 A lithium secondary battery was manufactured in the same manner as in Examples 1-6, except that O2 was used.

[0132] (evaluation) Evaluation 1: High temperature storage characteristic evaluation The initial DC resistance (DCIR) was measured as a ΔV / ΔI (change in voltage / change in current) value for the lithium secondary batteries of the examples and comparative examples. The maximum energy state inside the battery was then set to a fully charged state (SOC 100%), and after storing the battery in this state at high temperature (60°C) for 30 days, the DC resistance was measured and the DCIR increase rate (%) was calculated using the following formula 1. The results are shown in Table 1 below: [Formula 1] DCIR increase rate = {(DCIR after 30 days - initial DCIR) / initial DCIR} x 100%

[0133] [Table 1]

[0134] Evaluation 2: Gas generation measurement after high temperature storage The lithium secondary batteries of the Examples and Comparative Examples were left at 60° C. for 10 or 30 days, and the amount of gas generated (ml) on the 10th or 30th day was measured using a refinery gas analyzer (RGA), and the results are shown in Table 2 below.

[0135] [Table 2]

[0136] Evaluation 3: High temperature life characteristics evaluation The lithium secondary batteries of the examples and comparative examples were charged and discharged once at 0.2 C to measure the charge and discharge capacity.

[0137] In addition, the lithium secondary batteries of the examples and comparative examples were charged at a maximum charging voltage (4.35V or 4.45V) and then discharged at a constant current of 0.2C to 2.5V to measure the initial discharge capacity for each charging voltage.

[0138] The discharge capacity was measured again by performing 200 charge / discharge cycles at 0.33 C charge (CC / CV, 4.35 V or 4.45 V, 0.025 C cut-off) / 1.0 C discharge (CC, 2.5 V cut-off) at 45° C. The ratio of the discharge capacity to the initial discharge capacity is shown as the capacity retention rate in Table 3 below.

[0139] [Table 3]

[0140] According to Table 1, when a cobalt-free lithium nickel manganese oxide positive electrode active material is used, the DCIR increase rate of the lithium secondary battery tends to decrease compared to when a cobalt-containing positive electrode active material is used.

[0141] Furthermore, according to Tables 2 and 3, even when a cobalt-free lithium nickel manganese oxide-based positive electrode active material is used, the stability and life characteristics of the lithium secondary battery are all improved when used together with an electrolyte containing an additive including a lithium salt, a non-aqueous organic solvent, and a phosphorus-based compound containing a trialkylsilyl group.

[0142] In addition, in the examples, the DCIR increase rate, high temperature storage characteristics, and high temperature charge / discharge characteristics change depending on the content of the additive, so that the content of the additive can be appropriately controlled in consideration of this.

[0143] Although the above describes a preferred embodiment of the present invention, the present invention is not limited thereto, and can be embodied in various modified forms within the scope of the claims, the detailed description of the invention, and the accompanying drawings, which of course also fall within the scope of the present invention. [Explanation of symbols]

[0144] 100: Lithium secondary battery 10: Positive electrode 20: Negative electrode 30: Separator 50: Case 60: Sealing material

Claims

1. a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and an electrolyte solution including a lithium salt, a non-aqueous organic solvent, and an additive; The positive electrode active material includes a cobalt-free lithium nickel manganese oxide, The non-aqueous organic solvent contains 5% by weight or less of ethylene carbonate; The additive comprises a phosphorus-based compound containing a trialkylsilyl group; Lithium secondary battery.

2. 2. The lithium secondary battery of claim 1, wherein the additive comprises a phosphate-based compound containing a trialkylsilyl group, a phosphite-based compound containing a trialkylsilyl group, or a combination thereof.

3. 2. The lithium secondary battery of claim 1, wherein the additive comprises a compound represented by the following Chemical Formula 1, a compound represented by the following Chemical Formula 2, or a combination thereof: 【Chemistry 1】 【Chemistry 2】 In the above chemical formulas 1 and 2, R 1 ~R 6 are each independently the same or different and are a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

4. 2. The lithium secondary battery of claim 1, wherein the additive comprises trimethylsilyl phosphate, trimethylsilyl phosphite, or a combination thereof.

5. 2. The lithium secondary battery according to claim 1, wherein the additive is contained in an amount of 0.1 to 10.0% by weight based on the total amount of the electrolyte.

6. The additives include 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), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 2. The lithium secondary battery according to claim 1, further comprising at least one additive selected from the group consisting of 2-fluorobiphenyl (2-FBP) and 2-fluorobiphenyl (2-FBP).

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

8. The lithium secondary battery according to claim 7, wherein the chain carbonate is represented by the following chemical formula 3: 【Chemistry 3】 In the above formula 3 R 7 and R 8 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms.

9. 9. The lithium secondary battery according to claim 8, 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).

10. 10. The lithium secondary battery according to claim 9, wherein the non-aqueous organic solvent comprises ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 10:90 to 50:

50.

11. The lithium salt is LiPF 6 , LiBF 4 , lithium difluoro(oxalate)borate (LiDFOB), LiPO 2 F 2 , LiSbF 6 , LiAsF 6 , Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN (C p F 2p+1 SO 2 ) (C q F 2q+1 SO 2 ) (where p and q are integers from 1 to 20), LiCl, LiI, and LiB (C 2 O 4 ) 2 2. The lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of lithium bis(oxalato) borate (LiBOB).

12. 2. The lithium secondary battery of claim 1, wherein the cobalt-free lithium nickel manganese oxide includes a lithium composite oxide represented by the following Chemical Formula 4: [Chemical formula 4] Li a Ni x Mn y M 1 z M 2 w O 2±b X c In the above chemical formula 4, 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; M 1 and M. 2 are each independently one or more elements selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

13. The lithium secondary battery according to claim 12, wherein the chemical formula 4 is represented by the following chemical formula 4-1: [Chemical formula 4-1] Li a Ni x1 Mn y1 Al z1 M 2 w1 O 2±b X c In the above chemical formula 4-1, 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 are each independently one or more elements selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb, and X is one or more elements selected from S, F, P, and Cl.

14. 14. The lithium secondary battery according to claim 13, wherein x1 in the formula 4-1 is 0.6≦x1≦0.79, y1 is 0.2≦y1≦0.39, and z1 is 0.01≦z1<0.

1.

15. 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has an upper limit charging voltage of 4.35 V or higher.

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