Electrolyte additive, non-aqueous electrolyte comprising same for secondary battery, and lithium secondary battery

Abstract

The present invention provides an electrolyte additive, a non-aqueous electrolyte comprising same for a secondary battery, and a lithium secondary battery. Specifically, the present invention provides: an electrolyte additive comprising a compound represented by chemical formula 1 and enabling the formation of a film with excellent mechanical durability on the surface of a positive electrode; a non-aqueous electrolyte comprising same for a secondary battery; and a lithium secondary battery.

Description

Electrolyte additive, non-aqueous electrolyte for secondary batteries containing the same, and lithium secondary battery

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0154768 filed November 4, 2024 and Korean Patent Application No. 10-2025-0159735 filed October 29, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0003]

[0004] Technology field

[0005] The present invention relates to an electrolyte additive, a non-aqueous electrolyte for a secondary battery containing the same, and a lithium secondary battery.

[0006] As dependence on electrical energy gradually increases in modern society, the development of large-capacity power storage devices capable of stably supplying power while simultaneously increasing production is emerging. Furthermore, the need for high-capacity portable power is growing due to the performance improvements of electronic products, ranging from small devices such as mobile phones to medium-to-large devices such as electric vehicles. Lithium-ion batteries, which possess the highest potential, satisfy high-capacity power storage performance requirements and are therefore being utilized in a wide range of applications, from small electronic devices to electric vehicles (EVs) and energy storage systems (ESS).

[0007] The above lithium secondary battery generally consists of a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transporting lithium ions, and a separator. In this case, carbon-based active materials, silicon-based active materials, lithium transition metal oxides, lithium metal, etc., may be used as the negative electrode active material. Additionally, lithium transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium nickel-cobalt-manganese composite oxide, and lithium iron phosphate may be used as the positive electrode active material.

[0008] During the charging of a lithium secondary battery, lithium ions are generated from the positive electrode and can be converted into stacked or alloyed forms for storage on the negative electrode, while discharge proceeds in the opposite direction. Theoretically, the movement of lithium ions to the positive and negative electrodes during charging and discharging of such lithium secondary batteries should be reversible; however, in reality, the movement of lithium within the battery may be partially irreversible. Specifically, the medium through which lithium ions can move is the electrolyte. During charging, most lithium ions are stacked or alloyed within the negative electrode active material, but some are reduced together with the organic and inorganic materials constituting the electrolyte to form nano-sized organic-inorganic composites on the surface of the negative electrode material. This formed organic-inorganic film is called a solid electrolyte interface layer (SEI layer). Meanwhile, a solid electrolyte interface layer can also be formed on the surface of the positive electrode active material through the oxidation reaction of the materials constituting the electrolyte.

[0009] Although the formation of such a solid-electrolyte interface layer causes irreversible loss of lithium ions supplied by the anode, once the layer is formed, this irreversible loss is reduced, and a wide driving potential of the electrolyte is secured, enabling smooth reversible movement of lithium ions between the anode and cathode. Depending on its internal composition, this solid-electrolyte interface layer can contribute to lowering the energy barrier required for charge transfer of lithium ions to the cathode or anode, or its stability can determine the lifespan characteristics and durability of the lithium secondary battery.

[0010] Meanwhile, as the charging and discharging of the lithium secondary battery progresses, the deterioration of the initially formed solid-electrolyte interface layer causes the decomposition of the electrolyte, leading to an increase in resistance and structural degradation of the cathode material, which results in the leaching of transition metals from the cathode. The transition metal ions leached out in this way are re-deposited on the cathode, which causes an increase in the resistance of the cathode. Conversely, they move through the electrolyte to the anode and are electrodeposited on the anode, causing self-discharge of the anode. Furthermore, due to the destruction and regeneration of the solid-electrolyte interface layer, additional lithium ions are consumed, causing an increase in resistance and a deterioration of lifespan.

[0011] Therefore, strengthening the stability of the solid-electrolyte interface layer is emerging as an important task to improve the performance of lithium secondary batteries.

[0012] One objective of the present invention is to solve the above-mentioned problems by providing an electrolyte additive capable of increasing the stability of the solid-electrolyte interface layer formed on the surfaces of the cathode and the anode.

[0013] In addition, the present invention provides a non-aqueous electrolyte for a secondary battery that can secure excellent durability and stability at low and high temperatures by including the above-mentioned electrolyte additive.

[0014] In addition, the present invention provides a lithium secondary battery with improved overall performance by including the above-described non-aqueous electrolyte for the secondary battery, thereby improving low-temperature life, low-temperature output, fast charging, room-temperature life, high-temperature storage characteristics, and high-temperature life characteristics.

[0015] [1] The present invention provides an electrolyte additive comprising a compound represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017]

[0018] In the above chemical formula 1,

[0019] R is an alkylene group having 1 to 5 carbon atoms.

[0020] [2] The present invention provides an electrolyte additive in which, in [1], R in Formula 1 is an alkylene group having 1 to 3 carbon atoms.

[0021] [3] The present invention provides an electrolyte additive in which, in [1] or [2], the compound represented by Formula 1 is selected from the group consisting of at least one compound represented by Formulas 1A to 1C below.

[0022] [Chemical Formula 1A]

[0023]

[0024] [Chemical Formula 1B]

[0025]

[0026] [Chemical Formula 1C]

[0027]

[0028] [4] The present invention provides a non-aqueous electrolyte for a secondary battery comprising an electrolyte additive according to [1].

[0029] [5] The present invention provides a non-aqueous electrolyte for a secondary battery, wherein the electrolyte additive in [4] is included in an amount of 0.05% to 9% by weight based on the total weight of the non-aqueous electrolyte for a secondary battery.

[0030] [6] The present invention provides a non-aqueous electrolyte for a secondary battery, wherein, in [4] or [5], the electrolyte additive is included in an amount of 0.05% to 5% by weight based on the total weight of the non-aqueous electrolyte for a secondary battery.

[0031] [7] The present invention provides a non-aqueous electrolyte for a secondary battery, wherein, in at least one of [4] to [6], the non-aqueous electrolyte for a secondary battery further comprises a lithium salt and an organic solvent.

[0032] [8] The present invention provides a non-aqueous electrolyte for a secondary battery, wherein, in at least one of [4] to [7], the non-aqueous electrolyte for a secondary battery further comprises at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds and lithium salt compounds.

[0033] [9] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte for a secondary battery according to [4].

[0034]

[0010] The present invention provides a lithium secondary battery according to [9], wherein the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises a lithium iron phosphate.

[0035]

[0011] The present invention provides a lithium secondary battery, wherein, in [9] or

[0010] , the positive active material further comprises a lithium nickel-cobalt-manganese composite oxide.

[0036] The electrolyte additive represented by Chemical Formula 1 of the present invention has a lithium sulfonate group (-SO3) in a 1,3,2-dioxaborole-4,5-dione structure. - Li + It is characterized by the substitution of ). The electrolyte additive of the present invention can prevent adverse reactions between the electrolyte and the electrode and suppress electrode degradation by forming a boron (B)-containing solid-electrolyte interface layer that can function as an effective ion carrier on the electrode surface. Therefore, when a non-aqueous electrolyte containing such an electrolyte additive is applied to a lithium secondary battery, a lithium secondary battery capable of exhibiting excellent lifespan performance and storage performance even under conditions such as high temperature and high voltage can be manufactured.

[0037] First, prior to describing the present invention, the terms and words used in this specification and claims are used merely to describe exemplary embodiments and should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, they should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0038] For example, in this specification, terms such as “comprising,” “having,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0039] Additionally, in this specification, “substitution” means that at least one hydrogen bonded to carbon is substituted with another element, such as fluorine, unless otherwise defined.

[0040] Additionally, in this specification, “%” means weight % unless otherwise explicitly indicated.

[0041]

[0042] The present invention will be described in detail below.

[0043] The electrolyte additive according to the present invention, the non-aqueous electrolyte for a secondary battery including the same, and the lithium secondary battery comprise at least one of the configurations disclosed below, and may comprise any combination of technically feasible configurations among the configurations below.

[0044]

[0045] Electrolyte additive

[0046] According to one embodiment of the present invention, the present invention provides an electrolyte additive comprising a compound represented by the following chemical formula 1.

[0047] [Chemical Formula 1]

[0048]

[0049] In the above chemical formula 1,

[0050] R is an alkylene group having 1 to 5 carbon atoms.

[0051]

[0052] The compound represented by Chemical Formula 1 above contains a 1,3,2-dioxaborole-4,5-dione structure within its structure, thereby forming a boron (B)-containing solid-electrolyte interface layer with excellent durability that does not decompose at high temperatures on the electrode surface through a ring-opening reaction of the compound in which the BO bond is broken during charging and discharging. As a result, side reactions between the electrolyte and the electrode can be prevented, transition metal leaching from the anode caused by the deterioration of the solid-electrolyte interface layer can be suppressed, and anode degradation can be suppressed by minimizing reversible lithium ion loss.

[0053] In addition, the compound represented by the above chemical formula 1 has a lithium sulfonate group (-SO3) in its structure- Li + It contains ) so that the solid-electrolyte interface layer formed on the electrode surface can function as an effective ion carrier, thereby improving the lithium ion diffusion within the solid-electrolyte interface layer and reducing the resistance in the solid-electrolyte interface layer. In addition, it can suppress the degradation of the cathode and prevent transition metal ions leached from the anode from being electrodeposited on the cathode during high-temperature storage.

[0054]

[0055] Meanwhile, in the above chemical formula 1, R may be an alkylene group having 1 to 3 carbon atoms.

[0056] Specifically, the compound represented by the above chemical formula 1 may be at least one selected from the group consisting of compounds represented by the following chemical formulas 1A to 1C.

[0057] [Chemical Formula 1A]

[0058]

[0059] [Chemical Formula 1B]

[0060]

[0061] [Chemical Formula 1C]

[0062] .

[0063]

[0064] Non-aqueous electrolyte for lithium secondary batteries

[0065] In addition, in one embodiment of the present invention, the non-aqueous electrolyte for a secondary battery of the present invention may include the aforementioned electrolyte additive. Specifically, the non-aqueous electrolyte may further include a lithium salt, an organic solvent, and an auxiliary additive.

[0066]

[0067] (1) Electrolyte additive

[0068] The non-aqueous electrolyte for a lithium secondary battery of the present invention may include an electrolyte additive comprising a compound represented by the above chemical formula 1, and since the description of the electrolyte additive overlaps with the above description, the description thereof is omitted.

[0069]

[0070] Meanwhile, considering the effect of forming a stable film on the electrode surface and the effect of removing thermal decomposition products of the lithium salt, the above electrolyte additive may be included in an amount of 0.05 wt% or more, 0.06 wt% or more, 0.07 wt% or more, 0.08 wt% or more, 0.09 wt% or more, 0.1 wt% or more, 0.2 wt% or more, or 0.3 wt% or more based on the total weight of the non-aqueous electrolyte. In addition, the above electrolyte additive may be included in an amount of 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less based on the total weight of the non-aqueous electrolyte.

[0071] The above ranges may be combined with one another without limitation. For example, the electrolyte additive may be included in an amount of 0.05 wt% to 9 wt%, 0.05 wt% to 8 wt%, 0.05 wt% to 7 wt%, 0.05 wt% to 6 wt%, 0.05 wt% to 5 wt%, or 0.1 wt% to 4 wt% based on the total weight of the non-aqueous electrolyte.

[0072] When the content range of the above electrolyte additive satisfies the above range, it is possible to effectively suppress the leaching of transition metals from the cathode active material at high temperatures by forming a robust film on the cathode surface while minimizing disadvantages such as side reactions caused by the additive, capacity reduction, and increased resistance, and to effectively remove thermal decomposition products of the lithium salt, thereby achieving excellent high-temperature durability. That is, if the content of the above electrolyte additive is 0.05 weight% or more, the effect of removing thermal decomposition products of the lithium salt can be maintained even if the operating time increases, and the effect of suppressing transition metal leaching can be further improved by forming a stable film on the electrode surface. In addition, if the content of the above electrolyte additive is 9 weight% or less, side reactions caused by the additive included in a somewhat large amount can be prevented.

[0073]

[0074] (2) Lithium salt

[0075] The above lithium salts can be those commonly used in non-aqueous electrolytes for lithium secondary batteries without limitation, for example, Li as a cation + It includes, and as anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N -, BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - At least one type selected from the group consisting of can be cited.

[0076] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 It may include a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), and LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI). In addition to these, lithium salts commonly used in the electrolytes of lithium secondary batteries may be used without limitation.

[0077] The above lithium salt can be appropriately modified within a range that is typically usable, but in order to obtain the effect of forming a corrosion-preventing film on the optimal electrode surface, it may be included in the electrolyte at a concentration of 0.8M to 4.0M, specifically at a concentration of 1.0M to 3.0M.

[0078] When the concentration of the above lithium salt is included within the above range, the viscosity of the non-aqueous electrolyte can be controlled to achieve optimal impregnation, and the mobility of lithium ions can be improved to obtain the effect of improving the capacity characteristics and cycle characteristics of the lithium secondary battery.

[0079]

[0080] (3) Non-aqueous organic solvents

[0081] In addition, the description of the above-mentioned non-aqueous organic solvent is as follows.

[0082] As the above-mentioned non-aqueous organic solvent, various organic solvents commonly used in non-aqueous electrolytes may be used without limitation; there are no restrictions on the type of solvent as long as it can minimize decomposition due to oxidation reactions, etc., during the charging and discharging process of the secondary battery and exhibit the desired characteristics in combination with additives.

[0083] Specifically, the above-mentioned non-aqueous organic solvent may include (i) a cyclic carbonate-based organic solvent, (ii) a linear carbonate-based organic solvent, or (iii) a mixture of these organic solvents.

[0084] The above (i) cyclic carbonate-based organic solvent is a high-viscosity organic solvent that has a high dielectric constant and effectively dissociates lithium salts in a non-aqueous electrolyte, and may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate as specific examples, and may include at least one of ethylene carbonate and propylene carbonate.

[0085] The above (ii) linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate as specific examples, and specifically may include one of dimethyl carbonate and ethyl methyl carbonate.

[0086] In order to secure a higher ion conductivity, the non-aqueous electrolyte for a lithium secondary battery of the present invention may use (iii) the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent in combination, in which case the cyclic carbonate-based organic solvent and the linear carbonate-based organic solvent may be mixed and used in a volume ratio of 10:90 to 50:50, specifically 20:80 to 40:60.

[0087] In addition, the non-aqueous electrolyte for a lithium secondary battery of the present invention may further include at least one organic solvent among (iv) a linear ester-based organic solvent and (v) a cyclic ester-based organic solvent, which has a lower melting point and higher stability at high temperatures compared to the cyclic carbonate-based organic solvent and / or the linear carbonate-based organic solvent.

[0088] The above (iv) linear ester-based organic solvent may include, as a representative example, at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, and specifically may include at least one of ethyl propionate and propyl propionate.

[0089] The above (v) cyclic ester-based organic solvent may include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0090] Meanwhile, among the non-aqueous electrolyte for a lithium secondary battery of the present invention, the remainder excluding the lithium salt, the electrolyte additive, and the auxiliary additive described below may all be organic solvents unless otherwise noted.

[0091]

[0092] (4) Auxiliary additives

[0093] In addition, the non-aqueous electrolyte for a lithium secondary battery according to the present invention may additionally include auxiliary additives within the electrolyte as needed to prevent the electrolyte from decomposing and causing cathode collapse in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, prevention of overcharging, and suppression of battery expansion at high temperatures. If auxiliary additives are additionally included in the non-aqueous electrolyte of the present invention, the aforementioned additive may be named the first additive, and the auxiliary additive may be named the second additive.

[0094] These auxiliary additives may include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds as representative examples.

[0095] Specifically, the above-mentioned cyclic carbonate compounds may include vinylene carbonate (VC) or vinylethylene carbonate.

[0096] Examples of the above halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0097] The above sulfone-based compound may include at least one compound selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethen sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone.

[0098] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0099] The above phosphate-based compounds may include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphate.

[0100] Examples of the above borate compounds include tetraphenylborate and lithium oxalyl difluoroborate.

[0101] The above nitrile-based compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0102] Examples of the above benzene-based compounds include fluorobenzene, and examples of the above amine-based compounds include triethanolamine or ethylenediamine.

[0103] Tetravinylsilane can be cited as the above silane compound.

[0104] The above lithium salt-based compound is a compound different from the lithium salt included in the electrolyte, and may include one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate toborate (LiB(C2O4)2)) and LiBF4.

[0105] Among these auxiliary additives, if vinylene carbonate, vinylethylene carbonate, or succinonitrile is included, a more robust SEI film can be formed on the negative electrode surface during the initial activation process of the secondary battery.

[0106]

[0107] Meanwhile, the above auxiliary additives may be used in a mixture of two or more types and may be included in an amount of 30% by weight or less, specifically 0.01 to 10.0% by weight, based on the total weight of the electrolyte, and preferably 0.05 to 5.0% by weight. If the content of the above auxiliary additive is less than 0.01% by weight, the effect of improving low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is negligible, and if the content of the above auxiliary additive exceeds 30% by weight, there is a possibility that excessive side reactions may occur within the electrolyte during charging and discharging of the battery. In particular, when the above SEI film-forming additives are added in excess, they may not decompose sufficiently at high temperatures and may remain as unreacted substances or precipitated within the electrolyte at room temperature. Accordingly, side reactions that degrade the lifespan or resistance characteristics of the secondary battery may occur.

[0108]

[0109] lithium secondary battery

[0110] In addition, another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the electrolyte comprises the non-aqueous electrolyte for a lithium secondary battery according to the present invention.

[0111] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a separator, and a negative electrode are sequentially stacked, housing this in a battery case, and then introducing the electrolyte of the present invention.

[0112] The method for manufacturing the lithium secondary battery of the present invention can be manufactured and applied according to conventional methods known in the art, as specifically described below.

[0113]

[0114] (1) positive electrode

[0115] The anode according to the present invention may include an anode active material.

[0116] The above positive active material may include at least one positive active material selected from the group consisting of lithium iron phosphate, lithium nickel-cobalt-manganese composite oxide, or a mixture thereof.

[0117] Meanwhile, the above lithium iron phosphate can be represented by the following chemical formula P-1.

[0118] [Chemical Formula P-1]

[0119] Li 1+e Fe 1-g M 2 g (PO 4-f )X f

[0120] In the above chemical formula P-1, M 2 is one or more elements selected from Co, Ni, Mn, Al, Mg, Ti and V, X is F, S, or N, and 0≤g≤0.5; -0.5≤e≤+0.5; 0≤f≤0.1.

[0121] Specifically, representative examples of compounds represented by the above chemical formula P-1 include LiFePO4(LFP) (g=0, e=0, and f=0) and LiMn 0.5 Fe 0.5 PO4 (g=0.5, e=0, and f=0) and LiMn 0.6 Fe 0.4It may include PO4 (g=0.4, e=0, and f=0).

[0122]

[0123] For the above-described olivine-structured lithium iron phosphate, primary particles of nanometer size may be used for high lithium ion input / output, or these primary particles may be assembled to form secondary particles that are aggregates thereof. For example, when primary particles are used as the above-described olivine-structured lithium iron phosphate, the particle size may be 50 nm to 2000 nm, more specifically 200 nm to 1100 nm. In addition, when these primary particles are assembled to form secondary particles that are aggregates thereof, the average particle size (D50) of the secondary particles may be 0.5 μm to 30 μm.

[0124] Meanwhile, the above-mentioned olivine-structured lithium iron phosphate may have an amorphous layer of carbon or metal oxide coated on its surface. In this case, since the amorphous layer of carbon or metal oxide coated on the surface is not crystalline, the insertion and extraction of lithium ions into and out of the olivine-structured lithium iron phosphate in the core portion occurs through the amorphous layer of the shell. The amorphous layer of carbon or metal oxide coated on the surface allows lithium ions to pass through while also possessing excellent electronic conductivity; thus, it can act as a current path to the olivine-structured lithium iron phosphate core, which is the active material, thereby enabling charging and discharging at a high rate. Furthermore, when the surface of the olivine-structured lithium iron phosphate is coated with the above-mentioned amorphous layer of carbon or metal oxide, safety can be further enhanced in that unnecessary reactions between the core material and the electrolyte can be controlled.

[0125] Meanwhile, the lithium iron phosphate with an olivine structure represented by the above chemical formula P-1 has structural stability against volume changes due to charging and discharging and high thermal stability because the PO4 tetrahedra form strong covalent bonds between phosphorus and oxygen. However, it has the disadvantage of low electrical conductivity and energy density because the oxygen structure is tightly bound in a hexagonal close-packed manner, which hinders the movement of lithium ions and the flow of electrons.

[0126] Accordingly, in the present invention, the electrical conductivity of the anode can be further improved by additionally including a lithium nickel-cobalt-manganese complex oxide represented by the following chemical formula P-2, which has significantly higher electrical conductivity, together with the lithium iron phosphate of the olivine structure.

[0127] [Chemical Formula P-2]

[0128] Li 1+a1 Ni x1 Co y1 M 1 z M 2 w O2

[0129] In the above chemical formula P-2,

[0130] M 1 is Mn, Al, or a combination thereof, and

[0131] M 2 is at least one selected from the group consisting of Al, Zr, W, Ti, Mg, Ca, and Sr, and 0≤a1≤0.5, 0.55 <x1<1.0, 0<y1≤0.4, 0<z≤0.4, 0≤w≤0.1 이다. 이때, x1+y1+z+w는 1일 수 있다.

[0132] In the above chemical formula P-2, 1+a1 represents the molar ratio of lithium in the lithium nickel-cobalt-manganese composite oxide, and may be 0≤a1≤0.5, preferably 0≤a1≤0.2, more preferably 0≤a1≤0.1.

[0133] In the above chemical formula P-2, x1 represents the molar ratio of nickel among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese composite oxide, 0.55 <x1<1.0, 더욱 구체적으로는 0.6≤x1≤0.98, 보다 더 구체적으로는 0.6≤x1≤0.95일 수 있다.

[0134] In the above chemical formula P-2, y1 represents the molar ratio of cobalt among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese composite oxide, where 0 <y1≤0.4, 구체적으로 0<y1≤0.3, 더욱 구체적으로는 0.05≤y1≤0.3일 수 있다.

[0135] In the above chemical formula P-2, z is M among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese complex oxide. 1 Representing the molar ratio of elements, 0 <z≤0.4, 바람직하게는 0<z≤0.3, 더 바람직하게는 0.01≤z≤0.3일 수 있다.

[0136] In the above chemical formula P-2, w is M among the total transition metals excluding lithium in the lithium nickel-cobalt-manganese complex oxide. 2 It represents the molar ratio of the elements, 0≤w≤0.1, preferably 0≤w≤0.05, more preferably 0≤w≤0.02.

[0137] In order to realize a high-capacity battery, the above-mentioned lithium nickel-cobalt-manganese composite oxide comprises Li(Ni) with a Ni content of 0.55 atm% or more. 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al0.05 )O2, Li(Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 )O2, Li(Ni 0.90 Mn 0.05 Co 0.05 )O2 or Li(Ni 0.9 Mn 0.03 Co 0.06 Al 0.01 It can be )O2).

[0138]

[0139] Meanwhile, the anode may include an anode current collector; and an anode active material layer disposed on at least one surface of the anode current collector.

[0140] At this time, the positive active material layer may include the aforementioned positive active material.

[0141] The thickness of the above positive current collector can typically be 3 to 500 μm.

[0142] The above positive current collector may form fine irregularities on its surface to strengthen the bonding force of the positive active material. For example, the above positive current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0143] The positive active material layer is disposed on at least one surface of the positive current collector. Specifically, the positive active material layer may be disposed on one or both surfaces of the positive current collector.

[0144] The above-mentioned positive active material may be included in the positive active material layer in an amount of 80 to 98 weight%, more specifically 85 to 98 weight%, considering the sufficient capacity exertion of the positive active material. When the positive active material is included in the above range, it can exhibit excellent capacity characteristics.

[0145] In addition, the positive active material layer may further include a binder and / or a conductive material together with the aforementioned positive active material.

[0146] The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector.

[0147] Examples of such binders include fluoropolymer binders comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders comprising styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose binders comprising carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyalcohol binders comprising polyvinyl alcohol; polyolefin binders comprising polyethylene or polypropylene; polyimide binders; polyester binders; and silane binders, either alone or as a mixture of two or more.

[0148] The above binder may be included in an amount of 0.1 to 15.0 weight%, preferably 0.1 to 10.0 weight%, based on the total weight of the positive active material layer.

[0149]

[0150] Next, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include carbon black such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, etc., and one of these alone or a mixture of two or more may be used.

[0151] The above conductive material may be included in an amount of 0.1 to 10.0 weight%, preferably 0.1 to 5.0 weight%, based on the total weight of the positive active material layer.

[0152] The thickness of the above positive active material layer may be 5㎛ to 500㎛, preferably 20㎛ to 200㎛.

[0153] The anode may be manufactured by coating an anode slurry comprising an anode active material and optionally a binder, a conductive material, and a solvent for forming an anode slurry onto the anode current collector, and then drying and rolling. Alternatively, the anode may be manufactured by mixing an anode active material and optionally a binder, a conductive material, etc. to produce a film, and then laminating it onto an anode current collector.

[0154] The solvent for forming the anode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, and isopropyl alcohol, preferably N-methylpyrrolidone, in order to facilitate the dispersion of the anode active material, binder, and / or conductive material. The amount of the solvent used is not particularly limited, provided that it is sufficient to allow the anode composite to have an appropriate viscosity, taking into account the coating thickness, manufacturing yield, workability, etc. of the anode composite.

[0155]

[0156] (2) Cathode

[0157] Next, the cathode is explained.

[0158] The cathode according to the present invention may include a cathode active material.

[0159] The above negative electrode active material may include a silicon-based negative electrode active material.

[0160] The above silicon-based negative electrode active material is, for example, metallic silicon (Si) or silicon oxide (SiO). x , here 0 <x<2) 및 실리콘 탄소 복합체(SiC)로 이루어진 군으로부터 선택된 1종 이상을 포함할 수 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택될 수 있으며, 바람직하게는 실리콘 산화물(SiO x , 0 <x<2) 또는 실리콘 탄소 복합체를 포함할 수 있다.

[0161] In addition, the above-mentioned negative electrode active material may include a carbon-based negative electrode active material along with a silicon-based negative electrode active material.

[0162] The above carbon-based cathode active material may be various carbon-based cathode active materials used in the industry, such as graphite-based materials like natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon, soft carbon, and hard carbon such as petroleum or coal tar pitch-derived cokes. The shape of the above carbon-based cathode active material is not particularly limited, and materials of various shapes such as amorphous, plate-like, flake-like, spherical, or fibrous can be used.

[0163] Preferably, the above-mentioned cathode active material may use at least one carbon-based cathode active material among natural graphite and artificial graphite, and natural graphite and artificial graphite may be used together to increase adhesion with the current collector and suppress the detachment of the active material.

[0164] Meanwhile, the weight ratio of the carbon-based negative electrode active material and the silicon-based negative electrode active material may be 1:99 to 99:1, specifically 70:30 to 99:1, specifically 80:20 to 98:2, and more specifically 85:15 to 97:3. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, excellent cycle performance can be secured by suppressing the volume expansion of the silicon-based negative electrode active material while improving capacity characteristics.

[0165]

[0166] Meanwhile, the above-mentioned cathode may include a cathode current collector; and a cathode active material layer disposed on at least one surface of the cathode current collector. In this case, the cathode active material may be included in the cathode active material layer.

[0167] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above-mentioned negative current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0168] The above-mentioned cathode current collector can typically have a thickness of 3 to 500 μm.

[0169] The above-mentioned negative current collector may form fine irregularities on its surface to strengthen the bonding force of the negative active material. For example, the above-mentioned negative current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0170] The above-mentioned negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0171] The above negative electrode active material may be included in the negative electrode active material layer in an amount of 60% to 99% by weight in order to sufficiently express capacity in the secondary battery while minimizing the effect of volume expansion / contraction on the battery.

[0172] The above cathode active material layer may further include a conductive material and / or a binder together with the cathode active material.

[0173] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, specifically 0.1% to 5% by weight, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, carbon black such as carbon black, acetylene black (or Denka black), Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, etc. may be used.

[0174] The above binder is a component that assists in the bonding between a conductive material, an active material, and a current collector, and specific examples include a fluoropolymer-based binder comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber-based binder comprising styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; a cellulose-based binder comprising carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyalcohol-based binder comprising polyvinyl alcohol; a polyolefin-based binder comprising polyethylene or polypropylene; a polyimide-based binder; a polyester-based binder; and a silane-based binder.

[0175] The above binder may be included in an amount of 0.1 to 15.0 weight%, preferably 0.1 to 10.0 weight%, based on the total weight of the negative electrode active material layer.

[0176]

[0177] The thickness of the above negative electrode active material layer may be 5㎛ to 500㎛, preferably 5㎛ to 100㎛.

[0178] The above cathode may be manufactured by coating a cathode slurry comprising a cathode active material and optionally a binder, a conductive material, and a solvent for forming a cathode slurry onto the cathode current collector, and then drying and rolling. Alternatively, the cathode may be manufactured by mixing a cathode active material and optionally a binder, a conductive material, etc. to produce a film, and then laminating it onto a cathode current collector.

[0179] The solvent for forming the above cathode slurry may include, for example, at least one selected from the group consisting of distilled water, N-methylpyrrolidone, ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the cathode active material, binder, and / or conductive material.

[0180]

[0181] (3) Separator

[0182] The lithium secondary battery according to the present invention further includes a separator.

[0183] The above separator separates the negative and positive electrodes and provides a pathway for the movement of lithium ions. It can be used without any specific restrictions as long as it is a separator typically used in lithium secondary batteries, and it is particularly desirable that it has low resistance to the movement of lithium salt ions while having excellent electrolyte moisture retention capacity.

[0184] Specifically, as a separator, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0185]

[0186] The lithium secondary battery according to the present invention as described above can be usefully applied in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0187] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0188] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0189]

[0190] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0191]

[0192] Examples

[0193] Example 1.

[0194] (Manufacture of electrolytes for lithium secondary batteries)

[0195] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 1A and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 1A and vinylene carbonate (VC) were included in the non-aqueous electrolyte at concentrations of 0.2 wt% and 0.5 wt%, respectively (see Table 1 below).

[0196]

[0197] (Secondary battery manufacturing)

[0198] An anode slurry (solid content 60.0 wt%) was prepared by adding an anode active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride) to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.6:0.8:1.6. The anode slurry was coated onto an anode current collector (Al thin film) with a thickness of 13.5 μm and dried, and then a roll press was performed to produce an anode.

[0199] A cathode slurry (solid content: 60 wt%) was prepared by adding a cathode active material (synthetic graphite), a binder (SBR-CMC), and a conductive material (carbon black) to water, a solvent, in a weight ratio of 97.6:0.8:1.6. The cathode slurry was applied to a 6 μm thick copper (Cu) thin film serving as a cathode current collector, dried, and then subjected to a roll press to manufacture the cathode.

[0200] An electrode assembly was manufactured by interposing a porous polypropylene separator between the anode and cathode manufactured above, then housing it in a battery case, and a lithium secondary battery was manufactured by injecting the electrolyte for the lithium secondary battery manufactured above.

[0201]

[0202] Example 2.

[0203] (Manufacture of electrolytes for lithium secondary batteries)

[0204] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 1B and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 1B and vinylene carbonate (VC) were included in the non-aqueous electrolyte at concentrations of 0.2 wt% and 0.5 wt%, respectively (see Table 1 below).

[0205]

[0206] (Secondary battery manufacturing)

[0207] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte for the lithium secondary battery manufactured above was injected.

[0208]

[0209] Example 3.

[0210] (Manufacture of electrolytes for lithium secondary batteries)

[0211] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Formula 1C and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Formula 1C and vinylene carbonate (VC) were included in the non-aqueous electrolyte at concentrations of 0.2 wt% and 0.5 wt%, respectively (see Table 1 below).

[0212]

[0213] (Secondary battery manufacturing)

[0214] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte for the lithium secondary battery manufactured above was injected.

[0215]

[0216] Example 4.

[0217] (Manufacture of electrolytes for lithium secondary batteries)

[0218] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 1A and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 1A and vinylene carbonate (VC) were included in the non-aqueous electrolyte at 0.5 wt% and 0.5 wt%, respectively (see Table 1 below).

[0219]

[0220] (Secondary battery manufacturing)

[0221] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte for the lithium secondary battery manufactured above was injected.

[0222]

[0223] Example 5.

[0224] (Manufacture of electrolytes for lithium secondary batteries)

[0225] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 1A and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 1A and vinylene carbonate (VC) were included in the non-aqueous electrolyte at 1 wt% and 0.5 wt%, respectively (see Table 1 below).

[0226]

[0227] (Secondary battery manufacturing)

[0228] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte for the lithium secondary battery manufactured above was injected.

[0229]

[0230] Example 6.

[0231] (Manufacture of electrolytes for lithium secondary batteries)

[0232] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 1A and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 1A and vinylene carbonate (VC) were included in the non-aqueous electrolyte at 5 wt% and 0.5 wt%, respectively (see Table 1 below).

[0233]

[0234] (Secondary battery manufacturing)

[0235] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte for the lithium secondary battery manufactured above was injected.

[0236]

[0237] Example 7.

[0238] (Manufacture of electrolytes for lithium secondary batteries)

[0239] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 1A and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 1A and vinylene carbonate (VC) were included in the non-aqueous electrolyte at 8 wt% and 0.5 wt%, respectively (see Table 1 below).

[0240]

[0241] (Secondary battery manufacturing)

[0242] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte for the lithium secondary battery manufactured above was injected.

[0243]

[0244] Example 8.

[0245] (Secondary battery manufacturing)

[0246] Anode active material (Li(Ni) in solvent N-methyl-2-pyrrolidone (NMP) 0.8 Mn 0.1 Co 0.1 An anode slurry (solid content 60.0 wt%) was prepared by adding O2), a conductive material (carbon black), and a binder (polyvinylidene fluoride) in a weight ratio of 97.6:0.8:1.6. The anode slurry was applied to an anode current collector (Al thin film) with a thickness of 13.5 μm and dried, then a roll press was performed to produce an anode.

[0247] A cathode slurry (solid content: 60 wt%) was prepared by adding a cathode active material (synthetic graphite), a binder (SBR-CMC), and a conductive material (carbon black) to water, a solvent, in a weight ratio of 97.6:0.8:1.6. The cathode slurry was applied to a 6 μm thick copper (Cu) thin film serving as a cathode current collector, dried, and then subjected to a roll press to manufacture the cathode.

[0248] An electrode assembly was manufactured by interposing a porous separator polypropylene between the anode and cathode manufactured above, then placed in a battery case, and a lithium secondary battery was manufactured by injecting the electrolyte for a lithium secondary battery manufactured in Example 1.

[0249]

[0250] Comparative Example 1.

[0251] (Manufacture of electrolytes for lithium secondary batteries)

[0252] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 in a non-aqueous organic solvent to a concentration of 1.0 M, and then adding vinylene carbonate (VC) as an additive to a concentration of 0.5 wt% (see Table 1 below).

[0253]

[0254] (Secondary battery manufacturing)

[0255] An anode slurry (solid content 60.0 wt%) was prepared by adding an anode active material (LiFePO4), a conductive material (carbon black), and a binder (polyvinylidene fluoride) to the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.6:0.8:1.6. The anode slurry was coated onto an anode current collector (Al thin film) with a thickness of 13.5 μm and dried, and then a roll press was performed to produce an anode.

[0256] A cathode slurry (solid content: 60 wt%) was prepared by adding a cathode active material (synthetic graphite), a binder (SBR-CMC), and a conductive material (carbon black) to water, a solvent, in a weight ratio of 97.6:0.8:1.6. The cathode slurry was applied to a 6 μm thick copper (Cu) thin film serving as a cathode current collector, dried, and then subjected to a roll press to manufacture the cathode.

[0257] An electrode assembly was manufactured by interposing a porous polypropylene separator between the anode and cathode manufactured above, then housing it in a battery case, and a lithium secondary battery was manufactured by injecting the electrolyte for the lithium secondary battery manufactured above.

[0258]

[0259] Comparative Example 2.

[0260] (Manufacture of electrolytes for lithium secondary batteries)

[0261] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 2 and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 2 and vinylene carbonate (VC) were included in the non-aqueous electrolyte at concentrations of 0.2 wt% and 0.5 wt%, respectively (see Table 1 below).

[0262] [Chemical Formula 2]

[0263]

[0264]

[0265] (Secondary battery manufacturing)

[0266] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the fact that the electrolyte for the lithium secondary battery manufactured above was injected.

[0267]

[0268] Comparative Example 3.

[0269] (Manufacture of electrolytes for lithium secondary batteries)

[0270] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 3 and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 3 and vinylene carbonate (VC) were included in the non-aqueous electrolyte at concentrations of 0.2 wt% and 0.5 wt%, respectively (see Table 1 below).

[0271] [Chemical Formula 3]

[0272]

[0273]

[0274] (Secondary battery manufacturing)

[0275] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the fact that the electrolyte for the lithium secondary battery manufactured above was injected.

[0276]

[0277] Comparative Example 4.

[0278] (Manufacture of electrolytes for lithium secondary batteries)

[0279] A non-aqueous electrolyte for a lithium secondary battery was prepared by dissolving LiPF6 to a concentration of 1.0 M in a non-aqueous organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:70:10, and then adding a compound represented by Chemical Formula 4 and vinylene carbonate (VC) as electrolyte additives. At this time, the compound represented by Chemical Formula 4 and vinylene carbonate (VC) were included in the non-aqueous electrolyte at concentrations of 0.2 wt% and 0.5 wt%, respectively (see Table 1 below).

[0280] [Chemical Formula 4]

[0281]

[0282]

[0283] (Secondary battery manufacturing)

[0284] A lithium secondary battery was manufactured in the same manner as Comparative Example 1, except for the fact that the electrolyte for the lithium secondary battery manufactured above was injected.

[0285]

[0286] Non-aqueous Organic Solvent Lithium Salt Additive Auxiliary Additive (Weight%) Type Content (Weight%) Example 1 EC:EMC=30:70 Volume Ratio 1.0M LiPF6 Chemical Formula 1A 0.2VC (0.5) Example 2 Chemical Formula 1B 0.2 Example 3 Chemical Formula 1C 0.2 Example 4 Chemical Formula 1A 0.5 Example 5 Chemical Formula 1A 1.0 Example 6 Chemical Formula 1A 5.0 Example 7 Chemical Formula 1A 8.0 Example 8 Chemical Formula 1A 0.2 Comparative Example 1 -- Comparative Example 2 Chemical Formula 20.2 Comparative Example 3 Chemical Formula 30.2 Comparative Example 4 Chemical Formula 40.2

[0287] Meanwhile, in Table 1 above, the abbreviations of the compounds refer to the following: EC: Ethylene carbonate

[0288] EMC: Ethylmethyl carbonate

[0289] VC: Vinylene carbonate

[0290]

[0291] Experimental Example

[0292] Experimental Example 1. Evaluation of High-Temperature Storage Characteristics

[0293] For the lithium secondary batteries prepared in the examples and comparative examples, respectively, a formation process was performed by charging at a rate of 0.1C for 3 hours, and then the batteries were fully charged to 100% SOC by charging under constant current / constant voltage conditions (0.05C cut-off) at a rate of 0.33C at 25℃ up to 4.2V, and stored at a high temperature (60℃) for 16 weeks. Afterward, the batteries were transferred to a charge / discharger at room temperature (25℃) to measure the resistance, and the resistance increase rate was calculated using Equation 1 below, and the results are shown in Table 2 below.

[0294] [Equation 1]

[0295] Resistance increase rate (%) = {(Resistance after high-temperature storage - Initial resistance) / Initial resistance} × 100

[0296]

[0297] Experimental Example 2. Evaluation of High-Temperature Cycle Characteristics

[0298] For the lithium secondary batteries prepared in the examples and comparative examples, a formation process was performed by charging at a rate of 0.1C for 3 hours, and then the batteries were fully charged to 100% SOC by charging at 25°C at a rate of 0.33C under constant current / constant voltage conditions to 4.2V (0.05C cut-off). The fully charged batteries were charged at 45°C at a rate of 0.33C under constant current / constant voltage conditions to 4.2V, and discharged at a rate of 0.33C under constant current conditions to 2.8V; this constituted one cycle, and 300 th After performing the cycle, use Equation 2 below to 300 th The capacity retention rate after the cycle was calculated, and the results are shown in Table 2 below.

[0299] [Equation 2]

[0300] Capacity retention rate (%) = (300 th Capacity after cycle / Capacity after 1 cycle) × 100

[0301]

[0302] Resistance increase rate after high-temperature storage (%) Capacity retention rate after high-temperature cycling (%) Example 1 4.69 5.8 Example 2 11.98 8.2 Example 3 18.88 2.4 Example 4 5.99 2.3 Example 5 16.78 4.7 Example 6 22.48 0.4 Example 7 28.97 4.6 Example 8 12.18 9.2 Comparative Example 1 35.86 5.4 Comparative Example 2 32.47 0.8 Comparative Example 3 30.26 8.9 Comparative Example 4 42.76 9.4

[0303] Looking at Table 2 above, it can be seen that in the case of the secondary batteries of Examples 1 to 8 of the present invention, the resistance increase rate (%) after high-temperature storage and the capacity retention rate (%) after high-temperature cycling are both improved compared to the lithium secondary batteries of Comparative Examples 1 to 4.

[0304] Meanwhile, in the case of the lithium secondary battery of Example 8, which uses a lithium nickel-cobalt-manganese composite oxide containing a high content of Ni without including lithium phosphate as the positive electrode active material, the radical oxidation reaction is active when operating at high voltage, and as a result, the overpolymerization reaction of the additive occurs, causing a somewhat excessive film formation effect on the electrode surface. Consequently, compared to the lithium secondary battery of Example 1, which includes lithium phosphate as the positive electrode active material, it can be seen that the resistance increase rate (%) after high-temperature storage and the capacity retention rate (%) after high-temperature cycling are somewhat lower.

Claims

1. Electrolyte additive comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R is an alkylene group having 1 to 5 carbon atoms.

2. In Paragraph 1, In the above chemical formula 1, R is an electrolyte additive having 1 to 3 carbon atoms and is an alkylene group.

3. In Paragraph 1, The electrolyte additive represented by the above chemical formula 1 is at least one selected from the group consisting of compounds represented by the following chemical formulas 1A to 1C: [Chemical Formula 1A] [Chemical Formula 1B] [Chemical Formula 1C] .

4. A non-aqueous electrolyte for a secondary battery comprising the electrolyte additive of Claim 1.

5. In Paragraph 4, The above electrolyte additive is included in an amount of 0.05% to 9% by weight based on the total weight of the above non-aqueous electrolyte for a secondary battery.

6. In Paragraph 4, The above electrolyte additive is included in an amount of 0.05% to 5% by weight based on the total weight of the above non-aqueous electrolyte for a secondary battery.

7. In Paragraph 4, The above-mentioned non-aqueous electrolyte for a secondary battery is a non-aqueous electrolyte for a secondary battery that further comprises a lithium salt and an organic solvent.

8. In Paragraph 4, The above-mentioned non-aqueous electrolyte for a secondary battery further comprises at least one auxiliary additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

9. Anode; A cathode facing the anode above; A separator interposed between the above cathode and the above anode; and A lithium secondary battery comprising a non-aqueous electrolyte for a secondary battery according to claim 4.

10. In Paragraph 9, The above-mentioned positive electrode includes a positive electrode active material, and The above positive active material is a lithium secondary battery containing lithium iron phosphate.

11. In Paragraph 10, The above positive active material is a lithium secondary battery further comprising a lithium nickel-cobalt-manganese composite oxide.

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