Lithium secondary battery having improved safety

Abstract

The present invention relates to a lithium secondary battery. The lithium secondary battery includes, in a positive electrode, an NCM-based positive electrode active material having a high nickel (Ni) content, and thus has excellent energy density, and has the benefit of ameliorating safety issues caused by positive electrode active material at high temperatures, by adjusting the heat flow rate between the positive electrode active material and an electrolyte composition to be low, within a predetermined range.

Description

Lithium secondary batteries with improved safety

[0001] The present invention relates to a lithium secondary battery having excellent energy density and improved high-temperature safety.

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2023-0080465, filed June 22, 2023, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Recently, secondary batteries are widely used not only in small devices such as portable electronic devices, but also in medium and large devices such as battery packs for hybrid or electric vehicles or power storage devices.

[0005] These secondary batteries are manufactured by applying and drying a composition containing an electrode active material to a current collector in an appropriate thickness and length, or by forming the electrode active material itself into a film shape to produce a positive electrode and a negative electrode, winding or laminating them together with an insulator, a separator, in between to produce an electrode assembly, and then placing the electrode assembly in a can or similar container and injecting an electrolyte.

[0006] In order to apply these secondary batteries to medium and large devices, high energy density is required, so LiNi with a nickel (Ni) content of 60% or more is used. a Co b Mn c High capacity is achieved by using lithium nickel metal oxide with a layered structure such as O2 (0.6<a≤0.9, a+b+c=1, hereinafter referred to as 'NCM compound') as a cathode active material.

[0007]

[0008] [Prior Art Literature]

[0009] [Patent Document]

[0010] Republic of Korea Patent Publication No. 10-2018-0116564

[0011] Republic of Korea Patent Publication No. 10-2144056

[0012]

[0013] The purpose of the present invention is to provide a lithium secondary battery having excellent energy density by including an NCM-based cathode active material having a high nickel (Ni) content in the cathode, and also having improved safety by suppressing structural collapse of the NCM-based active material at high temperatures or improving gas generation due to structural collapse.

[0014]

[0015] To solve the above-mentioned problem,

[0016] In one embodiment of the present invention,

[0017] An electrode assembly comprising an anode, a cathode, and a separator disposed between the anode and the cathode, and

[0018] The electrode assembly comprises an electrolyte composition impregnated therein;

[0019] The above positive electrode is provided on at least one side of the positive electrode current collector and has a positive electrode active layer including a lithium metal oxide represented by the following chemical formula 1 as a positive electrode active material;

[0020] The above electrolyte composition comprises a lithium salt and a non-aqueous organic solvent containing at least 60 wt% of a cyclic ester solvent represented by the following chemical formula 2 based on the total weight;

[0021] A lithium secondary battery is provided, which exhibits a heat flux of 6.0 W / g or less within a range of 200 to 300°C when measuring a heat flux for a mixture containing a positive electrode active material and an electrolyte composition at a weight ratio of 1:1 with a 100% state of charge:

[0022] [Chemical Formula 1]

[0023] Li x [Ni y Co z Mn w M 1 v ]O2

[0024] [Chemical Formula 2]

[0025]

[0026] In the above chemical formulas 1 and 2,

[0027] M 1 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0028] x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이며,

[0029] is a single bond or double bond,

[0030] X is hydrogen, fluoro, or vinyl,

[0031] p is an integer from 1 to 5.

[0032]

[0033] At this time, the positive electrode active material is LiNi 0.95 Co 0.03 Mn 0.02 O2, LiNi 0.9 Co 0.6 Mn 0.4 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.85 Co 0.1 Mn 0.05 O2, LiNi 0.85 Co 0.05 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.75 Co 0.2 Mn 0.15 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.7Co 0.15 Mn 0.15 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may contain one or more types of O2.

[0034] In addition, the cyclic ester solvent represented by the above chemical formula 2 may include at least one of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, tetrahydropyranone, methyldihydrofuranone, propyltetrahydropyranone, and oxepanone.

[0035] In addition, the lithium salt has Li as a cation. + , and contains BF4 as anion. - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , B(C2O4)2 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - ,CF3SO3- , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - and ((C(CN))2NC(CF3))N - It may include one or more of the following:

[0036] As an example, the lithium salt has Li as the cation. + , and contains BF2C2O4 as anion. - , B(C2O4)2 - , (CF3SO2)2N - , (FSO2)2N - , (CF3CF2SO2)2N - or ((C(CN))2NC(CF3))N - may include.

[0037] As another example, the lithium salt has Li as the cation. + , and contains BF4 as anion. - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 -, (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - ,CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - and SCN - It may include two or more types.

[0038] In addition, the non-aqueous organic solvent may further include one or more auxiliary solvents selected from the group consisting of a fluorine-containing ether solvent, a fluorine-containing cyclic carbonate solvent, a linear carbonate solvent, a phosphate solvent, and a sulfone solvent, together with an ester solvent.

[0039] In addition, the electrolyte composition may further include an electrolyte additive represented by the following chemical formula 3:

[0040] [Chemical Formula 3]

[0041]

[0042] In the above chemical formula 3,

[0043] R1 is , or And,

[0044] R1' and R1" are each hydrogen or methyl group,

[0045] R2 is an arylene group having 6 to 20 carbon atoms; an aryleneoxy group having 6 to 20 carbon atoms; a heteroarylene group having 5 to 10 carbon atoms containing at least one heteroatom selected from N, S and O; a heteroaryleneoxy group having 5 to 10 carbon atoms containing at least one heteroatom selected from N, S and O; an alkyl group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a cycloalkyl group having 5 to 10 carbon atoms; and Contains at least one of the following:

[0046] R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or However,

[0047] The above alkyl group, alkoxy group, cycloalkyl group, and One or more of the hydrogens contained in may be replaced by a fluorine atom,

[0048] M includes at least one selected from the group consisting of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms,

[0049] l is an integer from 1 to 6,

[0050] m and n are integers from 2 to 20, respectively.

[0051]

[0052] Specifically, the electrolyte additive represented by the above chemical formula 3 may include one or more compounds of the following <structural formula 1> to <structural formula 17>:

[0053]

[0054]

[0055]

[0056]

[0057] At this time, the electrolyte additive may be included in an amount of 5 wt% or less based on the total weight of the electrolyte composition.

[0058] Meanwhile, the negative electrode is provided on at least one side of the negative electrode collector and has a negative electrode active layer including a carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0059] The above carbon-based negative electrode active material may include at least one of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, acetylene black, and Ketjen black as a carbon material.

[0060] In addition, the above silicon-based negative electrode active material is a silicon material such as silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q , but may include one or more of the following (0.8≤q≤2.5).

[0061] Here, the silicon-based negative electrode active material may be included in an amount of 0.1 to 30 wt% based on the total weight of the negative electrode active material.

[0062]

[0063] Furthermore, in one embodiment of the present invention,

[0064] A method for manufacturing a lithium secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte composition in which the electrode assembly is impregnated.

[0065] The above positive electrode is provided on at least one surface of the positive electrode current collector and has a positive electrode active layer including a lithium metal oxide represented by the following chemical formula 1 as a positive electrode active material;

[0066] The above electrolyte composition comprises a lithium salt and a non-aqueous organic solvent, and the non-aqueous organic solvent comprises a cyclic ester solvent represented by the following chemical formula 2 in an amount of 60 wt% or more based on the total weight;

[0067] A method for manufacturing a lithium secondary battery is provided, wherein the heat flux of a mixture containing a positive electrode active material and an electrolyte composition at a weight ratio of 1:1 with a 100% state of charge is measured, and the heat flux is 6.0 W / g or less within a range of 200°C to 300°C.

[0068] [Chemical Formula 1]

[0069] Li x [Ni y Co z Mn w M 1 v ]O2

[0070] [Chemical Formula 2]

[0071]

[0072] In the above chemical formulas 1 and 2,

[0073] M 1 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0074] x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이며,

[0075] is a single bond or double bond,

[0076] X is hydrogen, fluoro, or vinyl,

[0077] p is an integer from 1 to 5.

[0078]

[0079] The lithium secondary battery according to the present invention has an excellent energy density by including an NCM type cathode active material having a high nickel (Ni) content in the cathode, and has an excellent effect of improving safety issues caused by the cathode active material at high temperatures by controlling the heat flow between the cathode active material and the electrolyte composition to a low level within a predetermined range at high temperatures.

[0080]

[0081] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0082] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

[0083] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0084] Additionally, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "directly above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "directly below" the other part, but also cases where there is another part in between. Furthermore, in the present application, "on" may include cases where it is placed below as well as above.

[0085] In addition, in the present invention, "comprising as a main component" may mean comprising a defined component at 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of the total weight (or total volume). For example, "comprising a carbon-based negative electrode active material as a main component" may mean comprising a carbon-based negative electrode active material at 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more of the total weight of the negative electrode active material, and in some cases, it may mean that the entire negative electrode active material is composed of a carbon-based negative electrode active material and comprises 100 wt%.

[0086] Lithium secondary batteries are used as power sources for various electronic devices, including electric vehicles, due to their high energy density and superior output performance. To power these diverse electronic devices, they require high-temperature electrochemical properties. Furthermore, lithium secondary battery electrodes undergo an exothermic reaction with the electrolyte when exposed to high temperatures, making thermal stability crucial.

[0087] NCM compounds are considered the most promising candidates to replace cathode active materials such as LiCoO2 due to their overall superior properties, including high capacity, high-rate characteristics, and excellent stability, as well as their low cost, which makes them suitable for small- to medium- to large-sized batteries. However, NCM compounds have low ionic conductivity, low cycle performance and tap density, and a complex manufacturing process. Furthermore, increasing the nickel (Ni) ratio to achieve high capacity leads to reduced rate capability and reduced capacity during charge and discharge.

[0088] The two main causes of the decrease in electrochemical properties due to the increase in nickel (Ni) content are side reactions and structural degradation. Among these, the side reaction is when lithium salts present on the particle surface of NCM compounds used as cathode active materials react with the electrolyte of the battery to form an insulator on the surface of the NCM compounds, or Ni 4+ This refers to a reaction in which ions accelerate the decomposition of electrolytes, forming a thick solid-state electrolyte interface (SEI). In addition, structural collapse occurs in Ni 2+ Wow Li + This refers to a structural change (or collapse) of the layered structure due to the loss of oxygen caused by the site exchange reaction (cation mixing) and the escape of oxygen radicals from the lattice. The above structural collapse has a limitation in that it hinders the movement of Li ions during charge and discharge, thereby reducing the electrochemical characteristics. In particular, when the structure of the NCM-based active material collapses at high temperatures, the electrolyte decomposition occurs at the collapsed site, and the oxidized carbon (CO or CO2) during the decomposition process of the electrolyte generates water molecules in the process of combining with LiOH, etc. The water molecules generated in this way react with HF or LiF to rapidly generate a large amount of gas inside the battery, which can cause an explosion of the battery, thus reducing the safety of the battery.

[0089] To address these issues, a technology has been developed to coat the surface of conventional NCM-based compounds. However, this surface coating requires an additional calcination process after the NCM-based active material is manufactured, which increases manufacturing costs and makes it difficult to obtain a uniform coating layer. Furthermore, it is difficult to effectively suppress structural collapse.

[0090] Therefore, there is a need for the development of a technology that can improve the safety of secondary batteries by applying NCM-based active materials with a high nickel (Ni) content, thereby improving the energy density of secondary batteries and suppressing structural collapse of NCM-based active materials at high temperatures.

[0091] The lithium secondary battery according to the present invention has excellent energy density by including an NCM type cathode active material having a high nickel (Ni) content in the cathode, and has the characteristic of improving safety issues caused by the cathode active material at high temperatures by appropriately controlling the electrolyte material to lower the heat flow between the cathode active material and the electrolyte composition to a predetermined range at high temperatures.

[0092] Hereinafter, the present invention will be described in more detail.

[0093]

[0094] lithium secondary battery

[0095] In one embodiment of the present invention,

[0096] An electrode assembly comprising an anode, a cathode, and a separator disposed between the anode and the cathode, and an electrolyte composition in which the electrode assembly is impregnated;

[0097] The above positive electrode is provided on at least one side of the positive electrode current collector and has a positive electrode active layer including a lithium metal oxide represented by the following chemical formula 1 as a positive electrode active material;

[0098] A lithium secondary battery is provided that exhibits a heat flow of 6.0 W / g or less within a range of 200 to 300°C when measuring heat flow for a mixture containing a positive electrode active material and an electrolyte composition at a weight ratio of 1:1 with a 100% state of charge:

[0099] [Chemical Formula 1]

[0100] Li x [Ni y Co z Mn w M 1 v ]O2

[0101] In the above chemical formula 1,

[0102] M 1 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0103] x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이다.

[0104]

[0105] A lithium secondary battery according to the present invention comprises an electrode assembly having a structure in which a separator is disposed between a plurality of positive electrodes and a plurality of negative electrodes alternately stacked; and an electrolyte composition in which the electrode assembly is impregnated.

[0106] Here, the positive electrode included in the electrode assembly has a positive electrode active layer on at least one surface of the positive electrode current collector, and the positive electrode active layer is a material capable of implementing electrical activity by causing an electrochemical reaction on the positive electrode current collector, and includes a lithium metal oxide represented by the chemical formula 1 as a main component, which is capable of reversibly intercalating and deintercalating lithium ions.

[0107] The lithium metal oxide represented by the above chemical formula 1 is an oxide mixed with lithium (Li) and transition metals nickel (Ni), cobalt (Co), and manganese (Mn), and is characterized in that the content of nickel (Ni) is 60% or more (i.e., 60 mol%) of the total mole fraction of transition metals.

[0108] The ternary NCM cathode active material, which is mainly composed of nickel (Ni), cobalt (Co), and manganese (Mn), has the advantages of high capacity of LiNiO2 (LNO), excellent electrochemical performance of LiCoO2 (LCO), and stability of LiMn2O4 (LMO). However, despite these advantages, as the nickel (Ni) content increases, Li becomes unavailable during the synthesis process and / or charge / discharge process in a high-temperature environment. + Ni, which is similar in size to (0.76 Å) 2+ (0.69 Å) cation mixing occurs, which is a phenomenon in which lithium layers of a layered structure are occupied. Ni mixed in this way 2+ The rock-salt structure of Ni-O, which does not locally undergo electrochemical reaction, is formed, which hinders the movement of lithium ions and thus adversely affects electrochemical performance such as high-rate characteristics and discharge capacity. In addition, due to this structural instability, when charging and discharging a secondary battery under high-temperature conditions, water molecules are generated along with the decomposition of the electrolyte, which rapidly generates a large amount of gas inside the battery, thus limiting the high-temperature safety of the secondary battery.

[0109] However, the present invention can solve this problem by including a nickel metal oxide represented by chemical formula 1, in which the content of nickel (Ni) as a cathode active material is 60% or more (i.e., 60 mol%) with respect to the total molar fraction of transition metal, and lowering the heat flow between the cathode active material and the electrolyte composition at high temperature to satisfy a predetermined range.

[0110] "Heat flow rate" refers to the amount of heat flowing per unit weight, and can particularly indicate the degree of heat generation of a secondary battery. The electrolyte composition according to the present invention can have high thermal stability by showing a difference in the reaction between the positive electrode active material and the electrolyte composition under high temperature conditions compared to the conventional electrolyte composition as a result of thermal analysis simulating a deterioration phenomenon in which a secondary battery spontaneously generates heat due to high temperature exposure or external mechanical factors and the performance of the secondary battery deteriorates. Specifically, the heat flow measured according to the thermal analysis results indicates the degree of heat (e.g., heat amount) generated by the high temperature reaction between the electrolyte composition and the charged positive electrode active material when simulating the high temperature deterioration phenomenon of a secondary battery.

[0111] The above heat flux can increase or decrease depending on the type or content ratio of each component constituting the electrolyte composition, and can increase or decrease depending on whether an inorganic positive electrode film containing lithium ions is formed on the surface of the positive electrode active layer. A decrease in this heat flux means that the amount of heat generated between the positive electrode active material and the electrolyte composition is reduced. Accordingly, under high temperature conditions, the positive electrode active material included in the secondary battery is i) Ni 2+ Wow Li + The structural change (or collapse) of the layered structure due to ii) oxygen loss caused by the exchange reaction (cation mixing) and iii) oxygen radicals, etc. leaving the lattice may be delayed.

[0112] At this time, the heat flux between the cathode active material and the electrolyte composition according to the present invention may be 6.0 W / g or less within the range of 200°C to 300°C. More specifically, the heat flux may have an upper limit of 5.5 W / g or less; 5.0 W / g or less; 4.0 W / g or less; or 3.0 W / g or less, and a lower limit of more than 0 W / g; 0.5 W / g or more; 0.8 W / g or more; 1.0 W / g or more; or 2.0 W / g or more. As an example, the heat flux between the cathode active material and the electrolyte composition may be 0.5 W / g to 6.0 W / g; 0.5 W / g to 5 W / g; 0.5 W / g to 4.5 W / g; 0.5 W / g to 4.0 W / g within the range of 200°C to 300°C. Or it may be 0.5 W / g to 3.5 W / g. Here, the heat flow may be performed under predetermined conditions. Each material has its own thermal conductivity constant, and the cathode active material and the electrolyte composition may also have different thermal conductivity constants. Due to this difference, the amount of heat transferred between the cathode active material and the electrolyte composition may vary depending on the temperature conditions to which they are exposed. That is, the heat flow between the cathode active material and the electrolyte composition may have different values ​​depending on the temperature conditions to which they are exposed. Therefore, the heat flow according to the present invention can be measured under predetermined measurement conditions, specifically, a heating rate.

[0113] As an example, the heat flow between the positive electrode active material and the electrolyte composition can be measured using a differential scanning calorimeter (DSC) at a temperature increase condition of 10±1°C / min in the range of 100°C to 400°C after mixing the positive electrode active material and the electrolyte composition charged to 100% of SOC at 4.25 V in a 1:1 weight ratio.

[0114] In addition, the above cathode active material can be applied without any particular limitation as long as it is a lithium metal oxide represented by chemical formula 1, but specifically, LiNi 0.95 Co 0.03 Mn 0.02 O2, LiNi0.9 Co 0.6 Mn 0.4 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.85 Co 0.1 Mn 0.05 O2, LiNi 0.85 Co 0.05 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.75 Co 0.2 Mn 0.15 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may include one or more selected from the group consisting of O2.

[0115] In addition, the electrolyte composition is a liquid electrolyte, and includes a lithium salt and a non-aqueous organic solvent. Here, the composition of the non-aqueous organic solvent may be adjusted so that the lithium salt and the non-aqueous organic solvent include specific components to minimize the transfer of thermal energy from outside the secondary battery to the cathode active material inside the secondary battery.

[0116] Specifically, the non-aqueous organic solvent may include a cyclic ester solvent represented by the following chemical formula 2 as a main component:

[0117] [Chemical Formula 2]

[0118]

[0119] In the above chemical formula 2,

[0120] is a single bond or double bond,

[0121] X is hydrogen, fluoro, or vinyl,

[0122] p is an integer from 1 to 5.

[0123]

[0124] Specifically, the cyclic ester solvent represented by the above chemical formula 2 may include one or more of the ester cyclic compounds shown below:

[0125]

[0126]

[0127] In general, cyclic ester solvents such as dihydrofuranone have good solubility in lithium salts, but lithium bis(oxalato)borate (LiBOB, cation: Li + , anion: BF2C2O4 - ) etc., there is a limitation in the application of lithium secondary batteries because the cycle characteristics of the secondary battery are lowered. However, the present invention can have an excellent feature of improving the high-temperature safety of lithium secondary batteries because it can minimize the transfer of external heat to the positive electrode active material when the lithium secondary battery is exposed to high temperatures by including an excessive amount of a cyclic ester solvent represented by Chemical Formula 2 as a nonaqueous solvent of the electrolyte composition.

[0128] At this time, the cyclic ester solvent may be included in an amount of 60 wt% or more based on the total weight of the non-aqueous solvent of the electrolyte composition, and more specifically, may be included in an amount of 70 wt% or more, 75 wt% or more, 80 wt% or more, 85 wt% or more, 90 wt% or more, 60 wt% to 99 wt%, 70 wt% to 99 wt%, 80 wt% to 99 wt%, 90 wt% to 99 wt%, 95 wt% to 99 wt%, 60 wt% to 80 wt%, or 70 wt% to 90 wt%. In some cases, the cyclic ester solvent may be applied as a non-aqueous solvent itself and included in an amount of 100 wt% based on the total weight of the non-aqueous solvent. The present invention can prevent the problem of heat transferred to a cathode active material not being sufficiently reduced when a lithium secondary battery is exposed to high temperatures by controlling the content of a cyclic ester solvent contained in a non-aqueous solvent as described above to less than 60 wt%. In addition, since the cyclic ester solvent has excellent heat resistance, when the content of the cyclic ester solvent in the non-aqueous organic solvent is controlled within the above range, the electrolyte composition is not easily decomposed at high temperatures, and when combined with a predetermined lithium salt according to the present invention, there is an advantage of being able to minimize the amount of heat transferred to the cathode active material.

[0129] In addition, the electrolyte composition may include a specific lithium salt to reduce the amount of heat transferred to the cathode active material. Specifically, the lithium salt may be Li as a cation. + , and contains BF4 as anion. - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , B(C2O4)2 -, PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - ,CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - and ((C(CN))2NC(CF3))N - It may include one or more of the following:

[0130] Lithium salts fundamentally impart conductivity to the organic solvent constituting the electrolyte, while also inducing passivation of the negative electrode through the formation of an SEI. In the present invention, the lithium salt is dissolved in a cyclic ester solvent and decomposes on the surface of the positive electrode when the lithium secondary battery is exposed to high temperatures, thereby delaying the structural collapse of the positive electrode active material. To this end, the lithium salt used in the present invention may optionally include the lithium salts described above.

[0131] As an example, the lithium salt has Li as the cation. + , and contains BF2C2O4 as anion. - , BC4O8 - , (CF3SO2)2N - , (FSO2)2N -, (CF3CF2SO2)2N - or ((C(CN))2NC(CF3))N - may include. In this case, the lithium salt may include a borate group or a sulfonamide group in the anion, thereby performing a function of increasing the heat resistance of the electrolyte composition including the lithium salt. In addition, the lithium salt may include a borate group or a sulfonamide group, thereby forming a protective film through a reaction between the positive electrode active material and the electrolyte composition, thereby delaying the structural collapse of the positive electrode, thereby achieving an effect of significantly reducing the heat flow.

[0132] As another example, the lithium salt has Li as the cation. + , and contains BF4 as anion. - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - ,CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 -and SCN - It may include two or more kinds of lithium salts. In this case, the lithium salts are applied in the form of a basalt in which different salts are used in combination, thereby exhibiting a synergistic effect that significantly increases the heat flow reduction effect of the electrolyte composition, which was minimal when applied as a single component.

[0133] For example, PF6 as a dissociative anion - LiPF6, which represents Li, is a lithium salt commonly applied to the electrolyte composition of lithium secondary batteries, and has the characteristic of providing high conductivity to carbonate-based electrolytes. However, when LiPF6 is applied alone as a lithium salt, it decomposes into PF5 at about 200℃ or higher when exposed to high temperatures. This is very unstable, and since it is located on the surface of the positive electrode active layer and removes the positive electrode film derived from organic substances such as solvents and the positive electrode active material, there is a problem of reducing the high-temperature durability of the positive electrode active material. However, LiBF4 decomposes into BF3 at about 300℃ or higher, and thus has the characteristic of having a higher decomposition temperature than the decomposition temperature of the positive electrode active material. In other words, LiBF4 does not damage or remove the positive electrode film formed on the surface of the positive electrode active layer inside the secondary battery when exposed to high temperatures, so it can maintain the high-temperature durability of the positive electrode active material. However, LiBF4 has a minimal effect on increasing the conductivity of the electrolyte composition, and there is a limitation in that the performance of the negative electrode is reduced when an electrolyte containing it is applied to a secondary battery. Although LiPF6 and LiBF4 have limitations when applied to the electrolyte composition alone, when applied together to the lithium salt in the form of bisalt, not only does it have the effect of significantly improving the low high temperature safety of LiPF6, but it can also have the effect of significantly reducing the heat flow through which the electrolyte composition transfers heat to the cathode active material.

[0134] At this time, when the lithium salts used in combination are the first lithium salt and the second lithium salt, the mixing ratio of the first lithium salt and the second lithium salt may be 1:0.5 to 2.0 based on the molal concentration, and specifically, may be 1:0.5 to 1.5 or 1:0.8 to 1.2. The present invention can maximize the effect of lowering the heat flow of the electrolyte composition while minimizing the disadvantages of each lithium salt by controlling the ratio of the first lithium salt and the second lithium salt forming the bisalt as described above.

[0135] The concentration of these lithium salts is not particularly limited, but a preferable concentration may have a lower limit of 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more; and an upper limit of 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the concentration of the lithium salt is less than 0.5 mol / L, the ionic conductivity decreases, so there is a concern that the cycle characteristics and output characteristics of the non-aqueous electrolyte battery may decrease. In addition, if the concentration of the lithium salt exceeds 2.5 mol / L, the viscosity of the electrolyte for the non-aqueous electrolyte battery increases, so there is a concern that the ionic conductivity may decrease, and there is a concern that the cycle characteristics and output characteristics of the non-aqueous electrolyte battery may decrease.

[0136] In addition, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the liquid temperature may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt in this way, in the case of a lithium salt containing fluorine, there is a concern that decomposition may be accelerated and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is not desirable because it causes deterioration of battery performance. Therefore, the temperature when dissolving the lithium salt in the non-aqueous organic solvent is not particularly limited, but can be controlled to -20°C to 80°C, and specifically, can be controlled to 0°C to 60°C.

[0137] In addition, the non-aqueous organic solvent may further include one or more auxiliary solvents selected from the group consisting of a fluorine-containing ether solvent, a fluorine-containing cyclic carbonate solvent, a linear carbonate solvent, a phosphate solvent, and a sulfone solvent, together with the above-described ester solvent.

[0138] Specifically, the fluorine-containing ether solvent may be 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), etc., and the fluorine-containing cyclic carbonate solvent may be fluoroethylene carbonate (FEC), etc. In addition, the linear carbonate solvent may be ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), etc., the phosphate solvent may be trimethyl phosphate (TMP), etc., and the sulfone solvent may be sulfolane, methyl sulfolane, dimethyl sulfoxide, etc. In addition, in some cases, a cyclic carbonate solvent such as ethylene carbonate (EC) may be further included together with the non-aqueous organic solvents.

[0139] The above auxiliary solvents can improve the low-temperature performance of the electrolyte composition and can perform the function of preventing the generation of gas due to side reactions of the electrolyte composition induced when exposed to high temperatures. Accordingly, the above auxiliary solvents may be used alone or mixed with an ester solvent, or two or more types may be mixed with an ester solvent in any combination according to the intended use, from the perspectives of electrochemical stability against redox reactions and chemical stability with respect to reactions with heat or solutes.

[0140] In addition, the auxiliary solvent may be mixed so as to satisfy a certain volume ratio when mixed with the ester solvent. Specifically, the auxiliary solvent may be included in an amount of less than 40% by volume based on the total volume of the non-aqueous organic solvent, and more specifically, may be included in an amount of 30% by volume or less, 20% by volume or less, 1 to 30% by volume, 1 to 20% by volume, 1 to 10% by volume, 5 to 15% by volume, 5 to 20% by volume, 10 to 20% by volume, 20 to 30% by volume, 1 to 10% by volume, or 0.5 to 5% by volume based on the total volume of the non-aqueous organic solvent.

[0141] The present invention can maintain high compatibility between the ester solvent and the auxiliary solvent by controlling the content of the auxiliary solvent in the entire non-aqueous organic solvent to the above ratio, and at the same time, improve the performance of the battery by increasing the charge mobility and / or ion mobility of the battery.

[0142] In addition, the non-aqueous organic solvent may be additionally mixed with an organic solvent used in non-aqueous electrolytes in the art for the purpose of lowering the viscosity of the electrolyte composition at 25°C and improving the compatibility of the ester solvent represented by Chemical Formula 2 and the auxiliary solvent. At this time, the content of the organic solvent may be less than 10 wt% based on the total weight of the non-aqueous organic solvent of the electrolyte composition. As the miscible non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, 1,2-dimethoxyethane (DME), tetrahydrofuran, 2-methyl tetrahydrofuran, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, 1,3-dimethyl-2-imidazolidinone, ether, methyl pyrropionate, ethyl propionate, etc. can be used.

[0143] In addition, the electrolyte composition may further include additives in addition to the basic components described above. Any additives commonly used in the non-aqueous electrolyte of the present invention may be added in any proportion, as long as the gist of the present invention is not impaired.

[0144] Specifically, the electrolyte composition may further include an electrolyte additive represented by the following chemical formula 3 together with a non-aqueous organic solvent and a lithium salt:

[0145] [Chemical Formula 3]

[0146]

[0147] In the above chemical formula 3,

[0148] R1 is , or And,

[0149] R1' and R1" are each hydrogen or methyl group,

[0150] R2 is an arylene group having 6 to 20 carbon atoms; an aryleneoxy group having 6 to 20 carbon atoms; a heteroarylene group having 5 to 10 carbon atoms containing at least one heteroatom selected from N, S and O; a heteroaryleneoxy group having 5 to 10 carbon atoms containing at least one heteroatom selected from N, S and O; an alkyl group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a cycloalkyl group having 5 to 10 carbon atoms; and Contains at least one of the following:

[0151] R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or However,

[0152] The above alkyl group, alkoxy group, cycloalkyl group, and One or more of the hydrogens contained in may be replaced by a fluorine atom,

[0153] M includes at least one selected from the group consisting of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms,

[0154] l is an integer from 1 to 6,

[0155] m and n are integers from 2 to 20, respectively.

[0156]

[0157] The above electrolyte additive comprises an ionic compound having a nucleus in which a vinyl group, a (meth)acrylate group or an acrylamide group is bonded to a sulfonylimide group as a center, as shown in the above chemical formula 3, on one side of which i) a structure including a saturated hydrocarbon group or an oxygen atom introduced into a saturated hydrocarbon group or ii) a structure extending the conjugation of the sulfonylimide group or having a polyglycol unit is bonded.

[0158] The electrolyte additive has a chemical structure as represented by Chemical Formula 3, and thus can uniformly form an organic and / or inorganic film on the surfaces of the positive and negative electrodes when the secondary battery is activated. That is, the electrolyte additive can be directly incorporated in the form of a single molecule into the organic and / or inorganic film formed on the surfaces of the positive and / or negative electrodes when the secondary battery is activated. Through this, the electrolyte additive can suppress side reactions between the positive and / or negative electrodes and the electrolyte composition, and thus the electrical performance of the secondary battery including the electrolyte additive can be improved.

[0159] For this purpose, in the compound represented by the above chemical formula 1,

[0160] R2 is an ethylene group, a propylene group, a cyclohexylene group, a phenylene group, an oxymethylene group, a pyrrole group, an oxyphenylene group, an oxynaphthalene group, an oxypyrrole group, an oxythiophenylene group, an oxyfuranyl group, or And,

[0161] R3 is a fluoro group, a methyl group, a methyl fluoride group, a methoxy group, a methoxy fluoride group, or However, the above One or more of the hydrogens contained in may be replaced by a fluorine atom,

[0162] M is lithium, l is an integer of 1 or 2, and m can be an integer from 2 to 10.

[0163]

[0164] As an example, the compound represented by the above chemical formula 1 may be any one or more compounds of the following <structural formula 1> to <structural formula 17>:

[0165]

[0166]

[0167]

[0168]

[0169] A cathode active material including a lithium metal oxide represented by Chemical Formula 1 exhibits a high potential during charge and discharge compared to a cathode active material such as iron phosphate (LiFePO4). In this regard, when the electrolyte additive represented by the above <Structural Formula 1> to <Structural Formula 17> is applied to a lithium secondary battery together with a cathode active material such as a lithium metal oxide represented by Chemical Formula 1, organic and inorganic coating layers can be uniformly formed on the surfaces of the cathode and anode, respectively, due to the high charge and discharge potential of the cathode active material during the activation process of the secondary battery. The organic and inorganic coating layers thus formed can effectively suppress side reactions occurring in the electrolyte composition when the secondary battery is exposed to high temperatures. In addition, since the electrolyte additive can easily increase the oxidation potential window of the electrolyte composition, it can prevent the electrolyte composition from being decomposed during charge and discharge of the secondary battery.

[0170] As an example, the electrolyte composition according to the present invention may have an oxidation potential window of 4.5 V or higher. More specifically, the oxidation potential window of the electrolyte composition may be within a range of 4.5 V to 7.0 V, 5.0 V to 6.5 V, 5.0 V to 6.0 V, 5.3 V to 6.5 V, or 5.5 V to 6.0 V.

[0171] The above oxidation potential window refers to a voltage range in which no additional electrochemical reaction occurs inside the secondary battery other than the electrochemical oxidation-reduction occurring between the positive and negative electrodes, and here, a value relative to Li / Li+ is used as a reference electrode. In the present invention, if the oxidation potential window of the electrolyte is outside the above range, the potential window narrows, so that the non-aqueous electrolyte itself causes electrolysis during charging and discharging of the battery, shortening the lifespan of the lithium secondary battery and causing safety issues due to the generated gas. In addition, if the electrolyte composition according to the present invention satisfies the range of the above-described oxidation potential window or more, it is stable with respect to the potential applied during charging and discharging of the secondary battery, so that not only the lifespan of the battery is improved, but also the risk of explosion, etc., can be reduced.

[0172] In addition, the electrolyte additive may be included in the electrolyte composition in a specific content. Specifically, the electrolyte additive including the compound represented by the above chemical formula 1 may be included in an amount of 5 wt% or less, specifically 0.01 to 5 wt%, based on the total weight of the electrolyte composition. More specifically, the electrolyte additive may be included in an amount of 0.05 to 3 wt% or 1.0 to 2.5 wt% based on the total weight of the electrolyte composition. The present invention can prevent the electrolyte composition from being used in an excessive amount outside the above range to increase the viscosity of the electrolyte composition and thereby reduce wettability for electrodes and separators, while preventing the ion conductivity of the electrolyte composition from being reduced and thus deteriorating battery performance. In addition, the present invention can prevent the effect of the additive from being minimally implemented due to the use of a trace amount outside the above range of the electrolyte additive.

[0173] The lithium secondary battery according to the present invention can exhibit excellent high-temperature safety even if it includes a lithium metal oxide having a nickel (Ni) content of 60% or more of the total molar fraction as a cathode active material by including an electrolyte composition having the configuration described above.

[0174]

[0175] Hereinafter, each component of the lithium secondary battery will be described in more detail.

[0176] An electrode assembly provided in a lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, and a separator.

[0177] At this time, the positive electrode has a positive electrode active layer manufactured by applying, drying, and pressing a positive electrode slurry containing a positive electrode active material to at least one surface of a positive electrode current collector.

[0178] The cathode active material contained in the above cathode active layer has the advantage of being able to stably supply high-capacity and / or high-voltage electricity by including a lithium metal oxide represented by chemical formula 1 in which the nickel (Ni) content is 60% or more of the total molar fraction as described above.

[0179] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more based on the total weight of the positive electrode active layer, and specifically, may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0180] In addition, the positive electrode active layer may further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material, as needed.

[0181] At this time, the conductive material is used to improve the electrical performance of the anode, and can be applied as a material commonly used in the art. Specifically, it can include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

[0182] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on the total weight of the positive electrode active layer, and specifically, may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 0.5 to 3.5 parts by weight; 1 to 3 parts by weight; 0.1 to 2.5 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight.

[0183] In addition, the binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride (PVdF).

[0184] In addition, the binder may be included in an amount of 0.1 to 5 parts by weight based on the total weight of the positive electrode active layer, and specifically, may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 0.5 to 3.5 parts by weight; 1 to 3 parts by weight; 0.1 to 2.5 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight.

[0185] The total thickness of the above-mentioned positive electrode active layer is not particularly limited, but may be specifically 50 µm to 300 µm, and more specifically 100 µm to 200 µm; 80 µm to 150 µm; 120 µm to 170 µm; 150 µm to 300 µm; 200 µm to 300 µm; or 150 µm to 190 µm.

[0186] In addition, the positive electrode can be used as a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately applied in the range of 3 to 500 ㎛, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0187] Furthermore, the negative electrode, like the positive electrode, has a negative electrode active layer manufactured by applying, drying, and pressing a negative electrode slurry containing a negative electrode active material to at least one surface of a negative electrode current collector.

[0188] The above-mentioned negative electrode active layer may have a structure in which two individual layers are laminated depending on the battery model or product use to which the negative electrode of the present invention is applied, but is not limited thereto.

[0189] Specifically, the negative electrode according to the present invention may have a structure in which a first negative electrode active layer is provided on a negative electrode current collector, and a second negative electrode active layer is provided on the first negative electrode active layer. At this time, the first negative electrode active layer and the second negative electrode active layer each contain a negative electrode active material, and the negative electrode active materials contained in each layer may be the same or different. When a two-layer negative electrode active layer is provided on a negative electrode current collector, the composition of each negative electrode active layer can be easily controlled, so that an active material having excellent energy efficiency of the battery can be applied as the negative electrode active material to improve the electrical performance of the negative electrode, and there is an advantage in that a negative electrode active layer composition that can improve and / or prevent problems arising therefrom (e.g., deterioration of the interfacial adhesion between the negative electrode current collector and the negative electrode active layer, etc.) is possible.

[0190] In addition, the negative electrode active layer includes a carbon-based negative electrode active material as a negative electrode active material to implement electrical activity through a reversible redox reaction during charging and discharging of the battery.

[0191] The above carbon-based negative electrode active material refers to a material whose main component is carbon atoms, and such carbon-based negative electrode active material may include graphite. The graphite may include at least one of natural graphite and artificial graphite.

[0192] As an example, the carbon-based negative electrode active material may include mixed graphite, which is a mixture of natural graphite and artificial graphite. In this case, the mixed graphite may be a mixture of natural graphite and artificial graphite in a weight ratio of 10 to 50:50 to 90, or 10 to 30:70 to 90. By controlling the content ratio of natural graphite and artificial graphite as described above, the mixed graphite can prevent the adhesion between the negative electrode current collector and the negative electrode active layer from being reduced due to less than 10 parts by weight of natural graphite with respect to the total weight, and can prevent the charge / discharge capacity of the negative electrode from being reduced due to more than 50 parts by weight of natural graphite.

[0193] In addition, the carbon-based negative electrode active material is not particularly limited in its shape, but it is preferable to have a spherical graphite assembly formed by aggregating a plurality of flake-shaped graphite. Examples of the flake graphite include, in addition to natural graphite and artificial graphite, mesophase calcined carbon (bulk mesophase) using tar and pitch as raw materials, and graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.). In particular, it is preferable that the carbon-based negative electrode active material be assembled using a plurality of highly crystalline natural graphites. In addition, one graphite assembly can be formed by aggregating 2 to 100, preferably 3 to 20, flake-shaped graphite.

[0194] In addition, the carbon-based negative electrode active material has an average particle diameter (D) of 0.5 μm to 20 μm. 50 ) can be represented, and specifically, the average particle diameter (D) of 0.5 ㎛ to 15 ㎛; 0.5 ㎛ to 10 ㎛; 5 ㎛ to 20 ㎛; 10 ㎛ to 20 ㎛; 12 ㎛ to 18 ㎛; 2 ㎛ to 7 ㎛; 0.5 ㎛ to 5 ㎛; or 1 ㎛ to 3 ㎛ 50 ) can be expressed.

[0195] The average particle size of the carbon-based negative electrode material can be advantageously made smaller to maximize the degree of disorder in the direction of expansion of each particle, thereby preventing expansion of the particles due to lithium ion charging. However, when the graphite particle size is less than 0.5 ㎛, a large amount of binder may be required due to the increase in the number of particles per unit volume. On the other hand, when the maximum particle size exceeds 20 ㎛, expansion becomes severe, and as charge and discharge are repeated, the adhesion between particles and the adhesion between the particles and the current collector deteriorates, which can significantly reduce the cycle characteristics.

[0196] Furthermore, the negative electrode according to the present invention may include a silicon-based negative electrode active material together with a carbon-based negative electrode active material in the negative electrode active layer. The silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and may contain silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), or silicon dioxide (SiO2) alone or in combination. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited and included in the negative electrode active layer as the silicon-based negative electrode active material, they are silicon oxide (SiO q , but can be expressed as 0.8≤q≤2.5).

[0197] In addition, the negative electrode active material may be included in an amount of 85 parts by weight or more based on the total weight of the negative electrode active layer, and specifically, may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0198] In addition, among these, the silicon-based negative electrode active material may be included in an amount of 0.1 to 30 wt% based on the total weight of the negative electrode active material, and specifically, may be included in an amount of 0.5 to 20 wt%, 1 to 9 wt%, 5 to 15 wt%, 3 to 7 wt%, 11 to 19 wt%, 13 to 17 wt%, 15 to 20 wt%, 10 to 30 wt%, 20 to 30 wt%, 15 to 25 wt%, or 9 to 22 wt%. The present invention can reduce lithium consumption and irreversible capacity loss during initial charge and discharge of a secondary battery while improving the charge capacity per unit mass by controlling the contents of the carbon-based negative electrode active material and the silicon-based negative electrode active material included in the negative electrode active material within the above range. In addition, the structural stability of the negative electrode active layer can be improved by minimizing the change in volume of the negative electrode active layer during charging and discharging of the secondary battery, thereby increasing the lifespan of the secondary battery.

[0199] Meanwhile, the negative electrode active layer according to the present invention may optionally further include a conductive agent, a binder, other additives, etc., as needed, in addition to the carbon-based negative electrode active material as the main component.

[0200] The above-mentioned challenge material may include, but is not limited to, one or more types of carbon black such as acetylene black and Ketjen black; carbon nanotubes; and carbon fibers.

[0201] As an example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0202] At this time, the content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent the resistance of the negative electrode from increasing due to a low content of the conductive material, thereby reducing the charging capacity, and can prevent the problem of the content of the negative electrode active material decreasing due to an excessive amount of the conductive material, thereby reducing the charging capacity, or the problem of the rapid charging characteristics from decreasing due to an increase in the loading amount of the negative electrode active layer.

[0203] In addition, the binder may be appropriately applied as a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and may be applied within a range that does not deteriorate the electrical properties of the electrode. Specifically, the binder may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0204] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the electrode from being lowered due to an excessive amount of binder.

[0205] Furthermore, the average thickness of the negative electrode active layer may be 100 ㎛ to 300 ㎛, specifically 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or 130 ㎛ to 190 ㎛, and the average thickness may be the same as the average thickness of the flat region. The present invention can uniformly align the crystal plane of the carbon-based negative electrode active material contained in each region by controlling the average thickness of the negative electrode active layer within the above range, thereby improving the high-rate charge / discharge performance and energy density of a battery including the negative electrode.

[0206] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the negative electrode current collector can be appropriately applied from 1㎛ to 500㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0207]

[0208] Meanwhile, the separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the art, but specifically, one containing at least one polymer selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers having chemical resistance and hydrophobicity can be used. The separator may have a porous polymer substrate form such as a sheet or non-woven fabric containing the above-described polymer, and in some cases, may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate using an organic binder. In addition, the separator may have an average pore diameter of 0.01 to 10 μm, and an average thickness of 5 to 300 μm.

[0209] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but can be applied in various shapes such as cylindrical, square, pouch, or coin depending on the purpose of performance. The lithium secondary battery according to one embodiment of the present invention may be a pouch-type secondary battery.

[0210]

[0211] Manufacturing method of lithium secondary battery

[0212] Furthermore, in one embodiment of the present invention,

[0213] A method for manufacturing a lithium secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte composition in which the electrode assembly is impregnated.

[0214] The above positive electrode is provided on at least one surface of the positive electrode current collector and has a positive electrode active layer including a lithium metal oxide represented by the following chemical formula 1 as a positive electrode active material;

[0215] The above electrolyte composition comprises a lithium salt and a non-aqueous organic solvent, and the non-aqueous organic solvent comprises a cyclic ester solvent represented by the following chemical formula 2 in an amount of 60 wt% or more based on the total weight;

[0216] A method for manufacturing a lithium secondary battery is provided, wherein the heat flux of a mixture containing a positive electrode active material and an electrolyte composition at a weight ratio of 1:1 with a 100% state of charge is measured, and the heat flux is 6.0 W / g or less within a range of 200°C to 300°C.

[0217] [Chemical Formula 1]

[0218] Li x [Ni y Co z Mn w M 1 v ]O2

[0219] [Chemical Formula 2]

[0220]

[0221] In the above chemical formulas 1 and 2,

[0222] M 1 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0223] x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이며,

[0224] is a single bond or double bond,

[0225] X is hydrogen, fluoro, or vinyl,

[0226] p is an integer from 1 to 5.

[0227]

[0228] The method for manufacturing a lithium secondary battery according to the present invention refers to the method for manufacturing the lithium secondary battery of the present invention described above. The method includes a step of impregnating an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode with an electrolyte composition. At this time, the positive electrode of the electrode assembly includes an NCM-based positive electrode active material having a high nickel (Ni) content, and the electrolyte composition has an excellent advantage in that the heat flow between the positive electrode active material and the electrolyte composition is controlled to be low within a predetermined range at high temperatures, thereby improving safety issues caused by the positive electrode active material at high temperatures.

[0229] Since the specific description of the above positive electrode active material and electrolyte composition is the same as described above, a detailed description is omitted.

[0230]

[0231] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0232] However, the following examples and experimental examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0233]

[0234] Manufacturing Examples 1 to 17. Manufacturing of electrolyte composition for lithium secondary batteries.

[0235] As non-aqueous solvents, dihydrofuranone (DHF), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were prepared, and as lithium salts, LiPF6, LiBF4, LiN(FSO2)2, and LiBF2(CO2)2 were prepared.

[0236] Each prepared lithium salt was dissolved in a non-aqueous organic solvent at a concentration of 1.0 M (≒ 1.0 mol / g) at 30 to 40°C, and an electrolyte additive was added at 2.0 wt% based on the total weight of the electrolyte composition to prepare an electrolyte composition. At this time, the composition of the non-aqueous organic solvent used and the types of the lithium salt and electrolyte additive are shown in Table 1 below.

[0237] Non-aqueous organic solvent composition [unit: vol.%] Lithium salt composition [unit: M concentration] Electrolyte additive Manufacturing example 1 FDHF = 100 LiFSI - Manufacturing example 2 DHF = 100 LiFSI - Manufacturing example 3 DHF = 100 LiFSI <Structural formula 1> Manufacturing Example 4 DHF=100LiODFB-Manufacturing Example 5 DHF=100LiPF6:LiBF4=1:1-Manufacturing Example 6 DHF:FEC=90:10LiFSI-Manufacturing Example 7 DHF:EMC=90:10LiFSI-Manufacturing Example 8 DHF:EMC=60:40LiFSI-Manufacturing Example 9 DHF=100LiPF6:LiBF4=1:0.1-Manufacturing Example 10 DHF=100LiPF6:LiBF4=1:5-Manufacturing Example 11 DHF:EMC=40:60LiFSI-Manufacturing Example 12 DHF=100LiPF6-Manufacturing Example 13 DHF=100LiBF4-Manufacturing Example 14 EC:EMC=30:70LiFSI-Manufacturing Example 15EC:EMC=30:70LiODFB-Preparation example 16EC:EMC=30:70LiPF6-Preparation example 17EC:EMC=30:70LiBF4-DHF: dihydrofurane FDHF: fluorodihydrofurane EMC: ethyl methyl carbonate FEC: fluoro ethylene carbonate LiFSI: Lithium bis(trifluoromethanesulfonyl)imide, LiN(FSO2)2 LiODFB: Lithium difluoro(oxalato)borate, LiBF2(CO2)2

[0238]

[0239]

[0240]

[0241] Examples 1 to 8 and Comparative Examples 1 to 9. Manufacturing of lithium secondary batteries

[0242] LiNi with a particle size of 5㎛ as a cathode active material 0.86 Co 0.05 Mn 0.07Al 0.02 O2 was prepared, and polyvinylidene fluoride as a carbon-based conductive agent and binder was mixed with N-methyl pyrrolidone (NMP) in a weight ratio of 94:3:3 to prepare a cathode slurry having a solid content of 45%. The prepared cathode slurry was cast on an aluminum foil, dried in a vacuum oven at 120°C, and then rolled to prepare a cathode having a cathode active layer with a thickness of 160 μm.

[0243] Separately, a carbon-based negative electrode active material containing natural graphite and artificial graphite in a weight ratio of 3:7 and a silicon-based negative electrode active material containing SiO2 in a weight ratio of 88:12 were mixed to prepare a negative electrode active material. 97 parts by weight of the prepared negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to prepare a negative electrode slurry having a solid content of 40%. The negative electrode slurry was cast on a copper foil, dried in a vacuum oven at 130°C, and then rolled to prepare a negative electrode having a 180 μm thick negative electrode active layer.

[0244] A separator made of 18 μm polypropylene was interposed between the positive and negative electrodes obtained above, inserted into a case, and then the electrolyte composition manufactured in the manufacturing example was injected as shown in Table 2 below to assemble a lithium secondary battery.

[0245] Each assembled lithium secondary battery was initially charged. Specifically, the lithium secondary batteries were initially charged to a charge end voltage of 4.2 V at 55±2°C under the conditions shown in Table 2 below, thereby manufacturing activated lithium secondary batteries.

[0246] Electrolyte composition type Example 1 Electrolyte composition of Manufacturing Example 1 Example 2 Electrolyte composition of Manufacturing Example 2 Example 3 Electrolyte composition of Manufacturing Example 3 Example 4 Electrolyte composition of Manufacturing Example 4 Example 5 Electrolyte composition of Manufacturing Example 5 Example 6 Electrolyte composition of Manufacturing Example 6 Example 7 Electrolyte composition of Manufacturing Example 7 Example 8 Electrolyte composition of Manufacturing Example 8 Comparative Example 1 Electrolyte composition of Manufacturing Example 9 Comparative Example 2 Electrolyte composition of Manufacturing Example 10 Comparative Example 3 Electrolyte composition of Manufacturing Example 11 Comparative Example 4 Electrolyte composition of Manufacturing Example 12 Comparative Example 5 Electrolyte composition of Manufacturing Example 13 Comparative Example 6 Electrolyte composition of Manufacturing Example 14 Comparative Example 7 Electrolyte composition of Manufacturing Example 15 Comparative Example 8 Electrolyte composition of Manufacturing Example 16 Comparative Example 9 Manufacturing Example Electrolyte composition of 17

[0247]

[0248]

[0249] Experimental example.

[0250] In order to evaluate the safety and charge / discharge performance of the lithium secondary battery according to the present invention, the following experiments were conducted.

[0251]

[0252] 1) Measurement of heat flow between the cathode active material and electrolyte composition

[0253] Each lithium secondary battery manufactured in the examples and comparative examples was fully charged to 4.25 V at a rate of 0.5 C at 25°C under constant current (CC)-constant voltage (CV) conditions, and the fully charged lithium secondary batteries were disassembled to obtain the positive electrode active material, LiNi. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 and electrolyte composition were weighed and mixed in a 1:1 weight ratio.

[0254] The prepared mixture was injected into the sample can of a differential scanning calorimeter (DSC) to prepare a sample, and the heat flow for the prepared sample was measured. At this time, the heat flow was measured in the range of 100°C to 350°C while increasing the temperature at a heating rate of 10±0.1°C / min.

[0255] From the measured results, the heat flow between the cathode active material and electrolyte composition included in each lithium secondary battery was evaluated. Among the measured results, if there were two or more valid heat flow peaks within the temperature range of 100 to 350°C, the value of the peak showing the largest heat flow was determined as the corresponding heat flow. The results are shown in Table 3 below.

[0256]

[0257] 2) Thermal runaway test evaluation

[0258] The lithium secondary batteries manufactured in the examples and comparative examples were charged under constant current (CC) conditions maintained at 1.25 A until they reached 4.2 V at 25°C, and maintained at 4.2 V. After charging was completed, they were activated by discharging under constant current (CC) conditions maintained at 1.25 A until 2.85 V. After that, each activated lithium secondary battery was allowed to rest for 6 hours at 25°C.

[0259] Then, the batteries were fully charged under constant current (CC) conditions maintained at 1.25 A until they reached 4.2 V at 25°C, and a thermal runaway test was performed using an accelerating rate calorimetry (ARC). The ARC was manufactured by Thermal Hazard Technology (THT), and the thermal runaway test was performed using the heat-wait-search (HWS) method. In the HWS method, the temperature of the insulated oven chamber in which each lithium secondary battery was mounted was increased from 50°C to 190°C at a rate of 10°C / min by 5°C and then waited for 10 minutes. Here, when each heated lithium secondary battery showed a temperature change of 0.02℃ / min or more during a 10-minute standby, self-heating corresponding to thermal runaway (TR) was recognized to have occurred, and from then on, no separate thermal energy was applied so that the temperature would change due to self-heating of each secondary battery. After the self-heating of the secondary battery, the self-heating profile of the secondary battery was measured, and the maximum temperature of the secondary battery was calculated from the measured self-heating profile. The results are shown in Table 3 below.

[0260] Heat flux [W / g] Maximum temperature during thermal runaway test [℃] Example 12.5±0.125 1.7 Example 22.4±0.125 3.2 Example 32.6±0.124 7.0 Example 42.7±0.125 4.5 Example 54.9±0.127 1.8 Example 62.9±0.125 8.8 Example 73.0±0.126 0.3 Example 83.5±0.127 2.1 Comparative Example 16.5±0.145 1.7 Comparative Example 26.8±0.131 9.5 Comparative Example 37.0±0.132 3.6 Comparative Example 47.2±0.146 8.6 Comparative Example 57.0±0.129 9.9 Comparative Example 67.4±0.1324.9Comparative example 77.7±0.1337.4Comparative example 830.5±0.2513.8Comparative example 97.9±0.1347.2

[0261]

[0262]

[0263] It can be seen that the lithium secondary battery according to the present invention has excellent high-temperature safety and battery life despite including an NCM-based cathode active material in the cathode having a high nickel (Ni) content of 80% or more of the total molar fraction of transition metals by controlling the heat flow between the cathode active material and the electrolyte composition to a low level within a predetermined range.

[0264] Specifically, lithium secondary batteries of the examples in which the heat flow between the cathode active material and the electrolyte composition was 6 W / g or less exhibited a maximum temperature of less than about 275°C in a thermal runaway test.

[0265] On the other hand, the lithium secondary batteries of the comparative examples, in which the heat flow between the cathode active material and the electrolyte composition exceeds 6 W / g, showed a high maximum temperature of about 299℃ or higher in the thermal runaway test.

[0266] This means that when the heat flow between the cathode active material and the electrolyte composition is controlled to be below a predetermined range, even if an NCM cathode active material with a high nickel (Ni) content and low structural stability at high temperatures is included, damage to the cathode active material such as structural collapse can be suppressed, thereby preventing a significant increase in the temperature of the secondary battery at high temperatures.

[0267] From these results, it can be seen that the lithium secondary battery according to the present invention has excellent energy density by including an NCM-based cathode active material having a high nickel (Ni) content in the cathode, and has an excellent effect of improving safety issues caused by the cathode active material at high temperatures by controlling the heat flow between the cathode active material and the electrolyte composition to a low level within a predetermined range.

[0268]

[0269] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes to the present invention can be made without departing from the spirit and technical scope of the present invention as set forth in the claims to be described below.

[0270] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

Claims

1. An electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and an electrolyte composition in which the electrode assembly is impregnated; The above positive electrode is provided on at least one side of the positive electrode current collector and has a positive electrode active layer including a lithium metal oxide represented by the following chemical formula 1 as a positive electrode active material; The above electrolyte composition includes a lithium salt and a non-aqueous organic solvent, and the non-aqueous organic solvent includes a cyclic ester solvent represented by the following chemical formula 2 in an amount of 60 wt% or more based on the total weight of the non-aqueous organic solvent; A lithium secondary battery that exhibits a heat flux of 6.0 W / g or less within a range of 200°C to 300°C when measuring the heat flux of a mixture containing a positive electrode active material and an electrolyte composition in a 1:1 weight ratio with a 100% state of charge: [Chemical Formula 1] Li x [Ni y Co z Mr w M 1 v ]O2 [Chemical Formula 2] In the above chemical formulas 1 and 2, M 1 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이며, is a single bond or double bond, X is hydrogen, fluoro, or vinyl, p is an integer from 1 to 5.

2. In paragraph 1, The cathode active material is LiNi 0.95 Co 0.03 Mn 0.02 O2, LiNi 0.9 Co 0.6 Mn 0.4 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.85 Co 0.1 Mn 0.05 O2, LiNi 0.85 Co 0.05 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.75 Co 0.2 Mn 0.15 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 A lithium secondary battery containing at least one type of O2.

3. In paragraph 1, A lithium secondary battery, wherein the cyclic ester solvent represented by chemical formula 2 includes at least one of dihydrofuranone, vinyldihydrofuranone, fluorodihydrofuranone, furanone, tetrahydropyranone, methyldihydrofuranone, propyltetrahydropyranone, and oxepanone.

4. In paragraph 1, Lithium salts, Li as a cation + Including, BF4 as anion - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , B(C2O4)2 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - ,CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - and ((C(CN))2NC(CF3))N - A lithium secondary battery containing at least one of the following:

5. In paragraph 1, Lithium salts, Li as a cation + Including, BF2C2O4 as anion - , B(C2O4)2 - , (CF3SO2)2N - , (FSO2)2N - , (CF3CF2SO2)2N - or ((C(CN))2NC(CF3))N - A lithium secondary battery comprising:

6. In paragraph 1, Lithium salts, Li as a cation + Including, BF4 as anion - , B 10 Cl 10 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , (C2O4)2PF2 - ,CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - and SCN - A lithium secondary battery containing two or more types of lithium.

7. In paragraph 1, A lithium secondary battery further comprising at least one auxiliary solvent selected from the group consisting of a non-aqueous organic solvent, a fluorine-containing ether solvent, a fluorine-containing cyclic carbonate solvent, a linear carbonate solvent, a phosphate solvent, and a sulfone solvent.

8. In paragraph 1, A lithium secondary battery further comprising an electrolyte additive represented by the following chemical formula 3: [Chemical Formula 3] In the above chemical formula 3, R1 is , or And, R1' and R1" are each hydrogen or methyl group, R2 is an arylene group having 6 to 20 carbon atoms; an aryleneoxy group having 6 to 20 carbon atoms; a heteroarylene group having 5 to 10 carbon atoms containing at least one heteroatom selected from N, S and O; a heteroaryleneoxy group having 5 to 10 carbon atoms containing at least one heteroatom selected from N, S and O; an alkyl group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a cycloalkyl group having 5 to 10 carbon atoms; and Contains at least one of the following: R3 is a fluoro group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or However, The above alkyl group, alkoxy group, cycloalkyl group, and One or more of the hydrogens contained in may be replaced by a fluorine atom, M includes at least one selected from the group consisting of lithium, sodium, potassium, tetraalkylammonium having 1 to 4 carbon atoms, and tetraalkylphosphonium having 1 to 4 carbon atoms, l is an integer from 1 to 6, m and n are integers from 2 to 20, respectively.

9. In paragraph 8, A lithium secondary battery comprising an electrolyte additive represented by Chemical Formula 3, wherein the electrolyte additive comprises at least one compound selected from the following <Structural Formula 1> to <Structural Formula 17>:

10. In paragraph 8, A lithium secondary battery in which the electrolyte additive is included in an amount of 5 wt% or less based on the total weight of the electrolyte composition.

11. In paragraph 1, The negative electrode is provided on at least one side of the negative electrode collector and has a negative electrode active layer including a carbon-based negative electrode active material and a silicon-based negative electrode active material. A lithium secondary battery comprising the carbon-based negative electrode active material as a carbon material, at least one of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, acetylene black, and Ketjen black.

12. In paragraph 11, Silicon-based negative electrode active materials are silicon materials such as silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q , but a lithium secondary battery including at least one of 0.8≤q≤2.5).

13. In paragraph 11, A lithium secondary battery in which the silicon-based negative electrode active material is included in an amount of 0.1 to 30 wt% based on the total weight of the negative electrode active material.

14. A method for manufacturing a lithium secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte composition in which the electrode assembly is impregnated. The above positive electrode is provided on at least one surface of the positive electrode current collector and has a positive electrode active layer including a lithium metal oxide represented by the following chemical formula 1 as a positive electrode active material; The above electrolyte composition comprises a lithium salt and a non-aqueous organic solvent, and the non-aqueous organic solvent comprises a cyclic ester solvent represented by the following chemical formula 2 in an amount of 60 wt% or more based on the total weight; A method for manufacturing a lithium secondary battery, wherein the heat flux is measured for a mixture containing a positive electrode active material and an electrolyte composition at a weight ratio of 1:1 with a 100% state of charge, and the mixture exhibits a heat flux of 6.0 W / g or less within a range of 200°C to 300°C: [Chemical Formula 1] Li x [Ni y Co z Mr w M 1 v ]O2 [Chemical Formula 2] In the above chemical formulas 1 and 2, M 1 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, x, y, z, w, and v are 0.9≤x≤1.30, 0.6≤y<1, 0, respectively. <z≤0.2, 0<w≤0.2, 0≤v≤0.1이되, y+z+w+v=1이며, is a single bond or double bond, X is hydrogen, fluoro, or vinyl, p is an integer from 1 to 5.

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