Lithium secondary battery

Abstract

A lithium secondary battery according to the present invention comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises 1,3-propane sultone (PS) and / or lithium bis(oxalate)borate (LiBOB) as main additives, and has a full charge voltage exceeding 4.35 V.

Description

lithium secondary battery

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0141281 filed on October 16, 2024.

[0002] The present invention relates to a lithium secondary battery.

[0003]

[0004] In lithium secondary batteries, olivine-structured compounds have a voltage of ~3.5 V and 3.6 g / cm³ relative to lithium. 3 It has a high bulk density and a theoretical capacity of 170 mAh / g, and is widely used as a positive electrode active material because it has excellent high-temperature stability compared to cobalt (Co).

[0005] Recently, among compounds with an olivine structure, attempts have been made to use LMFP containing manganese as a positive electrode active material. LMFP has the effect of improving energy density due to its high average operating voltage.

[0006] Currently, general lithium secondary batteries are typically operated at 4.35V or lower, and if operated at a higher potential, the energy retention rate decreases.

[0007]

[0008] The problem that the technical concept of the present invention aims to solve is to mitigate the decrease in energy retention rate when a lithium secondary battery is operated at a high potential.

[0009] The problem that the technical concept of the present invention aims to solve is to provide a lithium secondary battery capable of realizing high energy density and high discharge voltage.

[0010] Furthermore, the problem that the technical concept of the present invention aims to solve is to provide a lithium secondary battery capable of realizing high energy density while having excellent high-temperature safety.

[0011]

[0012] A lithium secondary battery according to exemplary embodiments of the present invention is a lithium secondary battery comprising a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the electrolyte comprises 1,3-propane sultone (PS) and / or lithium bis(oxalate)borate (LiBOB) as a main additive and is characterized by having a full charge voltage exceeding 4.35V.

[0013] A lithium secondary battery according to exemplary embodiments may have a full charge voltage in the range of 4.4V to 4.5V.

[0014] In exemplary embodiments, the anode comprises a first anode active material and a second anode active material, wherein the first anode active material is a lithium composite metal oxide having a layered crystal structure and the second anode active material is a lithium transition metal phosphate having an olivine structure.

[0015] In exemplary embodiments, the first positive active material may be a compound represented by the following chemical formula 1.

[0016] [Chemical Formula 1]

[0017] Li 1+y Ni p Co q Mn r M 1 -(p+q+r) O 2-z A z

[0018] In the above chemical formula 1,

[0019] M 1 is at least one selected from the group consisting of Cu, Ti, Mg, Al, Pt, and Zr, and A is an oxygen-substituted halogen, 0≤y≤0.5, 0.4≤p≤1, 0≤q≤0.6, 0≤r≤0.6, 0.9≤p+q+r≤1, and 0≤z≤0.001.

[0020] In exemplary embodiments, the second positive active material may be a compound represented by the following chemical formula 2.

[0021] [Chemical Formula 2]

[0022] Li 1+a M x Fe 1-x (PO 4-b )X b

[0023] In the above chemical formula 2,

[0024] M is one or more elements selected from the group consisting of Mn, Al, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X is one or more elements selected from the group consisting of F, Cl, Br, I, At, N, and S, and a, b, and x are 0≤a≤0.1, 0≤b≤0.1, and 0, respectively. <x≤0.9 범위이다. 예시적인 실시예들에 있어서, 상기 제1 양극 활물질은, 니켈의 몰분율이 60% 이상, 및 70% 미만이다.

[0025] In exemplary embodiments, in the above formula 2, M is manganese, and the molar ratio of manganese to iron is 50:50 to 70:30.

[0026] In exemplary embodiments, the main additive is included in a range of 0.001 to 2 weight percent with respect to the total weight of the electrolyte.

[0027] In exemplary embodiments, the main additive is 1,3-propanesulfone.

[0028] In exemplary embodiments, 1,3-propanesulfone is included in a range of 0.25 to 1.75 weight percent with respect to the total weight of the electrolyte.

[0029] In exemplary embodiments, the main additive is lithium bisoxalate toborate.

[0030] In exemplary embodiments, the lithium bisoxalate is included in a range of 0.1% to 1.5% by weight relative to the total weight of the electrolyte.

[0031] In exemplary embodiments, the weight ratio of the first positive active material and the second positive active material is in the range of 4:6 to 9:1.

[0032] In exemplary embodiments, the cathode comprises natural graphite and / or artificial graphite as a cathode active material.

[0033]

[0034] According to the present invention, a lithium secondary battery is provided in which the decrease in energy retention rate is mitigated when driven at a voltage range exceeding 4.35V.

[0035] In addition, according to the present invention, a lithium secondary battery capable of realizing high energy density and high temperature safety is provided.

[0036]

[0037] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0038] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall 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.

[0039] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0040] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0041] In this specification, the description “A and / or B” means “A or B or both.”

[0042] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0043] In this specification, the average particle size (D 50 ) refers to the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The above D 50 For example, it can be measured using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0044] In this specification, "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BEL SORP-mino II of BEL Japan.

[0045]

[0046] A lithium secondary battery according to exemplary embodiments of the present invention comprises a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the electrolyte comprises 1,3-propane sultone (PS) and / or lithium bis(oxalate)borate (LiBOB) as a main additive, and the full charge voltage exceeds 4.35 V. The full charge voltage in this specification refers to the potential of the battery when the state of charge (SOC) of the battery is 100%.

[0047] The inventors of the present invention discovered that when the electrolyte in a lithium secondary battery includes 1,3-propanesulfone or lithium bis-oxalate toborate, the energy retention rate of the lithium secondary battery is improved in a voltage range greater than 4.35V compared to when the electrolyte does not include the said additive, and thus arrived at the present invention. Although 1,3-propanesulfone and lithium bis-oxalate toborate are known as additives that can be included in an electrolyte, the present invention is significant in that it is based on the technical concept that said additives improve the lifespan characteristics of the lithium secondary battery in a voltage range greater than 4.35V.

[0048] The components of the lithium secondary battery according to the present invention will be described in detail below.

[0049]

[0050] anode

[0051] A positive electrode according to exemplary embodiments comprises: a positive electrode current collector; and a positive electrode active material layer provided on at least one surface of the positive electrode current collector and comprising a positive electrode active material. The positive electrode active material layer is a layer that implements the electrical activity of the positive electrode and comprises a positive electrode active material as a main component that implements an electrochemical redox reaction during charging and discharging of the battery. Specifically, the positive electrode active material may be included in an amount of 80% to 99.8% by weight with respect to the total weight of the positive electrode active material layer, and specifically, may be included in an amount of 95% or more, 98% or more, 84% to 99.8% by weight, 90% to 99.8% by weight, 94% to 99.8% by weight, 88% to 96% by weight, or 92% to 97.5% by weight.

[0052] The above-mentioned positive electrode may include both a first positive electrode active material and a second positive electrode active material. The first positive electrode active material may be a lithium complex metal oxide having a layered crystal structure. The second positive electrode active material may be a lithium transition metal phosphate having an olivine structure. In exemplary embodiments, the first positive electrode active material may be a compound represented by the following Chemical Formula 1. In exemplary embodiments, the second positive electrode active material may be a compound represented by the following Chemical Formula 2.

[0053] [Chemical Formula 1]

[0054] Li 1+y Ni p Co q Mn r M 1 -(p+q+r) O 2-z A z

[0055] [Chemical Formula 2]

[0056] Li 1+a M x Fe 1-x (PO 4-b )X b

[0057] In the above chemical formula 1,

[0058] M 1 is at least one selected from the group consisting of Cu, Ti, Mg, Al, Pt, and Zr, and A is an oxygen-substituted halogen, 0≤y≤0.5, 0.4≤p≤1, 0≤q≤0.6, 0≤r≤0.6, 0.9≤p+q+r≤1, and 0≤z≤0.001.

[0059] In the above chemical formula 2,

[0060] M is one or more elements selected from the group consisting of Mn, Al, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X is one or more elements selected from the group consisting of F, Cl, Br, I, At, N, and S, and a, b, and x are 0≤a≤0.1, 0≤b≤0.1, and 0, respectively. <x≤0.9 범위이다.

[0061] The above-mentioned first cathode active material is a lithium composite metal oxide having a layered crystal structure, which facilitates the storage of lithium ions and possesses a high lithium ion diffusion rate, making it suitable for use as a cathode active material in high-capacity / high-output secondary batteries. However, compounds having a layered crystal structure have low chemical and structural stability, so they can easily decompose under high-temperature conditions. This acts as a factor that reduces the safety of the secondary battery.

[0062] On the other hand, the second cathode active material is a lithium transition metal phosphate having an olivine crystal structure, which exhibits high structural stability due to its hexahedral crystal form in which phosphorus (P) and oxygen (O) are strongly bonded. As a result, the lithium transition metal phosphate having an olivine crystal structure can easily maintain its crystal structure even if all lithium ions are released during charging, and the crystal structure does not easily decompose even under high temperature conditions.

[0063] According to the present invention, the positive electrode comprises a lithium composite metal oxide having a layered crystal structure as a positive electrode active material and a lithium transition metal phosphate having an olivine structure, thereby complementing or mitigating the limitations of metal oxides having different crystal structures, and thus the safety and electrical performance of the positive electrode can be further improved.

[0064] Meanwhile, traditional lithium transition metal phosphates have a low energy density, which indicates the amount of energy a battery can store per unit weight / volume. To compensate for this disadvantage, the present invention may select a compound represented by Chemical Formula 2 among transition metal phosphates with an olivine crystal structure. The compound represented by Chemical Formula 2 is a conventional lithium transition metal phosphate in which a portion of the iron is substituted with a metal such as manganese. Since it has a high driving voltage, it is possible to achieve high energy density compared to conventional lithium transition metal phosphates. Therefore, it is preferred as a positive electrode active material for the lithium secondary battery of the present invention, which must be charged within a voltage range exceeding 4.35V.

[0065] In a preferred embodiment, M of Formula 2 may be manganese. To achieve high energy density, the molar ratio of manganese to iron in this lithium manganese iron phosphate may be 50:50 to 70:30, preferably in the range of 55:45 to 65:35.

[0066] The above second positive active material may have a predetermined size. For example, average particle size (D 50 ) may be 0.5㎛ to 10㎛, and specifically, 0.5㎛ to 8㎛; 0.5㎛ to 6㎛; 0.5㎛ to 4㎛; 0.5㎛ to 2㎛; 1㎛ to 5㎛; 2㎛ to 4㎛; 4㎛ to 8㎛; 5㎛ to 9㎛; 3㎛ to 6㎛; 0.5㎛ to 1.5㎛; or 0.7㎛ to 1.4㎛.

[0067] The present invention relates to the average particle size (D) of the second positive active material. 50 By adjusting the range to the range described above, it is possible to prevent the anode active materials from aggregating due to particle sizes lower than the lower limit of the range, thereby reducing processability and reliability during anode manufacturing. Additionally, it is possible to prevent the problem of reduced electrical performance caused by damage to the anode active materials, such as breakage during the rolling process, due to particle sizes higher than the upper limit of the range.

[0068] In addition, the second positive electrode active material may have a structure in which a carbon layer is coated on its surface. The carbon layer may have a porous structure that not only has a high surface area but also has a form that uniformly surrounds the core surface with high crystallinity. Since a carbon layer with such a structure can further enhance the electrochemical reactivity and electrical properties of the positive electrode active material, the output and lifespan characteristics of the positive electrode can be improved.

[0069] Here, the thickness of the carbon layer can be controlled within a range that does not reduce the energy density of the cathode active material. Specifically, the carbon layer may have an average thickness of 50 nm or less, and more specifically, may have an average thickness of 40 nm or less; 30 nm or less; 20 nm or less; 10 nm or less; 5 nm to 40 nm; 5 nm to 20 nm; 10 nm to 30 nm; 20 nm to 45 nm; 10 nm to 20 nm; 5 nm to 10 nm; 1 nm to 10 nm; or 3 nm to 9 nm.

[0070] The layered lithium composite metal oxide represented by Chemical Formula 1 above is a metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn) along with lithium, and in some cases, other transition metals (M 1 It can have a doped form. For example, the lithium composite metal oxide is Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O2, Li(Ni0.6 Co 0.2 Mn 0.15 Zr 0.05 )O2, Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Al 0.2 )O2, Li(Ni 0.7 Co 0.15 Al 0.15 )O2, Li(Ni 0.8 Co 0.1 Al 0.1 )O2, Li(Ni 0.9 Co 0.05 Al 0.05 )O2, Li(Ni 0.6 Co 0.2 Al 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Al 0.15 Zr 0.05 )O2 and Li(Ni 0.7 Co 0.1 Al 0.1 Zr 0.1 It may include one or more types of O2.

[0071] In a preferred embodiment, the first cathode active material may have a mole fraction of nickel of 60% or more and less than 70%. In this case, there is an advantage of superior thermal safety compared to the case where the mole fraction of nickel is 70% or more.

[0072] The above-mentioned first positive active material may have a predetermined size. For example, the average particle size (D 50 ) may be 2㎛ to 10㎛, and specifically 2.5㎛ to 9㎛; 3㎛ to 8.5㎛; 3㎛ to 8㎛; 3.5㎛ to 7.5㎛; 3㎛ to 6㎛; 2㎛ to 4㎛; 4㎛ to 8㎛; 5㎛ to 9㎛; 3㎛ to 6㎛; 2.5㎛ to 3.5㎛; or 3.5㎛ to 6㎛.

[0073] Average particle size (D) of the first positive active material above 50If ) is less than 2㎛, the relative specific surface area increases and electrolyte side reactions intensify, which is undesirable in terms of lifespan performance, and the average particle size (D) of the first cathode active material is 50 If ) exceeds 10㎛, the diffusion path of lithium ions becomes long, which is undesirable in terms of resistance and output characteristics.

[0074] The BET specific surface area of ​​the first anode active material may be 0.2 m² / g to 3 m² / g, specifically 0.4 m² / g to 1 m² / g, and more specifically 0.7 m² / g to 1 m² / g. Being within this range is desirable in terms of suppressing gas generation due to side reactions on the anode surface.

[0075] The first and second positive electrode active materials may each be single-crystal particles. Cracks may occur in the particles during the rolling process for manufacturing the positive electrode and during the charging and discharging process of the manufactured positive electrode, and these cracks may cause destruction as charging and discharging are repeated. Such particle destruction increases the amount of gas generated within the battery and reduces the number of charge-discharge cycles, leading to a decrease in lifespan. If the first and second positive electrode active materials are single-crystal particles, the particles do not easily break during the rolling process and the charging and discharging process, which is desirable in terms of the battery's lifespan characteristics.

[0076] Here, a single crystal particle refers to a structure composed of primary particles rather than secondary particles, meaning a primary structure of a single particle.

[0077] The weight ratio of the first positive active material and the second positive active material may be in the range of 4:6 to 9:1, preferably 45:55 to 8:2, and more preferably 5:5 to 7:3. When the weight ratio of the first positive active material and the second positive active material is in the above range, it is possible to realize a battery having high energy density, and the full charge voltage of the battery may exceed 4.35V.

[0078] Meanwhile, the above-mentioned positive active material layer may optionally further include a binder, a conductive material, and other additives, along with the positive active material which is the main component.

[0079] The above binder may be appropriately applied as a component that assists in the bonding of the positive active material and the conductive material and the bonding to the current collector, within a range that does not degrade the electrical properties of the positive electrode, but specifically, it may include one or more of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0080] The content of the binder may be 0.1 to 10 parts by weight per 100 parts by weight of the entire positive 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 positive active material layer to the above range, the present invention can prevent the adhesion of the active material layer from being reduced due to a low content of binder or the electrical properties of the positive electrode from being reduced due to an excessive amount of binder.

[0081] The above conductive material may include one or more types such as acetylene black, Denka black, Ketjen black, Super-P, Channel black, furnace black, lamp black, thermal black, graphene, carbon nanotubes, and carbon fibers, but is not limited thereto.

[0082] The content of the conductive material may be 0.1 to 10 parts by weight per 100 parts by weight of the total electrode active material 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 decrease in charging capacity caused by an increase in the resistance of the electrode due to a low content of the conductive material, and can prevent problems such as a decrease in charging capacity caused by a decrease in the content of the active material due to an excessive amount of conductive material, or a decrease in rapid charging characteristics due to an increase in the loading amount of the active material layer.

[0083] The average thickness of the positive active material layer may be 50 μm to 500 μm. Specifically, the average thickness of the positive active material layer may be 100 μm to 400 μm; 200 μm to 350 μm; 50 μm to 180 μm; 80 μm to 150 μm; 100 μm to 250 μm; 100 μm to 250 μm; or 130 μm to 190 μm. By controlling the average thickness of the positive active material layer to the above range, the present invention can not only achieve high adhesion between the positive active material layer and the positive current collector, but also achieve high energy density of the positive.

[0084] Furthermore, the above-mentioned positive current collector may be one that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, one that has been surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the average thickness of the above-mentioned current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0085] The above anode may be manufactured according to a conventional anode manufacturing method. For example, the above anode may be manufactured by dissolving or dispersing the components constituting the anode active material layer, namely the anode active material, a conductive material, a binder, etc., in a solvent to prepare an anode slurry, applying the anode slurry to at least one surface of an anode current collector, and then drying and rolling, or by casting the anode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto an anode current collector.

[0086] The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for anode manufacturing thereafter.

[0087]

[0088] cathode

[0089] A cathode according to exemplary embodiments comprises: a cathode current collector; and a cathode active material layer provided on at least one surface of the cathode current collector and comprising a cathode active material. The cathode active material layer is a layer that implements electrical activity of the cathode and comprises a cathode active material as a main component that implements an electrochemical redox reaction during charging and discharging of the battery. Specifically, the cathode active material may be included in an amount of 80% to 99.8% by weight based on the total weight of the cathode active material layer, and specifically, may be included in an amount of 95% or more, 98% or more, 84% to 99.8% by weight, 90% to 99.8% by weight, 94% to 99.8% by weight, 88% to 96% by weight, or 92% to 97.5% by weight.

[0090] The above-mentioned negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiOv(0 <v<2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속산화물; 또는 Si-C 복합체 또는 Sn-C 복합체과 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 또한, 상기 음극 활물질로서 금속 리튬 박막이 사용될 수도 있다. 또, 탄소질 재료는 저결정 탄소 및 고결정성 탄소 등이 모두 사용될 수 있다. 저결정성 탄소로는 연화탄소(soft carbon) 및 경화탄소 (hard carbon)가 대표적이며, 고결정성 탄소로는 무정형, 판상, 인편상, 구형 또는 섬유형의 천연 흑연 또는 인조 흑연, 키시흑연 (Kish graphite), 열분해 탄소 (pyrolytic carbon), 액정피치계 탄소섬유 (mesophase pitch based carbon fiber), 탄소 미소구체 (meso-carbon microbeads), 액정피치(Mesophase pitches) 및 석유와 석탄계 코크스 (petroleum or coal tar pitch derived cokes) 등의 고온 소성 탄소가 대표적이다. 특히 음극 활물질로서 천연 흑연 및 / 또는 인조 흑연을 포함하는 경우, 용량 특성, 수명 특성 면에서 바람직하다.

[0091] In addition to the aforementioned cathode active material layer, the above-mentioned cathode active material layer may optionally further include a cathode binder, a cathode conductive material and / or a thickener, etc.

[0092] The above-mentioned cathode binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, and fluororubber, preferably at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.

[0093] The above-mentioned negative electrode binder is a component that assists in bonding between the active material and / or the current collector, and can typically be included in the negative electrode active material layer in an amount of 1% to 30% by weight, preferably 1% to 10% by weight.

[0094] As the above-mentioned thickener, any thickener conventionally used in lithium secondary batteries can be used, and an example is carboxymethylcellulose (CMC).

[0095] The above-mentioned cathode conductive material is not particularly limited as long as it possesses conductivity without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; carbon nanotubes; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0096] The above-mentioned cathode conductive material may typically be included in the cathode active material layer in an amount of 0% to 30% by weight, preferably 1% to 10% by weight.

[0097] The above-mentioned cathode may be manufactured according to a conventional cathode manufacturing method generally known in the relevant technical field. For example, the above-mentioned cathode may be manufactured by dissolving or dispersing components constituting a cathode active material layer, namely a cathode active material, a cathode conductive material and / or a cathode binder, in a solvent to prepare a cathode slurry, applying the cathode slurry to at least one surface of a cathode current collector, and then drying and rolling, or by casting the cathode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0098]

[0099] Separator

[0100] In a lithium secondary battery, the separator separates the positive electrode and the negative electrode and provides a pathway for the movement of lithium ions. In the present invention, the separator can be used without special limitations as long as it is a separator commonly used in secondary batteries, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an 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 fibers or polyethylene terephthalate fibers, 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 it may optionally be used in a single-layer or multi-layer structure.

[0101]

[0102] electrolytes

[0103] The electrolyte includes an organic solvent; a lithium salt; and an additive.

[0104] The above-mentioned organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above-mentioned organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as Ra-CN (Ra is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to 9 can result in excellent performance of the electrolyte.

[0105] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the above lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Among these, when the lithium salt is LiPF6, it can exhibit a synergistic effect in terms of the capacity retention rate improvement effect by the main additive described later. It is preferable to use the lithium salt within the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0106] The additive according to the present invention is a main additive, and the main additive comprises 1,3-propane sultone (PS) and / or lithium bis(oxalate)borate (LiBOB).

[0107] Generally, electrolytes contain additives to form a solid electrolyte interphase (SEI) on the surface of the cathode, such as vinylene carbonate, vinylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propanesulfone, and lithium bisoxalate toborate.

[0108] In a lithium secondary battery comprising the first and second positive active materials as positive active materials, 1,3-propanesulfone and lithium bisoxalate toborate have no or minimal effect of improving the energy retention rate of the battery in a voltage range of 4.35V or lower, but can improve the energy retention rate of the battery in a voltage range exceeding 4.35V. Accordingly, in the lithium secondary battery of the present invention, it is preferable that the full charge voltage is greater than 4.35V, specifically in the range of 4.4V to 4.6V, and more specifically in the range of 4.4V to 4.55V. Since the battery is charged within the above range, the energy density can be increased to raise the average discharge voltage.

[0109] The above main additive may be in the range of 0.001 wt% to 2 wt%, specifically 0.01 wt% to 1.5 wt% with respect to the total weight of the electrolyte. When the main additive is 1,3-propanesulfone, 1,3-propanesulfone may be included in the range of 0.001 to 2 wt% with respect to the total weight of the electrolyte, preferably 0.25 wt% to 1.75 wt%, more preferably 0.5 wt% to 1.5 wt%, and most preferably 0.75 to 1.25 wt%. When the main additive is lithium bisoxalate toborate, lithium bisoxalate toborate may be included in the range of 0.001 to 2 wt% with respect to the total weight of the electrolyte, preferably 0.1 wt% to 1.5 wt%, more preferably 0.2 wt% to 1.0 wt%, and most preferably 0.3 wt% to 0.7 wt%. When the main additive is included within the above content range, the energy retention rate of the battery can be improved, while the initial resistance characteristics and output performance can be appropriately maintained.

[0110] The lithium secondary battery according to the present invention, by having the above-described configuration, enables a high-energy density battery while maintaining excellent high-temperature safety. In addition, it has an excellent energy retention rate, allowing for the realization of a long-life battery.

[0111]

[0112] The present invention will be explained in more detail below through examples and comparative examples.

[0113] However, the following examples and comparative examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0114]

[0115] Preparation Example 1: Preparation of a lithium secondary battery

[0116] As the first positive active material, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiMn as the second positive active material 0.6 Fe 0.4 PO4 was prepared. At this time, the weight ratio of the first positive active material to the second positive active material was 5:5. N-methylpyrrolidone solvent was injected into a homo mixer, and 97.2 parts by weight of the prepared positive active material; 0.7 parts by weight of carbon nanotubes as a conductive material; and 2.1 parts by weight of polyvinylidene fluoride (PVdF) as a binder were each added. The prepared positive slurry was coated onto an aluminum current collector, and then dried and rolled to produce a positive electrode.

[0117] Water solvent was injected into a homo mixer, and synthetic graphite as the cathode active material, styrene-butadiene rubber as the binder, and carboxymethylcellulose (CMC) as the thickener were added in a weight ratio of 98:1:1. The prepared cathode slurry was coated onto a copper current collector, and then dried and rolled to produce a cathode.

[0118] Ethylene carbonate (EC):dimethyl carbonate (DMC):ethylmethyl carbonate (EMC) were mixed in a volume ratio of 20:75:5, and then dissolved to make LiPF6 1.25 M to prepare a non-aqueous organic solution. Then, 1,3-propanesulfone (PS) was added at a content of 1.0 wt% relative to the total weight of the non-aqueous organic solution to prepare an electrolyte.

[0119] An electrode assembly was manufactured by interposing a polyethylene porous separator between the anode and the cathode. The electrode assembly was housed in a pouch-type battery case, and the electrolyte was injected to assemble a lithium secondary battery.

[0120] The assembled lithium secondary battery was pre-aged at room temperature (22±2℃) for 1 day, and then activated by charging at 0.1C until the state of charge (SOC) reached 60%. Then, each activated lithium secondary battery was aged at room temperature (22±2℃) and 60℃ for 1 day each, and the manufacturing of the lithium secondary battery was completed.

[0121]

[0122] Preparation Example 2: Preparation of a lithium secondary battery

[0123] A lithium secondary battery was manufactured in the same manner as in Manufacturing Example 1, except that 0.5 wt% of lithium bisoxalate toborate (LiBOB) was added instead of 1,3-propanesulfone when preparing the electrolyte in Manufacturing Example 1.

[0124]

[0125] Preparation Example 3: Preparation of a lithium secondary battery

[0126] A lithium secondary battery was manufactured in the same manner as in Manufacturing Example 1, except that 1,3-propanesulfone was not added when manufacturing the electrolyte in Manufacturing Example 1.

[0127]

[0128] Preparation Example 4: Preparation of a lithium secondary battery

[0129] A lithium secondary battery was manufactured in the same manner as in Manufacturing Example 1, except that 1% by weight of vinylene carbonate (VC) was added instead of 1,3-propanesulfone when preparing the electrolyte in Manufacturing Example 1.

[0130]

[0131] Examples 1–6, Comparative Examples 1–6

[0132] Each of the lithium secondary batteries of Preparation Examples 1 to 3 above was subjected to 200 cycles of charge and discharge under the following charge and discharge conditions. During charging, the full charge voltage was set to the voltage listed in Table 1 below.

[0133] [Charging] 0.33C CC / CV, full charge voltage and 0.05C cut-off

[0134] [Discharge] 0.5C CC, 2.5V cut-off

[0135] The capacity retention rate was calculated from the discharge capacity measured in the first charge-discharge cycle and the discharge capacity measured in 200 charge-discharge cycles, and the results are shown in Table 1.

[0136] Capacity Retention Rate (%) = (Discharge Capacity in First Cycle / Discharge Capacity in 200 Charge-Discharge Cycles) × 100

[0137] Type of Lithium Secondary Battery Type of Additive Only Charge Voltage (V) Capacity Retention Rate (%) Comparative Example 1 Manufacturing Example 1 PS 4.35 9 4.6 Comparative Example 2 Manufacturing Example 2 LiBO B 9 4.8 Comparative Example 3 Manufacturing Example 3 - 9 4.7 Example 1 Manufacturing Example 1 PS 4.4 9 0.6 Example 2 Manufacturing Example 2 LiBO B 9 2.1 Comparative Example 4 Manufacturing Example 3 - 9 0.3 Example 3 Manufacturing Example 1 PS 4.45 8 6.9 Example 4 Manufacturing Example 2 LiBO B 8 8.1 Comparative Example 5 Manufacturing Example 3 - 8 6.8 Example 5 Manufacturing Example 1 PS 4.5 8 1.4 Example 6 Manufacturing Example 2 LiBO B 8 2.5 Comparative Example 6 Manufacturing Example 3 - 8 0.8 Comparative Example 7 Manufacturing Example 4 VC 8 0.7

[0138] Referring to Table 1, when the operating voltage of the battery is 4.35V or lower, even if the battery contains PS or LiBOB, there is no increase in capacity retention rate compared to a battery that does not contain these additives, or the capacity retention rate is at a similar level.

[0139] On the other hand, when the battery contains PS or LiBOB and the operating voltage of the battery is in the range of 4.4 to 4.5 V, these additives have the effect of improving the capacity retention rate of the battery. Therefore, in a lithium secondary battery with a full charge voltage of more than 4.35 V, if PS and / or LiBOB are selected as the main additive of the electrolyte, it is expected that the capacity retention rate of the lithium secondary battery can be improved and a long-life battery can be realized.

[0140]

[0141] The present invention has been described in more detail above through examples and other means. However, the configurations described in the examples and other means of this specification are merely one embodiment of the present invention and do not represent all technical concepts of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

Claims

1. A lithium secondary battery comprising a positive electrode; a negative electrode; a separator; and an electrolyte, wherein The above electrolyte comprises 1,3-propane sultone (PS) and / or lithium bis(oxalate)borate (LiBOB) as a main additive, and A lithium secondary battery with a full charge voltage exceeding 4.35V.

2. In Claim 1, A lithium secondary battery with a full charge voltage in the range of 4.4V to 4.5V.

3. In Claim 1, The above-mentioned positive electrode includes a first positive electrode active material and a second positive electrode active material, and A lithium secondary battery, wherein the first positive active material is a lithium composite metal oxide having a layered crystal structure and the second positive active material is a lithium transition metal phosphate having an olivine structure.

4. In Claim 3, A lithium secondary battery, wherein the first positive electrode active material is a compound represented by the following chemical formula 1: [Chemical Formula 1] Li 1+y Ni p Co q Mr r M 1 -(p+q+r) O 2-z A z In the above chemical formula 1, M 1 is at least one selected from the group consisting of Cu, Ti, Mg, Al, Pt, and Zr, and A is an oxygen-substituted halogen, 0≤y≤0.5, 0.4≤p≤1, 0≤q≤0.6, 0≤r≤0.6, 0.9≤p+q+r≤1, and 0≤z≤0.

001.

5. In Claim 3, A lithium secondary battery, wherein the second positive active material is a compound represented by the following chemical formula 2: [Chemical Formula 2] Li 1+a M x Fe 1-x (PO 4-b )X b In the above chemical formula 2, M is one or more elements selected from the group consisting of Mn, Al, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X is one or more elements selected from the group consisting of F, Cl, Br, I, At, N, and S, and a, b, and x are 0≤a≤0.1, 0≤b≤0.1, and 0, respectively. <x≤0.9 범위이다.

6. In Claim 4, The above-mentioned first positive active material is a lithium secondary battery having a mole fraction of nickel of 60% or more and less than 70%.

7. In Claim 5, In the above chemical formula 2, M is manganese, and A lithium secondary battery with a molar ratio of manganese to iron of 50:50 to 70:

30.

8. A lithium secondary battery according to claim 1, wherein the main additive is included in a range of 0.001 to 2 weight% with respect to the total weight of the electrolyte.

9. A lithium secondary battery according to claim 1, wherein the main additive is 1,3-propanesulfone.

10. A lithium secondary battery according to claim 9, wherein the 1,3-propanesulfone is included in a range of 0.25 to 1.75 weight% with respect to the total weight of the electrolyte.

11. A lithium secondary battery according to claim 1, wherein the main additive is lithium bis-oxalate toborate.

12. A lithium secondary battery according to claim 11, wherein the lithium bisoxalate toborate is included in a range of 0.1% to 1.5% by weight relative to the weight of the electrolyte.

13. A lithium secondary battery according to claim 1, wherein the weight ratio of the first positive active material and the second positive active material is in the range of 4:6 to 9:

1.

14. A lithium secondary battery according to claim 1, wherein the cathode comprises natural graphite and / or artificial graphite as a cathode active material.