Lithium secondary battery

Abstract

Provided is a lithium secondary battery including a negative electrode including a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, a positive electrode, and an electrolyte including a lithium salt, an organic solvent, and an additive, in which the negative electrode active material layer includes Si as a negative electrode active material, the organic solvent contains fluoroethylene carbonate, and the following Z has a value of 0.1 to 0.2. Z =, X is the content (wt%) of Si with respect to the total weight of the negative electrode active material contained in the negative electrode active material layer, and Y is the content (wt%) of fluoroethylene carbonate with respect to the total weight of the electrolyte after activation of the lithium secondary battery.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0142496 filed with the Korean Intellectual Property Office on October 23, 2023 and Korean Patent Application No. 10-2024-0091397 filed on July 10, 2024, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a lithium secondary battery. Background Technology

[0004] In recent years, as the application fields of lithium secondary batteries have rapidly expanded to power supply for electronic devices such as power, electronics, communications and computers, as well as power storage supply for large equipment such as automobiles and power storage devices, the demand for secondary batteries with high capacity, high output and high stability is increasing.

[0005] In particular, high capacity, high power, and long lifespan are becoming increasingly important in lithium-ion batteries used in automobiles. Therefore, to achieve high capacity in lithium-ion batteries, silicon-based anode active materials with high energy density but low stability can be used.

[0006] However, if silicon-based anode active materials are used in lithium-ion batteries to improve capacity, the shrinkage and expansion of the anode during cycling are drastic, resulting in poor long-term lifespan performance or battery durability. Typical lithium-ion batteries focus on forming a stable SEI layer on the initial anode, but silicon-based anode active materials undergo drastic volume changes with repeated charging and discharging, making it difficult to achieve sufficient long-term lifespan performance or battery durability. Summary of the Invention

[0007] Technical issues

[0008] The present invention aims to solve the above-mentioned problems and provide a lithium secondary battery that can stabilize the degradation caused by volume changes in silicon-based anode active materials even during cycling. Furthermore, the present invention also aims to provide a lithium secondary battery with excellent overall battery performance.

[0009] Technical solution

[0010] After repeated and careful research, the inventors of this invention discovered that the objectives of this disclosure can be achieved in the following aspects, and thus completed this invention.

[0011] [1] A lithium secondary battery is provided, comprising: a negative electrode comprising a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, a positive electrode, and an electrolyte comprising a lithium salt, an organic solvent and an additive, wherein the negative electrode active material layer comprises Si as a negative electrode active material, the organic solvent comprises fluoroethylene carbonate, and the value of Z is 0.1 to 0.2.

[0012] Z=

[0013] X is the content of Si relative to the total weight of the negative electrode active material contained in the negative electrode active material layer (weight %), and Y is the content of fluorinated ethylene carbonate relative to the total weight of the electrolyte after activation of the lithium secondary battery (weight %).

[0014] [2] In the above [1], the present invention can provide a lithium secondary battery, wherein the negative electrode active material contained in the negative electrode active material layer is composed of a mixture of Si and graphite.

[0015] [3] In [1] or [2] above, the present invention can provide a lithium secondary battery, wherein X is 1% to 10% by weight.

[0016] [4] In any of [1] to [3] above, the present invention can provide a lithium secondary battery, wherein the Y is 12% to 24% by weight.

[0017] [5] In any of [1] to [4] above, the present invention can provide a lithium secondary battery, wherein the organic solvent further comprises ethyl methyl carbonate and dimethyl carbonate.

[0018] [6] In the above [5], the present invention can provide a lithium secondary battery, wherein the content of dimethyl carbonate is 20% to 70% by weight based on the total weight of the electrolyte.

[0019] [7] In any of [1] to [6] above, the present invention can provide a lithium secondary battery, wherein the additives include vinylene carbonate, ethylene sulfate and propane sulpholactone.

[0020] [8] In the above [7], the present invention can provide a lithium secondary battery, wherein the content of the additive is from 1% to 10% by weight based on the total weight of the electrolyte.

[0021] [9]In any one of the above [1] to [8], the present invention may provide a lithium secondary battery, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material contained in the positive electrode active material layer is a lithium nickel-based oxide represented by the following [Formula 1].

[0022] [Formula 1]

[0023] Li a Ni b Co c M 1 d M 2 e O2

[0024] In the above Formula 1, M 1 may be Mn, Al or a combination thereof, M 2 may be one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0.8 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2, and 0 ≤ e ≤ 0.1.

[0025]

[10] In any one of the above [1] to [9], the present invention may provide a lithium secondary battery, wherein the lithium secondary battery has a cylindrical shape.

[0026] Advantageous Effects

[0027] In the present invention, the value of Z is controlled so that the amount of fluoroethylene carbonate after activation satisfies a specific range that varies with the amount of Si, which is the negative electrode active material contained in the lithium secondary battery and causes the collapse of the SEI film due to a drastic volume change, i.e., the volume change amount. As the amount of Si increases, the volume expansion / contraction during cycling intensifies, and cracks are generated in the initially formed SEI film, thereby accelerating deterioration. However, the remaining fluoroethylene carbonate after activation causes ring-opening reaction and defluorination reaction, thereby forming a new negative electrode film in each cycle. Therefore, it has the effect of ensuring the interfacial stability between Si and the electrolyte and suppressing further decomposition of the electrolyte.

[0028] In addition, by controlling the value of Z so that the amount of fluoroethylene carbonate satisfies a specific range that varies with the amount of Si, the amount of excessively present fluoroethylene carbonate can be reduced without forming a new negative electrode film, thereby minimizing the adverse effects on battery stability caused by the generation of by-product gases such as carbon dioxide (CO2) and ethylene (C2H4). Detailed Embodiments

[0029] Hereinafter, the present invention will be described in more detail.

[0030] The negative electrode, positive electrode, electrolyte, and / or lithium secondary battery of the present invention include at least one of the configurations disclosed below, and may include any combination of the technically possible configurations below.

[0031] It will be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical ideas of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best interpret the invention.

[0032] The lithium secondary battery of the present invention comprises: a negative electrode containing a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, a positive electrode, and an electrolyte containing a lithium salt, an organic solvent, and additives.

[0033] In particular, the negative electrode active material layer contains Si as the negative electrode active material. Si refers to pure Si particles, not silicon oxide or silicon-carbon composites. Furthermore, the organic solvent contained in the electrolyte of this invention contains ethylene fluorocarbonate.

[0034] The value of Z in the lithium secondary battery of the present invention is 0.1 to 0.2. Preferably, Z is 0.10 to 0.15, and more preferably 0.11 to 0.13.

[0035] Z=

[0036] The above X represents the content (wt%) of Si relative to the total weight of the negative electrode active material contained in the negative electrode active material layer. X can be from 1 wt% to 10 wt%, preferably from 1 wt% to 8 wt%, and more preferably from 4 wt% to 6 wt%.

[0037] As a negative electrode active material other than Si, compounds capable of reversibly inserting and deintercalating lithium can be used. Specific examples can include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers and amorphous carbon, lithium metal films, metallic materials that can be alloyed with lithium such as Sn and Al, and any one or a mixture of two or more of them can be used.

[0038] While Si-containing anodes can achieve high capacity, they suffer from reduced structural stability due to drastic contraction and expansion during charging and discharging. Therefore, it is preferable to mix Si with a carbon-based anode active material and use this mixture. Most preferably, a mixture comprising Si and graphite is preferred as the anode active material.

[0039] In the negative electrode active material layer of the present invention, the weight ratio of Si to graphite may be 1:99 to 20:80, 2:98 to 10:90, or 2.5:97.5 to 8.0:92.0.

[0040] The above Y represents the content (by weight%) of fluoroethylene carbonate relative to the total weight of the electrolyte after activation of the lithium secondary battery. Lithium secondary batteries are assembled by embedding the electrode components and electrolyte together in a battery casing, and then manufactured through an activation process. The activation process includes charging, aging, and discharging the assembled battery to stabilize the battery structure and bring it to a usable state.

[0041] The Y mentioned above can be from 12% to 24% by weight, preferably from 12% to 16% by weight, and more preferably from 13% to 15% by weight.

[0042] In addition, prior to activation, the content of fluoroethylene carbonate can be from 0.5% to 40% by weight, based on the total weight of the electrolyte.

[0043] The negative electrode of the present invention may have a structure in which a negative electrode active material layer is formed on one or both surfaces of a long sheet-shaped negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material containing Si, a conductive material and a binder.

[0044] Specifically, the negative electrode can be manufactured by coating a negative electrode slurry on one or both surfaces of a long sheet-shaped negative electrode current collector, removing the solvent from the negative electrode slurry through a drying process, and then rolling it. The negative electrode slurry is prepared by dispersing the negative electrode active material, conductive material, and binder in solvents such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water.

[0045] As the negative electrode current collector, commonly used negative electrode current collectors in the art can be used, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel surface-treated with one of carbon, nickel, titanium, and silver, or aluminum-cadmium alloys, etc. The negative electrode current collector can typically have a thickness from 3 μm to 500 μm, and as with the positive electrode current collector, microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0046] Conductive materials are used to impart conductivity to the negative electrode, and any conductive material can be used without particular limitation, as long as it is electronically conductive and does not cause chemical changes in the battery to be constructed. Specific examples may include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used.

[0047] Based on the total weight of the negative electrode active material layer, the content of conductive material can typically be from 0.01% to 0.2% by weight, preferably from 0.01% to 0.15% by weight, and more preferably from 0.05% to 0.12% by weight.

[0048] Adhesives are used to improve the bonding between particles of the negative electrode active material and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more of them may be used.

[0049] Based on the total weight of the negative electrode active material layer, the content of the binder can be from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 5% by weight.

[0050] The electrolyte contained in the lithium secondary battery of the present invention includes lithium salt, organic solvent and additives.

[0051] As organic solvents, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as organic solvents, the following can be used: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane.

[0052] In order to control the Z value within a specific range after activation, the preferred organic solvent is a mixture of fluoroethylene carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0053] For example, as a factor controlling the residual FEC content, the dimethyl carbonate content can be from 20% to 70% by weight, based on the total weight of the electrolyte. This is believed to be because dimethyl carbonate is oxidized before fluoroethylene carbonate, thus increasing the amount of residual fluoroethylene carbonate in the electrolyte. For instance, after activation, the dimethyl carbonate content can be from 50% to 70% by weight, based on the total electrolyte.

[0054] Any compound can be used as a lithium salt without particular limitation, as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F... - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN -and (CF3CF2SO2)2N - At least one of the following groups can be used as lithium salts: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, and LiN(CF3SO2). 2。 LiCl, LiI, or LiB(C₂O₄)₂, etc. Lithium salts can be used in concentration ranges from 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, and lithium ions can move efficiently.

[0055] In addition to the electrolyte components mentioned above, the electrolyte may further include one or more film-forming additives, such as vinylene carbonate, ethylene sulfate, and propane sulcolone, in order to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity.

[0056] In the electrolyte of the present invention, the content of the additive can be from 1% to 10% by weight, preferably from 1% to 5% by weight, and most preferably from 1% to 3% by weight, based on the total weight of the electrolyte. The type and content of the additive can be selected to control the amount of residual fluoroethylene carbonate after activation, thereby satisfying a specific range regarding the Si content.

[0057] The positive electrode of the present invention may have a structure in which a positive electrode active material layer is formed on one or both surfaces of a long sheet-like positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material, a conductive material and an adhesive.

[0058] Specifically, the positive electrode can be manufactured by coating a positive electrode slurry on one or both surfaces of a long sheet-shaped positive electrode current collector, removing the solvent from the positive electrode slurry through a positive electrode drying process, and then rolling it. The positive electrode slurry is prepared by dispersing positive electrode active materials, conductive materials, and binders in solvents such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water.

[0059] As the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector generally can have a thickness of 3 μm to 500 μm, and microscopic irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion of the positive electrode active material. The positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies. Most preferably, an aluminum thin film can be used in terms of elongation control, etc.

[0060] Meanwhile, as the positive electrode active material, positive electrode active materials commonly used in the art can be used.

[0061] The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, and specifically, can include lithium metal oxides containing lithium and one or more metals such as cobalt, manganese, nickel, and aluminum. More specifically, the lithium metal oxide can be a lithium manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium cobalt-based oxide (e.g., LiCoO2, etc.), a lithium nickel-based oxide (e.g., LiNiO2, etc.), a lithium nickel manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2(where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1 and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2 and p1 + q1 + r1 = 2), etc.), or a lithium nickel cobalt transition metal (M) oxide (e.g., Li(Ni p2 Co[[ID=​​​​)O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and p2 are each atomic fractions of independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc., and may include any one or two or more of these compounds.

[0062] Among them, since it can improve the capacity performance and stability of the battery, the lithium metal oxide can be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 [[ID=二十九]]Mn 0.1 Co 0.1 )O2, etc.), lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) or lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2), etc., and any one or a mixture of two or more of them can be used.

[0063] More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by the following [Formula 1].

[0064] [Formula 1] - 0>Li a Ni b Co c M 1 d M 2 e O2

[0066] In the above Formula 1, M 1 can be Mn, Al, or a combination thereof, preferably Mn, or Mn and Al.

[0067] M 2is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb. Preferably, it can be one or more selected from the group consisting of Zr, Y, Mg, and Ti. More preferably, it can be Zr, Y, or a combination thereof. It does not necessarily contain the M 2 element, but when contained in an appropriate amount, the M 2 element can play a role in promoting particle growth or improving the crystal structure stability during firing.

[0068] a represents the molar ratio of lithium in the lithium nickel-based oxide, where a can satisfy 0.8 ≤ a ≤ 1.2, 0.85 ≤ a ≤ 1.15, or 0.9 ≤ a ≤ 1. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be formed stably.

[0069] b represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide, and b can satisfy 0.8 ≤ b < 1, 0.85 ≤ b < 1, 0.86 ≤ b < 1, or 0.88 ≤ b < 1. When the molar ratio of nickel satisfies the above range, a high energy density can be achieved to realize a high capacity.

[0070] c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide, and c can satisfy 0 < c < 0.2, 0 < c < 0.15, 0 < c < 0.14, or 0.01 ≤ c ≤ 0.12. When the molar ratio of cobalt satisfies the above range, good resistance performance and output performance can be achieved.

[0071] d represents the molar ratio of the M 1 element in all metals other than lithium in the lithium nickel-based oxide, and d can satisfy 0 < d < 0.2, 0 < d < 0.15, 0 < d < 0.14, or 0.01 ≤ d ≤ 0.12. When the molar ratio of the M 1 element satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0072] e represents the molar ratio of the M 2 element in all metals other than lithium in the lithium nickel-based oxide, where e can satisfy 0 ≤ e ≤ 0.1, or 0 ≤ e ≤ 0.05.

[0073] Meanwhile, if necessary, the positive electrode active material of the present invention can also include a coating on the surface of the lithium nickel-based oxide particles, and the coating contains one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element can be Al, B, Co, or a combination thereof. Most preferably, the coating element can be B.

[0074] If the coating is present on the surface of lithium nickel-based oxide particles, the contact between the electrolyte and the lithium complex transition metal oxide is suppressed by the coating, thus reducing the dissolution of transition metals or the generation of gases due to side reactions with the electrolyte.

[0075] Next, a conductive material is used to impart conductivity to the electrode, and any conductive material can be used without particular limitation, as long as it is electronically conductive and does not cause chemical changes in the battery to be constructed. Specific examples may include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used.

[0076] Based on the total weight of the positive electrode active material layer, the content of conductive material can be from 0.1% to 10% by weight, preferably from 0.1% to 5% by weight, and more preferably from 1% to 3% by weight.

[0077] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0078] Based on the total weight of the positive electrode active material layer, the content of the binder can be from 1% to 30% by weight, preferably from 1% to 15% by weight, and more preferably from 1% to 4% by weight.

[0079] The lithium secondary battery of the present invention can have a cylindrical or square shape, etc., as used in the can. If the lithium secondary battery of the present invention has a cylindrical shape, the cylindrical lithium secondary battery may include a jelly-roll type electrode assembly having a positive electrode plate, a negative electrode plate, and a separator between the positive electrode plate and the negative electrode plate wound in one direction, a battery can containing the electrode assembly, and a sealing body that seals the opening end of the battery can.

[0080] In addition to the aforementioned positive and negative electrodes, the separator between the positive and negative electrodes separates them and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a commonly used separator in lithium-ion secondary batteries. Specifically, as the separator, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or laminated structures having two or more layers. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0081] The lithium secondary battery of the present invention can be used in battery cells for use as power sources in small devices, and can also preferably be used as a unit cell in medium and large battery modules comprising multiple battery cells.

[0082] Examples of medium to large-sized equipment include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0083] The invention will be described in more detail below with reference to specific embodiments. However, the following embodiments are for illustrative purposes only to help understand the invention and do not limit the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the invention, and that such changes and modifications are obviously within the scope of the appended claims.

[0084] Example

[0085] Example 1

[0086] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfite, and 2.0 wt% propane sulcolone as additives to an organic solvent (ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 5:75:20 by weight).

[0087] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0088] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 94.5:5.5 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0089] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0090] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 17.0% by weight.

[0091] Example 2

[0092] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfite, and 2.0 wt% propane sulcolone as additives to an organic solvent (ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 5:75:20 by weight).

[0093] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0094] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 97.0:3.0 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0095] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0096] The electrode assembly manufactured as described above was inserted into a cylindrical battery can with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the can to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 15.8% by weight.

[0097] Example 3

[0098] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfite, and 2.0 wt% propane sulcolone as additives to an organic solvent (ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 5:75:20 by weight).

[0099] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0100] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 97.0:3.0 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0101] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0102] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.1 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 14.3% by weight.

[0103] Comparative Example 1

[0104] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6 and 1 wt% fluoroethylene carbonate, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfate and 2.0 wt% propane sulcolone as additives to an organic solvent (ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): ethylene carbonate (EC) = 5:75:20 by weight).

[0105] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0106] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 94.5:5.5 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0107] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0108] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 0% by weight.

[0109] Comparative Example 2

[0110] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfide, and 2.0 wt% propanesulfonyl lactone as additives to an organic solvent (ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): ethylene carbonate (EC): fluoroethylene carbonate (FEC) = 5:65:20:10 by weight).

[0111] Will Li[Ni 0.9 Co0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0112] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 94.5:5.5 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0113] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0114] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 6.5% by weight.

[0115] Comparative Example 3

[0116] A non-aqueous electrolyte was prepared by dissolving 1.3 M LiPF6 in 80 wt% dimethyl carbonate (DMC) and 20 wt% fluoroethylene carbonate (FEC).

[0117] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0118] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 94.5:5.5 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0119] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0120] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 10.1% by weight.

[0121] Comparative Example 4

[0122] 1.3 M LiPF6 and 2.5 wt% vinylene carbonate were added as additives to an organic solvent (dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 80:20 by weight) to prepare a non-aqueous electrolyte.

[0123] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0124] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 94.5:5.5 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0125] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0126] The electrode assembly manufactured as described above was inserted into a cylindrical battery can with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the can to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 10.5% by weight.

[0127] Comparative Example 5

[0128] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfate, and 2.0 wt% propanesulfonyl lactone as additives to an organic solvent (diethyl carbonate (DEC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 10:60:30 by weight).

[0129] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0130] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 94.5:5.5 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0131] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0132] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of fluoroethylene carbonate relative to the total weight of the electrolyte was 27.4% by weight.

[0133] Comparative Example 6

[0134] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfide, and 2.0 wt% propanesulfonyl lactone as additives to an organic solvent (ethylene carbonate (EC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 20:75:5 by weight).

[0135] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0136] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 98.0:2.0 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0137] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0138] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of ethylene fluorocarbonate relative to the total weight of the electrolyte was 1.9% by weight.

[0139] Comparative Example 7

[0140] A non-aqueous electrolyte was prepared by adding 1.3 M LiPF6, 2.0 wt% vinylene carbonate, 1.3 wt% ethylene sulfite, and 2.0 wt% propane sulcolone as additives to an organic solvent (ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): fluoroethylene carbonate (FEC) = 5:75:20 by weight).

[0141] Will Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01O2, carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector with a thickness of 15.0 μm, dried at 120°C, and then rolled to manufacture the positive electrode.

[0142] A negative electrode slurry was prepared by mixing the negative electrode active material (graphite:Si = 98.2:1.8 by weight), the conductive material (super C), the styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) in water at a weight ratio of 98:0.1:1.5:0.4. This negative electrode slurry was coated onto one surface of a copper current collector, dried at 150°C, and then rolled to manufacture the negative electrode.

[0143] The separator is placed between the positive and negative electrodes manufactured as described above, and the separator, positive electrode and negative electrode are stacked in the order of separator / positive electrode / separator / negative electrode, and then wound to manufacture a wound electrode assembly.

[0144] The electrode assembly manufactured as described above was inserted into a cylindrical battery canister with a diameter of 21 mm and a height of 70 mm, and the electrolyte described above was injected into the canister to manufacture a cylindrical lithium secondary battery. After the prepared cylindrical lithium secondary battery was activated by charging it to 4.2 V at 0.5 C, the content of ethylene fluorocarbonate relative to the total weight of the electrolyte was 16.3% by weight.

[0145] Experimental Example

[0146] High-temperature life performance was evaluated for each cylindrical lithium secondary battery manufactured in Examples 1 to 3 and Comparative Examples 1 to 7.

[0147] Specifically, each cylindrical lithium secondary battery manufactured in Examples 1 to 3 and Comparative Examples 1 to 7 was charged to 4.25 V at 0.3 C under CC-CV conditions at 40°C, and then discharged to 2.85 V at 0.5 C under CC conditions. This charge / discharge cycle was defined as one cycle, and the number of cycles was measured until the capacity retention reached 80% based on the initial capacity. The Z-values ​​of Examples 1 to 3 and Comparative Examples 1 to 7, along with the number of cycles described above, are shown in Table 1 below.

[0148] [Table 1]

[0149] As shown in Table 1 above, the lithium secondary batteries of Examples 1 to 3, whose Z values ​​are in the range of 0.1 to 0.2, are confirmed to have superior life performance at high temperatures compared with the lithium secondary batteries of Comparative Examples 1 to 7.

Claims

1. A lithium secondary battery, comprising: The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector; Positive electrode; and Electrolytes, the electrolyte comprising lithium salts, organic solvents, and additives, in: The negative electrode active material layer contains Si as the negative electrode active material; The organic solvent contains fluoroethylene carbonate; The following values ​​for Z range from 0.1 to 0.2: Z= Wherein, X is the content of Si relative to the total weight of the negative electrode active material contained in the negative electrode active material layer, in weight%; and Y is the content of fluorinated ethylene carbonate relative to the total weight of the electrolyte after activation of the lithium secondary battery, in weight%.

2. The lithium secondary battery according to claim 1, wherein, The negative electrode active material layer contains a negative electrode active material composed of a mixture of Si and graphite.

3. The lithium secondary battery according to claim 1, wherein, The above X is 1% to 10% by weight.

4. The lithium secondary battery according to claim 1, wherein, The above Y ranges from 12% to 24% by weight.

5. The lithium secondary battery according to claim 1, wherein, The organic solvent also includes ethyl methyl carbonate and dimethyl carbonate.

6. The lithium secondary battery according to claim 5, wherein, Based on the total weight of the electrolyte, the content of dimethyl carbonate is from 20% to 70% by weight.

7. The lithium secondary battery according to claim 1, wherein, The additives include vinylene carbonate, ethylene sulfate, and propane sulpholactone.

8. The lithium secondary battery according to claim 7, wherein, The content of the additive is from 1% to 10% by weight, based on the total weight of the electrolyte.

9. The lithium secondary battery according to claim 1, wherein, The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer contains a lithium nickel-based oxide represented by the following formula 1: [Formula 1] Li a Ni b Co c M 1 d M 2 e O2 Among them, in the above formula (1), M 1 is Mn, Al or a combination thereof, and M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0.8 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2, and 0 ≤ e ≤ 0.

1.

10. The lithium secondary battery according to claim 1, wherein, The lithium secondary battery has a cylindrical shape.

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